Ion beam hydrogenation of polysilicon coated thermal oxide on silicon

Abstract

Abstract The annealing of bare thermal oxide on silicon at 400–500°C in a hydrogen bearing gas results in a reduced density of states Nss at the substrate silicon/oxide interface. Treatments of this type have played a role in MOS processing schedules for several years. However, a similar approach applied to large areas (cm2) of poly-silicon coated oxide appears to be less effective in reducing Nss. This may be due to the polysilicon acting as a partially impermeable barrier which tends to starve the substrate/oxide interface of hydrogen. In the present work hydrogenation of 2-inch diameter, polysilicon coated wafers has been accomplished by hydrogen ion implantation. H2+ ions of 135 kV energy were implanted (to a dose of 1015 cm−2) through a 7000 A polysilicon coating into an underlying 1400 A SiO2 layer. The polysilicon was removed after 30-min anneals carried out in pure N2 at 300, 400 or 500°C. Aluminium dots, 1 mm in diameter were then deposited on to the oxide and high frequency (1 MHz) and quasistat...