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 ${\mathrm{La}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}{\mathrm{/SiO}}_{\mathrm{2}}\mathrm{/Si}$ structures. The ${\mathrm{La}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ layers were deposited on thermal ${\mathrm{SiO}}_{\mathrm{2}}$ 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 ${\mathrm{La}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ layer, and the total oxide layer thickness increased by 17%, most likely due to the oxygen diffusion and reaction at the ${\mathrm{Si/SiO}}_{\mathrm{2}}$ interface. EELS, using a 0.2 nm probe, showed that rapid thermal annealing at 600 °C did not cause significant La diffusion into the ${\mathrm{SiO}}_{\mathrm{2}}$ 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 ${\mathrm{SiO}}_{\mathrm{2}}$ thickness need to be carefully controlled to control ${\mathrm{SiO}}_{\mathrm{2}}$ formation at the Si interface and to achieve target equivalent oxide thickness.