Manufacturing method for 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 making a master mold for imprinting. [Background technology]

[0002] The present applicant has proposed a technique disclosed in Patent Document 1 (hereinafter referred to as the "conventional technique") 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 having 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 (pressure welding) to transfer the conductive paste 22 in the recesses 21 of the replica mold 20 to the substrate 10, thereby forming wiring 11 and 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 (convex body) 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 structures of the master mold are formed from a resist, the resist is conventionally exposed to a sufficient amount of light so that the side shapes of the structures are nearly 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 manufacture replica molds smoothly and with good 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 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 ratio. Therefore, rather than simply having a tapered shape, the shape must be 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] JP 2021-111668 A 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 shape of the master mold structure, and currently, in order to make the side shape of the master mold structure into a forward taper shape with the desired taper angle, many complicated operations are required, which is labor-intensive and costly.

[0010] The present invention has been made in consideration of the above-mentioned current situation, and has an object to provide a method for producing a master mold for imprinting, which 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 desired pattern. [Means for solving the problem]

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

[0012] B Pump putter N A method for producing an imprint master mould having a formed structure 2, comprising the steps of: a mask forming step of forming a mask 4 on a surface of a light-transmitting substrate 1; The above Mask 4 On top of the specified thickness Negative type A coating step of coating a resist 3, and the substrate 1 The mask 4 is irradiated with light from the rear side of the mask 4. The resist 3 applied 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 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, 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, and The exposure step is performed so that the side shape of the structure 2 formed of the resist 3 by development in the development step is forward tapered. The amount of exposure light at a predetermined thickness of the resist 3 is determined based on the relationship between the amount of exposure light and the forward taper angle through the gray scale mask. The following D 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 a master mold for imprinting, comprising the steps of: Note Df: the 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 a master mold for imprinting 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 a master mold for imprinting, which is characterized by being 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 positive resist 3 of a predetermined thickness on a substrate 1, an exposure step of irradiating light from the front side of the substrate 1 to expose the resist 3 coated on the substrate 1 through a photomask, and a development step of developing the exposed resist 3, the photomask being 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 surrounding the light-shielding portion 4b. the exposure step is a step of exposing a predetermined portion of the resist 3 through the grayscale mask with an exposure amount equal to or less than the following Df, which is determined based on a previously determined relationship between the exposure amount at a predetermined thickness of the resist 3 and a taper angle of the forward taper, so that the side shape of the structure 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 Effect of the Invention

[0015] As described above, the present invention provides a method for producing a master mold for imprinting 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 target pattern size, pitch, aspect, etc. [Brief description of the drawings]

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

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

[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 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 is weaker near the edge of the light-transmitting portion 4a of the mask 4 compared to the center due to the diffraction of light, and therefore the photosensitivity in the film thickness direction of the resist 3 decreases near the edge of the light-transmitting portion 4a of the mask 4. 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, the exposure amount decreases toward the edge near the edge of the light-transmitting portion 4a of the mask 4 as shown in Fig. 2, and accordingly the photosensitivity in the film thickness direction of the resist 3 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 on 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. EXAMPLES

[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 base material 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 onto 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 embodiment, a photomask is not used in the exposure step, and a resist 3 is formed in a predetermined pattern through a mask 4 formed on a substrate 1, thereby forming a structure 2 made of the resist 3.

[0026] In this embodiment, 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 base material 1, so light is irradiated from the base material 1 side. For this reason, a light-transmitting base material 1 is used.

[0027] Specifically, in this embodiment, 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 embodiment 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 a mask 4 is formed on the substrate 1, and the mask film 5 is etched to a predetermined pattern. In this embodiment, Cr is sputtered onto the substrate 1 as the mask film 5 (see FIG. 3(b)), a resist (in this embodiment, a positive resist OFPR manufactured by Tokyo Ohka Kogyo Co., Ltd. is used) is applied onto the Cr film 5, and after exposure and development through a predetermined photomask, the Cr film 5 is 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 blocking 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 suitable material may be used as long as it can provide the same effects as those of this embodiment.

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

[0034] Specifically, a resist 3 (SU-8) is applied to a predetermined thickness on 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] Next, in an 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 within the range of 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 become sensitive Df: the 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 embodiment, D0 and Df are determined from the data sheet for SU-8 of 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. 4.

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

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

[0043] For example, from FIG. 5, the relationship data between the exposure dose and the taper angle, as shown in Table 1 below, can be obtained, and the exposure dose can be set based on this data (taper angle), or a calculation formula for determining the exposure dose can be created and the exposure dose can be set using this calculation formula.

[0044] [Table 1]

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

[0046] In this embodiment, a negative resist 3 is used, so that the resist 3 remains in the exposed portion, and this remaining resist 3 forms a structure 2 having a side shape formed into the desired tapered shape (taper angle), completing the master mold (see FIG. 3(g)).

[0047] As described above, the present 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 that in the exposure step, the resist 3 is exposed from the front side, and the remaining resist 3 becomes the structures 2, as shown in FIG.

[0050] FIG. 6 shows the shape of the structure 2 in a sample exposed to different exposure doses at a specified 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 FIG. 6, in the case of the positive resist 3, it can be confirmed that the taper angle of the structure 2 changes by changing the exposure dose, just like the negative resist 3. The taper angle can be obtained from SEM images of the bump pattern or 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 embodiment provides a method for producing a master mold for imprinting 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 amount of the resist 3 forming the structure 2 is set to D0 (the exposure amount at which the resist 3 applied on the substrate 1 begins to be exposed) to Df (the minimum exposure amount at which the entire thickness of the resist 3 applied on the substrate 1 is exposed), so that in the vicinity of the edge of the light-transmitting portion 4a of the mask 4, the exposure amount decreases toward the edge side, and accordingly the exposure effect in the film thickness direction of the resist 3 also decreases toward the edge side, 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 taper shape is prevented, and a master mold can be produced that allows pattern transfer to be performed smoothly and with good yield. EXAMPLES

[0055] A specific embodiment 2 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] The present embodiment will be described in detail below, but since the process flow of the present embodiment is the same as that of the first embodiment except for the mask formation process, the description of the processes other than the mask formation process will be omitted.

[0059] When a grayscale mask is used for the mask 4 as in this embodiment, there is no limit to the exposure amount, but it is preferable to use the exposure conditions in the exposure step of embodiment 1, that is, an exposure amount of less than twice Df.

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

[0061] Next, a film 5b for the grayscale portion is formed on the substrate 1 including the light-shielding portion 4b to form the grayscale portion 4c of the mask 4, and the film 5b for the grayscale portion is formed into a predetermined pattern by etching. In this embodiment, CrO3 is formed as the film 5b for the grayscale portion on the substrate 1 including the light-shielding portion 4b by sputtering (see FIG. 7(e)), a resist 6 (in this embodiment, a positive resist OFPR manufactured by Tokyo Ohka Kogyo Co., Ltd. is used) is applied onto the CrO3 film 5b, and after exposure and development through a predetermined photomask (see FIG. 7(f)), the CrO3 film 5b is etched through the resist 6 (see FIG. 7(g)), and the resist 6 is removed after the etching process to form the light-transmitting portion 4a and the grayscale portion 4c on the substrate 1 (see FIG. 7(h)), and a grayscale mask consisting of the light-transmitting portion 4a, the light-shielding portion 4b, and the grayscale portion 4c is formed on the substrate 1.

[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 a grayscale portion 4c that is provided along the periphery of the light-transmitting portion 4a at the boundary between the light-transmitting portion 4a and the light-shielding portion 4b, and the amount of exposure is reduced by passing through this grayscale portion 4c, and the photosensitivity in the film thickness direction of the resist 3 is also reduced accordingly, and due to the interaction with the diffraction effect of light, it is possible to easily form the structure 2 that has 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 an intensity distribution (upper part) derived based on the Fresnel diffraction of light that has passed through light-transmitting portion 4a, and an intensity distribution (lower part) derived based on the Fresnel diffraction of light that has passed through grayscale portion 4c in a grayscale mask as shown in this embodiment.

[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, so 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 with respect 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 becomes larger by the amount of the grayscale portion 4c, and accordingly the taper angle of the side surface of the structure 2 also becomes larger.

[0068] Table 2 below shows the results of measuring the side taper angle in a structure 2 with a bump diameter of 10 μm when a resist 3 with a thickness of 40 μm is exposed using a binary mask and when it is exposed using a grayscale mask. Note that 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 be used as the resist 3.

[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 blocking portion, and 4c denotes a gray scale portion) is preferable.

[0074] It should be noted that 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 shielding part 4c Grayscale section

Claims

1. A method for producing an imprint master mold having structures formed in a bump pattern, comprising: a mask formation step of forming a mask on a 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 to expose the resist coated on the mask through the mask; and a development step of developing the exposed resist, wherein the mask formation step includes forming a film for a light-shielding portion and a film for a grayscale portion on the surface of the substrate, to form a light-transmitting portion, a light-shielding portion, and a grayscale portion provided at a boundary between the light-transmitting portion and the light-shielding portion on the surface of the substrate. the grayscale portion is provided along an 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, the exposure amount being determined based on a previously determined relationship between the exposure amount at 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: the minimum exposure dose at which the entire thickness of the resist applied to the substrate is exposed

2. A method for producing a master mold for imprinting 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 positive resist of a predetermined thickness on a substrate; an exposure step of irradiating light from the front side of the substrate to expose the resist coated on the substrate through 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 the grayscale portion is provided along the entire circumference of the peripheral portion 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 through the grayscale mask with an exposure amount equal to or less than Df below, the exposure amount being determined based on a previously determined relationship between the exposure amount at a predetermined thickness of the resist and a taper angle of the forward taper, so that the side shape of the structure composed of the resist 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

Images