Trench photosensor for a CMOS imager

• US 7,655,494 B2
• Filed: 10/01/2008
• Issued: 02/02/2010
• Est. Priority Date: 02/01/1999
• Status: Expired due to Term

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Inventors: Rhodes, Howard E.
• Primary Examiner(s): Blum; David S
• Application Number:
  US12/285,313
• Publication Number:
  US 20090032685A1
• Time in Patent Office: 489 Days
• Field of Search: 438/48, 438/57, 438/73, 257/E21.001, 257/E27.13, 356/435
• 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 sensing photons comprising:

receiving said photons into a trench, said trench disposed in a doped layer of a first conductivity type formed in a semiconductor substrate;

activating a diode formed in said substrate adjacent said trench by absorbing said photons, said diode including a first doped region of a second conductivity type formed in a sidewall and bottom of said trench;

receiving charges from said first doped region into a second doped region of said second conductivity type formed in said doped layer; and

resetting a charge level of said second doped region by receiving charges from said second doped region into a conductive signal line.

2. A method of sensing photons as defined in claim 1 wherein said resetting a charge level of said second doped region comprises transferring charges through a reset transistor.

3. A method of sensing photons as defined in claim 2 wherein said reset transistor includes a drain region and a gate and wherein said second doped region includes a source of said reset transistor.

4. A method of sensing photons as defined in claim 1 wherein receiving said photons into said trench comprises receiving said photons through an aperture in an upper surface of said semiconductor substrate.

5. A method of sensing photons as defined in claim 1 wherein activating said diode comprises energizing electrons in response to absorbing said photons into said semiconductor substrate.

6. A method of sensing photons as defined in claim 1 wherein activating said diode comprises absorbing said photons in a first region of a surface of said trench after reflecting said photons from a second region of said surface of said trench.

7. A method of sensing photons as defined in claim 1 wherein activating said diode comprises:

conducting said photons through a transparent layer disposed above an internal surface of said trench; and

absorbing said photons into said semiconductor substrate.

8. A method of sensing light comprising:

receiving said light through an aperture in a surface of a semiconductor substrate;

absorbing said light into an internal surface of said semiconductor substrate, said internal surface defining a cavity within said semiconductor substrate;

energizing an electron of said semiconductor substrate with said absorbed light; and

activating a switching device using said energized electron.

9. A method of sensing light as defined in claim 8 wherein said activating a switching device comprises activating a field effect transistor.

10. A method of sensing light as defined in claim 8 wherein said absorbing said light into said internal surface comprises receiving said light into said substrate through a layer of conductive material.

11. A method of sensing light as defined in claim 10 wherein said layer of conductive material comprises a photo-gate said method including applying an electrical potential to said photo-gate.

12. A method of sensing light as defined in claim 8 wherein said absorbing said light into said internal surface comprises receiving said light into said substrate through a layer of insulating material.

13. A method of sensing light as defined in claim 8 wherein said absorbing said light into said internal surface comprises receiving said light through a first region of substrate material having a first doping characteristic into a second region of substrate material having a second doping characteristic.

14. A method of sensing light as defined in claim 8 wherein said switching device includes a field effect transistor and wherein said activating a switching device using said energized electron comprises:

passing said energized electron through a first transistor to a floating diffusion region; and

elevating an electrical potential of a gate of said field effect transistor, said gate being electrically coupled to said floating diffusion region.