Mechanisms of temperature dependence of threshold voltage in high-k/metal gate transistors with different TiN thicknesses

The change in temperature coefficient of the threshold voltage (=dV(th)/dT) for poly-Si/TiN/high-k gate insulator metal-oxide-semiconductor field-effect transistors (MOSFETs) was systematically investigated with respect to various TiN thicknesses for both n- and p-channel MOSFETs. With increasing TiN thickness, dV(th)/dT shifts towards negative values for both n- and p-MOSFETs. A mechanism that changes dV(th)/dT, depending on TiN thickness is proposed. The main origins are the work function of TiN (phi(TiN)) and its temperature coefficient (d phi(TiN)/dT). These are revealed to change when decreasing the thickness of the TiN layer, because the crystallinity of the TiN layer is degraded for thinner films, which was confirmed by ultraviolet photoelectron spectroscopy (UPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD).