Multi-color anti-reflection coating with silicon micro-lens photodiode for image sensor

A silicon micro-lens is proposed and analyzed when it is integrated into the photodiode for the application of a backside illuminated (BSI) image sensor (Pixel size is around 1 um). Due to the small dimension of the BSI pixel, each pixel of the image sensor receives from its adjacent pixels cross-talk (x-talk) due to large light incident angle and light diffraction, resulting in reduced sensor MTF and possible color artifacts. A silicon ulens formed between the photodiode and RGB color filter works as an inner lens to improve the focus of the light and guide it into its corresponding pixel, thus decreasing optical x-talk and reducing noise. Since the silicon ulens is integrated into the photodiode and could be doped as part of the photodiode, this design would eliminate any internal reflection caused by traditional inner micro lens solutions (made of Si oxide, Si nitride or polymer). 'By color' anti-reflection coatings (ARC) on top of the silicon ulens can work as a versatile optical filter to compensate the light spectrum and angular mismatch. Our design and analysis provide a solution to improve the quantum efficiency (QE) and x-talk of the BSI image sensor and the QE enhancement for each pixel are discussed in detail.