JP2016221980A - Method of manufacturing optical element and method of manufacturing shaping die for optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a shaping die that can form a fine uneven structure, having a wide range of pitch including an infrared region, on a surface including a large area surface and a curved surface.SOLUTION: In a method of manufacturing a shaping die for an optical element, a substrate made of a semiconductor or metal material reactive with sulfur hexafluoride is placed in a reactive ion etching apparatus, a mixed gas of sulfur hexafluoride and oxygen is introduced, and in a plasma dry etching process, oxides are scattered on a surface of the substrate and etching is made to progress on the surface of the substrate by the sulfur hexafluoride using the oxides as an etching prevention mask to form on the surface of the substrate a fine uneven structure having a pitch larger than 0.35 μm and having an upper limit of the pitch in an infrared region.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing an optical element having a fine concavo-convex structure on the surface and a method for manufacturing a mold for an optical element.

  An antireflection structure composed of fine concavo-convex structures arranged at a pitch (period) smaller than the wavelength of light is used for an optical element. As a method of manufacturing a mold for such a fine concavo-convex structure, a method is known in which resist is patterned using interference exposure or an electron beam drawing apparatus, and etching or electroforming is performed (for example, Patent Document 1). . However, it is difficult to form a fine concavo-convex structure on a large area surface or curved surface by these methods.

  Recently, a method for producing an antireflection structure without a resist patterning step has been developed. Mainly, a method of forming a fine concavo-convex structure by applying nanoparticles to the substrate surface (for example, Patent Document 2) or a method of forming a fine concavo-convex structure using anodized porous alumina as a mold (for example, Patent There is literature 3). Although these methods are expected to be applied to large-area surfaces and curved surfaces, the pitch size of the fine concavo-convex structure is limited to 1 micrometer or less because of process characteristics. Therefore, it is difficult to apply to, for example, an infrared optical element.

  Thus, a mold and an optical element manufacturing method that can form a fine concavo-convex structure with a wide range of pitches including the infrared region on a surface having a large area or a curved surface have not been developed.

WO2006 / 129514 JP2012-40878 JP2014-51710

  Accordingly, there is a need for a mold and an optical element manufacturing method that can form a fine concavo-convex structure with a wide range of pitches including the infrared region on a surface having a large area or a curved surface.

  The mold manufacturing method according to the first aspect of the present invention is a mold manufacturing method using a reactive ion etching apparatus. A mixed gas of sulfur hexafluoride and oxygen is introduced into the apparatus, a base material made of a semiconductor or metal material that reacts with sulfur hexafluoride is disposed, and oxides are scattered on the surface of the base material. Then, etching is performed on the surface of the base material with sulfur hexafluoride using the oxide as an etching prevention mask, thereby forming a fine concavo-convex structure with an upper limit of the pitch in the infrared region on the surface of the base material.

  Since the manufacturing method of this aspect does not require patterning for the etching prevention mask, it does not take time. Moreover, according to the manufacturing method of this aspect, a fine uneven structure having a wide range of pitches including the infrared region can be formed on a surface having a large area or a curved surface.

  In the mold manufacturing method according to the first embodiment of the first aspect of the present invention, the mold is for an optical element.

  In the method for manufacturing a molding die according to the second embodiment of the first aspect of the present invention, the molding die is for an antireflection structure.

  In the method for manufacturing a mold according to the third embodiment of the first aspect of the present invention, the mold is for an infrared antireflection structure.

  In the method for manufacturing a mold according to the fourth embodiment of the first aspect of the present invention, the mold is for a diffusion plate.

  The mold according to the second aspect of the present invention is a substrate made of a semiconductor or metal material that reacts with sulfur hexafluoride by introducing a mixed gas of sulfur hexafluoride and oxygen into a reactive ion etching apparatus. Is disposed on the surface of the base material, and the oxide is used as an anti-etching mask, and etching is performed on the surface of the base material with sulfur hexafluoride on the surface of the base material. A fine concavo-convex structure in which the upper limit of the pitch is in the infrared region is formed.

  The mold according to this aspect can be manufactured by a simple process without using patterning for an etching prevention mask. Moreover, a mold having a fine concavo-convex structure with a wide range of pitches including the infrared region on a surface having a large area or a curved surface is obtained.

  The optical element manufacturing method according to the third aspect of the present invention is an optical element manufacturing method using a reactive ion etching apparatus. A mixed gas of sulfur hexafluoride and oxygen is introduced into the apparatus, a base material made of a semiconductor that reacts with sulfur hexafluoride is disposed, oxides are scattered on the surface of the base material, and the oxidation is performed. Using the object as an etching prevention mask, etching is performed on the surface of the base material by sulfur hexafluoride, thereby forming a fine uneven structure having an upper limit of the pitch in the infrared region on the surface of the base material.

  Since the manufacturing method of this aspect does not require patterning for the etching prevention mask, it does not take time. Moreover, according to the manufacturing method of this aspect, a fine uneven structure having a wide range of pitches including the infrared region can be formed on a surface having a large area or a curved surface.

  The optical element according to the fourth aspect of the present invention introduces a mixed gas of sulfur hexafluoride and oxygen into a reactive ion etching apparatus, and disposes a substrate made of a semiconductor that reacts with sulfur hexafluoride, An oxide is scattered on the surface of the base material, and etching is performed on the surface of the base material with sulfur hexafluoride using the oxide as an etching prevention mask, whereby the upper limit of the pitch is increased on the surface of the base material. A fine uneven structure in the infrared region is formed.

  The optical element of this aspect can be manufactured by a simple process without using patterning for an etching prevention mask. In addition, an optical element having a fine concavo-convex structure with a wide range of pitches including the infrared region on a surface having a large area or a curved surface can be obtained.

It is a figure which shows the structure of the reactive ion etching apparatus 200 used for the shaping | molding die or optical element which provided the fine uneven structure on the surface by this invention. It is a flowchart for demonstrating the principle of the shaping | molding die manufacturing method by this invention. It is a figure for demonstrating the method to manufacture the shaping | molding die provided with the fine uneven structure on the plane. It is a figure for demonstrating the method to manufacture the optical element provided with the fine concavo-convex structure on the surface. It is a flowchart which shows the method of determining the etching conditions of the metal mold | die manufacturing method for antireflection structures as an example of the manufacturing method of the shaping | molding die by this invention. It is a figure which shows the relationship between the etching time at the time of maintaining the etching conditions of Table 1, and making the electric power of a high frequency power supply into 100 watts and 200 watts, and the pitch of a fine concavo-convex structure. It is a figure which shows the relationship between the etching time at the time of maintaining the etching conditions of Table 1, and making the electric power of a high frequency power supply into 100 watts and 200 watts, and the depth of a fine concavo-convex structure. It is a figure which shows the relationship between the wavelength of the infrared rays which inject into a base material provided with the fine concavo-convex structure, and the transmittance | permeability. It is a figure for demonstrating the transmittance | permeability. It is a figure which shows the relationship between the wavelength of the light which wants to improve the transmittance | permeability, and the pitch of the uneven | corrugated microstructure which improves the transmittance | permeability. It is a figure which shows the external appearance photograph of the board | substrate 1 which is not provided with the fine uneven structure on the surface, the board | substrate 2 provided with the fine uneven structure for visible light on the surface, and the substrate 3 provided with the fine uneven structure on the surface. 3 is a scanning electron micrograph of the fine concavo-convex structure 3.

  FIG. 1 is a diagram showing a configuration of a reactive ion etching apparatus 200 used for manufacturing a mold or an optical element having a fine concavo-convex structure on the surface according to the present invention. The reactive ion etching apparatus 200 has an etching chamber 201. A gas is supplied from the gas supply port 207 to the evacuated etching chamber 201. Further, the etching chamber 201 is provided with a gas exhaust port 209, and a valve 217 is attached to the gas exhaust port 209. The gas pressure in the etching chamber 201 can be set to a desired pressure value by causing the control device 215 to operate the valve 217 in accordance with the measured value of the gas pressure gauge 213 attached to the etching chamber 201. The etching chamber 201 is provided with an upper electrode 203 and a lower electrode 205, and plasma can be generated by applying a high-frequency voltage by a high-frequency power source 211 between both electrodes. The lower electrode 205 is provided with a base material 101 which is a base material of a mold. The lower electrode 205 can be cooled to a desired temperature by the cooling device 219. The cooling device 219 uses, for example, a water-cooled chiller for cooling. The reason why the lower electrode 205 is cooled is to control the etching reaction by setting the temperature of the substrate 101 to a desired temperature.

  Here, the gas supplied to the etching chamber 201 is a mixed gas of sulfur hexafluoride and oxygen. The base material is a semiconductor or metal that reacts with sulfur hexafluoride.

  FIG. 2 is a flowchart for explaining the principle of the mold manufacturing method according to the present invention.

  In step S1010 of FIG. 2, the mixed gas is turned into plasma by applying a high-frequency voltage so as to perform plasma dry etching.

  In step S1020 of FIG. 2, the oxygen ions in the plasma and the metal or semiconductor ions of the base material reacted with the fluorine-based gas (sulfur hexafluoride) are combined and attached as oxides at random positions on the surface of the base material. To do. The above oxide is hardly etched with sulfur hexafluoride and functions as an etching prevention mask.

  In step S1030 of FIG. 2, the etching of the portion not covered with the oxide on the substrate surface by sulfur hexafluoride proceeds using the above-mentioned oxide attached to the substrate surface as a mask. As a result, a fine uneven structure is formed on the substrate surface.

The gas to be used is a mixed gas of sulfur hexafluoride (SF ₆ ) and oxygen as described above.

  The base material is a semiconductor or metal that reacts with sulfur hexafluoride. Specific examples include silicon, titanium, tungsten, tantalum, a titanium alloy in which other elements are added to titanium, and a tungsten alloy in which other elements are added to tungsten.

  FIG. 3 is a diagram for explaining a method of manufacturing a mold having a fine concavo-convex structure on a plane.

  FIG. 3A is a diagram showing a cross section of the base material 101 before etching.

  FIG. 3B is a view showing a cross section of the surface of the substrate 101 obtained by etching the shape of the fine concavo-convex structure using a reactive ion etching apparatus. In FIG. 3B, the dimensions of the fine concavo-convex structure are illustrated in an enlarged manner as compared with the base material for easy understanding.

  FIG. 4 is a diagram for explaining a method of manufacturing an optical element having a fine concavo-convex structure on the surface.

  FIG. 4A is a diagram showing a cross section of a silicon optical element processed into a curved surface by cutting or the like. A silicon optical element is used for infrared rays.

  FIG. 4B is a view showing a cross section of the surface of a silicon optical element obtained by etching the shape of the fine concavo-convex structure using a reactive ion etching apparatus. The fine uneven structure on the surface of the optical element functions as an antireflection structure. For easy understanding, in FIG. 4B, the dimensions of the fine concavo-convex structure are illustrated in an enlarged manner as compared with the optical element.

  FIG. 5 is a flowchart showing a method for determining etching conditions of a method for manufacturing a mold for an antireflection structure as an example of a method for manufacturing a mold according to the present invention.

  In step S2010 of FIG. 5, initial values of etching conditions are set.

  In step S2020 of FIG. 5, the substrate is etched using a reactive ion etching apparatus in accordance with the set etching conditions.

  In step S2030 of FIG. 5, the reflectance of the manufactured mold is evaluated.

  In step S2040 of FIG. 5, the shape of the manufactured mold is evaluated. The shape is evaluated using, for example, a scanning electron microscope.

  In step S2050 of FIG. 5, it is determined whether or not the manufactured mold is appropriate as an antireflection structure mold. If appropriate, terminate the process. If not appropriate, the process proceeds to step S2060.

  In step S2060 of FIG. 5, the etching conditions are corrected.

  The etching conditions will be described in detail below.

Table 1 is a table showing a part of the etching conditions.

  A mixed gas of sulfur hexafluoride and oxygen is supplied from the gas supply port 207 to the etching chamber 201 of the reactive ion etching apparatus 200. The supply flow rates of sulfur hexafluoride and oxygen are 50 milliliters per minute, respectively. The pressure in the etching chamber 201 is controlled to 1 pascal. The temperature of the lower electrode 205 on which the substrate 101 is disposed is controlled to 3 degrees Celsius. The base material 101 is made of silicon.

  FIG. 6 is a diagram showing the relationship between the etching time and the pitch of the fine concavo-convex structure when the etching conditions in Table 1 are maintained and the power of the high frequency power supply 211 is 100 watts and 200 watts. The horizontal axis in FIG. 6 represents the etching time, and the vertical axis in FIG. 6 represents the pitch of the fine relief structure. The unit of time is minutes and the unit of pitch is micrometers. The frequency of the high frequency power supply 211 is 13.56 MHz.

  Here, the pitch of the fine concavo-convex structure is the average value of the distance in the direction parallel to the substrate surface between adjacent convex parts or between adjacent concave parts in the cross section of the fine concavo-convex structure obtained by an atomic force microscope or the like. is there. You may obtain | require by the Fourier analysis of the cross section of a fine concavo-convex structure.

  According to FIG. 6, the pitch of the fine relief structure increases as the etching time increases. Further, the increasing rate of the pitch of the fine concavo-convex structure with respect to time increases as the power of the high-frequency power source 211 increases.

  FIG. 7 is a diagram showing the relationship between the etching time and the depth of the fine concavo-convex structure when the etching conditions in Table 1 are maintained and the power of the high frequency power supply 211 is 100 watts and 200 watts. The base material 101 is made of silicon. The horizontal axis in FIG. 7 represents the etching time, and the vertical axis in FIG. 7 represents the depth of the fine relief structure. The unit of time is minutes and the unit of depth is micrometers.

  Here, the depth of the fine concavo-convex structure is an average value of distances in the direction perpendicular to the substrate surface between adjacent convex portions and concave portions in a cross section of the fine concavo-convex structure obtained by an atomic force microscope or the like.

  According to FIG. 7, the depth of the fine relief structure increases as the etching time increases. Moreover, the increasing rate of the depth of the fine concavo-convex structure with respect to time increases as the power of the high-frequency power source 211 increases.

  Thus, by adjusting the etching conditions including the power of the high-frequency power source 211 and the etching time, a fine concavo-convex structure having a pitch and a depth corresponding to the visible light region and the infrared region can be manufactured.

  FIG. 8 is a diagram showing the relationship between the wavelength of infrared light incident on a substrate having a fine relief structure and the transmittance. The horizontal axis of FIG. 8 represents the wavelength of infrared rays incident on the substrate, and the vertical axis of FIG. 8 represents infrared transmittance. In FIG. 8, the solid line indicates the relationship between the wavelength and transmittance of infrared rays incident on a substrate that does not have a fine concavo-convex structure, and the two-dot chain line has a fine concavo-convex structure manufactured under etching conditions 1 described below. The relationship between the wavelength of infrared rays incident on the substrate and the transmittance is shown, and the broken line indicates the relationship between the wavelength and transmittance of infrared rays incident on the substrate having a fine concavo-convex structure manufactured under the etching condition 2 described below. Show the relationship.

  FIG. 9 is a diagram for explaining the transmittance. The transmittance is a ratio of transmitted light to incident light. The transmittance varies depending on the function of the fine concavo-convex structure 1011 installed on the surface of the substrate 101.

Table 2 is a table showing the etching conditions 1 and 2.

  The pitch of the fine concavo-convex structure manufactured under the etching condition 1 (hereinafter referred to as the fine concavo-convex structure 1) is 1.0 micrometers, and the depth is 1.21 micrometers. The ratio of the pitch to the depth of the fine concavo-convex structure 1 is 0.83. The pitch of the fine concavo-convex structure manufactured under the etching condition 2 (hereinafter referred to as the fine concavo-convex structure 2) is 3.0 micrometers and the depth is 2.79 micrometers. The ratio of the pitch to the depth of the fine concavo-convex structure 2 is 1.1.

  According to FIG. 8, the base material provided with the fine concavo-convex structure 1 has a higher transmittance in the wavelength range of 2 to 15 micrometers than the base material not provided with the fine concavo-convex structure. In particular, in the wavelength range of 3 to 7 micrometers, the transmittance is about 10% or more higher than that of a substrate not having a fine relief structure. The base material provided with the fine concavo-convex structure 2 has a higher transmittance in the wavelength range of 6 to 15 micrometers compared to the base material not provided with the fine concavo-convex structure. In particular, in the wavelength range of 7 to 12 micrometers, the transmittance is about 7% or more higher than that of a substrate not having a fine relief structure. From the above results, it is preferable that the pitch of the fine concavo-convex structure that improves the transmittance, that is, reduces the reflectance, is in the range of 1/5 to 1/2 of the wavelength for which the transmittance is desired to be improved.

  FIG. 10 is a diagram illustrating an example of the relationship between the wavelength of light for which the transmittance is to be improved and the pitch of the uneven microstructure that is to improve the transmittance. The horizontal axis in FIG. 10 represents the wavelength of light for which the transmittance is desired to be improved, and the vertical axis in FIG. 10 represents the pitch of the concavo-convex microstructure that improves the transmittance.

  A fine concavo-convex structure (hereinafter referred to as fine concavo-convex structure 3) having a pitch in the infrared region larger than the pitch of the fine concavo-convex structure 2 was produced.

Table 3 is a table showing the etching conditions of the fine relief structure 3.

  The pitch of the fine concavo-convex structure 3 is 18.0 micrometers, and the depth is 6.0 micrometers. The ratio of the pitch to the depth of the fine relief structure 3 is 3.0.

  Under the etching conditions shown in Table 3, the supply amount of oxygen is made smaller than the supply amount of sulfur hexafluoride. As a result, the distance between oxides that adhere to the substrate surface and function as an etching mask increases. Therefore, the ratio of the pitch to the depth of the fine concavo-convex structure 3 is larger than the ratio of the pitch to the depth of the fine concavo-convex structures 1 and 2. Thus, by changing the ratio between the supply amount of sulfur hexafluoride and the supply amount of oxygen, the ratio of the pitch to the depth of the fine relief structure can be changed.

  FIG. 11 is a view showing external photographs of the substrate 1 having no fine uneven structure on the surface, the substrate 2 having a fine uneven structure for visible light on the surface, and the substrate 3 having the fine uneven structure 3 on the surface. is there. The pitch of the fine structure of the substrate 2 is 0.2 micrometers. Since reflection on the surface of the substrate 2 is reduced by the fine concavo-convex structure, the substrate 2 appears black compared to the substrate 1. The pitch of the fine concavo-convex structure 3 is sufficiently larger than the wavelength of visible light. On the other hand, the distance in the direction parallel to the substrate surface between adjacent convex portions or concave portions of the fine concavo-convex structure 3 is not constant but distributed in a predetermined range. Therefore, diffracted light of various orders with various wavelengths is generated by the fine concavo-convex structure 3 of the substrate 3, and the substrate 3 appears cloudy compared to the substrate 1. That is, the substrate 3 provided with the fine concavo-convex structure 3 on the surface diffuses visible light.

  Thus, the board | substrate 3 provided with the fine uneven structure 3 functions as a diffusion plate.

  FIG. 12 is a scanning electron micrograph of the fine relief structure 3.

Claims (3)

A substrate made of a semiconductor or metal material that reacts with sulfur hexafluoride is placed in a reactive ion etching apparatus, and a mixed gas of sulfur hexafluoride and oxygen is introduced. The oxygen ions of the base material and the base material material reacted with sulfur hexafluoride are bonded together, and an oxide is scattered on the surface of the base material. A method for manufacturing a molding die for an optical element, wherein a fine uneven structure is formed on the surface of the substrate by causing etching to proceed on the surface of the substrate, wherein the mold is for a diffusion structure, and the fine unevenness large in the cross section of the structure, the pitch of the fine unevenness of the average value of the distance in a direction parallel to the substrate surface between recesses or adjacent between adjacent convex portions, than the wavelength pitch of the visible light of the fine unevenness Ku, as the upper limit of the pitch of the fine unevenness are infrared region, method for producing a mold for an optical element for determining the pitch of the fine unevenness. A mold is produced by the method of claim 1 ,
An optical element manufacturing method for manufacturing an optical element by molding using the mold. A substrate made of a semiconductor material that reacts with sulfur hexafluoride is placed in a reactive ion etching apparatus, and a mixed gas of sulfur hexafluoride and oxygen is introduced. Ions and the material of the base material reacted with sulfur hexafluoride are bonded, and an oxide of the material of the base material is scattered on the surface of the base material. A method of manufacturing a diffusing optical element that forms a fine concavo-convex structure on the surface of the base material by causing etching to proceed on the surface of the base material with sulfur fluoride, wherein adjacent convex portions in the cross section of the fine concavo-convex structure are formed. the average value of the distance of the substrate plane direction parallel to between recess part between or adjacent as the pitch of the fine unevenness, the pitch of the fine unevenness is larger than the wavelength of visible light, on the pitch of the fine unevenness So it is infrared region, method of manufacturing an optical element defining the pitch of the fine unevenness.