Patent Publication Number: US-10790393-B2

Title: Utilizing multilayer gate spacer to reduce erosion of semiconductor Fin during spacer patterning

Description:
TECHNICAL FIELD 
     This disclosure generally relates to semiconductor fabrication techniques and, in particular, techniques for fabricating FET (field effect transistor) devices. 
     BACKGROUND 
     As semiconductor manufacturing technologies continue to evolve toward smaller design rules and higher integration densities (e.g., 14 nm technology node and beyond), integrated circuit devices and components become increasingly smaller, creating challenges in layout formation and device optimization. Currently, FinFET technologies are typically implemented for FET fabrication, as such technologies provide effective CMOS scaling solutions for FET fabrication at, and below, the 14 nm technology node. A FinFET device comprises a three-dimensional fin-shaped FET structure which includes at least one vertical semiconductor fin structure formed on a substrate, a gate structure formed over a portion of the vertical semiconductor fin, and source/drain regions formed from portions of the vertical semiconductor fin which extend from both sides of the gate structure. The portion of the vertical semiconductor fin that is covered by the gate structure between the source/drain regions comprises a channel region of the FinFET device. 
     The gate structures of FinFET devices can be formed using various techniques. For example, a FinFET gate structure can be fabricated using a “gate-last” process, which involves, for example, forming a dummy gate structure and a gate spacer over a portion of a vertical semiconductor fin, fabricating other FinFET device elements (e.g., source/drain regions), and then replacing the dummy gate structure with a metal gate structure using a replacement metal gate (RMG) process. For advanced FinFET technologies, it is important to prevent etch damage to the vertical semiconductor fins when etching a dielectric layer to form the gate spacers. 
     With conventional methods, a gate spacer is formed by depositing and patterning a layer of dielectric material using, e.g., RIE (reactive ion etching). Due to the limited selectivity of the RIE process, the vertical semiconductor fins can be subjected to significant etch damage when patterning the layer of dielectric material to form the gate spacers. While the spacer RIE process can be tuned to minimize etch erosion of vertical semiconductor fins formed of silicon (Si) or silicon-germanium (SiGe), the selectively of the RIE process decreases with the scaling of fin pitch (e.g., reducing inter fin spacing), and as the fin height increases (e.g., increasing aspect ratio for spacer RIE). 
     SUMMARY 
     Embodiments of the invention include FinFET devices comprising multilayer gate spacers, as well as methods for fabricating FinFET devices in which multilayer gate spacers are utilized to prevent or otherwise minimize the erosion of vertical semiconductor fins when forming the gate spacers. For example, in one embodiment, a method for fabricating a semiconductor device comprises forming a dummy gate structure over a portion of a vertical semiconductor fin of a FinFET device, and forming a multilayer gate spacer on the dummy gate structure. The multilayer gate spacer comprises a first dielectric layer and a second dielectric layer, wherein the first dielectric layer has etch selectivity with respect to the vertical semiconductor fin and the second dielectric layer. In one embodiment, the first dielectric layer comprises silicon oxycarbonitride (SiOCN) and the second dielectric layer comprises silicon boron carbon nitride (SiBCN). 
     Another embodiment includes a semiconductor device which comprises a gate structure formed over a portion of a vertical semiconductor fin of a FinFET device, and a multilayer gate spacer formed on sidewalls of the gate structure. The multilayer gate spacer comprises a first dielectric layer and a second dielectric layer, wherein the first dielectric layer has etch selectivity with respect to the vertical semiconductor fin and the second dielectric layer. In one embodiment, the first dielectric layer comprises SiOCN, and the second dielectric layer comprises SiBCN. 
     Other embodiments will be described in the following detailed description of embodiments, which is to be read in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A through 6B  schematically illustrate a process for fabricating FinFET devices according to an embodiment of the invention, wherein: 
         FIGS. 1A, 1B, 1C, and 1D  are schematic views of a semiconductor device at an intermediate stage of fabrication in which dummy gate structures are formed over vertical semiconductor fins of FinFET devices; 
         FIGS. 2A, 2B, and 2C  are schematic views of the semiconductor device of  FIGS. 1A, 1B , and  1 C, respectively, after depositing first and second dielectric layers over the dummy gate structures, which are subsequently patterned to form a multilayer gate spacer; 
         FIGS. 3A, 3B, and 3C  are schematic views of the semiconductor device of  FIGS. 2A, 2B , and  2 C, respectively, after etching the second dielectric layer selective to the first dielectric layer; 
         FIGS. 4A, 4B, and 4C  are schematic views of the semiconductor device of  FIGS. 3A, 3B , and  3 C, respectively, after etching the first dielectric layer selective to the second dielectric layer and the vertical semiconductor fins, and after forming epitaxial source/drain layers on exposed portions of the vertical semiconductor fins of the FinFET devices; 
         FIG. 4D  is a schematic top plan view of the semiconductor device shown in  FIGS. 4A, 4B and 4C ; 
         FIGS. 5A, 5B, and 5C  are schematic views of the semiconductor device of  FIGS. 4A, 4B , and  4 C, respectively, after depositing and planarizing a layer of dielectric material to form an interlevel dielectric (ILD) layer; and 
         FIGS. 6A and 6B  are schematic views of the semiconductor device of  FIGS. 5A and 5B , respectively, after performing a replacement metal gate process to replace the dummy gate structures with a high-k metal gate structure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will now be described in further detail with regard to FinFET devices comprising multilayer gate spacers, as well as method for fabricating FinFET devices in which multilayer gate spacers are utilized to prevent or otherwise minimize the erosion of vertical semiconductor fins when forming the gate spacers. It is to be understood that the various layers, structures, and regions shown in the accompanying drawings are schematic illustrations that are not drawn to scale. In addition, for ease of explanation, one or more layers, structures, and regions of a type commonly used to form semiconductor devices or structures may not be explicitly shown in a given drawing. This does not imply that any layers, structures, and regions not explicitly shown are omitted from the actual semiconductor structures. 
     Furthermore, it is to be understood that the embodiments discussed herein are not limited to the particular materials, features, and processing steps shown and described herein. In particular, with respect to semiconductor processing steps, it is to be emphasized that the descriptions provided herein are not intended to encompass all of the processing steps that may be required to form a functional semiconductor integrated circuit device. Rather, certain processing steps that are commonly used in forming semiconductor devices, such as, for example, wet cleaning and annealing steps, are purposefully not described herein for economy of description. 
     Moreover, the same or similar reference numbers are used throughout the drawings to denote the same or similar features, elements, or structures, and thus, a detailed explanation of the same or similar features, elements, or structures will not be repeated for each of the drawings. It is to be understood that the terms “about” or “substantially” as used herein with regard to thicknesses, widths, percentages, ranges, etc., are meant to denote being close or approximate to, but not exactly. For example, the term “about” or “substantially” as used herein implies that a small margin of error may be present, such as 1% or less than the stated amount. 
     To provide spatial context, XYZ Cartesian coordinates are shown in the drawings of semiconductor structures. It is to be understood that the term “vertical” as used herein denotes a Z-direction of the Cartesian coordinates shown in the drawings, and that the terms “horizontal” or “lateral” as used herein denotes an X-direction and/or Y-direction of the Cartesian coordinates shown in the drawings, which is perpendicular to the Z-direction. 
       FIGS. 1A through 6B  schematically illustrate a process for fabricating FinFET devices with multilayer gate spacer structures, according to an embodiment of the invention. To begin,  FIGS. 1A, 1B, 1C, and 1D  are schematic views of a semiconductor device  100  at an intermediate stage of fabrication in which dummy gate structures and are formed over vertical semiconductor fins of FinFET devices.  FIG. 1D  is a schematic top plan view (X-Y plane) of the semiconductor device  100 , while  FIGS. 1A, 1B and 1C  are cross-sectional side views of the semiconductor device  100  along planes that are represented by respective lines shown in  FIG. 1D . In particular,  FIG. 1A  is a cross-sectional side view (Y-Z plane) of the semiconductor device  100  along line  1 A- 1 A in  FIG. 1D .  FIG. 1B  is a cross-sectional side view (X-Z plane) of the semiconductor device  100  along line  1 B- 1 B in  FIG. 1D , and  FIG. 1C  is a cross-sectional side view (X-Z plane) of the semiconductor device  100  along line  1 C- 1 C in  FIG. 1D . 
     As shown in  FIGS. 1A, 1B, 1C and 1D , the semiconductor device  100  comprises a semiconductor substrate  110 , an isolation layer  120 , a plurality of vertical semiconductor fins  130 , dummy gate structures G 1  and G 2 , and capping layers  150  formed on top of the dummy gate structures G 1  and G 2 . The dummy gate structures G 1  and G 2  each comprise a dummy gate electrode layer  140  and a dummy gate oxide layer  142 , which are formed over respective channel (C) regions of the vertical semiconductor fins  130 . The dummy gate structures are replaced with metallic gate structures as part of a RMG process, as will be explained in further detail below. As shown in  FIG. 1D , for example, portions of the vertical semiconductor fins  130  which extend from the sides of the dummy gate structures G 1  and G 2  serve as source/drain (S/D) regions for FinFET devices D 1  and D 2 . As illustrated in the example embodiment of  FIGS. 1B and 1D , each FinFET device D 1  and D 2  comprises a common gate structure that is formed over a portion of three vertical semiconductor fins  130 . In this regard, each FinFET device D 1  and D 2  may be configured as a multi-fin FinFET structure when the respective source/drain regions on each side of the gate structure are commonly connected to a respective single vertical source/drain contact (i.e., three FinFET segments connected in parallel to form a multi-fin FinFET device). Further, in the example shown in  FIG. 1D , the FinFET devices D 1  and D 2  share a common source/drain (S/D) region between the dummy gate structures G 1  and G 2 , such that the FinFET devices D 1  and D 2  are connected in series. 
     The semiconductor device  100  shown in  FIGS. 1A, 1B, 1C and 1D  can be fabricated using known semiconductor fabrication techniques and suitable semiconductor materials. For example, the semiconductor substrate  110  is illustrated as a generic substrate layer, and may comprise various structures and layers of semiconductor material. In one embodiment, the semiconductor substrate  110  comprises a bulk semiconductor substrate (e.g., wafer) formed of, e.g., silicon (Si), or other types of semiconductor substrate materials that are commonly used in bulk semiconductor fabrication processes such as germanium (Ge), a silicon-germanium (SiGe) alloy, silicon carbide (SiC), silicon-germanium carbide alloy, or compound semiconductor materials (e.g. III-V or II-VI, etc.). Non-limiting examples of III-V compound semiconductor materials include gallium arsenide, indium arsenide, and indium phosphide. In another embodiment, the semiconductor substrate  110  comprises a SOI (silicon on insulator) substrate, which comprises an insulating layer (e.g., oxide layer) disposed between a base substrate layer (e.g., silicon substrate) and an active semiconductor layer (e.g., active Si or SiGe layer) in which active circuit components are formed as part of a FEOL (front end of line) structure. 
     The isolation layer  120  and vertical semiconductor fins  130  can be fabricated using various methods. For example, for bulk and SOI substrate embodiments, the vertical semiconductor fins  130  can be formed by patterning an active silicon layer (e.g., crystalline silicon, crystalline SiGe, III-V compound semiconductor material, etc.) at the surface of a bulk semiconductor substrate or the SOI substrate to form a pattern of vertical semiconductor fins in different device regions across the semiconductor wafer, three of which are shown in  FIGS. 1B, 1C and 1D  for ease of illustration. In one embodiment, the vertical semiconductor fins  130  may be patterned from a crystalline SiGe layer that is epitaxially grown on top of a bulk silicon substrate or a bulk germanium substrate. A crystalline SiGe layer that is formed using an epitaxial growth process may comprise a relaxed SiGe layer or a strained SiGe layer. As is known in the art, strain engineering is utilized to enhance the carrier mobility for MOS transistors, wherein different types of Si—SiGe heterostructures can be fabricated to obtain and/or optimize different properties for CMOS FET devices. For example, silicon can be epitaxially grown on a SiGe substrate layer to form a strained Si layer. Moreover, a strained SiGe layer can be epitaxially grown on silicon substrate layer. A strained-Si/relaxed-SiGe structure produces tensile strain which primarily improves electron mobility for n-type FET devices, while a strained-SiGe/relaxed-Si structure produces a compressive strain which primarily improves hole mobility for p-type FET devices. 
     After forming the vertical semiconductor fins  130 , a layer of insulating material can be deposited to cover the vertical semiconductor fins  130 , and then planarized (via chemical-mechanical planarization (CMP)) down to the top of the vertical semiconductor fins  130 , and then further recessed using an etch-back process (e.g., selective RIE process) to form the isolation layer  120 . As shown in  FIG. 1C , the layer of insulating material is etched down to a target level to expose upper portions of the vertical semiconductor fin structures  130 , which define a baseline active fin height H for the FinFET devices D 1  and D 2 . In one embodiment of the invention, the isolation layer  120  can be selectively etched using RIE, although other etching processes may be employed. A timed etch can be performed to remove a desired amount of insulating material to expose the upper portions of the vertical semiconductor fin structures  130 . 
     In other embodiment, the vertical semiconductor fins  130  can be formed using a process in which the isolation layer  120  is first deposited and then etched using RIE or deep RIE to form a pattern of trenches in the isolation layer  120  down to the semiconductor substrate  110 , which corresponds to a pattern of vertical semiconductor fins to be formed. The vertical semiconductor fins  130  are then formed by epitaxially growing crystalline semiconductor material, starting on the exposed surfaces of the semiconductor substrate  110  at the bottom of the trenches, using ART (aspect ratio trapping) techniques. ART enables selective epitaxial growth of crystalline Si, SiGe, or III-V compound semiconductor material, for example, to fill high aspect ratio trenches formed in an insulating layer, and thereby form high quality active channel layers for FinFET devices. The crystalline SiGe layer (or other types of epitaxial semiconductor layers) can be epitaxially grown using known techniques, such as CVD (chemical vapor deposition), MOCVD (metal-organic chemical vapor deposition), LPCVD (low pressure chemical vapor deposition), MBE (molecular beam epitaxy), VPE (vapor-phase epitaxy), MOMBE (metal organic molecular beam epitaxy), or other known epitaxial growth techniques. 
     Next, the dummy gate structures G 1  and G 2  can be fabricated using known process flows. For example, the dummy gate structures G 1  and G 2  can be fabricated by forming a conformal oxide layer over the surface of the semiconductor substrate to cover the vertical semiconductor fins  130 . The conformal oxide layer can be formed by growing an oxide layer (e.g., silicon oxide) on the exposed surfaces of semiconductor fin material (e.g., Si or SiGe surfaces, etc.) using known techniques, or by depositing a conformal layer of oxide material (e.g., silicon dioxide) over the surface of the semiconductor substrate using a known process such as atomic layer deposition (ALD), chemical vapor deposition (CVD), etc. A layer of sacrificial silicon material, such as polysilicon or amorphous silicon, is then blanket deposited over the semiconductor substrate and then planarized. The layer of sacrificial silicon material can be deposited using known methods such as CVD, physical vapor deposition (PVD), electro-chemical deposition, and other suitable deposition methods. The layer of sacrificial silicon material can be planarized using CMP. 
     The conformal oxide layer and sacrificial silicon layer are then patterned to form the dummy gate oxide layers  142  and dummy gate electrode layers  140  of the dummy gate structures G 1  and G 2 . For example, one or more layers of insulating material are deposited on the planarized surface of the sacrificial silicon layer, and then patterned using a photolithographic process to form the capping layers  150 . In the example embodiment shown in  FIG. 1A , for example, the capping layers  150  comprise a first insulating layer  152  and a second insulating layer  154 . In one embodiment, the first insulating layer  152  comprises silicon nitride and the second insulating layer  154  comprises silicon oxide, although the capping layers  150  can be formed of any suitable combinations of insulating materials depending on the fabrication process flow implemented. The capping layers  150  define an image of the dummy gate structures G 1  and G 2 , and can be utilized as an etch mask to etch the underlying conformal oxide layer and sacrificial silicon layer. 
     A dry etch process (e.g., RIE) can be used to etch portions of the sacrificial silicon layer exposed through the etch mask (capping layers  150 ), to thereby form the dummy gate electrode layers  140  of the dummy gate structures G 1  and G 2 . With this process, the underlying oxide layer serves as an etch buffer layer (or etch stop layer) when etching the sacrificial silicon layer (e.g., polysilicon layer) to prevent the poly etch process from etching through the oxide layer and damaging the semiconductor material of the vertical semiconductor fins  130 . Next, the exposed portions of the underlying oxide layer are etched to form the dummy gate oxide layers  142  of the dummy gate structures G 1  and G 2 , resulting in the intermediate semiconductor device shown in  FIGS. 1A, 1B, 1C, and 1D . 
     After forming the dummy gate structures G 1  and G 2 , the fabrication process continues with forming multilayer gate spacers for gate structures of the FinFET devices D 1  and D 2 . For example,  FIGS. 2A, 2B, and 2C  are schematic views of the semiconductor device of  FIGS. 1A, 1B, and 1C , respectively, after sequentially depositing a first dielectric layer  160  and a second dielectric layer  170  over the surface of the substrate to cover the dummy gate structures G 1  and G 2  and the exposed portions of the vertical semiconductor fins  130 . The first and second dielectric layers  160  and  170  are subsequently patterned using a process flow as discussed in further detail below to form insulating gate spacers for the FinFET devices D 1  and D 2 . 
     In one embodiment, the first dielectric layer  160  comprises a conformal dielectric film that is formed with a thickness in a range of about 2 nm to about 5 nm, and the second dielectric layer  170  comprises a conformal dielectric film that is formed with a thickness in a range of about 5 nm to about 20 nm. The first and second dielectric layers  160  and  170  can be deposited using known techniques such as plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), or other suitable deposition methods which enable the deposition of the first and second dielectric layers  160  and  170  with high conformality. 
     In one embodiment of the invention, the second dielectric layer  170  is formed of a dielectric material that can be etched selective to the first dielectric layer  160  (e.g., with an etch selectivity of about 10:1 or greater), and the first dielectric layer  160  is formed of a dielectric material that can be etched selective to (i) the second dielectric layer  170  (e.g., with an etch selectivity of about 10:1 or greater), and (ii) the semiconductor material that forms the vertical semiconductor fins  130  (e.g., with an etch selectivity of about 10:1 or greater). For example, in one embodiment, the first dielectric layer  160  is formed of thin silicon oxycarbonitride (SiOCN) film, and the second dielectric layer  170  is formed of a thin silicon boron carbon nitride (SiBCN) film. Other low-k dielectric materials which are suitable for use as gate insulating spacers for gate structures of FinFET devices can be used to form the first and second dielectric layers  160  and  170 , assuming that such dielectric materials provide the etch selectivity as discussed above. The first and second dielectric layers  160  and  170  are patterned using a process flow as schematically illustrated in  FIGS. 3A, 3B, 3C, 4A, 4B, and 4C . 
     In particular,  FIGS. 3A, 3B, and 3C  are schematic views of the semiconductor device of  FIGS. 2A, 2B, and 2C , respectively, after etching the second dielectric layer  170  selective to the first dielectric layer  160 . As shown in  FIGS. 3A and 3B , the etch process results in the removal of horizontal portions of the second dielectric layer  170  from horizontal surface features, and pulling down (recessing) portions of the second dielectric layer  170  on the vertical sidewalls of the dummy gate/capping layer stacks G 1 / 150  and G 2 / 150 . As shown in  FIG. 3C , the second dielectric layer  170  is completely removed in the regions between the dummy gate structures G 1  and G 2  over the S/D regions of the vertical semiconductor fins  130 . In one embodiment, the second dielectric layer  170  is etched using a directional (e.g., anisotropic) dry etch process (e.g., RIE) with an etch chemistry and etch environment that is configured to etch the second dielectric layer  170  highly selective to the first dielectric layer  160 , such that the first dielectric layer  160  serves as an etch stop for the etch process. In this etch process, the second dielectric layer  170  is vertically recessed on the vertical sidewalls of the dummy gate/capping layer stacks G 1 / 150  and G 2 / 150  to a target level which is sufficient to completely etch away the second dielectric layer  170  disposed adjacent to the sidewalls of the active S/D regions of the vertical semiconductor fins  130  (see  FIG. 3C ), while ensuring that the second dielectric layer  170  is not recessed below the first insulating layer  152  of the capping layer  150  on top of each dummy gate structure G 1  and G 2 . For example, as shown in the example embodiment of  FIG. 3A , the second dielectric layer  170  is vertically recessed to a level that is above the first insulating layer  152  of the capping layer  150  on the dummy gate structures G 1  and G 2 . 
     Next,  FIGS. 4A, 4B, and 4C  are schematic views of the semiconductor device of  FIGS. 3A, 3B, and 3C , respectively, after etching the first dielectric layer  160  selective to the second dielectric layer  170  and the vertical semiconductor fins  130 , and after forming epitaxial source/drain layers  180  on exposed portions of the S/D regions of the vertical semiconductor fins  130  of the FinFET devices D 1  and D 2 .  FIG. 4D  is a schematic top plan view of the semiconductor device shown in  FIGS. 4A, 4B and 4C , wherein  FIG. 4A  is a cross-sectional side view (Y-Z plane) of the semiconductor device  100  along line  4 A- 4 A in  FIG. 4D , wherein  FIG. 4B  is a cross-sectional side view (X-Z plane) of the semiconductor device  100  along line  4 B- 4 B in  FIG. 4D , and wherein FIG.  4 C is a cross-sectional side view (X-Z plane) of the semiconductor device  100  along line  4 C- 4 C in  FIG. 4D . 
     In one embodiment, an isotropic etch process is performed to selectively etch away exposed portions of the first dielectric layer  160 , while other portions of the first dielectric layer  160  which are covered by the second dielectric layer  170  are not etched. The etch process is also selective to the semiconductor material of the vertical semiconductor fins  130  to prevent or otherwise minimize any etch damage to the S/D regions of the vertical semiconductor fins  130  when etching the first dielectric layer  160 . In one embodiment of the invention, assuming that the first dielectric layer  160  is formed of SiOCN and the second dielectric layer  170  is formed of SiBCN, the isotropic etch process may be implemented using a hydrofluoric acid (HF)-based wet etch process to etch away the exposed portions of the first dielectric layer  160  highly selective to the second dielectric layer  170  and the vertical semiconductor fins  130 . In one embodiment of the invention, the HF-based etch chemistry comprises a diluted HF-based etch chemistry with enhanced acidity using other mineral acids. 
     As shown in  FIGS. 4A, 4B and 4D , the etching of the first dielectric layer  160  results in the formation of multilayer gate spacers  175  which are disposed on the vertical sidewalls of the dummy gate structures G 1  and G 2 , and which surround the dummy gate structures G 1  and G 2 . The fabrication of a multilayer gate spacer according to an embodiment of the invention enables the deposition and patterning of multiple thin low-k dielectric layers to form insulating gate spacers with uniform profiles and with lower effective dielectric constants, as compared to conventional spacers that are formed of a single layer of SiN or SiBCN, for example. Further, as shown above, the use of different low-k dielectric layers, with different etch properties, enables patterning of the low-k dielectric layers to form the gate spacers  175 , while preventing or otherwise minimizing etching of the vertical semiconductor fins  130  during spacer fabrication. 
     After forming the multilayer gate spacers  175 , the process flow continues with forming the source/drain layers  180  on the exposed S/D regions of the vertical semiconductor fins  130 . In one embodiment of the invention, as shown in  FIGS. 4A, 4C, and 4D , the source/drain layers  180  are formed by growing epitaxial semiconductor material on the exposed surfaces of the S/D regions of the vertical semiconductor fins  130  adjacent to the dummy gate structures G 1  and G 2 . The type of epitaxial material and doping used to form the source/drain layers  180  will vary depending on whether the FinFET devices D 1  and D 2  are P-type or N-type devices. In another embodiment, the source/drain layers  180  may be silicide layers that are formed on the exposed surfaces of the S/D regions of the vertical semiconductor fins  130  using known methods. 
     Next,  FIGS. 5A, 5B, and 5C  are schematic views of the semiconductor device of  FIGS. 4A, 4B, and 4C , respectively, after depositing and planarizing a layer of dielectric material to form an ILD layer  190 . The ILD layer  190  is formed, for example, by depositing one or more layers of insulating material over the surface of the semiconductor substrate to cover the dummy gate structures G 1  and G 2 , and then planarizing the surface of the semiconductor substrate down to a level which exposes the upper surface of the first insulating layer  152  of the capping layers  150  on the dummy gate structures G 1  and G 2 . The ILD layer  190  can be formed using suitable dielectric materials including, but not limited to, silicon oxide, hydrogenated silicon carbon oxide (SiCOH), SiCH, SiCNH, or other types of silicon based low-k dielectrics (e.g., k less than about 4.0), porous dielectrics, or known ULK (ultra-low-k) dielectric materials (with k less than about 2.5). For example, the ILD layer  190  may comprise a single deposited layer of insulating material, or multiple layers of insulating material (e.g., a first layer of a flowable oxide and a second layer of insulating material formed on the first layer). The ILD layer  190  may be deposited using known deposition techniques, such as, for example, ALD, CVD, PECVD (plasma-enhanced CVD), or PVD, or spin-on deposition. 
     Following formation of the ILD layer  190 , the process flow continues with a RMG process to replace the dummy gate structures G 1  and G 2  with metallic gate structures. For example,  FIGS. 6A and 6B  are schematic views of the semiconductor device of  FIGS. 5A and 5B , respectively, after performing a replacement metal gate process to remove the dummy gate structures G 1  and G 2  and form high-k metal gate structures  200 . In one embodiment, the high-k metal gate structures  200  each comprise a high-k gate dielectric layer  202  and a metallic gate electrode  204 . The dummy gate structure G 1  and G 2  can be removed, and the high-k metal gate structures  200  can be formed, using various methods. 
     For example, the first insulating layer  152  of each capping layer  150  can be etched away selective to the materials of the ILD layer  190  and the gate spacers  175 , to expose the dummy gate electrode layers  140  of the dummy gate structures G 1  and G 2 . The dummy gate electrode layers  140  are then removed using a wet etch process (e.g., TetraMethyl Ammonium Hydroxide (TMAH) chemical etch solution), or a dry etch process (e.g., NF 3 +H 2  gas phase chemical etch) to etch away the sacrificial silicon material of the dummy gate structures G 1  and G 2  selective to the dielectric and insulating materials of the ILD layer  190 , the gate spacers  175 , and the dummy gate oxide layers  142 . This etch process exposes the dummy gate oxide layers  142  of the dummy gate structures G 1  and G 2 . The dummy gate oxide layers  142  are then etched away using an etch chemistry and etch environment in which the oxide layers  142  are etched selective to the materials of the vertical semiconductor fins  130 , the gate spacers  175 , and the ILD layer  190 . For example, in one embodiment of the invention where the dummy gate oxide layers  142  are formed of silicon oxide, an oxide etch process can be performed using a mixture of NH 3  (ammonia) and HF (Hydrogen Fluoride) reaction gases (or etchant gases). 
     Following removal of the dummy gate oxide layers  142 , the metal gate structures  200  are formed by depositing one or more conformal layers of gate dielectric material over the surface of the semiconductor structure, and depositing one or more layers of conductive material over the gate dielectric material. A planarization process (e.g., CMP) is then performed to polish the surface of the semiconductor structure down to the ILD layer  190 , thereby removing the overburden portions of the gate dielectric and conductive materials, resulting in the semiconductor structure shown in  FIGS. 6A and 6B  with metal gate structures  200 . 
     The gate dielectric layers  202  are formed with any suitable dielectric material including, for example, nitride, oxynitride, or oxide or a high-k dielectric material having a dielectric constant of about 3.9 or greater. In particular, the conformal layer of gate dielectric material  202  can include silicon oxide, silicon nitride, silicon oxynitride, boron nitride, high-k materials, or any combination of these materials. Examples of high-k materials include, but are not limited to, metal oxides such as hafnium oxide, hafnium silicon oxide, hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide, zirconium silicon oxynitride, tantalum oxide, titanium oxide, barium strontium titanium oxide, barium titanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. The high-k gate dielectric material may further include dopants such as lanthanum, aluminum. In one embodiment of the invention, the conformal layer of gate dielectric material is formed with a thickness in a range of about 0.5 nm to about 2.5 nm, which will vary depending on the target application. The dielectric material that forms the gate dielectric layers  202  is deposited using known methods such as ALD, which allows for high conformality of the gate dielectric material. 
     The gate electrode layers  204  are formed with any suitable conductive material including, for example, doped polycrystalline or amorphous silicon, germanium, silicon germanium, a metal (e.g., tungsten, titanium, tantalum, ruthenium, zirconium, cobalt, copper, aluminum, lead, platinum, tin, silver, gold), a conducting metallic compound material (e.g., tantalum nitride, titanium nitride, tantalum carbide, titanium carbide, titanium aluminum carbide, tungsten silicide, tungsten nitride, ruthenium oxide, cobalt silicide, nickel silicide), carbon nanotube, conductive carbon, graphene, or any suitable combination of such conductive materials. The layer of conductive material may further comprise dopants that are incorporated during or after deposition. The layer of conductive material is deposited using a suitable deposition process, for example, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, sputtering, etc. 
     In another embodiment, a thin conformal layer of work function metal (WFM) may be deposited over the conformal layer of gate dielectric material  202  prior to depositing the layer of conductive material  204 . The thin conformal WFM layer can be formed of one or more types of metallic materials, including, but not limited to, TiN, TaN, TiAlC, Zr, W, Hf, Ti, Al, Ru, Pa, TiAl, ZrAl, WAl, TaAl, HfAl, TiAlC, TaC, TiC, TaMgC, or other work function metals or alloys that are commonly used to obtain target work functions which are suitable for the type (e.g., n-type or p-type) of vertical FET devices that are to be formed. The conformal WFM layer is deposited using known methods such as ALD, CVD, etc. In one embodiment, the conformal WFM layer is formed with a thickness in a range of about 2 nm to about 5 nm. In another embodiment, the conductive material that forms the gate electrode layers  204  can serve as a WFM layer. 
     Following the formation of the metallic gate structures  200 , any suitable sequence of processing steps can be implemented to complete the fabrication of n-type and/or p-type FinFET devices and other elements of a semiconductor integrated circuit being fabricated as part of the FEOL layer, the details of which are not needed to understand embodiments of the invention. Moreover, a MOL (middle of the line) process is performed to form conductive via contacts in the ILD layer  190  (and one or more other layers of insulating material that may be formed over the ILD layer  190 ). The via contacts are formed by etching openings in the ILD layer  190  (and any overlying insulating layer) down to the source/drain layers  180  formed on the S/D regions of the vertical semiconductor fins  130 , and to the metal gate structures  200 , and then filling the openings with a conductive material to form the device contacts in the ILD layer  190 . Following formation of the MOL device contacts, a BEOL (back end of line) interconnect structure is formed using well known fabrication process flows to provide connections between the FinFET devices and other active or passive devices that are formed as part of the FEOL layer. 
     It is to be understood that the methods discussed herein for fabricating FinFET devices with multilayer gate structures can be incorporated as part of various semiconductor processing flows for fabricating other types of semiconductor devices and integrated circuits with various analog and digital circuitry or mixed-signal circuitry. The integrated circuit dies can be fabricated with various devices such as field-effect transistors, bipolar transistors, metal-oxide-semiconductor transistors, diodes, capacitors, inductors, etc. An integrated circuit in accordance with the present invention can be employed in applications, hardware, and/or electronic systems. Suitable hardware and systems for implementing the invention may include, but are not limited to, personal computers, communication networks, electronic commerce systems, portable communications devices (e.g., cell phones), solid-state media storage devices, functional circuitry, etc. Systems and hardware incorporating such integrated circuits are considered part of the embodiments described herein. Given the teachings of the invention provided herein, one of ordinary skill in the art will be able to contemplate other implementations and applications of the techniques of the invention. 
     Although exemplary embodiments have been described herein with reference to the accompanying figures, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be made therein by one skilled in the art without departing from the scope of the appended claims.