Mechanism of immersion specific defects with high receding-angle topcoat

Abstract

A dynamic receding contact angle (RCA) is a well-known guideline to estimate the degree of watermark (WM) defects, which shapes circle and bridges inside of the defect and reduces with enlarging the RCA of topcoat (TC). However, our recent investigation revealed the occurrence of the circular shape defects in spite of using the TC with a large RCA, bringing about a change of line and space pattern pitch. In this paper, we clarify the origin of these defects and propose a new key factor of the dynamic surface properties of immersion-specific defects. It was found that the pitch-change defect is caused by the lens effect of the air bubbles embedded between advancing water meniscus and the TC. To well understand generation of the bubble defects, we defined the "effective" hysteresis (EH) as the hysteresis of dynamic contact angle taken the effects of water-absorption into account. An analysis with the EH indicates that the bubble defect arises from not only to the large ACA but also small amount of water uptake and the amount of water-absorption could be substituted by the dissolution rate of TC. It was demonstrated that the EH proposed is a new key factor for estimating the number of bubble defects. The EH is very useful for analyzing the bubble defects in immersion lithography. The characteristics of the bubble defect are also discussed with a focus on the structure of the polymer attached to water.