Investigations of Fast Vacuum Pump-Down Processes Between Parallel Isothermal Disks

To obtain optimal system throughput for semiconductor device fabrications, fast vacuum pump-down operations are frequently performed to quickly depressurize processing chambers for desirable pressure conditions. However, sudden and drastic temperature variations could occur at the beginning of a fast vacuum pump-down session, resulting in catastrophic consequences such as thermal shock and condensation-induced contamination, profoundly disturbing the otherwise well-conditioned mini-environment. To this end, the vacuum pump-down processes taking place between a pair of parallel isothermal disks resembling typical industrial applications (e.g., high-throughput load lock) are investigated by computational fluid dynamics (CFD) simulation and space-invariant theoretical modeling. It is discovered that the gas temperature first drops rapidly in a manner resembling isentropic gas expansion, and then quickly recovers at a rate governed by the pumping speed and a near-constant Nusselt number. In addition, it is discovered that attenuated temperature variations can be achieved with smaller disk separations and lower pumping speeds. Furthermore, a new empirical formula is proposed to calculate the Nusselt number based on a normalized time parameter, which not only better reflects the heat-transfer characteristics during pump-down than its well-known counterparts based on the Rayleigh number, but also enable efficient evaluations of various pump-down configurations with the space-invariant theoretical modeling.