JP3917822B2 - Optical filter having laminated film and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical filter in which a plurality of films whose refractive index changes stepwise and a manufacturing method thereof.
[0002]
[Prior art]
In the field of optical communications, a wavelength division multiplexing (WDM) transmission system is known in which a plurality of light beams having different wavelengths are simultaneously sent into one optical fiber in order to enable transmission of a large amount of data. As this type of optical filter, a multi-cavity optical filter is known, and is used for a bandpass filter (BPF), an edge filter, and the like.
[0003]
As a manufacturing method of this multicavity type optical filter, a vapor deposition method or an ion beam sputtering method is used. The vapor deposition method is performed by heating a material as a raw material in the chamber with an electron beam and attaching the evaporated material to a glass substrate. In the ion beam sputtering method, the target material, the ion gun, and the glass substrate are arranged in the same chamber, and the target material is irradiated with the ion beam to attach particles ejected from the target to the substrate.
[0004]
[Problems to be solved by the invention]
However, the optical filter used in the multi-cavity method or the like needs to control the optical film thickness of each layer very precisely, and the number of laminated layers needs to be more than one hundred layers. Since refractive index uniformity, non-polarization, smoothness of laminated film boundaries, stress relaxation, etc. are required with high accuracy, the above-described conventional manufacturing method can manufacture a high-precision optical filter in a short time. It was difficult.
[0005]
When this type of optical filter is performed by the above-described vapor deposition method, although there is an advantage that the film forming speed is high, it has a low-density structure with many gaps between particles, and unevenness occurs at the boundary between the films. The boundary portion of the film becomes unclear, and a film having a uniform refractive index cannot be formed. For example, as shown in the schematic diagram of FIG. 6, when the film 11 and the film 12 are formed on the glass substrate 4 by vapor deposition, a large number of gaps are formed between the films 11 and 12, and at the boundary between the film 11 and the film 12. Since the smoothness is lost, the boundary between the films becomes unclear, and a highly accurate film cannot be formed.
[0006]
FIG. 7 shows a cross-sectional SEM photograph of a single layer film of TiO _{2 formed} by the vapor deposition method, and FIG. 8 shows an SEM photograph showing a cross section of the TiO ₂ / SiO ₂ multilayer film formed by the vapor deposition method. In FIG. 7, a cluster configured in a columnar shape is formed, and a considerably rough columnar structure is formed. Many voids are generated between the columns, and in FIG. 8, a cluster configured in a grape shape is formed. It can be confirmed that voids are generated so as to surround the fine particles. These voids cause non-uniform refractive index and light scattering, resulting in light loss.
[0007]
The ion sputtering method can form a very dense film, and can form a film having a uniform refractive index within a single film. However, the film formation rate is very slow compared with the vapor deposition method, and the internal stress of the film is also large, which causes defects such as distortion.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical filter that can form a film having a uniform refractive index in a shorter time and further has a clear boundary between the films, and a method for manufacturing the same.
[0009]
[Means for Solving the Problems]
The present invention provides an optical filter in which a plurality of films having different refractive indexes are laminated on a substrate.
The film has a cluster-like microcrystal aggregate structure and an amorphous structure arranged so as to fill voids generated in the microcrystal aggregate structure, and the refractive index is uniform within a single film. It is characterized by.
[0010]
In the above, the material used for the cluster-like microcrystalline aggregate structure, and materials in which the use in the amorphous structure is preferably a wood charge of the same refractive index.
[0011]
In the optical filter of the present invention, a gap between microcrystalline grains having a particle size constituting a cluster structure of several nanometers (nm) to several hundred nanometers (nm) can be filled with a highly dense composition. A multilayer film having a uniform refractive index and no light scattering in a single film can be formed in a short time. Furthermore, since the composite has a different structure within a single film, the internal stress of the film can be relaxed by controlling the composition ratio, and distortion and cracks can be prevented.
[0012]
Moreover, it is preferable that the boundary of the film is formed only of an amorphous structure. As a result, the boundary surface of the film is formed only with dense particles, and thus the boundary surface is smoothed.
[0013]
Moreover, the manufacturing method of the optical filter of the present invention is a manufacturing method of an optical filter in which a plurality of films having different refractive indexes are laminated on a substrate.
Vapor deposition or chemical vapor deposition (CVD) is applied to the formation of a cluster-like microcrystalline aggregate structure, and sputtering is applied to film formation of an amorphous structure. The sputtering method is applied at the same time to form a multilayer film having a refractive index that changes stepwise on the substrate.
[0014]
In this case, it is preferable to stop film formation by the vapor deposition method or chemical vapor deposition method immediately after the start of film formation and immediately before the end of film formation.
[0015]
The manufacturing method of the present invention is suitable for forming a highly accurate multilayer optical filter because a large number of films having a uniform refractive index can be stacked in a short time.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
1A and 1B are explanatory views showing a manufacturing process of the optical filter of the present invention, wherein FIG. 1A shows a first process, FIG. 1B shows a second process, and FIG. 1C shows a third process. FIG. 2 is a schematic diagram showing the internal structure of the film. 4 is a scanning electron microscope (SEM) photograph of the cross section of the TiO ₂ film of the optical filter, and FIG. 5 is a transmission electron microscope (TEM) photograph of a part of FIG.
[0017]
A manufacturing apparatus 20 shown in FIG. 1 includes an ion beam sputtering apparatus 1 that performs an ion beam sputtering method and a vapor deposition apparatus 10 that performs a vapor deposition method. A glass substrate 4 is disposed at a predetermined position.
[0018]
The ion beam sputtering apparatus 1 includes an ion gun 2 and a target material 3 formed from a metal oxide or the like. The ion gun 2 is arranged toward the target material 3, and includes an argon ion (Ar ⁺ ) generating portion 2a, a discharge chamber 2b for converting argon ions into plasma, and a plurality of grids 2c for accelerating the argon ions. It is provided in parallel. By applying a high voltage of 1100 volts, for example, between the grids 2c, the argon ions are accelerated between the grids 2c, and a high-speed argon ion beam is emitted. Then, by applying an ion beam to the target material 3, sputtered particles are generated from the target material 3, and a film made of a radical metal oxide or the like is formed on the surface of the glass substrate 4. The ions are not limited to argon, but may be an inert gas having a higher specific gravity such as krypton or xenon.
[0019]
The vapor deposition apparatus 10 includes a container 11b containing a vapor deposition material 11a in the form of powder or pellets of metal oxide or the like and an electron gun 11c, and the electron beam (e) emitted from the electron gun 11c is vapor deposited. The vapor deposition material 11a is heated and evaporated by being applied to the material 11a. At this time, particles such as evaporated metal oxide are attached to the glass substrate 4 to form a film.
[0020]
The target material 3 and the vapor deposition material 11a are of the same type so that the refractive indexes are the same. For example, the materials 3 and 11a are metals, metal oxides, fluorides, and the like. Specifically, titanium dioxide (TiO ₂ ), silicon dioxide (SiO ₂ ), tantalum oxide (TaO _x ), alumina (Al ₂ O ₃ ), magnesium fluoride (MgF ₂ ), niobium oxide (NbO _x ), aluminum fluoride (AlF), magnesium oxide (MgO), zirconium oxide (ZrO ₂ ), calcium fluoride (CaF ₂ ), bismuth oxide ( Bi ₂ O ₃ ), cadmium selenium (CdSe), cadmium sulfa (CdS), silicon (Si), lanthanum fluoride (LaF ₃ ), antimony oxide (Sb ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ) and these It is selected from such alloy oxides . Also, from the viewpoint of the film internal stress and refractive index, the combination of the combination or titanium oxide and silicon dioxide and tantalum oxide and silicon dioxide it is most preferred.
[0021]
Next, an optical filter manufacturing method using the manufacturing apparatus 20 will be described with reference to FIG. The present embodiment shown in FIG. 1 is a method for forming a film by using an ion beam sputtering apparatus 1 and a vapor deposition apparatus 10 in combination. FIG. 2 schematically shows a state in which two layers of films are laminated on the glass substrate 4 using TiO ₂ and SiO ₂ as an example of the target material.
[0022]
First, as shown in FIG. 1A, TiO ₂ is placed on the target material 3 and only the ion beam sputtering apparatus 1 is operated. As a result, argon ions generated by the ion gun 2 strike the target material 3, and a layer (amorphous structure) 5 consisting only of a dense structure in which fine particles 8a are aggregated on the glass substrate 4 is formed. And wherein the process proceeds to steps subsequent to the steps of (A) (B), an ion beam sputtering apparatus 1 and the vapor deposition apparatus 10 to be operated simultaneously with the cluster-like microcrystalline aggregate structure on the prior SL layer 5 And a layer 6 having a dense structure as a whole by filling the voids (voids) formed between the particles 8b with a low-density structure (aggregate of coarse particles 8b). It is formed. Then, the process moves from the step (B) to the step (C), the vapor deposition apparatus 10 is stopped, and only the ion beam sputtering apparatus 1 is operated, so that only the dense particles 8a are formed on the layer 6. A layer (amorphous structure) 7 having the following structure is formed. As a result, a film 8 made of a single composition of TiO ₂ is formed.
[0023]
Furthermore, the target material 3 and the vapor deposition material 11a are changed from TiO ₂ to SiO ₂ , respectively, and the steps of FIGS. 1A to 1C are performed in the same manner as described above.
[0024]
In the step (A), by operating only the ion beam sputtering apparatus 1, the layer 15 composed only of an aggregate of dense SiO ₂ particles 18 a as an amorphous structure is formed on the layer 7. By simultaneously operating the ion beam sputtering apparatus 1 and the vapor deposition apparatus 10, an aggregate of fine particles 18a is formed in the gaps between the aggregates of coarse particles 18b (cluster-like microcrystal aggregate structure) on the layer 15. A layer 16 of filled structure is formed. Further, by operating only the ion beam sputtering apparatus 1, a layer 17 composed only of an aggregate of dense particles 18 a having an amorphous structure is formed on the layer 16. In this way, a film 18 having a single composition of SiO ₂ is formed.
[0025]
By selecting the target material 3 and the vapor deposition material 11a as described above and repeating the steps (A) to (C), a quasi-gradient type laminated film in which films having different refractive indexes are formed in stages is provided. An optical filter is obtained. The selection of the refractive index, the film thickness, and the number of stacked layers at this time are appropriately selected according to the purpose of use of the optical filter. Therefore, it is possible to form a high-precision optical filter composed of a film having the number of stacked layers on the order of 2 digits to 3 digits in a shorter time than conventional.
[0026]
For example, by setting the ratio of film formation by vapor deposition and the ratio of film formation by ion beam sputtering to 80:20 by volume, the film formation speed is five times as high as the film formation speed only by ion beam sputtering. Can be executed with The ratio can be appropriately changed according to the state of the film density and the film formation rate of each apparatus, but it is preferable to adjust the film formation rate by the vapor deposition method so as not to exceed the film formation rate of the ion beam sputtering method.
[0027]
Furthermore, it is also effective to install an ion gun or an electron gun with a configuration along the scattering direction of the substrate and vapor deposition particles as an assist for substrate cleaning and vapor deposition.
[0028]
In the films 8 and 18 formed by the manufacturing method described above, the joint surfaces of the layer 7 of the film 8 and the layer 15 of the film 18 are each an aggregate of dense particles. The boundary becomes clear. Therefore, the refractive index can be made uniform in a single film, and a highly accurate optical filter can be obtained by stacking a plurality of these. Further, in the films 8 and 18, since the high density particles are filled in the gap formed by the low density particles and are in a dense state, the light cannot recognize the structural difference although there is a structural difference. It can be recognized as a film having a uniform composition.
[0029]
For example, as shown in FIG. 4, when a film is formed by applying a vapor deposition method and an ion beam sputtering method, each film is formed densely and the boundary surface of each film is smoothed. Further, as shown in FIG. 5, it can be confirmed that a film in which an amorphous structure is buried as an amorphous structure is formed in a gap between cluster-like microcrystal aggregate structures.
[0030]
In this way, a laminated film such as a multi-cavity type bandpass filter or a random film thickness type gain guarantee filter can be formed, and a highly accurate optical filter can be obtained. It is also possible to form a refractive index gradient type optical filter having a so-called step gradient structure by changing the refractive index stepwise for each film. In this gradient index type optical filter, the effect of alleviating the film stress can be exhibited particularly by adopting a composite configuration with a uniform refractive index.
[0031]
FIG. 3 shows a manufacturing apparatus 30 which is a modification of the manufacturing apparatus 20. This manufacturing apparatus 30 is an apparatus capable of forming a film by using both the ion beam sputtering method and the vapor deposition method in the same manner as the manufacturing apparatus 20.
[0032]
The manufacturing apparatus 30 is provided with a selection plate 31, and a plurality of glass substrates 4 a, 4 b,... Are provided on the selection plate 31, and other configurations are the same as those of the manufacturing apparatus 20. Is omitted. The selection plate 31 is a disk that is rotatably supported. Glass substrates 4a, 4b,... Are placed on the disk, and when the film formation on the glass substrate 4a is completed, the selection plate 31 is rotated. Another glass substrate 4b can be selected. In this case, the selection plate 31 may be switched every time the layers 5, 6, 7 (15, 16, 17) in the single film are formed, or the selection plate 31 is formed every time the film 8 (18) is formed. 31 may be switched. Therefore, since the film forming process of another glass substrate 4b can be started immediately after the film forming of the glass substrate 4a is completed, the film forming time of the optical filter can be further shortened.
[0033]
Note that the present invention is not limited to the above embodiment, and a plurality of sets of ion beam sputtering apparatuses and vapor deposition apparatuses may be provided to form a film on a plurality of glass substrates at the same time. In addition, the target material and the vapor deposition material may be rotatably supported so as to eliminate the material exchange loss and reduce the film formation time.
[0034]
In the present embodiment, the combination of the vapor deposition method and the ion beam sputtering method has been described. However, the present invention is not limited to this. For example, a combination of the vapor deposition method and the helicon beam sputtering method may be used, or a chemical vapor phase using a chemical catalytic reaction may be used. A combination of a growth method (CVD) and a beam sputtering method can be appropriately changed.
[0035]
【The invention's effect】
In the present invention described above, an optical filter in which a film having a uniform refractive index can be formed in a short time in a single film, the internal stress of the film is small, and the boundary portion of the film is smoothed so that the boundary surface is clear. Can be obtained.
[0036]
As a result, it is possible to supply a large amount of demultiplexing filters necessary for high-density wavelength division multiplexing communication or polarization division communication such as high-accuracy bandpass filters, bandpass filters, and gain guarantee filters.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a manufacturing process of an optical filter of the present invention, (A) is a first process, (B) is a second process, (C) is a third process,
FIG. 2 is a schematic diagram showing the internal structure of an optical filter film;
FIG. 3 is a schematic diagram showing a modification of the manufacturing apparatus;
FIG. 4 is an SEM photograph showing a cross section of the TiO ₂ film of the optical filter of the present invention;
5 is an enlarged TEM photograph of a part of FIG.
FIG. 6 is a schematic diagram showing the structure inside the film when it is formed by vapor deposition;
FIG. 7 is a SEM photograph showing a cross section of a TiO ₂ single layer film when deposited by an evaporation method;
FIG. 8 is a SEM photograph showing a cross section of a TiO ₂ / SiO ₂ multilayer film formed by vapor deposition.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ion beam sputtering apparatus 2 Ion gun 3 Target material 4 Glass substrate 5, 6, 7 Layer 8, 18 Film 10 Deposition apparatus 11a Deposition material 11b Container 11c Electron gun 20, 30 Manufacturing apparatus

Claims (5)

In an optical filter in which a plurality of films having different refractive indexes are laminated on a substrate,
The film has a cluster-like microcrystal aggregate structure and an amorphous structure arranged so as to fill voids generated in the microcrystal aggregate structure, and the refractive index is uniform within a single film An optical filter characterized by. Material and the the materials used in the amorphous structure, the optical filter according to claim 1, wherein the wood charge of the same refractive index to be used for the cluster-like microcrystalline aggregate structure. The optical filter according to claim 1, wherein the boundary of the film is formed only of an amorphous structure. In the method of manufacturing an optical filter in which a plurality of layers having different refractive indexes are laminated on a substrate,
Vapor deposition or chemical vapor deposition (CVD) is applied in the formation of a cluster-like microcrystalline aggregate structure, and sputtering is applied in formation of an amorphous structure. A method for producing an optical filter, wherein the sputtering method is simultaneously applied to form a multi-layered film having a refractive index that changes stepwise on the substrate. The manufacturing method according to claim 4, wherein film formation by the vapor deposition method or chemical vapor deposition method is stopped immediately after the start of film formation and immediately before the end of film formation.

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