Multi-thickness gate dielectric

Patent metadata

Field	Value
Publication number	US-2020105807-A1
Application number	US-201816149544-A
Country	US
Kind code	A1
Filing date	Oct 2, 2018
Priority date	Oct 2, 2018
Publication date	Apr 2, 2020
Grant date	—

Abstract

An image sensor includes one or more photodiodes disposed in a semiconductor material to receive image light and generate image charge, and a floating diffusion to receive the image charge from the one or more photodiodes. One or more transfer transistors is coupled to transfer image charge in the one or more photodiodes to the floating diffusion, and a source follower transistor is coupled to amplify the image charge in the floating diffusion. The source follower includes a gate electrode (coupled to the floating diffusion), source and drain electrodes, and an active region disposed in the semiconductor material between the source and drain electrodes. A dielectric material is disposed between the gate electrode and the active region and has a first thickness and a second thickness. The second thickness is greater than the first thickness, and the second thickness is disposed closer to the drain electrode than the first thickness.

First claim

What is claimed is:

1 . An image sensor, comprising:
one or more photodiodes disposed in a semiconductor material to receive image light and generate image charge; a floating diffusion to receive the image charge from the one or more photodiodes; one or more transfer transistors coupled to transfer image charge in the one or more photodiodes to the floating diffusion; and a source follower transistor coupled to amplify the image charge in the floating diffusion, including: a gate electrode coupled to the floating diffusion; a source electrode and a drain electrode; an active region disposed in the semiconductor material between the source electrode and the drain electrode; and a dielectric material disposed between the gate electrode and the active region having a first thickness and a second thickness, wherein the second thickness is greater than the first thickness, and wherein the second thickness is disposed closer to the drain electrode than the first thickness.

2 . The image sensor of claim 1 , wherein the first thickness is 30 Å or less.

3 . The image sensor of claim 1 , wherein the second thickness is greater than or equal to a thickness required to prevent breakdown when the source follower transistor is operating in a saturation regime.

4 . The image sensor of claim 3 , wherein the second thickness is at least twice as thick as the first thickness.

5 . The image sensor of claim 3 , wherein the dielectric material gradually transitions from the first thickness to the second thickness.

6 . The image sensor of claim 1 , further comprising a reset transistor coupled to the floating diffusion to reset charge in the floating diffusion in response to a rest signal being applied to a second gate terminal of the reset transistor.

7 . The image sensor of claim 4 , further comprising a row select transistor coupled between an output of the source follower transistor and a bit line output.

8 . The image sensor of claim 1 , wherein the dielectric material includes at least one of hafnium oxide, silicon oxide, silicon nitride, or aluminum oxide.

9 . The image sensor of claim 1 , further comprising control circuitry coupled to control operation of the one or more photodiodes; and
readout circuitry coupled to the bitline to read out image data from the one or more photodiodes.

10 . The image sensor of claim 9 , further comprising function logic coupled to the readout circuitry to manipulate the image data.

11 . A method of image sensor fabrication, comprising:
forming one or more photodiodes in a semiconductor material to receive image light and generate image charge; implanting a floating diffusion in the semiconductor material to receive the image charge from the one or more photodiodes; forming one or more transfer transistors coupled to transfer image charge in the one or more photodiodes to the floating diffusion; and forming a source follower transistor coupled to amplify the image charge in the floating diffusion, including:
forming a gate electrode coupled to the floating diffusion;
forming a source electrode and a drain electrode;
implanting an active region in the semiconductor material between the source electrode and the drain electrode; and
forming a dielectric material disposed between the gate electrode and the active region having a first thickness and a second thickness, wherein the second thickness is greater than the first thickness, and wherein the second thickness is disposed closer to the drain electrode than the first thickness.

12 . The method of claim 11 , wherein forming the dielectric material includes forming the first thickness of the dielectric material of 30 Å or less.

13 . The method of claim 11 , wherein forming the dielectric includes forming the second thickness, which is greater than or equal to a thickness required to prevent breakdown when the source follower transistor is operating in a saturation regime.

14 . The method of claim 13 , wherein the second thickness is at least twice as thick as the first thickness.

15 . The method of claim 13 , wherein the dielectric material gradually transitions from the first thickness to the second thickness.

16 . The method of claim 1 , further comprising forming a reset transistor coupled to the floating diffusion to reset charge in the floating diffusion in response to a rest signal being applied to a second gate terminal of the reset transistor.

17 . The method of claim 4 , further comprising forming a row select transistor coupled between an output of the source follower transistor and a bit line output.

18 . The method of claim 1 , wherein forming the dielectric material includes depositing or growing at least one of hafnium oxide, silicon oxide, silicon nitride, or aluminum oxide.

19 . The method of claim 1 , further comprising:
forming control circuitry coupled to control operation of the one or more photodiodes; and forming readout circuitry coupled to the bitline to read out image data from the one or more photodiodes.

20 . The method of claim 9 , further comprising forming function logic coupled to the readout circuitry to manipulate the image data.

Assignees

• Omnivision Tech Inc

Inventors

• Chen Gang
• Zheng Yuanwei
• Wang Qin
• Yang Cunyu
• Chen Guannan
• Mao Duli
• Tai Dyson
• Grant Lindsay
• Webster Eric
• Hu Sing-Chung

Classifications

• H01L27/14614 Primary

  Electricity · mapped topic

• H04N9/0455

  Electricity · mapped topic

• H04N5/378

  Electricity · mapped topic

• H01L27/14689

  Electricity · mapped topic

• H01L27/14645

  Electricity · mapped topic