Backside illuminated image sensor having deep light reflective trenches
An array of pixels is formed using a substrate having a frontside and a backside that is for receiving incident light. Each pixel typically includes metallization layers included in the frontside of the substrate, a photosensitive region formed in the backside of the substrate, and a trench formed around the photosensitive region in the backside of the substrate. The trench causes the incident light to be directed away from the trench and towards the photosensitive region.
1. An image sensor, comprising:
an array of pixels formed using a substrate having a frontside and a backside, wherein the backside is to receive incident light, each pixel including:
metallization layers disposed on the frontside of the substrate;
a photosensitive region disposed within the substrate; and
a trench formed around at least a portion of the photosensitive region and extending from the frontside of the substrate past the photosensitive region towards the backside of the substrate, the trench causing the incident light received from the backside to be directed away from the trench and towards the photosensitive region,
wherein material filling the trench has a refractive index that is less than a refractive index of the substrate.
2. The image sensor of claim 1 , wherein the trench is filled with a gas or evacuated to generate a vacuum or partial-vacuum.
3. The image sensor of claim 1 , wherein a portion of the trench lies in an area that is at least partially peripheral to adjacent pixels.
4. The image sensor of claim 1 , wherein the trench is formed after thinning the backside of the substrate.
5. The image sensor of claim 4 , wherein the substrate is thinned using a chemical or mechanical planarization (CMP) process.
6. The image sensor of claim 4 , wherein the substrate is thinned using a chemical etching process using a shallow trench isolation (STI) region as an etch stop layer.
7. The image sensor of claim 1 , wherein the incident light received at the backside of the substrate is reflected from the trench in response to total internal reflection at an interface between the trench and the substrate.
8. The image sensor of claim 1 , wherein the trench is sealed using a non-conformably deposited dielectric film.
9. The image sensor of claim 1 , wherein the trench is formed by backside etching of a shallow trench isolation (STI) region in a portion of a peripheral region that is around the photosensitive region.
10. The image sensor of claim 1 , wherein the backside of the substrate is patterned and etched to expose a shallow trench isolation (STI) region.
11. The image sensor of claim 1 , wherein the trench is formed by etching the shallow trench isolation (STI) region and by filling the etched STI region with silicon dioxide.
12. The image sensor of claim 1 , wherein the trench is formed by etching the shallow trench isolation (STI) region such that a layer of silicon remains in the STI region.
13. The image sensor of claim 1 , wherein the trench extends through the entire substrate from the frontside of the substrate to the backside of the substrate.
14. The image sensor of claim 1 , wherein a portion of the trench physically abuts a side of the photosensitive region.
15. An image sensor, comprising:
an array of pixels formed using a substrate having a frontside and a backside, wherein the backside is to receive incident light, each pixel including:
metallization layers disposed over the frontside of the substrate;
a photosensitive region disposed within the substrate; and
a trench formed around at least a portion of the photosensitive region and extending from the frontside of the substrate past the photosensitive region towards the backside of the substrate, the trench causing the incident light received from the backside to be directed away from the trench and towards the photosensitive region,
wherein the trench has a reflective metal disposed at an interface of the trench and the photosensitive region.
16. An image sensor, comprising:
an array of pixels formed using a substrate having a frontside and a backside, wherein the backside is to receive incident light, each pixel including:
metallization layers disposed over the frontside of the substrate;
a photosensitive region disposed within the substrate; and
a trench formed around at least a portion of the photosensitive region and extending from the frontside of the substrate past the photosensitive region towards the backside of the substrate, the trench causing the incident light received from the backside to be directed away from the trench and towards the photosensitive region,
wherein a portion of the trench physically abuts a side of the photosensitive region.