Liquid discharge head manufacturing method and processing method

Abstract

To suppress generation of residue when forming an open hole by performing metal assist chemical etching from both surfaces of a substrate.SOLUTION: A liquid discharge head manufacturing method includes: a first etching process in which a first metal film is formed on a first face which is one plate face of a semiconductor substrate, and a first hole is formed at a position of a first flow path by metal assist chemical etching using the first metal film; and a second etching process in which after the first etching process, a second metal film is formed on a second face which is a plate face opposite to the first face of the semiconductor substrate, and a second hole is formed at a position of a second flow path by metal assist chemical etching using the second metal film. A first region, in which the first metal film is provided, involves a second region in which the second metal film is provided when viewed in a thickness direction of the semiconductor substrate.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a manufacturing method and a processing method for a liquid ejection head. [Background technology]

[0002] A liquid ejection head, typified by an inkjet head, generally includes a substrate having a flow path for a liquid such as ink. Patent Document 1 describes that a through hole that constitutes part of the flow path is formed by metal-assisted etching of a single crystal silicon substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-167472 Summary of the Invention [Problem to be solved by the invention]

[0004] When through-holes are formed by metal-assisted chemical etching from both sides of the substrate, residue or burrs may be generated. [Means for solving the problem]

[0005] A preferred embodiment of the present invention provides a method for manufacturing a liquid ejection head, which includes a flow path substrate having a first flow path opening on one plate surface and a second flow path opening on the other plate surface and communicating with the first flow path, and includes a first etching step of forming a first hole at a position that will become the first flow path by metal-assisted chemical etching using a first metal film formed on a first surface, which is one of the plate surfaces of the substrate, and a second etching step of forming a second hole at a position that will become the second flow path by metal-assisted chemical etching using a second metal film formed on a second surface, which is the plate surface opposite to the first surface of the substrate, after the first etching step, and wherein, when viewed in the thickness direction of the substrate, the first region, which is the region where the first metal film is provided, encompasses a second region, which is the region where the second metal film is provided.

[0006] A preferred embodiment of the processing method of the present invention is a processing method for forming a through hole in a substrate by metal-assisted chemical etching, comprising: a first etching step for forming a first hole by metal-assisted chemical etching using a first metal film formed on a first surface, which is one of the surfaces of the substrate; and a second etching step for forming a second hole penetrating the first hole by metal-assisted chemical etching using a second metal film formed on a second surface, which is the surface of the substrate opposite to the first surface, after the first etching step, wherein, when viewed in the thickness direction of the substrate, the first region, which is the region where the first metal film is provided, encompasses the second region, which is the region where the second metal film is provided. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of the configuration of a liquid ejection device. [Figure 2] FIG. 2 is an exploded perspective view of the liquid ejection head shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line aa in FIG. 2. [Figure 4] FIG. 4 is a plan view of the flow path substrate shown in FIG. [Figure 5] FIG. 5 is an enlarged view of a portion of the flow path substrate shown in FIG. [Figure 6]5A to 5C are diagrams illustrating a flow of a manufacturing method of a liquid ejection head according to an embodiment. [Figure 7] 7A to 7D are diagrams for explaining the steps from protective film forming step S1 to protective film forming step S4 shown in FIG. 6. [Figure 8] 7A to 7C are diagrams for explaining the steps from the second metal film forming step S5 to the third etching step S7 shown in FIG. 6. [Figure 9] 10 is a cross-sectional view of a substrate to which a processing method according to Modification 1 can be applied. FIG. [Figure 10] 10A to 10D are diagrams for explaining each step from a protective film forming step S1A to a protective film forming step S4A in Modification 1. [Figure 11] 10A to 10C are diagrams for explaining each step from a second metal film forming step S5A to a third etching step S7A in Modification 1. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the dimensions and scale of each part in the drawings may differ from the actual dimensions and are shown schematically to facilitate understanding. Furthermore, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited thereto.

[0009] In the following description, the mutually intersecting X-axis, Y-axis, and Z-axis will be used as appropriate. Furthermore, one direction along the X-axis will be referred to as the X1 direction, and the direction opposite to the X1 direction will be referred to as the X2 direction. Similarly, opposite directions along the Y-axis will be referred to as the Y1 direction and the Y2 direction. Furthermore, opposite directions along the Z-axis will be referred to as the Z1 direction and the Z2 direction. Furthermore, viewing in the direction along the Z-axis is referred to as "planar view."

[0010] The relationship between these axes and the vertical axis is not particularly limited and can be arbitrary. Furthermore, the X-axis, Y-axis, and Z-axis are typically perpendicular to each other, but are not limited to this and may intersect at an angle between 80° and 100°, for example.

[0011] 1. Embodiment 1-1. Overall configuration of the liquid ejection device 1 is a schematic diagram showing an example of the configuration of a liquid ejection device 1. The liquid ejection device 1 is an inkjet printing device that ejects ink, an example of a liquid, as droplets onto a medium 12. The medium 12 is typically printing paper. However, the medium 12 is not limited to printing paper and may be a printing target made of any material, such as a resin film or fabric.

[0012] As shown in FIG. 1, the liquid ejection device 1 includes a liquid container 14, a control unit 20, a transport mechanism 22, a moving mechanism 24, and a liquid ejection head 3.

[0013] The liquid container 14 is a container that stores ink. Specific examples of the liquid container 14 include a cartridge that is detachable from the liquid ejection device 1, a bag-shaped ink pack made of flexible film, and an ink tank that can be refilled with ink. The type of ink stored in the liquid container 14 is arbitrary.

[0014] The control unit 20 includes one or more processing circuits such as a CPU (Central Processing Unit) or FPGA (Field Programmable Gate Array) and one or more storage circuits such as semiconductor memory, and controls each element of the liquid ejection device 1 in an integrated manner.

[0015] The transport mechanism 22 transports the medium 12 in a direction along the Y axis under the control of the control unit 20. The movement mechanism 24 reciprocates the liquid ejection head 3 along the X axis under the control of the control unit 20. In the example shown in FIG. 1, the movement mechanism 24 includes a substantially box-shaped transport body 242 that houses the liquid ejection head 3, and a transport belt 244 to which the transport body 242 is fixed. Note that the number of liquid ejection heads 3 mounted on the transport body 242 is not limited to one, and may be two or more. In addition to the liquid ejection heads 3, the transport body 242 may also be equipped with liquid containers 14.

[0016] The liquid ejection head 3 ejects ink supplied from the liquid container 14 from multiple nozzles onto the medium 12 under the control of the control unit 20. This ejection is performed in parallel with the transportation of the medium 12 by the transport mechanism 22 and the repeated reciprocation of the transport body 242, thereby forming an ink image on the surface of the medium 12.

[0017] 1-2. Overall configuration of liquid ejection head 3 Fig. 2 is an exploded perspective view of the liquid ejection head 3 shown in Fig. 1. Fig. 3 is a cross-sectional view taken along line aa in Fig. 2. Fig. 3 shows a cross section of the liquid ejection head 3 cut along the XZ plane.

[0018] As shown in Fig. 2, the liquid ejection head 3 includes a plurality of nozzles N arranged along the Y axis. The plurality of nozzles N are divided into a first row La and a second row Lb arranged side by side at intervals along the X axis. Each of the first row La and the second row Lb is a collection of a plurality of nozzles N arranged linearly along the Y axis. The liquid ejection head 3 has a structure in which elements related to each nozzle N in the first row La and elements related to each nozzle N in the second row Lb are arranged in approximate plane symmetry.

[0019] 2 and 3, the liquid ejection head 3 includes a flow path structure 30, a plurality of piezoelectric elements 34, a sealing substrate 35, a housing 36, and a wiring substrate 40. The flow path structure 30 is a structure in which flow paths are formed to supply ink to each of a plurality of nozzles N. The flow path structure 30 includes a flow path substrate 31, a pressure chamber substrate 32, a vibration plate 33, a nozzle substrate 37, and a vibration absorber 38.

[0020] Each member constituting the flow path structure 30 is a long plate-like member extending along the Y axis. A pressure chamber substrate 32 and a housing 36 are disposed on the surface of the flow path substrate 31 facing in the Z2 direction. A nozzle substrate 37 and a vibration absorber 38 are disposed on the surface of the flow path substrate 31 facing in the Z1 direction. These members are fixed together, for example, by adhesive.

[0021] The nozzle substrate 37 is a plate-like member on which a plurality of nozzles N are formed. Each of the plurality of nozzles N is a through-hole that ejects ink. The nozzle substrate 37 is manufactured by processing a single crystal silicon (Si) substrate using semiconductor manufacturing techniques such as photolithography and etching.

[0022] The flow path substrate 31 is formed with a plurality of throttle portions 312, a plurality of communication flow paths 314, a communication space Ra, and a common flow path Rb. The common flow path Rb is an example of a "first flow path" and opens onto one plate surface of the flow path substrate 31 facing the Z1 direction. The throttle portion 312 is an example of a "second flow path" and opens onto the other plate surface of the flow path substrate 31 facing the Z2 direction, and damps vibrations of the liquid generated in the pressure chamber C1. The throttle portion 312 and the communication flow path 314 each extend along the Z axis and are through-holes formed for each nozzle N. The communication flow path 314 overlaps the nozzle N in a planar view. The communication space Ra is an opening formed in an elongated shape along the Y axis. The communication space Ra extends along the Y axis. The common flow path Rb is in communication with the communication space Ra and overlaps the communication space Ra in a planar view. The common flow path Rb extends along the Y axis. The common flow path Rb communicates with a plurality of throttle portions 312. Furthermore, the communication space Ra communicates the common flow path Rb with an external flow path of the liquid ejection head 3 via a space Rc, which will be described later.

[0023] The common flow path Rb may be an individual flow path provided for each pressure chamber C1. In this case, the flow path resistance of the throttle portion 312 and the individual flow paths can be reduced compared to a case where the throttle portion 312 and the individual flow paths are formed by dry etching. This is because, when holes are formed by dry etching, grooves are formed along a direction intersecting the depth direction of the holes, whereas when holes are formed by metal-assisted chemical etching, grooves are formed along the depth direction of the holes.

[0024] A plurality of pressure chambers C1 are formed in the pressure chamber substrate 32. The pressure chambers C1 are located between the flow path substrate 31 and the vibration plate 33, and are spaces formed by the wall surface 320 of the pressure chamber substrate 32. A pressure chamber C1 is formed for each nozzle N. The pressure chamber C1 is an elongated space extending in the X1 direction. The plurality of pressure chambers C1 are arranged along the Y axis. One end of the pressure chamber C1 in the X1 direction is connected to the nozzle N via a communicating flow path 314. The other end of the pressure chamber C1 in the X1 direction is connected to a throttle portion 312. The throttle portion 312 has a smaller cross-sectional area than the pressure chamber C1. By providing the communicating flow path 314 and the throttle portion 312 in the Z1 direction for the pressure chamber C1, nozzles can be arranged at a high density, and the liquid ejection head 3 can be made smaller and more densely packed.

[0025] Each of the flow path substrate 31 and the pressure chamber substrate 32 is manufactured by processing a semiconductor substrate such as a silicon single crystal substrate.

[0026] An elastically deformable vibration plate 33 is disposed on the surface of the pressure chamber substrate 32 facing the Z2 direction. The vibration plate 33 is laminated on the pressure chamber substrate 32 and contacts the surface of the pressure chamber substrate 32 opposite the flow path substrate 31. The vibration plate 33 is a plate-like member formed in an elongated rectangular shape along the Y axis in a plan view. The thickness direction of the vibration plate 33 is parallel to the Z1 direction. The pressure chamber C1 communicates with the communicating flow path 314 and the throttle portion 312. Therefore, the pressure chamber C1 communicates with the nozzle N via the communicating flow path 314, and also communicates with the communication space Ra via the throttle portion 312.

[0027] A piezoelectric element 34 is formed for each pressure chamber C1 on the surface of the vibration plate 33 opposite to the pressure chamber C1. The piezoelectric element 34 is a passive element that is elongated along the X-axis in a plan view. When a drive signal is applied to the piezoelectric element 34, it generates pressure fluctuations in the pressure chamber C1 to eject ink. Note that instead of the piezoelectric element 34, a heater may be used that heats the pressure chamber C1 to generate pressure fluctuations to eject ink.

[0028] The housing 36 is a case for storing ink to be supplied to the multiple pressure chambers C1, and is formed, for example, by injection molding of a resin material. A space Rc and a supply port 361 are formed in the housing 36. The supply port 361 is a conduit through which ink is supplied from the liquid container 14, and is connected to the space Rc. The space Rc in the housing 36 and the communication space Ra in the flow path substrate 31 are connected to each other. The communication space Ra, the common flow path Rb, and the space Rc form a common space R that is shared by the multiple nozzles N. The common space R functions as a liquid storage chamber that stores ink to be supplied to the multiple pressure chambers C1. The ink stored in the common space R branches off to each of the throttle sections 312 and is supplied to and filled in parallel into the multiple pressure chambers C1.

[0029] The vibration absorber 38 is a flexible film that forms the wall surface of the communication space Ra, and absorbs pressure fluctuations of the ink in the common space R. The vibration absorber 38 is, for example, a laminate of an ink-resistant resin film, a SUS (stainless steel) member that holds the resin film and has spring properties, and a fixing plate that protects the resin film and the SUS member. By providing the vibration absorber 38, the natural frequency of the flow path from the nozzle N through the pressure chamber C1 to the throttle section 312 is stabilized regardless of the nozzle N that is driven.

[0030] The sealing substrate 35 is a structure that protects the multiple piezoelectric elements 34 and reinforces the mechanical strength of the pressure chamber substrate 32 and the vibration plate 33, and is fixed to the surface of the vibration plate 33 with, for example, an adhesive. The multiple piezoelectric elements 34 are housed inside a recess formed on the surface of the sealing substrate 35 facing the vibration plate 33. A wiring board 40 is inserted through a through hole 362 of the housing part 36 and a through hole 353 of the sealing substrate 35. The wiring board 40 is bonded to the surface of the vibration plate 33. The wiring board 40 is a mounting component on which multiple wiring lines are formed for electrically connecting the control unit 20 and the liquid ejection head 3. For example, a TCP (Tape Carrier Package) or an FPC (Flexible Printed Circuit) is used as the wiring board 40. A drive signal and a reference voltage for driving the piezoelectric elements 34 are supplied to each piezoelectric element 34 from the wiring board 40.

[0031] In the liquid ejection head 3, when the piezoelectric element 34 contracts due to energization, the vibration plate 33 is bent and deflected in a direction that reduces the volume of the pressure chamber C1, and the pressure inside the pressure chamber C1 increases, causing an ink droplet to be ejected from the nozzle N. At this time, pressure also propagates from the pressure chamber C1 toward the throttle portion 312, causing ink to flow into the common flow path Rb through the throttle portion 312. After the ink is ejected, the piezoelectric element 34 returns to its original position. At this time, the ink in the common flow path Rb from the nozzle N also vibrates. Then, at the same time as the meniscus of the nozzle N restores its original shape, ink is supplied from the throttle portion 312. Through the above series of operations, ink is ejected from the nozzle N.

[0032] 1-3. Flow path substrate 31 FIG. 4 is a plan view of the flow path substrate 31 shown in FIG. 3. As shown in FIG. 4, the flow path substrate 31 is formed with a communication space Ra, a common flow path Rb, multiple throttle portions 312, and multiple communicating flow paths 314. The communication space Ra extends along the Y axis. The common flow path Rb extends along the Y axis and encompasses the communication space Ra and the multiple throttle portions 312 when viewed in the thickness direction of the flow path substrate 31, i.e., when viewed in the direction along the Z axis. The multiple throttle portions 312 and the multiple communicating flow paths 314 are provided, for example, in one-to-one correspondence with the multiple nozzles N. Note that several throttle portions 312 may correspond to one nozzle N. The multiple throttle portions 312 are spaced apart from one another and aligned along the Y axis. The multiple communicating flow paths 314 are spaced apart from one another and aligned along the Y axis. The multiple communicating flow paths 314 are spaced apart from the common flow path Rb and the multiple throttle portions 312.

[0033] Fig. 5 is an enlarged view of a portion of the flow path substrate 31 shown in Fig. 4. As shown in Fig. 5, the cross-sectional area of ​​the throttle section 312 parallel to the XY plane is smaller than the cross-sectional area of ​​the communicating flow path 314 parallel to the XY plane. Furthermore, the cross-sectional area of ​​the throttle section 312 parallel to the XY plane is smaller than the cross-sectional area of ​​the common flow path Rb along the Z axis. Furthermore, the shape and the like of the common flow path Rb are designed so that the flow path resistances of the multiple throttle sections 312 are equal to each other.

[0034] In the series of ink ejection operations described above, vibrations that occur when ink is ejected are damped by the flow path resistance within the flow path that runs from the nozzle N through the pressure chamber C1 to the throttle section 312. The flow path resistance within this flow path is mainly due to the flow path resistance of the throttle section 312. This is because the cross-sectional area of ​​the throttle section 312 parallel to the XY plane is smaller than both the cross-sectional area of ​​the common flow path Rb parallel to the Z axis and the cross-sectional area of ​​the pressure chamber C1 along the Z axis. The flow path resistance within this flow path can be adjusted by adjusting the number of throttle sections 312 or their cross-sectional areas.

[0035] In the example shown in Fig. 5, the cross-sectional shape of the throttle portion 312 is rectangular. Note that the cross-sectional shape of the throttle portion 312 is not limited to the example shown in Fig. 5, i.e., is not limited to a square, and may be, for example, a circle, an ellipse, or a polygon other than a square. Furthermore, the throttle portion 312 may be configured with two or more holes for one pressure chamber C1.

[0036] 1-4. Manufacturing method of liquid ejection head 6 is a diagram showing the flow of a manufacturing method of a liquid ejection head 3 according to an embodiment. The manufacturing method of a liquid ejection head includes a manufacturing method of a flow path substrate 31. As shown in FIG. 6, the manufacturing method of the flow path substrate 31 includes, in this order, a protective film forming step S1, a first metal film forming step S2, a first etching step S3, a protective film forming step S4, a second metal film forming step S5, a second etching step S6, and a third etching step S7. Note that the manufacturing method of the flow path substrate 31 can also be said to be a processing method for forming through holes in a substrate 31a by metal-assisted chemical etching.

[0037] As will be described later, metal-assisted chemical etching is used in each of the first etching step S3 and the second etching step S6. Metal-assisted chemical etching is abbreviated as MACE (Metal-Assisted Chemical Etching). By using metal-assisted chemical etching, it is possible to realize the constricted portion 312 having a configuration that is difficult to process using conventional methods. Furthermore, by performing the first etching step S3 before the second etching step S6, in other words, by performing the second etching step S6 after the first etching step S3, it is possible to prevent residue or burrs from being generated near the connection portion between the constricted portion 312 and the common flow path Rb.

[0038] Furthermore, dry etching, which processes each wafer individually, requires an extremely long processing time, potentially reducing productivity and the investment efficiency of the vacuum equipment used for manufacturing. However, metal-assisted chemical etching allows for simultaneous etching of multiple wafers, reducing the processing time required. Furthermore, while anisotropic wet etching along the crystal orientation makes it difficult to control the aspect ratio of the constricted portion 312, metal-assisted chemical etching makes it easy to form the constricted portion 312 with the desired aspect ratio. Therefore, metal-assisted chemical etching allows for the highly precise formation of the constricted portion 312 with the desired aspect ratio through the through-hole. This allows the movement of the meniscus to be controlled by the constricted portion 312, providing a compact liquid ejection head 3 with excellent ejection performance.

[0039] Fig. 7 is a diagram for explaining each step from protective film forming step S1 to protective film forming step S4 shown in Fig. 6. As shown in Fig. 7, first, in protective film forming step S1, a protective film 41 is formed on a first surface 301 of the substrate 31a, and a protective film 42 is formed on a second surface 302 of the substrate 31a.

[0040] The substrate 31a is a base material that becomes the flow path substrate 31, and is, for example, a semiconductor substrate such as an N-type single crystal silicon substrate with a (100) crystal orientation. The first surface 301 is one of the surfaces of the substrate 31a. The second surface 302 is the other surface, i.e., the surface opposite to the first surface 301 of the substrate 31a.

[0041] The substrate 31a is not limited to an N-type single crystal silicon substrate, but may be any substrate containing a semiconductor material. However, by using an N-type single crystal silicon substrate, metal-assisted chemical etching can be performed efficiently due to the action of carrier electrons. Furthermore, surface roughness is unlikely to occur even with a high etching rate.

[0042] Each of the protective films 41, 42 is made of, for example, diamond-like carbon. Diamond-like carbon is abbreviated as DLC. For example, the protective films 41, 42 are formed by a CVD (chemical vapor deposition) method or a sputtering method. The material of the protective films 41, 42 is not limited to diamond-like carbon as long as it is resistant to hydrofluoric acid. For example, silicon carbide (SiC), silicon nitride, rubber-based resist material, etc. may be used. Each of the protective films 41, 42 may be made of multiple films made of different materials. Another film, such as a silicon oxide film, may be interposed between the protective film 41 and the substrate 31a. Similarly, another film, such as a silicon oxide film, may be interposed between the protective film 42 and the substrate 31a.

[0043] After the protective film forming step S1, in the first metal film forming step S2, the first metal film 44 is formed on the first surface 301 of the substrate 31a.

[0044] In the first metal film forming step S2, although not shown, first, portions of the protective film 41 corresponding to the communicating flow paths 314 and the common flow path Rb are removed by etching with oxygen plasma or the like. Then, a resist pattern having openings corresponding to the communicating flow paths 314 and the common flow path Rb is formed on the protective film 41, and then a constituent material of the first metal film 44 is uniformly formed by a film forming method such as sputtering so as to cover the openings. Thereafter, the resist pattern is lifted off to form the first metal film 44 in the first region R1, which is the portion of the first surface 301 corresponding to the communicating flow paths 314 and the common flow path Rb.

[0045] The constituent material of the first metal film 44 is a metal that can be used in metal-assisted chemical etching. Specifically, examples of the constituent material of the first metal film 44 include gold (Au), platinum (Pt), ruthenium (Ru), palladium (Pd), molybdenum (Mo), chromium (Cr), copper (Cu), tantalum (Ta), titanium (Ti), iridium (Ir), silver (Ag), and rhodium (Rh). Among these, the first metal film 44 is preferably made of gold (Au). This allows metal-assisted chemical etching using the first metal film 44 to be performed efficiently.

[0046] After the first metal film forming step S2, in the first etching step S3, the first holes H1a and H1b are formed by metal-assisted chemical etching using the first metal film 44.

[0047] The first hole H1a is a bottomed hole formed in the first surface 301 at a position that will become the common flow path Rb, and constitutes at least a part of the common flow path Rb. The hole H1b is a bottomed hole formed in the first surface 301 at a position that will become the communicating flow path 314, and constitutes a part of the communicating flow path 314. In this embodiment, the first hole H1a becomes the common flow path Rb after undergoing a third etching step S7, which will be described later, but it can also be said that it constitutes the common flow path Rb.

[0048] The metal-assisted chemical etching in the first etching step S3 uses, for example, a solvent containing hydrogen fluoride and an oxidizing agent, and repeats the following cycles: oxidation of the substrate 31a due to the catalytic action of the material constituting the first metal film 44, etching of the oxide on the substrate 31a by the solvent, and adsorption between the first metal film 44 and the substrate 31a due to Coulomb force. As a result, first holes H1a and H1b are formed as bottomed holes opening in the first surface 301. Here, the first hole H1a is formed in the first region R1 of the first surface 301.

[0049] The oxidizing agent is not particularly limited, but examples thereof include hydrogen peroxide (H2O2) and nitric acid (HNO3). In particular, when the substrate 31a is a silicon substrate, the oxidizing agent is preferably hydrogen peroxide for efficient formation of an oxide on the substrate 31a. Note that the type of solvent is not limited to containing hydrogen fluoride and an oxidizing agent, as long as metal-assisted chemical etching is possible.

[0050] After the first etching step S3, in the protective film forming step S4, the first metal film 44 is removed, and then the protective films 41 and 42 are removed by plasma ashing or the like. Then, a protective film 51 is formed on the first surface 301 of the substrate 31a, and a protective film 52 is formed on the second surface 302 of the substrate 31a. Here, the protective film 51 has portions provided on the side surfaces and bottom surfaces of the first holes H1a and H1b. In this way, the protective film forming step S4 forms the etching protective film 51 for the first holes H1a between the first etching step S3 and the second etching step S6.

[0051] Like the protective films 41 and 42 described above, each of the protective films 51 and 52 is made of, for example, diamond-like carbon. For example, the protective film 42 is formed by a CVD method or a sputtering method. The material of the protective films 51 and 52 is not limited to diamond-like carbon as long as it is resistant to hydrofluoric acid. For example, silicon carbide (SiC), silicon nitride, a rubber-based resist material, or the like may be used. Each of the protective films 51 and 52 may be made of a plurality of films made of different materials. Another film, such as a silicon oxide film, may be interposed between the protective film 51 and the substrate 31a. Similarly, another film, such as a silicon oxide film, may be interposed between the protective film 52 and the substrate 31a.

[0052] Fig. 8 is a diagram for explaining each step from the second metal film forming step S5 to the third etching step S7 shown in Fig. 6. After the above-described protective film forming step S4, as shown in Fig. 8, in the second metal film forming step S5, a second metal film 54 is formed on the second surface 302 of the substrate 31a.

[0053] In the second metal film forming step S5, although not shown, first, portions of the protective film 52 corresponding to the constricted portion 312, the communicating flow path 314, and the communicating space Ra are removed by etching with oxygen plasma or the like. Then, a resist pattern having openings in portions corresponding to the constricted portion 312, the communicating flow path 314, and the communicating space Ra is formed on the protective film 52, and then a constituent material of the second metal film 54 is uniformly formed by a film forming method such as sputtering so as to cover the openings. Thereafter, the second metal film 54 is formed on the second surface 302 in portions corresponding to the constricted portion 312, the communicating flow path 314, and the communicating space Ra by lifting off the resist pattern.

[0054] The material of the second metal film 54 is a metal that can be used in metal-assisted chemical etching, similar to the first metal film 44. Specific examples of materials that can be used in the second metal film 54 include gold (Au), platinum (Pt), ruthenium (Ru), palladium (Pd), molybdenum (Mo), chromium (Cr), copper (Cu), tantalum (Ta), titanium (Ti), iridium (Ir), silver (Ag), and rhodium (Rh). Of these, the second metal film 54 is preferably made of gold (Au). This allows efficient metal-assisted chemical etching using the second metal film 54.

[0055] After the second metal film forming step S5, in the second etching step S6, the second hole H2a and holes H2b and H2c are formed by metal-assisted chemical etching using the second metal film 54.

[0056] The second hole H2a is a through-hole formed in a position on the second surface 302 that will become the throttle portion 312, and constitutes at least a part of the throttle portion 312. The hole H2b is a through-hole formed in a position on the second surface 302 that will become the communication space Ra, and constitutes at least a part of the communication space Ra. The hole H2c is a through-hole formed in a position on the second surface 302 that will become the communication flow path 314, and constitutes a part of the communication flow path 314. In this embodiment, the second hole H2a becomes the throttle portion 312 after undergoing a third etching step S7, which will be described later, but it can also be said that the second hole H2a constitutes the throttle portion 312.

[0057] In the metal-assisted chemical etching of the second etching step S6, similar to the first etching step S3, a solvent containing, for example, hydrogen fluoride and an oxidizing agent is used, and the following processes are repeated: oxidation of the substrate 31a due to the catalytic action of the constituent material of the second metal film 54, etching of the oxide on the substrate 31a by the solvent, and adsorption between the second metal film 54 and the substrate 31a due to Coulomb force. As a result, second holes H2a and holes H2b and H2c are formed as bottomed holes opening on the second surface 302.

[0058] Here, when viewed in the thickness direction of the substrate 31a, the second region R2, which is the region where the second metal film 54 is provided, is included in the first region R1, which is the region where the first metal film 44 is provided. In other words, when viewed in the thickness direction of the substrate 31a, the first region R1, which is the region where the first metal film 44 is provided, includes the second region R2, which is the region where the second metal film 54 is provided. The second hole H2a is formed in the second region R2 of the second surface 302.

[0059] In this way, the first region R1 encompasses the second region R2 in the thickness direction of the substrate 31a, which prevents residue or burrs from forming near the connection between the first hole H1a and the second hole H2a. In contrast, in an embodiment in which the second etching step S6 is performed before the first etching step S3, the second region R2 does not encompass the first region R1 in the thickness direction of the substrate 31a in the first etching step S3. Therefore, when the first hole H1a reaches the second hole H2a, over-etching occurs in the thickness direction in the region of the second region R2 that is not encompassed by the first region R1. Therefore, in an embodiment in which the second etching step is performed before the first etching step S3, there is a risk of residue or burrs forming near the connection between the first hole H1a and the second hole H2a.

[0060] Because the first region R1 encompasses the second region R2 in the thickness direction of the substrate 31a, as etching progresses in the second etching step S6, the second metal film 54 in the second hole H2a reaches the protective film 51 provided on the bottom surface of the first hole H1a. At this time, the protective film 51 functions as a stop layer for the etching. Therefore, in the second etching step, the etching is stopped when the second metal film 54 in the second hole H2a reaches the protective film 51 provided on the bottom surface of the first hole H1a. As a result, over-etching by the second metal film 54 in the second hole H2a can be suppressed, and the generation of residue or burrs near the connection portion between the first hole H1a and the second hole H2a can be suppressed.

[0061] Here, if the second metal film 54 is made of gold and the protective film 51 is made of diamond-like carbon, in the second etching step S6, when the etching to form the second hole H2a is stopped by the protective film 51 acting as an etching stop layer, the second metal film 54 is adsorbed to the protective film 51 due to the intermolecular force between the gold and the diamond-like carbon, thereby suppressing etching and over-etching due to unintended movement of the second metal film 54.

[0062] Similarly, the second metal film 54 in the hole H2b reaches the protective film 51 provided on the bottom surface of the first hole H1a. Moreover, the second metal film 54 in the hole H2c reaches the protective film 51 provided on the bottom surface of the hole H1b.

[0063] After the second etching step S6, in a third etching step S7, the second metal film 54 is removed, and then the protective films 51 and 52 are removed by plasma ashing or the like, and the wall surfaces of the first hole H1a, hole H1b, second hole H2a, hole H2b, and hole H2c are smoothed by etching. Here, the removal of the protective film 51 causes the first hole H1a to communicate with the second hole H2 and hole H2b. Furthermore, the removal of the protective film 51 causes hole H1b to communicate with hole H2c.

[0064] The etching in the third etching step S7 is not particularly limited as long as it is capable of smoothing, and may be anisotropic etching or isotropic etching. Furthermore, the third etching step S7 may perform smoothing by forming an oxide film by oxidizing the surface of the substrate 31a and then removing the oxide film by etching. In addition to the smoothing process, the third etching step S7 may also form other holes or recesses by etching. Furthermore, the third etching step S7 may be performed until the unevenness disappears, or the unevenness may remain. The smoothing process in the third etching step S7 may be performed as needed or may be omitted.

[0065] In the above-described manufacturing method of the liquid ejection head 3, as described above, the first region R1 encompasses the second region R2 when viewed in the thickness direction of the substrate 31a, and therefore, it is possible to prevent residues or burrs from being generated near the connection between the first hole H1a and the second hole H2a.

[0066] As described above, the protective film forming step S4 forms an etching protective film 51 for the first hole H1a between the first etching step S3 and the second etching step S6. This allows the protective film 51 to be used as an etching stop layer for the etching that forms the second hole H2a in the second etching step S6. This prevents over-etching of the second hole H2a. This also prevents roughening of the wall surface of the first hole H1a due to etching in the second etching step S6.

[0067] Furthermore, as described above, when the first metal film 44 and the second metal film 54 are each made of gold and the protective film 51 is made of diamond-like carbon, metal-assisted chemical etching can be performed efficiently because the first metal film 44 and the second metal film 54 are each made of gold. Also, in the second etching step S6, when the etching to form the second hole H2a is stopped by the protective film 51 acting as an etching stop layer, the second metal film 54 is adsorbed to the protective film 51 due to the intermolecular force between the gold and the diamond-like carbon, so that etching and over-etching due to unintended movement of the second metal film 54 can be suppressed.

[0068] As described above, the third etching step S7 etches the side surfaces of the first hole H1a and the second hole H2a after the second etching step S6. This allows the third etching step S7 to smooth out any irregularities that may be formed on the side surfaces of the first hole H1a and the second hole H2a by metal-assisted chemical etching. As a result, the flow path resistance of the common flow path Rb and the throttle portion 312 can be reduced.

[0069] 2. Variations The above-described exemplary embodiments may be modified in various ways. Specific modifications that may be applied to the above-described embodiments are exemplified below. Two or more modifications arbitrarily selected from the following examples may be combined as appropriate to the extent that they are not mutually inconsistent.

[0070] 2-1. Variation 1 9 is a cross-sectional view of a substrate 100 to which the processing method according to Modification 1 can be applied. Modification 1 will be described below, focusing on differences from the above-described embodiment, and omitting descriptions of similar points as appropriate.

[0071] The substrate 100 is a substrate such as a silicon substrate, whose thickness direction is along the Z axis. As shown in Fig. 9, the substrate 100 has two through holes HL1 and one through hole HL2.

[0072] The through-hole HL1 penetrates the substrate 100 in the thickness direction and is composed of a first hole H1c and a second hole H2d. The first hole H1c is a hole that opens into one of the surfaces of the substrate 100 facing the Z1 direction. The second hole H2d is a hole that opens into one of the surfaces of the substrate 100 facing the Z2 direction. Here, when viewed in the thickness direction of the substrate 100, the first hole H1c encompasses the second hole H2d, and the second hole H2d opens into the bottom surface of the first hole H1c. The cross-sectional shapes of the first hole H1c and the second hole H2d are not particularly limited and can be any. Furthermore, as long as the first hole H1c encompasses the second hole H2d when viewed in the thickness direction of the substrate 100, the size ratio of the first hole H1c to the second hole H2d is also not particularly limited and can be any.

[0073] The through hole HL2 penetrates the substrate 100 in the thickness direction and is composed of a third hole H1d and a fourth hole H2e. The third hole H1d is a hole that opens into one of the surfaces of the substrate 100 facing the Z2 direction. The fourth hole H2e is a hole that opens into one of the surfaces of the substrate 100 facing the Z1 direction. Here, when viewed in the thickness direction of the substrate 100, the third hole H1d encompasses the fourth hole H2e, and the fourth hole H2e opens into the bottom surface of the third hole H1d. The cross-sectional shapes of the third hole H1d and the fourth hole H2e are not particularly limited and can be any. Furthermore, as long as the third hole H1d encompasses the fourth hole H2e when viewed in the thickness direction of the substrate 100, the size ratio of the third hole H1d to the fourth hole H2e is also not particularly limited and can be any.

[0074] Fig. 10 is a diagram for explaining each step from protective film forming step S1A to protective film forming step S4A in Modification 1. Fig. 11 is a diagram for explaining each step from second metal film forming step S5A to third etching step S7A in Modification 1. As shown in Figs. 10 and 11, the processing method of Modification 1 includes, in this order, a protective film forming step S1A, a first metal film forming step S2A, a first etching step S3A, a protective film forming step S4A, a second metal film forming step S5A, a second etching step S6A, and a third etching step S7A.

[0075] First, as shown in FIG. 10, in the protective film forming step S1A, a protective film 41 is formed on the first surface 301 of the substrate 100a, and a protective film 42 is formed on the second surface 302 of the substrate 100a.

[0076] The substrate 100a is a base material that will become the substrate 100, and similar to the substrate 31a described above, is a semiconductor substrate such as an N-type single crystal silicon substrate with a crystal orientation (100).

[0077] After the protective film forming step S1A, in the first metal film forming step S2A, a first metal film 44 is formed on the first surface 301 of the substrate 100a, and a third metal film 45 is formed on the second surface 302 of the substrate 100a.

[0078] In the first metal film forming process S2A, the first metal film 44 is formed at a position that will become the first hole H1c on the first surface 301. In addition, in the first metal film forming process S2A, the third metal film 45 is formed at a position that will become the third hole H1d on the second surface 302. Note that the third metal film 45 is formed in the same manner as the first metal film 44, except that it is formed on the second surface 302.

[0079] After the first metal film forming step S2A, in the first etching step S3A, the first hole H1c and the third hole H1d are formed by metal-assisted chemical etching using the first metal film 44 and the third metal film 45.

[0080] After the first etching step S3A, in a protective film forming step S4A, the first metal film 44 and the third metal film 45 are removed, and then the protective films 41 and 42 are removed by plasma ashing or the like. Thereafter, a protective film 51 is formed on the first surface 301 of the substrate 100a, and a protective film 52 is formed on the second surface 302 of the substrate 100a. Here, the protective film 51 has portions provided on the side surfaces and bottom surfaces of the first holes H1c. The protective film 52 has portions provided on the side surfaces and bottom surfaces of the third holes H1d.

[0081] After the above protective film forming process S4A, as shown in FIG. 11, in the second metal film forming process S5A, a second metal film 54 is formed on the second surface 302 of the substrate 100a, and a fourth metal film 55 is formed on the first surface 301 of the substrate 100a.

[0082] In the second metal film forming process S5A, the second metal film 54 is formed at a position that will become the second hole H2d on the second surface 302. Also, in the second metal film forming process S5A, the fourth metal film 55 is formed at a position that will become the fourth hole H2e on the first surface 301. Note that the fourth metal film 55 is formed in the same manner as the second metal film 54, except that it is formed on the first surface 301.

[0083] Here, when viewed in the thickness direction of the substrate 100a, the second region R2, which is the region where the second metal film 54 is provided, is included in the first region R1, which is the region where the above-mentioned first metal film 44 is provided. In other words, when viewed in the thickness direction of the substrate 100a, the first region R1, which is the region where the first metal film 44 is provided, includes the second region R2, which is the region where the second metal film 54 is provided.

[0084] Further, when viewed in the thickness direction of the substrate 100a, the fourth region R4, which is the region where the fourth metal film 55 is provided, is included in the third region R3, which is the region where the above-mentioned third metal film 45 is provided. In other words, when viewed in the thickness direction of the substrate 100a, the third region R3, which is the region where the third metal film 45 is provided, includes the fourth region R4, which is the region where the fourth metal film 55 is provided.

[0085] After the second metal film forming step S5A, in the second etching step S6A, the second hole H2d and the fourth hole H2e are formed by metal-assisted chemical etching using the second metal film 54 and the fourth metal film 55.

[0086] As described above, since the first region R1 encompasses the second region R2 in the thickness direction of the substrate 100a, it is possible to prevent residues or burrs from being generated near the connection between the first hole H1a and the second hole H2a. Furthermore, as etching progresses in the second etching step S6A, the second metal film 54 in the second hole H2d reaches the protective film 51 provided on the bottom surface of the first hole H1c. At this time, the protective film 51 functions as a stop layer for the etching.

[0087] Similarly, because the third region R3 encompasses the fourth region R4 in the thickness direction of the substrate 100a, it is possible to prevent residues or burrs from being generated near the connection between the third hole H3d and the fourth hole H2e. Furthermore, as etching progresses in the second etching step S6A, the fourth metal film 55 in the fourth hole H2e reaches the protective film 52 provided on the bottom surface of the third hole H1d. At this time, the protective film 52 functions as a stop layer for the etching.

[0088] After the second etching step S6A, in a third etching step S7A, the second metal film 54 and the fourth metal film 55 are removed, and then the protective films 51 and 52 are removed by plasma ashing or the like, thereby obtaining the substrate 100. Note that in the third etching step S7A, the wall surfaces of the through holes HL1 and HL2 may be smoothed by etching, similar to the third etching step S7 in the previous embodiment.

[0089] According to the above-described first modification, the through holes HL1 and HL2 can be formed while suppressing the generation of residues or burrs.

[0090] 2-2. Variation 2 In the above embodiment, a liquid ejection head has been described as an example, but the processing method of the present disclosure is applicable not only to the manufacture of the flow path substrate 31 of the liquid ejection head 3, but also to the manufacture of components other than the flow path substrate 31 of the liquid ejection head 3, and is also applicable to the manufacture of various components and electronic devices having through holes other than the liquid ejection head 3. For example, the processing method of the present disclosure may be applied to the manufacture of the nozzles N of the nozzle substrate 37, or may be applied to the manufacture of the communicating flow paths 314 of the flow path substrate 31. Furthermore, when the common flow path Rb is the "first flow path," the communicating space Ra may be the "first flow path" instead of or in addition to the restricting portion 312.

[0091] 2-3. Variation 3 The liquid ejection head 3 may be a so-called circulation type head. In this case, the liquid ejection head 3 further includes a circulation mechanism 26. In this case, the throttle section 312 functions as a supply port, but may also function as a discharge port.

[0092] 2-4. Variation 4 In the above-described embodiment, the first metal film 44 and the second metal film 54 are formed by sputtering or the like, but the present invention is not limited to this. For example, the first metal film 44 and the second metal film 54 may be formed by electroless plating. In this case, a resist film is used as a mask.

[0093] 2-5. Variation 5 The liquid ejection device 1 exemplified in the first embodiment can be employed in various devices such as facsimile machines and copiers, as well as devices dedicated to printing. The uses of the liquid ejection device are not limited to printing. For example, a liquid ejection device that ejects a solution of a color material is used as a manufacturing device for forming color filters for display devices such as liquid crystal display panels. Furthermore, a liquid ejection device that ejects a solution of a conductive material is used as a manufacturing device for forming wiring and electrodes on a wiring board. Furthermore, a liquid ejection device that ejects a solution of an organic substance related to a living organism is used as a manufacturing device for manufacturing biochips, for example. 3. Notes A summary of this disclosure is provided below.

[0094] (Appendix 1) A first aspect, which is a preferred example of the method for manufacturing a liquid ejection head of the present disclosure, is a method for manufacturing a liquid ejection head including a flow path substrate having a first flow path opening on one plate surface and a second flow path opening on the other plate surface and communicating with the first flow path, and includes a first etching step of forming a first hole at a position that will become the first flow path by metal-assisted chemical etching using a first metal film formed on a first surface, which is one plate surface of the substrate, and a second etching step of forming a second hole at a position that will become the second flow path by metal-assisted chemical etching using a second metal film formed on a second surface, which is the plate surface opposite to the first surface of the substrate, after the first etching step, and wherein, when viewed in the thickness direction of the substrate, the first region, which is the region where the first metal film is provided, encompasses a second region, which is the region where the second metal film is provided.

[0095] In the above-described embodiment, it is possible to prevent residues or burrs from forming near the connection between the first hole and the second hole. In contrast, in an embodiment in which the second etching step is performed before the first etching step, the second region does not encompass the first region in the thickness direction of the substrate in the first etching step. Therefore, when the first hole reaches the second hole, over-etching occurs in the thickness direction in the region where the second region R2 is not encompassed by the first region R1. Therefore, in an embodiment in which the second etching step is performed before the first etching step, there is a risk of residues or burrs forming near the connection between the first hole and the second hole.

[0096] (Supplementary Note 2) In the second embodiment, which is a preferred example of the first embodiment, a protective film formation step of forming an etching protective film on the first hole is further included between the first etching step and the second etching step. In the above embodiment, the protective film can be used as an etching stop layer for the etching that forms the second hole in the second etching step. This makes it possible to prevent over-etching of the second hole. It is also possible to prevent roughening of the wall surface of the first hole due to etching in the second etching step.

[0097] (Supplementary Note 3) In a third aspect, which is a preferred example of the second aspect, the first metal film and the second metal film are each made of gold, and the protective film is made of diamond-like carbon. In the above aspect, since the first metal film and the second metal film are each made of gold, metal-assisted chemical etching can be performed efficiently. Furthermore, in the second etching step, when the etching to form the second hole is stopped by the protective film acting as an etching stop layer, the second metal film is adsorbed to the protective film due to the intermolecular force between gold and diamond-like carbon, which can prevent etching and over-etching due to unintended movement of the second metal film.

[0098] (Supplementary Note 4) In a fourth embodiment, which is a preferred example of any of the first to third embodiments, the method further includes a third etching step of etching the side surfaces of the first hole and the second hole after the second etching step. In this embodiment, even if irregularities are formed on the side surfaces of the first hole and the second hole by metal-assisted chemical etching, the irregularities can be smoothed out by the third etching step. As a result, the flow path resistance of each of the first flow path and the second flow path can be reduced.

[0099] (Supplementary Note 5) In a fifth aspect, which is a preferred example of any of the first to fourth aspects, the first flow path is an individual flow path provided for each pressure chamber, and the second flow path is a throttle portion that reduces vibrations of the liquid generated in the pressure chamber. In the above aspect, throttle portions and individual flow paths with lower flow path resistance can be obtained compared to aspects in which the throttle portions and individual flow paths are formed by dry etching. This is because, when holes are formed by dry etching, grooves are formed that run along a direction intersecting the depth direction of the holes, whereas when holes are formed by metal-assisted chemical etching, grooves are formed that run along the depth direction of the holes.

[0100] (Appendix 6) A sixth aspect, which is a preferred example of the processing method of the present disclosure, is a processing method for forming a through hole in a substrate by metal-assisted chemical etching, and includes a first etching step of forming a first hole by metal-assisted chemical etching using a first metal film formed on a first surface, which is one of the plate surfaces of the substrate, and a second etching step of forming a second hole penetrating the first hole by metal-assisted chemical etching using a second metal film formed on a second surface, which is the plate surface opposite to the first surface of the substrate, after the first etching step, wherein, when viewed in the thickness direction of the substrate, the first region, which is the region where the first metal film is provided, encompasses a second region, which is the region where the second metal film is provided.

[0101] In the above embodiment, it is possible to prevent residue or burrs from being generated near the connection between the first hole and the second hole. [Explanation of symbols]

[0102] 1...liquid ejection device, 3...liquid ejection head, 12...medium, 14...liquid container, 20...control unit, 22...transport mechanism, 24...movement mechanism, 26...circulation mechanism, 30...flow path structure, 31...flow path substrate, 31a...substrate, 32...pressure chamber substrate, 33...vibration plate, 34...piezoelectric element, 35...sealing substrate, 36...casing, 37...nozzle substrate, 38...vibration absorber, 40...wiring substrate, 41...protective film, 42...protective film, 44...first Metal film, 45...third metal film, 51...protective film, 52...protective film, 54...second metal film, 55...fourth metal film, 100...substrate, 100a...substrate, 242...transport body, 244...transport belt, 301...first surface, 302...second surface, 312...throttling portion (second flow path), 314...communicating flow path, 320...wall surface, 353...through hole, 361...supply port, 362...through hole, C1...pressure chamber, H1a...first hole, H1b...hole, H1c... 1st hole, H1d...3rd hole, H2...2nd hole, H2a...2nd hole, H2b...hole, H2c...hole, H2d...2nd hole, H2e...4th hole, H3d...3rd hole, HL1...through hole, HL2...through hole, La...1st row, Lb...Second row, N...Nozzle, R...Common space, R1...First region, R2...Second region, R3...Third region, R4...Fourth region, Ra...Communication space, Rb...Common channel (first channel), Rc...Space, S1...Protective film type formation process, S1A...protective film formation process, S2...first metal film formation process, S2A...first metal film formation process, S3...first etching process, S3A...first etching process, S4...protective film formation process, S4A...protection Film forming step, S5...second metal film forming step, S5A...second metal film forming step, S6...second etching step, S6A...second etching step, S7...third etching step, S7A...third etching step.

Claims

1. A method for manufacturing a liquid ejection head including a flow path substrate having a first flow path opening on one plate surface and a second flow path opening on the other plate surface and communicating with the first flow path, a first etching step of forming a first hole at a position that will become the first flow path by metal-assisted chemical etching using a first metal film formed on a first surface that is one of the plate surfaces of the substrate; a second etching step of forming, after the first etching step, a second hole at a position to become the second flow path by metal-assisted chemical etching using a second metal film formed on a second surface of the substrate opposite to the first surface, a first region in which the first metal film is provided encompasses a second region in which the second metal film is provided, as viewed in a thickness direction of the substrate; A method for manufacturing a liquid ejection head, comprising:

2. a protective film forming step of forming an etching protective film on the first hole between the first etching step and the second etching step, The method for manufacturing a liquid ejection head according to claim 1 .

3. each of the first metal film and the second metal film is made of gold; The protective film is made of diamond-like carbon. The method for manufacturing a liquid ejection head according to claim 2 .

4. a third etching step of etching each side surface of the first hole and the second hole after the second etching step; The method for manufacturing a liquid ejection head according to claim 1 .

5. the first flow path is an individual flow path provided for each pressure chamber, the second flow path is a throttle portion that reduces vibrations of the liquid generated in the pressure chamber. The method for manufacturing a liquid ejection head according to any one of claims 1 to 4.

6. A processing method for forming a through hole in a substrate by metal-assisted chemical etching, comprising: a first etching step of forming a first hole by metal-assisted chemical etching using a first metal film formed on a first surface, which is one of the plate surfaces of the substrate; a second etching step of forming a second hole penetrating the first hole by metal-assisted chemical etching using a second metal film formed on a second surface of the substrate opposite to the first surface, after the first etching step; a first region in which the first metal film is provided encompasses a second region in which the second metal film is provided, as viewed in a thickness direction of the substrate; A processing method characterized by:

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