Method for Improving Sensitivity of Backside Illuminated Image Sensors

• US 20080079108A1
• Filed: 07/09/2007
• Published: 04/03/2008
• Est. Priority Date: 09/29/2006
• Status: Abandoned Application

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: HSU, Tzu-Hsuan, YAUNG, Dun-Nian
• Application Number:
  US11/774,681
• Publication Number:
  US 20080079108A1
• Time in Patent Office: Days
• US Class Current: 257/460
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• CPC Class Codes: H01L 27/14621 Colour filter arrangements
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures
• CPC Class Codes: H01L 27/14683 Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof not peculiar thereto H01L21/00

Abstract

A method for improving sensitivity of backside illuminated image sensor. A substrate having a first conductivity type and a first potential. A depletion region having a second conductivity type is formed within the substrate. The depletion region is extended. The thickness of the substrate is reduced. First type conductivity ions having a second potential are implanted at backside surface of the substrate to form a doping layer. Laser annealing on the doping layer is performed to activate the first type conductivity ions.

Claims

1. A backside illuminated image sensor comprising:

a substrate having a first conductivity type and a first potential;

a depletion region having a second conductivity type formed within the substrate;

a doping layer having the first conductivity type and a second potential formed at a backside surface of the substrate; and

a photodiode formed at a front side surface of the substrate.

2. The backside illuminated image sensor of claim 1, wherein the depletion region extends to the backside surface of the substrate.

3. The backside illuminated image sensor of claim 1, wherein a thickness of the substrate is less than 3.5 um.

4. The backside illuminated image sensor of claim 1, wherein the depletion region comprises second conductivity type ions.

5. The backside illuminated image sensor of claim 1, wherein the doping layer comprises first conductivity type ions having a concentration of about 1e16 cm⁻

3 to about 1e21 cm<sup>−

3</sup>.

6. The backside illuminated image sensor of claim 1, wherein a thickness of the doping layer is less than about 1 um.

7. The backside illuminated image sensor of claim 1, wherein a thickness of the doping layer is less than about 1000 A.

8. The backside illuminated image sensor of claim 1, wherein the first conductivity type is p type and the second conductivity type is n type.

9. A method for improving sensitivity of backside illuminated image sensor, the method comprising:

providing a substrate having a first conductivity type and a first potential;

forming a depletion region having a second conductivity type within the substrate;

extending the depletion region;

reducing thickness of the substrate;

implanting first type conductivity ions having a second potential at backside surface of the substrate to form a doping layer; and

performing laser annealing on the doping layer to activate the first type conductivity ions.

10. The method of claim 10, wherein forming a depletion region having a second conductivity type within a substrate comprises:

implanting second conductivity type ions within the substrate.

11. The method of claim 10, wherein extending the depletion region comprises:

increasing resistance of the substrate to extend the depletion region to near the backside surface of the substrate.

12. The method of claim 10, wherein reducing thickness of the substrate comprises:

grinding down the substrate; and

performing a multi-step wet etching to reduce the substrate to a desired thickness.

13. The method of claim 10, wherein implanting first type conductivity ions comprises:

implanting first conductivity type ions using an energy of about 5 KeV to about 500 KeV.

14. The method of claim 10, wherein reducing thickness of the substrate comprises reducing the thickness of the substrate to less than about 3.5 um.

15. The method of claim 10, wherein the doping layer comprises first conductivity type ions having a concentration of about 1e16 cm⁻

3 to about 1e21 cm<sup>−

3</sup>

16. The method of claim 10, wherein the first conductivity type is a p-type.

17. The method of claim 10, wherein a thickness of the doping layer is less than about 1 um.

18. The method of claim 10, wherein a thickness of the doping layer is less than about 1000 A.

19. The method of claim 10, wherein the second conductivity type is n-type