To prevent overshoot of inner temperature of an electric furnace when transferring a wafer boat into the electric furnace without lowering a transfer speed.
When transferring a wafer boat 12 into an electric furnace 11, the positions of temperature sensors 18 (18A-18D) in the furnace are changed. The inner temperature of the furnace is feed-back controlled based on detection values from the sensors. Otherwise, in accordance with elevation of the wafer boat 12, the inner temperature is detected by other temperature sensors comprising a plurality of thermoelectric couples provided at a position b (overshoot- upon-transfer preventing position) in place of the temperature sensors 18. As a result, upon transferring a wafer boat, the inner temperature of the furnace can be feed-back controlled via a heater 15, based on the detection values from the sensors at appropriate positions. Accordingly, overshoot of the inner temperature can be prevented, especially overshoot of the inner temperature at the highest part can be prevented in a case where the furnace has a long upright shape. Thus, the inner temperature of the furnace when transferring a wafer boat can be stabilized in a short period.
NAKANO MINORU
TANAKA KAZUO
AKITA YUKIO
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