A STUDY ON REACTION CONTROL BETWEEN SILICON SURFACES AND OXYGEN-FREE WATER/WATER-FREE OXYGEN IN COMPLETELY CLOSED SYSTEMS

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A combination method of heating-up process with cooling-down in thermal desorption spectroscopy has been proposed in order to reveal the chemical reaction of hydrogen-terminated Si surfaces with water at elevated temperatures. It has been found for the first time that an HF-cleaned Si (100) surface reacts with water at approximate 400℃ or higher. HF-cleaned Si (100) surfaces have been analyzed with a thermal desorption spectroscopy system under introducing oxygen gas into the analytical chamber so as to characterize chemical reactions of Si surfaces with oxygen. It has been demonstrated that the HF-cleaned Si (100) surface reacts with oxygen or water after the hydrogen desorption at approximate 510℃ under introducing oxygen gas. The thermal oxidation of HF-cleaned Si (100) surfaces in the heating-up has been characterized with an oxidation system. It has been demonstrated that the oxide film thickness grown during the heating-up in oxygen gas at an atmospheric pressure to 900℃ begins to increase beyond approximate 550℃. Metal-oxide-semiconductor (MOS) diode characteristics have shown that leak current densities through silicon dioxide films with thinner preoxide grown during the heating-up to thermal oxidation at 900℃ are lower than that with thicker preoxide for the film with the total thickness of approximate 3 nm. The preoxide with the thickness of 0.3-0.4 nm, which corresponds to one molecular layer of oxide, has been grown during the heating-up to 900℃ at the rate of 50 deg/sec in 0.3% oxygen gas diluted with nitrogen. It has been demonstrated for the first time that the electrical insulating performance and reliability of ultrathin silicon dioxide films depends on the ultrapure water cleaning time of silicon wafers before MOS diode fabrication because of atomic structure change of silicon surface by ultrapure water cleaning.