Ge Surface Displacements Due to Low Energy Particles
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Ge SURFACE DISPLACEMENTS DUE TO LOW ENERGY PARTICLES
S. T. Picraux, K. M. Horn, E. Chason, J. Y. Tsao, P. Klitsner and D. K. Brice Sandia National Laboratories, Albuquerque, NM 87185 USA
Bedrossian,
T.
ABSTRACT 4
The production of surface defects by low energy He and Xe ions incident on very smooth Ge(001)2x1 surfaces is reported. Roughening at -50°C by 100-500 eV ions is measured by RHEED in real-time using the intensity of the out-of-phase specular beam. For He, the surface displacements per ion range from 0.05 to 0.3 and are comparable to our binary collision calculated surface vacancy production rate for a displacement threshold energy of 11 eV (3/4 of bulk value). For Xe, the displacement rate ranges from 2 to 10 (-30x higher) and falls between the calculated total vacancy and total defect (vacancy + interstitial) production rates.
INTRODUCTION The processing of semiconductor surfaces often involves the use of beams of low energy particles to stimulate or control cleaning, deposition and etching processes. However, progressive reductions in the feature size of semiconductor devices increases their sensitivity to low levels of defects produced during such processing. Quantitative measurements of the energy-dependent rate at which ions induce damage on well-defined surfaces provide fundamental information about the influence of low energy particles on processing. Relatively few results are available for UHV clean surfaces near the threshold energy (!100 eV) for surface or bulk atom displacements. Thus it has not previously been possible to compare actual defect production rates to theoretical prediction. In the present preliminary study we examine the surface disordering of Ge(001)2xl surfaces caused by low energy He and Xe ions and compare these results to binary collision simulations of the displacement disordering rates.
EXPERIMENTAL 10
The measurements were carried out in a UHV chamber with a lx10" Torr base pressure. Extremely smooth Ge(00l)2xl surfaces (0.5* miscut) were prepared by repeated sputter cleaning and high temperature annealing. The surface was bombarded using a non-mass separated, high gas purity sputter ion gun with He or Xe ions ranging in energy from 100 to 500 eV 2 with an incident ion current density from 10 to 200 nA/cm . The sample was maintained at -50°C during ion bombardment unless otherwise noted. The ion beam is incident on the target at an azimuthal angle of 38* relative to the crystalline direction and 60* relative to the surface normal. The relative accuracy of the damage production rates obtained from these measurements is estimated to be about +25% and the absolute values +50%. The 20 keV reflection high energy electron diffraction (RHEED) measurements were made in situ with the specular beam set in the out-of-phase condition at an azimuth of 8* off the axis. Under these conditions, electron scattering from atoms on adjacent atomic layers interferes destructively and the measured intensity is quite Mat. Res. Soc. Symp. Proc. Vol. 236. 01992 Materials Research Society
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