Use of transient enhanced diffusion to tailor boron out-diffusion

We report experimental results demonstrating the use of transient enhanced diffusion (TED) caused by silicon implant for “tuning” boron out-diffusion. The effect was measured as a function of the silicon implant dose and anneal temperature, and a range of boron junction depth movement from almost none up to 81 nm was observed with increasing TED at 750°C. The diffused profiles could be approximated by using a modified solubility limit model to describe the enhanced boron diffusion and clustering. However, by using a more sophisticated continuum model based on atomistic calculations, excellent agreement with the measured profiles could he obtained. In addition, the fit to the measured data yields the fraction of boron present in BI₂ precursor clusters after silicon implant as a function of the silicon implant dose. Two possible applications of the TED “tuning” are discussed, with device simulations which show that the effect is sufficiently large to tune the base width of a bipolar device from being depleted to that suitable for a high performance device