JP2009128541A - 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; and forming a plurality of 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 by electron beam lithography using a surface electron source 23. <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;
Forming a plurality of micro concavo-convex portions on the rough surface of the substrate by electron beam lithography using a surface electron source, and having an average pitch of the predetermined wavelength or less;
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,
A step of producing a sheet member or a prototype having a plurality of minute irregularities having an average pitch of the predetermined wavelength or less by electron beam lithography using a surface electron source;
Preparing a substrate having a rough surface with a surface roughness greater than a predetermined wavelength;
Bonding the sheet member formed using the sheet member or the prototype to the rough surface of the substrate;
A method for manufacturing an antireflection structure is provided.

  According to the present invention, the fine irregularities are formed on the rough surface of the substrate by electron beam lithography using a surface electron source capable of nanometer-size fine processing. Therefore, it is possible to form a minute uneven portion with high accuracy. Further, in electron beam lithography using a surface electron source, since a parallel electron flow is irradiated toward the substrate, exposure is performed without focusing the beam. Therefore, the substrate can be processed without depending on the depth of focus as in normal electron beam drawing. Further, since the parallel electron flow (ballistic electron emission) has a small electron emission angle and velocity dispersion, the rough surface can be processed. For this reason, according to the electron beam lithography of the present invention, it is possible to reliably form a minute uneven portion on a rough surface. In addition, the present invention has an advantage that throughput is higher than that of a point electron beam or the like because batch exposure is performed using a surface electron beam.

  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, an antireflection structure may be manufactured by first producing a prototype, then producing a replica from the prototype, and finally molding a material such as a resin using the replica. Since the latter is suitable for mass production, the latter method will be mainly described in this specification.

<< Making prototype >>
1. Substrate roughening First, a substrate to be used for producing a prototype is prepared. The material for the substrate is not particularly limited, and may be any one selected from glass, metal, ceramic, and resin. Further, the substrate may be transparent or opaque. As will be described later, in the present embodiment, the minute uneven portions are formed by electron beam lithography using a surface electron source.

  The roughening of the surface of the substrate can be performed by mechanical and / or chemical methods. 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 substrate becomes a rough surface having non-periodic irregularities.

  The roughening of the surface of the substrate is performed so that the surface roughness of the rough surface to be formed is larger than a predetermined wavelength. Specifically, as described with reference to FIG. 7, the average value of the angle formed by the normal vector of the tangent plane of the rough surface of the substrate and the normal vector of the reference surface of the substrate is 5 degrees or more. You can go to 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.

  Further, the surface of the substrate may be directly roughened by finely processing (grinding or cutting) the surface of the 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 substrate. That is, the method of directly processing the surface of the substrate is a recommended method when it is desired to set the angle θ strictly or to form a rough surface having periodic unevenness. Further, the surface of the 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, examples of the chemical method include a method in which an acid or alkali is brought into contact with the surface of the substrate to corrode the surface of the substrate. For example, in the case where the substrate is made of an anisotropic material such as single crystal (for example, single crystal silicon), by using anisotropic etching, the surface of the substrate is micrometer-sized unevenness ( For example, a texture structure) can be formed. Of course, a mechanical method and a chemical method may be combined.

2. Formation of micro uneven portions by electron beam lithography using a surface electron source Next, micro uneven portions are formed on the rough surface of the substrate by electron beam lithography using a surface electron source. Hereinafter, in this specification, the electron beam lithography using the surface electron source may be simply referred to as “electron beam lithography”. The material used as the substrate is not sensitive to electron beams. Therefore, in the present embodiment, as the electron beam lithography process, a process of forming a resist layer on the rough surface of the substrate, an exposure process of irradiating the resist layer with a surface electron beam, a development process of removing the photosensitive region, An etching process is performed using the patterned resist layer as a mask.

  FIG. 8 is an explanatory diagram illustrating an example of a process of forming minute uneven portions. Electron beam lithography using a surface electron source is a technique for forming a fine pattern using a surface electron beam. In the exposure process of the present invention, a known exposure apparatus including a surface electron source and an absorbent material arranged between the surface electron source and the object to be exposed and patterned into a predetermined shape can be used. For example, an exposure apparatus described in JP-A-2004-103942 can be used.

  First, as shown in FIG. 8A, a resist layer 28 that is sensitive to an electron beam is formed on the rough surface 27 p of the substrate 27. The resist layer 28 can be formed by applying a liquid electron beam resist by a method such as spin coating, spray coating, or dip coating. As the electron beam resist, for example, an acrylic resist can be used. The thickness of the resist layer 28 is, for example, 100 nm to 500 nm. A pre-filmed electron beam resist may be laminated and pressure-bonded to the substrate 27. A method is also conceivable in which a resist layer is formed on a non-roughened substrate, and then the substrate is made uneven with the resist layer by embossing.

  Next, as shown in FIG. 8B, the surface electron beam 24 is irradiated from the surface electron source 23 through the absorber 22 onto the substrate 27 from the side having the rough surface 27p (exposure process). The absorber 22 is made of a material having a predetermined pattern and absorbing an electron beam. That is, the absorber 22 has an electron beam transmission region and an electron beam absorption region, and functions as a mask. A region where the absorber 22 does not exist is an electron beam transmission region. The absorber 22 can be formed using materials such as Ta, Ni, Au, Ag, Cu, Cr, Fe, W, and Pt. A step of forming the absorbent 22 may be further included before the exposure step. In that case, for example, a material that absorbs an electron beam is used, and a predetermined pattern is formed on the material by drawing a dotted electron beam, so that the absorber 22 is manufactured. In the present embodiment, the pattern shape of the absorbent 22 is, for example, a lattice pattern or a dot pattern that reflects the arrangement of minute uneven portions. In the case of a dot pattern, the shape of the dot is not limited to a circle, and may be a triangle or a hexagon. The thickness of the absorber 22 may be a thickness that can completely absorb the electron beam, or may be partially changed. By partially changing the thickness of the absorber 22, the transmittance of the electron beam in the absorber 22 can be partially varied. As a result, it is possible to expose the rough surface 27p of the substrate 27 to a three-dimensional pattern corresponding to the thickness of the patterned absorber 22, and to form a minute uneven portion with high accuracy.

  After the exposure process is completed, the substrate 27 is immersed in a developer containing xylene or the like as a main component (development process). The portion exposed by the electron beam is dissolved in the developer because the molecular chain is cut. Unexposed parts do not dissolve. Through the development process, as shown in FIG. 8C, a fine structure 28 made of an electron beam resist is formed on the substrate 27. The electron beam resist may be either a negative type or a positive type.

Next, the substrate 27 is etched using the developed resist layer (fine structure 28 made of an electron beam resist) as a mask (etching step). For etching the substrate 27, wet etching or dry etching may be employed. For example, when the substrate 27 is made of quartz glass, dry etching may be performed using a mixed gas of CHF ₃ and O ₂ . Through the etching process, as shown in FIG. 8 (d), minute uneven portions 29 are formed on the rough surface 27 p of the substrate 27.

  The time used for etching the substrate 27 can be determined based on the time required for the disappearance of the microstructure 28 made of the electron beam resist. Specifically, the etching time may be set slightly longer than the time required for the disappearance of the fine structure 28. In this way, it is possible to accurately form the minute concavo-convex portion 29 with little blunting at the top. If the resist layer 28 (fine structure 28) remains even after a sufficiently high minute uneven portion 29 is formed through the etching process, an ashing process for removing the resist layer 28 may be performed.

  As shown in FIG. 9A, the underlayer 30 may be formed on the rough surface 27p of the substrate 27 before applying the electron beam resist. The underlayer 30 can be a layer containing as a main component a material that is not sensitive to electron beams. Specifically, a material having no photosensitivity, for example, a metal such as Cr, Ni, or Fe, is deposited on the rough surface 27p of the substrate 27 as a base layer 30 by a method such as sputtering, vapor deposition, or plating. Next, as shown in FIG. 9B, an electron beam resist is applied on the base layer 30 to form a resist layer 28.

  Next, an exposure process and a development process are performed according to the procedure described with reference to FIG. 8 to form a fine structure 28 made of an electron beam resist (FIG. 9C). Next, the underlying layer 30 is selectively etched using the developed fine structure 28 which is a resist layer as a mask. For selective etching of the underlayer 30, wet etching can be employed. In this way, the composite structure 31 including the resist layer 28 and the underlayer 30 is formed. Finally, the substrate 27 is dry-etched using the composite structure 31 as a mask in the procedure described with reference to FIG. According to such a method, it is easier to earn the height of the minute uneven portion 29 than the method described with reference to FIG. This is because if the base layer 30 (metal mask) is sandwiched between the substrate 27 and the resist layer 28, the etching selectivity can be increased. In order to increase the height of the minute uneven portion 29, it is necessary to form the resist layer 28 to be thick to some extent. However, since the electron beam resist is significantly deteriorated by long-time etching, there is a problem that it is too thick. The underlayer 30 contributes to solving these problems.

<< Production of replication type >>
Next, a replica mold is produced from the substrate having minute uneven portions. FIG. 10 is an explanatory diagram of a process for producing a replica mold by electroforming from a substrate having minute uneven portions. First, as shown in FIGS. 10A and 10B, the substrate 27 having the minute uneven portions 29 is immersed in the electroless Ni plating bath 63 to form the electroless Ni plating layer 64 that covers the minute uneven portions 29. . Next, as shown in FIG. 10C, 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. 10B may be omitted.

  Finally, as shown in FIG. 10 (d), the substrate 27 having the electroless Ni plating layer 64 and the electrolytic Ni plating layer 66 is dipped in a base solution 67, so that the Ni plating layers 64 and 66 are part of the substrate 27. Remove. Thereby, the Ni replication mold 66 in which the minute uneven portions 68 are formed on the surface 66p (rough surface) is obtained (FIG. 10E). If it is difficult to remove the substrate 27, the substrate 27 may be dissolved by selective etching. 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.

  Furthermore, the secondary replication mold can be manufactured using the Ni replication mold 66 manufactured by the above method as the primary replication mold. First, as shown in FIGS. 11A and 11B, a release film 69 is formed on a Ni replication mold 66 as a primary replication mold. The release film 69 is, for example, a nickel oxide layer formed by oxidizing the surface layer portion of the Ni replication mold 66. Next, as shown in FIG. 11 (c), the Ni replica mold 66 is immersed in an electrolytic Ni plating bath 65 and energized to form an electrolytic Ni plating layer 80 on the Ni replica mold 66 through the release film 69. To do. After that, as shown in FIG. 11 (d), the electrolytic Ni plating layer 80 and the Ni replica mold 66 are mechanically separated at the position of the release film 69. As a result, the Ni replica mold 80 as the secondary replica mold having the minute uneven portions 81 is obtained (FIG. 11E).

  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.

  Next, with reference to FIG. 12, a method for producing a replication mold by press molding from a substrate having minute uneven portions will be described. The gist of this method is to press a substrate having minute uneven portions against a separately prepared material and transfer the shape of the surface of the substrate to the material. The substrate 27 described with reference to FIG. 8 can be used as the substrate having minute uneven portions. It is preferable that the substrate 27 is made of a hard material such as quartz glass because minute irregularities are hardly damaged by pressurization.

  As shown in FIG. 12, first, a protective film 91 is formed on the rough surface 27 p of the substrate 27 having the minute uneven portions 29. The protective layer 91 is a layer containing, for example, an Ir—Rh alloy as a main component, and can be formed to a thickness of about 10 to 150 nm by a method such as sputtering. On the other hand, the lower mold | type 93 which has the recessed part 93g is prepared. The lower mold 93 is preferably made of a material having excellent heat resistance, for example, a cemented carbide such as WC. After the protective layer 97 is formed on the inner surface of the recess 93g of the lower mold 93, the glass material 94 to which the shape of the substrate 27 is to be transferred is accommodated in the recess 93g. The protective layer 97 can be made of, for example, an Ir—Rh alloy. As the glass material 94, a glass having a glass transition point lower than that of the constituent material of the substrate 27, for example, a crown borosilicate glass (glass transition point Tg: 501 ° C., yield point At: 549 ° C.) may be used. A release film 95 for facilitating release is formed on the surface of the glass material 94.

  The release film 95 is one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W, and Ta, an alloy containing these metals, carbon (including diamond-like carbon DLC). It may be composed of boron nitride or the like. The thickness of the release film 95 is about 10 to 150 nm. By setting the thickness within such a range, the fine structure is not easily depressed. Further, by providing the release film 95, it is possible to prevent the glass material 94 from coming into direct contact with the substrate 27 and being fused.

  Next, as shown in FIG. 12B, the substrate 27 and the lower mold 93 are accommodated in a heating furnace 96 whose atmosphere is replaced with an inert gas such as nitrogen gas. Then, the temperature in the heating furnace 93 is raised to a temperature exceeding the glass transition point Tg of the glass material 94, preferably a temperature slightly exceeding the yield point At (for example, around 590 ° C.). Thereafter, a pressing force is applied between the substrate 27 and the glass material 94 (FIG. 12C). After maintaining a state in which a pressing force is applied between the two for a predetermined time (for example, several minutes), the substrate 27 as the upper mold is separated from the glass material 94 without performing active cooling. Thereafter, the glass material 94 is gradually cooled to obtain a glass secondary replication mold 94 in which fine uneven portions 98 are formed on the surface (rough surface).

<< Molding diffusion plate >>
A molded product such as the diffusion plate 1 can be manufactured by an injection molding method using the replication mold 66 described with reference to FIG. As shown in FIG. 13A, first, the produced replica mold 66 is inserted 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. 13B and 13C, the molds 101 and 102 are heated, and the molten resin is injected into the cavity SH. As shown in FIG. 13D, 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. 14A and 14B, first, a prototype 120 having a plurality of minute concavo-convex portions 122 having an average pitch of a predetermined wavelength or less is produced by electron beam lithography. That is, the minute uneven portion 122 is formed on a smooth surface. Next, as shown in FIG. 14C, the surface shape of the master 120 is transferred to the sheet member 124 by press molding. Instead of the original pattern 120, a minute uneven portion may be directly formed on a sheet member made of an electron beam photosensitive material.

  On the other hand, a substrate 128 (see FIG. 14E) having a rough surface with a surface roughness larger than a predetermined wavelength is separately prepared. The substrate 128 may be a component constituting the final product such as a lens barrel. Then, a sheet member 124 (or a sheet member in which minute uneven portions are directly formed by electron beam lithography) formed using the prototype 120 is bonded to the rough surface 128p of the 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 substrate 128 (for example, an optical component) having the minute uneven portions 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. 15 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. 15, 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. 16 is a front view of the lens barrel 205.

  FIG. 17 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 by, for example, the injection molding method described with reference to FIG. 14, 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. 18 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 basic structure portion 7 can be formed by grinding the surface of the substrate using a cutting tool, and the minute uneven portion 11 can be formed by electron beam lithography.

  In the diffusing plate 50 shown in FIG. 18, 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 with reference to FIG. 7. 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. 19A, 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. 19B, 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.

  Next, as shown in FIG. 19 (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. 19D, 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. 19E). 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 Explanatory drawing of the process of forming minute uneven parts when the substrate does not have photosensitivity Explanatory drawing of other processes for forming minute irregularities when substrate does not have photosensitivity Explanatory drawing of the process of producing a replica mold by electroforming from a substrate having minute irregularities Explanatory drawing of the process of producing a secondary replication mold from a primary replication mold Explanatory drawing of the process of producing a replication mold by press molding from a substrate having minute uneven parts 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

1,50 Diffuser (Antireflection structure)
10, 27p, 66p Surface (rough surface)
11, 29, 68, 81, 98 Micro uneven portion 12, 51 Reference surface 13 Tangent plane 22 Absorber 23 Surface electron source 24 Surface electron beam 27 Substrate (or antireflection structure)
28 Resist layer 30 Underlayer 66, 80, 94 Replica type (antireflection structure)
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;
Forming a plurality of micro concavo-convex portions on the rough surface of the substrate by electron beam lithography using a surface electron source, and having an average pitch of the predetermined wavelength or less;
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.   2. The step of forming the minute concavo-convex portion by the electron beam lithography includes a step of irradiating the substrate with a surface electron beam through an absorber having a predetermined pattern and absorbing the electron beam. The manufacturing method of the reflection preventing structure of Claim 2.   The manufacturing of the antireflection structure according to claim 3, further comprising a step of forming the absorber by using a material that absorbs an electron beam, forming the predetermined pattern on the material by dot-like electron beam drawing, and producing the absorber. Method.   The step of forming the micro concavo-convex portion by the electron beam lithography includes the step of forming a resist layer having sensitivity to the electron beam on the rough surface of the substrate, and having an electron beam having a predetermined pattern. The method includes: irradiating the substrate with the surface electron beam through an absorbing material to be absorbed; developing the resist layer; and etching the substrate using the developed resist layer as a mask. The manufacturing method of the reflection preventing structure of any one of Claim 1 thru | or 4.   The step of forming the micro concavo-convex portion by the electron beam lithography includes the step of forming a base layer containing as a main component a material having no sensitivity to the electron beam on the rough surface of the substrate, Forming a resist layer sensitive to an electron beam on the base layer; irradiating the substrate with a surface electron beam through an absorber having a predetermined pattern and absorbing the electron beam; Developing the resist layer, forming the composite structure including the resist layer and the base layer by selectively etching the base layer using the developed resist layer as a mask, and using the composite structure as a mask The manufacturing method of the antireflection structure of any one of Claims 1 thru | or 4 including the process of etching a board | substrate.   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,
A step of producing a sheet member or a prototype having a plurality of minute irregularities having an average pitch of the predetermined wavelength or less by electron beam lithography using a surface electron source;
Preparing a substrate having a rough surface with a surface roughness greater than a predetermined wavelength;
Bonding the sheet member formed using the sheet member or the prototype to the rough surface of the 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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