A microstrip-line microwave interferometer for monitoring of plasma density of processing plasmas

C. Hsieh, Y.W. Liang, C. Lin, K. Leou
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引用次数: 2

Abstract

Summary form only given. We developed a planar transmission-line microwave interferometer for monitoring of electron density for applications in process real-time feedback control of plasma based semiconductor fabrication tools, such plasma etchers or PECVDs. The principle of this technique is the same as the conventional microwave interferometers except that the sensing microwave propagates along a transmission line structure. In this study, the sensor was a microstrip transmission-line where microwave propagates at a phase velocity determined by the structure and the electron density of the surrounding plasma. Thus the variation of plasma density can be estimated from the phase shift of the transmitted microwave from one to the other end of the transmission-line. Compared to the conventional microwave interferometers where line-averaged plasma density is measured, the transmission-line type microwave sensor will be less susceptive to the interference caused by multi-passes reflection/refraction effect resulting from nonuniformity of the plasma density profiles. Therefore, it provides a measurement of higher sensitivity and wider dynamic range. In this work, an U-shaped transmission line with 3 mm in width and 86 mm in length, the quartz based substrate thickness is 3.5 mm, and the distance between input and output ports is 23 mm. The dispersion characteristics of this microstrip line immersed in a plasma of different electron densities was simulated by using a commercial tool, High Frequency Structure Simulation code (Ansoft HFSS), a full- wave electromagnetic simulator using the finite element method. The simulation results show that the phase shift increases gradually with the plasma electron density with a sensitivity 12 degree / 1010 cm"3. Experimental demonstration has been performed with an inductively coupled plasma. The sensor was mounted on the inner wall of plasma chamber. Measurement results show that the dependence of electron density of plasma source RF power predicted by the sensor agrees with the Hairpin probe measurements.
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用于监测加工等离子体等离子体密度的微带线微波干涉仪
只提供摘要形式。我们开发了一种平面传输在线微波干涉仪,用于监测电子密度,用于等离子体半导体制造工具(如等离子体蚀刻器或pecvd)的过程实时反馈控制。该技术的原理与传统的微波干涉仪相同,只是感测微波沿传输线结构传播。在本研究中,传感器是微带在线传输线,微波以由周围等离子体的结构和电子密度决定的相速度传播。因此,等离子体密度的变化可以通过发射微波从传输线上一端到另一端的相移来估计。与测量等离子体密度线平均的传统微波干涉仪相比,传输在线型微波干涉仪不易受等离子体密度分布不均匀性引起的多道反射/折射效应的干扰。因此,它提供了更高的灵敏度和更宽的动态范围的测量。本作品采用宽3mm,长86mm的u型传输线,石英基衬底厚度为3.5 mm,输入输出端口之间的距离为23mm。利用商用全波电磁仿真软件Ansoft HFSS对微带线在不同电子密度等离子体中的色散特性进行了有限元模拟。仿真结果表明,随着等离子体电子密度的增大,相移逐渐增大,灵敏度为12度/ 1010 cm”3。用电感耦合等离子体进行了实验验证。传感器安装在等离子腔内壁上。测量结果表明,传感器预测的等离子体源射频功率的电子密度依赖关系与发夹探针的测量结果吻合。
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