Raman-scattering elucidation of the giant isotope effect in hydrogen-ion blistering of silicon.
In this work, we investigate the origin of a giant isotope effect discovered in the blistering of hydrogen-ion-implanted and annealed silicon. Si(001) samples were implanted or co-implanted with 5 keV of H and/or D ions to total fluences of 2 x 10(16) and 6 x 10(16) ion/cm(2). The lower fluence is sufficient for blistering by pure H, but the higher one is required for the maximum blister coverage whenever D is involved. On these samples, we carried out Raman-scattering investigations of the evolution of Si-H/D complexes upon a stepwise thermal annealing from 200 to 550 degrees C. We have identified the critical chemical transformations characterizing the hydrogen-deuterium-induced blistering of silicon. The puzzling dependence on ion mass appears to be mainly connected with the nature of the radiation damage. We have found that H is more efficient in "preparing the ground" for blistering by nucleating platelets parallel to the surface, essentially due to its ability to agglomerate in the multihydride monovacancy complexes that evolve into hydrogenated extended internal surfaces. By contrast, D is preferentially trapped in the surprisingly stable monodeuteride multivacancies.
Systematics of the giant isotope effect in hydrogen ion blistering of materials
Abstract The giant isotope effect, observed when D ions were substituted for H ions in low energy blistering of silicon, challenged common assumptions based on ion irradiation theory and H–Si chemistry. We report a systematic investigation of the effect in several materials, in an attempt to identify its origin. Samples of Si, Ge, GaAs, 6H–SiC and SrTiO3 (STO) were implanted at 5 keV with various H or D doses (1 × 1016 to 2 × 1017 cm− 2) and rapid thermal annealed. The resulting surface morphology was examined by atomic force microscopy. On Si and GaAs, D-ion blistering requires 2 to 3 times higher doses than H-ion blistering. On SiC, no D-ion blistering whatsoever is observed. On the other hand, on Ge and STO, there is little difference between H and D-induced blistering. For Si, Raman spectroscopy of Si–H/D bonding in conjunction with lattice kinetic Monte-Carlo calculations led to an interpretation of the effect in terms of reactions between the mobile entities, i.e. H (or D) atoms, vacancies and interstitials. The new data will be discussed by reference to this scenario.
Effect of uniaxial stress on local vibrational modes of hydrogen in ion-implanted silicon.
The interactions of hydrogen with intrinsic defects in proton-implanted silicon crystals have been studied by infrared absorption spectroscopy in conjunction with uniaxial stress. After implantation at room temperature numerous lines, associated with local vibrational Si-H stretching modes, have been revealed, in accordance with previous reports. The measurements have been carried out at low temperatures to reduce the linewidths. Only the lines observed at 1839, 1934, 2062, and 2166 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ have been investigated in detail. From the analysis of the stress-induced shifts and splittings of the lines, the symmetries of the relevant defect centers have been deduced. It has been found that the 1839-, 2062-, and 2166-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ lines originate from defects with trigonal symmetries, whereas the 1934-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ line corresponds to a monoclinic center of type I. The annealing behaviors of the lines have been determined and the results have been used to indicate whether different stretching modes are related to the same center. Moreover, from measurements on samples, where hydrogen atoms are partially substituted by deuterium atoms, some information about the number of hydrogen atoms involved in the various defects has been obtained. The 1839- and 2062-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ centers each involve a single Si-H bond. Detailed models for these two centers, consistent with the present observations and recent channeling experiments, are suggested. The 1934-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ line is tentatively assigned to a divacancy, having one or two dangling bonds saturated by hydrogen atoms. The 2166-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ line is ascribed to the activation of a twofold degenerate stretching mode, while another line at 2162 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, related to the same center, is believed to be associated with a nondegenerate mode. The 2166-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ center contains more than one hydrogen atom, and various models are briefly discussed.