Low temperature direct Cu-Cu bonding with low energy ion activation method

This paper describes a copper wafer bonding process for three-dimensional integration and wafer-level packaging applications. Cu-Cu direct bonding at low temperature using a low energy ion activation method was investigated. 8-inch silicon wafers were coated with 80 nm copper and the copper surfaces were cleaned by irradiation of 50-100 eV argon ion beam before mating them together. The cleaned surfaces were examined by Auger electron spectroscopy (AES). It was observed that carbon contamination and the native oxide layer on the copper surface were effectively removed by 1 min ion beam irradiation without any wet cleaning process. After cleaning the surfaces, two wafers were brought into contact and pressed up to 1000 kgf in the bonding chamber at ultra high vacuum (UHV) pressure. The surfaces were examined by atomic force microscopy (AFM) and the bonded interface was investigated by tensile tests. Details of characterization of bonding interface of Cu-Cu and the effects of low energy ion beam on the bonding are described.