| 摘要 |
PURPOSE:To enable to detect always the etching finishing point precisely by a method wherein the etching finishing point is detected by detecting reflected light quantity or transmitted light quantity of light irradiated to an original plate of mask to be etched. CONSTITUTION:When light is irradiated onto the original plate of mask from the light emitting part 8, reflected light therefrom is detected by the light receiving part 11, and a light quantity signal is sent out to a comparator circuit 12. When etching of a chromium film 2b is advanced according to the progress of etching, the area of surface of the film 2b is reduced gradually, and light quantity of reflected light is reduced gradually being in proportion thereto. The light quantity signal sent from the light receiving part 11 is reduced correspondingly according to the reduction of light quantity, and becomes to have the value being close to the reference signal by approaching to the finishing point. The optical signal thereof is compared with a signal of the reference signal source 13 in the comparator circuit 12, and when the light quantity signal reached within the range of error, it is judged as the finishing point of etching. |
