Measurements of the dynamic contact angle for conditions relevant to immersion lithography

Abstract

The semiconductor industry has used optical lithography to create impressively small features. However, the resolution of optical lithography is approaching limits based on light wavelength and numerical aperture. Immersion lithography is a means to extend the resolution by inserting a liquid with a high index of refraction between the lens and wafer. This enables the use of higher numerical aperture optics. Several engineering obstacles must be overcome before immersion lithography can be used on an industry-wide scale. One such challenge is the deposition of the immersion liquid onto the wafer during the scanning process; any residual liquid left on the wafer is a potential defect mechanism. The residual liquid deposition is controlled by the details of the fluid management system, and is strongly dependent on the three-phase contact line. Therefore, this work concentrates on understanding the behavior of this contact line, specifically by measuring the dynamic contact angle and the critical velocity for liquid deposition. A contact angle measurement technique is developed and verified; the technique is subsequently applied to measure the dynamic advancing and receding contact angle for a series of resist-covered surfaces under conditions that are relevant to immersion lithography.