A substantially low pressure is required to prevent film oxidation and reduce the
contaminant density. A pressure of 10−5 Torr is sufficient, but lower pressures would
help reduce the density of contaminants in the film. At 10−5 Torr the mean free
path of gas in the chamber is approximately 8 meters, which without the unit of
measurement is often referred to as the Knudsen number. The mean free path can