飞秒激光在空气和水中对硅片烧蚀加工的实验研究

采用1 kHz，800 nm，50 fs—24 ps的钛宝石激光脉冲对单晶硅样品在空气和水溶液环境中的烧蚀加工特性进行了研究.实验观察到了超短脉冲激光在空气氛围中烧蚀形成的双层环状结构，分析揭示了加工区域中心和边缘的烧蚀物理机制分别为热熔化和库仑爆炸，并测量了双层环状结构半径随入射激光能量、脉冲数及持续时间等的变化关系，结果表明获取较大深-宽比的加工效果需选择小能量脉冲激光的多次作用.在水溶液环境中，实验发现飞秒激光在样品表面诱导产生了亚微米量级的多孔状结构，而皮秒激光则更容易实现对硅表面的非热性去除.这是由于激光诱导的光机械应力和空泡效应随脉冲宽度变大而增强所致，在实验上确立了区分这两种不同加工状态的临界脉冲宽度. 关键词： 飞秒激光 硅片 激光加工

Femtosecond laser ablation of silicon wafers in air and water

In this paper, we investigate laser ablation of silicon wafers in air and water through using Ti:sapphire femtosecond laser with central wavelength of 800 nm and pulse duration of 50 fs—24 ps at a repetition rate of 1 kHz. Unique concentric rings are observed on the sample surfaces during the laser ablation in ambient air. Formation mechanisms of the inner and outer ablative structures are attributed to the thermal melting and Coulomb explosion, respectively. The influence of laser parameters, such as the laser energy, the number of pulses and the pulse duration on the radius of the ablation ring is observed experimentally. It is found that drilling a blind hole with large aspect ratio usually requires multiple laser shots with relatively small pulse energy. In the water surroundings, femtosecond laser ablation results in porous microstructure formation in the irradiated area. However, laser pulses with picosecond duration lead to large material removal by evidently nonthermal processes. Theoretical analysis suggests that this phenomenon could be explained by the photo-mechanical stress and bubble cavitation, which are strengthened with increasing pulse duration. The critical pulse width separating the two different ablation processes in the water ambience is determined experimentally for the first time.