Thin film deposition method

A method for depositing a thin film, the method comprising:

• a first process of supplying a first diffusion gas and a source gas through a first gas supply path formed in a gas injection part and supplying a second diffusion gas through a second gas supply path formed in the gas injection part;
• and
• a second process of supplying the first diffusion gas through the first gas supply path and supplying the second diffusion gas and the reactant gas through the second gas supply path,
• wherein a process cycle in which the second process is performed without supplying a purge gas after the first process is performed repeatedly.