The detection and prevention of air bubbles in immersion liquid

Immersion lithography has been proposed as a method for improving optical lithography resolution to 45 nm and below. The premise behind the concept is to increase the refraction index in the space between the lens and wafer by insertion of a high refractive index liquid in place of the low refractive index air that currently fills the gap. During the scanning and exposure process, immersion liquid is injected into the space between wafer and lens with certain inlet pressure and angle. Because the liquid will act as a lens component during the lithographic process, it must maintain high uniform optical quality. Air bubbles in immersion liquid will decay the optical quality of the fluid and must be concerned. In this paper, some preliminary experimental results are included. Four types of bubble formation during lithographic process are defined and discussed, and the corresponding preventive means are also proposed.