Development of ionic liquid circulation system in high-vacuum chamber for semiconductor device fabrication

In this study, a high-vacuum-compatible liquid circulation system was developed using an ionic liquid with a very low vapor pressure as the working fluid. The rationale for the development of this device is the increasing need for wet processing under vacuum conditions for application to semiconductor fabrication, such as developing and rinsing. Wet processes generally use a large volume of liquid; therefore, they need to be conducted under atmospheric pressure. However, vacuum-compatible wet processes are desirable because high vacuum is beneficial for cleanliness and use of beam progression in fabrication processes. Therefore, a liquid circulation system that can be directly used under a high vacuum is needed. The system developed in this study can circulate over 100 mL ionic liquid under direct vacuum exposure, regardless of the inner chamber pressure. The usefulness of a prototype of this system was experimentally investigated. The system reached an ultra-high vacuum pressure of 10−5 Pa. Outgassed ionic liquid fragments were detected with low partial pressures of the order of <10−6 Pa. We concluded that this device can be exploited for semiconductor fabrication application.