Inductive Operating Life Stress Metal Breakdown Mechanism

Abstract

Experimental devices in a deteriorated state were encountered after 168 hours of inductive operating life stress, (IOL) testing. A metal grain boundary breakdown mechanism was found during the analysis of the device, which was creating a low resistance current path between terminals. The AlSiCu top metal was breaking down along the grain boundaries. In addition there was alloying of the Aluminum into the underlying silicon. This alloying was creating a short to the gate, source, and drain. Several variations in the metal stack, testing conditions, number, and dimensions of bond wires die size and mold compound were evaluated to better understand the cause of the inability to withstand IOL stress and to provide a process solution. The prevention of the AlSiCu front metal grain boundary breakdown during inductive life stress testing required a die size, bond wire dimension, and testing condition change to meet the performance specification. This change resulted in a reduced grain boundary breakdown and consequently prevented Al grain boundary breakdown, TiW barrier breakdown, and Al alloy spiking. The die change and modified testing conditions resulted in a successful pass through the IOL stress testing.