Kinetics of vacancy diffusion on Si(111) surfaces studied by scanning reflection electron microscopy

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Abstract
The kinetics of vacancy diffusion on Si(111) surfaces is studied by using scanning reflection electron microscopy (SREM). Two types of layer-by-layer etching are observed during low-energy Ar ion irradiation (500 eV) at elevated substrate temperatures. One is step retreat, which is a reversal of step-flow growth, and the other is two-dimensional vacancy island nucleation. These results show that vacancies created by low-energy ion impact diffuse on the surfaces, and are annihilated at the step edges. The vacancy diffusion kinetics on the surfaces are examined by using a SREM technique. An activation energy of 3.0±0.2 eV is obtained from the vacancy diffusion length estimated from the width of the denuded zone, which is created on both sides of the atomic step by thermal heating after vacancy introduction by ion irradiation at room substrate temperature. These results indicate that vacancy diffusion kinetics is dominated by monovacancy formation and diffusion. These processes require thermal excitation to overcome the potential barrier for surface diffusion of adatoms, and to overcome the barrier for lateral binding energy to release adatoms from the step edges. © 1996 The American Physical Society.