Method for fabricating MOS transistors having gates with different work functions
First Claim
1. A method for fabricating an insulated gate field effect transistor (IGFET) comprising the steps of:
- providing a semiconductor substrate;
forming a layer of gate dielectric material on the semiconductor substrate;
forming a layer of semiconductor material on the gate dielectric material layer;
providing a pattern of masking material on the layer of semiconductor material, through which selected areas of the layer of semiconductor material are exposed;
introducing an impurity of a first conductivity type into the selected areas of the semiconductor material layer;
diffusing the impurity of the first conductivity type a selected distance into the semiconductor material layer laterally under the masking material pattern, wherein the selected distance is less than that required to completely dope the semiconductor material under the masking material pattern, leaving a central portion of the conductive material pattern undoped with the impurity of the first conductivity type; and
providing an impurity of a second conductivity type into the central portion.
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Accused Products
Abstract
A method for fabricating an insulated gate field effect transistor (IGFET) having a semiconductor gate with a first portion and a second portion where the portions are of two different conductivity types. Typically, a central portion of the gate, such as a doped polysilicon gate of a first conductivity type, is flanked by end portions near the source/drain regions, where the end portions are doped with an impurity of a second conductivity type. A semiconductor material layer, such as polycrystalline silicon (polysilicon) is selectively protected by a gate pattern mask whereby the end portions of the gates are produced by the lateral diffusion of the dopant under the edges of the gate pattern mask. Thus, the technique for defining the different portions of the gate uses other than photolithographic techniques which are limited in their resolution capabilities, and thus is readily implementable in submicron device feature processes.
138 Citations
21 Claims
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1. A method for fabricating an insulated gate field effect transistor (IGFET) comprising the steps of:
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providing a semiconductor substrate; forming a layer of gate dielectric material on the semiconductor substrate; forming a layer of semiconductor material on the gate dielectric material layer; providing a pattern of masking material on the layer of semiconductor material, through which selected areas of the layer of semiconductor material are exposed; introducing an impurity of a first conductivity type into the selected areas of the semiconductor material layer; diffusing the impurity of the first conductivity type a selected distance into the semiconductor material layer laterally under the masking material pattern, wherein the selected distance is less than that required to completely dope the semiconductor material under the masking material pattern, leaving a central portion of the conductive material pattern undoped with the impurity of the first conductivity type; and providing an impurity of a second conductivity type into the central portion. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for fabricating an insulated gate field effect transistor (IGFET) comprising the steps of:
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providing a semiconductor substrate lightly doped with an impurity; forming a layer of gate dielectric material on the semiconductor substrate; forming a layer of semiconductor material on the gate dielectric material layer; providing a pattern of masking material on the layer of semiconductor material, through which selected areas of the layer of semiconductor material are exposed; introducing an impurity of a first conductivity type into the selected areas of the semiconductor material layer; diffusing the impurity of the first conductivity type in the selected areas of the semiconductor material layer a selected distance into the semiconductor material layer laterally under the masking material pattern, wherein the selected distance is less than that required to completely dope the semiconductor material under the masking layer, leaving a central portion of the conductive material pattern undoped with the impurity of the first conductivity type; removing the selected areas of the semiconductor material to leave a gate of semiconductor material having end portions and the central portion between the end portions, the end portions being lightly doped with the impurity of the first conductivity type; and providing an impurity of a second conductivity type in the central portion. - View Dependent Claims (9, 10, 11, 12, 13)
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14. A process for fabricating an insulated gate field effect transistor (IGFET) comprising the steps of:
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providing a monocrystalline silicon substrate lightly doped with an impurity of a first conductivity type; forming a layer of gate silicon oxide on the silicon substrate; forming a layer of undoped polycrystalline silicon on the gate silicon oxide layer; providing a pattern of masking material on the layer of polycrystalline silicon, through which selected areas of the layer of polycrystalline silicon are exposed; introducing an impurity of the first conductivity type into the selected areas of the polycrystalline silicon layer; diffusing the impurity of the first conductivity type in the selected areas of the polycrystalline silicon layer a selected distance into the polycrystalline silicon layer laterally under the masking material pattern; removing the selected areas of the polycrystalline silicon to leave a polycrystalline silicon gate having end portions and a central portion therebetween, the end portions being lightly doped with the impurity of a first conductivity type; and introducing an impurity of a second conductivity type into the central portion of the gate and the silicon substrate using the gate as mask to simultaneously form a heavily doped central portion and heavily doped source/drain regions respectively, of a second conductivity type. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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Specification