Hole and electron trapping in ion implanted thermal oxides and SIMOX

Optically assisted methods of injecting either electrons or holes into SiO₂ layers were used to determine the effect of ion implantation on charge trapping in oxides. Dry-grown thermal oxides and the buried oxides of material grown by the SIMOX (separation by implantation of oxygen) process were studied. Al, Si, and P ions were implanted into the oxides at doses of 1×10¹³ to 1×10¹⁶ and the oxides were annealed at 700, 900, or 1050°C after implantation. High dose implantations were found to create electron traps having high capture cross sections, the density of which depends on the implant species, suggesting that electron trapping is related to chemical aspects of the implanted ion. This was supported by measurements on an oxide implanted with a large dose of Ar, which showed no increase in electron trapping. It was found that the shift in the flatband voltage resulting from hole trapping could be reduced by high dose implantations, and that this effect is only weakly dependent on implant species. The hole trapping results are explained in terms of the effect of implantation on the oxide structure