Patent Publication Number: US-10790148-B2

Title: Method to increase effective gate height

Description:
BACKGROUND 
     The present application relates generally to methods for forming semiconductor devices, and more specifically to methods for forming devices such as fin field effect transistors (FinFETs) having a reduced risk of electrical shorts between gate and source/drain contacts. 
     A trend in the development of semiconductor manufacturing technologies has been to increase the density of devices per chip, and hence decrease the size of active structures as well as the distances between such structures. An increase in device density may advantageously affect device performance such as circuit speed, and may allow also for increasingly complex designs and functionality. However, the decrease in size and the attendant increase in density may also generate undesirable effects, including unwanted short circuits between adjacent conductive elements. 
     In advanced node FinFET devices, for instance, the proximity of gate contacts and source/drain contacts may lead to unwanted parasitic capacitance or conduction, i.e., leakage, between these adjacent structures, particularly at the respective top and bottom portions of the structures, which can adversely affect performance and yield. 
     SUMMARY 
     It is therefore desirable to develop semiconductor device architectures and methods for fabricating semiconductor device architectures that have a decreased propensity for unwanted short circuits or parasitic capacitance between adjacent conductive elements, such as between adjacent gate and source/drain contacts. 
     In accordance with various embodiments, the formation of a semiconductor device includes the formation of a supplemental sacrificial gate that extends the height of a sacrificial gate and enables the formation of an improved gate cap, which provides an effective gate-to-source/drain dielectric barrier. In certain embodiments, the enhanced sacrificial gate height enables the formation of a thicker T-shaped gate cap as well as a thicker cap over source/drain contacts. 
     An exemplary device includes a layer of semiconductor material having a source/drain region and a channel region adjacent to the source/drain region, a conductive contact disposed over the source/drain region, a gate stack disposed over the channel region, and a capping layer disposed over the gate stack, where the gate cap has a lower portion having a first width, an upper portion having a second width greater than the first width, and the lower portion and the upper portion have substantially vertical sidewalls. The semiconductor layer may include a layer of an SOI substrate, or a portion of a semiconductor fin formed over a substrate. 
     A further device includes a semiconductor layer having a source/drain region and a channel region adjacent to the source/drain region, a conductive contact disposed over the source/drain region, a gate stack disposed over the channel region, a gate cap disposed over the gate stack, where the gate cap has a lower portion having a first width, an upper portion having a second width greater than the first width, and a low-k spacer layer disposed between the conductive contact and the lower portion of the gate cap. 
     According to various embodiments, a method of forming a semiconductor device includes forming a semiconductor layer over a semiconductor substrate, where the semiconductor layer has a source/drain region and a channel region adjacent to the source/drain region, forming a sacrificial gate over the channel region of the semiconductor layer, and forming a hard mask over the sacrificial gate. 
     A first spacer layer is deposited over sidewalls of the sacrificial gate and over sidewalls of the hard mask, and a second spacer layer is deposited over sidewalls of the first spacer layer. Thereafter, the hard mask and portions of the first spacer layer are removed to form an opening over the sacrificial gate, and a supplemental sacrificial gate is formed within the opening. 
     The method further includes etching the second spacer layer to form a recess, forming a sacrificial capping layer within the recess, removing the supplemental sacrificial gate and the sacrificial gate to form a gate opening, removing the second spacer layer from upper sidewalls of the gate opening above the first spacer layer, forming a functional gate within the gate opening over the channel region of the semiconductor layer, and forming a gate cap within the gate opening over the functional gate. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description of specific embodiments of the present application can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  is a schematic cross-sectional diagram of a FinFET device at an intermediate stage of fabrication including a semiconductor fin having alternating source/drain and channel regions, a sacrificial gate and a sacrificial gate hard mask disposed over the channel regions of the fin, and a composite spacer layer disposed over sidewalls of the sacrificial gate and the sacrificial gate hard mask; 
         FIG. 2  shows a cross-section of the FinFET device of  FIG. 1  after the formation of epitaxial source/drain junctions over the source/drain regions of the fin; 
         FIG. 3  shows the formation of a conformal contact etch stop layer within contact locations over the source/drain junctions and a dielectric fill layer over the contact etch stop layer; 
         FIG. 4  depicts removal of the sacrificial gate hard mask from over the sacrificial gate; 
         FIG. 5  depicts the formation of a supplemental sacrificial gate over the sacrificial gate; 
         FIG. 6  shows a recess etch of a sidewall spacer layer, the contact etch stop layer and the dielectric fill layer between adjacent sacrificial gates; 
         FIG. 7  depicts the formation of a sacrificial capping layer over the recessed architecture of  FIG. 6 ; 
         FIG. 8  shows the selective removal of the supplemental sacrificial gate and the sacrificial gate; 
         FIG. 9  shows the FinFET device structure following partial removal of the sidewall spacer layer from under the sacrificial capping layer; 
         FIG. 10  depicts the FinFET device structure following a replacement metal gate module and the deposition and planarization of a self-aligned gate cap over functional gates; 
         FIG. 11  shows the formation of an interlayer dielectric and metallization of the source/drain junctions; 
         FIG. 12  is a schematic cross-sectional view of a planar device structure at an intermediate stage of fabrication, including a semiconductor substrate having alternating source/drain and channel regions, a sacrificial gate and a sacrificial gate hard mask disposed over the channel regions, and a composite spacer layer disposed over sidewalls of the sacrificial gate and the sacrificial gate hard mask; 
         FIG. 13  shows a cross-section of the device of  FIG. 12  after the formation of raised source/drain junctions over the source/drain regions of the substrate; 
         FIG. 14  depicts the formation of a conformal contact etch stop layer within contact locations over the source/drain junctions and a dielectric fill layer over the contact etch stop layer; 
         FIG. 15  depicts the planar device architecture following a replacement metal gate (RMG) module and the deposition and planarization of a self-aligned gate cap over functional gates; and 
         FIG. 16  shows the formation of an interlayer dielectric over the structure of  FIG. 15  and metallization of the source/drain junctions. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in greater detail to various embodiments of the subject matter of the present application, some embodiments of which are illustrated in the accompanying drawings. The same reference numerals will be used throughout the drawings to refer to the same or similar parts. 
     As used herein, the formation or deposition of a layer or structure may involve one or more techniques suitable for the material or layer being deposited or the structure being formed. Such techniques include, but are not limited to, chemical vapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), metal organic CVD (MOCVD), atomic layer deposition (ALD), molecular beam epitaxy (MBE), electroplating, electroless plating, ion beam deposition, and physical vapor deposition (PVD) techniques such as sputtering or evaporation. 
     Disclosed in various embodiments is a method of manufacturing a semiconductor device such as a FinFET (3D) device where a composite spacer architecture is formed over sidewalls of a sacrificial gate, and the subsequent deposition of a supplemental sacrificial gate over the sacrificial gate enables the composite spacer topology to be maintained prior to a recess etch thereof and the formation within the recess of a sacrificial capping layer. Removal of the supplemental sacrificial gate and the sacrificial gate re-exposes the composite spacer architecture, which is selectively etched to form a T-shaped cavity overlying a channel region of the fin. A replacement metal gate is formed within a lower region of the T-shaped cavity, and a self-aligned contact (SAC) capping layer is formed within an upper region of the T-shaped cavity prior to metallization of the replacement metal gate and source/drain regions of the device. In various embodiments, the self-aligned contact (SAC) capping layer is T-shaped. As used herein, a “T-shaped” structure such as a T-shaped cavity or a T-shaped capping layer has an upper region and a lower region, where the upper region is wider than the lower region, and the upper region extends laterally beyond each of at least one pair of opposing sidewalls of the lower region. 
     The formation of a T-shaped self-aligned contact (SAC) capping layer, which provides an effective barrier between adjacent conductive structures, as well as the use of a supplemental sacrificial gate to form the T-shaped capping layer, is described in connection with a FinFET device architecture in  FIGS. 1-11 . An abbreviated process flow for forming a T-shaped self-aligned contact capping layer for a planar device is described with reference to  FIGS. 12-16 . 
     Referring to  FIG. 1 , a FinFET structure at an intermediate stage of fabrication includes a semiconductor fin  120  formed over a semiconductor substrate  100 . The semiconductor substrate  100  may be a bulk substrate or a composite substrate such as a semiconductor-on-insulator (SOI) substrate, and may include any suitable semiconductor material as known to those skilled in the art. Portions of the semiconductor substrate may be amorphous, polycrystalline, or single crystalline. Although a single fin  120  is shown in the illustrated cross-section, it will be appreciated that an array of fins  120  may be formed over the substrate  100 . 
     In various embodiments, each fin  120  includes a semiconductor material such as silicon, and may be formed by patterning and then etching the semiconductor substrate  100 , e.g., a top portion of the semiconductor substrate. In several embodiments, a fin  120  is etched from, and is therefore contiguous with the semiconductor substrate. For instance, fin  120  may be formed using a sidewall image transfer (SIT) process as known to those skilled in the art. 
     Each fin  120  can include a single crystal semiconductor material that extends along a lengthwise direction. As used herein, a “lengthwise direction” is a horizontal direction along with an object extends the most. A “widthwise direction” is a horizontal direction that is perpendicular to the lengthwise direction. 
     As used here, “horizontal” refers to a general direction along a primary surface of a substrate, and “vertical” is a direction generally orthogonal thereto. Furthermore, “vertical” and “horizontal” are generally perpendicular directions relative to one another independent of orientation of the substrate in three-dimensional space. 
     In certain embodiments, the fins  120  can have a width of 5 nm to 20 nm, and a height of 40 nm to 150 nm, although other dimensions are also contemplated. In structures including plural fins, i.e., a fin array, each fin may be spaced apart from its nearest neighbor by a periodicity or pitch (d) of 20 nm to 100 nm, e.g., 20, 30, 40, 50, 60, 70, 80, 90 or 100 nm, including ranges between any of the foregoing values. As used herein, the term “pitch” refers to the sum of the fin width and the spacing between neighboring fins. 
     Such plural fins are typically oriented parallel to each other and perpendicular to the library logic flow of a circuit. After fin formation, a fin cut or fin removal process may be used to eliminate unwanted fins or unwanted portions thereof for the particular circuit or device being fabricated. Thus, the fin-to-fin periodicity may be constant or variable over an array of fins. 
     The fin  120  includes alternating source/drain regions  122  and channel regions  124  as will be appreciated by those skilled in the art. A shallow trench isolation (STI) layer  200  may be used to provide electrical isolation between the fins  120  and between adjacent devices as is needed for the circuit(s) being formed. An STI process for FinFET devices involves creating isolation trenches in the semiconductor substrate  100  through an anisotropic etch process. The isolation trench between each adjacent fin may have a relatively low aspect ratio (e.g., ratio of the depth of the isolation trench to its width). According to certain embodiments, a dielectric filler material, such as silicon dioxide, is deposited into the isolation trenches, for example, using an enhanced high aspect ratio process (eHARP) to fill the isolation trenches. The deposited dielectric material may then be polished by a chemical-mechanical polishing (CMP) process that removes the excess dielectric material and creates a planar STI structure. The planarized oxide is then etched back to form a recessed, uniformly thick oxide isolation layer  200  between the fins  120 , where upper sidewalls of the fins  120  can be exposed for further processing. 
     “Planarization” and “planarize” as used herein refer to a material removal process that employs at least mechanical forces, such as frictional media, to produce a substantially two-dimensional surface. A planarization process may include chemical mechanical polishing (CMP) or grinding. Chemical mechanical polishing (CMP) is a material removal process that uses both chemical reactions and mechanical forces to remove material and planarize a surface. 
     Referring still to  FIG. 1 , the structure includes a sacrificial gate  310  formed over each channel region  124  of fin  120 . According to various embodiments, a sacrificial gate oxide layer  320  is formed over the sacrificial gate  310 , and a sacrificial gate hard mask  330  is formed over the sacrificial gate oxide layer  320 . 
     The sacrificial gate  310  may be formed using conventional deposition, photolithography and etching processes. The sacrificial gate  310  may include a layer of amorphous silicon (a-Si) or polycrystalline silicon, for example. Amorphous elemental silicon can be deposited using chemical vapor deposition, such as low pressure chemical vapor deposition (LPCVD) at temperatures ranging from 450° C. to 700° C. Silane (SiH 4 ) can be used as the precursor for CVD silicon deposition. 
     The sacrificial gate  310  extends over the top surface and sidewall surfaces of the fin  120  and may have a thickness sufficient to completely cover the fin. For instance, a thickness of sacrificial gate  310  may range from 50 to 200 nm, e.g., 50, 75, 100, 125, 150, 175 or 200 nm, including ranges between any of the foregoing values, although lesser and greater thicknesses may be used. 
     In certain embodiments, a sacrificial gate  310  may be formed from a blanket sacrificial gate layer that is deposited over the fins. Sacrificial gate oxide layer  320  and hard mask  330  are formed in succession over the sacrificial gate layer and patterned, for example, using conventional photolithography and etching techniques. The hard mask  330  may include a dielectric material such as silicon nitride, and may be formed using chemical vapor deposition. An example hard mask  330  has a thickness of 20 to 30 nm. 
     According to various embodiments, the sacrificial gate  310 , sacrificial gate oxide layer  320  and hard mask  330  template the formation of a first spacer layer  410  is over sidewalls thereof, and a second spacer layer  420  over sidewalls of the first spacer layer  410 . First and second spacer layers  410 ,  420  may be formed by blanket deposition of a spacer material (e.g., using atomic layer deposition) followed by a directional etch such as reactive ion etching (RIE) to remove the spacer materials from horizontal surfaces. Suitable materials for first spacer layer  410  include oxides, nitrides and oxynitrides, such as silicon dioxide, silicon nitride, silicon oxynitride, and low dielectric constant (low-k) materials such as amorphous carbon, SiOC, SiCN, SiOCN and SiBCN. As used herein, a “low-k” material has a dielectric constant less than that of silicon dioxide. In certain embodiments, the thickness of the first spacer layer  410  may be 2 to 5 nm, e.g., 2, 3, 4, or 5 nm, including ranges between any of the foregoing values. 
     As will be appreciated, the compounds silicon dioxide and silicon nitride have compositions that are nominally represented as SiO 2  and Si 3 N 4 , respectively. The terms silicon dioxide and silicon nitride, refer to not only these stoichiometric compositions, but also to oxide and nitride compositions that deviate from the stoichiometric compositions. 
     A second spacer layer  420  is formed over the first spacer layer  410 . According to various embodiments, the methods and materials used to form first spacer layer  410  may be used to form second spacer layer  420 . In certain embodiments, the thickness of the second spacer layer  420  may be 5 to 10 nm, e.g., 5, 8 or 10 nm, including ranges between any of the foregoing values. 
     According to certain embodiments, the first and second spacer layer materials are etch selective with respect to silicon dioxide and amorphous silicon. In an example structure, the first spacer layer  410  includes silicon nitride and the second spacer layer  420  includes a low-k material. 
     In an example structure, one or both of the first and second spacer layers  410 ,  420  may have a dielectric constant less than that of silicon dioxide. By way of example, first spacer layer  410  and second spacer layer  420  may independently have a dielectric constant of 2.8 to 3.8, e.g., 2.8, 3.0, 3.2, 3.4, 3.6 or 3.8, including ranges between any of the foregoing values. 
     Referring to  FIG. 2 , source/drain junctions  500  are formed over source/drain regions  122  of fin  120 . Source/drain junctions  500  may be formed by ion implantation or selective epitaxy following formation of the sacrificial gate  310  and spacer layers  410 ,  420 , e.g., using the spacer layers  410 ,  420  as an alignment mask. 
     According to various embodiments, source/drain junctions  500  may include silicon (e.g., Si) or a silicon-containing material such as silicon germanium (SiGe). For instance, SiGe source/drain junctions may be incorporated into a p-MOS device to provide compressive stress to the channel, which can improve carrier mobility. 
     The terms “epitaxy,” “epitaxial” and/or “epitaxial growth and/or deposition” refer to the growth of a semiconductor material layer on a deposition surface of a semiconductor material, in which the semiconductor material layer being grown assumes the same crystalline habit as the semiconductor material of the deposition surface. For example, in an epitaxial deposition process, chemical reactants provided by source gases are controlled and the system parameters are set so that depositing atoms alight on the deposition surface and remain sufficiently mobile via surface diffusion to orient themselves according to the crystalline orientation of the atoms of the deposition surface. Therefore, an epitaxial semiconductor material has the same crystalline characteristics as the deposition surface on which it is formed. For example, an epitaxial semiconductor material deposited on a (100) crystal surface will take on a (100) orientation. Example epitaxial growth processes include low energy plasma deposition, liquid phase epitaxy, molecular beam epitaxy, and atmospheric pressure chemical vapor deposition. 
     The source/drain junctions  500  may be doped, which may be performed in situ, i.e., during epitaxial growth, or following epitaxial growth, for example, using ion implantation or plasma doping. Doping changes the electron and hole carrier concentrations of an intrinsic semiconductor at thermal equilibrium. A doped layer or region may be p-type or n-type. 
     As used herein, “p-type” refers to the addition of impurities to an intrinsic semiconductor that creates a deficiency of valence electrons. In a silicon-containing fin, example p-type dopants, i.e., impurities, include but are not limited to boron, aluminum, gallium, and indium. As used herein, “n-type” refers to the addition of impurities that contribute free electrons to an intrinsic semiconductor. In a silicon-containing fin, example n-type dopants, i.e., impurities, include but are not limited to, antimony, arsenic, and phosphorus. 
     An optional drive-in anneal can be used to diffuse dopant species and generate a desired dopant profile. In certain embodiments, dopant atoms within the source/drain junctions  500  may be diffused into the semiconductor fin  120  using a post-epitaxy or post-implantation anneal (e.g., at a temperature of 600° C. to 1400° C.) to create a desired dopant profile within the fin. 
     Referring to  FIG. 3 , a conformal liner  510  is formed within contact locations over the source/drain junctions  500 , and a dielectric fill layer  520  is formed directly over the conformal liner  510 . The conformal liner  510  is adapted to function as a contact etch stop layer (CESL). As will be appreciated, conformal liner  510  and dielectric fill layer  520  extend over non-contact locations between fins, i.e., over STI layer  200 . 
     Conformal liner  510  may be formed by blanket deposition of a suitable contact etch stop material (e.g., using atomic layer deposition). In certain embodiments, the conformal liner  510  thickness is 2 to 10 nm, e.g., 2, 4, 6, 8 or 10 nm, including ranges between any of the foregoing values. 
     In various embodiments, the second spacer layer  420  and the conformal liner  510  are formed from materials that can be etched selectively to one another. In particular embodiments, the second spacer layer  420  includes SiOC or SiOCN and the conformal liner (i.e., contact etch stop layer)  510  includes silicon nitride. 
     The dielectric fill layer  520  may include any dielectric material including, for example, oxides, nitrides or oxynitrides. In one embodiment, the dielectric fill layer  520  includes silicon dioxide. By way of example, dielectric fill layer  520  may be a composite layer that includes an initially-deposited flowable oxide (FOX) layer, i.e., a flowable oxide layer deposited directly over the conformal liner  510 , and a high density plasma (HDP) oxide gap fill layer deposited over the flowable oxide layer. In various embodiments, the dielectric fill layer  520  may be self-planarizing, or the top surface of the dielectric fill layer  520  can be planarized by chemical mechanical polishing (CMP). 
     Referring to  FIG. 4 , a selective etch is used to remove the hard mask  330  and the sacrificial gate oxide layer  320  from over the sacrificial gate  310  to form openings  312 . The selective etch also removes exposed portions of the first spacer layer  410  above the sacrificial gate  310 . As used herein, the terms “selective” or “selectively” in reference to a material removal or etch process denote that the rate of material removal for a first material is greater than the rate of removal for at least another material of the structure to which the material removal process is applied. For example, in certain embodiments, a selective etch may include an etch chemistry that removes a first material selectively to a second material by a ratio of 2:1 or greater, e.g., 5:1, 10:1 or 20:1. 
     Referring to  FIG. 5 , a supplemental sacrificial gate  315  is formed within each opening  312  directly over sacrificial gate  310 . The supplemental sacrificial gate  315  may include a layer of amorphous silicon (a-Si) or polycrystalline silicon. As seen with reference to  FIG. 5 , sacrificial gate  310  is disposed directly over sidewalls of the first spacer layer  410 , while supplemental sacrificial gate  315  is formed within opening  312  directly over sidewalls of the second spacer layer  420 . 
     Referring to  FIG. 6 , a further selective etching step is used to recess the second spacer layer  420 , conformal liner  510  and dielectric fill layer  520  with respect to the supplemental sacrificial gate  315 . The recess etch exposes sidewalls of the supplemental sacrificial gate  315  without exposing the first spacer layer  410  or the sacrificial gate  310 . Dielectric layers  420 ,  510  and  520  may be recessed using a reactive ion etching (RIE) process. 
     Referring to  FIG. 7 , a sacrificial capping layer  550  is formed by depositing a dielectric material into the recesses, such that a bottom surface of the sacrificial capping layer  550  is disposed above a top surface of the sacrificial gate  310 . A polishing step may be used to remove the overburden and expose a top surface of the supplemental sacrificial gate  315 , e.g., using the supplemental sacrificial gate  315  as an etch stop layer. Sacrificial capping layer  550  may include silicon nitride or silicon dioxide, for example. 
     Referring to  FIG. 8 , the supplemental sacrificial gate  315  and the sacrificial gate  310  are etched selectively with respect to sacrificial capping layer  550 , first spacer layer  410  and second spacer layer  420  to form gate openings  610  and expose channel regions  124  of fin  120 . Within an upper region of the gate openings  610 , sidewalls thereof are defined by the second spacer layer  420 , while within a lower region of the gate openings  610 , sidewalls thereof are defined by first spacer layer  410 . Thus, at this stage of processing, a width (w 1 ) of a lower region of the gate opening  610  is less than a width (w 2 ) of an upper region of the gate opening  610 . In certain embodiments, the width (w 1 ) may range from 10 to 40 nm, e.g., 10, 15, 20, 25, 30, 35 or 40 nm, including ranges between any of the foregoing values, and the width (w 2 ) may range from 14 to 50 nm, e.g., 15, 20, 30, 40 or 50 nm, including ranges between any of the foregoing values. 
     As seen with reference to  FIG. 9 , a further etching step is used to remove the second spacer layer  420  proximate to the upper region of the gate opening  610 . Following the selective etch of the second spacer layer  420 , the upper region of the gate opening  610  has a width (w 3 ), where sidewalls of the upper region of the gate opening are now defined by conformal liner  510 . According to certain embodiments, width (w 3 ) may range from 20 to 70 nm, e.g., 20, 30, 40, 50, 60 or 70 nm, including ranges between any of the foregoing values. 
     Referring to  FIG. 10 , a replacement metal gate (RMG) module is used to form a functional gate stack  700  over channel regions  124  of the fin  120 . The functional gate stack  700  includes a gate dielectric and an overlying gate conductor (not separately shown). 
     As used herein, a “functional gate” or “gate” refers to a structure used to control output current (i.e., the flow of carriers through a channel) of a semiconductor device using an electrical field or, in some instances, a magnetic field, and includes a gate dielectric and a gate conductor. 
     The gate dielectric may include silicon dioxide, silicon nitride, silicon oxynitride, a high-k dielectric, or other suitable material. As used herein, a high-k material has a dielectric constant greater than that of silicon dioxide. A high-k dielectric may include a binary or ternary compound such as hafnium oxide (HfO 2 ). Further exemplary high-k dielectrics include, but are not limited to, ZrO 2 , La 2 O 3 , Al 2 O 3 , TiO 2 , SrTiO 3 , BaTiO 3 , LaAlO 3 , Y 2 O 3 , HfO x N y , HfSiO x N y , ZrO x N y , La 2 O x N y , Al 2 O x N y , TiO x N y , SrTiO x N y , LaAlO x N y , Y 2 O x N y , SiO x N y , SiN x , a silicate thereof, and an alloy thereof. Each value of x may independently vary from 0.5 to 3, and each value of y may independently vary from 0 to 2. The gate dielectric thickness may range from 1 nm to 10 nm, e.g., 1, 2, 4, 6, 8 or 10 nm, including ranges between any of the foregoing. 
     The gate conductor may include a conductive material such as polysilicon, silicon-germanium, a conductive metal such as Al, W, Cu, Ti, Ta, W, Co, Pt, Ag, Au, Ru, Ir, Rh and Re, alloys of conductive metals, e.g., Al—Cu, silicides of a conductive metal, e.g., W silicide, and Pt silicide, or other conductive metal compounds such as TiN, TiC, TiSiN, TiTaN, TaN, TaAlN, TaSiN, TaRuN, WSiN, NiSi, CoSi, as well as combinations thereof. The gate conductor may include one or more layers of such materials such as, for example, a metal stack including a work function metal layer and/or a conductive liner, and may have a thickness of 20 to 40 nm. In certain embodiments, the gate conductor includes a titanium nitride (TiN) layer directly over the gate dielectric and a tungsten (W) or cobalt (Co) fill layer over the titanium nitride layer. 
     Prior to forming gate stack  700 , an etching step may be used to remove native oxide and an extended gate (EG) oxide from over the channel regions  124  of the fins  120 . In certain embodiments, a single etching step may be used to strip native oxide and an EG oxide, if present, and laterally etch second spacer layer  620 . 
     Referring still to  FIG. 10 , a self-aligned gate cap  710  is formed directly over the gate stack  700 . Following deposition of the gate cap material, a polishing step may be used to remove the overburden and form a planarized structure. In certain embodiments, the polishing step removes the sacrificial capping layer  550 . By way of example, the gate cap  710  may include a nitride material such as silicon nitride or silicon oxynitride (SiON). 
     In the illustrated embodiment, a sidewall surface of an upper portion of the gate cap  710  directly contacts conformal liner  510 , while a sidewall surface of a lower portion of the gate cap  710  directly contacts first spacer layer  410 . The gate cap  710  thus has a T-shape. In various embodiments, within both the upper portion and the lower portion, the gate cap  710  has substantially vertical sidewalls. As used herein, “substantially vertical” sidewalls deviate from a direction normal to a major surface of the substrate by less than 5°, e.g., 0, 1, 2, 3, 4, or 5°, including ranges between any of the foregoing values. 
     Referring to  FIG. 11 , the dielectric fill layer  520  and conformal liner  510  can be removed from over source/drain junctions  500  to form self-aligned contact openings. Removal of the dielectric fill layer  520  and conformal liner  510  can be performed using an etch that is selective to the adjacent, exposed layers. For instance, the dielectric fill layer  520  and the conformal liner  510  can be removed by a reactive ion etch or isotropic etch such as a wet etch or an isotropic plasma etch. An example wet etch chemistry that can be used to remove the CESL layer  510  includes phosphoric acid. 
     Prior to metallization of the source/drain region, a wet etch can be used to remove native oxide from over the source/drain junctions  500 . An example wet etch for stripping oxide includes hydrofluoric acid or a solution that includes dilute hydrofluoric acid (d-HF). 
     As shown in  FIG. 11 , a conductive contact  810  is formed within the contact openings and over exposed surfaces of the source/drain junctions  500  by depositing, for example, a conductive liner and a barrier layer (not separately shown) and then filling the contact openings with a contact layer such as tungsten or cobalt. The conductive liner is typically titanium and the barrier layer may be titanium nitride (TiN). 
     Conductive contacts  810  may include a metal that forms an ohmic contact with the source/drain junctions  500 . A silicide layer (e.g., titanium silicide) may be formed in situ via reaction between the conductive liner (e.g., titanium) and the source/drain junctions  500  to form a trench silicide contact. 
     After formation of the conductive contacts  810 , a planarization process may be used to form a structure where a top surface of a conductive contact  810  is co-planar with a top surface of the neighboring gate capping layers  710 . 
     Additional processing may be used to form a functional device, including middle-of-the line and back-of-the line metallization and interconnect modules to form suitable electrical connections. As shown in  FIG. 11 , for instance, an interlayer dielectric  900  may be formed over the gate capping layers  710  and the conductive contact  810 . Conventional photolithography, etching and deposition processes may be used to form metal interconnects  910  within openings in the interlayer dielectric  900  and in electrical contact with conductive contacts  810 . According to further embodiments, conductive contacts  810  and metal interconnects  910  may be formed concurrently, as a single contact. 
     Although the foregoing methods and structures are described in connection with a FinFET device, it will be appreciated that the disclosed isolation architecture may be incorporated into various additional device structures, including planar, e.g., partially-depleted or fully-depleted SOI-based device structures. 
     In example planar devices, as an alternative to a conventional bulk silicon wafer platform for integrated circuit (IC) manufacture, SOI (silicon-on-insulator or semiconductor-on-insulator) substrates have been embraced by the microelectronics industry. SOI substrates are composite structures that include two semiconductor layers separated by an isolation layer. Compared to bulk silicon substrates, SOI substrates provide a number of advantages to circuit designers, including faster switching speeds, greater resistance to radiation effects, higher component packing densities, smaller leakage currents and parasitic capacitances, and the avoidance of low-impedance paths between power supply rails, i.e., “SCR latch-up.” 
     An SOI substrate can be formed using a variety of methods such as, for example, SiMOX or bonding methods known to those skilled in the art. According to various embodiments, a wafer bonding process for manufacturing SOI wafers includes physically uniting two single crystal semiconductor wafers. For instance, one of the wafers can be thermally oxidized to form the isolation layer and, after cleaning operations, bonded to the other. Bringing two hydrophilic surfaces (such as SiO 2 ) into direct contact can result in a strong interfacial bond. Following a thermal anneal at temperatures as high as 1100° C. (e.g., 1000° C.), the bond strength can be increased to that of bulk material. The outer surface of the composite wafer can be ground and polished to the desired thickness (e.g., 1-3 microns) using, for example, chemical mechanical polishing. 
     A further example wafer bonding method can be performed in conjunction with a layer transfer process where, by way of example, a gallium arsenide surface to be bonded is cleaved from a source wafer of gallium arsenide. In such a process, a single crystal wafer of gallium arsenide (GaAs) is ion implanted, e.g., with hydrogen, to a desired depth to define a thin layer of gallium arsenide to be transferred. The implanted wafer is then pre-bonded to the isolation layer of a support substrate such as an oxidized silicon substrate. The pre-bonded assembly is heated to cause eruption of the hydrogen-rich plane and cleavage of the defined gallium arsenide layer from the gallium arsenide wafer. The support substrate with the transferred layer can then be heated to improve the bonding between the substrate and the transferred layer. The excess support substrate can be removed and the gallium arsenide layer polished to form an SOI structure. The gallium arsenide source wafer and the excess support substrate can each be recycled back into the process. 
     An abbreviated process flow depicting the formation of a T-shaped capping layer in connection with a planar device is described with reference to  FIGS. 12-16 . Referring to  FIG. 12 , a device structure at an intermediate stage of fabrication includes an SOI substrate  100  having, from bottom to top, a handle portion  102 , an isolation layer  104 , and a semiconductor layer  106 . Handle portion  102  and semiconductor layer  106  may each include a silicon-containing material such as single crystal Si, polycrystalline Si, single crystal silicon germanium (SiGe), polycrystalline silicon germanium, silicon doped with carbon (Si:C), amorphous Si, as well as combinations and multi-layers thereof. As used herein, the term “single crystal” denotes a crystalline solid, in which the crystal lattice of the entire sample is substantially continuous and substantially unbroken to the edges of the sample with substantially no grain boundaries. 
     According to various embodiments, the handle portion  102  and the semiconductor layer  106  may include the same semiconductor material or different semiconductor materials. The handle portion  102  of an example semiconductor substrate may include (100)-oriented silicon or (111)-oriented silicon, for example, and the semiconductor layer  106  may include (100)-oriented silicon, single crystal SiGe or single crystal GaAs, although other materials and material combinations are contemplated. The thickness of the semiconductor layer  106  can be 10 to 100 nm, for example, although smaller and larger values are contemplated. 
     The isolation layer  104  between the handle portion  102  and the semiconductor layer  106  is often referred to as a buried oxide (BOX) layer. The thickness of the isolation layer  104  may range from 30 to 300 nm, e.g., 30, 50, 100, 150, 200, 250 or 300 nm, including ranges between any of the foregoing values, although lesser and greater thicknesses may be used. The isolation layer  104  may include, for example, silicon dioxide (SiO 2 ). Alternatively, isolation layer  104  may include silicon nitride, silicon oxynitride, a low-k material, or any suitable combination of these materials. 
     A shallow trench isolation (STI) layer  200  may be used to provide electrical isolation between adjacent devices as is needed for the circuit(s) being formed. As illustrated, a sacrificial gate  310  is disposed over each channel region  124  of the semiconductor layer  106 , a sacrificial gate oxide layer  320  is disposed over the sacrificial gate  310 , and a sacrificial gate hard mask  330  is disposed over the sacrificial gate oxide layer  320 . In an example method, a first spacer layer  410  is formed over sidewalls of the sacrificial gate  310 , the sacrificial gate oxide layer  320 , and the sacrificial gate hard mask  330 , and a second spacer layer  420  is formed over sidewalls of the first spacer layer  410 . The methods and materials used to form the sacrificial gate structure  310 ,  320 ,  330  as well as spacer layers  410 ,  420  in connection with the FinFET device illustrated in  FIG. 1 , may be used to form the structure illustrated in  FIG. 12 . 
     Referring to  FIG. 13 , raised source/drain junctions  500  are formed over source/drain regions  122  of semiconductor layer  106  and, as illustrated in  FIG. 14 , a conformal liner  510  is formed within contact locations over the source/drain junctions  500 , and a dielectric fill layer  520  is formed directly over the conformal liner  510 . 
     As will be appreciated, according to various embodiments, the processing may continue for the planar device in the manner disclosed herein with reference to  FIGS. 4-9  and, as shown in  FIG. 15 , include a replacement metal gate (RMG) module as described with reference to  FIG. 10 , including the formation of a functional gate stack  700  over channel regions  124  of the semiconductor layer  104 . Gate stack  700  includes a gate dielectric layer and a gate conductor layer (not separately shown). 
     A planar device architecture according to certain embodiments, and including a T-shaped capping layer  710  over the gate  700 , is illustrated in  FIG. 16  following the formation of conductive contacts  810  within contact openings and over exposed surfaces of the source/drain junctions  500 . An interlayer dielectric  900  may be formed over the gate capping layers  710  and the conductive contacts  810 . Conventional photolithography, etching and deposition processes may be used to form metal interconnects  910  within openings in the interlayer dielectric  900  and in electrical contact with conductive contacts  810 . 
     As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an “etching step” includes examples having two or more such “etching steps” unless the context clearly indicates otherwise. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred. Any recited single or multiple feature or aspect in any one claim can be combined or permuted with any other recited feature or aspect in any other claim or claims. 
     It will be understood that when an element such as a layer, region or substrate is referred to as being formed on, deposited on, or disposed “on” or “over” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, no intervening elements are present. 
     While various features, elements or steps of particular embodiments may be disclosed using the transitional phrase “comprising,” it is to be understood that alternative embodiments, including those that may be described using the transitional phrases “consisting” or “consisting essentially of,” are implied. Thus, for example, implied alternative embodiments to a high-k spacer that comprises aluminum oxide include embodiments where a high-k spacer consists essentially of aluminum oxide and embodiments where a high-k spacer consists of aluminum oxide. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.