Patent Publication Number: US-11049773-B2

Title: Art trench spacers to enable fin release for non-lattice matched channels

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/US2016/055028, filed Sep. 30, 2016, entitled “ART TRENCH SPACERS TO ENABLE FIN RELEASE FOR NON-LATTICE MATCHED CHANNELS,” which designates the United States of America, the entire disclosure of which is hereby incorporated by reference in its entirety and for all purposes. 
     BACKGROUND 
     Field 
     Integrated circuit devices. 
     Description of Related Art 
     Power consumption is a major consideration in circuit development. When transistors are in their off state, the current draw through unintentional leakage paths of the transistors should preferably be minimized. A major leakage path in planar and FinFET transistors is in the sub-channel region (sometimes referred to as a “sub-fin” region in FinFETs or in general, “sub-structure”). To limit this path, designers of conventional transistors attempt to employ sharp positive/negative (p/n) junctions between the source and channel/sub-channel region and between the drain and channel/sub-channel region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cross-sectional side view of an embodiment of a non-planar field effect transistor device. 
         FIG. 2  shows a cross-sectional side view of the structure of  FIG. 1  through line  2 - 2 ′. 
         FIG. 3  shows a perspective side view of a substrate having a sacrificial fin formed therein. 
         FIG. 4  shows the structure of  FIG. 3  following a deposition of a trench dielectric layer on the substrate. 
         FIG. 5  shows the structure of  FIG. 4  following a removal of a portion of the sacrificial fin to form a trench and the lining of the trench with a spacer material. 
         FIG. 6  shows the structure of  FIG. 5  through line  6 - 6 ′. 
         FIG. 7  shows the structure of  FIG. 5  following the removal of a remaining portion of the sacrificial fin to form a trench of a controlled size and shape. 
         FIG. 8  shows the structure of  FIG. 7  through line  8 - 8 ′. 
         FIG. 9  shows the structure of  FIG. 7  following the introduction of a buffer material in the trench. 
         FIG. 10  shows the structure of  FIG. 9  through line  10 - 10 ′. 
         FIG. 11  shows the structure of  FIG. 9  following a removal of a portion of the buffer material in the trench to a level below the spacer layer. 
         FIG. 12  shows the structure of  FIG. 11  through line  12 - 12 ′. 
         FIG. 13  shows the structure of  FIG. 11  following the introduction of an intrinsic material into trench. 
         FIG. 14  shows the structure of  FIG. 13  through line  14 - 14 ′. 
         FIG. 15  shows the structure of  FIG. 13  following a recession of the dielectric layer to define a transistor body or fin. 
         FIG. 16  shows the structure of  FIG. 15  through line  16 - 16 ′. 
         FIG. 17  shows the structure of  FIG. 15  following the formation of a sacrificial or dummy gate stack on the fin. 
         FIG. 18  shows the structure of  FIG. 17  through line  18 - 18 ′. 
         FIG. 19  shows the structure of  FIG. 17  following the definition of junction regions and a deposition of a dielectric material on the structure. 
         FIG. 20  shows the structure of  FIG. 19  through line  20 - 20 ′. 
         FIG. 21  shows the structure of  FIG. 20  through line  21 - 21 ′ following a removal of the sacrificial or dummy gate stack (gate dielectric  260  and dummy gate  265 ) and exposure of a channel region of intrinsic layer  240 . 
         FIG. 22  shows the structure of  FIG. 21  undergoing an etch to thin a width dimension of the fin (a width of intrinsic layer) in a channel region of the device and release the fin in the channel region from material in the trench. 
         FIG. 23  shows the structure of  FIG. 22  following the formation of a gate stack on the channel of the structure. 
         FIG. 24  shows a flow chart of the process described with reference to  FIGS. 3-23 . 
         FIG. 25  shows a cross-sectional side view of a portion of an integrated circuit substrate following the formation of a trench in a dielectric layer and a spacer layer in the trench according to another embodiment. 
         FIG. 26  shows the structure of  FIG. 25  following the formation of an intrinsic layer of a channel material in the trench. 
         FIG. 27  shows the structure of  FIG. 26  following a recession of the dielectric layer to expose a portion of the intrinsic layer as a transistor body or fin. 
         FIG. 28  shows the structure of  FIG. 27  following a removal of a sacrificial or dummy gate stack (gate dielectric and dummy gate) and exposure of a channel region of the intrinsic layer and a removal of the spacer layer. 
         FIG. 29  shows the structure of  FIG. 28  following an etch to thin a width dimension of the fin (intrinsic layer) in a channel region of the device and release the fin in the channel region from material (intrinsic layer) in the trench. 
         FIG. 30  shows the structure of  FIG. 29  following the formation of a gate stack on the channel of the structure. 
         FIG. 31  is an interposer implementing one or more embodiments. 
         FIG. 32  illustrates an embodiment of a computing device. 
     
    
    
     DETAILED DESCRIPTION 
     A technique to integrate low leakage non-lattice matched materials on an integrated circuit substrate is described. The technique enables removal of material below a transistor gate without a need for multiple material depositions selected for etch selectivities. An apparatus is also described that includes a transistor device including a channel disposed on a substrate between a source and a drain and a gate electrode disposed on the channel. The channel includes a channel material that is separated from a body of the same material on the substrate. 
       FIG. 1  shows a cross-sectional side view of an embodiment of a field effect transistor (FET) device such as a metal oxide semiconductor field effect transistor (MOSFET) device, a tunneling field effect transistor (TFET) device or other FET device.  FIG. 2  shows the structure of  FIG. 1  through line  2 - 2 ′. In this embodiment, a non-planar transistor is described that includes a conducting channel above a level of a dielectric layer as part of a transistor body or fin. A gate electrode is disposed on adjacent sides of the transistor body or fin allowing multiple gates to operate on a single transistor. It is appreciated that the techniques described are applicable to other transistors including gate all-around devices. 
     Referring to  FIG. 1  and  FIG. 2 , device  100  includes substrate  110  that is, for example, a single crystal silicon substrate such as a bulk substrate or a silicon on insulator substrate. Disposed on substrate  110 , in this embodiment, is buffer or sub-fin layer  120 . Buffer layer  120  contains, for example, a material that has a larger lattice than a material of the substrate (e.g., silicon substrate  110 ). A suitable material for buffer layer includes but is not limited to indium phosphate (InP), germanium (Ge), silicon germanium (SiGe), gallium arsenide (GaAs), gallium phosphide (GaP), gallium arsenide antimony (GaAsSb), indium aluminum arsenide (InAlAs), indium aluminum antimony (InAlSb), gallium antimony (GaSb), or other group III-V compound semiconductor. To reduce a threading dislocation density, a material in buffer layer  120  may be graded with, for example, a material of the underlying substrate (e.g., silicon) to gradually increase a material composition of buffer layer in an epitaxially grown film such that closer to substrate  110 , a material concentration of buffer layer is less and increases away from the substrate. In another embodiment, two or more different materials may be present in buffer layer  120  such as a first material at the base of the buffer layer and a second material on the first material. 
     In the embodiment in  FIGS. 1-2 , disposed on buffer layer  120  is intrinsic layer  140 . In one embodiment, intrinsic layer  140  is a channel material for the particular transistor device. In one embodiment, intrinsic layer  140  includes silicon, germanium, silicon germanium or a group III-V compound material. In one embodiment, the group III-V compound material includes indium (In) (i.e., has a concentration of indium). An example of a group III-V compound material including indium, particularly for an n-type transistor device is InGaAs. Germanium and silicon germanium are examples of material for intrinsic layer  140  for a p-type transistor device. 
     As illustrated in  FIG. 1 , disposed in intrinsic layer  140  is diffusion or junction region  150  and diffusion or junction region  155 . In one embodiment, diffusion region  150  is a source of a MOSFET (e.g., an n +  source) and diffusion region  155  is a drain of the MOSFET (e.g., n +  drain). Disposed between diffusion regions  150  and  155  is channel  1400  of a material of intrinsic layer  140  (e.g., InGaAs) having a length dimension, L of, for example, 10-30 nm. 
     As illustrated in  FIGS. 1 and 2 , below the gate stack of the transistor device (below channel  1400 ) is a void. Void  142 , in this embodiment, separates a portion of intrinsic layer  140 . A portion of intrinsic layer  140  is operable to function as a channel of the transistor device. Channel  1400  of intrinsic layer  140  is separated from another portion of intrinsic layer  140  by void  142 . In one aspect, void  142  minimizes device leakage below channel  1400 . 
     As illustrated in  FIG. 2 , in one embodiment, intrinsic layer  140  below channel  1400  is a body having representative width dimension, W 1 , defined by opposing sidewalls on the order of between 10 nm and 20 nm. Channel  1400  of intrinsic layer  140  has a width dimension, W 2 , that is less than W 1 . In one embodiment, a representative width, W 2 , of channel  1400  is on the order of 5 nm to 10 nm. The reduced width, in one aspect, improves carrier control in the channel for a multi-gate device such as described because the reduced width means a distance between opposing sidewalls of a gate electrode that is disposed on channel  1400  are closer to one another. A representative height dimension, h, of channel  1400  is on the order of 10 nm to 100 nm. 
       FIG. 2  is a cross-section through a channel region of the transistor of  FIG. 1  and shows that the body of intrinsic layer  140  in this region has a generally rectangular profile that, in one embodiment, has a superior surface that appears substantially parallel to a surface of substrate  110 . It is appreciated that a profile of the body of intrinsic layer will depend in part on the processing techniques (e.g., polish, etching, etc.) used to form the body. Accordingly, a body targeted to have a rectangular profile may have a profile approximating a rectangular profile (e.g., a profile with rounded edges, a trapezoidal profile, etc.). The rectangular profile is prescribed for explanation purposes and is intended as but one example of a profile employed in a transistor device. Alternative profiles are also contemplated. 
     Overlying channel region  1400  is gate dielectric layer  170  of, for example, a silicon dioxide or a dielectric material having a dielectric constant greater than silicon dioxide (a high-k material) or a combination of silicon dioxide and a high-k and a thickness on the order of a few nanometers. As illustrated in  FIG. 2 , gate dielectric layer  170  is disposed on sidewalls of a length dimension, L, of the body of channel  1400  exposed above dielectric layer  125  and on a superior surface as viewed. In one embodiment, gate electric layer  170  also conforms to an inferior surface of a body of channel  1400 . Disposed on gate dielectric  170  is gate electrode  175  of, for example, an electrically conductive material such as a metal material (e.g., tantalum), a metal nitride, or a silicide. In one embodiment, as shown in  FIG. 2 , gate electrode  175  wraps around (on all four sides) of channel  1400 . For representative purposes, in one embodiment, gate electrode  175  has a total thickness on the order of 5-50 nm and dielectric layer  170  has a thickness of 1-15 nm. 
       FIGS. 3-23  describe a process of forming an FET device such as is illustrated in  FIGS. 1-2 .  FIG. 24  presents a flow chart of the process. A formation process for an N-type FET is described. It should be appreciated that the techniques of forming a transistor presented herein are not limited to any particular device conductivity. Referring to  FIG. 3  and with reference to the flow chart of  FIG. 24 , the process begins by defining sacrificial fin structures in a substrate material (block  310 ,  FIG. 24 ).  FIG. 3  shows a perspective side view of substrate  210  that may be any material that may serve as a foundation of which a multi-gate FET may be constructed. Representatively, substrate  210  is a portion of a larger substrate such as wafer. In one embodiment, substrate  210  is a semiconductor material such as single crystal silicon. Substrate  210  may be a bulk substrate or, in another embodiment, a silicon on insulator (SOI) structure.  FIG. 3  shows substrate  210  following a patterning of the substrate to define sacrificial fin  2100 . The sacrificial fin may one of many sacrificial fins formed across a wafer. Sacrificial fin  2100  may be formed by a mask and etch process wherein a mask (e.g., a hard mask) is introduced on a surface (superior surface) of substrate  210  to protect areas of the substrate where the sacrificial fins will be defined and to provide openings in non-fin areas. Once the mask is patterned, substrate  210  may be etched to remove material in unprotected areas. A substrate of silicon may be etched with a wet or dry etch. Representatively, a suitable etchant is HF based chemistry. Sacrificial fin  2100  is etched, in one embodiment, to have a height, H, on the order of 100-400 nm. 
       FIG. 4  shows the structure of  FIG. 3  following a removal of the mask on the sacrificial fin and following the deposition of a trench dielectric layer on the substrate (block  320 ,  FIG. 24 ). In one embodiment, dielectric layer  225  is silicon dioxide or a low-k dielectric material. Following deposition of dielectric layer  225 , the surface (a superior surface as viewed) of the structure is polished to the level of the top of sacrificial fin  2100  so that the fin is exposed. 
       FIG. 5  shows the structure of  FIG. 4  following the removal of a portion of sacrificial fin  2100  to form a portion of a trench of a controlled size and shape (block  330 ,  FIG. 24 ).  FIG. 6  shows the structure of  FIG. 5  through line  6 - 6 ′. Referring to  FIGS. 5 and 6 , the sacrificial fin material may be removed by a mask and etch process wherein a mask is patterned on a surface of dielectric layer  225  leaving the sacrificial fin exposed followed by an etch process. A sacrificial fin of a silicon material may be etched by a dry or wet etch or a combination of the two. Suitable etchants for etching sacrificial fins of a silicon material include potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH). The removal of a portion of the sacrificial fin forms trench  218 . In one embodiment, approximately one-half of sacrificial fin  2100  is removed (one-half the height of sacrificial fin  2100 ). 
       FIGS. 5 and 6  also show the structure following a formation of a spacer layer or spacers along sidewalls of dielectric layer  225  in trench  218  (block  335 ,  FIG. 24 ). In one embodiment, for a generally rectangular- or other quadrilateral-shaped trench, spacer layer  215  is formed on opposing sidewalls of dielectric layer  225  along a length, l, of the trench. In one embodiment, spacer layer is formed on sidewalls of dielectric layer  225  from a superior surface of sacrificial fin  2100  to a superior surface of dielectric layer  225  as viewed. Spacer layer  215  is deposited to a collective thickness to narrow a portion of trench  218  (minimize a width dimension) while leaving access or an opening to sacrificial fin  2100  below so that the remaining portion of sacrificial fin  2100  may subsequently be removed and replaced with a material or materials. For a trench having a width, W T , on the order of 10 nm to 20 nm, spacer layer  215  has a width, W S , on each of opposing sides of dielectric layer  225  on the order of 2 nm to 6 nm, with thickness of at least 5 nm or greater being limited to trenches having a width, W T , greater than 10 nm. In one embodiment, a material for spacer layer  215  is a material that can be conformally deposited on sidewalls of dielectric layer  225  and can be selectively removed relative to a material of dielectric layer  225  and allow selective removal of sacrificial fin  2100  and other materials that might be added to trench  218  (e.g., buffer or sub-fin material). Where dielectric layer  225  is silicon dioxide, a material for spacer layer  215  may also be silicon dioxide (e.g., a doped silicon dioxide) or other material such as aluminum oxide (Al 2 O 3 ), silicon nitride (SiN), silicon carbide (SiC), titanium oxide nitride (TiO x N), silicon oxide nitride (SiON), hafnium oxide (HfO 2 ) or zirconium oxide (ZrO 2 ). 
       FIG. 7  shows the structure of  FIG. 5  following a removal of the remaining portion of sacrificial fin  2100  (block  340 ,  FIG. 24 ).  FIG. 8  shows the structure of  FIG. 7  through line  8 - 8 ′. In one embodiment, the remaining portion of sacrificial fin  2100  is removed by a mask and etch process. An etchant is selected that selectively etches sacrificial fin material relative to spacer layer  215  so that spacer layer  215  predominantly remains. The removal of the remaining portion of sacrificial fin  2100  increases a depth of trench  218 . In one embodiment, the etching of sacrificial fin  2100  may be performed to provide a {111} faceting at the bottom of trench  218  to facilitate a growth of a group III-V compound material in the trench. Such faceting may be achieved using TMAH-like or any equivalent chemistry. Alternative geometries are also contemplated. The trench confined growth of materials offer an advantage of aspect ratio trapping (ART) whereby a crystalline quality of the epitaxial layer is enhanced through trapping of threading dislocations, stacking faults, twins, etc., at sidewalls of trench  218  where defects terminate such that overlying layers may be increasingly defect-free. In one embodiment, to achieve ART, trench  218  has dimensions such that its height, h t , is on the order of twice its width, w t . 
       FIG. 7  and  FIG. 8  also show the structure following a reduction of a height of spacer layer  215  selective of dielectric layer  225  (block  345 ,  FIG. 24 ). In one embodiment, spacer layer  215  is recessed from a superior surface of dielectric layer  225  as viewed (a top of trench  218 ) a distance, d, to a position below the superior surface. In one embodiment, a distance, d, from a superior surface of dielectric layer  225  to a superior surface of spacer layer  215  on each of opposing sidewalls of dielectric layer  225  is a height of a desired or targeted projection of a transistor body or fin as an intrinsic material (channel material) that will be formed in the region of trench  218  above spacer layer  215 . In this embodiment, the region of trench  218  defined by a distance, d, provides a mold to control a shape of a channel material (e.g., as a transistor body or fin having a generally rectangular profile across its length). In another embodiment, spacer layer  215  may not be recessed and a formation of a channel material may be controlled through the addition and patterning of additional dielectric material on dielectric layer  225  or by controlling growth conditions of a channel material (e.g., controlling growth conditions so that lateral growth of channel material is constrained in favor of vertical growth). In the embodiment illustrated in  FIG. 7  and  FIG. 8 , in one embodiment, a height of dielectric layer  225  may optimally be reduced prior to recessing spacer layer  215 . Such reduction may be motivated by a desire to reduce an ultimate device height of a transistor. Representatively, a height of dielectric layer  225  of silicon dioxide may be reduced by a chemical mechanical polish (CMP). 
       FIG. 9  shows the structure of  FIG. 7  following the introduction of a buffer or sub-fin material in trench  218  (block  350 ,  FIG. 24 ).  FIG. 10  shows the structure of  FIG. 9  through line  10 - 10 ′. In one embodiment, buffer material  220  is a group III-V compound material such as, but not limited to, gallium arsenide (GaAs), indium phosphide (InP); germanium (Ge), gallium phosphide (GaP), gallium arsenide antimony (GaAsSb), indium aluminum arsenide (InAlAs) and gallium antimony (GaSb). In one embodiment, where an intrinsic or channel material subsequently introduced on buffer material  220  is InGaAs, buffer material  220  is GaAs as GaAs has relatively good etch selectively relative to InGaAs. Buffer material  220  may be introduced by an epitaxial growth process. In another embodiment, the trench may be filled with a first buffer of one of the noted materials followed by a second buffer of another of the noted materials.  FIG. 9  shows buffer material  220  completely filling trench  218  on both sides of spacer layer  215 .  FIG. 9  and  FIG. 10  show structure  200  following a planarization of a superior surface of the structure by, for example, a CMP to planarize buffer material  220  with a superior surface of dielectric layer  225 . 
       FIG. 11  shows the structure of  FIG. 9  following a removal of a portion of buffer material  220  in trench  218  (block  355 ,  FIG. 24 ).  FIG. 12  shows the structure of  FIG. 11  through line  12 - 12 ′. Buffer material  220 , in one embodiment, is recessed in trench  218  to a level below spacer layer  215  so spacer layer  215  is completely exposed in trench  218  both a superior surface and an underside surface (buffer material  220  does not contact spacer layer  215  after the recess of the buffer material). A wet or dry etch process may be utilized. A suitable etchant for etching a buffer material of GaAs is, for example, a two-step etchant process where the buffer material is first oxidized and, once oxidized, then removed. Suitable etchants include citric acid/peroxide, hydrochloric acid/peroxide, ozone and citric acid or ozone and hydrochloric acid. 
       FIG. 13  shows the structure of  FIG. 12  following the introduction of an intrinsic material into trench  218  (block  360 ,  FIG. 24 ).  FIG. 14  shows the structure of  FIG. 13  through line  14 - 14 ′. Intrinsic layer  240  is formed on buffer material  220 . In this manner, intrinsic layer  240  is disposed in trench  218  on both sides of spacer layer  215 . By recessing buffer material  220  to a level below spacer layer  215 , intrinsic layer  240  has space to grow in the ART trench to terminate any defects. The intrinsic layer may be epitaxially grown. In one embodiment, intrinsic layer  240  is an indium-containing group III-V compound material that may be lightly doped n-type or p-type to the extent of, for example, 1E16 atoms per cubic centimeters. In one embodiment, intrinsic layer  240  is InGaAs. Intrinsic layer  240  has a representative height above a superior surface of spacer layer  215  on the order of 40 nm to 100 nm.  FIGS. 13 and 14  show the structure following a polish of intrinsic layer  240  to a plane defined by dielectric layer  225 . In another embodiment, intrinsic layer  240  may be grown or otherwise formed to extent beyond a superior surface of dielectric layer  225 . 
       FIG. 15  shows the structure of  FIG. 13  following a recession of dielectric layer  225  to define a transistor body or fin (block  365 ,  FIG. 24 ).  FIG. 16  shows the structure of  FIG. 15  through line  16 - 16 ′. In one embodiment, dielectric layer  225  is recessed depth defined by a height of spacer layer  215 . Dielectric layer  225  may be recessed by a mask and etch process whereby a superior surface of intrinsic layer  240  is protected followed by an etch of dielectric layer  225 . 
       FIG. 17  shows the structure of  FIG. 15  following the formation of a sacrificial or dummy gate stack on the fin portion of intrinsic layer  240  extending above dielectric layer  225  (block  370 ,  FIG. 24 ).  FIG. 18  shows the structure of  FIG. 17  through line  18 - 18 ′. In one embodiment, a gate stack includes gate dielectric layer  260  of, for example, silicon dioxide or a high-k dielectric material. Disposed on the gate dielectric layer, in one embodiment, is dummy gate  265  of, for example, polysilicon. In one embodiment, to form the gate stack, gate dielectric layer  260  and dummy gate  265  may each be introduced as a blanket deposition one over the other then patterned. Alternatively, a mask material may be introduced over the structure and patterned to have an opening for the dummy gate stack. The gate stack is then introduced in the opening in a conventional gate-last process. A spacer dielectric layer defining spacers  285  may be placed on opposite sides of the sacrificial gate by, for example, depositing a dielectric material such as silicon dioxide or a low-k dielectric material on structure  200  and patterning the dielectric material into spacers. 
       FIG. 19  shows the structure of  FIG. 17  following the definition of junction regions (block  375 ,  FIG. 24 ).  FIG. 20  shows the structure of  FIG. 19  through line  20 - 20 ′.  FIGS. 19 and 20  show structure  200  including junction region or source  250  and junction region or drain  255 . Representatively, the junction regions (source and drain) are defined, in one embodiment, of a material of intrinsic layer  240  (InGaAs) in designated source and drain regions on the opposite sides of the sacrificial or dummy gate  265  (block  380 ,  FIG. 24 ). In another embodiment, the junction regions may be formed by doping of such fin portions. In a further embodiment, the junction regions may be formed by removing portions of the fin of intrinsic layer  240  in an etch undercut (EUC) process in regions corresponding to a source and a drain with the dummy gate stack and optional spacers  285  protecting a channel region of the fin. Following removal of fin material in source and drain regions to leave voids, source  250  and drain  255  are formed in respective voids. In one embodiment, a suitable material for an n-type transistor device is heavily n-type doped InGaAs or InAs or a combination of the two that may be epitaxially grown. 
     Following formation of junction regions (source  250 /drain  255 ), a dielectric material may be introduced on the structure (on structure  200  (on a surface including the junction region and sacrificial gate  265 )). In one embodiment, dielectric material  245  (shown in dashed lines) is an interlayer dielectric material (ILDO) such as silicon dioxide or a low-k material or a combination of materials (e.g., multiple low-k material of silicon dioxide and one or more low-k materials). 
       FIG. 21  shows the structure of  FIG. 20  through line  21 - 21 ′ following a removal of the sacrificial or dummy gate stack (gate dielectric  260  and dummy gate  265 ) and exposure of a channel region of intrinsic layer  240 . The sacrificial gate stack may be removed by a mask and etch process. Representatively, a mask is formed on dielectric layer  245  having an open area over the dummy gate stack. An etch is then performed to remove the sacrificial gate stack leaving intrinsic layer  240  and a portion of a surface of dielectric layer  225  exposed.  FIG. 21  also shows the structure following a recession of exposed dielectric layer  225  to expose spacer layer  215  and the removal of spacer layer  215  (block  385 ,  FIG. 24 ). Dielectric layer  225  may be recessed and spacer layer  215  removed by a mask and etch process using, for example, the same mask that was patterned for the dummy gate stack removal. In one embodiment, the etch or etches are selective for dielectric layer  225  and spacer layer  215  relative to intrinsic layer  240  (the etch or etches removes dielectric layer  225  and spacer layer  215  without removing intrinsic layer  240 ). 
       FIG. 22  shows the structure of  FIG. 21  undergoing an etch to thin a width dimension of the fin (intrinsic layer  240 ) in a channel region of the device and release the fin in the channel region from material (intrinsic layer  240 ) in the trench (block  390 ,  FIG. 24 ). The thinning and releasing of the fin may be done with the same etchant  247 . A suitable etchant for InGaAs is, for example, a two-step etchant process where the material is first oxidized and then the oxidized material removed. Suitable two-step etchants include citric acid and peroxide; hydrochloric acid and peroxide; ozone and citric acid; and ozone and hydrochloric acid.  FIG. 22  shows the fin of intrinsic layer  240  having a width, W 2 , that is less than a width, W 1 , of the fin in  FIG. 21 . The fin is released at the portion of intrinsic layer  240  that was formed between spacer layer  215  (an intentionally narrow portion). Releasing the fin from material in the trench creates void  242  between a transistor channel and material below the channel. By creating void  242 , a sub-channel leakage path is eliminated. 
       FIG. 23  shows the structure of  FIG. 22  following the formation of a gate stack on the channel of the structure (block  395 ,  FIG. 24 ). A gate stack includes gate dielectric  270  and gate electrode  275 . Suitable gate dielectric  270  is silicon dioxide or a high-k dielectric material or a combination of silicon dioxide and a high-k dielectric material. The presence of void  242  under the channel allows gate dielectric to optionally be formed on each side of the rectangular or otherwise quadrilateral-shaped or similar channel.  FIG. 23  shows gate dielectric  270  on each side of the channel (on each of four sides). Gate electrode  275  is disposed on gate dielectric  270 . Representative materials for a metal gate electrode include tungsten, tantalum, titanium or a nitride, a metal alloy, silicide or another material. The presence of void  242  under the channel also optionally allows gate electrode  275  to be formed on each side of the rectangular or otherwise quadrilateral-shaped or similar channel. 
     In the above embodiment, a channel material was formed on a buffer or sub-fin material in a trench. In another embodiment, a channel material may be formed in the trench without the need for the buffer or sub-fin material. As noted above, a trench having suitable dimensions (e.g., a height dimension twice a width dimensions) provides confined growth conditions including ART of defects at sidewalls of a trench and thereby improvement of a crystalline quality of a material at the top of the trench. Also, because the technique for releasing a channel material from a material in the trench does not rely on etch selectivities of different materials, different materials in a trench are not necessary.  FIGS. 25-30  describe another embodiment of a process of forming an FET device. The process is similar to the process described with respect to  FIGS. 3-24  except a buffer or sub-fin material is omitted and only a channel material is used in a trench fill process. 
       FIG. 25  shows a cross-sectional side view of a portion of an integrated circuit substrate following the formation of a trench in a dielectric layer and a spacer layer in the trench. The method of forming the structure, in one embodiment, is similar to that described with reference to  FIGS. 3-8 .  FIG. 25  shows substrate  410  of, for example, a silicon substrate; dielectric layer  425  formed on substrate  410 ; and trench  418  formed in dielectric layer  425 . Spacer layer  415  is formed on opposing sidewalls of trench  418  and is recessed below a superior surface of the trench. It is appreciated that the recessed spacer layer is one embodiment and, in another embodiment, the spacer layer may extend to a superior surface of trench  418 . 
       FIG. 26  shows the structure of  FIG. 25  following the formation of intrinsic layer  440  of a channel material such as InGaAs in trench  418 . As illustrated, intrinsic layer  440  is formed in the entire trench, from a base to a superior surface and is thus on both sides of spacer layer  415 . In one embodiment, intrinsic layer  440  of InGaAs may be epitaxially grown. 
       FIG. 27  shows the structure of  FIG. 26  following a recession of dielectric layer  425  to expose a portion of intrinsic layer  440  as a transistor body or fin. In this embodiment, dielectric layer  425  is recessed to a level of spacer layer  415 . Following the definition of a fin of intrinsic layer  440 , a transistor formation process may follow the process of  FIGS. 17-20  including forming of a sacrificial gate structure and a source and a drain in portions of the fin. 
       FIG. 28  shows the structure of  FIG. 27  following a removal of the sacrificial or dummy gate stack (gate dielectric and dummy gate) and exposure of a channel region of intrinsic layer  440  and a removal of spacer layer  415 . The sacrificial gate stack and spacer layer  415  may be removed by a mask and etch process. In one embodiment, the process is similar to that described with reference to  FIG. 21 . 
       FIG. 29  shows the structure of  FIG. 28  following an etch to thin a width dimension of the fin (intrinsic layer  440 ) in a channel region of the device and release the fin in the channel region from material (intrinsic layer  440 ) in the trench. The thinning and releasing of the fin may be done with the same etchant. In one embodiment, the process is similar to that described with reference to  FIG. 22 . The fin is released at the portion of intrinsic layer  440  that was formed between spacer layer  415  (an intentionally narrow portion). Releasing the fin from material in the trench creates void  442  between a transistor channel and material below the channel. 
       FIG. 30  shows the structure of  FIG. 29  following the formation of a gate stack on the channel of the structure. A gate stack includes gate dielectric  470  and gate electrode  475 . Suitable gate dielectric  470  is silicon dioxide or a high-k dielectric material or a combination of silicon dioxide and a high-k dielectric material. The presence of void  442  under the channel allows gate dielectric to optionally be formed on each side of the rectangular or otherwise quadrilateral-shaped or similar channel.  FIG. 30  shows gate dielectric  470  on each side of the channel (on each of four sides). Gate electrode  475  is disposed on gate dielectric  470 . Representative materials for a metal gate electrode include tungsten, tantalum, titanium or a nitride, a metal alloy, silicide or another material. The presence of void  442  under the channel also optionally allows gate electrode  475  to be formed on each side of the rectangular or otherwise quadrilateral-shaped or similar channel. 
       FIG. 31  illustrates interposer  500  that includes one or more embodiments. Interposer  500  is an intervening substrate used to bridge first substrate  502  to second substrate  504 . First substrate  502  may be, for instance, an integrated circuit die including multigate transistor devices of the type described above. Second substrate  504  may be, for instance, a memory module, a computer motherboard, or another integrated circuit die. Generally, the purpose of interposer  500  is to spread a connection to a wider pitch or to reroute a connection to a different connection. For example, interposer  500  may connect an integrated circuit die to ball grid array (BGA)  506  that can subsequently be coupled to second substrate  504 . In some embodiments, first and second substrates  502 / 504  are attached to opposing sides of interposer  500 . In other embodiments, first and second substrates  502 / 504  are attached to the same side of interposer  500 . In further embodiments, three or more substrates are interconnected by way of interposer  500 . 
     Interposer  500  may be formed of an epoxy resin, a fiberglass-reinforced epoxy resin, a ceramic material, or a polymer material such as polyimide. In further implementations, the interposer may be formed of alternate rigid or flexible materials that may include the same materials described above for use in a semiconductor substrate, such as silicon, germanium, and other group III-V and group IV materials. 
     The interposer may include metal interconnects  508  and vias  510 , including but not limited to through-silicon vias (TSVs)  512 . Interposer  500  may further include embedded devices  514 , including both passive and active devices. Such devices include, but are not limited to, capacitors, decoupling capacitors, resistors, inductors, fuses, diodes, transformers, sensors, and electrostatic discharge (ESD) devices. More complex devices such as radio-frequency (RF) devices, power amplifiers, power management devices, antennas, arrays, sensors, and MEMS devices may also be formed on interposer  500 . 
       FIG. 32  illustrates computing device  600  in accordance with one embodiment. Computing device  600  may include a number of components. In one embodiment, these components are attached to one or more motherboards. In an alternate embodiment, these components are fabricated onto a single system-on-a-chip (SoC) die rather than a motherboard. The components in computing device  600  include, but are not limited to, integrated circuit die  602  and at least one communication chip  608 . In some implementations communication chip  608  is fabricated as part of integrated circuit die  602 . Integrated circuit die  602  may include CPU  604  as well as on-die memory  606 , often used as cache memory, that can be provided by technologies such as embedded DRAM (eDRAM) or spin-transfer torque memory (STTM or STTM-RAM). 
     Computing device  600  may include other components that may or may not be physically and electrically coupled to the motherboard or fabricated within an SoC die. These other components include, but are not limited to, volatile memory  610  (e.g., DRAM), non-volatile memory  612  (e.g., ROM or flash memory), graphics processing unit  614  (GPU), digital signal processor  616 , crypto processor  642  (a specialized processor that executes cryptographic algorithms within hardware), chipset  620 , antenna  622 , display or touchscreen display  624 , touchscreen controller  626 , battery  628  or other power source, a power amplifier (not shown), global positioning system (GPS) device  644 , compass  630 , motion coprocessor or sensors  632  (that may include an accelerometer, a gyroscope, and a compass), speaker  634 , camera  636 , user input devices  638  (such as a keyboard, mouse, stylus, and touchpad), and mass storage device  640  (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth). 
     Communications chip  608  enables wireless communications for the transfer of data to and from computing device  600 . The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. Communication chip  608  may implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. Computing device  600  may include a plurality of communication chips  608 . For instance, a first communication chip may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others. 
     Processor  604  of computing device  600  includes one or more devices, such as multigate transistors, that are formed in accordance with embodiments described above. The term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. 
     Communication chip  608  may also include one or more devices, such as transistors, that are formed in accordance with embodiments. 
     In further embodiments, another component housed within computing device  600  may contain one or more devices, such as multigate transistors, that are formed in accordance with implementations. 
     In various embodiments, computing device  600  may be a laptop computer, a netbook computer, a notebook computer, an ultrabook computer, a smartphone, a tablet, a personal digital assistant (PDA), an ultra mobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, computing device  600  may be any other electronic device that processes data. 
     EXAMPLES 
     The following examples pertain to embodiments: 
     Example 1 is a transistor device including a transistor device including a channel disposed on a substrate between a source and a drain, a gate electrode disposed on the channel, wherein the channel includes a length dimension between the source and the drain wherein the channel includes a channel material that is separated from a body of the same material on a substrate. 
     In Example 2, a width dimension of the channel of the transistor device of Example 1 includes less than 10 nanometers. 
     In Example 3, the body of the transistor device of Example 1 or 2 includes the channel material formed on a buffer material. 
     In Example 4, the channel material of any of the transistor devices of Examples 1-3 includes a different lattice structure than a material of the substrate. 
     In Example 5, the channel material of any of the transistor devices of Examples 1-4 includes a group III-V compound semiconductor material. 
     In Example 6, the channel material of any of the transistor devices of Examples 1-4 includes germanium. 
     Example 7 is a method of forming a transistor device including forming a trench in a dielectric layer on an integrated circuit substrate, the trench including dimensions for a transistor body including a width; depositing a spacer layer in a portion of the trench, the spacer layer narrowing the width of the trench; forming a channel material in the trench through the spacer layer; recessing the dielectric layer to define a first portion of the channel material exposed and a second portion of the channel material in the trench; and separating the first portion of the channel material from the second portion of the channel material. 
     In Example 7, prior to forming the channel material in the trench, the method of Example 7 includes forming a buffer material in the trench and forming the channel material includes forming the channel material on the buffer material. 
     In Example 9, forming the buffer material of the method of Example 8 includes forming the buffer material below the spacer layer. 
     In Example 10, forming the buffer material below the spacer layer of the method of Example 9 includes forming the buffer material in the trench including through the spacer layer and then recessing the buffer material to a level below the spacer layer. 
     In Example 11, after recessing the dielectric layer, any of the methods of Examples 7-10 includes forming a source and a drain of a transistor on the transistor body, wherein the source and drain are separated by a channel region. 
     In Example 12, separating the first portion of the channel material from the second portion of channel material of any of the methods of Examples 7-10 includes separating in the channel region. 
     In Example 13, the method of any of Examples 7-12 further includes reducing a width of the first portion of the channel material. 
     In Example 14, the channel material of any of the methods of Examples 7-13 includes a different lattice structure than a material of the substrate. 
     Example 15 is a method of forming a transistor device including forming a sacrificial fin in a substrate, the sacrificial fin projecting a height dimension above a surface of the substrate; forming a dielectric material on opposite sides of the sacrificial fin; removing a first portion of the sacrificial fin to define a a first portion of a trench, wherein the first portion of the sacrificial fin is less than an entire portion of the sacrificial fin; depositing a spacer layer in the first portion of the trench, the spacer layer narrowing a width of the first portion of the trench; removing a second portion of the sacrificial fin to define a second portion of the trench; forming a channel material in the first portion and the second portion of the trench; recessing the dielectric layer to define a first portion of the channel material exposed and a second portion of the channel material in the second portion of the trench; and separating the first portion of the channel material from the second portion of the channel material. 
     In Example 16, prior to forming the channel material in the first portion and the second portion of the trench, the method of Example 15 includes forming a buffer material in the second portion of the trench and forming the channel material includes forming the channel material on the buffer material. 
     In Example 17, forming the buffer material in the second portion of the trench of the method of Example 16 includes forming the buffer material in the first portion of the trench and the second portion of the trench and then removing the buffer material from the first portion of the trench. 
     In Example 18, after recessing the dielectric layer, the methods of Example 15-17 includes forming a source and a drain of a transistor in regions of the channel material, wherein the source and drain are separated by a channel region. 
     In Example 19, separating the first portion of the channel material from the second portion of channel material of the method of Example 18 includes separating in the channel region. 
     In Example 20, the method of Example 19 further includes reducing a width of the first portion of the channel material in the channel region. 
     In Example 21, the channel material of any of the methods of Examples 15-20 includes a different lattice structure than a material of the substrate. 
     The above description of illustrated implementations, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific implementations of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope, as those skilled in the relevant art will recognize. 
     These modifications may be made in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific implementations disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.