Oxygen-impervious pad structure on a semiconductor substrate

Claim 1

An oxygen-impervious pad on a silicon substrate for integrated circuit devices, the pad preventing the formation of bird's beak profiles in recessed oxide isolation (ROX) structures, comprising: a layer (12) of silicon oxide overlaying the silicon substrate - (10); a layer (1 4 ) of silicon nitride overlaying said layer of silicon oxide, said layer of silicon nitride and said layer of silicon oxide being etched to form a pad structure (100) having substantially vertical sidewalls; a first oxygen-impervious layer (20) coated on said sidewalls of said structure to form spacers (20A) thereon, said first oxygen-impervious layer producing a negligible amount of film stress on the silicon substrate as compared to a silicon nitride layer; and a second oxygen-impervious layer ( 1 8) disposed between said first oxygen-impervious layer (20) and the silicon substrate (10); said first oxygen-impervious layer preventing diffusion of oxygen through said sidewalls of said structure and said second oxygen-impervious layer preventing diffusion of oxygen into the regions of the substrate lying beneath the pad.

Claim 6

A method of forming an oxygen-impervious pad on a semiconductor substrate, comprising the steps of: forming an oxide layer (12) on a surface of the semiconductor substrate (10); forming a layer (14) of silicon nitride on said oxide layer; etching said layer of silicon nitride and said oxide layer through a mask (16) to define a structure (100) having substantially vertical sidewalls; forming a thin oxygen-impervious layer (18) on the semiconductor substrate (10); forming a thick oxygen-impervious layer (20) on said structure and on said thin oxygen-impervious layer (18); and anisotropically etching said thick oxygen-impervious layer - (20) to form spacers (20A) on said vertical sidewalls of said structure (100), said spacers overlying portions of said thin oxygen-impervious layer (18) to protect said portions from removal during said step of etching said thick oxygen--impervious layer (20).

Claim 7

A method of forming an oxygen-impervious pad on a semiconductor substrate, comprising the steps of: forming an oxide layer (12) on a surface of the semiconductor substrate (10); forming a layer (14) of silicon nitride on said oxide layer; etching said layer of silicon nitride and said oxide layer through a mask (16) to define a structure (100) having substantially vertical sidewalls; forming a thin oxygen-impervious layer (18) on the semiconductor substrate (10); forming a thick oxygen-impervious layer (20) on said structure and on said thin oxygen-impervious layer (18); and anisotropically etching said thick oxygen-impervious layer - (20) to form spacers (20A) on said vertical sidewalls of said structure (100), said spacers overlying portions of said thin oxygen-impervious layer (18) to protect said portions from removal during said step of etching said thick oxygen--impervious layer (20).

Claim 9

The method as recited in claims 5 or 6, wherein said thin and thick oxygen-impervious layers (18, 20) are comprised of oxynitride.

Claim 10

The method as recited in claims 5 to 7, with the thickness ratio of said thin and thick oxygen-impervious layers (18, 20) being in the order of about 50Å/500-1000Å.

Claim 11

The method as recited in one of claims 5 to 8, wherein said oxygen-impervious layer has a refractive index in the order of 1.75 to 1.80.