溝槽天線耦合式表面波電漿放電數值模擬研究

Numerical Simulation Study of Slot Antenna Coupled Surface Wave Plasma Discharges

賴柏廷(Po-Ting Lai)

指導教授 ： 柳克強

國立清華大學/原子科學院/工程與系統科學系/碩士(2020年)

摘要

表面波電漿(surface wave plasma)具有大面積、高密度、高均勻度等優點，在半導體工業朝向大面積晶圓製程、極短製程時間、奈米等級關鍵尺寸方向發展的現在，表面波電漿為理想的製程電漿來源。控制表面波電漿源效能之關鍵主要為微波耦合結構，根據過去的研究，耦合結構有許多不同的設計，包含波導管開槽天線、環形溝槽天線、Radial Line溝槽天線(Radial Line Slot Antenna)等結構，其具有不同的表面波電漿特徵。本研究主旨為建立表面波電漿源之數值模擬模型，模型包含電漿理論、電磁波理論以及流場與熱傳理論，透過探討表面波電漿的操作條件與電漿隨參數之變化，掌握表面波電漿的基本特性，並且依據所建立之基本表面波電漿數值模擬模型設計出具有大面積、高密度、高均勻度的表面波電漿源。
模擬結果顯示，微波由溝槽天線耦合進介電質窗，在介電質窗表面形成駐波之表面波結構，並成功點起電漿，在微波功率為1 kW，氬氣氣壓為30 mTorr時，電子密度約為1018 m-3，電漿主要區域電子溫度約為1-3 eV；頂部表面波電漿源(TP-SWP)之表面波集中在介電質窗表面中心，電子加熱集中於該處，因此造成電漿分布不均勻；側壁表面波電漿源(SW-SWP)之表面波均勻分布於介電質窗表面，電子在此表面均勻加熱，因此具有較均勻之電漿分布。
進一步探討SW-SWP氬氣電漿與氫氣電漿之分子效應，模擬結果表示在相同操作條件下氫氣電漿電子密度會小於氬氣電漿，而將氫氣電漿電子密度提升則可以獲得與氬氣電漿在SW-SWP中類似的電漿特性。研究中調整腔體高度進一步提升電漿均勻度，並探討操作參數電於電漿特性的效應，模擬結果表示電子密度達到1017 1/m3，電漿均勻度50%落在半徑170 mm以內，最後則是提出SW-SWP電漿腔體外部的微波耦合結構，實際做出整體為軸對稱之幾何模型。

關鍵字

電漿 ； 數值模擬 ； 微波電漿 ； 表面波

並列摘要

Surface wave plasma has the benefits of large plasma area, high plasma density, and high plasma uniformity, and therefore it is an ideal plasma source of semiconductor industry pursuing large area wafer process, extremely rapid process period, and nanometer critical dimension. The key point of performance of surface wave plasma source is the microwave coupling structure. According the previous studies, there are several designs of coupling structures, including slot antenna at the bottom of waveguides, annular slot antenna, and radial line slot antenna (RLSA). Each coupling structures has distinct surface wave plasma characteristics. The objective of this work is building a numerical simulation model of surface wave plasma, model including the plasma theory, electromagnetic wave theory, as well as gas flow and heating transfer theory. Realizing the features of surface wave plasma by analyzing the simulation. Next, design a surface wave plasma source requiring large plasma area, high plasma density, and high plasma uniformity.
The simulation results showed that microwave coupling into the dielectric window, forming the surface wave structure in the standing wave form, and the plasma ignited successfully. As microwave power is 1 kW, Ar gas pressure is 30 mTorr, the electron density is about 1018 m-3, electron temperature in the bulk plasma is around 1-3 eV. For the top wall surface wave plasma (TP-SWP), surface wave concentrated at the center of the quartz plate surface, where is the main electron heating region, resulting the low uniformity of plasma; for the side wall surface wave plasma (SW-SWP), surface wave evenly distributed at the quartz surface, in where electron heating smoothly, so the plasma is more uniform.
The comparison between the molecular effect of argon plasma and hydrogen plasma shows that in the same operation conditions, the electron density of hydrogen plasma is lower than argon plasma. Once increasing the electron density, hydrogen plasma will show the same plasma characteristics as argon plasma. In the study, the chamber height is modified to increase the plasma uniformity, and the effects of operation conditions are discussed. The simulation results show that the electron density is up to 1017 1/m3, and for the plasma uniformity, the 50% of uniformity is in the radius of 170 mm. In the final part this study proposed a microwave coupling structure outside the plasma chamber so as to build an axisymmetric model geometry.

並列關鍵字

plasma ； numerical simulation ； microwave plasma ； surface wave

參考文獻

[1] H. Kokura, S. Yoneda, K. Nakamura, N. Mitsuhira, M. Nakamura, and H. Sugai, "Diagnostic of surface wave plasma for oxide etching in comparison with inductive RF plasma,", Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap., Article vol. 38, no. 9A, pp. 5256-5261, Sep 1999, doi: 10.1143/jjap.38.5256.

[2] H. Sugai, I. Ghanashev, and M. Nagatsu, "High-density flat plasma production based on surface waves,", Plasma Sources Sci. Technol., Article vol. 7, no. 2, pp. 192-205, May 1998, doi: 10.1088/0963-0252/7/2/014.

[3] C. M. Ferreira, "MODELING OF A LOW-PRESSURE PLASMA-COLUMN SUSTAINED BY A SURFACE-WAVE,", J. Phys. D-Appl. Phys., Article vol. 16, no. 9, pp. 1673-1685, 1983, doi: 10.1088/0022-3727/16/9/013.

[4] M. Kanoh, K. Aoki, T. Yamauchi, and Y. Kataoka, "Microwave-excited large-area plasma source using a slot antenna,", Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap., Article vol. 39, no. 9A, pp. 5292-5296, Sep 2000, doi: 10.1143/jjap.39.5292.

[5] T. Akimoto, E. Ikawa, T. Sango, K. Komachi, K. Katayama, and T. Ebata, "OXIDE ETCHING USING SURFACE-WAVE COUPLED PLASMA,", Jpn. J. Appl. Phys. Part 1 - Regul. Pap. Short Notes Rev. Pap., Article; Proceedings Paper vol. 33, no. 12B, pp. 7037-7041, Dec 1994, doi: 10.1143/jjap.33.7037.