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Title: Multi-foci division of nonlinear energy absorption on ultrashort pulse laser singulation of sapphire wafers
Authors: Lye, Celescia Siew Mun
Wang, Zhongke
Lam, Yee Cheong
Keywords: Engineering::Mechanical engineering
Issue Date: 2021
Source: Lye, C. S. M., Wang, Z. & Lam, Y. C. (2021). Multi-foci division of nonlinear energy absorption on ultrashort pulse laser singulation of sapphire wafers. Micromachines, 12(11), 1328-.
Project: U12-M-007JL 
Journal: Micromachines 
Abstract: The multi-foci division of through thickness nonlinear pulse energy absorption on ultrashort pulse laser singulation of single side polished sapphire wafers has been investigated. Firstly, it disclosed the enhancement of energy absorption by the total internal reflection of the laser beam exiting from an unpolished rough surface. Secondly, by optimizing energy distribution between foci and their proximity, favorable multi-foci energy absorption was induced. Lastly, for effective nonlinear energy absorption for wafer separation, it highlighted the importance of high laser pulse energy fluence at low pulse repetition rates with optimized energy distribution, and the inadequacy of increasing energy deposition through reducing scanning speed alone. This study concluded that for effective wafer separation, despite the lower pulse energy per focus, energy should be divided over more foci with closer spatial proximity. Once the power density per pulse per focus reached a threshold in the order of 1012 W/cm2, with approximately 15 μm between two adjacent foci, wafer could be separated with foci evenly distributed over the entire wafer thickness. When the foci spacing reduced to 5 μm, wafer separation could be achieved with pulse energy concentrated only at foci distributed over only the upper or middle one-third wafer thickness.
ISSN: 2072-666X
DOI: 10.3390/mi12111328
Rights: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// 4.0/).
Fulltext Permission: open
Fulltext Availability: With Fulltext
Appears in Collections:MAE Journal Articles
SIMTech Journal Articles

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