Back-illuminated image sensor with three-dimensional transistor structure and forming method thereof

[0033] In existing image sensors, transistors (such as source follower transistors, transfer transistors, and reset transistors, etc.) are usually planar structures. Therefore, the corresponding pixel units have many defects. For example, it is difficult to further reduce the chip area of ​​image sensors. The cost remains high, the image quality formed by the image sensor is difficult to further improve, the noise level of the image sensor is difficult to reduce, and the area occupancy rate of the photoelectric conversion element in the pixel unit is difficult to increase.

[0034] In existing image sensors, 3D transistors may be used in the process design of image sensors, but during the formation of the gate region of the transistor, the polysilicon etching of the gate region is difficult to control, resulting in the performance of the formed gate region Not good, poor interface goodness.

[0035] The present invention provides a method for forming a back-illuminated image sens