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A critical evalution of thermal mass flow meters



S A. Tison


Many semiconductor processes require that stable and known flows of gas be delivered to the processing chamber. The thermal mass flow meter (TMFM) is used almost exclusively in the semiconductor industry for the admission of process gases. While TMFM’s have been used in the semiconductor industry for over twenty years, much still remains to be understood about their behavior. The abundance of TMFM manufacturers that make instruments which are supposedly interchangeable complicates the use of TMFM’s because the instruments generally have different designs and performance. While some attempt has been made via written standards to address the specifications of the instruments, these standards do not address all performance issues and cannot eliminate the systematic errors in the original manufacturers calibration of the TMFM's. Further, the TMFM's used to measure the process gases are generally calibrated with nitrogen and "corrected" for other gases, but the correction factors are not well understood and are of questionable reliability. It is also important to understand how the TMFM's perform under conditions that differ from the laboratory conditions where they were calibrated and the measurement errors that are introduced as a result of these different operating conditions. This article presents data on the performance of five low-flow TMFM's, from different manufacturers, with full scale ranges of 1.5x10^-6-3.7x10^-6 mol/s (2-5 sccm).
Journal of Vacuum Science & Technology A


Tison, S. (1996), A critical evalution of thermal mass flow meters, Journal of Vacuum Science & Technology A, [online], (Accessed February 23, 2024)
Created January 5, 1996, Updated February 17, 2017