Joint and method for manufacturing the joint

Abstract

A joined body 1 comprises: a piezoelectric layer 11a formed from a piezoelectric material; a dielectric film 13 arranged under the piezoelectric layer 11a; a support substrate 14 joined to the piezoelectric layer 11a via the dielectric film 13; and a sacrificial layer that is provided between the support substrate 14 and the piezoelectric layer 11a and that is capable of forming a hollow section 17, wherein the dielectric film 13 includes SiO2 as a main component, and the hydrogen content, in terms of atomic ratio, is 0% to 1%. A joined body having a desired hollow section is provided thereby. Also provided is a method of manufacturing a joined body, in which method the etching rate of the dielectric film is small and it is possible to selectively remove the sacrificial layer when etching is performed.

Description

[Technical Field]

[0001] The present invention relates to a bonded body and a method for manufacturing the bonded body. [Background technology]

[0002] Among acoustic wave devices with a hollow structure, there is known a device in which SiO2 is provided as a dielectric film between a support substrate such as a silicon substrate and a piezoelectric substrate.

[0003] Patent Document 1 discloses an acoustic wave device having a hollow structure. The acoustic wave device includes a support substrate having a recess on its upper surface, a thin film disposed on the support substrate, a first main surface, and a second main surface opposing the first main surface, a piezoelectric substrate with the first main surface side disposed on the thin film, and an IDT electrode provided on the second main surface, in which a cavity is formed surrounded by the support substrate, the thin film, and at least the thin film of the piezoelectric substrate, and the thin film is disposed in a region on the first main surface of the piezoelectric substrate that is bonded to the support substrate via the thin film and in at least a portion of a region above the cavity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 147687 Summary of the Invention [Problem to be solved by the invention]

[0005] To form a hollow structure, for example, a method is used in which a film (sacrificial layer) made of a material different from the dielectric film is formed in the hollow portion, and then the sacrificial layer is removed by etching from a hole formed in the support substrate or piezoelectric substrate. In this case, if the difference in etching rate between the dielectric film and the sacrificial layer is small, there is a concern that not only the sacrificial layer but also the dielectric film will be etched, which may result in a bonded body having a desired hollow portion not being obtained. An object of the present invention is to provide a bonded structure having a desired hollow portion, and a method for manufacturing a bonded structure having a large difference in etching rate from a sacrificial layer, which allows the sacrificial layer to be selectively removed during etching. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a bonded body comprising: a piezoelectric layer made of a piezoelectric material; a dielectric film disposed below the piezoelectric layer; a support substrate bonded to the piezoelectric layer via the dielectric film; and a sacrificial layer provided between the support substrate and the piezoelectric layer and capable of forming a hollow portion, wherein the dielectric film is mainly composed of SiO2 and has an H content of 0% or more and 1% or less in atomic ratio.

[0007] The present invention also provides a bonded body comprising: a piezoelectric layer made of a piezoelectric material; a dielectric film disposed below the piezoelectric layer; a support substrate bonded to the piezoelectric layer via the dielectric film; and a hollow portion provided between the support substrate and the piezoelectric layer, wherein the dielectric film is mainly composed of SiO2 and has an H content of 0% or more and 1% or less in atomic ratio.

[0008] Furthermore, the present invention provides a method for manufacturing a bonded body, including a sacrificial layer formation step of forming a sacrificial layer on a piezoelectric substrate, a dielectric film formation step of forming a dielectric film mainly composed of SiO2 and having an H content of 0% or more and 1% or less in atomic ratio on the piezoelectric substrate and the sacrificial layer, a bonding step of bonding the dielectric film to a support substrate, a thinning step of thinning the piezoelectric substrate to obtain a piezoelectric layer, and a removal step of removing the sacrificial layer to form a hollow space between the support substrate and the piezoelectric layer.

[0009] Furthermore, the present invention provides a method for manufacturing a bonded body, including a sacrificial layer formation step of forming a sacrificial layer on a piezoelectric substrate, a dielectric film formation step of forming a dielectric film containing SiO2 as a main component and having a refractive index of 1.468 or more and 1.471 or less on the piezoelectric substrate and the sacrificial layer, a bonding step of bonding the dielectric film to a support substrate, a thinning step of thinning the piezoelectric substrate to obtain a piezoelectric layer, and a removal step of removing the sacrificial layer to form a hollow space between the support substrate and the piezoelectric layer. [Effects of the Invention]

[0010] It is possible to provide a bonded body having a desired hollow portion, and also to provide a method for manufacturing a bonded body in which the difference in etching rate between the bonded body and the sacrificial layer is large, and the sacrificial layer can be selectively removed during etching. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are diagrams illustrating a bonded body according to an embodiment of the present invention. [Figure 2] 10 is a flowchart illustrating a method for manufacturing a bonded body. [Figure 3] 3A to 3E are diagrams showing the states of the respective steps shown in FIG. [Figure 4] FIG. 1 is a diagram showing a reactive sputtering apparatus used when forming a dielectric film. [Figure 5] FIG. 1 is a diagram showing etching rates for levels 1 to 16. [Figure 6] FIG. 10 is a diagram showing the relationship between oxygen radical discharge output and etching rate. [Figure 7] FIG. 10 is a diagram showing the relationship between the flow rate of argon gas and the etching rate. [Figure 8] FIG. 10 is a diagram showing the relationship between the refractive index of SiO 2 and the etching rate. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0013] <Explanation of the structure of the junction> FIG. 1 is a diagram showing a bonded body 1 of the present embodiment. The bonded body 1 shown in the figure has a structure in which, from the top in the figure, a piezoelectric layer 11a, a dielectric film 13, and a support substrate 14 are laminated in this order. In addition, a hollow portion 17 is provided between the support substrate 14 and the piezoelectric layer 11a.

[0014] The piezoelectric layer 11a is a layer made of a piezoelectric material. The piezoelectric material is selected depending on the application of the bonded body 1. Examples of the piezoelectric material include, but are not limited to, LiNbO3 (LN) and LiTaO3 (LT), and examples of the piezoelectric material include silicon (Si), gallium arsenide (GaAs), silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), and solid solution ceramics (PZT).

[0015] The dielectric film 13 is a layer disposed below the piezoelectric layer 11a. As will be described in detail later, the dielectric film 13 is mainly composed of SiO2. That is, the dielectric film 13 can also be said to be an SiO2 film or an SiO2 layer. The dielectric film 13 has an H (hydrogen) content of 0% or more and 1% or less in terms of atomic ratio. In the dielectric film 13 mainly composed of SiO2, the refractive index of SiO2 is preferably 1.468 or more and 1.471 or less. Within this range, it is easy to control the etching rate to 200 nm / min or less. The refractive index of SiO2 can be measured, for example, using a spectroscopic ellipsometer, and a wavelength of 633 nm can be used.

[0016] The support substrate 14 serves as a support for the entire bonded body 1. The support substrate 14 is bonded to the piezoelectric layer 11a via the dielectric film 13. Any appropriate substrate can be used as the support substrate 14. The support substrate 14 may be made of a single crystal or a polycrystalline material. It may also be made of a metal.

[0017] The material constituting the support substrate 14 is preferably selected from the group consisting of silicon, sialon, sapphire, cordierite, mullite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), and brass. The thickness of the support substrate 14 is, for example, 0.3 to 1 mm, but any other appropriate thickness can be adopted.

[0018] The silicon may be single crystal silicon, polycrystalline silicon, or high resistance silicon, and the support substrate 14 may be SOI (Silicon on Insulator).

[0019] Typically, the sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina. For example, Si 6-w Al w O w N 8-w Specifically, sialon has a composition in which alumina is mixed into silicon nitride, and w in the formula indicates the mixing ratio of alumina. w is preferably 0.5 or more and 4.0 or less.

[0020] Typically, the sapphire is a single crystal having a composition of Al2O3, and the alumina is a polycrystalline material having a composition of Al2O3. The alumina is preferably translucent alumina.

[0021] Typically, the cordierite is a ceramic having a composition of 2MgO·2Al2O3·5SiO2, and the mullite is a ceramic having a composition in the range of 3Al2O3·2SiO2 to 2Al2O3·SiO2.

[0022] In this embodiment, the hollow portion 17 is formed in a recess provided in the dielectric film 13. Holes 16a and 16b are formed in the piezoelectric layer 11a, and the holes 16a and 16b communicate with the hollow portion 17.

[0023] <device> The structure of the bonded body 1 shown in the figure can be used as the structure of various devices, such as high-frequency devices, power semiconductors, semiconductor lasers, surface acoustic wave filters (SAW (Surface Acoustic Wave) filters), thin-film piezoelectric MEMS (Micro Electro Mechanical Systems), etc.

[0024] <Description of Manufacturing Method of Bonded Body 1> Next, a method for manufacturing the bonded body 1 will be described. 2 is a flowchart illustrating a method for manufacturing the bonded body 1. Also, FIGS. 3(A) to 3(E) are diagrams showing the states corresponding to the respective steps shown in FIG. First, a piezoelectric substrate 11 is prepared, and a sacrificial layer 12 is formed on the piezoelectric substrate 11 (step 101: sacrificial layer formation process) (FIG. 3(A)). The sacrificial layer 12 will be removed in a later process to form a hollow portion 17. Therefore, the sacrificial layer 12 is formed where the hollow portion 17 is to be formed. The sacrificial layer 12 can be made of metals such as Ni, Cu, Al, Si, insulating films such as SiO2, ZnO, and PSG (phosphosilicate glass), organic films, etc. The sacrificial layer 12 can be formed by vapor deposition, sputtering, CVD, spin coating, etc.

[0025] Furthermore, a dielectric film 13 containing SiO2 as a main component and having an H content of 0% to 1% in terms of atomic ratio is formed on the piezoelectric substrate 11 and the sacrificial layer 12 (step 102: dielectric film forming step) (FIG. 3(B)). In this case, the dielectric film 13 is formed so as to cover the piezoelectric substrate 11 and the sacrificial layer 12. The method for forming the dielectric film 13 will be described in detail later.

[0026] Next, a support substrate 14 is prepared, and the dielectric film 13 and the support substrate 14 are bonded together (step 103: bonding step) (FIG. 3(C)). This step is performed, for example, by using a plasma activated bonding (PAB) method in which the bonding surfaces of the dielectric film 13 and the support substrate 14 are surface-treated and activated in a vacuum, thereby bonding them together at room temperature. When bonding the dielectric film 13 and the support substrate 14, a dielectric film (SiO2) may be formed on a portion of the support substrate 14, and the portion of the dielectric film formed on the support substrate 14 may be plasma-activatedly bonded to the dielectric film 13 formed on the piezoelectric substrate 11.

[0027] Then, the piezoelectric substrate 11 is polished to form the piezoelectric layer 11a (step 104) (FIG. 3(D)).

[0028] Alternatively, a method may be used in which hydrogen ions or helium ions are implanted into the surface of the piezoelectric substrate 11 in step 101, and the depth at which the ions are implanted is used as the separation surface in step 104, thereby separating the piezoelectric substrate 11a. Either method may be employed in this embodiment. Regardless of which method is employed, step 104 can be considered as a thinning process in which the piezoelectric substrate 11 is thinned to obtain the piezoelectric layer 11a.

[0029] To function as a surface acoustic wave filter, an upper electrode and an IDT (Interdigital Transducer) electrode may be formed on the piezoelectric layer 11a. These electrodes are made of a conductive material such as Al (aluminum). These electrodes can be formed by, for example, a deposition lift-off method.

[0030] Furthermore, the sacrificial layer 12 is removed to form a hollow portion 17 between the support substrate 14 and the piezoelectric layer 11a (step 105: removal process) (FIG. 3(E)). To do this, first, a resist film is patterned by photolithography, and then an etching gas is introduced to form holes 16a and 16b. These holes 16a and 16b penetrate the piezoelectric layer 11a and reach the sacrificial layer 12. Then, an etching gas or an etching solution is introduced through the holes 16a and 16b to remove the sacrificial layer 12. As a result, the location where the sacrificial layer 12 was formed becomes a hollow portion 17. That is, the sacrificial layer 12 is removed by dry etching or wet etching to form the hollow portion 17.

[0031] 3(E), a protective layer made of an insulating film may be formed on the piezoelectric layer 11a, the upper electrode, and the IDT electrode. Furthermore, external terminals may be formed on the upper electrode and the IDT electrode. The above steps can be considered to be the bonded body of this embodiment as shown in FIG. 3(D) and FIG. 3(E).

[0032] <Method for forming dielectric film 13> Next, a method for forming the dielectric film 13 will be described in detail. Fig. 4 is a diagram showing a reactive sputtering apparatus 100 used when forming the dielectric film 13. That is, Fig. 4 shows an apparatus used when performing step 102 in Fig. 2 and the process in Fig. 3(B). The illustrated reactive sputtering apparatus 100 includes a chamber 110, a rotating drum-type substrate holder 120 disposed within the chamber 110, a target 131 disposed within the reactive sputtering apparatus 100, a sputtering power supply 132, a radical oxidation source 141, and a radical source power supply 142.

[0033] The reactive sputtering apparatus 100 performs reactive sputtering using silicon (Si) as a target 131, oxygen (O) gas, and argon (Ar) gas. A piezoelectric substrate 11 (FIG. 3A) with a sacrificial layer 12 formed thereon is placed on a rotating drum-type substrate holder 120. Argon gas is introduced directly into the chamber 110, while oxygen gas is first radicalized by a radical oxidation source 141 and then introduced into the chamber 110 as oxygen radicals. The silicon constituting the target 131 is then sputtered by a sputtering power supply 132 to form a silicon film on the piezoelectric substrate 11 and the sacrificial layer 12. This silicon film is then oxidized by the oxygen radicals to form a silicon oxide (SiO) film. This allows the formation of a dielectric film 13 primarily composed of SiO. The rotating drum-type substrate holder 120 can accommodate multiple film-forming targets. By rotating the rotating drum-type substrate holder 120 and changing the film-forming conditions, the dielectric film 13 can be formed under various film-forming conditions. The film formation conditions include the flow rate of argon gas, the flow rate of oxygen gas, the oxygen radical discharge output, and the sputtering discharge output.

[0034] In this embodiment, a dielectric film 13 is formed that is mainly composed of SiO2 and has an H content of 0% to 1% in atomic ratio. From the viewpoint of making the dielectric film 13 less susceptible to etching and making it easier to selectively etch the sacrificial layer 12, the H content is preferably 0.1% to 1.0%, and more preferably 0.2% to 0.9%. To obtain such a dielectric film 12, it is preferable to use at least one of the following (1) and (2) as film formation conditions. (1) The discharge output of oxygen radicals is 3000 W as the standard, and the ratio is between 1 and 1.5. In other words, the discharge output of oxygen radicals is between 3000 W and 4500 W. (2) When introducing argon gas, the flow rate is 400 sccm (Standard Cubic Centimeter per Minute), and the ratio is 0.81 or more and 1 or less. In other words, the flow rate of argon gas is 324 sccm or more and 400 sccm or less. Note that sccm is the gas flow rate (cm) converted to the value at 1 atmosphere and 0°C. 3 / min).

[0035] This makes it possible to form a dielectric film 13 with a low etching rate. This also means that it is possible to form a dielectric film 13 with a large difference in etching rate from the sacrificial layer 12. As a result, it is possible to provide a bonded body 1 having a hollow portion 17 of a desired size at a desired position. It is also possible to provide a method for manufacturing a bonded body having a large difference in etching rate from the sacrificial layer 12, allowing the sacrificial layer 12 to be selectively removed during etching. [Example]

[0036] <Preparation of Dielectric Film 13> Using the reactive sputtering apparatus 100 shown in Figure 4, a dielectric film 13 made of SiO2 was produced under the film formation conditions shown in Table 1 below. The thickness of the dielectric film 13 was set to 500 nm. Hereinafter, the case where the discharge output of oxygen radicals was 3000 W or the flow rate of argon gas when introduced was 400 sccm may be referred to as the standard conditions. Table 1 below shows the ratio of each parameter when the standard condition is set to 1. The flow rate of oxygen gas and the sputtering discharge output were all constant.

[0037] As shown in Table 1, the dielectric film 13 was formed under 16 film formation conditions, levels 1 to 16. Of these, levels 1 to 4, 11, and 16 satisfy both the film formation conditions (1) and (2) above. Levels 5, 8, 12, 13, and 15 satisfy the film formation condition (2) above, but do not satisfy the film formation condition (1) above. Furthermore, levels 6, 7, and 10 satisfy the film formation condition (1) above, but do not satisfy the film formation condition (2) above. Furthermore, levels 9 and 14 do not satisfy both the film formation conditions (1) and (2) above.

[0038] [Table 1]

[0039] <Evaluation> The etching rate of the dielectric film 13 was evaluated. Buffered hydrofluoric acid was used for etching. The thickness of the dielectric film 13 before and after etching was calculated using a spectroscopic ellipsometer, and the etching rate was calculated from the difference in film thickness and the etching time. In this case, an etching rate of 200 nm / min or less was considered to be acceptable, and an etching rate of more than 200 nm / min was considered to be unacceptable.

[0040] <Evaluation results> The evaluation results are explained below. FIG. 5 is a diagram showing the etching rates of levels 1 to 16. In FIG. 5, the horizontal axis represents levels 1 to 16, and the vertical axis represents the etching rate of the dielectric film 13. As shown in FIG. 5, in levels 8, 9, 12, and 14, the etching rate of the dielectric film 13 exceeded 200 nm / min and the results were unacceptable. It can be said that these dielectric films 13 are easily etched together with the sacrificial layer 12 during etching. In contrast, the others had etching rates of 200 nm / min or less and were acceptable. It can be said that these dielectric films 13 are difficult to etch and are easy to selectively etch the sacrificial layer 12. Therefore, it can be said that levels 1 to 7, 10, 11, 13, 15 and 16 are examples of the present invention, and levels 8, 9, 12 and 14 are comparative examples of the present invention.

[0041] Using the results of Figure 5, a regression analysis was performed to obtain a leverage plot for each deposition parameter, and the following relationship was obtained.

[0042] FIG. 6 is a diagram showing the relationship between oxygen radical discharge output and etching rate. In FIG. 6, the horizontal axis represents the oxygen radical discharge output, and the vertical axis represents the etching rate. 6 shows a regression curve K and a reliability curve S for the regression line. According to this, it can be said that the etching rate depends on the oxygen radical discharge output.

[0043] FIG. 7 is a diagram showing the relationship between the flow rate of argon gas and the etching rate. In FIG. 7, the horizontal axis represents the flow rate of argon gas (illustrated as Ar flow rate), and the vertical axis represents the etching rate. 7, the regression curve K and the reliability curve S for the regression line are shown by dotted lines. According to this, it can be said that the etching rate depends on the flow rate of argon gas.

[0044] Furthermore, the compositions of the dielectric films 13 of levels 1, 3, 7, 8, 12, 14, 15, and 16 were analyzed by RBS (Rutherford Backscattering Spectrometry). The results are shown in Table 2 below.

[0045]

Table 2

[0046] According to Table 2, the higher the etching rate, the higher the H content. When it exceeds 1% as in level 8, the etching rate becomes about 1.5 times that under standard conditions.

[0047] When performing the etching to form the hollow portion 17, in order to increase the etching rate difference from the sacrificial layer 12, a dielectric film 13 made of SiO2 with a low etching rate is desirable. From the results of this time, it can be seen that in order to obtain a dielectric film 13 with an etching rate of 200 nm / min or less, the H content in SiO2 is desirably 0% or more and 1% or less. Also, the higher the oxygen radical discharge output, the more difficult it is to perform etching (Fig. 6), and the lower the flow rate of argon gas, the more difficult it is to perform etching (Fig. 7). As standard conditions, when the oxygen radical discharge output is set to 3000 W and the standard condition is set to 1, the oxygen radical discharge output is preferably 1 or more and 1.5 or less. On the other hand, when the flow rate of argon gas is set to the standard 400 sccm and the standard condition is set to 1, it is preferably 0.81 or more and 1 or less. Also, when both of these film formation conditions for the oxygen radical discharge output and the flow rate of argon gas are satisfied, the etching rate becomes even smaller, which is more preferable as the film formation condition.

[0048] <Relationship between refractive index of SiO2 and etching rate> The refractive index of SiO2 formed as the dielectric 13 under the film formation conditions of this time was measured. The measurement of the refractive index was performed using a spectroscopic ellipsometer, and the refractive index at a wavelength of 633 nm was obtained. Fig. 8 is a diagram showing the relationship between the refractive index of SiO2 and the etching rate. According to Fig. 8, it can be seen that there is a correlation between the refractive index of SiO2 and the etching rate. In order to obtain a dielectric film 13 with an etching rate of 200 nm / min, the refractive index is preferably 1.468 or more and 1.471 or less.

[0049] Although the present embodiment has been described above, the technical scope of the present invention is not limited to the scope of the above embodiment. It is clear from the claims that various modifications and improvements to the above embodiment are also included in the technical scope of the present invention. [Explanation of symbols]

[0050] 1...bonded body, 11...piezoelectric substrate, 11a...piezoelectric layer, 12...sacrificial layer, 13...dielectric film, 14...support substrate, 17...hollow portion

Claims

1. a piezoelectric layer made of a piezoelectric material; a dielectric film disposed under the piezoelectric layer; a support substrate bonded to the piezoelectric layer via the dielectric film; a sacrificial layer provided between the support substrate and the piezoelectric layer, the sacrificial layer being capable of forming a hollow portion by selectively removing the sacrificial layer by etching after the dielectric film is formed; Equipped with The dielectric film is provided on the sacrificial layer and is made of SiO ２ The main component is a ferroelectric material having a hydrogen content of 0.1% or more and 1.0% or less in terms of atomic ratio. zygote.

2. The dielectric film is made of SiO ２ 2. The bonded body according to claim 1, wherein the bonded body has a refractive index of 1.468 or more and 1.471 or less.

3. a piezoelectric layer made of a piezoelectric material; a dielectric film disposed on the piezoelectric layer; a support substrate bonded to the piezoelectric layer via the dielectric film; a hollow portion provided in the dielectric film between the support substrate and the piezoelectric layer, the hollow portion being formed by selectively removing a sacrificial layer by etching after the dielectric film is formed; Equipped with The dielectric film is made of SiO ２ The main component is a ferroelectric material having a hydrogen content of 0.1% or more and 1.0% or less in terms of atomic ratio. zygote.

4. a sacrificial layer forming step of forming a sacrificial layer on the piezoelectric substrate; On the piezoelectric substrate and the sacrificial layer, SiO ２ a dielectric film forming step of forming a dielectric film having a main component of the above and a hydrogen content of 0.1% or more and 1.0% or less in terms of atomic ratio; a bonding step of bonding the dielectric film to a support substrate; a thinning step of thinning the piezoelectric substrate to obtain a piezoelectric layer; a removing step of selectively removing the sacrificial layer by etching to form a hollow portion between the support substrate and the piezoelectric layer; A method for producing a bonded body comprising the steps of:

5. the dielectric film forming step includes forming the dielectric film using a reactive sputtering apparatus that uses silicon as a target and introduces oxygen radicals and argon gas; 5. The method for producing a bonded body according to claim 4, wherein the discharge output of the oxygen radicals is 3000 W as a standard, and the ratio of the discharge output to the oxygen radicals is 1 or more and 1.5 or less.

6. the dielectric film forming step includes forming the dielectric film using a reactive sputtering apparatus that uses silicon as a target and introduces oxygen radicals and argon gas; 6. The method for producing a bonded body according to claim 4, wherein the flow rate of the argon gas when introduced is 400 sccm (Standard Cubic Centimeter per Minute) and the ratio of the flow rate to the standard is 0.81 or more and 1 or less.

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