A MECHANISM OF GATE OXIDE DETERIORATION DURING AS+ ION-IMPLANTATION

The ion implantation process involves the problem of wafer charging which may result in deterioration or catastrophic breakdown of thin gate oxides. In this paper, we have investigated how the deterioration of the oxide occurs during ion implantation. The effect of ion beam density, the distribution of the gate oxide deterioration over a wafer, and the effect of photoresist coverage are shown quantitatively by measuring the number of interface states generated in MOS capacitors. It is shown that the four charge sources contribute to the deterioration of gate oxide: the irradiated ion beam, the secondary electrons emitted from the gate electrode, the charges accumulated on the photoresist surface around the gate electrode, and the secondary electrons emitted from a wafer holder. The former three charges accelerate the deterioration of the gate oxide and the latter one reduces it. A model of the gate oxide deterioration in ion implantation is presented, which is very useful to find methods to reduce the charging damage.