<111>奈米雙晶銅在<100>優選方向與無優選方向之銅薄膜上之晶粒成長之研究

Abstract

奈米雙晶銅已經被許多人深入研究，極有潛力應用在下一代先進封裝製程。本研究是利用背向散射電子繞射分析（EBSD）、X射線繞射儀（XRD）及聚焦離子束系統（FIB）來對電鍍在<100>優選方向及無優選方向上之<111>奈米雙晶銅的熱穩定性與晶粒成長進行研究。 首先，奈米雙晶銅被電鍍在具有<111>優選方向之銅的晶種層之上。將試片進行200至400°C之退火1小時並進行比較。在低溫時奈米雙晶銅仍然有穩定之柱狀晶結構，反之在高溫時奈米雙晶銅異方向大晶粒成長，成為晶粒尺寸73.4微米之<100>方向大晶粒。 接著在<100>優選方向之銅薄膜上電鍍高密度之<111>奈米雙晶銅。對此<111>/<100>雙層膜進行退火。在200°C退火一小時後，<111>奈米雙晶銅仍有穩定之柱狀晶結構而非成長為<100>方向之大晶粒。隨著溫度上升，<100>方向之晶粒尺寸逐漸提升。經過400°C退火一小時後，FIB橫截面影像顯示雙層膜完全轉變為單顆<100>方向之大晶粒。 本研究也在同一溫度下進行連續及分段之退火來對晶粒成長進行研究。通過FIB橫截面影像可以得知，在15及30分鐘退火後，奈米雙晶銅仍有穩定之柱狀晶結構。隨著時間拉長，雙晶晶界逐漸消失，柱狀晶彼此混合，底部的<100>優選方向之銅逐漸將上方之<111>奈米雙晶銅轉變為<100>優選方向之大晶粒。 最後，使用無優選方向之銅薄膜作為基板電鍍<111>奈米雙晶銅與前面的研究進行比較。我們選用200 ℃、250 ℃ 及400 ℃作為退火溫度。在奈米雙晶銅穩定之溫度200℃ 退火一小時之後，有些較為筆直的<111>奈米雙晶銅晶粒有向下晶粒成長的情形，而且許多的奈米雙晶也生成。

Nanotwinned copper (nt-Cu) has been investigated intensively by many researchers mainly due to its potential of application in the next generation of advanced packaging process. In this study, the grain growth and thermal stability of <111> nt-Cu on <100>-oriented and random Cu films were investigated by using electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and focused ion beam (FIB). First, nt-Cu samples were produced by electroplating on <111>-oriented Cu seed layer. Samples Compared annealed at 200°C to 400°C for an hour were then compared. Nt-Cu remained as columnar structures at lower annealing temperatures, while anisotropic large grain growth to <100>-oriented grains occurred at higher annealing temperatures. Second, we electroplated highly-textured <111> nt-Cu films on <100>-oriented Cu substrates. After annealing at 200°C for an hour, nanotwins showed stable columnar structures instead of growing into larger grains. With the increase of annealing temperature, the <100> grain growth was enhanced. After annealing at 400°C for an hour, the cross-sectional FIB image showed that the bilayer completely transformed into <100>-oriented large grains. Third, we investigated the grain growth process by observing the same sample while extending the annealing time at a fixed temperature. By observing cross-sectional FIB image, after annealing for 15 and 30 minutes, Nt-Cu with columnar structure were shown to be stable. However, as the time extended, the <100>-oriented Cu at the bottom gradually transformed <111> nt-Cu grains into <100>-oriented larger grains. Last, we used random Cu films as substrates to examine the grain growth behavior of <111>-oriented nt-Cu films. After electroplating <111> nt-Cu on random Cu films, we annealed the specimen at 200°C since it is the most favorable temperature for the growth of <111> nt-Cu. After annealing for an hour, some of the <111>-oriented nt-Cu grains grew downward to consume the random-oriented grains, and nanotwins formed simultaneously.