Image sensors with optical trench

• US 20070045513A1
• Filed: 08/30/2005
• Published: 03/01/2007
• Est. Priority Date: 08/30/2005
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Mouli, Chandra, Lee, Ji
• Granted Patent: US 7,315,014 B2
• Time in Patent Office: Days
• US Class Current: 250/208.100
• CPC Class Codes: H01L 27/14627 Microlenses
• CPC Class Codes: H01L 27/14629 Reflectors
• CPC Class Codes: H01L 27/1463 Pixel isolation structures
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures

Abstract

A device and method for providing an optical trench structure for a pixel which guides incoming light onto the photosensor of the pixel. The optical trench structure has an optically reflecting barrier that substantially mitigates optical crosstalk. The optical trench structure is made of low dielectric constant material with an index of refraction that is less than the index of refraction of the material of surrounding layers (e.g., the substrate). This difference in refractive index causes an internal reflection into an optical path existing between a lens and pixel.

Claims

1. An image pixel comprising:

a photo-conversion device formed over a substrate;

at least one optically transmissive layer formed over a backside of said substrate;

a trench formed within at least a portion of said substrate and defining an optical guide structure over the photo-conversion device; and

at least one material filling said trench, said material having a lower refractive index than a refractive index of said substrate such that said reflection is produced by a refractive index difference.

2. The pixel of claim 1, wherein said trench is continuous and surrounds a lateral area of said photo-conversion device.

3. The pixel of claim 1, wherein said at least one material has a lower refractive index than a refractive index of said substrate such that said reflection is produced by a refractive index difference.

4. The pixel of claim 1, wherein said at least one material has a dielectric constant less than 1.45.

5. The pixel of claim 1, wherein said at least one material comprises carbon doped silicon dioxide.

6. The pixel of claim 1, wherein said at least one material comprises fluorinated silica glass oxide.

7. The pixel of claim 1, wherein said at least one material comprises metal.

8. The pixel of claim 1, wherein said at least one material comprises silver.

9. The pixel of claim 1, wherein said at least one material comprises copper.

10. The pixel of claim 1, wherein said at least one material comprises a plurality of materials layered within the interior surface of said trench.

11. The pixel of claim 1, wherein an outermost layer of said plurality of materials comprises silicon nitride.

12. The pixel of claim 1, wherein said photo-conversion device is a photosensor.

13. The pixel of claim 1, wherein said photo-conversion device is a photo emitter.

14. An image sensor comprising:

a plurality of pixels in an array, at least one of said pixels comprising;

a photosensor;

a lens for receiving incident light;

at least optically transmissive layer formed over a backside of said substrate; and

a trench formed within at least a portion of said substrate and defining an optical guide structure over the photo-conversion device; and

at least one material filling said trench, said material having a lower refractive index than a refractive index of said substrate such that said reflection is produced by a refractive index difference.

15. The image sensor of claim 14, wherein each trench is formed to surround a lateral area defined by said photosensor.

16. The image sensor of claim 14, wherein said at least one material has a lower refractive index than a refractive index of a material contained in said substrate.

17. The image sensor of claim 14, wherein said at least one material has a low-dielectric constant less than 1.45.

18. The image sensor of claim 14, wherein said at least one material comprises a metal.

19. The image sensor of claim 14, wherein said at least one material comprises a plurality of materials layered within the interior surface of said trench.

20. The image sensor of claim 19, wherein an outermost layer of said plurality of materials comprises silicon nitride.

21. A system comprising:

a processor coupled to an image sensor, said image sensor comprising;

a photosensor;

a lens for receiving incident light;

at least one optically transmissive layer formed over a backside of said substrate; and

an optical guide structure formed in said substrate, said optical guide structure comprising;

a trench defining said optical guide; and

at least one material filling said trench, said at least one material having a property of producing reflection of light within said optical guide structure.

22. The system of claim 21, wherein each trench is formed to surround a lateral area defined by said photosensor.

23. The system of claim 21, wherein said at least one material has a lower refractive index than a refractive index of a material contained in said substrate.

24. The system of claim 21, wherein said at least one material has a low-dielectric constant less than 1.45.

25. The system of claim 21, wherein said at least one material comprises a metal.

26. The system of claim 21, wherein said at least one material comprises a plurality of materials layered within the interior surface of said trench.

27. The system of claim 26, wherein an outermost layer of said plurality of materials comprises silicon nitride.

28. A method of forming an optical guide structure within a pixel of an imaging device, comprising the steps of:

forming a photo-conversion device over a substrate;

forming at least one optically transmissive layer over a backside of said substrate;

etching a trench into at least a portion of said substrate; and

filling said trench with at least one material suitable for producing an internal reflection of light within an area defined by said trench.

29. The method of claim 28, wherein said etching step comprises etching the trench to surround a lateral area defined by the photo-conversion device.

30. The method of claim 28 wherein said filling step comprises coating an interior surface of said trench with a first of said at least one material, thereby producing a first partially filled trench having an interior surface.

31. The method of claim 30, wherein said filling step further comprises filling an interior surface of said partially filled trench with a second of said at least one material, said second material being different from said first material.

32. The method of claim 30, wherein said filling step further comprises:

coating an interior surface of said partially filled trench with a second of said at least one material, thereby producing a second partially filled trench having an interior surface; and

filling the interior surface of said second partially filled trench with a third of said at least one material, said third material being different from said second material.

33. The method of claim 28 wherein said at least one material has a refractive index different from a refractive index of said substrate material.

34. The method of claim 28, wherein said at least one material has a dielectric constant less than 1.45.

35. The method of claim 28, wherein said at least one material comprises carbon doped silicon dioxide.

36. The method of claim 28, wherein said at least one material comprises fluorinated silica glass oxide.

37. The method of claim 28, wherein said at least one material comprises metal.

38. The method of claim 28, wherein said at least one material comprises silver.

39. The method of claim 28, wherein said at least one material comprises copper.