Tungsten oxide thin films chemically vapor deposited at low pressure by W(CO)(6) pyrolysis

Tungsten oxide thin films were grown by chemical vapor deposition at low pressure (0.1 Torr) and at temperatures ranging between 450 and 600 degrees C, in a cold wall horizontal reactor by pyrolysis of W(CO)(6) vapors. A small air flow through the reactor induces the growth of remarkably well-textured polycrystalline WO3 films, oriented with the < 010 > crystallographic axis perpendicular to the substrate as shown by x-ray diffraction and atomic force microscopy measurements. The films were grown on silicon wafers covered by SiO2, Si3N4, and polycrystalline silicon; the film texture was not influenced by the nature of the substrate. In the absence of oxygen during deposition the x-ray diffraction patterns show peaks corresponding to W3O (beta-tungsten) and to body centered cubic tungsten. These films exhibited metallic or insulating properties depending on the deposition temperature, as determined by resistivity measurements within the range 77 to 350 K. The metallic character was enhanced at lower temperatures. After thermal annealing of these films at 1000 degrees C for 10 s in medium vacuum (2 x 10(-2) Torr) their character changed to purely metallic. The x-ray diffraction patterns taken after annealing show peaks corresponding to body centered cubic W and WO2.