Effect of Y Content in (TaC)1-xYx Gate Electrodes on Flatband Voltage Control for Hf-Based High-k Gate Stacks

Abstract

The effects of varying the yttrium (Y) level in a (TaC)1-xYx gate electrode on the structural and electrical properties of a hafnium (Hf)-based high-k metal–oxide–semiconductor (MOS) capacitor, including flatband voltage (Vfb), were evaluated. The composition of (TaC)1-xYx was controlled by the power of pure TaC and Y targets in magnetron sputtering. The structure of the formed (TaC)1-xYx film was that of either a face-center cubic (fcc) at all compositions of x≤0.4 or amorphous at x≥0.5 after annealing at temperatures below 600 °C. X-ray photoelectron spectroscopy (XPS) analysis revealed that the TaC and (TaC)1-xYx films all contained about 10% oxygen. The resistivity of the (TaC)1-xYx films was invariant for all compositions of x≤0.5, but it increased with increasing annealing temperature up to 600 °C for compositions of x≥0.68. In the as-deposited case, the effective work function, which was estimated from the relationship between Vfb and the equivalent oxide thickness of the HfO2 film, clearly changed from 4.8 to 4.3 eV as x increased. The Vfb of HfO2 and HfSiOx dielectrics could be controlled within 0.5 V after annealing at 500 °C by changing the composition of the (TaC)1-xYx film (in terms of x). Based on the experimental data, it is clear that (TaC)1-xYx composites are candidate materials for n-metal gate electrodes in the gate-last process.