銅在酸性溶液之蝕刻研究

Abstract

本實驗針對銅溼式蝕刻之蝕刻液分為三個部分討論：第一部分為氯化銅-鹽酸-氯化銨系統研究，第二部分為硫酸-雙氧水與添加劑之作用，最後一個部分為低蝕刻速率之硫酸-雙氧水-醋酸系統的研究。利用秤重法量測各種蝕刻液的銅蝕刻速率，利用電化學直流極化技術，探討蝕刻過程中界面處可能發生的作用現象。藉由XPS及XRD分析表面組成，SEM及AFM觀察表面形貌及分析表面粗糙度。 實驗結果發現在氯化銅-鹽酸-氯化銨系統中，蝕刻速率的快慢與氯化亞銅（CuCl）的生成溶除速率有很大的關係，此現象可藉由電化學直流極化曲線圖之陽極電流轉折現象觀察到。增加溶液中Cu+2、Cl-離子、提高系統攪拌速度以及通入氧氣均可提升蝕刻速率。 在硫酸-雙氧水與添加劑作用實驗方面，發現添加檸檬酸、草酸、甘醇酸等有機錯合劑及醋酸、丙酸，因本身的吸附或與銅反應所生成之錯合物的吸附作用會造成蝕刻速率下降。添加氧化劑硝酸則因和雙氧水產生競爭作用，並無法有效提升蝕刻速率。添加NH4Cl，則因Cl-的錯合效果，能有效提升蝕刻速率。抑制劑BTA則能有效抑制陰極反應而減緩蝕刻速率。 在低蝕刻速率之硫酸-雙氧水-醋酸的實驗方面，由於醋酸會吸附在銅氧化物上，故會減緩蝕刻速率，蝕刻速率則隨醋酸添加量的增加而減緩至一定值。銅氧化物或醋酸吸附之氧化物的溶除速率與pH值有關，在pH較低的環境下，其溶除速率較快，蝕刻速率則能增加。無論是否添加醋酸，活化能介於44~46 kJ/mol，為反應控制。蝕刻後之銅表面則隨蝕刻速率的下降，而有較佳之粗糙度。

This thesis on wet copper etching has been investigated in three acid systems. CuCl2-HCl-NH4Cl system was investigated in the first part of study. The effects of H2SO4-H2O2 with various additives were investigated in the second part of study. H2SO4-H2O2-Acetic acid system for lower etching rate was investigated in the final part of study. In the experiments, the etching rates were measured by the weight-loss method and the interface phenomena in the etching process were also investigated by electrochemical polarization technique. We also analyzed the surface compositions by XPS or XRD, and observed the surface morphology and roughness by SEM and AFM. The results of CuCl2-HCl-NH4 system indicated that etching rate depended on the formation and dissolution of CuCl. The process would be observed on Tafel plot in which current was reduced at some anodic potential region. Etching rates could be increased by increasing Cu+2 or Cl- concentrations, aeration and stirring. By studying the effect of H2SO4-H2O2 with various additives, it has been found that adding citric acid, oxalic acid or glycolic acid would decrease etching rate. The results could be due to the adsorption of the organic acid or copper complex formed by reaction of copper ion and organic acid. However, adding nitric acid or other oxidants would not increase etching rate because nitric acid would compete with H2O2 for oxidizing copper. With complexing effect, adding Cl- ion increased etching rate, but on the contrary, adding inhibitor BTA decreased etching rate due to its inhibition for cathodic reaction. In the study of H2SO4-H2O2-Acetic acid system, etching rate decreased gradually to a certain value with increasing acetic acid concentration. It can deduced that acetic acid would be absorbed on the copper oxide surface. The dissolution rate of copper oxides or copper oxide adsorbed by AA depended on pH value. In lower pH environments, the dissolution rate was faster to make etching rate increased. Whether acetic acid was added or not, the etching process was reaction controlled and the activation energy is about 45 kJ/mol