Si ion implantation-induced damage in fused silica probed by variable-energy positrons

Abstract

Samples of synthetic fused silica have been implanted at room temperature with silicon ions of energy 1.5 MeV. Fluences ranged from 10 11 to 10 13 cm Ϫ2. Samples were probed using variable-energy positron annihilation spectroscopy. The Doppler-broadening S parameter corresponding to the implanted region decreased with increasing fluence and saturated at a fluence of 10 13 cm Ϫ2. It is shown that the decrease in the S parameter is due to the suppression of positronium ͑Ps͒ which is formed in the preimplanted material, due to the competing process of implantation-induced trapping of positrons. In order to satisfactorily model the positron data it was necessary to account for positron trapping due to defects created by both electronic and nuclear stopping of the implanted ions. Annealing of the 10 13 cm Ϫ2 sample resulted in measurable recovery of the preimplanted S parameter spectrum at 350°C and complete recovery to the preimplanted condition at 600°C. Volume compaction was also observed after implantation. Upon annealing, the compaction was seen to decrease by 75%.

Characterization of the interface region during the agglomeration of silicon nanocrystals in silicon dioxide

“…This is not due to the implantation-induced defects, which can be annealed out at 600°C. 22 The Si nanocrystals themselves cannot account for this decrease, either. The diffusion length of positrons in defect-free Si is usually 215-250 nm, 23 which is significantly larger than the sizes of nc-Si in our sample.…”

“…We should be also aware of the implantation-induced volume compaction in the structure of SiO 2 . This leads to the suppression of the formation of positronium, also contributing to the decrease of S. 22 After 400°C annealing in nitrogen, the trapping of nitrogen in the interface regions is saturated. This explains why S values decrease and then hardly change until 700°C ͑Fig.…”

Characterization of Implantation Induced Defects in Si-Implanted SiO2 Film

“…The S parameter versus positron incident energy (S-E) plots for this un-implanted sample at energies less than ∼2 keV are contributed by positrons diffusing from the implanted region to the region near the sample surface (corresponding to ∼100 eV positron incident energy). 8 Meanwhile, the S-E plots for implantated samples with different ion fluencies and annealing temperatures are shown in Figure 1(b). However, the difference in S parameter is due to the difference of the fraction of positrons able to diffuse to the surface.…”

Positron annihilation spectroscopy of the interface between nanocrystalline Si and SiO2

“…Impurities are also preferentially trapped in such voids, so that nitrogen incorporated during annealing reduces the S values seen by PAS. Implantation-induced volume compaction of SiO 2 leads to the suppression of the formation of positronium, also contributing to the decrease of S [18].…”

“…2). This is not due to the implantation-induced defects, which can be annealed out at 600 C [18], or the nc-Si, because the diffusion length of positrons in defect-free Si is significantly larger than the sizes of nc-Si in our sample [19,20]. The mismatch between nc-Si and the SiO 2 matrix leaves open-volume spaces (voids) in the interface regions; these trap positrons more effectively than both the normal SiO 2 structure and nc-Si.…”