Nitride film forming method and storage medium

A nitride film forming method, comprising:

• performing a pretreatment of adsorbing a chlorine-containing gas onto a surface of a first base film and a surface of a second base film, the first base film and the second base film being formed on a substrate to be processed, by supplying the chlorine-containing gas while heating the substrate to be processed to a predetermined temperature;
• and
• forming a nitride film on the first base film and the second base film subjected to the pretreatment, by an ALD method or a CVD method, using a raw material gas and a nitriding gas, while heating the substrate to be processed to a predetermined temperature,
• wherein the chlorine-containing gas used in the step of performing the pretreatment is at least one gas selected from a group consisting of a Cl2 gas, a HCl gas and a BCl3 gas.