Observation of metal-layer stress on Si nanowires in gate-all-around high-κ/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 similar to 5 nm) and metal-gate (TaN similar to 100 nm) are evaluated on Si nanowires having similar to 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 (similar to 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 similar to 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.