To study Ru electromigration, the single damascene lines were stressed by 5 MA/cm2 at 300°C for 1000 hours. No failures of Ru interconnects for half pitches of (sub-)10 nm were observed. Although the direct comparison to Cu structures is not straightforward, it should be noted that Cu lines typically show failures under such conditions even for larger line widths of the order of 20 nm and for optimized liner and cap combinations. This demonstrates the excellent electromigra-tion properties of Ru due to its refractory nature.