Effect of Nitrogen Incorporation in a Gd Cap Layer on the Reliability of Deep-Submicrometer Hf-Based High- $k$ /Metal-Gate nMOSFETs

In this letter, the effect of nitrogen incorporation in a Gd cap layer on the reliability of Hf-based high- k/metal-gate nMOSFETs is investigated in detail. NH₃ post plasma treatment was implemented after deposition of the Hf-silicate (HfO₂ or HfSiOx) to improve the channel interface state. The Gd cap layer was added on the top of the Hf-based high-k/metal gate for reducing the threshold voltage. However, the nitrogen atoms incorporated in the gate stack via the NH₃ plasma treatment could also diffuse into the Gd cap layer, thus blocking the Gd ions at the top of the Hf-based high-k /metal gate, which then generate bulk charges to degrade the device´s positive bias instability significantly. We identify the diffusion of nitrogen in the Gd cap layer as well as the location of trap defects in the Hf-based high-k/metal gate with secondary ion mass spectrometry, flicker-noise, and charge-pumping measurements.