Control of photoresist thickness uniformity in the microlithography process

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 standard PI controller, the temperature distribution of the bakeplate is manipulated in real-time to reduce photoresist thickness nonuniformity. We have experimentally obtained a repeatable improvement in resist thickness uniformity from wafer-to-wafer and across each wafer. Thickness nonuniformity of less than 10 nm has been obtained. On average, there is a 10× improvement in the thickness uniformity as compared to conventional softbake process.