Double exposure stabilization of positive photoresist

Positive photoresists appeared to be the most promising material in VLSI microfabrication for ten or more years from now. Thus, processing know-how needs to be accumulated continuously. This work deals with thermal characteristics of positive photoresist. The following facts were declared experimentally. The quinone diazide, photosensitizer, was thermally decomposed at around 140°C to release N₂. Simultaneously the surface layer of resist film was changed into innert state, called as ‘husk’, with low gas permeability and high chemical resistance. These thermal changes in resist film affect the photoresist to SiO₂ adhesion. In this work a noble process, named double exposure stabilization, is developed to get sufficient chemical resistance and good adhesion simultaneously.