Back-illuminated, thin photodiode arrays with isolating etched trenches between elements
Back-illuminated, thin photodiode arrays with trench isolation. The trenches are formed on one or both sides of a substrate, and after doping the sides of the trenches, are filled to provide electrical isolation between adjacent photodiodes. Various embodiments of the photodiode arrays and methods of forming such arrays are disclosed.
1. In a back-illuminated photodiode array, a device comprising:
a structure comprised of a semiconductor of a first conductivity type, having a first conductivity, and having first and second sides;
an array of photodiodes formed from the first side of the structure, each photodiode having a region of a second conductivity type with a concentration gradually decreasing towards the second side of the structure;
trenches in the semiconductor structure forming an interconnected matrix surrounding each photodiode, wherein the trenches extend from the second side of the structure;
the walls of the trenches doped with the first conductivity type to a second conductivity higher than the first conductivity;
the trenches being filled with electrical isolation material to provide electrical isolation between adjacent photodiodes; and
a region of the first conductivity type proximate to the second side of the structure, the region having a third conductivity higher than the first conductivity.
2. The device of claim 1 wherein the trenches also extend from the first side of the structure.
3. The device of claim 2 further comprising a matrix of regions of the same conductivity type as the walls of the trenches and having higher concentration than the first concentration and extending from the second side of the structure, the said matrix of regions of the same conductivity type as the walls of the trenches also surrounding each photodiode and aligned with the interconnected matrix of trenches surrounding each photodiode.
4. The device of claim 1 further comprising a matrix of regions of the same conductivity type as the walls of the trenches and having higher concentration than the first concentration extending from the first side of the structure, the said matrix of regions of the same conductivity type as the walls of the etched trenches also surrounding each photodiode and aligned with the interconnected matrix of etched trenches surrounding each photodiode.
5. The device of claim 1 wherein the trenches extend from the first and second sides of the structure.
6. The device of claim 5 wherein the photodiodes are formed by a diffusion of the second conductivity type from the first side of the structure.
7. The device of claim 6 wherein the diffusion of the second conductivity type is below the first side of the structure.
8. The device of claim 7 further comprising a region more conductive than the substrate extending from the diffusion of the second conductivity type to the first side of the structure.
9. The device of claim 1 further comprising a blanket diffusion of the first conductivity type with a concentration heavier than the first concentration in the second side of the substrate.
10. The device of claim 9 further comprising an antireflective coating on the blanket diffusion of the first conductivity type.
11. The device of claim 1 wherein the structure has a thickness of approximately 300 um or less.
12. The device of claim 1 wherein the second conductivity and the third conductivity are equal.