Substrate for liquid discharge head, liquid discharge head, and manufacturing method for substrate for liquid discharge head

Abstract

To provide a substrate for a liquid discharge head equipped with an electrode pad which is high in electrical reliability and power efficiency.SOLUTION: A substrate for a liquid discharge head is provided with: a heater element that generates energy for discharging liquid; an electrode pad part having a wiring layer in a lower layer, which is electrically connected to the heater element through the wiring layer and is electrically connected to the outside through a bonding material; and an insulation protective layer. The electrode pad part further has a lower electrode layer and an upper electrode layer. The insulation protective layer arranged in a first region overlapping in a film thickness direction with the wiring layer has a first opening through which the lower electrode layer is connected to the upper electrode layer. The insulation protective layer, arranged at a position including at least a second region overlapping in the film thickness direction with the bonding material, has a second opening through which the lower electrode layer is connected to the upper electrode layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a substrate for a liquid ejection head, a liquid ejection head, and a method for manufacturing a substrate for a liquid ejection head. [Background technology]

[0002] A bonding method such as wire bonding is used to electrically connect a liquid ejection head substrate (hereinafter sometimes simply referred to as an element substrate) constituting a liquid ejection head to an external substrate. The material of the electrode pad portion arranged on the element substrate is selected in consideration of the connection reliability with the bonding material and the chemical resistance to chemicals such as acid, alkali, and organic solvents used in the manufacturing process of the nozzle formed after the element substrate is manufactured. The electrode pad portion has a laminated structure, from the bottom up, of an aluminum layer used as a wiring layer of the element substrate, a barrier metal layer made of a material such as TiW, and an Au layer for connection with the bonding material. Then, the element substrate is connected to the external substrate by wire bonding connection using a gold wire or the like to such an electrode pad portion. At this time, the surface of the electrode pad portion is required to be as flat as possible to ensure the connection reliability with the bonding material.

[0003] On the other hand, before connecting the element substrate and the external substrate by wire bonding, an electrical test is performed to prevent mounting of an electrically defective element substrate (chip). In this electrical test, probing is performed by applying a test probe to the electrode pad portion. Here, in the case of a laminated film of Au layer / TiW layer / aluminum layer as described above, since the Au layer and the aluminum layer are relatively soft materials, the electrode pad portion may be damaged (gouged) by probing. As a result, irregularities (probe marks) having a height difference of about 1 μm or more may be formed on the surface of the electrode pad portion. If bonding is performed at the probe mark portion, the connection reliability between the electrode pad and the bonding material may be impaired. There is a technology in Patent Document 1 for the occurrence of such large irregularities on the electrode pad.

[0004] Patent Document 1 discloses a configuration in which an iridium film, which is used as a protective layer (cavitation-resistant layer) for protecting a heating element from physical impact, is also used as a wiring layer for an electrode pad section. According to the technology of Patent Document 1, in electrical testing before mounting, a relatively hard metal material such as iridium is used as a constituent material for the electrode pad, making it unnecessary to form a thick film to hide probe marks. By adopting such a configuration, a liquid ejection head substrate with a reduced film thickness for the electrode pad section is formed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-17054 Summary of the Invention [Problem to be solved by the invention]

[0006] From the viewpoint of thermal efficiency, the cavitation-resistant layer is required to be formed as thin as possible. On the other hand, it is desirable for the electrode pad portion to generate the necessary current with as little power as possible, and from the viewpoint of low resistance, it is preferable to form it thick. An electrode pad with high electrical reliability and power efficiency is required.

[0007] An object of the present disclosure is to provide a liquid ejection head substrate provided with electrode pads that have high electrical reliability and power efficiency. [Means for solving the problem]

[0008] A substrate for a liquid ejection head according to one aspect of the present disclosure is a substrate for a liquid ejection head comprising: a heat generating element that generates energy for ejecting liquid; an electrode pad portion having a wiring layer on a lower layer, electrically connected to the heat generating element via the wiring layer and electrically connected to the outside via a bonding material; and an insulating protective layer, wherein the electrode pad portion further has a lower electrode layer and an upper electrode layer, the insulating protective layer disposed in a first region overlapping with the wiring layer in the film thickness direction has a first opening connecting the lower electrode layer and the upper electrode layer, and the insulating protective layer disposed at a position including at least a second region overlapping with the bonding material in the film thickness direction has a second opening connecting the lower electrode layer and the upper electrode layer. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a liquid ejection head substrate equipped with electrode pads having high electrical reliability and power efficiency. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a perspective view that illustrates a substrate for a liquid ejection head. [Diagram 2] FIG. 2 is a diagram illustrating a substrate for a liquid ejection head. [Diagram 3] FIG. 2 is a cross-sectional view of a substrate for a liquid ejection head. [Figure 4] FIG. 2 is a cross-sectional view of a substrate for a liquid ejection head. [Diagram 5] FIG. [Figure 6] 5A to 5C are cross-sectional views illustrating the manufacturing process. [Figure 7] FIG. 2 is a schematic cross-sectional view of Comparative Example 1. [Figure 8] FIG. 11 is a schematic cross-sectional view of Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that the following embodiments do not limit the subject matter of the present disclosure, and not all combinations of features described in the following embodiments are necessarily essential to the solution of the present disclosure. Note that the same components will be described with the same reference numerals.

[0012] <<First embodiment>> <Configuration of Liquid Ejection Head> The liquid ejection head substrate described in this embodiment is mounted on a liquid ejection head. The liquid ejection head is mounted on a liquid ejection device. The liquid ejection device is equipped with a liquid ejection head in which the liquid inside the liquid chamber is heated by passing electricity through a recording element (heating resistor), which causes film boiling of the liquid to cause bubbles in the liquid chamber, and the resulting bubble-forming energy ejects droplets from the ejection orifices. Note that, in this embodiment, an example will be described in which ink is used as the liquid, but the liquid is not limited to ink.

[0013] When such a liquid ejection device ejects liquid, the area above the heating resistor may be subjected to physical effects such as cavitation shocks that occur when the liquid foams, contracts, and disappears in the area above the heating resistor. In order to protect the heating resistor from these physical or chemical effects, a cavitation-resistant layer may be disposed on the heating resistor. The cavitation-resistant layer is usually made of a metal material such as tantalum or iridium, and is disposed in a position that contacts the liquid.

[0014] In this embodiment, the metal material formed as the cavitation-resistant layer and having a relatively high hardness is also used for the electrode pad. In addition, an example of a configuration in which the electrical reliability and power efficiency are increased will be described.

[0015] <Explanation of the structure of the liquid ejection head substrate> FIG. 1 is a perspective view showing a liquid ejection head substrate (hereinafter, simply referred to as an element substrate) 10 according to the present embodiment. The element substrate 10 has a substrate 11 on which a liquid supply path and the like are formed. In the element substrate 10, an ejection port forming member 12 is formed on the front side (+Z direction side) of the substrate 11, and a cover plate 20 is formed on the back side (-Z direction side) of the substrate 11. The ejection port forming member 12 of the element substrate 10 has four ejection port arrays corresponding to each ink color. Hereinafter, the direction (arrow A, Y direction) in which the ejection port array in which a plurality of liquid ejection ports (hereinafter, simply referred to as ejection ports) 13 are arranged extends will be referred to as the "ejection port array direction". In addition, in this embodiment, an example in which a plurality of types of liquid (ink) are used will be described, but a single type of liquid (ink) may be used.

[0016] As shown in Fig. 1, recording elements 14 that generate energy for ejecting liquid are arranged on the substrate 11 at positions corresponding to the ejection ports 13. The recording elements 14 are arranged in liquid flow paths that communicate with the ejection ports 13. In the example of Fig. 1, the recording elements 14 are heating resistor elements that use thermal energy to bubble the liquid. The ejection port forming member 12 defines liquid flow paths (called pressure chambers) 23 that communicate between the ejection ports 13 and the recording elements 14.

[0017] The recording element 14 is electrically connected to the electrode pad portion 16 arranged at the end of the substrate 11 by an electric wiring (not shown) provided on the element substrate 10. The recording element 14 of this embodiment is a heating element that generates heat based on a pulse signal input via an external wiring substrate (not shown) to boil the liquid, and ejects the liquid from the ejection port 13 by the force of bubbling caused by the boiling. In the example of FIG. 1, a liquid supply path 18 and a liquid recovery path 19, which are flow paths extending in the ejection port row direction and provided on the element substrate 10, communicate with the ejection port 13 via a supply port (not shown) and a recovery port (not shown), respectively. The cover plate 20 is provided with an inlet (not shown) for supplying liquid from the outside to the liquid supply path 18, and an outlet (not shown) for discharging the liquid from the liquid recovery path 19 to the outside. By circulating the liquid between the liquid supply path 18 and the outside in the direction of the arrow B via the liquid supply path 18 and the liquid recovery path 19, it is possible to suppress the thickening of the liquid near the ejection port 13 and stabilize the ejection performance of the liquid.

[0018] In this embodiment, the recording element 14 is covered with a cavitation-resistant layer made of tantalum (Ta), iridium (Ir), or a laminated film thereof facing the pressure chamber 23. In this embodiment, the portion shown as the recording element 14 in FIG. 1 is provided with a cavitation-resistant layer, and the cavitation-resistant layer comes into contact with the liquid. In this embodiment, iridium metal alone is used as at least a part of the material of the cavitation-resistant layer, but it may be an iridium alloy containing a small amount of elements such as osmium (Os) or platinum (Pt). Each recording element 14 is provided inside the substrate 11, and is connected to the electrode pad portion 16 through wiring connected to each other. An external voltage is applied to the recording element 14 through the electrode pad portion 16.

[0019] Fig. 2 is a diagram for explaining a liquid ejection head substrate in this embodiment. Fig. 2(a) corresponds to a cross section of the element substrate 10 shown in Fig. 1 taken along line IIA-IIA. Fig. 2(b) is a diagram showing a schematic cross section of the vicinity of the electrode pad portion 16 after wire bonding. Fig. 2(c) is a schematic plan view of Fig. 2(a).

[0020] FIG. 2(a) shows the vicinity of the discharge port forming member 12 and the electrode pad portion 16, and the vicinity of the heating resistor element (also called heating element) 31, which is the recording element 14 arranged directly below the discharge port 13 (so as to face the discharge port 13). The lower layer part of the substrate 11 and the cover plate 20 arranged below (in the -Z direction) are omitted from the illustration. The element substrate 10 is constructed by laminating a plurality of layers. Hereinafter, in the lamination direction of the element substrate 10, the direction in which the discharge port 13 is provided is referred to as the upward direction (+Z direction), and the opposite direction is referred to as the downward direction (-Z direction). The lamination direction is also the film thickness direction of each film constituting each layer.

[0021] As shown in FIG. 2(a), a heating element 31 made of a cermet material such as TaSiN (tantalum silicon nitride) or WSiN (tungsten silicon nitride) is formed on a heat storage layer 32 made of silicon oxide. The heating element 31 is electrically connected to an electrode plug 33 made of tungsten (W). Furthermore, a first insulating protective layer 34 made of a SiN film, a SiC film, a SiCN film, or a laminate of these is formed so as to cover the heating element 31 and the electrical wiring. Furthermore, a cavitation-resistant layer 35 is formed on the first insulating protective layer 34 above the heating element 31, the outermost layer of which is a material such as Ir that has a relatively high hardness and is resistant to deformation or destruction due to physical force. That is, the heating element 31 is covered by the cavitation-resistant layer 35 via the first insulating protective layer 34.

[0022] Here, as shown on the right side of FIG. 2(a), a wiring lead-out layer 36 (also called a wiring layer) electrically connected to the heating element 31 is provided near the electrode pad portion 16. The wiring lead-out layer 36 is formed of, for example, aluminum or an alloy of aluminum and copper. The wiring lead-out layer 36 is the lower layer of the electrode pad portion 16. The wiring lead-out layer 36 is electrically connected to an intermediate layer 38 of the electrode pad portion 16, which is formed of the same material as the cavitation-resistant layer 35, the outermost layer of which is Ir, via a through hole 37 formed in the first insulating protective layer 34. The intermediate layer 38 is the lower electrode layer in the electrode pad portion 16. In this embodiment, as described above, the intermediate layer 38 of the electrode pad portion 16 and the cavitation-resistant layer 35 on the heating element 31 are formed simultaneously (i.e., in the same manufacturing process). This makes it possible to reduce the manufacturing load. As long as the intermediate layer 38 of the electrode pad portion 16 is formed of the same material as the cavitation-resistant layer 35, they may be formed in separate processes.

[0023] The wiring lead-out layer 36 constituting the lower layer of the electrode pad portion 16 may be an extension of a part of a wiring layer (not shown) or may be formed separately. The electrode pad portion 16 can be divided into a first pad region 16a where the wiring lead-out layer 36 and the middle layer 38 of the electrode pad portion 16 overlap, and a second pad region 16b excluding the first pad region 16a. A second insulating protective layer 39 made of SiN, SiC, SiCN, SiO, or SiOC, or a laminate of materials selected from the group, is formed so as to cover at least a part of the cavitation-resistant layer 35. Here, the second insulating protective layer 39 can also serve as an adhesion improving layer between the substrate 11 and the discharge port forming member 12. In particular, in the vicinity of the electrode pad portion 16, a first opening 17a is formed in the first pad region 16a and a second opening 17b is formed in the second pad region 16b in the second insulating protective layer 39. An upper layer 40 of the electrode pad portion 16 made of Au (gold) is formed on the electrode pad portion 16 so as to cover at least both the first opening 17a and the second opening 17b. The upper layer 40 is an upper electrode layer of the electrode pad portion 16.

[0024] Here, the first opening 17a and the second opening 17b are formed as independent patterns. The first opening 17a is an area where probing or bonding is not performed, and is therefore formed smaller than the second opening 17b in order to reduce the pad size. On the other hand, in order to ensure electrical connectivity when the opening size is reduced, a plurality of second openings 17b may be arranged. It is preferable that the second openings 17b are arranged at positions that do not unnecessarily increase the size of the pad portion. For example, an arrangement as shown in FIG. 2(c) is a suitable example. FIG. 2(c) shows an example in which three first openings 17a are provided for one second opening 17b. Also, FIG. 2(c) shows an example in which the first openings 17a are provided in the direction of the ejection port array in which the heating elements 31 are arranged (i.e., the ejection ports 13 are arranged).

[0025] At the boundary between the first pad region 16a and the second pad region 16b, there is a step due to the pattern of the wiring lead-out layer 36. At this step, the thickness of the middle layer 38 is likely to become thin, which raises concerns about electrical reliability. That is, when the thickness of the middle layer 38 becomes thin, a high-resistance region is generated in the electrode pad portion 16. This high-resistance region generates unnecessary parasitic resistance, which causes more power consumption than necessary and raises concerns about electrical reliability such as disconnection due to current concentration. However, by forming the second insulating protection layer 39 and the upper layer 40 as described above, the current flowing in the planar direction of the step can be suppressed, thereby improving reliability. That is, by providing the first opening 17a and the second opening 17b in the second insulating protection layer 39 as described above and forming the upper layer 40 so as to cover at least both the first opening 17a and the second opening 17b, electrical reliability is improved. Specifically, since current flows through upper layer 40 above second opening 17b, upper layer 40 above first opening 17a, middle layer 38 above first opening 17a, and a path leading to wiring extraction layer 36, the current flowing in the planar direction of the step portion can be suppressed, improving reliability.

[0026] With regard to the layered structure of the electrode pad portion 16, the side electrically connected to the outside is described as the top or front, and the opposite side as the bottom; however, these tops and bottoms do not change depending on the position of the substrate 10 for the liquid ejection head.

[0027] The material forming the upper layer 40 of the electrode pad portion 16 is Au, and therefore has resistance (chemical resistance) to acids, alkalis, or organic stripping liquids used in the subsequent manufacturing process of the ejection port forming member 12, and is not easily dissolved. In addition, in this embodiment, from the viewpoint of cost, an electrical inspection of the element substrate 10 is performed after the middle layer 38 or the upper layer 40 of the electrode pad portion 16 is formed and before wire bonding of the wire member 41 shown in FIG. 2(b) is performed. This prevents defective chips from being mounted.

[0028] In the electrode pad portion 16, electrical connection to an external substrate is performed by wire bonding or lead bonding. When wire bonding is performed on the first pad region 16a, the wiring lead-out layer 36 may be deformed by pressure during bonding, and abnormalities such as cracks may occur in the first insulating protection layer 34 or the second insulating protection layer 39. In contrast, the second pad region 16b does not have a layer that deforms under pressure. For this reason, it is preferable to perform wire bonding on the second pad region 16b. In addition, a barrier metal layer such as TiW (titanium tungsten) may be formed between the middle layer 38 and the upper layer 40. This can suppress the diffusion of Au into the lower layer.

[0029] 2(b) shows a schematic cross-sectional view of the vicinity of the electrode pad portion 16 after wire bonding of the wire member 41, which is a bonding material. As shown in FIG. 2(b), the flatness of the surface of the electrode pad portion 16 is maintained, so that deterioration of the connectivity and electrical reliability in the wire bonding can be suppressed. In addition, since the flatness of the electrode pad portion 16 can be maintained even when an electrical inspection is performed as described above, it is possible to perform bonding on the second pad region 16b.

[0030] As a comparative example not based on this embodiment, there is an example in which the electrode pad portion 16 is formed of AL (aluminum). Since AL is a relatively soft material, the electrode pad portion may be damaged (gouged) by probing, and as a result, unevenness (probe mark) having a height difference of about 1 μm or more may be formed on the surface of the electrode pad portion. If bonding is performed at this probe mark portion, the connection reliability between the electrode pad and the bonding material may be impaired. For this reason, in such a pad formed of AL, it is necessary to separate the probing area and the bonding area. For example, in many cases, a width of about 80 μm is required for the probing area and a width of about 80 μm is required for the bonding area, and the chip becomes larger than necessary due to the large width of the pad. In this embodiment, the middle layer 38 of the electrode pad portion 16 is formed of the same material as the cavitation-resistant layer 35, and the influence of the probe mark is small, so there is no need to separate the probing area and the bonding area. For this reason, it is also possible to reduce the area of ​​the electrode pad portion 16.

[0031] Furthermore, since the middle layer 38 of the electrode pad portion 16 is made of Ir, which is a precious metal film that does not form a natural oxide film in the air at room temperature, there is no need to perform a process to remove the oxide film on the upper surface of the middle layer 38 during the manufacturing process, which reduces the load on the manufacturing process.

[0032] The configuration of the electrode pad section 16 is not limited to the configuration having the intermediate layer 38 of a single layer structure shown in this embodiment, but may be a configuration having an intermediate layer 38 of a multi-layer structure. In the case of a multi-layer structure, it is sufficient that the surface on which probing is performed is formed of the same material as the cavitation-resistant layer. Also, probing is preferably performed on the second pad region 16b.

[0033] As described above, according to this embodiment, it is possible to provide a liquid ejection head substrate having electrode pads with high electrical reliability and power efficiency. That is, in this embodiment, when the element substrate 10 is electrically connected to the outside of the element substrate 10, the electrode pad portion 16 is formed in the same layer as the cavitation-resistant layer 35. This makes it possible to reduce the area of ​​the electrode pad portion 16. In this embodiment, the first opening 17a and the second opening 17b are provided in the second insulating protection layer 39 in the electrode pad portion 16, and the upper layer 40 is formed so as to cover at least both the first opening 17a and the second opening 17b. This allows a current to flow through the upper layer 40 on the second opening 17b, the upper layer 40 on the first opening 17a, the middle layer 38 on the first opening 17a, and the first path leading to the wiring lead-out layer 36. In addition, even in the second path in which a current flows in a planar direction through the middle layer 38 from the upper layer 40 on the second opening 17b through the middle layer 38 on the second opening 17b to the wiring lead-out layer 36, if the middle layer 38 is not physically interrupted, the electrical connection is maintained. However, the sheet resistance value of the middle layer 38 is greater than the sheet resistance value of the upper layer 40. That is, since the resistance ratio between the first path and the second path is large, only a substantially negligible current flows in the second path, and the current in the second path does not contribute to driving the liquid ejection head. In this way, in the element substrate 10 of this embodiment, since a current substantially flows through the first path, it is possible to suppress the current flowing in the planar direction (second path) of the step portion. Therefore, a large current does not flow through the thin film region of the electrode pad portion 16, and electrical reliability is improved. In addition, since the current paths with high resistance in the planar direction can be reduced, it is possible to provide a substrate for a liquid ejection head equipped with an electrode pad with high power efficiency. In addition, it is possible to provide a substrate for a liquid ejection head in which the occurrence of probe marks is suppressed.

[0034] In this embodiment, as described above, in order to ensure the reliability of the step portion of the electrode pad portion 16, the thickness of the upper layer 40 is sufficient to be 500 nm or less. The lower limit of the upper layer 40 is not particularly limited as long as the electrical connection is ensured, but 50 nm or more is preferable, and 100 nm or more is more preferable. In addition, it is preferable to make the upper surface of the upper layer 40 lower than the formation surface of the discharge port 13 in the discharge port formation member 12. This prevents the thickness of the electrode pad portion 16 and the sealant covering the electrode pad portion 16 from interfering with the distance between the formation surface of the discharge port 13 and a recording medium such as paper. Therefore, the distance between the formation surface of the discharge port 13 and a recording medium such as paper can be shortened, and image quality can be improved.

[0035] <<Second embodiment>> In the first embodiment, an example was described in which the middle layer 38 of the electrode pad portion 16 and the cavitation-resistant layer 35 have a single-layer structure. In the present embodiment, an example is described in which the middle layer 38 of the electrode pad portion 16 and the cavitation-resistant layer 35 have a two-layer structure. Since the basic configuration is similar to the example described in the first embodiment, the differences will be mainly described.

[0036] 3 shows a cross-sectional view of a liquid ejection head substrate in which the middle layer 38 of the electrode pad section 16 and the anti-cavitation layer 35 each have a two-layer laminate structure of a first adhesive layer and a second Ir film. That is, the middle layer 38 of the electrode pad section 16 has a first adhesive layer 38a and a second Ir film 38b. The anti-cavitation layer 35 has a first adhesive layer 35a and a second Ir film 35b. The first layer is a layer below the second layer.

[0037] Fig. 3 is a view corresponding to Fig. 2(a). By disposing the adhesion layer 35a in this manner, it is possible to improve the adhesion between the first insulating protective layer 34 and the anti-cavitation layer 35. Note that the adhesion layer 35a may be any conductive layer that has adhesion to the first insulating protective layer 34 and the anti-cavitation layer 35, and may be formed using, for example, a Ta film.

[0038] As described above, in this embodiment, it is possible to provide a liquid ejection head substrate having electrode pads that suppress the occurrence of probe marks and have high electrical reliability and power efficiency. In addition, it is possible to improve the adhesion between the first insulating protection layer 34 and the anti-cavitation layer 35.

[0039] <<Third embodiment>> In the first embodiment, an example was described in which the middle layer 38 of the electrode pad portion 16 and the cavitation-resistant layer 35 have a single-layer structure. In the present embodiment, an example is described in which the middle layer 38 of the electrode pad portion 16 and the cavitation-resistant layer 35 each have a three-layer structure. Since the basic configuration is similar to the example described in the first embodiment, the differences will be mainly described.

[0040] FIG. 4 shows a cross-sectional view of a liquid ejection head substrate in which the middle layer 38 of the electrode pad section 16 and the cavitation-resistant layer 35 each have a three-layer laminated structure. FIG. 4 is a view corresponding to FIG. 2(a). This laminated structure has a first layer of Ta film, a second layer of Ir film, and a third layer of Ta film. That is, the middle layer 38 of the electrode pad section 16 has a first layer of Ta film 38a, a second layer of Ir film 38b, and a third layer of Ta film 38c. The cavitation-resistant layer 35 has a first layer of Ta film 35a, a second layer of Ir film 35b, and a third layer of Ta film 35c. The first layer is a layer below the second layer, and the second layer is a layer below the third layer.

[0041] As shown in FIG. 4, on the electrode pad portion 16 and the heating element 31, the second insulating protective layer 39 is opened, and the third layer of Ta film (35c and 38c) is removed to expose the second layer of Ir film (35b and 38b). In this case, from the viewpoint of manufacturing load, it is preferable to remove the second insulating protective layer 39 and the third layer of Ta film (35c and 38c) in the same manufacturing process. That is, in this embodiment, of the three-layer laminated structure, the layers used as the cavitation-resistant layer 35 covering the electrode pad portion 16 and the heating element 31 are the first layer and the second layer. In this case, too, the Ir film, which is less likely to cause probe marks, is exposed on the surface of the electrode pad portion 16, and by probing this surface, an electrode pad in which probe marks are suppressed is obtained. Here, the first layer, the second layer, and the third layer of films are specifically described as Ta, Ir, and Ta, but other metal materials, etc. may be used.

[0042] Furthermore, by disposing the third layer Ta film (35c and 38c) in any region other than on the heating element 31 and the electrode pad portion 16, it can also be used as low-resistance electrical wiring, improving the degree of freedom in circuit layout. In this case, however, in order to reduce the amount of warping of the wafer, it is preferable that the thickness of the third layer Ta film 35c is 200 nm or less. Also, taking into account the electrical resistance, it is more preferable that the thickness of the third layer Ta film 35c is 50 nm or more and 200 nm or less.

[0043] In addition, in FIG. 4, the electrode pad portion 16 and the anti-cavitation layer 35 have a common laminated structure, but as long as the Ir film is common (formed in the same manufacturing process), the laminated structure does not have to be entirely common.

[0044] FIG. 5 is a diagram showing a modified example of this embodiment. FIG. 5 is a diagram showing a cross-sectional view of a substrate for a liquid ejection head, similar to FIG. 2(a). FIG. 5 is a diagram showing a modified example in which the electrode pad portion 16 and the cavitation-resistant layer 35 do not all have the same laminated structure. In FIG. 5, the electrode pad portion 16 is composed of a first layer of Ta film 38a and a second layer of Ir film 38b. On the other hand, the cavitation-resistant layer 35 is composed of a first layer of Ta film 35a, a second layer of Ir film 35b, and a third layer of Ta film 35c. In this modified example, the outermost layer of the cavitation-resistant layer 35 is a Ta film in order to protect the heating element 31, while the outermost layer of the electrode pad portion 16 is an Ir film in order to suppress probe marks in an electrical test. In other words, the cavitation-resistant layer 35 and the middle layer 38 of the electrode pad portion 16 do not have a completely identical layer structure.

[0045] In addition, since the Ir film 38b constituting the electrode pad portion 16 can prevent Au constituting the upper layer 40 from diffusing into the lower layer, there is no need to provide a separate barrier metal layer such as TiW. In other words, it is sufficient that the lower surface of the upper layer 40 is provided so as to be in contact with the Ir film. This configuration is preferable in that it can reduce manufacturing costs. In addition, if a barrier metal layer such as TiW is used, depending on the configuration, there is a risk that the barrier metal layer will be dissolved by a solvent used in the manufacturing process. On the other hand, the Ir film 38b is preferable in that it is resistant to such solvents and there is no risk of dissolution.

[0046] <<Example>> Specific examples of the configurations of the anti-cavitation layer 35 and the electrode pad portion 16 will be described below with reference to the drawings.

[0047] <Example 1> Example 1 corresponds to the above-mentioned first embodiment. In this example, a configuration and a manufacturing method in which an Ir film is used for the cavitation-resistant layer 35 in the same manner as in the first embodiment will be described with reference to FIG.

[0048] Fig. 6 is a process cross-sectional view explaining the manufacturing process of this embodiment. Fig. 6 is a schematic cross-sectional view of a substrate for a liquid ejection head, similar to Fig. 2(a). Also, in Fig. 6, the lower layer portion of the substrate 11 and the cover plate 20 are omitted, similar to Fig. 2(a).

[0049] As shown in FIG. 6(a), a heat storage layer 32 made of SiO and having a thickness of 1 μm was formed on a substrate (not shown) on which a driving element (not shown) and wiring (not shown) for driving the driving element were formed. Then, a part of the heat storage layer 32 was opened by dry etching to provide a through hole. An electrode plug 33 was formed by using tungsten (W) so as to fill the through hole. Furthermore, as shown in FIG. 6(a), a cermet material made of TaSiN was formed to a thickness of 15 nm. Also, a wiring electrode layer made of an alloy of aluminum and copper was formed on the cermet material, and a wiring take-out layer 36 and a heating element 31 were formed by photolithography and dry etching. A connection layer 30 was formed under the wiring take-out layer 36 using the same material as the heating element 31. The heating element 31 was formed to have a size of 15 μm. For example, after the lamination of the wiring electrode layer and the cermet material is dry etched, the wiring electrode layer on the cermet material is removed, and the cermet material is further dry etched as necessary to form the heating element 31. The lower layer driving element (not shown) is connected to the heating element 31 and wiring electrode layer formed in a later process via the electrode plug 33. However, the electrical connection to the heating element 31 can be made by supplying power from the wiring electrode layer in addition to using the electrode plug.

[0050] Next, as shown in FIG. 6(b), a first insulating protective layer 34 made of SiN was formed to a thickness of 200 nm so as to cover the heating element 31 and the wiring lead-out layer 36. Here, the film thickness of the first insulating protective layer 34 was set to 200 nm from the viewpoint of insulation, but a thickness of 100 nm or more is sufficient, and more preferably, a thickness of 100 nm to 500 nm is sufficient from the viewpoint of thermal conduction to the liquid. Next, a mask (not shown) was formed on the first insulating protective layer 34 by photolithography, and a through hole 37 was formed in the first insulating protective layer 34 to expose a part of the wiring lead-out layer 36, as shown in FIG. 6(b).

[0051] Next, as shown in FIG. 6(c), a layer made of iridium (Ir) was formed on the entire surface to a thickness of 100 nm, and the layer made of Ir was etched to form the intermediate layer 38 of the electrode pad portion 16 and the cavitation-resistant layer 35. The thickness of the Ir film may be any thickness that satisfies the cavitation resistance, and is preferably 20 nm or more. Furthermore, taking into consideration the viewpoint of processability, it is more preferable that the thickness is 20 nm or more and 300 nm or less. In addition, in the electrode pad portion 16, the intermediate layer 38 made of Ir formed in the same layer as the cavitation-resistant layer 35 is connected to the wiring lead-out layer 36 via a through hole 37. Thereafter, as shown in FIG. 6(c), a layer made of SiCN was formed to a thickness of 200 nm, and etched using a photolithography method and a dry etching method to form a second insulating protective layer 39. By disposing such a second insulating protective layer 39, the reliability of the liquid ejection head, especially for the liquid contact portion, is further improved. Here, as shown in Fig. 6(c), the second insulating protective layer 39 is removed from directly above the heating element 31 in terms of thermal efficiency. Also, for the electrode pad portion 16, a first opening 17a and a second opening 17b are formed for connection to the upper layer 40 in a later process. Thus, as shown in Fig. 6(c), in the outermost layer of the electrode pad portion 16, Ir, which is the middle layer 38, is exposed in each of the first pad region 16a and the second pad region 16b.

[0052] At this stage, the second pad region 16b was probed and an electrical test was performed. Since Ir is a precious metal film that does not form a natural oxide film in the air at room temperature, probing was performed stably, but the measured values ​​were unstable in some terminals. Later, when the terminals with unstable measurements were observed in detail, a part where Ir was partially interrupted was confirmed at the step part of the wiring lead-out layer 36 of the electrode pad part 16. In addition, the surface of the electrode pad part 16 after the electrical test was observed with a laser microscope, and no physical damage or deformation due to probing occurred. In other words, even when the electrical test was performed during the process as in this embodiment, no influence due to probing was observed. For the electrical test, a general probe made of rhenium tungsten with a tip diameter of φ20 μm was used. In addition, the overdrive amount during probing was set to 60 μm.

[0053] Next, as shown in FIG. 6(d), a layer made of gold (Au) was formed to a thickness of 400 nm on the entire surface of the substrate, and the upper layer 40 of the electrode pad portion 16 was formed by photolithography and wet etching using an etchant containing iodine. After that, as shown in FIG. 6(d), the liquid supply path and the discharge port 13 were formed using the discharge port forming member 12, and a cover plate was formed on the back side of the substrate (not shown), and the same electrical inspection was performed again. Probing was also performed stably, and the measured values ​​were stable, and the inspection was performed without any problems. At this time, the path of the current is the path (the first path described above) that flows from the upper layer 40 through the first opening 17a in the film thickness direction, so that a stable electrical inspection can be performed even if the middle layer 38 is interrupted halfway.

[0054] Next, as shown in Fig. 6(e), wire bonding was performed on the upper layer 40 of the electrode pad portion 16 using a wire member 41 made of gold for electrical connection to an external substrate. Wire bonding can be performed by ball bonding or wedge bonding, but in this embodiment, the ball bonding method was used. The wire member 41 used had a wire diameter of 25 µm.

[0055] In this embodiment, as described above, there is no physical damage or deformation on the surface of the electrode pad portion 16 due to probing, and therefore the electrical connection reliability of the electrode pad portion 16 is improved compared to the case where there is damage due to probing. Furthermore, even if the middle layer 38 of the electrode pad portion 16 is interrupted at the step portion, the influence can be eliminated by appropriately forming the upper layer 40. In addition, since it is not necessary to form a thick film to hide the probe mark, it is possible to provide a liquid ejection head that corresponds to miniaturization of ejection. Furthermore, when the liquid ejection head thus manufactured is driven and an operation of actually ejecting ink is performed, the liquid ejection can be continued without any problem.

[0056] <Example 2> Example 2 is an example corresponding to the above-mentioned second embodiment. In this example, the cavitation-resistant layer 35 in Example 1 was changed to a two-layer structure of an upper Ir film 35b and a lower Ta film 35a, as shown in Fig. 3. The other steps were the same as those in Example 1, and the liquid ejection head in this example was obtained. In this case, the Ir film and the Ta film were formed to have thicknesses of 70 nm and 30 nm, respectively.

[0057] With this configuration, the adhesion between the lower first insulating protection layer 34 and the cavitation-resistant layer 35 is further improved, and a more reliable liquid ejection head can be provided. In addition, in the electrode pad portion 16, as shown in Fig. 3, the middle layer 38 has a two-layer configuration of a first layer 38a formed in the same layer as the Ta film 35a, and a second layer 38b formed in the same layer as the Ir film 35b.

[0058] <Example 3> Example 3 is an example corresponding to the above-mentioned third embodiment. Fig. 4 is a schematic cross-sectional view of this example. Differences from Example 1 will be described below. A substrate similar to that of Example 1 was prepared, and the same process was used to fabricate the substrate up to the stage before the formation of the cavitation-resistant layer 35 (Fig. 6(b)).

[0059] Then, in this embodiment, the layer that becomes the cavitation-resistant layer 35 is formed from three layers, namely, the third layer Ta film 35c, the second layer Ir film 35b, and the first layer Ta film 35a, from the top. The thickness of the Ta film 35c is 70 nm, the thickness of the Ir film 35b is 70 nm, and the thickness of the Ta film 35a is 30 nm. In the electrode pad portion 16, the layer that becomes the middle layer 38 is also composed of the first layer 38a in the same layer as the Ta film 35a, the second layer 38b in the same layer as the Ir film 35b, and the third layer 38c in the same layer as the Ta film 35c. Then, on the cavitation-resistant layer 35 and the middle layer 38, a second insulating protective layer 39 made of SiCN is formed to a thickness of 200 nm so as to cover the entire substrate. Thereafter, the second insulating protective layer 39 on the heating element 31 and on the electrode pad portion 16, as well as the upper Ta film 35c and the third layer 38c, were removed by dry etching to expose the Ir film 35b and the second layer 38b, thereby forming the first opening 17a and the second opening 17b. By performing chemical etching using chlorine gas or fluorine gas during etching, the Ir surface can be exposed without significantly reducing the thickness of the Ir film.

[0060] In this embodiment, an electrical inspection of the substrate was also carried out immediately after the opening of the pad portion, that is, after FIG. 6(c). As described in the first embodiment, in this embodiment, the exposed surface of the electrode pad portion 16 during probing was the second layer 38b made of Ir, and it was confirmed that the second layer 38b had no physical damage or deformation, but the measured values ​​were unstable. Thereafter, the upper layer 40 was formed in the same manner as in the first embodiment, and an electrical inspection was carried out. As in the first embodiment, probing was also performed stably, the measured values ​​were also stable, and the inspection was carried out without problems. In the subsequent process, as in the first embodiment, a liquid supply path and a discharge port forming member 12 were formed on the substrate, and a cover plate was also formed on the back side of the substrate. Thereafter, as in the first embodiment, bonding was performed on the electrode pad portion 16 using a gold wire. In this embodiment, as in the first and second embodiments, the electrical connection reliability of the electrode pad portion 16 is improved compared to the case where damage is caused by probing.

[0061] <Comparative Example 1> 7 is a schematic cross-sectional view of Comparative Example 1. In this comparative example, the process up to the formation of the second insulating protective layer 39 was the same as in Example 3, and the opening 17 of the electrode pad portion 16 was formed as one large opening. In other words, the first opening 17a and the second opening 17b were not formed. When an electrical inspection was carried out after the opening 17 of the electrode pad portion 16 was formed as one large opening, probing was stably performed as in Example 1, but the measured values ​​were sometimes unstable at some terminals.

[0062] Subsequently, the upper layer 40 was formed in the same manner as in Examples 1 to 3, but the pattern of the upper layer 40 was lifted at the step between the first pad region 16a and the second pad region 16b. When this portion was observed in detail, an altered layer due to etching residue of the Ta film 38c was present at the step. When the subsequent process was carried out, peeling of the upper layer 40 occurred starting from the lifted portion, and there were cases where the desired head could not be manufactured.

[0063] <Comparative Example 2> 8 is a schematic cross-sectional view of Comparative Example 2. In this Comparative Example, a substrate was produced in the same process as in Example 1, except that the substrate was produced without forming only the first opening 17a. As in Example 1, electrical testing was performed twice, once with Ir exposed on the electrode pad portion 16 and once after the upper layer 40 was formed, and in both measurements, terminals with unstable measurement values ​​were observed. As in Example 1, it was observed that Ir was interrupted at a step portion present in the pad portion 16 for terminals with unstable measurement.

[0064] <<Other embodiments>> The disclosure of the present embodiment includes configurations represented by the following examples of a substrate for a liquid ejection head, examples of a liquid ejection head, and an example of a method for manufacturing a substrate for a liquid ejection head.

[0065] <Configuration 1> a heating element that generates energy for ejecting liquid; a wiring layer provided in a lower layer, electrically connected to the heat generating element via the wiring layer, an electrode pad portion electrically connected to the outside via a bonding material; An insulating protective layer; A liquid ejection head substrate comprising: The electrode pad portion is Further comprising a lower electrode layer and an upper electrode layer; the insulating protection layer disposed in a first region overlapping with the wiring layer in a film thickness direction has a first opening connecting the lower electrode layer and the upper electrode layer; the insulating protection layer disposed at a position including at least a second region overlapping with the bonding material in a thickness direction has a second opening connecting the lower electrode layer and the upper electrode layer; A substrate for a liquid ejection head.

[0066] <Configuration 2> The heating element further includes an anti-cavitation layer formed to cover the heating element, 2. The liquid ejection head substrate according to claim 1, wherein the lower electrode layer includes a layer formed of the same material as at least a portion of the anti-cavitation layer.

[0067] <Configuration 3> 3. The liquid ejection head substrate according to configuration 2, wherein the anti-cavitation layer has a thickness of 20 nm or more and 300 nm or less.

[0068] <Configuration 4> A first insulating protective layer electrically insulates the heating element from the anti-cavitation layer, 4. The liquid ejection head substrate according to configuration 2 or 3, wherein the insulating protective layer is a second insulating protective layer that covers at least a portion of the anti-cavitation layer.

[0069] <Component 5> 5. The liquid ejection head substrate according to any one of configurations 2 to 4, wherein the number of layers constituting the lower electrode layer is the same as the number of layers constituting the anti-cavitation layer.

[0070] <Component 6> 5. The substrate for a liquid ejection head according to any one of configurations 2 to 4, wherein the number of layers constituting the lower electrode layer is different from the number of layers constituting the anti-cavitation layer.

[0071] <Component 7> 7. The liquid ejection head substrate according to any one of configurations 2 to 6, wherein the anti-cavitation layer is a layer including a laminate of iridium metal and tantalum.

[0072] <Component 8> 8. The liquid ejection head substrate according to any one of configurations 1 to 7, wherein the wiring layer is connected to the lower electrode layer.

[0073] <Component 9> 9. The liquid ejection head substrate according to any one of configurations 1 to 8, wherein the lower electrode layer of the electrode pad portion is a layer containing iridium metal or an iridium alloy.

[0074] <Component 10> 10. The liquid ejection head substrate according to any one of configurations 1 to 9, wherein the upper electrode layer of the electrode pad portion is a layer containing gold.

[0075] <Component 11> 11. The liquid ejection head substrate according to any one of configurations 1 to 10, wherein the wiring layer is a layer containing aluminum.

[0076] <Component 12> 12. The liquid ejection head substrate according to any one of configurations 1 to 11, wherein no probe mark is formed on the wiring layer.

[0077] <Component 13> 13. The liquid ejection head substrate according to any one of configurations 1 to 12, wherein a plurality of the first openings are provided for one of the electrode pad portions.

[0078] <Component 14> 14. The liquid ejection head substrate according to configuration 13, wherein the first openings are provided in a direction in which the heat generating elements are arranged.

[0079] <Component 15> 15. The liquid ejection head substrate according to any one of configurations 1 to 14, wherein the second opening has an area larger than that of the first opening.

[0080] <Component 16> 16. The liquid ejection head substrate according to any one of configurations 1 to 15, wherein the sheet resistance of the lower electrode layer is greater than the sheet resistance of the upper electrode layer.

[0081] <Component 17> 17. The liquid ejection head substrate according to any one of configurations 1 to 16, wherein the first opening and the second opening are independent of each other.

[0082] <Component 18> 18. A liquid ejection head using the liquid ejection head substrate according to any one of configurations 1 to 17.

[0083] <Component 19> a heating element that generates energy for ejecting liquid; a wiring layer provided in a lower layer, electrically connected to the heat generating element via the wiring layer, an electrode pad portion electrically connected to the outside via a bonding material; an anti-cavitation layer formed to cover the heating element; An insulating protective layer; A method for manufacturing a liquid ejection head substrate, comprising: And, forming a wiring layer below the electrode pad portion; forming a lower electrode layer made of the same material as at least a portion of the cavitation-resistant layer in a region including a first region overlapping with the wiring layer in a thickness direction and a second region overlapping with the bonding material in a thickness direction; forming the insulating protection layer so as to form a first opening connecting the lower electrode layer and the upper electrode layer in the first region and to form a second opening connecting the lower electrode layer and the upper electrode layer in the second region; forming the upper electrode layer so as to cover the first opening and the second opening; bonding the bonding material to the top electrode layer; 2. A method for manufacturing a substrate for a liquid ejection head, comprising:

[0084] <Component 20> The heating element is formed in the step of forming the wiring layer, 20. The method of manufacturing a substrate for a liquid ejection head according to Configuration 19, wherein the anti-cavitation layer is formed in the step of forming the lower electrode layer. [Explanation of symbols]

[0085] 10. Liquid ejection head substrate 16 Electrode pad section 31 Heating element 34 First insulating protective layer 35 Cavitation-resistant layer 36 Wiring layer 38 Middle class 39 Second insulating protective layer 40 upper layer 41 Wire material

Claims

1. a heating element that generates energy for ejecting liquid; a wiring layer provided in a lower layer, electrically connected to the heat generating element via the wiring layer, an electrode pad portion electrically connected to the outside via a bonding material; An insulating protective layer; A liquid ejection head substrate comprising: The electrode pad portion is Further comprising a lower electrode layer and an upper electrode layer; the insulating protection layer disposed in a first region overlapping with the wiring layer in a film thickness direction has a first opening connecting the lower electrode layer and the upper electrode layer; the insulating protection layer disposed at a position including at least a second region overlapping with the bonding material in a thickness direction has a second opening connecting the lower electrode layer and the upper electrode layer; A substrate for a liquid ejection head.

2. The heating element further includes an anti-cavitation layer formed to cover the heating element, The liquid ejection head substrate according to claim 1 , wherein the lower electrode layer includes a layer formed of the same material as at least a portion of the anti-cavitation layer.

3. 3. The liquid ejection head substrate according to claim 2, wherein the cavitation-resistant layer has a thickness of 20 nm or more and 300 nm or less.

4. A first insulating protective layer electrically insulates the heating element from the anti-cavitation layer, The liquid ejection head substrate according to claim 2 , wherein the insulating protective layer is a second insulating protective layer that covers at least a portion of the anti-cavitation layer.

5. 3. The liquid ejection head substrate according to claim 2, wherein the number of layers constituting the lower electrode layer is the same as the number of layers constituting the anti-cavitation layer.

6. 3. The liquid ejection head substrate according to claim 2, wherein the number of layers constituting the lower electrode layer is different from the number of layers constituting the anti-cavitation layer.

7. 3. The liquid ejection head substrate according to claim 2, wherein the cavitation-resistant layer is a layer including a laminate of iridium metal and tantalum.

8. The liquid ejection head substrate according to claim 1 , wherein the wiring layer is connected to the lower electrode layer.

9. 2. The liquid ejection head substrate according to claim 1, wherein the lower electrode layer of the electrode pad portion is a layer containing iridium metal or an iridium alloy.

10. 2. The liquid ejection head substrate according to claim 1, wherein the upper electrode layer of the electrode pad portion is a layer containing gold.

11. 2. The liquid ejection head substrate according to claim 1, wherein the wiring layer is a layer containing aluminum.

12. The liquid ejection head substrate according to claim 1 , wherein the wiring layer is free of probe marks.

13. The liquid ejection head substrate according to claim 1 , wherein a plurality of the first openings are provided for one of the electrode pad portions.

14. The liquid ejection head substrate according to claim 13 , wherein the first openings are provided in a direction in which the heat generating elements are arranged.

15. The liquid ejection head substrate according to claim 1 , wherein the second opening has an area larger than that of the first opening.

16. 2. The liquid ejection head substrate according to claim 1, wherein the sheet resistance of the lower electrode layer is greater than the sheet resistance of the upper electrode layer.

17. The liquid ejection head substrate according to claim 1 , wherein the first opening and the second opening are independent of each other.

18. A liquid ejection head using the liquid ejection head substrate according to any one of claims 1 to 17.

19. a heating element that generates energy for ejecting liquid; a wiring layer provided in a lower layer, electrically connected to the heat generating element via the wiring layer, an electrode pad portion electrically connected to the outside via a bonding material; an anti-cavitation layer formed to cover the heating element; An insulating protective layer; A method for manufacturing a liquid ejection head substrate, comprising: And, forming a wiring layer below the electrode pad portion; forming a lower electrode layer made of the same material as at least a portion of the cavitation-resistant layer in a region including a first region overlapping with the wiring layer in a thickness direction and a second region overlapping with the bonding material in a thickness direction; forming the insulating protection layer so as to form a first opening connecting the lower electrode layer and the upper electrode layer in the first region and to form a second opening connecting the lower electrode layer and the upper electrode layer in the second region; forming the upper electrode layer so as to cover the first opening and the second opening; bonding the bonding material to the top electrode layer; 2. A method for manufacturing a substrate for a liquid ejection head, comprising:

20. The heating element is formed in the step of forming the wiring layer, The method for manufacturing a substrate for a liquid ejection head according to claim 19, wherein the anti-cavitation layer is formed in the step of forming the lower electrode layer.

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