Film forming method and film forming apparatus

A film forming method of forming a thin film by repeating a cycle of separately supplying a plurality of kinds of reaction gases that react with each other to a substrate in a process vessel, which is in a vacuum atmosphere, via a reaction gas supply passage provided for each of the plurality of kinds of the reaction gases continuously and laminating a reaction product thereon, while continuously supplying a counter gas from a counter gas supply passage provided separately from the reaction gas supply passage provided for each kind of the reaction gases, the method comprising:

• forming a film on the substrate loaded in the process vessel until a predetermined thickness of the film is formed on the substrate by repeating another cycle of separately performing operations for each of the plurality of kinds of reaction gases, the operations including storing the reaction gas in a storage part provided in the reaction gas supply passage to raise a pressure in the storage part to a first pressure and then discharging the reaction gas from the storage part into the process vessel, while continuously supplying the counter gas;
• and
• responsive to the predetermined thickness of the film being formed on the substrate, purging, by repeating multiple times operations of storing a purge gas in the storage part provided in the reaction gas supply passage to raise the pressure in the storage part to a second pressure higher than the first pressure, and discharging the purge gas from the storage part into the process vessel via a flow path at a downstream side of the storage part leading to the process vessel,
• wherein a flow rate of the counter gas supplied into the process vessel via the flow path in the purging is smaller than a flow rate of the counter gas supplied into the process vessel in the forming the film.