JP6867148B2 - Optical filter and imaging optical system - Google Patents

Description

The present invention relates to an optical filter and an imaging optical system having an optical filter.

An image pickup element such as a CCD or CMOS is mounted on an image pickup optical system such as a camera, and an image is obtained by converting light incident on the image pickup element into an electric signal. The image pickup optical system is provided with an optical filter such as an aperture mechanism or an ND filter that adjusts the amount of light incident on the image pickup device according to the shooting conditions.

The light amount adjusting filter has a function of attenuating the transmittance substantially uniformly in the light wavelength band used for photographing, and can adjust the amount of light incident on the image sensor while maintaining color reproducibility. By using the optical adjustment filter, it is possible to reduce the hunting phenomenon that can occur by adjusting the amount of light only by the aperture mechanism and the deterioration of the image due to the diffraction of light, and to obtain a higher quality image.

An optical filter mounted on an imaging optical system such as a camera has a substantially uniform transmittance in a target light wavelength region, that is, a transmittance flatness is regarded as important, and as shown in Patent Document 1, it is on a substrate. Generally, a light absorbing layer made of a metal or a metal compound and a dielectric layer made of a metal oxide are formed in a laminated structure.

Japanese Unexamined Patent Publication No. 2003-43211

Here, in an optical filter such as a conventional ND filter, for example, the optical characteristics of the light absorption layer among the light absorption layer and the dielectric layer are not stable, and the light amount adjustment performance cannot be stably obtained. there were.

The present invention provides an optical filter and an image pickup device having a function of stably adjusting the amount of light.

In order to solve the above problems, the optical filter of the present invention includes a substrate having light transmission and an optical adjustment layer provided on at least one surface of the substrate, and the optical adjustment layer has light absorption characteristics. first and second light absorbing layer formed at least one light-absorbing material metal a, chosen from the group consisting of nitrides aN oxide AO and metal a metal a having a pre-Symbol metal a It has first and second intermediate layers formed of oxide BO of metal B, which is a different metal element.
The optical adjustment layer is laminated in the order of the first light absorption layer, the first intermediate layer, the second intermediate layer, and the second light absorption layer from the substrate side, and the oxidation number of the second intermediate layer is the first intermediate layer. It is characterized by being larger than the oxidation number of.
Further, in order to solve the above problems, the optical filter of the present invention includes a substrate having light transmittance and an optical adjustment layer provided on at least one surface of the substrate, and the optical adjustment layer is provided with light. The first and second light absorption layers formed of at least one light absorption material selected from the group consisting of metal A having absorption characteristics, oxide AO of metal A, and nitride AN of metal A, and the metal A. It has a first intermediate layer formed of an oxide BO of metal B, which is a metal element different from the above, and a second intermediate layer formed of a nitride BN of the metal B, and the optical adjustment layer is the substrate. It is characterized in that the first light absorption layer, the first intermediate layer, the second intermediate layer, and the second light absorption layer are laminated in this order from the side.

According to the present invention, it is possible to realize an optical filter and an image pickup device having a function of stably adjusting the amount of light.

The block diagram of the optical filter which concerns on this invention. The block diagram of the optical filter which concerns on Example 1. FIG. The figure which shows the spectral transmittance characteristic of the optical filter which concerns on design examples 1 to 3. The block diagram of the optical filter which concerns on Example 2. FIG. The figure which shows the spectral transmittance characteristic of the optical filter which concerns on design example 4. FIG. The block diagram of the optical filter which concerns on Example 3. FIG. The figure which shows the spectral transmittance characteristic of the optical filter which concerns on design example 5. The figure which shows the transmittance characteristic of an infrared cut film. The block diagram which shows the modification of the optical adjustment filter in Example 3. FIG. The figure which shows the transmittance characteristic of the infrared cut film in the modification of the optical adjustment filter of Example 3. FIG. The block diagram which shows the image pickup optical system using the optical filter which concerns on this invention.

Hereinafter, the structure of the optical filter according to the embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration diagram of an optical filter according to an embodiment of the present invention as an example.
In the optical filter of the present invention, an optical adjustment layer provided on at least one surface of a transparent transparent substrate at a desired light wavelength is formed of metal A, an oxide AO of metal A, and a nitride AN of metal A. A compound of an oxide BO or a nitride BN of a metal B, which is a metal element different from the metal A formed between the first and second light absorbing layers selected from the above and the first and second light absorbing layers. It is obtained by forming it with an intermediate layer having a multi-layer structure formed by.

In the present invention, among the intermediate layers having a multi-layer structure, the layer on the first light absorption layer side has a larger extinction coefficient in the visible light wavelength region than the layer on the second light absorption layer side, and , The film thickness is thin. Further, preferably, an antireflection layer is formed on the outermost layer of the optical filter.

Here, as described above, the optical adjustment layer in the present invention constitutes one optical adjustment layer by the first and second light absorption layers and the intermediate layer having a multilayer structure provided between them. For example, when a plurality of optical adjustment layers are provided on the substrate, the light absorption layer and the intermediate layer may be alternately laminated to form one optical adjustment layer with one light absorption layer and the intermediate layer. When a plurality of optical adjustment layers are provided, the intermediate layer may be a combination of a one-layer structure and a multi-layer structure (two or more layers).

In the present invention, one or a plurality of optical adjustment layers may be provided on at least one surface of the substrate to form an optical filter, but one or a plurality of optical adjustment layers are provided on both sides of the substrate, respectively. An optical filter may be configured. One or more optical adjusting layers and an antireflection layer are combined to form a light amount adjusting film.

The elements constituting the optical filter of the present invention will be described below.
(Transparent board)
As the transparent substrate used in the present invention, any substrate can be used as long as it is a transparent substrate in a desired light wavelength region. For example, substrates made of inorganic materials such as glass and crystal, polyester-based, norbornene-based, polyether-based, acrylic-based, styrene-based, PET (polyethylene terephthalate), PES (polyethersulfone) -based, polysulfone-based, and PEN (polyethylenena). Various synthetic resin substrates such as phthalate) type, PC (polycarbonate) type, and polyimide type can be used.

Synthetic resin substrates are more flexible, lighter, and have better workability than inorganic substrates such as glass, but are prone to deformation due to film stress and thermal stress, and characteristic changes due to moisture. Therefore, when using a synthetic resin substrate, it is desirable to use a material having high heat resistance (high glass transition temperature Tg), high flexural modulus, and low water absorption. For example, a polyimide-based or PES-based substrate is used as a highly heat-resistant substrate, PET is used as a substrate having a large flexural modulus, and norbornene-based is used as a low water-absorbing substrate. Further, if necessary, a substrate made of an organic-inorganic hybrid material, for example, a substrate having a silsesquioxane skeleton may be used.

In the present invention, the transparent substrate is a substrate having light transmission at least in the visible light wavelength, and even if a substrate having light absorption in the ultraviolet wavelength region or the infrared wavelength region is used, for example. Good. Examples of such a substrate include an ultraviolet absorbing substrate in which an ultraviolet absorber is kneaded into glass or resin, a dye or pigment having infrared absorption performance, or a metal ion typified by copper is kneaded into glass or resin. Examples include an infrared absorption substrate.

Further, the thickness of the substrate is preferably as thin as possible within the range where rigidity can be maintained, and specifically, about 20 μm to 1 mm and 25 μm to 400 μm are preferable in consideration of miniaturization and weight reduction. When a substrate having light absorption other than the transmission band formed by the light interference thin film laminate is used, the thickness of the base material is determined in consideration of the light absorption characteristics of the substrate.

(1st and 2nd light absorption layers)
The first and second light absorbing layers of the present invention are at least one light absorbing layer selected from the group consisting of a metal A having a light absorbing property, an oxide of the metal A (AO), and a nitride of the metal A (AN). Examples thereof include metal A such as Ti, Ni, Cr, Fe, Nb, and Ta, alloys, oxides, nitrides, and the like, as the light absorbing material.

The first light absorbing layer and the second light absorbing layer may be formed by using the same light absorbing material, but may be formed by different light absorbing materials. When the metal A is used as the first and second light absorption layers, it is preferable that the plasma frequency is higher than the frequency of light in the wavelength region in which light absorption is desired to be exhibited.

Here, the plasma frequency refers to the limit frequency at which the free electrons of the metal oscillate in plasma. When the plasma frequency is higher than the frequency of the light, it prevents the light from entering the metal and reflects it. On the contrary, when the frequency of light is higher than the plasma frequency, the light penetrates into the metal and is absorbed by the metal. Therefore, by selecting a material in which the plasma frequency of the metal A is higher than the frequency of light in the wavelength region in which light absorption is desired to be exhibited, an optical filter having higher transmittance and flatness in a desired region can be obtained. ..

When an oxide of metal A (AO) and a nitride of metal A (AN) are used as the first and second light absorption layers, the extinction coefficient of the first and second light absorption layers is 0.5 or more. Is preferable. Here, the extinction coefficient indicates how much the light is attenuated when the light is incident on the substance, and the larger this value is, the stronger the incident light is attenuated.

Here, as compared with metals and alloys, the oxide (AO) of the metal A or the nitride (AN) of the metal A has a smaller extinction coefficient. If the extinction coefficient of the first and second light absorption layers is too small, the number of layers and the film thickness required to attenuate the desired amount of light become thick, which causes warpage and cracks of the optical filter. is there. Further, the first and second light absorption layers are preferably layers made of an oxide of metal A (AO) or a nitride of metal A (AN). Since metal oxides or nitrides have a smaller extinction coefficient than metals, the film thickness of each layer can be kept thick to some extent.

Therefore, the degree of freedom in film design is increased, the stability of film thickness control of the light absorption layer is improved, and an optical filter having good spectral characteristics and good reproducibility of optical characteristics can be obtained. When the oxide of metal A (AO) or the nitride of metal A (AN) is used for the first and second absorption films, it is particularly preferable to use titanium oxide (TiOx 0 <x <2). is there. This is because TiOx has a relatively linear absorption characteristic in the visible region, and can be used as an optical filter having a flatter transmittance characteristic.

The first and second light absorption layers can be formed by various known methods such as vacuum deposition, ion plating method, and ion assist method.

(Middle layer)
The intermediate layer of the present invention is formed from a compound of an oxide BO of a metal B or a nitride BN, which is a metal element different from the metal A formed between the first and second light absorbing layers, and is, for example, Si. It is formed from oxides, nitrides or oxide nitrides such as Al, Mg, La, Zr, Ti, Nb and Ta. In the present invention, when the intermediate layer is formed by a multilayer structure, for example, a first intermediate layer and a second intermediate layer, the first intermediate layer and the second intermediate layer may be made of the same material, or may be different. Materials may be used.

The intermediate layer has a multi-layer structure. For example, when it is composed of two layers (first and second intermediate layers), the first intermediate layer is formed on the first light absorption layer, and the first intermediate layer is on the first intermediate layer. 2 Form an intermediate layer. Then, by forming the second light absorption layer on the second intermediate layer, one optical adjustment layer is formed.

In this case, the first intermediate layer is provided so that the extinction coefficient in the visible light wavelength region of the first intermediate layer is larger than the extinction coefficient in the visible light wavelength region of the second intermediate layer. At this time, the extinction coefficient of the compound forming the first intermediate layer and the extinction coefficient of the compound forming the second intermediate layer are defined to have a magnitude relationship at the same wavelength.

The intermediate layer may be provided in three or more layers. In that case, it is advantageous to reduce the difference in refractive index and improve the adhesion by using the compound forming each intermediate layer as a similar material.

For example, when the first intermediate layer and the second intermediate layer are laminated with aluminum oxide on the first light absorbing layer formed of an oxide of titanium oxide (TiO _{x), the oxidation forming the first intermediate layer is performed. The oxidation number of aluminum oxide (Al 2 Oz} ) forming the second intermediate layer is larger than the oxidation number of aluminum (Al ₂ O _y ), that is, it is formed so as to satisfy the condition of y <z. It is preferable that the second intermediate layer is _{formed so as to be, for example, Al 2} O ₃ , so that the extinction coefficient at the visible light wavelength is as small as possible.

For example, when the first intermediate layer is formed, the first intermediate layer is formed without introducing a reactive gas, and when the second intermediate layer is formed, the first intermediate layer is formed while sufficiently introducing a reactive gas such as oxygen. The extinction coefficient in the visible light wavelength region of the second intermediate layer becomes larger than the extinction coefficient in the visible light wavelength region of the second intermediate layer, and the extinction coefficient in the visible light wavelength region of the second intermediate layer becomes close to zero. By not introducing a reactive gas during the film formation of the first intermediate layer, it is possible to suppress fluctuations in the extinction coefficient of the first absorption layer during the film formation of the intermediate layer.

Here, if the extinction coefficient of the first intermediate layer is set to be larger than that of the second intermediate layer, the light absorption rate of the first intermediate layer becomes large, but in the present invention, a factor of fluctuation in the light absorption characteristics of the optical filter. The thickness of the first intermediate layer should be as thin as possible, preferably less than half the thickness of the second intermediate layer, and more preferably less than 1/4 of the thickness of the second intermediate layer. ..

That is, the first intermediate layer is provided so as to have an extinction coefficient larger than that of the second intermediate layer, the fluctuation of the extinction coefficient of the first light absorption layer due to the film formation of the second intermediate layer is suppressed, and in addition, the first intermediate By making the thickness of the layer as thin as possible to minimize the influence on the light absorption characteristics of the optical filter, and by providing the second intermediate layer so that the extinction coefficient of the second intermediate layer becomes substantially zero, the entire optical filter is provided. The light absorption characteristics can be determined by the first and second light absorption layers. That is, the first and second light absorption layers provide a stable function of adjusting the amount of light without being affected by the intermediate layer.

Further, the extinction coefficient of the first intermediate layer is preferably 0.1 or less. This is because if the extinction coefficient is larger than 0.1, the influence on the transmittance characteristic of the optical filter becomes large, which may lead to a significant deterioration of the transmittance characteristic.

Further, as described above, the first intermediate layer has a thinner film thickness than the second intermediate layer, and specifically, it is preferably 60 Å to 200 Å. If the film thickness is thinner than 60 Å, the first intermediate layer has a sea-island structure, and there is a risk that a sufficient layer may not be formed. Nitriding may not be sufficiently prevented. On the other hand, if it is thicker than 200 Å, the minute light absorption characteristic of the first intermediate layer in the visible light wavelength region may adversely affect the transmittance flatness of the optical filter.

The intermediate layer has a function for making the transmittance flatness of the optical filter flatter. The extinction coefficient of the light absorption layer is not always uniform in the visible light wavelength region. Therefore, in order to make the amount of light absorbed by the entire light absorption layer substantially uniform in the visible light wavelength region, light interference is caused at the interface between the light absorption layer and the intermediate layer, and light is transmitted or reflected under optimum conditions. There is a need.

Although it depends on the material of the light absorption layer and the required transmittance flatness, a film thickness of about 60 to 1500 Å is required as the intermediate layer in order to obtain optimum light interference at the interface between the light absorption layer and the intermediate layer. It becomes. As described above, since the first intermediate layer has a large extinction coefficient, if the film thickness of the intermediate layer is larger than 200 Å, a multilayer structure of the first intermediate layer and the second intermediate layer is used, and the film thickness of the first intermediate layer is changed. It is preferably 200 Å or less.

Here, it is the light absorption layer that the intermediate layer is a compound of the oxide BO or the nitride BN of the metal B, which is a metal element different from the metal A formed between the first and second light absorption layers. This is to effectively have a difference in refractive index from the intermediate layer.

As described above, it is necessary to utilize the light interference effect between the light absorption layer and the intermediate layer in order to improve the transmittance flatness of the optical filter. However, when the light absorption layer and the intermediate layer are made of the same metal element, This is because there is a possibility that a sufficient refractive index difference cannot be obtained, and an effective optical interference effect may not be obtained.

Specifically, the first and second intermediate layers can be formed by various known methods such as vacuum deposition, ion plating method, and ion assist method. For example, the first and second intermediate layers are formed using metal B or metal oxide BO as a starting material, the first intermediate layer is formed without introducing a reactive gas such as oxygen, and the second intermediate layer is sufficiently oxygen. Alternatively, a reactive gas composed of nitrogen is introduced to form a film.

The first and second intermediate layers are preferably compounds made of metal oxide BO or metal nitride BN formed from the same metal B. By forming from the same metal, the difference in refractive index between the first and second intermediate layers can be made very small, and the transmittance characteristics of the optical filter deteriorate due to optical interference with the first and second intermediate layers. Can be suppressed.

Further, by making the first and second intermediate layers a compound made of a metal oxide BO made of the same metal B or a metal nitride BN, it is possible to strengthen the adhesion between the first and second intermediate layers. It becomes.

(Anti-reflective layer)
An antireflection layer is preferably formed on the outermost layer of the optical filter of the present invention. The antireflection layer is made _{of a material having a small refractive index such as SiO 2} and Mg F _2, and is formed so that the optical film thickness is about λ / 4 when the central wavelength of the wavelength region for suppressing reflection is λ. .. Here, the optical film thickness is represented by the product of the refractive index and the physical film thickness. The antireflection layer can be formed by various known methods such as a vacuum deposition method, an ion plating method, and an ion assist method. The antireflection layer may be formed of a plurality of thin films having different refractive indexes, if necessary. Even when formed from a plurality of thin films, the optical film thickness of the outermost layer is preferably about λ / 4. Here, about λ / 4 means a film thickness of about 0.7 to 1.3 λ / 4.

<Example 1>
FIG. 2 shows a block diagram of the optical filter according to this embodiment. The optical filter of this embodiment has a configuration in which a light amount adjusting film 8 composed of a plurality of optical adjusting layers and an antireflection layer is formed on both sides of a transparent substrate. Table 1 shows a design example of the optical filter according to the first embodiment as a design example 1.

The optical filter 11 of Design Example 1 has a transparent substrate made of a PET substrate having a thickness of 75 μm, _{first and second light absorption layers made of TiO x} (0 <x <2), and Al _{2 Oy} (first oxide). _{) And a second} intermediate layer made of Al _{2 Oz} (second oxide) are formed.

Here, y <z, and the _{extinction coefficient of Al 2} O _{y at} the visible light wavelength is larger than the extinction coefficient _{of Al 2} O _{z at the visible light wavelength.} Further, an antireflection layer made of MgF2 is formed on the outermost layer.

In the light amount adjusting film 8 of this embodiment, the light absorbing layers of all the optical adjusting layers are TiO _x , the first intermediate layer is the first compound Al ₂ O _y , and the second intermediate film is the second compound Al _{2 Oz.} ing. FIG. 3 shows the spectral transmittance characteristics of the optical filter of Design Example 1.

The method of manufacturing the optical filter of this embodiment will be described. The optical filter of Example 1 was produced by a vacuum vapor deposition method. First, the PET substrate is set on the film forming jig, and the PET substrate is attached to the vapor deposition dome so that the film forming surface of the PET substrate faces the vapor deposition material. The vapor deposition dome is put into the vapor deposition chamber and exhausted. When the vacuum inside the vapor deposition chamber reaches a desired degree of vacuum, for example, ^{about 1.0 × 10 -3} Pa, the film formation of the first light absorption layer is started.

The first light absorption layer uses titanium oxide as a starting material, and the titanium oxide stored in the crucible is heated by an electron beam to be deposited on a PET substrate. Titanium oxide is deposited on the PET substrate as a _{TiO x film.} In this embodiment, a reactive gas such as oxygen was not introduced at the time of forming the first light absorption layer, but it may be introduced as appropriate if necessary.

Subsequently, after the first light absorption layer is formed with a desired film thickness, the first intermediate layer is then formed. Aluminum oxide is used as a starting material for the first intermediate layer. Aluminum oxide, which is the starting material filled in the crucible, is heated with an electron beam and vapor-deposited without introducing oxygen gas.

When the film is formed without introducing oxygen gas, the oxygen deficiency of aluminum oxide, which is a starting material generated by the energy of the electron beam, is not sufficiently complemented until the PET substrate is reached, and the film is formed. By not introducing oxygen gas at the time of forming the first intermediate layer, it is possible to suppress the fluctuation of the extinction coefficient of the first absorbing layer and form the intermediate layer.

Further, when the film formation of the first intermediate layer is completed, the film formation of the second intermediate layer is performed. As with the first intermediate layer, aluminum oxide is used as a starting material for the second intermediate layer. In the second intermediate layer, aluminum oxide, which is a starting material, is heated by an electron beam, and oxygen gas is introduced so that ^{the pressure in the chamber becomes 3.0 × 10 -3 Pa to form a film.}

By forming the film in this way, the oxygen deficiency of the starting material aluminum oxide generated by the energy of the electron beam can be made into a layer sufficiently complemented by the oxygen introduced into the chamber.

In this embodiment, the pressure at the time of forming the second intermediate layer is 3.0 × 10 ^-3 Pa, but the pressure is not limited to this, and the optimum oxygen gas is used according to the film forming rate and the pressure at the start of film formation. The amount to be introduced may be used. Here, the first intermediate layer has a thinner film thickness than the second intermediate layer.

Both the first intermediate layer and the second intermediate layer are oxides of aluminum, but the first intermediate layer is in a state of oxygen deficiency and has weak absorption in the visible light wavelength region, so that the first intermediate layer has weak absorption. This is because if the layer is a thick film, the transmittance flatness of the light amount adjusting film may be deteriorated.

Subsequently, when the film formation of the second intermediate layer is completed, the TiO _x which is the second absorption layer is formed. The second absorption layer can be formed in the same manner as the first absorption layer. The light absorption layer and the intermediate layer are sequentially formed in the same manner as described above, and when the formation of the ninth layer is completed, the antireflection layer is formed. It is not necessary to provide such an antireflection layer.

In this example, MgF ₂ was formed as an antireflection layer. The antireflection layer heats a crucible filled with magnesium fluoride, which is a starting material, with an electron beam _{to form MgF 2} with a desired film thickness. After the film formation of the antireflection layer is completed, venting is performed, the pressure in the vapor deposition machine chamber is set to normal pressure, and the PET substrate is taken out. Further, a light amount adjusting film composed of a light absorbing layer, an intermediate layer and an antireflection layer is similarly formed on the opposite surface of the PET substrate.

In particular, when a resin substrate or the like is used as the transparent substrate as in this embodiment, it is preferable to provide light intensity adjusting films on both sides of the transparent substrate, and the light intensity adjusting films provided on both sides of the substrate are designed to be substantially the same. Is more preferable. With such a configuration, even if a resin substrate having a relatively low rigidity is used as the transparent substrate, an optical filter having a small warp or waviness can be obtained.

In this embodiment, the light amount adjusting film of the same design is formed on both sides of the transparent substrate, but the light amount adjusting film may be formed on only one side of the transparent substrate, or different films on each surface. It may be used as a design light amount adjusting film. Further, the light amount adjusting film may be formed only on one surface of the substrate.

Further, a base layer may be provided at the interface between the transparent substrate and the light amount adjusting film. As the base layer, a metal oxide is preferable, and for example, SiO ₂ , Al ₂ O ₃ , TIO _{2 and the} like are suitable. The base layer preferably does not affect the transmittance flatness of the light amount adjusting film, and preferably has low light absorption in the visible light wavelength region.

Specifically, it is preferable that the oxidation number is about the same as that of the second intermediate layer, that is, the metal oxide is substantially completely oxidized. By providing these base layers, the adhesion between the transparent substrate and the light amount adjusting film can be improved. Further, particularly when a transparent substrate made of resin having a higher water absorption rate than that made of glass is used as in this embodiment, water vapor, oxygen, etc. move from the transparent substrate to the first layer by providing the base layer. Can also be expected to have the effect of suppressing.

In Design Example 1, all the intermediate layers have a multi-layer structure, but as shown in Design Example 2 in Table 2, for example, a part of the intermediate layers may be composed of one layer. Intermediate layer between the design example In 2 fourth layer and the sixth layer of the light absorbing layer is made only Al ₃ O _y.

In Design Example 2, the film thickness required for the fifth intermediate layer is sufficiently thin, and light absorption due to oxygen deficiency in the fifth intermediate layer does not affect the flatness of the light amount adjusting film. This is because it is thick. FIG. 3 shows the spectral transmittance characteristics of the optical filter of Design Example 2.

In the design example 1, both the metal oxide of the first intermediate layer and the second intermediate layer _(Al 2 _{O y} or Al2O _z) and the but, as shown in the design example 3, for example the first intermediate layer first compound SiO _n, a second intermediate layer as the second compound Si ₃ n _m, one of the metal oxides (the first oxide), may be the other as a metal nitride (second nitride). Also in this case, the extinction coefficient in the visible light wavelength region of the first intermediate layer is larger than the extinction coefficient in the visible light wavelength region of the second intermediate layer, and the first intermediate layer is thinner than the second intermediate layer. It is a layer.

It is preferable that the Si ₃ N _m of the second intermediate layer is formed so as to be in a sufficiently nitrided state, that is, Si ₃ N _4, and the extinction coefficient in the visible light wavelength region is substantially zero. Here, SiO _n is obtained by heating silicon oxide with an electron beam using silicon oxide as a starting material and forming a film without introducing a reactive gas, and the nitride film SiN _m uses silicon as a starting material and has electrons. It is obtained by heating silicon, which is a starting material, with a beam and introducing nitrogen gas so that ^{the pressure in the chamber becomes 8.0 × 10 -3 Pa to form a film.}

By forming the film in this way, it is possible to suppress fluctuations in the extinction coefficient of the first light absorption layer due to the film formation of the intermediate layer, and it is possible to obtain an optical adjustment film having stable optical characteristics. FIG. 3 shows the spectral transmittance characteristics of the optical filter of Design Example 3 (Table 3).

The light amount adjusting film may have a region in which the transmittance changes stepwise or continuously in the plane direction. Optical filters having stepwise different transmittance densities can be produced, for example, by using a plurality of film forming masks having different openings when forming an optical adjusting film.

The film-forming mask determines the range of the thin-film film formed on the transparent substrate, and the opening of the film-forming mask is the film-forming region on the transparent substrate. By depositing multiple times using a plurality of film forming masks having different openings, the area formed in each vapor deposition process is different, so that a light amount adjusting film having a stepwise different transmittance can be obtained. ..

An optical filter having a continuously changing transmittance can be used, for example, to continuously change the film thickness of the light absorbing layer, which mainly determines the transmittance of the light amount adjusting film, in the plane direction, or to form a light absorbing layer. It can be produced by adjusting the amount of reactive gas introduced at the time and continuously changing the oxidation number or the nitrided number in the plane direction.

When the transmittance changes stepwise or continuously, it is preferable that a region in which the light absorption layer is not formed, that is, a substantially transparent region exists in the optical filter. The light amount adjusting film whose transmittance changes stepwise or continuously is not limited to the above-mentioned method, and can be produced by various already known methods.

<Example 2>
FIG. 4 shows a block diagram of the optical filter according to this embodiment. The optical filter of this embodiment has a structure in which a light amount adjusting film 8 is formed on one surface of the transparent substrate 1 and an antireflection film 9 is formed on the other surface. Table 4 shows a design example of the optical adjustment filter according to the second embodiment as a design example 4.

In the optical filter of this embodiment, an optical adjustment layer composed of a light absorption layer and an intermediate layer is formed on one surface of a glass substrate (B270i: manufactured by Schott AG) having a plate thickness of 400 μm, which is a transparent substrate, and the other. It has a structure in which an antireflection film composed of a plurality of layers is formed on the surface. The optical filter of Design Example 4 has the spectral transmittance characteristics as shown in FIG. 5, and the spectral transmittance in the visible light wavelength region is substantially uniform.

The optical adjustment film of Design Example 4 _{uses TiO x} and Ti as the light absorption layer. In Design Example 4, the light amount adjusting film is required to attenuate light only on one side of the transparent substrate. Therefore, in Design Example 4, Ti, which is a metal film, is used as a part of the light absorption layer. Ti has a _{larger extinction coefficient than TiO x,} and by using Ti, the total film thickness of the light absorption layer can be reduced.

Ti is formed by using metallic titanium as a vapor deposition material, irradiating a crucible filled with metallic titanium with an electron beam, and forming a film without introducing a reactive gas such as oxygen gas at the time of film formation. The other light absorption layers, TiO _x , the first and second intermediate layers, were formed under the same conditions as in Example 1.

In Design Example 4, only a part of the light absorption layer is a metal film, but all the layers of the light absorption layer may be a metal film, or a metal film may not be used. Further, the metal elements forming the first absorption layer and the second absorption layer may be different.

Here, the antireflection film will be described. In Design Example 4, the antireflection film is provided to suppress surface reflection on the surface of the transparent substrate on which the light amount adjusting film is not formed. The antireflection film is formed by laminating a plurality of thin films having different refractive indexes, and in Design Example 4, TiO ₂ and SiO ₂ are alternately laminated in four layers.

In Design Example 4, TiO ₂ and SiO ₂ are used, but the present invention is not limited to MgF ₂ , SiO, Si ₃ H ₄ , Al ₂ O ₃ , MgO, LaTIO ₃ , ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O. _{Various materials such as 5} can be used in any combination.

The outermost surface layer of the antireflection film is preferably made of a material having a low refractive index, and although SiO ₂ is used in _{Example 4, MgF 2} can also be preferably used. In this embodiment, the antireflection film is composed of a plurality of layers in order to minimize the influence on the transmittance flatness of the light amount adjusting film.

The single-layer antireflection film has the lowest reflectance at the central wavelength, and the reflectance gradually increases as the distance from the central wavelength increases. That is, in the case of an antireflection film formed from a single layer, the transmittance of the optical filter decreases due to the influence of the antireflection film as the distance from the center wavelength of the antireflection film increases, which may lead to deterioration of the transmittance flatness. .. On the other hand, by forming the antireflection film into a laminated structure composed of a plurality of layers, reflection can be suppressed in a wider wavelength range as compared with a single layer antireflection film, and the transmittance flatness of the optical filter is significantly deteriorated. Can be suppressed.

In this embodiment, metal oxides are used for the first intermediate layer and the second intermediate layer, but as in Design Example 2, a single intermediate layer may be included, or as in Design Example 3, the first A metal oxide may be used for the intermediate layer, and a metal nitride may be used for the second intermediate layer. As in Example 1, the light amount adjusting film in this example may also have a region in which the transmittance changes stepwise or continuously.

<Example 3>
FIG. 6 shows a block diagram of the optical filter according to this embodiment. The optical filter of this embodiment has a structure in which a light amount adjusting film is formed on one surface of a transparent substrate and an infrared cut film is formed on the other surface. Table 5 shows a design example of the optical filter according to the third embodiment as a design example 5.

In the optical filter of this embodiment, an infrared absorption glass (NF50T: manufactured by Asahi Glass Co., Ltd.) having a plate thickness of 400 μm, which substantially transmits visible light and has an absorption function in the infrared light wavelength region, is used as a transparent substrate 1, and is an infrared absorption glass. A light amount adjusting film 8 having an optical adjusting layer composed of a light absorbing layer and an intermediate layer is formed on one surface, and an infrared cut film composed of a laminate of a plurality of thin films having different refractive coefficients on the other surface. 10 is formed. The spectral characteristics of the optical filter of Design Example 5 are shown in FIG.

In the optical filter of Design Example 5, the transmittance in the visible light wavelength region is attenuated substantially uniformly by the light amount adjusting film, and at the same time, the transmission of light in the near infrared wavelength region is blocked by the infrared cut film.

The method of manufacturing the optical filter of this embodiment will be described. The infrared absorbing glass is set on the film forming jig, and a light amount adjusting film is formed on one surface of the infrared absorbing glass by the same method as in Example 1. Next, an infrared cut film is formed on the surface opposite to the surface on which the light amount adjusting film of the infrared absorbing glass is formed.

Here, the infrared cut film will be described. The infrared cut film is a plurality of thin film laminated structures having different refractive indexes. Light interference is expressed by utilizing the difference in refractive index of the thin films, and the thin films are laminated so as to reflect light in the infrared wavelength region. As the thin film material, MgF ₂ , SiO ₂ , SiO, Si ₃ H ₄ , Al ₂ O ₃ , MgO, LaTIO ₃ , ZrO ₂ , TiO ₂ , Nb ₂ O ₅ , Ta ₂ O _{5 and the} like can be used.

The infrared cut film has a refractive index of about λ / 4, specifically about 0.7 to 1.3 λ / 4, assuming that the central wavelength in the cut wavelength region formed by the infrared cut film is λ. The basic configuration is a structure in which a plurality of inorganic thin films having different rates are laminated. However, in order to reduce the ripple in the transmission band, a layer far away from λ / 4 may be provided. In particular, it is effective to form a plurality of layers for reducing ripple at the interface with the transparent substrate.

The infrared cut film has the spectral characteristics as shown in FIG. 8, has a transition wavelength region that transitions from the transmission region to the cut region, and red having a transmittance of 50% in this transition wavelength region. There is an outer half wavelength. The infrared absorption glass used in this example also has an infrared half-value wavelength, but the infrared half-value wavelength formed by the infrared cut film is longer than the infrared half-value wavelength of the infrared absorption glass. It is preferable to be on the side.

Compared with the infrared cut film, the infrared half-value wavelength of the infrared absorbing glass is less likely to vary in the manufacturing method. Therefore, it is possible to obtain a stable optical filter having an infrared half-value wavelength by configuring the infrared absorption glass to determine the infrared half-value wavelength.

In the infrared cut film, the larger the difference in the refractive index of the thin films, the smaller the number of layers required to obtain the desired spectral characteristics. Therefore, it is preferable to use a combination having the largest difference in the refractive index as much as possible. An infrared cut film was formed from _{SiO 2} and TiO _2. This combination is used because it is the combination in which the difference in refractive index is substantially the largest.

The infrared cut film is prepared as follows. The surface opposite to the surface on which the optical adjustment layer of the infrared absorbing glass is formed is set in the vapor deposition dome so as to correspond to the vapor deposition material, and exhausted until ^{the pressure in the deposition chamber reaches 1.0 × 10 -3 Pa.} I do. When the pressure in the chamber ^{reaches 1.0 × 10 -3} _{Pa, silicon oxide, which is the starting material of the SiO 2} layer filled in the crucible, is heated by an electron beam to be vapor-deposited.

At this time, plasma is generated in the vapor deposition chamber, and the vapor deposition component is formed so as to reach the infrared absorbing glass through the plasma atmosphere. When the SiO ₂ layer has a predetermined thickness, the TiO ₂ layer is then formed. Titanium oxide is used as the starting material for the TiO ₂ layer, and the titanium oxide filled in the pit is heated with an electron beam to generate plasma in the vapor deposition chamber and pass through the plasma atmosphere in the same way as when _{the SiO 2 layer is formed.} A film is formed so that the deposited components reach the infrared absorbing glass. In this way, the desired number of laminated SiO ₂ layers and the TiO ₂ layers are alternately laminated.

In Design Example 5, the infrared cut film was laminated on one surface, but as shown in FIG. 9A, the infrared cut film 10a and the infrared cut film 10b were divided into the respective surfaces of the transparent substrate 1. A film may be formed. When the infrared cut film 10 is divided and formed into a film, as shown in FIG. 10, the cut wavelengths of the infrared cut films 10a and 10b formed on the respective surfaces of the transparent substrate are different, and at least a part thereof is formed. It is preferable to have optical characteristics that overlap. By forming in this way, it is possible to efficiently cut the infrared light wavelength, and it is possible to eliminate a region in which the cutting function is insufficient in the infrared wavelength region.

Further, although the light amount adjusting film is formed on one surface of the transparent substrate in Design Example 5, the light amount adjusting film 8a and the light amount adjusting film 8b may be formed on both sides of the transparent substrate as shown in FIG. 9B. .. At this time, the light amount adjusting films formed on both sides of the transparent substrate are combined to form a desired amount of light so as to be attenuated.

When the infrared cut film and the light amount adjusting film are provided on the same surface of the substrate, the optical filter having an antistatic function can be obtained by forming the light amount adjusting film on the infrared cut film. The light amount adjusting film has a conductive light absorption layer (metal or metal oxide or nitride), and even if it has an antireflection layer, the surface resistivity is about 10 × 10 ¹⁰ Ω / □ or less. This is because it has a sufficient antistatic function. Therefore, it is possible to obtain an optical filter to which foreign matter and the like are less likely to adhere.

On the other hand, by forming an infrared cut film on the light amount adjusting film, the optical characteristics can be stabilized for a long period of time. In the light amount adjusting film, the light absorption layer made of metal or metal oxide or nitride comes into contact with oxygen or water vapor in the atmosphere to promote oxidation, and the transmittance may increase with time. By forming the cut film on the light amount adjusting film, the first layer is suppressed from coming into contact with oxygen and water vapor, and the change in transmittance is less likely to occur.

Further, it is preferable that the infrared cut film including the end face is covered with the light amount adjusting film, or the light amount adjusting film including the end face is covered with the infrared cut film. By doing so, the long-term stability of the above-mentioned antistatic function or optical characteristics can be further improved.

The stress direction of the light amount adjusting film and the infrared cut film may differ depending on the forming method. Therefore, when the light amount adjusting film and the infrared cut film are formed on the same surface of the transparent substrate, the adhesion at the interface between the light amount adjusting film and the infrared cut film may become a problem. In such a case, it is preferable to provide an adhesion layer at the interface between the light amount adjusting film and the infrared cut film. As the adhesion layer, a stress relaxation layer that relaxes the stress difference between the light amount adjusting film and the infrared cut film is optimal, and a layer in which the stress changes continuously is preferable.

Examples of such a stress relaxation layer include a layer in which the oxidation number continuously changes in the film thickness direction and a layer in which the film density continuously changes. The layer in which the oxidation number continuously changes in the film thickness direction can be obtained, for example, by forming a plurality of vapor-deposited materials at the same time and changing the mixing ratio thereof. Further, the layer whose film density changes continuously can be obtained, for example, by continuously changing the pressure in the vapor deposition chamber at the time of film formation. Further, the stress relaxation layer may be a metal film.

The metal film is a film made of metal bonds, and has excellent ductility as compared with a film made of covalent bonds or ionic bonds, and can be deformed relatively freely. Therefore, by arranging a metal film between the light amount adjusting film and the infrared cut film having different stress directions, the stress energy of the light amount adjusting film and the infrared cut film is used for deformation of the metal film, and the light amount is adjusted. Peeling at the interface between the film and the infrared cut film can be suppressed.

Further, when the light amount adjusting film and the infrared cut film are provided on the same surface of the transparent substrate, an interference adjusting layer may be introduced between the light amount adjusting film and the infrared cut film. The interference adjusting layer is a layer for adjusting the interference conditions between the light amount adjusting film and the infrared cut film, and adjusts the ripple generated by laminating the light amount adjusting film and the infrared cut film.

For example, TiO ₂ can be preferably used as the interference adjusting film, but in addition to this, MgF ₂ , SiO ₂ , SiO, Si ₃ H ₄ , Al ₂ O ₃ , MgO, LaTIO ₃ , ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O _{5 and the} like can also be preferably used, and may be configured as either a single layer or a laminated body.

The infrared cut film may have a function of cutting the transmission in the ultraviolet region. The ultraviolet cut function is provided by an ultraviolet cut film obtained by laminating thin films having different refractive indexes so that the optical film thickness of each layer is approximately λ / 4, when the wavelength of the ultraviolet region to be cut is λ. Brought to you.

As the ultraviolet cut film, the same material as the infrared cut film can be used, and the larger the difference in refractive index between the thin films, the smaller the number of layers. For example, _{the combination of the SiO 2} layer and the TiO ₂ layer is suitable because it is a combination having substantially the largest difference in refractive index.

In this embodiment, metal oxides are used for the first intermediate layer and the second intermediate layer of the light amount adjusting film, but a single intermediate layer may be included as in Design Example 2, or as in Design Example 3. A metal oxide may be used for the first intermediate layer and a metal nitride may be used for the second intermediate layer. As in Example 1, the light amount adjusting film may have a region in which the transmittance changes stepwise or continuously with respect to the surface direction of the substrate.

FIG. 11 shows an imaging optical system such as a camera. The incident light passes through the light amount adjusting device 20 formed of the lenses 12, 15 to 17, diaphragm blades 13a and 13b, the optical filter 11, etc., and is incident on the image sensor 18 composed of a CCD or CMOS sensor and converted into an electric signal. It is visualized.

The position information of the diaphragm blades 13a and 13b is transmitted to the light amount control unit 19, and the light amount control unit 19 uses the light amount information from the image sensor 18 and the position information of the diaphragm blades 13a and 13b to obtain the optimum opening. , 13b is driven.

The optical filter 11 is inserted into the optical path by the optical filter driving unit 14 when the aperture blades 13a and 13b are equal to or less than a certain opening, and suppresses harmful effects such as flare caused by the apertures of the diaphragm blades 13a and 13b becoming too small. ..

The optical filter produced in Examples 1 to 3 is inserted into the optical filter 11, and is appropriately inserted into the optical path according to the amount of light at the time of photographing.

Here, when the optical filter of Example 3 is used, it is preferable that the optical filter is arranged so that the light amount adjusting film exists between the infrared cut film having the infrared half-value wavelength and the image pickup device. By arranging in this way, the occurrence of ghost can be suppressed.

Note that ghosts are generated by multiple reflections of light in the imaging optical system, and the formula for simply obtaining the ghost intensity caused by the optical filter is (transmittance of optical filter) × (reflectance of optical filter) × ( It is represented by the sensitivity of the image pickup element). In the vicinity of the infrared half-value wavelength of the infrared cut film, the wavelength in the infrared large region of transmittance and reflectance is included, and the wavelength in the limit region that can be recognized by the human eye is included, so that the influence of ghost becomes particularly large.

When a light amount adjusting film is arranged between the infrared cut film and the image pickup element, the light transmitted through the infrared cut film is attenuated by the light amount adjustment film, and further incident on the light amount adjustment film reflected by the image pickup element or the like. This is because the light reaches the infrared cut film after being attenuated by the light amount adjusting film, so that the reflection caused by the infrared cut film can be efficiently attenuated.

Further, it is preferable to use infrared absorbing glass for the transparent substrate and to provide infrared absorbing glass between the infrared cut film having an infrared half-value wavelength and the image sensor. The infrared absorbing glass has a light absorption function in the infrared half-value wavelength region of the infrared cut film, and can effectively attenuate light that causes ghosting in the vicinity of the half-value wavelength of the infrared cut film.

Since the optical filter according to the present invention has good transmittance flatness, the amount of light reaching the image sensor can be appropriately attenuated without disturbing the color balance of the subject.

1 Transparent substrate 2 First and second light absorption layers 3 First intermediate layer 4 Second intermediate layer 5 Intermediate layer 6 Optical adjustment layer 7 Antireflection layers 8, 8a, 8b Light amount adjustment film 9 Antireflection films 10, 10a, 10b Infrared cut film

11 Optical filter 12, 15-17 Lens 13a, 13b Aperture blade 14 Optical filter drive unit 18 Image sensor 19 Light amount control unit 20 Light amount adjustment device

Claims (11)

A substrate with light transmission and
An optical adjustment layer provided on at least one surface of the substrate is provided.
The optical adjustment layer is formed of first and second light absorbing materials selected from the group consisting of metal A having light absorption characteristics, oxide AO of metal A, and nitride AN of metal A. has an absorbent layer, and first and second intermediate layer formed of an oxide of Al is different from the metal element and the metal a,
The optical adjustment layer, said from the substrate side first light-absorbing layer, the first intermediate layer is stacked directly on top of each layer in the order of the second intermediate layer and the second light-absorbing layer, the second the oxidation number of the intermediate layer is much larger than the oxidation number of the first intermediate layer,
An optical filter characterized in that the thickness of the second intermediate layer is thicker than the thickness of the first intermediate layer. The optical filter according to claim 1, wherein the extinction coefficient of the first intermediate layer at a visible wavelength is larger than the extinction coefficient of the second intermediate layer at a visible wavelength. The optical filter according to claim 1 or 2, wherein the light absorbing material is an oxide AO or a nitride AN. The metal A is, Ti, Ni, Cr, Fe , Nb, optical filter according to any one of claims 1 to 3, characterized in that Ru Ta der. The optical filter according to any one of claims 1 to 4, wherein the thickness of the first intermediate layer is 60 Å to 200 Å. An oxide layer formed of an oxide of Al is provided on one surface of the substrate and on the optical adjustment layer, and the thickness of the oxide layer is equal to or less than the thickness of the first intermediate layer. The optical filter according to any one of claims 1 to 5, wherein the oxidation number of the oxide layer is smaller than the oxidation number of the second intermediate layer. A plurality of layers of the optical adjustment layer are provided on one surface of the substrate.
The optical filter according to claim 6, characterized in that between the optical adjustment layer formed of a plurality of layers, the oxide layer is Ru provided. Claims 1 to 6 , wherein the optical adjustment layer has a first optical adjustment layer provided on one surface of the substrate and a second optical adjustment layer provided on the other surface of the substrate. The optical filter according to any one item. An underlayer formed of an oxide BO of a metal B, which is a metal element different from the metal A, is provided on one surface of the substrate.
The optical filter according to any one of claims 1 to 8 , wherein the optical adjustment layer is laminated on the base layer. The optical filter according to any one of claims 1 to 9, wherein an infrared cut film is formed on at least one surface of the substrate. An image pickup apparatus comprising the optical filter according to any one of claims 1 to 10 and an image pickup element that captures an image that has passed through the optical filter.

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