Temperature Effects of Constant Bias Stress on n-Channel FETs with Hf-based Gate Dielectric

摘要

Temperature dependence of degradation and breakdown behavior of hafnium silicate gate dielectrics in n-channel field-effect transistors (NFET) with polysilicon and TiN gate electrodes has been investigated. At elevated temperatures under positive gate bias, devices with polysilicon gate electrodes exhibit a so-called V_(th) turn around phenomenon (a change of the direction of the V_(th) shift from positive to negative), accompanied by decreasing transconductance and increasing gate leakage current. Hot-holes generation in the poly-Si gate by the injected electrons and a subsequent hole diffusion and trapping near the high-k/Si-substrate interface is proposed to contribute to the turn around behavior. No V_(th) turn around phenomenon was observed in devices with the TiN gate electrode. This hole induced degradation of the high-k/poly-Si gate stack may further complicate integration of the polysilicon gate electrode with high-k dielectrics.