A bulk acoustic wave resonator and a method for manufacturing the same

Abstract

The present application relates to the technical field of bulk acoustic wave resonators, and specifically provides a bulk acoustic wave resonator and a preparation method thereof. The resonator comprises: a substrate, a bottom electrode, a piezoelectric layer, and a top electrode connected in sequence from bottom to top, wherein an acoustic reflector is provided on the substrate; a first groove is provided on the piezoelectric layer, wherein the edge of the projection of the first groove in the top-view direction does not exceed the edge of the projection of the acoustic reflector in the top-view direction; a second groove is provided on the top electrode, wherein the edge of the projection of the second groove in the top-view direction does not exceed the edge of the projection of the first groove in the top-view direction; the resonator can effectively solve the problems that the air gap cannot fully play its role in reducing energy leakage due to morphological defects in the air gap, the improvement effect of the quality factor and parallel resonance impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external part of the top electrode is reduced due to the loss of support of the external part of the top electrode.

Description

Technical Field

[0001] The present application relates to the technical field of bulk acoustic wave resonators, and in particular to a bulk acoustic wave resonator and a method for preparing the same. Background Art

[0002] In the field of bulk acoustic wave resonator technology, related technologies usually reduce energy leakage by forming an air gap between the top electrode and the piezoelectric layer to improve the quality factor and parallel resonance impedance of the bulk acoustic wave resonator. The air gap can be divided into an air gap located in the non-external area of ​​the top electrode and an air gap located in the external area of ​​the top electrode. The process of forming the air gap located in the non-external area of ​​the top electrode in the related technology is as follows: first, a dielectric layer is formed on the piezoelectric layer located in the projection area of ​​the acoustic reflector, then a top electrode is formed on the dielectric layer, and finally the dielectric layer is removed. The process of forming the air gap located in the external area of ​​the top electrode in the related technology is as follows: first, a sacrificial layer is formed on the piezoelectric layer outside the projection area of ​​the acoustic reflector, then a top electrode is formed on the sacrificial layer, and finally the sacrificial layer is released.

[0003] Due to the limitation of process bottleneck, both the dielectric layer and the sacrificial layer formed on the piezoelectric layer have morphological defects, and the morphological defects will cause the air gap formed in the end to also have morphological defects. Therefore, the related art has the problem that the air gap cannot fully play the role of reducing energy leakage due to the morphological defects in the air gap, and the quality factor of the bulk acoustic wave resonator and the effect of improving the parallel resonance impedance are limited. Moreover, since the external part of the top electrode will lose support after the sacrificial layer is released, the related art also has the problem that the mechanical stability of the external part of the top electrode is reduced due to the loss of support of the external part of the top electrode.

[0004] There is no effective technical solution to the above problems. It should be noted that the above information disclosed in this section is only used to understand the background of the present invention, and therefore may contain information that does not constitute prior art. Summary of the Invention

[0005] The purpose of the present application is to provide a bulk acoustic wave resonator and a preparation method thereof, which can effectively solve the problems that the air gap cannot fully play its role in reducing energy leakage due to the presence of morphological defects in the air gap, the quality factor of the bulk acoustic wave resonator and the improvement effect of the parallel resonance impedance are limited, and the mechanical stability of the external part of the top electrode is reduced due to the loss of support of the external part of the top electrode.

[0006] In a first aspect, the present application provides a bulk acoustic wave resonator, comprising:

[0007] A substrate, a bottom electrode, a piezoelectric layer and a top electrode are sequentially connected from bottom to top, and an acoustic reflector is provided on the substrate;

[0008] A first groove is provided on the piezoelectric layer, and the edge of the projection of the first groove in the top view direction does not exceed the edge of the projection of the acoustic reflector in the top view direction. A second groove is provided on the top electrode, and the edge of the projection of the second groove in the top view direction does not exceed the edge of the projection of the first groove in the top view direction.

[0009] The present application provides a bulk acoustic wave resonator that can reduce acoustic wave leakage and energy leakage by forming a first groove on the piezoelectric layer and a second groove on the top electrode. That is, the present application is equivalent to using the first groove and the second groove to replace the air gap in the prior art, that is, the present application can improve the quality factor and parallel resonant impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problem that the air gap cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the air gap, the improvement effect of the quality factor and parallel resonant impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external part of the top electrode is reduced due to the loss of support of the external part of the top electrode.

[0010] Optionally, the piezoelectric layer has a step group, which is located in the first groove. The step group includes at least one step portion, and the height of the step portion is less than the depth of the first groove. When there are multiple step portions, the multiple step portions are distributed inside and outside the center of the piezoelectric layer and are spaced apart.

[0011] Since there is an acoustic impedance difference between the area where the step portion is located and the area outside the step portion, and under the action of this acoustic impedance difference, the step portion can hinder and reflect the lateral transmission of the sound wave. Therefore, this technical solution is equivalent to increasing the number and amount of reflections of the sound wave by arranging a step group in the first groove, thereby effectively improving the suppression effect of sound wave leakage and further reducing the amount of sound wave leakage and energy leakage, thereby further improving the quality factor and parallel resonant impedance of the bulk acoustic wave resonator.

[0012] Optionally, a minimum distance between the step portion and the top of the piezoelectric layer is greater than a minimum distance between the top of the step portion and the bottom of the first groove.

[0013] This technical solution can improve the sound wave leakage suppression effect of the step portion by making the minimum distance between the step portion and the top of the piezoelectric layer greater than the minimum distance between the top of the step portion and the bottom of the first groove. Therefore, this technical solution can further reduce the amount of sound wave leakage and energy leakage.

[0014] Optionally, the step portion is an annular structure, and the outermost step portion is in contact with the side wall of the first groove.

[0015] Optionally, the top electrode has at least one external connection portion, and the step portion is arranged in the first groove on a side close to the external connection portion.

[0016] The step portion of this technical solution is only arranged on one side of the first groove close to the external connection portion. Therefore, this technical solution can reduce the coverage area of ​​the step portion while ensuring the sound wave leakage suppression effect, thereby effectively reducing the production difficulty and production cost of the step portion, and further effectively reducing the production difficulty and production cost of the bulk acoustic wave resonator.

[0017] Optionally, the BAW resonator further includes a passivation layer, wherein the passivation layer is disposed above the top electrode.

[0018] In a second aspect, the present application further provides a method for preparing a bulk acoustic wave resonator, which comprises the following steps:

[0019] S1. forming a cavity on a substrate and forming an acoustic reflector in the cavity;

[0020] S2. forming a bottom electrode, a piezoelectric layer, and a first patterned photoresist layer on the substrate in sequence, wherein the inner boundary of the projection of the first patterned photoresist layer in the top view direction does not exceed the edge of the projection of the acoustic reflector in the top view direction;

[0021] S3, etching the piezoelectric layer based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of which, when projected in the top view, does not exceed the edge of the projection of the acoustic reflector in the top view;

[0022] S4, removing the first patterned photoresist layer;

[0023] S5. forming a top electrode and a second patterned photoresist layer in sequence on the piezoelectric layer, wherein an inner boundary of a projection of the second patterned photoresist layer in a top view direction is located at an edge of a projection of the first groove in a top view direction;

[0024] S6. Etching the top electrode based on the second patterned photoresist layer to form a second groove on the top electrode, the edge of which projection in the top view direction does not exceed the edge of the projection of the first groove in the top view direction.

[0025] The present application provides a method for preparing a bulk acoustic resonator, which can reduce the amount of acoustic wave leakage and energy leakage by forming a first groove on the piezoelectric layer and a second groove on the top electrode. That is, the present application is equivalent to using the first groove and the second groove to replace the air gap in the prior art, that is, the present application can improve the quality factor and parallel resonant impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problem that the air gap cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the air gap, the effect of improving the quality factor and parallel resonant impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external part of the top electrode is reduced due to the loss of support of the external part of the top electrode.

[0026] Optionally, the method for preparing a bulk acoustic wave resonator further includes a step performed between step S2 and step S3:

[0027] A1. Surface treatment is performed on the first patterned photoresist layer and the piezoelectric layer using oxygen.

[0028] This technical solution can use oxygen to perform surface treatment on the first patterned photoresist layer and the piezoelectric layer so that the side walls of the first patterned photoresist layer and the exposed surface of the piezoelectric layer have good morphology. Therefore, this technical solution can make the first groove formed on the piezoelectric layer have good morphology by performing surface treatment on the first patterned photoresist layer and the piezoelectric layer before etching the piezoelectric layer, thereby effectively avoiding the situation where the first groove cannot fully play the role of reducing energy leakage due to morphological defects in the first groove.

[0029] Optionally, step S3 includes:

[0030] S31, etching the piezoelectric layer using the TRIM technology based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of which, when projected in the top view, does not exceed the edge of the acoustic reflector, when projected in the top view;

[0031] Step S6 includes:

[0032] S61 , etching the top electrode using the TRIM technology based on the second patterned photoresist layer to form a second groove on the top electrode, the edge of which projection in the top view direction does not exceed the edge of the projection of the first groove in the top view direction.

[0033] Since TRIM technology has the advantage of high etching precision, this technical solution can ensure that the first groove and the second groove formed have precise depth and low surface roughness, thereby effectively improving the suppression effect of the first groove and the second groove on acoustic wave leakage, and further improving the quality factor and parallel resonant impedance of the bulk acoustic wave resonator.

[0034] Optionally, step S2 includes:

[0035] S21, forming a bottom electrode, a piezoelectric layer, a protective layer, and a first patterned photoresist layer in sequence on the substrate, wherein the inner boundary of the projection of the first patterned photoresist layer in the top view direction is located at the edge of the projection of the acoustic reflector in the top view direction;

[0036] Step S3 includes:

[0037] S31′, etching the piezoelectric layer and the protective layer based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of which, when projected in the top view, does not exceed the edge of the acoustic reflector, when projected in the top view;

[0038] Step S4 includes:

[0039] S41 , removing the first patterned photoresist layer and the protective layer.

[0040] From the above, it can be seen that the bulk acoustic wave resonator and the preparation method thereof provided by the present application can reduce the amount of acoustic wave leakage and energy leakage by forming a first groove on the piezoelectric layer and a second groove on the top electrode, that is, the present application is equivalent to using the first groove and the second groove to replace the air gap in the prior art, that is, the present application can improve the quality factor and parallel resonant impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problem that the air gap cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the air gap, the improvement effect of the quality factor and parallel resonant impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external part of the top electrode is reduced due to the loss of support of the external part of the top electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic cross-sectional view of a bulk acoustic wave resonator provided in the first embodiment of the present application.

[0042] Figure 2 A schematic cross-sectional view of a bulk acoustic wave resonator without a passivation layer provided in the second embodiment of the present application.

[0043] Figure 3 Schematic diagram of the cross-sectional structure of the substrate, bottom electrode, piezoelectric layer and step portion provided in the third embodiment of the present application.

[0044] Figure 4 A schematic structural diagram of the substrate, bottom electrode, piezoelectric layer and step portion provided for the third embodiment of the present application.

[0045] Figure 5 Schematic diagram of the cross-sectional structure of the substrate, bottom electrode, piezoelectric layer and step portion provided in the fourth embodiment of the present application.

[0046] Figure 6 This is a schematic structural diagram of the substrate, bottom electrode, piezoelectric layer and step portion provided in the fourth embodiment of the present application.

[0047] Figure 7 A schematic structural diagram of the substrate, bottom electrode, piezoelectric layer and step portion provided for the fifth embodiment of the present application.

[0048] Figure 8 A flow chart of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application.

[0049] Figure 9 A schematic flow chart of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application.

[0050] Figure 10 This is a scanning electron microscope image of the piezoelectric layer and the first groove after surface treatment with oxygen.

[0051] Figure 11 : SEM images of the piezoelectric layer and the first groove without oxygen surface treatment.

[0052] Figure numerals: 1. substrate; 2. bottom electrode; 3. piezoelectric layer; 4. top electrode; 5. acoustic reflector; 6. first groove; 7. second groove; 8. step portion; 9. passivation layer; 10. first patterned photoresist layer; 11. second patterned photoresist layer; 12. protective layer. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work fall within the scope of protection of the present application.

[0054] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0055] First, as Figure 1-Figure 7 As shown, the present application provides a bulk acoustic wave resonator, which includes:

[0056] A substrate 1, a bottom electrode 2, a piezoelectric layer 3 and a top electrode 4 are connected in sequence from bottom to top, and an acoustic reflector 5 is provided on the substrate 1;

[0057] A first groove 6 is provided on the piezoelectric layer 3, and the edge of the projection of the first groove 6 in the top view direction does not exceed the edge of the projection of the acoustic reflector 5 in the top view direction. A second groove 7 is provided on the top electrode 4, and the edge of the projection of the second groove 7 in the top view direction does not exceed the edge of the projection of the first groove 6 in the top view direction.

[0058] Among them, the material of the substrate 1 of this embodiment is preferably silicon material, the material of the bottom electrode 2 and the top electrode 4 of this embodiment is preferably a metal material with high electrical conductivity, large acoustic impedance and large Young's modulus (such as any one or more of gold, molybdenum, ruthenium and platinum), the material of the bottom electrode 2 of this embodiment is preferably the same as the material of the top electrode 4 of this embodiment, and the material of the piezoelectric layer 3 of this embodiment is preferably aluminum nitride. Specifically, when the top electrode 4 and the bottom electrode 2 are externally connected to a signal source (equivalent to applying a voltage signal or an electrical signal to the top electrode 4 and the bottom electrode 2), an electric field is formed at both ends of the piezoelectric layer 3 to excite a bulk acoustic wave (equivalent to exciting the piezoelectric layer 3 to generate a longitudinal wave), thereby realizing the mutual conversion of electrical energy and mechanical energy and the frequency selection of the bulk acoustic wave resonator. It should be understood that if it is necessary to improve the effective electromechanical coupling coefficient of the bulk acoustic wave resonator, this embodiment can select scandium-doped aluminum nitride as the material of the piezoelectric layer 3. Those skilled in the art can determine the specific scandium doping amount based on the actual effective electromechanical coupling coefficient requirements. An acoustic reflector 5 is provided on the substrate 1 of this embodiment. The acoustic reflector 5 can be an air cavity or several layers of Bragg reflective layers. Each Bragg reflective layer is composed of a low acoustic impedance layer and a high acoustic impedance layer. In this embodiment, the substrate 1 can be first etched to form a groove on the substrate 1, and then several layers of Bragg reflective layers are formed in the groove based on the existing Bragg reflective layer formation process. It should be understood that if the acoustic reflector 5 is an air cavity, the bulk acoustic wave resonator of this embodiment is essentially a film bulk acoustic resonator (FBAR); if the acoustic reflector 5 is a Bragg reflective layer, the bulk acoustic wave resonator of this embodiment is essentially a solid-mounted resonator (SMR). A first groove 6 is provided on the piezoelectric layer 3 of this embodiment. Since the difference between the acoustic impedance in the area where the first groove 6 is located and the acoustic impedance of the area outside the first groove 6 is large, and under the action of this acoustic impedance difference, the sound wave will encounter obstruction and reflection when entering the area outside the first groove 6 from the area where the first groove 6 is located. Therefore, this embodiment can reduce the amount of sound wave leakage by forming a first groove 6 on the piezoelectric layer 3 to reduce energy leakage. It should be understood that if the edge of the projection of the first groove 6 in the top view direction exceeds the edge of the projection of the acoustic reflector 5 in the top view direction, the sound wave will leak from the area of ​​the first groove 6 that exceeds the edge of the projection of the acoustic reflector 5 in the top view direction. At this time, the quality factor and parallel resonance impedance of the bulk acoustic wave resonator cannot be improved by reducing the amount of sound wave leakage. Therefore, this embodiment requires that the edge of the projection of the first groove 6 in the top view direction does not exceed the edge of the projection of the acoustic reflector 5 in the top view direction.Based on the same principle as the first groove 6, the second groove 7 of this embodiment plays a role in reducing acoustic wave leakage. Therefore, this embodiment can further reduce the amount of acoustic wave leakage and energy leakage by setting the second groove 7 on the top electrode 4, that is, this embodiment is equivalent to performing secondary confinement on the acoustic wave by setting the first groove 6 and the second groove 7.

[0059] The present application provides a bulk acoustic wave resonator that can reduce the amount of acoustic wave leakage and energy leakage by forming a first groove 6 on the piezoelectric layer 3 and a second groove 7 on the top electrode 4. That is, the present application is equivalent to using the first groove 6 and the second groove 7 to replace the air gap in the prior art, that is, the present application can improve the quality factor and parallel resonant impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problem that the air gap cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the air gap, the effect of improving the quality factor and parallel resonant impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external part of the top electrode 4 is reduced due to the loss of support of the external part of the top electrode 4.

[0060] In some preferred embodiments, Figure 3-Figure 7 As shown, the piezoelectric layer 3 has a step group, which is located in the first groove 6. The step group includes at least one step portion 8. The height of the step portion 8 is less than the depth of the first groove 6. When there are multiple step portions 8, the multiple step portions 8 are distributed inside and outside the center of the piezoelectric layer 3 and are spaced apart (refer to Figure 7 ). Because there is an acoustic impedance difference between the area where the step portion 8 is located and the area outside the step portion 8, and under the action of this acoustic impedance difference, the step portion 8 can hinder and reflect the lateral transmission of the sound wave. Therefore, this embodiment is equivalent to increasing the number and amount of sound wave reflections by providing a step group in the first groove 6, thereby effectively improving the suppression effect of sound wave leakage and further reducing the amount of sound wave leakage and energy leakage, thereby further improving the quality factor and parallel resonance impedance of the bulk acoustic wave resonator. It should be understood that the step group of this embodiment is part of the piezoelectric layer 3. The more step groups there are, the better the suppression effect of sound wave leakage, and the higher the production difficulty and production cost of the step group. Therefore, those skilled in the art can change the number of step portions 8 included in the step group according to the actual suppression effect, production difficulty and production cost requirements. Preferably, the number of step portions 8 in this embodiment is less than or equal to three to avoid the situation where the resonator frequency of the bulk acoustic wave resonator is affected by the excessive number of step portions 8. It should also be understood that those skilled in the art can adjust the length, width and / or height of the step portion 8 according to the performance requirements of the bulk acoustic wave resonator.

[0061] In some preferred embodiments, the minimum distance between the step portion 8 and the top of the piezoelectric layer 3 is greater than the minimum distance between the top of the step portion 8 and the bottom of the first groove 6. This embodiment can improve the acoustic wave leakage suppression effect of the step portion 8 by making the minimum distance between the step portion 8 and the top of the piezoelectric layer 3 greater than the minimum distance between the top of the step portion 8 and the bottom of the first groove 6. Therefore, this embodiment can further reduce the amount of acoustic wave leakage and energy leakage.

[0062] In some preferred embodiments, reference Figure 3 and Figure 4 The step portion 8 is an annular structure, and the outermost step portion 8 is in contact with the side wall of the first groove 6. The step portion 8 of this embodiment is preferably a polygonal annular structure, that is, the cross-sectional shape of the step portion 8 is polygonal. Since the step portion 8 of this embodiment is an annular structure, that is, the step portion 8 of this embodiment can suppress sound wave leakage in all directions, so this embodiment can achieve the best sound wave leakage suppression effect of the step portion 8.

[0063] In some preferred embodiments, the top electrode 4 has at least one external portion, and the step portion 8 is provided on one side of the first groove 6 close to the external portion. The top electrode 4 of this embodiment has at least one external portion, which extends to the area outside the acoustic reflector 5. Since the leakage of acoustic waves usually occurs at the external portion of the top electrode 4, the step portion 8 is provided on one side of the first groove 6 close to the external portion (refer to FIG. Figure 5 and Figure 6 ), therefore, this embodiment can reduce the coverage area of ​​the step portion 8 while ensuring the acoustic wave leakage suppression effect, thereby effectively reducing the production difficulty and production cost of the step portion 8, and further effectively reducing the production difficulty and production cost of the bulk acoustic wave resonator.

[0064] In some preferred embodiments, the BAW resonator further includes a passivation layer 9, which is disposed above the top electrode 4. The material of the passivation layer 9 in this embodiment may be aluminum nitride, silicon dioxide, or nitrogen dioxide. Since the passivation layer 9 in this embodiment is disposed above the top electrode 4, the passivation layer 9 can protect the top electrode 4. Therefore, this embodiment can effectively prevent the top electrode 4 from being oxidized, corroded, or contaminated due to contact with the external environment, so that the top electrode 4 can maintain good electrical conductivity and structural integrity, thereby effectively improving the stability of the BAW resonator and extending the service life of the BAW resonator.

[0065] In some preferred embodiments, the ratio of the depth of the first groove 6 to the thickness of the piezoelectric layer 3 is 5%-30%. This embodiment can effectively avoid the situation where the improvement effect of the quality factor of the BAW resonator is limited due to the first groove 6 being too shallow, and the resonator frequency and effective electromechanical coupling coefficient of the BAW resonator are significantly affected due to the first groove 6 being too deep, by setting the ratio of the depth of the first groove 6 to the thickness of the piezoelectric layer 3 to 5%-30%.

[0066] From the above, it can be seen that the bulk acoustic wave resonator provided by the present application can reduce the amount of acoustic wave leakage and energy leakage by forming a first groove 6 on the piezoelectric layer 3 and a second groove 7 on the top electrode 4, that is, the present application is equivalent to using the first groove 6 and the second groove 7 to replace the air gap in the prior art, that is, the present application can improve the quality factor and parallel resonant impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problem that the air gap cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the air gap, the improvement effect of the quality factor and parallel resonant impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external part of the top electrode 4 is reduced due to the loss of support of the external part of the top electrode 4.

[0067] Second, as Figures 8-11 As shown, the present application also provides a method for preparing a bulk acoustic wave resonator, which includes the following steps:

[0068] S1, forming a cavity on a substrate 1, and forming an acoustic reflector 5 in the cavity;

[0069] S2. Forming a bottom electrode 2, a piezoelectric layer 3, and a first patterned photoresist layer 10 in sequence on the substrate 1, wherein the inner boundary of the projection of the first patterned photoresist layer 10 in the top view direction does not exceed the edge of the projection of the acoustic reflector 5 in the top view direction;

[0070] S3, etching the piezoelectric layer 3 based on the first patterned photoresist layer 10 to form a first groove 6 on the piezoelectric layer 3, the edge of which, when projected in the top view, does not exceed the edge of the projection of the acoustic reflector 5 in the top view;

[0071] S4, removing the first patterned photoresist layer 10;

[0072] S5. Forming a top electrode 4 and a second patterned photoresist layer 11 in sequence on the piezoelectric layer 3, wherein the inner boundary of the projection of the second patterned photoresist layer 11 in the top view direction is located at the edge of the projection of the first groove 6 in the top view direction;

[0073] S6. Etching the top electrode 4 based on the second patterned photoresist layer 11 to form a second groove 7 on the top electrode 4, the edge of which is projected in the top view direction but does not exceed the edge of the projection of the first groove 6 in the top view direction.

[0074] Step S1 can use the existing etching process to etch the substrate 1 to form a cavity on the substrate 1. Step S1 can use the existing acoustic reflector 5 formation process to form an acoustic reflector 5 in the cavity. It should be understood that if the acoustic reflector 5 is an air cavity, step S1 fills the cavity with a sacrificial layer and releases the sacrificial layer after executing step S5.

[0075] In step S2, a bottom electrode 2 and a piezoelectric layer 3 can be sequentially formed on the substrate 1 by depositing electrode material and piezoelectric material on the substrate 1 in sequence. In step S2, a first patterned photoresist layer 10 can be formed on the piezoelectric layer 3 using an existing photoresist layer forming process. The first patterned photoresist layer 10 has an opening, and the inner boundary of the projection of the first patterned photoresist layer 10 in the top-view direction does not exceed the edge of the projection of the acoustic reflector 5 in the top-view direction, that is, the edge of the projection of the opening of the first patterned photoresist layer 10 in the top-view direction does not exceed the edge of the projection of the acoustic reflector 5 in the top-view direction, so as to ensure that the edge of the projection of the formed first groove 6 in the top-view direction does not exceed the edge of the projection of the acoustic reflector 5 in the top-view direction. It should be understood that the shape of the opening of this embodiment is the same as the shape of the first groove 6.

[0076] In step S3, the piezoelectric layer 3 can be etched based on the first patterned photoresist layer 10 using existing RIE technology, so as to form a first groove 6 on the piezoelectric layer 3, the edge of which, when projected in the top view, does not extend beyond the edge of the projection of the acoustic reflector 5 in the top view. In step S4, the first patterned photoresist layer 10 can be removed using an existing photoresist removal process.

[0077] In step S5, an electrode material can be deposited on the piezoelectric layer 3 using an existing physical deposition process or a chemical deposition process to form a top electrode 4 on the piezoelectric layer 3. In step S5, a second patterned photoresist layer 11 can be formed on the top electrode 4 using an existing photoresist layer formation process. The second patterned photoresist layer 11 has an opening, and the inner boundary of the projection of the second patterned photoresist layer 11 in the top view direction is located at the edge of the projection of the first groove 6 in the top view direction, that is, the edge of the projection of the opening of the second patterned photoresist layer 11 in the top view direction is located within the edge of the projection of the first groove 6 in the top view direction, so as to ensure that the edge of the projection of the formed second groove 7 in the top view direction does not exceed the edge of the projection of the first groove 6 in the top view direction. In step S6, the top electrode 4 can be etched based on the second patterned photoresist layer 11 using an existing RIE technology to form a second groove 7 on the top electrode 4, the edge of which does not exceed the edge of the projection of the first groove 6 in the top view direction.

[0078] The method for preparing a bulk acoustic resonator provided in this embodiment is preferably used to prepare the bulk acoustic wave resonator provided in the first aspect above. The principle of the method for preparing a bulk acoustic resonator provided in this embodiment is the same as the principle of the bulk acoustic wave resonator provided in the first aspect above, and will not be discussed in detail here.

[0079] In some preferred embodiments, the method for preparing a bulk acoustic wave resonator further includes the following steps performed between step S2 and step S3:

[0080] A1. Surface treatment is performed on the first patterned photoresist layer 10 and the piezoelectric layer 3 using oxygen.

[0081] In this embodiment, the first patterned photoresist layer 10 and the piezoelectric layer 3 can be surface treated with oxygen so that the sidewalls of the first patterned photoresist layer 10 and the exposed surface of the piezoelectric layer 3 have good morphology. Therefore, in this embodiment, the first groove 6 formed on the piezoelectric layer 3 can have a good morphology by surface treating the first patterned photoresist layer 10 and the piezoelectric layer 3 before etching the piezoelectric layer 3 (refer to FIG. Figure 10 and Figure 11 The morphology of the first groove 6 after the surface treatment with oxygen is better than that of the first groove 6 without the surface treatment with oxygen), thereby effectively avoiding the situation where the first groove 6 cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the first groove 6. Preferably, between steps S5 and S6, this embodiment also uses oxygen to surface treat the second patterned photoresist layer 11 and the top electrode 4.

[0082] In some preferred embodiments, step S3 includes:

[0083] S31, etching the piezoelectric layer 3 using the TRIM technology based on the first patterned photoresist layer 10 to form a first groove 6 on the piezoelectric layer 3, the edge of which, when projected in the top view, does not exceed the edge of the projection of the acoustic reflector 5 in the top view;

[0084] Step S6 includes:

[0085] S61 , etching the top electrode 4 using the TRIM technology based on the second patterned photoresist layer 11 to form a second groove 7 on the top electrode 4 , the edge of which projection in the top view direction does not exceed the edge of the projection of the first groove 6 in the top view direction.

[0086] This embodiment etches the piezoelectric layer 3 using TRIM technology (Triple Ion Modified Etching) based on the first patterned photoresist layer 10. Due to the high etching precision of TRIM technology, this embodiment can ensure that the first groove 6 and the second groove 7 formed have precise depth and low surface roughness, thereby effectively improving the first groove 6 and the second groove 7's ability to suppress acoustic wave leakage, thereby further improving the quality factor and parallel resonant impedance of the bulk acoustic wave resonator. Preferably, this embodiment selects a mixed gas of argon and sulfur hexafluoride as the etching gas. The ratio of the argon flow rate to the sulfur hexafluoride flow rate in this embodiment is preferably 1:5-1:3, and the etching gas pressure in this embodiment is preferably 5-10mt.

[0087] In some preferred embodiments, step S2 includes:

[0088] S21, forming a bottom electrode 2, a piezoelectric layer 3, a protective layer 12 and a first patterned photoresist layer 10 in sequence on the substrate 1, wherein the inner boundary of the projection of the first patterned photoresist layer 10 in the top view direction is located at the edge of the projection of the acoustic reflector 5 in the top view direction;

[0089] Step S3 includes:

[0090] S31′, etching the piezoelectric layer 3 and the protective layer 12 based on the first patterned photoresist layer 10 to form a first groove 6 on the piezoelectric layer 3, the edge of which, when projected in the top view, does not exceed the edge of the projection of the acoustic reflector 5 in the top view;

[0091] Step S4 includes:

[0092] S41 , removing the first patterned photoresist layer 10 and the protective layer 12 .

[0093] The material of the protective layer 12 of this embodiment is preferably silicon dioxide. The protective layer 12 of this embodiment can prevent the piezoelectric layer 3 from being corroded by the first patterned photoresist layer 10. Therefore, this embodiment can effectively avoid the situation where the piezoelectric layer 3 has morphological defects due to the corrosion of the piezoelectric layer 3 by the first patterned photoresist layer 10.

[0094] From the above, it can be seen that the method for preparing a bulk acoustic wave resonator provided by the present application can reduce the amount of acoustic wave leakage and energy leakage by forming a first groove 6 on the piezoelectric layer 3 and a second groove 7 on the top electrode 4, that is, the present application is equivalent to using the first groove 6 and the second groove 7 to replace the air gap in the prior art, that is, the present application can improve the quality factor and parallel resonant impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problem that the air gap cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the air gap, the effect of improving the quality factor and parallel resonant impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external part of the top electrode 4 is reduced due to the loss of support of the external part of the top electrode 4.

[0095] From the above, it can be seen that the bulk acoustic wave resonator and the preparation method thereof provided by the present application can reduce the amount of acoustic wave leakage and energy leakage by forming a first groove 6 on the piezoelectric layer 3 and a second groove 7 on the top electrode 4, that is, the present application is equivalent to using the first groove 6 and the second groove 7 to replace the air gap in the prior art, that is, the present application can improve the quality factor and parallel resonant impedance of the bulk acoustic wave resonator without forming an air gap. Therefore, the present application can effectively solve the problem that the air gap cannot fully play the role of reducing energy leakage due to the presence of morphological defects in the air gap, the improvement effect of the quality factor and parallel resonant impedance of the bulk acoustic wave resonator is limited, and the mechanical stability of the external part of the top electrode 4 is reduced due to the loss of support of the external part of the top electrode 4.

[0096] In the embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely schematic. For example, the division of the above-mentioned units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another robot, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some communication interface, the indirect coupling or communication connection of the device or unit can be electrical, mechanical or other forms.

[0097] In addition, the units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0098] Furthermore, the functional modules in each embodiment of the present application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0099] In this document, relational terms such as first and second, etc. are used merely to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any actual relationship or order between these entities or operations.

[0100] The above description is merely an embodiment of the present application and is not intended to limit the scope of protection of the present application. For those skilled in the art, various modifications and variations of the present application are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A bulk acoustic wave resonator, characterized in that: The bulk acoustic wave resonator comprises: A substrate, a bottom electrode, a piezoelectric layer and a top electrode are sequentially connected from bottom to top, wherein an acoustic reflector is provided on the substrate; The piezoelectric layer is provided with a first groove, the edge of the projection of the first groove in the top view direction does not exceed the edge of the projection of the acoustic reflector in the top view direction, and the top electrode is provided with a second groove, the edge of the projection of the second groove in the top view direction does not exceed the edge of the projection of the first groove in the top view direction; The piezoelectric layer has a step group, the step group is located in the first groove, the step group includes at least one step portion, the height of the step portion is less than the depth of the first groove, and when there are multiple step portions, the multiple step portions are distributed inside and outside the center of the piezoelectric layer and are spaced apart; The top electrode has at least one external connection portion, and the step portion is arranged in the first groove on a side close to the external connection portion.

2. The bulk acoustic wave resonator according to claim 1, wherein The minimum distance between the step portion and the top of the piezoelectric layer is greater than the minimum distance between the top of the step portion and the bottom of the first groove.

3. The bulk acoustic wave resonator according to claim 1, wherein The BAW resonator further includes a passivation layer disposed above the top electrode.

4. A method for preparing a bulk acoustic wave resonator, characterized in that: The bulk acoustic wave resonator preparation method is used to prepare the bulk acoustic wave resonator according to any one of claims 1 to 3, and the bulk acoustic wave resonator preparation method comprises the following steps: S1. forming a cavity on a substrate and forming an acoustic reflection mirror in the cavity; S2. Forming a bottom electrode, a piezoelectric layer, and a first patterned photoresist layer in sequence on the substrate, wherein an inner boundary of a projection of the first patterned photoresist layer in a top-view direction does not exceed an edge of a projection of the acoustic reflector in the top-view direction; S3. Etching the piezoelectric layer based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of which, when projected in a top view, does not exceed the edge of the acoustic reflector, when projected in a top view; S4, removing the first patterned photoresist layer; S5. Forming a top electrode and a second patterned photoresist layer in sequence on the piezoelectric layer, wherein an inner boundary of a projection of the second patterned photoresist layer in a top view direction is located at an edge of a projection of the first groove in a top view direction; S6. Etching the top electrode based on the second patterned photoresist layer to form a second groove on the top electrode, the edge of which projection in the top view direction does not exceed the edge of the projection of the first groove in the top view direction.

5. The method for preparing a bulk acoustic wave resonator according to claim 4, wherein: The method for preparing a bulk acoustic wave resonator further includes a step performed between step S2 and step S3: A1. Surface treatment is performed on the first patterned photoresist layer and the piezoelectric layer using oxygen.

6. The method for preparing a bulk acoustic wave resonator according to claim 4, wherein: Step S3 includes: S31, etching the piezoelectric layer using the TRIM technology based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of which, when projected in a top view, does not exceed the edge of the acoustic reflector, when projected in a top view; Step S6 includes: S61. Etch the top electrode using the TRIM technology based on the second patterned photoresist layer to form a second groove on the top electrode, the edge of which projection in the top view direction does not exceed the edge of the projection of the first groove in the top view direction.

7. The method for preparing a bulk acoustic wave resonator according to claim 4, wherein: Step S2 includes: S21, forming a bottom electrode, a piezoelectric layer, a protective layer, and a first patterned photoresist layer in sequence on the substrate, wherein an inner boundary of a projection of the first patterned photoresist layer in a top view direction is located at an edge of a projection of the acoustic reflector in a top view direction; Step S3 includes: S31′, etching the piezoelectric layer and the protective layer based on the first patterned photoresist layer to form a first groove on the piezoelectric layer, the edge of which, when projected in a top view, does not exceed the edge of the acoustic reflector, when projected in a top view; Step S4 includes: S41 , removing the first patterned photoresist layer and the protective layer.

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