Reduction of water contamination in a vacuum load lock during pumping from atmosphere

摘要

Rapid pumping causes adiabatic cooling. A dramatic drop in temperature (-35°C) causes the formation of a dense water aerosol in an ordinary vacuum chamber or load lock during routine pumping from atmosphere. In this study we have carefully measured the dynamic temperature response between parallel wafers located in load locks whose time constants are of pratical interest using a unique thermocouple technique. We have also measured the water aerosol formation with particle counters located in the foreline of a load lock as a function of chamber wall spacing. Finally, a model for a load lock which will not transport particles, or cause water vapor condensation has been constructed. This model shows that the water aerosol will not form, if parallel wafers located in the x—y plane are spaced less than or equal to 5 mm apart, and the pump port is located on the (0, 0, z) axis.