工作参数对容性耦合O₂等离子体中活性物种空间分布的影响

Influence of Operating Conditions on Spatial Distributions of Reactive Species in Capacitively Coupled O₂ Plasma

摘要: 容性耦合氧等离子体(CCP)在光刻胶灰化与表面改性中具有重要应用，其工艺性能高度依赖于活性粒子(如O原子、$O_2^{+}$ 离子等)密度的空间分布特性。本文基于流体力学思想，对容性耦合O₂等离子体放电系统建立二维流体模型，模型的可靠性通过与粒子模拟的结果进行对比得到了验证。本文系统研究了驱动频率(13.56~60 MHz)、施加电压(50~125 V)和工作气压(0.25~1 Torr)对$O_2^{+}$ 离子与O原子密度空间分布的影响机制。研究发现：频率升高能够显著提升O原子和$O_2^{+}$ 离子的密度。值得注意的是，虽然通过$O_2\left(a^1{\Delta }_g\right)$ 生成O原子的反应对O原子总产率的贡献相对较小，但O原子密度的空间分布与$O_2\left(a^1{\Delta }_g\right)$ 一致。电压增大也能有效提高活性粒子的浓度，然而随着气压的增加，O原子和$O_2^{+}$ 离子的密度的变化趋势是相反的。此外，结果表明：O原子密度随着其在材料表面的黏附系数的增加而降低，因此通过合理选择腔壁材料或表面涂层以调控该系数，可以实现对O原子密度的调控。本研究揭示了关键放电参数对O₂等离子体中活性粒子分布的调控规律，为优化实际工艺中的刻蚀速率、均匀性与材料兼容性提供了理论依据。

Abstract: Capacitively coupled oxygen plasma (CCP) is widely used in photoresist ashing and surface modification, and its process performance strongly depends on the spatial distribution characteristics of reactive species, such as O atoms and $O_2^{+}$ ions. A two-dimensional fluid model is developed in this paper for the capacitively coupled O₂ plasma discharge system. The validity of the model is first verified by comparing the results from a particle-in-cell/Monte Carlo collision model. This work systematically investigates the influences of driving frequency (13.56~60 MHz), applied voltage (50~125 V), and operating pressure (0.25~1 Torr) on the spatial distribution of $O_2^{+}$ ion and O atom density. It is found that increasing the frequency can significantly raise the density of O atoms and $O_2^{+}$ ions. Notably, although the contribution of the $O_2\left(a^1{\Delta }_g\right)$ reactions for O atom generation is relatively small, the spatial distribution of O atom density is consistent with that of $O_2\left(a^1{\Delta }_g\right)$ . Increasing the applied voltage can also effectively enhance the concentration of reactive species. However, with the rise of pressure, the density of O atoms and $O_2^{+}$ ions exhibits opposite trends. In addition, the results show that O atom density decreases with the increase of the sticking coefficient on material surface. Thus, tuning this coefficient by reasonably selecting chamber materials or surface coatings can regulate O atom density. This study reveals the effects of key discharge parameters on the distributions of reactive species in capacitively coupled O₂ plasma, providing a theoretical basis for optimizing the etching rate, uniformity, and material compatibility in practical processes.