Field dependent electrical conduction in HfO₂/SiO₂ gate stack for before and after constant voltage stressing

The electrical conduction mechanisms contributing to the leakage current at different field regions and different temperatures have been studied in this work. The current-voltage (I-V) measurement of TiN/HfO₂/SiO ₂/P-Si nMOS capacitor in the temperature range from 25 °C to 125 °C, taken before stressing and in the temperature range of 25 C to 65 C after constant voltage stressing (CVS) at 3 V suggests that the Poole-Frenkel mechanism is the dominant conduction mechanism in the high field region. It was also observed that in the low electric field region Ohmic conduction is the dominant mechanism. Trap energy level (φ_t) of 0.36 eV, obtained from the Poole-Frenkel mechanism indicates that the defect is oxygen-related and is a good match with the reported value for V^-/V^- in HfO₂. Significant charge trapping at low level stress was observed whereas at high level and elevated temperature stressing suggests a variation of trap energy level indicating new defect formation. It is observed that the stress induced gate leakage current for the high temperature stressed devices is about three orders of magnitude more than that of room temperature stressed devices for the whole field range.