Abstract: A method of manufacturing a mask support or diaphragm of SiC for X-ray lithography masks is set forth in which a SiC layer is deposited by means of chemical vapor deposition (CVD) on a substrate in the form of a monocrystalline silicon wafer on at least one of the two major surfaces of the monocrystalline silicon wafer, after which the monocrystalline silicon wafer is removed except an edge region in a selective etching step. According to the invention the following processing steps are used:(a) deposition of the SiC layer with the monocrystalline silicon wafer first being heated in the apparatus provided for the deposition process to a temperature in the range of 1000.degree. to 1350.degree. C. in a H.sub.2 atmosphere and then being etched by a suitable etchant and subsequently being rinsed under the influence of H.sub.2, whereupon the SiC layer is provided from a gas atmosphere containing silicon and hydrocarbons, after which the coated substrate is cooled in a H.sub.