Joined body and method of manufacturing joined body

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

Joint and method for manufacturing the joint

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

[0002] In an acoustic wave device with a hollow structure, a dielectric film of SiO is placed between a support substrate such as a silicon substrate and a piezoelectric substrate. ２ Devices having such a configuration are known.

[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, wherein 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.

[0004] International Publication No. 2016 / 147687

[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 through a hole formed in a support substrate or a 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. As a result, it may be impossible to obtain a bonded body with a desired hollow portion. The present invention aims to provide a bonded body with a desired hollow portion. Another aim of the present invention is to provide a method for manufacturing a bonded body in which the difference in etching rate between the dielectric film and the sacrificial layer is large, allowing the sacrificial layer to be selectively removed during etching.

[0006] In order to solve the above problems, the present invention provides a piezoelectric element comprising: 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; 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 made of SiO ２The present invention provides a bonded body having a main component of the above and a hydrogen content of 0% or more and 1% or less in terms of atomic ratio.

[0007] The present invention also provides a piezoelectric element comprising 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, and a hollow portion provided between the support substrate and the piezoelectric layer, wherein the dielectric film is made of SiO ２ The present invention provides a bonded body having a main component of the above and a hydrogen content of 0% or more and 1% or less in terms of atomic ratio.

[0008] Furthermore, the present invention provides a method for forming a sacrificial layer on a piezoelectric substrate, and a method for forming a sacrificial layer on the piezoelectric substrate and the sacrificial layer. ２ The present invention provides a method for manufacturing a bonded body, the method including: a dielectric film formation step of forming a dielectric film having a main component of SiO 2 and having an H content of 0% or more and 1% 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; and a removal step of removing a sacrificial layer to form a hollow portion between the support substrate and the piezoelectric layer.

[0009] Furthermore, the present invention also provides a method for forming a sacrificial layer on a piezoelectric substrate, and a method for forming a sacrificial layer on the piezoelectric substrate and the sacrificial layer. ２ The present invention provides a method for manufacturing a bonded body, the method including: a dielectric film formation step of forming a dielectric film having a refractive index of 1.468 or more and 1.471 or less, the dielectric film being mainly composed of a material selected from the group consisting of methyl methacrylate and methyl methacrylate; 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 a sacrificial layer to form a hollow space between the support substrate and the piezoelectric layer.

[0010] It is possible to provide a bonded body having a desired hollow portion. It is also possible 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.

[0011] FIG. 1 is a diagram showing a bonded body according to the present embodiment; FIG. 2 is a flowchart illustrating a method for manufacturing a bonded body; (A) to (E) are diagrams illustrating the states for each step shown in FIG. 2; FIG. 1 is a diagram showing a reactive sputtering apparatus used when forming a dielectric film; FIG. 2 is a diagram showing etching rates for levels 1 to 16; FIG. 3 is a diagram showing the relationship between oxygen radical discharge output and etching rate; FIG. 3 is a diagram showing the relationship between the flow rate of argon gas and etching rate; ２ 1 is a diagram showing the relationship between the refractive index and the etching rate.

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

[0013] 1 is a diagram showing a bonded body 1 according to 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. 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. For example, the piezoelectric material is LiNbO ３ (LN) and LiTaO ３ (LT), but is not limited to this, and silicon (Si), gallium arsenide (GaAs), silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), solid solution ceramics (PZT), etc. may be appropriately selected.

[0015] The dielectric film 13 is a layer disposed under the piezoelectric layer 11a. As will be described in detail later, the dielectric film 13 is made of SiO ２ That is, the dielectric film 13 is mainly composed of SiO ２ Film and SiO ２ The dielectric film 13 has an H (hydrogen) content of 0% or more and 1% or less in terms of atomic ratio. ２ The dielectric film 13 mainly contains SiO ２The refractive index of SiO is preferably 1.468 or more and 1.471 or less. When the refractive index is in this range, the etching rate can be easily controlled to 200 nm / min or less. ２ The refractive index can be measured, for example, by a spectroscopic ellipsometer, using a wavelength of 633 nm.

[0016] The support substrate 14 serves as a support for the entire bonded structure 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-resistivity silicon. 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, and for example, Si ６－ｗ Al ｗ O ｗ N ８－ｗ Specifically, sialon has a composition in which alumina is mixed in 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 Al ２ O ３ The alumina is a single crystal having a composition of Al ２ O ３The alumina is preferably a translucent alumina.

[0021] Typically, the cordierite is 2MgO.2Al ２ O ３ 5SiO ２ The mullite is a ceramic having a composition of 3Al ２ O ３ 2SiO ２ ~2Al ２ O ３ SiO ２ It is a ceramic having a composition in the range of

[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 (SAW) filters, thin-film piezoelectric MEMS (Micro Electro Mechanical Systems), etc.

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

[0025] Furthermore, on the piezoelectric substrate 11 and the sacrificial layer 12, SiO ２ A dielectric film 13 is formed having a main component of SiO 2 and an H content of 0% to 1% in terms of atomic ratio (step 102: dielectric film formation step) (FIG. 3B). 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. 3C). This step is performed, for example, by using a plasma activated bonding (PAB) method, which bonds the dielectric film 13 and the support substrate 14 at room temperature by surface treating and activating the bonding surfaces of the dielectric film 13 and the support substrate 14 in a vacuum. When bonding the dielectric film 13 and the support substrate 14 together, a dielectric film (SiO ２ ) may be formed, and a part of the dielectric film formed on this support substrate 14 may be plasma activated and bonded to the dielectric film 13 formed on the piezoelectric substrate 11 described above.

[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 represent the bonded body of this embodiment, as shown in FIGS. 3(D) and 3(E).

[0032] <Method of Forming Dielectric Film 13> Next, a method of 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 of Fig. 3(B). The reactive sputtering apparatus 100 shown in the figure includes a chamber 110, a rotary drum type substrate holder 120 arranged in the chamber 110, a target 131 arranged in 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 device 100 uses silicon (Si) as a target 131 and oxygen (O ２This is an apparatus for performing reactive sputtering using oxygen (O) gas and argon (Ar) gas. A piezoelectric substrate 11 (FIG. 3A) on which a sacrificial layer 12 is formed is placed on a rotary drum type substrate holder 120. In this case, argon gas is introduced directly into the chamber 110, but oxygen gas is radicalized in advance by a radical oxidation source 141 and introduced into the chamber 110 as oxygen radicals. 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, which is then oxidized by oxygen radicals to form silicon oxide (SiO ２ ) film. ２ It is possible to form a dielectric film 13 containing a main component of the above. Furthermore, a plurality of film formation targets can be placed on the rotary drum type substrate holder 120, and by changing the film formation conditions while rotating the rotary drum type substrate holder 120, it is possible to form the dielectric film 13 under various film formation 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, SiO ２ The dielectric film 13 is formed using a material having a hydrogen content of 0% to 1% in atomic ratio as a main component. 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 hydrogen 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, for example, at least one of the following (1) and (2) as film formation conditions. (1) The oxygen radical discharge output is 3000 W, and the ratio is 1 to 1.5. That is, the oxygen radical discharge output is 3000 W to 4500 W. (2) The flow rate of argon gas introduced is 400 sccm (standard cubic centimeter per minute), and the ratio is 0.81 to 1. That is, the argon gas flow rate is 324 sccm to 400 sccm. Note that sccm is the gas flow rate (cm) converted to a value at 1 atmosphere and 0°C. ３ / min).

[0035] This makes it possible to form the dielectric film 13 with a low etching rate. This also means that it is possible to form the dielectric film 13 with a large difference in etching rate from the sacrificial layer 12. As a result, it is possible to provide the bonded body 1 having the 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.

[0036] <Preparation of Dielectric Film 13> Using the reactive sputtering apparatus 100 shown in FIG. 4, a SiO ２ A dielectric film 13 made of the above was fabricated. 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 will be referred to as the standard conditions. Table 1 below shows the ratio of each parameter when the standard conditions are set to 1. The flow rate of oxygen gas and the sputtering discharge output were set to the same value.

[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 either the film formation conditions (1) or (2) above.

[0038]

[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 described below. FIG. 5 shows the etching rates for 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, levels 8, 9, 12, and 14 failed because the etching rate of the dielectric film 13 exceeded 200 nm / min. These dielectric films 13 are easily etched along with the sacrificial layer 12 during etching. In contrast, the other levels passed because the etching rate was 200 nm / min or less. These dielectric films 13 are difficult to etch and easily selectively etch the sacrificial layer 12. Therefore, levels 1 to 7, 10, 11, 13, and 15 to 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 oxygen radical discharge output, and the vertical axis represents etching rate. Fig. 6 also shows a regression curve K and a reliability curve S for the regression line. From this, it can be said that the etching rate depends on the oxygen radical discharge output.

[0043] 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 (shown as Ar flow rate), and the vertical axis represents the etching rate. In FIG. 7, the regression curve K and the reliability curve S for the regression line are shown by dotted lines. From this, it can be said that the etching rate depends on the flow rate of argon gas.

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

[0045]

[0046] According to Table 2, the higher the etching rate, the greater the H content, and when it exceeded 1%, as in level 8, the etching rate was about 1.5 times that of the standard conditions.

[0047] When etching is performed to form the hollow portion 17, in order to make a large difference in etching rate with the sacrificial layer 12, SiO ２ From the results of this study, in order to obtain a dielectric film 13 having an etching rate of 200 nm / min or less, it is necessary to use SiO ２ It can be seen that the H content in the film is preferably 0% or more and 1% or less. Furthermore, the higher the oxygen radical discharge output, the more difficult the etching (FIG. 6), and the lower the argon gas flow rate, the more difficult the etching (FIG. 7). When the oxygen radical discharge output is set to 3000 W as the standard condition and the standard condition is defined as 1, the oxygen radical discharge output is preferably 1 or more and 1.5 or less. On the other hand, when the argon gas flow rate is set to 400 sccm as the standard condition and the standard condition is defined as 1, the oxygen radical discharge output is preferably 0.81 or more and 1 or less. Furthermore, when these film formation conditions are satisfied for both the oxygen radical discharge output and the argon gas flow rate, the etching rate becomes even smaller, which is even more preferable as a film formation condition.

[0048] <SiO ２Relationship between refractive index and etching rate of SiO ２ The refractive index was measured using a spectroscopic ellipsometer, and the refractive index at a wavelength of 633 nm was obtained. ２ 8 is a graph showing the relationship between the refractive index and the etching rate of SiO ２ It can be seen that there is a correlation between the refractive index and the etching rate. 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.

[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; 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.

2. The dielectric film is made of SiO ２ The bonded body according to claim 1 , which 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 between the support substrate and the piezoelectric layer; 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 and an H 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 removing the sacrificial layer 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 forms the dielectric film by using a reactive sputtering apparatus that uses silicon as a target and introduces oxygen radicals and argon gas; 5. The method for producing a joint body according to claim 4, wherein a ratio of a discharge output of the oxygen radicals to a standard output of 3000 W is 1 or more and 1.5 or less.

6. The dielectric film forming step forms the dielectric film by 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 being introduced is 0.81 or more and 1 or less when 400 sccm (Standard Cubic Centimeter per Minute) is used as a standard.