スパッタ率測定へのマイクロバランスの応用

Abstract

The torsion vacuum microbalance technique useful for the determination of the sputtering yield of wall materials for fusion reactors was developed. In order to measure the rate of weight change of the samples during sputtering continuously, it is very important to keep the null point drift of the microbalance as small as possible. The deflection angle of the balance beam was detected and amplified by optical lever, and was transformed to electrical output by linear photopotentiometer. The null point drift was mainly caused by temperature change in the laboratory, which induced relative displacement by thermal expansion between the balance system and the optical measuring system. The drift was reduced less than the equivalent weight of 4 × 10 -7 g/hr when the balance system wosset in the thermostat kept at 20 ± 0.5 °C. The sensitivity of the balance was 8.3 × 10 -7 g/mV.The microbalance technique developed was applied to the measurement of sputtering yield of Cu by Ar+. The measurement was carried out with Ar+ ion energy of 0.22 keV, beam current of 0.51.5 μA, and sputtering time of 2 hrs. The initial weight of Cu sample was 0.4g (15 mm × 15 mm sheet) and the sample temperature during sputtering was about 120 °C. The sputtering yields obtained show good agreement with the results reported by Wehner et al. [8] and Weijsenfeld [9].