Manufacturing method for wafer slice starting material to optimize

Abstract

A method of manufacturing a silicon substrate which optimizes extrinsic gettering during semiconductor fabrication is provided in which phosphorous ions are diffused into the backside surface of a silicon substrate during wafer slice manufacture. Forming gettering sites at the backside surface prior to gate polysilicon deposition, extrinsic gettering is optimized. Initially, both the frontside and backside surfaces of a silicon substrate are subjected to dopant materials. Thereafter, at least one thin film is formed on both the frontside and backside surfaces. The thin films are then removed from the frontside surface along with a layer of the silicon substrate immediately below the frontside surface to a depth of about 10.0 .mu.m. The final polishing step of a typical silicon wafer manufacturing process removes a layer of silicon to a depth of about 10.0 .mu.m at the frontside surface of the silicon wafer, thus allowing the wafer slice material manufacturing method of the present invention to be easily be incorporated into a standard silicon wafer manufacturing process. It is estimated that at least 99 percent of the dopants introduced into the frontside surface are removed with the upper 10.0 .mu.m of silicon. The thin films formed on the backside surface of the silicon substrate remain, preventing outgassing of dopant impurities during subsequent thermal processing steps. A polysilicon thin film formed over the backside surface may also provide an additional source of extrinsic gettering.