Modelling of sputtering yield amplification in serial reactive magnetron co-sputtering T. Kubart a, ⁎, R.M. Schmidt b , M. Austgen b , T. Nyberg a , A. Pflug c , M. Siemers c , M. Wuttig b , S. Berg a a Solid State Electronics, The Ångström Laboratory, Uppsala University, Box 534, 751 21 Uppsala, Sweden b Institute of Physics (IA), RWTH Aachen University, 52056 Aachen, Germany c Fraunhofer IST, 38108 Braunschweig, Germany abstract article info Article history: Received 1 December 2011 Accepted in revised form 1 June 2012 Available online 9 June 2012 Keywords: Reactive sputtering Magnetron sputtering Deposition rate Oxide thin films TRIDYN Sputtering yield amplification Serial magnetron co-sputtering can be used to increase the deposition rate in reactive deposition of thin films. The increase in deposition rate is achieved by sputtering yield amplification through doping the sputtering target by a heavy element. The dopant is introduced by means of sputtering from an auxiliary tar- get onto a rotating primary magnetron. During sputtering of the primary target, the dopant is implanted into the target surface. Here we present a model describing the serial co-sputtering technique. The model is based on the binary collision approximation and takes into account the dynamical sputtering and mixing at the tar- get surface. As an example, W and Bi doping in reactive sputter deposition of Al 2 O 3 is analyzed. W is shown to be very efficient dopant which can increase the deposition rate for oxide up to 100% with 1.6 at.% of W in the resulting coating. Doping by Bi is not very effective due to the low surface binding energy of Bi. The simula- tions show that sputtering yield amplification can be realized in the serial co-sputtering setup with rotating magnetrons. © 2012 Elsevier B.V. All rights reserved. 1. Introduction One of the most common techniques for the deposition of com- pound thin films is reactive magnetron sputtering [1]. Due to its ver- satility and ease of up-scaling, it has many applications ranging from microelectronics to large area coatings on glass. Especially in the field of large area coatings, the low deposition rate and thus limited pro- ductivity for oxides is a major concern. This is related to the low sputtering yield of most oxides used as optical films [2]. In reactive magnetron sputtering, two distinct modes of operation exist. Stoi- chiometric oxide can be grown either at low rate in the so called oxide mode with a fully oxidized target, or in the transition region [3]. High deposition rates are possible in the transition region since the target is kept in the metallic state. Due to the hysteresis effect, however, this transition region is not stable and a feedback control is necessary [4]. As an alternative for the stabilization of the transition region [5], increasing the sputtering yield of the target material is another way to achieve a higher deposition rate for the same discharge power [6]. Recently, we have predicted that sputtering yield amplification (SYA) can be applied to reactive sputtering and leads to a very high deposition rate increase [7]. In SYA, the target material is doped by a heavy element in order to reduce the depth of the collision cascade. This increases the sputtering yield of the target atoms. As the doping element is sputtered together with the target atoms, the method is inherently limited to those applications which can tolerate the incor- poration of the dopant in the deposited coating. The model used in the previous study [7] assumed homogenous targets where the dop- ing element is evenly distributed. Production of such targets requires mixing on an atomic scale [6] and presents serious limitation for the practical realization of SYA. Serial co-sputtering is a technique to real- ize SYA as the dopant is deposited on the target surface and incorpo- rated by recoil implantation. This can be achieved using rotating systems where the target is periodically coated with a thin layer of a heavy element and sputtered [8]. Initial experiments showed about 80% increase in the deposition rate of Al 2 O 3 by W doping using serial co-sputtering [9]. Cylindrical rotating magnetrons are frequently used in industrial applications especially for large area coatings because they can be scaled up easily. The serial co-sputtering was shown to be a reliable technique for deposition of alloys combining the advantages of co- sputtering and sputtering from alloy targets [8]. If SYA can be realized using such a setup, the whole process is suitable for industrial appli- cations. A schematic sketch of a serial co-sputtering arrangement is shown in Fig. 1. It consists of a cylindrical rotating primary magnetron with a target made of the metal to be deposited. Doping is introduced by means of an auxiliary planar magnetron, which deposits the dop- ant on the back side of the primary target. It is then brought to the primary erosion zone by target rotation. Subsequently it is implanted into the primary target surface by recoil implantation. In order to assess the industrial potential of SYA in serial co-sputtering, it is necessary to evaluate the range of operating conditions for SYA as well as the enhancement of sputtering yield for different materials. There- fore, we present here a model for serial co-sputtering with cylindrical Surface & Coatings Technology 206 (2012) 5055–5059 ⁎ Corresponding author. Tel.: +46 18 471 7257; fax: +46 18 55 50 95. E-mail address: Tomas.Kubart@angstrom.uu.se (T. Kubart). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2012.06.005 Contents lists available at SciVerse ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat