Method of making trench photosensor for a CMOS imager

• US 6,500,692 B1
• Filed: 02/14/2001
• Issued: 12/31/2002
• Est. Priority Date: 02/01/1999
• Status: Expired due to Term

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Rhodes, Howard E.
• Primary Examiner(s): CHAUDHARI, CHANDRA P
• Application Number:
  US09/782,060
• Publication Number:
  US 20010032979A1
• Time in Patent Office: 685 Days
• Field of Search: 438/48, 438/57, 438/73, 438/74, 438/80, 438/200, 438/524, 438/525
• US Class Current: 438/73
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H01L 27/14689 MOS based technologies

Abstract

A trench photosensor for use in a CMOS imager having an improved charge capacity. The trench photosensor may be either a photogate or photodiode structure. The trench shape of the photosensor provides the photosensitive element with an increased surface area compared to a flat photosensor occupying a comparable area on a substrate. The trench photosensor also exhibits a higher charge capacity, improved dynamic range, and a better signal-to-noise ratio. Also disclosed are processes for forming the trench photosensor.

Claims

1. A method of forming a photosensor, comprising the steps of:

providing a semiconductor substrate having a doped layer of a first conductivity type;

forming a trench in said doped layer;

doping the sides and bottom of said trench to form a doped region of a second conductivity type; and

forming an insulating layer on the sides and bottom of said trench over said doped region.

2. The method of claim 1, wherein the photosensor is a photodiode sensor.

3. The method of claims 1, further comprising a step of forming a conductive layer on substantially all of an upper surface of the insulating layer.

4. The method of claim 3, wherein the photosensor is a photogate sensor.

5. The method of claim 3, wherein the step of forming said conductive layer comprises a chemical vapor deposition step.

6. The method of claim 3, wherein the step of forming said conductive layer comprises a sputtering step.

7. The method of claim 1, wherein said insulating layer is a layer of silicon dioxide.

8. The method of claim 1, wherein the first conductivity type is p-type, and the second conductivity type is n-type.

9. The method of claim 1, wherein the semiconductor substrate is a silicon substrate.

10. The method of claim 1, wherein the trench forming step comprises a reactive ion etching process.

11. The method of claim 1, wherein the doping step comprises ion implantation.

12. The method of claim 11, wherein the doping step comprises multiple angled ion implantation.

13. The method of claim 12, wherein the multiple angled ion implantation comprises four orthogonal angled implants at a dose of 1×

10¹² to 1×

10¹⁶ ions/cm², wherein a resist is placed on top of the substrate while implanting, and wherein the angle of implantation for each angled implant is greater than θ

_c, where tan θ

_c=[(t+d)/(w)], where t is the thickness of the resist, d is the depth of the trench, and w is the width of the trench.

14. The method of claim 13, wherein the dose of each implant is 1×

10¹³ to 1×

10¹⁵ ions/cm².

15. The method of claim 13, wherein the dose of each implant is 5×

10¹³ ions/cm².

16. A method of forming a photosensor, comprising the steps of:

providing a semiconductor substrate having a doped layer of a first conductivity type;

forming a doped region of a second conductivity type in the doped layer;

forming a trench in said doped region so that the sides and bottom of said trench are of the second conductivity type; and

forming an insulating layer on the sides and bottom of said trench.

17. The method of claim 16, wherein the photosensor is a photodiode sensor.

18. The method of claim 16, further comprising forming a conductive layer on the sides and bottom of the trench, and wherein the photosensor is a photogate sensor.

19. The method of claim 16, wherein the first conductivity type is p-type, and the second conductivity type is n-type.

20. The method of claim 16, wherein the trench forming step comprises a reactive ion etching process.

21. The method of claim 16, wherein the doping step comprises ion implantation.