PHOTO-SENSOR AND PIXEL ARRAY WITH BACKSIDE ILLUMINATION AND METHOD OF FORMING THE PHOTO-SENSOR

• US 20070194397A1
• Filed: 02/17/2006
• Published: 08/23/2007
• Est. Priority Date: 02/17/2006
• Status: Active Grant

• Current Assignee: Smartsens Technology (Cayman) Co., Ltd.
• Original Assignee: International Business Machines Corporation
• Inventors: Gambino, Jeffrey, Rassel, Richard, Jaffe, Mark, Loiseau, Alan, Adkisson, James
• Granted Patent: US 7,586,139 B2
• Time in Patent Office: Days
• US Class Current: 257/432
• CPC Class Codes: H01L 27/14621 Colour filter arrangements
• CPC Class Codes: H01L 27/1463 Pixel isolation structures
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H01L 27/14689 MOS based technologies

Abstract

An imaging sensor with an array of FET pixels and method of forming the imaging sensor. Each pixel is a semiconductor island, e.g., N-type silicon on a Silicon on insulator (SOI) wafer. FETs are formed in one photodiode electrode, e.g., a P-well cathode. A color filter may be attached to an opposite surface of island. A protective layer (e.g., glass or quartz) or window is fixed to the pixel array at the color filters. The image sensor may be illuminated from the backside with cell wiring above the cell. So, an optical signal passes through the protective layer is filtered by the color filters and selectively sensed by a corresponding photo-sensor.

Claims

1. An imaging sensor cell comprising:

a semiconductor layer;

a photo-sensor on one surface of said semiconductor layer; and

a color filter at an opposite surface of said semiconductor layer, light filtered by said color filter being selectively sensed by said photo-sensor.

2. An imaging sensor cell as in claim 1, wherein said semiconductor layer is an active silicon layer and said color filter is separated from said active silicon layer by a dielectric layer.

3. An imaging sensor cell as in claim 2, wherein said active silicon layer is doped with an N-type dopant and a P-well in said N-type active silicon layer forms a photodiode, said imaging sensor cell further comprising a plurality of NFETs formed in said P-well, said NFETs connected to selectively sense an optical signal to said photodiode.

4. An imaging sensor cell as in claim 3, wherein said plurality of NFETs comprises:

a first NFET connected between the cathode of said photodiode and a supply voltage (V_dd), said first NFET being gated by a reset signal;

a second NFET connected at the drain to said supply voltage and gated by said cathode; and

a third NFET connected between the source of said second NFET and a data output, said third NFET being gated by a pixel select signal.

5. An imaging sensor cell as in claim 2, wherein said active silicon layer is about 2-6 μ

m thick and said dielectric layer is about 0.1-1.0 μ

m.

6. An imaging sensor cell as in claim 1, wherein said color filter is in a layer of color filters, said imaging sensor further comprising:

a protective layer on said layer of color filters, light passing through said protective layer being filtered by color filters in said layer of color filters.

7. An imaging sensor cell as in claim 6, wherein said protective layer is a quartz layer.

8. An imaging sensor cell as in claim 6, wherein said protective layer further filters out invisible light.

9. An imaging sensor cell as in claim 1, wherein wiring to said cell extends away from said semiconductor layer from photo-sensor structures in said one surface.

10. An imaging sensor comprising:

a pixel array, each pixel comprising;

a semiconductor island,

a photo-sensor on one surface of said semiconductor island,

cell wiring to said cell extending from photo-sensor structures in said one surface, and

a color filter at an opposite surface of said semiconductor layer; and

a protective layer on said pixel array at pixel color filters, an optical signal passing through said protective layer being filtered by said color filters and selectively sensed by a corresponding said photo-sensor.

11. An imaging sensor as in claim 10, wherein said semiconductor island is about 2-6 μ

m thick silicon island separated from adjacent silicon islands by shallow trench isolation and said color filter is about 0.5-1.5 μ

m thick and separated from said semiconductor island by a dielectric layer about 0.1-1.0 μ

m thick.

12. An imaging sensor as in claim 11, wherein said silicon island is doped N-type, a P-well in said N-type silicon island forms a photodiode and NFETs on said P-well are connected to said photodiode to selectively sense said optical signal.

13. An imaging sensor as in claim 12, wherein said NFETs comprise:

a first NFET connected between the cathode of said photodiode and a supply voltage (V_dd), said first NFET being gated by a reset signal;

a second NFET connected at the drain to said supply voltage and gated by said cathode; and

a third NFET connected between the source of said second NFET and a data output, said third NFET being gated by a pixel select signal.

14. An imaging sensor as in claim 11, wherein a handle layer bonded to a surface above said cell wiring, said pixel array being sandwiched between said protective layer and said handle layer.

15. A method of forming an imaging sensor comprising the steps of:

a) defining an array of islands in a semiconductor layer;

b) forming a photo-sensor on a first surface of each of said islands;

c) forming connections to each said photo-sensor, said connections extending from said first surface;

d) forming a color filter on a second surface of each of said islands, said second surface being opposite said first surface;

e) packaging said imaging sensor, said second surface remaining exposed such that light to the packaged said imaging sensor is filtered by a respective said color filter and selectively sensed by a corresponding said photo-sensor.

16. A method of forming an imaging sensor as in claim 15, wherein said semiconductor layer is a silicon layer and the step (a) of defining the island array comprises the steps of:

i) bonding a handle layer to said second surface; and

ii) patterning said silicon layer using shallow trench isolation to define silicon islands.

17. A method of forming an imaging sensor as in claim 16, wherein the bonding step (i) comprises:

A) forming thermal oxide on said silicon layer; and

B) forming a nitride layer on said thermal oxide, said bonding layer being bonded to said nitride layer.

18. A method of forming an imaging sensor as in claim 15, wherein said silicon layer is doped N-type and the step (b) of forming the photo-sensor comprises:

i) forming a P-well in each said N-type island, said P-well forming a photodiode with said N-type island; and

ii) forming a plurality of NFETs in said P-well, connections formed in step (c) being to said NFETs and connecting each said N-type island to ground.

19. A method of forming an imaging sensor as in claim 15, wherein the step (d) of forming color filters comprises:

i) bonding a handle layer to an upper wiring layer at said first surface;

ii) removing a back-side handle layer from said second surface; and

iii) forming said color filters on said second surface.

20. A method of forming an imaging sensor as in claim 15, before the packaging step (e), further comprising:

e1) forming a protective layer on color filters formed on said second surface.