Fabrication of high resolution x-ray masks using diamond membrane for second generation x-ray lithography

Abstract

Second generation x-ray lithography (PXL-II) has been proposed to extend proximity x-ray lithography to the 50 nm generation and beyond while keeping a high throughput. Diamond membrane, which enables high power and shorter x-ray irradiation, is a key material for PXL-II. In this article, we describe the fabrication of ultrafine patterns of W–Ti absorber on thinned diamond membranes. By optimization of the etching conditions, about 30 nm W–Ti patterns with aspect ratios of about 10 were successfully fabricated. The dependence of pattern edge roughness of the absorber on the surface roughness of the diamond has also been investigated, and it has been shown that 3 nm rms roughness was enough to obtain the pattern quality equivalent to that on a SiC membrane. For narrower gap exposure with x-ray masks with thick diamond membrane in PXL-II, the flatness of the mask top surface has been studied, and we developed x-ray masks with a flatness of less than 1 μm by modifying the support ring geometry.