Back-illuminated imaging device and method of fabricating same

• US 20060186560A1
• Filed: 02/09/2006
• Published: 08/24/2006
• Est. Priority Date: 02/11/2005
• Status: Active Grant

• Current Assignee: Samoff Corporation, SRI International, Inc.
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Bhaskaran, Mahalingam, Swain, Pradyumna
• Granted Patent: US 7,238,583 B2
• Time in Patent Office: Days
• US Class Current: 257/460
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H01L 27/148 Charge coupled imagers individual charge coupled devices H01L29/765
• CPC Class Codes: H01L 31/18 Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
• CPC Class Codes: H01L 31/1892 methods involving the use of temporary, removable substrates
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

A method for fabricating a back-illuminated semiconductor imaging device on a thin semiconductor-on-insulator substrate, and resulting imaging device. Resulting device has a monotonically varying doping profile which provides a desired electric field and eliminates a dead band proximate to the backside surface.

Claims

1. A method for fabricating a back-illuminated semiconductor imaging device, comprising the steps of:

growing an epitaxial layer on a substrate, the substrate comprising;

a mechanical substrate,

an insulator layer, and

a doped semiconductor substrate,

the epitaxial layer being grown on the doped semiconductor substrate, whereby the epitaxial growth process causes dopants from the doped semiconductor substrate to diffuse into the epitaxial layer, and;

fabricating one or more imaging components in the epitaxial layer.

2. The method of claim 1, further comprising the step of removing at least a portion of the mechanical substrate.

3. The method of claim 1, wherein the semiconductor substrate has a thickness in the range from about 5 nanometers to about 100 nanometers.

4. The method of claim 1, wherein the step of fabricating one or more imaging components in the epitaxial layer includes one or more steps of fabricating junctions in proximity to a face of the epitaxial layer, the face of the epitaxial layer being opposite a boundary between the semiconductor substrate and the epitaxial layer.

5. The method of claim 4, further comprising the step of introducing one or more dopants in a semiconductor substrate to form the doped semiconductor substrate such that, upon completion of the step of fabricating one or more imaging components in the epitaxial layer, a net dopant concentration profile in the semiconductor substrate and the epitaxial layer results, the profile having a maximum value at an interface of the doped semiconductor substrate and the insulator layer and decreasing monotonically with increasing distance from the interface within a portion of the doped semiconductor substrate and the epitaxial layer between the interface and the junctions.

6. The method of claim 5, wherein the step of introducing one or more dopants includes the step of applying dopants to the semiconductor substrate through a face of the semiconductor substrate opposite an interface of the semiconductor substrate and the insulator layer, the dopants being applied in sufficient concentration and over a sufficient distance within the doped semiconductor substrate such that, upon completion of the step of fabricating one or more imaging components in the epitaxial layer, a net dopant concentration profile in the doped semiconductor substrate and the epitaxial layer results, the profile having a maximum value at the interface of the semiconductor substrate and the insulator layer and decreasing monotonically with increasing distance from the interface within a portion of the doped semiconductor substrate and the epitaxial layer between the interface and the junctions.

7. The method of claim 2 further comprising the step of:

removing at least a portion of the insulator layer following complete removal of the mechanical substrate.

8. The method of claim 7, wherein the step of removing at least a portion of the insulator layer results in a remaining insulator layer having a thickness such that the remaining insulator layer functions as an anti-reflection coating for electromagnetic radiation over a predetermined range of wavelengths.

9. The method of claim 8, wherein the predetermined range of wavelengths includes an ultraviolet range of wavelengths.

10. The method of claim 1, wherein the step of fabricating one or more imaging components includes the step of fabricating CMOS imaging components, charge-coupled device components, photodiodes, avalanche photodiodes, or phototransistors in any combination.

11. A method for fabricating a back-illuminated semiconductor imaging device, comprising the steps of:

providing a substrate comprising;

a mechanical substrate,

an insulator layer, and

a semiconductor substrate;

applying one or more dopants to the semiconductor substrate;

growing an epitaxial layer on the semiconductor substrate while simultaneously causing diffusion of the one or more dopants into the epitaxial layer such that, at completion of the growing of the epitaxial layer, there exists a net dopant concentration profile in the semiconductor substrate and the epitaxial layer which has an initial maximum value at an interface of the semiconductor substrate and the insulator layer and which decreases monotonically with increasing distance from the interface within an initial portion of the semiconductor substrate and the epitaxial layer, and;

fabricating one or more imaging components in the epitaxial layer such that, upon completion of the fabrication of the one or more imaging components, the net dopant concentration profile has a final maximum value at the interface of the semiconductor substrate and the insulator layer and decreases monotonically with increasing distance from the interface within a portion of the semiconductor substrate and the epitaxial layer.

12. The method of claim 11 further comprising the step of removing at least a portion of the mechanical substrate.

13. The method of claim 12 further comprising the step of:

removing at least a portion of the insulator layer following complete removal of the mechanical substrate.

14. The method of claim 13, wherein the step of removing at least a portion of the insulator layer results in a remaining insulator layer having a thickness such that the remaining insulator layer functions as an anti-reflection coating for electromagnetic radiation over a predetermined range of wavelengths.

15. The method of claim 14, wherein the predetermined range of wavelengths includes an ultraviolet range of wavelengths.

16. The method of claim 11, wherein the step of fabricating one or more imaging components includes the step of fabricating CMOS imaging components, charge-coupled device components, photodiodes, avalanche photodiodes, or phototransistors, in any combination.

17. A back-illuminated semiconductor imaging device configured to operate over a predetermined range of wavelengths, comprising:

an insulator layer;

a semiconductor substrate, having an interface with the insulator layer;

an epitaxial layer grown on the semiconductor substrate by epitaxial growth; and

one or more imaging components in the epitaxial layer in proximity to a face of the epitaxial layer, the face being opposite the interface of the semiconductor substrate and the insulator layer, the imaging components comprising junctions within the epitaxial layer;

wherein the semiconductor substrate and the epitaxial layer exhibit a net doping concentration having a maximum value at the interface of the semiconductor substrate and the insulator layer and decreasing monotonically with increasing distance from the interface within a portion of the semiconductor substrate and the epitaxial layer between the interface and the junctions.

18. The imaging device of claim 17, wherein a doping concentration at the interface of the semiconductor substrate and the insulator layer is high enough to stabilize a quantum efficiency of the device with respect to time and incident flux.

19. The imaging device of claim 17, wherein the epitaxial layer and semiconductor substrate both comprise silicon and the insulator layer comprises an oxide of silicon.

20. The imaging device of claim 17, wherein the insulator layer has a thickness selected to function as an anti-reflection coating over the predetermined range of wavelengths.

21. The device of claim 17, wherein light detected by the imaging components is incident on a face of the insulator layer opposite the interface between the semiconductor substrate and the insulator layer.

22. The device of claim 17, wherein the predetermined range of wavelengths includes an ultraviolet range.

23. The imaging device of claim 17, wherein the one or more imaging components includes CMOS imaging components, charge-coupled device components, photodiodes, avalanche photodiodes, or phototransistors, in any combination.

24. The imaging device of claim 17, wherein the semiconductor substrate has a thickness in the range from about 5 nanometers to about 100 nanometers.

25. The imaging device of claim 17, wherein the epitaxial layer has a thickness in the range from about 1 micrometer to about 400 micrometers.

26. The imaging device of claim 17, wherein the epitaxial layer has a thickness in the range from greater than about 1 micrometer to about 20 micrometers.