Oxide film preparation method

An oxide film preparation method comprising:

• placing a wafer on a base of a reaction chamber;
• and
• sequentially forming an oxide film on the wafer, a first oxynitride film on the oxide film, and a second oxynitride film on the first oxynitride film by following processes:
• performing a first process after placing the wafer on the base, the first process including introducing a first mixed gas of a first bombardment gas and a first oxidization gas into the reaction chamber, applying first DC power and first radio frequency (RF) power to a target, and exciting the first mixed gas to form a first plasma to bombard the target to form the oxide film on the wafer;
• performing a second process after performing the first process, the second process including introducing a second mixed gas of a second bombardment gas, a second oxidization gas, and first nitrogen into the reaction chamber, applying second RF power to the base, and exciting the second mixed gas to form a second plasma to bombard the oxide film to form the first oxynitride film by reacting with a surface of the oxide film;
• and
• performing a third process after performing the second process, the third process including introducing a third mixed gas of a third bombardment gas, a third oxidization gas, and second nitrogen into the reaction chamber, applying second DC power and third RF power to the target, applying fourth RF power to the base, and exciting the third mixed gas to form a third plasma to bombard the target and the first oxynitride film formed on the oxide film to form the second oxynitride film on the first oxynitride film that is arranged on the oxide film.