Observation of Metal-Layer Stress on Si Nanowires in Gate-All-Around High- $\kappa$ /Metal-Gate Device Structures

This letter reports, for the first time, the observation of mechanical stress from metal-gate layer on the Si nanowires formed by the top-down scheme. High-kappa (HfO2 ~ 5 nm) and metal-gate (TaN ~ 100 nm) are evaluated on Si nanowires having ~5-7 nm diameter. While no significant mechanical effect is observed after high-kappa deposition, the TaN metal layer is found to viciously stretch and twist the straight wires. The wire lengths increase significantly (~3%), which suggests that the Si nanowires are subjected to large tensile strain ( > 4 GPa), assuming that the wires obey Hooke's law with Young's modulus ~150 GPa for bulk Si. Interestingly, the twisted nanowires maintained their physical continuity, as demonstrated by the excellent performance of the fully functional gate-all-around MOSFETs fabricated with the wires as channels.