On control of resist film uniformity in the microlithography process

Abstract

A novel approach to improve photoresist thickness uniformity after the conventional spin-coating and softbake process is proposed in this paper. Using an array of thickness sensors, a multizone programmable bakeplate, and model-based control techniques, the temperature distribution of the bakeplate is manipulated in real-time to reduce photoresist thickness non-uniformity. To prevent the decomposition of photoactive compound in the photoresist, the bakeplate temperature is constrained. We have experimentally obtained a repeatable improvement in resist thickness uniformity from wafer-to-wafer and across each wafer. Thickness non-uniformity of less than 10 Å has been obtained. On average, there is a 10× improvement in the thickness uniformity as compared to conventional softbake process. © 2004 Elsevier Ltd. All rights reserved.