Microfabrication of X-Ray Absorber W Utilizing Al2O3 as an Etching Mask

Microfabrication of W X-ray absorber for X-ray masks was studied. The absorber patterns were fabricated by etching processes using double layer resists which consist of a top resist and second Al2O3 layers. The thickness of the top layer was 0.3 µm to relieve the effect of both forward and backward scattering in electron beam writing. The etching gases for W patterning were SF6 and CHF3. The selectivity between W and Al2O3 was more than 20 by properly adjusting the gas mixture ratio, pressure and etching power. The required thickness of the second Al2O3 layer was only 0.05 µm which could easily be etched using BCl3 gas. Nearly vertical 0.2 µm lines and spaces were fabricated for 0.5 µm thick W absorber.