硅的干/湿氧化：反应力场的开发

分子动力学（MD）是一种重要的数值模拟方法,通过求解所有相互作用，模拟原子的运动方程，实现目标系统时间演化的模拟，从而计算给定模拟时间内组成能量与其他热力学量等材料性质。MD的中心问题是构建足够有效和准确的模型，将量子尺度的相互作用适应到经典方程中。

Fig. 1 Comparison of the bond energies or the penalty energies on the basic test molecules.

在众多的势模型中，反应力场（ReaxFF）势由于其物理现象的再现性和准确性，被广泛应用于材料领域的研究。然而，迄今为止，许多引起人们兴趣的系统都没有在文献中涵盖，即使有也需要基于先前开发的参数集进行进一步的调整，以组成一个可靠的MD模型来解决实际问题。因此，发展ReaxFF参数是很有必要的。

Fig. 2 Results of the c-SiO2 thermal expansion.

来自三星日本公司Junichi Noaki等，开发了Si/O/H反应力场参数集，并将其应用于硅干/湿氧化过程中，以理解Si(100)表面热氧化的基本物理原理。

Fig. 3 Total energies calculated on small c-SiO2 test structures in different phases as a function of the volume per atom.

作者利用SiO₂晶体体积的实验数据作为训练数据，对Si/O参数进行了系统开发，完成了在300-1300K温度范围内的真实热行为。通过对Si/O/H系统相关的参数战略调整，作者进行了湿和干过程的模拟对比。

在所得到的ReaxFF中，研究结果提供了原位蒸汽生成（ISSG）氧化过程中H原子的一些关键特征，包括对逐层氧化性能的影响和氧化速率的提高。通过将获得的ReaxFF结果与其他作者最近开发的参数集获得的结果进行比较，深入理解了H原子在氧化过程中的作用。

Fig. 5 Time evolution of the number of O atoms retained in the system through the thermal oxidation of Si.

该工作提供的ReaxFF参数，为未来各种环境下的制造工艺的研究提供了有用的信息和见解。该文近期发表于npj Computational Materials 9: 161 (2023)。

Editorial Summary

Molecular dynamics (MD) is an important numerical simulation method, which can carry out the time evolution of the target system by solving the equation of motions for all simulated atoms that are interacting with each other, thereby investigate the properties of materials from the coordination of individual atoms in the system at a given simulation time by calculating the constituent energy and other thermodynamic quantities.

The central issue of MD is how to accommodate the quantum-scale interactions into the classical equations and construct a sufficiently effective and accurate model. Among numerous potential models, the reactive force field (ReaxFF) potential is widely used in extensive studies in the field of material because of its reproducibility of physical phenomena with great accuracy. However, so far many systems of interest are simply not covered in the literature, or, if any, further elaborate tuning is required based on previously developed parameter sets to make up a reliable MD model to answer practical questions. Therefore, it is of great importance to develop the ReaxFF parameter sets. 

Junichi Noaki et al. from Samsung Japan Corporation, developed the Si/O/H reactive force field parameter set and applied to silicon dry/wet oxidation process to understand the underlying physics of the thermal oxidation of the Si(100) surface. Employing the experimental volume of the SiO₂ crystal at different temperatures as training data, a realistic thermal behavior was accomplished, finishing the same result over the temperature range of 300–1300 K. With strategic tunings of parameters related to Si/O/H system, the authors carried out the simulation comparing the wet-and dry processes. 

In the demonstration of the resulting ReaxFF, results provided some key characteristics of the H atoms in the ‘in-situ-steam-generation (ISSG)’ oxidation processes, including the effect on the layer-by-layer oxidation property and the oxidation rate enhancement. Via comparing the results with those obtained by using parameter set recently developed by other authors, an insight into the role of H atoms in the oxidation process was acquired. ReaxFF parameters in this work provide useful information and insight into the study of manufacturing processes for various settings in the future. This article was recently published in npj Computational Materials 9: 161 (2023).

原文Abstract及其翻译

Development of the reactive force field and silicon dry/wet oxidation process modeling (开发反应力场模拟硅干/湿氧化过程)

Junichi Noaki, Satoshi Numazawa, Joohyun Jeon & Shuntaro Kochi 

Abstract

We developed the Si/O/H reactive force field parameter set and applied to silicon dry/wet oxidation process to understand the underlying physics of the thermal oxidation of the Si(100) surface. Through a systematic development of the Si/O parameter using the experimental data of the volumes of the SiO₂ crystal as a reference, we reproduced the same result over the temperature range of 300–1300 K. With strategic tunings of parameters related to Si/O/H system, we carried out the simulation comparing the wet-and dry processes. A significant acceleration of the oxide film growth seen in the ‘in-situ-steam-generation (ISSG)’ is successfully represented. These properties of our model imply its applicability in wider scope. We compare our results with those obtained by using parameter set recently developed by other authors. Investigating the configuration of atoms near the interface of the SiO₂ film, our model is found to be able to study the role of hydrogen atoms for the ISSG acceleration.

摘要

我们开发了Si/O/H反应力场参数集，并将其应用于硅干/湿氧化过程中，以理解Si(100)表面热氧化的基本物理原理。利用SiO₂晶体体积的实验数据作为参考，我们对Si/O参数进行了系统开发，在300-1300K温度范围内重现了相同的结果。通过对Si/O/H系统相关的参数战略调整，我们进行了湿和干过程的模拟对比。在“原位蒸汽生成（ISSG）”中所看到的氧化膜增长显著加速被成功展示。我们模型的这些特性暗示了其在更大范围内的适用性。我们将结果与其他作者最近开发的参数集获得的结果进行了比较。通过研究了二氧化硅薄膜界面附近的原子构型，我们发现该模型能够研究氢原子在ISSG加速中的作用。