JP2005026567A - Solid state imaging device and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small solid-state imaging device having a low loss and a high condensing efficiency. <P>SOLUTION: The imaging device comprises solid-state imaging elements 11a, 11b, and 11c wherein a photonic crystal having a periodic refractive-index structure having low refractive-index materials 1 and high refractive-index materials 2 alternately laminated and having a periodic refractive-index structure of a similar shape (circle or polygon) concentric to an in-plane direction is located on photoelectric conversion elements. Only by the photonic crystal, the color separation and condensation of RGB can be simultaneously realized. Further the photonic crystal can be manufactured by a method for providing cavities of similar shapes concentric to the in-plane direction by lithography and etching in multiple layer films having a periodic refractive-index structure in a lamination direction or by a method for providing a periodic refractive-index structure of the in-plane and lamination directions by self cloning on a base of a similar shape concentric to the in-plane direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state imaging device having a large number of photoelectric conversion elements formed on a semiconductor substrate and optical elements formed on the photoelectric conversion elements, and more particularly to a solid-state imaging device using a photonic crystal as an optical element. .
[0002]
[Prior art]
Conventionally, various technologies have been proposed as solid-state imaging devices. For example, in the solid-state imaging device 30 shown in FIG. 9, in order to collect incident light to the photoelectric conversion element 27, a microlens 21 is formed on the upper part of the device, and an in-layer lens 24 is formed inside the device, thereby increasing the light collection efficiency. Yes. In addition, a color filter 22 is provided for each pixel in order to detect each RGB light signal.
[0003]
Furthermore, various techniques have been proposed (for example, Patent Documents 1 and 2). In the solid-state imaging device disclosed in Patent Document 1, a photonic crystal in which substances having different refractive indexes are periodically stacked is provided in a region surrounding a window on a photoelectric conversion element, so that light in a predetermined wavelength region can be obtained. It has a structure that does not allow intrusion. Therefore, it is possible to prevent light from entering the peripheral region of the photoelectric conversion element without using a light shielding film of metal or the like.
[0004]
In the solid-state imaging device disclosed in Patent Document 2, a reflective film having a taper shape and light reflectivity is formed on a photoelectric conversion element. Further, a transmissive film whose refractive index increases from the periphery to the center is formed on the photoelectric conversion element in the portion surrounded by the reflective film. As a result, the light incident on the solid-state imaging device is efficiently condensed in the direction of the photoelectric conversion element, and the sensitivity is improved.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2003-133536 [0006]
[Patent Document 2]
Japanese Patent Laid-Open No. 2001-44401
[Problems to be solved by the invention]
However, since all of the conventional solid-state imaging devices as described above perform light collection and color separation by a plurality of elements, there is a limit in light collection efficiency due to reflection loss and coupling loss between each element, and the number of pixels There is a problem that it is difficult to reduce the size of pixels for improvement.
[0008]
In addition, since a color filter has to be installed separately, the resin and pigment constituting the color filter approach the same size as the pixel, so that there is a problem that color separation becomes difficult as the pixel becomes smaller.
[0009]
Furthermore, the light is incident on the pixels in the center of the device perpendicularly and obliquely on the peripheral pixels, but since the microlens is formed by reflow, it is difficult to control the shape between the device center and the periphery. There is a problem that the light collection efficiency of pixels around the apparatus is lower than that at the center.
[0010]
Furthermore, the solid-state imaging device disclosed in Patent Document 1 has a limitation in light collection efficiency because of a method of focusing with a mirror.
[0011]
Accordingly, the present invention has been made to solve such problems, and an object thereof is to provide a small solid-state imaging device with low loss and high light collection efficiency.
[0012]
[Means for Solving the Problems]
In order to solve the above-described problems, a solid-state imaging device according to the present invention is a solid-state imaging device having a large number of photoelectric conversion elements formed on a semiconductor substrate and optical elements formed on the photoelectric conversion elements. The optical element is formed of a photonic crystal having a refractive index periodic structure in a stacking direction and a concentric similar refractive index periodic structure in an in-plane direction.
[0013]
In the method for manufacturing a photonic crystal of a solid-state imaging device according to the present invention, concentric cavities in the in-plane direction are formed by lithography and etching on a multilayer film having a refractive index periodic structure in the stacking direction. A method of manufacturing a cylindrical photonic crystal provided, and a photonic in which a refractive index periodic structure in the in-plane direction and the stacking direction is provided by self-cloning on a base having a concentric similar shape in the in-plane direction There are two types of methods for producing crystals.
[0014]
As a result, the solid-state imaging device according to the present invention realizes color separation and light collection simultaneously with a single element, eliminating reflection loss and coupling loss due to the configuration of multiple elements. A small solid-state imaging device with high light efficiency can be realized.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a solid-state imaging device according to an embodiment of the present invention will be described with reference to the drawings.
[0016]
(Embodiment 1)
FIG. 1 is an external view of solid-state imaging devices 11a, 11b, and 11c according to Embodiment 1 of the present invention. For example, in the solid-state imaging device 11c, a photoelectric conversion element 4c that converts incident light into signal charges is provided on the surface of the semiconductor substrate 5, and a light shielding unit that blocks light from the side surface around the upper window. 3 is provided, and a planarizing layer 7 is provided thereon. Further, a photonic crystal to be described later is provided as an optical element so that the center of the concentric shape coincides with the center of the photoelectric conversion element 4c. Yes.
[0017]
The photonic crystal is for simultaneously performing color separation and light collection of light. A refractive index periodic structure similar to the multilayer filter is formed in the stacking direction. That is, the structure is 11 layers as a whole, and the low refractive index material 1 is arranged in the odd layer including the uppermost layer, and the high refractive index material 2 is arranged in the even layer including the second layer from the top. Note that the sixth layer of the high refractive index material 2 from the top is a stacking fault resonator.
[0018]
As the material of the photonic crystal, for example, SiO ₂ and Al ₂ O ₃ can be used as the low refractive index material 1, and TiO ₂ and Ta ₂ O ₅ can be used as the high refractive index material 2. In order to avoid loss due to absorption, any material that is transparent in the visible range may be used. When SiO ₂ and Ta ₂ O ₅ are used, the thickness of SiO ₂ is 217 nm, and the thickness of Ta ₂ O ₅ is 141 nm (however, the stacking fault resonator is 282 nm).
[0019]
On the other hand, in the in-plane direction of the photonic crystal, three concentric cavities are provided per element. That is, the central opening of the uppermost layer and the two donut-shaped openings vertically penetrate to the lowermost layer of the photonic crystal. Both the central opening diameter and the donut-shaped opening width are 180 nm, 210 nm, and 250 nm in the photonic crystals of the solid-state imaging devices 11a, 11b, and 11c, respectively (the pitches of the donut-shaped openings are all 600 nm).
[0020]
The transmission wavelength is determined by the respective film thicknesses and refractive indexes of the low refractive index material 1 and the high refractive index material 2 in the stacking direction of the photonic crystal, but the effective refractive index changes as the concentric circle period changes as described above. The transmission wavelength changes, and RGB color separation of light of R, G, and B becomes possible by the photonic crystals of the solid-state imaging devices 11a, 11b, and 11c, respectively (wavelength filter function). Further, a condensing function is generated by the similar refractive index periodic structure in the in-plane direction of the photonic crystal.
[0021]
FIG. 2 is a cross-sectional view in the stacking direction of the solid-state imaging device 11a according to Embodiment 1 of the present invention. Incident light is transmitted and collected only in a specific wavelength region (red) by the photonic crystal 10a having a refractive index periodic structure in the stacking direction and a similar refractive index periodic structure in the in-plane direction, It reaches the conversion element 4a.
[0022]
FIG. 3 is a diagram illustrating a modification of the solid-state imaging device according to Embodiment 1 of the present invention. In FIG. 1, the similar shape in the in-plane direction is a circle, but the solid-state imaging device 11 d illustrated in FIG. 3A is a regular hexagon, and the solid-state imaging device 11 e illustrated in FIG. is there.
[0023]
FIG. 4 is a diagram illustrating a planar arrangement example of the solid-state imaging device 11f according to Embodiment 1 of the present invention. Three types of regular hexagonal solid-state imaging devices with a refractive index periodic structure set in the in-plane direction so that only each light component of RGB is transmitted are optimal in a plane so that the same types are not adjacent to each other without gaps. It is arranged. When the solid-state imaging devices are arranged in a honeycomb shape as described above, a region that cannot be condensed by an optical element made of a photonic crystal, such as a corner of each solid-state imaging device, is reduced as compared with a case where the solid-state imaging devices are arranged in a square lattice shape. Therefore, the light collection efficiency is improved. Furthermore, when the solid-state imaging devices are arranged in a honeycomb shape and the concentric similar shape in the in-plane direction of the optical element made of a photonic crystal is a hexagon, almost no light condensing region is generated. Therefore, the light collection efficiency is further improved.
[0024]
FIG. 5 is a flowchart showing a photonic crystal manufacturing method of the solid-state imaging devices 11a, 11b, and 11c according to Embodiment 1 of the present invention. First, a multilayered film is formed by sputtering or the like to provide a refractive index periodic structure in the stacking direction (S1). Next, concentric similar shapes in the in-plane direction are formed by lithography and dry etching such as electron beam exposure. A step of providing a cavity is performed (S2), and finally a cylindrical shape having a refractive index periodic structure in the stacking direction as shown in FIG. 1 and a refractive index periodic structure having a concentric similar shape in the in-plane direction. Of photonic crystals.
[0025]
As described above, since the solid-state imaging device according to the present embodiment performs condensing and color separation using only an optical element formed of a photonic crystal, it is composed of a plurality of elements, which is a conventional problem. Since there is no reflection loss or coupling loss due to this, and no color filter is required, a small solid-state imaging device with extremely low loss and high light collection efficiency can be realized.
[0026]
In the present embodiment, the concentric similar shape in the in-plane direction is a circle, a regular hexagon, or a square, but may be implemented by other polygons.
[0027]
(Embodiment 2)
Next, a solid-state imaging device according to Embodiment 2 of the present invention will be described. The difference from the first embodiment is the structure and manufacturing method of the photonic crystal.
[0028]
FIG. 6 is an external view of the solid-state imaging devices 12a, 12b, and 12c according to Embodiment 2 of the present invention. For example, in the solid-state imaging device 12c, a photoelectric conversion element 6c that converts incident light into signal charges is provided on the surface of the semiconductor substrate 5a, and a light shielding unit that blocks light from the side surface around the upper window. 3a is provided, and further, a photonic crystal, which will be described later, is provided as an optical element so that the center of the concentric shape coincides with the center of the photoelectric conversion element 6c.
[0029]
In the photonic crystal, the same refractive index periodic structure as that of the multilayer filter is formed in the stacking direction. As in the first embodiment, the structure is 11 layers as a whole, and the low refractive index material 1a is formed on the odd layers including the uppermost layer, and the high refractive index material 2a is formed on the even layers including the second layer from the top. Are arranged respectively. The sixth layer of the high refractive index material 2a from the top is a stacking fault resonator. The material examples of the low refractive index material 1a and the high refractive index material 2a are the same as those in the first embodiment. For example, when SiO ₂ and Ta ₂ O ₅ are used, the thickness of SiO ₂ is 92 nm (however, the lowest layer is 200 nm), and the thickness of Ta ₂ O ₅ is 60 nm (however, the stacking fault resonator is 120 nm).
[0030]
On the other hand, in the in-plane direction of the photonic crystal, from the top layer to the tenth layer, the projections having a triangular shape in cross section form three concentric circles, thereby taking a refractive index periodic structure. The structure of the eleventh layer, that is, the lowermost layer will be described later.
[0031]
FIG. 7 is an external view of a base for manufacturing a photonic crystal of a solid-state imaging device according to Embodiment 2 of the present invention. The bases 13a, 13b, and 13c serve as bases for manufacturing the photonic crystals of the solid-state imaging devices 12a, 12b, and 12c shown in FIG. 6 by self-cloning, respectively. That is, it is the lowest layer of the photonic crystal of the solid-state imaging devices 12a, 12b and 12c shown in FIG. Three concentric projections having a rectangular cross-sectional shape and a height of 100 nm are provided on top of SiO _{2 having} a thickness of 200 nm. The width of the protrusion and the pitch of adjacent concentric circles are 80 nm and 160 nm, 100 nm and 200 nm, and 120 nm and 240 nm, respectively, in the bases 13a, 13b, and 13c. The diameter of the central part is the same as the pitch of the concentric circles.
[0032]
The transmission wavelength is determined by the respective film thicknesses and refractive indexes of the low refractive index material 1 and the high refractive index material 2 in the stacking direction of the photonic crystal, but the effective refractive index changes as the concentric circle period changes as described above. The transmission wavelength changes, and the RGB color separation of B, G, and R light becomes possible by the photonic crystals of the solid-state imaging devices 12a, 12b, and 12c in FIG. 6 (wavelength filter function). Further, a condensing function is generated by the similar refractive index periodic structure in the in-plane direction of the photonic crystal.
[0033]
FIG. 8 is a flowchart showing a photonic crystal manufacturing method of the solid-state imaging device according to Embodiment 2 of the present invention. First, a base manufacturing process in which concentric similar shapes in the in-plane direction as shown in FIG. 7 are formed is performed (S11), and then a high refractive index material and a low refractive index material are alternately laminated by self-cloning. Then, a step of providing a refractive index periodic structure in the in-plane direction and the stacking direction is performed (S12). Finally, the refractive index periodic structure in the stacking direction as shown in FIG. The photonic crystals of the solid-state imaging devices 12a, 12b and 12c having a similar refractive index periodic structure are manufactured.
[0034]
As described above, since the solid-state imaging device according to the second embodiment performs color separation and condensing using an optical element formed only by a photonic crystal manufactured by self-cloning, a color filter becomes unnecessary, Since there is no reflection loss or coupling loss due to the configuration of a plurality of elements, a small solid-state imaging device with extremely low loss and high light collection efficiency can be realized. Therefore, the size in the in-plane direction of one solid-state imaging device can be made smaller than before.
[0035]
In the present embodiment, the concentric similar shape in the in-plane direction is a circle, but may be a polygon such as a regular hexagon or a square.
[0036]
As described above, the solid-state imaging device according to the present invention has been described based on the embodiments. However, the present invention is not limited to these embodiments. For example, in the first and second embodiments of the present invention, the photonic crystal has a laminated structure of 11 layers, but may have a laminated structure of more layers. Further, the concentric periodic structure in the in-plane direction is regular with three periods, but may be four periods or more, or may be irregular. Moreover, the manufacturing method of a photonic crystal is not limited to multilayer film formation technology, lithography, etching, and self-cloning, and may be manufactured by other methods.
[0037]
【The invention's effect】
As is apparent from the above description, the solid-state imaging device according to the present invention can simultaneously realize color separation and a light collecting function with only one photonic crystal. Therefore, a color filter is not required, and reflection loss and coupling loss due to the configuration of a plurality of elements are eliminated, so that a reduction in loss can be realized. Therefore, the size in the in-plane direction of one solid-state imaging device can be made smaller than before. Furthermore, because photonic crystals are manufactured using precise multilayer film formation technology and lithography and etching, or self-cloning of semiconductor processes, the optimal period and structure can be easily formed with good controllability according to the position of RGB and equipment. it can. Therefore, it is possible to improve the decrease in the light collection efficiency of the pixels around the device, which is a conventional problem.
[0038]
As described above, the solid-state imaging device according to the present invention can realize a small-sized solid-state imaging device with low loss and high light collection efficiency, and its practical value is extremely high.
[Brief description of the drawings]
FIG. 1 is an external view of a solid-state imaging apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a cross-sectional view of the solid-state imaging device according to Embodiment 1 of the present invention.
FIG. 3 is a diagram showing a modification of the solid-state imaging device according to Embodiment 1 of the present invention.
FIG. 4 is a diagram illustrating a planar arrangement example of the solid-state imaging device according to Embodiment 1 of the present invention.
FIG. 5 is a flowchart showing a method for manufacturing a photonic crystal of the solid-state imaging device according to Embodiment 1 of the present invention.
FIG. 6 is an external view of a solid-state imaging device according to Embodiment 2 of the present invention.
FIG. 7 is an external view of a base of a photonic crystal of a solid-state imaging device according to Embodiment 2 of the present invention.
FIG. 8 is a flowchart showing a method for manufacturing a photonic crystal of a solid-state imaging device according to Embodiment 2 of the present invention.
FIGS. 9A and 9B are a cross-sectional view and a top view of a solid-state imaging device according to the related art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 1a Low refractive index material 2, 2a High refractive index material 3, 3a Light-shielding part 4a, 4c Photoelectric conversion element 5, 5a Semiconductor substrate 6c Photoelectric conversion element 7 Planarization layer 10a Photonic crystal 11a, 11b, 11c, 11d, 11e, 11f Solid-state imaging devices 12a, 12b, 12c Solid-state imaging devices 13a, 13b, 13c Base 21 Micro lens 22 Color filter 23 Flattening layer 24 In-layer lens 25 Flattening layer 26 Light-shielding portion 27 Photoelectric conversion element 28 Semiconductor substrate 30 Solid Imaging device

Claims (7)

A solid-state imaging device having a plurality of photoelectric conversion elements formed on a semiconductor substrate and an optical element formed on the photoelectric conversion elements,
The optical element is formed of a photonic crystal having a refractive index periodic structure in a stacking direction and a concentric similar refractive index periodic structure in an in-plane direction. The solid-state imaging device according to claim 1, wherein the photonic crystal has a cylindrical shape. The solid-state imaging device according to claim 1, wherein the photonic crystal is a self-cloning type. 4. The solid-state imaging device according to claim 1, wherein the concentric similar shape in the in-plane direction of the photonic crystal is one of a circle and a polygon. The solid-state imaging device according to claim 1, wherein the array is in a honeycomb shape. A method of manufacturing a solid-state imaging device,
A solid-state imaging device comprising a step of manufacturing a photonic crystal by providing a concentric, similar cavity in the in-plane direction by lithography and etching for a multilayer film having a refractive index periodic structure in a stacking direction Manufacturing method. A method of manufacturing a solid-state imaging device,
A solid-state imaging device comprising: a step of producing a photonic crystal by providing a refractive index periodic structure in an in-plane direction and a stacking direction by self-cloning on a base having a concentric similar shape in an in-plane direction Production method.

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