A semiconductor structure in which a power rail is located below the active gate

Abstract

A semiconductor structure is disclosed that includes a semiconductor device having a buried power rail. In one example, the semiconductor structure includes a plurality of semiconductor devices. Each of the semiconductor devices is insulated from an adjacent semiconductor device by a dielectric layer. The semiconductor structure further includes a first diffusion isolation extending across the plurality of semiconductor devices, a second diffusion isolation extending across the plurality of semiconductor devices, and a plurality of gates extending across the plurality of semiconductor devices. The gates are disposed between the first diffusion isolation and the second diffusion isolation. Each semiconductor device includes a power rail extending between the first diffusion isolation and the second diffusion isolation beneath the plurality of gates.

Description

[Technical Field]

[0001] The present invention relates generally to the field of semiconductor devices, and more particularly to semiconductor devices that include power rails. [Background technology]

[0002] Continued innovations in semiconductor process technology are enabling higher integration densities and device scaling. As the semiconductor industry advances toward and beyond the 7 nm technology node, semiconductor FET device structures must be scaled to smaller dimensions to increase device width per footprint. In this regard, non-planar FET devices, such as nanosheet FET devices, nanowire FET devices, vertical FET devices, and FinFET devices, have become viable options for continued CMOS scaling. Generally, nanowire FET devices include a device channel comprising one or more nanowire layers in a stacked configuration, with each nanowire comprising an elongated semiconductor layer having a width substantially equal to or slightly greater than the thickness of the elongated semiconductor layer. Nanosheet FET devices are similar to nanowire FET device sheets in that the device channel comprises one or more nanosheet layers in a stacked configuration, but each nanosheet layer has a width significantly greater than the nanosheet layer thickness. In nanowire / nanosheet FET devices, common gate structures are formed above and below each nanowire / nanosheet layer in a stacked configuration, thereby increasing the width (or channel width) of the FET device and therefore the drive current for a given footprint. Summary of the Invention

[0003] Disclosed embodiments include semiconductor structures that include buried power rails (BPRs) and techniques for fabricating semiconductor structures that include BPRs.

[0004] For example, one embodiment includes a semiconductor structure including a gate, a first source / drain region, a second source / drain region, and a power rail disposed below the gate, the first source / drain region, and the second source / drain region, the power rail being in electrical contact with the first source / drain region.

[0005] Another embodiment includes a semiconductor structure including a first active gate and a diffusion break. The diffusion break includes an isolation region configured to electrically isolate the first active gate from at least a second active gate. The semiconductor structure further includes a power rail disposed below the first active gate and extending to the diffusion break. The diffusion break includes a contact electrically coupled to the power rail.

[0006] Another embodiment includes a semiconductor structure including a semiconductor substrate, a first dielectric layer disposed on the semiconductor substrate, a power rail disposed on the first dielectric layer, a second dielectric layer disposed on the power rail, and a gate extending from the second dielectric layer.

[0007] Another embodiment includes a semiconductor structure including a plurality of semiconductor devices, each of which is insulated from an adjacent semiconductor device by a dielectric layer. The semiconductor structure further includes a first diffusion isolation extending across the plurality of semiconductor devices, a second diffusion isolation extending across the plurality of semiconductor devices, and a plurality of gates extending across the plurality of semiconductor devices. The gates are disposed between the first diffusion isolation and the second diffusion isolation. Each semiconductor device includes a power rail extending between the first diffusion isolation and the second diffusion isolation beneath the plurality of gates.

[0008] Another embodiment includes a method for fabricating a semiconductor structure, including forming a stack structure on a semiconductor substrate. The stack structure includes a first sacrificial layer, a second sacrificial layer, a third sacrificial layer disposed between the first and second sacrificial layers, multiple additional sacrificial layers, and multiple channel layers. The method further includes forming multiple gate structures on the stack structure and replacing the first and second sacrificial layers with a dielectric material to form corresponding first and second dielectric layers. The dielectric material also forms sidewalls on the gate structures. The method further includes etching the multiple additional sacrificial layers, the multiple channel layers, and the second dielectric layer between a first gate structure and a second gate structure of the multiple gate structures to expose the third sacrificial layer through the second dielectric layer, and forming source / drain regions between the first gate structure and the second gate structure in contact with the third sacrificial layer. The method further includes opening a particular gate structure of the plurality of gate structures to expose a third sacrificial layer, and replacing the third sacrificial layer with a power rail, the power rail contacting the source / drain region.

[0009] Other embodiments are described in the following detailed description of embodiments, which should be read in conjunction with the accompanying figures. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic top view of a semiconductor structure according to an embodiment of the present invention. [Figure 2] 2 is a schematic top view of a portion of the semiconductor structure of FIG. 1, in accordance with an embodiment of the present invention. [Figure 3] 3A and 3B are schematic cross-sectional side views of the semiconductor structure of FIG. 2 at intermediate stages of fabrication, taken along section lines AA and BB, respectively, of FIG. 2, in accordance with an embodiment of the present invention. [Figure 4] 3A and 3B are cross-sectional views of the semiconductor structure of FIGS. 3A and 3B at intermediate stages of fabrication after etching has been performed to form semiconductor regions, according to an embodiment of the present invention. [Figure 5]4A and 4B are cross-sectional views of the semiconductor structure of FIGS. 4A and 4B at intermediate stages of fabrication after the formation of a shallow trench isolation (STI) layer, according to an embodiment of the present invention. [Figure 6] 5A and 5B are cross-sectional views of the semiconductor structure of FIGS. 5A and 5B at intermediate stages of fabrication after formation of a gate structure, according to an embodiment of the present invention. [Figure 7] 6(A) and 6(B) are cross-sectional views of the semiconductor structure of FIG. 6(A) and FIG. 6(B) at intermediate stages of fabrication after removal of a sacrificial nanosheet layer, according to an embodiment of the present invention. [Figure 8] 7A and 7B are cross-sectional views of the semiconductor structure of FIGS. 7A and 7B at intermediate stages of fabrication after the formation of a dielectric layer, according to an embodiment of the present invention. [Figure 9] (A) and (B) are cross-sectional views of the semiconductor structure of Figures 8(A) and 8(B) at intermediate stages of fabrication after etching of exposed layers of the nanosheet stack structure, including a portion of the sacrificial nanosheet layer and a portion of the nanosheet channel layer, according to an embodiment of the present invention. [Figure 10] 9(A) and 9(B) are cross-sectional views of the semiconductor structure of FIG. 9(A) and FIG. 9(B) at intermediate stages of fabrication after etching of exposed portions of the sacrificial nanosheet layer and formation of internal spacers according to an embodiment of the present invention. [Figure 11] 10(A) and 10(B) are cross-sectional views of the semiconductor structure of FIG. 10(A) and FIG. 10(B) at intermediate stages of fabrication after forming and patterning an etching mask and etching channels through the dielectric layer 800 to expose the sacrificial nanosheet layer, according to an embodiment of the present invention. [Figure 12] 11(A) and 11(B) are cross-sectional views of the semiconductor structure of FIG. 11(A) and FIG. 11(B) at intermediate stages of fabrication after formation of source / drain regions on the exposed portions of the sacrificial nanosheet layer and the exposed portions of the dielectric layer, according to an embodiment of the present invention. [Figure 13] 12(A) and 12(B) are cross-sectional views of the semiconductor structure of FIGS. 12(A) and 12(B) at intermediate stages of fabrication after formation of an interlevel dielectric, according to an embodiment of the present invention. [Figure 14] 13A and 13B are cross-sectional views of the semiconductor structure of FIGS. 13A and 13B at intermediate stages of fabrication after formation of a sacrificial cap and an etch mask on a gate structure corresponding to single diffusion breaks (SDBs), in accordance with an embodiment of the present invention. [Figure 15] 14(A) and 14(B) are cross-sectional views of the semiconductor structure of FIG. 14(A) and FIG. 14(B) at intermediate stages of fabrication after removal of the dummy gate electrode and sacrificial nanosheet layer of the gate structure, according to an embodiment of the present invention. [Figure 16] 15(A) and 15(B) are cross-sectional views of the semiconductor structure of FIG. 15(A) and FIG. 15(B) at intermediate stages of fabrication after formation of a gate conductor layer in a gate structure and removal of a sacrificial cap, according to an embodiment of the present invention. [Figure 17] 16(A) and 16(B) are cross-sectional views of the semiconductor structure of FIG. 16(A) and FIG. 16(B) at intermediate stages of fabrication after opening the gate structure down to the sacrificial nanosheet layer and removing the sacrificial nanosheet layer, according to an embodiment of the present invention. [Figure 18] 17(A) and 17(B) are cross-sectional views of the semiconductor structure of FIG. 17(A) and FIG. 17(B) at intermediate stages of fabrication after formation of a BPR in an opened gate structure and a BPR in a channel exposed by removal of a sacrificial nanosheet layer, according to an embodiment of the present invention. [Figure 19] 18(A) and 18(B) are cross-sectional views of the semiconductor structure of FIGS. 18(A) and 18(B) at intermediate stages of fabrication after the gate conductor layer and BPR in the gate structure have been recessed, according to an embodiment of the present invention. [Figure 20]19(A) and 19(B) are cross-sectional views of the semiconductor structure of FIGS. 19(A) and 19(B) at intermediate stages of fabrication after an etching mask exposing the gate structure has been formed and the BPR has been etched down to the height of a portion of the dielectric layer to open the gate structure, according to an embodiment of the present invention. [Figure 21] 19(A) and 19(B) are cross-sectional views of the semiconductor structure of FIG. 2 at an intermediate stage of fabrication after an etch mask has been formed to expose the gate structure and the BPR has been etched down to the level of a portion of the dielectric layer to open the gate structure, in accordance with an embodiment of the present invention. The views are taken along section line CC in FIG. [Figure 22] 19(A) and 19(B) are cross-sectional views of the semiconductor structure of FIG. 2 at an intermediate stage of fabrication after an etch mask has been formed to expose the gate structure and the BPR has been etched down to the level of a portion of the dielectric layer to open the gate structure, in accordance with an embodiment of the present invention. [Figure 23] 20(A) and 20(B) are cross-sectional views of the semiconductor structure of FIG. 20(A) and FIG. 20(B) at intermediate stages of fabrication after forming an etching mask and performing gate cuts to separate the BPR between n-type and p-type semiconductor devices, according to an embodiment of the present invention. [Figure 24] 22 is a cross-sectional view of the semiconductor structure of FIG. 21 at an intermediate stage of fabrication after forming an etch mask and performing a gate cut to separate the BPR between n-type and p-type semiconductor devices in accordance with an embodiment of the present invention. [Figure 25] 23 is a cross-sectional view of the semiconductor structure of FIG. 22 at an intermediate stage of fabrication after forming an etch mask and performing a gate cut to separate the BPR between n-type and p-type semiconductor devices, in accordance with an embodiment of the present invention. [Figure 26] 2A and 2B are cross-sectional views of the semiconductor structure of FIGS. 23A and 23B at intermediate stages of fabrication after removal of the etching mask and formation of an ILD layer in exposed portions of the gate structure and between pillars of the BPR to electrically isolate the pillars from each other, according to an embodiment of the present invention. [Figure 27] 25 is a cross-sectional view of the semiconductor structure of FIG. 24 at an intermediate stage of fabrication after removal of the etch mask and formation of an ILD layer in exposed portions of the gate structure and between pillars of the BPR to electrically isolate the pillars from each other, in accordance with an embodiment of the present invention. [Figure 28] 26 is a cross-sectional view of the semiconductor structure of FIG. 25 at an intermediate stage of fabrication after removal of the etch mask and formation of an ILD layer in exposed portions of the gate structure and between pillars of the BPR to electrically isolate the pillars from each other, in accordance with an embodiment of the present invention. [Figure 29] 26(A) and 26(B) are cross-sectional views of the semiconductor structure of FIG. 26(A) and FIG. 26(B) at intermediate stages of fabrication after formation of gate contacts to source / drain regions electrically isolated from the BPR of the corresponding semiconductor device and formation of top contacts, according to an embodiment of the present invention. [Figure 30] 28 is a cross-sectional view of the semiconductor structure of FIG. 27 at an intermediate stage of fabrication after formation of a gate contact to a source / drain region electrically isolated from a BPR of a corresponding semiconductor device and formation of a top contact, according to an embodiment of the present invention. [Figure 31] 29 is a cross-sectional view of the semiconductor structure of FIG. 28 at an intermediate stage of fabrication after formation of a gate contact to a source / drain region electrically isolated from a BPR of a corresponding semiconductor device and formation of a top contact, according to an embodiment of the present invention. [Figure 32] 2 is a schematic top view of a semiconductor structure according to another embodiment of the present invention. [Figure 33] 33 is a schematic top view of a portion of the semiconductor structure of FIG. 32, in accordance with an embodiment of the present invention. [Figure 34] 34(A) and 34(B) are cross-sectional views of the semiconductor structure of FIG. 33 at intermediate stages of fabrication similar to those seen in FIG. 29(A) and FIG. 29(B), in accordance with an embodiment of the present invention. FIG. 34(A) is a view along section line A'-A' in FIG. 33, and FIG. 34(B) is a view along section line B'-B' in FIG. [Figure 35]34 is a cross-sectional view of the semiconductor structure of FIG. 33 at an intermediate stage of fabrication similar to that seen in FIG. 30, in accordance with an embodiment of the present invention. [Figure 36] 34 is a cross-sectional view of the semiconductor structure of FIG. 33 at an intermediate stage of fabrication similar to that seen in FIG. 31, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the following, embodiments of the present invention are described in further detail: Devices and methods are provided for fabricating nanosheet field effect transistor devices that utilize diffusion break contacts and include buried power rails beneath the active device.

[0012] It should be understood that the various layers, structures, and regions illustrated in the accompanying drawings are schematic representations that are not drawn to scale. Additionally, for simplicity of explanation, one or more layers, structures, and regions of a type commonly used in forming semiconductor devices or semiconductor structures may not be explicitly shown in a particular drawing. This does not mean that any layers, structures, and regions not explicitly shown are omitted from an actual semiconductor device structure. Furthermore, it should be understood that the embodiments described herein are not limited to the specific materials, features, and processing steps shown and described herein. In particular, with respect to semiconductor processing steps, it should be emphasized that the descriptions provided herein are not intended to encompass all of the processing steps that may be required to form a functional semiconductor integrated circuit device. Rather, certain processing steps commonly used in forming semiconductor devices, such as, for example, wet cleaning steps and annealing steps, are intentionally not described herein for the sake of brevity.

[0013] Furthermore, the same or similar reference numbers are used throughout the drawings to indicate the same or similar features, elements, or structures, and therefore, detailed descriptions of the same or similar features, elements, or structures will not be repeated in each of the drawings. It should be understood that the terms "about" or "substantially," when used herein with respect to thickness, width, proportion, range, etc., are intended to indicate closeness or approximation rather than precision. For example, the terms "about" or "substantially," when used herein, mean that there is a small range of error, such as less than 1% of the stated amount.

[0014] XYZ Cartesian coordinates are shown in each of the figures to provide spatial context for the orientation of the different structures of the semiconductor device structures shown throughout the figures. The terms "vertical" or "vertical" or "vertical height" as used herein refer to the Z direction of the Cartesian coordinates shown in the figures, and the terms "horizontal" or "horizontal" or "lateral" as used herein refer to the X and / or Y directions of the Cartesian coordinates shown in the figures.

[0015] FIG. 1 is a schematic top view (XY plane) of a semiconductor integrated circuit structure 100, also referred to herein as semiconductor structure 100, according to a first embodiment. For clarity, some elements of semiconductor structure 100 are not shown in FIG. 1. Semiconductor structure 100 includes a group of active gates 102 separated by single diffusion isolations (SDBs) 104, each of which includes an inactive gate. As described and illustrated in further detail below with reference to FIGS. 2-31 , power is supplied to the source / drain regions associated with the active gates 102 through either top-down contacts 106 or bottom-up contacts 108. The bottom-up contacts 108 are electrically connected to buried power rails (BPRs) 110 disposed below the source / drain regions. For example, in some embodiments, the source / drain regions on one side of the active gate 102 are connected to the top-down contacts 106, while the source / drain regions on the other side of the active gate 102 are connected to the BPR 110 via the bottom-up contacts 108. Although described with reference to top-down and bottom-up contacts, the semiconductor structure 100 may be formed using contacts in any orientation. The use of both the top-down contacts 106 and the bottom-up contacts 108 reduces tip-to-tip spacing, thereby reducing the occurrence of shorts and allowing for improved source / drain density.

[0016] 2 is a schematic top view (XY plane) of portion 112 of semiconductor structure 100 and is utilized to further illustrate features of semiconductor structure 100. As shown in FIG. 2, semiconductor structure 100 includes semiconductor regions 200-1, 200-2, 200-3, and 200-4 (collectively and individually referred to as semiconductor regions 200) across which SDBs 202-1 and 202-2 (collectively and individually referred to as SDBs 202) and active gates 204-1, 204-2, 204-3, and 204-4 (collectively and individually referred to as active gates 204) are formed. Each semiconductor region 200-1, 200-2, 200-3, and 200-4 includes a corresponding BPR 110-1, 110-2, 110-3, and 110-4 (collectively and individually referred to as BPR 110).

[0017] Although shown as including four semiconductor regions 200 with four active gates 204 between two SDBs 202, any number of semiconductor regions 200, SDBs 202, and active gates 204 may be included, with any number of active gates 204 disposed between each pair of SDBs 202. In some embodiments, for example, semiconductor regions 200 may be formed as nFET or pFET devices. In some embodiments, semiconductor regions 200-1 and 200-4 may include pFET devices, while semiconductor regions 200-2 and 200-3 may include nFET devices. In other embodiments, semiconductor regions 200 may alternate between nFET and pFET devices, for example, semiconductor regions 200-1 and 200-3 may include pFET devices, while semiconductor regions 200-2 and 200-4 include nFET devices, or vice versa.

[0018] For each semiconductor region 200, power is supplied to the BPR 110 through one or more corresponding top-down contacts 206 or 208 in the SDB 202. For example, the top-down contact 206 may be set to a first voltage, while the top-down contact 208 may be set to a second voltage different from the first voltage. The top-down contact 206 supplies power to the BPR 110 in semiconductor regions 200-1 and 200-4, while the top-down contact 208 supplies power to the BPR 110 in semiconductor regions 200-2 and 200-3. The use of the top-down contacts 206 and 208 in the SDB 202 to supply power to the BPR 110 enables reduced N-to-P spacing because the BPR 110 is self-aligned with the semiconductor device and formed under the active gate instead of in a shallow trench isolation (STI) layer. FIG. 2 also defines cross sections AA, BB, CC, and DD that are utilized in FIGS.

[0019] 3(A)-31 schematically illustrate an exemplary method for fabricating a semiconductor structure 100, according to an exemplary embodiment.

[0020] 3(A) and 3(B) are cross-sectional views of a semiconductor structure 100 at intermediate stages of fabrication. FIG. 3(A) is a schematic side view (YZ plane) of the semiconductor structure 100 taken along section line AA in FIG. 2, and FIG. 3(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 taken along section line BB in FIG. 2. As shown in FIGS. 3(A) and 3(B), the semiconductor structure 100 includes a semiconductor substrate 300 and a nanosheet stack structure formed on the semiconductor substrate 300. The nanosheet stack structure includes a stack of semiconductor layers 302-1, 302-2, 304-1, 304-2, 304-3, 304-4, 306-1, 306-2, and 306-3. In some embodiments, the semiconductor structure 100 includes an oxide layer disposed between the semiconductor substrate 300 and the nanosheet stack structure, which may, for example, provide etch selectivity between the layer of the nanosheet stack structure and the semiconductor substrate 300.

[0021] Although semiconductor substrate 300 is shown as a general substrate layer, it should be understood that semiconductor substrate 300 may comprise one of a variety of types of semiconductor substrate structures and materials. For example, in one embodiment, semiconductor substrate 300 may be a bulk semiconductor substrate (e.g., a wafer) formed of silicon (Si) or germanium (Ge), or other types of semiconductor substrate materials commonly used in bulk semiconductor manufacturing processes, such as silicon-germanium alloys, compound semiconductor materials (e.g., III-V), etc. In another embodiment, the semiconductor substrate 300 may be the active semiconductor layer of a silicon-on-insulator (SOI) substrate, a germanium-on-insulator (GeOI) substrate, or other type of semiconductor-on-insulator substrate, including an insulating layer (e.g., an oxide layer) disposed between a base substrate layer (e.g., a silicon substrate) and an active semiconductor layer (e.g., Si, Ge, etc.) in which active line components are formed as part of a front-end-of-line (FEOL) structure.

[0022] The stack of semiconductor layers 302-1 to 306-3 in the nanosheet stack structure includes sacrificial nanosheet layers 302-1, 302-2, 304-1, 304-2, 304-3, and 304-4, and nanosheet channel layers 306-1, 306-2, and 306-3. The sacrificial nanosheet layers 302-1 and 302-2 are collectively and individually referred to as sacrificial nanosheet layers 302. The sacrificial nanosheet layers 304-1, 304-2, 304-3, and 304-4 are collectively and individually referred to as sacrificial nanosheet layers 304. The nanosheet channel layers 306-1, 306-2, and 306-3 are collectively and individually referred to as nanosheet channel layers 306. Each nanosheet channel layer 306 is disposed between a pair of sacrificial nanosheet layers 304 in the nanosheet stack structure. The stack of semiconductor layers 302-1 to 302-3 includes successively grown epitaxial semiconductor layers.

[0023] For example, the sacrificial nanosheet layer 302-1 is epitaxially grown on the surface of the semiconductor substrate 300, the sacrificial nanosheet layer 304-1 is epitaxially grown on the sacrificial nanosheet layer 302-1, the sacrificial nanosheet layer 302-2 is epitaxially grown on the sacrificial nanosheet layer 304-1, the sacrificial nanosheet layer 304-2 is epitaxially grown on the sacrificial nanosheet layer 302-2, and the nanosheet channel layer 306-1 is epitaxially grown on the sacrificial nanosheet layer 304-1. 4-2, sacrificial nanosheet layer 304-3 is epitaxially grown on nanosheet channel layer 306-1, nanosheet channel layer 306-2 is epitaxially grown on sacrificial nanosheet layer 304-3, sacrificial nanosheet layer 304-4 is epitaxially grown on nanosheet channel layer 306-2, and nanosheet channel layer 306-3 is epitaxially grown on sacrificial nanosheet layer 304-4.

[0024] In one embodiment, epitaxial semiconductor layers 302-1 through 306-3 are deposited by chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD), low pressure chemical vapor deposition (LPCVD), molecular beam epitaxy (MBE), vapor-phase epitaxy (VPE), liquid-phase epitaxy (LPE), metal organic molecular beam epitaxy (MOMBE), rapid thermal chemical vapor deposition (RTCVD), low-energy plasma deposition (LEPD), ultra-high vacuum chemical vapor deposition (UHVCVD), atmospheric pressure chemical vapor deposition (APCVD), liquid-phase epitaxy (LPE), or other suitable deposition methods. The epitaxial semiconductor layers 302-1 through 306-3 may comprise single crystal (monocrystalline) semiconductor materials epitaxially grown using known methods, such as nanosheet FET device type (p-type or n-type), and the desired level of etch selectivity between the spacer and the semiconductor layer, as well as providing sufficient lattice match between the spacer and semiconductor layer materials to ensure proper (e.g., defect-free) epitaxial growth of the crystalline semiconductor layers 302-1 through 306-3.

[0025] For example, in one embodiment, the nanosheet channel layer 306 is formed of epitaxial silicon (Si), which is suitable for functioning as a semiconductor channel layer in a nanosheet FET device. If the nanosheet channel layer 306 is formed of crystalline Si, the sacrificial nanosheet layers 302 and 304, which function as sacrificial layers that are later etched and removed to release the nanosheet channel layer 306, can be formed of an epitaxial silicon-germanium (SiGe) alloy. This allows the epitaxial SiGe material of the sacrificial nanosheet layers 302 and 304 to be selectively etched relative to the epitaxial Si material of the nanosheet channel layer 306 in a subsequent process step to "release" the nanosheet channel layer 306. In some embodiments, the Ge concentration of one or more of the sacrificial nanosheet layers 302 and 304 may be varied to provide etch selectivity between the sacrificial nanosheet layer 302 and the sacrificial nanosheet layer 304. In other embodiments, Si, SiGe, or other materials may be utilized for the nanosheet channel layer 306 and the sacrificial nanosheet layers 302 and 304 .

[0026] Although the nanosheet stack structure is shown as including three nanosheet channel layers 306, in other embodiments, the nanosheet stack structure can be fabricated using more or fewer nanosheet channel layers. Similarly, although the nanosheet stack structure is shown as including two sacrificial nanosheet layers 302 and four sacrificial nanosheet layers 304, in other embodiments, the nanosheet stack structure can be fabricated using more or fewer sacrificial nanosheet layers 302 and 304.

[0027] In some embodiments, the sacrificial nanosheet layer 302 may comprise a SiGe alloy containing a high percentage of Ge, while the sacrificial nanosheet layer 304 may comprise a SiGe alloy containing a lower percentage of Ge than the sacrificial nanosheet layer 302, such that the sacrificial nanosheet layer 302 can be selectively etched relative to the sacrificial nanosheet layer 304. For example, in some embodiments, the sacrificial nanosheet layer 302 may comprise a SiGe alloy containing Ge in the range of about 50% to about 90%, the sacrificial nanosheet layer 304 may comprise a SiGe alloy containing Ge in the range of about 25% to about 40%, and the nanosheet channel layer 306 may comprise Si or a SiGe alloy containing Ge in the range of about 5% to about 15%, such that the sacrificial nanosheet layer 302 and the sacrificial nanosheet layer 304 can be selectively etched relative to each other and the nanosheet channel layer 306. In one example embodiment, the sacrificial nanosheet layer 302 comprises a SiGe alloy containing about 60% Ge, the sacrificial nanosheet layer 304 comprises a SiGe alloy containing about 25% Ge, and the nanosheet channel layer 306 comprises Si. In other embodiments, the sacrificial nanosheet layer 302, the sacrificial nanosheet layer 304, and the nanosheet channel layer 306 may comprise any other concentration of Ge, or other alloys of Si, or other semiconductor materials.

[0028] In some embodiments, the sacrificial nanosheet layer 304-1 may comprise a different SiGe alloy than the sacrificial nanosheet layers 304-2, 304-3, and 304-4. For example, in some embodiments, the sacrificial nanosheet layer 302 comprises a SiGe alloy containing 60% Ge, the sacrificial nanosheet layer 304-1 comprises a SiGe alloy containing 15% Ge, the sacrificial nanosheet layers 304-2, 304-3, and 304-4 comprise a SiGe alloy containing 30% Ge, and the nanosheet channel layer 306 comprises Si. In this manner, the sacrificial nanosheet layers 304-2, 304-3, and 304-4 may be selectively etched relative to the sacrificial nanosheet layer 304-1.

[0029] Continuing with reference to FIGS. 3(A) and 3(B), sacrificial nanosheet layers 304-2, 304-3, and 304-4 may be formed with thicknesses that determine the size of the gaps above and below nanosheet channel layers 306-1, 306-2, and 306-3, where high-k dielectric materials and work function metals are formed. The size of the gaps and the type of WFM material formed in the spaces above and below nanosheet channel layer 306 determine, in part, the threshold voltage (Vt) of the nanosheet FET device. In some embodiments, the thicknesses of sacrificial nanosheet layers 304-2 through 304-4 are in the range of about 8 nm to about 15 nm. In some embodiments, sacrificial nanosheet layer 302 may be formed with a thickness similar to that of sacrificial nanosheet layer 304.

[0030] The sacrificial nanosheet layer 304-1 may be formed between the sacrificial nanosheet layer 302-1 and the sacrificial nanosheet layer 302-2 with a thickness greater than the other sacrificial nanosheet layers 304-2, 304-3, and 304-4, because the sacrificial nanosheet layer 304-1 is replaced by the BPR 110 during fabrication.

[0031] In one embodiment, the thickness of the nanosheet channel layer 306 is in the range of about 4 nm to about 8 nm, but the nanosheet channel layer 306 can be formed in other thickness ranges depending on the application.

[0032] 4(A) and 4(B) are cross-sectional views of semiconductor structure 100 at an intermediate stage of fabrication after etching has been performed to form semiconductor region 200. FIG. 4(A) is a schematic side view (YZ plane) of semiconductor structure 100 taken along section line AA in FIG. 2, and FIG. 4(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 taken along section line BB in FIG. 2. As shown in FIGS. 4(A) and 4(B), etching is performed on semiconductor layers 302-1 through 306-3 and semiconductor substrate 300 using standard etching techniques to form semiconductor regions 200-1, 200-2, 200-3, and 200-4.

[0033] A nanosheet capping layer 400 may be formed on the nanosheet stack structure by depositing a layer of dielectric material, such as silicon nitride (SiN), silicon carbon nitride (SiCN), silicon oxynitride (SiON), boron nitride (BN), silicon boron nitride (SiBN), silicon boron carbon nitride (SiBCN), silicon oxycarbonitride (SiOCN), or other similar materials commonly used to form gate capping layers and gate sidewall spacers. Next, a hard mask layer is patterned to form the nanosheet capping layer 400. The nanosheet capping layer 400 is utilized as an etch hard mask to anisotropically etch (e.g., RIE) to remove layers of the nanosheet stack structure and form the semiconductor region 200 as shown in FIG. 4(A). As seen in FIG. 4(A), the etching process also forms a trench at a depth below the top surface of the semiconductor substrate 300.

[0034] 5(A) and 5(B) are cross-sectional views of the semiconductor structure 100 at an intermediate stage of fabrication after the formation of a shallow trench isolation (STI) layer 500. FIG. 5(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along section line AA in FIG. 2 , and FIG. 5(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line BB in FIG. 2 . The STI layer 500 is formed of any type of insulating material, such as an oxide material, that is suitable for a particular fabrication process flow. The insulating material (e.g., silicon oxide) is deposited and patterned using known techniques to form the STI layer 500 within the trenches of the semiconductor substrate 300. For example, the insulating material may be deposited on the semiconductor structure 100 and planarized down to the nanosheet capping layer 400, followed by a combination of dry and wet etching processes to selectively recess the insulating material below the nanosheet stack structure. The nanosheet capping layer 400 may then be removed using, for example, an RIE process, a CMP process, or another similar process that is selective to the materials of the semiconductor layers 302-1 to 306-3, the semiconductor substrate 300, and the STI layer 500 of the nanosheet stack structure.

[0035] 6(A) and 6(B) are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication after the formation of gate structures 604-1 through 604-6. Fig. 6(A) is a schematic side view (YZ plane) of semiconductor structure 100 taken along section line AA in Fig. 2, and Fig. 6(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 taken along section line BB in Fig. 2.

[0036] As part of the formation of gate structures 604-1 through 604-6, dummy gate electrode material and gate capping material are formed and patterned over the semiconductor device structures using, for example, standard deposition and lithography processes.

[0037] For example, a dummy gate electrode layer may be formed on the semiconductor structure 100 by blanket deposition of a sacrificial material, such as a polysilicon or amorphous silicon material. In some embodiments, a conformal layer of silicon oxide may be deposited prior to the formation of the dummy gate electrode layer. A CMP process is performed to planarize the layer of sacrificial material, and a hard mask layer is formed on the planarized surface of the polysilicon layer by depositing a layer of dielectric material, such as silicon nitride (SiN), silicon carbon nitride (SiCN), silicon oxynitride (SiON), boron nitride (BN), silicon boron nitride (SiBN), silicon boron carbon nitride (SiBCN), silicon oxycarbonitride (SiOCN), or other similar materials commonly used to form gate capping layers.

[0038] The hard mask layer is then patterned to form gate capping layer 602 of gate structures 604, which define dummy gate structures. Gate structures 604-1 through 604-6 are also referred to herein collectively and individually as gate structures 604.

[0039] The gate capping layer 602 is then utilized as an etch hard mask to anisotropically etch (e.g., RIE) the sacrificial polysilicon layer, thereby forming the dummy gate electrode 600 of the gate structure 604. In an exemplary embodiment, the etch chemistry is selective to the materials of the nanosheet stack structure (including the nanosheet channel layer 306-3) and the STI layer 500.

[0040] 7(A) and 7(B) are cross-sectional views of the semiconductor structure 100 at intermediate stages of fabrication after removal of the sacrificial nanosheet layers 302-1 and 302-2. Fig. 7(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along section line AA in Fig. 2, and Fig. 7(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line BB in Fig. 2.

[0041] As shown in FIGS. 7(A) and 7(B), one or more etching processes are utilized to remove the sacrificial nanosheet layer 302. In some embodiments, a dry etching process or a wet etching process may be utilized to etch the sacrificial nanosheet layer 302 without removing other semiconductor layers of the nanosheet stack structure. For example, the etching chemistry and etching process may be selective to the materials of the semiconductor substrate 300, the STI layer 500, the semiconductor layers 304 and 306, the dummy gate electrode 600, and the gate capping layer 602. For example, the etching chemistry may be configured to remove, e.g., a 60% concentration of SiGe alloy in the sacrificial nanosheet layer 302 while being selective to the lower concentration (e.g., 25%) of Ge found in the sacrificial nanosheet layer 304 and the nanosheet channel layer 306 when the SiGe alloy is present. In some embodiments, a dry vapor phase etch process may be utilized to remove the sacrificial nanosheet layer 302. In one embodiment, the SiGe material of the sacrificial nanosheet layer 302 can be selectively etched (with high etch selectivity) using gas-phase HCl (hydrochloric acid) or a wet etching solution that is selective to the Si and SiGe materials of the sacrificial nanosheet layer 304 and the nanosheet channel layer 306 to laterally etch the SiGe material of the sacrificial nanosheet layer 302. For example, if the sacrificial nanosheet layer 304 and the nanosheet channel layer 306 are formed of SiGe, which has a lower Ge concentration than Si or the SiGe material of the sacrificial nanosheet layer 302, gas-phase HCl (hydrochloric acid) will provide high etch selectivity.

[0042] 8(A) and 8(B) are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication after the formation of portions 800-1, 800-2, and 800-3 of dielectric layers (collectively and individually also referred to as dielectric layers 800). Figure 8(A) is a schematic side view (YZ plane) of semiconductor structure 100 along section line AA in Figure 2, and Figure 8(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line BB in Figure 2.

[0043] For example, a dielectric layer 800 is formed on the semiconductor structure 100 to fill the space left by the removal of the sacrificial nanosheet layer 302 and to form sidewalls of the gate structure 604 on the outer surfaces of the dummy gate electrode 600 and the gate capping layer 602. For example, the dielectric layer 800 may be formed by depositing one or more conformal layers of a dielectric material over exposed surfaces of the semiconductor structure 100, including the exposed surfaces of the nanosheet stack structure, the dummy gate electrode 600, and the gate capping layer 602. A dielectric material is also deposited over surfaces of the semiconductor substrate 300 and the sacrificial nanosheet layer 304 exposed by the removal of the sacrificial nanosheet layer 302. In some embodiments, the dielectric layer 800 is formed of a low-k dielectric material. For example, dielectric layer 800 can be formed of SiN, SiBCN, SiOCN, SiOC, SiO2, or any other type of dielectric material commonly used to form insulated gate sidewall spacers in FET devices (e.g., a low-k dielectric material having a dielectric constant (k) less than 5). In one embodiment, to ensure that the recess is fully filled with the dielectric material, the dielectric material is conformally deposited using a highly conformal deposition process such as ALD. Other deposition methods, such as CVD and PVD, can be utilized to deposit a highly conformal layer of dielectric material to fill the recess.

[0044] The conformal layer of dielectric material can be etched back using an anisotropic etching process that reduces over-etching. The anisotropic etching process removes the dielectric material from the surfaces of the sacrificial nanosheet layers 304-3 and 304-4 and the nanosheet channel layer 306 of the semiconductor device 200, while maintaining the dielectric layer 800 as sidewalls of the exposed portions of the sacrificial nanosheet layers 304-1 and 304-2, as shown in FIG. 8(A). In some embodiments, only a portion of the sacrificial nanosheet layer 304-2 may be covered by the dielectric layer 800. The anisotropic etching process also maintains the dielectric layer 800 as sidewalls of the gate structures 604, while exposing portions of the nanosheet channel layer 306-3 between the gate structures 604. The anisotropic etching also exposes the gate capping layer 602.

[0045] 8(A), for example, the dielectric layer 800 surrounds the sacrificial nanosheet layer 304-1 and at least partially surrounds the sacrificial nanosheet layer 304-2 in the YZ plane. As shown in FIG. 8(B), for example, the portions 800-1 and 800-2 of the dielectric layer 800 fill the channel exposed by the removal of the sacrificial nanosheet layer 302, and the portion 800-3 of the dielectric layer 800 also forms a sidewall spacer for the gate structure 604, leaving a portion of the nanosheet channel layer 306-3 exposed between the gate structures 604.

[0046] 9(A) and 9(B) are cross-sectional views of the semiconductor structure 100 at intermediate stages of fabrication after etching of exposed layers of the nanosheet stack structure, including portions of the sacrificial nanosheet layers 304-2, 304-3, and 304-4 and portions of the nanosheet channel layers 306-1, 306-2, and 306-3. FIG. 9(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along section line AA in FIG. 2, and FIG. 9(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line BB in FIG. 2.

[0047] For example, one or more etching processes (e.g., directional RIE processes) may be utilized to etch the nanosheet stack structure down to portion 800-2 of dielectric layer 800 and remove exposed portions of semiconductor layers 304-2 through 304-4 and 306-1 through 306-3 between and around gate structure 604. As an example, during an etching process that is selective to the materials of dielectric layer 800 and gate capping layer 602, portion 800-3 of dielectric layer 800 and gate capping layer 602 may be used as an etch mask for removal of semiconductor layers 304-2 through 304-4 and 306-1 through 306-3 of the nanosheet stack structure.

[0048] 10(A) and 10(B) are cross-sectional views of the semiconductor structure 100 at intermediate stages of fabrication after etching of exposed portions of the sacrificial nanosheet layers 304-2, 304-3, and 304-4 and formation of the interior spacers 1000. Fig. 10(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along section line AA in Fig. 2, and Fig. 10(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line BB in Fig. 2.

[0049] In one embodiment, the interior spacer 1000 is formed by a process that includes laterally recessing the exposed sidewall surfaces of the sacrificial nanosheet layers 304-2, 304-3, and 304-4 of the nanosheet stack structure to form recesses in the sidewalls of the nanosheet stack structure that are not protected by the portion 800-3 of the dielectric layer 800. As shown in FIG. 10(B), the exposed sidewall surfaces of the sacrificial nanosheet layers 304-2, 304-3, and 304-4 are recessed laterally (e.g., in the x-direction) to a predetermined depth. The amount of lateral recessing is controlled by timed etching. In one embodiment, the depth of the recess is substantially equal to the thickness of the adjacent portion 800-3 of the dielectric layer 800.

[0050] In one exemplary embodiment, the lateral etching process can be performed using an isotropic wet etching process with an etching solution suitable for etching the semiconductor material (e.g., SiGe) of the sacrificial nanosheet layers 304-2, 304-3, and 304-4 selective to the semiconductor material (e.g., Si) of the nanosheet channel layer 306, the dielectric layer 800, and other exposed elements. In another embodiment, an isotropic dry plasma etching process selective to the nanosheet channel layer 306, the dielectric layer 800, and other exposed elements can be performed to laterally etch the exposed sidewall surfaces of the sacrificial nanosheet layers 304-2, 304-3, and 304-4.

[0051] The recesses are then filled with a dielectric material to form interior spacers 1000 (or buried spacers) on the sidewalls of the nanosheet stack structure. In one embodiment, the interior spacers 1000 are formed by depositing a conformal layer of dielectric material over the semiconductor device structure until the recesses are filled with the dielectric material, followed by an etch-back process to remove the excess dielectric material. In one embodiment, the interior spacers 1000 are formed of the same dielectric material used to form the dielectric layer 800. For example, the interior spacers 1000 can be formed of SiN, SiBCN, SiOCN, SiOC, SiO, or any other type of dielectric material commonly used to form insulated gate sidewall spacers for FET devices (e.g., low-k dielectric materials having a dielectric constant less than 5). In one embodiment, to ensure that the recesses are fully filled with the dielectric material, the dielectric material is conformally deposited using a highly conformal deposition process, such as ALD. Other deposition methods, such as CVD and PVD, can be utilized to deposit a highly conformal layer of dielectric material to fill the recesses. The conformal layer of dielectric material can be etched back using an isotropic wet etching process to remove excess dielectric material at the sidewalls of the nanosheet stack structure and expose the sidewalls of the nanosheet channel layer 306, while leaving the dielectric material in the recesses to form the interior spacers 1000. The wet etching process may include, but is not limited to, buffered hydrofluoric acid (BHF), diluted hydrofluoric acid (DHC), hydrofluoric nitric acid (HNA), phosphoric acid, HF diluted with ethylene glycol (HF / EG), hydrochloric acid (HCl), or any combination thereof.

[0052] 11(A) and 11(B) are cross-sectional views of the semiconductor structure 100 at intermediate stages of fabrication after forming and patterning an etching mask 1100 and etching a channel through a portion 800-2 of the dielectric layer 800 with the etching mask 1100 to expose the sacrificial nanosheet layer 304-1. FIG. 11(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along section line AA in FIG. 2, and FIG. 11(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line BB in FIG. 2.

[0053] As shown in FIGS. 11(A) and 11(B), a lithography process is utilized to form an etch mask 1100 over a portion of semiconductor structure 100, including gate structure 604. For example, an OPL may be coated over semiconductor structure 100, followed by a lithography process to pattern the OPL and form etch mask 1100. The OPL may include, for example, a resin material that is applied by spin coating and baked to enhance planarization. The patterned portions of the OPL are removed such that etch mask 1100 exposes portions 800-2 of dielectric layer 800 in the region adjacent to gate structure 604-1, in the region between gate structures 604-3 and 604-4, and in the region adjacent to gate structure 604-6. For example, the etching mask 1100 may expose the regions between every other pair of gate structures 604 and, in some embodiments, the regions on either side of the gate structures 604 that will become SDBs (e.g., in the embodiment shown in FIG. 11(B) ). As shown in FIG. 11(A) , patterning the etching mask may expose portions 800-2 of the dielectric layer 800 of semiconductor devices 200-1 and 200-3 while covering portions 800-2 of the dielectric layer 800 of semiconductor devices 200-2 and 200-4. The pattern of the etching mask 1100 allows a directional etching process (e.g., a directional RIE process) to be utilized to etch the exposed portions 800-2 of the dielectric layer 800 down to the sacrificial nanosheet layer 304-1. For example, the etching chemistry may be selective to the materials of the gate capping layer 602, the sacrificial nanosheet layer 304-1, and the etching mask 1100. Etch mask 1100 may then be removed using, for example, a plasma etching process or an ashing process.

[0054] 12(A) and 12(B) are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication after formation of source / drain regions 1200 and 1202 on exposed portions of sacrificial nanosheet layer 304-1 and part 800-2 of dielectric layer 800. Figure 12(A) is a schematic side view (YZ plane) of semiconductor structure 100 along section line AA in Figure 2, and Figure 12(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line BB in Figure 2.

[0055] The source / drain regions 1200 and 1202 may be formed by implantation of appropriate dopants, such as using ion implantation, gas-phase doping, plasma doping, plasma immersion ion implantation, cluster doping, implantation doping, liquid-phase doping, or solid-phase doping. N-type dopants may be selected from the group of phosphorus (P), arsenic (As), and antimony (Sb), and p-type dopants may be selected from the group of boron (B), boron fluoride (BF), gallium (Ga), indium (In), and thallium (Ti). The source / drain regions 1200 and 1202 may be formed by an epitaxial growth process. In some embodiments, the epitaxy process includes in-situ doping (dopants are incorporated into the epitaxy material during epitaxy). The epitaxial material may be grown from gas or liquid precursors. Epitaxial materials may be grown using vapor phase epitaxy (VPE), molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), rapid thermal chemical vapor deposition (RTCVD), metalorganic chemical vapor deposition (MOCVD), ultrahigh vacuum chemical vapor deposition (UHVCVD), low pressure chemical vapor deposition (LPCVD), limited reaction processing CVD (LRPCVD), or other suitable processes. Depending on the type of transistor, epitaxial silicon, silicon-germanium (SiGe), germanium (Ge), or carbon-doped silicon (Si:C), or combinations thereof, can be doped during deposition (in-situ doped) by adding dopants such as n-type dopants (e.g., phosphorus or arsenic) or p-type dopants (e.g., boron or gallium). Dopant concentrations range from 1x10 19 cm -3 ~3x10 21 cm -3 , or preferably, 2x10 20 cm -3 ~3x10 21 cm -3 It can be.

[0056] In some embodiments, the source / drain regions 1200 and 1202 may be formed or grown on the sacrificial nanosheet layer 304-1 adjacent to the nanosheet stack structure and on the portion 800-2 of the dielectric layer 800, down to the portion 800-3 of the dielectric layer 800 above the nanosheet channel layer 306-3, so that the nanosheet channel layer 306-3 is not exposed. In some embodiments, the source / drain regions 1200 and 1202 may be formed or grown on the nanosheet channel layer 306-3 and then recessed or patterned in the z-direction to a desired height relative to the nanosheet channel layer 306-3. It is important to note that FIG. 12(B) illustrates cross section B-B of FIG. 2 along either the nFET or pFET semiconductor device 200. Accordingly, the source / drain regions 1200 in FIG. 12(B) comprise the same material or dopant, etc. (e.g., n-type material or p-type material, but not both). In contrast, Figure 12(A) shows cross section AA of Figure 2 through multiple semiconductor devices 200 of different types. In this case, both n-type and p-type materials are shown. For example, if source / drain region 1200 includes n-type material or n-type dopants, source / drain region 1202 includes p-type material, and vice versa.

[0057] 13(A) and 13(B) are cross-sectional views of the semiconductor structure 100 at intermediate stages of fabrication after the formation of an inter-layer dielectric (ILD) 1300. Fig. 13(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along section line AA in Fig. 2, and Fig. 13(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line BB in Fig. 2.

[0058] A dielectric material, such as, but not limited to, SiOx, low temperature oxide (LTO), high temperature oxide (HTO), flowable oxide (FOX), or some other dielectric, is deposited to form ILD 1300 over gate structure 604 and source / drain regions 1200 and 1202. ILD 1300 can be deposited using deposition techniques, such as, but not limited to, CVD, PECVD, RFCVD, PVD, ALD, MLD, MBD, PLD, or LSMCD, or a combination thereof, sputtering, or plating. Planarization, such as chemical mechanical polishing (CMP), can be performed to remove excess material from ILD 1300 and planarize the resulting structure. Planarization can be performed down to dummy gate electrode 600 of gate structure 604, such that gate capping layer 602 is removed and dummy gate electrode 600 is exposed. According to an exemplary embodiment, the ILD 1300 electrically isolates the different gate structures 604 from each other.

[0059] 14(A) and (B) are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication after formation of a sacrificial cap 1400 and an etching mask 1402 on gate structures 604-1 and 604-6 corresponding to the SDBs. FIG. 14(A) is a schematic side view (YZ plane) of semiconductor structure 100 along section line AA in FIG. 2, and FIG. 14(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line BB in FIG. 2.

[0060] A hard mask is formed on the planarized surfaces of ILD 1300, portion 800-3 of dielectric layer 800, and dummy gate electrode 600 by depositing a layer of dielectric material, such as silicon nitride (SiN), silicon carbon nitride (SiCN), silicon oxynitride (SiON), boron nitride (BN), silicon boron nitride (SiBN), silicon boron carbon nitride (SiBCN), silicon oxycarbonitride (SiOCN), or other similar materials commonly used to form sacrificial capping layers.

[0061] Next, a hard mask is patterned to form a sacrificial cap 1400 over gate structures 604-1 and 604-6. For example, a lithography process is utilized to form an etch mask 1402 over a portion of semiconductor structure 100, including gate structures 604-1 and 604-6. For example, an OPL may be coated over semiconductor structure 100, followed by a lithography process to pattern the OPL and form etch mask 1402. The OPL may include a resin material that is applied, for example, by spin coating and baked to enhance planarization. The patterned portions of the OPL are removed such that etch mask 1402 exposes the hard mask over the dummy gate electrodes 600 of gate structures 604-2 through 604-5, while etch mask 1402 remains over gate structures 604-1 and 604-6. A directional etching process (e.g., a directional RIE process) is utilized to etch the exposed hard mask down to the dummy gate structures 604-2 through 604-5 according to the pattern of the etch mask 1402 and form a sacrificial cap 1400 over the gate structures 604-1 and 604-6. For example, the etching chemistry may be selective to the materials of the ILD 1300, the dummy gate electrodes 600, and the dielectric layer 800.

[0062] 15(A) and 15(B) are cross-sectional views of the semiconductor structure 100 at intermediate stages of fabrication after removal of the dummy gate electrodes 600 of the gate structures 604-2 to 604-5 and the sacrificial nanosheet layers 304-2, 304-3, and 304-4. FIG. 15(A) is a schematic side view (YZ plane) of the semiconductor structure 100 taken along section line AA in FIG. 2, and FIG. 15(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 taken along section line BB in FIG. 2.

[0063] The dummy gate electrode 600 is etched away using known etching techniques and etch chemistries. For example, a selective dry or wet etch process can be used with appropriate etch chemistries, including ammonium hydroxide (NH4OH), tetramethylammonium hydroxide (TMAH), or SF6 plasma, to remove the dummy gate material. The etch of the dummy gate electrode 600 is selective to, for example, the ILD1300, the dielectric layer 800, the sacrificial nanosheet layer 304, and the nanosheet channel layer 306, thereby protecting the semiconductor material of the nanosheet stack structure from being etched during the poly etch process. The etch of the dummy gate electrode 600 opens the gate structures 604-2 through 604-5.

[0064] The sacrificial nanosheet layers 304-2, 304-3, and 304-4 are selectively etched away to release the nanosheet channel layer 306, thereby allowing the opened gate structures 604-2 through 604-5 to extend into the spaces between and adjacent to the nanosheet channel layer 306. In this embodiment, the opened gate structures 604-2 through 604-5 include the open space within the interior region defined by the portion 800-3 of the dielectric layer 800 and the interior spacer 1000.

[0065] The sacrificial nanosheet layers 304-2, 304-3, and 304-4 (e.g., SiGe layers) can be etched away using, for example, a wet etching process that is selective to the nanosheet channel layer 306 (e.g., Si layer). In one embodiment, the SiGe material of the sacrificial nanosheet layers 304-2, 304-3, and 304-4 can be selectively etched (with high etch selectivity) using gas-phase HCl (hydrochloric acid) or a wet etching solution that is selective to the Si material of the nanosheet channel layer 306 to laterally etch the SiGe material of the sacrificial nanosheet layers 304-2, 304-3, and 304-4. For example, if the nanosheet channel layer 306 is formed of Si or SiGe having a lower Ge concentration than the SiGe material of the sacrificial nanosheet layers 304-2, 304-3, and 304-4, gas-phase HCl (hydrochloric acid) provides high etch selectivity. As can be seen from FIG. 15(B), the sacrificial nanosheet layer 304-1 is protected by the portion 800-2 of the dielectric layer 800 and is therefore not etched away at this point.

[0066] In some embodiments, the etching mask 1402 may be removed by etching the dummy gate electrode 600 or the sacrificial nanosheet layer 304. In other embodiments, the etching mask 1402 may be removed using another process, such as, for example, a plasma etching process or an ashing process. In some embodiments, the etching mask 1402 is removed before etching the dummy gate electrode 600.

[0067] 16(A) and 16(B) are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication after formation of gate conductor layer 1600 in gate structures 604-2 through 604-5 and removal of sacrificial cap 1400. FIG. 16(A) is a schematic side view (YZ plane) of semiconductor structure 100 along section line AA in FIG. 2, and FIG. 16(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line BB in FIG. 2.

[0068] In some embodiments, an optional gate dielectric layer (not shown) is formed prior to the formation of the gate conductor layer 1600. The gate dielectric layer comprises a high-k dielectric layer, including, but not necessarily limited to, for example, HfO (hafnium oxide), ZrO (zirconium dioxide), hafnium zirconium oxide, AlO (aluminum oxide), and TaO (tantalum pentoxide), or other electronic grade (EG) oxides. Examples of high-k materials also include, but are not limited to, metal oxides such as silicon hafnium oxynitride, lanthanum oxide, aluminum lanthanum oxide, zirconium oxide, silicon zirconium oxide, silicon zirconium oxynitride, tantalum oxide, titanium oxide, titanium barium strontium oxide, titanium barium oxide, titanium strontium oxide, yttrium oxide, aluminum oxide, tantalum lead scandium oxide, and lead zinc niobate. In one embodiment, the dielectric material of the gate dielectric layer is conformally deposited using a highly conformal deposition process, such as ALD. Other deposition methods, such as CVD and PVD, can be utilized to deposit a highly conformal layer of dielectric material to cover the exposed portions of the gate structure 604 .

[0069] The gate conductor layer 1600 may include a metal gate or a work function metal (WFM). In an exemplary embodiment, the gate conductor layer 1600 includes a WFM for either an nFET device or a pFET device. For an nFET device, the WFM of the gate conductor may include titanium (Ti), aluminum (Al), titanium aluminum (TiAl), titanium aluminum carbon (TiAlC), a combination of a Ti alloy and an Al alloy, a stack including a barrier layer (e.g., titanium nitride (TiN) or another suitable material) followed by one or more of the aforementioned WFM materials, or the like. For a pFET device, the WFM of the gate conductor may include TiN, tantalum nitride (TaN), or another suitable material. In some embodiments, the pFET WFM may include a metal stack in which a thicker barrier layer (e.g., TiN, TaN, etc.) is formed followed by a WFM such as Ti, Al, TiAl, TiAlC, or any combination of a Ti alloy and an Al alloy. It should be understood that a variety of other materials may be used for the gate conductor layer 1600, if desired.

[0070] The gate conductor layer 1600 is formed using a deposition technique, for example, but not limited to, CVD, PECVD, RFCVD, PVD, ALD, MLD, MBD, PLD, LSMCD, sputtering, or plating, or a combination thereof. In an exemplary embodiment, the gate conductor layer 1600 is deposited over the semiconductor device structure including the STI layer 1300, over and between the nanosheet channel layer 306 of the nanosheet stack structure, and within the gate structures 604-2 through 604-5, as shown in FIG. 16(B). Excess WFM material may be removed, for example, using an etching or CMP process. In some embodiments, the etching or CMP process may remove the sacrificial cap 1400 and expose the dummy gate electrodes 600 of the gate structures 604-1 through 604-6.

[0071] 17(A) and 17(B) are cross-sectional views of the semiconductor structure 100 at intermediate stages of fabrication after opening the gate structures 604-1 and 604-6 down to the sacrificial nanosheet layer 304-1 and removing the sacrificial nanosheet layer 304-1. FIG. 17(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along section line AA in FIG. 2, and FIG. 17(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line BB in FIG. 2.

[0072] The gate structures 604-1 and 604-6 are opened using one or more etching processes to remove the dummy gate electrode 600, the sacrificial layers 304-2, 304-3, and 304-4, the nanosheet channel layer 306, and the portion 800-2 of the dielectric layer 800 to expose the sacrificial nanosheet layer 304-1 underneath the gate structures 604-1 and 604-6. For example, a directional anisotropic RIE process that is selective to the STI layer 1300 and the gate conductor layer 1600 may be utilized. The anisotropic RIE is configured to etch and remove all layers in the gate structures 604-1 and 604-6, including the dummy gate electrode 600, the sacrificial layers 304-2, 304-3, and 304-4, the nanosheet channel layer 306, and the portion 800-2 of the dielectric layer 800, to expose the sacrificial nanosheet layer 304-1, in a single process. In some embodiments, anisotropic RIE may at least partially etch into the sacrificial nanosheet layer 304-1. The SiGe material of the sacrificial nanosheet layer 304-1 can then be selectively etched (with high etch selectivity) using gas-phase HCl (hydrochloric acid) or a wet etching solution that is selective to the dielectric layer 800 and the inner spacer 1000 to laterally etch the SiGe material of the sacrificial nanosheet layer 304-1. In other embodiments, multiple etching processes may etch and remove the dummy gate electrode 600, the sacrificial layers 304-2, 304-3, and 304-4, the nanosheet channel layer 306, and the portion 800-2 of the dielectric layer 800.

[0073] 18(A) and 18(B) are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication after formation of BPR 1800 in opened gate structures 604-1 and 604-6 and in channels exposed by removal of sacrificial nanosheet layer 304-1. FIG. 18(A) is a schematic side view (YZ plane) of semiconductor structure 100 along section line AA in FIG. 2, and FIG. 18(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line BB in FIG. 2.

[0074] The BPR 1800 may include a metal-based material, such as tungsten, cobalt, zirconium, tantalum, titanium, aluminum, ruthenium, or copper, or a combination thereof. The BPR 1800 may be formed by conformal deposition using deposition techniques, including, but not limited to, CVD, PECVD, RFCVD, PVD, ALD, MLD, MBD, PLD, LSMCD, sputtering, or plating, or a combination thereof. In some embodiments, the metal-based material of the BPR 1800 is deposited to fill the channels exposed by the removal of the sacrificial nanosheet channel layer 304-1 and to fill the opened gate structures 604-1 and 604-6. CMP may be used to planarize the semiconductor structure 100 and etch away unwanted metal-based material.

[0075] 19(A) and 19(B) are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication after the gate conductor layer 1600 and BPR 1800 in gate structures 604-1 through 604-6 have been recessed. FIG. 19(A) is a schematic side view (YZ plane) of semiconductor structure 100 taken along section line AA in FIG. 2, and FIG. 19(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 taken along section line BB in FIG. 2.

[0076] The gate conductor layer 1600 and the BPR 1800 may be recessed using one or more etching processes. For example, if the metal-based materials of the gate conductor layer 1600 and the BPR 1800 are different, two different etching processes may be utilized. As an example, a first isotropic wet etching process selective to the material of the BPR 1800 may be used to recess the gate conductor layer 1600, and a second isotropic wet etching process selective to the material of the gate conductor layer 1600 may be used to recess the BPR 1800.

[0077] 20(A), 20(B), 21, and 22 are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication after an etch mask 2000 exposing gate structures 604-1 and 604-6 has been formed and BPR 1800 has been etched down to the level of portion 800-2 of dielectric layer 800 to open gate structures 604-1 and 604-6. FIG. 20(A) is a schematic side view (YZ plane) of semiconductor structure 100 along section line AA in FIG. 2, FIG. 20(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line BB in FIG. 2, FIG. 21 is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line CC in FIG. 2, and FIG. 22 is a schematic side view (YZ plane) of semiconductor structure 100 along section line DD in FIG. 2.

[0078] An etch mask 2000 may be formed and patterned in the manner described above with respect to etch mask 1402 to expose portions of BPR 1800 and ILD 1300 adjacent gate structures 604-1 and 604-6, as well as dielectric layer 800.

[0079] BPR 1800 may be etched in the z-direction down to the height of portion 800-2 of dielectric layer 800 using, for example, a timed anisotropic etch, although other etching processes may alternatively be utilized, configured to leave portions of BPR 1800 within each of gate structures 604-1 and 604-6 and to avoid over-etching into BPR 1800 disposed between portions 800-1 and 800-2 of dielectric layer 800.

[0080] As can be seen in Figure 21, the BPR 1800 material in gate structures 604-1 and 604-6 is not etched back in the CC cross section because it is used as a contact for electrical connection of upper layers to BPR 1800. As can be seen in Figure 22, for example, BPR 1800, along with the top etch mask 2000, forms contact pillars 1800-1, 1800-2, and 1800-3 for each semiconductor device 200, separated by recessed valleys corresponding to SDB gate structure 604-1. As can be seen in Figure 22, the nanosheet channel layers are indicated by the black dashed lines, indicating that they are etched away in the DD cross section but extend, e.g., in the x-direction, through the semiconductor device 200 at those locations. Similarly, the white dashed lines shown in FIG. 21 indicate positions where the BPR 1800 extends through the SDB, e.g., in the y direction, and the white dashed lines shown in FIG. 22 indicate positions where the BPR 1800 extends through the semiconductor device 200, e.g., in the x direction.

[0081] 23(A), 23(B), 24, and 25 are cross-sectional views of the semiconductor structure 100 at intermediate stages of fabrication after forming an etch mask 2300 and performing a gate cut to separate the BPR 1800 between the n-type and p-type semiconductor devices 200. FIG. 23(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along section line AA in FIG. 2, FIG. 23(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line BB in FIG. 2, FIG. 24 is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along section line CC in FIG. 2, and FIG. 25 is a schematic side view (YZ plane) of the semiconductor structure 100 along section line DD in FIG. 2.

[0082] In some embodiments, etch mask 2000 may be removed, e.g., using a plasma etching or ashing process, and a new etch mask 2300 may be formed and patterned, e.g., using the techniques described above, to expose BPR 1800 over portions of STI layer 500 disposed between pillars 1800-1, 1800-2, and 1800-3 of BPR 1800. The exposed portions of BPR 1800 are then etched down to STI layer 500, e.g., using RIE selective to etch mask 2300 and STI layer 500, to sever the connections between pillars 1800-1, 1800-2, and 1800-3 of BPR 1800. Thus, after severing, each pillar 1800-1, 1800-2, and 1800-3 includes its own BPR 1800, as shown, e.g., in FIG. 25 .

[0083] 26(A), 26(B), 27, and 28 are cross-sectional views of semiconductor structure 100 at an intermediate stage of fabrication after removal of etch mask 2300 and formation of ILD layer 2600 within exposed portions of gate structures 604-1 through 604-6 and between pillars 1800-1, 1800-2, and 1800-3 of BPR 1800 to electrically isolate pillars 1800-1, 1800-2, and 1800-3 from one another. 26(A) is a schematic side view (YZ plane) of the semiconductor structure 100 along the cutting line AA in FIG. 2, FIG. 26(B) is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along the cutting line BB in FIG. 2, FIG. 27 is a schematic side cross-sectional view (XZ plane) of the semiconductor structure 100 along the cutting line CC in FIG. 2, and FIG. 28 is a schematic side view (YZ plane) of the semiconductor structure 100 along the cutting line DD in FIG. 2.

[0084] In some embodiments, the etch mask 2000 may be removed, for example, using a plasma etching process or an ashing process, and the ILD 2600 may be formed by depositing a dielectric material, for example, including but not limited to, SiN, SiOx, low-temperature oxide (LTO), high-temperature oxide (HTO), flowable oxide (FOX), or some other dielectric, to form the ILD 2600 within the gate structure 604 and between the pillars 1800-1, 1800-2, and 1800-3 of the BPR 1800. The ILD 2600 may be deposited using deposition techniques, including, but not limited to, CVD, PECVD, RFCVD, PVD, ALD, MLD, MBD, PLD, or LSMCD, or combinations thereof, sputtering, or plating, or combinations thereof. Planarization, for example, chemical-mechanical polishing (CMP), may be performed to remove excess material from the ILD 2600 and planarize the resulting structure.

[0085] 29(A), 29(B), 30, and 31 are cross-sectional views of semiconductor structure 100 at intermediate stages of fabrication, after formation of gate contact 2900 to source / drain regions 1200 and 1202 electrically isolated from BPR 1800 of corresponding semiconductor device 200, formation of additional ILDs 1300 and 2600, and trenching and formation of top contact 3000. FIG. 29(A) is a schematic side view (YZ plane) of semiconductor structure 100 along section line AA in FIG. 2, FIG. 29(B) is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line BB in FIG. 2, FIG. 30 is a schematic side cross-sectional view (XZ plane) of semiconductor structure 100 along section line CC in FIG. 2, and FIG. 31 is a schematic side view (YZ plane) of semiconductor structure 100 along section line DD in FIG. 2.

[0086] For example, an etch mask is formed by coating a layer of OPL material over semiconductor structure 100, followed by performing a lithography process to pattern the OPL so that the etch mask exposes ILD 1300 disposed above source / drain regions 1200 and 1202 isolated from BPR 1800. The OPL may comprise a resin material that is applied, for example, by spin coating and baked to enhance planarization. For example, as seen in Figures 29(A) and 29(B), patterned portions of the OPL are removed, and the pattern is etched down into ILD 1300, opening and exposing source / drain regions 1200 and 1202 electrically isolated from BPR 1800. In an exemplary embodiment, the etch process (e.g., a directional RIE process) is selective to the materials of source / drain regions 1200 and 1202, dielectric layer 800, and BRP 1800. In some embodiments, multiple etch processes selective to one or more of these materials may be utilized. For example, the etch mask may be removed using a plasma etching process or an ashing process.

[0087] Gate contact 2900 is formed in contact with exposed source / drain regions 1200 and 1202 by depositing a contact material, such as a conductive material including, but not limited to, tungsten, cobalt, zirconium, tantalum, titanium, aluminum, ruthenium, or copper, or a combination thereof. In some embodiments, a liner layer (not shown), including, for example, titanium and / or titanium nitride, may be formed over exposed source / drain regions 1200 and 1202 prior to depositing the contact material. Deposition of the contact material may be performed using one or more deposition techniques, including, but not limited to, CVD, PECVD, PVD, ALD, MBD, PLD, LSMCD, or spin-on coating, or a combination thereof, followed by planarization using a planarization process such as CMP.

[0088] Following the formation of gate contact 2900, ILD material is again deposited to form the remaining ILD 1300 and 2600 over semiconductor structure 100. The ILD material is deposited using a deposition technique, for example, but not limited to, CVD, PECVD, RFCVD, PVD, ALD, MLD, MBD, PLD, LSMCD, sputtering, or plating, or a combination thereof, followed by a planarization process, for example, CMP.

[0089] For example, using lithography and a subsequent RIE process, contact trenches are etched down to gate contact 2900 and pillars 1800-1, 1800-2, and 1800-3, exposing the top surfaces of gate contact 2900 and pillars 1800-1, 1800-2, and 1800-3, and contact trenches or contact vias are opened in ILD 1300 and ILD 2600 above gate contact 2900 and pillars 1800-1, 1800-2, and 1800-3, respectively. For example, by depositing a contact material, such as a conductive material including, but not necessarily limited to, tungsten, cobalt, zirconium, tantalum, titanium, aluminum, ruthenium, or copper, or a combination thereof, a contact layer top contact 3000 is formed on the gate contact 2900 in the contact trench and on the exposed surfaces of pillars 1800-1, 1800-2, and 1800-3, as seen in Figures 29(A), 29(B), 30, and 31. Deposition of the contact material can be performed using one or more deposition techniques, including, but not necessarily limited to, CVD, PECVD, PVD, ALD, MBD, PLD, LSMCD, or spin-on coating, or a combination thereof, followed by planarization using a planarization process such as CMP.

[0090] 29(A) and 29(B), in one example embodiment and layout, the source / drain regions 1200 and 1202 alternate between contacts containing the BPR 1800 and the gate contact 2900 in both the x and y directions. This allows for increased density in these regions and the gate structure 604 itself, since the likelihood of shorts occurring between the contact materials is reduced. Additionally, as seen in FIGS. 30 and 31, power is supplied to the BPR 1800 for each semiconductor device 200 via each pillar 1800-1, 1800-2, and 1800-3 located in the SDB and the corresponding top contact 3000, allowing power to be supplied to the BPR 1800 of each semiconductor device 200 from above, in areas where no active gate is located, instead of from the side of the semiconductor structure 100. Additionally, because BPR 1800 is disconnected between pillars 1800-1, 1800-2, and 1800-3 by ILD 2600, different voltages may be supplied to pillars 1800-1, 1800-2, and 1800-3. For example, in some embodiments, pillars 1800-1 and 1800-3 may be in electrical communication, e.g., via their corresponding top contacts 3000, and supply power of the same voltage to semiconductor devices 200 of the same type (e.g., pFET or nFET), while pillar 1800-2 may supply power of a different voltage to semiconductor devices 200 of a different type. In one example, semiconductor devices 200-1 and 200-4 are pFET type devices, while semiconductor devices 200-2 and 200-3 are nFET type devices. In such an example, pillars 1800-1 and 1800-3 supply power at a first voltage to BPR 1800 of pFET semiconductor devices 200-1 and 200-4, while pillar 1800-2 supplies power at a second voltage to BPR 1800 of nFET semiconductor devices 200-2 and 200-4.

[0091] Any known sequence of processing steps can then be performed to complete the fabrication of the semiconductor structure, and details thereof are not required for understanding the exemplary embodiments. As a simple example, middle-of-the-line (MOL) processing can continue with the formation of MOL contacts (e.g., gate contacts, source / drain contacts, etc.). Back-end-of-line (BEOL) process modules can then be performed to fabricate BEOL interconnect structures that provide connections to / between the MOL contacts, as well as other active or passive devices formed as part of the front-end-of-line (FEOL) layers.

[0092] FIG. 32 is a schematic top view (XY plane) of a semiconductor integrated circuit structure 3200, also referred to herein as semiconductor structure 3200, according to a second embodiment. For clarity, some elements of the semiconductor structure 3200 are not shown in FIG. 32. The semiconductor structure 3200 includes double diffusion breaks (DDBs) 3202, each including a pair of inactive gates that separates a group of active gates 3204, as compared to the SDBs 104 of the first embodiment of FIG. 1, each including a single inactive gate. Power is supplied to the source / drain regions associated with the active gates 3204 via either a top-down contact 3206 or a bottom-up contact 3208, in a manner similar to the semiconductor integrated circuit structure 100, as described and illustrated in further detail below with reference to FIGS. 33-36. The bottom-up contact 3208 is electrically connected to a buried power rail (BPR) 3210 disposed below the source / drain regions. For example, in some embodiments, the source / drain regions on one side of the active gate 3204 are connected to the top-down contact 3206, while the source / drain regions on the other side of the active gate 3204 are connected to the BPR 3210 via the bottom-up contact 3208. While described with reference to top-down and bottom-up contacts, the semiconductor structure 3200 may be formed using contacts in any orientation. The use of both the top-down contact 3206 and the bottom-up contact 3208 reduces tip-to-tip spacing, thereby reducing the occurrence of shorts and enabling improved source / drain density. As can be seen in FIG. 32 , the BPR 3210 does not extend beyond the DDB 3202 in the x-direction, in contrast to the BPR 110, which extends beyond the SDB 104 of the first embodiment of FIG. 1 .

[0093] Figure 33 is a schematic top view (XY plane) of section 3212 of semiconductor structure 3200 and is utilized to further illustrate features of semiconductor structure 3200. As shown in Figure 33, semiconductor structure 3200 includes semiconductor regions 3302-1, 3302-2, 3302-3, and 3302-4 (collectively and individually referred to as semiconductor regions 3302) across which DDBs 3304-1 and 3304-2 (collectively and individually referred to as DDBs 3304), and active gates 3306-1, 3306-2, 3306-3, and 3306-4 (collectively and individually referred to as active gates 3306) are formed. Each semiconductor region 3302-1, 3302-2, 3302-3, and 3302-4 includes a corresponding BPR 3210-1, 3210-2, 3210-3, and 3210-4 (collectively and individually referred to as BPR 3210) that extends between, but not beyond, each DDB 3304. For example, a portion of a particular BPR 3210 extends to, but does not extend between, the first inactive gates of the corresponding DDB 3304.

[0094] Although shown as including four semiconductor devices 3302 with four active gates 3306 between two DDBs 3304, any number of semiconductor regions 3302, DDBs 3304, and active gates 3306 may be included, with any number of active gates 3306 disposed between each pair of DDBs 3304. In some embodiments, for example, semiconductor regions 3302 may be formed as nFET or pFET devices. In some embodiments, semiconductor regions 3302-1 and 3302-4 may include pFET devices, while semiconductor regions 3302-2 and 3302-3 may include nFET devices. In other embodiments, semiconductor regions 3302 may alternate between nFET and pFET devices, for example, semiconductor regions 3302-1 and 3302-3 may include pFET devices, while semiconductor regions 3302-2 and 3302-4 include nFET devices, or vice versa.

[0095] For each semiconductor region 3302, power is supplied to the BPR 3210 between the DDBs 3304 via one or more corresponding top-down contacts 3308 or 3310 in the DDBs 3304. For example, the top-down contact 3308 may be set to a first voltage, while the top-down contact 3310 may be set to a second voltage different from the first voltage. The top-down contact 3308 supplies power to the BPRs 3210 in the semiconductor regions 3302-1 and 3302-4, while the top-down contact 3310 supplies power to the BPRs 3210 in the semiconductor regions 3302-2 and 3302-3. The use of the top-down contacts 3308 and 3310 in the DDBs 3304 to supply power to the BPRs 3210 enables reduced n-to-p spacing because the BPRs do not need to be formed in a shallow trench isolation (STI) layer. In some embodiments, the same contact 3308 or 3310 may be used on both sides of the DDB 3304 to provide power to the BPR 3210. Figure 33 also defines cross sections A'-A', B'-B', C'-C', and D'-D', which are similar to cross sections AA, BB, CC, and DD, except that cross section D'-D' corresponds to a portion of the DDB 3302-1 where the BPR 3210 is not present. Cross sections A'-A', B'-B', C'-C', and D'-D' are utilized in Figures 34(A)-36.

[0096] 34(A), 34(B), 35, and 36 are cross-sectional views of the semiconductor structure 3200 of FIG. 32 at intermediate stages in fabrication, at points similar to FIGS. 29(A), 29(B), 30, and 31 of the semiconductor structure 100 of FIG. 1. FIG. 34(A) is a schematic side view (Y-Z plane) of the semiconductor structure 3200 along section line A'-A' in FIG. 32, FIG. 34(B) is a schematic side cross-sectional view (X-Z plane) of the semiconductor structure 3200 along section line B'-B' in FIG. 32, FIG. 35 is a schematic side cross-sectional view (X-Z plane) of the semiconductor structure 3200 along section line C'-C' in FIG. 32, and FIG. 36 is a schematic side view (Y-Z plane) of the semiconductor structure 3200 along section line D'-D' in FIG.

[0097] In an exemplary embodiment, the semiconductor structure 3200 shown in Figures 34(A), 34(B), 35, and 36 is formed using similar processes and steps as the semiconductor structure 100 shown in Figures 29(A), 29(B), 30, and 31, e.g., like numbers indicate like features. For example, the semiconductor structure 3200 includes a semiconductor substrate 3300, an STI layer 3500, gate structures 3604-1 through 3604-6, portions 3800-1, 3800-2, and 3800-3 of a dielectric layer 3800, an inner spacer 4000, source / drain regions 4200 and 4202, an ILD 4300, an ILD, a gate conductor layer 4600, a BPR 4800, an ILD 5600, a gate contact 5900, and a top contact 6000. For example, some or all of the steps and processes described in Figures 3-31 may be utilized to form semiconductor structure 3200 in a manner similar to the formation of semiconductor structure 100. The differences between these processes and structures will now be described in further detail.

[0098] 33, 34(A), and 34(B), as the semiconductor device 3302 is cut at the DDB 3304, additional etching is performed to expand the STI layer 3500 to include the edges of the semiconductor device 3302 below the DDB 3304. For example, during the step of forming the STI layer 3500, similar to the steps shown and described with reference to FIGS. 4(A)-5(A), etching and formation of the STI layer 3500 is also performed on the edges of the nanosheet stack structure and the semiconductor substrate 3300, such that the STI layer 3500 is formed adjacent to and at least partially underlies the gate structures 3604-1 and 3604-6 of the DDB, as shown in FIG. 34(B). Additionally, compared to the first embodiment in which the STI layer 500 is formed only under the cuts between pillars 1800-1, 1800-2, and 1800-3 and BPR 1800, as shown in FIG. 31, the STI layer 3500 extends across the entire DDB along cross section D'-D', as shown in FIG. 36.

[0099] 34(B), gate structures 3604-1 and 3604-6 of the DDB extend down the sides of BPR 4800 such that BPR 4800 is capped off at both ends by portions 3800-3 of dielectric layer 3800 of gate structures 3604-1 and 3604-6 and by STI layer 3500, and portions of ILD 4300 also insulate BPR 4800 from the DDB, e.g., in the x-direction. In some embodiments, for example, instead of forming dummy gate electrodes and dielectric layer 3800 of gate structures 3604-1 and 3604-6 in the manner shown in FIG. 8(B), dummy gate electrodes and portions of dielectric layer 3800 of gate structures 3604-1 and 3604-6 may be formed down to STI layer 3500 adjacent to the nanosheet stack structure. For example, when the dummy gate electrode and the bottom sacrificial layer are removed to form the BPR 4800 using the process described above with reference to FIGS. 17(A)-18(B), a portion 3800-3 of the dielectric layer 3800 remains, as shown in FIG. 34(B). When the BPR 4800 material is deposited on the exposed portions 3800-1, 3800-2, and 3800-3 of the dielectric layer 3800, it is also deposited on the exposed portions of the STI layer 3500 that contacted the portion of the dummy gate electrode. In this manner, a semiconductor structure 3200 may be fabricated that provides power to the BPR via contacts disposed in the DDB. This semiconductor structure 3200 provides the benefits of the DDB while providing high density capabilities.

[0100] The disclosed semiconductor structures 100 and 3200 allow for cell height scaling and improved wiring density, for example, without the BPR being constrained by the pitch of gates per semiconductor device because the BPR traverses underneath the gate structure and extends between single or double diffusion isolations. By forming the BPR underneath the gate structure, the BPR also provides backside shielding for the semiconductor device, limiting the potential impact of backside electromagnetic insertion attacks on the gate structure.

[0101] It should be understood that the methods described herein for fabricating semiconductor structures can be readily incorporated into semiconductor process flows, semiconductor devices, and integrated circuits including various analog and digital or mixed-signal circuits. In particular, integrated circuit dies can be fabricated using a variety of devices, such as field-effect transistors, bipolar transistors, metal-oxide-semiconductor transistors, diodes, capacitors, inductors, and the like. Integrated circuits according to the present invention can be employed in applications, hardware, or electronic systems, or combinations thereof. Suitable hardware and systems for implementing the present invention may include, but are not limited to, personal computers, communications networks, electronic commerce systems, portable communications devices (e.g., mobile phones), solid-state media storage devices, functional circuits, and the like. Systems and hardware incorporating such integrated circuits are considered part of the embodiments described herein. Given the teachings of the present invention provided herein, those skilled in the art will be able to contemplate other implementations and applications of the techniques of the present invention.

[0102] Although exemplary embodiments have been described herein with reference to the accompanying figures, it should be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications can be made in those embodiments by those skilled in the art without departing from the scope of the appended claims.

Claims

1. Gate and a first source / drain region; a second source / drain region; a power rail disposed below the gate, the first source / drain region, and the second source / drain region; wherein the power rail extends to a diffusion isolation, the power rail being in electrical contact with the first source / drain region and the diffusion isolation.

2. 2. The semiconductor structure of claim 1 wherein said first source / drain region is disposed on a first side of said gate and said second source / drain region is disposed on a second side of said gate.

3. 2. The semiconductor structure of claim 1 wherein said second source / drain regions are insulated from said power rail by a dielectric layer.

4. 10. The semiconductor structure of claim 1 wherein said gate is insulated from said power rail by a dielectric layer.

5. 10. The semiconductor structure of claim 1 further comprising a contact, said second source / drain region being disposed between said contact and said power rail.

6. 6. The semiconductor structure of claim 5 wherein said contacts are electrically isolated from said power rails by a dielectric layer.

7. a first active gate; a diffusion isolation including an isolation region configured to electrically isolate the first active gate from at least a second active gate; a power rail disposed below the first active gate and extending to the diffusion isolation; wherein the diffusion isolation includes a contact electrically coupled to the power rail.

8. the isolation region of the diffusion isolation includes an inactive gate structure, and the second active gate is disposed on an opposite side of the inactive gate structure from the first active gate; the power rail extends through the diffusion isolation and underneath the second active gate; 8. The semiconductor structure of claim 7.

9. the isolation region of the diffusion isolation includes first and second isolation regions, and the second active gate is disposed on an opposite side of the first and second isolation regions from the first active gate; the power rail extends to the first isolation region; a second power rail extending from the second isolation region to beneath the second active gate; 8. The semiconductor structure of claim 7.

10. the contact extends between the first isolation region and the second isolation region of the diffusion isolation; the power rail is electrically coupled to the contact in the first isolation region; the second power rail is electrically coupled to the contact in the second isolation region; 10. The semiconductor structure of claim 9.

11. 10. The semiconductor structure of claim 9 wherein the first and second isolation regions each comprise an inactive gate filled with a dielectric material.

12. 8. The semiconductor structure of claim 7, wherein said contact comprises a first contact on said diffusion isolation, said diffusion isolation comprising at least a second contact electrically insulated from said first contact by a dielectric layer, said second contact electrically coupled to a second power rail extending from said diffusion isolation under a third gate.

13. a semiconductor substrate; a first dielectric layer disposed on the semiconductor substrate; a power rail disposed on the first dielectric layer; a second dielectric layer disposed on the power rail; a gate extending from the second dielectric layer; and Including, A semiconductor structure wherein at least a portion of said power rail is disposed on a shallow trench isolation layer.

14. a semiconductor substrate; a first dielectric layer disposed on the semiconductor substrate; a power rail disposed on the first dielectric layer; a second dielectric layer disposed on the power rail; a gate extending from the second dielectric layer; and Including, The semiconductor structure, wherein the second dielectric layer includes at least one gap, and the power rail is in electrical communication with at least one source / drain region through the at least one gap.

15. 15. The semiconductor structure of claim 14 wherein said power rail is electrically isolated from at least another source / drain region by said second dielectric layer.

16. 15. The semiconductor structure of claim 14 wherein said power rail is electrically isolated from said gate by said second dielectric layer.

17. a plurality of semiconductor devices, each of the semiconductor devices being insulated from an adjacent semiconductor device by a dielectric layer; a first diffusion isolation extending across the plurality of semiconductor devices; a second diffusion isolation extending across the plurality of semiconductor devices; a plurality of active gates extending across the plurality of semiconductor devices; wherein the plurality of active gates are disposed between the first diffusion isolation and the second diffusion isolation, and each semiconductor device includes a power rail extending between the first diffusion isolation and the second diffusion isolation beneath the plurality of active gates.

18. 18. The semiconductor structure of claim 17, wherein said first diffusion isolation comprises a first contact and a second contact, said first contact insulated from said second contact by said dielectric layer, said first contact electrically coupled to said power rail of a first semiconductor device of said plurality of semiconductor devices, and said second contact electrically coupled to said power rail of a second semiconductor device of said plurality of semiconductor devices.

19. 20. The semiconductor structure of claim 18, wherein said second diffusion isolation comprises a third contact and a fourth contact, said third contact insulated from said fourth contact by said dielectric layer, said third contact electrically coupled to said power rail of said first semiconductor device, and said fourth contact electrically coupled to said power rail of said second semiconductor device.

20. each semiconductor device includes a plurality of source / drain regions interposed between said gates; a first source / drain region of a first semiconductor device of the plurality of semiconductor devices is disposed in electrical contact with the power rail of the first semiconductor device; 20. The semiconductor structure of claim 17 wherein a second source / drain region of said first semiconductor device is electrically isolated from said power rail of said first semiconductor device.

21. 21. The semiconductor structure of claim 20, wherein said first source / drain region is disposed on a first side of a particular active gate of said plurality of active gates and said second source / drain region is disposed on a second side of said particular active gate.

22. forming a stack structure on a semiconductor substrate, the stack structure including a first sacrificial layer, a second sacrificial layer, a third sacrificial layer disposed between the first sacrificial layer and the second sacrificial layer, a plurality of additional sacrificial layers, and a plurality of channel layers; forming a plurality of gate structures on the stack structure; replacing the first and second sacrificial layers with a dielectric material to form corresponding first and second dielectric layers, the dielectric material also forming sidewalls on the gate structure; etching the plurality of additional sacrificial layers, the plurality of channel layers, and the second dielectric layer between a first gate structure and a second gate structure of the plurality of gate structures to expose the third sacrificial layer through the second dielectric layer; forming source / drain regions between the first gate structure and the second gate structure in contact with the third sacrificial layer; opening a specific gate structure among the plurality of gate structures to expose the third sacrificial layer; replacing the third sacrificial layer with a power rail, the power rail contacting the source / drain regions; 1. A method for fabricating a semiconductor structure, comprising:

23. 23. The method of claim 22, wherein the thickness of the third sacrificial layer is greater than the thickness of the second sacrificial layer.

24. 23. The method of claim 22, further comprising filling the particular gate structure with a dielectric material to form a diffusion isolation isolation region, the diffusion isolation including a contact electrically coupled to the power rail for supplying power to the power rail.

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