JPWO2006092919A1 - Optical element and optical element manufacturing method - Google Patents

Abstract

A multilayer optical thin film 4 is formed by alternately depositing about 100 layers of SiO 2 thin films 2 and Nb 2 O 5 thin films 3 on the surface of a quartz substrate 1 having a thickness of 0.8 mm or less. Since the linear expansion coefficient of the substrate 1 is small and the difference from the multilayer optical thin film 4 is large, the compression stress and temperature of the multilayer optical thin film 4 when the substrate 1 is brought to room temperature from the film formation state which is usually about 200 ° C. The thermal stress generated by the descent cancels out, and the deformation (warpage) of the substrate 1 is reduced. Therefore, when the substrate 1 is cut with a dicing saw or the like, the processing is easy, the damage is less, and the surface accuracy of the cut out optical element is improved.

Description

  The present invention relates to an optical element formed by forming a thin film such as a dielectric film on a substrate, and a method for manufacturing such an optical element.

  In optical elements such as interference filters and antireflection films used for optical communications, etc., a thin film is formed on a glass with a thickness of 1 mm or less, and light interference in the multilayer thin film is utilized. Some have desired optical characteristics.

Such optical elements are, for example, 50 mm square, on a glass substrate having a thickness of about 0.3 mm (BK7), and SiO ₂ which is a low refractive _{material, Nb 2 O 5, Ta 2} O is a high refractive material ₅ , thin films of TiO ₂ , ZrO ₂ , HfO _2, etc. are alternately stacked (the thickness of each thin film is typically several tens to several hundreds of nanometers). Further, a thin film having a refractive index intermediate between the low refractive index material thin film and the high refractive index material thin film such as Al ₂ O ₃ is appropriately interposed between the low refractive index material and the high refractive index material. The film structure may be a multilayer thin film.

  A sputtering method or an ion beam assist method is often used for film formation. After the film formation is completed, the substrate having the multilayer thin film on the surface is cooled to room temperature, cut into a predetermined size by a dicing saw or the like, and used as an optical element.

When manufacturing such an optical element, there is a problem that the substrate is warped due to the compressive stress of the multilayer thin film. In this case, the compressive stress is a stress that works so as to stretch the surface of the substrate on which the multilayer thin film is formed. Deform to be convex. Such compressive stress is estimated to be 50 to 150 MPa in the case of Nb ₂ O ₅ and 150 to 350 MPa in the case of SiO ₂ .

  If the deformation of the substrate exceeds the allowable limit, there is a problem that it becomes difficult to cut with a dicing saw or the like, or breaks during handling. Further, there may be a problem that the surface of the cut out optical element is not flat. If the surface of the cut out optical element does not become flat, the optical characteristics change depending on the position of light incident on the optical element, or when these micro optical elements are arranged and sandwiched between other optical elements such as glass In addition, there are problems such as uneven surface and poor adhesion.

  The present invention has been made in view of such circumstances, and there is little deformation after film formation is completed, and therefore, handling such as cutting is easy, optical elements with good optical properties, and manufacture of such optical elements are provided. It is an object to provide a method.

  A first means for solving the problem is an optical element formed by forming a thin film having a compressive stress on a substrate, and the substrate has a linear expansion smaller than a linear expansion coefficient of the thin film. An optical element having a coefficient and having a thickness of 0.8 mm or less is used.

  In general, a thin film is formed by a sputtering method, an ion beam assist method, or the like, and these are performed at a high temperature. Therefore, if a material having a linear expansion coefficient smaller than that of the thin film is used as the substrate, the amount of contraction of the thin film becomes larger than the amount of contraction of the substrate when the room temperature is reached after completion of film formation. Therefore, the thermal stress generated between the substrate and the thin film cancels out due to the compressive stress and temperature drop of the thin film. can do. When the thickness of the substrate is 0.8 mm or more, deformation due to film stress is reduced and the effect of this means is reduced. Therefore, the thickness of the substrate is limited to 0.8 mm or less.

  As the thickness of the substrate is reduced to 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, and 0.1 mm, the effect of this means increases. Note that this means is not necessarily limited to a thin film formed by the sputtering method or the ion beam assist method.

  The second means for solving the above-mentioned problem is the first means, characterized in that the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 and 3: 1. To do.

  In most cases, the thickness of the thin film of the optical element formed by forming a thin film such as a dielectric film on the substrate is 10 μm to 30 μm. The thickness of the substrate is 10 μm to 0.8 mm. Therefore, when the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 and 3: 1, the effect of the first means is particularly great.

  A third means for solving the problem is the first means or the second means, wherein the thin film has a multilayer film structure.

  The first means and the second means may have a multilayer film structure that forms an interference filter or the like, and when the number of layers increases, it becomes easier to realize various spectral transmittance characteristics. Since the stress of the thin film itself also increases, the effect obtained by applying the first means and the second means is particularly great when the thin film has a multilayer structure.

  A fourth means for solving the problem is any one of the first means to the third means, wherein the material is quartz.

Generally, the linear expansion coefficient of a thin film is about 50 × 10 ⁻⁷ / K. On the other hand, the coefficient of linear expansion of quartz is about 5 × 10 ⁻⁷ / K, which is an order of magnitude smaller, so that it is particularly effective when used as a material for the first means or the second means.

  A fifth means for solving the above problem is a method of manufacturing an optical element including a step of forming a thin film having a compressive stress on a substrate, wherein the substrate is formed on the basis of a linear expansion coefficient of the thin film. When a substrate having a small coefficient of linear expansion and a thickness of 0.8 mm or less is used, and the substrate having a thin film formed on the surface is returned to room temperature after completion of film formation, the deformation of the substrate falls within an allowable range. An optical element manufacturing method is characterized in that film formation is performed at such a temperature.

  As described above, when a material having a linear expansion coefficient smaller than that of the thin film is used as the substrate, the compressive stress and thermal stress of the thin film cancel each other, and the deformation of the substrate at room temperature can be reduced. Since the magnitude of the thermal stress when the substrate is returned to room temperature increases as the temperature of the substrate during film formation increases, the compressive stress and thermal stress of the thin film can be reduced by adjusting the temperature of the substrate during film formation. By canceling out, the amount of deformation when the substrate is returned to room temperature can be reduced. The reason for limiting the thickness of the substrate to 0.8 mm or less is the same as in the first means.

  As the thickness of the substrate is reduced to 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, and 0.1 mm, the effect of this means increases.

  A sixth means for solving the above-mentioned problem is the fifth means, characterized in that the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 and 3: 1. To do.

  A seventh means for solving the above-mentioned problems is the fifth means or the sixth means, wherein the thin film has a multilayer film structure.

  An eighth means for solving the above-mentioned problem is any one of the fifth to seventh means, wherein the material is quartz.

It is a figure for demonstrating the manufacturing method of the optical element which is an example of embodiment of this invention.

Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a method of manufacturing an optical element which is an example of an embodiment of the present invention. Quartz substrate 1 (approximately 50mm square, a thickness of about 0.3 mm) on the surface of, by using a sputtering apparatus, a SiO ₂ thin film 2 and Nb ₂ O ₅ thin film 3, and a total of about 100 layer deposition alternately Then, the multilayer optical thin film 4 is formed. The thickness of the multilayer optical thin film 4 is about 30 μm.

  As the substrate 1, for example, in addition to quartz, for example, Clear Serum Z made by OHARA, Zerodur made by Shot, Pyrex glass made by Corning, Tempax glass made by Shot, etc. have a small linear expansion coefficient. Optical materials can be used.

The linear optical expansion coefficient of the multilayer optical thin film 4 is about 50 × 10 ⁻⁷ / K (the linear expansion coefficient of Nb ₂ 0 ₅ is 6.5 × 10 ⁻⁵ / K, and the linear expansion coefficient of SiO ₂ is 4 to 5 × 10 ⁻⁵ / K.) Since the conventional glass (BK7) has a linear expansion coefficient of about 75 × 10 ⁻⁷ / K and is larger than the linear expansion coefficient of the multilayer optical thin film 4, when the substrate 1 after film formation is at room temperature, the compressive stress and The thermal stress worked in the same direction, and the deformation of the substrate 1 was further increased.

  In this embodiment, since the linear expansion coefficient of the substrate 1 is smaller than the linear expansion coefficient of the multilayer optical thin film 4, when the substrate 1 is brought to room temperature from a film formation state that is usually about 200 ° C., the multilayer optical thin film 4 The compressive stress and the thermal stress generated by the temperature drop cancel each other, and the deformation (warpage) of the substrate 1 is reduced. Therefore, when the substrate 1 is cut with a dicing saw or the like, the processing is easy, the damage is less, and the surface accuracy of the cut out optical element is improved.

  Further, when the multilayer optical thin film 4 is formed, the film forming temperature is adjusted within a range that does not affect the film forming conditions, thereby adjusting the thermal stress when the substrate 1 is at room temperature. The deformation of the substrate 1 can be reduced. As the method, for example, after determining the material of the substrate 1, the film formation temperature is changed and the film formation is performed, and then the film formation temperature is set such that the deformation amount becomes the smallest when the substrate 1 is brought to a normal temperature state. Find it and deposit at that temperature.

  Further, when the film forming temperature is limited, for example, the amount of deformation is minimized when the material of the substrate 1 is changed and the film is formed at a predetermined film forming temperature and then the substrate 1 is brought to a room temperature. What is necessary is just to find the material of such a board | substrate 1 and to use the material as a material of the board | substrate 1.

As materials constituting the thin film used in the present invention, in addition to materials such as SiO ₂ and Nb ₂ O ₅ , in addition to materials such as Ta ₂ O ₅ , TiO ₂ , ZrO ₂ , HfO ₂ , and Al ₂ O ₃ , A material that generates compressive stress during film formation can be used.

As a substrate 1 as shown in FIG. 1, quartz having a size of 50 mm square and a thickness of 0.3 mm was used, and 51 layers of SiO ₂ and 50 layers of Nb ₂ 0 ₅ were alternately formed on the surface thereof by a sputtering apparatus. The film forming temperature was about 200 ° C. The average thickness of one layer of SiO ₂ was about 150 nm, and the average thickness of one layer of Nb ₂ 0 ₅ was about 250 nm. The thickness of the multilayer optical thin film 4 thus formed was about 20 μm.

  When the amount of warpage of the substrate 1 during the film formation was observed, it was about 1.1 mm. When the substrate 1 was brought to room temperature after the film formation was completed, the warpage amount of the substrate 1 was improved to 0.5 mm.

  By cutting this substrate with a dicing saw, a large number of optical elements having a thickness of 0.3 mm and 8 mm × 0.3 mm square were cut out. When these elements were sandwiched between the waveguides, they were able to be fitted into the grooves formed in the waveguides without any problems. Moreover, desired optical characteristics could be obtained.

Comparative example

  An optical element was manufactured in the same manner as in Example 1 except that glass (BK7) was used as the substrate 1.

  When the amount of warpage of the substrate 1 during the film formation was observed, it was about 0.9 mm. After the film formation was completed, when the substrate 1 was brought to room temperature, the warpage amount of the substrate 1 deteriorated to 1.4 mm. That is, the amount of warpage was about three times that of the example.

By cutting this substrate with a dicing saw, a large number of optical elements having a thickness of 0.3 mm and 8 mm × 0.3 mm square were cut out. When these elements are sandwiched and used in a waveguide, there are some that cannot be fitted in a groove formed in the waveguide. In addition, some optical fibers cannot obtain desired optical characteristics, which is presumed to be caused by fluctuations in the incident angle due to surface warpage.

Claims (8)

  An optical element formed by forming a thin film having a compressive stress on a substrate, wherein the substrate has a material having a linear expansion coefficient smaller than that of the thin film and a thickness of 0.8 mm or less. An optical element being used.   2. The optical element according to claim 1, wherein the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 and 3: 1.   The optical element according to claim 1, wherein the thin film has a multilayer film structure.   The optical element according to claim 1, wherein the material is quartz.   A method of manufacturing an optical element including a step of forming a thin film having compressive stress on a substrate, wherein the substrate has a linear expansion coefficient smaller than a linear expansion coefficient of the thin film, and a thickness of 0.8 mm or less The film is formed at a temperature such that the deformation of the substrate falls within an allowable range when the substrate having the thin film formed on the surface is returned to room temperature after the film formation is completed. Device manufacturing method.   6. The method of manufacturing an optical element according to claim 5, wherein the ratio of the thickness of the thin film to the thickness of the substrate is between 1:80 and 3: 1.   The optical thin film manufacturing method according to claim 5, wherein the thin film has a multilayer structure. The method for manufacturing an optical element according to claim 5, wherein the material is quartz.

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