Patent ID: 7534469

Claim:
A method of cleaning a CVD apparatus, comprising the steps of: removing contaminants adhering to the interior of a CVD by activating a cleaning gas; detecting a removal state of contaminants adhering to an inner surface of said reactor by irradiating the inner surface of said reactor with light having monochromaticity through an optical window provided on an inner wall of said reactor at a bottom of said reactor and receiving its reflected light; and controlling the cleaning step based on the detection of results, wherein prior to removing contaminants a purge gas is supplied, Directed to the vicinity of the optical window and exhausted to protect the optical window from reaction products while inhibiting the purge gas from flowing into a reaction space of the CVD reactor and the vicinity of a semiconductor wafer placed in the reaction space, wherein the purge gas is exhausted though one of two openings of an exhaust balancer, said one of the two openings being closer to the optical window than is another of the two openings, wherein the one of the two openings of the balancer is provided along a bottom surface of the reactor, and the another of the two openings of the balancer is provided along an inner wall of a reactor, wherein purge gas flows along the bottom surface of the reactor and an upper surface of the optical window and is exhausted through one of the two openings.