One-Step Femtosecond Laser Irradiation of Single-Crystal Silicon: Evolution of Micro-Nano Structures and Damage Investigation

Abstract

As a pillar material of semiconductors, single-crystal silicon (Si) has attracted much attention due to its excellent electronic properties. Meanwhile, femtosecond laser processing as a convenient fabrication method for miniaturized structures provides an effective way to improve the performance of Si-based devices. However, the final-state analysis of femtosecond laser-induced Si micro-nano structures remains to be explored. In this study, the evolution of the micro-nano structures and the variation of surface and subsurface damage with pulse number were studied. Based on the atomic structure, the amorphous layer, dislocation layer, and unaffected layer were found. The amorphous layer resulted from the re-solidification of melted materials. The dislocation layer consisted of dislocations and lattice distortion. The unaffected layer retained the initial lattice structure and was not affected by laser irradiation. The high temperature and stress induced by multiple pulses led to the stacking faults and nano-twins in the subsurface layer. The evolution of the Si structure was essentially a transition process from a dislocation layer to a high-density defect layer and a transition process from nanotips to laser-induced periodic surface structures. During this process, dislocations dominated the femtosecond laser-induced microstructural deformation, affecting the nano-hardness of the irradiated surface. As a result, the nano-hardness of Si structures fabricated using femtosecond laser processing was maximally enhanced by 9.54%. This work provides new information about ultrafast laser-induced surface and subsurface damage, which is significant for the efficient and high-precision fabrication of Si-based functional micro-nano devices.