Bulk acoustic wave resonator and method of forming the same

Abstract

An embodiment of the present invention provides a bulk acoustic wave resonator and a method for forming the same. The method for forming the foregoing bulk acoustic wave resonator includes: forming a sacrificial structure on a substrate, forming a seed layer on the sacrificial structure, forming a bottom electrode on the seed layer, forming a piezoelectric layer on the bottom electrode, forming a top electrode on the piezoelectric layer, removing the sacrificial structure to form a cavity, and etching the seed layer through the cavity. In the embodiment of the present invention, after forming the bottom electrode and the piezoelectric layer, the seed layer in the active region of the bulk acoustic wave resonator is selectively removed. Therefore, the quality factor and / or the electromechanical coupling coefficient of the bulk acoustic wave resonator can be improved without deteriorating the quality of the bottom electrode and the piezoelectric layer.

Description

Technical Field

[0001] Some embodiments of the present invention relate to bulk acoustic wave resonators and methods of forming the same, and more particularly to bulk acoustic wave resonators having openings in a seed layer and methods of forming the same. Background Art

[0002] Based on the latest developments in wireless communication technologies, filters capable of separating signals into individual frequency bands have been developed to meet the user's requirements for high-frequency selectivity, high bandwidth, and low acoustic loss. Currently, existing filters may include surface acoustic wave resonators (SAWRs) and bulk acoustic wave resonators (BAWRs). In bulk acoustic wave resonators, since the characteristics of thin film bulk acoustic wave resonators (FBARs) mainly depend on the film thickness and the overall structure, the thin film bulk acoustic wave resonators can be adjusted with respect to technical details related to film growth, and thus the thin film bulk acoustic wave resonators are widely used in various applications.

[0003] Although existing resonator structures generally meet the requirements of their intended uses, these existing resonator structures are not entirely satisfactory in all aspects (e.g., the quality factor needs to be improved). Therefore, there are still some problems to be solved regarding the search for resonator structures with higher performance and methods of forming the aforementioned resonator structures. Summary of the Invention

[0004] In view of the above problems, some embodiments of the present invention include a seed layer having an opening to improve the quality factor and reliability of a bulk acoustic wave resonator including the seed layer.

[0005] According to some embodiments, a method of forming a bulk acoustic wave resonator is provided. The method of forming the bulk acoustic wave resonator includes forming a sacrificial structure on a substrate. Forming a seed layer on the sacrificial structure. Forming a bottom electrode on the seed layer. Forming a piezoelectric layer on the bottom electrode. Forming a top electrode on the piezoelectric layer. Removing the sacrificial structure to form a cavity. Etching the seed layer via the cavity.

[0006] According to some embodiments, a bulk acoustic wave resonator is provided. The aforementioned bulk acoustic wave resonator includes a substrate, a seed layer, a bottom electrode, a piezoelectric layer, and a top electrode. The seed layer is disposed on the substrate. The bottom electrode is disposed on the seed layer. The piezoelectric layer is disposed on the bottom electrode. The top electrode is disposed on the piezoelectric layer. The substrate has a cavity on the substrate. The seed layer has an opening. The opening exposes a bottom surface of the bottom electrode and communicates with the cavity.

[0007] According to some embodiments, the bulk acoustic wave resonator is used in various types of electronic devices (e.g., filters and duplexers). In some embodiments, the bulk acoustic wave resonator is used in a ladder-type filter. To make the components and advantages of the embodiments of the present invention more understandable, some embodiments of the embodiments of the present invention are listed below in conjunction with the accompanying drawings and will be described in detail hereinafter.

[0008] After forming the bottom electrode and the piezoelectric layer in the embodiments of the present invention, the seed layer in the active region of the bulk acoustic wave resonator is selectively removed. Therefore, the quality factor and / or the electromechanical coupling coefficient of the bulk acoustic wave resonator can be improved without deteriorating the quality of the bottom electrode and the piezoelectric layer. Description of the Drawings

[0009] Those skilled in the art will better understand the viewpoints of some embodiments of the embodiments of the present invention through the following detailed description in conjunction with the accompanying drawings. It should be noted that, according to the standard operations of the industry, various components are not drawn to scale and are only for illustrative purposes. In fact, for clear illustration, the sizes of various components may be arbitrarily enlarged or reduced.

[0010] Figures 1 to 9 An exemplary cross-sectional view of the bulk acoustic wave resonator according to an embodiment of the present invention at various stages of manufacturing.

[0011] Figure 10 An exemplary top view of the bulk acoustic wave resonator according to an embodiment of the present invention.

[0012] Figures 11 to 14 An exemplary cross-sectional view of the bulk acoustic wave resonator according to an embodiment of the present invention.

[0013] Reference Numerals

[0014] 10, 10a, 10b, 10c, 10d: Bulk acoustic wave resonator

[0015] 100: Substrate

[0016] 210: First sacrificial layer

[0017] 220: Second sacrificial layer

[0018] 221: Sacrificial structure

[0019] 222: Side wall

[0020] 223: Groove

[0021] 230: Support layer

[0022] 231, 311: Frame element

[0023] 240: Cavity

[0024] 300: Seed layer

[0025] 310, 320: Opening

[0026] 330: Frame

[0027] 400: Bottom electrode

[0028] 500: Piezoelectric layer

[0029] 510, 520: Recess

[0030] 600: Top electrode

[0031] 700: Passivation layer

[0032] 800, 810: Via hole

[0033] T1: First thickness

[0034] T2: Second thickness

[0035] T3: Third thickness Detailed implementation manners

[0036] The following invention provides many different embodiments or examples for implementing different components of the bulk acoustic wave resonator invented herein. Specific examples of each component and its configuration are described below to simplify the embodiments of the present invention. Of course, these are only examples and are not intended to limit the embodiments of the present invention. For example, when it is mentioned in the description that the first component is formed on the second component, it may represent an embodiment where the first component is in direct contact with the second component, or it may represent an embodiment where additional components are formed between the first component and the second component, such that the first component and the second component are not in direct contact. In addition, the embodiments of the present invention may repeat element symbols and / or characters in different examples. Such repetition is for the sake of simplicity and clarity, and is not used to represent the relationship between different embodiments and / or aspects discussed herein.

[0037] Some variations of the embodiments are described below. In the different figures and the illustrated embodiments, like or identical element symbols are used to denote like or identical components. It should be understood that additional operations and / or processes may be provided before, during, and after the methods described herein, and in some embodiments, some of the operations described may be replaced or deleted with other embodiments of the foregoing methods.

[0038] Furthermore, to facilitate the description of the relationship between one component of an embodiment of the present invention and other components, spatial relative terms are used, for example: "on", "over", "upper", "lower", "above", "below", and their like. The spatial relative terms are intended to cover different orientations of the components in use or operation in addition to the orientations shown in the figures. When the component is turned to other orientations (e.g., rotated 90 degrees or other orientations), the spatial relative terms used herein can be interpreted according to this orientation.

[0039] Hereinafter, the terms "about", "approximately", "substantially" generally mean within ±20% of a given value or a given range, for example, within ±10%, within ±5%, within ±3%, within ±2%, within ±1%, or within ±0.5%. It should be noted that the numerical values provided in the specification are approximate values, that is, the meanings of "about", "approximately", "substantially" can still be implied without specific indication of "about", "approximately", "substantially".

[0040] Each embodiment generally relates to a bulk acoustic wave resonator and a method of forming the same, and more particularly to a bulk acoustic wave resonator having an opening in a seed layer and a method of forming the same. The bulk acoustic wave resonator may include a substrate having a cavity and a seed layer having an opening, and the foregoing opening exposes the bottom surface of the bottom electrode and communicates with the cavity. Accordingly, the performance of the bulk acoustic wave resonator can be improved.

[0041] Figures 1 to 9 FIGS. are exemplary cross-sectional views of a bulk acoustic wave resonator according to an embodiment of the present invention at various stages of manufacture.

[0042] Referring to Figure 1 , in some embodiments, a substrate 100 is provided, and a first sacrificial layer 210 and a second sacrificial layer 220 are formed on the substrate 100. In some embodiments, the first sacrificial layer 210 is disposed between the substrate 100 and the second sacrificial layer 220. However, in some other embodiments, the first sacrificial layer 210 is omitted, and the second sacrificial layer 220 is directly formed on the substrate 100.

[0043] The substrate 100 may be or include a bulk semiconductor substrate, a semiconductor-on-insulator (SOI) substrate, or other similar substrates. For example, the substrate 100 may be a doped substrate doped with p-type dopants or n-type dopants, or an undoped substrate. Generally, a semiconductor-on-insulator substrate includes a film layer of semiconductor material formed on an insulating layer. For example, the insulating layer may be a silicon oxide layer, a silicon nitride layer, a poly-silicon layer, a combination thereof, or a stack of the foregoing film layers. The insulating layer is disposed on a substrate such as a silicon (Si) substrate. Other substrates such as a multi-layer substrate or a gradient substrate may be used. In some embodiments, the semiconductor material of the substrate 100 includes silicon having different crystal planes. In some embodiments, the substrate 100 is a gallium arsenide (GaAs) substrate, a gallium nitride (GaN) substrate, a silicon carbide (SiC) substrate, an aluminum nitride (AlN) substrate, or a sapphire substrate.

[0044] In some embodiments, the first sacrificial layer 210 and / or the second sacrificial layer 220 is (or includes) a sacrificial material that can be removed in a subsequent process. For example, the sacrificial material may be a binary compound semiconductor such as gallium arsenide; a ternary compound semiconductor such as indium gallium phosphide (InGaP), indium gallium arsenide (InGaAs); a quaternary compound semiconductor such as aluminium gallium indium phosphide (AlInGaP); analogs thereof; other suitable sacrificial materials or combinations thereof, but the embodiments of the present invention are not limited thereto. The first sacrificial layer 210 and the second sacrificial layer 220 may be made of different materials. In some embodiments, the first sacrificial layer 210 and the second sacrificial layer 220 have different etching rates. In some embodiments, the first sacrificial layer 210 is made of indium gallium phosphide, and the second sacrificial layer 220 is made of gallium arsenide.

[0045] For example, the first sacrificial layer 210 and / or the second sacrificial layer 220 can be formed by a deposition process. The deposition process can be metal organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), similar processes, other suitable processes, or a combination thereof, but the present disclosure is not limited thereto.

[0046] Referring to Figure 2 , in some embodiments, the second sacrificial layer 220 is patterned to form a sacrificial structure 221 on the substrate 100. When viewed in cross-section, the sacrificial structure 221 can be platform-shaped, island-shaped, mesa-shaped, or other suitable shapes. In some embodiments, the first sacrificial layer 210 exposed by the sacrificial structure 221 is bombarded by ion implantation to adjust the conductive characteristics of the first sacrificial layer 210 exposed by the sacrificial structure 221.

[0047] In some embodiments, the sacrificial structure 221 is formed by successive etching processes after a process. In some embodiments, in the etching process for forming the sacrificial structure 221, the first sacrificial layer 210 serves as an etch stop layer. In some embodiments, by adjusting the etching parameters of the etching process, the sacrificial structure 221 has tapered sidewalls 222.

[0048] In some embodiments, the sacrificial structure 221 has a trench 223 on its top surface. In some embodiments, the trench 223 is located on the top surface of the sacrificial structure 221. The trench 223 can be formed by successive etching processes after a photolithography process.

[0049] In some embodiments, when viewed in a top view, the trench 223 on the sacrificial structure 221 is ring-shaped. The shape of the area surrounded by the trench 223 can be the shape of an opening to be subsequently formed in the seed layer. In some embodiments, the trench 223 on the sacrificial structure 221 has a depth, and the aforementioned depth corresponds to the thickness of the material to be subsequently formed in the trench 223. It should be noted that the ring-shaped trench 223 of the sacrificial structure 221 can be used to define a frame (or at least a part of the frame) for trapping energy in the active region of the bulk acoustic wave resonator. Details will be discussed below.

[0050] Referring to Figure 3, in some embodiments, the support layer 230 is formed on the sacrificial structure 221 and the first sacrificial layer 210. By a deposition process, the support layer 230 can be conformally formed on the first sacrificial layer 210 and the sacrificial structure 221. In some embodiments, the support layer 230 fills into the trench 223. In some embodiments, the trench 223 is filled with a portion of the support layer 230, and the aforementioned portion of the support layer 230 is retained in the trench 223 in subsequent processes. The deposition process for forming the support layer 230 can be chemical vapor deposition (CVD), atomic layer deposition, similar processes, other suitable processes, or combinations thereof, but the embodiments of the present invention are not limited thereto. In some embodiments, the support layer 230 is (or includes) a nitride, an oxide, a nitrogen oxide, a polymer, an analogue thereof, other suitable materials, or combinations thereof, but the embodiments of the present invention are not limited thereto. In some embodiments, the support layer 230 is silicon nitride or silicon oxide.

[0051] Refer to Figure 4 , in some embodiments, the support layer 230 is planarized to expose the top surface of the sacrificial structure 221. In some embodiments, a portion of the support layer 230 on the sacrificial structure 221 is removed to expose the top surface of the sacrificial structure 221, and another portion of the support layer 230 is retained in the trench 223. The aforementioned another portion of the support layer 230 can be referred to as the frame element 231. The planarization process can be a chemical mechanical polishing (CMP) process. In some embodiments, after performing the planarization process, the top surface of the support layer 230 is substantially coplanar with the top surface of the sacrificial structure 221.

[0052] In some other embodiments, the first sacrificial layer 210 is omitted, the sacrificial structure 221 is directly on the substrate 100, and the support layer 230 is directly on the substrate 100 and integrated with the substrate 100. For example, the substrate 100 and the support layer 230 can be an integrated substrate (base), an opening can be formed in this substrate, and then the sacrificial structure 221 is formed in this opening.

[0053] Refer to Figure 5, in some embodiments, a seed layer 300 is formed on the support layer 230 and the sacrificial structure 221. The seed layer 300 can improve the quality of the film layer formed on the seed layer 300 because the mismatch between the seed layer 300 and the layer formed on the seed layer 300 is reduced. In some embodiments, the seed layer 300 is (or includes) aluminum nitride (AlN), aluminum oxynitride (AlON), silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), silicon carbide, aluminum scandium nitride (AlScN), titanium (Ti), its analogs, other suitable materials, or a combination thereof. In some embodiments, the material of the seed layer 300 is the same as the material of the subsequent formed piezoelectric layer.

[0054] In some embodiments, the seed layer 300 and the support layer 230 are made of different materials. In some embodiments, the seed layer 300 is formed by a deposition process. The deposition process can be physical vapor deposition (PVD) (e.g., sputtering), atomic layer deposition, its analogs, other suitable processes, or a combination thereof, but the embodiments of the present invention are not limited thereto. In some embodiments, the seed layer 300 is doped with a transition element (e.g., scandium (Sc)).

[0055] Continuing to refer to Figure 5 , in some embodiments, a bottom electrode 400 is formed on the top surface of the seed layer 300. In some embodiments, the bottom electrode 400 is (or includes) a conductive material such as a metal. In some embodiments, the metal includes titanium (Ti), molybdenum (Mo), platinum (Pt), aluminum (Al), gold (Au), tungsten (W), ruthenium (Ru), its analogs, or a combination thereof.

[0056] In some embodiments, the bottom electrode 400 is formed by a deposition process. The deposition process can be PVD (e.g., sputtering), electroplating, similar processes, other suitable processes, or a combination thereof, but the embodiments of the present invention are not limited thereto. For example, the material of the bottom electrode 400 is deposited on the seed layer 300, and the material of the bottom electrode 400 is patterned to form the bottom electrode 400 with vertical sidewalls or tapered sidewalls. In some embodiments, the bottom electrode 400 is directly above the sacrificial structure 221. In some embodiments, the area of the sacrificial structure 221 projected onto the substrate 100 is within the area of the bottom electrode 400 projected onto the substrate 100.

[0057] Referring Figure 6 , in some embodiments, the piezoelectric layer 500 is formed on the top surface of the bottom electrode 400. In some embodiments, the piezoelectric layer 500 is (or includes) aluminum nitride, scandium aluminum nitride, analogs thereof, other suitable materials, or a combination thereof. In some embodiments, the piezoelectric layer 500 is conformally formed on the top surface of the seed layer 300 and the top surface of the bottom electrode 400. Since the piezoelectric layer 500 is formed on the bottom electrode 400 formed on the seed layer 300, the quality of the piezoelectric layer 500 can be improved. In some embodiments, the piezoelectric layer 500 is doped to increase the electromechanical coupling coefficient of the piezoelectric layer 500. The dopant used in the seed layer 300 can be the same as or different from the dopant used in the piezoelectric layer 500. In some embodiments, the piezoelectric layer 500 is doped with scandium. The piezoelectric layer 500 can be formed by a deposition process (e.g., sputtering).

[0058] Continuing to refer Figure 6 , in some embodiments, the top electrode 600 is formed on the top surface of the piezoelectric layer 500. The top electrode 600 and the bottom electrode 400 can be made of the same or different materials. The material and formation method of the top electrode 600 can be the same as or similar to those of the bottom electrode 400, and the details are not repeated herein.

[0059] In some embodiments, the top electrode 600 is directly above the bottom electrode 400. In some embodiments, the area of the bottom electrode 400 is larger than the area of the top electrode 600 to facilitate alignment of the bottom electrode 400 and the top electrode 600.

[0060] In some embodiments, since the top electrode 600 and the bottom electrode 400 are used for electrical connection to an external circuit, the piezoelectric layer 500 is sandwiched between the top electrode 600 and the bottom electrode 400.

[0061] Referring Figure 7, in some embodiments, a passivation layer 700 is formed on the top electrode 600. Specifically, the passivation layer 700 is formed on the top electrode 600 and the piezoelectric layer 500 to protect the underlying components. In some embodiments, the passivation layer 700 is conformally formed on the top electrode 600 and the piezoelectric layer 500 to enhance the protection effect. In some embodiments, the passivation layer 700 is (or includes) nitride, oxide, oxynitride, polymer, analogs thereof, combinations thereof, or other suitable materials with high etch resistance, but the embodiments of the present invention are not limited thereto.

[0062] Referring to Figure 8 , in some embodiments, the sacrificial structure 221 is removed via the vias 800 to form the cavity 240. Since the etchant can reach and etch the sacrificial structure 221 via the vias 800, the vias 800 can also be referred to as etch channels. The vias 800 can be formed by etching the topmost component of the bulk acoustic wave resonator to the sacrificial structure 221. Therefore, the topmost component of the bulk acoustic wave resonator is etched from the top side of the substrate 100. In some embodiments, the etching process is performed from the top side of the resonator to form the vias 800, and is referred to as a top-down etching process. In some embodiments, during the removal of the sacrificial structure 221 to form the cavity 240, the frame element 231 is left. The cavity 240 can be directly below the top electrode 600 and the bottom electrode 400, and on the substrate 100. In some embodiments, the active region of the bulk acoustic wave resonator is the region where the cavity 240, the bottom electrode 400, the piezoelectric layer 500, and the top electrode 600 overlap. In some embodiments, in order to remove the sacrificial structure 221, the vias 800 are connected to the sacrificial structure 221. A detailed description of the vias 800 is provided below.

[0063] In some embodiments, in order to improve the conductivity of the bottom electrode 400 and the top electrode 600, the vias 800 bypass the bottom electrode 400 and the top electrode 600, and extend through the passivation layer 700 and the piezoelectric layer 500 to the sacrificial structure 221. In some embodiments, the vias 800 extend through the passivation layer 700, the piezoelectric layer 500, and / or the bottom electrode 400 and / or the top electrode 600 to the sacrificial structure 221.

[0064] In some embodiments, the sacrificial structure 221 is removed by a wet etching process using an etchant. In some embodiments, the etchant is (or includes) an acidic etchant, an alkaline etchant, or a combination thereof. For example, acidic etchants include solutions of acidic compounds such as hydrofluoric acid, hydrochloric acid, chloric-based acids, bromic-based acids, iodic-based acids, sulfuric acid, sulfurous acid, hyposulfurous acid, nitric acid, nitrous acid, phosphoric acid, phosphorous acid, phosphinic acid, boric acid, tetrafluoroboric acid, formic acid, acetic acid, propionic acid, butanoic acid, trifluoroacetic acid, oxalic acid, lactic acid, methanesulfonic acid, p-toluene sulfonic acid, trifluoromethane sulfonic acid, fluorosulfonic acid, analogs thereof, or combinations thereof.For example, the alkaline etchant includes an organic alkaline solution or an alkaline compound, such as cyclohexylamine, ethylenediamine, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, ammonia solution, analogs thereof, or combinations thereof. In some embodiments, the sacrificial structure 221 is removed while removing a portion of the first sacrificial layer 210 beneath the sacrificial structure 221. However, in some other embodiments, the first sacrificial layer 210 has an etch resistance higher than that of the sacrificial structure 221, and thus the first sacrificial layer 210 is not removed while removing the sacrificial structure 221.

[0065] Referring Figure 9 , in some embodiments, the seed layer 300 is etched via the cavity 240. The etchant for etching the seed layer 300 can enter the cavity 240 via the vias 800 and then etch the seed layer 300. In some embodiments, the bottom electrode 400 serves as an etch stop layer during the etching of the seed layer 300. In some embodiments, during the etching of the seed layer 300 via the cavity 240, the frame element 231 serves as an etch mask to form the openings 310 and 320 in the seed layer 300. Specifically, the pattern of the transfer frame element 231 can be transferred to the seed layer 300 to form the patterned seed layer 300 including the openings 310 and 320 therein. In some embodiments, a portion of the seed layer 300 is removed to form the openings 310 and 320, and another portion of the seed layer 300 is left. In some embodiments, the aforementioned portion of the seed layer 300 remaining beneath the bottom surface of the bottom electrode 400 is referred to as the frame element 311. The frame element 311 can be interposed between the frame element 231 and the bottom electrode 400. A detailed description of the arrangement of the openings 310 and 320 and the frame element 311 is provided below.

[0066] In some embodiments, the etching process for etching the seed layer 300 is the same as or different from the etching process for removing the sacrificial structure 221. In some embodiments, the etching process for etching the seed layer 300 is an anisotropic etching process to prevent the frame element 231 and the frame element 311 from peeling off the bulk acoustic wave resonator 10. In some embodiments, the seed layer 300 is removed by a wet etching process using the etchant for removing the sacrificial structure 221. In some embodiments, etching the seed layer 300 via the cavity 240 and etching the sacrificial structure 221 via the vias 800 to form the cavity 240 are performed in the same process to reduce the manufacturing cost, or are continuously performed in different processes. In some embodiments, the seed layer 300 is etched via the cavity 240 after the bottom electrode 400 and / or the top electrode 600 are formed.

[0067] In some embodiments, the openings 310 and 320 expose the bottom surface of the bottom electrode 400. In some embodiments, the shape of the opening 310 corresponds to the frame element 311, and specifically, is the same as the shape of the region surrounded by the frame element 311. For example, when viewed from a top view, the shape of the opening 310 may be circular, rectangular, polygonal, irregular, or the like. In some embodiments, the opening 310 communicates with the cavity 240 to form a cavity having a volume larger than that of the cavity 240.

[0068] In some embodiments, when viewed in a cross-sectional view, the opening 310 is located between the sidewalls of the bottom electrode 400 and / or between the sidewalls of the top electrode 600. In some embodiments, the region surrounded by the frame element 311 and projected onto the substrate 100 is within the region where the bottom electrode 400 is projected onto the substrate 100. In some embodiments, the region surrounded by the frame element 311 and projected onto the substrate 100 is within the region where the bottom electrode 400, the piezoelectric layer 500, and the top electrode 600 overlap. In some embodiments, the region surrounded by the frame element 311 and projected onto the substrate 100 is within the active region of the bulk acoustic wave resonator 10 projected onto the substrate 100.

[0069] Refer to Figure 9, in some embodiments, the frame element 311 and the frame element 231 are connected to each other. The frame element 311 and the frame element 231 may be referred to as the frame 330. In some embodiments, the frame 330 includes a first portion (e.g., the frame element 231) and a second portion (e.g., the frame element 311) disposed between the first portion and the bottom electrode 400. In some embodiments, since the frame element 311 and the frame element 231 are made of different materials, the first portion and the second portion included in the frame 330 are made of different materials. In some embodiments, the frame 330 can enclose the acoustic wave within the active region of the bulk acoustic wave resonator 10 to improve the quality factor of the bulk acoustic wave resonator. In some embodiments, the frame 330 is directly below the active region of the bulk acoustic wave resonator 10.

[0070] As Figure 9 shown, in some embodiments, the frame element 231 has a first thickness T1, the frame element 311 has a second thickness T2, and the ratio of the first thickness T1 to the second thickness T2 is in the range between 0.2 and 15. In some embodiments, the frame element 231 having the first thickness T1 is made of silicon nitride, and the frame element 311 having the second thickness T2 is made of aluminum nitride. The materials of the frame elements 311 and 231 and the ratio of the first thickness T1 to the second thickness T2 can be adjusted to improve the performance of the bulk acoustic wave resonator.

[0071] In some embodiments, since the piezoelectric layer 500 is formed on the bottom electrode 400 formed on the seed layer 300, the quality of the piezoelectric layer 500 can be improved. However, the seed layer 300 may deteriorate the quality factor and / or the electromechanical coupling coefficient of the bulk acoustic wave resonator. Embodiments of the present invention selectively remove the seed layer 300 within the active region of the bulk acoustic wave resonator after forming the bottom electrode 400 and the piezoelectric layer 500. Therefore, the quality factor and / or the electromechanical coupling coefficient of the bulk acoustic wave resonator can be improved.

[0072] In some embodiments, a bulk acoustic wave resonator having an opening in the seed layer is used as a resonator in a filter (e.g., a transmit filter (Tx filter) or a receive filter (Rx filter)). In some embodiments, a bulk acoustic wave resonator having an opening in the seed layer is used as a series resonator or a shunt resonator in a ladder filter. By using a bulk acoustic wave resonator having an opening in the seed layer as a resonator in a filter, the performance of the filter can be improved.

[0073] Figure 10 is an exemplary top view of a bulk acoustic wave resonator according to an embodiment of the present invention.

[0074] Referring toFigure 10 , which is a state of the top view of the bulk acoustic wave resonator shown in Figure 9 . For the sake of convenience of illustration, the sacrificial structure 221, the bottom electrode 400, the top electrode 600 and the vias 800 are shown and other components are omitted. Figure 9 Show Figure 10 The cross-sectional view of the bulk acoustic wave resonator taken along the section line A-A'.

[0075] In some embodiments, as shown in Figure 10 , the sacrificial structure 221 has an extension outside the edges of the bottom electrode 400 and the top electrode 600, and the vias 800 are disposed on the region of the sacrificial structure 221 outside the bottom electrode 400 and the top electrode 600. Therefore, the etchant passing through the vias 800 will not damage the bottom electrode 400 and the top electrode 600 in the active region. The extension of the sacrificial structure 221 can be of various shapes based on requirements. In some embodiments, the number of vias 800 can be adjusted based on the required removal speed of the sacrificial structure 221 or the shape of the extension of the sacrificial structure 221. In some embodiments, the arrangement of the vias 800, the bottom electrode 400 and the top electrode 600 can be adjusted based on requirements.

[0076] Referring to Figures 11 to 14 , which is a cross-sectional view of a bulk acoustic wave resonator according to some other embodiments of the present invention. In Figure 11 , the vias 810 for etching the sacrificial structure 221 and the seed layer 300 are shown as dotted lines.

[0077] Figure 11 According to some embodiments, a cross-sectional view of the bulk acoustic wave resonator 10a is shown. In some embodiments, the top electrode 600 and the bottom electrode 400 partially overlap. In some embodiments, the area where the top electrode 600 projects onto the substrate 100 is not completely within the area where the bottom electrode 400 projects onto the substrate 100. Figure 11 Show the conductive portion extending from the top electrode 600, and the conductive portion can be used as a wire. In some embodiments, Figure 11 Show another conductive portion extending from the bottom electrode 400, and the another conductive portion can also be used as a wire.

[0078] Figure 12 According to some embodiments, a cross-sectional view of the bulk acoustic wave resonator 10b is shown. In some embodiments, the piezoelectric layer 500 is etched to form a recess outside the overlapping region of the bottom electrode 400, the piezoelectric layer 500 and the top electrode 600. The piezoelectric layer 500 can be etched from the top surface of the piezoelectric layer 500 or from the bottom surface of the piezoelectric layer 500. In some embodiments, the recess is disposed adjacent to the active region of the bulk acoustic wave resonator.

[0079] In some embodiments, the piezoelectric layer 500 is etched via the cavity 240 and the opening 320 to form the recess 510. In some embodiments, the recess 510 communicates with the cavity 240. In some embodiments, the etching process is performed from the bottom side of the resonator to form the recess 510, and is referred to as a down-top etching process. The process for etching the piezoelectric layer 500 to form the recess 510 may be the same as or different from the process for etching the seed layer 300 and / or the process for etching the sacrificial structure 221. In some embodiments, as Figure 12 shown, the recess 510 exposes the bottom surface of the top electrode 600. In some embodiments, the recess 510 is substantially aligned with the edge of the bottom electrode 400 to maintain the integrity of the bottom electrode 400.

[0080] In some embodiments, the piezoelectric layer 500 is etched from the top of the substrate 100 to form the recess 520 outside the overlapping region of the bottom electrode 400, the piezoelectric layer 500, and the top electrode 600. In some embodiments, the piezoelectric layer 500 is etched from the top surface of the piezoelectric layer 500. In some embodiments, the etching process is performed from the top side of the resonator to form the recess 520, and is referred to as an up-down etching process. In some embodiments, the recess 520 exposes the top surface of the bottom electrode 400. In some embodiments, the recess 520 is substantially aligned with the edge of the top electrode 600 to maintain the integrity of the top electrode 600.

[0081] Accordingly, the foregoing recesses 510 and 520 can surround the active region of the bulk acoustic wave resonator and can be used as an air-edge to further reduce the acoustic loss of the bulk acoustic wave resonator 10b. Therefore, the quality factor can be further improved.

[0082] Figure 13 According to some embodiments, a cross-sectional view of the bulk acoustic wave resonator 10c is shown. In some embodiments, the piezoelectric layer 500 is etched to form the recess 510 that does not expose the bottom surface of the top electrode 600. In some embodiments, a portion of the piezoelectric layer 500 directly above the recess 510 remains below the bottom surface of the top electrode 600, and the foregoing portion of the piezoelectric layer 500 has a third thickness T3. The foregoing portion of the piezoelectric layer 500 can enhance the support force of the underlying components. The third thickness T3 can be adjusted based on the requirement of the support force.

[0083] Figure 14 According to some embodiments, a cross-sectional view of the bulk acoustic wave resonator 10d is shown. In some embodiments, as Figure 14 shown, the via hole 800 communicates with the cavity 240 and the opening 310. In some embodiments, since the same via hole 800 is used as an etching channel to form the cavity 240, the opening 310, and / or the recess 510, the manufacturing cost can be reduced.

[0084] In summary, after forming the bottom electrode and the piezoelectric layer, the seed layer 300 in the active region of the bulk acoustic wave resonator is selectively removed in an embodiment of the present invention. Therefore, the quality factor and / or the electromechanical coupling coefficient of the bulk acoustic wave resonator can be improved without degrading the quality of the bottom electrode and the piezoelectric layer.

[0085] The foregoing outlines components of several embodiments of the present invention, enabling those skilled in the art to better understand aspects of this air edge. Those skilled in the art should understand that they can readily use the embodiments of the present invention as a basis for changing, substituting, replacing, and / or modifying other processes and structures to achieve the same purposes and / or attain the same advantages as the embodiments described herein. Those skilled in the art should also understand that such equivalent configurations do not depart from the spirit and scope of the embodiments of the present invention, and that they can make various changes, substitutions, and alterations herein without departing from the spirit and scope of the embodiments of the present invention.

Claims

1. A method for forming a bulk acoustic wave resonator, characterized in that, comprising: forming a sacrificial structure on a substrate; forming a seed layer on the sacrificial structure; forming a bottom electrode on the seed layer; forming a piezoelectric layer on the bottom electrode; forming a top electrode on the piezoelectric layer; removing the sacrificial structure to form a cavity; etching the seed layer through the cavity; and forming an opening in the seed layer, and the opening exposes at least a part of a bottom surface of the bottom electrode and a bottom surface of the bottom electrode.

2. The forming method according to claim 1, characterized in that, after forming the bottom electrode, etching the seed layer through the cavity.

3. The forming method according to claim 1, characterized in that, during the etching of the seed layer, the bottom electrode serves as an etch stop layer.

4. The forming method according to claim 1, characterized in that, the sacrificial structure has a groove on a top surface of the sacrificial structure.

5. The forming method according to claim 4, characterized in that, further comprising: forming a support layer on the sacrificial structure and the substrate, wherein a part of the support layer fills the groove; and planarizing the support layer, wherein the sacrificial structure is exposed and the part of the support layer in the groove is retained.

6. The forming method according to claim 5, characterized in that, during the etching of the seed layer, the part of the support layer serves as an etch mask, so that a part of the seed layer between the part of the support layer and the bottom electrode is retained under the bottom electrode.

7. The forming method according to claim 6, characterized in that, the part of the support layer and the part of the seed layer form a frame under the bottom electrode.

8. The forming method according to claim 5, characterized in that, the seed layer and the support layer are made of different materials.

9. The forming method according to claim 5, characterized in that, the seed layer comprises aluminum nitride, aluminum oxynitride, silicon dioxide, silicon nitride, silicon carbide, aluminum scandium nitride, titanium or a combination thereof.

10. The forming method according to claim 1, characterized in that, further comprising: etching the piezoelectric layer to form a recess, and the recess is outside an overlapping region of the bottom electrode, the piezoelectric layer and the top electrode.

11. The forming method according to claim 10, characterized in that, the recess communicates with the cavity.

12. The forming method according to claim 10, characterized in that, the recess exposes a bottom surface of the top electrode or a top surface of the bottom electrode.

13. The forming method according to claim 10, characterized in that, the recess is substantially aligned with an edge of the bottom electrode or an edge of the top electrode.

14. A bulk acoustic wave resonator, characterized in that, comprising: a substrate; a seed layer disposed on the substrate; a bottom electrode disposed on the seed layer; a piezoelectric layer disposed on the bottom electrode; a top electrode disposed on the piezoelectric layer, and a via hole disposed outside an overlapping region of the bottom electrode, the piezoelectric layer and the top electrode, The substrate has a cavity on the substrate, and the seed layer has an opening that exposes at least a part of a bottom surface of the piezoelectric layer and a bottom surface of the bottom electrode, and the opening communicates with the cavity and the via hole.

15. The bulk acoustic wave resonator according to claim 14, wherein, the opening is between sidewalls of the bottom electrode.

16. The bulk acoustic wave resonator according to claim 14, further comprising a frame below the bottom surface of the bottom electrode, and wherein the frame includes a part of the seed layer.

17. The bulk acoustic wave resonator according to claim 14, wherein, further comprising: a recess in the piezoelectric layer and outside an overlapping region of the bottom electrode, the piezoelectric layer, and the top electrode.

18. The bulk acoustic wave resonator according to claim 17, wherein, the recess communicates with the cavity.

19. The bulk acoustic wave resonator according to claim 17, wherein, the recess exposes a bottom surface of the top electrode or a top surface of the bottom electrode.

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