Imager having a reduced dark current through an increased bulk doping level
The disclosure relates to an image sensor comprising a substrate region in a semiconductor material; an active layer in contact with the substrate region; and a photodiode array formed in the active layer. The substrate region has a doping level such that the resistivity of the substrate region is less than 6 mOhm·cm.
1. An image sensor comprising:
a substrate region in a semiconductor material having a doping level such that the substrate region has a resistivity that is less than 6 mOhm·cm;
an active layer in the semiconductor material and in contact with the substrate region;
an array of photodiodes formed in the active layer;
deep trench isolators in contact with the substrate region and structured to isolate the photodiodes from each other; and
a semiconductor layer lining the trench isolators, in contact with the substrate region and having a higher doping level than the active layer.
2. The sensor of claim 1 , comprising:
a substrate having a doping level greater than that of the active layer; wherein said substrate region has a doping level greater than the doping level of the substrate and is an intermediate layer positioned between the substrate and the active layer.
3. The sensor of claim 2 , wherein the intermediate layer is epitaxial and has a resistivity between 1 and 6 mOhm·cm.
4. The sensor of claim 2 , wherein the intermediate layer has a thickness between 1 and 10 microns.
5. The sensor of claim 1 , wherein the substrate region is an integral part of a substrate having a uniform doping level.
6. The sensor of claim 1 , comprising:
a passivation layer on the active layer;
an array of colored filters on the passivation layer; and
an array of collimating lenses on the array of colored filters.
7. A method of manufacturing an image sensor, the method comprising:
forming a substrate region in a semiconductor material, the substrate region having a doping level such that the substrate region has a resistivity that is less than 6 mOhm·cm;
forming an active layer in the semiconductor material and in contact with the substrate region;
forming an array of photodiodes formed in the active layer;
forming deep trench isolators in contact with the substrate region and structured to isolate the photodiodes from each other; and
forming a semiconductor layer lining the trench isolators, in contact with the substrate region and having a higher doping level than the active layer.
8. The method of claim 7 , wherein:
said substrate region has a doping level greater than the doping level of the substrate and is an intermediate layer positioned between a substrate and the active layer, the substrate having a doping level greater than that of the active layer.
9. The method of claim 8 , wherein forming the substrate region includes epitaxially growing the substrate region, the substrate region having a resistivity between 1 and 6 mOhm·cm.
10. The method of claim 8 , wherein the intermediate layer has a thickness between 1 and 10 microns.
11. The method of claim 7 , wherein the substrate region is an integral part of a substrate having a uniform doping level.
12. The method of claim 7 , comprising:
forming a passivation layer on the active layer;
forming an array of colored filters on the passivation layer; and
forming an array of collimating lenses on the array of colored filters.