High-transmission CNT-based membrane for EUV

A highly transmissive membrane for EUV and Soft X-ray wavelengths has been developed, based on CNT’s (Carbon Nano Tubes). These are capable of withstanding high EUV loads and harsh chemical environments and may be used to protect EUV lithography masks from particles, or as basis for a transmissive diffuser or spectral filter. As EUV and Soft X-ray systems run in vacuum environments, the finite absorption and poor thermal conductivity combine to lead to very high temperatures in the membrane. This puts stringent requirements on the membrane material, manufacturing and pretreatment. For application in EUV lithography, the membrane must be able to withstand source powers of at least 1000 W and must be compatible with the stringent imaging requirements of upcoming <2 nm nodes. In this paper, we will give an overview of CNT-based membranes and zoom in on recent improvements for high-power compatibility, both in the membrane and in environment control. Robustness against high EUV power and EUV-induced hydrogen plasma will be discussed, as well as transmission, imaging and overlay.