Microstructure and formation of copper oxide in the Cu electro-polishing process.
In this study, the formation of Cu oxide on Cu film is studied during Cu electropolishing in a phosphoric acid-based electrolyte with various Cu ion concentrations, from 2.28% to 10.08%. In cyclic voltammetry measurement, the maximum current density of the anodic peak (Imax) decreases from 38.87 to 28.13 mA/cm2 with increasing Cu ion concentration, indicating that an oxide film forms on the Cu film surface and the thickness increases with Cu ion concentration. Microstructures and crystallography of the oxide film are examined by transmission electron microscopy, which confirms the increase of the oxide film thickness due to the high Cu ion concentration in a H3PO4 electrolyte. Three types of Cu oxide are detected using X-ray photoelectron spectroscopy, namely Cu2O, Cu(OH)2, and CuO. With a Cu-ion electrolyte concentration of less than 6.99%, Cu(OH)2 is dominant, while at higher Cu-ion concentrations, CuO predominates. The formation of CuO protects Cu from corrosion in the electrolyte with the Cu-ion concentration of over 6.99%.
Department of Materials Science and Engineering, National Chen-Kung University, Tainan 701, Taiwan, Republic of China.
Te-Ming
TM
Kung
Michael Rong-Shie
MR
Huang
Jung-Chih
JC
Tsao
Chuan-Pu
CP
Liu
Ying-Lang
YL
Wang