Mask surrogate semiconductor process with polysilicon gate protection
First Claim
1. A method, employing no more than one independent mask to form a mask-surrogate pattern definer, of producing a field-effect power MOS semiconductor device in a substrate structure including a gate oxide layer on an upper surface of a semiconductor substrate, the method comprising:
- forming a dopant protective layer over the gate oxide layer;
masking and patterning the dopant protective layer to form a mask-surrogate pattern-definer having a defined outline characteristic so that the pattern-definer protects an underlying gate oxide region and a first portion of the upper surface of the substrate;
selectively removing a portion of the dopant protective layer and of the oxide layer to expose a second portion of the upper surface of the substrate within a region defined by the defined outline characteristic;
performing a first doping step to introduce first dopant into said exposed second upper surface portion of the substrate so as to form a first region of a first conductivity type, defining a MOS body region, said first region extending to an extent under a peripheral edge of the protective layer;
performing a second doping step to introduce second dopant into said exposed second upper surface portion so as to form a second region of a second conductivity type, opposite the first conductivity type, defining a MOS source region;
said second MOS region being wholly contained in said first MOS region and not extending to said extent along the upper surface of the substrate, thereby to define a MOS channel beneath said gate oxide region;
the dopant protective layer including a dopant opaque polysilicon layer of a sufficient thickness to prevent the introduced dopants from penetrating the underlying gate oxide region, the polysilicon layer having an exposed upper surface;
reducing the thickness of the polysilicon layer; and
depositing a conductive material layer to form a gate conductive layer over the gate oxide region without a second masking step.
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Accused Products
Abstract
A dopant-opaque layer of polysilicon is deposited on gate oxide on the upper substrate surface to serve as a pattern definer during fabrication of the device. It provides control over successive P and N doping steps used to create the necessary operative junctions within a silicon substrate and the conductive structures formed atop the substrate. A trench is formed in the upper silicon surface and a source conductive layer is deposited to electrically contact the source region as a gate conductive layer is deposited atop the gate oxide layer. The trench sidewall is profile tailored using a novel O2 -SF6 plasma etch technique. An oxide sidewall spacer is formed on the sides of the pattern definer and gate oxide structures, before depositing the conductive material. A planarizing layer is applied and used as a mask for selectively removing any conductive material deposited atop the oxide spacer. The polysilicon layer on the oxide is reduced in thickness during trenching so that any conductive material deposited atop the spacers protrude upward for easy removal of excess, conductive material. The sidewall spacers can be sized, either alone or in combination with profile tailoring of the trench, to control source-region width (i.e., parasitic pinched base width) and proximity of the source conductor to the FET channel. Electrical contact between the source conductive layer and the source regions is enhanced by forming a low-resistivity layer between them.
20 Citations
10 Claims
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1. A method, employing no more than one independent mask to form a mask-surrogate pattern definer, of producing a field-effect power MOS semiconductor device in a substrate structure including a gate oxide layer on an upper surface of a semiconductor substrate, the method comprising:
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forming a dopant protective layer over the gate oxide layer; masking and patterning the dopant protective layer to form a mask-surrogate pattern-definer having a defined outline characteristic so that the pattern-definer protects an underlying gate oxide region and a first portion of the upper surface of the substrate; selectively removing a portion of the dopant protective layer and of the oxide layer to expose a second portion of the upper surface of the substrate within a region defined by the defined outline characteristic; performing a first doping step to introduce first dopant into said exposed second upper surface portion of the substrate so as to form a first region of a first conductivity type, defining a MOS body region, said first region extending to an extent under a peripheral edge of the protective layer; performing a second doping step to introduce second dopant into said exposed second upper surface portion so as to form a second region of a second conductivity type, opposite the first conductivity type, defining a MOS source region; said second MOS region being wholly contained in said first MOS region and not extending to said extent along the upper surface of the substrate, thereby to define a MOS channel beneath said gate oxide region; the dopant protective layer including a dopant opaque polysilicon layer of a sufficient thickness to prevent the introduced dopants from penetrating the underlying gate oxide region, the polysilicon layer having an exposed upper surface;
reducing the thickness of the polysilicon layer; anddepositing a conductive material layer to form a gate conductive layer over the gate oxide region without a second masking step. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification