CMOS image sensors

1. A CMOS image sensor comprising:

a semiconductor substrate;

a photodiode on the semiconductor substrate;

an insulating film on the semiconductor substrate, over the photodiode;

a microlens that is wider than the photodiode, comprising:

i) a first dielectric film on the insulating film and over the photodiode, the first dielectric film having a first refractive index;

ii) a second dielectric directly film on the first dielectric film, the second dielectric film having a second refractive index lower than the first refractive index; and

iii) a sidewall dielectric film directly on at sidewalls of each of the first and second dielectric films and on the insulating film, the sidewall dielectric film having a curved outer surface and a refractive index equal to the first refractive index; and

a fourth dielectric film on the insulating film and on the microlens.

2. A CMOS image sensor as claimed in claim 1 , wherein the first index of refraction is higher than an index of refraction of the second and fourth dielectric film.

3. A CMOS image sensor as claimed in claim 1 , wherein the indices of refraction of the first dielectric and sidewall dielectric films are about 1.8˜2.2, and the indices of refraction of the second and fourth dielectric films are about 1.3˜1.7.

4. A CMOS image sensor as claimed in claim 1 , wherein widths of the first and second dielectric films are substantially identical to a width of the photodiode.

5. A CMOS image sensor as claimed in claim 1 , wherein the first dielectric and sidewall dielectric films comprise nitride films.

6. A CMOS image sensor as claimed in claim 1 , further comprising a color filter layer located on the fourth dielectric film over the photodiode.

7. A CMOS image sensor as claimed in claim 1 , wherein the photodiode is in an epitaxial layer on the substrate.

8. A CMOS image sensor as claimed in claim 7 , further comprising a device isolation layer in the epitaxial layer and adjacent to the photodiode.

9. A CMOS image sensor as claimed in claim 4 , wherein the width of each of the first and second dielectric films are about 05˜2 μm.

10. A CMOS image sensor as claimed in claim 7 , further comprising a depletion region in the epitaxial layer.

11. A CMOS image sensor as claimed in claim 1 , wherein the insulating film comprises a light shielding layer.

12. A CMOS image sensor as claimed in claim 7 , wherein the photodiode comprises a region of the epitaxial layer containing N-type impurity ions.

13. A CMOS image sensor as claimed in claim 1 , wherein the first dielectric film has a thickness of about 5,000˜15,000 Å.

14. A CMOS image sensor as claimed in claim 1 , wherein the second dielectric film has a thickness of about 5,000˜15,000 Å.

15. A CMOS image sensor as claimed in claim 1 , wherein the sidewall dielectric film forms a sidewall spacer at the sidewalls of the first and second dielectric films.

16. A CMOS image sensor as claimed in claim 15 , wherein the sidewall dielectric film has a thickness at an interface wit the sidewalls of the first and second dielectric films about equal to a combined thickness of the first and second dielectric films.

17. A CMOS image sensor as claimed in claim 7 , wherein the first and second dielectric films are substantially aligned with the underlying photodiode, and substantially all of the sidewall dielectric film is over the area of the epitaxial layer that is lateral to die photodiode and surrounds the photodiode.

18. A CMOS image sensor as claimed in claim 1 , wherein the second and fourth dielectric films each comprise an oxide film.

19. A CMOS image sensor as claimed in claim 1 , wherein the insulating layer comprises an oxide film.

20. A CMOS image sensor as claimed in claim 6 , wherein the color filter layer is over the first and second dielectric layers and at least a portion of the sidewall dielectric layer.