Pinned photodiode with a low dark current
A method of manufacturing a pinned photodiode, including: forming a region of photon conversion into electric charges of a first conductivity type on a substrate of the second conductivity type; coating said region with a layer of a heavily-doped insulator of the second conductivity type; and annealing to ensure a dopant diffusion from the heavily-doped insulator layer.
1. A method comprising:
manufacturing a pinned photodiode, the manufacturing including:
forming a conversion region of a first conductivity type on a substrate of a second conductivity type, the conversion region being configured to convert photons into electric charges;
forming a shallow semiconductor region of the second conductivity type on the conversion region;
coating said shallow semiconductor region with a heavily-doped insulator layer that is doped with dopants of the second conductivity type, the shallow semiconductor region being positioned between the conversion region and the heavily-doped insulation layer; and
providing a dopant diffusion from the heavily-doped insulator layer into the shallow semiconductor region, wherein:
the shallow semiconductor region is formed on the conversion region prior to coating said shallow semiconductor region with the heavily-doped insulator layer; and
providing the dopant diffusion includes forming a diffusion layer of the second conductivity type in an upper portion of the shallow semiconductor region, the diffusion layer having a doping level that is higher than a doping level of the shallow semiconductor region.
2. The method of claim 1 , wherein the conversion region is of type N and the layer of a heavily-doped insulator is a boron-doped silicon oxide layer.
3. The method of claim 1 , wherein providing the dopant diffusion includes diffusing dopants from the heavily-doped insulator layer into the shallow semiconductor region to a penetration depth smaller than 50 nm.
4. The method of claim 1 , wherein forming the shallow semiconductor region includes coating the conversion region with the shallow semiconductor region with a maximum doping level in a range from 10 17 to 10 18 at./cm 3 before coating the shallow semiconductor region with the heavily-doped insulator layer.
5. The method of claim 1 , wherein providing the dopant diffusion includes annealing the heavily-doped insulator layer and forming a heavily-doped diffusion layer of the second conductivity type having a doping level that is greater than a doping level of the shallow semiconductor region.
6. The method of claim 2 , wherein the boron-doped silicon oxide layer is doped with a boron concentration from 5×10 21 to 2×10 22 at./cm 3 .
7. The method of claim 3 , wherein the penetration depth is smaller than 10 nm.
8. A pinned photodiode, comprising:
a conversion region of a first conductivity type formed on a substrate of a second conductivity type, the conversion region being configured to convert photons into electric charges;
a diffusion layer of the second conductivity type formed on the conversion region;
a shallow semiconductor region of the second conductivity type positioned between the diffusion layer and the conversion region; and
a heavily-doped insulator layer that coats the diffusion layer, the heavily-doped insulator layer being of the second conductivity type.
9. The pinned photodiode of claim 8 , wherein the heavily-doped insulator layer is boron-doped silicon oxide at a boron concentration from 5×10 21 to 2×10 22 at./cm 3 .
10. The pinned photodiode of claim 8 , wherein the diffusion layer has a depth of less than 50 nm.
11. The pinned photodiode of claim 8 , wherein the shallow semiconductor region has a maximum doping on the order 10 18 at./cm 3 and the diffusion layer has a maximum doping on the order 10 20 at./cm 3 .
12. The pinned photodiode of claim 8 , wherein said diffusion layer has a doping level that is higher than a doping level of the shallow semiconductor region.
13. A device, comprising:
a transfer transistor; and
a pinned photodiode, the pinned photodiode including:
a conversion region of a first conductivity type formed on a substrate of a second conductivity type, the conversion region being configured to convert photons into electric charges;
a diffusion layer of the second conductivity type formed on the conversion region;
a shallow semiconductor region of the second conductivity type positioned between the diffusion layer and the conversion region; and
a heavily-doped insulator layer that coats the diffusion layer, the heavily-doped insulator layer being of the second conductivity type.
14. The device of claim 13 , wherein the heavily-doped insulator layer is boron-doped silicon oxide at a boron concentration from 5×10 21 to 2×10 22 at./cm 3 .
15. The device of claim 13 , wherein the diffusion layer has a depth of less than 10 nm.
16. The device of claim 13 , wherein the transfer transistor includes an insulated gate, a drain, and a source, the source being at least a portion of the conversion region.
17. The device of claim 13 , wherein said diffusion layer has a doping level that is higher than a doping level of the shallow semiconductor region.
18. The device of claim 15 , wherein the shallow semiconductor region has a maximum doping on the order 10 18 at./cm 3 and the diffusion layer has a maximum doping on the order 10 20 at./cm 3 .