Boron, fluorine, and carrier profiles for B and BF2 implants into crystalline and amorphous Si

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Abstract
Depth distributions, measured by secondary ion mass spectrometry (SIMS), and carrier profiles, measured by differential capacitance‐voltage (C‐V) profiling, of boron and fluorine implanted as B, F, BF, or BF2 ions into random and channeling orientations of crystalline silicon, and into silicon amorphized by silicon ion implantation are reported. Low boron energies of 8 and 10 keV and the corresponding energies of 36 and 45 keV for BF2 ions are emphasized because of their use for high resolution device and circuit applications in silicon and silicon‐on‐sapphire. Amorphizing crystalline silicon prior to boron implantation eliminates the significant channeling tails on 8‐ or 10‐keV boron profiles. Fluorine penetrates more deeply into crystalline silicon than boron does. Both boron and fluorine redistribute during annealing at 925 °C/20 min for B, F, BF, or BF2 implants, but with quite different characteristics as illustrated, and depend on the implantation fluence (5×1014 and 2×1015 cm−2 reported here). The fluorine redistribution profiles are strongly influenced by the magnitude and distribution of damage that remains after annealing. Fair agreement is shown between boron atom depth distributions measured by SIMS and C‐V electrical profiles measured for a fluence of 1.5×1012 cm−2. Differential C‐V profiles indicate that the entire ion spectrum from BF3 can be implanted and electrically activated (for a fluence of 1.5×1012 cm−2), as can a BF2 implant. Implantation through a 20‐nm layer of SiO2 has no significant effect on the boron depth distribution in crystalline silicon. Pearson IV moments are given for the low energy boron profiles. The use of these profiles for modeling calculations is discussed. The suprem model of an exponential for the channeling tail of boron implants in crystalline silicon is fairly good for fluences greater than about 1015 cm−2, but poorer for lower fluences, but the slope and matching to the random portion of the profiles are difficult to predict. In order for modeling calculations to reasonably represent boron profiles, either the silicon substrate should be amorphized prior to boron implantation, or the modeling should be modified to use experimental data measured for the implant and silicon conditions.