Abstract:
An intermediate semiconductor structure in fabrication includes a silicon semiconductor substrate, a hard mask of silicon nitride (SiN) over the substrate and a sacrificial layer of polysilicon or amorphous silicon over the hard mask. The sacrificial layer is patterned into sidewall spacers, each of the sidewall spacers having vertically tapered inner and outer sidewalls providing a rough triangular shape. The rough triangular sidewall spacers are used as a temporary hard mask to pattern the SiN hard mask.

Description:
TECHNICAL FIELD 
     This invention relates to vertical field effect transistors (VFET) and more particularly to forming self-aligned replacement metal gates therefor. 
     BACKGROUND INFORMATION 
     Currently, the fabrication of VFETs utilize a gate first fabrication technique. Gate first fabrication techniques refer to a situation where the gate is patterned prior to the annealing step used to activate the source and drain. However, in gate last techniques, a dummy gate is used to occupy the gate space during the annealing process and a replacement metal gate is inserted into the dummy gate area after the anneal. The gate last technique and the use of replacement metal gates avoids the difficult thermal issues normally encountered with use of the gate first technique. 
     Accordingly, it is desirable to provide a self-aligned replacement metal gate method and structure for forming self-aligned replacement metal gates for vertical field effect transistors to provide desired thermal characteristics and effective area scaling. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, a method of providing a fin structure is disclosed. The fin structure includes a fin with sacrificial material above and adjacent the fin, with the fin structure being above a substrate adjacent a source or drain. The method includes removing a first portion of the sacrificial material above the fin to form an opening within the sacrificial material on top of the fin, forming a top source or drain within the opening on top of the fin, removing a second portion of the sacrificial material adjacent the top source or drain, depositing a spacer above and adjacent the top source or drain, depositing a gate material above the spacer and below the spacer to the sides of the fin, and removing the gate material above the bottom portion of the spacer to form a self aligned gate around the fin and a vertical field effect transistor. 
     The sacrificial material includes a first sacrificial material. A top portion of the first sacrificial material located above and adjacent said fin structure is removed to allow a remaining portion of the first sacrificial material to remain adjacent said fin. A second sacrificial material may be deposited above the remaining first sacrificial material so that the sacrificial material includes a first sacrificial material, the second sacrificial material, and a hard mask on the top of the fin. 
     The first sacrificial material may be a thin oxide surrounding the fin structure and an amorphous silicon deposited on top of the thin oxide. The second sacrificial material may be an oxide. The removing of a first portion of the sacrificial material above the fin to form an opening within the sacrificial material on top of the fin may include removing the hard mask above or on top of said fin. The self-aligned contact (SAC) cap may be deposited above the top source or drain within the oxide. The method may also include removing the oxide prior to depositing a spacer above and adjacent the top source or drain. Also, removing a third portion of the sacrificial material adjacent the fin may include removing the amorphous silicon. 
     The method may further include removing the thin oxide, which may be a silicon oxide. The method may also include providing a bottom spacer above the source or drain and substrate adjacent the fin. And, may include depositing a high K dielectric material on the bottom spacer, where the spacer and the fin form an intermediate structure, and annealing the intermediate structure. 
     The method may also include depositing a work function metal as part of the gate material and a metal over the work function metal as part of the gate material. 
     Removing the gate material above the bottom portion of the spacer may include removing the work function metal and the metal. 
     The method may further include removing annealed high K material above the spacer above and adjacent the top source or drain, depositing a second lithography stack over the barrier stack, performing a second lithography to pattern the at least one via opening, and etching to form at least one via opening. 
     The method may also include providing multiple fin structures, multiple top sources or drains to form multiple vertical field effect transistors. The fin structures may be parallel spaced with at least two vertical field effect transistors spaced apart and aligned along lengths thereof and forming at least one additional gate connecting aligned on parallel spaced vertical field effect transistors. 
     In another aspect of the invention, the method includes providing a fin structure having a fin with a hard mask on top of the fin. The fin structure is above a substrate adjacent a source or drain. The method includes depositing one or more sacrificial materials above and along sides of the fin structure, removing a top portion of the one or more sacrificial materials above a top of the fin to form an opening within the one or more sacrificial materials, forming a top source or drain within the opening on the top of said fin, removing a portion of the one or more sacrificial materials above and adjacent the top source or drain, depositing a spacer above the top source or drain, removing additional portions of the one or more sacrificial materials surrounding sides of the fin, depositing gate material above the spacer and below the spacer to the sides of the fin, and removing the gate material above the bottom portion of the spacer to form a self aligned gate around the fin and vertical field effort transistor. 
     In another aspect of the invention, the invention includes an intermediate semiconductor structure having a fin structure. The fin structure includes a fin above a substrate adjacent a bottom source or drain, a top source or drain located on the top of the fin, a spacer located above and surrounding the top source or drain and adjacent a top portion of the fin, a self-aligned gate structure located below the top spacer and above a bottom spacer located above said substrate and source or drain, and one or more work function layers located between the bottom spacer and side walls of the fin and top spacer. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       One or more aspects of the present invention are particularly pointed out and distinctly claimed as examples in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1A  depicts a cross sectional view of a fin of negative channel field-effect transistor device (nFET) including hardmask material which may be situated above and or included adjacent as a bottom spacer to the fin and can include a bottom source drain region and insulator region; 
         FIG. 1B  depicts a cross sectional view of a fin of a positive channel field-effect transistor device (pFET) including hardmask material which may be situated above and or included adjacent as a bottom to the fin and can include a bottom source drain region and insulator region; 
         FIG. 2A  depicts a cross sectional view of the structure of  FIG. 1A  after application of a first sacrificial material which may be in the form of a thin oxide surrounding said fin structure, and a second sacrificial material which may be in the form of an amorphous silicon layer deposed upon the first sacrificial material; 
         FIG. 2B  depicts a cross sectional view of the structure of  FIG. 1B  after application of a first sacrificial material which may be in the form of a thin oxide surrounding said fin structure, and a second sacrificial material which may be in the form of an amorphous silicon layer deposed upon the first sacrificial material; 
         FIG. 3A  depicts a cross sectional view of the structure of  FIG. 2A  after removing of a first portion of the first sacrificial material a first portion of the second sacrificial material thereby exposing the hardmask material located above the fin; 
         FIG. 3B  depicts a cross sectional view of the structure of  FIG. 2B  after removing of a first portion of the first sacrificial material a first portion of the second sacrificial material thereby exposing the hardmask material located above the fin; 
         FIG. 4A  depicts a cross sectional view of the structure of  FIG. 3A  after the recessing of a second portion of the first sacrificial further exposing the second sacrificial material; 
         FIG. 4B  depicts a cross sectional view of the structure of  FIG. 3B  after the recessing of a second portion of the first sacrificial further exposing the second sacrificial material; 
         FIG. 5A  depicts a cross sectional view of the structure of  FIG. 4A  after application of a third sacrificial material which may include an oxide; 
         FIG. 5B  depicts a cross sectional view of the structure of  FIG. 4B  after application of a third sacrificial material which may include an oxide; 
         FIG. 6A  depicts a cross sectional view of the structure of  FIG. 5A  after removal of the exposed hardmask material, and formation of an upper source drain junction; 
         FIG. 6B  depicts a cross sectional view of the structure of  FIG. 5B  after removal of the exposed hardmask material, and deposition of an upper source drain junction; 
         FIG. 7A  depicts a cross sectional view of the structure of  FIG. 6A  after application of a cap, which may be composed of a self aligned contact nitride above the upper source drain junction; 
         FIG. 7B  depicts a cross sectional view of the structure of  FIG. 6B  after application of a cap, which may be composed of a self aligned contact nitride above the upper source drain junction; 
         FIG. 8A  depicts a cross sectional view of the structure of  FIG. 7A  after removal of the third sacrificial material; 
         FIG. 8B  depicts a cross sectional view of the structure of  FIG. 7B  after removal of the third sacrificial material; 
         FIG. 9A  depicts a cross sectional view of the structure of  FIG. 8A  after adding a top spacer by means which may include deposition consisting of a material that may include SiN; 
         FIG. 9B  depicts a cross sectional view of the structure of  FIG. 8B  after adding a top spacer by means which may include deposition consisting of a material that may include SiN; 
         FIG. 10A  depicts a cross sectional view of the structure of  FIG. 9A  after removal of the second sacrificial material; 
         FIG. 10B  depicts a cross sectional view of the structure of  FIG. 9B  after removal of the second sacrificial material; 
         FIG. 11A  depicts a cross sectional view of the structure of  FIG. 10A  after removal of the first sacrificial material; 
         FIG. 11B  depicts a cross sectional view of the structure of  FIG. 10B  after removal of the first sacrificial material; 
         FIG. 12A  depicts a cross sectional view of the structure of  FIG. 11A  after application of a material layer through means such as chemical deposition wherein the material contains the property of having a high dielectric constant; 
         FIG. 12B  depicts a cross sectional view of the structure of  FIG. 11B  after application of a material layer through means such as chemical deposition wherein the material contains the property of having a high dielectric constant; 
         FIG. 13A  depicts a cross sectional view of the structure of  FIG. 12A  after deposition of a work function metal layer; 
         FIG. 13B  depicts a cross sectional view of the structure of  FIG. 12B  after deposition of a work function metal layer; 
         FIG. 14A  depicts a cross sectional view of the structure of  FIG. 13A  after deposition of a gate metal; 
         FIG. 14B  depicts a cross sectional view of the structure of  FIG. 13B  after deposition of a gate metal; 
         FIG. 15A  depicts a cross sectional view of the structure of  FIG. 14A  after removal of the gate metal except for the portions located under the top spacer and above the bottom spacer; 
         FIG. 15B  depicts a cross sectional view of the structure of  FIG. 14B  after removal of the gate metal except for the portions located under the top spacer and above the bottom spacer; 
         FIG. 16A  depicts a cross sectional view of the structure of  FIG. 15A  after the high K dielectric layer is removed except for the portions located under the top spacer and above the bottom spacer; 
         FIG. 16B  depicts a cross sectional view of the structure of  FIG. 15B  after the high K dielectric layer is removed except for the portions located under the top spacer and above the bottom spacer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Aspects of the present invention and certain features, advantages, and details thereof, are explained more fully below with reference to the non-limiting examples illustrated in the accompanying drawings. Descriptions of well-known materials, fabrication tools, processing techniques, etc., are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating aspects of the invention, are given by way of illustration only, and are not by way of limitation. Various substitutions, modifications, additions, and/or arrangements, within the spirit and/or scope of the underlying inventive concepts will be apparent to those skilled in the art from this disclosure. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. 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 “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include (and any form of include, such as “includes” and “including”)”, and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     As used herein, the terms “may” and “may be” indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances the modified term may sometimes not be appropriate, capable or suitable. For example, in some circumstances, an event or capacity can be expected, while in other circumstances the event or capacity cannot occur—this distinction is captured by the terms “may” and “may be.” 
     As used herein, “depositing” may include any now known or later developed techniques appropriate for the material to be deposited including but not limited to, for example: chemical vapor deposition (CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD), semi-atmosphere CVD (SACVD) and high density plasma CVD (HDPCVD), rapid thermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reaction processing CVD (LRPCVD), metal-organic CVD (MOCVD), sputtering deposition, ion beam deposition, electron beam deposition, laser assisted deposition, thermal oxidation, thermal nitridation, spin-on methods, physical vapor deposition (PVD), atomic layer deposition (ALD), chemical oxidation, molecular beam epitaxy (MBE), plating, evaporation. 
     Reference is made below to the drawings, which are not drawn to scale for ease of understanding, wherein the same reference numbers are used throughout different figures designate the same or similar components. 
     In accordance with one aspect of this invention, the following describes a method for manufacturing a fin structure, wherein this fin structure includes a fin with a sacrificial material above and/or adjacent to the fin. The fin structure also being above a substrate while being adjacent to a source or drain. The figures referenced are numbered and are labeled (A) and (B) to show the corresponding method for a negative channel field-effect transistor on the figures labeled with (A) and the corresponding method for a positive channel field-effect transistor on the figures labeled with (B). 
     Referring to  FIG. 1A , a n-type vertical FIN field-effect-transistor (n-VFINFET) is initially fabricated in a conventional manner. The structure includes hardmask material  12  which is situated above the vertical FIN channel, and a bottom spacer  16 , to a fin  14  and can include a bottom source/drain region  18  and a substrate  20 . There may also be an isolation region (not shown) between adjacent devices  10  if more than one device is fabricated. Referring to  FIG. 1B  a structure of a p-type VFINFET is fabricated in a conventional manner. The structure includes a hardmask material  12 , including but not limited to a nitride such as silicon nitride, which may be situated above and/or included adjacent a bottom spacer  16  (typically a nitride material) to a fin  14  and can include a bottom source/drain region  18  and an insulator region  20 . The n-VFINFET and p-VFINFET regions may be located on the same semiconductor wafer, for example in different, yet adjacent areas of a wafer separated by any distance that will not interfere with the operation of a VFET device. The fin  14  may include semiconductor materials, including but not limited to silicon, silicon germanium, and any III-V type materials. The bottom source/drain region  18  may include silicon, silicon germanium, or any other semiconductor material, and may be doped, often at high concentrations. The doping will vary for the device, but for an NFET it may be phosphorous doped and for a PFET it may be boron doped. Additionally, the source/drain region  18  in  FIG. 1A  may be different from the source/drain region  18  of  FIG. 1B , and both may be doped differently. The substrate region  20  can include silicon, silicon germanium, and any III-V type materials 
     Referring to  FIG. 2A , a first sacrificial material  34  and a second sacrificial material  36  are deposited onto the structure shown in  FIG. 1A . The first sacrificial material  34  may be in the form of a thin oxide deposed on and surrounding the hardmask material  12  above the bottom spacer  16 , the fin  14  and the bottom spacer  16  itself. The second sacrificial material  36  may be an amorphous silicon layer and may be deposited over and surrounding the first sacrificial material  34 . Referring to  FIG. 2B , the first sacrificial material  34  and second sacrificial material  36  are deposited onto the structure shown in  FIG. 1A . The first sacrificial material  34  may be a thin oxide deposed on and surrounding the hardmask material  12  above the bottom spacer  16 , the fin  14  and the bottom spacer  16  itself. The second sacrificial material  36  which may be an amorphous silicon layer may be deposited over and surrounding said first sacrificial material  34 . First and Second sacrificial material  34  and  36  may be deposited, for instance, by atomic layer deposition (ALD), physical vapor deposition (PVD), or any other chemical vapor depositions (CVD) capable of applying thin films consistently. 
     Referring to  FIG. 3A , the structure of  FIG. 2A  is planarized by, for example, a chemical mechanical polishing (CMP) technique. During planarization, the first sacrificial material  34  and the second sacrificial material  36  is removed from a first portion  42 , i.e., the top of device  10 , exposing the top section of the hardmask material  12 . Then, as shown in  FIG. 4A , a portion of the second sacrificial material  36 , adjacent to hardmask  12  and a top portion of fin  14 , is removed by, for example, etching using any wet or dry etch techniques to recess the second sacrificial material  36  below a top surface of device  10 . 
       FIG. 3B  illustrates the planarization of the structure of  FIG. 2B  by, for example, CMP. During planarization, as described in reference to  FIG. 3A , the first and second sacrificial material  34  and  36  is removed from a first portion  42 . Then as shown in  FIG. 4B , a portion of the second sacrificial material  36 , adjacent to hardmask  12  and a top portion of fin  14 , is removed by, for example, etching using any wet or dry etch techniques to recess the second sacrificial material  36  below a top surface of device  10 . 
     Referring to  FIG. 5A , a third sacrificial material  54 , which may include an oxide material, is deposited by ALD, CVD, or PVD in some embodiments, in the region shown in  FIG. 4A  which has been etched to recess the second sacrificial material  36 . Referring to  FIG. 5B , third sacrificial material  54  is similarly deposited on the positive channel. 
     Referring to  FIG. 6A , the remaining hardmask material  12  is removed by selective etching processes to expose the fin  14 . This can include any etch that is selective for a nitride material, and may include plasma etching. In its place, an upper source-drain  58  can be formed by selective epitaxy process, including but not limited to silicon and silicon germanium. The material and doping of upper source-drain  58  may be a different material for the n-VFINFET and p-VFINFET of  FIGS. 6A and 6B . For instance, the n-VFINFET ( FIG. 6A ) may include a heavily phosphorus doped silicon material, and the p-VFINFET ( FIG. 6B ) may be a heavily boron doped SiGe material. The patterning processes to form separate top S/D materials are not shown in detail here, because it is not the main focus of this disclosure. As shown in  FIG. 7A , a cap  62  is placed above the upper source-drain junction  58 . The cap  62  may be composed of a nitride, which will assist in subsequent self-aligned contact (SAC) etching to mask the upper source/drain junction  58  below. Similarly, referring to  FIG. 6B , the hardmask material  12  is removed on the p-VFINFET area by selective etching, to expose the fin  14 . In its place an upper source-drain junction  58  can be formed. As shown in  FIG. 7B , the nitride SAC cap  62  is also deposited above the upper source-drain junction  58  of the pFET region. 
     Referring to  FIG. 8A , what remains of the third sacrificial material  54  is removed, for instance, by buffered hydrofluoric acid (BHF) oxide etch, from the structure of  FIG. 7A . This may also remove the exposed portion of the first sacrificial material  34  below upper source/drain junction  58  and above the second sacrificial material  36 . Then, depicted in  FIG. 9A , a spacer  66  may be deposited adjacent the nitride cap  62  and around exposed source/drain region  58 . Spacer  66  can be of the same material as nitride cap  62 , and thus is shown as a single feature. Deposition can include any of CVD, PVD, and ALD. The Spacer  66  may then be etched back, if necessary, so as not to cover the entirety of the second sacrificial material  36 . The spacer  66  is deposited over and surrounding the upper source-drain junction  58 . Similarly, referring to  FIG. 8B , the third sacrificial material  54  may be removed from the pFET regions as well as described above. Thereafter, as shown in  FIG. 9B , spacer  66  is deposited adjacent the pFET nitride cap  62  and upper source-drain region  58 , creating a single spacer  66  merging with the nitride cap  62 . 
     Referring to  FIGS. 10A and 10B , the second sacrificial material  36  may then be removed by wet etching, such as hot ammonia or tetra methyl ammonia hydroxide (TMAH). Then, as shown in  FIGS. 11A and 11B , the first sacrificial material  34  may then be removed by, for example, selective oxide etching or any other suitable techniques such as wet dilute hydrofluoric (DHF) etching, or dry chemical oxide removal (COR) process. 
     Referring to  FIGS. 12A and 12B , a high K dielectric material is conformally deposited over the spacers  66 , the fin  14  and the bottom spacer  16  on both the n-VFINFET and p-VFINFET regions. The high K dielectric can include HfO 2 , ZrO 2 , Al 2 O 3 , TiO 2 , Ta 2 O 5 , lanthanide oxides and mixtures thereof, silicates and materials such as YSZ (yttria-stabilized zirconia), BST, BT, ST, and SBT. Then, as shown in  FIGS. 13A and 13B , a work function metal (WFM) layer  74  is conformally deposited over the high K layer and remaining structure. The WFM layer  74  can include a single-element metal, for instance cobalt, titanium, aluminum, or other metals alloys that will allow proper workfunction to give desired threshold voltage (Vt), such as TiN, TaN, TiC, TiAl, etc, and may be deposited, for instance, using ALD. Additionally, the WFM layer  74  for n-VFINFET and p-VFINFET may be different, and can be formed by, e.g, depositing first WFM for both p-VFINFET and n-VFINFET first, followed by a lithography process to block the p-VFINVET region, and remove the first WFM layer from the n-VFINFET, followed by resist strip, and followed by second WFM deposition over both n-VFINFET and p-VFINFET. Thus, the WFM layer  74  for n and p-VFINFET could be different materials which also may have different thickness. Then, as depicted in  FIGS. 14A and 14B , a gate metal  78 , for example tungsten or any other suitable metal typically used in a replacement metal gate (RMG) process, may be deposited on and surrounding the WFM layer  74  using ALD or other deposition techniques. 
     Referring to  FIGS. 15A and 15B , the gate metal  78  and WFM layer  74  may be selectively removed from the sides of the structure, but remaining between the upper source/drain junction  58  and adjacent the fin  14  and in the recess between spacer  66 . In some embodiments, the selective removal includes RIE, wherein the high K dielectric  70  layer, in some embodiments hafnium oxide (HfO 2 ), acts like a mask and protects the rest of the structure, essentially a gate that has been formed self-aligned to the top S/D region to the VFINFET device, from erosion. Finally, as shown in  FIGS. 16A and 16B , the exposed portions of the high K dielectric layer  70  are then removed, leaving only a lining in the recesses adjacent the fins  14 , forming a self-aligned RMG gate in device  10  for both the n-VINFET side ( FIG. 16A ) and the p-VFINFET side ( FIG. 16B ). 
     Following these steps, device  10  may be further processed following a known set of steps for conventional VFINFET device flow to form a connecting wire to bottom S/D, gate, and top S/D, followed by a back-end-of build. 
     Thus, as described above, methods according to certain embodiments allow for an RMG gate that has been self-aligned to a vertical fin using the above patterning techniques. The whole high-k/metal gate formation is after bottom and top S/D formation, thus, the high-k and WFM won&#39;t see any thermal impact due to the thermal budget during S/D formation. Also, due to the unique shape of the structure, different metal gate  78  materials can be used to vary the threshold voltage (Vt) without concern for how to recess the different metals in order to define the gate length, since the unique shape of the high K dielectric layer  70  allows for self-patterning. Additionally, in recessing the gate, this also allows for protection from any plasma damage to the gate during the recessing.