An ultrasensitive silicon pressure-based flowmeter

An ultrasensitive silicon pressure-based flowmeter has been developed for use in measuring sub-SCCM gas flows in semiconductor process equipment. The device utilizes a capacitive pressure sensor to measure the pressure drop induced by flow across a micromachined silicon microchannel. The flowmeter is fabricated using a single-sided dissolved-wafer process and requires only six masks. The processed silicon wafer is electrostatically bonded to a glass substrate and the wafer is selectively etched away, using boron etch-stops to define the final silicon-on-glass device structure. The capacitive pressure sensor uses a thin (2.2- mu m) stress-compensated membrane, which enables the sensor to monitor differential pressure as low as 1 mtorr while withstanding overpressures greater than 700 torr. The flowmeter is capable of measuring flows in the 10/sup -5/ SCCM range.<>