Thermal shock and degradation of metallization systems on silicon

Abstract

Purpose: The purpose of this study is to investigate the mechanisms of degradation of aluminum metallization under conditions of thermal shock caused by rectangular current pulses (amplitude j < 8 × 10¹⁰ A/m², duration t < 800 μs). Design/methodology/approach: The results were obtained using oscillography and optical microscopy and through the construction of an empirical model of the thermal degradation of metallization systems. Findings: Initially, for the authors’ studies, they deduced an equation that associated the depth of melting with the parameters of a current pulse. Research limitations/implications: The authors were able to observe effects only in systems with appropriate adhesion of the thin metal films. For the systems with bad adhesion, the main mechanisms of degradation were associated with the melting of the metal, the formation of melted drops (up to 20 mcm in size) and the movement of these drops along the electrical field due to the electrocapillary effect. Practical/implications: The mechanisms the authors studied could only occur in high-power semiconductor devices. Originality/value: The principal mechanism of melting of a metallization track is linked to the heat dissipation at the interface of solid and liquid phases under conditions of thermal shock. The authors estimated the mechanical stresses in subsurface layers of silicon in the proximity of a non-stationary thermal source. The authors’ results show that the mechanical stresses that are strong enough to form dislocations emerge with current flow with power measuring approximately 0.7 Pkr.