Structure and stability of La₂O₃/SiO₂ layers on Si(001)

High-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) were used to investigate La₂O₃/SiO₂/Si structures. The La₂O₃ layers were deposited on thermal SiO₂ on silicon, followed by rapid thermal annealing treatments at 600°C and 800°C in a nitrogen ambient. After annealing at 600°C, the oxide layers were amorphous. After an 800°C treatment, crystallites appeared in the original La₂O₃ layer, and the total oxide layer thickness increased by 17%, most likely due to the oxygen diffusion and reaction at the Si/SiO₂ interface. EELS, using a 0.2 nm probe, showed that rapid thermal annealing at 600°C did not cause significant La diffusion into the SiO₂ layer, whereas some intermixing was observed at 800°C. We use the observed microstructures to estimate equivalent oxide thicknesses. The results demonstrate that oxygen partial pressures and initial SiO₂ thickness need to be carefully controlled to control SiO₂ formation at the Si interface and to achieve target equivalent oxide thickness.