JP2008283070A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fill intervals of a plurality of electrodes, for reading charges generated at a photoelectric conversion section, with optical waveguide materials. <P>SOLUTION: An imaging device 1 comprises a photoelectric conversion section 11, multiple electrode layers for reading charges generated at the photoelectric conversion section 11; and optical waveguides 41', 41" formed of optical waveguide materials for guiding light to the photoelectric conversion section 11, on at least one of the electrode layers. At least one of the multiple electrode layers includes a plurality of electrodes 31a', 31b', and intervals of the plurality of electrodes 31a', 31b' are filled with the optical waveguide materials. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image sensor used for a digital still camera, a camcorder, and the like.

  In recent years, in addition to CCD-type image sensors, CMOS-type image sensors with low current consumption have been used as image sensors used for digital still cameras, camcorders, and the like. However, since the CMOS type image pickup device has a multilayer electrode layer, there is a drawback that light having a large incident angle cannot be efficiently guided to the photoelectric conversion unit.

Patent Document 1 discloses an imaging device in which an optical waveguide is provided between the light incident surface of the imaging device and the photoelectric conversion unit in order to improve the efficiency of capturing light with a large incident angle, thereby improving the light collection characteristics. Yes. This imaging element includes an optical waveguide made of silicon nitride (SiN), which is a high refractive index material, on the light incident side of the photoelectric conversion unit. The surrounding interlayer insulating film layer is made of silicon oxide (SiO ₂ ), which is a low refractive index material, so that incident light is totally reflected at the boundary surface, thereby improving the light collection characteristics.

  FIG. 3 is a partial cross-sectional view of a conventional CMOS image sensor having an optical waveguide. FIG. 3 exemplarily shows two pixels of the CMOS image sensor.

  In the imaging element 1, a photoelectric conversion unit 11 is formed inside a silicon substrate 10. On the silicon substrate 10, a first electrode disposed on a first electrode layer for transferring charges generated in the photoelectric conversion unit 11 to a floating diffusion unit (not shown) so as to partially overlap the photoelectric conversion unit 11. An electrode 12 is provided. A second electrode layer 30 is disposed on the first interlayer insulating film 21 made of silicon oxide, and a third electrode layer 31 is disposed on the second interlayer insulating film 22. . A third interlayer insulating film 23 is formed so as to cover the third electrode layer 31. The second electrode layer 30 and the third electrode layer 31 constitute an electrode for outputting the charge generated in the photoelectric conversion unit 11 to the outside of the image pickup device 1 as an image pickup signal. An optical waveguide 41 made of silicon nitride is formed in a region where the third electrode layer 31 and the second electrode layer 30 are opened. On the optical waveguide 41, a planarization layer 50, a color filter layer 51, a planarization layer 52, and a microlens 53 are formed of a resin material.

In the third electrode layer 31, two electrodes are formed per pixel. Assuming that the two electrodes 31a and 31b having the narrowest electrode interval a in the third electrode layer 31 are 31a and 31b, the interval a is substantially equal to the electrode width a so as not to block the light incident on the photoelectric conversion unit 11. It is configured to be the same. Since the distance a between the electrode 31a and the electrode 31b is narrow, the optical waveguide material (silicon nitride) cannot be filled between them. Therefore, the third electrode layer 31 is covered with the interlayer insulating film 23 made of silicon oxide. Then, after the third interlayer insulating film 23 is formed so as to cover the third electrode layer 31, the optical waveguide 41 is formed.
Japanese Patent Laying-Open No. 2006-040948 (5th page, FIG. 2)

  However, as the resolution of digital still cameras, camcorders, and the like increases and the pixel size of the CMOS image sensor decreases, the ratio of the height of the optical waveguide to the opening of the optical waveguide increases. As a result, there has been a problem that the optical waveguide material cannot be sufficiently filled between a plurality of electrodes for transferring (reading out) charges generated in the photoelectric conversion unit to the floating diffusion unit.

  The present invention has been made in view of the above-described problems, and an object thereof is to fill an optical waveguide material between a plurality of electrodes for reading out charges generated in a photoelectric conversion unit.

  The present invention is formed of a photoelectric conversion unit, a multilayer electrode layer for reading out charges generated in the photoelectric conversion unit, an optical waveguide material for guiding light to the photoelectric conversion unit, and the at least one layer And an optical waveguide formed on the electrode layer, wherein at least one of the multilayer electrode layers includes a plurality of electrodes, and the light guide is provided between the plurality of electrodes. It is filled with waveguide material

  According to the present invention, the optical waveguide material can be filled between the plurality of electrodes for reading out the electric charges generated in the photoelectric conversion unit.

  Hereinafter, a CMOS image sensor (hereinafter referred to as “image sensor”) according to a preferred embodiment of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view of a part of an image sensor according to the first embodiment of the present invention. Components similar to those in FIG. 3 are denoted by the same reference numerals.

  FIG. 1 exemplarily shows two pixels of the image sensor 100, but the number of pixels of the present invention is not limited to this. The photoelectric conversion unit 11 of the image sensor 100 is wired with a plurality of electrodes formed on at least one electrode layer among the multilayer electrode layers. In the following description, one of the two electrodes formed on the third electrode layer 31 is wired to the first electrode 12, and the other electrode is wired to a floating diffusion portion (not shown). Illustratively.

  In the image sensor 100 according to the present embodiment, the optical waveguide 41 ′ is formed immediately after the third electrode layer 31 ′ is formed. Two electrodes are formed per pixel on the third electrode layer 31 '. When the two electrodes having the narrowest distance b between the electrodes in the third electrode layer 31 are 31 a ′ and 31 b ′, the distance b is configured to be wider than the electrode width a. With such a configuration, the optical waveguide material (silicon nitride) can be filled in the distance b between the electrode 31a 'and the electrode 31b'.

  A planarizing layer 50, a color filter layer 51, a planarizing layer 52, and a microlens 53 are formed of a resin material on the optical waveguide 41 '.

  The light incident on the image sensor 100 is condensed on the optical waveguide 41 ′ by the microlens 53. The optical waveguide 41 'is made of an optical waveguide material such as silicon nitride, and its refractive index is about 1.9. The periphery of the optical waveguide 41 ′ is surrounded by the first interlayer insulating film 21 and the second interlayer insulating film 22 having a refractive index of about 1.46. Therefore, the light that has reached the wall surface of the optical waveguide 41 ′ is totally reflected at the interface between the first interlayer insulating film 21 and the second interlayer insulating film 22 and guided to the photoelectric conversion unit 11.

  As a result, the image sensor 100 of the present invention can efficiently receive even light having a large incident angle.

  Hereinafter, a method for manufacturing the image sensor 100 of the present invention will be described.

  First, ions are implanted into the photoelectric conversion region of the silicon substrate 10 to form the photoelectric conversion unit 11. Next, the silicon substrate 10 is thermally oxidized to form an insulating film made of silicon oxide (not shown) on the surface of the silicon substrate 10. Polysilicon is deposited on the insulating film formed on the surface of the silicon substrate 10, and the first electrode 12 is fabricated by patterning the electrode pattern.

  When the first electrode 12 is formed, a silicon nitride film is formed thereon to form an etching stopper film (not shown). The etching stopper film has a function of stopping the etching of the interlayer insulating film 21 and the interlayer insulating film 22 when forming the optical waveguide.

  When the etching stopper film is formed, a first interlayer insulating film 21 for forming the second electrode layer 30 is formed and planarization is performed. The first interlayer insulating film 21 is made of silicon oxide having a refractive index of about 1.46. A second electrode layer 30 made of aluminum is formed on the planarized first interlayer insulating film 21.

  Next, a second interlayer insulating film 22 for forming a third electrode is formed, and planarization is performed. The second interlayer insulating film 22 is also formed of silicon oxide having a refractive index of about 1.46. On the planarized second interlayer insulating film 22, a third electrode 31 'made of aluminum is formed.

  In the imaging device 100 of the present invention, the optical waveguide 41 ′ is formed after the third electrode layer 31 ′ is formed.

  First, an opening for forming the optical waveguide 41 ′ is formed in the first interlayer insulating film 21 and the second interlayer insulating film 22. The opening for forming the optical waveguide 41 ′ is formed by dry etching the second interlayer insulating film 22 and the first interlayer insulating film 21. At this time, since an etching stopper film is formed between the first interlayer insulating film 21 and the photoelectric conversion unit 11, the opening for forming the optical waveguide 41 ′ is the photoelectric conversion unit of the silicon substrate 10. Does not reach 11.

  Furthermore, in order to form the optical waveguide 41 ′, silicon nitride is formed by a high density plasma CVD method. The refractive index of silicon nitride formed by the high-density plasma CVD method is about 1.9. Here, the depth of the opening for forming the optical waveguide 41 ′ corresponds to the thickness of the interlayer insulating films 21 and 22. For this reason, the ratio of the depth of the opening to the opening is small. As a result, the opening can be satisfactorily filled with silicon nitride, which is an optical waveguide material.

  The third electrode layer 31 ′ is also covered with silicon nitride by forming a silicon nitride film. Here, the electrode layer 31 'is configured such that the narrowest gap b between the electrodes is wider than the electrode width a. Therefore, the optical waveguide material (silicon nitride) is satisfactorily embedded even at the narrowest distance b between the electrodes. When the optical waveguide 41 ′ is formed, the planarization layer 50 for forming the color filter layer 51 is formed. Further, when the color filter layer 51 is formed, the microlens 53 is formed after the planarization layer 52 for forming the microlens 53 is formed. The microlens 53 is formed by a known registry flow method.

(Second Embodiment)
FIG. 2 is a partial cross-sectional view of a CMOS type image pickup device according to a preferred second embodiment of the present invention. Components similar to those in FIG. 3 are denoted by the same reference numerals. FIG. 2 exemplarily shows two pixels of the image sensor 200, but the number of pixels of the present invention is not limited to this. In addition, the image sensor according to the present embodiment can be manufactured by the same manufacturing method as the image sensor according to the first embodiment.

  In the imaging device 200 according to the present embodiment, the optical waveguide 41 ″ is formed after the third electrode layer 31 ″ is formed. In the third electrode layer 31 ″, two electrodes are formed per pixel. Two electrodes having the narrowest distance c between the electrodes in the third electrode layer 31 ″ are 31 a ″ and 31 b ″. In this case, the distance c should be larger than 2/3 times the height h of the electrodes 31a ″ and 31b ″ and not more than twice the height h of the electrodes 31a ″ and 31b ″. That's fine. That is, the interval c is configured to satisfy the relationship of Equation 1 so that the optical waveguide material (silicon nitride) can be filled.

2 / 3h <c ≦ 2h (Formula 1)
Here, h is With such a configuration, the optical waveguide material (silicon nitride) can be satisfactorily filled even with the narrowest distance c between the electrodes. In the present embodiment, the interval c between the electrodes is configured to be substantially equal to the height h of the electrodes. At this time, the distance c between the electrodes may be equal to the width of the electrodes.

  Further, a planarizing layer 50, a color filter layer 51, a planarizing layer 52, and a microlens 53 are formed of a resin material on the optical waveguide 41 ''.

  In the imaging device 200 according to the present embodiment, since the optical waveguide 41 ″ is formed on the photoelectric conversion unit 11 side from the upper surface of the second interlayer insulating film 22, the height of the optical waveguide portion is low. Therefore, even in an image sensor with a small pixel size, the ratio of the height of the optical waveguide 41 ″ to the opening of the opening of the optical waveguide 41 can be reduced, and the optical waveguide material can be satisfactorily filled.

  The light incident on the image sensor 200 is collected by the microlens 53 onto the optical waveguide 41 ″. The optical waveguide 41 ″ is made of an optical waveguide material such as silicon nitride and has a refractive index of about 1.9. The periphery of the optical waveguide 41 ″ is surrounded by the first interlayer insulating film 21 and the second interlayer insulating film 22 having a refractive index of about 1.46. Therefore, the light reaching the wall surface of the optical waveguide 41 ″ is totally reflected at the interface between the first interlayer insulating film 21 and the second interlayer insulating film 22 and is guided to the photoelectric conversion unit 11.

  As a result, the image sensor 200 of the present invention can efficiently receive even light having a large incident angle.

It is a partial sectional view of an image sensor concerning a 1st embodiment of the present invention. FIG. 5 is a partial cross-sectional view of an image sensor according to a second embodiment of the present invention. It is sectional drawing of a part of conventional image pick-up element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up element 11 Photoelectric conversion part 41 ', 41''Optical waveguide 31a', 31b 'Electrode

Claims (3)

A photoelectric conversion unit, a multilayer electrode layer for reading out charges generated in the photoelectric conversion unit, and an optical waveguide material for guiding light to the photoelectric conversion unit, and at least of the multilayer electrode layers An imaging device comprising an optical waveguide formed on one electrode layer,
The at least one electrode layer has a plurality of electrodes,
An imaging device, wherein the optical waveguide material is filled between the plurality of electrodes.   The imaging device according to claim 1, wherein the narrowest interval among the intervals between the plurality of electrodes is larger than a width of the plurality of electrodes.   The narrowest interval among the intervals between the plurality of electrodes is greater than 2/3 times the height of the plurality of electrodes and less than or equal to twice the height of the plurality of electrodes. The imaging device according to claim 1.

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