Bulk acoustic wave resonator and manufacturing method thereof

Abstract

The invention discloses a bulk acoustic wave resonator and a manufacturing method thereof, and the bulk acoustic wave resonator comprises a substrate; the piezoelectric laminated structure is located on the substrate, and the piezoelectric laminated structure comprises a lower electrode layer, a piezoelectric layer and an upper electrode layer which are sequentially laminated from bottom to top; the reflection ring structure is located on the upper electrode layer and distributed along the edge of the effective resonance area with the resonators, the reflection ring structure comprises an annular supporting part and an annular mass adjusting part which are stacked from bottom to top, and the section width of the annular supporting part is smaller than the section width of the annular mass adjusting part on the section, perpendicular to the direction of the piezoelectric stacked layer, of the reflection ring structure. According to the invention, the transverse wave of the resonator can be effectively suppressed, the performance of the resonator is improved, the technological process for simultaneously manufacturing resonators with different frequencies is simplified, and the technological cost is reduced.

Description

Technical Field

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

[0002] The most basic structure of a bulk acoustic wave filter (BAW filter) is a "sandwich" structure consisting of two metal electrodes sandwiching a layer of piezoelectric film and an acoustic reflection structure (cavity or Bragg reflector) on the bottom substrate. When a high-frequency electrical signal is applied between the electrodes, a vertically propagating bulk acoustic wave is generated inside the piezoelectric material due to the piezoelectric effect. Sound waves of appropriate wavelength oscillate in the composite film layer to form standing waves. At this time, the signal resonates inside the material and the equivalent impedance of the device reaches an extreme value.

[0003] BAW filters produce lateral stray resonances because the Rayleigh surface wave reflects back and forth at the edge of the electrode in the plane, which is not perpendicular to the C-axis orientation of the piezoelectric film, and the longitudinal wave is not incident at 90°, reflecting the lateral shear wave, thus generating stray resonance peaks and causing device performance degradation. The commonly used solutions in the industry are:

[0004] 1. Make the work area into an irregular polygon (without parallel edges);

[0005] 2. Forming an electrode with a raised or recessed structural border.

[0006] The above two solutions can solve the problem of lateral clutter suppression to a certain extent, but the improvement on resonator performance is limited.

[0007] In addition, solutions for making resonators of different frequencies in BAW filters are needed. The commonly used practices in the industry are:

[0008] 1. Make the composite film layers (sandwich structures) of different resonators into different thicknesses. The advantage of this solution is that the frequency adjustment has little effect on the performance of the resonator, but the disadvantage is that the process steps are many and the cost is high;

[0009] 2. Make a tuning pattern on the electrode surface, adjust the frequency by the duty cycle of the tuning pattern, and form resonators of different frequencies. The advantage of this solution is that it has fewer process steps and low cost, but the disadvantage is that it will affect the performance of the resonator. Summary of the invention

[0010] The object of the present invention is to provide a bulk acoustic wave resonator and a method for manufacturing the same, so as to achieve effective suppression of the resonator transverse waves, improve the resonator performance, simplify the process of simultaneously manufacturing resonators of different frequencies, and reduce the process cost.

[0011] In order to achieve the above object, in a first aspect, the present invention provides a bulk acoustic wave resonator, comprising:

[0012] substrate;

[0013] A piezoelectric stack structure is located on the substrate, and the piezoelectric stack structure includes a lower electrode layer, a piezoelectric layer and an upper electrode layer stacked in sequence from bottom to top;

[0014] A reflection ring structure is located on the upper electrode layer and distributed along the edge of the effective resonance area of ​​the resonator. The reflection ring structure includes an annular support portion and an annular mass adjustment portion stacked from bottom to top. In the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion is smaller than the cross-sectional width of the annular mass adjustment portion.

[0015] In a second aspect, the present invention provides a method for manufacturing a bulk acoustic wave resonator, comprising:

[0016] Forming a piezoelectric stack structure on a substrate, the piezoelectric stack structure comprising a lower electrode layer, a piezoelectric layer and an upper electrode layer stacked in sequence from bottom to top;

[0017] A reflection ring structure is formed on the upper electrode layer. The reflection ring structure is distributed along the edge of the working area of ​​the resonator. The reflection ring structure includes an annular support portion and an annular quality adjustment portion stacked from bottom to top. In the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion is smaller than the cross-sectional width of the annular quality adjustment portion.

[0018] In a third aspect, the present invention further provides another method for manufacturing a bulk acoustic wave resonator, comprising:

[0019] Forming a piezoelectric stack structure on a substrate, the piezoelectric stack structure comprising a lower electrode layer, a piezoelectric layer and an upper electrode layer stacked in sequence from bottom to top;

[0020] A plurality of reflection ring structures are formed on the upper electrode layer. Each reflection ring structure is distributed along the edge of a working area of ​​a resonator. The reflection ring structure includes an annular support portion and an annular mass adjustment portion stacked from bottom to top. In a cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion is smaller than the cross-sectional width of the annular mass adjustment portion. The cross-sectional widths of the annular mass adjustment portions of different reflection ring structures are different in the direction perpendicular to the piezoelectric layer.

[0021] The beneficial effects of the present invention are:

[0022] The bulk acoustic wave resonator structure of the present invention is provided with a reflection ring structure at the edge of the working area on the piezoelectric stack structure, and the reflection ring structure includes an annular support portion and an annular mass adjustment portion stacked from bottom to top, and in the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion is smaller than the cross-sectional width of the annular mass adjustment portion, that is, the reflection ring structure has the characteristics of being wide at the top and narrow at the bottom. The reflection ring structure can not only suppress the reflection of shear waves at the edge of the working area of ​​the resonator, but also can play the function of mass load due to its structure of being wide at the top and narrow at the bottom, which concentrates a large weight in a narrow area. Different mass loads can also be achieved by adjusting the width of the upper annular mass adjustment portion, thereby achieving frequency adjustment of the resonator.

[0023] Furthermore, the bulk acoustic wave resonator manufacturing method of the present invention can adjust the weight of the mass load by controlling the width of the upper ring mass adjustment part of the reflection ring of different resonators in a layer of photolithography process, thereby producing resonators of different frequencies. It can also simultaneously produce multiple resonators of different frequencies in a layer of photolithography process, which has the advantages of fewer process steps and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 paying creative work.

[0025] Figure 1 This is a schematic cross-sectional structure diagram of a bulk acoustic wave resonator according to Example 1 of the present invention.

[0026] Figure 2 This is a top view of the working area of ​​a bulk acoustic wave resonator according to Example 1 of the present invention.

[0027] Figure 3 This is a schematic cross-sectional structure diagram of another BAW resonator according to Embodiment 1 of the present invention.

[0028] Figure 4 This is a schematic diagram of the device structure corresponding to each step of a method for manufacturing a bulk acoustic wave resonator according to Example 2 of the present invention.

[0029] Figure 5 This is a schematic diagram of the device structure corresponding to each step of a method for manufacturing a bulk acoustic wave resonator according to Example 3 of the present invention.

[0030] Figure 6 This is a schematic diagram of the device structure corresponding to each step of a method for manufacturing a bulk acoustic wave resonator according to Example 4 of the present invention.

[0031] Figure 7 This is a schematic diagram of the device structure corresponding to each step of a method for manufacturing a bulk acoustic wave resonator according to Example 5 of the present invention. DETAILED DESCRIPTION

[0032] The following is a further detailed description of a filter chip packaging structure and a wafer-level packaging method of the present invention in combination with the accompanying drawings and specific embodiments. According to the following description and drawings, the advantages and features of the present invention will be clearer. However, it should be noted that the concept of the technical solution of the present invention can be implemented in a variety of different forms and is not limited to the specific embodiments described herein. The drawings are all in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0033] The terms "first", "second", etc. in the specification and claims are used to distinguish between similar elements and are not necessarily used to describe a specific order or time sequence. It is to be understood that, where appropriate, these terms used in this way are interchangeable, for example, so that the embodiments of the invention described herein can be operated in an order other than that described or shown herein. Similarly, if the method described herein includes a series of steps, the order of these steps presented herein is not necessarily the only order in which these steps can be performed, and some of the steps described may be omitted and / or some other steps not described herein may be added to the method. If the components in a certain figure are the same as the components in other figures, although these components can be easily identified in all figures, in order to make the description of the figures clearer, this specification will not mark all the same component numbers in each figure.

[0034] Example 1

[0035] like Figure 1 As shown, this embodiment provides a bulk acoustic wave resonator, including:

[0036] A substrate 1, wherein the front surface of the substrate 1 in this embodiment has a cavity 7, the piezoelectric stack structure encloses the cavity 7, and the resonator working area is located above the cavity 7;

[0037] A piezoelectric stack structure, located on the substrate 1, the piezoelectric stack structure comprises 2 layers of lower electrodes, 3 layers of piezoelectric layers and 4 layers of upper electrodes stacked in sequence from bottom to top;

[0038] The reflection ring structure is located on the upper electrode 4 layer and distributed along the edge of the effective resonance area of ​​the resonator. The reflection ring structure includes an annular support portion 5 and an annular mass adjustment portion 6 stacked from bottom to top. In the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion 5 is smaller than the cross-sectional width of the annular mass adjustment portion 6.

[0039] In this embodiment, in the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the ratio of the cross-sectional width of the annular support portion 5 to the cross-sectional width of the annular mass adjustment portion 6 is preferably in the range of 1:2 to 1:5. In the specific implementation process, the mass load of the reflection ring structure can be adjusted by adjusting the width of the mass adjustment portion, thereby controlling the frequency range of the resonator. For example, when the cross-sectional width of the annular mass adjustment portion 6 is small, the mass load of the reflection ring structure is small, and the frequency of the resonator is high, which is a high-frequency resonator. When the cross-sectional width of the annular mass adjustment portion 6 is large, the mass load of the reflection ring structure is large, and the frequency of the resonator is low, which is a low-frequency resonator.

[0040] In this embodiment, the materials of the annular support portion 5 and the annular mass adjustment portion 6 are the same or different. The materials of the annular support portion 5 and the annular mass adjustment portion 6 can be metal or semiconductor material.

[0041] like Figure 2 As shown, in this embodiment, the projection of the reflection ring structure on the piezoelectric layer 3 is an irregular polygon, and any two sides of the polygon are not parallel. That is, the projection shape of the reflection ring structure as a whole on the piezoelectric layer 3 is the same as the shape of the working area.

[0042] In other embodiments, Figure 3 As shown, the substrate 1 may also have a Bragg reflector 8 inside, and the resonator working area is located above the Bragg reflector 8 .

[0043] In the BAW resonator of the present embodiment, since the reflection ring structure is wide at the top and narrow at the bottom, the reflection ring structure can not only suppress the reflection of the transverse wave at the edge of the working area of ​​the resonator, but also can play the role of mass load due to its wide at the top and narrow at the bottom structure, which concentrates a larger weight in a narrower area. Different mass loads can also be achieved by adjusting the width of the upper annular mass adjustment portion 6, thereby achieving frequency adjustment of the resonator.

[0044] Example 2

[0045] like Figure 4 As shown, this embodiment provides a method for manufacturing a bulk acoustic wave resonator, comprising:

[0046] S1: forming a piezoelectric stack structure on a substrate 1, wherein the piezoelectric stack structure comprises 2 layers of lower electrodes, 3 layers of piezoelectric layers and 4 layers of upper electrodes stacked in sequence from bottom to top;

[0047] In this step, a lower electrode 2 layer, a piezoelectric layer 3 and an upper electrode 4 layer can be formed on the substrate 1 in sequence through a deposition process.

[0048] In this embodiment, the substrate 1 can be any suitable substrate known to those skilled in the art, for example, it can be at least one of the following materials: silicon (Si), germanium (Ge), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), silicon germanium (SiGe), silicon carbon (SiC), carbon germanium silicon (SiGeC), indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP) or other III / V compound semiconductors, including multilayer structures composed of these semiconductors, or silicon on insulator (SOI), stacked silicon on insulator (SSOI), stacked silicon germanium on insulator (S-SiGeOI), silicon germanium on insulator (SiGeOI) and germanium on insulator (GeOI), or double-sided polished silicon wafers (Double Side Polished Wafers, DSP), ceramic substrates such as aluminum oxide, quartz, sapphire or glass substrates, etc. The substrate 1 described in this embodiment is a silicon substrate 1.

[0049] The front side of the substrate 1 has a cavity 7, and the piezoelectric stack structure closes the cavity 7. During the process, a sacrificial layer can be deposited in the cavity 7 on the front side of the substrate 1 before making the piezoelectric stack structure. The sacrificial layer in the cavity 7 can be released after the reflection ring structure is made. The projection of the cavity 7 on the piezoelectric layer 3 is preferably an irregular pentagon whose two sides are not parallel, that is, the shape of the resonator working area, which is consistent with the projection shape of the reflection ring structure formed later on the piezoelectric layer 3. In other embodiments, the substrate 1 may also have a Bragg reflector 8 (formed by alternating low-sound-velocity materials and high-sound-velocity materials), and the piezoelectric stack structure can be directly made on the substrate 1.

[0050] The material of the upper electrode 4 layer and the lower electrode 2 layer can be any suitable conductive material known in the art, and the conductive material can be a metal material with conductive properties, for example, made of one of the metals such as molybdenum (Mo), aluminum (Al), copper (Cu), tungsten (W), tantalum (Ta), platinum (Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), chromium (Cr), titanium (Ti), gold (Au), osmium (Os), rhenium (Re), palladium (Pd), or a laminated layer formed by the above metals. The upper and lower electrode 2 layers can be formed by physical vapor deposition such as magnetron sputtering and evaporation, or chemical vapor deposition, physical vapor deposition, or atomic layer deposition.

[0051] The material of the piezoelectric layer 3 can be aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO3), quartz (Quartz), potassium niobate (KNbO3) or lithium tantalate (LiTaO3) and other piezoelectric materials with a wurtzite crystal structure and their combinations. When the piezoelectric layer 3 includes aluminum nitride (AlN), the piezoelectric layer 3 may also include rare earth metals, such as scandium (Sc), erbium (Er), yttrium (Y) and lanthanum (La). In addition, when the piezoelectric layer 3 includes aluminum nitride (AlN), the piezoelectric layer 3 may also include transition metals, such as zirconium (Zr), titanium (Ti), manganese (Mn) and hafnium (Hf). The piezoelectric layer 3 can be formed by deposition using any suitable method known to those skilled in the art, such as chemical vapor deposition, physical vapor deposition or atomic layer deposition. In the present embodiment, the piezoelectric layer 3 is made of aluminum nitride (AlN).

[0052] S2: A reflection ring structure is formed on the upper electrode 4 layer, and the reflection ring structure is distributed along the edge of the working area of ​​the resonator. The reflection ring structure includes an annular support portion 5 and an annular mass adjustment portion 6 stacked from bottom to top. In the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion 5 is smaller than the cross-sectional width of the annular mass adjustment portion 6.

[0053] refer to Figure 4 In this embodiment, forming a reflection ring structure on the upper electrode 4 layer includes:

[0054] S201: forming a sacrificial layer 9 on the upper electrode 4 layer;

[0055] The material of the sacrificial layer 9 can be silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), aluminum oxide (Al 2 O 3 ) and aluminum nitride (AlN), carbon, germanium, silicon and other materials that can be bonded to the silicon wafer. The sacrificial layer 9 can be formed by chemical vapor deposition, magnetron sputtering or evaporation.

[0056] S202: patterning the sacrificial layer 9, forming an annular groove 10 distributed along the edge of the working area on the sacrificial layer 9, and the bottom of the annular groove 10 exposes the surface of the upper electrode 4 layer;

[0057] The sacrificial layer 9 can be patterned by a photolithography process, specifically including forming a patterned photoresist on the sacrificial layer 9, and then etching the sacrificial layer 9 by a dry etching process to form an annular groove 10, the projection of the annular groove 10 on the piezoelectric layer 3 is a pentagon with any two sides not parallel.

[0058] S203: forming a first material layer 11 on the sacrificial layer 9, wherein the first material layer 11 fills the annular groove 10 and covers the surface of the sacrificial layer 9, the thickness of the first material layer 11 is greater than the thickness of the sacrificial layer 9, and the first material layer 11 in the annular groove 10 forms the annular support portion 5;

[0059] The thickness of the first material layer 11 is greater than the thickness of the sacrificial layer 9, which can ensure that the first material layer 11 filled in the groove is connected to the first material layer 11 on the sacrificial layer 9, and ensure that the annular quality adjustment part 6 formed by subsequent etching of the first material layer 11 and the annular support part 5 in the groove are an integrated structure.

[0060] The material of the first material layer 11 can be a dielectric material or a metal material. The metal material includes one or more of Mo, W, Al, Cu, Au, Pt, and Ti. The dielectric material includes SiO 2 , SiN, AlN or one or more thereof. The first material layer 11 may be formed by chemical vapor deposition, magnetron sputtering or evaporation.

[0061] S204: forming a first photoresist layer on the first material layer 11; patterning the first photoresist layer, forming a first annular photoresist mask 12 corresponding to the annular groove 10 on the first material layer 11, wherein the annular groove 10 is located within a coverage range of the first annular photoresist mask 12, and a width of the first annular photoresist mask 12 is greater than a width of the annular groove 10;

[0062] In this step, the first photoresist layer is exposed and developed to form a first annular photoresist mask 12. The first annular photoresist mask 12 is used to define the width of the annular mass adjustment portion 6 on the upper layer of the reflective ring structure. By controlling the width of the first annular photoresist mask 12, the width of the subsequently formed annular mass adjustment portion 6 is controlled, and then the mass load of the reflective ring structure is controlled, so that the manufactured resonator reaches the required frequency.

[0063] S205: etching and removing the first material layer 11 outside the coverage of the first annular photoresist mask 12, and forming the annular quality adjustment portion 6 on the annular support portion 5;

[0064] By forming an annular photoresist mask having a width greater than that of the annular groove 10 above the annular support portion 5 in the annular groove 10, and then etching the first material layer 11 using the annular photoresist mask, a wider annular quality adjustment portion 6 connected to the annular support portion 5 in the groove can be formed above the annular support portion 5, thereby forming a reflective ring structure that is wider at the top and narrower at the bottom.

[0065] S206: removing the first annular photoresist mask 12;

[0066] The first annular photoresist mask 12 may be removed by a dry stripping process or a wet stripping process.

[0067] S207: removing the sacrificial layer 9.

[0068] The sacrificial layer 9 on the upper electrode 4 can be removed by wet etching. In addition, the sacrificial layer filled in the front cavity 7 of the substrate 1 can also be removed in this step, specifically by releasing it by wet process after forming a release hole on the piezoelectric stack structure.

[0069] The method of this embodiment can adjust the weight of the mass load in one layer of photolithography process by controlling the width of the upper ring-shaped mass adjustment portion 6 of the reflection ring of different resonators, thereby manufacturing resonators with different frequencies.

[0070] Example 3

[0071] This embodiment provides a method for manufacturing a bulk acoustic wave resonator. The difference between this embodiment and embodiment 2 is that the method for forming the reflection ring structure in step S2 is different. Figure 5 As shown, the method of this embodiment includes:

[0072] S1: forming a piezoelectric stack structure on a substrate 1, wherein the piezoelectric stack structure comprises 2 layers of lower electrodes, 3 layers of piezoelectric layers and 4 layers of upper electrodes stacked in sequence from bottom to top;

[0073] The film layer materials and film layer manufacturing processes involved in this step refer to Example 2 and are not described in detail here.

[0074] S2: A reflection ring structure is formed on the upper electrode 4 layer, and the reflection ring structure is distributed along the edge of the working area of ​​the resonator. The reflection ring structure includes an annular support portion 5 and an annular mass adjustment portion 6 stacked from bottom to top. In the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion 5 is smaller than the cross-sectional width of the annular mass adjustment portion 6.

[0075] refer to Figure 5 In this embodiment, forming a reflection ring structure on the upper electrode 4 layer includes:

[0076] S211: forming a second material layer 13 on the upper electrode layer 4; forming a third material layer 14 on the second material layer 13;

[0077] The material of the second material layer 13 is a metal material, and the material of the third material layer 14 is a dielectric material. The metal material includes one or more of Mo, W, Al, Cu, Au, Pt, and Ti. The dielectric material includes SiO 2 , SiN, AlN or more.

[0078] S212: forming a second photoresist layer on the third material layer 14; patterning the second photoresist layer to form a second annular photoresist mask 15 distributed along the edge of the working area;

[0079] The second annular photoresist mask 15 formed in this step is used to define the width of the upper annular quality adjustment portion 6 of the reflective ring structure.

[0080] S213: etching and removing the third material layer 14 and the second material layer 13 outside the coverage of the second annular photoresist mask 15, and the remaining third material layer 14 and the second material layer 13 form an annular structure 16 stacked up and down on the upper electrode 4 layer, and the third material layer 14 located at the upper layer of the annular structure 16 forms the annular quality adjustment portion 6;

[0081] S214: removing the second annular photoresist mask 15;

[0082] The formation and removal method of the second annular photoresist mask 15 is consistent with the relevant process of the first annular photoresist mask 12 in Example 2, and will not be described here.

[0083] S215: performing side etching on the sidewall of the second material layer 13 located at the lower layer in the annular structure 16 to reduce the width of the second material layer 13 to form the annular support portion 5;

[0084] In this step, a wet metal etching process may be used to perform side etching on the sidewall of the second material layer 13, thereby reducing the width of the bottom of the annular structure 16, and finally forming a reflective ring structure that is wide at the top and narrow at the bottom.

[0085] Example 4

[0086] This embodiment provides a method for manufacturing a bulk acoustic wave resonator. The difference between this embodiment and embodiment 2 is that the method of this embodiment forms multiple reflection ring structures with different top layer widths on a substrate 1 (wafer) at the same time, so that different resonators have different mass loads, thereby realizing the simultaneous manufacture of multiple resonators with different frequencies. The process used in each step and the material of each film layer are the same as those in embodiment 2.

[0087] like Figure 6 As shown, a method for manufacturing a bulk acoustic wave resonator in this embodiment includes:

[0088] S01: forming a piezoelectric stacked structure on a substrate 1, wherein the piezoelectric stacked structure comprises a lower electrode 2 layer, a piezoelectric layer 3 and an upper electrode 4 layer stacked sequentially from bottom to top;

[0089] S02: A plurality of reflection ring structures are formed on the upper electrode 4 layer, each reflection ring structure is distributed along the edge of the working area of ​​a resonator, the reflection ring structure includes an annular support portion 5 and an annular mass adjustment portion 6 stacked from bottom to top, and in a cross section perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion 5 is smaller than the cross-sectional width of the annular mass adjustment portion 6, and the cross-sectional widths of the annular mass adjustment portions 6 of different reflection ring structures are different in the direction perpendicular to the piezoelectric layer 3.

[0090] refer to Figure 6 In the above step S02, forming a plurality of reflective ring structures spaced apart on the upper electrode 4 layer specifically includes:

[0091] S301: forming a sacrificial layer 9 on the upper electrode 4 layer;

[0092] S302: patterning the sacrificial layer 9 to form a plurality of annular grooves 10 on the sacrificial layer 9, each annular groove 10 being distributed along an edge of a working area of ​​a resonator, and the bottom of the annular groove 10 exposing the surface of the upper electrode 4 layer;

[0093] S303: forming a first material layer 11 on the sacrificial layer 9, wherein the first material layer 11 fills the annular groove 10 and covers the surface of the sacrificial layer 9, the thickness of the first material layer 11 is greater than the thickness of the sacrificial layer 9, and the first material layer 11 in each annular groove 10 forms an annular support portion 5 of a reflective ring;

[0094] S304: forming a first photoresist layer on the first material layer 11;

[0095] S305: patterning the first photoresist layer, forming a plurality of first annular photoresist masks 12 corresponding to the plurality of annular grooves 10 on the first material layer 11, wherein different first annular photoresist masks 12 have different cross-sectional widths in a direction perpendicular to the piezoelectric layer 3, each annular groove 10 is located within a coverage range of a first annular photoresist mask 12, and a cross-sectional width of each first annular photoresist mask 12 in a direction perpendicular to the piezoelectric layer 3 is greater than a cross-sectional width of the corresponding annular groove 10 in a direction perpendicular to the piezoelectric layer 3;

[0096] S306: etching and removing the first material layer 11 outside the coverage of the plurality of first annular photoresist masks 12, and forming an annular quality adjustment portion 6 on each annular support portion 5;

[0097] S307: removing the first annular photoresist mask 12;

[0098] S308: removing the sacrificial layer 9.

[0099] In this embodiment, the front surface of the substrate 1 has a plurality of cavities 7, and the piezoelectric stack structure closes the cavities 7. Each of the reflection ring structures is located above one of the cavities 7. In other embodiments, the substrate 1 has a plurality of Bragg reflectors 8, and each of the reflection ring structures is located above one of the Bragg reflectors 8.

[0100] The method of this embodiment can fabricate reflection ring structures with different top widths by using one layer of photolithography process. As Figure 6 shown, the widths of the top annular mass adjustment parts in the reflection ring structures corresponding to the two resonators are different (W1 < W2), realizing different mass loads respectively, so as to fabricate resonators with multiple different frequencies simultaneously in one layer of photolithography process, which has the advantages of fewer process steps and low cost.

[0101] Embodiment 5

[0102] This embodiment provides a method for fabricating a bulk acoustic wave resonator. The main difference between this embodiment and Embodiment 4 is that the method of fabricating a plurality of reflection ring structures in step S02 is different in this embodiment. The processes adopted in each step and the materials of each film layer are the same as those in Embodiment 3.

[0103] As Figure 7 shown, a method for fabricating a bulk acoustic wave resonator in this embodiment includes:

[0104] S01: Form a piezoelectric stack structure on the substrate 1. The piezoelectric stack structure includes a lower electrode layer 2, a piezoelectric layer 3, and an upper electrode layer 4 stacked in sequence from bottom to top;

[0105] S02: Form a plurality of spaced-apart reflection ring structures on the upper electrode layer 4. Each reflection ring structure is distributed along the edge of the working area of one resonator. The reflection ring structure includes an annular support part 5 and an annular mass adjustment part 6 stacked from bottom to top. In the cross-section of the reflection ring structure perpendicular to the piezoelectric stack direction, the cross-section width of the annular support part 5 is smaller than the cross-section width of the annular mass adjustment part 6, and the cross-section widths of the annular mass adjustment parts 6 of different reflection ring structures are different in the cross-section perpendicular to the piezoelectric layer 3 direction.

[0106] Referring to Figure 7 , in step S02 of this embodiment, forming a plurality of spaced-apart reflection ring structures on the upper electrode layer 4 specifically includes:

[0107] S401: Form a second material layer 13 on the upper electrode layer 4; form a third material layer 14 on the second material layer 13;

[0108] S402: Form a second photoresist layer on the third material layer 14; pattern the second photoresist layer to form a plurality of second annular photoresist masks 15 distributed at intervals on the third material layer 14. The cross-sectional widths of different second annular photoresist masks 15 in a section perpendicular to the piezoelectric layer 3 are different, and each second annular photoresist mask 15 is distributed along the edge of the working area of a resonator.

[0109] S403: Etch away the third material layer 14 and the second material layer 13 outside the coverage of the plurality of second annular photoresist masks 15. The remaining third material layer 14 and second material layer 13 form a plurality of stacked annular structures 16 on the upper electrode 4 layer. The third material layers 14 located in the upper layer of the plurality of annular structures 16 respectively form annular mass adjustment portions 6 with different widths.

[0110] S404: Remove the second annular photoresist masks 15.

[0111] S405: Perform lateral etching on the side walls of the second material layer 13 located in the lower layer of the plurality of annular structures 16 to reduce the width of the second material layer 13 and form a plurality of annular support portions 5.

[0112] The method of this embodiment also uses a single-layer photolithography process to fabricate a reflection ring structure with different top-layer widths. As Figure 7 shown, the widths of the top-layer annular mass adjustment portions in the reflection ring structures corresponding to the two resonators are different (W1 < W2), realizing different mass loads respectively, so that resonators with multiple different frequencies can be fabricated simultaneously in a single-layer photolithography process, which has the advantages of fewer process steps and lower cost.

[0113] It should be noted that each embodiment in this specification is described in a related manner. The same or similar parts between each embodiment can be referred to each other, and the differences between each embodiment and other embodiments are emphasized. In particular, for the structural embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0114] The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention in any way. Any changes and modifications made by those of ordinary skill in the art of the present invention according to the above disclosure are within the protection scope of the claims.

Claims

1. A bulk acoustic wave resonator, characterized in that: include: substrate; A piezoelectric stack structure is located on the substrate, and the piezoelectric stack structure includes a lower electrode layer, a piezoelectric layer and an upper electrode layer stacked in sequence from bottom to top; A reflection ring structure is located on the upper electrode layer and distributed along the edge of the effective resonance area of ​​the resonator. The reflection ring structure includes an annular support portion and an annular mass adjustment portion stacked from bottom to top. In the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion is smaller than the cross-sectional width of the annular mass adjustment portion.

2. The bulk acoustic wave resonator according to claim 1, characterized in that In the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the ratio of the cross-sectional width of the annular support portion to the cross-sectional width of the annular mass adjustment portion is in the range of 1:2 to 1:

5.

3. The bulk acoustic wave resonator according to claim 1, characterized in that: The annular supporting portion and the annular mass adjustment portion may be made of the same or different materials.

4. The bulk acoustic wave resonator according to claim 1, characterized in that The projection of the reflection ring structure on the piezoelectric layer is an irregular polygon, and any two sides of the polygon are not parallel.

5. The bulk acoustic wave resonator according to claim 1, characterized in that: The front surface of the substrate has a cavity, and the piezoelectric stack structure closes the cavity, or a Bragg reflector is provided inside the substrate.

6. A method for manufacturing a bulk acoustic wave resonator, characterized in that: include: Forming a piezoelectric stack structure on a substrate, the piezoelectric stack structure comprising a lower electrode layer, a piezoelectric layer and an upper electrode layer stacked in sequence from bottom to top; A reflection ring structure is formed on the upper electrode layer. The reflection ring structure is distributed along the edge of the working area of ​​the resonator. The reflection ring structure includes an annular support portion and an annular quality adjustment portion stacked from bottom to top. In the cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion is smaller than the cross-sectional width of the annular quality adjustment portion.

7. The method for manufacturing a bulk acoustic wave resonator according to claim 6, characterized in that: Forming a reflective ring structure on the upper electrode layer includes: forming a sacrificial layer on the upper electrode layer; Patterning the sacrificial layer to form an annular groove distributed along the edge of the working area on the sacrificial layer, wherein the bottom of the annular groove exposes the surface of the upper electrode layer; forming a first material layer on the sacrificial layer, the first material layer filling the annular groove and covering the surface of the sacrificial layer, the thickness of the first material layer being greater than the thickness of the sacrificial layer, and the first material layer in the annular groove forming the annular support portion; forming a first photoresist layer on the first material layer; Patterning the first photoresist layer, forming a first annular photoresist mask corresponding to the annular groove on the first material layer, wherein the annular groove is located within the coverage range of the first annular photoresist mask, and the width of the first annular photoresist mask is greater than the width of the annular groove; Etching and removing the first material layer outside the coverage of the first annular photoresist mask, and forming the annular quality adjustment portion on the annular support portion; removing the first annular photoresist mask; The sacrificial layer is removed.

8. The method for manufacturing a bulk acoustic wave resonator according to claim 7, characterized in that: The material of the first material layer is a metal material or a dielectric material, the metal material includes one or more of Mo, W, Al, Cu, Au, Pt, and Ti, and the dielectric material includes one or more of SiO2, SiN, and AlN.

9. The method for manufacturing a bulk acoustic wave resonator according to claim 6, characterized in that: Forming a reflective ring structure on the upper electrode layer includes: forming a second material layer on the upper electrode layer; forming a third material layer on the second material layer; forming a second photoresist layer on the third material layer; Patterning the second photoresist layer to form a second annular photoresist mask distributed along the edge of the working area; The third material layer and the second material layer outside the coverage of the second annular photoresist mask are removed by etching, and the remaining third material layer and the second material layer form an annular structure stacked up and down on the upper electrode layer, and the third material layer located at the upper layer of the annular structure forms the annular quality adjustment part; removing the second annular photoresist mask; The sidewall of the second material layer located at the lower layer in the annular structure is laterally etched to reduce the width of the second material layer to form the annular support portion.

10. The method for manufacturing a bulk acoustic wave resonator according to claim 9, characterized in that: The material of the second material layer is a metal material, and the material of the third material layer is a dielectric material.

11. The method according to claim 10, characterized in that The method for manufacturing a bulk acoustic wave resonator comprises performing side etching on the side wall of the second material layer by a wet etching process.

12. The method for manufacturing a bulk acoustic wave resonator according to claim 6, characterized in that: The front surface of the substrate has a cavity, and the piezoelectric stack structure closes the cavity, or a Bragg reflector is provided inside the substrate.

13. A method for manufacturing a bulk acoustic wave resonator, characterized in that: include: Forming a piezoelectric stack structure on a substrate, the piezoelectric stack structure comprising a lower electrode layer, a piezoelectric layer and an upper electrode layer stacked in sequence from bottom to top; A plurality of reflection ring structures are formed on the upper electrode layer. Each reflection ring structure is distributed along the edge of a working area of ​​a resonator. The reflection ring structure includes an annular support portion and an annular mass adjustment portion stacked from bottom to top. In a cross section of the reflection ring structure perpendicular to the direction of the piezoelectric stack, the cross-sectional width of the annular support portion is smaller than the cross-sectional width of the annular mass adjustment portion. The cross-sectional widths of the annular mass adjustment portions of different reflection ring structures are different in the direction perpendicular to the piezoelectric layer.

14. The method for manufacturing a bulk acoustic wave resonator according to claim 13, characterized in that: Forming a plurality of reflective ring structures spaced apart from each other on the upper electrode layer comprises: forming a sacrificial layer on the upper electrode layer; Patterning the sacrificial layer to form a plurality of annular grooves on the sacrificial layer, each annular groove being distributed along an edge of a working area of ​​a resonator, and the bottom of the annular groove exposing the surface of the upper electrode layer; Forming a first material layer on the sacrificial layer, the first material layer filling the annular groove and covering the surface of the sacrificial layer, the thickness of the first material layer being greater than the thickness of the sacrificial layer, and the first material layer in each annular groove forming an annular support portion of a reflective ring; forming a first photoresist layer on the first material layer; Patterning the first photoresist layer, forming a plurality of first annular photoresist masks corresponding to the plurality of annular grooves on the first material layer, wherein different first annular photoresist masks have different cross-sectional widths in a direction perpendicular to the piezoelectric layer, each annular groove is located within a coverage range of a first annular photoresist mask, and the cross-sectional width of each first annular photoresist mask in a direction perpendicular to the piezoelectric layer is greater than the cross-sectional width of the corresponding annular groove in a direction perpendicular to the piezoelectric layer; Etching and removing the first material layer outside the coverage of the plurality of first annular photoresist masks, and forming an annular quality adjustment portion on each annular support portion; removing the first annular photoresist mask; The sacrificial layer is removed.

15. The method for manufacturing a bulk acoustic wave resonator according to claim 13, characterized in that: Forming a plurality of reflective ring structures spaced apart from each other on the upper electrode layer comprises: forming a second material layer on the upper electrode layer; forming a third material layer on the second material layer; forming a second photoresist layer on the third material layer; Patterning the second photoresist layer, forming a plurality of second annular photoresist masks distributed at intervals on the third material layer, wherein different second annular photoresist masks have different cross-sectional widths in a direction perpendicular to the piezoelectric layer, and each second annular photoresist mask is distributed along an edge of a working area of ​​a resonator; The third material layer and the second material layer outside the coverage of the plurality of second annular photoresist masks are removed by etching, and the remaining third material layer and the second material layer form a plurality of annular structures stacked up and down on the upper electrode layer, and the third material layer located at the upper layer of the plurality of annular structures respectively forms annular quality adjustment parts with different widths; removing the second annular photoresist mask; The sidewall of the second material layer located at the bottom layer in the plurality of annular structures is laterally etched to reduce the width of the second material layer and form a plurality of annular support parts.

16. The method for manufacturing a bulk acoustic wave resonator according to claim 13, characterized in that: The front side of the substrate has a plurality of cavities, the piezoelectric stack structure seals the cavities, and each of the reflection ring structures is located above a cavity; or, the substrate has a plurality of Bragg reflectors, and each of the reflection ring structures is located above a Bragg reflector.

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