The present invention relates to microstructures processed using the Talbot effect and a method for producing the same.
Submicron three-dimensional structures have drawn attention recently. Examples of the submicron three-dimensional structures include microstructured parts for semiconductor devices and microelectromechanical systems (MEMS), biomimetic structures that imitate functional microstructures of living organisms, and nanostructured photonic crystals composed of substances with different refractive indexes arranged at intervals almost the same as light wavelength. These submicron three-dimensional structures, particularly those having a periodic structure, are attracting attention as functional materials. Techniques for fabricating microstructures include lithography, etching, nanoimprint, laser micromachining, atomic manipulation using an atomic force microscope (AFM), and self-organization. These techniques require longer processing time as structures are formed multidimensionally, and improved processing efficiency is required. A high degree of freedom and high accuracy in processing are also required, along with more complicated structures, to control the periodic structure as desired. However, the efficiency and the degree of freedom in processing are in a trade-off relationship, and technologies for fabricating multi-dimensional microstructures with a simple technique have not yet been established and are under development. Together with the improvement in the processing accuracy, it also is desired to broaden a processing area to the order of millimeters in the production of microstructures.
One simple method for producing microstructures is a three-dimensional lithography technique using a resist resin material. Specifically, three-dimensional lithography using the Talbot effect facilitates the formation of a periodic pattern in a large area at once by using a specific wavelength and a diffraction grating, and highly improves the processing efficiency. In the lithography using the Talbot effect, however, the degree of freedom in processing is low, because the parameters for controlling the periodicity are the wavelength and the grating pitch, and thus the period control is limited to two dimensions. No technologies have been established for processing three-dimensional structures into desired shapes without limiting the processing area to the “surface” or “inside”.
Patent Document 1 discloses lithography techniques using the Talbot effect. These techniques are intended for processing with use of etching screen masks and do not involve internal processing of structures. Patent Document 2 discloses masks and pattern forming methods that enable highly accurate patterns to be formed using the Talbot effect, but the technique is not intended for fabrication of structures. Patent Document 3 discloses formation of periodic recesses or pores by etching, but it is not easy to fabricate microstructures with this technique. Non-Patent Document 1 proposes a structure in which metal nanoparticles are dispersed by applying stereolithography using the Talbot effect, but the technique has not reached fabricating clear layer structures using the Talbot effect. Non-Patent Document 2 discloses fabrication of nanostructures in a large area in one-dimensional layer structures and two-dimensional periodic structures, but the accuracy and the maintenance of the structures are unsatisfactory, and the technique has not reached fabricating periodic structures. Non-Patent Document 3 and Non-Patent Document 4 suggest the possibility of fabricating three-dimensional periodic nanostructures based on the results of numerical analysis of multiple exposures, but the accuracy and the maintenance of the structures are unsatisfactory, and the technique has not yet reached fabricating commercially practical structures.
Fabrication of such three-dimensional structures using resist resins is receiving attention and has been researched as a useful technique as described above, but they are not yet commercially practical because the periodicity of the three-dimensional structures is difficult to control.
To solve the above conventional problems, the present invention provides three-dimensional microfabricated structures having controlled periodicity from the surface to the inside.
The present invention relates to a microstructure having pores on its surface or inside,
wherein the microstructure is a sheet containing 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
T=(2nd2)/λ [Formula 1]
where ZT 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 and the vertical direction.
A method for producing the microstructure of the present invention is a method for producing the microstructure according to any of claims 1 to 6, including:
(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.
Multiple exposure, including exposure with rotation and/or shifting in the triaxial direction of energy ray obtained by the Talbot effect, enables formation of pores on the surface or inside of structures, whereby the microstructure of the present invention has controlled periodicity from the surface to the inside.
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.
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.
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.
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.
The production method of the microstructure of the present invention includes the following steps:
(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 obtained by the Talbot effect 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 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
(5) washing the resin obtained in (4) with pure water to remove the dissolved portion to obtain a microstructure.
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.
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.
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/cm2. 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.
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.
An exemplary technique for the washing in (5) is spin coating.
The following describes an exemplary microstructure of the present invention.
(1) The processible area is up to 20 mm per side in each exposure. Exposures are repeated to process a wider area.
(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.
(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.
(4) The periodicity of the structure is 1 to 20 times, and preferably about 1 to 10 times.
The Talbot effect used in the present invention is as follows.
(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.
(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.
Hereinafter, the present invention will be described using drawings. In the following drawings, the same reference numeral denotes the same element.
(1)
(2)
(3)
(4)
(5)
Preferable processing conditions according to the present invention are as follows.
(1) Resin Material
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.
(2) Cleaning liquid: Any liquid that is noninvasive to the resin can be used. Pure water is preferably used.
(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.
(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.
(5) Processing Pattern
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.
(6) Processing Characteristics
(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.
(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.
(c) The irradiation light vertically enters the substrate surface.
(d) The Talbot distance is determined by Formula 1.
This results in the following.
(i) Adjacent processing areas are connected by reducing the Talbot distance.
(ii) Prior and subsequent processing areas are connected by controlling a periodic distance.
(iii) Adjacent processing areas are made independent of each other by increasing the Talbot distance.
(iv) Prior and subsequent processing areas are independent of each other by controlling the periodic distance.
Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.
The experiment was performed in the following manner.
(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 (
(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 (
(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 (
(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 (
(5) The resin 19 obtained in (4) was washed with pure water to remove the dissolved portion to obtain a microstructure (
Microstructures of Examples 2 to 7 were produced in the same manner as in Example 1 except for conditions described in Table 2.
Tables 2 and 3 summarize the conditions and results.
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.
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.
Number | Date | Country | Kind |
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2019-203528 | Nov 2019 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2020/039865 | 10/23/2020 | WO |