Electrical Measurements to Detect Liquid Concentration

A special container is made to detect the liquid contents used in the semiconductor manufacturing process by electrical measurements in both static and dynamic conditions. For static measurements, the capacitance measurement shows the dispersive capacitance resulting from ionic response at low frequency (<2 kHz). However, it has negligible dispersion and is immune from the air exposure at high frequency (≥2 kHz). In addition, the capacitance and the corresponding dielectric constant show good linearity with respect to the IPA concentration at 20 kHz, indicating that it is a sweet spot to determine the liquid contents. The resistivity is independent of the measurement frequency (20 Hz to 200 kHz). However, it is sensitive to the exposure time to the air due to the atmospheric moisture and carbon dioxide dissolved in the liquid. For dynamic measurement, the longer transition time is observed when high-density liquid is flushed with low-density liquid, as compared to the other way around.