| 摘要 |
PURPOSE:To form a sublimable transparent dielectric film with stable film thickness, by attaching a pressure control valve controlling the evaporation pressure of an evaporation substance to a cover put on a boat made of W on which the evaporation substance is placed. CONSTITUTION:A boat 2 made of W is placed on a Cu hearth liner 3, and an evaporation substance 4 is placed on the boat 2, and then, a cover 1 to which a rivet-shaped pressure control valve 6 is attached is put on the above boat 2. The pressure control valve 6 attached to the central position of the cover 1 moves vertically and control the evaporation pressure of the evaporation substance 4 so as to prevent the bumping of the evaporation substance 4. Further, a step is made in the inner wall of the boat 2 so as to hold the cover 1, and the evaporated substance 4 sprung out of the gap between the boat 2 and the cover 1 is allowed to adhere to the wall of the second step and reevaporated by means of an electron beam applied from above, so that sticking to the periphery is inhibited. By this method, the cover 1 capable of attaining the refractive index and film thickness of the sublimable transparent dielectric film with highly stabilized mass productivity can be obtained.
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