Donut-Tungsten-Via in a Highly Robust Metallization Stack

In CMOS technologies with AlCu metallization, the common via shape is cylindrical. The size of the via is as small as possible for the related process and a maximum current per via is specified. Huge via arrays are in use for high current tracks. For future applications especially for automotive customers, the mission profiles of the products will be more challenging. Higher temperature, thermal expansion and cycling, higher current and high current pulses will require higher robustness of the metallization system.

The reliability of high current interconnections of wide metal tracks with via arrays with high via density is determined by electromigration performance but also limited by mechanical properties. The highly robust metallization concept considers the higher requirements regarding higher currents and temperatures as well as mechanical stress. For high current, slotted metal tracks are connected by Donut-Vias. First simulations and investigation showed an improved reliability for a Donut-Via layout. This paper will show a comparison of different geometries for Donut-Vias between metal layers with different thickness and design rules.