Pattern etching of Ta X-ray mask absorber on SiC membrane by inductively coupled plasma

Patterning of an X-ray mask absorber after Si back-etching is desirable from the viewpoint of the pattern placement accuracy. We investigated Ta X-ray absorber etching on an SiC membrane equipped on a mask frame using a low-stress CrN hard mask and an ICP etcher with a He cooling system. In this system, the membrane temperature and the self-bias voltage could be controlled. A 40-nm-thick CrN film was etched using a 200-nm-thick resist and Cl-2 and O-2 gases with a selectivity of 0.72 and a vertical sidewall. A 400-nm-thick Ta film was etched using Cl-2 gas at an electrode temperature of - 10 degrees C and a low gas pressure of 0.1 Pa. A high selectivity of Ta to CrN, 42, was obtained, and lines and spaces patterns below 0.1 mu m with vertical sidewalls could be fabricated.