High-performance surface acoustic wave device and preparation process thereof

Abstract

The invention belongs to the technical field of microelectronic devices, and particularly relates to a high-performance surface acoustic wave device and a preparation process thereof. Comprising the following steps: preparing a polycrystalline diamond film layer on a low-resistance silicon substrate; preparing a temperature compensation layer on the polycrystalline diamond film layer; helium ions are injected into the bulk piezoelectric precursor to form a piezoelectric film layer to be transferred; the bulk piezoelectric precursor is bonded to the temperature compensation layer through a bonding technology, the piezoelectric film layer is reserved in a heat treatment mode, and a piezoelectric layer is obtained; preparing an interdigital electrode on the surface of the piezoelectric layer; and preparing a protection layer on the surface of the interdigital electrode and the non-designated area of the low-resistance silicon substrate, and etching the low-resistance silicon substrate on the designated area. According to the method, the polycrystalline diamond film layer is prepared on the low-resistance silicon substrate, the polycrystalline diamond film layer has high sound velocity and can restrain energy from leaking to the substrate, and the low-resistance silicon in the designated area is etched to reduce the radio frequency loss of the device, improve the quality factor of the surface acoustic wave device and improve the performance of the surface acoustic wave device.

Description

Technical Field

[0001] The invention belongs to the technical field of microelectronic devices, and in particular relates to a high-performance surface acoustic wave device and a preparation process thereof. Background Art

[0002] Surface acoustic wave devices are small in size and light in weight and are widely used in radio frequency communication systems. With the further development of mobile communication technology, higher requirements are placed on the performance of surface acoustic wave devices, such as higher operating frequency and higher quality factor. The bonding scheme using piezoelectric single crystal film and non-piezoelectric substrate is one of the most effective ways to improve device performance. For example, a surface acoustic wave device with a high quality factor can be made by stimulating a horizontal shear surface acoustic wave mode in a piezoelectric film, or a surface acoustic wave device with a high operating frequency can be made by stimulating a longitudinal leakage surface acoustic wave mode in a piezoelectric film.

[0003] Since diamond substrates have extremely high sound velocity, surface acoustic wave devices based on diamond substrates have attracted widespread attention. Since diamond has extremely high hardness, high thermal conductivity and other characteristics, the use of low-resistance silicon-based diamond film substrates has been widely used in the fields of micro-electromechanical and electronic devices. However, for radio frequency devices such as surface acoustic waves, the preparation of surface acoustic wave devices using low-resistance silicon substrates brings additional radio frequency losses. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a high-performance surface acoustic wave device and its preparation process. The present invention prepares a polycrystalline diamond film layer on a low-resistance silicon substrate, wherein the resistivity of the low-resistance silicon substrate is 0.001Ω·cm~1kΩ·cm, to obtain a low-resistance silicon-based diamond film substrate, and sequentially prepares a temperature compensation layer, a bonding piezoelectric layer and a forked electrode on the polycrystalline diamond film layer, and removes the area corresponding to the forked electrode on the low-resistance silicon substrate by etching, retaining the low-resistance silicon substrate corresponding to the forked electrode area on the low-resistance silicon substrate as the outside, for supporting the device, to obtain a high-performance surface acoustic wave device. By preparing a crystalline diamond film layer with a high sound velocity on a low-resistance silicon substrate, acoustic energy leakage can be suppressed, and at the same time, the device RF loss can be reduced by etching away the low-resistance silicon in a specified area, thereby improving the quality factor of the surface acoustic wave device and greatly improving the performance of the surface acoustic wave device.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] One of the purposes of the present invention is to provide a process for preparing a high-performance surface acoustic wave device, comprising the following steps:

[0007] A low-resistance silicon substrate is provided, and a polycrystalline diamond film layer is prepared on the low-resistance silicon substrate, wherein the resistivity of the low-resistance silicon substrate is 0.001Ω·cm-1kΩ·cm.

[0008] A temperature compensation layer is prepared on the polycrystalline diamond film layer.

[0009] Helium ions are implanted into the bulk piezoelectric precursor to define the piezoelectric film layer to be transferred.

[0010] The bulk piezoelectric precursor is bonded to the temperature compensation layer by a bonding process, and the piezoelectric film layer is retained by a thermal annealing process to obtain a piezoelectric layer arranged on the temperature compensation layer.

[0011] The surface of the piezoelectric layer is polished to reduce the roughness, and then interdigital electrodes are prepared.

[0012] A protective layer is prepared on the surface of the interdigital electrode and the non-designated area of ​​the low-resistance silicon substrate. The designated area is the area on the low-resistance silicon substrate corresponding to the interdigital electrode. The low-resistance silicon substrate on the designated area is then etched to obtain a high-performance surface acoustic wave device.

[0013] The present invention forms a low-resistance silicon-based diamond film substrate by preparing a polycrystalline diamond film layer on a low-resistance silicon substrate, and sequentially prepares a temperature compensation layer, a bonding piezoelectric layer, and a forked electrode on the polycrystalline diamond film layer, and removes the area corresponding to the forked electrode on the low-resistance silicon substrate by etching, and retains the low-resistance silicon substrate corresponding to the forked electrode area on the low-resistance silicon substrate as the outside, which is used to support the device. The use of polycrystalline diamond sound velocity can suppress acoustic energy leakage, and at the same time, by etching away the low-resistance silicon in the specified area, the device radio frequency loss is reduced, thereby improving the quality factor of the surface acoustic wave device, manufacturing a high-performance surface acoustic wave device, and greatly improving the performance of the surface acoustic wave device.

[0014] It should be noted that the present invention does not make any specific limitation on the bonding process. Its purpose is to use a conventional bonding process to bond the support layer to the temperature compensation layer, and to obtain a bulk piezoelectric precursor with a piezoelectric film by injecting helium ions into the bulk piezoelectric material. The bulk piezoelectric precursor is then bonded to the temperature compensation layer, and the piezoelectric film layer is retained by thermal annealing to obtain the corresponding piezoelectric layer.

[0015] It should be noted that the present invention does not specifically limit the preparation method of polycrystalline diamond, temperature compensation layer, and interdigital electrodes. Its purpose is to use conventional preparation methods to prepare a polycrystalline diamond film layer on the surface of a low-resistance silicon substrate, or to prepare a temperature compensation layer on a polycrystalline diamond film layer, or to prepare interdigital electrodes on a piezoelectric layer, etc. The preparation methods of polycrystalline diamond film include microwave plasma chemical vapor preparation; the preparation methods of temperature compensation layer include plasma enhanced chemical vapor deposition, dry oxidation or wet oxidation, etc.; the preparation methods of interdigital electrodes include thermal evaporation, electron beam evaporation or magnetron sputtering, etc.

[0016] It should be noted that the entire surface of the interdigitated electrode side needs to be protected from damage during the etching process; the silicon at the corresponding position of the surface acoustic wave device electrode needs to be retained, that is, the silicon under the electrode is etched, and the silicon in other areas is retained to support the device.

[0017] It should be noted that after preparing the interdigitated electrodes, the low-resistance silicon substrate can be thinned to 0.1 um to 0.3 um to facilitate etching.

[0018] In some embodiments, the thickness of the low-resistance silicon substrate is 0.2 mm to 1 mm. It should be noted that if the low-resistance silicon is too thin, it is easy to break during the diamond preparation / piezoelectric layer bonding process; if the low-resistance silicon is too thick, it is more difficult to etch the low-resistance silicon.

[0019] In some embodiments, the thickness of the polycrystalline diamond film layer is 0.1 μm to 100 μm. It should be noted that the polycrystalline diamond film layer has a high sound velocity, which can suppress the leakage of energy to the substrate. The diamond can also be a single crystal diamond, but it is very difficult to grow a single crystal diamond of the required thickness of the present invention in terms of technology. If the thickness of the polycrystalline diamond film layer is too low, the effect of suppressing energy leakage will be poor, but if the thickness is increased, the roughness inside the wafer will increase, the stress of the substrate will increase, and the substrate will be easily broken.

[0020] In some embodiments, the thickness of the temperature compensation layer is 0.05 μm to 10 μm, and the material of the temperature compensation layer is silicon dioxide. It should be noted that the temperature compensation layer provides a better interface for bonding the piezoelectric layer and facilitates bonding; on the other hand, it can improve the frequency-temperature characteristics of the surface acoustic wave device.

[0021] In some embodiments, the bulk piezoelectric material is lithium niobate or lithium tantalate, and the thickness of the piezoelectric layer is 0.1 μm to 2 μm. It should be noted that the present invention controls the type, cut and thickness of the piezoelectric material to stimulate surface acoustic waves with different characteristics to meet different device requirements.

[0022] In some embodiments, the material of the interdigital electrodes is titanium, aluminum, chromium, silver, gold or copper, and the thickness of the interdigital electrodes is 0.05 μm to 1 μm. It should be noted that the material of the interdigital electrodes can be any one or more combinations of titanium, aluminum, chromium, silver, gold or copper. The present invention changes the operating frequency of the device and reduces the acoustic wave loss by controlling the type and thickness of the electrode material.

[0023] The second object of the present invention is to provide a high-performance surface acoustic wave device prepared by the above-mentioned preparation process. The high-performance surface acoustic wave device provided by the present invention can suppress the leakage of energy to the substrate due to the high sound velocity of the polycrystalline diamond film layer, and at the same time, the device radio frequency loss is reduced by etching away the low-resistance silicon in the specified area, thereby improving the quality factor of the surface acoustic wave device and greatly improving the performance of the surface acoustic wave device.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The invention prepares a polycrystalline diamond film layer on a low-resistance silicon substrate, the resistivity of the low-resistance silicon substrate is 0.001Ω·cm-1kΩ·cm, and a low-resistance silicon-based diamond film substrate is formed. A temperature compensation layer, a bonding piezoelectric layer and an interdigital electrode are sequentially prepared on the polycrystalline diamond film layer, and the area corresponding to the interdigital electrode on the low-resistance silicon substrate is removed by etching, and the low-resistance silicon substrate outside the area corresponding to the interdigital electrode on the low-resistance silicon substrate is retained for supporting the device. Since the high sound velocity of the polycrystalline diamond can suppress the leakage of acoustic energy, the radio frequency loss of the device is reduced by etching away the low-resistance silicon in the specified area, and the quality factor of the surface acoustic wave device is improved, so as to manufacture a high-performance surface acoustic wave device, and greatly improve the performance of the surface acoustic wave device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the process flow for preparing a high-performance surface acoustic wave resonator according to Example 1 of the present invention.

[0027] Figure 2 This is a schematic structural diagram of a high-performance surface acoustic wave resonator according to Example 1 of the present invention.

[0028] Figure 3 It is a schematic structural diagram of the high-performance surface acoustic wave resonator of comparative example 1 of the present invention.

[0029] Figure 4 1 and 2. The displacement distribution diagram of the high-performance surface acoustic wave resonator of Example 1 of the present invention and the surface acoustic wave resonator of Comparative Example 1.

[0030] Description of reference numerals:

[0031] 1. Low-resistance silicon substrate, 2. Polycrystalline diamond film layer, 3. Temperature compensation layer, 4. Piezoelectric layer, 5. Interdigital electrodes, 6. Protective layer.

[0032] 1-1, high-resistance silicon support substrate, 1-2, trap-rich layer, 1-3, temperature compensation layer, 1-4, piezoelectric layer, 1-5, interdigital electrode. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Certain words are used in the present invention to refer to specific components. Those skilled in the art should understand that technicians will use different nouns to refer to the same component. The present invention does not distinguish between components by the difference in nouns, but by the difference in the functions of the components. As mentioned throughout the specification and claims, "including" is an open term and should be understood as "including but not limited to".

[0035] The invention is further described below through specific examples.

[0036] Example 1

[0037] A process for preparing a high performance surface acoustic wave device, such as Figure 1 As shown, the following steps are included:

[0038] S1. Provide a low-resistance silicon substrate 1, the thickness of the low-resistance silicon substrate 1 is 0.725 mm, wherein the resistivity of the low-resistance silicon substrate 1 is 0.5 Ω·cm, and prepare a polycrystalline diamond film layer 2 on the low-resistance silicon substrate 1 by microwave plasma chemical vapor preparation method, the thickness of the polycrystalline diamond film layer 2 is 2 μm.

[0039] S2. Prepare a temperature compensation layer 3 on the polycrystalline diamond film layer 2 by plasma enhanced chemical vapor preparation. The material of the temperature compensation layer 3 is silicon dioxide, and the thickness of the temperature compensation layer 3 is 0.5 μm.

[0040] S3. Inject helium ions into the bulk piezoelectric material, the bulk piezoelectric material is 42° YX lithium tantalate, and define the piezoelectric film layer to be transferred, the thickness of the piezoelectric film layer is 0.6 μm.

[0041] S4. Bonding the piezoelectric thin film layer of the bulk piezoelectric precursor to the temperature compensation layer 3 using a bonding process.

[0042] S5. The piezoelectric film layer is retained by thermal annealing to obtain a piezoelectric layer 4 disposed on the temperature compensation layer 3. The thickness of the piezoelectric layer 4 is 0.6 μm.

[0043] S6. Polish the surface of the piezoelectric layer 4 to reduce the roughness.

[0044] S7. Prepare interdigital electrodes 5 on the piezoelectric layer 4 by electron beam evaporation. The interdigital electrodes are a combination of 10 nm titanium and 160 nm aluminum.

[0045] S8 . Form a protective layer 6 on the surface of the interdigital electrode 5 and on a non-designated area of ​​the low-resistance silicon substrate 1 . The designated area is an area on the low-resistance silicon substrate 1 corresponding to the interdigital electrode 5 .

[0046] S9, then etching the low-resistance silicon substrate 1 on the designated area by etching, thus obtaining a high-performance surface acoustic wave device. The structure of the high-performance surface acoustic wave device is as follows: Figure 2 shown.

[0047] Example 2

[0048] A process for preparing a high performance surface acoustic wave device, such as Figure 1 As shown, the following steps are included:

[0049] S1. Provide a low-resistance silicon substrate 1, the thickness of the low-resistance silicon substrate 1 is 1 mm, wherein the resistivity of the low-resistance silicon substrate 1 is 0.01 Ω·cm, and prepare a polycrystalline diamond film layer 2 on the low-resistance silicon substrate 1 by microwave plasma chemical vapor preparation, the thickness of the polycrystalline diamond film layer 2 is 100 μm.

[0050] S2. Prepare a temperature compensation layer 3 on the polycrystalline diamond film layer 2 by plasma enhanced chemical vapor preparation. The material of the temperature compensation layer 3 is silicon dioxide, and the thickness of the temperature compensation layer 3 is 5 μm.

[0051] S3. Inject helium ions into the bulk piezoelectric material, the bulk piezoelectric material is 42° YX lithium tantalate, define the piezoelectric film layer to be transferred, and the thickness of the piezoelectric film is 2 μm.

[0052] S4, bonding the piezoelectric film of the bulk piezoelectric precursor to the temperature compensation layer 3 using a bonding process.

[0053] S5. The piezoelectric film is retained by thermal annealing to obtain a piezoelectric layer 4 disposed on the temperature compensation layer 3. The thickness of the piezoelectric layer 4 is 2 μm.

[0054] S6. Polish the surface of the piezoelectric layer 4 to reduce the roughness.

[0055] S7. Prepare interdigital electrodes 5 on the piezoelectric layer 4 by electron beam evaporation. The thickness of the interdigital electrodes 5 is 0.5 μm, and the material of the interdigital electrodes 5 is aluminum.

[0056] S8 . Form a protective layer 6 on the surface of the interdigital electrode 5 and on a non-designated area of ​​the low-resistance silicon substrate 1 . The designated area is an area on the low-resistance silicon substrate 1 corresponding to the interdigital electrode 5 .

[0057] S9, then etching the low-resistance silicon substrate 1 on the designated area by etching, thus obtaining a high-performance surface acoustic wave device. The structure of the high-performance surface acoustic wave device is as follows: Figure 2 shown.

[0058] Example 3

[0059] A process for preparing a high performance surface acoustic wave device, such as Figure 1 As shown, the following steps are included:

[0060] S1. Provide a low-resistance silicon substrate 1, the thickness of the low-resistance silicon substrate 1 is 0.1um, wherein the resistivity of the low-resistance silicon substrate 1 is 1000Ω·cm, and prepare a polycrystalline diamond film layer 2 on the low-resistance silicon substrate 1 by microwave plasma chemical vapor preparation method, the thickness of the polycrystalline diamond film layer 2 is 0.1μm.

[0061] S2. Prepare a temperature compensation layer 3 on the polycrystalline diamond film layer 2 by plasma enhanced chemical vapor preparation. The material of the temperature compensation layer 3 is silicon dioxide, and the thickness of the temperature compensation layer 3 is 0.05 um.

[0062] S3. Inject helium ions into the bulk piezoelectric material, the bulk piezoelectric material is 42° YX lithium tantalate, define the piezoelectric film layer to be transferred, and the thickness of the piezoelectric film is 0.1 μm.

[0063] S4. Bonding the piezoelectric thin film layer of the bulk piezoelectric precursor to the temperature compensation layer 3 using a bonding process.

[0064] S5. The piezoelectric film layer is retained by thermal annealing to obtain a piezoelectric layer 4 disposed on the temperature compensation layer 3. The thickness of the piezoelectric layer 4 is 0.1 μm.

[0065] S6. Polish the surface of the piezoelectric layer 4 to reduce the roughness.

[0066] S7. Prepare interdigital electrodes 5 on the piezoelectric layer 4 by electron beam evaporation. The thickness of the interdigital electrodes 5 is 0.05 μm, and the material of the interdigital electrodes 5 is copper.

[0067] S8 . Form a protective layer 6 on the surface of the interdigital electrode 5 and on a non-designated area of ​​the low-resistance silicon substrate 1 . The designated area is an area on the low-resistance silicon substrate 1 corresponding to the interdigital electrode 5 .

[0068] S9, then etching the low-resistance silicon substrate 1 on the designated area by etching, thus obtaining a high-performance surface acoustic wave device. The structure of the high-performance surface acoustic wave device is as follows: Figure 2 shown.

[0069] Comparative Example 1

[0070] A method for preparing a surface acoustic wave resonator comprises the following steps:

[0071] S1. Provide a high-resistance silicon support substrate 1-1.

[0072] S2. Prepare a trap-rich layer 1-2 on the high-resistance silicon support substrate 1-1 by chemical vapor preparation. The thickness of the trap-rich layer 1-2 is 1 μm, and the material of the trap-rich layer is polycrystalline silicon.

[0073] S3, forming a temperature compensating layer 1-3 on the trap-rich layer 1-2, wherein the material of the temperature compensating layer 1-3 is silicon dioxide, and the thickness of the temperature compensating layer 1-3 is 0.5 μm.

[0074] S4. Bonding a piezoelectric layer 1-4 on the temperature compensation layer 1-3, the thickness of the piezoelectric layer 1-4 is 0.6 μm, and the material of the piezoelectric layer 1-4 is 42° YX lithium tantalate.

[0075] S5. Prepare interdigital electrodes 1-5 on the piezoelectric layer 1-4 by photolithography and lift-off process. The interdigital electrodes are a combination of 10 nm titanium and 160 nm aluminum.

[0076] S6. A surface acoustic wave resonator is obtained. The structure of the surface acoustic wave resonator is as follows: Figure 3 shown.

[0077] The high-performance surface acoustic wave resonators prepared in Examples 1 to 3 have similar structures and similar effects. The performance of the high-performance surface acoustic wave resonator prepared in Example 1 is taken as an example for further description.

[0078] Figure 4 1 is a displacement distribution diagram of the high-performance surface acoustic wave resonator of Example 1 of the present invention and the surface acoustic wave resonator of Comparative Example 1. The horizontal axis is the distance from the substrate surface, and the vertical axis is the normalized displacement value. Figure 4 As shown, by using a substrate with a diamond film, the leakage of surface acoustic wave energy into the substrate is greatly suppressed due to the high acoustic velocity of the diamond film.

[0079] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0080] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A process for preparing a high-performance surface acoustic wave device, characterized in that: The following steps are involved: A low-resistance silicon substrate (1) is provided, and a polycrystalline diamond film layer (2) is prepared on the low-resistance silicon substrate (1), wherein the resistivity of the low-resistance silicon substrate (1) is 0.001Ω·cm to 1kΩ·cm; Preparing a temperature compensation layer (3) on the polycrystalline diamond film layer (2); implanting helium ions into a bulk piezoelectric precursor to define a piezoelectric film layer to be transferred; The bulk piezoelectric precursor is bonded to the temperature compensation layer (3) by a bonding process, and the piezoelectric film layer is retained by thermal annealing to obtain a piezoelectric layer (4) disposed on the temperature compensation layer (3); Polishing the surface of the piezoelectric layer (4) to reduce the roughness, and then preparing interdigital electrodes (5); A protective layer (6) is prepared on the surface of the interdigital electrode (5) and on a non-designated area of ​​the low-resistance silicon substrate (1), wherein the designated area is an area on the low-resistance silicon substrate (1) corresponding to the interdigital electrode (5), and then the low-resistance silicon substrate (1) on the designated area is etched to obtain a high-performance surface acoustic wave device.

2. The process for preparing a high performance surface acoustic wave device according to claim 1, characterized in that: The thickness of the low-resistance silicon substrate (1) is 0.2 mm to 1 mm.

3. The process for preparing a high performance surface acoustic wave device according to claim 1, characterized in that: The thickness of the polycrystalline diamond film layer (2) is 0.1 μm to 100 μm.

4. The process for preparing a high performance surface acoustic wave device according to claim 1, characterized in that: The thickness of the temperature compensation layer (3) is 0.05 μm to 10 μm.

5. The process for preparing a high performance surface acoustic wave device according to claim 4, characterized in that: The material of the temperature compensation layer (3) is silicon dioxide.

6. The process for preparing a high-performance surface acoustic wave device according to claim 1, characterized in that: The thickness of the piezoelectric layer (4) is 0.1 μm to 2 μm.

7. The process for preparing a high performance surface acoustic wave device according to claim 1, characterized in that: The bulk piezoelectric material is lithium niobate or lithium tantalate.

8. The process for preparing a high performance surface acoustic wave device according to claim 1, characterized in that: The thickness of the interdigital electrode (5) is 0.05 μm to 1 μm.

9. The process for preparing a high performance surface acoustic wave device according to claim 1, characterized in that: The material of the interdigital electrodes (5) is titanium, aluminum, chromium, silver, gold or copper.

10. A high performance surface acoustic wave device prepared by the preparation process according to any one of claims 1 to 9.

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