Method for making an imprint master mold

Abstract

To provide a manufacturing method for an imprint master mold, capable of forming a structure in a predetermined tapered shape on a base material.SOLUTION: A manufacturing method includes an applying step of applying resist 3 with a predetermined thickness on a base material 1, a light-exposing step of exposing the resist 3 applied on the base material 1 to light through a mask 4, and a developing step of developing the resist 3 exposed to light. In the light-exposing step, a predetermined part of the resist 3 is exposed to light in such a way that the amount of light exposure is set to be twice or less the minimum amount of light exposure (Df) with which the entire thickness of the resist 3 applied on the base material 1 is exposed, so that a side surface shape of a structure 2 formed of the resist 3 formed by the development in the developing step becomes forwardly-tapered.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing an imprint master mold. [Background technology]

[0002] The present applicant has proposed a technique disclosed in Patent Document 1 (hereinafter referred to as "prior art") regarding a wiring formation method using an imprint method.

[0003] As shown in Figure 13, this conventional technology involves filling a conductive paste 22 into the recesses 21 of a replica mold 20, which has recesses 21 formed in a pattern similar to the wiring pattern or bump pattern to be formed on a substrate 10, and then overlapping the replica mold 20 with the recesses 21 filled with the conductive paste 22 on the substrate 10 and applying pressure (press-welding) to transfer the conductive paste 22 in the recesses 21 of the replica mold 20 to the substrate 10, thereby forming wiring 11 or bumps of a predetermined pattern on the substrate 10.

[0004] Incidentally, the replica mold 20 used in this conventional technology is produced using a master mold 30 (original plate) having a structure (protrusion) that represents a wiring pattern or a bump pattern on a substrate, as shown in Figure 14. The structure of this master mold 30 is formed by etching the substrate 31 itself (see Figure 14(a)), or by patterning a resist 32 applied to the substrate 31 (see Figure 14(b)).

[0005] When the structure of this master mold is formed from a resist, the resist is conventionally exposed to a sufficient amount of light, so that the side shape of the structure is almost perpendicular to the substrate.

[0006] However, if the side shape of the structure is nearly perpendicular to the substrate, the structure of the master mold may temporarily deform into an inverted tapered shape during polymerization and pressure application to form the replica mold, which may prevent proper transfer.

[0007] Therefore, in order to produce replica molds smoothly and with a high yield, it is preferable that the side shape of the master mold structure relative to the base material be a forward tapered shape; however, the shape of the master mold structure is directly reflected in the shape of the recesses in the replica mold, and further, the shape of the recesses in the replica mold is directly reflected in the shapes of the wiring and bumps formed on the substrate; for example, if the taper angle is too large, it will hinder miniaturization and high aspect ratios. Therefore, rather than simply giving the shape a tapered shape, it is necessary to form a forward tapered shape with an appropriate taper angle that takes into account the size, pitch, aspect ratio, etc. of the desired pattern. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2021-111668 Summary of the Invention [Problem to be solved by the invention]

[0009] However, to date, no method has been established for easily controlling the taper angle of the side surface shape of the master mold structure, and currently, in order to make the side surface shape of the master mold structure a forward tapered shape with a desired taper angle, many complicated operations are required, which is labor-intensive and costly.

[0010] The present invention has been made in view of the above-described current situation, and has an object to provide a method for producing an imprint master mold that can easily form, on a substrate, a structure formed in a forward tapered shape with an optimal taper angle taking into consideration the size, pitch, aspect, etc. of the target pattern. [Means for solving the problem]

[0011] The gist of the present invention will be explained with reference to the accompanying drawings.

[0012] B Pump putter N 1. A method for making an imprint master mold having a formed structure 2, comprising: a mask forming step of forming a mask 4 on the surface of a light-transmitting substrate 1; The aforementioned Mask 4 On top of that, a specified film thickness Negative type a coating step of coating the substrate 1 with a resist 3; Light is irradiated from the rear side of the mask 4 through the mask 4. The resist 3 coated on Dew and a developing step of developing the exposed resist 3. The mask forming step is a step of forming a grayscale mask on the surface of the base material 1 by depositing a film 5a for a light-shielding portion and a film 5b for a grayscale portion, and forming a grayscale mask on the surface of the base material 1, the grayscale mask being configured to be composed of a light-transmitting portion 4a, a light-shielding portion 4b, and a grayscale portion 4c provided at the boundary between the light-transmitting portion 4a and the light-shielding portion 4b, and the grayscale portion 4c being provided along the entire periphery of the light-transmitting portion 4a so as to surround the light-transmitting portion 4a; The exposure step is performed so that the side surface shape of the structure 2 formed by the resist 3, which is formed by development in the development step, becomes forward tapered. The exposure amount is determined based on the relationship between the predetermined thickness of the resist 3 and the taper angle of the forward taper through the gray scale mask. D below f or more Bottom Exposure In front A predetermined portion of the resist 3 is exposed to light. It is a process The present invention relates to a method for producing an imprint master mold, characterized in that: Note Df: minimum exposure dose at which the entire thickness of the resist 3 applied on the substrate 1 is exposed

[0013] In the method for producing an imprint master mold according to claim 1, the light-shielding portion film 5a is a Cr film, and the grayscale portion film 5b is a CrO 3 The present invention relates to a method for producing an imprint master mold that is a film.

[0014] Also, a method for producing an imprint master mold having structures 2 formed in a bump pattern includes a coating step of coating a substrate 1 with a positive resist 3 of a predetermined thickness, an exposure step of irradiating light from the front side of the substrate 1 and exposing the resist 3 coated on the substrate 1 through a photomask, and a development step of developing the exposed resist 3, wherein the photomask is composed of a light-transmitting portion 4a, a light-shielding portion 4b, and a grayscale portion 4c provided at the boundary between the light-transmitting portion 4a and the light-shielding portion 4b, and the grayscale portion 4c surrounds the light-shielding portion 4b. the exposure step is a step of exposing predetermined portions of the resist 3 through the grayscale mask with an exposure amount equal to or less than Df, which is determined based on a previously determined relationship between the exposure amount for a predetermined thickness of the resist 3 and a taper angle of the forward taper, so that the side shape of structures 2 made of the resist 3 formed by development in the development step has a forward taper. Note Df: The minimum exposure dose at which the entire thickness of the resist applied to the substrate is exposed [Effects of the Invention]

[0015] As described above, the present invention provides a method for producing an imprint master mold that can easily form, on a substrate, a structure made of resist formed in a forward tapered shape with an optimal taper angle taking into consideration the size, pitch, aspect, etc. of the target pattern. [Brief explanation of the drawings]

[0016] [Figure 1] 1A to 1C are schematic explanatory views of examples of forming structures in the present invention. [Figure 2]FIG. 2 is a diagram illustrating the photosensitivity characteristics of the resist in Example 1. [Figure 3] FIG. 1 is a process flow diagram for the first embodiment. [Figure 4] 1 is a graph showing the photosensitivity characteristics of a resist (SU-8) in Example 1. [Figure 5] 10 shows SEM images of a structure exposed to light at different exposure doses at a predetermined film thickness when the negative resist of Example 1 is used. [Figure 6] 10 shows SEM images of a structure exposed to light at different exposure doses at a predetermined film thickness when the positive resist of Example 1 is used. [Figure 7] FIG. 10 is a process flow diagram for the second embodiment. [Figure 8] FIG. 10 is a schematic diagram showing a mask (grayscale mask) when a negative resist is used in Example 2. [Figure 9] FIG. 10 is an explanatory diagram (explaining the principle) showing the light intensity distribution during exposure when a grayscale mask is used in the second embodiment. [Figure 10] FIG. 10 is an explanatory diagram (actual distribution) showing the light intensity distribution during exposure when a grayscale mask is used in Example 2. [Figure 11] FIG. 10 is an explanatory diagram (actual distribution) showing the light intensity distribution during exposure when a binary mask is used in Example 2. [Figure 12] FIG. 10 is a schematic diagram showing a mask (grayscale mask) when a positive resist is used in Example 2. [Figure 13] 10A and 10B are cross-sectional views illustrating a conventional wiring formation method using a replica mold. [Figure 14] 1A to 1C are cross-sectional views showing a conventional method for producing a master mold and a conventional method for producing a replica mold using the master mold. DETAILED DESCRIPTION OF THE INVENTION

[0017] A preferred embodiment of the present invention will be briefly described below, illustrating the operation of the present invention with reference to the drawings.

[0018] A resist 3 is applied onto a substrate 1, the resist 3 applied onto the substrate 1 is exposed through a mask 4, and the exposed resist 3 is developed to form a structure 2 made of the resist 3.

[0019] In the present invention, in the above-mentioned operation, the exposure dose when exposing the resist 3 is set to be equal to or less than twice Df (the minimum exposure dose at which the entire thickness of the resist 3 applied on the substrate 1 is exposed). Therefore, as shown in FIG. 1(a), the resist 3 near the edge (end) of the light-transmitting portion 4a (opening) of the mask 4 is exposed under conditions in which the amount of light attenuates in the film thickness direction of the resist 3 (exposure dose smaller than Df). This makes it possible to easily form a structure 2 whose side shape is a forward tapered shape relative to the substrate 1 as shown in FIG. 1(b).

[0020] That is, for example, when the resist 3 is exposed through the mask 4, the amount of light near the edges of the light-transmitting portions 4a of the mask 4 is weaker than that at the center due to the phenomenon of light diffraction, resulting in a phenomenon in which the photosensitivity of the resist 3 in the film thickness direction near the edges of the light-transmitting portions 4a of the mask 4 decreases. Therefore, by setting the exposure amount to be equal to or less than twice the minimum exposure amount (Df) at which the entire thickness of the resist 3 applied on the substrate 1 is exposed, as shown in Fig. 2, the exposure amount decreases toward the edge near the edges of the light-transmitting portions 4a of the mask 4, and accordingly the photosensitivity of the resist 3 in the film thickness direction also decreases toward the edge, making it possible to obtain a structure 2 having a forward tapered shape.

[0021] Furthermore, for example, by using a grayscale mask having grayscale portions 4c at the edges of the light-transmitting portions 4a of the mask 4, in addition to the above-mentioned light diffraction phenomenon, the exposure amount can be spatially changed by the action of the grayscale portions 4c, making it possible to obtain a structure 2 with a forward tapered shape having a larger taper angle. [Example]

[0022] A specific embodiment 1 of the present invention will be described with reference to FIGS. 1 to 6. FIG.

[0023] This example is a method for producing an imprint master mold having structures 2 formed on a substrate 1 in a predetermined pattern such as a wiring pattern or a bump pattern.

[0024] Specifically, it includes a mask formation process for forming a mask 4 on a substrate 1, a coating process for coating a resist 3 on the mask 4, an exposure process for exposing the resist 3 coated on the mask 4 through the mask 4, and a development process for developing the exposed resist 3.

[0025] That is, in this example, a photomask is not used in the exposure process, but a resist 3 is formed in a predetermined pattern through a mask 4 formed on a substrate 1, and a structure 2 made of the resist 3 is formed.

[0026] In this example, a thick-film negative resist 3 is used as the resist 3. When this negative resist 3 is used, if light is irradiated from the front surface side of the resist 3 during exposure, the structures 2 will have an inverse tapered shape relative to the substrate 1, so the light is irradiated from the substrate 1 side. Therefore, a light-transmitting substrate 1 is used.

[0027] Specifically, in this example, SU-8 manufactured by Nippon Kayaku Co., Ltd. is used as the resist 3, and the substrate 1 is made of glass.

[0028] Hereinafter, each step in the method for producing an imprint master mold of this example using the above-mentioned substrate 1 and resist 3 will be described in detail.

[0029] First, in the mask formation step, a mask 4 having a predetermined pattern is formed on a glass substrate 1 .

[0030] Specifically, a mask film 5 for forming the mask 4 is formed on the substrate 1, and the mask film 5 is etched into a predetermined pattern. In this example, Cr is sputtered onto the substrate 1 to form the mask film 5 (see FIG. 3(b)). A resist (in this example, a positive resist OFPR manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied to the Cr film 5, and the resist is exposed and developed through a predetermined photomask. The Cr film 5 is then etched through the resist (see FIG. 3(c)). After the etching, the resist is removed to form a binary mask consisting of light-transmitting portions 4a (openings) and light-shielding portions 4b (see FIG. 3(d)).

[0031] The mask film 5 may have any thickness as long as it can exhibit light-shielding properties during exposure in the exposure step (in this embodiment, it is set to 60 nm to 120 nm (adjustable depending on the exposure conditions)).

[0032] Furthermore, the mask film 5 is not limited to Cr, and any other material that can achieve the same effects as those of this embodiment can be used.

[0033] Subsequently, in the coating step, a resist 3 for forming the structures 2, in other words, a resist 3 that will become the structures 2, is coated on the substrate 1.

[0034] Specifically, a resist 3 (SU-8) having a predetermined thickness is applied onto a mask 4 formed on a substrate 1 (see FIG. 3(e)).

[0035] The resist 3 for forming the structures 2 is not limited to the above.

[0036] Subsequently, in the exposure step, the resist 3 is exposed to light.

[0037] Specifically, light is irradiated from the rear side of the glass substrate 1, and the resist 3 is exposed through a mask 4 provided between the glass substrate 1 and the resist 3 (see FIG. 3(f)).

[0038] The exposure dose is set to not more than twice the following Df, preferably to any of the following D0 to Df, so that the side shape of the structures 2 formed by development relative to the base material 1 has a forward taper. Note D0: Exposure amount at which the resist 3 applied on the substrate 1 begins to be exposed to light Df: minimum exposure dose at which the entire thickness of the resist 3 applied on the substrate 1 is exposed

[0039] More specifically, the exposure amount is set to within the above range according to the target taper angle based on the relationship data between the exposure amount for a predetermined thickness of the resist 3 and the taper angle of the forward taper, which is previously determined.

[0040] D0 and Df can be determined, for example, from a data sheet disclosed by a manufacturer. In this example, D0 and Df are determined from the data sheet for SU-8 from Kayaku Advanced Materials, Inc. (https: / / kayakuam.com / wp-content / uploads / 2020 / 09 / KAM-SU-8-2-25-Datasheet-9.3.20-final.pdf) shown in FIG.

[0041] In this embodiment, based on the determined D0 and Df, relationship data between the exposure dose at a predetermined film thickness of the resist 3 and the taper angle of the forward taper is obtained through experiments, and based on this relationship data, the exposure dose is set according to the target taper angle.

[0042] Specifically, in this example, a TEG pattern having bump patterns with different diameters and wiring patterns with different line widths was used, and samples were prepared by exposing the samples to different exposure doses at a predetermined film thickness, as shown in FIG. 5. The taper angle was determined from SEM images of the bump pattern and wiring pattern (FIG. 5 shows the bump pattern) in these samples, and data on the relationship between the exposure dose at a predetermined film thickness and the taper angle of the forward taper was obtained.

[0043] For example, from Figure 5, it is possible to obtain data on the relationship between the exposure dose and taper angle, as shown in Table 1 below, and based on this data (taper angle), the exposure dose can be set, or a calculation formula for determining the exposure dose can be created and used to set the exposure dose.

[0044] [Table 1]

[0045] Finally, in the development step, the exposed resist 3 is developed.

[0046] In this example, a negative resist 3 is used, so the resist 3 remains in the exposed area, and this remaining resist 3 forms a structure 2 whose side surface has the desired tapered shape (taper angle), thereby completing the master mold (see Figure 3(g)).

[0047] As described above, this embodiment uses a negative resist 3, but a positive resist 3 may also be used.

[0048] When a positive resist 3 is used, the mask formation step is not necessary, and a photomask is used in the exposure step.

[0049] In contrast to the negative resist 3, the positive resist 3 has no exposed area, so in the exposure process, the resist 3 is exposed from the front side, and the remaining resist 3 becomes the structure 2, as shown in Figure 1.

[0050] Figure 6 shows the shape of the structure 2 in a sample exposed to different exposure doses at a predetermined film thickness using PMER P-LA900 manufactured by Tokyo Ohka Kogyo Co., Ltd. as the resist 3 and the same TEG pattern as in the case of the negative resist 3.

[0051] As shown in Figure 6, in the case of the positive resist 3, it can be confirmed that the taper angle of the structure 2 changes when the exposure dose is changed, just like in the case of the negative resist 3.The taper angle can be obtained from SEM images of the bump pattern and wiring pattern of this sample, and data on the relationship between the exposure dose at a specified film thickness and the taper angle of the forward taper can be obtained.

[0052] As described above, this example provides a method for producing an imprint master mold that can easily form, on a substrate 1, structures 2 formed in a forward tapered shape with an optimal taper angle taking into consideration the size, pitch, aspect, etc. of the desired pattern.

[0053] That is, in this embodiment, the exposure dose of the resist 3 forming the structure 2 is set to D0 (the exposure dose at which the resist 3 applied on the substrate 1 begins to be exposed) to Df (the minimum exposure dose at which the entire thickness of the resist 3 applied on the substrate 1 is exposed), so that the exposure dose decreases near the edge of the light-transmitting portion 4a of the mask 4 toward the edge, and accordingly the photosensitivity in the film thickness direction of the resist 3 also decreases toward the edge, thereby making it possible to reliably form a structure 2 whose side shape has a forward tapered shape.

[0054] Therefore, even if the structure of the master mold is deformed during polymerization and pressure application to form the replica mold, the occurrence of an inverse tapered shape is prevented, and a master mold can be produced that allows pattern transfer to be performed smoothly and with high yield. [Example]

[0055] A specific second embodiment of the present invention will be described with reference to FIGS.

[0056] In this embodiment, a mask 4 different from that in the first embodiment is used.

[0057] Specifically, in this embodiment, a grayscale mask is used as the mask 4, and this grayscale mask is made up of a light-transmitting portion 4a, a light-shielding portion 4b, and a grayscale portion 4c.

[0058] This embodiment will be described in detail below, but the process flow of this embodiment is the same as that of the first embodiment except for the mask formation process, so a description of the processes other than the mask formation process will be omitted.

[0059] When a grayscale mask is used as the mask 4 as in this embodiment, there is no limit to the exposure amount, but it is desirable to use the exposure conditions in the exposure step of embodiment 1, that is, an exposure amount of not more than twice Df.

[0060] In the mask forming process of this example, first, a light-shielding film 5a for forming the light-shielding portions 4b of the mask 4 is formed on the substrate 1, and then the light-shielding film 5a is etched into a predetermined pattern. In this example, as in Example 1, Cr is formed on the substrate 1 by sputtering as the light-shielding film 5a (see FIG. 7(b)). A resist 6 (in this example, a positive resist OFPR manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied to the Cr film 5a, and the resist 6 is exposed and developed through a predetermined photomask. The Cr film 5a is then etched through the resist 6 (see FIG. 7(c)). After the etching, the resist 6 is removed to form the light-shielding portions 4b made of the Cr film 5a on the substrate 1 (see FIG. 7(d)).

[0061] Next, a grayscale film 5b for forming the grayscale portion 4c of the mask 4 is formed on the substrate 1 including the light-shielding portion 4b, and the grayscale film 5b is etched into a predetermined pattern. In this example, CrO3 is sputtered onto the substrate 1 including the light-shielding portion 4b to form the grayscale film 5b (see FIG. 7(e)). A resist 6 (a positive resist OFPR manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied to the CrO3 film 5b, and the resist 6 is exposed and developed using a predetermined photomask (see FIG. 7(f)). The CrO3 film 5b is then etched through the resist 6 (see FIG. 7(g)). After the etching, the resist 6 is removed to form the light-transmitting portion 4a and the grayscale portion 4c on the substrate 1 (see FIG. 7(h)). This forms a grayscale mask on the substrate 1, consisting of the light-transmitting portion 4a, the light-shielding portion 4b, and the grayscale portion 4c.

[0062] In this embodiment, in order to improve the adhesion of the resist 3, an adhesive film 5c (SiO2 film) is formed on the mask 4 formed as described above (see FIG. 7(i)).

[0063] Fig. 8 shows an example of the configuration of the mask 4 (grayscale mask) for the bump pattern formed as described above. As shown in Fig. 8, the mask 4 of this embodiment has grayscale portion 4c, which is provided at the boundary between the light-transmitting portion 4a and the light-shielding portion 4b and along the periphery of the light-transmitting portion 4a. The amount of exposure light passes through this grayscale portion 4c, which reduces the photosensitivity of the resist 3 in the film thickness direction. Due to this interaction with the diffraction effect of light, it is possible to easily form structures 2 that have a forward tapered shape with a larger taper angle than when a binary mask is used (see Figs. 7(k) and (j)).

[0064] The exposure mechanism when a grayscale mask is used will be described below.

[0065] FIG. 9 shows the intensity distribution (upper row) derived based on the Fresnel diffraction of light that has passed through the light-transmitting portion 4a in the grayscale mask of this embodiment, and the intensity distribution (lower row) derived based on the Fresnel diffraction of light that has passed through the grayscale portion 4c.

[0066] In the configuration of the grayscale portion 4c as shown in FIG. 9, the grayscale portion 4c is located within the range where Fresnel diffraction occurs, and therefore it is possible to superimpose (combine) the intensity distribution derived based on the Fresnel diffraction of light that has passed through the light-transmitting portion 4a and the intensity distribution derived based on the Fresnel diffraction of light that has passed through the grayscale portion 4c. As a result, the grayscale mask of this embodiment results in a light intensity distribution as shown in FIG. 10.

[0067] The light intensity distribution when the grayscale mask shown in Fig. 10 is used corresponds to a light intensity distribution shifted toward the light-shielding portion 4b (to the left in the figure) by the area (width) of the grayscale portion 4c relative to the light intensity distribution when the binary mask shown in Fig. 11 is used. Therefore, by using the grayscale mask, the recession amount of the side surface of the structure 2 increases by the amount of the grayscale portion 4c, and accordingly the taper angle of the side surface of the structure 2 also increases.

[0068] Table 2 below shows the results of measuring the side taper angle of a structure 2 with a bump diameter of 10 μm when a 40 μm-thick resist 3 was exposed using a binary mask and when it was exposed using a grayscale mask. The grayscale mask used had a region (width) of the grayscale portion 4c of 1.5 μm.

[0069] [Table 2]

[0070] The results shown in Table 2 also confirm that the use of a grayscale mask makes it possible to increase the taper angle of the side surface of the structure 2.

[0071] As described above, this embodiment uses a negative resist 3, but a positive resist 3 (for example, PMER P-LA900 manufactured by Tokyo Ohka Kogyo Co., Ltd.) may also be used.

[0072] When a positive resist 3 is used, the mask formation step is not necessary, and a photomask is used in the exposure step.

[0073] Moreover, a photomask having a mask configuration as shown in FIG. 12 (in the figure, reference numeral 4a denotes a light-transmitting portion, 4b denotes a light-shielding portion, and 4c denotes a grayscale portion) is suitable.

[0074] The present invention is not limited to the present embodiment, and the specific configuration of each component can be designed as appropriate. [Explanation of symbols]

[0075] 1 Base material 2 structure 3. Resist 4. Mask 4a Translucent part 4b Light blocking part 4c Grayscale section

Claims

1. A method for producing an imprint master mold having a structure formed in a bump pattern, comprising: a mask forming step of forming a mask on the surface of a light-transmitting substrate; a coating step of coating a negative resist of a predetermined thickness on the mask; an exposure step of irradiating light from the back side of the substrate and exposing the resist coated on the mask through the mask; and a development step of developing the exposed resist, wherein the mask forming step comprises forming a film for a light-shielding portion and a film for a grayscale portion on the surface of the substrate, and forming a light-transmitting portion, a light-shielding portion, and a grayscale portion provided at the boundary between the light-transmitting portion and the light-shielding portion on the surface of the substrate. the grayscale portion is provided along the entire periphery of the light-transmitting portion so as to surround the light-transmitting portion; and the exposure step is a step of exposing a predetermined portion of the resist through the grayscale mask with an exposure amount equal to or less than Df below, which is determined based on a predetermined relationship between the exposure amount for a predetermined thickness of the resist and a taper angle of the forward taper, so that a side shape of a structure formed by development in the development step is forward tapered. Note Df: minimum exposure dose at which the entire thickness of the resist applied to the substrate is exposed

2. A method for producing an imprinting master mold as described in claim 1, characterized in that the film for the light-shielding portion is a Cr film, and the film for the grayscale portion is a CrO 3 film.

3. A method for producing an imprint master mold having a structure formed in a bump pattern, comprising: a coating step of coating a substrate with a positive resist of a predetermined thickness; an exposure step of irradiating the surface side of the substrate with light and exposing the resist coated on the substrate via a photomask; and a development step of developing the exposed resist, wherein the photomask is a grayscale mask composed of a light-transmitting portion, a light-shielding portion, and a grayscale portion provided at the boundary between the light-transmitting portion and the light-shielding portion, and wherein this grayscale portion is provided along the entire periphery of the light-shielding portion so as to surround the light-shielding portion, and the exposure step is a step of exposing a predetermined portion of the resist via the grayscale mask with an exposure amount not exceeding Df below, which is determined based on a predetermined relationship between the exposure amount at a predetermined thickness of the resist and the taper angle of the forward taper, so that the side shape of the structure formed by development in the development step is forward tapered. Note Df: minimum exposure dose at which the entire thickness of the resist applied to the substrate is exposed

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