Removal of charging on SiO 2/Si structure during photoelectron spectroscopy measurements by metal overlayer

Abstract

When a silicon dioxide (SiO 2) layer is formed on Si, the energy shift of the Si 2p peak due to SiO 2 with respect to the Si substrate peak is relatively high, but the magnitude of the shift is decreased by the deposition of a ∼3 nm metal overlayer which is connected to the ground. Positive charges resulting from photoemission on the SiO 2 surface induce downward potential gradient toward the SiO 2 surface. This downward potential gradient in SiO 2 increases the energy difference between the SiO 2 Si 2p level at the surface and the substrate Si 2p level at the SiO 2/Si interface. The shift of the SiO 2 Si 2p peak due to charging increases with the thickness whereas the thickness dependence is decreased by the earthed Pd overlayer. Since the density of charges resulting from photoemission on SiO 2 strongly depends on the leakage characteristic, the magnitude of the shift of the SiO 2 Si 2p peak from the substrate Si 2p peak becomes higher with a decrease in the leakage current density. The SiO 2 layer formed with 98 wt% HNO 3 aqueous solutions possesses a lower leakage current density than that fabricated with 40 wt% HNO 3 solutions, resulting in the higher shift of the SiO 2 Si 2p peak. The lower leakage current density results from a higher atomic density of the SiO 2 layer and a lower density of suboxide species.