To provide a treatment apparatus and a method for a substrate for reducing the working time and the number of repetitions of maintenance, by preventing a byproduct from being deposited by a gas flow around the substrate.

A semiconductor processing apparatus 100 in a single wafer processing cold-wall method has a nitrogen purge lines 61, 62, and 63 connected to a turbomolecular pump connection flange 21, an interface flange 22, and a bellows 23. While a film is formed in a process, a semiconductor wafer 32 is heated by a plate heater 31, and at the same time, the nitrogen a flow of a process gas 41 is purged by a nitrogen gas from the purge lines 61, 62, and 63 to prevent a wrap around flow of the process gas 41. Then, a byproduct caused by the accumulation of the process gas 41 is prevented from being deposited thereon.