JP7570110B2 - Method for manufacturing a microstructure - Google Patents

Description

The present invention relates to a method for manufacturing a microstructure by using the Talbot effect.

In recent years, attention has been focused on three-dimensional structures on the submicron order. These include microstructured components in semiconductor devices and microelectromechanical systems (MEMS), biomimetic structures that mimic the functional microstructures of living organisms, and nanostructured photonic crystals that are composed of materials with different refractive indices arranged at intervals similar to the wavelength of light. These three-dimensional structures on the submicron order, especially those with periodic structures, are attracting attention as functional materials. Methods for fabricating microstructures include lithography, etching, nanoimprinting, laser microfabrication, atomic manipulation and self-organization methods using atomic force microscopes (AFMs). In these methods, the time required for processing increases as the structure becomes more multidimensional, and there is a demand for improving processing efficiency. In addition, there is a demand for the fabrication of complex structures, and high processing freedom and processing accuracy that allow the periodicity to be arbitrarily controlled are also required. However, there is a trade-off between processing efficiency and processing freedom, and no technology has been established that can realize multidimensional processing molding using a simple method, so structures are being developed. In addition to improving the processing accuracy, there is also a demand for wide processing areas on the order of millimeters in the manufacture of structures.

One method for easily manufacturing microstructures is to use three-dimensional lithography technology with a resist resin as the material. In particular, three-dimensional lithography processing using the Talbot effect uses a specific wavelength and diffraction grating, making it easy to mold periodic patterns over a large area all at once, and has extremely high processing efficiency. However, lithography using the Talbot effect has the problem that the parameters that control the period are the wavelength and grating pitch, and period control is limited to two dimensions, resulting in low processing freedom. As a result, no technology had been established for processing any shape without limiting the processing area to the "surface" or "interior" of a three-dimensional structure.

Patent Document 1 discloses a lithography processing technique using the Talbot effect, but since this technique is intended for processing an etching screen mask, internal processing of the structure is not performed. Patent Document 2 discloses a mask and a pattern forming method capable of forming a highly accurate pattern using the Talbot effect, but is not a technique for fabricating a structure. Patent Document 3 discloses forming recesses or holes of a periodic structure by etching, but it is difficult to easily fabricate a fine structure. Non-Patent Document 1 proposes a structure in which metal nanoparticles are dispersed by applying a photo-shaping technique based on the Talbot effect, but it has not yet been able to fabricate a clear hierarchical structure based on the Talbot effect. Non-Patent Document 2 discloses the fabrication of a wide range of nanostructures in a one-dimensional layer structure and a two-dimensional periodic structure, but there are problems with the accuracy and structure maintenance of the structure, and a structure with periodicity has not been created. Non-Patent Document 3 and Non-Patent Document 4 suggest the possibility of fabricating a three-dimensional nano-periodic structure based on the results of a numerical analysis of multiple exposures, but there are problems with the accuracy and structure maintenance of the structure, and a structure at a practical level has not been created.

WO2016-190247 specification JP 2015-169803 A JP 2006-343671 A

Fabrication of 3D metallic nanostructures using the Talbot effect (1st report), analysis of the influence of lattice shape and verification of the fabrication process (Proceedings of the 2016 Japan Society for Precision Engineering Spring Meeting) Large-area 3D lithography using the Talbot effect (Part 1), fabrication of functional structures using wavefront control and standing waves (Proceedings of the 2017 Japan Society for Precision Engineering Spring Meeting) Large-area 3D lithography using the Talbot effect (Part 2), Fabrication of 3D nano-periodic structures using multiple exposure (Proceedings of the 2019 Japan Society for Precision Engineering Spring Meeting) Fabrication of three-dimensional nano-periodic structures using multiple exposure lithography based on the Talbot effect (Journal of the Japan Society for Precision Engineering Vol.85, No.8, 2019)

As explained above, three-dimensional structures using resist resins have been attracting attention as a useful technology and have been researched, but have not yet been put to full-scale practical use because it is difficult to control the periodicity of the three-dimensional structure.
In order to solve these conventional problems, the present invention provides a three-dimensional structure that can be subjected to micro-molding processing with the periodicity of the surface and interior of the structure being controlled.

The present invention relates to a method for producing a microstructure containing a hole therein, comprising the steps of:
(1) applying an energy ray active resin to a substrate in a uniform thickness;
(2) pre-baking (heating) the applied energy ray active resin layer;
(3) placing a diffraction grating on the resin layer obtained in (2) above, and irradiating the resin layer with an energy beam from an oblique direction to generate a pattern in the resin layer;
(4) a step of chemically reacting the resin layer obtained in (3) with a developer to dissolve the portion irradiated with energy rays exceeding the curing threshold and to cure the portion not reaching the energy ray curing threshold, or a step of curing the portion irradiated with energy rays exceeding the curing threshold and dissolving the portion not reaching the energy ray curing threshold;
(5) A step of washing the substrate obtained by (4) with pure water to dissolve the dissolved portion, thereby obtaining a microstructure ,
the microstructure is a sheet containing an energy ray-activatable resin,
A hole having a slope is formed at least to the inside,
The hole inside the microstructure has a shape of a shaping pattern in which the Talbot distance is defined by the following (Equation 1),
The relationship between adjacent Talbot structures satisfies the following (Equation 2) and (Equation 3),
However, in (Equation 1) to (Equation 3),
Z _T : Talbot distance (nm)
n: the refractive index of the ultraviolet (UV) light irradiated onto the diffraction grating of the exposure mask
d: Pitch distance of the diffraction grating of the exposure mask (nm)
λ: wavelength (nm) of ultraviolet (UV) light irradiated during the manufacture of the microstructure
ΔX: Horizontal distance (nm) between the first row irradiation spot portion and the adjacent third row irradiation spot portion as viewed from the irradiation surface
θi: UV irradiation angle
This is a method for manufacturing a microstructure having a shape that is periodic in the planar direction .

The microstructure of the present invention can be processed to have holes drilled on its surface or inside by adjusting the exposure light incidence angle and the Talbot distance, and the periodicity can be controlled both on the surface and inside of the structure to perform micromolding processing.

FIG. 1A is a schematic cross-sectional view illustrating a process of placing an exposure mask on the upper surface of a photoresist resin and irradiating it with ultraviolet (UV) light in order to explain the basic concept of the present invention, and FIG. 1B is a schematic cross-sectional view illustrating a portion of the photoresist resin irradiated with light. FIG. 2A is a schematic cross-sectional view showing exposure in a conventional example, and FIG. 2B is a schematic cross-sectional view showing exposure in one embodiment of the present invention. 3A-E are schematic cross-sectional views showing a manufacturing method of one embodiment of the present invention, and FIG. 3F is a schematic perspective view. FIG. 4A is a schematic perspective view showing the inside of the microstructure of Example 1 of the present invention, and FIG. 4B is a photograph of the same. FIG. 5A is a schematic perspective view showing the inside of a microstructure of a comparative example, and FIG. 5B is a photograph of the same.

In the present invention, inclined holes are formed in a sheet containing an energy beam-activated resin. The inclined holes are preferably inclined at an angle of 15 to 30 degrees from the vertical direction. More preferably, the angle is in the range of 16 to 27 degrees. This allows the formation of continuous holes. The holes inside the structure have a shape of a shaping pattern in which the Talbot distance is defined by the above (Equation 1), the relationship between adjacent Talbot structures (holes) satisfies the following (Equation 2) and (Equation 3), and the shape is periodic in the planar direction.

The energy beam-activated resin is preferably a resist resin, more preferably a positive resist resin. Positive resist resins have the property that when exposed to energy beams, the exposed areas dissolve in solution, making them suitable for microfabrication. Negative resist resins are exposed to high temperatures during post-baking, which causes distortion in the resin and makes it difficult to obtain microstructures with accurate periodicity.

The periodic shape preferably has a grating pitch of wavelength λ≦grating pitch d and a pitch duty ratio of 0.2 to 0.7. This allows for finer processing. The periodic shape preferably has a regular shape. This results in a highly uniform microstructure.

The holes inside the structure may be present from the surface to the inside, or may penetrate from the front to the back. The hole is a concept that includes grooves and/or holes.

The method for producing a microstructure of the present invention includes the following steps.
(1) A step of applying an energy ray active resin to a substrate in a uniform thickness.
(2) A step of pre-baking (heating) the applied energy ray active resin layer.
(3) A process of placing a diffraction grating on the upper surface of the resin layer obtained in (2) above, and irradiating the resin layer with an energy beam capable of producing the Talbot effect from an oblique direction to generate a pattern in the resin layer.
(4) A process of chemically reacting the resin layer obtained in (3) with a developer to dissolve the resin portion that has been irradiated with energy rays exceeding the curing threshold and to cure the resin portion that has not reached the energy ray curing threshold, or a process of curing the portion that has been irradiated with energy rays exceeding the curing threshold and dissolving the portion that has not reached the energy ray curing threshold.
(5) A process of washing the resin obtained in (4) above with pure water to dissolve the dissolved portion, thereby obtaining a microstructure.

The method for applying the energy ray-activatable resin to a uniform thickness as described above in (1) can be, for example, a spin coating method, which can apply a thin, uniform thickness to a relatively small area.
The pre-baking (heating) conditions in (2) above are preferably 0 to 100° C. and about 1 to 5 minutes, which are the manufacturer's recommended values.
The oblique irradiation of the energy beam in the pattern generating step (3) is preferably at an angle of 30 to 50° from the vertical direction, more preferably at an angle of 35 to 45°. This allows the formation of continuous holes. The exposure dose is preferably 100 to 300 mJ/ ^cm2 , and the number of exposures is preferably one.
It is preferable to perform post-baking (heating) between the steps (3) and (4) in order to stabilize the resist after exposure. The post-baking conditions are preferably 30 to 100° C. and about 1 to 60 minutes.
The cleaning treatment of (5) above can be performed, for example, by spin coating.

An example of the microstructure of the present invention is as follows.
(1) The processing area can be up to 20 mm on a side with one exposure. To process a larger area, it is possible to do so by repeating the exposure.
(2) The thickness of the structure can be from 500 nm to 100 μm, more preferably from 700 nm to 50 μm, and even more preferably from 1 to 20 μm.
(3) The length (depth) of a hole that can be microfabricated is preferably 10 nm to 3000 nm, and more preferably 100 to 1500 nm.
(4) The periodicity can be from 1 to 20 cycles, and is preferably from about 2 to 10 cycles.

The Talbot effect used in the present invention is as follows.
(1) When a plane wave is incident on a diffraction grating, the diffracted lights in the Fresnel region interfere with each other, resulting in a periodic light intensity distribution that is repeated three-dimensionally.
(2) By generating a periodic light intensity distribution using a diffraction grating and using it for lithography exposure, it is possible to process periodic fine structures in a large area in three dimensions in one go.

The following description will be given with reference to the drawings. In the following drawings, the same reference numerals indicate the same objects. FIG. 1A is a diagram for explaining the basic concept of the present invention, and is a schematic cross-sectional view in which an optical filter (exposure mask) 2 is placed on the upper surface of a photoresist resin 3 and ultraviolet (UV) light 1 is irradiated. The photoresist resin 3 is a resin for positive photoresist, and the optical filter (exposure mask) 2 is, for example, a diffraction grating made of polycarbonate. The distance between the photoresist resin 3 and the optical filter (exposure mask) 2 is the distance l. X and Y are the surface directions, and Z is the depth direction. Details are as shown in the drawings. FIG. 1B is a schematic cross-sectional view for explaining an exposed portion 4 in the photoresist resin 3 where light is irradiated. The exposed light intensity distribution is shown in a dot pattern, and the greater the number of dots, the higher the exposure intensity. The exposure intensity is normalized by the strongest light intensity, so it is expressed in arbitrary units (denoted as a.u.).

2A is a schematic cross-sectional view showing a conventional exposure example. When ultraviolet (UV) rays 1 are irradiated perpendicularly to the surface of the photoresist resin 3, exposed portions 5a and 5b are formed. _ZT is the Talbot distance (nm). That is, it is the vertical distance (nm) between the center point of the irradiation spot portion in the first row and the center point of the irradiation spot portion in the third row of the same irradiation line as seen from the irradiation surface.

2B is a schematic cross-sectional view of exposure according to one embodiment of the present invention. The irradiation angle Θ _i of the ultraviolet (UV) 1 is preferably 30 to 50°. When irradiated in this range, a continuous exposed portion 6 is formed inside the photoresist resin 3. When the exposed portion 6 is later dissolved, this portion becomes a continuous hole. Δx is the horizontal distance (nm) between the center point P1 of the irradiation spot portion in the first row and the center point P2 of the irradiation spot portion in the adjacent third row as viewed from the irradiation surface.

3A-E are schematic cross-sectional views showing a manufacturing method of one embodiment of the present invention, and FIG. 3F is a schematic perspective view.
(1) FIG. 3A shows a state in which a 10 μm-thick sheet of hardened photoresist resin is placed on a substrate 10 as a buffer layer 11, and a photoresist resin liquid 13 is applied thereon by spin coating to form a photoresist resin layer 12 a.
(2) FIG. 3B shows the state in which the coated photoresist resin layer 12a is pre-baked (heated) on a hot plate 14 to form a photoresist resin layer 12b.
(3) FIG. 3C shows a state in which an optical filter (exposure mask) 15 is placed on the photoresist resin layer 12b obtained in (2) above, and ultraviolet (UV) rays 16 are irradiated from an oblique direction to form an exposure pattern 17 in the photoresist resin layer 12c.
(4) Fig. 3D shows a state where the photoresist resin layer 12c obtained in (3) is post-baked (heated) to stabilize it. Next, Fig. 3E shows a state where the post-baked (heated) photoresist resin layer 12d is spin-coated and chemically reacted with a developer to dissolve the parts 17 that have been irradiated with ultraviolet (UV) rays exceeding the curing threshold, and harden the resin parts 19 that have not reached the energy ray curing threshold. The photoresist resin layer 12e has holes 18.
(5) FIG. 3F shows the state in which the resin 19 obtained in (4) above is washed with pure water to dissolve the dissolved portion, resulting in a microstructure.

The preferred processing conditions of the present invention are as follows.
(1) Resin material It is preferable to use a positive resist. For example, a positive UV-curable resin is preferable. If a negative resist is used, a process of arranging a buffer layer is required. In addition, if a negative resist is used, the resin is exposed to high temperatures during post-baking, which causes distortion in the resin and makes it difficult to manufacture a microstructure with accurate periodicity. The resin processing temperature (pre-baking) is preferably 0 to 100°C. This is the resin curing temperature range recommended by the resin manufacturer.
(2) Cleaning liquid: Any liquid that is non-invasive to the resin is acceptable. It is preferable to use pure water.
(3) Light wavelength: UV light from a laser is used. For example, λ=360 nm. The wavelength range that can be used is from 0.1 nm to 380 nm. The energy rays that can be used include ultraviolet rays (UV-A, B, C), X-rays, electron beams, etc.
(4) Diffraction grating: one or more optical filters are used. For example, a polycarbonate optical filter is used. Grating pitch: defined as wavelength λ≦grating pitch d. Pitch duty ratio: 0.2 to 0.7, preferably 0.4 to 0.6. As an example, a grating pitch of 747 nm and a grating height of 150 nm are used. This can be the surface of a DVD. As diffraction gratings other than DVD, those listed in Table 1 can be used.

(5) Processing pattern A regular groove structure can be formed. It has periodicity and can be changed arbitrarily from 1 to 20 periods. The surface can be shaped to have sharp angles or flat surfaces.
(6) Processing Features (a) One-shot exposure is performed, and precise processing is performed without relying on phase shift.
(b) The processing state can be changed by changing the exposure state and time. When the light threshold is exceeded, the resin hardens. The hardening is controlled by the exposure time.
(c) The irradiating light is set at an incident angle of 30 to 50° from the perpendicular direction to the substrate surface.
(d) The Talbot distance is calculated using the formula (1) above. This is the range in which the Talbot effect is exerted. The processing characteristics are defined by the formulas (2) and (3) above.
This results in the following:
(i) Adjacent processed regions are joined by increasing the Talbot distance between them.
(ii) By controlling the adjacent wavelength distance X, the front and rear processed regions are joined.

The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.
Example 1
The experiment was carried out as follows.
(1) Using a spin coater, a resin layer 12a of SIPR-3251-6.0 (manufactured by ShinEtsu MicroSi) made of UV-curable resin was formed with a uniform thickness on the buffer layer 11 on the substrate 10. The thickness was 6 μm ( FIG. 3A ).
(2) The resin layer 12a formed in (1) was placed on a hot plate 14 and pre-baked (heated) for 2 minutes at 100° C. to volatilize the solvent contained in the resin layer 12a, thereby forming a resin layer 12b (FIG. 3B).
(3) A polycarbonate diffraction grating 15 (pitch width: 747 nm) with a refractive index n=1.59 was placed on the resin layer 12b obtained in (2). A pattern was generated in the resin layer 12c by exposing it to light 16 from an ultraviolet LED surface light source (wavelength λ=360 nm) at an angle of 40° from the vertical direction (FIG. 3C). At this time, the above formulas 1 to 3 were satisfied.
(4) The resin layer 12c obtained in (3) was chemically reacted with a developer for SIPR-3251 (the developer was included when the resin was purchased) to dissolve the portion irradiated with light exceeding the photocuring threshold of SIPR-3251, forming a resin layer 12d (FIG. 3D). Next, the resin layer 12d was chemically reacted with the developer by spin coating to dissolve the portion 18 irradiated with ultraviolet (UV) light exceeding the curing threshold, and harden the resin portion 19 that did not reach the energy ray curing threshold. The photoresist resin layer 12e was in a state in which holes 18 were formed in the resin portion 19 (FIG. 3E).
(5) The resin 19 obtained in (4) above was washed with pure water to elute the dissolved portion, thereby obtaining a microstructure (FIG. 3F).

(Comparative Example 1)
The same procedure as in Example 1 was carried out, except that light 16 from an ultraviolet LED surface light source (wavelength λ=360 nm) was irradiated from a vertical direction.
The above conditions and results are shown in Table 2.

As shown in FIGS. 4A and 4B, in the microstructure (sheet) 20 obtained in Example 1, continuous pores 22 having an inclination were formed with periodicity all the way to the inside of the resin portion 21.
In contrast, in the microstructure (sheet) 23 obtained in Comparative Example 1, as shown in FIGS. 5A and 5B, holes 25 in a state of isolated bubbles were formed inside the resin portion 24.

The microstructure of the present invention has grooves, through holes, open cells, etc. formed inside the resin layer, and can be applied to photonic structures including filters, biomimetic structures, functional components, etc.

1,16 Ultraviolet light (UV)
2, 15 Optical filter (exposure mask)
Reference Signs List 3: Photoresist resin 4, 5a, 5b; Exposed portion 6: Continuous exposed portion 10: Substrate 11: Buffer layer 12a-12f; Photoresist resin layer 13: Photoresist resin liquid 14: Hot plate 17: Exposed pattern 18: Hole 19: Resin portion 20, 23: Microstructure 21, 24 Resin part (sheet)
22 Continuous pores having an inclination 25 Holes in a closed cell state

Claims (10)

A method for producing a microstructure containing a hole therein, comprising the steps of:
(1) applying an energy ray active resin to a substrate in a uniform thickness;
(2) pre-baking (heating) the applied energy ray active resin layer;
(3) placing a diffraction grating on the resin layer obtained in (2) above, and irradiating the resin layer with an energy beam from an oblique direction to generate a pattern in the resin layer;
(4) a step of chemically reacting the resin layer obtained in (3) with a developer to dissolve the portion irradiated with energy rays exceeding the curing threshold and to cure the portion not reaching the energy ray curing threshold, or a step of curing the portion irradiated with energy rays exceeding the curing threshold and dissolving the portion not reaching the energy ray curing threshold;
(5) A step of washing the substrate obtained by (4) with pure water to dissolve the dissolved portion, thereby obtaining a microstructure ,
the microstructure is a sheet containing an energy ray-activatable resin,
A hole having a slope is formed at least to the inside,
The hole inside the microstructure has a shape of a shaping pattern in which the Talbot distance is defined by the following (Equation 1),
The relationship between adjacent Talbot structures satisfies the following (Equation 2) and (Equation 3),
However, in (Equation 1) to (Equation 3),
Z _T : Talbot distance (nm)
n: the refractive index of the ultraviolet (UV) light irradiated onto the diffraction grating of the exposure mask
d: Pitch distance of the diffraction grating of the exposure mask (nm)
λ: wavelength (nm) of ultraviolet (UV) light irradiated during the manufacture of the microstructure
ΔX: Horizontal distance (nm) between the first row irradiation spot portion and the adjacent third row irradiation spot portion as viewed from the irradiation surface
θi: UV irradiation angle
A method for producing a microstructure having a shape that is periodic in the planar direction . The method for manufacturing a microstructure according to claim 1, wherein the energy beam is irradiated from an oblique direction at an inclination of 30 to 50 degrees from the vertical direction. 3. The method for producing a microstructure according to claim 1, wherein the energy ray active resin is a resist resin. 4. The method for producing a microstructure according to claim 1, wherein the energy ray active resin is a resin for a positive resist. 5. The method for producing a microstructure according to claim 1, wherein the periodic shape has a grating pitch: wavelength λ≦grating pitch d, and a pitch duty ratio: 0.2 to 0.7. 6. The method for producing a microstructure according to claim 1, wherein the holes inside the structure penetrate from the front to the back surface. The method for producing a microstructure according to any one of claims 1 to 6 , wherein the pores inside the structure include grooves and/or holes. 8. The method for producing a microstructure according to claim 1, wherein the pores inside the structure are in a closed bubble state. The method for producing a microstructure according to any one of claims 1 to 8 , wherein the periodic shape is a regular shape. 10. The method for producing a microstructure according to claim 1, wherein the inclined holes are inclined at an angle of 15 to 30 degrees from the vertical direction.

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