Progress in SiC membrane for X-ray mask

In 1992, we began development of SiC membranes for X-ray masks using a prototype LPCVD system. A production type LPCVD system had been newly designed to provide significant improvements in film uniformity and achieved high productivity. SiC films of 2 mu m in thickness produced by the new system showed uniform thickness distribution of +/-0.6% in an area of 50 mm in diameter, and uniform stress of +/-1 % in an area of 25 mm square. SiC films in the suitable stress range of 100 to 350 MPa in tensile, with excellent thickness repeatability of +/-0.06 mu m, have been produced by the optimized process. SiC membrane of 3 mu m in thickness, which are more effective for obtaining precise masks, showed uniformity similar to the membrane of 2 mu m in thickness.