US 5,510,288 A · Buried bit line mask ROM process

Abstract

A MOSFET device is formed on a lightly doped semiconductor substrate, starting by forming a first dielectric layer on the substrate; forming a mask with an array of openings therein over the dielectric layer, and forming thick silicon dioxide regions through openings in the mask. Dopant is ion implanted into the substrate through the mask between the thick silicon dioxide regions to form an array of buried bitline conductors. Perform an etch back through the mask of the thick silicon dioxide regions removing material to form channel openings in the thick silicon dioxide regions down to the substrate. Then deposit a gate oxide layer over the exposed substrate, forming a conformal array of conductors over the device extending down into the channel openings forming sidewalls therein narrowing the channel openings. Then, form a ROM code mask over the device with a ROM code opening over one of the channel openings; and ion implant dopant into the ROM code opening.

Claims20

Dependent claims

A method of fabricating an MOSFET device on a lightly doped semiconductor substrate comprising,

forming a first dielectric layer on said substrate,
forming over said dielectric layer a masking layer with an array of openings therein,
forming field oxide regions through said openings in said masking layer,
ion implanting dopant into said substrate through said masking layer between said thick silicon dioxide regions forming an array of buried conductors therein,
performing an anisotropic etch back through said masking layer of said field oxide regions to form channel openings in said field oxide regions down to expose the surface of said substrate,
forming a gate oxide layer over said substrate where exposed by said etch back,
forming a conformal array of conductors over said device extending down into said channel openings forming sidewalls therein narrowing said channel openings,
forming a ROM code mask over said device with a ROM code opening over one of said channel openings, and
ion implanting dopant into said ROM code opening.

6 more elements

Dependencies are inferred from the claim text.

Buried bit line mask ROM process

Life of this patent

Buried bit line mask ROM process

Life of this patent

Abstract

Claims20