JP4495722B2 - Microstructure creation method - Google Patents

Description

The present invention relates to a work Narukata method microstructure formed by overlapping at least one second relief structure in the first uneven structure.

  Microstructures that diffract light typically have a large number of recesses in the form of parallel grooves and form an optical grating with, for example, a microscopic relief structure. Light incident on the microstructure is diffracted or scattered by the microstructure in a predetermined manner. The microstructured mosaic is formed, for example, in a plastic material or metal and serves as a feature that indicates the authenticity of the valuable article. These authentic features exhibit optically conspicuous behavior and make counterfeiting difficult.

  Several methods are known for forming this type of microstructure. For example, there is a method of forming a microstructure by scratching the surface of a substrate using a mechanical device to form a large number of parallel grooves. The shape of the scratching tool determines the cross-sectional shape of the concavo-convex structure. However, as the number of lines per millimeter increases, the operation of forming the concavo-convex structure by scratching becomes dramatically more difficult and therefore expensive. A holographic method of causing two coherent light beams from a laser light source to interfere on the photoresist photosensitive layer is less expensive. An image of interference fringes with bright and dark light stripes sensitizes the photoresist depending on the level of light brightness. After development, a concavo-convex structure having a symmetrical cross-sectional shape is formed on the surface of the photoresist. In yet another method, the electron beam draws concave and convex grooves one after another in the photoresist, but in this case, the groove also becomes a curve. The shape of the microstructure master formed by these methods is replicated by a plating method, and a metal stamp can be produced by the replication, and this microstructure stamp can be used to change the shape of the microstructure to metal or plastic. Can be formed into material. However, using these methods significantly increases the cost of the apparatus for forming the microstructure.

A novel microstructure synthesized in the form of a mosaic is known from Patent Document 1, in which case one of a set of different concavo-convex structures oriented in a predetermined orientation is present on each surface element of the mosaic. Mechanically formed.
European Patent Application Publication No. 0 105 099

The object of the present invention is to form a microstructure with a high degree of accuracy, for example for a replication master, which is complex and thus difficult to counterfeit, despite being relatively easy to fabricate . It is to provide an inexpensive work Narukata method microstructure is formed by at least a superposition of two uneven structure.

According to the present invention, an object of the present invention is achieved by the features claimed in claim 1, its features are the embossing or other mechanical forming forming step, a complex microstructure despite the low cost It lies in a combination of photo-forming shaped step to create. Advantageous embodiments of the invention are described in the dependent claims.

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

  Referring to FIG. 1, a first step of a method for making an optical diffractive structure is shown in cross section. A layer 2 of photoresist is applied on a flat substrate 1 made of metal, glass, ceramic or plastic material. The thickness d of the layer 2 is in the range from 0.1 μm to 100 μm and depends on the depth T of the diffractive structure to be produced. As a photosensitive photoresist material, for example, Mikroposit S 1813 sold by Shipley is known. The photoresist material is applied on the substrate 1 in a liquid state and cured by heating. The concavo-convex mother die 4 provided on the embossing stamp 3 is lowered onto the exposed flat surface of the layer 2 and pressed into the exposed surface of the layer 2, so that the shape of the concavo-convex mother die 4 becomes the layer 2. Formed on the exposed surface.

  When the embossing stamp 3 (FIG. 1) is pulled up, as shown in FIG. 2, the layer 2 in the area of the embossing stamp 3 has a concavo-convex structure 5 which is a negative image of the concavo-convex mother die 4 (FIG. 1). Prepare. Since the substrate 1 does not deform or bend during this embossing operation, the concavo-convex matrix 4 transfers the concavo-convex structure 5 onto the layer 2 with the highest fidelity with respect to shape.

"Uneven structure 5" without being restricted by means of the concept, Figure 1 shows a cross-sectional shape of the concave-convex mold 4 having a symmetrical sawtooth cross-section of the periodic grating, for example. One of the other well-known cross-sectional shapes, such as an asymmetric sawtooth cross-section, square cross-section, sinusoidal or sinusoidal cross-section, regular array of pyramids, etc., which also form a periodic primary or cross grating, in particular a relief structure 5 is suitable. Spatial frequency of the concavo-convex structure 5 can be selected from a wide range of between 1 line / mm to 2-3 thousand / mm. The depth T of the concavo-convex structure 5 made of a periodic lattice is usually in the range of 0.1 μm to 100 μm. 5 generally has a smaller spatial frequency value.

In another method, an isotropic or anisotropic mat structure forming a relief structure is formed on the surface of the layer 2. These mat structures include microscopic microrelief structure elements that determine the scattering ability and can only be expressed by statistical parameters such as, for example, average roughness R _a , correlation distance I _c, etc. _The value for a is between 20 nm and 2500 nm, preferably between 50 nm and 500 nm. In at least one direction, the correlation distance I _c is a value between 200 nm and 50000 nm, preferably between 1000 nm and 10000 nm. The microscopic uneven structure element with an isotropic mat structure does not have a preferred direction in terms of orientation because, for example, scattered light having an intensity greater than a predetermined limit is visually observed in the mat structure. This is because it is uniformly distributed in all azimuth directions within a predetermined spatial angle due to the scattering ability. A strongly scattering mat structure distributes scattered light within a larger spatial angle than a weakly scattering mat structure.

  On the other hand, if the microscopic concavo-convex structure element has a preferable azimuth direction, the mat structure scatters incident light with anisotropy. Due to the scattering ability of the mat structure, the predetermined spatial angle has an elliptical cross-sectional shape whose major axis is perpendicular to the preferred direction of the concavo-convex structure element. In contrast to a diffractive structure, a mat structure scatters incident light regardless of its wavelength, ie, the color of the scattered light roughly corresponds to the color of light incident on the mat structure.

FIG. 3 shows a cross-sectional view of an example of the mat structure, and the shape thereof is formed in the layer 2 as the concavo-convex structure 5. Instead of the depth T (FIG. 1) in the lattice, the cross-sectional shape of the mat structure has a mean roughness R _a. Fine unevenness element of the mat structure indicates a maximum difference in height H up to about 10 times the average roughness R _a. Thus, the maximum difference in the height H of the mat structure corresponds to the depth T for the periodic grating. The value of the difference in the height H of the mat structure is in the range of the depth T described above. Therefore, the detailed description to be described later regarding the range of the depth T applies to both the concavo-convex structure 5 having a periodic grating and the concavo-convex structure 5 having a mat structure.

  Referring to FIG. 4, a holographic process is shown in which a diffraction grating (not shown in FIG. 4) is additionally superimposed by exposing and shaping the concavo-convex structure 5. For example, a coherent light beam 6 having a wavelength of 400 nm is generated by the laser light source 7. The light beam 6 hits the beam splitter 8. The beam splitter 8 reflects a part of the light beam 6 as a branched beam 9 in the direction of the concavo-convex structure 5. The remaining light that has passed through the beam splitter 8 forms a reference beam 10. A polarizing mirror 11 guides the reference beam 10 onto the concavo-convex structure 5. The branched beam 9 and the reference beam 10 spread in a fan shape so that the entire concavo-convex structure 5 is individually illuminated by parallel light beams. Since the direction of the branch beam 9 is different from the direction of the reference beam 10, it intersects with a predetermined intersection angle in the surface area provided with the concavo-convex structure 5. Due to the fact that the light wave is coherent and the wavelengths of the two beams 9 and 10 are different, the branched beam 9 and the reference beam 10 interfere with each other to generate interference fringes on the concavo-convex structure 5. This interference fringe comprises parallel stripes consisting of bright fringes separated by dark fringes, where the interference fringes are traces of the surface defined on the concavo-convex structure 5 by the branched beam 9 and the reference beam 10. Intersect at right angles. The number of fringes per millimeter is determined by the wavelength of the light forming the beams 6, 9, 10 and the angle of intersection at which the branched beam 9 and the reference beam 10 intersect.

  Prior to the exposure operation, the orientation of the substrate 1 and the concavo-convex structure 5 provided in the substrate 1 with respect to the interference fringes is determined by rotating the substrate 1 around the normal line 15, and a predetermined orientation value is obtained. Is set.

  The above-described photoresist material is modified so that only bright light fringes of the interference fringes are exposed, and after exposure, the photoresist material is dissolved by the action of a developer such as Mikroposit 351 from Shipley. In that case, recesses are formed on the surface of the photoresist in the form of parallel grooves made of diffraction gratings having a grating period equal to the spacing of the interference fringes. The grating period can be adjusted by changing the angle at which the branched beam 9 and the reference beam 10 intersect. The wavelength of the light beam 6 is predetermined by the laser light source, but must be suitable for the exposure of the photoresist forming the layer 2.

  The cross-sectional shape of the groove and its geometric depth t are determined by the exposure time, the development time, and the light intensity. The depth of the groove usually reaches a predetermined value of 250 nm. The cross-sectional shape ranges from a symmetric and simple sinusoidal cross section to a square wave cross section. The position of the grating is determined by the interference fringes. Therefore, the azimuths of the grating lines of the concavo-convex structure 5 and the grooves of the diffractive structure differ depending on the preset azimuth value.

  FIG. 5 shows the surface of the layer 2 after the concavo-convex structure 5 (FIG. 4) is shaped by exposure. A microstructure 12 is formed on the surface of the layer 2, and this microstructure 12 is formed by additionally superimposing a holographically generated diffraction structure on the concavo-convex structure 5. In the embodiment, the lattice lines of the concavo-convex structure 5 and the grooves 13 of the diffractive structure are included in the same orientation. In FIG. 5, the original uneven structure 5 is indicated by a broken line 14. The photoresist that originally existed between the broken line 14 and the microstructure 12 has been removed by a development operation.

  After the photoresist is dried, the microstructure 12 is formed by nickel plating by a well-known method, and a master of the microstructure 12 is born. The reflective master is inspected to determine if it has optical properties that correspond to the desired properties. The master is then combined with other diffractive structures, mirrors, etc. in a plastic material or metal to produce a mosaic pattern for the optical security element.

  In the above forming step, a plurality of structures, that is, the concavo-convex structure 5 and the diffractive structure are additionally combined, and the microstructure 12 in which the geometric shape of the concavo-convex structure 5 and the diffractive structure substantially remains (other methods) The advantage is that it is almost certain that it will be obtained (better than used).

  In this case, it is also possible to combine structures having significantly different dimensions. For example, the concavo-convex structure 5 may have a depth T exceeding 2 μm, and may include one of a mat structure, one of gratings, or a microprism constituting a retroreflector. Can do. The concavo-convex structure 5 is overlaid with a diffractive structure having a low grating period value.

In the first method for creating a microstructure 12, a periodic grating described above is formed in the layer 2 as a concavo-convex structure 5, the periodic grating is photo shaped with diffractive structures. In certain embodiments, the spatial frequency of the diffractive structure is at least five times higher than the spatial frequency of the relief structure 5.

In a second method for creating a microstructure 12, one of the above-mentioned mat structure is formed in the layer 2, the mat structure is photo shaped with diffractive structures. The grating period of the diffractive structure is at most 500 nm so that light is reflected only in the zeroth diffraction order. The advantage of the microstructure 12 is that the microstructure 12 can combine the scattering capabilities of the mat structure with properties such as the wavelength selective reflection capability, polarization capability, etc. of the diffraction grating.

How to create the micro structure 12, after the previous photograph shaping work is performed, the branch beam 9 (Fig. 4) and a reference beam 10 (FIG. 4) and the first by changing the intersection angle at the point of intersection The method can be expanded, in which case further photo-sculpting work is performed with interference fringes that differ in the number of fringes per mm of the striped pattern compared to the previous photo-sculpting work. The method expansion with different settings regarding the spatial frequency of the striped pattern is performed once or a plurality of times with different spatial frequencies until a predetermined microstructure 12 is obtained.

How to create the micro structure 12, after the previous photograph shaping work is performed, the branch beam 9 (Fig. 4) and the reference beam 10 azimuth orientation of the substrate 1 to interference fringes formed by (Figure 4) It can be magnified by a second way of doing a different photo-formation task. The method expansion with different settings regarding the orientation of the azimuth is performed once or a plurality of times while changing the orientation of the orientation until a predetermined microstructure 12 is obtained.

The method of creating the microstructure 12 can be changed by a third method in which both the spatial frequency and orientation of the interference fringes are changed and then further photo-sculpting work is performed after the previous photo-sculpting work. . The enlargement of the photo modeling work performed with different settings regarding the spatial frequency and the orientation of the stripe pattern is performed once or a plurality of times while changing the settings until a predetermined microstructure 12 is obtained.

  In the method described here as a preferred method, the step a) includes using an embossing method for forming the shape of the concavo-convex structure 5. However, the step a) can be changed to a mode in which the concavo-convex structure 5 is already formed when the layer 2 is cast. In that case, a liquid photoresist is injected into a molding die comprising a substrate 1 and an uneven mother die 4 (FIG. 1) disposed opposite to the substrate 1. The concavo-convex mold 4 is removed after the photoresist is cured by heating. The exposed surface of the layer 2 includes a concavo-convex structure 5 as a negative image of the concavo-convex matrix 4.

  In still another method, in the step a), the concavo-convex structure 5 can be mechanically cut directly into the layer 2 by a cutting stylus instead of embossing or casting.

In another method shown in FIG. 6, at least one rotating paraboloid 16 and / or conical tip 17 is used as the concave-convex matrix 4. The paraboloid 16 and / or the conical tip 17 may be combined with the periodic grating described above. The shape of the concavo-convex matrix 4 is formed in the layer 2 on the substrate 1. Next, a photo modeling work is performed.

In still another method for forming the microstructure 12, instead of using a lattice structure or a mat structure as the concave / convex matrix 4, a combination structure that already exists by superposition of a plurality of structures is used, and this combination structure is described above. In the process, the surface of the layer 2 made of photoresist is first shaped to form the concavo-convex structure 5, and then further photographic modeling work is performed.

  In addition to the positive photoresist described above, it is also known to use a negative photoresist (Futurrex NR7-1000PY) which is extremely suitable for this formation method.

It is sectional drawing which shows the substrate provided with the layer which consists of photoresists. It is sectional drawing which shows the surface by which the layer which consists of photoresists was embossed. It is sectional drawing which shows a mat structure. It is sectional drawing which shows the exposure operation | work of a photoresist. It is sectional drawing which shows the shape of a microstructure. It is a perspective view which shows the embossing stamp provided with the uneven | corrugated mother block.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Photoresist layer 4 Concavity and convexity mold 5 Concavity and convexity structure 6 Light beam 7 Laser light source 8 Beam splitter 9 Branch beam 10 Reference beam 12 Microstructure 13 Groove

Claims (13)

A microscopic structure that diffracts light into the photoresist layer (2) on the substrate (1) by superimposing at least one second uneven structure serving as a diffraction structure (12) on the first uneven structure (5). A method of creating a structure (13) comprising:
a) A first concavo-convex structure (5) formed by molding the shape of the concavo-convex matrix (4) disposed facing the substrate (1) on the exposed surface of the photoresist layer (2). On a flat substrate (1) with a photoresist layer (2) comprising
b) removing the concave / convex matrix (4),
c) The coherent light is decomposed into a branched beam (9) and a reference beam (10), and the branched beam (9) and the reference beam (10) are caused to interfere with each other at a predetermined intersection angle. Create interference fringes on the concavo-convex structure (5) of 1,
d) by rotating the substrate (1) around a normal (15) to the plane of the substrate (1), by dark light fringes with respect to the orientation with respect to the first relief structure (5) Determine the direction of the interference fringes with the bright light stripes separated,
e) exposing the first relief structure (5) in the photoresist layer (2) for a predetermined time using the interference fringes;
f) The photoresist is developed for a predetermined time, and the photoresist material altered by the exposure is partially removed to form a groove (13) of the diffraction structure (12) in the first concavo-convex structure (5). Let
g) drying the photoresist;
How to create a microstructure characterized by including that each step. In the step a), the photoresist layer (2) is first formed on the substrate (1), the photoresist layer (2) is cured by the action of heat, and then on the stamp (3). The provided concavo-convex matrix (4) is lowered to the surface of the photoresist layer (2), and the shape of the first concavo-convex structure (5) is formed as a negative of the concavo-convex matrix (4). The method according to claim 1 . In the step a), the photoresist layer (2) is formed by casting. In this case, a liquid photoresist is injected between the substrate (1) and the concave-convex matrix (4), and the photoresist is formed. After being cured by heating and releasing, the exposed surface of the photoresist layer (2) is provided with the first concavo-convex structure (5) as a negative image of the concavo-convex matrix (4). The method according to claim 1 or 2 . The method according to any one of claims 1 to 3 , wherein in step a), a periodic grating is formed on the photoresist layer (2) as the first relief structure (5). The method according to any one of claims 1 to 3 , wherein in step a), an intersecting lattice is formed on the photoresist layer (2) as the first relief structure (5). In the step a), a periodic grating having a spatial frequency in the range of 1 line / mm to 1000 lines / mm is formed on the photoresist layer (2) as the first uneven structure (5). 6. A method according to any one of claims 1 to 5 , characterized in that In step c), the branch beam (9) and the reference are formed so that a diffractive structure (12) having a spatial frequency corresponding to at least five times the spatial frequency of the first concavo-convex structure (5) is formed. 6. A method as claimed in claim 4 or 5 , characterized in that the angle of intersection with the beam (10) is set. In the step a), any one of the preceding claims, characterized in that formed on the photoresist layer as a single mat structure for scattering light the first relief structure (5) (2) 3 The method described. In the step a), an uneven matrix (4) having a structure having at least one rotational paraboloid (16) and / or conical tip (17) is formed into the shape of the first uneven structure (5). any one process of claim 1 3, characterized by using in formation. It said first concave-convex structure (5), 0.1 [mu] m and a method according to any one of claims 1-9, characterized in that formed at a depth ranging between 100 [mu] m (T). Prior to the execution of the step g), at least one additional diffractive structure (12) is formed by repeating the photographic molding operation from the step c) to the step f), in which case the step d) The first concavo-convex structure (5) provided with a groove (13) of the diffractive structure (12) for new interference fringes by rotating the substrate (1) around the normal (15). The method according to any one of claims 1 to 10 , characterized in that the direction is determined. 12. Method according to claim 11 , characterized in that in the repetition of the photographic shaping operation in step c), the angle of intersection between the branch beam (9) and the reference beam (10) is changed. The intersection angle between the branched beam (9) and the reference beam (10) is set so that a diffractive structure (12) having a grating period of maximum 500 nm is formed in the step c). The method according to any one of claims 1 to 12 .

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