A stacked global exposure pixel unit structure and its forming method

Abstract

The present invention discloses a stacked-type global exposure pixel unit structure and a method for forming the same. The method comprises of forming a lower electrode plate and a top electrode plate of a capacitor by using the top metal in the top dielectric layer and the adhesive layer of the stacked first chip and the second chip to replace the MOS capacitor originally located in the first chip silicon substrate wherein the capacitor dielectric layer can also be made with a high dielectric constant so that the effective area of the capacitor can be greatly increased, that the storage capacitance value of the global exposure pixel unit is increased, and that the readout noise is reduced effectively. Meanwhile, through the use of the opaque top metal material to make the lower electrode plate for the capacitor as a light shielding structure, it is possible to prevent the incidence light rays that penetrate the silicon substrate and the back dielectric layer from affecting the capacitance storage signal. In addition, since it is no longer necessary to form an MOS capacitor structure in the silicon substrate of the first chip, the photosensitive area of the photodiode can be increased to the position occupied by the original MOS capacitor so as to improve the sensitivity of the pixel unit.

Description

technical field [0001] The present invention relates to the field of image sensors, in particular to a structure and a forming method of global exposure pixel units of a stacked CMOS image sensor using a back-illumination process. 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 medicine. [0004] In...

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Problems solved by technology

like figure 2 As shown, incident light with a certain incident angle is only reflected on the metal isolation 101 used to prevent crosstalk between pixel units (as indicated by the dotted arrow pointing upwards in the figure), since the peripheral area of ​​the lower plate of the capacitor is silicon substrate, and the silicon substrate is light-transmissive, so some light will still pass through the silicon substrate and enter the lower plate of the storage capacitor, that is, the MOS capacitor, affecting the charge signal stored on the MOS capacitor, resulting in distortion of the stored signal

[0013] In addition, since the lower plate 104 of the MOS capacitor and the photodiode 102 for the pixel unit to receive light are located in the silicon substrate 103 of the first chip, in order to ensure the sensitivity of the pixel unit, we hope to increase the area of ​​the photosensitive area, that is, the photodiode as much as possible. , so the area of ​​the MOS capacitor is limited by the photodiode, that is, the capacitance value of the MOS capacitor is limited, that is, the readout noise of the pixel unit cannot be effectively reduced

At the same time, the area of ​​the photodiode is also limited by the lower plate of the capacitor. The part of the silicon substrate occupied by the lower plate cannot be used for light sensing, which affects the sensitivity of the pixel unit.

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