科研之友
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摘要
The measurement and control of trace moisture, where the water concentration is lower than 1 ppmv [-76.2 degrees Cfor the frost point (degrees CFP)], are essential for improving the yield rate of semiconductor devices and for ensuring their reliability. Aball surface acousticwave (SAW) sensor with a sol-gel silica coating exhibited useful characteristics for a trace moisture analyzer (TMA) when the temperature drift of the delay time output was precisely compensated using two-frequency measurement (TFM), where the temperature-compensated relative delay time change (RDTC) was obtained by subtracting the RDTC at the fundamental frequency from that at the third harmonic frequency on an identical propagation path. However, the cost of the measurement circuit was a problem. In this study, a burst waveform undersampling (BUS) circuit based on the theory of undersampling measurement was developed as a practical means. The BUS circuit was useful for precise temperature compensation of the RDTC, and the ball SAWTMA was prototyped by calibrating the RDTC using a TMA based on cavity ring-down spectroscopy (CRDS), which is the most reliable method for trace moisture measurement. The ball SAW TMA outputted a similar concentration to that obtained by the CRDS TMA, and its response time at a set concentration in N-2 with a flow rate of 1 l/min was about half that of the CRDS TMA, suggesting that moisture of -80 degrees CFP was measured within only 1 min. The detection limit at a signal-to-noise ratio of 3 was estimated to be 0.05 ppbv, comparable with that of the CRDS TMA. From these results, it was demonstrated that a practical ball SAWTMA can be realized using the developed BUS circuit. Published by AIP Publishing.
- 出版日期2018-5
