Substrate processing apparatus and method of manufacturing semiconductor device

A substrate processing apparatus comprising:

• a process chamber configured to process a substrate;
• a buffer chamber installed above the process chamber, the buffer chamber including a dispersion unit configured to uniformly supply gases into the process chamber;
• a process gas supply hole installed in a ceiling portion of the buffer chamber, where a process gas supply unit is connected to an upstream side thereof in a gas supply direction;
• an inert gas supply hole installed in the ceiling portion of the buffer chamber, where an inert gas supply unit is connected to an upstream side thereof in the gas supply direction;
• a gas guide disposed in a gap between the dispersion unit and the ceiling portion, the gas guide including a base end portion disposed at a side of the process gas supply hole, a leading end portion disposed closer to the inert gas supply hole than to the process gas supply hole, and a plate portion connecting the base end portion and the leading end portion;
• a process chamber exhaust unit configured to exhaust an atmosphere of the process chamber;
• and
• a control unit configured to control at least the process gas supply unit, the inert gas supply unit, and the process chamber exhaust unit.