A polyimide film and a method for producing the same

Abstract

The application provides a polyimide film and a preparation method thereof. The preparation method comprises the following steps: providing a substrate and fixing the substrate on a rotating platform of a spin coating machine; rotating the substrate at a first rotating speed and spraying an adhesive on the upper surface of the substrate; after rotating for a first preset time, rotating at a second rotating speed for a second preset time to obtain an adhesive layer; rotating the substrate at a third rotating speed, spraying polyimide on the upper surface of the rotating adhesive layer, and after rotating for a third preset time, rotating at a fourth rotating speed for a fourth preset time, and after rotating for the fourth preset time, rotating at a fifth rotating speed for a fifth preset time; baking the substrate at a first preset temperature; placing the baked substrate in a furnace tube and annealing the substrate at a second preset temperature to obtain the polyimide film. The application improves the process of forming the polyimide film, improves the quality of the polyimide film, and shortens the preparation time.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor integrated circuit manufacturing and relates to a polyimide film and its preparation method. Background Technology

[0002] In microbolometer-type uncooled infrared focal plane detectors, the absorption of incident infrared radiation can be enhanced by designing an optical resonant cavity, further improving the detector's sensitivity. The cavity structure within the resonant cavity can be obtained by etching or corroding a sacrificial layer, typically made of materials such as silicon dioxide, phosphosilicate glass, or polyimide. Polyimide, in particular, possesses characteristics such as high temperature resistance, high insulation, good chemical stability, and strong strain resistance, making it frequently used as a sacrificial layer or passivation layer in MEMS device structures. The conventional approach involves static droplet spin coating, where an adhesive and polyimide solution are spin-coated onto a static substrate. However, this method results in a film that is thicker in the center, and often exhibits abnormal dots in the substrate center. Furthermore, to obtain a film without peeling and with good stability, multiple baking steps are required, leading to a prolonged polyimide film preparation time.

[0003] Therefore, there is an urgent need to find a method for preparing polyimide films that can improve the thickness uniformity and film quality of polyimide films formed during semiconductor device fabrication and shorten the film preparation cycle. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a polyimide film and its preparation method, which solves the problems of long film formation time, poor thickness uniformity and poor quality of polyimide films formed in the semiconductor device preparation process in the prior art.

[0005] To achieve the above and other related objectives, the present invention provides a method for preparing a polyimide film, comprising the following steps:

[0006] A substrate is provided and the substrate is fixed on the rotating platform of a spin coating machine;

[0007] Turn on the spin coating machine, rotate the substrate at a first rotation speed, spray a first preset dose of adhesive on the upper surface of the rotating substrate, and after rotating the substrate for a first preset time, rotate the substrate at a second rotation speed for a second preset time to obtain an adhesive layer attached to the upper surface of the substrate.

[0008] The substrate is rotated at a third rotation speed, and a second preset dose of polyimide is sprayed onto the upper surface of the rotating adhesive layer. After rotating the substrate for a third preset time, the substrate is rotated at a fourth rotation speed for a fourth preset time. After rotating the substrate for a fourth preset time, the substrate is rotated at a fifth rotation speed for a fifth preset time to obtain a polyimide film.

[0009] At a first preset temperature, the substrate on which the polyimide film is formed is baked for a sixth preset time;

[0010] The baked substrate is placed in an oven tube and annealed at a second preset temperature for a seventh preset time on the substrate on which the polyimide film is formed.

[0011] Optionally, the substrate includes a conductive glass plate, a silicon plate, or a silicon oxide plate.

[0012] Optionally, before fixing the substrate to the rotating platform, the step of cleaning the substrate is further included.

[0013] Optionally, the first rotational speed ranges from 300 rpm / s to 500 rpm / s; the second rotational speed ranges from 600 rpm / s to 800 rpm / s; the third rotational speed ranges from 300 rpm / s to 500 rpm / s; the fourth rotational speed ranges from 1200 rpm / s to 2100 rpm / s; and the fifth rotational speed ranges from 600 rpm / s to 800 rpm / s.

[0014] Optionally, the first preset time ranges from 15s to 30s; the second preset time ranges from 30s to 50s; the third preset time ranges from 15s to 30s; the fourth preset time ranges from 40s to 60s; the fifth preset time ranges from 15s to 30s; the sixth preset time ranges from 60s to 90s; and the seventh preset time ranges from 30min to 50min.

[0015] Optionally, the first preset temperature ranges from 100℃ to 130℃; the second preset temperature ranges from 300℃ to 350℃.

[0016] Optionally, during the annealing process of the substrate on which the polyimide film is formed, the substrate is in an atmosphere of protective gas and reducing gas.

[0017] Optionally, the protective gas includes an inert gas.

[0018] Optionally, after annealing the substrate on which the polyimide film is formed, a natural cooling step is also included.

[0019] The present invention also provides a polyimide film, which is prepared by the polyimide film preparation method described above.

[0020] As described above, the polyimide film and its preparation method of the present invention, through improved preparation process, involves rotating the rotating platform before spraying the adhesive onto the upper surface of the substrate, causing the substrate to rotate. This allows the adhesive to diffuse directly from the center of the substrate outwards at the instant of contact with the upper surface of the substrate, under the action of centripetal force, thus avoiding the accumulation of the adhesive. The substrate is then rotated at the first rotation speed for the first preset time to allow the adhesive to diffuse to a large area of ​​the center of the substrate. The second rotation speed is then used to improve the uniformity of the thickness of the formed adhesive layer, providing a better process platform for forming the polyimide film. Furthermore, before spraying the polyimide onto the upper surface of the adhesive layer, rotating the rotating platform causes the substrate to rotate. This allows the polyimide to diffuse directly from the center of the adhesive layer outwards at the instant of contact with the upper surface of the adhesive layer, under the action of centripetal force, thus avoiding the accumulation of the adhesive. This method avoids the accumulation of polyimide and rotates the substrate at the third rotation speed for the third preset time, allowing the polyimide to diffuse to most of the center area of ​​the adhesion layer. Then, the rotation speed of the substrate is changed sequentially to the fourth rotation speed and the fifth rotation speed to obtain the polyimide film. This improves the uniformity of the thickness of the formed polyimide film. At the same time, after using low-temperature baking to improve the adhesion between the adhesion layer and the substrate and the polyimide film, annealing is performed directly, avoiding multiple baking and shortening the preparation time. During the annealing process, protective gas and reducing gas are used to repair the surface and inner surface defects of the polyimide film caused by moisture evaporation, improving the surface roughness of the formed polyimide film and enhancing the density and stability of the polyimide film. Moreover, the preparation process is simple, requires no complex instruments and equipment, is low-cost, suitable for industrialization, can be mass-produced, and has high industrial application value. Attached Figure Description

[0021] Figure 1 The diagram shown is a process flow chart of the method for preparing the polyimide film of the present invention.

[0022] Figure 2 The diagram shows a spray adhesive used in the preparation method of the polyimide film of the present invention.

[0023] Figure 3 The diagram shown is a structural schematic of the polyimide film prepared according to the present invention after the formation of the adhesion layer.

[0024] Figure 4The diagram shows a method for preparing polyimide film according to the present invention, specifically a method for spraying polyimide.

[0025] Figure 5 The diagram shown is a structural schematic of the polyimide film after its formation, as described in the preparation method of the polyimide film of the present invention.

[0026] Figure 6 The image shown is a SEM image of a polyimide film formed at a fourth rotation speed (A) according to the preparation method of the polyimide film of the present invention.

[0027] Figure 7 The image shown is a SEM image of a polyimide film formed at a fourth rotation speed of B, as described in the preparation method of the polyimide film of the present invention.

[0028] Figure 8 The table showing the properties of the polyimide film prepared by the method of the present invention is a table of properties formed at a fourth rotation speed of A and B.

[0029] Explanation of icon numbers

[0030] 1 Substrate

[0031] 2 Adhesion layer

[0032] 21 Adhesives

[0033] 3. Polyimide film

[0034] 31 Polyimide Detailed Implementation

[0035] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] Please see Figures 1 to 8 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0037] Example 1

[0038] This embodiment provides a method for preparing a polyimide film, such as... Figure 1The diagram shown is a process flow chart of the preparation method of the polyimide film, including the following steps:

[0039] S1: Provide a substrate and fix the substrate on the rotating platform of a spin coating machine;

[0040] S2: Turn on the spin coating machine, rotate the substrate at a first rotation speed, spray a first preset dose of adhesive on the upper surface of the rotating substrate, and after rotating the substrate for a first preset time, rotate the substrate at a second rotation speed for a second preset time to obtain an adhesive layer attached to the upper surface of the substrate.

[0041] S3: Rotate the substrate at a third rotation speed, spray a second preset dose of polyimide onto the upper surface of the rotating adhesive layer, and after rotating the substrate for a third preset time, rotate the substrate at a fourth rotation speed for a fourth preset time, and after rotating the substrate for a fourth preset time, rotate the substrate at a fifth rotation speed for a fifth preset time to obtain a polyimide film.

[0042] S4: At a first preset temperature, the substrate on which the polyimide film is formed is baked for a sixth preset time;

[0043] S5: Place the baked substrate in an oven tube and anneal the substrate with the polyimide film formed thereon at a second preset temperature for a seventh preset time.

[0044] Please see Figures 2 to 3 Perform steps S1 and S2: provide a substrate 1 and fix the substrate 1 on the rotating platform of the spin coater; turn on the spin coater, rotate the substrate 1 at a first rotation speed, spray a first preset dose of adhesive 21 on the upper surface of the rotating substrate 1, and after rotating the substrate 1 for a first preset time, rotate the substrate 1 at a second rotation speed for a second preset time to obtain an adhesive layer 2 attached to the upper surface of the substrate 1.

[0045] As an example, the substrate 1 may include a conductive glass plate, a silicon plate, a silicon oxide plate, or other suitable flat plate material.

[0046] Specifically, while ensuring the performance of the formed polyimide film, the thickness and size of the substrate 1 can be selected according to the actual situation, and are not limited here.

[0047] As an example, before fixing the substrate 1 to the rotating platform, a step of cleaning the substrate 1 is included. In this embodiment, deionized water is used to clean the surface of the substrate 1 to remove impurities from the surface of the substrate 1.

[0048] Specifically, after cleaning the substrate 1, the process also includes drying the substrate 1. In this embodiment, after cleaning the substrate 1 with deionized water, the residual deionized water on the surface of the substrate 1 is first shaken off, and then the moisture on the surface of the substrate 1 is removed by drying to obtain a dry substrate 1.

[0049] Specifically, the spin coating machine mentioned is a commonly used spin coating instrument, and relevant information about spin coating machines will not be elaborated here.

[0050] Specifically, the method for fixing the substrate 1 to the rotating platform includes clamping, adsorption fixation, or other suitable fixation methods.

[0051] As an example, the range of the first speed is 300 rpm / s to 500 rpm / s, for example, the first speed can be 300 rpm / s, 400 rpm / s or 500 rpm / s.

[0052] Specifically, such as Figure 2 The diagram shown is a schematic of the application of the adhesive 21. As long as the adhesive layer 2 is evenly distributed on the upper surface of the substrate 1, the amount of the adhesive 21 applied can be selected according to the actual situation, and is not limited here.

[0053] Specifically, during the spraying process of the adhesive 21, the substrate 1 is in a low-speed rotation state. The centripetal force generated by the rotation causes the adhesive 21 to start spreading from the center of the substrate 1 to the surrounding area the moment it comes into contact with the upper surface of the substrate 1. This allows the adhesive 21 to spread to the upper surface of the substrate 1 more quickly, while avoiding the accumulation of the adhesive 21 on the upper surface of the substrate 1 during the spraying process, which would affect the uniformity of the thickness of the adhesive layer 2 formed after spin coating.

[0054] As an example, the first preset time ranges from 15s to 30s, for example, it can be 15s, 20s, or 30s.

[0055] Specifically, after the adhesive 21 is sprayed, the substrate is rotated for 15s to 30s so that the adhesive 21 is distributed over most of the center area of ​​the substrate 1.

[0056] As an example, the range of the second speed is 600 rpm / s to 800 rpm / s, for example, the second speed can be 600 rpm / s, 700 rpm / s or 800 rpm / s.

[0057] As an example, the second preset time ranges from 30s to 50s, for example, it can be 30s, 40s, or 50s.

[0058] Specifically, by using the first rotation speed to rotate the substrate 1 for the first preset time, and using the second rotation speed to rotate the substrate 1 for the second preset time, the adhesive 21 is evenly distributed on the upper surface of the substrate 1 to obtain the adhesive layer 2 with a more uniform thickness, thereby improving the flatness of the subsequent process platform.

[0059] Specifically, such as Figure 3 The diagram shown is a structural schematic after the adhesion layer 2 is formed. As long as the adhesion layer 2 can firmly adhere to the substrate 1 and the object on the upper surface of the adhesion layer 2, the thickness of the adhesion layer 2 can be selected according to the actual situation, and is not limited here.

[0060] Please see again Figures 4 to 5 The following steps are performed: Step S3, Step S4, and Step S5: The substrate 1 is rotated at a third rotation speed, and a second preset dose of polyimide 31 is sprayed onto the upper surface of the rotating adhesion layer 2. After rotating the substrate 1 for a third preset time, the substrate 1 is rotated at a fourth rotation speed for a fourth preset time. After rotating the substrate 1 for a fourth preset time, the substrate 1 is rotated at a fifth rotation speed for a fifth preset time to obtain a polyimide film 3. The substrate 1 with the polyimide film 3 is baked at a first preset temperature for a sixth preset time. The baked substrate 1 is placed in an oven tube and annealed at a second preset temperature for a seventh preset time.

[0061] Specifically, after the adhesion layer 2 is formed, the rotation speed of the rotating platform is adjusted to the third rotation speed.

[0062] As an example, the range of the third speed is 300 rpm / s to 500 rpm / s, that is, the third speed can be 300 rpm / s, 400 rpm / s or 500 rpm / s.

[0063] Specifically, such as Figure 4 The diagram shows a schematic of spraying the polyimide 31. As long as the polyimide 31 can form a polyimide film 3 of a preset thickness on the upper surface of the substrate 1, the amount of polyimide 31 sprayed can be selected according to the actual situation, and is not limited here.

[0064] Specifically, during the spraying process of the polyimide 31, the substrate 1 is in a low-speed rotation state. The centripetal force generated by the rotation causes the polyimide 31 to begin to diffuse from the center of the adhesive layer 2 outwards the instant it contacts the upper surface of the adhesive layer 2. This allows the polyimide 31 to spread more quickly to the upper surface of the adhesive layer 2, while avoiding the accumulation of the polyimide 31 on the upper surface of the adhesive layer 2 during the spraying process, which would affect the uniformity of the thickness of the polyimide film 3 formed after subsequent spin coating.

[0065] As an example, the range of the third preset time is 15s to 30s, for example, it can be 15s, 20s, or 30s.

[0066] Specifically, after the polyimide 31 is sprayed, the substrate 1 is rotated for 15s to 30s to distribute the polyimide 31 in most of the central area of ​​the adhesive layer 2, so as to avoid excessive accumulation of the polyimide 31 in the center of the adhesive layer 2, which would affect the film formation quality of the polyimide film 3.

[0067] As an example, the range of the fourth speed is 1200 rpm / s to 2100 rpm / s, that is, the third speed can be 1200 rpm / s, 1500 rpm / s, 1800 rpm / s or 2100 rpm / s.

[0068] Specifically, the fourth rotation speed is a key step in forming the polyimide film 3. By adjusting the rotation speed value of the fourth rotation speed, the thickness of the polyimide film 3 can be adjusted so that the thickness of the polyimide film 3 reaches a preset film thickness value.

[0069] As an example, the range of the fourth preset time is 40s to 60s, for example, it can be 40s, 50s or 60s.

[0070] Specifically, the rotating platform is rotated at the fourth rotation speed for the fourth preset time so that the polyimide 31 diffuses to the upper surface of the adhesive layer 2 and the polyimide 31 completely covers the upper surface of the adhesive layer 2. At the same time, due to the high speed of the rotating platform, the large centripetal force generated causes the excess polyimide 31 to be thrown out, so as to obtain the polyimide film 3 of the preset thickness.

[0071] As an example, the range of the fifth rotational speed is 600 rpm / s to 800 rpm / s, that is, the third rotational speed can be 600 rpm / s, 700 rpm / s or 800 rpm / s.

[0072] As an example, the range of the fifth preset time is 15s to 30s, for example, the fifth preset time can be 15s, 20s or 30s.

[0073] Specifically, such as Figure 5 The diagram shows the structure after the polyimide film 3 is formed. The rotating platform rotates at the fifth rotation speed for the fifth preset time to stabilize the thickness of the polyimide film 3 and allow the polyimide film 3 to dry initially.

[0074] Specifically, during the formation of the polyimide film 3, the combination of the third rotation speed, the fourth rotation speed, and the fifth rotation speed improves the quality of the polyimide film 3, making the distribution of the polyimide 31 more uniform, and consequently making the film thickness of the polyimide film 3 more uniform.

[0075] As an example, the range of the first preset temperature is 100℃ to 130℃. For example, the first preset temperature can be 100℃, 110℃, 120℃ or 130℃.

[0076] As an example, the range of the sixth preset time is 60s to 90s. For example, the sixth preset time can be 60s, 70s, 80s, or 90s.

[0077] Specifically, the adhesive layer 2 and the polyimide film 3, which are sequentially formed on the substrate 1, are baked at the first preset temperature for the sixth preset time, so as to allow the formed adhesive layer 2 and the polyimide film 3 to initially remove moisture at this temperature, thereby enhancing the interfacial contact between the adhesive layer 2, the polyimide film 3 and the substrate 1, reducing the occurrence of voids at the contact interface between the adhesive layer 2, the polyimide film 3 and the substrate 1, and improving the quality of the formed polyimide film 3.

[0078] As an example, the range of the second preset temperature is 300℃ to 350℃. For example, the second preset temperature can be 300℃, 325℃, or 350℃.

[0079] As an example, the range of the seventh preset time is 30 minutes to 50 minutes. For example, the seventh preset time can be 30 minutes, 40 minutes, or 50 minutes.

[0080] Specifically, the substrate 1 after the formation of the polyimide film 3 is placed in the furnace tube to facilitate the efficient removal of moisture from the film.

[0081] As an example, during the annealing process of the substrate 1 on which the polyimide film 3 is formed, the substrate 1 is in an atmosphere of protective gas and reducing gas.

[0082] As an example, the protective gas includes an inert gas or other suitable protective gas.

[0083] Specifically, the reducing gas is the reducing gas used in the preparation of the polyimide 31 by a gas-phase method.

[0084] Specifically, due to the improved density and stability of the polyimide film 3, voids caused by metal ion oxidation are prevented, thus avoiding bubbling or peeling during subsequent photolithography, etching, cleaning and other processes.

[0085] As an example, after annealing the substrate 1 on which the polyimide film 3 is formed, a natural cooling step is also included.

[0086] Specifically, after annealing the substrate 1 on which the polyimide film 3 is formed, the polyimide film 3 is cooled by natural cooling. This avoids uneven temperature formation of the polyimide film 3 due to excessively rapid temperature drop, which could cause uneven thermal stress in some areas of the polyimide film 3, leading to deformation or detachment of the polyimide film 3. This further ensures the quality of the polyimide film 3.

[0087] Specifically, such as Figure 6 , Figure 7 and Figure 8 The figures show SEM images of the polyimide film 3 formed at the fourth rotation speed of A and B, respectively, and a film characteristic table for the polyimide film 3 formed at the fourth rotation speeds of A and B. When the fourth rotation speed is A, the thickness of the polyimide film 3 is 1.65 μm, and the inter-film uniformity is 4.3%; when the fourth rotation speed is B, the thickness of the polyimide film 3 is 2.72 μm, and the inter-film uniformity is 4%. Figure 6 , Figure 7 and Figure 8 The data shows that the formed polyimide film 3 has good stability, high flatness, and low overall surface roughness, resulting in a smooth surface.

[0088] Specifically, due to the improved spin-coating process of the polyimide film 3, the protective gas and the reducing gas are used to repair surface and inner surface defects caused by moisture evaporation, eliminating the need for step-by-step baking, shortening the preparation time, simplifying the baking process after the formation of the polyimide film 3, and improving the preparation efficiency.

[0089] The method for preparing the polyimide film in this embodiment improves the process of forming the polyimide film 3. Before spraying the adhesive 21, the substrate 1 is rotated at the first rotation speed to utilize the centripetal force of rotation to diffuse the adhesive 21 from the center of the substrate 1 outwards, avoiding the accumulation of the adhesive 21. After spraying the adhesive 21, the substrate 1 is rotated at the first rotation speed for a first preset time to distribute the adhesive 21 in most of the central area of ​​the substrate 1. Then, the substrate 1 is rotated at the second rotation speed for a second preset time to ensure that the adhesive 21 is evenly distributed on the upper surface of the substrate 1, resulting in an adhesive layer 2 with a more uniform thickness, providing a smoother process platform for subsequent processes. Before spraying the polyimide 31, the substrate 1 is rotated at the third rotation speed. The centripetal force generated by the rotation causes the polyimide 31 to diffuse from the center of the adhesive layer 2 outwards at the instant it contacts the upper surface of the adhesive layer 2, avoiding the accumulation of the polyimide 31. After the polyimide 31 is sprayed, it is rotated at the third rotation speed for the third preset time to distribute the polyimide 31 in most of the central area of ​​the adhesive layer 2. Then, it is rotated at the fourth rotation speed for the fourth preset time to make the polyimide 31 evenly distributed on the upper surface of the adhesive layer 2, while obtaining the polyimide film 3 of the preset thickness. After the polyimide film 3 is formed, it is baked at the first preset temperature for the sixth preset time to initially remove moisture from the structure in which the polyimide film 3 is formed, so that the adhesion between the adhesive layer 2 and the substrate 1 and the polyimide film 3 is stronger, and the phenomenon of voids appearing at the contact interface between the adhesive layer 2, the polyimide film 3 and the substrate 1 is reduced. It is annealed at the second preset temperature for the seventh preset time, and the annealing process is carried out in the protective gas and the reducing gas, which improves the surface roughness of the formed polyimide film 3, eliminates the need for step-by-step baking, and shortens the preparation time.

[0090] Example 2

[0091] This embodiment provides a polyimide film, which is prepared using the polyimide film preparation method described in Example 1.

[0092] Specifically, by using the polyimide film preparation method described in Example 1 to prepare the polyimide film 3, the film defects in the polyimide film 3 are reduced, the uniformity of the thickness of the obtained polyimide film 3 is improved, and thus the quality of the polyimide film 3 is improved.

[0093] Specifically, since the polyimide film 3 is formed using the polyimide film preparation method described in Example 1, after the polyimide film 3 is formed, a low-temperature baking method is used to initially remove the moisture in the adhesive layer 2 and the polyimide film 3, thereby enhancing the adhesion of the adhesive layer 2 and subsequently enhancing the bonding force of the adhesive layer 2 to the substrate 1 and the polyimide film 3, thus avoiding the phenomenon of the polyimide film 3 formed by annealing falling off.

[0094] Specifically, when the polyimide film 3 is formed using the polyimide film preparation method described in Example 1, during the annealing process, the substrate 1 on which the polyimide film 3 is formed is placed in the atmosphere of the protective gas and the reducing gas. The protective gas and the reducing gas are used to repair surface and internal surface defects caused by moisture evaporation, eliminating the need for step-by-step baking, shortening the preparation time, improving the surface roughness of the formed polyimide film 3, and enhancing the density and stability of the polyimide film 3.

[0095] Specifically, since the polyimide film 3 is formed by using the polyimide film preparation method described in Example 1, the preparation efficiency is improved, and the preparation process is simple, requiring no complex instruments and equipment, and is low-cost, suitable for industrialization and large-scale production.

[0096] The polyimide film of this embodiment is prepared by the polyimide film preparation method described in Example 1. The resulting polyimide film has fewer defects, higher density and stability, and the surface roughness of the polyimide film is also improved. The preparation efficiency is also improved, and the preparation process is simple, requiring no complex instruments and equipment, with low cost, suitable for industrialization and large-scale production.

[0097] In summary, the polyimide film and its preparation method of the present invention improve the process of preparing the polyimide film. Before spraying the adhesive to form the adhesive layer, the substrate is rotated at a first preset speed. Centripetal force is used to cause the adhesive to diffuse from the center of the substrate to the surrounding area during the spraying process, avoiding the accumulation of adhesive and improving the uniformity of the adhesive layer thickness, thus providing a better process platform for forming the polyimide film. Before spraying the polyimide to form the polyimide film, the substrate is rotated at a third preset speed. Centripetal force is used to cause the polyimide to diffuse from the center of the adhesive layer to the surrounding area during the spraying process, avoiding the accumulation of polyimide and improving the uniformity of the thickness of the formed polyimide film. At the same time, after baking at a low temperature for a sixth preset time, the adhesion between the adhesive layer and the substrate and the polyimide film is improved, and then annealing is performed directly, avoiding multiple baking and shortening the preparation time. Furthermore, during the annealing process, protective and reducing gases are introduced to repair surface and internal surface defects in the polyimide film caused by moisture evaporation. This improves the surface roughness of the formed polyimide film, enhancing its density and stability. The preparation process is simple, requires no complex equipment, is low-cost, and suitable for industrialization and large-scale production. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial applicability.

[0098] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a polyimide film, characterized in that, Includes the following steps: A substrate is provided and the substrate is fixed on the rotating platform of a spin coating machine; The spin coater is turned on, the substrate is rotated at a first rotation speed, a first preset dose of adhesive is sprayed onto the upper surface of the rotating substrate, and after rotating the substrate for a first preset time, the substrate is rotated at a second rotation speed for a second preset time to obtain an adhesive layer attached to the upper surface of the substrate. The range of the first rotation speed is 300 rpm / s to 500 rpm / s, and the range of the second rotation speed is 600 rpm / s to 800 rpm / s. The substrate is rotated at a third rotation speed, and a second preset dose of polyimide is sprayed onto the upper surface of the rotating adhesive layer. After rotating the substrate for a third preset time, the substrate is rotated at a fourth rotation speed for a fourth preset time. After rotating the substrate for a fourth preset time, the substrate is rotated at a fifth rotation speed for a fifth preset time to obtain a polyimide film. The range of the third rotation speed is 300 rpm / s to 500 rpm / s, the range of the fourth rotation speed is 1200 rpm / s to 2100 rpm / s, and the range of the fifth rotation speed is 600 rpm / s to 800 rpm / s. At a first preset temperature, the substrate on which the polyimide film is formed is baked for a sixth preset time; The baked substrate is placed in a furnace tube and annealed at a second preset temperature for a seventh preset time. During the annealing process, the substrate is in an atmosphere of protective gas and reducing gas.

2. The method for preparing the polyimide film according to claim 1, characterized in that: The substrate includes a conductive glass plate, a silicon plate, and a silicon oxide plate.

3. The method for preparing the polyimide film according to claim 1, characterized in that: Before fixing the substrate to the rotating platform, the method further includes a step of cleaning the substrate.

4. The method for preparing the polyimide film according to claim 1, characterized in that: The first preset time ranges from 15 s to 30 s; the second preset time ranges from 30 s to 50 s; the third preset time ranges from 15 s to 30 s; the fourth preset time ranges from 40 s to 60 s; the fifth preset time ranges from 15 s to 30 s; the sixth preset time ranges from 60 s to 90 s; and the seventh preset time ranges from 30 min to 50 min.

5. The method for preparing the polyimide film according to claim 1, characterized in that: The first preset temperature ranges from 100 ℃ to 130 ℃; the second preset temperature ranges from 300 ℃ to 350 ℃.

6. The method for preparing the polyimide film according to claim 1, characterized in that: The protective gas includes an inert gas.

7. The method for preparing the polyimide film according to claim 1, characterized in that: After annealing the substrate on which the polyimide film is formed, the process further includes a natural cooling step.

8. A polyimide film, characterized in that: The polyimide film is prepared by the polyimide film preparation method according to any one of claims 1 to 7.

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