常壓射頻電容耦合式電漿束之研究

Abstract

在過去十年中，大氣電漿逐漸替代低壓電漿作為材料表面處理的應用。其重要性是由於它 相對低廉的設備費用，及更容易的操作條件和在更高的靈活性在工業上的應用。其中已經發展 的大氣電漿源之中，又以非熱平衡『常壓射頻電容耦合式電漿束』(簡稱常壓電漿束) 引起了最 多的注意。主要乃因為其應用範圍相當廣闊，包括半導體製程光阻去除，清潔，消毒，表面改 質和薄膜沈積等等，相當廣泛。 在這三年的計畫中，我們準備發展和系統化方式來研究非熱平衡『常壓電漿束』，並利用 其產生易反應之自由基原子，並進行相關方面的特性瞭解與應用。其中又以氧基(負電性)和氮基 (正電性)氣體種類有極佳的應用性。研究主軸包括實驗和電漿系統數值模擬兩大部份。整體來 說，實驗部份包含：1)建立和驗證常氣電漿束實驗設備和電漿量測儀器；2)定義各種測試條件操 作參數；3)量測常氣電漿束出口區域速度, 溫度分佈，電漿參數和氣體種類混合比例；4)結合理 論分析及數值模擬比對實驗結果。另外，電漿系統之數值模擬部分則包含：1)修改實驗室現有 已發展平行化流體數值模組(從2D改為軸對稱)，並考慮加入N-S 相關方程式；2)運用軸對稱流體 數值模組預測在各種測試條件下常氣電漿束行為；3)與實驗結果比較並結合電漿物理理論基 礎。最後，經過此計畫後希望能提供常氣電漿束的標準設計參數及見立常氣電漿束的數值模擬 能力。以下簡潔的說明每一年的主要任務及工作。 第一年，在實驗部分中我們將設計，建立和驗證基本常氣電漿束設備。基本先已氦氣及氬 氣或是兩者混合氣體做為量測實驗參數定義(電壓-電流、電流-功率參數關係)。我們將在常氣電 漿束出口位置使用幾種量測方式定義電漿特性。這幾種量測方式包括使用高速攝影機觀察流 場；使用粒子影像測速儀(PIV)量測速度；使用熱電偶線量測溫度分佈；及使用蘭牟耳探針量測 電漿參數。另外在電漿系統數值模擬部份中我們以全域式流體數值模組技術估計為電漿密度及 電子溫度。然後, 我們將修改並驗證實驗室現有已發展平行化流體數值模組有線差分法架構從 2D改為軸對稱，並加入軸對稱N-S 方程式。 第二年，在實驗部分中，早期焦點放在改變各種測試條件下量測其電漿束出口處電漿相關 的流體，化學及物理性質;後期再將焦點放在加入氧氣到原先氦或氬的氣體以及混合氣體對電漿 性質的影響。並分別把氧氣加入常氣電漿束之機制，於出口區域延長自由基氧原子存活距離及 增加其成份作為三個重要研究任務。除了重複第一年的量測外，在常氣電漿束出口位置針對不 同混合氣體的比例(特別是氧氣部份)使用光譜儀(OES)量測自由基原子種類及強度。另外在電漿 系統數值模擬部份中，我們將針對以流體數值模組來預測常氣電漿束各種測試條件實驗準確性。 第三年，初期我們將繼續第二年氧氣及氦或者氬的混合氣體電漿方面的研究。另開始以氮 氣加入氦或氬的混合氣體為電漿氣體之研究，並重複所有與氧氣相同或類似之實驗及數值模 擬。亦計畫應用常氣電漿束處理聚合物薄膜表面，並分析處理前後表面性質差異。 預計本計劃之完成將可提供常氣電漿束設計之系統參數，並培養相關模擬之能力。

In this proposed three-year project, we intend to develop and systematically characterize a non-thermal atomospheric-pressure capacitively coupled plasma jet (APPJ), which is able to generate reactive atoms or radicals of practical interest. Interested radicals may include oxygen- (electronegative) and nitrogen-based (electropositve) species, which have tremendous practical applications. Reseach approaches include both experiments and modelings. Overall speaking, proposed experiments shall include: 1) To set up and verify experimental facilty and instrumentation of the APPJ; 2) To identify the operating windows under various test conditions; 3) To measure the distirbutions of velocity, temperature, plasma parameters and species concentrations in the postglow region; 4) To intepretate the results with the help of theory and modelings. In addition, proposed modelings include: 1) To modify and verify a previously in-house developed parallel fluid modeling code from 2-D into axisymmetric 2-D, which shall consider the N-S equations; 2) To apply the fluid modeling code to simulate the APPJ flow under various test conditions; 3) To compare with experimental results and to help intepretate the underlying plasma physics. Finally, design crteria of APPJs shall be proposed based on the what we have learned from this project. Specific major tasks of each year are shown in the following for brevity. In the first year, in the experimental part we shall design, construct and verify a tesing rig for the basic APPJ experiment. Operating window (e.g., I-V ad I-P characteristics) for the basic configuration using helium, argon gas or mixture of both shall be identified. We shall made several measurements in the postglow region to chracterize the plasma. These measurements include flow visualization using a high-speed CCD camera, velocity field using a particle image velocimeter (PIV), temperature distribution using a thermocouple, and plasma parameters using a Langmuir probe. In the modeling part we shall estimate the plasma number density and electron temperature based on the global modeling technique. Then we shall modify and verify an existing in-house parallelized finite-difference fluid modeling code from two-dimensional into axisymmetric two-dimensional by also including the modeling of axisymmetric N-S equations. In the second year, in the experimental part in the earlier stage we will focus on examining the postglow fluid dynamics, plasma physics and chemistry by varying all kinds of test conditions. In later stage of this period, we will shift our focus to study the effects of the discharge by adding oxygen into the helium or argon gas or mixture of both. Mechanism of introducing oxygen into the discharge, how to extend the downstream distance of the 「alived」 reactive oxygen atoms, and increase the oxygen atoms are the three most important tasks. In addition to all the measurements in the first year, distirbution of the species concentrations, especially the oxygen atoms, shall be measured in the postglow region using the OES system. In the modeling part, we shall continue verifying the fluid modeling code and apply it to predict the APPJ under various test conditions that are comparable to those in experiments. In the third year, we will continue the experiments of adding oxygen into the carrier gas and repeat all the experiments and modeling considering the addition of nitrogen gas into the discharge. We will also apply the APPJ to treat some surfaces such as polymer and compare the surface properties before and after treatment. Completion of this project shall provide more fundamental understanding and design criteria of APPJ, as well as the capability of simulating AP plasmas.