In-situ observation of thermal oxidation on the Si surface by RHEED-AES CL

为了阐明金属-氧化物-半导体场效应晶体管（MOSFET）栅绝缘体极薄SiO_2层的生长模型，采用俄歇电子能谱结合反射高能电子衍射（RHEED-AES）实时监测方法研究了干燥O_2在Si（001）表面热氧化的初始阶段。RHEED-AES方法可以同时测量硅热氧化过程中的氧化物覆盖率和蚀刻速率。O - KLL俄热电子强度随时间的演化明确区分了langmuir型氧化、二维氧化岛生长和活性氧化三种氧化方案，并给出了氧化方案随o2压力和温度变化的相图。在langmuir型氧化区，半阶RHED点强度的时间演化表明氧化物中有Si原子发射，这可以用氧化引起的体积膨胀引起的界面应变来解释。在二维氧化岛生长和活性氧化区，半阶RHEED光斑强度表现出振荡行为，振荡周期与温度、氧化物覆盖和氧化方案无关，但与O_2压力成比例减小。这意味着蚀刻反应不受SiO脱附的速率限制，而是受O_2吸附的速率限制。基于实验结果，提出了二维氧化岛生长的表面反应模型，其中SiO在表面迁移的解吸前驱体之间的碰撞导致氧化岛成核和生长，因此表面的蚀刻源于氧化物的生长和SiO的解吸。结果表明，在Si热氧化初期出现的所有氧化方案的表面反应模型中，都应考虑Si原子的发射和表面迁移。

The initial stage of thermal oxidation on the Si(001) surface with dry O_2 was investigated by a realtime monitoring method of Auger electron spectroscopy combined with reflection high energy electron diffraction (RHEED-AES) in order to clarify the growth model of very thin SiO_2 layers for the gate insulator of metal-oxide-semiconductor field effect transistor (MOSFET). The RHEED-AES method made it possible to measure simultaneously the oxide coverage and etching rate during Si thermal oxidation. The time evolution of O KLL Auger electron intensity discriminated clearly three oxidation schemes of Langmuir-type oxidation, two-dimensional oxide island growth and active oxidation, and gave a phase diagram of the oxidation scheme as a function of O_2 pressure and temperature. In the Langmuir-type oxidation region, emission of Si atoms from oxides was suggested by the time evolution of half-order RHED spot intensities, which was interpreted in terms of the interfacial strain due to volume expansion associated with oxidation. In the two-dimensional oxide island growth and active oxidation region, the half-order RHEED spot intensities showed a oscillatory behavior, the oscillation period of which was independent of temperature, oxide coverage and oxidation scheme, but decreased in proportion to O_2 pressure. This means that the etching reaction is not rate-limited by SiO desorption but by O_2 adsorption. Based on the experimental results, a surface reaction model of two-dimensional oxide island growth was proposed, in which collisions between desorption precursors of SiO migrating on the surface lead to nucleation and growth of oxide islands and therefore etching of the surface originates from oxide growth as well as SiO desorption. As a result, it was concluded that the emission and surface migration of Si atoms should be considered in the surface reaction model of all oxidation schemes appearing at the initial Si thermal oxidation.