Photodetector for backside-illuminated sensor

• US 7,939,903 B2
• Filed: 12/31/2009
• Issued: 05/10/2011
• Est. Priority Date: 05/24/2007
• Status: Expired due to Fees

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: Hsu, Tzu-Hsuan, Wang, Ching-Chun, Yaung, Dun-Nian
• Primary Examiner(s): Nguyen; Dao H
• Assistant Examiner(s): NGUYEN, TRAM HOANG
• Application Number:
  US12/651,236
• Publication Number:
  US 20100102411A1
• Time in Patent Office: 495 Days
• Field of Search: 257/223, 257/228, 257/245, 257445-447, 257/448, 257/449, 257451-456, 257/229, 257/460, 257/E33.068, 257/219, 257/225, 257/239, 257/240, 257/241, 257/246, 257E27082-E27083, 257E2715-E27163, 257/E29.065, 257E29227-E2924, 257/E21.029, 257/144, 257/113, 257/E33.076, 257/184, 257/257, 257/290, 257/461, 257/154, 257/444, 257/458, 257/749, 257/E33.079, 257/436, 438/48, 438/72, 438/636, 438/952, 438/60, 438/75, 438/144
• US Class Current: 257/460
• CPC Class Codes: H01L 27/14625 Optical elements or arrangements associated with the device
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers

Abstract

A backside-illuminated sensor including a semiconductor substrate. The semiconductor substrate has a front surface and a back surface. A plurality of pixels are formed on the front surface of the semiconductor substrate. At least one pixel includes a photogate structure. The photogate structure has a metal gate that includes a reflective layer.

Claims

1. An active pixel sensor comprising:

a semiconductor substrate having a front surface and a back surface, wherein the semiconductor substrate is configured such that light incident the back surface is sensed by a pixel formed in the front surface; and

wherein the pixel formed in the front surface of the semiconductor substrate comprises a photodetector, the photodetector having a metal gate with a reflective layer positioned on a side of the gate opposite an entry location of light to be sensed by the sensor.

2. The sensor of claim 1, wherein the sensor is configured as a complimentary metal-oxide semiconductor (CMOS) image sensor (CIS).

3. The sensor of claim 1, further comprising:

a transfer transistor, a reset transistor, a source follower transistor, and a selector transistor coupled to the sensor.

4. The sensor of claim 1, wherein the gate further includes a gate dielectric layer and a gate electrode layer underlying the reflective layer.

5. The sensor of claim 1, wherein the pixel is an n-type photosensor.

6. A method of forming an image sensor comprising:

providing a semiconductor substrate; and

forming a photodetector on the substrate, forming the photodetector comprises;

forming a gate, forming the gate comprises;

forming a gate dielectric layer on the substrate; and

forming a reflective layer on the gate dielectric layer, wherein the reflective layer is formed on the semiconductor substrate on a side of the semiconductor substrate opposite an incident radiation beam, wherein the incident radiation beam enters the photodetector.

7. The method of claim 6, further comprising:

detecting light in infrared (IR), visual, or ultraviolet (UV) wavelengths using the image sensor.

8. The method of claim 6, including forming the reflective layer by depositing a metal layer and annealing the metal layer to form a silicide.

9. The method of claim 6, further comprising:

forming a transfer transistor on the substrate proximate the photodetector.

10. The method of claim 6, further comprising:

exposing a photogeneration region in the substrate below the reflective layer to light that is to be detected using the image sensor.

11. The method of claim 6, wherein the forming the reflective layer includes forming at least one of a silicide and a metal layer.

12. The method of claim 6, further comprising:

forming a photogeneration region coupled to a gate on the photodetector.

13. The method of claim 12, further comprising:

positioning the reflective layer over the photogeneration region.

14. A radiation sensor circuit comprising:

a transfer transistor;

a reset transistor coupled to the transfer transistor forming a floating diffusion region therebetween; and

a photodetector transistor configured to detect radiation and coupled to the transfer transistor, wherein the transfer transistor moves a signal charge accumulated in the photodetector transistor to the diffusion region, and wherein the photodetector transistor is formed on a substrate and includes a gate with a reflective layer formed on the substrate on a side of the substrate opposite entry of a the radiation.

15. The sensor of claim 14, wherein the transfer transistor is formed on the substrate proximate the photodetector transistor.

16. The sensor of claim 15, wherein the transfer transistor and the photodetector transistor arc formed concurrently.

17. The sensor of claim 14, wherein the gate includes a dielectric layer adjacent the substrate.

18. The sensor of claim 17, wherein the gate includes a electrode layer formed between the reflective layer and the dielectric layer.

19. The sensor of claim 14, wherein the electrode layer is formed as one of polysilicon and metal.

20. The sensor of claim 14, wherein the reflective layer is a silicide layer.