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How Low Can You Go? In Pressure That Is.

Designed for semiconductor, MOCVD, and other gas flow control applications that require a high purity all-metal flow path, the Brooks GF100 Series mass flow controllers deliver outstanding performance, reliability, and flexibility. Highlights of the GF100 series industry leading features include: ultra fast 300 millisecond settling time, MultiFlo™ gas and range programmability, optional pressure transient insensitivity (PTI), local display, extremely low wetted surface area, and corrosion resistant Hastelloy® sensor tube and valve seat. GF120XSD is an extension to Brooks GF100 Series thermal mass flow controller family (MFC). Designed for extreme low pressure operation, the GF120XSD has been optimized for the precise delivery of high value, low pressure specialty gases. At the heart of mass flow controller is the flow sensor which consists of two temperature controlled windings around a thin walled capillary tube. As flow passes through the tube (in a precise ratio to the main flow of gas through the body of the MFC), the gas molecules carry heat down the sensor tube from the first heated zone, raising the temperature in the second heated zone. The change in temperature is directly proportional to the mass flow rate of the gas in the tube. Due to the precise sampling (or flow-splitting) the sensor output is proportional to the total flow of gas flowing through the instrument. As the sensor tube ID is typically very small (0.010" ID), and due to the fact that control valves require some pressure drop for stable control, mass flow controller's generally require a differential pressure of 5-10 psid to drive the gas through the device. In microelectronic manufacturing, a wide range of gases are used including highly toxic gases for implant and deposition process.  For safe handling, these gases are often contained in specialty cylinders that can hold large quantities of the toxic gas at sub atmospheric pressures. This simplifies the transportation, handling and delivery of the gas, but creates challenges for the mass flow controllers used to precisely control the flow of gas to the process chamber.   As the gas is consumed the pressure drops, causing significant challenges to traditional mass flow controllers that require a relatively high differential pressure to drive the flow through the device. The Brooks GF120XSD utilizes a large bore, low pressure drop thermal flow sensor. By increasing the conductance of the flow sensor, less pressure is required to split off the sample gas for measurement. Combined with a high stoke precision control valve to further minimize the pressure drop, the GF120XSD can precisely control flow with <1/100th of an atmosphere of inlet pressure (and vacuum outlet pressure). This very low pressure operation makes it possible to utilize as much as 90% of the valuable low pressure specialty process gases, a ~ 40% improvement over conventional mass flow controllers. In a recent OEM qualification, the GF120XSD demonstrated best accuracy and flow stability at very low pressures, with flow stabilization time reduced by seconds compared to previous generations of Brooks low pressure mass flow controllers, further improving the efficiency of gas usage.

About The Author

Alexandra Davila
Global Product Manager

Alexandra is a global product manager for mass flow and pressure control products for semiconductor applications at Brooks Instrument.

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