Improving Overlay in Nanolithography with a Deformable Mask Holder

摘要

In very fine-line VLSI photolithography, alignment and overlay errors due to distortion in the projected image of a photomask relative to an existing pattern on a silicon wafer are becoming such serious problems :hat product-yield is beginning to drop precipitously. We propose to solve these problems by deliberately deforming a mask with a system of piezoelectric actuators in such a way that its induced deformations precisely match those of the wafer and so that all of the alignment marks at each chip site can be pulled into registration simultaneously during exposure. The centerpiece of our program is a proof-of-concept demonstration of inducing predictable distortions in a photomask by means of piezoelectric transducers in a deformable mask holder. In this report, we outline our program and provide a status report of the ongoing work. We have constructed and tested the deformable mask holder for the proof-of concept demonstration and performed measurements of mask distortions as a function of applied force.