Oxidation Structure Change of Copper Surface Depending on Accelerated Humidity

Nonlinear dependence of sheet resistance change for Cu film on humidity was observed during temperature humidity storage (THS) test to evaluate the lifetime of Cu film in long-term storage in an environment. X-ray photoelectron spectroscopy (XPS) was adopted to investigate the change of oxidation structure depending on the humidity. Relative volume ratio of Cu, Cu20, and CuO was considered as the reason for the nonlinear dependence. The dominant reaction of oxidation changed from Cu20 to CuO between 75 and 85% relative humidity (RH) at 85 °C, leading to almost no reduction of Cu film thickness in spite of higher humidity.