試作マイクロバランスにおける微小重量変化の検出

概要

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With objection of absolute measurement of sputtering yield, the microbalance has been constructed. In the balance system, weight change was followed from observation of the deflection of the balance. The deflection was optically magnified and was converted to electrical output by means of a linear photopotentiometer. To the weaker deflection signal due to smaller weight change than the noise, separation of the signal from the noise was an important problem. Of the noises, the fluctuating noises were induced from 1) propagation of mechanical vibration (1070 Hz) to the balance and the optical alignment, and 2) propagation of sample oscillation to the balance (1Hz), and periodical thermal expansion or shrink of the optical alignment in the thermostatic room (0.02 Hz). The amplitude of fluctuating noises having higher frequency components than 1 Hz could be damped by a factor of 5 by the use of a low pass filter (cutoff frequency is 0.1 Hz). Then the amplifier gain to the deflection signal could be increased by a factor of 5. As a result of the improvement of S/N, the increase of the sensitivity from 5×10-7 g/mV to 7.3×10-8 g/mV was achieved. The minimum detectable weight change per hour was also reduced from 10-6 g/hr to 3.7×10-8 g/hr.
日本真空協会の論文