Structures and methods to improve the crosstalk between adjacent pixels of back-illuminated photodiode arrays
Structures and methods to improve the crosstalk between adjacent pixels of back-illuminated photodiode arrays on a substrate having first and second surfaces, including providing a first matrix of regions of a first conductivity type of a higher conductivity than the substrate extending into the substrate from the first surface and surrounding each photodiode of the array, and providing a second matrix of regions of a first conductivity type of a higher conductivity than the substrate extending into the substrate from the second surface, the second matrix being a mirror image of and aligned with the first matrix, the matrices extending into the substrate less than one half the thickness of the substrate so as to not touch each other. The methods and corresponding structures may be applied to p/n diodes, pin diodes, avalanche photodiodes, photoconductive cells (no p-n junction at all), or similar photosensitive device arrays.
1. A method of fabrication of a photodiode array on a silicon substrate having first and second surfaces comprising:
providing a first matrix of regions of a first conductivity type of a higher conductivity than the substrate extending into the substrate from the first surface and surrounding each photodiode of the array;
providing a plurality of regions of a second conductivity type interspersed within the first matrix of regions of the first conductivity type;
providing a second matrix of regions of a first conductivity type of a higher conductivity than the substrate extending into the substrate from the second surface, the second matrix being aligned with the first matrix, the first and second matrices extending into the substrate but not touching each other; and,
providing a plurality of contacts on the first surface for making electrical contact to the first matrix of regions of the first conductivity type and the plurality of regions of the second conductivity type.
2. The method of claim 1 wherein the substrate provided is an n-type silicon substrate having a resistivity of approximately 500 ohm-cm.
3. The method of claim 1 wherein the substrate has a thickness of less than approximately 200 μm.
4. The method of claim 1 wherein the substrate has a thickness of less than approximately 120 μm.
5. A back illuminated photodiode array comprising:
a substrate of a first conductivity type having first and second surfaces;
a first matrix of regions of a first conductivity type of a higher conductivity than the substrate extending into the substrate from the first surface of the substrate;
a plurality of regions of a second conductivity type interspersed within the matrix of regions of the first conductivity type, extending into the substrate from the first surface, each region of the second conductivity type being within a respective region defined by the first matrix of regions of a first conductivity type;
a second matrix of regions of the first conductivity type of a higher conductivity than the substrate extending into the substrate from the second surface of the substrate and aligned with the first matrix, the first and second matrices not extending into the substrate to touch each other;
the second surface of the substrate having a layer of the first conductivity type having a greater conductivity than the substrate; and,
a plurality of contacts on the first surface for making electrical contact to the first matrix of regions of the first conductivity type and the plurality of regions of the second conductivity type;
there being no electrical contact to the second matrix of regions of a first conductivity type or to the layer of the first conductivity type having a greater conductivity than the substrate on the second surface of the substrate other than through the substrate itself.