Low-pressure oxidation of silicon stimulated by low-energy electron bombardment

The mechanisms of silicon oxide growth stimulated by electronic bombardment have been studied. Silicon single crystals, after cleaning by ion bombardment in UHV, were submitted to a low-energy (<100eV) electron irradiation (∼ 1 mA cm−2), under low oxygen pressure (10−4 Torr) in the temperature range 25–700°C. Oxide thicknesses less than 10 nm were thereby achieved. There is a strong increase of the initial growth rate when the electron energy decreases to 10eV. The oxidation kinetics can be fitted by a direct logarithmic law: X = X 0 log [(t/τ) + 1] where X is the thickness of oxide grown during time t and U = X 0/τ is the initial growth rate. Using the results of 18O tracing experiments, the growth mechanism is explained by a step-by-step motion of charged oxygen species under a constant electric field.