A New Quality Metric for III-V/High-k MOS Gate Stacks Based on the Frequency Dispersion of Accumulation Capacitance and the CET

This letter proposes a metric to assess the quality of high-k dielectrics on III-V substrates and a benchmarking methodology for the gate stack qualification in the region of MOS device operation above threshold voltage, V-t. The metric is based on a capacitive equivalent thickness (CET) - normalized frequency dispersion (D-eff) evaluated in the accumulation region of capacitance voltage (C-V) measurements of III-V MOS devices. Deff is found to be CET independent, which allows for a preliminary assessment of the dielectric quality by using relatively thick layers. Several gate stacks, single layer or bi-layer, including those with Al2O3, and the recently reported ASM-imec interfacial layer (IL) with HfO2 are evaluated and compared against Si MOS devices. Using the proposed technique, a clear difference between the various deposition processes is observed. The results indicate that the quality of a single layer Al2O3 or a bi-layer stack of Al2O3/HfO2 on InGaAs is significantly lower compared with Si gate stacks while the ASM-imec IL yields a gate-stack with good performance on the proposed quality metric. In addition, these results correlate well with the reliability performance of the studied gate stacks.