PARAMAGNETIC POINT-DEFECTS IN SILICON-NITRIDE AND SILICON OXYNITRIDE THIN-FILMS ON SILICON

Silicon nitride and silicon oxynitride thin films on silicon often con tain paramagnetic point defects. In the nitride, major defects are the K-0 center (Si-.=N-3) and the N-2(0) center (N-.=Si-2), with possibly an NN20 center (Si-N-.-N=Si-2). In the dark, the K center normally ex ists as nonparamagnetic K- and K+. It may be (temporarily) put into th e K-0 state by UV excitation. The behavior of K-0 is consistent with a model in which the two-electron state is more stable than the single- electron state; other explanations are possible. A change in compositi on from Si-rich to N-rich SixNy reduces [K-0] and, due to the wider ba ndgap, allows the singly-occupied N-2(0) state to emerge from the vale nce band E(s)' (Si-.=O-3) and E(gamma)' (O-3=Si+...Si-.=O-3); and a te ntatively-assigned nitroxide-like N-x center. Since most oxynitride de fects contain either N or O, but not both, a multiphase material is su ggested.