Oxygen self-diffusion in silicon dioxide:: Effect of the Si/SiO2 interface

The effect of the SiO2/Si interface on oxygen self-diffusion in SiO2 during thermal oxidation was investigated using oxygen isotopes. A (SiO2)-O-18 layer was first grown in O-18(2) and then the sample was reoxidized in O-16(2) at 900 similar to 1100 degrees C. The O diffusion in SiO2 during the O-16(2) oxidation was investigated by secondary ion mass spectrometry (SIMS) measurements. Near the SiO2/Si interface, a significant broadening of the O-18 profile toward the newly grown (SiO2)-O-16 was observed. This O-18 diffusion became slower with oxidation time and hence with increasing distance between O-18 diffusion region and the interface. This distance-dependent O-18 self-diffusion was simulated taking into account the effect of SiO generated at the interface upon oxidation and diffusing into SiO2 to enhance O self-diffusion. The simulation fits the SIMS profiles and shows that the SiO diffusion is greatly retarded by the oxidation with O-2 from the oxygen-containing atmosphere and that the O self-diffusion therefore becomes distance-dependent. In addition, near the SiO2 surface, O-16 diffusion profiles develop with the O-16(2) oxidation time from the surface into the initially grown (SiO2)-O-18. The integrated surface O-16 concentration increases with oxidation time and the SiO from the interface affects the O self-diffusion near the surface as well.