Plasma-enhanced atomic layer deposition of WO3-SiO2 films using a heteronuclear precursor

Tungsten oxide-silicon dioxide (WOx-SiOy) composite thin films were deposited for the first time via the remote oxygen plasma-enhanced atomic layer deposition (ALD) process using a novel metal-organic heteronuclear and heteroleptic precursor, bis(tert-butylimido)bis(trimethylsilylmethyl)tungsten. Self-limiting ALD growth was demonstrated over a wide temperature window of 203-328 degrees C with growth per cycle decreasing with increasing temperature from 0.75 to 0.4 angstrom/cycle, respectively. Residual gas analysis revealed ligand competition and showed that ligand reaction during ALD nucleation and growth was a function of deposition temperature, thereby affecting the film composition. As the temperature increased from 203 to 328 degrees C, the film composition [W/(Si + W)] ranged from 0.45 to 0.53. In addition, the carbon impurity content was reduced and the refractive index increased from 1.73 to 1.96, the density increased from 4.63 to 5.6 g/cm(3), and the optical bandgap decreased from 3.45 to 3.27 eV. Grazing angle x-ray diffraction indicated that as-deposited films were amorphous. Upon annealing in O-2 at 500 degrees C or higher, depending on deposition temperature, films are crystalized into the triclinic WO3 phase. At the same time, WO3 is sublimed from the surface and films are reduced in thickness. Published under an exclusive license by the AVS.