Development on copper to copper bonding optimization on low-k structure integrated circuit device

Wire bonding technology has been widely used in the semiconductor industry for interconnection between chip and lead frame or substrate.Gold (Au) is the most widely used metal for Integrated Circuit (IC) wire bonding because of its resistance to surface corrosion and high productivity through the Au ball bonding process.However,the upward trend in gold price has prompted the industry interest in gold wire replacement.Copper (Cu) would be one of the best selections as an interconnection material in semiconductor packaging because of its obvious advantages over gold in cost comparison.Cu wire also has lower resistivity where could offer improvement in circuit performance.Despite its material properties advantages,Cu wire bonding technology has still facing many technical challenges due to its characteristic.Copper are very corrosive.Oxidation could easily happen on copper wire and bond pad which cause poor interconnect.In order to solve the bondability issue of Cu wire bonding,the selection of wire capillary and bonding parameters are among key factor must be considered.Design of Experiment (DOE)and evaluations were carried out to have better understanding of this technology.Ball bond diameter, ball height,ball pull and ball shear are among key wire bonding responses been analysed.This development covered the impact analysis of bond pad and circuitry underneath using pad cratering method.Experiment results shown that all bonding responses are meeting targeted results even with additional welded area and cross-section check.One of the key findings was the pre-bonding and initial bonding parameters are crucial for good bondability in Cu-Cu bonding technology.This new understanding becomes a gate opener for further Cu-Cu package development