Stealth dicing of sapphire sheets with low surface roughness, zero kerf width, debris/crack-free and zero taper using a femtosecond Bessel beam
Stealth dicing of sapphire sheets with low surface roughness, zero kerf width, debris/crack-free and zero taper using a femtosecond Bessel beam
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DOI：
10.1016/j.optlastec.2020.106713
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发表时间：
2021-03-01
影响因子：
5
通讯作者：
Li, Lin
中科院分区：
文献类型：
--
作者：
Li, Zhaoqing;Wang, Xuefeng;Li, Lin
用于蓝宝石的激光束切割的先前方法通常导致碎裂、碎片、大切口宽度、渐缩和高表面粗糙度或不均匀表面。激光隐形切割可以消除切缝宽度和锥度，减少缺陷。然而，侧壁均匀性差，因为材料的一部分被激光切割，并且一部分被外部机械力破坏。在蓝宝石的贝塞尔光束全深度切割的先前方法中，可以改善均匀性。然而，侧壁表面粗糙度较差。一直缺乏实现最小缺陷和低表面粗糙度的理想解决方案。在这里，我们展示了一种大大改进的蓝宝石切割方法，其具有飞秒贝塞尔光束，实现了200 nm Ra的切割表面粗糙度，这比先前的贝塞尔光束切割方法几乎提高了一个数量级，而不会失去均匀性。通过使用通过20度物理角轴棱锥透镜的直径减小的高斯光束，产生高度均匀的非衍射贝塞尔光束。在圆偏振状态下，分析了贝塞尔光束扫描速度对切割0.38mm、1 mm和1.5mm厚蓝宝石板的抗弯强度和侧壁表面粗糙度的影响。零锥度、零切口宽度、无碎屑/碎屑蓝宝石直线和曲线切割都得到了证明。所涉及的基本机制进行了讨论。贝塞尔光束的均匀性和适当的脉冲间隔已被确定为实现低表面粗糙度的关键因素。
Previous approaches for laser beam cutting of sapphire often lead to chipping, debris, large kerf widths, tapering and high surface roughness or nonuniform surfaces. Laser beam stealth dicing can remove kerf width and tapering, reduce defects. However, sidewall uniformity is poor as part of the material is laser cut and part is broken by an external mechanical force. In previous approaches of Bessel beam full depth cutting of sapphire, uniformity can be improved. However, the sidewall surface roughness is poor. There has been lack of an ideal solution to achieving minimum defects and low surface roughness. Here we show a much improved sapphire cutting method with a femtosecond Bessel beam achieving a 200 nm Ra cut surface roughness, which is almost an order of magnitude improvement over the previous Bessel beam cutting approaches without losing the uniformity. By using a diameter reduced Gaussian beam passing through a 20 degrees physical angle axicon lens, a highly uniform non-diffraction Bessel beam is generated. Under circular polarization, the effects of Bessel beam scanning speed on flexural strength and the sidewall surface roughness are analyzed for cutting sapphire sheets of 0.38 mm, 1 mm, and 1.5 mm in thickness. Zero taper, zero kerf width, free of debris/chipping sapphire cutting with both straight and curved lines are demonstrated. The fundamental mechanisms involved are discussed. The uniformity of Bessel beam and appropriate separation of pulses have been identified as the key factors for achieving the low surface roughness.