Rapid freeze-cleaning method

Abstract

Freeze cleaning involves the selective separation of particles from the substrate surface by utilizing the volume expansion that occurs when water in a supercooling state changes to ice. This allows particles to be efficiently and easily removed without causing pattern collapse. However, this method has a long processing time because of the following two factors: (i) the particles tend to remain at the four corners of a rectangular substrate; (ii) particle removal efficiency (PRE) per freeze-thaw cycle is low. These factors necessitated 30 repetitions of the freeze-thaw cycle to obtain sufficient removability over the entire substrate surface, which prolonged the processing time. Therefore, we attempted to improve the removability at the four corners of the substrate and PRE per freeze-thaw cycle. The experimental results showed that removability at the four corners of the substrate was enhanced by improving the discharge efficiency of particles separated from the substrate. Furthermore, the PRE per freeze-thaw cycle was improved by achieving a uniform temperature distribution across the substrate at the end of supercooling. These measures reduced the processing time to 1/6 and allowed us to successfully develop a device for mass production.