Method of forming a photosensor comprising a plurality of trenches
View Patent ↗A method of forming a multiple-trench photosensor for use in a CMOS imager having an improved charge capacity. The multi-trench photosensor may be either a photogate or photodiode structure. The multi-trench photosensor provides the photosensitive element with an increased surface area compared to a flat photosensor occupying a comparable area on a substrate. The multi-trench photosensor also exhibits a higher charge capacity, improved dynamic range, and a better signal-to-noise ratio. Also disclosed are processes for forming the multi-trench photosensor.
1. A method of forming a photosensor, comprising the steps of:
providing a semiconductor substrate having a doped layer of a first conductivity type;
forming a doped region of a second conductivity type in the doped layer;
forming a plurality of trenches in said doped region so that the sides and bottom of each of said plurality of trenches are of the second conductivity type; and
forming an insulating layer on the sides and bottom of each of said plurality of trenches of the photosensor.
2. The method of claim 1 , wherein the photosensor is a photodiode sensor.
3. The method of claim 1 , further comprising forming a conductive layer on the sides and bottom of each of said plurality of trenches, and wherein the photosensor is a photogate sensor.
4. The method of claim 1 , wherein the first conductivity type is p-type, and the second conductivity type is n-type.
5. The method of claim 1 , wherein the step of forming a plurality of trenches comprises a reactive ion etching process.
6. The method of claim 1 , wherein the of forming a doped region comprises ion implantation.
7. A method of forming a photosensor comprising:
forming a doped layer in a semiconductor substrate;
forming a plurality of trenches in said doped layer to define a photosensistive area of the photosensor, wherein each of said plurality of trenches further comprises a plurality of sidewalls and a bottom;
forming a doped region on the sidewalls and bottom of each of said plurality of trenches, wherein said doped region is opposite in conductivity type from said doped layer; and
forming an insulating layer on the sidewalls and bottom of each of said plurality of trenches.
8. The method of claim 7 , further comprising forming a conductive layer over said insulating layer.
9. The method of claim 7 , wherein said photosensor is a photodiode sensor.
10. The method of claim 7 , wherein said photosensor is a photogate sensor.
11. A method of forming a single photosensor comprising:
providing a semiconductor substrate;
forming a doped region in said semiconductor substrate;
forming a photosensitive area comprising at least two trenches in said doped region, wherein each of said at least two trenches further comprises sidewalls and a bottom;
forming a dielectric layer over said sidewalls and bottom of each of said at least two trenches of the single photosensor.
12. The method of claim 11 , further comprising forming a conductive layer over said dielectric layer.
13. The method of claim 11 , wherein said single photosensor is a photodiode sensor.
14. The method of claim 11 , wherein said single photosensor is a photogate sensor.