以甲烷/氨氣和乙炔/氨氣混合物研製n型非晶質 射頻電漿輔助化學汽相沉積碳薄膜

n-Type amorphous carbon films prepared by radio frequency plasma enhanced chemical vapor deposition using methane/ammonia and acetylene/ammonia mixtures

薛翔峻

指導教授 ： 李三保

國立清華大學/工學院/材料科學工程學系/博士(2013年)

https://doi.org/10.6843/NTHU.2013.00486

摘要

本論文以甲烷/氨氣和乙炔/氨氣混合物研製n型非晶質射頻電漿輔助化學汽相沉積碳薄膜。當氨氣/甲烷比從0增加到0.2時，氮/碳比從0增加到5.4%。氮碳鍵結、氮氫鍵結和sp2碳比例隨著氨氣/甲烷比增加而增加，但碳薄膜的沉積速率、有序程度、光學能隙、楊氏模數、硬度和殘留應力隨著氨氣/甲烷比增加而減少。非晶質碳薄膜/p型矽元件在氨氣/甲烷比為0.15時(氮/碳比為4.7%)具有最佳的電學特性。另一方面，當氨氣/乙炔比從0增加到1.4時，氮/碳比從0增加到6.9%。氮碳鍵結和sp2碳比例隨著氨氣/甲烷比增加而增加，但碳薄膜的有序程度、楊氏模數和硬度隨著氨氣/乙炔比增加而減少。非晶質碳薄膜/p型矽元件在氨氣/乙炔比為1時(氮/碳比為5.8%)有最佳的電學特性，其理想因子為1.59。
另外，本論文也利用黏彈性力學探討在薄膜/基材系統中的殘留應力。首先，本論文推導出在多層薄膜/基材系統中，一個簡化的黏彈性應力封閉解。如果總薄膜剛性和基材剛性的比例小於0.02時，本研究的公式可以有效地顯示出多層薄膜/基材系統中殘留應力的鬆弛。基材和薄膜中的應力隨著薄膜和基材的熱膨脹係數差、溫度差、薄膜楊氏模數和薄膜黏性係數的增加而增加，但隨著時間的增加而減少。其次，本論文也推導出在雙層馬斯威爾材料系統中，其黏彈性應力的真實解。如果其中一層的厚度遠小於另外一層，在雙層系統中的黏彈性應力可以被簡化為薄膜/基材系統中的黏彈性應力。薄膜/基材系統的黏彈性應力解包含了薄膜厚度和位置。分析結果顯示平均薄膜應力隨著正規化時間的增加而減少，且到很長的時間後變成零。本真實解可用來評估其他近似解的準確性。

關鍵字

電漿輔助化學汽相沉積法 ； 碳薄膜 ； 殘留應力

並列摘要

This study investigates the effect of ammonia/methane (NH3/CH4) and ammonia/acetylene (NH3/C2H2) mixtures on characteristics of nitrogen-doped amorphous hydrogenated carbon (a-C:H(N)) films prepared by plasma enhanced chemical vapor deposition. As the NH3/CH4 ratio increases from 0 to 0.2, the nitrogen/carbon ratio increases from 0 to 5.4%. The nitrogen-carbon bonds, nitrogen-hydrogen bonds, and sp2 carbon fraction of carbon films enlarge with increasing the NH3/CH4 ratio, while the deposition rate, ordered degree, optical band gap, reduced Young’s modulus, hardness, and residual stress of carbon films decrease. The a-C:H(N)/p-Si device has an optimum electrical property at the NH3/CH4 ratio of 0.15 (or at the N/C ratio of 4.7%). On the other hand, as the NH3/C2H2 ratio increases from 0 to 1.4, the nitrogen/carbon ratio increases from 0 to 6.9%. The nitrogen-carbon bonds and sp2 carbon fraction of carbon films enlarge with increasing the NH3/C2H2 ratio, while the ordered degree, Young’s modulus, and hardness of carbon films decrease. Furthermore, the a-C:H(N)/p-Si device has an optimal electrical property at the NH3/C2H2 ratio of 1 (or at the N/C ratio of 5.8%), which has an ideality factor of 1.59.
Additionally, this study also investigates the residual stresses in thin films/substrate systems using viscoelastic theory. First, a simplified closed-form solution for viscoelastic deformation of multilayers due to residual stresses is derived. If the ratio of the total axial rigidity of thin films to that of the substrate is smaller than 0.02, the formulas of this study are valid to evaluate the relaxation of residual stresses in multi-layered thin films/substrate systems. The magnitude of stresses in the substrate and fims increases with increasing the difference of the thin film and substrate thermal expansion coefficients, the temperature change, and Young’s modulus and viscous coefficient of thin films, but it decreases with increasing the time. Second, the exact solution of viscoelastic stresses in the bilayer system is derived if both layers are Maxwell materials. As the thickness of one layer is much smaller than that of the other layer, the viscoelastic stress in the bilayer system can be reduced to that of the thin film/substrate system. The relative film thickness and the position in the thin film/ substrate system are included in this solution. The analytic result shows that the average film stress decreases with increasing the normalized time and finally equals zero in a long time. This exact solution can be used to evaluate the accurary of other approximate solutions.

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