Isolator for electrically isolating semiconductor devices in an integrated circuit

Claim 1

An isolator for isolating semiconductor devices in an integrated circuit on a semiconductor substrate comprising a trench of a predetermined depth and width formed on a top surface of the semiconductor substrate and having sidewalls, the trench is substantially filled wit ha silicon oxide layer grown by a chemical vapor deposition method, a silicon nitride layer in said trench is located between said sidewalls of said trench and said silicon oxide layer, and a small ditch created, by the use of a hydrofluoric acid to treat said silicon oxide layer, in the middle of a top surface of the silicon oxide layer in the trench is filled with a silicon layer, at least a top surface of which is thermally oxidized to form another silicon oxide layer, said small ditch extends from a top of said trench toward a bottom of said trench and has a wedge shape which has a wider width at the top of said trench, said width of said small ditch being the same width irrespective of said width of said trench.

Claim 3

A method of forming an isolator for isolating semiconductor devices in an integrated circuit on a semiconductor substrate comprising etching a trench having a predetermined width and depth in a semiconductor substrate surface, forming p+ regions on the bottom and sides of said trench growing a first silicon dioxide layer on said semiconductor surface including in said trench, depositing a second silicon dioxide layer on said silicon nitride layer and completely filling said trench with said second silicon dioxide layer, removing said second silicon dioxide layer from said silicon nitride layer except for a remaining thin film and except for that located in said trench, removing said thin film by treating it with a hydrofluoric acid, generating a small wedge-shaped ditch having a predetermined width and depth in said second silicon dioxide layer in the middle of said trench by said treating, said predetermined width of said small wedge-shaped ditch being the same width, irrespective of said width of said trench, depositing a polycrystalline silicon layer in said small ditch, oxidating said polycrystalline silicon layer so that a third silicon dioxide layer is obtained, and removing said silicon nitride layer and said first silicon dioxide layer from said semiconductor substrate surface except in said trench.

Claim 4

A method of forming an isolator for isolating semiconductor devices in an integrated circuit on a semiconductor substrate comprising etching a trench having a predetermined width and depth in a semiconductor substrate surface, forming p+ regions on the bottom and sides of said trench growing a first silicon dioxide layer on said semiconductor surface including in said trench, depositing a second silicon dioxide layer on said silicon nitride layer and completely filling said trench with said second silicon dioxide layer, removing said second silicon dioxide layer from said silicon nitride layer except for a remaining thin film and except for that located in said trench, removing said thin film by treating it with a hydrofluoric acid, generating a small wedge-shaped ditch having a predetermined width and depth in said second silicon dioxide layer in the middle of said trench by said treating, said predetermined width of said small wedge-shaped ditch being the same width, irrespective of said width of said trench, depositing a polycrystalline silicon layer in said small ditch, oxidating said polycrystalline silicon layer so that a third silicon dioxide layer is obtained, and removing said silicon nitride layer and said first silicon dioxide layer from said semiconductor substrate surface except in said trench.