JPH04221904A - Optical multiplayered interference film - Google Patents

Abstract

PURPOSE:To additionally improve the spectral transmittance characteristic of transparent parts, namely to additionally improve and flatten the transmittance and to simultaneously obtain a sharp cut characteristic at the time of obtaining the characteristics of a short-pass filter. CONSTITUTION:This interference film has a multilayered film group A in which high-refractive index films H and low-refractive index films L are alternately formed in multiple layers on a base material 1 and the respective layers have the large optical film thicknesses a equal to each other successively from the base material 1 side, an intermediate layer group B which is formed by superposing one layer each of the high-refractive index films and the low-refractive index films and a multilayered film group C' in which the respective layers have the small optical film thicknesses c equal to each other. The optical film thicknesses b of the respective layers of the intermediate layer group are c+(a-c)/6<=b<=a-(a-c)/6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an optical multilayer interference film used in filters and the like.

0002

2. Description of the Related Art Multilayer films using optical multilayer films have already been produced by methods such as vacuum evaporation, ion plating, and sputtering, and have been put into practical use for various purposes. Among them, those that transmit only wavelengths shorter than a certain wavelength are called short-pass filters. Generally, in a short-pass filter, it is necessary that the transmittance distribution in the transmitting part be as high and flat as possible, and the transmittance distribution in the non-transmissive (reflecting) part be as low and flat as possible. If you want to widen the reflection band, you can stack multilayer films with two different reflection wavelengths (optical film thicknesses) and connect the two reflection bands to expand the band.

[0003] These short-pass filters are usually
It is produced by utilizing the boundary between the reflection region and the transmission region on the shorter wavelength side of an optical multilayer interference film, which is made by alternately laminating high refractive index films and low refractive index films with the same optical film thickness. However, in this part,
As shown in FIG. 3, a ripple-like characteristic called ripple appears, and unless this is suppressed, excellent short-pass characteristics cannot be obtained.

[0004] The most common method for suppressing ripples in a multilayer film (single wavelength configuration) in which all optical film thicknesses are equal and has a single main reflection wavelength is to The structure is such that it becomes a low refractive index film, and its optical thickness is half that of the other layers. In this way, ripples are considerably suppressed and excellent characteristics can be obtained.

[0005]

[Problem to be solved by the invention] However, in this way,
The method of placing a low refractive index film with half the optical thickness on the bottom layer (here, the first layer) has a manufacturing problem. Generally, when producing optical thin films, methods such as vacuum evaporation are used, but the film thickness can be controlled most accurately by using a photoelectric film thickness meter. This is a mechanism that controls the film thickness by measuring changes in the reflectance of a film formed on the surface of a monitor glass installed near the evaporation substrate in the chamber of a vacuum evaporation machine. At this time, the following problems arise. First of all, when a low refractive index film is deposited on the monitor glass,
Generally, a decrease in reflectance occurs, resulting in smaller measured values and lower measurement accuracy. Second, if the film thickness is significantly different from that of other layers, it will either go out of the film thickness measurement range of the instrument, or even if it does not go out, the measurement will be performed near the measurement limit.
Film thickness control is often difficult.

For the above reasons, when a low refractive index film with half the optical thickness is placed in the bottom layer, it is difficult to accurately control the film thickness. If the second layer is formed on this inaccurate first layer, the thickness of the second layer will also be inaccurate, which may require replacing the monitor glass, leading to an increase in costs. Another method to widen the reflection band is to stack multilayer films with two different main reflection wavelengths (optical film thicknesses) and connect the two reflection bands to expand the band (2
Regarding ripple control of wavelength configuration), since two multilayer film groups with different optical film thicknesses interfere with each other, a much more complex interference effect occurs. For this reason, it is difficult to suppress ripples even if a multilayer film group with two wavelengths, long and short, is subjected to the single wavelength ripple treatment and laminated.

Conventionally, as a method for suppressing ripples in a two-wavelength configuration, there has been a method of ``optimizing'' the film configuration through computer simulation. However, this method not only makes manufacturing difficult because the film thickness of each layer varies, but also increases the number of elements to be managed during mass production, making it difficult to suppress variations in characteristics.

[0008] The present invention solves these problems, and when trying to obtain broadband reflection characteristics and short-pass filter characteristics, it improves the spectral transmittance characteristics of the transmitting part, that is, It is an object of the present invention to provide an optical multilayer interference film that can have higher transmittance, flatness, and sharp cut characteristics at the same time.

[0009]

[Means for Solving the Problems] In order to solve the above problems, the present invention has an optical multilayer interference thin film in which high refractive index films and low refractive index films are alternately formed on a base material, In order from the base material side; multilayer film group A in which high refractive index films and low refractive index films having mutually equal optical film thicknesses are formed in multiple layers alternately;
; intermediate layer group B formed by overlapping one high refractive index film and one low refractive index film having mutually equal optical film thicknesses b;
; and a multilayer film group C in which high refractive index films and low refractive index films having mutually equal optical film thicknesses c are alternately formed;
, the optical film thickness a is larger than the optical film thickness c, and
An optical multilayer interference film having an optical thickness b in the range of c+(ac)/6≦b≦a-(ac)/6 is provided. This film thickness b is the film thickness a
and larger than the film thickness c.

In the present invention, film groups A, B, and C having three different optical film thicknesses have a high refractive index film as the first layer and a low refractive index film as the final layer, counting from the respective base material sides. It may have a membrane. In this invention, the final layer of multilayer film group C and the layer two layers before the final layer are low refractive index films, the optical thickness of the final layer is in the range of 0.4c to 0.7c, and the two final layers are low refractive index films. The optical thickness of the front layer may be in the range of 1.05c to 1.25c.

The total number of layers in the multilayer film group A having a large optical thickness is, for example, 10 to 20 layers, and the total number of layers in the multilayer film group C having a small optical thickness is, for example, 10 to 20 layers. Ru. It is preferable that there is no significant difference between these two A and B.

0012

[Function] When the film structure is made up of the above-mentioned three specific film groups A, B and C, for example, FIGS. 3 and 4
As shown in , a short-pass filter with extremely flat and high transmission characteristics can be created. If the film thickness or structure deviates from the range shown in claim 1, the ripple suppressing effect will be weakened or the short-pass characteristics will deteriorate, making it impossible to obtain practical characteristics.

[0013] In this invention, since there is no layer other than the final layer whose thickness differs greatly from other layers, it is easy to measure the thickness. It is inevitable that the final layer should be a low refractive index film with half the film thickness, but in this case, a high refractive index film has been deposited as a previous layer before the final layer, and the reflectance of the monitor glass has already been is considerably high, so the reduction in measurement accuracy due to the reduction in reflectance due to the deposition of a low refractive index film is no longer a problem. Furthermore, since it is the final layer, there is no adverse effect on the thickness of subsequent layers.

[0014] Also from the vapor deposition procedure, all film thickness changes start with the vapor deposition of a high refractive index film, so if the monitor glass is replaced each time, there is no need to start vapor deposition from a low refractive index film. The intermediate layer group B must have one high refractive index film and one low refractive index film. This is because ripple cannot be suppressed sufficiently. If the order of multilayer film groups A and C is reversed, ripples cannot be suppressed sufficiently.

The optical thickness of the layer two layers before the final layer (the third layer from the final layer) (low refractive index film) is set to 1.5 times the thickness of the other alternating layers.
A range of 0.05 to 1.25 times has a subtle effect on ripple suppression. Even if the thickness of this layer is made the same as that of the other basic constituent layers without using such a structure, ripples can be sufficiently suppressed (see FIG. 5). However, since the characteristics will be slightly different, it is only necessary to appropriately select one according to the purpose and use of the optical multilayer interference film.

[0016]

[Embodiments] The present invention will be explained in detail below with reference to drawings showing embodiments thereof. FIG. 1 shows one embodiment of the optical multilayer interference film of the present invention. A multilayer film group A, an intermediate layer group B, and a multilayer film group C are formed on a base material 1 so as to be laminated in this order.

The multilayer film group A is a film group on the long wavelength side, and is a film group with a large optical film thickness (main reflection wavelength; the same applies hereinafter) a. High refractive index films H1 and low refractive index films L1 having the same optical film thickness a are alternately formed in multiple layers. The multilayer film group C is a film group on the short wavelength side, and is a film group with a small optical film thickness c (c<a). High refractive index films H3 and low refractive index films L3 having the same optical film thickness c are alternately formed in multiple layers.

The intermediate layer group B is an intermediate adjustment layer, and is formed by overlapping one high refractive index film H2 and one low refractive index film L2 having the same optical film thickness b. The optical thickness b of each layer of the intermediate layer group B is in the range of c+(ac)/6≦b≦a−(ac)/6. When b is out of this range, the ripple suppression effect disappears (see FIGS. 11 and 12).

The high refractive index film is made of, for example, titanium dioxide, and the low refractive index film is made of, for example, silicon dioxide. As the formation method, for example, the above-mentioned film formation method such as vacuum evaporation is employed. Although the above-mentioned photoelectric film thickness meter and the like are used to manage the film thickness, it is not limited thereto. FIG. 2 shows another embodiment of the optical multilayer interference film of the present invention. This optical multilayer interference film is the same as that shown in FIG. 1 except that the multilayer film group is different (indicated by C' in the figure). In the multilayer film group C', the final layer L5 and the layer L4 two layers before the final layer are low refractive index films, and the optical film thickness of the final layer L5 is 0.4c~
The optical film thickness of the layer L4 two layers before the final layer is in the range of 1.05c to 1.25c.

[0020] Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the following examples. -Example 1- This example is an example in which the optical multilayer interference film of the present invention is a blue filter.

A blue illumination filter for use in stage lighting etc. was produced as follows. The optical thickness a of each layer of the long wavelength side reflective layer (multilayer film group A; the same applies hereinafter) is 194 nm, and the main reflection wavelength is 775 nm; the optical thickness c of the short wavelength side reflective layer (multilayer film group C; the same applies below) is 155 nm. , main reflection wavelength 620 nm;
The optical thickness b of each layer of intermediate layer group B was 174 nm, and the main reflection wavelength was 698 nm. Titanium dioxide was used for the high refractive index film, and silicon dioxide was used for the low refractive index film. 1 reflective layer on the long wavelength side
2 layers, 2 layers of intermediate layer groups, 16 layers of short wavelength side reflective layers, and in this order, the first layer of each layer group is a high refractive index film, and the second layer is a high refractive index film. was formed so that it became a low refractive index film. High refractive index films and low refractive index films were arranged alternately. Among the short wavelength side reflective layers, the optical film thickness of the final layer (first layer as viewed from the air side: low refractive index film) is increased by 0.5 times, and that of the third layer film (low refractive index film) from the air side. The optical film thickness was increased by 1.1 times. As a result, a good blue filter was obtained. As shown in Figure 6, this filter has a high transmittance for the necessary blue color.
Since red and other components on the long wavelength side can be almost completely removed, it has demonstrated excellent efficiency and beautiful light color for lighting applications.

- Example 2 - This example is an example in which the optical multilayer interference film of the present invention is a violet filter. A lighting purple filter used for stage lighting etc. was produced as follows. The optical thickness a of each layer of the long wavelength side reflective layer is 1
69 nm, main reflection wavelength 675 nm; optical film thickness c of the short wavelength side reflection layer is 135 nm, main reflection wavelength 540 nm; optical film thickness b of each layer of intermediate layer group B is 152 nm, main reflection wavelength 60
It was set to 8 nm. Titanium dioxide was used for the high refractive index film, and silicon dioxide was used for the low refractive index film. 12 long wavelength side reflective layers,
Two intermediate layers and 16 short-wavelength reflective layers are deposited in this order on a glass substrate using a vacuum evaporation method, so that the first layer of each layer group is a high refractive index film and the second layer is a low refractive index film from the substrate side. It was formed so as to form a film with a high density. High refractive index films and low refractive index films were arranged alternately. Among the short wavelength side reflective layers, the optical film thickness of the final layer (first layer as viewed from the air side: low refractive index film) is increased by 0.5 times, and that of the third layer film (low refractive index film) from the air side. The optical film thickness was increased by 1.1 times. This resulted in a good purple filter. As shown in Figure 7, this filter has a high transmittance for the necessary violet color and can almost eliminate components such as red on the long wavelength side, so it was able to exhibit excellent efficiency and beautiful light color for lighting applications. .

- Example 3 - This example is an example in which the optical multilayer interference film of the present invention is an infrared cut filter. An infrared cut filter used for lighting was produced as follows. Optical film thickness a of each layer of the long wavelength side reflective layer
269 nm, main reflection wavelength 1075 nm; optical film thickness c of the short wavelength side reflection layer 215 nm, main reflection wavelength 860 nm;
The optical thickness b of each layer of intermediate layer group B was 241 nm, and the main reflection wavelength was 968 nm. Titanium dioxide was used for the high refractive index film, and silicon dioxide was used for the low refractive index film. 1 reflective layer on the long wavelength side
2 layers, 2 layers of intermediate layer groups, 16 layers of short wavelength side reflective layers, and in this order, the first layer of each layer group is a high refractive index film, and the second layer is a high refractive index film. was formed so that it became a low refractive index film. High refractive index films and low refractive index films were arranged alternately. Among the short wavelength side reflective layers, the optical film thickness of the final layer (first layer as viewed from the air side: low refractive index film) is increased by 0.5 times, and that of the third layer film (low refractive index film) from the air side. The optical film thickness was increased by 1.1 times. As a result, a filter with good characteristics was obtained. As shown in Figure 8, this filter has almost uniformly high transmittance in the necessary visible range, and has a wide reflection range, so it can reflect most of the infrared radiation range of incandescent bulbs, making it an excellent choice for lighting. We were able to demonstrate efficiency and a high heat ray cutting rate of over 90%.

Example 4 This example is an example in which the optical multilayer interference film of the present invention is a blue separation mirror. LCD projection televisions (projection televisions) have R. (red), G. (green), B. In order to separate and combine the three primary colors (blue), a 45° selective reflection reflector is used. Of these, B. A blue selective transmission mirror for decomposition of (blue) was prepared as follows.

The optical thickness a of each layer of the long wavelength side reflective layer is 20
0 nm, main reflection wavelength 800 nm; optical film thickness c of the short wavelength side reflection layer is 160 nm, main reflection wavelength 640 nm; optical film thickness b of each layer of intermediate layer group B is 180 nm, main reflection wavelength 720
It was set as nm. Titanium dioxide was used for the high refractive index film, and silicon dioxide was used for the low refractive index film. 12 long-wavelength reflecting layers, 2 intermediate layer groups, and 16 short-wavelength reflecting layers are deposited in this order onto a glass substrate using a vacuum evaporation method, so that the first layer of each layer group has a high refractive index from the substrate side. The second layer was formed as a low refractive index film. High refractive index films and low refractive index films were arranged alternately. Among the short wavelength side reflective layers, the optical film thickness of the final layer (first layer as seen from the air side: low refractive index film) was increased by 0.5 times, and the third layer film (from the air side) was increased by 0.5 times.
The optical film thickness of the low refractive index film) was increased to 1.1 times.

[0026] As a result, a sharp-cut filter with a flat transmission part and high transmittance was obtained. As shown in FIG. 9, this filter has a wide reflection range and can almost completely remove components such as red on the long wavelength side, so that pure light color can be obtained. The characteristics shown in FIG. 9 are those when used at 45°. -Example 5- This example is an example in which the optical multilayer interference film of the present invention is an ultraviolet filter.

An ultraviolet filter for use in an ultraviolet irradiation device was produced as follows. This filter transmits only ultraviolet rays among components emitted from a light source such as a mercury lamp. Since mercury lamps emit a large amount of radiation in the visible range, this leads to the generation of heat, which is an obstacle to low-temperature treatment. The optical thickness a of each layer of the long wavelength side reflective layer is 144
nm, main reflection wavelength 575 nm; optical film thickness c of short wavelength side reflection layer 115 nm, main reflection wavelength 460 nm; intermediate layer group B
The optical thickness b of each layer is 129 nm, and the main reflection wavelength is 518 nm.
It was set as m. Titanium dioxide was used for the high refractive index film, and silicon dioxide was used for the low refractive index film. 12 long-wavelength reflecting layers, 2 intermediate layer groups, and 16 short-wavelength reflecting layers are deposited in this order onto a glass substrate using a vacuum evaporation method, so that the first layer of each layer group has a high refractive index from the substrate side. The second layer was formed as a low refractive index film. High refractive index films and low refractive index films were arranged alternately. Among the short wavelength side reflective layers, the optical film thickness of the final layer (first layer as viewed from the air side: low refractive index film) is increased by 0.5 times, and that of the third layer film (low refractive index film) from the air side. The optical film thickness was increased by 1.1 times.

[0028] As a result, a filter with good characteristics was obtained. As shown in FIG. 10, this filter had a flat and high transmittance in the necessary ultraviolet region, a nearly uniformly high reflectance in the visible region, and was able to exhibit excellent efficiency and high heat ray cut. - Comparative Example 1 - In Example 1, the optical thickness of each layer of the intermediate layer was 160n.
The same procedure as in Example 1 was carried out except that m was used.

The transmission characteristics of the obtained filter are as shown in FIG. 11, and there is no ripple suppressing effect. - Comparative Example 2 - In Example 1, the optical thickness of each layer of the intermediate layer was 187n.
The same procedure as in Example 1 was carried out except that m was used.

The transmission characteristics of the obtained filter are as shown in FIG. 12, and there is no ripple suppressing effect. - Comparative Example 3 - Example 1 except that the intermediate layer was made of two high refractive index films and two low refractive index films (total 4 layers).
I did the same thing.

The transmission characteristics of the obtained filter are as shown in FIG. 13, and ripple suppression is not sufficient. - Comparative Example 4 - Example 1 was carried out in the same manner as in Example 1 except that the order of multilayer film group A and multilayer film group C was reversed.

The transmission characteristics of the obtained filter are as shown in FIG. 14, and ripple suppression is not sufficient. - Example 6 - In Example 1, ripple treatment was not performed (the optical thickness of the final layer and the third layer from the air side (low refractive index film) was made the same as the thickness of the other alternating layers. The same procedure as in Example 1 was carried out except for the following.

The transmission characteristics of the obtained filter are as shown in FIG. -Example 7- In Example 2, the same procedure as Example 2 was carried out except that the ripple treatment was not performed. The transmission characteristics of the obtained filter are as shown in FIG.

-Example 8- The same procedure as Example 5 was carried out except that the ripple treatment was not performed. The transmission characteristics of the obtained filter are as shown in FIG. In addition, in FIGS. 3 to 17, the horizontal axis represents wavelength [nm], and the vertical axis represents transmittance (tra).
nsmittance) [%].

[0035]

[Effects of the Invention] The present invention has the following effects. The overall membrane structure is simple, easy to manufacture, and stable production with good reproducibility is possible. Yield can be improved and costs can be reduced. It is possible to achieve better ripple suppression than other ripple suppression methods, and it is possible to obtain an excellent broadband reflective short-pass filter.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one embodiment of an optical multilayer interference film of the present invention.

FIG. 2 is an explanatory diagram showing the film structure of another embodiment of the optical multilayer interference film of the present invention (an example of a ripple suppressed product).

FIG. 3 is a graph showing the characteristics of a conventional optical multilayer interference film consisting of alternating layers.

FIG. 4 is a graph showing the characteristics of the optical multilayer interference film of the present invention treated for ripple suppression.

FIG. 5 is a graph showing the characteristics of the optical multilayer interference film of the present invention when the third to last layer is not processed.

6 is a graph showing the characteristics of the optical multilayer interference film (blue filter) of Example 1. FIG.

7 is a graph showing the characteristics of the optical multilayer interference film (purple filter) of Example 2. FIG.

8 is a graph showing the characteristics of the optical multilayer interference film (infrared cut filter) of Example 3. FIG.

9 is a graph showing the characteristics of the optical multilayer interference film (blue resolving mirror) of Example 4. FIG.

10 is a graph showing the characteristics of the optical multilayer interference film (ultraviolet transmission filter) of Example 5. FIG.

11 is a graph showing the characteristics of the optical multilayer interference film of Comparative Example 1. FIG.

12 is a graph showing the characteristics of the optical multilayer interference film of Comparative Example 2. FIG.

13 is a graph showing the characteristics of the optical multilayer interference film of Comparative Example 3. FIG.

14 is a graph showing the characteristics of the optical multilayer interference film of Comparative Example 4. FIG.

15 is a graph showing the characteristics of the optical multilayer interference film of Example 6. FIG.

16 is a graph showing the characteristics of the optical multilayer interference film of Example 7. FIG.

17 is a graph showing the characteristics of the optical multilayer interference film of Example 8. FIG.

[Explanation of symbols]

1 Base material A Multilayer film group with large optical thickness B Intermediate film group C. Multilayer film group with small optical film thickness H1 High refractive index film H2 High refractive index film H3 High refractive index film L1 Low refractive index film L2 Low refractive index film L3 Low refractive index film L4 Low refractive index film L5 Low refractive index film

Claims (3)

[Claims] Claim 1: An optical multilayer interference thin film in which a high refractive index film and a low refractive index film are alternately formed in multiple layers on a base material, in order from the base material side; a high refractive index film having mutually equal optical film thickness a; Multilayer film group A in which a high refractive index film and a low refractive index film are alternately formed in multiple layers.
; intermediate layer group B formed by overlapping one high refractive index film and one low refractive index film having mutually equal optical film thicknesses b;
; and a multilayer film group C in which high refractive index films and low refractive index films having mutually equal optical film thicknesses c are alternately formed;
, the optical film thickness a is larger than the optical film thickness c, and
Optical film thickness b is c+(a-c)/6≦b≦a-(a-c)
/6 optical multilayer interference film. 2. Film groups A, B, and C having three different optical film thicknesses all have the first layer counted from the respective substrate side.
2. The optical multilayer interference film according to claim 1, comprising a high refractive index film in each layer and a low refractive index film in the final layer. [Claim 3] Final layer and final layer 2 of multilayer film group C
The previous layer is a low refractive index film, and the optical thickness of the final layer is 0.
．． 3. The optical multilayer interference film according to claim 1, wherein the optical thickness of the layer two layers before the final layer is in the range of 1.05c to 1.25c.