Co-implantation of boron and fluorine in silicon

It was shown recently that co-implantation of fluorine with boron limits boron transient enhanced diffusion. This effect was shown to be a chemical species effect by eliminating extraneous damage effects through the use of pre-amorphized silicon. However, the nature of the fluorine interaction with boron remained in question. In order to answer this question, a series of experiments have been performed. Amorphization of a n-type Czochralski wafer was achieved with a 70 keV Si/sup +/ implantation at a dose of 1/spl times/10/sup 15//cm/sup 2/. The Si/sup +/ implant produced a 1400/spl Aring/ deep amorphous layer, which was then implanted with a 1/spl times/10/sup 15//cm/sup 2/ B/sup +/ dose at an energy of either 1.1 keV or 500 eV. The samples were then implanted with a dose of 2/spl times/10/sup 15//cm/sup 2/ F/sup +/ at various energies ranging from 2 keV to 36 keV. By varying the F/sup +/ energy it was possible to change the position and concentration of the fluorine relative to the boron and the end-of-range interstitial source. After annealing at 550/spl deg/C, 750/spl deg/ C, and 1050/spl deg/C the wafers were analyzed by secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM). Fluorine co-implantation with boron causes the diffusion of boron to exhibit two stages of diffusion during time frame that the control sample exhibits transient enhanced diffusion. The results from this experiment and supporting experiments suggest the fluorine is reducing the TED of the boron by trapping silicon interstitials.