鍍液溫度對電鍍奈米雙晶銅膜成長之研究

Abstract

奈米雙晶銅的熱穩定性與機械性質皆比無雙晶結構的一般銅較佳，因此，是一能應用在接點技術上之具有潛力的材料，若是透過製程上許多不同參數的調整，將能使其性質達到最佳化，因此，過去已有許多研究在探討不同參數對奈米雙晶銅的影響，包括電流密度、薄膜厚度、附著層等。 溫度會影響原子的能量狀態及擴散速率，進而影響材料的微結構狀態，因此，在材料科學當中，溫度一直都是扮演重要的關鍵角色，本實驗將以不同的電鍍方式，透過不同溫度的鍍液製備奈米雙晶銅膜，觀察其微結構受溫度變化的影響，在這之後，將進一步對不同電鍍溫度下所製備出之銅膜進行400˚C，持續一小時的退火之熱穩定及晶粒成長性質測試，以及DC-15˚C、DC-35˚C銅膜進行拉伸之機械性質測試，由結果顯示，透過鍍液溫度的變化對晶粒大小的改變，可推測不同的電鍍模式其成長主導機制不同，且雙晶密度亦會因溫度降低而提高。 另一方面，由退火後之銅膜之分析結果，成功地找到各個電鍍模式下，欲使雙晶銅膜產生極度的異向性晶粒成長之最佳溫度條件，另一方面，由微結構的分析，可推測影響奈米雙晶銅的晶粒成長機制可能有銅膜的殘餘應力、雙晶晶界與柱狀晶界的交點所產生的釘札效應，以及過渡層中的細晶粒等因素同時交互競合影響，而由DC-15˚C、DC-35˚C銅膜拉伸測試結果可知，雖然雙晶結構可有效提升機械強度，然而，當銅膜本身的細晶粒仍佔不少，且晶粒狀態趨於混亂時，雙晶結構的對機械強度的提升效果會降低。

It has been suggested that thermal stability and mechanical property of Cu with nanotwinned structure be superior to those of normal Cu. Therefore, plenty of parameters including current density, film thickness, and substrates had been modified in order to obtain the optimization of properties of nanotwinned copper in many researches. Temperature has a great effect on the motion of atoms, further influencing the microstructure of the Cu films prepared by electrodeposition. Hence, temperature always plays a key role when speaking of materials science. In the present study, nanotwinned Cu films were fabricated with different bath temperatures under three electroplating modes, direct-current mode, pulsed mode, and pulse-reversed mode, respectively, for further microstructure analysis. Moreover, a lot of interests were raised in thermal stability and mechanical strength of nanotwinned Cu films electroplated with different temperatures under distinct modes. Annealing at 400˚C for 1 h for all films and tensile tests for DC-15˚C, DC-35˚C films were both conducted so that thermal stability and mechanical strength could be determined. It had been shown from the grain size analysis that the rate-determined factor under three modes would be different during Cu films electrodeposition. Furthermore, the results also indicate that twin spacing varies with bath temperatures. Nanotwinned Cu films produced under different conditions also have dissimilar thermal and mechanical behaviors after annealing and tensile test. If one aims at gaining films with extra large grains after the heat treatment, the best conditions had been found to be DC-30˚C, PED-20˚C, and PR-30˚C through orientation analysis. In addition, the grain growth might depend on residual stress, thickness of the transition layer, and the pinning effect associated with twin boundaries and columnar grain boundaries. For the tensile test of DC-15˚C, DC-35˚C films, it clearly pointed out that despite of the strengthening effect of twins on the tensile strength, temperature effect would be weakened if too many fine grains were present.