Oxide film preparation method

An oxide film preparation method comprising:

• placing a wafer that is to be deposited with a film on a base of a reaction chamber;
• introducing a first mixed gas of a bombardment gas and an oxidization gas into the reaction chamber, applying DC power and radio frequency (RF) power to a target, and exciting the first mixed gas to form a plasma to bombard the target to form an oxide film on the wafer;
• stopping applying the DC power and the RF power to the target, introducing a second mixed gas of a bombardment gas, an oxidization gas, and nitrogen into the reaction chamber, applying the RF power to the base, and exciting the second mixed gas to form a plasma to bombard the oxide film to form an oxynitride film;
• and
• continuing to introduce the second mixed gas into the reaction chamber, applying the DC power and the RF power to the target, continuing to apply the RF power to the base, and exciting the second mixed gas to form the plasma to bombard the target and the oxynitride film formed above to form another oxynitride film on the oxynitride film formed above.