Electrical and bias temperature instability characteristics of n-type field-effect transistors using HfO_x N_y gate dielectrics

The dielectric properties and n-type metal oxide semiconductor field-effect transistor (nMOSFET) positive bias temperature instability (PBTI) characteristics of in situ nitrogen-incorporated plasma-enhanced atomic layer deposited HfO_x N_y gate dielectrics were compared with those of the HfO₂ films. Although the physical thickness of the HfO_x N_y and HfO₂ films were almost identical (∼4.1 nm), the capacitance equivalent oxide thickness of HfO_x N_y (1.43 nm) was much lower than that of HfO₂ (2.28 nm), suggesting that HfO_x N_y has a larger dielectric constant. However, HfO_x N_y showed a higher leakage current than HfO₂ due to a decrease in bandgap. HfO_x N_y showed a turnaround effect under a positive gate stress bias in nMOSFET. The threshold voltage (Vth) shifted to the positive direction during the first second due to the trapping of electrons at pre-existing trap sites in Hf-based gate dielectrics. Subsequently, the Vth shifted in the negative direction due to hole trapping, which originated from the generation of electron-hole pairs related to the surface plasmon. HfO_x N_y showed a higher initial interface trap density but a lower interface trap generation rate during n-type MOS PBTI stress than HfO₂.