Effect of nitrogen addition on the properties of C:F thin films deposited by RF sputtering

Laboratory for Electrostatics and Dielectric Materials (LEMD), French National Centre for Scientific Research (CNRS) and Joseph Fourier University (UJF), LEMD-CNRS, BP 166, 38042 Grenoble Cedex 9, France

Corresponding author: patrice.gonon@grenoble.cnrs.fr

Received: 14 December 2004
Revised: 29 March 2005
Accepted: 24 June 2005
Published online: 25 October 2005

Abstract

Fluorocarbon (C:F) and nitrogen-doped fluorocarbon (C:F:N) thin films are deposited by RF magnetron sputtering using a polytetrafluoroethylene (PTFE) target and Ar or Ar/N₂ sputtering gas. Properties of C:F:N films are compared to those of C:F films. They are studied using X-ray Photoelectron Spectroscopy (XPS), Infra-Red (IR) transmission spectroscopy, Thermo-Gravimetric Analysis (TGA), impedance spectroscopy, and current-voltage measurements. By adding nitrogen to the sputtering gas, XPS shows that nitrogen substitutes for fluorine leading to a decrease in the relative concentration of CF_x species, to an increase in C-C bonds, and to the appearance of specific CFN bonds. There is also a new IR band at 1350 cm^-1 whose origin is uncertain (CN bonds or disordered sp² carbon). Thermal stability is not improved upon nitrogen addition (the C:F and C:F:N films both decompose above 200 °C). Dielectric properties (dielectric constant and loss) are only slightly affected by nitrogen doping. The DC transport properties are modified upon nitrogen addition (C:F:N films display a higher resistivity and a supra-linear behaviour at high fields indicative of field-enhanced tunnelling transport).