A method for processing a semiconductor substrate in a chamber includes forming a silicon oxynitride film using a two-step anneal process. The first anneal step includes annealing the silicon oxynitride film in the presence of an oxidizing gas that has a partial pressure of about 1 to about 100 mTorr, and the second anneal step includes annealing the silicon oxynitride film with oxygen gas that has a flow rate of about 1 slm. The first anneal step is performed at a higher chamber temperature and higher chamber pressure than the second anneal step.