Image sensor and preparation method thereof

Abstract

The invention relates to the technical field of semiconductors, and discloses an image sensor and a preparation method thereof. The image sensor comprises a photodiode and a pixel reading circuit, wherein the photodiode comprises a first doped region and a second doped region; a PN junction is formed by the first doped region and the second doped region by using the surface of a substrate as an interface; the first doped region is positioned in the substrate; the second doped region is positioned on the surface of the substrate; a part of the first doped region is not covered by the second doped region on the surface of the substrate; and the part of the first doped region, which is not covered by the second doped region, is used as an active region of a metal oxide semiconductor (MOS) tube in the pixel reading circuit. Therefore, the potential deviation of the photodiode can be effectively reduced and even eliminated, a photo-generated charge transport effect of the image sensor is improved, and the performance of a device is improved; and in addition, the image sensor is prepared by the traditional process technologies such as graphical reduction, epitaxy and ion implantation, is easy and convenient to operate and is easy to produce in batches.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to an image sensor. Background technique [0002] An image sensor is an electronic component widely used in the fields of digital imaging, aerospace and medical imaging. A charge coupled device (Charge Coupled Device, CCD) image sensor and a complementary metal oxide semiconductor (C1mplementary Metal Oxide Semiconductor, CMOS) image sensor are two common image sensors. [0003] CCD has low readout noise and dark current noise, and has high photon conversion efficiency, so it has high signal-to-noise ratio and high sensitivity. Incident light with very low light intensity can also be detected, and its signal will not be covered up. In addition, the CCD also has a high dynamic range, which improves the use range of the system environment and does not cause signal contrast due to large brightness differences. However, its power consumption is relatively large, the supply vol...

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Problems solved by technology

[0007] if used Figure 4 The shown PN junction photosensitive diode is used to make a CMOS image sensor. Similarly, when an operating voltage is applied to the gate TX of the transfer transistor and the transfer transistor is turned on, under the action of the grid voltage of the transfer transistor gate TX, the semiconductor substrate The part below the gate TX forms an N-type inversion layer, but it is affected by the carrier movement of the P+ doped region of the PN junction photodiode close to the gate of the transfer transistor TX, which is shown on the energy band diagram, located at the transfer Part of the N-doped region below the transistor gate TX (that is, the part of the N-well region in the PN junction photodiode that exceeds the P+ doped region in the horizontal direction) will form a potential sink (pocket), and its potential Distribution map such as Figure 5 As shown, due to the existence of the sink, during the pixel readout process, when the photogenerated charge transfer occurs in the PN junction photodiode PD, some charges will be confined in the potential sink pocket area, and cannot be used due to the inability to jump over the sink potential. Control of gate TX moves down to floating diffusion FD for readout

[0008] Therefore, in the prior art, the barrier effect and pocket effect in the PN junction photodiode hinder the transmission of the photogenerated charge, and the readout process of the photogenerated charge in the image sensor is greatly affected, thereby affecting the device sensitivity, dynamic range, and response. Parameter performance such as speed and signal-to-noise ratio

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