JP7475129B2 - Light shielding member and imaging device using the light shielding member - Google Patents

Description

The present invention relates to a light blocking member such as an aperture plate mounted in an imaging system such as a camera, and an imaging device.

Conventionally, cameras and other imaging devices are provided with an aperture plate to adjust the amount of light that enters the imaging element. The aperture plate allows light to pass through the main optical path and prevents other light from entering the imaging element. However, light that passes through the main optical path is reflected by a lens or optical filter, and this reflected light is further reflected by the aperture plate and enters the imaging element, causing ghosts and flares.

Patent Document 1 discloses a black anti-reflective film that reduces reflectance by forming a black coating on a substrate and then forming an anti-reflective film on the black coating. Patent Document 2 discloses a film in which TiN and SiN are alternately laminated on a SUS substrate.

JP 2001-350003 A JP 2012-163756 A

However, in Patent Document 1, the black coating with light absorbing function is a single layer, and merely provides low reflection for a specific wavelength, and since the black coating is made of resin, there is a problem with environmental stability. Cited Document 2 does not mention environmental stability focusing on the light absorbing layer.

The present invention can provide a light-shielding member with excellent environmental stability due to the composition of the light-absorbing layer.

In order to solve the above problems, the present invention provides a light-shielding member including a light-damping film in which a dielectric layer and a light-absorbing layer are alternately laminated on a light-shielding substrate having an opening, the light-shielding member comprising:
The light-attenuating film has a plurality of the light-absorbing layers, each of which includes a first light-absorbing layer made of a metal compound and a second light-absorbing layer made of a metal compound provided at a position farther from the light-shielding substrate in the stacking direction than the first light-absorbing layer, and an oxidation number of a metal in the second light-absorbing layer is larger than an oxidation number of a metal in the first light-absorbing layer.

The configuration of the present invention makes it possible to provide a light-shielding member with excellent environmental stability due to the composition of the light-absorbing layer.

FIG. 2 is a cross-sectional view of a light-shielding member according to the present invention. 3A and 3B are cross-sectional views showing the configuration of each layer of a light-shielding member according to an embodiment. 4 shows reflectance characteristics of a light blocking member according to an embodiment. An optical system according to the present invention. FIG. 2 is a cross-sectional view of a light-shielding member according to the present invention. A cross-sectional view of a light absorbing laminate according to Example 2 and a graph showing the oxidation number of the light absorbing layer A cross-sectional view of a light absorbing laminate according to Example 3 and a graph showing the oxidation number of the light absorbing layer A cross-sectional view of a light absorbing laminate according to a modified example of Example 3 and a graph showing the oxidation number of the light absorbing layer A cross-sectional view of a light absorbing laminate according to Example 4 and a graph showing the oxidation number of the light absorbing layer A graph comparing the amount of change in optical density in a high-temperature, high-humidity test in Examples 2 to 4 and Comparative Examples 2 to 4

An embodiment of the present invention will be explained with reference to Figures 1 to 4.

As shown in FIG. 1, the light-shielding member of the present invention has a light-damping film 5 formed on a light-shielding substrate 1, in which a dielectric layer 2 and a light-absorbing layer 3 are alternately laminated. If an anti-reflection film 4 having a lower refractive index than the dielectric layer 2 and the light-absorbing layer 3 is provided on the light-damping film 5, a low-reflection configuration is easily achieved. The multiple light-absorbing layers include a first light-absorbing layer of a metal compound and a second light-absorbing layer of a metal compound provided at a position farther from the light-shielding substrate in the stacking direction than the first light-absorbing layer. The oxidation number of the metal of the second light-absorbing layer is larger than the oxidation number of the metal of the first light-absorbing layer, thereby increasing environmental stability. In addition, other metal compound layers, etc. may be provided between the above-mentioned layers.

(substrate)
The light-shielding substrate 1 in the present invention has a light-shielding function against visible light wavelengths (400 to 700 nm). Here, the light-shielding function refers to an optical density of 2.0 or more (transmittance of about 1% or less), and the light-shielding substrate 1 preferably has an optical density of 2.5 or more (transmittance of about 0.32% or less). By increasing the optical density of the light-shielding substrate 1, it is possible to increase the degree of freedom in the film design of the light-damping film 5 formed on the light-shielding substrate 1. Note that, unless otherwise specified in the present invention, the optical density and transmittance are values at a light wavelength of 550 nm.

The light-shielding substrate 1 may be, for example, a resin sheet in which a pigment or dye with light absorption in the visible light range, such as carbon black, is dispersed, a resin sheet in which a thin film with visible light absorption function, such as a metal, is formed on the resin sheet, or a metal sheet, but a metal sheet is most preferable in terms of light-shielding properties and rigidity. Metal substrates such as stainless steel, aluminum alloys, and copper alloys can be suitably used as the metal sheet. From the viewpoint of reducing the size and weight of the optical system in which the light-shielding member is mounted, it is preferable that the thickness of the light-shielding substrate 1 is as thin as possible while maintaining rigidity, for example, 100 μm or less is preferable, and about 10 to 50 μm is even more preferable.

The light-shielding substrate 1 preferably has a surface roughness sufficient to scatter light. By causing scattering by the light-shielding substrate 1, the regular reflectance of the light-shielding member can be reduced, and the occurrence of strong ghosts and flares can be suppressed. Furthermore, by having the light-shielding substrate 1 have a surface roughness of at least a certain level, the area of the interface between the light-shielding substrate 1 and the light-damping film 5 can be increased, improving adhesion. The surface roughness can be obtained, for example, by performing a process such as shot blasting or etching.

In the present invention, the light-shielding substrate 1 has an opening. The opening can be formed by punching or etching, but considering the precision of the opening diameter and the shape of the opening end, it is preferable to form the opening by etching.

(Light attenuation film)
Next, the light attenuating film 5 will be described. The light attenuating film 5 of the present invention has a structure in which dielectric layers 2 and light absorbing layers 3 are alternately laminated. By using such a laminated structure, it is possible to utilize the optical interference effect and to effectively absorb light in the light absorbing layers 3 in a wide wavelength range of the target wavelengths (visible light wavelengths), thereby enabling lower reflection than before in this range.

The dielectric layer 2 is a film formed of a metal compound, and may be, for example, MgF ₂ , or may be a metal oxide, metal nitride, or the like. The dielectric layer 2 is preferably one having high gas barrier properties, and is preferably, for example, Al ₂ O ₃ , SiO ₂ , or the like. Here, the dielectric layer 2 is preferably a stoichiometric metal compound layer. The stoichiometric metal compound refers to a metal compound that has completely reacted with oxygen, nitrogen, fluorine, or the like. These metal compounds are characterized in that they are poorly reactive and have little change in optical properties due to changes over time, etc., since they have already been sufficiently oxidized, nitrided, and fluorinated. Here, the stoichiometric metal compound in the present invention refers to a composition in which oxygen, nitrogen, fluorine, or the like is contained in 90% or more of the stoichiometric composition relative to the corresponding stoichiometric composition. For example, the stoichiometric composition of aluminum oxide is Al ₂ O ₃ , and the stoichiometric metal compound in the present invention is Al ₂ Oy (y≧2.7).

The light absorbing layer 3 is a film formed of a metal compound having absorption in visible light wavelengths, and for example, an oxide or nitride made of Ti, Ni, Cr, Fe, Nb, Ta, or an alloy thereof can be used. Here, the light absorbing layer 3 is preferably a substoichiometric metal compound, and more preferably a substoichiometric metal oxide or a substoichiometric metal nitride. In general, substoichiometric metal oxides or substoichiometric metal nitrides have a large extinction coefficient compared to the corresponding stoichiometric metal oxides and stoichiometric metal nitrides. This makes it possible to reduce the film thickness of the light absorbing layer 3. Note that when a metal layer is used as the light absorbing layer 3, although the extinction coefficient is large, it is difficult to achieve a sufficiently low reflectance as a light blocking member due to its high reflectance.

In the embodiment of the present invention, substoichiometric refers to a state in which oxygen and nitrogen, or the total of them, are deficient by 10 to 70% with respect to the corresponding stoichiometric composition. For example, in the case of titanium oxide, the stoichiometric composition is _TiO2 , and the substoichiometric composition is TiOx (0.6≦x≦1.8). If oxygen and nitrogen, or both, are deficient by more than 30% with respect to the stoichiometric composition, the optical properties become close to those of metal, making it difficult to achieve low reflectance. On the other hand, if oxygen and nitrogen, or the total of them, are contained by more than 90% with respect to the stoichiometric composition, it becomes difficult to obtain sufficient light absorption.

By the way, substoichiometric metal compounds have higher chemical reactivity than the corresponding stoichiometric metal compounds. For this reason, it is preferable that the light absorbing layer 3, which is a substoichiometric metal compound, is sandwiched between the dielectric layer 2, which is a stoichiometric metal compound. By adopting such a configuration, it is possible to suppress chemical reactions (mainly oxidation) of the light absorbing layer 3, and it is possible to stabilize the reflectance characteristics of the light attenuating film 5. The film thickness of the dielectric layer 2 is a film thickness that can maintain the protective function of the light absorbing layer 3, and is preferably 60 Å or more, and more preferably 80 Å or more.

The light absorbing layer 3 may have layers with substantially the same oxidation number or nitridation number within the layer, or may have layers with different oxidation numbers or nitridation numbers continuously or stepwise. The light absorbing layer 3 has different optical properties such as refractive index and extinction coefficient, and when the same physical film thickness is formed, the wavelength dependency of the transmittance may tend to be different. For example, in the case of titanium oxide, in the case of a TiO layer, when the physical film thickness is 200 Å, the transmittance tends to gradually decrease toward the short wavelength side (400 nm side) of the visible light wavelength. In the case of a Ti ₂ O ₃ layer, when the physical film thickness is 200 Å, the transmittance also tends to decrease toward the long wavelength side (700 nm side) of the visible light wavelength. That is, TiO and Ti ₂ O ₃ have wavelength-dependent characteristics with different tendencies in the transmittance characteristics of the visible light wavelength. As a result, by using, for example, both a TiO layer and _{a Ti2O3} layer in the light absorbing layer 3, it becomes easy to reduce the wavelength dependency of the transmittance in the visible light wavelength as the light attenuation film 5, and the degree of freedom in film design for realizing low reflection in this wavelength region increases. In order to make the oxidation number or nitridation number in the light absorbing layer 3 different, a method of adjusting the oxidation number of the starting material for each layer or adjusting the ratio of air, oxygen, nitrogen, etc. introduced during film formation can be used.

When the oxidation number or nitridation number is approximately the same in each light absorbing layer 3, a method for reducing the wavelength dependency of the transmittance of the light attenuating film 5 at visible light wavelengths can be, for example, a method of making the light absorbing layer a mixed layer of TiO and Ti ₂ O _3. In this way, it is possible to reduce the wavelength dependency of the transmittance at visible light wavelengths in each layer of the light absorbing layer. For example, when a mixed layer of TiO and Ti ₂ O ₃ is used, the oxidation number of the starting material may be adjusted to an arbitrary oxidation number, the ratio of oxygen introduced during film formation may be adjusted, or, for example, TiO and Ti ₂ O ₃ may be simultaneously formed by a two-source evaporation method.

When the oxidation number or nitridation number is made different for each layer of the light absorbing layer 3, it is preferable that the oxidation number or nitridation number of the light absorbing layer closest to the substrate side is the smallest among the light absorbing layers. In general, the smaller the oxidation number or nitridation number, the higher the light absorption, and when a substrate having a high reflectance such as a metal is used for the light-shielding substrate 1, the reflected light of the substrate can be effectively absorbed. On the other hand, among the light absorbing layers forming the light-damping film 5, it is preferable that the oxidation number or nitridation number of the light absorbing layer closest to the surface layer is the largest. In general, as the oxidation number or nitridation number increases, the reflection of the light absorbing layer tends to decrease. In other words, by adopting such a configuration, the reflection of the light-shielding substrate 1 can be effectively absorbed while effectively suppressing the reflection as the light-shielding member 10. The light absorbing layers present between the light absorbing layer closest to the light-shielding substrate 1 and the light absorbing layer closest to the surface layer of the light-damping film 5 may have substantially uniform oxidation numbers and nitridation numbers in each layer, or may have different oxidation numbers and nitridation numbers, or may change continuously, for example, so that the oxidation number and nitridation number gradually increase toward the surface layer.

On the other hand, by making the oxidation number or nitridation number of each light absorbing layer approximately equal, the optical constants of the light absorbing layers can be made the same for each layer, which has the advantage of making film design easier.

In this embodiment, the light absorbing layer 3 is described using TiO and Ti ₂ O ₃ , but it is not limited thereto, and any material can be used. In addition, when forming a light absorbing layer (TiOx: x<1) having a smaller oxygen ratio than TiO in the light absorbing layer 3, for example, Ti may be used as a starting material and oxygen may be introduced while the film is formed, or a method of intentionally obtaining oxygen deficiency by irradiating high energy at a level that causes oxygen dissociation during film formation with TiO as a starting material can be used. On the other hand, when forming a light absorbing layer (TiOx: 1.5<x) having a larger oxygen ratio than Ti ₂ O ₃ , for example, Ti ₄ O ₇ may be selected as a starting material, or for example, Ti ₂ O ₃ may be used as a starting material and oxygen may be introduced while the film is formed.

As shown in FIG. 5, the light-shielding member of the present invention is a light-absorbing laminate 6 formed of at least a first light-absorbing layer 33a, a second light-absorbing layer 33b, and a dielectric layer 2, which are provided on a light-shielding substrate 1 and have oxidation numbers that increase in the stacking direction from the light-shielding substrate 1 side. The light-absorbing layers 33a and 33b constituting the light-absorbing laminate 6 are made of metal oxide (MxOy), and the difference in absolute value of the oxidation numbers between the first light-absorbing layer 33a and the second light-absorbing layer 33b is smaller than the value given by formula 1 when MxOy is a saturated oxide.

((y/x)-1)/((y/x)+1) .....Equation 1

In addition, it is preferable to form an anti-reflection film 4 on the outermost layer of the light absorbing laminate 6, which is the farthest from the light-shielding substrate 1, to form a low-reflectivity light-damping film 5.

Metals and metal oxides generally tend to be less susceptible to oxidation as their oxidation number increases. For example, in titanium oxide, TiO is less susceptible to oxidation than Ti, and Ti ₂ O ₃ is more susceptible to oxidation than TiO. That is, in consideration of the stability of optical properties after film formation, it is advantageous for the light absorbing layer to have a larger oxidation number. However, as described above, if the oxidation number is large, sufficient light absorption cannot be ensured, and the film thickness of the light absorbing layer becomes thicker or the number of layers required increases, which increases the risk of cracks and the like occurring. Therefore, the light absorbing laminate 6 of the present invention is configured so that the oxidation number of the light absorbing layer on the side opposite to the substrate side, which is susceptible to oxidation from the atmosphere, is larger than the oxidation number of the light absorbing layer on the light-shielding substrate side, which is less susceptible to oxidation from the atmosphere. That is, when the light absorbing layers forming the light absorbing laminate are arranged in order from the light-shielding substrate side to the first light absorbing layer 33a and the second light absorbing layer 33b, the second light absorbing layer 33b has a larger oxidation number. By configuring in this way, it is possible to obtain a light absorbing laminate 6 with excellent environmental stability without excessively increasing the film thickness and number of layers. Furthermore, the difference in oxidation number between the first light absorbing layer 33a and the second light absorbing layer 33b constituting the light absorbing laminate 6 is smaller than the value given by formula 1 when the metal oxide (MxOy) used in the light absorbing layer is a saturated oxide. For example, in the case of titanium oxide, the saturated oxide is _TiO2 , and the value of formula 1 is 0.333. Furthermore, it is more preferable that the difference in oxidation number between the first light absorbing layer 33a and the second light absorbing layer 33b is 0.2 or less.

Here, it is preferable that the interface between the light-shielding substrate 1 and the light-damping film 5 is a dielectric layer 2. If the chemicals used in forming the openings or modifying the surface of the light-shielding substrate 1 remain in the light-shielding substrate 1, a relatively highly reactive light-absorbing layer 3 (substoichiometric compound layer) may cause a chemical reaction at the interface between the light-shielding substrate 1 and the light-damping film 5, which may cause changes in optical properties and a decrease in adhesion. However, by making the interface between the light-shielding substrate 1 and the light-damping film 5 a dielectric layer 2 (stoichiometric compound layer) with low reactivity, these effects can be minimized. In particular, when the surface of the light-shielding substrate 1 is roughened and the interface area between the light-shielding substrate 1 and the light-damping film 5 is large, it is effective to make the interface a chemically stable dielectric layer 2.

In the present invention, the light attenuation film 5 has a laminated structure of six or more layers. By configuring it to have six or more layers, it is possible to ensure a certain number of laminated layers of the light absorbing layer 3, and the film thickness of each layer of the light absorbing layer 3 can be thinned, and a film configuration in which the light absorbing layer 3 effectively absorbs light by utilizing the interference of light can be obtained. In the present invention, the film thickness of each layer of the light absorbing layer 3 is preferably 350 Å or less. If the film thickness of each layer of the light absorbing layer 3 becomes thick, the difference in composition (oxidation number) in the layer between the initial film formation and the later film formation is likely to become large, and the optical characteristics are likely to vary from the design value, making it difficult to obtain stable optical characteristics. It is preferable that the light absorbing layer 3 has a film thickness of 30 Å or more. If the light absorbing layer 3 is less than 30 Å, it may become a sea-island structure, and light may not be absorbed uniformly in the formed region. In addition, if the light absorbing layer 3 does not form a layer, optical interference with the dielectric layer 2 is not expressed, and the light absorbing layer 3 cannot effectively absorb light. In addition, it is preferable that the light attenuation film 5 of the present invention has a laminated number of 24 layers or less. By limiting the number of layers to 24 or less, the thickness of the light-damping film 5 does not become too thick, and the light-shielding member 10 can be prevented from becoming thicker than necessary. More preferably, the light-damping film 5 has a number of layers of 14 or less. The thickness of the light-damping film 5 is preferably 1 μm or less, and more preferably 0.5 μm or less. If the thickness of the light-damping film 5 is about 1 μm or less, when the light-shielding member 10 is placed in the optical system, it can be used suitably without impairing the freedom of lens design or the miniaturization of the optical system.

In the present invention, in order to sufficiently absorb the reflection of the light-shielding substrate 1 and achieve low reflectivity as the light-shielding member 10, it is preferable that the optical density of the light-damping film 5 is 0.9 or more (transmittance 12.5% or less), and more preferably, the optical density is 1.5 or more (transmittance 3.2% or less). In addition, it is preferable that the optical density of the light-damping film 5 is 3.0 or less. If an attempt is made to increase the optical density of the light-damping film 5 more than necessary, the film thickness of the light-damping film 5 will be large, which is contrary to the aim of making the imaging device in which the light-shielding member 1 is mounted small and lightweight, and also makes it easier for the light-shielding substrate 1 to warp or undulate due to the stress of the film.

To achieve low reflectance in the light attenuating film 5, it is preferable that the optical thickness of the light absorbing layer 3, which is the closest to the surface of the light attenuating film 5, is about 0.01 to 0.1 when the central wavelength of the wavelength range that achieves low reflectance is 550 nm, and that the optical thickness of the dielectric film 2, which is the outermost layer of the light attenuating film 5, is about 0.01 to 0.1. Here, the optical thickness is expressed as the product of the refractive index and the physical thickness.

The light attenuation film 5 is preferably formed on both sides of the light-shielding substrate 1. By forming the light attenuation film 5 on both sides of the light-shielding substrate 1, when the substrate is mounted in an optical system, low reflection can be achieved for light other than the main light path, while low reflection can also be achieved for light that passes through the main light path, is reflected by a lens or an image sensor, and is incident on the light-shielding member 10. Furthermore, by forming the light attenuation film 5 on both sides of the light-shielding substrate 1, the light attenuation film 5 is easily attached to the opening end, and reflection at the opening end can be effectively suppressed. In addition, when the light attenuation film 5 is formed on both sides of the light-shielding substrate 1, it is preferable that the film thickness of each side is approximately the same, and further, it is preferable that the film thickness of the dielectric layer 2 and the light absorption layer 3 is approximately the same, and most preferably, the film configuration of each side is approximately the same. With such a configuration, even if a light-shielding substrate 1 with a thin plate thickness is used, warping and waviness can be reduced.

(Anti-reflection coating)
Next, the anti-reflection film 4 will be described. In the present invention, the anti-reflection film 4 is preferably made of a low refractive index material, such as SiO ₂ or MgF _2. When the anti-reflection film 4 is made of a single layer, it is formed so that the optical thickness is about λ/4 when the central wavelength of the wavelength region that realizes low reflection is λ, together with the optical thickness of the dielectric layer 2, which is the outermost layer of the light attenuation film 5. When the anti-reflection film 4 has a laminated structure of multiple thin films with different refractive indexes, the outermost layer of the anti-reflection film 4 is the layer with the smallest refractive index among the layers that form the anti-reflection film 4, and its optical thickness is about λ/4. In the present invention, about λ/4 refers to a thickness of about (0.7×λ/4) to (1.3×λ/4). In the examples described later, Al ₂ O ₃ is used as the dielectric layer 2 and MgF ₂ is used as the anti-reflection film 4, but both the dielectric layer 2 and the anti-reflection film 4 may be made of SiO ₂ as long as the conditions of the refractive index difference and film thickness are satisfied. When the antireflection film 4 made of a dielectric material is formed, the antireflection film 4 may be formed adjacent to the light absorbing layer 3. In this case, the antireflection film 4 is preferably a stoichiometric metal compound.

(Production method)
A method for manufacturing the light-shielding member according to the present invention will be described. The light-shielding member 10 of the present invention is formed by forming a light-damping film 5 and an anti-reflection film 4 on a light-shielding substrate 1 by a vapor phase deposition method. Here, a manufacturing method using a vacuum deposition method among vapor phase deposition methods will be described, but the manufacturing method is not limited to the vacuum deposition method, and various other known methods such as a sputtering method, an ion plating method, and an ion-assisted method can also be used for manufacturing.

The light-shielding substrate 1 with an opening formed by etching or the like is set on a film-forming jig, which is attached to a deposition dome so that the film-forming surface faces the deposition source. Next, the deposition dome is put into a deposition chamber and evacuated. When the interior of the deposition chamber reaches a desired degree of vacuum, for example, about 1.0×10 ⁻³ Pa, the first step of forming the first dielectric layer is performed. Specifically, the starting material for the dielectric layer filled in the crucible is heated by an electron beam and evaporated onto the light-shielding substrate 1. When the dielectric layer formed on the light-shielding substrate 1 reaches a desired thickness, the heating of the starting material for the dielectric layer by the electron beam is stopped, and the second step of forming the light-absorbing layer 3 is performed. The starting material for the light-absorbing layer filled in the crucible is heated by an electron beam to form a film having a desired thickness. The oxidation number can be adjusted by the amount of oxygen introduced at this time and the time. Furthermore, in the third step, a dielectric layer is formed on the light-absorbing layer formed in the second step to a desired thickness in the same manner as in the first step. After the second and third steps are repeated a desired number of times, an anti-reflection film is finally formed. The starting material for the anti-reflection film filled in the crucible is heated by an electron beam to form the anti-reflection film to a desired thickness. After the formation of the anti-reflection film is completed, the chamber is vented, the pressure in the deposition chamber is set to atmospheric pressure, and the light-shielding substrate 1 is removed. During the film formation, the deposition dome rotates at a predetermined speed, which makes the film thickness on the same circumference of the dome uniform, thereby improving the reproducibility of the optical characteristics between film formation lots. When a light-attenuating film and an anti-reflection film are formed on both sides of the light-shielding substrate 1, the first to third steps and the formation of the anti-reflection film are performed with the surface of the light-shielding substrate 1 on which the film has not been formed facing the deposition source.

In this embodiment, the starting materials are heated by electron beams in the formation of the dielectric layer, light absorbing layer, and anti-reflective film, but this is not limited to this, and resistance heating methods can be used depending on the starting material. In addition, when forming each layer of the dielectric layer, light absorbing layer, and anti-reflective film, gases such as air, oxygen, and nitrogen can be introduced as necessary to adjust the chemical composition of each layer.

Example 1
2 is a cross-sectional view of the light-shielding member 10 according to this embodiment, and film design values of the light-shielding film and the anti-reflection film according to this embodiment are shown in Table 1. In this embodiment, the light-damping film 5 and the anti-reflection film 4 having the same film configuration are provided on both sides of the light-shielding substrate 1.

In this embodiment, the light-shielding substrate 1 is made of SUS with a thickness of 20 μm. The SUS substrate has openings formed by etching.

In this embodiment, the light attenuating film 5 is composed of 11 layers, and Al ₂ Oy is used for the dielectric layer 2, and TiOx is used for the light absorbing layer 3. The y value of Al ₂ Oy determined by XPS (x-ray photoelectron spectroscopy) is about 3, and the x values of TiOx are about 1.0, 1.1, 1.2, 1.3, and 1.4 for the 2nd, 4th, 6th, 8th, and 10th layers counting from the light-shielding substrate 1 side, respectively. That is, the light attenuating film 5 in this embodiment is configured so that the light absorbing layer close to the light-shielding substrate 1 effectively absorbs the reflection of the light-shielding substrate 1. In this embodiment, the interface between the light-shielding substrate 1 and the light attenuating film 5 is an Al ₂ Oy layer which is the dielectric layer 2, and all the TiOx layers which are the light absorbing layers 3 are sandwiched between the Al ₂ Oy layers which are the dielectric layers 2. Furthermore, in this embodiment, the antireflection film 4 has a single layer structure and uses _MgF2 . The thickness of _{the MgF2} , together with the thickness of the _Al2Oy layer, which is the outermost layer of the light-damping film 5, is about λ/4 in optical thickness with a central wavelength of 550 nm. In this embodiment, the light-damping film 5 and the antireflection film 4 were formed by vacuum deposition, and oxygen was introduced when forming the _Al2Oy layer, which is a dielectric layer.

Figure 3 shows the measurement results of the total reflectance and regular reflectance of the light-shielding member 10 in this embodiment. The total reflectance was measured using a UV2600 (manufactured by Shimadzu Corporation), and the regular reflectance was measured using a U-4100 (manufactured by Hitachi High-Technologies Corporation), with the regular reflectance measured at an incident angle of 5°. As shown in Figure 3, the light-shielding member 10 in this embodiment has a total reflectance of 1% or less, and a regular reflectance of 0.1% or less, which is an extremely low reflectance characteristic. The optical density of the light-damping film 5 in this embodiment was approximately 1.9 (transmittance 1.25%).

Example 2
6 is a cross-sectional view of the light-attenuating film according to Example 2 and a graph showing the oxidation number of the light-absorbing layer. In Example 2, the light-attenuating film 5 has a 10-layer structure, and is composed of one light-absorbing stack 6 and an anti-reflection film 4. The light-absorbing layers 33a to 33d constituting the light-absorbing stack 24 are configured so that the oxidation number gradually increases from the light-shielding substrate side (light-absorbing layer 33a) to the opposite side to the light-shielding substrate (light-absorbing layer 33d). In Example 2, SUS having a thickness of 20 μm is used as the light-shielding substrate 1, Al ₂ O ₃ is used as the dielectric layer 2, TixOy (0.6≦y/x≦1.8) is used as the light-absorbing layers 33a to 33d, and MgF ₂ is used as the anti-reflection film 4. Here, the y/x values of the light absorbing layers TixOy 22a to 22d obtained by XPS (x-ray Photoelectron Spectroscopy) (apparatus name: PHI Quantera II) were approximately 1.0, 1.1, 1.2, and 1.3, respectively. All the light absorbing layers 33a to 33d included in the light attenuation film of this embodiment are sandwiched between the dielectric layers 2, which are Al ₂ O ₃ .

In this embodiment, the light attenuation film 5 is made up of 10 layers, but the number of layers can be adjusted as desired.

Example 3
7 is a cross-sectional view of the light attenuation film according to Example 3 and a graph showing the oxidation number of the light absorbing layer. In Example 3, the light attenuation film 5 has a 12-layer structure, and the light absorbing stack 6 and the antireflection layer 4 are formed on the light absorbing layers 33, 33' and the dielectric layer 2. The light absorbing layers 33 and 33' have a substantially uniform oxidation number, and the light absorbing layers 33a to 33c forming the light absorbing stack 6 have a gradually increasing oxidation number from the substrate side to the opposite substrate side. In Example 3, the light-shielding substrate, the dielectric layer, the light absorbing layer, and the antireflection layer are made of SUS, Al ₂ O ₃ , Ti x O y , and MgF ₂ , each having a thickness of 20 μm, as in Example 2. Here, the y/x values of the light absorbing layers 33, 33', and 33a to 33c obtained by XPS were 1.0, 1.0, 1.0, 1.1, and 1.3, respectively. As in the second embodiment, all the light absorbing layers included in the light attenuating film are sandwiched between the dielectric layers 2 made of Al ₂ O ₃ .

In Example 3, the light absorbing layers 33, 33' and the dielectric layer 2 are provided between the light-shielding substrate 1 and the light-absorbing laminate 6, but as shown in FIG. 8, the light absorbing layers 33, 33' and the dielectric layer 2 may be provided between the light-absorbing laminate 6 and the anti-reflection film 4. In addition, other functional films, such as an adhesive layer, may be provided between the light-shielding substrate 1 and the light-absorbing laminate 6, and between the light-absorbing laminate 6 and the anti-reflection film 4.

In this embodiment, the light absorbing layer forming the light absorbing stack 6 is three layers, but the light absorbing layer forming the light absorbing stack may be two or more layers. Also, the light absorbing layer provided between the light absorbing stack 6 and the light shielding substrate 1 or the anti-reflection film 4 is two layers in this embodiment, but there is no limit to the number of layers, and it may be one layer or three or more layers.

Example 4
9 is a cross-sectional view of the light-attenuating film according to Example 4 and a graph showing the oxidation number of the light-absorbing layer. In Example 4, the light-attenuating film 5 is composed of two light-absorbing laminates 6a and 6b and an anti-reflection film 4, and the light-absorbing layers forming the light-absorbing laminates 6a and 6b are each configured so that the oxidation number gradually increases from the light-shielding substrate side toward the opposite substrate side. In Example 4, the light-shielding substrate, the dielectric layer, the light-absorbing layer, and the anti-reflection film are made of SUS, Al ₂ O ₃ , Ti x O y , and MgF ₂ , each having a thickness of 20 μm, as in Example 2. Here, the values of x in the light-absorbing layers 33a to 33f obtained by XPS were approximately 1.0, 1.2, 1.3, 1.0, 1.2, and 1.4, respectively.

Also, as in the second embodiment, all the light absorbing layers included in the light attenuation film are sandwiched between the dielectric layers, Al ₂ O _3. Here, the oxidation number of the light absorbing layer 33d of the light absorbing stack 6b that is closest to the light-shielding substrate 1 is preferably smaller than that of the light absorbing layer 33c of the light absorbing stack 6a that is farthest from the light-shielding substrate 1. The extinction coefficient of the light absorbing layer decreases as the oxidation number increases, but if the oxidation number of the light absorbing layer closest to the substrate of the light absorbing stack is large, it becomes difficult to give the light absorbing stack a sufficient light absorbing function. Furthermore, it is preferable that the light absorbing layers 33a and 33d of the light absorbing stacks 6a and 6b that are closest to the light-shielding substrate 1, respectively, have approximately the same oxidation number. In this way, when designing the light attenuation film 5, the optical constants of the light absorbing layers of the light absorbing stacks 6a and 6b can be designed to be approximately the same, making the film design easier. For example, in this embodiment, the starting material is TiO, and after a TiO layer is formed as the first light absorbing layer 33a in the lower light absorbing laminate 6a, a TiO layer is formed as the first light absorbing layer 33d in the upper light absorbing laminate 6b. Therefore, the same starting material can be used between light absorbing laminates, and productivity is high.

In addition, after the TixOy layer (y/x=1.3) which is the third light absorbing layer 33c of the lower light absorbing laminate 6a, the first light absorbing layer 33d of the upper light absorbing laminate 6b is formed with a TiO layer having a larger extinction coefficient than the third light absorbing layer 33c of the lower light absorbing laminate 6a, so that it can have sufficient light absorbing function. In addition, the TixOy layer (y/x=1.4) which is the third light absorbing layer 33f of the upper light absorbing laminate 6b has an oxidation number that is 0.33 or more different from the TiO layers which are the first light absorbing layers 33a and 33d of the light absorbing laminate 6a and the light absorbing laminate 6b, respectively, but the oxidation number is within 0.33 of the TixOy layer (y/x=1.2) which is the second light absorbing layer 33e of the upper light absorbing laminate 6b, making it easy to adjust the optical properties.

In this embodiment, two light absorbing laminates are laminated, but three or more light absorbing laminates may be provided. A single layer or multiple layers of a dielectric layer, light absorbing layer, other functional film, etc. may be formed between the light absorbing laminates. Furthermore, while the light absorbing laminates 6a and 6b in this embodiment each consist of three light absorbing layers, this is not limited to this as long as there are two or more layers. From the viewpoint of simplicity of film design, it is more preferable that the light absorbing layers forming the light absorbing laminates 6a and 6b have the same number of layers as in this embodiment, but this is not limited to this.

As in Example 4, in multiple light absorbing laminates, the light absorbing layers contained in the light absorbing laminate are configured so that their oxidation number gradually increases from the light-shielding substrate side to the opposite substrate side. This makes it possible to obtain a light absorbing film that is easy to design and has good oxidation resistance, without the difference in oxidation number of the light absorbing layers in the light absorbing laminate becoming too large, even if a strong light attenuation function is required for the light absorbing film.

Comparative Example
Comparative Examples 2, 3, and 4 are light-attenuating films having the same number of layers as those in Examples 2, 3, and 4, respectively, and the light-shielding substrate, dielectric layer, light-absorbing layer, and anti-reflection film are made of SUS, Al ₂ O ₃ , TixOy, and MgF ₂ with a thickness of 20 μm as in Examples 2 to 4, and the oxidation numbers of all the light-absorbing layers constituting the light-absorbing stack are set to 1.0.

Figure 10 shows the change in optical density (OD) between Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, and Example 4 and Comparative Example 4 in the high temperature and high humidity test (temperature: 85°C, humidity: 85%). From Figure 10, Examples 2 to 4 have a smaller change in optical density in the high temperature and high humidity test compared to Comparative Examples 2 to 4, respectively. From this, it can be seen that the change in extinction coefficient of the light absorbing layer forming the light absorbing film of Examples 2 to 4 is small, that is, the change in oxidation number of the light absorbing layer is small. In other words, the same effect can be obtained with the configuration of Example 1, which has a similar oxidation number configuration to Example 2. In addition, the oxidation number of all the light absorbing layers constituting the light absorbing laminate of the above-mentioned comparative example is set to 1.5, and the change in optical density can be equal to or less than that of the examples, but if an attempt is made to have the same optical density as the examples, the film thickness of the light absorbing layer becomes thick, and there is a risk of occurrence of adverse effects such as cracks and warping. Furthermore, if the light absorbing layer close to the light-shielding substrate does not have sufficient light absorption function, it becomes difficult to effectively suppress reflection caused by the light-shielding substrate.

By providing the light-damping film 5 shown in Examples 1 to 4 on a light-shielding substrate, it is possible to provide light-shielding components such as aperture blades and light-shielding plates that have good environmental stability.

Figure 4 shows a cross section of an optical system equipped with the light shielding member 10 of the present invention. A light ray passes through the opening 10a of the light shielding member 10 and an image formed on the image sensor 15 is photoelectrically converted to be imaged. The light shielding member 10 of the present invention is disposed near the lenses 11 to 14 mounted on the optical system, and may be directly attached to the lenses or may be provided independently of the lenses. The light incident on the optical system is focused on the image sensor by the lenses, but the light shielding member 10 suppresses unnecessary incident light from passing through the lenses. At this time, since the light shielding member 10 of the present invention has a very low reflectance, stray light that causes flare and ghosting is unlikely to occur. Furthermore, since the light shielding member 10 of the present invention does not have a light absorbing layer 3 having a certain thickness or more in the light attenuation film 5, the optical constant does not vary significantly within the light absorbing layer, and the variation in reflectance characteristics is small. In addition, the light shielding member 10 of the present invention has excellent environmental stability because the oxidation number of the light absorbing layer (second light absorbing layer) further away from the light shielding substrate 1 in the stacking direction is greater than the oxidation number of the light absorbing layer (first light absorbing layer) closer to the light shielding substrate 10. Furthermore, the light shielding member 10 of the present invention has a characteristic that the reflectance is stable because the light absorbing layer 3, whose optical properties are easily changed, of the light attenuation film 5 is sandwiched between the chemically stable dielectric layer 2. In FIG. 4, the light shielding member 10 is disposed outside the lenses 11 to 14, but the light shielding member 10 may be included in the lenses.

The optical system according to the present invention can be suitably used for camera applications, such as vehicle-mounted cameras, cameras for smartphones and tablet terminals, and other imaging devices and devices incorporating imaging devices that require a particularly thin design.

1 Light-shielding substrate 2 Dielectric layer (stoichiometric metal compound layer)
3, 3', 33a to 33f Light absorbing layer (substoichiometric metal compound layer)
4 Anti-reflection film 5 Light attenuation films 6, 6a, 6b Light absorbing laminate 10 Light shielding members 11 to 14 Lens 15 Imaging element

Claims (7)

A light-shielding member including a light-damping film in which a dielectric layer and a light-absorbing layer are alternately laminated on a light-shielding substrate having an opening,
The light attenuating film has a plurality of the light absorbing layers,
The plurality of light absorbing layers include a first light absorbing layer of a metal compound;
The first light absorbing layer is provided at a position farther from the light shielding substrate in a stacking direction than the first light absorbing layer.
a second light absorbing layer of a metal compound;
A light-shielding member, wherein an oxidation number of a metal of the second light-absorbing layer is greater than an oxidation number of a metal of the first light-absorbing layer. The light-shielding member according to claim 1, characterized in that another dielectric layer is provided between the light-shielding substrate and the light-damping film. The light-shielding member according to claim 1 or 2, characterized in that the absolute value of the difference between the oxidation number of the first light-absorbing layer and the oxidation number of the second light-absorbing layer is 0.2 or less. an anti-reflection film provided on the light-damping film,
4. The light-shielding member according to claim 1, wherein the light-shielding substrate is a metal substrate, the dielectric layer is made of Al ₂ O ₃ , and the anti-reflection film is made of MgF ₂ . 5. The light-shielding member according to claim 1, wherein the light-absorbing layer closest to the light- shielding substrate side among the light-absorbing layers has the smallest oxidation number or nitridation number among the light-absorbing layers. The light-shielding member according to any one of claims 1 to 5, characterized in that the light-damping film has a laminated structure of six or more layers. An imaging device comprising the light shielding member according to any one of claims 1 to 6 and an imaging element that captures light that has passed through an opening in the light shielding member.

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