Smoothing Roughness of SiC Membrane Surface for X-Ray Masks

We have obtained a smoother surface of SiC membranes than that of as-deposited SiC using etch-back and polishing methods, and investigated the influence of surface roughness of SiC films on internal stress and film structure of X-ray absorber films and optical transmittance of SiC membrane. Surface roughness for the as-deposited SiC surface is 15 nm (Ra), whereas that for etch-backed SiC is 6.9 nm (Ra) and that for polished SiC is 4.3 nm (Ra). Optical transmittance of as-deposited SiC membrane is 48% (λ=633 nm) and increases by a few percent with decrease in the Ra value. Internal stress of sputtered Ta tends to show gentler change with increasing surface roughness of SiC film. Film structure of Ta film is largely influenced by the surface roughness of SiC films at low Ar pressure. Sub-half micron absorber patterns with vertical walls, however, have been obtained even on rough surface SiC.