Mechanism of ultra low force probing on Al electrodes

We report on the breakdown of thin native oxide film formed on aluminum electrodes contacting metal probes at the contact force smaller than 0.1 mN when the surface aluminum oxide is difficult to break mechanically. The contact method with low contact force on aluminum electrodes is required for test probing of LSI for the next generation. A gold wire was used as a contact probe on aluminum electrode formed on Si wafer. To investigate the initial stage of the breakdown, the current flow is limited to the value below 1 muA using a large resistance inserted to the current circuit. It was found that ohmic contacts with resistance of about 10-100 Omega were obtained after the breakdown at 2-10 V. The contact resistance was found to be affected by the breakdown voltage, not by the current. Adhesion forces between the probe and the wafer were found to be 40-80 muN. A small current was observed before breakdown and may have influences on the breakdown voltage.