Progress in EUV optics lifetime expectations

Optics lifetime and contamination is one of the major challenges for extreme ultraviolet (EUV) lithography. The basic contamination and lifetime limiting processes are carbon growth and oxidation of the mirrors. Without appropriate measures, optics lifetime will be limited to a few hours. Within the EUV α-tool project of ASML and Carl Zeiss, several potential solutions towards improvement of optics life time are being studied: vacuum improvement, capping layers for oxidation protection, mitigation of carbon growth and development of efficient cleaning techniques that are soft to the mirror. For instance, we have been able to identify a capping layer that shows carbon growth even under extremely oxidizing conditions. The current status of our experiments leads us to believe that a lifetime of 1000 h is within reach.