Impact of transmission non-uniformity of a wrinkled EUV pellicle for N5 patterning under various illuminations

Abstract

To solve the defect problem during the exposure process of EUV lithography (EUVL), an EUV pellicle is suggested as a solution. Even though use of an EUV pellicle is considered an essential solution for defect control during the exposure process, it is not ready for application in real commercial processes due to how difficult it is to manufacture. Due to tight requirements for an EUV pellicle, flawless fabrication is impossible and deformations such as a wrinkle would result in serious patterning problems. These deformations lead to critical dimension (CD) non-uniformity due to the non-uniform transmission distribution caused by a pellicle wrinkle. In this paper, we discuss the impact of transmission non-uniformity caused by a wrinkled pellicle. When we treat the effects of a wrinkled pellicle, we considered off-axis-illumination, which is a promising resolution enhancement technology. By shrinking the target pattern size down to 7nm nodes (N7) or 5nm nodes (N5), a flexible illumination system is required to enhance the resolution ability. With dipole illuminations, resolution is varied by partial coherence and by not only the beam size at the pellicle, but also by the incident angle distribution. For these reasons, a non-uniform intensity distribution caused by a wrinkled pellicle is modified with changes in off-axis illumination conditions, including spatial coherence and the aperture shape. For N5 patterning, the CD non-uniformity of 0.2nm occurs at 1.7% transmission variation (2-pass). However, the intensity distribution is varied under various illumination conditions in spite of the same pellicle conditions. The intensity non-uniformity goes up with increasing spatial coherence. Even though feature conditions of the wrinkled pellicle are the same, the transmission non-uniformity is changed with illumination conditions. Thus, the allowable feature conditions of the wrinkled pellicle may be changed. For achieving good CD uniformity, the allowable limit of the pellicle wrinkle is carefully studied because the impact of the wrinkled pellicle varies with the illumination conditions.