Highly Sensitive Trace Moisture Ball Surface Acoustic Wave Sensor Using Siox Film

Regarding the gases for the manufacturing process of semiconductor devices, fast and sensitive sensors are needed to control trace moisture to less than 1 mu mol/mol. A ball surface acoustic wave (SAW) sensor is promising technology for this purpose. In this study, we verify the response of a sol-gel SiOx film-coated ball SAW sensor to extremely low-concentration moisture using a cavity ring down spectroscopy (CRDS), the most sensitive commercially available moisture sensor, as a reference sensor. We clearly measured 17 nmol/mol moisture by developing a sensor cell using metal O-rings reducing the leakage of moisture. The response time from 390 to 790 nmol/mol was one tenth of that for the CRDS, and the detection limit was estimated to be as low as 0.2 nmol/mol. (C) 2014 The Japan Society of Applied Physics