JP7459656B2 - Anti-reflection structure - Google Patents

Description

The present invention relates to an anti-reflection structure.

Conventionally, there is known a technique for forming an anti-reflection structure having a diffraction pattern or fine irregularities on the surface in order to prevent light reflection on the surfaces of optical disks such as CDs and DVDs, and on the surfaces of lenses, etc., and to prevent glare on the surfaces of displays, etc. (Patent Documents 1 and 2).

Patent No. 5162585 JP 2018-120047 Publication

The antireflection structure of Patent Document 1 does not necessarily have sufficient antireflection performance (antireflection properties).
On the other hand, the antireflection structure of Patent Document 2 requires a high wall portion with an average height of 13 μm in order to obtain excellent antireflection performance. Therefore, when an attempt is made to manufacture an antireflection structure using a mold, the releasability when transferring the uneven structure of the mold to the material of the antireflection structure is poor. Therefore, there have been problems in that the production efficiency of the antireflection structure is low and transfer defects from the mold are likely to occur. In addition, as the number of transfers increases, poor transfer causes further deterioration of mold releasability, which becomes a factor in deterioration of production efficiency and anti-reflection properties.
An object of the present invention is to provide an antireflection structure that has excellent antireflection performance and antiglare properties, has high production efficiency using a mold, and is less prone to transfer defects from the mold.

In order to achieve the above object, the present invention employs the following configuration.
[1] A container having a plurality of bottoms each having a substantially circular outer edge and a large protrusion that separates the plurality of bottoms from one another;
The average diameter of the smallest circle including the outer edge of the bottom is 500 nm or more and 20 μm or less,
A microstructure is formed on the bottom, the microprotrusions being clustered together at an average pitch of 10 nm or more and 500 nm or less;
The large protrusion has a multi-peaked structure in which the height of the upper surface changes irregularly along the outer edge portion,
An anti-reflection structure, wherein a maximum height H of the large protrusions is greater than a maximum height M of the small protrusions at the bottom.
[2] The anti-reflection structure according to [1], wherein the large protrusions have a maximum height H of 3 to 12 μm.
[3] The anti-reflection structure according to [1] or [2], wherein the maximum height M of the minute protrusions at the bottom is 0.1 μm or more and 2 μm or less.
[4] The anti-reflection structure according to any one of [1] to [3], wherein the ratio [H/M] of the maximum height H of the large protrusions to the maximum height M of the microprotrusions at the base is 3 to 120.
[5] The anti-reflection structure according to any one of [1] to [4], wherein the large protrusions have a microstructure formed on at least a part of their upper surface, the microstructure being made up of microprotrusions standing in clusters at an average pitch of 10 nm or more and 500 nm or less.
[6] The anti-reflection structure according to [5], wherein the maximum height N of the minute protrusions on the upper surface of the large protrusions is 0.1 μm or more and 2 μm or less.
[7] The anti-reflection structure according to any one of [1] to [6], wherein the diameter of the smallest circle including the outer edge of the bottom has a distribution having two or more peaks in increments of 0.1 μm.
[8] The anti-reflection structure according to [7], wherein the two or more peaks include a pair of peaks adjacent to each other and the difference in diameter is 0.3 μm or more.
[9] The anti-reflection structure according to any one of [1] to [8], which is made of a black material.
[10] The anti-reflection structure according to any one of [1] to [9], which has a layer of a black material on the surface opposite to the surface on which the large protrusions are formed.

The anti-reflection structure of the present invention has excellent anti-reflection and anti-glare properties, while also being highly efficient in production using a mold and being less susceptible to transfer defects from the mold.

1 is a SEM image of an anti-reflection structure 1 according to an example of the present invention, viewed downward in the height direction. 1 is a perspective SEM image of an antireflection structure 1 that is an example of the present invention. 3 is an enlarged SEM image of a part of FIG. 2. FIG. 2 is a schematic perspective view illustrating a partial structure of the antireflection structure 1. FIG. 3 is a schematic cross-sectional view of the antireflection structure 1 cut along the height direction of a large protrusion 3. FIG. 2 is a schematic cross-sectional view showing how light incident on the antireflection structure 1 is absorbed. FIG. 1 is an example of a distribution diagram showing the diameter distribution of the smallest circle that includes the outer edge of each bottom of an antireflection structure 1. FIG. 1 is a schematic cross-sectional view illustrating an example of a method for manufacturing a mold for manufacturing an antireflection structure 1. FIG. 10A to 10C are schematic cross-sectional views illustrating another example of a method for producing a mold for producing the antireflection structure 1. This is a SEM image of an example of a mold for manufacturing the antireflection structure 1, looking down along the height direction. 1 is a perspective SEM image of an example of a mold for producing an antireflection structure 1. 1A to 1C are schematic cross-sectional views showing a method for producing an anti-reflection structure 1 using a mold. FIG. 2 is a cross-sectional view showing an antireflection structure according to another embodiment of the present invention.

[Anti-reflection structure]
An antireflection structure according to an embodiment of the present invention has a plurality of bottom portions each having a substantially circular outer edge portion, and a large protrusion that defines the plurality of bottom portions from each other.
The average diameter of the smallest circle including the outer edge of the bottom is 500 nm or more and 20 μm or less.
Further, a microstructure consisting of microprotrusions clustered at an average pitch of 10 nm or more and 500 nm or less is formed on the bottom.
The large protrusion has a multimodal structure in which the height of the upper surface changes irregularly along the outer edge of the bottom.
The maximum height H of the large protrusion is higher than the maximum height L of the small protrusion at the bottom.

Hereinafter, an example of the antireflection structure according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an electron micrograph of an antireflection structure 1 according to an embodiment of the present invention viewed from above along the height direction, and FIG. 2 shows an electron micrograph of the antireflection structure 1 viewed diagonally from above.
Note that in this specification, the height direction means a direction perpendicular to the main surface of the antireflection structure 1. Further, the term "above" means a direction away from the main surface of the antireflection structure 1, and the term "bottom" means a direction approaching the main surface of the antireflection structure 1.

As shown in FIGS. 1 and 2, the anti-reflection structure 1 has a plurality of substantially circular base portions 2 and large protrusions 3 that separate adjacent base portions 2 from one another.
A fine structure consisting of upper surface micro-protrusions 5 standing in clusters is formed on part of the upper surface of the large protrusions 3. The fine structure consisting of the upper surface micro-protrusions 5 has a pin-holder structure in which the upper surface micro-protrusions 5 stand in clusters at high density.
It is preferable that the microstructure consisting of a group of upper surface microprotrusions 5 is formed mainly in the upper surface portion where the area of the large protrusions 3 is large, such as a portion separating bottom portions 2 that are slightly spaced apart, or a portion separating three or more bottom portions 2 from one another.

Figure 3 is an enlarged photograph of the large protrusion 3 in Figure 2, near where a microstructure consisting of a group of micro-protrusions 5 on the upper surface is formed. Also, Figure 4 is a schematic diagram showing one bottom 2 and the large protrusion 3 that separates that bottom 2 from the other bottoms 2, and Figure 5 is a schematic cross-sectional view of the anti-reflection structure 1 cut along the height direction. Note that Figure 5 and Figure 6 described below show an array of bottoms 2 in which the diameter of the smallest circle that includes the outer edge 2a is approximately the same.

1 and 3, the outer edge 2a of the bottom 2 is substantially circular. That the outer edge 2a, which is the outline of the bottom 2, is substantially circular means that the shape of the outer edge 2a can be approximated to a circle or an ellipse when viewed down in the height direction (a circle or ellipse close to that shape can be assumed).
3 to 5, a microstructure consisting of a group of bottom microprotrusions 4 is formed on each bottom 2. The microstructure consisting of the bottom microprotrusions 4 has a pin-frog structure in which the bottom microprotrusions 4 are grouped together at a high density.

The large protrusions 3 are formed to rise between the outer edge 2a of the bottom 2 and the outer edge 2a of the other bottom 2. The outer edge 2a side of each large protrusion 3 may rise vertically along the outer edge 2a, or may have a larger or smaller diameter than the outer edge 2a as it goes up. For ease of manufacture and to increase anti-reflection properties, it is preferable that the diameter is larger than the outer edge 2a as it goes up, as shown in Figure 5.

As shown in FIGS. 3 and 4, the large protrusion 3 has a multimodal structure in which the height of the upper surface changes irregularly along the outer edge 2a of the bottom 2. As shown in FIGS.
The large protrusion 3 surrounding the outer edge 2a may be continuous while changing the height along the outer edge 2a, or may be discontinuous with a portion completely missing. When a part of the large protrusion 3 surrounding the outer edge 2a is completely missing and discontinuous, the two adjacent bottom parts 2 communicate at that part.

The average (hereinafter referred to as "average bottom diameter R") of the diameter R1 of the smallest circle including the outer edge 2a of the bottom 2 (hereinafter referred to as "bottom diameter R1") is 500 nm or more and 20 μm or less.
The average diameter R of the bottom portion is preferably 1 μm or more and 10 μm or less, and more preferably 1.5 μm or more and 6.0 μm or less.
When the average bottom diameter R is 500 nm or more and 20 μm or less, regular reflection of incident light is sufficiently prevented, and the antireflection properties achieved by the antireflection structure 1 can be further improved.

The average base diameter R is determined as follows.
The antireflection structure 1 is observed under an electron microscope looking down along the height direction, a square region containing 100 to 200 bases 2 is arbitrarily set, and the base diameter R1 is measured for each of the bases 2 that cross two diagonals of the square, and the arithmetic average of these base diameters R1 is calculated.

The average pitch P1 of the bottom microprojections 4 standing in clusters on the bottom 2 (hereinafter referred to as the "bottom microprojection average pitch P") is 10 nm or more and 500 nm or less.
The average bottom minute projection pitch P is preferably 50 nm or more and 300 nm or less, and more preferably 80 nm or more and 200 nm or less.
When the average bottom microprotrusion pitch P is 10 nm or more and 500 nm or less, incident light that reaches the bottom 2 is easily taken into the fine structure consisting of the bottom microprotrusions 4, and reflection of the incident light can be prevented.

The average pitch P of the bottom microprotrusions is determined as follows.
A 10 mm x 10 mm sample for surface observation is prepared by cutting out the antireflection structure 1 at an arbitrary position using a microtome or CP processing (ion milling). The produced surface observation sample was observed with an electron microscope, and in each of the ten bottom parts 2, any ten bottom microprotrusions 4 and the pitch P1 of the adjacent bottom microprotrusions 4 (the top of the adjacent bottom microprotrusions 4) were observed. (distances between vertices) are measured and determined as the arithmetic mean of their pitches P1.

The average pitch Q1 of the upper surface microprotrusions 5 standing in clusters on the upper surface of the large protrusions 3 (hereinafter referred to as the "average upper surface microprotrusion pitch Q") is preferably 10 nm or more and 500 nm or less.
The upper surface microprotrusion average pitch Q is more preferably 50 nm or more and 300 nm or less, and further preferably 80 nm or more and 200 nm or less.
When the upper surface microprotrusion average pitch Q is 10 nm or more and 500 nm or less, light incident on the upper surface of the large protrusions is easily taken into the fine structure consisting of the upper surface microprotrusions 5, and reflection of the incident light can be prevented.

The average upper surface minute protrusion pitch Q is calculated as follows.
An arbitrary position of the antireflection structure 1 is cut out by a microtome or CP processing (ion milling) to prepare a 10 mm x 10 mm surface observation sample. The top surfaces of the 10 large protrusions 3 on which a microstructure consisting of upper surface microprotrusions 5 is formed in the prepared surface observation sample are observed by an electron microscope.
For each of the 10 large protrusions 3 observed, the pitch Q1 (the distance between the tops (apexes) of adjacent upper surface microprotrusions 5) of any 10 upper surface microprotrusions 5 and their adjacent upper surface microprotrusions 5 is measured, and the arithmetic average of these Q1s is calculated.
In addition, if it is not possible to extract 10 large protrusions 3 each having a fine structure formed from upper surface microprotrusions 5 from one surface observation sample, multiple surface observation samples are prepared by cutting out the samples at different positions, and 10 large protrusions 3 each having a fine structure formed from upper surface microprotrusions 5 are extracted.

The maximum height H of the large protrusion (hereinafter referred to as "large protrusion maximum height H") is larger than the maximum height M of the bottom microprotrusion 4 (hereinafter referred to as "bottom microprotrusion average height M").
The ratio [H/M] of the maximum height H of the large protrusion to the maximum height M of the bottom microprotrusion is preferably 3 to 120, more preferably 4 to 30, and still more preferably 5 to 12. preferable.
When the ratio [H/M] is 3 to 120, a good result is obtained due to the synergistic effect of the anti-reflection effect against vertical or angular incident light by the large projections and the effect of minimizing reflection by the bottom micro projections. Provides anti-reflection properties.

The maximum height H of the large protrusion is preferably 3 to 12 μm, more preferably 4 to 10 μm, and even more preferably 5 to 8 μm.
When the maximum height H of the large protrusions is 3 μm or more, specular reflection of incident light can be sufficiently prevented, and the antireflection properties of the antireflection structure 1 can be further enhanced. When the maximum height H of the large protrusions is 12 μm or less, it is easy to maintain the mechanical strength of the antireflection structure 1. Further, when manufactured by a manufacturing method using a mold described below, the mold releasability is excellent and production efficiency is high. In addition, transfer defects from the mold are less likely to occur.

The maximum height H of the large protrusion is determined as follows.
A cross-sectional sample is prepared by cutting out the anti-reflection structure 1 at an arbitrary different cross-section along the height direction using a microtome or CP processing (ion milling). For each cross-sectional sample, 10 to 20 points were observed using an electron microscope in a range including 3 to 10 bottom parts 2, and the height H1 of the highest large protrusion 3 within each observation range was measured. Calculated as the arithmetic mean of

H1 in the cross-sectional sample is determined as follows. That is, the distance between the top (apex) of the highest large protrusion 3 within the observation range of the cross-sectional sample and the horizontal line at the lowest position of the large protrusion 3 is determined as H1.

The maximum height M of the bottom minute projections is preferably 0.1 μm or more and 2 μm or less, more preferably 0.2 to 1.5 μm, and even more preferably 0.3 to 1.0 μm.
When the maximum height M of the bottom microprotrusions is 0.1 μm or more, the refractive index changes continuously and gradually from the air layer to the substrate, which tends to produce anti-reflection properties. Also, when the maximum height M of the bottom microprotrusions is 2 μm or less, the mechanical strength of the anti-reflection structure 1 tends to be maintained.

The maximum height M of the bottom microprotrusion is determined as follows.
A cross-sectional sample is prepared by cutting out the anti-reflection structure 1 at an arbitrary different cross-section along the height direction using a microtome or CP processing (ion milling). Regarding the cross-sectional sample, 10 to 20 points are observed using an electron microscope in a range including 1 to 5 bottom parts 2, and the height M1 of the highest bottom microprotrusion 4 in each observation range is measured. Obtained as the arithmetic mean.

M1 in each cross-sectional sample is determined as follows. That is, the distance between the top (apex) of the highest bottom microprotrusion 4 within the observation range of the cross-sectional sample and the horizontal line of the lowest position of the bottom microprotrusion 4 is determined as M1.

The maximum height N of the upper surface microprotrusion 5 (hereinafter referred to as "upper surface microprotrusion maximum height N") is preferably 0.1 μm or more and 2 μm or less, more preferably 0.2 to 1.5 μm. , more preferably 0.3 to 1.0 μm.
When the maximum height N of the upper surface microprotrusions is 0.1 μm or more, the refractive index changes continuously and gently from the air layer toward the base material, so that antireflection properties are likely to occur. Further, when the maximum height N of the upper surface microprotrusions is 2 μm or less, it is easy to maintain the mechanical strength of the antireflection structure 1.

The maximum height N of the upper surface microprotrusions is determined as follows.
A cross-sectional sample is prepared by cutting out an arbitrary different cross-section of the anti-reflection structure 1 along the height direction using a microtome or CP processing (ion milling). The upper surfaces of the 10 large protrusions 3 on which the fine structure consisting of the upper surface microprotrusions 5 was formed in the produced cross-sectional sample are observed using an electron microscope.
For each of the ten large protrusions 3 observed, the height N1 of the highest upper surface microprotrusion 5 is measured, and the arithmetic mean of these N1 is determined.
In addition, if it is not possible to extract ten large protrusions 3 in which a fine structure consisting of upper surface microprotrusions 5 is formed with one cross-sectional sample, multiple cross-sectional samples cut out with different cross sections are prepared and the upper surface micro-protrusions 5 are extracted. Ten large protrusions 3 having a fine structure formed thereon are extracted, and N1 of each is measured.

N1 in each large protrusion 3 is determined as follows. That is, the distance between the top (vertex) of the highest upper surface microprotrusion 5 in the large protrusion 3 having the upper surface microprotrusion 5 and the horizontal line of the lowest position of the upper surface microprotrusion 5 is determined as N1.
Note that when selecting the highest peak (apex), upper surface microprotrusions 5 where there is no upper surface microprotrusion 5 adjacent to the left or right side are not considered.

Among the above-mentioned measurement methods, in a measurement method using a cross-sectional sample, if the uneven structure is crushed when cutting out the cross-section of the antireflection structure 1, the following alternative method may be applied.
That is, first, a resin composition is applied to the surface of the antireflection structure 1 on which the large protrusions 3 and the like are formed and then cured to prepare a sample onto which a concave-convex structure including the bottom microprotrusions 4 and the top surface microprotrusions 5 is transferred, or a sample in which the concave-convex structure is protected by the resin composition. Next, a cross section along the height direction of the sample is cut out.
Then, the pitch and height of the target portion of the antireflection structure 1 or the transferred portion are measured.

For example, when determining the average height M of the bottom microprotrusions, ten arbitrary protrusions corresponding to the bottom 2 are observed in the sample onto which the uneven structure has been transferred. Then, the heights of the concave portion (or the convex portion next to it) to which any ten arbitrary bottom microprotrusions 4 have been transferred in each convex portion and the concave portion adjacent to it (or the convex portion next to it) are measured, and It is calculated as the arithmetic mean of the heights of
Other values (maximum height H of large protrusions, maximum height N of small protrusions on the top surface) can also be determined using a sample onto which the uneven structure has been transferred in the same manner.

The mechanism by which reflection is prevented in the antireflection structure 1 of this embodiment will be described with reference to FIG.
As shown in Figure 6, a light ray L1 that enters the anti-reflection structure 1 and reaches the bottom 2 directly is suppressed from being reflected and is taken into the anti-reflection structure 1 due to the anti-reflection property (moth-eye effect) of the group of bottom microprotrusions 4, which has a refractive index that changes continuously and gradually from the air layer toward the substrate.
Furthermore, like light rays L2 and L3, light that reaches the side of the large protrusion 3 is reflected by the side of the large protrusion 3 and reaches the bottom 2, where reflection is suppressed by the moth-eye effect of the cluster of bottom micro-protrusions 4 and the light is taken into the anti-reflection structure 1.

As with light ray L4, light that reaches the upper surface of the large protrusion 3 is reflected, but as with light ray L5, light that reaches the upper surface of the large protrusion 3 having a group of upper surface microprotrusions 5 is suppressed in reflection by the moth-eye effect of the group of upper surface microprotrusions 5 and is taken into the anti-reflection structure 1.
In addition, the large projections 3 having a multi-peaked structure can be manufactured by a manufacturing method using a mold described below, which reduces the gap area between adjacent bottom portions 2 and narrows the width of the upper surface of the large projections 3 to the limit.
Therefore, it is possible to extremely reduce the probability that a light ray, like the light ray L4, hits the upper surface of the large protrusion 3 and is reflected.

Furthermore, if a fine structure consisting of upper surface microprotrusions 5 standing in clusters is formed on the upper surface of the large protrusions 3 as in this embodiment, light rays that strike the upper surface of the large protrusions 3 can also be taken in by the antireflection structure 1. If a fine structure consisting of upper surface microprotrusions 5 standing in clusters is formed on the upper surface of the large protrusions 3, particularly in the portion having a large area, the effect is great.
According to a manufacturing method using a mold described later, a fine structure consisting of upper surface minute protrusions 5 can be easily formed on the upper surface of the large protrusions 3, particularly on the portion having a large area.

The bottom diameter R1 of each bottom portion 2 may be the same or different. In order to close-pack the bottom parts 2 in the two-dimensional plane of the anti-reflection structure 1 and to make the area of the upper surface of the large protrusion 3 as small as possible, it is preferable that the bottom diameter R1 of each bottom part 2 is the same. .

However, if the arrangement of the bottoms 2 becomes regular due to this close packing, optical interference may occur in the light incident on the antireflection structure 1. From the viewpoint of preventing this optical interference, it is preferable to have bottoms 2 with bottom diameters R1 different from one another, as in the examples shown in Figures 1 to 3.
The bottom diameter R1 of the bottom portion 2 preferably has a distribution having two or more peaks at intervals of 0.1 μm, and more preferably has a distribution having three or more peaks.

The distribution of the bottom diameter R1 of the bottom portion 2 is determined as follows.
Observe the antireflection structure 1 with an electron microscope while looking down in the height direction, arbitrarily set a square area containing 100 to 200 bottoms 2, and for each bottom 2 included in the area, Measure the bottom diameter R1 of each.
Then, as shown in FIG. 7, a distribution map is created in which the diameter is plotted on the horizontal axis and the number of bottom portions 2 having the bottom diameter R1 is plotted on the vertical axis in increments of 0.1 μm.
FIG. 7 shows a distribution map in which the bottom diameter R1 is determined in 0.1 μm increments: (a) a distribution diagram with two peaks, and (b) a distribution diagram with three peaks. Ta. Note that FIG. 7(a) is a distribution diagram of the bottom diameter R1 of the antireflection structure of Example 1, which will be described later, and FIG. 7(b) is a distribution diagram of the bottom diameter R1 of the antireflection structure of Example 2, which will be described later. It is a diagram.

When the bottom diameter R1 has a distribution having two or more peaks at intervals of 0.1 μm, it is preferable that the two or more peaks include a pair of adjacent peaks whose diameter difference is 0.3 μm or more. It is more preferable that the diameter difference between the pair of adjacent peaks is all 0.3 μm or more.

The difference in diameter between a pair of adjacent peaks is preferably 0.3 μm or more, more preferably 0.4 μm or more, and even more preferably 0.5 μm or more.
If the difference in diameter between a pair of adjacent peaks is 0.3 μm or more, the arrangement of the bottom portion 2 will not be too regular and will have appropriate randomness, which will facilitate optical interference. It can be prevented.

The difference in diameter between a pair of adjacent peaks is preferably 2.0 μm or less, more preferably 1.5 μm or less, and even more preferably 1.0 μm or less.
If the difference in diameter between a pair of adjacent peaks is 2.0 μm or less, it is easy to arrange the bottom portions 2 in a high density on the two-dimensional plane of the antireflection structure 1, so that the antireflection properties can be further improved. Can be done.

The ratio of the total area of the bottom portion 2 to the total area of the antireflection structure 1 is preferably from 40 to 85%, more preferably from 50 to 85%, and even more preferably from 55 to 85%.
From the viewpoint of further enhancing these effects, the higher the upper limit of the above range, the better. However, it is impossible to achieve 100%, and about 85% can be said to be the practical limit.

The ratio of the total area of the bottom portion 2 to the total area of the antireflection structure 1 is determined as follows.
The antireflection structure 1 is observed with an electron microscope while looking down along the height direction, and a square area containing 100 to 200 bottoms 2 is arbitrarily set.
The total area of the bottom portions 2 in this square area is determined by visually observing or image processing the area of each bottom portion 2. If a part of the large protrusion 3 is missing and adjacent bottom parts 2 are in communication with each other, the area is determined on the assumption that the large protrusion 3 continues to exist in the missing part.

It is preferable that the total area occupancy of the area in which the fine structure consisting of clustered bottom microprotrusions 4 is formed with respect to the total area (100%) of the bottom part 2 is 60 to 100%, and 65 to 100%. More preferably, 70 to 100% is even more preferable.
By setting the area occupancy of the region in which the fine structure is formed to be 70% or more, the light rays reaching the bottom part 2 can be taken into the antireflection structure 1 more reliably.

The percentage of the total area of the region in which the microstructure consisting of the standing bottom minute projections 4 is formed relative to the total area (100%) of the bottom 2 is calculated as follows.
The antireflection structure 1 is observed with an electron microscope looking down along the height direction, and a square region containing 100 to 200 bases 2 is arbitrarily set.

The total area of the bottom 2 in this square region is the sum of the areas of the individual bottoms 2 determined by visual inspection or image processing. When adjacent bottoms 2 are connected due to a loss of a portion of the large protrusions 3, the area is determined on the assumption that the large protrusions 3 continue to exist in the missing portion. In addition, the total area of the region in this square region where a fine structure consisting of clusters of bottom microprotrusions 4 is formed is the sum of the areas in each bottom 2 where a fine structure consisting of clusters of bottom microprotrusions 4 is formed, determined by visual inspection or image processing.

The overall shape of the antireflection structure 1 is not particularly limited, and may be, for example, film-like, sheet-like, plate-like, block-like, lens-like, spherical, or the like. The antireflection structure 1 can have an appropriate specific shape depending on its intended use.

From the viewpoint of improving anti-glare properties, the antireflection structure 1 is preferably partially or entirely formed of a dark-colored material, and more preferably entirely formed of a dark-colored material. Among dark colors, black is particularly preferred.
By making part or all of the antireflection structure 1 dark-colored, especially black, it becomes easier to absorb the light rays incident on the antireflection structure 1, and the anti-glare properties are enhanced.

[Method of manufacturing anti-reflection structure]
The anti-reflection structure according to the present invention can be mass-produced, for example, by using a mold produced as follows.
FIG. 8 shows one example of a method for manufacturing the mold 10, and FIG. 9 shows another example.

In both the methods of Fig. 8 and Fig. 9, the surface of the substrate 21 that is the material of the mold 10 may be flat or rough. The rough surface may be an uneven structure produced by a known method such as blasting, or dry etching using an existing photomask. In order to simplify the process, it is preferable that the surface of the substrate 21 is roughened in advance by a known method such as blasting. The surface of the substrate 21 is preferably roughened to an arithmetic mean roughness Ra of about 0.01 to 0.5 µm, and more preferably about 0.05 to 0.45 µm.
By previously roughening the surface of the substrate 21, a large number of convex micro-holes 14 corresponding to the bottom micro-projections 4 can be easily formed.

The substrate 21 may be a single base material or a composite base material. Examples of the single base material include silicon, silicon carbide, glass, and quartz. Examples of the composite base material include a base material in which a film of Si or SiC is formed on a base material. The material of the base material is not particularly limited, and glass (quartz, alkali glass, non-alkali glass, sapphire), ceramics, and metals (iron, stainless steel, nickel, etc.) can be used. Among these, silicon is preferred because it has good processability and is widely used as an etching target.
The surface of the substrate 21 is not limited to a flat surface, and may have a curved surface.

(Example of manufacturing method of the first mold)
In the method of Fig. 8, first, as shown in Fig. 8(a), a large number of particles 22 are scattered on the surface of a substrate 21, and the particles 22 are densely packed so that they are in contact with each other. However, the particles 22 are prevented from piling up on other particles 22, so that a layer of particles 22 is formed on the surface of the substrate 21. The shape of each particle 22 may be a perfect sphere, or a shape other than a perfect sphere, such as a spheroid. The diameter of each particle 22 is slightly larger than the bottom average diameter R of the bottom 2 of the anti-reflection structure 1.

Materials for the particles 22 include metals such as Al, Au, Ti, Pt, Ag, Cu, Cr, Fe, Ni, Si, and W, and metals such as SiO ₂ , Al ₂ O ₃ , TiO ₂ , MgO ₂ , and CaO ₂ . Examples include metal oxides. Other examples include nitrides such as SiN and TiN, carbides such as SiC and WC, organic polymers such as polystyrene and polymethyl methacrylate, other semiconductor materials, and inorganic polymers. Furthermore, at least two of these materials can also be used in combination. Among the above-mentioned materials, inorganic oxides are preferable from the viewpoint of having a high degree of freedom in etching selectivity with respect to the substrate 21. Moreover, among the inorganic oxides, SiO ₂ (silica) is more preferable.

Next, as shown in FIG. 8(b), when the substrate 21 covered with particles 22 is processed with etching gas plasma G (ions, radicals, gas, etc.) generated in the etching chamber, the particles 22 prevent etching. The substrate 21 is etched by the etching gas plasma G that functions as a mask and passes through the gaps between the particles 22 . At this time, the etching is performed under conditions that make it difficult for the particles 22 to be etched as much as possible. As a result, relatively narrow grooves 13 are formed in portions of the substrate 21 corresponding to the gaps between the particles 22 .

In order to create conditions in which the particles 22 are less likely to be etched, the type of gas of the etching gas plasma G, gas flow rate, gas ratio, pressure, bias power, etc. may be appropriately selected.
For example, when the substrate 21 is silicon and the particles 22 are SiO ₂ , the gas species used in the etching gas plasma G include Ar, SF ₆ , F ₂ , CF ₄ , C ₄ F ₈ , C ₅ F ₈ , C _{2F6 , C3F6} , _{C4F6 , CHF3} , _CH2F2 , _{CH3F , C3F8 , Cl2 , CCl4 , SiCl4} , _BCl2 , _BCl3 , _BC2 , Br ₂ , _Br3 , HBr, _CBrF3 , HCl, _CH4 , _NH3 , _O2 , _H2 , _N2 , CO, _CO2 can be used. Among them, Ar, SF ₆ , CF ₄ , C ₂ F ₆ , C ₃ F 6 , C ₄ F ₆ , CHF ₃ , Cl ₂ , BCl _{3 ,} CH ₄ , One or more gases selected from the group consisting of NH ₃ , O ₂ , H ₂ , and N ₂ are preferred.

Note that if the etching is performed under conditions where the particles 22 are relatively easily etched, the grooves 13 tend to have a wide overall width and a uniform depth.
On the other hand, if etching is performed under conditions that make it difficult for particles 22 to be etched as much as possible, the depth of the grooves 13 will be very shallow in areas where adjacent particles 22 are in contact, and in areas where there is a certain distance between adjacent particles 22. For example, in a portion surrounded by three or more particles 22, the groove 13 becomes deeper. Therefore, the groove 13 according to this example of the manufacturing method has a multimodal structure in which the depth varies irregularly along the contour of the particle 22.

For example, if the particles 22 are all the same size and hexagonally close-packed, there will be a portion around one particle 22 where six other particles 22 are in contact. In between, there will be a portion surrounded by the particle 22 in question and two other particles 22, that is, a portion where there is a certain distance between adjacent particles 22. Therefore, the groove 13 in this case will have a multi-peaked structure with six deep portions along the contour of one particle 22 and six shallow portions between them.

8C, the particles 22 are removed from the etched surface of the substrate 21. Thereafter, a roughening process is performed in which the surface of the substrate 21 is roughened to form an upper rough surface 24, and the bottom of the groove 13 is roughened to form an inner groove rough surface 25.
When the substrate 21 is a silicon substrate, prior to the surface roughening treatment, an etching treatment is performed to remove an oxide film from the silicon surface, and then the exposed silicon surface is roughened by etching to perform the surface roughening treatment.

In order to obtain etching conditions that can remove the silicon oxide film, the type of etching gas, the gas flow rate, the gas ratio, the pressure, the bias power, and the like may be appropriately selected.
As _the etching gas, _Ar , _{SF6 , CF4} , _{C2F6, C3F6 , C4F6} , _CHF3 , _Cl2 , _CH4 , _NH3 , _O2 , _H2 , and _N2 can be used. Among them, one or more gases selected from the group consisting of Ar, _NH3 , _O2 , _{H2 ,} and _N2 , or a mixed gas of these gases further containing one or more gases selected from the group consisting of _SF6 , _CF4 , _C2F6 , _C3F6 , _C4F6 , _{and CHF3 ,} is preferred.

In order to obtain etching conditions that roughen the exposed silicon surface, the type of etching gas, gas flow rate, pressure, bias voltage, etc. may be appropriately selected.
SF ₆ , Cl ₂ , and HCl can be used as the etching gas. Cl ₂ is preferred because it has high etching properties on Si-based substrates and is generally widely used. Further, at least one kind selected from the group consisting of Ar, O ₂ , H ₂ and N ₂ may be added as a diluent gas. The diluent gas is used to make the etching gas uniform (to improve the processing distribution of the Si-based substrate) and to adjust the etching rate of the Si-based substrate.

Note that if the upper rough surface 24 and the groove inner rough surface 25 have already been formed when the particles 22 are removed, the roughening process may be omitted. Even if surface roughening treatment is not performed, residues originating from the particles 22 may remain, or the etching gas that has flowed under the particles 22 during etching may unevenly etch the surface of the substrate 21. may have a roughened surface.

Finally, as shown in FIG. 8D, the rough substrate 21 on which the rough upper surface 24 and the rough inner groove surface 25 are formed is processed by an etching gas plasma G generated in an etching chamber.
Due to the roughness, differences occur in the etching rates at the upper rough surface 24 and the inner groove rough surface 25 of the substrate 21, so as the etching proceeds, a large number of convex microholes 14 corresponding to the bottom microprotrusions 4 are formed on the surface of the antireflection structure 1. Also, a large number of groove microholes 15 corresponding to the upper surface microprotrusions 5 are formed on the bottom of the groove 13.
This results in the desired mold 10.

In order to obtain etching conditions that allow micropores to be formed in the roughened portion, the type of etching gas, gas flow rate, gas ratio, pressure, bias power, etc. may be appropriately selected.
As the etching gas, _{at least} one gas selected from the group _consisting of _CF4 , _{C4F8 , C5F8 , C2F6 , C3F6} , _C4F6 , CHF3, _CH2F2 , _CH3F , _C3F8 , _SF6 , _{Cl2 ,} HCl, _SiCl4 , _BCl2 , _BCl3 , _CCl4 , and _BC2 , or a mixed gas of two or more gases can be used. In _addition , as a dilution gas, at least one gas selected from the group consisting of Ar, _H2 , and _N2 may be further added. Among them, a mixed gas containing _SF6 or _Cl2 is preferable because it is easy to control the diameter and depth of the microhole.

In each etching step, the flow rate of the etching gas differs depending on the capacity of the dry etching chamber and the size of the Si-based substrate to be processed, and therefore must be adjusted appropriately.
The ratio of the flow rate (sccm) of the etching gas to the flow rate (sccm) of the dilution gas (etching gas/dilution gas) is, for example, 100/0 to 10/90.
When the size of the Si-based substrate is large, the distribution of the etching gas within the surface of the Si-based substrate tends to deteriorate. In that case, it is preferable to increase the ratio of the dilution gas in order to reduce the fluctuation range of the etching rate of the entire Si-based substrate.

(Example of manufacturing method of the second mold)
9(a), a large number of resist films 23 patterned by known photolithography or nanoimprinting are first arranged. Each resist film 23 has a substantially circular shape when viewed from above, that is, a circular or elliptical shape or a shape that can be approximated to these when viewed from above in the height direction (a circular or elliptical shape close to this shape can be assumed).

Since the resist film 23 has a cylindrical (elliptical cylinder) shape, if it is densely spread so as to contact each other, it will be in line contact in the z direction, and gaps are unlikely to occur even as etching progresses. Therefore, it is spread densely within a range where it does not contact each other.
The distance between the resist films 23 and the adjacent resist films 23 (the distance at the closest portions) is preferably 1 to 40% of the average bottom diameter R of the bottom 2 of the antireflection structure 1, more preferably 3 to 30%, and even more preferably 5 to 20%.
The diameter of each resist film 23 is slightly larger than the bottom diameter R 1 of each bottom portion 2 of the anti-reflection structure 1 .

Examples of the material for the resist film 23 include photoresist made of an organic-inorganic hybrid material. A material, such as a known photosensitive functional polymer material, that allows suitable patterning and is suitable as a mask in the etching process is used. A liquid material containing a resist material used in photolithography is, for example, a mixture whose main components are a polymer, a photosensitizer, an additive, and a solvent. In addition, the resist film 23 may be a hard mask made of an inorganic compound formed by photolithography and reactive ion etching. For example, the resist film 23 may be formed by high-density plasma CVD or LP-CVD. It may be formed of a silicon nitride film or a silicon oxide film.
Among the above materials, photoresist is preferable as the material for the resist film 23 because it allows easy patterning of an etching mask.

Next, as shown in FIG. 9(b), when the substrate 21 covered with the resist film 23 is processed with an etching gas plasma G generated in an etching chamber, the resist film 23 functions as a mask to prevent etching, and the substrate 21 is etched by the etching gas plasma G blown through the gaps between the resist films 23. At this time, the etching is performed under conditions that make etching of the resist film 23 as difficult as possible. As a result, a relatively narrow groove 13 is formed in the portion of the substrate 21 that corresponds to the gaps between the resist films 23.

In order to make the resist film 23 less susceptible to etching, the type of gas, gas flow rate, gas ratio, pressure, bias power, etc. of the etching gas plasma G may be appropriately selected.
For example, when the substrate 21 is silicon and the resist film 23 is photoresist, the following etching gases can be used: Ar, _SF6 , _F2 , _CF4 , _C4F8 , _{C5F8 , C2F6, C3F6, C4F6, CHF3, CH2F2, CH3F , C3F8 , Cl2 , CCl4 , SiCl4 , BCl2 , BCl3} , _{BC2 , Br2} , _{Br3 , HBr , CBrF3 ,} HCl, _CH4 , _NH3 , _O2 , _H2 , _N2 , CO, and _CO2 . Among these, one _or more gases selected from _{the group consisting of Ar, SF6, CF4, C2F6, C3F6 , C4F6 , CHF3 , Cl2 , BCl3} , CH4, _NH3 , _O2 , _H2 , _{and N2} are preferred because _they are commonly and widely used gases.

Note that if the resist film 23 is etched under conditions that make it relatively easy to be etched, the groove 13 will have a wide width and a uniform depth as a whole.
On the other hand, if the resist film 23 is etched under conditions that make it as difficult as possible to etch the resist film 23, the depth of the groove 13 will be very shallow in the areas where the adjacent resist films 23 are close, and there will be a certain amount of space between the adjacent resist films 23. The groove 13 becomes deeper in a part where there is a distance, for example, in a part surrounded by three or more resist films 23. Therefore, the groove 13 according to this manufacturing method example has a multimodal structure in which the depth changes irregularly along the contour of the resist film 23, similarly to the first type manufacturing method example.

Subsequently, as shown in FIG. 9(c), the resist film 23 is removed from the etched surface of the substrate 21. Thereafter, a roughening process is performed to roughen the surface of the substrate 21 to form an upper rough surface 24 and to roughen the bottom of the groove 13 to form an inner rough surface 25.
When the substrate 21 is a silicon substrate, an etching process is performed to remove an oxide film from the silicon surface prior to the roughening process. Thereafter, the exposed silicon surface is roughened by etching. The etching conditions in this case are the same as those described in the first mold manufacturing method example.
Note that, similarly to the first mold manufacturing method example, if the upper rough surface 24 and the groove inner rough surface 25 are already formed when the resist film 23 is removed, the roughening process is omitted. It's okay.

Finally, as shown in FIG. 9D, the rough substrate 21 on which the rough upper surface 24 and the rough inner groove surfaces 25 are formed is processed by an etching gas plasma G generated in an etching chamber.
Due to the roughness, differences occur in the etching rates at the upper rough surface 24 and the inner groove rough surface 25 of the substrate 21, so as the etching proceeds, a large number of convex microholes 14 corresponding to the bottom microprotrusions 4 are formed on the surface of the antireflection structure 1. Also, a large number of groove microholes 15 corresponding to the upper surface microprotrusions 5 are formed on the bottom of the groove 13.
This results in the desired mold 10.
The etching conditions for forming the micropores in the roughened portion are the same as those explained in the example of the manufacturing method for the first mold.

An example of the mold 10 manufactured by the method described in the first mold manufacturing method example is shown in FIGS. 10 and 11. FIG. 10 is an electron micrograph of an example of the manufactured mold 10 viewed from above in the height direction, and FIG. 2 is an electron micrograph of an example of the manufactured mold 10 viewed from diagonally above.
In FIGS. 10 and 11, it is observed that the convex portions 12 are clustered together, and a fine structure consisting of a large number of convex microholes 14 is formed on the upper surface of the convex portions 12. The part that looks black on the outside of the convex part 12 is the groove 13.

(Method of manufacturing an anti-reflection structure using a mold)
The antireflection structure 1 is obtained by transferring the uneven structure of the mold 10 produced by the above-mentioned method or the like to the material of the antireflection structure 1 by a known technique such as nanoimprinting, press molding, or injection molding.

As shown in FIG. 12, the part corresponding to the upper surface of the convex part 12 of the mold 10 becomes the bottom part 2 of the antireflection structure 1, and the bottom part 2 has bottom microprotrusions 4 corresponding to the convex micropores 14 of the mold 10. are formed in large numbers.
Further, the portion corresponding to the groove 13 of the antireflection structure 1 becomes the large protrusion 3 of the antireflection structure 1, and the upper surface of the large protrusion 3 has a large number of upper surface microprotrusions 5 corresponding to the groove microholes 15 of the mold 10. It is formed.

The material of the anti-reflection structure 1 is preferably a synthetic resin. Examples of synthetic resins include known synthetic resins such as thermoplastic resins, thermosetting resins, and photocurable resins. Suitable materials include synthetic resins such as polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), triacetyl cellulose (TAC), polycarbonate (PC), cycloolefin polymer (COP), cycloolefin copolymer (COC), and acrylic resin. The synthetic resin may be transparent or black.

The antireflection structure 1 can obtain a high antireflection effect even if the height of the large protrusions 3 is reduced. Therefore, the depth of the grooves 13 in the mold 10 can be reduced, and the releasability when the concave-convex structure of the mold 10 is transferred to the material of the antireflection structure 1 can be improved.
Therefore, the production efficiency of the antireflection structure 1 can be improved and transfer defects can be prevented.

[Other embodiments]
FIG. 13 is a sectional view showing another embodiment of the present invention.
The antireflection structure 100 in FIG. 13 is composed of an antireflection structure 1 and a dark-colored material layer 30 laminated on the antireflection structure 1.

The dark-colored material layer 30 is provided on the surface of the antireflection structure 1 opposite to the surface on which the large projections 3 are formed, that is, on the surface opposite to the surface on which the uneven structure is formed. The dark-colored material layer 30 may be provided on a part of the surface of the antireflection structure 1 opposite to the surface on which the large protrusion 3 is formed, but it is preferably provided on the entire surface.

There is no particular limitation on the form of the dark-colored material layer 30. For example, it can be a layer of paint applied to the antireflection structure 1 or a layer of ink printed on the antireflection structure 1. Alternatively, a sheet may be laminated on the antireflection structure 1 via an adhesive layer or directly. Further, when the antireflection structure 1 is attached inside a black casing of an optical device, the casing becomes the dark-colored material layer 30.

The color of the dark color material layer 30 may be any dark color, but it is particularly preferable that the color is black.
By providing a dark color material layer 30, particularly a dark color material layer 30 which is a black material layer, on a part or all of the surface opposite to the surface on which the concave-convex structure of the antireflection structure 1 is formed, it is possible to absorb light rays that are taken into the antireflection structure 1 and reach the dark color material layer 30. Therefore, it is possible to prevent light that has once been taken into the antireflection structure 1 from being reflected at the interface between the antireflection structure 1 and the outside and being released to the outside again, thereby improving antiglare properties.

[Evaluation method, etc.]
(Evaluation of mold releasability)
When manufacturing the antireflection structures of the following Examples and Comparative Examples, the releasability of the COP film to which the uneven structure of the mold was transferred from the mold was evaluated based on the following criteria.
◎: The COP film was naturally peeled off from the mold at the same time as the pressure was released.
○: The COP film and the mold were integrated when the pressure was released, but when the COP film was slightly peeled off from the mold, it was peeled off without resistance.
Δ: When the pressure was released, the COP film and the mold were integrated, and there was resistance when peeling the COP film from the mold.
×: When the pressure is released, the film and mold are integrated, and there is a large resistance when peeling the COP film from the mold, so it is difficult to peel off.

(Evaluation of anti-reflection properties)
In order to confirm the antireflection properties of the antireflection structures produced in the Examples and Comparative Examples, the luminosity-corrected reflectance (Y value) was evaluated using a spectrophotometer V-770 manufactured by JASCO Corporation. The lower the Y value, the lower the reflectance and the better the antireflection properties.

[Example 1]
An antireflection structure was produced by making a mold according to the first example of the manufacturing method of the mold shown in FIG. 8, and transferring it to the uneven structure thermoplastic resin of the mold by thermal nanoimprinting. The specific steps will be explained below.

Two types of spherical colloidal silica having a nominal diameter of 3.0 μm and 4.0 μm were prepared as 20% by mass aqueous dispersions, and these were mixed in a weight ratio of 1:1 to prepare an aqueous dispersion.
This aqueous dispersion was filtered through a membrane filter with a pore size of 10 μmφ. A 1.0% by mass aqueous solution of phenyltriethoxysilane hydrolysate was added to the aqueous dispersion that had passed through the membrane filter, and the mixture was reacted at about 40° C. for 3 hours to obtain a reaction liquid. At this time, the aqueous dispersion and the aqueous hydrolysate solution were mixed so that the mass of phenyltriethoxysilane was 0.02 times the mass of the colloidal silica particles.
To the resulting reaction liquid, methyl ethyl ketone was added in an amount four times the volume of the reaction liquid, and the mixture was thoroughly stirred to extract the hydrophobic colloidal silica into an oil phase, thereby obtaining a hydrophobic colloidal silica dispersion having a concentration of 0.91 mass%.

The obtained hydrophobic colloidal silica dispersion was dropped at a rate of 0.01 mL/sec onto the liquid surface (water was used as the sublayer water, water temperature 25°C) in a water tank (LB trough device) equipped with a surface pressure sensor that measures the surface pressure of the monoparticle film and a movable barrier that compresses the monoparticle film in the direction along the liquid surface. A flat-surfaced Si substrate (6 inches) was previously immersed in the sublayer water of the tank in an approximately vertical direction as a substrate.

After that, ultrasonic waves (output 300 W, frequency 950 kHz) are irradiated from the lower water toward the water surface for 10 minutes to promote two-dimensional close packing of particles, while evaporating methyl ethyl ketone, which is the solvent of the dispersion. A single particle film was formed.
This single particle film was then compressed by a movable barrier until the diffusion pressure reached 25 mNm ^-1 , and the substrate was pulled up at a speed of 5 mm/min and transferred onto one side of the substrate.

Subsequently, a hydrolyzed solution of 1% by mass monomethyltrimethoxysilane as a binder was infiltrated onto the substrate on which the single particle film was formed, and then the excess of the hydrolyzed solution was treated with a spin coater (3000 rpm) for 1 minute. Removed. Thereafter, this was heated at 100° C. for 10 minutes to cause the binder to react, thereby obtaining a substrate with a single particle film.

The substrate with the monolayer particle film was dry etched with a mixed gas of BCl ₃ and Cl ₂ to form a groove. The etching conditions were antenna power 1500 W, bias power 500 W, gas flow rate 100 sccm, and etching time 1200 seconds. The etched particles were then removed by wiping and washing with water.
Next, the substrate from which the particles had been removed was etched with a mixed gas of CF ₄ and O ₂ at an antenna power of 1500 W, a bias power of 300 W, a gas flow rate of 200 sccm, and an etching time of 300 seconds to remove the oxide film.

Thereafter, a roughening process was performed by etching using Cl ₂ gas at an antenna power of 1500 W, a bias power of 800 W, a gas flow rate of 100 sccm, and an etching time of 240 seconds.
Further, etching was performed using a mixed gas of _BCl3 and _Cl2 with an antenna power of 1500 W, a bias power of 800 W, a gas flow rate of 100 sccm, and an etching time of 400 seconds to form a large number of microholes in the roughened portion, thereby obtaining the mold of Example 1. Figures 10 and 11 are photographs of the mold of Example 1.

Thermal nanoimprinting was performed on a COP film having a thickness of 0.188 mm at a pressure of 6.0 MPa and a processing temperature of 170° C. using the mold of Example 1, and after cooling to room temperature, the pressure was released and the COP film to which the concave-convex structure of the mold had been transferred was peeled off from the mold to obtain the antireflection structure of Example 1. Figures 1 to 3 are photographs of the antireflection structure of Example 1.
The sizes of the various parts of the antireflection structure of Example 1 were determined by the above-mentioned method, and were as follows:

Bottom average diameter R: 2.9 μm
Distribution of bottom diameter R1 in 0.1 μm increments: Peaks at 2.6 μm and 3.6 μm. Average bottom microprojection pitch P: 98 nm
Average pitch Q of microprojections on upper surface: 98 nm
Maximum height H of large protrusion: 6.3 μm
Maximum height of bottom microprojection M: 750 nm
Maximum height N of upper surface microprotrusion: 750 nm
Ratio [H/M]: 8.4
Proportion of the total area of the bottom to the total area of the anti-reflection structure: 61.2%
The ratio of the total area of the region in which the microstructure consisting of the standing bottom microprotrusions is formed to the total area of the bottom: 70.4%

[Example 2]
A 20% by mass aqueous dispersion of three types of spherical colloidal silica having nominal sizes of 2.0 μm, 3.0 μm, and 4.0 μm was prepared, and an aqueous dispersion was prepared by mixing the three types at a weight ratio of 1:1:1. A mold for Example 2 was then produced using the same method as in Example 1. Then, an antireflection structure for Example 2 was obtained using the same method as in Example 1.
The sizes of the various parts of the antireflection structure of Example 2 were determined by the above-mentioned method, and were as follows:

Bottom average diameter R: 2.3μm
Distribution of bottom diameter R1 in 0.1 μm increments: Peaks at 1.8 μm, 2.6 μm, and 3.6 μm Bottom microprotrusion average pitch P: 98 nm Top surface microprotrusion average pitch Q: 98 nm
Maximum height H of large protrusion: 5.6μm
Bottom microprotrusion maximum height M: 750nm
Maximum height N of top surface microprotrusions: 750nm
Ratio [H/M]: 7.5
Ratio of the total area of the bottom to the total area of the anti-reflection structure: 72.3%
Occupancy rate of the total area of the region where the microstructure consisting of clustered bottom microprotrusions is formed relative to the total area of the bottom: 69.7%

[Example 3]
A mold of Example 3 was produced using the same method as Example 1 except that the dry etching time using a mixed gas of BCl ₃ and Cl ₂ was changed to 1650 seconds. Thereafter, the antireflection structure of Example 3 was obtained using the same method as in Example 1.
The sizes of each part of the antireflection structure of Example 3 were determined by the method described above, and were as follows. Note that no upper microprotrusions were formed on the upper surface of the large protrusion of the antireflection structure of Example 3.

Bottom average diameter R: 2.9 μm
Distribution of bottom diameter R1 in 0.1 μm increments: Peaks at 2.6 μm and 3.6 μm Bottom microprojection average pitch P: 98 nm
Maximum height H of large protrusion: 7.5 μm
Maximum height of bottom microprojection M: 750 nm
Maximum height N of upper surface microprotrusion: 750 nm
Ratio [H/M]: 10
Proportion of the total area of the bottom to the total area of the anti-reflection structure: 61.6%
The ratio of the total area of the region in which the microstructure consisting of the standing bottom microprotrusions is formed to the total area of the bottom: 68.7%

[Comparative Example 1]
The antireflection structure having a cylindrical opening in Example 2 of Patent Document 2 was used as the antireflection structure in Comparative Example 1.
That is, three types of 20 mass % aqueous dispersions of spherical colloidal silica having nominal diameters of 3.0 μm, 4.0 μm, and 5.0 μm were prepared, and aqueous dispersions were prepared by mixing them in a weight ratio of 1:1:1. The same method as in Example 1 was used to obtain a substrate with a monoparticle film.

The substrate with the monolayer particle film was dry-etched with a mixed gas of CF ₄ , Cl ₂ , and O _2. The etching conditions were: antenna power 1500 W, bias power 1000 W, gas flow rate 100 sccm, and etching time 1000 seconds. The etched particles were then removed by wiping and washing with water, and further dry-etched with Cl ₂ gas to produce a mold for Comparative Example 1.
Thereafter, using the same method as in Example 1, an antireflection structure having a cylindrical opening of Comparative Example 1 was obtained.

The size of each part of the antireflection structure of Comparative Example 1 was determined by the method described in Patent Document 2, and was as follows. No microprotrusions were formed on the upper surface of the wall of the antireflection structure of Comparative Example 1.
Note that the average height of the wall portions in Comparative Example 1 and Comparative Example 2 described below are values determined by the method described in paragraph [0019] of Patent Document 2. The aperture diameter distribution is the distribution of the aperture diameter p1 of the light absorption unit 2 obtained by the method described in paragraph [0028] of Patent Document 2. The aperture ratio is a value determined by the method described in paragraph [0032] of Patent Document 2. The average pitch of the bottom microprotrusions is a value determined by the method described in paragraph [0026] of Patent Document 2. The average height of the bottom microprotrusions is a value determined by the method described in paragraph [0023] of Patent Document 2.

Average height of wall: 7.0μm
Opening diameter distribution: peaks at 2.6 μm, 3.5 μm, and 4.3 μm Opening ratio: 55.2%
Bottom microprotrusion average pitch: 110nm
Bottom microprotrusion average height: 750nm

[Comparative Example 2]
The antireflection structure having a cylindrical opening in Example 3 of Patent Document 2 was used as the antireflection structure in Comparative Example 2.
That is, a substrate with a monoparticle film was obtained by the same method as in Comparative Example 1. Then, dry etching was performed using a mixed gas of CF ₄ and Cl _2. The etching conditions were antenna power 1500 W, bias power 800 W, gas flow rate 100 sccm, and etching time 1500 seconds. Then, the etched fine particles were removed by wiping and washing with water, and further dry etching was performed using Cl ₂ gas to prepare a mold of Comparative Example 2. Then, an antireflection structure of Comparative Example 2 was obtained using the same method as in Example 1.

The size of each part of the antireflection structure of Comparative Example 2 was determined by the method described in Patent Document 2, and was as follows. No microprotrusions were formed on the upper surface of the wall of the antireflection structure of Comparative Example 2.
Average height of wall: 13.0μm
Aperture diameter distribution: Peaks at 2.6 μm, 3.5 μm, 4.3 μm Aperture ratio: 56.1%
Average pitch of microprotrusions in the bottom Kenzan structure: 110 nm
Average height of microprotrusions in the bottom Kenzan structure: 750 nm

The evaluation results of the anti-reflection structures of Examples 1 to 3 are shown in Table 1, and the evaluation results of Comparative Examples 1 and 2 are shown in Table 2.

As shown in Table 1, the antireflection structures of the Examples all had excellent releasability and antireflection properties.
In contrast, as shown in Table 2, the antireflection structures of Comparative Examples 1 and 2 both had problems with releasability. Comparative Example 2, in which the wall was made high enough to obtain good antireflection properties, had particularly poor releasability. Comparative Example 1, in which the wall was made low to ensure a certain degree of releasability, also had poor antireflection properties.

The anti-reflection structure according to the present invention can be used, for example, on the surfaces of optical discs such as CDs and DVDs, the surfaces of optical components such as lenses, protective films used on the surfaces of displays, and the inner surfaces of housings of optical devices such as telescopes and spectrophotometers.
It may also be applied to black painted surfaces for decorative purposes to accentuate the black color.

Reference Signs List 1 Anti-reflection structure 2 Bottom 2a Outer edge 3 Large projections 4 Bottom microprojections 5 Top microprojections 10 Mold 12 Convex portions 13 Grooves 14 Convex microholes 15 Groove microholes 21 Substrate 22 Particles 23 Resist film 24 Top rough surface 25 In-groove rough surface 30 Dark color material layer 100 Anti-reflection structure R Bottom average diameter H Large projection maximum height M Bottom microprojection maximum height N Top microprojection maximum height P Bottom microprojection average pitch Q Top microprojection average pitch G Etching gas

Claims (9)

a plurality of bottoms having a substantially circular outer edge, and a large protrusion that is formed to stand up between the plurality of bottoms and demarcates the plurality of bottoms from each other;
The average diameter of the smallest circle including the outer edge of the bottom is 1 μm or more and 20 μm or less,
A microstructure consisting of microprotrusions clustered at an average pitch of 10 nm or more and 300 nm or less is formed on the bottom,
The large protrusion has a multimodal structure in which the height of the upper surface rising between the plurality of bottoms changes so that a plurality of peaks can be observed along the outer edge,
The maximum height H of the large protrusion is greater than the maximum height M of the micro protrusion at the bottom,
A microstructure consisting of microprotrusions clustered at an average pitch of 10 nm or more and 300 nm or less is formed on at least a part of the upper surface of the large protrusion rising between the plurality of bottoms.
An anti-reflection structure characterized by: The anti-reflection structure according to claim 1, wherein the maximum height H of the large protrusions is 3 to 12 μm. The anti-reflection structure according to claim 1 or 2, wherein the maximum height M of the microprotrusions at the bottom is 0.1 μm or more and 2 μm or less. An anti-reflection structure according to any one of claims 1 to 3, in which the ratio [H/M] of the maximum height H of the large protrusions to the maximum height M of the small protrusions at the base is 3 to 120. The antireflection structure according to any one of claims 1 to 4, wherein the maximum height N of the microprotrusions on the upper surface of the large protrusions is 0.1 μm or more and 2 μm or less. The antireflection structure according to any one of claims 1 to 5, wherein the diameter of the smallest circle including the outer edge of the bottom has a distribution having two or more peaks in 0.1 μm increments. The anti-reflection structure according to claim 6, wherein the two or more peaks include a pair of adjacent peaks whose diameter difference is 0.3 μm or more. An anti-reflection structure according to any one of claims 1 to 7, which is made of a black material. An anti-reflection structure according to any one of claims 1 to 8, having a layer of black material on the surface opposite to the surface on which the large protrusions are formed.

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