Impact of EUV absorber variations on wafer patterning

Mask absorber variations are known to impact wafer imaging. To understand these impacts, absorber variations around SRAF and line-end features are studied on both bright and dark field masks. The primary areas of investigation are SRAF absorber thickness and sidewall angle variation. The working hypothesis was that these two variations are most prevalent in EUV mask absorber processing and could limit EUV imaging. In addition, this study will investigate whether Optical Proximity Correction (OPC) and can compensate for absorber thickness and sidewall variations. AFM data were collected to identify whether qualitative variations between SRAF and main features in the mask absorber were present. Simulations were deployed to quantify the response of wafer images to mask absorber variations. The study found sensitivity to SRAF SWA and thickness variations in the dark field and bright field cases. The study also found that OPC mitigates a large part of the mask SRAF shape variations, if the OPC model includes the quantified variation. Consequently, mask characterization and inclusion in OPC models is needed to reduce model errors.