Thermal Nitridation of Si(111) Surfaces with N2 Molecules Studied by X-Ray Photoelectron Spectroscopy

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Abstract
The initial stage of thermal nitridation of Si (111) surfaces using N2 gas has been studied by X-ray photoelectron spectroscopy. It was found, for the first time, that under N2 pressure of 1.3×10-3 Pa the nitridation rate increases with temperature from 600 to 700° C, reaches a constant value and then falls off abruptly at the critical temperature (∼880° C). Since the critical temperature coincides with that of the transformation of Si (111) from 7×7 to 1×1, we ascribe the abrupt change to significant differences in reactivity with nitrogen between 7×7 and 1×1 surfaces. This interpretation is supported by a smoother temperature dependence of nitridation on (100) 2×1 surfaces.