Tungsten-carbon thin films deposited using screen grid technique in an electron cyclotron resonance chemical vapour deposition system

Abstract

A new technique for depositing metal-carbon (Me-C:H) thin films is proposed based on two metal screen grids embedded within an electron cyclotron resonance chemical vapour deposition (ECR-CVD) system. The grids are negatively biased and supported at adjustable distances above the substrate holder in the deposition chamber. With source gases of methane and argon, sputtering of the metal grids by Ar+ results in the incorporation of metal in the growing carbon films. The amount of metal in the films can be very well controlled over a wide range by varying the bias voltage of the grids, the separation of the grids from the substrate holder and the ratio of CH4/Ar. Furthermore, by separately biasing the substrate holder, the properties of the films can be varied resulting in the formation of a great variety of Me-C:H films with very different mechanical and structural properties. Tungsten incorporated carbon films (W-C:H) were deposited using this technique with two tungsten (W) grids biased at -330 V. The fraction of W in the films was controlled by varying the flow ratio of CH4/Ar. The films were characterized using Rutherford backscattering and X-ray photoelectron spectroscopy measurements, and also in terms of their conductivity, optical absorption and hardness. The conductivity was found to increase by six orders of magnitude whereas the optical gap decreased by 1.5 eV with an increasing atomic fraction of W in the films from 2% to 8%. WC bonds were not detected, and the W detected was mainly in the form of WO2 and WO3. (C) 2000 Elsevier Science S.A. All rights reserved.