Blind-zone formation in laser shockwave nano-cleaning

• Published in: Optics express Vol. 29; no. 17; pp. 27587 - 27599
• Main Authors: Zhang, Shuowen, Yan, Qingyu, Lin, Jian, Zhang, Qunli, Ding, Xiaoyu, Lu, Yongfeng, Guo, Lianbo, Kovalenko, Volodymyr S., Fan, Lisha, Yao, Jianhua
• Format: Journal Article
• Language: English
• Published: 16.08.2021
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.428610

Laser shockwave cleaning (LSC) has attracted growing attention due to its advantages in non-contact, site-selective nanoparticle removal on microelectronic/optical devices. However, an uncleaned blind-zone formed directly under the laser-induced plasma kernel severely affects the cleaning effect. Laser shockwave cleaning of 300 nm polystyrene latex nanoparticles on silicon wafers is fully explored to understand the blind-zone formation mechanism. The size of the uncleaned blind-zone quickly increases from 0.84 to 19.50 mm 2 associated with a growing fraction of the uncleaned blind-zone area within the whole cleaned area from 0.05 to 0.93 as the plasma-substrate gap distance is increased from 0.5 to 2 mm and the laser fluence is increased from 75 to 150 J/cm 2 . Besides, the variation of the blind-zone size is more strongly dependent on the plasma-substrate gap distance than the laser fluence. A time-resolved analysis of the laser-induced plasma evolution shows an inseparable relationship between the blind-zone and the geometric location of the plasma kernel. Theoretical analysis of the removal force in LSC based on the rolling mode reveals that the lack of dragging force acting on the nanoparticles in the region right under the plasma kernel impedes their removal and causes the uncleaned blind-zone formation.