Effect of an Si_3N_4/PSG/SiO_2 Multilayer Dielectric Coating on the Spectral Sensitivity of Elements in CMOS Area Imagers

摘要

Spectral dependences of the transmittance of the IC-protecting multilayer dielectric coating are theoretically and experimentally studied to facilitate the development and design of CMOS color area imagers. The results obtained demonstrate the modulation of the spectral sensitivity of photodiodes with conventional multilayer dielectric coatings, a characteristic that substantially impedes color separation of a photosignal. Numerical simulation of the spectral transparency of the conventional dielectric coating employed indicates that interference in the upper dielectric layer whose refractive index appears significantly higher than the tabulated value plays the main role. A brief review of the methods for correction of the undesirable features of the spectral transparency that are caused by the maximum possible refractive index of an Si_3N_4 protective coating are reviewed.