JP7483495B2 - Substrate for liquid ejection head and manufacturing method thereof - Google Patents

Description

The present invention relates to a substrate for a liquid ejection head that ejects liquid to record on a recording medium, and a method for manufacturing the substrate for the liquid ejection head.

Conventionally, bonding methods such as wire bonding have been 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 acids, alkalis, and organic solvents used in the nozzle manufacturing process formed after the element substrate is manufactured. Currently, the electrode pad portion has a laminated structure from the bottom, such as an aluminum layer used as the 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, such an electrode pad portion is connected to an external substrate by wire bonding connection using a gold wire or the like. 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.

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 the electrical test, probing is performed by placing a test probe on the electrode pad portion. However, in the case of the current Au layer/TiW layer/aluminum layer laminated film, the Au layer and the aluminum layer are relatively soft materials, so the electrode pad portion may be damaged (gouged) by probing. As a result, unevenness (called probe marks) with a height difference of about 1 μm or more may be formed on the surface of the electrode pad portion. Figure 10 is a diagram showing the occurrence of probe marks 105 when an electrical test is performed on an electrode pad portion having a conventional aluminum layer 102 using a probe 103. As shown in Figure 10 (a), the probe 103 is placed on the aluminum layer 102 and scanned in the direction of the arrow. This scanning distance is called the overdrive amount, and the area where the probe 103 contacts is called the probing area 104. As shown in FIG. 10B, in the probing region 104, the aluminum layer 102 is gouged out, and the residue becomes a large unevenness (probe mark 105) as a protrusion. 101 indicates a contact via to the lower wiring (not shown).

To deal with the occurrence of such large irregularities, a method is known in which after the process of exposing the aluminum layer, an electrical test of the board is carried out on the aluminum layer, then a TiW layer is sputtered, and then a thick Au layer is formed by plating. By probing the thin aluminum layer and filling the probe marks with a thick Au layer, the effects of probing in the electrical test are minimized, ensuring the reliability of the connection during wire bonding. Another method is to form a thick insulating layer instead of a thick Au layer to hide the probe marks, and to form a through hole in the area without the probe marks to form a pad electrode.

However, forming a thick Au layer is costly, and the formation of thick film protrusions on the substrate can impair uniformity within the substrate surface. Forming a thick insulating layer can also cause stress to be applied to the entire substrate, resulting in problems such as substrate warping. Therefore, the following techniques have been proposed to thin the Au layer without forming a thick insulating layer.

Patent Document 1 discloses a method of forming a film by electroless plating, instead of forming an electrode film by sputtering and electrolytic plating. Here, a thin Au layer is formed on a nickel layer. By forming a thick nickel layer, the probe marks are covered.

In Patent Document 2, an opening is formed in an insulating layer that covers the wiring aluminum layer, leaving the surrounding aluminum layer as the electrode pad portion, and the aluminum layer exposed in the opening is removed, after which a barrier metal and a gold layer are formed. Before removing the aluminum layer exposed in the insulating layer, the aluminum layer is probed, and the probe marks are removed by removing the aluminum layer in the exposed portion, making it possible to form an electrode with a thin Au layer.

JP 2000-43271 A JP 2018-154090 A

Miniaturization of ejection requires a design with a low ink flow path and short ejection ports (i.e., a thin orifice plate). In Patent Document 1, the thickness of the Au layer can be made thin, keeping costs low, but the nickel layer is thick, so it may not be possible to meet the demand for miniaturization. In Patent Document 2, each layer can be made thin, so it can meet the demand for miniaturization, but it may be necessary to form a mask to remove the aluminum layer and form a step accordingly. In addition, the aluminum layer and Au layer come into contact on the side of the aluminum layer, and there is a concern that the contact resistance will increase as the pad area is reduced.

The present invention aims to provide a liquid ejection head with a reduced film thickness in the electrode pad area and a method for manufacturing the liquid ejection head, including electrical testing using probing.

One aspect of the present invention is a liquid ejection head comprising: a heating element that generates thermal energy for ejecting liquid;
an electrode pad portion for electrical connection to an external device, the electrode pad portion being electrically connected to the heat generating element;
an anti-cavitation layer formed to cover the heating element;
A liquid ejection head substrate comprising:
the electrode pad portion includes a layer containing iridium metal or an iridium alloy,
The present invention relates to a liquid ejection head substrate, wherein at least a portion of the cavitation-resistant layer is made of the same material as the layer containing iridium metal or iridium alloy and is provided in the same layer.

The present invention provides a liquid ejection head substrate with a reduced film thickness on the electrode pad section, as the electrode pad section is configured to be subjected to less physical damage and deformation caused by probing during electrical testing prior to mounting, eliminating the need to form a thick film to hide probe marks.

1 is a schematic perspective view of a liquid ejection head substrate according to an embodiment to which the present invention can be applied. 1 is a schematic cross-sectional view of a liquid ejection head substrate according to a first embodiment to which the present invention can be applied. 3A to 3C are cross-sectional flow diagrams illustrating a manufacturing process of a liquid ejection head substrate according to a first embodiment to which the present invention can be applied. 10 is a flowchart illustrating the timing of an electrical inspection in a manufacturing method for a liquid ejection head substrate according to an embodiment to which the present invention can be applied. 5 is a schematic cross-sectional view of a liquid ejection head substrate according to a second embodiment to which the present invention can be applied. FIG. FIG. 11 is a schematic cross-sectional view of a liquid ejection head substrate according to a third embodiment to which the present invention can be applied. 7A to 7C are cross-sectional flow diagrams illustrating a manufacturing process of the liquid ejection head substrate according to the embodiment shown in FIGS. 6A to 6C. FIG. 7 is a schematic cross-sectional view showing a modification of the embodiment shown in FIG. 6 . FIG. 13 is a schematic cross-sectional view of a liquid ejection head substrate according to a fourth embodiment to which the present invention can be applied. FIG. 1 is a schematic cross-sectional view illustrating a problem with a conventional aluminum pad.

1. Embodiments to which the present invention can be applied 1.1 Configuration of a liquid ejection head Hereinafter, examples of embodiments to which the present invention can be applied will be described with reference to the drawings. However, the following description does not limit the scope of the present invention.
Many recording devices are equipped with a liquid ejection head in which the liquid in the liquid chamber is heated by passing electricity through a recording element (heating resistor), which causes film boiling of the liquid to bubble in the liquid chamber, and the resulting bubble-emission energy ejects droplets from the ejection port. When recording is performed using such a recording device, physical effects such as impacts due to cavitation that occur when the liquid bubbles, contracts, and disappears in the area above the heating resistor may be applied to the area above the heating resistor. In order to protect the heating resistor from these physical or chemical effects on the heating resistor, 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 at a position in contact with the liquid.
In the present invention, attention has been focused on iridium or an iridium alloy formed as an anti-cavitation layer, and the application of this to electrode pads has been considered.

(Description of the Structure of the Substrate for Liquid Ejection Head)
1 is a perspective view showing a liquid ejection head substrate (hereinafter, simply referred to as an element substrate) 10 according to an embodiment to which the present invention can be applied. The element substrate 10 comprises a substrate 11 in which a liquid supply path and the like are formed, an ejection port forming member 12 on the front side of the substrate 11, and a cover plate 20 on the rear side of the substrate 11. Four ejection port arrays corresponding to each ink color are formed in the ejection port forming member 12 of the element substrate 10. Hereinafter, the direction (arrow A) 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".

As shown in FIG. 1, a recording element 14 that generates energy for ejecting liquid is disposed in a liquid flow path that communicates with each ejection port 13 at a position corresponding to the ejection port 13. In this example, the recording element 14 is a heat generating resistor element that uses thermal energy to foam the liquid, and the ejection port forming member 12 defines a liquid flow path (called a pressure chamber) 23 that communicates with the ejection port having the recording element 14 inside. The recording element 14 is electrically connected to an electrode pad portion 16 disposed at the end of the substrate 11 by electrical wiring (not shown) provided on the element substrate 10, and generates heat based on a pulse signal input via an external wiring substrate (not shown) to boil the liquid. The liquid is ejected from the ejection port 13 by the force of foaming caused by this boiling. In this example, a liquid supply path 18 and a liquid recovery path 19 are provided as flow paths extending in the ejection port row direction provided on the element substrate 10, and communicate with the ejection port 13 via a supply port 17a and a recovery port 17b, respectively. The cover plate 20 has an inlet 21 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 with the outside in the direction of the arrow B through the liquid supply path 18 and the liquid recovery path 19, the viscosity of the liquid near the ejection port 13 is suppressed, and the ejection performance of the liquid is stabilized. In this embodiment, the heating element is covered with a cavitation-resistant layer made of tantalum (Ta), iridium (Ir) or a laminated film thereof facing the pressure chamber. In this embodiment, the portion shown as the recording element 14 in FIG. 1 is provided with a cavitation-resistant layer and 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 an iridium alloy containing a small amount of elements such as osmium (Os) or platinum (Pt) may be used. Each recording element 14 is connected to an electrode pad portion 16 through wiring provided inside the substrate 11, and a voltage is applied to the recording element 14 from the outside through this electrode pad portion 16.

Fig. 2(a) is a schematic cross-sectional view of a liquid ejection head substrate according to a first embodiment to which the present invention can be applied. It corresponds to a cross section of the element substrate 10 shown in Fig. 1 taken along the line X-X'. The figure shows the vicinity of the ejection 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 a recording element arranged directly below the ejection port 13 (so as to face the ejection port 13). The lower layer portion of the substrate 11 and the cover plate 20 arranged below these are omitted.
As shown in FIG. 2A, a heating element 31 made of a cermet material such as TaSiN or WSiN is formed on a heat storage layer 32 made of silicon oxide, and is electrically connected to an electrode plug 33 made of tungsten (W). Furthermore, an insulating protective layer 34 made of SiN, SiC, SiCN, 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 having a noble metal material such as Ir as the outermost layer is formed on the insulating protective layer 34 above the heating element 31. That is, the heating element 31 is covered by the cavitation-resistant layer 35 via the insulating protective layer 34. Here, as shown on the left side of FIG. 2A, a wiring lead-out layer 36 is disposed near the electrode pad portion 16, which is electrically connected to the heating element 31 and is the lower layer of the electrode pad portion 16 and is formed of, for example, aluminum or an alloy of aluminum and copper. The wiring lead-out layer 36 is electrically connected to the upper layer 38 of the electrode pad section 16, which is formed in the same layer and of the same material as the cavitation-resistant layer 35 made of Ir, through a through hole 37 formed in the insulating protective layer 34. In this embodiment, as described above, the upper layer 38 of the electrode pad section 16 and the cavitation-resistant layer 35 on the heating element 31 are formed simultaneously (in the same manufacturing process). This makes it possible to reduce the manufacturing load. However, as long as the upper layer 38 of the electrode pad section is formed of iridium or an iridium alloy, they may be formed in separate processes. The wiring lead-out layer 36 constituting the lower layer of the electrode pad section 16 may be an extension of a part of a wiring layer (not shown) or may be formed separately.
With regard to the layered structure of the electrode pad portion 16, the side electrically connected to the outside is referred to as the top or front, and the opposite side is referred to as the bottom, and these tops and bottoms do not change depending on the position of the substrate 10 for the liquid ejection head.

The material forming the upper layer 38 of the electrode pad portion 16 is Ir (containing Ir), so it is resistant (chemical resistant) to acids, alkalis, or organic stripping liquids used in the subsequent manufacturing process of the ejection port forming material, and is not easily dissolved. Also, from the perspective of cost, after the formation of the upper layer 38 of the electrode pad portion 16 and before performing the wire bonding shown in FIG. 2(b), an electrical inspection of the element substrate is performed to prevent the mounting of defective chips. The electrode pad portion 16 is electrically connected to an external substrate by wire bonding, lead bonding, or the like.

Figure 4 is a flow chart explaining the timing of electrical testing. (a) shows a form in which electrical testing is performed after the electrode pad portion 16 is formed and before the formation of the ejection port forming member 12, etc., and (b) shows a form in which electrical testing is performed after the ejection port forming member 12, etc. are formed and before wire bonding is performed.

In the case of conventional aluminum pads, as shown in FIG. 10, probing during electrical testing would leave large unevenness, i.e., probe marks 105. On the other hand, in the pad configuration of this embodiment, the upper layer 38 on the insulating protective layer is made of Ir, which has a higher hardness than aluminum, so that even when probing during electrical testing, no probe marks are left and flatness is maintained.

FIG. 2(b) shows a schematic cross-sectional view of the vicinity of the pad portion 16 after wire bonding. As shown in FIG. 2(b), the flatness of the surface of the pad portion 16 is maintained, so that the deterioration of the connectivity and electrical reliability in wire bonding can be suppressed without the need for a process of burying or removing the probe marks as in the conventional electrode pad configuration. 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 also possible to bond on the probing region 104. Therefore, there is no need to separate the probing region 104 and the bonding region as in the conventional AL pad, and it is also possible to reduce the area of the electrode pad portion 16.
Furthermore, since the upper layer 38 of the 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 top surface of the upper layer 38 during the manufacturing process, thereby reducing the load on the manufacturing process.

The configuration of the electrode pad section 16 is not limited to the configuration having the upper layer 38 of a single layer structure shown in this embodiment, but may be a configuration having an upper 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 a layer containing iridium or an iridium alloy. In addition, probing is preferably performed in an area (near the center of the electrode pad section 16) where there is no lower wiring layer such as the wiring extraction layer 36. However, depending on the thickness of the insulating protection layer 34, it may be possible to perform probing without affecting the lower layer, so the wiring layer 36, which is the lower layer of the electrode pad section, may be arranged below the probing area.

Figure 5 shows a cross-sectional view of a liquid ejection head substrate according to a second embodiment, in which the upper layer 38 of the electrode pad portion 16 and the cavitation-resistant layer 35 are made of a two-layer laminate structure of a first layer of Ta film (35a and 38a) and a second layer of Ir film (35b and 38b). Figure 5 corresponds to Figure 2(a), and the ejection port forming member 12 is omitted. By arranging the Ta film 35a in this manner, it is possible to improve the adhesion between the insulating protection layer 34 and the cavitation-resistant layer 35.

Figure 6 is a cross-sectional view of a liquid ejection head substrate according to a third embodiment in which the upper layer 38 of the electrode pad portion 16 and the cavitation-resistant layer 35 are made of a three-layer laminated structure, and corresponds to Figure 2 (a). This laminated structure is made of a first layer of Ta film (35a and 38a), a second layer of Ir film (35b and 38b), and a third layer of Ta film (35c and 38c). Furthermore, an adhesion improving layer 39 is arranged to cover this laminated structure and improve the adhesion between the ejection port forming member and the substrate. On the electrode pad portion 16 and the heating element 31, the adhesion improving 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). At this time, from the viewpoint of manufacturing load, it is preferable to remove the adhesion improving 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 laminate structure, the layers used as the cavitation-resistant layer 35 that covers the electrode pad portion 16 and the heating element 31 are the first and second layers. 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 that suppresses probe marks can be obtained.

Furthermore, by disposing the upper layer Ta film 35c in any area 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 freedom of circuit layout. However, in this case, in order to reduce the amount of warping of the wafer, it is preferable that the thickness of the upper 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 upper layer Ta film 35c is 50 nm or more and 200 nm or less.

The adhesion improving layer 39 is a layer that improves adhesion with the discharge port forming member 12 more than the insulating protective layer 34, and is not particularly limited as long as it is made of an insulating material. For example, inorganic materials such as SiC and SiCN are preferably used.

As shown in FIG. 6, if the third layer Ta film 38c located above the through hole 37 is left, the step caused by the through hole 37 can be covered and flatness can be ensured.
In the electrode pad portion 16, the third layer of Ta film 38c may be further removed to expand the pad area as shown in Fig. 8(a). Specifically, in Fig. 8(a), the Ta film 38c above the wiring extraction layer 36 and the through hole 37 is removed from the configuration shown in Fig. 6.
6, the electrode pad portion 16 and the cavitation-resistant 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 the same. For example, in FIG. 8(b) showing a modification of this embodiment, the electrode pad portion 16 is composed of a first layer of Ta film 38a and a second layer of Ir film 38b, and 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 modification, the outermost layer of the cavitation-resistant layer 35 is a Ta film from the viewpoint of protecting the heating element 31, while the outermost layer of the electrode pad portion 16 is an Ir film to suppress probe marks during electrical testing.

9 shows a schematic cross-sectional view of a liquid ejection head substrate according to a fourth embodiment to which the present invention can be applied. In FIG. 9, a configuration in which a connection member 40 containing gold (Au) is arranged on the electrode pad portion 16 is shown in comparison with the configuration shown in FIG. 6. By arranging the connection member 40 containing Au, the connection reliability with the wire member mainly made of gold wire is further improved. The connection member can be formed in the same manner as a conventional gold bump, but since it is not necessary to make it a thick film, it can be easily formed as a thin film by film formation in a vacuum device such as a sputtering method. In addition, a barrier metal layer such as TiW may be formed between the Ir film and the gold layer. This suppresses the diffusion of gold into the lower layer.
In addition, since the Ir film 38b constituting the electrode pad portion 16 can suppress the diffusion of gold of the connection member 40 to the lower layer, it is not necessary to separately provide a barrier metal layer such as TiW. In other words, it is sufficient that the lower surface of the connection member 40 is provided so as to be in contact with the Ir film. Such a configuration is preferable in that it is possible to suppress manufacturing costs. In addition, when a barrier metal layer such as TiW is used, depending on the configuration, the barrier metal layer may be dissolved by a solvent used in the manufacturing process, but the Ir film 38b is resistant to such a solvent and is preferable in that there is no concern of dissolution.

As described above, the purpose of the present invention is to prevent the electrode pad portion 16 from becoming thick, and a thickness of 500 nm or less is sufficient for the connection member 40. There is no particular lower limit, 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 connection member 40 lower than the formation surface (discharge port surface) of the discharge port 13 in the discharge port forming member 12. This makes it possible to shorten the distance between the formation surface of the discharge port 12 and a recording medium such as paper without being hindered by the thickness of the electrode pad portion 16 or the sealant that covers it, thereby improving image quality.

Specific examples of the configuration of the cavitation-resistant layer 35 and the electrode pad portion 16 are described below with reference to the drawings.

Example 1
In this embodiment, a configuration and a manufacturing method in which an Ir film is used for the cavitation-resistant layer 35 as in the above embodiment will be described with reference to FIG.
3A to 3C are cross-sectional views illustrating the manufacturing process of this embodiment.
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 for driving the driving element (not shown) were formed, and 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 (FIG. 3(a)). Furthermore, a cermet material made of TaSiN was formed to a thickness of 15 nm, a wiring electrode layer made of an alloy of aluminum and copper was formed thereon, and a wiring take-out layer 36 and a heating element 31 were formed by photolithography and dry etching (FIG. 3(b)). 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 square. For example, after dry etching the lamination of the wiring electrode layer and the cermet material, the wiring electrode layer on the cermet material was removed, and the cermet material was further dry etched as necessary to form the heating element 31. Note that the lower layer driving element (not shown) is configured to be connected to the heating element 31 and the wiring electrode layer to be formed in a later process via the electrode plug 33, but the electrical connection to the heating element 31 can also be made by supplying power from the wiring electrode layer in addition to using the electrode plug.

Next, an insulating protective layer 34 made of SiN was formed to a thickness of 200 nm to cover the heating element 31 and the wiring lead-out layer 36 (FIG. 3(c)). Here, the insulating protective layer 34 was set to a thickness of 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 insulating protective layer 34 by photolithography, and a through hole 37 was formed in the insulating protective layer 34 to expose a part of the wiring lead-out layer 36.

Next, a layer of iridium (Ir) was formed to a thickness of 100 nm on the entire surface, and this Ir layer was etched to form the upper layer 38 of the electrode pad section 16 and the cavitation-resistant layer 35 (Figure 3 (d)). 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 account the viewpoint of processability, it is more preferable that it is 20 nm or more and 300 nm or less. In addition, in the electrode pad section 16, the upper layer 38 made of Ir formed in the same layer as the cavitation-resistant layer 35 is connected to the wiring extraction layer 36 via a through hole 37, and the outermost layer of the electrode pad section 16 is configured so that Ir is exposed.

Next, after forming the liquid supply path and nozzle material on the substrate and forming a cover plate on the back side of the substrate (not shown), an electrical test was performed. A rhenium-tungsten probe with a tip diameter of φ20 μm, which is a common probe, was used for the electrical test. The overdrive amount during probing was set to 60 μm. The surface of the electrode pad portion 16 after the electrical test was observed with a laser microscope, but 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 effects due to probing were observed. In addition, Ir is a precious metal film that does not form a natural oxide film in the air at room temperature, so probing could be performed stably and the test was performed without any problems.

Next, wire bonding (Fig. 2(b)) was performed on the Ir of the electrode pad portion 16 to connect electrically to an external substrate with a wire member 41 made of gold. There are ball bonding and wedge bonding methods for wire bonding, but in this example, the ball bonding method was used. The wire member 41 used had a wire diameter of 25 μm.

In this embodiment, as described above, there is no physical damage or deformation to 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. In addition, since it is not necessary to form a thick film to hide the probe marks, it is possible to provide a liquid ejection head that can handle miniaturized ejection.

Example 2
In this embodiment, the anti-cavitation film 35 in Example 1 was changed to a two-layer structure consisting of an upper Ir layer 35b and a lower Ta layer 35a, as shown in Fig. 5. The other steps were the same as those in Example 1, and the liquid ejection head in this embodiment was obtained. In this case, the Ir layer and the Ta layer were formed to have thicknesses of 70 nm and 30 nm, respectively.
With this configuration, the adhesion between the lower insulating protection layer 34 and the anti-cavitation layer 35 is further improved, providing a liquid ejection head with higher reliability.
In the electrode pad portion 16, as shown in FIG. 5, the upper layer 38 has a two-layer structure including a first layer 38a formed in the same layer as the Ta layer 35a and a second layer 38b formed in the same layer as the Ir layer 35b.

Example 3
7A to 7C are cross-sectional views for explaining the manufacturing process of this embodiment. Differences from the first embodiment will be explained below.
A substrate similar to that in 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. 3(c)).
7(a), in this embodiment, the cavitation-resistant layer was formed from three layers, from the top, the third layer Ta film 35c, the second layer Ir film 35b, and the first layer Ta film 35a. The thickness of the Ta film 35c was 70 nm, the thickness of the Ir film 35b was 70 nm, and the thickness of the Ta film 35a was 30 nm. The electrode pad portion 16 also had an upper layer 38, which was a first layer 38a in the same layer as the Ta film 35a, a second layer 38b in the same layer as the Ir film 35b, and a third layer 38c in the same layer as the Ta film 35c.
On top of that, a layer 39 for improving adhesion between the ejection port forming member 12 and the substrate was formed of SiCN to a thickness of 200 nm so as to cover the entire substrate (FIG. 7B). By providing such an adhesion improving layer 39, the reliability of the liquid ejection head is further improved, particularly with respect to the liquid contact portion.
Thereafter, the adhesion improving layer 39 on the heating element 31 and the electrode pad portion 16, and the upper layer Ta film 35c and the third layer 38c were removed by dry etching to expose the Ir film 35b and the second layer 38b (FIG. 7(c)). In this case, by performing chemical etching using chlorine gas or fluorine gas during etching, the Ir surface can be exposed without reducing the thickness of the Ir film.

In this embodiment, an electrical inspection of the board was performed immediately after the pad portion was opened, i.e., after Fig. 7(c) As described in the first embodiment, in this embodiment, too, it was confirmed that the exposed surface of the electrode pad portion 16 during probing was the second layer 38b made of Ir, and that the second layer 38b was not physically damaged or deformed.
As in Example 1, in the subsequent steps, liquid supply paths and ejection port forming members were formed in the substrate, and a cover plate was formed on the rear surface side of the substrate.
Thereafter, the electrode pad portion 16 was bonded to a gold wire in the same manner as in Example 1. In this example, similar to Examples 1 and 2, the electrical connection reliability of the electrode pad portion 16 is improved compared to the case where damage is caused by probing.

Example 4
FIG. 9 is a schematic cross-sectional view of this embodiment.
In this embodiment, electrical testing was performed after opening the electrode pad portion 16 (FIG. 7(c)) in the same manner as in embodiment 3. Furthermore, in order to improve the connection reliability during wire bonding of the electrode pad portion 16, a connection member made of Au was formed on the electrode pad portion 16 by sputtering before forming the liquid supply path and the discharge port forming member 12. The thickness of the connection member 40 was set to 500 nm. In this configuration, a barrier metal layer made of TiW (not shown) may be inserted between the connection member and Ir.
Thereafter, in the same manner as in Example 3, a liquid supply path and a discharge port forming member 12 were formed, and a wire made of gold was connected to the electrode pad portion 16 having gold exposed on the outermost surface layer.
In this embodiment, the outermost layer of the electrode pad portion and the bonding material are made of the same material, gold, so that the configuration has higher electrical connection reliability than the electrode pad portion of the other embodiments, which has an Ir outermost layer.

10 Substrate for liquid ejection head 11 Substrate 12 Ejection port forming member 13 Ejection port 14 Recording element 16 Electrode pad portion 23 Pressure chamber 31 Heat generating element 32 Heat storage layer 33 Electrode plug 34 Insulating protective layer 35 Cavitation resistant layer 36 Lower layer of electrode pad portion (wiring lead layer)
37: through hole 38: upper layer of electrode pad portion 39: adhesion improving layer 40: connecting member 41: wire member

Claims (18)

a heating element that generates thermal energy for discharging the liquid;
an electrode pad portion for electrical connection to an external device, the electrode pad portion being electrically connected to the heat generating element;
an anti-cavitation layer formed to cover the heating element;
A liquid ejection head substrate comprising:
the electrode pad portion includes a layer containing iridium metal or an iridium alloy,
A liquid ejection head substrate, wherein at least a portion of the cavitation-resistant layer is made of the same material as the layer containing iridium metal or iridium alloy and is provided in the same layer. The liquid ejection head substrate according to claim 1, wherein the outermost layer of the electrode pad portion is a layer containing the iridium metal or iridium alloy. The liquid ejection head substrate according to claim 1, wherein the electrode pad portion has a connection member containing gold in the outermost layer. The liquid ejection head substrate according to claim 3, wherein the connection member is formed of a gold-containing layer having a thickness of 500 nm or less. The liquid ejection head substrate according to claim 3 or 4, wherein the layer containing the iridium metal or iridium alloy is in contact with the lower surface of the connection member. a discharge port forming member having a discharge port surface on which a liquid discharge port for discharging a liquid is provided;
The liquid ejection head substrate according to claim 3 , wherein an upper surface of the connection member is located lower than the ejection port surface. The liquid ejection head substrate according to any one of claims 1 to 6, wherein the layer containing the iridium metal or iridium alloy in the electrode pad portion has a thickness of 20 nm to 300 nm. the electrode pad portion includes a wiring lead-out layer formed under the layer containing iridium metal or iridium alloy and for electrically connecting the layer containing iridium metal or iridium alloy and the heat generating element,
8. A substrate for a liquid ejection head as described in any one of claims 1 to 7, wherein the layer containing iridium metal or iridium alloy and the wiring lead-out layer are connected via a through hole formed in an insulating protective layer between the layer containing iridium metal or iridium alloy and the wiring lead-out layer. The liquid ejection head substrate according to claim 8, wherein the wiring lead-out layer is a layer containing aluminum. The liquid ejection head substrate according to claim 8 or 9, in which no probe marks are formed on the wiring extraction layer. The liquid ejection head substrate according to any one of claims 8 to 10, further comprising an upper layer covering the layer containing iridium metal or iridium alloy at a position of the layer containing iridium metal or iridium alloy corresponding to the through hole. forming an element that generates energy for ejecting liquid on a substrate;
forming an electrode pad portion for electrical connection to an external device, the electrode pad portion including a layer containing iridium metal or an iridium alloy, the electrode pad portion being electrically connected to the element;
having
A method for manufacturing a substrate for a liquid ejection head, comprising the steps of: probing the layer containing iridium metal or iridium alloy to carry out an electrical test prior to electrical connection of the electrode pad portion with an external device; the element is a heating element, and a step of forming an anti-cavitation layer to cover the heating element is included;
The method for manufacturing a substrate for a liquid ejection head according to claim 12, wherein the layer containing the iridium metal or the iridium alloy of the electrode pad portion is formed in the same layer and using the same material as at least a part of the cavitation-resistant layer. The method for manufacturing a substrate for a liquid ejection head according to claim 12 or 13, comprising a step of forming an ejection port forming member having a liquid ejection port for ejecting liquid. The method for manufacturing a liquid ejection head substrate according to claim 14, wherein the electrical inspection is performed before the step of forming the ejection port forming member. The method for manufacturing a liquid ejection head substrate according to claim 14, wherein the electrical inspection is performed after the step of forming the ejection port forming member. The method for manufacturing a substrate for a liquid ejection head according to any one of claims 12 to 16, further comprising the step of forming a connection member containing gold on the layer containing iridium metal or iridium alloy of the electrode pad portion after the electrical inspection. The method for manufacturing a substrate for a liquid ejection head according to any one of claims 12 to 17, wherein the step of forming the electrode pad portion includes a step of forming a wiring lead-out layer for electrically connecting the element and the layer containing the iridium metal or the iridium alloy, and a step of forming the layer containing the iridium metal or the iridium alloy after the step of forming the wiring lead-out layer.

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