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

为了揭示端氢硅表面与水在高温下的化学反应，提出了热解吸光谱中加热与冷却相结合的方法。首次发现hf清洗的Si（100）表面与水在约400℃或更高的温度下发生反应。在分析室内引入氧气的情况下，用热解吸光谱系统对hf清洗过的Si（100）表面进行了分析，以表征Si表面与氧气的化学反应。结果表明，在引入氧气的条件下，在510℃左右的温度下，经hf清洗后的Si（100）表面与氧或水发生反应。用氧化系统表征了高频清洗硅（100）表面在加热过程中的热氧化。结果表明，在大气压900℃的氧气中升温过程中，氧化膜厚度在约550℃以上开始增大。金属氧化物半导体（MOS）二极管的特性表明，对于总厚度约为3 nm的二氧化硅薄膜，在900℃加热至热氧化过程中生长的预氧化物较薄的二氧化硅薄膜，其漏电流密度低于预氧化物较厚的二氧化硅薄膜。在0.3%的氧气和氮气中，以50℃/秒的速度加热到900℃，生长出厚度为0.3 ~ 0.4 nm的预氧化物，相当于1个分子层的氧化物。首次证明了超薄二氧化硅薄膜的电绝缘性能和可靠性取决于超纯水清洗硅片的时间，因为超纯水清洗会改变硅表面的原子结构。

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.