Thin Solid Films, 193/194(1990) 171-180 171 AN INVESTIGATION INTO THE VARIATION IN BOMBARDMENT INTENSITY FROM ION PLATING DISCHARGES BY SPUTTER WEIGHT LOSS EXPERIMENTS K. S. FANCEY AND A. MATTHEWS Research Centre in SurJace Engineering, Department oJ l~ngineering Design and Manufacture, University of Hull. Hull HU6 7RX ( U. K. ) Work is reported on the use of sputter weight loss measurements to characterize the spatial distribution of energetic species in typical d.c. diode and thermionic triode discharges. The findings highlight the influence of workpiece geometry on uniformity of bombardment in diode configurations. Furthermore, the use of an ionization-enhancing thermionic emitter is quantified, indicating that (i) it can impart an exponentially decreasing bombardment effect with distance from the emitter and (ii) bombardment has a preferred direction. We show that (i) is primarily related to the mean free path for impact ionization by thermionically emitted electrons and suggest that (ii) may be caused by anisotropic charge carrier motion in the plasma. These effects are discussed in relation to the relative location of ionization-intensifying electrodes and vapour sources in practical deposition systems. 1. INTRODUCTION Deposition plasmas can be investigated by a variety of techniques; for example, the use of electrostatic probes to measure plasma parameters is well documented. Provided that they can be operated without significantly distorting the plasma and that probe contamination does not cause measurement errors, information such as local charge carrier variations in the plasma volume may be evaluated (e.g. refs. 1 and 2). Optical emission spectroscopy can also provide spatially resolved infor- mation about the discharge (e.g. refs. 3-5). However, the inherent deficiency in these two methods is that they do not provide direct information on effects occurring at the substrate surface. We believe that the influence of the plasma at the substrate surface is of greater interest to practitioners of ion plating than a direct knowledge of spatial variations in fundamental plasma volume parameters. In view of this, we report on the results of sputter weight loss experiments, which provide direct information on plasma effects on samples mounted at different locations within the deposition chamber. The work expands on preliminary investigations which have been previously reported 6. Our aim here is to evaluate variations in bombardment intensity from argon d.c. discharges operated under conditions typically used in ion plating systems. 0040-6090/90/$3.50 © Elsevier Sequoia/Printed in The Netherlands