Metal mask and internal electrode for multilayer ceramic capacitor

Abstract

The present invention is a metal mask which is for producing an internal electrode of a multilayer ceramic capacitor and in which a through hole having a rectangular shape in plan view is formed in a metal base material, wherein the ratio (short side length / step height in short side direction) of the length of a short side of the through hole to a step height in the short side direction of the through hole is not less than 44.6.

Description

Metal masks and internal electrodes for multilayer ceramic capacitors

[0001] The present invention relates to a metal mask, more specifically, a metal mask for forming components of a multilayer ceramic capacitor (MLCC). The present invention also relates to an internal electrode for an MLCC formed using the metal mask. This application claims priority to Japanese Patent Application No. 2024-106955 filed on July 2, 2024, Japanese Patent Application No. 2024-228714 filed on December 25, 2024, Japanese Patent Application No. 2025-003034 filed on January 8, 2025, and Japanese Patent Application No. 2025-080220 filed on May 13, 2025, the contents of which are incorporated herein by reference.

[0002] MLCCs are chip-type capacitors in which internal electrodes and dielectric sheets (sometimes called green sheets) are stacked in multiple layers. While MLCCs are becoming increasingly smaller, they are still required to have sufficient capacitance as capacitors. Increasing capacitance without increasing size requires reducing the thickness of the internal electrodes and increasing the number of layers. While screen printing has traditionally been used to form the internal electrodes, sputtering is expected to enable thinner internal electrodes and a greater number of layers than conventional methods (see, for example, Patent Document 1).

[0003] One method for producing a metal mask used in sputtering or the like is to wet-etch a thin metal substrate (see, for example, Patent Document 2). Material flying from a target passes through through holes formed by etching, and is deposited at a predetermined position with predetermined dimensions and shape.

[0004] International Publication No. 2005 / 117040 Japanese Patent No. 6168944

[0005] In the above-mentioned film formation, it is ideal that the areas of the bottom and top surfaces are the same, but in reality this is not the case, and the top surface is usually smaller than the bottom surface. When these members are stacked, the size of the area that functions as a capacitor is determined by the area of ​​the smaller top surface, so it is preferable to make the area of ​​the top surface as close to the area of ​​the bottom surface as possible.

[0006] From the above viewpoint, the inventors have conducted various studies on the shape of the through holes in the metal mask and have completed the present invention.

[0007] In view of the above circumstances, an object of the present invention is to provide a metal mask that can form a metal thin film with a small difference in area between the bottom surface and the top surface.

[0008] A first aspect of the present invention is a metal mask for manufacturing an internal electrode of a multilayer ceramic capacitor, the metal mask having a metal substrate with a through hole that is rectangular in plan view formed therein, wherein the ratio of the length of a short side of the through hole to a step height in the short side direction of the through hole (length of the short side / step height in the short side direction) is 44.6 or more.

[0009] A second aspect of the present invention is the metal mask of the first aspect, wherein the step height is 0.3 μm or more.

[0010] A third aspect of the present invention is the metal mask according to the second aspect, wherein the step height is 6.3 μm or less.

[0011] A fourth aspect of the present invention is the metal mask according to the second aspect, wherein the step height is 4.0 μm or less.

[0012] A fifth aspect of the present invention is the metal mask of the first aspect, wherein the through holes have a taper angle in the short side direction of 44.0° or more.

[0013] A sixth aspect of the present invention is the metal mask according to the fifth aspect, wherein the taper angle is 61° or less.

[0014] A seventh aspect of the present invention is a metal mask for manufacturing an internal electrode of a multilayer ceramic capacitor, the metal mask having a metal substrate with a through hole that is rectangular in plan view formed therein, wherein the ratio of the length of a long side of the through hole to a step height in the long side direction of the through hole (the length of the long side / the step height in the long side direction) is 315.5 or more.

[0015] An eighth aspect of the present invention is the metal mask of the seventh aspect, wherein the ratio of the length of the long side of the through hole to the step width in the long side direction of the through hole (the length of the long side / the step width in the long side direction) is 419.6 or more.

[0016] A ninth aspect of the present invention is the metal mask according to the eighth aspect, wherein the step height is 0.3 μm or more.

[0017] A tenth aspect of the present invention is the metal mask according to the ninth aspect, wherein the step height is 3.0 μm or less.

[0018] An eleventh aspect of the present invention is the metal mask according to the ninth or tenth aspect, wherein the step width is 0.3 μm or more.

[0019] A twelfth aspect of the present invention is the metal mask according to the ninth or tenth aspect, wherein the step width is 2.4 μm or less.

[0020] A thirteenth aspect of the present invention is the metal mask according to the seventh aspect, wherein the through holes have a taper angle in the direction of the long sides of the through holes of 47.5° or more.

[0021] A fourteenth aspect of the present invention is a metal mask for manufacturing an internal electrode of a multilayer ceramic capacitor, the metal mask having a through hole formed in a metal substrate that is rectangular in plan view, wherein the ratio of the length of the short side of the through hole to the step width in the short side direction of the through hole (the length of the short side / the step width in the short side direction) is 85.1 or more.

[0022] A fifteenth aspect of the present invention is the metal mask according to the fourteenth aspect, wherein the step width is 0.2 μm or more.

[0023] A sixteenth aspect of the present invention is the metal mask according to the fifteenth aspect, wherein the step width is 3.5 μm or less.

[0024] A seventeenth aspect of the present invention is the metal mask according to the fifteenth aspect, wherein the step width is 2.1 μm or less.

[0025] An eighteenth aspect of the present invention is the metal mask of any one of the first to seventeenth aspects, wherein the substrate is made of a magnetic alloy.

[0026] A nineteenth aspect of the present invention is the metal mask according to the eighteenth aspect, wherein the alloy is any one of SUS430, Invar, and Super Invar.

[0027] A twentieth aspect of the present invention is an internal electrode for a multilayer ceramic capacitor in which a thin film made of a conductor is formed on a dielectric substrate, and the ratio of the area of ​​the top surface to the area of ​​the bottom surface in a plan view of the thin film (the area of ​​the top surface / the area of ​​the bottom surface) is 0.80 or more.

[0028] According to the present invention, it is possible to provide a metal mask that can form a thin metal film with a small difference in area between the bottom surface and the top surface.

[0029] 1 is a schematic diagram showing the positional relationship of the metal mask and the like according to the first embodiment during film formation; FIG. 2 is a diagram showing the relationship between the cross-sectional shape of the through hole of the metal mask according to the present embodiment and the film-formed object (a view of the through hole from the long side direction); FIG. 3 is an example of a thickness profile of a nickel film according to a study; FIG. 4 is a table showing the measurement results of Sample A; FIG. 5 is a table showing the measurement results of Sample B; FIG. 6 is a schematic plan view showing an example of a member formed using the metal mask according to the present embodiment; FIG. 7 is a schematic diagram showing an example of a layered structure of the same member; FIG. 8 is a schematic diagram showing the positional relationship of the metal mask and the like according to the second embodiment during film formation; FIG. 9 is a diagram showing the cross-sectional shape of the through hole of the metal mask according to the present embodiment and the relationship between the film-formed object (a view of the through hole from the short side direction); FIG. 10 is an example of a thickness profile of a nickel film according to a study; FIG. 11 is a table showing the measurement results of Sample A; 1 is a diagram showing the relationship between the cross-sectional shape of a through hole of a metal mask according to an embodiment of the present invention and the cross-sectional shape of a metal thin film (a diagram of the through hole viewed from its long side direction); FIG. 2 is an example of a thickness profile of a deposited metal thin film; FIG. 3 is a table showing the measurement results of sample A; FIG. 4 is a schematic plan view showing an example of a member formed using a metal mask according to an embodiment of the present invention; and FIG. 5 is a schematic view showing an example of a layered configuration of the same member.

[0030] (First embodiment) A first embodiment of the present invention will be described with reference to Fig. 1 to Fig. 7. As shown schematically in Fig. 1, a metal mask 1 according to this embodiment is placed so as to overlap a dielectric sheet 100 serving as a substrate. In the sputtering process, of the material flying from the target T toward the metal mask 1, only that which passes through the through holes 1a is deposited on the dielectric sheet 100 to form a film.

[0031] FIG. 2 is an enlarged cross-sectional view of one through hole 1a in the metal mask 1. The through hole 1a is formed by etching the sheet-like metal member (hereinafter simply referred to as the "substrate") constituting the metal mask from both sides in the thickness direction. When the through hole 1a is formed by wet etching, the etching is often performed in two stages. Typically, the surface of the substrate facing the dielectric sheet 100 is etched first, followed by the surface facing the target T. This results in the formation of the through hole 1a. Because etching is isotropic, the planar dimensions of the through hole 1a are larger closer to the surface of the substrate and smaller as they move away from the surface. Therefore, when two-stage etching is performed on both sides of the substrate to fabricate the metal mask 1, the planar dimensions of the formed through hole are smallest at the through portion 1b in the middle of the substrate in the thickness direction. The planar shape and dimensions of the through portion 1b determine the planar shape of the film-formed structure.

[0032] The penetration portion 1b, where the planar dimensions are smallest, is formed at the location where etching from both sides meet. Therefore, the position of the penetration portion 1b in the thickness direction of the substrate changes depending on the degree of etching from each side. The film formation material flies radially from the target. Therefore, if the film formation material enters the through hole 1a at an angle, as shown by the arrow in Figure 2, it may fly beyond the range of the penetration portion 1b in the planar view and reach the dielectric sheet 100 after passing through the penetration portion 1b. This phenomenon is sometimes called the "shadow effect." The probability of this phenomenon occurring increases as the penetration portion 1b is farther from the dielectric sheet 100. Furthermore, the stronger the shadow effect, the smaller the area of ​​the top surface of the formed thin film becomes relative to the area of ​​the bottom surface.

[0033] Based on this, the inventors studied the step height (shown by the symbol h1 in Figure 2 ), which is the distance in the thickness direction of the metal mask 1 from the surface located on the dielectric sheet 100 side to the penetration portion 1b, and the taper angle (shown by the symbol θ in Figure 2 ), and investigated the conditions for a metal mask suitable for manufacturing internal electrodes for MLCCs.

[0034] (Preparation of Metal Mask Samples) A ​​50 μm-thick stainless steel SUS430 sheet (planar dimensions: 350 mm × 715 mm) was prepared as a substrate. The substrate was etched on both sides using a two-stage etching method to create a large number of through holes at a constant pitch. By varying the amount of etching from both sides, samples with 13 different step heights (step heights on both sides of the short side of the through holes) were prepared, as shown in FIGS. 4 and 5 .

[0035] For each step height, two types of samples were prepared, each with different planar dimensions of the through portion as shown below. Through hole A was intended for producing two internal electrodes for a 0603-type MLCC at a time, and through hole B was intended for producing two internal electrodes for a 0402-type MLCC at a time. In the following description, the metal mask sample with through hole A formed therein will be referred to as sample A, and the metal mask sample with through hole B formed therein will be referred to as sample B. Through hole A (design value): Rectangle with short sides of 280 μm and long sides of 1180 μm Through hole B (design value): Rectangle with short sides of 180 μm and long sides of 780 μm After each sample was completed, the planar dimensions of the through portion 1b of five selected through holes were measured using a measuring device (Nikon NEXIV VMZ-H3030), and the arithmetic mean of the measured values ​​was recorded. In the following discussion, the short side, long side and step height of the through holes are average values ​​based on the actual measurements of the penetration portion 1b of each through hole.

[0036] (Film formation and measurement using metal mask samples) The dielectric sheets used were PET sheets in which a slurry containing barium titanate as the main component was die coated on the surface and then dried to form a 1 μm thick layer on the surface. The dielectric sheets were placed in a sputtering device, and the metal masks for each sample were attached to the dielectric sheets, and films were formed on the dielectric sheets under the following conditions: Target material: nickel Ultimate pressure: 1.0 × 10-5 Pa or less Film formation pressure: 0.65 Pa Input voltage (power): 1.0 kW Input gas type: argon Input gas flow rate: 100 sccm Film thickness: 150 nm (target value)

[0037] Next, the nickel film of each sample was measured to obtain a thickness profile. A Keyence VK-X3000 laser microscope was used as the measurement device. Profiles were taken in two directions: from the midpoint of the long side toward the short side, and from the midpoint of the short side toward the long side. An example of a profile obtained in the short side direction is shown in Figure 3. As shown in Figure 3, the profile was approximately trapezoidal, with upper and lower bases. The starting and ending points of the upper and lower bases were determined using the following criteria: Based on the profile, the height change from the previous point at each measurement point was calculated. The point showing the minimum change before the film thickness began to increase was defined as the starting point of the lower base. If there were multiple points showing the same minimum value, the position farthest from the upper base was used as the starting point of the lower base. The point where the change increased from the starting point of the lower base and exceeded its peak and reached 0.002 μm for the first time was defined as the starting point of the upper base. The upper base was not completely horizontal (zero change). Therefore, after the start point of the upper base, as long as the amount of change is less than ±0.002, the upper base is considered to continue, and the point where the amount of change first reached -0.002 μm is defined as the end point of the upper base, and the distance between the start point and the end point is taken as the length of the upper base. ・After the end point of the upper base, the point where the amount of change is maximum is taken as the end point of the lower base. If there are multiple points showing the maximum value, the position farthest from the upper base is used.

[0038] Based on the four points identified in the above manner, the approximately trapezoidal shape of the nickel film for each sample in the long and short side directions was identified, and the dimensions of the long and short sides of the top surface of the approximately rectangular shape were obtained. Based on this, the areas of the bottom and top surfaces of the nickel film were calculated. The results are shown in Figures 4 and 5. When the nickel film for each sample is used as an internal electrode for an MLCC, as described below, it is divided into two equal parts in the long side direction. Therefore, in Figures 4 and 5, half of the actual measured value is shown as the dimension in the long side direction.

[0039] For both sample A shown in Figure 4 and sample B shown in Figure 5, a tendency was observed in which the lower base dimension increased and the upper base dimension decreased as the step height in the short-side direction of the through-hole increased. The capacitance of capacitors, including MLCCs, is generally required to be guaranteed to be within ±20% of the set value. Therefore, the area of ​​the top surface of the film-formed structure, as determined by the upper base dimension, must be 80% or more of the area of ​​the bottom surface, as determined by the lower base dimension.

[0040] The results of Figure 4 reveal that, for metal masks used to manufacture internal electrodes for 0603-type MLCCs, by setting the step height in the short side direction to 6.3 μm or less, a film with an area ratio (top surface area / bottom surface area) of 0.80 or more can be formed, satisfying this condition. Furthermore, it was also found that by setting the step height in the short side direction to 2.77 μm or less, the area ratio becomes greater than 0.90, resulting in better film formation. The results of Figure 5 reveal that, for metal masks used to manufacture internal electrodes for 0402-type MLCCs, by setting the step height in the short side direction to 4.0 μm or less, a film with an area ratio of 0.80 or more can be formed. Furthermore, it was also found that by setting the step height in the short side direction to 1.5 μm or less, the area ratio of the top surface to the bottom surface (top surface area / bottom surface area) becomes greater than 0.90, resulting in better film formation.

[0041] In order to find a metal mask index that universally indicates the upper limit of the suitable step height in the short side direction for each sample found in this study, we attempted to calculate an index, which is the ratio of the dimension of the short side of a substantially rectangular through hole to the step height in the short side direction (short side dimension / step height in the short side direction). As shown in Figure 4, if the index value is 44.6 or more for a 0603-type metal mask and 44.7 or more for a 0402-type metal mask, it is believed that a film with an area ratio (top surface area / bottom surface area) of 0.80 or more, which satisfies the above-mentioned conditions, can be formed.

[0042] Looking at the relationship between the taper angle and the area ratio, it was shown that Sample A had a taper angle of 43.1° or more, and Sample B had a taper angle of 44.0° or more, and thus a film could be formed with an area ratio (top surface area / bottom surface area) of 0.80 or more. The larger the taper angle, the more difficult it becomes for the film-forming material to pass through the through-holes, which would cause a shadow effect. Therefore, although there is no particular upper limit to the taper angle, in this study, the upper limit of the taper angle was around 61°.

[0043] In both samples A and B, the area ratio of the top and bottom surfaces was greatest at the lowest step height in the short side direction of 0.2 μm, but a decrease in the linearity of the periphery was observed in the planar view of the film-formed structure. Investigation into the cause of this finding revealed that excessive etching from one side caused excessive etching of the substrate at the penetration portion, resulting in the periphery of the through-hole expanding beyond the set point. While the change in the planar shape of the film-formed structure due to this decrease does not immediately adversely affect its performance as an internal electrode for an MLCC, based on this finding, a step height value in the short side direction of 0.3 μm or more was considered more preferable, as it maintained a good planar shape of the film-formed structure.

[0044] FIG. 6 shows an example of a component 50 serving as an internal electrode for an MLCC, formed using the metal mask according to this embodiment. The component 50 has a structure in which a thin film 20 made of a conductor is formed on a substrate 10, such as a dielectric sheet, by sputtering using the metal mask according to this embodiment. Because the thin film 20 is formed using the metal mask according to this embodiment, the ratio of the area of ​​the top surface 21 to the area of ​​the bottom surface 22 in a plan view (top surface area / bottom surface area) is 0.80 or greater. The component 50 is divided into two equal parts in the longitudinal direction, as shown by the dashed-dotted line, to form an internal electrode for an MLCC. The internal electrode for an MLCC is formed by stacking multiple components so that the margins 11 without the thin film 20 are staggered. Even after the component 50 is divided into two equal parts, the area ratio of the top surface 21 to the bottom surface 22 of the thin film 20 remains unchanged, which contributes to the optimal fabrication of an MLCC that guarantees the above-mentioned capacitance. FIG. 7 shows an example of the positional relationship when the internal electrodes for an MLCC are alternately stacked after the component 50 is divided into two equal parts. In practice, a combination of these two MLCC internal electrodes constitutes one set, and many such sets are stacked. The area R1 enclosed by the dashed line is the region that essentially functions as a capacitor. The larger the area of ​​the upper surface within this range, the better the capacitor performance. External terminals are arranged left and right in Figure 7, and are connected to the thin film 20 extending to the left end and the thin film 20 extending to the right end, respectively.

[0045] Although the present invention has been described above, the specific configuration is not limited to this embodiment, and modifications and combinations of the configuration within the scope of the gist of the present invention are also included.

[0046] For example, the substrate of the metal mask according to the present invention is not limited to stainless steel such as SUS430 used in the above study. Therefore, other magnetic metal substrates made of alloys such as Invar and Super Invar may also be used. Forming a thin-film metal substrate from a magnetic metal material as described above offers the advantage of being able to be fixed to a film-forming apparatus using magnetic force. Furthermore, the thickness of the substrate is not limited to 50 μm as used in the above study. Even if the substrate has a different thickness, the same effect can be achieved by setting the step height or index in the short-side direction within the above-mentioned range. When fabricating a metal mask, the substrate may be in the form of a sheet cut to a predetermined length, or may be wound into a roll. Using a roll-shaped substrate allows for continuous and efficient production of metal masks.

[0047] Note that when the metal mask according to the present invention is mounted in a typical film deposition apparatus, either surface in the thickness direction can be placed facing the substrate. Accordingly, the step height in the short-side direction also changes, but the step height in the short-side direction in the present invention is defined as the lower of the two values. Furthermore, due to the manufacturing process, the step height in the metal mask according to the present invention tends to be lower in the short-side direction of the through hole than in the long-side direction. The inventors also conducted a similar study on the step height in the long-side direction and found that the step height in the short-side direction was more closely related to the area of ​​the top surface. Therefore, the step height in the short-side direction is considered to be more useful as an indicator.

[0048] Second Embodiment A second embodiment of the present invention will be described with reference to Figs. 8 to 14. Components of the second embodiment that are common to the first embodiment are given the same reference numerals as in the first embodiment. As shown schematically in Fig. 8, the metal mask 1 according to this embodiment is placed so as to overlap a dielectric sheet 100 as a substrate. In the sputtering process, of the material that flies from the target T toward the metal mask 1, only that which passes through the through holes 1a is deposited on the dielectric sheet 100 to form a film.

[0049] FIG. 9 is an enlarged cross-sectional view of one through hole 1a in the metal mask 1. The through hole 1a is formed by etching the sheet-like metal member (hereinafter simply referred to as the "substrate") constituting the metal mask from both sides in the thickness direction. When the through hole 1a is formed by wet etching, the etching is often performed in two stages. Typically, the surface of the substrate facing the dielectric sheet 100 is etched first, followed by the surface facing the target T. This results in the formation of the through hole 1a. Because etching is isotropic, the planar dimensions of the through hole 1a are larger closer to the surface of the substrate and smaller as they move away from the surface. Therefore, when two-stage etching is performed from both sides of the substrate to fabricate the metal mask 1, the planar dimensions of the formed through hole are smallest at the through portion 1b in the middle of the substrate in the thickness direction. The planar shape and dimensions of the through portion 1b determine the planar shape of the film-formed structure.

[0050] The penetration portion 1b, where the planar dimensions are smallest, is formed at the location where etching from both sides meet. Therefore, the position of the penetration portion 1b in the thickness direction of the substrate changes depending on the degree of etching from each side. The film formation material flies radially from the target. Therefore, if the film formation material enters the through hole 1a at an angle, as shown by the arrow in Figure 9, it may fly beyond the range of the penetration portion 1b in the planar view and reach the dielectric sheet 100 after passing through the penetration portion 1b. This phenomenon is sometimes called the "shadow effect." The probability of this phenomenon occurring increases as the penetration portion 1b is farther from the dielectric sheet 100. Furthermore, the stronger the shadow effect, the smaller the area of ​​the top surface of the formed thin film becomes relative to the area of ​​the bottom surface.

[0051] Based on this, the inventors investigated the step height (shown by the symbol h1 in FIG. 9 ), which is the distance in the thickness direction of the metal mask 1 from the surface located on the dielectric sheet 100 side to the penetration portion 1 b, the step width (shown by the symbol w1 in FIG. 9 ), and the taper angle (shown by the symbol θ in FIG. 9 ), and investigated the conditions for a metal mask suitable for manufacturing internal electrodes for MLCCs.

[0052] (Preparation of Metal Mask Samples) A ​​50 μm-thick stainless steel SUS430 sheet (planar dimensions: 350 mm × 715 mm) was prepared as a substrate. The substrate was etched on both sides using a two-stage etching method to create a large number of through holes at a constant pitch. By varying the amount of etching from both sides, samples with 15 different step heights (step heights on both sides of the long side of the through holes) were prepared, as shown in FIGS. 11 and 12 .

[0053] For each step height, two types of samples were prepared, each with different planar dimensions of the through portion as shown below. Through hole A was intended for producing two internal electrodes for a 0603-type MLCC at a time, and through hole B was intended for producing two internal electrodes for a 0402-type MLCC at a time. In the following description, the metal mask sample with through hole A formed therein will be referred to as sample A, and the metal mask sample with through hole B formed therein will be referred to as sample B. Through hole A (design value): Rectangle with short sides of 280 μm and long sides of 1180 μm Through hole B (design value): Rectangle with short sides of 180 μm and long sides of 780 μm After each sample was completed, the planar dimensions of the through portion 1b of five selected through holes were measured using a measuring device (Nikon NEXIV VMZ-H3030), and the arithmetic mean of the measured values ​​was recorded. In the following discussion, the short side, long side and step height of the through holes are average values ​​based on the actual measurements of the penetration portion 1b of each through hole.

[0054] (Film formation and measurement using metal mask samples) The dielectric sheets used were PET sheets in which a slurry containing barium titanate as the main component was die coated on the surface and then dried to form a 1 μm thick layer on the surface. The dielectric sheets were placed in a sputtering device, and the metal masks for each sample were attached to the dielectric sheets, and films were formed on the dielectric sheets under the following conditions: Target material: nickel Ultimate pressure: 1.0 × 10-5 Pa or less Film formation pressure: 0.65 Pa Input voltage (power): 1.0 kW Input gas type: argon Input gas flow rate: 100 sccm Film thickness: 150 nm (target value)

[0055] Next, the nickel film of each sample was measured to obtain a thickness profile. A Keyence VK-X3000 laser microscope was used as the measurement device. Profiles were taken in two directions: from the midpoint of the long side toward the short side, and from the midpoint of the short side toward the long side. An example of a profile obtained in the short side direction is shown in Figure 10. As shown in Figure 10, the profile was approximately trapezoidal, with upper and lower bases. The starting and ending points of the upper and lower bases were determined based on the following criteria: Based on the profile, the height change from the previous point at each measurement point was calculated. The point where the change was minimal before the film thickness began to increase was defined as the starting point of the lower base. If there were multiple points showing the same minimum value, the position farthest from the upper base was used as the starting point of the lower base. The point where the change increased from the starting point of the lower base and exceeded its peak and reached 0.002 μm for the first time was defined as the starting point of the upper base. The upper base was not completely horizontal (zero change). Therefore, after the start point of the upper base, as long as the amount of change is less than ±0.002, the upper base is considered to continue, and the point where the amount of change first reached -0.002 μm is defined as the end point of the upper base, and the distance between the start point and the end point is taken as the length of the upper base. ・After the end point of the upper base, the point where the amount of change is maximum is taken as the end point of the lower base. If there are multiple points showing the maximum value, the position farthest from the upper base is used.

[0056] Based on the four points identified in the above manner, the approximately trapezoidal shape of the nickel film for each sample in the long and short side directions was identified, and the dimensions of the long and short sides of the top surface of the approximately rectangular shape were obtained. Based on this, the areas of the bottom and top surfaces of the nickel film were calculated. The results are shown in Figures 11 and 12. When the nickel film for each sample is used as an internal electrode for an MLCC, as described below, it is divided into two equal parts in the long side direction. Therefore, in Figures 11 and 12, half of the actual measured value is shown as the dimension in the long side direction.

[0057] For both sample A shown in Figure 11 and sample B shown in Figure 12, a tendency was observed in which the lower base dimension increased and the upper base dimension decreased as the step height in the long side direction of the through hole increased. The capacitance of capacitors, including MLCCs, is generally required to be guaranteed to be within ±20% of the set value. Therefore, the area of ​​the top surface of the film-formed structure, as determined by the upper base dimension, must be 80% or more of the area of ​​the bottom surface, as determined by the lower base dimension.

[0058] The results of Figure 11 reveal that, for metal masks used to manufacture internal electrodes for 0603-type MLCCs, by setting the step height in the long side direction to 3.74 μm or less, a film with an area ratio (top surface area / bottom surface area) of 0.80 or more, which satisfies this condition, can be formed. Furthermore, it was also found that by setting the step height in the long side direction to 1.55 μm or less, the area ratio becomes 0.90 or more, enabling even better film formation. The results of Figure 12 reveal that, for metal masks used to manufacture internal electrodes for 0402-type MLCCs, by setting the step height in the long side direction to 3.03 μm or less, a film with the above area ratio of 0.80 or more can be formed. Furthermore, when an approximation formula was calculated for the graph in which No. 1 to No. 5 of Sample B in FIG. 12 were plotted, it was found that by setting the step height in the long side direction to 1.18 μm or less, the area ratio of the top surface to the bottom surface (top surface area / bottom surface area) became 0.90 or more, and better film formation could be achieved.

[0059] In order to find a metal mask index that universally indicates the preferred upper limit of the step height in the long side direction for each sample found in this study, we attempted to calculate an index, which is the ratio of the long side dimension of a substantially rectangular through hole to the step height in the long side direction (long side dimension / long side step height). As shown in Figure 11, it was believed that if the index value was 315.5 or greater for a 0603-type metal mask and 259.3 or greater for a 0402-type metal mask, it would be possible to form a film with an area ratio (top surface area / bottom surface area) of 0.80 or greater, which satisfies the above-mentioned conditions.

[0060] A similar study was also performed on the step width in the long side direction. The results of Figure 11 revealed that, for metal masks used to manufacture internal electrodes for 0603-type MLCCs, a film with an area ratio (top surface area / bottom surface area) of 0.80 or more, which satisfies this condition, can be formed by setting the step width in the long side direction to 2.81 μm or less. Furthermore, it was also found that an area ratio of 0.96 or more can be achieved by setting the step width in the long side direction to 0.30 μm or less, resulting in even better film formation. The results of Figure 12 revealed that, for metal masks used to manufacture internal electrodes for 0402-type MLCCs, a film with an area ratio of 0.80 or more can be formed by setting the step width in the long side direction to 2.43 μm or less. Furthermore, when an approximation formula was calculated for the graph plotting No. 1 to No. 5 of Sample B in Figure 12, it was found that by setting the step width in the long side direction to 0.73 μm or less, the area ratio of the top surface to the bottom surface (top surface area / bottom surface area) becomes 0.90 or more, thereby enabling better film formation. As shown in Figure 11, it was thought that if the ratio of the long side dimension to the step width in the long side direction (long side dimension / long side step width) is 419.6 or more for the 0603 type metal mask, and if the index value is 323.3 or more for the 0402 type metal mask, it would be possible to form a film with an area ratio (top surface area / bottom surface area) of 0.80 or more that satisfies the above-mentioned conditions.

[0061] Looking at the relationship between the taper angle and the area ratio, it was shown that a film with an area ratio (top surface area / bottom surface area) of 0.80 or more could be formed when the taper angle was 46.5° or more for Sample A and 47.5° or more for Sample B. The larger the taper angle, the less likely it is that the film material will pass through the through-holes, causing a shadow effect. Therefore, although there is no particular upper limit for the taper angle, in this study the upper limit for the taper angle was around 60°.

[0062] In both samples A and B, the area ratio of the top and bottom surfaces was greatest at the lowest step height in the long side direction of 0.2 μm, but a decrease in the linearity of the periphery was observed in the planar view of the film-formed structure. Investigation into the cause of this finding suggested that excessive etching from one side resulted in excessive etching of the substrate at the penetration portion, causing the periphery of the through-hole to expand beyond the specified range. While the change in the planar shape of the film-formed structure due to this decrease does not immediately adversely affect its performance as an internal electrode for an MLCC, given this finding, a step height of 0.3 μm or greater in the long side direction was considered preferable because it maintained a good planar shape of the film-formed structure. A similar tendency was observed for the step width. Therefore, a step width of 0.3 μm or greater in the long side direction was considered preferable because it maintained a good planar shape of the film-formed structure.

[0063] FIG. 13 shows an example of a component 50 serving as an internal electrode for an MLCC, formed using the metal mask according to this embodiment. The component 50 has a structure in which a thin film 20 made of a conductor is formed on a substrate 10, such as a dielectric sheet, by sputtering using the metal mask according to this embodiment. Because the thin film 20 is formed using the metal mask according to this embodiment, the ratio of the area of ​​the top surface 21 to the area of ​​the bottom surface 22 in a plan view (top surface area / bottom surface area) is 0.80 or greater. The component 50 is divided into two equal parts in the longitudinal direction, as shown by the dashed-dotted line, to form an internal electrode for an MLCC. The internal electrode for an MLCC is formed by stacking multiple components so that the margins 11 without the thin film 20 are staggered. Even after the component 50 is divided into two equal parts, the area ratio of the top surface 21 to the bottom surface 22 of the thin film 20 remains unchanged, which contributes to the optimal fabrication of an MLCC that guarantees the above-mentioned capacitance. FIG. 14 shows an example of the positional relationship when the internal electrodes for an MLCC are alternately stacked after the component 50 is divided into two equal parts. In practice, a combination of these two MLCC internal electrodes constitutes one set, and many such sets are stacked. The area R1 enclosed by the dashed line is the region that essentially functions as a capacitor. The larger the area of ​​the upper surface within this range, the better the capacitor performance. External terminals are arranged in the left-right direction of Figure 14, and are connected to the thin film 20 extending to the left end and the thin film 20 extending to the right end, respectively.

[0064] Although the present invention has been described above, the specific configuration is not limited to this embodiment, and modifications and combinations of the configuration within the scope of the gist of the present invention are also included.

[0065] For example, the substrate of the metal mask according to the present invention is not limited to stainless steel such as SUS430 used in the above study. Therefore, other magnetic metal substrates made of alloys such as Invar and Super Invar may also be used. Forming a thin-film metal substrate from a magnetic metal material as described above offers the advantage of being able to be fixed to a film-forming apparatus using magnetic force. Furthermore, the thickness of the substrate is not limited to 50 μm as used in the above study. Even if the thickness is different, similar effects can be achieved by setting the step height and step width in the long-side direction or the corresponding index within the above-mentioned ranges. When fabricating a metal mask, the substrate may be in the form of a sheet cut to a predetermined length, or may be wound into a roll. Using a roll-shaped substrate allows for continuous and efficient production of metal masks.

[0066] The metal mask according to the present invention can be mounted in a normal film forming apparatus with either surface in the thickness direction facing the substrate. The step height and step width in the long side direction also change accordingly, but the step height and step width in the long side direction in the present invention are defined as the lower of the above values.

[0067] (Third Embodiment) A third embodiment of the present invention will be described with reference to Figures 15 to 21. The dimensions of the drawings illustrated in the following description are merely examples, and the present invention is not necessarily limited thereto. Appropriate changes can be made without departing from the spirit of the present invention. In the following drawings, the scale and number of each structure may differ from the actual structure to make each structure easier to understand. The same reference numerals as in the first embodiment are used for the components of the third embodiment.

[0068] In each drawing, the Z axis is indicated as appropriate. In this embodiment, the direction in which Z extends is the direction in which the plate surface of the metal mask faces. In the following description, the direction in which the plate surface of the metal mask faces is simply referred to as the "thickness direction." In the following description, the side in the thickness direction toward which the Z axis arrow faces (+Z side) is referred to as the "back side," and the side in the thickness direction opposite to the side toward which the Z axis arrow faces (-Z side) is referred to as the "front side." Note that the back side and front side are simply names used to describe the relative positional relationships of the various parts of the metal mask, and the actual positional relationships may be other than those indicated by these names.

[0069] In each drawing, the X-axis is indicated as appropriate. In this embodiment, the direction in which the X-axis extends is the long side direction of the through-hole in the metal mask. In the following description, the long side direction of the through-hole in the metal mask will be simply referred to as the "long side direction." The long side direction is perpendicular to the thickness direction.

[0070] In each drawing, the Y axis is indicated as appropriate. In this embodiment, the direction in which the Y axis extends is the short side direction of the through hole in the metal mask. In the following description, the short side direction of the through hole in the metal mask will be simply referred to as the "short side direction." The short side direction is perpendicular to both the thickness direction and the long side direction.

[0071] A third embodiment of the present invention will be described with reference to FIGS. 15 to 21 . FIG. 15 is a schematic diagram showing the positional relationship of a metal mask 1 and other components during film formation. The metal mask 1 of this embodiment is used to manufacture internal electrodes of a multilayer ceramic capacitor (MLCC). As shown in FIG. 15 , the metal mask 1 of this embodiment is placed so as to overlap a dielectric sheet 100 serving as a substrate. In the sputtering process, of the material flying from the target T toward the metal mask 1, only that which passes through the through holes 1 a is deposited on the dielectric sheet 100 to form a film, and as shown in FIG. 16 , a metal thin film 20 is formed on the dielectric sheet 100.

[0072] FIG. 16 is a diagram showing the relationship between the cross-sectional shape of the through hole 1a in the metal mask 1 and the cross-sectional shape of the metal thin film 20. FIG. 16 shows an enlarged cross-sectional shape of the through hole 1a as viewed from the long side direction (X-axis direction). As shown in FIG. 15, in the metal mask 1 of this embodiment, multiple through holes 1a are formed in a metal plate-shaped substrate 15. Each through hole 1a penetrates the substrate 15 in the thickness direction (Z-axis direction). Although not shown, the through holes 1a are rectangular holes in a plan view, with their long sides extending in the long side direction. The through holes 1a are formed by etching the substrate 15 from both sides in the thickness direction.

[0073] When the through hole 1a is formed by wet etching, the etching is often performed in two stages. Typically, first, the first surface 1c of the substrate 15, which faces the dielectric sheet 100, is etched. This forms the first hole 13 shown in FIG. 16. The first hole 13 is a hole recessed from the first surface 1c toward the front surface (-Z side). Then, the second surface 10d, which faces the target T, is etched. This forms the second hole 14 shown in FIG. 16, and the through hole 1a is formed. The second hole 14 is a hole recessed from the second surface 10d toward the back surface (+Z side). Because the etching is isotropic, the planar dimensions of the through hole 1a are larger closer to the surfaces 1c and 10d of the substrate 15 and smaller as they move away from the surfaces 1c and 10d. That is, the planar dimensions of the first hole portions 13 are larger the closer to the first surface 1c, and the planar dimensions of the second hole portions 14 are larger the closer to the second surface 10d. Therefore, when two-stage etching is performed from both sides of the substrate 15 to fabricate the metal mask 1, the planar dimensions of the through holes 1a are smallest at the penetrating portion 1b in the middle in the thickness direction (Z-axis direction) of the substrate 15. The planar shape and dimensions of the penetrating portion 1b determine the planar shape of the metal thin film 20.

[0074] The penetrating portion 1b, which has the smallest size in plan view, is formed at a location where etching from both sides meets, and therefore the position of the penetrating portion 1b in the thickness direction of the substrate 15 changes depending on the extent to which etching is performed from the first surface 1c and the second surface 10d.

[0075] As shown in FIG. 15 , in the sputtering process, the film forming material flies radially from the target T. Therefore, when the film forming material enters the through-hole 1a at an angle, as shown by arrows N in FIG. 16 , after passing through the through-hole 1b, the film forming material flies beyond the range of the through-hole 1b in a plan view and reaches the dielectric sheet 100. This phenomenon is sometimes called the "shadow effect." The probability of this phenomenon occurring increases as the position of the through-hole 1b in the thickness direction (Z-axis direction) becomes farther from the dielectric sheet 100. Furthermore, the stronger the shadow effect, the smaller the area of ​​the top surface 21 of the formed metal thin film 20 becomes relative to the area of ​​the bottom surface 22.

[0076] Based on this, the inventors investigated the step width w1 in the short side direction (Y-axis direction) of the through hole 1a, the length L1 of the short side of the through hole 1a, and the taper angle θ of the through hole 1a shown in Fig. 16, and found the conditions for a metal mask 1 suitable for manufacturing an internal electrode for an MLCC. Note that the step height h1 shown in Fig. 16 is the distance in the thickness direction (Z-axis direction) from the first surface 1c to the through portion 1b.

[0077] In this embodiment, the length L1 of the short side of the through hole 1a is the dimension in the short side direction (Y-axis direction) of the through portion 1b. As described above, the planar dimension of the through hole 1a is smallest at the through portion 1b. Therefore, the length L1 of the short side of the through hole 1a is the smallest dimension of the through hole 1a in the short side direction.

[0078] In this embodiment, the step width w1 in the short-side direction of the through hole 1a is the dimension of the gap between the end of the first hole portion 13 on the back side (+Z side) and the through portion 1b in the short-side direction (Y-axis direction). In the following description, the step width w1 in the short-side direction of the through hole 1a may be simply referred to as the "step width w1." As the step width w1 increases, the film-forming material that enters the through hole 1a at an angle is more likely to reach a portion of the dielectric sheet 100 outside the through portion 1b in a planar view. Therefore, as the step width w1 increases, the shadow effect becomes stronger, and the length Lb1 (see FIG. 17 ) of the short side of the bottom surface 22 of the metal thin film 20 becomes longer. On the other hand, as the step width w1 decreases, the film-forming material that enters the through hole 1a at an angle is less likely to reach a portion of the dielectric sheet 100 outside the through portion 1b in a planar view. Therefore, the smaller the step width w1, the weaker the shadow effect, and therefore the shorter the length Lb1 of the short side of the bottom surface 22 of the metal thin film 20. As a result, the smaller the step width w1, the smaller the difference between the length Lb1 of the short side of the bottom surface 22 of the metal thin film 20 and the length Lu1 of the short side of the top surface 21 of the metal thin film 20 (see FIG. 17 ).

[0079] In this embodiment, the step width w1, i.e., the step width in the short side direction of the through hole 1a, is preferably 3.5 μm or less to reduce the shadow effect. The step width w1 is more preferably 2.1 μm or less. Furthermore, as will be described later, the step width w1 is preferably 0.2 μm or more to ensure good linearity of the peripheral edge of the deposited metal thin film 20.

[0080] In this embodiment, the taper angle θ of the through hole 1a is the angle between a first imaginary line V1 passing through the end of the second hole portion 14 on the surface side (-Z side) and the through portion 1b, and a second imaginary line V2 passing through the through portion 1b and extending in the short side direction (Y axis direction), as viewed from the long side direction (X axis direction). In the following description, the taper angle θ of the through hole 1a may be simply referred to as the "taper angle θ." As indicated by arrow N, the film-forming material entering the through hole 1a at the greatest inclination with respect to the thickness direction (Z axis direction) flies in a direction parallel to the first imaginary line V1. Therefore, the smaller the taper angle θ, the more easily the film-forming material flying in a direction with a greater inclination with respect to the thickness direction reaches the dielectric sheet 100. Therefore, as the taper angle θ becomes smaller, the shadow effect becomes stronger, and therefore the length Lb1 of the short side of the bottom surface 22 of the metal thin film 20 (see FIG. 17) becomes longer than the length Lu1 of the short side of the top surface 21 of the metal thin film 20 (see FIG. 17). On the other hand, as the taper angle θ becomes larger, it becomes more difficult for the film formation material flying in a direction with a large inclination relative to the thickness direction to reach the dielectric sheet 100. Therefore, as the taper angle θ becomes larger, the shadow effect becomes weaker, and therefore the length Lb1 of the short side of the bottom surface 22 of the metal thin film 20 becomes shorter. As a result, as the taper angle θ becomes larger, the difference between the length Lb1 of the short side of the bottom surface 22 of the metal thin film 20 and the length Lu1 of the short side of the top surface 21 of the metal thin film 20 becomes smaller.

[0081] (Preparation of Metal Mask Samples) A ​​50 μm-thick stainless steel SUS430 sheet (planar dimensions: 350 mm × 715 mm) was prepared as the substrate 15. Two-stage etching was performed on both sides of the substrate 15 to create multiple through holes 1 a at a constant pitch. By varying the amount of etching from both sides, multiple samples with different step widths w1, step width indexes Is, and taper angles θ were prepared, as shown in FIGS. 18 and 19 . The substrate 15 used to prepare the metal mask may be in the form of a sheet cut to a predetermined length, or may be wound into a roll. Using a roll-shaped substrate 15 allows for continuous and efficient production of metal masks.

[0082] In this embodiment, the step width index Is is the ratio of the length L1 of the short side of the through hole 1a to the step width w1 in the short side direction of the through hole 1a (length L1 of the short side of the through hole 1a / step width w1 in the short side direction of the through hole 1a). As will be described later, the step width index Is was calculated with the aim of finding an index of the metal mask 1 that universally indicates the upper limit of the suitable step width w1 in the short side direction for each sample found in this study. In this embodiment, the step width index Is is 85.1 or greater.

[0083] In this embodiment, two types of samples were prepared, with different planar dimensions of the through hole 1a, i.e., the planar dimensions of the through portion 1b, as follows: Through hole A is intended for producing two internal electrodes for a 0603 type MLCC at a time, and through hole B is intended for producing two internal electrodes for a 0402 type MLCC at a time. In the following explanation, the metal mask sample with through hole A formed therein will be referred to as sample A, and the metal mask sample with through hole B formed therein will be referred to as sample B. Through hole A (design value): Rectangle with short sides of 280 μm and long sides of 1180 μm Through hole B (design value): Rectangle with short sides of 180 μm and long sides of 780 μm

[0084] In this embodiment, 15 types of samples A were fabricated, each having a different step width w1, step width index Is, and taper angle θ, as shown in Fig. 18. In addition, in this embodiment, 15 types of samples B were fabricated, each having a different step width w1, step width index Is, and taper angle θ, as shown in Fig. 19.

[0085] After each sample shown in FIGS. 18 and 19 was completed, a measuring device (Nikon NEXIV VMZ-H3030) was used to measure the planar dimensions of the through portions 1b in five arbitrarily selected through holes 1a, and the arithmetic mean values ​​of the measured values ​​were defined as the length L1 of the short side of the through hole 1a and the length L2 of the long side of the through hole 1a shown in FIGS. 18 and 19, respectively.

[0086] Furthermore, a laser microscope (Keyence VK-X3000) was used to observe an arbitrarily selected through hole 1a from the back surface side (+Z side), i.e., the dielectric sheet 100 side, to obtain cross-sectional profile data of the through hole 1a, and the cross-sectional profile data was processed to calculate the step width w1 in the short side direction of the through hole 1a, which was defined as the step width w1 in the short side direction shown in each of Figures 18 and 19. Furthermore, the ratio of the length L1 of the short side of the through hole 1a to the step width w1 in the short side direction was calculated, which was defined as the step width index Is shown in each of Figures 18 and 19.

[0087] Furthermore, a laser microscope (Keyence VK-X3000) was used to observe an arbitrarily selected through hole 1a from the front surface side (-Z side), i.e., the target T side, to obtain cross-sectional profile data of the through hole 1a. By processing the cross-sectional profile data, the taper angle θ of the through hole 1a in the short side direction was calculated, and this was set as the taper angle θ in the short side direction shown in each of FIGS.

[0088] (Film formation and shape measurement using metal mask samples) The dielectric sheet 100 used was a PET sheet in which a slurry containing barium titanate as a main component was die coated on the surface of the sheet and then dried to form a layer of 1 μm in thickness on the surface of the sheet. The dielectric sheet 100 was placed in a sputtering device, and the metal mask 1 for each sample was attached to the dielectric sheet 100, and a metal thin film 20 was formed on the dielectric sheet 100 under the following conditions: Target material: nickel Ultimate pressure: 1.0 × 10-5 Pa or less Film formation pressure: 0.65 Pa Input voltage (power): 1.0 kW Input gas type: argon Input gas flow rate: 100 sccm Film thickness: 150 nm (target value)

[0089] Next, a laser microscope (Keyence VK-X3000) was used to obtain a thickness profile of the metal thin film 20 formed on the dielectric sheet 100 using the metal mask 1 of each sample. The thickness profile of the metal thin film 20 was obtained in two directions: from the midpoint of the long side of the metal thin film 20 in the short side direction (Y-axis direction), and from the midpoint of the short side of the metal thin film 20 in the long side direction (X-axis direction).

[0090] Fig. 17 is an example of a thickness profile of the deposited metal thin film 20. Fig. 17 is an example of a thickness profile of the metal thin film 20 obtained in the short side direction (Y-axis direction). The thickness profile of the metal thin film 20 is substantially trapezoidal having an upper surface (upper base) 21 and a bottom surface (lower base) 22, and the start and end points of the upper surface 21 and the bottom surface 22 are specified according to the following criteria.

[0091] The amount of change in height from the previous point at each measurement point was determined based on the thickness profile shown in Fig. 17. The point at which the amount of change was minimum before the thickness of the metal thin film 20 began to increase was taken as the starting point of the bottom surface 22. Note that if there were multiple points at which the same minimum value was observed, the position farthest from the top surface 21 was taken as the starting point of the bottom surface 22.

[0092] Next, the point where the change in height from the previous point increased from the start point of the bottom surface 22 and exceeded the maximum value, and then reached 0.002 μm for the first time, was determined as the start point of the top surface 21. The top surface 21 is not perfectly horizontal (zero change). Therefore, as long as the change in height from the previous point after the start point of the top surface 21 is less than ±0.002 μm, the top surface 21 is considered to be continuous, and the point where the change in height first reached −0.002 μm was determined as the end point of the top surface 21. The distance between the start point and end point of the top surface 21 was determined as the length Lu1 of the short side of the top surface 21 or the length of the long side (not shown).

[0093] Next, after the end point of the top surface 21, the portion where the amount of change in height from the previous point shows the maximum value was determined as the end point of the bottom surface 22. If there are multiple portions where the amount of change in height from the previous point shows the maximum value, the position farthest from the top surface 21 was determined as the end point of the bottom surface 22. The distance between the start point and end point of the bottom surface 22 was determined as the length Lb1 of the short side of the bottom surface 22 or the length of the long side (not shown).

[0094] Based on the four points, i.e., the start and end points of the top surface 21 and the start and end points of the bottom surface 22, identified as described above, the approximately trapezoidal shape of the metal thin film 20 formed using each sample in the long and short side directions was identified, and the length Lu1 of the short side of the approximately rectangular top surface 21, the length of the long side of the top surface 21, the length Lb1 of the short side of the approximately rectangular bottom surface 22, and the length of the long side of the bottom surface 22 were obtained. Furthermore, the area of ​​the top surface 21 of the metal thin film 20 was calculated based on the length Lu1 of the short side of the top surface 21 and the length of the long side of the top surface 21, and the area of ​​the bottom surface 22 of the metal thin film 20 was calculated based on the length Lb1 of the short side of the bottom surface 22 of the metal thin film 20 and the length of the long side of the bottom surface 22.

[0095] Note that the metal thin film 20 formed by each sample is divided into two equal parts in the long side direction (X-axis direction) when used as an internal electrode for an MLCC, as described below (see FIG. 21 ). Therefore, in FIGS. 18 and 19 , half of the measured areas of the top surface 21 and bottom surface 22 of the metal thin film 20 are shown as the area Su of the top surface 21 and the area Sb of the bottom surface 22, respectively. Additionally, the area ratio Rs, which is the ratio of the area Su of the top surface to the area Sb of the bottom surface 22 (Su / Sb), was calculated and shown in FIGS. 18 and 19 . The stronger the shadow effect, the smaller the area ratio Rs, and the weaker the shadow effect, the larger the area ratio Rs. Furthermore, the larger the area ratio Rs, the smaller the area difference between the bottom surface 22 and the top surface 21.

[0096] Although not shown, for both Sample A and Sample B, the length Lu1 of the short side of the top surface 21 tended to increase as the step width index Is increased. Furthermore, the length Lb1 of the short side of the bottom surface 22 tended to decrease as the step width index Is increased. This is because, as described above, as the step width w1 decreases, it becomes more difficult for the film-forming material entering the through-hole 1a at an angle to reach areas outside the through-hole 1b in the planar view of the dielectric sheet 100, weakening the shadow effect. Furthermore, as shown in FIGS. 18 and 19 , the area Su of the top surface 21 tended to increase and the area Sb of the bottom surface 22 tended to decrease as the step width index Is increased. Therefore, the area ratio Rs tended to increase as the step width index Is increased. In other words, the area difference between the bottom surface 22 and the top surface 21 decreased as the step width index Is increased.

[0097] Although not shown, for both Sample A and Sample B, the length Lu1 of the short side of the top surface 21 tended to increase as the step width w1 decreased. Furthermore, the length Lb1 of the short side of the bottom surface 22 tended to decrease as the step width w1 decreased. This is due to the fact that the shadow effect weakens as the step width w1 decreases, as described above. As a result, as shown in FIGS. 18 and 19 , the area Su of the top surface 21 tended to increase and the area Sb of the bottom surface 22 tended to decrease as the step width w1 decreased. Therefore, the area ratio Rs increased and the area difference between the bottom surface 22 and the top surface 21 decreased as the step width w1 decreased.

[0098] Although not shown, for both Sample A and Sample B, the length Lu1 of the short side of the top surface 21 tended to increase as the taper angle θ increased. Furthermore, the length Lb1 of the short side of the bottom surface 22 tended to decrease as the taper angle θ increased. This is because, as described above, as the taper angle θ increases, it becomes more difficult for the film-forming material flying in a direction with a greater inclination relative to the thickness direction (Z-axis direction) to reach the dielectric sheet 100, weakening the shadow effect. Furthermore, as shown in Figures 18 and 19, the area Su of the top surface 21 tended to increase and the area Sb of the bottom surface 22 tended to decrease as the taper angle θ increased. Therefore, the area ratio Rs tended to increase as the taper angle θ increased. In other words, the area difference between the bottom surface 22 and the top surface 21 decreased as the taper angle θ increased.

[0099] The capacitance of capacitors, including MLCCs, is generally required to be within ±20% of the set value. Therefore, the area Su of the top surface 21 of the metal thin film 20 is required to be 80% or more of the area Sb of the bottom surface 22 formed according to the target value. In other words, the area ratio Rs is required to be 0.80. In the results columns of each of Figures 18 and 19, samples with an area ratio Rs of 0.80 or more are marked with a circle (Good), and samples with an area ratio Rs of less than 0.80 are marked with an × (Poor).

[0100] As shown in Figure 18, in the metal mask 1 of sample A used for manufacturing internal electrodes for 0603-type MLCCs, it was found that a metal thin film 20 with an area ratio Rs of 0.80 or more can be formed by setting the step width index Is, i.e., the ratio of the length L1 of the short side of the through hole 1a to the step width w1 in the short side direction of the through hole 1a, to 79.3 or more. Also, as shown in Figure 18, it was found that a metal thin film 20 with an area ratio Rs of 0.80 or more can be formed by setting the step width w1, i.e., the step width in the short side direction, to 3.5 μm or less. Furthermore, as shown in Figure 18, it was found that a metal thin film 20 with an area ratio Rs of 0.80 or more can be formed by setting the taper angle θ to 43.1° or more.

[0101] 19 , it was revealed that, in the metal mask 1 of sample B used to manufacture internal electrodes for 0402-type MLCCs, a metal thin film 20 with an area ratio Rs of 0.80 or more can be formed by setting the step width index Is, i.e., the ratio of the length L1 of the short side of the through hole 1a to the step width w1 in the short side direction of the through hole 1a, to 85.1 or more. Therefore, it was revealed that, by setting the step width index Is to 85.1, a metal thin film 20 with an area ratio Rs of 0.80 or more can be formed in both the metal mask 1 used to manufacture internal electrodes for 0402-type MLCCs and the metal mask 1 used to manufacture internal electrodes for 0603-type MLCCs. This ensures stable capacitance of the MLCC.

[0102] 19, it was also revealed that by setting the step width w1 to 2.1 μm or less, a metal thin film 20 having an area ratio Rs of 0.80 or more can be formed. Therefore, it was revealed that by setting the step width w1, i.e., the step width in the short side direction, to 2.1 μm or less, a metal thin film 20 having an area ratio Rs of 0.80 or more can be formed in both the metal mask 1 used to manufacture internal electrodes for 0603 type MLCCs and the metal mask 1 used to manufacture internal electrodes for 0402 type MLCCs. This makes it possible to stably guarantee the capacitance of the MLCC.

[0103] Furthermore, it was found that by setting the taper angle θ to 44.0° or more, it is possible to form a metal thin film 20 having an area ratio Rs of 0.80 or more. Therefore, it was found that by setting the taper angle θ to 44.0° or more, it is possible to form a metal thin film 20 having an area ratio Rs of 0.80 or more in both the metal mask 1 used to manufacture internal electrodes for 0603 type MLCCs and the metal mask 1 used to manufacture internal electrodes for 0402 type MLCCs. This makes it possible to stably guarantee the capacitance of the MLCC.

[0104] For both metal mask samples A and B, the area ratio Rs was greatest in the sample with the narrowest step width w1 in the short side direction of 0.1 μm, but a decrease in the linearity of the periphery of the metal thin film 20 was observed in plan view. Investigation into the cause of this suggests that excessive etching from the first surface 1 c resulted in excessive etching of the substrate 15 at the penetration portion 1 b, causing the periphery of the through hole 1 a to expand beyond the set point. While this decrease in the linearity of the periphery of the metal thin film 20 does not immediately adversely affect its performance as an internal electrode for an MLCC, given this finding, it is considered more preferable to set the step width w1 in the short side direction to 0.2 μm or more, as this allows for a good planar shape of the metal thin film 20 to be formed.

[0105] FIG. 20 is a schematic plan view showing an example of a member 50 formed using the metal mask 1 according to this embodiment. Next, an example of a member 50 serving as an internal electrode for an MLCC, formed using the metal mask 1 according to this embodiment, will be described. The member 50 has a structure in which a thin metal film 20 made of a conductor is formed on a substrate such as a dielectric sheet 100 by sputtering using the metal mask 1 according to this embodiment. Because the thin metal film 20 is formed using the metal mask 1 according to this embodiment, the area ratio Rs, i.e., the ratio of the area Su of the top surface to the area Sb of the bottom surface 22 (Su / Sb), is 0.80 or greater. The member 50 is divided into two equal parts in the long side direction (X-axis direction) at the portion indicated by the dashed dotted line to form an internal electrode for an MLCC. The internal electrode for an MLCC is formed by stacking multiple members so that the margins 11 without the thin metal film 20 are staggered. Since the area ratio Rs of the thin metal film 20 remains unchanged even after the member 50 is divided into two equal parts, this contributes to the favorable fabrication of an MLCC with guaranteed capacitance.

[0106] FIG. 21 is a schematic diagram showing an example of a lamination pattern of the member 50. FIG. 21 shows an example of the positional relationship when the member 50 is divided into two equal parts and then the MLCC internal electrodes are alternately laminated. In practice, a combination of two MLCC internal electrodes forms one set, and many sets are stacked. The area R1 surrounded by the dashed line is the region that essentially functions as a capacitor. The larger the area Su of the upper surface 21 within this range, the better the performance of the capacitor. External terminals are arranged in the left-right direction of FIG. 21, and the external terminals are connected to the metal thin film 20 extending to the left end and the metal thin film 20 extending to the right end, respectively.

[0107] According to this embodiment, the metal mask 1 is a metal mask for manufacturing internal electrodes of a multilayer ceramic capacitor, having a metal substrate 15 with through holes 1a that are rectangular in plan view. The step width index Is, i.e., the ratio of the short-side length L1 of the through holes 1a to the step width w1 in the short-side direction of the through holes 1a (short-side length L1 / short-side step width w1), is 85.1 or greater. Therefore, as described above, it is possible to form a metal thin film 20 having an area ratio Rs, which is the ratio of the area Su of the top surface 21 to the area Sb of the bottom surface 22, of 0.80 or greater. This allows the formation of a metal thin film 20 with a small area difference between the bottom surface 22 and the top surface 21. This ensures stable capacitance of the MLCC.

[0108] According to this embodiment, the step width w1 in the short side direction is 0.2 μm or more. Therefore, as described above, it is possible to prevent the linearity of the peripheral edge of the deposited metal thin film 20 from decreasing. Therefore, it is possible to deposit a metal thin film 20 with a good shape in plan view.

[0109] According to this embodiment, the step width w1 in the short side direction is 3.5 μm or less. Therefore, as described above, the metal mask 1 of sample A used in manufacturing an internal electrode for a 0603-type MLCC can form a metal thin film 20 with an area ratio Rs of 0.80 or more. This allows the metal thin film 20 to be formed with a small area difference between the bottom surface 22 and the top surface 21, thereby ensuring a stable capacitance of the MLCC.

[0110] According to this embodiment, the step width w1 in the short side direction is 2.1 μm or less. Therefore, as described above, in each of sample A used to manufacture an internal electrode for a 0603-type MLCC and sample B used to manufacture an internal electrode for a 0402-type MLCC, a metal thin film 20 having an area ratio Rs of 0.80 or more can be formed. This allows the metal thin film 20 to be formed with a small area difference between the bottom surface 22 and the top surface 21, thereby ensuring a stable capacitance of the MLCC.

[0111] Although the present invention has been described above, the specific configuration is not limited to this embodiment, and modifications and combinations of the configuration within the scope of the gist of the present invention are also included.

[0112] For example, the substrate of the metal mask according to the present invention is not limited to stainless steel such as SUS430 used in the above study. Therefore, other magnetic metal substrates made of alloys such as Invar and Super Invar may also be used. Metal substrates made of magnetic metal materials such as those described above have the advantage of being able to be fixed to a film deposition apparatus using magnetic force. Furthermore, the thickness of the substrate is not limited to 50 μm as in the above study, but may be a different thickness. By setting the step width index, step width, or step angle within the above ranges, a metal thin film with a small area difference between the bottom and top surfaces can be deposited.

[0113] Although the present invention has been described above, the specific configurations are not limited to the first to third embodiments, and include modifications and combinations of the configurations within the scope of the present invention. For example, it is possible to replace part of the configurations of the above embodiments with well-known configurations, or to combine the configurations of the above embodiments with each other, as appropriate, within the scope of the present invention.

[0114] In the present application, the three embodiments measure samples A and B, which are partially identical. As a basis for this, in FIGS. 4 and 5 for the first embodiment, FIGS. 11 and 12 for the second embodiment, and FIGS. 18 and 19 for the third embodiment, samples A and B are shown with the same values ​​for the upper and lower surface areas of the film-formed object in the three embodiments. Therefore, for example, it is possible to combine the configurations of the first and third embodiments. According to the measurement results of the first and third embodiments, it is believed that rectangularity is good if two of the three parameters related to the through-hole shape, namely, the step height in the short side direction and the taper angle in the short side direction, or two of the step width in the short side direction and the taper angle in the short side direction, are within the above-mentioned ranges. It is believed that rectangularity is even better if all of the step height in the short side direction, the taper angle in the short side direction, and the step width in the short side direction are within the above-mentioned ranges.

[0115] According to the present invention, it is possible to provide a metal mask that can form a metal thin film with a small difference in area between the bottom surface and the top surface.

[0116] REFERENCE SIGNS LIST 1 metal mask 1a through hole 10 substrate 20 thin film 21 upper surface 22 bottom surface h1 step height in the short side direction of the through hole h2 step height in the long side direction of the through hole w2 step width in the long side direction of the through hole 15 base material L1 length of the short side of the through hole w1 step width in the short side direction of the through hole

Claims

1. A metal mask for manufacturing internal electrodes of a multilayer ceramic capacitor, in which a through hole that is rectangular in plan view is formed in a metal substrate, wherein the ratio of the length of the short side of the through hole to the step height in the short side direction of the through hole (the length of the short side / the step height in the short side direction) is 44.6 or more.

2. The metal mask according to claim 1, wherein the step height is 0.3 μm or more.

3. The metal mask according to claim 2, wherein the step height is 6.3 μm or less.

4. The metal mask according to claim 2, wherein the step height is 4.0 μm or less.

5. The metal mask according to claim 1, wherein the through hole has a taper angle in the direction of its short side of 44.0° or more.

6. The metal mask according to claim 5, wherein the taper angle is 61° or less.

7. A metal mask for manufacturing internal electrodes of a multilayer ceramic capacitor, in which a through hole that is rectangular in plan view is formed in a metal substrate, wherein the ratio of the length of the long side of the through hole to the step height in the long side direction of the through hole (the length of the long side / the step height in the long side direction) is 315.5 or more.

8. The metal mask according to claim 7, wherein the ratio of the length of the long side of the through hole to the step width in the long side direction of the through hole (the length of the long side / the step width in the long side direction) is 419.6 or more.

9. The metal mask according to claim 8, wherein the step height is 0.3 μm or more.

10. The metal mask according to claim 9, wherein the step height is 3.0 μm or less.

11. The metal mask according to claim 9 or 10, wherein the step width is 0.3 μm or more.

12. The metal mask according to claim 9 or 10, wherein the step width is 2.4 μm or less.

13. The metal mask according to claim 7, wherein the taper angle of the through hole in the direction of the long side is 47.5° or more.

14. A metal mask for manufacturing internal electrodes of a multilayer ceramic capacitor, in which a through hole that is rectangular in plan view is formed in a metal substrate, wherein the ratio of the length of the short side of the through hole to the step width in the short side direction of the through hole (length of the short side / step width in the short side direction) is 85.1 or more.

15. The metal mask according to claim 14, wherein the step width is 0.2 μm or more.

16. The metal mask according to claim 15, wherein the step width is 3.5 μm or less.

17. The metal mask according to claim 15, wherein the step width is 2.1 μm or less.

18. The metal mask according to any one of claims 1 to 17, wherein the substrate is made of a magnetic alloy.

19. The metal mask according to claim 18, wherein the alloy is one of SUS430, Invar, and Super Invar.

20. An internal electrode for a multilayer ceramic capacitor in which a thin film made of a conductor is formed on a dielectric substrate, wherein the ratio of the area of ​​the top surface to the area of ​​the bottom surface in a plan view of the thin film (the area of ​​the top surface / the area of ​​the bottom surface) is 0.80 or more.

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