Back-illuminated global pixel unit structure and preparation method thereof

Abstract

The invention provides a backside illumination global pixel unit structure and a preparation method thereof. The preparation method includes the following steps: conducting reflection of incident light by using a light-blocking isolation groove and an additional capacitance top crown, preventing the incident light from entering a charge signal memory block of a capacitor structure, and forming an additional capacitor structure on a back surface of a silicon lining in correspondence to the capacitor structure, the additional capacitor structure being in parallel to the capacitor structure. The backside illumination global pixel unit structure does not take too much an area of a pixel unit, does not influence a photosensitive area of a photodiode in the pixel unit, does not low agility of a device, can increase memory capacitance of the global pixel unit, lowers readout noise of the global pixel unit and increases entire performance of the global pixel unit.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to a back-illuminated global pixel unit structure and a preparation method thereof. Background technique [0002] An image sensor refers to a device that converts optical signals into electrical signals. Generally, large-scale commercial image sensor chips include charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) image sensor chips. [0003] Compared with traditional CCD sensors, CMOS image sensors have the characteristics of low power consumption, low cost and compatibility with CMOS technology, so they are more and more widely used. CMOS image sensors are now not only used in consumer electronics, such as miniature digital cameras (DSC), mobile phone cameras, video cameras and digital single-lens reflex (DSLR), but also in automotive electronics, monitoring, biotechnology and medical fields. . [0004] The pixel unit of the CMOS image sensor i...

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Problems solved by technology

[0011] At the same time, the capacitance values ​​of storage capacitors C1 and C2 also directly affect the readout noise of the global pixel unit. The larger the capacitance value of storage capacitors C1 and C2, the smaller the readout noise of the pixel unit and the better its performance. Conventional storage capacitors C1 and C2 use MOS capacitors, and the capacitance value is proportional to its area, but if the area of ​​the storage capacitor is increased, the photosensitive area of ​​the photodiode needs to be reduced, which will reduce the sensitivity of the pixel unit. Therefore, in order to ensure that the photodiode in the pixel unit area of ​​the photosensitive area, the area of ​​the storage capacitor is limited

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