PURPOSE: To reduce the concentration of a precursor radical outside a cover and improve the uniformity of the thickness of an accumulating film of a wafer by increasing the ratio of the area that faces a space surrounding the cover to the volume of the space.
CONSTITUTION: The same number of absorbing plates 12 as slits 7 are concentrically arranged between an internal reaction tube 2 and a cover 11 so as to overlap the slits 7. The precursor radical generated between the cover 11 and the internal reaction tube 2 is absorbed by the absorbing plates 12, and the precursor radical contained in reaction gas at the time of filling the slits 7 is reduced. It is desirable that the ratio of the surface area of the absorbing plate 12 to the volume of a space between the cover 11 and the internal reaction tube 2 becomes almost the same as the ratio of the volume of a space between the cover 11 and the internal reaction tube 2 to the surface area of the wafer 13. Thus, the uniformity of the film thickness is improved.
SATO TAKETOSHI
MAEDA KIYOHIKO
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