A Study on the Effect of Microstructure Evolution of the Aluminum Metallization Layer on Its Electrical Performance During Power Cycling

The study presented in this paper contributes to the quantification of the correlations between resistance degradation and Al metallization layer reconstruction observed in high-power insulated gate bipolar transistor (IGBT) modules during power cycling. The microstructure evolution that occurs in the Al metallization layer during power cycling was investigated via electron and ion microscopy, and the surface roughness was measured and used to characterize Al metallization degradation. An electrical four-point probe method was used to examine the change in the electrical parameter (resistance) of the Al metallization layer in the IGBT modules. The effect of the Al metallization layer reconstruction on its electrical performance was investigated by experimental observation and finite-element analysis (FEA). The results show that both the Al metallization layer surface morphology and cracks propagating across the Al metallization layer thickness significantly affect the metallization resistance. In the initial and mid-point stages of power cycling, the increase in the Al metallization layer resistance is consistent with the surface roughness evolution. Near the ultimate lifetime of the IGBT module, the change in the resistance strongly depends on the crack density.