Process techniques have been developed to produce diamond membranes for application as x-ray lithography masks. Residual stress and grain size of the films are influenced by substrate temperature, chamber pressure, and methane concentration, and optimization of these parameters narrows the range of acceptable process conditions. A reactor geometry was chosen which has the capability to produce membranes with thickness uniformity of ± 7 percent across a 50 mm diameter. A cyclic renucleation technique was developed to maintain the grain size at low levels independent of film thickness. Membranes with RMS roughness of about 25 nm, as determined by atomic force microscopy, are fabricated reproducibly. The elastic modulus of small grained membranes deviates from that of larger grained membranes. This deviation must be taken into account in membrane distortion modeling calculations.