Annealing of intrinsic stresses in sputtered TiN films: The role of thickness-dependent gradients of point defect density Harald Köstenbauer a, ⁎ , Gerardo A. Fontalvo a , Marianne Kapp b,c , Jozef Keckes b,c , Christian Mitterer a a Department of Physical Metallurgy and Materials Testing, University of Leoben, A-8700 Leoben, Austria b Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, A-8700 Leoben, Austria c Materials Center Leoben, A-8700 Leoben, Austria Received 3 August 2006; accepted in revised form 10 October 2006 Available online 20 November 2006 Abstract Morphology, structure and thermal behavior of magnetron sputtered TiN thin films with the thickness in the range 100–2900 nm are characterized. The films are thermally cycled and the relationship between film thickness, defect density and the intrinsic stress relaxation is analyzed. The results indicate that the residual stresses in the as-deposited films and the amount of stress relaxation depend decisively on the specific depth gradient of point defects originating from film evolution during growth. The compressive stresses, representing different driving forces and the amount of stress relaxation decrease, while the onset temperature of stress relaxation increases with increasing film thickness. © 2006 Elsevier B.V. All rights reserved. Keywords: Defects; Reactive sputtering; Titanium nitride; Stress relaxation 1. Introduction Understanding residual stresses in hard coatings is a pre- requisite for stress engineering, which could be a powerful tool to increase the lifetime of wear-protecting coatings on e.g. tools or engineering components. These stresses are composed of an intrinsic part resulting from growth defects and a thermal part caused by the mismatch in thermal expansion coefficients of coating and substrate. Previously, stress investigations were conducted on metal films up to 6 μm thickness where tensile residual stresses caused by grain boundary shrinkage obey a power law dependence on coating thickness [1,2]. For sputtered TiN hard coatings above 1 μm thickness a slight stress– thickness dependence was found [3,4]. The authors related this effect to the formation of point defects like implanted sputter gas atoms, self-interstitials, vacancies, line defects like disloca- tions [5], where the thickness influence was explained by an increasing coating porosity [4]. According to Kamminga et al. [3], it can be assumed that in sputtered TiN films point defects determine the growth stress. Not only residual stresses but also stress relaxation due to defect annihilation at elevated temperatures (often referred to as recovery), are of vital importance for high-temperature applications. Only a few investigations have been published on stress relaxation of hard coatings [4,6,7], and essentially nothing is known about thickness-dependent stress relaxation at elevated temperatures. Thus, it is the aim of this work to investigate the effect of thickness-dependent gradients of point defect densities present in sputtered TiN films in the thickness range between 100 and 2900 nm on residual stress and stress relaxation at elevated temperatures. 2. Experimental details TiN films of thicknesses between 100 and 2900 nm were deposited onto silicon (100) substrates (20 × 7 mm 2 , thick- nesses: 200, 300 and 450 μm) by reactive sputtering from a Ti target (∅ 75×6 mm 3 ) in an Ar + N 2 atmosphere using a laboratory-scale unbalanced DC magnetron sputtering system [8]. There, the substrates are stationary positioned in a distance of about 6 cm above the target. The substrate temperature and Surface & Coatings Technology 201 (2007) 4777 – 4780 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. E-mail address: harald.koestenbauer@mu-leoben.at (H. Köstenbauer). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.10.017