Image sensors with phase detection auto-focus pixels

1. An image sensor pixel array, comprising:

a plurality of image pixels to gather image information; and

a plurality of phase detection auto-focus (PDAF) pixel units to gather phase information,

wherein:

each of the PDAF pixel units is substantially surrounded by the image pixels;

each of the PDAF pixel units includes at least one PDAF pixel, wherein:

the PDAF pixel includes a first photodiode (PD) disposed in a semiconductor substrate and a first micro-lens covers the PDAF pixel;

the image pixel includes a second PD disposed in the semiconductor substrate and it second micro-lens covers the image pixel, wherein:

the first PD is identical to the second PD, and the first micro-lens is identical to the second micro-lens; and

a coating layer disposed on both the first micro-lenses and the second micro-lenses, wherein the coating layer forms a flattened surface across the image sensor pixel array;

a PDAF micro-lens disposed on the coating layer, wherein the PDAF micro-lens covers a PDAF pixel unit;

wherein a refractive index of the coating layer is lower than a refractive index of the first micro-lens and the second micro-lens; and

wherein a refractive index of the PDAF micro-lens is lower than the refractive index of the coating layer.

2. The image sensor pixel array of claim 1 , further comprising:

a first interlayer dielectric layer disposed on the semiconductor substrate;

a color filter array disposed on the first interlayer dielectric layer;

a second interlayer dielectric layer disposed on the color filter array.

3. The image sensor pixel array of claim 2 , wherein a refractive index of the second interlayer dielectric layer is not lower than a refractive index of the first micro-lens and the second micro-lens.

4. The image sensor pixel array of claim 1 , wherein a PDAF pixel unit includes two PDAF pixels adjacent to each other arranged to form a 2×1 pattern.

5. The image sensor pixel array of claim 1 , wherein a PDAF pixel unit includes four PDAF pixels adjacent to each other arranged to form a 2×2 pattern.

6. The image sensor pixel array of claim 4 , wherein the PDAF micro-lens covers both PDAF pixels of the PDAF pixel units.

7. The image sensor pixel array of claim 6 , wherein the PDAF pixels of the PDAF pixel units include green color filters aligned with first micro-lenses of the PDAF pixels.

8. The image sensor pixel array of claim 4 , wherein a left half of the incident light is directed and focused to a first PDAF pixel of the PDAF pixel unit, and a right half of the incident light is directed and focused to a second pixel of the PDAF pixel unit.

9. The image sensor pixel array of claim 1 , further comprising isolation regions between adjacent PDs in the semiconductor substrate.

10. The image sensor pixel array of claim 1 , further comprising isolation regions between adjacent PDs in the semiconductor substrate, except between adjacent PDs of the PDAF pixels.

11. The image sensor pixel array of claim 1 , wherein the PDAF pixel unit includes a single half-shield (HS) PDAF pixel.

12. The image sensor pixel array of claim 11 , wherein the HS PDAF pixel includes a half shield, wherein the half shield blocks a first half of the incident light, and a second half of the incident light passes through a clear filter in the HS PDAF pixel.

13. The image sensor pixel array of claim 12 , wherein the half shield blocks a left half of the incident light, and a right half of the incident light passes through the clear filter in the left half of the HS PDAF pixel.

14. The linage sensor pixel array of claim 12 , wherein the half shield blocks a right half of the incident light, and a left half of the incident light passes through the clear filter in the right half of the HS PDAF pixel.

15. A method for manufacturing an image sensor, comprising:

forming a micro-lens array on an image sensor pixel array, wherein the image sensor pixel array comprising:

a plurality of image pixel units for gathering image information; and

a plurality of phase detection auto-focus (PDAF) pixel units for gathering phase information;

forming a coating layer on the micro-lens array;

flattening a surface of the coating layer across the micro-lens array;

forming a PDAF micro-lens on the coating layer, wherein the PDAF micro-lens covers a PDAF pixel unit;

wherein a refractive index of the coating layer is lower than a refractive index of the micro-lens array; and

wherein a refractive index of the PDAF micro-lens is lower than the refractive index of the coating layer.