US20020045362A1 - Method of forming a silicon nitride layer on a semiconductor wafer - Google Patents

Abstract

The invention provides methods and apparatuses of forming a silicon nitride layer on a semiconductor wafer is located on a susceptor within a semiconductor processing chamber. A carrier gas, a nitrogen source gas, and a silicon source gas are introduced into the semiconductor processing chamber and a semiconductor wafer is exposed to the mixture of gases at a pressure in the chamber in the range of approximately 100 on to 500 Torr.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention[0001]
• This invention relates generally to deposition technologies in integrated circuit chip processing and more particularly to the deposition of silicon nitride films.[0002]
• 2. Discussion of Related Art[0003]
• The manufacture of semiconductor integrated circuits generally involves the formation of a plurality of layers of material on a semiconductor (e.g. silicon) wafer, each layer serving specific functions generally related to the routing and isolating of specific signals. One or more of these layers may comprise silicon nitride (Si[0004]₃N₄) as an insulator or mask. A conventional method of forming a silicon nitride layer on a wafer involves locating the wafer on a susceptor within a processing chamber and introducing a mixture of gases such as a silicon source gas, a nitrogen source gas, and a carrier gas into the processing chamber. The gases combine in the processing chamber at generally a pressure of about 300 millitorr (mTorr) to form the silicon nitride layer or film.
• The processing chamber is heated by a heat source such as external heat lamps that direct light through transparent walls of the semiconductor processing a chamber to heat the chamber. A temperature measurement device such as a thermocouple, pyrometer, or a thermal camera may be used for detecting a temperature at a location on the susceptor.[0005]
• The deposition rate, thickness, and uniformity of the silicon nitride layer may depend on a variety of parameters such as the pressure or the temperature in the chamber, or the amount and type of gas and flow rate of the gas across the wafer introduced into a chamber. Additionally, increasing one parameter such as temperature may affect another parameter such as pressure. For example, using a higher temperature generally allows for a lower pressure (e.g. 300 mTorr) to be used. Although higher temperatures result in a higher deposition rate of the silicon nitride layer on a wafer, high temperature deposition has its disadvantages. One disadvantage is that high temperature processing causes outdiffusion of dopants from, for example, P-type conductivity or N-type conductivity regions (P- or N-doped regions) of a semiconductor wafer. Outdiffusion may result in the breakdown of the electrical elements (e.g., transistors, capacitor, diodes, etc.) that are formed from doped regions. Avoidance of such outdiffusion is particularly important as device dimensions decrease below 0.25 μm.[0006]
• It is desirable to provide a method of increasing the deposition of a silicon nitride layer on a wafer while avoiding the negative consequences seen in the prior art.[0007]
SUMMARY OF THE INVENTION
• Methods and apparatuses of forming a silicon nitride layer on a semiconductor wafer are disclosed. In one embodiment of the invention, a mixture of gases that include a carrier gas, a nitrogen source gas, and a silicon source gas are introduced into the processing chamber at a pressure of approximately in the range of 100 to 500 Torr to form a Si[0008]₃N₄film on a wafer in the processing chamber. In another embodiment of the Invention a silicon nitride film is formed using an annular-shaped pumping plate that has a sidewall with a plurality of gas holes that communicate with a pumping channel to introduce the reactants into the chamber. Other aspects and methods of the invention as well as apparatuses formed using these methods are described further below in conjunction with the following figures.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention is further described by way of example with reference to the accompanying drawings wherein:[0009]
• FIG. 1 shows cross-sectional side views of a processing chamber comprising a resistive heater in a “wafer process” position in accordance with an embodiment of the invention through a first cross-section and a section cross-section each through one-half of the chamber.[0010]
• FIG. 2 shows similar cross-sectional side views as in FIG. 1 in a wafer-separate position.[0011]
• FIG. 3 shows similar cross-sectional side views as in FIG. 1 in a wafer-separate position.[0012]
• FIG. 4 shows another cross-sectional side view of a portion of a processing chamber position in accordance with an embodiment of the invention.[0013]
• FIG. 5 shows yet another cross-sectional side view of a portion of a processing chamber position in accordance with an embodiment of the invention.[0014]
• FIG. 6 shows a top perspective view of a portion of a processing chamber with the chamber lid removed in accordance with an embodiment of the invention.[0015]
• FIG. 7 shows a top perspective view of a pumping plate in accordance with an embodiment of the invention.[0016]
• FIG. 8 shows a side plan view of a pumping plate in accordance with an embodiment of the invention.[0017]
• FIG. 9 shows a top plan view of a pumping plate in accordance with an embodiment of the invention.[0018]
• FIG. 10 shows a bottom plan view of a pumping plate in accordance with an embodiment of the invention.[0019]
• FIG. 11 shows a cross-sectional side view of portion of a pumping plate in accordance with an embodiment of the invention.[0020]
• FIG. 12 shows side plan view of a portion of a pumping plate having a single gas hole plate in accordance with an embodiment of the invention.[0021]
• FIG. 13 shows a top plan view of a portion of a pumping plate having a single gas hole plate in accordance with an embodiment of the invention.[0022]
• FIG. 14 shows a top plan view of a face plate in accordance with an embodiment of the invention.[0023]
• FIG. 15 shows a cross-sectional side view of a face plate in accordance with an embodiment of the invention.[0024]
• FIG. 16 shows a cross-sectional side view of a portion of a face plate in accordance with an embodiment of the invention.[0025]
• FIG. 17 is a cross-sectional schematic view of a single substrate radiantly-heated deposition chamber.[0026]
• FIG. 18 is a schematic block diagram illustrating a system used for carrying out a method according to one embodiment of the invention.[0027]
• FIG. 19 is a thickness map illustrating a thickness measurement of a film deposited in accordance with an embodiment of a process of the invention.[0028]
• FIG. 20 is a thickness map illustrating a thickness measurement of a film deposited in accordance with an embodiment of a process of the invention.[0029]
• FIG. 21 shows one embodiment of the invention wherein the rate of deposition of silicon nitride on a wafer is shown relative to the pressure in the chamber, the flow rate of silane gas, and the ratio of ammonia gas to silane gas.[0030]
• FIG. 22 shows one embodiment of the invention in which the deposition rate of silicon nitride is shown relative to temperature wherein the pressure is approximately 100 Torr.[0031]
DESCRIPTION OF PREFERRED EMBODIMENT
• In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident, however, to one skilled in the art that the present invention may be practiced without these specific details. In certain instances specific apparatus, structures, and methods have not been described so as not to obscure the present invention.[0032]
• The invention relates to methods and apparatuses of forming a silicon nitride film layer on a substrate such as a semiconductor wafer. In one embodiment, the film or layer is formed on a semiconductor wafer that is located on a susceptor within a single wafer processing chamber that is heated by using radiant or resistive heat. A mixture of gases, including a nitrogen source gas, a silicon source gas, and a carrier gas, are introduced into the chamber to form the Si[0033]₃N₄film or layer. The wafer is exposed to the mixture with at a wafer temperature of between 600° C. and 800° C. To form a suitable Si₃N₄film or layer, the pressure in the processing chamber is maintained approximately in the range of 100-500 Torr. In an embodiment of the invention, a silicon nitride layer is formed using a pumping plate wherein the pumping plate has a first stepped portion, a second stepped portion, and a third stepped portion. A silicon source gas and a nitrogen source gas are introduced into the chamber to form the Si₃N₄layer or film. In one embodiment, the partial pressure of the silicon source gas such as silane is approximately in the range of 0.05 to 5 Torr and the nitrogen source gas such as ammonia has a partial pressure equal to or less than 300 Torr in chamber. Other partial pressures may be used for the silicon and nitrogen source gases which depend, in part, upon the particular gas used.
• The invention contemplates processing conditions that offer an improved deposition rate and uniformity of the Si[0034]₃N₄layer. By increasing the reaction pressure beyond prior art teachings, the process of the invention may be operated at a lower temperature without deleteriously affecting the Si₃N₄deposition or the wafer. Si₃N₄layers may be used to form spacers, an etch stop, a hard mask, or dielectric elements.
• Although the claimed invention is described relative to a resistively-heated processing chamber (FIGS. 1 through 3) and a radiantly-heated processing chamber (FIGS. 10 through 11), it is to be appreciated that other types of processing chambers may be used in conjunction with the techniques described herein.[0035]
• Referring to the drawings, a low pressure chemical vapor deposition (LPCVD) chamber is described. FIGS.[0036]1-3 show cross-sectional views of one type of reactor such as a resistive reactor used to practice the invention. FIG. 3 each show cross-sectional views of a chamber through two different cross-sections, each cross-section representing a view through approximately one-half of the chamber.
• The LPCVD chamber illustrated in FIGS.[0037]1-3 is constructed of materials such that, in this embodiment, a pressure of greater than or equal to 100 Torr can be maintained. For the purpose of illustration, a chamber of approximately in the range of eight liters is described. FIG. 1 illustrates the inside ofprocess chamber body45 in a “wafer-process” position. FIG. 2 shows the same view of the chamber in a “wafer-separate” position. FIG. 3 shows the same cross-sectional side view of the chamber in a “wafer-load” position. In each case a wafer is indicated in dashed lines to indicate its location in the chamber.
• FIGS.[0038]1-3show chamber body45 that defines reaction chamber90 in which the reaction between a process gas or gases and the water takes place (e.g., a CVD reaction).Chamber body45 is constructed in one embodiment of aluminum and haspassages55 for water to be pumped therethrough to cool chamber body45 (e.g., a “cold-wall” reaction chamber). Resident in chamber90 isresistive heater80 including, in this view,susceptor5 supported byshaft65.Susceptor5 has a surface area sufficient to support a substrate such as a semiconductor wafer (shown in dashed lines).
• Process gas enters otherwise sealed chamber[0039]90 throughgas distribution port20 in a top surface ofchamber lid30 ofchamber body45. The process gas then goes throughblocker plate24 to distribute the gas about an area consistent with the surface area of a wafer. Thereafter, the process gas is distributed through perforated face plate located, in this view, aboveresistive heater80 and coupled tochamber lid30 inside chamber90. One objective of the combination ofblocker plate24 withface plate25 in this embodiment is to create a uniform distribution of process gas at the substrate, e.g., wafer.
• A substrate such as a wafer is placed in chamber[0040]90 onsusceptor5 ofheater80 throughentry port40 in a side portion ofchamber body45. To accommodate a wafer for processing,heater80 is lowered so that the surface ofsusceptor5 is belowentry port40 as shown in FIG. 3. Typically by a robotic transfer mechanism, a wafer is loaded by way of, for example, a transfer blade into chamber90 onto the superior surface ofsusceptor5. Once loaded,entry port40 is scaled andheater80 is advanced in a superior (e.g., upward) direction towardface plate25 bylifter assembly60 that is, for example, a step motor. The advancement stops when the wafer is a short distance (e.g., 400-700 mils) from face plate25 (see FIG. 1). In the wafer-process position, chamber90 is effectively divided into two zones, a first zone above the superior surface ofsusceptor5 and a second zone below the inferior surface ofsusceptor5. It is generally desirable to confine the film formation to the first zone.
• At this point, process gas controlled by a gas panel flows into chamber[0041]90 throughgas distribution port20, throughblocker plate24 andperforated face plate25. Process gas typically reacts or contacts a wafer to form a film on the wafer. At the same time, an inert bottom-purge gas, e.g., nitrogen, is introduced into the second chamber zone to inhibit film formation in that zone. In a pressure controlled system, the pressure in chamber90 is established and maintained by a pressure regulator or regulators coupled to chamber90. In one embodiment, for example, the pressure is established and maintained by baretone pressure regulator(s) coupled tochamber body45 as known in the art. In this embodiment, the baretone pressure regulator(s) maintains pressure at a level of equal to or greater than 100 Torr. A suitable mid-level pressure range is approximately 100-300 Torr.
• Residual process gas is pumped from chamber[0042]90 through pumpingplate85 to a collection vessel at a side of chamber body45 (vacuum pump-out31). Pumping plate creates two flow regions resulting in a gas flow pattern that creates a uniform Si₃N₄layer on a substrate.
• [0043]Pump32 disposed exterior to apparatus2 provides vacuum pressure within pumping channel4140 (belowchannel414 in FIGS.1-3) to draw both the process and purge gases out of the chamber90) through vacuum pump-out31. The gas is discharged from chamber90) along adischarge conduit33. The flow rate of the discharged gas throughchannel4140 is preferably control led by athrottle valve34 disposed alongconduit33. The pressure within processing chamber90 is monitored with sensors (not shown) and controlled by varying the cross-sectional area ofconduit33 withthrottle valve34. Preferably, a controller or processor receives signals from the sensors that indicate the chamber pressure and adjuststhrottle valve34 accordingly to maintain the desired pressure within chamber90. A suitable throttle valve for use with the present invention is described in U.S. Pat. No. 5,000,225 issued to Murdoch and assigned to Applied Materials, Inc., the complete disclosure of which is incorporated herein by reference.
• Once wafer processing is complete, chamber[0044]90 may be purged, for example, with in inert gas, such as nitrogen. After processing and purging,heater80 is advanced in an inferior direction (e.g., lowered) bylifter assembly60 to the position shown in FIG. 2. Asheater80 is moved, lift pins95, having an end extending through openings or throughbores in a surface ofsusceptor5 and a second end extending in a cantilevered fashion from an inferior (e.g., lower) surface ofsusceptor5, contactlift plate75 positioned at the base of chamber90. As is illustrated in FIG. 2, in one embodiment, at this point,lift plate75 remains at a wafer-process position (i.e., the same position the plate was in FIG. 1). Asheater80 continues to move in an inferior direction through the action oflifter assembly60, lift pins95 remain stationary and ultimately extend above the superior or top surface ofsusceptor5 to separate a processed wafer from the surface ofsusceptor5. The surface ofsusceptor5 is moved to a position belowopening40.
• Once a processed wafer is separated from the surface of[0045]susceptor5,transfer blade41 of a robotic mechanism is inserted through opening40 beneath the heads of lift pins95 and a wafer supported by the lift pins. Next,lifter assembly60 inferiorly moves (e.g., lowers)heater80 andlift plate75 to a “wafer-load” position. By movinglift plate75 in an inferior direction, lift pins95 are also moved in an inferior direction, until the surface of the processed wafer contacts the transfer blade. The processed wafer is then removed throughentry port40 by, for example, a robotic transfer mechanism that removes the wafer and transfers the wafer to the next processing step. A second wafer may then be loaded into chamber90. The steps described above are generally reversed to bring the wafer into a process position. A detailed description of onesuitable lifter assembly60 is described in U.S. Pat. No. 5,772,773, assigned to Applied Materials, Inc. of Santa Clara, Calif.
• In a high temperature operation, such as LPCVD processing to form a Si[0046]₃N₄film, the reaction temperature inside chamber90 can be as high as 750° C. or more. Accordingly, the exposed components in chamber90 must be compatible with such high temperature processing. Such materials should also be compatible with the process gases and other chemicals, such as cleaning chemicals (e.g., NF₃) that may be introduced into chamber90. Exposed surfaces ofheater80 may be comprised of a variety of materials provided that the materials are compatible with the process. For example,susceptor5 andshaft65 ofheater80 may be comprised of similar aluminum nitride material. Alternatively, the surface ofsusceptor5 may be comprised of high thermally conductive aluminum nitride material (on the order of 95% purity with a thermal conductivity from 140 W/mK to 200 W/mK) whileshaft65 is comprised of a lower thermally conductive aluminum nitride.Susceptor5 ofheater80 is typically bonded toshaft65 through diffusion bonding or brazing as such coupling will similarly withstand the environment of chamber90.
• FIG. 1 also shows a cross-section of a portion of[0047]heater80, including a cross-section of the body ofsusceptor5 and a cross-section ofshaft65. In this illustration, FIG. 1 shows the body ofsusceptor5 having two heating elements formed therein,first heating element50 andsecond heating element57. Each heating element (e.g.,heating element50 and heating element57) is made of a material with thermal expansion properties similar to the material of the susceptor. A suitable material includes molybdenum (Mo). Each heating element includes a thin layer of molybdenum material in a coiled configuration.
• In FIG. 1,[0048]second heating element57 is formed in a plane of the body ofsusceptor5 that is located inferior (relative to the surface of susceptor in the figure) toFirst heating element50.First heating element50 andsecond heating element57 are separately coupled to power terminals. The power terminals extend in an inferior direction as conductive leads through a longitudinally extending opening throughshaft65 to a power source that supplies the requisite energy to heat the surface ofsusceptor5. Extending through openings in chamber lid are two pyrometers, first pyrometer10 and second pyrometer15. Each pyrometer provides data about the temperature at the surface of susceptor5 (or at the surface of a wafer on susceptor5). Also of note in the cross-section ofheater80 as shown in FIG. 1 is the presence ofthermocouple70.Thermocouple70 extends through the longitudinally extending opening throughshaft65 to a point just below the superior or top surface ofsusceptor5.
• In accordance with one embodiment of the invention to form a Si[0049]₃N₄film on a wafer, the gases include acarrier gas200, anitrogen source gas220, and asilicon source gas210. Suitable carrier gas sources include, but are not limited to, hydrogen (H₂), nitrogen (N₂), argon (Ar), and helium (He). Suitable nitrogen source gas includes, but is not limited to, ammonia (NH₃). Suitable silicon source gas includes, but is not limited to, silane, dichlorosilane, and disilene. The nitrogen source gas and the silicon source gas combine to produce a Si₃N₄layer on the wafer.
• In use,[0050]silicon source gas210 may be mixed withcarrier gas200 before or during introduction into the processing chamber90. The mixture of the carrier gas and the silicon source gas is then introduced intogas inlet20 of chamber90.Nitrogen source gas220 is also introduced intogas inlet20 and allowed to mix with the mixture of the carrier gas and the silicon source gas. The process gas passes through the plurality of holes in ablocker plate24 and then through the plurality of holes in theface plate25. These gases then flow into chamber so wherein the gases are exposed to a wafer. Thereafter, the process gas exits through the pumpingplate85 into the pumpingchannel414.
• The flow rate of the gases is dependent upon the size of semiconductor processing chamber[0051]90. In one embodiment, the total flow rate of the gases ranges iffy, from five to fifteen liters per minute based upon a total effective volume of a processing chamber of one to nine liters. The ratio of at least one of the gases or the total gas flow rate relative to the chamber is 0.50 to 5 liters per minute per liter of chamber volume.
• Exposure of the wafer to the mixture of gases causes deposition of a silicon nitride (Si[0052]₃N₄) layer on the wafer according to thermal chemical vapor deposition principles. Exposure of the gases to the wafer at an elevated temperature causes dissociation of the molecules of the silicon source gas and the nitrogen source gas into smaller molecules. The smaller molecules then recombine with one another. Provided below is a general chemical reaction that occurs in this process. Silane generally reacts with ammonia according to the chemical equation
• 3SiH₄+4NH₃->Si₃N₄+12H₂
• As a general rule, the higher the temperature in chamber[0053]90, and therefore of wafer and susceptor, the quicker the silicon nitride layer will form.
• In one embodiment, SiH[0054]₄, NH₃, and N₂are introduced with 100 standard cubic centimeters per minute (sccm) of SiH₄, 5 standard liters per minute (slm) of NH₃, and 10 slm of N₂, while wafer is heated to a temperature of between 600° C. and 800° C. During deposition, pressure in the chamber of between 100 to 500 Torr is maintained. A suitable mid-level pressure range is greater than 100 Torr to 350 Torr. In one embodiment, the partial pressure of silane is approximately in the range of 0.05 to 5 Torr and ammonia has a partial pressure equal to or less than 300 Torr in chamber. However, other partial pressures may be used for the silicon and nitrogen source gases which may depend upon the particular gas used.
• In another embodiment, gases may be used in the following proportions: SiH[0055]₄: 70 sccm, NH₃: 2 slm, and N₂: 8 slm. In yet another embodiment, gases may be used in the following proportions: dichlorosilane (SiH₂Cl₂): 230 sccm NH₃: 1,000 sccm, and H₂: 9,000 sccm. If N₂is used as a carrier gas, a deposition rate of about 50 to 5,000 Å per minute may be achieved at a temperature as low as 600° C.
• The above embodiment described controlling conditions in a reaction chamber to form a Si[0056]₃N₄film on a wafer. It is to be appreciated that such control may be done manually or with the aid of a system controller. In the former instance, an operator may monitor and adjust the power supply to the heater to control the temperature, and a vacuum source to control the pressures. The operator may also manually adjust valves associated with the individual gases to regulate the mixture and flow rate of the gases.
• A system controller may also be employed to handle the control tasks associated with system control. FIG. 1 illustrates a system controller or processor coupled to a power supply and a gas manifold. The controller may be configured to record the temperature measured by the temperature indicators and control the power supplied to the heating elements based, for example, on an algorithm that determines a relative value of the temperature difference and adjusts the heating elements accordingly. The controller may also be configured to control the mixture and flow of gases to the processing chamber. In an LPCVD reaction process, the controller may further be coupled to a pressure indicator that measures the pressure in the chamber as well as a vacuum source to adjust the pressure in the chamber.[0057]
• The system controller is supplied with control signal generation logic. The controller may also be coupled to a user interface that allows an operator to enter the reaction parameters, such as the desired reaction temperature, the acceptable tolerance of a temperature difference between indicators (e.g., ±3° C.), the reaction pressure, and the flow of gases to the processing chamber.[0058]
• Control signal generation logic is supplied to the system controller in the form of, for example, software instruction logic that is a computer program stored in a computer-readable medium such as the memory of the controller. The computer program includes sets of instructions that dictate the timing, mixture of gases, chamber pressure, chamber temperature, and other parameters of a particular process. It is to be appreciated that other computer programs such as one stored on another memory device, including but not limited to, a floppy disk, may also be used to operate the system, controller.[0059]
• The computer program code can be written in a computer-readable programming language such as, for example, 68000 assembly language, C, C++, Pascal, Fortran or others. Suitable program code is generally entered into a single file or multiple files using a text editor. If the entered code text is in a high level language, the code is compiled, and the resultant compiler code is then linked with an object code or precompiled object code, the system invokes the object ode, causing the computer system to load the code in memory, from which the central processing unit reads and executes the code to perform the task identified in the program.[0060]
• In one aspect of the invention, an apparatus and method of improving the uniformity of process/reactant gas distribution is described. As described above, process gas such as a silicon source gas and a nitrogen source gas (along with a carrier gas) is introduced into chamber[0061]91) throughgas distribution port20. The process gas flows throughblocker plate24 andface plate25 which create a shower-head like cascade of the process gas over a surface of a wafer on the surface ofsusceptor5. As gas is introduced into chamber90 gas is also removed so that a pre-determined pressure may be maintained during processing. In the configuration of the chamber shown in FIGS.1-3, gas is removed from a side of the chamber, e.g., pumped out at one side designated vacuum pump-out31. In prior art systems, the asymmetrical removal of gases from one side of the chamber created pressure differences in the chamber; for example, a pressure measured at a point in the chamber nearer a chamber pump-out was different (e.g., less) than a pressure measured at a point distant from the pump-out. The pressure difference contributed to non-uniformity of deposition of a film on a wafer.
• In one embodiment of the invention, a pumping plate is provided to direct the flow of gases in the chamber. The pumping plate of the invention defines two gas flow regions: a first flow region of process gases directed at a wafer on the surface of[0062]susceptor5 and a second flow region defined by a radial channel about the pumping plate of gases primarily to be discharged from the chamber. By creating the two regions, a more uniform pressure may be maintained in the chamber. The invention contemplates that a static pressure difference between the two flow regions can be established throughout the chamber contributing to more uniform deposition of films across a wafer.
• Referring to FIGS. 4 through 10, components of the invention utilized to coordinate a uniform flow of process gas in the chamber will now be described in detail relative to their use in the relatively-heated processing chamber described in FIGS. 1 through 3. FIG. 4 shows a schematic cross-sectional side view of a portion of a processing chamber. FIG. 4 illustrates a portion of a chamber in a position through a single cross-section to illustrate the two gas flow regions. The cross-section is through a center axis of the chamber to illustrate the location of[0063]susceptor5 relative to pumpingplate85. In the wafer-process position, a portion ofsusceptor5 sits within an annular opening of pumping plate85 (a portion of pumpingplate85 surroundingsusceptor5 is cut-away in this cross-section).
• As seen in the illustration of FIG. 4, pumping[0064]plate85 rests oninner chamber portion41 ofchamber wall45. An underside of pumpingplate85 andinner chamber portion41 defineschannel4140 extending circumferentially around the chamber.Channel4140 does not extend completely around the chamber as a portion of a similar chamber area is utilized byentry port40 to load and remove a wafer. In one embodiment,channel4140 extends approximately 270° around the chamber. Vacuum pump-out31 is linked tochannel4140 to discharge gases from the chamber.
• As shown in FIG. 4, pumping[0065]plate85 includes (in this view) a vertical annular first steppedportion464 that forms a circumferential edge of a longitudinal or vertical wall to faceplate25. Second steppedportion466 comprises a lateral position that protrudes from the circumferential edge. Together, first steppedportion464 and second steppedportion466 definechannel414 betweenface plate25,chamber wall40 and pumpingplate85. The vertical wall separatesfirst flow region1000 where process gas is directed at a wafer (to be seated in wafer inwafer pocket6 of susceptor5) fromsecond region1010 where gas is discharged from the chamber. Gas fromfirst flow region1000 enterssecond flow region1010 through circumferentially located holes (gas holes490) extending aroundfirst portion464 of pumpingplate85. The flow of gas insecond flow region1010 is radial andsecond flow region1010 communicates withchannel4140 to remove gas from the chamber.
• FIGS. 5 and 6 show schematic views of the general flow direction of process gases through the chamber. FIG. 5 is a cross-section through the chamber that shows pumping[0066]plate85 surrounding a portion ofsusceptor5. In FIG. 5, process gas is illustrated entering through the gas inlet of the chamber and passing through blockingplate24 andface plate25. Infirst flow region1000, process gas arrives at the surface ofsusceptor5 to react with a wafer inpocket6 ofsusceptor5 and form a film of, for example, Si₃N₄or other desired material (e.g., SiO₂, polysilicon, etc.). Residual process gas as well asbottom purge gas1030 is directed tosecond flow region1010 to be discharged from the chamber. Gas enterssecond flow region1010 bygas holes490 circumferentially spaced around pumpingplate85. In this embodiment, the gas holes490 are positioned to be above the top surface of a wafer onsusceptor5 during processing. In general, gas holes490 are positioned at least at the level of a wafer or above the wafer when the heater is in the “wafer process” position.
• FIG. 6 further show the process flow of gas entering and exiting[0067]pumping plate85. FIG. 6 is a top perspective view without the resistive heater, the chamber lid, blocking plate, and face plate. FIG. 6 shows generallyU-shaped pumping channel414 that substantially surrounds a susceptor and definessecond flow region1010. Radially oriented gas holes490 are positioned around the entire perimeter of the pumping plate and communicate with pumpingchannel414. Gas holes490 in the side wall of pumpingplate95 allow gas to flow horizontally into pumpingchannel414.Pumping channel414 communicates withchannel4140 through two large openings inchannel414; openings defined by the absence of sections of lateral second steppedportion466 of pumpingplate85. Second steppedportion466 is comprised of two flange portions (see FIG. 7). One flange portion isolateschannel414 fromentry port40 while a second flange portion separateschannel414 from a region ofchannel4140 occupied by vacuum pump-out31. Configuring the flange portions in this manner helps to maintain a uniform pressure inchannel414.
• Gas holes[0068]490 in first steppedportion464 of pumpingplate85 are shown in FIG. 6 substantially evenly spaced apart from one another. Additionally, the gas holes are generally centered in first steppedportion464 of pumpingplate85. The placement of gas hole,498 in the side wall of pumpingplate85 and the division offirst flow region1000 andsecond flow region1010 creates a consistent pressure difference betweenfirst flow region1000 andsecond flow region1010. This feature allows the gas flow within the chamber to be more uniform that prior art configurations. In the prior art, a pumping plate had varying pressure differentials at various points along the pumping plate which resulted in non-uniform gas flow regions.
• FIGS.[0069]7-12 illustrate different views of an embodiment, or a portion of an embodiment, of a pumping plate of the invention. FIG. 7 illustrates a perspective top view, FIG. 8 a planar side view, FIG. 9 a planar top view, and FIG. 10 a planar bottom view. FIGS.11-12 show portions of the pumping plate to more clearly describe certain features.
• Pumping[0070]plate85 comprises generallyannular member460. In one embodiment,member460 is an integral piece comprising a process compatible metal, such as aluminum alloy or preferably C275 aluminum alloy, that will be suitably shaped to fit within a particular semiconductor processing chamber. C275 aluminum alloy is commercially available from Alcoa Advanced Technologies of Engelwood, Colo. Althoughmember460 is preferably constructed of a single integral piece of metal with different portions ofmember460, the pumpingplate85 may be comprised of pieces connected or coupled together.
• In the specific configuration described herein,[0071]member460 includes first steppedportion464, second steppedportion466, and third steppedportion468. First steppedportion464 forms a vertical side wall to definechannel414 and separatesecond flow region1010 fromfirst flow region1000. Second steppedportion466 defines the lateral portion or floor of pumpingchannel414. Third steppedportion468 serves to align pumpingplate85 in a predetermined position within a processing chamber.
• In the eight liter processing chamber described with reference to FIGS.[0072]1-3, the thickness of first steppedportion468 ranges from approximately 0.06 inches to 0.10 inches and is preferable 0.06 inches. With reference to FIGS.8-9, inner diameter ID₁₀of second steppedportion466 is, for example, 9.572 inches, and the outer diameter OD₁₀is, for example 11.25 inches. Inner diameter ID₁₀of second steppedportion466 is slightly larger than the diameter ofsusceptor5 so thatsusceptor5 will fit within the opening inannular member460 of pumpingplate85. In one embodiment, there is approximately 0.12 to 0.18 inches spacing betweensusceptor5 and second steppedportion466. ID₂₀of first steppedportion464 is 10.4 inches. OD₂₀of first steppedportion464 is 10.9 inches. As shown in FIG. 11, height488 of pumpingplate85 in this embodiment is 1.20 inches. The distance betweenbase489 of the pumping plate (the base of third stepped portion468) and the central point ofgas hole490 extending through the first steppedportion464 is 0.728 inches.
• Second stepped[0073]portion466 comprises two flange portions which extend the outside diameter from OD₁₀to OD₁₁. OD₁₁ranges from a diameter of 12.93 inches. Each flange portion has an area in proportion to an arc defined between two radii of first and second portion ofannular member460, respectively. FIG. 9 shows each flange with a bisection having an area in proportion to an arc of 55°.
• The flange portions of second stepped portion[0074]466 (i.e., the lateral portions) define the base ofchannel414 andsecond flow region1010. Between each flange portion are provided openings tochannel4140 and vacuum pump-out31. In one embodiment, an area between flange portions is in proportion to an arc of 70°.
• As illustrated by the bottom plan view of FIG. 10, third stepped portion creates a seat for pumping[0075]plate85 to rest oninner chamber portion41. In this embodiment, third steppedportion469 includes a single lip portion coinciding with an area similar to an area of one of the flange portions of second steppedportion466. The lip portion serves, in one aspect, to orient pumpingplate85 in the chamber.
• The diameters of the first, second, and third stepped portions of the pumping plate will depend on the characteristics of the individual deposition apparatus, such as the diameter of the perforated[0076]face plate25, the radial distance between pumpingchannel414 and chamber90, the height Of susceptor5 (i.e., the axial distance betweenchannel414 and chamber90 ), and the diameter of thesusceptor5.
• Pumping[0077]plate85 comprises a plurality ofgas holes490 through the side wall of first steppedportion464 that communicatefirst flow region1000 withchannel414 andsecond flow region1010. In one embodiment, forty-eightgas holes490 are located in pumpingplate85. As shown in particular in FIGS.7-8, gas holes490 are circumferentially spaced aroundannular opening462 ofbody member460 to facilitate uniform discharge of process gas through gas holes490. In one configuration, onegas hole490 is spaced a distance of 7.5° from anothergas hole490. FIG. 11 shows a magnified side plan view of a portion of pumpingplate85. FIG. 12 shows a magnified plan view of one gas hole. FIG. 12 showsgas holes490 having concave sidewalls so that theirouter diameter496 is larger than theirinner diameter494 at both the inlet and the outlet of the gas hole. The concave sidewalls are preferably smooth to reduce the creation of turbulence of the gas that might contribute to non-uniform gas flow. The concave shape ofgas holes490 also serves to restrict the flow through each particular gas hole which contributes to increased uniformity of flow through all of the gas holes. As seen in FIGS.11-12, gas holes490 extend substantially straight through pumpingplate85. In one embodiment, gas holes490 have a diameter approximately in the range of 0.120 to 0.130 inches and more preferably in the range of 0.122 to 0.125 inches.
• Process gas enters the processing chamber through relatively narrow gas distribution port[0078]20 (FIG. 1-3). To distribute the process gas evenly, the processing chamber of the invention is equipped withblocker plate24 andface plate25. FIG. 13 shows a top plan view ofblocker plate24.Blocker plate24 is substantially circular in shape and is coupled tochamber lid30 through the circumferentially-arranged fastening holes.Blocker plate24 has throughholes23 forcoupling blocker plate24 toperforated face plate25. In an embodiment suitable for the eight liter processing chamber described with reference to FIGS.1-3,blocker plate24 has approximately1,122 throughholes23 having a diameter in the range of 0.010 inches to 0.020 inches and preferably in the range of 0.014 inches to 0.016 inches. Throughholes23 are arranged, in this embodiment, in a generally circular pattern.Blocker plate24 has a thickness approximately in the range of 0.180 to approximately 0.190 inches. Preferably, the thickness ofblocker plate24 is 0.185 inches.Blocker plate24 assists in creating uniform flow of gas inchamber body45 by spreading the relatively narrow stream of process gas throughgas distribution port20 over the area ofblocker plate24.
• FIGS.[0079]14-15 show a top and side plan view, respectively offace plate25. FIG. 16 shows a cross-sectional side plan view of a portion offace plate25.Face plate25 is circular in shape.Face plate25 serves in one aspect to assist in the uniform distribution of process gas over a wafer. Process gas already redistributed to the circumferential area ofblocker plate24 is further restricted as the gas contacts faceplate25. In one embodiment, through holes inface plate25 have a similar diameter as through holes inblocker plate24.
• [0080]Face plate25 is substantially circular in shape and is coupled tochamber lid30 through circumferentially-arranged fastening holes26. Thoughholes27 in the central portion of theface plate25 extend throughface plate25. In the embodiment of an eight liter processing chamber described above, the inner diameter of a perforated face plate may range from approximately 9.10 to 9.30 inches and an outer diameter that may range from approximately 10.7 to 10.10 inches ofperforated face plate25.Face plate25 includes two stepped portions. A thickness ofexterior portion31 to coupleface plate25 to a chamber is approximately 0.800 inches while theinner portion32 having throughholes27 is approximately 0.400 inches.
• In one embodiment, though[0081]holes27 in the inlet side ofperforated face plate25 have a larger diameter than the outlet side where the process gas enters the reaction portion of the chamber. One reason for this is mechanical constraints of forming appropriate diameter through hole, in the material, e.g., damaging drill bits. FIG. 16 shows the difference in diameters between the inlets and outlets of throughholes27 inperforated face plate25.Inlet28A to each through hole (gas inlets are located at the superior side ofperforated face plate25 adjacent to blocker plate24) has a diameter of about 0.62 inches which is larger thanoutlet diameter28B of 0.016 inches. The depth of the gas hole is approximately 0.400 inches. The smaller diameter opening has a length (numerically represented by reference numeral29) of approximately 0.030 inches.
• The method for processing a semiconductor wafer according to the invention will now be described. Wafer is first positioned onto the upper surface of[0082]susceptor5 with a support blade (not shown) of the robotic wafer transfer system.Susceptor5 is raised into the upper processing position withinprocess chamber45 via conventional means, such as a hydraulic lift, so that wafer resides within central opening ofplate85.Chamber45 is then evacuated to a suitable vacuum pressure, while the wafer andsusceptor5 are suitably heated. Process gases, such as SiH₄and NH₃, are mixed in a chamber of a manifold head (not shown) and introduced throughinlet20 throughblocker plate24 and distributed uniformly over wafer viaperforated face plate25. Depending on the particular process, the process gas will contact the wafer and form a film, such as an oxide or nitride film.
• During the deposition process, pump[0083]32 is activated to generate vacuum pressure within pumpingchannel414, thereby drawing the process gases and/or plasma residue out of processing chamber90 throughgas holes490 of pumpingplate85. In addition, purge gas (bottom purge gas)1030 such as nitrogen may be directed through inlet18 and into processing chamber90 through the gap between susceptor and pumpingplate85. The purge gas minimizes leakage of process gas into the lower portion of the chamber. The residual gas and purge gas flow uniformly intogas holes490 and into pumpingchannel414. The exiting gases are discharged through vacuum pump-out31 and discharged alongline33.
• Pumping[0084]plate85 separates the gas flow into two flow regions: afirst flow region1000 directed at the surface of susceptor5 (or a wafer on susceptor5) and asecond flow region1010 inchannel414 and in communication withchannel4140. In one aspect, the invention contemplates that a pressure difference between a pressure measured in first flow region and a pressure measured insecond flow region1030 will be similar at all points around the chamber. The consistent pressure difference contributes to a uniform flow of gas through the chamber and a more uniform film deposition on a wafer. By operating in ranges of chamber pressure greater than 100 Torr, the process offers greater flexibility in deposition rate and a reduction in temperature sensitivity across the wafer than prior processes operating in ranges of less than 100 Torr. The reduction in temperature sensitivity yields a more uniform film deposition across a wafer than prior art processes.
• Referring to the drawings, a low pressure chemical vapor deposition (LPCVD) chamber is described. FIGS.[0085]1-3 show cross-sectional views of one type or reactor such as a resistive reactor used to practice the invention. FIGS.1-3 each show cross-sectional views of a chamber through two different cross-sections, each cross-section representing a view through approximately one-half of the chamber.
• The LCVD chamber illustrated in FIGS.[0086]1-3 is constructed of materials such that, in this embodiment, a pressure of greater than or equal to 100 Torr can be maintained. For the purpose of illustration, a chamber of approximately in the range of eight liters is described. FIG. 1 illustrates the inside ofprocess chamber body45 in a “wafer-process” position. FIG. 2 shows the same view of the chamber in a “wafer-separate” position. FIG. 3 shows the same cross-sectional side view of the chamber in a “wafer-load” position. In each case, a wafer is indicated in dashed lines to indicate its location in the chamber.
• FIGS.[0087]1-3show chamber body45 that defines reaction chamber90 in which the reaction between a process gas or gases and the wafer takes place (e.g., a CVD reaction).Chamber body45 is constructed, in one embodiment, of aluminum and haspassages55 for water to be pumped therethrough to cool chamber body45 (e.g., a “cold-wall” reaction chamber). Resident in chamber90 isresistive heater80 including, in this view,susceptor5 supported byshaft65.Susceptor5 has a surface area sufficient to support a substrate such as a semiconductor wafer (shown in dashed lines).
• Process gas enters otherwise sealed chamber[0088]90 throughgas distribution port20 in a top surface ofchamber lid30 ofchamber body45. The process gas then goes throughblocker plate24 to distribute the gas about an area consistent with the surface area of a wafer. Thereafter, the process gas is distributed throughperforated face plate25 located, in this view, aboveresistive heater80 and coupled tochamber lid30 inside chamber90. One objective of the combination ofblocker plate24 withface plate25 in this embodiment is to create a uniform distribution of process gas at the substrate, e.g., wafer.
• A substrate such as a wafer is placed in chamber[0089]90 onsusceptor5 ofheater80 throughentry port40 in a side portion ofchamber body45. To accommodate a wafer for processing,heater80 is lowered so that the surface ofsusceptor5 is belowentry port40 as shown in FIG. 3. Typically by a robotic transfer mechanism, a wafer is loaded by way of, for example, a transfer blade into chamber90 onto the superior surface ofsusceptor5. Once loaded,entry port40 is sealed andheater80 is advanced in a superior (e.g., upward) direction towardface place25 bylifter assembly60 that is, for example, a step motor. The advancement stops when the wafer is a short distance (e.g., 400-700 mils) from face plate25 (see FIG. 1). In the wafer-process position, chamber90 is effectively divided into two zones, a first zone above the superior surface ofsusceptor5 and a second zone below the inferior surface ofsusceptor5. It is generally desirable to confine the film formation to the first zone.
• At this point, process gas controlled by a gas panel flows into chamber[0090]90 throughgas distribution port20, throughblocker plate24 andperforated face plate25. Process gas typically reacts or contacts a wafer to form a film on the wafer. At the same time, an inert bottom-purge gas, e.g., nitrogen, is introduced into the second chamber zone to inhibit film formation in that zone. In a pressure controlled system, the pressure in chamber90 is established and maintained by a pressure regulator or regulators coupled to chamber90. In one embodiment, for example, the pressure is established and maintained by baretone pressure regulator(s) coupled tochamber body45 as known in the art. In this embodiment, the baretone pressure regulator(s) maintains pressure at a level of equal to or greater than 100 Torr. A suitable mid-level pressure range is approximately 100-300 Torr.
• Residual process gas is pumped from chamber[0091]90 through pumpingplate85 to a collection vessel at a side of chamber body45 (vacuum pump-out31). Pumpingplate85 creates two flow regions resulting in gas flow pattern that creates a uniform Si₃N₄layer on a substrate.
• [0092]Pump32 disposed exterior to apparatus2 provides vacuum pressure within pumping channel4140 (belowchannel414 in FIGS.1-3) to draw both the process and purge gases out of the chamber90 through vacuum pump-out31. The gas is discharged from chamber90 along adischarge conduit33. The flow rate of the discharged gas throughchannel4140 is preferably controlled by athrottle valve34 disposed alongconduit33. The pressure within processing chamber90 is monitored with sensors (not shown) and controlled by varying the cross-sectional area ofconduit33 withthrottle valve34. Preferably, a controller or processor receives signals from the sensors that indicate the chamber pressure and adjuststhrottle valve34 accordingly to maintain the desired pressure within chamber90. A suitable throttle valve for use with the present invention is described in U.S. Pat. No. 5,000,225 issued to Murdoch and assigned to Applied Materials, Inc., the complete disclosure of which is incorporated herein by reference.
• Once wafer processing is complete, chamber[0093]90 may be purged, for example, with an inert gas, such as nitrogen. After processing and purging,heater80 is advanced in an inferior direction (e.g., lowered) bylifter assembly60 to the position shown in FIG. 2. Asheater80 is moved, lift pins95, having an end extending through openings or throughbores in a surface ofsusceptor5 and a second end extending in a cantilevered fashion from an inferior (e.g., lower) surface ofsusceptor5, contactlift plate75 positioned at the base of chamber90. As is illustrated in FIG. 2, in one embodiment, at this point,lift plate75 remains at a wafer-process position (i.e., the same position the plate was in FIG. 1). Asheater80 continues to move in an inferior direction through the action oflifter assembly60, lift pins95 remain stationary and ultimately extend above the superior or top surface ofsusceptor5 to separate a processed wafer from the surface ofsusceptor5. The surface ofsusceptor5 is moved to a position belowopening40.
• Once a processed wafer is separated from the surface of[0094]susceptor5,transfer blade41 of a robotic mechanism is inserted through opening40 beneath the heads of lift pins95 and a wafer supported by the lift pins. Next,lifter assembly60 inferiorly moves (e.g., lowers)heater80 andlift plate75 to a “wafer load” position. By movinglift plate75 in an inferior direction, lift pins95 are also moved in an inferior direction, until the surface of the processed wafer contacts the transfer blade. The processed wafer is then removed throughentry port40 by, for example, a robotic transfer mechanism that removes the wafer and transfers the wafer to the next processing step. A second wafer may then be loaded into chamber90. The steps described above are generally reversed to bring the wafer into a process position. A detailed description of onesuitable lifter assembly60 is described in U.S. Pat. No. 5,772,773, assigned to Applied Materials, Inc., of Santa Clara, Calif.
• In a high temperature operation, such as LPCVD processing to form a Si[0095]₃N₄film, the reaction temperature inside chamber90 can be as high as 750° C. or more. Accordingly, the exposed components in chamber90 must be compatible with such high temperature processing. Such materials should also be compatible with the process gases and other chemicals, such as cleaning chemicals (e.g., NF₃) that may be introduced into chamber90. Exposed surfaces ofheater80 may be comprised of a variety of materials provided that the materials are compatible with the process. For example,susceptor5 andshaft65 ofheater80 may be comprised of high thermally conductive aluminum nitride material (on the order of 95% purity with a thermal conductivity from 140 W/mK to 200 W/mK) whileshaft65 is comprised of a lower thermally conductive aluminum nitride.Susceptor5 ofheater80 is typically bonded toshaft65 through diffusion bonding or brazing as such coupling will similarly withstand the environment of chamber90.
• FIG. 1 also shows a cross-section of a portion of[0096]heater80, including a cross-section of the body ofsusceptor5 and a cross-section ofshaft65. In this illustration, FIG. 1 shows the body ofsusceptor5 having two heating elements formed therein,first heating element50 andsecond heating element57. Each heating element (e.g.,heating element50 and heating element57) is made of a material with thermal expansion properties similar to the material of the susceptor. A suitable material includes molybdenum (Mo). Each heating element includes a thin layer of molybdenum material in a coiled configuration.
• In FIG. 1,[0097]second heating element57 is formed in a plane of the body ofsusceptor5 that is located inferior (relative to the surface of susceptor in the figure) tofirst heating element50.First heating element50 andsecond heating element57 are separately coupled to power terminals. The power terminals extend in an inferior direction as conductive leads through a longitudinally extending opening throughshaft65 to a power source that supplies the requisite energy to heat the surface ofsusceptor5. Extending through openings in chamber lid are two pyrometers, first pyrometer10 and second pyrometer15. Each pyrometer provides data about the temperature at the surface of susceptor5 (or at the surface of a wafer on susceptor5). Also of note in the cross-section ofheater80 as shown in FIG. 1 is the presence ofthermocouple70.Thermocouple70 extends through the longitudinally extending opening throughshaft65 to a point just below the superior or top surface ofsusceptor5.
• In accordance with one embodiment of the invention to form a Si[0098]₃N₄film on a wafer, the gases include a carrier gas200), anitrogen source gas220, and asilicon source gas210. Suitable carrier gas sources include, but are not limited to, hydrogen (H₂), nitrogen (N₂), argon (Ar), and helium (He). Suitable nitrogen source gas includes, but is not limited to, ammonia (NH₃). Suitable silicon source gas includes, but is not limited to, silane, dichlorosilane, and disilene. The nitrogen source gas and the silicon source gas combine to produce a Si₃N₄layer on the wafer.
• In use,[0099]silicon source gas210 may be mixed withcarrier gas200 before or during introduction into the processing chamber90. The mixture of the carrier gas and the silicon source gas is then introduced intogas inlet20 of chamber90.Nitrogen source gas220 is also introduced intogas inlet20 and allowed to mix with the mixture of the carrier gas and the silicon source gas. The process gas passes through the plurality of holes in ablocker plate24 and then through the plurality of holes in theface plate25. These gases then flow into chamber90 wherein the gases are exposed to a wafer. Thereafter, the process gas exits through the pumpingplate85 into the pumpingchannel414.
• The flow rate of the gases is dependent upon the size of semiconductor processing chamber[0100]90. In one embodiment, the total flow rate of the gases ranges from five to fifteen liters per minute based upon a total effective volume of a processing chamber of one to nine liters. The ratio of at least one of the gases or the total gas flow rate relative to the chamber is 0.50 to 8 liters per minute per liter of chamber volume.
• Exposure of the wafer to the mixture of gases causes deposition of a silicon nitride (Si[0101]₃N₄) layer on the wafer according to thermal chemical vapor deposition principles. Exposure of the gases to the wafer at an elevated temperature causes dissociation of the molecules of the silicon source gas and the nitrogen source gas into smaller molecules. The smaller molecules then recombine with one another. Provided below is a general chemical reaction that occurs in this process. Silane generally reacts with ammonia according to the chemical equation
• 3SiH₄+4NH₃−>Si₃N₄+12H₂
• As a general rule, the higher the temperature in chamber[0102]90, and therefore of wafer and susceptor, the quicker the silicon nitride layer will form.
• In one embodiment, SiH[0103]₄, NH₃, and N₂are introduced with 100 standard cubic centimeters per minute (sccm) of SiH₄, 5 standard liters per minute (slm) of NH₃, and 10 slm of N₂, while wafer is heated to a temperature of between 600° C. and 800° C. During deposition, pressure in the chamber of between 100 to 500 Torr is maintained. A suitable mid-level pressure range is greater than 100 Torr to 350 Torr. In one embodiment, the partial pressure of silane is approximately in the range of 0.05 to 5 Torr and ammonia has a partial pressure equal to or less than 300 Torr in chamber. However, other partial pressures may be used for the silicon and nitrogen source gases which may depend upon the particular gas used.
• In another embodiment, gases may be used in the following proportions: SiH[0104]₄: 70 sccm, NH₃: 2 slm, and N₂: 8 slm. In yet another embodiment, gases may be used in the following proportions: dichlorosilane (SiH₂Cl₂): 230 sccm, NH₃: 1,000 sccm, and H₂: 9,000 sccm. If N₂is used as a carrier gas, a deposition rate of about 50 to 5,000 Å per minute may be achieved at a temperature as low as 600° C.
• The above embodiment described controlling conditions in a reaction chamber to form a Si[0105]₃N₄film on a wafer. It is to be appreciated that such control may be done manually or with the aid of a system controller. In the former instance, an operator may monitor and adjust the power supply to the heater to control the temperature, and a vacuum source to control the pressures. The operator may also manually adjust valves associated with the individual gases to regulate the mixture and flow rate of the gases.
• A system controller may also be employed to handle the control tasks associated with system control. FIG. 1 illustrates a system controller or processor coupled to a power supply and a gas manifold. The controller may be configured to record the temperature measured by the temperature indicators and control the power supplied to the heating elements based, for example, on an algorithm that determines a relative value of the temperature difference and adjusts the heating elements accordingly. The controller may also be configured to control the mixture and flow of gases to the processing chamber. In an LPCVD reaction process, the controller may further be coupled to a pressure indicator that measures the pressure in the chamber as well as a vacuum source to adjust the pressure in the chamber.[0106]
• The system controller is supplied with control signal generation logic. The controller may also be coupled to a user interface that allows an operator to enter the reaction parameters, such as the desired reaction temperature, the acceptable tolerance of a temperature difference between indicators (e.g., ±3° C.), the reaction pressure, and the flow of gases to the processing chamber.[0107]
• Control signal generation logic is supplied to the system controller in the form of, for example, software instruction logic that is a computer program stored in a computer-readable medium such as the memory of the controller. The computer program includes sets of instructions that dictate the timing, mixture of gases, chamber pressure, chamber temperature, and other parameters of a particular process. It is to be place appreciated that other computer programs such as one stored on another memory device, including but not limited to, a floppy disk, may also be used to operate the system, controller.[0108]
• The computer program code can be written in a computer-readable programming language such as, for examples 68000 assembly language, C, C++, Pascal, Fortran or others. Suitable program code is generally entered into a single file or multiple files using a text editor. If the entered code text is in a high level language, the cede is compiled, and the resultant compiler code is then linked with an object code or precompiled object code, the system invokes the object code causing the computer system to load the code in memory, from which the central processing unlit reads and executes the code to perform the task identified in the program.[0109]
• In one aspect of the invention, an apparatus and method of improving the uniformity of process/reactant gas distribution is described. As described above, process gas such as a silicon source gas and a nitrogen source gas (along with a carrier gas) is introduced into chamber[0110]90 throughgas distribution port20. The process gas flows throughblocker plate24 andface plate25 which create a shower-head like cascade of the process gas over a surface of a wafer on the surface ofsusceptor5. As gas is introduced into chamber90 gas is also removed so that a pre-determined pressure may be maintained during processing. In the configuration of the chamber shown in FIGS.1-3, gas is removed from a side of the chamber, e.g., pumped out at one side designated vacuum pump-out31. In prior art systems, the asymmetrical removal of gases from one side of the chamber created pressure differences in the chamber; for example, a pressure measured at a point in the chamber nearer a chamber pump-out was different (e.g., less) than a pressure measured at a point distant from the pump-out. The pressure difference contributed to non-uniformity of deposition of a film on a wafer.
• In one embodiment of the invention, a pumping plate is provided to direct the flow of gases in the chamber. The pumping plate of the invention defines two gas flow regions: a first flow region of process gases directed at a wafer on the surface of[0111]susceptor5 and a second flow region defined by a radial channel about the pumping plate of gases primarily to be discharged from the chamber. By creating the two regions, a more uniform pressure may be maintained in the chamber. The invention contemplates that a static pressure difference between the two flow regions can be established throughout the chamber contributing to more uniform deposition of films across a wafer.
• Referring to FIGS. 4 through 10, components of the invention utilized to coordinate a uniform flow of process gas in the chamber will now be described in detail relative to their use in the resistively-heated processing chamber described in FIGS. 1 through 3. FIG. 4 shows a schematic cross-sectional side view of a portion of a processing chamber. FIG. 4 illustrates a portion of a chamber in a position through a single cross-section to illustrate the two gas flow regions. The cross-section is through a center axis of the chamber to illustrate the location of[0112]susceptor5 relative to pumpingplate85. In the wafer-process position, a portion ofsusceptor5 sits within an annular opening of pumping plate85 (a portion of pumpingplate85 surroundingsusceptor5 is cut-away in this cross-section).
• As seen in the illustration of FIG. 4, pumping[0113]plate85 rests oninner chamber portion41 ofchamber wall45. An underside of pumpingplate85 andinner chamber portion41 defineschannel4140 extending circumferentially around the chamber.Channel4140 does not extend completely around the chamber as a portion of a similar chamber area is utilized byentry port40 to load and remove a wafer. In one embodiment,channel4140 extend approximately 270° around the chamber. Vacuum pump-out31 is linked tochannel4140 to discharge gases from the chamber.
• As shown in FIG. 4, pumping[0114]plate25 includes (in this view) a vertical annular first steppedportion464 that forms a circumferential edge of a longitudinal or vertical wall to faceplate25. Second steppedportion466 comprises a lateral portion that protrudes from the circumferential edge. Together, first steppedportion464 and second steppedportion466 definechannel414 betweenface plate25,chamber wall40 and pumpingplate85. The vertical wall separatesfirst flow region1000 where process gas is directed at a wafer (to be seated inwafer pocket6 of susceptor5) fromsecond region1010 where gas is discharged from the chamber. Gas fromfirst flow region1000 enterssecond flow region1010 through circumferentially located holes (gas holes490) extending aroundfirst portion464 of pumpingplate85. The flow of gas insecond flow region1010 is radially andsecond flow region1010 communicates withchannel4140 to remove gas from the chamber.
• FIGS. 5 and 6 show schematic views of the general flow direction of process gases through the chamber. FIG. 5 is a cross-section through the chamber that shows pumping[0115]plate85 surrounding a portion ofsusceptor5. In FIG. 5, process gas is illustrated entering through the gas inlet of the chamber and passing through blockingplate24 andface plate25. Infirst flow region1000, process gas arrives at the surface ofsusceptor5 to react with a wafer inpocket6 ofsusceptor5 and form a film of, for example, Si₃N₄or other desired material (e.g., SiO₂, polysilicon, etc.). Residual process gas as well asbottom purge gas1030 is directed tosecond flow region1010 to be discharged from the chamber. Gas enterssecond flow region1010 bygas holes490 circumferentially spaced around pumpingplate85. In this embodiment, the gas holes490 are positioned to be above the top surface of awafer oil susceptor5 during processing. In general, gas holes490 are positioned it least at the level of a wafer or above the wafer when the heater is in the “wafer process” position.
• FIG. 6 further shows the process flow of gas entering and exiting[0116]pumping plate85. FIG. 6 is a top perspective view without the resistive heater, the chamber lid, blocking plate, and face plate. FIG. 6 shows generallyU-shaped pumping channel414 that substantially surrounds a susceptor and definessecond flow region1010. Radially oriented gas holes490 are positioned around the entire perimeter of the pumping plate and communicate with pumpingchannel414. Gas holes490 in the side wall of pumpingplate85 allow gas to now horizontally into pumpingchannel414.Pumping channel414 communicates withchannel4140 through two large openings inchannel414; openings defined by the absence of sections of lateral second steppedportion466 of pumpingplate85. Second steppedportion466 is comprised of two flange portions (see FIG. 7). One flange portion isolateschannel414 fromentry port40 while a second flange portion separateschannel414 from a region ofchannel4140 occupied by vacuum pump-out31. Configuring the flange portions in this manner helps to maintain a uniform pressure inchannel414.
• Gas holes[0117]490 in first steppedportion464 of pumpingplate85 are shown in FIG. 6 substantially evenly spaced apart from one another. Additionally, the gas holes are generally centered in first steppedportion464 of pumpingplate85. The placement of gas holes498 in the side wall of pumpingplate85 and the division offirst flow region1000 andsecond flow region1010 creates a consistent pressure difference betweenfirst flow region1000 andsecond flow region1010. This feature allows the gas flow within the chamber to the more uniform than prior art configurations. In the prior art, a pumping plate had varying pressure differentials at various points along the pumping plate which resulted in non-uniform gas flow regions.
• FIGS.[0118]7-12 illustrate different views of an embodiment, or a portion of an embodiment, of a pumping plate of the invention. FIG. 7 illustrates a perspective top view, FIG. 8 a planar side view, FIG. 9 a planar top view, and FIG. 10 a planar bottom view. FIGS.11-12 show portions of the pumping plate to more clearly describe certain features.
• Pumping[0119]plate85 comprises generallyannular member460. In one embodiment,member460 is an integral piece comprising a process compatible metal, such as aluminum alloy or preferably C275 aluminum alloy, that will be suitably shaped to fit within a particular semiconductor processing chamber. C275 aluminum alloy is commercially available from Alcoa Advanced Technologies of Engelwood, Colo. Althoughmember460 is preferably constructed of a single integral piece of metal with different portions ofmember460, the pumpingplate85 may be comprised of pieces connected or coupled together.
• In the specific configuration described herein,[0120]member460 includes first steppedportion464, second steppedportion466, and third steppedportion468. First steppedportion464 forms a vertical side wall to definechannel414 and separatesecond flow region1010 fromfirst flow region1000. Second steppedportion466 defines the lateral portion or floor of pumpingchannel414. Third steppedportion468 serves to align pumpingplate85 in a predetermined position within a processing chamber.
• In the eight liter processing chamber described with reference to FIGS.[0121]1-3, the thickness of first steppedportion468 ranges from approximately 0.06 inches to 0.10 inches and is preferably 0.06 inches. With reference to FIGS.8-9, inner diameter ID₁₀of second steppedportion466 is, for example, 9.572 inches, and the outer diameter OD₁₀is, for example, 11.25 inches. Inner diameter ID₁₀of second steppedportion466 is slightly larger than the diameter ofsusceptor5 so thatsusceptor5 will fit within the opening inannular member460 of pumpingplate85. In one embodiment, there is approximately 0.12 to 0.18 inches spacing betweensusceptor5 and second steppedportion466. ID₂₀of first steppedportion464 is 10.4 inches. OD₂₀of first steppedportion464 is 10.9 inches. As shown in FIG. 11, height488 of pumpingplate85 in this embodiment is 1.20 inches. The distance betweenbase489 of the pumping plate (the base of third stepped portion468) and the central point ofgas hole490 extending through the first steppedportion464 is 0.728 inches.
• Second stepped[0122]portion466 comprises two flange portions which extend the outside diameter from OD₁₀to OD₁₁. OD₁₁ranges from a diameter of 12.93 inches. Each flange portion has an area in proportion to an arc defined between two radii of first and second portion ofannular member460, respectively. FIG. 9 shows each flange with a bi-section having an area in proportion to an arc of 55°.
• The flange portions of second stepped portion[0123]466 (i.e., the lateral positions) define the base ofchannel414 andsecond flow region1010. Between each flange portion are provided openings tochannel4140 and vacuum pump-out31. In one embodiment, an area between flange portions is in proportion to an arc of 70°.
• As illustrated by the bottom plan view of FIG. 10, third stepped portion creates a seat for pumping[0124]plate85 to rest oninner chamber portion41. In this embodiment, third steppedportion468 includes a single lip portion coinciding with an area similar to an area of one of the flange portions of second steppedportion466. The lip portion serves, in one aspect, to orient pumpingplate85 in the chamber.
• The diameters of the first, second, and third stepped portions of the pumping plate will depend on the characteristics of the individual deposition apparatus, such as the diameter of the perforated[0125]face plate25, the radial distance between pumpingchannel414 and chamber90, the height of susceptor5 (i.e., the axial distance betweenchannel414 and chamber90), and the diameter of thesusceptor5.
• Pumping[0126]plate85 comprises a plurality ofgas holes490 through the side wall of first steppedportion464 that communicatefirst flow region1000 withchannel414 andsecond flow region1010. In one embodiment, forty-eightgas holes490 are located in pumpingplate85. As shown in particular in FIGS.7-8, gas holes490 are circumferentially spaced aroundannular opening462 ofbody member460 to facilitate uniform discharge of process gas through gas holes490. In one configuration, onegas hole490 is spaced a distance of 7.5° from anothergas hole490. FIG. 11 shows a magnified side plan view of a portion of pumpingplate85. FIG. 12 shows a its magnified plan view of one gas hole. FIG. 12 showsgas holes490 having concave sidewalls so that theirouter diameter496 is larger than theirinner diameter494 at both the inlet and the outlet of the gas hole. The concave sidewalls are preferably smooth to reduce the creation of turbulence of the gas that might contribute to non-uniform gas flow. The concave shape ofgas holes490 also serves to restrict the flow through each particular gas hole which contributes to increased uniformity of flow through all of the gas holes. As seen in FIGS.11-12, gas holes490 extend substantially straight through pumpingplate85. In one embodiment, gas holes490 have a diameter approximately in the range of 0.120 to 0.130 inches and more preferably in the range of 0.122 to 0.125 inches.
• Process gas enters the processing chamber through relatively narrow gas distribution port[0127]20 (FIGS.1-3). To distribute the process gas evenly, the processing chamber of the invention is equipped withblocker plate24 andface plate25. FIG. 13 shows a top plan view ofblocker plate24.Blocker plate24 is substantially circular in shape and is coupled tochamber lid30 through the circumferentially-arranged fastening holes.Blocker plate24 has throughholes23 forcoupling blocker plate24 toperforated face plate25. In an embodiment suitable for the eight liter processing chamber described with reference to FIGS.1-3,blocker plate24 has approximately1,122 throughholes23 having a diameter in the range of 0.110 inches to 0.020 inches and preferably in the range of 0.014 inches to 0.016 inches. Throughholes23 are arranged, in this embodiment, in a generally circular pattern.Blocker plate24 has a thickness approximately in the range of 0.180 to approximately 0.190 inches. Preferably, the thickness ofblocker plate24 is 0.185 inches.Blocker plate24 assists in creating a uniform flow of gas inchamber body45 by spreading the relatively narrow stream of process gas throughgas distribution port20 over the area ofblocker plate24.
• FIGS.[0128]14-15 show a top and side plan view, respectively offace plate25. FIG. 16 shows a cross-sectional side plan view of a portion offace plate25.Face plate25 is circular in shape.Face plate25 serves in one aspect to assist in the uniform distribution of process gas over a wafer. Process gas already redistributed to the circumferential area ofblocker plate24 is further restricted as the gas contacts faceplate25. In one embodiment, through holes inface plate25 have a similar diameter as through holes inblocker plate24.
• [0129]Face plate25 is substantially circular in shape and is coupled tochamber lid30 through circumferentially-arranged fastening holes26. Thoughholes27 in the central portion of theface plate25 extend throughface plate25. In the embodiment of an eight liter processing chamber described above, the inner diameter of a perforated face plate may range from approximately 9.10 to 9.30 inches and an outer diameter that may range from approximately 10.7 to 10.10 inches ofperforated face plate25.Face plate25 includes two stepped portions. A thickness ofexterior portion31 to coupleface plate25 to a chamber is approximately 0.800 inches while theinner portion32 having throughholes27 is approximately 0.400 inches.
• In one embodiment, though[0130]holes27 in the inlet side ofperforated face plate25 have a larger diameter than the outlet side where the process gas enters the reaction portion of the chamber. One reason for this is mechanical constraints of forming appropriate diameter through holes in the material, e.g., damaging drill bits. FIG. 16 shows the difference in diameters between the inlets and outlets of throughholes27 inperforated face plate25.Inlet28A to each through hole (gas inlets are located at the superior side ofperforated face plate25 adjacent to blocker plate24) has a diameter of about 0.62 inches which is larger than outlet diameter29B of 0.016 inches. The depth of the gas hole is approximately 0.400 inches. The smaller diameter opening has a length (numerically represented by reference numeral29) of approximately 0.030 inches.
• The method for processing a semiconductor wafer according to the invention will now be described. Wafer is first positioned onto the upper surface of[0131]susceptor5 with a support blade (not shown) of the robotic wafer transfer system.Susceptor5 is raised into the upper processing position withinprocess chamber45 via conventional means, such as a hydraulic lift, so that wafer resides within central opening ofplate85.Chamber45 is then evacuated to a suitable vacuum pressure, while the wafer andsusceptor5 are suitably heated. Process gases, such as SiH₄and NH₃, are mixed in a chamber of a manifold head (not shown) and introduced throughinlet20 throughblocker plate24 and distributed uniformly over wafer viaperforated face plate25. Depending on the particular process, the process gas will contact tie wafer and form a film, such as an oxide or nitride film.
• During the deposition process, pump[0132]32 is activated to generate vacuum pressure within pumpingchannel414, thereby drawing the process gases and/or plasma residue out of processing chamber90 throughgas holes490 of pumpingplate85. In addition, purge gas (bottom purge gas)1030 such as nitrogen may be directed through inlet18 and into processing chamber90 through the gap between susceptor and pumpingplate85. The purge gas minimizes leakage of process gas into the lower portion of the chamber. The residual gas an purge gas flow uniformly intogas holes490 and into pumpingchannel414. The exiting gases are discharged through vacuum pump-out31 and discharged alongline33.
• Pumping[0133]plate85 separates the gas flow into two flow regions: afirst flow region1000 directed at the surface of susceptor5 (or a wafer on susceptor5) and asecond flow region1010 inchannel414 and in communication withchannel4140. In one aspect, the invention contemplates that a pressure difference between a pressure measured in first flow region and a pressure measured insecond flow region1030 will be similar at all points around the chamber. The consistent pressure difference contributes to a uniform flow of gas through the chamber and a more uniform film deposition on a wafer. By operating in ranges of chamber pressure greater than 100 Torr, the process offers greater flexibility in deposition rate and a reduction in temperature sensitivity across the wafer than prior processes operating in ranges of less than 100 Torr. The reduction in temperature sensitivity yields a more uniform film deposition across a wafer than prior art processes.
• FIG. 17 illustrates an example of a radiantly-heated processing chamber. Although heretofore such chambers have been used at process pressures less than or approaching 100 Torr, their use may also be suitable for higher pressure processes. Design considerations for operating at pressures, greater than 100 Torr are to be contemplated. The[0134]single substrate reactor131 includestop wall132,sidewalls133 andbottom wall134 that defines thereactor131 into which a single substrate, such as a wafer, can be loaded. The wafer is mounted onsusceptor105 that is rotated bymotor137 to provide a time averaged environment for the wafer that is cylindrically symmetric. Preheatring140 is supported in thechamber130 and surrounds the wafer. The wafer andpreheat ring140 are heated by light from a plurality ofhigh intensity lamps138 and139 mounted outside ofreactor131.Top wall132 andbottom wall134 ofchamber130 are substantially transparent to light to enable the light fromexternal lamps138 and139 to enterreactor131 andheat susceptor105, the wafer, andpreheat ring140. Quartz is a useful material fortop wall132 andbottom wall134 because it is transparent to light of visible and infrared (IR) frequencies; it is a relatively high strength material that can support a large pressure difference across these walls; and because it has a low rate of outgassing.
• During deposition, the reactant gas stream flows front gas input port across preheat[0135]ring140 where the reactant gases are heated, across the surface of the wafer in the direction of thearrows141 to deposit the desired films thereon, and intoexhaust port311. The gas input port is connected to a gas manifold (not shown) that provides one or a mixture of gases to enterreactor131 via a plurality of pipes into this port. The locations of the input ends of these pipes, the gas concentrations, and/or flow rates through each of these pipes are selected to produce reactant gas flows and concentration profiles that optimize processing uniformity. Although the rotation of the substrate and thermal gradients caused by the heat fromlamps138 and139 can affect the flow profile of the gases, inreactor131, the dominant shape of the flow profile is a laminar flow from the gas input port and across preheatring140 and the wafer to exhaustport311. In one embodiment, the temperature of the wafer may range from approximately 600° C. to approximately 800° C. The pressure in the chamber may range from approximately 100 to approximately 500 Torr, with a suitable mid-level pressure range of greater than 100 Torr to 350 Torr. Again, it is to be appreciated that higher pressures (e.g., approaching 500 Torr) contribute to deposition rate flexibility and reduced temperature sensitivity across the wafer.
• FIG. 18 is a block[0136]diagram illustrating system100 for carrying out a method according to the invention in a radiantly-heated processing chamber such as described with respect to FIG. 17.System100 includesgas manifold120, processingchamber250housing susceptor160, andsystem180 for heating the confines ofsemiconductor processing chamber250, and, in this example, a radiant heat system.Processing chamber250 has a slit (not shown) through which substrate (e.g., wafer)260 is insertable intoprocessing chamber250 and then located onsusceptor160. A portion ofprocessing chamber250 may be made of transparent material such as quartz or the like.
• [0137]System180 for heating the confines ofsemiconductor processing chamber250 includesheat lamps240A,240B,240C, and240D located above and below theprocessing chamber250 and positioned to direct light energy intosemiconductor processing chamber250,temperature detector300, such as a pyrometer or thermal camera, that measures a temperature withinprocessing chamber250, andcontroller280.
• [0138]Temperature detector300 is positioned and aligned to detect a temperature on a lower surface of the susceptor.Temperature detector300 sends a signal tocontroller280 which is indicative of the temperature measured onsusceptor160.Controller280 is connected topower supply290.Controller280 adjusts power supplied bypower supply290 torespective heat lamps240A,240B,240C,240D depending on the temperature measured bytemperature detector300. For example, if the measured temperature drops too low, power supplied toheat lamps240A,240B,240C,240D would be increased. Power supplied to therespective heat lamps240A,240B.240C, or240D may be selected differently from one another.
• [0139]Gas manifold120 is capable of supplying multiple gases (e.g., three) to theprocessing chamber250. In this example, the gases includecarrier gas200,nitrogen source gas220, andsilicon source gas210. Suitable carrier gas sources include but are not limited to hydrogen (H₂), nitrogen (N₂), argon (Ar), and helium (He). Suitable nitrogen source gas includes but is not limited to ammonia (NH₃). Suitable silicon source gas includes but is not limited to silane, dichlorosilane, and disilene. The nitrogen source gas and the silicon source gas combine to produce a Si₃N₄layer on thewafer260.
• In use,[0140]silicon source gas210 may be mixed withcarrier gas200 before or during introduction intoprocessing chamber250. The mixture of the carrier gas and the silicon source gas is then introduced into a base ring (not shown) ofsemiconductor processing chamber250.Nitrogen source gas220 is also introduced into the base ring and allowed to mix with the mixture of the carrier gas and the silicon source gas. These gases flow into thesemiconductor processing chamber250 wherein the gases are exposed towafer260. The flow rate of the gases is dependent upon the size ofprocessing chamber250. In one embodiment, the total flow rate of the gases ranges from five to fifteen liters per minute based upon a total effective volume of a processing chamber of one to nine liters. The ratio of at least one of the gases or the total gas flow rate relative to the chamber is 0.7 to 5 liters per minute per liter. Exposure of the wafer to the mixture of gases causes deposition of a silicon nitride (Si₃N₄) layer onwafer260 according to thermal chemical vapor deposition principles. The wafer is heated bylamps240A and240B and by thesusceptor160.Lamps240C and240D also may be used for generating heat in the chamber. Exposure of the gases to the wafer at an elevated temperature causes dissociation of the molecules of the silicon source gas and the nitrogen source gas into smaller molecules. The smaller molecules then recombine with one another.
• In one embodiment, SiH[0141]₄, NH₃, and N₂are introduced with 100 standard cubic centimeters per minute (sccm) of SiH₄, 5 standard liters per minute (slm) of NH₃, and 10 slm of N₂, whilewafer260 is heated to a temperature of between 600° C. and 800° C. During deposition, pressure in the chamber of between 100 to 500 Torr is maintained. In another embodiment, gases may be used in the following proportions: SiH₄: 70 sccm, NH₃: 2 slm, and N₂: 8 slm. In yet another embodiment, gases may be used in the following proportions: dichlorosilane: 230 sccm, NH₃: 1,000 sccm, and H₂: 9,000 sccm. If N₂is used as a carrier gas, a deposition rate of about 50 to 5,000 Å per minute may be achieved at a temperature as low as 600° C.
• By using higher pressure (e.g., greater than 100 Torr) in the processing chamber described above, lower temperatures in the chamber may be used. Low temperature deposition is desirable for a number of reasons. For example, lower temperature deposition decreases the risk of outdiffusion of dopants in P or N doped regions of the wafer. Outdiffusion of the P or N doped regions may cause breakdown in the operation of electrical elements such as a transistor, to prevent or reduce outdiffusion of dopants from doped regions that are less than 0.25 μm apart, a pressure range of 100-500 Torr is preferable.[0142]
• FIG. 19 is a thickness map of the thin silicon nitride film deposited on a wafer in accordance with a first example set forth in Table 1. Forty-nine points were measured for the thickness map shown in FIG. 18. Using an ellipsometer, the average thickness was 1004.6 Å with a 1% degree of accuracy indicating excellent uniformity of the film and a deposition rate of about 2.000 Å/minute.[0143]

  TABLE I
  Deposition Recipe for 1000 Å Si3N4Film

  Step number, name	1, POSITION	2, GAS ON	3, HEATUP
  Chamber Selection	D ALL CLR	D ALL CLR	D ALL CLR
  Step and control	By Time	By Time	By Time
  Maximum step time	5.0 seconds	5.0 seconds	10.0 seconds
  Endpoint selection	No Endpoint	No Endpoint	No Endpoint
  Pressure	Throttle fully open	Throttle fully open	Servo 275.0 Torr
  Heater Temperature	Servo 800°	Servo 800°	Servo 800°
  Heater spacing	550 mils	550 mils	550 mils
  Gas names and flows
  		N2 5000 scc	N2 9800 scc
  BP = Bottom Purge		N2-BP 4000 scc	N2-BP 5000 scc
  Step number, name	4, NH3 PRETREATMENT	5, DEPOSITION	6, PURGE
  Chamber Selection	D ALL CLR	B ALL CLR	D ALL CLR
  Step and control	By Time	By Time	By Time
  Maximum step time	10.0 seconds	29.0 seconds	5.0 seconds
  Endpoint selection	No Endpoint	No Endpoint	No Endpoint
  Pressure	Servo 275.0 Torr	Servo 275.0 Torr	Throttle fully open
  Heater Temperature	Servo 800°	Servo 800°	Servo 800°
  Heater spacing	550 mils	550 mils	550 mils
  Gas names and flows	NH3 3000 scc	NH3 3000 scc
  	N2 7000 scc	N2 7000 scc	N2 5000 scc
  		SIH4 50 scc
  	N2-BP 5000 scc	N2-BP 5000 scc
  Step number, name	7, POSITION
  Chamber Selection	D ALL CLR
  Step and control	By Time
  Maximum step time	5.0 seconds
  Endpoint selection	No Endpoint
  Pressure	Throttle fully open
  Heater Temperature	Servo 800°
  Heater spacing	1600 mils
  Gas names and flows
  	N2  5000 scc

• FIG. 20 is a thickness map of the thin silicon nitride film deposited on the wafer in accordance with a second example set forth in Table II. Again, forty nine points were measured for the thickness map shown in FIG. 20. Using an ellipsometer, the average thickness was 99.72 Å with a 1% degree of accuracy indicating excellent uniformity of the film. The deposition rate was about 300 Å/minute. The measured refractive index of this film indicated that a stoichiometric film was obtained.[0144]

  TABLE II
  Deposition Recipe for 100 Å Si3N4Film

  Step number, name	1, POSITION	2, GAS ON	3, HEATUP
  Chamber Selection	D ALL CLR	D ALL CLR	D ALL CLR
  Step and control	By Time	By Time	By Time
  Maximum step time	5.0 seconds	5.0 seconds	20.0 seconds
  Endpoint selection	No Endpoint	No Endpoint	No Endpoint
  Pressure	Throttle fully open	Throttle fully open	Servo 275.0 Torr
  Heater Temperature	Servo 800°	Servo 800°	Servo 800°
  Heater spacing	550 mils	550 mils	550 mils
  Gas names and flows
  		N2 5000 scc	N2 5000 scc
  BP = Bottom Purge		N2-BP 2000 scc	N2-BP 2000 scc
  Step number, name	4, NH3 PRETREATMENT	5, DEPOSITION	6, PURGE
  Chamber Selection	D ALL CLR	B ALL CLR	D ALL CLR
  Step and control	By Time	By Time	By Time
  Maximum step time	10.0 seconds	19.0 seconds	5.0 seconds
  Endpoint selection	No Endpoint	No Endpoint	No Endpoint
  Pressure	Servo 275.0 Torr	Servo 275.0 Torr	Throttle fully open
  Heater Temperature	Servo 800°	Servo 800°	Servo 800°
  Heater spacing	550 mil	550 mils	550 mils
  Gas names and flows	NH3 500 scc	NH3 500 scc
  	N2 4500 scc	N2 4500 scc	N2 5000 scc
  		S1H4 5 scc
  	N2-BP 2000 scc	N2-BP 2000 scc
  Step number, name	7, POSITION
  Chamber Selection	D ALL CLR
  Step and control	By Time
  Maximum step time	5.0 seconds
  Endpoint selection	No Endpoint
  Pressure	Throttle fully open
  Heater Temperature	Servo 800°
  Heater spacing	1600 mils
  Gas names and flows
  	N2 5000 scc

• The thin silicon nitride films of the invention can be deposited, for example, over silicon substrates, over silicon oxide, or sandwiched between silicon oxide layers, in accordance with standard semiconductor device processing. No particular pretreatment of the substrate prior to silicon nitride deposition is required, although native silicon oxide may be desired to be removed prior to deposition of the silicon nitride film directly onto silicon, whether single crystal silicon or polycrystalline silicon. This may be accomplished by a standard preclean etch process, either in the same chamber employed for the silicon nitride deposition, or in another chamber of a multi-chamber vacuum processing system.[0145]
• Processing parameters can be varied to obtain the desired thickness of the silicon nitride films. The temperature during deposition can be varied from about approximately 600 to approximately 800° C. For example, the deposition rate can be increased by increasing the temperature of deposition up to about 800° C., that may be desirable if thicker films, on the order of about 1000 Å in thickness, are to be deposited at practicable rates in a single substrate processing chamber. The pressure can also be varied to affect a change in the deposition rate: in general, the rate of deposition increases as the pressure increases.[0146]
• The silicon nitride films can he deposited in a stand-alone LPCVD chamber, or, preferably such chamber can be part of a multi-chamber vacuum processing system. In that case the processing chamber of the invention has a port in a sidewall thereof for transferring substrates into and out of the LPCVD chamber from a central transfer chamber.[0147]
• FIG. 21 shows one embodiment of the invention wherein the rate of deposition of silicon nitride on a wafer is shown relative to the wafer temperature, the pressure in the chambers the flow rate of ratio of ammonia gas to silane gas. The pressure in the chamber ranged from approximately 100 Torr to 275 Torr.[0148]
• FIG. 22 shows another embodiment of the invention wherein the pressure in, the chamber is maintained at approximately 100 Torr. As the temperature increases, the deposition rate of silicon nitride generally increases.[0149]
• Although the invention has been described with respect to certain types of substrate processing chamber, variations in equipment and design can he made by one skilled in the art and are meant to he included herein. The invention is only to be limited by the scope of the appended claims[0150]

Claims (26)

What is claimed:

1. A method of depositing a film of silicon nitride comprising:

placing a single substrate in a substrate low pressure chemical vapor deposition chamber;

generating a pressure to from about 100 Torr to about 500 Torr and heating the substrate to a temperature of front about 600° C. to about 800° C., and

providing a gas mixture comprising a silicon source gas and a nitrogen source gas into the chamber.

2. The method ofclaim 1 wherein the gas mixture further includes a carrier gas.

3. The method ofclaim 2 wherein the carrier gas is selected from the group consisting of hydrogen, nitrogen, argon, and helium.

4. The method ofclaim 1 wherein the silicon source gas is selected from the group consisting of silane, disilane and dichlorosilane.

5. The method ofclaim 4 wherein the gas mixture comprises about 230 sccm of dichlorosilane about 1000 sccm of ammonia and about 9000 sccm of hydrogen.

6. The method ofclaim 1 wherein a rate of deposition ranges from approximately 40 Å per minute to about 5,000 Å per minute.

7. The method ofclaim 1, wherein nitrogen source gas is ammonia.

8. The method ofclaim 1, wherein the partial pressure of silane is approximately in the range of 0.05 to 5 Torr.

9. The method ofclaim 1, wherein ammonia has a partial pressure equal to or less than 300 Torr.

10. A method of forming a silicon nitride layer on a semiconductor wafer, comprising the steps of:

locating a semiconductor wafer on a susceptor within a processing chamber;

mixing at least three gases comprising

a carrier gas selected from the group consisting of H₂, N₂, He, and Ar,

a nitrogen source gas, and

a silicon source gas;

introducing the mixture of gases into the semiconductor processing chamber;

exposing the wafer to the mixture; and

maintaining a pressure in the semiconductor processing chamber in the range of 100 to 500 Torr.

11. The method ofclaim 10 wherein the flow rate of at least one of the gases is 5 liters per minute to 15 liters per minute for a semiconductor processing chamber having a volume in the range of 1 to 9 liters.

12. The method ofclaim 10 wherein the ratio of a flow rate of at least one gas to the volume of a semiconductor processing chamber is 0.7 to 5.

13. The method ofclaim 10 wherein at least two of the gases are at least partially mixed within the semiconductor processing chamber.

14. The method ofclaim 10 wherein the nitrogen source gas is NH₃.

15. The method ofclaim 10 wherein the silicon source gas is selected from the group consisting of SiH₄, Si₂H₆, and SiH₂Cl₂.

16. The method ofclaim 10 further comprising heating the wafer to a temperature of between 600° C. and 800° C. prior to exposing the wafer to the mixture of gases.

17. A method of forming a silicon nitride layer on a semiconductor wafer, comprising the steps of:

locating the semiconductor wafer on a susceptor within a semiconductor processing chamber;

mixing at least two gases in the semiconductor processing chamber selected from the group consisting of

a carrier gas,

a NH₃source gas, and

a silicon source gas, a silicon source gas selected from the group consisting of

exposing the semiconductor wafer to the mixture of gases, and

maintaining a pressure in the semiconductor processing chamber in the range of 100 to 500 Torr.

18. The method ofclaim 17 wherein the flow rate of at least one of the gases is in the range of 1 slm to 12 slm.

19. The method ofclaim 17 further comprising heating the wafer to a temperature of between 600° C. and 900° C. prior to exposing the wafer to the mixture of gases.

20. The method ofclaim 17 wherein the nitride layer forms at a rate in the range of between 40 Å per minute and 5,000 Å per minute.

21. The method ofclaim 17 wherein the carrier gas is selected from the carrier gas selected from the group consisting of H₂, N₂, He, and Ar.

22. A method of depositing films of silicon nitride onto a substrate in a chemical vapor deposition chamber, comprising:

(a) supporting a single substrate in the chamber,

(b) adjusting the pressure from about 100 to about 500 Torr and heating the substrate to a temperature from about 600° C. to 800° C.; and

(c) passing a silicon source gas into the chamber.

23. The method ofclaim 22 wherein the nitride layer forms at a rate in the range of between 40 Å per minute and 5,000 Å per minute.

24. The method ofclaim 22 further comprising:

removing a gas from the chamber through a pumping plate, the pumping plate has a first stepped portion, a second stepped portion, and a third stepped portion, wherein the third stepped portion has a plurality of holes circumferentially spaced.

25. An apparatus comprising:

a chamber configured to house a substrate for processing;

a nitrogen source gas coupled to the chamber;

a silicon source gas coupled to the chamber;

a system controller configured to control the introduction of a nitrogen gas from the nitrogen gas source and a silicon gas from the silicon gas source into the chamber;

at least one pump coupled to the chamber, wherein the pump is capable of creating a pressure greater than 100 Torr;

a memory coupled to the controller comprising a computer-readable medium having a computer-readable program embodied therein for directing operation of the system, the computer-readable program comprising instructions for controlling the nitrogen source gas and the silicon source gas and a pressure in the chamber and the instructions comprise parameters for maintaining a pressure in the range of approximately 100 Torr to approximately 500 Torr in the chamber.

26. The apparatus ofclaim 25 further comprising:

a blocker plate coupled to a chamber lid and a perforated face plate wherein the perforated face plate is coupled to a pumping plate;

the pumping plate having a first stepped portion, a second stepped portion, and a third stepped portion, wherein the third stepped portion has a plurality of gas holes and the gas holes are substantially circumferentially spaced; and

the second stepped portion has two flanges wherein the flanges restrict gas flow.

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