Effect of oxygen pressure on the structure and thermal stability of ultrathin Al2O3 films on Si(001)

${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/Si(001)}$ 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 ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ film of about 0.6 nm was grown on an atomically flat $\mathrm{Si(001)-2\times 1}$ surface, and the resulting ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/Si(001)}$ interface was atomically abrupt. An intentional reoxidation of the ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/Si(001)}$ system under low oxygen pressure ${\text{(2×10}}^{\text{−6}},$ ${\text{5×10}}^{\text{−6}},$ and ${\text{2×10}}^{\text{−5}} \mathrm{Torr}$ ${\mathrm{O}}_{\mathrm{2}})$ showed that the ultrathin ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ 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 °C). A high-pressure reoxidation of the ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/Si(001)}$ system at ${\text{5×10}}^{\text{−5}} \mathrm{Torr}$ ${\mathrm{O}}_{\mathrm{2}}$ resulted in the formation of an interfacial ${\mathrm{SiO}}_{\mathrm{2}}$ 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 °C. Additionally, a very weak temperature dependence of the growth of interfacial ${\mathrm{SiO}}_{\mathrm{2}}$ was observed. A high-pressure reoxidation at 750 °C led to the formation of crystalline ultrathin ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ film and also caused degradation of the film by formation of ${\mathrm{SiO}}_{\mathrm{2}}$ in the near-surface region, where a slight decrease in the ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ film thickness was observed. This was attributed to the formation of interstitial Si in the interfacial ${\mathrm{SiO}}_{\mathrm{2}}$ 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 ${\mathrm{SiO}}_{\mathrm{2}}$ layer at the ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/Si(001)}$ interface. These results indicate that the oxygen pressure of the ambience plays an important role in the oxidation of the ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/Si(001)}$ interface, and the mobility, transport, and chemical reactions at various oxidation temperatures...