Mechanical distortions in advanced optical reticles

Finite element models have been developed and refined to simulate the mechanical distortions associated with mask blank fabrication, pattern transfer, and exposure clamping. By modeling the substrate with layers associated with the mask fabrication process and then by prestressing specified layers, the resulting out-of-plane and in-plane distortions of the mask blank have been determined. Etching procedures were subsequently simulated to assess the pattern transfer distortions associated with both dark and bright field masks. Investigations included substrate materials which have acceptable optical transmission for wavelengths below 180 nm. Additional mechanical distortions associated with clamping the reticle into the exposure mount have also been considered.