Free-standing carbon nanotube films for extreme ultraviolet pellicle application

Abstract

To enable high volume manufacturing with extreme ultraviolet (EUV) lithography, a pellicle membrane is needed to protect the reticle from particles at EUV source powers beyond 250 W. Identifying a membrane with high EUV transmission, mechanical integrity, thermal stability, and chemical resistance to the scanner environment is extremely challenging; yet, these properties are required to realize next-generation EUV pellicle solutions. Free-standing carbon nanotube (CNT) film as an alternative next-generation core pellicle material is proposed. We demonstrate that free-standing CNT films possess very high EUV transmission (up to 99%) and good transmission uniformity (∼0.4 % half range), mechanical stability (maximum deflection ∼0.08 mm at 2 Pa), thermal stability (no transmission change under greater than 250 W equivalent EUV power in vacuum), and scalability to a full pellicle size (∼15 × 12 cm2). The capability of the CNT membrane to withstand high EUV power in the presence of H2 for a limited time is demonstrated. Other CNT membrane properties are presented that are important for the pellicle application: low EUV scattering, low EUV reflectivity, and sufficient transmission to enable through-pellicle inspection with DUV light or electrons. The ability of the CNT film to stop particles is tested. The influence of hydrogen at higher EUV powers and prolonged exposures on the lifetime of the CNT pellicle remains the current research focus. Approaches for coating the free-standing CNT films for protection are discussed.