Effect of Y Content in (TaC)_1-xY_x 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) 1Àx 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 fb ), were evaluated. The composition of (TaC) 1Àx Y x was controlled by the power of pure TaC and Y targets in magnetron sputtering. The structure of the formed (TaC) 1Àx Y x 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) 1Àx Y x films all contained about 10% oxygen. The resistivity of the (TaC) 1Àx Y x 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 asdeposited case, the effective work function, which was estimated from the relationship between V fb and the equivalent oxide thickness of the HfO 2 film, clearly changed from 4.8 to 4.3 eV as x increased. The V fb of HfO 2 and HfSiO x dielectrics could be controlled within 0.5 V after annealing at 500 C by changing the composition of the (TaC) 1Àx Y x film (in terms of x ). Based on the experimental data, it is clear that (TaC) 1Àx Y x composites are candidate materials for n-metal gate electrodes in the gate-last process. #

(Invited) Mechanism of Vfb Shift in HfO2 Gate Stack by Al Diffusion from (TaC)1-xAlx Gate Electrode

“…We confirmed that the structure of (TaC) 1-x Al x films consist of the FCC of TaC in all compositions. The lattice constant of (TaC) 1-x Al x films shows almost same value in all compositions, while the lattice constant value of the (TaC) 1-x Y x films increased with increasing Y content (21). This behavior can be explained by the difference in the ionic radius among Ta (0.068 nm), Y (0.106 nm) and Al (0.057 nm) atoms.…”

“…Figure 3 shows the Vfb change as a function of x value in (TaC) 1-x Al x gate electrodes after PMA at 400 -600 °C. The Vfb data for (TaC) 1-x Y x /HfO 2 MOS capacitors are also plotted in the figure (21). It is clear that the Vfb shift towards a negative direction as the x value in (TaC) 1-x Al x gate electrodes increases regardless of the annealing temperature.…”

“…On the other hand, nitrogen-free TaC has emerged as a promising gate electrode because of high mobility and thermal stability (18)(19)(20). We reported that the φ m,eff could be easily controlled by introducing a Y atom with a low work function of 3.1 eV to TaC materials (21). However, effect of Al atoms in Al-incorporated TaC ((TaC) 1-x Al x ) gate electrodes on Vfb has not been understand yet.…”

Mechanism of Vfb Shift in HfO2 Gate Stack by Al Diffusion from (TaC)1-xAlx Gate Electrode

“…On the other hand, nitrogen-free TaC has emerged as a promising gate electrode because of high mobility and thermal stability [6,7]. However, effect of Al atoms in Al-incorporated TaC ((TaC) 1-x Al x ) gate electrodes on Vfb has not been understand yet.…”