Method of making dense vertical programmable read only memory cell structure

A method of forming a memory device on a semiconductor substrate, comprising the steps of:

• forming source and drain regions within the substrate at one surface thereof,
• depositing a layer of isolation dielectric to a thickness on said substrate surface,
• removing an initial portion of the isolation dielectric by an isotropic etch through a mask opening positioned between said source and drain regions,
• thereafter removing a remaining portion of the isolation dielectric by an anisotropic etch through said mask opening, thereby to form a trench in said isolation dielectric that exposes the substrate surface to a pattern substantially that of said mask opening,
• depositing a second dielectric layer over said trench,
• anisotropically etching away said second dielectric in a manner to leave dielectric spacers along sidewalls of said trench, and
• forming at least one conductive element within said trench and along said sidewall spacers thereof in a manner to form a memory cell therein.