Many semiconductor manufacturing process steps require a mid- to high-level of vacuum in the process chamber to operate effectively. The optimum pumping package for each application depends on the type and amount of gases to be pumped (which are typically reaction byproducts or purge gas), the chamber size, pumping speed required and ultimate pressure required.
These include CVD, silicon epitaxy, plasma etch, ion implantation, PVD/sputtering and plasma stripping. Gas loads vary from a few sccm in ion implant systems to over a hundred sccm in CVD and etch.
Typically wafers are transferred to the chamber through a load-lock. So-called “roughing” pumps — which can be rotary vane, dry pumps (claw, screw or scroll) or “Roots blowers” – are used to take the pressure from atmospheric pressures to around 10-2 to 10-3 Torr. Then high vacuum pumps, typically turbomolecular pumps or cryogenic pumps take over to achieve process-level pressure. Roughing pumps are often located in the sub-fab below the tool. Turbos and cryos are often located very close to the process chamber, inside the tool, but can also be located in the sub-fab.
Turbo pumps use rapidly spinning blades to impart direction to gas molecules, propelling them through multiple stages of increasing pressure. Magnetic bearings are used to levitate the pump drive shaft and eliminate the need for lubricating oil.
The latest primary pumping mechanism to be introduced is the regenerative pump, which uses a single, high-speed rotor to impart momentum to the gas, compressing it through several stages to atmospheric pressure.
Fundamentals of Vacuum Technology
Current and future trends in vacuum process technology