A thin-film bulk acoustic wave resonator and a method for fabricating the thin-film bulk acoustic wave resonator using a wet chemical substrate lift-off technique.

Abstract

This application proposes a thin-film bulk acoustic wave resonator and a method for fabricating the thin-film bulk acoustic wave resonator using a wet chemical substrate lift-off technique. The method involves growing a BaF2 and / or CaF2 lift-off layer, an AlN piezoelectric layer, a bottom electrode layer, and a support layer on the surface of substrate A; growing a cavity layer on the surface of substrate B; bonding substrate A and substrate B together; etching the lift-off layer; and lifting substrate A. A patterned top electrode is then grown on the exposed piezoelectric layer surface. Utilizing the different solubility of the solvent in the lift-off layer and functional layer, the thin film is effectively lifted off, reducing damage to the film during the lift-off process. This effectively improves the resonator's performance, reduces energy loss during operation, and significantly ensures the signal quality of the filter formed by the resonator.

Description

Technical Field

[0001] This application relates to the field of semiconductor device technology, and in particular to a thin-film bulk acoustic wave resonator and a method for fabricating a thin-film bulk acoustic wave resonator using a wet chemical substrate peeling technique. Background Technology

[0002] The development of artificial intelligence technology has placed higher demands on communication performance, creating an urgent need for low-latency, high-data-capacity communication methods. This has greatly promoted the development of high-frequency communication technology, characterized by high transmission speeds and large data bandwidth. Among these technologies, radio frequency (RF) filters are one of the core components in high-frequency communication, and their operating frequency primarily depends on the resonator's operating frequency band. Therefore, the development of high-frequency communication technology places higher demands on the energy loss of resonators. Developing high-quality bulk acoustic wave (BAW) resonators is of great significance to the development of communication technology.

[0003] In traditional cavity-type bulk acoustic wave resonators, the sacrificial layer release process can lead to thin film damage and incomplete release, resulting in serious consequences such as resonator performance loss. Therefore, using flip-chip bonding and substrate peeling during fabrication reduces damage to the device thin film during sacrificial layer release, significantly improving resonator performance and consequently enhancing the filtering performance of bulk acoustic wave filters. Furthermore, with the continuous advancement of intelligent technology, flexible wearable communication and other bendable communication components have seen significant development; flip-chip bonding and substrate peeling technologies are also reliable solutions for fabricating flexible filter chips.

[0004] However, current mainstream lift-off techniques mainly utilize physical and chemical polishing (CMP) or laser lift-off. These techniques not only damage the substrate, increasing fabrication costs, but also introduce additional surface damage to the thin film during physical lift-off, leading to performance degradation. Therefore, it is necessary to provide a more reliable method for resonator fabrication. Summary of the Invention

[0005] This application provides a thin-film bulk acoustic wave resonator and a method for fabricating the thin-film bulk acoustic wave resonator using a wet chemical substrate lift-off technique, in order to solve the problems existing in related technologies. The technical solution is as follows:

[0006] In a first aspect, embodiments of this application provide a method for fabricating a thin-film bulk acoustic resonator using a wet chemical substrate lift-off technique, comprising the following steps:

[0007] Step S1: A release layer, a piezoelectric layer, a bottom electrode layer, and a support layer are grown on the surface of substrate A; the release layer is BaF2 and / or CaF2.

[0008] Step S2: A cavity layer is grown on the surface of substrate B;

[0009] Step S3: Bond substrate A and substrate B together, etch the release layer, and peel off substrate A;

[0010] Step S4: A patterned top electrode is grown on the surface of the piezoelectric layer exposed after stripping.

[0011] In one embodiment, substrate A is any one of Si, sapphire, or SiC.

[0012] In one embodiment, the piezoelectric layer is AlN or Al x Ga 1-x N、ScxAl 1-x N or Al x Si 1-x Any of N.

[0013] In one embodiment, the bottom electrode layer is one or a combination of two or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb or Hf.

[0014] In one embodiment, the support layer is one or a combination of two or more of Si3N4, SiO2 or SiC.

[0015] In one embodiment, substrate B is any one of Si, SiC, glass, or organic flexible substrate.

[0016] In one embodiment, the cavity layer is patterned SiO2 or Si3N4 with a cavity structure.

[0017] In one embodiment, a cavity structure is grown on the surface of substrate B using photolithography, photomask, or etching techniques.

[0018] In one embodiment, the bonding is a metallic bond, a non-metallic bond, or an organic adhesive.

[0019] In one embodiment, an alcohol solvent is used to etch the release layer.

[0020] In one embodiment, the alcohol solvent is one or a combination of two or more of ethanol, methanol, or glycerol.

[0021] In one embodiment, the thickness of the release layer is 30-100 nm.

[0022] Secondly, embodiments of this application provide a thin-film bulk acoustic resonator, which is prepared by any of the methods described above for preparing a thin-film bulk acoustic resonator using wet chemical substrate lift-off technology.

[0023] In one embodiment, the thickness of the bottom electrode and the top electrode is 200-1500 nm, the thickness of the cavity layer is 0.5-4 μm, the thickness of the piezoelectric layer is 0.1-3.5 μm, and the thickness of the support layer is 20-300 nm.

[0024] In one embodiment, the surface roughness of the piezoelectric layer is less than 2.5 nm.

[0025] In one embodiment, the surface roughness of the piezoelectric layer is 0.1-2 nm.

[0026] The advantages or beneficial effects of the above technical solutions include at least the following:

[0027] This application discloses a method for fabricating thin-film bulk acoustic wave resonators using a wet chemical substrate peeling technique. This technique effectively avoids damage to the functional layer film caused by traditional peeling techniques, thus improving the quality factor of the fabricated resonator. Simultaneously, it effectively reduces damage to the substrate during the physical peeling process, facilitating substrate reuse and lowering production costs.

[0028] In particular, the lattice mismatch between the release layer and the piezoelectric layer provided in this application is small. Therefore, when growing the piezoelectric layer on the release layer, it is beneficial to obtain a piezoelectric layer film with high crystal quality; the defect density is reduced, thereby reducing the energy loss of the device.

[0029] Therefore, the fabrication method of this application can effectively improve the performance of the resonator and reduce the fabrication cost, thereby obtaining a low-energy-loss, easily integrated, and flexible bulk acoustic resonator.

[0030] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of this application will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0031] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0032] Figure 1 This is a schematic diagram of the resonator structure in Example 1;

[0033] Figure 2 A cross-sectional view of substrate A prepared in Example 1;

[0034] Figure 3This is a cross-sectional view of the cavity layer structure grown on substrate B in Example 1;

[0035] Figure 4 This is a cross-sectional view of the structure after bonding in Example 1;

[0036] Figure 5 This is a schematic diagram of the preparation process of the present invention;

[0037] Figure 6 AFM image of AlN after peeling in Example 1;

[0038] Figure 7 The quality factor curve of the resonator prepared in Example 1;

[0039] Figure 8 AFM image of AlN after stripping in Comparative Example 1;

[0040] Figure 9 The quality factor curve of the resonator prepared in Comparative Example 1 is shown. Detailed Implementation

[0041] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this application. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0042] Regardless of whether physical or chemical polishing (CMP) or laser lift-off techniques are used, they all damage the substrate, increasing fabrication costs. Furthermore, physical lift-off introduces additional surface damage to the thin film, leading to performance degradation. In device fabrication, directly growing piezoelectric layers, especially AlN piezoelectric layers, on Si-containing substrates can also limit the crystal quality of the AlN film due to lattice mismatch between Si and AlN, increasing defect density and consequently increasing energy loss. Therefore, effectively lifting the thin film while minimizing damage during the lift-off process, thereby significantly improving resonator performance, reducing energy loss during operation, and ensuring the signal quality of the filter formed by the resonator, is a problem that needs to be solved in device fabrication.

[0043] To address the aforementioned issues, this application provides a method for fabricating thin-film bulk acoustic wave resonators using a wet chemical substrate lift-off technique. This method effectively avoids damage to the thin film during cavity release and prevents damage to the functional layer during substrate lift-off, thereby greatly ensuring the resonator's performance. This method can effectively improve the resonator's performance and reduce fabrication costs, resulting in a low-energy-loss, easily integrated, and flexible bulk acoustic wave resonator.

[0044] This application provides a method for fabricating a thin-film bulk acoustic wave resonator using a wet chemical substrate lift-off technique, comprising the following steps:

[0045] Step S1: A release layer, a piezoelectric layer, a bottom electrode layer, and a support layer are grown on the surface of substrate A; the release layer is BaF2 and / or CaF2.

[0046] Step S2: A cavity layer is grown on the surface of substrate B;

[0047] Step S3: Bond substrate A and substrate B together, etch the release layer, and peel off substrate A;

[0048] Step S4: A patterned top electrode is grown on the surface of the piezoelectric layer exposed after stripping.

[0049] A release layer and a piezoelectric layer are grown on the surface of substrate A and bonded to substrate B. The release layer is then etched to remove substrate A. The release layer is BaF2 and / or CaF2, which can be grown on the substrate using PVD. A piezoelectric layer can then be grown on the formed BaF2 and / or CaF2 release layer. Since BaF2 and / or CaF2 are soluble, the differential solubility of the solvent in the release layer and functional layer is utilized to etch away the release layer through dissolution. This etching process causes the substrate to detach from the piezoelectric layer, exposing it and achieving substrate removal. The etching of the release layer does not cause physical damage to the substrate or the contact surface between the piezoelectric layer and the release layer, thus facilitating substrate reuse and reducing production costs. Simultaneously, it improves the quality of the piezoelectric layer, thereby enhancing the resonator's performance.

[0050] In one embodiment, substrate A is any one of Si, sapphire, or SiC.

[0051] As one implementation method, the piezoelectric layer is AlN or Al x Ga 1-x N、ScxAl 1-x N or Al x Si 1-x Any of N.

[0052] When growing a piezoelectric layer, if the substrate is Si-containing and the piezoelectric layer is AlN, the lattice mismatch between Si and AlN limits the crystal quality of the AlN film, increases defect density, and consequently increases device power loss. The method in this application, however, grows an exfoliation layer between the substrate and the piezoelectric layer, allowing AlN to grow on BaF2 and CaF2. This prevents direct contact between the AlN and the Si-containing substrate, reducing lattice mismatch and facilitating the production of high-crystallinity AlN piezoelectric films, thus further improving device performance.

[0053] In one embodiment, the bottom electrode layer is one or a combination of two or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb or Hf.

[0054] As one implementation, the support layer is one or a combination of two or more of Si3N4, SiO2, or SiC.

[0055] In one embodiment, substrate B is any one of Si, SiC, glass, or organic flexible substrate.

[0056] In one implementation, the cavity layer is a patterned SiO2 or Si3N4 with a cavity structure.

[0057] As one implementation method, a cavity structure is grown on the surface of substrate B using photolithography, photomask, or etching techniques.

[0058] As one implementation method, the bonding is a metallic bond, a non-metallic bond, or an organic adhesive.

[0059] As one implementation method, an alcohol solvent is used to etch the release layer.

[0060] As one embodiment, the alcohol solvent is one or a combination of two or more of ethanol, methanol, or glycerol.

[0061] Alcohol solvents, especially ethanol, methanol, or glycerol, exhibit good solubility for the BaF2 and CaF2 of the release layer, while remaining undissolved in the AlN piezoelectric layer, support layer, cavity layer, and substrate. This allows for the use of the difference in solubility of alcohol solvents in the release layer and functional layers to etch the release layer, thereby separating the substrate from the piezoelectric layer without affecting the substrate or other layers. Alcohol solvents are highly volatile and can be easily removed after use, leaving no residue in the device. Preferably, the alcohol solvents on the device are dried by purging with an inert gas.

[0062] In one embodiment, the thickness of the release layer is 30-100 nm. The thickness of the release layer can be adjusted according to actual needs.

[0063] In one embodiment, substrate A and substrate B are cleaned before use; preferably, acetone and hydrofluoric acid are used to clean and dry the substrates.

[0064] This application also provides a thin-film bulk acoustic wave resonator, which is prepared by any of the methods described above for preparing thin-film bulk acoustic wave resonators using wet chemical substrate peeling technology.

[0065] The thin-film bulk acoustic resonator prepared by the method described in this application has low surface roughness of the piezoelectric layer and high growth quality; therefore, the overall quality factor of the resonator is significantly improved.

[0066] In one embodiment, the thickness of the bottom electrode and the top electrode is 200-1500 nm, the thickness of the cavity layer is 0.5-4 μm, the thickness of the piezoelectric layer is 0.1-3.5 μm, and the thickness of the support layer is 20-300 nm.

[0067] As one embodiment, the surface roughness of the piezoelectric layer is less than 2.5 nm.

[0068] As one embodiment, the surface roughness of the piezoelectric layer is 0.1-2 nm.

[0069] The following provides a further explanation using specific implementation methods.

[0070] Example 1

[0071] This embodiment provides a method for fabricating a thin-film bulk acoustic resonator using a wet chemical substrate lift-off technique, wherein the resonator is as follows: Figure 1 As shown, it includes a silicon substrate 101, a cavity layer 102, a support layer 103, a bottom electrode 104, a piezoelectric layer 105, and a top electrode 106.

[0072] Preparation method as follows Figure 5 As shown, it includes the following steps:

[0073] like Figure 2 As shown, a (111) Si substrate was selected as substrate A107, and the substrate was cleaned and dried using acetone and hydrofluoric acid.

[0074] A 50 nm thick BaF2 release layer 108 and a 1 μm thick AlN piezoelectric layer 105 are grown by PVD; a 500 nm thick layer of metallic Mo is deposited on the surface of the piezoelectric layer 105 as a bottom electrode 104 by PVD; and a 50 nm thick Si3N4 support layer 103 is grown by plasma-enhanced CVD.

[0075] like Figure 3 As shown, a Si substrate was selected as substrate B 101. The substrate was cleaned and dried using acetone and hydrofluoric acid. A 3 μm patterned SiO2 thin film 109 was grown using PVD technology to form a cavity structure, forming a cavity layer 102.

[0076] like Figure 4 As shown, two wafers are bonded together using amorphous bonding technology;

[0077] The substrate was then immersed in an ethanol solution to etch the release layer and peel off substrate A. After peeling, the substrate was dried with nitrogen gas. The surface of the AlN piezoelectric layer was observed using an atomic force microscope (AFM), and the AFM images are shown below. Figure 6 As shown, a 500 nm thick layer of metallic Mo is grown on the AlN piezoelectric layer 105 using PVD as the top electrode 106, thereby fabricating a material as shown. Figure 1 The resonator shown.

[0078] Example 2

[0079] This embodiment provides a method for fabricating a thin-film bulk acoustic resonator using a wet chemical substrate lift-off technique, wherein the resonator is as follows: Figure 1 As shown, it includes a silicon substrate 101, a cavity layer 102, a support layer 103, a bottom electrode 104, a piezoelectric layer 105, and a top electrode 106.

[0080] Preparation method as follows Figure 5 As shown, it includes the following steps:

[0081] like Figure 2 As shown, a sapphire substrate was selected as substrate A107, and the substrate was cleaned and dried using acetone and hydrofluoric acid.

[0082] A 100 nm CaF2 release layer 108 and a 2 μm AlN piezoelectric layer 105 are grown by PVD; a 200 nm thick layer of metallic Mo is deposited on the surface of the piezoelectric layer 105 as a bottom electrode 104 by PVD; and a 20 nm thick Si3N4 support layer 103 is grown by plasma-enhanced CVD.

[0083] like Figure 3 As shown, a SiC substrate was selected as substrate B 101. The substrate was cleaned and dried using acetone and hydrofluoric acid. A 4μm patterned Si3N4 thin film 109 was grown using PVD technology to form a cavity structure, forming a cavity layer 102.

[0084] like Figure 4 As shown, two wafers are bonded together using amorphous bonding technology;

[0085] Then, it was immersed in a solution of methanol and glycerol in a volume ratio of 9:1 to etch the release layer and peel off the substrate A; after peeling, it was dried with nitrogen gas; a 1000 nm thick layer of metallic Mo was grown on the AlN piezoelectric layer 105 using PVD as the top electrode 106, thereby preparing the substrate A. Figure 1 The resonator shown.

[0086] Example 3

[0087] This embodiment provides a method for fabricating a thin-film bulk acoustic resonator using a wet chemical substrate lift-off technique, wherein the resonator is as follows: Figure 1 As shown, it includes a silicon substrate 101, a cavity layer 102, a support layer 103, a bottom electrode 104, a piezoelectric layer 105, and a top electrode 106.

[0088] Preparation method as follows Figure 5 As shown, it includes the following steps:

[0089] like Figure 2 As shown, a SiC substrate was selected as substrate A107, and the substrate was cleaned and dried using acetone and hydrofluoric acid.

[0090] A 30 nm thick CaF2 and BaF2 lift-off layer 108 with a mass ratio of 1:1 and a 3 μm thick AlN piezoelectric layer 105 are grown by PVD; a 1500 nm thick layer of metallic Mo is deposited on the surface of the piezoelectric layer 105 as a bottom electrode 104 by PVD; and a 300 nm thick SiO2 support layer 103 is grown by plasma-enhanced CVD.

[0091] like Figure 3 As shown, an organic flexible substrate was selected as substrate B 101. The substrate was cleaned and dried using acetone and hydrofluoric acid. A 1 μm patterned Si3N4 thin film 109 was grown using PVD technology to form a cavity structure, forming a cavity layer 102.

[0092] like Figure 4 As shown, two wafers are bonded together using amorphous bonding technology;

[0093] Then, it was immersed in a solution of methanol and glycerol in a volume ratio of 9:1 to etch the release layer and peel off the substrate A; after peeling, it was dried with nitrogen gas; a 500 nm thick layer of metallic Mo was grown on the AlN piezoelectric layer 105 using PVD as the top electrode 106, thereby preparing the substrate A. Figure 1 The resonator shown.

[0094] Comparative Example 1

[0095] A thin-film bulk acoustic wave resonator is disclosed in this embodiment. The resonator is fabricated using a wet chemical substrate lift-off technique. The resonator includes a silicon substrate, a cavity, a support layer, a bottom electrode, a piezoelectric layer, and a top electrode.

[0096] The preparation method includes the following steps:

[0097] A (111) Si substrate was selected as substrate A. The substrate was cleaned and dried using acetone and hydrofluoric acid.

[0098] A 500 nm thick layer of metallic Mo was deposited on the surface of the piezoelectric layer using PVD as the bottom electrode; and a 50 nm thick Si3N4 support layer was grown using plasma-enhanced CVD.

[0099] A Si substrate was selected as substrate B. The substrate was cleaned and dried using acetone and hydrofluoric acid. A 3μm patterned SiO2 thin film was grown using PVD technology to form a cavity structure and a cavity layer.

[0100] Two wafers are bonded together using amorphous bonding technology;

[0101] Substrate A was removed using laser lift-off technology, exposing the AlN piezoelectric layer. The surface of the AlN piezoelectric layer was observed using atomic force microscopy (AFM), and the AFM images are shown below. Figure 8 As shown, a resonator was fabricated by growing a 500 nm thick layer of metallic Mo on an AlN piezoelectric layer using PVD as the top electrode.

[0102] from Figure 6 The AFM image of the AlN surface after peeling in Example 1 shows a surface roughness of 0.51 nm, indicating that the damage to the film during the peeling process is negligible. Figure 8 The AFM image of the AlN surface after peeling in Comparative Example 1 shows that its surface roughness is 4.46 nm, indicating that the damage to the film caused by the peeling process is much greater than that in Example 1.

[0103] The quality factor of the resonator prepared in Example 1 is as follows: Figure 7 As shown, the quality factor of the resonator prepared in Comparative Example 1 is as follows: Figure 9 As shown; from Figure 7 and Figure 9 It can be seen that the maximum quality factor of the resonator prepared in Example 1 is 2780; while the maximum quality factor of the resonator prepared in Comparative Example 1 is only 1909. It is evident that the performance of the resonator prepared in Comparative Example 1 is far inferior to that of the resonator prepared in Example 1.

[0104] Therefore, it is shown that the wet chemical stripping technique of this application effectively reduces the damage to the substrate caused by the physical stripping process and improves the performance of the resonator.

[0105] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0106] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0107] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this application, and these should all be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for fabricating a thin-film bulk acoustic resonator using a wet chemical substrate lift-off technique, characterized in that, Includes the following steps: Step S1: A release layer, a piezoelectric layer, a bottom electrode layer, and a support layer are grown on the surface of substrate A; the release layer is BaF2 and / or CaF2; the release layer is etched using an alcohol solvent; the alcohol solvent is one or a combination of two or more of ethanol, methanol, or glycerol; substrate A is any one of Si, sapphire, or SiC. The piezoelectric layer is AlN, Al x Ga 1-x N、ScxAl 1-x N or Al x Si 1-x Any one of N; The bottom electrode layer is one or a combination of two or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb or Hf; The support layer is one or a combination of two or more of Si3N4, SiO2 or SiC; The thickness of the release layer is 30-100 nm; Step S2, a cavity layer is grown on the surface of substrate B; Step S3: Bond substrate A and substrate B together, etch the release layer, and peel off substrate A; Step S4: A patterned top electrode is grown on the surface of the piezoelectric layer exposed after peeling. The bottom and top electrodes have a thickness of 200-1500 nm, the cavity layer has a thickness of 0.5-4 μm, the piezoelectric layer has a thickness of 0.1-3.5 μm, and the support layer has a thickness of 20-300 nm.

2. The method for fabricating a thin-film bulk acoustic resonator using a wet chemical substrate lift-off technique according to claim 1, characterized in that, Substrate B is any one of Si, SiC, glass, or organic flexible substrate; The cavity layer is a patterned SiO2 or Si3N4 with a cavity structure.

3. The method for preparing a thin-film bulk acoustic resonator using a wet chemical substrate lift-off technique according to claim 2, characterized in that, A cavity structure is grown on the surface of substrate B using photolithography, photomask, or etching techniques.

4. The method for preparing a thin-film bulk acoustic resonator using wet chemical substrate lift-off technology according to claim 1, characterized in that, The bonding can be metallic, non-metallic, or organic.

5. A thin-film bulk acoustic resonator, characterized in that, It is prepared by the method for preparing a thin-film bulk acoustic resonator using wet chemical substrate peeling technology as described in any one of claims 1-4.

6. A thin-film bulk acoustic resonator according to claim 5, characterized in that, The surface roughness of the piezoelectric layer is less than 2.5 nm.

7. A thin-film bulk acoustic resonator according to claim 6, characterized in that, The surface roughness of the piezoelectric layer is 0.1-2 nm.

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