Features of semiconductor irradiation with low-energy caesium ions

Abstract

The paper considers the emission of secondary cluster ions when Si and GaAs surfaces are simultaneously sputtered with low-energy caesium ions (0.5–2 keV) and a pulsing beam of bismuth ions with an energy of 30 keV. It is shown that the observed mass spectra can be obtained if the caesium atoms implanted during irradiation form nano-islands (nanoparticles) at the irradiated surface. It was found that these Cs nanoparticles are formed under the surface due to the so-called Ostwald ripening process and come to the surface during the ongoing sputtering. The composition of the experimental mass spectra with 6–7 target and caesium atoms of a sufficiently high intensity leads to the conclusion that neither the recombination model nor the direct emission model can explain the observed emission. We explain the observed yield of cluster ions by the sputtering mode with the formation of “thermal spots”. These high-temperature spots resulting from collisions of primary bismuth ions with target atoms give rise to the generation of elastic waves in the target. These waves reach the surface and lead to a simultaneous escape of several atoms from the surface layer, or, in other words, to the formation of a secondary cluster.