Morphology of Tantalum Nitride Thin Films Grown on Fused Quartz by Reactive High Power Impulse Magnetron Sputtering (HiP
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Morphology of Tantalum Nitride Thin Films Grown on Fused Quartz by Reactive High Power Impulse Magnetron Sputtering (HiPIMS) D. O. Thorsteinsson1, T. K. Tryggvason1 and J. T. Gudmundsson1,2 Institute, University of Iceland, Dunhaga 3, IS-107 Reykjavik, Iceland 2Department of Space and Plasma Physics, School of Electrical Engineering, KTH Royal Institute of Technology, SE-100 44, Stockholm, Sweden
1Science
ABSTRACT Thin tantalum nitride films were grown on fused quartz by reactive high power impulse magnetron sputtering (HiPIMS) while varying the fractional N2 flow rate at fixed substrate temperature of 400°C. The film properties were compared to films grown by conventional dc magnetron sputtering (dcMS) at similar conditions. Structural characterization was carried out using X-ray diffraction and reflection methods. The HiPIMS process produces slightly less dense films than does dcMS and the surface roughness is similar for both the HiPIMS and dcMS grown films. The deposition rate for HiPIMS is up to 80 % lower than for dcMS but it can be roughly doubled by lowering the magnetic field strength by 30 %. INTRODUCTION Thin films of sputter deposited tantalum nitride are widely used in microelectronics. Tantalum nitride is a chemically inert refractory compound, with good physical properties including high hardness, mechanical strength, and chemical thermal stability [1]. Furthermore, it has a high melting point of 3090°C and heat of formation ∆Hf of about −60 kcal/mol. The physical and mechanical properties of tantalum nitride thin films are largely dependent on the phase composition. By changing the growth conditions, tantalum nitride films can be used in wide ranges of applications, as structural elements in integrated circuits [2], as thin-film resistors [3], and as a diffusion barrier in copper based conductor lines for microelectronic applications [4, 5]. Furthermore, tantalum nitride thin films are also used as wear and corrosion resistant layers. The Ta-N system is inherently complex with more than 11 reported equilibrium and metastable phases [6]. The chemical and phase composition of as deposited TaNx films is known to be highly dependent on the growth conditions such as substrate temperature and the N2 fraction in the Ar/N2 mix [6]. High power impulse magnetron sputtering (HiPIMS) is a novel ionized physical vapor deposition (IPVD) technique that has received significant interest lately [7, 8]. By pulsing the target to a high power density with unipolar voltage pulses, a low duty cycle, and low frequency a high electron density is achieved [8]. Thus, it provides a high ionization fraction of the sputtered vapor and increased dissociation of the molecular gas in reactive sputtering. Increased ionization of the sputtered vapor has been demonstrated to improve the quality of the deposited film, such as increasing film density, in particular for substrates of complex shape, and improving surface roughness [7]. Tantalum nitride films have been deposited by reactive sputtering using dc sputtering [9], and both dc
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