Backside-illuminated photodetector structure and method of making the same

1. A backside-illuminated (BSI) photodetector structure comprising:

a first reflecting region comprising a first distributed Bragg reflector;

a second reflecting region comprising a second distributed Bragg reflector; and

a semiconductor region, wherein the semiconductor region is between the first reflecting region and the second reflecting region, and the semiconductor region comprises:

a first doped region extending from a first surface of the semiconductor region to a first intermediate level of the semiconductor region, wherein the first doped region is of a first conductivity type and has a first dopant concentration, and the first doped region comprises:

a contact region; and

a transverse region, wherein the contact region extends deeper than the transverse region in a direction pointing from the first surface to an opposite second surface of the semiconductor region;

a recess extending from an additional top surface of the semiconductor region to the first surface, with the additional top surface being higher than the first surface, wherein an entirety of the first doped region is underlying and overlapped by the recess;

a second doped region extending from the second surface of the semiconductor region to a second intermediate level of the semiconductor region, wherein the second doped region is of a second conductivity type and has a second dopant concentration, with the second conductivity type opposite to the first conductivity type; and

a third doped region extending from the first intermediate level to the second intermediate level, wherein the third doped region has the first conductivity type, and a third dopant concentration of the third doped region is lower than the first dopant concentration and the second dopant concentration.

2. The BSI photodetector of claim 1 , wherein the first doped region comprises one of a P-doped region or an N-doped region.

3. The BSI photodetector of claim 1 , wherein the first reflecting region or the second reflecting region comprises SiNx, AlN, Si or a high-k dielectric material.

4. The BSI photodetector of claim 1 , wherein the first reflecting region or the second reflecting region comprises SiO 2 or a low-k dielectric material.

5. A backside-illuminated (BSI) photodetector structure comprising:

a semiconductor region, wherein the semiconductor region comprises:

a first doped region;

a second doped region, wherein the first doped region and the second doped region are parts of a photodetector;

a first surface, with a recess extending from the first surface into the semiconductor region, wherein an entirety of the first doped region is under and overlapped by the recess, and the first doped region comprises:

a contact region; and

a transverse region; and

a second surface, wherein the first surface and the second surface are opposite surfaces of the semiconductor region, and the contact region extends further than the transverse region in a direction pointing from the first surface to the second surface of the semiconductor region;

a first reflecting region on a first side of the semiconductor region, the first reflecting region comprising a first distributed Bragg reflector in contact with the first surface of the semiconductor region; and

a second reflecting region on a second side of the semiconductor region and underlying the semiconductor region, the second reflecting region comprising a second distributed Bragg reflector in contact with the second surface of the semiconductor region.

6. The BSI photodetector of claim 5 , wherein the recess comprises:

a first recess surface, wherein the first recess surface is substantially horizontal;

a second recess surface, wherein the second recess surface is vertical; and

a third recess surface, wherein the third recess surface is substantially vertical.

7. The BSI photodetector of claim 5 , wherein the first distributed Bragg reflector reflecting region or the second distributed Bragg reflector reflecting region comprises a number of reflecting layers ranging from about 2 layers to about 20 layers.

8. The BSI photodetector of claim 5 , wherein the first distributed Bragg reflector reflecting region or the second distributed Bragg reflector reflecting region comprises:

a first layer, wherein the first layer is associated with a corresponding first refraction index; and

a second layer, wherein the second layer is associated with a corresponding second refraction index.

9. The BSI photodetector of claim 8 , wherein the first refraction index and the second refraction index comprises a refraction index contrast between the first refraction index and the second refraction index, wherein the refraction index contrast is greater than 0.5.

10. A method of making a backside-illuminated (BSI) photodetector device, the method comprising:

forming a recess extending from a first surface of a semiconductor region into the semiconductor region and toward an opposite second surface of the semiconductor region;

forming a first doped region and a second doped region in a semiconductor region, wherein an entirety of the first doped region is under and overlapped by the recess, and the first doped region comprises:

a contact region; and

a transverse region, wherein the contact region extends further than the transverse region in a direction pointing from the first surface to the second surface of the semiconductor region;

forming a first reflecting region on a first side of a semiconductor region, the first reflecting region comprising a first distributed Bragg reflector in contact with the first surface of the semiconductor region; and

forming a second reflecting region on a second side of a semiconductor region and underlying the semiconductor region, the second reflecting region comprising a second distributed Bragg reflector in contact with a second surface of the semiconductor region, wherein the first surface and the second surface are opposite surfaces of the semiconductor region.

11. The method of claim 10 , further comprising:

forming a conductive line in the semiconductor region, wherein the conductive line is electrically connected to the first doped region or the second doped region; and

forming a conductive layer adjacent to the first reflecting region.

12. The method of claim 10 , further comprising:

grinding the second side of the semiconductor region; and

performing an etch of the second side of the semiconductor region.

13. The BSI photodetector of claim 1 , wherein the first distributed Bragg reflector is in physical contact with the first surface of the semiconductor region, and the second distributed Bragg reflector is in physical contact with the second surface of the semiconductor region.

14. The BSI photodetector of claim 1 further comprising:

a conductive feature penetrating through the semiconductor region and electrically coupling to the first doped region.

15. The BSI photodetector of claim 5 , wherein the first distributed Bragg reflector extends into the recess.

16. The BSI photodetector of claim 5 , wherein the second distributed Bragg reflector is in physical contact with the second surface of the semiconductor region.

17. The method of claim 10 , wherein the forming the first doped region and the second doped region comprises:

implanting the semiconductor region to form the first doped region extending from the first surface of the semiconductor region into the semiconductor region; and

implanting the semiconductor region to form the second doped region extending from the second surface of the semiconductor region into the semiconductor region, wherein the first surface and the second surface are opposite surfaces of the semiconductor region.

18. The BSI photodetector of claim 5 , wherein the first distributed Bragg reflector extends into the recess.

19. The BSI photodetector of claim 1 , wherein edges of the recess are substantially aligned to respective edges of the semiconductor region.

20. The BSI photodetector of claim 14 further comprising an insulating region in the semiconductor region, wherein the conductive feature is separated from the semiconductor region by the insulating region.