Prevention of oil vapor backstreaming in vacuum systems by gas purge method

Mechanical pumps have been used as roughing pumps in many vacuum systems because of the ease of their operation. However, it is a well known fact that heavy oil vapor backstreaming occurs when mechanical pumps are operated at pressures close to their ultimate pressure. This backstreaming oil vapor contaminates the vacuum system. Recently, oil contamination has become a serious problem in the semiconductor manufacturing process. In this paper, the results from experiments to prevent oil vapor backstreaming in a pipe that is 9 cm in diam. and 220 cm in length in the transition flow region, using gas purge is examined. Backstreaming oil is measured quantitatively with and without gas purge using a quadrupole mass analyzer and a differential pumping system. The results show that even in the transition flow region, oil vapor backstreaming is prevented by a small flow rate of purge gas.