Trench photosensor for a CMOS imager

• US 7,445,951 B2
• Filed: 11/07/2006
• Issued: 11/04/2008
• Est. Priority Date: 02/01/1999
• Status: Expired due to Fees

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Rhodes, Howard E.
• Primary Examiner(s): Nguyen; Tuan H
• Application Number:
  US11/593,589
• Publication Number:
  US 20070051989A1
• Time in Patent Office: 728 Days
• Field of Search: 438/48, 438/57, 438/73, 438/75, 438/200, 257/216, 257/244
• US Class Current: 438/57
• CPC Class Codes: H01L 27/14601 Structural or functional details thereof
• 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 converting an optical signal to an electrical signal, comprising:

receiving said optical signal at a surface of a photoreceptor;

absorbing said optical signal through said surface of said photoreceptor;

generating electrons with said photoreceptor in relation to an intensity of said optical signal;

storing said electrons in sidewalls and a bottom of a substantially concave cavity within a substrate, said sidewalls and bottom of said cavity forming a part of said photoreceptor; and

adjusting an electrical output signal in relation to a magnitude of said stored electrons.

2. A method of converting an optical signal to an electrical signal as in claim 1, wherein said substantially concave cavity is a trench formed in a surface of said substrate.

3. A method of converting an optical signal to an electrical signal as in claim 1, wherein said surface of said photoreceptor and said surface of said cavity are substantially coextensive.

4. A method of converting an optical signal to an electrical signal as in claim 1, wherein said substrate is doped to a first conductivity type and said sidewalls and bottom of said cavity comprise a doped region of a second conductivity type, an insulator, and a transparent conductor.

5. A method of converting an optical signal to an electrical signal as in claim 1, further comprising:

selectively transferring said electrical output signal to a floating diffusion region via a transfer gate.

6. A method of converting an optical signal to an electrical signal as in claim 1, further comprising:

converting said electrical output signal from analog to digital.

7. A method of converting an optical signal to an electrical signal as in claim 6, wherein said converting comprises:

receiving said electrical output signal at an input of a sample and hold circuit;

sampling said electrical output signal; and

digitizing said electrical output signal to produce a digital output signal.

8. A method of converting an optical signal to an electrical signal as in claim 7, further comprising:

storing said digital output signal in a digital electronic memory.

9. A method of converting an optical signal to an electrical signal as in claim 1, wherein said receiving said optical signal comprises receiving an electromagnetic signal having a wavelength of about 400 nanometers to about 700 nanometers.

10. A method of converting an optical signal to an electrical signal as in claim 1, wherein said absorbing said optical signal through said surface of said photoreceptor comprises absorbing said optical signal through a layer of insulating material disposed above a surface of said substrate.

11. A method of converting an optical signal to an electrical signal as in claim 1, wherein said absorbing said optical signal through said surface of said photoreceptor comprises absorbing said optical signal through a layer of conductive material disposed above a surface of said substrate.

12. A method of converting an optical signal to an electrical signal as in claim 11, wherein said layer of conductive material comprises a metallic material.