Thin-film formation by spin coating: Characteristics of a positive photoresist

Thin-film formation of a positive photoresist was investigated experimentally in terms of weight loss and temperature shift of the photoresist solution on a glass wafer during the spinning process. The former is analyzed by gravimetry and the latter by thermometry. The results show that weight loss of the photoresist solution is dominated mainly by outflow and is influenced only slightly by the evaporation of the solvent during the spinning process. Furthermore, film uniformity has been improved by a large quantity of radial flow, during which the solution behaved as a Newtonian fluid, at the middle stages of the spinning process. Film uniformity is degraded by non-Newtonian flow and the temperature difference in the glass wafer at the later stages of the spinning process. Consequently, a most suitable spinning time (minimum thickness deviation) exists for each spin velocity.