Method for inspecting photomask blank, production of photomask, photomask blank and glass substrate for photomask blank

PURPOSE:To provide the method for inspecting a photomask blank which can exactly decide the normal/defective condition of the photomask blank, the process for production of the photomask blank which can produce the photomask blank with good productivity by using this inspecting method and the photomask blank and glass substrate for the photomask blank to be used in this process for production. CONSTITUTION:The above-mentioned inspecting method and process for production of the photomask blank by using this inspecting method consist in measuring the rugged shape of the main surface 1 of the photomask blank and decides the normal/defective conditions of the photomask blank according to whether the rugged shape of the main surface 1 is a plane approximately parallel with a reference plane 2 approximately parallel with the main surface or is a curved surface having a nearly simple projecting or recessed shape, thereby greatly improving the accuracy in the decision of the normal/defective conditions of the photomask blank and enabling the production of the good-quality photomask blank with good productivity. In addition, the photomask blank and glass substrate for the photomask blank are accepted as non-defectives by the decision and, therefore, the good-quality photomask is obtd. with the good productivity by using such photomask blank and glass substrate for the photomask blank.