利用Nd:YAG纳秒脉冲激光(波长532 nm)在空气中对单晶硅表面进行单脉冲辐照，研究了激光能量密度和光斑面积变化对微结构的影响。通过场发射扫描电子显微镜和原子力显微镜(AFM)对样品表征，并对纳秒激光辐照硅的热力学过程进行分析。结果显示：当脉冲激光的能量密度接近硅的熔融阈值且光斑直径小于8 μm时，形成尖峰微结构;随着能量密度或光斑面积增大，尖峰结构消失，形成边缘隆起和弹坑微结构。通过流体动力学模型得到微结构形貌的解析解，模拟得到的微结构形貌与实验测得的AFM数据一致。研究表明微结构的形成主要是由于表面张力引起的熔融硅流动。表面张力与表面温度和表面活性剂的质量浓度有关。温度梯度引起的热毛细流作用和表面活性剂浓度引起的毛细作用共同影响下形成尖峰、边缘隆起和弹坑微结构。

The morphologies of silicon surfaces are modified with the single Nd:YAG nanosecond laser pulse (wavelength 532 nm) in air. The influence of single pulse laser energy density and spot size on the morphology is studied. The field emission scanning electron microscope (FESEM) and the atomic force microscope (AFM) measurement results show the formation of completely different morphologies in different conditions, and the thermodynamic process of nanosecond laser irradiating silicon is analyzed. We find that when the energy density is close to the melting threshold of silicon, and the spot size is as small as 8 μm, the spike structures are fabricated. While increasing the energy density and the spot size, the conical spike structures gradually disappear, and the profile of the irradiated surface shows swellings and craters. We obtain approximate analytical solutions for the morphology by the hydrodynamic model, and the theoretical data show good agreement with AFM data for microstructures. The reason of the microstructure formation is that surface tension force drives the molten silicon to flow. The surface tension depends on the surface temperature gradient and the surfactant concentration. With the total effects of thermocapillary by the surface temperature gradient and surfactant compositional capillarity, the spike, swelling and craters can be fabricated.