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低温感应耦合射频等离子体作为半导体制造中的关键等离子体源, 其中性气体温度通过调控化学反应动力学、活性自由基分布以及等离子体-表面相互作用, 对高质量芯片制造工艺具有重要影响. 本文通过光谱法、布拉格光栅和光纤传感测温等3种测温手段, 系统研究了氮气以及氮氩混合等离子体在不同射频功率、气体压力和气体组分条件下的中性气体温度(Tg)的变化规律. 另外, 还结合Langmuir探针测量的电子密度、电子温度、电子能量概率函数以及整体模型模拟, 分析了中性气体加热的物理机制. 结果表明, 当射频功率增大时, 耦合到等离子体的能量增大, 电离反应增强, 电子-中性粒子之间的碰撞过程和能量传递增大, 使Tg呈单调递增趋势. 而当气压升高初期, 电子密度和背景气体密度增大共同提升了加热效率, Tg快速上升, 但在气压超过3 Pa后, 电子平均自由程缩短, 电子密度下降, 而背景气体密度持续增大, 因而导致Tg 增大变缓. 在氮/氩混合体系放电中, 氩气比例增大显著提高了Tg的上升速率, 这是由于随着氩气比例增大, 高能电子比例和电子密度上升, 增强了电离和中性气体加热, 同时氩亚稳态原子通过 Penning过程提高了氮激发态粒子密度, 并促使氮分子向高能级激发, 进一步加热气体. 此外, 研究发现纯氮等离子体的径向温度分布在轴向高度增大时呈现由抛物线形向马鞍形的转变, 这是因为离线圈越近, 受到电磁场的影响电子碰撞激发反应越强. 研究还发现了径向边缘处的Tg随气压的升高几乎不发生变化, 这是由于当气压不断升高时, 线圈下方的电子很难运动到径向边缘处与中性粒子发生碰撞, 从而限制了边缘中性粒子的加热.Low-temperature inductively coupled radio-frequency plasma is a key plasma source in semiconductor fabrication, where the neutral gas temperature (Tg) is one of the critical parameters influencing chemical reactions and plasma characteristics. Precise control of Tg significantly influences processes such as thin-film deposition and reactive ion etching, with its synergistic interaction with plasma parameters (ne, Te) often determining process outcomes. Consequently, a thorough understanding of the evolution of Tg and its correlation with discharge parameters has become a critical issue for optimizing semiconductor manufacturing processes. To achieve more accurate measurements of neutral gas temperature, this work employs three temperature measurement techniques: spectroscopy, Bragg grating, and fiber optic sensing. These methods are used to systematically investigate the variation patterns of neutral gas temperature (Tg) in nitrogen plasma and nitrogen-argon mixed plasma under different radio-frequency power, gas pressure, and gas composition conditions. To elucidate the gas heating mechanism, this work combines Langmuir probe measurements of electron density, electron temperature, electron energy probability distribution with a global model simulation. The results show that as the RF power increases, the energy coupled to the plasma increases, the ionization reaction is enhanced, and the collision process and energy transfer between electrons and neutral particles increase, resulting in a monotonically increasing trend of Tg. When gas pressure initially increases, both electron density and background gas density rise together, enhancing heating efficiency and driving rapid Tg growth. However, beyond 3 Pa, electron mean free path shortens and electron density declines. In contrast, background gas density continues to increase, leading to slower Tg growth. In nitrogen/argon mixed system discharges, increasing the argon proportion significantly enhances the rate of Tg increase. This occurs because a higher argon ratio elevates the proportion of high-energy electrons and electron density, thereby strengthening ionization and neutral gas heating. At the same time, argon metastable atoms enhance the density of excited nitrogen particles through the Penning process, which promotes nitrogen molecular excitation to higher energy levels and further heats the gas. Additionally, we observe that the radial temperature distribution in pure nitrogen plasma shifts from parabolic to saddle-type with axial height increasing, due to intensified electron collision excitation near the coil under electromagnetic field effects. In this study, it is also found that the glass transition temperature at the radial edge remains virtually unchanged as atmospheric pressure increases. This is because, as pressure continues to rise, electrons beneath the coil struggle to migrate to the radial edge to collide with neutral particles, thereby limiting the heating of edge neutral particles.
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Keywords:
- neutral gas temperature /
- inductively coupled plasma /
- fiber optic sensing temperature measurement /
- radial distribution
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图 1 ICP中性气体温度多手段测量实验装置
Fig. 1. ICP neutral gas temperature multi-method measurement experimental apparatus.
图 2 气压为 1 Pa, 气体流量为50 mL/min (标准状况)时, 腔室中心处氮气中性气体温度随功率的变化 (a)光纤测温、布拉格光栅、发射光谱测量方法对比; (b)模拟结果
Fig. 2. Temperature of nitrogen neutral gas at the center of the chamber as a function of power at a pressure of 1 Pa and gas flow rate of 50 mL/min (standard condition): (a) Comparison of three measurement methods of fiber optic temperature measurement, Bragg grating, and emission spectroscopy; (b) simulation results.
图 3 气压为1 Pa, 气体流量为50 mL/min (标准状况)时, 腔室中心处氮气电子密度和电子温度随功率的变化 (a), (c) 探针测量结果; (b), (d) 模拟结果
Fig. 3. Nitrogen electron density and electron temperature at the center of the chamber as a function of power at a pressure of 1 Pa and gas flow rate of 50 mL/min (standard condition): (a), (c) Probe measurement results; (b), (d) simulation results.
图 4 气压为 1 Pa, 气体流量为50 mL/min (标准状况) 时, 纯氮气放电的EEPF随功率的变化
Fig. 4. EEPF of pure nitrogen discharge as a function of power at a pressure of 1 Pa and gas flow rate of 50 mL/min (standard condition).
图 5 功率为600 W, 气体流量为50 mL/min (标准状况)时, 腔室中心处氮气中性气体温度随气压的变化 (a) 光纤测温、布拉格光栅、发射光谱测量方法对比; (b) 电子密度; (c) 电子温度; (d) EEPF
Fig. 5. Temperature of nitrogen neutral gas at the center of the chamber as a function of pressure at a power of 600 W and gas flow rate of 50 mL/min (standard condition): (a) Comparison of measurement methods of fiber optic temperature measurement, Bragg grating, and emission spectroscopy; (b) electron density; (c) electron temperature; (d) EEPF.
图 6 功率为300 W, 气压为1 Pa, 气体流量为70 mL/min (标准状况)时, 腔室中心处氮气中性气体温度随氩含量的变化 (a) 光纤测温、布拉格光栅、发射光谱测量方法对比; (b) 电子密度; (c) 电子温度; (d) EEPF
Fig. 6. Temperature of nitrogen neutral gas at the center of the chamber as a function of argon content at a power of 300 W, a pressure of 1 Pa, and gas flow rate of 70 mL/min (standard condition): (a) Comparison of measurement methods of fiber optic temperature measurement, Bragg grating, and emission spectroscopy; (b) electron density; (c) electron temperature; (d) EEPF.
图 7 固定气压为1 Pa、气体流量为50 mL/min (标准状况)时, 纯氮气放电中在不同高度不同功率下的Tg径向分布特征 (a) 30 mm; (b) 50 mm; (c) 70 mm; (d) 不同轴向高度、不同功率条件下的温度极差趋势图
Fig. 7. Under fixed gas pressure of 1 Pa and gas flow rate of 50 mL/min (standard condition) the radial distribution characteristics of Tg during pure nitrogen discharge at different power levels at different height: (a) 30 mm; (b) 50 mm; (c) 70 mm; (d) temperature gradient trend diagram under varying axial heights and power conditions.
图 8 固定功率为 300 W、气体流量为50 mL/min(标准状况)时, 纯氮气放电中在不同高度不同气压下的 Tg径向分布特征 (a) 30 mm; (b) 50 mm; (c) 70 mm; (d) 不同轴向高度、不同功率条件下的温度极差趋势图
Fig. 8. At a fixed power of 300 W and gas flow rate of 50 mL/min (standard condition), the radial distribution characteristics of Tg under different gas pressures during pure nitrogen discharge at different height: (a) 30 mm; (b) 50 mm; (c) 70 mm; (d) temperature gradient trend diagram under varying axial heights and power conditions.
表 1 模型中考虑的氮相关反应及系数
Table 1. Nitrogen-related reactions and coefficients considered in the model.
编号 反应表达式 反应系数/(cm3·s–1) 文献 1 $ \text{e}+{\text{N}}_{2}\rightarrow \text{N}_{2}^{+}+2\text{e} $ $ 7.76\times {10}^{-9}T_{\text{e}}^{0.79}\text{exp}(-16.75/{T}_{\text{e}}) $ [43] 2 $ \text{e}+\text{N}\rightarrow {\text{N}}^{+}+2\text{e} $ $ 3.87\times {10}^{-9}T_{\text{e}}^{0.86}\text{exp}(-14.62/{T}_{\text{e}}) $ [43] 3 $ \text{e}+{\text{N}}_{2}\rightarrow {\text{N}}^{+}+\text{N}+2\text{e} $ $ 2.90\times {10}^{-9}T_{\text{e}}^{0.72}\text{exp}(-29.71\text{/}{T}_{\text{e}}) $ [44] 4 $ \text{e}+{\text{N}}_{2}\rightarrow \text{N}+\text{N}+\text{e} $ $ 2.15\times {10}^{-8}\text{exp}(-14.39/{T}_{\text{e}}) $ [43] 5 $ \text{e}+{\text{N}}_{2}\rightarrow {\text{N}}_{2}\left(\text{A}\right)+\text{e} $ $ 8.06\times {10}^{-10}T_{\text{e}}^{-0.306}\text{exp}(-8.87/{T}_{\text{e}}) $ [43] 6 $ \text{e}+{\text{N}}_{2}\rightarrow {\text{N}}_{2}\left(\text{B}\right)+\text{e} $ $ 1.56\times {10}^{-8}T_{\text{e}}^{-0.52}\text{exp}(-9.16/{T}_{\text{e}}) $ [43] 7 $ \text{e}+{\text{N}}_{2}\rightarrow {\text{N}}_{2}\left({a}^{\prime} \right)+\text{e} $ $ 6.6\times {10}^{-9}T_{\text{e}}^{-0.66}\text{exp}(-11.05/{T}_{\text{e}}) $ [43] 8 $ \text{e}+\text{N}_{2}^{+}\rightarrow \text{N}+\text{N} $ $ 4.8\times {10}^{-7}\left(0.026/{T}_{\text{e}}\right) $ [45] 9 $ {\text{N}}_{2}\left(\text{A}\right)+{\text{N}}_{2}\left({a}^{\prime} \right)\rightarrow \text{N}_{2}^{+}+{\text{N}}_{2}+\text{e} $ $ 3.2\times {10}^{-12} $ [46] 10 $ {\text{N}}_{2}\left({a}^{\prime} \right)+{\text{N}}_{2}\left({a}^{\prime} \right)\rightarrow \text{N}_{2}^{+}+{\text{N}}_{2}+\text{e} $ $ 5.0\times {10}^{-11} $ [47] 11 $ {\text{N}}_{2}\left(\text{A}\right)+\text{N}\rightarrow {\text{N}}_{2}+\text{N} $ $ 2.0\times {10}^{-12} $ [44] 12 $ {\text{N}}_{2}\left(\text{A}\right)+{\text{N}}_{2}\rightarrow {\text{N}}_{2}+{\text{N}}_{2} $ $ 3.0\times {10}^{-18} $ [48] 13 $ {\text{N}}_{2}\left(\text{A}\right)+{\text{N}}_{2}\left(\text{A}\right)\rightarrow {\text{N}}_{2}\left(\text{B}\right)+{\text{N}}_{2} $ $ 7.7\times {10}^{-11} $ [47] 14 $ {\text{N}}_{2}\left(\text{B}\right)+{\text{N}}_{2}\rightarrow {\text{N}}_{2}+{\text{N}}_{2} $ $ 1.5\times {10}^{-12} $ [47] 15 $ {\text{N}}_{2}\left({a}^{\prime} \right)+{\text{N}}_{2}\rightarrow {\text{N}}_{2}\left(\text{B}\right)+{\text{N}}_{2} $ $ 1.9\times {10}^{-13} $ [49] 16 $ \text{N}+\text{N}+\text{N}\rightarrow {\text{N}}_{2}+\text{N} $ $ 1.0\times {10}^{-32} $(cm6·s–1) [50] 17 $ {\text{N}}_{2}\left(\text{B}\right)\rightarrow {\text{N}}_{2}\left(\text{A}\right)+\text{hν} $ $ 2.0\times {10}^{-5} $ [51] 注: 其中电子温度用电子伏(eV)为单位 
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