Bulk acoustic wave resonator, preparation method, filter, and preparation method

Abstract

The present invention discloses a bulk acoustic wave resonator, a preparation method, and a filter, and a preparation method. The preparation method of the bulk acoustic wave resonator includes: providing a substrate, wherein a sound reflection structure is arranged on the surface or inside of the substrate; forming a lower electrode and a piezoelectric layer in sequence on the substrate; forming a mask layer on the surface of the piezoelectric layer away from the lower electrode, wherein the mask layer is provided with a microstructure window, and the microstructure window includes a convex structure window; forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure; removing the mask layer and the convex structure film layer on the surface of the mask layer; forming an upper electrode, and the upper electrode covers the convex structure and the piezoelectric layer. The technical solution provided by the embodiment of the present invention simplifies the preparation process of the bulk acoustic wave resonator and reduces the production 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 microstructures such as convex structures and concave structures 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-surface film layer of the convex structure, and then perform the first photolithography and etching on the whole-surface 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 microstructure 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:

[0006] Providing a substrate, wherein a sound reflection structure is disposed on a surface or inside of the substrate;

[0007] forming a lower electrode and a piezoelectric layer in sequence on the substrate;

[0008] Forming a mask layer on a surface of the piezoelectric layer away from the lower electrode, wherein the mask layer is provided with a microstructure window, and the microstructure window includes a convex structure window;

[0009] Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure;

[0010] removing the mask layer and the convex structure film layer on the surface of the mask layer;

[0011] An upper electrode is formed, the upper electrode covering the protruding structure and the piezoelectric layer.

[0012] Optionally, the microstructure window further includes a recessed structure window, and forming a mask layer on a surface of the piezoelectric layer away from the lower electrode includes:

[0013] forming a first mask layer and a second mask layer in sequence on a surface of the piezoelectric layer away from the lower electrode;

[0014] forming a first portion of a protruding structure window on the second mask layer;

[0015] A second portion of the convex structure window and a concave structure window are formed on the first mask layer, wherein the convex structure window is connected to the concave structure window, and the concave structure window is located at the inner side and the outer side of the convex structure window.

[0016] Optionally, removing the mask layer and the protruding structure film layer on the surface of the mask layer includes:

[0017] removing the second mask layer and the protruding structure film layer on the surface of the second mask layer;

[0018] Using the first mask layer as a mask, forming a concave structure on the surface of the piezoelectric layer, wherein the orthographic projection of the concave structure on the substrate coincides with the orthographic projection of the concave structure window on the substrate, and the depth of the concave structure is less than the thickness of the piezoelectric layer;

[0019] The first mask layer is removed.

[0020] Optionally, after forming an upper electrode, wherein the upper electrode covers the protruding structure and the piezoelectric layer, the method further comprises:

[0021] The protruding structure and the upper electrode outside the edge of the working area of ​​the BAW resonator are removed, and the protruding structure and the upper electrode within the working area of ​​the BAW resonator are retained.

[0022] Optionally, forming the second part of the protruding structure window and the recessed structure window in the first mask layer includes:

[0023] forming a second portion of the protruding structure window on the first mask layer;

[0024] The sidewall of the first mask layer is etched by a wet etching process to form a recessed structure window, wherein the convex structure window is connected to the recessed structure window, and the recessed structure window is located inside and outside the convex structure window.

[0025] Optionally, the wet etching rate is greater than or equal to and less than or equal to

[0026] Optionally, the first mask layer includes any one of undoped silicon dioxide, phosphosilicate glass, borophosphosilicate glass and photoresist;

[0027] The second mask layer includes photoresist.

[0028] Optionally, the thickness of the first mask layer is greater than or equal to And less than or equal to 2um;

[0029] The thickness of the second mask layer is greater than or equal to And less than or equal to 10um.

[0030] According to another aspect of the present invention, a method for preparing a filter is provided. The filter includes at least one BAW resonator. The method for preparing the BAW resonator is the method for preparing the BAW resonator according to any embodiment of the present invention.

[0031] According to another aspect of the present invention, there is provided a bulk acoustic wave resonator, comprising:

[0032] A substrate, wherein a sound reflection structure is provided on the surface or inside of the substrate;

[0033] A lower electrode and a piezoelectric layer, wherein the lower electrode and the piezoelectric layer are sequentially arranged on the substrate;

[0034] A microstructure, wherein the microstructure includes a protrusion structure, and the protrusion structure is located on the surface of the piezoelectric layer;

[0035] an upper electrode, the upper electrode covering the protrusion structure and the piezoelectric layer;

[0036] The method for preparing the protruding structure comprises: forming a mask layer on a surface of the piezoelectric layer away from the lower electrode, wherein the mask layer is provided with a microstructure window, and the microstructure window comprises a protruding structure window;

[0037] Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure;

[0038] The mask layer and the protruding structure film layer on the surface of the mask layer are removed.

[0039] Optionally, the microstructure further includes a concave structure, the concave structure is located on the surface of the piezoelectric layer, and the concave structure is located on the inner side of the convex structure, and the depth of the concave structure is less than the thickness of the piezoelectric layer.

[0040] Optionally, the method for preparing the recessed structure includes:

[0041] forming a first mask layer and a second mask layer in sequence on a surface of the piezoelectric layer away from the lower electrode;

[0042] forming a first portion of a protruding structure window on the second mask layer;

[0043] forming a second portion of a convex structure window and a concave structure window on the first mask layer, wherein the convex structure window is connected to the concave structure window, and the concave structure window is located at the inner side and the outer side of the convex structure window;

[0044] Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the second mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure;

[0045] removing the second mask layer and the protruding structure film layer on the surface of the second mask layer;

[0046] Using the first mask layer as a mask, forming a concave structure on the surface of the piezoelectric layer, wherein the orthographic projection of the concave structure on the substrate coincides with the orthographic projection of the concave structure window on the substrate, and the depth of the concave structure is less than the thickness of the piezoelectric layer;

[0047] The first mask layer is removed.

[0048] Optionally, the protruding structure is located in the working area of ​​the BAW resonator;

[0049] The upper electrode covers the protruding structure and a surface of the piezoelectric layer surrounded by the protruding structure.

[0050] Optionally, the material of the protrusion structure is the same as or different from the material of the upper electrode.

[0051] According to another aspect of the present invention, a filter is provided, comprising at least one BAW resonator according to any one of the embodiments of the present invention.

[0052] The technical solution provided in this embodiment is that before forming the convex structure film layer, a mask layer provided with a convex structure window is formed on the surface of the piezoelectric layer. After forming the convex structure film layer, the mask layer and the convex structure film layer on the surface of the mask layer are removed, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure. The convex structure is located under the upper electrode. The convex structure makes the upper electrode include a middle planar area and a convex reflective structure surrounded by the edge. The convex reflective structure surrounded by the edge serves as a structure to avoid the loss of sound wave energy, and can achieve the effect of reflecting the sound wave back to the piezoelectric layer, reducing the loss of the sound 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 need to etch the convex structure film layer, which simplifies the preparation process of the bulk acoustic wave resonator and reduces the preparation cost of the bulk acoustic wave resonator.

[0053] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended 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

[0054] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 is a schematic flow chart of a method for preparing a bulk acoustic wave resonator provided according to an embodiment of the present invention;

[0056] Figure 2-Figure 9 is a structural schematic diagram corresponding to each step of a method for preparing a bulk acoustic wave resonator provided by an embodiment of the present invention;

[0057] Fig.10 is a schematic flow chart of another method for preparing a bulk acoustic wave resonator provided according to an embodiment of the present invention;

[0058] Figure 11-Figure 20 is a schematic structural diagram corresponding to each step of another method for preparing a bulk acoustic wave resonator provided by an embodiment of the present invention;

[0059] Fig.21 yes Fig.10 A schematic diagram of the process flow included in S250;

[0060] Fig. 22 yes Fig.10 Schematic diagram of the process included in S270. DETAILED DESCRIPTION

[0061] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0062] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, 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 "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, 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 clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0063] In order to simplify the preparation process of a BAW resonator and reduce the preparation cost of the BAW resonator, an embodiment of the present invention provides a method for preparing a BAW resonator. Figure 1 It is a schematic flow chart of a method for preparing a bulk acoustic wave resonator provided according to an embodiment of the present invention. Figure 2-Figure 9 1 is a schematic diagram of the structure corresponding to each step of a method for preparing a bulk acoustic wave resonator according to an embodiment of the present invention. Figure 1 The preparation method of the bulk acoustic wave resonator comprises the following steps:

[0064] S110, providing a substrate, wherein a sound reflection structure is disposed inside the substrate.

[0065] See also Figure 2 , providing a substrate 10. The substrate 10 can be made of materials such as single crystal silicon, gallium arsenide, sapphire, and quartz.

[0066] An acoustic reflection structure is provided in the substrate 10. Figure 2The acoustic reflection structure is a cavity structure 10a. In S110, the cavity structure 10a is filled with a material containing silicon oxide, such as phosphosilicic glass (PSG) as a sacrificial layer. In a subsequent step, the sacrificial layer is corroded by 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 alternating high and low acoustic impedance layers, a groove on the back of the substrate 10, or a cavity structure surrounded by the substrate 10, a lower electrode, and a support structure located between the substrate 10 and the lower electrode.

[0067] S120, forming a lower electrode and a piezoelectric layer in sequence on the substrate.

[0068] See also Figure 3 , a lower electrode 20 is formed on the substrate 10 by sputtering or evaporation process, and then a piezoelectric layer 30 is formed on the surface of the lower electrode 20 by a deposition process. The lower electrode 20 can be made of at least one of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper and titanium with good conductivity. The piezoelectric layer 30 can be made of at least one of single crystal piezoelectric film materials and polycrystalline piezoelectric 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.

[0069] S130, forming a mask layer on the surface of the piezoelectric layer facing away from the lower electrode, wherein the mask layer is provided with a microstructure window, and the microstructure window includes a protruding structure window.

[0070] See also Figure 4 The mask layer 40 can be formed on the surface of the piezoelectric layer 30 away from the lower electrode 20 by a low temperature deposition process or a coating process. The mask layer 40 can be made of insulating materials such as silicon oxide and photoresist. Figure 5 , through a patterning process, a microstructure window is formed on the mask layer 40, and the microstructure window includes a convex structure window 41. Wherein, the mask layer 40 is provided with a microstructure window, and the microstructure window includes a convex structure window 41.

[0071] S140, forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure.

[0072] See also Figure 6 The mask layer 40 includes a microstructure window. During the process of forming the raised structure film layer 50, a portion of the raised structure film layer 50 is located in the raised structure window 41 on the piezoelectric layer 30, and the portion of the raised structure film layer 50 is the raised structure 50a. The other portion of the raised structure film layer 50 is located on the surface of the mask layer 40.

[0073] S150, removing the mask layer and the raised structure film layer on the surface of the mask layer.

[0074] See also Figure 7 The mask layer 40 and the protruding structure film layer 50 on the surface of the mask layer 40 are removed by a metal lift-off process, and an annular protruding structure 50 a is retained on the surface of the piezoelectric layer 30 .

[0075] Compared with the prior art, when preparing the protruding structure, it is necessary to first form a film layer of the entire surface of the protruding structure, and then perform the first photolithography and etching on the entire surface of the film layer to obtain the protruding structure, see Figure 6 and Figure 7 In the process of forming the protruding structure 50a on the surface of the piezoelectric layer 30 in this embodiment, there is no need to etch the protruding structure film layer 50, which simplifies the preparation process of the BAW resonator and reduces the preparation cost of the BAW resonator.

[0076] S160, forming an upper electrode, wherein the upper electrode covers the protruding structure and the piezoelectric layer.

[0077] See also Figure 8 , an upper electrode 60 is formed by sputtering or evaporation process, and the upper electrode 60 covers the protruding structure 50a and the piezoelectric layer 30. The upper electrode 60 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 60, the piezoelectric layer 30 and the lower electrode 20 serves as a resonant unit of the bulk acoustic wave resonator. The orthographic projections of the upper electrode 60, the piezoelectric layer 30 and the lower electrode 20 overlap on the substrate 10, and the part where the orthographic projection and the orthographic projection of the acoustic reflection structure overlap on the substrate 10 belongs to the working area, and the part outside the working area is called the non-working area.

[0078] Optionally, S160 forms an upper electrode, and after the upper electrode covers the protruding structure and the piezoelectric layer, it also includes:

[0079] The protruding structure 50a and the upper electrode 60 may be patterned according to the preset size of the upper electrode 60. Fig. 9 , removing the protruding structure 50a and the upper electrode 60 outside the edge of the BAW resonator working area, retaining the protruding structure 50a and the upper electrode 60 in the working area of ​​the BAW resonator, forming Fig. 9 The bulk acoustic wave resonator in .

[0080] Specifically, the raised structure 50a is located under the upper electrode 60. The raised structure 50a makes the upper electrode 60 include a middle planar area and a raised reflective structure surrounded by the edge. The raised reflective structure surrounded by the edge serves as a structure to avoid the loss of sound wave energy. It can achieve the effect of reflecting the sound waves back to the piezoelectric layer 30, reducing the loss of sound waves, thereby improving the quality factor of the bulk acoustic wave resonator.

[0081] Optionally, the materials of the protruding structure 50a and the upper electrode 60 are the same or different. When the materials of the protruding structure 50a and the upper electrode 60 are the same, the ability of the upper electrode 60 to transmit large current can be increased while avoiding the loss of acoustic wave energy.

[0082] The technical solution provided in this embodiment is that before forming the convex structure film layer 50, a mask layer 40 provided with a convex structure window 41 is formed on the surface of the piezoelectric layer 30. After forming the convex structure film layer 50, the mask layer 40 and the convex structure film layer 50 on the surface of the mask layer 40 are removed, and the convex structure film layer 50 located in the convex structure window 41 on the piezoelectric layer 30 is a convex structure 50a. The convex structure 50a is located below the upper electrode 60. The convex structure 50a makes the upper electrode 60 include a middle plane area and a convex reflective structure surrounded by the edge. The convex reflective structure surrounded by the edge serves as a structure to avoid the loss of sound wave energy, and can achieve the effect of reflecting the sound wave back to the piezoelectric layer 30, reducing the loss of the sound 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 need to etch the convex structure film layer 50, which simplifies the preparation process of the bulk acoustic wave resonator and reduces the preparation cost of the bulk acoustic wave resonator.

[0083] The embodiment of the present invention also provides another method for preparing a bulk acoustic wave resonator. Fig.10 Another method for preparing a bulk acoustic wave resonator is provided according to an embodiment of the present invention. Figure 11-Figure 20 Schematic diagram of the structure corresponding to each step of another method for preparing a bulk acoustic wave resonator according to an embodiment of the present invention. Based on the above technical solution, in this embodiment, the mask layer 40 includes a recessed structure window 44 in addition to the microstructure window including a protruding structure window 41. Fig.10 , the method comprises the following steps:

[0084] S210, providing a substrate, wherein a sound reflection structure is disposed inside the substrate.

[0085] S220, forming a lower electrode and a piezoelectric layer in sequence on the surface of the substrate.

[0086] The implementation methods and beneficial effects of S210 and S220 may refer to the implementation methods and beneficial effects of S110 and S120.

[0087] S230 , sequentially forming a first mask layer and a second mask layer on a surface of the piezoelectric layer facing away from the lower electrode.

[0088] See also Fig.11, a first mask layer 42 is first formed on the surface of the piezoelectric layer 30 away from the lower electrode 20 by a low temperature deposition process or a coating process, and then a second mask layer 43 is formed. The materials of the first mask layer 42 and the second mask layer 43 can be the same or different. Optionally, the first mask layer 42 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 42 is greater than or equal to The second mask layer 43 can be made of positive or negative photoresist; the thickness of the second mask layer 43 is greater than or equal to And less than or equal to 10um.

[0089] S240 , forming a first portion of a protruding structure window on the second mask layer.

[0090] See also Fig.12 When the second mask layer 43 can be made of positive or negative photoresist, the second mask layer 43 can be quickly patterned through exposure and development processes to form the first portion 41a of the protruding structure window 41.

[0091] S250, forming a second part of the convex structure window and a concave structure window on the first mask layer, wherein the convex structure window and the concave structure window are connected, and the concave structure window is located at the inner side and the outer side of the convex structure window.

[0092] Optional, see Fig.21 S250 forms the second part of the protruding structure window and the recessed structure window in the first mask layer, specifically including the following steps:

[0093] S2501, forming a second part of the protruding structure window on the first mask layer;

[0094] See also Fig.13 , the first mask layer 42 may be etched through a wet etching process to form the second portion 41 b of the protruding structure window 41 .

[0095] S2502, etching the sidewall of the first mask layer through a wet etching process to form a recessed structure window, wherein the raised structure window and the recessed structure window are connected, and the recessed structure window is located on the inner side and the outer side of the raised structure window.

[0096] See also Fig.14 The first mask layer 42 is etched by a wet process, and by controlling the etching time, a recessed structure window 44 is formed on both sides of the raised structure window 41, wherein the inner recessed structure window 44a is located on the inner side of the raised structure window 41, and the outer recessed structure window 44b is located on the outer side of the raised structure window 41, and the raised structure window 41 and the recessed structure window 44 are connected.

[0097] It should be noted that the second portion 41 b of the protruding structure window 41 and the recessed structure window 44 may be formed together by a wet etching process.

[0098] Optionally, the wet etching rate is greater than or equal to and less than or equal to Specifically, the wet etching rate can be controlled to be greater than or equal to 100% by controlling the concentration of the wet etching solution and the etching time. and less than or equal to , so as to realize that the outer recessed structure window 44b and the inner recessed structure window 44a are within the preset size.

[0099] It should be noted that the widths of the outer recessed structure window 44b and the inner recessed structure window 44a may be the same or different.

[0100] S260, forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure.

[0101] See also Fig.14 , the first mask layer 42 includes the second portion 41b of the protruding structure window 41, and the second mask layer 43 includes the first portion 41a of the protruding structure window 41. Fig.15 In the process of forming the raised structure film layer 50 , a portion of the raised structure film layer 50 is located in the raised structure window 41 on the piezoelectric layer 30 , and the portion of the raised structure film layer 50 is the raised structure 50 a , and another portion of the raised structure film layer 50 is located on the surface of the second mask layer 43 .

[0102] S270, removing the mask layer and the raised structure film layer on the surface of the mask layer.

[0103] Optional, see Fig. 22 , S270 removes the mask layer and the raised structure film layer on the surface of the mask layer including:

[0104] S2701, removing the second mask layer and the raised structure film layer on the surface of the second mask layer.

[0105] See also Fig.16 The second mask layer 43 and the protruding structure film layer 50 on the surface of the second mask layer 43 are removed by an etching process or an exposure and development process, and an annular protruding structure 50 a is retained on the surface of the piezoelectric layer 30 .

[0106] Compared with the prior art, when preparing the protruding structure, it is necessary to first form a film layer of the entire surface of the protruding structure, and then perform the first photolithography and etching on the entire surface of the film layer to obtain the protruding structure, see Fig.15 and Fig.16 In the process of forming the protruding structure 50a on the surface of the piezoelectric layer 30 in this embodiment, there is no need to etch the protruding structure film layer 50, which simplifies the preparation process of the BAW resonator and reduces the preparation cost of the BAW resonator.

[0107] S2702, using the first mask layer as a mask plate, forming a recessed structure on the surface of the piezoelectric layer, wherein the orthographic projection of the recessed structure on the substrate and the orthographic projection of the recessed structure window on the substrate coincide with each other, and the depth of the recessed structure is less than the thickness of the piezoelectric layer.

[0108] See also Fig.17 In the process of forming the recessed structure 70, the piezoelectric layer 30 is dry-etched using the first mask layer 42 as a mask, and the recessed structure 70 is formed on the surface of the piezoelectric layer 30, thereby achieving self-alignment of the convex structure 50a and the recessed structure 70, avoiding the deviation of the relative positions of the convex structure 50a and the recessed structure 70, thereby improving the yield of the BAW resonator. Fig.16 The orthographic projection of the recessed structure window 44 in the substrate 10 coincides, and the depth of the recessed structure 70 is less than the thickness of the piezoelectric layer 30. The recessed structure 70 includes an inner recessed structure 70a and an outer recessed structure 70b. The orthographic projection of the inner recessed structure 70a and the inner recessed structure window 44a on the substrate 10 coincides. The orthographic projection of the outer recessed structure 70b and the outer recessed structure window 44b on the substrate 10 coincides.

[0109] It should be noted that, when the piezoelectric layer 30 is dry-etched using the first mask layer 42 as a mask, the protruding structure 50a will also be etched, so that the thickness of the protruding structure 50a will also decrease. Therefore, the thickness of the protruding structure film layer 50 needs to be greater than the depth of the recessed structure 70 to ensure that the protruding structure 50a remains on the surface of the piezoelectric layer 30 after the recessed structure 70 is formed.

[0110] S2703, removing the first mask layer.

[0111] See also Fig.18 , the first mask layer 42 may be removed by a wet etching process.

[0112] S280, forming an upper electrode, wherein the upper electrode covers the protruding structure and the piezoelectric layer.

[0113] See also Fig.19 , an upper electrode 60 is formed by a sputtering or evaporation process, and the upper electrode 60 covers the protruding structure 50 a and the piezoelectric layer 30 .

[0114] Optionally, S280 forms an upper electrode, and after the upper electrode covers the protruding structure, the method further includes:

[0115] S290, removing the protruding structure and the upper electrode outside the edge of the working area of ​​the BAW resonator, and retaining the protruding structure and the upper electrode within the working area of ​​the BAW resonator.

[0116] See also Fig. 20 , the protruding structure 50a and the upper electrode 60 can be patterned according to the preset size of the upper electrode 60, the protruding structure 50a and the upper electrode 60 outside the edge of the working area of ​​the BAW resonator are removed, and the protruding structure 50a and the upper electrode 60 in the working area of ​​the BAW resonator are retained, so as to form Fig. 20 The bulk acoustic wave resonator in .

[0117] Specifically, the protruding structure 50a and the recessed structure 70 are located under the upper electrode 60. The protruding structure 50a and the recessed structure 70 make the upper electrode 60 include a middle planar area and a concave reflective structure and a convex reflective structure surrounded by the edge. The concave reflective structure and the convex reflective structure surrounded by the edge serve as structures for avoiding the loss of sound wave energy. They can achieve the effect of reflecting the sound waves back to the piezoelectric layer 30, reduce the loss of sound waves, and thus further improve the quality factor of the bulk acoustic wave resonator.

[0118] On the basis of the above technical solutions, the technical solutions provided in this embodiment, in the first aspect, before forming the convex structure film layer 50, a mask layer 40 provided with a convex structure window 41 is formed on the surface of the piezoelectric layer 30, and after forming the convex structure film layer 50, the mask layer 40 and the convex structure film layer 50 on the surface of the mask layer 40 are removed, and the convex structure film layer 50 located in the convex structure window 41 on the piezoelectric layer 30 is the convex structure 50a. The preparation process of the above-mentioned bulk acoustic wave resonator does not need to etch the convex structure film layer 50, which simplifies the preparation process of the bulk acoustic wave resonator and reduces the preparation cost of the bulk acoustic wave resonator. On the second hand, in the process of forming the recessed structure 70, the piezoelectric layer 30 is dry-etched using the first mask layer 42 as a mask plate, and the recessed structure 70 is formed on the surface of the piezoelectric layer 30, thereby realizing the self-alignment of the convex structure 50a and the recessed structure 70, avoiding the deviation of the relative positions of the convex structure 50a and the recessed structure 70, thereby improving the yield of the bulk acoustic wave resonator. On the third hand, the convex structure 50a and the recessed structure 70 are located below the upper electrode 60, and the convex structure 50a and the recessed structure 70 make the upper electrode 60 include a middle planar area and a concave reflection structure and a convex reflection structure surrounded by the edge. The concave reflection structure and the convex reflection structure surrounded by the edge serve as structures to avoid the loss of sound wave energy, and can achieve the effect of reflecting the sound wave back to the piezoelectric layer 30, reducing the loss of the sound wave, thereby further improving the quality factor of the bulk acoustic wave resonator.

[0119] The embodiment of the present invention also provides a method for preparing a filter. The filter includes at least one BAW resonator, and the BAW resonator adopts the method for preparing the BAW resonator described in any of the above embodiments. Therefore, the method for preparing the filter provided by the embodiment of the present invention also has the beneficial effects described in the above embodiments, which will not be described in detail here.

[0120] The embodiment of the present invention also provides a bulk acoustic wave resonator. Figure 8 The BAW resonator comprises: a substrate 10, wherein an acoustic reflection structure such as a cavity structure 10a is arranged on the substrate 10; a lower electrode 20 and a piezoelectric layer 30, which are arranged on the surface of the substrate 10 in sequence; a microstructure, wherein the microstructure comprises a protruding structure 50a, which is located on the surface of the piezoelectric layer 30; and an upper electrode 60, which covers the protruding structure 50a and the piezoelectric layer 30. Figure 4-Figure 7 The method for preparing the protruding structure 50a includes: forming a mask layer 40 on the surface of the piezoelectric layer 30 away from the lower electrode 20. The mask layer 40 is provided with a microstructure window, and the microstructure window includes a protruding structure window 41. Forming a protruding structure film layer 50, wherein the protruding structure film layer 50 is located on the surface of the mask layer 40 and in the protruding structure window 41 on the piezoelectric layer 30, and the protruding structure film layer 50 located in the protruding structure window 41 on the piezoelectric layer 30 is a protruding structure 50a. Removing the mask layer 40 and the protruding structure film layer 50 on the surface of the mask layer 40.

[0121] The technical solution provided in this embodiment is that the raised structure 50a is located below the upper electrode 60. The raised structure 50a makes the upper electrode 60 include a middle plane area and a raised reflective structure surrounded by the edge. The raised reflective structure surrounded by the edge is a structure to avoid the loss of sound wave energy, which can achieve the effect of reflecting the sound wave back to the piezoelectric layer 30, reducing the loss of sound waves, thereby improving the quality factor of the bulk acoustic wave resonator. Specifically, before forming the raised structure film layer 50, a mask layer 40 with a raised structure window 41 is formed on the surface of the piezoelectric layer 30. After forming the raised structure film layer 50, the mask layer 40 and the raised structure film layer 50 on the surface of the mask layer 40 are removed, and the raised structure film layer 50 located in the raised structure window 41 on the piezoelectric layer 30 is the raised structure 50a. The preparation process of the above-mentioned raised structure 50a does not require etching of the raised structure film layer 50, which simplifies the preparation process of the bulk acoustic wave resonator and reduces the preparation cost of the bulk acoustic wave resonator.

[0122] Optional, see Fig.19The microstructure also includes a recessed structure 70, which is located on the surface of the piezoelectric layer 30, and the recessed structure 70 is located on the inner side of the protruding structure 50a, and the recessed structure 70 is formed by a groove on the piezoelectric layer 30, and the depth of the recessed structure 70 is less than the thickness of the piezoelectric layer 30.

[0123] Optional, see Fig.11 – Fig.18 , the preparation method of the recessed structure 70 includes: first forming a first mask layer 42 and a second mask layer 43 on the surface of the piezoelectric layer 30 away from the lower electrode 20. Forming a first part 41a of the convex structure window 41 on the second mask layer 43. Forming a second part 41b of the convex structure window 41 and a recessed structure window 44 on the first mask layer 42, wherein the convex structure window 41 and the recessed structure window 44 are connected, and the recessed structure window 44 is located on the inner and outer sides of the convex structure window 41. Forming a convex structure film layer 50, wherein the convex structure film layer 50 is located on the surface of the second mask layer 43 and in the convex structure window 41 on the piezoelectric layer 30, and the convex structure film layer 50 located in the convex structure window 41 on the piezoelectric layer 30 is a convex structure 50a. Removing the second mask layer 43 and the convex structure film layer 50 on the surface of the second mask layer 43. Using the first mask layer 42 as a mask, a recessed structure 70 is formed on the surface of the piezoelectric layer 30, wherein the orthographic projection of the recessed structure 70 on the substrate 10 coincides with the orthographic projection of the recessed structure window 44 on the substrate 10, and the depth of the recessed structure 44 is less than the thickness of the piezoelectric layer 30. The first mask layer 42 is removed. The recessed structure 44 is a groove on the piezoelectric layer 30.

[0124] See also Fig.14 , the first mask layer 42 is etched by a wet process, and by controlling the etching time, a recessed structure window 44 is formed on both sides of the convex structure window 41, wherein the inner recessed structure window 44a is located inside the convex structure window 41, and the outer recessed structure window 44b is located outside the convex structure window 41, and the convex structure window 41 and the recessed structure window 44 are connected. The width of the outer recessed structure window 44b and the inner recessed structure window 44a can be the same or different. The recessed structure 70 includes an inner recessed structure 70a and an outer recessed structure 70b. The orthographic projections of the inner recessed structure 70a and the inner recessed structure window 44a on the substrate 10 overlap. The orthographic projections of the outer recessed structure 70b and the outer recessed structure window 44b on the substrate 10 overlap. The widths of the outer recessed structure 70b and the inner recessed structure 70a can be the same or different.

[0125] Specifically, the convex structure 50a and the concave structure 70 are located below the upper electrode 60. The convex structure 50a and the concave structure 70 make the upper electrode 60 include a middle plane area and a concave reflection structure and a convex reflection structure surrounded by the edge. The concave reflection structure and the convex reflection structure surrounded by the edge are structures to avoid the loss of sound wave energy, which can achieve the effect of reflecting the sound wave back to the piezoelectric layer 30, reduce the loss of the sound wave, and further improve the quality factor of the bulk acoustic wave resonator. In the process of forming the concave structure 70, the first mask layer 42 is used as a mask plate to wet-etch the piezoelectric layer 30, and the concave structure 70 is formed on the surface of the piezoelectric layer 30, so as to achieve self-alignment of the convex structure 50a and the concave structure 70, and avoid the relative position deviation of the convex structure 50a and the concave structure 70, thereby improving the yield of the bulk acoustic wave resonator.

[0126] Optional, see Fig. 9 and Fig. 20 , the protruding structure 50 a is located in the working area of ​​the BAW resonator; the upper electrode 60 covers the protruding structure 50 a and the surface of the piezoelectric layer 30 surrounded by the protruding structure 50 a.

[0127] Specifically, the sandwich structure composed of the upper electrode 60, the piezoelectric layer 30 and the lower electrode 20 is used as a resonant unit of the bulk acoustic wave resonator. The orthographic projections of the upper electrode 60, the piezoelectric layer 30 and the lower electrode 20 on the substrate 10 overlap, and the part where the orthographic projection overlaps with the orthographic projection of the acoustic reflection structure on the substrate 10 belongs to the working area, and the part outside the working area is called the non-working area.

[0128] The protruding structure 50a and the upper electrode 60 may be patterned according to the preset size of the upper electrode 60. Fig. 9 and Fig. 20 , removing the protruding structure 50a and the upper electrode 60 outside the edge of the BAW resonator working area, retaining the protruding structure 50a and the upper electrode 60 in the working area of ​​the BAW resonator, forming Fig. 9 and Fig. 20 The bulk acoustic wave resonator in .

[0129] Optionally, the materials of the protruding structure 50a and the upper electrode 60 are the same or different. When the materials of the protruding structure 50a and the upper electrode 60 are the same, the ability of the upper electrode 60 to transmit large current can be increased while avoiding the loss of acoustic wave energy.

[0130] The embodiment of the present invention further provides a filter. The filter includes at least one BAW resonator, and the BAW resonator includes any BAW resonator described in the above embodiment. Therefore, the filter provided by the embodiment of the present invention also has the beneficial effects described in the above embodiment, which will not be described in detail here.

[0131] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0132] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a bulk acoustic wave resonator, characterized in that: include: Providing a substrate, wherein a sound reflection structure is disposed on a surface or inside of the substrate; forming a lower electrode and a piezoelectric layer in sequence on the substrate; Forming a mask layer on a surface of the piezoelectric layer away from the lower electrode, wherein the mask layer is provided with a microstructure window, and the microstructure window includes a convex structure window; Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure; removing the mask layer and the convex structure film layer on the surface of the mask layer; forming an upper electrode, wherein the upper electrode covers the protruding structure and the piezoelectric layer; The microstructure window further includes a recessed structure window, and forming a mask layer on a surface of the piezoelectric layer away from the lower electrode includes: forming a first mask layer and a second mask layer in sequence on a surface of the piezoelectric layer away from the lower electrode; forming a first portion of a raised structure window on the second mask layer; forming a second portion of a convex structure window and a concave structure window on the first mask layer, wherein the convex structure window is connected to the concave structure window, and the concave structure window is located at the inner side and the outer side of the convex structure 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 protruding structure film layer on the surface of the second mask layer; Using the first mask layer as a mask, a concave structure is formed on the surface of the piezoelectric layer, wherein the orthographic projection of the concave structure on the substrate coincides with the orthographic projection of the concave structure window on the substrate, and the depth of the concave structure is less than the thickness of the piezoelectric layer; The first mask layer is removed.

2. The method for preparing a bulk acoustic wave resonator according to claim 1, characterized in that: The method further comprises: forming an upper electrode, wherein the upper electrode covers the protruding structure and the piezoelectric layer; The protruding structure and the upper electrode outside the edge of the working area of ​​the BAW resonator are removed, and the protruding structure and the upper electrode within the working area of ​​the BAW resonator are retained.

3. The method for preparing a bulk acoustic wave resonator according to claim 1, characterized in that: Forming the second part of the protruding structure window and the recessed structure window on the first mask layer includes: forming a second portion of the protruding structure window on the first mask layer; The sidewall of the first mask layer is etched by a wet etching process to form a recessed structure window, wherein the convex structure window is connected to the recessed structure window, and the recessed structure window is located inside and outside the convex structure window.

4. The method for preparing a bulk acoustic wave resonator according to claim 3, characterized in that: The wet etching rate is greater than or equal to 5000 Å / min and less than or equal to 10000 Å / min.

5. The method for preparing a bulk acoustic wave resonator according to claim 1, characterized in that: 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 preparing a bulk acoustic wave resonator according to claim 1, characterized in that: The thickness of the first mask layer is greater than or equal to 2000 Å and less than or equal to 2 um; The thickness of the second mask layer is greater than or equal to 1000 Å and less than or equal to 10 um.

7. A method for preparing a filter, characterized in that: include: The filter comprises at least one BAW resonator, and a method for preparing the BAW resonator is the method for preparing the BAW resonator according to any one of claims 1 to 6.

8. A bulk acoustic wave resonator, characterized in that: include: A substrate, wherein a sound reflection structure is provided on the surface or inside of the substrate; A lower electrode and a piezoelectric layer, wherein the lower electrode and the piezoelectric layer are sequentially arranged on the substrate; A microstructure, wherein the microstructure includes a protrusion structure, and the protrusion structure is located on the surface of the piezoelectric layer; an upper electrode, the upper electrode covering the protrusion structure and the piezoelectric layer; The method for preparing the protruding structure comprises: forming a mask layer on a surface of the piezoelectric layer away from the lower electrode, wherein the mask layer is provided with a microstructure window, and the microstructure window comprises a protruding structure window; Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure; removing the mask layer and the convex structure film layer on the surface of the mask layer; The microstructure also includes a recessed structure, which is located on the surface of the piezoelectric layer and the inner side of the protruding structure. The recessed structure is formed by a groove on the piezoelectric layer, and the depth of the recessed structure is less than the thickness of the piezoelectric layer.

9. The BAW resonator according to claim 8, characterized in that: The method for preparing the recessed structure comprises: forming a first mask layer and a second mask layer in sequence on a surface of the piezoelectric layer away from the lower electrode; forming a first portion of a raised structure window on the second mask layer; forming a second portion of a convex structure window and a concave structure window on the first mask layer, wherein the convex structure window is connected to the concave structure window, and the concave structure window is located at the inner side and the outer side of the convex structure window; Forming a convex structure film layer, wherein the convex structure film layer is located on the surface of the second mask layer and in the convex structure window on the piezoelectric layer, and the convex structure film layer located in the convex structure window on the piezoelectric layer is a convex structure; removing the second mask layer and the protruding structure film layer on the surface of the second mask layer; Using the first mask layer as a mask, a concave structure is formed on the surface of the piezoelectric layer, wherein the orthographic projection of the concave structure on the substrate coincides with the orthographic projection of the concave structure window on the substrate, and the depth of the concave structure is less than the thickness of the piezoelectric layer; The first mask layer is removed.

10. The bulk acoustic wave resonator according to claim 8, characterized in that The protruding structure is located in the working area of ​​the BAW resonator; The upper electrode covers the protruding structure and a surface of the piezoelectric layer surrounded by the protruding structure.

11. The bulk acoustic wave resonator according to claim 8, characterized in that The material of the protrusion structure is the same as or different from the material of the upper electrode.

12. A filter, characterized in that: Comprising at least one BAW resonator according to any one of claims 8 to 11.

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