Passivation scheme for image sensor substrate

1. A method for forming an integrated chip, the method comprising:

forming a photodetector in a substrate;

patterning the substrate to form a trench in the substrate, wherein the trench is formed by sidewalls of the substrate, and wherein the trench surrounds the photodetector;

depositing a first passivation layer on the sidewalls of the substrate that form the trench, the first passivation layer comprising hydrogenated amorphous silicon; and

depositing a dielectric layer over the first passivation layer and in a remainder of the trench to form a trench isolation structure over the first passivation layer and surrounding the photodetector.

2. The method of claim 1 , wherein the hydrogenated amorphous silicon of the first passivation layer is undoped, and wherein the method further comprises:

depositing a second passivation layer over the first passivation layer, the second passivation layer comprising hydrogenated amorphous silicon that has p-type doping.

3. The method of claim 2 , further comprising:

depositing a third passivation layer over the second passivation layer, the third passivation layer comprising aluminum oxide.

4. The method of claim 2 , further comprising:

annealing the first passivation layer at a temperature of less than 250 degrees Celsius.

5. The method of claim 2 , wherein the first passivation layer is deposited along a backside of the substrate, wherein the dielectric layer is deposited along the backside of the substrate, and wherein the method further comprises:

performing a planarization process on the dielectric layer and the first passivation layer to remove the dielectric layer and the first passivation layer from along the backside of the substrate.

6. The method of claim 1 , wherein the substrate has a n-type doping type along the sidewalls of the substrate, and wherein the hydrogenated amorphous silicon has p-type doping.

7. The method of claim 1 , wherein the substrate has p-type doping along the sidewalls of the substrate, wherein the hydrogenated amorphous silicon has p-type doping, and wherein a dopant concentration of the hydrogenated amorphous silicon is greater than a dopant concentration of the substrate along the sidewalls of the substrate.

8. The method of claim 1 , wherein a hydrogen concentration of the hydrogenated amorphous silicon ranges from 4% to 35%.

9. A method for forming an integrated chip, the method comprising:

forming a photodetector in a substrate;

etching the substrate to form a trench in the substrate, wherein the trench surrounds the photodetector and the trench is delimited by sidewalls of the substrate;

forming a passivation structure along the sidewalls of the substrate, the passivation structure comprising hydrogenated amorphous silicon having p-type doping; and

depositing a dielectric layer over of the passivation structure to from a trench isolation structure in the trench, wherein the trench isolation structure is separated from the substrate by the passivation structure.

10. The method of claim 9 , wherein forming the passivation structure comprises depositing a first passivation layer on the sidewalls of the substrate, the first passivation layer comprising the hydrogenated amorphous silicon having the p-type doping, and wherein the dielectric layer is deposited on the first passivation layer.

11. The method of claim 9 , wherein forming the passivation structure comprises depositing a first passivation layer on the sidewalls of the substrate and depositing a second passivation layer over the first passivation layer, the first passivation layer comprising hydrogenated amorphous silicon having intrinsic doping and the second passivation layer comprising the hydrogenated amorphous silicon having the p-type doping, and wherein the dielectric layer is deposited on the second passivation layer.

12. The method of claim 9 , wherein forming the passivation structure comprises depositing a first passivation layer on the sidewalls of the substrate, depositing a second passivation layer over the first passivation layer, and depositing a third passivation layer over the second passivation layer, the first passivation layer comprising hydrogenated amorphous silicon having intrinsic doping, the second passivation layer comprising the hydrogenated amorphous silicon having the p-type doping, and the third passivation layer comprising aluminum oxide, and wherein the dielectric layer is deposited on the third passivation layer.

13. The method of claim 9 , wherein the substrate has n-type doping along the sidewalls of the substrate.

14. The method of claim 9 , wherein the substrate has p-type doping along the sidewalls of the substrate, and wherein a dopant concentration of the hydrogenated amorphous silicon is greater than a dopant concentration of the substrate at along the sidewalls of the substrate.

15. The method of claim 9 , wherein forming the photodetector in the substrate comprises forming a first semiconductor well having a first doping type in a substrate along a first side of the substrate, the method further comprising:

forming second semiconductor well having a second doping type, different than the first doping type, in the substrate along a second side of the substrate, opposite the first side,

wherein the first semiconductor well extends along sidewalls of the passivation structure, and wherein the second semiconductor well extends along a bottom surface of the passivation structure.

16. A method for forming an integrated chip, the method comprising:

forming a first semiconductor well having a first doping type in a substrate along a first side of the substrate;

forming second semiconductor well having a second doping type, different than the first doping type, in the substrate along a second side of the substrate, opposite the first side;

etching the first side of the substrate to form a trench in the substrate, wherein the trench surrounds a photodetector in the first semiconductor well, wherein the trench is delimited by sidewalls of the substrate and an upper surface of the substrate, and wherein the first semiconductor well extends along the sidewalls of the substrate and the second semiconductor well extends along the upper surface of the substrate;

depositing a first passivation layer on the sidewalls of the substrate and the upper surface of the substrate, the first passivation layer comprising hydrogenated amorphous silicon; and

depositing a dielectric layer over sidewalls and an upper surface of the first passivation layer to form a trench isolation structure surrounding the photodetector.

17. The method of claim 16 , wherein a hydrogen concentration of the hydrogenated amorphous silicon is controlled during the depositing of the first passivation layer by controlling an amount of hydrogen gas used during the depositing of the first passivation layer.

18. The method of claim 16 , wherein the hydrogenated amorphous silicon has p-type doping, and wherein a dopant concentration of the hydrogenated amorphous silicon is controlled during the depositing of the first passivation layer by controlling an amount dopant gas used during the depositing of the first passivation layer.

19. The method of claim 16 , further comprising:

depositing a second passivation layer on the sidewalls and the upper surface of the first passivation layer, wherein the first passivation layer comprises intrinsic hydrogenated amorphous silicon and the second passivation layer comprises hydrogenated amorphous silicon having p-type doping, and wherein the dielectric layer is deposited over sidewalls and an upper surface of the second passivation layer.

20. The method of claim 19 , further comprising:

depositing a third passivation layer on the sidewalls and the upper surface of the second passivation layer, wherein the third passivation layer comprises aluminum oxide, and wherein the dielectric layer is deposited over sidewalls and an upper surface of the third passivation layer.