Method for producing liquid-ejection head substrate

A method for producing a liquid-ejection head substrate includes forming a protective film covering the surface of a portion of a cavitation resistant film provided at a position where the heating resistor is covered with a metallic material containing at least one of titanium, tungsten, and titanium tungsten and etching the substrate after forming the protective film.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a method for producing a liquid-ejection head substrate for use in a liquid ejection head that ejects liquid.

Description of the Related Art

The microfabricated structure of a semiconductor substrate is widely used in functional devices of a micro electromechanical system (MEMS) and electromechanical fields. One example is a liquid ejection head that performs printing by ejecting liquid droplets onto print media. Thermal liquid ejection heads perform printing by causing film boiling of liquid, such as ink, using thermal energy generated by supplying power to a heating resistor and by ejecting the liquid through ejection ports using pressure caused by the film-boiling.

These liquid ejection heads include a liquid-ejection head substrate, which is a semiconductor substrate including heating resistors, and a channel member in which ejection ports and channels are formed. The heating resistors are driven by an electrical signal and a voltage supplied from a liquid ejection apparatus main body including the liquid ejection head via electrode pads provided on the liquid-ejection head substrate.

Each heating resistor is coated with an insulating protection layer having electrical insulating properties. A thermic effect unit, which is an ink contact portion above the heating resistor, is exposed to high temperature by the heat generated from the heating resistor and is subjected to multiple actions including a physical action, such as an impact due to cavitation caused by foaming and shrinkage of the ink and a chemical action of the ink. To protect the heating resistor from these influences, a cavitation resistant film is provided on a portion of the insulating protection layer covering the heating resistor, and a portion of the cavitation resistant film above the heating resistor functions as a thermic effect unit. Thus, the liquid-ejection head substrate extends the life of the head and improves the reliability by providing the cavitation resistant film. The cavitation resistant film is generally made of a metallic material, such as tantalum or niobium. Japanese Patent Laid-Open No. 2012-101557 discloses a configuration for extending the life of the head by uniformly removing a burnt deposit on the surface of the thermic effect unit, in which the cavitation resistant film is made of a metallic material, such as iridium or ruthenium.

The electrode pads provided on the liquid-ejection head substrate have a structure in which multiple kinds of metal film, such as an electrode layer provided on the wiring lines and a diffusion prevention layer for preventing the metal of the electrode layer from diffusing to the substrate, are laminated. In forming the electrode pads, an oxide layer and organic pollutants formed on the surface of the wiring lines are removed to provide sufficient electrical conductivity. Next, the formed metal films are patterned to a desired shape to form the electrode pads. The metal films are generally continuously formed by sputter etching (reverse sputtering) in vacuum using a sputter system to remove the oxide film and organic pollutants.

In forming the channel member on the liquid-ejection head substrate, the altered substances, such as an oxide film and organic pollutants, on the surface of the substrate need to be removed to provide sufficient adhesion between the substate and the channel member. These oxide film and organic pollutants are removed by a dry etching or wet etching method.

Since the above etching method is performed over the entire substrate, the cavitation resistant film serving as a thermic effect unit is also etched to decrease in thickness. The decrease in the thickness of the cavitation resistant film can decrease the life of the head.

In particular, if the cavitation resistant film is made of iridium, the decrease of iridium due to sputter etching is more than five times that of tantalum or niobium. This may increase variations in the thickness of the cavitation resistant film in the wafer surface or the chip. For this reason, particular attention should be paid to the thickness of the cavitation resistant film.

If the thickness of the cavitation resistant film is increased in consideration of a decrease in the thickness of the cavitation resistant film, consumption of raw materials for the cavitation resistant film is increased, leading to increased production cost.

SUMMARY OF THE INVENTION

Accordingly, an embodiment of the present disclosure reduces or eliminates a decrease in the thickness of the cavitation resistant film of a liquid-ejection head substrate.

A method for producing a liquid-ejection head substrate according to an aspect of the present disclosure includes preparing a substrate including a heating resistor and a cavitation resistant film including a portion provided at a position where the heating resistor is covered, a surface of the portion being exposed to an outside, forming a protective film covering the surface of the portion of the cavitation resistant film with a metallic material containing at least one of titanium, tungsten, and titanium tungsten, etching the substrate after forming the protective film, and removing the protective film after etching the etching.

DESCRIPTION OF THE EMBODIMENTS

Methods for producing liquid ejection head substrates according to embodiments of the present disclosure will be described with reference to the drawings. Although the embodiments illustrate specific examples of the present disclosure, these are technically preferable examples and do not limit the scope of the present disclosure.

First Embodiment

FIG.1Ais a schematic plan view of a liquid-ejection head substrate1according to an embodiment to which the present disclosure can be applied.FIG.1Bis a schematic plan view of a liquid ejection head100to which this embodiment can be applied. The liquid-ejection head substrate1includes a plurality of electrode pads2and a plurality of thermic effect units3. The liquid ejection head100includes the liquid-ejection head substrate1and a channel member15which is provided on the surface of the liquid-ejection head substrate1adjacent to the thermic effect units3and in which ejection ports16and channels are to be formed.

FIGS.2A to2Eare schematic diagrams illustrating a method for producing the liquid-ejection head substrate1of this embodiment.FIGS.2A to2Eare schematic diagrams illustrating, in particular, how the electrode pads2and the thermic effect units3are formed in a II-II cross-section ofFIG.1A. In this specification, the liquid ejecting direction is defined as upward, and the opposite direction is defined as downward, but this is defined only for convenience.

As shown inFIG.2A, first, a substrate serving as a first metal film constituting part of the electrode pads2, in which the wiring lines4and the thermic effect units3are provided, is prepared. Referring toFIG.2A, the cross-sectional configuration of the part constituting the electrode pads2will be described. An insulating protection layer5with electrical insulating properties is provided on the wiring lines4provided on an interlaminar film8on a base substrate (not shown). The insulating protection layer5has openings14. The wiring lines4are generally made of metal with low specific resistivity, such as aluminum or copper. The insulating protection layer5is made of a silicon compound, such as silicon carbonitride film or silicon acid carbonitride film. Part of the wiring lines4is exposed from the openings14of the insulating protection layer5, and the surface of the exposed part of the wiring lines4made of the above metal is covered with an oxide film6. The oxide film6is removed by a later process.

Next, the cross-sectional configuration of the thermic effect units3will be described. The interlaminar film8with electrical insulating properties is provided on heating resistors7on the base substrate. Cavitation resistant films9are provided on the interlaminar film8. The cavitation resistant films9protects the heating resistors7from the influence of a physical action, such as an impact due to cavitation caused by foaming and shrinking of liquid, such as ink, and chemical actions due to ink. The cavitation resistant films9are made of tantalum, niobium, iridium, or ruthenium which is resistant to a mechanical impact. Each cavitation resistant film9may be a lamination of these metallic materials. In this embodiment, the insulating protection layer5is provided also on the cavitation resistant film9. To form the thermic effect unit3, the insulating protection layer5has openings13from which the surface of the cavitation resistant film9is exposed to the outside.

Most of the surface of the liquid-ejection head substrate1, other than the electrode pads2and the thermic effect units3, is covered with the insulating protection layer5, and at last part of the surface is stained with an oxide film and altered substances17, such as organic pollutants. The presence of the altered substances17causes the channel member15, which is formed on the surface of the liquid-ejection head substrate1later, to peel off. For this reason, the altered substances17are removed in a later process.

Referring next toFIG.2B, a protective film10is formed so as to cover the top of the cavitation resistant film9of each thermic effect unit3.FIG.3is a schematic plan view of the substrate on which the protective film10is formed, illustrating areas with the protective film10, an area without the protective film10, that is, an area in which the oxide film6and the altered substances17are to be removed. The protective film10is disposed on at least areas that cover the surfaces of the cavitation resistant films9serving as the thermic effect units3.

The protective film10has a role in preventing a decrease in the thickness of the cavitation resistant film9due to sputter etching (reverse sputtering) described later. If the thickness of the protective film10is increased, film that is scraped and scattered by sputter etching can adhere to the side wall of the protective film10to form a fence. The fence adhering to the side wall of the protective film10can remain on the substrate even after the protective film10is removed and is separated in a later process into particles. For this reason, the thickness of the protective film10is preferably 60 nm or less. The lower limit of the thickness of the protective film10is preferably 20 nm in consideration of the performance of coating the cavitation resistant film9and the decrease in the thickness due to the sputter etching.

A material for the protective film10may be a metallic material, in particular, a metallic material containing at least, titanium, tungsten, and titanium tungsten in the following point of view. In other words, these metallic materials are highly resistant to sputter etching and can therefore sufficiently reduce a decrease in the thickness of the cavitation resistant film9. These metallic materials have a high level of adhesion to the cavitation resistant film9made of tantalum, niobium, iridium, or ruthenium and the insulating protection layer5made of a silicon compound. This allows for reducing or eliminating peeling of the protective film10after the sputter etching process. Other materials for the protective film10include an organic material and an inorganic material. However, the organic material has lower sputter etching resistance than that of the metallic materials described above and may not be able to sufficiently reduce the decrease in the thickness of the cavitation resistant film9compared with the above metallic materials. The inorganic material has lower adhesion to the cavitation resistant film9than that of the above metallic materials and may cause peeling of the inorganic material from the protective film10after the sputter etching process. Accordingly, the metallic materials may be used for the protective film10.

Referring next toFIG.2C, the substrate is set at a deposition system and is subjected to sputter etching (reverse sputtering) with inert-gas plasma, such as argon, to remove the oxide films6on the surfaces of the wiring lines4. The removal of the oxide films6provides sufficient electrical conductivity to the electrode pads2.

The reverse sputtering process removes the altered substances17(altered layers and organic pollutants) on the surface of the insulating protection layer5. This exposes a clear surface of the substrate to provide high adhesion to the channel member provided in a later process.

The protective film10formed on the top of the cavitation resistant film9prevents a decrease in the thickness of the cavitation resistant film9due to the reverse sputtering process. This can extend the life of the liquid ejection head100.

Referring next toFIG.2D, a diffusion prevention layer11, which is an intermediate metallic film, and an electrode layer12, which is a second metallic film, are formed on the entire surface of the substrate with the deposition system next to the reverse sputtering process. The diffusion prevention layer11is made of a metallic material with high adhesion to the wiring line4and the electrode layer12, with stability to temperature to cause no diffusion, and with low specific resistivity or a compound thereof. In this embodiment, examples of the metallic material include titanium tungsten and tungsten. The electrode layer12is made of a metallic material with low specific resistivity and high corrosion resistance. In this embodiment, the electrode layer12is made of gold.

Referring next toFIG.2E, the electrode layer12and the diffusion prevention layer11are patterned using a photolithography method to form the electrode pads2. In this embodiment, each electrode pad2is a lamination of the wiring line4, the diffusion prevention layer11, and the electrode layer12.

Unnecessary part of the electrode layer12and the diffusion prevention layer11are etched by wet etching.

Forming the diffusion prevention layer11and the protective film10with the same material allows removing the diffusion prevention layer11and the protective film10using the same etching process, which may reduce the processing load. The electrode layer12made of gold can be etched using an etchant containing iodine and potassium iodide. The diffusion prevention layer11and the protective film10made of titanium tungsten or the like can be etched using a 30% hydrogen peroxide solution. Employing wet etching with a hydrogen peroxide solution for etching the protective film10provides sufficient options for the cavitation resistant film9, allowing for preventing a decrease in the thickness of the cavitation resistant film9in etching the protective film10.

FIG.4is a schematic plan view of the protective films10formed in the thermic effect units3.FIGS.5A and5Bare detailed drawings of the thermic effect unit3before and after the reverse sputtering process, respectively.FIG.5Ais a cross-sectional view taken along line VA-VA ofFIG.4, illustrating the state of the substrate before the reverse sputtering process.

FIG.5Bis a diagram illustrating a state in which the protective film10is removed after the reverse sputtering process.

The liquid-ejection head substrate1includes the plurality of heating resistors7. In this embodiment, the cavitation resistant films9are provided so as to cover the individual heating resistors7, as shown inFIG.4. The insulating protection layer5covering the cavitation resistant films9has openings13in correspondence with the cavitation resistant films9in such a manner that the outer rims of the openings13are positioned inside the outer rims of the cavitation resistant films9. The liquid-ejection head substrate1are provided with the plurality of thermic effect units3in this manner. The protective films10may be disposed in independent patterns so as to cover the individual thermic effect units3. This is because providing the protective films10only at necessary portions allows for reliably removing altered layers in the insulating protection layer5and organic pollutants due to the reverse sputtering process.

As shown inFIG.5B, the insulating protection layer5in the area where the protective film10is not disposed is reduced in thickness by more than 10 nm because of the reverse sputtering process, and the cavitation resistant film9and the insulating protection layer5in the area where the protective film10is disposed is not reduced in the thickness. This causes a level difference of more than 10 nm between a surface5aof the insulating protection layer5where the protective film10is disposed and a surface5bof the insulating protection layer5where the protective film10is not disposed.FIG.5Billustrates the decreased portions of the insulating protection layer5with broken lines. If the protective films10are thin and the level difference due to the decrease in the thickness of the insulating protection layer5is minute, generation of fences at the portions where the protective films10were present before being removed can be prevented.

Second Embodiment

FIGS.6A to6Eare schematic diagrams illustrating a method for producing a liquid-ejection head substrate1of this embodiment.FIGS.6A to6Eare schematic diagrams illustrating, in particular, how electrode pads2and thermic effect units3are formed in a VI-VI cross-section ofFIG.1A. The configurations and processes similar to the above are sometimes omitted.

As shown inFIG.6A, first, a substrate serving as a first metal film constituting part of the electrode pads2, in which wiring lines4and thermic effect units3are provided, is prepared. Referring toFIG.6A, the cross-sectional configuration of the part constituting the electrode pads2will be described. An insulating protection layer5with electrical insulating properties is provided on the wiring lines4provided on an interlaminar film8on a base substrate (not shown). The insulating protection layer5has openings14. The wiring lines4are made of noble metal such as iridium. Since the wiring lines4are made of noble metal, the oxide film as in the first embodiment is not formed on the surface of the wiring lines4of the insulating protection layer5exposed from the opening14.

The configuration of the thermic effect units3is the same as that of the first embodiment. Forming the cavitation resistant films9and the wiring lines4with the same material in the same process will reduce the production load.

Referring next toFIG.6B, a protective film10is formed so as to cover the top of the cavitation resistant film9of each thermic effect unit3. The protective film10is also formed so as to cover the wiring line4exposed from the opening14of the insulating protection layer5. The protective film10that covers the cavitation resistant film9is also referred to as a first protective film, and the protective film10that covers the wiring line4is also referred to as a second protective film. The plurality of protective films10(first protective films) are provided in independent patterns so as to cover the individual thermic effect units3, as in the first embodiment. The liquid-ejection head substrate1is provided with multiple electrode pads2, as shown inFIGS.1A and1B. Correspondingly, the insulating protection layer5is provided with a plurality of openings14. The protective films10(second protective films) are provided in independent patterns so as to cover the individual surfaces of the wiring lines4exposed from the openings14.

Not removing the protective film10provided at the portion of each electrode pad2in a later process allows the protective film10to be used as an adhesion-level enhancing film between the wiring line4and the insulating protection layer5and an electrode layer12described later. This allows for omitting the process of forming the diffusion prevention layer11on the electrode pad2, as in the first embodiment. The protective films10may be made of the metallic material, such as titanium, tungsten, or titanium tungsten, described above, because of the resistance to sputter etching and the high adhesion to the wiring lines4, the insulating protection layer5, and the electrode layer12.

Referring next toFIG.6C, the substrate is set in a deposition system and is subjected to a sputter etching (reverse sputtering) process to remove the altered substances17of the insulating protection layer5. This exposes a clear surface of the substrate to provide high adhesion to the channel member. Since the cavitation resistant film9and the wiring line4are covered with the protective film10, a decrease in the thickness due to the reverse sputtering process can be prevented. This can extend the life of the liquid ejection head100.

Referring next toFIG.6D, the electrode layer12, which is the second metallic film, is formed on the entire surface of the substrate with the deposition system next to the reverse sputtering process. Since the protective film10has high adhesion to the wiring line4and the electrode layer12, as described above, the protective film10functions as an adhesion-level enhancing film between the wiring line4and part of the insulating protection layer5and the electrode layer12and has no problem in electrical conduction. The electrode layer12is made of gold, which has low specific resistivity and high corrosion resistance.

Referring next toFIG.6E, the electrode layer12is patterned using a photolithography method to form the electrode pads2. In this embodiment, each electrode pad2is a lamination of the wiring line4, the second protective film, and the electrode layer12. Next, the protective film10of the thermic effect unit3is etched. At that time, part of the protective film10disposed on the electrode pad2is also etched so that the protective film10is left only under the electrode layer12.

The above embodiments will be described more specifically with reference to examples.

In EXAMPLE 1, the liquid-ejection head substrate1shown inFIGS.1A and1Bwas formed using the production method shown inFIGS.2A to2E. In EXAMPLE 1, the wiring lines4were made of aluminum, the insulating protection layer5was made of silicon carbonitride, and the cavitation resistant film9was made of iridium inFIG.2A. An altered layer was formed in the surface layer of the insulating protection layer5, and a small amount of organic pollutants were attached to the surface layer.

Referring next toFIG.2B, the protective film10was formed so as to cover only the top of the cavitation resistant film9of each thermic effect unit3. The protective film10was made of titanium tungsten with a thickness of 50 nm in the viewpoint of preventing the generation of a fence and the performance of coating the cavitation resistant film9. The titanium tungsten exhibited high resistance to sputter etching and high adhesion to the cavitation resistant film9and the insulating protection layer5.

Referring next toFIG.2C, the substrate was set to a deposition system and was subjected to a sputter etching (reverse sputtering) process to remove the oxide film6formed on the wiring line4. The sputter etching was performed under the conditions of a flow rate of argon gas of 30 sccm, a power of 400 W, and a processing time of 20 seconds. Thus, the altered layer and the organic pollutants on the surface of the insulating protection layer5were removed. Since the protective film10was provided on the top of the cavitation resistant film9, the cavitation resistant film9was not decreased in thickness by the reverse sputtering. In contrast, the insulating protection layer5in the area where the protective film10is not disposed decreased by a thickness of more than 10 nm.

Referring next toFIG.2D, the diffusion prevention layer11and the electrode layer12were formed on the entire surface of the substrate by the deposition system, subsequent to the reverse sputtering process. The diffusion prevention layer11was formed of titanium tungsten with a thickness of 200 nm, which is a metallic material that has high adhesion to the wiring line4and the electrode layer12, stability to temperature to cause no diffusion, and low specific resistivity. The electrode layer12was made of gold, which has low specific resistively and high corrosion resistance, in a thickness of 400 nm.

Referring next toFIG.2E, the electrode layer12and the diffusion prevention layer11were patterned using a photolithography method to form the electrode pads2. Thereafter, unnecessary part of the electrode layer12and the diffusion prevention layer11were etched by wet etching. Since the diffusion prevention layer11and the protective film10were made of the same material, the diffusion prevention layer11and the protective film10could be removed by the same etching method. The electrode layer12made of gold was etched for a desired time using an etchant containing iodine and potassium iodide. The diffusion prevention layer11and the protective film10made of titanium tungsten were etched using a 30% hydrogen peroxide solution. Employing wet etching with a hydrogen peroxide solution for etching the protective film10provides sufficient options for the cavitation resistant film9, allowing for preventing a decrease in the thickness of the cavitation resistant film9. The protective film10was formed in a small thickness of 50 nm, and the level difference due to the decrease in the thickness of the insulating protection layer5caused by the reverse sputtering was as small as a dozen nm. For this reason, the result of observation of the portion of the protective film10after the protective film10was etched showed that no fence was formed.

In EXAMPLE 2, the liquid-ejection head substrate1shown inFIGS.1A and1Bwas formed using the production method shown inFIGS.6A to6E. In EXAMPLE 2, the wiring lines4were made of iridium, the insulating protection layer5was made of silicon carbonitride, and the cavitation resistant film9was made of iridium inFIG.6A. No oxide film was formed on part of the wiring line4exposed from the opening14of the insulating protection layer5because the wiring line4was made of noble metal. An altered layer was formed in the surface layer of the insulating protection layer5, and a small amount of organic pollutants were attached to the surface layer.

Referring next toFIG.6B, the protective films10were formed so as to cover the top of the cavitation resistant film9of each thermic effect unit3and the portion of the wiring line exposed from the opening14. The protective film10was made of titanium tungsten with a thickness of 50 nm in the viewpoint of preventing the generation of a fence and the performance of coating the cavitation resistant film9.

Referring next toFIG.6C, the substrate was set in a deposition system and is subjected to a sputter etching (reverse sputtering) process to remove the altered surface layer of the insulating protection layer5. The sputter etching was performed under the conditions of a flow rate of argon gas of 30 sccm, a power of 400 W, and a processing time of 20 seconds. This exposed a clear surface of the substrate to provide high adhesion to the channel member. Since the protective film10was provided on the top of the cavitation resistant film9, the cavitation resistant film9was not decreased in thickness by the reverse sputtering.

In contrast, the insulating protection layer5at the area where the protective film10is not disposed decreased by a thickness of more than 10 nm.

Referring next toFIG.6D, the electrode layer12was formed on the entire surface of the substrate by the deposition system, subsequent to the reverse sputtering process. The electrode layer12was formed with gold in a thickness of 400 nm.

Referring next toFIG.6E, the electrode layer12was patterned using a photolithography method to form the electrode pads2. The electrode layer12made of gold was etched for a desired time using an etchant containing iodine and potassium iodide.

Next, the protective film10of the thermic effect unit3was etched. The protective film10made of titanium tungsten was etched for a desired time using a 30% hydrogen peroxide solution. At the same time, part of the protective film10disposed on the electrode pad2was also etched to leave the protective film10only under the electrode layer12. Employing wet etching with a hydrogen peroxide solution for etching the protective film10provides sufficient options for the cavitation resistant film9, allowing for preventing a decrease in the thickness of the cavitation resistant film9. The protective film10was formed in a small thickness of 50 nm, and the level difference due to the decrease in the thickness of the insulating protection layer5caused by the reverse sputtering was as small as a dozen nm. For this reason, the result of observation of the portion of the protective film10after the protective film10was etched showed that no fence was formed.

The embodiments of the present disclosure allow reducing or eliminating a decrease in the thickness of the cavitation resistant film of the liquid-ejection head substrate.

This application claims the benefit of Japanese Patent Application No. 2021-047215, filed Mar. 22, 2021, which is hereby incorporated by reference herein in its entirety.