Thermal response of EUVL mask substrate during dry etching process

In the fabrication of an EUVL mask, some of the highest temperatures probably occur during the dry etching step. The thermal response of an EUVL mask during dry etching was investigated through simulations. 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 pasted on it. The measured results were compared with simulation results obtained using a lumped heat capacity model. The absorption ration was found to be 0.25-0.35, and there was good agreement between the measured and simulation data. In order to calculate the time-wise change in temperature, an internal energy balance model based on a large number of small elements was developed. To handle mask deflection caused by the temperature gradient in the thickness direction, 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 clarified. The amount of thermal deflection was found to be much smaller when masks are made on ULE of Si substrates than on quartz.