Fabrication of image sensor with improved signal to noise ratio

摘要

For fabricating an image sensor, an isolation structure is formed to define a first active region of a semiconductor substrate. A first transistor and a second transistor of a unit pixel are formed in the first active region. In addition, a threshold voltage lowering region is formed in a portion of the semiconductor substrate near a portion of the isolation structure abutting the second transistor in the first active region. The threshold voltage lowering region causes the second transistor to have a respective threshold voltage magnitude that is lower than for the first transistor. The threshold voltage lowering region is formed simultaneously with a passivation region in a second active region having a photodiode formed therein.