Silicon-based Micro-nanostructures Fabricated By Femtosecond Laser And Wet Etching

Micro-electromechanical system(MEMS) is a new technology which combines microelectronic with micromachining technology, it shows great application value in the fields of industrial, military, medical owing to the advantages of the miniaturization integration, diversification. The mainly processing material of MEMS is excellent semiconductor silicon and silicon is a good sensitive material with the ideal elastic, thermal conductivity and perfect stability. It also can be applicable to a variety of complex environments and be integrated easily which caters to the needs of the development of science and technology. Therefore, the technology of silicon-based micro-nanostructures fabrication is particularly important. Traditional technologies include surface micro machining technology, bulk micro processing technology and LIGA technology, but their technical processes require multiple deposition of sacrifice layer, etching and the overall layout which is very complex, so we need to seek a simple and flexible technology. Femtosecond laser micro-nano processing technology has a unique advantage in high resolution, high accuracy, complex three-dimensional micro-nanostructures fabrication, but silicon material has a strong absorption of UV-VIS-IR. So the laser focus is difficult to enter into the interior of silicon to direct write processing. Wet etching can be used to prepare silicon micro-nanostructures, but the design of masks membrane limits the flexibility of the structure, and it is very difficult to achieve small area structures. Femtosecond laser wet etching technology combines the technical advantages of the above two methods and makes up for their disadvantages.In this paper, we prepared a variety of silicon micro-nanostructures by femtosecond laser and wet etching technique successfully. Firstly polygon and double coil two-dimensional structures were obtained by ablating silicon with high power femtosecond laser oscillator, then the results were analyze. Then HF and KOH were used as isotropic and anisotropic etchants to do deal with silicon wafers. It was found that HF enhanced the effect of ablation, but KOH solution weakened. The part of ablation with HF is etched, and with KOH is preserved. Through further characterization it was confirmed that silicon formed silica on the surface during the process of the laser ablation, KOH is very selective to silicon and silicon dioxide, so ablation structure plays a role of mask which can effectively prevent the underlying silicon is etched during the corrosion process. We successfully prepared three-dimensional micro-nanostructures by properly prolonging the KOH etching time. During the experiment, we found that lateral etching effects also exists at the same time and floating disc, spiral coil and hexagonal structure were obtained though the clever use of the lateral etching effect.A new silicon micro-nanostructures fabrication technology was proposed, this method can shorten the process time and improve the processing efficiency. Because the mask membrane structure can be fabricated in any position of the silicon wafer, it greatly improved the flexibility of preparation process. Therefore femtosecond laser wet etching technology could be widely used in the field of MEMS.