Adhesion and Removal of Micro Bubbles for Immersion Lithography

摘要

It is necessary to develop a nano-bubble detector similar as a conventional particle counter for reducing micro and nano defects caused by nano-bubble (NB) in immersion lithography. In this regard, we discuss adhesion and removal mechanisms of NB adhered on a resist surface for immersion lithography. The micro and nano bubbles are more likely to adhere to the micro defect on the resist surface and lens surface. Keeping cleanness of lens and resist surface is necessary in order to prevent the micro bubble adhesion. We employed the AFM (Atomic Force Microscope) for the observation of NBs on a Si substrate and a resist surface. The diameter and height of NBs observed are approximately 40～100nm and 3～8nm, respectively. By approaching the AFM tip onto the NBs, the repulsive force can be detected but the attractive force on the resist surface. The interaction analysis between the AFM tip and the ArF excimer resist surface is effective in order to identify the NBs and to distinguish from solid particles. These phenomena can be discussed on the basis of Lifshitz theory. The separation procedure of the NB is accomplished with the AFM tip. The applying load at which the NB can be separated into the minute one is approximately 5nN. In addition, by the thermodynamic analysis, it can be considered that the NB adhered on the resist surface tends to be a flat shape and spread on the resist surface. It is difficult to adhere the bubbles on the resist surface.