Method of making wafer structure for backside illuminated color image sensor

1. A method comprising:

providing a semiconductor substrate having a substantially planar front surface and a back surface;

forming a first pixel and a second pixel on the substantially planar front surface of the semiconductor substrate; and

forming a first portion of the semiconductor substrate having a first thickness and a second portion of the semiconductor substrate having a second thickness, wherein the first portion having the first thickness is aligned with the first pixel and the second portion having the second thickness is aligned with the second pixel.

2. The method of claim 1 , further comprising forming a planarization layer over the back surface of the semiconductor substrate.

3. The method of claim 2 , wherein forming the planarization layer over the back surface of the semiconductor substrate includes forming the planarization layer directly on the first and second portions of the semiconductor substrate.

4. The method of claim 1 , wherein forming the first portion of the semiconductor substrate having the first thickness and the second portion of the semiconductor substrate having the second thickness includes performing an etching process to the back surface of the semiconductor substrate.

5. The method of claim 4 , wherein the etching process includes a wet etching process.

6. The method of claim 1 , further comprising forming a color filter layer over the first and second portions of the semiconductor substrate.

7. The method of claim 6 , wherein the color filter layer includes a first type of color filter aligned with the first portion and a second color filter aligned with the second portion.

8. A method comprising:

forming a first radiation-sensing element and a second radiation-sensing element on a substantially planar first surface of a substrate; and

removing portions of the substrate such that the substrate has a first thickness and a second thickness, wherein the first thickness and the second thickness are between the substantially planar first surface and a second surface of the substrate, and wherein the first thickness is aligned with the first radiation-sensing element and the second thickness is aligned with the second radiation-sensing element.

9. The method of claim 8 , wherein forming the first radiation-sensing element and the second radiation-sensing element on the substantially planar first surface of the substrate further includes forming a third radiation-sensing element on the substantially planar first surface of the substrate.

10. The method of claim 9 , further comprising forming red, green, and blue color filters over the second surface of the substrate that are aligned with the first, second, and third radiation-sensing elements, respectively.

11. The method of claim 9 , wherein removing portions of the substrate such that the substrate has the first thickness and the second thickness further includes removing additional portions of the substrate such that the substrate has a third thickness, and

wherein the third thickness is between the substantially planar first surface and the second surface of the substrate, and

wherein the third thickness is aligned with the third radiation-sensing element.

12. The method of claim 11 , wherein the first thickness defines a first absorption depth for a first radiation directed towards the first radiation-sensing element from the second surface,

wherein the second thickness defines a second absorption depth for a second radiation directed towards the second radiation-sensing element from the second surface, and

wherein the third thickness defines a third absorption depth for a third radiation directed towards the third radiation-sensing element from the second surface.

13. The method of claim 8 , wherein the substrate is a silicon-on-insulator substrate.

14. The method of claim 8 , further comprising forming one of an organic material layer or a polymeric material layer over the second surface of the substrate.

15. A method comprising:

providing a substrate having a substantially planar first surface and an opposing second surface;

forming a first pixel and a second pixel on the substantially planar first surface of the substrate; and

removing portions of the substrate such that the substrate has a first thickness and a second a second thickness, wherein the first thickness is aligned with the first pixel and the second thickness is aligned with the second pixel.

16. The method of claim 15 , furthering including forming a plurality of metal layers over the substantially planar first surface of the substrate.

17. The method of claim 15 , further comprising forming a planarization layer over the second surface of the substrate.

18. The method of claim 17 , wherein the planarization layer includes a first surface facing the second surface of the semiconductor substrate and an opposing substantially planar second surface,

wherein the planarization layer has a first portion having a first thickness extending from the first surface of the planarization layer to the substantially planar second surface and a second portion having a second thickness extending from the first surface of the planarization layer to the substantially planar second surface, and

wherein the first portion of the planarization layer is aligned with the first pixel and the second portion of the planarization layer is aligned with the second pixel.

19. The method of claim 17 , further comprising forming a color filter layer over the planarization layer; and

forming a lens over the color filter layer.

20. The method of claim 19 , wherein forming the color filter layer over the planarization layer includes forming a first type of color filter over the planarization layer that is aligned with the first thickness and a second type of color filter over the planarization layer that is aligned with the second thickness.