Abstract
The temperature rise of an X-ray mask irradiated by synchrotron radiation (SR) emitted from the SORTEC storage ring has been measured in situ using the thermography technique. In order to detect IR rays in the range of 2.5-5.6 µ m wavelength, emissivities for masks with and without an absorber were measured in advance by using Fourier transform infrared spectroscopy. After measuring the temperature rise of the mask as a function of helium (He) pressure, the heat transfer coefficient was analyzed for estimating the thermal effect on the mask-wafer assembly. Using this heat transfer coefficient, the temperature rises of 20 and 0.3° C in vacuum and under atmospheric He pressure were successfully calculated at a ring current of 200 mA, respectively. The He pressure above 10 Torr in the exposure chamber is sufficient in SR lithography to minimize the temperature rises of the mask membrane and wafer.