Method of forming isolation film in semiconductor device

Abstract

There is disclosed a method of forming an isolation film in a semiconductor device, the method including the steps of: forming a silicon oxide film and a silicon nitride film in that order on a silicon substrate, using a resist pattern as a mask, etching the silicon nitride film and silicon oxide film, and forming trenches in the substrate. In the substrate, the respective trenches form a region in which isolation films are to be formed, and the region between the trenches forms an active region. In this case, each dimension is set so that a ratio W/t of width W to thickness t of the patterned silicon nitride film is 3.8 or more. Subsequently, by removing the resist pattern, subsequently using the silicon nitride film as the mask, and performing thermal oxidation at a temperature of 1050° C. to 1150° C. in an oxygen atmosphere, an isolation film is formed in the trench.