The influence of boron ion implantation on hydrogen blister formation in n-type silicon
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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 1014 to 1019cm3. These substrates were implanted with 240 keV B+ ions to a dose of 1015cm2, followed by a rapid thermal anneal at 900C for 3060 s to force the boron atoms into substitutional lattice positions (activation). The samples were then implanted with 40 keV H+ to a dose of 51016cm2. The implanted H+ distribution peaks at a depth of about 475 nm, whereas the distribution in the implanted B+ is broader and peaks at about 705 nm. To evaluate the role of the B+ implantation, control samples were prepared by implanting with H+ only. Following the H+ implantation, all the samples were vacuum annealed at 390C for 10 min. Blisters resulting from subsurface cracking at depths of about 400 nm, were observed in most of the B+ implanted samples, but not in the samples implanted with H+ 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 H+ 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 B+ and H+ doping, the blister density was found to decrease with increasing n-type doping, when the boron is activated. Blister formation was also observed in B+ implanted samples which had not been activated. In this case, the blister density was found to increase with increasing value of n-type doping.
