IMAGE SENSOR WITH RAISED PHOTOSENSITIVE ELEMENTS

• US 20100059802A1
• Filed: 09/11/2008
• Published: 03/11/2010
• Est. Priority Date: 09/11/2008
• Status: Active Grant

• Current Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Original Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Inventors: Chen, Shenlin
• Granted Patent: US 8,211,732 B2
• Time in Patent Office: Days
• US Class Current: 257/292
• CPC Class Codes: H01L 27/14632 Wafer-level processed structures
• CPC Class Codes: H01L 27/14634 Assemblies, i.e. Hybrid structures
• CPC Class Codes: H01L 27/14636 Interconnect structures
• CPC Class Codes: H01L 27/14687 Wafer level processing
• CPC Class Codes: H01L 27/1469 Assemblies, i.e. hybrid integration

Abstract

An image sensor having a pixel array comprises periphery elements formed over a substrate, an oxide layer formed over the periphery elements, an epitaxial layer formed in an opening in the oxide layer in a pixel array area, and a plurality of photosensitive elements of the pixel array formed in the epitaxial layer. Formation of an initial metallization layer occurs after the formation of the photosensitive elements in the epitaxial layer. The photosensitive elements can thus be formed in the epitaxial layer at a higher level within an image sensor stack than that of the initial metallization layer. This advantageously allows stack height and pixel size to be reduced, and fill factor to be increased. The image sensor may be implemented in a digital camera or other type of digital imaging device.

Claims

1. A method of forming an image sensor having a pixel array, the method comprising the steps of:

forming periphery elements of the image sensor over a substrate;

forming an oxide layer over the periphery elements;

forming an opening in the oxide layer in a pixel array area;

forming an epitaxial layer in the opening; and

forming photosensitive elements of the pixel array in the epitaxial layer.

2. The method of claim 1 wherein the periphery elements comprise polysilicon gates of periphery transistors.

3. The method of claim 1 further including the step of forming an initial metallization layer comprising periphery metal conductors overlying one or more of the periphery elements.

4. The method of claim 3 wherein the step of forming the initial metallization layer is performed subsequent to the steps of forming the oxide layer, forming the opening in the oxide layer, forming the epitaxial layer in the opening, and forming the photosensitive elements of the pixel array.

5. The method of claim 4 further including the step of forming a plurality of additional metallization layers subsequent to the step of forming the initial metallization layer.

6. The method of claim 1 wherein the step of forming the epitaxial layer in the opening further comprises performing a selective epitaxial growth process such that the epitaxial layer is confined substantially to the pixel array area.

7. The method of claim 6 wherein the selective epitaxial growth process is controlled to provide a designated depletion region characteristic for the photosensitive elements.

8. The method of claim 1 further comprising the step of forming metal conductors interconnecting pixel array circuitry with periphery circuitry.

9. The method of claim 8 wherein the metal conductors comprise final metallization layer conductors.

10. The method of claim 1 further comprising the steps of:

forming a nitride layer over the photosensitive elements of the pixel array;

forming multiple metallization layers and associated vias in periphery areas of the image sensor; and

removing the nitride layer.

11. The method of claim 1 wherein the steps are implemented as part of a wafer level process for forming a plurality of image sensors utilizing an image sensor wafer and the image sensor wafer is subsequently separated into the plurality of image sensors.

12. An image sensor having a pixel array, the image sensor comprising:

periphery elements formed over a substrate;

an oxide layer formed over the periphery elements;

an epitaxial layer formed in an opening in the oxide layer in a pixel array area; and

a plurality of photosensitive elements of the pixel array formed in the epitaxial layer.

13. The image sensor of claim 12 wherein the periphery elements comprise polysilicon gates of periphery transistors.

14. The image sensor of claim 12 farther comprising an initial metallization layer comprising periphery metal conductors overlying one or more of the periphery elements.

15. The image sensor of claim 14 wherein the photosensitive elements are formed in the epitaxial layer at a higher level within an image sensor stack than that of the initial metallization layer.

16. The image sensor of claim 14 further comprising a plurality of additional metallization layers formed over the initial metallization layer.

17. The image sensor of claim 12 further comprising metal conductors interconnecting pixel array circuitry with periphery circuitry, wherein the metal conductors comprise final metallization layer conductors.

18. The image sensor of claim 12 wherein said image sensor comprises a CMOS image sensor.

19. A digital imaging device comprising:

an image sensor having a pixel array; and

one or more processing elements configured to process outputs of the image sensor to generate a digital image;

wherein said image sensor comprises;

periphery elements formed over a substrate;

an oxide layer formed over the periphery elements;

an epitaxial layer formed in an opening in the oxide layer in a pixel array area; and

a plurality of photosensitive elements of the pixel array formed in the epitaxial layer.

20. The digital imaging device of claim 19 wherein said imaging device comprises a digital camera.