Light Guide Array for An Image Sensor
An image sensor pixel that includes a photoelectric conversion unit ( 102 ) supported by a substrate ( 106 ) and an insulator ( 110 ) adjacent to the substrate. The pixel includes a cascaded light guide ( 116,130 ) that is located within an opening of the insulator and extends above the insulator such that a portion ( 130 ) of the cascaded light guide has an air interface ( 424 ). The air interface improves the internal reflection of the cascaded light guide. The cascaded light guide may include a self-aligned color filter ( 114 B, 114 G) having, air-gaps (. 422 ). between adjacent color filters. These characteristics of the light guide eliminate the need for a microlens. Additionally, an anti-reflection stack ( 230 ) is interposed between the substrate ( 106 ) and the light guide ( 116 ) to reduce backward reflection from the image sensor. Two pixels of having different color filters may have a difference in the thickness of an anti-reflection film within the anti-reflection stack.
1 . An image sensor pixel, comprising:
a substrate;
a photoelectric conversion unit supported by the substrate;
an protection film extending over and across the substrate; and,
a cascaded light guide wherein a first portion of said cascaded light guide is between the protection film and the substrate and a second portion extends above the protection film.
2 . The pixel of claim 1 , wherein each cascaded light guide includes a transparent portion and a color filter that is contiguous with said transparent portion and extends above said insulator.
3 . The pixel of claim 1 , wherein the second portion includes a color filter.
4 . The pixel of claim 3 , wherein the color filters from cascaded light guides of adjacent pixels are separated by a first air gap that has a width no more than 0.45 um.
5 . The pixel of claim 4 , wherein said first air gap has a depth at least 1.0 times a wavelength of light.
6 . The pixel of claim 5 , where said wavelength of light is 450 nm.
7 . The pixel of claim 3 , wherein the color filter self-aligns within the cascaded light guide.
8 . The pixel of claim 3 , wherein the top surface of the color filter is an air interface.
9 . (canceled)
10 . The pixel of claim 1 , wherein all optical interfaces along the vertical axis of the cascaded light guide and above the protection film are flat and parallel.
11 . (canceled)
12 . The pixel of claim 1 , wherein at least two cascaded light guides from two different pixels have different cross-sectional profiles.
13 . The pixel of claim 1 , wherein the vertical centerlines of the first and second portions are mutually offset.
14 . The pixel of claim 13 , wherein the cascaded light guide is configured so that light exits and re-enters said cascaded light guide.
15 . A method for fabricating an image sensor pixel, comprising:
forming a support film with an opening and over a substrate that supports a photoelectric conversion unit; and,
forming a color filter in the opening of the support film.
16 . The method of claim 15 , further comprising forming a protection film between the color filter and the substrate.
17 . The method of claim 15 , further comprising removing at least a portion of the support film between two adjacent color filters.
18 . The method of claim 15 , further comprising forming a transparent light guide in the opening of the support film.
19 . The method of claim 18 , further comprising removing a portion of the support film adjacent the transparent light guide.
20 . The method of claim 18 , further comprising forming a lower transparent light guide between the transparent light guide and the substrate.
21 . The method of claim 20 , where the vertical centerline of the lower transparent light guide is offset from the vertical centerline of the opening of the support film.
22 . The method of claim 18 , wherein the forming of the color filter creates a flat air interface on a top surface of the color filter.
23 . A method for fabricating an image sensor pixel array, comprising:
forming an insulator over a substrate that supports a photoelectric conversion unit;
forming a plurality of walls adjacent to the insulator;
forming a plurality of light guides between the walls;
forming a plurality of color filters adjacent to the light guides; and,
removing at least a portion of the walls so that there is an air gap between adjacent color filters.
24 . The method of claim 23 , wherein the walls are formed by forming a support film and creating openings within the support film.
25 . The method of claim 23 , further comprising forming a protection film over the insulator.
26 . The method of claim 23 , wherein a portion of the support film is removed so that a portion of each light guide has an air interface.
27 . An image sensor pixel, comprising:
a substrate;
a photoelectric conversion unit supported by said substrate;
a light guide coupled to said photoelectric conversion unit;
anti-reflection means for reducing reflection between said light guide and said photoelectric conversion unit.
28 . The pixel of claim 27 , wherein said anti-reflection means includes a first anti-reflection film and a second anti-reflection film, said first anti-reflection film having an index of refraction lower than an index of refraction of said second anti-reflection film and an index of refraction of said light guide, and said first anti-reflection film located between the second anti-reflection film and the light guide.
29 . The pixel of claim 28 , wherein said anti-reflection means includes a third anti-reflection film which has an index of refraction lower than an index of refraction of said second anti-reflection film and wherein said second anti-reflection film is between said first anti-reflection film and said third anti-reflection film.
30 . The pixel of claim 28 , wherein a first pixel has a thinner anti-reflection film than a corresponding anti-reflection film of a second pixel having a color filter of a different color.
31 . (canceled)
32 . (canceled)
33 . The pixel of claim 28 , wherein said second anti-reflection film is a contact etch stop.
34 . The pixel of claim 28 , wherein said second anti-reflection film includes silicon nitride.
35 . The pixel of claim 27 , further comprising a light-guide etch-stop layer between said light guide and said anti-reflection means.
36 . A method for fabricating an image sensor pixel, comprising:
forming an anti-reflection stack on a photoelectric conversion unit supported by a substrate; and,
forming a light guide adjacent to the photoelectric conversion unit.
37 . (canceled)
38 . (canceled)
39 . A method for forming a portion of an image sensor pixel, comprising:
forming a first anti-reflection film over a substrate that supports a photoelectric conversion unit;
forming an insulator over said first anti-reflection film;
etching an opening in the insulator with an etchant that etches the insulator faster than the first anti-reflection film;
forming a second anti-reflection film within the opening; and
forming light guide material within the opening.
40 . The method of claim 39 , further comprising etching a vertical sidewall portion of the second anti-reflection film.
41 . (canceled)
42 . A method for fabricating a color filter for an image sensor pixel, comprising:
forming at least one wall;
forming a color filter within the wall;
removing at least a portion of the wall.