JP2002182016A - Method for producing diffusion plate and display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffusion plate in which the peak-to-valley height or refractive index difference can easily be adjusted to <=100 nm and made variable and to provide a method for producing the diffusion plate. SOLUTION: A substrate 2 comprising a metal such as aluminum is anodically oxidized to form a porous alumina layer 3 with crystals of alumina 5 grown with a prescribed period. The metal part 2a of the substrate 2 is dissolved by immersing the substrate 2 in a dissolving liquid such as phosphoric acid to form a rugged surface comprising the interface 2b between the metal part 2a having a projecting face for every crystal and the alumina 5. A reflecting film 6 is then formed on the interface 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a diffusion plate and a method of manufacturing a display device, in which light is diffused by providing fine periodic irregularities or refractive index differences on an incident surface or an exit surface of light.

[0002]

2. Description of the Related Art A diffusion plate widely used for a single-lens reflex camera, a backlight of a liquid crystal display device, a lighting device, etc. is a diffusion surface having a fine periodic unevenness or a refractive index difference on a light incident surface or a light exit surface. The light is diffused by the refraction of the light, and uniform light is emitted. For example, when a diffusion plate is used for a backlight of a transmission type liquid crystal display device, the configuration is as shown in FIG. A linear light source 11 composed of a fluorescent tube is arranged on the side of the light guide plate 12. In the drawing of the light guide plate 12, the diffusion plate 1 is disposed above and the backlight 15 is configured. A liquid crystal panel 13 is arranged above the diffusion plate 1.

A light beam emitted from the light source 11 is transmitted through the light guide plate 1.
By 0, the light is guided upward in the figure and enters the diffusion plate 1. Light beam diffused by the diffusion plate 1 is adapted to an image is projected uniformly irradiate the liquid crystal panel 13. Reference numeral 14 denotes a reflection plate that guides light from the light source 11 to the light guide plate 12.

FIG. 13 is a diagram showing a configuration in which a diffusion plate is used in a reflection type liquid crystal display device. The diffusion plate 1 arranged above the liquid crystal panel 13 also serves as a light guide plate,
The light beam emitted from 1 is incident on the side surface of the diffusion plate 1 and irradiates the liquid crystal panel 13 by the diffusion surface 1a on the lower surface. If the period of the unevenness of the diffusion surface 1a is on the order of the wavelength, the diffusion is too strong to visually recognize the image. For this reason, a diffusion surface 1a provided with irregularities having a period equal to or less than the wavelength is formed.

The diffusion surface 1a of the conventional diffusion plate 1 is formed by a method such as mechanical processing such as polishing or blasting, dry etching or wet etching, irradiation of a diffusion plate made of a polymer material with ultraviolet light, or laser processing. Is formed. In the machining by polishing, the surface of a substrate such as glass is polished with coarse abrasive grains to form a diffusion surface 1a having irregularities of a desired period. In the machining by blasting, abrasive grains are sprayed onto the surface of the substrate by high pressure to form a diffusion surface 1a having irregularities.

In the processing method by etching, first, a pattern made of a resist is formed at predetermined intervals on the surface of a substrate such as glass by photolithography. Next, dry etching or wet etching such as RIE is performed to remove a portion of the substrate surface where the pattern is not formed. Then, the resist is removed to form a diffusion surface 1a having irregularities of a desired period on the substrate surface.

In the processing method by irradiation with ultraviolet rays, a substrate made of a polymer material is irradiated with ultraviolet rays at a predetermined cycle. As a result, the polymeric material of the portion ultraviolet is irradiated is decomposed or polymerized, the refractive index is varied. As a result, a diffusion surface 1a having a periodic refractive index difference is formed on the surface of the substrate.

In the method using laser processing, a surface of a substrate such as glass is irradiated with laser light and scanned to form a concave portion at a predetermined cycle. As a result, a diffusion surface 1a having irregularities with a desired period is formed on the substrate surface.

[0009]

The outgoing light is diffused more uniformly when the period of the minute unevenness and the refractive index difference of the diffusing surface 1a is made sufficiently smaller than the wavelength of the light. For example, in order to uniformly diffuse visible light, it is desirable to form irregularities and refractive index differences with a period of 100 nm or less. Further, in FIG. 12 described above, the light intensity of the light beam A1 incident on the central portion of the diffuser plate 1 is weaker than the light beam A2 incident on the peripheral portion by the longer distance from the light source 11. Therefore, in order to irradiate the liquid crystal panel 13 uniformly, it is necessary to change the period of the unevenness and the refractive index difference between the central part and the peripheral part of the diffusion plate 1.

However, according to the above-mentioned conventional method for processing a diffusion surface, there are the following problems. That is, when forming the diffusion surface by machining the diffuser 1
It is difficult to change the period of the irregularities between the peripheral portion and the central portion of the above. Also, it is difficult to provide partial unevenness.

When a diffusion surface is formed by etching, irregularities having a period of about 1 μm can be easily formed. However, the process becomes complicated, and the limit resolution of an exposure apparatus for patterning is about 200 nm.
It is difficult to form irregularities having the following periods.

According to the processing method in which the refractive index difference is provided by irradiating ultraviolet rays, the durability is low and the reliability is low because the diffusion plate is made of an organic material. In the case of forming irregularities by laser processing, since laser light is scanned over the entire substrate, processing time is increased and manufacturing cost is increased.

Therefore, 1
It is difficult to form a diffusion surface having irregularities or a refractive index difference with a period of 00 nm or less and variable in the period of the irregularities or the refractive index difference with low cost and high reliability.

According to the present invention, there is provided a method of manufacturing a diffusion plate having irregularities or refractive index differences having a period of 100 nm or less and capable of forming a diffusion surface capable of varying the period of irregularities or the refractive index difference at low cost and high reliability. And a method for manufacturing a display device using the diffusion plate.

[0015]

According to a first aspect of the present invention, there is provided a method for manufacturing a diffusion plate, comprising: anodizing a substrate made of a metal to grow an oxide; The method is characterized in that an uneven surface comprising a boundary surface between a metal and an oxide is formed on the surface by dissolving one of the objects.

According to this structure, an oxide having pores for each crystal is generated by anodizing a metal substrate. The boundary between the oxide and the metal is formed on a curved surface for each crystal. When the substrate is immersed in a predetermined solution, for example, the metal portion is dissolved and the boundary between the oxide and the metal is exposed on the surface. As a result, a diffusion plate having an uneven surface formed on each oxide crystal as a convex surface is obtained.

According to a second aspect of the present invention, there is provided a method for manufacturing a diffusion plate, wherein an oxide is grown by anodizing a substrate made of a metal, and one of the metal and the oxide is dissolved. and an uneven surface formed from the boundary surface between the oxide to form a mold having a surface, is characterized in that molding using the mold.

According to this configuration, an oxide having pores for each crystal is generated by anodizing a substrate made of metal. The boundary between the oxide and the metal is formed on a curved surface for each crystal. When the substrate is immersed in a predetermined solution, for example, the metal portion is dissolved and the boundary between the oxide and the metal is exposed on the surface. As a result, a mold having an uneven surface formed in a convex surface for each oxide crystal can be obtained. The transmission type diffusion plate is formed by molding using this mold.

According to a third aspect of the present invention, in the method for manufacturing a diffusion plate according to the first or second aspect, the substrate is made of aluminum. According to this configuration, the substrate made of aluminum is anodized to generate porous alumina having pores for each crystal.

According to a fourth aspect of the present invention, in the method for manufacturing a diffusion plate according to any one of the first to third aspects, the distance between the unevenness of the uneven surface is controlled. .

According to a fifth aspect of the present invention, in the method for manufacturing a diffusion plate according to the invention, a metal plate is anodically oxidized, and a mask having through holes arranged at predetermined intervals is arranged on a substrate. The surface of the substrate is ion-exchanged at predetermined intervals by contacting the substrate with an ion-exchange fluid.

According to this configuration, an oxide having pores for each crystal is generated by anodizing the metal plate. For example, when the oxide is cut along a plane perpendicular to the pores, through holes are formed at predetermined intervals. Mask is obtained. By disposing the mask on a substrate such as glass and disposing the substrate in the ion exchange fluid, the ion exchange fluid comes into contact with the substrate through the through hole. Thereby, the portion of the through-hole on the surface of the substrate is ion-exchanged, and portions having a different refractive index from the substrate are formed at predetermined intervals.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a display device, comprising: anodizing a substrate made of a metal to grow an oxide; and dissolving one of the metal and the oxide. A diffusion plate having an uneven surface composed of a boundary surface between the diffusion plate and the oxide is formed on the surface, and the diffusion plate is disposed to face the display element.

Further a method of manufacturing a display device of the invention described in claim 7, a substrate made of a metal is grown oxide by anodizing, by dissolving one of metal and oxide, metal A mold having a concave-convex surface formed of a boundary surface between a metal and an oxide is formed on the surface, and a diffusion plate formed by using the mold is arranged to face a display element.

According to a eighth aspect of the present invention, in the method of manufacturing a display device according to the invention, a metal plate is formed by anodizing a metal plate and a mask having through holes arranged at predetermined intervals is arranged on a substrate. A diffusion plate in which the surface of the substrate is ion-exchanged at a predetermined interval by contacting an ion exchange fluid with the substrate through the substrate, and the diffusion plate is arranged to face a display element.

According to a ninth aspect of the present invention, in the method for manufacturing a display device according to any one of the sixth to eighth aspects, the display element comprises a liquid crystal display element.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. Figure 1-4 is a side sectional view showing the manufacturing method of the diffuser plate of the first embodiment. FIG. 1 shows a side sectional view of the pit forming step. In the pit forming step, the pits 10 are formed on the surface of the substrate 2 made of aluminum at a predetermined two-dimensional cycle by fine processing means such as drawing with an electron beam.

Next, as shown in FIG. 2, in the anodic oxidation step, the substrate 2 is placed on the anode, immersed in an acidic electrolytic solution such as oxalic acid, and the substrate 2 is anodized by applying a voltage. Alumina 5 is generated by anodic oxidation, and a crystal having hole 4 at the position where pit 10 is formed grows.

As a result, the pores 4 composed of pores having a very high aspect ratio having a diameter of several nanometers to several hundreds of nanometers are formed by several tens of holes.
The porous alumina layer 3 arranged with a period of nm to several hundreds of nm is obtained. The diameter and period of the hole 4 can be controlled by the type, concentration or applied voltage of the acidic electrolytic solution. For example, as shown in Table 1, the pores 4 having a desired period can be obtained by changing the applied voltage and the concentration of oxalic acid to oxalic acid as the acidic electrolytic solution.

[0030]

[Table 1]

The alumina 5 crystal usually grows in a hexagonal lattice even without providing the pits 10 (see FIG. 1), and the holes 4 formed for each crystal are arranged at substantially predetermined intervals. However, by providing the pit 10, the pit 1
0 triggers the formation of the hole 4 and the diameter and the period of the hole 4 can be controlled with high accuracy. In addition, crystals having another arrangement such as a square lattice can be easily formed.

The oxide may be formed by anodic oxidation using a substrate made of a metal other than aluminum. However, by using an inexpensive aluminum substrate to produce alumina having excellent corrosion resistance, This is more desirable because the cost of the diffusion plate can be reduced and high reliability can be obtained.

Next, in the immersion step, the substrate 2 is
_{2 or} a saturated solution of Br ₂ in methanol. Porous alumina layer 3 and metal part 2a of substrate 2
The boundary surface 2 b is curved for each crystal of the alumina 5 along the shape of the hole 4. Therefore, as shown in FIG.
The metal part 2a is dissolved by the solution to expose the boundary surface 2b, and the porous alumina layer 3 having a convex surface for each crystal on the surface remains.

Then, as shown in FIG. 4, in the reflection film forming step, a reflection film 6 made of a metal such as aluminum is formed on the boundary surface 2b by vapor deposition, sputtering or the like. Thereby, it is possible to obtain the reflection type diffusion plate 1 having the diffusion surface 1a on which the irregularities are formed at a predetermined period.

When the substrate 2 is immersed in phosphoric acid or oxalic acid without applying a voltage in the immersion step, as shown in FIG. 5, the porous alumina layer 3 is dissolved to expose the interface 2b. The metal part 2a having a concave surface for each crystal on the surface remains. Even in this way, it is possible to obtain the reflection type diffusion plate 1 having the diffusion surface 1a on which the irregularities are formed at a predetermined period.

According to the present embodiment, it is possible to easily obtain the diffusion plate 1 having irregularities with a period of 100 nm or less, and to reduce the cost of the diffusion plate 1. Further, since the diffusion plate 1 is made of an oxide or a metal, higher durability than an organic material can be secured.

FIG. 11 shows a configuration in which the diffusion plate 1 according to the present embodiment is used in a transmission type liquid crystal display device using a transmission type liquid crystal panel 13. The diffusion plate 1 is disposed below the liquid crystal panel 13, and a light beam emitted from the light source 11 from an oblique side is reflected and diffused by the diffusion surface 1 a of the diffusion plate 1. Then, an image is projected through the liquid crystal panel 13.

At this time, by changing the interval between the holes 4 according to the position of the substrate 2 of the diffusion plate 1, it is possible to obtain the diffusion plate 1 having a different period of unevenness depending on the position. Therefore, the light intensity of the light beam A1 incident on the central portion of the diffuser plate 1 and the light intensity of the light beam A2 incident on the peripheral portion can be equalized,
The image quality of the liquid crystal display device can be easily improved.
It is also possible to form partial unevenness.

The distance between the holes 4 can be controlled by changing the distance between the pits 10 (see FIG. 1). Further, the control can also be performed by changing the applied voltage of the substrate 2 according to the position of the substrate 2.

Next, a second embodiment will be described with reference to the drawings. This embodiment corresponds to FIGS. 1 to 3 and FIG.
As in the first embodiment, a pit forming step (see FIG. 1), an anodizing step (see FIG. 2), and a dipping step (see FIGS. 3 and 5) are performed on the metal substrate 2. Thereafter, the molding step shown in FIG. 6 the diffusion plate 1 obtained in the mold is to be carried out.

In the molding step, as in the first embodiment, a lower mold 19 composed of a diffusion plate 1 (see FIG. 5) obtained by dissolving alumina is attached to a molding apparatus 20, and an upper mold 1 is formed.
And an optical resin is poured into the gap. And the lower mold 19
A diffusion plate 21 having a diffusion surface 21a composed of irregularities corresponding to the uneven portion 19a (equivalent to the diffusion surface 1a in FIG. 5) is injection-molded. Thereby, the transmission type diffusion plate 21 can be easily obtained. A reflective film may be formed on the surface to form a reflective diffusion plate. Alternatively, the lower mold may be made of alumina 5 (see FIG. 3) in which the metal portion 2b (see FIG. 2) is dissolved.

As the optical resin, PC (polycarbonate), PMMA (polymethyl methacrylate) or the like can be used. Further, in order to improve the releasability and durability, the uneven portion 19a of the lower mold 19 may be coated with a suitable material.

According to the present embodiment, it is possible to easily form the transmission type diffusion plate 21 which can change the period of the unevenness.
Thus, as shown in FIG. 13 described above, the present invention can be used for a reflection type liquid crystal display device in which the reflection type liquid crystal panel 13 and the diffusion plate 21 are arranged to face each other. Further, as shown in FIG. 12, the present invention can be used for a transmission type liquid crystal display device using a transmission type liquid crystal panel.

Next, FIGS. 7 and 8 are side sectional views showing a method for manufacturing a diffuser plate according to the third embodiment. The diffusion plate 1 is formed by performing ion exchange at a predetermined position on the surface of a substrate 8 made of glass in an ion exchange step. As shown in FIG.
A mask 9 having through holes 9a at predetermined intervals is arranged on the substrate 8, and an ion exchange gas G is supplied to the substrate 8 through the through holes 9a.
Contact surface. As a result, the substrate 8 made of glass
Na and K in the gas are replaced with monovalent metals in the ion exchange gas G.

As a result, as shown in FIG.
An ion exchange portion 8a having a different refractive index from glass is formed at a position corresponding to a. Therefore, it is possible to obtain the transmission type diffusion plate 1 having a predetermined period of the refractive index difference on the surface.
The substrate 8 may be immersed in the ion exchange solution instead of the ion exchange gas G. However, when the substrate 8 is immersed in the liquid, the mask 9 and the substrate 8 need to be brought into close contact with each other without a gap, which requires a lot of man-hours. Therefore, it is more preferable to use the ion exchange gas G.

The mask 9 is made of an oxide such as alumina, and is formed by anodizing a metal substrate. 9 and 10 show a method of manufacturing the mask 9, similarly to FIG. 1 described above, as shown in FIG. 9, drawing by an electron beam on the surface of the mask substrate 7 made of aluminum in the pit forming step. The pits 10 are formed at a two-dimensional predetermined period by the fine processing means.

Next, as shown in FIG. 10, in the anodic oxidation step, the mask substrate 7 is placed on the anode, immersed in an acidic electrolytic solution such as oxalic acid, and a voltage is applied to anodic oxidize the mask substrate 7. I do. Alumina 5 is generated by anodic oxidation, and a crystal having hole 4 at the position where pit 10 is formed grows. As a result, the pores 4 composed of pores having a very high aspect ratio having a diameter of several nm to several hundreds of nm are formed by several tens of holes.
The porous alumina layer 3 arranged with a period of nm to several hundreds of nm is obtained. As described above, the diameter and period of the hole 4 may control the type of acid electrolyte solution, the concentration or the applied voltage.

Next, in the cutting step, the porous alumina layer 3 is cut along the dashed line D. Thereby, the mask 9 having the through holes 9a (see FIG. 7) formed of the holes 4 at a predetermined interval.
Is obtained. Therefore, it is possible to cycle the ion exchange unit 8a (see FIG. 8) can be easily obtained following diffuser 1 100 nm, reducing the cost of diffusion plates 1.

Further, similarly to the first embodiment, since the diffusion plate 1 is made of an inorganic material such as glass, it is possible to secure higher durability than an organic material conventionally used. Furthermore, by making the interval between the holes 4 variable according to the position of the mask substrate 7, it is possible to easily obtain the diffusion plate 1 having a different refractive index difference cycle depending on the position.

Therefore, as shown in FIG. 12, when the diffusion plate 1 is used for the backlight 15 of the liquid crystal display device,
The intensity of the light beam A1 emitted from the central portion of the diffuser 1 away from the light source 11 and the intensity of the light beam A2 emitted from the peripheral portion of the diffuser 1 closer to the light source 11 can be made equal.
As described above, the interval between the holes 4 can be controlled by changing the interval between the pits 10. Further, it is also possible to control the spacing of the holes 4 and variable according to the applied voltage of the mask substrate 7 in the position of the mask substrate 7.

In the anodic oxidation step, alumina 5 may be grown until the hole 4 penetrates to form a through hole. The oxide may be formed by anodic oxidation using a mask substrate made of a metal other than aluminum. However, by using a mask substrate made of inexpensive aluminum to produce alumina having excellent corrosion resistance, the mask can be formed. 9
This is more preferable because the cost of the mask 9 can be reduced and the mask 9 can be prevented from deteriorating during ion exchange.

[0052]

According to the present invention, a metal substrate is anodically oxidized to form a diffusion surface by irregularities formed by a boundary surface between a metal portion and an oxide. Therefore, a reflection type diffusion plate having a period of 100 nm or less can be easily formed. Thus, the cost of the diffusion plate can be reduced. Further, it is possible to secure a high durable than organic materials the diffusion plate is formed of an oxide or metal. Further, by controlling the positions of the holes, it is possible to easily obtain a diffuser plate having different periods of irregularities and refractive index differences depending on the positions.

When used in a display device in which a diffusion plate is arranged to face a transmission type liquid crystal display element, light emitted from a central portion of the diffusion plate distant from the light source and a peripheral portion of the diffusion plate close to the light source. Can be made uniform, and a display with less uneven brightness can be realized.

Further, according to the present invention, the diffusion plate can be obtained by anodizing the metal substrate to form a mold having irregularities composed of the interface between the metal portion and the oxide, and forming the diffusion plate. Can easily be obtained, and the cost of the diffusion plate can be reduced. This makes it possible to easily manufacture a display device in which a diffusion plate is arranged to face a reflective liquid crystal display element.

Further, according to the present invention, the cost of the diffusion plate or the mold can be reduced by forming the diffusion plate or the mold using inexpensive aluminum as the metal to be anodized. In addition, high reliability can be obtained by using a diffusion plate or a mold made of alumina having excellent corrosion resistance obtained by oxidizing aluminum.

Further, according to the present invention, since the interval between the holes is controlled to a desired interval, the diameter and the period of the holes can be accurately controlled. Further, crystals having various lattice shapes can be easily formed.

According to the present invention, the period of the refractive index difference is 1 by ion-exchanging the substrate using a mask having a through-hole formed by anodization.
A diffusion plate of 00 nm or less can be easily obtained, and the cost of the diffusion plate can be reduced. Further, since the diffusion plate is made of an inorganic material such as glass, it is possible to ensure higher durability than an organic material.

Further, it is possible to easily obtain a diffusing plate having a different period of the refractive index difference depending on the position, and to easily form a partial refractive index difference. Therefore, it is possible to easily manufacture a display device in which a diffusion plate is disposed opposite to a reflection type liquid crystal display element, and when a transmission type diffusion plate is disposed oppositely and used as a backlight of a liquid crystal display device, a diffusion device that is far from a light source is provided. The intensity of light emitted from the central portion of the plate and the peripheral portion of the diffuser plate close to the light source can be made uniform.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a pit forming step in a manufacturing process of a diffusion plate according to a first embodiment of the present invention.

FIG. 2 is a side sectional view showing an anodic oxidation step in a manufacturing process of the diffusion plate according to the first embodiment of the present invention.

3 is a side sectional view showing the immersion step of the manufacturing process of the diffuser plate of the first embodiment of the present invention.

FIG. 4 is a side cross-sectional view showing a reflection film forming step in the manufacturing process of the diffusion plate according to the first embodiment of the present invention.

FIG. 5 is a side cross-sectional view showing another immersion step of the manufacturing process of the diffusion plate according to the first embodiment of the present invention.

FIG. 6 is a side cross-sectional view showing a forming step in a manufacturing process of a diffusion plate according to a second embodiment of the present invention.

FIG. 7 is a side cross-sectional view illustrating an ion exchange step of a manufacturing process of a diffusion plate according to a third embodiment of the present invention.

FIG. 8 is a side sectional view showing a diffusion plate according to a third embodiment of the present invention.

FIG. 9 is a side cross-sectional view showing a pit forming step of a mask used in a manufacturing process of a diffusion plate according to a third embodiment of the present invention.

FIG. 10 is a side cross-sectional view showing an anodizing step and a cutting step of a mask used in a manufacturing process of a diffusion plate according to a third embodiment of the present invention.

FIG. 11 is a side sectional view showing a configuration of a transmission type liquid crystal display device using a reflection type diffusion plate.

FIG. 12 is a side sectional view showing a configuration of a transmission type liquid crystal display device using a transmission type diffusion plate.

FIG. 13 is a side sectional view showing a configuration of a reflection type liquid crystal display device using a transmission type diffusion plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 21 Diffusion plate 2, 7, 8 Substrate 3 Porous alumina layer 4 Hole 5 Alumina 6 Reflection film 9 Mask 10 Pit 11 Light source 12 Light guide plate 13 Liquid crystal panel 14 Reflection plate 15 Backlight

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takashi Hatano 2-3-13 Azuchicho, Chuo-ku, Osaka-shi F-term in Osaka International Building Minolta Co., Ltd. 2H042 BA03 BA15 BA20 2H091 FA31Z FB06 FB08 FC14 FC28 LA18 5G435 AA02 AA17 BB12 BB15 DD13 DD14 FF06 KK05

Claims (9)

[Claims] An oxide is grown by anodizing a substrate made of a metal, and one of the metal and the oxide is dissolved to form an uneven surface formed of a boundary surface between the metal and the oxide on the surface. A method for manufacturing a diffusion plate, comprising: 2. A substrate made of metal is anodically oxidized to grow an oxide, and one of the metal and the oxide is dissolved, so that the surface has an uneven surface formed of a boundary surface between the metal and the oxide. A method for manufacturing a diffusion plate, comprising: forming a mold and performing molding using the mold. 3. The process for producing a diffusion plate according to claim 1 or claim 2 wherein the substrate is characterized in that it consists of aluminum. 4. The method for manufacturing a diffusion plate according to claim 1, wherein an interval between the irregularities on the irregular surface is controlled. 5. A method in which a metal plate is anodized and a mask having through holes arranged at predetermined intervals is arranged on a substrate, and an ion exchange fluid is brought into contact with the substrate through the through holes. A method for producing a diffusion plate, wherein the surface of the substrate is ion-exchanged at predetermined intervals. 6. An anodization of a substrate made of a metal to grow an oxide, and by dissolving either the metal or the oxide, the surface has an uneven surface formed of a boundary surface between the metal and the oxide. A method for manufacturing a display device, comprising: forming a diffusion plate, and disposing the diffusion plate so as to face a display element. 7. An oxide is grown by anodizing a substrate made of a metal, and one of the metal and the oxide is dissolved, so that the surface has an uneven surface formed of a boundary surface between the metal and the oxide. A method for manufacturing a diffusion plate, comprising: forming a die, and disposing a diffusion plate formed by using the die to face a display element. 8. A method in which a metal plate is anodized and a mask having through holes arranged at predetermined intervals is arranged on a substrate, and an ion exchange fluid is brought into contact with the substrate through the through holes. Forming a diffusion plate obtained by ion-exchanging the surface of the substrate at predetermined intervals, and disposing the diffusion plate to face a display element. 9. The method according to claim 6, wherein the display element comprises a liquid crystal display element.