Impact of Aluminum Metallization Reconstruction on the Current Distribution in Power Semiconductors

For optimized performance of the semiconductor switch in a power electronic module a uniform current distribution in the active volume of the chip is desirable. Since the bottom side of the semiconductor die is fully connected to a substrate by a soldered or even a sintered layer, the vertical current distribution is mainly determined by the top side interconnection technology and the ability of the top side aluminum metallization to spread the current in lateral direction. The focus of this paper is on the influence of the metallization and the top side connection, realized by heavy wire bonds. Sheet resistance and roughness measurements were taken on power modules, aged by active power cycling, in order to evaluate degradation during regular operation. Voltage mapping measurements across the metallization layer during operation were correlated to finite element simulation results, revealing inhomogeneities in the current density distribution in the metallization layer as well as the semiconductor die.