Improvement of Photoresist Planarization Properties by Thermal Cure: Role of the PAC

Photoresist planarization properties are shown to be improved by a subsequent thermal cure. In order to understand the effects of thermal processing on photoresists, this paper discusses their thermal chemistry in relation to their thermal flow properties. The photoactive compound (PAC) is shown to hinder the thermal flow of the photoresist by ester‐linkage up to the temperature where the resin undergoes complete thermal cross‐linking. Transformation of the PAC by a suitable exposure to UV light will let the resin flow up to its own limits. The thermal flow behavior is shown to be dependent on the feature size. The thickness shrinking due to the loss of weight occurring all along the thermal cure is shown to degrade the planarization properties and to compete with thermal flow.