CMOS image sensor and method for forming same

Abstract

A CMOS image sensor comprises at least one CMOS image sensor pixel unit pair which comprises a first pixel unit and a second pixel unit. Each pixel unit in the CMOS image sensor comprises a photodiode area and a drive circuit area, wherein the drive circuit area comprises output transistors. Drain electrodes of the two output transistors adjacent to the first pixel unit and the second pixel unit are connected to be a common output end. The invention further provides another CMOS image sensor, wherein the amount of effective contact holes can be reduced through an output contact hole and a power contact hole of a common output transistor of the adjacent pixel units, thereby effectively decreasing the amount of the contact holes. The structure enables pixel units with smaller dimension to be designed under the condition of unreduced technical nodes without modifying a peripheral circuit and the processing parameter, which can not increase the mask and processing cost, but reduces the output capacitance and increases the filling ratio and the optical path.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to a CMOS image sensor and a forming method thereof. Background technique [0002] At present, the charge coupled device (CCD) is the main practical solid-state image sensing device, which has the advantages of low read noise, large dynamic range, and high response sensitivity. The disadvantage of Complementary-Metal-Oxide-Semiconductor (CMOS) technology compatibility is that it is difficult to achieve single-chip integration with CCD-based image sensors. The CMOS image sensor (CMOS Image sensor, CIS) adopts the same CMOS technology, which can integrate the pixel array and peripheral circuits on the same chip. Compared with CCD, CIS has the advantages of small size, light weight, low power consumption, programming Convenience, ease of control, and low average cost. [0003] At present, the patent application documents related to CMOS image sensors basically focus on how to ...

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Problems solved by technology

However, CIS designers use the widely used 0.18μm technology to design very small pixel units (pixel unit size is less than 2.8×2.8μm 2 ) is more difficult

There are two main reasons. First, as the size of the pixel unit shrinks, if the technology node is the same, the operating voltage of the pixel unit is the same, which means that the threshold voltage Vt of the three transistors must be maintained at a given level. Therefore, the transistor The channel length of the channel cannot be reduced with the reduction of the size of the pixel unit; second, the CMOS image sensor needs to have a contact hole in contact with the metal line to transmit signals and provide power. route them within the pixel area

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