Method for manufacturing semiconductor device

Claim 1

A method for manufacturing a semiconductor device, comprising the steps of: forming a SiO 2 film on a semiconductor layer; laying down a first mask pattern on said SiO 2 film; using said first mask pattern, ion-implanting in said semiconductor layer an impurity of the conductivity type opposite to that of said semiconductor layer to form an ion injection layer of a conductivity type opposite to that of said semiconductor layer buried in said semiconductor layer; forming a thin layer on at least the side surfaces of said first mask pattern; selectively forming a second mask pattern on the portion of said SiO 2 film located between, and abutting, portions of said thin layer formed on said side surfaces of said first mask pattern, the material of said thin layer being different from the materials of said first and second mask patterns; selectively etching said portions of said thin layer formed on at least said side surfaces of said first mask pattern and said SiO 2 film under said latter portions and lying between said first and second mask patterns to expose said semiconductor layer; selectively etching the exposed portion of said semiconductor layer to form a trench substantially surrounding the implanted ions; forming an element isolation region by burying an insulating material in said trench; annealing said semiconductor layer to diffuse said impurity from said ion injection layer and thereby forming a well region of a conductivity type opposite to that of said semiconductor layer self-aligned with, and having a depth smaller than the depth of, said element isolation region in that portion of said semiconductor layer isolated by said element region; forming an electronic element on said well region; and wiring said element for connection.

Claim 2

A method for manufacturing a semiconductor device, comprising the steps of: forming a SiO 2 film on a semiconductor layer; laying down a first mask pattern on said SiO 2 film; using said first mask pattern, ion-implanting in said semiconductor layer an impurity of the conductivity type opposite to that of said semiconductor layer to form an ion injection layer of a conductivity type opposite to that of said semiconductor layer buried in said semiconductor layer; forming a thin layer on at least the side surfaces of said first mask pattern; selectively forming a second mask pattern on the portion of said SiO 2 film located between, and abutting, portions of said thin layer formed on said side surfaces of said first mask pattern, the material of said thin layer being different from the materials of said first and second mask patterns; selectively etching said portions of said thin layer formed on at least said side surfaces of said first mask pattern and said SiO 2 film under said latter portions and lying between said first and second mask patterns to expose said semiconductor layer; selectively etching the exposed portion of said semiconductor layer to form a trench substantially surrounding the implanted ions; forming an element isolation region by burying an insulating material in said trench; annealing said semiconductor layer to diffuse said impurity from said ion injection layer and thereby forming a well region of a conductivity type opposite to that of said semiconductor layer self-aligned with, and having a depth smaller than the depth of, said element isolation region in that portion of said semiconductor layer isolated by said element region; forming an electronic element on said well region; and wiring said element for connection.