Investigating EUV degradation with in-situ EUV transmission measurements

The degradation resistance of materials in EUV and H2 plasma is critical for EUV lithography processes and equipment. Therefore, our study investigates in-situ time-resolved EUV- and plasma-driven degradation of transition metal oxides (TMO) to understand EUV degradation. The hypothesized mechanism is based on Auger decay due to photoelectrons. Thus, we predict that the electronic structure of a TMO determines its EUV stability.

For a first exposure run, two TMOs were chosen according to their hypothesized stability. The stability was monitored with in-situ EUV transmission (EUVT) measurements. The stable material had no significant change in EUVT, while the EUVT of the unstable material decreased, which is in line with the hypothesis. Ex-situ EUV reflectivity and X-ray reflectivity show an increase in layer thickness, indicating oxidation, for which a more detailed model is proposed. In addition, the EUV degradation in a hydrogen environment was investigated, where the effect of hydrogen was not significant, confirming out hypothesis that materials stable in “offline” hydrogen exposures are also stable in EUV plasma.

These findings will increase the understanding of EUV and H2 plasma stability of different materials in EUV lithography processes.