激光量热法测量深紫外氟化物薄膜吸收

Abstract

To obtain the relationship between the absorptances of thin-film materials and the incoming ultraviolet laser energy density, it is better to establish a standard measurement method. The principle and measurement process of laser calorimetry is introduced, the dose depending effect, nonlinear absorption, and unrecoverable absorption phenomenon that might influence the measurement results are analyzed, a method based on the laser calorimetry is proposed, which is used to measure the absorptance of fluoride coatings that can be used in 193 nm ultraviolet photolithography systems, and experiments. According to the new proposed method, the dose depending effect, the corresponding laser energy density while the unrecoverable absorption phenomenon appears when the fused silica substrates are irradiated by 193 nm laser are measured; the relationship between absorptances of substrates and the laser energy density are calculated. After that, two substrates are coated with LaF3 and MgF2 separately by boat evaporation; the relationships between absorptances of the coated samples and laser energy density are measured. By the comparison of absorptances before and after coating, the relationships of the two thin-film materials between absorptances and laser energy densities are calculated, and the absorptances of LaF3 and MgF2 in actual working condition are figured out, also the relationship between deposited temperature and absorptance, roughness, waviness of LaF3 is obtained. The experimental results confirm the feasibility of the proposed method, which help to improve the imaging quality and prolong the working life of the objective system that can be used in the photolithography system.