The Study of Copper Etching in Acid Solutions
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
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