Surface acoustic wave device and method for manufacturing same

Abstract

The invention provides a surface acoustic wave device and a manufacturing method thereof. The surface acoustic wave device includes: a semiconductor support substrate; a modified substrate surface layer formed on the surface of the support substrate; a low sound velocity layer formed on the modified substrate surface layer; a piezoelectric layer formed on the low sound velocity layer; and a plurality of I DT electrodes disposed on the piezoelectric layer, in which the surface roughness on the surface layer side of the modified substrate is 0.2 nm or less.

Description

Technical Field

[0001] The present invention relates to a surface acoustic wave device and a method for manufacturing the same, and in particular to a surface acoustic wave device and a method for manufacturing the same that can prevent high-frequency loss increase and Q value degradation and simplify the manufacturing process by forming a modified substrate surface layer on the surface of a supporting substrate. Background Art

[0002] like Figure 1 As shown in FIG. 3 , a structure in which a high acoustic velocity layer 110, a low acoustic velocity layer 120, and a piezoelectric layer 130 are sequentially stacked on a support substrate 100 is well known as a technique for improving the Q value of a surface acoustic wave (SAW) resonator. Alternatively, when a high acoustic velocity support substrate 101 as shown in FIG. 3 is used, the high acoustic velocity layer is acoustically unnecessary and can be omitted.

[0003] When a silicon substrate as a semiconductor is used as a high acoustic velocity support substrate, a problem is that a parasitic conductive layer is generated at the silicon substrate interface due to the interaction between carriers contained in SiO2 as an oxide and the silicon substrate as a semiconductor, and high-frequency loss increases, and the Qmax of the SAW resonator is significantly deteriorated. Even if the silicon substrate is designed to have a high resistivity of 4 to 10 kΩ·cm, high-frequency loss is still not resolved.

[0004] In order to suppress the carriers passing through the silicon interface, one can Figure 2 As shown, amorphous silicon (a-Si) or polycrystalline silicon (poly Si) is stacked on a silicon substrate, or a trap-rich layer 102 is formed by ion implantation. The trap-rich layer 102 can prevent the reduction of silicon interface resistance by reducing the mobility of carriers. Amorphous silicon or polycrystalline silicon can also serve as a high acoustic velocity layer because its surface acoustic wave velocity is higher than that of LiTaO3 or LiNbO3 used as a piezoelectric layer.

[0005] In order to fully suppress high-frequency loss, it is necessary to use low-pressure chemical vapor deposition (LPCVD) equipment, plasma-enhanced chemical vapor deposition (PECVD) equipment, or sputtering equipment to deposit an amorphous silicon or polycrystalline silicon layer to a thickness of about 400 to 1000 nm. Compared with PECVD or sputtering equipment, LPCVD equipment is suitable for depositing a trap-rich layer because it has lower equipment cost and higher productivity.

[0006] In the case of implanting ions on the silicon surface, when argon (Ar) is used as the ion, an amorphous layer of about 50 nm in depth may be formed. The problem with ion implantation equipment is that it requires investment in high-cost equipment compared to LPCVD equipment, and the manufacturing cost increases due to reduced productivity. Summary of the invention

[0007] The present invention aims to solve the technical problem and provide a surface acoustic wave device with reduced manufacturing cost compared with a four-layer stacked structure while reducing high-frequency losses and minimizing the degradation of Q performance.

[0008] The technical problems of the present invention are not limited to the above-mentioned technical problems, and other unmentioned technical problems will be clearly understood by those skilled in the art from the following description.

[0009] In order to solve the technical problem, a surface acoustic wave device according to some embodiments of the present invention includes: a supporting substrate; a modified substrate surface layer formed on the surface of the supporting substrate; a low acoustic velocity layer formed on one side of the modified substrate surface layer; a piezoelectric layer formed on the low acoustic velocity layer; and a plurality of IDT electrodes arranged on the piezoelectric layer, wherein the surface roughness of one side of the modified substrate surface layer can be 0.2 nm or less.

[0010] In some embodiments of the present invention, the modified substrate surface layer may include an amorphous layer of a material constituting the support substrate, and the surface roughness may be the roughness of an interface between the support substrate and the low acoustic velocity layer.

[0011] In some embodiments of the present invention, the modified substrate surface layer may contain any one of argon, helium, krypton, and xenon.

[0012] In some embodiments of the present invention, the thickness of the modified substrate surface layer may be 10 nm or less.

[0013] In some embodiments of the present invention, when the wavelength of the surface elastic wave determined by the arrangement interval of the plurality of IDT electrodes is λ, the thicknesses of the piezoelectric layer and the low acoustic velocity layer may be 1λ or less.

[0014] In some embodiments of the present invention, the support substrate may include at least one of a silicon substrate, silicon carbide and gallium nitride.

[0015] In order to solve the technical problem, a surface acoustic wave device manufacturing method according to some embodiments of the present invention includes the following steps: forming a modified substrate surface layer by plasma surface treatment of the surface of a supporting substrate; forming a low acoustic velocity layer on the piezoelectric layer; and bonding the surfaces of the substrate surface layer and the low acoustic velocity layer.

[0016] In some embodiments of the present invention, the plasma surface treatment process may include plasma treatment using any one of argon, helium, krypton, and xenon, and the modified substrate surface layer may partially contain any one of the argon, helium, krypton, and xenon used in the plasma treatment.

[0017] In some embodiments of the present invention, the method for manufacturing a surface acoustic wave device may further include the step of forming a plurality of IDT electrodes on the piezoelectric layer, and when the wavelength of the surface elastic wave determined by the configuration interval of the plurality of IDT electrodes is λ, the thickness of the piezoelectric layer and the low acoustic velocity layer may be 1λ or less.

[0018] Details of other embodiments are included in the detailed description and accompanying drawings.

[0019] A surface acoustic wave device according to one embodiment of the present invention may provide almost the same performance as a surface acoustic wave device including a trap-rich layer while simplifying the manufacturing process, and thus may have significant advantages in terms of manufacturing cost and throughput.

[0020] The effects of the present invention are not limited to the above-mentioned effects, and other unmentioned effects will be clearly understood by those skilled in the art from the description of the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figures 1 to 3b is a diagram explaining a surface acoustic wave device according to the prior art.

[0022] Figure 4 is a cross-sectional view showing the configuration of a surface acoustic wave device according to one embodiment of the present invention.

[0023] Figure 5 1 is a diagram explaining the results of EDX analysis performed on a bonding unit between a supporting substrate having a modified substrate surface layer on the surface and a low acoustic velocity layer in a surface acoustic wave device according to an embodiment of the present invention.

[0024] Figure 6 This is a diagram comparing the surface roughness of the trap-rich layer formed by ion implantation.

[0025] Figure 7 1 is a graph explaining the relationship between the plasma process time and the thickness of the surface layer of the substrate modified into the amorphous layer in the surface acoustic wave device according to one embodiment of the present invention.

[0026] Figure 8 and 9 is a graph explaining the performance of a surface acoustic wave device according to one embodiment of the present invention.

[0027] Fig.10 is a flow chart illustrating a method for manufacturing a surface acoustic wave device according to an embodiment of the present invention.

[0028] Figures 11 to 13 FIG. 1 is a diagram showing intermediate steps for explaining a method for manufacturing a surface acoustic wave device according to an embodiment of the present invention.

[0029] Description of symbols

[0030] 100, 101: Support substrate

[0031] 105: Modified substrate surface layer

[0032] 110: High sound velocity layer

[0033] 120: Low sound velocity layer

[0034] 130: Piezoelectric layer

[0035] 150: IDT electrode DETAILED DESCRIPTION

[0036] By referring to the following and attached Figure 1 The advantages and features of the present invention and the methods for achieving them will become clear from the detailed description of the embodiments. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various different forms. These embodiments are only used to make the disclosure of the present invention complete and fully convey the scope of the present invention to those skilled in the art. The present invention is defined only by the scope of the claims. The same reference numerals represent the same elements throughout the specification.

[0037] When a component is referred to as being "connected to" or "coupled to" another component, it includes the case where it is directly connected or coupled to the other component and the case where other components are interposed therebetween. Conversely, when a component is referred to as being "directly connected to" or "directly coupled to" another component, it means that no other components are interposed therebetween. "And / or" includes each of the mentioned items and all combinations of one or more of the mentioned items.

[0038] The terms used in this specification are used to describe the embodiments rather than to limit the present invention. In this specification, the singular form also includes the plural form unless otherwise specified in a sentence. The terms "include ..." and / or "comprising ..." used in this specification mean that the components, steps, operations and / or elements mentioned do not exclude the existence or addition of one or more other components, steps, operations and / or elements.

[0039] Although the terms first, second, etc. are used to describe various components, these components are certainly not limited by these terms. These terms are only used to distinguish one component from another. Therefore, it goes without saying that the first component mentioned below may also be the second component within the technical spirit of the present invention.

[0040] Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used as the meanings commonly understood by those skilled in the art. In addition, unless clearly and specifically defined, terms defined in commonly used dictionaries will not be idealized or over-interpreted.

[0041] Figure 4is a cross-sectional view showing the configuration of a surface acoustic wave device according to one embodiment of the present invention.

[0042] refer to Figure 4 , a surface acoustic wave device according to an embodiment of the present invention may include a supporting substrate 101 , a modified substrate surface layer 105 , a low acoustic velocity layer 120 , a piezoelectric layer 130 , and a plurality of IDT electrodes 150 .

[0043] The support substrate 101 may include a material whose acoustic velocity of slow transverse waves is higher than the acoustic velocity of surface acoustic waves propagating in the piezoelectric layer 130, and may be made of any one of a silicon substrate, silicon carbide, and gallium nitride, but the present invention is not limited thereto. Hereinafter, the support substrate 101 is described as a high-resistivity silicon substrate having a resistivity of 4 kΩcm or more.

[0044] The low acoustic velocity layer 120 may be made of a material having an acoustic velocity lower than the acoustic velocity of the surface elastic wave of the piezoelectric layer 130, and may include, for example, one or more of silicon oxide (SiO2), tantalum pentoxide (Ta2O5), tellurium dioxide (TeO2), and the like.

[0045] The piezoelectric layer 130 includes a piezoelectric element and may generate an elastic wave from a signal applied to the plurality of IDT electrodes 150 , and may include a material such as LiTaO 3 (LT), LiNbO 3 (LN), or the like.

[0046] The plurality of IDT electrodes 150 are arranged on the piezoelectric layer 130 , and when the wavelength of the surface elastic wave determined by the arrangement interval of the plurality of IDT electrodes 150 is λ, the thickness of the piezoelectric layer 130 and the low acoustic velocity layer 120 may be 1λ or less.

[0047] The modified substrate surface layer 105 may be formed on the surface of the support substrate 101. The modified substrate surface layer 105 may include, for example, an amorphous layer formed by surface treating the support substrate 101 using argon plasma or the like. Therefore, the modified substrate surface layer 105 may include a material forming the support substrate 101 and a material for plasma surface treatment. Meanwhile, in addition to argon, an inert gas such as helium (He), neon (Ne), krypton (Kr), xenon (Xe), etc. may be used to perform plasma treatment on the support substrate 101, in which case the modified substrate surface layer 105 may partially contain the corresponding material.

[0048] Figure 51 is a diagram for explaining the results of energy dispersive spectroscopy (EDX) analysis performed on a bonding unit between a support substrate 101 having a modified substrate surface layer 105 on the surface and a low acoustic velocity layer 120 in a surface acoustic wave device according to an embodiment of the present invention. For the EDX analysis, a silicon substrate was used as the support substrate 101, silicon oxide was used as the low acoustic velocity layer 120, and the modified substrate surface layer 105 was formed for argon plasma surface treatment.

[0049] refer to Figure 5 , the upper part shows a transmission electron microscope (TEM) image of the bonding unit, and the lower part shows a graph of the EDX analysis results. In the graph, the horizontal axis represents depth and the vertical axis represents the content ratio of each material.

[0050] As shown in the EDX chart, the modified substrate surface layer 105 whose interface material is amorphous silicon is formed between the low acoustic velocity layer 120 and the supporting substrate 101, and it can be confirmed that a small amount of argon is detected inside the modified substrate surface layer 105 having a thickness of 10 nm or less. Since argon is not detected in the low acoustic velocity layer 120, the argon contained in the modified substrate surface layer 105 is not introduced when the low acoustic velocity layer 120 is deposited.

[0051] Since the modified substrate surface layer 105 is only thinly formed on the surface of the support substrate 101, its thickness may be much lower than that of the modified substrate surface layer 105 formed by using the above Figure 2 The described deposition process forms a thickness of 400 to 600 nm for the trap rich layer 102. The modified substrate surface layer 105 may be formed to have a thickness of 10 nm or less, which is a considerably lower thickness compared to the at least 50 nm thickness of the trap rich layer 102 formed by the deposition process.

[0052] When argon or the like is ion-implanted into the support substrate 101, the surface roughness of the support substrate 101 changes. As the acceleration voltage increases, the implant amount increases, and the implantation angle is optimized to increase the throughput of the ion implantation, the surface roughness increases.

[0053] Figure 6 This is a diagram comparing the surface roughness of the trap-rich layer formed by ion implantation.

[0054] refer to Figure 6 , the surface roughness Ra before ion implantation was 0.15 nm, but it was observed that the surface roughness Ra increased to about 1 to 2 nm after ion implantation. In order to bond the support substrate and the piezoelectric layer together by wafer bonding, the surface roughness must be 0.5 nm or less, preferably, 0.2 nm or less. Therefore, in order to apply wafer bonding to a piezoelectric layer having Figure 6 The support substrate with the surface roughness shown requires additional processing separately.

[0055] In contrast, when a modified substrate surface layer 105 is formed by plasma surface treatment, such as a surface acoustic wave device according to an embodiment of the present invention, the above-mentioned effect of increasing surface roughness does not occur, and a surface roughness of 0.2 nm or less can be easily obtained, which allows wafer bonding to be formed on one side 106 of the modified substrate surface layer 105 bonded to the low acoustic velocity layer 120.

[0056] Figure 7 1 is a graph explaining the relationship between the plasma process time and the thickness of the substrate surface layer 105 modified into an amorphous layer in the surface acoustic wave device according to one embodiment of the present invention.

[0057] refer to Figure 7 It is observed that as the duration of the plasma treatment increases, the thickness of the modified substrate surface layer 105 converges to about 10 nm. When the trap-rich layer is formed by the above-mentioned ion implantation or the like, a thickness as low as 50 nm to several hundred nanometers can be relatively easily obtained. However, in the case of plasma treatment using argon or the like, it is somewhat difficult to deeply modify the surface of the support substrate 101 by a much less energy-intensive process, rather than ion implantation. Therefore, a surface acoustic wave device according to one embodiment of the present invention includes a modified substrate surface layer 105 having a thickness as low as about 10 nm while maintaining a small change in surface roughness.

[0058] Figure 8 and 9 is a graph explaining the performance of a surface acoustic wave device according to one embodiment of the present invention.

[0059] First, refer to Figure 8 , which shows a graph of high frequency loss measured in a surface acoustic wave device according to an embodiment of the present invention. The yellow graph corresponds to Figure 4 The high frequency loss measured in the surface acoustic wave device of the present invention is shown in FIG. 1 , and the blue graph, the green graph, and the red graph correspond to the high frequency loss measured in FIG. Figure 2 , 3a Measured high frequency loss in the surface acoustic wave devices shown in 3a and 3b. In each case, the insertion loss method was used by patterning a coplanar waveguide (CPW) with aluminum on the surface of the stacked structure. The length of the CPW was 2 mm.

[0060] First, we see the high-frequency loss of the device with a three-layer structure of a supporting substrate, a low acoustic velocity layer, and a piezoelectric layer ( Figure 3a ), which shows a variation of 0.6 to 0.9 dB in each frequency band, while the high frequency loss of the device with only the piezoelectric layer ( Figure 3b ) varies from 0.19 to 0.32dB.

[0061] At the same time, it includes Figure 2 The four-layer structure of the trap-rich layer shown has an insertion loss of 0.14 to 0.24 dB in each band, which is a significant difference considering that the difference in insertion loss in a bandpass SAW filter is 0.1 dB.

[0062] Finally, it was confirmed that the insertion loss measured in the surface acoustic wave device having the structure formed with the modified surface substrate layer as shown in one embodiment of the present invention was 0.15 to 0.21 dB, which showed an insertion loss level similar to that of the surface acoustic wave device including the trap rich layer.

[0063] refer to Fig. 9 , which shows graphs of the admittance characteristic and the Q characteristic measured in a surface acoustic wave device according to an embodiment of the present invention. The yellow graph corresponds to Figure 5 The admittance and Q value measured in the surface acoustic wave device of the present invention are shown in FIG. 1 , and the blue graph, the green graph and the red graph correspond to the Figure 2 , 3a Measured admittance and Q values ​​in the SAW device shown in 3a and 3b.

[0064] First, a device having a three-layer structure of a support substrate, a low acoustic velocity layer, and a piezoelectric layer ( Figure 3a ) and devices with only piezoelectric layers ( Figure 3b ) have maximum Q values ​​of 1600 and 1800 respectively, which is similar to Figure 2 Compared with the maximum Q value of the device having the four-layer structure including the trap-rich layer shown, which is about 3900, it can be confirmed that the performance is significantly deteriorated.

[0065] In contrast, the maximum value of the Q value measured in the surface acoustic wave device having the structure in which the modified surface substrate layer is formed as shown in one embodiment of the present invention is about 3600, which is almost the same as Figure 2 The maximum values ​​of the devices in the same figure are the same, and the resonant frequency, antiresonant frequency, and electrostatic capacitance shown in the admittance characteristics are almost the same. Figure 2 The resonant frequency, anti-resonant frequency and electrostatic capacitance of the device are the same.

[0066] In summary, a surface acoustic wave device including a modified substrate surface layer according to an embodiment of the present invention can provide almost the same performance as a surface acoustic wave device including a trap-rich layer while simplifying the manufacturing process, thus potentially having significant advantages in manufacturing cost and throughput.

[0067] Fig.10 is a flow chart illustrating a method for manufacturing a surface acoustic wave device according to an embodiment of the present invention, Figures 11 to 13 are diagrams showing intermediate steps for explaining the manufacturing method.

[0068] refer to Fig.10According to an embodiment of the present invention, a surface acoustic wave device manufacturing method may include: a step S110 of depositing a low acoustic velocity layer on one side of a piezoelectric layer; a step S120 of forming a modified substrate surface layer by performing plasma surface treatment on a supporting substrate; and a step S130 of bonding the supporting substrate and the piezoelectric layer.

[0069] refer to Fig.11 , a step of depositing a low acoustic velocity layer 120 on one side of the piezoelectric layer 130 is performed. The piezoelectric layer 130 may include materials such as LiTaO3 (LT), LiNbO3 (LN), etc. The low acoustic velocity layer 120 may be formed by generating a material selected from silicon oxide (SiO2), tantalum pentoxide (Ta2O5), tellurium dioxide (TeO2), etc. by methods such as thermal oxidation, or by depositing the material by methods such as chemical vapor deposition (CVD), sputtering, etc. If necessary, the surface of the low acoustic velocity layer 120 may be ground by chemical mechanical polishing (CMP) or the like to reduce the surface roughness.

[0070] refer to Fig.12 , a modified substrate surface layer 105 is formed by performing plasma surface treatment on a support substrate 101. The surface of the support substrate 101 is modified into an amorphous layer by performing argon plasma surface treatment on the support substrate 101, thereby forming the modified substrate surface layer 105, wherein the support substrate 101 includes any one of a silicon substrate, silicon carbide, and gallium nitride, and has a surface treated like a mirror. In this case, the modified substrate surface layer 105 can be formed to have a thickness of 10 nm or less and can contain some materials for plasma surface treatment. Before the surface treatment, a process of removing a natural oxide film formed on the support substrate 101 can be performed.

[0071] In some embodiments of the present invention, by performing plasma surface treatment to form the modified substrate surface layer 105, impurities on the surface of the support substrate 101 may also be removed and the surface roughness may be reduced.

[0072] refer to Fig.13 , the support substrate 101 and the piezoelectric layer 130 are bonded together. That is, one side of the support substrate 101 formed with the modified substrate surface layer 105 and one side of the low acoustic velocity layer 120 formed on the piezoelectric layer 130 may be bonded together. For bonding, a hydrophilic treatment process may be performed after activating the bonding surfaces of the two substrates using a N2 / O2 mixed gas. After bonding is completed, a process of thinning the piezoelectric layer 130 to a desired thickness may be additionally performed.

[0073] In this way, according to an embodiment of the present invention, a method for manufacturing a surface acoustic wave device including a modified substrate surface layer does not require a separate deposition process to form a trap-rich layer. In order to ensure the performance of a conventional trap-rich layer, it is necessary to deposit the trap-rich layer by LPCVD, PECVD or sputtering equipment to make it about 400 to 1000 nm thick. Even if the trap-rich layer is formed by ion implantation, it is necessary to form a thickness of at least 50 nm by ion implantation equipment. In contrast, the method for manufacturing a surface acoustic wave device according to an embodiment of the present invention only requires a process for forming a modified substrate surface layer 105 by performing plasma surface treatment on the surface of a supporting substrate 101, which can reduce the manufacturing time and cost required to ensure the same performance.

[0074] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, it will be appreciated by those skilled in the art that the present invention can be implemented in other specific forms without changing the technical spirit or basic features. Therefore, the embodiments described above should be understood to be illustrative in all aspects, rather than restrictive.

Claims

1. A surface acoustic wave device, comprising: Semiconductor support substrate; a modified substrate surface layer formed on the surface of the supporting substrate; a low acoustic velocity layer formed on one side of the modified substrate surface layer; A piezoelectric layer formed on the low acoustic velocity layer; as well as A plurality of IDT electrodes are arranged on the piezoelectric layer, wherein: The surface roughness of the modified substrate surface layer side is 0.2 nm or less.

2. The device according to claim 1, wherein: The modified substrate surface layer includes an amorphous layer of a material constituting the supporting substrate, and the surface roughness is the roughness of the interface between the supporting substrate and the low acoustic velocity layer.

3. The device according to claim 2, wherein: The modified substrate surface layer contains any one of argon, helium, krypton and xenon.

4. The device according to claim 2, wherein: The thickness of the modified substrate surface layer is 10 nm or less.

5. The device according to claim 1, wherein: When the wavelength of the surface elastic wave determined by the arrangement interval of the plurality of IDT electrodes is λ, the thicknesses of the piezoelectric layer and the low acoustic velocity layer are 1λ or less.

6. The device according to claim 1, wherein: The support substrate includes at least one material among a silicon substrate, silicon carbide and gallium nitride.

7. A method for manufacturing a surface acoustic wave device, the method comprising the following steps: Forming a modified substrate surface layer by performing plasma surface treatment on the surface of the supporting substrate; forming a low acoustic velocity layer on the piezoelectric layer; as well as The substrate surface layer and the surface of the low acoustic velocity layer are bonded together.

8. The method according to claim 7, wherein: The plasma surface treatment process includes plasma treatment using any one of argon, helium, krypton, and xenon, and the modified substrate surface layer portion contains any one of the argon, helium, krypton, and xenon used in the plasma treatment.

9. The method according to claim 7, wherein: The thickness of the modified substrate surface layer is 10 nm or less.

10. The method according to claim 7, wherein: The modified substrate surface layer includes an amorphous layer of the material constituting the supporting substrate.

11. The method according to claim 7, further comprising the step of forming a plurality of IDT electrodes on the piezoelectric layer, wherein: When the wavelength of the surface elastic wave determined by the arrangement interval of the plurality of IDT electrodes is λ, the thicknesses of the piezoelectric layer and the low acoustic velocity layer are 1λ or less.

12. The method according to claim 11, wherein: The support substrate includes at least one material among a silicon substrate, silicon carbide and gallium nitride.

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