Patent Grant
11951742
The present disclosure relates to a substrate joined body.
A liquid discharge head (also referred to as an inkjet recording head or a liquid ejection head) that discharges a liquid is an example of a functional device such as a MEMS (Micro Electro Mechanical System) such as a pressure sensor or an acceleration sensor, a micro fluid device, and the like. In the manufacture of these devices, a device configured of a substrate joined body in which substrates are joined to each other with an organic film (adhesive) interposed therebetween is manufactured.
In the liquid discharge head, the inner wall surface of an ink flow path is easily eroded by the ink, and when exposed to the ink for a long period of time, the flow path structure may collapse. In particular, when the substrate is a silicon substrate, such damage caused by ink is likely to occur. Further, when the ink flow path is formed by joining substrates in which flow path shapes have been machined with an organic film (adhesive) interposed therebetween, ink penetrates into the interfaces between the substrates and the organic film, and the adhesive strength may decrease.
As a method for reducing such damage caused by ink to the substrate and the organic film (adhesive), a method for protecting the surface of the substrate joined body with a protective film (liquid resistant film) that is not easily eroded by ink has been proposed (Japanese Patent Application Laid-open No. 2014-124887).
However, the present inventors have found that even when the protective film is formed from the inner wall surface of the ink flow path over the top of the organic film (adhesive) as in Japanese Patent Application Laid-open No. 2014-124887, the high quality protective film can be difficult to form on the organic film (adhesive).
This is presumably because the organic film (adhesive) is slightly deformed due to temperature changes, pressure changes, and the like applied to the substrate joined body in the manufacturing process, stress is applied to the protective film, and cracks (hair cracks) occur in the protective film due to the adhesive force between the protective film and the organic film and the rigidity of the protective film.
In particular, where a protective film including an inorganic element such as shown in Japanese Patent Application Laid-open No. 2014-124887 is directly formed on an organic film (adhesive), when the adhesive force between the protective film and the organic film (adhesive) is weak and/or when the protective film is not rigid enough even if the adhesive force is ensured, the protective film may be peeled off by the force acting on the interface between the protective film and the organic film (adhesive). It is considered that where the protective film is peeled off, ink infiltrates from the peeled segment and damages the organic film (adhesive), which results in poor bonding between the substrates. In addition, it is considered that the protective film may peel off and become dust that floats in the flow path, which may affect the discharge performance.
Further, such a problem may occur when a protective film is formed on an organic film attached to or formed on at least a part of the substrate not only in the abovementioned substrate joined body. That is, when a protective film (for example, a film that protects some functional element, wiring, or the like) is formed on an organic film and the protective film is formed satisfactorily, peeling and hair cracking of the protective film becomes a problem.
This disclosure was made in view of the above issues. That is, the present disclosure provides a substrate joined body in which cracking and peeling of a protective film can be suppressed.
The present invention discloses a substrate joined body comprising:
According to the present disclosure, a substrate joined body in which cracking and peeling of a protective film can be suppressed is provided.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the following description, the substrate joined body and the manufacturing method thereof according to the present disclosure will be described by taking a liquid discharge head as an example, but the present disclosure is not limited to the application to the liquid discharge head.
In the present disclosure, the expression of “from XX to YY” or “XX to YY” indicating a numerical range means a numerical range including a lower limit and an upper limit which are end points, unless otherwise specified. Also, when a numerical range is described in a stepwise manner, the upper and lower limits of each numerical range can be arbitrarily combined. In the following description, the same number is assigned in the figures to structures that have the same function, and in some instances a description thereof may be omitted.
The present invention discloses a substrate joined body comprising:
The symbols in
The symbols in
The present invention discloses a liquid discharge head comprising:
A method for forming the protective film 125 will be described hereinbelow. The protective film 125 of the present embodiment is formed using a technique for forming a film by repeating surface saturation adsorption of at least one agent selected from the group consisting of an oxidizing agent and a nitriding agent and a raw material gas by an atomic layer deposition method (ALD method).
The protective film preferably comprises at least one element selected from the group consisting of Ta, Ti, Zr, Nb, V, Hf, and Si as a simple substance, an oxide, a nitride, or a carbide. Among these, the protective film preferably comprises an oxide of at least one element selected from the group consisting of Ta, Ti, Zr, Nb, V, Hf, and Si, and more preferably comprises at least one compound selected from the group consisting of TaO, TiO, SiOC, SiC, SiCN, TaN, and TiN.
The thickness of the protective film is not particularly limited, but is preferably from 10 to 300 nm, and more preferably from 50 to 200 nm. The amount of the inorganic element in the protective film is preferably from 25 to 75% by mass, and more preferably from 30 to 70% by mass. Further, the amount of the abovementioned compound in the protective film is preferably from 50 to 100% by mass, and more preferably from 80 to 100% by mass.
Among them, an ALD-TiO film formed by using titanium tetrachloride (TiCl4) as the raw material gas and pure water as the oxidizing agent will be specifically described as an example.
A film is formed by alternately supplying TiCl4 and pure water and repeating surface saturation adsorption of the oxidizing agent and the raw material gas, and the precursor molecules and water molecules that are the raw materials are delivered into the substrate in a vacuum chamber to cause the adsorption of molecules targeted at about one molecular layer on the substrate surface. At this time, the functional group in the precursor is adsorbed on the hydroxyl group present on the substrate surface, and the functional group detaches a hydrogen atom from the hydroxyl group and is desorbed as a volatile molecule. After that, the remaining oxygen atom and the inorganic element (here, Ti element) in the precursor are bonded by a covalent bond. In the exhaust step, the molecules that were not completely adsorbed on the substrate surface in the deposition step and stayed in the chamber are exhausted.
In the atomic layer deposition method, since a strong bond is formed by covalent bonds, it is possible to form a protective film with a high adhesive force. In addition, since the atomic layer deposition method is a film formation method that uses saturated chemical adsorption rather than plasma excitation or ion acceleration energy, a single-phase adsorption layer can be formed equally on all surfaces exposed to the raw material gas, and since the film thickness is the same in all places where the raw material gas can flow in, the protective film has good throwing power with respect to grooves and holes having a high aspect ratio.
Since a protective film is formed by the reaction between the hydroxyl groups chemically adsorbed on the surface of the organic film and the raw material gas, the properties and adhesive force of the protective film are greatly affected by how many hydroxyl groups the organic film has. The state of the organic film surface suitable for the atomic layer deposition method is an active state showing hydrophilicity like an oxide crystal, and where the surface is hydrophilic, it has a strong affinity with water molecules, and a monomolecular layer of water is easily formed by chemical adsorption. Further, where the organic film surface is in a hydrophobic state such as that of carbon and carbides, the affinity with water molecules is low and a monomolecular layer of water is unlikely to be formed. When the organic film includes silicon, many hydroxyl groups can be introduced into the organic film, so that the organic film surface can be controlled to be in an active state exhibiting hydrophilicity as described above.
For this reason, in order to form a dense film that adheres well to the organic film surface, it is important to have an oxidized surface with a small amount of carbon. Therefore, it is conceivable to oxidize the organic film. It is known that carbon can be easily sublimated by using an oxidation treatment such as oxygen ashing. In order to form a protective film on the organic film, it is important that the organic film have a structure that can form an oxide layer after reducing the carbon on the surface of the organic film by using a carbon reduction step such as oxidation treatment. For this reason, it is important that the organic film of the present disclosure includes at least one selected from the group consisting of an organosilicon compound to which a hydroxyl group can be adsorbed and a polymer of the organosilicon compound. Where the organic film of the present disclosure includes at least one selected from the group consisting of an organosilicon compound and a polymer of the organosilicon compound, more hydroxyl groups can be introduced into the organic film, so that the organic film surface can be more easily controlled to the active state showing hydrophilicity such as described above.
In the present embodiment, a sample obtained by using a compound having a structure in which benzocyclobutene has a siloxane bond and/or a polysiloxane bond, specifically, divinyltetramethylsiloxane benzocyclobutene, as the organosilicon compound, and subjecting the organic film surface to oxygen ashing by plasma oxidation using O2 plasma (carbon reduction step), and a sample that has not been subjected to the oxygen ashing were prepared, and a protective film was grown on each sample for verification. The protective film was an ALD-TiO film formed by using titanium tetrachloride (TiCl4) as the raw material gas and pure water as the oxidizing agent.
In oxygen ashing, oxygen ions and oxygen radicals were generated by high frequency in an oxygen gas flow. Oxygen ions and oxygen radicals only thinly oxidize the surface of the silicon film, but volatilize the carbon, which is the main component of the organic film, to reduce the amount of carbon in the organic film.
In the present embodiment, ashing was performed for 1 min without applying RF bias power at a stage temperature of 250° C. Then, a protective film was formed with an ALD-TiO film formed from titanium tetrachloride (TiCl4) and pure water. The film formation temperature at this time was 300° C., and the film thickness of the protective film was 130 nm.
Ti, O, Si, and C elements were measured by X-ray photoelectron spectroscopy (XPS) in the depth direction while sputtering the organic film, which was treated under such conditions and on which the protective film was formed, with He gas from the surface on the protective film side, and elemental analysis of the protective film and the organic film was performed. The results are shown in
From the results obtained by this measurement method, it is possible to determine the oxygen ashing conditions for improving the adhesiveness by regulating the carbon reduction amount in the organic film within a certain range.
As a result, it was found that a region in which the ratio of carbon to silicon based on atomic percentage (referred to hereinbelow simply as “carbon/silicon ratio”) was greater than 0.0 and less than or equal to 5.0 was formed within 50 nm from the surface of the oxygen-ashed organic film on the protective film side, and the carbon/silicon ratio exceeded 5.0 in the portion of the organic film exceeding 50 nm from the surface on the protective film side.
This indicates that oxygen ashing reduced the amount of carbon in at least a part of the region within 50 nm from the surface of the organic film on the protective film side. Further, as a result of performing the same XPS measurement using a sample not subjected to oxygen ashing, it was found that, as shown in
When a test was conducted at 121° C. for 20 h with a PCT test device (pressure cooker test) while the substrate joined body produced in this step was immersed in ink, there was no peeling of the protective film in the sample subjected to oxygen ashing treatment. By contrast, the protective film of the sample not subjected to the oxygen ashing treatment was peeled off from the interface between the organic film and the protective film.
This result shows that a protective film that is less likely to be cracked and is unlikely to peel off can be formed on an organic film on which the protective film is formed by creating a region in which the carbon/silicon ratio is greater than 0.0 and less than or equal to 5.0 in at least a part of the region within 50 nm from the surface of the organic film on the protective film side.
Further, it is preferable that a region in which the carbon/silicon ratio is from 10.0 to 30.0 (preferably from 8.0 to 25.0, and more preferably from 6.0 to 20.0) be not present in the region within 50 nm from the surface on the protective film side.
The carbon/silicon ratio is preferably from 1.0 to 4.0, and more preferably from 1.5 to 3.5. The carbon/silicon ratio can be controlled by varying the stage temperature, ashing time, and RF bias power.
As the carbon amount reduction step, oxygen ashing, which is a kind of oxidation treatment, was used in the above embodiment, but this step is not limited to the oxidation treatment. Further, when the oxidation treatment is adopted as the carbon amount reduction step, the treatment is not limited to the oxygen ashing by plasma oxidation using O2 plasma, and the oxygen ashing may be performed by ozone oxidation using ozone.
When oxygen ashing is adopted as the carbon amount reduction step, the stage temperature can be preferably from 5 to 350° C. Further, the RF bias power may or may not be applied, and the RF bias power when applied is preferably from 50 to 200 W. Further, the ashing time is preferably from 0.5 to 10 min.
Titanium tetrachloride was used as the raw material gas in the above embodiment, but the raw material gas is not limited to titanium tetrachloride.
Further, as the oxidizing agent, pure water was used in the above embodiment, but the oxidizing agent is not limited to pure water.
Furthermore, the film formation temperature of the protective film is preferably from 150 to 500° C.
Divinyltetramethylsiloxane benzocyclobutene was used in the above embodiment as the organosilicon compound capable of forming an organic film (adhesive), but this organosilicon compound is not limiting. As the organosilicon compound, for example, at least one compound selected from the group consisting of divinyltetramethylsiloxane benzocyclobutene and bis-vinylsiloxane benzocyclobutene can be used. The organic compound can be used as a solution, and the solvent of the solution can be, for example, 1,3,5-trimethylbenzene. The solution can be adjusted to have a viscosity of from 15 to 50 cps (for example, 35 cps).
The thickness of the organic film is not particularly limited, but is preferably from 0.1 to 10 μm, and more preferably from 1 to 5 μm.
As the first substrate and second substrate, known substrates used as substrates for functional devices such as MEMS and microfluidic devices can be used without particular limitation, but silicon substrates are preferable. The thickness of the first substrate and second substrate is also not particularly limited, but may be preferably from 500 to 1000 μm.
In
Although the aspects of the present disclosure have been described with reference to the substrate joined body, the aspects of the present disclosure are not limited to the substrate joined body as described above, and application is also possible to a structure including a substrate, an organic film that is present on the substrate and includes silicon and carbon, and a protective film that includes an inorganic element and is formed on the organic film.
As the substrate of the structure, the same one as the first substrate or the second substrate of the substrate joined body can be used.
Further, the organic film of the structure is present on the substrate, for example, the organic film may be attached to at least a part of the substrate, or the organic film may be formed on the substrate. Further, for the organic film of the structure, a compound including silicon and carbon, for example, a compound of a structure in which benzocyclobutene similar to the organic film of the abovementioned substrate joined body has a siloxane bond and/or a polysiloxane bond, specifically, divinyltetramethylsiloxane benzocyclobutene, bis-vinylsiloxane benzocyclobutene, and the like can be used. The compound can be a solution using 1,3,5-trimethylbenzene or the like as a solvent, similarly to the organic film of the abovementioned substrate joined body, and the viscosity of the solution can be adjusted from 15 to 50 cps (for example, 35 cps).
Furthermore, the protective film of the structure includes an inorganic element, and can include, for example, the same element as the protective film of the substrate joined body. In addition, the protective film of the structure is formed on the organic film, and can be formed, for example, by the same method as the protective film of the substrate joined body.
The present invention is more specifically described herebelow using examples. The present invention is not limited by the examples that follow. The number of parts in the following formulations is on a mass basis in all instances unless specifically indicated otherwise.
As an example in the present embodiment, a substrate joined body was manufactured as shown in
An ultraviolet radiation-curable tape having a thickness of 180 μm was attached as a protective tape to the front surface of the first substrate, and the back surface of the first substrate was thinly processed with a grinding device until the substrate thickness became 500 μm. Then the ground surface was smoothed by polishing with a CMP device. The polishing was performed using a slurry containing colloidal silica as a main component and a polyurethane-based polishing pad. Then, the polished surface was washed with a washing liquid consisting of a mixed liquid of 8% by mass of ammonia, 8% by mass of hydrogen peroxide solution, and 84% by mass of pure water to remove the slurry.
Next, a groove serving as a second flow path 113 was formed by etching (
Next, a protective tape was attached to the back surface of the first substrate 131, a resist mask was formed on the front surface by the same means as above, and dry etching was performed from the front surface side of the first substrate 131 to form a first flow path 112 composed of a plurality of holes. After the etching, the protective tape was removed, and the resist and deposits were removed with the stripping solution.
Next, a silicon substrate with a thickness of 500 μm was prepared as the second substrate 132 (
Next, an adhesive 123 was applied to the back surface of the first substrate 131. First, an 8-inch silicon substrate was separately prepared, and a 1,3,5-trimethylbenzene solution (viscosity=35 cps) of divinyltetramethylsiloxane benzocyclobutene as the adhesive 123 was spin-coated on the substrate to a thickness of 2 μm. Then, the adhesive 123 was transferred to the back surface of the first substrate 131 by bringing the joint surface of the first substrate 131 into contact with the coated adhesive 123.
Next, the first substrate 131 and the second substrate 132 were aligned using a joint alignment device, and the two ends of the substrates were temporarily fixed by pressurizing with a clamp jig (not shown) (
Next, ashing treatment was performed for 1 min, without applying RF bias power to the lower electrode, with O2 plasma excited at a stage temperature of 250° C. and at 200 W, the amount of carbon was reduced from the surface of the adhesive 123 spreading from the joint portion of the first substrate 131 and the second substrate 132, and a region 124 having a carbon/silicon ratio of greater than 0.0 and less than or equal to 5.0 was formed (
Further, a TiO film was formed as a protective film 125 with a thickness of 130 nm (
In this example, the thermal ALD-TiO film was formed by using TiCl4 and pure water, and the film was formed by alternately supplying TiCl4 and pure water. At this time, in the film-forming cycle, the gas obtained by vaporizing TiCl4 was transported into the furnace together with nitrogen and sprayed for 5 sec, followed by sufficient purging with nitrogen and discharge. Next, the gas obtained by vaporizing pure water was transported into the furnace together with nitrogen and sprayed for 5 sec, followed by sufficient purging with nitrogen and discharge. This cycle was regarded as one cycle, the same cycle was repeated about 2000 times, and the titanium oxide film was layered to 130 nm at a film formation temperature controlled at 300° C.±10° C. to obtain a substrate joined body 130. As for the film forming method, a thermal atomic layer deposition method was adopted as the atomic layer deposition method in this example, but the film forming method based on the plasma atomic layer deposition method may also be used. Further, the protective film may be formed by a method other than the atomic layer deposition method.
The substrate joined body 130 is a structure in which the first substrate 131 and the second substrate 132 are joined and which has a flow path (second flow path 113 and third flow path 114). An organic film (adhesive) 123 that joins these substrates is present between the first substrate 131 and the second substrate 132. The protective film 125 is formed over the organic film 123 from at least a part of the surface of the first substrate 131 and at least a part of the surface of the second substrate 132. Then, a dry film resist composed of a positive resist was laminated on the front surface of the first substrate 131 of the substrate joined body to form an etching mask. The protective film 125 on the contact pad 103 was removed by etching with a fluorine-based etching solution.
Next, a negative-type dry film made of an epoxy resin was attached to the front surface of the first substrate 131 and exposed to form a wall 118 of a discharge port forming member 119. Further, a dry film was attached from thereabove and exposed to form a top plate 117 of the discharge port forming member 119. Then, the unexposed portion was removed by development to form a discharge port 101 and a pressure chamber 102 (
A manufacturing method in which the conditions of reducing the amount of carbon (
Next, the step of reducing the amount of carbon that is shown in
In Example 2, an RF bias power of 120 W was applied at a stage temperature of 16° C., an ashing treatment using O2 plasma was performed for 5 min, and the amount of carbon was reduced from the surface of the adhesive 123 spreading from the joint portion between the first substrate 131 and the second substrate 132. As a result, as in the first embodiment, it was possible to obtain a substrate joined body and a liquid discharge head in which cracking and peeling of the protective film could be suppressed.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. This application claims the benefit of Japanese Patent Application No. 2021-091395, filed May 31, 2021, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-091395 | May 2021 | JP | national |
| Number | Date | Country |
|---|---|---|
| 2014-124887 | Jul 2014 | JP |
| 2019209573 | Dec 2019 | JP |
| Entry |
|---|
| Machine Translation of Manufacturing Method of Liquid Discharge Head (JP 2019-209573) to Fukumoto Takayuki et al., Dec. 12, 2019, [Description of Embodiments, Embodiment 1] (Year: 2019). |
| Shimoda et al., U.S. Appl. No. 17/751,916, filed May 24, 2022. |
| Number | Date | Country | |
|---|---|---|---|
| 20220379606 A1 | Dec 2022 | US |
