Room temperature oxidation enhancement of porous Si(001) using ultraviolet-ozone exposure

The interaction of porous silicon (001) with ozone and ultraviolet (uv) was investigated at room temperature and ambient pressure. The O/Si atomic ratio in oxidized samples, as measured by Auger depth profiling, was similar to those measured from thermally oxidized samples. For long exposure times (>15 min), the O/Si ratio stayed constant throughout the porous layer, indicating full oxidation of the porous structure. Additionally, the carbon concentration decreased significantly in the uv-ozone oxidized layers as compared to the untreated porous layers. Oxide layers up to 400 nm were measured. Fourier transform ir absorption measurements show both an increase in the oxygen concentration and a decrease in hydrogen concentration after oxidation. Photoluminescence data show that this method of oxidation quenches light emission from the porous layer. We believe that uv induced excitation of valence electrons results in higher reactivity and diffusion of oxygen and ozone as well as bond softening. The large volume of voids in the porous structure assist penetration of ozone and atomic oxygen throughout the porous structure while the narrow lateral dimensions of the Si skeleton requires a short diffusion length for full oxidation.