Electron and hole trapping in irradiated SIMOX, ZMR and BESOI buried oxides

Shallow electron and deep hole trapping in the buried oxides of SIMOX (separation by implantation of oxygen), ZMR, and BESOI (bond and etchback silicon-on-insulator) material are examined. By irradiating the oxides with X-rays at cryogenic temperatures, 40-50 K, hole motion is frozen and electrons are trapped. The oxide charge is determined by C-V measurements. Following the cryogenic irradiation, the electrons are detrapped by field stressing (tunneling) or by annealing (thermal excitation). Hole trapping is examined by annealing after the trapped electrons are removed by field stressing. Substantial shallow electron and deep hole trapping distributed uniformly through the oxide is observed for all buried oxides that are processed above about 1100°C. A comparison to thermal oxides grown at 850°C and annealed at 1300°C with and without a polysilicon capping layer shows that the top silicon layer significantly increases trap formation. These results indicate that the oxide defects responsible for the electron and hole trapping are produced by chemically reducing the oxide and producing defects such as Si-Si pairs