SLowFlowS: A novel flow standard for semiconductor process gases

Numerous process gases are used in the production of semiconductor chips. Accurate metering of these gases into process chambers is critical for maximizing device throughput and yield. A national flow standard for semiconductor process gases does not exist, forcing the industry to rely on approximate "meter factors" to extrapolate a meter calibration carried out with nitrogen to the actual process gas. To address this issue the National Institute of Standards and Technology (NIST) developed a novel rate-of-rise flow standard featuring long, slender tubing for the collection tank geometry. This design, paired with an air bath for thermal stability, ensures efficient heat transfer and accurate temperature prediction during the filling process. This standard will enable modeling the species effects of commercial flow meters and controllers. These models will enable a meter calibrated with nitrogen to provide accurate measurements of hazardous semiconductor process gases. We describe the design, experimental validation of the thermodynamic model, tests of the new flow standard, and uncertainty analysis. The standard is called SLowFlowS (Semiconductor Low Flow Standard), and it has an expanded uncertainty (95 % confidence level) between 0.056 % and 0.098 % of the flow and covers a flow range of 0.01 cm³/min to 1000 cm³/min at the standard conditions of 273.15 K and 101.325 kPa.