Etching method of metal mask

Abstract

The application provides an etching method of a metal mask, which is used for forming a large hole on a first surface of a substrate. The specific steps include: forming a first opening on the first surface of the substrate, forming an oxidation film with gradually changed thickness on the surface of the first opening, and etching the first opening to form a large hole. The opening angle of the large hole is in the range of 40°-65°. In the application, the active and accurate control of the side wall etching profile is realized by forming the oxidation film with gradually changed thickness, so as to form a large hole with extremely high etching factor and verticality on the first surface of the metal mask. The side etching amount of the hole is reduced, the etching factor is greatly improved, and the opening angle of the large hole is in the range of 40°-65°. In addition, after the etching factor is improved by using the technical solution of the application, the anti-bending damage ability of the high-resolution metal mask is significantly improved, and the production defects caused by bending damage are reduced.

Description

Etching methods for metal photomasks Technical Field

[0001] This invention belongs to the field of fine metal mask manufacturing technology, and specifically relates to an etching method for metal masks. Background Technology

[0002] Currently, Organic Light Emitting Diode (OLED) display panels are a type of panel that uses OLEDs as display pixels. Compared to traditional LCD panels, OLED display panels are becoming increasingly popular in the market due to their numerous advantages, such as self-illumination, low power consumption, excellent color performance, and applicability to flexible displays.

[0003] OLED light-emitting devices are generally fabricated by vapor-depositing organic materials onto a substrate. Vapor deposition of organic materials typically requires a mask. Masks primarily serve as pattern transfer masters and are typically customized. Masks are divided into photomasks (photomasks) and metal masks (shadow masks). Photomasks are mainly used in photolithography processes, are made of high-purity quartz glass, and are used to create circuit patterns. Fine metal masks (FMMs) are a key component in OLED display manufacturing, primarily used for the precise deposition of organic materials to form pixel patterns.

[0004] Traditional FMM etching process typically employs a double-sided etching process. A typical process flow is as follows: raw material cleaning → lamination (coating photoresist) → exposure (patterning) → development → small hole surface (single-sided) etching to form an opening → small hole surface opening protection → large hole surface (single-sided) etching to form an opening → wafer separation → finished product.

[0005] Researchers discovered that in traditional FMM etching processes, during large-aperture etching, the etchant not only etches the metal vertically downwards but also laterally corrodes the already formed hole walls. As the aperture size and aspect ratio increase, the undercut increases significantly, severely affecting the accuracy of the aperture pattern and limiting the fabrication capability of high-resolution FMM products.

[0006] Therefore, there is an urgent need to provide an etching method for metal photomasks that can improve the accuracy of the opening pattern. Summary of the Invention

[0007] In view of this, this application provides an etching method for metal masks, which belongs to the high-precision etching process for metal foils. It is particularly suitable for improving the side etching problem of high-resolution, high aspect ratio etched patterns, increasing the etch factor, and improving the accuracy of the opening pattern.

[0008] The technical solution provided in this application is as follows:

[0009] An etching method for a metal mask involves forming large holes on a first surface of a substrate through the following steps:

[0010] S1, a first opening is formed on the first surface of the substrate;

[0011] S2, an oxide film with gradually varying thickness is formed on the surface of the first opening;

[0012] S3, etch the first opening to form the large hole, the opening angle of the large hole being in the range of 40°~65°.

[0013] In one embodiment, the formation process of the oxide film with gradually varying thickness includes:

[0014] S201, the substrate with the first opening is immersed in a first working tank, and the surface of the substrate is brought into full contact with an acidic solution of a first concentration, wherein the first working tank contains the acidic solution of the first concentration;

[0015] S202, the substrate immersed in the first working tank is subjected to roller sensing to remove the acidic solution with a first concentration from the surface of the substrate, and then moved to the second working tank, the second working tank containing an acidic solution with a second concentration, the second concentration being greater than the first concentration;

[0016] S203, the first surface is sprayed with the acidic solution of the second concentration so that the growth rate of the oxide film on the sidewall of the first opening is greater than the growth rate on the bottom wall of the first opening, thereby forming the oxide film with a gradually varying thickness.

[0017] In one embodiment, during step S201, when the surface of the substrate is in full contact with an acidic solution of a first concentration, the following parameters are used:

[0018] The acidic solution with the first concentration is concentrated nitric acid with a concentration of 20% to 35%, the sufficient contact temperature is 20°C to 30°C, and the sufficient contact time is 5 minutes to 8 minutes.

[0019] In one embodiment, in S203, when the first surface is sprayed with the acidic solution having a second concentration, the following parameters are used:

[0020] The acidic solution with the second concentration is concentrated nitric acid with a concentration of 35% to 50%, the spray pressure is 0.1 MPa to 0.3 MPa, the temperature of the acidic solution with the second concentration in the second working tank is 35°C to 50°C, and the reaction time of the acidic solution with the second concentration is 15 minutes to 45 minutes.

[0021] In one embodiment, the thickness of the oxide film located on the sidewall of the first opening is d1, and the thickness of the oxide film located on the bottom wall of the first opening is d2, with a thickness difference... Within the range of 2nm to 6nm.

[0022] In one embodiment, as the oxide film gradually decreases from the two sidewalls of the first opening to the center of the bottom wall of the first opening, the thickness of the oxide film located on the bottom wall of the first opening is 1 nm to 2 nm; the thickness of the oxide film located on the sidewall of the first opening is 4 nm to 8 nm.

[0023] In one embodiment, the oxide film with gradually varying thickness comprises oxides formed by metallic elements in the Invar alloy substrate, including Fe2O3 and NiO.

[0024] In one embodiment, the maximum depth of the first opening is set to 0.2*d1~0.3*d1, where d1 is the depth of the large hole in the metal mask.

[0025] In one embodiment, the thickness of the substrate is 15 micrometers to 35 micrometers, and the substrate is an Invar alloy material.

[0026] In one embodiment, when etching the first opening in step S3, the etching solution is a ferric chloride solution, the etching temperature is 25℃~40℃, and the etching time is 10 minutes~25 minutes.

[0027] The solution provided in this application has the following beneficial effects:

[0028] In this embodiment, an oxide film with gradually varying thickness is first formed on the surface of the first opening, and then the first opening is etched. The resulting large hole has extremely high etch factor and perpendicularity, reduces lateral etching, significantly increases the etch factor, and has an opening angle in the range of 40° to 65°. Furthermore, because high-resolution metal mask products have high pattern opening density, at low etch factors, large lateral etching can easily lead to insufficient structural strength between pixel holes in the metal mask. When the technical solution in this embodiment is adopted, the etch factor is increased, significantly improving the high-resolution metal mask's resistance to breakage and reducing production defects caused by breakage.

[0029] In this embodiment, the metal mask etching method provides active and precise control over the sidewall etching profile by forming an oxide film with gradually varying thickness. Compared to traditional uniform protective films that can only suppress lateral etching (generating vertical sidewalls), this method actively guides the etching direction in subsequent etching by adjusting the different thicknesses of the oxide film in specific regions (the sidewall or bottom wall of the first opening). This enables the reliable and repeatable fabrication of holes with large opening angles of 40° to 65° on Invar alloy substrates, solving the problem that traditional processes struggle to form controllable conical holes in a single etching operation.

[0030] In this embodiment, by forming an oxide film with gradually varying thickness, the verticality and consistency of the aperture shape are significantly improved. Since the oxide film with varying thickness provides the strongest protection at the root of the sidewall and the weakest at the opening, during the subsequent second etching of the large aperture surface, the etching solution naturally performs slight lateral etching downwards from the opening, forming a smooth and uniform positive taper. This effectively eliminates defects such as undercut and "flared" edges caused by uneven etching solution attack, resulting in steep and smooth opening sidewalls, and significantly improving the pattern fidelity and deposition accuracy of the FMM.

[0031] In this embodiment, a protective layer gradient model is constructed by limiting the thickness of the oxide film to gradually decrease from the sidewall to the center of the bottom wall. This structure ensures that in subsequent etching (secondary etching), the etchant has the strongest attack on the bottom wall, while the protection of the sidewall increases with the height of the sidewall (i.e., the protection is strongest at the root of the sidewall). This differentiated etching rate can actively guide the etching direction, accurately "carve" the sidewall contour, and achieve an opening angle of 40°~65°, effectively avoiding the problems of vapor deposition shadows caused by too small an angle or pattern distortion caused by too large an angle.

[0032] In this embodiment, a dual-tank acid treatment process of "immersion-drying transfer-immersion + spraying" is used to achieve selective growth of oxide films on a three-dimensional structure. The initial immersion stage generates a uniform oxide film substrate across the entire surface; while the subsequent directional spraying of high-concentration acid utilizes fluid dynamics principles to ensure that the sidewalls continuously contact and react with newer, higher-concentration acid compared to the bottom wall, thereby actively promoting a higher oxide film formation rate on the sidewalls than on the bottom wall. This process offers strong controllability and good film uniformity, providing an efficient and reliable implementation scheme for the large-scale, stable preparation of gradient oxide films.

[0033] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figures 1A, 1B, 1C, and 1D are schematic diagrams of steps 1, 2, 3, and 4 in the traditional method for preparing a metal photomask.

[0036] Figure 2 is a schematic diagram of an etching method for a metal mask provided in an embodiment of this application;

[0037] Figure 3 is a comparative schematic diagram of the large-aperture surface of the metal mask formed using the prior art and the technical solution of this application;

[0038] Figure 4 is a confocal microscope image of the metal mask plate forming Comparative Example 1 prepared using the existing technology.

[0039] Figure 5A is a confocal microscope image of the large-aperture surface of the metal mask formed by the etching method of the metal mask described in Example 1.

[0040] Figure 5B is a confocal microscope image of the large-aperture surface of the metal mask formed by the etching method of the metal mask described in Example 2.

[0041] Figure 5C is a confocal microscope image of the large-aperture surface of the metal mask formed by the etching method of the metal mask described in Example 3.

[0042] Figure 6 is a schematic SEM scan of the large-aperture surface of the metal mask plate of Comparative Example 1 prepared using the existing technical solution.

[0043] Figure 7 is a schematic SEM scan of the large-aperture surface of the metal mask formed by the etching method of the metal mask described in Example 2. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0045] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0046] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0047] In the description of this application, it should be noted that the terms "inner," "outer," "upper," "lower," "vertical," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0048] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, features in the following embodiments can be combined with each other.

[0049] In view of the shortcomings of the prior art, the technical solution of this application is proposed. The technical solution of this application will be described in detail below.

[0050] Please refer to Figures 1A, 1B, 1C, and 1D for the traditional method of fabricating a metal photomask, which includes the following process steps:

[0051] Step 1, as shown in Figure 1A, involves pretreatment and patterning / processing of the aperture surface. A 20μm thick Invar alloy foil is provided. After cleaning and drying, it is sequentially laminated, exposed, and developed on both sides to form a photoresist mask pattern that meets design requirements. Subsequently, the side defining the pixel aperture size (the second surface) is etched to form a single-sided blind aperture.

[0052] Step 2, as shown in Figure 1B, involves protecting the small-hole surface. After etching the small-hole surface, a peelable polymer protective adhesive is used to completely cover and cure the surface to prevent the etching solution from damaging or contaminating the pattern formed on the small-hole surface during subsequent large-hole etching.

[0053] Step 3, as shown in Figure 1C, involves etching the large-aperture surface. After the small-aperture surface is protected, the other side (the first surface) defining the pixel opening size is etched to form a large-aperture. Once the small-aperture surface is unprotected, a mask via is formed.

[0054] Step 4, as shown in Figure 1D, involves subsequent processing. After all etching is completed, the protective adhesive and photoresist on the workpiece surface are removed. Then, the workpiece is sliced ​​and inspected to obtain the finished FMM.

[0055] The etching method for metal masks involved in this application mainly focuses on the improvement of the etching step for large-hole surfaces in step 3.

[0056] Referring to Figure 2, this application provides an etching method for a metal mask, which involves forming large holes on a first surface of a substrate through the following steps. The substrate can be Invar alloy foil or other materials used to prepare the metal mask. The metal mask has large holes and small holes (the large holes and small holes are holes used to form specific pixel images during the vapor deposition of organic materials) on two surfaces of the substrate, respectively. The large holes and small holes have through-holes that penetrate the substrate for vapor deposition of organic materials.

[0057] S1, A first opening is formed on the first surface of the substrate. In this step, the first opening of a specific size can be formed by etching the first surface of the substrate in one step.

[0058] In some embodiments of this step, the maximum depth of the first opening can be controlled to be 0.2*d1~0.3*d1, where d1 is the opening depth of the large hole in the metal mask. By controlling the maximum depth of the first opening, the stability of the etching process and the accuracy of the hole shape control can be controlled.

[0059] In this step, when forming the first opening, only a portion of the substrate on the first surface needs to be removed, leaving enough substrate for subsequent shaping of the large hole. This reduces etching time and chemical consumption, while also lowering the risk of undercut, thus balancing etching efficiency and precision.

[0060] If the maximum depth of the first opening is not within the range of 0.2*d1~0.3*d1, if it is less than 0.2*d1, it means that the sidewall area is small, resulting in insufficient protection during S3 etching, intensified lateral etching, and the opening angle of the large hole is less than 40°; if it is greater than 0.3*d1, and because the thickness of the substrate itself is thin (generally only 15 micrometers~35 micrometers), the etching of S3 is not easy to control, and over-etching is very likely to occur.

[0061] Therefore, the maximum depth of the first opening can be set to 0.2*d1~0.3*d1. The first opening provides a sufficient surface area so that the oxide film formed in subsequent steps can form a protective layer on the sidewall, avoiding insufficient or excessive local protection, thereby precisely controlling the etching direction.

[0062] S2, an oxide film of gradually varying thickness is formed on the surface of the first opening. In this step, forming an oxide film of gradually varying thickness is to create a larger opening angle on the first surface of the substrate. In this step, the oxide film acts as a protective layer, guiding the etchant to preferentially attack the bottom wall of the first opening during subsequent etching, thereby forming the opening angle required for a large hole. In this step, the oxide film of gradually varying thickness can be understood as the thickness of the oxide film gradually decreasing from the two sidewalls of the first opening towards the bottom wall. The oxide film of gradually varying thickness comprises oxides formed by metallic elements in the Invar alloy substrate, and can be a metal oxide film, such as an Fe2O3 film and / or a NiO film.

[0063] S3, the first opening is etched to form a macropore with an opening angle in the range of 40° to 65°. In this step, the gradually varying thickness of the oxide film during etching of the first opening significantly reduces the risk of undercut, resulting in a significantly higher etching rate for the bottom wall of the first opening compared to the side walls, thus balancing etching efficiency and precision. During this step, the etching solution rapidly and vertically etches the metal of the bottom wall of the first opening, which is protected by a thin oxide film, while etching the side walls, which are protected by a thicker oxide film, is extremely slow. This mechanism forces the etching reaction to proceed primarily downwards, thereby minimizing undercut and effectively increasing the etching factor to form near-vertical etched side walls. In one embodiment, in step S3, the etching solution for etching the first opening is a ferric chloride solution, the etching temperature is 25°C to 40°C, and the etching time is 10 to 25 minutes.

[0064] In this embodiment, an oxide film with gradually varying thickness is first formed on the surface of the first opening, and then the first opening is etched. The resulting large hole has an extremely high etching factor and perpendicularity, with reduced lateral etching and a significantly increased etching factor. The opening angle is within the range of 40° to 65°. Furthermore, because high-resolution metal mask products have high pattern opening density, a large lateral etching at a low etching factor can easily lead to insufficient structural strength between pixel holes in the metal mask. By adopting the technical solution in this embodiment, the etching factor is increased, significantly improving the high-resolution metal mask's resistance to breakage and reducing production defects caused by breakage.

[0065] In one embodiment, the oxide film with gradually decreasing thickness includes an oxide film whose thickness gradually decreases as it transitions from the two sidewalls of the first opening to the center of the bottom wall of the first opening.

[0066] In this embodiment, the provided etching method for a metal mask achieves active and precise control over the sidewall etching profile by forming an oxide film with gradually varying thickness. Compared to traditional uniform protective films that can only suppress lateral etching (generating vertical sidewalls), this method actively guides the etching direction in subsequent etching by adjusting the different thicknesses of the oxide film in specific regions (the sidewall or bottom wall of the first opening). This enables the reliable and repeatable fabrication of holes with large opening angles of 40° to 65° on Invar alloy substrates, solving the problem that traditional processes struggle to form controllable conical holes in a single etching operation.

[0067] In this embodiment, by forming an oxide film with gradually varying thickness, the verticality and consistency of the aperture shape are significantly improved. Since the oxide film with varying thickness has the strongest protection at the root of the sidewall and the weakest at the opening, during the subsequent second etching of the large aperture surface, the etching solution will naturally perform slight lateral etching from the opening downwards, forming a smooth and uniform positive taper. This effectively eliminates defects such as undercut and "trumpet mouth" caused by uneven etching solution attack, making the opening sidewalls steep and smooth, and greatly improving the pattern fidelity and evaporation accuracy of the FMM.

[0068] In one embodiment, the oxide film with gradually decreasing thickness includes an oxide film whose thickness gradually decreases as it transitions from the two sidewalls of the first opening to the center of the bottom wall of the first opening.

[0069] In this embodiment, a protective layer gradient model is constructed by limiting the thickness of the oxide film to gradually decrease from the sidewall to the center of the bottom wall. This structure ensures that in subsequent etching (secondary etching), the etchant has the strongest attack on the bottom wall, while the protection of the sidewall increases with the height of the sidewall (i.e., the protection is strongest at the root of the sidewall). This differentiated etching rate can actively guide the etching direction, accurately "carve" the sidewall contour, and achieve an opening angle of 40°~65°, effectively avoiding the problems of vapor deposition shadows caused by too small an angle or pattern distortion caused by too large an angle.

[0070] In one embodiment, the formation process of an oxide film with gradually varying thickness includes:

[0071] S201, the substrate with the first opening is immersed in the first working tank and the surface of the substrate is brought into full contact with the acidic solution with the first concentration. The first working tank contains the acidic solution with the first concentration.

[0072] S202, the substrate immersed in the first working tank is subjected to a roller sensor to remove the acidic solution with a first concentration from the surface of the substrate, and then moved to the second working tank, which contains an acidic solution with a second concentration, which is greater than the first concentration.

[0073] In step S203, an acidic solution of a second concentration is sprayed onto the first surface to ensure that the growth rate of the oxide film on the sidewall of the first opening is greater than that on the bottom wall of the first opening, thereby forming an oxide film with a gradually varying thickness. In this step, the fluidity of the acidic solution of the second concentration differs between the sidewall and the bottom wall of the first opening. Therefore, the oxide film formation rates differ between the sidewall and the bottom wall of the first opening, with the less fluid solution at the sidewall, which is more conducive to the reaction between the acidic solution and the alloy, resulting in a thicker oxide film.

[0074] In this embodiment, a dual-tank acid treatment process of "immersion-drying transfer-immersion + spraying" is used to achieve selective growth of the oxide film on a three-dimensional structure. The initial immersion stage generates a uniform oxide film substrate across the entire surface; while the subsequent directional spraying of high-concentration acid utilizes fluid dynamics principles to ensure that the sidewalls continuously contact and react with newer, higher-concentration acid compared to the bottom wall, thereby actively promoting a higher oxide film formation rate on the sidewalls than on the bottom wall. This process offers strong controllability and good film uniformity, providing an efficient and reliable implementation scheme for the large-scale, stable preparation of gradient oxide films.

[0075] In one embodiment, in S201, when the surface of the substrate is in full contact with an acidic solution of a first concentration, the following parameters are used: the acidic solution of the first concentration is concentrated nitric acid with a concentration of 20% to 35%; the full contact temperature is 20°C to 30°C; and the full contact time is 5 minutes to 8 minutes. Specifically, the acidic solution of the first concentration can be concentrated nitric acid with a concentration of 23%, 25%, 27%, 29%, or 30%. The full contact temperature can be set to room temperature, 25°C, 28°C, or 30°C. The full contact time can be set to 5 minutes or 7 minutes.

[0076] In this embodiment, by precisely defining the concentration, temperature, and processing time of the acidic solution in the first working tank, an optimal window for oxide film substrate formation is established. A concentrated nitric acid concentration of 20%–35%, combined with room temperature (20°C–30°C) and a processing time of 5–8 minutes, can form a dense and moderately thick initial oxide layer on the Invar alloy surface. This provides good basic protection while avoiding the difficulties in subsequent process adjustments caused by an excessively thick oxide film. These parameters collectively ensure the high quality and batch-to-batch consistency of the initial film, laying a solid foundation for the subsequent formation of a precise thickness gradient.

[0077] In one embodiment, in S203, when spraying the first surface with an acidic solution of a second concentration, the following parameters are used: the acidic solution of the second concentration is concentrated nitric acid with a concentration of 35% to 50%; the spraying pressure is 0.1 MPa to 0.3 MPa; the temperature of the acidic solution of the second concentration in the second working tank is 35°C to 50°C; and the reaction time of the acidic solution of the second concentration is 15 minutes to 45 minutes. Specifically, the acidic solution of the second concentration can be concentrated nitric acid with a concentration of 35%, 37%, 40%, 43%, 46%, or 50%. The spraying pressure can be set to 0.1 MPa, 0.2 MPa, or 0.3 MPa. The sufficient contact temperature can be set to 35°C, 38°C, 42°C, 46°C, or 49°C. The sufficient contact time can be set to 18 minutes, 24 minutes, 30 minutes, 36 minutes, 40 minutes, or 43 minutes.

[0078] In this embodiment, the formation process of the gradient oxide film was precisely controlled by limiting the spray parameters of the second working tank. A relatively high acid concentration of 35%–50%, a heating environment of 35°C–50°C, and a spray pressure of 0.1 MPa–0.3 MPa together created reaction conditions that promoted the selective and rapid growth of the sidewall film. The increased temperature accelerated the reaction rate, the spray pressure ensured continuous flushing and renewal of the sidewalls by the fresh acidic solution, and the reaction time of 15–45 minutes guaranteed sufficient gradient formation. This combination of parameters significantly improved the contrast and uniformity of the gradient oxide film, thereby ultimately optimizing the etch morphology of the macropores.

[0079] In one embodiment, the elemental composition ratio of the thin film on the surface of the first opening is measured by XPS analysis to determine the oxide film thickness on the sidewall and bottom wall of the first opening, respectively. The thickness of the oxide film on the sidewall of the first opening is d1, and the thickness of the oxide film on the bottom wall of the first opening is d2, with a thickness difference of... Within the range of 2nm to 6nm. In different embodiments, an oxide film with a gradient thickness on the surface of the first opening is fabricated, and the difference in oxide film thickness between the sidewalls and the bottom can be 2nm, 3nm, 4nm, 5nm, or 6nm.

[0080] In this embodiment, by limiting the thickness difference between the sidewall and bottom oxide films to a precise range of 2nm to 6nm, an optimal balance between protection and etching is achieved. This thickness difference ensures that, during subsequent etching, there is a sufficiently significant difference in etching rate between the bottom and sidewalls to effectively drive the etching direction vertically downwards, thereby keeping the undercut at an extremely low level. Simultaneously, this moderate difference avoids the problem of uneven sidewall contours that may be caused by an excessively steep gradient, contributing to the formation of steep and smooth hole walls and significantly improving the etching factor.

[0081] In one embodiment, the thickness of the oxide film located on the bottom wall of the first opening is 1 nm to 2 nm; the thickness of the oxide film located on the side wall of the first opening is 4 nm to 8 nm.

[0082] In this embodiment, the absolute range of the generated oxide film thickness is further clarified, namely 1nm~2nm for the bottom wall and 4nm~8nm for the sidewalls. The extremely thin bottom wall oxide film (1nm~2nm) minimizes its obstruction to vertical etching, ensuring etching efficiency; while the sufficiently thick sidewall oxide film (4nm~8nm) provides robust and reliable protection, effectively resisting the lateral attack of the etching solution. This combination achieves a state of "nearly unobstructed bottom and robust sidewall protection" at the molecular level, representing a superior process window for achieving high etching factors and excellent aperture angles.

[0083] In one embodiment, the substrate may be made of Invar alloy material. The thickness of the substrate may be set to 15 micrometers to 35 micrometers, and in some embodiments, the thickness of the substrate is set to 20 micrometers to 30 micrometers, such as in one embodiment where the thickness of the substrate is set to 28 micrometers.

[0084] Please refer to Figure 3, which shows a comparison of the large-aperture surfaces of metal masks formed using the prior art and the technical solution of this application. It can be clearly seen that, under the premise that the opening depth of the large aperture is the same, the opening angle θ1 of the large aperture formed in the prior art is less than the opening angle θ2 of the large aperture formed in this solution.

[0085] Please refer to Table 1 below. To verify the technical effect, this application provides the following Comparative Example 1, Example 1, Example 2, and Example 3. In Examples 1 to 3, the maximum depth of the first opening is selected to be equal to 0.25*d1. In the three embodiments provided by this application, the thickness of the oxide film forming a complete surface on the surface of the first opening is different, and the opening angle of the final macropore is different, but all are greater than 40° (and the opening angle of the final macropore formed in the three different embodiments is greater than the opening angle of the final macropore formed in Comparative Example 1).

[0086] Comparative Example 1: The steps for etching the large-hole surface include:

[0087] Provide Invar alloy substrate;

[0088] On the first surface of the Invar alloy substrate, a 37% ferric chloride solution was used to etch the macropores to a predetermined opening depth d1 for 35 minutes. As shown in Table 1, the final opening angle of the macropores formed on the first surface of the Invar alloy substrate was 28°.

[0089] Example 1: The steps for etching the large-hole surface include:

[0090] Provide Invar alloy substrate;

[0091] A first opening is formed on the first surface of the Invar alloy substrate, and the depth of the first opening is 25% of the preset opening depth d1 of the macrohole;

[0092] An oxide film of gradually varying thickness is formed on the surface of the first opening. Specifically, this includes:

[0093] S201, the substrate with the first opening is immersed in the first working tank, and the surface of the substrate is brought into full contact with a 28% concentrated nitric acid solution at a temperature of 25°C for 5 minutes. The first working tank contains a 28% concentrated nitric acid solution, which can submerge the substrate.

[0094] S202, the substrate immersed in the first working tank is subjected to roller induction to remove the 28% concentrated nitric acid solution from the surface of the substrate, and then moved to the second working tank, which contains a 36% concentrated nitric acid solution.

[0095] S203, a 36% concentrated nitric acid solution is sprayed onto the first surface at a pressure of 0.3 MPa. The temperature in the second working tank is 45°C, and the reaction time is 25 minutes. In this embodiment, the growth rate of the oxide film on the sidewall of the first opening is greater than that on the bottom wall of the first opening, thus forming an oxide film with a gradually changing thickness. In this embodiment, the thickness difference between the oxide film thickness d1 on the sidewall of the first opening and the oxide film thickness d2 on the bottom wall of the first opening is... It is 2nm.

[0096] On the surface of the first opening where an oxide film of gradually varying thickness is formed, a 40% ferric chloride solution is used for etching at a preset opening depth d1 for 10 minutes to form the macropore. As shown in Table 1 below, the final opening angle of the macropore formed on the first surface of the Invar alloy substrate is 40°.

[0097] Example 2: The steps for etching the large-hole surface include:

[0098] Provide Invar alloy substrate;

[0099] A first opening is formed on the first surface of the Invar alloy substrate, and the depth of the first opening is 25% of the preset opening depth d1 of the macrohole;

[0100] An oxide film of gradually varying thickness is formed on the surface of the first opening. Specifically, this includes:

[0101] S201, the substrate with the first opening is immersed in the first working tank, and the surface of the substrate is brought into full contact with a 28% concentrated nitric acid solution at a temperature of 25°C for 5 minutes. The first working tank contains a 28% concentrated nitric acid solution, which can submerge the substrate.

[0102] S202, the substrate immersed in the first working tank is subjected to roller induction to remove the 28% concentrated nitric acid solution from the surface of the substrate, and then moved to the second working tank, which contains a 36% concentrated nitric acid solution.

[0103] S203, a 36% concentrated nitric acid solution is sprayed onto the first surface at a pressure of 0.3 MPa. The temperature in the second working tank is 48°C, and the reaction time is 30 minutes. In this embodiment, the growth rate of the oxide film on the sidewall of the first opening is greater than that on the bottom wall of the first opening, thus forming an oxide film with a gradually changing thickness. In this embodiment, the thickness difference between the oxide film thickness d1 on the sidewall of the first opening and the oxide film thickness d2 on the bottom wall of the first opening is... It is 4nm.

[0104] On the surface of the first opening where an oxide film of gradually varying thickness is formed, a 40% ferric chloride solution is used for etching at a preset opening depth d1 for 10 minutes to form the macropore. As shown in Table 1 below, the final opening angle of the macropore formed on the first surface of the Invar alloy substrate is 50°.

[0105] Example 3: The steps for etching the large-hole surface include:

[0106] Provide Invar alloy substrate;

[0107] A first opening is formed on the first surface of the Invar alloy substrate, and the depth of the first opening is 25% of the preset opening depth d1 of the macrohole;

[0108] An oxide film of gradually varying thickness is formed on the surface of the first opening. Specifically, this includes:

[0109] S201, the substrate with the first opening is immersed in the first working tank, and the surface of the substrate is brought into full contact with a 28% concentrated nitric acid solution at a temperature of 25°C for 5 minutes. The first working tank contains a 28% concentrated nitric acid solution, which can submerge the substrate.

[0110] S202, the substrate immersed in the first working tank is subjected to roller induction to remove the 28% concentrated nitric acid solution from the surface of the substrate, and then moved to the second working tank, which contains a 36% concentrated nitric acid solution.

[0111] S203, a 36% concentrated nitric acid solution is sprayed onto the first surface at a pressure of 0.3 MPa. The temperature in the second working tank is 48°C, and the reaction time is 40 minutes. In this embodiment, the growth rate of the oxide film on the sidewall of the first opening is greater than that on the bottom wall of the first opening, thus forming an oxide film with a gradually changing thickness. In this embodiment, the thickness difference between the oxide film thickness d1 on the sidewall of the first opening and the oxide film thickness d2 on the bottom wall of the first opening is... It is 6nm.

[0112] On the surface of the first opening where an oxide film of gradually varying thickness is formed, a 40% ferric chloride solution is used for etching at a preset opening depth d1 for 10 minutes to form the macropore. As shown in Table 1 below, the final opening angle of the macropore formed on the first surface of the Invar alloy substrate is 65°.

[0113] Table 1 shows the experimental parameters for a comparative example and three embodiments:

[0114]

[0115] Please refer to Figures 4, 5A, 5B, and 5C, which are confocal microscope images of the large-aperture surfaces of metal masks formed using the etching methods of Comparative Example 1, Example 1, Example 2, and Example 3, respectively. In Figure 4 formed using the method of Comparative Example 1, the black area represents the large-aperture area, and the opening angle of the large-aperture is θ1. In Figure 5A formed using the method of Example 1, the black area represents the large-aperture area, and the opening angle of the large-aperture is θ21. In Figure 5B formed using the method of Example 2, the black area represents the large-aperture area, and the opening angle of the large-aperture is θ22. In Figure 5C formed using the method of Example 3, the black area represents the large-aperture area, and the opening angle of the large-aperture is θ23. Comparing Figures 4, 5A, 5B, and 5C, it is clear that the opening angle of the large-aperture is θ1 < θ21 < θ22 < θ23. It can be seen that the metal mask prepared by the etching method of the metal mask involved in the embodiments of this application has a larger opening angle for the large holes.

[0116] Please refer to Figures 6 and 7. Figure 6 is a SEM scan diagram of the large-aperture surface of the metal mask prepared using the technical solution of Comparative Example 1 in the prior art, with the corresponding large-aperture opening angle θ1 being 28°. Figure 7 is a SEM scan diagram of the large-aperture surface of the metal mask prepared using the etching method of the metal mask in Example 2, with the corresponding large-aperture opening angle θ22 being 50°. The comparison of the large-aperture opening angles in Figures 6 and 7 is obvious. The metal mask prepared using the technical solution in this application can stably and repeatedly prepare large-aperture structures with steep sidewalls, excellent morphology, and flexible adjustable angles between 40° and 65°. This completely solves the industry problems of severe side etching, inconsistent hole shapes, and difficulty in precise control in traditional processes, providing a key guarantee for the performance improvement and reliable manufacturing of high-resolution metal masks.

[0117] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application. It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0118] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for etching a metal photomask, characterized in that, A macropore is formed on the first surface of a substrate by the following steps: S1, forming a first opening on the first surface of the substrate; S2, forming an oxide film with a gradually varying thickness on the surface of the first opening; the thickness of the oxide film gradually decreases from the two sidewalls of the first opening to the center of the bottom wall of the first opening; S3, etching the first opening to form the macropore, the opening angle of the macropore being in the range of 40° to 65°; the oxide film formation process includes: S201, immersing the substrate with the first opening formed in a first working tank, and exposing the surface of the substrate to an acid with a first concentration. The solution is fully in contact with the substrate, and the first working tank contains the acidic solution with a first concentration; S202, the substrate immersed in the first working tank is subjected to roller induction to remove the acidic solution with the first concentration from the surface of the substrate, and is moved to the second working tank, the second working tank containing the acidic solution with a second concentration, the second concentration being greater than the first concentration; S203, the first surface is sprayed with the acidic solution with the second concentration, so that the growth rate of the oxide film on the sidewall of the first opening is greater than the growth rate on the bottom wall of the first opening, thereby forming the oxide film with a gradually changing thickness.

2. The etching method for a metal mask according to claim 1, characterized in that, In S201, when the surface of the substrate is in full contact with an acidic solution of a first concentration, the following parameters are used: the acidic solution of the first concentration is concentrated nitric acid with a concentration of 20% to 35%, the full contact temperature is 20°C to 30°C, and the full contact time is 5 minutes to 8 minutes.

3. The etching method for a metal mask according to claim 1, characterized in that, In S203, when the first surface is sprayed with the acidic solution of the second concentration, the following parameters are used: the acidic solution of the second concentration is concentrated nitric acid with a concentration of 35% to 50%, the spraying pressure is 0.1 MPa to 0.3 MPa, the temperature of the acidic solution of the second concentration in the second working tank is 35°C to 50°C, and the reaction time of the acidic solution of the second concentration is 15 minutes to 45 minutes.

4. The etching method for a metal mask according to claim 1, characterized in that, The thickness of the oxide film located on the sidewall of the first opening is d1, and the thickness of the oxide film located on the bottom wall of the first opening is d2, with the thickness difference ranging from 2nm to 6nm.

5. The etching method for a metal mask according to claim 1, characterized in that, The oxide film located on the bottom wall of the first opening has a thickness of 1 nm to 2 nm; the oxide film located on the side wall of the first opening has a thickness of 4 nm to 8 nm.

6. The etching method for a metal mask according to claim 1, characterized in that, The oxide film with gradually varying thickness comprises oxides formed by metallic elements in the Invar alloy substrate, including Fe2O3 and NiO.

7. The etching method for a metal mask according to claim 1, characterized in that, The maximum depth of the first opening is set to 0.2*d1~0.3*d1, where d1 is the depth of the large hole in the metal mask.

8. The etching method for a metal mask according to claim 1, characterized in that, The thickness of the substrate is 15 micrometers to 35 micrometers, and the substrate is an Invar alloy material.

9. The etching method for a metal mask according to claim 1, characterized in that, In step S3, when etching the first opening, the etching solution is ferric chloride solution, the etching temperature is 25℃~40℃, and the etching time is 10 minutes~25 minutes.

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