Patent Publication Number: US-9905651-B2

Title: GE and III-V channel semiconductor devices having maximized compliance and free surface relaxation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/914,102, filed on Feb. 24, 2016, which is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/US2013/062447, filed Sep. 27, 2013, entitled “GE AND III-V CHANNEL SEMICONDUCTOR DEVICES HAVING MAXIMIZED COMPLIANCE AND FREE SURFACE RELAXATION” the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the invention are in the field of semiconductor devices and processing and, in particular, Ge and III-V channel semiconductor devices having maximized compliance and free surface relaxation and methods of fabricating such Ge and III-V channel semiconductor devices. 
     BACKGROUND 
     For the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of memory or logic devices on a chip, lending to the fabrication of products with increased capacity. The drive for ever-more capacity, however, is not without issue. The necessity to optimize the performance of each device becomes increasingly significant. 
     In the manufacture of integrated circuit devices, multi-gate transistors, such as fin field effect transistors (fin-FETs), have become more prevalent as device dimensions continue to scale down. In conventional processes, fin-FETs are generally fabricated on either bulk silicon substrates or silicon-on-insulator substrates. In some instances, bulk silicon substrates are preferred due to their lower cost and compatibility with the existing high-yielding bulk silicon substrate infrastructure. 
     Scaling multi-gate transistors has not been without consequence, however. As the dimensions of these fundamental building blocks of microelectronic circuitry are reduced and as the sheer number of fundamental building blocks fabricated in a given region is increased, the constraints on the semiconductor processes used to fabricate these building blocks have become overwhelming. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an angled three-dimensional cross-sectional view of a state-of-the-art Ge/III-V-on Si non-planar device. 
         FIG. 1B  illustrates a plan view of the Ge/III-V-on Si non-planar device of  FIG. 1A  having a gate line and source/drain contacts thereon. 
         FIG. 1C  is a plot showing relative cladding layer parameters for a variety of device architectures, in accordance with an embodiment of the present invention. 
         FIGS. 2A-2C  illustrate cross-sectional views of various operations in a method of fabricating a short fin device with a retained 2× gate pitch accommodation, in accordance with an embodiment of the present invention, where: 
         FIG. 2A  illustrates a plan view and cross-sectional view depicting a semiconductor fin having a total length of 2× gate pitch, but having a central segment isolated from outer segments; 
         FIG. 2B  illustrates a cross-sectional view depicting growth of a cladding layer on the structure of  FIG. 2A ; and 
         FIG. 2C  illustrates a cross-sectional view depicting formation of a gate line and source/drain contacts on the structure of  FIG. 2B . 
         FIGS. 3A-3D  illustrate cross-sectional views of various operations in a method of fabricating a fin device with axial channel growth and a retained 2× gate pitch accommodation, in accordance with an embodiment of the present invention, where: 
         FIG. 3A  illustrates a plan view and cross-sectional view depicting a semiconductor fin having a total length of 2× gate pitch, but having a central segment isolated from outer segments; 
         FIG. 3B  illustrates a cross-sectional view depicting recessing of the central segment of the fin of  FIG. 3A ; 
         FIG. 3C  illustrates a cross-sectional view depicting growth of a cladding layer on the structure of  FIG. 3B ; and 
         FIG. 3D  illustrates a cross-sectional view depicting formation of a gate line and source/drain contacts on the structure of  FIG. 3C . 
         FIG. 4  is a plot of simulated epitaxial layer stress (in GPa) as a function of cladding layer composition, in accordance with an embodiment of the present invention. 
         FIG. 5A  illustrates a cross-sectional view of a Ge or III-V channel semiconductor device having maximized compliance and free surface relaxation, in accordance with an embodiment of the present invention. 
         FIG. 5B  illustrates a plan view taken along the a-a′ axis of the semiconductor device of  FIG. 5A , in accordance with an embodiment of the present invention. 
         FIG. 6  illustrates a computing device in accordance with one implementation of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Ge and III-V channel semiconductor devices having maximized compliance and free surface relaxation and methods of fabricating such Ge and III-V channel semiconductor devices are described. In the following description, numerous specific details are set forth, such as specific integration and material regimes, in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known features, such as integrated circuit design layouts, are not described in detail in order to not unnecessarily obscure embodiments of the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale. 
     One potential way to integrate high mobility channel materials on silicon (Si) is with thin cladding layers on Si nanoscale templates. One or more embodiments described herein are directed to techniques for maximizing compliance and free surface relaxation in germanium (Ge) and III-V Transistors. One or more embodiments may be directed to one or more of cladding layers, compliant expitaxy, germanium channel regions, III-V material channel regions, transistor fabrication including metal oxide semiconductor (MOS) and complementary metal oxide semiconductor (CMOS) devices, and compound semiconductor (III thru V) devices. 
     More specifically, one or more embodiments described herein provides approaches for improving epitaxial growth quality of compliant III-V and Ge channel transistor devices. To provide context, for state of the art trigate transistors, fin length is set at approximately 2× gate pitch. Hence, if used, cladding layers must be grown on fins of this length. By contrast, one or more embodiments described herein decouples the active channel fin length from the typical fin length set at 2× gate pitch. Such decoupling can enable improved compliant growth on shorter fin portions or segments. Additionally, in one such embodiment, the active channel fin can also be recessed, to provide further improved compliance/free surface relaxation for the most ideal III-V material or Ge epitaxial growth in the channel region of high performance devices. 
     A compliant substrate, or a non-planar semiconductor body having a cladding layer to provide a compliance effect typically involves growing a Ge or III-V film on a thin fin silicon fin or substrate. Such an arrangement allows not only the film being deposited but also the thin Si-Fin (compliant) to accommodate some of the lattice mismatch and strain in the films, enabling defect reduction. As a reference point, a silicon fin having a cladding layer formed thereon can provide a compliant substrate. The cladding layer of Ge or III-V is formed on a portion of the fin to provide a high mobility channel layer. The cladding layer has a larger lattice constant than the silicon fin and, as such, both layers are strained. Compliance of the fin to the cladding layer may be achieved when a narrow fin Wsi is used, resulting in a beneficial free surface effect. In particular, the thin silicon fin and cladding layer ultimately “comply” or stretch to accommodate epitaxial growth at free surfaces thereof. 
     As mentioned above, state of the art non-planar devices have a fin length set at twice the gate line pitch. A cladding layer formed on such a fin, e.g., a silicon fin, is formed on the entire length of the fin. The resulting compliance effect may not be optimal on such a scale, and an increased number of defects may result. As an example of a prior approach,  FIGS. 1A and 1B  illustrate an angled three-dimensional cross-sectional view and a plan view, respectively, of a Ge/III-V-on Si non-planar device. Referring to  FIG. 1A , a device  100  includes a silicon fin  102  having a width (d) and a length (L). The silicon fin  102  is shown as a bulk silicon fin in that the fin extends through an isolation region  104  and coupled to an underlying silicon substrate (not shown). A Ge or III-V material cladding layer  106  is disposed on the surface of the exposed or protruding portion of fin  102 . As shown in  FIG. 1A , the cladding layer has a thickness (t) and extends along the entire length (L) of the fin  102 . Referring to  FIG. 1B , the device  100  is shown from above the fin with a gate line  108  and source/drain contacts  110  formed over the fin, i.e., formed over the cladding layer  106 . As shown in  FIG. 1B , the fin  102  has a length equal to twice the gate pitch. As such, the cladding layer  106  of device  100  runs a length of twice the gate line pitch. 
       FIG. 1C  is a plot  150  showing relative cladding layer parameters for a variety of device architectures, in accordance with an embodiment of the present invention. Referring to plot  150 , matched minimum template dimensions are determined for a thin silicon device  152  having a cladding layer  154  on an active region  156  with a thickness (d) above an isolation layer  158 , for a conventional trigate fin device  162  having a cladding layer  164  on an active region  166  with a width (d) and protruding above an isolation layer  168 , for a nanoribbon device  172  having a cladding layer  174  surrounding an active region  176  having a height (d), for a core-shell nanowire device  182  having a cladding layer  184  surrounding an active region  186  having a diameter (d), and for an axial nanowire  192  having a cladding layer  194  on an active region  196  with a width (d). Relative substrate compliance, free surface relaxation and critical thickness (t C ) are shown in plot  150  for devices  152 ,  162 ,  172 ,  182  and  192 . Referring again to  FIG. 1C , one potential drawback to a traditional trigate device is that fin length is tied to gate pitch which requires that (i) the entire fin length (which is 2× gate pitch) has to be cladded, (ii) the active cladded fin channel cannot be made shorter because of this constraint (which would otherwise be an improvement for compliance), and (iii) the axial cladding structure in the active channel cannot be utilized, which would otherwise provide an optimal structure for compliance. 
     In contrast to the cladded trigate structure of  FIGS. 1A and 1B , which is benchmarked in  FIG. 1C , generally, one or more embodiments described herein provide an approach to fabricating shorter fin Si base segments for improved growth/compliance. In a first example,  FIGS. 2A-2C  illustrate cross-sectional views of various operations in a method of fabricating a short fin device with a retained 2× gate pitch accommodation, in accordance with an embodiment of the present invention. 
     Referring to  FIG. 2A , a plan view and cross-sectional view depict a semiconductor fin  202  having a total length of 2× gate pitch, but having a central segment  204  isolated from outer segments  206 . The fin  202  protrudes above an isolation region  208  which is further disposed between the central segment  204  and the outer segments  206  of the fin  202 . As such, fin  202  effectively represents a conventional fin cut into three segments. In one embodiment, the fin  202  is a bulk silicon fin silicon and the isolation region is composed of silicon dioxide, as shown. In an embodiment, in keeping with traditional bulk trigate manufacturing approaches, the fin  202  is first formed within an underlying bulk substrate. An isolation material is then formed over the fin and subsequently recessed to expose the protruding portions of the fin. In accordance with an embodiment of the present invention, however, fin formation further includes cutting of the segments as shown (e.g., by a patterning and etch process) prior to isolation deposition and recessing. It is to be appreciated that the resulting fin  202  is a single fin as shown along source to drain regions, and is not merely a plurality of fins. 
     Referring to  FIG. 2B , a cross-sectional view depicts growth of a cladding layer  210  on the structure of  FIG. 2A . In particular, the cladding layer  210  is grown epitaxially on the central segment  204  and the outer segments  206  of the fin  202 . However, instead of growing a single cladding layer region along the entire length of the fin, a first cladding layer region  210 A is grown on the central segment  204  of the fin  202 . Second cladding layer regions  210 B are grown on the outer segments  206  of the fin  202 . The cladding layer regions  210 A and  210 B merge at interfaces  211 . However, the cladding layer region  210 A is formed as a distinct region. This enables the highest quality cladding layer growth, and best substrate compliance, since the growth of region  210 A is confined to the central segment  204  of fin  202 . The effect is to shorten the length of the grown cladding layer  210 A relative to the entire length of the fin. By reducing the length, the compliance is enhanced at the channel region of the fin  202 , where it is most needed. It is to be appreciated that the regions  210 B very well may run along longer portions of the fin  202  and, accordingly, have less compliance effect and/or have lower quality than region  210 A. 
     Referring to  FIG. 2C , a cross-sectional view depicts formation of a gate line  212  and source/drain contacts  214  on the structure of  FIG. 2B . In particular, the gate line  212  is formed above/over the cladding layer region  210 A. The source/drain contacts  214  are formed above/over the cladding layer regions  210 B. The resulting device, then, provides a high compliance cladding layer region  210 A underneath the gate line  212 . The total fin  202  of the semiconductor device includes the regions  206  and  204  along with cladding layer regions  210 A and  210 B. It is to be appreciated that the structure of  FIG. 2C  may subsequently be subjected to further processing, such as back end metallization, in order to incorporate the device into an integrated circuit such as a CMOS integrated circuit. 
     In a second example,  FIGS. 3A-3D  illustrate cross-sectional views of various operations in a method of fabricating a fin device with axial channel growth and a retained 2× gate pitch accommodation, in accordance with an embodiment of the present invention. 
     Referring to  FIG. 3A , a plan view and cross-sectional view depict a semiconductor fin  302  having a total length of 2× gate pitch, but having a central segment  304  isolated from outer segments  306 . The fin  302  protrudes above an isolation region  308  which is further disposed between the central segment  304  and the outer segments  306  of the fin  302 . As such, fin  302  effectively represents a conventional fin cut into three segments. In one embodiment, the fin  302  is a bulk silicon fin silicon and the isolation region is composed of silicon dioxide, as shown. In an embodiment, in keeping with traditional bulk trigate manufacturing approaches, the fin  302  is first formed within an underlying bulk substrate. An isolation material is then formed over the fin and subsequently recessed to expose the protruding portions of the fin. In accordance with an embodiment of the present invention, however, fin formation further includes cutting of the segments as shown (e.g., by a patterning and etch process) prior to isolation deposition and recessing. 
     Referring to  FIG. 3B , a cross-sectional view depicts recessing of the central segment  304  of the fin  302 . In particular, the central segment  304  is recessed to provide a recessed central segment  304 A of a modified fin  302 A. It is to be appreciated that the resulting fin  302 A is a single fin as shown along source to drain regions, and is not merely a plurality of fins. The recessing may be performed by a patterning and etch process. In one embodiment, the recessing is performed to provide the recessed central segment  304 A at approximately the level of the isolation region  308 , as is depicted in  FIG. 3B . 
     Referring to  FIG. 3C , a cross-sectional view depicts growth of a cladding layer  310  on the structure of  FIG. 3B . In particular, the cladding layer  310  is grown epitaxially on the recessed central segment  304 A and the outer segments  306  of the fin  302 . However, instead of growing a single cladding layer region along the entire length of the fin, a first cladding layer region  310 A is grown on the recessed central segment  304 A of the fin  302 A. Second cladding layer regions  310 B are grown on the outer segments  306  of the fin  302 A. The cladding layer regions  310 A and  310 B merge at interfaces  311 . However, the cladding layer region  310 A is formed as a distinct region. This enables the highest quality cladding layer growth, and best substrate compliance, since the growth of region  310 A is confined to the recessed central segment  304 A of fin  302 A. The effect is to shorten the length of the grown cladding layer  310 A relative to the entire length of the fin. By reducing the length, the compliance is enhanced at the channel region of the fin  302 A, where it is most needed. It is to be appreciated that the regions  310 B very well may run along longer portions of the fin  302 A and, accordingly, have less compliance effect and/or have lower quality than region  310 A. 
     Referring to  FIG. 3D , a cross-sectional view depicts formation of a gate line  312  and source/drain contacts  314  on the structure of  FIG. 3C . In particular, the gate line  312  is formed above/over the cladding layer region  310 A. The source/drain contacts  314  are formed above/over the cladding layer regions  310 B. The resulting device, then, provides a high compliance cladding layer region  310 A underneath the gate line  312 . The total fin  302 A of the semiconductor device includes the regions  306  and  304 A along with cladding layer regions  310 A and  310 B. It is to be appreciated that the structure of  FIG. 3D  may subsequently be subjected to further processing, such as back end metallization, in order to incorporate the device into an integrated circuit such as a CMOS integrated circuit. 
     In an embodiment, the cladding layer  310  has a lower band gap yet larger lattice constant than underlying Si. The cladding layer  310  may have a thickness suitable to propagate a substantial portion of a wave-function, e.g. suitable to inhibit a significant portion of the wave-function from entering the Si fin. However, the cladding layer  310  may be sufficiently thin for compliance. In one embodiment, cladding layer  310  has a thickness approximately in the range of 10-50 Angstroms. The cladding layer  310  may be formed by a technique such as, but not limited to, chemical vapor deposition (CVD) or molecular beam epitaxy (MBE), or other like processes. 
     In a first embodiment, the cladding layer  310  is a germanium (Ge) cladding layer, such as a pure or essentially pure germanium cladding layer. As used throughout, the terms pure or essentially pure germanium may be used to describe a germanium material composed of a very substantial amount of, if not all, germanium. However, it is to be understood that, practically, 100% pure Ge may be difficult to form and, hence, could include a tiny percentage of Si. The Si may be included as an unavoidable impurity or component during deposition of Ge or may “contaminate” the Ge upon diffusion during post deposition processing. As such, embodiments described herein directed to a Ge cladding layer may include Ge materials that contain a relatively small amount, e.g., “impurity” level, non-Ge atoms or species, such as Si. Also, in alternative embodiments, SiGe is used, e.g., a Si x Ge y  layer, where 0&lt;x&lt;100, and 0&lt;y&lt;100, with a high % Ge content relative to silicon. 
     In a second embodiment, the cladding layer  310  is a III-V material cladding layer. That is, in one embodiment, the cladding layer  310  is composed of groups III (e.g. boron, aluminum, gallium or indium) and V (e.g. nitrogen, phosphorous, arsenic or antimony) elements. In one embodiment, cladding layer  310  is composed of binary (e.g., GaAs) but can also be ternary or quarternary based III-V materials, etc. 
     As mentioned above, in one embodiment, the illustrations of  FIGS. 2A and 3A  begins the processs flow descriptions post fin etch and shallow trench isolation (STI) polish following isolation oxide deposition. It is to be appreciated that artifacts that may have at one point remained from the fabrication of fins  202  or  302  have also been removed. For example, in one embodiment, a hardmask layer, such as a silicon nitride hardmask layer, and a pad oxide layer, such as a silicon dioxide layer, have been removed from the top surface of fins  202  or  302 . In one embodiment, a corresponding bulk substrate and, hence, the fins  202  or  302 , are undoped or lightly doped at this stage. For example, in a particular embodiment, the bulk substrate and, hence, the fins  202  or  302 , have a concentration of less than approximately 1E17 atoms/cm 3  of boron dopant impurity atoms. However, in other embodiments, well and/or retrograde implants have been, or will be, provided to the fins  202  or  302  and the underlying substrate. In one such example, such doping of the exposed fins  202  or  302  may lead to doping within the corresponding bulk substrate portion, where adjacent fins share a common doped region in the bulk substrate. 
     In an embodiment, referring again to  FIGS. 2A and 3A , the dielectric layer  208  or  308  is composed of silicon dioxide, such as is used in a shallow trench isolation fabrication process. The dielectric layer  208  or  308  may be deposited by a chemical vapor deposition (CVD) or other deposition process (e.g., ALD, PECVD, PVD, HDP assisted CVD, low temp CVD) and may be planarized by a chemical mechanical polishing (CMP) technique. The planarization may also removes any artifacts from fin patterning, such as a hardmask layer and/or pad oxide layer, as mentioned above. In an embodiment, recessing of a dielectric layer to provide isolation regions  208  or  308  defines the initial Si channel height (HSI). The recessing may be performed by a plasma, vapor or wet etch process. In one embodiment, a dry etch process selective to silicon fins  202  or  302  is used, the dry etch process based on a plasma generated from gases such as, but not limited to NF 3 , CHF 3 , C 4 F 8 , HBr and O 2  with typically pressures in the range of 30-100 mTorr and a plasma bias of 50-1000 Watts. In the case of the process described in association with  FIGS. 2A-2C , the initial Si channel height (HSI) is retained. However, the case of the process described in association with  FIGS. 3A-3D , the initial Si channel height (HSI) is reduced upon recessing of the central fin portion. It is to be appreciated that cladding layer growth for compliant substrate fabrication increases the total fin height which is based on HSI and top cladding layer thickness. 
     In an embodiment, gate line  212  or  312  patterning involves poly lithography to define a polysilicon gate (permanent or placeholder for a replacement gate process) by etch of an SiN hardmask and polysilicon subsequently. In one embodiment, a mask is formed on the hardmask, the mask composed of a topographic masking portion and an anti-reflective coating (ARC) layer. In a particular such embodiment, the topographic masking portion is a carbon hardmask (CHM) layer and the anti-reflective coating layer is a silicon ARC layer. The topographic masking portion and the ARC layer may be patterned with conventional lithography and etching process techniques. In one embodiment, the mask also includes and uppermost photo-resist layer, as is known in the art, and may be patterned by conventional lithography and development processes. In a particular embodiment, the portions of the photo-resist layer exposed to the light source are removed upon developing the photo-resist layer. Thus, patterned photo-resist layer is composed of a positive photo-resist material. In a specific embodiment, the photo-resist layer is composed of a positive photo-resist material such as, but not limited to, a 248 nm resist, a 193 nm resist, a 157 nm resist, an extreme ultra violet (EUV) resist, an e-beam imprint layer, or a phenolic resin matrix with a diazonaphthoquinone sensitizer. In another particular embodiment, the portions of the photo-resist layer exposed to the light source are retained upon developing the photo-resist layer. Thus, the photo-resist layer is composed of a negative photo-resist material. In a specific embodiment, the photo-resist layer is composed of a negative photo-resist material such as, but not limited to, consisting of poly-cis-isoprene or poly-vinyl-cinnamate. 
     Pertinent to the structures shown in both  FIGS. 2C and 3D ,  FIG. 4  is a plot  400  of simulated epitaxial layer stress (in GPa) as a function of cladding layer composition, in accordance with an embodiment of the present invention. Referring to plot  400 , stress of an InxGal-xAs cladding layer on a silicon fin is plotted as a function of increasing value for x. Data line  402  represents stress for a 2 nm thick cladding layer on a 4 nm wide Si fin of infinite length. Data line  404  represents stress for a 2 nm thick cladding layer on a 4 nm wide Si fin of 84 nm length. The relative stress is lowered in shorter fins due to free surface relaxation. 
     In general, referring again to  FIGS. 2A-2C and 3A-3D , in an embodiment, the approach described can be used for N-type (e.g., NMOS) or P-type (e.g., PMOS), or both, device fabrication. It is to be understood that the structures resulting from the above exemplary processing schemes, e.g., the structures from  FIGS. 2C and 3D , may be used in a same or similar form for subsequent processing operations to complete device fabrication, such as PMOS and NMOS device fabrication. As an example of a completed device,  FIGS. 5A and 5B  illustrate a cross-sectional view and a plan view (taken along the a-a′ axis of the cross-sectional view), respectively, of a Ge or III-V channel semiconductor devices having maximized compliance and free surface relaxation, in accordance with an embodiment of the present invention. 
     Referring to  FIG. 5A , a semiconductor structure or device  500  includes a non-planar active region (e.g., a fin structure including protruding fin portion  504  and sub-fin region  505 ) formed from substrate  502 , and within isolation region  506 . In the case shown, three distinct fins are included in a single device. A channel region cladding layer  597  is formed to surround the protruding region  504  of each of the fins. Although not shown, it is to be appreciated that the cladding layer  597  of each fin (as considered in a direction normal to the page) does not run the length of the entire fin. Instead, it is shortened in the manner described in association with  FIGS. 2A-2C and 3A-3D  to provide an enhanced compliance effect. 
     Referring again to  FIG. 5A , a gate line  508  is disposed over the protruding portions  504  of the non-planar active region as well as over a portion of the isolation region  506 . As shown, gate line  508  includes a gate electrode  550  and a gate dielectric layer  552 . In one embodiment, gate line  508  may also include a dielectric cap layer  554 . A gate contact  514 , and overlying gate contact via  516  are also seen from this perspective, along with an overlying metal interconnect  560 , all of which are disposed in inter-layer dielectric stacks or layers  570 . Also seen from the perspective of  FIG. 5A , the gate contact  514  is, in one embodiment, disposed over isolation region  506 , but not over the non-planar active regions. 
     Referring to  FIG. 5B , the gate line  508  is shown as disposed over the protruding fin portions  504 . Source and drain regions  504 A and  504 B of the protruding fin portions  504  can be seen from this perspective. In one embodiment, the source and drain regions  504 A and  504 B are doped portions of original material of the protruding fin portions  504 / 597 . In another embodiment, the material of the protruding fin portions  504 / 597  is removed and replaced with another semiconductor material, e.g., by epitaxial deposition. In that case, portions of a cladding layer confined to the source and drain regions are also removed. In either case, the source and drain regions  504 A and  504 B may extend below the height of dielectric layer  506 , i.e., into the sub-fin region  505 . Alternatively, the source and drain regions  504 A and  504 B do not extend below the height of dielectric layer  506 , and are either above or co-planar with the height of dielectric layer  506 . 
     In an embodiment, the semiconductor structure or device  500  is a non-planar device such as, but not limited to, a fin-FET. However, a tri-gate or similar device may also be fabricated. In such an embodiment, a corresponding semiconducting channel region is composed of or is formed in a three-dimensional body. In one such embodiment, the gate electrode stacks of gate lines  508  surround at least a top surface and a pair of sidewalls of the three-dimensional body, as depicted in  FIG. 5A . 
     Substrate  502  may be composed of a semiconductor material that can withstand a manufacturing process and in which charge can migrate. In an embodiment, substrate  502  is a bulk substrate composed of a crystalline silicon layer doped with a charge carrier, such as but not limited to phosphorus, arsenic, boron or a combination thereof, to form active region  504 / 505 . In one embodiment, the concentration of silicon atoms in bulk substrate  502  is greater than 99%. In another embodiment, bulk substrate  502  is composed of an epitaxial layer grown atop a distinct crystalline substrate, e.g. a silicon epitaxial layer grown atop a boron-doped bulk silicon mono-crystalline substrate. Alternatively, in place of a bulk substrate, a silicon-on-insulator (SOI) substrate may be used. In a particular embodiments, substrate  502  and, hence, protruding portions  504  of the fins, is composed of single crystalline silicon, and the cladding layer  597  is a Ge cladding layer or a III-V material cladding layer, as described above. 
     Isolation region  506  may be composed of a material suitable to ultimately electrically isolate, or contribute to the isolation of, portions of a permanent gate structure from an underlying bulk substrate or isolate active regions formed within an underlying bulk substrate, such as isolating fin active regions. For example, in one embodiment, the isolation region  506  is composed of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride. 
     Gate line  508  may be composed of a gate electrode stack which includes a gate dielectric layer  552  and a gate electrode layer  550 . In an embodiment, the gate electrode of the gate electrode stack is composed of a metal gate and the gate dielectric layer is composed of a high-K material. For example, in one embodiment, the gate dielectric layer is composed of a material such as, but not limited to, hafnium oxide, hafnium oxy-nitride, hafnium silicate, lanthanum oxide, zirconium oxide, zirconium silicate, tantalum oxide, barium strontium titanate, barium titanate, strontium titanate, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, lead zinc niobate, or a combination thereof. Furthermore, a portion of gate dielectric layer may include one or a few monolayers of native oxide formed from the top few layers of the cladding layer  597 . 
     In one embodiment, the gate electrode is composed of a metal layer such as, but not limited to, metal nitrides, metal carbides, metal silicides, metal aluminides, hafnium, zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum, cobalt, nickel or conductive metal oxides. In a specific embodiment, the gate electrode is composed of a non-workfunction-setting fill material formed above a metal workfunction-setting layer. 
     Spacers associated with the gate electrode stacks (not shown) may be composed of a material suitable to ultimately electrically isolate, or contribute to the isolation of, a permanent gate structure from adjacent conductive contacts, such as self-aligned contacts. For example, in one embodiment, the spacers are composed of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride. 
     Gate contact  514  and overlying gate contact via  516  may be composed of a conductive material. In an embodiment, one or more of the contacts or vias are composed of a metal species. The metal species may be a pure metal, such as tungsten, nickel, or cobalt, or may be an alloy such as a metal-metal alloy or a metal-semiconductor alloy (e.g., such as a silicide material). 
     In an embodiment (although not shown), providing structure  500  involves formation of a contact pattern which is essentially perfectly aligned to an existing gate pattern while eliminating the use of a lithographic step with exceedingly tight registration budget. In one such embodiment, this approach enables the use of intrinsically highly selective wet etching (e.g., versus conventionally implemented dry or plasma etching) to generate contact openings. In an embodiment, a contact pattern is formed by utilizing an existing gate pattern in combination with a contact plug lithography operation. In one such embodiment, the approach enables elimination of the need for an otherwise critical lithography operation to generate a contact pattern, as used in conventional approaches. In an embodiment, a trench contact grid is not separately patterned, but is rather formed between poly (gate) lines. For example, in one such embodiment, a trench contact grid is formed subsequent to gate grating patterning but prior to gate grating cuts. 
     Furthermore, the gate stack structure  508  may be fabricated by a replacement gate process. In such a scheme, dummy gate material such as polysilicon or silicon nitride pillar material, may be removed and replaced with permanent gate electrode material. In one such embodiment, a permanent gate dielectric layer is also formed in this process, as opposed to being carried through from earlier processing. In an embodiment, dummy gates are removed by a dry etch or wet etch process. In one embodiment, dummy gates are composed of polycrystalline silicon or amorphous silicon and are removed with a dry etch process including use of SF 6 . In another embodiment, dummy gates are composed of polycrystalline silicon or amorphous silicon and are removed with a wet etch process including use of aqueous NH 4 OH or tetramethylammonium hydroxide. In one embodiment, dummy gates are composed of silicon nitride and are removed with a wet etch including aqueous phosphoric acid. In an embodiment, replacement of a dummy gate dielectric layer with a permanent gate dielectric layer is additionally performed. 
     In an embodiment, one or more approaches described herein contemplate essentially a dummy and replacement gate process in combination with a dummy and replacement contact process to arrive at structure  500 . In one such embodiment, the replacement contact process is performed after the replacement gate process to allow high temperature anneal of at least a portion of the permanent gate stack. For example, in a specific such embodiment, an anneal of at least a portion of the permanent gate structures, e.g., after a gate dielectric layer is formed, is performed at a temperature greater than approximately 600 degrees Celsius. The anneal is performed prior to formation of the permanent contacts. 
     Referring again to  FIG. 5A , the arrangement of semiconductor structure or device  500  places the gate contact over isolation regions. Such an arrangement may be viewed as inefficient use of layout space. In another embodiment, however, a semiconductor device has contact structures that contact portions of a gate electrode formed over an active region. In general, prior to (e.g., in addition to) forming a gate contact structure (such as a via) over an active portion of a gate and in a same layer as a trench contact via, one or more embodiments of the present invention include first using a gate aligned trench contact process. Such a process may be implemented to form trench contact structures for semiconductor structure fabrication, e.g., for integrated circuit fabrication. In an embodiment, a trench contact pattern is formed as aligned to an existing gate pattern. By contrast, conventional approaches typically involve an additional lithography process with tight registration of a lithographic contact pattern to an existing gate pattern in combination with selective contact etches. For example, a conventional process may include patterning of a poly (gate) grid with separate patterning of contact features. 
     It is to be understood that not all aspects of the processes described above need be practiced to fall within the spirit and scope of embodiments of the present invention. For example, in one embodiment, dummy gates need not ever be formed prior to fabricating gate contacts over active portions of the gate stacks. The gate stacks described above may actually be permanent gate stacks as initially formed. Also, the processes described herein may be used to fabricate one or a plurality of semiconductor devices. The semiconductor devices may be transistors or like devices. For example, in an embodiment, the semiconductor devices are a metal-oxide semiconductor field effect transistors (MOS) transistors for logic or memory, or are bipolar transistors. Also, in an embodiment, the semiconductor devices have a three-dimensional architecture, such as a fin-FET device, a trigate device, or an independently accessed double gate device. One or more embodiments may be particularly useful for fabricating semiconductor devices at a 14 nanometer (14 nm) or smaller technology node. 
     In general, then, one or more embodiments described above allow for decoupling the active channel fin length from the typical fin length=2× gate pitch. This allows for better compliant growth since the fin is shortened. Additionally, the active channel fin can also be recessed, to provide even better compliance/free surface relaxation for III-V or Ge epitaxial growth in the channel. Thus, novel high mobility materials such Ge or III-V may be introduced into the transistor channel, e.g., PMOS for the former and NMOS for the latter. 
       FIG. 6  illustrates a computing device  600  in accordance with one implementation of the invention. The computing device  600  houses a board  602 . The board  602  may include a number of components, including but not limited to a processor  604  and at least one communication chip  606 . The processor  604  is physically and electrically coupled to the board  602 . In some implementations the at least one communication chip  606  is also physically and electrically coupled to the board  602 . In further implementations, the communication chip  606  is part of the processor  604 . 
     Depending on its applications, computing device  600  may include other components that may or may not be physically and electrically coupled to the board  602 . These other components include, but are not limited to, volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flash memory, a graphics processor, a digital signal processor, a crypto processor, a chipset, an antenna, a display, a touchscreen display, a touchscreen controller, a battery, an audio codec, a video codec, a power amplifier, a global positioning system (GPS) device, a compass, an accelerometer, a gyroscope, a speaker, a camera, and a mass storage device (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth). 
     The communication chip  606  enables wireless communications for the transfer of data to and from the 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. The communication chip  606  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. The computing device  600  may include a plurality of communication chips  606 . For instance, a first communication chip  606  may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip  606  may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others. 
     The processor  604  of the computing device  600  includes an integrated circuit die packaged within the processor  604 . In some implementations of embodiments of the invention, the integrated circuit die of the processor includes one or more devices, such as Ge or III-V channel semiconductor devices having maximized compliance and free surface relaxation built in accordance with implementations of the invention. 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. 
     The communication chip  606  also includes an integrated circuit die packaged within the communication chip  606 . In accordance with another implementation of the invention, the integrated circuit die of the communication chip includes one or more devices, such as Ge or III-V channel semiconductor devices having maximized compliance and free surface relaxation built in accordance with implementations of the invention. 
     In further implementations, another component housed within the computing device  600  may contain an integrated circuit die that includes one or more devices, such as Ge or III-V channel semiconductor devices having maximized compliance and free surface relaxation built in accordance with implementations of embodiments of the invention. 
     In various embodiments, the computing device  600  may be a laptop, a netbook, a notebook, an ultrabook, 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, the computing device  600  may be any other electronic device that processes data. 
     Thus, embodiments of the present invention include Ge and III-V channel semiconductor devices having maximized compliance and free surface relaxation and methods of fabricating such Ge and III-V channel semiconductor devices. 
     In an embodiment, a semiconductor device includes a semiconductor fin disposed above a semiconductor substrate. The semiconductor fin has a central protruding segment spaced apart from a pair of protruding outer segments along a length of the semiconductor fin. A cladding layer region is disposed on the central protruding segment of the semiconductor fin. A gate stack is disposed on the cladding layer region. Source/drain regions are disposed in the pair of protruding outer segments of the semiconductor fin. 
     In one embodiment, the semiconductor device further includes a second cladding layer region disposed on one of the pair of protruding outer segments. A third cladding layer region is disposed on the other of the pair of protruding outer segments. The second and third cladding regions are discrete from, but contiguous with, the cladding layer region disposed on the central protruding segment of the semiconductor fin. 
     In one embodiment, the semiconductor fin and the cladding layer region together provide a compliant substrate. 
     In one embodiment, the central protruding segment is spaced apart from the pair of protruding outer segments by an isolation layer. 
     In one embodiment, the semiconductor fin consists essentially of silicon, and the cladding layer region consists essentially of germanium. 
     In one embodiment, the semiconductor device is a PMOS device. 
     In one embodiment, the semiconductor fin consists essentially of silicon, and the cladding layer region consists essentially of a III-V material. 
     In one embodiment, the semiconductor device is an NMOS device. 
     In an embodiment, a semiconductor device includes a semiconductor fin disposed above a semiconductor substrate. The semiconductor fin has a central recessed segment spaced apart from a pair of protruding outer segments along a length of the semiconductor fin. A cladding layer region is disposed on the central recessed segment of the semiconductor fin. A gate stack is disposed on the cladding layer region. Source/drain regions are disposed in the pair of protruding outer segments of the semiconductor fin. 
     In one embodiment, the semiconductor device further includes a second cladding layer region disposed on one of the pair of protruding outer segments. A third cladding layer region is disposed on the other of the pair of protruding outer segments. The second and third cladding regions are discrete from, but contiguous with, the cladding layer region disposed on the central recessed segment of the semiconductor fin. 
     In one embodiment, the semiconductor fin and the cladding layer region together provide a compliant substrate. 
     In one embodiment, the central recessed segment is spaced apart from the pair of protruding outer segments by an isolation layer. 
     In one embodiment, the semiconductor fin consists essentially of silicon, and the cladding layer region consists essentially of germanium. 
     In one embodiment, the semiconductor device is a PMOS device. 
     In one embodiment, the semiconductor fin consists essentially of silicon, and the cladding layer region consists essentially of a III-V material. 
     In one embodiment, the semiconductor device is an NMOS device. 
     In an embodiment, a method of fabricating a semiconductor device involves forming a semiconductor fin above a substrate. The method also involves etching the semiconductor fin to provide a central protruding segment spaced apart from a pair of protruding outer segments along a length of the semiconductor fin. The method also involves forming an isolation layer between the central protruding segment and each of the pair of protruding outer segments, the isolation layer having a top surface below a top surface of the central protruding segment. The method also involves, subsequent to forming the isolation layer, forming a cladding layer on exposed surfaces of the semiconductor fin. The method also involves forming a gate stack on the cladding layer. The method also involves forming source/drain regions in the pair of protruding outer segments of the semiconductor fin. 
     In one embodiment, the method of claim further involves, subsequent to forming the isolation region and prior to forming the cladding layer, recessing the central protruding segment to approximately the top surface of the isolation region. 
     In one embodiment, forming the cladding layer region involves forming a first cladding layer region on the central protruding segment, forming a second cladding layer region on one of the pair of protruding outer segments, and forming a third cladding layer region on the other of the pair of protruding outer segments. The second and third cladding regions are discrete from, but contiguous with, the first cladding layer region. 
     In one embodiment, forming the cladding layer region involves forming a first cladding layer region on the central recessed segment, forming a second cladding layer region on one of the pair of protruding outer segments, and forming a third cladding layer region on the other of the pair of protruding outer segments. The second and third cladding regions are discrete from, but contiguous with, the first cladding layer region. 
     In one embodiment, forming the cladding layer on exposed surfaces of the semiconductor fin provides a compliant substrate.