Pinned photodiode with high storage capacity, method of manufacture and image sensor incorporating same
In a photodiode formed by a region of a first type inside a region of a second type, of a semiconductor substrate, the region of the first type includes a first zone including a dopant of the first type having a first concentration and a first depth. The region of the first type also has a second zone adjacent to the first zone in the dopant of the first type has a second concentration higher than the first concentration and a second depth smaller than the first depth. A method for making such a diode is also disclosed.
1. A device located between an isolating region and a transfer gate of a charge transfer transistor, comprising:
a first photodiode having a doping profile; and
a second photodiode having a doping profile reinforced relative to the doping profile of the first photodiode,
wherein said device is formed by a first region of a first conductivity type above a second region of a second conductivity type formed on a semiconductor substrate, said first region comprising (a) a first zone comprising a dopant of the first conductivity type with a first concentration and having a first depth and (b) a second zone adjacent to the first zone, comprising the dopant of the first conductivity type with a second concentration higher than the first concentration and having a second depth smaller than the first depth,
wherein the first photodiode comprises at least the first zone of the first region and the second photodiode comprises at least the second zone of the first region.
2. A device according to the claim 1 , wherein a pinching of the second photodiode is reinforced relative to a pinching of the first photodiode.
3. A device according to claim 1 , wherein the first zone extends over a first length and wherein the second zone extends over a second length of the order of 0.2 to 4 times the first length.
4. A device according to claim 3 , wherein the first length is substantially equal to the second length.
5. A device according to claim 1 , wherein the second concentration is of the order of 0.5 to 3 times the first concentration.
6. A device according to claim 1 , wherein the second region comprises a third zone adjacent to the first zone and positioned underneath the second zone on a third depth, and comprising a dopant of the second conductivity type.
7. A device according to claim 1 , wherein the first conductivity type is an N type and wherein the second conductivity type is a P type.
8. A device according to claim 1 wherein the first zone is situated between the second zone and the transfer gate.
9. A device according to claim 1 wherein the second zone is situated between the first zone and the transfer gate.