利用電滲流蝕刻微/奈米管道之輸送現象之理論研究

Abstract

濕蝕刻，是通過液體環境中的化學反應以及流體流動的攪動來去除固體材料的過程，在半導體製造中是一個重要的製程。隨著半導體器件的關鍵尺寸縮小到奈米級，在製造過程中基板上會出現微米和奈米通道。通常在進行進一步製程之前，會需要清潔通道底部，而濕蝕刻是其中一個有發展性的清潔方法。本研究提出使用電滲流來增強蝕刻性能，因為其與晶圓和拋光板相對運動所產生的庫埃特流動（Couette flow）相比，電滲流可能可以提供更大及均勻的壁面剪切應力、而剪切應力的大小與濕蝕刻的效果呈正相關的變化。本研究回顧傳統濕蝕刻所使用之剪切機制驅動與具平移效應驅動之剪切機制對其進行理論分析，並將其與電滲機制驅動之理論進行比較，研究電滲機制驅動之濕蝕刻是否具有優勢。 在假設二維電滲流和均勻電滲流速度的情況下，通過解連續方程式、含靜電力項的Navier-Stokes方程式和質量傳遞方程式，本文解得速度場、蝕刻劑濃度場和材料去除率（Material Remove Rate，簡稱為MRR）之分析解。另通過使用COMSOL軟件本文也進行了詳細的數值計算（本文所有蝕刻的質傳模擬均為三維，並採用電滲流速度的解析解），進一步計算MRR與不均勻度（Degree of Non-Uniformity of Material Removal Rate，簡稱為MRRNU），並和分析解結果相互驗證。對於純庫埃特驅動情況，本研究亦進行分析與計算，其所獲的MRR與文獻中銅蝕刻的實驗結果相符（解析和計算的誤差分別為10.1%和10.3%）。比較庫埃特流和電滲流驅動機制的結果，以對銅進行蝕刻為例，當輸入電場為1000 V/m時，前者的MRR及MRRNU分別比後者高10.8%及低6.2%；當輸入電場提升為10000 V/m時，則分別高出8.3%及高15.8%。電滲流驅動所得之MRR在輸入電場為10000 V/m時雖稍差於傳統的庫埃特流所驅動者，但其蝕刻的均勻度(MRRNU愈低)卻可獲相當幅度的提升。若要同時提升電滲機制蝕刻之MRR與MRRNU，可將流場效電晶體(FlowFET)結合電滲機制，以提升電滲機制濕蝕刻之應用潛力。

Wet etching, removing solid material via chemical reaction in liquid environment together with the agitation from fluid flow, is an important process in semiconductor manufacturing. As the critical dimensions of semiconductor devices are down to nano sizes, micro and nano channels occur on the substrate during the manufacturing processes. It is usually required to clean the bottom of the channels prior to further processes, and wet etching is one of the promising tools for cleaning. It is proposed in this study to enhance the etching performance using electroosmosis as it might provide larger and more uniform shear stress at wall in comparing with that through the relative motion of the wafer and the polishing pad (Couette-type). This study reviews and theoretically analyzes the Couette-type and sweeping Couette-type driving mechanisms used in traditional wet etching, comparing them with the theory of electroosmotic mechanisms to investigate whether electroosmotic-driven wet etching has advantages. The velocity field, the concentration field of the etchant and the material removal rate (MRR), were obtained analytically by solving the continuity, the Navier-Stokes equation with electrical force term, and the mass transfer equation, under the assumptions of 2D electroosmosis flow and uniform electroosmosis velocity. The degree of nonuniformity in polishing rate (MRRNU) and the analytical results were further calculated/validated through detailed numerical calculation via the aid of COMSOL software (etching simulation are all 3D with substituting analytical solution of electroosmosis velocity). For the purely Couette-type driving case, the present study for MRR agrees with the experiment in literatures of copper etching (with discrepancies 10.1% and 10.3% for analysis and calculation). For the comparison of the Couette-type and electroosmotic driving mechanisms, the former is 10.8% better for MRR and 6.2% better for MRRNU than the latter when the applied electric field for electroosmosis is 1000 V/m. For the comparison of the 10000 V/m and 1000 V/m electric field condition, the former is 8.3% better for MRR and 15.8% better for MRRNU. The MRR driven by electroosmosis at an electric field of 10,000 V/m is slightly less than that driven by traditional Couette flow, but the etching uniformity (with a lower MRRNU) is significantly improved. To simultaneously enhance the MRR and MRRNU of the electroosmotic driving mechanism, a flow field-effect transistor (FlowFET) can be combined with the electroosmotic driving mechanism to increase the application potential of electroosmotic wet etching.