Patent ID: 9613998
Date: 2017-04-04
CPC Classifications: H01L

Claim:
1. A method for reducing dark current of a Back Side Illumination (BSI) image sensor, wherein the BSI image sensor comprises: a photodiode formed by forming an area with a second type conductivity in a semiconductor substrate with a first type conductivity, wherein the area with the second type conductivity is defined as an area for collecting photo-generated carriers; an isolation layer with the first type conductivity formed in the semiconductor substrate with the first type conductivity and above the photodiode; a gate structure of a pass transistor formed on a top surface of the semiconductor substrate with the first type conductivity and being corresponding to the isolation layer with the first type conductivity, wherein the gate structure comprises a gate oxide layer, a gate electrode layer and a gate spacer, and the gate structure covers the photodiode correspondingly; and a floating diffusion area formed in the semiconductor substrate with the first type conductivity and being heavily doped with the second type conductivity; and wherein the method comprises: when the semiconductor substrate with the first type conductivity is a P-type semiconductor substrate, applying a voltage ranging from −3.0V to −0.5V to the gate structure, wherein the voltage makes holes accumulate at a portion of the P-type semiconductor substrate corresponding to the gate structure, such that the defects at the interface between the P-type semiconductor substrate and the gate oxide layer are isolated from the N-type area of the photodiode to reduce the dark current; and when the semiconductor substrate with the first type conductivity is a N-type semiconductor substrate, applying a voltage ranging from +0.5V to +3.0V to the gate structure, wherein the voltage makes electrons accumulate at a portion of the N-type semiconductor substrate corresponding to the gate structure, such that the defects at the interface between the N-type semiconductor substrate and the gate oxide layer are isolated from the P-type area of the photodiode to reduce the dark current.