Patent Publication Number: US-10332800-B2

Title: Vertical field effect transistor having U-shaped top spacer

Description:
BACKGROUND 
     Technical Field 
     The present invention relates generally to semiconductor devices, and more specifically, to a vertical field effect transistor (VFET) having a U-shaped top spacer. 
     Description of the Related Art 
     A fin metal-oxide-semiconductor field effect transistor (finMOSFET or FinFET) can provide solutions to metal-oxide-semiconductor field effect transistor (MOSFET) scaling issues at and below, for example, the 22 nanometer (nm) node of semiconductor technology. A FinFET includes at least one narrow semiconductor fin (e.g., less than 30 nm wide) gated on at least two opposing sides of each of the at least one semiconductor fin. FinFET structures can, for example, typically be formed on either a semiconductor-on-insulator (SOI) substrate or a bulk semiconductor substrate. 
     SUMMARY 
     In accordance with an embodiment, a method is provided for forming a semiconductor structure. The method includes forming a plurality of fins over a source/drain region, forming a first spacer within troughs defined by the plurality of fins and depositing a high-k dielectric layer, a work function material layer, and a conducting layer. The method further includes etching the high-k dielectric layer, the work function material layer, and the conducting layer to form recesses between the plurality of fins, depositing a liner dielectric, and etching portions of the liner dielectric to form a plurality of second spacers having a U-shaped configuration. The method further includes forming an epitaxial layer over the plurality of fins such that a gap region is defined between the plurality of second spacers and the epitaxial layer. 
     In accordance with an embodiment, a method is provided for forming a semiconductor structure. The method includes forming a plurality of fins over a substrate, forming a spacer adjacent a lower section of the plurality of fins, depositing a liner dielectric, and etching portions of the liner dielectric to form a plurality U-shaped spacers adjacent an upper section of the plurality of fins. 
     In accordance with another embodiment, a semiconductor device is provided. The semiconductor device includes a plurality of fins formed over a source/drain region, a first spacer formed within troughs defined by the plurality of fins, a high-k dielectric layer, a work function material layer, and a conducting layer deposited over the plurality of fins, where the high-k dielectric layer, the work function material layer, and the conducting layer are etched to form recesses between the plurality of fins, a liner dielectric etched to form a plurality of second spacers having a U-shaped configuration, and an epitaxial layer formed over the plurality of fins such that a gap region is defined between the plurality of second spacers and the epitaxial layer. 
     It should be noted that the exemplary embodiments are described with reference to different subject-matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments have been described with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject-matter, also any combination between features relating to different subject-matters, in particular, between features of the method type claims, and features of the apparatus type claims, is considered as to be described within this document. 
     These and other features and advantages will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will provide details in the following description of preferred embodiments with reference to the following figures wherein: 
         FIG. 1  is a cross-sectional view of a semiconductor structure including an undoped channel region, in accordance with an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the semiconductor structure of  FIG. 1  where a plurality of fins are formed from the undoped channel region, in accordance with an embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of the semiconductor structure of  FIG. 2  where a high-k layer, a work function material layer, and a conducting layer are deposited over the plurality of fins, in accordance with an embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of the semiconductor structure of  FIG. 3  where an ILD oxide fill takes place, in accordance with an embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of the semiconductor device of  FIG. 4  where the high-k layer, the work function material layer, and the conducting layer are recessed to expose a top portion of the plurality of fins, in accordance with an embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of the semiconductor device of  FIG. 5  where a dielectric liner is deposited over the plurality of fins, as well as over the ILD oxide, in accordance with an embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of the semiconductor device of  FIG. 6  where an organic planarization layer (OPL) is deposited within recesses or troughs formed between the plurality of fins, in accordance with an embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of the semiconductor device of  FIG. 7  where a silicon nitride (SiN) mask positioned over the plurality of fins is etched away to form top spacers, in accordance with an embodiment of the present invention; 
         FIG. 9  is a cross-sectional view of the semiconductor device of  FIG. 8  where the OPL is removed and an epitaxially growth layer is formed over the plurality of fins such that a gap region is defined between the epitaxially grown layer and the top spacers, in accordance with an embodiment of the present invention; 
         FIG. 10  is a cross-sectional view of the semiconductor device of  FIG. 9  where a SiN cap is deposited over the epitaxially grown layer, in accordance with an embodiment of the present invention; and 
         FIG. 11  is a block/flow diagram of an exemplary method for forming U-shaped top spacers adjacent top portions of a plurality of fins, in accordance with an embodiment of the present invention. 
     
    
    
     Throughout the drawings, same or similar reference numerals represent the same or similar elements. 
     DETAILED DESCRIPTION 
     In one or more embodiments, a method includes forming a plurality of fins over a source/drain region, forming a first spacer within troughs defined by the plurality of fins and depositing a high-k dielectric layer, a work function material layer, and a conducting layer. The method further includes etching the high-k dielectric layer, the work function material layer, and the conducting layer to form recesses between the plurality of fins, depositing a liner dielectric, and etching portions of the liner dielectric to form a plurality of second spacers having a U-shaped configuration. The method further includes forming an epitaxial layer over the plurality of fins such that a gap region is defined between the plurality of second spacers and the epitaxial layer. 
     In one or more embodiments, a method includes forming a plurality of fins over a substrate, forming a spacer adjacent a lower section of the plurality of fins, depositing a liner dielectric, and etching portions of the liner dielectric to form a plurality U-shaped spacers adjacent an upper section of the plurality of fins. 
     In one or more embodiments, a semiconductor structure includes a plurality of fins formed over a source/drain region, a first spacer formed within troughs defined by the plurality of fins, a high-k dielectric layer, a work function material layer, and a conducting layer deposited over the plurality of fins, where the high-k dielectric layer, the work function material layer, and the conducting layer are etched to form recesses between the plurality of fins, a liner dielectric etched to form a plurality of second spacers having a U-shaped configuration, and an epitaxial layer formed over the plurality of fins such that a gap region is defined between the plurality of second spacers and the epitaxial layer. 
     In one or more embodiments, a U-shaped top spacer that can naturally form an air gap between the top source/drain epi and the gate is presented, which reduces parasitic capacitance. The goal is to utilize the fact that the top source/drain epi sits on top of the vertical fins. In this case, when forming the top source/drain that is larger than the fin underneath it, an air gap is formed underneath. Therefore, parasitic capacitance between the gate and the top S/D epi for the VFET is reduced by forming top U-shaped spacers that naturally form air gaps between the top S/D epi and the gate. 
     The work function is the minimum energy (usually measured in electron volts) needed to remove an electron from a solid to a point immediately outside the solid surface (or energy needed to move an electron from the Fermi energy level into vacuum). Here “immediately” means that the final electron position is far from the surface on the atomic scale but still close to the solid on the macroscopic scale. The work function is an important property of metals. The magnitude of the work function is usually about a half of the ionization energy of a free atom of the metal. The threshold voltage of a MOSFET is usually defined as the gate voltage where an inversion layer forms at the interface between the insulating layer (oxide) and the substrate (body) of the transistor. 
     As used herein, “semiconductor device” refers to an intrinsic semiconductor material that has been doped, that is, into which a doping agent has been introduced, giving it different electrical properties than the intrinsic semiconductor. Doping involves adding dopant atoms to an intrinsic semiconductor, which changes the electron and hole carrier concentrations of the intrinsic semiconductor at thermal equilibrium. Dominant carrier concentration in an extrinsic semiconductor determines the conductivity type of the semiconductor. 
     As used herein, the term “drain” means a doped region in the semiconductor device located at the end of the channel, in which carriers are flowing out of the transistor through the drain. 
     As used herein, the term “source” is a doped region in the semiconductor device, in which majority carriers are flowing into the channel. 
     The term “direct contact” or “directly on” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary conducting, insulating or semiconductor layers at the interface of the two elements. 
     The terms “overlying”, “atop”, “positioned on” or “positioned atop” means that a first element, such as a first structure, is present on a second element, such as a second structure, wherein intervening elements, such as an interface structure can be present between the first element and the second element. 
     The term “electrically connected” means either directly electrically connected, or indirectly electrically connected, such that intervening elements are present; in an indirect electrical connection, the intervening elements can include inductors and/or transformers. 
     The term “crystalline material” means any material that is single-crystalline, multi-crystalline, or polycrystalline. 
     The term “non-crystalline material” means any material that is not crystalline; including any material that is amorphous, nano-crystalline, or micro-crystalline. 
     The term “intrinsic material” means a semiconductor material which is substantially free of doping atoms, or in which the concentration of dopant atoms is less than 10 15  atoms/cm 3 . 
     As used herein, “p-type” refers to the addition of impurities to an intrinsic semiconductor that creates deficiencies of valence electrons. In a silicon-containing substrate, examples of n-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 contributes free electrons to an intrinsic semiconductor. In a silicon containing substrate examples of n-type dopants, i.e., impurities, include but are not limited to antimony, arsenic and phosphorous. 
     As used herein, an “anisotropic etch process” denotes a material removal process in which the etch rate in the direction normal to the surface to be etched is greater than in the direction parallel to the surface to be etched. The anisotropic etch can include reactive-ion etching (RIE). Other examples of anisotropic etching that can be used include ion beam etching, plasma etching or laser ablation. 
     As used herein, the term “fin structure” refers to a semiconductor material, which can be employed as the body of a semiconductor device, in which a gate structure is positioned around the fin structure such that charge flows down the channel on the two sidewalls of the fin structure. The fin structures are processed to provide FinFETs. A field effect transistor (FET) is a semiconductor device in which output current, i.e., source-drain current, is controlled by the voltage applied to the gate structure to the channel of a semiconductor device. A finFET is a semiconductor device that positions the channel region of the semiconductor device in a fin structure. 
     The term “processing” as used herein includes deposition of material or photoresist, patterning, exposure, development, etching, cleaning, stripping, implanting, doping, stressing, layering, and/or removal of the material or photoresist as required in forming a described structure. 
     Exemplary types of semiconductor devices include planar field effect transistors (FETs), fin-type field effect transistors (FinFETs), nanowire/nanosheet devices, vertical field effect transistors (VFETs), or other devices. 
     It is to be understood that the present invention will be described in terms of a given illustrative architecture; however, other architectures, structures, substrate materials and process features and steps/blocks can be varied within the scope of the present invention. It should be noted that certain features cannot be shown in all figures for the sake of clarity. This is not intended to be interpreted as a limitation of any particular embodiment, or illustration, or scope of the claims. 
     Various illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this invention. 
     The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present invention with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
       FIG. 1  is a cross-sectional view of a semiconductor structure including an undoped channel region, in accordance with an embodiment of the present invention. 
     A semiconductor structure  5  includes a semiconductor substrate  10 . A doped bottom source/drain (S/D) layer  12  is deposited over the substrate  10 . An undoped channel region  14  is deposited over the bottom S/D layer  12 . The undoped channel region  14  is used to form a plurality of fins, as described below. 
     In one or more embodiments, the substrate  10  can be a semiconductor or an insulator with an active surface semiconductor layer. The substrate  10  can be crystalline, semi-crystalline, microcrystalline, or amorphous. The substrate  10  can be essentially (i.e., except for contaminants) a single element (e.g., silicon), primarily (i.e., with doping) of a single element, for example, silicon (Si) or germanium (Ge), or the substrate  10  can include a compound, for example, Al 2 O 3 , SiO 2 , GaAs, SiC, or SiGe. The substrate  10  can also have multiple material layers, for example, a semiconductor-on-insulator substrate (SeOI), a silicon-on-insulator substrate (SOI), germanium-on-insulator substrate (GeOI), or silicon-germanium-on-insulator substrate (SGOI). The substrate  10  can also have other layers forming the substrate  10 , including high-k oxides and/or nitrides. In one or more embodiments, the substrate  10  can be a silicon wafer. In an embodiment, the substrate  10  is a single crystal silicon wafer. 
       FIG. 2  is a cross-sectional view of the semiconductor structure of  FIG. 1  where a plurality of fins are formed from the undoped channel region, in accordance with an embodiment of the present invention. 
     In various embodiments, the undoped channel region  14  is etched to form fins  16 . A hard mask  18  is also deposited over the fins  16 . The hard mask  18  can be, e.g., a silicon nitride (SiN) hard mask  18 . A proximal portion of the fin  16  extends up to the doped S/D layer  14 . The fin  16  extend vertically from the substrate  10 . Stated differently, the fin  16  is normal to or perpendicular to the substrate  10 . 
     As used herein, a “semiconductor fin” refers to a semiconductor structure including a portion having a shape of a rectangular parallelepiped. The direction along which a semiconductor fin  16  laterally extends the most is herein referred to as a “lengthwise direction” of the semiconductor fin  16 . The height of each semiconductor fin  16  can be in a range from 5 nm to 300 nm, although lesser and greater heights can also be employed. The width of each semiconductor fin  16  can be in a range from 5 nm to 100 nm, although lesser and greater widths can also be employed. In various embodiments, the fins  16  can have a width in the range of about 6 nm to about 20 nm, or can have a width in the range of about 8 nm to about 15 nm, or in the range of about 10 nm to about 12 nm. In various embodiments, the fin  16  can have a height in the range of about 25 nm to about 75 nm, or in the range of about 40 nm to about 50 nm. 
     Multiple semiconductor fins  16  can be arranged such that the multiple semiconductor fins  16  have the same lengthwise direction, and are laterally spaced from each other along a horizontal direction that is perpendicular to the lengthwise direction. In this case, the horizontal direction that is perpendicular to the common lengthwise direction is referred to as a “widthwise direction.” Each semiconductor fin  16  includes a pair of parallel sidewalls along the lengthwise direction. 
     In one embodiment, each semiconductor fin  16  can be formed by lithography and etching. The lithographic step can include forming a photoresist (not shown) atop a substrate including a topmost semiconductor material, exposing the photoresist to a desired pattern of radiation and then developing the exposed photoresist utilizing a conventional resist developer. The pattern within the photoresist is then transferred into the topmost semiconductor material. The etch can include a dry etch process, a chemical wet etch process, or any combination thereof. When a dry etch is used, the dry etch can be a reactive ion etch process, a plasma etch process, ion beam etching or laser ablation. The patterned photoresist material can be removed after transferring the pattern utilizing a conventional stripping process. 
     In another embodiment of the present application, each semiconductor fin  16  can be formed utilizing a SIT (sidewall image transfer) process. In a typical SIT process, spacers are formed on sidewall surfaces of a sacrificial mandrel that is formed on a topmost semiconductor material of a substrate. The sacrificial mandrel is removed and the remaining spacers are used as a hard mask to etch the topmost semiconductor material of the substrate. The spacers are then removed after each semiconductor fin  16  has been formed. In another embodiment, sequential SIT processes can be utilized to form fins with highly scaled fin width and pitches. 
     In some embodiments, the fins  16  in the plurality of semiconductor fins can have a fin width between 5 nm and 10 nm. The combination of the fin width and the width of the trough equals, in embodiments, the fin pitch. The fin width and the fin pitch can vary in different areas of a fin array, and can vary from one fin array to another on a semiconductor wafer, according to the design parameters of the integrated circuit that is being made. For example, fins of negatively doped FinFETs can have a different fin size than positively doped FinFETs because of the electrical properties of the materials they are made of. 
     The block masks  18  can comprise soft and/or hard mask materials and can be formed using deposition, photolithography and etching. In one embodiment, the block mask  18  comprises a photoresist. A photoresist block mask can be produced by applying a photoresist layer, exposing the photoresist layer to a pattern of radiation, and then developing the pattern into the photoresist layer utilizing conventional resist developer. Typically, the block masks have a thickness ranging from 10 nm to 300 nm. 
     The block mask  18  can comprise soft and/or hard mask materials and can be formed using deposition, photolithography and etching. In one embodiment, the block mask  18  is a hard mask composed of a nitride-containing material, such as silicon nitride (SiN). It is noted that it is not intended that the block mask be limited to only silicon nitride, as the composition of the hard mask can include any dielectric material that can be deposited by chemical vapor deposition (CVD) and related methods. Other hard mask compositions for the block mask can include silicon oxides, silicon oxynitrides, silicon carbides, silicon carbonitrides, etc. Spin-on dielectrics can also be utilized as a hard mask material including, but not limited to: silsequioxanes, siloxanes, and boron phosphate silicate glass (BPSG). 
     In one embodiment, a block mask comprising a hard mask material can be formed by blanket depositing a layer of hard mask material, providing a patterned photoresist atop the layer of hard mask material, and then etching the layer of hard mask material to provide a block mask protecting at least one portion of the dummy gate. A patterned photoresist can be produced by applying a blanket photoresist layer to the surface of the hard mask, exposing the photoresist layer to a pattern of radiation, and then developing the pattern into the photoresist layer utilizing resist developer. Etching of the exposed portion of the block mask can include an etch chemistry for removing the exposed portion of the hard mask material and having a high selectivity to at least the block mask. In one embodiment, the etch process can be an anisotropic etch process, such as reactive ion etch (RIE). In another embodiment, the replacement gate can be formed by utilizing the SIT patterning and etching process described above. 
     The etching can include a dry etching process such as, for example, reactive ion etching, plasma etching, ion etching or laser ablation. The etching can further include a wet chemical etching process in which one or more chemical etchants are used to remove portions of the blanket layers that are not protected by the patterned photoresist. The patterned photoresist can be removed utilizing an ashing process. 
     As used herein, the term “selective” in reference to a material removal process denotes 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 being applied. For example, in one embodiment, a selective etch can include an etch chemistry that removes a first material selectively to a second material by a ratio of 10:1 or greater, e.g., 100:1 or greater, or 1000:1 or greater. 
       FIG. 3  is a cross-sectional view of the semiconductor structure of  FIG. 2  where a high-k layer, a work function material layer, and a conducting layer are deposited over the plurality of fins, in accordance with an embodiment of the present invention. 
     In various embodiments, spacers  20  are formed by, e.g., directional deposition or dielectric fill and CMP and etch back/recess. The spacers  20  can be, e.g., a nitride film. In an embodiment, the spacer  20  can be an oxide, for example, silicon oxide (SiO), a nitride, for example, a silicon nitride (SiN), or an oxynitride, for example, silicon oxynitride (SiON). In an embodiment, the spacer  20  can be, e.g., SiOCN, SiBCN, or similar film types. The spacer  20  can also be referred to as a non-conducting dielectric layer. 
     In some exemplary embodiments, the spacer  20  can include a material that is resistant to some etching processes such as, for example, HF chemical etching or chemical oxide removal etching. 
     In one or more embodiments, the spacer  20  can have a thickness in the range of about 3 nm to about 10 nm, or in the range of about 3 nm to about 5 nm. 
     In various embodiments, a high-k dielectric  22  is deposited over the plurality of fins. A work function material layer  24  is then deposited over the high-k dielectric  22 . The work function  24  can be, e.g., a work function metal. A conducting layer  26  is then deposited over the work function material layer  24 . The conducting layer  26  can be a metal. The metal can be, e.g., Tungsten (W). The layers  22 ,  24 ,  26  can form, e.g., a HKMG (high-k metal gate). 
     In various embodiments, the HKMG can include but is not limited to metal oxides such as hafnium oxide (e.g., HfO 2 ), hafnium silicon oxide (e.g., HfSiO 4 ), hafnium silicon oxynitride (Hf w Si x O y N z ), lanthanum oxide (e.g., La 2 O 3 ), lanthanum aluminum oxide (e.g., LaAlO 3 ), zirconium oxide (e.g., ZrO 2 ), zirconium silicon oxide (e.g., ZrSiO 4 ), zirconium silicon oxynitride (Zr w Si x O y N z ), tantalum oxide (e.g., TaO 2 , Ta 2 O 5 ), titanium oxide (e.g., TiO 2 ), barium strontium titanium oxide (e.g., BaTiO 3 —SrTiO 3 ), barium titanium oxide (e.g., BaTiO 3 ), strontium titanium oxide (e.g., SrTiO 3 ), yttrium oxide (e.g., Y 2 O 3 ), aluminum oxide (e.g., Al 2 O 3 ), lead scandium tantalum oxide (Pb(Sc x Ta 1-x )O 3 ), and lead zinc niobate (e.g., PbZn 1/3 Nb 2/3 O 3 ). The high-k material can further include dopants such as lanthanum and/or aluminum. The stoichiometry of the high-K compounds can vary. 
     In various embodiments, the HKMG can have a thickness in the range of about 1.5 nm to about 2.5 nm. 
       FIG. 4  is a cross-sectional view of the semiconductor structure of  FIG. 3  where an ILD oxide fill takes place, in accordance with an embodiment of the present invention. 
     In various embodiments, an oxide gap fill takes place. The ILD oxide  28  is planarized. The ILD oxide  28  fills the remaining gap or recess between the fins  16 . The top sections or portions of the structure can be etched. As such, high-k dielectric  22 , the work function material layer  24 , and the conducting layer  26  are selective etched to expose the top surface  17  of the SiN hard mask  18 . Thus, the ILD oxide  28  extends beyond a top surface of the fins  16 . The ILD oxide  28  extends up to a top surface of the SiN mask  18 . In other words, the ILD oxide  28  is flush with the top surface  17  of the SiN hard mask  18 . Additionally, the top surface  21  of the high-k dielectric  22  is exposed, the top surface  23  of the work function material layer  24  is exposed, and the top surface  25  of the conducting layer  26  is exposed adjacent the top portion of the SiN hard mask  18 . 
     In various embodiments, the height of the ILD oxide fill  28  can be reduced by chemical-mechanical polishing (CMP) and/or etching. Therefore, the planarization process can be provided by CMP. Other planarization process can include grinding and polishing. 
     In one or more embodiments, the ILD oxide  28  can have a height of about 20 nm to about 200 nm. 
     The ILD  28  can be selected from the group consisting of silicon containing materials such as SiO 2 , Si 3 N 4 , SiO x N y , SiC, 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 ILD  28  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. 
     In various embodiments, the top sections formed over the structure are removed by, e.g., CMP. Therefore, the planarization process can be provided by CMP. Other planarization process can include grinding and polishing. In particular, the conducting layer  26 , the work function material layer  24  and the high-k dielectric  22  are selectively removed or stripped. The removal of such top section results in the exposure of the top surface  17  of the SiN mask  18 . 
       FIG. 5  is a cross-sectional view of the semiconductor device of  FIG. 4  where the high-k layer, the work function material layer, and the conducting layer are recessed to expose a top portion of the plurality of fins, in accordance with an embodiment of the present invention. 
     In various embodiments, the high-k dielectric  22 , the work function material layer  24 , and the conducting layer  26  are selective etched to expose the hark mask  18 , as well as the top portion  15  of the plurality of fins  16 . Thus, gaps or recesses  30  are formed between the SiN hard masks  18  and between the top portions  15  of the plurality of fins  16 . The height of the recess  30  is designated by “X.” The height of the recess “X” extends from a top surface of the high-k dielectric  22 , the work function material layer  24 , and the conducting layer  26  to a top surface of the hard mask  18 . 
     RIE is a form of plasma etching in which during etching the surface to be etched is placed on the RF powered electrode. Moreover, during RIE the surface to be etched takes on a potential that accelerates the etching species extracted from plasma toward the surface, in which the chemical etching reaction is taking place in the direction normal to the surface. Other examples of anisotropic etching that can be used at this point of the present invention include ion beam etching, plasma etching or laser ablation. 
     In various embodiments, the materials and layers can be deposited by physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), molecular beam epitaxy (MBE), or any of the various modifications thereof, for example plasma-enhanced chemical vapor deposition (PECVD), metal-organic chemical vapor deposition (MOCVD), low pressure chemical vapor deposition (LPCVD), electron-beam physical vapor deposition (EB-PVD), and plasma-enhanced atomic layer deposition (PE-ALD). The depositions can be epitaxial processes, and the deposited material can be crystalline. In various embodiments, formation of a layer can be by one or more deposition processes, where, for example, a conformal layer can be formed by a first process (e.g., ALD, PE-ALD, etc.) and a fill can be formed by a second process (e.g., CVD, electrodeposition, PVD, etc.). 
       FIG. 6  is a cross-sectional view of the semiconductor device of  FIG. 5  where a dielectric liner is deposited over the plurality of fins, as well as over the ILD oxide, in accordance with an embodiment of the present invention. 
     In various embodiments, a dielectric liner  32  is deposited over the structure. The dielectric liner  32  can be, e.g., a silicon nitride (SiN) liner. The liner material can also be another dielectric material, such as a low k material (e.g., SiBCN, SiOC, etc.). The SiN liner  32  covers sidewalls of the exposed top portion  15  of the fin  16 , as well as sidewalls/top surface of the hard mask  18 . The SiN liner  32  also covers the exposed portions/sections of the ILD oxide  28 . 
       FIG. 7  is a cross-sectional view of the semiconductor device of  FIG. 6  where an organic planarization layer (OPL) is deposited within recesses or troughs formed between the plurality of fins, in accordance with an embodiment of the present invention. 
     In one example, an organic planarization layer (OPL)  34  is formed within the U-shaped regions of the SiN liner  32 . The OPL  34  can be formed utilizing a deposition process such as, for example, spin-on, CVD, PECVD, evaporation, chemical solution deposition and other like deposition techniques. 
     The thickness of the OPL  34  can vary so long as its thickness is greater than the total thickness of each gate line and of the plurality of gate lines (not shown). In one embodiment, the OPL  34  has a thickness from 50 nm to 500 nm. In another embodiment, the OPL  34  has a thickness from 150 nm to 300 nm. The OPL  34  can have a thickness greater than the thickness of the SiN layer  32 . The thickness of the OPL  34  can be, e.g., approximately equal to the thickness of the top portion  15  of the fin  16 . 
       FIG. 8  is a cross-sectional view of the semiconductor device of  FIG. 7  where a silicon nitride (SiN) mask positioned over the plurality of fins is etched away to form top spacers, in accordance with an embodiment of the present invention. 
     In various embodiments, etching takes place to remove the hard mask  18 , as well portions/sections as the SiN mask  32  contacting or engaging the hard mark  18 . The etching creates a recess “D” that extends from a top surface of the OPL  34  to a top surface of the  29  of the ILD oxide  28 . The removal of the hard mask  18  allows for the exposure of the top surface  13  of the fin  16 . The removal of the hard mask  18  further allows for the exposure of the top surface  29  of the ILD oxide  28 . Additionally, the top surface  13  of the fin  16  is flush with the top surface of the OPL  34 . 
     Moreover, U-shaped top spacers  38  are now formed adjacent the top portion of the fin  16 . The U-shaped top spacers  38  hold the OPL  34 . The U-shaped top spacers  38  are defined by a first section  37 , a second section  36 , and a third section  39 . The first and third sections  37 ,  39  are parallel to each other, whereas the second section  36  is perpendicular to the first and third sections  37 ,  39 . The first and third sections  37 ,  39  of the U-shaped top spacer  38  can be parallel to the fin  16 . The U-shaped top spacers  38  are offset from the fins  16 . Stated differently, the U-shaped top spacers  38  are positioned or formed between the fins  16 . The U-shaped top spacers  38  are configured to contact or engage or be adjacent to at least a portion of the fins  16 . The U-shaped top spacers  38  selectively contact the HKMG. The U-shaped top spacers  38  are in alignment with their respective HKMG. 
       FIG. 9  is a cross-sectional view of the semiconductor device of  FIG. 8  where the OPL is removed and an epitaxially growth layer is formed over the plurality of fins such that a gap region is defined between the epitaxially grown layer and the top spacers, in accordance with an embodiment of the present invention. 
     In one or more embodiments, a top source/drain  42  is epitaxially grown after the HKMG is defined in the VFET structure. The deposition of the S/D epi  42  results in the creation of voids or gaps  40  between the U-shaped top spacers  38  and the S/D epi  42 . The gaps  40  are created in a region where the OPL  34  used to be. Therefore, a U-shaped top spacer  38  can naturally form an air gap  40  between the top source/drain epi  42  and the gate, which reduces parasitic capacitance. The goal is to utilize the fact that the top source/drain epi  42  sits on top of the vertical fins  16 . In this case, when forming the top source/drain epi  42  that is larger than the fin  16  underneath it, an air gap  40  is formed underneath. Therefore, parasitic capacitance between the gate and the top S/D epi  42  for the VFET is reduced by forming top U-shaped spacers  38  that naturally form air gaps  40  between the top S/D epi  42  and the gate. 
     In another embodiment, the HKMG is defined by a replacement metal gate (RMG) process. It is advantageous and useful to form the epitaxial growth layer  42  after formation of the HKMG. 
     In one or more embodiments, enablement of a higher thermal budget for the top epitaxially grown source/drain regions is advantageously achieved, as well as higher epitaxial growth quality, higher in-situ doping, and lower resistance. In another embodiment, multi-Vt is advantageously enabled through a poly open process. 
     In one or more embodiments, a VFET process is defined which advantageously enables the top source/drain epitaxial region  42  to be formed with a high thermal budget, to minimize defects stemming from epitaxial growth, and to minimize sheet resistance. In one or more embodiments, a VFET replacement metal gate (RMG) process is defined that is compatible with tight fin pitches to advantageously enable multi-Vt processing. 
     In various embodiments, the in-situ doped source/drain  42  is advantageously deposited or formed via epitaxial growth. Depending on how the epitaxial growth develops, it can be necessary to anisotropically etch the epitaxial growth, in order to result in a top surface of the source/drain region  42  that is suitable for subsequent processing. 
     The doped region  42  can be formed above the vertical fin  16 . The dopant can be provided to the doped region(s)  42  (i.e., source/drain region(s)) by ion implantation, and source/drains formed by annealing the doped region(s)  42 . In various embodiments, the doped region  42  can be n-doped or p-doped. It should be noted that the source and drain can be interchangeable between the top and bottom locations of a vertical fin, where the doped region in the substrate can act as a source or a drain. 
     In various embodiments, the bottom source can be doped in-situ or ex-situ, for example, through ion implantation or thermal diffusion of dopants into the substrate. The dopant of the source can be activated by annealing. Other suitable doping techniques can also be used, including but not limited to, gas phase doping, plasma doping, plasma immersion ion implantation, cluster doping, infusion doping, liquid phase doping, solid phase doping, or combinations thereof. 
     Forming the source and drain regions  42  can include forming an in situ doped epitaxial semiconductor material on the source and drain region portions of the fin structures  16 . The term “epitaxial semiconductor material” denotes a semiconductor material that has been formed using an epitaxial deposition or growth process. “Epitaxial growth and/or deposition” means the growth of a semiconductor material on a deposition surface of a semiconductor material, in which the semiconductor material being grown has substantially the same crystalline characteristics as the semiconductor material of the deposition surface. In some embodiments, when the chemical reactants are controlled and the system parameters set correctly, the depositing atoms arrive at the deposition surface with sufficient energy to move around on the surface and orient themselves to the crystal arrangement of the atoms of the deposition surface. Thus, in some examples, an epitaxial film deposited on a {100} crystal surface will take on a {100} orientation. In some embodiments, the epitaxial deposition process is a selective deposition method, in which the epitaxial semiconductor material is formed only on semiconductor material deposition surfaces. The epitaxial deposition process will not form epitaxial semiconductor material on dielectric surfaces. 
     In some embodiments, the epitaxial semiconductor material that provides the source and drain regions  42  can be composed of silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon doped with carbon (Si:C) or a combination thereof. In one example, the p-type source and drain regions are provided by silicon germanium (SiGe) epitaxial semiconductor material. In one embodiment, a number of different sources can be used for the epitaxial deposition of the epitaxial semiconductor material that provides the source and drain regions  42 . 
     Examples of silicon including source gasses can include silane, disilane, trisilane, tetrasilane, hexachlorodisilane, tetrachlorosilane, dichlorosilane, trichlorosilane, methylsilane, dimethylsilane, ethylsilane, methyldisilane, dimethyldisilane, hexamethyldisilane and combinations thereof. 
     Examples of germanium including source gasses for epitaxially forming the epitaxial semiconductor material of a germanium containing semiconductor include germane, digermane, halogermane, dichlorogermane, trichlorogermane, tetrachlorogermane and combinations thereof. 
     Epitaxial deposition can be carried out in a chemical vapor deposition apparatus, such as a metal organic chemical vapor deposition (MOCVD) apparatus or a plasma enhanced chemical vapor deposition (PECVD) apparatus. The temperature for epitaxial deposition typically ranges from 550° C. to 900° C. Although higher temperature typically results in faster deposition, the faster deposition can result in crystal defects and film cracking. 
     The epitaxial semiconductor material that provides the source and drain regions  42  can be in situ doped to a p-type conductivity or an n-type conductivity. The term “in situ” denotes that a dopant, e.g., n-type or p-type dopant, is introduced to the base semiconductor material, e.g., silicon or silicon germanium, during the formation of the base material. For example, an in situ doped epitaxial semiconductor material can introduce p-type dopants to the material being formed during the epitaxial deposition process that includes p-type source gasses. 
     As used herein, “p-type” refers to the addition of impurities to an intrinsic semiconductor that creates deficiencies of valence electrons. In a type IV semiconductor, such as silicon, examples of p-type dopants, i.e., impurities, include but are not limited to, boron, aluminum, gallium and indium. The p-type gas dopant source can include diborane (B 2 H 6 ). In some embodiments, the epitaxial deposition process for forming the epitaxial semiconductor material for the source and drain regions  32  can continue until the epitaxial semiconductor material that is formed on adjacent fin structures contact one another to form merged epitaxial semiconductor material. 
     As used herein, “n-type” refers to the addition of impurities that contributes free electrons to an intrinsic semiconductor. In a type IV semiconductor, such as silicon, examples of n-type dopants, i.e., impurities, include but are not limited to antimony, arsenic and phosphorous. 
       FIG. 10  is a cross-sectional view of the semiconductor device of  FIG. 9  where a SiN cap is deposited over the epitaxially grown layer, in accordance with an embodiment of the present invention. 
     In various embodiments, a SiN cap  44  is deposited over the epitaxially grown layer  42 , as well as the exposed portions of the ILD oxide  28 . 
       FIG. 11  is a block/flow diagram of an exemplary method for forming U-shaped top spacers adjacent top portions of a plurality of fins, in accordance with an embodiment of the present invention. 
     At block  102 , a plurality of fins are formed over a source/drain region. 
     At block  104 , a first spacer is formed within troughs defined by the plurality of fins. 
     At block  106 , a high-k dielectric layer, a work function material layer, and a conducting layer are deposited. 
     At block  108 , the high-k dielectric layer, the work function material layer, and the conducting layer are etched to form recesses between the plurality of fins. 
     At block  110 , a liner dielectric is deposited. 
     At block  112 , portions of the liner dielectric are etched to form a plurality of second spacers having a U-shaped configuration. 
     At block  114 , an epitaxial layer is formed over the plurality of fins such that a gap region is defined between the plurality of second spacers and the epitaxial layer. 
     It is to be understood that the present invention will be described in terms of a given illustrative architecture; however, other architectures, structures, substrate materials and process features and steps/blocks can be varied within the scope of the present invention. 
     It will also be understood that when an element such as a layer, region or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     The present embodiments can include a design for an integrated circuit chip, which can be created in a graphical computer programming language, and stored in a computer storage medium (such as a disk, tape, physical hard drive, or virtual hard drive such as in a storage access network). If the designer does not fabricate chips or the photolithographic masks used to fabricate chips, the designer can transmit the resulting design by physical mechanisms (e.g., by providing a copy of the storage medium storing the design) or electronically (e.g., through the Internet) to such entities, directly or indirectly. The stored design is then converted into the appropriate format (e.g., GDSII) for the fabrication of photolithographic masks, which typically include multiple copies of the chip design in question that are to be formed on a wafer. The photolithographic masks are utilized to define areas of the wafer (and/or the layers thereon) to be etched or otherwise processed. 
     Methods as described herein can be used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case, the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case, the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor. 
     It should also be understood that material compounds will be described in terms of listed elements, e.g., SiGe. These compounds include different proportions of the elements within the compound, e.g., SiGe includes Si x Ge 1-x  where x is less than or equal to 1, etc. In addition, other elements can be included in the compound and still function in accordance with the present embodiments. The compounds with additional elements will be referred to herein as alloys. 
     Reference in the specification to “one embodiment” or “an embodiment” of the present invention, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment”, as well any other variations, appearing in various places throughout the specification are not necessarily all referring to the same embodiment. 
     It is to be appreciated that the use of any of the following “/”, “and/or”, and “at least one of”, for example, in the cases of “A/B”, “A and/or B” and “at least one of A and B”, is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of both options (A and B). As a further example, in the cases of “A, B, and/or C” and “at least one of A, B, and C”, such phrasing is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of the third listed option (C) only, or the selection of the first and the second listed options (A and B) only, or the selection of the first and third listed options (A and C) only, or the selection of the second and third listed options (B and C) only, or the selection of all three options (A and B and C). This can be extended, as readily apparent by one of ordinary skill in this and related arts, for as many items listed. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, can be used herein for ease of description to describe one element&#39;s or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the FIGS. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the FIGS. For example, if the device in the FIGS. is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein can be interpreted accordingly. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers can also be present. 
     It will be understood that, although the terms first, second, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first element discussed below could be termed a second element without departing from the scope of the present concept. 
     Having described preferred embodiments of a method of device fabrication and a semiconductor device thereby fabricated to form U-shaped top spacers adjacent top portions of a plurality of fins (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments described which are within the scope of the invention as outlined by the appended claims. Having thus described aspects of the invention, with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.