JP2008116935A - Optical low-pass filter and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical low-pass filter which is inexpensive, has a suppressed thickness, hardly changes diffraction efficiency even when dirt and dust are attached and the height of a recessed and projection structure slightly deviates from a design value and, even in such a shape that the pitch of the recessed and projection structure is broad and the Raman Nath diffraction is caused, can suppress multiple light intensity low, and to provide a manufacturing method of the optical low-pass filter. <P>SOLUTION: The optical low-pass filter 1 includes: a sheet-like recessed and projection structural body 12 having a large number of recessed and projection parts 10 which are formed with a first transparent resin and have a height of 1 μm to 100 μm on the surface; and a cover layer 14 which is formed with a second transparent resin and covers the sheet-like recessed and projection structural body, wherein the sheet-like recessed and projection structural body is extended in the thickness direction of the first transparent resin layer, the recessed and projection parts are periodically arranged in the order of 80 nm to 1,000 nm in a matrix in a face vertical to the thickness direction of the first transparent resin layer and the difference of refractive index between the first and second transparent resins is 0.001 to 0.4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical low-pass filter and a manufacturing method thereof, and more particularly, to an optical low-pass filter used in a digital camera or the like attached to a mobile phone in order to prevent moire and a manufacturing method thereof.

  2. Description of the Related Art In recent years, home video cameras and digital still cameras whose performance has been remarkably improved have used CCD area image sensors and CMOS area image sensors as imaging means.

  These sensors are configured to perform photoelectric conversion with a large number of light receiving elements arranged two-dimensionally on a silicon substrate, and transfer charges generated by each light receiving element to the outside with an image pickup element such as a CCD element or a CMOS circuit. It has. In these sensors, in order to obtain color information for each light receiving element (pixel), for example, RGB color filters are arranged in a stripe pattern or four types of filters in a square mosaic pattern on each pixel. Are regularly arranged in a grid pattern.

  As described above, in the CCD area image sensor and the like described above, since the image pickup elements and the like are regularly arranged in a grid pattern, color reproduction such as generation of a pseudo signal (moire) in the generated image of the subject is performed. Inconvenience may occur. In order to solve such a problem, an optical low-pass filter (OLPF) that cuts over a specific frequency is used. As such an optical low-pass filter, a quartz OLPF utilizing the birefringence of quartz is most often used.

  However, the quartz OLPF has a structure in which two quartz plates are arranged on both sides of a quarter-wave plate or a structure in which three quartz plates are combined. There is a problem that it is not suitable for an optical system in which it is required to shorten the optical length, such as a camera optical system, and it is also expensive.

  For this reason, a method has also been proposed in which an uneven phase grating having an uneven structure on the surface of a transparent resin or the like is used as an optical low-pass filter. (See Patent Document 1 and Patent Document 2).

JP-A-8-212336 Japanese Patent Laid-Open No. 7-5394

However, the concavo-convex phase grating having the concavo-convex structure on the surface of the transparent resin has a problem that the diffraction ability is greatly reduced by dust and dirt adhering to the concavo-convex surface.
Furthermore, since the concavo-convex phase grating has a large refractive index difference Δn between the transparent resin and air, a large difference in diffraction efficiency occurs when the concavo-convex height slightly deviates from the design value, making it impossible to exhibit the desired performance. Also, there is a problem that the yield is poor at the time of mass production.
In addition, since the concavo-convex phase grating has a large refractive index difference Δn between the transparent resin and air, if the concavo-convex structure has a wide pitch and a shape that causes Raman / Nas diffraction, the multi-order light intensity increases and is incorporated into the camera. In this case, the resolution is lowered.

  The present invention has been made to solve such problems, is inexpensive and has a reduced thickness, and dust or dirt adheres to it, and the height of the unevenness slightly deviates from the design value. However, the present invention provides an optical low-pass filter that can suppress the multi-order light intensity and a method of manufacturing the same even when the change in diffraction efficiency is small and the pitch of the concavo-convex structure is wide to cause Raman / Nass diffraction. For the purpose.

According to the present invention,
An optical low-pass filter,
A sheet-like concavo-convex structure formed of a first transparent resin and provided with a large number of concavo-convex portions having a height of 1 μm to 100 μm on the surface;
A cover layer formed of a second transparent resin covering the sheet-like uneven structure,
The sheet-like concavo-convex structure extends in the thickness direction of the first transparent resin layer, and the concavo-convex portion is periodically on the order of 80 nm to 1000 μm in a plane perpendicular to the thickness direction of the first transparent resin layer. Arranged in a grid,
The difference in refractive index between the first transparent resin and the second transparent resin is 0.001 to 0.4.
An optical low-pass filter is provided.

  The concavo-convex portion basically includes a cylindrical convex portion, but may be a prism, or may be a cone, an elliptical cone, a triangular pyramid, a truncated cone, an elliptical truncated cone, a truncated pyramid, or the like.

In addition, the higher the ratio of the flat portion in the cross-sectional shape of the concavo-convex portion, the greater the intensity of light that goes straight without diffraction, making it difficult to obtain high diffraction efficiency. An elliptical cone and a triangular pyramid shape are preferable.
The optical low-pass filter of the present invention is disposed, for example, on the light receiving surface of a solid-state image sensor.

  In the optical low-pass filter having such a configuration, the uneven portion formed in the first resin having a refractive index difference of 0.001 to 0.4 with the second transparent resin forming the cover layer covering the surface Are regularly arranged in a lattice pattern on the order of 80 nm to 1000 μm, and has a highly regular structure in which the refractive index changes periodically on the order of 80 nm to 1000 μm. Therefore, it is possible to effectively prevent the occurrence of moire while having a thin structure. Furthermore, it is less expensive than an optical low-pass filter made of quartz.

  In addition, in the optical low-pass filter having a fine uneven portion on the surface, there is a risk that the diffraction ability is greatly reduced by dust or dirt adhering to the uneven surface, but the optical low-pass filter of the present invention having the above-described configuration. Then, since the fine uneven part formed in the first transparent resin is covered with the second transparent resin having a refractive index different from that of the first transparent resin, the diffraction ability is reduced due to the adhesion of dust and dirt. The degree to which is reduced.

Further, the Q value, which is an index representing the thickness of the diffraction grating, is obtained by the equation (1). When the Q value is sufficiently larger than 1, the diffraction efficiency of the diffraction grating is determined by the Bragg equation (equation (2)). It is known that the diffraction efficiency depends on the thickness L of the diffraction grating.
The conventional optical low-pass filter with a fine uneven structure on the surface of the transparent resin has a large refractive index difference Δn between the transparent resin and air. A big difference will occur (see Table 1).
Q = 2π · λ · L / n · Λ2 (1)
η = sin2 (π · Δn · L / λ) (2)

Further, when the Q value is sufficiently smaller than 1, it is known that the diffraction efficiency of the diffraction grating is obtained by the Raman-Nas formula, and the diffraction efficiency depends on the thickness L of the diffraction grating.
A conventional optical low-pass filter with fine irregularities on the surface of a transparent resin has a large refractive index difference Δn between the transparent resin and air, which increases the intensity of multi-order light and lowers the resolution when incorporated in a camera. It also has the problem of becoming.

  On the other hand, in the optical low-pass filter of the present invention having the above-described configuration, the fine irregularities formed by the first transparent resin are formed by the second transparent resin having a refractive index different from that of the first transparent resin. Since it is covered, Δn can be set small. When Δn is small, the effect on the diffraction efficiency due to the difference in height of the concavo-convex portion is small, yield improvement can be expected in mass production, and even when the pitch of the concavo-convex portion is wide and causes a Raman-Nas diffraction, It can be expected that the next light intensity can be kept low.

According to another aspect of the invention,
A method for manufacturing an optical low-pass filter, comprising:
Disposing a first transparent resin layer on a smooth substrate;
Forming fine irregularities periodically arranged on the surface of the first transparent resin layer by photolithography;
Forming on the smooth substrate an optical low-pass filter that covers the surface of the first transparent resin layer and includes a second transparent resin layer having a refractive index different from that of the first transparent resin layer. A method for manufacturing an optical low-pass filter is provided.

  The concavo-convex portion basically includes a cylindrical convex portion, but may be a prism, or may be a cone, an elliptical cone, a triangular pyramid, a truncated cone, an elliptical truncated cone, a truncated pyramid, or the like.

  In addition, the higher the ratio of the flat portion in the cross-sectional shape of the concavo-convex portion, the greater the intensity of light that goes straight without diffraction, making it difficult to obtain high diffraction efficiency. An elliptical cone and a triangular pyramid shape are preferable.

  Photolithography is preferable as a method for forming the concavo-convex portion, but a sheet-like concavo-convex structure having an concavo-convex portion with an aspect ratio of about 20 can be produced by using X-ray lithography.

According to another preferred aspect of the present invention, the smooth substrate is the light receiving surface of the image sensor.
According to such a configuration, the generation of moire can be effectively prevented even with a thin structure, so that an optical low-pass filter can be directly built on the solid-state imaging device, thus simplifying the work process. The cost and labor of manufacturing a camera or the like equipped with a solid-state image sensor can be reduced.

According to another aspect of the invention,
A method for manufacturing an optical low-pass filter, comprising:
Applying a first transparent resin on a mold on which fine irregularities are formed;
Disposing a translucent film on the first transparent resin, irradiating an active energy ray from above the translucent film, polymerizing and curing the first transparent resin layer, and an uneven portion that is complementary to the uneven portion. Forming a sheet-like uneven structure formed on the surface;
Separating the mold from the sheet-like uneven structure, and applying a second transparent resin to the surface of the sheet-like uneven structure;
Arranging a translucent film on the second transparent resin, and irradiating an active energy ray from above the translucent film to polymerize and cure the second transparent resin layer,
An optical low-pass filter manufacturing method is provided.

  The mold basically includes a cylindrical convex portion, but may be a prism, or may be a cone, an elliptical cone, a triangular pyramid, a truncated cone, an elliptical truncated cone, a truncated pyramid, or the like.

  According to the present invention, the change in the diffraction efficiency is small even if the thickness is low, the thickness is suppressed, dust or dirt adheres, or the height of the sheet-like uneven structure slightly deviates from the design value. In addition, an optical low-pass filter that can suppress the multi-order light intensity low and a method for manufacturing the same are provided even in the case where the pitch of the concavo-convex structure is wide and causes a Raman-Nas diffraction.

  Hereinafter, an optical system using an optical low-pass filter 1 according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a drawing schematically showing a configuration of an imaging optical system 2 using an optical low-pass filter 1 according to an embodiment of the present invention.

  The imaging optical system 2 is used as an imaging optical system that takes an image with a solid-state imaging device having pixels of a predetermined pitch, such as an optical system for a digital still camera, an optical system for a digital camera mounted on a mobile phone, or the like. .

  As shown in FIG. 1, in the imaging optical system 2, the optical low-pass filter 1 is disposed on the front side of the light receiving surface of the solid-state imaging device 4. The imaging optical system 2 of the present embodiment further includes a lens 6 that forms an image on the light receiving surface and an infrared cut filter 8.

  The solid-state imaging device 4 of the present embodiment is a two-dimensional arrangement of a large number of light receiving elements on a silicon substrate, and charges generated by each light receiving element are externally output by the imaging element (CCD element or CMOS circuit). It is an area image sensor that can be transferred as a signal.

  The lens 6 is composed of a glass lens made of inorganic glass or a plastic lens made of polycarbonate resin, acrylic resin, polystyrene resin, polyolefin resin, or the like.

  The infrared cut filter 8 is composed of a glass filter made of inorganic glass or a plastic filter made of polycarbonate resin, acrylic resin, polystyrene resin, or polyolefin resin to which an organic dye is added.

  FIG. 2 is a drawing schematically showing the internal structure of the optical low-pass filter 1. The optical low-pass filter 1 includes a sheet-like concavo-convex structure body 12 having a plurality of concavo-convex portions 10 having a height of 1 μm to 100 μm formed of a first transparent resin on the surface, and covers the sheet-like concavo-convex structure body 12. A cover layer 14 made of a transparent resin, and a cover layer 14.

  In the optical low-pass filter 1 of the present embodiment, a large number of cylindrical shapes provided on the surface of the first transparent resin layer so as to extend in the thickness direction of the first transparent resin layer (sheet-like structure 12). Consists of convex portions 10, and these convex portions 10 are arranged with two-dimensional regularity in a plane perpendicular to the thickness direction of the first transparent resin layer (sheet-like structure 12).

  In the optical low-pass filter 1 of the present embodiment, the convex portions 10 are regularly arranged so as to form a hexagonal lattice as shown in FIG. 3, and by this regularity, six-point separation (three directions) is performed. Can be performed by a single filter. The hexagonal lattice includes a triangular lattice and a honeycomb lattice. In addition to the hexagonal lattice, the sheet-like concavo-convex structure may be arranged to form a square lattice or an oblique lattice.

  The arrangement period of the sheet-like concavo-convex structure, that is, the interval between the convex portions 10 is 80 nm to 1000 μm, preferably 90 nm to 100 μm, more preferably 100 nm to 50 μm.

The concavo-convex portion basically consists of a columnar convex portion, but as shown in FIG. 4, a prism (a), a truncated cone, an elliptical truncated cone or a truncated pyramid (b), a hemispherical (c) , Water drops (d), or conical, elliptical or pyramid (e).
In addition, since the uneven portion has a higher proportion of the flat portion in the cross-sectional shape, the intensity of light that goes straight without being diffracted increases, and it becomes difficult to obtain high diffraction efficiency. A conical shape or an elliptical cone shape is preferred.

In the optical low-pass filter 1 of the present embodiment, the height of the convex portion (the height difference of the concave and convex portions) is 1 μm to 100 μm.
Further, the diameter of the convex portion (in the case of a prism, the diameter of the circumscribed circle of the cross section) is 80 nm to 1000 μm, preferably 90 nm to 100 μm, more preferably 100 nm to 50 μm.

  The difference in refractive index between the first transparent resin forming the sheet-like uneven structure 12 and the second transparent resin forming the cover layer 14 is 0.001 to 0.4.

As a preferable aspect of the present invention, the height (the height difference) of the convex portion 10 is 1 μm to 10 μm, the arrangement period of the convex portions 10, that is, the interval is 5 μm to 50 μm, and
A value obtained by multiplying the arrangement period, that is, the interval of the convex portions 10 by the refractive index difference between the first transparent resin forming the sheet-like uneven structure and the second transparent resin forming the cover layer is 0.12 μm to 0 .15 μm, more preferably 0.13 μm to 0.14 μm.

  By adopting such an aspect, since the aspect ratio of the convex portion 10 is low, in the case where the sheet-like concavo-convex structure 12 is formed with a mold or the like, the possibility that the resin remains in the mold or the like is reduced, and productivity is reduced. It becomes possible to raise.

  Further, even when the optical low-pass filter 1 having such a configuration has a periodic structure that causes Raman-Nath diffraction, the intensity of multi-order diffracted light can be suppressed, so that a reduction in resolution of the imaging optical system can be suppressed.

  By setting the height, diameter, and arrangement period of the convex portions 10 and the refractive index difference between the sheet-like concavo-convex structure 12 and the cover layer 14 within the above range, the optical low-pass filter 1 has a thickness of 80 nm to 1000 μm. It has a highly regular structure in which the refractive index changes periodically on the order, and as an optical product, an interference effect on light in the wavelength range of 350 nm to 2000 nm can be sufficiently exhibited. As a result, the optical low-pass filter 1 can perform advanced light control such as diffraction and deflection.

  The sheet-like concavo-convex structure 12 and the cover layer 14 constituting the optical low-pass filter 1 of the present embodiment are made of polycarbonate resin, acrylic resin, polystyrene resin, or polyimide resin, but may be any transparent material. However, it is not particularly limited to these. The above-mentioned transparent material is formed by irradiating the photopolymerizable composition with light and curing it. As the photopolymerizable composition, one containing a monofunctional monomer or a polyfunctional monomer or oligomer having two or more functions and a photopolymerization initiator is used.

  Specific examples of the monofunctional monomer include methyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, ethyl carbitol (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, isobornyl (meth) acrylate, and phenyl carbitol. (Meth) acrylate, nonylphenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, (meth) acryloyloxyethyl succinate, (meth) acryloyloxyethyl phthalate, phenyl (meth) acrylate, cyanoethyl (Meth) acrylate, tribromophenyl (meth) acrylate, pentabromophenyl (meth) acrylate, phenoxyethyl (meth) acrylate, tribromophenoxy Ethyl (meth) acrylate, benzyl (meth) acrylate, p-bromobenzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, trifluoroethyl (meth) acrylate, pentadecafluorooctyl (meth) (Meth) acrylate compounds such as acrylate and 2,2,3,3-tetrafluoropropyl (meth) acrylate; vinyl compounds such as styrene, p-chlorostyrene, vinyl acetate, acrylonitrile, N-vinylpyrrolidone and vinylnaphthalene; ethylene Examples include allyl compounds such as glycol bisallyl carbonate, diallyl phthalate, and diallyl isophthalate.

  Specific examples of the bifunctional or higher polyfunctional monomer include triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and 1,4-butanediol di (meth) acrylate. 1,6-hexanediol di (meth) acrylate, hydrogenated dicyclopentadienyl di (meth) acrylate, ethylene oxide modified bisphenol A di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra ( (Meth) acrylate, tetramethylolmethane tetra (meth) acrylate, pentaerythritol hexa (meth) acrylate, polyfunctional epoxy (meth) acrylate, polyfunctional urethane (meth) acrylate, divinyl Zenene, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl chlorendate, N, N′-m-phenylene bismaleimide, diallyl phthalate, etc. It can be used as a mixture.

  For example, when a sheet-like uneven structure is formed by polymerizing and curing pentadecafluorooctyl acrylate, and a cover layer is formed by polymerizing and curing pentabromophenyl methacrylate, a sheet-like uneven structure is produced. The refractive index difference between the body and the cover layer is 0.371.

  In this embodiment, the photopolymerization initiator used in the photopolymerizable composition is not particularly limited as long as it is used in normal photopolymerization in which polymerization is performed by irradiating active energy rays such as ultraviolet rays. Absent. For example, benzophenone, benzyl, Michler's ketone, 2-chlorothioxanthone, benzoin ethyl ether, diethoxyacetophenone, pt-butyltrichloroacetophenone, benzyldimethyl ketal, 2-hydroxy-2-methylpropylphenone, 1-hydroxycyclohexyl phenyl ketone, 2-Benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, dibenzosuberone and the like.

  The amount of these photopolymerization initiators used is preferably in the range of 0.001 to 10 parts by weight with respect to 100 parts by weight of the other photopolymerizable composition so as not to deteriorate the transparency of the optical low-pass filter. Therefore, it is more preferable to use 0.01 to 5 parts by weight.

In this embodiment, a monofunctional monomer or oligomer having one polymerizable carbon-carbon double bond in the molecule may be used as the photopolymerizable composition together with the polyfunctional monomer or oligomer as described above. Good.
As such a monofunctional monomer or oligomer, those containing (meth) acryloyl group, vinyl group, allyl group and the like are particularly preferable.

  These monofunctional monomers or oligomers are used for imparting flexibility to the optical low-pass filter. The amount of the monofunctional monomer or oligomer is preferably in the range of 10 to 99% by mass, more preferably in the range of 10 to 50% by mass, of the total amount with the polyfunctional monomer or oligomer.

Further, as the photopolymerizable composition, a homogeneous dissolution mixture containing the polyfunctional monomer or oligomer and a compound having no polymerizable carbon-carbon double bond can be used.
Examples of the compound having no polymerizable carbon-carbon double bond include polymers such as polystyrene, polymethyl methacrylate, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl alcohol, and nylon, toluene, n-hexane, cyclohexane, acetone, and methyl ethyl ketone. , Methyl alcohol, ethyl alcohol, ethyl acetate, acetonitrile, dimethylacetamide, dimethylformamide, low molecular compounds such as tetrahydrofuran, organic halogen compounds, organic silicon compounds, plasticizers, additives such as stabilizers, and the like.

  The amount of the compound having no polymerizable carbon-carbon double bond is used to reduce the viscosity of the photopolymerizable composition and improve the handleability when producing an optical low-pass filter. Or it is preferable to set it as the range of 1 to 99 mass% among the total amount with an oligomer.

Next, a method for manufacturing the optical low-pass filter 1 by photolithography will be described. The optical low-pass filter 1 of the present embodiment is manufactured on the light receiving surface of the solid-state image sensor 4.
First, a transparent resin substrate made of a photopolymerizable resin (first transparent resin) or the like is disposed on the light receiving surface of the solid-state imaging device 4. Such a transparent resin substrate may be fixed on the solid-state image sensor with an adhesive or the like, and a photopolymerizable resin composition is formed on the solid-state image sensor by a spin coat method or the like, and diffused light or the like is formed. It may be cured with ultraviolet rays. Alternatively, a film-like product may be used in which a solution obtained by dissolving a thermoplastic resin or the like in a solvent is used to form a coating film by a spin coating method or the like, and the solvent is evaporated to solidify.

  Next, the step of forming the sheet-like concavo-convex structure 12 on the surface of the transparent resin substrate by a photolithography technique, and the difference in refractive index between the transparent resin substrate on the sheet-like concavo-convex structure 12 is 0.001 to 0.4. The optical low-pass filter 1 is manufactured by forming the cover layer 14 with the transparent resin (second transparent resin).

As a method of forming a sheet-like concavo-convex structure by photolithography, first, a photoresist layer is formed on a transparent resin substrate by a spin coating method, then a photomask is arranged on the photoresist layer, and ultraviolet rays or the like is applied by a mask aligner. The active energy rays of the photoresist layer are irradiated to cure only the active energy ray irradiated or unirradiated portions of the photoresist layer.
As a photomask to be used, a photomask in which circular or polygonal shapes on the order of 80 nm to 1000 μm in diameter (referred to as circumscribed circle diameter in the case of a rectangular wave shape) are regularly arranged in a hexagonal lattice structure is used.

  Further, after removing the uncured portion by development processing, the portion not covered with the photoresist is etched by a dry etching apparatus, and a sheet-like concavo-convex structure in which convex portions are arranged on the surface of the transparent resin substrate Form the body. The depth of the etching process is preferably in the range of 1 μm to 100 μm.

The photoresist layer is removed from the transparent resin substrate subjected to the etching treatment, and a transparent resin (second resin) having a refractive index difference of 0.001 to 0.4 with respect to the transparent resin substrate is formed on the sheet-like uneven structure by spin coating or the like. In addition, the second transparent resin is photocured with an active energy ray such as ultraviolet rays, and a sheet-like uneven structure formed of the first transparent resin is formed of the second transparent resin. An optical low-pass filter covered with the covered cover layer is obtained.
The thickness of the optical low-pass filter is not particularly limited, but is preferably in the range of 1 μm to 1000 μm, more preferably in the range of 5 μm to 500 μm.

Next, a method for manufacturing the optical low-pass filter 1 by mold shaping will be described. The optical low-pass filter 1 of this embodiment is manufactured on a translucent film such as a PET film.
First, a photopolymerizable resin (first transparent resin) is applied onto a mold having a fine concavo-convex structure that is complementary to the fine concavo-convex portion to be formed.

  Next, a step of arranging a translucent film on the photopolymerizable resin, and polymerizing and curing the photopolymerizable resin by irradiating the photopolymerizable resin with active energy rays such as ultraviolet rays through the translucent film. By the step, a plastic film formed with a fine uneven structure is formed on the mold.

  The plastic film is peeled from the mold, and a photopolymerizable resin (second transparent resin) is applied onto the concavo-convex structure formed on one side of the plastic film.

  Next, a step of arranging a translucent film on the photopolymerizable resin, and polymerizing and curing the photopolymerizable resin by irradiating the photopolymerizable resin with active energy rays such as ultraviolet rays through the translucent film. By the step, the optical low-pass filter 1 in which the concavo-convex structures having different refractive indexes are adhered to each other is manufactured.

  Without being limited to the above-described embodiment of the present invention, various changes and modifications can be made within the scope of the technical idea described in the claims.

Examples of the present invention will be described.
(Example 1)
A photopolymerizable composition obtained by dissolving 1 part by weight of 1-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator in trimethylolpropane triacrylate having a refractive index of a single polymer of 1.535, 100 mm × A plastic film with a thickness of 100 μm is applied on a glass plate by applying it onto a glass plate with a thickness of 100 mm and a thickness of 1 mm by a spin coating method, covering the PET film and irradiating with an ultraviolet ray using an ultra-high pressure mercury lamp. Obtained.

  On the resulting plastic film, a negative photoresist was applied by spin coating, and heated at 100 ° C. for 120 seconds for soft baking. The obtained plastic film was covered with a photomask, and an i-line stepper was used to irradiate parallel light with an integrated light amount of 160 mJ / cm 2 to partially photocure the photoresist layer. In the photomask, holes having a diameter of 2 μm are arranged in a hexagonal lattice pattern with a period of 5 μm.

  Further, the photoresist layer was post-baked by heating at 90 ° C. for 120 seconds. Furthermore, the plastic film was immersed in isopropyl alcohol to remove the uncured portion of the photoresist layer from the plastic film, and heated at 180 ° C. for 1 hour to hard-bake the photoresist layer.

  Further, a portion of the plastic film where the photoresist layer is not formed is selectively etched by a dry etching apparatus, and holes having a diameter of 2 μm and a depth of 5 μm are arranged in a hexagonal lattice pattern with a period of 5 μm, and a fine surface is formed. A sheet-like concavo-convex structure in which convex portions were arranged was formed. The convex portion has a cylindrical shape having a rectangular wave-like cross-sectional shape. Further, the plastic film was immersed in a release agent to completely remove the photoresist layer.

  Further, a photopolymerizable composition obtained by dissolving 1 part by mass of 1-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator in EO-modified bisphenol A dimethacrylate having a refractive index of a single polymer of 1.572. A 200 μm thick plastic is applied by applying a spin coat method on a plastic film having the fine projections formed on the surface, covering the PET film, and irradiating with an ultraviolet ray using an ultra-high pressure mercury lamp. A film was obtained.

  In the obtained plastic film, cylindrical convex portions having a diameter of 2 μm and having a refractive index different from that of the cover layer are arranged in a hexagonal lattice pattern with a period of 5 μm in a plane perpendicular to the film thickness direction.

  When this plastic film was irradiated with laser light having a center wavelength of 532 nm and the intensity of the diffracted light was measured, the proportion of ± 2nd order diffracted light to the total diffracted light was less than 1%.

  This plastic film was placed on a CMOS solid-state imaging device in a camera module and a circular zone plate was photographed to evaluate its function as an optical low-pass filter.

  FIG. 5 shows an image of a circular zone plate used for evaluation of the optical low-pass filter function, taken by a camera without an optical low-pass filter. FIG. 5 shows an image taken by a camera with an optical low-pass filter. It is shown in FIG. In FIG. 6, it can be confirmed that most of the moire image observed in FIG. 5 has disappeared and the function of the optical low-pass filter is exhibited.

In addition, even if dust or dirt adheres to the optical low-pass filter or the height (difference in height) of the convex part slightly deviates from the design value, it is confirmed that the function of the optical low-pass filter is manifested. did it.
(Example 2)
Photopolymerizable composition obtained by dissolving 1.2 parts by mass of 1-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator in polyoxytetramethylene glycol dimethacrylate having a refractive index of a single polymer of 1.482 Was coated on a mold, covered with a PET film, and irradiated with ultraviolet rays by an ultraviolet irradiation apparatus using an ultra-high pressure mercury lamp, to obtain a plastic film having a thickness of 25 μm on the mold.

  The fine unevenness on the mold surface is a pyramid structure having a base of 32.7 μm and a height of 9.2 μm arranged in a square lattice pattern with a period of 32.7 μm.

  The obtained plastic film was peeled from the mold, and 1,2-bis [4- (methacryloxypolyethoxy) phenyl] propane having a refractive index of 1.537 as a single polymer was used as a photopolymerization initiator. Ultraviolet irradiation using a super high pressure mercury lamp using a photopolymerizable composition obtained by dissolving 1.2 parts by weight of hydroxycyclohexyl phenyl ketone on the surface of the peeled plastic film on which the concavo-convex structure is formed, and covering the PET film By irradiating the apparatus with ultraviolet rays, a plastic film having a thickness of 50 μm in which a plastic layer having a thickness of 25 μm was formed on the plastic film was obtained.

  In the obtained plastic film, pyramid-shaped convex portions with a base of 32.7 μm having a refractive index different from that of the cover layer are arranged in a square lattice pattern with a period of 32.7 μm in a plane perpendicular to the film thickness direction inside.

  When this plastic film was irradiated with laser light having a center wavelength of 532 nm and the intensity of the diffracted light was measured, the proportion of ± 2nd order diffracted light to the total diffracted light was less than 1%.

  This plastic film was placed on a CMOS solid-state imaging device in a camera module and a circular zone plate was photographed to evaluate its function as an optical low-pass filter.

  FIG. 5 shows an image of a circular zone plate used for evaluation of the optical low-pass filter function, taken by a camera without an optical low-pass filter. FIG. 5 shows an image taken by a camera with an optical low-pass filter. 7 shows. In FIG. 7, it can be confirmed that most of the moire image observed in FIG. 5 has disappeared, and the function of the optical low-pass filter is expressed.

  In addition, even if dust or dirt adheres to the optical low-pass filter or the height (difference in height) of the convex part slightly deviates from the design value, it is confirmed that the function of the optical low-pass filter is manifested. did it.

It is drawing which shows typically the structure of the imaging optical system using the optical low-pass filter of one Embodiment of this invention. It is drawing which shows typically the structure of the optical low-pass filter of FIG. It is drawing which shows typically arrangement | positioning of the convex part of the optical low-pass filter of FIG. It is drawing which shows the other aspect of a convex part. It is the image which image | photographed the circular zone plate with the camera which has not arrange | positioned the optical low-pass filter. 2 is an image obtained by photographing a circular zone plate with a camera in which the optical low-pass filter of Example 1 is arranged. 6 is an image obtained by photographing a circular zone plate with a camera in which the optical low-pass filter of Example 2 is arranged.

Explanation of symbols

1: Optical low-pass filter 2: Imaging optical system 4: Solid-state imaging device 5: Lens 8: Infrared cut filter 10: Convex portion 12: Sheet-like concavo-convex structure 14: Cover layer

Claims (3)

An optical low-pass filter,
A sheet-like concavo-convex structure formed of a first transparent resin and provided with a large number of concavo-convex portions having a height of 1 μm to 100 μm on the surface;
A cover layer formed of a second transparent resin covering the sheet-like uneven structure,
The sheet-like concavo-convex structure extends in the thickness direction of the first transparent resin layer, and the concavo-convex portion is periodically on the order of 80 nm to 1000 μm in a plane perpendicular to the thickness direction of the first transparent resin layer. Arranged in a grid,
The difference in refractive index between the first transparent resin and the second transparent resin is 0.001 to 0.4.
An optical low-pass filter characterized by that. A method for manufacturing an optical low-pass filter, comprising:
Disposing a first transparent resin layer on a smooth substrate;
Forming fine irregularities periodically arranged on the surface of the first transparent resin layer by photolithography;
An optical low-pass filter having a cover layer made of a second transparent resin having a refractive index different from that of the first transparent resin layer is formed on a smooth substrate so as to cover the surface of the first transparent resin layer. A step, and
An optical low-pass filter manufacturing method characterized by the above. A method for manufacturing an optical low-pass filter, comprising:
Applying a first transparent resin on a mold having fine irregularities formed thereon;
A translucent film is arranged on the first transparent resin, the active energy rays are irradiated from above the translucent film, the first transparent resin is polymerized and cured, and the concave and convex portions complementary to the concave and convex portions are surfaces. Forming a sheet-like concavo-convex structure formed on,
Separating the mold from the sheet-like uneven structure, and applying a second transparent resin to the surface of the sheet-like uneven structure;
Disposing a translucent film on the second transparent resin, and irradiating an active energy ray from above the translucent film to polymerize and cure the second transparent resin.
An optical low-pass filter manufacturing method characterized by the above.