Method for manufacturing substrate structure

Abstract

To provide a method of manufacturing a substrate structure capable of suppressing peeling of a protective film.SOLUTION: A method of manufacturing a substrate structure including an organic film and a silicon substrate, the method comprising: performing an ashing process on the substrate structure at a first temperature while applying a first bias; performing an ashing process on the substrate structure subjected to the first ashing process at a second temperature higher than the first temperature while applying a second bias lower than the first bias or without applying a bias; and forming a protective film on the substrate structure subjected to the second ashing process.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a substrate structure. [Background technology]

[0002] An inkjet head used in an inkjet recording device has a nozzle substrate, which is formed by bonding substrates together with an adhesive and has ink channels, nozzles, and ejection ports. In the nozzle substrate, the inner wall surfaces of the channels are easily eroded by ink, and prolonged exposure to ink can cause changes in the channel structure. Silicon substrates are particularly susceptible to such ink damage. Furthermore, ink can penetrate the interface between the substrate and the organic film (adhesive), reducing the adhesive strength between the substrates. Patent Document 1 describes a technology for protecting the surfaces of the substrate assembly and the inner walls of the channels from ink by forming a protective film that is resistant to ink on them. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-124887 Summary of the Invention [Problem to be solved by the invention]

[0004] If the surface on which the protective film is to be formed (film formation surface) is contaminated with organic matter (for example, resist residue), the formed protective film may peel off from the organic matter.

[0005] An object of the present invention is to provide a method for manufacturing a substrate structure that can suppress peeling of a protective film. [Means for solving the problem]

[0006] The present invention provides a method for manufacturing a substrate structure having an organic film and a silicon substrate, a first ashing step of performing an ashing process on the substrate structure using oxygen plasma to remove organic matter at a first temperature while applying a first bias; a second ashing step of performing an ashing process at a second temperature higher than the first temperature while applying a second bias lower than the first bias to the substrate structure after the first ashing step, or without applying a bias; a film forming step of forming a protective film on the substrate structure that has been subjected to the second ashing step; The present invention relates to a method for manufacturing a substrate structure having the above structure. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for manufacturing a substrate structure that can suppress peeling of a protective film. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view of a substrate assembly according to an embodiment. [Figure 2] 3A to 3C are diagrams illustrating a method for manufacturing a substrate assembly according to Example 1. [Figure 3] 10A and 10B are diagrams illustrating a method for manufacturing a substrate assembly of Comparative Example 1. [Figure 4] 10A and 10B are diagrams illustrating a method for manufacturing a substrate assembly of Comparative Example 2. [Figure 5] 10A and 10B are diagrams illustrating a method for manufacturing a substrate assembly of Comparative Example 3. [Figure 6] 10A and 10B are diagrams illustrating peeling of a protective film when bias ashing is performed. [Figure 7] FIG. 1 is a diagram showing the oxygen concentration at the interface between an oxide film and a silicon substrate. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, exemplary embodiments for carrying out the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described in the following examples may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and the scope of the present invention is not intended to be limited to the following examples.

[0010] FIG. 1 is a cross-sectional view of a substrate assembly 15 of this embodiment.

[0011] The substrate assembly 15 includes a first substrate 1 and a second substrate 5 bonded together via an adhesive 4, which is an organic film, and a third substrate 8 bonded together via an adhesive 14. The substrate assembly 15 has an ink flow path 2 extending across the first substrate 1, the second substrate 5, and the third substrate 8, and the first substrate 1 has an ejection port 9 formed therein for ejecting ink. A protective film 10 formed by atomic layer deposition (ALD) extends from the inner wall surface of the ink flow path 2 to the adhesive 4. The material of the protective film 10 can be selected from the group consisting of TaO, TiO, SiOC, SiCN, TaN, TiN, HfO2, and ZrO2, for example. This prevents the first substrate 1, the second substrate 5, the third substrate 8, the adhesive 4, and the adhesive 14 from being eroded by the ink.

[0012] A liquid ejection head formed of a substrate assembly 15 has an ink flow path 2 with a complex shape, and it is desirable to protect the inner wall of the ink flow path 2 inside the substrate assembly 15. A method for forming a protective film 10 on the inner wall of the ink flow path 2 will be described. The protective film 10 of the embodiment can be formed by repeating surface saturation adsorption of an oxidizing agent (or a nitriding agent) and a source gas using atomic layer deposition (ALD). The material of the protective film 10 preferably contains a simple substance, oxide, nitride, or carbide of any element selected from the group consisting of Ta, Ti, Zr, Nb, V, Hf, and Si.

[0013] The ALD method forms strong covalent bonds, allowing for the formation of films with high adhesion. In addition, the ALD method is a film formation method that utilizes saturated chemical adsorption, so the film adheres well to grooves and holes with high aspect ratios.

[0014] In the ALD method, a film is formed by the reaction of source gas with hydroxyl groups chemically adsorbed on the substrate surface, so the amount of hydroxyl groups on the substrate surface has a significant effect on the film quality and adhesion. A substrate surface suitable for the ALD method is one that is hydrophilic, such as an oxide crystal. This is because a hydrophilic substrate surface has a high affinity for water molecules, making it easier for a water monolayer to form through chemical adsorption.

[0015] On the other hand, if the substrate surface is contaminated with organic matter, the hydroxyl groups are covered with the organic matter, and in this case, there are not enough hydroxyl groups to obtain good adhesion to the substrate surface. Organic contamination can occur due to various factors within the process.

[0016] For this reason, when using the ALD method, it is desirable to remove organic substances that contaminate the substrate surface before film formation and turn the film formation surface into an activated surface that exhibits hydrophilicity, such as oxide crystals. One method for removing organic contamination is ashing, which uses oxygen plasma to remove organic substances (O2 ashing).

[0017] This ashing process also contributes to improving the adhesion of films formed by the ALD method to adhesives containing siloxane, such as benzocyclobutene (BCB), which are organic resins used as adhesives for bonding substrates. The silicon and oxygen contained in the resin react with each other. This is because a silicon oxide film is formed on the surface in response to the heat.

[0018] This step allows the adhesive layer to have many hydroxyl groups on its surface, which improves adhesion to the film formed by the ALD method, making it preferable as an adhesive.

[0019] However, the process of removing organic contamination from substrate assemblies with complex ink flow paths by ashing has the following problems: (1) Even after ashing, thick organic contamination remains and cannot be completely removed; (2) the organic substances used in the adhesive used to bond the substrates are damaged by ashing, such as cracking and scraping; and (3) a fragile oxide layer is formed on the surface of the substrate due to ashing.

[0020] Regarding point (1), the ability to remove organic matter can be improved by setting the ashing temperature higher. However, ashing at high temperatures can cause the adhesive to crack or the adhesive to be worn away deep into the bonding surface. This occurs when the oxide film formed on the surface of the adhesive layer becomes too thick, causing the oxide film to crack due to the difference in thermal expansion coefficients between the adhesive layer and the oxide film, and the cracks reach the adhesive layer. With organic resins that do not contain silicon, the amount of wear increases, penetrating deep into the bonding surface and causing wear. Residues of the organic resin tend to remain in the worn areas on the bonding surface, which can cause the protective film to peel off.

[0021] In cracked or deeply scraped areas, the formed protective film does not have sufficient mechanical strength or adhesion, and may crack during ink immersion, thereby failing to perform its function. For this reason, it is not desirable to perform the ashing process at an excessively high temperature in substrate assemblies containing organic resins.

[0022] Regarding (2), cracking and scraping of the adhesive can be suppressed by setting the ashing temperature low. However, lowering the ashing temperature reduces the ability to remove organic contaminants (ashing rate), making it impossible to remove resist residues and organic residues generated during the process.

[0023] Lowering the ashing temperature can prevent cracking and chipping of the adhesive layer, but lowering the temperature to a temperature where cracking and chipping of the adhesive layer no longer occur makes it impossible to sufficiently remove thick organic contaminants, which results in residues that cause the protective film to peel off.

[0024] By using a low ashing temperature and applying a bias during the ashing process, it is possible to suppress the effects of cracking and scraping on the adhesive layer and maintain a high ability to remove thick organic contaminants, because the ion bombardment promotes reactivity.

[0025] However, when a protective film is formed on the surface of a silicon substrate that has undergone low-temperature bias ashing, the protective film may peel off. This is the problem (3). The cause of this peeling is not a lack of hydroxyl groups on the substrate surface, but rather, as shown in Figure 6(A), the oxide film 13 that grows rapidly on the surface of the silicon substrate 1 due to ashing is broken, and as shown in Figure 6(B), it peels off from the silicon substrate 1. The oxide film 13 formed by bias ashing is fragile due to ion bombardment, so even if a protective film 10 is formed on this oxide film 13, the oxide film 13 will peel off at the interface with the base silicon substrate 1.

[0026] FIG. 7 shows the oxygen concentration at the interface between an oxide film (SiO) and a silicon substrate (Si) under various ashing conditions. Medium-temperature ashing is performed at a temperature range where cracks do not occur in the adhesive layer. High-temperature ashing is performed at a temperature range where cracks occur in the adhesive layer. Low-temperature bias ashing is performed at a lower temperature than medium-temperature ashing while applying a bias. Only when low-temperature bias ashing is performed does the oxygen concentration at the interface between the oxide film and the silicon substrate decrease more rapidly than in the other cases.

[0027] However, if intermediate-temperature ashing is performed after low-temperature bias ashing, the oxygen concentration at the interface between the oxide film and the silicon substrate does not decrease sharply. When a protective film was formed on the oxide film after intermediate-temperature ashing following low-temperature bias ashing, the protective film did not peel off. This is thought to be because oxygen diffused into the fragile oxide film formed by bias ashing during intermediate-temperature ashing, restoring the fragility of the oxide film at the interface.

[0028] The processing temperature range for mid-temperature ashing, which can restore the brittleness of the oxide film formed by low-temperature bias ashing without causing cracking or chipping of the organic resin, is 60 to 100° C. The upper limits of the processing temperature and processing time for mid-temperature ashing are 100° C. and 150 seconds, respectively.

[0029] The organic contamination removal capacity in medium-temperature ashing (no-bias ashing) without applying a bias is approximately 0.86 μm when the processing temperature is 100°C and the processing time is 150 seconds. The organic contamination removal capacity in low-temperature ashing (processing temperature less than 60°C) is 0.0 μm / min.

[0030] On the other hand, the organic contamination removal capacity of low-temperature bias ashing is approximately 2.5 μm at a processing temperature of 16° C. and a processing time of 150 seconds, which is 2.9 times that of medium-temperature ashing.

[0031] Medium-temperature ashing is effective for organic contamination caused by the resist stripping process, but it is not sufficient to remove thick organic contaminants. Low-temperature bias ashing may be required to remove thick organic contaminants.

[0032] By performing intermediate temperature ashing immediately after low-temperature bias ashing on a substrate, or by performing intermediate temperature ashing on a substrate that has previously undergone low-temperature bias ashing, it is possible to restore the fragility of the Si / SiO interface. This achieves sufficient organic contamination removal, suppresses cracking and chipping of the adhesive layer (organic resin), and prevents peeling of the protective film due to rupture between the silicon and oxide film.

[0033] In the intermediate temperature ashing performed after the low temperature bias ashing, no bias may be applied, or a bias may be applied to the extent that the oxide film does not become brittle. In this case, the bias applied should be lower than the bias applied in the low temperature bias ashing. When applying a bias in the intermediate temperature ashing, up to about 50 W is acceptable.

[0034] It should be noted that low-temperature bias ashing does not have sufficient cleaning power for organic contamination inside the ink flow path 2 where ions are difficult to hit. However, medium-temperature ashing can reinforce this.

[0035] Examples and comparative examples will be described below.

[0036] Example 1 A method for manufacturing a substrate assembly 15 in Example 1 will be described with reference to FIG. 2. The substrate assembly 15 is an example of a substrate structure having silicon substrates, including layers of adhesives 4 and 14 as organic films. The substrate assembly 15 is an assembly in which a plurality of silicon substrates are bonded together with an adhesive. The adhesive is made of an organic material containing silicon. The adhesive can be, for example, benzocyclohexane. An example is butene.

[0037] First, as shown in Fig. 2(a), an ink flow path 2 and a piezoelectric element housing portion 3 are formed on a first substrate 1. An adhesive 4 is formed on the first substrate 1 by transfer. At this time, the adhesive 4 is not transferred to the ink flow path 2 or the piezoelectric element housing portion 3.

[0038] Next, as shown in FIG. 2(b), the first substrate 1 and the second substrate 5 are bonded together and the adhesive 4 is cured. After that, organic matter that adhered during processing is removed by an ashing process. This ashing is performed by low-temperature bias ashing to minimize its effect on the adhesive 4. In this example, an O2 plasma excited by microwaves (MW) was used at a processing temperature of 16°C, and an RF bias power of 120 W was applied to the lower electrode, and the ashing process was performed for 1 minute.

[0039] Next, as shown in Figure 2(c), the second substrate 5 is thinned. This process is performed by attaching protective tape to the first substrate 1. After that, areas that will become pressure chambers 7 are formed in positions corresponding to the piezoelectric elements 6. The pressure chambers 7 are formed by performing resist patterning and silicon etching on the thinned surface using known methods.

[0040] Next, as shown in FIG. 2(d), adhesive 14 is transferred to second substrate 5, and second substrate 5 and third substrate 8 are bonded together. After that, organic matter that adhered during processing is removed by an ashing process. This ashing is performed by low-temperature bias ashing to minimize its effect on adhesive 14. In this example, an O2 plasma excited by MW at a processing temperature of 16°C was used, and an RF bias power of 120 W was applied to the lower electrode, and the ashing process was performed for 1 minute.

[0041] 2(e), the third substrate 8 is thinned, and the thinned surface is subjected to resist patterning and silicon etching by known methods to form discharge ports 9, which are openings for discharging liquid. This results in a substrate assembly 15. Note that, although an example has been shown in which the discharge ports 9 are formed after the third substrates 8 are bonded and thinned, the present invention is not limited to this, and the third substrates 8 having discharge ports 9 formed therein may also be bonded.

[0042] Next, as shown in FIG. 2(f), in the first ashing step, low-temperature bias ashing is performed on the substrate assembly 15 at a first temperature while applying a first bias. In this example, the stage 11 is kept at a temperature of 16°C, and an RF bias power of 120 W is applied to the lower electrode using O2 plasma 12 (oxygen plasma) excited by MW, and the ashing process is performed for 1 minute. This removes thick organic contamination adhering to the surface of the first substrate 1.

[0043] Next, as shown in FIG. 2(g), in the second ashing step, medium-temperature ashing is performed on the substrate assembly 15 at a second temperature higher than the first temperature without applying a bias. In this example, the stage 11 is kept at a temperature of 88°C, and the ashing process is performed for 2 minutes and 30 seconds using O2 plasma excited by MW without applying RF bias power to the lower electrode. This restores the fragile oxide film formed by the low-temperature bias ashing and removes organic contamination accumulated in the ink flow path 2.

[0044] 2(h), a film-forming step is performed to form a protective film 10 on the substrate assembly 15 that has been subjected to the second ashing step. In this example, the protective film 10 is formed by depositing 130 nm of TaO at a film-forming temperature of 230°C by the ALD method while alternately supplying TBTEMT and pure water. In this film-forming step, the protective film 10 is formed on the surface of the substrate assembly 15 and on the inner wall of the ink flow path 2 that communicates with the ejection orifice 9.

[0045] In the substrate assembly 15 manufactured by the above steps, the protective film 10 is removed from the silicon substrate. It was possible to prevent the protective film 10 from breaking and peeling off together with the oxide film formed on the surface. It was also possible to prevent peeling off of the protective film 10 due to organic contamination on the silicon substrate and the oxide film on its surface. It was also possible to prevent cracks and the like from occurring in the adhesive layer due to ashing.

[0046] As mentioned above, low-temperature bias ashing may be performed not only at the timing shown in Fig. 2(f) immediately before the protective film deposition process shown in Fig. 2(h), but also in an earlier process (after Fig. 2(b) or Fig. 2(d)). Even in such cases, the fragile oxide film formed by the low-temperature bias ashing can be restored by the medium-temperature ashing process shown in Fig. 2(g).

[0047] Although an example in which no bias is applied during the medium-temperature ashing in Fig. 2(g) has been described, medium-temperature bias ashing may be performed while applying a second bias lower than the first bias in the low-temperature bias ashing. The first temperature during the first ashing step in Fig. 2(f) is lower than 60°C. The second temperature during the second ashing step in Fig. 2(g) is equal to or higher than 60°C and lower than 100°C. The material of the protective film formed in Fig. 2(h) is any one of TaO, TiO, SiOC, SiCN, TaN, and TiN.

[0048] (Comparative Example 1) FIG. 3 shows a method for manufacturing a substrate assembly of Comparative Example 1 in which ashing is not performed before the formation of the protective film.

[0049] 3(a) to 3(e) are similar to FIGS. 2(a) to 2(e) of the embodiment.

[0050] In Comparative Example 1, the process shown in Fig. 2(f) (first ashing process) and the process shown in Fig. 2(g) (second ashing process) of the embodiment are not performed, and the process shown in Fig. 3(e) is followed by the process shown in Fig. 3(h) of forming the protective film 10. Fig. 3(h) is the same as Fig. 2(h) of the embodiment.

[0051] In Comparative Example 1, peeling occurred in the protective film 10 formed in FIG. 3(h) due to the influence of adhesive residue from the tape and organic residues left behind when the resist was peeled off.

[0052] (Comparative Example 2) 4 shows a manufacturing method of a substrate assembly of Comparative Example 2 in which high-temperature ashing is performed before forming a protective film. Figures 4(a) to 4(e) and 4(h) are similar to Figures 3(a) to 3(e) and 3(h) of Comparative Example 1.

[0053] In Comparative Example 2, after Fig. 4(e), high-temperature ashing was performed as shown in Fig. 4(f). In Comparative Example 2, the stage 11 was kept at a temperature of 200°C, and an ashing process was performed for 2 minutes and 30 seconds using O2 plasma 12 excited by MW without applying RF bias power to the lower electrode. In Comparative Example 2, cracks occurred in the adhesive.

[0054] (Comparative Example 3) FIG. 5 shows a method for manufacturing a substrate assembly in Comparative Example 3, in which low-temperature bias ashing is performed before the formation of a protective film. 5(a) to 5(e) and 5(h) are similar to FIGS. 3(a) to 3(e) and 3(h) of Comparative Example 1.

[0055] In Comparative Example 3, after Fig. 5(e), low-temperature bias ashing is performed as shown in Fig. 5(f). In Comparative Example 3, the temperature of the stage 11 is controlled at 16°C, and an RF bias power of 120 W is applied to the lower electrode using O2 plasma excited by MW, and ashing processing is performed for 1 minute.

[0056] In Comparative Example 3, a break occurred between the silicon substrate (Si) and the oxide film (SiO) formed by ashing, and the protective film 10 peeled off together with the oxide film.

[0057] The results of the above examples and comparative examples are summarized in Table 1. As shown in Table 1, by performing low-temperature bias ashing followed by medium-temperature ashing, it is possible to prevent cracking of the adhesive layer, peeling of the protective film due to organic contamination, and peeling of the protective film due to fracture from the oxide film on the surface of the silicon substrate. [Table 1]

[0058] The disclosure of this embodiment includes the following configuration. (Method 1) A method for manufacturing a substrate structure having an organic film and a silicon substrate, comprising: a first ashing step of performing an ashing process on the substrate structure using oxygen plasma to remove organic matter at a first temperature while applying a first bias; a second ashing step of performing an ashing process at a second temperature higher than the first temperature while applying a second bias lower than the first bias to the substrate structure after the first ashing step, or without applying a bias; a film forming step of forming a protective film on the substrate structure that has been subjected to the second ashing step; A method for manufacturing a substrate structure having the above structure. (Method 2) the organic film is an adhesive; The method for manufacturing a substrate structure according to Method 1, wherein the substrate structure is a bonded body in which a plurality of the silicon substrates are bonded with the adhesive. (Method 3) 3. The method for manufacturing a substrate structure according to method 2, wherein the adhesive is made of an organic material containing silicon. (Method 4) 4. The method for producing a substrate structure according to Method 3, wherein the adhesive is benzocyclobutene. (Method 5) 5. The method for manufacturing a substrate structure according to any one of methods 1 to 4, wherein the first temperature is lower than 60°C. (Method 6) 6. The method for manufacturing a substrate structure according to any one of methods 1 to 5, wherein the second temperature is 60°C or higher and lower than 100°C. (Method 7) 7. The method for manufacturing a substrate structure according to any one of Methods 1 to 6, wherein the material of the protective film is any one of TaO, TiO, SiOC, SiCN, TaN, and TiN. (Method 8) 8. The method for producing a substrate structure according to any one of methods 1 to 7, wherein the film formation step is performed by atomic layer deposition. (Method 9) the substrate structure is provided with an opening for discharging a liquid and a flow path communicating with the opening; The protective film is formed on the surface of the substrate structure and on the inner wall of the flow channel. 10. A method for manufacturing the substrate structure according to claim 9. [Explanation of symbols]

[0059] 1: first substrate, 4: adhesive, 5: second substrate, 8: third substrate, 10: protective film, 14: adhesive, 15: substrate assembly

Claims

1. A method for manufacturing a substrate structure having an organic film and a silicon substrate, comprising: a first ashing step of performing an ashing process on the substrate structure using oxygen plasma to remove organic matter at a first temperature while applying a first bias; a second ashing step of performing an ashing process at a second temperature higher than the first temperature while applying a second bias lower than the first bias to the substrate structure after the first ashing step, or without applying a bias; a film forming step of forming a protective film on the substrate structure that has been subjected to the second ashing step; A method for manufacturing a substrate structure having the above structure.

2. the organic film is an adhesive; 2. The method for manufacturing a substrate structure according to claim 1, wherein the substrate structure is a bonded body in which a plurality of the silicon substrates are bonded together with the adhesive.

3. The method for manufacturing a substrate structure according to claim 2 , wherein the adhesive is made of an organic material containing silicon.

4. 4. The method for manufacturing a substrate structure according to claim 3, wherein the adhesive is benzocyclobutene.

5. 5. The method for manufacturing a substrate structure according to claim 1, wherein the first temperature is lower than 60.degree.

6. 5. The method for manufacturing a substrate structure according to claim 1, wherein the second temperature is 60.degree. C. or higher and lower than 100.degree.

7. 5. The method for manufacturing a substrate structure according to claim 1, wherein the material of the protective film is any one of TaO, TiO, SiOC, SiCN, TaN, and TiN.

8. 5. The method for manufacturing a substrate structure according to claim 1, wherein the film formation step is performed by atomic layer deposition.

9. the substrate structure is provided with an opening for discharging a liquid and a flow path communicating with the opening; 5. The method for manufacturing a substrate structure according to claim 1, wherein the protective film is formed on the surface of the substrate structure and on the inner wall of the flow path.

Images