Method for manufacturing substrate for liquid ejection head

Abstract

To suppress a reduction in a cavitation-resistant film for a substrate for liquid discharge head.SOLUTION: A method of manufacturing a substrate for a liquid discharge head includes the steps of: forming a protective film for coating a partial surface of a cavitation-resistant film, which is provided in a position to coat a heat element, from a metallic material including at least any one of titanium, tungsten and titanium tungsten; and performing etching for the substrate after the step of forming the protective film.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a liquid ejection head substrate used in a liquid ejection head that ejects liquid. [Background technology]

[0002] Microfabricated structures on semiconductor substrates are widely used in the fields of MEMS and electromechanical functional devices. One example is a liquid ejection head for liquid ejection recording, which ejects droplets onto a recording medium to perform recording. Thermal liquid ejection heads use thermal energy generated by passing electricity through a heating resistor to cause film boiling of liquid such as ink, and then use the resulting pressure to eject the liquid from the ejection orifices to perform the recording operation.

[0003] The liquid ejection head used in this manner has a liquid ejection head substrate, which is a semiconductor substrate equipped with a heating resistor, and a flow path member for forming the ejection ports and flow paths. The heating resistor is driven by receiving an electric signal or voltage from the liquid ejection device body on which the liquid ejection head is mounted, via an electrode pad provided on the liquid ejection head substrate.

[0004] The heating resistor is covered with an electrically insulating protective layer. The heating element, which is the ink-contacting portion above the heating resistor, is exposed to high temperatures due to the heat generated by the heating resistor and is also subjected to a combination of physical effects, such as cavitation shocks caused by ink bubbling and contraction, and chemical effects from the ink. To protect the heating resistor from these influences, a cavitation-resistant film is provided on the insulating protective layer covering the heating resistor. The portion of this cavitation-resistant film above the heating resistor functions as the heating element. Thus, the provision of a cavitation-resistant film on a liquid ejection head substrate aims to extend the head's life and reliability. Typically, metallic materials such as tantalum and niobium are used for the cavitation-resistant film. Patent Document 1 also discloses a configuration for uniformly removing kogation accumulated on the heating element surface to extend the head's life. The cavitation-resistant film is made of metallic materials such as iridium and ruthenium.

[0005] The electrode pads provided on the substrate for liquid ejection heads have a structure in which multiple types of metal films are laminated, including an electrode layer provided on the wiring and a diffusion prevention layer that prevents the metal of the electrode layer from diffusing into the substrate. When forming the electrode pads, first, oxide films and organic contaminants formed on the surface of the wiring are removed to ensure conductivity. Next, a metal film is formed and then patterned into the desired shape to form the electrode pad. Generally, metal films are formed by sputter etching (reverse sputtering) in a vacuum using a sputtering device, and after the oxide films and organic contaminants are removed, the metal film is continuously formed.

[0006] Furthermore, when forming a flow path member on a substrate for a liquid ejection head, it is necessary to remove any alterations, such as oxide films and organic contaminants, from the surface of the substrate in order to ensure adhesion between the substrate and the flow path member. These oxide films and organic contaminants can be removed by dry etching or wet etching. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-101557 Summary of the Invention [Problem to be solved by the invention]

[0008] When etching is performed as described above, the entire substrate is etched, and the cavitation-resistant film, which acts as the heat-sensitive part, is also etched, reducing its thickness. This reduction in the cavitation-resistant film can have a negative impact on the lifespan of the head.

[0009] In particular, when iridium is used for the cavitation-resistant film, the amount of film loss caused by sputter etching is more than five times that of tantalum or niobium. Therefore, there is a concern that the film thickness of the cavitation-resistant film will vary greatly across the wafer surface or within a chip, so particular care must be taken to control the film thickness of the cavitation-resistant film.

[0010] Furthermore, if the anti-cavitation film is formed thicker in consideration of the reduction in the thickness of the anti-cavitation film, the consumption of raw materials for the anti-cavitation film increases, leading to an increase in manufacturing costs.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to suppress the reduction in thickness of the cavitation-resistant film on the liquid ejection head substrate. [Means for solving the problem]

[0012] A method for manufacturing a substrate for a liquid ejection head, comprising the steps of: preparing a substrate having a heating resistor; and an anti-cavitation film having a portion disposed in a position covering the heating resistor, the surface of the portion being exposed to the outside; forming a protective film covering the surface of the portion of the anti-cavitation film from a metal material containing at least one of titanium, tungsten, and titanium tungsten; etching the substrate after the protective film forming step; and removing the protective film after the etching step. The method further includes the steps of: preparing a substrate; preparing the substrate further having a first metal film that will become a part of an electrode pad; and an oxide film formed on a surface of the first metal film; removing the oxide film in the etching step; and forming an intermediate metal film that contains the same material as the protective film and covers the surface of the protective film and the surface of the first metal film after the etching step; and removing the intermediate metal film that covers the protective film while leaving a portion of the intermediate metal film that covers the surface of the first metal film that will become a part of the electrode pad; and performing the steps of removing the intermediate metal film and removing the protective film in the same process. It is characterized by: [Effects of the Invention]

[0013] According to the present invention, it is possible to suppress the reduction in thickness of the cavitation-resistant film on the liquid ejection head substrate. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic plan view illustrating a liquid ejection head substrate and a liquid ejection head to which the present invention can be applied. [Figure 2] 3A to 3C are schematic diagrams illustrating a method for manufacturing a substrate for a liquid ejection head according to the first embodiment. [Figure 3] 1 is a schematic plan view showing an area where a protective film is formed on a liquid ejection head substrate and an area where an oxide film or deteriorated material is to be removed. [Figure 4] FIG. 10 is an enlarged view of the heat application portion, and is a schematic plan view showing a state in which a protective film is formed. [Figure 5] 3A to 3C are schematic diagrams showing the state of a heat application part before and after a reverse sputtering process. [Figure 6] 10A to 10C are schematic diagrams illustrating a method for manufacturing a liquid ejection head substrate according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a method for manufacturing a substrate for a liquid ejection head according to an embodiment of the present invention will be described with reference to the drawings. Note that, although specific descriptions may be used in the following embodiments to fully explain the present invention, these are merely examples that are technically preferred and do not particularly limit the scope of the present invention.

[0016] (First embodiment) Fig. 1(a) is a schematic plan view illustrating a liquid ejection head substrate 1 as an embodiment to which the present invention can be applied. Fig. 1(b) is a schematic plan view illustrating a liquid ejection head 100 to which this embodiment can be applied. A plurality of electrode pads 2 and a plurality of thermal application portions 3 are formed on the liquid ejection head substrate 1. The liquid ejection head 100 also has the liquid ejection head substrate 1 and a flow path member 15 that is provided on the surface of the liquid ejection head substrate 1 facing the thermal application portion 3 and that forms ejection ports 16 and flow paths.

[0017] 2(a) to 2(e) are schematic diagrams illustrating the manufacturing method of the liquid ejection head substrate of this embodiment. 2(a) to 2(e) are schematic diagrams illustrating the process of forming the electrode pad 2 and the thermal application portion 3 in the AA' cross section of FIG. 1. Note that in this specification, the liquid ejection direction is described as up and the opposite direction is described as down, but this is for convenience's sake.

[0018] First, as shown in FIG. 2(a), a substrate is prepared on which wiring 4 and a thermal application portion 3 are provided as a first metal film constituting part of the electrode pad 2. Referring to FIG. 2(a), the cross-sectional structure of the portion constituting the electrode pad 2 will be described. An electrically insulating protective layer 5 is provided on wiring 4 provided on an interlayer film 8 provided on a substrate (not shown). Furthermore, an opening 14 is provided in the insulating protective layer 5. Metals with low resistivity, such as aluminum and copper, are typically used for the wiring 4. Silicon compounds, such as silicon carbonitride and silicon oxycarbonitride, are used for the insulating protective layer 5. A portion of the wiring 4 is exposed through the opening 14 in the insulating protective layer 5, and the surface of the exposed portion of the wiring 4, formed using the metal, is covered with an oxide film 6. This oxide film 6 is removed in a later process.

[0019] Next, the cross-sectional structure of the thermal application unit 3 will be described. An electrically insulating interlayer film 8 is provided on the heating resistor 7 provided on the substrate. Next, a cavitation-resistant film 9 is provided on the interlayer film 8. The cavitation-resistant film 9 protects the heating resistor 7 from physical effects such as cavitation shock caused by bubbling and contraction of liquids such as ink, and from the effects of chemical reactions caused by the ink. Tantalum, niobium, iridium, ruthenium, and other materials that are resistant to mechanical shock are used for the cavitation-resistant film 9. The cavitation-resistant film 9 may also be formed by laminating these metal materials. In this embodiment, the insulating protective layer 5 described above is also provided on the cavitation-resistant film 9, and an opening 13 is provided in the insulating protective layer 5 to expose the surface of the cavitation-resistant film 9 to the outside in order to form the thermal application unit 3.

[0020] Furthermore, most of the surface of the liquid ejection head substrate 1, except for the electrode pads 2 and the heat application portion 3, is covered with an insulating protective layer 5, and at least a portion of the surface layer has degraded materials 17, such as oxide films and organic contaminants, attached to it. If such degraded materials 17 are present, they can cause the flow path member 15, which will be provided on the surface of the liquid ejection head substrate 1 later, to peel off, so the degraded materials 17 are removed in a later process.

[0021] Next, as shown in Fig. 2(b), a protective film 10 is formed so as to cover the top of the cavitation-resistant film 9 of the heat application part 3. Fig. 3 shows a schematic plan view of the substrate provided with the protective film 10, showing the area where the protective film 10 is provided and the area where the protective film 10 is not provided, i.e., the area where the oxide film 6 and the altered material 17 are removed. The protective film 10 is disposed at least in the area that covers the surface of the cavitation-resistant film 9 that becomes the heat application part 3.

[0022] The protective film 10 serves to prevent the cavitation-resistant film 9 from being thinned by sputter etching (reverse sputtering), which will be described later. If the protective film 10 is made thick, the film scraped off and scattered by the sputter etching may adhere to the sidewalls of the protective film 10, forming a fence. The fences attached to the sidewalls of the protective film 10 may remain on the substrate even after the protective film 10 is removed, and may break off and become particles in a later process. Therefore, the thickness of the protective film 10 is preferably 60 nm or less. Regarding the lower limit of the thickness of the protective film 10, taking into consideration the coverage of the cavitation-resistant film 9 and the amount of film thinning due to sputter etching, the thickness of the protective film 10 is preferably 20 nm or more.

[0023] Furthermore, the protective film 10 is preferably made of a metal material, and is particularly preferably made of a metal material containing at least one of titanium, tungsten, and titanium-tungsten for the following reasons. These metal materials have high resistance to sputter etching, making it possible to sufficiently suppress film loss of the cavitation-resistant film 9 due to sputter etching. Furthermore, these metal materials also have good adhesion to the cavitation-resistant film 9 formed of tantalum, niobium, iridium, ruthenium, etc., and the insulating protective layer 5 formed of a silicon compound. This makes it possible to suppress the risk of peeling of the protective film 10 after sputter etching. Other materials for the protective film 10, such as organic and inorganic materials, may also be used. However, organic materials have lower sputter etching resistance than the above-mentioned metal materials and may not be able to sufficiently suppress film loss of the cavitation-resistant film 9 compared to the above-mentioned metal materials. Furthermore, inorganic materials have lower adhesion to the cavitation-resistant film 9 compared to the above-mentioned metal materials, making it possible for the inorganic materials to peel off from the protective film 10 after sputter etching. Therefore, it is desirable to use the above-mentioned metal materials as the material for the protective film 10.

[0024] 2(c), the substrate is placed in a film forming device and etching such as sputter etching (reverse sputtering) is performed using an inert gas plasma such as argon to remove the oxide film 6 on the surface of the wiring 4. By removing the oxide film 6, the conductivity of the electrode pad 2 can be ensured.

[0025] This reverse sputtering process also removes altered materials 17 (altered layers and organic contaminants) on the surface of the insulating protective layer 5. This exposes a clean surface on the surface of the substrate, which is in a suitable state for adhesion to a flow path member to be provided later.

[0026] Here, when etching is performed, since the protective film 10 is formed on the top of the cavitation-resistant film 9, it is possible to prevent the cavitation-resistant film 9 from being thinned by the reverse sputtering process, thereby achieving a longer lifespan of the liquid ejection head.

[0027] Next, as shown in FIG. 2(d), following the reverse sputtering process in a film formation apparatus, a diffusion prevention layer 11 as an intermediate metal film and an electrode layer 12 as a second metal film are formed over the entire surface of the substrate. The diffusion prevention layer 11 uses a metal material or a compound thereof that has excellent adhesion to the wiring 4 and the electrode layer 12, is stable against temperature, does not diffuse, and has a low specific resistance. In this embodiment, such a metal material is titanium tungsten or tungsten. In addition, the electrode layer 12 uses a metal material with low specific resistance and excellent corrosion resistance, such as gold in this embodiment.

[0028] 2(e), the electrode layer 12 and the diffusion prevention layer 11 are patterned using photolithography to form the electrode pad 2. In this embodiment, the electrode pad 2 is configured by laminating the wiring 4, the diffusion prevention layer 11, and the electrode layer 12.

[0029] The unnecessary electrode layer 12 and diffusion prevention layer 11 are etched using a wet etching method. Forming the diffusion prevention layer 11 and protective film 10 from the same material allows the diffusion prevention layer 11 and protective film 10 to be removed in the same etching process, which is preferable from the perspective of reducing process load. The electrode layer 12, which is made of gold, can be etched using an etching solution containing iodine and potassium iodide. The diffusion prevention layer 11 and protective film 10, which are made of titanium tungsten or the like, can be etched using a 30% concentration hydrogen peroxide solution. Using wet etching with hydrogen peroxide to etch the protective film 10 provides sufficient selectivity to the cavitation-resistant film 9, preventing the cavitation-resistant film 9 from being thinned during etching of the protective film 10.

[0030] Fig. 4 is a schematic plan view showing the state in which the protective film 10 has been formed on the thermal action part 3, and Fig. 5 is a diagram illustrating in detail the state of the thermal action part 3 before and after the reverse sputtering process. Fig. 5(a) is a cross-sectional view taken along line AA' in Fig. 4, showing the state of the substrate during the reverse sputtering process. Fig. 5(b) is a diagram showing the state in which the protective film 10 has been removed after the reverse sputtering process has been performed.

[0031] The liquid ejection head substrate 1 is provided with a plurality of heating resistors 7, and in this embodiment, as shown in FIG. 4, an anti-cavitation film 9 is provided to cover each of the plurality of heating resistors 7. Furthermore, the insulating protective layer 5 covering the plurality of anti-cavitation films 9 is provided with openings 13 corresponding to each of the plurality of anti-cavitation films 9, so that the outer edges of the openings 13 are positioned inside the outer edges of the anti-cavitation films 9. In this manner, a plurality of heat application portions 3 are provided on the liquid ejection head substrate 1. It is preferable that the plurality of protective films 10 are provided as independent patterns so as to cover each of the plurality of heat application portions 3. By providing the protective films 10 only in necessary areas, it is possible to reliably remove altered layers and organic contaminants from the insulating protective layer 5 by reverse sputtering.

[0032] As shown in FIG. 5(b), the insulating protective layer 5 in the region where the protective film 10 was not formed is thinned by a few tens of nanometers due to the reverse sputtering process, while the anti-cavitation film 9 and insulating protective layer 5 in the region where the protective film 10 was formed are not thinned. As a result, a step of a few tens of nanometers is generated between the surface 5a of the insulating protective layer 5 where the protective film 10 was formed and the surface 5b of the insulating protective layer 5 where the protective film 10 was not formed. In FIG. 5(b), the thinned insulating protective layer 5 is indicated by a dashed line. Furthermore, if the protective film 10 is formed as a thin film and the step resulting from the thinning of the insulating protective layer 5 caused by the reverse sputtering is small, it is possible to prevent the generation of a fence in the region where the protective film 10 was formed after the protective film 10 was removed.

[0033] (Second embodiment) Figures 6(a) to 6(e) are schematic diagrams for explaining the manufacturing method of the liquid ejection head substrate of this embodiment. Figures 6(a) to 6(e) are schematic diagrams for explaining the process of forming the electrode pad 2 and the thermal application part 3 in the AA' cross section of Figure 1. Note that the description of the same configurations and processes as those described above may be omitted.

[0034] First, as shown in FIG. 6(a), a substrate is prepared on which wiring 4 as a first metal film constituting part of the electrode pad 2 and a thermal application portion 3 are provided. Referring to FIG. 6(a), the cross-sectional structure of the portion constituting the electrode pad 2 will be described. The electrode pad 2 has an electrically insulating protective layer 5 provided on wiring 4 provided on an interlayer film 8 provided on a base (not shown). Furthermore, openings 14 are provided in the insulating protective layer 5. The wiring 4 is made of a noble metal such as iridium. Because the wiring 4 is made of a noble metal, no oxide film is formed on the surface of the wiring 4 exposed from the openings 14 in the insulating protective layer 5, as in the above-described embodiment.

[0035] The configuration of the heat application portion 3 is the same as in the above-described embodiment. Note that the anti-cavitation film 9 and the wiring 4 are formed in the same layer using the same material in the same process, thereby reducing the manufacturing load.

[0036] Next, as shown in FIG. 6(b), a protective film 10 is formed so as to cover the upper part of the anti-cavitation film 9 of the heat application portion 3. The protective film 10 is also formed so as to cover the surface of the wiring 4 exposed from the openings 14 of the insulating protective layer 5. Here, the protective film 10 covering the anti-cavitation film 9 is also referred to as the first protective film, and the protective film 10 covering the wiring 4 is also referred to as the second protective film. As in the above-described embodiment, a plurality of protective films 10 (first protective films) are provided as independent patterns so as to cover the plurality of heat application portions 3, respectively. As shown in FIG. 1, a plurality of electrode pads 2 are provided on the liquid ejection head substrate 1, and a plurality of openings 14 are provided in the insulating protective layer 5 corresponding to these electrode pads. When providing the protective film 10, a plurality of protective films 10 (second protective films) are also provided as independent patterns so as to cover the surface of the wiring 4 exposed from the plurality of openings 14, respectively.

[0037] Here, by leaving the protective film 10 provided on the portion that will become the electrode pad 2 without removing it in a later step, it can be used as an adhesion-improving film interposed between the wiring 4 and insulating protective layer 5 and the electrode layer 12 that will be provided later. This makes it possible to omit the step of providing the diffusion prevention layer 11 on the electrode pad 2 as in the above-mentioned embodiment. Metal materials such as titanium, tungsten, and titanium tungsten as mentioned above are preferred as materials for the protective film 10 because they have good adhesion to the wiring 4, insulating protective layer 5, and electrode layer 12 in addition to being resistant to sputter etching.

[0038] Next, as shown in FIG. 6(c), to remove the altered material 17 from the insulating protective layer 5, the substrate is set in a film-forming device and subjected to sputter etching (reverse sputtering). This exposes a clean surface on the substrate, creating a favorable condition for adhesion to the flow path member. Because the anti-cavitation film 9 and wiring 4 are covered with the protective film 10, film reduction due to the reverse sputtering process can be prevented. This contributes to extending the life of the liquid ejection head.

[0039] Next, as shown in Figure 6(d), following the reverse sputtering process in a film formation device, an electrode layer 12 is formed as a second metal film over the entire surface of the substrate. As described above, the protective film 10 has excellent adhesion to the wiring 4 and the electrode layer 12, and therefore functions as a film for improving adhesion between the wiring 4 and part of the insulating protective layer 5 and the electrode layer 12. There are also no problems with electrical conductivity. Furthermore, gold, which has low resistivity and excellent corrosion resistance, is used for the electrode layer 12.

[0040] Next, as shown in FIG. 6(e), the electrode layer 12 is patterned using photolithography to form the electrode pad 2. In this embodiment, the electrode pad 2 is configured by laminating the wiring 4, the second protective film, and the electrode layer 12. Next, the protective film 10 of the thermal action part 3 is etched. At this time, a part of the protective film 10 disposed on the electrode pad 2 is also etched at the same time, so that the protective film 10 remains only under the electrode layer 12.

[0041] Example 1 The above-described embodiment will be described in more detail below using examples.

[0042] In Example 1, the liquid ejection head substrate 1 shown in Fig. 1 was formed using the manufacturing method shown in Fig. 2. In Example 1, in Fig. 2(a), the wiring 4 was made of aluminum, the insulating protective layer 5 was made of silicon carbonitride film, and the anti-cavitation film 9 was made of iridium. A deteriorated layer was formed on the surface of the insulating protective layer 5, and a small amount of organic contaminants were also attached.

[0043] Next, as shown in Figure 2(b), a protective film 10 was formed so as to cover only the upper part of the cavitation-resistant film 9 of the heat application part 3. Here, from the viewpoint of suppressing the occurrence of fences and the coverage of the cavitation-resistant film 9, the thickness of the protective film 10 was set to 50 nm, and titanium tungsten was used as the material for the protective film 10. Titanium tungsten has high resistance to sputter etching and also has good adhesion to the cavitation-resistant film 9 and the insulating protective layer 5.

[0044] Next, as shown in FIG. 2(c), the substrate was set in a film-forming apparatus and subjected to sputter etching (reverse sputtering) to remove the oxide film 6 formed on the surface of the wiring 4. The sputter etching conditions were an argon gas flow rate of 30 sccm, power of 400 W, and processing time of 20 seconds. This also removed the altered layer and organic contaminants on the surface of the insulating protective layer 5. Here, because the protective film 10 was formed on top of the cavitation-resistant film 9, the cavitation-resistant film 9 was not thinned by the reverse sputtering. However, a thickness loss of several tens of nanometers was confirmed in the insulating protective layer 5 in the areas where the protective film 10 was not formed.

[0045] Next, as shown in Fig. 2(d), following the reverse sputtering process, a diffusion prevention layer 11 and an electrode layer 12 were formed on the entire surface of the substrate in a film formation apparatus. The diffusion prevention layer 11 was formed using titanium tungsten, a metal material that has excellent adhesion to the wiring 4 and the electrode layer 12, is stable against temperature, does not diffuse, and has a low specific resistance, and was formed to a thickness of 200 nm. The electrode layer 12 was formed using gold, which has low specific resistance and excellent corrosion resistance, and was formed to a thickness of 400 nm.

[0046] Next, as shown in FIG. 2(e), the electrode layer 12 and the diffusion prevention layer 11 were patterned using photolithography to form the electrode pad 2. The unnecessary electrode layer 12 and diffusion prevention layer 11 were then etched away using a wet etching method. Furthermore, because the diffusion prevention layer 11 and the protective film 10 were made of the same material, the diffusion prevention layer 11 and the protective film 10 could be removed in the same etching process. The electrode layer 12, made of gold, was etched for a desired time using an etching solution containing iodine and potassium iodide. The diffusion prevention layer 11 and the protective film 10, made of titanium tungsten, were etched for a desired time using a 30% hydrogen peroxide solution. The protective film 10 was etched using wet etching with hydrogen peroxide, which provided sufficient selectivity to the cavitation-resistant film 9, preventing the cavitation-resistant film 9 from being thinned. Furthermore, the protective film 10 was formed as a thin film of 50 nm, and the step caused by the reduction in the insulating protective layer 5 due to reverse sputtering was minute, at just over 10 nm. Therefore, after etching the protective film 10, the area where the protective film 10 had been formed was observed, but no fences were found.

[0047] Example 2 In Example 2, the liquid ejection head substrate 1 shown in Fig. 1 was formed using the manufacturing method shown in Fig. 6. In Example 2, in Fig. 6(a), the wiring 4 was made of iridium, the insulating protective layer 5 was made of silicon carbonitride film, and the anti-cavitation film 9 was made of iridium. Because the wiring 4 was a precious metal, no oxide film was formed on the part of the wiring 4 exposed from the opening 14 of the insulating protective layer 5. A modified layer was formed on the surface of the insulating protective layer 5, and a small amount of organic contaminants were also attached.

[0048] 6(b), a protective film 10 was formed to cover the upper part of the cavitation-resistant film 9 of the heat application part 3 and the part of the wiring 4 exposed from the opening 14. Here, from the viewpoint of fence suppression and coverage of the cavitation-resistant film, the thickness of the protective film 10 was set to 50 nm, and titanium tungsten was used as the material of the protective film 10.

[0049] Next, as shown in FIG. 6(c), to remove the altered surface layer of the insulating protective layer 5, the substrate was set in a film-forming device and subjected to sputter etching (reverse sputtering). The sputter etching conditions were an argon gas flow rate of 30 sccm, power of 400 W, and processing time of 20 seconds. This exposed a clean surface on the substrate, creating a state suitable for adhesion to the flow path member. Here, because the protective film 10 was formed on top of the cavitation-resistant film 9, the cavitation-resistant film 9 was not thinned by the reverse sputtering. However, a thickness loss of several tens of nanometers was confirmed in the insulating protective layer 5 in the areas where the protective film 10 was not formed.

[0050] 6(d), the electrode layer 12 was formed on the entire surface of the substrate using a film forming apparatus, following the reverse sputtering process. The electrode layer 12 was formed using gold to a thickness of 400 nm.

[0051] 6(e), the electrode layer 12 was patterned using photolithography to form the electrode pad 2. The electrode layer 12 formed of gold was etched for a desired time using an etching solution containing iodine and potassium iodide.

[0052] Next, the protective film 10 on the thermal application portion 3 was etched. The protective film 10, made of titanium tungsten, was etched using a 30% hydrogen peroxide solution for the desired time. At this time, a portion of the protective film 10 disposed on the electrode pad 2 was also etched simultaneously, leaving only the protective film 10 below the electrode layer 12. The use of wet etching with hydrogen peroxide for the protective film 10 ensured sufficient selectivity to the cavitation-resistant film 9, preventing the cavitation-resistant film 9 from being thinned. Furthermore, the protective film 10 was formed to a thickness of 50 nm, and the step caused by the thinning of the insulating protective layer 5 by reverse sputtering was minimal, at just over 10 nm. Therefore, after etching the protective film 10, the area where the protective film 10 had been formed was observed, but no fences were found. [Explanation of symbols]

[0053] 1. Liquid ejection head substrate 7 Heating resistor 9. Cavitation-resistant membrane 10 Protective film

Claims

1. A method for manufacturing a substrate for a liquid ejection head, comprising the steps of: A step of preparing a substrate having a heating resistor and an anti-cavitation film including a portion provided in a position covering the heating resistor, the surface of the portion being exposed to the outside; forming a protective film covering the surface of the portion of the cavitation-resistant film from a metal material containing at least one of titanium, tungsten, and titanium tungsten; performing an etching process on the substrate after the step of forming the protective film; removing the protective film after the etching step; having In the step of preparing the substrate, the substrate further includes a first metal film that is to become a part of the electrode pad, and an oxide film formed on a surface of the first metal film; In the etching step, the oxide film is removed, forming an intermediate metal film, which contains the same material as the protective film and covers a surface of the protective film and a surface of the first metal film, after the etching step; removing the intermediate metal film covering the protective film while leaving a portion of the intermediate metal film covering the surface of the first metal film, which becomes a part of the electrode pad; and A method for manufacturing a substrate for a liquid ejection head, comprising the steps of removing the intermediate metal film and removing the protective film in a same process.

2. In the step of preparing the substrate, the substrate further includes an insulating protective layer provided on the surface side of the portion of the anti-cavitation film and having a surface exposed to the outside; The method for manufacturing a substrate for a liquid ejection head according to claim 1 , wherein in the step of performing etching, altered matter on the surface of the insulating protective layer is removed.

3. 3. The method for manufacturing a substrate for a liquid ejection head according to claim 1, wherein said etching step comprises sputter etching.

4. The method for manufacturing a substrate for a liquid ejection head according to claim 1 , wherein the protective film has a thickness of 60 nm or less.

5. The method for manufacturing a substrate for a liquid ejection head according to claim 1 , wherein the protective film has a thickness of 20 nm or more.

6. The method for manufacturing a substrate for a liquid ejection head according to claim 1 , wherein the cavitation-resistant film contains at least one of tantalum, niobium, iridium, and ruthenium.

7. In the step of preparing a substrate, a substrate having a plurality of the heating resistors is prepared, 7. The method for manufacturing a substrate for a liquid ejection head according to claim 1, wherein in the step of forming the protective film, a protective film is formed so as to cover each of the plurality of heating resistors.

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