Ion Channeling Analysis of Disorder
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ION CHANNELING ANALYSIS OF DISORDER*
S. T. PICRAUX Sandia National Laboratoriest,
Albuquerque, New Mexico,
87185,
USA
Abstract The use of ion channeling to characterize disorder in semiconductors is briefly reviewed. At high defect densities the ion channeling/backscattering technique can give the depth distribution of defects with a resolution 10 nm. Quantitative analysis of the defect depth profile 1 requires that a single type of defect dominates the scattering of partiicles out of channeling trajectories. This scattering process is characterized by two defect-specific quantities: the direct scattering factor and the dechanneling cross-section. For impurity-associated defects the lattice location of the impurity atoms can be determined to within - 0.1 A by simultaneously measuring the impurity and host atom signals as a function of tilt angle about channeling directions. The channeling technique can detect a wide range of intrinsic defects including interstitials, dislocations, stacking faults, microtwins, and amorphous clusters. Examples of the application of channeling to study defects in silicon will be given for the cases: 1) hydrogen trapping at defects; 2) ion implantation doping; and 3) epitaxial growth of layers. INTRODUCTION The study of disorder by the ion channeling technique [El is based on the principle that channeled ions detect displacements from regular lattice sites. Thus, ion channeling is sensitive to interstitial host atoms or changes in the host periodicity, e.g., stacking faults, but is insensitive to isolated vacancies, except for a very small contribution in the case of lattice relaxations > 0.1 X around the vacancy. Some examples of defects which have been detected by the channeling effect are given in Table I. The technique is versatile but relatively insensitive. However, this can be an advantage in studies which involve high densities of defects. Ion channeling is a direct lattice technique. It contrasts to diffraction-based, reciprocal lattice techniques in that the interpretation of channeling data is very geometrical and qualitative aspects are subject to little uncertainty. However channeling is a spectroscopy only in the sense that by ion beam techniques impurity and host atom signals can be separated and resolved in depth. Therefore if a variety of defects involving a single impurity or the host atoms are present simultaneously, their respective signals will be summed together complicating interpretation. For this reason transmission electron microscopy is an important complementary technique to ion channeling studies of disorder.
*This work was supported by the Department of Energy, Energy Sciences, under contract DE-AC04-76-DP00789. tA U. S. Department of Energy facility.
Division of Basic
136 TABLE I Some defects which have been studied by the ion channeling technique.
Defect
Representative Study
Typical Concentrations Needed
Reference
Substitutional impurity
0.1 at.%
Si(As) laser annealing
2
Near substitutional impurity
0.1 at.%
Si(Bi) defect as
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