Arrayed silicon-based concave microlens fabricated by single mask ultraviolet-photolithography and dual-step KOH etching

Background: As an important optical element, concave microlens arrays are utilized in many applications. How to fabricate a mass of concave microlens arrays efficiently at a low cost is a key problem to be solved. Aim: We propose a method of fabricating a concave microlens array based on single mask ultraviolet (UV)-photolithography and dual-step potassium hydroxide (KOH) etching, which has proven to be efficient. Approach: An arrayed silicon-based concave microlens utilized in the infrared wavelength range was designed and fabricated based on single mask UV-photolithography and dual-step KOH etching. Combining the computation simulation and the evolving microstructural mechanism based on the silicon anisotropic corrosion characteristics in a common KOH solution with several control factors such as the solution concentration, temperature, and corrosion period, an arrayed concave microlens with a spherical profile over a silicon wafer with the required crystal orientation was simulated, designed, and fabricated effectively. Results: Both the scanning electron microscopy and the surface profile measurements indicate that the fabricated concave microlens arrays present a high filling-factor of more than 80% and a small surface roughness with a root mean square value in several tens of nanometer scale. The common optical measurements demonstrate that the fabricated silicon-based concave microlens presents a good infrared beam divergence performance. Conclusions: The method highlights the prospect of the industrial production of large-area silicon-based concave microlens arrays for infrared beam shaping and control light applications.