JP2005210013A - Solid-state image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging device which has high light-utilization efficiency and can be miniaturized and thin-shaped. <P>SOLUTION: The solid-state imaging device comprises a plurality of light receiving parts and a planar light-condensing lens arranged via at least a planarization layer and a color-filter layer on a light receiving plane which is constituted by arranging the light receiving parts. The light-condensing lens is constituted by arranging a plurality of microlenses at positions so as to correspond to the respective light receiving parts. Each microlens has a refractive index distribution in which a refractive index increases from the peripheral edge to the center. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device such as a CCD or CMOS, and more particularly to a thin solid-state imaging device with high light utilization efficiency.

In order to improve the light collection efficiency of each pixel, a solid-state imaging device such as a CCD or CMOS generally has a plurality of fine light receiving portions (pixels) arranged thereon, and a flattening layer and a color filter layer are provided thereon. In addition, a condensing lens in which a plurality of fine convex lenses are arranged is provided.
The condensing lens, for example, forms a photosensitive thermoplastic resin layer on the arranged light receiving portions, and this thermoplastic resin layer is exposed and developed using a photomask having a predetermined lens pattern, It is manufactured by forming a planar pattern of a thermoplastic resin at a position corresponding to each light receiving portion, and then heat-treating the thermoplastic resin to cause it to flow into a convex lens shape using surface tension. (Patent Document 1)

In addition, a photosensitive resist film is formed on a flat lens resin layer, and the photosensitive resist film is exposed and developed through a photomask having a light-shielding film pattern in which the light-shielding dot density is changed stepwise. Then, a resist film patterned into a lens shape is formed, and then etched back to remove the resist film. At the same time, a convex lens is formed on the lens resin layer to form a condensing lens. (Patent Document 2)
JP 61-67003 A Japanese Patent Laid-Open No. 5-142752

However, since the above condenser lens has a lens effect due to the three-dimensional shape of a fine convex lens, when an infrared cut filter or a cover glass is attached, the periphery of the fine convex lens is filled with the adhesive when an adhesive is used. The lens effect will be impaired. For this reason, it is necessary to provide a gap between the condenser lens and the infrared cut filter or the cover glass, which increases the thickness of the solid-state imaging device, which hinders downsizing and thinning.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid-state imaging device that has high light utilization efficiency and can be reduced in size and thickness.

  In order to achieve such an object, the present invention is provided with an element main body in which a plurality of light receiving portions are disposed, and a light receiving surface of the element main body via at least a planarizing layer and a color filter layer. And a plurality of microlenses arranged at positions corresponding to the respective light receiving portions, and each microlens has a large refractive index from the peripheral portion toward the central portion. It was set as the structure which has such refractive index distribution.

As a preferred aspect of the present invention, a flattening layer and a color filter layer are laminated in this order between the light receiving surface and the planar condenser lens.
Moreover, as a preferable aspect of the present invention, the first planarizing layer, the color filter layer, and the second planarizing layer are laminated in this order between the light receiving surface and the planar condenser lens.
As a preferred embodiment of the present invention, the planar condenser lens has a thickness in the range of 0.5 to 5 μm.
Furthermore, as a preferable aspect of the present invention, the micro lens has a refractive index distribution width in the range of 1.4 to 1.8.

According to the present invention, since the flat condensing lens is provided, it is possible to attach an infrared cut filter, a cover glass or the like without providing a gap, and it is possible to reduce the size and thickness.
The effective area of each microlens that composes a flat condensing lens is expanded compared to the conventional micro-convex lens that obtains the lens effect by a three-dimensional shape, and the condensing efficiency is higher, and the light receiving part from the infrared cut filter, cover glass, etc. Distance can be shortened, and the sensitivity dependency on the incident angle of light is reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of an embodiment of a solid-state imaging device of the present invention. In FIG. 1, a solid-state imaging device 1 of the present invention includes an element body 2 in which a plurality of light receiving portions 3 are disposed, a first planarization layer 5 and a color filter layer that are sequentially stacked on the light receiving surface 4 of the element body 2. 6. A second planarizing layer 7 and a planar condenser lens 8 provided on the second planarizing layer 7 are provided.
The element body 2 constituting the solid-state imaging device 1 has a configuration corresponding to a solid-state imaging device such as a CCD or CMOS. For example, a plurality of light receiving portions 3 are arranged on one surface of a silicon wafer, a glass wafer, or the like. It is a thing. The light receiving section 3 may be a photodiode, CdS or the like, and a signal electrode (not shown) is formed corresponding to each light receiving section 3.

  The first planarization layer 5 constituting the solid-state imaging device 1 is a layer for relaxing and leveling the unevenness of the light receiving surface 4. Such a 1st planarization layer 5 can be formed using transparent resin materials, such as an acrylic resin, a styrene resin, a phenol resin, a polyimide resin, for example. The thickness of the 1st planarization layer 5 can be suitably set within the range of 0.5-3 micrometers, for example. Such a first planarizing layer 5 is formed by applying a composition containing the above-described transparent resin material onto the light receiving surface 4 using a method such as spin coating or flow coating, and drying (curing) it. Can be formed.

The color filter layer 6 constituting the solid-state imaging device 1 has a coloring pattern of red (R), green (G), and blue (B). For example, after applying a colored resist layer of each color, photolithography is applied. It can be formed by the method.
The second flattening layer 7 constituting the solid-state imaging device 1 is a layer for relaxing and flattening the difference in thickness of each color pattern of the color filter layer 6 and the unevenness due to the overlapping portion. The second planarizing layer 7 can be formed by the same material and forming method as the first planarizing layer 5 described above, and the thickness can be appropriately set within a range of 0.5 to 2 μm, for example. it can.

The flat condensing lens 8 constituting the solid-state imaging device 1 has a plurality of microlenses 9 arranged at positions corresponding to the respective light receiving portions 3, and each microlens 9 has a refractive index from the peripheral portion toward the central portion. Has a refractive index distribution that increases. FIG. 2 is a view for explaining the structure of the microlens 9 constituting the planar condenser lens 8. As shown in FIG. 2, the microlens 9 has a refractive index n _{0 at the} central portion 9a larger than the refractive index n _{1 at the} peripheral portion 9b. Then, the refractive index change (refractive index distribution) from the refractive index n ₀ to the refractive index n ₁ can be appropriately set within a range of 1.4 to 1.8, for example, in order to obtain a desired condensing distance. it can. For example, when the distance from the interface between the flat condensing lens 8 and the second flattening layer 7 to the light receiving unit 3 is the condensing distance S1, the refractive index distribution constant A is calculated from the following formula 1, and the following formula 2 The refractive index distribution N (r) [n ₁ ≦ N (r) ≦ n ₀ ] can be set.

S1 = 1 / [n ₀ √A · tan (√A · (Z))] Equation 1
N (r) = n ₀ [1- (A / 2) r ² ]... Formula 2
Where N (r): refractive index at point r
n ₀ : Refractive index on the central axis L
A: Refractive index distribution constant
Z: thickness of the flat condenser lens 8
r: Distance from the lens center axis L (μm)

For example, as shown in FIG. 3, the planar condensing lens 8 is formed by exposing and developing a photosensitive resin composition film 8 ′ for forming a lens through a photomask M, so that a plurality of microlenses can be simultaneously formed. 9 can be provided.
As the photomask M, it is possible to use a photomask M in which a plurality of fine light-transmitting regions composed of an aggregate pattern of fine light-transmitting dots that are not resolved at the exposure wavelength are arranged on the mask base material corresponding to the light receiving unit 3. In the above-described minute light-transmitting region, the density of the minute light-transmitting dots decreases from the peripheral edge toward the center.

  FIG. 4 is a diagram for explaining a minute light-transmitting region of the photomask M when using a photosensitive resin composition film 8 ′ for forming a lens whose refractive index decreases when exposed. As shown in FIG. 4, the minute light-transmitting region 11 is a set pattern of minute light-transmitting dots 12 (indicated by white squares in the illustrated example). The density of the fine light transmitting dots 12 in the peripheral edge portion 11b of the minute light transmitting region 11 is larger than the density of the fine light transmitting dots 12 in the central portion 11a. The collective pattern of the fine light-transmitting dots 12 can be set as appropriate using a binarization process, a light proximity effect, or the like. The dimension of the fine translucent dot 12 can be appropriately set to a dimension close to the exposure wavelength. When the dimension of the fine light transmitting dots 12 overlaps with a part of the exposure wavelength band and resolution occurs, the gap between the photomask M and the photosensitive resin composition film 8 ′ is set to about 10 to 20 μm. The resolution may be blurred.

For such a photomask M, for example, a light-shielding film such as a Cr thin film is formed on a transparent base material such as a glass substrate, and the light-shielding film is subjected to pattern etching to form an aggregate pattern of fine light-transmitting dots 12. Can be produced.
The light irradiated to the photomask M passes through the photomask M, and has a light amount distribution corresponding to the aggregate pattern of the fine light-transmitting dots 12 in each minute light-transmitting region 11. The resin composition film 8 'is exposed.
When a photosensitive resin composition film 8 ′ for forming a lens that has a refractive index that increases when exposed to light is used, a photomask M in which the fine light-transmitting dots 12 are fine light-shielding dots is used.

  Among the resin compositions that can be used for the photosensitive resin composition film 8 ′, examples of the photosensitive resin composition that decreases in refractive index upon exposure include trifluoroethyl acrylate, polymethylphenylsilane (Osaka Gas). Chemical Co., Ltd. PMPS, Nippon Paint Co., Ltd. Gracia etc.) etc. can be mentioned. Examples of the photosensitive resin composition having a refractive index that increases upon exposure include, for example, tribromophenoxyethyl acrylate, a photopolymer (such as OmniDex manufactured by DuPont, etc., but if it is a material for visible light exposure, It is necessary to stop photopolymerization by post-baking or the like.

The photosensitive resin composition is a mixture of such a refractive index distribution type monomer and a transparent polymer, and, if necessary, a photopolymerization initiator, a photosensitizer, a heat improver, a chemical resistance improver, etc. Can be used. Examples of the transparent polymer include polymethyl acrylate, polyolefin, polyester, polyurethane, epoxy acrylate, polyimide, and the like, and examples of the heat resistance improver and the chemical resistance improver include polysilazane. The refractive index distribution type monomer and the transparent polymer can be appropriately selected from the above exemplified materials and the like in consideration of the refractive index, but have the same light collection distance by using a material having a large refractive index. The thickness of the planar condenser lens can be made thinner.
The thickness of the planar condenser lens 8 described above can be in the range of 0.5 to 5 μm, preferably 0.7 to 3 μm. Alternatively, the flat condensing lens 8 may be provided by transferring and bonding a flat condensing lens formed on the transfer substrate in the same manner as described above onto the second planarizing layer 7.

  FIG. 5 is a schematic configuration diagram showing another example of the embodiment of the solid-state imaging device of the present invention. In FIG. 5, the solid-state imaging device 21 of the present invention includes an element main body 22 provided with a plurality of light receiving portions 23, a planarization layer 25 and a color filter layer 26 that are sequentially stacked on the light receiving surface 24 of the element main body 22. And a flat condensing lens 28 provided on the color filter layer 26. The solid-state imaging device 21 is different from the above-described solid-state imaging device 1 in that it does not include the second planarization layer. In the present embodiment, the planar condenser lens 28 also serves as the second planarization layer. Yes. The flat condensing lens 28 has a plurality of microlenses 29 arranged at positions corresponding to the respective light receiving portions 23, and each microlens 29 has a refractive index that increases in refractive index from the peripheral portion toward the central portion. Have a distribution. The planar condenser lens 28 may have the same configuration as the planar condenser lens 8 described above, and can be formed on the color filter layer 26 in the same manner as the planar condenser lens 8 described above. In addition, the element main body 22, the light receiving unit 23, the planarization layer 25, and the color filter layer 26 that configure the solid-state imaging device 21 are the element main body 2, the light receiving unit 3, and the first planarization layer that configure the solid-state imaging device 1. 5. It can be the same as the color filter layer 6.

  Since the solid-state imaging device of the present invention as described above includes a planar condenser lens, the lens effect is impaired even if an infrared cut filter or a cover glass is attached to the outside of the planar condenser lens using an adhesive. This makes it possible to reduce the size and thickness of the solid-state imaging device. In addition, the effective area where the lens effect can be obtained is larger than the conventional condensing lens having a plurality of fine convex lenses, and the condensing efficiency is improved.

Next, the present invention will be described in more detail by showing more specific examples.
[Example 1]
A planarization layer composition (CT-2000L manufactured by Fuji Film Arch Co., Ltd.) is applied to the light-receiving surface of the element body (silicon wafer) on which the CCD is formed by spin coating, followed by drying at 220 ° C. for 12 minutes. Thermal curing was performed to form a first planarization layer having a thickness of about 1.5 μm.
Next, a composition for red (R) color pattern (SR-3000L manufactured by Fuji Film Arch Co., Ltd.), a composition for green (G) color pattern (SG-3000L manufactured by Fuji Film Arch Co., Ltd.), and blue (B ) After applying each colored pattern composition of the color pattern composition (SB-3000L manufactured by Fuji Film Arch Co., Ltd.) in the order of R, G, and B, the pattern is formed by photolithography. A color filter layer (the thickness of each layer was about 1 μm) was provided.

Next, the above planarization layer composition is applied onto the color filter layer by a spin coating method, followed by drying and thermal curing at 220 ° C. for 12 minutes to form a second planarization layer having a thickness of about 1 μm. Formed.
Next, a photosensitive resin composition for lens formation having the following composition is applied onto the second planarizing layer by spin coating, and dried at 120 ° C. for 2 minutes to form a photosensitive resin composition film (thickness 3 μm). Formed.
(Photosensitive resin composition for lens formation)
・ Polymethylphenylsilane: 50 parts by weight (PMPS manufactured by Osaka Gas Chemical Co., Ltd.)
・ Propylene glycol monomethyl ether acetate: 50 parts by weight

  Next, the above-described photosensitive resin composition film for lens formation was exposed under the following conditions with an exposure apparatus (UIV-570 manufactured by Ushio Electric Co., Ltd.) through a binary photomask having the following specifications. The exposure apparatus was used by exchanging the lens with a quartz lens so as to transmit the short wavelength light. Further, the photomask was obtained by forming a Cr vapor deposition film on one side of a glass substrate and forming fine light-transmitting dots by pattern etching, and the distance between the photomask and the photosensitive resin composition film was set to 18 μm.

(Photomask specifications)
-Fine translucent dot diameter: 0.4 μm
-Aggregation pattern of fine light-transmitting dots: Aggregation pattern shown in Fig. 4 (exposure conditions)
・ Light source: Ultra high pressure mercury lamp (USH-500D manufactured by USHIO INC.)
-Input power: 500W
-Exposure time: 10 minutes Thereby, the planar condensing lens provided with the some microlens corresponding to CCD on the 2nd planarization layer was formed. This planar condenser lens had a thickness of 3 μm.

[Example 2]
In the same manner as in Example 1, the first planarizing layer and the color filter layer were formed on the light receiving surface of the element body (silicon wafer) on which the CCD was formed.
Next, the same lens-forming photosensitive resin composition as in Example 1 was applied onto the color filter layer by spin coating, and dried at 120 ° C. for 2 minutes to form a photosensitive resin composition film (thickness 3 μm). ) Was formed.
Next, the above-described photosensitive resin composition film for lens formation was exposed using the same photomask and exposure conditions as in Example 1.
As a result, a planar condenser lens having a plurality of microlenses corresponding to the CCD was formed on the color filter layer. This planar condenser lens had a thickness of 3 μm.

[Evaluation 1]
A glass substrate is used instead of the element main body (silicon wafer) on which the CCD is formed, and a laminated structure (samples 1 and 2) having a planar condenser lens on the glass substrate in the same manner as in the first and second embodiments. ) Was produced. That is, as shown in FIG. 6, a Cr thin film 32 is formed on one surface of a glass substrate 31, and an opening 33 (5 mm × 5 mm) for sample preparation and two reference openings are formed in the Cr thin film 32. (5 μm × 5 μm) 34a and 34b were formed by etching. A laminated structure (samples 1 and 2) was produced in the opening 33 on the Cr thin film forming surface side of the glass substrate 31.
As a result of measuring the condensing distance of each of the microlenses of Samples 1 and 2 by the following method, it was 4 μm for Sample 1 and 5 μm for Sample 2, and it was confirmed that the condensing distance was extremely small.

(Condensing distance measurement method)
As shown in FIG. 7, the glass substrate 31 is fixed to a stage 41, and a parallel light source 42 and an optical microscope 43 (objective lens magnification = 60 times, NA = 0.85, through the glass substrate 31). The eyepiece magnification is 5 times. However, the glass substrate 31 was disposed such that the surface on which the laminated structure (samples 1 and 2) having the flat condensing lens and the Cr thin film 32 were formed was on the light source 42 side. Further, a neutral density filter (ND filter) 44 for adjusting the amount of light is disposed between the light source 42 and the glass substrate 31.
Next, as shown in FIG. 8 which is an enlarged view of the opening 33, the reference opening 34a, and the reference opening 34b, the stage 41 while observing the reference opening 34a and the reference opening 34b with the optical microscope 43, respectively. Were moved in the Z-axis direction to determine the Z-axis positions Z1 and Z2 of the reference opening. Note that the position of the Z-axis was a position where the reference opening could be seen to the minimum (focused).
Next, the stage 41 is moved in the Z-axis direction while observing the opening portion 33 in which the laminated structure (samples 1 and 2) having the planar condensing lens is manufactured with the optical microscope 43, and the position Z3 (where the light spot can be minimized) Beam waist) was determined.
Further, in order to correct the inclination of the glass substrate 31, the average of the positions Z1 and Z2 of the reference opening was calculated and set as the plane position Z4 of the planar condenser lens portion.
The distance between the position Z3 and the position Z4 was defined as the distance from the flat condensing lens to the condensing position.

[Evaluation 2]
A device body (silicon wafer) on which a CMOS sensor was formed was used, and a laminated structure (samples 3 and 4) each having a planar condenser lens was produced on the device body in the same manner as in Examples 1 and 2. . In addition, a laminated structure (Comparative Samples 1 and 2) was prepared in the same manner as Samples 3 and 4 except that the flat condenser lens was not provided.
With respect to Samples 3 and 4 and Comparative Samples 1 and 2, sensor outputs were measured in a wafer state using a CCD-CMOS area sensor tester TS6600 manufactured by Yokogawa Electric Corporation. As a result, the sensor outputs of Samples 3 and 4 were about three times as high as the sensor outputs of Comparative Samples 1 and 2, and it was confirmed that the light collection efficiency was high.

  The present invention can be applied to a solid-state imaging device such as a small and thin CCD or CMOS.

It is a schematic block diagram which shows an example of embodiment of the solid-state image sensor of this invention. It is a figure for demonstrating the structure of the micro lens which comprises a planar condensing lens. It is a figure for demonstrating the formation method of a plane condensing lens. It is a figure for demonstrating the fine translucent area | region which comprises a photomask. It is a schematic block diagram which shows the other example of embodiment of the solid-state image sensor of this invention. It is a figure for demonstrating the sample for condensing distance measurement in an Example. It is a figure for demonstrating the measuring method of the condensing distance in an Example. It is a figure for demonstrating the measuring method of the condensing distance in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,21 ... Solid-state image sensor 2,22 ... Element main body 3,23 ... Light-receiving part 4,24 ... Light-receiving surface 5,25 ... 1st planarization layer (flattening layer)
6, 26 ... Color filter layer 7 ... Second flattening layer 8, 28 ... Planar condenser lens 9, 29 ... Micro lens M ... Photomask

Claims (5)

  An element main body provided with a plurality of light receiving portions, and a planar condensing lens provided on the light receiving surface of the element main body via at least a planarizing layer and a color filter layer, the planar condensing lens Has a plurality of microlenses arranged at positions corresponding to the respective light receiving portions, and each microlens has a refractive index distribution such that the refractive index increases from the peripheral portion toward the central portion. Image sensor.   2. The solid-state imaging device according to claim 1, wherein a planarization layer and a color filter layer are laminated in this order between the light receiving surface and the planar condenser lens.   2. The solid-state imaging device according to claim 1, wherein a first planarizing layer, a color filter layer, and a second planarizing layer are laminated in this order between the light receiving surface and the planar condenser lens.   4. The solid-state imaging device according to claim 1, wherein a thickness of the planar condenser lens is in a range of 0.5 to 5 μm.   The solid-state imaging device according to any one of claims 1 to 4, wherein a width of a refractive index distribution in the microlens is in a range of 1.4 to 1.8.

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