Novel membrane solutions for the EUV pellicle: better or not?

A protective membrane – a pellicle – must be used to prevent yield loss during EUV lithography exposure, just as it was for 193nm lithography. The pellicle must be thin enough to transmit EUV light, yet strong enough to withstand the scanner environment. Membrane solutions for ~ 80W exposure exist. Our focus is developing a membrane solution for 250W exposure power. The main pellicle challenge here is still the identification of a membrane material that has very high transmission at EUV wavelengths. Additionally, absorption during lithographic exposure results in high thermal and mechanical load for the pellicle, which can cause yield problems. The current candidates for pellicle membranes such as poly-silicon and silicon nitride cannot withstand 250W power conditions, therefore alternative materials will be required for the future HVM pellicle. At imec, a variety of novel membrane material options are investigated for the HVM pellicle application. One promising approach is based on carbon nanotubes (CNT). In this paper we outline different CNT based process options, and report results on their optical, thermal, and mechanical performance. In addition, we will report on their uniformity and robustness towards scanner application. Finally, the family of CNT-based membrane options will be compared to promising candidates fabricated using conventional film approaches that do not have a CNT layer.