A Photodiode Structure for Improving the Quantum Efficiency of CMOS Image Sensors

Abstract

The invention discloses a photodiode structure for improving the quantum efficiency of a CMOS image sensor. The photodiode structure is located in a lightly-doped substrate. The photodiode structure comprises a reset transistor, a transmission transistor, a PN photodiode, a pixel unit isolation region, a well region and an annular silicon region. The two ends of the transmission transistor are connected with the reset transistor and the PN photodiode respectively. A region formed by the reset transistor, the transmission transistor and the PN photodiode is surrounded by the annular pixel unitisolation region. The part of the pixel unit isolation region, adjacent to the reset transistor, is isolated from a shallow trench. The P-type region and the N-shaped region in the PN photodiode are distributed up and down in the vertical direction, and the lower part of the above space comprises a region I, a region II and a region III, wherein the three regions are different in doping concentration and are arranged from top to bottom. An annular silicon region is arranged below the well region and the pixel unit isolation region. According to the photodiode structure provided by the invention, the quantum efficiency of a long-wave section can be improved, and an inter-band tunneling electric leakage is avoided.

Description

technical field [0001] The invention relates to the field of semiconductors, in particular to a photodiode structure for improving the quantum efficiency of a CMOS image sensor. Background technique [0002] The CMOS image sensor is a photoelectric conversion device. The incident photons excite the electrons in the valence band of the semiconductor to the conduction band, store them in the reverse PN junction, and then transfer them to the capacitor through a transfer MOS transistor. [0003] The PN junction is reverse biased, that is, the drain of the reset transistor is connected to a high potential, the drain of the pass transistor is suspended, the gate of the reset transistor is set to high voltage and turned on, and the gate of the pass transistor is turned on at high voltage, at this time, the PN junction in the photodiode is clamped The charges (electrons) in the N region of the clamped photodiode are extracted, and the PN junction in the clamped photodiode is placed...

AI Technical Summary

Problems solved by technology

There are two ways to increase the width of the depletion region. First, you can increase the voltage, but after increasing the voltage, it will introduce band-to-band tunneling (BTBT) leakage, resulting in an increase in dark current.

The second can increase the depth of the N region of the PN junction, but after increasing the depth of the N region of the PN junction, the residual electrons after reset will be increased, resulting in poor dark light response effect

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