Time-varying wetting behavior on copper wafer treated by wet-etching

- A thin oxide layer always remains on surfaces of Cu wafers after aqueous etching.
- A pure Cu wafer is obtained by the HAc treatment and the water CA is about 45°.
- The oxide layer and CA grow with time after the Cu wafer is exposed to air.
- Surface roughness and hydrophobicity of pure Cu wafers grow rapidly in vacuum.