ION-ENERGY EFFECTS IN SILICON ION-BEAM EPITAXY

Direct ion-beam deposition of Si-28(+) ions for homoepitaxial film gro wth on Si{100} has been studied over the ion-energy range of 8-80 eV i n the low-temperature range of 40-500 degrees C. Deposition was perfor med 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 Delta E = +/- 3 eV. The films were analyzed in situ at growth inte rvals by reflection high-energy electron diffraction and Auger-electro n spectroscopy, and ex situ by cross-section high-resolution transmiss ion electron microscopy, Rutherford backscattering spectrometry, and s econdary-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 temperat ure) and ion energy (at low energy). Layer-by-layer epitaxial growth i s observed down to similar to 160 degrees C with appropriate ion energ ies; below this temperature, island growth with a transition to an amo rphous 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 illustr ates ion beam enhanced epitaxy, is extremely narrow at low temperature , i.e., similar to 20 +/- 10 eV at 160 degrees C, and broadens out on the low-energy side at higher temperatures, e.g., at 290 degrees C. Wi thin this energy window, the films have the same level of crystallinit y as the single-crystal silicon substrate. This behavior is discussed in terms df the changes in the phenomena which dominate the growth pro cess as a function of ion energy and temperature. For the conditions 2 90 degrees C and 20 eV, epitaxial high crystalline quality films up to 352 nm thick have been grown, and there is no indication of a limitin g epitaxial layer thickness. SIMS analysis shows that the isotropic en hancement ratio is Si-28/(Si-29 + Si-30) > 10(4).[SD163-1829(96)05316- 7]