Impact of Laser-Induced Oxidation on Laser-Induced Damage Thresholds of Copper Thin Films

Laser-induced damage studies have applications in optical techniques using high-powered lasers, such as materials processing and metrology. Here we investigate laser-induced chemical changes using thin copper films exposed to a nanosecond UV laser due to their prevalence in electronics and material processing. In particular potential oxidation with atmospheric oxygen is studied due to Cu’s readiness to form oxide species (Cu2O, CuO and Cu(OH)2). Regions exposed to different laser fluences in ultra-high vacuum, 10−2 mbar O2 and air are characterized using optical microscopy to determine their damage threshold. The surface composition and oxidation state changes of the Cu layers close to the damage threshold are analyzed using ex situ X-ray Photo-electron Spectroscopy (XPS). The results show significant differences in damage behavior for UV illumination in ambient versus ultra-high vacuum, confirming the significance of atmospheric effects. XPS results suggest a possible systematic reduction of divalent Cu oxide species due to UV exposure, which can be the result of multiple damage-related mechanisms such as water film evaporation and different ablation thresholds of different species.