JP7162867B2 - ND filter and its manufacturing method - Google Patents

Description

The present invention relates to an ND (Neutral Density) filter and a method for manufacturing an ND filter.

As an ND filter, one described in Japanese Patent No. 5909523 (Patent Document 1) is known. In this ND filter, the Si ₃ N ₄ film as the water vapor barrier layer is arranged above (on the surface side) the Ti _x O _y film as the light absorption layer, so that deterioration of the Ti _x O _y film due to water vapor is prevented. prevented.
Further, as an ND filter, one described in Japanese Patent Application Laid-Open No. 2003-322709 (Patent Document 2) is known. In this ND filter, the light-absorbing film is a low-grade metal nitride film ( _NbNx film), and the light-absorbing film is oxidized by a transparent dielectric film ( _SiO2 film) that is usually placed adjacent to the light-absorbing film. is prevented, and furthermore, the transmittance change is prevented, or the spectral characteristic of the ND filter is prevented from changing.

Japanese Patent No. 5909523 JP-A-2003-322709

In the ND filter of Japanese Patent No. 5909523, the Si ₃ N ₄ film is a water vapor barrier layer, and no particular consideration is given to the interaction between the Si ₃ N ₄ film itself and the Ti _x O _y film itself.
In the ND filter disclosed in Japanese Unexamined Patent Application Publication No. _2003-322709 , the light absorption film is an NbN _x film to prevent oxidation due to the SiO ₂ film. is relatively difficult due to severe reaction conditions such as requiring high temperature.
SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an ND filter and a method for manufacturing an ND filter in which the interaction between the light absorbing film and the film adjacent thereto is suppressed and the formation of these films is facilitated. be.

The invention according to claim 1 is an ND filter, comprising: a substrate; a light absorbing layer made of a mixture of Nb and Si disposed on one or more surfaces of the substrate; and disposed adjacent to the light absorbing layer. and a light-absorbing adjacent layer made of _SiNx .
A related invention is an ND filter comprising a substrate, a light absorbing layer comprising a mixture of Nb and Si disposed on one or more surfaces of the substrate, and a SiN layer disposed adjacent to the light absorbing layer. a light-absorbing adjacent layer consisting of _x , said light-absorbing layer comprising a first sputtering source for sputtering Nb and a second sputtering source for sputtering Si; It is characterized by being formed by a drum-type sputtering deposition apparatus having a drum that rotates while holding the substrate so as to repeatedly pass through two sputtering sources. Incidentally, in the present invention, the light absorption layer is considered to have a density of a degree that is formed by a drum-type sputtering deposition apparatus having the first sputtering source, the second sputtering source, and the drum. Also good.
According to a second aspect of the present invention, there is provided an ND filter, comprising a substrate and a light absorption layer made of a mixture of Nb and Si disposed on one or more surfaces of the substrate, and The content of Si in is 6.7% or more and 51.1% or less.
The invention according to claim 3 is characterized in that, in the above invention, the substrate cannot be wound up.

According to a fourth aspect of the present invention, a light absorbing layer made of a mixture of Nb and Si and a _SiNx layer disposed adjacent to the light absorbing layer are formed on at least one surface of a substrate by a drum-type sputtering deposition apparatus. A method of manufacturing an ND filter by forming a light absorbing adjacent layer consisting of a radical source capable of radicalizing gas for irradiation; and a drum rotating while holding the substrate such that the substrate repeatedly passes through the first sputtering source, the second sputtering source, and the radical source. , wherein the light absorbing layer is deposited by simultaneous operation of the first sputtering source and the second sputtering source and the drum; and the light absorbing adjacent layer is formed by the second sputtering source and the gas. is characterized in that the film is formed by the simultaneous operation of the radical source and the drum using N ₂ gas.
According to a fifth aspect of the present invention, in the above invention, a SiO ₂ layer made of SiO ₂ is further formed, and the SiO ₂ layer is formed by using the second sputtering source and the gas as O ₂ gas. The film is formed by the simultaneous operation of the radical source and the drum.
The invention according to claim 6 is characterized in that, in the above invention, the substrate cannot be wound up.

The main effect of the present invention is to provide an ND filter and a method for manufacturing an ND filter in which the interaction between the light absorbing film and the film adjacent thereto is suppressed and these films are easily formed. .

1 is a schematic cross-sectional view of a drum-type sputtering film deposition apparatus; FIG. 5 is a graph of spectral transmittance and spectral reflectance in designs of Example 1 and Comparative Example 1. FIG. 4 is a graph of optical constants of SiN _x ; It is a graph related to the optical constant of Nb. 1 is a graph of optical constants of SiO ₂ ; 4 is a graph of measured spectral transmittance and spectral reflectance of Example 1. FIG. 4 is a graph of measured spectral transmittance and spectral reflectance of Comparative Example 1. FIG. 4 is a graph of optical constants of Nb ₂ O ₅ ; 7 is a graph of spectral transmittance measured in a heating test of Example 2. FIG. 4 is a graph of measured spectral transmittance and spectral reflectance of Example 3. FIG. 10 is a graph of measured spectral transmittance and spectral reflectance of Example 4. FIG. It is a graph related to the optical constants of Nb (6 kW input power during sputtering) + Si (4 kW power input during sputtering). 10 is a graph of measured spectral transmittance and spectral reflectance of Example 5. FIG. It is a graph related to the optical constants of Nb (6 kW input power for sputtering) + Si (8.5 kW for the same). 10 is a graph of measured spectral transmittance and spectral reflectance of Example 6. FIG. 11 is a graph of spectral transmittance measured in a heating test of Example 7. FIG. 10 is a graph of spectral transmittance measured in a heating test of Example 8. FIG. It is a graph relating to optical constants of Nb (6 kW input power during sputtering)+Si (1.5 kW in the same case). 10 is a graph of spectral transmittance measured in a heating test of Example 9. FIG. It is a graph related to the optical constants of Nb (9 kW input power during sputtering) + Si (3 kW power). 10 is a graph of spectral transmittance measured in a heating test of Example 10. FIG. It is a graph related to the optical constants of Nb (4 kW input power during sputtering) + Si (10 kW power). 11 is a graph of spectral transmittance measured in a heating test of Example 11. FIG. It is a graph related to the optical constants of Nb (3 kW input power for sputtering) + Si (10 kW for the same). 10 is a graph of spectral transmittance measured in a heating test of Example 12. FIG. 5 is a graph showing the relationship between the Si content (%, horizontal axis) in the Nb+Si layer and the amount of change in transmittance (point, vertical axis) in a heating test in Examples 2 and 7 to 12;

Hereinafter, examples of embodiments according to the present invention will be described with appropriate reference to the drawings.
In addition, the present invention is not limited to the following examples.

INDUSTRIAL APPLICABILITY The ND filter according to the present invention is a filter that has a substantially flat transmittance distribution with respect to light in a specific wavelength band and that transmits the light substantially uniformly. For example, the difference between the maximum value and the minimum value of transmittance [%] in the wavelength range is preferably within 15 points, more preferably within 10 points, and still more preferably within 5 points.
The specific wavelength range includes, for example, the visible range. The visible region is, for example, 400 nanometers (nm) or more and 780 nm or less. .
Also, the specific wavelength range may be an ultraviolet range or an infrared range instead of the visible range, or together with the visible range, or a combination thereof.
In the following description, the specific wavelength range to be uniformly transmitted is the visible range, but the description does not limit the specific wavelength range to the visible range.

In the ND filter according to the present invention, a light absorbing film is formed on either one side or both sides of the substrate. One or more films such as a hard coat film, an antifouling film, an antireflection film, and a conductive film may be applied to at least one of the substrate side and the surface side of the light absorbing film. Incidentally, the hard coat film, the conductive film, and the like may be treated as being included in the light absorption film.
The substrate may be made of any material, including resin such as polycarbonate and glass, as long as it is transparent (including translucent as appropriate), preferably glass containing an alkali element, and more preferably tempered glass. Yes, for example chemically strengthened glass.
A tempered glass substrate has a compressive stress layer formed on its surface, so even if cracks occur on the surface, the crack growth is suppressed by the compressive stress, making it more resistant to impact than ordinary (non-strengthened) glass substrates. Strong against
Also, the substrate is preferably non-rollable and non-rollable. If the substrate is not so flexible that it cannot be wound unless it is deformed, the light absorbing film and the like can be formed more stably, and the ND filter can be made more robust.

The light-absorbing film is a film containing one or more layers, and has one or more light-absorbing layers that absorb visible light whose wavelength range is light in the visible range, and the uniform transmission of the visible light (ND ).
When the light absorbing films are formed on both sides, it is preferable that both films have the same structure when viewed from the substrate.
The light absorbing layer is a layer made of Nb (niobium) or a Nb+Si layer made of a mixture of Nb and Si (silicon, silicon). A plurality of light absorption layers may be provided, and a part thereof may be formed of another material such as a metal or metal oxide other than the Nb layer or the Nb + Si layer, but preferably one or more light absorption layers All of the layers are Nb layers or Nb+Si layers.
Regarding absorption for uniform transmission of visible light, absorption [%] is simply expressed as "100-(transmittance [%] + reflectance [%])", so spectral transmission in the visible range It can be grasped by the flatness of the index distribution and the spectral reflectance distribution, and when the reflectance is small, it can be grasped by the flatness of the spectral transmittance distribution. The flatness of absorption is evaluated by the difference between the maximum and minimum values of absorption, and the flatness of spectral transmittance distribution is evaluated by the difference between the maximum and minimum values of transmittance. High flatness. There is a strong need for high flatness as it provides uniform light attenuation. There is also a need to provide a wide variety of variations by increasing the transmittance or decreasing the transmittance in the red region from that in the blue region.
For example, the light used by the imaging device of a camera with an ND filter is light transmitted through the ND filter, and the reflected light from the ND filter causes noise in the imaging device and optical system. % or less, and uniform absorption is required for the above-mentioned flat spectral transmittance distribution.
Further, when the light absorbing film is a multilayer film having a plurality of layers, in order to achieve a desired transmittance for the ND filter as a whole, absorption of visible light by the light absorbing layer may Alternatively, it may be a distribution corresponding to the distribution of absorption, transmittance, or reflectance in the substrate.

In addition, since the light absorption film whose light absorption layer is an Nb layer has functions other than the flat absorption function, such as the function of preventing the reflection of visible light, it is made of a low-temperature material containing SiN _x (silicon nitride). It includes a low refractive index layer made of a refractive index material.
A SiN _x film is also called a silicon nitride film. For example, in a vacuum chamber having a sputtering source, nitrogen gas discharged by a high frequency, that is, radical nitrogen is introduced into the sputtering source, and Si set in the sputtering source is used as a target. As a result of the sputtering, deposition and nitridation of Si are repeated to form a film on the substrate. The value of x in SiN _x depends on the film formation conditions, that is, the degree of vacuum in the vacuum chamber, the input power of the high frequency, the flow rate of the nitrogen gas, whether or not radicals other than radical nitrogen are used in combination, and the type of radical when used in combination, input power, and It varies depending on the flow rate, the vacuum chamber temperature, the temperature of the sputtering source, the target temperature, the substrate temperature, etc. For example, it is any value in the range of more than 0 and 1.5 or less, and the radical nitrogen is introduced to some extent. For example, it falls within the range of 1.0 or more and 1.5 or less or 1.2 or more and 1.5 or less, which is approximately 1.33.
The value of x can be controlled to some extent by adjusting the film formation conditions, but direct identification is not realistic because it is necessary to observe the entire layer with an electron microscope or the like that can see atoms. Direct measurement is extremely difficult. Therefore, the specification of SiN _x or SiN _x layer is useful, and the specification of SiN _x or SiN _x layer under suitable film formation conditions during sputtering is useful and easy to understand for those skilled in the art.

A low refractive index layer formed by a film of _SiNx , ie a layer made of _SiNx , is arranged adjacent to the Nb layer ₍ light absorbing adjacent layer, Nb adjacent layer). The Nb layer is more difficult to be nitrided than oxidized, and compared to the case where the Nb adjacent layer is an oxide such as a _SiO2 layer, the _Nb layer , and the Nb layer is protected from changes during manufacturing and aging.
A low refractive index layer made of a low refractive index material other than _SiNx may be disposed in the layers other than the Nb adjacent layer. Silicon oxide (particularly SiO ₂ ) is exemplified as such a low refractive index material. Also, other dielectric materials, metal materials, or metal oxide materials may be used as the low refractive index material.
Furthermore, a high refractive index layer made of a high refractive index material may be arranged separately from the light absorption layer. Examples of such high refractive index materials include dielectric materials, metal materials, and metal oxide materials. More specific examples include zirconium oxide (especially ZrO ₂ ), titanium oxide (especially TiO ₂ ), At least one of tantalum oxide (particularly Ta ₂ O ₅ ) and niobium oxide (particularly Nb ₂ O ₅ ) can be used.
The low refractive index layers and the high refractive index layers in the light absorbing film are preferably alternately arranged. Although the number of layers in such a light absorption film is not particularly limited, it is preferably 5 layers or more, more preferably 7 layers or more, from the viewpoint of providing an excellent antireflection function and the like. Since the light absorbing layer has a higher refractive index than most dielectric materials, it can be treated primarily as a high refractive index layer. When the layer closest to the substrate (the layer closest to the substrate) in such a light absorption film is the first layer, the first layer may be a low refractive index layer or a high refractive index layer. However, the odd-numbered layers are preferably low refractive index layers, and the even-numbered layers are preferably high refractive index layers.

On the other hand, the light-absorbing film whose light-absorbing layer is an Nb+Si layer may be a film having only a light-absorbing layer, a film consisting of a light-absorbing layer and a low refractive index layer, or a film composed of these layers. and a high refractive index layer, preferably a film in which a _SiNx layer is arranged as an Nb+Si adjacent layer (light absorbing adjacent layer).
Further, the light absorbing film whose light absorbing layer is an Nb+Si film may be formed in the same manner as the light absorbing film whose light absorbing layer is an Nb layer. For example, low refractive index layers and high refractive index layers are alternately arranged. may be formed by

The Nb+Si layer is preferably deposited by sputtering, and in case the _SiNx layer is co-located, preferably by sputtering in the same vacuum chamber as the deposition of the _SiNx layer.
That is, the Nb+Si layer was formed by introducing radicals of a rare gas such as Ar (argon) into a first sputtering source and a second sputtering source in a vacuum chamber having a plurality of sputtering sources, and setting the first sputtering source. The sputtering with Nb as the target and the sputtering with Si as the target set in the second sputtering source are performed while the substrate is moved between the first sputtering source and the second sputtering source, whereby the substrate Deposition of Nb and deposition of Si are repeated to form a film on the top. The ratio Nb/Si of Nb and Si in the Nb+Si layer depends on the film formation conditions, that is, the degree of vacuum in the vacuum chamber, the common or individual input power and introduction flow rate of radicals to each sputtering source, and whether or not other radicals are used in combination. Also, it changes depending on the type of radical, input power, flow rate, vacuum chamber temperature, temperature of each sputtering source, target temperature, substrate temperature, etc. when used in combination.

An ND filter including a substrate having such a light absorbing film disposed thereon is preferably used for cameras.
The camera ND filter may be retrofitted in front of the camera lens or the like, or may be incorporated in the optical system of the camera (built into the camera).
Further, the camera ND filter may be used for a vehicle-mounted camera, a security camera, or a camera attached to a medical device.

Next, preferred examples of the present invention and comparative examples not belonging to the present invention will be described (Examples 1 to 8, Comparative Example 1).
In addition, the present invention is not limited to the following examples. Moreover, depending on how the present invention is understood, the following examples may substantially become comparative examples, and the following comparative examples may substantially become working examples.

<<Example 1 and Comparative Example 1, etc.>>
Both Example 1 and Comparative Example 1 are ND filters in which a light absorbing film is formed on one side of a flat transparent white plate glass substrate by a drum type sputtering film forming apparatus 1 as shown in FIG. .
A drum-type sputtering deposition apparatus 1 includes a vacuum chamber 2 and a cylindrical drum 4 rotatably arranged in the center thereof about its own axis. A substrate 6 to be film-formed is held on the outer cylindrical surface of the drum 4 with the film-forming surface facing outward.
A first sputtering source 10 is arranged on one side of the vacuum chamber 2 . The first sputtering source 10 includes a sputtering cathode 12 on which a first target T1 is set, a pair of anti-adhesion plates 14, and a sputtering gas introduction port 16 into which the sputtering gas is introduced after appropriately adjusting the flow rate. . The sputtering cathode 12 is connected to an external AC power supply (not shown). The anti-adhesion plate 14 is arranged so as to separate the portion of the drum 4 facing the first target T<b>1 from other internal portions of the vacuum chamber 2 . The sputtering gas introduction port 16 allows the sputtering gas to flow toward the space separated by the anti-adhesion plate 14 .
A second sputtering source 20 is arranged on the other side of the vacuum chamber 2 . The second sputtering source 20, like the first sputtering source 10, includes a sputtering cathode 22 on which the second target T2 is set, a pair of anti-adhesion plates 24, and a sputtering gas inlet .
Furthermore, a radical source 30 is arranged on the other side of the vacuum chamber 2 . The radical source 30 includes a radical gas inlet 34 through which a gas can be introduced after adjusting the flow rate by a valve 32, a gun 36 capable of generating plasma by applying a voltage from an accelerating voltage power supply (not shown), have The gas introduced into the vacuum chamber 2 through the radical gas introduction port 34 is radicalized by the plasma generated by the gun 36 and irradiated toward the substrate 6 in the form of a beam.

In Example 1, on one side of a substrate 6 made of white sheet glass (B270 manufactured by Corning Incorporated), a seven-layer light absorption film having an _SiNx layer as an odd-numbered layer and an Nb layer as an even-numbered layer, and a light absorption film disposed thereon. By forming a SiO ₂ film as the eighth layer, as shown in FIG. was designed to flatten out at 25%. In such a design, previously known optical constants of SiN _x , Nb, and SiO ₂ were used, as shown sequentially in FIGS. In FIG. 2, the left scale indicates the transmittance, and the right scale indicates the reflectance. In FIGS. 3 to 5, the left scale indicates the refractive index, and the right scale indicates the extinction coefficient.
The physical film thickness of each layer in Example 1, including the thickness of the substrate 6, is shown in [Table 1] below.
The _SiO2 film is a low-refractive-index film provided to reduce the spectral reflectance in the visible range or to protect the light-absorbing film. It may be grasped including. Instead of or together with the SiO ₂ film, another low refractive index film such as magnesium fluoride (MgF ₂ ) may be used.

Example 1 was formed by the drum-type sputtering deposition apparatus 1 as follows. The following formation may be automatically controlled by a control means (not shown) of the drum-type sputtering film forming apparatus 1, may be manually performed by an operator, or may be performed by a mixture of these methods. .
First, the substrate 6 was set on the drum 4, Nb was set as the first target T1, and Si was set as the second target T2.
Next, the inside of the vacuum chamber 2 was evacuated to 9×10 ⁻⁴ Pa (Pascal).
Subsequently, the drum 4 is rotated at 100 rpm (rotations per minute) so that the substrate 6 held by the drum 4 passes through the first sputtering source 10, the radical source 30, and the second sputtering source 20 in order repeatedly at high speed. was done.
The substrate 6 was then cleaned. That is, in a state in which oxygen (O ₂ ) gas was introduced from the radical gas inlet 34 of the radical source 30 at a flow rate of 500 ccm (500 milliliters per minute), a high frequency voltage was applied to the gun 36 at an input power of 3 kW (kilowatt). Then, radical oxygen was generated and irradiated to the moving substrate 6 for 30 seconds. By such irradiation of radical oxygen, even if organic substances adhere to the surface of the substrate 6, the organic substances are decomposed and peeled off by the radical oxygen and the ultraviolet rays generated by the plasma, and the surface of the substrate 6 is cleaned. Such cleaning improves the adhesion of the film to be formed later.
The drum-type sputtering deposition apparatus 1 is placed in a room temperature environment, and the vacuum chamber 2, the drum 4, and the substrate 6 are not heated. The maximum temperature of the substrate 6 was 80°C.

Subsequently, Si deposition and nitridation were repeated to form a first SiN _x layer.
That is, while the rotation of the drum 4 is maintained, 100 ccm of Ar gas is introduced from the sputtering gas inlet 26 of the second sputtering source 20, and a high-frequency voltage of 8 kW is applied to the sputtering cathode 22. , Si on the surface of the second target T2 was deposited on the surface of the substrate 6 by sputtering with Ar.
At the same time, in a state in which 80 ccm of nitrogen (N ₂ ) gas was introduced from the radical gas inlet 34 of the radical source 30, a high frequency voltage was applied to the gun 36 at an input power of 3 kW to generate radical nitrogen and deposit Si. Nitriding of Si was performed by irradiating the moving substrate 6 .
The film thickness of the SiN _x layer is controlled by the length of the sputtering time because the power supplied to the sputtering cathode 22 is constant and the film formation rate, which is the physical film thickness formed per unit time, is constant. , the voltage application to the sputtering cathode 22 was stopped when the time corresponding to the desired film thickness had elapsed, and the film formation of the first SiN _x layer was completed.

Then, Nb was deposited to form a second Nb layer.
That is, while the rotation of the drum 4 is maintained, 120 ccm of Ar gas is introduced from the sputtering gas inlet 16 of the first sputtering source 10, and a high frequency voltage of 6 kW is applied to the sputtering cathode 12. , Nb on the surface of the first target T1 was deposited on the surface of the substrate 6 by sputtering with Ar. Here, the radical source 30 was inoperative. The rotation of the drum 4 may be temporarily changed or temporarily stopped after the first layer is formed and before the second layer is formed.
At the time of forming the Nb layer, even if the radical nitrogen associated with the _SiNx layer formation in the previous step remains, Nb is relatively difficult to be nitrided, and the Nb layer forming conditions including the above temperature conditions No nitriding was observed.
The film thickness of the Nb layer can be controlled by time similarly to the _SiNx layer, and when the time corresponding to the desired film thickness has passed, the voltage application to the sputtering cathode 12 is stopped, and the second Nb layer is formed. Layer deposition is complete.

By repeating the film formation of the SiN _x layer and the film formation of the Nb layer in the same manner, up to the seventh light absorption film was formed.

Furthermore, the SiO ₂ film as the eighth layer was formed as follows.
That is, while the rotation of the drum 4 is maintained, 100 ccm of Ar gas is introduced from the sputtering gas inlet 26 of the second sputtering source 20, and a high-frequency voltage of 8 kW is applied to the sputtering cathode 22. , Si on the surface of the second target T2 was deposited on the surface of the substrate 6 by sputtering with Ar.
At the same time, in a state in which 80 ccm of O ₂ gas is introduced from the radical gas inlet 34 of the radical source 30, a high-frequency voltage is applied to the gun 36 at an input power of 3 kW, radical oxygen is generated, and Si is deposited and moved. The substrate 6 was irradiated to oxidize Si.
The film thickness of the SiO ₂ film is also controlled in the same manner as the other layers, and when the time corresponding to the desired film thickness has elapsed, the voltage application to the sputtering cathode 22 is stopped, and the final SiO ₂ film is deposited. was completed, and the formation of Example 1 was completed.

On the other hand, Comparative Example 1 was designed similarly to Example 1, except that the low refractive index layer as the Nb adjacent layer was a _SiO2 layer instead of a _SiNx layer. The physical film thickness of each layer according to the design of Comparative Example 1, including the thickness of the substrate, is shown in [Table 2] below. In Comparative Example 1, the seventh layer, which is the outermost layer of the light absorbing film, is a _SiO2 layer, so the _SiO2 film in Example 1 is not necessary, and only seven light absorbing films are formed. It has become.

Comparative Example 1 was formed by the drum-type sputtering deposition apparatus 1 as follows.
That is, the steps from setting the substrate 6 to cleaning the substrate 6 were performed in the same manner as in the first embodiment.
Next, a first SiO ₂ layer was formed in the same manner as the SiO ₂ film in Example 1.
Subsequently, a second Nb layer was formed in the same manner as in Example 1.
The physical thicknesses of the _SiO2 and Nb layers were controlled as designed.
These formations were repeated up to the seventh layer, and the formation of Comparative Example 1 was completed.

The spectral transmittance and spectral reflectance measured in Example 1 are shown in FIG. 6, and the spectral transmittance and spectral reflectance measured in Comparative Example 1 are shown in FIG.
The actual spectral transmittance in Example 1 flattened out at 25% as designed (FIG. 2). Moreover, the actual spectral reflectance in Example 1 was suppressed to 3% or less in the above-described visible range and adjacent range (400 nm or more and 800 nm or less).
In the ND filter, the flatness and value of the spectral transmittance in the visible region are relatively important compared to the distribution shape of the spectral reflectance. Although the distribution shape of the spectral reflectance is different from that of , there is no problem. As for the spectral reflectance, as long as the magnitude of the reflectance is suppressed, the antireflection function is sufficient.

On the other hand, the actual spectral transmittance in Comparative Example 1 was flat at 45%, significantly different from the design (FIG. 2).
This is because the Nb layer during and after deposition is partially oxidized due to the action of the _SiO2 layer itself and the _O2 gas and radical oxygen that remain even after the deposition. This is thought to be due to
Therefore, assuming that one Nb layer in Comparative Example 1 actually has a three-layer structure of an Nb layer sandwiched between _five upper and lower Nb ₂ O layers, unlike the design, the actual spectral transmittance and spectral reflection The laminate structure of Comparative Example 1 was analyzed to match the ratio (FIG. 7). In this analysis, the optical constants of Nb, SiO ₂ (FIGS. 4-5) and the previously known optical constants of Nb ₂ O ₅ shown in FIG. 8 were used.
As a result, it was found that the laminated structure shown in [Table 3] below matches the actual spectral transmittance and spectral reflectance.

From this analysis result, the following can be understood about Comparative Example 1.
That is, when the Nb adjacent layer is SiO ₂ , the surface of Nb is oxidized during manufacturing, etc., and an Nb ₂ O ₅ layer having characteristics different from those of Nb is generated. Since such an Nb ₂ O ₅ layer is not considered in the design, the actual spectral transmittance and the like of Comparative Example 1 deviate from the design.
Since the degree of oxidation of Nb varies depending on various conditions, even if the generation of the Nb ₂ O ₅ layer is taken into account at the time of design, the physical thickness of the Nb ₂ O ₅ layer will be determined. It cannot be assumed, and after all it is difficult to design.

In contrast to Comparative Example 1, in Example 1, the Nb adjacent layer is a _SiNx layer, and _NbNx is _more difficult to form than _{Nb2O5 .} is easily prevented, the Nb film is manufactured with a physical film thickness as designed, and manufacturing is easy.

<<Example 2, etc.>>
Example 2 is the same as Example 1 except for the physical thickness of each layer.
The physical film thickness of each layer of each film in Example 2, including the thickness of the substrate 6, is shown in [Table 4] below.

In Example 2, as in Example 1, the Nb-adjacent layer is a _SiNx layer, and Nb is difficult to be nitrided. is prevented, the Nb film is manufactured with a physical film thickness as designed, and is easy to manufacture.

Further, the following heat resistance test was conducted on Example 2.
That is, Example 2 after measurement of spectral transmittance and the like was continuously heated at 200° C. for 10 hours in the air. Then, the spectral transmittance of Example 2 after heating was measured and compared with the spectral transmittance before heating.
FIG. 9 shows the spectral transmittance of Example 2 before and after heating in the above-described visible range and adjacent range.
After heating, the spectral transmittance in the wavelength range was generally slightly lower than before heating. The change in average transmittance in the visible range was -1 point.
Example 2 has such a slight change in spectral transmittance due to heating, and is somewhat resistant to heat.

<<Example 3, etc.>>
In Example 3, a film having the same structure as the film structure on one side in Example 1 is also formed on the other side.
The physical film thickness of each layer of each film in Example 3, including the thickness of the substrate 6, is shown in [Table 5] below.
The design value of flat transmittance in Example 3 is 25%×25%=6.25%, since the design value of transmittance on one side is 25% (see Example 1).
In Example 3, after the film on one side is produced in the same manner as in Example 1, the substrate 6 is turned over and set again on the drum 4, and the film on the other side is produced in the same manner. be done.

FIG. 10 shows the spectral transmittance and spectral reflectance measured in Example 3. FIG.
The actual spectral transmittance in Example 3 flattened out at about 6.5%, as designed. Further, the actual spectral reflectance in Example 1 was suppressed to 3% or less in the above-described visible range and adjacent range.

<<Example 4, etc.>>
In Example 4, two substrates 6 with a multilayer film having the same configuration as in Example 1 are formed in the same manner as in Example 1, and the multilayer film sides of these substrates are bonded to each other with an adhesive while facing inward. be done. The adhesive that bonds the SiO ₂ films of _each multilayer film to each other may be UV (ultraviolet) curable or heat curable, and may have any other properties. It is preferable to have a refractive index after curing that is the same or close to the refractive index of the film or _SiNx layer, etc. Here, it is cured by UV irradiation and has a refractive index (1.477) that is close to that of the _SiO2 film. Optical adhesive Optodyne UV manufactured by Daikin Industries, Ltd. was used.
The physical film thickness of each layer of each film in Example 4, including the thickness of the substrate 6 (2 mm) and the thickness of the adhesive (20 μm (micrometers)), is shown in [Table 6] below.
The design value of flat transmittance in Example 4 is 6.25% as in Example 3.

FIG. 11 shows the spectral transmittance and spectral reflectance measured in Example 4. FIG.
The actual spectral transmittance in Example 4 flattened out at about 6.5%, as designed. Further, the actual spectral reflectance in Example 4 was suppressed to 7% or less (5% or less at 410 nm or longer) in the above-mentioned visible range and adjacent range.
In the ND filter of Example 4, the two substrates 6 are the outer surfaces of each surface, so the multilayer film including the light absorbing film is protected. Therefore, the ND filter of Example 4 is more resistant to impacts and scratches.

<<Example 5, etc.>>
Example 5 was formed to have the same structure as Example 1 except that the light absorption layer in the light absorption film was replaced with an Nb+Si layer made of Nb+Si instead of the Nb layer.
Example 5, like Example 1, was designed so that the spectral transmittance in the visible range was flat at 25%. In such a design, in addition to the previously grasped optical constants of SiN _x (FIG. 3) and SiO ₂ (FIG. 5), the previously grasped input power for Nb sputtering as shown in FIG. The optical constants of Nb+Si were used, where σ was 6 kW and the input power for sputtering Si was 4 kW.
The physical film thickness of each layer of each film in Example 5, including the thickness of the substrate 6, is shown in [Table 7] below.

Example 5 was formed by the drum-type sputtering deposition apparatus 1 as follows.
That is, the steps from setting the substrate 6 to forming the first SiN _x layer were performed in the same manner as in the first embodiment.
A second Nb+Si layer was then deposited by deposition of Nb and Si. That is, while the rotation of the drum 4 is maintained, 120 ccm of Ar gas is introduced from the sputtering gas inlet 16 of the first sputtering source 10, and a high frequency voltage of 6 kW is applied to the sputtering cathode 12. , Nb on the surface of the first target T1 was deposited on the surface of the substrate 6 by sputtering with Ar. At the same time, 200 ccm of Ar gas is introduced from the sputtering gas inlet 26 of the second sputtering source 20, and a high-frequency voltage with an input power of 4 kW is applied to the sputtering cathode 22, so that Si on the surface of the second target T2 is transformed into Ar was deposited on the surface of the substrate 6 by sputtering. Here, the radical source 30 was not used. The film thickness of the Nb+Si layer is also controlled in the same manner as the other layers, and when the time corresponding to the desired film thickness has passed, the voltage application to the sputtering cathodes 12 and 22 is stopped, and the film formation of the Nb+Si layer is completed. did.
Then, after the third layer, the film formation of the _SiNx layer and the film formation of the Nb+Si layer are repeated up to the seventh layer, and the SiO film as the eighth layer is formed in the same manner as in Example ₁ . The formation of Example 5 was completed.

Nb and Si in each Nb+Si layer of Example 5 are sputtered while the substrate 6 on the drum 4 rotating at high speed is successively passed through the first sputtering source 10 and the second sputtering source 20. It is thought that it is uniformly mixed at Determining microscopic structures and bonding states related to mixing requires a great deal of cost and is not realistic at present.
The ratio of Nb and Si can be estimated from the increment of the deposition rate during deposition of the Nb+Si layer with respect to the deposition rate during deposition of the Nb layer. That is, the film formation rate at the time of forming the Nb layer (input power for Nb: 6 kW) was 0.2006 nm/sec in Example 1. On the other hand, the film formation rate at the time of forming the Nb+Si layer (6 kW input power for Nb, 4 kW input power for Si) was 0.2400 nm/sec in Example 5, and the increment was 0.0394. . If this increment were applied to Si, then Si/(Nb+Si)×100=0.0394/0.2400×100≈16.4% with a ratio of 16.4% Si and 83.6% Nb. presumed to be.

FIG. 13 shows the spectral transmittance and spectral reflectance measured in Example 5. FIG.
The actual spectral transmittance in Example 5 flattened out at about 25% as designed. Further, the actual spectral reflectance in Example 5 was suppressed to 4% or less in the above-described visible range and adjacent range.
A mixture of Nb and Si is more difficult to nitridate than to oxidize, and it is difficult to form a nitride thin film on the surface of the Nb+Si layer. .

<<Example 6, etc.>>
Example 6 was formed in the same manner as Example 5, except that the input power for Si and the amount of Ar gas introduced during the formation of the Nb+Si layer were changed.
Example 6, like Examples 1 and 5, was designed so that the spectral transmittance in the visible range was flat at 25%. In such a design, as shown in FIG. 14, the power input for Nb sputtering is 6 kW and the input power for Si sputtering is 8.5 kW. A constant was used.
The physical film thickness of each layer of each film in Example 6, including the thickness of the substrate 6, is shown in [Table 8] below.

In the formation of Example 6 by the drum-type sputtering deposition apparatus 1, the input power for Si sputtering was 8.5 kW, and the Ar gas introduction amount for Si sputtering was 120 ccm.
The ratio of Nb and Si in Example 6 is estimated in the same manner as in Example 5. That is, the film formation rate at the time of forming the Nb layer (input power for Nb: 6 kW) was 0.2006 nm/sec in Example 1. On the other hand, the film formation rate at the time of forming the Nb+Si layer (6 kW input power for Nb, 8.5 kW input power for Si) was 0.2921 nm/sec in Example 6, and the increment was 0.0915. there were. If this increment were applied to Si, then Si/(Nb+Si)×100=0.0915/0.2921×100≈31.3% with a ratio of 31.3% Si and 68.7% Nb. presumed to be.

FIG. 15 shows the spectral transmittance and spectral reflectance measured in Example 6. FIG.
The actual spectral transmittance in Example 6 flattened out at about 25%, as designed. Further, the actual spectral reflectance in Example 6 was suppressed to 3% or less in the above-described visible range and adjacent range.
Also in Example 6, similarly to Example 5, a nitride thin film is hardly formed on the surface of the Nb+Si layer, and the spectral transmittance and the like can be easily obtained as designed.

<<Example 7, etc.>>
Example 7 is similar to Example 5 except for the physical thickness of each layer.
The input power for the sputtering of Si during the formation of the Nb+Si layer of Example 7 was 4 kW as in Example 5, and the ratio of Nb and Si in the Nb+Si layer of Example 7 was also the same as in Example 5. is presumed to be
The physical film thickness of each layer of each film in Example 7, including the thickness of the substrate 6, is shown in [Table 9] below.

Similarly to Example 5, Example 7 has flat spectral transmittance and low spectral reflectance, is manufactured with a physical film thickness as designed, and is easy to manufacture.

Further, the ND filter of Example 7 was subjected to a heat resistance test in the same manner as in Example 2.
The spectral transmittance of Example 7 before and after heating is shown in FIG.
There was almost no change in spectral transmittance before and after heating. The change in average transmittance in the visible range was -0.07 points.
According to the results of the heat resistance test, even Example 2, in which the light absorption layer is the Nb layer, has a certain degree of heat resistance. It can be said that 7 is more excellent in heat resistance.

<<Example 8, etc.>>
Example 8 is similar to Example 6 except for the physical thickness of each layer.
The input power for the sputtering of Si during the formation of the Nb+Si layer of Example 8 was 8.5 kW as in Example 6, and the ratio of Nb and Si in the Nb+Si layer of Example 8 was also is presumed to be similar to
The physical film thickness of each layer of each film in Example 8, including the thickness of the substrate 6, is shown in [Table 10] below.

Similarly to Example 6, Example 8 has a flat spectral transmittance and a low spectral reflectance, is manufactured with a physical film thickness as designed, and is easy to manufacture.

Further, a heat resistance test was conducted on Example 8 in the same manner as Examples 2 and 7.
The spectral transmittance of Example 8 before and after heating is shown in FIG.
There was almost no change in spectral transmittance before and after heating. The change in average transmittance in the visible range was +0.26 points.
According to the results of the heat resistance test, it can be said that Example 8, in which the light absorption layer is the Nb+Si layer, has better heat resistance than Example 2, in which the light absorption layer is the Nb layer.

<<Example 9, etc.>>
Example 9 was formed in the same manner as Example 5, except that the operation of the radical source 30 during the formation of the Nb+Si layer, the input power related to Si, and the amount of Ar gas introduced were changed.
Example 9 was designed to have a flat spectral transmittance of 20% in the visible region. In such a design, as shown in FIG. 18, the power input for Nb sputtering is 6 kW and the input power for Si sputtering is 1.5 kW. A constant was used.
The first layer in Example 9 is a SiO ₂ film, which, like the outermost SiO ₂ film, is used to reduce the spectral reflectance in the visible region or to ensure the adhesion of the light absorbing film to the substrate. It may be included in the light absorption film as one layer belonging to the light absorption film, which is a film having a low refractive index. Instead of or together with the SiO ₂ film, another low refractive index film such as magnesium fluoride (MgF ₂ ) may be used.
The 2nd to 9th layers in Example 9 are the same as the 1st to 8th layers in Example 5 except for the physical film thickness and the proportion of Si in the Nb+Si layer.
The physical film thickness of each layer of each film in Example 9, including the thickness of the substrate 6, is shown in [Table 11] below.

In the formation of the Nb+Si layer of Example 9 by the drum-type sputtering deposition apparatus 1, the input power for Si sputtering was 1.5 kW, and the Ar gas introduction amount for Si sputtering was 350 ccm. Also, the radical source 30 is activated by the introduction of Ar gas, and the amount of Ar gas introduced is 100 ccm with an input power of 1 kW.
The ratio of Nb and Si in Example 9 is estimated in the same manner as in Example 5. That is, the film formation rate at the time of forming the Nb layer (input power for Nb: 6 kW) was 0.2006 nm/sec in Example 1. On the other hand, the film formation rate at the time of forming the Nb+Si layer (input power for Nb: 6 kW, power for Si: 1.5 kW) was 0.215 nm/sec in Example 9, and the increment was 0.0144. there were. If this increment were applied to Si, then Si/(Nb+Si)×100=0.0144/0.215×100≈6.697% with a ratio of 6.7% Si and 93.3% Nb. presumed to be.

Also in Example 9, it has a flat spectral transmittance and a low spectral reflectance, is manufactured with a physical film thickness as designed, and is easy to manufacture.

Further, the heat resistance test of Example 9 was conducted in the same manner as in Examples 2, 7 and 8.
The spectral transmittance of Example 9 before and after heating is shown in FIG.
There was almost no change in spectral transmittance before and after heating. The change in average transmittance in the visible range was -0.10 points.
According to the results of the heat resistance test, it can be said that Example 9, in which the light absorption layer is the Nb+Si layer, has better heat resistance than Example 2, in which the light absorption layer is the Nb layer.

<<Example 10, etc.>>
Example 10 was formed in the same manner as Example 9, except that the input power for sputtering of Nb and Si and the introduction amount of Ar gas for Si were changed during the formation of the Nb+Si layer. In Example 10, the radical source 30 does not operate during the formation of the Nb+Si layer.
Example 10 was designed to have a flat spectral transmittance of 22% in the visible region. In such a design, as shown in FIG. 20, the optical constant of Nb+Si when the input power for Nb sputtering is 9 kW and the input power for Si sputtering is 3 kW is ascertained in advance. used.
The physical film thickness of each layer of each film in Example 10, including the thickness of the substrate 6, is shown in [Table 12] below.

In the formation of Example 10 by the drum-type sputtering deposition apparatus 1, the input power for Nb sputtering was 9 kW, and the Ar gas introduction amount for Nb sputtering was 120 ccm. Also, the input power for Si sputtering is 3 kW, and the Ar gas introduction amount for Si sputtering is 120 ccm.
The ratio of Nb and Si in Example 10 is estimated in the same manner as in Examples 5-9. That is, the film formation rate at the time of forming the Nb layer (input power for Nb: 6 kW) was 0.2006 nm/sec in Example 1. On the other hand, the film formation rate during Nb+Si layer formation (input power for Nb: 9 kW, input power for Si: 3 kW) was 0.22 nm/sec in Example 10, and the increment was 0.0194. . If this increment were applied to Si, then Si/(Nb+Si)×100=0.0194/0.22×100≈8.81% with a ratio of 8.8% Si and 91.2% Nb. presumed to be.

Also in Example 10, it has a flat spectral transmittance and a low spectral reflectance, is manufactured with a physical film thickness as designed, and is easy to manufacture.

Further, the heat resistance test of Example 10 was conducted in the same manner as Examples 2 and 7-9.
The spectral transmittance of Example 10 before and after heating is shown in FIG.
There was almost no change in spectral transmittance before and after heating. The change in average transmittance in the visible range was -0.20 points.
According to the results of the heat resistance test, it can be said that Example 10, in which the light absorption layer is the Nb+Si layer, has better heat resistance than Example 2, in which the light absorption layer is the Nb layer.

<<Example 11, etc.>>
Example 11 was formed in the same manner as Example 10, except that the input powers for the sputtering of Nb and Si during the formation of the Nb+Si layer were changed.
Example 11 was designed to have a flat spectral transmittance of 25% in the visible region. In such a design, as shown in FIG. 22, when the input power for Nb sputtering is 4 kW and the input power for Si sputtering is 10 kW, the optical constant of Nb+Si is used.
The physical film thickness of each layer of each film in Example 11, including the thickness of the substrate 6, is shown in [Table 13] below.

In the formation of Example 11 by the drum-type sputtering deposition apparatus 1, the input power for sputtering Nb was 4 kW. Also, the input power for Si sputtering is 10 kW.
The ratio of Nb and Si in Example 11 is estimated in the same manner as in Examples 5-10. That is, the film formation rate at the time of forming the Nb layer (input power for Nb: 6 kW) was 0.2006 nm/sec in Example 1. On the other hand, the film formation rate at the time of forming the Nb+Si layer (4 kW input power for Nb, 10 kW input power for Si) was 0.36 nm/sec in Example 11, and the increment was 0.1594. . If this increment were applied to Si, then Si/(Nb+Si)×100=0.1594/0.36×100≈44.27% with a ratio of 44.3% Si and 55.7% Nb. presumed to be.

Also in Example 11, it has a flat spectral transmittance and a low spectral reflectance, is manufactured with a physical film thickness as designed, and is easy to manufacture.

Further, the heat resistance test of Example 11 was conducted in the same manner as in Examples 2 and 7-10.
The spectral transmittance of Example 11 before and after heating is shown in FIG.
There was almost no change in spectral transmittance before and after heating. The change in average transmittance in the visible range was +0.41 points.
According to the results of the heat resistance test, it can be said that Example 11, in which the light absorption layer is the Nb+Si layer, has better heat resistance than Example 1, in which the light absorption layer is the Nb layer.

<<Example 12, etc.>>
Example 12 was formed in the same manner as Example 11, except that the input power for Nb during the formation of the Nb+Si layer was changed.
Example 12 was designed to have a flat spectral transmittance of 26% in the visible region. In such a design, as shown in FIG. 24, the optical constant of Nb+Si when the input power for Nb sputtering is 3 kW and the input power for Si sputtering is 10 kW is ascertained in advance. used.
The physical film thickness of each layer of each film in Example 12, including the thickness of the substrate 6, is shown in [Table 14] below.

In the formation of Example 12 by the drum-type sputtering deposition apparatus 1, the input power for Si sputtering is 3 kW.
The ratio of Nb and Si in Example 12 is estimated in the same manner as in Examples 5-11. That is, the film formation rate at the time of forming the Nb layer (input power for Nb: 6 kW) was 0.2006 nm/sec in Example 1. On the other hand, the film formation rate when forming the Nb+Si layer (3 kW input power for Nb, 10 kW input power for Si) was 0.41 nm/sec in Example 12, and the increment was 0.2094. . If this increment were applied to Si, then Si/(Nb+Si)×100=0.2094/0.41×100≈51.07% with a ratio of 51.1% Si and 48.9% Nb. presumed to be.

Also in Example 12, it has a flat spectral transmittance and a low spectral reflectance, is manufactured with a physical film thickness as designed, and is easy to manufacture.

Further, a heat resistance test was conducted on Example 12 in the same manner as Examples 2 and 7-11.
The spectral transmittance of Example 12 before and after heating is shown in FIG.
There was almost no change in spectral transmittance before and after heating. The change in average transmittance in the visible range was +0.78 points.
According to the results of the heat resistance test, it can be said that Example 12, in which the light absorption layer is the Nb+Si layer, has better heat resistance than Example 2, in which the light absorption layer is the Nb layer.

The input electric power and the Ar gas flow rate for Nb and Si during the Nb+Si layer formation are not limited to those of Examples 5-12. The input power during sputtering for Si is adjusted to the values of Examples 5 to 12 or other values, or instead of or in conjunction with the adjustment, other film formation including the input power during sputtering for Nb If the conditions are adjusted, the ratio and state of the mixture of Nb and Si are changed according to the adjustment. It is possible to adjust the characteristics of the filter, the manufacturing process, and the like.

≪Summary of heating test, etc.≫
The properties of Examples 2 and 7 to 12 and the results of the heating test (change in transmittance before and after heating) are summarized in the following [Table 15] and FIG.
In [Table 15], the Si contents in the Nb+Si layer are arranged in ascending order.

When the Si content in the Nb+Si layer reached 16.4% (Example 7), the change in transmittance before and after heating was 0. When the Si content decreased below this value, the transmittance decreased after heating (transmittance The amount of change becomes negative), and if the Si content increases beyond this, the transmittance after heating becomes large (the amount of change in transmittance becomes positive).
In addition, the amount of change in transmittance is proportional to the Si content from the value at which the Si content is about 6.7% (Example 9) to the value at which it is about 51.1% (Example 12). (See long auxiliary straight line in FIG. 26).

DESCRIPTION OF SYMBOLS 1... Drum-type sputtering film-forming apparatus, 4... Drum, 6... Substrate, 10... First sputtering source, 20... Second sputtering source, 30... Radical source, T1... First target (Nb ), T2 . . . second target (Si).

Claims (6)

a substrate;
a light absorbing layer of a mixture of Nb and Si disposed on one or more surfaces of the substrate;
a light-absorbing adjacent layer of SiN _x positioned adjacent to the light-absorbing layer;
An ND filter characterized by comprising: a substrate;
a light absorbing layer of a mixture of Nb and Si disposed on one or more surfaces of the substrate;
and
The ND filter, wherein the content of Si in the light absorption layer is 6.7% or more and 51.1% or less. 3. The ND filter according to claim 1, wherein said substrate cannot be wound. A light absorbing layer made of a mixture of Nb and Si and a light absorbing adjacent layer made of _SiNx and arranged adjacent to the light absorbing layer were formed on at least one surface of the substrate by a drum-type sputtering deposition apparatus. A method for manufacturing an ND filter by forming a film,
The drum-type sputtering film forming apparatus is
a first sputtering source for sputtering Nb;
a second sputtering source for sputtering Si;
a radical source capable of radicalizing and irradiating gas;
a drum rotating while holding the substrate such that the substrate repeatedly passes through the first sputtering source, the second sputtering source, and the radical source;
and
The light absorbing layer is deposited by simultaneous operation of the first sputtering source, the second sputtering source and the drum,
A method for manufacturing an ND filter, wherein the light-absorbing adjacent layer is formed by simultaneous operation of the second sputtering source, the radical source using _N2 gas as the gas, and the drum. Furthermore, a SiO ₂ layer made of SiO ₂ is deposited,
5. The manufacture of the ND filter according to claim 4 , wherein the _SiO2 layer is formed by simultaneous operation of the second sputtering source, the radical source using _O2 gas as the gas, and the drum. Method. 6. The method of manufacturing an ND filter according to claim 4 , wherein the substrate cannot be wound.

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