Film forming apparatus, gas supply device and film forming method

A gas supply device used in a film forming apparatus for forming a thin film by sequentially supplying different kinds of mutually-reacting reaction gases to a substrate held within a process chamber of vacuum atmosphere and depositing reaction products on the substrate, the gas supply device comprising:

• gas supply paths formed in a corresponding relationship with the different kinds of the mutually-reacting reaction gases, and configured to supply the mutually-reacting reaction gases into the process chamber;
• valves installed in the gas supply paths at upstream and downstream sides of retaining units;
• a purge gas supply unit configured to supply a purge gas to the retaining units;
• the retaining units installed in the gas supply paths, an internal pressures of the retaining units being increased by retaining at least one of the mutually-reacting reaction gases and the purge gas;
• and
• a control unit configured to control:
• a film forming process for sequentially performing operations of actuating the valves such that the mutually-reacting reaction gases are retained in the retaining units, the internal pressures of the retaining units are increased to a first pressure and then the mutually-reacting reaction gases are supplied from the retaining units into the process chamber;
• and a purging process including a degassing operation of evacuating the gas supply paths to remove the mutually-reacting reaction gases remained from the film forming process, a purging operation including performing a purging gas filling action of simultaneously and continuously supplying the purging gas to the retaining units to increase the internal pressures of the retaining units to a second pressure higher than a first pressure, and subsequently performing and repeating a plurality number of times a purging action of actuating the valves to supply the purging gas from the retaining units sequentially and non-simultaneously to the process chamber, and a vacuum operation, performed after the purging action, of evacuating the gas supply paths to remove the purging gas.