電漿在半導體製程有著廣泛的應用，如PECVD、Sputtering、及Plasma etching，而電漿特性主要由電漿密度所決定，因此電漿密度量測為重要的技術。本研究使用電漿吸收探針(Plasma Absorption Probe, PAP)作為電漿密度量測的工具，其運作原理是當表面波與電漿中的電子發生共振時，表面波會被電漿吸收，因此量測到的反射係數將呈現最低值，此時的頻率為共振吸收頻率，藉此可以推算出在探針頭附近的電漿密度，而PAP對電漿密度量測的靈敏度透過實驗量測與數值模擬得知與天線結構有關，如Compact PAP、Dielectric Loaded PAP、Flat-Head PAP。
在先前PAP的電磁數值模擬中，建立理論鞘層、前鞘層模型(Theory Sheath Pre-Sheath Model, TSPM)來模擬探針周圍電漿的狀態，並將電漿前鞘層模型簡化為均勻空間分佈於PAP，然而在進行量測時，探針伸入腔體的行為會干擾電漿密度分佈，使得TSPM將不再適用。因此，本研究第一部分，提出模擬鞘層模型(Simulation Sheath Model, SSM)來模擬電漿受PAP干擾後的微波量測，此模型電漿前鞘層的電漿密度分佈是基於流體數值模擬的結果所建立，考慮較完整的物理模型以貼近實際量測情況。
在製程上，會透過外加射頻偏壓以提升蝕刻率，因此射頻偏壓對PAP量測的影響變為重要。本研究第二部分，使用Flat-Head PAP在射頻偏壓電漿環境中進行實驗量測，發現當探針量測位置接近腔壁時，量測到的共振吸收峰之半高寬有上升的現象。為了探討此現象，本研究透過流體數值模擬建立ICP電漿源，並置入PAP以及射頻偏壓，並由模擬結果發現射頻鞘層現象，進一步使用本研究第一部分的SSM模型模擬微波量測，發現在一個射頻偏壓週期內PAP模擬出的共振吸收頻率發生位移。由此看出在使用PAP於射頻偏壓電漿環境中進行量測時，隨著量測位置越靠近腔壁，射頻鞘層對量測的共振吸收峰影響越大，因此證明射頻鞘層對電漿量測影響的重要性。

Plasma has a wide range of applications in semiconductor manufacturing processes, such as PECVD, sputtering, and plasma etching. The characteristics of plasma are mainly determined by plasma density, so plasma density measurement is an important technology. This study uses plasma absorption probe (PAP) as a tool for plasma density measurement. The principle of PAP is that surface wave will be absorbed by the plasma at resonance, so the reflection coefficient will be the lowest value, which frequency is the resonant absorption frequency. It can be used to calculate the plasma density near the probe head. The sensitivity of PAP is related to the antenna structure which has been studied from experimental measurements and numerical simulation, such as Compact PAP, Dielectric Loaded PAP, and Flat-Head PAP.
In the previous electromagnetic numerical simulation model of PAP, the theoretical sheath and pre-sheath model (TSPM), were established to simulate the state of the plasma around the probe. However, TSPM is over simplified on plasma distribution. Therefore, a new model, simulation sheath model (SSM), is proposed to PAP simulation. In SSM, plasma density distribution is based on fluid numerical simulation which consider more complete physical module to be close to the actual measurement situation.
In the manufacturing process, an external RF bias voltage is applied to increase the etching rate. Therefore, the influence of the RF bias voltage on the PAP measurement is important. In the second part of this study, the Flat-Head PAP was used to measurements in the RF biased plasma environment. It was found that when the probe measurement position was close to the chamber wall, the FWHM of the resonant absorption peak increased which is RF sheath affect on PAP. In order to explore RF sheath effect, this study establishes an ICP plasma source with PAP and RF bias in fluid numerical simulations. Further uses the SSM model to simulate microwave characteristics. It is found that the resonant absorption frequency shifts in one RF bias cycle. Which show when measurement position is closer to the chamber wall, the radio frequency sheath has a greater influence on the resonant absorption peak. Therefore, it is nesscery to consider RF sheath effect in PAP measurement when an external RF bias affect on plasma.

[1] H. Kokura, K. Nakamura, I. P. Ghanashev, and H. Sugai, "Plasma absorption probe for measuring electron density in an environment soiled with processing plasmas," Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers, vol. 38 (9A), 5262-5266 (1999)
[2] H. Sugai and K. Nakamura, "Novel Plasma Monitoring by Surface Wave Probe," Proceedings of Frontiers in Low Temperature Plasma Diagnostics V, 30-39 (2003)
[3] K. Nakamura, M. Ohata, and H. Sugai, "Highly sensitive plasma absorption probe for measuring low-density high-pressure plasmas," Journal of Vacuum Science & Technology A, vol. 21 (1), 325-331 (2003)
[4] M. A. Lieberman and A. J. Lichtenberg, "Principles of Plasma Discharges and Materials Processing," John wiley & sons, (2005)
[5] A. Meige, O. Sutherland, H. B. Smith, and R. W. Boswell, "Ion heating in the presheath," Physics of Plasmas, vol. 14 (3), 032104 (2007)
[6] M. Lapke, T. Mussenbrock, R. P. Brinkmann, C. Scharwitz, M. Boke, and J. Winter, "Modeling and simulation of the plasma absorption probe," Applied Physics Letters, vol. 90 (12), (2007)
[7] C. Scharwitz, "The Plasma Absorption Probe: Optimisation by model-based design variations," PhD thesis, Ruhr-University Bochum, Germany, (2007)
[8] C. Scharwitz, M. Boeke, S. H. Hong, and J. Winter, "Experimental characterisation of the plasma absorption probe," Plasma Processes and Polymers, vol. 4 (6), 605-611 (2007)
[9] C. Scharwitz, M. Boke, and J. Winter, "Optimised Plasma Absorption Probe for the Electron Density Determination in Reactive Plasmas," Plasma Processes and Polymers, vol. 6 (1), pp. 76-85 (2009)
[10] B. Li, H. Li, Z. P. Chen, J. L. Xie, G. Y. Feng, and W. D. Liu, "Experimental and Simulational Studies on the Theoretical Model of the Plasma Absorption Probe," Plasma Science and Technology, vol. 12 (5), 513-518, (2010)
[11] D. M. Pozar, "Microwave Engineering," John wiley & sons, 30-35 (2011)
[12] CFDRC, "CFD-ACE+ V2020.0 Manual_Plasma Module," ESI Group, 1388-1392 (2020)
[13] 陳穩智, "電漿吸收探針模擬與實驗分析," 碩士論文, 工程與系統科學系, 國立清華大學, 新竹市, (2012)
[14] 邱晉陞, "高靈敏度微波共振探針研製及其射頻電漿鞘層影響分析," 碩士論文, 工程與系統科學系, 國立清華大學, 新竹市, (2015)
[15] 陳博志, "平頭式電漿吸收探針之研製," 碩士論文, 工程與系統科學系, 國立清華大學, 新竹市, (2018)