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

摘要

The effects of varying the yttrium (Y) level in a (TaC)_(1-x)Y_x gate electrode on the structural and electrical properties of a hafnium (Hf)-based high-k metal-oxide-semiconductor (MOS) capacitor, including flatband voltage (V_(tb)), were evaluated. The composition of (TaC)_(1-x)Y_x was controlled by the power of pure TaC and Y targets in magnetron sputtering. The structure of the formed (TaC)_(1-x)Y_x film was that of either a face-center cubic (fcc) at all compositions of × ≤ 0.4 or amorphous at × > 0.5 after annealing at temperatures below 600℃. X-ray photoelectron spectroscopy (XPS) analysis revealed that the TaC and (TaC)I_xYx films all contained about 10% oxygen. The resistivity of the (TaC)_(1-x)Y_x films was invariant for all compositions of × < 0.5, but it increased with increasing annealing temperature up to 600℃ for compositions of × > 0.68. In the as-deposited case, the effective work function, which was estimated from the relationship between V_(tb) and the equivalent oxide thickness of the HfO_2 film, clearly changed from 4.8 to 4.3 eV as × increased. The V_(tb) of HfO_2 and HfSiO_x dielectrics could be controlled within 0.5 V after annealing at 500 ℃ by changing the composition of the (TaC)I_xYx film (in terms of x). Based on the experimental data, it is clear that (TaC)_(1-x)Y_x composites are candidate materials for n-metal gate electrodes in the gate-last process.