Microvoids and defect chemistry at the SiSiO₂ interface studied by positron annihilation depth profiling

A low energy positron beam (few keV) has been used to study device quality dry thermal SiO2 layers (∼ 50 nm thick) on Si(100). By tuning the beam energy over the range 0-10 keV to vary implantation depth, and by accounting for positron diffusion as well as annihilation in SiO2 and Si, depth profiles of material properties are obtained which sense material, defect, and electric field properties. The unusual observation of ortho-positronium 3γ-decay at the interface demonstrates that microvoids > 1 nm in size are present in these oxides, apparently an intrinsic consequence of the thermal oxidation process. The microvoid signal increases with annealing, possibly due to initiation of the interfacial oxide decomposition reaction. Reversible hydrogen uptake and desorption are also observed, illustrating the interface sensitivity of positron studies. © 1990.