Femtosecond laser multi-beam interference lithography anti-reflective microstructure on silicon surface

In order to obtain uniform distribution silicon surface microstructure, a new method was proposed based on multi-beam interference lithography to relaise the controlling of the distribution character of the microstructure. Femtosecond laser multi-beam interference was formed by Spatial Light Modulator (SLM), and the uniform distribution multi-spots with the controllable period were generated. By using these multi-spots, the regular distribution concave structures were fabricated on silicon surface, and the distribution character and period was flexiblly controlled by shift the phase masks on SLM. The morphology and optical character of the microstructure were measured with Scanning Electron Microscopy (SEM) and spectrophotometer. Experimental results show that the close-packed concave structure with the period of about 3.3 μm can be fabricated on the silicon surface under special parameters (10× focusing lens, laser power of 25 mW, exposing time of 30 s) by loading the phase of 4-facet pyramid lens with the base angle of 2°; the formed structure shows good effect of anti-reflection; its transmission at the near infrared band of 1.2~2 μm enhances 11.5% in comparison with the polished silicon.