US20080083703A1 - Method of plasma processing - Google Patents

Abstract

Plasma processing apparatus and plasma processing methods capable of maintaining etching characteristics and to prevent degradation of a lower electrode even when the focus ring is severely eroded by the plasma are disclosed. According to an exemplary embodiment, a side-surface protecting ring formed of a ceramic material having an erosion rate by the plasma lower than an erosion rate of the material of the focus ring is provided to cover the side surface of the lower electrode. As a result, it becomes possible to prevent the side surface of the lower electrode from being exposed to the plasma and maintain the etching characteristics even after the focus ring is severely eroded. Further, degradation of the lower electrode is decreased.

Description

• This is a Division of application Ser. No. 11/057,164 filed Feb. 15, 2005. The entire disclosure of the prior applications is hereby incorporated by reference herein in its entirety. This invention is first described in a Japanese Application No. 2004-53275, which is incorporated by reference in its entirety.
BACKGROUND
• This invention relates to a plasma processing apparatus for processing a surface of a substrate using plasma and also relates to methods of plasma processing a surface of a substrate.
• Plasma processing techniques, such as, for example, dry etching techniques, have been widely used for manufacturing semiconductor devices such as semiconductor integrated circuits. The plasma processing processes various films formed on a surface of a substrate to be processed, such as a semiconductor wafer, using reactive gases activated by plasma. The dry etching, for example, etches various films and forms fine circuit patterns such as electrode and wiring patterns using resist patterns formed by the lithography as masks.
• In any application of the plasma processing, it is inevitable that the reactive gas activated by the plasma touches and erodes components within the processing chamber. Especially, the processing of silicon oxide films requires high radio frequency power, because the bonding energy of Si—O bonds is high. Accordingly, the processing of silicon oxide films causes severe damage to the components.
• In general, so-called parallel-plate RIE (Reactive Ion Etching) apparatus is mainly used as the dry etching apparatus for processing silicon oxide films. In the parallel-plate RIE apparatus, radio-frequency power is applied to an upper and a lower electrode that face in parallel with each other. In such an apparatus, usually, the wafer to be processed is placed on the lower electrode and the plasma is concentrated between the electrodes to process the surface of the wafer.
• In order to concentrate the plasma between the electrodes, peripheries of the upper and the lower electrodes are surrounded by ring-shaped components formed of, for example, quartz. Hereafter, the ring-shaped components that surrounds the upper electrode will be called “shield ring”, while the ring-shaped component that surround the lower electrode will be called “focus ring”.
• Moreover, in order to improve processing accuracy, an electro-static chuck has been widely employed as the means to hold the wafer on the wafer-supporting surface of the plasma processing apparatus. Compared with a mechanical chuck, the electro-static chuck improves the uniformity of the surface temperature of the wafer and improves the uniformity of the processing.
• Electro-static chucks are generally classified into two types. One is formed of fluorocarbon resin, and the other is formed of ceramics. The dry etching apparatus for processing silicon oxide films mainly utilize the electro-static chuck formed of fluorocarbon resin, in which a conductive film is inserted into a fluorocarbon resin film. A high DC voltage is applied to the conductive film, and the wafer is chucked onto the upper surface of the electro-static chuck by the Coulomb force generated between the wafer and the conductive film.
• FIG. 10 is a partial cross-sectional view showing the periphery of the lower electrode of a plasma processing apparatus. As shown inFIG. 10, theupper surface118aof thelower electrode118 has an electro-static chuck120, which is formed of, for example, afluorocarbon resin film120aand aconductive film120binserted within theresin film120a. Thefluorocarbon resin film120aalso covers theside surface118bof thelower electrode118.
• Afocus ring124 is detachably placed so as to surround the periphery of thelower electrode118. The height of the upper surface124bof thefocus ring124 generally matches the height of theupper surface118aof thelower electrode118. The wafer W to be processed is placed on the upper surface, or the wafer-supporting surface,118aof thelower electrode118 and is chucked by the electro-static chuck120.
• In the dry etching apparatus for processing silicon oxide films described above, a component that is generally most severely damaged by the plasma is thefocus ring124 that surrounds thelower electrode118. When the focus ring is continuously used in the processing apparatus, it gradually erodes. The erosion generally proceeds in the vertical direction, mainly at thestepped region124anear the inner perimeter of thefocus ring124, and a groove is formed. In other words, the erosion proceeds mainly at the area near the outer perimeter of the wafer W.
• When the erosion reaches the extent shown inFIG. 11, the side surface of thelower electrode118bbecomes exposed to the plasma. Thereafter, the plasma may influence the temperature of the wafer W chucked by the electro-static chuck120 onto the supportingsurface118aof thelower electrode118.
• As discussed above, the control of the wafer temperature is crucial for etching fine patterns. However, as discussed above, the amount of plasma radiation to thelower electrode118 increases as the erosion of thefocus ring124 increases. The increased plasma radiation increases the surface temperature of the wafer W, especially at the region near the edge. As a result, it becomes difficult to maintain an acceptable uniformity of etching.
• Moreover, exposure of thelower electrode118 to the plasma accelerates the degradation and shortens the usable life of thelower electrode118. Thelower electrode118, to which theelectrostatic chuck120 is attached, is one of the most expensive components in the dry etching apparatus. Therefore, the shortened life of thelower electrode118 markedly increases the operation cost of the apparatus.
• As such, the erosion of thefocus ring124 causes two problems, change of the etching characteristics, and rapid degradation of thelower electrode118. Therefore, thefocus ring124 is generally replaced or repaired at short intervals before it becomes severely damaged. As a result, the replacement and/or repair of the focus ring has to be made frequently, and the throughput and the cost of production of semiconductor devices by the processing apparatus are thus adversely affected.
• In regards to the focus ring that is eroded by the plasma, various improvements have been proposed in, for example, the following references:
• Japanese Laid-open Patent No. 2003-100713 (Patent Document 1) discloses an electrode cover which is divided into an inner portion and an outer portion. The inner portion, which is further divided into a plurality of sections in the circumferential direction, surrounds the side surface of the lower electrode. The outer portion is attached to the outside of the inner portion. Thereby, a plurality of sections and portions are combined to form a cover, or a focus ring, having an inner periphery that surrounds closely the side surface of the lower electrode.
• Japanese Laid-open Patent No. 8-339895 (Patent Document 2) discloses a quartz component, or a focus ring, coated with an insulating film having a high resistance to the erosion by the plasma.
• The focus ring disclosed in Patent Document 1 aims to minimize the clearance between the lower electrode and the focus ring, but does not suppress the erosion of the focus ring.
• In the quartz component disclosed in Patent Document 2, the insulating film having a high erosion resistance is coated on the surface of a quartz component, which is designed to have a shape suitable to be used in a processing apparatus. Therefore, the thickness of the resistive coating film is limited so that the coating film does not materially change the shape of the component. Therefore, the ability to improve the erosion resistance is limited.
SUMMARY
• Accordingly, in order to solve the above-mentioned problems, an exemplary object of this invention is to provide a processing apparatus and methods of plasma processing to maintain acceptable etching characteristics, even when the focus ring is severely eroded by the plasma. Another exemplary object of this invention is to provide an apparatus and methods that diminish the degradation of the lower electrode even when the focus ring is severely eroded. Another exemplary object of this invention is to provide an apparatus and methods to leave the plasma discharge conditions used in the conventional apparatus and methods substantially unchanged, while maintaining acceptable etching characteristics, even when the focus ring is severely eroded. In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing apparatus for processing a substrate using plasma. The exemplary apparatus includes a lower electrode comprising a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, a side surface protecting ring that covers the side surface of the lower electrode, and a focus ring that surrounds the side surface of the lower electrode covered by the side surface protecting ring. The supporting surface may have a dimension approximately the same as, or smaller than, that of the substrate. The side surface protecting ring may be formed of a ceramic material, and an outer perimeter of the side surface protecting ring may be approximately aligned with, or inside of, an outer perimeter of the substrate supported on the supporting surface. The focus ring is formed of a first material, and the ceramic material has an erosion rate by the plasma lower than that of the first material.
• In the exemplary apparatus, an outer perimeter of the side surface protecting ring may be positioned inside of an outer perimeter of the substrate supported on the supporting surface.
• In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing apparatus for processing a substrate using plasma. The exemplary apparatus includes a lower electrode comprising a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, a side surface protecting ring that covers the side surface of the lower electrode, and a focus ring that surrounds the side surface of the lower electrode covered by the side surface protecting ring. The supporting surface may have a dimension approximately the same as, or smaller than, that of the substrate. The side surface protecting ring may be formed of a ceramic material selected from a group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution, and an outer perimeter of the side surface protecting ring may be approximately aligned with, or inside of, an outer perimeter of the substrate supported on the supporting surface. The focus ring may be formed of a first material selected from a group consisting of quartz, silicon, and engineering plastics.
• In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing apparatus for processing a substrate using plasma. The exemplary apparatus includes a lower electrode comprising a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, a side surface protecting ring that covers the side surface of the lower electrode, and a focus ring that surrounds the side surface of the lower electrode covered by the side surface protecting ring. The supporting surface may have a dimension approximately the same as, or smaller than, that of the substrate. The side surface protecting ring may be formed of a ceramic material, and an outer perimeter of the side surface protecting ring may be positioned inside of an outer perimeter of the substrate supported on the supporting surface. The focus ring is formed of a first material different from the ceramic material.
• In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing method of processing a substrate using plasma. The exemplary method includes providing a lower electrode in a processing chamber, the lower electrode having a supporting surface and a side surface connected to an outer perimeter of the supporting surface, covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material, and surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of a first material. The supporting surface may have a dimension approximately the same as, or smaller than, that of the substrate, and the ceramic material may have an erosion rate by the plasma lower than that of the first material. The exemplary method further includes supporting the substrate on the supporting surface, and processing a surface of the substrate by generating plasma in the processing chamber. Processing the surface includes i) preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode, and ii) preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.
• In the exemplary method, the focus ring may prevent the plasma from touching the side surface protecting ring before the focus ring is eroded by the plasma; and the side surface protecting ring may prevent the plasma from touching the side surface of the lower electrode even after the focus ring is eroded by the plasma to an extent that the focus ring cannot prevent the plasma from touching the side surface of the lower electrode.
• Furthermore, in the exemplary method, the covering may include positioning an outer perimeter of the side surface protecting ring inside of an outer perimeter of the substrate supported on the supporting surface.
• In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing method of processing a substrate using plasma. The exemplary method includes providing a lower electrode in a processing chamber, the lower electrode having a supporting surface and a side surface connected to an outer perimeter of the supporting surface, covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material selected from the group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution, and surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of a first material selected from a group consisting of quartz, silicon, and engineering plastics. The supporting surface may have a dimension approximately the same as, or smaller than, that of the substrate. The exemplary method further includes supporting the substrate on the supporting surface, and processing a surface of the substrate by generating plasma in the processing chamber. The processing includes i) preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode, and ii) preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.
• In order to solve the above-mentioned problems, various exemplary embodiments according to this invention provide an exemplary plasma processing method of processing a substrate using plasma. The exemplary method includes providing a lower electrode in a processing chamber, the lower electrode having a supporting surface and a side surface connected to an outer perimeter of the supporting surface, covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material, and surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of a first material different from the ceramic material. The supporting surface has a dimension approximately the same as, or smaller than, that of the substrate. The exemplary method may further include supporting the substrate on the supporting surface, and processing a surface of the substrate by generating plasma in the processing chamber. The processing includes i) preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode, and ii) preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic drawing of an exemplary plasma processing apparatus according to an exemplary embodiment of this invention;
• FIG. 2 is a magnified view showing the relationship between the focus ring and the lower electrode, to which the ceramic ring is fitted, in the plasma processing apparatus shown inFIG. 1;
• FIG. 3 is a curve illustrating a relationship between the amount of erosion of the focus ring and the cumulative RF discharge time of the focus ring in a conventional plasma processing apparatus;
• FIG. 4 is a curve illustrating a relationship between the temperature near the edge of a wafer and the cumulative RF discharge time of the focus ring in a conventional plasma processing apparatus;
• FIG. 5 is a cross-sectional view showing the structure of a wafer W processed in an exemplary plasma processing apparatus;
• FIG. 6 is a curve illustrating a relationship between the etching rate of silicon dioxide film near the edge of the wafer and the cumulative RF discharge time of the focus ring in a conventional plasma processing apparatus;
• FIG. 7 is a curve illustrating a relationship between the etching rate of silicon dioxide film near the edge of the wafer and the cumulative RF discharge time of the focus ring in an exemplary plasma processing apparatus according to this invention;
• FIG. 8 is a curve illustrating a relationship between the silicon dioxide etching rate near the edge of the wafer and the cumulative RF discharge time of two focus rings used alternately in the exemplary plasma processing apparatus according to this invention;
• FIG. 9 is a curve illustrating a relationship between the amount of erosion of the ceramic ring and the cumulative RF discharge time of the ceramic ring;
• FIG. 10 is a magnified view showing the relationship between an uneroded focus ring and the lower electrode in a conventional plasma processing apparatus; and
• FIG. 11 is a magnified view showing the relationship between an eroded focus ring and the lower electrode in a conventional plasma processing apparatus.
DETAILED DESCRIPTION OF EMBODIMENTS
• An exemplary plasma processing apparatus and plasma processing methods according to this invention are explained in detail with reference to various exemplary embodiments shown in the drawings.
• FIG. 1 is a schematic drawing of an exemplary plasma processing apparatus according to this invention. As shown inFIG. 1, an exemplaryplasma processing apparatus10 is a dry etching apparatus for manufacturing semiconductor devices. Theapparatus10 may have a narrow-gap parallel-plate construction and etches oxide films such as silicon oxide films using high-frequency (radio frequency) plasma.
• Theprocessing chamber12 for accommodating a wafer W, which is a substrate to be processed, can be evacuated to a pressure of, for example, about 10⁻⁶Torr (10⁻⁴Pa). Various components are provided within thechamber12.
• In the upper center of thechamber12, anupper electrode16, which is connected to agas inlet14 for introducing an etching gas, is provided. In the lower center of thechamber12, alower electrode18 is provided.
• According to various exemplary embodiments, thelower electrode18 is formed of alumite-coated aluminum. The upper surface, a wafer-supportingsurface18aof thelower electrode18, has a dimension approximately the same as or is slightly smaller than the dimension of the wafer W. The inside of thelower electrode18 has a circulation path for circulating coolant supplied from the chiller (not shown), which is placed outside thechamber12. Thereby, theupper surface18aof thelower electrode18 can be maintained to a desired temperature.
• According to various exemplary embodiments, on theupper surface18aof thelower electrode18, an electro-static chuck20 for chucking the wafer W is provided. The electro-static chuck20 is formed of a fluorocarbon resin film in which a metal film is inserted. The fluorocarbon resin film, forming the electro-static chuck20, also covers theside surface18bof thelower electrode18.
• Applying a voltage to the metal film from a high voltage DC power source (not shown), which is placed outside of thechamber12, produces a Coulomb force between the metal film and thewafer20. Thereby, the wafer W is chucked on the upper surface of the electro-static chuck20. That is, the wafer W is chucked on the wafer-supportingsurface18aof thelower electrode18 by the electro-static chuck20.
• According to various exemplary embodiments, thelower electrode18 also has passages (not shown) to supply He gas. Supplying He gas to the rear side of the wafer W chucked on the electro-static chuck20 improves the thermal conduction between the wafer W and thelower electrode18. The passages are divided into two groups so that the pressures of He gas supplied to the central portion and to the outer portion of the wafer W can be controlled independently.
• According to various exemplary embodiments, on theside surface18bof thelower electrode18, a side-surface protecting ring30 formed of a ceramic material (which will be called as a “ceramic ring” hereinafter) is placed. That is, theceramic ring30 covers theside surface18bof thelower electrode18, or, more exactly, thefluorocarbon resin film20acovering theside surface18bof thelower electrode18.
• Ashield ring22 and afocus ring24 may surround peripheries of theupper electrode16 and of thelower electrode18, respectively. Theshield ring22 and thefocus ring24 concentrate the plasma between the parallel-plate electrodes. Theshield ring22 and thefocus ring24 are detachable in order to perform, for example, a mechanical cleaning.
• According to various exemplary embodiments, aRF power splitter26 and aRF power source28 are placed outside of thechamber12. TheRF power source28 supplies a high-frequency (radio frequency) power to theRF power splitter26, and theRF power splitter26 applies RF power to both thelower electrode18 and theupper electrode16. Thus, RF plasma is generated within thechamber12 and dry etching is performed.
• Theplasma processing apparatus10 shown inFIG. 1 employs, as an example, a split-coupling configuration by using theRF power splitter26. However, any one of the configurations including an anode-coupling, a cathode-coupling, or a split-coupling configurations may be selected.
• FIG. 2 is a magnified view showing the relationship between thelower electrode18, to which theceramic ring30 is fitted, and thefocus ring24.
• According to various exemplary embodiments, theceramic ring30 has a ring shape, and is formed of a ceramic material having an erosion rate by the plasma lower than that of the material forming thefocus ring24.
• According to various exemplary embodiments, theside surface18bof thelower electrode18 is covered with thefluorocarbon resin film20athat constitutes the electro-static chuck20, and is surrounded by thefocus ring24. Theceramic ring30 is inserted between thefluorocarbon resin film20acovering theside surface18bof thelower electrode18 and the inner-side surface of thefocus ring24. That is, theside surface18bof thelower electrode18 is covered by thefluorocarbon resin film20aand further by theceramic ring30, and then surrounded by thefocus ring24.
• In the exemplaryplasma processing apparatus10 shown inFIG. 2, theceramic ring30 has a thickness (a dimension perpendicular to theside surface18bof the lower electrode) such that it is fitted inside the outer perimeter of the wafer W.
• When the erosion of thefocus ring24 reaches a certain extent, theceramic ring30 becomes directly exposed to the plasma. Therefore, theceramic ring30 should preferably have a sufficient thickness in order to improve the durability and the mechanical strength.
• However, if theceramic ring30 is too thick and extends outwardly from the outer perimeter of the wafer W, charged particles, which are accelerated toward a direction perpendicular to the surface of the wafer W, may irradiate the surface of theceramic ring30. As a result, the plasma characteristics may change due to the difference between the secondary electron emission coefficients of theceramic ring30 and thequartz focus ring24. Such change in the plasma characteristics changes the etching characteristics. Thus, the etching condition should be adjusted differently. Further, depending on the etching process, small particles emitted from the ceramic ring may alter the electrical characteristics of the semiconductor device processed by the apparatus.
• Thus, it may be preferable to make the dimension of the wafer-supportingsurface18aof thelower electrode18 smaller than that of the wafer W, and position the outer surface of theceramic ring30 approximately aligned with, or inside of, the outer perimeter of the wafer W.
• According to the various exemplary embodiments of this invention, the fluorocarbonresin coating film20aon theside surface18bof thelower electrode18 may be omitted. The material of thefocus ring24 is not limited to quartz. For example, silicon may be used as the material to form thefocus ring24. Other kinds of engineering plastics having high operation temperatures, which are also called super engineering plastics, may also be used. For example, Vespel® Polyimide from DuPont, and Celazole® PolyBenzlmidazole from Celanese Advanced Materials may be used.
• The material of the side-surface protecting ring30 may preferably be, for example, alumina, but is not limited to specific materials among various ceramic materials. Other ceramic materials such as aluminum nitride, silicon nitride, and silicon carbide may also be used. Further, at least in processing apparatus for use in BEOL (Back-end of the line) processes in the semiconductor device production, zirconia, titanium nitride, and YGA (Y₃Al₅O₁₂) may also be used. Moreover, solid solutions including one or more of these materials, such as solid solutions of alumina and silicates, alumina and silicon nitride, and the like, may also be used. These ceramic materials may also contain various additives.
• Generally, these ceramic materials have lower erosion rates that those of the materials used for forming thefocus ring24, although the ratios between erosion rates are different for different combinations of materials. The ratio for a specific combination also varies depending on various conditions such as the etching gas and the plasma discharge condition.
• According to various exemplary embodiments, in order to perform etching using theplasma processing apparatus10, after evacuating thechamber12 to a predetermined pressure, a fluorocarbon-based etching gas is introduced from thegas inlet14, and an etching gas atmosphere with a predetermined pressure is produced within the space between theelectrodes16 and18. By applying an RF power, through theRF power splitter26, to theelectrodes16 and18 between which the etching gas atmosphere is produced, fluorocarbon-based plasma is generated. As a result, charged particles within the plasma are accelerated toward the direction perpendicular to the surface of the wafer W placed on the wafer-supportingsurface18aof thelower electrode18, and the surface of the wafer W becomes etched.
• In the various exemplary embodiments according to this invention, the side surface of thelower electrode18 is protected by aceramic ring30 formed of a material having a lower erosion rate than that of the material of thefocus ring24. Therefore, even after thefocus ring24 is severely eroded, theside surface18bof thelower electrode18 is not exposed to the plasma and is not damaged. As a result, increase of the surface temperature near the edge of the wafer W is diminished, and the etching characteristics can be maintained.
• Moreover, because the etching characteristics can be maintained even after the focus ring is severely eroded, the interval for replacing thefocus ring24 can be extended. As a result, the costs incurred for the maintenance is reduced.
• Furthermore, because theceramic ring30 protects theside surface18bof thelower electrode18, the mechanical damage to the fluorocarbon resin film covering theside surface18bof thelower electrode18 during the attaching and detaching of the focus ring34 is prevented.
• In the exemplary plasma processing apparatus, before the erosion of the focus ring proceeds, the wafer W and thefocus ring24 prevent theceramic ring30 and theside surface18bof thelower electrode18 from being exposed to the plasma. After thefocus ring24 is eroded to an extent that it cannot prevent theceramic ring30 from being exposed to the plasma, theceramic ring30 then prevents theside surface18bof thelower electrode18 from being exposed to the plasma. In other words, after thefocus ring24 is eroded to an extent that thefocus ring24 alone cannot prevent theside surface18bof thelower electrode18 from being exposed to the plasma, theceramic ring30 prevents theside surface18bof thelower electrode18 being exposed to the plasma.
• Moreover, in the exemplary embodiment of theplasma processing apparatus10, the dimension of the wafer-supportingsurface18aof thelower electrode18 is made smaller than the dimension of the wafer W, and the outer perimeter of theceramic ring30 is positioned approximately aligned with, or inside, the outer perimeter of the wafer W. Accordingly, it is possible to prevent charged particles in the plasma accelerated to the direction perpendicular to the surface of the wafer W from irradiating theceramic ring30, even after thefocus ring24 is eroded.
• The exemplary plasma processing apparatus and plasma processing methods according to this invention are not limited to the embodiments described above. For example, the plasma processing apparatus may be any type of plasma processing apparatus that comprises an electrode having a substrate-supporting surface. Further, the exemplary plasma processing apparatus according to this invention is not limited to semiconductor manufacturing apparatuses for processing surfaces of semiconductor substrates, but may be various apparatuses for processing various other substrates. Moreover, various reaction gases other than the fluorocarbon-based gas may be used.
Comparative Example 1
• In order to confirm the effect of theceramic ring30 in the exemplaryplasma processing apparatus10, etching is performed using a conventional plasma processing apparatus that does not have aceramic ring30.
• FIG. 3 is a curve illustrating a relationship between an amount of erosion of thefocus ring124 of a conventional plasma processing apparatus in the vertical direction, or in the direction perpendicular to the surface of the wafer W supported on the wafer-supportingsurface18a, and a cumulative RF discharge time of the focus ring124 (i.e., a cumulative time of RF discharge made using the same focus ring124).
• FIG. 11 described above shows the shape of thefocus ring124 when the amount of erosion is about 1 mm.FIG. 3 indicates that thefocus ring124 reaches this shape when the cumulative RF discharge time reaches about 300 hours. It is found that the desired etching characteristics cannot be maintained when thefocus ring124 has the shape shown inFIG. 11.
• At first, in order to investigate the relationship between the surface temperature of the wafer W and the amount of erosion of thefocus ring124, the surface temperature of the wafer W is measured while the plasma is generated. Specifically, the surface temperature of the wafer W at 5 mm from the edge is measured.
• As the dry etching process gas, a mixture of etchant gases (CF₄and C₄F₈), CO and Ar is used. Table 1 shows the plasma discharge condition during the measurement of the surface temperature. However, theplasma processing apparatus10 is used for the production of semiconductor devices with a different process gas and a different plasma discharge condition shown in Table 2. That is, thefocus ring124 is mainly eroded by the plasma with the condition shown in Table 2.

  TABLE 1
  			Coolant temperature	Rear side He
  Discharge	RF Power		[° C.]	pressure

  pressure

  density

  Gas flow rate [sccm]

  upper

  lower

  [Torr]

  [mTorr]	[Wcm−2]	CF4	C4F8	CO	Ar	electrode	electrode	center	edge
  150	4.65	10	8	120	350	30	−10	10	19

• TABLE 2
  	RF		Coolant temperature
  Discharge	Power	Gas flow rate	[° C.]	Rear side He

  pressure

  density

  [sccm]

  upper

  lower

  pressure [Torr]

  [mTorr]	[Wcm−2]	CF4	CHF3	Ar	electrode	electrode	center	edge
  300	4.65	40	30	500	30	−10	10	22

• FIG. 4 is a curve illustrating the result of measurements, where the surface temperature near the edge of the wafer W is shown in relation to the cumulative RF discharge time of thefocus ring124.FIG. 4 indicates that the surface temperature near the edge of the wafer W increases after the cumulative RF discharge time exceeds 300 hours.
• A coolant with the temperature shown in Table 1 is circulated within thelower electrode118. Because there is a certain distance between the circulation path and theside surface118bof thelower electrode118, however, the temperature of thelower electrode118 near theside surface118bincreases when theside surface118bis exposed to the plasma. Accordingly, the temperature of the edge portion of the wafer W increases.
• In order to evaluate the change of etching rate of small holes near the edge of the wafer W by the increase of the cumulative RF discharge time of the focus ring, dry etching is conducted. Specifically, the surface of the wafer W shown inFIG. 5 is etched under the conditions shown in Table 1.
• As discussed above, however, the apparatus is used for the production with the condition shown in Table 2. Here, the condition shown in Table 1 is more suitable for etching small holes, but is more strongly influenced by the surface temperature of the wafer W.
• According to various exemplary embodiments, in the wafer W shown inFIG. 5, on a silicon substrate S1, a 2.0 μm thick silicon dioxide film S2 is formed, and a 1.2 μm thick photoresist mask pattern M is formed on the silicon dioxide film. The mask M has 0.30 μm^Φ holes H. A mixture of etchant gases (CF₄and C₄F₈) and CO and Ar is used as the dry etching process gas. The etching rate is measured at the position of 5 mm from the edge of the wafer W.
• FIG. 6 is a curve illustrating the change of the silicon dioxide film etching rate in relation to the cumulative RF discharge time of thefocus ring124.FIG. 6 shows that the etching rate near the edge of the wafer W significantly decreases after the cumulative RF discharge time exceeds 300 hours.
• This result indicates that, 1) when the cumulative RF discharge time exceeds 300 hours, thefocus ring124 is severely damaged and irradiation of the plasma to the side surface of thelower electrode118 increases, and 2) as a result, the surface temperature near the edge of the wafer W increases and the etching rate near the edge of the wafer W decreases. In other words, it is impossible to maintain desired etching characteristics when the cumulative RF discharge time exceeds 300 hours.
• Moreover, in the conventional plasma processing apparatus illustrated inFIG. 10, thelower electrode118 is also damaged when the erosion of thefocus ring124 proceeds to the extent shown inFIG. 11.
• Thefluorocarbon resin film120acovering theside surface118bof thelower electrode118 is not highly resistant to the plasma. Therefore, when thefocus ring124 is eroded as shown inFIG. 11, thefluorocarbon resin film120aon theside surface118bof thelower electrode118 may easily be degraded. Moreover, in the conventional plasma processing apparatus illustrated inFIGS. 10 and 11, it is difficult to prevent thefluorocarbon resin film120aon theside surface118afrom being damaged during attaching and detaching of thefocus ring124.
• As a result, when thefocus ring124 is severely eroded as shown inFIG. 11, thefluorocarbon resin film120adisappears at least partly on theside surface118bof thelower electrode118, and portions of theside surface118bof thelower electrode118 are directly exposed to the plasma. The direct exposure to the plasma degrades the alumite coating on theside surface118bof thelower electrode118, and causes abnormal discharge, or arcing, from the portion that is dielectrically destructed.
• When the abnormal discharge occurs, thelower electrode118 cannot be used anymore. Therefore, the operation of the apparatus must be stopped, and the replacement to a newlower electrode118 must be made.
• As discussed above, in the conventional plasma processing apparatus that does not have theceramic ring30, the etching rate changes and the lower electrode degrades when thefocus ring124 is eroded. Therefore, thefocus ring124 should be replaced when the cumulative RF discharge time exceeds 300 hours, or when the amount of erosion in the vertical direction reaches about 1 mm by a visual inspection. The usedfocus ring124 should be discarded or repaired.
Example 1
• Using the exemplaryplasma processing apparatus10 shown inFIG. 1, dry etching of silicon dioxide films S2 on the surface of the wafers W shown inFIG. 5 is conducted, and the change of the etching rate is examined.
• As shown inFIG. 2, theceramic ring30 has a dimension such that the outer perimeter of theceramic ring30 is positioned inside of the outer perimeter of the wafer W. Specifically, the dimension, or the diameter, of the wafer-supportingsurface18aof thelower electrode18 is about 6 mm smaller than that of the wafer W, and the thickness, or the width, of theceramic ring30 is 2 mm. Therefore, the outer perimeter of theceramic ring30 is positioned about 1 mm inside the outer perimeter of the wafer W. In this example, the material of the ceramic ring is alumina.
• In this example, afocus ring24 that is already severely eroded is used. Specifically, afocus ring24 that is already eroded to a depth of 3 mm in the vertical direction at the steppedportion24anear the inner perimeter, which faces thelower electrode18, is used. This amount of erosion corresponds to three times the maximum allowable erosion depth (1 mm) in a conventional apparatus. In other words, a focus ring that has been used for a cumulative RF discharge time of about 900 hours, is used.
• The etching for measuring the etching rate is conducted using the plasma discharge condition shown in Table 3. Theapparatus10 is also used for the production of semiconductor devices using the condition shown in Table 2.

  TABLE 3
  			Coolant temperature	Rear side He
  Discharge	RF Power		[° C.]	pressure

  pressure

  density

  Gas flow rate [sccm]

  upper

  lower

  [Torr]

  [mTorr]	[Wcm−2]	CF4	C4F8	CO	Ar	electrode	electrode	center	edge
  150	4.65	10	8	120	350	30	−10	10	16

• According to various exemplary embodiments, when theceramic ring30 is fitted around theside surface18bof thelower electrode18, the surface temperature within about 5 mm from the edge of the wafer decreases with an amount of about 5° C. if the discharge condition shown in Table 1 is used. Such decrease in the temperature is due to the fact that, different from the conventional apparatus, theside surface18bof thelower electrode18 is not exposed to the plasma, and the thermal conductivity of theceramic ring30 is high. Especially, the fact that theceramic ring30 is made of alumina and has a thermal conductivity more than 20 times higher than that of quartz, which is the material of thefocus ring30, significantly improves the cooling efficiency of the edge portion of the wafer W.
• Therefore, according to various exemplary embodiments, in order to improve the uniformity of the surface temperature of the wafer W, the condition shown in Table 3 is used to measure the etching rate. Specifically, as shown in Table 3, the pressure of He gas supplied to the peripheral portion of the rear side of the wafer W is decreased to an amount of about 3 Torr, compared to the condition shown in Table 1. Otherwise the condition shown in Table 3 is the same as that shown in Table 1.
• FIG. 7 is a curve illustrating the change of the silicon dioxide film etching rate in relation to the cumulative RF discharge time of thefocus ring24. As shown inFIG. 7, the etching rate of 0.30 μm^Φ hole does not significantly change even when thefocus ring24, which has already been eroded to the depth of 3 mm, is further used for 400 hours.
• This result indicates that theceramic ring30 enables to maintain a uniform surface temperature of the wafer W and a stable etching rate irrespective of the amount of erosion of thefocus ring24. Further, because the etching rate is stable irrespective of the amount of erosion, the usable life of thefocus ring24 can be extended.
• That is, according to various exemplary embodiments of this invention, a protecting ring formed of a ceramic material that has an erosion rate lower than that of the material of the focus ring covers the side surface of the lower electrode. Accordingly, even after the focus ring is severely eroded, the etching characteristics can be maintained and the degradation of the lower electrode is prevented. Moreover, an interval to replace the focus ring can be extended, and a cost incurred for replacing the focus ring can be reduced.
• Moreover, as discussed above, it is not necessary to materially change the etching condition when theceramic ring30 is used. Specifically, the etching condition shown in Table 3, which is the same as the conventional condition shown in Table 1, except that the pressure of He supplied to the rear side of the wafer W is adjusted, can be used in theapparatus10 that utilizes theceramic ring30. This result indicates that theceramic ring30 does not materially influence the plasma characteristics.
• In this exemplary embodiment, because afocus ring24 that is already severely eroded is used, theceramic ring30 is exposed to the plasma. Because the outer perimeter of theceramic ring30 is positioned inside of the outer perimeter of the wafer W, however, charged particles in the plasma accelerated toward the direction perpendicular to the surface of the wafer W do not irradiate theceramic ring30. Accordingly, theceramic ring30 does not materially change the plasma characteristics.
Example 2
• Using theplasma processing apparatus10 shown inFIG. 1, an exemplary etching process is performed for a plurality of wafers W having the structure shown inFIG. 5. The thickness of theceramic ring30 is 2 mm. Two focus rings24, which have not been eroded, are prepared, and a running experiment is conducted by alternately using the two focus rings24. That is, the operation of theapparatus10 is stopped every 50 hours of cumulative RF discharge time for a mechanical cleaning. During the mechanical cleaning, thefocus ring24 is substituted with another one.
• Measurement of the etching rate of 0.30 μm^Φ hole is made with a predetermined interval using the plasma discharge condition shown in Table 3. The apparatus may be operated for other purposes with the condition shown in Table 2.
• FIG. 8 is a curve illustrating the change of the etching rate of 0.30 μm^Φ hole in relation to the cumulative RF discharge time of the two focus rings24 (i.e., the cumulative time of RF discharge made using the two focus rings24).FIG. 8 shows that the change of the etching rate is small even when the cumulative RF discharge time reaches 1200 hours, or when the cumulative RF discharge time of eachfocus ring24reaches 600 hours.
• On the other hand, as shown inFIG. 6, the etching rate in the conventional apparatus changes significantly when the cumulative RF discharge time of the focus ring exceeds 300 hours. Accordingly, it can be understood that by employing theceramic ring30, the life, or the maximum usable period of thefocus ring24, can be extended at least by two times.
• During the experiment, thelower electrode18 is not damaged. In this experiment, theceramic ring30 is prepared separately from thelower electrode18 and fitted to theside surface18bof thelower electrode18 when starting the experiment. Because theceramic ring30 has a smaller outer diameter, and a smaller weight, than those of thefocus ring24, it can be easily fitted to thelower electrode18. Therefore, there is no risk of damaging thefluorocarbon resin film20aon theside surface18bof thelower electrode18 when fitting theceramic ring30. Moreover, it is not necessary to detach the ceramic ring for mechanical cleaning.
• Finally,FIG. 9 is a curve illustrating the amount of erosion of theceramic ring30 in relation to the cumulative RF discharge time of theceramic ring30, or the cumulative time of RF discharge made using the two focus rings24 and theceramic ring30.FIG. 9 indicates that the amount of erosion is about 1 mm when the cumulative RF discharge time is 1200 hours. That is, for example, theceramic ring30 with a width of 2 mm has a sufficient shielding ability to prevent the plasma from touching theside surface18bof thelower electrode18, at least to the cumulative RF discharge time of 1200 hours.
• FIG. 9 shows that, during the initial period before the cumulative RF discharge time of less than about 300 hours, the erosion rate of the ceramic material measured by the amount of erosion of theceramic ring30 in the direction perpendicular to theside surface18bof thelower electrode18 is about 25 nm/min. On the other hand,FIG. 3 shows that, during the same time period, the erosion rate of quartz measure by the amount of increase in the erosion of the focus ring in the vertical direction, or in the direction perpendicular to the surface of the wafer W, is about 56 nm/min. That is, the erosion rate of the ceramic material measured by the amount of erosion of theceramic ring30 in the direction perpendicular to theside surface18bof thelower electrode18 is less than a half of the erosion rate of quartz measured by the amount of erosion of thefocus ring24 in the direction perpendicular to the surface of the wafer W.
• FIG. 9 further indicates that, when the cumulative RF discharge time increases, the amount of erosion of theceramic ring30 tends to saturate. That is, the erosion rate of the ceramic ring decreases as the cumulative RF discharge time increases. The lower erosion rate of theceramic ring30, compared with that of thefocus ring24, enables to use theceramic ring30 for a long period even after thefocus ring24 is severely eroded.
• It should be noted that the erosion rates and the ratios thereof thus calculated from the data shown inFIGS. 3 and 9 are determined not only by the difference of the properties of the materials but also by the positions of theceramic ring30 and thefocus ring24 in theplasma processing apparatus10. In fact, it is found that the erosion rate of alumina measured by an etching rate of aluminum oxide film on the surface of a wafer W placed on the wafer-supportingsurface18bof theplasma processing apparatus10 is about 30 times lower than the erosion of quartz measured by an etching ration of silicon dioxide film on the surface of a wafer W placed on the wafer-supportingsurface18b. It is clear however that the actual erosion rate in theceramic ring30 fitted in theprocessing apparatus10 determines the usable life of theceramic ring30.
• This invention is not limited to the specific embodiments described above. Various improvements or modifications may be made within the spirit of this invention.
• For example, in the exemplary embodiment described above, alower electrode18 having afluorocarbon resin film20aon theside surface18bmay be used in order to be compared to the conventional plasma processing apparatus. However, theceramic ring30 prevents the plasma from touching theside surface18bof thelower electrode18 even after thefocus ring24 is severely eroded. Therefore, essentially the same usable life of thelower electrode18 is realized even without thefluorocarbon resin film20aon theside surface18bof thelower electrode18.
• Further, in the exemplary embodiments described above, thelower electrode18 having anelectrostatic chuck20 formed of fluorocarbon resin is used. However, this invention may also be applied to an apparatus having an electrostatic chuck formed of ceramics. In that case, similarly to a case where an electrostatic chuck formed of fluorocarbon resin is used, a ceramic coating film on theside surface18bof thelower electrode18 is not always required.
• According to various exemplary embodiments, when the ceramic coating film on theside surface18bof thelower electrode18 is made, however, theceramic ring30 prevents the plasma from touching the ceramic coating film on theside surface18bof thelower electrode18 even after thefocus ring24 is severely eroded. Accordingly, theceramic ring30 significantly extends the life of the ceramic coating.

Claims (11)

1. A method of processing a substrate using a plasma, comprising:

providing a lower electrode in a processing chamber, the lower electrode having a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, the supporting surface having a size approximately the same as, or smaller than, a size of the substrate;

supporting the substrate on the supporting surface;

covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material;

positioning an outer perimeter of the most outside part of the side surface protecting ring inside an outer perimeter of the substrate supported on the supporting surface;

surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of a first material different from the ceramic material; and

processing a surface of the substrate by generating a plasma in the processing chamber, the processing including:

preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode; and

preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.

2. The method according toclaim 1, wherein:

the focus ring prevents the plasma from touching the side surface protecting ring before the focus ring is eroded by the plasma; and

the side surface protecting ring prevents the plasma from touching the side surface of the lower electrode even after the focus ring is eroded by the plasma to an extent that the focus ring cannot prevent the plasma from touching the side surface of the lower electrode.

3. The method according toclaim 1, wherein the ceramic material has a different secondary electron emission coefficient than that of the first material.

4. The method according toclaim 1, wherein the side surface protecting ring is prevented by the substrate from being irradiated by the charged particles in the plasma accelerated toward the direction perpendicular to the surface of the substrate, even after the focus ring is eroded.

5. The method according toclaim 1, wherein said covering includes fitting the side surface protecting ring, which is prepared separately from the lower electrode, to the side surface of the lower electrode.

6. The method according toclaim 1, wherein:

the ceramic material is selected from the group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution; and

the first material is selected from a group consisting of quartz, silicon, and engineering plastics.

7. The method according toclaim 1, wherein the ceramic material is alumina and the first material is quartz.

8. A method of processing a substrate using a plasma, comprising:

providing a lower electrode in a processing chamber, the lower electrode having a supporting surface for supporting the substrate and a side surface connected to an outer perimeter of the supporting surface, the supporting surface having a size smaller than a size of the substrate;

supporting the substrate on the supporting surface;

covering the side surface of the lower electrode by a side surface protecting ring formed of a ceramic material;

positioning an outer perimeter of the most outside part of the side surface protecting ring inside an outer perimeter of the substrate supported on the supporting surface;

surrounding the side surface of the lower electrode, which is covered by the side surface protecting ring, by a focus ring formed of quartz;

processing a surface of the substrate by generating a plasma in the processing chamber, the processing including:

preventing, by the side surface protecting ring, the plasma from touching the side surface of the lower electrode; and

preventing, by the substrate supported on the supporting surface, charged particles in the plasma accelerated toward a direction perpendicular to the surface of the substrate from irradiating the side surface protecting ring.

9. The method according toclaim 8, wherein the ceramic material is selected from a group consisting of alumina, aluminum nitride, silicon carbide, silicon nitride, zirconia, titanium nitride, YAG, alumina-silicate solid solution, and alumina-silicon nitride solid solution.

10. The method according toclaim 8, wherein the ceramic material is alumina.

11. The method according toclaim 8, wherein said covering includes fitting the side surface protecting ring, which is prepared separately from the lower electrode, to the side surface of the lower electrode.

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