| 摘要: | 在以電漿輔助化學氣相法類鑽碳膜的製程中，許多參數影響著成膜速率與成膜品質，包含氣體濃度、氣體溫度與壓力、離子能量和碳源氣體種類等。為釐清影響成膜速率的因素，本文參考以往學者的文獻與其實驗設備，取其圓柱型反應腔軸對稱特性建立 r－z 系統的幾何模型，再以連續體模型模擬電漿流場，並採用 CFD-ACE+ 商 業套裝軟體進行數值計算，最後再根據結果探討控制環境參數對各氣體密度、電子能量或電場等電漿參數的影響。在數值計算模型中，包含電子、離子和不帶電物質等各物質密度（或濃度）皆以連續體方程式表示；電子能量由能量守恆式為之；電場強度或電位勢分佈則以泊松（Poisson）方程式表示。最後，再利用有限體積法進行數值計算。最終模擬結果分三大類逐一討論：流速、溫度與壓力。流速對原料氣體甲烷的濃度是有增益的，當原料注入並產生流速時，對甲烷而言是補充遠大於消耗。然而流速對其他不帶電物質則為損益，即電漿中不帶電物質的產生速率遠不及流出反應腔的部 份，同時也造成沉積物質的流失，薄膜沉積速率因為流速的提升而降低。至於溫度和壓力對各參數的影響皆可由理想氣體定律解釋：定壓下溫度與物質密度成反比，定溫下壓力與物質密度成正比。因此在定壓時，由於沉積物質的密度隨溫度提高而降低，造成沉積速率的下降。而在定溫時，沉積物質的密度隨著壓力升高而增加，沉積速率也隨之提升。總而言之，在本文的模擬結果中，在有入口流速的情況下，以0.01 m/s 有最快的沉積速率，流速過高則會稀釋沉積物質造成反效果。而在環境條件溫度與壓力的控制上，則以高壓低溫環境可得到較快速的沉積速率。 During the process of depositing diamond-like carbon films with plasma-enhanced chemical vapor deposition, deposition rate and the quality of the films were effected by some parameters, like gas concentration, temperature, pressure, ion energy and carbon sources. In order to clarify how these parameters influence the deposition rate, in this paper we consulted to the former work and their experimental setup to create a 2-D physical model. And adopting commercial software CFD-ACE+ as a solver. Finally, we discuss the simulation results. In mathematical model, all species were expressed with continuity equations, while electron energy was solved by energy conservation equation. Besides, electric field or electric potential was in the form of Poisson’s equation. And then the mathematical model was solved with finite volume method. We simulate different inlet flow velocity, gas temperature and pressure to see how the variables will change. Methane was supplied with inlet gas flow, though plasma reactions consumed some of them, methane got more than reaction loss. But the situation was quite different for other species, like the main deposition species methyl. For methyl, the reaction production rates were less than the flow rate that out of the chamber. Therefore, the larger inlet flow the greater loss of reaction products. This also decreases the deposition rate. Gas temperature and pressure followed ideal gas law. Under fixed pressure, temperature gets larger while the gas concentration gets fewer. Under fixed temperature, gas concentration is proportional to the pressure. In our simulation results, the highest deposition rate occurred while inlet velocity equals to 0.01 m/s. And the higher inlet velocity get worse deposition rate. Under control of gas temperature and pressure, high pressure and low temperature would increase deposition rate. |
