在磷酸銨鹽系統中電化學機械研磨金屬導線銅之電化學特性的研究

The Study on Electrochemical Mechanical Polishing of Cu Metal Wire in Ammonium Phosphate System and Its Electrochemical Characteristics

楊牧寰(Mu-Huan Yang)

指導教授 ： 顏溪成

國立臺灣大學/工學院/化學工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.01760

摘要

半導體製程中，隨著低介電常數之介電層的引入，傳統的平坦化技術，化學機械研磨(CMP)也面臨一些問題，如因過大的下壓力破壞了介電層的機械結構。有別於傳統CMP，電化學機械研磨(ECMP)可施加遠小於傳統CMP的下壓力進行研磨，並透過外加電場有效地提高移除速率。此外，隨著環保意識的抬頭，近年來ECMP已開發出不含氧化劑的研磨液系統，則可不需再使用對環境有害的氧化劑；ECMP更可在無研磨粒子下進行研磨，降低磨後清洗晶圓表面的製程複雜度以及汙染可能性。
本研究著重於銅的ECMP，並探討無額外添加氧化劑環境下，其在磷酸銨鹽系統中的電化學機械研磨時的最適化工作條件；除了利用直流極化技術外，也使用交流阻抗分析研究銅表面研磨時的動力學機制，更透過原子力學顯微鏡(AFM)了解研磨後銅表面平坦度以及組成成份。實驗結果顯示，磷酸銨鹽的酸鹼值若控制在pH 8時，銅表面生成鈍化層的效果最好；此外施加電壓0.4V時，相對應的電流較為穩定。加入咪唑後發現在0.3 wt%下有相對穩定的電流；而當使用苯咪唑作為抑制劑時，0.3 wt%的濃度可以較有效的抑制電流值。透過AFM量測表面平坦度後可發現，苯咪唑保護銅表面的效果較咪唑來的好。最後在加入研磨粒子的實驗結果中發現，雖然加入研磨粒子後，研磨速率提升了許多，但是另一方面，銅表面平坦度卻也降低，由此可看出加入研磨粒子並非改善平坦度的有效方法。
在本研究所得到的最佳工作條件下，亦即在pH值8的磷酸銨鹽溶液、0.3 wt%的苯咪唑添加、施加電壓0.4V、相對轉速300rpm以及施加下壓力0.6psi進行銅片的ECMP，可以得到最好的平坦化結果，其粗糙度為14.78nm。

關鍵字

電化學機械研磨 ； 腐蝕抑制劑 ； 咪唑 ； 苯咪唑

並列摘要

In this study, the electrochemical characteristics of Cu ECMP were investigated, and we also studied the best working condition during the process of Cu ECMP in ammonium phosphate slurry system. By performing electrochemical measurements such as polarization curves, current-time plot and impedance spectroscopy, the slurry compositions and electrochemical characteristics during ECMP were discussed; besides, surface morphological analysis after ECMP was carried out by atomic force microscopy (AFM). The experimental results showed that the effect of passivation on the Cu surface is better than others when the pH value of electrolyte is 8. As 0.4 voltage was applied during process, the current was more stable. In the case of adding imidazole as the inhibitor, the current would be more stable as the concentration of imidazole was chosen to be 0.3wt%. In the other case of adding benzimidazole as the inhibitor, the concentration of benzimidazole was also chosen to be 0.3wt% for the same reason. By the data of AFM, benzimidazole had better ability to protect Cu surface than imidazole. Finally, we found out that material removal rate would be enhanced by adding abrasive particles, but the effect on planarization of Cu surface would be reduced. So adding abrasive particles is not an effective way to improve the planarization.
The best result of planarization of Cu ECMP in our study is 14.78nm under the working condition: ammonium phosphate electrolyte at pH=8.0, concentration of benzimidazole = 0.3wt%, applied voltage = 0.4V, rotation speed = 300rpm, applied pressure = 0.6psi.

並列關鍵字

ECMP ； corrosion inhibitor ； imidazole ； benzimidazole

參考文獻

陳怡秀，化學機械研磨阻障層鉭與其電化學特性的研究，台大化工所博士學位論文(2010)

Ahn, Y., J.-Y. Yoon, et al. (2004). "Chemical mechanical polishing by colloidal silica-based slurry for micro-scratch reduction." Wear 257(7-8): 785-789.

Aksu, S. (2009). "Electrochemical Equilibria of Copper in Aqueous Phosphoric Acid Solutions." Journal of the Electrochemical Society 156(11): C387.

Armini, S., C. M. Whelan, et al. (2008). "Engineering Polymer Core–Silica Shell Size in the Composite Abrasives for CMP Applications." Electrochemical and Solid-State Letters 11(10): H280.

Bohr, M. T. (1995). “Interconnect Scaling - the Real Limiter to High Performance ULSI,” Technical Digest - International Electronic Devices Meeting: 241-244.