Analysis on Light Transmission through Multi-Metal-Layers for CMOS Image Sensors

Abstract

With the downscaling of CMOS technology, interconnect layers are multi-stratified since the number of metal levels has increased. However, this multi-metal-layer structure above the photodiodes affects sensitivity, which is important for obtaining optimal performance from CMOS image sensors. This paper analyzes the light-transmission characteristics on multi-metal layers (interconncet layers). To evaluate what effect standard CMOS-process technologies have on multi-metal layers, we developed a method of calculating the transmitted light intensity through the multi-metal layers. We found the transmitted light intensity from the calculated results using the transfer matrix method for standard CMOSs ranging in size from 1.2 μm to 22 nm.