Image sensor and forming method thereof

Abstract

The invention discloses an image sensor and a forming method thereof. The image sensor comprises a pixel array, and the pixel array comprises a plurality of pixel units which are arranged in an array mode. Each pixel unit comprises a semiconductor substrate, a photodiode, a floating diffusion region, a transfer transistor and a source-follower transistor, wherein the photodiode is placed in the semiconductor substrate, the floating diffusion region is placed in the semiconductor substrate, the transfer transistor comprises a source electrode and a drain electrode which are placed in the semiconductor substrate, the source electrode and the drain electrode are electrically connected with a photovoltaic conversion element and the floating diffusion region respectively, the source-follower transistor comprises a grid electrode placed on the semiconductor substrate, the grid electrode is electrically connected with the floating diffusion region, a channel region of the source-follower transistor is of a cross beam structure, the cross beam structure is provided with a top face and two side faces, and the grid electrode of the source-follower transistor covers at least one of the top face and the two side faces. The performance of the image sensor is improved, and cost is lowered.

Description

technical field [0001] The present invention relates to the field of image sensors, in particular to an image sensor and a forming method thereof. Background technique [0002] An image sensor is a semiconductor device that converts an optical signal into an electrical signal, and the image sensor has a photoelectric conversion element. [0003] Image sensors can be further divided into complementary metal oxide (CMOS) image sensors and charge-coupled device (CCD) image sensors. The advantage of the CCD image sensor is that it has high image sensitivity and low noise, but it is difficult to integrate the CCD image sensor with other devices, and the power consumption of the CCD image sensor is relatively high. In contrast, CMOS image sensors have the advantages of simple process, easy integration with other devices, small size, light weight, low power consumption, and low cost. Therefore, with the development of technology, CMOS image sensors are increasingly used in variou...

AI Technical Summary

Problems solved by technology

Therefore, although the circuits around the pixel array can further reduce the line width and size according to Moore's Law, the transistor devices in the pixel unit can only be reduced very slowly.

The area of ​​the entire image sensor chip is mainly determined by the pixel array. Therefore, the structure of the existing pixel unit limits the further reduction of the chip area, making the cost of the image sensor high.

[0014] 2. In the existing pixel unit, the four transistor devices are all planar structures. For a pixel unit of a certain size, after containing four transistor devices, the size can be further reduced. ratio is limited

In the traditional existing process, even though great effort is spent on these aspects, the ideal effect cannot be achieved because the process limit has been reached. Therefore, new image sensors and corresponding processes are urgently needed to further reduce dark current and noise. , white point and dark point etc. indicator levels

[0016] 4. In the existing pixel unit, since each transistor has a planar structure, the parasitic capacitance between the transfer transistor, the reset transistor and the source follower transistor cannot be further reduced as the size is reduced, and the parasitic capacitance basically plays a negative role. For example, reducing signal transmission speed, increasing low-frequency 1 / f noise, reducing dynamic range, etc., these are unacceptable for image sensors

Therefore, it is necessary to further reduce parasitic capacitance and reduce low-frequency 1 / f noise in order to increase signal transmission speed and increase dynamic range, which is a very difficult and expensive task for traditional image sensors and their formation processes

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