ELSEVIER Surfaceand Coatings Technology 99 (1998) 266-273 a'R/-AIgE COATINGS 17t##OLO6Y Spectroscopic studies of a magnetron sputtering discharge for boron nitride deposition R. Pintaske *, Th. Welzel, M. Schaller, N. Kahl, J. Hahn, F. Richter Technische Universitiit Chemnit:, Institut fiir Pt~ysik, D-09107 Chemnit:, Germany Received 17 June 1997: accepted 23 September 1997 Abstract Magnetron sputtering discharges for the deposition of cubic boron nitride have been investigated using optical emission spectroscopy and Langnmir double probes. Spatially resolved measurements revealed the inhomogeneous discharge structure with respect to the distribution of excited species, electron density and electron temperature. The optical emission spectra were analysed by means of the corona model. The vibrational excitation of the nitrogen molecule was examined. The ratio of selected Ar and N2 emission intensities provided a qualitative measure of the electron temperature, which was determined by probe measurements. However, the intensity ratios of Ar and Ar + lines did not correspond to changes in electron temperature. Varying the electron density in a wide range, it could be demonstrated that the excitation mechanisms do not remain constant, mainly due to multi- step excitation. The vibrational temperature of N2 (CaYI,) has been ~bund to be much higher in the case of r,f. sputtering than in the d.c. mode. © 1998 Elsevier Science S.A. Keywords: Magnetron sputtering; Optical emission spectroscopy: Corona model; Langmuir probe: Boron nitride 1. Introduction Low-pressure glow discharges have been widely used for thin film deposition and surface modification. In order to study their basic properties and behaviour, optical emission spectroscopy (OES) is a favoured in-situ diagnostic technique (e.g. for end-point detection [1,2], study of the temporal behaviour of discharges [3,4], determination of the velocity distribution [5,6], actinometry [7,8], and impurity detection), In most cases, optical emission spectra can be acquired without any problems. However, using OES only excited species can be detected. To obtain reliable information concern- ing ground-state densities or plasma excitation temper- atures, detailed knowledge of the excitation mechanisms is required. Other diagnostic methods are able to support OES (e.g. mass spectroscopy, electrostatic probes and laser-based techniques). In this paper we present a study of magnetron sputter- ing discharges used to deposit cubic boron-nitride thin films. The plasma was characterised by optical emission spectroscopy and Langmuir double probes. The aim of the current investigation was to check to what extent * Correspondingauthor. OES can supply reliable information on the discharge with regard to excitation mechanisms. 2. Experimental The circular magnetron sputtering system employed (see Fig. l ) has been used to deposit thin boron nitride films containing a considerable amount of the cubic phase [9]. The magnetron sputtering source could be driven by either an r.f. (13.56 MHz) or a d.c. power supply. Hexagonal boron nitride and pure boron disks == ( 100 mm in diameter) were used as the sputtering targets. On heating the boron target, its intrinsic electrical conductivity becomes high enough to sustain a stable sputtering discharge in the d.c. mode. The substrat~ holder ( 150 mm in diameter) was separately r.f.-powered yielding a d.c. bias voltage of up to -400V. Both electrodes formed a parallel plate arrangement with an electrode distance of 100 ram. The total pressure has been varied in the range from 0.1-4 Pa. The sputtering atmosphere consisted of nitrogen, argon, or a mixture of both gases. The observation axis for the OES was parallel to the surfaces of both electrodes. The light emitted by the 0257-8972/98/$19.00 ,~;, 1998Elsevier ScienceB.V. All rights reserved. PII S0257-8972(97)00566-5 =