Gettering of Iron and Surface Oxygen by High-Energy Boron ion Implantation in Silicon

Abstract

AbstractThe gettering of transition metals in silicon presents new challenges since older schemes such as internal gettering cease to be effective with newer technologies. The oxygen concentration in active regions is also a matter of concern when denuding cycles are not employed. Implantation of a deep layer of boron is a promising technique. The effects of boron implants at 1.7 MeV in the dose range 1014 – 1015 at./cm2 were studied with regard to the redistribution of both Fe and 0 after a thermal cycle. Fe was introduced onto the front surface of wafers by deposition after boron implantation. The redistribution of these species was monitored through SIMS depth profiles. In addition, diffusion length measurements from the back surface of the wafers were employed as a new means of assessing Fe gettering. In general there is a lowering of the surface oxygen concentration that increases with dose, or with temperature in the range 850-1000°C. The oxygen concentration can be lowered to a level comparable to denuded wafers at the upper end of this range. The amount of Fe gettering is higher after 850°C than after 1000°C at a given dose. Diffusion length measurements correlate well with SIMS data and provide a convenient method of investigating Fe gettering. This study has demonstrated the feasibility of optimizing a combination of dose and temperature for the gettering of Fe and the lowering of surface oxygen concentration to an acceptable level for device fabrication.