Method of making a substrate contact for an integrated circuit

Claim 1

An improved method for altering the threshold voltage characteristics of individual, isolated silicon gate IGFETs comprising the steps of: (a) forming a plurality of IGFETs having silicon gates on a single substrate; (b) forming metal contacts to said IGFETs, said metal contacts not overlying the gates of selected ones of said IGFETs; (c) forming a protective oxide layer over said IGFETs and over said metal contacts; wherein the improvement comprises: (a) photolithographically defining an etch resistant mask through which are exposed the portions of said protective oxide layer which overlie: (i) selected portions of said metal contacts, which selected portions of said metal contacts are used as bond pads; and (ii) selected ones of said silicon gates, which selected ones of said silicon gates are the individual, isolated silicon gate IGFETs whose threshold voltage characteristics are to be modified; (b) removing said exposed portions of said protective oxide layer by etching, thereby exposing said selected portions of said metal contacts and the silicon gates of said selected ones of said IGFETs; then (c) ion implanting selected conductivity modifiers through said selected isolated silicon gates, through the underlying gate insulator and into the channel region of the selected IGFETs, thereby modifying the threshold voltage characteristics of said selected IGFETs.