Li Shunping, Wang Xinchang, Chen Guojie, Wang Zhongke
Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan 528220, China.
Singapore Institute of Manufacturing Technology (SIMTech), A*Star, 2 Fusionopolis Way, Singapore 138634, Singapore.
Micromachines (Basel). 2022 Dec 31;14(1):119. doi: 10.3390/mi14010119.
Laser ablation of semiconductor silicon has been extensively studied in the past few decades. In the ultrashort pulse domain, whether in the fs scale or ps scale, the pulse energy fluence threshold in the ablation of silicon is strongly dependent on the pulse width. However, in the ns pulse scale, the energy fluence threshold dependence on the pulse width is not well understood. This study elucidates the interaction energy dependency on pulse width in ns NIR laser ablation of silicon. The level of ablation or melting was determined by the pulse energy deposition rate, which was proportional to laser peak power. Shorter pulse widths with high peak power were likely to induce surface ablation, while longer pulse widths were likely to induce surface melting. The ablation threshold increased from 5.63 to 24.84 J/cm as the pulse width increased from 26 to 500 ns. The melting threshold increased from 3.33 to 5.76 J/cm as the pulse width increased from 26 to 200 ns, and then remained constant until 500 ns, the longest width investigated. Distinct from a shorter pulse width, a longer pulse width did not require a higher power level for inducing surface melting, as surface melting can be induced at a lower power with the longer heating time of a longer pulse width. The line width from surface melting was less than the focused spot size; the line appeared either as a continuous line at slow scanning speed or as isolated dots at high scanning speed. In contrast, the line width from ablation significantly exceeded the focused spot size.
在过去几十年中，人们对半导体硅的激光烧蚀进行了广泛研究。在超短脉冲领域，无论是飞秒尺度还是皮秒尺度，硅烧蚀中的脉冲能量通量阈值都强烈依赖于脉冲宽度。然而，在纳秒脉冲尺度下，能量通量阈值对脉冲宽度的依赖性尚不清楚。本研究阐明了纳秒近红外激光烧蚀硅时相互作用能量对脉冲宽度的依赖性。烧蚀或熔化的程度由与激光峰值功率成正比的脉冲能量沉积速率决定。具有高峰值功率的较短脉冲宽度可能会引起表面烧蚀，而较长脉冲宽度可能会引起表面熔化。随着脉冲宽度从26纳秒增加到500纳秒，烧蚀阈值从5.63焦耳/平方厘米增加到24.84焦耳/平方厘米。随着脉冲宽度从26纳秒增加到200纳秒，熔化阈值从3.33焦耳/平方厘米增加到5.76焦耳/平方厘米，然后在直到500纳秒（所研究的最长宽度）时保持不变。与较短脉冲宽度不同，较长脉冲宽度在诱导表面熔化时不需要更高的功率水平，因为较长脉冲宽度的较长加热时间可以在较低功率下诱导表面熔化。表面熔化产生的线宽小于聚焦光斑尺寸；该线在慢扫描速度下呈现为连续线，在高扫描速度下呈现为孤立点。相比之下，烧蚀产生的线宽明显超过聚焦光斑尺寸。
