An AES-SIMS study of silicon oxidation induced by ion or electron bombardment

Abstract

We have investigated bombardment-induced oxidation of silicon at room temperature in an AES-SIMS system. Most of the results described were obtained by AES. SIMS was used only to reproduce previous work under the conditions of this study. It was found that bombardment of sputter-cleaned silicon with either electrons (2 keV) or argon ions (5-10 keV) at elevated oxygen pressures (up to 10-3 Pa) results in strongly enhanced oxygen uptake and oxidation of silicon, as evidenced by the appearance of a strong (SiO2)LVV line at ≈78 eV. At base pressure almost complete oxidation can be produced by direct implantation of oxygen (15 keV O+2) at normal incidence, whereas O+2 impact at 45° results in incomplete oxidation. The (SiO2)LVV intensity increases as the n-th power of the OKLL intensity, where n = 2.4 and 3.7 for argon and oxygen bombardment, respectively. Deviations from the expected growth kinetics (n = 2) are attributed mostly to differences in escape depth of the (SiO2)LVV and OKLL electrons. Electron impact results in oxide structures similar to those induced by ion impact, the main difference being that the thickness of the altered layer is apparently smaller under electron irradiation. Comparison of AES and SIMS results suggests that the oxygen-induced enhancement of the Si+ intensity is directly related (most likely proportional) to the concentration of SiO2. Oxygen uptake from the ambient has also been investigated by ion-excited AES. It was found that the ion excited Si signals are much less sensitive to variations in the average oxygen content than the respective electron-excited signals. This suggests rapid oxygen emission from the cascade center prior to deexcitation of the collisionally excited Si atom. © 1980.