Liquid ejection head and manufacturing method thereof

Abstract

To provide a highly reliable liquid discharge head that has its substrate suppressed from being fused and secures sufficient strength between the substrate and a member joined to the substrate.SOLUTION: A liquid discharge head 10 has: a substrate 3 which is made of silicon and has a first surface 3a and a second surface 3b on the opposite side from the first surface 3a; a discharge port formation member 8 which is joined to the first surface 3a of the substrate 3 and has a discharge port 9 formed to discharge liquid; and a joined member 20 which is joined to a second surface 3b of the substrate 3. The substrate 3 has a through flow passage 4 formed penetrating the substrate 3 and supplying the liquid to the discharge port 9, and also has a first protection film 5 formed of metal oxide on an inner surface of the through flow passage 4. A second protection film 7 is formed of a silicon compound entirely over the second surface 3b of the substrate 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In liquid ejection heads used in inkjet recording devices, etc., some substrates are provided with a protective film containing metal oxide on the areas of the substrate that come into contact with the liquid (such as the inner surfaces of through-holes that serve as liquid flow paths) to prevent dissolution (corrosion) of the silicon substrate by liquids such as ink. However, before the protective film is formed on the substrate, residues (organic residues) of resists used in forming the through-holes may re-adhere to the substrate, causing organic contamination. This may change the surface condition of the substrate and reduce the adhesion of the protective film that is formed. As a result, peeling phenomena such as blistering and lifting of the protective film may occur, which may lead to substrate dissolution from these areas. In response to this issue, Patent Document 1 describes a method in which a protective film formed on the back surface of the substrate is removed by etching and then a new protective film is formed in that area. This method removes the organic residues attached to the back surface of the substrate along with the protective film, cleaning the back surface of the substrate and thereby improving adhesion between the substrate and the protective film. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-103382 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the method described in Patent Document 1, the openings of the liquid flow paths on the back surface of the substrate are covered with a dry film resist before etching the protective film, so the protective film cannot be removed from the periphery of the openings covered with the resist, which leaves organic contamination in these areas and can cause the protective film to peel off, potentially making it difficult to ensure sufficient bonding strength with the member bonded to the back surface of the substrate. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a highly reliable liquid ejection head and a method for manufacturing the same, which can prevent dissolution of the substrate and ensure sufficient bonding strength between the substrate and the member bonded to the substrate. [Means for solving the problem]

[0005] In order to achieve the above-mentioned object, the liquid ejection head of the present invention comprises a silicon substrate having a first surface and a second surface opposite to the first surface, an ejection port forming member bonded to the first surface of the silicon substrate and having an ejection port formed therein for ejecting liquid, and a member to be bonded to the second surface of the silicon substrate, wherein a through-flow passage is formed in the silicon substrate to pass through the silicon substrate and supply liquid to the ejection port, and a first protective film made of a metal oxide is formed on the inner surface of the through-flow passage. In one embodiment, a second protective film made of a silicon compound is formed on the entire surface of the second surface of the silicon substrate. Silicon substrate Formed adjacent to the second surface The second protective film is formed so as to cover the end face of the first protective film on the second surface side. In another embodiment, a second protective film made of a silicon compound is formed on the second surface of the silicon substrate in contact with the second surface, and the first protective film has an end surface on the same plane as the second surface of the silicon substrate. In yet another embodiment, a second protective film made of a silicon compound is formed on the entire second surface of the silicon substrate in contact with the second surface of the silicon substrate, and the member to be joined is a flow path substrate in which a connecting flow path communicating with the through flow path is formed. . Furthermore, the present invention provides a method for manufacturing a liquid ejection head, which includes a silicon substrate having a first surface and a second surface opposite to the first surface, an ejection port forming member bonded to the first surface of the silicon substrate and having an ejection port formed therein for ejecting liquid, and a member to be bonded to the second surface of the silicon substrate, wherein the silicon substrate has a through-flow path formed therein for passing through the silicon substrate and supplying liquid to the ejection port, and a first protective film made of a metal oxide is formed on the inner surface of the through-flow path, and the method includes the steps of: forming the first protective film on at least the second surface of the silicon substrate; thinning the silicon substrate from the side of the second surface after forming the first protective film and removing the first protective film formed on the second surface to expose the entire surface of the second surface; and forming a second protective film made of a silicon compound on the entire surface of the exposed second surface. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a highly reliable liquid ejection head and a method for manufacturing the same, which can suppress dissolution of the substrate and ensure sufficient bonding strength between the substrate and the member bonded to the substrate. [Brief explanation of the drawings]

[0007] [Figure 1] 1A and 1B are a plan view and a cross-sectional view of a liquid ejection head according to a first embodiment. [Figure 2] 3A to 3C are cross-sectional views illustrating a method for manufacturing the liquid ejection head according to the first embodiment. [Figure 3] 10A and 10B are a plan view and a cross-sectional view of a liquid ejection head according to a second embodiment. [Figure 4] 10A and 10B are a plan view and a cross-sectional view of a liquid ejection head according to a third embodiment. [Figure 5] 10A to 10C are cross-sectional views illustrating a method for manufacturing a liquid ejection head according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] (First embodiment) Fig. 1(a) is a plan view of a liquid ejection head according to a first embodiment of the present invention, showing the surface on which ejection ports for ejecting liquid are formed, and Fig. 1(b) is a cross-sectional view taken along line AA in Fig. 1(a).

[0010] The liquid ejection head 10 ejects liquid such as ink to record an image on a recording medium, and has a recording element substrate 15 having a substrate 3 and an ejection port forming member 8. The recording element substrate 15 is bonded to a support member 20 with a resin adhesive 21. The silicon substrate 3 has a surface 3a (hereinafter also referred to as the "substrate surface") and an opposite back surface 3b (hereinafter also referred to as the "substrate back surface"), and a discharge port forming member 8 made of a photosensitive epoxy resin is bonded to the substrate surface 3a. The discharge port forming member 8 is formed with a plurality of discharge ports 9 for discharging liquid and pressure chambers 11 communicating with the plurality of discharge ports 9. The substrate 3 is formed with a plurality of individual flow paths (through-flow paths) 4 that penetrate the substrate 3 and communicate with the pressure chambers 11 to supply liquid to the discharge ports 9. The substrate surface 3a is provided with energy generating elements (heaters) 1 that generate energy used to discharge the liquid, at positions facing the discharge ports 9. The energy generated by the energy generating elements 1 causes the liquid in the pressure chambers 11 to bubble, thereby discharging the liquid from the discharge ports 9. An interlayer insulating film 2 including a wiring layer and a drive circuit made of semiconductor elements for driving the energy generating elements 1 is also formed on the substrate surface 3a using a multilayer wiring technology using photolithography. Furthermore, the support member 20 is formed with a common flow path 22 that passes through the support member 20 and communicates with the plurality of individual flow paths 4 .

[0011] A first protective film 5 made of a metal oxide is formed on the inner surface of each individual flow path 4 to prevent dissolution of the substrate 3 by a liquid such as ink. Dissolution of silicon often occurs when an alkaline ink is used as the liquid. Therefore, a specific material for the first protective film 5 is preferably one that has high corrosion resistance to alkaline solutions, such as oxides of Ti, Zr, Hf, V, Nb, and Ta, with TiO (titanium oxide) being particularly preferred. The first protective film 5 does not extend to the rear surface 3b of the substrate, and has an end surface 5a that is flush with the rear surface 3b of the substrate. However, this end surface 5a is a surface that is polished and formed during the manufacturing process of the liquid ejection head 10, which will be described later. In addition, a second protective film 7 made of a silicon compound is formed on the back surface 3b of the substrate to similarly suppress dissolution of the substrate 3 by a liquid such as ink. The second protective film 7 is formed to cover the end surface 5b of the first protective film 5 on the back surface 3b side of the substrate, extending to the inside of the individual flow paths 4. This prevents corrosion from progressing from the end surface 5a on the back surface 3b side of the substrate, which is the polished surface, as described above, and thus suppresses a decrease in the reliability of the first protective film 5. Since the second protective film 7 is formed on the bonding surface (back surface 3b) of the substrate 3 with the support member 20, it preferably has excellent adhesion to the substrate 3 and also preferably has liquid resistance such as ink resistance. Therefore, specific materials for the second protective film 7 include silicon compounds containing carbon, such as SiC, SiOC, SiCN, and SiOCN, and SiC (silicon carbide) is particularly preferred.

[0012] Here, a method for manufacturing a liquid ejection head according to this embodiment will be described with reference to Fig. 2. Fig. 2(a) to Fig. 2(h) are cross-sectional views of the liquid ejection head in each step of the manufacturing method according to this embodiment, and correspond to Fig. 1(b). Note that the order of the steps described below is merely an example, and the order of the steps may be changed as necessary.

[0013] First, as shown in Fig. 2(a), a substrate 3 having energy generating elements 1 and an interlayer insulating film 2 on a substrate surface 3a is prepared. Then, as shown in Fig. 2(b), etching is performed from the substrate surface 3a side to form a plurality of recesses 12 in the substrate surface 3a. As a method for etching the substrate 3, for example, a dry etching method using deep reactive ion etching (Deep-RIE) in which etching and film formation are performed alternately can be used. 2(c), a first protective film 5 made of a metal oxide is formed on the substrate front surface 3a, the substrate back surface 3b, and the inner surfaces of the recesses 12. The first protective film 5 can be formed by, for example, chemical vapor deposition (CVD), sputtering, or atomic layer deposition (ALD). Among these, ALD is preferred because of its excellent coating properties for steps and holes. This allows the first protective film 5 to be formed with a substantially uniform thickness on the substrate front surface 3a, the substrate back surface 3b, and the inner surfaces of the recesses 12.

[0014] 2(d), the first protective film 5 on the substrate surface 3a is patterned, and unnecessary portions of the first protective film 5, i.e., portions of the first protective film 5 corresponding to the region where the ejection port forming member 8 is bonded and the region where the pressure chambers 11 are formed, are removed. For patterning, a tenting method is used in which etching is performed after the openings of the recesses 12 are blocked with a dry film resist, and the etching method used may be, for example, wet etching using buffered hydrofluoric acid (BHF). 2(e), the substrate 3 is thinned from the rear surface 3b side, the first protective film 5 formed on the rear surface 3b is completely removed, and the recesses 12 are opened on the rear surface 3b to form the individual flow paths 4 made of through-holes. In this way, the entire rear surface 3b of the substrate is exposed, and the end surface 5a of the first protective film 5 on the rear surface 3b side of the substrate is exposed. Methods for thinning the substrate 3 include polishing such as chemical mechanical polishing (CMP).

[0015] Next, as shown in FIG. 2(f), a second protective film 7 made of a silicon compound is formed over the entire exposed back surface 3b of the substrate. The second protective film 7 can be formed by a common film formation method such as CVD or sputtering, but plasma CVD is preferred in terms of coverage. This ensures that the end surface 5a of the first protective film 5 on the back surface 3b side of the substrate is covered with the second protective film 7, thereby preventing corrosion from progressing from the polished end surface 5a, as described above. Next, as shown in FIG. 2(g), a dry film 13 containing a photosensitive epoxy resin is attached to the substrate surface 3a. Then, as shown in FIG. 2(h), the dry film 13 is partially exposed and developed to remove unnecessary portions, thereby forming a discharge port forming member 8 having discharge ports 9 and pressure chambers 11. Thereafter, a support member 20 having a common flow path 22 formed from a through groove is prepared, and the recording element substrate 15 including the discharge port forming member 8 and the substrate 3 is bonded to the support member 20 with a resin adhesive 21, thereby completing the liquid discharge head 10 shown in FIG. 1(b). The common flow path 22 can be formed in the support member 20 by anisotropic wet etching, a laser method, or a sandblasting method. Furthermore, the recording element substrate 15 and the support member 20 may be bonded by plasma activation bonding using an oxide film.

[0016] According to this embodiment, even if the rear surface 3b of the substrate is contaminated with organic residues before the first protective film 5 is formed, the organic residues can be removed from the rear surface 3b of the substrate together with the first protective film 5 by thinning the substrate 3 from the rear surface 3b side after the first protective film 5 is formed. Then, by forming the second protective film 7 on the entire surface of the rear surface 3b of the substrate thus cleaned, the adhesion between the substrate 3 and the second protective film 7 can be improved. Furthermore, since the support member 20 is bonded to the entire surface of the rear surface 3b of the substrate via the second protective film 7 formed with good adhesion, the bonding strength between the substrate 3 and the support member 20 can be ensured. Although there is a concern that thinning (polishing) the substrate 3 may cause corrosion to progress from the end surface 5a exposed on the rear surface 3b of the substrate, thereby reducing the reliability of the first protective film 5, such a concern does not arise because the end surface 5a of the first protective film 5 is covered by the second protective film 7. That is, since the inner surface of the individual flow path 4 is covered with the first protective film 5, and the rear surface 3b of the substrate and the end surface 5a of the first protective film 5 on the rear surface 3b side of the substrate are covered with the second protective film 7, dissolution of the substrate 3 by liquids such as ink can be suppressed.

[0017] (Second embodiment) Fig. 3(a) is a plan view of a liquid ejection head according to a second embodiment of the present invention, showing the surface on which ejection ports for ejecting liquid are formed. Fig. 3(b) is a cross-sectional view taken along line BB in Fig. 3(a). Hereinafter, the same components as those in the first embodiment will be assigned the same reference numerals in the drawings and their description will be omitted, and only the components different from the first embodiment will be described.

[0018] This embodiment differs from the first embodiment in that a flow path substrate 30 is incorporated between the recording element substrate 15 and the support member 20 (and accordingly, the shape of the common flow path 22 is changed). The flow path substrate 30 is formed with connection flow paths 23 that communicate with the common flow path 22 and the multiple individual flow paths 4 and facilitate the flow of liquid from the common flow path 22 to the multiple individual flow paths 4. The flow path substrate 30 is made of silicon, and the connection flow paths 23 can be formed, for example, by anisotropic wet etching. Furthermore, a third protective film 17 made of a silicon compound is formed on both the front and back surfaces of the flow path substrate 30 (the surface facing the substrate 3 and the surface opposite thereto) and on the inner surfaces of the connection flow paths 23 to suppress dissolution of the flow path substrate 30 by liquids such as ink. As with the second protective film 7, the specific material of the third protective film 17 is preferably a silicon compound containing carbon, such as SiC, SiOC, SiCN, or SiOCN, with SiC being particularly preferred. The third protective film 17 can be formed by a general film forming method such as CVD or sputtering, but in consideration of coverage, it is preferable to use plasma CVD. As described above, in this embodiment, the member to be bonded to the rear surface 3b of the substrate is different from that in the first embodiment, but the obtained effects are the same as those in the first embodiment. Note that the flow path substrate 30 is bonded to the recording element substrate 15 with a resin adhesive 31 and to the support member 20 with a resin adhesive 21, but at least one of the bonding may be performed by plasma activation bonding using an oxide film.

[0019] (Third embodiment) Fig. 4(a) is a plan view of a liquid ejection head according to a second embodiment of the present invention, showing the surface on which ejection ports for ejecting liquid are formed. Fig. 4(b) is a cross-sectional view taken along line CC in Fig. 4(a). Hereinafter, the same components as those in the above-described embodiment will be denoted by the same reference numerals in the drawings and their description will be omitted, and only the components different from the above-described embodiment will be described.

[0020] This embodiment differs from the first embodiment in that the flow path structure formed in the substrate 3 has been changed (and therefore the shape of the common flow path 22 has been changed). That is, the substrate 3 is formed with through-flow paths 4, 24, each of which is made up of a plurality of individual flow paths 4 opening on the substrate front surface 3a and a common flow path 24 opening on the substrate back surface 3b and communicating with the plurality of individual flow paths 4. Therefore, in this embodiment, the manufacturing method of the liquid ejection head 10 differs from that of the first embodiment, as will be described below, and the area of the bonding surface (substrate back surface 3b) between the substrate 3 and the support member 20 is smaller than in the first embodiment, but the obtained effects are the same as those of the first embodiment.

[0021] Here, the method for manufacturing the liquid ejection head of this embodiment will be described with reference to Fig. 5. Fig. 5(a) to Fig. 5(h) are cross-sectional views of the liquid ejection head in each step of the manufacturing method of this embodiment, and correspond to Fig. 4(b). Note that the order of the steps described below is merely an example, and the order of the steps may be changed as necessary.

[0022] First, as shown in Fig. 5(a), a substrate 3 having energy generating elements 1 and an interlayer insulating film 2 on a substrate surface 3a is prepared. Then, as shown in Fig. 5(b), etching is performed from both the substrate surface 3a side and the substrate back surface 3b side to form through-flow channels 4, 24 each consisting of a plurality of individual flow channels 4 opening on the substrate surface 3a and a common flow channel 24 opening on the substrate back surface 3b. As an etching method for the substrate 3, for example, a dry etching method using Deep-RIE in which etching and film formation are performed alternately can be mentioned. 5(c), a first protective film 5 made of a metal oxide is formed on the substrate front surface 3a, the substrate back surface 3b, and the inner surfaces of the through-channels 4 and 24. The first protective film 5 can be formed by, for example, CVD, sputtering, or ALD, among which ALD is preferred because of its excellent coating properties for steps and holes. This allows the first protective film 5 to be formed with a substantially uniform thickness on the substrate front surface 3a, the substrate back surface 3b, and the inner surfaces of the through-channels 4 and 24.

[0023] 5(d), the substrate 3 is thinned from the rear surface 3b side, and the first protective film 5 formed on the rear surface 3b is completely removed. In this way, the entire rear surface 3b of the substrate is exposed, and the end surface 5a of the first protective film 5 on the rear surface 3b side of the substrate is exposed. Examples of methods for thinning the substrate 3 include polishing such as CMP. Next, as shown in FIG. 5(e), a second protective film 7 made of a silicon compound is formed over the entire exposed back surface 3b of the substrate. The second protective film 7 can be formed by a common film formation method such as CVD or sputtering, but plasma CVD is preferred in terms of coverage. This ensures that the end surface 5a of the first protective film 5 on the back surface 3b side of the substrate is covered with the second protective film 7, thereby preventing corrosion from progressing from the polished end surface 5a, as described above.

[0024] 5(f), the first protective film 5 on the substrate surface 3a is patterned, and unnecessary portions of the first protective film 5, i.e., portions of the first protective film 5 corresponding to the region where the ejection port forming member 8 is bonded and the region where the pressure chambers 11 are formed, are removed. For the patterning, a tenting method is used in which etching is performed after the openings of the individual flow paths 4 are blocked with a dry film resist, and the etching method used may be, for example, wet etching using BHF. Next, as shown in Fig. 5(g), a dry film 13 containing a photosensitive epoxy resin is attached to the substrate surface 3a. Then, as shown in Fig. 5(h), the dry film 13 is partially exposed to light and developed to remove unnecessary portions, thereby forming an ejection port forming member 8 having ejection ports 9 and pressure chambers 11. Thereafter, a support member 20 is prepared in which a common flow path 22 made of a through groove is formed, and the recording element substrate 15 including the ejection port forming member 8 and the substrate 3 is bonded to the support member 20 with a resin adhesive 21, thereby completing the liquid ejection head 10 shown in Fig. 4(b).

[0025] The present invention will be described in more detail below with reference to specific examples.

[0026] Example 1 In this example, the liquid ejection head 10 shown in FIG. 1 was fabricated using the manufacturing method shown in FIG. 2. A 700-μm-thick silicon substrate with a 5-μm-thick interlayer insulating film 2 was prepared as the substrate 3. A prismatic recess 12 measuring 50 μm × 50 μm and 250 μm deep was formed by deep-RIE using SF6 and C4F8 as etching gases. An 85-nm-thick titanium oxide film was deposited as the first protective film 5 by ALD, and the first protective film 5 was etched by wet etching using BHF. The substrate 3 was polished to a thickness of 200 μm, and a 50-nm-thick silicon carbide film was deposited as the second protective film 7 by plasma CVD. A storage immersion test was carried out in which the liquid ejection head 10 thus produced was immersed in ink for a certain period of time, and no peeling or dissolution of the substrate 3 was observed.

[0027] Example 2 3 was produced using the same procedures as in Example 1, except for the following points. That is, a flow path substrate 30 having a connection flow path 23 formed therein was prepared, the recording element substrate 15 and the flow path substrate 30 were bonded with a resin adhesive 31, and the support member 20 and the flow path substrate 30 were bonded with a resin adhesive 21. A through groove was formed as the connection flow path 23 by anisotropic wet etching, and a silicon carbide film having a thickness of 50 nm was formed as the third protective film 17 by plasma CVD. A storage immersion test was carried out in which the liquid ejection head 10 thus produced was immersed in ink for a certain period of time, and no peeling or dissolution of the substrate 3 was observed.

[0028] Example 3 In this example, the liquid ejection head 10 shown in FIG. 4 was fabricated using the manufacturing method shown in FIG. 5. A 700-μm-thick silicon substrate with a 10-μm-thick interlayer insulating film 2 was prepared as the substrate 3. Using deep-RIE with SF6 and C4F8 as etching gases, rectangular recesses measuring 50 μm × 50 μm and 200 μm deep were formed as the individual flow channels 4, and a groove measuring 200 μm wide and 500 μm deep was formed as the common flow channel 24. An 85-nm-thick titanium oxide film was formed by ALD, and the substrate 3 was polished to a thickness of 650 μm. A 50-nm-thick silicon carbide film was formed as the second protective film 7 by plasma CVD, and the first protective film 5 was etched using wet etching with BHF. The liquid ejection head 10 thus fabricated was subjected to a storage immersion test in which it was immersed in ink for a certain period of time, and no peeling or dissolution of the substrate 3 was observed. [Explanation of symbols]

[0029] 3. Circuit Board 5 First protective film 7 Second protective film 8. Discharge port forming member 10 Liquid ejection head

Claims

1. a silicon substrate having a first surface and a second surface opposite the first surface; a discharge port forming member bonded to the first surface of the silicon substrate and having a discharge port formed therein for discharging a liquid; a bonded member bonded to the second surface of the silicon substrate, a through-flow passage that penetrates the silicon substrate and supplies liquid to the ejection port is formed in the silicon substrate, and a first protective film made of a metal oxide is formed on an inner surface of the through-flow passage; a second protective film made of a silicon compound is formed on the entire second surface of the silicon substrate in contact with the second surface of the silicon substrate; The liquid ejection head, wherein the second protective film is formed so as to cover an end face of the first protective film on the side of the second surface.

2. a silicon substrate having a first surface and a second surface opposite the first surface; a discharge port forming member bonded to the first surface of the silicon substrate and having a discharge port formed therein for discharging a liquid; a bonded member bonded to the second surface of the silicon substrate, a through-flow passage that penetrates the silicon substrate and supplies liquid to the ejection port is formed in the silicon substrate, and a first protective film made of a metal oxide is formed on an inner surface of the through-flow passage; a second protective film made of a silicon compound is formed on the second surface of the silicon substrate in contact with the second surface; The liquid ejection head according to claim 1, wherein the first protective film has an end surface on the same plane as the second surface of the silicon substrate.

3. The liquid ejection head according to claim 2 , wherein the second protective film is formed so as to cover the end surface of the first protective film.

4. 4. The liquid ejection head according to claim 1, wherein the silicon compound is silicon carbide.

5. 5. The liquid ejection head according to claim 1, wherein the metal oxide is titanium oxide.

6. The liquid ejection head according to claim 1 , wherein the member to be joined is a flow path substrate on which a connection flow path communicating with the through flow path is formed.

7. A silicon substrate having a first surface and a second surface opposite the first surface; a discharge port forming member bonded to the first surface of the silicon substrate and having a discharge port formed therein for discharging a liquid; a bonded member bonded to the second surface of the silicon substrate, a through-flow passage that penetrates the silicon substrate and supplies liquid to the ejection port is formed in the silicon substrate, and a first protective film made of a metal oxide is formed on an inner surface of the through-flow passage; a second protective film made of a silicon compound is formed on the entire second surface of the silicon substrate in contact with the second surface of the silicon substrate; A liquid ejection head, wherein the member to be joined is a flow path substrate on which a connection flow path communicating with the through flow path is formed.

8. 8. The liquid ejection head according to claim 7, wherein the flow path substrate is made of silicon, and a third protective film made of a silicon compound is formed on the surface of the flow path substrate facing the silicon substrate and on the opposite surface thereof, and on the inner surface of the connection flow path.

9. A method for manufacturing a liquid ejection head comprising: a silicon substrate having a first surface and a second surface opposite to the first surface; an ejection port forming member bonded to the first surface of the silicon substrate, the ejection port being formed therein and configured to eject a liquid; and a member to be bonded to the second surface of the silicon substrate; wherein a through-flow path is formed in the silicon substrate to pass through the silicon substrate and supply a liquid to the ejection port, and a first protective film made of a metal oxide is formed on an inner surface of the through-flow path, forming the first protective film on at least the second surface of the silicon substrate; after forming the first protective film, thinning the silicon substrate from the second surface side and removing the first protective film formed on the second surface to expose the entire second surface; and forming a second protective film made of a silicon compound on the entire exposed second surface.

10. The method further includes forming a recess on the first surface of the silicon substrate before forming the first protective film, the step of forming the first protective film includes forming the first protective film on the first and second surfaces of the silicon substrate and on an inner surface of the recess; the step of thinning the silicon substrate includes opening the recessed portion to the second surface to form the through-flow path and exposing an end face of the first protective film on the second surface side; The method for manufacturing a liquid ejection head according to claim 9 , wherein the step of forming the second protective film includes forming the second protective film so as to cover the exposed end surface of the first protective film.

11. The method further includes forming the through-channel in the silicon substrate before forming the first protective film, the step of forming the first protective film includes forming the first protective film on the first and second surfaces of the silicon substrate and on an inner surface of the through-channel; the step of thinning the silicon substrate includes exposing an end surface of the first protective film on the second surface side; The method for manufacturing a liquid ejection head according to claim 9 , wherein the step of forming the second protective film includes forming the second protective film so as to cover the exposed end surface of the first protective film.

12. 12. The method for manufacturing a liquid ejection head according to claim 9, wherein the step of forming the second protective film includes forming a silicon carbide film by plasma CVD.

13. The method for manufacturing a liquid ejection head according to claim 9 , wherein the step of forming the first protective film includes forming a titanium oxide film by an ALD method.

14. 14. The method for manufacturing a liquid ejection head according to claim 9, further comprising the step of bonding a flow path substrate, on the second surface of the silicon substrate on which the second protective film is formed, as the member to be bonded, the flow path substrate having a connection flow path formed thereon that communicates with the through flow path.

15. 15. The method for manufacturing a liquid ejection head according to claim 14, wherein the step of bonding the flow path substrate includes: preparing the flow path substrate made of silicon; and forming a third protective film made of a silicon compound on a surface of the flow path substrate facing the silicon substrate, a surface on the opposite side thereof, and an inner surface of the connection flow path, before bonding the flow path substrate to the second surface of the silicon substrate.

16. The method for manufacturing a liquid ejection head according to claim 9 , wherein the step of thinning the silicon substrate includes polishing the silicon substrate.

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