Strain determination and microstructural characterization of 50 keV Sn-ion-implanted Si(001)

Abstract

Si(001) structures, implanted with Sn at energy of 50 keV and with doses in the range 2–9×1015 cm−2, were investigated by multicrystal x-ray diffraction, reciprocal space mapping (RSM), high-resolution transmission electron microscopy, and secondary-ion-mass spectrometry (SIMS). For Sn doses up to 3.30×1015 cm−2, annealing at 600 °C for 30 min under dry N2 atmosphere resulted in recrystallization by solid-phase epitaxy (SPE) to a layer thickness of more than 50 nm. These SPE-grown layers were shown to be free of extended defects and Sn redistribution was negligible. As measured by x-ray diffraction, the Sn-induced strain in Si increased with the implant dose. From RSM measurements, this strain was shown to be tetragonal with negligible in-plane relaxation. Mosaicity and defect-related effects were shown to be negligible. Instead, limited thickness effects and strain variation due to the implantation profile appeared to be the major sources of the observed broadening in the diffraction peaks. The lattice expansion coefficient for Sn in Si was estimated from the measurements to be 2.5×10−24 cm3/atom. For Sn doses above 3.3×1015 cm−2, a reduction in the Sn-induced strain in Si was observed despite the fact that Sn concentrations were higher. In this high-dose regime, the SPE growth under the same annealing conditions was limited to ∼10 nm. The remainder of the structure showed a succession of layers dominated by twinned Si(001), polycrystalline Si, nanocrystalline Si:Sn, and an untransformed amorphous top layer. In addition, Sn redistribution was detected in the SIMS measurements at levels much higher than expected from trace-diffusivity values at the employed annealing conditions. The observed SPE retardation was related to the high concentrations of Sn in these structures.