Effect of MeV electron irradiation on Si-SiO2 structures

Abstract

The effect of 20-MeV electron-beam irradiation on Si-SiO2 structures was studied. The Si-SiO2 samples were fabricated on n-type <100>-oriented Si wafers with resistivity of 4.7 Ω cm. Following a standard cleaning procedures, thermal oxidation in dry O2 + 8 % HCl ambient was performed at 900 °C to produce oxide layer with a thickness of 20-nm. After oxidation, the samples were cooled at a rate of 1o C s−1 in the ambient where the oxidation was carried out. The samples were exposed to a beam of 20-MeV electrons with a flux of about 1.2×1015 cm−2. The oxide thickness was measured by ellipsometry before and after electron irradiation, which showed that the SiO2 thickness in the irradiated Si-SiO2 structures increases. This result can be connected with the increase of the oxygen content at the Si-SiO2 interface. If one takes into account the defect generation in the whole Si-SiO2 structure, it is reasonable to expect that the oxygen motion through the SiO2 oxide defects will be stimulated during MeV electron irradiation. The changes on the SiO2 surface roughness induced by the high-energy electron irradiation of the Si-SiO2 structures were observed by atomic force microscopy (AFM). It was seen that these changes consisted in the formation of nanocrystals at the SiO2 surface. We assume that the MeV electron irradiation breaks the Si-O bonds, the free oxygen moves through the radiation defects and creates conditions whereby Si nanostructures are generated in the oxide SiO2 and at the SiO2 surface of the structures.