Observation of Vacancy Clustering in Si Crystals During in Situ Electron Irradiation in a High Voltage Electron Microscope

Abstract

The formation of vacancy clusters in various Si crystals covered with SiO2 and Si₃N₄ films has been studied by means of high-voltage and high-resolution electron microscopy using electron beam energies of 1000 and 400 keV, respectively, and at temperatures between 20 and 250°C. Small vacancy clusters of about 2–5 nm in the form of Frank dislocation loops and stacking fault tetrahedra were observed by irradiating the thinnest areas (< 20 nm) of the investigated silicon specimens. Vacancy clustering seems to be more complicated in the thicker parts (> 20 nm) of irradiated crystals. We assume that in these areas vacancy clusters may be formed only in Si layers near the interfaces Si-SiO₂ or Si-Si₃N₄ and they may interact with interstitials without full recombination of the defects. This leads to the appearance of a new form of interstitial clusters such as {111}-defects as well as the usual interstitial {113}-defects associated with vacancy clusters during prolonged irradiation in the HVEM.