The 1640 was the first MFC to enable SDS gas utilization at source pressures below 10 Torr. Configurations of the 1640 have been designed specifically for the requirements needed for flow control in ion implanters utilizing SDS dopant sources. The SDS source pressure is typically at 650 Torr when the source is full, and drops as the source gas is extracted. The 1640 PMFC is designed to extract gas below source pressures of 10 Torr. The 1640 PMFC thus improves source utilization and reduces the frequency of source bottle changes.
The 1640 for SDS applications is designed to function over the wide SDS source pressure range from 650 Torr to below 10 Torr and provide Full Scale dopant flows as high as 10 sccm. Since flow is controlled by controlling pressure there is not as much pressure coefficient effect as there is with most thermal MFCs. The 1640 is in use today on medium and high current as well as high energy implanters throughout the world. 1640s are also available for high pressure implant gases.
In the 1640, a Baratron® capacitance manometer monitors the pressure upstream of the critical orifice. This pressure is proportional to mass flow. The measured pressure is compared in the control electronics to the flow set point. A control signal is then generated to drive the proportional control valve to the conductance required to bring the actual control pressure (flow) into agreement with the flow set point.