Metal mask and method for manufacturing a metal mask

Abstract

The application discloses a metal mask plate and a manufacturing method of the metal mask plate, and the metal mask plate is used for evaporating and depositing an organic light-emitting layer of an OLED device. The metal mask plate comprises a mask plate body, a plurality of mask holes are formed on the mask plate body, the mask plate body comprises a first surface and a second surface which are opposite to each other, the mask holes penetrate through the first surface and the second surface, the mask holes form first openings on the first surface, the mask holes form second openings on the second surface, and the ratio of the aperture of the first opening to the aperture of the second opening is between 1 and 1.5. The metal mask plate has the characteristics of high tensile strength and high resolution.

Description

Technical Field

[0001] This invention relates to the field of photomask manufacturing technology, specifically to a metal photomask and a method for manufacturing a metal photomask. Background Technology

[0002] In the commercial mass production methods of Organic Light Emitting Diode (OLED), vapor deposition is currently the mainstream technology. The vapor deposition process requires the use of a fine metal mask (FMM) to deposit the light-emitting layer of the OLED device. The quality of the fine metal mask determines the quality of the OLED screen it manufactures.

[0003] Currently, AMOLED (Active Matrix Organic Light Emitting Diode) products are mainly limited to resolutions below 600ppi, with display sizes ranging from 5 to 17 inches (foldable screens). This corresponds to the required red, green, and blue sub-pixel sizes of approximately 30 to 100 μm. To manufacture higher resolution screens, higher resolution precision metal masks must be used. Improving the resolution of these precision metal masks often involves reducing the spacing between adjacent apertures. Reducing the spacing between adjacent apertures places high demands on the thickness and thermal expansion coefficient of the foil material.

[0004] However, existing precision metal photomasks have the problem that the foil used in their manufacture cannot meet the requirements for producing high-resolution photomasks. Summary of the Invention

[0005] The present invention aims to provide a metal photomask and a method for manufacturing a metal photomask, which has the advantages of low coefficient of thermal expansion, good flatness, and high resolution.

[0006] To achieve the above objectives, a first aspect of the present invention discloses a metal mask for evaporating and depositing an organic light-emitting layer for an OLED device. The metal mask includes a mask body with a plurality of mask holes formed thereon. The mask body includes a first surface and a second surface opposite to each other. The mask holes penetrate the first surface and the second surface. The mask holes form a first opening on the first surface and a second opening on the second surface. The ratio of the aperture of the second opening to the aperture of the first opening is between 1 and 1.5.

[0007] When the apertures of the first and second openings are close, the pixel density of the first surface can be increased without affecting the pixel density of the second surface, significantly reducing the distance between adjacent apertures and increasing ppi (pixels per inch).

[0008] Optionally, the mask aperture has a stepped portion formed on the side near the first surface, the diameter of the stepped portion being larger than the aperture of the first opening, and the stepped portion being closer to the first surface relative to the first opening.

[0009] Optionally, the difference between the diameter of the stepped portion and the aperture of the first opening is less than or equal to 0.5 μm, and the height of the stepped portion is less than or equal to 0.5 μm.

[0010] The smaller the step height, the smaller the shadow area generated during the vapor deposition process, which can reduce the mura defects (local uneven brightness or color defects that occur during screen display).

[0011] Optionally, the aperture of the first opening is between 5 and 20 μm.

[0012] Optionally, the resolution of the metal mask is between 600 and 1500 ppi.

[0013] Optionally, the thickness of the metal mask is less than or equal to 20 μm.

[0014] A metal mask with a thickness of 20 μm or less can increase the upper limit of ppi for FMM products.

[0015] A second aspect of the present invention discloses a method for manufacturing a metal photomask, comprising the following steps: The substrate is placed in an electroforming solution for electrodeposition to form a first foil on the substrate; Separate the first foil from the substrate; The first foil is heat-treated to obtain a second foil; wherein the proportion of the body-centered cubic structure of the second foil does not exceed a set proportion. The second foil is etched to obtain a metal mask.

[0016] A first foil is formed by electrodeposition on a substrate, providing a deposition platform that allows the first foil to be shaped into a sheet. During the electrodeposition and separation steps, stress accumulates within the first foil. Without treatment, this stress will affect subsequent processing, specifically reducing the lifespan of the first foil or making it more prone to deformation. Furthermore, the first foil has a relatively high coefficient of thermal expansion, thus requiring heat treatment. In the heat treatment step, the first foil is heated to a certain temperature, causing changes in its crystal structure and balancing uneven stress. Maintaining this high temperature for a certain period allows for atomic rearrangement, promoting stress release. Finally, gradual cooling reduces thermal stress caused by temperature changes, preventing the generation of new residual stress and thus improving the foil's flatness. A second objective of the heat treatment step is to promote the transformation of the body-centered cubic structure to a face-centered cubic structure under high-temperature conditions, reducing the foil's coefficient of thermal expansion.

[0017] Optionally, the average coefficient of thermal expansion of the second foil at 20~200°C is less than or equal to 2 ppm / K.

[0018] Optionally, the first foil is subjected to heat treatment, including: applying a set tension to the first foil, wherein the set tension is between 5-1500 N / mm²; In a protective atmosphere, the first foil material with the set tension applied is heated to a set temperature, and each part of the first foil material is held at the set temperature for a set time, the set temperature being 300-600°C and the set time being between 0.5-10 minutes.

[0019] Heat treatment of the first foil yields a second foil with dimensions required by subsequent manufacturing processes. Applying a set tension to the first foil during heat treatment improves its strength and ductility, facilitates the transformation between body-centered cubic (BCC) and face-centered cubic (FCC) structures, reduces the proportion of BCC in the first foil, and consequently lowers its coefficient of thermal expansion. Placing the first foil in a protective atmosphere and heating it to a set temperature for a set time ensures that the foil surface does not oxidize. The tension applied to the first foil during heat treatment ranges from 5 to 1500 N / mm², with the appropriate tension selected based on the actual material of the first foil. The ambient temperature during heat treatment is between 300 and 600°C, facilitating complete phase transformation of the BCC structure within the first foil and eliminating residual stress. The heat treatment time is designed to maintain sufficient heating time, ensuring uniform temperature distribution throughout the first foil, enabling uniform phase transformation and improving the uniformity of the first foil.

[0020] Optionally, in the heat treatment step, the first foil is heated to the set temperature in a heat treatment furnace equipped with a foil inlet and a foil outlet. The unwinding and rewinding devices are controlled to ensure the first foil moves at a speed of 1-10 m / min within the heat treatment furnace. The first foil is placed in a reducing gas environment with an oxygen content below 100 ppm. During heat treatment, the first foil is placed in a protective atmosphere to prevent oxidizing gases such as oxygen from affecting the heat treatment process, avoiding oxidation, and preserving the physical and mechanical properties of the first foil. Simultaneously, since oxides typically have a higher coefficient of thermal expansion, the oxide content decreases in the protective atmosphere, reducing the internal stress of the first foil, which facilitates subsequent foil processing and improves the stability and reliability of the first foil.

[0021] Applying tension to both ends of the first foil maintains its direction of movement, ensuring it moves along a predetermined path during heat treatment and maintaining stability during the process. Furthermore, by controlling the first foil's speed through the heat treatment furnace, it is ensured that all parts of the first foil remain at the predetermined temperature for the specified time, allowing for thorough heat treatment across the entire foil. This ensures the first foil's coefficient of thermal expansion meets the requirements for subsequent metal mask manufacturing, reduces residual stress within the foil, and improves its flatness.

[0022] A photoresist film 4 is coated onto the surface of foil 1. The design pattern on the photomask is transferred to the photoresist film 4 through an exposure process. Unwanted portions of the photoresist 4 are removed, exposing the metal. The first surface 2 of foil 1 is etched. Etching is stopped once the target size is reached, and the pits on the first surface 2 of foil 1 are filled with photoresist 4. The second surface 3 of foil 1 is then etched, etching through the remaining thickness of the foil to form through-holes. Wherein, W1: aperture of the first surface 2; W2: aperture of the second surface 3; W3: hole spacing; W4: width of residual metal between holes; W5: width of the through hole step of the first surface 2; H1: height of the through hole step of the first surface 2; H2: product thickness.

[0023] The above-mentioned metal photomask features are: 1) W2 / W1 ratio range [1, 1.5]; 2) W5 ≤ 0.5 μm, H1 ≤ 0.5 μm; 3) W1 range [5, 20] μm; 4) resolution range [600, 1500] ppi; 5) thickness less than 20 μm.

[0024] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. The preferred embodiments or means of the present invention will be shown in detail in conjunction with the accompanying drawings, but are not intended to limit the technical solutions of the present invention. In addition, each of these features, elements and components appearing in the following text and drawings is a plurality of, and different symbols or numbers are used for convenience of representation, but all represent parts with the same or similar construction or function. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a flowchart of the metal photomask manufacturing method of the present invention.

[0026] Figure 2 This is a schematic diagram of the I-Unit calculation for the electroformed foil of the metal mask plate of the present invention.

[0027] Figure 3 This is a schematic diagram of the I-Unit-X curve of the electroformed foil material of the metal mask of the present invention.

[0028] Figure 4 This is a schematic diagram of the I-Unit-Y curve of the electroformed foil material of the metal mask of the present invention.

[0029] Figure 5 This is a schematic diagram showing the second foil material of the metal mask of the present invention before etching.

[0030] Figure 6 This is a schematic diagram of the first surface of the second foil material of the metal mask of the present invention after etching.

[0031] Figure 7 This is a schematic diagram showing how the second foil of the metal mask of the present invention fills the pits on the first surface.

[0032] Figure 8 This is a schematic diagram of the second surface of the second foil material of the metal mask of the present invention after etching.

[0033] Figure 9 This is a top view schematic diagram of the metal mask of the present invention.

[0034] Figure 10 For the present invention Figure 9 Schematic diagram of the C-plane cross section.

[0035] Figure 11 A schematic diagram of the through-hole cross-section after increasing the pixel density of a metal mask in the prior art.

[0036] Figure 12 A schematic diagram of the through-hole cross-section after increasing the pixel density of a metal mask in the prior art.

[0037] Explanation of reference numerals in the attached figures: 1. Second foil; 2. First surface; 3. Second surface; 4. Photoresist. Detailed Implementation

[0038] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are intended to explain the present invention and should not be construed as limiting the invention.

[0039] The terms "an embodiment," "example," or "trademark" used in this specification refer to a particular feature, structure, or characteristic described in connection with the embodiment itself that may be included in at least one embodiment disclosed in this invention. The phrase "in an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0040] In the commercial mass production of organic light-emitting diodes (OLEDs), metal masks are required to deposit the light-emitting layer of OLED devices, and the quality of the metal masks is subject to high requirements.

[0041] The main limitation to further improving the resolution of precision metal photomasks is the thickness of the metal foil. Currently, the thickness of precision metal photomasks is 25-40 μm, and the manufacturing technology for the raw foil is rolling. To break through the resolution barrier, the foil thickness must be less than 20 μm while maintaining consistent foil quality, which is difficult to achieve with current rolling processes. Electroforming can easily and cost-effectively produce foils with a thickness of less than 20 μm, but the resulting foils have poor flatness, coefficient of thermal expansion, and other qualities, failing to meet the production requirements of precision metal photomasks. Existing metal photomask production mainly uses rolled ultra-thin Invar foil combined with wet etching.

[0042] However, in existing methods for preparing metal photomasks, electroformed foil as a raw material has problems such as high residual stress, excessively high BCC (Body-Centered Cubic) phase content, and a large coefficient of thermal expansion, which do not meet the requirements for the preparation and production of metal photomasks.

[0043] To address the aforementioned problems, a first aspect of this application discloses a metal photomask, comprising a photomask body with a plurality of mask holes formed thereon. The photomask body includes a first surface 2 and a second surface 3 opposite to each other. The mask holes penetrate the first surface 2 and the second surface 3. The mask holes form a first opening on the first surface 2 and a second opening on the second surface 3. The ratio of the diameter of the second opening to the diameter of the first opening is between 1 and 1.5.

[0044] When the apertures of the first and second openings are similar, the pixel density of the first surface 2 can be increased without affecting the pixel density of the second surface 3, thereby significantly reducing the distance between adjacent apertures and increasing ppi.

[0045] Optionally, the mask hole forms a stepped portion on the side near the first surface 3, the diameter of the stepped portion is larger than the aperture of the first opening, and the stepped portion is closer to the first surface 3 relative to the first opening.

[0046] Optionally, the difference between the diameter of the stepped portion and the aperture of the first opening is less than or equal to 0.5 μm, and the height of the stepped portion is less than or equal to 0.5 μm.

[0047] The smaller the step height, the smaller the shadow area generated during the vapor deposition process, which can reduce the mura defects produced on the screen.

[0048] Optionally, the aperture of the first opening is between 5 and 20 μm.

[0049] Optionally, the resolution of the metal mask is between 600 and 1500 ppi.

[0050] Optionally, the thickness of the metal mask is less than or equal to 20 μm.

[0051] A metal mask with a thickness of 20 μm or less can increase the upper limit of ppi for FMM products.

[0052] A second aspect of the present invention discloses a method for manufacturing a metal photomask, comprising the following steps: S10. The substrate is placed in an electroforming solution for electrodeposition to form a first foil on the substrate; S20. Separate the first foil from the substrate; S30. The first foil is heat-treated to obtain the second foil 1; wherein the proportion of the body-centered cubic structure in the second foil 1 does not exceed a set proportion. S40. The second foil 1 is etched to obtain a metal mask.

[0053] A first foil is formed by electrodeposition on a substrate, providing a deposition platform that allows the first foil to be shaped into a sheet. During the electrodeposition and separation steps, stress accumulates within the first foil. Without treatment, this stress will affect subsequent processing, specifically reducing the foil's lifespan or making it more prone to deformation. Furthermore, the first foil has a high coefficient of thermal expansion, necessitating heat treatment. In the heat treatment step, the first foil is heated to a specific temperature, causing a change in its crystal structure and balancing uneven stress. Maintaining this high temperature for a certain period allows for atomic rearrangement, promoting stress release. Finally, gradual cooling reduces thermal stress caused by temperature changes, preventing the generation of new residual stress and thus improving the foil's flatness. A second objective of the heat treatment step is to promote the transformation of the body-centered cubic structure to a face-centered cubic structure under high-temperature conditions, reducing the foil's coefficient of thermal expansion.

[0054] Optionally, the average coefficient of thermal expansion of the second foil 1 at 20~200℃ is less than or equal to 2 ppm / K.

[0055] Optionally, the first foil is subjected to heat treatment, including: applying a set tension to the first foil, wherein the set tension is between 5-1500 N / mm²; In a protective atmosphere, the first foil material with the set tension applied is heated to a set temperature, and each part of the first foil material is held at the set temperature for a set time, the set temperature being 300-600°C and the set time being between 0.5-10 minutes.

[0056] Heat treatment of the first foil yields a second foil 1 with dimensions required by subsequent manufacturing processes. Applying a set tension to the first foil during heat treatment improves its strength and ductility, facilitates the transformation between body-centered cubic (BCC) and face-centered cubic (FCC) structures, reduces the proportion of BCC in the first foil, and consequently lowers its coefficient of thermal expansion. Placing the first foil in a protective atmosphere and heating it to a set temperature for a set time ensures that the foil surface does not oxidize. The tension applied to the first foil during heat treatment ranges from 5 to 1500 N / mm², with the appropriate tension selected based on the actual material of the first foil. The ambient temperature during heat treatment is 300-600℃ to facilitate complete phase transformation of the BCC structure within the first foil, eliminating residual stress. The heat treatment time is designed to maintain sufficient heating time to ensure uniform temperature distribution throughout the first foil, enabling uniform phase transformation and improving the uniformity of the first foil.

[0057] Optionally, in the heat treatment step, the first foil is heated to the set temperature in a heat treatment furnace equipped with a foil inlet and a foil outlet. The unwinding and rewinding devices are controlled to ensure the first foil moves at a speed of 1-10 m / min within the heat treatment furnace. The first foil is placed in a reducing gas environment with an oxygen content below 100 ppm. During heat treatment, the first foil is placed in a protective atmosphere to prevent oxidizing gases such as oxygen from affecting the heat treatment process, avoiding oxidation, and preserving the physical and mechanical properties of the first foil. Simultaneously, since oxides typically have a higher coefficient of thermal expansion, the oxide content decreases in the protective atmosphere, reducing the internal stress of the first foil, which facilitates subsequent foil processing and improves the stability and reliability of the first foil.

[0058] Applying tension to both ends of the first foil maintains its direction of movement, ensuring it moves along a set direction during heat treatment and maintaining stability during the process. The first foil undergoes heat treatment in the furnace; by controlling its speed through the furnace, it is ensured that all parts of the foil remain at the set temperature for the set time, allowing for thorough heat treatment. This ensures the first foil's coefficient of thermal expansion meets the requirements for subsequent metal mask manufacturing, reduces residual stress, and improves flatness. After heat treatment, the first foil yields the second foil 1.

[0059] A photoresist film is coated onto the surface of the second foil 1. The design pattern from the photomask is transferred onto the photoresist film through an exposure process. Unwanted portions of the photoresist 4 are removed, exposing the metal. The first surface 2 of the second foil 1 is etched. Etching stops when the aperture size of the first surface 2 reaches W1. The pits on the first surface 2 of the second foil 1 are filled with photoresist 4. The second surface 3 of the second foil 1 is then etched, etching through the remaining foil thickness to form a through-hole. Wherein, W1: aperture of the first surface 2; W2: aperture of the second surface 3; W3: hole spacing; W4: width of residual metal between holes; W5: width of the through hole step of the first surface 2; H1: height of the through hole step of the first surface 2; H2: product thickness.

[0060] The above-mentioned metal photomask features are: 1) W2 / W1 ratio range [1, 1.5]; 2) W5 ≤ 0.5 μm, H1 ≤ 0.5 μm; 3) W1 range [5, 20] μm; 4) resolution range [600, 1500] ppi; 5) thickness less than 20 μm.

[0061] In this embodiment, after the first foil is deposited on the substrate, the substrate-first foil mixture is peeled, cleaned and trimmed to separate the first foil from the substrate, and the residual electroplating solution on the surface of the first foil is washed and dried. Finally, the two sides of the first foil are trimmed to obtain the required size.

[0062] In this embodiment, the purpose of heat-treating the first foil is to reduce the proportion of the BCC phase. Specifically, the material of the Invar foil is Fe64Ni36, which is FCC (Face Centered Cubic, austenitic). However, electroformed Invar foil is prone to introducing BCC (Body Centered Cubic, ferrite). The proportion of the BCC phase must be lower than the set proportion in order to reduce the coefficient of thermal expansion of the first foil.

[0063] In this embodiment, the proportion of the BCC phase is set at 50%. When the proportion of the BCC phase is less than or equal to 50%, the coefficient of thermal expansion of the second foil 1 can meet the requirements of subsequent production.

[0064] In this embodiment, the proportion of the BCC phase is measured by calculating the percentage of different phases through the diffraction peak area.

[0065] In this embodiment, the first foil is prepared by an electrodeposition process. Electrodeposition can provide a uniform and controllable coating thickness, which can improve the material's performance and appearance, has high material utilization, and high production efficiency, thereby improving the mask preparation efficiency.

[0066] Further, the first foil is subjected to heat treatment, including: applying a set tension to the first foil; heating the first foil with the set tension applied to it to a set temperature in a protective atmosphere, and maintaining each part of the first foil at the set temperature for a set time.

[0067] Heat treatment of the first foil can yield a second foil 1 that meets the dimensional requirements of subsequent manufacturing methods. Applying a set tension to the first foil during heat treatment can improve its strength and ductility, and facilitate the transformation between body-centered cubic (BCC) and face-centered cubic (FCC) structures. Placing the first foil in a protective atmosphere and heating it to a set temperature for a set time can transform the BCC structure in the first foil into a FCC structure and eliminate residual stress in the first foil, thereby reducing the proportion of BCC structure in the first foil, which in turn reduces the coefficient of thermal expansion of the first foil. This improves the dimensional and strength data of the foil when manufacturing metal photomasks, and ultimately improves the quality of the obtained metal photomasks.

[0068] In this embodiment, the corresponding tension is first selected according to the material of the first foil, and then the first foil is controlled to undergo annealing while maintaining the set tension.

[0069] Furthermore, the set tension is 5-1500 N / mm²; the set temperature is 300-600 °C; and the heat treatment duration at each part of the first foil is 0.5-10 min.

[0070] The tension applied to the first foil during heat treatment ranges from 5 to 1500 N / mm², and the appropriate tension is selected based on the actual material of the first foil. The ambient temperature for heat treatment is 300-600℃, which facilitates the complete phase transformation of the body-centered cubic structure within the first foil and helps eliminate residual stress inside the first foil. The heat treatment time is designed to keep the first foil heated for a sufficient period of time to ensure uniform temperature distribution throughout the first foil, enabling uniform phase transformation and improving the uniformity of the first foil.

[0071] In this embodiment, the second foil 1 obtained after the first foil material undergoes heat treatment step S30 requires a thickness of less than or equal to 20 μm, a width between 300-1000 mm, an average thermal expansion coefficient of less than or equal to 2 ppm / K at 20~200℃, a yield strength greater than or equal to 800 MPa, a tensile strength greater than or equal to 950 MPa, a flat area width ratio greater than 60%, an edge I-Unit-X less than 10 and greater than 0, and an I-Unit-Y less than 4 and greater than 0.

[0072] Specifically, the flatness screening criterion for the second foil material 1 is the I-Unit value, see Appendix. Figure 2 Along the conveying direction or width direction of the first foil, the first foil is divided into thin strips. Due to the presence of edge ripples or bulges on the foil surface, the specific length of different thin strips will vary after straightening due to different surface undulations. A specified nominal length is taken as the base length L0, and the actual length of each thin strip is Ln. The length difference ΔL between the two is obtained using the formula: I-Unit=

[0073] The I-Unit value is calculated, and the length deviation calculated along the conveying direction is denoted as I-Unit-X, while the length deviation calculated along the width direction is denoted as I-Unit-Y. Theoretically, if the foil is completely flat, all the thin strips should be the same length, with a length deviation of 0. Therefore, the larger the length deviation, the more obvious the undulations such as edge waves or bulges at the corresponding position, i.e., the worse the flatness. If measuring a sample with a length of 1000mm, the reference length L0 in the conveying direction is 1000mm, and an appropriate step value is set in the width direction. The laser height gauge can non-destructively measure the actual length of Ln and calculate the I-Unit value. Connecting the I-Unit value points at each position yields the I-Unit-X curve diagram and the I-Unit-Y curve diagram.

[0074] like Figure 3 As shown, Figure 3 The length deviation I-Unit-X in the conveying direction is distributed along the width direction. A horizontal coordinate system is established with the midpoint of the width as the zero point. The middle 80% width area is called the middle region, and the remaining 10% on each side is called the edge region. Within the middle region, the continuous area satisfying the condition "I-Unit-X ≤ 1" is called the flat area. To meet the requirements of FMM (Fine Metal Mask) production, the foil must simultaneously meet the following requirements: the width of the flat area ≥ 60% of the width; the maximum value of I-Unit-X at the edges ≤ 10.

[0075] like Figure 4 As shown, Figure 4 It is the distribution curve of the length deviation I-Unit-Y in the width direction along the rolling direction. The horizontal coordinate system is established with the midpoint of the reference length L0 as the zero point. In order to meet the requirements of FMM production, the foil needs to meet the requirement that the maximum value of I-Unit-Y is ≤4.

[0076] Furthermore, in the step of applying a set tension to the first foil, the first end of the first foil is fixed to the unwinding device, and the second end of the first foil is fixed to the winding device, and the set tension is applied by unwinding and winding.

[0077] Applying tension to both ends of the first foil can keep the direction of movement of the first foil unchanged, ensuring that the first foil can move along the set direction during the heat treatment process and maintaining the stability of the heat treatment process of the first foil.

[0078] Furthermore, in the heat treatment step S30, the first foil is heated to the set temperature in a heat treatment furnace equipped with a foil inlet and a foil outlet, wherein the unwinding device and the winding device are controlled so that the moving speed of the first foil in the heat treatment furnace is 1-10 m / min.

[0079] The first foil is heat-treated in the heat treatment furnace. By controlling the moving speed of the first foil through the heat treatment furnace, it can be ensured that all parts of the first foil are kept at the set temperature for a set time during the heat treatment. This ensures that all parts of the first foil can be fully heat-treated, guaranteeing that the proportion of the body-centered cubic structure in the first foil meets the requirements for subsequent manufacturing of metal photomasks, and reducing residual stress in the first foil, thereby improving quality.

[0080] Furthermore, in the heat treatment step S30, the first foil is in a protective atmosphere and has an oxygen content of less than 100 ppm.

[0081] During heat treatment, the first foil is placed in a protective atmosphere to prevent oxidizing gases such as oxygen from affecting the heat treatment process, thus avoiding oxidation and preserving its physical and mechanical properties. Simultaneously, since oxides typically have a higher coefficient of thermal expansion, the oxide content decreases in the protective atmosphere, reducing the internal stress of the first foil. This facilitates subsequent processing of the foil and improves its stability and reliability.

[0082] Furthermore, in the heat treatment step S30, the protective atmosphere includes hydrogen, or the protective atmosphere includes a mixture of hydrogen and nitrogen, or the protective atmosphere includes an inert gas such as nitrogen or argon.

[0083] Hydrogen, as a reducing gas, can provide a reducing atmosphere for the first foil. Nitrogen or argon, as inert gases, will not react with metals or their oxides, thus preventing the first foil from undergoing an overly violent reduction reaction during heat treatment and improving the safety of the heat treatment.

[0084] Further, in the electrodeposition step S10, the substrate is made of titanium alloy or stainless steel, and the electroforming solution comprises: Nickel sulfate 40wt% to 50wt%; Ferrous sulfate 20wt% to 30wt%; Nickel chloride or ammonium chloride 5wt% to 10wt%; Boric acid 10wt% to 20wt%; Sodium dodecyl sulfate 2wt% to 10wt%; Saccharin 1wt% to 5wt%; Sodium benzoate 0 wt% to 3 wt%.

[0085] In this embodiment, the specific components are 43 wt% nickel sulfate, 27 wt% ferrous sulfate, 9 wt% nickel chloride, 12 wt% boric acid, 5 wt% sodium dodecyl sulfate, 3 wt% saccharin, and 1 wt% sodium benzene disulfonate. After mixing, the mixture is stirred thoroughly, and any missing or lower-than-set components are promptly added.

[0086] Furthermore, in the electrodeposition step S10, the pH value of the electroforming solution is 2.0-3.5, the temperature is 35-55℃, and the current density of the electroforming solution is 30-50mA / cm².

[0087] The concentration of the electroforming solution, the current density, and the time the substrate spends in the electroforming solution during electrodeposition all affect the first foil deposited on the substrate. Under these conditions, a first foil with a thickness that meets the processing requirements can be obtained, thereby improving the processing quality.

[0088] After obtaining the second foil 1 through the above steps, the second foil 1 is etched in step S40 to obtain a metal mask.

[0089] like Figure 5 As shown, specifically, a photoresist 4 film is coated onto the surface of the second foil 1 in sequence. The photomask is then irradiated with a light source of a certain wavelength to transfer the design pattern on the photomask onto the photoresist 4 film. Unwanted photoresist 4 parts are removed to expose the metal, which is then ready for etching.

[0090] like Figure 6 As shown, the first surface 2 of the second foil 1 is etched to create a design pit of the target size from the first surface 2 of the second foil 1. The aperture size of the first surface 2 is W1. When the etching reaches W1, the etching is stopped. Due to the characteristics of solution etching, the thickness direction of the second foil 1 is also etched to a certain depth, but a large amount of ingots are still not etched. At the same time, small steps will be generated at the edge of the through hole of the first surface 2.

[0091] like Figure 7 As shown, the pits on the first surface 2 of the second foil 1 are filled with photoresist 4.

[0092] like Figure 8 As shown, the remaining thickness of the foil is etched through the second surface 3 of the second foil 1 to form a through hole. Since there is a lot of remaining thickness, the designed size of the hole diameter W2 on the second surface 3 is larger than the set size of the hole diameter W1 on the first surface 2, thereby speeding up the etching and finally forming a bowl shape.

[0093] like Figure 9 and Figure 10 As shown, after removing the photoresist 4 from the first surface 2 and the second surface 3, the FMM is cut into sheets to obtain a metal mask.

[0094] Wherein, W1: aperture of the first surface 2; W2: aperture of the second surface 3; W3: hole spacing; W4: width of residual metal between holes; W5: width of the through hole step of the first surface 2; H1: height of the through hole step of the first surface 2; H2: product thickness.

[0095] like Figure 11 As shown, further, if the ppi increases, that is, the pixel density increases, then within the same screen area, the aperture W1 of the first surface 2 needs to be reduced, and the aperture spacing W3 becomes shorter. Since the aperture W2 of the second surface 3 is larger than the aperture W1 of the first surface 2, as W3 gradually shortens, the width W4 of the residual metal between the apertures will gradually shorten, and the through holes of the second surface 3 will partially overlap, that is, the metal connection between the through holes will be etched.

[0096] Figure 12The thickness H2 of the product remains the same as the foil thickness, but part of the middle connection has been etched away. As ppi continues to increase and pixel density continues to increase, W4 will also disappear.

[0097] The product thickness H3 is less than the foil thickness, resulting in increased etching of the metal at the through-hole connection. This reduced remaining metal at the connection point leads to decreased tensile strength in the FMM product, affecting deposition accuracy and product lifespan. This is also why current FMM products made with rolled Invar foil cannot achieve higher ppi (pixel density). The only solution is to further reduce the thickness of existing rolled foil to below 20 μm. Therefore, the second foil 1 obtained in the metal mask manufacturing method of this application can meet the subsequent production requirements of metal masks.

[0098] Furthermore, the smaller the step dimensions H1 and W5 in the first surface 2, the better, because the presence of steps can cause shadow areas to be generated during the vapor deposition process, resulting in mura defects in the fabricated screen.

[0099] The metal photomask in this application, manufactured using the method described in the second aspect above, employs an electroforming solution deposition process, which improves the strength of the metal photomask compared to traditional rolling processes. Specifically, the yield strength of the metal photomask in this application can reach over 800 MPa, and the tensile strength can reach over 950 MPa. Furthermore, in the processing of this application, after the electroforming solution deposition is completed, the first foil is heat-treated, resulting in a second foil with a flat area width ratio exceeding 60%, an edge I-Unit-X ratio below 10, and an edge I-Unit-Y ratio below 4, which can significantly improve the quality of the subsequent metal photomask.

[0100] To better illustrate the advantages of the metal mask manufacturing method in this application, the following specific embodiments are provided, including Embodiment 1: The metal substrate is pretreated to remove residues and contaminants from previous processes. A chemical cleaning agent is used to remove organic matter and oxide layers from the surface. The chemical cleaning agent is a sodium hydroxide solution with pH=12 and a temperature of 50°C. The substrate is then washed with water and air-dried. Next, the substrate surface is immersed in a high-concentration acid solution, specifically a hydrochloric acid solution with pH=1 and a temperature of 30°C. Finally, the substrate is washed with water and air-dried.

[0101] Prepare the electroforming solution by mixing nickel sulfate, ferrous sulfate, nickel chloride or ammonium chloride, boric acid, sodium dodecyl sulfate, saccharin, and sodium benzene disulfonate, wherein the proportions are 43 wt% nickel sulfate, 27 wt% ferrous sulfate, 9 wt% nickel chloride, 12 wt% boric acid, 5 wt% sodium dodecyl sulfate, 3 wt% saccharin, and 1 wt% sodium benzene disulfonate. Stir thoroughly and replenish as needed to obtain the electroforming solution.

[0102] Electrodeposition was performed using a metal substrate as the cathode and a nickel-iron alloy as the anode in an electroforming bath filled with electroforming solution. The pH of the electroforming solution was controlled at 2.5, the temperature at 45°C, and the solution was stirred in real time to ensure uniformity of the electroformed metal foil. The target thickness was obtained by electrodeposition at a current density of 35 mA / cm². The foil contained 35.4 wt% nickel, with the remainder being iron and trace elements. In this embodiment, the target thickness was 20 μm.

[0103] The electroformed metal foil is separated from the metal substrate. The residual chemical solution on the surface of the peeled foil is washed off and dried. The foil is then cut off from both sides to obtain the target width, thus obtaining the first foil. In this embodiment, the target width is 300 mm.

[0104] The first foil is heat-treated by applying a tension of 650 N / mm. 2 The annealing temperature was 415ºC, the annealing rate was 5m / min, and a protective atmosphere of hydrogen-nitrogen mixture was used.

[0105] Finally, after winding, the second foil material 1 is obtained.

[0106] Example 2 includes: The metal substrate is pretreated to remove residues and contaminants from previous processes. A chemical cleaning agent is used to remove organic matter and oxide layers from the surface. The chemical cleaning agent is a sodium hydroxide solution with pH=12 and a temperature of 50°C. The substrate is then washed with water and air-dried. Next, the substrate surface is immersed in a high-concentration acid solution, specifically a hydrochloric acid solution with pH=1 and a temperature of 30°C. Finally, the substrate is washed with water and air-dried.

[0107] Prepare the electroforming solution by mixing nickel sulfate, ferrous sulfate, nickel chloride or ammonium chloride, boric acid, sodium dodecyl sulfate, saccharin, and sodium benzene disulfonate, wherein the proportions are 43 wt% nickel sulfate, 27 wt% ferrous sulfate, 9 wt% nickel chloride, 12 wt% boric acid, 5 wt% sodium dodecyl sulfate, 3 wt% saccharin, and 1 wt% sodium benzene disulfonate. Stir thoroughly and replenish as needed to obtain the electroforming solution.

[0108] Electrodeposition was performed using a metal substrate as the cathode and a nickel-iron alloy as the anode in an electroforming bath filled with electroforming solution. The pH of the electroforming solution was controlled at 2.5, the temperature at 45°C, and the solution was stirred in real time to ensure uniformity of the electroformed metal foil. The target thickness was obtained by electrodeposition at a current density of 35 mA / cm². The foil contained 35.4 wt% nickel, with the remainder being iron and trace elements. In this embodiment, the target thickness was 20 μm.

[0109] The electroformed metal foil is separated from the metal substrate. The residual chemical solution on the surface of the peeled foil is washed off and dried. The foil is then cut off from both sides to obtain the target width, thus obtaining the first foil. In this embodiment, the target width is 300 mm.

[0110] Finally, after winding, the second foil material 1 is obtained.

[0111] Example 3 includes: The metal substrate is pretreated to remove residues and contaminants from previous processes. A chemical cleaning agent is used to remove organic matter and oxide layers from the surface. The chemical cleaning agent is a sodium hydroxide solution with pH=12 and a temperature of 50°C. The substrate is then washed with water and air-dried. Next, the substrate surface is immersed in a high-concentration acid solution, specifically a hydrochloric acid solution with pH=1 and a temperature of 30°C. Finally, the substrate is washed with water and air-dried.

[0112] Prepare the electroforming solution by mixing nickel sulfate, ferrous sulfate, nickel chloride or ammonium chloride, boric acid, sodium dodecyl sulfate, saccharin, and sodium benzene disulfonate, wherein the proportions are 43 wt% nickel sulfate, 27 wt% ferrous sulfate, 9 wt% nickel chloride, 12 wt% boric acid, 5 wt% sodium dodecyl sulfate, 3 wt% saccharin, and 1 wt% sodium benzene disulfonate. Stir thoroughly and replenish as needed to obtain the electroforming solution.

[0113] Electrodeposition was performed using a metal substrate as the cathode and a nickel-iron alloy as the anode in an electroforming bath filled with electroforming solution. The pH of the electroforming solution was controlled at 2.5, the temperature at 45°C, and the solution was stirred continuously to ensure uniformity of the electroformed metal foil. The target thickness was achieved by electrodeposition at a current density of 35 mA / cm². The foil contained 35.4 wt% nickel, with the remainder being iron and trace elements. In this embodiment, the target thickness was 11 μm.

[0114] The electroformed metal foil is separated from the metal substrate. The residual chemical solution on the surface of the peeled foil is washed off and dried. The foil is then cut off from both sides to obtain the target width, thus obtaining the first foil. In this embodiment, the target width is 300 mm.

[0115] The first foil is heat-treated by applying a tension of 650 N / mm. 2 The annealing temperature was 415ºC, the annealing rate was 5m / min, and a protective atmosphere of hydrogen-nitrogen mixture was used.

[0116] Finally, after winding, the second foil material 1 is obtained.

[0117] In addition, Comparative Example 1 provides the corresponding data for rolled foil.

[0118] As can be seen from the above process, the difference between Example 1 and Example 2 is that Example 1 performed the heat treatment step S30, while Example 2 did not perform the heat treatment step S30. The difference between Example 1 and Example 3 is that the thickness of Example 1 is 20 μm, while the thickness of Example 3 is 11 μm.

[0119] Table 1

[0120] CTE (Coefficient of Thermal Expansion) is the coefficient of thermal expansion.

[0121] The results in Table 1 show that Example 1, which underwent heat treatment step S30, has the same characteristics as Example 2, which did not undergo heat treatment step S30, with a higher proportion of flat area width, smaller I-Unit-X and I-Unit-Y at the edges, and a smaller linear thermal expansion coefficient. Furthermore, the resulting body-centered cubic structure has a lower proportion of phase and a higher yield strength, making it more suitable for subsequent processing.

[0122] Compared with Example 1 and Example 3, which also underwent heat treatment step S30, the thickness of Example 3 is smaller than that of Example 1, but the tensile strength and yield strength of the second foil 1 obtained in Example 3 are greater than those of the second foil 1 obtained in Example 1.

[0123] Therefore, it can be concluded that the heat treatment process of this application has a significant beneficial effect on the electroformed foil. After heat treatment, the flatness of the foil is significantly improved, the BCC phase is reduced, the CTE is reduced, and high strength is maintained. That is, the metal mask obtained by this application can meet the production requirements in terms of size, specifically in terms of thinner thickness, and improved yield strength and tensile strength while keeping other properties the same.

[0124] In this embodiment, the second foil 1 used to manufacture the metal mask is formed by electroforming. Metal masks were fabricated using foils obtained through different preparation methods, and the results are shown in Table 2. Example 4 uses 20μm electroformed Invar foil and processes the following steps: cleaning → lamination → exposure → development → etching A → filling A → etching B → film removal → cutting to produce a 20μm thick FMM product. Comparative Example 2 uses 40μm rolled Invar foil and processes the following steps: cleaning → thinning → lamination → exposure → development → etching A → filling A → etching B → film removal → cutting to produce a 20μm thick FMM product. The difference between the two is that the electroformed Invar foil does not use chemical etching to reduce the material thickness.

[0125] Example 4 includes: A second foil with a thickness of 20 μm is selected, and its surface is cleaned. A photoresist film is then coated onto the surface of the second foil. A photomask is illuminated by a light source of a specific wavelength, transferring the design pattern from the photomask onto the photoresist film. Unwanted photoresist is removed to expose the metal, ready for etching.

[0126] A design pit of the target size is etched from the first surface 2 of the second foil. The design size of the pit on the first surface 2 is W1. When the etching reaches the target size W1, the etching stops. Due to the characteristics of solution etching, a certain depth is also etched in the thickness direction of the second foil, but a large amount of ingots are still left unetched. At the same time, small steps will be generated at the edge of the through hole on the first surface 2.

[0127] The pits on the first surface 2 are filled with photoresist; The remaining thickness of the second foil is etched through the second surface 3 of the second foil to form a through hole. Since there is a lot of remaining thickness, the aperture W2 of the second surface 3 is designed to be larger than the aperture W1 of the first surface 2, thereby accelerating the etching and finally forming a bowl-shaped pit on the second surface 3.

[0128] Remove the photoresist from the second surface 3 of A; FMM is cut into pieces to obtain the finished product.

[0129] Comparative Example 2 includes: A 40μm thick rolled foil is selected, its surface is cleaned, and then thinned by chemical etching. A photoresist film is then coated onto the surface of the rolled foil. A photomask is illuminated by a light source of a specific wavelength, transferring the design pattern from the photomask onto the photoresist film. Unwanted photoresist is removed to expose the metal, ready for etching.

[0130] A design recess of the target size is etched from the first surface 2 of the rolled foil. The design size of the recess on the first surface 2 is W1. After the etching reaches the target size W1, the etching stops. Due to the characteristics of solution etching, a certain depth is also etched in the thickness direction of the rolled foil, but a large amount of foil remains unetched. Small steps will be generated at the edge of the through hole on the first surface 2.

[0131] The pits on the first surface 2 are filled with photoresist; The remaining thickness of the rolled foil is etched through from the second surface 3 of the rolled foil to form a through hole. Since there is a lot of remaining thickness, the aperture W2 of the second surface 3 is designed to be larger than the aperture W1 of the first surface 2, thereby accelerating the etching and finally forming a bowl shape.

[0132] Remove the photoresist from the second surface 3 of A; FMM is cut into pieces to obtain the finished product.

[0133] As can be seen from the above process, the difference between Example 4 and Comparative Example 2 is that the foil preparation process used is different and the FMM production process is slightly simplified. Electroforming foil does not require chemical etching to thin it.

[0134] Table 2

[0135] As shown in the table above, the step dimensions H1 and W5 of the first surface 2 in Example 4 are extremely small. Judging from the W2 / W1 results, the aperture size of the second surface 3 in Example 4 is almost the same as that of the first surface 2. Theoretically, with almost identical W1 dimensions, the aperture distribution density of Example 4 can be 1.7 times that of Comparative Example 2, corresponding to a 1.7 times higher ppi for the precision metal mask. Based on extensive data, the W2 / W1 range for rolled foil FMMs is [1.5, 3], and the W2 / W1 range for electroformed foil FMMs is [1, 1.5]. Currently, the resolution of rolled foil FMMs is 300-500 ppi, while the resolution of the electroformed foil FMM in this application can reach up to 1500 ppi.

[0136] In summary, this application involves a heat treatment step S30 on the first foil obtained after electrodeposition step S10 and separation step S20: applying a certain tension while annealing the foil. The applied tension ranges from 5 to 1500 N / mm. 2 (Approximately 0.5~150 kgf / mm) 2 The annealing temperature is 300ºC~600ºC, the annealing rate is 1~10m / min, and a protective atmosphere is used, such as hydrogen, nitrogen or a hydrogen-nitrogen mixture, with an oxygen content of less than 100ppm.

[0137] The second foil 1 obtained after heat treatment process S30 has the following characteristics: thickness ≤20μm, width 300~1000mm, flat area width ratio higher than 60%, edge I-Unit-X less than 10, I-Unit-Y less than 4, average thermal expansion coefficient ≤2ppm / K at 20~200℃, BCC phase ratio ≤50%, yield strength ≥800MPa and tensile strength ≥950MPa. By adding heat treatment step S30, a second foil 1 capable of preparing higher resolution metal photomasks can be obtained, thus improving the resolution of the metal photomask.

[0138] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A metal mask for depositing an organic light-emitting layer for an OLED device, the metal mask comprising a mask body having a plurality of mask holes formed thereon, the mask body including opposing first and second surfaces, the mask holes penetrating the first and second surfaces, characterized in that, The mask aperture forms a first opening on the first surface and a second opening on the second surface, wherein the ratio of the diameter of the second opening to the diameter of the first opening is between 1 and 1.

5. The mask aperture has a stepped portion formed on the side near the first surface. The diameter of the stepped portion is larger than the aperture of the first opening. The stepped portion is close to the first surface relative to the first opening. The axial height of the stepped portion is less than or equal to 0.5 μm.

2. The metal photomask according to claim 1, characterized in that, The difference between the diameter of the stepped portion and the aperture of the first opening is less than or equal to 0.5 μm.

3. The metal photomask according to claim 2, characterized in that, The aperture of the first opening is between 5 and 20 μm.

4. The metal photomask according to any one of claims 1-3, characterized in that, The resolution of the metal mask is between 600 and 1500 ppi.

5. The metal photomask according to any one of claims 1-3, characterized in that: The thickness of the metal mask is less than or equal to 20 μm.

6. A method for manufacturing a photomask, said method for manufacturing a metal photomask according to any one of claims 1 to 5, characterized in that, The manufacturing method includes the following steps: The substrate is placed in an electroforming solution for electrodeposition to form a first foil on the substrate; Separate the first foil from the substrate; The first foil is heat-treated to obtain a second foil; wherein the proportion of the body-centered cubic structure of the second foil does not exceed a set proportion. The second foil is etched to obtain a metal mask.

7. The manufacturing method according to claim 6, characterized in that, The average coefficient of thermal expansion of the second foil at 20~200℃ is less than or equal to 2 ppm / K.

8. The manufacturing method according to claim 6, characterized in that, The heat treatment of the first foil includes: applying a set tension to the first foil, wherein the set tension is between 5-1500 N / mm²; In a protective atmosphere, the first foil material with the set tension applied is heated to a set temperature, and each part of the first foil material is held at the set temperature for a set time; wherein the set temperature is 300-600°C, and the set time is between 0.5-10 min.

9. The manufacturing method according to claim 8, characterized in that, In the heat treatment step, the first foil is heated to the set temperature in a heat treatment furnace equipped with a foil inlet and a foil outlet. The first foil is moved at a speed of 1-10 m / min in the heat treatment furnace by controlling the unwinding and rewinding equipment. The first foil is in a protective atmosphere and has an oxygen content of less than 100 ppm.

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