Dry Etching Assisted Femtosecond Laser Fabrication

Nowadays,three-dimensional(3D)structures of hard materials,such as silicon,sapphire,and diamond,have been widely used in microelectronics,micro-optics,microelectromechanical systems and biosensors.The traditional micro/nano fabrication methods for constructing of microstructures are photolithography,electron beam lithography,nanoimprint lithography,and focused ion beam lithography.With high resolution of several nanometers,complex microstructures and devices can be precisely fabricated by these micro/nano fabrication methods.The above methods are always used for fabricating two-dimensional or quasi-three-dimensional microstructures and are difficult to construct 3D microstructures.In addition,the properties of high hardness and stability also made it difficult to process hard materials,especially for fabricating optical complex 3D microstructures.Femtosecond laser ablation technology can be used to fabricate micro/nano structures of hard materials.However,High laser energy density are required for process hard materials,which results in the decreasing of scanning rate.Moreover,the surface roughness of structures would be increased when process of hard materials with high laser energy density,which does not satisfy the requirement for surface smoothness of optical devicesIn order to solve the problem of low efficiency and high surface roughness about femtosecond laser process hard materials,dry etching assisted femtosecond laser process technology is proposed for fabricating 3D structures on the surface of hard materials in this paper.The technology concludes three schemes: First,dry etching transferring assisted femtosecond laser multiphoton polymerization is proposed for fabricating sapphire convex microlens and spiral phase plate.Second,dry etching assisted femtosecond laser modification is proposed for constructing of silicon and sapphire concave microlens arrays.Third,dry etching assisted gray scale femtosecond laser process is proposed for fabricating silicon 3D microstructures.In details:(1)Dry etching transferring assisted femtosecond laser multiphoton polymerization is proposed for fabricating sapphire 3D microstructures.The relationship of the morphology of sapphire microstructures with the parameters of femtosecond laser and ICP etching are investigated.Micro cone,step-like structures and slope-like structures are fabricated on sapphire substrate.Sapphire convex microlens and spiral phase plate with high quality are fabricated via optimizing the parameters of femtosecond laser and ICP etching.The feasibility of fabrication of three-dimensional structures by dry etching transferring assisted femtosecond laser multiphoton polymerization is verified.(2)Silicon concave microlens arrays are fabricated by dry etching assisted femtosecond laser modification.The diameter and depth of the silicon concave microlens can be adjusted by laser pulse energy,pulse number,and etching time.Honeycomb PDMS convex microlens array is fabricated by using silicon concave microlens array as a template.The compatibility of semiconductor technology with dry etching assisted femtosecond laser modification is studied and is preliminarily verified.(3)Sapphire concave microlens arrays are fabricated by dry etching assisted femtosecond laser modification.Corresponding on silicon concave microlens,the diameter and depth of the sapphire concave microlens can be adjusted by laser pulse energy,pulse number,and etching time.On this basis,centimeter-level large area sapphire concave microlens array is rapidly fabricated by the combination of scanning mirror and field lens.In addition,ultraviolet beam homogenization is realized by this large area sapphire concave microlens array.Finally,large area glass convex microlens array is fabricated by using silicon concave microlens array as a template,which provides a new way for construction of hard materials microstructures.(4)Controllable oxidization of silicon is realized by femtosecond laser modification.Followed with dry etching,a micro gear,micro comb actuator,micro Fresnel zone plate,and micro cantilever are fabricated on silicon wafer.Moreover,the concentration of oxygen in the surface of silicon wafer can be adjusted by changing the laser pulse power and scanning step.On this basis,step-like structures,a word of“LASER” on the step,rectangular pyramid and focal varying microlens array are realized on silicon wafer,indicates the ability of dry etching assisted gray scale femtosecond laser process for construction of arbitrary gradient height 3D microstructures.In summary,in order to solve the problem of low efficiency and high surface roughness about femtosecond laser process hard materials,dry etching assisted femtosecond laser process technology is proposed.Micro-optics elements and micromechanics devices can be fabricated on silicon and sapphire substrate.The compatibility of semiconductor technology with dry etching assisted femtosecond laser modification is studied and is preliminarily verified.It provides a new way for developing femtosecond laser micro/nano fabrication technology to industrial applications.