Back side illumination photodiode of high quantum efficiency
A back side illumination photodiode includes a light-receiving back side surface of a semiconductor material substrate. An area of the light-receiving back side surface includes a recess. The recess is filled with a material having an optical index that is lower than an optical index of the semiconductor material substrate. Both the substrate and the filling material are transparent to an operating wavelength of the photodiode. The recess may be formed to have a ring shape.
1. A method fabricating a back side illumination (BSI) photodiode, comprising:
forming a recess in at least one area of a light-receiving back surface of a semiconductor layer within which a photosensitive region for the back side illumination (BSI) photodiode is provided; and
filling the recess with a material having an optical index different from an optical index of the semiconductor layer to form a diffracting structure;
wherein said filling material is transparent to an operating wavelength of the BSI photodiode.
2. The method of claim 1 , further comprising, before forming and filling: performing a diffraction simulation regarding said BSI photodiode according to said material and an operating wavelength in order to determine dimensions of said recess.
3. The method of claim 1 , wherein the material has a lower optical index than the optical index of the semiconductor layer.
4. The method of claim 1 , wherein the recess in the shape of a ring having an inner diameter and an outer diameter.
5. The method of claim 4 , further comprising, before forming and filling: performing a diffraction simulation regarding said BSI photodiode according to said material and an operating wavelength in order to determine the inner and outer diameter dimensions of said recess.
6. The method of claim 4 , wherein the inner diameter is in the range between approximately 200 and approximately 500 nm and wherein the outer diameter is in the range between approximately 450 and approximately 650 nm.
7. The method of claim 1 , further comprising implanting dopant of a same conductivity type as present in the semiconductor layer, but at a higher dopant concentration, adjacent sides of the recess.
8. The method of claim 7 , wherein filling is performed after implanting.
9. The method of claim 1 , wherein the material is silicon oxide.
10. The method of claim 1 , further comprising implanting dopant of a same conductivity type as present in the semiconductor layer, but at a higher dopant concentration, adjacent a bottom of the recess.
11. The method of claim 10 , wherein filling is performed after implanting.
12. The method of claim 1 , further comprising implanting dopant of a same conductivity type as present in the semiconductor layer, but at a higher dopant concentration, at the light-receiving back surface.
13. The method of claim 1 , wherein a lateral dimension of said recess is smaller than an operating wavelength of the BSI photodiode.
14. The method of claim 1 , further comprising forming an an electrical interconnection network on a front side surface of the semiconductor layer opposite the light-receiving back surface.
15. The method of claim 1 , further comprising:
forming a color filter layer over the light-receiving back surface; and
forming a lens over the color filter layer.