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

• Published in: Applied surface science Vol. 341; pp. 37 - 42
• Main Authors: Tu, Sheng-Hung, Wu, Chuan-Chang, Wu, Hsing-Chen, Cheng, Shao-Liang, Sheng, Yu-Jane, Tsao, Heng-Kwong
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.06.2015
• Subjects: Acetic acid; Contact angle; Copper; Cuprous oxide; Etching; OXIDES; SEMICONDUCTORS; Wafers; Wetting; Wetting; Cuprous oxide; Contact angle
• ISSN: 0169-4332
• DOI: 10.1016/j.apsusc.2015.01.048

•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. The wet cleaning process in semiconductor fabrication often involves the immersion of the copper wafer into etching solutions and thereby its surface properties are significantly altered. The wetting behavior of a copper film deposited on silicon wafer is investigated after a short dip in various etching solutions. The etchants include glacial acetic acid and dilute solutions of nitric acid, hydrofluoric acid, and tetramethylammonium hydroxide. It was found that in most cases a thin oxide layer still remains on the surface of as-received Cu wafers when they are subject to etching treatments. However, a pure Cu wafer can be obtained by the glacial acetic acid treatment and its water contact angle (CA) is about 45°. As the pure Cu wafer is placed in the ambient condition, the oxide thickness grows rapidly to the range of 10–20Å within 3h and the CA on the hydrophilic surface also rises. In the vacuum, it is surprising to find that the CA and surface roughness of the pure Cu wafer can grow significantly. These interesting results may be attributed to the rearrangement of surface Cu atoms to reduce the surface free energy.