Patent ID: 7084035
Filing Date: 2006-08-01
Classification: H01L,Y10S

Abstract:
1. A method for forming three kinds of MOS transistors on a single semiconductor substrate, said three kinds of MOS transistors each being provided with gate oxides of differing thicknesses, comprising the steps of: (a) forming a dielectric layer for device isolation on a surface of the semiconductor substrate for defining first, second, and third regions; (b) depositing buffer oxide layers on a surface of said semiconductor substrate each overlying said first, second, and third regions; (c) forming an oxidation resistance layer to have an opening for exposing said first region and to mask said second and third regions; (d) performing a first thermal oxidation process for forming a first gate oxide layer by increasing a layer thickness of said oxide layer overlaying said first region; (e) removing said oxidation resistance layer; (f) depositing a first polysilicon layer over a surface of said semiconductor substrate to be pattered for forming a first gate electrode on said first gate oxide layer; (g) forming a resist pattern to have an opening for exposing said third region and to mask said first, and said second regions; (h) removing said buffer oxide layer on said third region using said resist pattern as a mask; (i) removing said resist pattern; (j) performing a second thermal oxidation process for forming a second gate oxide layer by increasing a layer thickness of said buffer oxide layer overlaying said second region, having a thickness different from said first gate oxide, and for forming a third gate oxide layer by increasing a layer thickness of said buffer oxide layer overlaying said third region, having a thickness different from said first, and said second gate oxides; (k) depositing a second polysilicon layer over the surface of said semiconductor substrate; and (l) patterning said second polysilicon layer for forming second, and third gate electrodes on said second, and third gate oxide layers, respectively.