銅的腐蝕研究與過硫酸銨研磨液對銅/釕化學機械研磨之效應

Abstract

本研究主要探討銅的腐蝕研究以及在過硫酸銨系統下的Cu/Ru化學機械研磨。在銅腐蝕方面，利用電化學三極系統探討銅在硫酸銨溶液中的腐蝕情形。首先利用電化學還原銅在白金旋轉電極上，銅的厚度大約為0.98μm，接著在不同環境下測試其腐蝕情況。實驗發現氮氣除氧時間10分鐘以上就可將大部分的氧氣排除。在溫度方面，腐蝕速率隨著溫度的升高而變高。在電解液中通入不同氣體，發現通入氧氣的腐蝕速率最高，氮氣與氫氣差不多，而通入氬氣的腐蝕速率則最低，而在氮氣的環境下腐蝕速率也很低。在不同pH值的情況下，pH為5或6時的腐蝕速率相較於pH 7-9時低，因此不再添加其他溶液調整電解液之pH值。銅在純水中的腐蝕速率比在0.1 M硫酸銨或硫酸鈉溶液低，其值為1.07 × 10-3 nm/s。本實驗也添加了兩種抑制劑，探討其對銅腐蝕之抑制效果。Benzotriazole (BTA)為Cu CMP中常見之抑制劑，其抑制腐蝕效果也較benzimidazole為佳。而比較添加不同濃度的BTA，發現濃度為10 ppm即可以降低腐蝕速率，且效果佳，Cu的腐蝕速率為1.2 × 10-3 nm/s (在0.1 M (NH4)2SO4溶液)。 在銅/釕化學機械研磨方面，除了利用直流極化技術外，也使用交流阻抗分析研究研磨時的動力學機制，更透過原子力學顯微鏡(AFM)了解研磨後的表面平坦度。實驗結果顯示，研磨液為pH 6的情況為最佳，金屬銅與釕的研磨速率最為相近，分別為225.0 nm/min及63.9 nm/min，而且研磨後，銅的表面粗糙度下降至14.3 nm；釕的表面粗糙度下降至19.0 nm。在交流阻抗分析方面，探討在化學機械研磨時釕在pH 6的過硫酸銨研磨液中表面的動力學機制，由浸漬時間的不同，了解金屬釕表面鈍化層的生成，而在化學機械研磨時，以機械力移除其表面的鈍化層。

This study includes two parts: copper corrosion and effect of ammonium persulfate-based slurry on Cu/Ru chemical mechanical polishing. We used three electrode-system to investigate the corrosion of copper in various conditions. Copper was electrodeposited on a rotating disk electrode with the thickness of 0.98 μm. After the corrosion experiments, the remaining copper was measured. We found that sparging nitrogen for 10 minutes could remove 90% oxygen in the solution. The corrosion rate of copper increases as temperature increases. Sparging oxygen in the electrolytes has the highest corrosion rate; on the other hand, sparging argon has the lowest corrosion rate. At various pH values, the corrosion rates at pH 5 and 6 are lower than pH 7-9. Two organic inhibitors has also been investigated: benzotriazole and benzimidazole, and it was found that benzotriazol is better than benzimidazole for copper corrosion inhibitor. Adding 10 ppm BTA in the solution can decrease the corrosion rate, and the corrosion rate is 1.2 × 10-3 nm/s in 0.1 M (NH4)2SO4 solution. In the Cu/Ru CMP experiments, by performing electrochemical measurements such as polarization and impedance spectroscopy, the electrochemical characteristics has been studied. Besides, surface morphological analysis after CMP was carried out by atomic force microscopy. The experimental results showed that the ammonium persulfate-based slurry at pH 6 has the best performance. At pH 6, there is the lowest galvanic corrosion, the removal rate of Ru was found to match that of Cu. After CMP in (NH4)2S2O8-based slurry, the copper surface roughness reduces to 14.3 nm; the ruthenium surface roughness reduces to 19.0 nm.