JPH0727907A - Optical multilayer film and forming method therefor - Google Patents

Abstract

PURPOSE:To provide an optical multilayer film with which the incident angle dependency of spectral characteristics can be largely decreased compare with a conventional film. CONSTITUTION:This optical multilayer film is obtd. by alternately laminating thin films 11(TiO2 films) having high refractive index of about >=2.5 and thin films (Ta2O5 films) having lower refractive index by about 0.3 than the thin films 11 on a substrate 10. Even when the incident angle is changed, the shift of spectral characteristics is largely decreased compared with a conventional film. For example, when this film is used as a color separation prism of a videocamera, the shading characteristics can be largely improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multilayer film for use in a three-color separation prism for separating incident light into blue, red, and green color components, and a film forming method thereof.

[0002]

2. Description of the Related Art An optical multi-layer film for color separation is used in a three-color separation prism for a three-plate camera. For example, a blue reflective film, a red reflective film, a green reflective film and the like correspond to this.

Conventionally, in these optical multilayer films, a TiO ₂ film having a refractive index of about 2.3 is mainly used as a high refractive index thin film, and a SiO having a refractive index of about 1.46 is used as a low refractive index thin film.
_Two films have been used, and these films have been formed by alternately laminating 10 to 10 layers.

A green reflective film is taken as an example of a conventional optical multilayer film, and a film forming method thereof will be described with reference to FIG.

An EB gun 52 in a vacuum chamber 51 kept in a high vacuum state by an exhaust pump 50 uses a vapor deposition material (Ti
O ₂ ) 53 is heated and melted and evaporated. At this time, oxygen gas is introduced from the oxygen inlet 54, and the pressure in the vacuum chamber is set to about 1 to 2 × 10 ⁻⁴ torr. The evaporated particles 55 that have evaporated reach the substrate 57 installed on the substrate holder 56 and form a thin film having a high refractive index of about 2.3.

Evaporated particles that have passed through the hole 58 of the substrate holder reach the optical film thickness monitor substrate 59 to form a thin film.

The light flux of a specific wavelength emitted from the light source 60 reaches the thin film formed on the optical film thickness monitor substrate 59, and the reflected light flux is detected by the detector 61. Since the amount of reflected light changes depending on the film thickness formed on the optical film thickness monitor substrate 59, when the predetermined amount of light is reached, the shutter 62 is rotated to close and complete the vapor deposition to form the first layer. Complete.

Next, the vapor deposition material was replaced with a SiO ₂ material,
Also replace the optical film thickness monitor board with a new board. Similar to the TiO ₂ film of the first layer, the SiO ₂ material is evaporated by heating and melting with an EB gun to form a second layer on the substrate.
As a result, a thin film having a low refractive index of about 1.46 is formed.

This operation is repeated many times to obtain TiO 2.
_The green multilayer film was formed by alternately stacking about 12 layers with the film thickness of ₂ being about 50 nm and the film thickness of SiO ₂ being about 330 nm.

The spectral characteristic of the green reflective film thus prepared is shown by a curve 65 in FIG. In FIG. 6, the horizontal axis represents wavelength (unit: nm) and the vertical axis represents reflectance (%).
Here, the refractive index of the substrate is about 1.6, the incident angle is about 26 degrees, and the spectral characteristic shows the spectral characteristic using the average value of the reflectance of S deflection and the reflectance of P deflection. Hereinafter, the spectral characteristics will be described using such average characteristics.

As described above, it can be seen that a green reflective film having a markedly increased reflectance can be formed in the green wavelength region of wavelengths of 490 nm to 560 nm.

[0012]

However, there will be explained a problem when such an optical multilayer film is used for an optical device for color separation such as a three-color separation prism.

That is, the angle of light incident on an optical device such as a three-color separation prism is not constant but may change as shown in the schematic view of FIG. That is, the light 71 emitted from the subject 70 is reflected by the green reflective film 72 and reaches the CCD 73 to obtain an image signal, but it is known that the emitted light 71 is inclined to some extent depending on the photographing conditions and the like. ing.

When the inclination angle is θ, the angle of light incident on the green reflective film 72 naturally changes, so that the spectral characteristic of the green reflective film 72 changes according to the incident angle. For example, taking the case where the incident angle changes by θ = ± 1.3 degrees as an example, the spectral characteristics at this time are shown by the curves 66, 6 in FIG.
Shown by 7. From this, the spectral characteristics change significantly, θ = 2
If the incident angle is as large as 7.3 degrees, the curve 67
It can be seen that the wavelength shifts to the short wavelength side as shown by, and when the incident angle becomes small as θ = 24.7 degrees, the wavelength shifts to the long wavelength side as shown by the curve 66.

When the shift amount is evaluated at a wavelength having a reflectance value half the maximum reflectance, that is, a half value wavelength amount, the shift amount is evaluated to be about 13 nm on the long wavelength side and about 9 n on the short wavelength side.
It can be seen that m is also shifted.

Such a shift of the half-value wavelength due to a change in angle causes, for example, in the case of a video camera, unevenness in color and brightness called shading to occur in the up-down direction, that is, the vertical direction of the photographic screen, resulting in deterioration of image quality. It had a problem of being lost.

In view of such a point, the present invention has an object to provide an optical multilayer film in which vertical shading is suppressed.

Note that the half-value wavelength shift amount will be described below by typifying the shift amount on the long wavelength side.

[0019]

Means for Solving the Problems A refractive index of 2.
An optical multilayer film in which a thin film having a high refractive index of 5 or more and a thin film having a low refractive index smaller than that of the thin film having a high refractive index by 0.3 or more are alternately laminated as a main thin film substance is used.

Further, on the substrate, a high refractive index thin film having a refractive index of 2.4 to 2.5, a refractive index of about 1.65 or more, and a refractive index higher than that of the high refractive index thin film. An optical multilayer film in which thin films having a low refractive index smaller by 0.3 or more are alternately laminated as a main constituent substance is used.

[0021]

According to the present invention, by using the optical multilayer film in which the above-mentioned thin films having the refractive index are alternately laminated, the wavelength shift amount with respect to the change of the incident angle can be remarkably suppressed, and as a result, the vertical shading can be suppressed. Becomes

[0022]

【Example】

(First Embodiment) An optical multilayer film according to the first embodiment of the present invention will be described. FIG. 1 shows the structure of the optical multilayer film of this example.

That is, a TiO ₂ film 11 having a refractive index of about 2.6 is used as a thin film having a high refractive index, and Ta ₂ O ₅ 12 having a refractive index of about 2.1 is used as a thin film having a low refractive index. Board 1
It has a structure in which 19 layers are alternately laminated on the 0. Here, the film thickness of TiO ₂ is about 53 nm and that of Ta ₂ O ₅ is about 65 nm.

A method of forming such an optical multilayer film will be described with reference to FIG. The inside of the vacuum chamber 51 is maintained in a high vacuum state by the exhaust pump 50. The vapor deposition material 53 in the crucible is heated and melted by the EB gun 52. Titanium oxide is used as the vapor deposition material. At this time, oxygen gas is introduced into the vacuum layer through the oxygen introduction port 54, and the pressure in the vacuum chamber is set to, for example, about 5 × 10 ⁻⁵ torr.

The molten titanium oxide evaporates and evaporates particles 5
5 reaches the substrate 57 set on the substrate holder 56 and forms a thin film. During this time, the evaporated particles react with oxygen introduced into the vacuum chamber, and a very transparent and stable TiO ₂ film having a refractive index of about 2.6 can be realized.

Thus, unlike the conventional case, the refractive index is about 2.6 by specifying the oxygen gas partial pressure in the higher vacuum region.
TiO ₂ film having a high refractive index can be realized.

As a result of evaluating the transparency, adhesion, reliability, etc., it is needless to say that it was as good as the conventional film. As the substrate, for example, optical glass such as BK or SK is used.

At this time, the vaporized particles passing through the hole portion 58 of the substrate holder reach the optical film thickness monitor substrate 59,
Form a thin film. The optical film thickness monitor substrate 59 is irradiated with the light flux of the specific wavelength emitted from the light source 60,
The reflected light reaches the detector 61. The amount of reflected light at this time varies depending on the refractive index and the film thickness of the thin film formed on the monitor substrate. When the amount of reflected light reaches a predetermined value, the shutter 62 is closed and the first film having a film thickness of about 53 nm. Layer T
The formation of the iO ₂ film is completed.

When the film formation of the first layer is completed, the vapor deposition material 53 in the crucible is replaced with Ta ₂ O ₅ and a new optical film thickness monitor substrate is set. And Ta ₂ O ₅ 5
3 is heated and melted by the EB gun 52 to fly as vaporized particles 55, and a second thin film is formed on the substrate 57.

This thin film is also formed on the exchanged optical film thickness monitor substrate 59, and when the reflected light is measured, it ends when the film thickness becomes about 65 nm.

The spectral characteristics of the optical multilayer film of this embodiment will be described below. FIG. 2 shows the spectral characteristics of the optical multilayer film of the present example formed by the above method. Curve 21 shows the case where the incident angle is 26 degrees. A good multi-layered film with improved reflectance in the green wavelength range of 490 nm to 560 nm, similar to the conventional green reflective film, even though the constituent materials and refractive index of the thin film were changed compared to the conventional one. You can see that it is done.

Next, the angle dependence of the green reflective film will be described. The incident angle of this green reflective film is 26 degrees ± 1.
When the change in the spectral characteristic with respect to the angle is examined by changing the angle by 3 degrees, as shown in the figure, when θ = 24.7 degrees, the wavelength shifts to the long wavelength side as shown by the curve 22, and θ = 2
It can be seen that in the case of 7.3 degrees, the wavelength shifts to the short wavelength side as shown by the curve 23.

When this shift width is evaluated, it is about 5.3.
It can be seen that this is significantly suppressed compared with the conventional configuration of about 13 nm.

Therefore, the optical multilayer film of the present invention can maintain the spectral characteristics almost the same as those of the conventional optical multilayer film, and can suppress the dependence on the incident angle to less than half that of the conventional optical multilayer film. It can be called a membrane.

Here, in the embodiment, Ti having a refractive index of 2.6 is used.
An example of an O ₂ film and a Ta ₂ O ₅ film with a refractive index of 2.1 was shown, but as a result of examination, unlike the conventional example, if the following conditions are satisfied, a very large angle dependence is obtained. I found that I could be.

That is, whether a high-refractive-index thin film having a refractive index of 2.5 or more and a low-refractive-index thin film having a refractive index of 0.3 or more smaller than that of the high-refractive index thin film are alternately laminated as main constituents When the refractive index of the high refractive index thin film is 2.4 to 2.5, the refractive index is about 1.65 or more, and the refractive index is 0.3 or more smaller than that of the high refractive index thin film. It was found that by alternately laminating thin films having a high refractive index as a main constituent substance, a very good optical multilayer film having a wavelength shift amount of 7 nm or less can be obtained.

As a result of the experiment, the high refractive index thin film was TiO ₂ , and the low refractive index thin film was Ta ₂ O ₅ , ZrTiO ₄ , Zn.
It was found that the effects are exhibited by S, ZrO ₂ , TiO ₂ , Al ₂ O ₃ , SiO ₂ , MgF _{2 and the} like.

In particular, as a thin film having a low refractive index, T
The use of a ₂ O ₅ , ZrTiO ₄ , ZnS, ZrO ₂ , and TiO ₂ is particularly good, and the wavelength shift amount is about 5 nm.
An extremely good optical multilayer film was realized as follows.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 3 shows its configuration diagram. That is,
1 to 19 layers of the same material Ti on the substrate 30
An O ₂ film is formed. However, the refractive index of each layer is changed so that the odd-numbered layers have a TiO ₂ film 31 with a refractive index of about 2.6.
And the even layer is a TiO ₂ film 32 having a refractive index of about 2.2. Here, the film thickness of the odd-numbered TiO ₂ film is about 53 nm.
The TiO ₂ film of the even layer has a thickness of about 63 nm.

A method for forming such an optical multilayer film will be described with reference to FIG. The inside of the vacuum chamber 51 is maintained in a high vacuum state by the exhaust pump 50. The evaporation material 53 is heated and melted by the EB gun 52. Titanium oxide is used as the vapor deposition material. At this time, oxygen gas is introduced into the vacuum layer through the oxygen inlet 54, and the pressure in the vacuum chamber is adjusted to, for example, about 5
Set to × 10 ^-5 torr.

The molten titanium oxide evaporates and evaporates particles 5
5 reaches the substrate 57 set on the substrate holder 56 and forms a thin film. During this time, the evaporated particles react with oxygen introduced into the vacuum chamber, and a very transparent and stable TiO ₂ film having a refractive index of about 2.6 can be realized.

At this time, the vaporized particles that have passed through the hole portion 58 of the substrate holder reach the optical film thickness monitor substrate 59,
Form a thin film. The optical film thickness monitor substrate 59 is irradiated with the light flux of the specific wavelength emitted from the light source 60,
The reflected light reaches the detector 61. The amount of reflected light at this time varies depending on the refractive index and the film thickness of the thin film formed on the monitor substrate. When the amount of reflected light reaches a predetermined value, the shutter 62 is closed and the first film having a film thickness of about 53 nm. Layer T
The formation of the iO ₂ film is completed.

When the film formation of the first layer is completed, a new optical film thickness monitor substrate is set. Then, the amount of oxygen gas introduced by the oxygen introduction 54 is increased, and the pressure in the vacuum chamber is set to about 1 × 10 ⁻⁴ torr. Then, the shutter 62 is opened to form a _second layer TiO ₂ film.

The oxygen partial pressure is changed to that of the first layer, and the specific pressure is changed.
With a refractive index of 2.2 ₂Create a membrane. This
The thin film is an optical film thickness monitor substrate 59 as in the first layer.
The film thickness is also formed by measuring the reflected light.
It ends when it reaches about 63 nm.

As described above, a high refractive index and a low refractive index can be realized only by changing the oxygen introduction pressure when forming the TiO ₂ film without using two kinds of evaporation substances.

This has the effect that it is not necessary to use a complicated mechanism for changing the material in the vacuum apparatus, and
Since only two kinds of materials are used, there is no problem that two kinds of materials are mixed and the refractive index changes.
In addition, the heating and melting time, which has been carried out each time the material is changed, is shortened, which shortens the film forming time, which can be said to be extremely useful in practice in the apparatus.

In FIG. 4, a curve 41 indicates the spectral characteristic of the optical multilayer film of this embodiment. Here, the incident angle is set to 26 degrees as an example.

As described above, even though it is made of one kind of material, the wavelength is 490n as in the conventional green reflective film.
It can be seen that a good multilayer film in which the reflectance in the green wavelength region of m to 560 nm is increased can be realized.

Next, the angle dependence of the green reflective film will be described. The incident angle of this green reflective film is 26 degrees ± 1.
When the change in the spectral characteristic with respect to the angle is examined by changing the angle by 3 degrees, as shown in FIG. 4, when θ = 24.7 degrees, the wavelength shifts to the long wavelength side as shown by the curve 42. θ = 2
It can be seen that in the case of 7.3 degrees, the wavelength shifts to the short wavelength side as shown by the curve 43. When the shift width is evaluated now, it is about 5.2 nm, and it can be seen that the shift width is remarkably suppressed as compared with the conventional structure of about 13 nm, as in Example 1.

Therefore, the optical multilayer film of the present embodiment can maintain the spectral characteristics almost the same as those of the conventional optical multilayer film, while suppressing the dependence on the incident angle to less than half that of the conventional optical multilayer film. It can be called a multilayer film.

Further, as described above, the effect of not using a complicated mechanism for changing the material in the vacuum apparatus because it is formed of one kind of material called TiO _{2 or two} kinds of materials The problem that the refractive index changes due to the mixing of the materials described above is eliminated, and the heating and melting time required each time the material is changed is also shortened, which shortens the film formation time, which is extremely useful in terms of equipment and practical use. Can be said.

Although the present invention has been described with respect to the green reflective film, it goes without saying that it is also useful for the red reflective film, the blue reflective film and the like.

Although the number of layers has been described as 19 layers, the present invention does not limit the number of layers in any way, and it goes without saying that an optical multilayer film of 12 layers or several tens layers is also useful.

Although the embodiment has been described by using two kinds or one kind of material, there is a problem even if several thin films having the third refractive index are inserted in order to obtain desired optical characteristics at a specific angle. Needless to say

Further, it is needless to say that the thin film layer itself does not have to be a single material, and is effective as long as the refractive index satisfies the conditions of the present invention.

Although the refractive index of the substrate has been described as about 1.6, BK7 having a refractive index of about 1.5 was also useful.

Although an angle of about 26 degrees has been described, it goes without saying that other incident angles are also useful.

Further, the chemical formulas such as TiO ₂ were used to indicate the materials, but Ti as shown in the chemical formulas is not necessarily used.
The ratio of and O need not be exactly 1: 2. It suffices that the refractive index satisfies the conditions of the present invention.

[0059]

By using the film forming apparatus or the film forming method of the present invention, it is possible to realize an optical multi-layer film in which the dependency performance on the incident angle can be suppressed more than ever before.

This can be said to be extremely useful because shading, which has been a problem up to now, which has been a problem in video cameras and the like, can be significantly suppressed.

Further, by using the forming method of forming with one kind of material called TiO ₂ , it is not necessary to use a complicated mechanism for changing the material in the vacuum apparatus, and 2
The problem that the refractive index changes due to mixing of different types of materials is eliminated, and the heating and melting time required each time the material is changed is shortened, which shortens the film formation time. It can be said that there is.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical multilayer film according to a first embodiment of the present invention.

FIG. 2 is an optical characteristic diagram of the optical multilayer film according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical multilayer film according to a second embodiment of the present invention.

FIG. 4 is an optical characteristic diagram of the optical multilayer film according to the second embodiment of the present invention.

FIG. 5 is a block diagram of a film forming apparatus for forming an optical multilayer film.

FIG. 6 is an optical characteristic diagram of a conventional optical multilayer film.

FIG. 7 is an explanatory diagram of incident angle dependence of spectral characteristics.

[Explanation of symbols]

10, 30 substrate 11 TiO ₂ film 12 Ta ₂ O ₅ film 30 TiO ₂ film (n = 2.6) 32 TiO ₂ film (n = 2.2) 50 exhaust pump 51 vacuum chamber 52 EB gun 53 vapor deposition material 54 oxygen Inlet 55 Evaporated particles 56 Substrate holder 57 Substrate 58 Hole 59 Optical film thickness monitor substrate 60 Light source 61 Detector 62 Shutter 70 Subject 71 Light 72 Green reflective film 73 CCD

Claims (3)

[Claims] 1. A thin film having a high refractive index of 2.5 or more and a low refractive index thin film having a refractive index of 0.3 or more smaller than that of the high refractive index thin film as a main constituent thin film on a substrate. An optical multilayer film which is alternately laminated or a high refractive index thin film having a refractive index of 2.4 to 2.5 and a refractive index of 1.65 on a substrate.
In addition to the above, an optical multi-layer film in which thin films having a low refractive index smaller than that of the thin film having a high refractive index by 0.3 or more are alternately laminated as main constituent thin films. 2. The high refractive index thin film is a TiO ₂ film, and the low refractive index substance is Ta ₂ O ₅ , ZrTiO ₄ , ZnS, Zr.
The optical multilayer film according to claim 1, which contains O ₂ and TiO ₂ as main components. 3. Ti having a high refractive index is obtained by introducing oxygen as a reaction gas into the vapor deposition apparatus and changing the amount of oxygen.
A method for forming an optical multilayer film, which comprises forming an O ₂ film and a TiO ₂ film having a low refractive index by vapor deposition.