Method for fabricating super-steep retrograde well MOSFET on SOI or bulk silicon substrate, and device fabricated in accordance with the method
View Patent ↗A method is provided to fabricate a semiconductor device, where the method includes providing a substrate comprised of crystalline silicon; implanting a ground plane in the crystalline silicon so as to be adjacent to a surface of the substrate, the ground plane being implanted to exhibit a desired super-steep retrograde well (SSRW) implant doping profile; annealing implant damage using a substantially diffusionless thermal annealing to maintain the desired super-steep retrograde well implant doping profile in the crystalline silicon and, prior to performing a shallow trench isolation process, depositing a silicon cap layer over the surface of the substrate. The substrate may be a bulk Si substrate or a Si-on-insulator substrate. The method accommodates the use of an oxynitride gate stack structure or a high dielectric constant oxide/metal (high-K/metal) gate stack structure. The various thermal processes used during fabrication are selected/controlled so as to maintain the desired super-steep retrograde well implant doping profile in the crystalline silicon.
1. A method to fabricate a semiconductor device, comprising:
providing a substrate comprised of crystalline silicon;
implanting a ground plane in the crystalline silicon so as to be adjacent to a surface of the substrate, the ground plane being implanted to exhibit a desired super-steep retrograde well implant doping profile;
annealing implant damage using a substantially diffusionless thermal annealing to maintain the desired super-steep retrograde well implant doping profile in the crystalline silicon; and
performing a silicon epitaxy to deposit a silicon cap layer of undoped silicon over the surface of the substrate in order to provide an undoped channel region for the semiconductor device; and thereafter forming a shallow trench isolation structure, where formation of the shallow trench isolation structure after deposition of the silicon cap layer of undoped silicon enables the silicon cap layer to remain free of faceting.
2. The method of claim 1 , where the silicon epitaxy is performed at a temperature at or below about 700° C. to maintain the desired super-steep retrograde well implant doping profile.
3. The method of claim 1 , where forming the shallow trench isolation structure comprises defining an active device area on top of the silicon cap layer with padfilms deposition processes controlled to maintain the desired super-steep retrograde well implant doping profile, photolithographically defining the active device area on the padfilm, retaining a portion of the padfilm over the active area, depositing shallow trench isolation oxide and selectively removing the shallow trench isolation oxide by a process that stops on the padfilm to form the shallow trench isolation structure that surrounds the active device area and extends through the silicon cap layer and into the substrate.
4. The method of claim 3 , further comprising removing the padfilm within the active area to expose the underlying silicon cap layer, forming a gate oxide structure upon the exposed silicon cap layer, and depositing a layer of polycrystalline silicon over the gate oxide structure.
5. The method of claim 4 , further comprising doping the polycrystalline silicon layer with a dopant species appropriate for whether the device within the active area is to be an N-type or a P-type field effect transistor, photolithographically defining an upstanding gate stack structure that includes the gate oxide structure and an overlying portion of the doped polycrystalline silicon layer, forming a reoxidation gate stack structure cap and performing a rapid thermal anneal to diffuse the doping in the overlying portion of the polycrystalline silicon layer while not appreciably affecting the desired super-steep retrograde well implant doping profile in the underlying crystalline silicon.
6. The method of claim 5 , further comprising forming an offset spacer over the reoxidation gate stack structure cap, implanting extensions, forming a final spacer over the offset spacer, implanting deep source and drain regions, annealing to activate the implanted extensions and source drain regions with a thermal process selected to not appreciably affect the desired super-steep retrograde well implant doping profile in the underlying crystalline silicon, and forming silicide regions over the implanted source and drain regions and over the gate stack structure.
7. The method of claim 6 , where the substrate is a silicon-on-insulator substrate, where the ground plane is formed in a crystalline silicon layer that overlies a buried oxide layer, and where the deep source and drain implants create deep source drain junctions that are butted against the layer of buried oxide.
8. The method of claim 6 , where substrate is a bulk crystalline silicon substrate, where implanting a ground plane further comprises implanting a higher energy well to provide well isolation, and where the deep source and drain implants create a graded junction at a bottom of the deep source and drain implant region.
9. The method of claim 3 , further comprising removing the padfilm within the active area to expose the silicon cap layer, forming a high dielectric constant oxide/metal gate structure upon the exposed silicon cap layer, and depositing a layer of polycrystalline silicon over the high dielectric constant oxide/metal gate structure.
10. The method of claim 9 , further comprising doping the polycrystalline silicon layer with a dopant species appropriate for whether the device within the active area is to be an N-type or a P-type field effect transistor, photolithographically defining an upstanding gate stack structure that includes the high dielectric constant oxide/metal gate structure and an overlying portion of the doped polycrystalline silicon layer, forming a nitride gate stack structure cap and performing a rapid thermal anneal to diffuse the doping in the overlying portion of the polycrystalline silicon layer while not appreciably affecting the desired super-steep retrograde well implant doping profile in the underlying crystalline silicon.
11. The method of claim 10 , further comprising forming an offset spacer over the nitride gate stack structure cap, implanting extensions, forming a final spacer over the offset spacer, implanting deep source and drain regions, annealing to activate the implanted extensions and source drain regions with a thermal process selected to not appreciably affect the desired super-steep retrograde well implant doping profile in the underlying crystalline silicon, and forming silicide regions over the implanted source and drain regions and over the gate stack structure.
12. The method of claim 11 , where the substrate is a bulk crystalline silicon substrate, where implanting a ground plane further comprises implanting a higher energy well to provide well isolation, and where the deep source and drain implants create a graded junction at a bottom of the deep source and drain implant region.
13. The method of claim 1 , where the substrate is a silicon on insulator substrate and where the ground plane is implanted in a crystalline silicon layer that overlies a buried oxide layer.
14. The method of claim 1 , where the substrate is a bulk crystalline silicon substrate, and where implanting a ground plane further comprises implanting a higher energy well to provide well isolation.
15. The method of claim 4 , where the gate oxide structure is comprised of one of silicon dioxide or silicon oxynitride.
16. The method of claim 9 , where the high dielectric constant oxide/metal gate structure is comprised of layers of at least one of HfO 2 , ZrO 2 , Ti 2 O 5 and TiN, TaN.
17. The method of claim 11 , where the substrate is a silicon-on-insulator substrate, where the ground plane is implanted in a crystalline silicon layer that overlies a buried oxide layer, and where the deep source and drain implants create deep source drain junctions that are butted against the buried oxide layer.
18. The method of claim 1 , where formation of the shallow trench isolation structure after deposition of the silicon cap layer of undoped silicon enables the silicon cap layer to remain substantially uniform in thickness.