Method of fabricating a semiconductor device having an asymmetrical dual-gate silicon-germanium (SiGe) channel MOSFET and a device thereby formed

[0002] Not Applicable.

[0003] Not Applicable.

[0004] Not Applicable.

[0005] 1. Field of the Invention

[0006] The present invention relates to semiconductor devices and their methods of fabrication. More particularly, the present invention relates to the formation of complimentary metal oxide semiconductor field effect transistors (MOSFETs). Even more particularly, the present invention relates to forming MOSFETs using differential silicides.

[0007] 2. Description of the Background Art

[0008] Currently, a double-gate silicon-on-insulator metal oxide semiconductor field effect transistor (SOI MOSFET) is receiving significant attention in the semiconductor industry due to its high current drive and high immunity to short-channel effects. As such, the dual-gate SOI MOSFET is a good candidate architecture for sub-0.25-μm gate length complementary metal oxide semiconductor (CMOS) technology. A dual-gate Fin-FET comprises an active layer being surrounded by a gate on both sides of a narrow silicon “fin.” However, only one gate electrode straddles across the silicon “fin” or active line. In some applications, a separate gate electrode may be required. By individually biasing two such gates (i.e., applying an “asymmetrical gate”), the threshold voltage of a MOSFET is more readily controllable. Dual-gate biasing of a transistor also potentially reduces standby power and/or improves on-state drive current through a “threshold dynamic voltage” design. However, these related art dual gates have limited carrier mobility (speed at which an electron or a hole can move). Therefore, a need exists for a method of fabricating a semiconductor device having an asymmetrical dual-gate MOSFET with a channel which improves carrier mobility.

[0009] Accordingly, the present invention provides a method of fabricating a semiconductor device having an asymmetrical dual-gate MOSFET with a silicon-germanium (SiGe) channel which improves carrier mobility, and a device thereby formed. Generally, the present invention device comprises a SiGe channel, which provides approximately 2 to 5 times more carrier mobility (especially with “holes”) than a related Si channel, because the present SiGe channel reduces carrier scattering and has a substantially lighter effective mass of “holes.” The present invention method for fabricating the present device, generally comprises: forming a dual-gate MOSFET having a SiGe/Si/SiGe sandwich structure; and forming a pair of asymmetrical gate electrodes. The unique features of the present method basically involve forming an epitaxial layer, comprising SiGe, on at least one sidewall of a narrow line, comprising Si; depositing a gate electrode material over the narrow line and the epitaxial layer; and polishing the gate electrode material, and thereby forming the pair of asymmetrical gate electrodes. This present invention dual-gate device, so formed, has the advantages of both a high drive current as well as a high immunity to short-channel effect (SCE), enabling further densification of transistors and circuits.

[0010] By way of example, and not of limitation, a semiconductor device, having an asymmetrical dual-gate MOSFET with a silicon-germanium (SiGe) channel, may be fabricated according to the present invention by: (a) patterning an active region of a silicon-on-insulator (SOI) structure (or wafer) with a first photoreist layer, wherein the SOI structure comprises a silicon dioxide (SiO₂) layer, a silicon (Si) layer deposited on the SiO₂layer, and a silicon nitride (Si₃N₄) layer deposited on the Si layer; (b) initiating formation of a SiGe/Si/SiGe sandwich fin structure from the SOI structure, wherein the step (b) comprises (b)(1) etching through the Si₃N₄and the Si layers, thereby forming a Si₃N₄/Si stack, the Si₃N₄/Si stack comprising a Si₃N₄cap layer and a reduced width Si layer, wherein the Si₃N₄/Si stack has a height in a range of approximately 800 Angstroms to approximately 1500 Angstroms, and (b)(2) further etching the Si layer by wet-etching, thereby forming a narrow line, comprising Si, under the Si₃N₄cap layer; (c) completing formation of the SiGe/Si/SiGe sandwich fin structure, wherein the step (c) comprises (c)(1) forming an epitaxial layer, comprising SiGe, on at least one sidewall of the narrow line, and (c)(2) depositing a thin gate dielectric layer, wherein the thin gate dielectric layer comprises a high dielectric constant material such as Si₃N₄; (d) depositing a thick gate material layer on SiGe/Si/SiGe sandwich fin structure, wherein the thick gate material layer has a thickness in a range of approximately 3000 Angstroms to approximately 6000 Angstroms, and wherein the thick gate material layer comprises a material selected from a group consisting essentially of polysilicon (poly-Si), poly-SiGe, and a metal; and (e) forming an asymmetrical dual gate, wherein the step (e) comprises (e)(1) polishing the gate material, thereby forming a polished gate material, whereby the Si₃N₄cap layer acts as a polishing-stop, wherein the polishing step (e)(1) may be performed by a technique such as chemical-mechanical polishing (CMP), (e)(2) patterning the polished gate material with a second photoreist layer; (e)(3) etching the patterned polished gate material, thereby forming a pair of asymmetrical gate electrodes, and (e)(4) completing processing of the asymmetrical gate electrodes, thereby forming the asymmetrical dual-gate, wherein the asymmetrical dual gate is separated by the Si₃N₄cap layer; and (f) completing fabrication of the semiconductor device (e.g., formation of source/drain structure).

[0011] An object of the present invention is to reduce carrier scattering and provide a substantially lighter effective mass of “holes” in a MOSFET.

[0012] Another object of the present invention is to provide a method for fabricating a semiconductor device, having an asymmetrical dual-gate MOSFET with a silicon-germanium (SiGe) channel which improves carrier mobility.

[0013] Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.

[0014] For a better understanding of the present invention, reference is made to the below-referenced accompanying drawing(s) which is/are for illustrative purposes and where like reference numbers denote like elements.

[0015] FIG. 1 through FIG. 6, together, constitute a process flow diagram of the fabrication of a semiconductor device, in accordance with the present invention, wherein the semiconductor device is shown in cross-section at various stages of the process.

[0016] Referring more specifically to the drawings for illustrative purposes, the present invention is embodied in the apparatus and method generally shown in FIG. 1 through FIG. 6. These figures depict an embodiment of a process for fabricating a semiconductor device, having an asymmetrical dual-gate MOSFET with a silicon-germanium (SiGe) channel which improves carrier mobility. Each figure illustrates a particular processing stage, and presents a side view in cross-section of the device at that stage of processing. However, that the apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein, will be appreciated.

[0017] Referring first to FIG. 1, in the first stage of processing, an active region of a silicon-on-insulator (SOI) structure (or wafer) 10 is patterned with a first photoreist layer 20, wherein the SOI structure 10 may comprise a silicon dioxide (SiO₂) layer 11, a silicon (Si) layer 12 is deposited on the SiO₂layer 11, and a silicon nitride (Si₃N₄) layer 13 is deposited on the Si layer 12.

[0018] Next, as shown in FIG. 2, an initial SiGe/Si/SiGe sandwich fin structure 30 is formed from the SOI structure 10, wherein the SiGe/Si/SiGe sandwich fin structure 30 is initially formed by etching through the Si₃N₄layer 13 and the Si layer 12, thereby forming a Si₃N₄/Si stack 15, the Si₃N₄/Si stack comprising a Si₃N₄cap layer 16 and a reduced width Si layer 17, and wherein the Si₃N₄/Si stack may have a height in a range of approximately 800 Angstroms to approximately 1500 Angstroms, and by further etching the reduced width Si layer 17 by wet-etching, thereby forming a narrow line 18, comprising Si, under the Si₃N₄cap layer 16.

[0019] Next, as shown in FIG. 3, a complete SiGe/Si/SiGe sandwich fin structure 35 is formed on the SiO₂layer 11, wherein the complete SiGe/Si/SiGe sandwich fin structure 35 is finally formed by forming an epitaxial layer 36, comprising SiGe, on at least one sidewall of the narrow line, and by depositing a thin gate dielectric layer 37 on the epitaxial layer 36, the cap layer 16, and any exposed portion of the SiO₂layer 11, wherein the thin gate dielectric layer 37 may comprise a high dielectric constant material such as Si₃N₄.

[0020] Next, as shown in FIG. 4, a thick gate material layer 40 is deposited on the thin gate dielectric layer 37 (i.e., over the complete SiGe/Si/SiGe sandwich fin structure 35), wherein the thick gate material layer 40 may have a thickness in a range of approximately 3000 Angstroms to approximately 6000 Angstroms, and wherein the thick gate material layer 40 may comprise a material selected from a group consisting essentially of polysilicon (poly-Si), polysilicon-germanium (poly-SiGe), and a metal.

[0021] Next, as shown in FIG. 5, an asymmetrical dual-gate 45 is formed, wherein the asymmetrical dual-gate 45 is formed by polishing the gate material 40, thereby forming a polished gate material 41, whereby the Si₃N₄cap layer 16 acts as a polishing-stop, wherein the polishing step may be performed by a technique such as chemical-mechanical polishing (CMP); by patterning the polished gate material 41 with a second photoreist layer (not shown); by etching the patterned polished gate material 41, thereby forming a pair of asymmetrical gate electrodes; and by completing processing of the asymmetrical gate electrodes, thereby forming the asymmetrical dual-gate 45, wherein each gate of the asymmetrical dual-gate 45 is separated by the Si₃N₄cap layer.

[0022] As depicted in FIG. 6, a source/drain structure 50 is formed in the substrate 10, wherein the source/drain structure 50 is disposed adjacent to the complete SiGe/Si/SiGe sandwich fin structure 35, and wherein the asymmetrical dual-gate 45 flanks the complete SiGe/Si/SiGe sandwich fin structure 35 and is disposed approximately 90° from the source/drain structure 50.

[0023] Information as herein shown and described in detail is fully capable of attaining the above-described object of the invention, the presently preferred embodiment of the invention, and is, thus, representative of the subject matter which is broadly contemplated by the present invention. The scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and is to be limited, accordingly, by nothing other than the appended claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described preferred embodiment and additional embodiments that are known to those of ordinary skill in the art are hereby expressly incorporated by reference and are intended to be encompassed by the present claims.

[0024] Moreover, no requirement exists for a device or method to address each and every problem sought to be resolved by the present invention, for such to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. However, it should be readily apparent to those of ordinary skill in the art that various changes and modifications in form, semiconductor material, and fabrication material detail may be made without departing from the spirit and scope of the inventions as set forth in the appended claims. No claim herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”