HYDROGEN AND OXYGEN EVOLUTION WITH TEMPERATURE IN NANOPOROUS SILICON

In this work, a porous layer on an n⁺ emitter by a chemical route was realized. The MEB observation shows a nanoporous shape of the surface. The subsequent contact depositions needs a heat treatment that has an influence on hydrogen and oxygen distributions in the porous layer. After heat treatments, the porous silicon layer is analyzed by secondary ion mass spectroscopy. The concentration profile of light elements like H, O, C, F and N are measured and compared with untreated porous layer. The results show that oxygen is present at high level at ambient temperature and then decreases from 25°C to 775°C. This means that oxygen desorption is observed on the surface. At 800°C the oxygen content increases again showing an oxidation of porous layer surface. For hydrogen, the concentration decreases from the ambient temperature until 750°C was noted. Then the hydrogen is restored at its first concentration. The FTIR spectra correlate this hydrogen distribution. The absorption spectra show the appearance of Si–H_x bonds (with x = 1, 2, 3) at 2089, 2115, and 2140 cm^-1, respectively. Both elements O and H are present deeply in the porous silicon layer as shown by the sputter time.