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）栅绝缘层极薄SiO2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）的实时监测方法，研究了Si（001）表面干氧热氧化的初始阶段。RHEED-AES法使硅热氧化过程中氧化层覆盖率和腐蚀速率的同时测量成为可能。O-KLL俄歇电子强度随时间的变化，区分了Langmuir型氧化、二维氧化岛生长和活性氧化三种氧化模式，并给出了氧化模式随O_2压力和温度变化的相图。在朗缪尔型氧化区，从氧化物中的Si原子的发射建议的半阶RHED斑点强度的时间演化，这是解释的界面应变，由于与氧化相关的体积膨胀。在二维氧化岛生长和活性氧化区，半阶RHEED光斑强度呈现振荡行为，其振荡周期与温度、氧化膜覆盖率和氧化方式无关，但与O_2压力成正比地减小。这表明，刻蚀反应的速率限制不是SiO的脱附，而是O_2的吸附。在此基础上，提出了二维氧化岛生长的表面反应模型，即迁移到表面的SiO脱附前驱体之间的碰撞导致氧化岛的成核和生长，因此表面的刻蚀既源于氧化物的生长，也源于SiO的脱附.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，均应考虑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.