Comparison of femtosecond laser-induced front- and rear-side ablation of films

• Published in: Proceedings of the Institution of Mechanical Engineers. Part B, Journal of engineering manufacture Journal of engineering manufacture, 2011-04, Vol.225 (4), p.520-527
• Main Authors: Wang, W J, Wang, K D, Jiang, G D, Mei, X S, Yang, C J
• Format: Article
• Language: English
• Subjects: Ablation; Applied sciences; Comparative analysis; Cross sections; Cutting forces; Exact sciences and technology; Femtosecond; Laser ablation; Lasers; Mechanical engineering. Machine design; Mechanical engineers; Microstructure; Morphology; Precision engineering, watch making; Ripples
• ISSN: 0954-4054; 2041-2975
• DOI: 10.1177/2041297510394071

Femtosecond laser rear-side ablation, in which the laser beam first passes through the substrate, then irradiates on the film at the substrate–film interface, can be used to fabricate films on a transparent substrate. In this method, the material removal mechanism is different from that in front-side ablation, and the ablation occurs in an enclosed space. The different material removal process in rear-side laser ablation will bring about some unique ablation results. In this paper, the material removal mechanisms and ablation results of Cr film in rear-side ablation are investigated by comparing with those in front-side ablation. It is found that rear-side ablation can achieve smaller feature size than front-side ablation, especially when the laser fluence is small. However, owing to its different material breaking and ejecting process, the rear-side ablation tends to have worse bottom morphology and irregular edge morphology. In addition, the microstructures in the two ablations have opposite cross-sectional shapes and the ripple period in rear-side ablation is larger than that in front-side ablation.