Investigation of the radiation-induced thermal flexure of an x-ray lithography mask during a tilted exposure.

Thermal deformations of the x-ray mask were simulated in the case of a synchrotron x-ray spectrum which was modified to decrease the incident power of synchrotron radiation (leaving the electron beam conditions at the storage ring unaltered). Effective methods are (1) the attenuation of the hard component with a grazing incidence x-ray mirror in combination with absorption filters or (2) the use of a central beamstop to suppress the center part of the synchrotron radiation beam where its harder component is concentrated. With a central beamstop combined with absorbing filters, the spectral bandwidth of the x-ray photons absorbed in a resist layer becomes narrower, which decreases the absorbed radiation power. The maximum of the spectral distribution remains at the same position for both variants by using an optimized filter combination. Also the thermal deviation of the microstructures is decreased below 3 μm in the case of an inclined exposure, and the reproducibility of the positioning precision has been demonstrated for tilted deep x-ray lithography with the necessary top and bottom dose ratios for thick SU-8 resist layers. [ABSTRACT FROM AUTHOR]