Thermal behavior along depth of extreme ultraviolet lithography mask during dry etching

The thermal response of an extreme ultraviolet lithography (EUVL) mask during dry etching was investigated through simulation. In order to estimate the power absorbed during dry etching, the temperature of a glass wafer was measured by observing the change in color of a heat-sensitive label. The experimental result was compared with the simulation result based on a lumped heat capacity model. The absorptance of power was found to be 0.25–0.35, and there was good agreement between the results of the experiment and simulation. To handle mask deflection caused by the temperature gradient, a first-approximation model based on spherical deformation and free boundary conditions was used. The temperature gradient in an EUVL mask that arises during dry etching was analyzed. Thermal deflection of EUVL masks was found to be much less when the masks were formed on an ultralow expansion (ULE) glass substrate or Si substrate rather than on quartz.