“Anomalous” Speed Dependence in Polyimide Spin Coating

Abstract

Thethickness of spun films is often represented as inversely proportionalto some power of the spin speed. For most materialsthis power is found to be one-half. However, polyamic acidsolutions show a much stronger dependence with exponents ranging fromabout 0.5 to almost 1. A simple model of spin-coatingis used to explain this difference. Using coating data forboth polyamic acid and photoresist solutions, it is shown thatin many experiments the coating process has not reached steadystate. When steady state is attained, the speed power isone-half; at shorter times, the power is greater. For somematerials, the time required to reach steady state may be10 min or more. ©1997 The Electrochemical Society, Inc.