The formation of a continuous amorphous layer by room . . temperature implantation of boron into silicon

Ion implantation of 60 ke V boron into {100} silicon at medium beam currents (150 ttA) was performed at 300-315 K over the dose range from 1 to 8 X 1016/cm2 • Diffraction contrast and high-resolution phase contrast transmission electron microscopy (TEM) were used on planview and 90· cross-section samples to study the formation of a continuous amorphous layer as a function of increasing dose. Our TEM results show that, unlike implantation of Si with heavier ions where amorphization initially occurs at or around the projected range, the amorphization by high dose ( > 5 X 1016/cm2) B-+-implanted Si first occurs at and/or near the surface. It is proposed that the buildup of a high concentration of vacancies which inevitably occurs near the surface during high-dose n-' implantation is primarily responsible for the observed near-surface amorphization. Based on the results of this investigation and those available in the published literature, it appears that low temperature (slow recombination rate for point defects) and high beam current (high generation rate for point defects) implantation may result in the optimum conditions for amorphous layer formation with boron.