A Study of Radiation Effects on SiO2 and Al2O3 Layers Using Thermoluminescence Glow Curve Techniques

Trap levels in thin layers (500 to 6000Å) of Al2O3 and various types of SiO2, all on Si substrates, were investigated using thermoluminescence glow curves in a temperature range from 30° to 300°C. Layers were studied which had been exposed to doses of Co60-gamma radiation up to several Mrads. Previously unirradiated SiO2 layers showed a small density of thermoluminescence traps (<1014 cm-3). Co60 -gamma radiation was found to increase the trap density by an order of magnitude, introducing five peaks in the glow curve. The glow curves were resolved into their component peaks revealing five trap levels with depths ~1 eV. Al2O3 layers were found to have a larger inherent density of traps than SiO2 layers, also with five levels having depths ~1 eV. Co60-gamma radiation in doses up to ~10 Mrads did not appreciably increase the density of traps. For both the SiO2 and Al2O3 layers, high-temperature baking increased the thermoluminescence output considerably and caused the five discrete levels to be replaced by a continuum. For the SiO2 layers, it was found that a proportionately larger part of the thermoluminescence output came from the region of the oxide layer close to the SiO2-Si interface. For the Al2O3 layers, the luminescence was more uniformly produced throughout the layer.