Mechanism of AC electromigration

Abstract

A model for the mechanism of AC electromigration based on the thermal response of Al stripes is proposed. The model is based on the temperature difference between the positive period and the negative period. The thermal time constant of the Al stripe, underlying SiO/sub 2/, and Si substrate is on the order of microseconds and that of the package and ambient is a few seconds. When the cycle time of the current is longer than thermal time constant, the temperature of the Al stripes obeys the current waveform. When the cycle time is shorter than the thermal time constant, the temperature keeps constant. Mean time to failure (MTF) depends on the temperature according to Arrhenius's equation. The temperature difference between positive and negative periods causes an unbalance of atomic flux between the periods. Thus, open-circuit failure can take place under AC conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>