添加劑對電鍍銅影響之電化學及微結構研究

Abstract

這篇論文主要針對電鍍過程中添加劑對電鍍銅影響之電化學及顯微結構研究。探討電鍍過程中添加硫脲對電鍍沈積銅退火行為之影響，以及硫酸鍍液內添加不同氯離子濃度，其對於電解沈積銅之結晶行為。實驗使用硫酸銅鍍液中添加不同濃度硫脲，在高溫高電流密度下進行電鍍，利用微硬度量測電鍍沈積銅退火前後硬度的變化，並以DSC量測並記錄沈積銅退火時吸、放熱行為，研究沈積銅抵抗退火軟化的能力。結果顯示鍍液中含硫脲濃度高於3ppm時，沈積銅抵抗退火軟化阻抗能力明顯得到改善。添加硫脲於電鍍液中，可使沈積銅的晶粒尺寸細化，並且當增加硫脲含量高於3ppm時，沈積銅的雙晶結構明顯增加，並且可發現許多含硫顆粒沿晶界共沈積，少數含硫顆粒存在於沈積晶粒內。這些含硫量高的顆粒阻礙晶界移動，因此提高沈積銅退火的軟化抵抗能力。上述沈積銅的顯微結構以穿透式電子顯微鏡（TEM）觀察，並以X-ray 能譜分析儀（EDS）來分析其化學組成。 在鍍液中添加不同氯離子濃度之沈積銅結晶行為，利用場射掃瞄式電子顯鏡(FESEM)及高解析穿透式電子顯鏡(HRTEM)附加成分分析，觀察分析電解沈積銅初始生長形貌及顯微結構。由陰極極化及定電流電鍍結果顯示，可知電鍍銅時陰極電位隨氯離子濃度提高而增加。由SEM觀察顯示在電鍍結晶過程，由於三角形氯化亞銅沈積物除了存在陰極的表面，而且形成在沈積群集銅上，造成陰極電位增加。在初始生長期間，顯示群集生長的銅和六角形的氯化亞銅沈積物同時被還原，最後可發現由許多平行之六角形面，以螺旋差排生長形成之金字塔形狀的氯化亞銅沈積物。氯化亞銅沈積物吸附上鈦陰極表面，造成極化影響更進一步證實並且驗證，透過陰極電位量測和FESEM研究沈積形貌，觀察在相同電鍍條件下，銅陰極表面比鈦陰極，吸附更少氯化亞銅沈積物，導致極化影響下降。

In this thesis, electrochemical and microstructure effects on copper electrodeposition with two additives, thiourea and chloride ion, were studied and reported. The copper electroplating was performed at relatively high temperature and high current density, which was conducted in a conventional copper sulfate-sulfuric acid bath with various concentrations of additives. The annealing behavior of electroplated copper deposits is reported in this study. Moreover, this thesis is also to study the electrocrystallization behavior of the copper deposit on pure titanium substrate.

The copper deposits were electroplated with a current density of 0.7 A/cm2 in a sulfuric acid bath containing various concentrations of thiourea. The hardness values of the copper deposits were measured before and after annealing, and the DSC diagrams of the as-electroplated copper deposits were recorded. An improvement of the softening resistance of the copper deposits was observed when the bath contained thiourea ≥3 ppm. By adding thiourea in the plating bath, smaller grain size of the copper deposits can be achieved. As thiourea content increased ≥3 ppm, the twin boundary of the copper deposits was significantly increased, and many sulfur-rich particles were deposited along the grain boundaries and a few within the grains of the deposit. These sulfur-rich particles are capable of impeding migration of the grain boundaries, and, hence, improving the softening resistance of the copper deposits during annealing. The aforementioned microstructures of the copper deposits were examined with transmission electron microscope (TEM) integrated with energy-dispersive x-ray spectrometer (EDS) for chemical composition analysis. The electroplating was conducted at 0.7 A/cm2 in cupric sulfate-sulfuric acid bath with various chloride additions. Initial growth morphology and microstructure of the deposit were examined with field-emission scanning electron microscope (FESEM) and high-resolution transmission electron microscope (HRTEM) integrated with energy dispersive X-ray spectrometer (EDS). Results of cathodic polarization and galvanostatic plating experiments show that the increasing concentration of chloride ion in the plating bath would significantly increase the cathodic potential. This cathodic potential increase was found to be induced by the presence of CuCl precipitates on the cathodic surface as well as on the copper cluster formed during electrocrystallization process. At initial plating stage both copper and hexagonal-shaped CuCl precipitate were produced simultaneously. Eventually, the pyramid-shaped CuCl precipitates were observed, which consisted of many parallel hexagonal planes stemming from a screw dislocation. The polarization effect of CuCl precipitate on the Ti-substrate was further confirmed and clarified. Through measurement of the electrode response and investigation of the deposit using FESEM, it was observed that under the identical electroplating conditions much less CuCl forms on a copper substrate in the initial stages than on a titanium substrate, leading to lower polarization.