Process method of source drain spacer engineering to improve transistor capacitance

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.

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 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.

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. 1illustrates a conventional semiconductor transistor device100that can be fabricated with conventional complimentary MOS (CMOS) processing techniques in a semiconductor substrate102. The device100includes a gate structure104comprising a gate electrode106and a gate dielectric108. The gate electrode106generally comprises polysilicon or SiGe and overlies the gate dielectric108. Sidewall spacers110,112are located upon either side of the gate structure104. As will be discussed further, the sidewall spacers110,112impede doping of certain areas or extension regions114,116underlying the spacers110,112. Two laterally spaced doped source/drain regions118and120are formed within the substrate102and a channel region122is defined therebetween under the gate structure104.

In operation, the resistivity of the channel122may be controlled by a voltage applied to the gate electrode106, where changing the gate voltage changes the amount of current flowing through the channel122between the source and drain. The gate contact or electrode106and the channel122are separated by the gate dielectric108, which is an insulator and which opposes current flow between the gate electrode106and the channel122, such that the device does not become activated until a sufficient voltage (at least larger than a threshold voltage Vt) is applied to the gate electrode106.

To form the device100, a layer of dielectric material124is 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). The gate electrode layer126and the layer of dielectric material124are then patterned (e.g., via etching) to develop the gate structure104(FIG.4). Dopant128is then applied to the gate electrode106and to exposed portions of the substrate102to form extension regions130,132therein (FIG.5). As will become apparent, the extension regions130,132are precursors to portions of the source and drain regions118,120formed within the substrate102.

A layer of an insulating material134(e.g., silicon nitride, silicon oxide) is then formed over the entire structure (FIG.6). The layer of insulating material134is selectively removed (e.g., via anisotropic etching) to form the sidewall spacers110,112on either side of the gate structure104(FIG.7). Additional dopant128is then applied to the gate electrode106and the substrate102, except for those portions114,116covered by the sidewall spacers110,112(FIG.8). The additional dopant128establishes the source and drain regions118,120within the substrate102on either side of the gate structure104. It will be appreciated that the additional dopant128is of substantially the same type as that previously applied in forming the extension regions130,132(e.g., FIG.5). The channel region122is thereby defined within the substrate102under the gate structure104as the source and drain regions118,120are formed (FIG.8).

Turning now toFIG. 9, a methodology200is illustrated for forming a MOS transistor according to one or more aspects of the present invention. Although the methodology200is 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.

The methodology200begins at202wherein 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 to204wherein 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 to206wherein 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, at208a 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 at210and212, 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 the first oxide layer208, nitride layer210and second oxide layer212can 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 milling, 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 at220to 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 at218and/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 at216may 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 at220is 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 gate dielectric material302is 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 gate dielectric material302can 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 gate dielectric material302can be formed across the substrate304in 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.

A gate electrode layer306is then formed over the layer of gate dielectric material302(e.g., via spin-on, sputtering, deposition, growth techniques, etc.) (FIG.11). The gate electrode layer306generally includes doped polysilicon, SiGe or metal, and can be formed to a thickness of about 200 nanometers or less, for example. The gate electrode layer306ultimately yields a contact area or surface that provides a means for applying a voltage to the transistor300or otherwise biasing the transistor300.

The gate electrode layer306and the layer of gate dielectric material302are then patterned to form a gate structure308(FIG.12). The gate structure308thus comprises a gate electrode310and a gate dielectric312. It will be appreciated that the layers can be patterned in any suitable manner(s), either alone or in combination, to form the gate structure308, such as by etching.

After the gate structure308is formed, a dopant314is applied to the substrate304to form source and drain extension regions316,318therein (FIG.13). Such extension regions may, for example, be formed according to HDD (highly doped drain) techniques. The extension regions abut a channel region320within the substrate304under the gate structure308and 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 the extension 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.

Another dopant322is then applied to the substrate304to form halo regions324,326over the extension 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.

A first oxide layer328is then formed over the gate structure308and exposed portions of the substrate304(FIG.15). The first oxide layer328can be formed to a thickness of about 20 to 120 Angstroms, for example. A nitride layer330is then formed over the first oxide layer328(FIG.16), and a second oxide layer332is formed over the nitride layer330(FIG.17). The nitride layer330can be formed to a thickness of about 50 to 200 Angstroms and the second oxide layer332can be formed to about 400 to 800 Angstroms, for example. It will be appreciated that the first oxide layer328, nitride layer330and second oxide layer332can 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. The layers328,330and332are 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.

The second oxide layer332is then processed (e.g., via dry etching or other suitable reduction techniques) to reveal oxide sidewall spacers334,336adjacent to the gate structure308(FIG.18). Such sidewall spacers can have a width338of about 300 to 800 Angstroms, for example. It will be appreciated that this processing is selective such that the underlying nitride layer330is substantially unaffected by the processing.

The nitride layer330is then processed (e.g., etched) to remove nitride material not covered/protected by the oxide sidewall spacers334,336(FIG.19). In the example shown the remaining or residual nitride material330has an “L” shape. It will be appreciated that this processing is also substantially selective such that the oxide sidewall spacers334,336are not affected thereby. It will be further appreciated that any differences in the height and/or other dimension(s) of the oxide spacers334,336depicted 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 the sidewall spacers334,336and to remove some or all of the exposed portions of the first oxide layer328(FIG.20). The width338(FIGS. 18 and 19) of the sidewall spacers334,336may, for example, be reduced to338′ (FIG.20), where338is greater than338′. Again, this processing is substantially selective such that the remaining (L shaped) nitride material330is not affected thereby. In this manner, portions of the first oxide layer328underlying the residual nitride material330are not affected by the processing. Moreover, the underlying L shaped nitride layer330can 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 shaped nitride material330depicted 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 the oxide sidewall spacers334,336and the nitride layer330are processed such that the sidewall spacers334,336are reduced more than the nitride layer330(FIG.20). In this manner, a portion339of the residual L shaped nitride material330having a width339′ overlies areas of the substrate304that are not covered by the oxide sidewall spacers334,336. This arrangement can be utilized to achieve certain doping profiles in the substrate304as will be described below.

Additional, dopant340is then implanted in forming the source and drain regions342,344(FIG.21). These implants are done at relatively low energies and are substantially blocked by the sidewall spacers334,336and the residual nitride material330. Accordingly, the sidewall spacers334,336and residual nitride material330together act as a boundary that guides the dopants340in forming the source and drain regions342,344in the substrate304. 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 drain regions342,344. 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 dopant346is then implanted into the source and drain regions in the substrate304to form compensation regions348,350(FIG.22). The dopant246in the compensation regions348,350are implanted relatively deeply into the substrate304. 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 the compensation dopant346penetrates deeper into the substrate304as a result of the different (e.g., greater) mass and/or energy level of the compensation dopant346relative to the other dopants314,322,340utilized in doping the substrate304. In general, the compensation dopant346is implanted into the substrate304to a depth about twice that of the dopant340utilized in establishing the source and drain regions342,344.

It will be appreciated that the selective oxide etching discussed above with respect toFIG. 20leaves a portion339of the L shaped nitride material uncovered by the oxide sidewall spacers334,336. The dopant346and/or energy level utilized in the compensation implant (FIG. 22) facilitates passage of the compensation dopant through the nitride material330, whereas the oxide spacers334,336substantially block the compensation dopant346, as well as the source/drain dopant340(FIG.21). Accordingly, the compensation dopant346is implanted in the substrate closer to the channel320than 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 a portion339of the L shaped nitride layer. This is evident by a comparison of the distance352between the deep compensation implants348,350where the sidewall spacers334,336have been processed further (FIG. 22) and the distance352′ between the deep compensation implants348,350in a situation where the sidewall spacers334,336have not been subsequently processed (FIG.23).

It can be seen inFIGS. 22 and 23that352′ is greater than352by an amount equal to two times the width339′ of the portion339of the L shaped nitride layer330that is not covered by the oxide spacers334,336. Since the source/drain regions342,344and the compensation regions348,350are somewhat alignedFIG. 23, the distance352′ can also be said to correspond to the distance between the source342and drain344regions. Moving the deep junctions towards the channel320in the manner illustrated inFIG. 22reduces 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).