JPH08254612A - Multilayer film optical component and manufacture thereof - Google Patents

Abstract

PURPOSE: To manufacture an inexpensive multilayer film having good quality by using TiO2 film layers and MgF2 film layers as its constituents. CONSTITUTION: In this manufacture, six TiO2 film layers 11 and six MgF2 film layers 12 are alternately formed on a glass substrate 10 respectively with an ion-assisted vapor deposition method using oxygen ions as the ion assistant to manufacture the objective high reflectance film. By forming each of the TiO2 film layers 11 with the ion-assisted vapor deposition method, its internal stress becomes a compression stress by which the tensile stress of the adjacent one of the MgF2 film layers 12 is canceled and therefore, the internal strain of the high reflectance film is drastically reduced to avoid the generation of cracks in the film. Also, by forming the MgF2 film layers 12 with the ion- assisted vapor deposition method, those in which the chlorine elimination is inhibited from occurring and also, the packing density is improved and further, the wavelength shift hardly occurs can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer optical component in which a multilayer film such as a highly reflective film (mirror) or a dichroic film (filter) is laminated on a substrate, and a method for manufacturing the same.

[0002]

2. Description of the Related Art For a multilayer optical component such as a mirror having a highly reflective film laminated on a substrate or a filter having a dichroic film laminated, a combination of a high refractive index material and a low refractive index material is appropriately selected from various dielectric materials. Then, each is formed into a multilayer film having a predetermined number of layers by a film forming method such as a vacuum evaporation method or a sputtering method.

Dielectric materials having a high refractive index (high refractive index materials) include TiO ₂ , Ta ₂ O ₅ , ZrO ₂ and HfO _2.
As a dielectric material having a low refractive index (low refractive index material), MgF ₂ , SiO ₂ , Al ₂ O _3, etc. are widely used individually or as a mixture, in order to reduce the manufacturing cost of a multilayer film. Therefore, it is desirable to design a multilayer film having a small number of layers by combining a high refractive index material having a high refractive index with a low refractive index material having a low refractive index as much as possible.

Theoretically, if TiO ₂ having the highest refractive index and MgF ₂ having the lowest refractive index are combined among the above-mentioned dielectric materials, the number of layers is the smallest and the bandwidth is wide and the quality is high. It should be possible to obtain a reflective film or the like.

[0005]

However, according to the above-mentioned conventional technique, when a multilayer film such as a highly reflective film made of TiO ₂ and MgF ₂ is actually manufactured by a vacuum deposition method or a sputtering method, fluorine is formed on the MgF ₂ layer. Internal defects such as desorption occur, and cracks occur due to internal strain of the multilayer film, so that it is not possible to obtain a high-quality multilayer film as designed.

That is, the internal defects of the MgF ₂ layer significantly impair the optical characteristics of the multilayer film due to the increase in absorption, and the cracks are generated in the TiO ₂ film formed by the vacuum deposition method. It is presumed that this is because the internal stress of the MgF ₂ film is a tensile stress, and therefore the internal strain of the multilayer film is significantly increased, which greatly reduces the strength and durability of the multilayer film.

The present invention has been made in view of the above-mentioned problems of the prior art, and is composed of a TiO ₂ film and a MgF ₂ film, which is the most desirable combination in order to reduce the number of layers, and also has no cracks or cracks. It is an object of the present invention to provide a multilayer optical component having a high quality and inexpensive multilayer film without internal defects and a method for manufacturing the same.

[0008]

In order to achieve the above object, the multilayer optical component of the present invention has a multilayer film composed of a plurality of pairs of TiO ₂ films and MgF ₂ films alternately laminated on the surface of a substrate. However, the internal stress of each pair of the TiO ₂ films is a compressive stress, and the internal stress of the MgF ₂ film is a tensile stress.

It is preferable to have four or more pairs of TiO ₂ film and MgF ₂ film.

The method for producing a multilayer optical component of the present invention has a step of alternately forming a plurality of pairs of TiO ₂ films and MgF ₂ films on the surface of a substrate, and at least the TiO ₂ films of each pair are ion-deposited. It is characterized in that the film is formed by the assisted vapor deposition method.

Oxygen ions may be used as ion assist in the ion assist deposition method.

The substrate may be unheated during the formation of each pair of TiO ₂ film and MgF ₂ film.

Before the step of forming a plurality of pairs of TiO ₂ film and MgF ₂ film on the surface of the substrate, the surface may be cleaned by ion irradiation.

[0014]

[Function] TiO _{2 formed} by a known vacuum deposition method
The internal stress of both the film and the MgF ₂ film is generally a tensile stress, but when the film forming conditions are controlled by using the ion assisted vapor deposition method for forming the TiO ₂ film, the internal stress becomes a compressive stress, and the MgF ₂ film Cancels the tensile stress of the film. As a result, the internal strain of the multilayer film is significantly reduced, and the occurrence of cracks can be avoided.

Further, when employing the ion-assisted deposition to the deposition of the MgF ₂ film, it is possible packing density to obtain a large MgF ₂ film without internal defects fluorine desorption like.

Therefore, by forming both the TiO ₂ film and the MgF ₂ film by the ion assisted vapor deposition method, the drawbacks such as cracks and internal defects of the multilayer film composed of the TiO ₂ film and the MgF ₂ film are easily avoided. It is possible to manufacture a high-quality and inexpensive multilayer optical component having excellent adhesion and environment resistance.

[0017]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view for explaining a film forming apparatus used in the method of manufacturing a multilayer optical component according to the first embodiment.
This is an exhaust port 1a connected to an exhaust pump (not shown).
And a reaction gas inlet 1b for introducing a reaction gas such as oxygen gas
A vacuum chamber 1 having a substrate 1 is provided inside the vacuum chamber 1.
A substrate holder 2 which holds 0 and rotates, a resistance heating evaporation source 3 used for forming a MgF ₂ film, an electron beam evaporation source 4 used for forming a TiO ₂ film, and an ion source 5 for generating ions are provided. . Further, a neutralizer 6 for preventing abnormal discharge due to ions generated from the ion source 5 is provided in the vicinity of the ion source 5, and in the center of the substrate holder 2,
A crystal oscillator 7 and an optical monitor 8 are provided on the substrate 10 to detect the film thickness of the thin film being formed and control the deposition rate of the resistance heating evaporation source 3 and the electron beam evaporation source 4.

The apparatus shown in FIG. 1 is used to fabricate a mirror having a multi-layered structure of 12 layers as shown in FIG.

First, the vacuum chamber 1 is depressurized to a predetermined vacuum degree, and the glass (BK7) substrate 10 is irradiated with ions such as Ar or O ₂ from the ion source 5 to clean the surface of the substrate 10 (cleaning). Then, the electron beam evaporation source 4 and the resistance heating evaporation source 3 are alternately heated to form TiO _{2 having an} optical film thickness nd = λ / 4 (λ = 550 nm) on the surface of the substrate 10.
The film 11 and the MgF ₂ film 12 were alternately laminated to form a total of 12 thin films, 6 layers each, to obtain a high reflection film.

The formation of each TiO ₂ film 11 is carried out by introducing oxygen gas as a reaction gas from the reaction gas introduction port 1b to obtain a vacuum degree of 1
The deposition rate was 0.5n in an oxygen atmosphere of × 10 ^-4 Torr.
Controlled to m / sec, ion source 5 as ion assist
To ion energy 500 eV, ion current density 50
It was performed by generating oxygen ions of μA / cm ² .

In forming each MgF ₂ film 12, a reaction gas is not introduced, the vapor deposition rate is controlled to 1.0 nm / sec, and ion energy 30 is supplied from the ion source 5 as ion assist.
Oxygen ions having an ion current density of 30 μA / cm ² were generated at 0 eV.

Each TiO ₂ film 11 and each MgF ₂ film 1
Neutralizer 6 is operated during the film formation of 2.
The substrate 10 was not heated. Further, MgF ₂ material and TiO ₂ material were used for the evaporation sources of the resistance heating evaporation source 3 and the electron beam evaporation source 4, respectively.

TiO ₂ film 1 formed under the above-mentioned film forming conditions
1 and the internal stress of the MgF ₂ film 12 were examined.
The internal stress of the O ₂ film 11 is a compressive stress and has a stress value of 3.
1 × 10 ⁸ N / m ² , the internal stress of the MgF ₂ film 12 is tensile stress, and the stress value is 2.3 × 10 ⁸ N / m ² ,
When the TiO ₂ films 11 and the MgF ₂ films 12 are alternately laminated, most of these internal stresses cancel each other out, and the internal strain is greatly reduced.

When a TiO ₂ film is formed by a known vacuum deposition method without using ion assist, Ti
Although the internal stress of the O ₂ film is a tensile stress, it is considered that the internal stress in the compression direction was generated in this example because the TiO ₂ film was formed by the ion assisted vapor deposition method using ion assist. Also in the case of the MgF ₂ film, it is considered that the stress value of the tensile stress is somewhat reduced by adopting the ion assisted vapor deposition method using the ion assist.

Experiments have shown that the compressive stress of the TiO ₂ film and the tensile stress of the MgF ₂ film can be controlled in a wide range by changing the kind of ion assist gas, ion energy and ion current density.

When the spectral reflectance of the mirror manufactured by the above method was examined, as shown in FIG.
It was found to be a very high quality mirror with a reflectance of 99.3% at 50 nm. When the MgF ₂ film is formed by a vacuum evaporation method or the like, fluorine desorption or the like is likely to occur,
It is speculated that the use of the ion assisted vapor deposition method using ion assist avoids such internal defects and greatly improves the optical characteristics.

Further, with respect to 30 samples, an adhesion test with an adhesive tape, a friction test with sillbon paper, and a solvent test with an organic solvent were carried out. As a result, no sample had a bad result.

Next, each sample was subjected to a temperature of 70 ° C. and a humidity of 80%.
After carrying out the environment resistance test of leaving it in the high temperature and high humidity environment for 500 hours, the same adhesion test, friction test and solvent test as above were carried out. When the reflectance was examined, the reflectance at the central wavelength was 99.2%, and the wavelength shift amount was ± 1 nm or less.

This is because the internal strain of the multilayer film (highly reflective film) is greatly reduced by controlling the internal stress of the TiO ₂ film by using the ion assist, as described above, so that the occurrence of cracks is avoided. The result is that the mechanical strength and the like are significantly improved, and that the wavelength shift after the environment resistance test is small is that both of the TiO ₂ film and the MgF ₂ film are formed by the ion assisted vapor deposition method. It is presumed that this is due to a significant improvement in the packing density of.

As a result of numerous experiments, it was found that the use of the ion assisted vapor deposition method can avoid the occurrence of cracks even if the total number of TiO ₂ films and MgF ₂ films is 20 or more.

According to this embodiment, the optical characteristics are excellent with a small number of layers, the mechanical strength such as adhesion and abrasion resistance, the solvent resistance, etc. are sufficient, and the environment resistance is also excellent. It is possible to obtain an extremely high-quality and inexpensive multilayer optical component.
In this example, the TiO ₂ material was used as the evaporation source when forming the TiO ₂ film, but Ti or T was used instead.
It is also possible to use iO _x (0 <x <2). If necessary, the substrate may be heated to, for example, 100 ° C to 300 ° C.

(Comparative Example) Using the apparatus of FIG. 1, a total of 12 layers of TiO ₂ film and MgF ₂ film were designed in the same manner as the mirror of FIG. 2, and the substrate made of BK7 was heated to 300 ° C. , Each TiO ₂ film and each MgF ₂ film were formed without using ion assist.

The deposition rate of the TiO ₂ film is 0.5 nm.
/ Sec and the degree of vacuum is 1 × 10 ⁻⁴ Torr in an oxygen atmosphere, and the MgF ₂ film is formed at a deposition rate of 1.0 nm /
sec, the reaction gas was not introduced. TiO ₂
Both the internal stress of the film and the MgF ₂ film are tensile stress, and the stress values are 2.1 × 10 ⁸ N / m ² and 2.5 × 10, respectively.
^{It is 8} N / m ² , and it is estimated that an extremely large internal strain is generated.

When the substrate was taken out after forming all the layers, many cracks were generated in the multilayer film.

Therefore, the number of pairs of the TiO ₂ film and the MgF ₂ film was reduced to design a mirror of 5 pairs (10 layers in total), and a multilayer film having a total film thickness of 780 nm was formed by the same method as described above. The measured spectral reflectance is shown in FIG. The reflectance at the center wavelength of 550 nm was 97.4%, and there were no cracks immediately after film formation, but many cracks were generated as a result of the above-mentioned environment resistance test.

It was found that the number of pairs of the TiO ₂ film and the MgF ₂ film must be 4 or less in order to prevent cracks from occurring even after the environment resistance test.

Next, as shown in FIG. 5, a TiO ₂ film 21 is formed.
A mirror having a total of 14 pairs of 7 pairs of SiO ₂ film 22 and SiO ₂ film 22 was designed, and each TiO ₂ film 21 and SiO ₂ film 22 were formed by heating the substrate 20 at 300 ° C. by a known film forming method. SiO ₂
Of the TiO ₂ film of this embodiment by using a combination of the film and the TiO ₂ film.
To obtain the same optical characteristics as a high reflection film composed of ₂ film and the MgF ₂ film 6 pairs requires 7 pairs, that much manufacturing cost is increased.

The TiO ₂ film 21 is formed at a vacuum degree of 1 × 10 ^-4.
Vapor deposition rate of 0.5 nm / se in oxygen atmosphere of Torr
The deposition rate of the SiO ₂ film 22 is 1.0 in an oxygen atmosphere with a vacuum degree of 1 × 10 ⁻⁵ Torr.
Control was performed at nm / sec. The internal stress of the SiO ₂ film 22 is a compressive stress and the stress value is 2.3 × 10 ⁸ N
/ M ² . When the spectral reflectance of this mirror was measured, as shown in FIG. 6, the reflectance at the central wavelength of 550 nm was 99.3%, and the mechanical strength immediately after film formation and after the above-mentioned environment resistance test was sufficient. However, the wavelength shift after the environment resistance test is 5 to 8 nm, and the center wavelength is 550 nm.
In some samples, the reflectance was 99% or less.

As described above, when the TiO ₂ film and the SiO ₂ film are combined, not only the number of layers required is higher and the cost is higher than the combination of the TiO ₂ film and the MgF ₂ film, but also the durability and the like are improved. Turned out to be insufficient.

FIG. 7 shows a film structure of an infrared cut filter which is a multilayer optical component according to the second embodiment. This is a glass (BK7) substrate 30 having a TiO ₂ film 31 and a MgF ₂ film on the upper surface thereof. A total of 14 layers of 7 layers of film 32, substrate 30
The TiO ₂ film 31 and the MgF ₂ film 32 are laminated on the lower surface of each of the above by a total of 10 layers by ion-assisted vapor deposition using the apparatus of FIG.

First, the vacuum chamber 1 was depressurized to a predetermined vacuum degree, and the substrate 30 was irradiated with ions such as Ar or O ₂ from the ion source 5 to clean the surface of the substrate 30.

The formation of each TiO ₂ film 31 is performed by introducing oxygen gas as a reaction gas from the reaction gas inlet 1b and setting the degree of vacuum to 1
The deposition rate was 0.4n in an oxygen atmosphere of × 10 ^-4 Torr.
Controlled to m / sec, ion source 5 as ion assist
From ion energy 500 eV, ion current density 40
It was performed by generating oxygen ions of μA / cm ² .

In forming each MgF ₂ film 32, the reaction gas is not introduced, the vapor deposition rate is controlled to 1.0 nm / sec, and the ion energy 40 from the ion source 5 is used as ion assist.
Oxygen ions having an ion current density of 35 μA / cm ² were generated at 0 eV.

Each TiO ₂ film 31 and each MgF ₂ film 3
Neutralizer 6 is operated during the film formation of 2.
The substrate 30 was not heated.

TiO ₂ film 3 formed under the above film forming conditions
1 and the internal stress of the MgF ₂ film 32 were examined.
The internal stress of the O ₂ film 31 is compressive stress and the stress value is 3.
5 × 10 ⁸ N / m ² , the internal stress of the MgF ₂ film 32 is tensile stress, and the stress value is 2.5 × 10 ⁸ N / m ² ,
It was found that most of the internal stresses of the TiO ₂ film 31 and the MgF ₂ film 32 cancel each other out and the internal strain is greatly reduced.

When the spectral characteristics of the manufactured infrared cut filter were examined by the above method, as shown in FIG. 8, the transmittance was 3% or less in the infrared region (wavelength 780 to 1150 nm) and the visible region (wavelength was It was found that the average transmittance was 85% or more in the range of 400 to 720 nm), and that the infrared cut filter had an extremely high quality.

Further, when 30 samples were subjected to an adhesion test with an adhesive tape, a friction test with sillbon paper, and a solvent test with an organic solvent, none of the samples had a bad result.

Next, each sample was subjected to a temperature of 70 ° C. and a humidity of 80%.
After carrying out the environment resistance test of leaving it in a high temperature and high humidity environment for 500 hours, the same adhesion test, friction test and solvent test as described above were carried out. When we examined the wavelength 740nm
The shift amount was ± 2 nm or less with respect to the transmittance of 50%.

(Comparative Example) As shown in FIG. 9, a TiO ₂ film 41 and SiO ₂ were formed on the upper surface of a glass (BK7) substrate 40.
16 layers of ₂ films 42 in total, and TiO ₂ film 41 and SiO _{2 on} the lower surface
_A total of 12 layers of the _two films 42 were laminated by a known film forming method to manufacture an infrared cut filter.

The TiO ₂ film 41 is formed at a vapor deposition rate of 0.5.
nm / sec and a vacuum degree of 1 × 10 ⁻⁴ Torr in an oxygen atmosphere, and the SiO ₂ film 42 is formed at a deposition rate of 1.
0 nm / sec, the reaction gas was not introduced.
The internal stress of the SiO ₂ film 42 was compressive stress, and the stress value was 2.3 × 10 ⁸ N / m ² , respectively. The measured spectral transmittance is shown in FIG. The mechanical strength was sufficient immediately after film formation and after the environment resistance test, but the shift amount for the 50% transmittance at the wavelength of 740 nm after the environment resistance test was +
In some samples, the transmittance was 5 to +10 nm, and the transmittance in the infrared region was 3% or more.

[0052]

Since the present invention is configured as described above, it has the following effects.

In order to reduce the number of layers, it is possible to avoid the defect that cracks and internal defects of the multilayer film composed of TiO ₂ film and MgF ₂ film, which are the most desirable combination, and to have excellent optical characteristics with a small number of layers. In addition, a multilayer film having sufficient mechanical strength and environmental resistance can be obtained. By using such a multilayer film, quality improvement and cost reduction of the multilayer film optical component such as a mirror and a filter can be greatly promoted.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a film forming apparatus.

FIG. 2 shows a film structure of a mirror according to the first embodiment.

FIG. 3 is a graph showing the spectral reflectance of the mirror of FIG.

FIG. 4 is a graph showing a spectral reflectance of a comparative example of the first embodiment.

FIG. 5 shows a film structure of another comparative example of the first embodiment.

6 is a graph showing the spectral reflectance of the mirror of FIG.

FIG. 7 shows a film structure of an infrared cut filter according to a second embodiment.

8 is a graph showing the spectral characteristics of the infrared cut filter of FIG.

FIG. 9 shows a film structure of a comparative example of the second embodiment.

10 is a graph showing the spectral characteristics of the infrared cut filter of FIG.

[Explanation of symbols]

10, 20, 30, 40 Substrate 11, 21, 31, 41 TiO ₂ film 12, 32 MgF ₂ film 22, 42 SiO ₂ film

Claims (9)

[Claims] 1. A multilayer film comprising a plurality of pairs of TiO ₂ films and MgF ₂ films alternately laminated on the surface of a substrate, wherein the internal stress of each pair of the TiO ₂ films is compressive stress, and the Mg
A multilayer optical component in which the internal stress of the F ₂ film is a tensile stress. 2. A multilayer film comprising a plurality of pairs of TiO ₂ films and MgF ₂ films alternately laminated on the surface of a substrate, and at least the TiO ₂ films of each pair are formed by an ion assisted vapor deposition method. A multilayer optical component characterized by being a thing. 3. The multilayer optical component according to claim 1, which has four or more pairs of TiO ₂ films and MgF ₂ films. 4. A step of alternately forming a plurality of pairs of TiO ₂ films and MgF ₂ films on the surface of a substrate, wherein at least the TiO ₂ films of each pair are formed by an ion assisted vapor deposition method. And a method for manufacturing a multilayer optical component. 5. A method for manufacturing a multilayer optical component, characterized in that both the TiO ₂ film and the MgF ₂ film of each pair are formed by an ion assisted vapor deposition method. 6. The method for producing a multilayer optical component according to claim 4, wherein oxygen ions are used as ion assist in the ion assisted vapor deposition method. 7. The multilayer film according to claim 4, wherein the internal stress of at least the TiO ₂ film of each pair is controlled by adjusting the film forming conditions in the ion assisted vapor deposition method. Optical component manufacturing method. 8. The substrate is not heated during formation of each pair of TiO ₂ film and MgF ₂ film.
A method for manufacturing a multilayer optical component according to any one of claims 1. 9. A plurality of pairs of TiO ₂ films and Mg are formed on the surface of a substrate.
9. The method for manufacturing a multilayer optical component according to claim 4, wherein the surface is cleaned by ion irradiation before the step of forming the F ₂ film.