Disclosed in the present invention is a method for manufacturing a back-illuminated CMOS image sensor structure, comprising: providing a silicon substrate which has been subjected to front processing and back thinning; forming a grid-shaped deep trench on the back of the silicon substrate; forming an insulating layer on the inner wall surface of the deep trench, so as to form a grid-shaped deep trench isolation structure; forming a diffusion barrier layer on the surface of the insulating layer; performing metal filling in the deep trench, so as to form a grid-shaped composite structure in which a metal gate is combined with the deep trench isolation. The present invention uses a one-step method for forming the deep trench isolation structure and the metal gate. The method can avoid the requirement that both the deep trench isolation structure and the metal gate need high precision alignment in the traditional process, and can make the deep trench isolation structure also serve as the metal gate, thereby not only improving the utilization rate of the material and saving costs, but also reducing the difficulty of the process, improving the production efficiency.
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