The mechanism of micro-cracks formation in ultrasonic-assisted water confined laser micromachining silicon

In the ultrasonic-assisted water confined laser micromachining silicon, micro-cracks may generate. The effect of ultrasonic power and thickness of the water layer on the groove section’s micro-cracks is discussed systematically to control the micro-cracks formation and improve the processing quality. The experimental and simulational results indicate the maximum radius of the bubbles and the bubble interference coefficient have an important effect on the micro-cracks formation. The larger the maximum radius of the bubble, the shorter the micro-cracks formed, and the smaller the bubble interference coefficient, it is easier to produce micro-cracks. The bubble interference coefficient and the maximum radius of the bubble can be affected by the water layer thickness and ultrasonic power. Therefore the micro-cracks can be effectively controlled by selecting the appropriate water layer thickness of 1.5mm and ultrasonic power of 195W in this study. The study is obtained from this study provides a guide for micro-cracks under ultrasonic-assisted solution confined laser processing. •The effects of ultrasonic power and water layer thickness on the micro-crack formation were experimentally investigated.•The influence of the laser-induced bubble size on micro-crack formation is analyzed by experiment and theoretical calculation.•The influence of the interference coefficient of bubbles on micro-crack formation is analyzed by numerical simulation.