Study of Cu-Cu low temperature direct bonding and contact resistance measurement on bonding interface

Cu surface oxide prevents Cu-Cu low temperature bonding and raises contact resistance on bonding interface. Therefore, in this study, formic acid gas was used to treat Cu surface oxide for low temperature bonding and decreasing contact resistance. A pair of new electrode samples were designed and fabricated for contact resistance measurement. It includes many small electrodes located on the whole upper sample surface for resistance measurement. Samples were treated using formic acid gas at 200°C for 20min first, then were bonded together at 200°C for 5min under the load of 1000N. Resistance on different electrodes chain was measured. It proved the bonding is good in most area of sample because the value of resistances for all electrodes chains maybe measured, which is not unlimited. Contact resistance was measured using 4-point measurement method. Average contact resistance for different measurement points on sample is about 0.17mΩ. It also means that the bonding is good.