Broadband antireflective light-blocking layer using nanoparticle suspension in photoresist with high-resolution patterning

Abstract. Background: Many MEMS and optical sensor devices can benefit from layers that block transmission and suppress reflection of light across the visible spectrum. Because these devices can include complicated topography, many existing methods for depositing antireflective layers are difficult, impractical, or unusable. Aim: To create a light-blocking antireflective layer that works well with complicated MEMS and sensor devices, a layer should be made that is cheap, simple, and can be deposited and patterned with high resolution at low temperatures. Approach: Light blocking is achieved using an aluminum layer. Suppressing reflection is achieved by mixing aluminum oxide nanoparticles in photoresist to create a layer that partially absorbs and partially scatters light. Results: The combination of a layer of metal and a layer of nanoparticles and photoresist completely blocks transmission of light and significantly reduces reflections across the visible spectrum, particularly for shorter wavelengths. The layer is also patternable to sizes as small as a few microns with high resolution. Conclusion: By combining a metal layer and a layer of nanoparticles in photoresist, a simple, cheap, and effective light-blocking antireflective layer can be created that is compatible with planar devices with complex topography.