A photomask blank has at least one layer of chromium base film on a transparent substrate. The chromium base film of chromium oxycarbide (CrCO) or chromium oxynitride carbide (CrCON) is formed by a reactive sputtering technique using chromium or chromium containing O, N or C as the target and a mixture of carbon dioxide gas and an inert gas as the sputtering gas. A photomask is manufactured by lithographically patterning the photomask blank. The photomask blank and photomask are of quality featuring high uniformity within the substrate plane and ease of control during manufacture.