Reduced crosstalk CMOS image sensors
View Patent ↗CMOS image sensor having high sensitivity and low crosstalk, particularly at far-red to infrared wavelengths, and a method for fabricating a CMOS image sensor. A CMOS image sensor has a substrate, an epitaxial layer above the substrate, and a plurality of pixels extending into the epitaxial layer for receiving light. The image sensor also includes at least one of a horizontal barrier layer between the substrate and the epitaxial layer for preventing carriers generated in the substrate from moving to the epitaxial layer, and a plurality of lateral barrier layers between adjacent ones of the plurality of pixels for preventing lateral diffusion of electrons in the epitaxial layer.
1. A CMOS image sensor, comprising:
a substrate;
a single epitaxial layer above the substrate;
a plurality of pixels extending into the epitaxial layer for receiving light;
a horizontal barrier layer between the substrate and the epitaxial layer for preventing carriers generated in the substrate from moving to the epitaxial layer; and
a plurality of lateral barrier layers between adjacent ones of the plurality of pixels for preventing lateral diffusion of electrons in the epitaxial layer, wherein the plurality of lateral barrier layers each comprise a deep P-well between adjacent pixels extending into the epitaxial layer to a depth of from about 2 μm to about 20 μm, and
the deep P-well is formed of P-dopant of a single conductivity type in the single epitaxial layer.
2. The CMOS image sensor according to claim 1 , wherein the horizontal barrier layer comprises very heavily-doped silicon.
3. The CMOS image sensor according to claim 2 , wherein the horizontal barrier layer includes one or more of boron, aluminum, gallium, indium, phosphorus, arsenic, antimony, germanium and carbon.
4. The CMOS image sensor according to claim 2 , wherein the horizontal barrier layer is encapsulated on one or both sides by a carbon containing layer.
5. The CMOS image sensor according to claim 2 , wherein the horizontal barrier layer has a thickness of greater than about 100 Å to less than 1 μm.
6. The CMOS image sensor according to claim 1 , wherein the epitaxial layer has a thickness of from about 2 μm to about 20 μm, and wherein the plurality of pixels each include a well portion that extends into the epitaxial layer to a depth of from about 1 μm to about 15 μm.
7. The CMOS image sensor according to claim 6 , wherein doping in the epitaxial layer is graded below a depletion depth to provide an electric field to direct carriers.
8. The CMOS image sensor according to claim 1 , wherein each of the plurality of lateral barrier layers further include trenches in the deep P-wells.
9. The CMOS image sensor according to claim 8 , wherein the trenches of the plurality of lateral barrier layers are filled with at least one of polysilicon, silicon oxide and silicon dioxide.
10. The CMOS image sensor according to claim 1 , wherein the light includes in a far-red to infrared wavelength range.
11. The CMOS image sensor according to claim 1 , wherein the epitaxial layer has a first thickness and the deep P-well extends into the epitaxial layer at a depth corresponding to the first thickness.
12. The CMOS image sensor according to claim 11 , wherein the epitaxial layer has a first thickness greater than 17 μm and the deep P-well extends into the epitaxial layer at a depth greater than 17 μm.
13. A CMOS image sensor, comprising:
a substrate;
a single epitaxial layer above the substrate;
a plurality of pixels for receiving light, wherein the light comprises light in a far-red to infrared wavelength range, and wherein each of the plurality of pixels extend into the epitaxial layer;
a horizontal barrier layer between the substrate and the epitaxial layer for preventing carriers generated in the substrate from moving to the epitaxial layer; and
a plurality of lateral barrier layers between adjacent ones of the plurality of pixels for preventing lateral diffusion of electrons in the epitaxial layer, wherein the plurality of lateral barrier layers each comprise a deep P-well between adjacent pixels extend into the epitaxial layer to a depth of from about 2 μm to about 20 μm, and
the deep P-well is formed of P-dopant of a single conductivity type in the single epitaxial layer.
14. The CMOS image sensor according to claim 13 , wherein the horizontal barrier layer comprises very heavily-doped silicon.
15. The CMOS image sensor according to claim 14 , wherein the doping in the epitaxial layer is graded below a depletion depth to provide an electric field to direct carriers.
16. The CMOS image sensor according to claim 13 , wherein the plurality of lateral barrier layers each comprise a deep P-well between adjacent pixels extending into the epi layer to a depth of from about 2 μm to about 20 μm, and a lateral trench in each of the deep P-wells.
17. The CMOS image sensor according to claim 16 , wherein the trenches of the plurality of lateral barrier layers are filled with at least one of polysilicon, silicon oxide and silicon dioxide.
18. The CMOS image sensor according to claim 13 , wherein the horizontal barrier layer includes one or more of boron, aluminum, gallium, indium, phosphorus, arsenic, antimony, germanium and carbon.
19. The CMOS image sensor according to claim 13 , wherein the horizontal barrier layer is encapsulated on one or both sides by a carbon containing layer.
20. The CMOS image sensor according to claim 13 , wherein the epitaxial layer has a first thickness and the deep P-well extends into the epitaxial layer at a depth corresponding to the first thickness.
21. The CMOS image sensor according to claim 20 , wherein the epitaxial layer has a first thickness greater than 17 μm and the deep P-well extends into the epitaxial layer at a depth greater than 17 μm.
22. A method for fabricating a CMOS image sensor that comprises a substrate, an epitaxial layer above the substrate, and a plurality of pixels extending into the epitaxial layer, the method comprising:
forming a horizontal barrier layer between the substrate and the epitaxial layer for preventing carriers generated in the substrate from moving to the epitaxial layer; and
forming a plurality of lateral barrier layers between adjacent ones of the plurality of pixels for preventing lateral diffusion of electrons in the epitaxial layer, wherein the plurality of lateral barrier layers each comprise a deep P-well between adjacent pixels extending into the epitaxial layer to a depth of from about 2 μm to about 20 μm,
the epitaxial layer is a single layer, and
the deep P-well is formed of P-dopant of a single conductivity type in the single epitaxial layer.
23. The method according to claim 22 , wherein the horizontal barrier layer comprises very heavily-doped silicon.
24. The method according to claim 22 , wherein the plurality of lateral barrier layers include deep P-wells and lateral trenches in the P-wells.
25. The CMOS image sensor according to claim 22 , wherein the epitaxial layer has a first thickness and the deep P-well extends into the epitaxial layer at a depth corresponding to the first thickness.