Nanosecond laser-induced surface damage growth and its mechanism of single crystal CaF₂ (111) at 193 nm.

The damage growth of calcium fluoride crystal (CaF2) induced by 193 nm laser irradiation poses a significant risk to the operation of deep-ultraviolet photolithography. It is crucial to explore the damage growth characteristics and mechanism of CaF2 crystal induced by a 193 nm laser for the safe operation of integrated photolithography systems. This paper analyzed the trend of 193 nm laser-induced damage growth of CaF2 crystal surfaces and obtained the damage growth coefficients and thresholds of three CaF2 crystal test samples. By analyzing the chemical composition variation and the electrical field modulation of initial damage, it was concluded that the laser-induced modification around initial damage and the electric field modulation at the center of initial damage would affect the damage growth properties. Meanwhile, the different absorption and growth thresholds of the same initial damage would also result in different damage growth characteristics. This research provides reliable information for improving CaF2 crystal's damage resistance ability and prolonging its lifetime in deep-ultraviolet lithography systems.