Characterization of alterations on power MOSFET devices under extreme electro-thermal fatigue

Extreme electro-thermal fatigue tests on power MOSFET-based switches for automotive applications have been performed in order to pinpoint their failure mechanisms. Contrary to devices from the former technology generation, the most important failure mode concentrates in the source metallization zone and consists in the degradation of the metallic layer. Intense intergranular and surface diffusion triggered by the thermal stresses between the Si substrate and the Al layer leads to intergranular crack formation. Around the ultimate life time (ULT) of the device, these intergranular cracks burrow almost down to the active transistor region and their density on the source surface is high enough to cause a loss of contact between the metal grains. The observed increase of the drain-source resistance could be attributed to this degradation that have qualitatively modeled. Observed melt down of the Al layer revealed by the formation of Al/Si eutectic could be the result of hot spots due to spikes in source resistance. (C) 2010 Elsevier Ltd. All rights reserved.