Semiconductor device including image sensor and method of forming the same
A semiconductor device includes a substrate having a front side and a back side opposite to each other. A plurality of photodetectors is disposed in the substrate within a pixel region. An isolation structure is disposed within the pixel region and between the photodetectors. The isolation structure includes a back side isolation structure extending from the back side of the substrate to a position in the substrate. A conductive plug structure is disposed in the substrate within a periphery region. A conductive cap is disposed on the back side of the substrate and extends from the pixel region to the periphery region and electrically connects the back side isolation structure to the conductive plug structure. A conductive contact lands on the conductive plug structure, and is electrically connected to the back side isolation structure through the conductive plug structure and the conductive cap.
1. A method of forming a semiconductor device, comprising:
providing a substrate having a front side and a back side opposite to each other;
forming a plurality of photodetectors in the substrate within a pixel region;
patterning the substrate from the back side of the substrate to form a first opening within the pixel region and a second opening within a periphery region;
forming a dielectric liner on sidewalls and bottom surfaces of the first and second openings;
removing a portion of the dielectric liner covering the bottom surfaces of the first and second openings;
forming a conductive material layer after the removing, wherein the conductive material layer is formed on the substrate and filling into the first and second openings, wherein the conductive material layer comprises a first conductive plug in the first opening, a second conductive plug in the second opening, and an upper portion over the back side of the substrate, and wherein the first conductive plug serves as a first portion of an isolation structure disposed between the plurality of photodetectors;
patterning the upper portion of the conductive material layer to form a conductive cap, wherein the conductive cap extends from the pixel region to the periphery region and is electrically connected to the first and second conductive plugs; and
forming a conductive contact on the second conductive plug over the front side of the substrate within the periphery region.
2. The method of claim 1 , further comprising:
forming a first well region and a second well region in the substrate within the pixel region and the periphery region from the front side of the substrate, respectively, wherein the first opening and the second opening are respectively formed to extend from the back side of the substrate to the first well region and the second well region, respectively, and wherein the first well region serves as a second portion of the isolation structure.
3. The method of claim 2 , further comprising:
forming a doped contact region on the second well region, wherein the doped contact region has a same doping type as, and a higher doping concentration than, the second well region, wherein the conductive contact extends to the doped contact region, and wherein the second well region has a lesser height than the first well region.
4. The method of claim 2 , wherein the conductive contact extends to a surface of the substrate and is spaced from the second well region, and wherein the first well region extends into the substrate from the surface of the substrate.
5. The method of claim 1 , wherein the first conductive plug has a grid-shaped top geometry, and wherein the second conductive plug has a ring-shaped top geometry surrounding the grid-shaped top geometry.
6. A method of forming a semiconductor device, comprising:
forming an array of photodetectors in a pixel region of a substrate;
forming a first well region and a second well region in the substrate, wherein the first well region extends into the substrate from a front side surface of the substrate and has a first grid-shaped top geometry separating each photodetector of the array of photodetectors from each other, and wherein the second well region is outside the pixel region;
forming a contact region in the substrate and separating the second well region from the front side surface of the substrate;
patterning the substrate to form a first opening and a second opening extending from a back side surface of the substrate, opposite the front side surface of the substrate, respectively to the first and second well regions, wherein the first opening has a second grid-shaped top geometry separating each photodetector of the array of photodetectors from each other;
depositing a metal layer filling the first and second openings; and
patterning the metal layer to form a plurality of third openings respectively overlying the array of photodetectors.
7. The method of claim 6 , wherein the patterning of the metal layer forms a first plurality of line-shaped metal segments extending in parallel along rows of the array of photodetectors, and further forms a second plurality of line-shaped metal segments extending in parallel along columns of the array of photodetectors, and wherein the second plurality of line-shaped metal segments intersect the first plurality of line-shaped metal segments.
8. The method of claim 6 , further comprising:
depositing a liner layer lining and partially filling the first opening;
depositing a dielectric layer covering the back side surface of the substrate, and further covering the first opening without filling the first opening, wherein a thickness of the dielectric layer is less directly over the first opening than directly over the back side surface of the substrate; and
performing a blanket etch into the liner layer and the dielectric layer to expose the first well region in the first opening before the depositing of the metal layer.
9. The method of claim 8 , wherein the liner layer is further deposited lining and partially filling the second opening, and wherein the dielectric layer is further deposited covering the second opening without filling the second opening.
10. The method of claim 6 , further comprising:
forming a doped region recessed into the first well region, wherein the doped region has an opposite doping type as the first well region; and
forming a pair of gate electrodes on the front side surface of the substrate, wherein a portion of the doped region is between and borders the pair of gate electrodes.
11. The method of claim 6 , wherein the contact region has a same doping type as the second well region and further has a different doping concentration than the second well region.
12. The method of claim 6 , wherein the second well region extends in a first closed path around the first grid-shaped top geometry, and wherein the second opening extends in a second closed path around the second grid-shaped top geometry.
13. A method of forming a semiconductor device, comprising:
forming an array of photodetectors in a substrate;
forming a front side isolation structure and a front side plug extending into the substrate from a front side of the substrate, wherein the front side isolation structure individually surrounds each photodetector of the array of photodetectors, and wherein the front side plug is laterally offset from the array of photodetectors;
patterning a back side of the substrate, opposite the front side of the substrate, to form a first opening and a second opening respectively exposing the front side isolation structure and the front side plug;
depositing a conductive layer filling the first and second openings, wherein the conductive layer forms a back side isolation structure and a back side plug extending into the substrate from the back side of the substrate respectively to the front side isolation structure and the front side plug; and
forming an interconnect structure on the front side of the substrate, wherein the interconnect structure directly contacts the front side plug while being spaced from the front side isolation structure, and further electrically couples to the front side isolation structure indirectly via the conductive layer and the front side plug.
14. The method of claim 13 , wherein the front side isolation structure consists essentially of a first well, and wherein the front side plug consists essentially of a contact region and a second well, and wherein the first well, the second well, and the contact region share a common doping type in the substrate.
15. The method of claim 14 , wherein the front side isolation structure and the front side plug have a same height.
16. The method of claim 14 , wherein the second opening is spaced from the contact region.
17. The method of claim 13 , further comprising:
performing an etch selectively into the conductive layer to remove portions of the conductive layer directly over the array of photodetectors.
18. The method of claim 13 , further comprising:
forming a doped semiconductor region recessed into the front side isolation structure; and
forming a pair of gate electrodes on the front side of the substrate, wherein a portion of the doped semiconductor region is between and borders the pair of gate electrodes.
19. The method of claim 13 , wherein the forming of the front side isolation structure and the front side plug comprises:
forming a first well region and a second well region in the substrate from the front side of the substrate, wherein the first opening and the second opening are respectively formed to extend from the back side of the substrate respectively to the first well region and the second well region, wherein the first well region forms the front side isolation structure, and wherein the second well region partially forms the front side plug.
20. The method of claim 13 , wherein the back side isolation structure has a grid-shaped top geometry, and wherein the back side plug has a ring-shaped top geometry surrounding the grid-shaped top geometry.