Isolation between diffusion lines in a memory array

Abstract

A method of forming a memory device with improved isolation between diffusion lines. Parallel, spaced apart thick oxide strips are grown on a substrate. Next, spaced apart, parallel strips having a polysilicon and nitride layer, oriented perpendicular to the first strips, are formed. The oxide between the second strips is removed, followed by an implantation to form source and drain regions. The nitride layer on the second strips is removed on those strips between two drain diffusions and an oxidation is performed to form self-aligned thick oxide over the source and drain regions. The strips from which the nitride has been removed are also oxidized, thus providing isolation between adjacent drain lines. In the formation of floating gate memory devices, a second polysilicon layer is deposited, and patterned in one direction to form strips overlying the second strips. After deposition of an intergate dielectric and a third polysilicon layer, a further patterning step is performed to form strips perpendicular to the second strips and second polysilicon layer and an etch is performed to etch the third polysilicon layer, intergate dielectric, second polysilicon layer and first polysilicon layer not covered by the patterning layer.