Nitrogen-purged Minienvironments Keep Wafers Cleaner

Wayland, MA–Portable Clean Rooms has just concluded extensive beta testing with advanced prototypes of its new, nitrogen-purged Class 1 minienvironments for IC fab use. Test results show that wafers stored in Portable Clean Rooms` minienvironments had one-third the amount of particles on them than wafers stored in polycarbonate wafer carrier boxes. In addition, test results show that isolation in a nitrogen-purged environment retards oxidation on semiconductor surfaces.

The company has produced two basic types of nitrogen-purged minienvironments–150 mm and 200 mm Portable Clean Rooms–to permit isolated transport of wafers and masks and other surface-sensitive substrates.

The 150 mm Portable Clean Room has a canister containing 57 liters of high purity (99.99999 percent) VLSI-grade nitrogen. The canister is covered with a bonnet that threads securely to the chamber-top via a large ring. The minienvironment is carried with a handle on the bonnet`s top. The nitrogen flows at a regulated rate through a pressure regulator. A separate fitting sits on the regulator mount to accept a house nitrogen fitting for quick filling of the chamber. Before the nitrogen enters the chamber, it passes through the last subsystem–a filter assembly containing a prefilter and an absolute filter. The supply of nitrogen is about 100 hours at a 100 percent duty cycle.

The 200 mm Portable Clean Room uses the same principle as the 150 mm unit. It maintains an overpressure condition with inert nitrogen. A set of handles on its base and the chamber-top allow portability.

For more information contact: Portable Clean Rooms, Wayland, MA (508) 358-4969–LC. n