Construction of short-length electrode in semiconductor device

Abstract

A construction process employs an insulating abutment which serves as a guide in the formation of a shortlength electrode in the fabrication of a semiconductor device. The process is particularly useful in construction of extremely short channel asymmetric lightly doped drain (LDD) silicon FET's in which case a bird beak is formed on the surface of a silicon wafer. The bird beak is composed of silicon dioxide produced by oxidation of the silicon substrate with the aid of an oxidation resistant covering of silicon nitride, the edge of which defines the location of the abutment. Reactive ion etching is employed to remove excess silicon dioxide leaving a vertical wall at one side of the abutment. Thereafter, the silicon nitride layer is stripped off leaving a slating roof to the abutment. A dope polysilicon layer is deposited conformally on the surface of the substrate and on the abutment to a depth equal to the desired length of the electrode. Further reactive ion etching removes all of the polysilicon except for the portion thereof appended to the vertical wall of the abutment. Thereafter, ion implantation establishes a drain region at the side of the abutment having the slanting roof and a source region at the side of the abutment facing the vertical wall. The profile of the ion implantation follows the profile of the abutment enabling the stopping properties of the abutment to constrict the amount of charge implanted in the drain side of the channel.