A bulk acoustic wave resonator, a preparation method thereof, a filter, and a preparation method thereof

Abstract

The present invention discloses a bulk acoustic wave resonator, a preparation method thereof, a filter, and a preparation method thereof. The preparation method of the bulk acoustic wave resonator includes: providing a substrate, wherein an acoustic reflection structure is disposed on the surface or inside of the substrate; sequentially forming a lower electrode, a piezoelectric layer, and an upper electrode on the substrate; forming a mask layer on the surface of the upper electrode facing away from the piezoelectric layer, wherein the mask layer is provided with a frame structure window, and the frame structure window includes a first window; forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and within the first window on the upper electrode, and the convex structure film layer within the first window on the upper electrode is a convex structure; removing the mask layer and the convex structure film layer on the surface of the mask layer. The technical solution provided by the embodiments of the present invention simplifies the preparation process of the bulk acoustic wave resonator and reduces the manufacturing cost.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a bulk acoustic wave resonator, a preparation method thereof, and a filter, and a preparation method thereof. Background Art

[0002] In recent years, with the development of communication technology, bulk acoustic wave resonators have played an important role in the field of wireless communications due to their small size, high operating frequency, low power consumption, high quality factor, and compatibility with CMOS process.

[0003] Among them, the sandwich structure composed of the lower electrode, the piezoelectric layer and the upper electrode serves as the resonant unit of the BAW resonator. In order to improve the quality factor of the BAW resonator, the prior art usually sets a frame structure such as a convex structure and a concave structure under the upper electrode to avoid the loss of acoustic wave energy. However, when preparing the convex structure, the prior art needs to first form a whole film layer of the convex structure, and then perform the first photolithography and etching on the whole film layer to obtain the convex structure; then form the concave structure, and in the process of forming the concave structure, it is necessary to perform a second photolithography and etching process on the film layer where the concave structure is located. Since one side of the concave structure in the frame structure needs to be aligned with one side of the convex structure, there are strict requirements on the position of the first and second photolithography and etching. However, it is easy to have deviations in the alignment process between the position of the second photolithography and etching process and the position of the first photolithography and etching process, so that the relative position between the concave structure and the convex structure does not match the preset relative position, which leads to a low yield of the BAW resonator. In addition, multiple etching processes also make the preparation process of the existing BAW resonator too complicated. Summary of the invention

[0004] The present invention provides a bulk acoustic wave resonator, a preparation method thereof, a filter and a preparation method thereof, so as to simplify the preparation process of the bulk acoustic wave resonator and reduce the production cost of the bulk acoustic wave resonator.

[0005] According to one aspect of the present invention, there is provided a method for preparing a bulk acoustic wave resonator, comprising: providing a substrate, wherein a sound reflection structure is disposed on a surface or inside of the substrate;

[0006] forming a lower electrode, a piezoelectric layer and an upper electrode in sequence on the substrate;

[0007] A mask layer is formed on a surface of the upper electrode facing away from the piezoelectric layer, wherein the mask layer is provided with a frame structure window, and the frame structure window includes a first window;

[0008] forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and in the first window on the upper electrode, and the convex structure film layer located in the first window on the upper electrode is a convex structure;

[0009] Remove the mask layer and the raised structure film layer on the surface of the mask layer.

[0010] Optionally, the frame structure window further includes a second window. Forming a mask layer on the surface of the upper electrode facing away from the piezoelectric layer includes:

[0011] Form a first mask layer and a second mask layer in sequence on the surface of the upper electrode facing away from the piezoelectric layer;

[0012] Form a first part of the first window in the second mask layer;

[0013] Form a second part of the first window and the second window in the first mask layer, wherein the first window and the second window communicate, and the second window is located inside and outside the first window.

[0014] Optionally, removing the mask layer and the raised structure film layer on the surface of the mask layer includes:

[0015] Remove the second mask layer and the raised structure film layer on the surface of the second mask layer;

[0016] Using the first mask layer as a mask plate, form a concave structure on the surface of the upper electrode, wherein the orthographic projection of the concave structure on the substrate coincides with the orthographic projection of the second window on the substrate, and the depth of the concave structure is less than the thickness of the upper electrode;

[0017] Remove the first mask layer.

[0018] Optionally, after removing the mask layer and the raised structure film layer on the surface of the mask layer, further include:

[0019] Remove the raised structures and the upper electrode outside the edge of the working area of the bulk acoustic wave resonator, and retain the raised structures and the upper electrode within the working area of the bulk acoustic wave resonator.

[0020] Optionally, forming a second part of the first window and the second window in the first mask layer includes:

[0021] Form a second part of the first window in the first mask layer;

[0022] Through a wet etching process, etch the sidewall of the first mask layer to form the second window, wherein the first window and the second window communicate, and the second window is located inside and outside the first window.

[0023] Optionally, the etching rate of the wet etching is greater than or equal to and less than or equal to

[0024] Optionally, the first mask layer includes any one of undoped silicon dioxide, phosphosilicate glass, borophosphosilicate glass, and photoresist;

[0025] The second mask layer includes photoresist.

[0026] Optionally, the thickness of the first mask layer is greater than or equal to and less than or equal to 2 μm;

[0027] The thickness of the second mask layer is greater than or equal to and less than or equal to 10 μm.

[0028] According to another aspect of the present invention, a method for manufacturing a filter is provided. The filter includes at least one bulk acoustic wave resonator, and the manufacturing method of the bulk acoustic wave resonator is the manufacturing method of the bulk acoustic wave resonator as described in any embodiment of the present invention.

[0029] According to another aspect of the present invention, a bulk acoustic wave resonator is provided, including:

[0030] A substrate, wherein an acoustic reflection structure is provided on the surface or inside of the substrate;

[0031] A lower electrode, a piezoelectric layer, and an upper electrode, which are sequentially disposed on the substrate;

[0032] A frame structure, the frame structure includes a convex structure, and the convex structure is located on the surface of the upper electrode;

[0033] The manufacturing method of the convex structure includes: forming a mask layer on the surface of the upper electrode facing away from the piezoelectric layer, wherein the mask layer is provided with a frame structure window, and the frame structure window includes a first window;

[0034] Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and within the first window on the upper electrode, and the convex structure film layer within the first window on the upper electrode is the convex structure;

[0035] Removing the mask layer and the convex structure film layer on the surface of the mask layer.

[0036] Optionally, the frame structure further includes a concave structure, the concave structure is located on the surface of the upper electrode, the concave structure is located inside the convex structure, and the concave structure is formed by a groove on the upper electrode, and the depth of the concave structure is less than the thickness of the upper electrode.

[0037] Optionally, the manufacturing method of the concave structure includes:

[0038] A first mask layer and a second mask layer are sequentially formed on the surface of the upper electrode facing away from the piezoelectric layer;

[0039] A first part of a first window is formed in the second mask layer;

[0040] A second part of the first window and a second window are formed in the first mask layer, wherein the first window and the second window are communicated, and the second window is located inside and outside the first window;

[0041] A raised structure film layer is formed, wherein the raised structure film layer is located on the surface of the second mask layer and inside the first window on the upper electrode, and the raised structure film layer inside the first window on the upper electrode is a raised structure;

[0042] The second mask layer and the raised structure film layer on the surface of the second mask layer are removed;

[0043] Using the first mask layer as a mask plate, a recessed structure is formed on the surface of the upper electrode, wherein the orthographic projection of the recessed structure on the substrate coincides with the orthographic projection of the second window on the substrate, and the depth of the recessed structure is less than the thickness of the upper electrode;

[0044] The first mask layer is removed.

[0045] Optionally, the raised structure and the upper electrode are located in the working area of the bulk acoustic wave resonator.

[0046] Optionally, the material of the raised structure is the same as or different from the material of the upper electrode.

[0047] According to another aspect of the present invention, a filter is provided, which includes at least one bulk acoustic wave resonator as described in any embodiment of the present invention.

[0048] In the technical solution provided in this embodiment, before forming the raised structure film layer, a mask layer provided with a first window is formed on the surface of the upper electrode. After forming the raised structure film layer, the mask layer and the raised structure film layer on the surface of the mask layer are removed, and the raised structure film layer inside the first window on the upper electrode is a raised structure. The raised structure, as a structure to avoid acoustic wave energy loss, can achieve the effect of reflecting the acoustic wave back to the piezoelectric layer, reducing the loss of the acoustic wave, thereby improving the quality factor of the bulk acoustic wave resonator. The preparation process of the above-mentioned bulk acoustic wave resonator does not require etching the raised structure film layer, simplifies the preparation process of the bulk acoustic wave resonator, and reduces the preparation cost of the bulk acoustic wave resonator. Moreover, the upper electrode is formed on the surface of the piezoelectric layer with good surface flatness, improving the yield of the upper electrode, and further improving the yield of the bulk acoustic wave resonator.

[0049] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0051] Figure 1 is a schematic flowchart of a method for manufacturing a bulk acoustic wave resonator according to an embodiment of the present invention;

[0052] Figures 2 - 8 is a schematic structural diagram corresponding to each step of a method for manufacturing a bulk acoustic wave resonator according to an embodiment of the present invention;

[0053] Figure 9 is a schematic flowchart of another method for manufacturing a bulk acoustic wave resonator according to an embodiment of the present invention;

[0054] Figures 10 - 18 is a schematic structural diagram corresponding to each step of another method for manufacturing a bulk acoustic wave resonator according to an embodiment of the present invention;

[0055] Figure 19 is Figure 9 a schematic flowchart included in S250;

[0056] Figure 20 is Figure 9 a schematic flowchart included in S270. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0057] In order to enable those skilled in the art to better understand the solutions of the present invention, the following clearly and completely describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0058] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily limit to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0059] In order to simplify the preparation process of the bulk acoustic wave resonator and reduce the preparation cost of the bulk acoustic wave resonator, an embodiment of the present invention provides a method for preparing a bulk acoustic wave resonator. Figure 1 It is a schematic flowchart of a method for preparing a bulk acoustic wave resonator according to an embodiment of the present invention. Figures 2 - 8 It is a schematic structural diagram corresponding to each step of a method for preparing a bulk acoustic wave resonator according to an embodiment of the present invention. Refer to Figure 1 The method for preparing the bulk acoustic wave resonator includes the following steps:

[0060] S110. Provide a substrate, wherein an acoustic reflection structure is provided on the surface or inside of the substrate.

[0061] Refer to Figure 2 A substrate 10 is provided. The substrate 10 can be selected from materials such as single crystal silicon, gallium arsenide, sapphire, and quartz.

[0062] An acoustic reflection structure is provided inside the substrate 10. Exemplarily, in Figure 2 the acoustic reflection structure is a cavity structure 10a. In S110, the cavity structure 10a is filled with a material containing silicon oxide, such as phosphosilicate glass (PSG), as a sacrificial layer. In subsequent steps, the sacrificial layer is etched with an etching solution to remove the filling material in the cavity structure 10a. It should be noted that the acoustic reflection structure may also include a Bragg reflection layer formed by alternately stacking high and low acoustic impedance layers, a groove on the back surface of the substrate 10, or a cavity structure surrounded by the substrate 10, a lower electrode, and a support structure between the substrate 10 and the lower electrode.

[0063] S120. Form a lower electrode, a piezoelectric layer, and an upper electrode on the substrate in sequence.

[0064] Refer to Figure 3, a lower electrode 20 is formed on a substrate 10 through a sputtering or evaporation process. After that, a piezoelectric layer 30 is formed on the surface of the lower electrode 20 through a deposition process. After forming the piezoelectric layer 30, an upper electrode 40 is formed through a sputtering or evaporation process. The upper electrode 40 is formed on the surface of the piezoelectric layer 30 with good surface flatness, improving the yield rate of the upper electrode 40, and thus improving the yield rate of the bulk acoustic wave resonator.

[0065] Among them, the lower electrode 20 can be selected from at least one of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, and titanium with good conductivity. The piezoelectric layer 30 can be selected from at least one of single-crystal piezoelectric thin film materials and polycrystalline piezoelectric thin film materials such as aluminum nitride, zinc oxide, lead zirconate titanate piezoelectric ceramics, lithium niobate, lithium tantalate, potassium niobate, etc. A certain proportion of rare earth elements can also be doped in the piezoelectric layer 30 to improve the performance of the piezoelectric material layer. The upper electrode 40 can be selected from at least one of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, and titanium with good conductivity. The sandwich structure composed of the upper electrode 40, the piezoelectric layer 30, and the lower electrode 20 serves as the resonant unit of the bulk acoustic wave resonator. The orthographic projections of the upper electrode 40, the piezoelectric layer 30, and the lower electrode 20 on the substrate 10 overlap, and the overlapping part of this orthographic projection and the orthographic projection of the acoustic reflection structure, such as the cavity structure 10a, on the substrate 10 belongs to the working area, and the part located outside the working area is called the non-working area.

[0066] S130. A mask layer is formed on the surface of the upper electrode facing away from the piezoelectric layer. Among them, the mask layer is provided with a frame structure window, and the frame structure window includes a first window.

[0067] See Figure 4 , a mask layer 50 can be formed on the surface of the upper electrode 40 facing away from the piezoelectric layer 30 through a low-temperature deposition process or a glue coating process. The mask layer 50 can be selected from insulating materials such as silicon oxide and photoresist. See Figure 5 , through a patterning process, a frame structure window is formed in the mask layer 50, and the frame structure window includes a first window 51.

[0068] S140. A raised structure film layer is formed. Among them, the raised structure film layer is located on the surface of the mask layer and within the first window on the upper electrode, and the raised structure film layer within the first window on the upper electrode is the raised structure.

[0069] See Figure 6 , the mask layer 50 includes a frame structure window. During the process of forming the raised structure film layer 60, a part of the raised structure film layer 60 is located within the first window 51 on the upper electrode 40, and this part of the raised structure film layer 60 is the raised structure 60a, and another part of the raised structure film layer 60 is located on the surface of the mask layer 50.

[0070] S150. Remove the mask layer and the raised structure film layer on the surface of the mask layer.

[0071] See Figure 7 , the mask layer 50 and the raised structure film layer 60 on the surface of the mask layer 50 are removed by a metal lift-off process, and an annular raised structure 60a is reserved on the surface of the upper electrode 40.

[0072] When preparing the raised structure with respect to the prior art, it is necessary to first form a whole film layer of the raised structure, and then perform the first photolithography and etching on the whole film layer to obtain the raised structure. See Figure 6 and Figure 7 . In this embodiment, the process of forming the raised structure 60a on the surface of the upper electrode 40 does not require etching the raised structure film layer 60, simplifies the preparation process of the bulk acoustic wave resonator, and reduces the preparation cost of the bulk acoustic wave resonator.

[0073] Optionally, after removing the mask layer and the raised structure film layer on the surface of the mask layer in S150, it further includes:

[0074] Removing the raised structure and the upper electrode outside the edge of the working area of the bulk acoustic wave resonator, and retaining the raised structure and the upper electrode within the working area of the bulk acoustic wave resonator.

[0075] The raised structure 60a and the upper electrode 40 can be patterned according to the preset size of the upper electrode 40. See Figure 8 , removing the raised structure 60a and the upper electrode 40 outside the edge of the working area of the bulk acoustic wave resonator, and retaining the raised structure 60a and the upper electrode 40 within the working area of the bulk acoustic wave resonator to form the Figure 8 bulk acoustic wave resonator in.

[0076] Specifically, the raised structure 60a is located above the upper electrode 40. The raised structure 60a serves as a raised reflection structure to avoid acoustic wave energy loss, and can achieve the effect of reflecting the acoustic wave back to the piezoelectric layer 30, reducing the loss of the acoustic wave, thereby improving the quality factor of the bulk acoustic wave resonator.

[0077] Optionally, the materials of the raised structure 60a and the upper electrode 40 are the same or different. When the materials of the raised structure 60a and the upper electrode 40 are the same, on the basis of avoiding acoustic wave energy loss, it can also increase the ability of the upper electrode 40 to transmit large currents.

[0078] In the technical solution provided in this embodiment, before forming the convex structure film layer 60, a mask layer 50 provided with a first window 51 is formed on the surface of the upper electrode 40. After forming the convex structure film layer 60, the mask layer 50 and the convex structure film layer 60 on the surface of the mask layer 50 are removed. The convex structure film layer 60 located within the first window 51 on the upper electrode 40 is the convex structure 60a. The convex structure 60a, as a structure for avoiding acoustic wave energy loss, can achieve the effect of reflecting acoustic waves back to the piezoelectric layer 30, reducing the loss of acoustic waves, thereby improving the quality factor of the bulk acoustic wave resonator. The preparation process of the above-mentioned bulk acoustic wave resonator does not require etching of the convex structure film layer 60, simplifies the preparation process of the bulk acoustic wave resonator, and reduces the preparation cost of the bulk acoustic wave resonator. Moreover, the upper electrode 40 is formed on the surface of the piezoelectric layer 30 with good surface flatness, improving the yield of the upper electrode 40, and further improving the yield of the bulk acoustic wave resonator.

[0079] The embodiment of the present invention also provides another method for manufacturing a bulk acoustic wave resonator. Figure 9 It is another method for manufacturing a bulk acoustic wave resonator provided according to the embodiment of the present invention. Figures 10 - 19 It is a schematic structural diagram corresponding to each step of another method for manufacturing a bulk acoustic wave resonator provided according to the embodiment of the present invention. On the basis of the above technical solution, in this embodiment, on the basis that the mask layer 50 further includes a first window in the frame structure window, it further includes a second window. See Figure 9 , and this method includes the following steps:

[0080] S210. Provide a substrate, wherein an acoustic reflection structure is provided on the surface or inside of the substrate.

[0081] S220. Sequentially form a lower electrode, a piezoelectric layer, and an upper electrode on the substrate.

[0082] For the implementation manners and beneficial effects of S210 and S220, reference can be made to the implementation manners and beneficial effects of S110 and S120.

[0083] S230. Sequentially form a first mask layer and a second mask layer on the surface of the upper electrode facing away from the piezoelectric layer.

[0084] See Figure 10 , first form a first mask layer 52 on the surface of the upper electrode 40 facing away from the piezoelectric layer 30 through a low-temperature deposition process or a spin-coating process, and then form a second mask layer 53. Among them, the materials of the first mask layer 52 and the second mask layer 53 can be the same or different. Optionally, the first mask layer 52 can be selected from any one of undoped silicon dioxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), and photoresist; the thickness of the first mask layer 52 is greater than or equal to and less than or equal to 2 um. The second mask layer 53 can be a positive or negative photoresist; the thickness of the second mask layer 53 is greater than or equal to and less than or equal to 10 um.

[0085] S240. Form the first part of the first window in the second mask layer.

[0086] Refer to Figure 11 , when the second mask layer 53 can be a positive or negative photoresist, the second mask layer 53 can be quickly patterned to form the first part 51a of the first window 51 through an exposure and development process.

[0087] S250. Form the second part of the first window and the second window in the first mask layer, wherein the first window and the second window are connected, and the second window is located inside and outside the first window.

[0088] Optionally, refer to Figure 19 , the specific steps of S250 for forming the second part of the first window and the second window in the first mask layer are as follows:

[0089] S2501. Form the second part of the first window in the first mask layer.

[0090] Refer to Figure 12 , the first mask layer 52 can be etched through a wet etching process to form the second part 51b of the first window 51.

[0091] S2502. Corrode the sidewall of the first mask layer through a wet etching process to form the second window, wherein the first window and the second window are connected, and the second window is located inside and outside the first window.

[0092] Refer to Figure 13 , etch the first mask layer 52 through a wet process, and by controlling the etching time, form the second window 54 on both sides of the first window 51, wherein the inner second window 54a is located inside the first window 51, and the outer second window 54b is located outside the first window 51, and the first window 51 and the second window 54 are connected.

[0093] It should be noted that the second part 51b of the first window 51 and the second window 54 can be formed together through a wet etching process.

[0094] Optionally, the rate of wet etching is greater than or equal to and less than or equal to Specifically, by controlling the concentration of the etching solution for wet etching and the etching time, the rate of wet etching can be controlled to be greater than or equal to and less than or equal to within a certain range to ensure that the second outer window 54b and the second inner window 54a are within the preset dimensions.

[0095] It should be noted that the widths of the second outer window 54b and the second inner window 54a can be the same or different.

[0096] S260. Form a convex structure film layer, where the convex structure film layer is located on the surface of the mask layer and within the first window on the upper electrode. The convex structure film layer within the first window on the upper electrode is the convex structure.

[0097] See Figure 13 , the first mask layer 52 includes the second part 51b of the first window 51, and the second mask layer 53 includes the first part 51a of the first window 51. See Figure 14 , during the formation of the convex structure film layer 60, a part of the convex structure film layer 60 is within the first window 51 on the upper electrode 40, and this part of the convex structure film layer 60 is the convex structure 60a, and another part of the convex structure film layer 60 is located on the surface of the second mask layer 53.

[0098] S270. Remove the mask layer and the convex structure film layer on the surface of the mask layer.

[0099] Optionally, see Figure 20 , S270 removing the mask layer and the convex structure film layer on the surface of the mask layer includes:

[0100] S2701. Remove the second mask layer and the convex structure film layer on the surface of the second mask layer.

[0101] See Figure 15 , through an etching process or an exposure and development process, remove the second mask layer 53 and the convex structure film layer 60 on the surface of the second mask layer 53, and a circular convex structure 60a is retained on the surface of the upper electrode 40.

[0102] Compared with the prior art in preparing a convex structure, it is necessary to first form a whole film layer of the convex structure, and then perform the first photolithography and etching on the whole film layer to obtain the convex structure. See Figure 14 and Figure 15 , in this embodiment, there is no need to etch the convex structure film layer 60 during the process of forming the convex structure 60a on the surface of the upper electrode 40, which simplifies the preparation process of the bulk acoustic wave resonator and reduces the preparation cost of the bulk acoustic wave resonator.

[0103] S2702. Using the first mask layer as a mask, form a concave structure on the surface of the upper electrode, where the orthographic projection of the concave structure on the substrate coincides with the orthographic projection of the second window on the substrate, and the depth of the concave structure is less than the thickness of the upper electrode.

[0104] See Figure 16 , in the process of forming the concave structure 70, using the first mask layer 52 as a mask, the upper electrode 40 is dry-etched, and a concave structure 70 is formed on the surface of the upper electrode 40, realizing the self-alignment of the convex structure 60a and the concave structure 70, avoiding the deviation of the relative positions of the convex structure 60a and the concave structure 70, thereby improving the yield of the bulk acoustic wave resonator. Among them, the orthographic projection of the concave structure 70 on the substrate 10 and Figure 15 the orthographic projection of the second window 54 in coincide on the substrate 10, and the depth of the concave structure 70 is less than the thickness of the upper electrode 40. Among them, the concave structure 70 includes an inner concave structure 70a and an outer concave structure 70b. The orthographic projection of the inner concave structure 70a and the inner second window 54a coincide on the substrate 10. The orthographic projection of the outer concave structure 70b and the outer second window 54b coincide on the substrate 10.

[0105] It should be noted that in the process of dry-etching the upper electrode 40 with the first mask layer 52 as a mask, the convex structure 60a will also be etched, so that the thickness of the convex structure 60a decreases accordingly. Therefore, the thickness of the convex structure film layer 60 needs to be greater than the depth of the concave structure 70 to ensure that after the concave structure 70 is formed, the convex structure 60a remains on the surface of the upper electrode 40.

[0106] S2703. Remove the first mask layer.

[0107] See Figure 17 , the first mask layer 52 can be removed by a wet etching process.

[0108] Optionally, see Figure 9 , after S270 removes the mask layer and the convex structure film layer on the mask layer surface, it further includes:

[0109] S280. Remove the convex structure and the upper electrode outside the edge of the working area of the bulk acoustic wave resonator, and retain the convex structure and the upper electrode within the working area of the bulk acoustic wave resonator.

[0110] See Figure 18 , the convex structure 60a and the upper electrode 40 can be patterned according to the preset size of the upper electrode 40, remove the convex structure 60a and the upper electrode 40 outside the edge of the working area of the bulk acoustic wave resonator, and retain the convex structure 60a and the upper electrode 40 within the working area of the bulk acoustic wave resonator, forming Figure 18 the bulk acoustic wave resonator in

[0111] Specifically, the convex structure 60a serves as a convex reflection structure, and the concave structure 70 serves as a concave reflection structure. The concave reflection structure and the convex reflection structure, as structures for avoiding acoustic wave energy loss, can achieve the effect of reflecting acoustic waves back to the piezoelectric layer 30, reducing the loss of acoustic waves, and thus further improving the quality factor of the bulk acoustic wave resonator.

[0112] Based on the above technical solution, in the technical solution provided in this embodiment, on the one hand, before forming the convex structure film layer 60, a mask layer 50 provided with a first window 51 is formed on the surface of the upper electrode 40. After forming the convex structure film layer 60, the mask layer 50 and the convex structure film layer 60 on the surface of the mask layer 50 are removed. The convex structure film layer 60 located within the first window 51 on the upper electrode 40 is the convex structure 60a. The preparation process of the above bulk acoustic wave resonator does not require etching of the convex structure film layer 60, simplifies the preparation process of the bulk acoustic wave resonator, and reduces the preparation cost of the bulk acoustic wave resonator. Moreover, the upper electrode 40 is formed on the surface of the piezoelectric layer 30 with good surface flatness, improving the yield of the upper electrode 40, and thus further improving the yield of the bulk acoustic wave resonator. On the other hand, during the formation of the concave structure 70, using the first mask layer 52 as a mask, the upper electrode 40 is dry-etched to form the concave structure 70 on the surface of the piezoelectric layer 30, achieving self-alignment of the convex structure 60a and the concave structure 70, avoiding deviation in the relative positions of the convex structure 60a and the concave structure 70, and thus improving the yield of the bulk acoustic wave resonator. On the third hand, the convex structure 60a serves as a convex reflection structure, and the concave structure 70 serves as a concave reflection structure. The concave reflection structure and the convex reflection structure, as structures for avoiding acoustic wave energy loss, can achieve the effect of reflecting acoustic waves back to the piezoelectric layer 30, reducing the loss of acoustic waves, and thus further improving the quality factor of the bulk acoustic wave resonator.

[0113] The embodiment of the present invention also provides a preparation method for a filter. The filter includes at least one bulk acoustic wave resonator, and the bulk acoustic wave resonator adopts the preparation method of the bulk acoustic wave resonator described in any of the above embodiments. Therefore, the preparation method for the filter provided in the embodiment of the present invention also has the beneficial effects described in the above embodiments, which will not be elaborated here.

[0114] The embodiment of the present invention also provides a bulk acoustic wave resonator. Refer to Figure 7 and this bulk acoustic wave resonator includes: a substrate 10, wherein a sound reflection structure such as a cavity structure 10a is provided on the surface or inside of the substrate 10; a lower electrode 20, a piezoelectric layer 30, and an upper electrode 40, and the lower electrode 20, the piezoelectric layer 30, and the upper electrode 40 are sequentially arranged on the substrate 10; a frame structure, and the frame structure includes a convex structure 60a, and the convex structure 60a is located on the surface of the upper electrode 40. Refer to Figure 4 – Figure 7, the preparation method of the convex structure 60a includes: forming a mask layer 50 on the surface of the upper electrode 40 facing away from the piezoelectric layer 30, wherein the mask layer 50 is provided with a frame structure window, and the frame structure window includes a first window 51; forming a convex structure film layer 60, wherein the convex structure film layer 60 is located on the surface of the mask layer 50 and within the first window 51 on the upper electrode 40, and the convex structure film layer 60 within the first window 51 on the upper electrode 40 is the convex structure 60a; removing the mask layer 50 and the convex structure film layer 60 on the surface of the mask layer 50.

[0115] In the technical solution provided in this embodiment, the convex structure 60a, as a structure to avoid acoustic wave energy loss, can achieve the effect of reflecting acoustic waves back to the piezoelectric layer 30, reducing the loss of acoustic waves, and thus improving the quality factor of the bulk acoustic wave resonator. The preparation process of the above-mentioned bulk acoustic wave resonator does not require etching of the convex structure film layer 60, simplifies the preparation process of the bulk acoustic wave resonator, and reduces the preparation cost of the bulk acoustic wave resonator. Moreover, the upper electrode 40 is formed on the surface of the piezoelectric layer 30 with good surface flatness, improving the yield of the upper electrode 40, and further improving the yield of the bulk acoustic wave resonator. Specifically, before forming the convex structure film layer 60, a mask layer 50 provided with a first window 51 is formed on the surface of the upper electrode 40. After forming the convex structure film layer 60, the mask layer 50 and the convex structure film layer 60 on the surface of the mask layer 50 are removed. The convex structure film layer 60 within the first window 51 on the upper electrode 40 is the convex structure 60a. The preparation process of the convex structure 60a does not require etching of the convex structure film layer 60, simplifies the preparation process of the bulk acoustic wave resonator, and reduces the preparation cost of the bulk acoustic wave resonator.

[0116] Optionally, referring to Figure 18 , the frame structure further includes a concave structure 70. The concave structure 70 is located on the surface of the upper electrode 40, the concave structure 70 is located inside the convex structure 60a, and the concave structure 70 is formed by a groove on the upper electrode 40, and the depth of the concave structure 70 is less than the thickness of the upper electrode 40.

[0117] Optionally, referring to Figures 10 - 17, the preparation method of the concave structure 70 includes: sequentially forming a first mask layer 52 and a second mask layer 53 on the surface of the upper electrode 40 facing away from the piezoelectric layer 30; forming a first part 51a of the first window 51 in the second mask layer 53; forming a second part 51b of the first window 51 and a second window 54 in the first mask layer 52, wherein the first window 51 and the second window 54 are communicated, and the second window 54 is located inside and outside the first window 51; forming a convex structure film layer 60, wherein the convex structure film layer 60 is located on the surface of the second mask layer 53 and in the first window 51 on the upper electrode 40, and the convex structure film layer 60 in the first window 51 on the upper electrode 40 is the convex structure 60a; removing the second mask layer 53 and the convex structure film layer 60 on the surface of the second mask layer 53; using the first mask layer 52 as a mask, forming a concave structure 70 on the surface of the upper electrode 40, wherein the orthographic projection of the concave structure 70 on the substrate 10 coincides with the orthographic projection of the second window 54 on the substrate 10, and the depth of the concave structure 70 is less than the thickness of the upper electrode 40; removing the first mask layer 52. It should be noted that the concave structure 70 is a groove on the upper electrode 40.

[0118] See Figure 13 , the first mask layer 52 is etched by a wet process, and by controlling the etching time, second windows 54 are formed on both sides of the first window 51, wherein the inner second window 54a is located inside the first window 51, and the outer second window 54b is located outside the first window 51, and the first window 51 and the second windows 54 are communicated.

[0119] The widths of the outer second window 54b and the inner second window 54a may be the same or different. The concave structure 70 includes an inner concave structure 70a and an outer concave structure 70b. The orthographic projections of the inner concave structure 70a and the inner second window 54a on the substrate 10 coincide. The orthographic projections of the outer concave structure 70b and the outer second window 54b on the substrate 10 coincide. The widths of the outer concave structure 70b and the inner concave structure 70a may be the same or different.

[0120] Specifically, the convex structure 60a serves as a convex reflection structure, and the concave structure 70 serves as a concave reflection structure. The concave reflection structure and the convex reflection structure are structures for avoiding acoustic wave energy loss, and can achieve the effect of reflecting acoustic waves back to the piezoelectric layer 30, reducing the loss of acoustic waves, thereby further improving the quality factor of the bulk acoustic wave resonator. And in the process of forming the concave structure 70, using the first mask layer 52 as a mask, the upper electrode 40 is dry-etched to form the concave structure 70 on the surface of the piezoelectric layer 30, realizing the self-alignment of the convex structure 60a and the concave structure 70, avoiding the deviation of the relative positions of the convex structure 60a and the concave structure 70, and thus improving the yield of the bulk acoustic wave resonator.

[0121] Optionally, refer to Figure 8 and Figure 18 , the protruding structure 60a and the upper electrode 40 are located within the working area of the bulk acoustic wave resonator.

[0122] The sandwich structure composed of the upper electrode 40, the piezoelectric layer 30, and the lower electrode 20 serves as the resonant unit of the bulk acoustic wave resonator. The upper electrode 40, the piezoelectric layer 30, and the lower electrode 20 overlap in the orthographic projection on the substrate 10, and the overlapping part of this orthographic projection and the orthographic projection of the acoustic reflection structure, such as the cavity structure 10a, on the substrate 10 belongs to the working area, and the part located outside the working area is called the non-working area.

[0123] The protruding structure 60a and the upper electrode 40 can be patterned according to the preset size of the upper electrode 40. Refer to Figure 8 and Figure 18 , remove the protruding structure 60a and the upper electrode 40 outside the edge of the working area of the bulk acoustic wave resonator, and retain the protruding structure 60a and the upper electrode 40 within the working area of the bulk acoustic wave resonator to form Figure 8 and Figure 18 the bulk acoustic wave resonator in

[0124] Optionally, the material of the protruding structure 60a is the same as or different from that of the upper electrode 40. When the materials of the protruding structure 60a and the upper electrode 40 are the same, on the basis of avoiding acoustic wave energy loss, the ability of the upper electrode 40 to transmit large currents can also be increased.

[0125] An embodiment of the present invention also provides a filter. The filter includes at least one bulk acoustic wave resonator, and the bulk acoustic wave resonator includes the bulk acoustic wave resonator described in any of the above embodiments. Therefore, the filter provided by the embodiment of the present invention also has the beneficial effects described in the above embodiments, which will not be elaborated here.

[0126] It should be understood that various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved, and no limitations are imposed herein.

[0127] The above specific embodiments do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a bulk acoustic wave resonator, characterized in that, Comprising: Providing a substrate, wherein an acoustic reflection structure is disposed on the surface or inside of the substrate; Successively forming a lower electrode, a piezoelectric layer, and an upper electrode on the substrate; Forming a mask layer on the surface of the upper electrode facing away from the piezoelectric layer, wherein the mask layer is provided with a frame structure window, and the frame structure window includes a first window; Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and within the first window on the upper electrode, and the convex structure film layer within the first window on the upper electrode is a convex structure; Removing the mask layer and the convex structure film layer on the surface of the mask layer; The frame structure window further includes a second window, and forming a mask layer on the surface of the upper electrode facing away from the piezoelectric layer includes: Successively forming a first mask layer and a second mask layer on the surface of the upper electrode facing away from the piezoelectric layer; Forming a first part of the first window in the second mask layer; Forming a second part of the first window and a second window in the first mask layer, wherein the first window and the second window communicate, and the second window is located inside and outside the first window; Removing the mask layer and the convex structure film layer on the surface of the mask layer includes: Removing the second mask layer and the convex structure film layer on the surface of the second mask layer; Using the first mask layer as a mask, forming a concave structure on the surface of the upper electrode, wherein the orthographic projection of the concave structure on the substrate coincides with the orthographic projection of the second window on the substrate, and the depth of the concave structure is less than the thickness of the upper electrode; Removing the first mask layer.

2. The method for manufacturing a bulk acoustic wave resonator according to claim 1, wherein After removing the mask layer and the convex structure film layer on the surface of the mask layer, further comprising: Removing the convex structure and the upper electrode outside the working area edge of the bulk acoustic wave resonator, and retaining the convex structure and the upper electrode within the working area of the bulk acoustic wave resonator.

3. The manufacturing method of the bulk acoustic wave resonator according to claim 1, characterized in that, Forming a second part of the first window and a second window in the first mask layer includes: Forming a second part of the first window in the first mask layer; By wet etching process, etching the sidewall of the first mask layer to form a second window, wherein the first window and the second window communicate, and the second window is located inside and outside the first window.

4. The method for manufacturing a bulk acoustic wave resonator according to claim 3, characterized in that, The rate of the wet etching is greater than or equal to and less than or equal to 5. The method for preparing a bulk acoustic wave resonator according to claim 1, wherein, The first mask layer includes any one of undoped silicon dioxide, phosphosilicate glass, borophosphosilicate glass, and photoresist; The second mask layer includes photoresist.

6. The method for manufacturing a bulk acoustic wave resonator according to claim 1, wherein: The thickness of the first mask layer is greater than or equal to and less than or equal to 2 um; The thickness of the second mask layer is greater than or equal to and less than or equal to 10 um.

7. A method for preparing a filter, characterized in that, Comprising: The filter includes at least one bulk acoustic wave resonator, wherein the method for manufacturing the bulk acoustic wave resonator is the method for manufacturing a bulk acoustic wave resonator according to any one of claims 1-6.

8. A bulk acoustic wave resonator, characterized in that, Comprising: A substrate, wherein an acoustic reflection structure is disposed on the surface or inside of the substrate; A lower electrode, a piezoelectric layer, and an upper electrode, the lower electrode, the piezoelectric layer, and the upper electrode are successively disposed on the substrate; A frame structure, the frame structure includes a convex structure, and the convex structure is located on the surface of the upper electrode; The preparation method of the convex structure includes: forming a mask layer on the surface of the upper electrode facing away from the piezoelectric layer, wherein the mask layer is provided with a frame structure window, and the frame structure window includes a first window; Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and within the first window on the upper electrode, and the convex structure film layer within the first window on the upper electrode is the convex structure; Removing the mask layer and the convex structure film layer on the surface of the mask layer; The frame structure further includes a concave structure, the concave structure is located on the surface of the upper electrode, the concave structure is located inside the convex structure, and the concave structure is formed by a groove on the upper electrode, and the depth of the concave structure is less than the thickness of the upper electrode; The preparation method of the concave structure includes: Sequentially forming a first mask layer and a second mask layer on the surface of the upper electrode facing away from the piezoelectric layer; Forming a first part of the first window in the second mask layer; Forming a second part of the first window and a second window in the first mask layer, wherein the first window and the second window are communicated, and the second window is located inside and outside the first window; Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the second mask layer and within the first window on the upper electrode, and the convex structure film layer within the first window on the upper electrode is the convex structure; Removing the second mask layer and the convex structure film layer on the surface of the second mask layer; Using the first mask layer as a mask plate, forming a concave structure on the surface of the upper electrode, wherein the orthographic projection of the concave structure on the substrate coincides with the orthographic projection of the second window on the substrate, and the depth of the concave structure is less than the thickness of the upper electrode; Removing the first mask layer.

9. The bulk acoustic wave resonator according to claim 8, wherein The convex structure and the upper electrode are located within the working area of the bulk acoustic wave resonator.

10. The bulk acoustic wave resonator according to claim 8, wherein The material of the convex structure and the material of the upper electrode are the same or different.

11. A filter, characterized in that, Comprising at least one bulk acoustic wave resonator according to any one of claims 8-10.

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