Thermally accelerated photochemical damage in CaF₂ under DUV irradiation

CaF₂ optical components are critical elements in DUV lithography systems, and their performance degradation directly impacts system reliability. The simultaneous thermal and photochemical effects of deep ultraviolet (DUV) nanosecond light source irradiation on optical elements' intricate component irradiation damage mechanisms, posing challenges for accelerated lifetime studies. Therefore, this study examines the combined accelerating impact of photothermal and photochemical effects on component damage by contrasting the damage evolution under different deep ultraviolet laser irradiation scenarios. The consistency observed between the absorption spectra and XRD characterization results indicates that photochemical effects dominate in the initial irradiation stage, manifested by the irradiation-induced generation of M centers and the development of tensile lattice strain. However, accelerated irradiation amplified the UV absorbance by about 10⁴ compared to real-time irradiation. Contamination increased the RMS roughness by 10∼10² relative to non-accelerated samples, and the average UV absorbance rose by 19.93%. Therefore, the thermal effects of irradiation influence the photochemical processes and surface roughness of optical elements by promoting defect generation and aggregation, internal stress states, and contaminant reaction rates, respectively.