Optical film, antireflection optical element and master

An optical element includes a base and a large number of structures arranged on the surface of the base, the structures being projections or depressions. The structures are arranged at a pitch shorter than or equal to a wavelength of light in a use environment. An effective refractive index in the depth direction of the structures gradually increases toward the base and has two or more inflection points.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national stage of International Application No. PCT/JP2009/066870 filed on Sep. 18, 2009 and claims priority to Japanese Patent Application No. 2008-250492 filed on Sep. 29, 2008 the disclosures of which are incorporated herein by reference.

BACKGROUND

The present invention relates to an optical element, an optical component having an anti-reflection function, and a master. Specifically, the present invention relates to an optical element in which structures are arranged at a pitch shorter than or equal to a wavelength of light in a use environment.

Conventionally, in an optical element that uses a light-transmissive substrate composed of glass, plastic, or the like, surface treatment is performed to suppress the surface reflection of light. A method in which a minute and dense uneven structure (moth-eye structure) is formed on the surface of the optical element is exemplified as the surface treatment (e.g., refer to refer to “Optical and Electro-Optical Engineering Contact” Vol. 43, No. 11 (2005), 630-637).

In general, in the case where a periodic uneven shape is formed on the surface of an optical element, diffraction is generated when light passes through the periodic uneven shape, which considerably reduces the amount of the light component of transmitted light that goes straight. However, when the pitch of the uneven shape is shorter than the wavelength of light transmitted, diffraction is not generated. For example, if the uneven shape is rectangular, an anti-reflection effect that is effective for single-wavelength light corresponding to the pitch, depth, or the like can be achieved.

Since the above-described optical element has good anti-reflection characteristics, it is expected that the optical element is applied to a solar cell and a display device. The following is proposed as the uneven structure in which anti-reflection characteristics are taken into account.

A minute tent-shaped uneven structure (pitch: about 300 nm, depth: about 400 nm) is proposed as a structure manufactured using electron-beam exposure (e.g., refer to NTT Advanced Technology Corporation, “Master Mold for Forming Anti-reflection (Moth-eye) Structure having no wavelength dependence”, [online], [accessed Sep. 1, 2008], Internet <http://keytech.ntt-at.co.jp/nano/prd—0033.html>).

Furthermore, a Super-RENS Technology Team, the Center for Applied Near-Field Optics Research of the Advanced Industrial Science and Technology has proposed a nano-hole structure with a diameter of 100 nm and a depth of 500 nm or more (e.g., refer to the National Institute of Advanced Industrial Science and Technology, “Development of Desktop Device Enabling Nanometer-scale Microfabrication”, [online], [accessed Sep. 1, 2008], Internet <http://aist.go.jp/aist_i/press_release/pr2006/pr20060306/pr20060306.html>). Such a structure can be formed by a microstructure formation method that uses an optical disc recording apparatus. Specifically, such a structure can be formed using a nanomachining device based on a thermal lithography technology in which a visible light laser lithography method using a semiconductor laser (wavelength 406 nm) is combined with a thermally nonlinear material (e.g., refer to non-Patent Document 3).

In addition, the inventors of the present invention have proposed a structure having a hanging bell shape or a truncated elliptic cone-like shape (e.g., refer to International Publication No. 08/023,816 Pamphlet). In this structure, anti-reflection characteristics close to those of a structure obtained by electron-beam exposure are achieved. Furthermore, the structure can be manufactured by a method in which a process for making a master of optical discs is combined with an etching process.

SUMMARY

Technical Problem

In recent years, it has been desired that the visibility of various display devices such as a liquid crystal display device is further improved. To satisfy such a demand, it is important to further improve the above-described anti-reflection characteristics of optical elements.

Accordingly, an object of the present invention is to provide an optical element having good anti-reflection characteristics, an optical component having an anti-reflection function, and a master.

Technical Solution

To solve the problems described above, a first invention provides an optical element having an anti-reflection function, including:

a base; and

a large number of structures arranged on a surface of the base, the structures being projections or depressions,

wherein the structures are arranged in a hexagonal lattice, a quasi-hexagonal lattice, a tetragonal lattice, or a quasi-tetragonal lattice at a pitch shorter than or equal to a wavelength of light in a use environment, and

an effective refractive index in a depth direction of the structures gradually increases toward the base and has two or more inflection points.

A second invention provides an optical component having an anti-reflection function, including:

an optical component; and

a large number of structures arranged on a light-entering surface of the optical component, the structures being projections or depressions,

wherein the structures are arranged in a hexagonal lattice, a quasi-hexagonal lattice, a tetragonal lattice, or a quasi-tetragonal lattice at a pitch shorter than or equal to a wavelength of light in a use environment, and

an effective refractive index in a depth direction of the structures gradually increases toward a base and has two or more inflection points.

A third invention provides a master including:

a base; and

a large number of structures arranged on a surface of the base, the structures being projections or depressions,

wherein the structures are used for forming a surface shape of an optical element having an anti-reflection function,

the structures are periodically arranged in a hexagonal lattice, a quasi-hexagonal lattice, a tetragonal lattice, or a quasi-tetragonal lattice at a pitch shorter than or equal to a wavelength of light in an environment where the optical element is used, and

an effective refractive index in a depth direction of the optical element formed by the structures gradually increases toward the base of the optical element and has two or more inflection points.

A fourth invention provides an optical element having an anti-reflection function, including:

a base; and

a large number of structures arranged on a surface of the base, the structures being projections or depressions,

wherein the structures are arranged at a pitch shorter than or equal to a wavelength of light in a use environment,

the structures have a cone-like shape or an elliptic cone-like shape whose top has a curvature, or a truncated cone-like shape or a truncated elliptic cone-like shape, and

an effective refractive index in a depth direction of the structures gradually increases toward the base and has two or more inflection points.

A fifth invention provides an optical element having an anti-reflection function, including:

a base; and

a gradient film formed on the base,

wherein an effective refractive index in a depth direction of the gradient film gradually increases toward the base and has two or more inflection points.

In the present invention, the term “depth direction” means a direction that perpendicularly extends from the surface of the base to the inside of the base. Specifically, when the structures are projections, the depth direction is a direction that perpendicularly extends from the top to the bottom of the projections. When the structures are depressions, the depth direction is a direction that perpendicularly extends from the opening portion to the bottom of the depressions.

In the present invention, the term “tetragonal lattice” means a regular tetragonal lattice. The term “quasi-tetragonal lattice” means, unlike a regular tetragonal lattice, a distorted regular tetragonal lattice.

Specifically, when the structures are arranged linearly, the quasi-tetragonal lattice is a tetragonal lattice obtained by stretching and distorting a regular tetragonal lattice in the direction of the linear arrangement. When the structures are arranged in an arc-like shape, the quasi-tetragonal lattice is a tetragonal lattice obtained by distorting a regular tetragonal lattice in an arc-like shape or a tetragonal lattice obtained by distorting a regular tetragonal lattice in an arc-like shape and stretching and distorting it in the direction of the arc-shaped arrangement. When the structures are arranged in a meandering manner, the quasi-tetragonal lattice is a tetragonal lattice obtained by distorting a regular tetragonal lattice through the meandering arrangement of the structures. Alternatively, the quasi-tetragonal lattice is a tetragonal lattice obtained by stretching and distorting a regular tetragonal lattice in the direction (track direction) of the linear arrangement and distorting through the meandering arrangement of the structures.

In the present invention, the term “hexagonal lattice” means a regular hexagonal lattice. The term “quasi-hexagonal lattice” means, unlike a regular hexagonal lattice, a distorted regular hexagonal lattice.

Specifically, when the structures are arranged linearly, the quasi-hexagonal lattice is a hexagonal lattice obtained by stretching and distorting a regular hexagonal lattice in the direction of the linear arrangement. When the structures are arranged in an arc-like shape, the quasi-hexagonal lattice is a hexagonal lattice obtained by distorting a regular hexagonal lattice in an arc-like shape or a hexagonal lattice obtained by distorting a regular hexagonal lattice in an arc-like shape and stretching and distorting it in the direction of the arc-shaped arrangement. When the structures are arranged in a meandering manner, the quasi-hexagonal lattice is a hexagonal lattice obtained by distorting a regular hexagonal lattice through the meandering arrangement of the structures. Alternatively, the quasi-hexagonal lattice is a hexagonal lattice obtained by stretching and distorting a regular hexagonal lattice in the direction (track direction) of the linear arrangement and distorting through the meandering arrangement of the structures.

In the present invention, the term “ellipse” includes not only mathematically defined perfect ellipses but also ellipses having some distortion. The term “circle” includes not only mathematically defined perfect circles but also circles having some distortion.

In the first to fourth inventions, the effective refractive index in the depth direction of the structures gradually increases and has two or more inflection points, whereby an interference effect can be produced on the surface of the base while a shape effect of the structures is used. Thus, the reflected light on the surface of the base can be reduced.

In the fifth invention, the effective refractive index in the depth direction of the gradient film gradually increases and has two or more inflection points, whereby an interference effect can be produced on the surface of the base. Thus, the reflected light on the surface of the base can be reduced.

Advantageous Effects

As described above, according to the present invention, an optical element having good anti-reflection characteristics can be provided.

DETAILED DESCRIPTION

Embodiments of the present invention are described with reference to the attached drawings in the following order.1. First Embodiment (an example in which structures are two-dimensionally arranged linearly in a hexagonal lattice: refer toFIGS. 1A and 1B)2. Second Embodiment (an example in which structures are two-dimensionally arranged in an arc-like shape in a hexagonal lattice: refer toFIGS. 10A and 10B)3. Third Embodiment (an example in which structures are two-dimensionally arranged linearly in a tetragonal lattice: refer toFIGS. 13A and 13B)4. Fourth Embodiment (an example in which secondary structures are arranged in addition to primary structures: refer toFIGS. 14C and 14D)5. Fifth Embodiment (an example in which structures that are depressions are formed on the surface of a base: refer toFIG. 17)6. Sixth Embodiment (an example in which pillar-shaped structures are one-dimensionally arranged: refer toFIG. 18)7. Seventh Embodiment (an example of structures having parallel steps: refer toFIG. 19)8. Eighth Embodiment (an example in which a thin film is formed instead of structures: refer toFIG. 20)9. Ninth Embodiment (an example in which structures are arranged in a meandering manner: refer toFIG. 21)10. Tenth Embodiment (an example of an optical element manufactured using a room-temperature nanoimprinting technology: refer toFIGS. 22A to 22D)11. Eleventh Embodiment (an example of an optical element without a base: refer toFIG. 23)12. Twelfth Embodiment (a first application example to a display device: refer toFIG. 24)13. Thirteenth Embodiment (a second application example to a display device: refer toFIG. 25)14. Fourteenth Embodiment (an application example to a package of an image sensor element: refer toFIG. 26)15. Fifteenth Embodiment (an example in which a light-absorbing layer is formed on the back of an optical element: refer toFIG. 27)16. Sixteenth Embodiment (an example in which an optical element itself has light absorbency: refer toFIG. 28)17. Seventeenth Embodiment (an example in which an optical element is provided in a barrel: refer toFIG. 29)18. Eighteenth Embodiment (an example in which a transparent conductive film is formed on one principal surface of an optical element: refer toFIG. 30)19. Nineteenth Embodiment (an example in which structures are formed on both principal surfaces of an optical element: refer toFIG. 31)20. Twentieth Embodiment (an application example to a touch panel: refer toFIGS. 32A and 32B)21. Twenty-first Embodiment (an application example to a dye-sensitized solar cell: refer toFIG. 33)22. Twenty-second Embodiment (an application example to a silicon solar cell: refer toFIG. 34)
<1. First Embodiment>
[Configuration of Optical Element]

FIG. 1Ais a schematic plan view showing an example of a configuration of an optical element according to a first embodiment of the present invention.FIG. 1Bis a partially enlarged plan view of the optical element shown inFIG. 1A.FIG. 1Cis a sectional view taken along track T1, T3, . . . ofFIG. 1B.FIG. 1Dis a sectional view taken along track T2, T4, . . . ofFIG. 1B.

An optical element1is suitably applied to various optical components used for displays, optoelectronics, optical communications (optical fibers), solar cells, and luminaries. Specifically, one of a polarizer, a lens, an optical waveguide, a window material, and a display element can be exemplified as the optical component, for example.

The optical element1includes a base2having a front surface (first principal surface) and a back surface (second principal surface) facing each other and structures3that are projections and are formed on the front surface of the base2. The optical element1has an anti-reflection function against light that enters the front surface of the base on which the structures3are formed. Hereinafter, as shown inFIG. 1, two axes orthogonal to each other in one principal surface of the base2are referred to as an X axis and a Y axis and an axis perpendicular to the principal surface of the base2is referred to as a Z axis. Furthermore, when gaps2aare present between the structures3, a minute uneven shape is preferably provided to the gaps2a. By providing such a minute uneven shape, the reflectivity of the optical element1can be further reduced.

FIG. 2shows an example of a refractive index profile of the optical element according to the first embodiment of the present invention. As shown inFIG. 2, the effective refractive index in the depth direction (−Z axis direction inFIG. 1) of the structures3gradually increases and has two or more inflection points N1, N2, . . . , Nn(n: an integer of 2 or more). This reduces reflected light because of an interference effect of light, which can improve the anti-reflection characteristics of the optical element. The change in the effective refractive index in the depth direction is preferably a monotonic increase. Furthermore, the change in the effective refractive index in the depth direction is preferably greater on the top side of the structures3than an average of a slope of the effective refractive index and is also preferably greater on the base side of the structures3. This can improve ease of transference while good optical characteristics are achieved.

Hereinafter, the base2and the structures3constituting the optical element1are described in order below.

The base2is a transparent base having transparency. The base2is mainly composed of, for example, a transparent synthetic resin such as polycarbonate (PC) or polyethylene terephthalate (PET) or glass, but the material of the base2is not particularly limited to these materials.

The base2is, for example, in the shape of a film, sheet, plate, or block, but the shape of the base2is not particularly limited to these shapes. The shape of the base2is preferably selected and determined in accordance with the shape of the main body of each of various optical devices that require predetermined anti-reflection functions such as displays, optoelectronic devices, optical communication devices, solar cells, and illuminating devices or in accordance with the shape of a sheet- or film-shaped anti-reflection component attached to each of the optical devices.

FIG. 3is a partially enlarged perspective view of the optical element shown inFIG. 1. A large number of structures3that are projections are arranged on the surface of the base2. The structures3are periodically and two-dimensionally arranged at a pitch shorter than or equal to a wavelength of light in a use environment, for example, at a pitch substantially equal to a wavelength of visible light. The light in the use environment is, for example, ultraviolet light, visible light, or infrared light. Herein, the ultraviolet light is light having a wavelength of 10 nm to 360 nm. The visible light is light having a wavelength of 360 nm to 830 nm. The infrared light is light having a wavelength of 830 nm to 1 mm.

The structures3of the optical element1has a configuration including multiple rows of tracks T1, T2, T3, . . . (hereinafter collectively referred to as “track T”) provided on the surface of the base2. Herein, the track is a region where the structures3are linearly arranged in rows.

In the two adjacent tracks T, the structures3arranged on one track are shifted by half a pitch from the structures3arranged on the other track. Specifically, in the two adjacent tracks T, at the intermediate positions (at the positions shifted by half a pitch) between the structures3arranged on one track (e.g., T1), the structures3on the other track (e.g., T2) are disposed. Consequently, as shown inFIG. 1B, in the three adjacent rows of tracks (T1to T3), the structures3are arranged so as to form a hexagonal lattice pattern or a quasi-hexagonal lattice pattern with the centers of the structures3being positioned at points a1to a7. In the first embodiment, the term “hexagonal lattice pattern” means a lattice pattern having a regular hexagonal shape. In addition, the term “quasi-hexagonal lattice pattern” means, unlike a lattice pattern having a regular hexagonal shape, a hexagonal lattice pattern that is stretched and distorted in the track extending direction (X axis direction).

When the structures3are arranged so as to form a quasi-hexagonal lattice pattern, as shown inFIG. 1B, the arrangement pitch P1(distance between a1and a2) of the structures3on the same track (e.g., T1) is preferably longer than the arrangement pitch of the structures3between the two adjacent tracks (e.g., T1and T2), that is, the arrangement pitch P2(e.g., distance between a1and a7or a2and a7) of the structures3in the ±θ direction with respect to the track extending direction. By arranging the structures3in such a manner, the packing density of the structures3can be further improved.

The height (depth) of the structures3is not particularly limited, and is appropriately set in accordance with the wavelength range of light to be transmitted. The height of the structures3is preferably smaller than or equal to the average wavelength of light in a use environment. Specifically, when visible light is transmitted, the height (depth) of the structures3is preferably 150 nm to 500 nm. The aspect ratio (height H/arrangement pitch P) of the structures3is preferably set in the range of 0.81 to 1.46. If the aspect ratio is less than 0.81, the reflection characteristics and transmission characteristics tend to decrease. If the aspect ratio is more than 1.46, the releasing property is decreased during manufacturing of the optical element1and it tends to be difficult to remove a replicated replica properly.

Note that, in the present invention, the aspect ratio is defined by formula (1) below:
Aspect ratio=H/P(1)
where H is the height of the structures3, and P is the average arrangement pitch (average period).

Herein, the average arrangement pitch P is defined by formula (2) below:
Average arrangement pitchP=(P1+P2+P2)/3  (2)
where P1is the arrangement pitch in the track extending direction (period in the track extending direction), and P2is the arrangement pitch in the ±θ direction with respect to the track extending direction (where θ=60°−δ, where preferably 0°<δ≦11°, and more preferably 3°≦δ≦6°) (period in the θ direction).

Furthermore, the height H of the structures3is the height H2in the column direction of the structures3(refer toFIG. 3). Herein, the term “column direction” means a direction (Y axis direction) orthogonal to the track extending direction (X axis direction) in the surface of the base. When the optical element1is manufactured by the manufacturing method described below, the height H1in the track extending direction of the structures3is preferably smaller than the height H2in the column direction. By satisfying such a relationship of the heights, in the manufacturing method described below, the height of portions other than the portions located in the track extending direction of the structures3is substantially the same as the height H2in the column direction. Therefore, the height H of the structures3is represented by the height H2in the column direction.

InFIG. 3, each of the structures3has the same shape. However, the shape of the structures3is not limited thereto. The structures3having two or more different shapes may be formed on the surface of the base. Furthermore, the structures3may be integrally formed with the base2.

In addition, the structures3do not necessarily have the same aspect ratio. The structures3may be configured so as to have a certain height distribution (e.g., in the range of about 0.83 to 1.46 in terms of an aspect ratio). By disposing the structures3having the height distribution, the wavelength dependence of reflection characteristics can be reduced. Consequently, an optical element1having good anti-reflection characteristics can be realized.

The term “height distribution” means that the structures3having two or more different heights (depths) are disposed on the surface of the base2. That is, it means that structures3having a reference height and structures3having a height different from the reference height are disposed on the surface of the base2. The structures3having a height different from the reference height are disposed, for example, on the surface of the base2periodically or aperiodically (at random). For example, the track extending direction, the column direction, or the like may be exemplified as the direction of the periodicity.

Preferably, the structures3are mainly composed of, for example, an ionizing radiation curable resin that is cured through ultraviolet rays or electron beams or a thermosetting resin that is cured through heat. Most preferably, the structures3are mainly composed of an ultraviolet curable resin that is cured through ultraviolet rays.

FIG. 4is a sectional view showing an example of the shape of the structures. The structures3preferably have a curved surface so as to become wider from the top3tto the bottom3bof the structures3. By providing such a shape, ease of transference can be improved.

The top3tof the structures3has, for example, a flat surface or a convex curved surface. Preferably, the top3thas a convex curved surface. By providing such a convex curved surface, the durability of the optical element1can be improved. Furthermore, a low refractive index layer having a lower refractive index than the structures3may be formed on the top3tof the structures3. By forming such a low refractive index layer, the reflectivity can be reduced.

The curved surface of the structures3preferably has two pairs or more of a first changing point Pa and a second changing point Pb formed in that order in the direction from the top3tto the bottom3b. As a result, the effective refractive index in the depth direction (−Z axis direction inFIG. 1) of the structures3can have two or more inflection points. Herein, the uppermost point of the top3tis also a first changing point Pa and the lowermost point of the bottom3bis also a second changing point Pb.

In addition, at least one pair of a first changing point and a second changing point formed in that order in the direction from the top3tto the bottom3bof the structures3are preferably formed on the side surface of the structures3excluding the top3tand the bottom3b. In this case, the slope in the direction from the top3tto the bottom3bof the structures3preferably becomes gentler at the first changing point Pa and then becomes steeper at the second changing point Pb. Moreover, as described above, when at least one pair of the first changing point Pa and the second changing point Pb formed in that order are formed, the top3tof the structures3preferably has a convex curved surface or a hem3cthat broadens with a gradually decreasing slope is preferably formed (refer toFIG. 4).

Herein, the first changing point and the second changing point are defined as follows.

As shown inFIGS. 5A and 5B, in the case where the surface from the top3tto the bottom3bof the structures3is formed by joining a plurality of smooth curved surfaces in a discontinuous manner in the direction from the top3tto the bottom3bof the structures3, the joining points are the changing points. The changing points match the inflection points. Although differentiation cannot be performed accurately at the joining points, the inflection points taken as limit are also referred to as an inflection point. When the structures3have the above-described curved surface, as shown inFIG. 4, the slope in the direction from the top3tto the bottom3bof the structures3preferably becomes gentler at the first changing point Pa and then becomes steeper at the second changing point Pb.

As shown inFIG. 5C, in the case where the surface from the top3tto the bottom3bof the structures3is formed by joining a plurality of smooth curved surfaces in a continuous manner in the direction from the top3tto the bottom3bof the structures3, the changing points are defined as follows. As shown inFIG. 5C, the points, on the curved line, closest from intersection points at which tangent lines of inflection points, the uppermost point, and the lowermost point intersect with each other are referred to as a changing point. Furthermore, as described above, the uppermost point is the first changing point at the top3tand the lowermost point is the second changing point at the bottom3b.

The structures3preferably have two or more slope steps St, more preferably two or more and ten or less slope steps St on the surface between the top3tand the bottom3b. Specifically, the structures3preferably have two or more steps between the top3tand the bottom3b, the steps including either the top3tor the bottom3bor both the top3tand the bottom3b. When the number of slope steps St is two or more, the effective refractive index in the depth direction (−Z axis direction inFIG. 1) of the structures3can have two or more inflection points N1, N2, . . . , Nn(n: an integer of 2 or more). Moreover, when the number of slope steps St is ten or less, the structures3can be easily manufactured.

The term “slope step St” means a step that is inclined but is not parallel to the surface of the base. By making the step St be inclined with respect to the surface of the base rather than making the step St be parallel with the surface of the base, ease of transference can be improved. Herein, the slope step St is a section defined by the above-described first changing point Pa and second changing point Pb. Furthermore, the slope step St is a concept including a protrusion at the top3tand a hem3cat the bottom3bas shown inFIG. 4. In other words, a section defined by the first changing point Pa and the second changing point at the top3tand a section defined by the first changing point Pa and second changing point Pb at the bottom3bare also referred to as slope steps St.

A conical form can be exemplified as the entire shape of the structures3. Examples of the conical form include a cone-like shape, a truncated cone-like shape, an elliptic cone-like shape, a truncated elliptic cone-like shape, a cone-like shape whose top has a curvature, and an elliptic cone-like shape whose top has a curvature. Herein, as described above, the conical form has a concept including an elliptic cone-like shape, a truncated elliptic cone-like shape, a cone-like shape whose top has a curvature, and an elliptic cone-like shape whose top has a curvature in addition to a cone-like shape and a truncated cone-like shape. Moreover, the truncated cone-like shape is a shape obtained by removing the top of a cone-like shape from the cone-like shape. The truncated elliptic cone-like shape is a shape obtained by removing the top of an elliptic cone-like shape from the elliptic cone-like shape. Furthermore, the entire shape of the structures3is not limited to these shapes, and needs only to be a shape in which the effective refractive index in the depth direction of the structures3gradually increases toward the base2and has two or more inflection points.

The structures3having an elliptic cone-like shape are structures having a conical form in which the bottom face is in the shape of an ellipse, an oblong, or an oval with a major axis and a minor axis, and the top has a curved surface. The structures3having a truncated elliptic cone-like shape are structures having a conical form in which the bottom face is in the shape of an ellipse, an oblong, or an oval with a major axis and a minor axis, and the top has a flat surface. When the structures3have an elliptic cone-like shape or a truncated elliptic cone-like shape, the structures3are preferably disposed on the surface of the base such that the major axis of the bottom face of the structures3is directed in the track extending direction (X axis direction).

The cross section of the structures3changes in the depth direction of the structures3so as to correspond to the above-described refractive index profile. Preferably, the cross section of the structures3monotonically increases as the depth of the structures3increases. Herein, the cross section of the structures3means an area of a section that is parallel to the surface of the base where the structures3are arranged.

[Configuration of Roll Master]

FIG. 6shows an example of a configuration of a roll master for manufacturing the optical element having the above-described configuration. As shown inFIG. 6, a roll master11includes a large number of structures13that are depressions and are arranged on the surface of a cylinder- or column-shaped master12. The structures13are periodically and two-dimensionally arranged at a pitch shorter than or equal to a wavelength of light in an environment where the optical element1is used, for example, at a pitch substantially equal to a wavelength of visible light. The structures13are arranged on the surface of the cylinder- or column-shaped master12, for example, in a concentric or spiral manner. The structures13are used for forming the structures3that are projections on the surface of the above-described base2. The master12can be composed of, for example, glass, but the material is not particularly limited thereto.

[Method for Manufacturing Optical Element]

Next, an example of a method for manufacturing the optical element having the above-described configuration will be described with reference toFIGS. 7 to 9.

A method for manufacturing an optical element according to the first embodiment is a method in which a process for making a master of optical discs is combined with an etching process. The manufacturing method includes a resist layer formation step of forming a resist layer on a master, an exposure step of forming a latent image of a moth-eye pattern on the resist layer using a roll master exposure apparatus, a development step of developing the resist layer on which the latent image has been formed, an etching step of making a roll master using plasma etching or the like, and a replication step of making a replica substrate using an ultraviolet curable resin. Herein, a RIE (reactive ion etching) apparatus may be used in the etching step.

(Configuration of Exposure Apparatus)

First, a configuration of the roll master exposure apparatus used in the moth-eye pattern exposure step will be described with reference toFIG. 7. The roll master exposure apparatus is configured on the basis of an optical disc recording apparatus.

A laser light source21is a light source for exposing the resist layer formed on the surface of the master12as a recording medium, and oscillates, for example, a laser beam15for recording with a wavelength λ of 266 nm. The laser beam15emitted from the laser light source21travels in a straight line as a collimated beam and enters an electro optical modulator (EOM)22. The laser beam15transmitted through the electro optical modulator22is reflected by a mirror23and guided to an optical modulation system25.

The mirror23includes a polarization beam splitter and has a function that reflects one polarized component and transmits the other polarized component. The polarized component transmitted through the mirror23is received by a photodiode24, and the electro optical modulator22is controlled in accordance with the signal of the received polarized component to perform phase modulation of the laser beam15.

In the optical modulation system25, the laser beam15is focused by a collective lens26on an acoust-optic modulator (AOM)27composed of glass (SiO2) or the like. After the laser beam15is intensity-modulated by the acoust-optic modulator27and diverged, the laser beam15is collimated by a collimating lens28. The laser beam15emitted from the optical modulation system25is reflected by a mirror31and guided onto a moving optical table32in a horizontal and parallel manner.

The moving optical table32includes a beam expander33and an objective lens34. The laser beam15guided to the moving optical table32is shaped into a desired beam form by the beam expander33, and then applied to the resist layer on the master12through the objective lens34. The master12is placed on a turntable36connected to a spindle motor35. Subsequently, the exposure step of the resist layer is performed by intermittently irradiating the resist layer with the laser beam15while the master12is rotated and the laser beam15is moved in the height direction of the master12. The resulting latent image has, for example, a substantially elliptical shape having a major axis in the circumferential direction. The laser beam15is moved by moving the moving optical table32in the direction indicated by arrow R.

The exposure apparatus includes a control mechanism37for forming, on the resist layer, a latent image corresponding to the two-dimensional pattern of the hexagonal lattice or quasi-hexagonal lattice shown inFIG. 1B. The control mechanism37includes a formatter29and a driver30. The formatter29includes a polarity inversion unit, and the polarity inversion unit controls the timing when the resist layer is irradiated with the laser beam15. The driver30controls the acoust-optical modulator27in response to the output from the polarity inversion unit.

In the roll master exposure apparatus, a polarity inversion formatter signal is synchronized to a rotation controller of the recording apparatus to generate a signal for each track so that two-dimensional patterns are spatially linked to one another, and intensity modulation is performed by the acoust-optical modulator27. By performing patterning at constant angular velocity (CAV) and at an appropriate number of revolutions, an appropriate modulation frequency, and an appropriate feed pitch, a hexagonal or quasi-hexagonal lattice pattern can be recorded on the resist layer.

Hereinafter, the individual steps in the method for manufacturing the optical element according to the first embodiment of the present invention will be described in order below.

First, as shown inFIG. 8A, a cylinder- or column-shaped master12is prepared. The master12is, for example, a glass master. Next, as shown inFIG. 8B, a resist layer14is formed on a surface of the master12. The resist layer14can be composed of, for example, either an organic resist or an inorganic resist. Examples of the organic resist include novolac resists and chemically-amplified resists. Furthermore, examples of the inorganic resist include metal oxides containing one, or two or more transition metals such as tungsten and molybdenum.

Next, as shown inFIG. 8C, using the roll master exposure apparatus described above, the resist layer14is irradiated with the laser beam (exposure beam)15while the master12is rotated. In this step, the entire surface of the resist layer14is exposed by intermittently irradiating the resist layer14with the laser beam15while the laser beam15is moved in the height direction of the master12. As a result, a latent image16following the trajectory of the laser beam15is formed over the entire surface of the resist layer14, for example, at a pitch substantially equal to a wavelength of visible light.

Next, a developer is dropwise applied onto the resist layer14while the master12is rotated, whereby the resist layer14is subjected to development treatment as shown inFIG. 9A. In the case where the resist layer14is formed using a positive resist, an exposed portion exposed to the laser beam15has an increased rate of dissolution in the developer compared with a non-exposed portion. As a result, as shown inFIG. 9A, a pattern corresponding to the latent image (exposed portion)16is formed on the resist layer14.

Next, the surface of the master12is etched using, as a mask, the pattern of the resist layer14(resist pattern) formed on the master12. Consequently, as shown inFIG. 9B, there can be obtained depressions of an elliptic cone-like shape or a truncated elliptic cone-like shape having a major axis directed in the track extending direction, that is, structures13. The etching is performed by dry etching or the like. In this step, by alternately carrying out etching treatment and ashing treatment, for example, a pattern of conical structures13can be formed, and also a glass master having a depth of three times or more the thickness of the resist layer14(selectivity: 3 or more) can be produced to achieve a high aspect ratio of the structures3. Furthermore, by appropriately adjusting the treatment time of the etching treatment and the ashing treatment, slope steps can be formed on a curved surface of the structures13.

Thereby, a roll master11having a hexagonal lattice pattern or a quasi-hexagonal lattice pattern can be obtained.

Next, the roll master11and the base2such as an acrylic sheet to which an ultraviolet curable resin has been applied are brought into close contact with each other. After the ultraviolet curable resin is cured by irradiation with ultraviolet rays, the base2is detached from the roll master11. Consequently, as shown inFIG. 9C, an intended optical element1is manufactured.

According to the first embodiment, the change in an effective refractive index in the depth direction is characterized by each of the structures3, and the effective refractive index gradually increases toward the base2and has two or more inflection points N1, N2, . . . , Nn(n: an integer of 2 or more). Therefore, reflected light can be reduced because of an interference effect of light combined with a shape effect of the structures3. Thus, an optical element having good anti-reflection characteristics can be realized.

Furthermore, when the optical element1is manufactured by a method in which a process for making a master of optical discs is combined with an etching process, the time (exposure time) required in the process for making a master can be considerably shortened compared with the case where the optical element1is manufactured using electron-beam exposure. Thus, the productivity of the optical element1can be significantly improved.

Moreover, when the shape of the top of the structures3is a smooth shape but not an acute shape, that is, when the shape of the top has a smooth curved surface that protrudes in the height direction, the durability of the optical element1can be improved. The releasing property of the optical element1from the roll master11can also be improved.

Furthermore, when a step of the structures3is a slope step, ease of transference can be improved compared with the case where a parallel step is used. Note that the parallel step will be described later.

[Configuration of Optical Element]

FIG. 10Ais a schematic plan view showing an example of a configuration of an optical element according to a second embodiment of the present invention.FIG. 10Bis a partially enlarged plan view of the optical element shown inFIG. 10A.FIG. 10Cis a sectional view taken along track T1, T3, . . . ofFIG. 10B.FIG. 10Dis a sectional view taken along track T2, T4, . . . ofFIG. 10B.

In an optical element1according to the second embodiment, tracks T have an arc-like shape and structures3are arranged in an arc-like shape. As shown inFIG. 10B, in the three adjacent rows of tracks (T1to T3), the structures3are arranged so as to form a quasi-hexagonal lattice pattern with the centers of the structures3being positioned at points a1to a7. Herein, the term “quasi-hexagonal lattice pattern” means, unlike a regular hexagonal lattice pattern, a hexagonal lattice pattern distorted in an arc-like shape of the tracks T. Alternatively, the quasi-hexagonal lattice pattern means a hexagonal lattice pattern that is distorted in an arc-like shape of the tracks T and stretched and distorted in the track extending direction (X axis direction).

Except for the configuration of the optical element1described above, the configuration is the same as that in the first embodiment, and the description thereof is omitted.

[Configuration of Disc Master]

FIG. 11shows an example of a configuration of a disc master for manufacturing the optical element having the above-described configuration. As shown inFIG. 11, a disc master41has a configuration in which a large number of structures43that are depressions are arranged on a surface of a disc-shaped master42. The structures13are periodically and two-dimensionally arranged at a pitch shorter than or equal to a wavelength of light in an environment where the optical element1is used, for example, at a pitch substantially equal to a wavelength of visible light. For example, the structures43are disposed on concentric or spiral tracks.

Except for the configuration of the disc master41described above, the configuration is the same as that of the roll master11in the first embodiment, and the description thereof is omitted.

[Method for Manufacturing Optical Element]

FIG. 12is a schematic view showing an example of a configuration of an exposure apparatus used for making a disc master having the above-described configuration.

A moving optical table32includes a beam expander33, a mirror38, and an objective lens34. The laser beam15guided to the moving optical table32is shaped into a desired beam form by the beam expander33, and then applied to the resist layer on the disc-shaped master42through the mirror38and the objective lens34. The master42is placed on a turntable (not shown) connected to a spindle motor35. Subsequently, the exposure step of the resist layer is performed by intermittently irradiating the resist layer on the master42with the laser beam while the master42is rotated and the laser beam15is moved in the radial direction of rotation of the master42. The resulting latent image has a substantially elliptical shape having a major axis in the circumferential direction. The laser beam15is moved by moving the moving optical table32in the direction indicated by arrow R.

The exposure apparatus shown inFIG. 12includes a control mechanism37for forming, on the resist layer, a latent image of the hexagonal lattice or quasi-hexagonal lattice two-dimensional pattern shown inFIG. 11. The control mechanism37includes a formatter29and a driver30. The formatter29includes a polarity inversion unit, and the polarity inversion unit controls the timing when the resist layer is irradiated with the laser beam15. The driver30controls an acoust-optical modulator27in response to the output from the polarity inversion unit.

The control mechanism37synchronizes the intensity modulation of the laser beam15performed by the AOM27, the driving rotational speed of the spindle motor35, and the moving speed of the moving optical table32for each track so that the two-dimensional patterns of the latent image are spatially linked to one another. The rotation of the master42is controlled at a constant angular velocity (CAV). In addition, patterning is performed using an appropriate number of revolutions of the master42provided by the spindle motor35, appropriate frequency modulation of laser intensity provided by the AOM27, and an appropriate feed pitch of the laser beam15provided by the moving optical table32. Thereby, a latent image of a hexagonal lattice pattern or a quasi-hexagonal lattice pattern is formed on the resist layer.

Furthermore, the control signal of the polarity inversion unit is gradually changed such that the spatial frequency (pattern density of the latent image: P1: 330, P2: 300 nm; P1: 315 nm, P2: 275 nm; or P1: 300 nm, P2: 265 nm) becomes uniform. More specifically, exposure is performed while an irradiation period of the resist layer with the laser beam15is changed for each track, and frequency modulation of the laser beam15is performed by the control mechanism37such that P1becomes about 330 nm (315 nm, or 300 nm) on each track T. That is, the modulation is controlled such that the irradiation period of the laser beam becomes shorter as the track position becomes distant from the center of the disc-shaped master42. Thereby, a nano-pattern in which the spatial frequency is uniform over the entire substrate can be formed.

Except for the method for manufacturing the optical element described above, the method is the same as that in the first embodiment, and the description thereof is omitted.

According to the second embodiment, as in the case where the structures3are linearly arranged, an optical element1having good anti-reflection characteristics can be obtained.

FIG. 13Ais a schematic plan view showing an example of a configuration of an optical element according to a third embodiment of the present invention.FIG. 13Bis a partially enlarged plan view of the optical element shown inFIG. 13A.FIG. 13Cis a sectional view taken along track T1, T3, . . . ofFIG. 13B.FIG. 13Dis a sectional view taken along track T2, T4, . . . ofFIG. 13B.

An optical element1according to the third embodiment differs from that of the first embodiment in that, in the three adjacent rows of tracks, structures3form a tetragonal lattice pattern or a quasi-tetragonal lattice pattern. Herein, the term “quasi-tetragonal lattice pattern” means, unlike a regular tetragonal lattice pattern, a tetragonal lattice pattern that is stretched and distorted in the track extending direction (X axis direction). When the structures3are periodically arranged in a tetragonal lattice pattern or in a quasi-tetragonal lattice pattern, for example, the structures3lie adjacent to one another in directions of 4-fold symmetry. Moreover, by further stretching and distorting the tetragonal lattice, a structure can also be laid adjacent to the structures on the same track, and an arrangement with high packing density is achieved in which one structure lies adjacent to structures not only in directions of 4-fold symmetry but also at two positions on the same track.

In the two adjacent tracks T, at the intermediate positions (at the positions shifted by half a pitch) between the structures3arranged on one track (e.g., T1), the structures3on the other track (e.g., T2) are disposed. Consequently, as shown inFIG. 13B, in the three adjacent rows of tracks (T1to T3), the structures3are arranged so as to form a tetragonal lattice pattern or a quasi-tetragonal lattice pattern with the centers of the structures3being positioned at points a1to a4.

The height (depth) of the structures3is not particularly limited, and is appropriately set in accordance with the wavelength range of light to be transmitted. For example, when visible light is transmitted, the height (depth) of the structures3is preferably 150 nm to 500 nm. The pitch P2in the θ direction with respect to the track T is, for example, about 275 nm to 297 nm. The aspect ratio (height H/arrangement pitch P) of the structures3is, for example, about 0.54 to 1.13. In addition, the structures3do not necessarily have the same aspect ratio. The structures3may be configured so as to have a certain height distribution.

The arrangement pitch P1of the structures3on the same track is preferably longer than the arrangement pitch P2of the structures3between the two adjacent tracks. Furthermore, the ratio P1/P2preferably satisfies the relationship 1.4<P1/P2≦1.5, where P1is the arrangement pitch of the structures3on the same track and P2is the arrangement pitch of the structures3between the two adjacent tracks. By selecting such a numerical range, the packing density of the structures having an elliptic cone-like shape or a truncated elliptic cone-like shape can be improved. Therefore, anti-reflection characteristics can be improved.

In the third embodiment, an optical element1having good anti-reflection characteristics can be obtained as in the first embodiment.

FIG. 14Ais a schematic plan view showing an example of a configuration of an optical element according to a fourth embodiment of the present invention.FIG. 14Bis a partially enlarged plan view of the optical element shown inFIG. 14A.FIG. 14Cis a sectional view taken along track T1, T3, . . . ofFIG. 14B.FIG. 14Dis a sectional view taken along track T2, T4, . . . ofFIG. 14B.FIG. 15is a partially enlarged perspective view of the optical element shown inFIG. 14.

An optical element1according to the fourth embodiment differs from that of the first embodiment in that the optical element1further includes secondary structures4formed on the surface of the base2. The same parts as those in the first embodiment are designated by the same reference numerals, and the descriptions thereof are omitted. Note that, in the fourth embodiment, the structures3are referred to as primary structures3to avoid the confusion between the structures3and the secondary structures4.

The secondary structures4are structures whose height is smaller than that of the primary structures3. For example, the secondary structures4are small protruding portions.

Furthermore, when the height of the secondary structures4is smaller than or equal to about ¼ the wavelength of light in a use environment on the basis of an optical path length adopted in consideration of a refractive index, the secondary structures4contribute to an anti-reflection function. For example, the height of the secondary structures4is about 10 nm to 150 nm. The secondary structures4can be composed of, for example, the same material as that of the base2and the primary structures3, but is preferably composed of a material having a lower refractive index than the materials constituting the base2and the primary structures3. This is because the reflectivity can be further reduced. Furthermore, in the above description, the case where both the primary structures3and the secondary structures4are projections has been mainly described, but the primary structures3and the secondary structures4may be depressions. Moreover, the projection-depression relationship may be reversed between the primary structures3and the secondary structures4. Specifically, when the primary structures3are projections, the secondary structures4may be depressions. When the primary structures3are depressions, the secondary structures4may be projections.

The secondary structures4are disposed, for example, between the primary structures3. Specifically, preferably, the secondary structures4are provided in the most adjacent portions of the primary structures3, and the primary structures3are connected to one another by the secondary structures4provided in the most adjacent portions. In such a manner, the packing density of the primary structures3can be improved. Furthermore, the spatial frequency component of the secondary structures4is preferably higher than the frequency component converted from the period of the primary structures3. Specifically, the spatial frequency component of the secondary structures4is preferably two times or higher and more preferably four times or higher the frequency component converted from the period of the primary structures3. Preferably, the spatial frequency component of the secondary structures4is not an integral multiple of the frequency component of the primary structures3.

From the standpoint of ease of formation of the secondary structures4, as shown inFIG. 14B, the secondary structures4are preferably arranged in positions indicated by black circles where the primary structures3of an elliptic cone-like shape, a truncated elliptic cone-like shape, or the like lie adjacent to one another. In such an arrangement, the secondary structures4may be formed in all the adjacent portions of the primary structures3or may be formed only in the track, such as T1or T2, extending direction. When the primary structures3are arranged periodically in a hexagonal lattice pattern or in a quasi-hexagonal lattice pattern, for example, the primary structures3lie adjacent to one another in directions of 6-fold symmetry. In this case, preferably, the secondary structures4are provided in the adjacent portions, and the primary structures3are connected to one another by the secondary structures4. Furthermore, when gaps2aare present between the primary structures3as shown inFIG. 14B, from the standpoint of improving the packing density, the secondary structures4are preferably formed in the gaps2abetween the primary structures3. The secondary structures4may be formed both in the adjacent portions of the primary structures3and in the gaps2a. Furthermore, the positions in which the secondary structures4are formed are not particularly limited to the examples described above. The secondary structures4may be formed on the entire surfaces of the primary structures3.

Furthermore, from the standpoint of improving the reflection characteristics and transmission characteristics, at least one type of minute projections and depressions, for example, minute uneven portions4aare preferably formed on the surfaces of the secondary structures4.

Furthermore, in order to obtain an optical element1having a good anti-reflection function and small wavelength dependence, minute projections or depressions of the secondary structures4are preferably formed so as to have a spatial frequency component of high-frequency wave that is shorter than the period of the primary structures3. For example, the secondary structures4preferably include corrugated, minute uneven portions4ahaving minute depressions and projections as shown inFIG. 15. The minute uneven portions4acan be formed, for example, by appropriately selecting the conditions of etching such as RIE (reactive ion etching) in the optical element manufacturing process or the material for the master. For example, the uneven portions4acan be formed using Pyrex (registered trademark) glass as the material for the master.

In the fourth embodiment, since the secondary structures4are further formed on the surface of the base2, the anti-reflection characteristics can be further improved compared with the first embodiment.

FIG. 16Ais a schematic plan view showing an example of a configuration of an optical element according to a fifth embodiment of the present invention.FIG. 16Bis a partially enlarged plan view of the optical element shown inFIG. 16A.FIG. 16Cis a sectional view taken along track T1, T3, . . . ofFIG. 16B.FIG. 16Dis a sectional view taken along track T2, T4, . . . ofFIG. 16B.FIG. 17is a partially enlarged perspective view of the optical element shown inFIG. 16.

An optical element1according to the fifth embodiment differs from that of the first embodiment in that a large number of structures3that are depressions are arranged on the surface of the base. The shape of the structures3is a depression obtained by reversing the projection of the structures3in the first embodiment. Therefore, the effective refractive index in the depth direction (−Z axis direction inFIG. 16) of the structures3gradually increases toward the base and has two or more inflection points N1, N2, . . . , Nn(n: an integer of 2 or more). Note that, when the structures3are depressions as described above, the opening portions (the entrance portions of the depressions) of the structures3that are depressions are defined as a bottom and the lowermost portions (the deepest portions of the depressions) in the depth direction of the base2are defined as a top. In other words, the top and bottom are defined using the structures3that are insubstantial spaces. In this case, the effective refractive index shown inFIG. 2gradually increases in the direction from the bottom to the top. The fifth embodiment is the same as the first embodiment except for the above description.

In the fifth embodiment, since the depressions obtained by reversing the projections of the structures3in the first embodiment are used, the same effects as in the first embodiment can be achieved.

FIG. 18is a perspective view showing an example of a configuration of an optical element according to a sixth embodiment of the present invention. As shown inFIG. 18, an optical element1according to the sixth embodiment differs from that of the first embodiment in that the optical element1includes pillar-shaped structures5that extend in a single direction on the surface of the base and the structures5are one-dimensionally arranged on the base2. Note that the same parts as those in the first embodiment are designated by the same reference numerals, and the descriptions thereof are omitted.

The effective refractive index in the depth direction (−Z axis direction inFIG. 18) of the structures5gradually increases toward the base2and has two or more inflection points N1, N2, . . . , Nn(n: an integer of 2 or more) in the depth direction.

The structures5have a curved surface that uniformly extends in a single direction (Y axis direction). The section (YZ section) obtained by cutting the structures5in the direction perpendicular to a ridgeline direction has a sectional shape similar to the refractive index profile shown inFIG. 2.

According to the sixth embodiment, the effective refractive index in the depth direction of the ridgeline gradually increases toward the base2and has two or more inflection points N1, N2, . . . , Nn(n: an integer of 2 or more). Therefore, reflected light can be reduced because of an interference effect of light combined with a shape effect of the structures5. Thus, an optical element having good anti-reflection characteristics can be achieved.

FIG. 19shows an example of a shape of structures of an optical element according to a seventh embodiment of the present invention. As shown inFIG. 19, the structures3include, on the surface between the top3tand the bottom3b, preferably two or more of at least one of parallel steps st and slope steps St, more preferably two or more and ten or less of at least one of parallel steps st and slope steps St. If the number of at least one of the parallel steps st and the slope steps St is two or less, the effective refractive index in the depth direction (−Z axis direction inFIG. 1) of the structures3can have two or more inflection points. Furthermore, when the number of at least one of the parallel steps st and the slope steps St is ten or less, the optical element can be easily manufactured.

The parallel step st is a step parallel to the surface of the base. Herein, the parallel step st is a section defined by the first changing point Pa and the second changing point Pb. Note that the parallel step st does not include the top3tand the bottom3bthat have a planar shape. That is, the steps that are formed between the top3tand the bottom3bof the structures3excluding the top3tand the bottom3band that are parallel to the surface of the base are called parallel steps.

The seventh embodiment is the same as the first embodiment except for the above description.

FIG. 20is a sectional view showing an example of a configuration of an optical element according to an eighth embodiment of the present invention. As shown inFIG. 20, an optical element1according to the eighth embodiment differs from that of the first embodiment in that a gradient film6is formed on the base instead of the structures3. Note that the same parts as those in the first embodiment are designated by the same reference numerals, and the descriptions thereof are omitted.

The gradient film6is a film composed of a material whose composition is gradually changed in the depth direction (thickness direction), whereby the refractive index in the depth direction is gradually changed. The refractive index on the surface side of the gradient film6is lower than that on the base side (interface side). The effective refractive index in the depth direction gradually increases toward the base2and has two or more inflection points N1, N2, . . . , Nn(n: an integer of 2 or more). Therefore, reflected light can be reduced because of an interference effect of light. Thus, the anti-reflection characteristics of the optical element can be degraded.

The gradient film6can be formed by, for example, sputtering. Examples of the film formation method performed by sputtering include a method in which two types of target materials are simultaneously sputtered at a certain ratio and a method in which the content of process gas contained in the film is appropriately changed by performing reactive sputtering while the flow rate of the process gas is changed.

According to the eighth embodiment, the same effects as in the first embodiment can be achieved.

FIG. 21Ais a schematic plan view showing an example of a configuration of an optical element according to a ninth embodiment of the present invention.FIG. 21Bis a partially enlarged plan view of the optical element shown inFIG. 21A.

An optical element1according to the ninth embodiment differs from that of the first embodiment in that a plurality of structures3are arranged on meandering tracks (hereinafter referred to as wobble tracks). The wobbles of the tracks on the base2are preferably synchronized with one another. That is, the wobbles are preferably synchronized wobbles. By synchronizing the wobbles in such a manner, a unit lattice shape of a hexagonal lattice or a quasi-hexagonal lattice can be held and high packing density can be maintained. Examples of the waveform of the wobble tracks include a sine wave and a triangular wave. The waveform of the wobble tracks is not limited to periodical waves, and may be a non-periodical wave. The wobble amplitude of the wobble tracks is set to, for example, about ±10 μm.

The ninth embodiment is the same as the first embodiment except for the above description.

According to the ninth embodiment, since the structures3are arranged on the wobble tracks, the occurrence of visual unevenness can be suppressed.

[Configuration of Optical Element]

An optical element1according to a tenth embodiment differs from that of the first embodiment in that structures3obtained using a siloxane resin are disposed on the base2.

The optical element1according to the tenth embodiment is suitably applied to optical elements such as a cover glass and a window material having thermal resistance and high transparency; and packages of an image sensor element (e.g., a CCD image sensor element and a CMOS image sensor element) including such an optical element, a photodiode, a semiconductor laser device, and the like. Furthermore, the optical element1according to the tenth embodiment is suitably applied to optical elements such as a front panel having high hardness and thermal resistance and displays including the optical elements. More specifically, the optical element1is suitably applied to the packages of image sensors provided to various cameras such as a digital camera (e.g., a single-lens reflex camera and a compact camera), a digital camera equipped in cellular phones, a camera for industrial machines, a security camera, and a camera for image recognition devices.

FIG. 22is a processing chart for describing a method for manufacturing an optical element according to the tenth embodiment of the present invention. The method for manufacturing an optical element uses a room-temperature nanoimprinting technology.

The method for manufacturing an optical element according to the tenth embodiment of the present invention is characterized by including a step of forming a resin layer by applying a film formation composition containing a siloxane resin on the base; a step of transferring a shape to the resin layer by pressing a mold against resin layer; a step of removing the mold from the resin layer; and a step of irradiating the resin layer from which the mold has been removed, with ultraviolet rays under a reduced pressure.

First, as shown inFIG. 22A, a resin layer61is formed by applying a film formation composition containing a siloxane resin on the base2. The application can be performed by, for example, spin coating, but the application method is not particularly limited thereto. The base2can be composed of, for example, a glass substrate (e.g., clear glass or quartz) mainly made of glass. A silsesquioxane resin is preferably used as the siloxane resin. The film formation composition is preferably used as the form of a solution by dissolving a component such as the siloxane resin in an appropriate organic solvent. Furthermore, an organic layer and an inorganic layer may be optionally formed on the base2. Moreover, the thickness of the resin layer61is preferably 300 nm or more and 500 nm or less, although depending on the kind of structures2to be manufactured.

Next, as shown inFIG. 22B, by pressing a mold62having a predetermined shape against the resin layer61formed on the base2, the shape of the mold is transferred to the resin layer61. For example, the die41used in the second embodiment can be used as the mold62, but the mold62is not particularly limited. For example, a die manufactured by performing plating on the optical element1or the like according to the first or third embodiment may be used. The pressing pressure of the mold62is preferably about 5 MPa to 100 MPa. Furthermore, the pressing time is preferably about 10 sec to 20 sec, although depending on the thickness of the resin layer61. The resin layer61having the shape is further hardened by performing pressing for a predetermined time while the mold62is pressed against the resin layer61.

Next, as shown inFIG. 22C, the mold62is removed from the resin layer61. As a result, structures3obtained by transferring the shape of the mold62are formed on the base2.

Next, as shown inFIG. 22D, preferably, the resin layer61from which the mold62has been removed is irradiated with ultraviolet rays L at a reduced pressure of about 10 Torr, and then heated to 300° C. to 400° C. The curing efficiency is increased by applying heat in such a manner. For example, a pencil hardness of 7 H to 9 H is obtained through the heating to 300° C. and a pencil hardness of 8 H to 9 H is obtained through the heating to 400° C. Moreover, when the resin layer61is cured at 300° C. to 400° C., the thermal resistance of the optical element1manufactured in such a manner is 500° C. or higher, which is sufficiently high thermal resistance for a reflow process.

Through the steps described above, the structures3obtained by transferring the shape of the mold62can be formed on the base2.

The optical element1according to the sixth embodiment can be used as, for example, a cover glass and a window material provided to the package of image sensor elements, a front panel of displays, and the like. Thus, there can be provided a cover glass or a window material having thermal resistance and high transparency, a front panel having high hardness and thermal resistance, a display including the same, and the like.

FIG. 23shows an example of a configuration of an optical element according to an eleventh embodiment. As shown inFIG. 23, the optical element1differs from that of the first embodiment in that there is no base2. The optical element1includes a plurality of structures3that are projections and are arranged at a fine pitch shorter than or equal to a wavelength of visible light, and the lower portions of the adjacent structures are connected to each other. The plurality of structures whose lower portions are connected to each other may constitute a mesh as a whole. When the optical element1has no base as described above, the flexibility is preferably imparted to the structures3by suitably adjusting the elastic modulus of the structures3. By imparting the flexibility in such a manner, the optical element1can be attached to an adherend without an adhesive. Furthermore, the optical element1can be attached to a three-dimensional curved surface.

[Configuration of Liquid Crystal Display Device]

FIG. 24shows an example of a configuration of a liquid crystal display device according to a twelfth embodiment of the present invention. As shown inFIG. 24, the liquid crystal display device includes a backlight53that emits light and a liquid crystal panel51that temporally and spatially modulates the light emitted from the backlight53to display an image. Polarizers51aand51bare respectively disposed on two surfaces of the liquid crystal panel51. An optical element1is disposed on the polarizer51bdisposed on the display surface side of the liquid crystal panel51. In the present invention, the polarizer51bhaving the optical element1disposed on one principal surface thereof is referred to as an anti-reflective polarizer52. The anti-reflective polarizer52is an example of optical elements having an anti-reflection function.

Hereinafter, the backlight53, the liquid crystal panel51, the polarizers51aand51b, and the optical element1constituting the liquid crystal display device will be described in order below.

For example, a direct-type backlight, an edge-type backlight, or a planar light source-type backlight can be used as the backlight53. The backlight53includes, for example, a light source, a reflecting plate, an optical film, and the like. For example, a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), an organic electroluminescence (OEL), an inorganic electroluminescence (IEL), a light emitting diode (LED), or the like is used as the light source.

Examples of the display mode that can be used for the liquid crystal panel51include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a vertically aligned (VA) mode, an in-plane switching (IPS) mode, an optically compensated birefringence (OCB) mode, a ferroelectric liquid crystal (FLC) mode, a polymer dispersed liquid crystal (PDLC) mode, and a phase change guest host (PCGH) mode.

The polarizers51aand51bare respectively provided on two surfaces of the liquid crystal panel51so that the transmission axes thereof are orthogonal to each other, for example. Each of the polarizers51aand51ballows only one of orthogonal polarized components of incident light to pass through and blocks the other component by absorption. Each of the polarizers51aand51bmay be a uniaxially stretched hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, an ethylene-vinyl acetate copolymer partially saponified film, or the like, with a dichroic substance, such as iodine or a dichroic dye, adsorbed thereto. A protective layer such as a triacetyl cellulose (TAC) film is preferably formed on two surfaces of each of the polarizers51aand51b. When the protective layer is formed in such a manner, the base2of the optical element1preferably also serves as the protective layer. This is because, in such a configuration, the anti-reflective polarizer52can be thinned.

The optical element1is the same as one of those in the first to eleventh embodiments, and the descriptions thereof is omitted.

According to the twelfth embodiment, since the optical element1is disposed on the display surface of the liquid crystal display device, the anti-reflection function of the display surface of the liquid crystal display device can be improved. Thus, the visibility of the liquid crystal display device can be improved.

[Configuration of Liquid Crystal Display Device]

FIG. 25shows an example of a configuration of a liquid crystal display device according to a thirteenth embodiment of the present invention. The liquid crystal display device differs from that of the twelfth embodiment in that the liquid crystal display device includes a front member54on the front side of the liquid crystal panel51and also includes the optical element1on at least one of the front surface of the liquid crystal panel51and the front and rear surfaces of the front member54.FIG. 25shows an example in which the optical element1is provided to all the front surface of the liquid crystal panel51and the front and rear surfaces of the front member54. For example, an airspace is formed between the liquid crystal panel51and the front member54. The same parts as those in the seventh embodiment are designated by the same reference numerals, and the descriptions thereof are omitted. Note that, in the present invention, the front surface is a surface on the display surface side, that is, a surface on the viewer's side, and the rear surface is a surface on the side opposite the display surface.

The front member54is used for the purpose of providing mechanical, thermal, and weather-resistant protections and a design function to the front surface (viewer's side) of the liquid crystal panel51. The front member54has, for example, a sheet shape, a film shape, or a plate shape. Examples of the material of the front member54include glass, triacetyl cellulose (TAC), polyester (TPEE), polyethylene terephthalate (PET), polyimide (PI), polyamide (PA), aramid, polyethylene (PE), polyacrylate, polyethersulfone, polysulfone, polypropylene (PP), diacetyl cellulose, polyvinyl chloride, acrylic resins (PMMA), and polycarbonate (PC). However, the material is not particularly limited to these materials and any material having transparency can be used.

According to the thirteenth embodiment, the visibility of the liquid crystal display device can be improved as in the twelfth embodiment.

FIG. 26is a sectional view showing an example of a configuration of a package of an image sensor element according to a fourteenth embodiment of the present invention. As shown inFIG. 26, a package71includes an image sensor element72and a cover glass73fixed so as to cover an opening window of the image sensor element72. The image sensor element72is, for example, a CCD (charge coupled device) image sensor element or a CMOS (complementary metal oxide semiconductor) image sensor element. For example, any one of the optical elements1according to the first to eleventh embodiments may be used as the cover glass73, but the optical element1according to the tenth embodiment is particularly preferred.

FIG. 27is a sectional view showing an example of a configuration of an optical element according to a fifteenth embodiment of the present invention. As shown inFIG. 27, an optical element1according to the fifteenth embodiment differs from that of the first embodiment in that the optical element1further includes a light-absorbing layer7on the back surface (second principal surface) thereof. Furthermore, the optical element1may optionally include an adhesive layer between the base2and the light-absorbing layer7to attach the light-absorbing layer7to the base2through the adhesive layer. When the adhesive layer is provided in such a manner, the refractive index of the base2is preferably equal to or substantially equal to that of the adhesive layer. This can suppress the interface reflection between the base2and the adhesive layer. The adhesive layer may have a light-absorbency as with the light-absorbing layer7. The light-absorbing layer itself may also serve as the adhesive layer.

Furthermore, the optical element1may optionally further include an adhesive layer8aand a detachment layer8bon the light-absorbing layer7in order to attach the optical element1to an adherend through the adhesive layer8a.

The light-absorbing layer7has absorbency for light in a use environment or light whose reflection is intended to be reduced. The light-absorbing layer7contains, for example, a binder resin and a black coloring agent. Moreover, the light-absorbing layer7may optionally further contain additives such as an organic pigment and an inorganic pigment and a dispersing agent for improving dispersion.

Examples of the black coloring agent include carbon black, titanium black, graphite, iron oxide, and titanium oxide. However, the black coloring agent is not particularly limited to these materials. Among them, carbon black, titanium black, and graphite are preferable, and carbon black is more preferable. These materials may be used alone or in combination.

Commercially available carbon black can be used as the carbon black. Examples of the carbon black include #980B, #850B, MCF88B, and #44B available from Mitsubishi Chemical Corporation; BP-800, BP-L, REGAL-660, and REGAL-330 available from Cabot Corporation; RAVEN-1255, RAVEN-1250, RAVEN-1020, RAVEN-780, and RAVEN-760 available from Columbian Chemicals Company; and Printex-55, Printex-75, Printex-25, Printex-45, and SB-550 available from Degussa Corporation. These carbon blacks may be used alone or in combination.

Examples of the binder resin include modified or unmodified vinyl chloride resins, polyurethane resins, phenoxy resins, and polyester resins, in addition to cellulose esters such as cellulose acetate butylate. Furthermore, a thermoplastic resin, a thermosetting resin, an ionizing radiation-curable resin, or the like that is used in a specific method may also be used. An electron beam-curable resin and an ultraviolet curable resin are preferred as the ionizing radiation-curable resin.

The adhesive layer8ais mainly composed of an adhesive. For example, an adhesive publicly known in the technical field of an optical sheet can be used as the adhesive. Note that, in this specification, a pressure sensitive adhesive (PSA) or the like is regarded as one type of an adhesive. The detachment layer8bis a detachment sheet for protecting the adhesive layer8a.

In the fifteenth embodiment, the light-absorbing layer7composed of a material having high absorbency for light such as visible light is formed on the back surface of the base, whereby most of the back side reflection can be eliminated. Consequently, there can be suppressed light reflection that occurs on the surface of an unit in the barrel of optical devices such as cameras and telescopes and on the inner periphery surface of the barrel. Thus, optical characteristics such as ghost, flare, and contrast can be improved.

When the adhesive layer8ais further disposed on the light-absorbing layer7, the optical element1can be easily attached to an adherend such as an optical device including a camera through the adhesive layer8a. When the detachment layer8bis further disposed on the adhesive layer8a, the optical element1can be easily handled.

An optical element1according to a sixteenth embodiment differs from that of the fifteenth embodiment in that, instead of the light-absorbing layer7, at least one of the base2and structures3contains a black coloring agent such as carbon black so as to have light absorbency.

FIG. 28Ais a sectional view showing a first configuration example of an optical element according to a sixteenth embodiment of the present invention. As shown inFIG. 28A, the optical element1includes the base2integrally formed with the structures3, and both the base2and the structures3contain the black coloring agent. Thus, both the base2and the structures3have light absorbency.

FIG. 28Bis a sectional view showing a second configuration example of the optical element according to the sixteenth embodiment of the present invention. As shown inFIG. 28B, the optical element1includes the independently formed base2and structures3, and at least one of the base2and the structures3contains the black coloring agent and has light absorbency. In view of reduction in reflectivity, preferably, only the base2contains the black coloring agent and has light absorbency while the structures3are transparent.

FIG. 28Cis a sectional view showing a third configuration example of the optical element according to the sixteenth embodiment of the present invention. As shown inFIG. 28C, the optical element1includes the independently formed base2and structures3, and the base2is a stacked body. The stacked body has a stacked structure obtained by stacking two or more layers, and at least one layer of the two or more layers contains the black coloring agent and has light absorbency. The structures3may contain the black coloring agent and have light absorbency. However, in view of reduction in reflectivity, preferably, only the base2contains the black coloring agent and has light absorbency as described above.

In the sixteenth embodiment, since the optical element itself contains the black coloring agent and has light absorbency, the formation of the light-absorbing layer7can be omitted. Thus, a light-absorbing layer formation step can be omitted, which can improve productivity. Furthermore, the optical element1can be thinned.

FIG. 29is a sectional view showing an example of a configuration of a barrel according to a seventeenth embodiment of the present invention. As shown inFIG. 29, a barrel81includes an optical element1therein. The specific positions in the barrel where the optical element1is provided are, for example, the inner periphery surface of the barrel and the surface of a unit in the barrel. At least one of the optical elements1according to the fifteenth and sixteenth embodiments can be used as the optical element1. Preferably, the optical element1is suitably selected in accordance with desired anti-reflection characteristics or the like. The optical element1is disposed, for example, in portions between a lens82and a lens83and between the lens83and a lens84on the inner periphery surface of the barrel81. The optical element1may be integrally formed with the barrel81.

In the eighth embodiment, since the optical element1is provided to the inner periphery surface of the barrel, the surface of a unit in the barrel, or the like, light reflection caused on the inner periphery surface of the barrel, the surface of a unit in the barrel, or the like can be reduced. Thus, the occurrence of ghost and flare on an image and an decrease in contrast can be suppressed.

FIG. 30Ais a schematic plan view showing an example of a configuration of an optical element according to an eighteenth embodiment of the present invention.FIG. 30Bis a partially enlarged plan view of the optical element shown inFIG. 30A.FIG. 30Cis a sectional view taken along track T1, T3, . . . ofFIG. 30B.FIG. 30Dis a sectional view taken along track T2, T4, . . . ofFIG. 30B.

An optical element1according to the eighteenth embodiment differs from that of the first embodiment in that the optical element1is so-called a conductive optical element and further includes a transparent conductive film9on the uneven surface of a plurality of structures2. Furthermore, in view of reduction in surface resistance, a metal film10is preferably further formed between the uneven surface of the optical element1and the transparent conductive film9.

Examples of the material constituting the transparent conductive film9include ITO (In2O3, SnO2), AZO (Al2O3, ZnO), SZO, FTO, SnO2, GZO, and IZO (In2O3, ZnO). However, in view of high reliability and low resistivity, ITO is preferred. The transparent conductive film9is formed along the surface shape of the structures3, and the surface shape of the transparent conductive film9is preferably substantially similar to that of the structures3. This is because the change in a refractive index profile caused by the formation of the transparent conductive film9can be suppressed and good anti-reflection characteristics and/or transmission characteristics can be maintained.

The metal film10is preferably formed as a base layer of the transparent conductive film9. This is because the resistivity can be reduced and the transparent conductive film9can be thinned, or when the electrical conductivity does not reach a sufficient value with only the transparent conductive film9, the electrical conductivity can be compensated. The thickness of the metal film10is not particularly limited, and is, for example, about several nanometers. Since the metal film10has high electrical conductivity, sufficient surface resistance can be achieved at a thickness of several nanometers. Furthermore, a thickness of about several nanometers hardly produces optical effects such as absorption and reflection due to the metal film10. The metal film10is preferably composed of a metal material having high electrical conductivity. Examples of the metal material include Ag, Al, Cu, Ti, Nb, and Si doped with impurities. However, in view of high electrical conductivity, the use results, and the like, Ag is preferred. Sufficient surface resistance can be achieved with only the metal film10. However, if the metal film10is extremely thin, the metal film10has an island structure, which makes it difficult to ensure continuity. In this case, it is important to form the transparent conductive film9that is an upper layer of the metal film10in order to electrically connect the island-shaped metal films10to one another.

FIG. 31is a sectional view showing an example of a configuration of a conductive optical element according to a nineteenth embodiment of the present invention. As shown inFIG. 31, an optical element1according to the nineteenth embodiment differs from that of the eighteenth embodiment in that, in addition to one principal surface (first principal surface) on which the structures3are formed, structures3are further formed on the other principal surface (second principal surface) opposite the first principal surface.

The arrangement patterns and aspect ratios of the structures3formed on both principal surfaces of the optical element1are not necessarily the same, and different arrangement patterns and aspect ratios may be selected in accordance with desired characteristics. For example, one principal surface may have a quasi-hexagonal lattice pattern as an arrangement pattern and the other principal surface may have a quasi-tetragonal lattice pattern as an arrangement pattern.

In the nineteenth embodiment, since a plurality of structures3are formed on both principal surfaces of the base2, an anti-reflection function of light can be imparted to the light-entering and light-emitting surfaces of the optical element1. Thus, light transmission characteristics can be further improved.

FIG. 32Ais a sectional view showing an example of a configuration of a touch panel according to a twentieth embodiment of the present invention. As shown inFIG. 32A, a touch panel90includes a first conductive substrate91and a second conductive substrate92facing the first conductive substrate91. The touch panel90preferably further includes a hard coat layer or an antifouling hard coat layer on the surface on the touch side of the first conductive substrate91. Moreover, a front panel may be optionally further disposed on the touch panel90. For example, the touch panel90is attached to a display device94through an adhesive layer93.

Examples of the display device include various display devices such as a liquid crystal display, a CRT (cathode ray tube) display, a plasma display panel (PDP), an electro luminescence (EL) display, and a surface-conduction electron-emitter display (SED).

One of the optical elements1according to the eighteenth and nineteenth embodiments is used as at least one of the first conductive substrate91and the second conductive substrate92. When one of the optical elements1according to the eighteenth and nineteenth embodiments is used as both the first conductive substrate91and the second conductive substrate92, the optical element1according to the same embodiment or the optical elements1according to the different embodiments can be used as the conductive substrates.

The structures3are formed on at least one of the two surfaces of the first conductive substrate91and the second conductive substrate92, the two surfaces facing each other. In view of anti-reflection characteristics and transmission characteristics, the structures3are preferably formed on both the two surfaces.

FIG. 32Bis a sectional view showing a modification of the touch panel according to the twentieth embodiment of the present invention. As shown inFIG. 32B, the optical element1according to the nineteenth embodiment is used as at least one of the first conductive substrate91and the second conductive substrate92.

A plurality of structures3are formed on at least one of the two surfaces of the first conductive substrate91and the second conductive substrate92, the two surfaces facing each other. Furthermore, a plurality of structures3are formed on at least one of the surface on the touch side of the first conductive substrate91and the surface on the display device94side of the second conductive substrate92. In view of anti-reflection characteristics and transmission characteristics, the structures3are preferably formed on both the surfaces.

In the twentieth embodiment, since the optical element1is used as at least one of the first conductive substrate91and the second conductive substrate92, a touch panel90having good anti-reflection characteristics and transmission characteristics can be obtained. Thus, the visibility of a display device having the touch panel90can be improved. In particular, the visibility of a display device in the outside can be improved.

FIG. 33shows a twenty-first embodiment of the present invention. In this embodiment, there is exemplified a dye-sensitized solar cell110in which any one of the optical elements1having the configurations described in the first to eleventh embodiments is used as a light guide window100.

The dye-sensitized solar cell110of this embodiment is constituted by a stacked body obtained by disposing a metal-oxide semiconductor layer105and an electrolyte layer106between the light guide window100having a transparent conductive film101and a substrate104having a current collector103and a (transparent) conductive film102that opposes the transparent conductive film101. The semiconductor layer105has, for example, an oxide semiconductor material and a sensitizing dye. Furthermore, the transparent conductive film101and the conductive film102are connected to each other through a conducting wire, and a current circuit having an ammeter (amperemeter)107is formed.

A glass substrates or a transparent plastic substrate is used for the light guide window100. The structures3described in the first embodiment and having a quasi-hexagonal lattice minute arrangement structure (sub-wavelength structure) are formed on the light-entering surface (light-receiving surface) on the outer side of the light guide window100and on the light-emitting surface on the inner side.

The metal-oxide semiconductor layer105constitutes a photoelectric conversion layer obtained by sintering metal-oxide particles onto the transparent conductive film101. Examples of the material of the metal-oxide semiconductor layer105include metal oxides such as TiO2, MgO, ZnO, SnO2, WO2, Nb2O5, and TiSrO3. Furthermore, a sensitizing dye is supported on the metal-oxide semiconductor layer105, and the metal-oxide semiconductor is sensitized by the sensitizing dye. The sensitizing dye is not particularly limited as long as it provides a sensitization action. Examples of the sensitizing dye include bipyridine, phenanthrene derivatives, xanthene dyes, cyanine dyes, basic dyes, porphyrin compounds, azo dyes, phthalocyanine compounds, anthraquinone dyes, and polycyclic quinone dyes.

The electrolyte layer106is obtained by dissolving, in an electrolyte, at least one material system that reversibly causes an oxidation-reduction state change (oxidation-reduction system). The electrolyte may be a liquid electrolyte or may be a gel electrolyte obtained by adding the liquid electrolyte to a polymer material, a polymer solid material, or an inorganic solid electrolyte. Examples of the oxidation-reduction system include halogens such as I−/I3−and Br−/Br2, pseudohalogens such as quinone/hydroquinone and SCN−/(SCN)2, iron (II) ions/iron (III) ions, and copper (I) ions/copper (II) ions. However, the oxidation-reduction system is not limited thereto. There can be used, as a solvent, nitriles such as acetonitrile, carbonates such as propylene carbonate and ethylene carbonate, gamma-butyrolactone, pyridine, dimethylacetamide, other polar solvents, room temperature molten salts such as methylpropylimidazolium-iodine, and mixtures thereof.

In the dye-sensitized solar cell110having the above-described configuration, light received on the light-receiving surface of the light guide window100excites the sensitizing dye supported on the surface of the metal-oxide semiconductor layer105, and the sensitizing dye immediately supplies electrons to the metal-oxide semiconductor layer105. On the other hand, the sensitizing dye that has lost electrons receives electrons from ions in the electrolyte layer106that is a carrier transport layer. The molecules that have supplied electrons receive electrons from the counter electrode102. In such a manner, a current flows between the electrodes101and102.

According to this embodiment, since the light-receiving surface of the dye-sensitized solar cell110is constituted by the light guide window100as the optical element according to the present invention, the surface reflection of light received on the light-receiving surface (light-entering surface) and the reflection of transmitted light caused on the rear surface (light-emitting surface) of the light guide window100can be effectively prevented. This can increase the use efficiency of the received light and can improve photoelectric conversion efficiency, that is, power generation efficiency.

Moreover, the light-entering and light-emitting surfaces of the light guide window100have a sub-wavelength structure in which the structures3(FIG. 1B) are finely arranged at a pitch shorter than a wavelength of visible light, which can effectively increase the photoelectric conversion efficiency of the photoelectric conversion portion having sensitivity in the range of the near-ultraviolet region to the visible light region and the near-infrared region.

FIG. 34shows a thirty-fourth embodiment of the present invention. In this embodiment, there is described an example in which the present invention is applied to a silicon solar cell120as a photoelectric conversion apparatus.

FIG. 34schematically shows a configuration of the silicon solar cell120. The silicon solar cell120includes a silicon substrate111, transparent conductive films114and115respectively formed on the front and back surfaces of the silicon substrate111, and a load116connected between the transparent conductive films114and115. The silicon substrate111is a junction Si substrate having an n-type semiconductor layer112and a p-type semiconductor layer113. A pn junction117of the n-type semiconductor layer112and the p-type semiconductor layer113constitutes a photoelectric conversion layer that generates electricity based on the intensity of incident light that enters the n-type semiconductor layer112.

In this embodiment, the surface of the n-type semiconductor layer112that constitutes a light-receiving surface has a sub-wavelength structure in which the structures3(FIG. 1B) are arranged in a quasi-hexagonal lattice at a fine pitch shorter than or equal to a wavelength of incident light to prevent the reflection of light on the light-entering surface of the n-type semiconductor layer112and to improve transmission characteristics. This can increase the photoelectric conversion efficiency at the pn junction117.

Furthermore, a minute arrangement structure of the structures3(FIG. 1B) formed on the light-entering surface of the silicon substrate111is formed at a fine pitch shorter than or equal to a wavelength of near-ultraviolet light, whereby the photoelectric conversion efficiency of a Si solar cell having sensitivity in the wide range of the near-ultraviolet region to the near-infrared region can be dramatically improved.

The silicon solar cell120having the above-described configuration can be manufactured by directly etching the surface of the silicon substrate111constituting the n-type semiconductor layer112.FIG. 35is a sectional view of a principal part of a processing chart for describing a method for manufacturing the silicon solar cell.

First, as shown inFIG. 35A, a resist layer130is formed on the surface of the silicon substrate111. A mask pattern of the resist layer130is formed on the surface of the silicon substrate111by using an exposure technology based on the optical disc recording technology described in the second embodiment and by performing development treatment. Next, etching is performed with fluorocarbon gas such as CF4using the mask pattern of the manufactured resist layer130as a mask to form an uneven pattern constituted by depressions131having a conical form on the surface of the silicon substrate111as shown inFIG. 35B. Through the steps described above, a silicon substrate111having a sub-wavelength structure surface is manufactured.

EXAMPLES

Hereinafter, the present invention is specifically described using Examples, but is not limited to only Examples. Note that a simulation used in Examples is a RCWA (Rigorous Coupled Wave Analysis) simulation.

Examples of the present invention are described in the following order.1. Investigation about the shape of structures through a simulation2. Investigation about the relationship between inflection point and reflectivity through a simulation (1)3. Investigation about the relationship between inflection point and reflectivity through a simulation (2)4. Evaluation about the reflection characteristics with an actually prepared sample
<1. Investigation about the Shape of Structures Through a Simulation>

The shape of structures whose effective refractive index monotonically increases and has two or more inflection points was investigated through a simulation. Note that the pitch of structures in the following Examples is a length of the short sides of a rectangular lattice as shown inFIG. 36A. However, when the lattice is a tetragonal lattice as shown inFIG. 36B, the sides are not particularly differentiated and the length of the sides is referred to as a pitch.

Examples 1-1 to 1-3

In the case where the structures are arranged in a hexagonal lattice, there were investigated the shapes of the structures whose effective refractive index in the depth direction thereof monotonically increases and has two inflection points.FIGS. 37A to 37Cshow the results.

Examples 2-1 to 2-3

In the case where the structures are arranged in a hexagonal lattice, there were investigated the shapes of the structures whose effective refractive index in the depth direction thereof monotonically increases and has three inflection points.FIGS. 38A to 38Cshow the results.

Examples 3-1 to 3-3

In the case where the structures are arranged in a hexagonal lattice, there were investigated the shapes of the structures whose effective refractive index in the depth direction thereof monotonically increases and has five inflection points.FIGS. 39A to 39Cshow the results.

Examples 4-2 to 4-3

In the case where the structures are arranged in a tetragonal lattice, there were investigated the shapes of the structures whose effective refractive index in the depth direction thereof monotonically increases and has five inflection points.FIGS. 40A to 40Cshow the results.

In the case where the structures are arranged in a quasi-hexagonal lattice, there was investigated the shape of the structures whose effective refractive index in the depth direction thereof monotonically increases and has three inflection points.FIG. 41Ashows the result.

In the case where the structures are arranged in a quasi-hexagonal lattice, there was investigated the shape of the structures whose effective refractive index in the depth direction thereof monotonically increases and has five inflection points.FIG. 41Bshows the result.

In the case where the structures are arranged in a hexagonal lattice, there was investigated the shape in which the projections/depressions of the structures whose effective refractive index in the depth direction thereof monotonically increases and has three inflection points are reversed.FIG. 41Cshows the result.

It is clear fromFIGS. 37A to 41Cthat the inflection point and the shape of the structures have the following relationships.

Examples 1-1 to 1-3 (two inflection points, hexagonal lattice): there are a slope step at the top and one slope step on the curved surface of structures.

Examples 2-1 to 2-3 (three inflection points, hexagonal lattice): there are a slope step at the top, one slope step on the curved surface of structures, and a slope step at the bottom.

Examples 3-1 to 3-3 (five inflection points, hexagonal lattice): there are a slope step at the top, two slope steps on the curved surface of structures, and a slope step at the bottom.

Examples 4-1 to 4-3 (five inflection points, tetragonal lattice): there are a slope step at the top, two slope steps on the curved surface of structures, and a slope step at the bottom.

Example 5 (three inflection points, quasi-hexagonal lattice): there are a slope step at the top, one slope step on the curved surface of structures, and a slope step at the bottom.

Example 6 (five inflection points, quasi-hexagonal lattice): there are a slope step at the top, two slope steps on the curved surface of structures, and a slope step at the bottom.

<2. Investigation about the Relationship Between Inflection Point and Reflectivity Through a Simulation (1)>

Assuming a refractive index profile having inflection points, the relationship between inflection point and reflectivity was investigated on the basis of the refractive index profile through a simulation.

Examples 8 to 10

First, as shown inFIGS. 42A and 42B, refractive index profiles were assumed in which the numbers of inflection points of effective refractive indices in the depth direction of structures are two, three, and five. Note that, since the optical thickness is based on the bottom surface of the structures inFIGS. 42A and 42B, the refractive index profile is opposite to that shown inFIG. 2. Next, the reflectivities of the optical elements were obtained on the basis of the refractive index profiles. Herein, the height of the structures was 250 nm.FIG. 42Cshows the results.

Comparative Example 1

First, as shown inFIG. 42A, a refractive index profile was assumed in which the number of inflection points of an effective refractive index in the depth direction of structures is one. Next, the reflectivity of the optical element was obtained on the basis of the refractive index profile. Herein, the height of the structure was 250 nm.FIG. 42Cshows the result.

Comparative Example 2

First, as shown inFIG. 42A, a refractive index profile was assumed in which an effective refractive index in the depth direction of structures has no inflection points and is linear. Next, the reflectivity of the optical element was obtained on the basis of the refractive index profile. Herein, the height of the structure was 250 nm.FIG. 42Cshows the result.

It is clear fromFIGS. 42A to 42Cthat the number of inflection points and reflectivity have the following relationships.

Comparative Example 1 (one inflection point): the reflectivity increases in the long wavelength region.

Comparative Example 2 (no inflection point): the reflectivity increases in the entire spectrum (in particular, in the short wavelength region).

Example 8 (two inflection points): the reflectivity tends to increase to some extent in the long wavelength region, but the amount of the increase is smaller than that in Comparative Example 1. The reflectivity is 0.1% or less in the substantially entire region of a visible light region of 400 nm to 700 nm.

Example 9 (three inflection points): the amount of the increase in the reflectivity is small in the long wavelength region, and the reflectivity is 0.1% or less in the entire region of a visible light region of 400 nm to 700 nm.

Example 10 (five inflection points): the reflectivity increases to some extent around a wavelength of 500 nm, but is extremely low in the short and long wavelength regions. The reflectivity decreases in the wide range of wavelength 350 to 800 nm.

<3. Investigation about the Relationship Between Inflection Point and Reflectivity Through a Simulation (2)>

Assuming a refractive index profile having inflection points, the relationship between inflection point and reflectivity was investigated on the basis of the refractive index profile through a simulation.

Examples 11 to 12

First, as shown inFIG. 43A, refractive index profiles were assumed in which the numbers of inflection points of effective refractive indices in the depth direction of structures are two and three. Next, the reflectivities of the optical elements were obtained on the basis of the refractive index profiles. Herein, the height of the structures was 250 nm.FIG. 43Bshows the results.

Comparative Example 3

First, as shown inFIG. 43A, a refractive index profile was assumed in which the number of inflection points of an effective refractive index in the depth direction of structures is one. Next, the reflectivity of the optical element was obtained on the basis of the refractive index profile. Herein, the height of the structures was 250 nm.FIG. 43Bshows the result.

Comparative Example 4

First, as shown inFIG. 43A, a refractive index profile was assumed in which an effective refractive index in the depth direction of structures has no inflection points and is linear. Next, the reflectivity of the optical element was obtained on the basis of the refractive index profile. Herein, the height of the structures was 250 nm.FIG. 43Bshows the result.

It is clear fromFIGS. 43A and 43Bthat the number of inflection points and reflectivity have the following relationships.

Comparative Example 3 (one inflection point): the reflectivity increases in the long wavelength region.

Comparative Example 4 (no inflection point): the reflectivity increases in the entire spectrum (in particular, in the short wavelength region).

Example 11 (two inflection points): the reflectivity tends to increase to some extent in the long wavelength region, but the amount of the increase is smaller than that in Comparative Example 1. The reflectivity is 0.1% or less in the substantially entire region of a visible light region of 400 nm to 700 nm.

Example 12 (three inflection points): the amount of the increase in the reflectivity is small in the long wavelength region, and the reflectivity is 0.1% or less in the entire region of a visible light region of 400 nm to 700 nm.

Up to this point, the embodiments and Examples of the present invention have been specifically described. However, the present invention is not limited to the above-described embodiments and Examples, and various modifications can be made on the basis of the technical ideas of the present invention.

For example, the numerical values, shapes, materials, and configurations exemplified in the embodiments and Examples are mere examples, and different numerical values, shapes, materials, and configurations may be optionally used.

<4. Evaluation about the Reflection Characteristics with an Actually Prepared Sample>

A sample was actually prepared and the reflection characteristics of the prepared sample were evaluated.

First, a glass roll master having an outer diameter of 126 mm was prepared, and a resist layer was formed on the surface of the glass roll master as follows. That is to say, a photoresist was diluted with a thinner by a factor of 1/10, and the diluted resist was applied on the columnar surface of the glass roll master by dipping so as to have a thickness of about 70 nm, whereby the resist layer was formed. Next, the glass roll master as a recording medium was transferred to the roll master exposure apparatus shown inFIG. 7. By exposing the resist layer, a latent image having a quasi-hexagonal lattice pattern in the three adjacent rows of tracks was patterned on the resist layer so as to form a single spiral shape.

Specifically, a region where a quasi-hexagonal lattice pattern was to be formed was irradiated with laser beams having a power of 0.50 mW/m that reach the surface of the glass roll master to form the quasi-hexagonal lattice pattern having depressions. Note that the thickness of the resist layer in the column direction of track rows was about 60 nm and the thickness of the resist layer in the track extending direction was about 50 nm.

Subsequently, by subjecting the resist layer on the glass roll master to development treatment, an exposed portion of the resist layer was dissolved to perform development. Specifically, an undeveloped glass roll master was placed on a turntable of a developing apparatus (not shown). A developer was dropwise applied onto the surface of the glass roll master while the glass roll master was rotated together with the turntable, to develop the resist layer on the surface. Thus, a resist glass roll master whose resist layer has openings in a quasi-hexagonal lattice pattern was obtained

Next, etching treatment and ashing treatment were alternately performed on the resist glass roll master using a roll etching machine. Thus, a pattern of structures (depressions) having a conical form was formed. Furthermore, by suitably adjusting the processing time of the etching treatment and ashing treatment, the top of the structures was shaped into a convex curved surface and steps were formed on the side surface. That is to say, steps were formed on the top and the side surface. Thus, the shape of the structures whose effective refractive index in the depth direction thereof gradually increases toward a base and has two inflection points was obtained.

Herein, the roll etching machine is a plasma etching apparatus having a pillar-shaped electrode, and is configured such that the pillar-shaped electrode is inserted into the hollow of the cylindrical glass roll master and plasma etching is performed on the cylindrical surface of the glass roll master.

Finally, by completely removing the resist layer by O2ashing, a moth-eye glass roll master having a depressed quasi-hexagonal lattice pattern was obtained. The depth of the depression in the column direction was larger than that in the track extending direction.

Subsequently, the moth-eye glass roll master was brought into close contact with an acrylic sheet to which an ultraviolet curable resin has been applied, and they were then detached from each other while being cured by applying ultraviolet rays. Consequently, an optical sheet having a surface on which a plurality of structures were arranged was obtained.

The uneven surface of the optical element of Example 13 manufactured as described above was observed using a scanning electron microscope (SEM).FIG. 44shows the result.

The pitch, height, and the like of the structures obtained from the SEM observation are shown below.

Shape: a shape having steps at the top and on the side surface (an effective refractive index has two inflection points)

The reflectivity of the optical element of Example 13 manufactured as described above was evaluated using an evaluation apparatus (V-550) available from JASCO Corporation.FIG. 45shows the result.

Comparative Example 5

The reflection characteristics of an optical element having a surface on which a plurality of structures having no inflection points have been arranged were obtained through a simulation.FIG. 45shows the result.

The conditions of the simulation are shown below.

Comparative Example 6

The reflection characteristics of an optical element having a surface on which a plurality of structures having no inflection points have been arranged were obtained through a simulation.FIG. 45shows the result.

The conditions of the simulation are shown below.

Shape: hanging bell shape

The following is clear fromFIG. 44.

There is obtained the shape of structures whose effective refractive index in the depth direction thereof gradually increases toward a base and has two inflection points.

Furthermore, such a shape is obtained using a method in which a process for making a master of optical discs is combined with an etching process, by adjusting the processing time of the etching treatment in the etching process and the ashing treatment.

The following is clear fromFIG. 45.

In Example 13 that represents a shape whose effective refractive index has two inflection points, the reflectivity is reduced in a visible light region of about 450 nm to 700 nm compared with Comparative Example 5 that represents a cone-like shape.

In Example 13, the reflectivity tends to increase in a wavelength region longer than about 580 nm compared with Comparative Example 6. This is because the structures in Example 13 are smaller in height than those in Comparative Example 6. If the height of the structures in Example 13 is about 300 nm that is the height in Comparative Example 6, it is believed that the increase in reflectivity is suppressed even in a longer wavelength region. Note that the reflectivity in Example 13 is reduced in a wavelength region of about 450 nm to 580 nm compared with Comparative Example 6.

It is clear from the above description that good reflection characteristics can be achieved when an effective refractive index in the depth direction of structures gradually increases toward a base and has two or more inflection points.

Furthermore, the configurations of the above-described embodiments can be combined with each other as long as they do not depart from the spirit of the present invention.

Furthermore, in the above-described embodiments, the case where the present invention is applied to a liquid crystal display device has been described as an example, but the present invention can also be applied to various display devices other than the liquid crystal display device. For example, the present invention can be applied to various display devices such as a CRT (cathode ray tube) display, a plasma display panel (PDP), an electro luminescence (EL) display, and a surface-conduction electron-emitter display (SED).

Furthermore, in the above-described embodiments, the case where the optical element1is manufactured by a method in which a process for making a master of optical discs is combined with an etching process has been described as an example. However, the method for manufacturing the optical element1is not limited thereto, and any method may be adopted as long as an optical element having an effective refractive index in the depth direction that gradually increases toward a base and has two or more inflection points can be manufactured. For example, the optical element may be manufactured using electron-beam exposure or the like. Alternatively, the optical element may be manufactured by performing coating with a gradient film obtained by blending hollow silica or the like while the ratio of the hollow silica is changed such that the effective refractive index gradually changes or with a gradient film obtained through reactive sputtering.

Furthermore, in the above-described embodiments, a low refractive index layer may be further formed on the surface, of the base2, where the structures3have been formed. Preferably, the low refractive index layer is mainly composed of a material having a lower refractive index than the materials constituting the base2, the structures3, and the secondary structures4. Examples of the material of such a low refractive index layer include organic materials such as fluorine resins and inorganic low refractive index materials such as LiF and MgF2.

Furthermore, in the above-described embodiments, the configuration in which the surface of the base has the structures3that are projections has been described as an example, but a configuration in which the surface of the base has structures that are depressions may be adopted. Herein, when the structures3are depressions, the height H of the structures3in formula (1) or the like is replaced with the depth H of the structures3.

Furthermore, in the above-described embodiments, the optical element may be manufactured by thermal transfer. Specifically, the optical element1may be manufactured by heating a base mainly composed of a thermoplastic resin and then by pressing a stamp (mold) such as the roll master11or the disc master41against the base sufficiently softened by the heat treatment. Moreover, the optical element may be manufactured by injection molding.

Furthermore, in the above-described embodiments, by suitably changing the pitch of structures, diffracted light is generated in the oblique direction from the front, whereby a peep prevention function may be imparted to the optical element.

Furthermore, in the above-described embodiments, the case where the structures that are depressions or projections are formed on the outer circumferential surface of the column- or cylinder-shaped master has been described as an example. However, when the master is cylinder-shaped, the structures that are depressions or projections may be formed on the inner circumferential surface of the master.

Furthermore, in the above-described embodiments, an example in which the present invention is applied to a resistive film touch panel has been described. However, the present invention is not limited to the example, and can be applied to, for example, a capacitive, ultrasonic, or optical touch panel.

Furthermore, in the above-described embodiments, the case where the plurality of structures are regularly arranged on the surface of the base in a hexagonal lattice, a tetragonal lattice, or the like has been described as an example, but the plurality of structures may be arranged on the surface of the base at random.

Furthermore, in the above-described embodiments, the case where a single thin film composed of a material whose composition is gradually (continuously) changed in the thickness direction is used as the gradient film has been described as an example, but a stacked film obtained by stacking, on the base, a plurality of thin films having slightly different refractive indices may be used as the gradient film.

Explanation of Reference Numerals

1: optical element

4: secondary structure

6: gradient film

9: transparent conductive film

10: metal film

11: roll master

51: liquid crystal panel

54: front member

72: image sensor element

73: cover glass

90: touch panel

Pa: first changing point

Pb: second changing point

St: slope step

st: parallel step