JP2007316107A - Infrared light cut filter, method of manufacturing the same and optical component having infrared cut filer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared cut filter and a method of manufacturing the same in which the attraction of dust due to static charge is prevented, the complication of processing steps is avoided and the cost is reduced, and an optical component having the infrared cut filter. <P>SOLUTION: In the infrared cut filter, a conductive anti-reflection film 12 comprising two layers of a conductive layer comprising a transparent conductive film and a low refractive index dielectric layer 15 having a refractive factor smaller than that of a high refractive index layer is formed on an alternative layer 13 formed by alternately laminating two layers of the high refractive index layer and a low refractive index layer each having different refractive index. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an infrared cut filter, a method for manufacturing the same, and an optical component having the infrared cut filter.

Currently, in an optical system of a digital camera, an optical low-pass filter is generally disposed on the front surface of an image sensor in order to reduce the generation of moire images by the image sensor.
However, unlike human visual sensitivity, the sensitivity of the image sensor is high in the near infrared region, so in order to correct this, a multilayer infrared cut filter is generally formed on the surface of the optical low-pass filter. Yes.
In general, the optical low-pass filter is often placed immediately before the image sensor, and the multilayer infrared cut filter on the surface of the optical low-pass filter has a low reflectance and a high transmittance in the visible region to prevent ghosting. Is required.
Furthermore, since the optical low-pass filter is often disposed immediately before the image sensor, dust adhesion to the surface of the optical low-pass filter causes a point-like defect on the photographed image. Is required to prevent the adhesion of dust.

In recent digital cameras, the optical low-pass filter is often placed immediately before the image sensor due to the miniaturization, and the adhesion of dust to the surface of the optical low-pass filter has a point-like defect on the photographed image. Will occur.
Therefore, it is required to prevent dust from adhering to the surface of the optical low-pass filter.
However, an optical low-pass filter usually used in a digital camera often uses a dielectric material such as quartz or lithium niobate as its material, and the surface is often charged to attract dust.
Furthermore, the multilayer infrared cut filter formed on the surface of the optical low-pass filter is often composed of a dielectric multilayer film and has no antistatic effect. For this reason, there is a problem that dust or the like in the surrounding atmosphere is attracted by electrostatic force due to charging of the optical low-pass filter surface.
For this reason, for example, in Patent Document 1, as a camera and an image sensor unit used therefor, it is proposed that dust attached to the surface is dropped by vibration.
Further, for example, Patent Document 2 proposes an antistatic low-reflection type cathode ray tube and a sol-gel method for providing a conductive antireflection film as a manufacturing method thereof, and Patent Document 3 proposes a plastic optical article having a multilayer antireflection film. Has been.
JP 2003-348401 A JP-A-8-279341 JP-A-9-197103

However, as in Patent Document 1 in the above-described conventional example, the method of dropping attached dust by vibration requires a mechanism for generating vibration, which leads to complication of the apparatus and an increase in price.
In the above conventional example,
(1) An antistatic effect and an antireflection effect are obtained, but there is no effect of an infrared cut filter for correcting visibility,
(2) Defects such as scratches are likely to occur in subsequent processes due to insufficient film hardness and adhesion.
There is a problem.
Therefore, in order to give the optical low-pass filter both the visibility correction effect and the antistatic effect, it is necessary to form an antireflection film in a separate process after the multilayer infrared cut filter is formed. Will bring about cost and cost increase.

In view of the above problems, an object of the present invention is to provide an infrared cut filter formed of a dielectric multilayer film that can prevent dust from being adsorbed by charging, and an optical component having the infrared cut filter. .
In addition, according to the present invention, when forming a two-layer antireflection film having an antistatic effect on an infrared cut filter made of a dielectric multilayer film, it is possible to avoid complication of processing steps and to reduce costs. It aims at providing the manufacturing method of an infrared cut filter.

In order to solve the above-described problems, the present invention provides an infrared cut filter configured as follows, a method for manufacturing the same, and an optical component having the infrared cut filter.
The infrared cut filter of the present invention comprises a conductive layer made of a transparent conductive film and a high refractive index layer on an alternating layer obtained by alternately laminating two thin films of a high refractive index layer and a low refractive index layer having different refractive indexes. A conductive antireflection film comprising two layers of a low refractive index dielectric layer having a low refractive index is formed. Thereby, it is possible to prevent dust from being adsorbed by charging.
The infrared cut filter of the present invention is characterized in that the low refractive index dielectric layer is made of a material selected from SiO ₂ or MgF ₂ .
Moreover, the infrared cut filter of the present invention is characterized in that the transparent conductive film is formed using ITO and has a physical film thickness of 20 nm or more and 100 nm or less. Thereby, the transmittance | permeability in a visible region and the improvement of an antistatic effect can be aimed at.
The infrared cut filter of the present invention is characterized in that the low refractive index dielectric layer is formed on the outermost surface using MgF ₂ and has a physical film thickness of 30 nm or more and 200 nm or less. This can improve the antireflection effect and the antistatic effect in the visible range.
Moreover, the manufacturing method of the infrared cut filter of the present invention includes:
A conductive layer made of a transparent conductive film is formed on the infrared cut filter made of a dielectric multilayer film, and an antireflection film made of a low refractive index dielectric film selected from SiO ₂ or MgF ₂ is formed on the conductive layer. An infrared cut filter manufacturing method comprising:
The method includes forming the transparent conductive film and the low refractive index dielectric film by vacuum film formation in the same vacuum chamber as the infrared cut filter made of the dielectric multilayer film. As a result, it is possible to avoid complication of processing steps and to reduce costs.
The infrared cut filter manufacturing method of the present invention is characterized in that the film is formed in a heated vacuum atmosphere of 200 ° C. or higher when the vacuum film is formed in the vacuum chamber. Thereby, film | membrane hardness and adhesive force can be improved.
Moreover, the optical component of this invention has the infrared cut filter manufactured by the infrared cut filter in any one of the above-mentioned, or the manufacturing method of the infrared cut filter described in any one of the above.

ADVANTAGE OF THE INVENTION According to this invention, the infrared cut filter formed of the dielectric multilayer film which can prevent the adsorption | suction of the dust by electrical charging, and the optical component which has this infrared cut filter are realizable.
Moreover, the manufacturing method of the infrared cut filter which can avoid complexity of a process and can aim at cost reduction is realizable.

Next, an embodiment of the present invention will be described with reference to FIG.
In the present embodiment, a transparent conductive layer is formed on a dielectric multilayer infrared cut filter 13 in which thin films composed of two high-refractive index layers and low-refractive index layers having different refractive indexes on the transparent dielectric substrate 11 are alternately stacked. It can be configured to include a two-layer antireflection film 12 having an antistatic effect comprising the film 14 and the low refractive index dielectric film 15.
When actually used as an optical component, the transparent conductive film 14 can be grounded by a component mounting frame or the like. The ground 16 shown in FIG. 1 schematically represents a ground by a metal frame.

In such a configuration, since the transparent conductive film 14 is normally insulated by the low refractive index dielectric film 15, the charge accumulated on the surface of the low refractive index dielectric film 15 flows through the transparent conductive film 14. There is no antistatic effect.
However, since the low-refractive-index dielectric film 15 is a thin film, it has been confirmed by actual experience and analysis that some moisture in the atmosphere is taken in due to the presence of many lattice defects and impurities.
In the present invention, as a result of optimizing the film thickness and processing conditions of the low-refractive-index dielectric film 15 from experimental results, it was confirmed by experiments that an antistatic effect is obtained when the optical film thickness is 200 nm or less.
This is considered to be due to the leakage of the electric charge stored on the surface of moisture or the like slightly present in the low refractive index dielectric film 15 to the earth 16 through the transparent conductive film 14.

Next, as a method of forming the transparent conductive film 14, wet film formation such as a sol-gel method or a coating method may be used.
However, such a method has problems such as (1) poor film thickness control accuracy, (2) low film strength, and (3) the need for additional steps. Usually, the dielectric multilayer infrared cut filter 13 is usually formed by a vacuum film forming method such as sputtering or vacuum deposition in order to obtain optical performance. Therefore, in the present invention, these problems are solved by forming the transparent conductive film 14 and the low refractive index dielectric film 15 by vacuum film formation in the same vacuum chamber as the dielectric multilayer infrared cut filter 13.

Next, the material of the transparent conductive film used in this embodiment will be described.
The transparent conductive film 14 is required to have (1) low resistance, (2) low film absorption and high transmittance, optically and physically stable properties, and the like.
As a result of examining transparent conductive film materials in the present invention, it was confirmed by experiments that an ITO film is suitable.
FIG. 2 shows optical constants of the ITO film obtained by this experiment. In order to reduce the resistance value of the transparent conductive film 14, it is desirable that the film thickness is large.
However, on the other hand, the presence of slight film absorption in the visible region is confirmed in FIG. 2 from FIG. 2, and when the thickness of the transparent conductive film 14 is increased, the transmittance in the visible region decreases. This is confirmed by an optical simulation using the optical constants shown in FIG.

In the present embodiment, as a result of considering the above, when ITO is selected as the material of the transparent conductive film 14, the following film thickness is desirable.
That is, in order to obtain 10 ¹⁰ to 10 ¹² Ω or less as the surface resistance value necessary for obtaining the antistatic effect, the physical film thickness is preferably 20 nm or more, ideally 40 nm or more. The thickness is preferably 100 nm or less, ideally 60 nm or less.

Next, the low refractive index dielectric film 15 used in the present embodiment will be described.
The low refractive index dielectric film 15 formed on the transparent conductive film 14 needs to have a refractive index lower than that of the transparent conductive film 14 in order to obtain an antireflection effect in terms of optical performance.
As materials satisfying this condition, SiO ₂ and MgF ₂ are desirable from the viewpoint of optical stability, physical strength, and ease of processing. In particular, MgF ₂ has a lower surface energy than SiO ₂ and has antifouling properties. It is more desirable because of its superiority.
In addition, when MgF ₂ is used as the film thickness of the low refractive index dielectric film 15, the physical film thickness is set to 200 nm or less, ideally 100 nm or less in order to obtain an antistatic effect. It is desirable.
Furthermore, as a result of performing an optical simulation to optimize the antireflection effect in the visible range, it was found that the physical film thickness is preferably 30 nm or more, ideally 60 nm or more and 120 nm or less.

Next, the film formation temperature in the processing step in this embodiment will be described.
In general, it is known that the film hardness and adhesion of a dielectric thin film obtained by vacuum film formation tend to be stronger as the substrate temperature is higher to some extent.
For example, it has been known from past experience that when the above-described low refractive index dielectric film is formed by depositing MgF ₂ by a vacuum deposition method, sufficient film hardness cannot be obtained at a heating temperature of 150 or less.
Therefore, in an actual processing step, processing in a heated vacuum atmosphere of 200 ° C. or higher is more desirable for improving film hardness and adhesion.
Thus, in the present invention, the antistatic effect can be further imparted to the surface layer while maintaining the performance of the infrared cut filter for normal visibility correction.

Finally, an example of this embodiment will be specifically described.
FIG. 3 shows a film configuration as an example of the present embodiment, and FIG. 4 shows a spectral characteristic diagram (transmittance and reflectance) obtained by the film configuration.
In this embodiment, a quartz plate is used as a substrate, Al ₂ O ₃ is used as an undercoat layer, and ITO is 50 nm and MgF ₂ is formed on a 23-layer infrared cut filter composed of alternating TiO ₂ / SiO ₂ layers. A 25-layer film having a thickness of 87.6 nm was formed. Thereby, an optical component having a sufficient optical performance such as a transmittance of 98% and a reflectance of 1% in the visible region can be obtained.
Further, FIG. 5 shows the results of evaluating the effects of antistatic and dust adhesion according to the above configuration example of the present embodiment.
In this evaluation method, an infrared cut filter having an antistatic effect according to the present embodiment is formed on one side of the substrate, and a conventional infrared cut filter is formed on the remaining portion, and the state of adhesion of the charged resin powder is checked. It is an evaluation of the difference.
According to the above configuration example of the present embodiment, it can be confirmed that the surface potential and the adhesion of dust are improved in the portion provided with conductivity on the surface as compared with the non-treated portion.

By using the infrared cut filter of the present embodiment as described above for an optical low-pass filter formed on a substrate such as quartz crystal lithium niobate, the adhesion of dust to the surface due to charging can be prevented while maintaining optical performance. Can be planned.
By using the optical component having the above configuration in a digital camera or the like, it is possible to further improve image quality while suppressing an increase in price.
The present embodiment described above is merely an example, and the present invention is not limited by these.

Examples of the present invention will be described below.
[Example 1]
As Example 1 of the present invention, FIG. 6 shows a film design example, and FIG. 7 shows a spectral characteristic diagram. In this embodiment, a quartz plate is used as a substrate, Al ₂ O ₃ is used as an undercoat layer, ITO is 100 nm on a 23-layer infrared cut filter composed of alternating TiO ₂ / SiO ₂ layers, and MgF ₂ is 75. This is an example of a 25-layer film having a thickness of 9 nm.
As the thickness of the ITO film increases, the transmittance in the visible short wavelength region is slightly reduced, but the optical performance is sufficient with a reflectance of 1%.
From this example, it can be confirmed that limiting the thickness of the ITO film is effective.

[Example 2]
As Example 2 of the present invention, FIG. 8 shows a film design example, and FIG. 9 shows a spectral characteristic diagram. In this embodiment, lithium niobate is used as a substrate, Al ₂ O ₃ is used as an undercoat layer, ITO is 100 nm on a 23-layer infrared cut filter composed of alternating TiO ₂ / SiO ₂ layers, and MgF ₂ is 75%. This is an example of a 25-layer film formed to a thickness of 9 nm.
As the thickness of the ITO film increases, the transmittance in the visible short wavelength region is slightly reduced, but the optical performance is sufficient with a reflectance of 1%.
From this example, it can be confirmed that the present invention is effective for a ferroelectric substrate such as lithium niobate.

[Example 3]
As Example 3 of the present invention, a usage example of an optical component to which the present invention is applied is shown in FIG.
FIG. 10 schematically shows the structure of a digital single-lens reflex camera. A low-pass filter 91 is arranged on the front surface of the image sensor 92.
Here, a multilayer infrared cut filter according to the present invention is formed on the surface of the low-pass filter 91.
According to the present embodiment, dust adhesion due to the antistatic effect can be reduced, and the image quality formed by the image sensor 92 can be improved.

(Comparative Example 1)
As a comparative example 1 for the present invention, FIG. 11 shows a film configuration of a normally used 23-layer dielectric multilayer infrared cut filter, and FIG. 12 shows a spectral characteristic diagram.
A normal dielectric multilayer infrared cut filter has sufficient optical performance, but has no antistatic effect, and a problem arises in that dust is adsorbed by surface charging during use.

(Comparative Example 2)
As Comparative Example 2 for the present invention, the film configuration is shown in FIG. 13 for the example in which only the ITO 50 nm single layer as the transparent conductive film is provided on the surface of the dielectric multilayer infrared cut filter of Comparative Example 1 above, and the spectral characteristic diagram. Is shown in FIG.
As described above, an antistatic effect can be obtained by simply providing a transparent conductive film on the surface of a normal dielectric multilayer infrared cut filter, but the optical characteristics are significantly deteriorated.

  As described above, the implementation of the present invention can reduce the adhesion of dust due to charging of the surface of the optical component, thereby contributing to the improvement of the image quality of a digital camera or the like.

1 is a representative diagram illustrating a configuration of the present invention. The optical constant of the ITO film used in the present invention. 1 is a film configuration of the best example for carrying out the present invention. The spectral characteristic figure of the best Example for implementing this invention. The figure which shows the result evaluated about the effect of invention. The figure which shows the film | membrane structure in Example 1 of this invention. The figure which shows the spectral characteristic in Example 1 of this invention. The figure which shows the film | membrane structure in Example 2 of this invention. The figure which shows the spectral characteristics in Example 2 of this invention. FIG. 6 is a diagram for explaining an example of using an optical component in Embodiment 3 of the present invention. The figure which shows the film structure of the comparative example 1. The figure which shows the spectral characteristic of the comparative example 1. FIG. The figure which shows the film structure of the comparative example 2. The figure which shows the spectral characteristics of the comparative example 2.

Explanation of symbols

11: Transparent dielectric substrate 12: Two-layer conductive antireflection film 13: Dielectric multilayer infrared cut filter 14: Transparent conductive film 15: Low-refractive-index dielectric film 16: Ground by holding metal frame 91: The present invention is implemented Optical low-pass filter 92: Image sensor

Claims (7)

  A low refractive index dielectric having a lower refractive index than that of a conductive layer made of a transparent conductive film and the high refractive index layer on an alternating layer obtained by alternately laminating two thin films of a high refractive index layer and a low refractive index layer having different refractive indexes. An infrared cut filter comprising a two-layer conductive antireflection film formed with a body layer. The infrared cut filter according to claim 1, wherein the low refractive index dielectric layer is made of a material selected from SiO ₂ or MgF ₂ .   The infrared cut filter according to claim 1, wherein the transparent conductive film is formed using ITO, and has a physical film thickness of 20 nm or more and 100 nm or less. The low refractive index dielectric layer is formed on the outermost surface using MgF ₂ and has a physical film thickness of 30 nm or more and 200 nm or less. Infrared cut filter. A conductive layer made of a transparent conductive film is formed on the infrared cut filter made of a dielectric multilayer film, and an antireflection film made of a low refractive index dielectric film selected from SiO ₂ or MgF ₂ is formed on the conductive layer. An infrared cut filter manufacturing method comprising:
A method of manufacturing an infrared cut filter, comprising: forming the transparent conductive film and the low refractive index dielectric film by vacuum film formation in the same vacuum chamber as the infrared cut filter made of the dielectric multilayer film. .   6. The method for manufacturing an infrared cut filter according to claim 5, wherein the film is formed in a heated vacuum atmosphere of 200 [deg.] C. or higher when vacuum film formation is performed in the vacuum chamber.   An optical component comprising the infrared cut filter according to any one of claims 1 to 4 or the infrared cut filter manufactured by the method for manufacturing an infrared cut filter according to any one of claims 5 to 6.

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