Correlation Between CD/LWR and Focus Level Fitting Error: A Process Quality Indicator

Achieving uniformity of patterns on photoresists is a significant challenge as process nodes get smaller. In practical production lines, the level sensor (LS) of the lithography system will record the focus level to calculate fitting errors and correct the focus level errors automatically during exposure. In this study, we present the analysis of the inherent adjustment errors stemming from the LS process dependency. Additionally, we propose a correlation analysis method that utilizes the focus level fitting errors alongside the measured data including uniformity of critical dimension (CD) and line width roughness (LWR). The correlation can serve as an indicator of process quality and offer guidance for further process optimization.