Method for manufacturing a film bulk acoustic resonator

Abstract

The application discloses a preparation method of a film bulk acoustic resonator and belongs to the technical field of microelectronic manufacturing. The preparation method specifically comprises the following steps: S100, providing a substrate, etching a concave cavity on a processing surface of the substrate; S200, sequentially covering a protection layer and a sacrifice layer on the processing surface of the substrate; S300, etching a groove on the protection layer and the sacrifice layer and depositing a longitudinal Bragg reflection layer in the groove; S400, depositing a piezoelectric stack structure on the protection layer, the sacrifice layer and the longitudinal Bragg reflection layer; S500, forming a transverse reflection layer on the piezoelectric stack structure; and S600, removing the sacrifice layer to form a cavity. The preparation method of the application omits a bonding process, reduces the flatness requirement of the substrate, reduces the implementation difficulty of the preparation method, shortens the process cycle of the preparation method, and adopts an etching process to replace an existing CMP process to make the longitudinal Bragg reflection layer on the protection layer, so that the longitudinal Bragg reflection layer is flush with the surface of the protection layer, thereby improving the Q value of the film bulk acoustic resonator.

Description

[Technical Field]

[0001] This invention relates to the field of microelectronics manufacturing technology, and in particular to a method for fabricating thin-film bulk acoustic resonators. [Background Technology]

[0002] Currently, the most mainstream implementation methods for radio frequency (RF) filters are surface acoustic wave (SAW) filters and filters based on film bulk acoustic resonator (FBAR) technology. Due to its inherent limitations, SAW filters are more suitable for use below 1.5 GHz. However, current wireless communication protocols have long used frequency bands above 2.5 GHz, necessitating the use of FBAR-based filters.

[0003] In recent years, thin-film bulk acoustic resonators (FBARs) have been developed with higher operating frequencies (1-10 GHz) than traditional surface acoustic wave (SAW) devices, quartz crystal resonators, and ceramic dielectric devices. They also have advantages such as small size, high Q value, and low loss. Therefore, FBARs have a very broad prospect for development and application in wireless communication.

[0004] There are many structures and fabrication methods for FBAR devices. One known method involves etching grooves on a first and second substrate, depositing a thin film material in the grooves of the second substrate, and then CMP polishing the surface of the thin film material to remove any undesigned material, forming a longitudinal reflective layer. The first and second substrates are then bonded together on the back of the second substrate to form a piezoelectric stack structure. A lateral reflective layer is formed at the edge region of the piezoelectric stack structure, completing the fabrication of the thin-film bulk acoustic resonator. This design can confine acoustic wave energy to the effective area of ​​the device using the longitudinal and lateral reflective layers, thereby improving the Q value of the FBAR device. However, this fabrication method uses bonding and CMP polishing processes. First, the physical meaning of bonding usually refers to cleaning the surfaces of two substrates and achieving atomic-level flatness. The technology of directly bonding homogeneous or heterogeneous semiconductor materials under certain conditions after surface cleaning and activation, using van der Waals forces, molecular forces, or even atomic forces to bond the wafers together, is difficult to implement due to the strict flatness requirements of the substrate material, and can easily become a bottleneck in the manufacturing process. Secondly, CMP polishing to remove undesigned reflective materials requires high-performance CMP equipment. Different polishing materials have different polishing rates after CMP polishing, which will generate a certain amount of dishing, making it difficult to ensure that the reflective layer is flush with the substrate surface. This affects the film quality of the piezoelectric stacked structure and leads to a decrease in the Q value of the FABR device. Therefore, the existing methods for fabricating thin-film bulk acoustic resonators have certain limitations in practical implementation. [Summary of the Invention]

[0005] The purpose of this invention is to provide a method for fabricating a thin-film bulk acoustic resonator, which can at least partially solve the aforementioned technical problems.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] The fabrication method of a thin-film bulk acoustic resonator includes the following steps:

[0008] S100, Provide a substrate, and etch a cavity into the processing surface of the substrate;

[0009] S200, A protective layer and a sacrificial layer are sequentially covered on the processed surface of the substrate;

[0010] S300: Grooves are etched into the protective layer and the sacrificial layer, and a longitudinal Bragg reflector layer is deposited in the grooves;

[0011] S400, depositing a piezoelectric stacked structure on a protective layer, a sacrificial layer and a longitudinal Bragg reflector layer;

[0012] S500, A transverse reflective layer is formed on the piezoelectric stacked structure;

[0013] S600, remove the sacrificial layer to form a cavity.

[0014] In the above method for fabricating a thin-film bulk acoustic resonator, step S200 includes:

[0015] S210. Deposit a protective layer on the processing surface of the substrate;

[0016] S220, Deposit a sacrificial layer on the protective layer;

[0017] S230. Remove excess sacrificial layer to make the surfaces of the protective layer and the sacrificial layer flush.

[0018] In the above-mentioned method for fabricating a thin-film bulk acoustic resonator, the sacrificial layer is removed in step S600 using a dry release process. The protective layer is a silicon dioxide layer formed by thermal oxidation, and the sacrificial layer is a polycrystalline silicon layer.

[0019] In the above method for fabricating a thin-film bulk acoustic resonator, step S300 includes:

[0020] S310. Pattern and etch the surface of the protective layer to form the first groove;

[0021] S320. Pattern and etch the surface of the sacrificial layer to form a second groove that communicates with the first groove;

[0022] S330, a longitudinal Bragg reflector layer is deposited in the first groove and the second groove.

[0023] In the above-mentioned method for fabricating a thin-film bulk acoustic resonator, at least one set of longitudinal Bragg reflector layers is deposited in step S330, and each set of longitudinal Bragg reflector layers includes at least two thin-film material layers with different acoustic impedances.

[0024] In the above-mentioned method for fabricating a thin-film bulk acoustic resonator, in step S330, photolithography is used to remove the undesigned longitudinal Bragg reflection layer, so that the thickness of the longitudinal Bragg reflection layer is consistent with the depth of the first groove and the second groove.

[0025] In the above method for fabricating a thin-film bulk acoustic resonator, step S400 includes:

[0026] S410. Deposit a seed layer on the protective layer, the sacrificial layer, and the longitudinal Bragg reflector layer;

[0027] S420. Deposit an electrode layer on a portion of the surface of the seed layer and pattern it.

[0028] S430. Deposit a piezoelectric layer on the remaining surface of the seed layer and on the lower electrode layer;

[0029] S440. An upper electrode layer and a passivation layer are sequentially deposited on the surface of the piezoelectric layer, and the upper electrode layer and passivation layer are patterned and etched to expose part of the surface of the piezoelectric layer.

[0030] In the above-described method for fabricating a thin-film bulk acoustic resonator, step S400 further includes:

[0031] S450. A lower electrode opening is provided through the piezoelectric layer along its thickness direction, and an upper electrode opening is provided through the passivation layer along its thickness direction.

[0032] S460, a lower electrode lead is deposited in the lower electrode opening to form a lower electrode lead in contact with the lower electrode layer, and an upper electrode lead is deposited in the upper electrode opening to form a upper electrode lead in contact with the upper electrode layer.

[0033] In the above-mentioned method for fabricating a thin-film bulk acoustic resonator, in step S500, a third groove is etched on the piezoelectric layer to form a transverse reflective layer based on an air gap, and the third groove and the adjacent piezoelectric layer form a transverse reflective layer.

[0034] In the above-mentioned method for fabricating a thin-film bulk acoustic resonator, in step S500, a third groove is etched on the piezoelectric layer, a thin film material is deposited in the third groove, and the thin film material and the adjacent piezoelectric layer form a Bragg-based lateral reflective layer.

[0035] The beneficial effects of this invention are:

[0036] In the fabrication method of the thin-film bulk acoustic resonator proposed in this invention, the protective layer, sacrificial layer, longitudinal Bragg reflector layer, and piezoelectric stacking structure are all continuously stacked and integrated on the same substrate, eliminating the bonding process, avoiding the technical difficulties brought about by the bonding process, reducing the flatness requirements of the substrate, reducing the implementation difficulty of the fabrication method, and shortening the process cycle of the fabrication method. Furthermore, the use of etching process to replace the existing CMP process to create the longitudinal Bragg reflector layer on the protective layer can ensure that the longitudinal Bragg reflector layer is flush with the surface of the protective layer, effectively reducing longitudinal acoustic wave leakage, thereby improving the Q value of the thin-film bulk acoustic resonator.

[0037] Furthermore, in step S330, at least one set of longitudinal Bragg reflector layers is deposited, each set comprising at least two thin film material layers with different acoustic impedances. This allows for the reflection of sound waves by utilizing the impedance difference between adjacent thin film material layers, thereby maximizing the utilization of sound wave energy.

[0038] Further, step S400 includes: S410, depositing a seed layer on the protective layer, sacrificial layer, and longitudinal Bragg reflector layer; S420, depositing a lower electrode layer on a portion of the surface of the seed layer and patterning it; S430, depositing a piezoelectric layer on the remaining surface of the seed layer and the lower electrode layer; S440, sequentially depositing an upper electrode layer and a passivation layer on the surface of the piezoelectric layer, and patterning and etching the upper electrode layer and passivation layer to expose a portion of the surface of the piezoelectric layer. It can be seen that in the piezoelectric stacked structure designed according to the steps of this scheme, a seed layer separates the lower electrode layer from the longitudinal Bragg reflector layer. On the one hand, the seed layer can improve the adhesion and crystal orientation of the film layer; on the other hand, it prevents the lower electrode layer from directly contacting the longitudinal Bragg reflector layer, allowing longitudinal and transverse acoustic waves to return to the effective area and reducing acoustic wave leakage.

[0039] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. [Attached Image Description]

[0040] The invention will be further described below with reference to the accompanying drawings:

[0041] Figure 1 This is a flowchart illustrating a method for fabricating a thin-film bulk acoustic resonator in one embodiment of the present invention;

[0042] Figure 2 This is a schematic diagram of step S100 in one embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram illustrating the fabrication of step S210 in one embodiment of the present invention;

[0044] Figure 4 This is a schematic diagram illustrating the fabrication of step S220 in one embodiment of the present invention;

[0045] Figure 5 This is a schematic diagram illustrating the fabrication of step S230 in one embodiment of the present invention;

[0046] Figure 6 This is a schematic diagram illustrating the fabrication of step S310 in one embodiment of the present invention;

[0047] Figure 7 This is a schematic diagram illustrating the fabrication of step S320 in one embodiment of the present invention;

[0048] Figure 8 This is a schematic diagram illustrating the fabrication of step S330 in one embodiment of the present invention;

[0049] Figure 9 This is a schematic diagram illustrating the fabrication of step S410 in one embodiment of the present invention;

[0050] Figure 10 This is a schematic diagram illustrating the fabrication of step S420 in one embodiment of the present invention;

[0051] Figure 11 This is a schematic diagram illustrating the fabrication of step S430 in one embodiment of the present invention;

[0052] Figure 12 This is a schematic diagram illustrating the fabrication of step S440 in one embodiment of the present invention;

[0053] Figure 13 This is a schematic diagram illustrating the fabrication of step S450 in one embodiment of the present invention;

[0054] Figure 14 This is a schematic diagram illustrating the fabrication of step S460 in one embodiment of the present invention;

[0055] Figure 15 This is a schematic diagram illustrating the fabrication of step S500 in one embodiment of the present invention;

[0056] Figure 16 This is a schematic diagram illustrating the fabrication of step S600 in one embodiment of the present invention;

[0057] Figure 17 The Q-simulation curves for existing thin-film bulk acoustic resonators;

[0058] Figure 18 The Q-simulation curve of a thin-film bulk acoustic resonator in one embodiment of the present invention is shown.

[0059] Figure label:

[0060] 100 substrate, 110 cavity;

[0061] 200 protective layer, 210 first groove;

[0062] 300 sacrificial layer, 310 second groove, 320 cavity;

[0063] 400 longitudinal Bragg reflector layer;

[0064] 500 seed layers;

[0065] 600 lower electrode layer;

[0066] 700 piezoelectric layer, 710 lower electrode opening, 720 lower electrode lead, 730 third groove;

[0067] 800 top electrode layer;

[0068] 900 passivation layer, 910 upper electrode opening, 920 upper electrode lead.

Detailed Implementation Methods

[0069] The technical solutions of the embodiments of the present invention will be explained and described below with reference to the accompanying drawings. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0070] The terms "exemplary" and "some embodiments" used below are meant to be "used as examples, embodiments, or illustrations," and any embodiment described as "exemplary" is not necessarily to be construed as superior to or better than other embodiments. Numerous specific details are set forth in the following detailed description to better illustrate the invention, and those skilled in the art will understand that this disclosure can be practiced without certain specific details.

[0071] Reference Figure 1 The method for fabricating a thin-film bulk acoustic resonator proposed in one embodiment of the present invention is characterized by comprising the following steps:

[0072] S100: Provide a substrate 100 and etch a cavity 110 on the processing surface of the substrate 100;

[0073] S200, a protective layer 200 and a sacrificial layer 300 are sequentially covered on the processing surface of the substrate 100;

[0074] S300, Grooves are etched on the protective layer 200 and the sacrificial layer 300, and a longitudinal Bragg reflector layer 400 is deposited in the grooves;

[0075] S400, a piezoelectric stacked structure is deposited on the protective layer 200, the sacrificial layer 300 and the longitudinal Bragg reflector layer 400;

[0076] S500, A transverse reflective layer is formed on the piezoelectric stacked structure;

[0077] S600, remove the sacrificial layer 300 to form a cavity 320.

[0078] Specifically, refer to Figure 2 In step S100 of this embodiment, the substrate 100 is preferably a Si wafer, which is easy to process. In other embodiments, SOI substrate 100 or SiC substrate 100 can also be selected according to actual process needs. The cavity 110 is etched on the processing surface of the substrate 100 by dry etching process. During the etching process, the angle between the side surface and the bottom surface of the cavity 110 is greater than 100°, which can improve the quality of the subsequent deposited film layer.

[0079] Reference Figure 3-5 Step S200 specifically includes:

[0080] S210. A protective layer 200 is deposited on the processing surface of the substrate 100. The protective layer 200 covers the entire processing surface of the substrate 100, including the surface of the cavity 110. In this embodiment, the protective layer 200 is a silicon dioxide layer formed by thermal oxidation. The protective layer 200 provides protection for the substrate 100 when the sacrificial layer 300 is removed in a subsequent process. In other embodiments, other materials may be selected depending on the process of removing the sacrificial layer 300.

[0081] S220. A sacrificial layer 300 is deposited on the protective layer 200. The sacrificial layer 300 completely covers the protective layer 200. Considering that the dry release process is used to remove the sacrificial layer 300 in step S600 of this embodiment, and the sacrificial layer 300 is a polycrystalline silicon layer, in other embodiments, other materials can be selected according to different processes for removing the sacrificial layer 300. For example, when the sacrificial layer 300 is removed by a wet release process, PSG can be used as the sacrificial layer 300 material. Finally, the cavity 320 is formed by etching the PSG sacrificial layer 300.

[0082] S230. Remove excess sacrificial layer 300 to make the surfaces of protective layer 200 and sacrificial layer 300 flush. This step uses a polishing process (such as CMP process) to remove excess sacrificial layer 300, exposing part of protective layer 200, and keeping the upper surfaces of the two flush.

[0083] Reference Figure 6-8 Step S300 specifically includes:

[0084] S310, The surface of the protective layer 200 is patterned and etched, and the part of the protective layer 200 near the sacrificial layer 300 is patterned and etched by photolithography to form the first groove 210.

[0085] S320. The surface of the sacrificial layer 300 is patterned and etched. The part of the surface of the sacrificial layer 300 near the protective layer 200 is patterned and etched to form a second groove 310. The first groove 210 and the second groove 310 are connected and have the same depth.

[0086] S330. A longitudinal Bragg reflector layer 400 is deposited in the first groove 210 and the second groove 310. Specifically, a thin film material is deposited into the first groove 210 and the second groove 310, and the undesigned longitudinal Bragg reflector layer 400 is removed by photolithography with photoresist coating, so that the thickness of the longitudinal Bragg reflector layer 400 is consistent with the depth of the first groove 210 and the second groove 310. Preferably, at least one set of longitudinal Bragg reflector layers 400 is deposited in the first groove 210 and the second groove 310, and each set of longitudinal Bragg reflector layers 400 includes at least two thin film material layers with different acoustic impedances. For example, each set of longitudinal Bragg reflector layers 400 includes a first thin film layer and a second thin film layer. The first thin film layer is made of silicon dioxide, and the second thin film layer is made of aluminum nitride. The difference in impedance between the first thin film layer material and the second thin film layer material is used to reflect sound waves, thereby maximizing the utilization of sound wave energy. When multiple sets of longitudinal Bragg reflector layers need to be set, the other sets of longitudinal Bragg reflector layers can also be designed with reference to the above-described stacked structure.

[0087] As can be seen from the above example, when the longitudinal Bragg reflector layer 400 includes a third thin film layer, the first thin film layer, the second thin film layer and the third thin film layer are stacked sequentially in the groove, and the third thin film layer and the second thin film layer are also thin film material layers with different acoustic impedances, it is sufficient to ensure that the thin film material layers with different acoustic impedances are stacked in layers.

[0088] In the above examples, the thin film material is not limited to silicon dioxide and aluminum nitride, but can also be silicon nitride, silicon oxynitride, silicon carbide, tungsten, titanium oxide, thallium oxide, etc. Those skilled in the art can also select other materials with different impedances according to actual needs, which are not specifically limited here.

[0089] Reference Figure 9-14 Step S400 specifically includes:

[0090] S410. A seed layer 500 is deposited on the protective layer 200, the sacrificial layer 300, and the longitudinal Bragg reflector layer 400. The seed layer 500 completely covers the protective layer 200, the sacrificial layer 300, and the longitudinal Bragg reflector layer 400. The material of the seed layer 500 can be one of aluminum, tungsten, or aluminum nitride. Those skilled in the art can also choose other materials according to actual needs, but no specific limitation is made here.

[0091] S420. Deposit and pattern a lower electrode layer 600 on a portion of the surface of the seed layer 500; the lower electrode layer 600 is typically a metallic material, such as tungsten, silver, copper, titanium, chromium, etc.

[0092] S430. A piezoelectric layer 700 is deposited on the remaining surface of the seed layer 500 and the lower electrode layer 600. The material of the piezoelectric layer 700 can be selected from aluminum nitride, zinc oxide, titanium oxide, and thallium oxide. Those skilled in the art can also select other materials according to actual needs, and no specific limitation is made here.

[0093] S440. An upper electrode layer 800 and a passivation layer 900 are sequentially deposited on the surface of the piezoelectric layer 700, and the upper electrode layer 800 and the passivation layer 900 are patterned and etched to expose a portion of the surface of the piezoelectric layer 700. The material of the upper electrode layer 800 is the same as that of the lower electrode layer 600 mentioned above, and the two materials can be the same or different. The material of the passivation layer 900 is aluminum nitride, but those skilled in the art can also use silicon dioxide, silicon nitride or other materials.

[0094] S450. A lower electrode opening 710 is provided through the piezoelectric layer 700 along its thickness direction, and an upper electrode opening 910 is provided through the passivation layer 900 along its thickness direction.

[0095] S460, a lower electrode lead 720 in contact with the lower electrode layer 600 is deposited in the lower electrode opening 710, and an upper electrode lead 920 in contact with the upper electrode layer 800 is deposited in the upper electrode opening 910.

[0096] As can be seen from step S400 above, a seed layer 500 is spaced between the lower electrode layer 600 and the longitudinal Bragg reflector layer 400. On the one hand, the seed layer 500 can improve the adhesion and crystal orientation of the film layer; on the other hand, other structural designs in the prior art, such as the invention patent with application number "202110682234" entitled "A High Q Value Thin Film Bulk Acoustic Resonator for Suppressing Energy Leakage and Parasitism", use other materials to replace the electrode edge to achieve impedance matching in order to return some acoustic energy to the effective area. In this way, the reflector layer must be in contact with the electrode layer. Although this can reduce energy leakage to a certain extent, there will still be acoustic energy leakage to the lateral and longitudinal directions. In this embodiment, the seed layer 500 makes the lower electrode layer 600 not in direct contact with the longitudinal Bragg reflector layer 400, which can return the longitudinal and lateral acoustic waves to the effective area and reduce the leakage of acoustic waves.

[0097] Reference Figure 15In step S500, a third groove 730 is etched on the piezoelectric layer 700. The third groove 730 and the adjacent piezoelectric layer 700 form a transverse reflective layer based on an air gap. Specifically, since the transverse reflective layer based on an air gap has the third groove 730 and the adjacent piezoelectric layer 700, it can utilize the different impedances of the air gap and the adjacent piezoelectric layer 700 to reflect sound waves, thereby maximizing the utilization of sound wave energy. Its structure is similar to the aforementioned longitudinal Bragg reflective layer 400 formed by two layers of thin film material with different acoustic impedances, but the effect is to effectively reduce the loss of transverse sound waves. Since the thin-film bulk acoustic resonator has both a transverse reflective layer and a longitudinal reflective layer, it can effectively reduce the loss of longitudinal and transverse sound waves, which is beneficial to confine the sound wave energy within the effective area of ​​the device, thereby improving the Q value of the device and enabling the thin-film bulk acoustic resonator to have higher frequency stability.

[0098] In other embodiments, step S500 may involve etching a third groove 730 on the piezoelectric layer 700, depositing a thin film material within the third groove 730, and forming a Bragg-based lateral reflective layer with the adjacent piezoelectric layer 700. This lateral reflective layer structure can also reduce lateral sound wave loss. Structurally, the thin film material within the third groove 730 and the piezoelectric layer 700 material have different acoustic impedances, allowing the difference in impedance between adjacent material layers to reflect sound waves and maximize the utilization of sound wave energy.

[0099] Reference Figure 16 In step S600, the sacrificial layer 300 is removed to form a cavity 320. Specifically, the sacrificial layer 300 is removed using a dry release process to ensure that the sacrificial layer material in the cavity 320 is completely released. In other embodiments, other known processes such as wet release processes can be used to remove the sacrificial layer.

[0100] As can be seen from the above embodiments, the protective layer 200, the sacrificial layer 300, the longitudinal Bragg reflector layer 400, and the piezoelectric stacked structure are all continuously stacked and integrated on the same substrate 100, eliminating the bonding process in the prior art, avoiding the technical difficulties brought about by the bonding process, reducing the flatness requirements of the substrate 100, reducing the implementation difficulty of the fabrication method, and shortening the process cycle of the fabrication method. In step 300, the etching process is used to replace the existing CMP process to make the longitudinal Bragg reflector layer 400 on the protective layer 200, which can ensure that the longitudinal Bragg reflector layer 400 is flush with the surface of the protective layer 200, effectively reducing the leakage of longitudinal acoustic waves, thereby improving the Q value of the thin film bulk acoustic resonator.

[0101] Compared to existing conventional processes, the Q-value of the thin-film bulk acoustic resonator prepared using the embodiments of this invention is further improved. Specifically, a comparison can be made... Figure 17 and Figure 18The Q value of the thin-film bulk acoustic wave resonator in this embodiment does not change much at the series frequency Fs, but the Q value at the parallel resonant frequency Fp can be improved by about 100. Before the series resonant frequency, the Q value of the thin-film bulk acoustic wave resonator in this embodiment is in the range of 1000-1600, while that of existing thin-film bulk acoustic wave resonators is only 600-1300. Between Fs and Fp, the Q value of the thin-film bulk acoustic wave resonator in this embodiment is in the range of 1200-1900, while that of existing thin-film bulk acoustic wave resonators is only 1160-1370. After Fp, the Q value of the thin-film bulk acoustic wave resonator in this embodiment is in the range of 1300-2600, while that of existing thin-film bulk acoustic wave resonators is only 1150-1400. It can be seen that the Q value of the thin-film bulk acoustic wave resonator prepared using the embodiment of the present invention is improved.

[0102] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A method for fabricating a thin-film bulk acoustic resonator, characterized in that, Includes the following steps: S100, Provide a substrate, and etch a cavity into the processing surface of the substrate; S200, A protective layer and a sacrificial layer are sequentially covered on the processed surface of the substrate; S300: Grooves are etched into the protective layer and the sacrificial layer, and a longitudinal Bragg reflector layer is deposited in the grooves; S400, depositing a piezoelectric stacked structure on a protective layer, a sacrificial layer and a longitudinal Bragg reflector layer; S500, A transverse reflective layer is formed on the piezoelectric stacked structure; S600, Remove the sacrificial layer to form a cavity; Step S200 includes: S210. Deposit a protective layer on the processing surface of the substrate; S220, Deposit a sacrificial layer on the protective layer; S230. Remove excess sacrificial layer to make the surfaces of the protective layer and the sacrificial layer flush. Step S300 includes: S310. Pattern and etch the surface of the protective layer to form the first groove; S320. Pattern and etch the surface of the sacrificial layer to form a second groove that communicates with the first groove; S330. Deposit a longitudinal Bragg reflector layer in the first groove and the second groove, so that the longitudinal Bragg reflector layer is flush with the surface of the protective layer. Step S400 includes: S410. Deposit a seed layer on the protective layer, the sacrificial layer, and the longitudinal Bragg reflector layer; S420, Deposit an electrode layer on a portion of the surface of the seed layer and pattern it.

2. The method for fabricating a thin-film bulk acoustic resonator as described in claim 1, characterized in that, In step S600, a dry release process is used to remove the sacrificial layer. The protective layer is a silicon dioxide layer formed by thermal oxidation, and the sacrificial layer is a polycrystalline silicon layer.

3. The method for fabricating a thin-film bulk acoustic resonator as described in claim 1, characterized in that, In step S330, at least one set of longitudinal Bragg reflector layers is deposited, and each set of longitudinal Bragg reflector layers includes at least two thin film material layers with different acoustic impedances.

4. The method for fabricating a thin-film bulk acoustic resonator as described in claim 1, characterized in that, In step S330, photolithography is used to remove the undesigned longitudinal Bragg reflection layer, so that the thickness of the longitudinal Bragg reflection layer is consistent with the depth of the first groove and the second groove.

5. The method for fabricating a thin-film bulk acoustic resonator as described in claim 1, characterized in that, Step S400 further includes: S430. Deposit a piezoelectric layer on the remaining surface of the seed layer and on the lower electrode layer; S440. An upper electrode layer and a passivation layer are sequentially deposited on the surface of the piezoelectric layer, and the upper electrode layer and passivation layer are patterned and etched to expose part of the surface of the piezoelectric layer.

6. The method for fabricating a thin-film bulk acoustic resonator as described in claim 5, characterized in that, Step S400 further includes: S450. A lower electrode opening is provided through the piezoelectric layer along its thickness direction, and an upper electrode opening is provided through the passivation layer along its thickness direction. S460, a lower electrode lead is deposited in the lower electrode opening to form a lower electrode lead in contact with the lower electrode layer, and an upper electrode lead is deposited in the upper electrode opening to form a upper electrode lead in contact with the upper electrode layer.

7. The method for fabricating a thin-film bulk acoustic resonator as described in claim 5, characterized in that, In step S500, a third groove is etched on the piezoelectric layer to form a transverse reflective layer based on an air gap with the adjacent piezoelectric layer.

8. The method for fabricating a thin-film bulk acoustic resonator as described in claim 5, characterized in that, In step S500, a third groove is etched on the piezoelectric layer, and a thin film material is deposited in the third groove. The thin film material and the adjacent piezoelectric layer form a Bragg-based lateral reflective layer.

Images