Image sensor having curved micro-mirrors over the sensing photodiode and method for fabricating

• US 20080099804A1
• Filed: 10/26/2006
• Published: 05/01/2008
• Est. Priority Date: 10/26/2006
• Status: Active Grant

• Current Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Original Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Inventors: Venezia, Vincent, Tai, Hsin-chih
• Granted Patent: US 7,888,159 B2
• Time in Patent Office: Days
• US Class Current: 257/291
• CPC Class Codes: H01L 27/14625 Optical elements or arrangements associated with the device
• CPC Class Codes: H01L 27/14629 Reflectors
• CPC Class Codes: H01L 27/14685 Process for coatings or optical elements

Abstract

The invention involves the integration of curved micro-mirrors over a photodiode active area (collection area) in a CMOS image sensor (CIS) process. The curved micro-mirrors reflect light that has passed through the collection area back into the photo diode. The curved micro-mirrors are best implemented in a backside illuminated device (BSI).

Claims

1. A method comprising:

fabricating an image sensor up to, but not including, a first metallization layer;

fabricating a micro-lens on a pre-metal dielectric layer;

depositing a metal layer of a reflective material on the micro-lens and pre-metal dielectric layer;

covering the metal layer with photoresist;

patterning the photoresist to remove the photoresist from all areas except the surface of the micro-lens;

etching exposed metal layer away;

removing remaining photoresist; and

covering the micro-mirror with a layer of dielectric material.

2. The method of claim 1, wherein the image sensor is a CMOS image sensor.

3. The method of claim 1, wherein the image sensor is a backside illuminated image sensor.

4. The method of claim 1, wherein the pre-metal dielectric layer is up to 800 nanometers thick.

5. The method of claim 1, wherein the layer of reflective material is a metal.

6. The method of claim 1, wherein the layer of reflective material is between 10 and 50 nanometers thick.

7. The method of claim 1, wherein the micro-lens is curved.

8. The method of claim 7, wherein the micro-lens is concave.

9. A method of fabricating micro-mirrors for an image sensor, the method comprising:

fabricating an image sensor up to, but not including, a first metallization layer;

fabricating a micro-lens on a first pre-metal dielectric layer where the first pre-metal dielectric layer is some portion of the PMD layer;

depositing a layer of a reflective material on the micro-lens and first portion of the PMD layer;

covering the layer of reflective material with photoresist;

patterning the photoresist to remove the photoresist from all areas except the surface of the microlens;

etching away exposed metal;

removing remaining photoresist; and

depositing a second pre-metal dielectric layer over the micro-lens where the second pre-metal dielectric layer is a remaining portion of the PMD.

10. The method of claim 9 wherein the PMD layer is planarized.

11. A method of fabricating micro-mirrors for an image sensor, the method comprising:

fabricating an image sensor up to, but not including, a first metallization layer;

fabricating a micro-lens on a silicon surface of the image sensor;

depositing a metal layer of a reflective material on the micro-lens and silicon surface;

depositing a layer of reflective material over the image sensor;

covering the image sensor with photoresist;

patterning the photoresist to remove the photoresist from all areas except the microlens;

etching exposed reflective layer away;

removing remaining photoresist; and

covering the micro-mirror with a layer of dielectric material.

12. An apparatus comprising an image sensor with a micro-mirror, the image sensor further comprising:

a pre-metal dielectric layer;

a micro-lens coupled to the pre-metal dielectric layer;

a metal layer coupled to the micro-lens forming a micro-mirror; and

a layer of dielectric material covering the micro-mirror.

13. The apparatus as in claim 12, further comprising a curved micro-mirror above the pre-metal dielectric layer.

14. The apparatus as in claim 12, further comprising a curved micro-mirror within the pre-metal dielectric layer.

15. An apparatus comprising an image sensor with a micro-mirror, the image sensor further comprising:

a backside illumination device;

a pre-metal dielectric layer;

a micro-lens coupled to the pre-metal dielectric layer;

a metal layer coupled to the micro-lens forming a micro-mirror; and

a layer of dielectric material covering the micro-mirror.

16. The apparatus as in claim 15, further comprising a curved micro-mirror above the pre-metal dielectric layer.

17. The apparatus as in claim 15, further comprising a curved micro-mirror within the pre-metal dielectric layer.

18. An apparatus comprising an image sensor with a micro-mirror, the image sensor further comprising:

a backside illumination device;

a micro-lens coupled to a surface of the backside illumination device;

a metal layer coupled to the micro-lens forming a micro-mirror; and

a layer of dielectric material covering the micro-mirror.

19. The apparatus of claim 18, further comprising a curved micro-lens.

20. The apparatus of claim 18, further comprising a concave micro-lens.