Background: Extreme ultraviolet (EUV) pellicles are affected by heat deformation due to energy absorption during EUV exposure. Defects can accelerate thermal deformation, thereby shortening pellicle lifetime.

Aim: We compared the thermal stress and thermomechanical stability with different defects, focusing on the internal defects that occur during the fabrication of EUV pellicles.

Approach: Pellicles resistant to high thermal stress can be fabricated based on mechanical properties. To evaluate this, we compared the mechanical stability based on robustness against thermal stress during exposure.

Results: Our results show that external contaminants had a greater contribution than internal defects on the mechanical stability of pellicles. However, pellicles with internal defects exhibited increased thermal stress and decreased mechanical stability compared with defect-free pellicles during EUV exposure.

Conclusions: Thermal stress is used as an indicator in most studies to predict pellicle lifetime, but evaluation of thermomechanical stability including thermal stress and mechanical durability is required because the material can break under low thermal stress depending on the mechanical properties, and pellicle defects can be a major cause of shortening the lifetime of pellicles.