| 摘要 |
1,219,290. Ultrasonic thickness measurement; ultrasonic couplings. SOUTH AFRICAN INVENTIONS DEVELOPMENT CORP. 19 June, 1968, No. 29197/68. Headings H4D and H4J. Thin film deposition on a substrate is monitored by detecting changes in the velocity of an ultrasonic surface wave transmitted along the film and/or the substrate surface on which the film is deposited. In the Fig. 4 embodiment a transducer assembly A is clamped to end region 11a of a substrate 9 in an evacuated deposition chamber. Plate 10 shields the assembly A from material x being evaporated on to the substrate. The assembly A is used for (preferably pulsed) transmission and reception of a surface wave B and a bulk wave C which are reflected from end region 11b and interfere to produce a resultant signal. The bulk wave is substantially unaffected by buildup of the deposited film, but the build-up results in a velocity change of the surface wave and hence an amplitude change of the said resultant signal. This resultant signal, after frequency conversion in mixer 15, is demodulated at 17 and fed via gated amplifier 18 and diode pump integrator 19 to a recorder or indicator 20: it may also be used to control the deposition. The gating of amplifier 18 is such that multiple echoes from end 11b do not affect indicator 20. In an alternative embodiment transducer assembly A is used for transmission only and a similar assembly, clamped at end region 11b, is used for reception. Transducer details.-The transducer assembly (Fig. 1) comprises an X-cut quartz crystal 1 cemented to a damping block 3 and to a coupling member 2 in the form of a comb (e.g. of photo-etched phosphor bronze). Members 4 and 7, attached to block 3 by springs 5, clamp the comb to the substrate 9. Spring tension is adjusted by screw 8.
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