Method for forming element isolating film of semiconductor device

Abstract

A method for forming an element isolating film of a semiconductor device, which is capable of achieving a reduction in topology and a reduction in the occurrence of a bird's beak phenomenon, so that subsequent processes can be easily carried out to fabricate highly integrated semiconductor devices. The method includes the steps of sequentially forming a pad oxide film and a first nitride film over a semiconductor substrate, over-etching the first nitride film and the pad oxide film by use of an element isolating mask, thereby forming a first hole in the semiconductor substrate, cleaning the entire upper surface of the resulting structure by use of an etch solution, forming second-nitride film spacers on side walls of the selectively etched first nitride film, pad oxide film and first hole, forming a second hole in the first hole of the semiconductor substrate by use of the first nitride film and second-nitride film spacers as a mask, thermally oxidizing the surface of the second hole, thereby forming a thermal oxide film, and removing the first nitride film, pad oxide film and second-nitride film spacers, thereby forming an element isolating film.