Reactive sputtering of TiN films at large substrate to target distances

Abstract

The paper is a critical review of the present status of the magnetron ion sputter plating of thin TiN films. Thus different possibilities of extracting high ion current l s from the magnetron discharge to substrates located not only at standard target to substrate distances d S-T of about 50 mm but also at larger distances d S-T are discussed in detail. Special attention is devoted to magnetron sputtering systems with enhanced ionization, to plasma confinement in the magnetron sputtering systems and to the discharge characteristics of an unbalanced magnetron (UM). It is shown that a UM can be operated in the regime of a double-site-sustained discharge (DSSD) and in this case large l s can be extracted to substrates located in large d S-T of about 200 mm and even at high pressures p = 5 Pa. A physical comparison of the conventional magnetron (CM), UM and DSSD is also given. Considerable attention is also devoted to the effect of ion bombardment on properties of TiN films created in the sputtering system using DSSD. It is shown that the microstructure of TiN films seems to be controlled by the combined parameter E p = e (U pl−U s) ν i/ ν m ∼ eU si s/a D, i.e by the energy delivered per condedering particle, where U pl is the plasma potential, U s is the substrate bias, ν i and ν m are the fluxes of ions and metal atoms impinging on the substrate, respectively, i s is the substrate ion current density, and a D is the deposition rate. At low negative biases | U s ⪅50 V, the microstructure of created TiN films strongly depends on i s . At low i s ⪅ 1 mA cm −2 porous black TiN films and at higher i s > 1 mA cm −2 compact, dense, bright golden TiN films are created independently of the distance d S-T . The colour of TiN films prepared in a DSSD, i.e. the brilliance L ∗ = 77–79 , the redness a ∗ = 0.3–0.8 and the yellowness b ∗ = 41–44 , compare well with the colour of the best TiN films prepared by standard ion plating and the cathodic arc processes. It has been shown that with DSSD good quality TiN films can be produced at distance d S-T up to 200 mm. In principle, the distance d S-T can be longer but the magnetic field strength must be sufficient at the substrate to ensure adequate plasma confinement in the space between the target and substrates. The DSSD represents a new qualitative step in magnetron sputter ion plating of thin films and the related sputtering system is also suitable for coating large three-dimensional parts and it is fully competitive with standard commercial deposition devices based on low voltage electron beam (LVEB), triode and arc evaporation.