Thermal Behavior of Porous Silicon

Thermal behavior of porous silicon formed by anodic reaction in 50 wt% hydrofluoric acid has been investigated. It was found that the porous silicon films (PSF) step height before and after heat treatment was a strong function of the apparent PSF density, atmosphere, temperature, and time. Particularly, the heat treatment in wet oxygen resulted in a change from PSF virtual volume increase to decrease with increasing oxidation time when the apparent PSF density is very small. In dry oxygen, PSF always caused a virtual volume increase. Three exothermic peaks, which were apparently caused by the oxidation reaction, were observed at approximately 300°C, 630°C, and 800°C. Si-Si bond in as-grown PSF was very unstable and the bond changed easily into Si-O bond as the oxidation temperature increased. Diffraction peaks, apparently caused by the formation of β-cristoballite, were observed at 1100°C in dry oxygen.