Low-Force Electric Contact Processes on Cu Electrodes

A contact process between large-scale integration (LSI) pads and test probes at low contact force is a key to developing a probe card with smaller pitch and higher pin count. In this paper, we report on the characteristics of low-force contact methods on Cu electrodes. One is the fritting process, in which an electric breakdown is utilized to break the surface oxide, and the other is the heating treatment in hydrogen gas aimed at deoxidizing the surface Cu oxide. Conventional tungsten needle probes were used as testing probes, and contact resistances at low contact force of 1-5 mN were measured. Contact resistances smaller than 1 Omega were obtained by the fritting processes, in which the voltage and the current were 10 V and 280-320 mA, respectively. A deoxidization process at over 260degC was found to be effective for decreasing the contact resistance. The X-ray photoelectron spectroscopy (XPS) was utilized to investigate the surface state of hydrogen-treated Cu, and the deoxidization of Cu₂O to Cu was observed in samples treated at 260degC, while no change was found in that at 150degC.