Effect of oxygen pressure on the structure and thermal stability of ultrathin Al_(2)O_(3) films on Si(001)

摘要

Al_(2)O_(3)/Si(001) surfaces and interfaces were investigated using scanning reflection electron microscopy, reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and Auger electron spectroscopy. A uniform, stoichiometric and ultrathin Al_(2)O_(3) film of about 0.6 nm was grown on an atomically flat Si(001)-2×1 surface, and the resulting Al_(2)O_(3)/Si(001) interface was atomically abrupt. An intentional reoxidation of the Al_(2)O_(3)/Si(001) system under low oxygen pressure (2×10~(-6), 5×10~(-6), and 2×10~(-5) Torr O_(2)) showed that the ultrathin Al_(2)O_(3) film stoichiometry and the interface abruptness were maintained with progress in reoxidation time. Furthermore, the film and the interface showed no degradation under low-pressure reoxidation at various temperatures (400-750℃). A high-pressure reoxidation of the Al_(2)O_(3)/Si(001) system at 5×10~(-5) Torr O_(2) resulted in the formation of an interfacial SiO_(2) layer which grew in a layer-by-layer mode with atomic-scale uniformity and had an atomically abrupt interface with Si(001) substrate up to 700℃. Additionally, a very weak temperature dependence of the growth of interfacial SiO_(2) was observed. A high-pressure reoxidation at 750℃ led to the formation of crystalline ultrathin Al_(2)O_(3) film and also caused degradation of the film by formation of SiO_(2) in the near-surface region, where a slight decrease in the Al_(2)O_(3) film thickness was observed. This was attributed to the formation of interstitial Si in the interfacial SiO_(2) layer and the subsequent mobility of Si and Al under this growth condition. Under low-pressure reoxidation, the Si and Al were immobile because of the absence of an interfacial SiO_(2) layer at the Al_(2)O_(3)/Si(001) interface. These results indicate that the oxygen pressure of the ambience plays an important role in the oxidation of the Al_(2)O_(3)/Si(001) interface, and the mobility, transport, and chemical reactions at various oxidation temperatures (400-750℃).