Method of forming a photosensor
View Patent ↗A trench photosensor for use in a CMOS imager having an improved charge capacity. The trench photosensor may be either a photogate or photodiode structure. The trench shape of the photosensor provides the photosensitive element with an increased surface area compared to a flat photosensor occupying a comparable area on a substrate. The 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 trench photosensor.
1. A method of forming a photosensor comprising:
excavating a trench within a semiconductor substrate of a first conductivity type, said trench having a substantially vertical internal surface region and bottom surface region;
performing a first ion implantation of a second conductivity type into said substantially vertical internal surface region and bottom surface region at a first ion implantation angle; and
performing a second ion implantation of said second conductivity type into said substantially vertical internal surface region and bottom surface region at a second ion implantation angle, wherein said first implantation angle is orthogonal to said second ion implantation angle.
2. A method of forming a photosensor as defined in claim 1 further comprising performing a plurality of ion implantations at a respective plurality of ion implantation angles.
3. A method of forming a photosensor as defined in claim 1 further comprising applying a passivation layer above said substantially vertical internal surface region.
4. A method of forming a photosensor as defined in claim 3 wherein said passivation layer comprises silicon dioxide.
5. A method of forming a photosensor as defined in claim 3 wherein said passivation layer comprises Borosilicate glass.
6. A method of forming a photosensor as defined in claim 3 wherein said passivation layer comprises phospho-silicate glass.
7. A method of forming a photosensor as defined in claim 3 wherein said passivation layer comprises boron-phospho-silicate glass.
8. A method of forming a photosensor as defined in claim 3 further comprising chemical mechanical planarizing said passivation layer.
9. A method of forming a photosensor as defined in claim 1 , wherein said step of excavating a trench further comprises anisotropically etching said semiconductor substrate.
10. A method of forming a photosensor as defined in claim 1 further comprising forming an insulating layer that covers the vertical internal surface region and bottom surface region of said trench.
11. A method of forming a photosensor as defined in claim 10 further comprising forming a conductive layer that covers a substantial portion of said insulating layer.
12. A method of forming a photosensor as defined in claim 1 , wherein the first conductivity type is p-type, and the second conductivity is n-type.