Channeling study of boron implanted silicon: Liquid nitrogen temperature implantation

Abstract

Silicon samples have been boron implanted at 150 keV at liquid nitrogen temperature to a dose of 3.6 × 10¹⁵/cm². This dose rendered the implanted layer amorphous as viewed by helium ion backscattering. Four kinds of room temperature measurements were made on the same set of samples as a function of the isochronal annealing temperature. The measurements made were the determination of the substitutional boron content by the channeling technique using the B¹¹(p, α) nuclear reaction, observation of the disorder by helium ion backscattering, determination of the carrier concentration by van der Pauw Hall measurements, and the sheet resistivity by four point probe measurements. These measurements are compared with results from samples implanted at room temperature. The carrier concentration correlates well with the substitutional boron content for both room temperature and liquid nitrogen temperature implantations. Following annealing temperatures in the 600 to 800°C range, a much larger percentage of the boron lies on substitutional lattice sites, and therefore the carrier concentration is larger, if the implantation is done at liquid nitrogen temperature rather than at room temperature. Following liquid nitrogen temperature implantation, reverse annealing is observed from 600 to 800°C in the substitutional boron content, carrier concentration and sheet resistivity. The boron is more than 90 per cent substitutional after annealing to 1100°C for both the room temperature and liquid nitrogen temperature implantations. The low temperature implantation produced a buried amorphous layer, and this layer was observed to regrow from both the surface and substrate sides at approximately equal rates.