Image sensor with improved color crosstalk
An image sensor comprises a substrate of a first conductivity type. First and second pixels are arrayed over the substrate. A potential barrier is formed in a region of the substrate corresponding to the first pixel but not in a region of the substrate corresponding to the second pixel. The second pixel is responsive to a color having a wavelength longer than the color to which the first pixel is responsive. The potential barrier is doped with dopants by a high energy ion implantation dopants or by an ion implantation or diffusion during epitaxial growth of the P-type epitaxial layer.
1. A method of forming an image sensor, the method comprising:
forming an epitaxial layer without a potential barrier and including a first region corresponding to a first photodiode, a second region corresponding to a second photodiode, and a thickness between a top surface of the epitaxial layer and an interface of the epitaxial layer with a substrate;
implanting ions within the epitaxial layer without the potential barrier to form a potential barrier in the first region but not in the second region;
wherein the potential barrier is separated from the top surface by an upper portion of the first region; and
wherein the potential barrier is separated from the interface by a lower portion of the first region.
2. The method of claim 1 , further comprising:
forming a first filter above the first region, wherein the first filter is configured to pass light of a first color into the first region; and
forming a second filter above the second region, wherein the second filter is configured to pass light of a second color into the second region.
3. The method of claim 2 , wherein the first color comprises at least one of blue or green, and wherein the second color comprises red.
4. The method of claim 2 , wherein the upper portion of the first region is arranged as an area where a majority of photons of the first color are converted to electrons.
5. The method of claim 1 , wherein the potential barrier is formed to prevent electrons formed in the lower portion of the first region from flowing into the upper portion of the first region.
6. The method of claim 1 , wherein the potential barrier is formed to sweep electrons formed in the lower portion of the first region into the second region.
7. The method of claim 1 , wherein the potential barrier comprises a P-type doped region.
8. A method of forming an image sensor, the method comprising:
forming an epitaxial layer without a potential barrier including a first region corresponding to a first photodiode, a second region corresponding to a second photodiode, a third region corresponding to a third photodiode, and a thickness between a top surface of the epitaxial layer and an interface of the epitaxial layer with a substrate;
implanting ions within the epitaxial layer without the potential barrier to form a potential barrier in the first region and the third region, but not in the second region;
wherein the potential barrier is separated from the top surface by an upper portion of the first region and an upper portion of the third region; and
wherein the potential barrier is separated from the interface by a lower portion of the first region and a lower portion of the third region.
9. The method of claim 8 , further comprising:
forming a first filter above the first region, wherein the first filter is configured to pass light of a first color into the first region;
forming a second filter above the second region, wherein the second filter is configured to pass light of a second color into the second region; and
forming a third filter above the third region, wherein the third filter is configured to pass light of a third color into the third region.
10. The method of claim 9 , wherein:
the first color comprises blue;
the second color comprises red; and
the third color comprises green.
11. The method of claim 9 , wherein:
the upper portion of the first region is arranged as an area where a majority of photons of the first color are converted to electrons; and
the upper portion of the third region is arranged as an area where a majority of photons of the third color are converted to electrons.
12. The method of claim 8 , wherein the potential barrier is formed to prevent electrons formed in the lower portion of the first region and the lower portion of the third region from flowing into the upper portion of the first region and the upper portion of the third region.
13. The method of claim 8 , wherein the potential barrier is formed to sweep electrons formed in the lower portion of the first region and the lower portion of the third region into the second region.
14. The method of claim 8 , wherein a thickness of the upper portion of the first region is different than a thickness of the upper portion of the third region.