Assessing the remnant of anti-oxidant agent on the processed copper bond pad surface by using XPS and TEM analysis

In copper leadframe fabrication process, anti-oxidant agent is a common chemical solution used to easily protect oxidize surface like copper bond pad surface. There are varieties of anti-oxidant solution available in the market. However, only certain group of anti-oxidant chemical solution can be applied on the copper leadframe or bond pad surface. This is mainly due to the specific and unique anti-tarnish properties, such as low evaporation point and high adhesion strength on specific metal or polymer surface. The application of this anti-oxidant in copper leadframe or bond pad application leads to some challenges like difficulty to examine or ensure the homogeneity of the coating thickness. Besides, in flip chip die bonding process, insufficient removal of the anti-oxidant protecting layer from the copper bond pad surface will cause copper pillar chip bonding quality issue, due to the organic residue left on the bond pad surface, which inhibits the intermetallic formation and contributes to solder voiding issue. Therefore, to accurately examine the existence of the anti-oxidant characteristics, high end analytical tools like X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) had been applied in this study. From the analysis, the properties of chemical bonding state on the anti-oxidant and coating thickness had been successfully determined. In term of verifying the coating thickness, a single analytical tool like XPS may not be able to provide an accurate information, due to the tool depth profiling setting. Therefore, a complimentary analytical tool like TEM is more suitable to be used to examine the nano thickness level anti-oxidant coating.