Method for producing an optical filter in an integrated circuit, and corresponding integrated circuit
An integrated circuit includes a substrate and an interconnect part above the substrate, and further includes a photosensitive region in the substrate. A filter is provided aligned with the photosensitive region. The filter is formed by at least one layer of filter material. In one implementation for front side illumination, the layer of filter material is positioned above the photosensitive region between the interconnect part and the substrate. In another implementation for back side illumination, the layer of filter material is positioned below the photosensitive region opposite the interconnect part. The layer of filter material is configured such that a product of the thickness of the layer of filter material and the imaginary part of the refractive index of the layer of filter material is above 1 nm.
1. An integrated circuit, comprising:
a substrate having a photosensitive region,
an interconnect part above the substrate, and
an optical filter configured to filter radiation, wherein the optical filter comprises: at least one layer of filter material made of an electrically conductive material, aligned with the photosensitive region situated in the substrate and extending laterally beyond the photosensitive region, said at least one layer of filter material being electrically connected to an electrical contact at a portion of the electrically conductive material located laterally beyond the photosensitive region, so as to generate, in the electrically conductive material of the optical filter, an electrical field that polarizes the at least one layer of filter material.
2. The integrated circuit of claim 1 , wherein the at least one layer of filter material is formed on a surface between the substrate and the interconnect part.
3. The integrated circuit of claim 1 , wherein the at least one layer of filter material is formed on a surface below the photosensitive region and opposite from the interconnect part.
4. The integrated circuit according to claim 1 , wherein a product of the thickness of the at least one layer of filter material and the imaginary part of the refractive index is above 10 nanometers for the wavelengths of the radiation to be filtered.
5. The integrated circuit according to claim 1 , wherein a product of the thickness of the at least one layer of filter material and the imaginary part of the refractive index is above 1 nanometer for the wavelengths of the radiation to be filtered.
6. The integrated circuit according to claim 1 , wherein the electrically conductive material for the at least one layer of filter material comprises one of polycrystalline silicon or amorphous silicon.
7. The integrated circuit according to claim 1 , wherein the electrically conductive material for the at least one layer of filter material comprises polycrystalline silicon having p-type doping.
8. The integrated circuit according to claim 7 , further comprising at least one transistor having a gate region which comprises polycrystalline silicon having p-type doping and having a same thickness as the layer of filter material.
9. The integrated circuit according to claim 1 , wherein the photosensitive region is a photosensitive region of a single photon avalanche diode.
10. The integrated circuit according to claim 1 , further comprising an additional layer of filter material situated above or inside the interconnect part.
11. The integrated circuit of claim 1 , wherein the electrical contact connects to a metal line controlling the polarization of the at least one layer of filter material.
12. An integrated circuit, comprising:
a substrate having a front side and a back side and including a photosensitive region;
an interconnect part above the front side of the substrate;
an optical filter comprising:
an electrically conductive material layer positioned in alignment with the photosensitive region and extending laterally beyond the photosensitive region, the electrically conductive material layer being electrically connected to an electrical contact at a portion of the optical filter located laterally beyond the photosensitive region, so as to generate, in the electrically conductive material layer of the optical filter, an electrical field that polarizes the electrically conductive material layer.
13. The integrated circuit of claim 12 , wherein the optical filter comprises a layer of filter material positioned between the front side of the substrate between the substrate and the interconnect part.
14. The integrated circuit of claim 13 , wherein the optical filter comprises a layer of filter material mounted to the back side of the substrate.
15. The integrated circuit of claim 14 , wherein a product of the thickness of the layer of filter material and the imaginary part of the refractive index is above 10 nanometers for a certain wavelength range to be filtered.
16. The integrated circuit of claim 14 , wherein a product of the thickness of the layer of filter material and the imaginary part of the refractive index is above 1 nanometer for a certain wavelength range to be filtered.
17. The integrated circuit of claim 14 , wherein said electrically conductive material layer comprises a layer of material selected from the group consisting of polycrystalline silicon and amorphous silicon.
18. The integrated circuit of claim 14 , wherein said electrically conductive material layer comprises a layer of polycrystalline silicon doped with p-type dopant.
19. The integrated circuit of claim 14 , wherein said electrically conductive material layer comprises a layer of filter material located at a same level as a gate region of a transistor of the integrated circuit.
20. The integrated circuit of claim 14 , wherein the photosensitive region comprises a single photon avalanche diode.
21. The integrated circuit of claim 14 , further comprising a layer of filter material situated above or inside the interconnect part.
22. The integrated circuit of claim 14 , wherein the optical filter comprises a plurality of filter layers.
23. The integrated circuit according to claim 14 , wherein the electrical contact connects to a metal line controlling the polarization of the at least one layer of filter material.