PURPOSE:To enhance the yield rate of a product without causing any trouble inside by installing a transparent viewing window, composed of heat-resisting glass, which can observe, with the naked eye, the inside of a heat-insulating cover covering a high-temperature exposure part. CONSTITUTION:While a baking process is executed, a cover 9 for thermal insulation always covers a stage 5. Because a sheet of transparent heat-resisting glass 10 is installed inside the cover 9, it is possible to always monitor, e.g., the state of a semiconductor wafer 6 while it is baked. In addition, a protective plate 11 where two or more openings are formed is installed at the upper part of the heat-resisting glass 10 and protects the heat-resisting glass 10. Because a heat-insulating material 12 is installed at the periphery inside the cover 9, the heating at the outer wall of the cover 9 due to the heat generated by the stage is prevented.
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