Oxygen-induced atomic desorptions in oxynitrides: Density functional calculations

The role of atomic oxygen, O2, and NO molecules in the nitrogen and oxygen removal processes observed during the thermal growth of oxynitride (SiOxNy) films is addressed by spin density functional calculations. Our results show that the energetically most favorable N-desorption mechanism would be induced by O2 reacting with the Si-[NO]-Si structure in SiO2, where nitrogen is released from the network as an interstitial NO molecule, leaving a peroxy linkage (Si-O-O-Si) in its place. Atomic O diffusing via peroxy linkage also removes nitrogen from the Si-[NO]-Si structure. However, this reaction has an occurrence rate of about 104 times smaller that the most favorable one. We also identify an oxygen exchange mechanism occurring through the annihilation of two peroxyl O atoms when they approach each other, where oxygen is released from the network as an O2 molecule leaving a perfect SiO2 structure. The energetics of other possible scenarios for atomic desorptions in SiOxNy are also discussed.