A method to improve setup and overlay performance on an excimer laser stepper using a unique DUV resist-KRS

Accurate stepper setup is essential for getting good overlay performance on product wafers. As part of a typical stepper setup procedure. one or more wafers are exposed, developed, aligned to the initial exposure, and then exposed again in order to determine the x/y baseline position and grid rotation. By removing the wafer from the chuck for processing (baking and development) before the alignment and exposure, both pre-aligner and stage errors are introduced. If the alignment and second exposure could be made without removing the wafer from the stepper chuck, these two sources of error could be eliminated. This is possible if the resist has a strong and immediate latent image after exposure.