Effects of material properties on patterning distortions of optical reticles

Bulk (or global) heating of photomasks due to e-beam energy deposition during patterning causes thermal expansion of the mask substrate and leads to pattern placement errors. Finite element calculations were performed to simulate the in-plane distortions (IPD) due to the single pass writing of a 6 in. x 6 in. optical reticle. Comparison studies were performed to identify the effects of material properties (such as thermal conductivity and the coefficient of thermal expansion) when patterning SiO2 and CaF2 substrates. Final IPD maps illustrate that thermal distortions of the CaF2 will need to be controlled in order to satisfy increasingly stringent error budgets.