Deposition parameters acting on nucleation and growth local conditions have been optimized in a bell jar microwave plasma reactor to obtain polycrystalline diamond thin films compatible with X-ray membrane requests. The microstructure and the chemical quality of the films were estimated by SEM and Raman spectroscopy respectively, the roughness was evaluated by AFM experiments and the residual stress was deduced from the substrate deflection method. Membranes were obtained by removing the silicon substrate on 15 mm diameter circular windows. The optical transparency depending on deposition conditions was optimized up to 65% at 630 nm for 1 μm thickness. A high resolution additive mask process, based on well taut membranes and low stress electroplated gold absorber, was carried out. Micrometric and submicrometric mask patterns were generated in photoresists both by electron beam lithography with a nanopattern generator and by X-ray lithography using the synchrotron radiation facility implemented at LURE-Orsay. Despite the diamond films roughness of the order of 30 nm, well defined dots and lines as narrow as 100–200 nm could be obtained.