JP2010277094A - Method for producing absorption type multi-layer film nd filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an absorption type multi-layer film ND filter whose substrate hardly warps and which can promise superior mass productivity and moreover can achieve transmittance attenuation that is flat for wavelengths. <P>SOLUTION: The absorption type multi-layer film ND filter comprises a film substrate 12 and absorption type multi-layer films 13, 16 constituted by alternately laminating dielectric layers 14, 17 formed of SiO<SB>2</SB>, Al<SB>2</SB>O<SB>3</SB>or the like and metal film layers 15, 18 formed of an Ni-based alloy on the film substrate. In the method for producing the absorption type multi-layer film ND filter, the absorption type multi-layer films are respectively formed so as to have a film structure symmetrical to each other interposing the substrate, warpage of the substrate is controlled at a curvature of radius of 500 mm or more and further the metal film layers are formed by a magnetron sputtering method using a nickel-based material target formed by adding to Ni one element selected from Al, V, W, Ta and Si in a prescribed range. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an absorptive multilayer ND filter that attenuates transmitted light in the visible range, and in particular, an absorptive multilayer ND filter to which a thin substrate such as a resin film, a resin plate, or a glass thin plate is applied. It is about the method.

  As this type of ND (Neutral Density Filter) filter, a reflection type ND filter that reflects and attenuates incident light and an absorption type ND filter that absorbs and attenuates incident light are known. When an ND filter is incorporated in a lens optical system in which reflected light is a problem, an absorption ND filter is generally used. In this absorption ND filter, an absorbing substance is mixed into the substrate itself (color glass ND). There are two types: a filter) type to be applied and a type in which a thin film formed on the surface of the substrate has no absorption and absorption. In the latter case, the thin film is formed of a multilayer film to prevent reflection on the surface of the thin film, and has an antireflection effect as well as a function of attenuating transmitted light.

  As an absorptive multilayer ND filter in which the thin film is a multilayer film, Patent Document 1 discloses a multilayer film in which a dielectric layer and a titanium oxide film layer are combined, and Patent Document 2 discloses a dielectric film. A multilayer film in which a niobium film layer is combined is disclosed.

  Further, Patent Document 3 discloses a technique of forming a dielectric hard film layer on at least one outermost surface in order to prevent scratches due to mechanical contact.

  By the way, since the absorption multilayer ND filter used for a small thin digital camera has a small installation space, it is necessary to thin the substrate itself, and a very thin glass plate, resin plate, or resin film is applied as the substrate.

  However, when a very thin glass plate, resin plate, or resin film is applied as the substrate, the following specific problems occur.

  That is, if a multilayer film having a different structure is formed on each side of a very thin glass sheet, resin plate, or resin film, the substrate may be warped on one side due to the film stress of each formed multilayer film. In this case, if film formation is performed under ideal film formation conditions in which the total film stress is canceled for each multilayer film on each side, that is, when the film is formed on only one side, the substrate does not warp. Even if a multilayer film is formed on the substrate, the substrate does not warp. As a method for canceling the overall film stress, there are a method for eliminating the film stress for each layer and a method for canceling the film stress by alternately laminating films of tensile stress and compressive stress. In reality, it is difficult to make the film stress of the multilayer film zero.

For example, in the case of a general absorptive multilayer ND filter in which the absorption multilayer film 1 is formed on one surface of the substrate 3 and the antireflection film 2 is formed on the other surface as shown in FIG. If the balance between the film stresses of the mold multilayer film 1 and the antireflection film 2 is poor, the substrate warps when the substrate 3 is made of a very thin glass plate, resin plate, or resin film. The thin metal film, a method most cases the absorption type multi-layer film 1 shown in composed Figure 1 with SiO _2, to cancel the film stress by alternately laminating a film of the above-mentioned tensile stress and compressive stress Since the metal film is thin, it cannot be used, and it is necessary to adjust the film stress of the SiO ₂ film to zero. However, it is actually difficult to set the film forming conditions for making the film stress of the SiO ₂ film zero.

  If the substrate is warped, there is a problem that handling becomes difficult when the ND filter is bonded or welded, and there is a concern that the image may be distorted when used in the vicinity of the image sensor.

Japanese Patent No. 3359114 JP 2002-350610 A JP-A-10-133253

  The present invention was made paying attention to such problems, and the problem is that even when a thin film substrate such as a resin film, a resin plate or a glass thin plate is applied, the substrate is hardly warped. Another object of the present invention is to provide a method for manufacturing an absorption-type multilayer ND filter that is excellent in mass productivity and that provides a flat transmittance attenuation with respect to the wavelength.

Therefore, as a result of intensive studies by the present inventors in order to solve the above-described problems, an absorption-type multilayer having a film structure that is symmetrical with respect to both sides of a thin substrate such as a resin film, a resin plate, a glass thin plate, etc. warpage of the substrate is easily reduced by canceling the both surfaces of the film stress to form a film, also a dielectric layer composed of the above absorption type multi-layer film of SiO _2, Al ₂ O _3, or which such mixtures and Ni It has been found that a flat transmittance attenuation with respect to the wavelength can be obtained by constituting a multilayer film with a single layer or a metal film layer made of a Ni-based alloy, and the present invention has been completed.

That is, the invention according to claim 1
An absorptive multilayer film for attenuating transmitted light is provided on a substrate made of a resin film, a resin plate or a glass thin plate, and the absorptive multilayer film comprises a dielectric layer made of SiO ₂ , Al ₂ O ₃ or a mixture thereof and Ti Absorption multilayer ND filter composed of a multilayer film in which metal film layers made of an Ni-based alloy to which one or more elements selected from Al, V, W, Ta, and Si are added are alternately laminated Assuming the manufacturing method of
Each of the absorption multilayer films is formed on both sides of the substrate so as to have a symmetrical film structure around the substrate, and the curvature radius of the warp of the substrate is adjusted to 500 mm or more, and addition of Ti element The proportion is 5 to 15% by weight, the addition rate of Al element is 3 to 8% by weight, the addition rate of V element is 3 to 9% by weight, the addition rate of W element is 18 to 32% by weight, and the addition rate of Ta element is The metal film layer is formed by a magnetron sputtering method using Ni-based material targets set in a range of 5 to 12% by weight and a Si element addition ratio of 2 to 6% by weight, respectively.

The invention according to claim 2
Based on the manufacturing method of the absorption multilayer ND filter according to the invention of claim 1,
The total film thickness of the dielectric layer on one side of the substrate made of SiO ₂ , Al ₂ O ₃ or a mixture thereof is set to 100 nm or more, and the total film thickness of the metal film layer on the side of the substrate made of Ni-based alloy is set to 30 nm or less. It is characterized by being,
The invention according to claim 3
Based on the manufacturing method of the absorption multilayer ND filter according to the invention of claim 1,
The thickness of each dielectric layer composed of the SiO _2, Al ₂ O _3, or which such mixtures are all set to the same thickness, and all the film thickness of each metal film layer made of Ni-based alloy in the same film thickness It is characterized by being set.

  According to the method for manufacturing an absorptive multilayer ND filter according to the present invention, an absorptive multilayer film having a film structure symmetric with respect to the substrate is formed on both surfaces of a substrate made of a resin film, a resin plate or a glass thin plate. Since the film stresses on both sides are canceled each other, it is possible to produce an absorption type multilayer ND filter having excellent flatness with a curvature radius adjusted to 500 mm or more even with a thin substrate.

  Further, the addition ratio of Ti element is 5 to 15 wt%, the addition ratio of Al element is 3 to 8 wt%, the addition ratio of V element is 3 to 9 wt%, the addition ratio of W element is 18 to 32 wt%, Spectral transmittance wavelength in the visible region by a magnetron sputtering method using Ni-based material targets in which the addition ratio of Ta element is 5 to 12% by weight and the addition ratio of Si element is 2 to 6% by weight. Since the metal film layer of the absorption multilayer film is formed of a Ni-based alloy having a small dependence, the effect of stably mass-producing the absorption multilayer film ND filter that can obtain a flat transmittance attenuation with respect to the wavelength is obtained. Have.

  Furthermore, since the absorption multilayer film having a film structure that is symmetric with respect to the substrate is formed on both sides of the substrate, the productivity of the absorption multilayer film ND filter is excellent and the distinction between the front and back sides is eliminated. It has the effect of facilitating management.

FIG. 7 is a structural cross-sectional view of an absorption multilayer ND filter according to a conventional example. FIG. 5 is a cross-sectional view of a configuration of an absorption multilayer ND filter according to a conventional example (comparative example). The graph which shows the theoretical spectral transmission characteristic in the absorption type multilayer film of the absorption type multilayer film ND filter which concerns on a prior art example. The graph which shows the theoretical spectral reflection characteristic in the absorption type multilayer film of the absorption type multilayer film ND filter which concerns on a prior art example. The graph which shows the theoretical spectral reflection characteristic in the multilayer anti-reflective film of the absorption type multilayer ND filter which concerns on a prior art example. FIG. 3 is a cross-sectional view of an absorption multilayer ND filter according to a reference example in which a metal film layer is composed of Ni alone and an absorption multilayer ND filter according to the present invention in which the metal film layer is composed of a Ni-based alloy. The graph which shows the theoretical spectral transmission characteristic in the absorption type multilayer film of the absorption type multilayer film ND filter which concerns on the reference example shown in Table 2. FIG. The graph which shows the theoretical spectral reflection characteristic in the absorption type multilayer film of the absorption type multilayer film ND filter which concerns on the reference example shown in Table 2. FIG. The graph which shows the spectral transmission characteristic of the absorption type multilayer ND filter which concerns on the reference example 1. FIG. The graph which shows the spectral transmission characteristic of the absorption type multilayer ND filter which concerns on a comparative example. The graph which shows the relationship between the transmittance | permeability and wavelength in Ni thin film, Cr thin film, Nb thin film, and Ta thin film. The graph which shows the theoretical spectral transmission characteristic in the absorption type multilayer film of the absorption type multilayer film ND filter which concerns on this invention shown in Table 3. FIG. The graph which shows the theoretical spectral reflection characteristic in the absorption type multilayer film of the absorption type multilayer film ND filter which concerns on this invention shown in Table 3. FIG. FIG. 9 is a graph showing the spectral transmission characteristics of the absorption multilayer ND filter according to Example 3. The graph which shows the theoretical spectral transmission characteristic in the absorption type multilayer film of the absorption type multilayer film ND filter which concerns on this invention shown in Table 4. FIG. The graph which shows the theoretical spectral reflection characteristic in the absorption type multilayer film of the absorption type multilayer film ND filter which concerns on this invention shown in Table 4. FIG. FIG. 9 is a graph showing the spectral transmission characteristics of the absorption multilayer ND filter according to Example 4.

  Hereinafter, the manufacturing method of the absorption type multilayer ND filter according to the present invention will be described in detail with reference to the drawings.

  In addition, when a thin substrate having no absorption in the used wavelength band is used, in order to form an absorption multilayer film having an antireflection function with the same film configuration on both surfaces of the substrate to obtain a desired transmittance, each absorption multilayer film It is necessary to set in consideration of the absorption by each. That is, in order to manufacture an ND filter with a transmittance of 25%, it is necessary to form an absorption multilayer film with a transmittance of 50% (= √25%) on both sides, and a transmittance of 12.5%. In order to manufacture an ND filter, it is necessary to form an absorption multilayer film having a transmittance of 35% (= √12.5%) on both sides.

  First, FIG. 2 shows an absorption multilayer ND filter according to a conventional example having a transmittance of 12.5%.

That is, the absorption multilayer ND filter according to this conventional example includes a film (PC: polycarbonate) substrate 5 and an absorption multilayer film (specifically “Ni” formed on the surface of the substrate 5 having an antireflection function). A single metal film layer 9 / dielectric layer 8 made of SiO ₂ / the metal film layer 9 / the dielectric layer 8 / the metal film layer 9 / the dielectric layer 8 ”). formed on the back surface multilayer antireflection film of the substrate 5 (specifically, _"Ta 2 _{O 5} made of a metal film layer 11 / SiO ₂ composed of dielectric layer 10 / the metal layer 11 / the dielectric layer 10 ' The main part is composed of 7). Table 1 below shows specific film configurations, constituent materials, film thicknesses and refractive indices of the respective layers of the absorption multilayer film and multilayer antireflection film. Further, the theoretical spectral transmission characteristics of the absorption multilayer film 6 of the absorption multilayer film ND filter according to the conventional example are shown in FIG. 3, the theoretical spectral reflection characteristics of the absorption multilayer film 6 are shown in FIG. 7 shows the theoretical spectral reflection characteristics in FIG.

On the other hand, an absorptive multilayer ND filter obtained by the manufacturing method according to the present invention is an absorptive multilayer ND filter in which an absorptive multilayer film that attenuates transmitted light is provided on a substrate made of a resin film, a resin plate, or a glass thin plate. a is, the absorption type multi-layer film is constituted by a multilayer film obtained by alternately stacking the metal film layer made of a dielectric layer and the Ni-based alloy consisting of SiO _2, Al ₂ O _3, or which such mixtures, and, The absorption multilayer film is formed on both surfaces of the substrate so as to have a symmetrical film structure with the substrate as a center, and the curvature radius of warpage of the substrate is adjusted to 500 mm or more. And

  And the said board | substrate is comprised with a resin film, a resin board, or a glass thin plate, Although the material is not specifically limited, A transparent thing is preferable and when considering mass productivity, the dry-type roll coating mentioned later is attained. A substrate having flexibility is preferable. A flexible substrate is superior in that it is cheaper, lighter, and more deformable than a conventional glass substrate. In particular, a resin plate or a resin film is preferable as the substrate.

  Specific examples of the resin plate or resin film constituting the substrate are selected from resin materials of polyethylene terephthalate (PET), polyether sulfone (PES), polyarylate (PAR), polycarbonate (PC), polyolefin (PO) and norbornene. Examples thereof include a single resin plate or resin film or a composite of a resin plate or resin film selected from the above resin materials and an acrylic organic film covering one or both surfaces of this single material. In particular, as for norbornene resin materials, representative examples include ZEONOR (trade name) manufactured by ZEON Corporation, and ARTON (trade name) manufactured by JSR Corporation.

  Further, as described above, the metal film layer is made of a Ni-based alloy, that is, a Ni-based alloy material in which one or more elements selected from Ti, Al, V, W, Ta, and Si are added to Ni. The

  The details of this reason will be described later, but are summarized as follows. That is, when the Ni film is formed using the sputtering method, if the thickness of the Ni target decreases with the continuous use of the Ni target, the leakage magnetic field in the plasma space becomes stronger in the thinned portion of the Ni target. come. When the leakage magnetic field in the plasma space becomes stronger, the discharge characteristics (discharge voltage, discharge current, etc.) change and the film formation rate changes. In other words, if the same Ni target is used continuously for a long time during production, there is a problem that the deposition rate of the Ni film changes as the Ni target is consumed, and the absorption multilayer ND filter with uniform characteristics is stabilized. This makes it difficult to produce. In order to avoid this problem, as described above, the metal film layer is formed using a Ni-based alloy material to which one or more elements selected from Ti, Al, V, W, Ta, and Si are added. That's fine.

  Next, a transmittance of 12.5%, the main part of which is composed of a film (PC: polycarbonate) substrate 12 and absorption multilayer films 13 and 16 each having an antireflection function formed on both surfaces of the substrate 12, respectively. A specific example of the absorption multilayer ND filter according to the reference example is shown in FIG. Table 2 below shows specific film configurations, constituent materials, film thicknesses and refractive indexes of the absorption multilayer films 13 and 16, respectively, and relates to a reference example in which the metal film layer is composed of Ni alone. The theoretical spectral transmission characteristics of the absorption multilayer films 13 and 16 of the absorption multilayer film ND filter are shown in FIG. 7, and the theoretical spectral reflection characteristics thereof are shown in FIG.

As shown in Table 2, the absorption multilayer films 13 and 16 include metal film layers 15 and 18 made of Ni alone and dielectric layers 14 and 17 made of SiO _{2 in} order from the substrate 12 side. It is configured by alternately stacking. Although the number of these layers is arbitrary, FIG. 6 shows the absorption type multilayer films 13 and 16 in which the metal film layers 15 and 18 and the dielectric layers 14 and 17 are composed of a total of four layers. ing. In Table 2, the metal film layers 15 and 18 and the dielectric layers 14 and 17 are set to the same film thickness, but the absorption multilayer films 13 and 16 are symmetrical with respect to the substrate 12. Each film thickness can be arbitrarily adjusted on condition that each film is formed so as to have a film structure.

  Here, it has been confirmed that the wavelength dependence of the transmittance of the Ni thin film constituting the metal film layers 15 and 18 is smaller than that of the Cr thin film, the Ta thin film, and the Nb thin film. That is, the variation width of the transmittance of the Cr thin film, the Ta thin film, and the Nb thin film at wavelengths of 0.400 to 0.800 μm is 14.7%, 13.5%, and 11.1 respectively, as shown in the graph of FIG. Although it is 8%, the fluctuation range of the transmittance in the Ni thin film is as low as 1.5%.

  However, the reflection on the surface of the absorption ND filter becomes stray light, which adversely affects the image quality of a digital camera or the like. For this reason, in order to give the absorption type ND filter surface the effect of preventing reflection, the absorption type multilayer films 13 and 16 are composed of multilayer films.

  In the absorption multilayer ND filter according to the reference example in which the metal film layer is composed of Ni alone, and in the absorption multilayer ND filter according to the present invention in which the metal film layer is composed of a Ni-based alloy, Since the thickness of the metal film layer is well controlled and the wavelength dependence of the transmittance in the visible range of a Ni-based thin film made of Ni alone or a Ni-based alloy is small, it is composed of a metal film layer and a dielectric layer. The absorption multilayer film thus obtained has a small wavelength dependency of the spectral transmittance in the visible region without increasing the number of layers, and can obtain a flat transmittance attenuation with respect to the wavelength.

Incidentally, the dielectric layer (except those shown in Table 2) 14 and 17 is a thin film made of SiO _2, the material (the SiO ₂ having a lowest possible refractive index with respect to the metal film layer 15 and 18 made of Ni alone In addition, it is preferably composed of Al ₂ O ₃ or a mixture of SiO ₂ and Al ₂ O ₃ . Further, it is preferable to control the film thickness of the dielectric layers 14 and 17 in order to provide the antireflection effect of the absorption multilayer film.

The thicknesses of the metal film layers 15 and 18 made of Ni alone and the dielectric layers 14 and 17 made of SiO ₂ are such that the absorptive multilayer films 13 and 16 have a predetermined transmittance and reflectance in the visible region (for example, The thickness of each of the metal film layers 15 and 18 is particularly preferably 2 to 15 nm. In this absorption multilayer ND filter, the absorption multilayer films 13 and 16 are formed including the metal film layers 15 and 18 made of Ni alone, so that even if the number of layers is as small as four layers, for example. It has a sufficiently flat transmittance spectral characteristic.

  Next, the absorptive multilayer film according to the present invention can be formed by a sputtering method.

  The sputtering method is an effective thin film formation method when a film is formed on a substrate using a material having a low vapor pressure or when precise film thickness control is required, and the operation is very simple. Widely used. In general, under an argon gas pressure of about 10 Pa or less, the substrate is used as an anode, the film source target is used as a cathode, glow discharge is caused between them to generate argon plasma, and This is a technique in which an argon cation collides with a cathode target to repel target component particles, and deposits the particles on a substrate to form a film.

  The above sputtering methods are classified according to the method of generating argon plasma, and those using radio frequency (RF) plasma are called high frequency sputtering methods and those using DC plasma are called DC sputtering methods. A method of forming a film by arranging a magnet on the back side of the target and concentrating argon plasma directly on the target and increasing the collision efficiency of argon ions even at a low gas pressure is called a magnetron sputtering method.

Each of the metal film layers in the absorption multilayer film according to the reference example and the absorption multilayer film according to the present invention is, for example, a direct current using a target of a Ni-based metal (Ni simple substance or Ni-based alloy) in an Ar atmosphere. It is formed by magnetron sputtering. The dielectric layer is formed, for example, by a high frequency magnetron sputtering method using a Si or Al target in an Ar and O ₂ atmosphere. By performing the dielectric layer by a high frequency sputtering method, abnormal discharge generated in reactive sputtering can be prevented, and stable film formation can be achieved.

  By the way, since pure Ni material is a ferromagnetic material, when the metal film layer is formed by DC magnetron sputtering, the magnetic force from the magnet arranged on the back side of the target for acting on the plasma between the target and the substrate is The magnetic field that is shielded by the Ni target material and leaks to the surface becomes weak, and it becomes difficult to concentrate the plasma and efficiently form a film. In order to avoid this, it is preferable to perform sputtering film formation by using a cathode (strong magnetic field cathode) in which the magnetic force of a magnet disposed on the back side of the target is increased (400 Gauss or more) and by increasing the magnetic field passing through the Ni target.

  However, even when such a method is adopted, another problem as described below may occur during production. That is, when the thickness of the target decreases with continuous use of the Ni target, the leakage magnetic field in the plasma space becomes stronger in the portion where the thickness of the target is reduced as described above. When the leakage magnetic field in the plasma space becomes stronger, the discharge characteristics (discharge voltage, discharge current, etc.) change and the film formation rate changes. In other words, if the same Ni target is used continuously for a long time during production, there is a problem that the deposition rate of the Ni film changes as the Ni target is consumed, and the absorption multilayer ND filter with uniform characteristics is stabilized. Making it difficult to produce. In order to avoid this problem, as described above, the metal film layer is formed using a Ni-based alloy material to which one or more elements selected from Ti, Al, V, W, Ta, and Si are added. Good.

  And in this invention, it is required to use the Ni type alloy material which contains Ti element in the range of 5 to 15 weight%. The reason why the lower limit of the amount of Ti is 5% by weight is that the ferromagnetic characteristics can be extremely weakened by including 5% by weight or more, and direct current magnetron sputtering film formation is performed even on a cathode on which a normal magnet having a low magnetic force is arranged. Because it can. Further, since the magnetic field shielding ability of the target is low, the change in the leakage magnetic field in the plasma space depending on the target consumption is small, and a constant film formation rate can be maintained, so that film formation can be performed stably. In addition, the reason why the upper limit of Ti amount is 15.0% by weight is that a material having a large amount of intermetallic compound when Ti is contained exceeding 15.0% by weight and the wavelength dependency in transmittance is small. It is because there is a risk of disappearing. Further, the addition amount of Al element, V element, W element, Ta element, Si element is also determined for the same reason, and when adding such Al element, V element, W element, Ta element, Si element, Al is added. The addition ratio of the element is 3 to 8 wt%, the addition ratio of the V element is 3 to 9 wt%, the addition ratio of the W element is 18 to 32 wt%, the addition ratio of the Ta element is 5 to 12 wt%, It is necessary to make the Ni-based alloy material added in an addition ratio of 2 to 6% by weight.

  However, when there are two or more elements to be added to Ni, it is preferable to adjust the amount to be lower than the upper limit of the amount of each element so as not to form a large amount of intermetallic compounds. For example, when two elements of Ti and Si are added to Ni, if the amount of Si element added exceeds 5% by weight with respect to the amount of Ti added of 7.5% by weight, the numerical values of these added amounts are as described above. Even in the composition range (Ti element is 5 to 15% by weight, Si element is 2 to 6% by weight), the formation of intermetallic compounds may be remarkable.

The metal film layer and the dielectric layer of SiO ₂ , Al ₂ O ₃ or a mixture thereof can be formed on a film-like substrate by using a dry roll coating method.

  By adopting the above-described configuration for the absorption multilayer film, the reflectance is 5% or less and the transmittance fluctuation range is within 10% in the entire visible range of 0.400 μm to 0.800 μm. An absorption multilayer ND filter can be provided.

  In addition, as confirmed from the numerical values described in Tables 1 and 2, the absorption multilayer ND filter according to the reference example in which the metal film layer is composed of Ni alone is compared with the ND filter according to the conventional example. Total film thickness on both sides of the substrate (in the conventional ND filter, the absorption multilayer film is 270 nm and the multilayer antireflection film is 256 nm, whereas in the absorption multilayer film ND filter according to the reference example, The absorption multi-layer film (154 nm) is thinned to about half, and furthermore, since only two kinds of film materials are used, the productivity is excellent.

Further, in the absorption type multi-layer film ND filter metal film layer according to the reference example composed of Ni alone, to increase the simplified and productivity deposition conditions, a dielectric made of SiO ₂ as shown in Table 2 The layers may be designed to have the same film thickness (70 nm) on both surfaces, and the metal film layer made of Ni alone may be designed to have the same film thickness (7 nm) on both surfaces. In order to form an absorption multilayer film on both sides of the substrate, the thin substrate may be fixed to the frame so that it does not warp due to film stress, but it may be formed on each side. Is.

  By setting it as such a structure, it can achieve that the curvature radius of the curvature of a board | substrate shall be 500 mm or more. When the curvature radius of the substrate warp is less than 500 mm, it becomes difficult to handle by an apparatus in a process of cutting, adhering or welding the absorption multilayer ND filter, and further, the absorption multilayer ND filter is transmitted. This is not preferable because the image may be distorted.

  When the absorption multilayer ND filter according to the reference example shown in FIG. 6 is placed on a surface plate (see reference numeral 4 in FIG. 1), there is almost no warping of the substrate, and the gap at the center is 0.2 mm or less. It was so difficult to measure accurately.

  On the other hand, when the absorption type multilayer ND filter according to the conventional example shown in FIG. 2 is placed on a surface plate (however, the absorption type multilayer film 6 of the absorption type multilayer ND filter is on the upper side and the multilayer antireflection film 7 is on the lower side). The substrate was warped, and a gap of about 2 mm was observed in the center. When the substrate size is 60 mm and a gap of 0.9 mm is generated at the center, the curvature radius of warping is 500 mm.

They note that the film thickness of the dielectric layer and the metal layer of the absorption type multi-layer film ND filter metal film layer according to the present invention consists of Ni-based alloy _is comprised of SiO 2, _Al 2 O _3, or which such mixture It is preferable that the total film thickness of the dielectric layers on one side of the substrate is set to 100 nm or more, and the total film thickness of the metal film layers on the one side of the substrate made of Ni-based alloy is set to 30 nm or less. If the total film thickness of the dielectric layer on one side of the substrate is less than 100 nm, it may be difficult to give the absorption multilayer film an antireflection function, and the total film thickness of the metal film layer on the one side of the substrate exceeds 30 nm. If the thickness is too thick, it is expected that the film stress will be reduced if the soft metal film layer is made thicker than the dielectric layer, but the spectral transmittance may be extremely lowered.

  Here, in the absorptive multilayer ND filter according to the present invention, when forming absorptive multilayer films having mutually symmetrical film structures around the substrate on both sides of the substrate, it is not always necessary to satisfy the complete symmetry condition. It is only necessary to satisfy a substantially symmetrical condition that can cancel the film stress. For example, after forming an absorptive multilayer film on the front side of the substrate and evaluating its optical characteristics, if the transmittance on the surface is higher than the expected value, the transmittance on the back side is lowered, and conversely the transmission on the surface If the rate is lower than the expected value, the transmittance can be corrected by finely adjusting the film configuration of the backside absorption multilayer film, such as increasing the transmittance on the back side.

  Next, specific examples of the present invention will be described. The absorption multilayer ND filter according to Reference Example 1 and Examples 3 and 4 and the absorption multilayer ND filter according to the comparative example were compared and evaluated.

[Reference Example 1]
As the substrate, a PC (polycarbonate) film having a thickness of 100 μm cut to 60 mm was used. This film was fixed with a metal frame that pressed a portion about 5 mm from the edge, and film formation was performed on one side. An RF magnetron sputtering apparatus (manufactured by ULVAC, Inc.) is used for film formation, and the film formation rate of the dielectric layer: SiO ₂ is 0.2 nm / second, and the film formation speed of the metal film layer: Ni is 0.1 nm / second. It was. Moreover, since this absorption type multilayer ND filter has the same film configuration on both sides, the film was formed in the same process on each side.

The film structure of the absorptive multilayer film formed on both surfaces of the film is the same as that of the absorptive multilayer film ND filter shown in FIG. 6, the dielectric layer: SiO _{2 has} a film thickness of 70 nm, and the metal film layer: Ni has a film thickness. Was 7 nm.

  And when the absorption type multilayer ND filter according to Reference Example 1 is placed on a surface plate, there is almost no warping of the film as a substrate, and the gap at the center is 0.2 mm or less and cannot be measured accurately. there were.

[Example 2]
In place of the Ni target used in Reference Example 1, a Ni-based alloy target containing 7.5% by weight of Ti (manufactured by Sumitomo Metal Mining Co., Ltd.) was used. An absorption multilayer ND filter according to Example 2 which is the same as the absorption multilayer ND filter shown in FIG. 6 having a layer: SiO ₂ film thickness of 70 nm and a metal film layer: Ni-based alloy film thickness of 7 nm is manufactured. did.

  When the absorption multilayer ND filter according to Example 2 was placed on a surface plate, there was almost no warping of the film as the substrate in this absorption multilayer ND filter, and the gap at the center was 0.2 mm. It was so difficult to measure accurately below.

[Example 3]
Instead of the Ni target used in Reference Example 1, a Ni-based alloy target containing 7.5% by weight of Ti (manufactured by Sumitomo Metal Mining Co., Ltd.) was used, and SiO ₂ as shown in Table 3 below. The same procedure as in Reference Example 1 was applied except that Al ₂ O ₃ was applied in place of the dielectric layer, and the dielectric layer: Al ₂ O _{3 had} a thickness of 60 nm, and the metal film layer: Ni-based alloy (Ni—Ti) An absorptive multilayer ND filter according to Example 3 having the same structure as that of the absorptive multilayer ND filter of FIG.

That is, a PC (polycarbonate) film with a thickness of 100 μm cut to φ60 mm was used as the substrate, and this film was fixed with a metal frame that pressed a portion about 5 mm from the edge, and film formation was performed on one side. An RF magnetron sputtering apparatus (manufactured by ULVAC, Inc.) was used for the film formation, the film formation rate of the dielectric layer: Al ₂ O ₃ was 0.2 nm / second, the metal film layer: the Ni-based alloy target [Sumitomo Metal Mining Co., Ltd.] The film formation rate of “made by Co., Ltd.” was 0.1 nm / second. Further, as shown in Table 3, since both surfaces have the same film configuration, film formation in the same process was performed on each side. FIG. 12 shows the theoretical spectral transmittance when the absorption multilayer film is formed on one side, FIG. 13 shows the theoretical spectral reflectance, and the absorption multilayer film ND according to Example 3 actually formed. The spectral transmittance of the filter is shown in FIG.

  When the absorption type multilayer ND filter according to Example 3 was placed on a surface plate, there was almost no warping of the film as the substrate, and the gap at the center was 0.2 mm or less, so that it could not be measured accurately. there were.

[Example 4]
In place of the Ni target used in Reference Example 1, a Ni-based alloy target containing 7.5 wt% Ti (manufactured by Sumitomo Metal Mining Co., Ltd.) was used, and SiO ₂ as shown in Table 4 below. The same procedure as in Reference Example 1 was performed except that a mixture of SiO ₂ and Al ₂ O ₃ (molar ratio 1: 1) was applied instead of the dielectric layer, and the dielectric layer: in the mixture of SiO ₂ and Al ₂ O ₃ Absorptive multilayer ND filter according to Example 4 having the same structure as the absorptive multilayer ND filter of FIG. 6 having a thickness of 67 nm and a metal film layer: Ni-based alloy (Ni—Ti) having a thickness of 7.3 nm Manufactured.

That is, a PC (polycarbonate) film with a thickness of 100 μm cut to φ60 mm was used as the substrate, and this film was fixed with a metal frame that pressed a portion about 5 mm from the edge, and film formation was performed on one side. An RF magnetron sputtering apparatus (manufactured by ULVAC, Inc.) was used for film formation, the film formation rate of the dielectric layer: the mixture of SiO ₂ and Al ₂ O ₃ was 0.2 nm / second, and the metal film layer: the above Ni-based alloy The film formation rate of the target [manufactured by Sumitomo Metal Mining Co., Ltd.] was 0.1 nm / second. In addition, as shown in Table 4, since both surfaces have the same film configuration, film formation in the same process was performed on each side. FIG. 15 shows the theoretical spectral transmittance when the absorption multilayer film is formed on one side, FIG. 16 shows the theoretical spectral reflectance, and the absorption multilayer film ND according to Example 4 actually formed. The spectral transmittance of the filter is shown in FIG.

  And when the absorption type multilayer ND filter according to Example 4 was placed on a surface plate, there was almost no warping of the film as a substrate, and the gap in the central part was 0.2 mm or less and could not be measured accurately. there were.

[Comparative example]
First, an absorption multilayer film was formed on a PC film, and then a multilayer antireflection film was formed to obtain an absorption multilayer film ND filter according to a comparative example.

An RF magnetron sputtering apparatus (manufactured by ULVAC, Inc.) was used for film formation, and the film formation rate of the dielectric layer: SiO ₂ in the absorption multilayer film was 0.2 nm / second, and the film formation rate of the metal film layer: Ni was 0. .1 nm / sec. The film formation rate of the dielectric layer: SiO ₂ in the multilayer antireflection film was 0.2 nm / second, and the film formation rate of the metal film layer: Ta ₂ O ₅ was also 0.2 nm / second.

The film structure of the absorptive multilayer film formed on one side of the PC film is the same as that of the absorptive multilayer film ND filter shown in FIG. 2, the dielectric layer: SiO _{2 has} a thickness of 80 nm, and the metal film layer: Ni has a thickness. Was 10 nm. Further, the film structure of the multilayer antireflection film formed on the other surface of the PC film was the same as that of the absorption multilayer film ND filter shown in FIG.

  When the absorption multilayer ND filter according to the comparative example is placed on a surface plate (however, the absorption multilayer film of the absorption multilayer ND filter is on the upper side and the multilayer antireflection film is on the lower side), A certain PC film was warped, and a gap of about 2 mm was observed at the center. When the substrate size is φ60 mm and a gap of 0.9 mm occurs in the center, the curvature radius of the warp is 500 mm, and the result shows that the curvature radius is smaller than that.

"Evaluation"
Next, spectral transmission characteristics of the absorption multilayer ND filter according to Reference Example 1 and Examples 3 and 4 and the absorption multilayer ND filter according to the comparative example were evaluated. Spectral transmission characteristics were measured with a self-recording spectrophotometer manufactured by Hitachi, Ltd.

  The spectral transmission characteristics of the absorption multilayer ND filter according to Reference Example 1, Examples 3 and 4 are shown in FIGS. 9, 14 and 17, and the spectral transmission characteristics of the absorption multilayer ND filter according to the comparative example are shown. 10 shows.

  As a result, both the absorption multilayer ND filter according to Reference Example 1 and Examples 3 and 4 and the absorption multilayer ND filter according to the comparative example have substantially the same transmission characteristics in the used wavelength band of 0.4 to 0.7 μm. Met.

  As described above, the absorption multilayer ND filter according to each embodiment has the same optical characteristics as the absorption multilayer ND filter according to the conventional example (comparative example), and obtains an ND filter without warping of the substrate. I was able to. Moreover, in addition to having the same film configuration on both sides, all the dielectric layers on both sides have the same thickness, and all the metal film layers have the same thickness. Also, productivity is excellent.

  The absorptive multilayer ND filter according to the present invention is a small thin digital camera with a small space for incorporating an absorptive ND filter mixed with an absorptive substance in the substrate itself or an absorptive multilayer ND filter using a thick glass substrate. There is a possibility of being used.

DESCRIPTION OF SYMBOLS 1 Absorption type multilayer film 2 Antireflection film 3 Substrate 4 Surface plate 5 Film substrate 6 Absorption type multilayer film 7 Multilayer antireflection film 8 Dielectric layer made of SiO ₂ 9 Metal film layer made of Ni simple substance 10 Dielectric made of SiO ₂ Layer 11 Metal film layer made of Ta ₂ O ₅ 12 Film substrate 13 Absorbing multilayer film 14 Dielectric layer made of SiO ₂ , Al ₂ O ₃ or a mixture thereof 15 Metal film layer made of Ni alone or Ni-based alloy 16 Absorption Type multilayer film 17 Dielectric layer made of SiO ₂ , Al ₂ O ₃ or a mixture thereof 18 Metal film layer made of Ni alone or Ni-based alloy

Claims (3)

Absorption type multi-layer film is a resin film to attenuate the transmitted light, provided on a substrate made of a resin plate or a glass sheet, the absorption type multilayer film, a dielectric layer made of SiO _2, Al ₂ O _3, or which such mixture of Ti Absorption multilayer ND filter composed of a multilayer film in which metal film layers made of an Ni-based alloy to which one or more elements selected from Al, V, W, Ta, and Si are added are alternately laminated In the manufacturing method of
Each of the absorption multilayer films is formed on both sides of the substrate so as to have a symmetrical film structure around the substrate, and the curvature radius of the warp of the substrate is adjusted to 500 mm or more, and addition of Ti element The proportion is 5 to 15% by weight, the addition rate of Al element is 3 to 8% by weight, the addition rate of V element is 3 to 9% by weight, the addition rate of W element is 18 to 32% by weight, and the addition rate of Ta element is Absorption type characterized in that said metal film layer is formed by magnetron sputtering method using Ni-based material target set in the range of 5 to 12% by weight and Si element addition ratio in the range of 2 to 6% by weight, respectively. Manufacturing method of multilayer ND filter. The total film thickness of the dielectric layer on one side of the substrate made of SiO ₂ , Al ₂ O ₃ or a mixture thereof is set to 100 nm or more, and the total film thickness of the metal film layer on the side of the substrate made of Ni-based alloy is set to 30 nm or less. The method for producing an absorptive multilayer ND filter according to claim 1, wherein: The thicknesses of the dielectric layers made of SiO ₂ , Al ₂ O ₃ or a mixture thereof are all set to the same thickness, and the thicknesses of the metal film layers made of the Ni-based alloy are all set to the same thickness. 2. The method for producing an absorptive multilayer ND filter according to claim 1, wherein the method is set.

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