JP2005156677A - Method for manufacturing optical component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical component, which can precisely and continuously control the etching quantity or the film deposition quantity, without deteriorating the characteristic of the optical component, even in the film for the optical component having the refractive index equivalent to that of a substrate. <P>SOLUTION: A reflective film 3 is prepared between the substrate 1 and the film 2 for the optical component. A monochromatic light is incident on the reflective film. The variation in the reflectance of the reflected light reflected by the interface between the film 2 for the optical component and the reflective film 3 and the variation in the etching thickness are used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing an optical component such as a diffraction grating used in an optical communication device.

  With the spread of optical communication systems in recent years, development of optical components such as diffraction gratings has been promoted. These optical components use films made on the substrate for the purpose of improving characteristics such as functional improvement and miniaturization, and solving manufacturing problems such as difficulty in processing the substrate. It is obtained by processing into a desired shape. The film thickness accuracy of the optical component affects the shape of the diffraction grating and the like, and thus greatly affects the characteristics of an optical communication device such as an optical multiplexer / demultiplexer incorporating the optical component. Therefore, a highly accurate film thickness control method is required in the manufacturing method of optical components. In order to solve this problem, the following methods have been proposed.

  In Patent Document 1, a method using transmitted light amount is shown as a film thickness control method in the case of manufacturing by alternately laminating films for optical components having two kinds of refractive indexes on a substrate. In this method, white light dispersed from the upper part of the film is irradiated during film formation, and the amount of light transmitted through the substrate and the optical component film is detected on the back surface of the substrate. The film thickness is controlled by utilizing the fact that the detected transmitted light amount repeatedly increases and decreases for each quarter-wavelength optical film thickness. Further, the light quantity of two wavelengths on both the long and short sides of the desired center wavelength determined by the material constant of the optical component film is measured, and the film thickness is controlled with high accuracy by using the point where the light quantity crosses.

In Patent Document 2, an etching stop film having an etching amount per unit time slower than that of the optical part film is formed between the substrate and the optical part film. By this etching stop, a film for an optical component having a required film thickness can be obtained without being etched beyond a desired depth. Further, since this method does not use transmitted light, it can be used for processing a film for an optical component having the same refractive index as that of the substrate.
JP 2003-215333 A Japanese Patent Laid-Open No. 7-168023

  The above two methods have the following problems.

  In Patent Document 1, since the point where the light amounts of two wavelengths cross is used, the film thickness can be controlled only by a discrete value, and it is difficult to control the film thickness to an arbitrary film thickness other than the quarter wavelength optical film thickness. There is a problem. In addition, when there is a film such as a metal film that hinders the transmission of light, such as a metal film, the film thickness cannot be controlled because the amount of transmitted light cannot be measured. Furthermore, when an optical component film having a refractive index equivalent to that of the substrate is produced, there is almost no change in the amount of transmitted light, and it is difficult to control the film thickness by changing the amount of light. Another mechanistic problem is that the use of two wavelengths complicates the film thickness control system.

  In the method of Patent Document 2, since etching stop is necessary on the entire surface of the substrate, there is a problem that the etching stop affects the characteristics of the optical component. As processing methods by etching, there are wet etching using an etchant and dry etching such as reactive ion etching. In both methods, since the entire surface of the substrate is etched simultaneously, it is necessary to stop etching on the entire surface in order to uniformly control the film thickness of the optical component film within the substrate. Further, since the end point of etching is detected by stopping etching, it is not possible to obtain a desired film thickness by stopping etching in the middle of the optical component film, and there is a restriction in controlling the film thickness.

  In order to solve the above-mentioned problems, the present invention is capable of continuously adjusting the etching amount or the film forming amount with high accuracy without degrading the characteristics of the optical component even in the optical component film having the same refractive index as that of the substrate. It is an object of the present invention to provide a method for manufacturing an optical component that can be controlled automatically.

  In order to solve the above problems, an optical component manufacturing method according to the present invention is an optical component manufacturing method in which a film having a refractive index equivalent to that of the substrate is formed on the substrate. A reflective film having a refractive index different from that of the substrate is made between the optical component films having a single-wavelength light incident on the reflective film from above the optical component film, While measuring the reflected light reflected at the interface of the reflective film, the etching amount or film forming amount is determined based on the change in the reflectance of the reflected light that changes with the etching amount or film forming amount of the optical component film. It is characterized by controlling.

  This method utilizes the fact that the reflectance of reflected light at the interface between the reflective film and the optical component film having the same refractive index as that of the substrate changes as the optical component film thickness increases or decreases. The reflectance of the optical component film repeatedly increases and decreases for each quarter wavelength optical film thickness. The relationship between the etching time and the change in reflectance is illustrated in FIG. 3, and this phenomenon has been experimentally verified. The relationship between the film thickness for optical parts and the etching time can also be obtained in advance by experiments. From these two relationships, the relationship between the change in reflectance and the film thickness can be obtained. Here, since the reflectivity is determined by a constant specific to the reflective film to be used and the optical part film, it is not affected by the experimental conditions. Therefore, the etching amount or film forming amount can be accurately grasped from the change in reflectance during etching or film formation, and highly accurate film thickness control independent of external factors such as experimental conditions can be performed. In addition, since the reflectance is constantly measured during film formation or etching, the film thickness can be accurately adjusted by stopping etching or film formation when the change in reflectance corresponding to an arbitrary film thickness is confirmed. It is also possible to control. Furthermore, since the reflective film only needs to be formed in the portion where the single wavelength light is incident, it does not affect the characteristics of the optical component. In addition, in terms of the mechanism, since the single wavelength light is used, the film thickness control system can be simplified. As described above, a film for an optical component having a refractive index equivalent to that of the substrate can be controlled to an arbitrary film thickness with high accuracy by a simple film thickness control mechanism without affecting the characteristics of the optical component.

  Further, in a method of manufacturing an optical component that forms a film having a refractive index different from that of the substrate on the substrate, single wavelength light is incident on the reflective film from above the optical component film formed on the substrate, and the substrate And the reflected light reflected at the interface between the optical component film and the etching amount of the film on the substrate, or the amount of etching or The amount of film formation can be controlled.

  In this method, an optical component is manufactured using a film for an optical component having a refractive index different from that of the substrate. In this case as well, single wavelength light is made incident from above the optical component film in the same manner as described above. However, since the refractive indexes of the substrate and the optical component film are different, the incident single wavelength light is reflected at the interface between the substrate and the optical component film. By detecting the change in reflectance, the same effect as the above method can be obtained.

  Further, as a configuration example in the manufacturing method, a metal may be used for the reflective film.

  When the refractive indexes of the substrate and the optical component film are the same, a change in reflectance on the reflective film is used for controlling the film thickness, and the reflectance is determined by the material constants specific to the reflective film and the optical component film. In general, a transparent or nearly transparent film is used for an optical component such as a diffraction grating in order to obtain optical characteristics. Therefore, by using an opaque film such as a metal that easily reflects light as the reflective film, it becomes easier to detect the reflected light, and the change in reflectivity as the film thickness for optical components increases or decreases can be judged more clearly. can do.

Furthermore, as a structural example in the manufacturing method, Ta ₂ O ₅ may be used for the optical component film. This is because Ta ₂ O ₅ has a high refractive index and is suitable as a film for optical parts.

  As described above, in the method of manufacturing an optical component according to the present invention, even a film for an optical component having a refractive index equivalent to that of a substrate can be formed with any film with a simple film thickness control mechanism without affecting the characteristics of the optical component. Thickness can be controlled with high accuracy.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an optical component produced using the method for producing an optical component of the present invention. The optical component includes a substrate 1 on which an optical component film is produced, an optical component film 2 and a reflective film 3. An example of these manufacturing methods will be described.

  A ceramic substrate 1 having a refractive index of 2.07 at a wavelength of 633 nm is prepared. As long as the substrate material has the above-mentioned refractive index, any kind of polycrystalline or single crystal ceramics or glass may be used. Next, the substrate is cleaned to remove dust and dirt on the substrate 1.

Thereafter, a material used as the reflective film 3 is formed. In this embodiment, Al is used as an example of the reflective film. The refractive index of Al is 1.0 (absorption coefficient is about 6.6), and the refractive index of the substrate 1 and the optical component film 2 is as follows. Therefore, the reflectance can be detected. In addition to Al, a similar effect can be obtained if a metal such as Au, Ag, Cu, or a dielectric film such as SiO ₂ (refractive index is 1.46) is a film having a refractive index different from that of the optical component film. be able to. An Al film having a film thickness of 30 nm is formed on the entire surface of one side of the substrate 1 placed in a vacuum evaporation apparatus by a vacuum evaporation method. As a film forming method, a sputtering method or an electroless plating method may be used. Next, an unnecessary portion of the Al film is removed from the reflective film using a photolithography technique. Specifically, this is performed as follows. A mask material is applied to the entire surface of the formed Al film, and the mask material is processed so that only the necessary portion of the reflective film 3 is left. At that time, the mask material is formed in a circular shape having a diameter of 5 to 10 mm, for example, in a portion that does not affect the characteristics of the optical component. Thereafter, the substrate 1 is immersed in a solution containing phosphoric acid, nitric acid, and acetic acid as main components, and a portion of the Al film not covered with the mask material is removed by a wet etching method, thereby forming a pattern of the reflective film 3. The shape of the reflective film 3 is not limited to a circle, a square, or the like.

  Although the above reflective film manufacturing process uses an etching method, it may be manufactured by a lift-off method. In the lift-off method, a mask material is first applied on the substrate 1 and the mask material is removed only at a portion where the reflective film 3 is to be formed using a photolithography technique. Thereafter, an Al film is formed by a vacuum deposition method, a sputtering method, an electroless plating method, or the like, and then the mask material is removed to obtain the reflective film 3.

Next, a material to be used for an optical component is formed. In this embodiment, a case where Ta ₂ O ₅ is used as the optical component film 2 is illustrated. First, the substrate is placed in a vacuum deposition apparatus and heated so that the substrate temperature becomes 300 ° C. Thereafter, Ta ₂ O ₅ is formed on the entire surface of the substrate by vacuum deposition. As a result of measuring the film thickness and refractive index of Ta ₂ O ₅ at this time, they were 1.0 μm and 2.07, respectively, and the refractive index was the same value as that of the substrate 1.

Next, the formed optical component film 2 is processed into a desired shape. A mask material is applied on the Ta ₂ O ₅ film formed on the entire surface of the substrate, and the mask material other than the portion corresponding to the structure of the desired optical component is removed by a photolithography technique. Next, the substrate is placed in a vacuum apparatus, and the Ta ₂ O ₅ film without the mask material is removed by reactive ion etching. At this time, a single wavelength light having a wavelength of 633 nm is irradiated from above the Al film, which is a reflective film prepared at a predetermined position of the substrate by the above-described process. During etching, single wavelength light is continuously irradiated. Single wavelength light incident on the Al film is reflected at the interface between the Al film and the Ta ₂ O ₅ film. This reflected light is detected at the upper part of the film formation surface, and the reflectance is measured. The relationship between the change amount of the reflectance and the etching time is known to be as shown in FIG. 3 by an experiment conducted in advance, and shows that the reflectance periodically changes depending on the etching time. In FIG. 3, the film thickness T corresponding to one period from the peak to the next peak of the change in reflectance depends on the refractive index (n) of the optical component film 2 and the wavelength (λ) of the irradiated light. , T = λ / 2n. In this embodiment, the used single-wavelength light of 633 nm is irradiated onto the Ta ₂ O ₅ film having a refractive index of 2.07. In this case, the film thickness corresponding to one period of the change amount of the reflectance. Is 153 nm from the above equation. For example, when the etching amount is set to 600 nm, the amount of change in reflectance is less than 4 cycles. Therefore, if the etching is stopped when the amount of change in the reflectance at the dotted line in the figure is reached, a Ta ₂ O ₅ film having a thickness of 400 nm can be obtained. Thus, if the relationship between the change amount of the reflectance and the etching time and the relationship between the etching time and the etching amount are obtained, the etching amount can be derived from the change in the reflectance continuously measured during the etching.

As described above, after etching the Ta ₂ O ₅ film to a desired film thickness, the mask material is removed using oxygen plasma, whereby an optical component having a desired shape can be obtained.

Here, as the optical component, for example, as shown in FIG. 4, there is a rectangular diffraction grating in which a concave portion 23 is formed after an optical component film 22 made of Ta ₂ O ₅ is formed on a substrate 21. In the case of producing such a structure, first, a mask material is produced on the optical component film 22 in a strip shape at intervals necessary for obtaining optical characteristics by the photolithography technique. Next, the optical component film 22 without the mask material is removed while controlling the etching amount with high accuracy by the reactive ion etching method or the like, thereby forming the recesses 23. Thereafter, the mask material is removed using oxygen plasma, whereby a diffraction grating having the recesses 23 whose film thickness is controlled with high accuracy can be obtained.

  The above is the manufacturing method of the optical component by the etching method, but it can also be manufactured by using the lift-off method in the same manner as the Al film. First, the reflective film 3 is produced by the same method as described above. Next, after the mask material is applied to the entire surface of the substrate 1 before the production of the optical component film 2, the mask material corresponding to the structure of the desired optical component is removed using a photolithography technique. Thereafter, the optical component film 2 is formed by a vacuum vapor deposition method, a sputtering method, or the like, and the optical material film 2 having a desired shape can be produced by removing the mask material.

  Next, a second embodiment of the present invention will be described with reference to FIG. First, a substrate 11 for preparing the optical component film 12 is prepared. Next, an optical component film 12 having a refractive index different from that of the substrate 11 is formed and processed on the substrate by the same method as in the first embodiment. When the optical component film 12 is etched by reactive ion etching or the like, single wavelength light is incident from above the surface of the substrate 11 on which the film is formed. The reflectance of the reflected light reflected at the interface between the substrate 11 and the optical component film 12 is always measured during etching. At the same time, if the relationship between the etching amount of the optical component film 12 and the etching time is obtained in advance, the change in reflectance during etching is measured in the same manner as in the first embodiment, whereby the optical component film 2 is measured. The etching amount can be controlled with high accuracy. Thereafter, a desired shape as an optical component can be obtained by the same process as in the first embodiment. Similarly to Example 1, the film 2 for optical components having a desired shape can also be produced by the lift-off method.

It is sectional drawing of the optical component produced using the 1st manufacturing method of this invention. It is sectional drawing of the optical component produced using the 2nd manufacturing method of this invention. It is the graph which showed the relationship between the change of the reflectance of the reflected light reflected in the interface of the reflecting film in the 1st manufacturing method of this invention, and the film for optical components, and the etching time of the film for optical components. It is a partially broken perspective view of the diffraction grating which is an example of the optical component produced using the manufacturing method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical component film having the same refractive index as the substrate 3 Reflective film 11 Substrate 12 Optical component film having a different refractive index from the substrate 21 Substrate 22 Optical component film 23 Recess

Claims (4)

In a method for manufacturing an optical component in which a film for optical components having a refractive index equivalent to that of the substrate is formed on the substrate,
A reflective film having a refractive index different from that of the substrate is produced between the substrate and the optical component film, and single wavelength light is incident on the reflective film from above the optical component film. Etching amount or film formation amount based on a change in reflectance of the reflected light, which varies with the etching amount or film formation amount of the optical component film, while measuring the reflected light reflected at the interface between and the reflection film A method for manufacturing an optical component, characterized in that the control is performed. In a manufacturing method of an optical component for forming a film for an optical component having a refractive index different from that of the substrate on the substrate,
A single wavelength light is incident on the optical component film from above the optical component film formed on the substrate, and the reflected light reflected at the interface between the substrate and the optical component film is measured. An optical component manufacturing method for controlling an etching amount or a film formation amount on the basis of a change in reflectance of the reflected light which varies with an etching amount or a film formation amount of the optical component film. In the manufacturing method of the optical component of Claim 1 and Claim 2,
A method of manufacturing an optical component, wherein a metal is used as the reflective film. In the manufacturing method of the optical component of Claim 1,
The method for manufacturing an optical component, wherein the optical component film is made of Ta ₂ O ₅ .

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