Phase explosion and Marangoni flow effects during laser micromachining of thin metal films

Abstract

Phase explosion and Marangoni flow during laser micromachining of thin metal films are studied in this paper. The purpose of this study was to improve understanding of the time scales by which these processes occur. The study was based on a time-resolved reflection imaging method. The method used a nitrogen-pumped dye laser to illuminate the surface of the films at a given time after the Nd:YAG laser heats the film. The dye laser irradiation reflected from the surface was then imaged by a CCD camera. The lasers were coupled by a digital pulse-delay generator, allowing the time delay between the two lasers to be controlled by the user. The effects of Marangoni flow and phase explosion can be seen on the starting and ending times of ablation. At all fluences in the study, holes were opened in the aluminum films and the hole formation process was completed in under 350 ns. Ablation of nickel films was very different however, with thin layers of the film surface removed at low fluences, a process which took on the order of microseconds to complete. At higher fluences the nickel films ruptured and the hold opening process was completed in less than 500 ns.