Method for reducing dark current of image sensor

Abstract

The invention provides a method for reducing dark current of an image sensor. The method comprises preparation of a photodiode and a transistor. The preparation of the transistor comprises following steps of firstly forming grid electrodes of four transistors; forming light dope drain regions of a reset pipe, an amplifying pipe and a selecting pipe; then, forming corresponding side walls on grid electrode side walls of the rest pipe, the amplifying pipe, the selection pipe and a transferring pipe; and at last, forming a light dope drain region of the transferring pipe on the substrate of a semiconductor at the bottom of the outer side of the side wall of the transferring pipe. Thus, effective channel length of the transferring pipe is increased, electric field in the channel direction is reduced and probability of generation of thermal electrons is reduced, thereby reducing dark current of the image sensor.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to a method for reducing dark current of an image sensor. Background technique [0002] CMOS image sensor (CIS) is compatible with the existing integrated circuit manufacturing process because of its manufacturing process, and has many advantages in performance compared with the original charge-coupled device CCD. The CMOS image sensor can integrate the driving circuit and the pixel together, which simplifies the hardware design and reduces the power consumption of the system at the same time. Because CIS can take out electrical signals while collecting optical signals, it can also process image information in real time, and its speed is faster than that of CCD image sensors. CMOS image sensors also have the advantages of low price, large bandwidth, anti-blur, flexible access and large fill factor. [0003] Traditional active pixels use photodiodes as image sensing devices....

AI Technical Summary

Problems solved by technology

However, as the size of the pixel unit shrinks, the size of the photodiode PD and the transfer transistor Tx will also continue to shrink. For the drain end of the transfer transistor Tx (ie, the floating diffusion point FD), the lightly doped drain region (LDD) is placed on the Before the formation of the side wall (spacer), the effective channel length of the transfer tube will be reduced, and the hot electron injection effect of the transfer tube will increase. These hot electrons break the original Si-H bond and increase the interface state.

Images