Atomic-Scale Simulation of Silicon Atomic Beam Deposition
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ATOMIC-SCALE SIMULATION OF SILICON ATOMIC BEAM DEPOSITION
BRIAN W. DODSON Sandia National Laboratories,
Albuquerque,
NM 87185
ABSTRACT The mechanisms which control low energy (10-100 eV) beam deposition of silicon onto a relaxed (111) silicon substrate have been studied using a molecular dynamics technique. A many-body empirical potential was used to describe the covalent Si-Si bonding. 10 eV silicon beams with near-perpendicular incidence were simulated to study capture mechanisms and the local lattice excitation resulting from impact. Grazing angles of incidence (3°-30°) were studied for beam energies of 20-100 eV. For incidence angles less than an energyand orientation-dependent critical value, the phenomenon of 'surface channeling' is predicted, in which the incoming particle is steered parallel to, and roughly 2 A above, the surface of the substrate through inelastic substrate interactions. The phenomena seen in low-energy beam deposition offer new avenues of control over growth of modulated semiconductor structures.
INTRODUCTION Devices which depend critically on modulated physical structure are currently of great interest. Examples of such structures include superlattices, strained-layer systems, devices with ultrathin layers, and related structures. The quality of such structures often correlates with substrate temperature during growth; thus one approach to reducing defect density while retaining conventional growth techniques is to optimize the growth temperature. This optimization involves balancing competing processes: if the temperature
is
too low,
defects
resulting
from unannealed
surface
configura-
tions will be formed, whereas at higher temperatures, thermally induced defects will nucleate. For some systems an adequate window of temperatures exists between these two limits, but this is not always the case. A nonequilibrium approach to reducing defects in the growth process is to keep the bulk of the structure relatively cool during deposition while annealing the surface in situ through direct excitation of the surface. One proposed technique is low energy ion beam deposition, in which experimental studies have recently begun [1]. To produce significant non-thermal effects, the beam energy must be larger than the energy of adsorption of a silicon atom onto a silicon surface. To investigate this approach, we have considered the near-perpendicular deposition of 10 eV silicon atoms onto, and the interaction of a grazing 20-100 eV silicon beam with, a relaxed Si (111) surface.
SIMULATION METHOD AND INTERACTION POTENTIAL Molecular dynamics techniques have been used with considerable success to simulate the microscopic response of atomistic systems to a given set of conditions [2]. The process of beam deposition has small enough length and time scales that they are easily accessible to such techniques. In molecular dynamics the classical equations of motion for an assembly of interacting particles are integrated numerically, resulting in a complete classical description of the system over the
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