AFM and AES studies on the electron-beam-irradiation-induced modifications in superficial and buried SiO2 layers

Abstract

The interactions between electrons and SiO 2 are of interest to modern materials characterization and processing technologies. In this work, electron-beam-irradiation-induced modification has been investigated in a superficial oxide (SiO 2 /Si) and a buried oxide in Cu/TaN/SiO 2 /Si using atomic force microscopy (AFM) and Auger electron spectroscopy (AES). In the superficial oxide layer, a hole of 15 nm deep and 2.5 μm wide was observed, after the oxide had been irradiated by a 20 keV 50 nA electron beam rastering over 1.5 x 1.5 μm 2 for 30 min. In the buried layer, however, bumps of 40-90 nm high and ∼10 μm wide were generated after irradiation of a 20 keV 150 nA electron beam rastering over 1.5 x 1.5 μm 2 for 5-40 min. Surrounding the hole and the bumps were halo-like features. In the bumps, small holes were visible. The observations have been explained by proposing a model whereby, upon irradiation by electron beams, both the swelling and the loss occur in the SiO 2 layer. The swelling happened as a result of the generation of voids inside the irradiated volume, whereas the loss was attributed to the desorption of O 2 formed by the oxygen atoms originally dwelling at the surface and those diffused to the surface. It is suggested that the TaN barrier layer, which prevented oxygen diffusion from the oxide, played a prominent role in the swelling of the buried SiO 2 . The damage to SiO 2 was demonstrated further with Auger depth profiling analyses, and the corresponding artefact appearing in the analysis was discussed.