JP2009098237A - Nonreflective structure, optical element, metallic mold and their manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonreflective structure which has a simple and easily producible structure and has the reflection suppressing effect that is equal to or higher than that of conventional structure. <P>SOLUTION: The nonreflective structure 1 constituted of innumerable cones 9 arranged at a pitch not exceeding a wavelength of the light, is formed on the surface where light not to be reflected is made incident. The height of the cone 9 is lower than the pitch and an aspect ratio is 1 or less. The flank of the cone 9 is concave toward a line connecting a point on a bottom surface periphery of the cone 9 and the apex of the cone 9. The nonreflective structure 1 is manufactured by patterning with lithography or transfer of a shape by a metallic mold. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-reflective structure having an antireflection effect, in which cones are arranged at a pitch equal to or less than the wavelength of light whose reflection should be suppressed.

  In various optical devices, reflection of incident light to an optical element is suppressed, and a connection portion of an optical fiber with a small loss, a bright lens, a display with little reflection, and the like can be realized. For this reason, in an optical element made of glass or the like, surface treatment is performed in order to reduce return light due to surface reflection and increase transmitted light (see, for example, Patent Document 1).

  As one of the conventional surface treatment methods, there is a method of forming a single layer or a plurality of layers of a thin film of a substance having a refractive index different from that of the material constituting the optical element on the surface of the optical element. In general, such an antireflection film is formed by a film formation method such as vacuum deposition (see, for example, Patent Document 1).

  As another surface treatment method, there is a method of forming a fine and dense uneven shape on the surface of the optical element (see, for example, Non-Patent Document 1). In order to obtain an antireflection structure having an antireflection effect for light having a wider wavelength range and having a small incident angle dependency, a cone shape having an aspect ratio of 1 or more is formed on the optical element. (For example, refer to Patent Document 1).

  In addition, in order to arrange protrusions with an aspect ratio of 1 or more as closely as possible, and to further enhance the reflection suppression effect, the cones to be formed are hexagonal pyramid shapes, and the hexagonal circumscribed circle on each bottom has a two-dimensional close-packed structure. None, and a non-reflective structure disposed so that adjacent hexagonal apexes are in contact with each other is disclosed (for example, see Patent Document 2).

JP 2001-272505 A (2nd and 4th pages) JP 2006-171229 A Hisao Kikuta and Koichi Iwata, “Optical Control by a Finer Grating Structure than Wavelength”, Optics, The Optical Society of Japan, 1998, Vol. 27, No. 1, p.12-17

  However, when the aspect ratio increases, there is a problem that microfabrication becomes difficult. Also, if the aspect ratio is large even if it is processed into a mold and the shape is transferred to increase the area and reduce costs, the mold and the surface processed product are not well separated and the mold cannot be formed accurately. There was a problem.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a non-reflective structure or the like that realizes high antireflection performance with a low aspect.

In order to achieve the above-described object, according to a first aspect of the present invention, cones are arranged at a pitch equal to or less than a wavelength of light to suppress reflection, and a side surface of the cone is a point on a circumference of a bottom surface of the cone. It is a nonreflective structure characterized by being concave with respect to a line connecting the apex.
Moreover, it is desirable that the aspect ratio of the cone is 1 or less.
Further, it is preferably formed on the surface of the optical element.

  In the second invention, the conical holes are arranged at a pitch equal to or less than the wavelength of the light whose reflection should be suppressed, and the side surface of the hole is a line connecting a point on the circumference of the hole entrance and a vertex of the hole. The mold is characterized by being convex.

  A third invention includes a step of forming a metal film on a surface of a substrate, a step of forming a photosensitive resist on the metal film, a step of forming a microstructure on the photosensitive resist, and the photosensitive property Using the resist as a mask, forming a fine structure on the metal film, removing the photosensitive resist, and using the finely processed metal film as an etching mask, the fine structure is formed on the substrate surface by a wet etching method. And a step of forming the non-reflective structure.

  4th invention is a manufacturing method of the metal mold | die characterized by including the process of forming a metal layer in the surface of a non-reflective structure, and the process of isolate | separating the said non-reflective structure from the said metal layer. is there.

  The fifth invention comprises a step of providing a mold inside the mold, a step of filling the mold with a fluid material, and a step of releasing the mold from the material. This is a method of manufacturing a non-reflective structure.

  6th invention is a manufacturing method of the non-reflective structure characterized by including the process of pressing a metal mold | die with the softened material, and the process of releasing the said metal mold | die.

  By arranging the cones at a pitch equal to or less than the wavelength of the light, an index gradient film in which the refractive index is inclined from the refractive index of the cone to the refractive index outside the cone is formed in the region from the bottom surface to the apex of the cone. An effect equal to the effect it has can be produced. Therefore, reflection caused by a difference in refractive index can be suppressed at the interface between the inside and the outside of the non-reflective structure.

  By optimizing the shape of the side surface of the cone and taking a concave structure with respect to the line connecting the point on the bottom circumference of the cone and the apex, the effect of sufficient reflectance reduction is achieved even for cones with an aspect ratio of 1 or less. Can be expressed.

  A non-reflective structure is produced by fine processing such as direct drawing with an electron beam or shape transfer using a mold. However, since the aspect ratio of the cone is 1 or less, the conventionally disclosed aspect ratio is 1 or more. Compared to this structure, it is easy to manufacture.

  According to the present invention, it is possible to provide a non-reflective structure or the like that achieves high antireflection performance with a low aspect.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a non-reflective structure 1 according to the first embodiment, and FIGS. 1A, 1B, and 1C are a perspective view, a plan view, and a plan view of the non-reflective structure 1, respectively. It is a front view. As shown to Fig.1 (a), the non-reflective structure 1 consists of the board | substrate 7 and many cones 9 arranged on it. The cones 9 are arranged in a simple lattice pattern with a pitch of 300 nm as shown in FIG. As shown in FIG. 1C, the cone 9 is a cone having a diameter of 300 nm and a height of 280 nm, and the side surface of the cone 9 has a generatrix 10 connecting a vertex with a point on the circumference of the bottom of the cone. From the perspective, it has a concave shape. Its aspect ratio is about 0.93, which is 1 or less.

  The bottom surface of the cone 9 is preferably a polygon such as a circle or a hexagon.

  The pitch of the cones 9 is set to 300 nm in order to suppress reflection of visible light. However, if the wavelength to be suppressed changes, the pitch may be changed accordingly. For example, if the reflection of infrared rays is to be suppressed, the pitch may be made larger, and if the reflection of ultraviolet rays is to be suppressed, the pitch may be made smaller.

  The height of the cone 9 directly affects the aspect ratio. When the aspect ratio is high, the antireflection effect is higher, and when the aspect ratio is low, it can be easily manufactured, and it becomes easy to process the mold or transfer the shape using the mold.

  The arrangement of the cones 9 is not limited to a simple lattice, and may be a close-packed lattice.

  As the material of the substrate 7 and the cone 9, various optical materials can be used. Preferred are glass such as quartz glass, crystals used for optical elements, resins such as acrylic resin, polycarbonate resin, polymethyl methacrylate resin, and epoxy resin.

  According to the first embodiment, higher antireflection performance can be obtained than when the side surface of the cone 9 is flat. Therefore, even if the aspect ratio is 1 or less, a sufficient antireflection effect can be obtained.

Next, the manufacturing method of the nonreflective structure 1 is demonstrated.
FIG. 2 is a diagram illustrating a manufacturing process of the non-reflective structure 1. As shown in FIG. 2A, the surface of the substrate 7 is smoothed. Thereafter, a metal layer 11 is formed on the substrate 7 as shown in FIG. Thereafter, a resist layer 13 is formed on the metal layer 11 as shown in FIG.

  As shown in FIG. 2D, the resist layer 13 is patterned and developed to form a cylindrical resist mask 15. Thereafter, the metal layer 11 is patterned by wet etching, the resist mask 15 is removed, and a metal mask 17 is formed as shown in FIG. Thereafter, wet etching with dilute hydrofluoric acid is performed to obtain a non-reflective structure 1 having a cone 9 on a substrate 7 as shown in FIG.

  The patterning is preferably performed by direct drawing with an electron beam, X-ray lithography, or photolithography.

  Examples of the material for the metal layer 11 and the metal mask 17 include chromium, nickel, aluminum, carbon, tantalum, molybdenum, iron, platinum, and gold.

  As a material of the resist layer 13 and the resist mask 15, a general resist material can be used, and polymethyl methacrylate (PMMA) is preferable.

  Since isotropic etching is performed by wet etching, a non-reflective structure in which the side wall of the cone 9 has a concave shape with respect to the bus bar 10 is formed (FIGS. 1A and 2F).

  FIG. 3 is a diagram illustrating a method for manufacturing the nonreflective structure 2 according to the second embodiment of the present invention. The nonreflective structure 2 has a cone 27 on the substrate 25 as shown in FIG. 3 (f), and has the same structure as the nonreflective structure 1. The non-reflective structure 2 can be mass-produced using the replica mold 23 made from the non-reflective structure 1.

  The manufacturing process of the nonreflective structure 2 is demonstrated using FIG. First, as shown to Fig.3 (a), the non-reflective structure 1 is prepared. The non-reflective structure 1 has a cone 9 on a substrate 7, and the side surface of the cone 9 has a concave shape when viewed from a generatrix 10 connecting a vertex and a vertex on the circumference of the bottom of the cone. It has become.

  As shown in FIG. 3B, electroless plating is performed on the surface of the cone 9 to form an electroless plating layer 19. Thereafter, as shown in FIG. 3C, electrolytic plating is performed using the electroless plating layer 19 to form a plating layer 21. As shown in FIG. 3D, the substrate 7 is removed to obtain a duplicate mold 23.

  The duplicate mold 23 is obtained by transferring the structure of the non-reflective structure 1. Thereafter, as shown in FIG. 3 (e), the structure is transferred to the substrate 25 using the replication mold 23 to form a cone 27. As shown in FIG. 3 (f), the non-reflective structure 2 Get.

  In the electroless plating, it is preferable to form the nickel electroless plating layer 19 using an electroless Ni / B solution.

  In the electroplating, it is preferable to immerse the antireflective structure 1 having the electroless plating layer 19 in a nickel sulfamate electrolytic solution to form a nickel plating layer 21.

  Since the non-reflective structure 1 is made of quartz glass, it does not have conductivity. Therefore, it is preferable to perform electroplating after performing electroless plating.

  When the substrate 25 is formed of a resin material such as acrylic resin, fluororesin, epoxy resin, polyethylene, or polyolefin, the transfer of the structure to the substrate 25 using the replica mold 23 is performed by injection molding or casting. Molding can be used.

  Here, injection molding refers to a method in which a softened resin material is filled in a mold by applying pressure to perform resin molding.

  Cast molding refers to a method in which a resin material dissolved in a solution is poured into a mold and solidified to mold the resin.

  When the substrate 25 is formed of a glass material such as borosilicate glass, the structure of the replication mold 23 is formed on the substrate 25 by press molding using the replication mold 23 at a temperature at which the substrate 25 is softened. Can be transferred.

  In such a second embodiment, the replica mold 23 can be used as a mold for directly molding a resin, glass or the like, without using a high-cost and low-productivity method such as electron beam drawing. The non-reflective structure 2 can be manufactured.

  In the second embodiment, since the aspect ratio of the cone 9 of the non-reflective structure 1 is 1 or less, the substrate 7 and the replication mold 23 are easily separated. Further, the replication mold 23 accurately transfers the structure of the non-reflective structure 1.

Next, examples of the present invention will be described.
<Example 1>
Quartz glass was cut into a size of 20 mm × 20 mm × 1.0 mm, and the surface was optically polished to obtain a substrate. A chromium thin film was formed on the surface of the substrate by sputtering. Next, a PMMA (polymethyl methacrylate) resist film having a thickness of 0.3 μm was formed on the surface of the chromium thin film by spin coating. Further, a circular shape having the arrangement shown in FIG. 1B was drawn directly on the PMMA resist film with an electron beam. As a result, the PMMA resist film was processed into a fine structure having a pitch of 300 nm with a circular unit.

  Subsequently, wet etching was performed on the chrome thin film to form an etching mask having a fine structure with a circular shape as a unit. Etching was performed using buffered hydrofluoric acid (BHF) in which hydrofluoric acid (50 wt%) and ammonium fluoride aqueous solution (40 wt%) were mixed 1:10 as an etching solution. At this time, quartz glass could be isotropically etched at room temperature (25 ° C.) at an etching rate of about 100 nm / min. The etching mask peeled off the substrate and disappeared automatically when the substrate was etched and cones were formed. By these treatments, a structure having a unit of a cone shape having a height of 280 nm and a pitch of 300 nm and an aspect ratio of 1 or less was formed on the surface of the substrate. Moreover, since it is isotropic etching by wet etching, the non-reflective structure 1 in which the cone-shaped side surface has a cone that is concave from the generatrix is formed.

  When the surface of the formed non-reflective structure 1 was inspected, the surface roughness after etching was small, and the surface roughness was almost equal to the polished surface before etching. Further, when the reflectance in the case of normal incidence on the surface of the substrate 7 on which the nonreflective structure 1 was formed was measured, a value of 0.86% was shown for light having a wavelength of 600 nm.

(Comparative Example 1)
An etching mask is formed on another quartz glass substrate 30 in the same manner as described above, and the substrate 30 and the etching mask are simultaneously etched by anisotropic dry etching using a mixed gas of CHF ₃ and O ₂ . A non-reflective structure 3 having a cone 29 having an aspect ratio of 1 as shown in a) was produced. The side surface of the cone 29 is the same as the bus bar 31, and the cone 29 has a conical shape. When the reflectance of the light with a wavelength of 600 nm was measured using the nonreflective structure 3, it was 1.11%.

(Comparative Example 2)
An etching mask is formed on another quartz glass substrate 34 in the same manner as described above, and the substrate 34 and the etching mask are simultaneously etched by anisotropic dry etching using a mixed gas of CHF ₃ and O ₂ . A non-reflective structure 4 having a cone 33 having an aspect ratio of about 1.5 as shown in b) was produced. In Comparative Example 1, etching was performed under the condition that the mixing ratio of CHF ₃ and O ₂ was changed and the etching rate of the Cr mask was slow. The side surface of the cone 33 is the same as the bus bar 35, and the cone 33 has a conical shape. When the reflectance of the light with a wavelength of 600 nm was measured using the non-reflective structure 4, it was 0.84%.

(Comparative Example 3)
A substrate 5 having only a flat surface obtained by polishing another quartz glass substrate smoothly without forming a non-reflective structure was obtained. When the reflectance of light having a wavelength of 600 nm was measured using the substrate 5, it was 4.65%.

  Furthermore, using the non-reflective structures 1, 3, 4, and the substrate 5, the reflectance when light with a wavelength of 600 nm was incident at different angles was also measured. The results are shown in Table 1. The reflectivity of Example 1 is very low as compared with the other comparative examples even when the incident angle is increased. Not only the reflectivity of the incident light from the front is reduced, but also the incident light from an oblique direction. The reflectance can also be suppressed.

<Example 2>
Since the electroreflective structure 1 produced in Example 1 is not conductive, it was immersed in an electroless Ni plating solution to form a nickel electroless plating layer on the surface of the antireflective structure 1. Next, the master mold on which the electroless plating layer was formed was immersed in a nickel sulfamate electrolyte, and electroplating was performed to form a nickel plating layer on the surface of the master mold. Thereafter, the nickel-plated master mold was immersed in a base solution, and the antireflective structure 1 was pulled away to obtain a replica mold 23.
Using this replication mold 23, the non-reflective structure 2 was formed on the epoxy resin surface. The reflectance at a wavelength of 600 nm was 0.92%. As a comparison, since the reflectance of the epoxy resin that was not surface-treated was 5.97%, a non-reflective structure excellent in performance could be formed even if the replication mold 23 was used.

  The preferred embodiments of the nonreflective structure according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

  The present invention can be used for the surface of an optical element such as a lens element, a prism element, and a mirror element, the surface of a display, a connection portion between optical fibers, and the like.

The figure which shows the non-reflective structure 1 which concerns on 1st Embodiment. The figure which shows the manufacturing process of the non-reflective structure. The figure which shows the manufacturing process of the non-reflective structure. The figure which shows the manufacturing process of the non-reflective structure. The figure which shows the manufacturing process of the non-reflective structure. The figure which shows the manufacturing process of the non-reflective structure. The figure which shows the manufacturing process of the non-reflective structure. The figure which shows the manufacturing process of the non-reflective structure 2 which concerns on 2nd Embodiment. The figure which shows the manufacturing process of the non-reflective structure 2 which concerns on 2nd Embodiment. The figure which shows the manufacturing process of the non-reflective structure 2 which concerns on 2nd Embodiment. The figure which shows the manufacturing process of the non-reflective structure 2 which concerns on 2nd Embodiment. The figure which shows the manufacturing process of the non-reflective structure 2 which concerns on 2nd Embodiment. The figure which shows the manufacturing process of the non-reflective structure 2 which concerns on 2nd Embodiment. The figure which shows various comparative examples.

Explanation of symbols

1, 2, 3, 4 ......... Non-reflective structure 5, 7, 25, 30, 34 ......... Substrate 9, 27, 29, 33 ...... Cone 10, 31, 35 ......... Bus 11 ... …… Metal layer 13 ……… Resist layer 15 ………… Resist mask 17 ………… Metal mask 19 ………… Electroless plating layer 21 ………… Plating layer 23 ………… Replication mold

Claims (8)

The cones are arranged at a pitch below the wavelength of the light whose reflection should be suppressed,
A non-reflective structure characterized in that a side surface of the cone is concave with respect to a line connecting a point and a vertex on the circumference of the bottom surface of the cone.   The nonreflective structure according to claim 1, wherein an aspect ratio of the cone is 1 or less.   An optical element comprising the nonreflective structure according to claim 1 or 2 formed on a surface thereof. The cone-shaped holes are arranged at a pitch equal to or less than the wavelength of the light whose reflection should be suppressed,
The mold characterized in that the side surface of the hole is convex with respect to a line connecting a point on the periphery of the hole entrance and a vertex of the hole. Forming a metal film on the surface of the substrate (a);
A step (b) of forming a photosensitive resist on the metal film;
Forming a microstructure in the photosensitive resist (c);
Forming a microstructure on the metal film using the photosensitive resist as a mask (d);
Removing the photosensitive resist (e);
Using the finely processed metal film as an etching mask and performing wet etching to form a fine structure on the substrate surface;
The manufacturing method of the non-reflective structure characterized by comprising. A step (g) of forming a metal layer on the surface of the non-reflective structure according to claim 1;
Separating the nonreflective structure from the metal layer (h),
A metal mold manufacturing method, wherein the metal layer is a metal mold. A step (i) of providing the mold according to claim 4 inside the mold; and
Filling the inside of the mold with a fluid material (j);
A step (k) of releasing the mold from the material;
The manufacturing method of the non-reflective structure characterized by comprising. Pressing the mold according to claim 4 against the softened material (l);
A step (m) of releasing the mold from the material;
The manufacturing method of the non-reflective structure characterized by comprising.

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