Control of Resist Processing in Lithography

Abstract

This thesis proposes control strategies to reduce critical dimension (CD) variations by improving various steps/aspects of the lithography process. Firstly, real-time control of develop step is performed using a reconfigurable bake/chill system with an online film thickness estimation. Then, a feed-forward control strategy is applied during post-exposure-bake step to reduce CD variations caused by poor temperature uniformity control and temperature disturbances caused by placement of cold wafers on the bakeplate of the same bake/chill system mentioned earlier. Lastly, variations in lithography process such as process drifts and deterioration of equipment often increase sensitivity of plant model to disturbances. A robust run-to-run controller that uses minimax function is proposed and used to minimize the worst predicted scenario when the bounds of these variations are known.