Backside illuminated image sensor and preparation method

Abstract

The invention provides a backside illuminated image sensor. An isolation ring surrounds a photodiode and a channel region of a second conductive type and penetrates through a semiconductor substrate and an epitaxial layer of the second conductive type; and the first conductive type source region extends into the second conductive type channel region from the surface of the second conductive type channel region along the inner wall of the isolation ring and surrounds the first conductive type charge accumulation region, and the second conductive type channel region isolates the first conductivetype source region from the first conductive type charge accumulation region. The isolation ring of the backside illuminated image sensor is completely compatible with the conventional CMOS process flow, and the vertically distributed photodiode and the first conductive type source region are formed in the isolation ring by adopting multiple times of injection, so that the parasitic capacitance of the charge transmission tube is reduced, the transmission rate of the charge transmission tube is improved, and the image frame rate of an image sensor chip is improved.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to a back-illuminated image sensor and a preparation method thereof. Background technique [0002] With the development of image recognition for autonomous driving and artificial intelligence, CMOS APS (CMOS active pixel sensor, CMOS active pixel sensor) has become an important component in image recognition due to its advantages of high integration, small size, and low power consumption. . [0003] Compared with the commonly used charge-coupled device (CCD), the dynamic range, sensitivity and noise index of the traditional CMOS APS are poor, mainly reflected in the crosstalk of adjacent pixels when the light intensity changes sharply, which seriously limits The use of CMOS APS in high-quality imaging. figure 1 A schematic diagram of a traditional back-illuminated pixel structure is shown. The traditional back-illuminated image sensor includes a photosensitive photodiode (P...

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Problems solved by technology

However, with the conventional backside illumination (BSI) image sensor with backside thinning, even with backside thinning, the thickness of the photosensitive layer is about 3 μm.

When a small-sized pixel is used, the energy of long-wavelength light is low, such as red light, and half of the far-red light is not absorbed by the image sensor, resulting in a low sensitivity to infrared light, resulting in an obvious lack of full well charge and poor image quality. bad question

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