Image twist and placement error caused by heat absorption during EUV exposure

초록

Background The thermal deformation during dose accumulation shifts the image transfer path, leading to significant distortion in the local image profile. This phenomenon underscores the necessity of evaluating thermal deformation not merely as static placement errors but as factors affecting imaging performance. Aim This work aims to clarify how the thermal deformation occurring during EUV exposure directly influences image degradation and placement error. Approach A thermomechanical wafer heating model is established to calculate transient deformation under EUV exposure. The resulting deformation data is subsequently coupled with lithography simulation results to calculate the local image profile. Finally, the image profile is analyzed to quantify the image twisting effect and placement error. Results Placement errors exhibit spatially diverse distributions dependent on global field location and intra-slit coordinates. Furthermore, the dynamic variability of deformation during exposure was found to be a systematic source of image performance reduction, particularly through NILS reduction in fine-pitch patterns. Conclusions These results show that wafer deformation should be treated not only as a source of overlay error but also as a contributor to image degradation. This finding provides a basis for understanding deformation-induced placement error and image twisting in EUV lithography and for improving future overlay and imaging control strategies.

키워드