In-situ critical dimension control during post-exposure bake with spectroscopic ellipsometry

Strong correlation between de-protection induced thickness reduction and amplified chemical reaction in the exposed area of the chemically amplified resist (CAR) during post-exposure bake (PEB) has been established. The optical properties of the resist film due to the thickness reduction can be detected using a spectroscopic ellipsometer. In this paper, a rotating polarizer spectroscopic ellipsometer is developed and a proposed control scheme is presented for signature profiles matching. With the implementation of the control scheme, wafer-towafer critical dimensions (CD) uniformity is improved by 5 times.

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