A method for fabricating a photomask and the photomask itself.

Abstract

This invention discloses a mask fabrication method and a mask, relating to the field of semiconductor display technology. The mask fabrication method includes the following steps: S10, preparing a metal substrate; S20, coating one surface of the metal substrate with a PI film; S30, etching a first opening through the metal substrate to form a semi-finished mask; S40, stretching the semi-finished mask onto a mesh and welding it to a frame; S50, using a laser to create a second opening on the PI film, the second opening and the first opening forming a continuous pattern. The mask is fabricated using this method, where the first opening forming the pattern is formed on the metal substrate before mesh stretching, and the second opening is formed on the PI film after mesh stretching and welding. This significantly improves production efficiency and allows the produced mask to achieve higher precision requirements.

Description

Technical Field

[0001] This invention relates to the field of semiconductor display technology, and in particular to a method for fabricating a photomask and the photomask itself. Background Technology

[0002] Common Metal Mask (CMM) plays a role in defining the active area (AA) of the panel during the vapor deposition process and is widely used in AMOLED, PMOLED and micro OLED fields.

[0003] Traditional CMM manufacturing involves first producing CMM sheets through processes such as cleaning, lamination, exposure, development, etching, and stripping of the invar material. Then, a screen tensioning device is used to apply tension to the CMM sheet and continuously adjust its positional accuracy before finally welding it to a metal frame. This method produces CMMs with relatively large errors. However, with the trend towards high PPI and narrow bezel products, the precision requirements for CMMs are further increasing, and existing processing methods struggle to meet these higher precision demands. Furthermore, the time spent adjusting positional accuracy during the screen tensioning process is relatively long, impacting production capacity. Additionally, screen tensioning equipment is expensive, and increasing production capacity by adding more equipment would require significant investment, leading to substantial pressure to meet mass production demands.

[0004] Therefore, a new processing method is urgently needed to solve the above problems. Summary of the Invention

[0005] To obtain a higher precision CMM, this invention provides a method for fabricating a photomask, the method comprising the following steps:

[0006] S10, Prepare the metal substrate;

[0007] S20. Coat one surface of the metal substrate with a PI film;

[0008] S30. An etching process is used to process a first opening on a metal substrate. The first opening penetrates the metal substrate to form a mask semi-finished product.

[0009] S40. Tension the mask semi-finished product into a mesh and weld it to the frame;

[0010] S50. A second opening is processed on the PI film using a laser. The second opening and the first opening form a patterned opening that runs vertically through the film.

[0011] Furthermore, the second opening corresponds one-to-one with the first opening.

[0012] Furthermore, the first opening is larger than the second opening, and the second opening is completely contained within the range of the first opening;

[0013] Preferably, the distance between the edge of the second opening and the edge of the first opening is d, where 10μm≤d≤100μm;

[0014] Preferably, the laser etching angle at the edge of the second opening is γ, where 45°≤γ≤80°.

[0015] Furthermore, the metal substrate is Invar alloy, SUS304, or SUS316, with a thickness of 100μm to 200μm; the coating thickness of the PI film is 10μm to 30μm.

[0016] Furthermore, the distance between the edge of the second opening and the edge of the first opening is d, and the thickness of the PI film is t, where t is positively correlated with d.

[0017] Furthermore, in step S20, the PI film is coated using spin coating, screen printing, or inkjet printing.

[0018] Furthermore, in step S30, the etching process sequentially includes pretreatment, coating, exposure, development, etching, and stripping steps.

[0019] Furthermore, in step S30, some steps of the etching process are performed as follows:

[0020] A photoresist film is coated on the surface of the metal substrate on the side away from the PI film;

[0021] Exposure and development pattern the photoresist film;

[0022] The surface of the metal substrate covered with photoresist film is etched.

[0023] Furthermore, in step S30, the etching process is performed at least once during the preparation of the first opening;

[0024] Preferably, the etching process is performed twice during the preparation of the first opening, wherein:

[0025] A first etching process creates groove A; a second etching process creates opening B at the bottom of groove A. Groove A and opening B together form the first opening; or...

[0026] The first etching process creates two C-grooves, and the second etching process removes the portion between the two C-grooves, forming the first opening.

[0027] In addition, a mask prepared using the above-mentioned mask preparation method is also proposed.

[0028] The beneficial effects of this invention are as follows:

[0029] 1) The pattern opening fabrication of the photomask involves processing a first opening on a metal substrate and a second opening on a PI film. The first opening is obtained by etching before screen stretching, which helps reduce the mutual influence of tension in different directions during screen stretching, improves the flatness of the stretched screen, and avoids the subsequent processing from substantially affecting the stress characteristics of the stretched photomask surface, ensuring that the photomask remains flat. The effective width of the opening corresponding to the target pattern is the width of the second opening, which is obtained by laser etching after screen stretching. Compared with traditional manufacturing methods, this reduces the cumulative error caused by the superposition of errors in photomask sheet fabrication and screen stretching machine deviations. In addition, since the second opening is directly processed by laser and formed on a PI film of a fixed thickness, the opening accuracy is easier to control precisely. Therefore, higher precision requirements can be achieved.

[0030] 2) Setting the PI film coating process before processing the first opening can effectively control the film thickness and uniformity of the PI film, and has a significant effect on suppressing the change of PI film surface stress before and after processing the second opening, which affects the opening accuracy.

[0031] 3) The second opening, which serves as an effective opening, is formed after the wire mesh stretching and welding steps. During the wire mesh stretching process, there is no need to repeatedly adjust the positional accuracy, saving the time cost required for continuous positional accuracy adjustments and significantly increasing production output.

[0032] Furthermore, other additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the photomask fabrication process.

[0034] Figure 2 A schematic diagram of the structure of the semi-finished mask obtained by etching;

[0035] Figure 3 This is a schematic diagram of the structure obtained after the mask semi-finished product is combined with the frame.

[0036] Figure 4 This is a schematic diagram of the structure of the finished photomask.

[0037] Figure 5 This is a schematic diagram of the cross-sectional structure of the opening at a single opening position in the finished mask.

[0038] Figure 6 This is a schematic diagram of the laser etching angle at the edge of the second opening;

[0039] Figure 7 Schematic diagrams illustrating different implementations of a multiple etching process for the first opening;

[0040] In the figure: 1. Frame; 11. Window; 2. Mask; 21. Metal substrate; 211. First opening; 211a. Groove A; 211b. Opening B; 211c. Groove C; 22. PI film; 221. Second opening; 200. Pattern opening; 2-a. Mask semi-finished product; 3. Photoresist film; 4. Photomask. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. For reference, the following description and accompanying drawings are brief examples to help understand this invention, and are not intended to limit the technical scope of this invention. In other words, the embodiments described below may have various modifications, which fall within the scope of the technical concept of this invention. Those skilled in the art can easily understand the technical concept of this invention through the following description. The invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] Appendix Figure 4 A photomask is shown, specifically a general-purpose metal photomask (CMM).

[0043] See appendix Figure 4 As shown, the photomask includes a frame 1 and a mask 2, with the mask 2 welded to one surface of the frame 1. The frame 1 is rectangular and has a vertically extending window 11 in the center. In some embodiments, multiple windows 11 may be provided in the frame 1, arranged in an array. The frame 1 is preferably made of Invar alloy to reduce thermal expansion deformation during use; in some embodiments, stainless steel or other alloy steels, such as SUS304 or SUS316, may also be used. The mask 2 has multiple patterned openings 200 located within the area of ​​the window 11, arranged in an array. In some embodiments, the number of patterned openings 200 can be increased or decreased as needed; for example, only one patterned opening 200 may be provided at a minimum.

[0044] Appendix Figure 5 The above appendix is ​​shown Figure 4 One of the patterns in the mask has an opening 200 in its cross-sectional structure.

[0045] See appendix Figure 4 and attached Figure 5As shown, the mask 2 includes a metal substrate 21 and a PI film 22 (polyimide film) coated on one surface of the metal substrate 21. The metal substrate 21 is preferably an Invar alloy sheet, but SUS304, SUS316, etc., can also be used. The structure of the patterned opening 200 on the mask 2 includes a first opening 211 and a second opening 221. The first opening 211 is formed on the metal substrate 21, penetrating the metal substrate 21 to the surface of the PI film 22; the second opening 221 is formed on the PI film 22, penetrating the PI film 22. The second opening 221 is formed within the area of ​​the first opening 211, and the two together constitute the patterned opening 200 penetrating the mask 2.

[0046] See appendix Figure 4 As shown, the preferred configuration is that the second opening 221 corresponds one-to-one with the first opening 211, meaning that any pattern opening 200 is formed by combining a first opening 211 and a second opening 221. For a common metal mask (CMM), the effective area of ​​its pattern opening 200 corresponds to the entire display panel, which is the second opening 221. If a large first opening 211 is opened on the metal substrate 21, and multiple second openings 221 are arranged within the area of ​​the larger first opening 211, the shielding portion between two adjacent second openings 221 will only consist of the PI film 22 layer, making it difficult to control the strength and sag. Based on this consideration, in this design, the shielding portion between two adjacent pattern openings 200 is composed of both the metal substrate 21 layer and the PI film 22 layer, ensuring that both the strength and sag are controllable, thus improving the mask accuracy.

[0047] In addition, see appendix Figure 5 As shown, the first opening 211 is larger than the second opening 221, and the second opening 221 is completely contained within the area of ​​the first opening 211. During processing, the first opening 211 is processed before the second opening 221, which can be used to position the area of ​​the pattern opening 200, facilitating the subsequent processing of the second opening 221. Furthermore, the size of the first opening 211 is slightly larger than that of the second opening 221, which helps to reduce the obstruction of the metal substrate 21 on the organic material entering the second opening 221, reducing the generation of shadows. More importantly, this design ensures that the second opening 221 is completely formed on the PI film 22 of a defined thickness, and the processing depth of the second opening 221 is a defined value, making the processing accuracy easier to control.

[0048] Appendix Figure 5As shown, the distance between the edge of the second opening 221 and the edge of its corresponding first opening 211 is d. During the design process, factors considered in determining the value of d include the mechanical properties of the PI film 22 and the shrinkage variation of the PI film 22 before and after the second opening 221 is opened. If the value of d is inappropriate, the strength of the PI film 22 may be insufficient to support the portion extending beyond the inner edge of the first opening 211 on the metal substrate 21, potentially resulting in significant sagging at the edge of the second opening 221, thus affecting the processing accuracy of the second opening 221. Furthermore, an unreasonable value of d can also lead to a large shrinkage variation of the PI film 22 before and after the second opening 221 is opened, or inconsistent shrinkage variations on each side when the second opening 221 is opened, which will also affect the processing accuracy of the second opening 221. Based on this consideration, this design preferably uses a d value between 10μm and 100μm, for example, d values ​​of 30μm, 50μm, or 70μm. This can significantly improve the processing accuracy of the second opening 221.

[0049] In addition, see appendix Figure 6 As shown, the laser etching angle at the edge of the second opening 221 is γ, 45°≤γ≤80°, for example: γ=50° or 60° or 70°. The aforementioned laser etching angle is the incident angle of the laser on the surface of the PI film 22. After controlling the laser etching angle, the thickness of the PI film 22 at the edge of the second opening 221 is reduced, which is beneficial to reduce the shadow during the vapor deposition process and realize the processing of products with narrower bezels. More preferably, 45°≤γ≤55°, for example: γ=50°, this angle is comparable to the incident angle of the organic material during the vapor deposition process, resulting in a smaller shadow.

[0050] Appendix Figure 4 and attached Figure 5 As shown, the thickness of the metal substrate 21 is between 100 μm and 200 μm, for example, using an Invar alloy sheet with a thickness of 150 μm as the metal substrate 21. The thickness of the PI film 22 on the surface of the metal substrate 21 is between 10 μm and 30 μm, for example, the thickness of the PI film 22 is 20 μm. Here, when designing the thickness of the PI film 22, both the mechanical properties of the PI film 22 and the shrinkage variation of the PI film 22 before and after the second opening 221 are opened are considered. Based on this consideration, the thickness of the PI film 22 in this design also helps to improve the processing accuracy of the second opening 221.

[0051] In addition, see appendix Figure 5As shown, the distance between the edge of the second opening 221 and the edge of the first opening 211 is d, and the thickness of the PI film 22 is t, where t is positively correlated with d. That is, the larger the distance between the edge of the second opening 221 and the edge of the first opening 211, the greater the thickness of the PI film 22; conversely, the smaller the distance between the edge of the second opening 221 and the edge of the first opening 211, the smaller the thickness of the PI film 22. For example: d takes a value of 10μm to 40μm, and t takes a value of 10μm; d takes a value of 40μm to 70μm, and t takes a value of 20μm; d takes a value of 70μm to 100μm, and t takes a value of 30μm. This ensures the mechanical strength of the PI film 22 and reduces the risk of deformation at the edge of the second opening 221.

[0052] In traditional photomask manufacturing methods, a finished photomask component is first fabricated, with etched patterns and openings. This component is then stretched and welded to a support frame, resulting in a usable photomask. However, this traditional method requires repeated adjustments to the tension applied to the photomask at various points during the stretching and welding process to achieve controlled precision. Furthermore, the relative position of the photomask to the support frame needs constant adjustment using the stretching machine. This process is time-consuming and significantly slows down production efficiency.

[0053] In addition, in traditional photomask manufacturing methods, there are sheet material manufacturing errors (including errors in pattern opening) when processing finished photomask parts, and errors (including alignment errors) are generated during the mesh welding process due to the mesh stretching machine. The accumulation of multiple errors makes it difficult to achieve a breakthrough in improving the processing accuracy of photomasks.

[0054] For this purpose, see Appendix Figure 1 As shown in the figure, this embodiment provides a method for preparing a photomask, which includes the following steps:

[0055] Step 1: Fabrication of the metal substrate 21. See Appendix. Figure 1 Step ① is shown in the diagram.

[0056] Invar alloy, SUS304, or SUS316 strip is selected as the raw material, with a thickness between 100μm and 200μm. For example, an Invar alloy strip with a thickness of 150μm is selected as the raw material. The Invar alloy, SUS304, or SUS316 roll is unwound by an unwinding machine, and then the portion used to make the mask 2 is cut out by cutting or other methods, which serves as the metal substrate 21.

[0057] It is worth noting that the “preparation” here is not limited to in-house processing, but also includes obtaining the metal substrate 21 by means of direct procurement.

[0058] Step two, a PI film 22 is coated on one surface of the metal substrate 21. See Appendix Figure 1 Step ② is shown in the diagram.

[0059] Before coating the PI film 22, the surface of the metal substrate 21 needs to be cleaned to remove any foreign matter that may adhere to the surface of the metal substrate 21, and finally a dry metal substrate 21 is obtained for use.

[0060] After pretreatment such as cleaning, a metal substrate 21 is taken, and polyimide is used as the coating material. The polyimide is coated onto one surface of the metal substrate 21 using methods such as spin coating, screen printing, or inkjet printing to form a PI film 22. The coating thickness is between 10 μm and 30 μm, for example, 20 μm. After coating, the substrate can be baked at a certain temperature (i.e., a baking process) to enhance the adhesion of the PI film 22 to the surface of the metal substrate 21 and reduce the possibility of peeling off.

[0061] Step 3: An etching process is used to fabricate a first opening 211 on the metal substrate 21. The first opening 211 penetrates the metal substrate 21, forming a mask semi-finished product 2-a. The etching process sequentially includes pretreatment, coating, exposure, development, etching, and stripping steps. See the appendix for details on the coating and stripping steps. Figure 1 Steps ③ to ⑦ are shown in the diagram.

[0062] Pretreatment: The uncoated surface of the metal substrate 21 is cleaned by means of fluid flushing, ultrasonic cleaning, etc., to remove impurities that adhered to the metal substrate 21 in the previous process, and then dried for later use.

[0063] Coating: A photoresist film 3 is attached to the surface of the metal substrate 21 that is not covered with the PI film 22. The photoresist film 3 is either a dry film photoresist or a wet film photoresist.

[0064] Exposure / Development: This refers to the patterning of the photoresist film 3. The surface of the metal substrate 21 coated with the photoresist film 3 is exposed and developed sequentially using exposure and development equipment to form a pattern structure corresponding to the first opening 211 on the photoresist film 3. The parameters of the pattern can be determined according to actual needs, such as the number, size, and spacing of the patterns.

[0065] Etching: Preset appropriate parameters such as etching solution concentration, number of nozzles, and etching solution flow rate to obtain a suitable etching speed. Draw etching lines according to predetermined parameters such as the number, size, and spacing of patterns, and etch along the etching lines to form the first opening 211 on the surface of the developed metal substrate 21.

[0066] See appendix Figure 5As shown, in the thickness direction of mask 2, the size of the first opening 211 formed by etching gradually decreases along the direction toward the PI film 22. In the overall structure of mask 2, the narrowest point of the etched first opening 211 should be larger than the predetermined size of the second opening 221 processed subsequently, see Appendix Figure 5 As shown, the distance d between the two opening edges should be between 10μm and 100μm.

[0067] Photoresist removal: Remove the photoresist film 3 attached to the metal substrate 21 to obtain the following result. Figure 2 The mask semi-finished product 2-a shown in the figure.

[0068] It is worth noting that the first opening 211 can be obtained by one etching process described above, or by performing multiple etching processes described above. Here, it is preferable to use two etching processes to process the first opening 211 on the metal substrate 21.

[0069] For example: see appendix Figure 7 As shown in (a), a first etching process is performed to create a groove A 211a, which is a semi-groove with a depth between 20% and 50% of the thickness of the metal substrate 21, for example, 30% or 40%. A second etching process is performed to create an opening B 211b at the bottom of the groove A 211a, which extends from the metal substrate 21 to the surface of the PI film 22. The groove A 211a and the opening B 211b constitute the first opening 211. This helps to reduce the generation of shadows during the vapor deposition process and increases the number of times the mask can be used for vapor deposition.

[0070] For example: see appendix Figure 7 As shown in (b). The first etching process is performed to process two C-grooves 211c, and the predetermined width of the first opening 211 is located. The C-grooves 211c are also half-grooves. The second etching process is performed to remove the part between the two C-grooves 211c to form the first opening 211.

[0071] In practice, the number of etching processes used to process the first opening 211 can be determined according to actual needs, either by increasing or decreasing the number of etching steps.

[0072] Furthermore, in cases where the first opening 211 is processed using multiple etching processes, the etching process for the second and subsequent etching processes should include situations where the pretreatment steps are not repeated. For example, if the surface of the product being prepared for the next etching process is sufficiently clean after the previous etching process, then the cleaning process need not be repeated.

[0073] Step four: Stretch the mesh onto the mask semi-finished product 2-a and weld it to frame 1. See appendix. Figure 1 Step ⑧ is shown in the diagram.

[0074] The film sheeting machine grips the edges of the semi-finished mask 2-a, applies tension to stretch it to a flat state, and then welds it onto the frame 1. (See attached diagram.) Figure 3 As shown in the diagram. During the netting process, precise alignment of the opening is not required.

[0075] Step 5: Process the second opening 221 to create the finished mask. See appendix. Figure 1 Step 9 is shown in the diagram.

[0076] This step eliminates the need for further lamination and other operations. Instead, a laser is used to directly etch the PI film 22, controlling the laser's incident angle on the PI film 22 surface between 45° and 80°, more preferably between 45° and 55°, to create a second opening 221. The second opening 221 is completely contained within the area of ​​the first opening 211, and the distance d between the edge of the second opening 221 and the edge of the first opening 211 meets the requirement of 10μm to 100μm. The second opening 221 and the first opening 211 form a vertically continuous patterned opening 200, thus producing the finished mask.

[0077] This design includes the production of attachments. Figure 4 and attached Figure 5 In the mask fabrication process shown, the first opening 211 is formed before the mesh is stretched, and the second opening 221 is formed after the mesh is stretched. Processing the first opening 211 before stretching the mesh allows for modification of the metal substrate 21 structure to achieve anisotropy, and makes it easier to ensure a flat mesh surface during stretching. When processing the second opening 221, the mask 2 has already been stretched and welded to the frame 1, and the tension state is essentially the same as the finished product state. Subsequent stretching is not repeated. After processing the second opening 221, a finished mask that can be directly used is produced.

[0078] Furthermore, compared to traditional manufacturing methods, this invention employs a process of first processing the first opening 211, then stretching the mesh before processing the second opening 221. During the processing of the second opening 221, the position of the second opening 221 is directly positioned using laser equipment, eliminating the cumulative errors caused by the combined effects of mask sheet manufacturing errors and stretching machine deviations. Moreover, the subsequent processing of the second opening 221 on the PI film 22 has virtually no impact on the stress of the entire PI film 22 mesh surface, and the PI film 22 at the edge of the second opening 221 exhibits minimal shrinkage. The processing accuracy of the second opening 221 fully meets quality control requirements. Therefore, the processing accuracy of the mask is significantly improved.

[0079] Furthermore, setting the PI film coating process before processing the first opening 211 can effectively control the film thickness and uniformity of the PI film, and this purpose can be achieved without the need for other fixtures. This has a significant effect on suppressing the change in surface stress of the PI film before and after processing the second opening 221, which affects the opening accuracy.

[0080] Furthermore, in the manufacturing method of this invention, precise positional control is not required during the mesh stretching step. The low precision alignment requirement eliminates the need for repeated adjustments to the mask 2's positional accuracy during mesh stretching, significantly improving processing efficiency.

[0081] Finally, it should be emphasized again that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fabricating a photomask, characterized in that, The steps for creating a general-purpose metal photomask include: S10, Prepare a metal substrate (21); S20. A PI film (22) is coated on one surface of the metal substrate (21), comprising: The metal substrate (21) is pretreated. Take the pretreated metal substrate (21) and coat it with coating material on one of the surfaces of the metal substrate (21) with a coating thickness between 10 μm and 30 μm to form a PI film (22). Then, a baking process is performed to enhance the adhesion of the PI film (22) to the surface of the metal substrate (21); S30. An etching process is used to process a first opening (211) on a metal substrate (21). The first opening (211) penetrates the metal substrate (21) to form a mask semi-finished product (2-a). S40. The mask semi-finished product (2-a) is stretched with a wire mesh and welded to the frame (1), wherein, The gripper of the stretching machine grabs the edges of the semi-finished mask (2-a) and applies tension to stretch the semi-finished mask (2-a) to a flat state. Precise control of the alignment of the opening is not required during the stretching process. S50. A second opening (221) is processed on the PI film (22) using a laser. The second opening (221) and the first opening (211) form a patterned opening (200) that runs vertically through the film. The second opening (221) corresponds one-to-one with the first opening (211). The first opening (211) is larger than the second opening (221). The second opening (221) is completely contained within the range of the first opening (211). The distance between the edge of the second opening (221) and the edge of the first opening (211) is d, 10μm≤d≤100μm.

2. The method for fabricating a photomask according to claim 1, characterized in that, The laser etching angle at the edge of the second opening (221) is γ, 45°≤γ≤80°.

3. The method for fabricating a photomask according to claim 1, characterized in that, The metal substrate (21) is Invar alloy, SUS304 or SUS316, with a thickness of 100μm to 200μm.

4. The method for fabricating a photomask according to claim 1, characterized in that, The distance between the edge of the second opening (221) and the edge of the first opening (211) is d, and the thickness of the PI film (22) is t, where t is positively correlated with d.

5. The method for fabricating a photomask according to claim 1, characterized in that, In step S20, the PI film (22) is coated by spin coating, screen printing, or inkjet printing.

6. The method for fabricating a photomask according to claim 1, characterized in that, In step S30, the etching process sequentially includes pretreatment, coating, exposure, development, etching, and stripping steps.

7. The method for fabricating a photomask according to claim 6, characterized in that, In step S30, some steps of the etching process are performed as follows: A photoresist film (3) is coated on the surface of the metal substrate (21) on the side away from the PI film (22). Exposure and development pattern the photoresist film (3); The surface of the metal substrate (21) covered with photoresist film (3) is etched.

8. The method for fabricating a photomask according to claim 6, characterized in that, In step S30, the etching process is performed at least once during the preparation of the first opening (211).

9. The method for fabricating a photomask according to claim 6, characterized in that, The etching process is performed twice during the preparation of the first opening (211), wherein: A first etching process is performed to create groove A (211a), and a second etching process is performed to create opening B (211b) at the bottom of groove A (211a). Groove A (211a) and opening B (211b) together form the first opening (211); or, The first etching process is performed to create two C-grooves (211c). The second etching process is performed to remove the portion between the two C-grooves (211c) to form the first opening (211).

10. A universal metal mask prepared using the mask fabrication method according to any one of claims 1 to 9.

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