Backside illuminated global shutter pixels
Global shutter imaging pixels may include a charge storage region that receives charge from a respective photodiode. Global shutter imaging pixels may be formed as frontside illuminated imaging pixels or backside illuminated imaging pixels. Shielding charge storage regions from incident light may be important for image sensor performance. To shield charge storage regions in backside illuminated global shutter imaging pixels, shielding structures may be included over the charge storage region. The shielding structures may include backside trench isolation structures, a metal layer formed in a backside trench between backside trench isolation structures, and frontside deep trench isolation structures. The metal layer may have angled portions that reflect light towards the photodiodes.
1. An image sensor comprising:
a substrate having a front surface and a back surface;
first and second photodiodes formed in the substrate;
a charge storage region formed in the substrate between the first and second photodiodes;
backside deep trench isolation having first and second portions between the first and second photodiodes;
a trench in between the first and second portions of backside deep trench isolation that extends from the back surface towards the front surface;
an opaque layer formed in the trench; and
an oxide layer formed over the opaque layer, wherein the oxide layer is formed in the trench.
2. The image sensor defined in claim 1 , wherein the opaque layer comprises a metal layer.
3. The image sensor defined in claim 1 , wherein the backside deep trench isolation comprises an additional trench that is filled with a filler material.
4. The image sensor defined in claim 3 , wherein the filler material comprises an oxide material.
5. The image sensor defined in claim 3 , wherein the filler material comprises a metal material.
6. The image sensor defined in claim 3 , wherein the backside deep trench isolation further comprises a passivation coating that is interposed between the filler material and the substrate.
7. The image sensor defined in claim 6 , wherein the passivation coating comprises a material selected from the group consisting of: p-type doped oxide, phosphorous doped oxide, hafnium oxide, titanium oxide, zirconium oxide, tantalum oxide, aluminum oxide, and silicon dioxide.
8. The image sensor defined in claim 1 , wherein the oxide layer is a silicon dioxide layer and wherein the silicon dioxide layer has an upper surface that is coplanar with an upper surface of the opaque layer.
9. The image sensor defined in claim 1 , wherein a width of the trench is less than a distance between the first and second portions of backside deep trench isolation.
10. The image sensor defined in claim 1 , further comprising:
frontside deep trench isolation having first and second portions between the first and second photodiodes, wherein the first and second portions of frontside deep trench isolation are respectively overlapped by the first and second portions of backside deep trench isolation.
11. A backside illuminated image sensor comprising:
a substrate having a front surface and a back surface;
a photodiode formed in the substrate;
a charge storage region that is formed in the substrate and that is configured to receive charge from the photodiode;
shielding structures formed in the substrate over the charge storage region, wherein the shielding structures comprise an opaque layer that is formed in a first trench between first and second backside deep trench isolation structures; and
a coating having a first portion formed on the back surface over the photodiode, a second portion formed in a second trench for the first backside deep trench isolation structure, a third portion formed in a third trench for the second backside deep trench isolation structure, and a fourth portion formed in the first trench.
12. The backside illuminated image sensor defined in claim 11 , wherein the shielding structures further comprise first and second frontside deep trench isolation structures and wherein the first and second backside deep trench isolation structures overlap the first and second frontside deep trench isolation structures.
13. An image sensor comprising:
a substrate having first and second opposing surfaces;
first and second photodiodes formed in the substrate;
first and second color filters formed over the substrate, wherein the first surface is interposed between the first and second color filters and the second surface;
a charge storage region formed in the substrate between the first and second photodiodes; and
a metal layer having first and second angled portions formed in at least one trench in the first surface of the substrate, wherein the metal layer covers the charge storage region, wherein the first angled portion is at a first angle relative to the first surface, wherein the second angled portion is at a second angle relative to the first surface, wherein the first angle is greater than 0 degrees and less than 90 degrees, and wherein the second angle is greater than 0 degrees and less than 90 degrees.
14. The image sensor defined in claim 13 , wherein the first and second angled portions extend away from the first surface and meet directly at a vertex below the first surface.
15. The image sensor defined in claim 13 , wherein the at least one trench comprises first and second trenches and wherein the first and second angled portions are respectively formed in the first and second trenches.
16. The image sensor defined in claim 14 , wherein metal layer has a horizontal portion that is parallel to the first surface of the substrate and wherein the horizontal portion is interposed between and directly connected to the first and second angled portions.
17. The image sensor defined in claim 1 , wherein the oxide layer has a first uppermost surface, wherein the opaque layer has a second uppermost surface, and wherein the first and second uppermost surfaces are coplanar.
18. The image sensor defined in claim 1 , wherein the oxide layer has a portion that is formed below a plane defined by the back surface of the substrate, wherein the oxide layer has first and second opposing sides connected by a third side, and wherein the first, second, and third sides of the oxide layer directly contact the opaque layer.
19. The image sensor defined in claim 1 , wherein the first portion of backside deep trench isolation comprises a first additional trench that is filled with a first filler material, wherein the second portion of backside deep trench isolation comprises a second additional trench that is filled with a second filler material, wherein the opaque layer has a first portion that is formed in the trench between the first and second portions of backside deep trench isolation, wherein the opaque layer has a second portion that serves as the first filler material for the first portion of backside deep trench isolation, and wherein the opaque layer has a third portion that serves as the second filler material for the second portion of backside deep trench isolation.
20. The backside illuminated image sensor defined in claim 11 , wherein the opaque layer has a first portion that is formed in the first trench between the first and second backside deep trench isolation structures, a second portion that extends below the first portion of the opaque layer to form part of the first backside deep trench isolation structure, and a third portion that extends below the first portion of the opaque layer to form part of the second backside deep trench isolation structure.