A method for fabricating an air gap film bulk acoustic wave filter

Abstract

The application discloses a preparation method of an air-gap thin film bulk acoustic wave filter, and comprises the following steps: S1, sequentially depositing a passivation layer, an upper electrode, a piezoelectric layer and a lower electrode on the surface of a first substrate, and patterning the lower electrode; S2, depositing a support layer on the lower electrode, polishing and patterning the support layer to form a cavity; S3, bonding the support layer with a second substrate; S4, removing the first substrate, and taking the second substrate as the substrate of the filter; S5, patterning the passivation layer, the upper electrode and the piezoelectric layer; S6, depositing a PAD material on the surface of the filter; and S7, adjusting the passivation layer according to the test result. The growth order of the passivation layer is changed, so that the purpose of not deteriorating the resonator Q value is achieved. The passivation layer is preferentially deposited, compared with the deposition after the cavity is formed, the stress of the material layer is not increased, and the Q value can be further improved. Meanwhile, there is no step generated by patterning, and the consistency of the passivation layer film is better.

Description

Technical Field

[0001] This invention relates to the field of filter fabrication technology, and in particular to a method for fabricating an air-gap thin-film bulk acoustic filter. Background Technology

[0002] There are generally two methods for fabricating air-gap thin-film bulk acoustic wave filters. One method involves pre-embedding a sacrificial layer and then releasing it to obtain the cavity; the other method involves obtaining the cavity through bonding. For bonding fabrication, SiN is often chosen as the passivation layer to achieve good airtightness. However, changes in SiN thickness have little effect on frequency change. Therefore, during frequency tuning, the Mo layer needs to be thinned accordingly before SiN deposition, and secondary frequency tuning is required after SiN deposition. Furthermore, SiN deposition significantly reduces the Q value of the resonator, leading to a deterioration in the filter's insertion loss and rectangularity.

[0003] In existing technologies for fabricating filters using bonding methods, the passivation layer is typically grown after the cavity is formed. However, this process significantly reduces the Q value, leading to a deterioration in the resonator's insertion loss and rectangularity. Furthermore, secondary frequency tuning is required. Summary of the Invention

[0004] To address the problem that passivation layers in existing technologies can lead to a decrease in Q-value, resulting in deterioration of filter insertion loss and rectangularity, this invention provides a method for fabricating an air-gap thin-film bulk acoustic filter. By changing the growth sequence of the passivation layer, the Q-value of the resonator is not deteriorated.

[0005] The following is the technical solution of the present invention.

[0006] A method for fabricating an air-gap thin-film bulk acoustic wave filter includes the following steps:

[0007] S1: A passivation layer, an upper electrode, a piezoelectric layer, and a lower electrode are sequentially deposited on the surface of the first substrate, and the lower electrode is patterned.

[0008] S2: A support layer is deposited on the lower electrode, and the support layer is polished and patterned to form a cavity;

[0009] S3: Bonding the second substrate to the support layer;

[0010] S4: Eliminate the first substrate and use the second substrate as the substrate for the filter;

[0011] S5: Pattern the passivation layer, top electrode, and piezoelectric layer;

[0012] S6: Deposit PAD material on the filter surface;

[0013] S7: Adjust the frequency of the passivation layer based on the test results.

[0014] This invention first deposits a passivation layer, a top electrode, a piezoelectric layer, and a bottom electrode sequentially on the surface of a first substrate, then bonds a second substrate, and finally removes the first substrate. Since the second substrate is the one that actually functions, the growth sequence of each layer is reversed compared to the conventional method. The passivation layer deposition process is adjusted to occur before cavity formation, prioritizing the deposition of the passivation layer. Compared to existing technologies where the passivation layer is deposited after cavity formation, this does not increase the stress on the material layers and can further improve the Q value. Simultaneously, there are no steps caused by patterning, resulting in better uniformity of the passivation layer film. Therefore, steps S2-S4 of this invention are crucial to the effectiveness and cannot be replaced.

[0015] Preferably, the method further includes depositing a mass loading layer that enhances the Q value on the surface of the piezoelectric layer before depositing the lower electrode.

[0016] Preferably, the complete removal of the first substrate includes: completely removing the first substrate using mechanical grinding and etching processes.

[0017] Preferably, the passivation layer is a two-layer passivation layer, including a first passivation layer and a second passivation layer.

[0018] Preferably, the first passivation layer is a combination layer of aluminum nitride and silicon nitride or a combination layer of aluminum nitride and silicon dioxide, and the second passivation layer is a combination layer of aluminum nitride and silicon nitride or a combination layer of aluminum nitride and silicon dioxide. These materials can ensure the hermeticity of the device, and only frequency modulation of the aluminum nitride is required. If silicon nitride or silicon dioxide is used, the thickness needs to be greater than 50 angstroms to ensure the hermeticity of the device.

[0019] Preferably, the first substrate and / or the second substrate are semiconductor materials, including one or more of high-resistivity silicon, silicon carbide, gallium nitride, aluminum oxide, and diamond.

[0020] Preferably, the piezoelectric material of the piezoelectric layer includes aluminum nitride.

[0021] Preferably, the materials of the upper and lower electrodes include one or more of aluminum, molybdenum, and tungsten.

[0022] Preferably, the material of the mass loading layer includes one or more of molybdenum, aluminum nitride, polycrystalline silicon, and silicon dioxide.

[0023] Preferably, the PAD material includes one or more of aluminum, gold, and copper.

[0024] The substantial effects of this invention include:

[0025] Using a bonding process, aluminum nitride and other materials are first deposited on the first substrate as a passivation layer, followed by the deposition of the upper electrode, piezoelectric layer, mass load layer, lower electrode, support layer, etc., and then the cavity is patterned to form a cavity. By depositing the passivation layer before the cavity is formed, the Q value is avoided from decreasing due to the deposition of the passivation layer after the cavity is formed.

[0026] Preferential deposition of passivation layer results in better uniformity of passivation film due to the absence of steps caused by patterning.

[0027] Choosing aluminum nitride or a combination of materials as the passivation layer only requires frequency tuning of the aluminum nitride, while ensuring the hermeticity of the device. More importantly, depositing the passivation layer before the cavity is formed will not cause the Q value to decrease. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the first stage of the preparation process according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the second stage of the preparation process according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the third stage of the preparation process according to an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the fourth stage of the preparation process in an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the fifth stage of the preparation process according to an embodiment of the present invention;

[0033] The figure includes: 1-first substrate, 2-first passivation layer, 3-second passivation layer, 4-upper electrode, 5-piezoelectric layer, 6-lower electrode, 7-support layer, 8-second substrate, and 9-PAD material. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be understood that in the various embodiments of the present invention, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0036] It should be understood that in this invention, "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0037] It should be understood that in this invention, "multiple" refers to two or more. "And / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, "and / or B" can represent: A existing alone, A and B existing simultaneously, and B existing alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "Contains A, B, and C", "Contains A, B, and C" means that all three A, B, and C are contained; "Contains A, B, or C" means that one of A, B, and C is contained; "Contains A, B, and / or C" means that any one, two, or three of A, B, and C are contained.

[0038] The technical solution of the present invention will be described in detail below with reference to specific embodiments. Embodiments may be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0039] Example:

[0040] A method for fabricating an air-gap thin-film bulk acoustic wave filter includes the following steps: S1: as Figure 1 As shown, a first passivation layer 2, a second passivation layer 3, an upper electrode 4, a piezoelectric layer 5, and a lower electrode 6 are sequentially deposited on the surface of the first substrate 1, and the lower electrode is patterned.

[0041] In terms of process sequence, two passivation layers are first deposited, followed by the deposition of the upper electrode and piezoelectric layer. Other structures such as the mass load layer can be processed on the surface of the piezoelectric layer. Then, the lower electrode is deposited on the surface of the piezoelectric layer and patterned.

[0042] In this embodiment, the passivation layer consists of two layers. The material of each layer can be selected from aluminum nitride, aluminum nitride and silicon nitride, or aluminum nitride and silicon dioxide. In this embodiment, one layer uses aluminum nitride and the other layer uses aluminum nitride and silicon nitride.

[0043] The above materials can ensure the hermeticity of the device, and only the aluminum nitride needs to be frequency tuned; if silicon nitride or silicon dioxide is used, the thickness needs to be greater than 50 angstroms to ensure the hermeticity of the device.

[0044] Furthermore, the piezoelectric material of the piezoelectric layer in this embodiment is aluminum nitride. The materials for the upper and lower electrodes include one or more of aluminum, molybdenum, and tungsten; in this embodiment, molybdenum is selected as the material for both the upper and lower electrodes. The materials for the mass load layer include one or more of molybdenum, aluminum nitride, polycrystalline silicon, and silicon dioxide; in this embodiment, polycrystalline silicon is used for the mass load layer.

[0045] S2: Deposit a support layer 7 on the lower electrode, and polish and pattern the support layer to form a cavity.

[0046] That is, a support layer 7 is deposited on the surface of the lower electrode, and then mechanically and chemically polished and patterned.

[0047] S3: As Figure 2 As shown, the second substrate 8 is bonded to the support layer.

[0048] In this embodiment, the first substrate and / or the second substrate are semiconductor materials, and the selection range includes one or more of high-resistivity silicon, silicon carbide, gallium nitride, aluminum oxide, and diamond. In this embodiment, silicon carbide is used.

[0049] S4: As Figure 3 As shown, the first substrate is completely removed, and the second substrate is used as the substrate for the filter. For ease of understanding, Figure 3 The schematic diagram has been flipped so that the second substrate is facing down.

[0050] S5: As Figure 4 As shown, the passivation layer, passivation layer, top electrode, and piezoelectric layer are patterned.

[0051] S6: As Figure 5 As shown, PAD material is deposited on the surface of the filter.

[0052] The PAD material can be selected from one or more of aluminum, gold, and copper. In this embodiment, copper is used as the PAD material.

[0053] S7: Adjust the frequency of the passivation layer based on the test results.

[0054] In this embodiment, a passivation layer, an upper electrode, a piezoelectric layer, and a lower electrode are sequentially deposited on the surface of a first substrate. A second substrate is then bonded, and the first substrate is removed. Since the second substrate is the one that actually functions, the growth sequence of each layer is reversed compared to the conventional method. The passivation layer deposition process is adjusted to occur before cavity formation, prioritizing the deposition of the passivation layer. Compared to depositing the passivation layer after cavity formation, this does not increase the stress on the material layers or cause a decrease in the Q value. Furthermore, there are no steps caused by patterning, resulting in better uniformity of the passivation layer film.

[0055] This embodiment employs a bonding process route, prioritizing the deposition of materials such as aluminum nitride as a passivation layer on the first substrate, followed by the deposition of the upper electrode, piezoelectric layer, mass load layer, and lower electrode. By depositing the passivation layer before the cavity is formed, the Q value is avoided from decreasing due to the deposition of the passivation layer after the cavity is formed.

[0056] Preferential deposition of passivation layer results in better uniformity of passivation film due to the absence of steps caused by patterning.

[0057] Choosing aluminum nitride or a combination of materials as the passivation layer only requires frequency tuning of the aluminum nitride, while ensuring the hermeticity of the device. More importantly, depositing the passivation layer before the cavity is formed will not cause the Q value to decrease.

[0058] Through the above description of the embodiments, those skilled in the art will understand that, for the sake of convenience and brevity, only the division of the above functional modules is used as an example. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the specific device can be divided into different functional modules to complete all or part of the functions described above.

[0059] In the embodiments provided in this application, it should be understood that the disclosed structures and methods can be implemented in other ways. For example, the structural embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another structure, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection of structures or units, and may be electrical, mechanical, or other forms.

[0060] The units described as separate components may or may not be physically separate. A component shown as a unit can be one or more physical units; that is, it can be located in one place or distributed in multiple different locations. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0061] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should 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 of making an air gap film bulk acoustic wave filter, comprising: The method comprises the following steps: S1: sequentially depositing a passivation layer, an upper electrode, a piezoelectric layer, and a lower electrode on the surface of a first substrate, and patterning the lower electrode; S2: depositing a support layer on the lower electrode, and forming a cavity after polishing and patterning the support layer; S3: bonding the support layer with a second substrate; S4: removing the first substrate, and taking the second substrate as the substrate of the filter; S5: patterning the passivation layer, the upper electrode, and the piezoelectric layer; S6: depositing a PAD material on the surface of the filter; S7: adjusting the passivation layer according to the test result.

2. The method of claim 1, wherein the air gap film bulk acoustic wave filter is prepared by the steps of: Further comprising: Before depositing the lower electrode, depositing a mass load layer for improving Q value on the surface of the piezoelectric layer.

3. The method of claim 1, wherein the method further comprises: In the S4, the first substrate is completely removed by mechanical grinding or etching process.

4. The method for fabricating an air-gap thin-film bulk acoustic filter according to claim 1, characterized in that, The passivation layer comprises two layers, i.e., a first passivation layer and a second passivation layer.

5. The method of claim 4, wherein the air gap FBAR is prepared by: The first passivation layer is a combined layer of aluminum nitride and silicon nitride or a combined layer of aluminum nitride and silicon dioxide, and the second passivation layer is a combined layer of aluminum nitride and silicon nitride or a combined layer of aluminum nitride and silicon dioxide, and the thickness of the single-layer passivation layer is greater than 50 angstroms.

6. The method of claim 1, wherein the air gap FBAR is prepared by the steps of: The first substrate and / or the second substrate is a semiconductor material, which comprises one or more of high-resistance silicon, silicon carbide, gallium nitride, aluminum oxide, and diamond.

7. The method for fabricating an air-gap thin-film bulk acoustic filter according to claim 1, characterized in that, The piezoelectric material of the piezoelectric layer comprises aluminum nitride.

8. The method of claim 1, wherein the air gap film bulk acoustic wave filter is prepared by the steps of: The material of the upper electrode and the lower electrode comprises one or more of aluminum, molybdenum, and tungsten.

9. The method for fabricating an air-gap thin-film bulk acoustic filter according to claim 2, characterized in that, The material of the mass load layer comprises one or more of molybdenum, aluminum nitride, polysilicon, and silicon dioxide.

10. The method of claim 1, wherein the air gap film bulk acoustic wave filter is prepared by the steps of: The PAD material comprises one or more of aluminum, gold, and copper.

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