Post treatment method for in-situ cleaning

A method for performing a post treatment comprising the steps of:

• introducing a post treatment gas into a reaction chamber after in-situ cleaning;
• applying electric power to the post treatment gas to generate a plasma so that a residual cleaning gas and the post treatment gas react with each other to form a volatile product;
• and
• removing the residual cleaning gas by expelling the volatile product out of the reaction chamber,
• wherein the post treatment gas is a reactive gas which contains an element in common with a thin film deposited on a substrate, and which reacts with the cleaning gas to form the volatile product,
• where the post treatment gas is introduced into the reaction chamber at a flow rate such that the deposition rate of thin film deposited by the post treatment gas is reaction-limited, and
• wherein the plasma is generated by applying electric power to the post treatment gas so that the deposition rate of the thin film formed by the post treatment gas is reaction-limited.