Patent Publication Number: US-11049979-B2

Title: Long channel nanosheet FET having tri-layer spacers

Description:
BACKGROUND 
     The disclosure relates generally to gate-all-around (GAA) transistor structures. The disclosure relates particularly to long channel GAA transistor structures having tri-layer inter-channel spacers. 
     Gate-all-around (GAA) vertical stacked field effect transistors (VFET) may include a stack of semiconductor nanosheets encased in a work function metal (WFM), as part of the gates of the structures. These structures may be used as part of device downscaling efforts. Long channel GAA structures may include channel structures having lengths in the range of AA to BB nanometers. 
     SUMMARY 
     The following presents a summary to provide a basic understanding of one or more embodiments of the disclosure. This summary is not intended to identify key or critical elements or delineate any scope of the particular embodiments or any scope of the claims. Its sole purpose is to present concepts in a simplified form as a prelude to the more detailed description that is presented later. 
     In one aspect, a semiconductor device and method of forming the same including a plurality of vertically aligned long channel semiconductor channel layers disposed above a substrate layer, a plurality of vertically aligned short channel semiconductor channel layers disposed above a substrate layer, and a plurality of tri-layer dielectric spacers disposed between the vertically aligned long channel semiconductor layers. 
     In one aspect, a method of forming a semiconductor device includes forming a stack of alternating long channel layers and sacrificial layers on a substrate layer, forming source and drain structures at ends of the long channel layers, etching away portions of the sacrificial layers exposing channel layer surfaces, leaving pillars of sacrificial material between long channel layers, and forming gate stacks on and around the channel layers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Through the more detailed description of some embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein the same reference generally refers to the same components in the embodiments of the present disclosure. 
         FIG. 1  provides a top view of a step in the fabrication of a semiconductor device, according to an embodiment of the invention. The figure illustrates the top view of a formed stack of alternating sacrificial and channel layers of short channel and long channel semiconductor field effect transistor devices disposed on a substrate. The figure includes section lines X 1 , Y 1 , X 2 , and X 22 , referred to in additional figures. 
         FIG. 2  provides a cross-sectional view along section line Y 1  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates etched stacks of alternating layers of sacrificial and channel layers and the addition of a shallow trench isolation layer to the short channel device. 
         FIG. 3  provides a cross-sectional view along section line X 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates etched stacks of alternating layers of sacrificial and channel layers and the addition of a shallow trench isolation layer to the long channel device. 
         FIG. 4  provides a cross-sectional view along section line Y 1  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a dummy gate and hard mask to the short channel devices. 
         FIG. 5  provides a cross-sectional view along section line X 2  of  FIG. 1  of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a dummy gate and hard mask to the long channel device. 
         FIG. 6  provides a cross-sectional view along section line Y 1  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the removal of a sacrificial layer from the short channel device. 
         FIG. 7  provides a cross-sectional view along section line X 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the removal of a sacrificial layer from the long channel device. 
         FIG. 8  provides a cross-sectional view along section line Y 1  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a bottom dielectric isolation layer to the short channel device. 
         FIG. 9  provides a cross-sectional view along section line X 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a bottom dielectric isolation layer and dielectric gate spacers to the long channel device. 
         FIG. 10  provides a cross-sectional view along section line X 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition source-drain regions, inter-layer dielectric, and inner spacers to the long channel device. 
         FIG. 11  provides a cross-sectional view along each of section lines Y 1  and Y 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a masking organic planarization layer to the long channel device and the removal of the sacrificial layers of the short channel device. 
         FIG. 12  provides a cross-sectional view along each of section lines X 1  and X 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a masking organic planarization layer to the long channel device and the removal of the sacrificial layers of the short channel device. 
         FIG. 13  provides a cross-sectional view along each of section lines Y 1  and Y 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a masking organic planarization layer to the short channel device and the removal of portions of the sacrificial layers of the long channel device. 
         FIG. 14  provides a cross-sectional view along each of section lines X 2  and X 22  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the removal of portions the sacrificial layers of the long channel device. 
         FIG. 15  provides a cross-sectional view along each of section lines Y 1  and Y 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a GeO 2  layer on and around the short channel and long channel devices. 
         FIG. 16  provides a cross-sectional view along each of section lines X 2  and X 22  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the addition of a GeO 2  layer on and around the short channel and long channel devices. 
         FIG. 17  provides a cross-sectional view along each of section lines Y 1  and Y 2  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the annealing of the central spacer pillars of the long channel device. 
         FIG. 18  provides a cross-sectional view along each of section lines X 2  and X 22  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the annealing of the central spacer pillars of the long channel device. 
         FIG. 19  provides a cross-sectional view along each of section lines X 2  and X 22  of  FIG. 1 , of a step in the fabrication of semiconductor devices, according to an embodiment of the invention. The figure illustrates the completion of the device gate stacks and the addition of source-drain and gate contacts. 
         FIG. 20  provides a flowchart depicting the steps of a semiconductor device fabrication method, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments will be described in more detail with reference to the accompanying drawings, in which the embodiments of the present disclosure have been illustrated. However, the present disclosure can be implemented in various manners, and thus should not be construed to be limited to the embodiments disclosed herein. 
     It is to be understood that aspects of the present invention will be described in terms of a given illustrative architecture; however, other architectures, structures, substrate materials, and process features, and steps can be varied within the scope of aspects of the present invention. 
     It will also be understood that when an element such as a layer, region or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     The present embodiments can include a design for an integrated circuit chip, which can be created in a graphical computer programming language and stored in a computer storage medium (such as a disk, tape, physical hard drive, or virtual hard drive such as in a storage access network). If the designer does not fabricate chips or the photolithographic masks used to fabricate chips, the designer can transmit the resulting design by physical means (e.g., by providing a copy of the storage medium storing the design) or electronically (e.g., through the Internet) to such entities, directly or indirectly. The stored design is then converted into the appropriate format (e.g., GDSII) for the fabrication of photolithographic masks, which typically include multiple copies of the chip design in question that are to be formed on a wafer. The photolithographic masks are utilized to define areas of the wafer (and/or the layers thereon) to be etched or otherwise processed. 
     Methods as described herein can be used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case, the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher-level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case, the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either: (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor. 
     It should also be understood that material compounds will be described in terms of listed elements, e.g., SiGe. These compounds include different proportions of the elements within the compound, e.g., SiGe includes SixGe1-x where x is less than or equal to 1, etc. In addition, other elements can be included in the compound and still function in accordance with the present principles. The compounds with additional elements will be referred to herein as alloys. 
     Reference in the specification to “one embodiment” or “an embodiment”, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment”, as well any other variations, appearing in various places throughout the specification are not necessarily all referring to the same embodiment. 
     It is to be appreciated that the use of any of the following “/”, “and/or”, and “at least one of”, for example, in the cases of “A/B”, “A and/or B” and “at least one of A and B”, is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of both options (A and B). As a further example, in the cases of “A, B, and/or C” and “at least one of A, B, and C”, such phrasing is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of the third listed option (C) only, or the selection of the first and the second listed options (A and B) only, or the selection of the first and third listed options (A and C) only, or the selection of the second and third listed options (B and C) only, or the selection of all three options (A and B and C). This can be extended, as readily apparent by one of ordinary skill in this and related arts, for as many items listed. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not tended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, can be used herein for ease of description to describe one element&#39;s or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the FIGS. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the FIGS. For example, if the device in the FIGS. is turned over, elements described as “below”, or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations and the spatially relative descriptors used herein can be interpreted accordingly. In addition, be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers cat also be present. 
     It will be understood that, although the terms first, second, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first element discussed below could be termed a second element without departing from the scope of the present concept. 
     The following description includes long channel gate-all-around (GAA) semiconductor devices having a plurality of long semiconductor channel layers aligned in a vertical stack. The channel layers are evenly separated. The stack also includes tri-layer spacers disposed between long channel layers. 
     Disposing the tri-layer spacers between the long channels reduces the occurrence of bending or sagging of the long channels during fabrication due to capillary and surface tension forces acting upon the long channels. 
     Reference is now made to the figures, in which identical reference numbers refer to the same or similar elements.  FIG. 1  provides a top view  100  of short  150  and long  160  channel devices at an early stage of the fabrication process. Section lines Y 1 , X 1 , Y 2 , X 2 , and X 22  relate to  FIGS. 2 through 19 . 
       FIG. 2  illustrates a cross-sectional view common to the short and long channel devices at an early stage in the method of forming the devices along section line Y 1  of  FIG. 1 .  FIG. 3  provides a cross-sectional view of the long channel device along section line X 1  of  FIG. 1 . The semiconductor structure of  FIGS. 2 and 3 , includes a semiconductor material stack of vertically aligned layers including a bottom sacrificial semiconductor layer  120 , alternating layers of a sacrificial semiconductor material layer  130  and a semiconductor channel material layer  140 , wherein the semiconductor material stack is located on a topmost surface of a semiconductor substrate  110 . 
     The semiconductor substrate  110  may include any semiconductor material including, for example, silicon. The term “semiconductor material” is used throughout the present application to denote a material that has semiconducting properties. Besides silicon, the semiconductor material may be strained Si, SiC (silicon carbide), Ge (germanium), SiGe (silicon germanium), SiGeC (silicon-germanium-carbon), Si alloys, Ge alloys, III-V semiconductor materials (e.g., GaAs (gallium arsenide), InAs (indium arsenide), InP (indium phosphide), or aluminum arsenide (AlAs)), II-VI materials (e.g., CaSe (cadmium selenide), CaS (cadmium sulfide), CaTe (cadmium telluride), ZnO (zinc oxide), ZnSe (zinc selenide), ZnS (zinc sulfide), or ZnTe (zinc telluride)), or any combination thereof. By “III-V semiconductor material” it is meant that the semiconductor material includes at least one element from Group IIIA (i.e., Group 13) of the Periodic Table of Elements and at least one element from Group VA (i.e., Group 15) of the Periodic Table of Elements. 
     The semiconductor material stack is then sequentially formed upon the semiconductor substrate  110 . As mentioned above, the semiconductor material stack includes a bottom most sacrificial semiconductor material layer  120  and alternating sacrificial semiconductor layers  130  and semiconductor channel material layer  140  one atop the other. In  FIGS. 2 and 3  and by way of one example, the semiconductor material stack includes one sacrificial semiconductor layer  120 , three sacrificial semiconductor material layers  130 , and three semiconductor channel material layers  140 . The semiconductor material stack that can be employed in the present application is not limited to the specific embodiment illustrated in  FIGS. 1 through 3 . Instead, the semiconductor material stack can include any number of sacrificial semiconductor material layers  130  and corresponding semiconductor channel material layers  140 , atop sacrificial semiconductor material layer  120 , so long as the semiconductor material stacks includes at least two sacrificial semiconductor material layers  130 , and two semiconductor channel material layers  140 . 
     Each sacrificial semiconductor material layer  120  and  130 , is composed of a first semiconductor material which differs in composition from at least an upper portion of the semiconductor substrate  110  and is resistant to Ge condensation. In one embodiment, the upper portion of the semiconductor substrate  110  is composed of silicon, while each sacrificial semiconductor material layers  120  and  130  is composed of a silicon germanium alloy. In such an embodiment, the SiGe alloy that provides each sacrificial semiconductor material layer  120  has a germanium content that is greater than 50 atomic percent germanium. In one example, the SiGe alloy that provides each sacrificial semiconductor material layer  120  has a germanium content from 50 atomic percent germanium to 70 atomic percent germanium. In such an embodiment, the SiGe alloy that provides each sacrificial semiconductor material layer  130  has a germanium content that is less than 50 atomic percent germanium. In one example, the SiGe alloy that provides each sacrificial semiconductor material layer  130  has a germanium content from 20 atomic percent germanium to 40 atomic percent germanium. The first semiconductor material that provides each sacrificial semiconductor material layers  120  and  130  can be formed utilizing an epitaxial growth (or deposition process) as defined in greater detail herein below. 
     Each semiconductor channel material layer  140 , is composed of a second semiconductor material that has a different etch rate than the first semiconductor material of the sacrificial semiconductor material layers  120  and  130  and is also resistant to Ge condensation. The second semiconductor material of each semiconductor channel material layer  140 , may be the same as, or different from, the semiconductor material of at least the upper portion of the semiconductor substrate  110 . The second semiconductor material can be a SiGe alloy provided that the SiGe alloy has a germanium content that is less than 50 atomic percent germanium, and that the first semiconductor material is different from the second semiconductor material. 
     In one example, at least the upper portion of the semiconductor substrate  110  and each semiconductor channel material layer  130  is composed of Si or a III-V compound semiconductor, while each sacrificial semiconductor material layer  120 ,  130  is composed of a silicon germanium alloy. The second semiconductor material of each semiconductor channel material layer  140 , can be formed utilizing an epitaxial growth (or deposition process) as defined in greater detail herein below. 
     The layers of channel material and sacrificial material  140 ,  130  and  120 , are formed on the substrate  110  by any appropriate deposition process. For example, the alternating layers may be formed by alternating deposition processes including, e.g., chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), or gas cluster ion beam (GCIB) deposition. CVD is a deposition process in which a deposited species is formed as a result of chemical reaction between gaseous reactants at greater than room temperature (e.g., from about 25° C. about 900° C.). The solid product of the reaction is deposited on the surface on which a film, coating, or layer of the solid product is to be formed. Variations of CVD processes include, but are not limited to, Atmospheric Pressure CVD (APCVD), Low Pressure CVD (LPCVD), Plasma Enhanced CVD (PECVD), and Metal-Organic CVD (MOCVD) and combinations thereof may also be employed. In alternative embodiments that use PVD, a sputtering apparatus may include direct-current diode systems, radio frequency sputtering, magnetron sputtering, or ionized metal plasma sputtering. In alternative embodiments that use ALD, chemical precursors react with the surface of a material one at a time to deposit a thin film on the surface. In alternative embodiments that use GCIB deposition, a high-pressure gas is allowed to expand in a vacuum, subsequently condensing into clusters. The clusters can be ionized and directed onto a surface, providing a highly anisotropic deposition. 
     Sacrificial semiconductor material layer  120 , may have a thickness from about 5 nanometers (nm) to about 15 nm, each nanosheet sacrificial semiconductor material layer  120 , may have a thickness from about 8 nm to about 12 nm, while each nanosheet semiconductor channel material layer  140 , may have a thickness from about 5 nm to about 15 nm. In an embodiment, each sacrificial semiconductor material layer  130  has an identical thickness, each semiconductor layer  140  has an identical thickness. The term “nanosheet” denotes a substantially two-dimensional structure with thickness in a scale ranging from 1 to 100 nm. The width and length dimensions of the nanosheet may be greater than the thickness dimensions. 
       FIG. 2  also illustrates shallow trench isolation (STI) regions  210  adjacent to the stacks of sacrificial semiconductor material layers  120 ,  130 , and semiconductor channel material layers  140  of the long and short channel devices. The STI regions  210  can be formed by, any suitable process including, for example, lithography or etching to form trenches, and then filling the trenches with an insulating material, such as silicon dioxide. Following the deposition of the STI material, an additional etching process can be performed to remove portions of the STI material and expose the stacks of layers  120 ,  130 , and  140 . The stacks of sacrificial semiconductor material layers  120 ,  130 , and semiconductor channel material layers  140 , are formed by, for example, a photolithographic patterning and etching process that removes exposed portions of the sacrificial semiconductor material layers  120 ,  130 , and semiconductor channel material layers  140 , to form the stacks of layers. This etching can be performed using a timed anisotropic etch such as reactive ion etching (RIE). The etch can be performed in a single etch that removes material from both the channel layers  140 , and the sacrificial layers  120 ,  130  or may, alternatively, be performed using alternating etching processes that selectively affect the channel layers  140 , and the sacrificial layers  120 ,  130 , in turn. As used herein, the term “selective” in reference to a material removal process denotes that the rate of material removal for a first material is greater than the rate of removal for at least another material of the structure to which the material removal process is being applied. 
     Reference is now made to  FIGS. 4 and 5 , illustrating a step in the formation of the semiconductor devices of an embodiment of the invention.  FIG. 4  provides a cross-sectional view along line Y 1  of  FIG. 1 , and common to both the long  160  and short  150  channel devices at this stage.  FIG. 5  provides a cross-sectional view along line X 2  of  FIG. 1 , illustrating the long channel device  160  at this stage.  FIGS. 5 and 6  illustrate stacks of vertically aligned nanosheet sacrificial semiconductor material layers  120 ,  130 , and semiconductor channel material layers  140 . As shown in the figures, portions of the stacks are covered and protected by a dummy gate structure  405  and hard mask layer  410 . Dummy gate  405  In one embodiment, dummy gate  405  is composed of silicon nitride, deposited using, for example, low pressure chemical vapor deposition (LPCVD). Other materials of which dummy gate  405  may be formed include, but are not limited to, silicon oxide, silicon oxide doped with carbon, titanium oxide, hafnium oxide, any other insulative material. In a preferred embodiment, dummy gate  405  is between 20 nm and 200 nm thick and is preferably about 70 nm thick. A person of ordinary skill in the art will recognize that chemical-mechanical-planarization (CMP) steps may be inserted before and after the deposition of dummy gate  405  and hard mask  410  to ensure that the top surface of dummy gate  405  and hard mask  410  are relatively flat. The process of patterning dummy gate  405  to define the desired shape of the nanosheet stacks to be created involves the use of standard photolithographic processes to define the desired shape in a layer of photoresist (not shown) deposited on the material of which dummy gate  405  is formed. In various embodiments, standard photolithographic processes are used to remove a portion of the photoresist layer corresponding to the area of the material of which dummy gate  405  is formed which is to be etched during the formation of dummy gate  405 . The pattern of dummy gate  405  defined in the photoresist layer is formed into dummy gate  405  by removing dummy gate  405  from the areas not protected by the pattern in the photoresist layer. The portion of the material of which dummy gate  405  is formed is removed using, for example, RIE. A person of ordinary skill in the art will recognize that the type of plasma used in the RIE process will depend on the material of which dummy gate  405  is composed, or that other etch processes, e.g., wet chemical etch, laser ablation, etc., may be used. 
     The hard mask  410  may be formed of a nitride, oxide, an oxide-nitride bilayer, or another suitable material. In some embodiments, the hard mask  410  may comprise an oxide such as silicon oxide (SiO), a nitride such as silicon nitride (SiN), an oxynitride such as silicon oxynitride (SiON), combinations thereof, etc. In some embodiments, the hard mask  410  is a silicon nitride such as Si 3 N 4 . The width or horizontal thickness (in direction X-X′) of the hard mask  410  matches that of the underlying dummy gate  405 . The hard mask  410  may have a height or vertical thickness in a Z or surface normal direction ranging from 10 nanometers (nm) to 50 nm. 
     Subsequent to the formation of dummy gate  405  and hard mask  410 , sacrificial semiconductor layer  120  is removed as illustrated in  FIGS. 6, and 7  along  FIG. 1  section lines Y 1  and X 2  respectively. In an embodiment, sacrificial semiconductor material layers  120  are etched away using an isotropic etch, such as a wet or dry chemical etch selective to the sacrificial semiconductor material. The removal of sacrificial semiconductor material layers  120  leave gaps between the substrate  110  and the lowest sacrificial semiconductor material layer  130  for each of the long and short channel devices. 
     Reference is now made to  FIGS. 8 and 9 , illustrating a step in the formation of the semiconductor devices of an embodiment of the invention. As shown in the figures, a dielectric isolation layer  910  has been disposed upon the short and long channel devices. In an embodiment, dielectric isolation layer  910  comprises silicon dioxide or another dielectric material disposed around and upon the short and long channel devices as described above. The dielectric layer  910  forms a bottom dielectric isolation layer isolating the nanosheet stacks from the substrate and also forms gate spaces adjacent to the dummy gate  405 , and portions of hard mask  410 . 
     Reference is now made to  FIG. 10 , illustrating a step in the formation of the semiconductor devices of an embodiment of the invention. As shown in  FIG. 10 , inner spacers  1010  have been formed between adjacent pairs of nanosheet semiconductor channel layers  140 . Prior to the formation of the inner spacers  1010 , portions of the nanosheet stacks of sacrificial  130 , and channel  140  layers are removed. The portions of the stacks of sacrificial semiconductor material layers  130 , and semiconductor channel material layers  140 , are removed by, for example, an etching process that removes horizontal exposed portions of the dielectric material  910 , sacrificial semiconductor material layers  130 , and semiconductor channel material layers  140 , to form the stacks of layers. This etching can be performed using a timed anisotropic etch such as reactive ion etching (RIE). The etch can be performed in a single etch that removes material from dielectric layer  910 , channel layers  140 , and the sacrificial layers  130  or may, alternatively, be performed using etching processes that selectively affect the dielectric layer  910 , channel layers  140 , and the sacrificial layers  130 , in turn. 
     In an embodiment, after removal of the nanosheet stacks in preparation for the inner spacers, portions of the sacrificial semiconductor layers  130  are etched away leaving gaps between the semiconductor channel layers  140 . In an embodiment, a layer of nitride dielectric or similar material, is deposited on the short and long channel devices after the spacer etching is completed. This layer fills the gaps and coats the devices. The coating of the dielectric is then removed by an ashing process. Ashing can be performed using a plasma etch with a suitable reaction gas, for example, O2, N2, H2/N2, O3, CF4, or any combination thereof. The ashing process leaves the inter-channel layer  140  gaps, filled with the dielectric material inner spacers  1010 . 
     As shown in  FIG. 10 , source and drain regions  1020  have been epitaxially grown adjacent to the sidewalls of layers  130  and  140  and the bottom dielectric isolation layer. After growth, the source-drain regions  1020  may be trimmed to an appropriate shape and size. Source-drain regions  1020  are grown after the formation of the inner spacers  1010 . 
     The terms “epitaxially growing and/or depositing” and “epitaxially grown and/or deposited” mean the growth of a semiconductor material on a deposition surface of a semiconductor material, in which the semiconductor material being grown has the same crystalline characteristics as the semiconductor material of the deposition surface. In an epitaxial deposition process, the chemical reactants provided by the source gases are controlled and the system parameters are set so that the depositing atoms arrive at the deposition surface of the semiconductor substrate with sufficient energy to move around on the surface and orient themselves to the crystal arrangement of the atoms of the deposition surface. Therefore, an epitaxial semiconductor material has the same crystalline characteristics as the deposition surface on which it is formed. 
     In the present embodiments, the source-drain regions  1020  may be doped in situ by adding one or more dopant species to the epitaxial material. The dopant used will depend on the type of FET being formed, whether p-type or n-type. As used herein, “p-type” refers to the addition of impurities to an intrinsic semiconductor that creates deficiencies of valence electrons. In a silicon-containing semiconductor, examples of p-type dopants, i.e., impurities, include but are not limited to: boron, aluminum, gallium and indium. As used herein, “n-type” refers to the addition of impurities that contributes free electrons to an intrinsic semiconductor. In a silicon containing substrate, examples of n-type dopants, i.e., impurities, include but are not limited to antimony, arsenic and phosphorous. 
     In an embodiment, after the source-drain regions  1020  have been grown, isolation layer dielectric (ILD)  1030 , are deposited adjacent to the source-drain regions  1020  and the gate spacer dielectric  910 . ILD  1030  are deposited as described above. 
     Reference is now made to  FIGS. 11 and 12 , illustrating a step in the formation of the semiconductor devices of an embodiment of the invention.  FIG. 11  is a view of short channel device  150  along section line Y 1  of  FIG. 1 , and also a view of long channel device  160  along section line Y 2  of  FIG. 1 .  FIG. 12  is a view of short channel device  150  along section line X 1  of  FIG. 1 , and also a view of long channel device  160  along section line X 2  of  FIG. 1 . Dummy gate  405  has been removed by etching as described above. A photoresist layer of organic planarization material (OPL)  1110  is deposited upon the long channel device  160  using a photolithographic process and masks long channel device  160 . After the deposition of the OPL, the sacrificial semiconductor layers  130  of the short channel device  150 , are etched away as illustrated in  FIGS. 11 and 12 . 
     In an embodiment, sacrificial semiconductor material layers  130  are etched away using an isotropic etch, such as a wet or dry chemical etch selective to the sacrificial semiconductor material. The removal of sacrificial semiconductor material layers  130  leave gaps between the bottom dielectric isolation layer  910  and the lowest semiconductor channel material layer  140 , as well as gaps between adjacent semiconductor material layers  130 . 
     Reference is now made to  FIGS. 13 and 14 , illustrating a step in the formation of the semiconductor devices of an embodiment of the invention.  FIG. 13  is a view of short channel device  150  along section line Y 1  of  FIG. 1 , and also a view of long channel device  160  along section line Y 2  of  FIG. 1 .  FIG. 14  is a view of long channel device  160  along section lines X 2  and X 22  of  FIG. 1 . As shown in the figures, OPL  1110  has been removed from long channel device  160 . In an embodiment, the OPL  1110  is removed using an ashing process as described above. A short channel device OPL  1310 , is then formed to mask the short channel device  150 . As shown in the figures, after masking short channel device  150 , portions of the sacrificial semiconductor material layers  130 , of long channel device  160 , are etched away. In an embodiment illustrated in  FIGS. 13 and 14 , the central portion of the sacrificial semiconductor layers  130  of the long channel device  160  are preserved between the channel layers  140  and between the bottom dielectric layer  910  and the lower most channel layer  140 . 
     Reference is now made to  FIGS. 15 and 16 , illustrating a step in the formation of the semiconductor devices of an embodiment of the invention.  FIG. 15  is a view of short channel device  150  along section line Y 1  of  FIG. 1 , and also a view of long channel device  160  along section line Y 2  of  FIG. 1 .  FIG. 16  is a view of long channel device  160  along each of section lines X 2  and X 22  of  FIG. 1 . Short channel device  150  OPL mask  1310  has been removed using an ashing process. A deposition process, as described above, applies a layer  1510  of GeO 2  or similar material on and around the surfaces of the short  150  and long  160  channel devices. 
     Reference is now made to  FIGS. 17 and 18 , illustrating a step in the formation of the semiconductor devices of an embodiment of the invention.  FIG. 15  is a view of short channel device  150  along section line Y 1  of  FIG. 1 , and also a view of long channel device  160  along section line Y 2  of  FIG. 1 .  FIG. 18  is a view of long channel device  160  along section lines X 2  and X 22  of  FIG. 1 . As shown in the figures, a two-stage process, first a low temperature (about 600 C) for 30 seconds in a Nitrogen atmosphere selectively oxidizes the outer portions of the sacrificial semiconductor material (SiGe) pillars into SiO 2 ,  1710  and leaves the core of the pillar of material with a higher Ge content. The second stage, 550 C for SS seconds in an Oxygen atmosphere, yields a pillar core of SiGeO x  material  1720 . After the two-stage process has completed, the remaining GeO 2  material  1510  is washed away. 
     Reference is now made to  FIG. 19 , illustrating a step in the formation of the semiconductor devices of an embodiment of the invention.  FIG. 19  is a view of long channel device  160  along section lines X 2  and X 22  of  FIG. 1 . As shown in the figure, gate formation is complete with the addition of a high-k dielectric layer  1910  and work function metal layer  1920 , to the semiconductor devices  150  and  160 . In an embodiment, work function metal layer  1920  is disposed using ALD as described above. 
     As used herein, “high-k” denotes a dielectric material featuring a dielectric constant (k) higher than the dielectric constant of silicon dioxide. The high-k gate dielectric layer  510 , can include at least one metallic element. Some examples of high-k dielectric materials suitable for the gate dielectric layer  510  include hafnium oxide, hafnium silicon oxide, hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide, zirconium silicon oxynitride, tantalum oxide, titanium oxide, barium strontium titanium oxide, barium titanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, lead zinc niobate and combinations thereof. In an embodiment, the gate dielectric layer  510  is disposed using a deposition method as described above. In one embodiment, the gate dielectric layer  510  has a thickness that ranges from about 1 nm to about 3 nm. In another embodiment, the gate dielectric layer  510  has a thickness that ranges from about 1.5 nm to about 2 nm. 
     Work function layer  1920  may comprise metals, such as tungsten, nickel, titanium, molybdenum, tantalum, copper, platinum, silver, gold, ruthenium, iridium, rhenium, and rhodium and alloys thereof including titanium aluminum and titanium nitride alloys, and doped semiconductor materials such as, e.g., doped polysilicon. In an embodiment, work function metal layer  1920  comprises multiple layers of different metals. 
     As shown in the figure, a layer of passivating dielectric  1930  (or inter-layer dielectric) is deposited over the device structure. It is specifically contemplated that the passivating dielectric  1930  may be, e.g., silicon dioxide, but any other appropriate dielectric material may be used instead. Openings in the passivating dielectric  1930  are formed using, for example, any appropriate anisotropic etch. Gate contacts  1940  and source-drain contacts  1950  are then formed in the openings to provide electrical connectivity to the gate work function metal  1920  and to the source-drain regions  1020 . 
     Reference is now made to  FIG. 20 , a flowchart depicting steps of a method of concurrently forming long channel and short channel semiconductor devices on a single die, according to an embodiment of the invention. As shown in the figure, at  2010 , the method deposits material and forms a stack of vertically aligned, alternating sacrificial and channel nanosheet layers formed on a base substrate. The stack begins with a first sacrificial layer having a first concentration of Germanium. This first layer is followed by alternating layers of sacrificial layers and channel material layers. These sacrificial layers are of uniform thickness and have a Germanium content which differs from that of the first sacrificial layer. Portions of the stacks are removed yielding vertically aligned stacks of nanosheets separated by shallow trench isolation dielectric regions. At  2020 , in an embodiment, the method deposits a dummy gate and a hard mask, providing protection for portions of the vertically aligned stacks of layers. The dummy gate and hard mask are patterned to match the shape of the final gate areas of the semiconductor device design. At  2030 , the method removes the bottom sacrificial layers of the short and long channel devices and deposits a bottom dielectric isolation layer between the base substrate and the next sacrificial layer. Dielectric material is also deposited along the sidewalls of the dummy gate during this process. In an embodiment, the sacrificial layer is removed by selective etching. At  2040 , portions of the dielectric material, the remaining sacrificial layers, and the channel layers are etched away. After the initial removal, edge portions of the remaining sacrificial layers are removed and replaced with inner spacer dielectric material. The dielectric material is deposited as a coating on the devices. The majority of the coating is removed by an ashing process, leaving only the inner spacer dielectric portions between the channel layers. After formation of the inner spacers, source-drain regions are epitaxially grown adjacent to the nanosheet stacks, the inner spacers, and upon the bottom dielectric isolation layer. At block  2050 , the long channel device is masked using an organic planarization material layer and the sacrificial spacer layers of the short channel device are etched away. At block  2060 , the long channel device OPL layer is removed by ashing, the short channel device is masked with an OPL layer and portions of the long channel sacrificial spacer layers are etched away, leaving a central pillar of sacrificial semiconductor material between the adjacent channel layers. At  2070 , the short channel OPL is washed away and a coating of GeO 2 , or similar material, is deposited upon and around the device elements. The devices are subjected to a two-stage annealing process which converts the central pillars of sacrificial material to tri-layer spacers. In an embodiment, the spacers have outer layers of SiO 2 , and an inner layer of SiGeO x . The remaining GeO 2  coating is washed off the devices. At block  2080 , the devices are completed with gate stacks including an interface high-k dielectric and a work function metal layer. A layer of passivating dielectric is added to the devices, contact regions are etched in the dielectric material and gate and source-drain contacts are disposed in the contact regions.