WO2003058330A1

WO2003058330A1 - Process for fabricating a mold of light-guide plate, which having non-isosceles triangled sectional shape on its surface, and the mold thereof

Info

Publication number: WO2003058330A1
Application number: PCT/KR2002/002380
Authority: WO
Inventors: Chul Park
Original assignee: Fineoptics Co.
Priority date: 2001-12-18
Filing date: 2002-12-18
Publication date: 2003-07-17
Also published as: KR20030050296A; AU2002359964A1

Abstract

Disclosed are a mold for a light-guide plate and a fabricating method thereof. The mold has unevenness, which has a non-isosceles triangular sectional shape. The method comprises the steps of: preparing a substrate having a surface which is parallel to neither of two crystal planes which can be anisotropically etched; forming an etching mask on the surface of the substrate; subjecting the substrate to an anisotropic etching to form the grooves on the surface of the substrate, each of the grooves having a non-isosceles triangular sectional shape; forming the mold for the light-guide plate after filling a material for the mold in the grooves and attaching the material onto the surface of the substrate; and separating the mold from the substrate.

Description

PROCESS FOR FABRICATING A MOLD OF LIGHT-GUIDE PLATE. WHICH HAVING NON-ISOSCELES TRIANGLED SECTIONAL SHAPE ON ITS SURFACE, AND THE MOLD THEREOF

Background of the invention

The present invention relates to a light-guide plate used in a backlight module system employed in such apparatuses as a liquid crystal display (LCD), and more particularly to a light-guide plate having at least one non-isosceles triangular groove, a method of fabricating the light-guide plate, a mold for fabricating the light-guide plate, and a method of fabricating the mold

Related Art Since liquid crystal cannot emit light by itself, a typical LCD requires a backlight module of a surface light source type, which supplies light to the entire screen of the LCD so as to keep the screen of the LCD bright. In general, a backlight section of an LCD basically includes a light source, and, especially when the light source is located at a side position of a screen of the LCD, the backlight section must be equipped with a special unit capable of directing the light from the side-positioned light source toward a front surface of the LCD.

In general, light-guide plates perform such a function as described above. A light-guide plate is one of the most important units of the backlight module, which reflects or refracts light incident into the transparent light- guide plate from a light source located at a side position or under-position thereof by means of dot-shaped printed patterns or minute mechanical unevenness on the surface of the plate, thereby directing and dispersing the light toward the front surface of the plate.

FIG. 1 is a schematic view showing changes in directions of light beams in a light-guide plate having grooves 14 formed on a lower surface thereof. As shown, a light source 11 is located at side position of a light- guide plate body 12 made of transparent acrylic resin, and the grooves 14 each having a triangular cross-sectional shape like a prism are formed on and a reflection film 13 is attached to the lower surface of the light-guide plate body 12.

Light beams emitted from the side-positioned light source 11 proceed at various angles in the transverse direction in the light-guide plate body 12. A light beam a, which is incident at an angle smaller than a predetermined angle with respect to the front surface of the light-guide plate, is reflected inward of the light-guide plate due to the total reflection, and thus cannot function as backlight. However, in the case where the light-guide plate has grooves 14 formed on the lower surface thereof, even a light beam b, which is incident at an angle smaller than that of the light beam a, can function as backlight since the light beam b escape the light-guide plate owing to the refraction or reflection by the grooves.

The degree of reflection or refraction of light beams largely depends on a shape of each groove. Especially, the light-guide plate has a larger optical efficiency when each groove has an non-isosceles triangular sectional shape than when each groove has a isosceles triangular sectional shape. Herein, the optical efficiency implies a degree or quantity of light beams from the side-positioned light source which are directed toward the front surface of the light-guide plate by the light-guide plate. The reason why the groove having a non-isosceles triangular sectional shape produces a larger optical efficiency can be easily understood through a comparison between FIGs. 2 and 3.

FIG. 2 schematically shows directions of light beams incident at various angles into a groove of a light-guide plate. The groove (each of) has an isosceles triangular sectional shape, that is, groove has two base angles x and y, which are identical to each other. In the light-guide plate, light beams proceed from the interior 12 of the light-guide plate, which is an optically dense medium, toward the air 14-1, which is an optically sparse medium. Therefore, a light beam incident to the groove at an angle smaller than the total reflection angle, that is, at an angle equal or similar to that of a light beam c as shown, is totally reflected to be directed toward the upper surface of the light-guide plate, and is then incident to the upper surface of the light- guide plate at an angle p, so that the light beam can escape from the light- guide plate.

However, a light beam which is incident at an angle equal to that of a light beam d is refracted at the boundary of the groove and air, and then reflected on the reflecting surface 13 as shown. After the reflection, it proceeds into the light-guide plate body again, and is then incident to the upper surface of the light-guide plate body at an angle q. This angle q is equal to the angle q' at which the light beam is initially incident to the upper surface of the light-guide plate, and is smaller than the total reflection angle, so that the light beam is directed inward of the light-guide plate and, as a result, cannot escape from the light-guide plate. In other words, the groove cannot affect or divert this light beam of d. Further, another light beam e is reflected as shown and thus cannot either escape from the light-guide plate or function as a backlight. As a result, those light beams incident at angles which cannot be utilized reduce the optical efficiency of the light-guide plate. Therefore, in order to overcome this problem, a new type of groove is required.

As a groove of the new type mentioned above, an asymmetric or non- isosceles triangular groove can be employed. In the present invention, an asymmetric or non-isosceles triangle generally represents all triangles, a base angle x'of which, nearer to a light source is different from the other base angle y', farther from the light source. Although the light source is not shown in FIG. 3, one skilled in the art will naturally understand that the light source be located on the left hand of the drawing.

In FIG. 3, light beams c', d', and e' are incident to the groove at the same angles as the angles of the light beams c, d, and e in FIG. 2. However, since base angles x' and y' are different from each other, differently from the same base angles x and y in FIG. 2, directions of the light beams are completely different from the directions in FIG. 2 after being incident to the groove. Specifically, the light beam c' is totally reflected by a surface 31 of the groove, which has a larger base angle x' than the base angle x in FIG. 2, and thus can egress through the upper surface of the light-guide plate, like the light beam c in FIG. 2 does. However, differently from the light beam d in FIG. 2, the light beam d' is not totally reflected into the light-guide plate but is refracted toward and can escape through the upper surface out of the light- guide plate. Also, since a side 32 of the groove has an inclination smaller than that of the other side 31 of the groove, the light beam e' is incident to the upper surface of the light-guide plate at an angle r' which is larger than the angle r in FIG. 2, and thus the light beam e' is not totally reflected by and can escape from the upper surface of the light-guide plate.

In a light-guide plate utilizing reflection by a groove as described above, each light beam incident as shown has a much higher possibility of escaping from an upper surface of the light-guide plate when the groove has a triangular sectional shape whose base angles are not equal to each other, especially when the groove has a triangular sectional shape in which a base angle nearer to a light source is larger than the other base angle farther from the light source, than when the groove has an isosceles triangular sectional shape.

In contrast, in a state where a reflection layer 41 is in close contact with a bottom surface of the groove as shown in FIG. 4, each light beam incident as shown has the highest possibility of escaping from an upper surface of the light-guide plate when the groove has a triangular sectional shape in which a base angle x" nearer to a light source is smaller than the other base angle y" farther from the light source.

It can be concluded that a light-guide plate utilizing grooves has a higher optical efficiency when the groove has a non-isosceles triangular sectional shape than when the groove has an isosceles triangular sectional shape. However, the problem is that it is not easy to form such a groove having a non-isosceles triangular sectional shape on a surface of the light- guide plate. In other words, since each of the grooves formed on a light- guide plate has a width of 100 μm to 10 μm, it is very difficult to form such grooves to have non-symmetric sectional shapes, moreover, uniformly.

According to typical methods, a groove or grooves can be formed by injection-molding process by utilizing a mold having embossments corresponding to asymmetric grooves, in which a material of a light-guide plate such as polymethylmethacrylate (PMMA) or resin is filled.

Another Method is pressing process, in which a stamp having sharp edges is lowered down and pressed onto a surface of a preform of the light-guide plate to form the grooves.

However, in order to employ these methods, the mold for the injection- molding or the stamp must be precisely machined, and particularly, blade- shaped portions of the mold for forming the minute grooves must be precisely machined again in asymmetric shapes. Therefore, such precise machining has a high possibility of failure, thereby increasing the manufacturing cost of the light-guide plate.

This problem still remains unsolved in the field of manufacturing the light-guide plates.

Summary of the invention

Therefore, the present invention has been made to solve the above-mentioned problems by employing microelectromechanical(MEMS) process. It is an object of the present invention to provide a method of fabricating a light-guide plate having unevenness, each having a non-isosceles triangular sectional shape, which employs a silicon mold.

It is another object of the present invention to provide a silicon mold and a method of fabricating the silicon mold, which can be used in fabricating a light-guide plate having unevenness, each having a non- isosceles triangular sectional shape.

It is another object of the present invention to provide a silicon mold and a method of fabricating the silicon mold, which is fabricated by anisotropically etching a silicon substrate and used in fabricating a light- guide plate having unevenness, each having a non-isosceles triangular sectional shape.

It is still another object of the present invention to provide a method capable of fabricating any mold which can be anisotropically etched in forming a groove having a non-isosceles triangular sectional shape.

According to an aspect of the present invention, there is provided a method of fabricating a mold for a light-guide plate having unevenness on its surface, the method comprising the steps of: preparing a substrate having a surface which is parallel to neither of two crystal planes which can be anisotropically etched; forming an etching mask on the surface of the substrate; subjecting the substrate to an anisotropic etching to form grooves on the surface of the substrate, the groove having a non-isosceles triangular sectional shape; forming the mold for the light-guide plate after filling a material for the mold in the grooves and attaching the material onto the surface of the substrate; and separating the mold from the substrate. The substrate may be made from various material, which can be anisotropically etched, including silicon. In the case where the substrate is made from silicon, the two crystal planes which can be anisotropically etched may be

(100) plane and (111) plane.

The present invention does not employ mechanical processing but employs chemical etching in fabricating a mold, and enables a mold having non-isosceles triangular grooves to be fabricated utilizing a substrate which can be anisotropically etched, thereby providing a means capable of solving the problems of the conventional methods in an epochal manner.

Brief Description of the drawings The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic view showing changes in directions of light beams in a light-guide plate having grooves formed on a lower surface thereof; FIG. 2 a schematic view showing directions of light beams incident at various angles into a groove of a light-guide plate, which has an isosceles triangular sectional shape;

FIG. 3 a schematic view showing directions of light beams incident at various angles into a groove of a light-guide plate, which has a non-isosceles triangular sectional shape;

FIG. 4 is a schematic view showing directions of light beams in a light-guide plate having a groove and a reflection plate attached to the groove;

FIG. 5 is a schematic view of a silicon ingot grown in a direction toward (100) plane;

FIG. 6 is a perspective view of a substrate obtained by slicing the ingot shown in FIG. 5 at an angle α ;

FIG. 7 is a schematic view showing an arrangement of crystal planes in the substrate shown in FIG. 6; FIGs. 8 to 10 sequentially show a method of fabricating a mold for a light-guide plate having grooves;

FIG. 11 is a perspective view of a silicon substrate fabricated according to a method of the present invention;

FIGs. 12 and 13 are perspective views showing a process of fabricating a mold for a light-guide plate utilizing the silicon substrate;

FIG. 14 is a perspective view of a light-guide plate fabricated according to a method of the present invention; and FIG. 15 a schematic view showing directions of light beams in a light-guide plate according to another embodiment of the present invention, which has non-isosceles triangular sectional protrusions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 5 is a schematic view showing a single crystal silicon ingot grown by a Czochralski (CZ) method. The ingot shown in FIG. 5 is, for example, an ingot grown in a direction toward (100) plane, and (111) plane makes an angle of 54.74° with respect to (100) plane in a crystallographic view. In the present invention, silicon wafer used as a substrate has a surface which is parallel to neither of the two crystal planes of the (111) and (100), and is prepared by slicing the ingot along a plane making an angle α with respect to (100) plane in a direction designated by an arrow 51 as shown.

When the ingot is sliced at an angle α , the sliced wafer has a shape of an ellipsoidal substrate as shown in FIG. 6. Although the angle α in the shown embodiment is larger than 0° and smaller than 54.74° , any angle, which is parallel to neither (100) plane nor (111) plane, and thereby can show anisotropic etching selectivity can be employed. The reason for selecting a plane between (100) plane and (111) plane is that the two crystal planes show large etching rates 'difference to make it easy to obtain a mold aimed by the present invention, which will be described later. However, the two crystal planes are taken only as one embodiment of the present invention and do not limit the scope of the invention. FIG. 6 shows an ellipsoidal silicon wafer 61 made by slicing the ingot in the direction designated by the arrow 51 in FIG. 5. (100) plane makes an angle of (90° - α ) and (111) plane makes an angle of {90° - (54.74° - α )}, that is, an angle of (35.26° + α ), with respect to an outer surface of the wafer 61. For example, when the angle α is 20° , (100) plane makes an angle of 70° and (111) plane makes an angle of 55.26° , with respect to the surface of the wafer 61.

FIG. 7 is a sectional view of the substrate 61, which shows (100) plane 71 and (111) planes 72 and 72'. Crystallographically, the angle between the two (111) planes 72 and 72'is 109.48° .

(100) plane and (111) plane show much different etching rates in an etching solution such as KOH solution. Specifically, (100) plane shows an etching rate faster by one hundred times than that of (111) plane, which is understood due to the fact that (111) plane has higher atom density than (100) plane. When crystal planes having large difference in etching rate are etched in the same etching solution, the planes can be etched to produce various shapes in structure due to the geometric relationship. This is called "anisotropic etching", and the difference in etching rate is called "etching selectivity". The MEMS process is a representative process by using such anisotropic etchings in microelectronics. The present invention is highly characterized in that a mold for a light-guide plate having grooves, each having a non-isosceles triangular sectional shape, is fabricated by etching crystal planes of a wafer anisotropically.

FIGs. 8 to 11 sequentially show a method of fabricating a mold for a light-guide plate having grooves, each having asymmetric triangular sectional shape, by means of the ellipsoidal wafer substrate 61. FIG. 8 is a sectional view of the wafer substrate 61 on which an etching mask 81 made of Si₃N₄ has been deposited. In general, this kind of etching mask prevents undesired portions of silicon from being etched by acid, KOH solution, or etc., which are used in etching the silicon. The mask may be deposited and processed by such methods as sputtering, Reactive Ion

Etching (RIE), or etc. Referring to FIG. 8, the etching mask 81 does not cover portions of the substrate on which grooves will be formed, and the substrate under the etching mask has such a crystallographic arrangement as shown in FIG. 7. Further, the etching mask described above is taken only as one embodiment, and instead, any film showing more than a predetermined degree of resistance to the silicon etching solution, such as nitride films including A1N or GaN films, oxide films such as Siθ₂ films or polymer mask may be employed.

FIG. 9 shows an intermediate step of the process, in which the wafer substrate 61 shown in FIG. 8 is etched in, for example, KOH solution, or etc.

As the etching solution, not only the KOH-based solution but also acid solution such as HF, NaOH solution, ethylene diamine-based solution, hydrazine-based solution, Buffered Oxide Etch (BOE) solution, or nitric acid- based solution such as HN0₃ may be utilized. Further, in addition to the etching method described above, any method capable of performing the anisotropic etching, such as chemical plasma etching, may be employed.

Since the substrate has a crystallographic arrangement as shown, the etching is carried out more rapidly in a direction toward (100) plane than in a direction toward (111) planes. As a result, the substrate is etched deeply in the direction toward (100) plane, while (111) planes extend from both ends of

(100) plane with inclinations which enable to form the groove having non- isosceles triangular sectional shape. FIG. 10 shows a state where the etching has been completed, so that two (111) planes meet each other to eliminate (100) plane, thereby producing a non-isosceles triangular sectional shaped groove aimed by the present invention. FIG. 11 shows a resultant shape of a silicon substrate mold 110 from which the etching mask is eliminated after the etching is completed. It is noted that a plurality of grooves, each having a non-isosceles triangular sectional shape are formed on a surface of the silicon substrate mold.

Hereinafter, a method of fabricating a hard light-guide plate mold by using the silicon substrate mold. The hard light-guide plate mold will be utilized in a stamping process or an injection-molding process for the light- guide plate. The method will be described with reference to FIGs. 12 to 14.

Referring to FIG. 12, the hard light-guide plate mold 120 is manufactured by filling metal, for example, Ni into the silicon substrate mold 110 using a method, for example, a plating. Not only nickel, which is usually utilized, but also various metal or ceramic may be utilized as a material of the hard light-guide plate mold. In the case of ceramic, a ceramic mold can be fabricated by filling ceramic powder in the silicon substrate mold and then subjecting the filled ceramic powder, with the silicon substrate mold, in heat treatment process.. After the hard light-guide plate mold 120 is completely fabricated, it is separated from the silicon substrate mold 110. Since the two kinds of molds are made of materials totally different from each other, the two molds are not attached to each other and thus can be easily separated from each other even by a small force. Of course, in order to facilitate separation between them, a lubricant may be applied onto the surface of the silicon substrate mold before the filling step shown in FIG. 12.

FIG. 13 schematically illustrates a process of forming grooves on a surface of a light-guide plate preform 130 in a stamping manner by using the hard light-guide plate mold 120 fabricated by the process described above, and FIG. 14 shows a light-guide plate 130' finally produced according to the process of the present invention. It is noted that the light-guide plate 130' has grooves formed on the surface thereof, each of which has a non-isosceles triangular sectional shape aimed by the present invention. When an LCD is manufactured, the shown light-guide plate will be located under an LCD panel. Although not shown, after the hard light-guide plate mold 120 fabricated as shown in FIG. 12 may be assembled with a mold system for injection-molding, in which material for a light-guide plate may be filled in the hard light-guide plate mold for injection-molding and then injection- molded, so as to produce the light-guide plate.

FIG. 15 shows a light-guide plate according to another embodiment of the present invention, which is different from the light-guide plate according to the previous embodiment. The light-guide plate shown in FIG.

15 has a protrusion having a non-isosceles triangular sectional shape instead of a groove. To briefly describe light beams paths in the protrusion described above, a light beam 140' is incident at an angle which causes the light beam 140 'to be totally reflected on the lower surface of the light-guide plate 141 and prevents the light beam 140' from escaping out of the light-guide plate

141 if there is no protrusions. However, the light beam 140, which has same incident angle as that of the light beam 140 'will be refracted and thus can escape out of the light-guide plate, if the protrusion having a non-isosceles triangular sectional shape according to the present embodiment of the invention is formed on the lower surface.

It is simple to fabricate such a light-guide plate having the protrusions. Since the silicon substrate mold described above has intaglio (grooves) formed thereon, the light-guide plate having embossment (protrusions as shown in FIG. 15) can be fabricated by filling material of the light-guide plate directly in the silicon substrate. Otherwise, the light-guide plate as shown in FIG. 15 can be fabricated by fabricating a nickel mold having embossment as described above, and fabricating a second hard mold having intaglio by means of the nickel mold, and then filling material of the light- guide plate in the second mold. Of course, lubricant, etc., may be applied onto a surface of the molds, so that the molds can be easily separated from each other.

I ndustr ial App l i cabi I i ty

As can be seen from the foregoing, the present invention provides a novel method of fabricating an asymmetric groove on a light-guide plate.

In the prior art, a mold for forming minute grooves is fabricated by subjecting a mold preform to a precise mechanical cutting. However, it is never easy to uniformly form fine grooves having an asymmetric, non- isosceles triangular sectional shape, even by the precise mechanical cutting. Moreover, once the mold has even a small defective portion, the entire mold must be abandoned, thereby increasing the manufacturing cost of the light- guide plate.

In order to solve the problems of the prior art, the present invention does not employ mechanical processing but employs MEMS or chemical etching process in fabricating a mold, and enables a mold having non- isosceles triangular grooves to be fabricated utilizing a substrate which can be anisotropically etched, thereby providing a means capable of solving the problems of the conventional methods in an epochal manner.

The method of the present invention enables grooves, each having a non-isosceles triangular sectional shape with uniform base angles, to be easily fabricated, and enables various factors to be precisely controlled and prevents errors to be generated in the process of fabricating the mold.

While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments and the drawings, but, on the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims. For example, a mold of the present invention can be fabricated by not only the silicon substrate described above but also various substrates which can be anisotropically etched. Further, once base angles of the non-isosceles triangle have been determined, an angle at which an ingot is sliced can be optionally selected within the limit of the base angles. Further, in the silicon substrate, not only (100) plane and (111) plane but also any combination of crystal planes, which show etching selectivity, such as (211) plane and (111) plane, or (110) plane and (111) plane, can be selected to be etched.

Further, according to the shape of the etching mask and the degree of etching, an island type mold having asymmetric pyramidal shape can be fabricated. A description of pyramidal shape will be omitted since it is well- known shape in the field of solar cells technology. However, it is necessary to use the substrate which can be anisotropically etched when fabricating the asymmetric pyramidal shape on the surface.

Therefore, the scope of the present invention is not limited to the described embodiments but is defined only by the following claims.

Claims

Claims A method of fabricating a mold for a light-guide plate having unevenness on its surface, wherein the shape of the unevenness is non-isosceles triangular sectional shape, the method comprising the steps of: preparing a substrate having a surface which is parallel to neither of two crystal planes which can be anisotropically etched; ^* forming an etching mask on the surface of the substrate; subjecting the substrate to an anisotropic etching to form grooves on the surface of the substrate, the groove having a non-isosceles triangular sectional shape; forming the mold for the light-guide plate after filling a material for the mold in the grooves; and separating the mold from the substrate.

2. The method according to claim 1, wherein the substrate is made of silicon.

3. The method according to claim 2, wherein the two crystal planes which can be anisotropically etched are (100) plane and (111) plane.

4. The method according to claim 1, wherein the material for the mold is nickel.

5. A method of fabricating a light-guide plate having non-isosceles triangular grooves, the method comprising the steps of: preparing a substrate having a surface which is parallel to neither of two crystal planes which can be anisotropically etched; forming an etching mask on the surface of the substrate; subjecting the substrate to an anisotropic etching to form grooves on the surface of the substrate, the grooves having a non-isosceles triangular sectional shape; forming the mold for the light-guide plate after filling a material for the mold in the grooves; separating the mold from the substrate; attaching a light-guide plate preform to the mold to transcribe a shape of the mold to the light-guide plate preform; and separating the light-guide plate from the mold, the light-guide plate having a shape transcribed from the mold.

6. A method of fabricating a light-guide plate having protrusions, each of the protrusions having a non-isosceles triangular sectional shape, the method comprising the steps of: preparing a substrate having a surface which is parallel to neither of two crystal planes which can be anisotropically etched; forming an etching mask on the surface of the substrate; subjecting the substrate to an anisotropic etching to form grooves on the surface of the substrate, each of the grooves having a non-isosceles triangular sectional shape; attaching a light-guide plate preform to the substrate to transcribe a shape of the substrate to the light-guide plate preform; and separating the light-guide plate from the substrate, the light-guide plate having the protrusions formed by transcription of the shape of the mold.

7. A method of fabricating a light-guide plate having protrusions, each of the protrusions having a non-isosceles triangular sectional shape, the method comprising the steps of: preparing a substrate having a surface which is parallel to neither of two crystal planes which can be anisotropically etched; forming an etching mask on the surface of the substrate; subjecting the substrate to an anisotropic etching to form grooves on the surface of the substrate, each of the grooves having a non-isosceles triangular sectional shape; attaching a first mold preform to the surface of the substrate, thereby forming a first mold for the light-guide plate, the first mold having embossment; separating the first mold from the substrate; attaching a second mold preform to the surface of the first mold, thereby forming a second mold for the light-guide plate, the second mold having intaglio; separating the second mold from the first mold; attaching a light-guide plate preform to the second mold to transcribe a shape of the second mold to the light-guide plate preform; and separating the light-guide plate from the second mold, the light-guide plate having the protrusions formed by transcription of the shape of the second mold.

8. A silicon mold for fabricating a light-guide plate having unevenness on its surface, wherein the shape of the unevenness is non- isosceles triangular sectional shape, comprising a surface being parallel to neither of the crystal planes which can be anisotropically etched.

9. The mold according to claim 8, wherein the crystal planes which can be anisotropically etched are (100) plane and (111) plane.

10. The method according to claim 1, wherein each of said unevenness of the mold has a shape of a groove.

11. The mold according to claim 8, wherein each of said unevenness of the mold has a shape of a groove.