Extension of shallow trench isolation by ion implantation

Abstract

A shallow trench isolation (STI) structure is formed by etching trenches into the surface of a substrate in alignment with a patterned masking layer. An ion implantation of, for example, carbon, nitrogen, or oxygen, is performed so as to create an electrically insulating layer extending downwardly from a bottom surface of the trench. By implanting such extensions, STI structures with greater effective aspect ratios may be obtained which, in turn, allow greater packing density in integrated circuits. Implanted isolation structures may be formed without etching a trench by implanting into regions of the substrate. In this way, trench etch, dielectric back-fill, and planarization operations can be eliminated. Furthermore the implanted regions may be formed by multiple implants at different energies so as to obtain multiple, typically contiguous, target ranges. Ions of various masses or charges may be used so as to obtain the desired implant depth and concentration profile in the isolation structures, independent of whether these structures are trench extensions or formed directly beneath a planarized substrate surface.