CNT pellicles: recent optimization and exposure results

EUV lithography has been implemented in high volume wafer production. Consequently, maximizing yield is of major importance. One key component to achieve optimal yield is using a pellicle to hold particles out of the focal plane and thereby minimize the printing of defects. The carbon nanotube (CNT) pellicle is a membrane consisting of a network of carbon nanotubes, which demonstrates EUV transmission up to 98%. The challenge is to balance the CNT material parameters for optimal performance in the EUV scanner: low probability for particles to pass, high durability in the scanner environment, while maintaining high transmission and low impact on imaging. While our earlier reporting on full-field CNT pellicle exposures demonstrated minimal impact on imaging, the focus of the current paper is on extended exposures on NXE:3400. In the scanner, the EUV light induces a hydrogen plasma that etches the CNTs, resulting in decreasing membrane density and increasing EUV transmission. In this work, we quantify the CNT pellicle etch rate in a real scanner environment and correlate the findings to those obtained in an offline test setup. Our exposures were performed using two different pellicles, with EUV transmission of 89% and 95%, for up to 3000 wafers. Additionally, we demonstrated the effectiveness of pellicle purification prior to mounting on the reticle, which is important to avoid contamination from the as-fabricated CNT pellicle onto the reticle surface. Current ongoing developments focus on further increasing the pellicle durability in the scanner environment. The presented results demonstrate the potential of a CNT-based pellicle at high EUV powers.