NOVEL DIELECTRIC STRUCTURES FOR OPTICAL PERFORMANCE ENHANCEMENT IN DEEP SUB-MICRON CMOS IMAGE SENSOR

摘要

Novel dielectric structures, light guide and air gap guard ring, have been successfully developed to improve pixel sensitivity and crosstalk in 0.18um technology. As the light transmission path surrounded by low RI (refraction index) dielectric films, the incident light will be confined to the selected pixels. Air-gap guard ring [FSG-oxide(RI-1.43)/air-gap(RI-1)] with larger RI difference shows better confinement than light guide [PE-oxide(RI-1.46)/FSG-oxide(RI-1.43)]. Small pixels with cell pitch 2.8um~4.0um have been characterized for excellent optical performance. For 3.0um pixel with air-gap guard ring operating at a 20° Incident angle, the pixel sensitivity is enhanced by 45% and the optical spatial crosstalk is reduced by 90%. In actual color image sensors, air-gap guard ring shows significant improvement in suppression of color mixing caused by oblique illumination.