K. Laing et al., The effect of ion current density on the adhesion and structure of coatings deposited by magnetron sputter ion plating, SURF COAT, 112(1-3), 1999, pp. 177-180
Recent work using an improved design of an unbalanced magnetron in a four-m
agnetron closed-field arrangement has resulted in exceptionally high ion cu
rrent densities at the substrates during both ion cleaning and deposition.
The ion current at the electrically biased substrate is increased by a fact
or of close to 100 as compared to balanced magnetrons of the same polarity.
The absolute ion current is dependent on a number of factors which are dis
cussed, the most important being the power applied to the magnetrons. The r
elationship between substrate bias and ion current is presented. It is foun
d that it is possible to achieve very high ion currents at bias voltages as
low as - 50 V. The effect of the substrate bias voltage and the substrate
ion current on the coating structure have been studied, and it is found tha
t the optimum conditions for the deposition of dense coherent coatings with
low internal stresses are a high ion current at a low bias voltage. These
conditions are readily achieved using the closed-field unbalanced magnetron
technique. It is shown that coating structure is almost independent of dep
osition rate, which is extremely important for the deposition of coatings w
ith excellent structures at low temperatures. Ion cleaning prior to deposit
ion is carried out with the magnetrons operating at low power. This allows
the plasma discharge to strike and be maintained at low arson a pressures,
thus avoiding contamination from the chamber walls, etc. The enhancement of
the ion current under these conditions is similar to that achieved during
deposition, i.e. around 100 x, and so the efficiency of ion cleaning is con
siderably enhanced, producing a "clean" surface which results in excellent
adhesion. Scratch adhesion testing has been used to compare the critical lo
ads for coatings deposited with different cleanings conditions and the exce
llent adhesion achievable is demonstrated. (C) 1999 Elsevier Science S.A. A
ll rights reserved.