Process for enhancing image quality of backside illuminated image sensor

Patent metadata

Field	Value
Publication number	US-9142709-B2
Application number	US-201414463151-A
Country	US
Kind code	B2
Filing date	Aug 19, 2014
Priority date	Sep 30, 2011
Publication date	Sep 22, 2015
Grant date	Sep 22, 2015

Abstract

A method includes providing a substrate having a first surface and a second surface, the first surface being opposite the second surface, forming a light sensing region at the first surface of the substrate, forming a doped layer at the second surface of the substrate using a laser annealing process, and performing a chemical mechanical polishing process on the annealed, doped layer.

First claim

What is claimed is:

1. A method comprising:
providing a substrate having a first surface and a second surface, the first surface being opposite the second surface;
forming a light sensing region at the first surface of the substrate;
forming a doped layer at the second surface of the substrate using a laser annealing process at a temperature greater than or equal to about 1100° C; and
performing a chemical mechanical polishing process on the annealed, doped layer.

2. The method of claim 1 wherein the laser annealing process is selected to provide a shallow depth anneal that does not modify a metal layer formed on the first surface.

3. The method of claim 1 wherein the laser annealing process uses a green light laser.

4. The method of claim 1 wherein the laser annealing process is for a duration of about 100 to about 400 nsec.

5. The method of claim 1 , further comprising, forming a metal layer above the first surface of the substrate.

6. The method of claim 1 wherein the performing the polishing process on the annealed, doped layer includes removing a portion of the doped layer, wherein the removed portion of the substrate has a thickness of about 0.02 μm to about 0.1 μm.

7. The method of claim 1 wherein the performing the polishing process on the annealed, doped layer includes:
polishing the second surface of the substrate with a first slurry of a first size; and
polishing the second surface of the substrate with a second slurry of a second size, the second size being less than the first size.

8. The method of claim 7 wherein the first size of the first slurry is between about 35 μm to about 70 μm, and the second size of the second slurry is less than about 35 μm.

9. The method of claim 1 wherein the performing the polishing process on the annealed, doped layer includes achieving total thickness variation of the substrate of less than or equal to about 0.2 μm.

10. The method of claim 1 wherein the performing the polishing process on the annealed, doped layer includes achieving a roughness of the second surface that is less than or equal to about 0.06 μm.

11. The method of claim 1 further comprising reducing a thickness of the substrate before forming the doped layer.

12. A method for forming an image sensor, the method comprising:
providing a substrate having a front surface and a back surface;
forming a light sensing region of the image sensor at the front surface of the substrate;
forming a layer above the front surface of the substrate;
implanting a dopant at the back surface of the substrate;
performing an annealing process to activate the dopant, such that the implanting and the annealing process form a doped layer disposed at the back surface of the substrate, wherein the activated dopant is of a relatively shallow depth in that it does not modify the layer above the front surface of the substrate; and
after annealing, performing a polishing process on the back surface of the substrate to achieve a roughness of the back surface that is less than or equal to about 0.06 μm.

13. The method of claim 12 wherein the performing the annealing process includes performing a laser annealing process.

14. The method of claim 13 wherein the laser annealing process uses a green light laser.

15. The method of claim 14 wherein the laser annealing process uses an annealing temperature greater than or equal to about 1100° C. for a duration of about 100 to about 400 nsec.

16. The method of claim 12 wherein the performing the polishing process includes performing a chemical mechanical polishing process on the back surface.

17. The method of claim 12 wherein the performing the polishing process includes reducing a surface roughness of the back surface of the substrate to less than about 0.02 μm.

18. The method of claim 12 further including:
after the annealing process, determining a surface roughness of the back surface of the substrate; and
determining a polishing time based on the determined surface roughness of the back surface of the substrate, wherein the performing the polishing process is performed for the polishing time.

19. A method comprising:
providing a substrate having a front surface and a back surface;
forming a light sensing region at the front surface of the substrate;
implanting a dopant at the back surface of the substrate;
performing an annealing process to activate the dopant, such that the implanting and the annealing process form a doped layer disposed at the back surface of the substrate with a surface roughness;
after the annealing process, polishing the back surface of the substrate to a reduced surface roughness that is less than or equal to about 0.02 μm.

20. The method of claim 19 further comprising:
forming a layer above the front surface of the substrate;
wherein the annealing process is a green light laser anneal process that anneals to a relatively shallow depth so that it does not modify the layer above the front surface of the substrate.

Assignees

• Taiwan Semiconductor Mfg

Inventors

• Lu Shou-Shu
• Huang Hsun-Ying
• Lin I-Chang
• Hsiao Chia-Chi
• Chang Yung-Cheng

Classifications

• H10P74/203

  Structural properties, e.g. testing or measuring thicknesses, line widths, warpage, bond strengths or physical defects · CPC title

• H10P74/23

  characterised by multiple measurements, corrections, marking or sorting processes · CPC title

• H10F39/807

  Pixel isolation structures · CPC title

• H10F39/199 Primary

  Back-illuminated image sensors · CPC title

• H10F39/028

  performed after manufacture of the image sensors, e.g. annealing, gettering of impurities, short-circuit elimination or recrystallisation · CPC title