US20050212041A1 - Novel process method of source drain spacer engineering to improve transistor capacitance - Google Patents

Abstract

A method of forming an associated transistor is presented whereby short channel effects and junction capacitances are mitigated and enhanced switching speeds are thereby facilitated. Compensation regions are formed within a substrate by implanting dopants relatively deeply over source and drain regions formed within the substrate. The compensation regions are spaced apart slightly less than are the source and drain regions. This spacing affects potential contours and reduces junction capacitances within the transistor. The different distances between the source and drain regions and the compensation regions are achieved by forming and selectively adjusting sidewall spacers adjacent to a gate structure of the transistor. These spacers serve as guides for the dopants implanted into the substrate to form the source and drain regions and the compensation regions.

Description

FIELD OF INVENTION
• The present invention relates generally to semiconductor processing, and more particularly to a methodology for source drain spacer engineering to improve transistor capacitance.
BACKGROUND OF THE INVENTION
• Several trends exist presently in the semiconductor and electronics industry. Devices are continually getting smaller, faster and requiring less power. A reason for these trends is that more personal devices are being fabricated which are relatively small and portable, thereby relying on a battery as its primary supply source. For example, cellular phones, personal computing devices, and personal sound systems are devices which are in great demand in the consumer market. In addition to being smaller and more portable, personal devices are requiring more computational power and speed. In light of all these trends, there is an ever increasing demand in the industry for smaller and faster transistors used to provide the core functionality of the integrated circuits used in these devices.
• Accordingly, in the semiconductor industry there is a continuing trend toward manufacturing integrated circuits (ICs) with higher densities. To achieve high densities, there has been and continues to be efforts toward scaling down dimensions (e.g., at submicron levels) on semiconductor wafers, which are generally produced from bulk silicon. In order to accomplish such high densities, smaller feature sizes, smaller separations between features and more precise feature shapes are required in integrated circuits (ICs) fabricated on small rectangular portions of the wafer, commonly known as dies. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, as well as the surface geometry of various other features (e.g., corners and edges). The scaling-down of integrated circuit dimensions can facilitate faster circuit performance and/or switching speeds, and can lead to higher effective yield in IC fabrication by providing more circuits on a die and/or more die per semiconductor wafer.
• The process of manufacturing integrated circuits typically consists of more than a hundred steps, during which hundreds of copies of an integrated circuit can be formed on a single wafer. This process can create electrically active regions in and on the semiconductor wafer surface. In MOS transistors, for example, a gate structure is created, which can be energized to establish an electric field within a semiconductor channel, by which current is enabled to flow between a source region and a drain region within the transistor. The source and drain regions facilitate this conductance by virtue of containing a majority of positively doped (p) or negatively doped (n) materials.
• As device sizes continue to shrink, however, the channel lengths continue to be scaled downward, and short channel effects can become significant. For example, hot carrier effects can be experienced in short channel devices. More particularly, during saturation operation of a MOS transistor, for example, electrons can gain kinetic energy and become “hot”. Some of these hot electrons traveling to the drain can be injected into a thin gate dielectric proximate the drain junction. The injected hot carriers, in turn, often lead to undesired degradation of the MOS device operating parameters, such as a shift in threshold voltage, changed transconductance, changed drive current/drain current exchange, device instability, etc.
• Similarly, unwanted source/drain leakage conduction or punchthrough current can occur as channel lengths shorten. Punchthrough current may be seen as a parasitic current path existing between the drain and source, which the gate has difficulty in controlling since the current path is located deep in the bulk (substrate) far away from the gate. The actual amount of punchthrough current depends mainly upon the potential distribution under the channel and on the source/drain junction depths. As the effective channel length gets shorter, the source/drain depletion regions get closer together. Punchthrough generally occurs when the effective channel length is decreased to roughly the sum of two junction depletion widths.
• In addition, as device densities and operational speeds continue to increase, reduction of the delay times in the MOS devices used in integrated circuits is desired. These delays are related to the on-state resistance as well as the junction capacitances of these MOS devices. Working with smaller and more densely packed devices, however, requires a greater precision in fabrication, which can provide opportunities for errors to occur. For example, dopant may be unintentionally placed in unwanted areas and may increase junction capacitance and cause body leakage, resulting in reduced switching speeds and higher source to drain resistance (Rsd). Imprecisely placed dopants may also migrate into a channel region, for example, and shorten the channel length adding to possible subsurface leakage current paths.
• Accordingly, improved techniques for fabricating densely packed semiconductor devices would be desirable. More particularly, it would be desirable to fabricate semiconductor devices in a manner that mitigates short channel effects. Similarly, it would also be desirable to fashion semiconductor devices such that junction capacitances are reduced and switching speeds are thereby enhanced.
SUMMARY OF THE INVENTION
• The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended neither to identify key or critical elements of the invention nor to delineate the scope of the invention. Rather, its primary purpose is merely to present one or more concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
• The present invention pertains to formation of a transistor in a manner that mitigates short channel effects and junction capacitances, thereby facilitating enhanced switching speeds. More particularly, compensation regions are formed with dopants implanted relatively deeply over source and drain regions within a substrate. The compensation regions are spaced apart slightly more than the source and drain regions to alter potential contours and reduce junction capacitances within the transistor. The different distances between the source and drain regions and the compensation regions are achieved by forming and selectively adjusting sidewall spacers adjacent to a gate structure of the transistor. These spacers effectively serve as guides for the dopants implanted into the substrate to form the source and drain regions and the compensation regions.
• According to one aspect of the present invention, a method of forming a transistor is disclosed. The method includes forming a first oxide layer over a gate structure. The first oxide layer is also formed over portions of a substrate not covered by the gate structure. These uncovered portions of the substrate also have source/drain extension regions and halo regions formed therein. The method further includes forming a nitride layer over the first oxide layer, forming a second oxide layer over the nitride layer and processing the second oxide layer and nitride layer to form oxide sidewall spacers adjacent the gate structure. In this manner, the oxide sidewall spacers are situated over a residual portion of nitride material. The method further includes processing the oxide sidewall spacers such that they are reduced in size relative to the underlying portions of nitride material. Regions of the substrate adjacent the gate structure are then doped with a first dopant to form source and drain regions within the substrate. The first dopant is, however, substantially blocked by the oxide sidewall spacers and the underlying portions of nitride material. Regions of the substrate adjacent the gate.structure are then doped again with a second dopant to form first and second compensation regions within the substrate. The second dopant is, however, substantially blocked by the oxide sidewall spacers.
• In accordance with one or more other aspects of the present invention, a method of forming a transistor includes forming source and drain regions within a substrate adjacent to a gate structure formed upon the substrate. The method also includes forming first and second compensation regions within the substrate to a depth about twice that of the source and drain regions. The source and drain regions and the first and second compensation regions are separated by a channel region underlying the gate structure. The source and drain regions are also separated by a first distance and the first and second compensation regions are separated by a second distance, where the first distance is greater than the second distance.
• According to one or more other aspects of the present invention, a transistor includes a gate structure formed over a substrate. The transistor also includes a source region formed within the substrate adjacent the gate structure and a drain region formed within the substrate adjacent the gate structure. A first compensation region is formed within the substrate adjacent the gate structure and within the source region. Similarly, a second compensation region is formed within the substrate adjacent the gate structure and within the drain region. The transistor also has a channel underlying the gate structure and separating the source and drain regions and the first and second compensation regions. The source and drain regions are also separated by a first distance and the first and second compensation regions are separated by a second distance, where the first distance is greater than the second distance.
• To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which one or more aspects of the present invention may be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the annexed drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a simplified, schematic cross-sectional illustration of a conventional transistor.
• FIG. 2-8 are cross-sectional illustrations depicting a conventional methodology for forming a PMOS transistor, such as that presented inFIG. 1.
• FIG. 9 is a flow diagram illustrating an example of a methodology of forming a transistor in accordance with one or more aspects of the present invention.
• FIGS. 10-23 are cross-sectional illustrations of a transistor formed according to one or more aspects of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• One or more aspects of the present invention are described with reference to the drawings, wherein like reference numerals are generally utilized to refer to like elements throughout, and wherein the various structures are not necessarily drawn to scale. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects of the present invention. It may be evident, however, to one skilled in the art that one or more aspects of the present invention may be practiced with a lesser degree of these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more aspects of the present invention.
• The present invention pertains to formation of a transistor in a manner that mitigates short channel effects and junction capacitances, thereby facilitating enhanced switching speeds. More particularly, compensation regions are formed with dopants implanted relatively deeply over source and drain regions within a substrate. The compensation regions are spaced apart slightly more than the source and drain regions to alter potential contours and reduce capacitive contact areas, thereby reducing junction capacitances within the transistor. The different distances between the source and drain regions and the compensation regions are achieved by forming and selectively adjusting sidewall spacers adjacent to a gate structure of the transistor. These spacers serve as guides for the dopants implanted into the substrate to form the source and drain regions and the compensation regions.
• In order to appreciate various aspects of the present invention, a brief description of a conventional MOS device and fabrication process follows below.FIG. 1 illustrates a conventionalsemiconductor transistor device100 that can be fabricated with conventional complimentary MOS (CMOS) processing techniques in asemiconductor substrate102. Thedevice100 includes agate structure104 comprising agate electrode106 and agate dielectric108. Thegate electrode106 generally comprises polysilicon or SiGe and overlies thegate dielectric108.Sidewall spacers110,112 are located upon either side of thegate structure104. As will be discussed further, thesidewall spacers110,112 impede doping of certain areas orextension regions114,116 underlying thespacers110,112. Two laterally spaced doped source/drain regions118 and120 are formed within thesubstrate102 and achannel region122 is defined therebetween under thegate structure104.
• In operation, the resistivity of thechannel122 may be controlled by a voltage applied to thegate electrode106, where changing the gate voltage changes the amount of current flowing through thechannel122 between the source and drain. The gate contact orelectrode106 and thechannel122 are separated by thegate dielectric108, which is an insulator and which opposes current flow between thegate electrode106 and thechannel122, such that the device does not become activated until a sufficient voltage (at least larger than a threshold voltage V_t) is applied to thegate electrode106.
• To form thedevice100, a layer ofdielectric material124 is initially formed over the substrate102 (FIG. 2). A gate electrode layer126 (e.g., polysilicon or SiGe) is then formed over the layer of dielectric material124 (FIG. 3). Thegate electrode layer126 and the layer ofdielectric material124 are then patterned (e.g., via etching) to develop the gate structure104 (FIG. 4).Dopant128 is then applied to thegate electrode106 and to exposed portions of thesubstrate102 to formextension regions130,132 therein (FIG. 5). As will become apparent, theextension regions130,132 are precursors to portions of the source and drainregions118,120 formed within thesubstrate102.
• A layer of an insulating material134 (e.g., silicon nitride, silicon oxide) is then formed over the entire structure (FIG. 6). The layer of insulatingmaterial134 is selectively removed (e.g., via anisotropic etching) to form thesidewall spacers110,112 on either side of the gate structure104 (FIG. 7).Additional dopant128 is then applied to thegate electrode106 and thesubstrate102, except for thoseportions114,116 covered by thesidewall spacers110,112 (FIG. 8). Theadditional dopant128 establishes the source and drainregions118,120 within thesubstrate102 on either side of thegate structure104. It will be appreciated that theadditional dopant128 is of substantially the same type as that previously applied in forming theextension regions130,132 (e.g.,FIG. 5). Thechannel region122 is thereby defined within thesubstrate102 under thegate structure104 as the source and drainregions118,120 are formed (FIG. 8).
• Turning now toFIG. 9, amethodology200 is illustrated for forming a MOS transistor according to one or more aspects of the present invention. Although themethodology200 is illustrated and described hereinafter as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated steps may be required to implement a methodology in accordance with one or more aspects of the present invention. Further, one or more of the acts may be carried out in one or more separate acts or phases.
• It will be appreciated that a methodology carried out according to one or more aspects of the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated or described herein. By way of example, the method or variants thereof may be used to fabricate a transistor as illustrated and described below with respect toFIGS. 10-23, as well as to devices not shown or described with regard toFIGS. 10-23.
• Themethodology200 begins at202 wherein a gate structure is formed over a semiconductor substrate. In particular, a layer of gate dielectric material is formed over the semiconductor substrate, a gate electrode layer is formed over the layer of gate dielectric material, and the gate electrode layer and the layer of gate dielectric material are patterned to form the gate structure. The gate structure thus comprises a gate electrode and a gate dielectric. It will be appreciated that the layers can be patterned in any suitable manner to form the gate structure, such as by etching, for example.
• Further, the layer of gate dielectric material and the gate electrode layer can be applied to the substrate in any number of ways, such as with spin-on techniques, sputtering techniques (e.g., magnetron or ion beam sputtering), growth and/or deposition techniques such as chemical vapor deposition (CVD), for example. The gate dielectric material can be formed to a thickness of about 1 nanometer or more, and can have an equivalent oxide thickness (EOT) of about 1 nanometer or less, for example, while the gate electrode layer can be formed to a thickness of about 50-200 nm, for example.
• Additionally, the substrate generally includes silicon, the gate electrode layer generally includes doped polysilicon, SiGe or metal, and the layer of gate dielectric material can comprise a high-k dielectric material, for example. The layer of gate dielectric material may include, for example, any one or more of the following, either alone or in combination: aluminum oxide (Al₂O₃), zirconium silicate, hafnium silicate, hafnium silicon oxynitride, hafnium oxynitride, zirconium oxynitride, zirconium silicon oxynitride, hafnium silicon nitride, lanthanum oxide (La₂O₃), hafnium oxide (HfO₂), zirconium oxide (ZrO₂), cerium oxide (CeO₂), bismuth silicon oxide (Bi₄Si₂O₁₂), titanium dioxide (TiO₂), tantalum oxide (Ta₂O₅), tungsten oxide (WO₃), yttrium oxide (Y₂O₃), lanthanum aluminum oxide (LaAlO₃), barium strontium titanate, barium strontium oxide, barium titanate, strontium titanate, PbZrO₃, PST, PZN, PZT and PMN.
• The gate structure may also include a thin oxide over the polysilicon (e.g., about 1.5 nm thick) and a thin offset spacer (e.g., deposited and dry etched to a thickness of about 2-20 nm) on the sidewall thereof. Such an initial gate structure and other variations are contemplated as falling within the scope of the present invention.
• After the gate structure is formed, the methodology proceeds to204 wherein source/drain extension regions are formed. Such extension regions may, for example, be formed according to HDD (highly doped drain) techniques. The extension regions are generally formed within the substrate and facilitate absorption of some of the potential associated with the drain. In this manner, some of this potential is directed away from the drain/channel interface, thereby mitigating the occurrence of channel hot carriers and the adverse effects associated therewith. By way of example, a p-type dopant having a concentration of about 1E19 to 5E20 atoms/cm³for a PMOS transistor, or an n-type dopant having concentration of about 1E19 to 9.5E20 atoms/cm³for an NMOS transistor can be implanted to a depth of about 100-350 Angstroms, for example. It will be appreciated, however, that other implant concentrations and penetration depths are contemplated as falling within the scope of the present invention.
• The methodology then proceeds to206 wherein halo regions are formed within the semiconductor substrate. Halo implants (or pocket implants) can facilitate scaling the device channel length by creating localized dopant distributions near the source/drain (S/D) regions, where the distributions may extend, at least partially, under the channel. In this manner, halos can mitigate unwanted source/drain leakage conduction, or punchthrough current, and as such are sometimes referred to as “punchthrough stoppers”. A quad high-angle implant may be utilized, for example, to place a halo dose around an edge of the gate structure in source/drain regions of the semiconductor substrate. In one example, such a high-angle implant can place a p-type halo dopant having a concentration of about 1 to 3E19 atoms/cm³at the center of the halos for an NMOS transistor. It will be appreciated, however, that other implant concentrations are contemplated as falling within the scope of the present invention.
• Then, at208 a first oxide layer is formed over the gate and exposed portions of the substrate. The first oxide layer can be formed to a thickness of about 20 to 120 Angstroms, for example. A nitride layer and a second oxide layer are then sequentially formed over the first oxide layer at210 and212, respectively. The nitride layer can be formed to a thickness of about 50 to 200 Angstroms and the second oxide layer can be formed to about 400 to 800 Angstroms, for example. It will be appreciated that thefirst oxide layer208,nitride layer210 andsecond oxide layer212 can be formed in any number of suitable ways, such as with spin-on techniques, sputtering techniques (e.g., magnetron or ion beam sputtering), growth and/or deposition techniques such as chemical vapor deposition (CVD), for example.
• At214, the second oxide layer is processed (e.g., via dry etching, ion miling, or other suitable reduction techniques) to reveal oxide sidewall spacers adjacent to the gate. Such sidewall spacers can have a width of about 300 to 800 Angstroms, for example. At216, some of the oxide material is processed to reduce the sidewall spacers and the nitride layer is processed to remove nitride material not covered/protected by the oxide sidewall spacers. It will be appreciated, however, that the processing of the nitride layer and the oxide sidewall spacers may be performed in separate acts, where nitride material is selectively removed and then oxide is subsequently selectively removed (e.g., via wet etching, CMP, other suitable reduction techniques), where the residual nitride material underlying the oxide sidewall spacers serves as a processing stopper. In one example, the second oxide layer on the nitride layer is partially removed, and in another example, the oxide material is completely removed.
• At218, source and drain implants are performed at relatively low energies. These implants are substantially blocked by the sidewall spacers and the residual nitride material as well as any residual second oxide material that may be residing there-over. Accordingly, the sidewall spacers and residual nitride material together act as a boundary that guides the dopants into source and drain regions of the substrate. By way of example, a dopant of Arsenic or other suitable substance having a peak concentration of about 0.5 to 5E20 atoms/cm³may be implanted at an energy level of about 20 to 50 KeV to provide dopant to an implant range into silicon of about 300-350 Angstroms, for example.
• A compensation implant is then performed at220 to place dopant deeper into the source and drain regions of the substrate. By way of example, a dopant of Phosphorous or other suitable substance having a peak concentration of about 5E17 to 5E19 atoms/cm³may be implanted at an energy level of about 30 to 40 KeV to provide dopant to an implant range into silicon of about 600-700 Angstroms. It will be appreciated that the compensation dopant penetrates deeper into the substrate as a result of the different (e.g., greater) mass of the compensation dopant relative to the dopant utilized for the source/drain implants at218 and/or a different (e.g., greater) energy level utilized during the compensation implant. Regardless, the compensation dopant is generally implanted into the substrate to a depth about twice that of the source/drain implant at218.
• It will be appreciated that the subsequent selective oxide etching performed at216 may result in a reduction in the oxide sidewall spacers such that they are not flush with remaining/underlying nitride material. In this manner, some of the remaining nitride material may overlie underlying substrate areas whereas the oxide spacers no longer cover these areas. The type of dopant and/or energy level utilized in the compensation implant facilitates passage of the compensation dopant through the nitride material, whereas the oxide portion of the spacers substantially block the compensation dopant (as well as the source/drain dopant implanted at218). Accordingly, a portion of the dopant implanted into the source and drain regions during the compensation implant at220 is implanted closer to the channel. Moving the deep source/drain junctions towards the channel in this fashion reduces gate sidewall junction capacitances by smoothing out the junctions, thus facilitating improved switching speeds, as will be further appreciated infra.
• Turning now toFIGS. 10-23, an exemplary technique for forming a transistor according to one or more aspects of the present invention is disclosed. Initially, a layer of gatedielectric material302 is formed upon a semiconductor substrate304 (FIG. 10). It is to be appreciated that the term “semiconductor substrate” as used herein can include a base semiconductor wafer (e.g., silicon, SiGe, or an SOI wafer) and any epitaxial layers or other type semiconductor layers formed thereover or associated therewith. It is to be further appreciated that elements depicted herein are illustrated with particular dimensions relative to one another (e.g., layer to layer dimensions and/or orientations) for purposes of simplicity and ease of understanding, and that actual dimensions of the elements may differ substantially from that illustrated herein.
• The layer of gatedielectric material302 can include any of a number of suitable materials. Some examples include silicon dioxide, high-k materials, or a stack of such layers. It will be appreciated that the layer of gatedielectric material302 can be formed across thesubstrate304 in any of a number of suitable manners, including, for example, sputtering techniques (e.g., magnetron or ion beam sputtering), growth and/or deposition techniques, such as chemical vapor deposition (CVD). The layer of gate dielectric material can also be formed to a thickness of about 2.0 nanometers or more to mitigate “tunneling”, and can have an equivalent oxide thickness (EOT) of about 2.0 nanometers or less, for example, so as to maintain and exhibit desired electrical properties. A dielectric material having a k of about 7.8 and a thickness of about 10 nm, for example, is substantially electrically equivalent to an oxide gate dielectric having a k of about 3.9 and a thickness of about 5 nm.
• Agate electrode layer306 is then formed over the layer of gate dielectric material302 (e.g., via spin-on, sputtering, deposition, growth techniques, etc.) (FIG. 11). Thegate electrode layer306 generally includes doped polysilicon, SiGe or metal, and can be formed to a thickness of about 200 nanometers or less, for example. Thegate electrode layer306 ultimately yields a contact area or surface that provides a means for applying a voltage to thetransistor300 or otherwise biasing thetransistor300.
• Thegate electrode layer306 and the layer of gatedielectric material302 are then patterned to form a gate structure308 (FIG. 12). Thegate structure308 thus comprises agate electrode310 and agate dielectric312. It will be appreciated that the layers can be patterned in any suitable manner(s), either alone or in combination, to form thegate structure308, such as by etching.
• After thegate structure308 is formed, adopant314 is applied to thesubstrate304 to form source anddrain extension regions316,318 therein (FIG. 13). Such extension regions may, for example, be formed according to HDD (highly doped drain) techniques. The extension regions abut achannel region320 within thesubstrate304 under thegate structure308 and facilitate absorption of some of the potential associated with the drain. In this manner, some of this potential is directed away from the drain/channel interface, thereby mitigating the occurrence of channel hot carriers and the adverse effects associated therewith. By way of example, a p-type dopant having a concentration of about 1E19 to 5E20 atoms/cm³for a PMOS transistor, or an n-type dopant having concentration of about 1E19 to 9.5E20 atoms/cm³for an NMOS transistor can be implanted to a depth of about 300-350 Angstroms, for example, to establish theextension regions316,318. It will be appreciated, however, that other implant concentrations and penetration depths are contemplated as falling within the scope of the present invention.
• Anotherdopant322 is then applied to thesubstrate304 to formhalo regions324,326 over theextension regions316,318 (FIG. 14). The halo implants (or pocket implants) can facilitate scaling channel length by creating localized dopant distributions near the source/drain (S/D) regions, where the distributions may extend, at least partially, under the channel. In this manner, halos can mitigate unwanted source/drain leakage conduction, or punchthrough current, and as such, are sometimes referred to as “punchthrough stoppers”. A quad high-angle implant may be utilized, for example, to place a halo dose around an edge of the gate structure in source/drain regions of the semiconductor substrate. In one example, such a high-angle implant can place a halo dopant having a concentration of about 1 to 3E19 atoms/cm³at the center of the halos for an NMOS transistor. It will be appreciated, however, that other implant concentrations are contemplated as falling within the scope of the present invention.
• Afirst oxide layer328 is then formed over thegate structure308 and exposed portions of the substrate304 (FIG. 15). Thefirst oxide layer328 can be formed to a thickness of about 20 to 120 Angstroms, for example. Anitride layer330 is then formed over the first oxide layer328 (FIG. 16), and asecond oxide layer332 is formed over the nitride layer330 (FIG. 17). Thenitride layer330 can be formed to a thickness of about 50 to 200 Angstroms and thesecond oxide layer332 can be formed to about 400 to 800 Angstroms, for example. It will be appreciated that thefirst oxide layer328,nitride layer330 andsecond oxide layer332 can be formed in any number of suitable ways, such as with spin-on techniques, sputtering techniques (e.g., magnetron or ion beam sputtering), growth and/or deposition techniques such as chemical vapor deposition (CVD), for example. Thelayers328,330 and332 are not drawn to scale in the figures, but instead are shown enlarged to help facilitate an understanding of one or more aspects of the present invention.
• Thesecond oxide layer332 is then processed (e.g., via dry etching or other suitable reduction techniques) to revealoxide sidewall spacers334,336 adjacent to the gate structure308 (FIG. 18). Such sidewall spacers can have awidth338 of about 300 to 800 Angstroms, for example. It will be appreciated that this processing is selective such that theunderlying nitride layer330 is substantially unaffected by the processing.
• Thenitride layer330 is then processed (e.g., etched) to remove nitride material not covered/protected by theoxide sidewall spacers334,336 (FIG. 19). In the example shown the remaining orresidual nitride material330 has an “L” shape. It will be appreciated that this processing is also substantially selective such that theoxide sidewall spacers334,336 are not affected thereby. It will be further appreciated that any differences in the height and/or other dimension(s) of theoxide spacers334,336 depicted in the Figures is merely incidental and/or the result of intermediate acts that are generally understood, but that are not shown or described herein.
• Alternatively, the “L” shaped region may comprise another material having a slower etch rate than oxide. For example, the layer may comprise polysilicon or other suitable material, and such alternatives are contemplated by the present invention. Similarly, the first oxide layer could be replaced with another suitable material in accordance with the present invention.
• A portion of the remaining oxide material is subsequently processed (e.g., etched) to reduce the size of thesidewall spacers334,336 and to remove some or all of the exposed portions of the first oxide layer328 (FIG. 20). The width338 (FIGS. 18 and 19) of thesidewall spacers334,336 may, for example, be reduced to338′ (FIG. 20), where338 is greater than338′. Again, this processing is substantially selective such that the remaining (L shaped)nitride material330 is not affected thereby. In this manner, portions of thefirst oxide layer328 underlying theresidual nitride material330 are not affected by the processing. Moreover, the underlying L shapednitride layer330 can serve as a process (e.g., etch) stopper as the spacers are being processed. It will be appreciated that any differences in the height and/or other dimension(s) of the residual L shapednitride material330 depicted in the Figures is merely incidental and/or the result of intermediate acts that are generally understood, but that are not shown or described herein.
• It will be appreciated that theoxide sidewall spacers334,336 and thenitride layer330 are processed such that thesidewall spacers334,336 are reduced more than the nitride layer330 (FIG. 20). In this manner, aportion339 of the residual L shapednitride material330 having awidth339′ overlies areas of thesubstrate304 that are not covered by theoxide sidewall spacers334,336. This arrangement can be utilized to achieve certain doping profiles in thesubstrate304 as will be described below.
• Additional,dopant340 is then implanted in forming the source and drainregions342,344 (FIG. 21). These implants are done at relatively low energies and are substantially blocked by thesidewall spacers334,336 and theresidual nitride material330. Accordingly, thesidewall spacers334,336 andresidual nitride material330 together act as a boundary that guides thedopants340 in forming the source and drainregions342,344 in thesubstrate304. By way of example, a dopant of Arsenic or other suitable substance having a concentration of about 0.5 to 5E20 atoms/cm³may be implanted at an energy level of about 20 to 50 KeV to provide dopant to an implant range into silicon of about 300-350 Angstroms to form the source and drainregions342,344. It will be appreciated, however, that other implant concentrations, energy levels and/or penetration depths are contemplated as falling within the scope of the present invention.
• More dopant346 is then implanted into the source and drain regions in thesubstrate304 to formcompensation regions348,350 (FIG. 22). The dopant246 in thecompensation regions348,350 are implanted relatively deeply into thesubstrate304. By way of example, a dopant of Phosphorous or other suitable substance having a concentration of about 5E17 to 5E19 atoms/cm³may be implanted at an energy level of about 30 to 40 KeV to provide dopant to an implant range into silicon of about 600-700 Angstroms, for example. It will be appreciated that thecompensation dopant346 penetrates deeper into thesubstrate304 as a result of the different (e.g., greater) mass and/or energy level of thecompensation dopant346 relative to theother dopants314,322,340 utilized in doping thesubstrate304. In general, thecompensation dopant346 is implanted into thesubstrate304 to a depth about twice that of thedopant340 utilized in establishing the source and drainregions342,344.
• It will be appreciated that the selective oxide etching discussed above with respect toFIG. 20 leaves aportion339 of the L shaped nitride material uncovered by theoxide sidewall spacers334,336. Thedopant346 and/or energy level utilized in the compensation implant (FIG. 22) facilitates passage of the compensation dopant through thenitride material330, whereas theoxide spacers334,336 substantially block thecompensation dopant346, as well as the source/drain dopant340 (FIG. 21). Accordingly, thecompensation dopant346 is implanted in the substrate closer to thechannel320 than the source/drain dopant340. The separation between the deep compensation implants is thus smaller than it would be had the oxide sidewall spacers not been subsequently selectively processed (e.g., etched) to remove some of the oxide material and expose aportion339 of the L shaped nitride layer. This is evident by a comparison of thedistance352 between thedeep compensation implants348,350 where thesidewall spacers334,336 have been processed further (FIG. 22) and thedistance352′ between thedeep compensation implants348,350 in a situation where thesidewall spacers334,336 have not been subsequently processed (FIG. 23).
• It can be seen inFIGS. 22 and 23 that352′ is greater than352 by an amount equal to two times thewidth339′ of theportion339 of the L shapednitride layer330 that is not covered by theoxide spacers334,336. Since the source/drain regions342,344 and thecompensation regions348,350 are somewhat alignedFIG. 23, thedistance352′ can also be said to correspond to the distance between thesource342 and drain344 regions. Moving the deep junctions towards thechannel320 in the manner illustrated inFIG. 22 reduces junction areas where capacitance can arise. Reducing bottom wall areas in this fashion mitigates the opportunity for capacitive build up to occur, and thereby facilitates improved switching speeds.
• Accordingly, it will be appreciated that one or more aspects of the present invention facilitate channel length scaling by altering short channel characteristics. By changing the doping profile in and around the channel region, the distribution of the dopants and potential contours can be changed to facilitate attaining higher switching speeds in a MOS transistor, at a higher drive current (Ids), but at a lower junction capacitance under the gate (Cjswg).
• Although the invention has been shown and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art based upon a reading and understanding of this specification and the annexed drawings. The invention includes all such modifications and alterations and is limited only by the scope of the following claims. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”

Claims (7)

1-27. (canceled)

28. A transistor comprising:

a gate structure formed over a substrate;

a source region formed within the substrate adjacent the gate structure;

a drain region formed within the substrate adjacent the gate structure;

a first compensation region formed within the substrate adjacent the gate structure and within the source region;

a second compensation region formed within the substrate adjacent the gate structure and within the drain region;

a channel underlying the gate structure and separating the source and drain regions and the first and second compensation regions, the source and drain regions being separated by a first distance and the first and second compensation regions being separated by a second distance, the first distance being greater than the second distance.

29-33. (canceled)

34. A transistor, comprising:

a gate structure overlying a semiconductor body;

source and drain regions having a first depth and a first conductivity type within the semiconductor body, and defining a channel region therebetween having a second conductivity type below the gate structure;

extension regions of the first conductivity type having a second depth within the semiconductor body, and disposed between the source and drain regions and the channel, respectively;

halo regions of the second conductivity type having a third depth within the semiconductor body, and extending below the extension regions, wherein the third depth is greater than the second depth;

compensation regions of the first conductivity type having a portion disposed between the source and drain regions and their corresponding extension regions with a fourth depth, wherein the fourth depth is greater than the second depth and less than the third depth, and wherein a dopant concentration of the compensation regions is less than a dopant concentration of the source and drain regions, thereby defining a generally laterally extending junction having a first portion nearest the channel corresponding to the extension regions and halo regions, and a second portion corresponding to the compensation regions and the halo regions, respectively.

35. The transistor ofclaim 34, further comprising a multi-component spacer associated with sidewalls of the gate structure, the multi-component spacer comprising:

an “L” shaped spacer generally adjacent the sidewalls of the gate structure; and

another spacer residing on a first portion of the “L” shaped spacer and exposing a second portion of the “L” shaped spacer,

wherein the exposed portion of the “L” shaped spacer has a width that corresponds to a width of the second portion of the generally laterally extending junction.

36. The transistor ofclaim 35, wherein the “L” shaped spacer comprises an “L” shaped oxide spacer and an “L” shaped nitride spacer lying thereover.

37. The transistor ofclaim 35, wherein the “L” shaped spacer comprises an “L” shaped oxide spacer and an “L” shaped polysilicon spacer lying thereover, and wherein the another spacer comprises an oxide overlying a portion of the polysilicon.

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