STRUCTURE AND OPTICAL-PROPERTIES OF TUNGSTEN THIN-FILMS DEPOSITED BY PYROLYSIS OF W(CO)(6) AT VARIOUS TEMPERATURES

Tungsten thin films, 200 nm thick, have been chemically vapor deposited by pyrolysis of W(CO)6 on oxidized silicon substrates at atmospheric pressure and temperatures varying from 350 to 500°C. The structure of the films has been studied with x-ray-diffraction measurements and it was found that at deposition temperature of 350°C a face-cubic-centered phase is formed with a unit-cell dimension of 0.4111 nm. At higher temperatures, up to 450°C, the deposited films crystallize in a body-cubic-centered phase of tungsten with a unit cell of 0.317 nm. The complex dielectric constant (ε=ε1+iε2) of the films has been measured with spectroscopic ellipsometry within the energy range 1.5-6.5 eV. The energy variation of ε1 changes with deposition temperature; instead, that of ε2 does not change significantly with it. The energy variation of ε1 for the films deposited at temperatures below 400°C corresponds to that of insulators while that of films deposited at higher temperatures, up to 450°C, reveals their metallic character. © 1995 American Institute of Physics.