Diamond layers are of special interest for x‐ray mask fabrication because of their excellent optical and mechanical properties. Using a plasma activated chemical vapor deposition process, 2–5 μm thick diamond layers were deposited and characterized. Microhardness and Young’s modulus are found to be very close to the literature values of bulk diamond. A standard isotropic etching process was applied for membrane fabrication. The optical transparency and the thickness homogeneity were measured. Concerning surface roughness, scanning electron micrographs and atomic force measurements were evaluated. After irradiation of diamond masks with synchrotron light, a slight increase of optical transparency was found.