Development of room-temperature oxidation method of Si due to pulsed hyperthermal atomic oxygen beam

本课题研究了利用脉冲超热原子氧束在室温下氧化硅片的新方法。一个广泛的-。利用激光诱导的氧气爆轰现象产生的脉冲-高热（5eV）原子氧束，在Si（001）表面形成了氧化薄膜。很清楚地观察到高温。L束即使在室温下也能形成<5 nm的氧化膜。这是可以应用于下一代ulsi的厚度。氧化膜的厚度取决于温度和原子氧通量。还观察到氧化膜的生长服从抛物线规律。利用x射线光电子能谱（XPS）对氧化膜的厚度进行了原位测量，结果表明氧化时间与氧化膜厚度之间存在线性关系。这一结果清楚地表明，生长机制受原子氧扩散的速率限制。结果表明，SiO_2薄膜中原子氧的扩散活化能低至0.15eV。在微波生成氧等离子体的出光区SiO_2膜中原子氧的扩散活化能为0.5eV，热氧化过程中分子氧的扩散活化能为1.2eV。氧原子在SiO_2膜中扩散的低活化能可能包括在Si/SiO_2界面处产生的高压应力导致间隙Si原子的逆扩散。为了降低如此高的界面应力，使用氧和少量氟的预混气是有效的。

This project dealt with the new method for room-temperature oxidation of Si wafers "using pulsed-hyperthermual atomic oxygen beam. A broad-. pulsed-, hyperthemial (5eV) atomic oxygen beam, generated by the laser-induced detonation phenomenon of oxygen gas, was applied to formation of thin oxide films on the Si (001) surface. It was clearly observed that the hypertherma.l beam can form thin oxide film (<5 nm) even at the room temperature. This is the thickness can be applied for the next generation ULSIs. The thickness of the oxide film depends on the temperatute and the atomic oxygen flux. It was also observed that the growth of oxide film obeyed the parabolic law. This was confirmed by the in-situ thickness measurement of the oxide film using X-ray photoelectron spectroscopy (XPS) which indicated the linear relationship between oxidation time versus thickness_2. This result clearly showed that the growth mechanism was rate-limited by the diffusion of atomic oxygen. It is, however, measured that the activation energy of diffusion of atomic oxygen in the SiO_2 film was as low as 0.15eV.The activation energy of diffusion of atomic oxygen in the SiO_2 film measure in the out-of-glow region of microwave- generated oxygen plasma was reported to be 0.5eV, and that of molecular oxygen in the thermal oxidation was 1.2eV.The low activation energy on diffusion of atomic oxygen in the SiO_2 film may include the inverse diffusion of interstitial Si atoms which is generated high compressive stresses applied at the Si/SiO_2 interface. In order to reduce such high interfacial stresses, it would be effective to use the premix gas of oxygen with small amount of fluorine.