Image sensors and methods of forming the same

1. An image sensor, comprising:

a semiconductor substrate containing a plurality of photodiodes formed therein;

a patterned buffer layer disposed above the semiconductor substrate;

a red (R) pixel, a green (G) pixel, a blue (B) pixel and an infrared (IR) pixel;

R, G and B filters respectively disposed at the R, G and B pixels;

an IR pass filter disposed at the IR pixel; and

an IR filter stacked with the R, G and B filters, wherein the IR filter cuts off at least IR light with a specific wavelength, the semiconductor substrate is disposed under the R, G and B filters, the IR filter and the IR pass filter, the R, G and B filters are disposed on the IR filter, the IR filter is formed on the patterned buffer layer, and the patterned buffer layer has an opening at the IR pixel.

2. The image sensor as claimed in claim 1 , further comprising a light source unit configured to radiate IR light with a wavelength of a specific band onto an object, wherein the specific wavelength of the IR light cut off by the IR filter is consistent with the wavelength of the specific band of the IR light of the light source unit.

3. The image sensor as claimed in claim 2 , wherein the R, G and B filters combined with the IR filter allows R, G and B lights with wavelengths of a visible band to be transmitted through and cuts off the IR light of the light source unit with the wavelength of the specific band.

4. The image sensor as claimed in claim 1 , wherein a top surface of the IR pass filter is higher than a top surface of the IR filter.

5. The image sensor as claimed in claim 1 , wherein a top surface of the IR pass filter is level with a top surface of the R, G and B filters.

6. The image sensor as claimed in claim 1 , wherein the IR filter comprises a selective IR filter cutting off IR light with the specific wavelength.

7. The image sensor as claimed in claim 1 , wherein the IR filter comprises an IR cut-off filter cutting off IR light with wavelengths of the entire IR band.

8. The image sensor as claimed in claim 1 , further comprising:

a light source unit configured to radiate IR light with a specific wavelength onto an object;

a microlens structure disposed above the R, G and B filters, the IR filter and the IR pass filter; and

a double band pass filter disposed above the microlens structure, wherein the double band pass filter allows a light with a first wavelength of a visible band and a light with a second wavelength of a specific IR band to be transmitted through, and the second wavelength of the specific IR band is consistent with the specific wavelength of the IR light of the light source unit.

9. A method of forming an image sensor, comprising:

providing a semiconductor substrate containing a plurality of photodiodes formed therein, wherein each of the photodiodes is disposed at one pixel of a red (R) pixel, a green (G) pixel, a blue (B) pixel and an infrared (IR) pixel;

forming a buffer material layer above the semiconductor substrate;

forming an IR filter material layer on the buffer material layer;

removing a portion of the buffer material layer at the IR pixel to form a patterned buffer layer;

removing a portion of the IR filter material layer at the IR pixel to form an IR filter, wherein the IR filter cuts off at least IR light with a specific wavelength, and the IR filter has an opening at the IR pixel;

forming R, G and filters respectively at the R, G and B pixels; and

forming an IR pass filter in the opening of the IR filter at the IR pixel.

10. The image sensor as claimed in claim 1 , wherein the R, G and B filters and the IR filter have an opening together, and the IR pass filter fills in the opening of the R, G and B filters and the IR filter.

11. An image sensor, having a pixel array area and a peripheral area surrounding the pixel array area, comprising:

a red (R) pixel, a green (G) pixel, a blue (B) pixel and an infrared (IR) pixel;

R, G and B filters respectively disposed at the R, G and B pixels;

an IR pass filter disposed at the IR pixel; and

an IR filter stacked with the R, G and B filters, wherein the IR filter cuts off at least IR light with a specific wavelength, the R, G and B filters, the IR filter and the IR pass filter are disposed in the pixel array area, and the IR pass filter is further disposed in the peripheral area as a light shielding element.

12. The image sensor as claimed in claim 11 , wherein the R, G and B filters are disposed underneath the IR filter.

13. The image sensor as claimed in claim 11 , wherein a top surface of the IR pass filter is lower than the top surface of the IR filter, and a cavity is formed on the IR pass filter.

14. The image sensor as claimed in claim 13 , further comprising a microlens structure disposed on the IR filter and the IR pass filter, wherein the microlens structure fills in the cavity formed on the IR pass filter.