AUGER SI-LVV, O-KLL AND N-KLL LINESHAPES AT AIR-EXPOSED SILICON-NITRIDE SURFACES - PATTERN-RECOGNITION ANALYSIS

Auger electron spectroscopy measurements have been performed on silicon nitride layers exposed to air. The layers were deposited on Si(100) wafers kept at 300 degrees C or 600 degrees C by excimer laser ablation of a silicon target under various ammonia pressures. The Si LVV, O KLL and N KLL lineshapes of silicon nitride layers and of in situ prepared clean surfaces of standards are compared by applying pattern recognition (PR) methods to obtain bonding information of elements within the analysed volume. The PR results based on Auger Si LVV, O KLL and N KLL spectra compare very well. They are also in agreement with the results of XPS. The chemical states of silicon atoms in all silicon nitride layers depend strongly on the deposition conditions used. For low ammonia pressures, surface regions of silicon nitride layers show a twofold coordination with oxygen to silicon atoms (SiO2), whereas for higher ammonia pressures there is a four fold coordination of silicon to nitrogen atoms (Si3N4). The results are interpreted as follows. The silicon-rich silicon nitride layers are formed at the lower ammonia pressure where the silicon oxide dominates over silicon nitride in the surface region, whereas for the higher ammonia pressure silicon nitride is prevalent. A new approach of the PR method, so-called 'cluster analysis', shows a close similarity in the chemical states of nitrogen atoms in the nitride layer formed at higher pressure and silicon nitride standard, indicating a threefold coordination of nitrogen to silicon atoms. Subtle differences revealed in the spectral shapes elucidate the strongly correlated behavior of the N KLL lineshapes with the deposition conditions used.