Investigation on the sputtering effects on r.f. plasma processing

The effects of plasma bombardment variations at the substrace surface in hihg-frequency (13.56 MHz) r.f. glow discharges, as are commonly utilized in various PVD processes, were investigated by means of a series of sputter weight loss experiments. The weight losses on small substrates, removable from a larger cathode arrangement, mounted in various positions in the chamber were recorded after exposure to a series of glow discharges maintained at a range of argon pressures and power densities. Therefore, the relationship between ion bombardment intensity and sputter removal at the substrate could be determined at different locations in the deposition volume. The results were compared with previous work in which similar experiments were performed in d.c. and low-frequency (380 kHz) glow discharges and hence the degree of sputtering uniformity in each of these discharge systems could be ranked. The findings show that high-frequency glow discharges behave similarly to the d.c. diode system at low pressures and at elevated pressures the bombardment characteristics are similar to a low-frequency discharge. The work is significant for coating and plasma treatment applications because of the profound effects that ion bombardment has, for example, on coating thickness uniformity, coating structure and diffusional effects.