Abstract:
A semiconductor device and a method of fabricating a semiconductor device are disclosed. In one embodiment, the method comprises providing a semiconductor substrate, epitaxially growing a Ge layer on the substrate, and epitaxially growing a semiconductor layer on the Ge layer, where the semiconductor layer has a thickness of 10 nm or less. This method further comprises removing at least a portion of the Ge layer to form a void beneath the Si layer, and filling the void at least partially with a dielectric material. In this way, the semiconductor layer becomes an extremely thin semiconductor-on-insulator layer. In one embodiment, after the void is filled with the dielectric material, in-situ doped source and drain regions are grown on the semiconductor layer. In one embodiment, the method further comprises annealing said source and drain regions to form doped extension regions in the semiconductor layer. Epitaxially growing the extremely thin semiconductor layer on the Ge layer ensures good thickness control across the wafer. This process could be used for SOI or bulk wafers.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to the field of semiconductors, and more particularly relates to extremely-thin silicon-on-insulator field-effect transistors having extremely-thin silicon layers, and a method of fabricating the same. 
         [0003]    2. Background Art 
         [0004]    In order to be able to make integrated circuits (ICs), such as memory, logic, and other devices, of higher integration density than currently feasible, one has to find ways to further downscale the dimensions of field effect transistors (FETs), such as metal-oxide-semiconductor field effect transistors (MOSFETs) and complementary metal oxide semiconductors (CMOS). Scaling achieves compactness and improves operating performance in devices by shrinking the overall dimensions and operating voltages of the device while maintaining the device&#39;s electrical properties. Additionally, all dimensions of the device must be scaled simultaneously in order to optimize the electrical performance of the device. 
         [0005]    With conventional planar FET scaling reaching fundamental limits, the semiconductor industry is looking at more unconventional geometries that will facilitate continued device performance improvements. As a result, attention has been given to using FETs with extremely thin silicon layers where the silicon or “device” layer has a thickness of from about seven run and about ten nm. When used with FETs having silicon on oxide, these devices are referred to as extremely thin silicon on oxide (ETSOI) devices. Extremely thin silicon layer technology can also be used with bulk wafers. 
         [0006]    ETSOI devices have very substantial advantages, however they also present difficult challenges. For instance, these devices can experience threshold-voltage and subthreshold slope fluctuation because of Si thickness variations across the wafer. For example, a typical SOI device may have a silicon layer thickness of from 4-8 nanometers (nm), with a variation of 1 or more nm across the wafer. 
         [0007]    Also, it has been determined that when implanting dopants into semiconductor layers that have a thickness of 10 nm or less, the ion implantation amorphizes the semiconductor layer. Recrystallizing the amorphous semiconductor layer is difficult, because of the limited amount of crystal seed layer that is available in semiconductor layers having a thickness of less than 10 nm that have been ion implanted into an amorphous crystal structure. The presence of an amorphous semiconductor material in a semiconductor device results in the semiconductor device having a high external resistance. Further, the resistance of the semiconductor device is increased by defects in the semiconductor layer that are produced by ion implantation. The ion implantation may also damage the gate dielectric. 
       BRIEF SUMMARY 
       [0008]    Embodiments of the invention provide a semiconductor device and a method of fabricating a semiconductor device. In one embodiment, the method comprises providing a semiconductor substrate, epitaxially growing a germanium-containing (Ge) layer on the substrate, and epitaxially growing a germanium-containing (Ge) layer, where the semiconductor layer has a thickness of 10 nm or less. This method further comprises removing at least a portion of the Ge layer to form a void beneath the semiconductor layer, and filling the void at least partially with a dielectric material. In this way, the semiconductor layer becomes an extremely thin semiconductor-on-insulator layer. 
         [0009]    Epitaxially growing the extremely thin semiconductor layer on the Ge layer ensures good thickness control across the wafer. This process could be used for SOI or bulk wafers. 
         [0010]    In one embodiment, after the void is filled with the dielectric material, in-situ doped source and drain regions are grown on the semiconductor layer. In one embodiment, the method further comprises annealing said source and drain regions to form doped extension regions in the semiconductor layer. 
         [0011]    In one embodiment, the removing includes dissolving said at least a portion of the Ge layer. In an embodiment, said removing includes etching away at least a part of the Ge layer. 
         [0012]    In an embodiment, the method further comprises forming isolation regions in the substrate, and anchoring the semiconductor layer at said isolation regions while removing said at least a portion of the Ge layer. 
         [0013]    In one embodiment, the semiconductor layer is comprised of Si. In an embodiment, the Ge layer is comprised of SiGe. In one embodiment, the dielectric material may be or include a single dielectric material; and in another embodiment, the dielectric material may be or include a multi-layer dielectric material. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]      FIG. 1   a  illustrates an initial structure used in one embodiment of the present invention, where the structure includes a bulk Si semiconductor. 
           [0015]      FIG. 2   a  shows an initial structure used in a second embodiment of the invention, where the structure includes a SOI substrate. 
           [0016]      FIGS. 1   b  and  2   b  show spacers formed on the gates of the structures shown in  FIGS. 1   a  and  2   a.    
           [0017]      FIGS. 1   c  and  2   c  depict shallow trench isolation regions that may be formed in the substrates of  FIGS. 1   a  and  2   a.    
           [0018]      FIGS. 1   d  and  2   d  illustrate etching or dissolving the SiGe layers of the structures of  FIGS. 1   a  and  2   a.    
           [0019]      FIGS. 1   e  and  2   e  show the voids that are formed when the SiGe layers are removed. 
           [0020]      FIGS. 1   f  and  2   f  depict doped source and drain regions that are grown on the structures of  FIGS. 1   e  and  2   e.    
           [0021]      FIGS. 1   g  and  2   g  show doped extension regions that are formed in the structures of  FIGS. 1   f  and  2   f.    
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention is intended to be illustrative, and not restrictive. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0023]    In one embodiment, the present invention relates to a method for forming a planar semiconductor device on a semiconductor on insulator (SOI) substrate having an extremely thin semiconductor on insulator (ETSOI) layer. An extremely thin semiconductor on insulator (ETSOI) layer is the semiconductor layer that is present atop the buried insulating layer of an SOI substrate, wherein the ETSOI layer has a thickness of 10 nm or less. In accordance with an embodiment of the present invention, source and drain extension regions are formed in the ETSOI layer using an in situ doped epitaxial growth process followed by an annealing process to drive the dopant from the in-situ doped epitaxial semiconductor material into the ETSOI layer to provide extension regions without utilizing ion implantation. 
         [0024]      FIGS. 1   a - 1   g  and  2   a - 2   g  show two embodiments of the present invention.  FIGS. 1   a - 1   g  illustrate a device  100 , and a method of fabricating the device, including an extremely thin silicon layer  102  above a bulk semiconductor substrate  104 .  FIGS. 2   a - 2   g  illustrate a device  200  including an extremely thin silicon layer  202  above a substrate  204 . This substrate  204 , in turn, includes semiconductor layers  206  and  210  and insulating layer  212 , such as a buried oxide (BOX) layer.  FIGS. 1   a  and  2   a  also show a SiGe layer  114 ,  214  directly beneath the silicon layers  102 ,  202 , and a gate  116 ,  216  extending upward from layers  102 ,  202 . 
         [0025]    With reference to  FIG. 1   a , substrate  104  typically is Si although other suitable semiconductor materials may be used. For example, SiC, SiGe, SiGeC, Si alloys, Ge, Ge alloys, GaAs, InAs, and InP, as well as other III/V and II/VI compound semiconductors, may be used. 
         [0026]    With reference to  FIG. 2   a , semiconductor layers  206  and  210  also typically are Si, although other suitable semiconductor materials may be used. For example, SiC, SiGe, SiGeC, Si alloys, Ge, Ge alloys, GaAs, InAs, and InP, as well as other III/V and II/VI compound semiconductors, may be used. 
         [0027]    The dielectric layer  212  present in device  200  may be formed in any suitable way. For instance, layer  212  may be formed by implanting a high-energy dopant into the substrate  204  and then annealing the structure to form a buried insulating layer, i.e., dielectric layer  212 . In another embodiment, the dielectric layer  212  may be deposited or grown prior to the formation of the silicon layer  210 . In yet another embodiment, the substrate  204  may be formed using wafer-bonding techniques, where a bonded wafer pair is formed utilizing glue, adhesive polymer, or direct bonding. 
         [0028]    Generally, the two devices  100  and  200 , and the processes by which they are fabricated, are basically similar, with the exception that the device  200  includes the above-mentioned insulating layer  212  and silicon layer  210  on top of that insulating layer. 
         [0029]    In both of these devices  100 ,  200 , the semiconductor layer  102 ,  202  has a thickness of less than 10 nm, and the devices are fabricated without using ion implantation to provide the source and drain regions and the extensions regions of the semiconductor device. It has been determined, as mentioned above, that when implanting dopants into semiconductor layers that have a thickness of 10 nm or less, the ion implantation amorphizes the semiconductor layer. Recrystallizing the amorphous semiconductor layer is difficult, because of the limited amount of crystal seed layer that is available in semiconductor layers having a thickness of less than 10 nm that have been ion implanted into an amorphous crystal structure. The presence of an amorphous semiconductor material in a semiconductor device results in the semiconductor device having a high external resistance. 
         [0030]    Further, the resistance of the semiconductor device is increased by defects in the semiconductor layer that are produced by ion implantation. The ion implantation may also damage the gate dielectric. In one embodiment, the invention disclosed herein overcomes the disadvantages that result from ion implantation, by forming the source and drain regions in an extremely thin silicon layer, i.e., semiconductor layer  102 ,  202 , using an in-situ doped epitaxial semiconductor growth process followed by an annealing process. The annealing process drives the dopant from the in-situ doped epitaxial semiconductor material  102 ,  202 , i.e., in-situ doped epitaxial semiconductor raised source and drain regions, to provide extension regions. 
         [0031]    The fabrication of both devices  100  and  200  may start with a respective substrate  104  and  204 . In both embodiments, a SiGe layer  114 ,  214  is formed at the top of the initial substrate  104 ,  204 , and a Si layer  102 ,  202  is epitaxially grown on top of the SiGe layer. 
         [0032]    In one embodiment, germanium ions are implanted into substrates  104 ,  204  to form a disposable SiGe layer  114 ,  214 . Any suitable procedure may be used to do this, and for example, in an embodiment, the dose of the germanium ion implant is approximately 10 15 /cm 2 , and the energy of the germanium ion implant is less than 200 KeV. In another embodiment, the disposable SiGe layer  114 ,  214  is formed by epitaxially growing SiGe on the substrate  104 ,  204 , respectively. 
         [0033]    The Ge content of the SiGe may range from 5% to 60%, by atomic weight %. In another embodiment, the Ge content of the epitaxial grown SiGe may range from 10% to 40%. The epitaxial grown SiGe may be under an intrinsic compressive strain, in which the compressive strain is produced by a lattice mismatch between the larger lattice dimension of the SiGe and the smaller lattice dimension of the layer on which the SiGe is epitaxially grown. In one embodiment, the epitaxial grown SiGe produces a compressive strain in a portion of the layer  102 ,  202 , in which the channel of a semiconductor device, such as a pFET device, is subsequently formed. 
         [0034]    The extremely thin silicon (ETS) layers  102 ,  202  are epitaxially grown on the SiGe layers  114 ,  214 . The ETS layers  102 ,  202  may comprise any semiconducting material including, but not limited to Si, strained Si, SiC, SiGe, SiGeC, Si alloys, Ge, Ge alloys, GaAs, InAs, and InP, or any combination thereof. In one embodiment, the ETS layer  102 ,  202  has a thickness ranging from 1.0 nm to 10.0 nm. In another embodiment, the ETS layer  102 ,  202  has a thickness ranging from 1.0 nm to 5.0 nm. In a further embodiment, the ETS layer has a thickness ranging from 3.0 nm to 8.0 nm. 
         [0035]    As mentioned above, layers  102  and  202  are undoped or in-situ doped semiconductor materials formed on exposed surfaces of SiGe layers  114 ,  214 . In one embodiment, the in-situ doped semiconductor material  102 ,  202  is formed using an epitaxial growth process. When the chemical reactants are controlled and the system parameters set correctly, the depositing atoms arrive at the surface of the layer  114 ,  214  with sufficient energy to move around on the surface and orient themselves to the crystal arrangement of the atoms of the deposition surface. Thus, an epitaxial film deposited on a {100} crystal surface will take on a {100} orientation. If, on the other hand, the wafer surface has an amorphous surface layer, possibly the result of implanting, the depositing atoms have no surface to align to, resulting in the formation of polysilicon instead of single crystal silicon. 
         [0036]    A number of different sources may be used for the deposition of epitaxial silicon. Silicon sources for epitaxial growth include silicon tetrachloride, dichlorosilane (SiH 2 Cl 2 ), and silane (SiH 4 ). The temperature for epitaxial silicon deposition typically ranges from 550° C. to 900° C. Although a higher temperature typically results in faster deposition, the faster deposition may result in crystal defects and film cracking. 
         [0037]    In one embodiment, the in-situ doped semiconductor material  102 ,  202  is doped with a first conductivity type dopant during the epitaxial growth process. In one embodiment, the in-situ doped semiconductor material  102 ,  202  provides the raised source and drain regions of a semiconductor device. P-type MOSFET devices are produced by doping the in-situ doped semiconductor material  116 ,  216  with elements from group III of the Periodic Table of Elements. In one embodiment, the group III element is boron, aluminum, gallium or indium. In one example, in which the in-situ doped semiconductor material  102 ,  202  is doped to provide a p-type conductivity, the dopant may be boron present in a concentration ranging from 1×10 18  atoms/cm 3  to 2×10 21  atoms/cm 3 . 
         [0038]    In one embodiment, the in-situ doped semiconductor material  102 ,  202  is doped with a second conductivity type dopant during the epitaxial growth process. In one embodiment, the in-situ semiconductor material  102 ,  202  provides the raised source and drain regions of a semiconductor device, in which n-type MOSFET devices are produced by doping the in-situ doped semiconductor material  102 ,  202  with elements from group V of the Periodic Table of Elements. In one embodiment, the group V element is phosphorus, antimony or arsenic. 
         [0039]      FIGS. 1   a  and  2   a  also depict a gate structure  116 ,  216  formed directly on the first semiconductor layer  102 ,  202 , in accordance with one embodiment of the present invention. The gate structure  116 ,  216  can be formed using deposition, photolithography, and a selective etching process. Specifically, a pattern is produced by applying a photoresist to the surface to be etched, exposing the photoresist to a pattern of radiation, and then developing the pattern into the photoresist utilizing a resist developer. Once the patterning of the photoresist is completed, the sections covered by the photoresist are protected while the exposed regions are removed using a selective etching process that removes the unprotected regions. 
         [0040]    In one embodiment, a hard mask (hereafter referred to as a dielectric cap) may be used to form the gate structure  116 ,  216 . The dielectric cap may be formed by first depositing a dielectric hard mask material, like silicon nitride or silicon oxide, atop a layer of gate electrode material and then applying a photoresist pattern to the hard mask material using a lithography process. The photoresist pattern is then transferred into the hard mask material using a dry etch process forming the dielectric cap. Next the photoresist pattern is removed and the dielectric cap pattern is then transferred into the gate electrode material during a selective etching process. The dielectric cap may be removed by a wet or dry etch prior to a silicide process. Alternatively, the gate structure  116 ,  216  can be formed by other patterning techniques such as spacer image transfer. 
         [0041]    The gate structures  116 ,  216  may include at least a gate conductor atop a gate dielectric. This gate conductor, in turn, may be a metal gate electrode and a second conductive material atop the metal gate electrode. The metal gate electrode may be any conductive metal including, but not limited to, W, Ni, Ti, Mo, Ta, Cu, Pt, Ag, Au, Ru, Ir, Rh, and Re, and alloys that include at least one of the aforementioned conductive elemental metals. In one example, the second conductive material atop the metal gate electrode may be a doped semiconductor material, such as a doped silicon containing material, e.g., doped polysilicon. When a combination of conductive elements is employed, an optional diffusion bather material such as TaN or WN may be formed between the conductive materials. 
         [0042]    The gate conductor of the gate structure  116 ,  216  is typically present on a gate dielectric that may be, for example, a dielectric material, such as silicon oxide, or alternatively high-k dielectrics, such as oxides of Ta, Zr, Al or combinations thereof. In another embodiment, the gate dielectric is comprised of an oxide, such as silicon oxide, ZrO 2 , Ta 2 O 5  or Al 2 O 3 . In one embodiment, the gate dielectric has a thickness ranging from 1 nm to 10 nm. In another embodiment, the gate dielectric has a thickness ranging from 1.5 nm to 5 nm. 
         [0043]      FIGS. 1   b  and  2   b  depict first spacers  120 ,  220  formed in direct contact with the sidewalls of the gate structures  116 ,  216 . The first spacers  120 ,  220  are typically narrow, having a width ranging from 2.0 nm to 15.0 nm. The first spacers  120 ,  220  can be formed using deposition and etch processing steps. The first spacers  120 ,  220  may be composed of a dielectric, such as nitride, oxide, oxynitride, or a combination thereof. The thickness of the first spacers  120 ,  220  determines the proximity of the subsequently formed raised source/drain (RSD) regions to the channel of the devices  100 ,  200 . 
         [0044]    With reference to  FIGS. 1   c  and  2   c , shallow trench isolation (STI) regions, represented at  124 ,  224 , are formed in devices  100  and  200 , on either sides of gates  120  and  220 . Any suitable procedure may be used to form these trenches. In one embodiment, the STI regions  124 ,  224  are formed in the substrate  104 ,  204  and filled with dielectric material, such as silicon oxide. Other types of isolation regions may also be used. STI can be formed before the formation of gate structure  116 ,  216 . 
         [0045]    Trenches  124  and  224  may be formed, for example, by lithography and etching. The lithography step includes applying a photoresist to the surface of the device substrate, exposing the photoresist, and developing the exposed photoresist using a conventional resist developer. The etching step used in forming the trenches  124 ,  224  may include, for example, any standard Si directional reactive ion etch process. Other dry etching processes such as plasma etching, ion beam etching and laser ablation may also be employed. Portions of the layer  102 ,  202  that are protected by the patterned photoresist are not removed during etching. After etching, the patterned photoresist is removed utilizing a conventional resist stripping process. 
         [0046]    SiGe underlayers  114 ,  214  are dissolved to form silicon-on-nothing, and any suitable procedure may be employed to do this. For example, access to the SiGe underlayers  114 ,  214  may be provided by a selective etching of the isolation trenches  124 ,  224  until lateral access is provided to the SiGe layers. This etching may be performed in a conventional manner, for example by an anisotropic plasma etch. The process then continues, as illustrated in  FIGS. 1   d  and  2   d , with the removal of the SiGe layer by selective lateral etching. SiGe can be removed, either by oxidizing chemistry (such as by etching with a solution having 40 ml of 70% HNO 3 +20 ml of H 2 O 2 +5 ml of 0.5% HF) or by isotropic plasma etching. During this process, the Si layers  102 ,  202  and the SiGe layers  114 ,  214  are anchored at the STI regions. 
         [0047]      FIGS. 1   d  and  2   d  illustrate perspective views of the devices  100  and  200  after the etching of the trenches and lateral etching of the SiGe or Ge layer  114 ,  214 . There is a void  130 ,  230  under the silicon epitaxial layer  102 ,  202 , inside or on top of the initial substrate  104 ,  204 . Supports (not shown) may be located around the perimeter of the void  130 ,  230  at predetermined intervals to maintain the structure. 
         [0048]    With reference to  FIGS. 1   e  and  2   e , the voids  130 ,  230  are then filled with a dielectric  132 ,  232  for the purpose of achieving an epitaxial SOI layer. Any suitable dielectric may be used, and for instance, silicon oxide may be used. The dielectric layer  132 ,  232  may be formed by thermal oxidation of the silicon layer, by a conventional deposition process, or else by a hybrid process. In one embodiment, the surfaces forming the voids  130 ,  230  may be passivated by thermal oxidation, and then the voids  130 ,  230  may be completely filled with a dielectric different from silicon oxide, such as silicon nitride. The process then continues with the filling of the trenches  124 ,  224  with a dielectric. This dielectric may be the same as that used in the STI process. 
         [0049]    As illustrated in  FIGS. 1   f  and  2   f , in-situ doped source regions  134 ,  234  and drain regions  136 ,  236  are then grown on substrates  104 ,  204 , and any suitable procedure may be used to grow these regions. For example, to form an N-type region, the region may be grown with elements from group V of the Periodic Table of Elements, such as phosphorus, antimony or arsenic. To form a P-type region, the region may be grown with elements, such as boron, aluminum, gallium or indium, from group III of the Periodic Table of Elements. 
         [0050]    An annealing process is used to drive dopant from the in-situ doped source regions  134 ,  234  and drain regions  136 ,  236  into the ETSOI layers  102 ,  202  to form extension regions, shown at  140 ,  240  in  FIGS. 1   g  and  2   g . In one embodiment, the dopant from the source and drain regions is diffused into the ETSOI layers  102 ,  202  by an annealing process including, but not limited to: rapid thermal annealing, furnace annealing, flash lamp annealing, laser annealing, or any suitable combination thereof. In one embodiment, thermal annealing to diffuse the dopant into the ETSOI layer  102 ,  202  is conducted at a temperature ranging from about 850° C. to about 1350° C. 
         [0051]    In one embodiment, the extension regions  140 ,  240  that are formed in the ETSOI layer  102 ,  202  have a p-type conductivity. Typically, the dopant concentration of the extension regions having the p-type conductivity ranges from 1×10 19  atoms/cm 3  to 2×10 21  atoms/cm 3 . In another embodiment, the extension regions  45  have the p-type conductivity ranging from 2×10 19  atoms/cm 3  to 5×10 20  atoms/cm 3 . 
         [0052]    In another embodiment, in which the source and drain regions are doped to an n-type conductivity, the extension regions  140 ,  240  that are formed in the ETSOI layer  102 ,  202  have an n-type conductivity. Typically, the dopant concentration of the extension regions having the n-type conductivity ranges from 1×10 19  atoms/cm 3  to 2×10 21  atoms/cm 3 . In another embodiment, the extension regions have the p-type conductivity ranging from 2×10 19  atoms/cm 3  to 5×10 20  atoms/cm 3 . 
         [0053]    In one embodiment, the extension regions  140 ,  240  have a depth that extends the entire depth of the ETSOI layer  102 ,  202 . Therefore, the extension regions have a depth of less than 10 nm, typically being 3 nm to 8 nm in depth, as measured from the upper surface of the ETSOI layer  102 ,  202 . 
         [0054]    Additional processing steps, if desired or appropriate, may be performed. For example, silicides may be formed on the raised source and drain regions of the device, i.e., the in-situ doped semiconductor material  102 ,  202 . Silicide formation typically requires depositing a refractory metal such as cobalt, nickel, or titanium onto the surface of a Si-containing material. Following deposition, the structure is subjected to an annealing step using conventional processes such as, but not limited to, rapid thermal annealing. During thermal annealing, the deposited metal reacts with Si forming a metal silicide. The remaining unreacted metal is removed by an etch process selective to silicides and spacers  120 ,  220 . A gate silicide may also be formed on the gate conductor. 
         [0055]    Following silicide formation, a layer of dielectric material can be blanket deposited atop the entire substrate and planarized. The blanket dielectric may be selected from the group comprising silicon-containing materials such as silicon oxide, silicon nitride, silicon oxynitride, carbon-containing silicon, SiCO, SiCOH, and SiCH compounds; the above-mentioned silicon-containing materials with some or all of the Si replaced by Ge; carbon-doped oxides; inorganic oxides; inorganic polymers; hybrid polymers; organic polymers such as polyamides or SiLK™; other carbon-containing materials; organo-inorganic materials such as spin-on glasses and silsesquioxane-based materials; and diamond-like carbon (DLC, also known as amorphous hydrogenated carbon, α-C:H). Additional choices for the blanket dielectric include: any of the aforementioned materials in porous form, or in a form that changes during processing to or from being porous and/or permeable to being non-porous and/or non-permeable. 
         [0056]    The deposited dielectric is then patterned and etched to form via holes to the various source/drain and gate conductor regions of the device. Following via formation interconnects may be formed by depositing a conductive metal into the via holes using deposition methods, such as CVD or plating. The conductive metal may include, but is not limited to: tungsten, copper, aluminum, silver, gold and alloys thereof. 
         [0057]    The above process may provide a planar semiconductor device that includes a substrate having an extremely thin layer of semiconductor material  102 ,  202  atop an insulating layer, wherein the layer of semiconductor material has a thickness of less than 10.0 nm. A gate structure  116 ,  126  is present on the semiconductor material. The planar semiconductor device includes doped epitaxial raised source and drain regions (in-situ doped semiconductor material  102 ,  202 ) that are present atop the semiconductor material, and extension diffusions  140 ,  240  extending from the doped epitaxial raised source and drain regions into the semiconductor material. 
         [0058]    While it is apparent that the invention herein disclosed is well calculated to fulfill objects discussed above, it will be appreciated that numerous modifications and embodiments may be devised by those skilled in the art, and it is intended that the appended claims cover all such modifications and embodiments as fall within the true spirit and scope of the present invention.