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. NH
₃
post plasma treatment was implemented after deposition of the Hf-silicate (HfO
₂
or HfSiO
x
) 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 NH
₃
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.