Introduction Polycold Cryochiller
Theory of Operation Installation and Operation Manual
Brooks Automation
1-6
214072 Revision B
Legend:
A. Polycold Cryochiller Refrigeration Unit
B. Refrigerant line
C. Cryogenic feedthrough
D. Vacuum chamber wall
E. Cryosurface
Minimizing Oil Backstreaming From Diffusion Pumps
Backstreaming can occur any time oil diffusion pumps are used in high vacuum systems. Hot oil vapor
from a diffusion pump can migrate into the vacuum chamber and contaminate the system.
An optically-opaque cryogenic chevron baffle that is cooled by the Polycold Cryochiller is placed over
the diffusion pump to greatly reduce oil contamination due to backstreaming. This baffle also provides
additional water vapor pumping speed to the vacuum tool. This greatly improves vacuum system clean-
liness and leads to greater product quality and yield. Quick cooling and defrosting is not typically
required for such an application because the cold cryobaffle remains isolated behind a high vacuum
valve whenever the chamber is vented to atmosphere. See Figure 1-4 on page 1-7.
Optically transparent cryobaffles are also available from Brooks Automation Polycold. These baffles are
appropriate for increased water vapor pumping speed in turbomolecular pump applications.
Figure 1-3: Polycold Cryochiller Used for Water Vapor Capture
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