Image sensor pixel with deep trench isolation structure
An image sensor device is disclosed. The image sensor device includes a number of pixels and neighboring pixels are isolated by deep trench isolation structures. In an embodiment, a method of forming a deep trench isolation structure includes performing a first etching process to remove a portion of a substrate, thereby forming a first trench in the substrate, performing a first doping process to form a first sidewall doped region along a sidewall surface of the first trench, after the performing of the first plasma doping process, performing a second etching process to extend the first trench, thereby forming a second trench in the substrate, and, after the performing of the second etching process, performing a second doping process to form a second sidewall doped region along a sidewall surface of the second trench, a portion of the second sidewall doped region overlaps with the first sidewall doped region.
1. A method of forming an image sensor device, comprising:
performing a first etching process to remove a portion of a substrate, thereby forming a first trench in the substrate;
before the performing of the first etching process, performing a first blanket doping process to form a first blanket doped region in the substrate;
after the performing of the first etching process, performing a first doping process to form a first sidewall doped region along a sidewall surface of the first trench;
performing a second etching process to extend the first trench, thereby forming a second trench in the substrate;
after the performing of the second etching process, performing a second doping process to form a second sidewall doped region along a sidewall surface of the second trench, a portion of the second sidewall doped region overlaps with the first sidewall doped region; and
after the performing of the second doping process, performing a second blanket doping process to form a second blanket doped region in the substrate and over the first blanket doped region,
wherein a dopant concentration of the second blanket doped region is greater than a dopant concentration of the first blanket doped region, and wherein a doping polarity of the first and second sidewall doped regions is opposite to a doping polarity of the first and second blanket doped regions.
2. The method of claim 1 , further comprising:
after the performing of the first doping process and before the performing of the second etching process, performing an annealing process.
3. The method of claim 1 , further comprising:
forming a patterned mask film over the substrate, the patterned mask film comprising an opening exposing the portion of the substrate.
4. The method of claim 3 , wherein the performing of the first etching process stops before reaching the first blanket doped region, and the second trench extends into the first blanket doped region.
5. The method of claim 1 ,
wherein the second sidewall doped region comprises an upper portion and a lower portion, the upper portion is overlapped with the first sidewall doped region,
wherein a top surface and a bottom surface of the upper portion are substantially coplanar with a top surface and a bottom surface of the second blanket doped region, respectively, and
wherein a top surface and a bottom surface of the lower portion are substantially coplanar with a top surface and a bottom surface of the first blanket doped region, respectively.
6. The method of claim 1 , further comprising:
performing a third etching process to extend the second trench, thereby forming a third trench in the substrate; and
after the performing of the third etching process, performing a third doping process to form a third sidewall doped region along a sidewall surface of the third trench,
wherein a portion of the third sidewall doped region overlaps with the second sidewall doped region.
7. The method of claim 1 , wherein an implant dosage of the first doping process is different than an implant dosage of the second doping process.
8. The method of claim 1 , wherein an energy of the first doping process is smaller than an energy of the second doping process.
9. The method of claim 1 , further comprising:
after the performing of the second doping process, forming a dielectric liner in the second trench; and
forming a conductive layer over the dielectric liner to fill the second trench.
10. The method of claim 9 , further comprising:
after forming the conductive layer and before the performing of the second blanket doping process, etching back the dielectric liner and the conductive layer to form a recess in the second trench; and
refilling the recess with a dielectric material.
11. The method of claim 9 , further comprising:
before the performing of the second blanket doping process, forming a gate dielectric layer over the substrate;
after the performing of the second blanket doping process, forming a gate electrode layer over the gate dielectric layer; and
patterning the gate electrode layer and the gate dielectric layer to form a gate structure over the substrate.
12. The method of claim 1 , wherein the first and second blanket doped regions comprise an n-type dopant, and the first and second sidewall doped regions comprise a p-type dopant.
13. A method of forming an image sensor device, comprising:
receiving a workpiece comprising:
a first isolation structure formed in a front side of a substrate,
a first doped region in a bottom portion the substrate and having a first dopant concentration and a first doping polarity, and
a trench extending through the first isolation structure and a portion of the substrate;
performing a first doping process to form a second doped region along a sidewall surface of the trench, the second doped region having a second doping polarity opposite to the first doping polarity;
after the forming of the second doped region, extending the trench downwardly into a portion of the substrate under the first doped region;
performing a second doping process to the workpiece to form a third doped region along a sidewall surface of the extended trench, a portion of the third doped region overlapping with the second doped region; and
performing a blanket doping process to the workpiece to form a fourth doped region in the substrate, wherein the fourth doped region has a second dopant concentration and the first doping polarity and is disposed laterally adjacent to the second doped region and over the first doped region.
14. The method of claim 13 , wherein the second dopant concentration is greater than the first dopant concentration.
15. The method of claim 13 , further comprising:
forming a dielectric liner in the extended trench;
forming a conductive layer over the dielectric liner to fill the extended trench;
after filling the extended trench, forming a gate trench extending into the portion of the substrate over the first doped region;
after the performing of the blanket doping process, forming a gate electrode layer in the gate trench;
performing a planarization process to a back side of the substrate to expose the conductive layer, the back side of the substrate being opposite to the front side of the substrate; and
forming a color filter under the back side of the substrate and directly under the fourth doped region.
16. A method of forming a semiconductor device, comprising:
forming a mask layer covering a first region of a substrate;
forming a trench by recessing a second region of the substrate not covered by the mask layer;
after the forming of the trench, performing a first plasma doping process to form a first p-type doped region in the substrate and adjacent to the trench;
after the performing of the first plasma doping process, further recessing the second region of the substrate to vertically extend the trench;
after the further recessing of the second region of the substrate, performing a second plasma doping process to form a second p-type doped region in the substrate and under the first p-type doped region;
forming an isolation feature in the extended trench, the isolation feature comprising a dielectric liner extending along bottom and sidewall surfaces of a conductive layer; and
after the forming of the isolation feature, removing the mask layer.
17. The method of claim 16 , wherein, after the performing of the second plasma doping process, a dopant concentration of the first p-type doped region is higher than a dopant concentration of the second p-type doped region.
18. The method of claim 16 , wherein, after the performing of the second plasma doping process, the first p-type doped region laterally spans a first width, the second p-type doped region laterally spans a second width, the second width is less than the first width.
19. The method of claim 16 , further comprising:
before the forming of the mask layer, performing a first blanket doping process to form a first n-type doped region in the substrate, wherein the first n-type doped region is disposed under the first p-type doped region; and
after the removing of the mask layer, performing a second blanket doping process to form a second n-type doped region in the substrate, wherein the second n-type doped region is disposed over the first n-type doped region and laterally adjacent to the first p-type doped region.
20. The method of claim 19 , wherein a top surface of the isolation feature is lower than a topmost surface of the substrate.