A novel refractive silicon microlens array using bulk micromachining technology

We propose a novel Si microlens array for enhancing the detectivity of IR detector using bulk micromachining technology. Boron diffusion and etching selectivity with respect to boron density in EDP etchant are utilized. Unlike conventional microlens, the focal length can be easily controlled with diffusion parameters such as diffusion temperature/time and diffusion window. In the experiment, the focal length can be controlled within 70% by varying the drive-in time between 0 and 8 hours. The measured focal spot size is 3.8 μm of which a theoretical diffraction-limited spot size is 3.3 μm. Arbitrary shaped-microlens can be fabricated by SiO₂ patterning. The peak-to-peak surface roughness is low, about 40 nm, due to self-stopping property