Electron trapping studies in multiple- and single-implant SIMOX oxides

A detailed study of electron traps in SIMOX buried oxides prepared by both single- and multiple-implant acid anneal technologies is reported. The techniques of avalanche electron injection and constant voltage stressing (CVS) have been used to reveal three distinct electron traps in SIMOX. The largest, with a capture cross section of the order 10 -14 cm 2 , is thought to be related to the so-called E' centres associated with excess Si in the oxide matrix. Its concentration is seen consistently to be higher in single-implant material which is known to contain a significantly higher concentration of excess Si than multiple-implant material. SIMOX also contains a smaller trap, with a cross section typically of the order 10 -16 cm 2 , and it is suggested that it is a result of contamination during implantation. The third and smallest trap has a cross section of the order 10 -17 cm 2 and may be the so-called water-related trap seen in thermal oxides. The experiments also show that useful quantitative information can be obtained from the relatively crude but simple technique of constant voltage stressing. This is mainly because the field necessary to induce significant electron current through the oxide is significantly lower than in conventional thermal oxide as the injection is aided by field intensification arising from interfacial asperities. CVS has therefore been developed into a simple oxide assessment technique which could be readily applied to starting substrates on simple, mesa-defined MOS capacitors.