Method of making a small geometry contact using sidewall spacers

Abstract

A contact between a heavily-doped region in the substrate and metal is made via a hole in a thick oxide layer and a polysilicon layer. The polysilicon layer is first etched to form a hole for establishing a mask for the eventual contact hole. Prior to forming the contact hole, a sidewall spacer of polysilicon is formed in the hole in the polysilicon layer. A thin oxide layer over the polysilicon layer is used for convenient end point detection during the formation of the polysilicon sidewall spacers. The sidewall spacer reduces the bore dimension of the hole in the polysilicon used for the mask for forming the contact hole. A hole is then etched in the thick oxide which is sloped and which has a bore dimension determined by the hole in the polysilicon which is reduced due to the sidewall spacer. The heavily-doped region, the contact hole, and the remaining polysilicon are coated with a barrier. The contact hole is then filled with a conductive material which also coats the barrier. The resulting conductive material, barrier, and polysilicon, are conveniently selectively etched in a single process step. The contact adheres well because polysilicon is in contact with the thick oxide in the locations where there is going to applied any physical stress, such as a bonding pad.