ELECTRON BEAM INDUCED CURRENT / TUNNELING CURRENT MICROSCOPY OF THIN SILICON DIOXIDE FILMS ON SILICON

Abstract

The purpose of this project is to characterize the defects in very thin silicon dioxide films on silicon with the Electron Beam Induced Current/Tunneling Current Microscopy (EBIC/TCM) technique. MOS (Metal-Oxide-Silicon) capacitors were used as test structures for oxide defect characterization. The characteristics of the electron beam induced current were examined first, followed by the investigation of the effects of electron beam irradiation and the SEM's (Scanning Electron Microscope) parameters. Various defects were studied and identified using the EBIC/TCM technique. The EBIC in the silicon oxide film was found to be better described by the columnar model, while the Fowler-Nordheim equation with modified parameters could still be used to describe the beam enhanced tunneling current at high electric field. It was found that thin oxide films under electron beam irradiation had different current-oxide thickness dependency at different electric field. This led to the observation of a reversal of contrast for local oxide thickness variation in the EBIC/TCM micrographs for the first time. The more severe beam irradiation damage was the accumulation of positive charges. Methods used to reduce this effect will be discussed. Surface, oxide and substrate defects were observed in the EBIC/TCM micrographs. Reversal of contrast due to local oxide variation was verified by a special MOS structure. A new method was used to distinguish between substrate and oxide defects. This method, together with other techniques, enabled us to identify and locate most of the defects seen in the EBIC/TCM micrographs.