Corrosion behavior of aluminum in fluoride-containing discharge condition for excimer laser structure application

Aluminum is widely used as the discharge chamber structures of excimer lasers which are important high-power UV-band lasers. Corrosion behavior of aluminum in fluoride-containing discharge condition greatly affects the laser output by consuming fluoride medium and generating gases. This paper characterizes the structure, morphology and element distribution of the corrosion layer by scanning electron microscope analysis, electron probe micro analysis, and glow discharge mass spectrometry analysis. The aluminum was fluorinated mainly by pitting corrosion and did not generate a dense passivation layer. Elements aggregated at the surface with different degrees: the elements of IA, IIA and VIB groups within 2.4 mu m from the surface aggregated over 10-1000 times, but Fe, Ni and Si, C elements aggregated only a few times. The serious element diffusion zone was about 5 mu m, and some elements diffused tens of microns. Considering the stability to fluorine medium and the ability to improve thermodynamic stability, the Ni element should be a good choice for anticorrosive layer. The aggregation of elements like Si greatly increases the possibility to form harmful gases, and their content should be strictly controlled. The physical models of passivation, operation, and air exposure of the excimer laser are established. The passivation effect largely depends on the surface content and state of harmful elements, but the long-term chemical stability in the operation is related to the surface quality, internal content of harmful elements and diffusion rate.