An x-ray photoelectron spectroscopy study of the thermal nitridation of SiO2/Si

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Abstract
X‐ray photoelectron spectroscopy (XPS) has been used to study the dependence of the nitrogen distribution in thermally nitrided SiO2 films on the nitridation time and temperature. Intensity analysis of the XPS data, of which a detailed derivation is presented, in conjunction with chemical depth profiling, has been used to determine the compositional variation with depth in the nitrided film. The experimental results show that, for a nitridation temperature of 1000 °C, the maximum nitrogen concentration in the interfacial region occurs at the interface in the initial stages of nitridation (within 10 min), while at later times (30 min and longer) the maximum occurs 20–25 Å away from the interface. For a nitridation temperature of 1150 °C, the maximum interfacial nitrogen concentration occurs 20 Å from the interface for nitridation times as short as 5 min, but saturates at a lower value than that observed at 1000 °C. For a nitridation temperature of 800 °C, the maximum interfacial nitrogen concentration remains at the interface for nitridation times up to 4 h. These data can be understood within a previously developed kinetic model which explicitly considers the effect of interfacial strain on the nitridation kinetics. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen concentration. It is postulated that the fluorine bonds preferentially to defects, and it is shown that this postulate and the measured fluorine intensities are consistent with a strain‐dependent energy of formation of defects, proposed recently to explain electrical results.

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