| 摘要 |
PURPOSE:To improve the dimensional accuracy of a pattern to be formed on a material without deteriorating the efficiency of the treatment, by providing a storage section for storing data of end points of materials already treated, and determining an unknown end point for a material now treated from the known data stored in the storage section. CONSTITUTION:As an area occupied by light transmitting sections 9 of a light transmission film 2 is increased progressively by etching action of an etching solution 7 given to the light transmitting film 8 of a photo mask blank 2, a progressively larger amount of light 12 is transmitted by the light transmitting sections 9, reflected by a corner cube 13, again transmitted by the light transmitting section 9 and reaches a light receiving section 11. A control section 14 calculates an arithmetical mean, for example, from data of elapsed times Ta and Tb from the initiation to end points for photo mask blanks 2 already treated, the data being held in a storage section 15, and determines a required time to the end point Tc. Thus, the end point is found automatically and precisely based on elapse of the time Tc, and supply of the etching solution 7 and rotation of a rotary table 1 are stopped.
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