JP2003279706A - Antireflection member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antireflection member having a low reflectance by easily and stably forming an antireflection face on a substrate. <P>SOLUTION: An uneven face composed of continuous patterns of minute pyramidal shapes 10 is formed on the surface of a translucent substrate 1. The uneven face composes a zero-order refractive face to visible light, and a refractive index is changed so that a refractive index of an apex side of projection parts of the uneven face is smaller than that of a bottom side of the substrate 1. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection member which is used in various optical devices such as spectroscopic analysis, optical electronics, optical communication, and lighting equipment, and which is suitable for preventing reflection of light having a wavelength range such as visible light. .

[0002]

2. Description of the Related Art Conventionally, in an optical element using a translucent substrate such as glass or plastic, surface treatment such as providing an antireflection film on the light incident surface of the substrate in order to reduce light due to surface reflection. Has been applied. As an antireflection film for light having a wavelength range such as visible light, a multilayer film in which thin dielectric films are superposed is known. These multilayer films are formed by depositing a thin film of metal oxide or the like on the surface of the transparent substrate by vacuum deposition or the like.

Further, as another method of surface treatment for preventing reflection, there is a method of forming a fine and fine uneven shape on the surface of an optical element. In general, when a periodic uneven shape is provided on the surface of the optical element, diffraction occurs when light passes through the surface, and the straight-ahead component of the transmitted light is significantly reduced. However, when the pitch of the uneven shape is shorter than the wavelength of the transmitted light, diffraction does not occur. For example, when the uneven shape is a rectangle as described later, a single wavelength corresponding to the pitch or depth. It is possible to obtain an effective antireflection effect against the above light.

Further, the uneven shape is not rectangular, but is formed by a so-called conical shape, which will be described later, so that the volume ratio between the peaks and valleys, that is, the optical element material side and the air side changes continuously. An antireflection effect can be obtained even for light having a wavelength range.

As a method for producing such a shape, for example, as described in JP-A-5-88001, a method in which fine particles of silicon oxide or aluminum oxide are mixed with an alcohol solution of ethyl silicate, It is a method of obtaining a film having an uneven shape by applying fine particles on a desired optical element surface and then removing the fine particles.

As another method for producing, as described in JP-A-62-96902, the surface of the molding die is cut from the depth of the wavelength of 1/3 of visible light to the same wavelength. There is a method in which a fine sawtooth (including a rounded tip) is processed to a predetermined depth of up to 1/50 of the above, and the mold is used for plastic molding.

[0007]

However, in the above-described method of forming an antireflection film using a dielectric thin film on the surface of an optical element, when the number of layers of the dielectric thin film is small, the wavelength range is reduced. It is difficult to obtain an antireflection effect for the light that it has. In order to obtain an antireflection effect in a wide wavelength range, it is necessary to form a large number of dielectric thin films. Furthermore, in order to suppress the change in reflectance depending on the incident angle of light, it is necessary to stack more dielectric thin films, and depending on the required performance, it may be 10 to 10 layers. is there.

Further, when the dielectric thin film is formed by vacuum evaporation, there is a problem that the film thickness varies and the performance is not stable. Furthermore, since the dielectric thin film must be formed on the surface of the substrate in a separate step after molding the substrate to be the optical element, the yield is deteriorated, which causes a cost increase.

Since the antireflection film basically cancels the reflected light by utilizing the interference of light, the refractive index and the film thickness of the material are controlled with high accuracy when each dielectric thin film is formed. Therefore, the cost increases as the number of layers for laminating thin films increases. Also, as the number of layers in which thin films are stacked increases, warpage of the substrate that is an optical element occurs,
There is a problem in that the yield is reduced.

Further, when forming a thin film, the spectral characteristics are affected by the physical properties of the film material, particularly the refractive index. There is also a problem that the refractive index varies depending on the film forming conditions. Furthermore, the film materials are also limited, and it is difficult to obtain ideal spectral characteristics.

On the other hand, it is effective to provide a pyramidal projection on the optical substrate. Further, in order to obtain an antireflection effect on light having a wider wavelength range, it is desirable that the aspect ratio, which is the ratio of the height of the protrusions to the pitch P, is large. However, it is difficult in principle to form a conical shape having an aspect ratio of 1 or more with the configuration described in Japanese Patent Laid-Open No. 5-88001.

Further, in the structure described in the above-mentioned Japanese Patent Laid-Open No. 62-96902, the irregular shape of the protrusions may cause irregular reflection of incident light, resulting in poor efficiency. Become.

In order to solve the above problems, Japanese Patent Laid-Open No.
In Japanese Patent Application Laid-Open No. 01-272505, a metal mask is formed in a dot array shape on an optical element, and then reactive ion etching is performed. At that time, the diameter of the metal mask is gradually reduced until it disappears. A method of forming a cone shape on an optical element by etching the optical element has been proposed.

In the above-mentioned Japanese Patent Laid-Open No. 2001-272505, there is proposed a surface treatment method for forming a cone shape having a large aspect ratio on an optical element. In this method, the optical element is made of Cr, Al or the like. There is a problem that the process becomes complicated and the cost increases, such as forming the metal mask and performing reactive ion etching on the optical element until the metal mask disappears.

Therefore, it is an object of the present invention to provide an antireflection material which can easily and stably form an antireflection surface on a substrate and has a low reflectance at a low cost.

[0016]

According to the present invention, an uneven surface is formed on a surface of a translucent substrate, the uneven surface being a fine conical continuous pattern, and the uneven surface is a diffractive surface of 0th order with respect to visible light. In addition, the convex portion of the uneven surface is characterized in that the refractive index is changed so that the refractive index becomes smaller on the apex side than on the substrate bottom surface side.

Here, the 0th-order diffraction means that the light goes straight as it is, and that the diffraction of the light does not occur.

Further, the refractive index of the convex portion of the uneven surface is changed so as to become continuously smaller from the bottom surface side of the substrate toward the apex side.

According to the above construction, the antireflection surface can be easily and stably formed on the substrate, and at the same time, stable spectral characteristics can be obtained. Moreover, the refractive index of the convex portion of the uneven surface is made smaller continuously from the substrate bottom side toward the apex side, so that even if the aspect ratio is small, the spectral characteristic of low reflectance over the visible light region is obtained. realizable.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a schematic shape of a surface of an antireflection member using the present invention, and FIG. 2 is a schematic view showing a pattern cross-sectional shape.

As shown in FIG. 1, the translucent substrate 1 is provided with a concavo-convex surface which is a continuous pattern in which fine pyramidal projections 10 are continuously formed. Although the pattern shape of the protrusion 10 in the embodiment is a quadrangular pyramid shape, the present invention may be a hexagonal pyramid shape or a conical shape.

The ratio D / p of the pattern height D to the pattern pitch p shown in FIG. 2 is defined as the aspect ratio.

FIG. 3 shows a simulation result of the spectral characteristics when the aspect ratio is changed in the quadrangular pyramid pattern. In this simulation, four kinds of aspect ratios with aspect ratios of 1, 1.5, 1.7, and 2 and the refractive index of the projections 10 on the uneven surface with the aspect ratio of 1 are The refractive index distributions (Type 1, 2) were used so that the refractive index was continuously reduced toward the apex (incident light side). That is, a pattern shape having a refractive index distribution substantially in the axial direction was used. Further, Type 2 has a larger refractive index distribution. In these simulations, the pattern pitch p is 300 nm.

In the spectral characteristics shown in FIG. 3, there is no great difference between the aspect ratios of 1 and 1.5.
It can be seen that the reflectance is considerably low when the aspect ratio is 2. On the other hand, Typ with a distribution of refractive index
At e1 and 2, the reflectance is low. The larger the refractive index distribution, the smaller the reflectance.

FIG. 4 is a plot of average reflectance values of the spectral characteristics of FIG. It can be seen that the relationship between the average reflectance and the aspect ratio can be temporarily approximated when the aspect ratio is between 1 and 2. Both Type 1 and 2 are examples in which the aspect ratio is 1, and the average value of Type 1 is 0.04.
7, the average value of Type2 is 0.022, and when applied to FIG. 3, it can be seen that Type1 corresponds to an aspect ratio of 1.65 and Type2 corresponds to an aspect ratio of 2 or more.

The pattern pitch p is preferably smaller than the wavelength of light. In this embodiment, 30
It is set to 0 nm. When the pattern pitch p is close to the visible wavelength, for example, when it is 550 nm, a light diffraction phenomenon occurs. When diffracted, the original antireflection effect is lost. On the other hand, when the wavelength is smaller than the visible wavelength, it is called zero-order diffraction, and no light diffraction occurs. Therefore, the continuous pattern formed on the surface of the transparent substrate 1 is configured to form a 0th-order diffractive surface for visible light.

As described above, when the refractive index is distributed such that it becomes smaller continuously from the bottom side of the substrate toward the apex side (incident light side), the aspect ratio is large even if the aspect ratio is small. The same reflectivity as that obtained is obtained. The smaller the aspect ratio, the easier the molding using the mold. In molding using a mold, the pattern shape is transferred to the pattern on the substrate. Even if the rate of transfer from the mold to the pattern to be molded, that is, the so-called transfer rate is lowered, a low reflectance can be obtained by slightly increasing the aspect ratio. From this, it is possible to manufacture a translucent substrate as an optical element that has been subjected to antireflection surface treatment using a mold.

In the case of organic compounds, ultraviolet laser irradiation, etc.
It is known that photoexcitation can induce a refractive index change. As a method of photoexciting a substance with laser irradiation or the like to change the refractive index, since the change in the refractive index is larger as the light intensity is stronger, the laser is focused on the cone-shaped bottom surface part where the refractive index should be maximized. A laser whose laser power decreases toward the apex of the cone is irradiated.

Further, in order to greatly stabilize the change in the refractive index, Ge, B, B is added to the acrylic (PMMA) base material.
It is also effective to add a substance such as i or Ti that promotes light induction.

As the material of the base material itself, a PVK-based organic photorefractive material, which has recently been receiving attention, can be used. The refractive index of the photorefractive material changes when it is exposed to light.

As a method other than photoexcitation, the injection pressure can be gradually increased by an injection molding method to continuously reduce the specific gravity from the pyramidal bottom surface to the apex. Since the higher the specific gravity is, the higher the refractive index is, it is possible to provide a continuous refractive index distribution.

Further, it is possible to adopt a method of using materials of different grades having different refractive indexes and changing from low refractive index to high refractive index at the time of molding.

As another method of changing the refractive index, the following method can be considered. There is a method in which monomers having different refractive indexes are contained in the acrylic agent of the substrate and photopolymerization is selectively performed. In the case of this method, for example, a photopolymerization initiator is mixed with a two-component monomer system that satisfies a certain relationship, and ultraviolet rays are irradiated. By doing so, the refractive index can be controlled to gradually increase in the opposite direction from the side irradiated with the ultraviolet rays. In the present invention, when the ultraviolet rays are irradiated from the apex side of the cone shape, the refractive index can be increased toward the bottom surface.

The refractive index can be changed by changing the fluorine content by copolymerization with a monomer containing fluorine. It is known that when fluorine is mixed with an acrylic agent, the refractive index changes in the range of about 1.36 to 1.49 depending on the fluorine content. In the pyramidal shape example, when fluorine is diffused so that the fluorine content increases from the bottom surface toward the apex, the refractive index becomes lower toward the apex.

As described above, the pattern pitch p is preferably smaller than the wavelength of light. In this embodiment, the thickness is 300 nm, but the smaller the pattern pitch p, the more difficult the molding becomes. Considering molding and the like, the thickness is preferably 100 nm or more and 300 nm or less.
The minimum fine pitch of recent semiconductors is 100 nm, and an F2 laser has a wavelength λ = 1 as a light source for laser exposure.
A wavelength of 157 nm in the generation of 00 nm has also been studied. The processing accuracy and resolution are determined by λ. Considering this, the minimum fine pattern pitch p is set to 100 nm or more.

If the above-mentioned cone-shaped pattern is provided on the surface as an antireflection member, dust may adhere to the pattern surface. For this reason, it is possible to provide an ITO film on which the dust is hard to adhere, or an anti-aging thin film such as TiO ₂ having a photocatalytic action on the uneven surface.

Next, a specific example of applying the antireflection member of the present invention will be described. FIG. 5 is a schematic view showing an example in which the present invention is applied to a light guide plate used in a surface light source device of a reflective liquid crystal display device.

As shown in the schematic sectional view of FIG. 5, the illuminating device 5 is provided as a front light on the reflective liquid crystal display means 51 side.
2 is arranged, and the illuminating device 52 is provided on the back surface of the linear light source 35, the light guide plate 54, and the light guide plate 54 to improve the visibility so as to face the reflective liquid crystal display means 51. The prevention member 55 is provided. The antireflection member 55 is integrally formed when the light guide plate 54 is molded, as will be described later. And this antireflection member 55
Is, for example, an uneven surface in which projections having a pattern pitch p of 300 nm and an aspect ratio of 1 are continuously formed, and the projections are made smaller continuously from the bottom surface side toward the apex (incident light side). The refractive index has a distribution.

Some linear light sources 53 use linear arc tubes, but in order to reduce power consumption, a point light source such as a light emitting diode and light from this point light source are dispersed. The thing provided with the linear or rod-shaped light-guide body which emits is used widely.

On the surface of the light guide plate 54, a reflection surface 56 for dispersing the light incident on the one end surface of the light guide plate 54 from the linear light source 53, that is, the incident surface and reflecting it on the back surface, and the liquid crystal display means 51.
The light that is reflected by the light and enters the back surface of the light guide plate 54
The transparent surfaces 57 that transmit light to the front surface side of No. 4 are alternately formed.

The light emitted from the linear light source 53 is guided by the light guide plate 5.
It is reflected by the reflecting surface 56 of No. 4 and given to the liquid crystal display means 51. The light modulated and reflected by the liquid crystal display means 51 is prevented from being reflected by the antireflection member 55 of the light guide plate 54, and visible light enters the light guide plate 54 without being diffracted. Then, the light is transmitted through the light guide plate 54 and is visually recognized.

An example of the method of forming the above-mentioned light guide plate will be described with reference to FIG. A front light mold 61 provided with a pattern for forming a reflection surface and a transmission surface on the front side of a light guide plate constituting a front light, and an antireflection member mold 62 having a continuous pattern of antireflection members. To prepare. The front light mold 61 is formed of a light transmissive member.

Then, a UV curable resin is filled between the molds 61 and 62. Then, ultraviolet (UV) light is irradiated to cure the UV curable resin. After that, the molds 61, 6
By removing 2, the antireflection member 55 can be integrally formed when the light guide plate 54 is molded. Then, laser irradiation may be applied to the antireflection member 55 in order to form the distribution of the refractive index.

According to the above method, it is possible to form the pattern of the mold with an extremely high transfer rate.

Another example of the method of forming the above-mentioned light guide plate will be described with reference to FIG. A front light mold 61 provided with a pattern for forming a reflection surface and a transmission surface on the front side of a light guide plate constituting a front light, and a mold for an antireflection member having a continuous pattern of antireflection members 6
Prepare 2. The front light mold 61 is formed of a light transmissive member.

Then, UV curable resin is filled between both the molds 61 and 62 on both sides of the transparent substrate. Then, ultraviolet (UV) light is irradiated to cure the UV curable resin. After that, by removing the molds 61 and 62, the antireflection member 55 and the pattern surface of the front light are respectively formed on both surfaces of the substrate, but the light guide plate can be integrally molded.
Then, laser irradiation may be applied to the antireflection member 55 in order to form the distribution of the refractive index.

According to the above method, it is possible to form the pattern of the mold with an extremely high transfer rate.

The present invention can be applied to various optical devices other than the above-mentioned light guide plate. For example, a spherical surface of a lens such as an optical pickup objective lens, a semiconductor laser,
The present invention can be applied to a cover glass of an LED, a resin cover for a liquid crystal display surface of a PDA device such as a mobile phone, a touch panel, and a light incident surface of a solar cell device.

[0049]

As described above, according to the present invention, the antireflection surface can be easily and stably formed on the substrate, and at the same time, stable spectral characteristics can be obtained. Moreover, the refractive index of the convex portion of the uneven surface is made smaller continuously from the substrate bottom side toward the apex side, so that even if the aspect ratio is small, the spectral characteristic of low reflectance over the visible light region is obtained. realizable.

[0050]

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic shape of a surface of an antireflection member using the present invention.

FIG. 2 is a schematic diagram showing a pattern cross-sectional shape.

FIG. 3 is a diagram showing simulation results of spectral characteristics when an aspect ratio is changed in a quadrangular pyramid pattern.

FIG. 4 is a reference diagram in which average values of reflectances of the spectral characteristics of FIG. 3 are plotted.

FIG. 5 is a schematic cross-sectional view showing an illumination device using a light guide plate to which the invention is applied.

FIG. 6 is a schematic cross-sectional view showing a method for forming a light guide plate to which the present invention is applied.

FIG. 7 is a schematic cross-sectional view showing a method of forming a light guide plate to which the present invention is applied.

[Explanation of symbols]

1 substrate 10 protrusions

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H042 BA04 BA11 BA13 BA20                 2H091 FA14Z FA23X FA37X FA42X                       FB04 FC19 LA03 LA12                 2K009 AA12 BB11 CC24 DD02 DD17

Claims (2)

[Claims] 1. A translucent substrate is provided with a concavo-convex surface formed of a fine conical continuous pattern on the surface thereof, and the concavo-convex surface constitutes a zero-order diffractive surface for visible light, and the concavo-convex surface is formed. The convex portion of the antireflection member is characterized in that the refractive index is changed so that the refractive index is smaller on the apex side than on the substrate bottom side. 2. The reflection according to claim 1, wherein the refractive index of the convex portion of the uneven surface is changed so as to become continuously smaller from the substrate bottom side toward the apex side. Prevention member.