JP2015138179A - Microstructure and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microstructure with micro-protrusions, which can be manufactured without the constraints of the etching rate of a base material to sufficiently achieve the desired performance and superior durability even if the etching condition varies, and to provide a manufacturing method therefor.SOLUTION: An anti-reflection structure (microstructure) 10 comprises a base material 11 and a surface concavo-convex layer 12 which is formed, with a micro concavo-convex pattern formed on a surface thereof, on at least a portion of the base material 11. The surface concavo-convex layer 12 has a refractive index that continuously decreases with a distance from a contact surface 12a in contact with the base material 11 toward a surface 12b thereof on a side opposite the contact surface 12a.

Description

  The present invention relates to a microstructure suitably used as an antireflection structure and a method for manufacturing the microstructure.

For example, a film-like antireflection structure for improving visibility is often provided on the surface of a display such as a personal computer. As such an antireflection structure, there is known a structure in which a fine concavo-convex pattern composed of conical fine protrusions is formed on the surface. In this structure, the arrangement pitch of the fine protrusions is set to be equal to or less than the wavelength of visible light, and thus, the refractive index continuously changes in the depth direction, and the incident light to be incident from the fine protrusion side is visually changed. Fresnel reflection is suppressed.
In such an antireflection structure, in order to exhibit excellent antireflection performance, it is required that the shape of the fine protrusion is accurately formed in a conical shape. As a method of forming a fine uneven pattern, there is a method of etching a target surface through a mask pattern (see Patent Document 1).

International Publication No. 2008/001670

However, the method of forming a fine concavo-convex pattern by etching has poor productivity when the substrate to be etched is a material having a low etching rate. Further, even when the etching rate is moderate, it is necessary to accurately form the shape of the fine protrusions in a conical shape. For this reason, the etching conditions must be strictly controlled. Even if the fine protrusions can be accurately formed into a conical shape, the conical fine protrusions have insufficient endurance (abrasion resistance) due to their shapes.
Further, when a material having a low etching rate is etched, it is very difficult to form a sufficiently high fine protrusion, and it is difficult to obtain necessary optical performance (antireflection performance). That is, in order to form fine protrusions at a sufficient height, it is necessary to increase the film thickness of the mask pattern or select a material having a lower etching rate than the material to be etched as the material of the mask pattern. . However, increasing the film thickness of the mask pattern has a limit in film forming conditions. In addition, when the etching rate of the material to be etched is low, it is practically difficult to use a mask pattern made of a material having a lower etching rate than such a material.

  The present invention has been made in view of the above circumstances, and is not limited to the etching rate of the substrate, and even if the etching conditions vary somewhat, the desired optical performance is sufficiently expressed and the fineness excellent in durability is also achieved. It is an object of the present invention to provide a microstructure having a protrusion and a manufacturing method thereof.

The present invention has the following configuration.
[1] A microstructure having a substrate and a surface uneven layer formed on at least a part of the substrate and having a fine uneven shape formed on a surface thereof, wherein the surface uneven layer includes the substrate The fine structure is characterized in that the refractive index continuously decreases from the contact surface to the surface of the surface uneven layer on the side opposite to the contact surface.
[2] The uneven surface layer contains silicon, oxygen, and nitrogen, and the nitrogen content continuously decreases from the contact surface toward the surface of the uneven surface layer. ] Fine structure.
[3] The microstructure according to [1] or [2], wherein the surface of the base material on which the surface uneven layer is formed has a center line average roughness Ra of 30 nm or less according to JIS B0601.
[4] The microstructure according to any one of [1] to [3], wherein the base material is made of YAG.
[5] A film forming step of sputtering a target with a sputtering gas to form a surface layer on a substrate, and an etching step of etching the surface layer through a mask pattern to make the surface layer a surface uneven layer In the film forming step, the refractive index in the film thickness direction of the surface layer is changed from the contact surface between the base material and the surface layer to the surface of the surface layer opposite to the contact surface. The surface layer is formed so as to become continuously smaller toward the surface, and the method for manufacturing a microstructure is characterized.
[6] In the film forming step, a film thickness of the surface layer formed by using a mixed gas of a rare gas and a reactive gas as the sputtering gas and continuously changing a gas composition of the mixed gas. The method for producing a microstructure according to [5], wherein the composition in the direction is continuously changed.
[7] The film forming process according to [6], wherein silicon is used as the target, oxygen and nitrogen are used as the reactive gas, and a ratio of the nitrogen in the mixed gas is continuously reduced. A manufacturing method of a fine structure.
[8] The fine film according to [6], wherein in the film forming step, silicon dioxide is used as the target, nitrogen is used as the reactive gas, and the ratio of the nitrogen in the mixed gas is continuously reduced. Manufacturing method of structure.

  According to the present invention, there is no limitation on the etching rate of the substrate, and even if the etching conditions vary somewhat, the microstructure having the fine protrusions that sufficiently express the target optical performance and is excellent in durability. And a manufacturing method thereof.

It is a longitudinal cross-sectional view which shows the reflection preventing structure which is an example of 1 embodiment of the microstructure of this invention. (A) The schematic diagram of the shape of the conventional fine protrusion, (b) The schematic diagram of the shape of the fine protrusion which the fine structure of FIG. 1 has. It is explanatory drawing about the manufacturing method of a microstructure, and is a longitudinal cross-sectional view which shows the state which formed the surface layer in the single side | surface of a base material. It is explanatory drawing about the manufacturing method of a microstructure, (a) A schematic diagram showing the initial stage of etching, (b) After the etching progresses and a cylinder appears at a position corresponding to each particle, on each cylinder It is the schematic diagram which shows the state which the particle | grains also etched and became small, (c) The schematic diagram which shows the state which each particle | grain disappeared by etching and the bell-shaped fine protrusion was formed. It is a graph (refractive index distribution curve) which shows the refractive index distribution of a surface uneven | corrugated layer (surface layer).

Hereinafter, the present invention will be described in detail.
<Microstructure>
FIG. 1 is a longitudinal sectional view showing a film-like antireflection structure which is an embodiment of the microstructure of the present invention.
The antireflection structure 10 of this example includes a plate-like base material 11 and a surface uneven layer 12 formed on the entire surface of one side of the base material 11. The surface uneven layer 12 has a fine uneven shape formed on the exposed surface 12 b (surface opposite to the contact surface 12 a with the substrate 11) 12 b. The surface irregularity layer 12 is a layer that functions as an antireflection layer, and has a large number of bell-shaped fine protrusions 13 having a circular bottom surface.

The base material 11 in this example is made of YAG (yttrium, aluminum, garnet), which is a phosphor and is a material that performs wavelength conversion, and at least the surface 11a on the side where the surface uneven layer 12 is formed is described in JIS B0601. The center line average roughness Ra is a smooth surface of 30 nm or less. YAG is a material having a low etching rate at which the etching itself hardly proceeds. The thickness of the substrate 11 is preferably, for example, 10 to 10,000 μm, and more preferably 50 to 2000 μm, from the viewpoint of simplicity of the film forming operation of the surface uneven layer 12.
In the present invention, any of a transparent substrate, a translucent substrate, and an opaque substrate can be used. A transparent substrate and a translucent substrate are more preferable as the optical absorption is lower. If the substrate has a low optical absorption, the optical absorption of the light entering the substrate can be suppressed, and the final light extraction efficiency can be increased.

  In addition, in the case of a transparent base material and a semi-transparent base material, the light extraction efficiency in consideration of optical absorption is represented by the following approximate expression (1).

The abbreviations in the formula have the following meanings.
R ₁ : Surface reflectance (%) of the surface uneven layer
R ₂ : Surface reflectance of substrate (%)
A ₁ : Optical absorptance (%) of surface uneven layer per unit length; eigenvalue depending on material.
A ₂ : Optical absorption rate (%) of base material per unit length; eigenvalue depending on material.
d ₁ : optical path length (mm) of light traveling through the surface uneven layer; corresponding to the thickness of the surface uneven layer.
d ₂ : optical path length (mm) of light traveling through the substrate; equivalent to the thickness of the substrate.
E _x : Wavelength conversion efficiency of the substrate; eigenvalue depending on the material; 1.0 for materials that do not perform wavelength conversion.

The surface reflectance can be measured by measuring 5 ° frontal reflection with a spectrophotometer such as “V-670 spectrophotometer” manufactured by JASCO Corporation. For example, when R ₂ is considered to be 0% as in Example 1 described later, a light absorbing tape (for example, “Super Black IR” manufactured by Tech World Co., Ltd.) is applied to the back surface of the base material on which the surface uneven layer is formed. R ₁ is obtained by measuring the reflectance of the surface of the surface irregularity layer after pasting and performing a backside light absorption treatment. In the case of measuring the surface reflectance of a fine structure having a transparent or translucent base material, the back surface light absorption treatment was emitted from the light source and incident on the base material, and then reflected at the interface between the back surface of the base material and air. This is performed in order to prevent light from being mixed into the reflected light of the surface of the fine structure.

  On the other hand, in the case of an opaque base material (total reflection), the light extraction efficiency in consideration of optical absorption is represented by the following approximate expression (2).

  The meaning of the abbreviations in the formula is the same as in formula (1).

From the above equations, it can be seen that the lower the surface reflectances R ₁ and R _{2, the} higher the light extraction efficiency. Further, it can be seen that the higher the optical absorptivity A ₁ is low light extraction efficiency of the surface irregularities layer. The transparent case of a substrate and semi-transparent substrate, it can be seen that a high extraction efficiency the lower the optical absorption factor A ₂ of the substrate light.

  The mode pitch P and the mode height H of the fine concavo-convex shape of the surface concavo-convex layer 12 vary depending on the use of the fine structure, but since the fine structure in this example is the antireflection structure 10, the fine protrusion 13 The pitch indicating the distance between the tops is preferably 300 nm or less, more preferably 150 nm or less, as the most frequent pitch P, which is smaller than the wavelength of visible light (about 400 nm to 750 nm). If it is 150 nm or less, diffracted light in the visible light region can be reduced. When used in an infrared region having a wavelength of about 750 nm to 10000 nm or less, the most frequent pitch P is preferably 5000 nm or less.

Specifically, the most frequent pitch P of the fine concavo-convex shape is obtained as follows.
First, in a randomly selected region on the surface 12b of the surface concavo-convex layer 12 on which the fine concavo-convex shape is formed, a square region with one side corresponding to 30 to 40 times the most frequent pitch P is scanned with a scanning microscope (SEM). ) Get an image. For example, when the most frequent pitch P is about 300 nm, an image of an area of 9 μm × 9 μm to 12 μm × 12 μm is obtained. Then, this image is waveform-separated by Fourier transform to obtain an FFT image (fast Fourier transform image). Next, the distance from the 0th order peak to the 1st order peak in the profile of the FFT image is obtained. The reciprocal of the distance thus obtained is the most frequent pitch P in this region. Such a process is similarly performed for a total of 25 or more regions of the same area selected at random, and the most frequent pitch in each region is obtained. The average value of the mode pitches P _{1 to} P _{25 in} the ₂₅ or more regions thus obtained is the mode pitch P. In this case, the regions are preferably selected at least 1 mm apart, more preferably 5 mm to 1 cm apart.

  In the case of the antireflection structure 10, the mode height H (= mode pitch P × aspect ratio) of the fine concavo-convex shape is preferably 0.5 or more, more preferably 1. The value is 0 or more, more preferably 2.0 or more. When the aspect ratio is not less than the lower limit, the antireflection property can be further increased.

Specifically, the most frequent height H is obtained as follows.
First, from a scanning microscope (SEM) image, a longitudinal sectional view as shown in FIG. 1 is obtained along a line of 1 mm length in an arbitrary direction and position. From this cross section, 30 fine protrusions 13 are extracted, and for each fine protrusion 13 included therein, the height H1 of the apex and two fine protrusions 13 adjacent to the fine protrusion 13 are formed. The difference between the height of the two valleys and the lower height H2 is obtained, and the obtained value is rounded by two effective digits to obtain the height of each fine protrusion 13, and the mode value is set to the maximum. Frequency H is assumed.

In this example, the surface uneven layer 12 having a fine uneven shape is made of an inorganic material. Specifically, it consists of a composition containing silicon, oxygen, and nitrogen. The composition in the film thickness direction (the height direction of the fine protrusions 13) continuously changes from the contact surface 12a with the base material 11 toward the surface 12b opposite to the contact surface 12a. ing. Specifically, the contact surface 12a side with the base material 11 is the composition A (Si—O—N) having a large nitrogen content (ratio), and as the surface 12b on the opposite side to the contact surface 12a is approached. The content (ratio) of nitrogen continuously decreases, and the surface 12b has a composition B (Si—O) composed only of silicon and oxygen.
Since the surface irregularity layer 12 changes in composition in the film thickness direction in this way, the refractive index in the film thickness direction of the surface irregularity layer 12 increases from the contact surface 12a toward the surface 12b as the composition changes. Continuously smaller.

For example, in this example, YAG is used for the base material 11 and the refractive index of YAG is 1.83. Therefore, the composition of the contact surface 12a with the base material 11 in the surface irregularity layer 12 is the same as that of YAG as the base material 11, or the refractive index is close to YAG. This is preferable from the viewpoint of preventing reflection at the interface with the layer 12. Specifically, when the refractive index of the substrate 11 was set to _{n i,} the refractive index _{n ii} of the contact surface 12a of the substrate 11 in the surface uneven layer _12, | a <0.1 | _{n i} -n ii It is preferable to satisfy. For example, Si ₅ ON ₅ having an atomic ratio of silicon: oxygen: nitrogen = 5: 1: ₅ has a refractive index of 1.83, which is the same as that of YAG. Therefore, when the base material 11 is YAG, Si ₅ ON ₅ is suitable as the composition of the contact surface 12 a with the base material 11 in the surface uneven layer 12. On the other hand, the composition consisting only of silicon and oxygen is usually SiO ₂ and its refractive index is 1.45.

  As described above, the surface uneven layer 12 included in the antireflection structure 10 of FIG. 1 is not only formed with a fine uneven shape that exhibits antireflection performance on the surface 12b, but also has a refractive index in the film thickness direction. The contact surface 12a is continuously reduced from the contact surface 12a with the base material 11 toward the surface 12b opposite to the contact surface 12a. That is, the refractive index of the material itself forming the surface uneven layer 12 changes. Therefore, although it has a fine concavo-convex shape, its refractive index as a material exhibits an excellent antireflection performance as compared with a conventional surface concavo-convex layer whose thickness direction is constant. In addition, it can be manufactured in a simpler process and the total film thickness is thinner than the case of laminating a layer whose refractive index changes in the film thickness direction and a surface uneven layer whose refractive index is constant in the film thickness direction. However, high antireflection ability can be exhibited.

In the present invention, since the component constituting the surface uneven layer 12 continuously changes in the thickness direction (film thickness direction), the refractive index also changes continuously in the thickness direction in conjunction with it. Here, the change in the refractive index is “continuous” is not stepwise and discrete, and the “local change rate” defined below is an arbitrary position in the thickness direction of the surface uneven layer 12. In the range of ± 50% of the “total average rate of change” defined below. Note that the “change amount (distance) in the thickness direction” of the “local change rate” is 10 nm. The “difference in refractive index between the air side and the substrate side of the surface uneven layer” is a difference between the refractive index of the surface 12 b of the surface uneven layer 12 and the refractive index of the contact surface 12 a.
The local change rate is easily obtained by a method using TOF-SIMS (time-of-flight secondary ion mass spectrometry). That is, by TOF-SIMS, elemental analysis of the vaporized component is performed while ion milling the uneven surface layer 12 with an argon ion beam or the like in the thickness direction. Then, a component distribution curve in the thickness direction is obtained, and a refractive index distribution curve in the thickness direction is further obtained from the component analysis curve, thereby obtaining a change in refractive index. When the refractive index distribution is obtained from the component distribution, a calibration curve indicating the relationship between the component (composition) and the refractive index prepared in advance can be used.

  In the case of a surface uneven layer having a fine uneven shape in which the refractive index of the material is constant in the film thickness direction as in the prior art, the optimum shape of the fine protrusion from the viewpoint of antireflection performance is shown in FIG. It was a tapered cone shape as shown in FIG. Such a tapered shape of the conventional fine protrusion 13 ″ has insufficient durability (abrasion resistance) at the tip. On the other hand, the fine protrusion 13 of the antireflection structure 10 of FIG. As described above, since the refractive index of the material continuously decreases as it approaches the surface 12b side, the optimum shape of the fine protrusion 13 from the viewpoint of antireflection ability is as shown in FIG. In addition, the ring-shaped fine protrusion 13 has a rounded tip, which is more durable than the tapered cone-shaped protrusion 13 ″ shown in FIG. Excellent scratch resistance.

  In addition, in the case of the tapered conical fine protrusion 13 ″ as shown in FIG. 2A, if it is attempted to form this by etching, strict control of the etching conditions is required. For example, the tip is thin. Even if the etching conditions vary slightly because the time required for turning the etching gas into plasma is slightly varied, the thin part at the tip will be etched away, and the desired tapered shape will not be obtained. On the other hand, as shown in FIG.2 (b), if the bell-shaped fine protrusion 13 having a rounded tip is used, even if the etching conditions are somewhat varied, the shape may be greatly affected. In addition, even if the shape is slightly changed, the refractive index of the material constituting the surface irregularity layer 12 is set so that the fine protrusions 13 have a high refractive index so as to be suitable for the expression of antireflection performance. Since the continuously changed in the direction to cover the adverse effect of the shape changes.

<Method for producing fine structure>
Next, a method for manufacturing the antireflection structure (fine structure) 10 of FIG. 1 will be described.
(Film forming process)
First, a target is sputtered with a sputtering gas, and a film forming step for forming a surface layer 12 ′ on one surface of the substrate 11 is performed as shown in FIG. The surface layer 12 ′ formed here is a flat layer in which no fine uneven shape is formed.
Specifically, in a vacuum state, a voltage is applied between the target and the substrate 11 while introducing the sputtering gas to cause the sputtering gas to collide with the target. Then, atoms constituting the target jump out and are deposited on the substrate 11 to form a surface layer 12 ′. Here, when silicon is used as a target, silicon jumps out of the target and deposits on the base material 11. At this time, argon (rare gas), oxygen (reactive gas), and nitrogen (reaction) are used as sputtering gases. When a mixed gas is used, the rare gas argon is not taken into the surface layer 12 ', but the reactive gases oxygen and nitrogen are taken into the surface layer 12'. Therefore, a compound (Si—O—N) composed of silicon derived from the target and oxygen and nitrogen that are reactive gases is first deposited on the substrate 11.

Here, the composition of the contact surface 12a ′ of the surface layer 12 ′ with the substrate 11 in the surface layer 12 ′ is adjusted as appropriate, as described above, by adjusting the initial ratio of argon, oxygen, and nitrogen. Are preferably the same or have a refractive index close to that of YAG. In this case, reflection at the interface between the substrate 11 and the uneven surface layer 12 formed later from the surface layer 12 ′ can be suitably prevented. The refractive index of YAG is 1.83. In this case, if the initial ratio of argon, oxygen and nitrogen (Ar / O ₂ / N ₂ ) is 2: 1: 2, the group in the surface layer 12 ′ It is easy to control the composition of the contact surface 12a ′ with the material 11 to the above-described Si ₅ ON ₅ having a refractive index of 1.83.

And sputtering is continued, controlling the gas composition of the mixed gas (sputtering gas) introduce | transduced, specifically, the ratio of argon, oxygen, and nitrogen so that nitrogen may reduce continuously.
Then, at the initial stage of sputtering, the material having the composition (Si—O—N) is deposited on the base material 11 as described above, but the deposit is reduced as the ratio of nitrogen in the mixed gas decreases. The nitrogen in it will also decrease. When the amount of nitrogen in the mixed gas is finally reduced to, for example, zero, the surface 12b ′ of the surface layer 12 ′ has a composition consisting mainly of silicon and oxygen (mainly SiO ₂ ).

In the mixed gas, a specific method for controlling the ratio of argon, oxygen, and nitrogen so that the nitrogen continuously decreases is a method of decreasing the nitrogen while increasing the argon and oxygen while keeping the flow rate of the mixed gas constant; A method of reducing the flow rate of nitrogen with a constant flow rate of argon and oxygen; a method of increasing the flow rate of argon and oxygen with a constant flow rate of nitrogen; and a method of increasing the flow rate of argon, oxygen, and nitrogen so that the ratio of nitrogen continuously decreases. There is a method of changing the flow rate at the same time. However, the flow rate of nitrogen is reduced by keeping the flow rates of argon and oxygen constant from the viewpoint that the surface layer 12 'can be stably formed and the control of the gas flow rate is easy. The method is preferred. Further, as long as the ratio of nitrogen in the mixed gas is continuously reduced, it may be finally reduced to zero or may not be reduced to zero.
As the rare gas, argon is preferable from the viewpoint of sputtering efficiency, but a rare gas other than argon (helium, neon, xenon, krypton) can also be used, and these may be mixed and used.

As a sputtering condition for making the surface layer 12 ′ have a composition in which nitrogen is continuously reduced in the film thickness direction, the degree of opening and closing of the main valve of the mixed gas is adjusted, and thereby the film forming pressure is set to 0.5 to 10 Pa. To. As a mixed gas flow rate, the conditions of an argon gas flow rate of 40 sccm at the initial stage of film formation, an oxygen gas flow rate of 20 sccm, and a nitrogen gas flow rate of 40 sccm (ratio of argon, oxygen, and nitrogen (Ar / O ₂ / N ₂ ) as a molar ratio are 2: 1: From 2), the nitrogen gas is finally reduced to 0 sccm. Among these conditions, the ratio of the mixed gas composition is particularly important.
Note that 1 sccm (Standard Cubic Centimeter per Minute) corresponds to 1.69 × 10 ⁻³ Pa · m ³ / sec.

By such a film forming process, the composition continuously changes so that the nitrogen content decreases from the contact surface 12a ′ with the base material 11 toward the surface 12b ′ opposite to the contact surface 12a ′. As a result, a surface layer 12 ′ having a refractive index that continuously decreases from the contact surface 12 a ′ with the base material 11 toward the surface 12 b ′ opposite to the contact surface 12 a ′ can be formed.
10-5000 nm is preferable and, as for the film thickness of surface layer 12 ', 300-500 nm is preferable. The film thickness of the surface layer 12 ′ is controlled by the time of the film forming process, the required film flatness, the film thickness uniformity, and the like.

(Etching process)
The surface layer 12 ′ formed by the film forming process described above is a flat layer that does not have a fine uneven shape. Therefore, a mask pattern is arranged on the surface layer 12 ′, and the surface layer 12 ′ is etched through the mask pattern to form a fine uneven shape. Thereby, the surface layer 12 ′ is converted to the surface uneven layer 12.

  As the mask pattern used here, it is preferable to use a single particle film mask by a known colloidal lithography method described in Patent Document 1, for example. Further, when the antireflection structure 10 as shown in FIG. 1 is manufactured, from the viewpoint of antireflection ability, the average particle diameter obtained by the dynamic light scattering method is 3 to 3 as particles constituting the single particle film mask. It is preferable to use one having a thickness of 5000 nm. The average particle diameter of the particles and the diameter of each circular bottom surface of the fine protrusion 13 to be formed are almost the same value. Further, when a particle having an average particle diameter of 3 nm or more is used, it is possible to sufficiently secure the distance of the space where the refractive index is inclined through which the incident light passes, and it is possible to obtain a good quenching effect by the so-called sub-wavelength grating.

  The particles constituting the single particle film mask preferably have a particle size variation coefficient (standard deviation divided by an average value) of 20% or less, more preferably 10% or less, and more preferably 5%. The following are more preferable. As described above, when using a particle having a small variation coefficient of particle size, that is, a particle having a small variation in particle size, it is difficult to generate a defective portion where no particle exists. When a single particle film mask having no defect is used, an antireflection structure that gives a uniform refractive index gradient effect to incident light can be easily obtained.

Particle materials include metals such as Al, Au, Ti, Pt, Ag, Cu, Cr, Fe, Ni, and Si, and metal oxides such as SiO ₂ , Al ₂ O ₃ , TiO ₂ , MgO ₂ , and CaO ₂ . In addition to organic polymers such as polystyrene and polymethyl methacrylate, one or more of semiconductor materials and inorganic polymers can be employed.

  As etching, it is preferable to employ vapor phase etching. When etching is started with the etching gas through the mask pattern, first, as shown in FIG. 4A, the etching gas passes through the gaps between the particles P constituting the single particle film mask F, and the surface layer 12 ' Reaching the surface, a groove is formed in that portion, and a cylinder 13 ′ appears at a position corresponding to each particle P. When the gas phase etching is continued, the particles P on each cylinder 13 'are gradually etched to become smaller, and at the same time, the groove of the surface layer 12' becomes deeper (FIG. 4B). Finally, each particle P disappears by etching, and at the same time, a large number of bell-shaped fine protrusions 13 are formed on the surface of the surface layer 12 ′, and converted from the flat surface layer 12 ′ to the surface uneven layer 12. (FIG. 4C).

  The mode pitch P of the fine irregularities formed here is mainly controlled by the average particle diameter of the particles constituting the single particle film mask F. The mode height H (= mode pitch P × aspect ratio) is controlled by the average particle size of the particles and the etching conditions.

Examples of the etching gas used for the vapor phase etching include Ar, SF ₆ , F ₂ , CF ₄ , C ₄ F ₈ , C ₅ F ₈ , C ₂ F ₆ , C ₃ F ₆ , C ₄ F ₆ , and CHF. ₃ , CH ₂ F ₂ , CH ₃ F, C ₃ F ₈ , Cl ₂ , CCl ₄ , SiCl ₄ , BCl ₂ , BCl ₃ , BC ₂ , Br ₂ , Br ₃ , HBr, CBrF ₃ , HCl, CH ₄ , NH ₃ , O ₂ , H ₂ , N ₂ , CO, CO _{2 and the} like can be mentioned, and one or more of these can be used.

  The gas phase etching is performed by anisotropic etching in which the etching rate in the vertical direction is larger than that in the horizontal direction of the surface layer 12 ′. As an etching apparatus that can be used, a reactive ion etching apparatus, an ion beam etching apparatus, or the like that can perform anisotropic etching and can generate a bias electric field of about 20 W at the minimum can generate plasma. There are no particular restrictions on specifications such as system, electrode structure, chamber structure, and frequency of the high-frequency power source.

  In order to carry out anisotropic etching, the etching rate of the single particle film mask F and the surface layer 12 'needs to be different, and the etching selectivity (surface layer etching rate / single particle film etching rate) is preferably 1. Each of the etching conditions (particle material constituting single particle film mask F, kind of etching gas, bias power, antenna power, gas flow rate and pressure, more preferably 2 or more, more preferably 3 or more. It is preferable to set the etching time and the like.

  Moreover, since the antireflective structure 10 of FIG. 1 is continuously decreasing as the refractive index of the material of the surface uneven | corrugated layer 12 formed approaches the surface 12b side as mentioned above, it is a viewpoint of antireflection ability. As shown in FIG. 2B, the optimum shape of the fine protrusion 13 from the top is a so-called bell shape with a rounded tip. In order to form the bell-shaped fine protrusion 13, it is necessary to suppress the etching of the side wall of the fine protrusion 13 (etching in the horizontal direction) in the etching process. Therefore, in the etching process, it is preferable to perform etching while introducing a side wall protective gas (deposition gas) that protects the side walls of the protrusions.

Side wall protective gases include C ₄ F ₈ , C ₅ F ₈ , C ₂ F ₆ , C ₃ F ₆ , C ₄ F ₆ , CHF ₃ , CH ₂ F ₂ , CH ₃ F, C ₃ F ₈ and the like Freon-based gas to be used, and one or more of them can be used. These gases are decomposed in a plasma state and then polymerized by bonding the decomposed materials to form a deposited film that acts as a protective film on the surface of the object to be etched. Thus, the bell-shaped fine protrusion 13 can be formed by performing an etching process by appropriately selecting the side wall protective gas.

In this way, when silicon is used as the sputtering target, nitrogen and oxygen are used as the reactive gas used in combination with the rare gas, and the surface layer 12 ′ is formed while changing the gas composition of the mixed gas, 12, the contact surface 12a with the base material 11 is, for example, Si ₅ ON ₅ , and the refractive index thereof can be 1.83. On the other hand, if the surface of the surface irregularity layer 12 and SiO _2, can be the refractive index 1.45. That is, with this system, the refractive index can be changed in the range of 1.45 to 1.83, for example.

The antireflection structure 10 manufactured in this way has not only the surface unevenness layer 12 formed with a fine unevenness shape that exhibits antireflection performance on the surface, but also the film thickness direction of the surface unevenness layer 12. The refractive index of the material itself forming the surface irregularity layer 12 is continuously reduced from the contact surface 12a with the substrate 11 toward the surface 12b opposite to the contact surface 12a. The rate is changing. Therefore, it exhibits excellent antireflection performance.
Further, since the refractive index of the material itself forming the surface irregularity layer 12 is changed as described above, the optimum shape of the fine protrusions from the viewpoint of antireflection performance is as shown in FIG. It is not a tapered cone shape but a bell shape with a rounded tip as shown in FIG. The bell-shaped fine protrusion 13 is excellent in durability (abrasion resistance) at the tip, and the formed shape hardly changes even if the etching conditions slightly vary. Further, even if the shape is slightly changed, the refractive index of the material itself constituting the surface uneven layer 12 is inclined in the height direction of the fine protrusions 13, so that the adverse effect due to the change in shape can be covered. .

<Other forms>
In the above example, YAG is mentioned as the base material 11, but it is not limited to YAG, and the following materials can also be used. Examples of the material of the base material include the following. The refractive index n is also described.
Soda lime glass ((alkali glass), n = 1.51), borosilicate glass ((non-alkali glass), n = 1.51 to 1.54 (for lenses)), SF (heavy flint) Glasses such as system high refractive index glass (n = 1.64 to 1.84 (for example, SF ₆ is n = 1.80 (for a lens)), and the like.
Also, ITO (indium tin oxide, n = 1.8), IZO (indium zinc oxide, n = 2.07), GaN (n = 2.4), TiO ₂ (n = 2.52), Al ₂ O ₃ (n = 1.76), MgO (n = 1.76), CaO (n = 1.83), sapphire (n = 1.76) and the like.
Moreover, resin materials, such as a polyethylene terephthalate (n = 1.65) and polymethyl methacrylate (n = 1.48-1.50), are mentioned.

Among these, although glass can be etched, a residue is generated as the etching progresses, and the progress of the etching is hindered by the generated residue. Therefore, the etching is substantially difficult. Further, YAG is a material having a low etching rate at which the etching itself hardly proceeds as described above. The manufacturing method of the microstructure of the present invention is a method of etching the surface layer 12 ′ provided on the base material 11 instead of etching the base material 11. Therefore, even if a material that is difficult to etch, such as glass or YAG, is used for the substrate, a fine uneven shape can be formed by etching.
Further, since the surface layer 12 ′ is directly processed by etching, the fine uneven shape can be easily controlled to a desired shape. Here, suppose that the substrate is etched to form a fine uneven shape on the surface, and a surface layer is formed on the surface by vapor deposition, sputtering, etc., thereby expressing the fine uneven shape on the surface layer. The surface shape of the base material formed by etching is not accurately reflected on the surface shape of the surface layer, and the fine uneven shape of the surface layer may be slightly flattened. In such a case, depending on the angle of incidence, sufficient antireflection performance cannot be exhibited.
Further, as an antireflection structure, a method in which a resin layer on which fine irregularities are formed by a nanoimprint method is provided on a base material made of YAG is also conceivable. However, since it is difficult to reduce the difference in refractive index between the resin and the base material, it is difficult to reduce the reflectance at this interface. Therefore, in the nanoimprint method, it is difficult to form a gradient structure having a refractive index from the base material to the air side as in the present invention.

In the above example, silicon is employed as a sputtering target, and oxygen and nitrogen are employed as a reactive gas used in combination with a rare gas, whereby the composition of the surface layer 12 ′ and the surface uneven layer 12 is changed between silicon and oxygen. It was set as the composition containing nitrogen. Then, the composition of the surface layer 12 ′ and the surface uneven layer 12 is changed from the contact surfaces 12a ′, 12a to the base material 11 toward the surfaces 12b ′, 12b on the opposite side to the contact surfaces 12a ′, 12a. The content of was changed so as to be continuously reduced.
However, the refractive indexes in the film thickness direction of the surface layer 12 ′ and the surface uneven layer 12 are continuously increased from the contact surface with the base material toward the surfaces 12b ′ and 12b opposite to the contact surfaces 12a ′ and 12a. As long as it can be formed as small as possible, the type of target and gas used, and the composition of the surface layer 12 ′ and the surface uneven layer 12 formed by the target and gas are not limited. For example, when the composition of the surface layer 12 ′ and the surface irregularity layer 12 is a composition containing silicon, oxygen, and nitrogen, silicon dioxide is used as a target, nitrogen is used as a reactive gas, and nitrogen in the mixed gas A method of continuously decreasing the ratio is also preferable.

Further, as a target to be sputtered, a method in which SiO ₂ and TiO ₂ are used in combination, and sputtering is performed with a rare gas while controlling the voltage applied to each of these targets can be mentioned. Thereby, the composition of the surface layer and the surface uneven layer is, for example, TiO ₂ (n = 2.70) on the contact surface side with the substrate, and for example, SiO ₂ (n = 1) on the surface opposite to the contact surface. .45) by continuously changing the amount of titanium contained from the contact surface with the substrate toward the surface opposite to the contact surface so that the amount of titanium decreases and the amount of silicon increases. The refractive index can be controlled to be continuously reduced. That is, with this system, the refractive index can be changed in the range of 2.70 to 1.45 at the maximum.

  Thus, by changing the type of the target layer, the type of sputtering gas, the composition, etc. used in the film-forming step and appropriately selecting the composition system of the surface layer and the surface uneven layer, the refraction that the surface uneven layer can take. The rate range can be adjusted. Therefore, it is preferable to appropriately select the type of target, the type of sputtering gas, the composition, and the like according to the refractive index of the substrate to be used. However, the method of sputtering while changing the gas composition in the sputtering gas is simpler and the operation is simpler than the method of sputtering while controlling the pressure applied to each target using a plurality of targets. Is preferable.

  The uneven surface layer only needs to be formed on at least a part of the substrate, that is, at least a part of the surface of the substrate. It may be formed on the end face of the material. In addition, the shape of the substrate is not limited to a plate shape, and may be a three-dimensional shape, and the surface of the substrate on which the surface layer is formed has a center line average roughness Ra described in JIS B0601 of 30 nm or less. A substrate having a curved surface such as a lens may be used.

Hereinafter, the present invention will be specifically described with reference to examples.
<Example 1>
First, a surface layer was formed on a base material made of YAG (surface has a centerline average roughness Ra of 30 nm or less) by sputtering using silicon as a target (film forming step). The molar ratio of the sputtering gas was changed from Ar: O ₂ : N _{2 =} 2: 1: 2 at the initial stage of sputtering to finally Ar: O ₂ : N ₂ = 2: 1: 0. At this time, the flow rates of Ar and O ₂ were kept constant, and the flow rate of N ₂ was continuously decreased.
The composition of the surface layer formed by such sputtering is from a composition rich in nitrogen to a composition rich in oxygen, from the contact surface with the base material to the surface (air side) opposite to the contact surface with the base material. Become. Therefore, the refractive index of the surface layer formed by sputtering decreases continuously from the contact surface with the substrate toward the surface (air side) opposite to the contact surface with the substrate. Specifically, the refractive index n = 1.83 of the base material (YAG), the refractive index n = 1.83 of the contact surface with the base material in the surface layer (composition is Si ₅ ON ₅ ), the base material in the surface layer The refractive index n of the surface (air side) opposite to the contact surface was 1.45. Each refractive index was measured using FilmTEK4000 manufactured by SCI.
The surface layer formed in the film forming step is a flat layer that does not have a fine uneven shape. Therefore, a mask pattern made of a single particle film of silica particles is disposed on the surface layer, and the surface layer is etched through the mask pattern to form a surface uneven layer having a fine uneven shape formed on the surface (etching step). ).
In the surface irregularity layer, the refractive index continuously decreases from the contact surface with the base material to the surface (air side) opposite to the contact surface with the base material, and the tips of the fine protrusions are rich in oxygen. It was SiO ₂ (refractive index n = 1.45).
Thus, about the fine structure in which the surface uneven | corrugated layer was formed, the reflectance of the surface, calculation of light extraction efficiency (refer said formula (1)), etc. were performed. The results are shown in Table 1.
The surface reflectance was measured at a measurement wavelength λ = 380 to 780 nm, and the average value is shown in Table 1.

<Comparative Example 1>
A film forming process was performed in the same manner as in Example 1 except that the film was formed while maintaining the molar ratio of the sputtering gas at Ar: O ₂ : N ₂ = 2: 1: 2. As a result, a surface layer made of Si ₅ ON ₅ having a constant refractive index in the film thickness direction (n = 1.83 equal to YAG) was formed.
Thereafter, a mask pattern made of a single particle film of silica particles similar to that used in Example 1 is placed on the surface layer, and the surface layer is etched through the mask pattern to form a fine uneven shape on the surface. The surface uneven | corrugated layer was formed (etching process). In the same manner as in Example 1, the surface reflectance was measured, the light extraction efficiency was calculated, and the like. The results are shown in Table 1.

<Comparative Example 2>
Measurement of the reflectance (surface reflectance) of a base material made of YAG (without the surface uneven layer) was performed. In addition, the light extraction efficiency was calculated. The results are shown in Table 1.

The thickness d ₁ of the surface uneven layer was obtained as follows by extracting 30 fine protrusions from the SEM image as shown in FIG. First, for each fine protrusion, the distance from the apex to the interface between the surface uneven layer and the substrate was measured. Further, for each of 29 valleys between the 30 fine protrusions, the distance from the valley to the interface between the surface uneven layer and the substrate was measured. The resulting measured values (number of data: 59) obtains an average value of, and the d _1.
Further, the radius of curvature (nm) of the tip of the fine protrusion was extracted from 30 SEM images as shown in FIG. 1, the minimum radius of curvature of each tip portion was measured, and the average value was obtained. Described.

In Example 1, since the refractive index of the contact surface with the base material of the surface uneven layer is the same as that of YAG, R ² is 0%. The same applies to Comparative Example 1. On the other hand, Comparative Example 2, since it does not have surface unevenness ^layer, (reflectance of the interface between YAG and air) R 2 was 10.20% (found).
Moreover, in Example 1, since the composition of a surface uneven | corrugated layer is changing continuously, the composition of a surface uneven | corrugated layer is the composition of a contact surface side with a base material, and a composition on the opposite side to this contact surface. regarded as the average composition, based on the average composition was determined a value of a _1.
d ₁ corresponds to a thickness of the surface uneven layer of 500 nm (= 0.005 mm), and d ₂ corresponds to a thickness of 1 mm of the substrate.
_Ex is an intrinsic property depending on the material of the base material, and is 26% in the case of YAG.
The light extraction efficiency of each example was calculated as follows.
Example 1: (1-0.005) × (1-0) × (1-0.002 × 0.0005) × (1-0.015 × 1) × 0.26 = 0.2548; 25.48%
Comparative Example 1: (1-0.039) × (1-0) × (1-0.002 × 0.0005) × (1-0.015 × 1) × 0.26 = 0.2460; 24.60%
Comparative Example 2: (1-0) × (1-0.1020) × (1-0 × 0) × (1-0.015 × 1) × 0.26 = 0.299; that is, 22.99%
Reflectance measurement method: “V-670 spectrophotometer” manufactured by JASCO Corporation was used to measure 5 ° frontal reflection. At the time of measuring R _{1, the} measurement was performed after the light absorption tape (Tech World Co., “Super Black IR”) was subjected to light absorption treatment on the back surface.

In addition, as the refractive index distribution curve of a surface uneven | corrugated layer is shown in FIG. 5, the refractive index of the surface uneven | corrugated layer of Example 1 is continuous as the height from the contact surface with a base material becomes large. It was getting smaller. And the "local change rate" (formula (3); distance = 10 nm) of the refractive index at an arbitrary position of the surface uneven layer is 100% when the "overall average change rate" (formula (4)) is 100%. , Within a range of ± 5%. ). On the other hand, the refractive index of the surface layer of Comparative Example 1 was constant.
The refractive index distribution curve of FIG. 5 was obtained as follows.
First, a plurality of samples in which the ratio of x and _y in SiO _x N _y is changed (in each sample, there is no composition gradient), and the refractive index of the sample is measured to obtain the composition (SiO _x A calibration curve of N _y ) -refractive index was obtained. At this time, a stylus type step gauge was used to measure the film thickness of a plurality of samples, and a spectroscopic ellipsometer was used to measure the refractive index. Next, in Example 1, the surface layer formed in the film forming process (the layer not subjected to the etching process) was subjected to TOF-SIMS by ion milling using an argon ion beam to form a region from the surface to a depth of 500 nm. The atoms were identified by performing mass analysis of the atoms while gradually digging by about 10 nm. Thus, at each position in the depth direction from the surface of the surface layer determines the x and y SiO _x N _y, was determined composition. And the refractive index was calculated | required from the composition of each position using the above-mentioned calibration curve, and FIG. 5 was obtained. The same operation was performed for Comparative Example 1.

<Discussion>
From the results in Table 1, it can be seen that the light extraction efficiency decreases in the order of Example 1, Comparative Example 1, and Comparative Example 2. Similarly, the reflectance of the surface also increases in the order of Example 1, Comparative Example 1, and Comparative Example 2, and it can be seen that the antireflection performance decreases.
Since Comparative Example 1 has a fine concavo-convex structure, the reflectance is lower than that of Comparative Example 2, but it is not sufficient. On the other hand, Example 1 was excellent in both light extraction efficiency and antireflection ability.
In addition, the fine protrusion of Example 1 had a larger radius of curvature at the tip than the fine protrusion of Comparative Example 1 and a rounded tip, but was excellent in antireflection performance. From this, it was suggested that the fine structure of Example 1 is excellent not only in antireflection performance but also in scratch resistance.

DESCRIPTION OF SYMBOLS 10 Antireflection structure 11 Base material 12 Surface uneven | corrugated layer 12 'Surface layer

Claims (8)

A microstructure having a substrate and a surface uneven layer formed on at least a part of the substrate and having a fine uneven shape formed on the surface,
The surface uneven layer has a fine structure in which the refractive index is continuously reduced from the contact surface with the base material toward the surface of the surface uneven layer on the opposite side of the contact surface. body.   The said surface uneven | corrugated layer contains silicon, oxygen, and nitrogen, and the content of the said nitrogen is continuously small toward the said surface of the said surface uneven | corrugated layer from the said contact surface. Fine structure.   The fine structure according to claim 1 or 2, wherein the surface of the base material on which the uneven surface layer is formed has a center line average roughness Ra of 30 nm or less according to JIS B0601.   The microstructure according to any one of claims 1 to 3, wherein the substrate is made of YAG. Sputtering the target with sputtering gas to form a surface layer on the substrate,
Etching the surface layer through a mask pattern, and making the surface layer a surface uneven layer,
In the film forming step, the refractive index in the film thickness direction of the surface layer is continuously increased from the contact surface between the base material and the surface layer toward the surface of the surface layer opposite to the contact surface. A method of manufacturing a fine structure, wherein the surface layer is formed to be small.   In the film forming step, a composition in the film thickness direction of the surface layer is formed by using a mixed gas of a rare gas and a reactive gas as the sputtering gas and continuously changing the gas composition of the mixed gas. The method for producing a fine structure according to claim 5, wherein the is continuously changed.   The microstructure according to claim 6, wherein in the film forming step, silicon is used as the target, oxygen and nitrogen are used as the reactive gas, and a ratio of the nitrogen in the mixed gas is continuously reduced. Manufacturing method.   7. The microstructure according to claim 6, wherein in the film forming step, silicon dioxide is used as the target, nitrogen is used as the reactive gas, and a ratio of the nitrogen in the mixed gas is continuously reduced. Production method.

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