Patent ID: 8282737

Claim:
A substrate processing apparatus comprising: a reaction furnace for processing a substrate which includes a process tube, an inlet flange for supporting the process tube, and a base flange for supporting the inlet flange; a seal cap for sealing the reaction furnace hermetically; a cover installed inside the base flange separately from the seal cap so as to cover approximately the entire surface of the seal cap facing the inner side of the reaction furnace; a small chamber formed by a space enclosed by the seal cap, the cover and the inner wall surface of the base flange; a feed opening facing the small chamber for supplying a first gas that is inert to the seal cap into the small chamber; a flow outlet formed by a clearance between the cover and the inner wall surface of the base flange, for making the first gas supplied to the small chamber flow into the reaction furnace; and a feed opening provided further downstream than the flow outlet, for supplying a second gas that is more active to the seal cap than the first gas into the reaction furnace.