Global shutter CMOS image sensor and method for forming the same

1. A global shutter Complementary Metal-Oxide-Semiconductor (CMOS) image sensor, comprising:

a photodiode disposed in an upper portion of the substrate;

a floating diffusion region disposed in the upper portion of the substrate;

a storage diode disposed in the upper portion of the substrate, and the storage diode is disposed between the photodiode and the floating diffusion region;

a first transfer gate disposed on the substrate between the photodiode and the storage diode;

a second transfer gate disposed on the substrate between the storage diode and the floating diffusion region;

a first dielectric layer that is disposed on the substrate and that covers the first transfer gate and the second transfer gate;

a light-shielding layer disposed on the first dielectric layer; and

a light pipe through the light-shielding layer and a portion of the first dielectric layer, and correspondingly disposed above the photodiode,

wherein a refractive index of the light pipe is higher than a refractive index of the first dielectric layer,

wherein the light-shielding layer comprises at least two film layers.

2. The global shutter CMOS image sensor as claimed in claim 1 , wherein a projection of the light pipe is within range of a projection of the photodiode in a top view.

3. The global shutter CMOS image sensor as claimed in claim 1 , wherein an upper diameter of the light pipe is greater than a lower diameter of the light pipe.

4. The global shutter CMOS image sensor as claimed in claim 1 , wherein a ratio of the upper diameter of the light pipe to the lower diameter of the light pipe is in a range from about 1 to about 3.

5. The global shutter CMOS image sensor as claimed in claim 1 , wherein a ratio of the upper diameter of the light pipe to a width of the photodiode is in a range from about 0.2 to about 1.

6. The global shutter CMOS image sensor as claimed in claim 1 , wherein a distance between a bottom surface of the light pipe and the photodiode is in a range from about 0 nm to about 600 nm.

7. The global shutter CMOS image sensor as claimed in claim 1 , wherein the light pipe comprises poly(methyl methacrylate) (PMMA), perfluorocyclobutyl (PFCB) polymer, polyimide, or epoxy resins.

8. The global shutter CMOS image sensor as claimed in claim 1 , wherein a refraction index of the light pipe is greater than 1.46.

9. The global shutter CMOS image sensor as claimed in claim 1 , wherein the light pipe comprises two or more materials with different refraction indexes.

10. The global shutter CMOS image sensor as claimed in claim 1 , wherein the light-shielding layer comprises tungsten, aluminum, silicon nitride, tungsten nitride, metal nitride, metal oxide, or a combination thereof.

11. The global shutter CMOS image sensor as claimed in claim 1 , wherein an extinction coefficient of the light-shielding layer is greater than 1, and a reflectivity of the light-shielding layer is greater than 90%.

12. The global shutter CMOS image sensor as claimed in claim 1 , further comprising:

a second dielectric layer disposed on the light-shielding layer and the light pipe.

13. The global shutter CMOS image sensor as claimed in claim 1 , further comprising:

a passivation layer blanketly covering the light-shielding layer;

an underlayer blanketly covering the passivation layer;

a color filter disposed on the underlayer and above the light pipe; and

a microlens disposed on the color filter and above the light pipe.

14. A method of forming a global shutter CMOS image sensor, comprising:

forming a photodiode, a floating diffusion region, and a storage diode in an upper portion of a substrate, wherein the storage diode is disposed between the photodiode and the floating diffusion region;

forming a first transfer gate on the substrate between the photodiode and the storage diode;

forming a second transfer gate on the substrate between the storage diode and the floating diffusion region;

forming a first dielectric layer on the substrate, wherein the first dielectric layer covers the first transfer gate and the second transfer gate;

forming a light-shielding layer on the first dielectric layer;

removing a portion of the light-shielding layer on the first dielectric layer;

forming a hole in an upper portion of the first dielectric layer with the remaining light-shielding layer being used as a mask, wherein the hole is above the photodiode; and

forming a light pipe in the hole, wherein a refraction index of the light pipe is greater than a refraction index of the first dielectric layer.

15. The method for forming a global shutter CMOS image sensor as claimed in claim 14 , wherein a projection of the light pipe is within range of a projection of the photodiode in a top view.

16. The method for forming a global shutter CMOS image sensor as claimed in claim 14 , wherein an upper diameter of the light pipe is greater than a lower diameter of the light pipe.

17. The method for forming a global shutter CMOS image sensor as claimed in claim 14 , wherein the light pipe comprises two or more materials with different refraction indexes.

18. The method for forming a global shutter CMOS image sensor as claimed in claim 14 , wherein the light-shielding layer comprises at least two film layers.

19. The method for forming a global shutter CMOS image sensor as claimed in claim 14 , further comprising:

forming a second dielectric layer on the light-shielding layer and the light pipe.