Method for implanting the sidewalls of isolation trenches

Claim 1

A method for making isolation trenches comprising substantially vertical sidewalls in a semiconductor substrate, said method comprising the steps of: (a) depositing a predetermined thickness of a masking material over said substrate; (b) patterning said masking material to indicate the placement of said isolation trenches; (c) forming a spaced succession of windows through the masking material formed in step (a) in accordance with the pattern established in step (b), said windows comprising substantially vertical sidewalls and having a substantially horizontal bottom which coincides with the top surface of said substrate; (d) performing a series of ion implantations through said windows at varying depths into said substrate to implant ions which will coincide with the substantially vertical trench sidewalls; (e) depositing a conformally coating cover layer over said masking material formed in step (a) such that said conformal coating is also deposited into the windows formed in step (c); (f) etching said cover layer to remove horizontally disposed conformal coating such that the remaining conformal coating completely covers the vertical sidewalls of said windows and also covers a predetermined portion of the bottom of the windows, said etched conformal coating thereby narrowing the width of said windows; (g) etching said substrate using said masking material to produce a spaced succession of isolation trenches, wherein said isolation trenches comprise a width determined by the portion of said windows not covered by said conformal coating cover layer; (h) removing the remaining portions of said conformal covering layer; (i) oxidizing said isolation trenches; (j) performing a final ion implantation to implant ions which will coincide with the substantially horizontal bottom of said isolation trench; and (k) thermally oxidizing and subsequently etching said substrate so as to completely fill said spaced succession of isolation trences and planarize the final structure.

Claim 2

A method for making isolation trenches comprising substantially vertical sidewalls in a semiconductor substrate, said method comprising the steps of: (a) depositing a predetermined thickness of a masking material over said substrate; (b) patterning said masking material to indicate the placement of said isolation trenches; (c) forming a spaced succession of windows through the masking material formed in step (a) in accordance with the pattern established in step (b), said windows comprising substantially vertical sidewalls and having a substantially horizontal bottom which coincides with the top surface of said substrate; (d) performing a series of ion implantations through said windows at varying depths into said substrate to implant ions which will coincide with the substantially vertical trench sidewalls; (e) depositing a conformally coating cover layer over said masking material formed in step (a) such that said conformal coating is also deposited into the windows formed in step (c); (f) etching said cover layer to remove horizontally disposed conformal coating such that the remaining conformal coating completely covers the vertical sidewalls of said windows and also covers a predetermined portion of the bottom of the windows, said etched conformal coating thereby narrowing the width of said windows; (g) etching said substrate using said masking material to produce a spaced succession of isolation trenches, wherein said isolation trenches comprise a width determined by the portion of said windows not covered by said conformal coating cover layer; (h) removing the remaining portions of said conformal covering layer; (i) oxidizing said isolation trenches; (j) performing a final ion implantation to implant ions which will coincide with the substantially horizontal bottom of said isolation trench; and (k) thermally oxidizing and subsequently etching said substrate so as to completely fill said spaced succession of isolation trences and planarize the final structure.