Influence of wafer warpage on photoresist film thickness and extinction coefficient measurements

Abstract

Photoresist film thickness and extinction coefficient are two important properties which has an impact on critical dimension (CD). Current approaches for estimating these resist film properties are based on the assumption of a flat wafer. However, wafer warpage is common in microelectronics processing. In this paper, the effect of wafer warpage on the accuracy of resist properties estimation is investigated and an in-situ calibration method is proposed. Based on the proposed approach, we demonstrate how wafer warpage can be detected in real-time using conventional reflectometers during the thermal processing steps in lithography.