Pressure based mass flow control for ion implant SDS applications

Thermal mass flow control (MFC) has been used to control the flow of gas in semiconductor process systems for many years. With the introduction of SDS gas sources for ion implantation, improvements in mass flow control technology were required to maximize cylinder yield and effect a corresponding reduction in operating cost. Pressure-based MFC (PMFC) is an alternative to thermal flow control technology. Discussed are the design and operating principles of PMFC´s utilizing the principal of “choked” (sonic) flow for applications with inlet pressures to below 10 torr. A comparison is made between the PMFC and thermal MFC techniques. A significant increase in throughput per bottle is presented for a device with 6 torr inlet pressure capability