JP2009128543A - Method for manufacturing antireflection structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture an antireflection structure having a finely rugged portion. <P>SOLUTION: A method for manufacturing an antireflection structure includes steps of: preparing a substrate 27 having a rough surface 27p with a surface roughness larger than a predetermined wavelength; depositing metal in an island state on the rough surface 27p of the substrate 27; and dry etching the substrate 27 by using the island-shaped deposited material 28 as a mask to form a plurality of acicular and finely rugged portions 29 having an average pitch equal to or less than the predetermined wavelength on the rough surface 27p of the substrate 27. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an antireflection structure.

  In recent years, various optical elements in which antireflection treatment for suppressing light reflection is performed on the surface have been proposed. Examples of the antireflection treatment include a film having a relatively low refractive index (low refractive index film) and a multilayer film in which a low refractive index film and a film having a relatively high refractive index (high refractive index film) are alternately laminated. The process which forms the antireflection film which consists of on the surface is mentioned (for example, patent document 1).

  However, such an antireflective film composed of a low refractive index film or a multilayer film requires complicated steps such as vapor deposition and sputtering. For this reason, there is a problem that productivity is low and production cost is high. Further, an antireflection film made of a low refractive index film or a multilayer film has a problem that the wavelength dependency and the incident angle dependency are relatively large.

  In view of such problems, as an anti-reflection process with relatively small incident angle dependency and wavelength dependency, for example, there is a process of regularly forming minute irregularities on the surface of the optical element with a pitch equal to or less than the wavelength of incident light. It has been proposed (for example, Non-Patent Document 1). By performing this process, a rapid change in refractive index at the interface between the element and air is suppressed, and the refractive index gradually changes at the interface between the element and air. For this reason, reflection on the surface of the optical element is reduced, and a high light incidence rate into the optical element can be realized.

Patent Document 2 discloses a technique for forming minute uneven portions on a rough surface.
JP 2001-127852 A JP-T-2001-517319 Daniel H. Lagunin (Daniel H. Raguin) By Michael Morris, “Analysis of antireflective-structured-pure-fused-constitutive-structured-frustrated-constitutive-constitutive-constitutive-constitutive-constitutive-constitutive ----------------- ), Vol. 32, No. 14 (Vol. 32, No. 14), p. 2582-2598, 1993

  An object of the present invention is to provide a method for manufacturing an antireflection structure having a minute uneven portion.

That is, the present invention
A method of manufacturing an antireflection structure that suppresses reflection of light having a predetermined wavelength or more,
Preparing a substrate having a rough surface with a surface roughness greater than the predetermined wavelength;
Depositing metal in an island shape on the rough surface of the substrate;
Using the metal island-shaped deposit as a mask, dry-etching the substrate, and forming a plurality of minute irregularities having an average pitch of the predetermined wavelength or less on the rough surface of the substrate;
A method for manufacturing an antireflection structure is provided.

In another aspect, the present invention provides:
A method of manufacturing an antireflection structure that suppresses reflection of light having a predetermined wavelength or more,
Depositing metal in an island shape on the surface of the first substrate;
Performing dry etching of the first substrate using the metal island deposit as a mask, and forming a plurality of minute uneven portions having an average pitch of the predetermined wavelength or less on the surface of the first substrate; ,
Preparing a second substrate having a rough surface with a surface roughness greater than the predetermined wavelength;
Forming a sheet member using the first substrate as a mold, and bonding the sheet member to the rough surface of the second substrate;
A method for manufacturing an antireflection structure is provided.

  According to the present invention, nanometer-sized minute uneven portions can be accurately formed on a substrate.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, the antireflection structure to be manufactured by the manufacturing method of the present invention will be described, and then the manufacturing method of the antireflection structure will be described.

  FIG. 1 is a perspective view of a diffusion plate 1 as an example of an antireflection structure. FIG. 2 is a partial cross-sectional view of the diffusion plate 1. The diffusing plate 1 can be applied to constituent members of optical devices such as a display device, an imaging device, a lighting device, and a projector. Light emitting elements such as semiconductor laser elements, LED elements, light bulbs, cold cathode fluorescent lamps, image sensors such as charge coupled devices (CCD) and CMOS, photodetectors such as power meters, energy meters, and reflectance measuring devices, micro lens arrays, etc. It can also be applied to.

  The diffusing plate 1 is a plane material having a substantially rectangular shape in a plan view, and diffuses and transmits light (specifically, diffuses and transmits at least light whose reflection is suppressed by the minute uneven portions 11 described below). . The diffusion plate 1 is disposed on the front surface of a display or the like, for example, and suppresses reflection of light on the display surface (reflection of external light or the like). The material of the diffusion plate 1 is not particularly limited, but may be made of resin or glass. Further, fine particles or the like may be dispersed and mixed.

  As shown in FIG. 2, the surface 10 of the diffusion plate 1 is regularly arranged with a period equal to or less than the wavelength of the incident light 20 (preferably, a period equal to or less than the wavelength of the shortest wavelength of the incident light 20). A plurality of minute uneven portions 11 are formed. For this reason, an abrupt refractive index change between the surface 10 of the diffusing plate 1 and the air layer is suppressed, and the refractive index gently changes in the surface layer portion of the surface 10 on which the minute uneven portions 11 are formed. Therefore, as shown in FIG. 3, the reflection on the surface 10 of the diffuser plate 1 is effectively suppressed by forming the minute irregularities 11.

  The minute irregularities 11 may be irregularly arranged as long as they have an average pitch of a predetermined wavelength (for example, 400 nm) or less, and the effect of suppressing reflection is obtained in the same manner as in the case of regular arrangement. . When the minute uneven portions 11 are regularly arranged, the average pitch matches the cycle.

  The shape of the minute uneven portion 11 is not particularly limited as long as it has a function of smoothing the refractive index change at the interface between the surface 10 and the air layer. May be chamfered or R-chamfered), a concave or convex portion having a truncated pyramid shape, a linear shape (the cross-sectional shape is triangular (the top portion may be R-chamfered), a trapezoidal shape, It may be a concave or convex portion having a rectangular shape.

  In addition, from the viewpoint of realizing a high reflection suppressing effect, it is preferable that the average pitch (or period) of the minute uneven portions 11 is equal to or less than the wavelength of the incident light 20. On the other hand, the height of the minute irregularities 11 is preferably 0.4 or more times the wavelength of the incident light 20, more preferably 1 or more times the wavelength of the incident light 20, and even more preferably 3 or more times. Strictly speaking, when the incident light 20 has a wavelength width, the period of the minute uneven portion 11 is preferably equal to or shorter than the shortest wavelength of the incident light 20, and the height of the minute uneven portion 11. Is preferably 0.4 times or more (preferably 1 time or more, more preferably 3 times or more) of the longest wavelength of the incident light 20.

  On the other hand, the surface 10 is a rough surface having a surface roughness Rc larger than a predetermined wavelength (for example, 400 nm). As will be described later, the surface roughness Rc of the surface 10 may be a value measured by filtering a roughness component derived from the minute irregularities 11. The surface 10 may be a surface having non-periodic unevenness as shown in FIG. 2 or may be a surface having periodic unevenness as described later with reference to FIG.

In the case where the arrangement of the micro concavo-convex portions 11 is periodic, the period of the micro concavo-convex portions 11 is the most from one arbitrary micro concavo-convex portion 11 observed when the surface 10 is viewed in plan view, It is prescribed | regulated by the distance P between tops with the other one minute uneven part 11 in the near position. The inter-top distance P can be accurately measured by surface observation means such as STM (Scanning Tunneling Microscope), AFM (Atomic Force Microscope), and SEM (Scanning Electron Microscope). Moreover, when the arrangement | sequence of the micro uneven | corrugated | grooved part 11 is aperiodic, the average value of the said distance P is prescribed | regulated as an average pitch. The height H of the micro concavo-convex portion 11 is defined by the average value of the distance from the valley bottom to the top of the micro concavo-convex portion 11 (for example, the average value of 10 micro concavo-convex portions 11). Since the definition of Rz _JIS (JIS B0601: 2001) is included in the above rules, the measured value of Rz _JIS may be used as the value of the minute uneven portion. In addition, Rz _JIS (JIS B0601: 2001) is the fifth from the highest peak that is measured from the roughness curve in the direction of the average line and measured in the direction of the vertical magnification from the average line of the extracted part. Is the sum of the absolute value of the absolute value of the altitude at the top of the mountain and the average value of the absolute value of the altitude of the bottom from the lowest valley floor to the fifth, and this value is expressed in micrometers (μm). .

  Note that the minute uneven portion 11 does not necessarily have to exhibit a reflection suppressing effect with respect to all of the incident light 20. For example, if the wavelength of the incident light 20 covers a wide wavelength range including ultraviolet light, near-ultraviolet light, visible light, near-infrared light, and infrared light, only reflection of light having a wavelength of 400 nm to 700 nm is suppressed. When good, it is preferable that the period of the micro uneven part 11 is 400 nm or less. On the other hand, the height of the minute uneven portion 11 is preferably 0.4 times or more of 700 nm, that is, 280 nm or more.

  The minute irregularities 11 may be formed so that their heights are different from each other on each part of the surface 10, but are formed so that their heights are substantially the same from the viewpoint of ease of manufacture. It is preferable. Further, for example, when the minute uneven portion 11 is a cone-shaped concave portion or a cone-shaped convex portion, the plurality of minute uneven portions 11 have a central axis connecting the bottom center and the top portion of the cone. Are preferably formed so as to be substantially parallel to each other. In this case, the diffusion plate 1 can be easily manufactured by injection molding. On the other hand, for the same reason, when the minute irregularities 11 are linear concave portions or linear convex portions having a triangular cross section, the plurality of minute irregularities 11 connect the bottom center and the top in the cross section. The central axes may be formed so as to be substantially parallel to each other (for example, each part having a size of 1 mm square).

  As described above, since the plurality of minute uneven portions 11 are formed on the surface 10, reflection of light on the surface 10 is suppressed. However, when the surface 10 is a smooth surface, regular reflection on the surface 10 cannot be sufficiently suppressed.

  FIG. 4 is a graph showing the reflected light intensity of light incident at an incident angle of 45 degrees.

  As shown in FIG. 4, when the minute uneven portion 11 is formed on the smooth surface, reflected light having an emission angle of about 45 degrees, that is, regular reflection is observed. Thus, when the surface 10 on which the minute irregularities 11 are formed is a smooth surface, regular reflection of the incident light 20 cannot be sufficiently suppressed. On the other hand, as shown in FIG. 4, when the fine uneven portion 11 is formed on a rough surface having a surface roughness larger than the wavelength of the incident light 20, regular reflection is not substantially observed. Here, in the diffusing plate 1 shown in FIG. 1, as shown in FIG. 2, the fine irregularities 11 are formed on the surface 10 which is a rough surface having a surface roughness larger than the wavelength of the incident light 20. Specifically, the surface 10 is formed with a surface roughness larger than the wavelength of the incident light 20 at an average height Rc defined by ISO 4287: 1997 (corresponding to JIS B0601: 2001). Therefore, in the diffusing plate 1, regular reflection on the surface 10 is also sufficiently suppressed. However, the effect of suppressing the occurrence of regular reflection tends to decrease if the surface roughness of the surface 10 is too large. A preferable range of the surface roughness Rc of the surface 10 is 100 μm or less. More preferably, it is 50 micrometers, More preferably, it is 30 micrometers.

  In addition, as shown in FIG. 3, when the minute uneven portion 11 is formed on the smooth surface, a sufficient reflection suppressing effect cannot be given to light having a relatively large incident angle. That is, the reflectance depends on the incident angle. On the other hand, when the surface 10 on which the minute concavo-convex portions 11 are formed has a surface roughness larger than the wavelength of incident light on the surface 10, as shown in FIG. Therefore, a high reflection suppression effect can be obtained even for light having a relatively large incident angle.

FIG. 5 is a graph showing the correlation between θ and reflectance. Note that θ shown in FIG. 5 is a rough tangent plane of the surface 10 (in other words, a tangential plane in a shape in which the fine irregularities 11 are cut off as a high frequency component from the shape including the minute irregularities 11 on the surface 10). 13 is a size of an angle formed by the normal vector N _{2 of} 13 and the normal vector N ₁ of the reference surface 12 of the surface 10 (see FIG. 7). A contact point between the tangent plane 13 and the surface 10 is determined at an intersection point CL between the surface 10 and the reference plane 12 (the intersection point CL becomes an annular line on three-dimensional coordinates). The reference plane 12 means “average line (filtered wave curve (cutoff wavelength λ _c : 0.5 mm))” defined in JIS B0601: 2001.

  As shown in FIG. 5, when θ is 0 degree (that is, a smooth surface), even if the minute uneven portion 11 is formed, for example, a large incident angle exceeding 50 degrees, In the case of a large incident angle exceeding 70 degrees, the reflectance tends to increase as the incident angle increases. On the other hand, as θ increases from 0 degrees, the dependency of the reflectance on the incident angle is reduced, and a high reflection suppression effect can be obtained even for light having a large incident angle.

  Specifically, it is preferable that the ratio per unit area (for example, 1 mm square) occupied by a portion where θ is 5 degrees or less is less than 80%. In other words, the ratio per unit area occupied by the portion where θ is 5 degrees or more is preferably 20% or more. In this case, the reflectance of light having an incident angle of 89 degrees can be reduced by about 30% or more as compared with the case where the minute irregularities 11 are formed on the smooth surface. Moreover, it is preferable that the ratio per unit area which the part whose (theta) is 10 degrees or less occupies is less than 90%. In other words, it is preferable that the ratio per unit area occupied by the portion where θ is 10 degrees or more is 10% or more. Also in this case, the reflectance of light having an incident angle of 89 degrees can be reduced by about 30% or more as compared with the case where the minute irregularities 11 are formed on the smooth surface.

  More preferably, the ratio per unit area occupied by the portion where θ is 5 degrees or less is preferably less than 50%. In other words, the ratio per unit area occupied by the portion where θ is 5 degrees or more is preferably 50% or more. Moreover, it is preferable that the ratio per unit area which the part whose (theta) is 10 degrees or less occupies is less than 80%. In other words, the ratio per unit area occupied by the portion where θ is 10 degrees or more is preferably 20% or more. In this case, the reflectance of light having an incident angle of 89 degrees can be reduced by about 50% or more compared to the case where the minute uneven portion 11 is formed on the smooth surface.

  More preferably, the ratio per unit area occupied by the portion where θ is 5 degrees or less is preferably less than 30%. In other words, it is preferable that the ratio per unit area occupied by the portion where θ is 5 degrees or more is 70% or more. Moreover, it is preferable that the ratio per unit area which the part whose (theta) is 10 degrees or less occupies is less than 50%. In other words, the ratio per unit area occupied by the portion where θ is 10 degrees or more is preferably 50% or more. In this case, the reflectance of light having an incident angle of 89 degrees can be reduced by about 70% or more as compared with the case where the minute irregularities 11 are formed on the smooth surface.

Next, a preferable range of the average value (θ _ave ) of θ will be described.

FIG. 6 is a graph showing the correlation between θ _ave and reflectance.

As shown in FIG. 6, as θ _ave increases, the incident angle dependency decreases, and a high reflection suppression effect can be obtained even for light having a relatively large incident angle. Specifically, it is preferable that θ _ave is 5 degrees or more. In this case, the reflectance of light having an incident angle of 89 degrees can be reduced by about 30% or more as compared with the case where the minute irregularities 11 are formed on the smooth surface. More preferably, θ _ave is 10 degrees or more. In this case, the reflectance of light having an incident angle of 89 degrees can be reduced by about 50% or more compared to the case where the minute uneven portion 11 is formed on the smooth surface. More preferably, θ _ave is 15 degrees or more. In this case, the reflectance of light having an incident angle of 89 degrees can be reduced by about 60% or more as compared with the case where the minute uneven portion 11 is formed on the smooth surface.

  Further, the peak of the distribution of θ (the value of θ having the highest frequency) is preferably larger than 0 degree, preferably 2 degrees or more, and more preferably 5 degrees or more.

  In addition, here, an example in which the minute uneven portion 11 is directly formed on the surface 10 of the diffusion plate 1 has been described, but the surface 10 is formed by sticking or adhering a seal on which the minute uneven portion 11 is formed. Also good. In other words, the diffusing plate 1 may not be integrated, and may be constituted by a plurality of constituent members.

  In addition, here, an example in which the minute concavo-convex portion 11 is formed over the entire surface 10 has been described. However, the minute concavo-convex portion 11 is not necessarily provided over the entire surface 10, and the minute concavo-convex portion is provided only in a necessary portion. The part 11 may be formed. In this case, not only the portion provided with the minute uneven portion 11 but also other portions of the surface 10 may be rough surfaces having the same surface roughness as the portion provided with the minute uneven portion 11, or less. It is good also as a smooth surface of surface roughness. Furthermore, another antireflection structure made of a multilayer film of a film having a relatively low reflectivity and a film having a relatively high reflectivity may be formed at a location where the minute uneven portion 11 is not provided. Further, the height and period (pitch) of the minute irregularities 11 may be adjusted as necessary even in the region where the minute irregularities 11 are formed.

  Next, a method for manufacturing the antireflection structure will be described. The antireflection structure such as the diffusing plate 1 can be manufactured by forming a rough surface by roughening the surface of the substrate to be the antireflection structure, and forming minute uneven portions on the rough surface. . Alternatively, the antireflection structure may be manufactured by first producing a mold and molding a material such as a resin using the mold. Since the latter is suitable for mass production, the latter method will be mainly described in this specification.

<< Making prototype >>
1. Roughening of the substrate First, a substrate to be used for producing a mold is prepared. The material of the substrate is not particularly limited, and the material of the substrate is not particularly limited, and may be composed of any one selected from glass, metal, semiconductor, ceramic, and resin. Specifically, glass materials such as boric acid glass and silicate glass, semiconductor materials such as silicon and GaAs, ceramic materials such as Si ₃ N _4, and metal materials such as Ta can be used. In this embodiment, a silicon single crystal substrate is used as such a substrate. As will be described later, the silicon single crystal substrate is suitable because the surface can be easily roughened and the minute uneven portions can be formed with extremely high accuracy.

  As the silicon single crystal substrate, a substrate having a {100} plane with a main surface produced by a CZ (Czochralski) method or an FZ (Floating Zone Melting) method can be used. A silicon single crystal substrate having a main surface of {100} is preferable because it can be easily roughened by a chemical method and can efficiently form minute irregularities. A silicon single crystal substrate having a {100} plane as the main surface is easily available. In terms of mechanical strength, a silicon single crystal substrate manufactured by the CZ method is excellent. The conductivity type may be n-type or p-type. However, a {110} plane silicon single crystal substrate or a polycrystalline substrate may be used.

  The roughening of the surface of the silicon single crystal substrate can be performed by a mechanical and / or chemical method. As a mechanical method, there is a method of roughening by sandblasting or sandpaper. Instead of sand blasting, shot blasting or wet blasting may be employed. If roughening is performed by these methods, the surface of the silicon single crystal substrate becomes a rough surface having non-periodic unevenness. The roughening of the substrate other than the silicon single crystal substrate may be basically performed by the same method as that for the silicon single crystal substrate.

  The surface of the silicon single crystal substrate is roughened so that the surface roughness of the rough surface to be formed is greater than a predetermined wavelength. Specifically, as described with reference to FIG. 7, the average value of the angles formed by the normal vector of the tangent plane of the rough surface of the silicon single crystal substrate and the normal vector of the reference surface of the silicon single crystal substrate is What is necessary is just to carry out so that it may become 5 degree | times or more. Alternatively, the average height Rc may be 100 μm or less (preferably 50 μm or less, more preferably 30 μm or less). When roughening by blasting, processing conditions such as the hardness of the projectile, the average particle size, and the projection speed may be determined so as to satisfy these requirements. When roughening is performed using sandpaper, an appropriate sandpaper count may be selected. If the unevenness is insufficient, the antireflection effect is insufficient as described above.

  Alternatively, the surface of the silicon single crystal substrate may be directly roughened by finely processing (grinding or cutting) the surface of the silicon single crystal substrate with a tool such as a tool. According to this method, the pitch and height of the unevenness can be set freely. Specifically, the angle θ shown in FIG. 7 can be freely set by controlling the angle of the cutting tool blade with respect to the surface of the silicon single crystal substrate. That is, the method of directly processing the surface of the silicon single crystal substrate is a method recommended when the angle θ is to be set strictly or when a rough surface having periodic irregularities is to be formed. Further, the surface of the silicon single crystal substrate may be roughened using a laser. By controlling the type and output of the laser used, it is possible to control the angle θ as in the case of machining with a tool.

  On the other hand, as a chemical method, a method of etching the surface of the silicon single crystal substrate by bringing acid or alkali into contact with the surface of the silicon single crystal substrate can be exemplified. Specifically, by using anisotropic etching, micrometer-sized irregularities (texture structure) can be formed on the surface of the silicon single crystal substrate. For example, an alkaline solution such as a sodium hydroxide solution, a potassium hydroxide solution, or a potassium carbonate solution is heated to 60 to 80 ° C., a silicon single crystal substrate is immersed in the solution, and anisotropic etching of the surface of the silicon single crystal substrate is performed. I do. By performing anisotropic etching of a silicon single crystal substrate having a main surface of {100} plane, as shown in FIG. 8, a collection of regular tetragonal pyramidal projections having a texture structure surrounded by four {111} planes Can be formed as The height difference of each protrusion is in the range of several μm to several tens of μm. When an alkaline solution used for etching contains an alcohol such as ethylene glycol or 2-propanol, there is an advantage that a texture structure having a uniform height can be quickly formed. In addition, you may implement such a chemical method in combination with a mechanical method.

2. Formation of micro uneven portions Next, micro uneven portions are formed on the rough surface of the silicon single crystal substrate. Specifically, the process of depositing metal in an island shape on the rough surface of the silicon single crystal substrate and the reactivity of the silicon single crystal substrate with a process gas including a carbon source gas using the metal island deposit as a mask. A step of performing ion etching and forming a plurality of needle-like fine irregularities having an average pitch of a predetermined wavelength or less on the rough surface of the silicon single crystal substrate. According to this method, nanometer-sized needle-like minute irregularities can be efficiently formed on the rough surface of the silicon single crystal substrate. Note that the etching method is not limited to reactive ion etching, and an appropriate dry etching method may be employed depending on the material of the substrate to be used.

  First, as shown in FIGS. 9A and 9B, a metal is deposited on a silicon single crystal substrate 27 having a roughened surface. Thereby, island-like deposits 28 are formed on the rough surface 27p of the silicon single crystal substrate 27. As the metal to be deposited, at least one selected from the group consisting of Fe, Ni, Co, Cu, Cr, W, Ta, and Pt can be used. The metal deposition method is not particularly limited, and a known method such as a sputtering method or a vapor deposition method can be employed. From the viewpoint of uniformly forming minute island deposits, a sputtering method performed in an inert gas atmosphere such as Ar is recommended.

  The island-like deposit 28 has an average diameter of a predetermined wavelength (for example, 400 nm) or less. When the island-like deposit 28 having such an average diameter is used, needle-like minute uneven portions having an average pitch of a predetermined wavelength (for example, 400 nm) or less can be formed. In order to deposit metal in an island shape, the deposition rate and deposition time of the metal may be mainly controlled. The average diameter of the island-like deposits 28 is an average value of a predetermined number (for example, 10), and can be measured by, for example, SEM observation.

  Next, as shown in FIG. 9C, the silicon single crystal substrate 27 is etched using the island-shaped deposit 28 as an etching mask (etching step). For the etching, reactive ion etching may be employed. The reactive ion etching may be performed using a process gas including a carbon source gas and a carrier gas. As the carbon source gas, a C1-C3 saturated or unsaturated hydrocarbon gas can be used, and methane is preferred. As the carrier gas, hydrogen, a rare gas, or a mixed gas of hydrogen and a rare gas can be used. The mixing ratio of the hydrocarbon gas and the carrier gas is a volume ratio in a standard state, for example, (hydrocarbon gas) :( carrier gas) = 10: 1 to 2: 1.

  The reactive ion etching of the silicon single crystal substrate 27 is preferably performed while heating the temperature of the silicon single crystal substrate 27 to 250 to 800 ° C. and applying a negative bias to the silicon single crystal substrate 27. Further, the pressure of the atmosphere is maintained at a pressure lower than atmospheric pressure, for example, in the range of several hundred to several tens of thousands Pa. The carbon source gas contained in the process gas is turned into plasma by microwaves and brings about the etching action of the silicon single crystal substrate 27.

  The etching of the silicon single crystal substrate 27 is preferably continued until the island-like deposit 28 as an etching mask disappears. This eliminates the need for an ashing process for removing the island-like deposits 28, and enables formation of sharp minute irregularities. The time for the reactive ion etching of the silicon single crystal substrate 27 can be determined based on the time required for the disappearance of the island-like deposit 28. Specifically, the etching time may be set slightly longer than the time required for the disappearance of the island deposit 28. In this way, it is possible to accurately form the minute concavo-convex portion 29 with little blunting at the top. In addition, when the island-like deposit 28 remains even after the minute uneven portion 29 having a sufficiently high height is formed through the etching process, an ashing step for removing the island-like deposit 28 may be performed. .

  Through the etching process, as shown in FIG. 9 (d), needle-like micro uneven portions 29 are formed on the rough surface 27 p of the silicon single crystal substrate 27. As for the size of each minute uneven portion 29, for example, the diameter of the bottom surface is 200 to 300 nm, and the height is about 1 μm. In addition, the needle-shaped minute uneven part 29 is covered with a carbon thin film. This carbon thin film can be changed into a silicon carbide film by annealing the silicon single crystal substrate 27. This silicon carbide film may be removed by etching using an acidic aqueous solution (for example, an aqueous solution containing nitric acid and hydrofluoric acid). The silicon single crystal substrate 27 having the needle-like minute uneven portions 29 can be handled as an antireflection structure or as a part of a mold for forming the antireflection structure. It can also be handled as a prototype for producing a replication mold.

<< Production of replication type >>
In order to increase the mass productivity, a replica mold of the substrate 27 having the minute uneven portions 29 may be produced, and the antireflection structure may be molded using the replica mold. FIG. 11 is an explanatory diagram of a process for producing a replication mold by electroforming from a substrate 27 having minute uneven portions 29. First, as shown in FIGS. 11A and 11B, the substrate 27 having the minute uneven portions 29 is immersed in an electroless Ni plating bath 63 to form an electroless Ni plating layer 64 that covers the minute uneven portions 29. . Next, as shown in FIG. 11C, the substrate 27 is immersed in an electrolytic Ni plating bath 65 and energized to form an electrolytic Ni plating layer 66 on the substrate 27. The thickness of the electrolytic Ni plating layer 66 is preferably about 0.3 to 40.0 mm, for example. As the electroless Ni plating bath 63, a known plating bath such as a Ni / B solution and as the electrolytic Ni plating bath 65 can be used a nickel sulfamate electrolytic solution. If the substrate 27 has conductivity, the electroless plating step shown in FIG. 11B may be omitted.

  Finally, as shown in FIG. 11D, the substrate 27 having the electroless Ni plating layer 64 and the electrolytic Ni plating layer 66 is immersed in a base solution 67, and the substrate 27 is dissolved by selective etching, so that the Ni plating layer 64 is obtained. , 66 part of the substrate 27 is removed. Thereby, the Ni replication mold 66 in which the minute uneven portions 68 are formed on the surface 66p (rough surface) is obtained (FIG. 11 (e)). Furthermore, the two may be separated using a difference in characteristics such as a linear expansion coefficient and an elastic coefficient between the substrate 27 and the replication mold 66. In place of Ni plating, other metal plating such as Cu plating or Sn plating may be employed, or two or more of these may be combined.

  By repeating the above operation, a duplicate mold having the same surface shape can be produced in layers. Since these replica molds can be used as resin or glass molds, they are suitable for mass production of antireflection structures.

<< Molding of antireflection structure (diffusion plate 1) >>
By using the substrate 27 (or the replication mold 66) produced as described above, the antireflection structure (diffusing plate 1) can be molded. FIG. 10 is an explanatory diagram of a process of manufacturing the antireflection structure by press molding. As shown in FIG. 10, an upper mold 35 including a substrate 27 and a lower mold 36 containing a material 38 (for example, glass or resin) to be molded face each other. The heaters 39 and 39 are energized to heat the molds 35 and 36 to a temperature exceeding the softening point of the material. After sufficiently softening the material 38, the molds 35 and 36 are clamped, and the substrate 27 is pressed against the softened material 38, thereby transferring the shape of the minute uneven portion 29 of the substrate 27 to the material 38. Thereafter, the molds 35 and 36 are gradually cooled to open the mold, and the molded body 41 having the minute uneven portions 40 is taken out. The molded body 41 can be used as a mold (replication mold) to mold the antireflection structure.

  Further, the antireflection structure can be manufactured by an injection molding method using the substrate 27 as a part of the mold. As shown in FIG. 12A, first, the substrate 27 on which the minute concavo-convex portion 29 is formed is incorporated between the upper mold 101 and the lower mold 102 as an insert mold. A release layer 103 is formed by applying a silane coupling agent to a portion where the cavity SH filled with resin is formed, and the mold is clamped. Next, as shown in FIGS. 12B and 12C, the molds 101 and 102 are heated, and the molten resin is injected into the cavity SH. As shown in FIG. 12D, the temperature of the molds 101 and 102 is lowered to solidify the resin, and the mold is opened. Thereby, the resin molded product 105A (diffusing plate 1) as an antireflection structure is obtained. There is no restriction | limiting in particular in the kind of resin to inject | pour, Various resin in which injection molding is possible, such as an acrylic resin, a fluororesin, an olefin resin, and a polycarbonate resin, can be used.

  Next, another method for manufacturing the antireflection structure will be described. The antireflection structure such as the diffusing plate 1 can also be manufactured by the method described below. As shown in FIGS. 13A and 13B, first, a prototype 120 having a plurality of minute concavo-convex portions 122 having an average pitch of a predetermined wavelength or less is manufactured by the method described above. That is, the minute uneven portion 122 is formed on the smooth surface of the first substrate 120 (for example, a silicon single crystal substrate). Next, as shown in FIGS. 13C and 13D, the surface shape of the master 120 is transferred to the sheet member 124 by press molding.

  On the other hand, a second substrate 128 (see FIG. 13E) having a rough surface with a surface roughness larger than a predetermined wavelength is separately prepared. The second substrate 128 may be a component constituting the final product such as a lens barrel. Then, the sheet member 124 formed using the prototype 120 is bonded to the rough surface 128p of the second substrate 128. Bonding can be performed using an adhesive. The thickness of the sheet member 124 may be adjusted so that the sheet member 124 can follow the rough surface 128p. As described above, the second substrate 128 (for example, an optical component) having the minute uneven portion 126 is obtained.

  Next, some other examples of the antireflection structure that can be manufactured by the method of the present invention will be described. The antireflection structure produced by the method of the present invention is not limited to the light transmissive structure like the diffusing plate 1, and may have a light absorptivity, for example.

  FIG. 14 is a schematic diagram illustrating a configuration of an imaging apparatus to which the antireflection structure is applied.

  The imaging apparatus 201 includes an apparatus main body 203 and a lens barrel unit 202 as an optical unit. Although an example in which the lens barrel unit 202 is attached to the apparatus main body 203 will be described here, the lens barrel unit 202 may be configured to be detachable from the apparatus main body 203, for example.

  The lens barrel unit 202 includes a cylindrical (specifically, cylindrical) lens barrel 205 and an optical system 204 housed inside the lens barrel 205. On the other hand, the apparatus main body 203 includes an image sensor 206 arranged so as to be positioned on the optical axis AX of the optical system 204. The optical system 204 is for forming an optical image on the image pickup surface of the image pickup device 206. The optical image formed on the image pickup surface by the optical system 204 is converted into an electric signal by the image pickup device 206. For example, it is stored in a memory (may be an external memory) provided in the apparatus main body 203 or output to another apparatus via a cable connected to the apparatus main body 203. Yes. Note that the image sensor 206 can be configured by, for example, a CCD (charge coupled device), a CMOS (complementary metal-oxide semiconductor), or the like.

  The optical system 204 is not particularly limited as long as it can form an optical image on the image pickup surface of the image pickup element 206. For example, as shown in FIG. 14, the first lens (group) L1 is used. The second lens (group) L2 and the third lens (group) L3 may be configured by three lenses (group). Further, at least one of the three lenses (groups) L1 to L3 may be displaceable in the direction of the optical axis AX so that focusing and / or zooming is possible.

  FIG. 15 is a front view of the lens barrel 205.

  FIG. 16 is an enlarged cross-sectional view of a part of the lens barrel 205. On the inner peripheral surface of the lens barrel 205, an antireflection structure having a minute uneven portion is provided. The antireflection structure provided in the lens barrel 205 can be manufactured, for example, by the injection molding method described with reference to FIG. 12, and may be a member itself constituting the lens barrel 205, or the lens barrel 205. The adhesive sheet affixed on the inner peripheral surface may be sufficient.

  The lens barrel 205 is configured to absorb light (generally visible light) incident on the optical system 204 from the image side. For this reason, the lens barrel 205 absorbs a light beam that is incident on the lens barrel unit 202 from the image side or more and has a comprehensive field angle of the optical system 204 or a reflection on the surface of the lens or the like constituting the optical system 204. . Therefore, the imaging apparatus 201 has high optical performance with the occurrence of ghost, flare, etc. suppressed.

  Specifically, a configuration in which a light-absorbing material (for example, a dye or a pigment) is dispersed and mixed in the lens barrel 205 may be employed. Alternatively, the lens barrel 205 may be formed of a substantially light absorbing material. As a light-absorbing material that absorbs visible light, black dyes obtained by mixing a plurality of pigments such as cyan, magenta, and yellow (for example, Plato Black 8950 and 8970 manufactured by Arimoto Chemical Co., Ltd.), Carbon black etc. are mentioned. The base material in which these pigments and dyes are dispersed and mixed is, for example, a resin such as glass, an acrylic resin or a polycarbonate resin (preferably a resin having a glass transition temperature of 90 ° C. or higher and 170 ° C. or lower) or a glass fiber-containing resin. May be. Furthermore, from the viewpoint of suppressing dust and dust from adhering to the lens barrel 205, the lens barrel 205 preferably contains an antistatic material. The lens barrel 205 preferably has high light resistance (particularly light resistance to ultraviolet light).

  The lens barrel 205 absorbs light incident on the lens barrel unit 202 from the image side (strictly, light having a wavelength that should be suppressed from reflection), and a minute amount for suppressing reflection of the light. Since a plurality of the concavo-convex portions 11 (see FIG. 2) are formed on the inner peripheral surface 210, the reflection of light on the inner peripheral surface 210 of the lens barrel 205 is greatly reduced.

  Usually, in an optical element such as a lens that transmits light, there is little need to consider reflection of large incident light exceeding 50 degrees, for example. However, in the case of the lens barrel unit 205, only light with a small incident angle is not necessarily incident. Therefore, it is preferable to have a configuration that suppresses reflection of incident light with a relatively large incident angle.

  FIG. 17 is a cross-sectional view of a diffusion plate (antireflection structure) in which fine irregularities are formed on a surface (rough surface) having periodic irregularities. On the surface (rough surface) of the diffusing plate 50, the base structure portion 7 is formed by periodically arranging conical (for example, quadrangular pyramid) structural units 70, 70, and the surface of the base structure portion 7 is formed. A large number of minute concavo-convex portions 11 are densely formed on the inclined surfaces 71 and 73 of the structural unit 70. As described above, the base structure portion 7 can be formed by grinding the surface of the substrate using a cutting tool, and the minute unevenness portion 11 is formed according to the procedure described with reference to FIGS. can do.

  In the diffusing plate 50 shown in FIG. 17, the angle α (inclination angle α) formed between the inclined surfaces 71 and 73 of each structural unit 70 and the reference surface 51 corresponds to the angle θ described in FIG. Specifically, the inclination angle α is preferably 5 ° or more. By setting the inclination angle α to 5 ° or more, the incident angle of incident light is reduced. Furthermore, the inclination angle α is preferably 45 °. By setting the inclination angle α to 45 °, incident light incident on the reference surface 51 at an incident angle of 0 ° to 90 ° is incident on the inclined surfaces 71 and 73 at an incident angle of −45 ° to 45 °. Therefore, the maximum absolute value of the incident angle with respect to the inclined surfaces 71 and 73 can be set to 45 ° or less with respect to incident light incident on the reference surface 51 at any incident angle.

  The lens barrel 205 can be manufactured by the method shown in FIG. As shown in FIG. 18A, first, a substrate 130 for preparing a molding die for the lens barrel 205 is prepared. The surface 130r of the substrate 130 is constituted by a part (for example, an angle range of 90 °) of a cylindrical surface having a diameter (specifically, an equal diameter) corresponding to the inner diameter of the lens barrel 205 to be manufactured. As shown in FIG. 18B, a rough surface 130p is formed by roughening the surface 130r of the substrate 130, and further, a minute uneven portion 132 is formed. The step of roughening the surface 130r of the substrate 130 and the step of forming the minute uneven portion 132 are as described above.

  In the present invention, etching is performed using a metal island-shaped deposit as a mask to form the minute uneven portion 132, so that there is essentially no problem of the depth of focus associated with the photolithography technique. Therefore, even if the radius of curvature of the surface 130r of the substrate 130 is relatively large, there is an advantage that the fine uneven portion 132 can be formed with high accuracy.

  Next, as shown in FIG. 18 (c), the substrate 130 having the minute uneven portions 132 is accommodated between the upper mold 134 and the lower mold 130, and after mold clamping, the resin is injected into the cavity CV. That is, the substrate 130 is used as an insert mold. A replica type of the substrate 130 may be used as an insert type.

  As shown in FIG. 18D, the component 140 obtained by resin molding is a part of the lens barrel 205. A cylindrical lens barrel 205 is completed by combining a plurality of parts manufactured by the same method (FIG. 18E). According to such a method, since the minute uneven portion can be formed in almost the entire inner peripheral surface of the lens barrel 205, it is extremely effective in reducing ghosts and flares.

  Since the antireflection structure according to the present invention sufficiently suppresses generation of unnecessary light such as reflected light, various optical devices such as an imaging device, an illumination device, an optical scanning device, an optical pickup device, and a display are used. Useful for.

Perspective view of diffuser plate as one example of antireflection structure Partial sectional view of diffuser plate Graph showing the correlation between incident angle and reflectance A graph representing the reflected light intensity of light incident at an incident angle of 45 degrees Graph showing the correlation between θ and reflectance Graph _showing the correlation between θ _ave and reflectance Sectional drawing showing the roughness shape of the part shown in FIG. 2 on the surface Illustration of texture structure of silicon single crystal substrate Explanatory drawing of the process of forming needle-like minute irregularities on the rough surface of a silicon single crystal substrate Explanatory drawing of the process of manufacturing an antireflection structure by press molding Explanatory drawing of the process of producing a replica mold by electroforming from a substrate having minute irregularities Explanatory drawing of process to mold resin using replication mold Process explanatory drawing of other manufacturing methods of antireflection structure Schematic showing the configuration of an imaging device to which an antireflection structure is applied Front view of lens barrel Sectional view enlarging a part of the lens barrel Cross-sectional view of an antireflection structure in which fine irregularities are formed on a surface having periodic irregularities Process explanatory drawing of the manufacturing method of the lens barrel

Explanation of symbols

1, 41, 50 Diffuser (Antireflection structure)
10, 27p, 66p Surface (rough surface)
11, 29, 40, 68 Minute irregularities 12, 51 Reference surface 13 Tangent plane 27 Silicon single crystal substrate 66 Replica mold 105A Resin molded product (antireflection structure)

Claims (9)

A method of manufacturing an antireflection structure that suppresses reflection of light having a predetermined wavelength or more,
Preparing a substrate having a rough surface with a surface roughness greater than the predetermined wavelength;
Depositing metal in an island shape on the rough surface of the substrate;
Using the metal island-shaped deposit as a mask, dry-etching the substrate, and forming a plurality of minute irregularities having an average pitch of the predetermined wavelength or less on the rough surface of the substrate;
A method for manufacturing an antireflection structure, comprising:   The step of preparing the substrate is such that an average value of an angle formed by a normal vector of a tangential plane of the rough surface of the substrate and a normal vector of a reference surface of the substrate is 5 degrees or more. The manufacturing method of the antireflection structure of Claim 1 including the process of roughening the surface.   The method for manufacturing an antireflection structure according to claim 1, wherein the substrate is a silicon single crystal substrate.   The method of manufacturing an antireflection structure according to claim 3, wherein in the step of forming the micro uneven portion, reactive ion etching of the silicon single crystal substrate is performed with a process gas containing a carbon source gas.   The method for manufacturing an antireflection structure according to claim 4, wherein the process gas includes methane as the carbon source gas and hydrogen.   The method for manufacturing an antireflection structure according to claim 1, wherein the etching of the substrate is continued until the mask disappears.   The method further comprises a step of producing a replica mold of the substrate having the minute irregularities by electroforming or press molding, and a step of molding the antireflection structure using the replica mold. The manufacturing method of the reflection preventing structure of any one of these. A method of manufacturing an antireflection structure that suppresses reflection of light having a predetermined wavelength or more,
Depositing metal in an island shape on the surface of the first substrate;
Performing dry etching of the first substrate using the metal island-shaped deposit as a mask, and forming a plurality of minute irregularities having an average pitch of the predetermined wavelength or less on the surface of the first substrate; ,
Preparing a second substrate having a rough surface with a surface roughness greater than the predetermined wavelength;
Forming a sheet member using the first substrate as a mold, and bonding the sheet member to the rough surface of the second substrate;
A method for manufacturing an antireflection structure, comprising:   An optical apparatus comprising the antireflection structure manufactured by the method according to claim 1.

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