The influence of boron ion implantation on hydrogen blister formation in n-type silicon

We have studied the formation of surface blisters in 〈100〉 n-type silicon following co-implantation with boron and hydrogen. The silicon substrates had four different n-type dopant levels, ranging from ${10}^{14}$ to ${10}^{19} {\mathrm{cm}}^{\mathrm{-3}}.$ These substrates were implanted with 240 keV ${\mathrm{B}}^{\mathrm{+}}$ ions to a dose of ${10}^{15} {\mathrm{cm}}^{\mathrm{-2}},$ followed by a rapid thermal anneal at 900 °C for 30–60 s to force the boron atoms into substitutional lattice positions (activation). The samples were then implanted with 40 keV ${\mathrm{H}}^{\mathrm{+}}$ to a dose of ${\text{5×10}}^{16} {\mathrm{cm}}^{\mathrm{-2}}.$ The implanted ${\mathrm{H}}^{\mathrm{+}}$ distribution peaks at a depth of about 475 nm, whereas the distribution in the implanted ${\mathrm{B}}^{\mathrm{+}}$ is broader and peaks at about 705 nm. To evaluate the role of the ${\mathrm{B}}^{\mathrm{+}}$ implantation, control samples were prepared by implanting with ${\mathrm{H}}^{\mathrm{+}}$ only. Following the ${\mathrm{H}}^{\mathrm{+}}$ implantation, all the samples were vacuum annealed at 390 °C for 10 min. Blisters resulting from subsurface cracking at depths of about 400 nm, were observed in most of the ${\mathrm{B}}^{\mathrm{+}}$ implanted samples, but not in the samples implanted with ${\mathrm{H}}^{\mathrm{+}}$ only. This study indicates that the blistering results from the coalescence of implanted H into bubbles. The doping with B facilitates the short-range migration of the H interstitials and the formation of bubbles. A comparison of the observed crack depth with the depth of the damage peak resulting from the ${\mathrm{H}}^{\mathrm{+}}$ implantation (evaluated by the computer code TRIM) suggests that the nucleation of H bubbles occurs at the regions of maximum radiation damage, and not at the regions of maximum H concentration. For given values of ${\mathrm{B}}^{\mathrm{+}}$ and ${\mathrm{H}}^{\mathrm{+}}$ doping, the blister density was found to decrease with increasing n-type doping, when the boron is activated. Blister formation was also observed in ${\mathrm{B}}^{\mathrm{+}}$ implanted samples which had not been activated. In this case, the blister density was found to increase with increasing value of n-type doping.