以脈衝電鍍製備具有 (111) 優選方向之奈米雙晶銅膜以及熱處理之後 (100) Cu異方性單晶成長

Abstract

本研究以脈衝電鍍系統使用硫酸銅溶液製備奈米雙晶銅金屬膜。主要以改變脈衝電鍍系統中電鍍參數，探討鍍層材料之結晶方向及雙晶結構生成以及其電性、機械性質等，並結合後續熱處理製程，同時探討熱處理對於脈衝電鍍製程所製備形成的奈米雙晶銅金屬膜之影響。 本實驗分別利用 X 光繞射儀、聚焦離子束、電子背向散射繞射系統、四點探針、奈米壓痕儀及穿透式電子顯微鏡等設備，分析脈衝電鍍銅薄膜晶體的優選成長方向及雙晶結構生成的情形。研究結果發現，在 50 mA/cm2 的電流密度下，所製備的銅金屬薄膜具有最佳的 <111> 優選方向，其內部微結構由微米級柱狀晶粒構成，晶粒內部有高密度平行於生長基材的奈米雙晶界面，其雙晶間距為 10~70 奈米間，隨著電流密度提高或下降，奈米雙晶銅薄膜的 {111} 晶面繞射強度隨之降低，而雙晶銅薄膜內部的平均雙晶間距也隨之上升。 高溫熱處理的過程中，我們發現此高度有序的 <111> 奈米雙晶銅薄膜，會發生極端的異方性晶粒成長。其側向成長的速度比垂直方向快非常多，因此可以長成很大的晶粒。例如，在7微米厚的銅薄膜內之 {111} 柱狀晶粒平均約 1.5 微米，經由熱處理溫度 400 °C 持溫一小時，可以長成平均 438 微米的銅 {200} 晶粒，且此極端的異常晶粒成長呈現常態的粒徑分佈曲線。藉由此獨特的異常晶粒成長模式，成功的大量製備 <100> 單晶銅微凸塊應用於三維積體電路封裝技術。

This study adopts pulsed deposition and CuSO4-based electrolytes to electroplate nanotwinned Cu (nt-Cu) film. We vary the parameters of electrodeposition, and investigate the properties of the nt-Cu films, including preferred orientation, twin structures, electrical conductivity, and hardness. In addition, the nt-Cu films are annealed to examine the effect of annealing conditions on the microstructure of the nt-Cu films. This study use X-ray diffraction, focused ion beam, back-scattered scanning electron microscopy, four-point probe, nano-indentation, and transmission electron microscope to characterize the nt-Cu films. We found that the nt-Cu films possess highest (111) preferred orientation of 50 mA/cm2. The (111) grains are columnar with highly-ordered nanotwins parallel to the substrate. The spacing of the nanotwins range from 10 nm to 70 nm. The refection (111) intensity decreases with a higher or a lower deposition current density. In addition, the average spacing of nanotwins increases if the current density deviate from 50 mA/cm2. It is interesting that extremely anisotropic grain growth occurs in (111)-oriented nt-Cu films during annealing. The lateral growth rate is much faster than the growth rate in the thickness direction. Therefore, huge (100) Cu grains can be obtained. For example, for a 7 um thick (111) nt-Cu films with an average grains size of 1.5 um, we can grow large {200} Cu grain with an average grain size of 438 um. In addition, the distribution of the {200} grain appears normal distribution. Thus it is different from traditional abnormal grain growth. We can fabricate arrays of <100>-oriented single crystals on si substrates using the extremely anisotropic grain growth. These large {100} Cu single crystals may have potential application in 3D IC packaging.