Pixel with asymmetric transfer gate channel doping and method for manufacturing pixel

Abstract

A pixel including a substrate of a first conductivity type, a photodetector of a second conductivity type that is opposite the first conductivity type and configured to convert incident light to a charge, a floating diffusion of the second conductivity, and a transfer region between the photodetector and floating diffusion. A gate is formed above the transfer region and partially overlaps the photodetector and is configured to transfer charge from the photodetector to the floating diffusion. A pinning layer of the first conductivity type extends at least across the photodetector from the gate. A channel region of the first conductivity type extends generally from a midpoint of the gate at least across the photodiode and is formed by an implant of a dopant of the first conductivity and having a concentration such that a dopant concentration of the transfer region is greater proximate to the photodetector than proximate to the floating diffusion.

Description

Background technique [0001] Digital cameras using a complementary metal-oxide-semiconductor (CMOS) image sensor with a 4-transistor pixel structure (which has buried gated diodes) typically provide better image quality than cameras using a 3-transistor CMOS image sensor because the buried The inset photodiode configuration reduces the amount of current generated at the surface, thereby reducing dark current, and also reduces noise because the transfer gate used to access the photodiode allows correlated double sampling to be used. However, as described below, dark current may be generated in pixel regions other than the photodiodes. [0002] A 4-transistor pixel typically includes a photodiode, a charge-to-voltage conversion region ("floating diffusion"), and a charge-transfer region. The photodiode and floating diffusion are built in a substrate (eg, silicon), and the charge transfer region is typically a MOSFET ("transfer gate") located between the diode and floating diffus...

AI Technical Summary

Problems solved by technology

This leakage will result in an incorrect reading of the amount of charge collected during the concentration period, thus degrading the image quality

[0008] Although the above structure is generally effective in reducing dark current by injecting dopants into the entire charge transport region to enhance the conductivity with respect to the substrate, this structure does not address the subsurface leakage current and the image lag issue

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