Light Guide Array for An Image Sensor

Abstract

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.