Enhanced utilization of SDS cylinder gases on the Eaton NV 8200P ion implanter

Safe delivery system (SDS) cylinders used in medium current ion implant applications deliver gas at flow rates of 0.2 to 2 sccm at cylinder pressures from 760 Torr to substantially below 50 Torr. Flow measurement and control using thermal methods has limitations in low flow, low inlet pressure applications that limit the amount of gas that can be extracted from an SDS cylinder. A flow control method using a capacitance manometer has been implemented on an Eaton NV-8200P ion implanter to increase the cylinder lifetime of a SDS gas cylinder. This paper presents flow data as a function of inlet pressure for several thermal mass flow controllers in a low flow/low inlet pressure application and shows the relative advantages of using a capacitance manometer flow measurement and control device to regulate the flow of gas to the source