FUNNELED LIGHT PIPE FOR PIXEL SENSORS
A photo sensing structure and methods for forming the same. The structure includes (a) a semiconductor substrate and (b) a photo collection region on the semiconductor substrate. The structure also includes a funneled light pipe on top of the photo collection region. The funneled light pipe includes (i) a bottom cylindrical portion on top of the photo collection region of the photo collection region, and (ii) a funneled portion which has a tapered shape and is on top and in direct physical contact with the bottom cylindrical portion. The structure further includes a color filter region on top of the funneled light pipe.
1. Technical Field
The present invention relates to pixel sensors, and more specifically, to pixel sensors that have funneled light pipes.
2. Related Art
Some advanced pixel sensors implement vertical light pipes with micro-lenses, wherein the micro-lenses are used to focus light into the light pipes. Therefore, there is a need for a pixel sensor structure that does not have the micro-lenses of the prior art.
SUMMARY OF THE INVENTIONThe present invention provides a pixel sensor structure, comprising (a) a semiconductor substrate; (b) a photo collection region on the semiconductor substrate; and (c) a funneled light pipe on top of the photo collection region, wherein the funneled light pipe comprises (i) a bottom cylindrical portion on top of the photo collection region of the photo collection region, and (ii) a funneled portion which has a tapered shape and is on top and in direct physical contact with the bottom cylindrical portion.
The present invention also provides a semiconductor structure fabrication method, comprising providing a structure that includes (i) a semiconductor substrate, (ii) a photo collection region on the semiconductor substrate, and (iii) a BEOL (Back End Of Line) layer on the photo collection region and the semiconductor substrate; etching the BEOL layer so as to form a funneled cavity in the BEOL layer, wherein a cross-section of the funneled cavity has a tapered shape; after said etching the BEOL layer so as to form the funneled cavity in the BEOL layer, further etching the BEOL layer through the funneled cavity so as to form a cylindrical cavity in the BEOL layer, wherein the cylindrical cavity are directly above the photo collection region and directly beneath the funneled cavity; and forming a funneled light pipe in the cylindrical cavity and the funneled cavity.
The present invention also provides a photo sensing structure, comprising (a) a semiconductor substrate; (b) a photo collection region on the semiconductor substrate; (c) a BEOL (Back End Of Line) layer on the semiconductor substrate and the photo collection region; and (d) a funneled light pipe on top of the photo collection region and in the BEOL layer, wherein the funneled light pipe comprises (i) a bottom cylindrical portion on top of the photo collection region of the photo collection region, (ii) a funneled portion which has a tapered shape and is on top and in direct physical contact with the bottom cylindrical portion, and (iii) a light reflective layer on side walls of the bottom cylindrical portion and the funneled portion.
The present invention provides a pixel sensor structure that does not have the micro-lens of the prior art.
BRIEF DESCRIPTION OF THE DRAWINGS
With reference to
Next, in one embodiment, four photo collection region 112a, 112b, 112c, and 112d are formed on top of the semiconductor substrate 110 as shown in
Next, with reference to
Next, in one embodiment, a dielectric layer 122 is formed on top of the nitride layer 116. Illustratively, the dielectric layer 122 comprises an electrically insulating material such as USG (Undoped Silicate Glass).
Next, in one embodiment, metal lines 124 are formed in the dielectric layer 122. Illustratively, the metal lines 124 comprise copper, aluminum, or any other electrically conductive metal. In one embodiment, the metal lines 124 are formed by using a conventional method.
Next, in one embodiment, a nitride layer 126 is formed on top of the dielectric layer 122. Illustratively, the nitride layer 126 is formed by CVD of silicon nitride on top of the dielectric layer 122. The dielectric layer 122, the metal lines 124, and the nitride layer 126 are collectively referred to as an interconnect layer 120.
Next, with reference to
Next, with reference to
Next, with reference to
Next, with reference to
Next, in one embodiment, the patterned photo-resist layer 160 is removed by using a wet etching step, resulting in the structure 100 of
Next, with reference to
In one embodiment, the transparent material of the funneled light pipes 170a, 170b, 170c, and 170d has a refractive index: (a) which is higher than the refractive index of the material of the dielectric layers 122, 132, 142, and 152 surrounding the funneled light pipes 170a, 170b, 170c, and 170d, and (b) but which is lower than the refractive index of the material of the nitride layer 116 above the photo diodes 112a, 112b, 112c, and 112d. In one embodiment, the transparent material of the funneled light pipes 170a, 170b, 170c, and 170d can be BPSG (boro-phospho-silicate glass), or silicon nitride.
In an alternative embodiment, the side walls 165a, 165b, 165c, 165d, 169a, 169b, 169c, and 169d of the funneled pipes 164a,168a; 164b,168b; 164c,168c and 164d,168d are coated with a light reflective material (such as aluminum) so as to form a light reflective layer (not shown) before the funneled light pipes 170a, 170b, 170c, and 170d are formed as described above. More specifically, the aluminum layer is formed by depositing aluminum on top of the entire structure 100 of
In yet another alternative embodiment, the side walls 165a, 165b, 165c, 165d, 169a, 169b, 169c, and 169d of the funneled pipes 164a,168a; 164b,168b; 164c,168c and 164d,168d can be first coated with a nitride film (not shown) so as to form a “cladding” and then an oxide material or a clear polymer can be used to fill the funneled pipes 164a, 168a; 164b,168b; 164c,168c and 164d,168d as described above.
Next, with reference to
In one embodiment, the operation of the pixel sensor 100 of
wherein ndielectric material is refractive index of the material of the dielectric layers 122, 132, 142, and 152 and ntransparent material is refractive index of the transparent material of the funneled light pipe 170a. If the incident angle θ of the photon 184 is greater than the critical angle θ0, the photon 184 will bounce back (i.e., reflect) into the funneled light pipe 170a. Then, the photon 184 can travel down the funneled light pipe 170a and arrive at the photo diode 112a, or hit the side walls 165a and 169a one or more times at possibly different incident angles (not shown). If these incident angles are also greater than the critical angle θ0, the photon 184 will travel down the funneled light pipe 170a and arrive at the photo diode 112a. The greater ntransparent material is, the smaller the critical angle θ0 is, and therefore, the more green photons (like the photon 184) that arrive at the photo diode 112a. Blue photons of the light beam that pass through the blue CFA region 180b will travel down along the funneled light pipe 170b and reach the photo diodes 112b in a similar manner. Red photons of the light beam that pass through the red CFA region 180d will travel down along the funneled light pipe 170d and reach the photo diodes 112d in a similar manner. As a result, the greater ntransparent material is, the more photons of the light beam that arrive at the photo diodes 112a, 112b, 112c and 112d. It should be noted that the description above is for the case where there is no light reflective coating layer on side walls 165a, 165b, 165c, 165d, 169a, 169b, 169c, and 169d. If the side walls 165a, 165b, 169a, 169b, 169c, and 169d of the funneled pipes 164a,168a; 164b,168b; 164c,168c and 164d,168d are coated with the light reflective material (such as aluminum) and then filled with the transparent material as describe above with reference to
In one embodiment, the operation of the pixel sensor 200 is similar to the operation of the pixel sensor 100 of
In one embodiment, the operation of the pixel sensor 300 is similar to the operation of the pixel sensor 100 of
In one embodiment, the operation of the pixel sensor 400 of
In the embodiments described above, with reference to
In the embodiments described above, with reference to
In the embodiments described above, the side walls of the funnels 164a, 164b, 164c, and 164d (
While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.
Claims
1. A pixel sensor structure, comprising:
- (a) a semiconductor substrate;
- (b) a photo collection region on the semiconductor substrate; and
- (c) a funneled light pipe on top of the photo collection region, wherein the funneled light pipe comprises (i) a bottom cylindrical portion on top of the photo collection region of the photo collection region, and (ii) a funneled portion which has a tapered shape and is on top and in direct physical contact with the bottom cylindrical portion.
2. The structure of claim 1, further comprising a color filter region on top of the funneled light pipe.
3. The structure of claim 2, further comprising a micro-lens on top of the color filter region.
4. The structure of claim 1, further comprising a micro-lens on top of the funneled light pipe.
5. The structure of claim 1, wherein a first horizontal cross-section of the funneled portion is larger in area than a second horizontal cross-section of the bottom cylindrical portion.
6. The structure of claim 1, wherein a cross-section of the funneled portion has a concave shape.
7. The structure of claim 6, wherein the concave shape has a hyperbolic shape.
8. The structure of claim 6, wherein the concave shape has a parabolic shape.
9. The structure of claim 1, wherein a cross-section of the funneled portion has a convex shape.
10. The structure of claim 9, wherein the convex shape has a hyperbolic shape.
11. The structure of claim 9, wherein the convex shape has a parabolic shape.
12. The structure of claim 1, wherein a cross-section of the funneled portion has a shape of a straight line.
13. The structure of claim 1, further comprising a BEOL (Back End Of Line) layer on top of the photo collection region and the semiconductor substrate,
- wherein the funneled light pipe resides in the BEOL layer, and
- wherein the BEOL layer comprises M interconnect layers, M being a positive integer.
14. The structure of claim 13, wherein the funneled portion resides in only one interconnect layer of the M interconnect layers.
15. The structure of claim 13, wherein the funneled portion resides in K interconnect layers of the M interconnect layers, wherein K is an integer, and wherein 1<K<M.
16. The structure of claim 13, wherein the funneled light pipe comprises a transparent material whose refractive index is higher than a refractive index of a material of the BEOL layer.
17. The structure of claim 1, further comprising a light reflective layer on side walls of the funneled light pipe.
18. A semiconductor structure fabrication method, comprising:
- providing a structure that includes (i) a semiconductor substrate, (ii) a photo collection region on the semiconductor substrate, and (iii) a BEOL (Back End Of Line) layer on the photo collection region and the semiconductor substrate;
- etching the BEOL layer so as to form a funneled cavity in the BEOL layer, wherein a cross-section of the funneled cavity has a tapered shape;
- after said etching the BEOL layer so as to form the funneled cavity in the BEOL layer, further etching the BEOL layer through the funneled cavity so as to form a cylindrical cavity in the BEOL layer, wherein the cylindrical cavity are directly above the photo collection region and directly beneath the funneled cavity; and
- forming a funneled light pipe in the cylindrical cavity and the funneled cavity.
19. The method of claim 18, further comprising forming a color filter region on top of the funneled light pipe.
20. The method of claim 19, further comprising the step of forming a micro-lens on top of the color filter region.
21. The method of claim 18, further comprising the step of forming a micro-lens on top of the funneled light pipe region.
22. The method of claim 18, wherein said etching the BEOL layer so as to form the funneled cavity in the BEOL layer is isotropic etching.
23. The method of claim 22, wherein said further etching the BEOL layer through the funneled cavity so as to form the cylindrical cavity in the BEOL layer is anisotropic etching.
24. The method of claim 18, wherein said forming the funneled light pipe in the cylindrical cavity and the funneled cavity comprises filling the funneled cavity and the cylindrical cavity with a transparent material whose refractive index is higher than a refractive index of a material of the BEOL layer.
25. The method of claim 18, wherein said forming the funneled light pipe in the cylindrical cavity and the funneled cavity comprises:
- forming a light reflective layer on side walls of the cylindrical cavity and the funneled cavity; and
- after said forming the light reflective layer is performed, filling the funneled cavity and the cylindrical cavity with a transparent material.
26. A pixel sensing structure, comprising:
- (a) a semiconductor substrate;
- (b) a photo collection region on the semiconductor substrate;
- (c) a BEOL (Back End Of Line) layer on the semiconductor substrate and the photo collection region; and
- (d) a funneled light pipe on top of the photo collection region and in the BEOL layer, wherein the funneled light pipe comprises (i) a bottom cylindrical portion on top of the photo collection region of the photo collection region, (ii) a funneled portion which has a tapered shape and is on top and in direct physical contact with the bottom cylindrical portion, and (iii) a light reflective layer on side walls of the bottom cylindrical portion and the funneled portion.
27. The structure of claim 26, further comprising a color filter region on top of the funneled light pipe.
28. The structure of claim 27, further comprising a micro-lens on top of the color filter region.
29. The structure of claim 26, further comprising a micro-lens on top of the funneled light pipe.
30. The structure of claim 26, wherein a first horizontal cross-section of the funneled portion is larger in area than a second horizontal cross-section of the bottom cylindrical portion.
Type: Application
Filed: Dec 16, 2005
Publication Date: Jun 21, 2007
Patent Grant number: 7524694
Inventors: James Adkisson (Jericho, VT), Jeffrey Gambino (Westford, VT), Robert Leidy (Burlington, VT), Richard Rassel (Colchester, VT)
Application Number: 11/275,171
International Classification: G01J 1/04 (20060101);