Physical Thickness 1.5-nm HfZrO Negative Capacitance NMOSFETs

This article focuses on how to improve the negative capacitance (NC) properties of NMOSFET in the gate-last process flow. The impacts of the HfZrO ferroelectric film thickness, metal gates with different work functions, stress of filled metal gate, the thickness of seed layer underneath HfZrO etc. on NC effect are investigated, and the corresponding possible mechanisms are discussed. These techniques have been successfully applied to the fabrication of NC-NMOSFETs with physical thickness 1.5-nm HfZrO, and underneath with 1.0-nm ZrO2 seed layer. The NC-NMOSFETs with much improved subthreshold swing (SS) of 38.6 mV/decade and nearly hysteresis free are developed with a gate length of 900 nm, and the SS is over 40 mV/decade smaller than that of the control-2 NMOSFETs with 2.5-nm HfO2 gate dielectric only.