Method of manufacturing field effect transistors having self-registering source and drain regions to minimize capacitances

Claim 1

A method of manufacturing a semiconductor device comprising the steps of (a) forming an insulating layer on a surface of a semiconductor substrate of silicon by oxidizing said substrate to form a layer of silicon dioxide, said insulating layer having a thickness of approximately 0.45 μm, (b) implanting ions through said insulating layer over said surface with an ion implantation dose of 1.5×10 13 ions/cm 2 at 150 kcV, said ion implantation forming an increased acceptor level at said surface, (c) forming at least one aperture through said insulating layer to said surface, (d) depositing a layer of polycrystalline silicon of a thickness ranging from 2 nm to at most 100 nm both on said surface in said aperture and on said insulating layer, said layer of polycrystalline silicon being deposited at a pressure rangiing from 0.01 to 10 Torr and at a temperature below 800° C., (e) thermally heating said layer of polycrystalline silicon to change said layer in said aperture to monocrystalline silicon by recrystallization, (f) depositing an epitaxial layer of silicon over said monocrystalline silicon and remaining portions of said polycrystalline silicon at a temperature of approximately 1050° C., said epitaxial layer forming a monocrystalline portion in said aperture and a polycrystalline portion outside said aperture, said epitaxial layer having a thickness ranging from 0.4 μm to 0.6 μm, (g) doping said epitaxial layer in said aperture with phosphorous by diffusion, (h) continuing said diffusion below said epitaxial layer into said substrate to a depth of 0.7 μm, (i) patterning said polycrystalline portion of said epitaxial layer into a first wiring layer, (j) covering the entire structure with a layer of silicon oxide, (k) photolithographically forming a window through said layer of silicon oxide at said at least one aperture, (l) anisotropically etching a recess into said substrate to a depth of 0.8 μm through said window at said at least one aperture, said recess forming source and drain regions in said substrate at said surface at opposite sides of said recess, (m) providing a channel between said source and drain regions, said channel extending below said recess, and (n) growing gate oxide in said recess by thermal oxidation, said oxidation continuing in said recess adjacent said channel region until an oxide thickness of approximately 50 nm is achieved, said oxidation proceeding faster adjacent doped regions of said substrate than adjacent undoped regions of said substrate, such that said gate oxide is considerably more thickener between a gate electrode and said source and drain regions than adjacent said channel region, wherein stray capacitances between said source and drain regions and said gate electrode are decreased.

Claim 2

A method of manufacturing a semiconductor device comprising the steps of (a) forming an insulating layer on a surface of a semiconductor substrate of silicon by oxidizing said substrate to form a layer of silicon dioxide, said insulating layer having a thickness of approximately 0.45 μm, (b) implanting ions through said insulating layer over said surface with an ion implantation dose of 1.5×10 13 ions/cm 2 at 150 kcV, said ion implantation forming an increased acceptor level at said surface, (c) forming at least one aperture through said insulating layer to said surface, (d) depositing a layer of polycrystalline silicon of a thickness ranging from 2 nm to at most 100 nm both on said surface in said aperture and on said insulating layer, said layer of polycrystalline silicon being deposited at a pressure rangiing from 0.01 to 10 Torr and at a temperature below 800° C., (e) thermally heating said layer of polycrystalline silicon to change said layer in said aperture to monocrystalline silicon by recrystallization, (f) depositing an epitaxial layer of silicon over said monocrystalline silicon and remaining portions of said polycrystalline silicon at a temperature of approximately 1050° C., said epitaxial layer forming a monocrystalline portion in said aperture and a polycrystalline portion outside said aperture, said epitaxial layer having a thickness ranging from 0.4 μm to 0.6 μm, (g) doping said epitaxial layer in said aperture with phosphorous by diffusion, (h) continuing said diffusion below said epitaxial layer into said substrate to a depth of 0.7 μm, (i) patterning said polycrystalline portion of said epitaxial layer into a first wiring layer, (j) covering the entire structure with a layer of silicon oxide, (k) photolithographically forming a window through said layer of silicon oxide at said at least one aperture, (l) anisotropically etching a recess into said substrate to a depth of 0.8 μm through said window at said at least one aperture, said recess forming source and drain regions in said substrate at said surface at opposite sides of said recess, (m) providing a channel between said source and drain regions, said channel extending below said recess, and (n) growing gate oxide in said recess by thermal oxidation, said oxidation continuing in said recess adjacent said channel region until an oxide thickness of approximately 50 nm is achieved, said oxidation proceeding faster adjacent doped regions of said substrate than adjacent undoped regions of said substrate, such that said gate oxide is considerably more thickener between a gate electrode and said source and drain regions than adjacent said channel region, wherein stray capacitances between said source and drain regions and said gate electrode are decreased.