Noble-gas ion bombardment on clean silicon surfaces

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Abstract
Under UHV conditions clean c-Si(111) surfaces have been bombarded at room temperature by noble gases (He,Ne,Ar,Kr). Using spectroscopic ellipsometry, the implantation processes were continuously recorded. A low-dose behavior (amorphization) and a high-dose behavior (dilution) are observed. After termination of the bombardment, a self-anneal behavior appears and some experiments are discussed in order to explain the observed phenomena. After applying a monotonous temperature increase up to 1100 K, the noble gas desorbs and the surface layer returns to the original state, as can be seen from a closed trajectory in the (δψ,δΔ) plane. The low-dose behavior is analyzed in the scope of a simple ellipsometric first-order approximation, and the results obtained are compared with theory. The dilution arising during the high-dose behavior can be explained ellipsometrically by means of microscopic surface roughness, and some complementary measurements are reported to verify this explanation.