Replication of 50-nm-linewidth device patterns using proximity x-ray lithography at large gaps

We demonstrate the replication of device patterns consisting of interdigital lines ∼50 nm wide on 100 nm pitch using 1.32 nm x rays at a mask-to-substrate gap of 2.72 μm. The exposure latitude exceeds the factor 2.3 at this gap. From the expression that relates gap, G, linewidth, W, and wavelength λ (i.e., G=αW2/λ), we obtain α=1.44, which is well beyond the predictions of previous theoretical analyses based on the Kirchhoff boundary conditions. We attribute this disparity to the fact that an x-ray absorber is a lossy dielectric, hundreds of wavelengths thick, and hence the Kirchhoff boundary conditions are not applicable.