Helium-implanted silicon: A study of bubble precursors

Abstract

The interaction of helium atoms with the radiation damage imparted to (100) silicon single crystal by He+ implantation at 5×1015 cm−2, 20 keV, and liquid–nitrogen temperature is investigated by means of various complementary techniques during and after thermal treatments. Thermal programmed desorption was used to study the dissociation kinetics of helium from the defects and to plan suitable heat treatments for the other techniques. The helium profiles were determined by 8 MeV N2+15 elastic recoil detection, quantitative data on damage were obtained by channeling Rutherford backscattering spectrometry, double crystal x-ray diffraction, and positron annihilation spectroscopy. Isothermal treatments at 250 °C produce first helium redistribution and trapping in vacancy-like defects, rather than helium desorption from traps. The process is thermally activated with an effective activation energy, dispersed in a band from 1.1 to about 1.7 eV. For higher temperature treatments (2 h at 500 °C) the traps are almost emptied and at 700 °C all vacancy-like defects are annealed out. No bubbles or voids are observed by transmission electron microscopy, either in the as-implanted or in annealed samples.

He migration in implanted UO2 sintered disks

“…The He shift towards the surface suggests that He atoms are mobile at temperatures as low as 600°C and are trapped at implantation induced defects as has already been observed in crystalline Si [10] and also in polycrystalline MgAl 2 O 4 [11]. Corni et al [10] observed a forward He profile shift of 45 nm in 20 keV heliumimplanted silicon (R p ¼ 215 nm) after annealing.…”

“…$1.6 lm). As it has been demonstrated in Si [10], one of the processes involved prior to He bubble formation is the He rearrangement in the high defect concentration region which occurs when the implanted samples are annealed. This would suggest that the vacancy defect profile in sintered UO 2 disks implanted with 1 MeV 3 He ions is indeed located at approximately 1.6 lm from the sample surface.…”

“…Corni et al [10] observed a forward He profile shift of 45 nm in 20 keV heliumimplanted silicon (R p ¼ 215 nm) after annealing. By correlating ERD, PAS and DC-XRD measurements, the authors ascribed this 14% shift to the interstitial helium movement and trapping in the vacancy-like defects produced by the implantation.…”

Iodine isothermal migration behaviour in titanium nitride

“…4 shows the distribution of nitrogen vacancy-like defects created by the initial implantation (calculated from SRIM Ò code [37]) together with the experimental iodine depth profiles before and after thermal treatment at 1500°C for 3 h. The vacancy concentration is theoretically high in the region between the surface and a depth of about 125 nm corresponding to the maximum defect concentration. It has been shown in many materials that vacancy-like defects created during implantation near the surface constitute potential traps for the implanted species [28,38]. In the case of titanium nitride, the presence of remaining point defects could explain the accumulation of iodine near the surface.…”

Vacancy Cluster Distributions in He Implanted Silicon Studied by Slow Positron Annihilation Spectroscopy

“…Recently, the subject was systematically investigated with several techniques applied at samples implanted at a He fluence below (5 x 10 15 cm -2 ) and above (2 x 10 16 cm -2 ) the threshold for cavities formation. Information about the evolution of He and of the displaced silicon atoms distributions was obtained by elastic recoil detection (ERD) and Rutherford backscattering in channelling (RBS-C) [3,4]. Thermal programmed desorption (TPD) [5] was employed to obtain information about thermodynamics and kinetics quantity.…”