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

• US 7,888,159 B2
• Filed: 10/26/2006
• Issued: 02/15/2011
• 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: Tai, Hsin-chih, Venezia, Vincent
• Primary Examiner(s): CHEN, JACK S J
• Application Number:
  US11/588,925
• Publication Number:
  US 20080099804A1
• Time in Patent Office: 1,573 Days
• Field of Search: 438/48, 438/69, 438/70, 438/72, 438/57, 257/E33.068
• US Class Current: 438/69
• 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, wherein the image sensor includes a light sensitive element configured to receive light from a light-incident side of the image sensor;

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, wherein the metal layer is exposed in areas where the photoresist is removed;

etching the exposed metal layer away to form a micro-mirror, wherein the light sensitive element is disposed between the light incident side of the image sensor and the micro-minor;

removing remaining photoresist; and

covering the micro-minor 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 between 10 and 50 nanometers thick.

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

7. The method of claim 6, wherein the micro-lens is concave.

8. The method of claim 1, wherein the micro-mirror is disposed to redirect incident light back through to the light sensitive element.

9. The method of claim 1, wherein the light sensitive element includes a photodiode.

10. The method of claim 1, wherein the micro-lens is a first micro-lens and wherein the image sensor includes a second micro-lens disposed on the light-incident side of the image sensor, such that the light sensitive element is disposed between the first micro-lens and the second micro-lens.

11. A method, comprising:

fabricating a first layer of an image sensor, wherein the image sensor includes a light sensitive element configured to receive light from a light-incident side of the image sensor;

fabricating a micro-lens on the first layer of the image sensor;

depositing a metal layer of reflective material on the micro-lens and on the first layer of the image sensor;

covering the image sensor with photoresist;

patterning the photoresist to remove the photoresist from all areas except the micro-lens, wherein the metal layer is exposed in areas where the photoresist is removed;

etching the exposed metal layer of reflective material away to form a micro-mirror, wherein the light sensitive element is disposed between the light incident side of the image sensor and the micro-minor; and

removing remaining photoresist.

12. The method of claim 11, wherein the image sensor is a CMOS image sensor.

13. The method of claim 11, wherein the image sensor is a backside illuminated image sensor.

14. The method of claim 11, wherein the micro-mirror is disposed to redirect incident light back through to the light sensitive element.

15. The method of claim 11, wherein the light sensitive element includes a photodiode.

16. The method of claim 11, wherein the micro-lens is a first micro-lens and wherein the image sensor includes a second micro-lens disposed on the light-incident side of the image sensor, such that the light sensitive element is disposed between the first micro-lens and the second micro-lens.