Piezoelectric layer with tilted c-axis orientation and method of manufacturing the same

Abstract

A structure includes a substrate, the substrate including a wafer or a portion thereof; and the structure includes a piezoelectric bulk material layer, the piezoelectric bulk material layer including a first portion deposited on the substrate and a second portion deposited on the first portion, the second portion including an outer surface having a surface roughness (Ra) of 4.5 nm or less. A method for depositing a piezoelectric bulk material layer includes depositing a first portion of a bulk layer material at a first angle of incidence to achieve a predetermined c-axis tilt, and depositing a second portion of the bulk material layer on the first portion at a second angle of incidence that is less than the first angle of incidence. The second portion has a second c-axis tilt that is substantially aligned with the first c-axis tilt.

Description

Technical Field

[0001] This disclosure relates to structures including tilted c-axis hexagonal crystal structure materials, and systems and methods for producing such materials. In particular, this disclosure relates to structures including tilted c-axis hexagonal crystal structure piezoelectric materials such as aluminum nitride (AlN) and zinc oxide (ZnO). For example, tilted c-axis hexagonal crystal structure piezoelectric materials can be used in various resonators and in thin-film electroacoustic and / or sensor devices, particularly for sensors operating in liquid / viscous media (e.g., chemical and biochemical sensors). Background Technology

[0002] For example, hexagonal piezoelectric materials such as AlN and ZnO have commercial value due to their piezoelectric and electroacoustic properties. The primary applications of electroacoustic technology are in communications (e.g., for oscillators, filters, delay lines, etc.). Recently, there has been increasing interest in the use of electroacoustic devices in high-frequency sensing applications, attributed to their potential for high sensitivity, resolution, and reliability. However, applying electroacoustic technology in certain sensor applications—particularly sensors operating in liquid or viscous media (e.g., chemical and biochemical sensors)—is not straightforward because longitudinal waves and surface waves exhibit considerable acoustic leakage in such media, leading to reduced resolution.

[0003] In the case of piezoelectric crystal resonators, sound waves can manifest as bulk acoustic waves (BAW) propagating through the interior (or 'body') of the piezoelectric material, or as surface acoustic waves (SAW) propagating on the surface of the piezoelectric material. SAW devices involve the propagation of sound waves (typically comprising two-dimensional Rayleigh waves) along the surface of the piezoelectric material using interdigitated transducers, where the wave is confined to a penetration depth of approximately one wavelength. BAW devices typically involve the propagation of sound waves using electrodes positioned on opposing top and bottom surfaces of the piezoelectric material. In BAW devices, different vibrational modes can propagate within the body material, including longitudinal modes and two distinctly polarized shear modes, where the longitudinal and shear bulk modes propagate at different velocities. The longitudinal modes are characterized by compression and elongation in the propagation direction, while the shear modes consist of motion perpendicular to the propagation direction without localized volumetric changes. The propagation characteristics of these bulk modes depend on the material properties and the direction of propagation relative to the crystal axis orientation. Because shear waves exhibit very low penetration depth in liquids, devices with pure or predominantly shear modes can operate in liquids without significant radiation losses (unlike longitudinal waves, which radiate in liquids and exhibit significant propagation losses). To reiterate, shear mode vibrations are advantageous for the operation of acoustic devices with fluids because shear waves do not transfer significant energy into the fluid.

[0004] Some piezoelectric thin films can excite longitudinal and shear mode resonances. In order to excite waves including shear modes using standard sandwich electrode configurations, the polarization axes in the piezoelectric thin film must generally not be perpendicular to the film plane (e.g., tilted relative to the film plane). Hexagonal piezoelectric materials, such as (but not limited to) aluminum nitride (AlN) and zinc oxide (ZnO), tend to develop their polarization axes (i.e., c-axis) perpendicular to the film plane because the (0001) plane typically has the lowest surface density and is thermodynamically preferred. Certain high-temperature (e.g., vapor phase epitaxy) processes can be used to grow tilted c-axis films, but low-temperature deposition processes (e.g., typically below approximately 300°C) are required for full compatibility with microelectronic structures such as metal electrodes or traces.

[0005] For example, low-temperature deposition methods such as reactive RF magnetron sputtering have been used to prepare tilted AlN thin films. However, these processes tend to result in deposition angles that vary significantly with position on the substrate region, causing the c-axis direction of the deposited piezoelectric material to vary with the radial position from the target to the source.

[0006] One consequence of the lack of uniformity in the c-axis tilt angle of the AlN thin film structure on the substrate is that if the AlN-covered substrate is sliced ​​into individual chips, each chip will exhibit a significant variation in the c-axis tilt angle, along with accompanying changes in acoustic wave propagation characteristics. This variation in the c-axis tilt angle makes it difficult to efficiently fabricate large quantities of resonator chips with consistent and repeatable performance.

[0007] Improved methods and systems for producing host thin films with a tilted c-axis have been described, wherein the c-axis tilt of the host layer is primarily controlled by controlling the deposition angle. For example, apparatus and methods for depositing seed and host layers with tilted c-axis are described in U.S. Patent Application No. 15 / 293 063 entitled “Deposition System for Growing Tilted C-Axis Piezoelectric Material Structures”, U.S. Patent Application No. 15 / 293 071 entitled “Method for Manufacturing Acoustic Structures with Tilted C-Axis Piezoelectrics and Seed Layers”, U.S. Patent Application No. 15 / 293 082 entitled “Acoustic Resonator Structures with Tilted C-Axis Piezoelectrics and Seed Layers”, U.S. Patent Application No. 15 / 293 091 entitled “Multi-Stage Deposition System for Growing Tilted C-Axis Piezoelectric Material Structures”, and U.S. Patent Application No. 15 / 293 108 entitled “Method for Producing Piezoelectrics and Seed Layers with Different C-Axis Orientation Distributions”. Among other things, these published patent applications also describe the use of collimators and control mechanisms to provide a more uniform c-axis tilted body film across the entire surface of the substrate. The use of collimators can result in a large amount of body layer being deposited on the collimator rather than on the substrate, which can lead to waste and inefficiency in the process.

[0008] These published patent applications also describe attempts to deposit the host layer directly onto the substrate without first depositing a seed layer (e.g., see U.S. Patent Application No. 15 / 293071). However, despite deposition under the same conditions as those used for depositing the host layer on the seed layer (which exhibits the desired performance), such a host layer does not exhibit the desired c-axis tilt angle distribution and fails to exhibit the required minimum shear mode to longitudinal coupling ratio of at least 1.25 (which would result in a structure unsuitable for use as a bulk acoustic sensor resonator in liquid / viscous media).

[0009] A host layer with improved performance is needed. Summary of the Invention

[0010] Among other things, this disclosure provides a bulk acoustic wave resonator structure and a method for manufacturing such a resonator structure. The bulk acoustic wave resonator structure includes a host layer of a hexagonal crystal structure material (e.g., a piezoelectric material) having a tilted c-axis. The hexagonal crystal host layer is supported by a substrate. The host layer can be formed in a two-step process. In the first step, a portion of the host layer is deposited at a non-perpendicular incident angle to achieve the desired c-axis tilt. Once the c-axis tilt is established, the remaining portion of the host layer is deposited at perpendicular incident angle. Despite being deposited at perpendicular incident angle, the remaining host layer tends to adopt the c-axis tilt of the previously deposited crystal layer. Such a process can be performed without using a conventional seed layer, a process that tends to promote a (103) texture without in-plane alignment along the (002) direction, or such a process can be performed using a conventional seed layer.

[0011] In some embodiments, the structure includes a substrate comprising a wafer or a portion thereof; and the structure includes a piezoelectric host material layer having a first portion deposited on the substrate and a second portion deposited on the first portion, the second portion having an outer surface having a surface roughness (Ra) of 4.5 nm or less. The piezoelectric host material layer may have a c-axis tilt of approximately 35 degrees to approximately 52 degrees. The crystalline host layer may exhibit a shear coupling to longitudinal coupling ratio of 1.25 or greater during excitation.

[0012] The structure may include bumps at least partially disposed on the body material layer. According to one embodiment, the bump contacts may exhibit shear strength that can resist forces of 80g or greater, 100g or greater, 110g or greater, 120g or greater, 130g or greater, or 140g or greater.

[0013] The host material layer can have a thickness ranging from approximately 1,000 angstroms to approximately 30,000 angstroms. The thickness variation over a region of the host material layer can be less than 2%.

[0014] In some embodiments, a crystalline host layer having a preselected c-axis tilt is prepared by a method comprising depositing a first portion in a first growth step under deposition conditions containing 5 mTorr or less. The first growth step is performed with non-perpendicular incidence. Preferably, the deposited host layer has a c-axis tilt of approximately 35 degrees or greater. For example, the host material layer may be deposited at a deposition angle of approximately 35 degrees to approximately 85 degrees. Preferably, the deposition in the first growth step is performed under conditions that slow the surface migration of the material to be deposited, such that the crystals in the host material layer are substantially parallel to each other and substantially oriented in the direction of the preselected angle. The method further comprises depositing a second portion in a second growth step, which comprises depositing the host material layer at a smaller incidence angle (e.g., approximately perpendicular incidence). Although deposited with approximately perpendicular incidence, the second portion of the host material layer deposited in the second growth step is oriented with a c-axis tilt of the first portion, for example, approximately 35 degrees or greater. The host material may exhibit a shear coupling to longitudinal coupling ratio of 1.25 or greater during excitation. The main layer (e.g., the second part) may have an outer surface with a surface roughness (Ra) of 4.5 nm or less.

[0015] In some embodiments, a crystalline host layer having a pre-selected c-axis tilt is prepared by a method comprising depositing a first portion of the host material layer onto a substrate at a first incident angle, the first portion having a first c-axis tilt; and depositing a second portion of the host material layer onto the first portion at a second incident angle smaller than the first incident angle, the second portion having a second c-axis tilt substantially aligned with the first c-axis tilt. The first portion may be deposited directly on the surface of the substrate. The host layer (e.g., the second portion) may have an outer surface having a surface roughness (Ra) of 4.5 nm or less.

[0016] In some embodiments, a crystalline host layer with a preselected c-axis tilt is prepared by a method comprising depositing a seed layer on a substrate under deposition conditions containing a pressure of 10 mTorr or greater; and depositing the crystalline host layer with a preselected c-axis tilt on the seed layer. The deposition of the host layer comprises a two-step process. A first portion is deposited in a first growth step performed at a first incident angle that is not perpendicular to the ground. Preferably, the first portion of the deposited host layer has a preselected c-axis tilt. The method further comprises a second growth step, which comprises depositing a second portion of the host material layer at a second incident angle smaller than the first incident angle. Although deposited at approximately perpendicular incident angle, the second portion of the host material layer deposited in the second growth step is oriented with respect to the c-axis tilt of the first portion. The host material may exhibit a shear coupling to longitudinal coupling ratio of 1.25 or greater during excitation. The host layer (e.g., the second portion) may have an outer surface with a surface roughness (Ra) of 4.5 nm or less.

[0017] In the various embodiments described herein, the host layer is fabricated such that the c-axis orientation of the crystals in the host layer is selectable in the range of approximately 0 degrees to approximately 90 degrees, for example, from approximately 30 degrees to approximately 52 degrees, or from approximately 35 degrees to approximately 46 degrees. The c-axis orientation distribution over a large substrate area is preferably substantially uniform (e.g., having a diameter in the range of at least approximately 50 mm or greater, approximately 100 mm or greater, or approximately 150 mm or greater), thereby enabling multiple chips to be produced from a single substrate and having the same or similar acoustic wave propagation characteristics.

[0018] In the various embodiments described herein, the host material layer has a thickness of approximately 1,000 angstroms to approximately 30,000 angstroms. The host material layer can be deposited at a deposition angle of approximately 35 degrees to approximately 85 degrees. The host material can exhibit a shear coupling to longitudinal coupling ratio of 1.25 or greater during activation.

[0019] In the various embodiments described herein, the structure includes a substrate comprising a wafer and a piezoelectric host material layer deposited on the surface of the wafer, wherein the host material layer has a c-axis tilt of approximately 32 degrees or greater. The structure may exhibit a shear coupling to longitudinal coupling ratio of 1.25 or greater during activation. The host layer (e.g., a second portion) may have an outer surface with a surface roughness (Ra) of 4.5 nm or less.

[0020] In the various embodiments described herein, the bulk acoustic resonator includes a structure comprising a substrate containing a wafer and a piezoelectric host material layer deposited on the surface of the wafer, wherein the host material layer has a c-axis tilt of approximately 32 degrees or greater, and wherein at least a portion of the piezoelectric host material layer is located between a first electrode and a second electrode. The host layer (e.g., a second portion) may have an outer surface having a surface roughness (Ra) of 4.5 nm or less. Attached Figure Description

[0021] Figure 1 This is a graph of the shear coupling coefficient (Ks) and longitudinal coupling coefficient (KI) as a function of the c-axis tilt angle of AlN;

[0022] Figures 2A-2D This is a schematic diagram illustrating a process for depositing a host layer on a substrate without a seed layer to achieve a desired c-axis tilt, according to an embodiment described herein.

[0023] Figures 3A-3D This is a schematic diagram illustrating a process for depositing a host layer on a substrate having a seed layer to achieve a desired c-axis tilt, according to an embodiment described herein.

[0024] Figure 4 This is an upper external perspective view of the reactor used in a deposition system for growing hexagonal piezoelectric materials with a tilted c-axis. The system includes a linear sputtering apparatus, a movable substrate stage for supporting multiple substrates, and a collimator.

[0025] Figure 5 yes Figure 4 The upper perspective view of some components of the reactor includes a linear sputtering device, a translation track for translating a movable substrate stage for supporting multiple substrates, and a collimator.

[0026] Figure 6 It is a schematic cross-sectional view of a portion of a bulk acoustic wave-mounted resonator device including a body layer of a tilted c-axis hexagonal crystal piezoelectric material as disclosed herein, wherein the resonator device includes an active region having a portion of the piezoelectric material disposed between overlapping portions of a top-side electrode and a bottom-side electrode.

[0027] Figure 7 This is a schematic cross-sectional view of a thin-film bulk acoustic resonator (FBAR) device according to one embodiment, comprising a body layer of tilted c-axis hexagonal piezoelectric material disposed on a seed layer as disclosed herein, wherein the FBAR device includes a substrate defining a cavity covered by a support layer and an active region registered with the cavity by a portion of piezoelectric material disposed between the overlapping portions of the top and bottom electrodes.

[0028] Figure 8A and8B It is a graphical representation of the c-axis angle of the example sample;

[0029] Figure 9A and 9B It is a graphical representation of the c-axis angle of the comparison samples based on the example;

[0030] Figure 10 It is a graphical representation of the electromechanical coupling of the example sample and the comparison sample;

[0031] Figure 11 This is a graphical representation of the wafer quality of the sample and comparison sample in Example 1;

[0032] Figure 12 SEM (scanning electron microscope) images of the sample and comparison sample in Example 2 are shown;

[0033] Figure 13 Show STEM images of the sample and comparison sample in Example 2;

[0034] Figure 14 Show STEM images of the sample and comparison sample in Example 2;

[0035] Figure 15 A schematic diagram of the bumps prepared in Example 3 is shown;

[0036] Figure 16 show Figure 15 Images of the shear failure test of the bumps;

[0037] Figure 17 This is a graphical representation of the result of Example 3. Detailed Implementation

[0038] This disclosure relates to a crystalline host layer and a method for depositing the crystalline host layer, which allows for the selection of a c-axis tilted crystalline material. This disclosure relates to a crystalline host layer with improved properties, such as an improved mechanical quality factor, reduced acoustic loss, reduced ohmic (electrical) loss, reduced surface roughness, and / or improved mechanical strength during device fabrication. The host layer can be formed in a two-step process. In a first step, a portion of the host layer is deposited at a non-perpendicular incident angle to achieve the desired c-axis tilt. Once the c-axis tilt is established, the remaining portion of the host layer is deposited at perpendicular incident angle. Although deposited at perpendicular or near-perpendicular incident angle, the remaining host layer tends to adopt the c-axis tilt of the previously deposited crystalline layer. The host layer can be deposited directly on a substrate or on a substrate having a seed layer.

[0039] This disclosure relates to a crystalline host layer exhibiting low surface roughness and low thickness variation. The crystalline host layer can be used to fabricate resonators exhibiting high shear strength, a high shear coupling to longitudinal coupling ratio, and small variations in resonant frequency and dry gain.

[0040] Improvements are needed in the crystalline host layer and the method for manufacturing the crystalline host layer to provide, for example, one or more of the following: additional control over the c-axis angle of the crystals in the host layer; improved characteristics such as reduced film surface roughness, increased mechanical quality factor, increased coupling coefficient, increased uniformity of host layer thickness, or increased shear-to-longitudinal coupling ratio; and improved manufacturing efficiency of the host layer, as well as improved performance of the device using the film.

[0041] Depositing the crystalline host layer with approximately perpendicular incidence and achieving the desired c-axis tilt reduces waste and processing efficiency. For example, perpendicular incidence deposition can be performed without a collimator, reducing material loss of the host layer material attributable to deposition on the collimator. Consequently, more host layer material can be directly transferred onto the substrate. Furthermore, the frequency of removing deposits accumulated on the collimator or the frequency of collimator replacement can be reduced. Moreover, perpendicular incidence deposition can be faster and can be performed using standard equipment and process conditions. These and other advantages will be readily understood by those skilled in the art.

[0042] This disclosure provides a method for preparing structures with a pre-selected c-axis tilt in the crystalline host layer. The desired c-axis tilt depends on the intended purpose, use, and effect of the host layer. Changing the c-axis tilt angle of a hexagonal piezoelectric material causes changes in the shear and longitudinal coupling coefficients, such as... Figure 1 As shown. Figure 1 Includes shear coupling coefficients (K) that are each a function of the c-axis tilt angle of AlN. sThe graph shows the electromechanical coupling coefficient (K1) and the longitudinal coupling coefficient (K1). It can be seen that the maximum electromechanical coupling coefficient of AlN's shear mode resonance is obtained at a c-axis tilt angle of approximately 35 degrees, the pure shear response (with zero longitudinal coupling) at approximately 46 degrees, and the shear coupling coefficient exceeds the longitudinal coupling coefficient in the range of approximately 19 to approximately 63 degrees. The longitudinal coupling coefficient is also zero at a c-axis tilt angle of 90 degrees, but growing AlN at very steep c-axis tilt angles is impractical. Other piezoelectric materials are expected to exhibit similar behavior, although the specific angular position can vary. For electroacoustic resonators designed to operate in liquids or other viscous media, providing the piezoelectric film with a c-axis tilt angle sufficient to provide a shear coupling coefficient exceeding the longitudinal coupling coefficient—in some embodiments, a c-axis tilt angle with a longitudinal coupling coefficient close to zero, or a c-axis tilt angle equal to or close to a value where shear coupling is maximized—would be desirable. Therefore, for electroacoustic resonators including an AlN piezoelectric layer, it is desirable to provide a c-axis tilt angle in the range of approximately 19 degrees to approximately 63 degrees, and a c-axis tilt angle between 35 degrees and 46 degrees is particularly desirable. Other c-axis tilt angles may be desirable when used for other applications or when materials other than AlN are used for deposition.

[0043] When the c-axis tilt angle is in the range of approximately 19 degrees to approximately 63 degrees, the shear coupling coefficient of the bulk acoustic resonator containing the AlN host layer exceeds the longitudinal coupling coefficient. A larger difference between the shear mode and longitudinal coupling is obtained approximately between 30 degrees and 52 degrees, and a pure shear mode resonant response (with zero longitudinal coupling) can be obtained at a c-axis tilt angle of approximately 46 degrees. Therefore, it is desirable to fabricate an AlN host layer with a c-axis tilt between approximately 30 degrees and approximately 52 degrees, between approximately 32 degrees and approximately 50 degrees, between approximately 35 degrees and approximately 50 degrees, between approximately 35 degrees and approximately 48 degrees, or approximately 46 degrees. In some embodiments, shear mode excitation can be increased by depositing a host layer with a c-axis tilt of approximately 30 degrees to approximately 52 degrees, approximately 32 degrees to approximately 50 degrees, or approximately 35 degrees to approximately 48 degrees. In other embodiments, other c-axis tilt angles may also be useful. For example, in some embodiments, a c-axis tilt of about 30 to about 45 degrees, about 32 degrees, or about 90 degrees may be beneficial.

[0044] The term "c-axis" is used here to refer to the (002) orientation of a deposited crystal with a hexagonal wurtzite structure. The c-axis is typically the longitudinal axis of the crystal.

[0045] The terms “c-axis tilt”, “c-axis orientation”, and “c-axis tilt” are used interchangeably here to refer to the angle of the c-axis relative to the normal of the surface plane of the deposited substrate.

[0046] When referring to c-axis tilt or c-axis orientation, it should be understood that even given a single angle value, the crystals in the deposited crystal layers (e.g., seed layer or host layer) can exhibit an angular distribution. The angular distribution typically approximates a normal (e.g., Gaussian) distribution, which can be graphically represented as, for example, a two-dimensional graph or pole figure resembling a bell curve.

[0047] The term “incident angle” is used here to refer to an angle at which atoms are deposited on a substrate. The “incident angle” is measured as the angle between the deposition path and the normal to the surface plane of the substrate.

[0048] The term "substrate" is used herein to refer to a material on which the seed layer or host layer may be deposited. For example, the substrate may be a wafer, or may be part of a resonator device complex or wafer, which may also include other components, such as electrode structures disposed on at least a portion of the substrate. In embodiments of this disclosure, the seed layer is not considered a "substrate".

[0049] When referring to crystal deposition "on a substrate," there may be an intermediate layer (e.g., a seed layer) between the substrate and the crystal. However, expressing "directly on the substrate" or "on the surface of the substrate" is intended to exclude any intermediate layer.

[0050] The term “seed layer” is used here to refer to a crystalline layer dominated by a (103) texture with little or no in-plane alignment along the (002) direction, on which a host material layer can be deposited.

[0051] The term “main body layer” is used herein to refer to the crystalline layer that primarily displays the (002) texture. The main body layer may be formed in one or more steps. The main body layer referred to in this disclosure refers to the entire main body layer, regardless of whether the main body layer is formed in a single step, two steps, or more than two steps. The term “first portion” is used herein to refer to the first deposited portion (e.g., layer) of the main body layer that primarily displays the (002) texture.

[0052] The term “basically” as used here has the same meaning as “almost entirely” and can be understood as modifying the term according to at least approximately 90%, at least approximately 95%, or at least approximately 98%.

[0053] The terms "parallel" and "substantially parallel" in relation to crystals refer to the orientation of the crystal. Substantially parallel crystals not only have the same or similar c-axis tilt, but also point in the same or similar directions.

[0054] The term “approximately” is used here in conjunction with numerical values ​​to include normal variation in measured values ​​as would be expected by those skilled in the art, and is understood to have the same meaning as “approximately” and to cover a typical range of error, such as ±5% of the specified value.

[0055] All scientific and technical terms used herein have their common meaning in the art, unless otherwise specified. The definitions provided herein are intended to aid in understanding certain terms frequently used herein and are not intended to limit the scope of this disclosure.

[0056] As used herein, the singular forms “a,” “an,” and “this” include embodiments with plural indicators, unless the context clearly specifies otherwise.

[0057] As used herein, the term "or" is generally used in its sense, including "and / or," unless the context expressly specifies otherwise. The term "and / or" means one or all of the listed elements or a combination of any two or more listed elements.

[0058] As used herein, "having," "including," "comprising," etc., are used in their open sense and generally mean "including, but not limited to." It will be understood that "substantially composed of," "consisting of," etc., are included within "comprising," etc. As used herein, "substantially composed of," because it relates to a composition, product, method, etc., means that the components of the composition, product, method, etc., are limited to the listed components and any other components that do not substantially affect the essential and novel characteristics of the composition, product, method, etc.

[0059] The terms "preferred" and "ideally" refer to embodiments of the invention that may provide certain benefits in certain circumstances. However, other embodiments may also be preferred in the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of protection of this disclosure (including the claims).

[0060] A range of values ​​defined by endpoints includes all numbers falling within that range (for example, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc., or 10 or less includes 10, 9.4, 7.6, 5, 4.3, 2.9, 1.62, 0.3, etc.). In this case, the range of values ​​is defined as "reaching" a specific value that is included within the range.

[0061] Any orientations mentioned herein, such as “top,” “bottom,” “left,” “right,” “above,” “below,” and other orientations and orientations, are described herein for clarity with reference to the accompanying drawings and are not limited to actual devices or systems or the use of such devices or systems. Devices or systems as described herein can be used in multiple orientations and directions.

[0062] This disclosure relates in various aspects to a crystalline host layer, a bulk acoustic wave resonator structure, and a method for manufacturing such a host layer and resonator structure. Compared to conventional resonator structures, manufacturing methods, and deposition systems, various embodiments of this disclosure include or implement a tilted c-axis piezoelectric thin film with a preselected c-axis tilt angle, the preselected c-axis tilt angle having an increased range of selectable angles. The tilted c-axis piezoelectric thin film can also exhibit improved mechanical quality factor, reduced acoustic loss, reduced ohmic (electrical) loss, reduced surface roughness, and / or improved mechanical strength when manufactured into an apparatus. The tilted c-axis piezoelectric thin film can be manufactured over a large area (e.g., a large-area substrate) with increased uniformity of the c-axis tilt angle. The method for fabricating a tilted c-axis piezoelectric thin film may be more efficient or reduce waste compared to prior art methods for preparing tilted c-axis piezoelectric thin films.

[0063] The methods described herein include a host layer deposition process having two or more steps. The process may further include depositing a seed layer on a substrate or may include depositing the host layer directly on the substrate (without an intermediate seed layer).

[0064] Now for reference Figures 2A-2D Figures 3A-3D show schematic diagrams of a two-step host layer deposition process. Figures 2A-2D This describes a process in which the main layer 40 is directly deposited on the substrate 4, which lacks a seed layer. The first growth step (in...) Figure 2A (As shown in the image) This includes ejecting metal atoms from a target 2 of a linear sputtering apparatus to react with a gas type to form a deposition flux 10 received by a substrate 4. The deposition system may include a porous collimator 17 disposed between the target and the substrate. The deposition flux 10 may be guided through holes 18 of the collimator 17 to help control the incident angle during deposition. The deposition flux 10 reaches the substrate 4 at a first incident angle α, forming the first portion 41 of the host layer 40 (in... Figure 2B (As shown in the image). The crystal of the first portion 41 of the main layer 40 has a c-axis tilt 41γ.

[0065] In the second growth step (in Figure 2CAs shown in the diagram, metal atoms are ejected from target 2 to react with the gas and are received by the first portion 41 already deposited on substrate 4. In the second growth step, target 2 can be positioned such that the second incident angle β is smaller than the first incident angle α (e.g., between the normal and the first incident angle α). For example, the second incident angle β can be approximately 0 degrees (i.e., perpendicular to the surface of substrate 4). The deposition flux 10 in the second growth step forms the second portion 42 of the host layer 40 (in... Figure 2D (As shown in the image). The crystal of the second portion 42 of the main layer 40 has a c-axis tilt of 42γ. The second growth step can be performed without a collimator.

[0066] According to one embodiment, the c-axis tilt 42γ of the second portion 42 follows or substantially follows the c-axis tilt 41γ of the first portion 41 of the host layer 40. In some embodiments, the c-axis tilts 41γ, 42γ of the first and second portions 41, 42 are aligned or at least substantially aligned with a first incident angle α used in the first growth step. The resulting host layer crystals of the first portion 41 and the second portion 42 may be substantially parallel to each other and at least substantially aligned with the desired c-axis tilt. The resulting host layer crystals of the first portion 41 and the second portion 42 may also be substantially parallel within each portion. For example, at least 50%, at least 75%, or at least 90% of the crystal of the first portion 41 may have a c-axis tilt 41γ and a direction that is within the range of an average c-axis tilt of 0 to 10 degrees, and that is within the range of an average crystal orientation of 0 to 45 degrees, or within the range of an average crystal orientation of 0 to 20 degrees. Similarly, at least 50%, at least 75%, or at least 90% of the crystal of the second part 42 may have a c-axis tilt 42γ and a direction in which the c-axis tilt 42γ is within the range of an average c-axis tilt of 0 to 10 degrees, and the direction is within the range of an average crystal orientation of 0 to 45 degrees, or within the range of an average crystal orientation of 0 to 20 degrees.

[0067] Figures 3A-3D This describes a process in which the main layer 50 is deposited on the seed layer 31, which has already been deposited on the substrate 4. Figure 3A In the first growth step shown, the first portion 51 of the crystalline host layer 50 ( Figure 3B The atoms (metal atoms reacting with the gas) in the deposition flux 10 are deposited on the seed layer 31. In the first growth step, the atoms in the deposition flux 10 are deposited at a first incident angle α. In the second growth step, in Figure 3C As shown, atoms in deposition flux 10 are deposited at a second incident angle β to produce a second portion 52 of the host layer 50. The second incident angle β can be smaller than the first incident angle α. For example, the second incident angle β may be approximately 0 degrees (i.e., perpendicular to the surface of the substrate 4). The crystals of the second portion 52 of the host layer 50 have a c-axis tilt 52γ.

[0068] According to one embodiment, the c-axis tilt 52γ of the second portion 52 follows or substantially follows the c-axis tilt 51γ of the first portion 51 of the host layer 50. In some embodiments, the c-axis tilts 51γ, 52γ of the first and second portions 51, 52 are aligned or at least substantially aligned with a first incident angle α used in the first growth step. The resulting host layer crystals of the first portion 51 and the second portion 52 may be substantially parallel to each other and at least substantially aligned with the desired c-axis tilt. The resulting host layer crystals of the first portion 51 and the second portion 52 may also be substantially parallel within each portion. For example, at least 50%, at least 75%, or at least 90% of the crystal of the first portion 51 may have a c-axis tilt 51γ and a direction that is within the range of an average c-axis tilt of 0 to 10 degrees, and that direction is within the range of an average crystal orientation of 0 to 45 degrees, or within the range of an average crystal orientation of 0 to 20 degrees. Similarly, at least 50%, at least 75%, or at least 90% of the crystal of the second part 52 may have a c-axis tilt 52γ and a direction, the c-axis tilt 52γ being within the range of an average c-axis tilt of 0 to 10 degrees, and the direction being within the range of an average crystal orientation of 0 to 45 degrees, or within the range of an average crystal orientation of 0 to 20 degrees.

[0069] exist Figures 2A-2D Both methods shown in 3A-3D can use collimator 17 in the first growth step (see reference). Figure 2A and 3A The first growth step includes positioning the target 2 with a non-perpendicular incidence relative to the substrate 4. The second step (see...) Figure 2C and 3C Preferably, without using a collimator, the second portions 42, 52 of the main body layers 40, 50 are deposited with approximately perpendicular incidence in the second step.

[0070] According to at least some embodiments of the present disclosure, the main body layers 40, 50 have a preselectable c-axis tilt. The method of the present disclosure produces the main body layers 40, 50, in which the crystals of the main body layers are aligned or substantially aligned with the preselected c-axis tilt. In some embodiments, the c-axis tilt distribution of the crystals is such that at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the crystals of the main body layers have a c-axis tilt within a preselected range of c-axis tilt, such as within a range of 1 to 10 degrees, 1 to 8 degrees, 1 to 5 degrees, or 1 to 3 degrees of the preselected c-axis tilt.

[0071] Without being bound by theory, it is assumed that deposition conditions in at least one growth step can be chosen such that they slow down the surface mobility of the atoms to be deposited. Deposition conditions that can have a surface mobility mitigation effect include many variables. These variables can be chosen such that the surface mobility is reduced to a degree to which the c-axis tilt of the seed layer and / or the host layer can be controlled. The surface mobility of atoms is a result of variables as a whole and not necessarily only of any single variable. Each variable may differ slightly when compared to conventional methods and deposition conditions used for depositing the host layer, or only some variables may differ while others may remain the same as in conventional methods. Since it is difficult to directly determine the surface mobility of atoms, a suitable combination of conditions can be determined based on the ability to change the c-axis tilt of the resulting crystalline layer to an angle typically available for depositing materials due to crystallographic limitations. For example, in the case of AlN, the ability to produce crystalline layers with a c-axis tilt aligned along 32 degrees (with an angular distribution ranging from approximately 25 to approximately 35 degrees) or greater can indicate deposition conditions that favor kinetics over thermodynamics and allow crystal growth to respond to changes in the deposition environment. Similarly, the ability to deposit the host layer directly onto the substrate (without a seed layer) at a c-axis tilt angle aligned at 20 degrees, above 25 degrees, above 30 degrees, or above 35 degrees can indicate deposition conditions that favor kinetics rather than thermodynamics. Crystals in the host layer can be aligned or substantially aligned over a region of the substrate (e.g., over the entire deposition area).

[0072] According to one embodiment, the initial (e.g., first) portion of the host layer can be deposited at a non-perpendicular incident angle under initial deposition conditions, such that the crystals in the resulting initial host layer have the desired c-axis tilt. The remaining host layer (e.g., a second or subsequent portion) can be deposited under the same initial deposition conditions or under different deposition conditions (e.g., conditions typically used for host layer deposition).

[0073] In some embodiments, the bulk acoustic resonator structure and the method for fabricating such a resonator structure include depositing a body layer directly onto a substrate (without a seed layer). Improved coupling efficiency and mechanical quality factor may result from the elimination of the seed layer, even if the seed layer is formed of the same material as the body layer. In some embodiments, the resonator structure is formed by depositing the body layer directly onto the substrate and exhibits improved mechanical quality factor, reduced acoustic loss, reduced ohmic (electrical) loss, high shear strength, high shear coupling to longitudinal coupling ratio, and / or small resonant frequency and dry gain variation. The resonator structure also exhibits increased uniformity of the c-axis tilt angle over a large area.

[0074] According to at least some embodiments of this disclosure, the c-axis tilt of the host layer can be adjusted by depositing a first portion of the host layer at a desired angle under initial deposition conditions. According to some embodiments, the initial deposition conditions are designed to slow the surface migration rate of atoms during the deposition of the host layer. In at least some embodiments, a host layer with a pre-selected c-axis tilt can be deposited under initial deposition conditions without first depositing a seed layer.

[0075] In some embodiments, the initial deposition conditions in the first growth step may include one or more of the following: incident angle, pressure, temperature, distance from the target to the substrate, and gas ratio. The incident angle may be non-perpendicular. For example, the incident angle may be greater than 10 degrees, greater than 27 degrees, greater than 30 degrees, greater than 32 degrees, greater than 33 degrees, greater than 34 degrees, greater than 35 degrees, greater than 36 degrees, or greater than 40 degrees. The incident angle may reach approximately 85 degrees, approximately 75 degrees, approximately 65 degrees, approximately 56 degrees, approximately 52 degrees, approximately 50 degrees, approximately 49 degrees, or approximately 48 degrees. Illustrative incident angles include 35 degrees, 40 degrees, 43 degrees, and 46 degrees. In some embodiments, the incident angle is less than 32 degrees or greater than 40 degrees.

[0076] The pressure in the first growth step can be at least about 0.5 mTorr, at least about 1 mTorr, or at least about 1.5 mTorr. The pressure can reach about 10 mTorr, about 8 mTorr, about 6 mTorr, about 5 mTorr, or about 4 mTorr. In some embodiments, the pressure is below 5 mTorr. For example, the pressure can be about 2 mTorr, about 2.5 mTorr, about 3 mTorr, about 3.5 mTorr, or about 4 mTorr. The temperature can be at least about 20°C, at least about 50°C, or at least about 100°C. The temperature can reach about 300°C, about 250°C, or about 200°C. In some embodiments, the deposition process can generate heat, but the deposition chamber is not heated by a heater (i.e., not intentionally heated), and deposition takes place in the deposition chamber.

[0077] In the first growth step, the distance from the target to the substrate can be at least about 50 mm, at least about 75 mm, at least about 80 mm, or at least about 90 mm. The distance can reach about 200 mm, about 150 mm, about 130 mm, or about 120 mm. In some embodiments, the distance from the target to the substrate during deposition can be from about 108 mm to about 115 mm.

[0078] The gas in the vapor space of the deposition system can be selected based on the expected composition of the deposition layer and can include argon and gases that react with the deposited atoms, such as nitrogen or oxygen. The gas ratio of argon to reactant gas (e.g., nitrogen) in the vapor space can be from about 1:10 to about 10:10, from about 2:10 to about 8:10, or about 4:10.

[0079] In some embodiments, the bulk acoustic resonator structure and the method for fabricating such a resonator structure include depositing a host layer on a seed layer. The seed layer may be used to provide a textured surface for depositing the host layer. The seed layer may exhibit different textures, most notably (103) and (002). Directional deposition flux and competing column growth may result in the host layer having a c-axis that is substantially oriented along the deposition flux.

[0080] In some embodiments, the seed layer is compositionally matched to the hexagonal piezoelectric material host layer. In some embodiments, the thickness of the seed layer is no greater than about 20%, about 15%, or about 10% of the combined thickness of the host layer and the seed layer. In some embodiments, the seed layer comprises a thickness in the range of about 500 angstroms to about 2000 angstroms and (for hexagonal seed materials such as AlN) may comprise a primary (103) texture.

[0081] Seed layers can be prepared (e.g., deposited on a substrate) according to known methods and conditions, such as those discussed in U.S. Patent Application No. 15 / 293071 entitled "Method for Fabricating an Acoustic Structure Having a Tilted C-Axis Piezoelectric and a Crystalline Seed Layer." In some embodiments, the seed layer is deposited at pressures of 8 mTorr or higher, 10 mTorr or higher, or 12 mTorr or higher, and reaching 25 mTorr, 20 mTorr, or 18 mTorr.

[0082] According to some embodiments, in a first growth step, a host layer is deposited on a seed layer under initial deposition conditions, which may include one or more of the following: incident angle, pressure, temperature, distance from target to substrate, and gas ratio.

[0083] The angle of incidence in the first growth step can be non-perpendicular. For example, the angle of incidence can be greater than 10 degrees, greater than 27 degrees, greater than 30 degrees, greater than 32 degrees, greater than 33 degrees, greater than 34 degrees, greater than 35 degrees, greater than 36 degrees, or greater than 40 degrees. The angle of incidence can reach approximately 85 degrees, approximately 75 degrees, approximately 65 degrees, approximately 56 degrees, approximately 52 degrees, approximately 50 degrees, approximately 49 degrees, or approximately 48 degrees. Illustrative angles of incidence include 35 degrees, 40 degrees, 43 degrees, and 46 degrees. In some embodiments, the angle of incidence is less than 32 degrees or greater than 40 degrees.

[0084] The pressure in the first growth step can be at least about 0.5 mTorr, at least about 1 mTorr, or at least about 1.5 mTorr. The pressure can reach about 10 mTorr, about 8 mTorr, or about 6 mTorr. In some embodiments, the pressure is below 5 mTorr. For example, the pressure can be about 2 mTorr, about 2.5 mTorr, about 3 mTorr, about 3.5 mTorr, or about 4 mTorr. The temperature can be at least about 20°C, at least about 50°C, or at least about 100°C. The temperature can reach greater than 300°C, greater than 250°C, or about 200°C. In some embodiments, the deposition process may generate heat, but the deposition chamber is not heated by a heater (i.e., not intentionally heated), and deposition takes place in the deposition chamber.

[0085] During deposition, the distance from the target to the substrate can be at least approximately 50 mm, at least approximately 75 mm, at least approximately 80 mm, or at least approximately 90 mm. The distance can reach approximately 200 mm, approximately 150 mm, approximately 130 mm, or approximately 120 mm. In some embodiments, the distance from the target to the substrate during deposition can be from approximately 108 mm to approximately 115 mm.

[0086] The gas in the vapor space of the deposition system can be selected based on the expected composition of the deposition layer and can include argon and gases that react with the deposited atoms, such as nitrogen or oxygen. The gas ratio of argon to reactant gas (e.g., nitrogen) in the vapor space can be from about 1:10 to about 10:10, from about 2:10 to about 8:10, or about 4:10.

[0087] The surfaces of the seed layer, the host layer, or a portion thereof may be optionally roughened prior to deposition. For example, the surface of the substrate, the surface of the seed layer, or the surface of a first portion of the host layer may be roughened. For instance, the surface may be roughened by atomic bombardment. Surface roughening can improve the orientation of the host layer crystals subsequently grown during deposition. It is thought that roughening the surface can lead to shading effects, which can help favor the orientation of crystals toward the deposition angle, without being bound by theory. For example, the surface of the substrate may be roughened by atomic bombardment to create “hills” and “valleys” on the surface.

[0088] According to some embodiments, a second portion of the host layer is deposited with perpendicular incidence or with an incidence angle between the first incidence and the normal to the plane of the substrate. The ability to deposit a portion or most of the host layer (e.g., a second portion of the host layer) with perpendicular incidence can make manufacturing faster and more efficient. Furthermore, deposition with perpendicular incidence may result in less material being deposited on the collimator.

[0089] The deposition conditions in the second growth step may include an incident angle and one or more of pressure, temperature, distance from the target to the substrate, and gas ratio. The second incident angle may be approximately 0 degrees, approximately 5 degrees, approximately 10 degrees, approximately 15 degrees, approximately 20 degrees, approximately 25 degrees, approximately 30 degrees, approximately 35 degrees, or approximately 40 degrees.

[0090] The deposition conditions in the second growth step may be the same as or different from the initial deposition conditions. The deposition conditions in the second growth step may include, for example, pressures from about 0.5 mTorr to about 15 mTorr, from about 0.8 mTorr to about 10 mTorr, or from about 1 mTorr to about 5 mTorr. In some embodiments, the pressure is below 5 mTorr. For example, the pressure may be about 2 mTorr, about 2.5 mTorr, about 3 mTorr, about 3.5 mTorr, or about 4 mTorr. The temperature range in the second growth step may be from about 20°C to about 300°C, from about 50°C to about 250°C, or from about 100°C to about 200°C. The gas ratio of argon to reactant gas (e.g., nitrogen) in the vapor space may be from about 1:10 to about 10:10, from about 2:10 to about 8:10, or about 4:10.

[0091] The materials used in the first and second growth steps may be the same or different. Suitable materials for the body layer include piezoelectric materials or other metallic materials with high melting points. In some embodiments, the material includes metal nitrides, such as aluminum nitride, titanium nitride, hafnium nitride, tantalum nitride, zirconium nitride, vanadium nitride, niobium nitride, etc. In some embodiments, the material includes metal oxides, such as zinc oxide, tungsten oxide, hafnium oxide, molybdenum oxide, etc. In some embodiments, the material comprises metal oxynitrides, such as hafnium oxynitride, titanium oxynitride, tantalum oxynitride, etc. In some embodiments, the material includes metal carbides, such as titanium carbide, niobium carbide, tungsten carbide, tantalum carbide, etc. In some embodiments, the material is a refractory metal, such as zirconium, hafnium, tungsten, molybdenum, etc. The body layer may comprise a combination of two or more of the above-described materials.

[0092] In some embodiments, the hexagonal piezoelectric material host layer includes a c-axis having an orientation distribution relative to the normal of the surface of the substrate or wafer supporting the hexagonal piezoelectric material host layer, the orientation distribution being primarily in the range of 12 degrees to 52 degrees, or in the range of 27 degrees to 37 degrees, or in the range of 75 degrees to 90 degrees.

[0093] The c-axis orientation distribution of the hexagonal piezoelectric material substrate layer can be normal or bimodal. In a preferred embodiment, the distribution is normal. In some embodiments, less than approximately 30%, approximately 25%, or approximately 20% of the c-axis orientation distribution of the hexagonal piezoelectric material substrate layer is within the range of 0 to 25 degrees relative to the normal to the surface of the substrate. In some embodiments, less than approximately 30%, approximately 25%, or approximately 20% of the c-axis orientation distribution of the hexagonal piezoelectric material substrate layer is within the range of 45 to 90 degrees relative to the normal to the surface of the substrate. At least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% of the c-axis orientation distribution of the hexagonal piezoelectric material substrate layer can be within the range of 25 to 45 degrees. In some embodiments, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% of the c-axis orientation of the hexagonal piezoelectric material host layer is in the range of 30 to 40 degrees.

[0094] The hexagonal piezoelectric material host layer also has a host grain orientation that differs from the c-axis tilt. The host grain orientation of a first portion of the host layer may differ from that of a second portion. In some embodiments, the host grain orientation of the second portion may be vertical or substantially vertical. For example, the host grain orientation of the second portion may be at an angle of up to 15°, 10°, or 5° to the normal to the surface of the substrate.

[0095] In some embodiments, the hexagonal piezoelectric material host layer (combining the first and second portions) may have approximately (E) or larger, approximately or larger, approximately or larger, approximately or larger, approximately Or larger, or approximately Or even thicker. The thickness of the main layer of a hexagonal crystal structure piezoelectric material can reach approximately... Reach approximately or reach approximately Such a hexagonal piezoelectric material substrate preferably comprises a substantially uniform thickness, nanostructure, and crystallinity, having a stress-controlled and dense columnar or recrystallized grain structure. In some embodiments, a seed layer includes... to The thickness is within a certain range, and (for hexagonal piezoelectric materials such as AlN) may include a primary (103) texture. In other embodiments, the structure does not include a seed layer.

[0096] Compared to existing techniques, the thickness variation of the host layer can be reduced. According to some embodiments, the hexagonal piezoelectric material host layer exhibits a film thickness variation of 2.0% or less, 1.9% or less, 1.8% or less, or 1.7% or less.

[0097] The hexagonal piezoelectric material host layer can also exhibit reduced surface roughness. According to some embodiments, the hexagonal piezoelectric material host layer has an outer surface with a surface roughness (Ra) of 4.5 nm or less, 4.2 nm or less, 4.0 nm or less, 3.8 nm or less, or 3.8 nm or less.

[0098] According to some embodiments, an acoustic resonator structure is fabricated in a deposition system in which at least one wafer containing a substrate is received by a support surface. The acoustic reflector structure may be disposed on the substrate, and electrode structures disposed on at least a portion of the acoustic reflector structure—this may be useful, for example, for producing at least one robustly mounted bulk acoustic resonator device. In some other embodiments, at least one wafer includes a substrate defining a recess, a support layer disposed over the recess, and electrode structures disposed on the support layer—this may be useful, for example, for producing at least one thin-film bulk acoustic resonator device. In the methods described herein, deposition simply on a “substrate” may be described. However, it should be understood that the substrate may be part of a resonator device complex or wafer that may also include other components, such as electrode structures disposed on at least a portion of the substrate.

[0099] Multiple acoustic resonator structures or devices (e.g., a batch of devices) can be fabricated from a single wafer manufactured according to the method of this disclosure. The batch of devices can be manufactured to specific specifications and quality parameters. Among other things, such specifications and quality parameters may include the operating resonant frequency, the variation in resonant frequency across the entire batch, and the variation in dry gain (quality sensitivity) across the entire batch. The variation in resonant frequency can be understood as the difference in actual frequency compared to the nominal or target frequency between batches. The variation in dry gain can be understood as the difference in dry gain across the entire batch under given test conditions. It has been found that the dry gain of an acoustic resonator structure is positively correlated with the device's resonant frequency. Therefore, the variation in dry gain in a batch of acoustic resonator structures fabricated from a given wafer is also positively correlated with the variation in resonant frequency across the entire batch. According to one embodiment, the variation in dry gain can be reduced by depositing a more uniform host layer. Therefore, the acoustic resonator structure fabricated according to this disclosure can exhibit smaller series resonant frequency (fs) variation and smaller dry gain variation compared to prior art structures.

[0100] In some embodiments, multiple acoustic resonator structures (e.g., BAW devices) fabricated from a single wafer exhibit a resonant frequency variation of + / -100 MHz or less, + / -90 MHz or less, or + / -80 MHz or less compared to the nominal frequency. Under test conditions, the dry gain variation of the multiple acoustic resonator structures may be 10% or less, 8% or less, 6% or less, 4% or less, 2% or less, 1.9% or less, or 1.8% or less. It can be assumed that the test conditions for the batch of structures are the same throughout the batch. In some embodiments, any number of acoustic resonator structures can be fabricated from a single wafer. For example, the wafer can be fabricated with 100 or more, 1000 or more, or 10000 or more acoustic resonator structures, up to 100,000 acoustic resonator structures. Any two or more structures can be tested and can exhibit the specified resonant frequency variation and dry gain variation. The acoustic resonator structure can have any suitable operating frequency, such as 2 GHz or higher, 2.5 GHz or higher, 2.75 GHz or higher, or 3 GHz or higher. In some embodiments, the multiple acoustic resonator structures are BAW devices having operating frequencies in the range of 2 GHz to 3 GHz.

[0101] In one exemplary embodiment, a wafer is fabricated by depositing a host material layer according to the method of this disclosure. A batch of BAW resonators is fabricated from the wafer. The BAW resonators have a nominal resonant frequency of approximately 2.7 GHz. Any two or more BAW resonators in this batch can be tested and can exhibit a resonant frequency variation of + / - 100 MHz or less. In other words, the tested BAW resonators can exhibit a resonant frequency between 2.6 GHz and 2.8 GHz. Any two or more BAW resonators in this batch can be tested under test conditions and can exhibit a dry gain variation of 10% or less. In other words, the dry gain of the test setup differs from each other by less than 10%.

[0102] Various devices, such as BAW resonators, manufactured using the acoustic resonator structures of this disclosure can exhibit greater mechanical strength compared to prior art devices. The device structure may include bumps at least partially disposed on a layer of body material. The bump structure is a strut configured to make electrical contact with a piezoelectric surface. During use of the device, the bumps may be subjected to shear forces. Therefore, higher shear strength and the ability to withstand higher shear forces are advantageous. The bump shear strength depends on various factors, such as the bump diameter, height, and underlying stack configuration. Bumps constructed using the methods of this disclosure can exhibit higher shear strength compared to similar bumps constructed using prior art methods. According to one embodiment, a bump structure fabricated on an acoustic resonator structure can exhibit shear strength (measured using an adhesive shear measuring tool) that can resist forces of 80g or greater, 100g or greater, 110g or greater, 120g or greater, 125g or greater, 130g or greater, 135g or greater, or 140g or greater. While there is no expected upper limit to the ability to withstand shear forces, in practice, bump structures may be able to withstand shear forces of up to 500g, 400g, 300g, 250g, or 200g. Increased mechanical strength can lead to improved performance during device use, as well as increased production throughput and lower manufacturing costs.

[0103] In one aspect, this disclosure relates to a method for fabricating at least one acoustic resonator structure, wherein a growth step (e.g., a first growth step and a second growth step) includes depositing a hexagonal crystal structure host layer on a substrate. The deposited material may be a piezoelectric material. The growth step includes ejecting metal atoms from a target surface of a linear sputtering apparatus to react with a gas species and be received by the substrate.

[0104] The acoustic resonator structure prepared according to the method of this disclosure, and the device manufactured using such an acoustic resonator structure, can be more robust and exhibit improved mechanical stability compared with structures prepared using previously known methods.

[0105] The seed layer and host layer of this disclosure can be prepared in any suitable deposition system. An example of a suitable deposition system is described in U.S. Patent Application No. 15 / 293063, entitled “Deposition System for Growing Tilted C-Axis Piezoelectric Material Structures.” The main aspects of the deposition system are summarized below. However, the method of this disclosure is not particularly limited to the system used, and other suitable systems can also be used.

[0106] The crystalline layer disclosed herein can be prepared in a deposition system comprising a porous collimator disposed between a target surface of a linear sputtering apparatus and a substrate stage supporting one or more wafers or substrates for receiving sputtered deposited material. In some embodiments, the wafer or substrate may be placed on a fixed pedestal for deposition at perpendicular incidence (0 degrees).

[0107] exist Figure 4 An exemplary deposition system is shown in the figure. Figure 4 This is an upper external perspective view of a reactor 100 used in a deposition system for growing hexagonal piezoelectric materials. The reactor 100 includes first, second, and third tubular sections 102, 120, and 108 for housing various elements used to deposit materials onto a substrate. Figure 5 The diagram depicts an upper perspective view of some components of the reactor 100, including a linear sputtering device 154, a translation track 115 for translating a movable substrate stage for supporting multiple substrates, and a collimator assembly 170.

[0108] The target surface may be non-parallel to the substrate stage, and the collimator disposed in the middle may be non-parallel to both the target surface and the substrate stage. Preferably, both the collimator and the substrate stage are movable (e.g., translated) during sputtering, and at least one of the substrate stage or the collimator is preferably biased to a potential other than ground. The system can be used to grow (e.g., deposit) a seed layer, followed by the growth of a hexagonal piezoelectric material host layer on the seed layer under conditions different from those used for seed layer deposition. Alternatively, according to the method of this disclosure, the host layer can be deposited directly on the substrate without first depositing a seed layer.

[0109] According to one embodiment, a host layer is grown (e.g., deposited) using a single sputtering apparatus. The growth steps (e.g., first and / or second growth steps) can be performed using a deposition system that utilizes a linear sputtering apparatus, a substrate stage transferable between different locations within the linear sputtering apparatus, and a collimator disposed between the substrate stage and the linear sputtering apparatus. The hexagonal piezoelectric host layer can be grown in a housing where at least one vacuum evacuation element can generate sub-atmospheric pressure conditions, and the wafer or substrate supporting the host layer can be translated within the housing.

[0110] In some embodiments, the host layer is grown (e.g., deposited) in two or more steps. These two or more steps can be performed using a deposition system that utilizes multiple linear sputtering devices and a substrate stage that is movable between different locations close to the different linear sputtering devices. A collimator can be positioned between the substrate stage and the respective linear sputtering devices. For example, according to a first growth step, a first collimator can be used at a first station to grow a seed layer and / or a first portion of a hexagonal piezoelectric host layer via reactive sputtering, and in a second growth step, a hexagonal piezoelectric host layer (or a second portion of the host layer) can be grown at a second station via reactive sputtering without a collimator. Both stations can be located in a single housing, where at least one vacuum evacuation element can be used to generate sub-atmospheric pressure conditions, and the wafer or substrate supporting the respective layer can be moved between stations without needing to be removed from the sub-atmospheric pressure conditions. In some embodiments, different process conditions and / or different angular positions between the target surface, collimator, and wafer or support surface can be used in the first and second growth steps.

[0111] A deposition system suitable for growing tilted c-axis hexagonal piezoelectric materials may include a linear sputtering apparatus, a porous collimator, and a transferable substrate stage having a support surface configured to be non-parallel to the target surface of the sputtering apparatus, wherein the substrate stage and / or collimator are electrically biased to a potential other than ground. A linear sputtering apparatus may include a linear magnetron or linear ion beam sputtering apparatus, comprising a target surface configured to eject metal (e.g., aluminum or zinc) atoms, wherein the target surface is non-parallel to the support surface (e.g., oriented at 0 to less than 90 degrees to the support surface). The collimator may also be configured to be non-parallel to the support surface. In some embodiments, for example, in a first growth step, the target surface is positioned at a first non-zero angle relative to the support surface, and the collimator is positioned at a second non-zero angle relative to the support surface, wherein the first non-zero angle is greater than the second non-zero angle. Metal atoms ejected from the target surface react with a gas species contained in a gas-containing environment to form the material to be deposited (e.g., a piezoelectric material). For example, aluminum atoms ejected from an aluminum or aluminum-containing target surface can react with nitrogen to form aluminum nitride, or zinc atoms ejected from a zinc or zinc-containing target surface can react with oxygen to form zinc oxide.

[0112] The support surface of the substrate stage can be configured to receive one or more wafers to be used as deposition substrates, preferably having a diameter in the range of at least about 50 mm, about 100 mm, or about 150 mm. The substrate stage can be coupled to a movable element (e.g., a translation element) configured to move the substrate stage during operation of the linear sputtering apparatus. Movement of the substrate stage can promote uniform material deposition over a large area by preventing localized areas of material deposition of varying thicknesses. An exemplary collimator includes multiple guide elements arranged non-parallel to the support surface, such as multiple longitudinal elements and multiple transverse elements forming a grid defining multiple collimator apertures. Electrically biasing the substrate stage and / or the collimator to a potential other than ground improves control of material deposition during sputtering apparatus operation. Collimator bias can also affect the development of the microstructure of tilted c-axis piezoelectric materials in a bulk acoustic resonator device. The substrate stage and collimator can be independently biased to a potential other than ground. The individual guide elements of the collimator can also be electrically biased differently relative to each other. The collimator can be configured to translate during linear sputtering operation to prevent the formation of a "shadow" pattern, which can otherwise be formed on the surface receiving the deposited piezoelectric material. Deposition holes can be positioned between the collimator and the substrate stage.

[0113] According to at least some embodiments, the resulting c-axis tilt of the main layer is the same as or within the range of the incident angle and / or the preselected angle. For example, the resulting c-axis tilt of the main layer may be within 1 degree, 2 degrees, 3 degrees, 5 degrees, 10 degrees, or 15 degrees of the incident angle and / or the preselected c-axis tilt. The c-axis tilt distribution of the crystals in the main layer may be such that at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the crystals in the main layer have a c-axis tilt within a range, such as within 1 degree, 2 degrees, 3 degrees, 5 degrees, 10 degrees, or 15 degrees of the incident angle and / or the preselected c-axis tilt.

[0114] In some embodiments, the substrate stage and / or collimator are configured to translate during the first and / or second growth steps to facilitate uniform material deposition. Electrode structures may be formed on at least a portion of the hexagonal piezoelectric material host layer to form at least one bulk acoustic wave resonator device. An active region of the bulk acoustic wave resonator device is provided in a region where the hexagonal piezoelectric material host layer is disposed between the first and second electrode structures. Such growth steps can be performed using a single sputtering apparatus or a deposition system utilizing multiple linear sputtering apparatuses, a substrate stage transferable between different locations near the different linear sputtering apparatuses, and collimators optionally disposed between the substrate stage and the respective linear sputtering apparatuses. In some embodiments, at least one resonator device composite is diced into multiple chips, such as rigidly mounted bulk acoustic wave resonator chips or thin-film bulk acoustic wave resonator chips, on which the hexagonal piezoelectric material host layer is deposited.

[0115] In another aspect of this disclosure, a method for fabricating at least one resonator structure includes using a first station comprising a first linear sputtering apparatus and a second station comprising a second linear sputtering apparatus, the first linear sputtering apparatus including a first target surface and the second linear sputtering apparatus including a second target surface. At least one wafer structure supported by a substrate stage is moved to the first station, where a first sub-atmospheric pressure condition is generated, and a first growth step is performed to deposit a first portion of a hexagonal piezoelectric material body layer onto the at least one wafer structure. At least one wafer structure supported by a substrate stage is moved to the second station, where a second sub-atmospheric pressure condition is generated, and a second growth step is performed to deposit a second portion of a hexagonal piezoelectric material body layer onto the first portion of the body layer, wherein the second portion of the hexagonal piezoelectric material body layer has a c-axis orientation distribution substantially similar to that of the first portion of the hexagonal piezoelectric material body layer. The first growth step includes ejecting metal atoms from a first target surface to (i) pass through a first deposition aperture (optionally before passing through a first collimator including a plurality of first collimator apertures), and (ii) react with a gas species and be received by at least one wafer structure to deposit a first portion of a hexagonal piezoelectric material body layer. The second growth step includes ejecting metal atoms from a second target surface to (i) pass through a second deposition aperture, and (ii) react with a gas species and be received by the first portion to deposit a second portion of the hexagonal piezoelectric material body layer. The second growth step may include the use of a collimator or may not include the use of a collimator. In some embodiments, the first growth step is configured to produce a first portion of a hexagonal piezoelectric material body layer having an orientation distribution primarily within a preselected angular range (e.g., within ±5 degrees or ±10 degrees); and the second growth step is configured to produce a second portion of a hexagonal piezoelectric material body layer including a c-axis having an orientation distribution primarily within the same preselected angular range (e.g., within ±5 degrees or ±10 degrees). The term primarily refers to at least 50%, at least approximately 75%, at least approximately 90%, or at least approximately 95% of the crystals in the layer.

[0116] In some embodiments, a substrate stage supporting at least one wafer structure is loaded into a load-locked chamber, and an initial sub-atmospheric pressure condition is created in the load-locked chamber before the at least one wafer structure supported by the substrate stage is moved to a first station. In some embodiments, the first and second stations are located within a single housing, in which a first and a second sub-atmospheric pressure condition are created. In other embodiments, the first station is located in a first chamber having an associated first vacuum venting element, and the second station is located in a second chamber having an associated second vacuum venting element.

[0117] In some embodiments, the substrate has a diameter of at least about 50 mm (or at least about 100 mm, or at least about 150 mm) and a hexagonal piezoelectric material host layer covers at least about 50% (or at least about 75%, or at least about 90%, or at least about 95%) of the substrate surface. In some embodiments, multiple bulk acoustic resonator devices, each comprising an active region between a first electrode structure and a second electrode structure, are disposed on a single substrate. Multiple bulk acoustic resonator chips can be obtained from such a substrate (e.g., by slicing) and can be integrated into one or more sensor and / or fluid devices.

[0118] In one embodiment, the deposition system is configured to directly grow a hexagonal piezoelectric material body layer on a substrate (without first depositing a seed layer). In another embodiment, the deposition system is configured to grow a hexagonal piezoelectric material body layer on a seed layer deposited on a substrate. The substrate may be a wafer received by a support surface, wherein at least 50% (or at least 75%, or at least 90%, or at least 95%) of the hexagonal piezoelectric material body layer comprises a c-axis relative to the surface of the substrate or wafer received by the support surface, the c-axis having an orientation distribution primarily in the range of 25 degrees to 50 degrees (or in a subrange of 30 degrees to 40 degrees, the subrange having a peak at approximately 35 degrees), or greater than 10 degrees, greater than 27 degrees, greater than 30 degrees, greater than 32 degrees, greater than 33 degrees, greater than 34 degrees, greater than 35 degrees, greater than 36 degrees, or greater than 40 degrees. The orientation distribution can reach approximately 85 degrees, approximately 80 degrees, approximately 75 degrees, approximately 65 degrees, approximately 56 degrees, approximately 52 degrees, approximately 50 degrees, approximately 49 degrees, or approximately 48 degrees. Such a c-axis orientation distribution is preferably substantially uniform over a large area of ​​the substrate (e.g., having a diameter in the range of at least approximately 50 mm, approximately 100 mm, or approximately 150 mm), thereby enabling the production of multiple chips with the same or similar acoustic wave propagation characteristics from a single substrate.

[0119] The host layer grown according to the method of this disclosure has a preselected c-axis tilt angle. The selection of the preselected c-axis tilt angle will depend on the desired or intended use of the resulting crystalline host layer structure (e.g., an acoustic resonator structure). For example, the preselected angle can be any angle greater than 0 degrees and less than 90 degrees. Selecting an angle that favors shear mode resonance may be desirable. For example, the preselected angle can be greater than 10 degrees, greater than 27 degrees, greater than 30 degrees, greater than 32 degrees, greater than 33 degrees, greater than 34 degrees, greater than 35 degrees, greater than 36 degrees, or greater than 40 degrees. The preselected angle can reach approximately 85 degrees, approximately 75 degrees, approximately 65 degrees, approximately 56 degrees, approximately 52 degrees, approximately 50 degrees, approximately 49 degrees, or approximately 48 degrees. Exemplary preselected angles include 35 degrees and 46 degrees. In some embodiments, the preselected angle is less than 32 degrees or greater than 46 degrees.

[0120] According to embodiments of this disclosure, a piezoelectric material thin film having a host layer can be used in various bulk acoustic wave (“BAW”) devices, such as BAW resonators. Figure 6-7 An exemplary BAW resonator using a piezoelectric material thin film of this disclosure is shown.

[0121] Figure 6This is a schematic cross-sectional view of a portion of a bulk acoustic wave-mounted resonator device 50, including a piezoelectric material body layer 64 embodying a tilted c-axis hexagonal crystal structure piezoelectric material (e.g., AlN or ZnO) as disclosed herein. The c-axis (or (002) direction) of the piezoelectric material body layer 64 is tilted away from a direction perpendicular to the substrate 52, as illustrated by two superimposed arrows on the piezoelectric material body layer 64. The resonator device 50 includes a substrate 52 (e.g., typically silicon or another semiconductor material), an acoustic reflector 54 disposed on the substrate 52, the piezoelectric material body layer 64, and bottom and top side electrodes 60, 68. The bottom side electrode 60 is disposed between the acoustic reflector 54 and the piezoelectric material body layer 64, and the top side electrode 68 is disposed along a portion of the upper surface 66 of the piezoelectric material body layer 64. A region is considered to be the active region 70 of the resonator device 50, in which the piezoelectric material body layer 64 is disposed between the overlapping portions of the top side electrode 68 and the bottom side electrode 60. Acoustic reflector 54 is used to reflect sound waves and thus reduce or avoid their dissipation in substrate 52. In some embodiments, acoustic reflector 54 comprises alternating thin layers 56, 58 of materials with different acoustic impedances (e.g., SiOC, Si3N4, SiO2, AlN, and Mo), optionally embodied as Bragg mirrors, deposited on substrate 52. In some embodiments, other types of acoustic reflectors may be used. The steps for forming resonator device 50 may include depositing acoustic reflector 54 on substrate 52, followed by depositing bottom-side electrode 60, followed by growing (e.g., by sputtering or other suitable method) piezoelectric material host layer 64, followed by depositing top-side electrode 68.

[0122] Figure 7 This is a schematic cross-sectional view of a thin-film bulk acoustic resonator (FBAR) device 72 according to one embodiment. The FBAR device 72 includes a substrate 74 (e.g., silicon or another semiconductor material) defining a cavity 76 covered by a support layer 78 (e.g., silicon dioxide). In the case of a bottom-side electrode 80 and a support layer 78, the bottom-side electrode 80 is disposed on a portion of the support layer 78. A piezoelectric material body layer 84 comprising a tilted c-axis hexagonal crystal structure piezoelectric material (e.g., AlN or ZnO) is disposed on the bottom-side electrode 80, and a top-side electrode 88 is disposed on at least a portion of the top surface 86 of the piezoelectric material body layer 84. A portion of the piezoelectric material body layer 84 disposed between the top-side electrode 88 and the bottom-side electrode 80 embodies an active region 90 of the FBAR device 72. The active region 90 is disposed above and aligned with the cavity 76, which is disposed below the support layer 78. Cavity 76 is used to confine the sound waves induced in the active region 90 by preventing sound energy from dissipating into the substrate 74, since sound waves cannot propagate effectively within cavity 76. In this respect, cavity 76 is Figure 6 and 7The acoustic reflector 54 described herein provides an alternative. Although Figure 7 The cavity 76 shown is bounded from below by the thinned portion of the substrate 74. In an alternative embodiment, at least a portion of the cavity 76 extends through the entire thickness of the substrate 74. The steps for forming the FBAR device 72 may include defining the cavity 76 in the substrate 74, filling the cavity 76 with a sacrificial material (not shown), optionally followed by planarizing the sacrificial material, depositing a support layer 78 on the substrate 74 and the sacrificial material, removing the sacrificial material (e.g., by allowing etchant to flow through a vertical opening defined in the substrate 74 or the support layer 78, or the side of the substrate 74), depositing a bottom-side electrode 80 on the support layer 78, growing a piezoelectric material body layer 84 (e.g., by sputtering or other suitable method), and depositing a top-side electrode 88.

[0123] In some embodiments, an acoustic reflector structure is disposed between a substrate and at least one first electrode structure to provide a robustly mounted bulk acoustic resonator device. Optionally, the back side of the substrate may include a roughened surface configured to reduce or eliminate backside acoustic reflections. In other embodiments, the substrate defines a recess, a support layer is disposed over the recess, and the support layer is disposed between the substrate and at least a portion of the at least one first electrode structure to provide a thin-film bulk acoustic resonator structure.

[0124] Based on the general principles of the invention disclosed above and the detailed description foregoing, those skilled in the art will readily appreciate the various modifications, rearrangements, and substitutions that are susceptible to the invention, as well as the various advantages and benefits that the invention can provide. Therefore, the scope of protection of the invention should be limited only to the following claims and their equivalents. Furthermore, it should be understood that within the scope of protection of the invention, the disclosed and claimed articles and methods may be useful in applications other than surgery. Therefore, the scope of protection of the invention can be extended to include the use of the claimed and disclosed methods for such other applications.

[0125] Example

[0126] Example 1

[0127] BAW wafers (samples) and cover films are prepared according to the methods of this disclosure and compared with a benchmark BAW wafer (comparison sample) and cover film prepared according to prior art methods.

[0128] All samples, including the comparative samples, were prepared using a deposition system as described in U.S. Patent Application No. 15 / 293 063 entitled “Deposition System for Growing Tilted C-Axis Piezoelectric Material Structures”.

[0129] Three sample wafers (150 mm in diameter) and a cover film were prepared by directly depositing an AlN crystalline host layer onto a substrate in two steps. The sample wafers were prepared by depositing a first portion of the AlN crystalline host layer at a deposition angle of 43 degrees in the first step and a second portion at a deposition angle of 0 degrees (perpendicular incidence) in the second step.

[0130] In the first step (at 43 degrees Celsius), with an argon to nitrogen ratio of 6:15, the deposition pressure was selected as 2.5 mTorr. The power was 3 kW, the DC current pulse was 250 kHz, and the target voltage was 250 V with a target current of 12 A. The distance from the target to the substrate was 100 mm. The deposition rate was... The space was not heated, but the temperature was estimated to be around 100°C due to the use of plasma.

[0131] In the second step (with perpendicular incidence), the wafer substrate was placed on a fixed pedestal. An argon to nitrogen ratio of 1:5 was used, and a deposition pressure of 3.0 mTorr was selected. The power was 6 kW, the DC current pulse was 100 kHz, and the target voltage was 250 V with a target current of 12 A. The space was heated to 300 °C. A 100 W bias voltage was applied to the pedestal. No collimator was used. The distance from the target to the substrate was 50 mm. The deposition rate was...

[0132] The comparative (benchmark) sample (150 mm in diameter) was prepared by depositing an AlN layer in a single step. The AlN layer was deposited at a 43-degree deposition angle. The deposition pressure was chosen to be 2.5 mTorr with an argon to nitrogen ratio of 6:15. The power was 3 kW, the DC current pulse was 250 kHz, and the target voltage was 250 V with a target current of 12 A. The deposition rate was... The space was not heated, but the temperature was estimated to be around 100°C due to the use of plasma.

[0133] A capping film was prepared to achieve X-ray diffraction measurements of the c-axis angle of the AlN host layer crystal. The AlN host layer crystal deposited on the capping film corresponds to the AlN host layer crystal deposited on the wafer under the same conditions.

[0134] The c-axis angles of the AlN host layer crystals on the sample and comparison capping films were measured using a standard X-ray diffractometer equipped with a goniometer for pole figure measurements. It should be noted that the deposition angles given in this example are nominal settings for the deposition system and may vary within the actual angular range of the deposition flux contact substrate. However, the relative magnitudes of the angles can still be compared.

[0135] exist Figure 8A and 8BThe image shows the results of covering the sample with a thin film, and... Figure 9A and 9B The results of the comparison (benchmark) covered film are illustrated.

[0136] It was observed that by applying the main portion of the body layer with perpendicular incidence, production volumes significantly higher than usual could be achieved. Without a collimator, this could be achieved... Vertical incidence deposition was performed. This deposition rate resulted in a significant increase in production and efficiency.

[0137] If they are in the polar regions Figure 8A and 9A The sample prepared by the two-step method, with an approximately 35-degree c-axis tilt angle, is similar to the comparison sample. The two-step method includes a second step with perpendicular incidence. It is observed that the host layer crystals deposited with perpendicular incidence are aligned with the crystals applied in the first step. It is assumed that the microcrystals from the first step act as templates for the subsequent host layer.

[0138] The effective electromechanical coupling coefficient and mechanical quality factor of each wafer were evaluated to extract resonator performance characteristics by studying the scattering (S-) parameter matrix of the samples using a vector network analyzer. Electrical probing was performed at all 100 locations on each wafer, and the results were calculated as normalized averages.

[0139] Used to calculate the quality factor (Q) and effective coupling coefficient (k 2 eff The method is based on the work published by KM. Larkin in the IEEE MTT-S Microwave Symposium Digest, 1992, pp. 149-152. The quality factor is determined using the following expression:

[0140]

[0141] The effective coupling coefficient is obtained by measuring the series resonant frequency (f). s ) and parallel resonant frequency (f p And it was determined using the following formula:

[0142] in

[0143] In displaying the electromechanical coupling coefficient (k) e ) 2 of Figure 10 Furthermore, it displays the mechanical quality factor (Q) normalized to the comparison (benchmark) sample. Figure 11 The results are shown in the diagram.

[0144] It was observed that the electrical properties of the sample films grown under the deposition conditions according to this disclosure were comparable to those of the comparative (benchmark) samples. The mechanical quality factor (Q) measured on the sample wafers was comparable to or slightly higher (approximately 1.1 times) the mechanical quality factor of the comparative (benchmark) samples.

[0145] Example 2

[0146] The sample and comparison films were prepared as described in Example 1. The surface roughness of the films was tested using an atomic force microscope (AFM) with a Dimension 5000 instrument from Brooke Company, Bill Ricard, Massachusetts (previously available from Digital Instruments).

[0147] Focused ion beam (FIB) was used to cut the thin film to obtain microscopic images of its cross-section. A FEI NovaNanolab 600I SEM (scanning electron microscope) equipped with FIB was used for cutting and for obtaining SEM images. High-resolution scanning tunneling electron microscopy (STEM) images were acquired using a Hitachi 2300ASTEM. Figure 12 The image shows SEM images (100,000x magnification) of the surfaces of the sample film and the comparison film. Figure 13 The image shows a cross-sectional STEM image (100,000x magnification). It should be noted that the dominant grain structure seen in the image is the bulk grain structure, contrasting with the c-axis tilt. Figure 14 The images show STEM images of cross-sections demonstrating fissures (sample film) or voids (comparison film) in the deposited layer. The results are shown in Table 1 below.

[0148] Table 1 Surface roughness results

[0149] Roughness Rq Roughness Ra Roughness Rmax Sample film, middle 5.4nm 4.40nm 49.1nm Sample film, edge 4.01nm 3.18nm 30.3nm Compared to thin films, the middle 6.37nm 5.10nm 48.6nm Compare the thin film, the edge 6.55nm 5.22nm 62.0nm

[0150] What was observed was that the sample film had a lower surface roughness than the comparison film. Further observation showed that the sample film had a more uniform film thickness, with a thickness variation of less than 2%, in contrast to the comparison film's thickness variation of more than 2%.

[0151] Assume that existing techniques cause voids to form at the edges of the host film due to shading effects during the deposition process. What is observed is that the sample film does not show voids, and when comparing films, only the seams are visible when voids are present.

[0152] Example 3

[0153] To test the shear strength of biosensor bumps made using a covered film, according to Figure 15 The schematic diagram illustrates the preparation of bump samples. Bump samples are fabricated on the sample film and comparison film prepared according to Example 1.

[0154] Shear tests were performed on the bump samples using an adhesive shear measurement tool, which can be used during manufacturing to test the product's resistance to shear forces. The shear tests were run at the wafer level, with 20 tests performed on a single wafer. Comparisons showed that the thin-film bumps exhibited some reliability issues attributed to tearing and cracking in the substrate. Figure 16 The images show typical failure modes of the bumps on the sample film and the comparison film. The bumps on the comparison film fail due to tearing in the substrate, unlike the bumps on the sample film. It can also be seen that the bumps on the sample film still have some copper residue after failure, while the comparison film does not. (As shown in...) Figure 17 As seen in the graphical representation, the sample film also exhibits bumps with higher tolerance to shear stress. The sample film bumps failed when subjected to shear forces ranging from 125g to 160g. The comparison film bumps failed when subjected to shear forces ranging from 50g to 150g. It was also observed that the comparison film bumps exhibited greater variability in shear strength.

[0155] Further observations revealed that the resonator fabricated using the sample film exhibited a smaller fs (series resonant frequency) and smaller dry gain variation compared to the resonator fabricated using the comparison film. The electrical performance of the resonator was measured through electrical contact with the film. The fs variation of the resonator fabricated using the sample film was below + / -100 MHz, while the fs variation of the resonator fabricated using the comparison film was above + / -100 MHz. The dry gain variation of the resonator fabricated using the sample film was less than 2%, while the dry gain variation of the resonator fabricated using the comparison film was greater than 2%.

[0156] The results in Examples 1-3 demonstrate that the method of this disclosure can be used to deposit a host layer in two steps, with the second step performed at a perpendicular incident angle, producing a host layer that is at least equivalent to or better than that deposited using prior art methods. The host layer exhibits lower surface roughness and greater thickness uniformity. Structures fabricated using the host layer exhibit greater shear strength. The improved quality of the host layer leads to process improvements, such as higher throughput and lower process costs.

Claims

1. A structure comprising: A substrate containing a wafer or a portion thereof; A piezoelectric host material layer comprising a first portion deposited on the substrate and a second portion deposited on the first portion, the first portion having a first c-axis tilt of 35 to 52 degrees, the second portion having a second c-axis tilt substantially aligned with the first c-axis tilt, the hexagonal crystal structure of the second portion comprising an outer surface having a reduced surface roughness (Ra) of 4.5 nm or less; and At least partially provided on the body material layer, the protrusions being capable of withstanding a shear force of 120g or greater; The piezoelectric host material layer has a thickness of about 1,000 angstroms to about 30,000 angstroms and the thickness variation from the center to the edge of the piezoelectric host material layer is less than 2%.

2. The structure according to claim 1, wherein the outer surface has a surface roughness (Ra) of 4 nm or less.

3. The structure according to any one of claims 1 to 2, wherein the protrusion is capable of withstanding a shear force of 125g or greater.

4. The structure according to claim 1, wherein the first portion has a first main grain orientation and the second portion has a second main grain orientation, and wherein the second main grain orientation is different from that of the first portion.

5. The structure according to claim 4, wherein the orientation of the second host grain is substantially vertical.

6. The structure according to claim 1, wherein the piezoelectric host material layer comprises AlN.

7. The structure according to claim 1, wherein the piezoelectric host material layer exhibits a shear coupling to longitudinal coupling ratio of 1.25 or greater during excitation.

8. The structure according to claim 1, wherein the structure is prepared by: A first portion of the main material layer is deposited on the substrate at a first incident angle, the first portion having a first c-axis tilt; and A second portion of the host material layer is deposited on the first portion at a second incident angle smaller than the first incident angle, and the second portion has a second c-axis tilt substantially aligned with the first c-axis tilt.

9. The structure of claim 8, wherein the first portion, the second portion, or both are deposited under deposition conditions containing a pressure of less than 5 mTorr.

10. The structure according to claim 9, wherein the pressure is from 1 mTorr to 4 mTorr.

11. A bulk acoustic resonator comprising the structure of any one of claims 1 to 10, the bulk acoustic resonator further comprising a first electrode and a second electrode, wherein at least a portion of the piezoelectric body material layer is located between the first electrode and the second electrode.

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