MICROSTRUCTURE AND METHOD FOR MANUFACTURING SAME

Abstract

The present invention relates to a microstructure 20 having pores 22 on its surface or inside. The microstructure is a sheet containing an energy ray active resin 21. The pores 22 are formed in a vertical array and are in a formation pattern with a Talbot distance being specified by Formula 1 below:

Z.sub.T=(2nd.sup.2)/λ  [Formula 1] where Z.sub.T represents a Talbot distance (nm), n represents a refractive index, d represents a pitch distance (nm), and λ represents a light wavelength (nm). The pores have a periodic shape in the planar direction. Thus, the present invention provides three-dimensional microfabricated structures through which the periodicity is controlled.

Claims

1. A microstructure comprising pores on its surface or inside, wherein the microstructure is a sheet comprising an energy ray active resin, the pores are formed in a vertical array, the pores in the microstructure are in a formation pattern with a Talbot distance being specified by Formula 1 below:
Z.sub.T=(2nd.sup.2)/λ  [Formula 1] where Z.sub.T represents a Talbot distance (nm), n represents a refractive index, d represents a pitch distance (nm), and λ represents a light wavelength (nm), and the pores have a periodic shape in the planar direction.

2. The microstructure according to claim 1, wherein the energy ray active resin is a resist resin.

3. The microstructure according to claim 1, wherein the energy ray active resin is a positive resist resin.

4. The microstructure according to claim 1, wherein the periodic shape satisfies a grating pitch of wavelength λ≤grating pitch d and a pitch duty cycle of 0.2 to 0.7.

5. The microstructure according to claim 1, wherein the pores on the surface or inside of the microstructure are at least one selected from closed cells, pores penetrating through the front and back surfaces of the microstructure, grooves, and holes.

6. The microstructure according to claim 1, wherein the periodic shape is a shape with regularity.

7. A method for producing a microstructure, comprising pores on its surface or inside, the microstructure being a sheet comprising an energy ray active resin, the pores being formed in a vertical array, the pores in the microstructure being in a formation pattern with a Talbot distance being specified by Formula 1 below:
Z.sub.T=(2nd.sup.2)/λ  [Formula 1] where Z.sub.T represents a Talbot distance (nm), n represents a refractive index, d represents a pitch distance (nm), and λ represents a light wavelength (nm), and the pores having a periodic shape in the planar direction, the method comprising: (1) applying an energy ray active resin to a substrate in a uniform thickness; (2) prebaking (heating) the applied energy ray active resin layer; (3) forming a pattern in the energy ray active resin layer obtained in (2) by placing a diffraction grating on an upper surface of the resin layer, and vertically irradiating the resin layer with energy ray through multiple exposures including exposure with at least one movement of the diffraction grating selected from rotation and shifting; (4) chemically reacting the resin layer obtained in (3) with a developer to dissolve a portion where an energy ray exposure dose reaches or exceeds an energy ray curing threshold and cure a portion where the exposure dose is below the curing threshold, or to cure a portion where an energy ray exposure dose reaches or exceeds an energy ray curing threshold and dissolve a portion where the exposure dose is below the curing threshold; and (5) washing the substrate obtained in (4) with pure water to remove the dissolved portion to obtain a microstructure.

8. The method according to claim 7, wherein the energy ray active resin is a resist resin.

9. The method according to claim 7, wherein the energy ray active resin is a positive resist resin.

10. The method according to claim 7, wherein the periodic shape satisfies a grating pitch of wavelength λ≤grating pitch d and a pitch duty cycle of 0.2 to 0.7.

11. The method according to claim 7, wherein the pores on the surface or inside of the microstructure are at least one selected from closed cells, pores penetrating through the front and back surfaces of the microstructure, grooves, and holes.

12. The method according to claim 7, wherein the periodic shape is a shape with regularity.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1A is a schematic cross-sectional view illustrating the basic concept of the present invention in which an exposure mask placed on the upper surface of a photoresist resin is irradiated with ultraviolet light (UV). FIG. 1B is a schematic cross-sectional view illustrating portions in the photoresist resin irradiated with light.

[0028] FIG. 2 is a schematic perspective view illustrating multiple exposures in one embodiment of the present invention. FIG. 2A is a schematic perspective view of the first exposure, and FIG. 2B is a schematic perspective view of the second exposure performed after rotation of a diffraction grating.

[0029] FIGS. 3A to 3E are schematic cross-sectional views and 3F is a schematic perspective view illustrating a production method in one embodiment of the present invention.

[0030] FIG. 4 is a schematic perspective view illustrating the inside of a microstructure of Example 1 of the present invention.

[0031] FIG. 5A is a schematic perspective view illustrating the inside of a microstructure of Example 2 of the present invention, and FIG. 5B is a photograph of the same.

[0032] FIG. 6 is a schematic perspective view illustrating the inside of a microstructure of Example 3 of the present invention.

[0033] FIG. 7 is a schematic perspective view illustrating the inside of a microstructure of Example 4 of the present invention.

[0034] FIG. 8 is a schematic perspective view illustrating the inside of a microstructure of Example 5 of the present invention.

[0035] FIG. 9A is a schematic perspective view illustrating the inside of a microstructure of Example 6 of the present invention, and FIG. 9B is a photograph of the same.

[0036] FIG. 10 is a schematic perspective view illustrating the inside of a microstructure of Example 7 of the present invention.

DESCRIPTION OF THE INVENTION

[0037] In the present invention, a sheet containing an energy ray active resin has pores formed in a vertical array. The pores may be present on the surface or inside of the sheet. The pores may be either closed or open. The pores in the microstructure are in a formation pattern with a Talbot distance being specified by Formula 1 above. The pores have a periodic shape in the planar direction.

[0038] The energy ray active resin is preferably a resist resin, and more preferably a positive resist resin. Portions in the positive resist resin exposed to energy ray dissolve in a solution, and such a property of the positive resist resin is suitable for microfabrication. A negative resist resin is exposed to high temperatures in postbaking, which strains resin and makes it difficult to produce microstructures with accurate periodicity.

[0039] The periodic shape preferably satisfies a grating pitch of wavelength λ≤grating pitch d and a pitch duty cycle of 0.2 to 0.7. This makes is possible to perform finer processing. The periodic shape is preferably a shape with regularity. Thus, microstructures with high uniformity are obtained.

[0040] The pores on the surface or inside of the microstructure include closed cells, pores penetrating through the front and back surfaces of the microstructure, grooves, holes, and other various pores.

[0041] The production method of the microstructure of the present invention includes the following steps:

[0042] (1) applying an energy ray active resin to a substrate in a uniform thickness;

[0043] (2) prebaking (heating) the applied energy ray active resin layer;

[0044] (3) forming a pattern in the energy ray active resin layer obtained in (2) by placing a diffraction grating on an upper surface of the resin layer, and vertically irradiating the resin layer with energy ray obtained by the Talbot effect through multiple exposures including exposure with at least one movement of the diffraction grating selected from rotation and shifting;

[0045] (4) chemically reacting the resin layer obtained in (3) with a developer to dissolve a resin portion where an energy ray exposure dose reaches or exceeds an energy ray curing threshold and leave a resin portion where the exposure dose is below the curing threshold, or leave a resin portion where an energy ray exposure dose reaches or exceeds an energy ray curing threshold and dissolve a resin portion where the exposure dose is below the curing threshold; and

[0046] (5) washing the resin obtained in (4) with pure water to remove the dissolved portion to obtain a microstructure.

[0047] An exemplary technique for the application of an energy ray active resin in a uniform thickness in (1) is spin coating. The spin coating enables thin and uniform application in a relatively small area.

[0048] Preferable conditions for the prebaking (heating) in (2) are the temperature of 0° C. to 100° C. and the time of about 1 to 5 minutes, according to the manufactures' recommendation.

[0049] Preferable conditions for the vertical irradiation with energy ray in the pattern forming step in (3) are the number of times of exposure of 2 to 10 times and the total exposure dose of 100 to 300 mJ/cm.sup.2. The exposure with energy ray obtained by the Talbot effect may be any of the following: multiple exposures from the vertical direction; multiple exposures with shifting in the triaxial direction or rotation: or multiple exposures with shifting in the triaxial direction and rotation. For pattern formation, either the substrate or the diffraction grating may be moved, and any common positioning device may be used.

[0050] Postbaking (heating) is preferably performed between (3) and (4) to stabilize the exposed resist. Preferable conditions for the postbaking are the temperature of 30° C. to 100° C. and the time of about 1 to 60 minutes.

[0051] An exemplary technique for the washing in (5) is spin coating.

[0052] The following describes an exemplary microstructure of the present invention.

[0053] (1) The processible area is up to 20 mm per side in each exposure. Exposures are repeated to process a wider area.

[0054] (2) The processible thickness of the structure is 500 nm to 100 μm. The thickness is more preferably 700 nm to 50 μm, and further preferably 1 to 20 μm.

[0055] (3) The microfabricable pore length (length in the depth direction) is preferably 10 nm to 3000 nm. The length is more preferably 100 to 1500 nm.

[0056] (4) The periodicity of the structure is 1 to 20 times, and preferably about 1 to 10 times.

[0057] The Talbot effect used in the present invention is as follows.

[0058] (1) The Talbot effect is a phenomenon in which when a plane wave is incident upon the diffraction grating, diffracted light in the Fresnel region interferes with each other, and the periodic light intensity distribution is repeated three-dimensionally.

[0059] (2) By generating the periodic light intensity distribution by the diffraction grating and using it for exposure in lithography, a periodic microstructure can be three-dimensionally processed at once in a large area.

[0060] Hereinafter, the present invention will be described using drawings. In the following drawings, the same reference numeral denotes the same element. FIG. 1A is a schematic cross-sectional view illustrating the basic concept of the present invention in which an optical filter (exposure mask) 2 is placed on the upper surface of a photoresist resin 3 and irradiated with ultraviolet light (UV) 1. The photoresist resin 3 is a positive photoresist resin, and the optical filter (exposure mask) 2 is, e.g., a polycarbonate diffraction grating. A space between the photoresist resin 3 and the optical filter (exposure mask) 2 is defined as a distance 1. X and Y indicate the planar direction, and Z indicates the depth direction. Details are shown in the drawing. FIG. 1B is a schematic cross-sectional view illustrating light exposed portions 4, irradiated with light, in the photoresist resin 3. The pattern of dots indicates the exposed light intensity distribution, where the larger the number of dots, the higher the exposure intensity. The exposure intensity is standardized by the strongest light intensity and expressed in an arbitrary unit, a.u.

[0061] FIG. 2A is a schematic perspective view illustrating multiple exposures in one embodiment of the present invention. Vertically irradiating the surface of the photoresist resin 3 with ultraviolet light (UV) 1 yields light exposed portions 5a and 5b. Z.sub.T is a Talbot distance (nm). In FIG. 2A, the Talbot distance is a vertical distance (nm) between the center of an irradiated spot in the first row and the center of an irradiated spot in the third row, these irradiated spots being on the same irradiation line as viewed from the irradiation surface. By performing multiple exposures, light exposed portions 6 inside the resin continuously extend in the planar direction and become continuous pores when dissolved in the following step.

[0062] FIG. 2B is a schematic perspective view illustrating an exposure involving rotation. The rotation is the rotation of the photoresist resin 3 by a predetermined angle θ. By performing exposure with rotation, light exposed portions 7 are independent of each other and become closed pores when dissolved in the following step.

[0063] FIGS. 3A to 3E are schematic cross-sectional views and FIG. 3F is a schematic perspective view illustrating a production method in one embodiment of the present invention.

[0064] (1) FIG. 3A illustrates a state in which a sheet obtained by curing a 10-μm-thick photoresist resin is placed as a buffer layer 11 on a substrate 10, onto which a photoresist resin liquid 13 is applied by spin coating to form a photoresist resin layer 12a on the buffer layer 11.

[0065] (2) FIG. 3B illustrates a state in which the applied photoresist resin layer 12a is prebaked (heated) on a hot plate 14 to prepare a prebaked photoresist resin layer 12b.

[0066] (3) FIG. 3C illustrates a state in which an optical filter (exposure mask) 15 is placed on the photoresist resin layer 12b obtained in (2) and vertically irradiated with ultraviolet light (UV) 16 to form an exposure pattern 17 in a photoresist resin layer 12c.

[0067] (4) FIG. 3D illustrates a state in which the photoresist resin layer 12c obtained in (3) is stabilized by postbaking (heating). Next, FIG. 3E illustrates a state in which a postbaked (heated) photoresist resin layer 12d is chemically reacted with a developer by spin coating to dissolve a portion where an ultraviolet light (UV) exposure dose reaches or exceeds an energy ray curing threshold and cure a resin portion 19 where the exposure dose is below the curing threshold. By doing so, pores 18 are formed in a photoresist resin layer 12e.

[0068] (5) FIG. 3F illustrates a state in which the resin 19 obtained in (4) is washed with pure water to remove the dissolved portion to obtain a microstructure.

[0069] Preferable processing conditions according to the present invention are as follows.

[0070] (1) Resin Material

[0071] A positive resist is preferably used. For example, a positive UV curable resin is preferred. A negative resist requires a step of arranging a buffer layer and involves high temperature exposure in postbaking, which strains the resin and makes it difficult to produce microstructures with accurate periodicity. The processing temperature (prebaking) of resin is preferably 0 to 100° C. This is the resin curing temperature range according to the resin manufactures' recommendation.

[0072] (2) Cleaning liquid: Any liquid that is noninvasive to the resin can be used. Pure water is preferably used.

[0073] (3) Light wavelength: Laser UV light is used. For example, λ=360 nm is used. The wavelength region is 0.1 nm to 380 nm. Examples of the energy ray include ultraviolet lights (UV-A, B, C), X-rays, and electron beams.

[0074] (4) Diffraction grating: One or more optical filters are used. For example, polycarbonate optical filters are used. The grating pitch is specified by wavelength λ≤grating pitch d. The pitch duty cycle is 0.2 to 0.7, and preferably 0.4 to 0.6. For example, the grating pitch is 747 nm, and the grating height is 150 nm. The DVD surface can be used as a diffraction grating. Examples of the diffraction grating other than DVDs include those described in Table 1.

TABLE-US-00001 TABLE 1 The number of grooves Pitch (number/mm) (μm) GTU13-06 manufactured by Thorlabs, Inc. 600 1.67 GTU13-08 manufactured by Thorlabs, Inc. 830 1.20 GTU13-12 manufactured by Thorlabs, Inc. 1200 0.833

[0075] (5) Processing Pattern

[0076] A groove structure with regularity can be formed. The periodicity of the structure is changeable between 1 time and 20 times inclusive. The surface to be processed of the structure may be formed to have an acute angle, or flat.

[0077] (6) Processing Characteristics

[0078] (a) Precise processing is performed by multiple exposures with shifting in the triaxial direction or/and rotation. A positioning device can be used to control the positions of the substrate and the diffraction grating for the movements in the X, Y, and Z-axes directions and rotation. The positioning device may be a piezo stage. For example, Melles Griot, 17MAX301 may be used.

[0079] (b) The processing conditions can be changed depending on the exposure conditions and exposure time. Resin cures when the exposure dose reaches or exceeds the light curing threshold. Curing is controlled by the exposure time.

[0080] (c) The irradiation light vertically enters the substrate surface.

[0081] (d) The Talbot distance is determined by Formula 1.

[0082] This results in the following.

[0083] (i) Adjacent processing areas are connected by reducing the Talbot distance.

[0084] (ii) Prior and subsequent processing areas are connected by controlling a periodic distance.

[0085] (iii) Adjacent processing areas are made independent of each other by increasing the Talbot distance.

[0086] (iv) Prior and subsequent processing areas are independent of each other by controlling the periodic distance.

EXAMPLES

[0087] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.

Example 1

[0088] The experiment was performed in the following manner.

[0089] (1) A resin layer 12a made of a UV curable resin SIPR-3251-6.0 (manufactured by Shin-Etsu Chemical Co., Ltd.) having a uniform thickness was formed on a buffer layer 11 on a substrate 10 using a spin coater. The thickness was 6 μm (FIG. 3A).

[0090] (2) The resin layer 12a formed in (1) was placed on a hot plate 14 and prebaked (heated) at 100° C. for 2 minutes to volatilize a solvent contained in the resin layer 12a to form a resin layer 12b (FIG. 3B).

[0091] (3) A polycarbonate diffraction grating 15 (pitch width: 747 nm) having a refractive index n of 1.59 was placed on the upper surface of the resin layer 12b obtained in (2). The resin layer was vertically irradiated with light 16 of an ultraviolet LED surface light source (wavelength λ=360 nm) two times, with shifting in the X-axis direction of 0.5×d (the unit is the same as the unit d and may be an arbitrary unit) to form a pattern in a resin layer 12c (FIG. 3C). At this time, the Formula 1 above was satisfied.

[0092] (4) The resin layer 12c obtained in (3) was chemically reacted with a SIPR-3251 developer (the developer supplied with the resin SIPR-3251) to dissolve a portion where the exposure dose reached or exceeded the light curing threshold of SIPR-3251 to form a resin layer 12d (FIG. 3D). Then, the resin layer 12d was chemically reacted with the developer by spin coating to dissolve a portion 18 where the ultraviolet light (UV) exposure dose reached or exceeded the energy ray curing threshold and cure a resin portion 19 where the exposure dose was below the curing threshold. Thus, a photoresist resin layer 12e was formed to have the pores 18 in the resin portion 19.

[0093] (5) The resin 19 obtained in (4) was washed with pure water to remove the dissolved portion to obtain a microstructure (FIG. 3F).

[0094] FIG. 4 shows an obtained microstructure (sheet) 20, in which closed pores 22 are regularly formed with periodicity inside a resin portion 21.

Examples 2 to 7

[0095] Microstructures of Examples 2 to 7 were produced in the same manner as in Example 1 except for conditions described in Table 2.

[0096] Tables 2 and 3 summarize the conditions and results. FIG. 5A is a schematic perspective view illustrating the inside of a microstructure of Example 2, and FIG. 5B is a photograph of the same. FIG. 6 is a schematic perspective view illustrating the inside of a microstructure of Example 3. FIG. 7 is a schematic perspective view illustrating the inside of a microstructure of Example 4. FIG. 8 is a schematic perspective view illustrating the inside of a microstructure of Example 5. FIG. 9A is a schematic perspective view illustrating the inside of a microstructure of Example 6, and FIG. 9B is a photograph of the same. FIG. 10 is a schematic perspective view illustrating the inside of a microstructure of Example 7. In FIGS. 5A to 10, reference numerals 20, 23, 26, 29, 32, 35, and 38 indicate microstructures, 21, 24, 27, 30, 33, 36, and 39 indicate resin portions, and 22, 25, 28, 31, 34, 37, and 40 indicate pores.

TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Example 4 Material of structure UV curable UV curable UV curable UV curable resin resin resin resin Light source Type Ultraviolet Ultraviolet Ultraviolet Ultraviolet fight light light light Wavelength (nm) λ = 360 λ = 360 λ = 360 λ = 360 Optical filter Height of diffraction 150 150 150 150 grating (h) (nm) Pitch of diffraction 747 747 747 747 grating (d) (nm) Duty cycle of 0.5 0.5 0.5 0.5 diffraction grating Material Polycarbonate Polycarbonate Polycarbonate Polycarbonate Distance between optical filter and 785.9 785.9 0 0 structure (l) (nm) Parameter of Talbot distance (nm) 3143.7 3143.7 3143.7 3143.7 Talbot effect Zt = (2nd.sup.2)/λ Application of Rotation speed of 3000 3000 3000 3000 UV curable spin coater (rpm) resin Thickness of resin 6 6 6 2 layer (μm) Prebaking Temperature (° C.) 100 100 100 100 Time (min) 2 2 2 2 Light Total exposure dose 80 150 160 150 exposure (mJ/cm.sup.2) The number of times 2 2 4 2 of exposure (times) Moving condition of 1st: 0 1st: 0 1st: 0 1st: 0 each exposure 2nd: 0.5 d in 2nd: 0.5 d in 2nd: 0.25 d in 2nd: 90 degree the X-axis the X-axis the X-axis rotation direction direction direction 3rd: 0.25 d in the X-axis direction 4th: 0.25 d in the X-axis direction Shape of structure FIG. 4 FIGS. 5A and FIG. 6 FIG. 7 5B

TABLE-US-00003 TABLE 3 Example 5 Example 6 Example 7 Material of structure UV curable UV curable UV curable resin resin resin Light source Type Ultraviolet light Ultraviolet light Ultraviolet light Wavelength (nm) λ = 360 λ = 360 λ = 360 Optical filter Height of diffraction 150 150 150 grating (h) (nm) Pitch of diffraction 747 747 747 grating (d) (nm) Duty cycle of 0.5 0.5 0.5 diffraction grating Material Polycarbonate Polycarbonate Polycarbonate Distance between optical filter and 785.9 785.9 785.9 structure (l) (nm) Parameter of Talbot distance (nm) 3143.7 3143.7 3143.7 Talbot effect Zt = (2nd.sup.2)/λ Application of Rotation speed of spin 3000 3000 3000 UV curable coater (rpm) resin Thickness of resin 2 6 6 layer (μm) Prebaking Temperature (° C.) 100 100 100 Time (min) 2 2 2 Light Exposure dose 150 200 300 exposure (mJ/cm.sup.2) The number of times 2 4 4 of exposure (times) Moving condition of 1st: 0 1st: 0 1st: 0 each exposure 2nd: 90 degree 2nd: 0.5 l in the 2nd: 0.5 d in the rotation Z-axis direction X-axis direction 3rd: 90 degree 3rd: 90 degree rotation rotation 4th: 0.5 l in the 4th: 0.5 d in the Z-axis direction Y-axis direction Shape of structure FIG. 8 FIGS. 9A and FIG. 10 9B

[0097] The above examples indicate that multiple exposure with shifting in the triaxial direction and/or rotation of energy ray obtained by the Talbot effect enables formation of pores in structures and microfabrication of structures having controlled periodicity to the inside.

INDUSTRIAL APPLICABILITY

[0098] The microstructures of the present invention having a resin layer in which grooves, through pores, open cells, and the like are formed, are applicable to photonic structures including filters, biomimetic structures, functional members, etc.

DESCRIPTION OF REFERENCE NUMERALS

[0099] 1, 16 Ultraviolet light (UV) [0100] 2, 15 Optical filter (exposure mask) [0101] 3 Photoresist resin [0102] 4, 5a, 5b Light exposed portion [0103] 6 Connected light exposed portion [0104] 10 Substrate [0105] 11 Buffer layer [0106] 12a-12f Photoresist resin layer [0107] 13 Photoresist resin liquid [0108] 14 Hot plate [0109] 7, 17 Exposure pattern [0110] 18 Pore [0111] 19 Resin portion [0112] 20, 23, 26, 29, 32, 35, 38 Microstructure [0113] 21, 24, 27, 30, 33, 36, 39 Resin portion [0114] 22, 25, 28, 31, 34, 37, 40 Pore