Impact of MOR anomalies on lithography and OPC: challenges and solutions

The enablement of High-NA EUV for high-volume manufacturing significantly relies on the performance of photoresists. As the depth of focus (DoF) decreases and feature sizes shrink, photoresists must fulfill additional requirements. They need to be thin to accommodate the reduced DoF, while also absorbing more photons to mitigate stochastic effects. Metal oxide resists (MOR) are among the few photoresists that meet these criteria, making their integration crucial for high-volume manufacturing. This study investigates the impact of density variations on wafer critical dimension (CD) for MOR. We conducted experiments using a fixed line-space design larger than 1 µm x 1 µm, while systematically varying the density of surrounding design. Our experimental results show that these density changes in proximity can significantly alter the CD of the fixed line-space design by more than 10%. Given that one half of the process margin is already consumed, the variation is significant from the process margin perspective. The density challenge extends to OPC as well, as traditional OPC models focus on the optical influence range, with flare being the sole long-range effect considered. However, these density effects extend beyond 10 µm, surpassing the visibility range of conventional OPC models. To address this, we propose incorporating long-range resist terms into OPC models and selecting appropriate features for model calibration to include the long-range effects in the current OPC solutions.