側壁表面波電漿放電研究-微波耦合結構設計與電漿/微波交互作用特性之分析

Study of Side Wall Surface Wave Plasma Discharge – Microwave Applicator Design and Plasma/Microwave Interaction Analysis

李修竹(Hsiu-Chu Lee)

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(2021年)

摘要

表面波電漿(surface wave plasma)的優點為大面積、高密度、高均勻度等，大面積晶圓製程、極短製程時間、奈米等級關鍵尺寸為目前半導體工業之趨勢
，表面波電漿為理想的製程電漿源。本研究根據側壁表面波電漿源結構，以數值模擬計算分析進一步探討電漿腔體與微波源耦合之特性，模型包括電漿理論、電磁波理論，同時考慮熱傳與流場影響，在頻域下以麥克斯韋方程求解電磁場與功率沉積，了解電漿腔體與微波源之耦合特性，
在側壁表面波電漿(Side Wall Surface Wave Plasma)腔體結構，微波由溝槽天線耦合至介電質腔壁，在介電質腔壁與高密度電漿間形成駐波之表面波結構。分析穩態電漿與功率源的功率反射頻譜分佈，分析在不同電漿吸收功率下穩態電漿的S11頻譜偏移，模擬結果顯示每提高1 kW的微波吸收功率，共振頻率約提高23 MHz，可藉由調整微波功率源的操作頻率達成功率源與電漿腔體的阻抗匹配。
為符合實務上固定輸入功率的微波功率源操作模式，進一步以微波端口設定固定輸入功率，探討調頻微波流程。先以符合表面波模態的微波頻率激發初步電漿分布，再調整微波功率源的頻率至共振頻率，可以提高微波吸收功率，其穩態結果之微波特性及電漿特性與固定吸收功率之結果相近。由於微波調頻耦合的阻抗匹配較機械式諧調器快之優勢，本研究將有助於脈衝表面波電漿源的研製。
許多製程機台為控制到達晶圓表面的離子能量，加入射頻偏壓影響電漿電位分布，因此本研究建立表面波電漿源並包含射頻偏壓之數值模擬模型，觀察到射頻偏壓電漿特性的增強與自偏壓現象。

關鍵字

表面波電漿 ； 數值模擬 ； COMSOL ； 氬氣電漿 ； 微波調頻 ； 微波特性

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.Based on the structure of the side wall surface wave plasma, this study further explores the coupling characteristics of the plasma cavity and the microwave source with numerical simulation calculations. The model includes plasma theory and electromagnetic wave theory. At the same time, the influence of heat transfer and flow field is considered. Maxwell’s equations are used to solve the electromagnetic field and power deposition, understand the coupling characteristics of the plasma cavity and the microwave source.
In the Side Wall Surface Wave Plasma cavity structure, microwaves are coupled to the dielectric cavity wall by the trench antenna, and a surface wave structure of standing waves is formed between the dielectric cavity wall and the high-density plasma. By analysis the power reflection spectrum distribution of steady-state plasma and power source, oberver that S11 spectrum shiftunder different plasma absorption power is analyzed. The simulation results show that the resonance frequency increases about 23 MHz for every 1 kW increase in microwave absorption power. The impedance matching between the power source and the plasma cavity can achieved by adjusting the operating frequency of the microwave power source. In order to comply with experimental operation mode of microwave power source with fixed input power, the microwave port is further used to set fixed input power, and the process of frequency tuning microwave is discussed. First, the initial plasma distribution is excited by the microwave frequency that conforms to the surface wave mode, then the frequency of the microwave power source is adjusted to the resonant frequency, which can increase the absorbed power. Because the impedance matching of microwave frequency tuning coupling is faster than that of mechanical tuner, this research will be helpful to the development of pulsed surface wave plasma source.
In order to control the ion energy on wafer surface, many process add RF bias to affect the plasma potential distribution. Therefore, in this study, a surface wave plasma source and a numerical simulation model including RF bias are established. It is observed that the RF bias will enhancement plasma characteristics and the phenomenon of self-biasing.

並列關鍵字

microwave_plasma ； simulation ； COMSOL ； tuning

參考文獻

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