Method for forming a resist film

Abstract

To provide a resist film forming method employing a resist with viscosity which is high at normal temperature but decreases upon heating, where the method enables formation of a resist film reduced in air bubbles.SOLUTION: A resist film forming method comprises: a step A of applying onto a substrate a resist whose viscosity at 23°C is 1000 mPa s to 30000 mPa s, thereby forming a film of the resist; and a step B of applying heat treatment to the film of the resist. The step B comprises: a step B-1 of decreasing the viscosity of the resist by stepwise or continuous increase of the temperature of the film of the resist; and a step B-2 of heating under a vacuum environment the film of the resist whose viscosity is 5000 mPa s or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for forming a resist film. [Background technology]

[0002] Conventionally, a resist film has been formed using a resist that has a high viscosity at room temperature and whose viscosity decreases when heated. For example, Patent Document 1 discloses a method for forming a resist film, which includes applying a solution of a resist having a glass transition temperature of 40° C. to 50° C. and softening upon slight heating onto a substrate by a spin coating method to form a coating film, heating the coating film to remove the solvent and obtain a resist film, arranging spacers having the same thickness as the required resist film thickness around the periphery of the substrate, and then heating the resist film again, and pressing the resist film softened by heating with a glass substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-207969 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a high-viscosity resist, once air bubbles are mixed in the resist, the air bubbles are difficult to remove. In addition, when the temperature of a high-viscosity resist, whose viscosity decreases when heated, is suddenly increased from a high-viscosity state, air bubbles are likely to occur. For this reason, a relatively large number of air bubbles tend to be observed in a resist film formed using a resist that has a high viscosity at room temperature and whose viscosity decreases when heated. If air bubbles exist in a resist film, for example, when the resist is a photoresist, a problem of light scattering may occur when the resist film is exposed to light.

[0005] Regarding the above-mentioned point, in Patent Document 1, when forming a resist film, a resist that has a high viscosity at room temperature and whose viscosity decreases when heated is used, but the problem of air bubbles is not addressed at all.

[0006] An object of the present invention is to provide a method for forming a resist film using a resist that has high viscosity at room temperature and that decreases in viscosity upon heating, and that is capable of forming a resist film with reduced bubbles. [Means for solving the problem]

[0007] Specific means for solving the above problems include the following embodiments. [1] A step A of applying a resist having a viscosity of 1000 mPa·s to 30000 mPa·s at 23°C onto a substrate to form a film of the resist; A step B of subjecting the resist film to a heat treatment, The above-mentioned step B is a method for forming a resist film, comprising: step B-1 of reducing the viscosity of the resist by stepwise or continuously increasing the temperature of the resist film; and step B-2 of heating the resist film having a viscosity of 5000 mPa s or less in a vacuum environment. [2] The method for forming a resist film according to [1], wherein the step B includes a step B-3 of further heating the resist film that has been subjected to the step B-2 under atmospheric pressure. [3] A method for forming a resist film according to claim 1 or claim 2, further comprising a step C of step of gradually or continuously lowering the temperature of the resist film after step B. [4] The method for forming a resist film according to [3], wherein in step C, the temperature of the resist film having been subjected to step B is lowered at a temperature lowering rate of 5° C. / min or less. Effect of the Invention

[0008] According to one embodiment of the present disclosure, there is provided a method for forming a resist film using a resist that has high viscosity at room temperature and whose viscosity decreases upon heating, and which can form a resist film with reduced bubbles. [Brief description of the drawings]

[0009] [Figure 1A] 1 is a photograph showing a resist film formed by the method of Example 1. [Figure 1B] 3 is a photograph showing a resist film formed by the method of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The resist film forming method of the present disclosure will be described in detail below. The following description of the requirements may be based on a representative embodiment of the present disclosure, but the present disclosure is not limited to such an embodiment, and can be modified as appropriate within the scope of the purpose of the present disclosure.

[0011] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the lower limit and upper limit, respectively. In the present disclosure, in which numerical ranges are described in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper limit or lower limit of a certain numerical range may be replaced with a value shown in the examples.

[0012] In the present disclosure, combinations of two or more preferred embodiments are more preferred embodiments.

[0013] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0014] The elements in the drawings illustrated in this disclosure are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. In each drawing, components having the same function are given the same reference numerals, and duplicated explanations are omitted.

[0015] In this disclosure, "room temperature" means 23°C. In this disclosure, "high viscosity" means a viscosity of 1000 mPa·s or greater.

[0016] [Method of forming resist film] The method for forming a resist film of the present disclosure includes step A of applying a resist having a viscosity of 1000 mPa·s to 30000 mPa·s at 23°C onto a substrate to form a resist film, and step B of performing a heat treatment on the resist film. Step B includes step B-1 of decreasing the viscosity of the resist film by increasing the temperature of the resist film stepwise or continuously, and step B-2 of heating the resist film having a viscosity of 5000 mPa·s or less in a vacuum environment. According to the method for forming a resist film of the present disclosure, a resist film with reduced bubbles can be formed by using a resist that has a high viscosity at room temperature and whose viscosity decreases when heated. Although the reason why the method for forming a resist film according to the present disclosure can achieve such an effect is unclear, the present inventors speculate as follows: However, the following speculation is not intended to limit the interpretation of the method for forming a resist film according to the present disclosure, but is merely an example.

[0017] In the method for forming a resist film of the present disclosure, a resist that has a high viscosity at room temperature and whose viscosity decreases when heated is used. In a high-viscosity resist, once air bubbles are mixed into the resist, the air bubbles are difficult to remove. In addition, if the temperature of a high-viscosity resist that decreases in viscosity when heated is suddenly increased from a high-viscosity state, air bubbles are likely to occur. In the resist film forming method of the present disclosure, when the resist film is subjected to a heat treatment (e.g., a heat treatment for removing a solvent), the temperature of the resist film is increased stepwise or continuously, thereby suppressing the generation of bubbles in the film caused by a sudden increase in temperature of the resist, and since a resist film having a specific viscosity or less is heated in a vacuum environment, the air and bubbles in the film are efficiently removed. From the above, it is presumed that the method for forming a resist film according to the present disclosure makes it possible to form a resist film with reduced bubbles.

[0018] The method for forming a resist film according to the present disclosure will be described in detail below.

[0019] [Process A] Step A is a step of applying a resist having a viscosity of 1000 mPa·s to 30000 mPa·s at 23° C. onto a substrate to form a film of the resist. In the present disclosure, "a resist having a viscosity of 1000 mPa·s to 30000 mPa·s at 23° C." is also referred to as "specific resist."

[0020] The material of the substrate is not particularly limited and can be appropriately selected depending on the purpose. Examples of the substrate include glass substrates, resin substrates (e.g., polyethylene terephthalate (PET) substrates, polyethylene naphthalate (PEN) substrates, polycarbonate (PC) substrates, polyimide (PI) substrates, and triacetyl cellulose (TAC) substrates), metal substrates (e.g., aluminum substrates and stainless steel substrates), and semiconductor substrates (e.g., silicon substrates). The shape and thickness of the substrate are not particularly limited and can be appropriately selected depending on the purpose.

[0021] In step A, a resist having a viscosity of 1000 mPa·s to 30000 mPa·s at 23° C. (that is, a specific resist) is applied onto a substrate. The specific resist in the present disclosure is not particularly limited as long as it has a viscosity at 23° C. of 1000 mPa·s to 30000 mPa·s and has the property of decreasing in viscosity upon heating. Examples of the specific resist include SU-8 3050 (trade name, viscosity at 23° C.: 12000 mPa·s) and KMPR-1035 (trade name, viscosity at 23° C.: 8300 mPa·s) manufactured by Nippon Kayaku Co., Ltd. These commercially available products can be used as the specific resist as they are. These commercially available products have a viscosity of 1000 mPa·s to 30000 mPa·s at 23°C, and may be used as a specific resist by diluting them with a solvent and / or adding various additives thereto, as long as the property of decreasing viscosity upon heating is not impaired.

[0022] The viscosity of the specific resist at 23° C. is, for example, preferably from 5000 mPa·s to 30000 mPa·s, more preferably from 8000 mPa·s to 25000 mPa·s, and even more preferably from 10000 mPa·s to 20000 mPa·s.

[0023] In the present disclosure, the viscosity of the resist at 23° C. is a value measured using a viscometer (including a rheometer; the same applies below). For example, the viscosity of the resist at 23° C. is measured using a viscometer after adjusting the temperature of the resist to 23° C. As the viscometer, for example, a rheometer (product name: HAAKE RheoStress 6000) manufactured by Thermo Fisher Scientific Co., Ltd. can be used. However, the viscometer is not limited to this.

[0024] The application of the specific resist onto the substrate is not limited to direct application onto the surface of the substrate. The particular resist may be applied, for example, onto a film base which is disposed on a substrate. When the film substrate is disposed on the substrate, the film substrate is preferably fixed on the substrate. The means for fixing the film substrate on the substrate is not particularly limited, but is preferably a means for removing the film substrate from the substrate when the fixing of the film substrate is no longer required. From this viewpoint, the means for fixing the film substrate on the substrate may be, for example, a peelable fixing means such as an adhesive or a double-sided adhesive sheet. When the film base is fixed onto the substrate, it is preferable to attach the substrate and the film base together in such a way that no air bubbles are trapped between the substrate and the film base. Examples of materials for the film substrate include resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyimide (PI), and triacetyl cellulose (TAC). Among these, polyethylene terephthalate (PET) is preferable as the material for the film substrate.

[0025] The thickness of the film substrate is not particularly limited, but is, for example, preferably from 100 μm to 500 μm, more preferably from 150 μm to 400 μm, and even more preferably from 200 μm to 300 μm. When the thickness of the film substrate is within the above range, for example, when the resist film is finally peeled off from the film substrate, the resist film tends to be peeled off without being damaged.

[0026] In the present disclosure, the thickness of the film substrate means the average thickness of the film substrate. The average thickness of the film substrate is a value determined by the following method. The arithmetic average value of the film thickness measured at 10 randomly selected points in the thickness direction of the film substrate is calculated, and the obtained value is regarded as the average film thickness of the film substrate. A micrometer is used to measure the film thickness of the film substrate. An example of the micrometer is a micrometer (product name: crimp height micrometer) manufactured by Mitutoyo Corporation. However, the micrometer is not limited to this.

[0027] The method for applying the specific resist onto the substrate is not particularly limited. Methods for applying the specific resist onto the substrate include, for example, coating methods (eg, slit coating, spin coating, and curtain coating) and inkjet methods. Also, for example, the specific resist may be applied onto the substrate by dropping.

[0028] The amount of the specific resist applied is not particularly limited, and is set appropriately depending on, for example, the desired thickness of the resist film.

[0029] [Process B] Step B is a step of performing a heat treatment on the specific resist film formed in step A. Step B includes step B-1 of gradually or continuously increasing the temperature of the specific resist film formed in step A to reduce the viscosity of the specific resist, and step B-2 of heating the specific resist film having a viscosity of 5000 mPa s or less in a vacuum environment. Step B preferably includes step B-3 of further heating the specific resist film that has been subjected to step B-2 under atmospheric pressure.

[0030] The heat treatment in step B can remove the solvent as well as the air and bubbles in the film of the specific resist. The heat treatment method is not particularly limited. Examples of the heat treatment means include a hot plate and a convection oven (a so-called hot air circulation dryer). Examples of the heat treatment means in the step B-2 include a vacuum heating dryer.

[0031] (Process B-1) Step B-1 is a step of increasing the temperature of the specific resist film formed in step A stepwise or continuously to reduce the viscosity of the specific resist. The specific resist has a property that the viscosity decreases when heated. If the temperature of the specific resist is suddenly increased from a high viscosity state, air bubbles are likely to occur in the film. In step B-1, the temperature of the specific resist film is increased stepwise or continuously, so that the generation of air bubbles in the film caused by a sudden increase in the temperature of the resist is suppressed. In addition, in step B-1, the viscosity of the specific resist is reduced, so that air bubbles in the film are more likely to escape when the specific resist film is heated in a vacuum environment in step B-2 described later.

[0032] When the viscosity of the specific resist at 23° C. is 5000 mPa·s or less, in step B-1, the temperature of the film of the specific resist is increased to a temperature at which the viscosity of the specific resist decreases. If the viscosity of the specific resist at 23° C. exceeds 5000 mPa·s, in step B-1, the temperature of the specific resist film is increased to a temperature at which the viscosity of the specific resist falls to 5000 mPa·s or less.

[0033] In the present disclosure, the viscosity of the resist forming a film is determined according to the following procedures (1) to (3). (1) In advance, create a calibration curve (also called a "temperature-viscosity curve") that shows the relationship between the temperature and viscosity of the resist to be applied to the substrate in process A. Specifically, while changing the temperature of the resist stepwise in 10°C increments from 23°C to 153°C, measure the viscosity of the resist at each temperature step using a viscometer, and create a temperature-viscosity curve based on the values ​​obtained. (2) The temperature of the resist film is measured using a radiation thermometer. (3) The viscosity of the resist film is calculated by applying the measured temperature of the resist film to the above-mentioned temperature-viscosity curve prepared in advance.

[0034] As the viscometer in (1) above, for example, a rheometer (product name: HAAKE RheoStress 6000) manufactured by Thermo Fisher Scientific Co., Ltd. can be used. However, the viscometer is not limited to this.

[0035] The temperature of the specific resist film may be increased stepwise or continuously, but it is more preferable to increase the temperature stepwise. When the temperature of the specific resist film is increased stepwise, the number of steps is not particularly limited as long as it is 2 or more. For example, from the viewpoint of reducing the complexity of the operation, the number of steps is preferably 5 or less, and more preferably 2. When the temperature of the specific resist film is increased stepwise, for example, a preferred embodiment is to increase the temperature of the specific resist film to 50°C to 70°C and then to 90°C to 130°C, a more preferred embodiment is to increase the temperature of the specific resist film to 55°C to 70°C and then to 90°C to 120°C, and a further more preferred embodiment is to increase the temperature of the specific resist film to 60°C to 70°C and then to 90°C to 110°C. The heating time in each stage is not particularly limited, but it is preferable that the heating time in the final stage is the longest.

[0036] When the temperature of the specific resist film is continuously increased, the temperature increase rate is not particularly limited, but is preferably, for example, 70° C. / min or less, more preferably 50° C. / min or less, and even more preferably 30° C. / min or less. The lower limit of the temperature rise rate is preferably, for example, 5° C. / min or more.

[0037] In the present disclosure, the temperature of the resist film refers to the temperature of the resist film surface measured using a radiation thermometer. As the radiation thermometer, for example, a radiation thermometer (model number: IT-314) manufactured by AS ONE Corporation can be used. However, the radiation thermometer is not limited to this.

[0038] In step B-1, the time for which the specific resist film is subjected to the heat treatment (i.e., the time for which the specific resist film is heated) is not particularly limited and is set appropriately depending on, for example, the type of specific resist and the heating temperature. The time for heating the specific resist film is, for example, preferably 0.5 to 3 hours, more preferably 0.5 to 2.5 hours, even more preferably 0.5 to 2.0 hours, and particularly preferably 0.5 to 1.5 hours. In step B-1, when the temperature of the specific resist film is increased stepwise, the heating time of the specific resist film means the total heating time of the specific resist film in each step.

[0039] (Process B-2) Step B-2 is a step of heating the specific resist film having a viscosity of 5000 mPa·s or less in a vacuum environment. In this disclosure, "vacuum" refers to a state in which the degree of vacuum is 0.1 MPa or less. In a high-viscosity resist film, once air bubbles are mixed in the film, they tend to be difficult to remove. In step B-2, the specific resist film with a viscosity of 5000 mPa·s or less is heated in a vacuum environment, so air bubbles in the film are efficiently removed. If the viscosity of the specific resist when heated in a vacuum environment is 5000 mPa·s or less, the air bubbles in the film are more likely to move, making them easier to remove from the film. In addition, when the specific resist film is heated in a vacuum environment, the volume of the air bubbles increases and expands, increasing the buoyancy of the air bubbles, making it easier for the air bubbles to remove from the film than when the specific resist film is heated under atmospheric pressure.

[0040] In step B-2, for example, from the viewpoint of more effectively removing bubbles in the specific resist film, it is desirable to heat the specific resist film in a vacuum environment, the specific resist film having a viscosity of preferably 4000 mPa·s or less, more preferably 3000 mPa·s or less, even more preferably 2000 mPa·s or less, and particularly preferably 1000 mPa·s or less.

[0041] The heating temperature when the specific resist film is heated in a vacuum environment is not particularly limited as long as the viscosity of the specific resist can be maintained at 5000 mPa·s or less. The heating temperature when the specific resist film is heated in a vacuum environment is, for example, preferably 70°C to 130°C, more preferably 90°C to 130°C, even more preferably 90°C to 120°C, and particularly preferably 90°C to 110°C.

[0042] In step B-2, the time for which the specific resist film is subjected to heat treatment (i.e., the time for which the specific resist film is heated in a vacuum environment) is not particularly limited, but is, for example, preferably 1 minute or more, more preferably 2 minutes or more, even more preferably 3 minutes or more, and particularly preferably 4 minutes or more. The upper limit is preferably, for example, 10 minutes or less.

[0043] (Process B-3) Step B preferably includes step B-3 of further heating the specific resist film that has been subjected to step B-2 under atmospheric pressure. In this disclosure, "under atmospheric pressure" means a range of more than 0.1 MPa to 0.12 MPa. When a film of a specific resist is heated in a vacuum environment, the marks caused by the bubbles bursting when the bubbles escape may remain on the surface of the film. When the film of a specific resist heated in a vacuum environment is further heated under atmospheric pressure, the surface of the film is leveled, so that the surface of the formed resist film can be made flat. In addition, the specific resist film heated in a vacuum environment can be further heated under atmospheric pressure to remove residual solvent in the specific resist film.

[0044] The heating temperature when the specific resist film is further heated under atmospheric pressure is not particularly limited, but is, for example, preferably 70°C to 130°C, more preferably 90°C to 130°C, further preferably 90°C to 120°C, and particularly preferably 90°C to 110°C. The heating temperature when the specific resist film is further heated under atmospheric pressure is, for example, preferably equal to or higher than the heating temperature when the specific resist film is heated in a vacuum environment, and more preferably equal to the heating temperature when the specific resist film is heated in a vacuum environment.

[0045] In step B-3, the time for which the specific resist film is subjected to heat treatment (i.e., the time for which the specific resist film is further heated under atmospheric pressure) is not particularly limited, but is, for example, preferably 3 hours or more, more preferably 3 to 8 hours, even more preferably 4 to 7 hours, and particularly preferably 4 to 6 hours.

[0046] [Process C] The method for forming a resist film according to the present disclosure preferably includes a step C of lowering the temperature of the specific resist film after the step B, either stepwise or continuously. If the temperature of the specific resist film after heating is suddenly lowered, stress is generated inside the specific resist film, which may affect the in-plane film thickness variation of the resist film. If the temperature of the specific resist film after heating is gradually or continuously lowered (so-called gradual cooling), the generation of stress inside the specific resist film due to the sudden drop in temperature of the specific resist film is suppressed.

[0047] In step C, the temperature of the specific resist film that has been subjected to step B may be lowered stepwise or continuously, but it is more preferable to lower it continuously. In step C, when the temperature of the specific resist film that has been subjected to step B is lowered stepwise, the temperature lowering rate is not particularly limited. In step C, for example, it is preferable to lower the temperature of the specific resist film at a temperature lowering rate of 5° C. / min or less. When the temperature of the specific resist film is lowered at a temperature lowering rate of 5° C. / min or less, the generation of stress inside the specific resist film due to a rapid drop in the temperature of the specific resist film is further suppressed. The temperature drop rate is preferably 4° C. / min or less, and more preferably 3° C. / min or less. The lower limit of the temperature drop rate is not particularly limited, but is preferably, for example, 0.1° C. / min or more.

[0048] The temperature of the specific resist film after cooling is not particularly limited, but is preferably from 5°C to 30°C, more preferably from 10°C to 25°C, and even more preferably from 15°C to 23°C, for example.

[0049] [Other steps] The method for forming a resist film of the present disclosure may include, as necessary, steps other than the above-described steps, i.e., step A and step B, which are essential steps, and step C, which is an optional step (so-called other steps), within the scope of the present disclosure. For example, when the specific resist is photocurable, the other step may be a step of irradiating the film of the specific resist after the cooling step with light (a so-called exposure step). Specific examples of the light source include various lasers, light emitting diodes (LEDs), ultra-high pressure mercury lamps, high pressure mercury lamps, and metal halide lamps. The amount of exposure (so-called integrated amount of light) is not particularly limited, and can be set appropriately depending on, for example, the type of a specific resist. Furthermore, other steps include, for example, a development step, a post-baking step, and the like.

[0050] -Thickness of resist film- The thickness of the resist film formed by the method for forming a resist film of the present disclosure is not particularly limited, but can be, for example, 50 μm to 1000 μm. In the present disclosure, the thickness of the resist film means the average thickness of the resist film. The average film thickness of the resist film is a value determined by the following method. The arithmetic average value of the thickness of the resist film measured at 10 randomly selected points in the thickness direction of the resist film is calculated, and the obtained value is regarded as the average thickness of the resist film. A laser displacement meter is used to measure the thickness of the resist film. An example of the laser displacement meter is a spectral interference laser displacement meter (model: SI-F10) manufactured by Keyence Corporation. However, the laser displacement meter is not limited to this. EXAMPLES

[0051] The method for forming a resist film according to the present disclosure will be described in more detail below with reference to examples. However, the method for forming a resist film according to the present disclosure is not limited to the following examples as long as it does not deviate from the gist of the method.

[0052] In the following examples, the thickness of the resist film was measured by the method described above using a spectroscopic interference laser displacement meter (model: SI-F10) manufactured by Keyence Corporation.

[0053] The viscosity of the resist was measured using a rheometer manufactured by Thermo Fisher Scientific (product name: HAAKE RheoStress 6000).

[0054] The temperature of the resist film was measured using a radiation thermometer (model number: IT-314) manufactured by AS ONE Corporation. The viscosity of the resist forming the film was obtained by the method described above. That is, a calibration curve (i.e., a temperature-viscosity curve) showing the relationship between the temperature and viscosity of the resist used in the following examples was prepared in advance, and the temperature of the resist film measured using the radiation thermometer was applied to the prepared temperature-viscosity curve to obtain the viscosity of the resist forming the film.

[0055] [Formation of resist film] Example 1 <Process A> A PET sheet (size: 110 mm x 80 mm, film thickness: 250 μm) was attached as a base material to one side of a substrate (trade name: SMS6025E2, size: 6025 (size: 152 mm x 152 mm, thickness: 6.35 mm), material: synthetic quartz glass, manufactured by Shin-Etsu Chemical Co., Ltd.) using a double-sided adhesive sheet. Next, SU-8 3050 (trade name, viscosity at 23 ° C: 12000 mPa s, manufactured by Nippon Kayaku Co., Ltd.) as a specific resist was slit-coated on the surface of the PET sheet to form a film of the specific resist. The amount of the specific resist applied was such that the film thickness of the resist film finally formed was 300 μm ± 15 μm.

[0056] <Process B> Next, a heat treatment was performed on the specific resist film formed in the step A. Specifically, the following operations were performed.

[0057] <<Process B-1>> A glass substrate having a PET sheet on which a specific resist film was formed (hereinafter also referred to as "PET sheet-attached substrate") was placed on a hot plate with a heating temperature set to 70°C and heated for 30 seconds (so-called first stage heating), and then moved onto a hot plate with a heating temperature set to 100°C and heated for a further hour (so-called second stage heating), thereby gradually increasing the temperature of the specific resist film. The temperature of the specific resist film after the first heating stage was 65°C, the temperature of the specific resist film after the second heating stage was 95°C, and the viscosity of the specific resist after the second heating stage was 4000 mPa s.

[0058] <<Process B-2>> Next, the substrate with the PET sheet having the specific resist film with a viscosity of 4000 mPa s was placed in a vacuum dryer (product name: ETTAS vacuum dryer, model number: AVO-200NS-D, manufactured by AS ONE Co., Ltd.) with the temperature inside the dryer set to 100°C, and vacuum-heated for 5 minutes. The degree of vacuum inside the dryer was 0.1 MPa.

[0059] <<Process B-3>> Next, the substrate with the PET sheet was removed from the vacuum dryer, placed on a hot plate with the heating temperature set to 100° C., and heated for an additional 5 hours under atmospheric pressure. The temperature of the specific resist film after heating was 95°C.

[0060] <Process C> Next, the substrate X with the PET sheet was removed from the hot plate, and the specific resist film was cooled to 23° C. over 6 hours at a temperature drop rate of 0.2° C. / min. In this manner, a resist film was formed. The resist film thus formed had a thickness of 300 μm.

[0061] Example 2 <Process A> A PET sheet (size: 110 mm x 80 mm, film thickness: 250 μm) was attached as a base material to one side of a substrate (trade name: SMS6025E2, size: 6025 (size: 152 mm x 152 mm, thickness: 6.35 mm), material: synthetic quartz glass, manufactured by Shin-Etsu Chemical Co., Ltd.) using a double-sided adhesive sheet. Next, KMPR-1035 (trade name, viscosity at 23 ° C: 8300 mPa s, manufactured by Nippon Kayaku Co., Ltd.) as a specific resist was slit-coated on the surface of the PET sheet to form a film of the specific resist. The amount of the specific resist applied was such that the film thickness of the resist film finally formed was 300 μm ± 15 μm.

[0062] <Process B> Next, a heat treatment was performed on the specific resist film formed in the step A. Specifically, the following operations were performed.

[0063] <<Process B-1>> A glass substrate having a PET sheet on which a specific resist film was formed (hereinafter also referred to as "PET sheet-attached substrate") was placed on a hot plate with a heating temperature set to 70°C and heated for 30 seconds (so-called first stage heating), and then moved onto a hot plate with a heating temperature set to 100°C and heated for a further hour (so-called second stage heating), thereby gradually increasing the temperature of the specific resist film. The temperature of the specific resist film after the first heating stage was 65°C, the temperature of the specific resist film after the second heating stage was 95°C, and the viscosity of the specific resist after the second heating stage was 4000 mPa s.

[0064] <<Process B-2>> Next, the substrate with the PET sheet having the specific resist film with a viscosity of 4000 mPa s was placed in a vacuum dryer (product name: ETTAS vacuum dryer, model number: AVO-200NS-D, manufactured by AS ONE Co., Ltd.) with the temperature inside the dryer set to 100°C, and vacuum-heated for 5 minutes. The degree of vacuum inside the dryer was 0.1 MPa.

[0065] <<Process B-3>> Next, the substrate with the PET sheet was removed from the vacuum dryer, placed on a hot plate with the heating temperature set to 100° C., and heated for an additional 5 hours under atmospheric pressure. The temperature of the specific resist film after heating was 95°C.

[0066] <Process C> Next, the substrate X with the PET sheet was removed from the hot plate, and the specific resist film was cooled to 23° C. over 6 hours at a temperature drop rate of 0.2° C. / min. In this manner, a resist film was formed. The resist film thus formed had a thickness of 300 μm.

[0067] Example 3 A resist film was formed in the same manner as in Example 1, except that step B-1 in Example 1 was changed as follows. The resist film thus formed had a thickness of 300 μm. "<<Process B-1>> The glass substrate provided with the PET sheet on which the specific resist film was formed (hereinafter also referred to as the "PET sheet-attached substrate") was placed in a hot air circulation dryer and heated at a temperature increase rate of 25°C / min until the temperature of the specific resist film reached 95°C. The viscosity of the specific resist when the film temperature was 95° C. was 4000 mPa·s.

[0068] Comparative Example 1 A resist film was formed in the same manner as in Example 1, except that steps B-2 and B-3 were not performed. Specifically, the following operations were performed. A PET sheet (size: 110 mm x 80 mm, film thickness: 250 μm) was attached as a base material to one side of a substrate (trade name: SMS6025E2, size: 6025 (size: 152 mm x 152 mm, thickness: 6.35 mm), material: synthetic quartz glass, manufactured by Shin-Etsu Chemical Co., Ltd.) using a double-sided adhesive sheet. Next, SU-8 3050 (trade name, viscosity at 23 ° C: 12000 mPa s, manufactured by Nippon Kayaku Co., Ltd.) as a specific resist was slit-coated on the surface of the PET sheet to form a film of the specific resist. The amount of the specific resist applied was such that the film thickness of the resist film finally formed was 300 μm ± 15 μm. Next, the glass substrate having a PET sheet on which a specific resist film was formed (hereinafter also referred to as "PET sheet-attached substrate") was placed on a hot plate with a heating temperature set to 70°C and heated for 30 seconds (so-called first stage heating), and then moved onto a hot plate with a heating temperature set to 100°C and heated for a further hour (so-called second stage heating), thereby gradually increasing the temperature of the specific resist film. The temperature of the specific resist film after the first heating stage was 65°C, the temperature of the specific resist film after the second heating stage was 95°C, and the viscosity of the specific resist after the second heating stage was 4000 mPa s. Next, the substrate with the PET sheet was removed from the hot plate, and the temperature of the specific resist film was cooled to 23° C. over 6 hours at a temperature drop rate of 0.2° C. / min. In this manner, a resist film was formed. The resist film thus formed had a thickness of 300 μm.

[0069] Comparative Example 2 A PET sheet (size: 110 mm x 80 mm, film thickness: 250 μm) was attached as a base material to one side of a substrate (trade name: SMS6025E2, size: 6025 (size: 152 mm x 152 mm, thickness: 6.35 mm), material: synthetic quartz glass, manufactured by Shin-Etsu Chemical Co., Ltd.) using a double-sided adhesive sheet. Next, SU-8 3050 (trade name, viscosity at 23 ° C: 12000 mPa s, manufactured by Nippon Kayaku Co., Ltd.) as a specific resist was slit-coated on the surface of the PET sheet to form a film of the specific resist. The amount of the specific resist applied was such that the film thickness of the resist film finally formed was 300 μm ± 15 μm.

[0070] Next, the glass substrate provided with the PET sheet on which the specific resist film was formed (so-called PET sheet-attached substrate) was placed on a hot plate with the heating temperature set to 30°C and heated for 30 seconds (so-called first stage heating), and then moved onto a hot plate with the heating temperature set to 45°C and heated for a further hour (so-called second stage heating), thereby gradually increasing the temperature of the specific resist film. The temperature of the specific resist film after the first heating stage was 25°C, the temperature of the specific resist film after the second heating stage was 40°C, and the viscosity of the specific resist after the second heating stage was 6000 mPa s. Next, the substrate with the PET sheet having the specific resist film with a viscosity of 6000 mPa s was placed in a vacuum dryer (product name: ETTAS vacuum dryer, model number: AVO-200NS-D, manufactured by AS ONE Co., Ltd.) with the temperature inside the dryer set to 45°C, and vacuum-heated for 5 minutes. The degree of vacuum inside the dryer was 0.1 MPa. Next, the substrate with the PET sheet was removed from the vacuum dryer, placed on a hot plate with the heating temperature set at 45° C., and heated for an additional 5 hours under atmospheric pressure. The temperature of the specific resist film after heating was 40°C. Next, the substrate with the PET sheet was removed from the hot plate, and the temperature of the specific resist film was cooled to 23° C. over 110 minutes. The temperature drop rate was 0.2° C. / min. In this manner, a resist film was formed. The resist film thus formed had a thickness of 300 μm.

[0071] Comparative Example 3 A resist film was formed in the same manner as in Example 1, except that step B-1 in Example 1 was changed as follows. The resist film thus formed had a thickness of 300 μm. "<<Process B-1>> A glass substrate provided with a PET sheet on which a specific resist film was formed (hereinafter also referred to as "PET sheet-attached substrate") was placed on a hot plate with the heating temperature set to 100°C, and heated for 1 hour. The temperature of the specific resist film after heating was 95°C, and the viscosity of the specific resist after heating was 4000 mPa·s.

[0072] When the resist films formed by the methods of Examples 1, 2, and 3 were visually observed, no air bubbles were found in any of the films. A photograph of the resist film formed by the method of Example 1 is shown in FIG. 1A.

[0073] On the other hand, when the resist films formed by the methods of Comparative Examples 1, 2, and 3 were visually observed, noticeable air bubbles were confirmed. The reason why air bubbles were significantly observed in the resist film formed by the method of Comparative Example 2 is thought to be that the high viscosity of the resist makes it difficult for air bubbles in the film to move, and therefore the air bubbles are difficult to remove from the film even when heated in a vacuum environment. The reason why air bubbles were prominently observed in the resist film formed by the method of Comparative Example 3 is thought to be that the temperature of the resist was raised so suddenly that a large number of air bubbles were generated in the film, and even when the film was heated in a vacuum environment, all the air bubbles could not be removed. A photograph of the resist film formed by the method of Comparative Example 1 is shown in FIG. 1B.

Claims

1. A step A of applying a resist having a viscosity of 1000 mPa·s to 30000 mPa·s at 23° C. onto a substrate to form a film of the resist; A step B of subjecting the resist film to a heat treatment, The process B is a method for forming a resist film, comprising: a process B-1 of reducing the viscosity of the resist by increasing the temperature of the resist film stepwise or continuously; and a process B-2 of heating the resist film having a viscosity of 5000 mPa·s or less in a vacuum environment.

2. 2. The method for forming a resist film according to claim 1, wherein the step B includes a step B-3 of further heating the resist film that has been subjected to the step B-2 under atmospheric pressure.

3. 3. The method for forming a resist film according to claim 1, further comprising a step C of step of lowering the temperature of the resist film after the step B in a stepwise or continuous manner.

4. 4. The method for forming a resist film according to claim 3, wherein in the step C, the temperature of the resist film having been subjected to the step B is lowered at a temperature lowering rate of 5[deg.] C. / min or less.

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