Method of forming isolation film for semiconductor devices

Abstract

A method of forming an isolation film forms a spacer for connecting the edge of an active region to the isolation film. The spacer is on the upper sidewall of a trench and smoothes the transition or step between the level of the isolation film and the level of the active region. Accordingly, a gate oxide film of a uniform thickness can be formed on the entire active region in a subsequent process, thus preventing degradation of the characteristics of the gate oxide film. The spacer can be formed using a sidewall spacer on the hard mask used for forming the trench. The sidewall spacer protects part of the isolation formed in the trench, and etching after removal of the sidewall spacer can round the protected portion to create the spacer. Furthermore, to dispel stresses and defects in the isolation film, annealing for densification of the isolation film can be performed at a high temperature such as about 1150° C. because the spacer mitigates the effects of shrinking or sagging of the isolation film.