Ion-energy effects in silicon ion-beam epitaxy

Abstract

Direct ion-beam deposition of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}_{}^{+}{}_{}{}^{}$ ions for homoepitaxial film growth on Si{100} has been studied over the ion-energy range of 8–80 eV in the low-temperature range of 40–500 °C. Deposition was performed by means of a mass-selected, low-energy, ultrahigh-vacuum ion-beam system with a well-defined ion energy (E) for which the energy spread is ΔE=±3 eV. The films were analyzed in situ at growth intervals by reflection high-energy electron diffraction and Auger-electron spectroscopy, and ex situ by cross-section high-resolution transmission electron microscopy, Rutherford backscattering spectrometry, and secondary-ion-mass spectrometry (SIMS) depth profiling. The growth mode, crystalline quality, and number of defects in the films are found to be extremely sensitive to both substrate temperature (at low temperature) and ion energy (at low energy). Layer-by-layer epitaxial growth is observed down to ∼160 °C with appropriate ion energies; below this temperature, island growth with a transition to an amorphous phase occurs. An optimum ion-energy window for achieving layer-by-layer epitaxial growth and high crystalline quality films which are relatively defect free is observed. This energy window, which illustrates ion beam enhanced epitaxy, is extremely narrow at low temperature, i.e., ∼20±10 eV at 160 °C, and broadens out on the low-energy side at higher temperatures, e.g., at 290 °C. Within this energy window, the films have the same level of crystallinity as the single-crystal silicon substrate. This behavior is discussed in terms of the changes in the phenomena which dominate the growth process as a function of ion energy and temperature. For the conditions 290 °C and 20 eV, epitaxial high crystalline quality films up to 352 nm thick have been grown, and there is no indication of a limiting epitaxial layer thickness. SIMS analysis shows that the isotropic enhancement ratio is ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$/${(}^{29}$Si ${+}^{30}$Si)≳${10}^4$. © 1996 The American Physical Society.