Piezoelectric bulk layers with tilted c-axis orientation and methods for making the same

Abstract

To provide piezoelectric bulk layers with improved properties, and methods for making the same.SOLUTION: A structure includes: a substrate including a wafer or a portion of the wafer; and a piezoelectric bulk material layer comprising a first portion deposited on the substrate and a second portion deposited on the first portion, the second portion comprising an outer surface having a surface roughness (Ra) of 4.5 nm or less. Methods for depositing a piezoelectric bulk material layer include: depositing a first portion of bulk layer material at a first incidence angle to achieve a predetermined c-axis tilt; and depositing a second portion of the bulk material layer on the first portion at a second incidence angle that is smaller than the first incidence angle. The second portion has a second c-axis tilt aligned substantially with the first c-axis tilt.SELECTED DRAWING: Figure 2D

Description

[Technical Field]

[0001] The present disclosure relates to structures including materials with a hexagonal c-axis tilted crystal structure, as well as systems and methods for fabricating such materials. In particular, the present disclosure relates to structures including piezoelectric materials with a hexagonal c-axis tilted crystal structure, such as aluminum nitride (AlN) and zinc oxide (ZnO). Piezoelectric materials with a hexagonal c-axis tilted crystal structure may be used, for example, in various resonators, thin film electroacoustic devices and / or thin film sensor devices, particularly sensors operating in liquid / viscous media (e.g., chemical and biochemical sensors) and the like. [Background technology]

[0002] Piezoelectric materials with a hexagonal crystal structure, such as AlN and ZnO, are of commercial interest due to their piezoelectric and electroacoustic properties. Electroacoustic technology has been used primarily in the telecommunications field (e.g., oscillators, filters, delay lines, etc.). More recently, there has been growing interest in using electroacoustic devices in high-frequency sensing applications due to their potential for high sensitivity, high resolution, and high reliability. However, applying electroacoustic technology to certain sensor applications, particularly sensors operating in liquid or viscous media (e.g., chemical and biochemical sensors), is challenging because longitudinal and surface waves exhibit significant acoustic leakage into such media, leading to reduced resolution.

[0003] Piezoelectric crystal resonators can embody either bulk acoustic waves (BAW), which propagate through the interior (or "bulk") of a piezoelectric material, or surface acoustic waves (SAW), which propagate along the surface of the piezoelectric material. SAW devices transduce acoustic waves (typically including two-dimensional Rayleigh waves) using interdigital transducers along the surface of the piezoelectric material, confining the waves to a penetration depth of approximately one wavelength. BAW devices typically transduce acoustic waves using electrodes positioned on opposing top and bottom surfaces of the piezoelectric material. In BAW devices, different vibration modes can propagate through the bulk material, including longitudinal modes and two differently polarized shear modes. The longitudinal and shear bulk modes propagate at different velocities. Longitudinal modes are characterized by compression and extension in the direction of propagation, while shear modes consist of motion perpendicular to the direction of propagation without local volume change. The propagation characteristics of these bulk modes are determined by the material properties relative to the crystallographic axis orientation and the propagation direction, respectively. Because shear waves exhibit a very small penetration depth in liquids, devices with pure or predominantly shear modes can operate in liquids without significant radiation losses (as opposed to longitudinal waves, which can propagate radially in liquids and exhibit significant propagation losses). In other words, shear mode vibrations are beneficial for the operation of fluid-based acoustic wave devices because shear waves do not transfer significant energy into the fluid.

[0004] Certain piezoelectric thin films can excite both longitudinal and shear mode resonances. To excite waves, including shear modes, using devices with standard sandwich-type electrode configurations, the polarization axis of the piezoelectric thin film generally needs to be non-perpendicular (e.g., tilted) to the film plane. Piezoelectric materials with hexagonal crystal structures, such as (but not limited to) aluminum nitride (AlN) and zinc oxide (ZnO), tend to grow with their polarization axis (i.e., c-axis) perpendicular to the film plane because the (0001) plane typically has the lowest surface density and is thermodynamically favored. While certain high-temperature (e.g., vapor deposition) processes can be used to grow c-axis tilted thin films, low-temperature deposition processes (e.g., typically below about 300 °C) are required to provide full compatibility with microelectronic structures such as metal electrodes and interconnects.

[0005] Low-temperature deposition methods such as reactive radio frequency magnetron sputtering have been used to create graded AlN films, but these processes tend to result in deposition angles that vary significantly with position across the area of ​​the substrate, which in turn results in the c-axis orientation of the deposited piezoelectric material varying with 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 film structure across the substrate is that when the AlN film-covered substrate is diced into individual chips, the individual chips will exhibit significant variations in c-axis tilt angle and concomitant variations in acoustic propagation characteristics. Such variations in c-axis tilt angle will make it difficult to efficiently manufacture large quantities of resonator chips with consistent and repeatable performance.

[0007] Improved methods and systems for fabricating bulk films with a c-axis tilt have been described, in which the c-axis tilt of the bulk layer is controlled primarily by controlling the deposition angle. For example, apparatus and methods for depositing seed layers and bulk layers with tilted c-axes are described in U.S. patent application Ser. No. 15 / 293,063, entitled "Deposition System for Growth of Inclined C-Axis Piezoelectric Material Structures," U.S. patent application Ser. No. 15 / 293,071, entitled "Methods for Fabricating Acoustic Structure with Inclined C-Axis Piezoelectric Bulk and Crystalline Seed Layers," U.S. patent application Ser. No. 15 / 293,071, entitled "Acoustic Resonator Structure with Inclined C-Axis Piezoelectric Bulk and Crystalline Seed Layers," and U.S. patent application Ser. No. 15 / 293,071, entitled "Methods for Fabricating Acoustic Structure with Inclined C-Axis Piezoelectric Bulk and Crystalline Seed Layers." No. 15 / 293,082 entitled "Multi-Stage Deposition System for Growth of Inclined C-Axis Piezoelectric Material Structures," U.S. Patent Application No. 15 / 293,091 entitled "Multi-Stage Deposition System for Growth of Inclined C-Axis Piezoelectric Material Structures," and U.S. Patent Application No. 15 / 293,108 entitled "Methods for Producing Piezoelectric Bulk and Crystalline Seed Layers of Different C-Axis Orientation Distributions."These published patent applications also describe, among other things, the use of collimators and control mechanisms to provide bulk films with more uniform c-axis tilt across the surface of a substrate. The use of collimators can result in deposition of a significant amount of the bulk layer onto the collimator rather than the substrate, which can lead to waste and inefficiencies in the process.

[0008] These published patent applications also describe attempts to deposit bulk layers directly onto a substrate without first depositing a seed layer (see, e.g., U.S. Patent Application No. 15 / 293,071). However, such bulk layers did not exhibit the desired c-axis tilt angle distribution and failed to exhibit the desired minimum shear mode-to-longitudinal coupling ratio of 1.25 or greater (which would result in a structure that would not be suitable for use as a resonator for bulk acoustic sensing in liquid / viscous media), even though they were deposited under the same conditions used to deposit the bulk layers (which exhibited the desired properties) onto the seed layer. Summary of the Invention [Problem to be solved by the invention]

[0009] A bulk layer with improved properties is desired. [Means for solving the problem]

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

[0011] In some embodiments, the structure includes a substrate comprising a wafer or a portion of a wafer; and a piezoelectric bulk 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 with a surface roughness (Ra) of 4.5 nm or less. The piezoelectric bulk material layer can have a c-axis tilt of about 35 degrees to about 52 degrees. The crystalline bulk layer can exhibit a shear bond to longitudinal bond ratio of 1.25 or greater during excitation.

[0012] The structure can include a bump disposed at least partially in the bulk material layer. According to one embodiment, the bump contact can exhibit a shear strength capable of withstanding a force of 80 g (0.78 N) or more, 100 g (0.98 N) or more, 110 g (1.08 N) or more, 120 g (1.18 N) or more, 130 g (1.27 N) or more, or 140 g (1.37 N) or more.

[0013] The bulk material layer may have a thickness of about 1,000 angstroms to about 30,000 angstroms, and the thickness may vary by less than 2% across the area of ​​the bulk material layer.

[0014] In some embodiments, a crystalline bulk layer having a c-axis at a preselected angle is produced by a method including depositing a first portion in a first growth step under deposition conditions including a pressure of 5 mTorr (0.67 Pa) or less. The first growth step is performed at a non-normal incidence. Preferably, the deposited bulk layer has a c-axis tilt of about 35 degrees or more. For example, the bulk material layer can be deposited at a deposition angle of about 35 degrees to about 85 degrees. Preferably, deposition in the first growth step is under conditions that inhibit the surface mobility of the deposited material, such that the crystals of the bulk material layer are approximately parallel to each other and oriented substantially at the preselected angle. The method further includes depositing a second portion in a second growth step, including depositing the bulk material layer at a smaller incidence angle, e.g., near-normal incidence. Despite deposition at near-normal incidence, the second portion of the bulk material layer deposited in the second growth step is oriented in the direction of the c-axis tilt of the first portion, e.g., about 35 degrees or more. The bulk material may exhibit a shear bond to longitudinal bond ratio of 1.25 or greater during excitation. The bulk layer (e.g., the second portion) may have an outer surface with a surface roughness (Ra) of 4.5 nm or less.

[0015] In some embodiments, a crystalline bulk layer having a c-axis tilt at a preselected angle is produced by a method including: depositing a first portion of the bulk material layer having a first c-axis tilt onto a substrate at a first angle of incidence; and depositing a second portion of the bulk material layer having a second c-axis tilt substantially aligned with the first c-axis tilt onto the first portion at a second angle of incidence less than the first angle of incidence. The first portion can be deposited directly onto a surface of the substrate. The bulk layer (e.g., the second portion) can have an outer surface with a surface roughness (Ra) of 4.5 nm or less.

[0016] In some embodiments, a crystalline bulk layer having a c-axis tilt at a preselected angle is produced by a method including: depositing a seed layer on a substrate under deposition conditions including a pressure of 10 mTorr (1.33 Pa) or greater; and depositing a crystalline bulk layer having a c-axis tilt at a preselected angle on the seed layer. Depositing the bulk layer includes a two-step process. A first portion is deposited in a first growth step performed at a first angle of incidence that is non-normal. Preferably, the deposited first portion of the bulk layer has a c-axis tilt at the preselected angle. The method further includes a second growth step including depositing a second portion of the bulk material layer at a second angle of incidence that is smaller than the first angle of incidence. Despite being deposited at near-normal incidence, the second portion of the bulk material layer deposited in the second growth step is oriented in the direction of the c-axis tilt of the first portion. The bulk material may exhibit a shear bond to longitudinal bond ratio of 1.25 or greater during excitation. The bulk layer (eg, the second portion) may have an outer surface with a surface roughness (Ra) of 4.5 nm or less.

[0017] In various embodiments described herein, the bulk layer is fabricated such that the c-axis orientation of the crystals within the bulk layer can be selected within a range of 0 degrees to 90 degrees, such as from about 30 degrees to about 52 degrees, or from about 35 degrees to about 46 degrees, etc. The c-axis orientation distribution is preferably substantially uniform across the entire area of ​​a large substrate (e.g., having a diameter in the range of about 50 mm or more, about 100 mm or more, or about 150 mm or more), thereby enabling multiple chips with the same or similar acoustic wave propagation characteristics to be obtained from a single substrate.

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

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

[0020] In various embodiments described herein, a bulk acoustic wave resonator (bulk acoustic wave resonator) includes a structure including a substrate having a wafer and a piezoelectric bulk material layer deposited on a surface of the wafer, the bulk material layer having a c-axis tilt of about 32 degrees or more, and at least a portion of the piezoelectric bulk material layer being between a first electrode and a second electrode. The bulk layer (e.g., the second portion) can have an outer surface with a surface roughness (Ra) of 4.5 nm or less. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a graph of the shear coupling coefficient (Ks) and longitudinal coupling coefficient (Kl) as a function of c-axis tilt angle for AlN. [Figure 2A] FIG. 2A is a schematic diagram illustrating the process of depositing a bulk layer on a substrate without a seed layer to obtain a desired c-axis tilt according to embodiments described herein. [Figure 2B] FIG. 2B is a schematic diagram illustrating the process of depositing a bulk layer on a substrate without a seed layer to obtain a desired c-axis tilt according to embodiments described herein. [Figure 2C] FIG. 2C is a schematic diagram illustrating the process of depositing a bulk layer on a substrate without a seed layer to obtain a desired c-axis tilt according to embodiments described herein. [Figure 2D] FIG. 2D is a schematic diagram illustrating the process of depositing a bulk layer on a substrate without a seed layer to obtain a desired c-axis tilt according to embodiments described herein. [Figure 3A] FIG. 3A is a schematic diagram illustrating the process of depositing a bulk layer onto a substrate with a seed layer to obtain a desired c-axis tilt according to embodiments described herein. [Figure 3B] FIG. 3B is a schematic diagram illustrating the process of depositing a bulk layer onto a substrate with a seed layer to obtain a desired c-axis tilt according to embodiments described herein. [Figure 3C] FIG. 3C is a schematic diagram illustrating the process of depositing a bulk layer onto a substrate with a seed layer to obtain a desired c-axis tilt according to embodiments described herein. [Figure 3D] FIG. 3D is a schematic diagram illustrating the process of depositing a bulk layer onto a substrate with a seed layer to obtain a desired c-axis tilt according to embodiments described herein. [Figure 4] FIG. 4 is a top exterior perspective view of a reactor of a deposition apparatus for growing piezoelectric material with a hexagonal crystal structure having a tilted c-axis, the deposition apparatus including a linear sputtering device, a movable substrate table supporting multiple substrates, and a collimator. [Figure 5] FIG. 5 is a top perspective view of some of the elements of the reactor of FIG. 4, including a linear sputtering apparatus, a translation rail for translating a movable substrate table that supports multiple substrates, and a collimator. [Figure 6] FIG. 6 is a schematic cross-sectional view of a portion of a bulk wave solid-state resonator device disclosed herein that includes a bulk layer of piezoelectric material with a c-axis tilted hexagonal crystal structure, the resonator device including an active region in which a portion of the piezoelectric material is disposed between overlapping portions of a top electrode and a bottom electrode. [Figure 7] FIG. 7 is a schematic cross-sectional view of a thin film bulk acoustic wave resonator (FBAR) device according to one embodiment disclosed herein, including a bulk layer of piezoelectric material with a c-axis tilted hexagonal crystal structure disposed on a crystalline seed layer, the FBAR device including a substrate defining a cavity covered by a support layer, a portion of the piezoelectric material disposed between overlapping portions of a top electrode and a bottom electrode, and an active region sensed using the cavity. [Figure 8A] FIG. 8A is a graphical representation of the c-axis angle of the sample in one example. [Figure 8B] FIG. 8B is a graphical representation of the c-axis angle of the sample in one example. [Figure 9A] FIG. 9A is a graphical representation of the c-axis angle of a comparative sample in one example. [Figure 9B] FIG. 9B is a graphical representation of the c-axis angle of the comparative sample in one example. [Figure 10] FIG. 10 is a graphical representation of the electromechanical coupling of an example sample and a comparative sample. [Figure 11] FIG. 11 is a graphical representation of wafer quality for the sample of Example 1 and the comparative sample. [Figure 12] FIG. 12 shows SEM images of the sample of Example 2 and the comparative sample. [Figure 13] FIG. 13 shows STEM images of the sample of Example 2 and the comparative sample. [Figure 14] FIG. 14 shows wafer-quality STEM images of the sample of Example 2 and the comparative sample. [Figure 15] FIG. 15 shows a schematic drawing of the bumps produced in Example 3. [Figure 16] FIG. 16 shows images of the shear fracture test of the bump of FIG. [Figure 17] FIG. 17 is a graphical representation of the results of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present disclosure relates to crystalline bulk layers and methods for depositing crystalline bulk layers that allow for selection of the c-axis tilt of the crystalline material. The present disclosure relates to crystalline bulk layers that, when processed into devices, have improved properties, such as improved mechanical quality factor, reduced acoustic loss, reduced resistive (electrical) loss, reduced surface roughness, and / or improved mechanical strength. The bulk layer can be formed in a two-step process. In the first step, a portion of the bulk layer is deposited at a non-normal incidence angle to achieve the desired c-axis tilt. Once the c-axis tilt is established, the remaining portion of the bulk layer is deposited at normal incidence. Whether deposited at normal or near-normal incidence, the remaining bulk layer tends to adopt the c-axis tilt of the previously deposited crystalline layer. The bulk layer can be deposited directly onto a substrate or onto a substrate with a seed layer.

[0023] The present disclosure relates to crystalline bulk layers that exhibit low surface roughness and small thickness variations, which can be used to create resonators that exhibit high shear strength and a high shear-to-longitudinal coupling ratio, and have small variations in resonant frequency and dry gain.

[0024] Improvements to crystalline bulk layers and methods for making crystalline bulk layers would be desirable, for example, to provide one or more of the following: greater control over the angle of the c-axis of the crystals within the bulk layer; improved properties (e.g., reduced thin film surface roughness, improved mechanical quality factor, improved coupling coefficient, improved bulk layer thickness uniformity, increased shear bond to longitudinal bond ratio, etc.); improved bulk layer manufacturing efficiency; and improved performance of thin film-based devices.

[0025] Depositing a crystalline bulk layer at near-normal incidence and achieving the desired c-axis tilt reduces waste and processing efficiency. For example, deposition at normal incidence can be performed without a collimator, thereby reducing material loss of bulk layer material resulting from deposition on the collimator. As a result, more bulk layer material can be transferred directly to the substrate. Furthermore, the frequency with which deposits on the collimator need to be cleaned or replaced can be reduced. In addition, deposition at normal incidence can be faster and can be performed using standard equipment and process conditions. These and other advantages will be readily apparent to those skilled in the art.

[0026] The disclosed method provides for the fabrication of structures having crystalline bulk layers whose c-axes are tilted at a preselected angle. The desired c-axis tilt is determined by the intended purpose, application, and bulk layer influence. Varying the c-axis tilt angle for piezoelectric materials with a hexagonal crystal structure varies the shear coupling coefficient and longitudinal coupling coefficient, as shown in Figure 1. Figure 1 shows graphs of the shear coupling coefficient (Ks) and longitudinal coupling coefficient (Kl) as a function of c-axis tilt angle for AlN. It can be seen that the maximum electromechanical coupling coefficient for shear mode resonance in AlN is obtained at a c-axis tilt angle of approximately 35 degrees, that a pure shear response (zero longitudinal coupling) is obtained at a c-axis tilt angle of approximately 46 degrees, and that the shear coupling coefficient exceeds the longitudinal coupling coefficient for c-axis tilt angles ranging from approximately 19 degrees to approximately 63 degrees. Furthermore, while the longitudinal coupling coefficient is zero at a c-axis tilt angle of 90 degrees, growing AlN at very steep c-axis tilt angles is not practical. Similar operation is contemplated for other piezoelectric materials, although the specific angular positions may vary. For electroacoustic resonators intended for operation in liquid or other viscous media, it is desirable to provide piezoelectric thin films with a c-axis tilt angle sufficient to provide a shear coupling coefficient that exceeds the longitudinal coupling coefficient, in certain embodiments at c-axis tilt angles where the longitudinal coupling coefficient approaches zero or near values ​​where shear coupling is maximized. Thus, for electroacoustic resonators including AlN piezoelectric layers, it is desirable to provide a c-axis tilt angle in the range of about 19 degrees to about 63 degrees, with a c-axis tilt angle of about 35 degrees to about 46 degrees being particularly desirable. Other c-axis tilt angles may be desirable for other purposes or when materials other than AlN are used for deposition.

[0027] The shear coupling coefficient in bulk wave resonators comprising AlN bulk layers exceeds the longitudinal coupling coefficient for c-axis tilt angle values ​​ranging from about 19 degrees to about 63 degrees. A larger difference between shear mode and longitudinal coupling is obtained for c-axis tilt angles between about 30 degrees and 52 degrees, and a pure shear mode resonant response (with zero longitudinal coupling) can be obtained for c-axis tilt angles of approximately 46 degrees. Therefore, it is desirable to be able to fabricate AlN bulk layers with c-axis tilt angles between about 30 degrees and about 52 degrees, between about 32 degrees and about 50 degrees, between about 35 degrees and about 50 degrees, between about 35 degrees and about 48 degrees, or between about 46 degrees. In some embodiments, shear mode excitation can be increased by depositing bulk layers with c-axis tilts between about 30 degrees and about 52 degrees, between about 32 degrees and about 50 degrees, or between about 35 degrees and about 48 degrees. Other c-axis tilt angles may also be useful in other embodiments. For example, a c-axis tilt of about 30 degrees to about 45 degrees, about 32 degrees, or about 90 degrees may be desired in some embodiments.

[0028] The term "c-axis" is used herein to refer to the (002) direction of deposited crystals having a hexagonal wurtzite structure. The c-axis is typically the longitudinal axis of the crystal.

[0029] The terms "c-axis tilt," "c-axis orientation," and "c-axis tilt" are used interchangeably herein to refer to the c-axis angle relative to the normal to the surface plane of the deposition substrate.

[0030] When referring to c-axis tilt or c-axis orientation, it should be understood that even if a single angular value is given, the crystals within a deposited crystalline layer (e.g., a seed layer or a bulk layer) may exhibit an angular distribution, which typically approximately follows a normal (e.g., Gaussian) distribution that can be practically depicted graphically, for example, as a two-dimensional graph resembling a bell curve or by a pole figure.

[0031] The term "angle of incidence" is used herein to refer to the angle at which atoms deposit onto a substrate, measured as the angle between the path of deposition and the normal to the plane of the substrate surface.

[0032] The term "substrate" is used herein to refer to a material on which a seed layer or bulk layer may be deposited. The substrate may be, for example, a wafer, or may be part of a composite resonant device or wafer, which may also include other components, such as electrode structures, disposed on at least a portion of the substrate. A seed layer is not considered a "substrate" in the embodiments of the present disclosure.

[0033] When referring to the deposition of a crystal "on a substrate," there may be an intervening layer (e.g., a seed layer) between the substrate and the crystal, although the phrases "directly onto the substrate" or "on the surface of the substrate" are intended to exclude intervening layers.

[0034] The term "seed layer" is used herein to refer to a crystalline layer onto which a bulk material layer may be deposited, dominated by a (103) texture with little or no in-plane orientation along the (002) direction.

[0035] The term "bulk layer" is used herein to refer to a crystalline layer that exhibits a predominantly (002) texture. The bulk layer can be formed in one or more steps. References to a bulk layer in this disclosure refer to the entire bulk layer, and the bulk layer may be formed in one step, two steps, or more than two steps. The term "first portion" is used in this disclosure to refer to a first deposited portion (e.g., layer) of the bulk layer that exhibits a predominantly (002) texture.

[0036] The term "substantially" is used herein to mean the same as "almost completely" and can be understood to modify the following term by about 90% or more, about 95% or more, or about 98% or more.

[0037] The terms "parallel" and "nearly parallel" with respect to crystals refer to the orientation of the crystals. Nearly parallel crystals not only have the same or similar c-axis tilt, but also point in the same or similar direction.

[0038] The term "about" is used herein in conjunction with numerical values ​​to include normal variations in measurement expected by one of ordinary skill in the art and is understood to have the same meaning as "approximately," encompassing a typical range of error, such as ±5% of the stated value.

[0039] All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are intended to aid in the understanding of certain terms used frequently herein and are not intended to limit the scope of the present disclosure.

[0040] As used herein, the singular forms "a," "an," and "the" include embodiments with plural referents unless the content clearly dictates otherwise.

[0041] As used herein, the term "or" is generally used in its inclusive sense unless the context clearly dictates otherwise. "And / or" means one or all of the listed elements or a combination of any two or more of the listed elements.

[0042] As used herein, the terms "have," "having," "including," "comprising," and the like are used in their open-ended sense and generally mean "including, but not limited to." "Consisting essentially of," "consisting of," and the like are encompassed by "comprising" and the like. As used herein, "consisting essentially of," as it relates to a composition, product, process, or the like, means that the components of the composition, product, process, or the like are limited to the recited components and any other components that do not materially affect the basic and novel characteristics of the composition, product, process, or the like.

[0043] The words "preferred" and "preferably" refer to embodiments of the invention that may provide certain benefits, under particular circumstances, although other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation 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 the present disclosure, including the claims.

[0044] The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.; 10 or less includes 10, 9.4, 7.6, 5, 4.3, 2.9, 1.62, 0.3, etc.), where a range of values ​​is "up to" a particular value, that value is included within the range.

[0045] Any directions referred to herein, such as "top," "bottom," "left," "right," "upper," "lower," and other directions and orientations, are described herein for clarity in connection with the figures and are not intended to limit the actual device or system or the use of the device or system. The devices or systems described herein can be used in numerous directions and orientations.

[0046] The present disclosure relates in various aspects to crystalline bulk layers, bulk wave resonator structures, and methods for fabricating such bulk layers and resonator structures. Compared to conventional resonator structures, fabrication methods, and deposition apparatus, various embodiments of the present disclosure include or enable c-axis tilted piezoelectric thin films (c-axis tilted piezoelectric thin films) with preselected c-axis tilt angles and an increased range of selectable angles. The c-axis tilted piezoelectric thin films may also exhibit improved mechanical quality factors, reduced acoustic losses, reduced resistive (electrical) losses, reduced surface roughness, and / or improved mechanical strength when processed into devices. The c-axis tilted piezoelectric thin films can be fabricated on large areas (e.g., large area substrates) with improved uniformity of the c-axis tilt angle. The methods for fabricating c-axis tilted piezoelectric thin films may be more efficient or reduce waste compared to prior art methods for fabricating c-axis tilted piezoelectric thin films.

[0047] The methods described herein include bulk layer deposition processes having two or more steps, which may further include depositing a seed layer onto a substrate, or may include depositing a bulk layer directly onto a substrate (without an intervening seed layer).

[0048] 2A-2D and 3A-3D, schematic diagrams of a two-step bulk layer deposition process are shown. FIGS. 2A-2D illustrate a process for depositing a bulk layer 40 directly onto a substrate 4 without a seed layer. The first growth step (shown in FIG. 2A) involves metal atoms being released from a target 2 in a linear sputtering system and reacting with gas species to form a deposition flux 10 that is received by the substrate 4. The deposition system may include a multi-aperture collimator 17 positioned between the target and the substrate. The deposition flux 10 can be directed through apertures 18 in the collimator 17 to help control the angle of incidence during deposition. The deposition flux 10 reaches the substrate 4 at a first angle of incidence α, forming a first portion 41 of the bulk layer 40 (shown in FIG. 2B). The crystal of the first portion 41 of the bulk layer 40 has a c-axis tilt 41γ.

[0049] In the second growth step (shown in FIG. 2C), metal atoms are released from the target 2, react with gas species, and are received by the first portion 41 already deposited on the substrate 4. In the second growth step, the target 2 can be positioned so that the second angle of incidence β is smaller than the first angle of incidence α (e.g., between the normal and the first angle of incidence α). For example, the second angle of incidence β can be approximately 0 degrees (i.e., perpendicular to the surface of the substrate 4). In the second growth step, the deposition flux 10 forms the second portion 42 of the bulk layer 40 (shown in FIG. 2D). The crystal of the second portion 42 of the bulk layer 40 has a c-axis tilt 42γ. The second growth step can be performed without a collimator.

[0050] 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 bulk 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 the first incidence angle α used during the first growth step. The resulting bulk layer crystals of the first and second portions 41, 42 can be substantially parallel to each other and at least substantially aligned with the desired c-axis tilt. The resulting bulk layer crystals of the first and second portions 41, 42 can also be substantially parallel within each portion. For example, at least 50%, 75%, or 90% of the crystals of the first portion 41 can have a c-axis tilt 41γ within 0 to 10 degrees of the average c-axis tilt and a direction within 0 to 45 degrees, or within 0 to 20 degrees, of the average crystal orientation. Similarly, 50% or more, 75% or more, or 90% or more of the crystals in the second portion 42 may have a c-axis tilt 42γ that is within 0 to 10 degrees of the average c-axis tilt and an orientation that is within 0 to 45 degrees, or within 0 to 20 degrees, of the average crystal direction.

[0051] 3A-3D illustrate a process in which a bulk layer 50 is deposited on a seed layer 31 deposited on a substrate 4. A first portion 51 (FIG. 3B) of the crystalline bulk layer 50 is deposited on the seed layer 31 in a first growth step shown in FIG. 3A. In the first growth step, atoms in the deposition flux 10 (metal atoms reacted with gas) are deposited at a first incident angle α. In a second growth step shown in FIG. 3C, atoms in the deposition flux 10 are deposited at a second incident angle β, resulting in a second portion 52 of the bulk layer 50. The second incident angle β can be smaller than the first incident angle α. For example, the second incident angle β can be approximately 0 degrees (i.e., perpendicular to the surface of the substrate 4). The crystal of the second portion 52 of the bulk layer 50 has a c-axis tilt 52γ.

[0052] 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 bulk 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 the first incidence angle α used during the first growth step. The resulting bulk layer crystals of the first and second portions 51, 52 can be substantially parallel to each other and at least substantially aligned with the desired c-axis tilt. The resulting bulk layer crystals of the first and second portions 51, 52 can also be substantially parallel within each portion. For example, 50% or more, 75% or more, or 90% or more of the crystals of the first portion 51 can have a c-axis tilt 51γ that is within 0 to 10 degrees of the average c-axis tilt and a direction that is within 0 to 45 degrees, or within 0 to 20 degrees, of the average crystal orientation. Similarly, 50% or more, 75% or more, or 90% or more of the crystals in the second portion 52 may have a c-axis tilt 52γ that is within 0 to 10 degrees from the average c-axis tilt and an orientation that is within 0 to 45 degrees, or within 0 to 20 degrees, from the average crystal direction.

[0053] 2A-2D and 3A-3D can both utilize a collimator 17 in the first growth step (see FIGS. 2A and 3A), which involves positioning the target 2 at a non-normal incidence relative to the substrate 4. The second step (see FIGS. 2C and 3C), in which the second portions 42, 52 of the bulk layers 40, 50 are deposited at near-normal incidence, preferably does not utilize a collimator.

[0054] According to at least some embodiments of the present disclosure, the bulk layer 40, 50 has a preselectable c-axis tilt. The methods of the present disclosure result in bulk layers 40, 50 in which the crystals within the bulk layer are aligned or substantially aligned with a preselected c-axis tilt. In some embodiments, the c-axis tilt of the crystals is distributed such that 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more of the crystals within the bulk layer have a c-axis tilt within a range of the preselected c-axis tilt, for example, within 1 to 10 degrees, 1 to 8 degrees, 1 to 5 degrees, or 1 to 3 degrees of the preselected c-axis tilt.

[0055] Without wishing to be bound by theory, it is hypothesized that the deposition conditions during at least one growth step can be selected to inhibit the surface mobility of the deposited atoms. Many variables can be included in the deposition conditions that can have a surface mobility inhibiting effect. These variables can be selected to reduce surface mobility to the point where the c-axis tilt of the seed layer and / or bulk layer is controllable. The surface mobility of atoms is the result of the overall set of variables, not necessarily the result of any single variable alone. When compared to conventional methods and the deposition conditions for depositing bulk layers, each of the variables may be slightly different, or only some of the variables may be different, while others may remain the same as in conventional methods. Because the surface mobility of atoms is difficult to determine directly, an appropriate combination of conditions can be determined based on the ability to change the c-axis tilt of the resulting crystalline layer beyond the angle normally available in the deposited material due to crystallographic constraints. For example, in the case of AlN, the ability to produce a crystalline layer with a c-axis tilt aligned along 32 degrees or greater (with an angular distribution ranging from about 25 degrees to about 35 degrees) may indicate deposition conditions favored by kinetics over thermodynamics, allowing crystals to grow in response to changes in the deposition environment. Also, the ability to deposit a bulk layer directly onto a substrate (without a seed layer) with a c-axis tilt angle aligned at 20 degrees, greater than 25 degrees, greater than 30 degrees, or greater than 35 degrees may indicate deposition conditions favored by kinetics over thermodynamics. The crystals within the bulk layer may be aligned or substantially aligned across the entire area of ​​the substrate (e.g., across the entire deposition area).

[0056] According to one embodiment, an initial (e.g., first) portion of the bulk layer can be deposited at a non-normal incidence angle under initial deposition conditions such that the resulting crystals in the initial bulk layer have a desired c-axis tilt. The remaining bulk layers (e.g., second, or subsequent portions) can be deposited under the same initial deposition conditions or under different deposition conditions (e.g., conditions normally used for depositing the bulk layers).

[0057] In some embodiments, bulk wave resonator structures and methods for fabricating such resonator structures include depositing a bulk layer directly onto a substrate (without a seed layer). Eliminating the seed layer can result in improved coupling efficiency and mechanical quality factor, even if the seed layer is formed of the same material as the bulk layer. In some embodiments, resonator structures formed by depositing a bulk layer directly onto a substrate exhibit improved mechanical quality factor, reduced acoustic loss, reduced resistive (electrical) loss, high shear strength, a high shear-to-longitudinal coupling ratio, and / or small resonant frequency and dry gain variations. The resonator structures also exhibit improved uniformity of the c-axis tilt angle over a large area.

[0058] In accordance with at least some embodiments of the present disclosure, the c-axis tilt of the bulk layer can be adjusted by depositing a first portion of the bulk layer at a desired angle under initial deposition conditions. In some embodiments, the initial deposition conditions are adapted to inhibit surface mobility of atoms while the bulk layer is being deposited. In at least some embodiments, a bulk layer having a preselected c-axis tilt can be deposited under the initial deposition conditions without first depositing a seed layer.

[0059] In some embodiments, the initial deposition conditions during the first growth step can include one or more of the angle of incidence, pressure, temperature, target-to-substrate distance, and gas ratio. The angle of incidence can be non-normal incidence. 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 be less than or equal to about 85 degrees, less than or equal to about 75 degrees, less than or equal to about 65 degrees, less than or equal to about 56 degrees, less than or equal to about 52 degrees, less than or equal to about 50 degrees, less than or equal to about 49 degrees, or less than or equal to about 48 degrees. Exemplary 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.

[0060] The pressure during the first growth step can be about 0.5 mTorr (0.07 Pa) or more, about 1 mTorr (0.13 Pa) or more, or about 1.5 mTorr (0.20 Pa) or more. The pressure can be about 10 mTorr (1.33 Pa) or less, about 8 mTorr (1.07 Pa) or less, about 6 mTorr (0.80 Pa) or less, about 5 mTorr (0.67 Pa) or less, or about 4 mTorr (0.53 Pa) or less. In some embodiments, the pressure is less than 5 mTorr (0.67 Pa). For example, the pressure can be about 2 mTorr (0.27 Pa), about 2.5 mTorr (0.33 Pa), about 3 mTorr (0.40 Pa), about 3.5 mTorr (0.47 Pa), or about 4 mTorr (0.53 Pa). The temperature can be about 20° C. or more, about 50° C. or more, or about 100° C. or more. The temperature can be about 300° C. or less, about 250° C. or less, or about 200° C. or less. In some embodiments, the deposition process may generate heat, but the deposition chamber in which deposition occurs is not heated by a heater (i.e., is not intentionally heated).

[0061] The target-to-substrate distance during the first growth step can be about 50 mm or more, about 75 mm or more, about 80 mm or more, or about 90 mm or more. The distance can be about 200 mm or less, about 150 mm or less, about 130 mm or less, or about 120 mm or less. In some embodiments, the target-to-substrate distance during deposition can be about 108 mm to about 115 mm.

[0062] The gas in the vapor space of the deposition apparatus can be selected based on the intended composition of the layer to be deposited and can include argon and a gas that reacts with the deposited atoms, such as nitrogen or oxygen. The gas ratio of argon to reactive gas (e.g., nitrogen) in the vapor space can be about 1:10 to about 10:10, about 2:10 to about 8:10, or about 4:10.

[0063] In some embodiments, bulk wave resonator structures and methods for fabricating such resonator structures include depositing a bulk layer onto a seed layer. The seed layer can be used to provide a textured surface on which the bulk layer is deposited. The seed layer can exhibit a variety of textures, most notably (103) and (002). A directional deposition flux and predominantly columnar growth can result in a bulk layer with a c-axis substantially oriented along the deposition flux.

[0064] In certain embodiments, the crystalline seed layer is compositionally matched to the bulk layer of the hexagonal crystal structure piezoelectric material. In some embodiments, the thickness of the crystalline seed layer is about 20% or less, about 15% or less, or about 10% or less of the combined thickness of the bulk layer and the seed layer. In certain embodiments, the seed layer comprises a thickness in the range of about 500 angstroms to about 2,000 angstroms and may comprise a predominant (103) texture (for hexagonal crystal structure seed materials such as AlN).

[0065] The seed layer can be prepared (e.g., deposited on a substrate) according to known methods and conditions, such as those described in U.S. Patent Application No. 15 / 293,071, entitled "Method for Fabricating Acoustic Structures Having C-Axis Tilted Piezoelectric Bulk Layers and Crystalline Seed Layers." In some embodiments, the seed layer is deposited at a pressure of 8 mTorr (1.07 Pa) or more, 10 mTorr (1.33 Pa) or more, or 12 mTorr (1.60 Pa) or more, or 25 mTorr (3.33 Pa) or less, 20 mTorr (2.67 Pa) or less, or 18 mTorr (2.40 Pa) or less.

[0066] According to some embodiments, in the first growth step, the bulk layer is deposited onto the seed layer during initial deposition conditions that may include one or more of the angle of incidence, pressure, temperature, target-to-substrate distance, and gas ratio.

[0067] The angle of incidence for the first growth step can be non-normal incidence. 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 be about 85 degrees or less, about 75 degrees or less, about 65 degrees or less, about 56 degrees or less, about 52 degrees or less, about 50 degrees or less, about 49 degrees or less, or about 48 degrees or less. Exemplary 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.

[0068] The pressure during the first growth step can be about 0.5 mTorr (0.07 Pa) or more, about 1 mTorr (0.13 Pa) or more, or about 1.5 mTorr (0.20 Pa) or more. The pressure can be about 10 mTorr (1.33 Pa) or less, about 8 mTorr (1.07 Pa) or less, or about 6 mTorr (0.80 Pa) or less. In some embodiments, the pressure is less than 5 mTorr (0.67 Pa). For example, the pressure can be about 2 mTorr (0.27 Pa), about 2.5 mTorr (0.33 Pa), about 3 mTorr (0.40 Pa), about 3.5 mTorr (0.47 Pa), or about 4 mTorr (0.53 Pa). The temperature can be about 20° C. or more, about 50° C. or more, or about 100° C. or more. The temperature can be about 300° C. or less, about 250° C. or less, or about 200° C. or less. In some embodiments, the deposition process may generate heat, but the deposition chamber in which the deposition occurs is not heated by a heater (i.e., is not intentionally heated).

[0069] The target-to-substrate distance during deposition can be about 50 mm or more, about 75 mm or more, about 80 mm or more, or about 90 mm or more. The distance can be about 200 mm or less, about 150 mm or less, about 130 mm or less, or about 120 mm or less. In some embodiments, the target-to-substrate distance during deposition can be about 108 mm to about 115 mm.

[0070] The gas in the vapor space of the deposition apparatus can be selected based on the intended composition of the layer to be deposited and can include argon and a gas that reacts with the deposited atoms, such as nitrogen or oxygen. The gas ratio of argon to reactive gas (e.g., nitrogen) in the vapor space can be about 1:10 to about 10:10, about 2:10 to about 8:10, or about 4:10.

[0071] The surface on which the seed layer, bulk layer, or portion of the bulk layer is deposited can optionally be roughened prior to deposition. For example, the surface of the substrate, the surface of the seed layer, or the surface of the first portion of the bulk layer can be roughened. The surface can be roughened, for example, by atomic bombardment. Roughening the surface can improve the ability to orient the crystals of the subsequently grown bulk layer during deposition. Without wishing to be bound by theory, it is believed that surface roughening can create a shadowing effect that helps to favor the orientation of the crystals toward the deposition angle. The surface of the substrate can be roughened, for example, by atomic bombardment, to create surface "peaks" and "valleys."

[0072] According to certain embodiments, the second portion of the bulk layer is deposited at normal incidence, or at an incidence angle between the first incidence and normal to the substrate plane. The ability to deposit a portion or most of the bulk layer (e.g., the second portion of the bulk layer) at normal incidence can allow for faster and more efficient manufacturing. Additionally, depositing at normal incidence allows for less material to be deposited on the collimator.

[0073] Deposition conditions during the second growth step can include an angle of incidence and one or more of pressure, temperature, target-to-substrate distance, and gas ratio. The second angle of incidence can be about 0 degrees, about 5 degrees or less, about 10 degrees or less, about 15 degrees or less, about 20 degrees or less, about 25 degrees or less, about 30 degrees or less, about 35 degrees or less, or about 40 degrees or less.

[0074] The deposition conditions during the second growth step can be the same as or different from the initial deposition conditions. Deposition conditions during the second growth step can include, for example, a pressure of 0.5 mTorr (0.07 Pa) to about 15 mTorr (2.00 Pa), about 0.8 mTorr (0.11 Pa) to about 10 mTorr (1.33 Pa), or about 1 mTorr (0.13 Pa) to about 5 mTorr (0.67 Pa). In some embodiments, the pressure is less than 5 mTorr (0.67 Pa). For example, the pressure can be about 2 mTorr (0.27 Pa), about 2.5 mTorr (0.33 Pa), about 3 mTorr (0.40 Pa), about 3.5 mTorr (0.47 Pa), or about 4 mTorr (0.53 Pa). The temperature during the second growth step can range 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 reactive 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.

[0075] The materials used in the first and second growth steps can be the same or different. Suitable materials for the bulk layer include piezoelectric materials and other metallic materials with high melting points. In some embodiments, the material includes a metal nitride, such as aluminum nitride, titanium nitride, hafnium nitride, tantalum nitride, zirconium nitride, vanadium nitride, or niobium nitride. In some embodiments, the material includes a metal oxide, such as zinc oxide, tungsten oxide, hafnium oxide, or molybdenum oxide. In some embodiments, the material includes a metal oxynitride, such as hafnium oxynitride, titanium oxynitride, or tantalum oxynitride. In some embodiments, the material includes a metal carbide, such as titanium carbide, niobium carbide, tungsten carbide, or tantalum carbide. In some embodiments, the material is a refractory metal, such as zirconium, hafnium, tungsten, or molybdenum. The bulk layer can include a combination of two or more of the above materials.

[0076] In certain embodiments, the bulk layer of hexagonal crystal structure piezoelectric material comprises a c-axis having an orientation distribution primarily in the range of 12 degrees to 52 degrees, 27 degrees to 37 degrees, or 75 degrees to 90 degrees relative to a normal to the surface of a substrate or wafer supporting the bulk layer of hexagonal crystal structure piezoelectric material.

[0077] The distribution of c-axis orientations in the bulk layer of the hexagonal crystal structure piezoelectric material can be normal or bimodal. In preferred embodiments, the distribution is normal. In certain embodiments, less than about 30%, less than about 25%, or less than about 20% of the c-axis orientations in the bulk layer of the hexagonal crystal structure piezoelectric material are in the range of 0 to 25 degrees relative to the normal to the surface of the substrate. In certain embodiments, less than about 30%, less than about 25%, or less than about 20% of the c-axis orientations in the bulk layer of the hexagonal crystal structure piezoelectric material are in 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 orientations in the bulk layer of the hexagonal crystal structure piezoelectric material can be in the range of 25 to 45 degrees. In some embodiments, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more of the c-axis orientation distribution of a bulk layer of a piezoelectric material having a hexagonal crystal structure is within the range of 30 degrees to 40 degrees.

[0078] Additionally, a bulk layer of the hexagonal crystal structure piezoelectric material has a bulk grain orientation that differs from the c-axis tilt. The bulk grain orientation of a first portion of the bulk layer can differ from a second portion of the bulk layer. In some embodiments, the bulk grain orientation of the second portion can be vertical or substantially vertical. For example, the bulk grain orientation of the second portion can be 15° or less, 10° or less, or 5° or less from the normal to the surface of the substrate.

[0079] In certain embodiments, the bulk layer of hexagonal crystal structure piezoelectric material (combined first and second portions) can have a thickness of about 1,000 Å (angstroms) or more, about 2,000 Å or more, about 3,000 Å or more, about 4,000 Å or more, about 6,000 Å or more, or about 10,000 Å or more. The thickness of the bulk layer of hexagonal crystal structure piezoelectric material can be about 30,000 Å or less, about 26,000 Å or less, or about 20,000 Å or less. Such bulk layer of hexagonal crystal structure piezoelectric material preferably has substantially uniform thickness, nanostructure, and crystalline properties, controlled stress, and a closely packed columnar grain or recrystallized grain structure. In certain embodiments, the crystalline seed layer can have a thickness in the range of 500 Å to 2,000 Å and (for hexagonal crystal structure piezoelectric materials such as AlN) a predominant (103) texture. In other embodiments, the structure does not include a seed layer.

[0080] The variation in thickness of the bulk layer can be reduced compared to prior art methods, and according to some embodiments, the bulk layer of hexagonal crystal structure piezoelectric material exhibits a variation in thickness of 2.0% or less, 1.9% or less, 1.8% or less, or 1.7% or less.

[0081] The bulk layer of hexagonal crystal structure piezoelectric material may also exhibit reduced surface roughness. According to some embodiments, the bulk layer of hexagonal crystal structure piezoelectric material 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.

[0082] According to some embodiments, the acoustic resonator structure is fabricated in a deposition apparatus in which at least one wafer comprising a substrate is received by a support surface. The acoustic reflector structure can be disposed on the substrate, and an electrode structure can be disposed on at least a portion of the acoustic reflector structure, such a structure can be useful for fabricating at least one solid-state bulk wave resonator device. In certain embodiments, the at least one wafer includes a substrate defining a recess, a support layer disposed on the recess, and an electrode structure disposed on the support layer, such a structure can be useful for fabricating at least one thin film bulk wave resonator device. When describing methods herein, deposition on a "substrate" may be referred to simply. However, it should be understood that the substrate may be part of a composite resonator device or wafer, and that the composite resonator device or wafer may also include other components, such as an electrode structure, disposed on at least a portion of the substrate.

[0083] A large number of acoustic resonator structures or devices (e.g., a group of devices) can be fabricated from a single wafer fabricated according to the methods of the present disclosure. The group of devices (a batch of devices) can be fabricated to specific specifications and quality parameters. Such specifications and quality parameters may include, among other things, operational resonant frequency, resonant frequency variation across the group, and dry gain (mass sensitivity) variation across the group. Resonant frequency variation can be understood as the difference in actual frequency compared to a nominal or target frequency within the group. Dry gain variation can be understood as the difference in dry gain across the group under given test conditions. The dry gain of acoustic resonator structures has been found to be positively correlated with the resonant frequency of the device. Therefore, dry gain variation across a group of acoustic resonator structures fabricated from a given wafer also positively correlates with resonant frequency variation across the group. According to one embodiment, dry gain variation can be reduced by depositing a more uniform bulk layer. Thus, acoustic resonator structures made in accordance with the present disclosure may exhibit less variation in series resonant frequency (fs) and less variation in dry gain compared to prior art structures.

[0084] According to 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 relative to the nominal frequency. 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 under test conditions. Test conditions for a group of structures may be assumed to be the same for the entire group. In some embodiments, any number of acoustic resonator structures may be fabricated from a single wafer. For example, a wafer may contain 100 or more, 1,000 or more, or 10,000 or more acoustic resonator structures, and up to 100,000 acoustic resonator structures. Any two or more structures may be tested and may exhibit a specified resonant frequency variation and dry gain variation. The acoustic resonator structures may have any suitable operating frequency, such as 2 GHz or greater, 2.5 GHz or greater, 2.75 GHz or greater, or 3 GHz or greater. In some embodiments, the plurality of acoustic resonator structures are BAW devices with an operating frequency in the range of 2 GHz to 3 GHz.

[0085] In a preferred embodiment, a wafer is prepared by depositing a bulk material layer according to the method of the present disclosure. A group 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 from the group may be tested and may exhibit a resonant frequency variation of ±100 MHz or less. That is, the tested BAW resonators may exhibit a resonant frequency between 2.6 GHz and 2.8 GHz. Any two or more BAW resonators from the group may be tested under test conditions and may exhibit a dry gain variation of 10% or less. That is, the dry gains of the tested devices are within ±10% of each other.

[0086] Various devices, such as BAW resonators, fabricated from the acoustic resonator structures of the present disclosure may exhibit greater mechanical strength than prior art devices. The device structures may include bumps disposed at least partially on a bulk material layer. The bump structures are post-shaped structures fabricated to provide electrical contact to the surface of the piezoelectric material. During device use, the bumps may be subjected to shear forces. Therefore, greater shear strength and the ability to withstand greater shear forces are beneficial. The shear strength of a bump is determined by various factors, such as the diameter, height, and underlying stack configuration of the bump. Bumps fabricated on stacks fabricated using the methods of the present disclosure may exhibit greater shear strength than similar bumps fabricated on stacks fabricated using prior art methods. According to one embodiment, a bump structure fabricated on an acoustic resonator structure may exhibit a shear strength (measured using a shear adhesion measurement tool) capable of withstanding a force of 80 g (0.78 N) or more, 100 g (0.98 N) or more, 110 g (1.08 N) or more, 120 g (1.18 N) or more, 125 g (1.22 N) or more, 130 g (1.27 N) or more, 135 g (1.32 N) or more, or 140 g (1.37 N) or more. While there is no desired upper limit to the ability to withstand shear force, in practice the bump structure may be able to withstand a shear force of 500 g (4.90 N) or less, 400 g (3.92 N) or less, 300 g (2.94 N) or less, 250 g (2.45 N) or less, or 200 g (1.96 N) or less. Improved mechanical strength may result in increased performance during use of the device, but may also result in increased process throughput and lower processing costs during manufacturing.

[0087] In one aspect, the present disclosure relates to a method for fabricating at least one acoustic resonator structure, wherein a growing step (e.g., a first growing step or a second growing step) includes depositing a bulk layer of a hexagonal crystal structure on a substrate. The deposited material can be a piezoelectric material. The growing step includes ejecting metal atoms from a target surface of a linear sputtering apparatus, reacting with gas species, and receiving them by the substrate.

[0088] Acoustic resonator structures made according to the methods of the present disclosure and devices made using such acoustic resonator structures can be more robust and exhibit improved mechanical stability compared to structures made using known methods.

[0089] The seed layer and bulk layer of the present disclosure can be prepared in any suitable deposition apparatus. One example of a suitable deposition apparatus is described in U.S. Patent Application No. 15 / 293,063, entitled "Deposition Apparatus for Growing C-Axis Tilted Piezoelectric Material Structures." Key aspects of the deposition apparatus are summarized below. However, the method of the present disclosure is not particularly limited by the deposition apparatus used, and other suitable deposition apparatus can also be used.

[0090] The crystalline layers of the present disclosure can be produced in a deposition apparatus incorporating a multi-aperture collimator positioned between the target surface of a linear sputtering apparatus and a substrate table supporting one or more wafers or substrates that receive the sputter-deposited material. In some embodiments, the wafer or substrate may be mounted on a fixed pedestal for deposition at normal incidence (0 degrees).

[0091] A preferred deposition apparatus is shown in Figure 4, which is a top exterior perspective view of a deposition apparatus reactor 100 for growing piezoelectric materials with a hexagonal crystal structure. The reactor 100 includes first, second, and third tubular sections 102, 120, 108 that store the various elements used in the material to be deposited on the substrate. Figure 5 shows a top perspective view of some of the elements of the reactor 100, including a linear sputtering apparatus 154, a translation rail 115 that translates a movable substrate table that supports multiple substrates, and a collimator assembly 170.

[0092] The target surface may be non-parallel to the substrate table, and the intermediate collimator may be non-parallel to both the target surface and the substrate table. The collimator and substrate table are preferably both movable (e.g., translated) during sputtering, and at least one of the substrate table and collimator is preferably biased to a potential other than ground. The deposition apparatus may be used to grow (e.g., deposit) a crystalline seed layer and then grow a bulk layer of hexagonal crystal structure piezoelectric material on the crystalline seed layer under conditions different from those for depositing the seed layer. Alternatively, the disclosed method may deposit the bulk layer directly onto the substrate without first depositing a seed layer.

[0093] According to one embodiment, the bulk layer is grown (e.g., deposited) using a single sputtering apparatus. The growth steps (e.g., the first growth step and / or the second growth step) can be performed using a deposition apparatus that utilizes a linear sputtering apparatus, a substrate table that can be moved between different positions within the linear sputtering apparatus, and a collimator positioned between the substrate table and the linear sputtering apparatus. The bulk layer of hexagonal crystal structure piezoelectric material can be grown in an enclosure in which sub-atmospheric conditions can be generated using at least one vacuum pumping element, and the wafer or substrate supporting the bulk layer can be translated within the enclosure.

[0094] In some embodiments, the bulk layer is grown (e.g., deposited) in two or more steps using a deposition apparatus that utilizes multiple linear sputtering devices and a substrate table that can be moved between different positions proximate to the different linear sputtering devices. A collimator can be positioned between the substrate table and each linear sputtering device. For example, a crystalline seed layer and / or a first portion of a bulk layer of hexagonal crystal structure piezoelectric material can be grown by reactive sputtering at a first position using a first collimator according to a first growth step, and a bulk layer of hexagonal crystal structure piezoelectric material (or a second portion of the bulk layer) can be grown by reactive sputtering at a second position without a collimator in a second growth step. All of these positions can be located within a single enclosure in which sub-atmospheric conditions can be generated using at least one vacuum pumping element, and the wafer or substrate supporting each layer can be moved between these positions without having to be removed from sub-atmospheric conditions. In some embodiments, different process conditions and / or different angular positions between the target surface, the collimator, and the wafer or support surface may be used in the first and second growth steps.

[0095] A deposition apparatus suitable for growing a piezoelectric material with a hexagonal crystal structure and a tilted c-axis may include a linear sputtering apparatus, a multi-aperture collimator, and a movable substrate table having a support surface positioned non-parallel to a target surface of the sputtering apparatus, with the substrate table and / or collimator electrically biased to a potential other than ground. The linear sputtering apparatus, which may include a linear magnetron or linear ion beam sputtering apparatus, includes a target surface configured to eject metal (e.g., aluminum or zinc) atoms, the target surface being non-parallel to the support surface (e.g., oriented at less than 0° to 90° from the support surface). The collimator may also be positioned non-parallel to the support surface. In certain embodiments, for example, during the 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, the first non-zero angle being greater than the second non-zero angle. The metal atoms ejected from the target surface react with gas species contained in a gas-containing environment to form the deposited material (e.g., piezoelectric material). For example, aluminum atoms released from an aluminum or aluminum-containing target surface can react with nitrogen gas species to form aluminum nitride, and zinc atoms released from a zinc or zinc-containing target surface can react with oxygen gas species to form zinc oxide.

[0096] The support surface of the substrate table can be configured to receive one or more wafers used as deposition substrates and preferably has a diameter in the range of about 50 mm or more, about 100 mm or more, or about 150 mm or more. The substrate table can be coupled to a movable element (e.g., a translation element) configured to move the substrate table during operation of the linear sputtering apparatus. Moving the substrate table can promote uniform material deposition over a large area by preventing localized deposition of material with different thicknesses. A preferred collimator includes multiple guide members arranged non-parallel to the support surface, such as multiple vertical members and multiple horizontal members, forming a grid that defines multiple collimator openings. Electrically biasing the substrate table and / or collimator to a potential other than ground enhances control of material deposition during operation of the sputtering apparatus. Biasing the collimator can also affect the microstructural growth of the c-axis tilted piezoelectric bulk material in the bulk wave resonator device. The substrate table and collimator can be individually electrically biased to a potential other than ground. Also, different guiding members of the collimator can be electrically biased differently from one another. The collimator can be configured to move during operation of the linear sputtering apparatus to prevent the formation of "shadow" patterns that might otherwise form on the surface receiving the deposited piezoelectric material. A deposition opening can be located between the collimator and the substrate table.

[0097] According to at least some embodiments, the c-axis tilt of the resulting bulk layer is the same as the preselected angle or is within a range of the angle of incidence and / or the preselected angle. For example, the c-axis tilt of the resulting bulk layer can be within 1 degree, 2 degrees, 3 degrees, 5 degrees, 10 degrees, or 15 degrees of the angle of incidence and / or the preselected c-axis tilt. The distribution of c-axis tilt of the bulk layer crystals can be such that 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more of the bulk layer crystals are within a range, such as within 1 degree, 2 degrees, 3 degrees, 5 degrees, 10 degrees, or 15 degrees, of the angle of incidence and / or the preselected c-axis tilt.

[0098] In certain embodiments, the substrate table and / or collimator are configured to move during the first and / or second growth steps to promote uniform material deposition. An electrode structure can be formed on at least a portion of the bulk layer of hexagonal crystal structure piezoelectric material to form at least one bulk wave resonator device. An active region of the bulk wave resonator device is provided within the area where the bulk layer of hexagonal crystal structure piezoelectric material is disposed between the first and second electrode structures. Such growth steps can be performed using a single sputtering apparatus or a deposition apparatus utilizing multiple linear sputtering apparatuses, a substrate table movable between different positions proximate to the different linear sputtering apparatuses, and optionally a collimator disposed between the substrate table and each linear sputtering apparatus. In certain embodiments, at least one composite resonator device, on which the bulk layer of hexagonal crystal structure piezoelectric material is deposited, is diced into multiple chips, such as solid-state bulk wave resonator chips or thin-film bulk wave resonator chips.

[0099] In another aspect of the present disclosure, a method for fabricating at least one resonator structure includes using a first position including a first linear sputtering apparatus including a first target surface and using a second position including a second linear sputtering apparatus including a second target surface, wherein at least one wafer structure supported by a substrate table is moved to the first position where a first sub-atmospheric pressure condition is created and a first growth step is performed to deposit a first portion of a bulk layer of a hexagonal crystal structured piezoelectric material on the at least one wafer structure, and wherein the at least one wafer structure supported by the substrate table is moved to a second position where a second sub-atmospheric pressure condition is created and a second growth step is performed to deposit a second portion of a bulk layer of a hexagonal crystal structured piezoelectric material on the first portion of the bulk layer, the second portion of the bulk layer of a hexagonal crystal structured piezoelectric material having a c-axis orientation distribution substantially similar to the c-axis orientation distribution of the first portion of the bulk layer of a hexagonal crystal structured piezoelectric material. The first growth step includes metal atoms being ejected from a first target surface, (i) passing through a first deposition opening (optionally after passing through a first collimator including multiple first collimator openings), and (ii) reacting with gas species and being received by at least one wafer structure to deposit a first portion of a bulk layer of hexagonal crystal structured piezoelectric material. The second growth step includes metal atoms being ejected from a second target surface, (i) passing through a second deposition opening, and (ii) reacting with gas species and being received by the first portion to deposit a second portion of a bulk layer of hexagonal crystal structured piezoelectric material. The second growth step may or may not include the use of a collimator. In certain embodiments, the first growth step is configured to produce a first portion of a bulk layer of piezoelectric material having a hexagonal crystal structure with an orientation distribution predominantly within a range (e.g., within ±5 degrees or ±10 degrees) of a preselected angle, and the second growth step is configured to produce a second portion of a bulk layer of piezoelectric material having a hexagonal crystal structure with a c-axis having an orientation distribution predominantly within a range (e.g., within ±5 degrees or ±10 degrees) of the same preselected angle, where predominantly is intended to mean 50% or more, about 75% or more, about 90% or more, or about 95% or more of the crystals in the layer.

[0100] In certain embodiments, a substrate table supporting at least one wafer structure is introduced into the load lock chamber prior to moving the at least one wafer structure supported by the substrate table to the first location to create an initial sub-atmospheric condition within the load lock chamber. In certain embodiments, the first location and the second location are located within a single enclosure in which the first sub-atmospheric pressure condition and the second sub-atmospheric pressure condition are created. In other embodiments, the first location is located within a first chamber having an associated first vacuum pumping element, and the second location is located within a second chamber having an associated second vacuum pumping element.

[0101] In certain embodiments, the substrate has a diameter of about 50 mm or more (or about 100 mm or more, or about 150 mm or more), and the bulk layer of piezoelectric material with a hexagonal crystal structure covers about 50% or more (or 75% or more, 90% or more, or 95% or more) of the surface of the substrate. In certain embodiments, multiple bulk wave resonating devices, each including an active region between a first electrode structure and a second electrode structure, are provided on a single substrate. Multiple bulk acoustic resonator chips can be obtained (e.g., by dicing) from such a substrate and incorporated into one or more sensors and / or fluidic devices.

[0102] In one embodiment, the deposition apparatus is configured to grow a bulk layer of hexagonal crystal structure piezoelectric material directly on a substrate (without first depositing a seed layer). In another embodiment, the deposition apparatus is configured to grow a bulk layer of hexagonal crystal structure piezoelectric material on a seed layer disposed on a substrate. The substrate may be a wafer supported on a support surface, and at least 50% (or 75% or more, 90% or more, or 95% or more) of the bulk layer of hexagonal crystal structure piezoelectric material includes a c-axis with an orientation distribution that is primarily in the range of 25° to 50° (or a subrange of 30° to 40° with a peak at about 35°), or in the range of greater than 10°, greater than 27°, greater than 30°, greater than 32°, greater than 33°, greater than 34°, greater than 35°, greater than 36°, or greater than 40° relative to a normal to the surface of the substrate or wafer supported on the support surface. The orientation distribution can be about 85 degrees or less, about 80 degrees or less, about 75 degrees or less, about 65 degrees or less, about 56 degrees or less, about 52 degrees or less, about 50 degrees or less, about 49 degrees or less, or about 48 degrees or less. Such a c-axis orientation distribution is preferably substantially uniform across the area of ​​a large-area substrate (e.g., having a diameter in the range of about 50 mm or more, about 100 mm or more, or about 150 mm or more), thereby enabling multiple chips having the same or similar acoustic wave propagation characteristics to be obtained from a single substrate.

[0103] Bulk layers grown according to the methods of the present disclosure have a preselected c-axis tilt angle. The choice of the preselected c-axis tilt angle depends on the desired or intended use of the resulting crystalline bulk 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. It may be desirable to select an angle that favors shear mode resonance. 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 be about 85 degrees or less, about 75 degrees or less, about 65 degrees or less, about 56 degrees or less, about 52 degrees or less, about 50 degrees or less, about 49 degrees or less, or about 48 degrees or less. Preferred preselected angles include 35 degrees and 46 degrees. In some embodiments, the preselected angle is less than 32 degrees or greater than 46 degrees.

[0104] Piezoelectric material thin films having bulk layers according to embodiments of the present disclosure can be used in a variety of bulk acoustic wave ("BAW") devices, such as BAW resonators. A preferred BAW resonator utilizing the piezoelectric material thin films of the present disclosure is shown in Figures 6-7.

[0105] 6 is a schematic cross-sectional view of a portion of a bulk wave solid-state resonator device 50 including a piezoelectric material bulk layer 64 embodying a c-axis tilted hexagonal crystal structure piezoelectric material (e.g., AlN or ZnO) as disclosed herein. The c-axis (i.e., (002) direction) of the piezoelectric material bulk layer 64 is tilted away from a direction perpendicular to the substrate 52, as indicated by the two arrows superimposed on the piezoelectric material bulk 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 bulk layer 64, and bottom and top electrodes 60, 68. The bottom electrode 60 is disposed between the acoustic reflector 54 and the piezoelectric material bulk layer 64, and the top electrode 68 is disposed along a portion of the top surface 66 of the piezoelectric material bulk layer 64. The region of the piezoelectric material bulk layer 64 located between the overlapping portions of the top electrode 68 and the bottom electrode 60 is considered the active region 70 of the resonant device 50. The acoustic reflector 54 serves to reflect acoustic waves, thereby reducing or preventing their dissipation within the substrate 52. In certain embodiments, the acoustic reflector 54 comprises alternating thin layers 56, 58 of materials of different acoustic impedances (e.g., SiOC, Si3N4, SiO2, AlN, Mo) deposited on the substrate 52, optionally embodied in Bragg reflectors. In certain embodiments, other types of acoustic reflectors may be used. Forming the resonant device 50 may include depositing the acoustic reflector 54 on the substrate 52, followed by depositing the bottom electrode 60, followed by growing (e.g., by sputtering or other suitable method) the piezoelectric material bulk layer 64, followed by depositing the top electrode 68.

[0106] FIG. 7 is a schematic cross-sectional view of a 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). A bottom electrode 80 is disposed on a portion of the support layer 78, and includes the bottom electrode 80 and the support layer 78. A piezoelectric material bulk layer 84, which embodies a piezoelectric material with a hexagonal crystal structure with a tilted c-axis (e.g., AlN or ZnO), is disposed on the bottom electrode 80, and a top electrode 88 is disposed on at least a portion of an upper surface 86 of the piezoelectric material bulk layer 84. The portion of the piezoelectric material bulk layer 84 disposed between the top electrode 88 and the bottom electrode 80 defines an active region 90 of the FBAR device 72. The active region 90 is disposed above the cavity 76, which is disposed below the support layer 78, and is sensed using the cavity 76. The cavity 76 serves to confine acoustic waves guided within the active region 90 by preventing acoustic energy from dissipating into the substrate 74, where the waves do not efficiently propagate across the cavity 76. In this respect, the cavity 76 provides an alternative to the acoustic reflector 54 shown in Figures 6 and 7. While the cavity 76 shown in Figure 7 is bounded from below by a thin portion of the substrate 74, in other embodiments, at least a portion of the cavity 76 extends through the entire thickness of the substrate 74. Steps for forming the FBAR device 72 may include defining a cavity 76 in a substrate 74, filling the cavity 76 with a sacrificial material (not shown) and then optionally planarizing the sacrificial material, depositing a support layer 78 over the substrate 74 and the sacrificial material, removing the sacrificial material (e.g., by flowing an etchant through vertical openings defined in the substrate 74 or support layer 78 or through the outer edges of the substrate 74), depositing a bottom electrode 80 on the support layer 78, growing a bulk layer of piezoelectric material 84 (e.g., by sputtering or other suitable method), and depositing a top electrode 88.

[0107] In certain embodiments, the acoustic reflector structure is disposed between the substrate and the at least one first electrode structure to provide a solid-state mounted bulk acoustic resonator device. Optionally, the back surface of the substrate may include a roughened surface configured to reduce or eliminate acoustic reflections from the back surface. In other embodiments, the substrate defines a recess, and the support layer is disposed over the recess, the support layer being 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.

[0108] From the above disclosure of the general principles of the present invention and the foregoing detailed description, those skilled in the art will readily appreciate the various modifications, rearrangements, and substitutions to which the present invention may be adapted, as well as the various advantages and benefits that the present invention may offer. Therefore, the scope of the present invention should be limited only by the following claims and their equivalents. Additionally, it is understood that within the scope of the present invention, the articles and methods disclosed and claimed may be useful in applications other than surgical procedures. Therefore, the scope of the present invention can be broadened to include the use of the claimed and disclosed methods in such applications. [Example]

[0109] Example 1 BAW wafers (samples) and blanket films were prepared according to the methods of the present disclosure and compared to reference BAW wafers (comparison samples) and blanket films prepared according to prior art methods.

[0110] All samples, including the comparative sample, were prepared using the deposition apparatus described in U.S. patent application Ser. No. 15 / 293,063, entitled "Deposition Apparatus for Growing C-Axis Tilted Piezoelectric Material Structures."

[0111] Three wafer samples (150 mm diameter) and a blanket film were prepared by depositing the AlN crystalline bulk layer directly onto the substrate in two steps. The wafer samples were prepared by depositing the first portion of the AlN crystalline bulk layer in the first step at a deposition angle of 43 degrees, and the second portion in the second step at a deposition angle of 0 degrees (normal incidence).

[0112] During the first step (at 43°C), the deposition pressure was chosen to be 2.5 mTorr (0.33 Pa) with a 6:15 argon / nitrogen mixture. The power was 3 kW, the DC current was pulsed at 250 kHz, the target voltage was 250 V, and the target current was 12 A. The target-to-substrate distance was 100 mm. The deposition rate was 40 Å / min. The space was not heated, but due to the use of plasma, the temperature was estimated to be approximately 100°C.

[0113] During the second step (at normal incidence), the wafer substrate was placed on a fixed pedestal. The deposition pressure was selected to be 3.0 mTorr (0.40 Pa) with a 1:5 argon / nitrogen mixture. The power was 6 kW, the DC current was pulsed at 100 kHz, the target voltage was 250 V, and the target current was 12 A. The space was heated to 300 °C. A bias of 100 W was applied to the pedestal. No collimator was used. The target-to-substrate distance was 50 mm. The deposition rate was 900 Å / min.

[0114] A comparative (reference) sample (150 mm diameter) was prepared by depositing an AlN layer in one step. The AlN layer was deposited at a deposition angle of 43 degrees. The deposition pressure was selected to be 2.5 mTorr (0.33 Pa) with a 6:15 argon / nitrogen mixture. The power was 3 kW, the DC current was pulsed at 250 kHz, the target voltage was 250 V, and the target current was 12 A. The deposition rate was 40 Å / min. The space was not heated, but due to the use of plasma, the temperature was estimated to be approximately 100°C.

[0115] Blanket films were prepared to enable measurement of the c-axis angle of the AlN bulk layer crystals by X-ray diffraction. The AlN bulk layer crystals deposited on blanket films correspond to the AlN bulk layer crystals deposited on wafers under the same conditions.

[0116] The c-axis angles of the AlN bulk layer crystals on the sample blanket films and on the control blanket films were measured using a standard X-ray diffractometer equipped with a pole figure goniometer. Note that the deposition angles given in this example are the nominal settings of the deposition equipment, and there may be some variation in the actual angular range over which the deposition flux contacts the substrate. However, the relative amplitudes of the angles are still comparable.

[0117] The results for the sample blanket membranes are shown graphically in Figures 8A and 8B, and the results for the comparative (reference) blanket membranes are shown graphically in Figures 9A and 9B.

[0118] It was observed that applying normal incidence to the bulk of the layer allowed for much higher throughput than usual. Deposition at normal incidence was achieved without a collimator at 900 Å / min. The deposition rate resulted in a significant improvement in throughput and efficiency.

[0119] The sample fabricated by the two-step method with a normal incidence second step had a c-axis tilt angle of approximately 35°, as seen in pole figures 8A and 9A, respectively, similar to the control sample. The bulk layer crystallites deposited at normal incidence were observed to be aligned with the crystallites applied in the first step. The crystallites in the first step are believed to act as a template for the subsequent bulk layer.

[0120] The effective electromechanical coupling coefficient and effective mechanical quality factor of each wafer were evaluated by probing the scattering (S) parameter matrix of the sample using a vector network analyzer to extract resonator performance characteristics. Electrical probing was performed at 100 locations on each wafer, and the results were calculated as normalized average values.

[0121] Quality factor (Q value) and effective coupling coefficient (k 2 effThe method for calculating the quality factor is based on KM Lakin's "Modeling of Thin Film Resonators and Filters," IEEE MTT-S Microwave Symposium Digest, 1992, pp. 149-152. The quality factor is determined using the following formula:

[0122]

number

[0123] The effective coupling coefficient is the series (f s ) resonant frequency and parallel (f p ) is determined by measuring the resonant frequency and using the following formula:

[0124]

number

[0125] The results are the electromechanical coupling coefficient (k e ) 2 This is shown graphically in Figure 10, which shows the mechanical quality factor (Q-factor) normalized to a comparative (reference) sample, and in Figure 11, which shows the mechanical quality factor (Q-factor) normalized to a comparative (reference) sample.

[0126] The electrical performance of sample thin films according to the present disclosure grown under deposition conditions was observed to be comparable to that of the control (baseline) sample, and the mechanical quality factor (Q) measured on wafer samples was comparable to or slightly greater (approximately 1.1 times) than the control (baseline) sample.

[0127] Example 2 Sample and control films were prepared as in Example 1. The surface roughness of the films was examined using atomic force microscopy (AFM) using a Dimension 5000 instrument from Bruker Corp., Billerica, Massachusetts (formerly available from Digital Instruments).

[0128] The thin films were sectioned using a focused ion beam (FIB) to obtain cross-sectional microscopy images. An FEI Nova Nanolab 600I SEM (scanning electron microscope) equipped with a FIB was used for sectioning and SEM imaging. High-resolution scanning tunneling electron microscope (STEM) images were obtained using a Hitachi 2300A STEM. SEM images of the surfaces of the sample and comparative thin films are shown in Figure 12 (100,000x magnification). Cross-sectional STEM images are shown in Figure 13 (100,000x magnification). Note that the predominant grain structure seen in the images is a bulk grain structure, as opposed to a c-axis tilt. Cross-sectional STEM images showing the seams (sample thin films) or gaps (comparative thin films) of the deposited layers are shown in Figure 14. The results are shown in Table 1 below. [Table 1]

[0129] The sample films were observed to have less surface roughness than the control films. Additionally, the sample films were observed to have a more uniform film thickness than the control films, with film thickness variations of less than 2%, as opposed to over 2% for the control films.

[0130] It is hypothesized that prior art methods result in the formation of gaps at the edges of the bulk film due to shadowing effects during deposition. It was observed that the sample thin films did not exhibit gaps, and only seams were visible where the comparative thin films exhibited gaps.

[0131] Example 3 To test the shear strength of the bumps on biosensors fabricated using blanket films, bump samples were fabricated according to the schematic diagram in Figure 15. The bump samples were fabricated on the sample thin film fabricated according to Example 1 and on the control thin film.

[0132] The bump samples were subjected to shear testing using a shear adhesion measurement tool, which is sometimes used to test the shear force resistance of products during manufacturing. The shear testing was performed at the wafer level, with 20 measurements performed on one wafer. The bumps on the comparative thin film showed some reliability issues due to substrate tearing and cracking. Typical failure modes for bumps on the sample thin film and the comparative thin film can be seen in the images in Figure 16. The bumps on the comparative thin film broke due to substrate tearing, unlike the bumps on the sample thin film. It can also be seen that the bumps on the sample thin film still retain some copper after failure, while the bumps on the comparative thin film do not. The sample thin film also produced bumps with greater resistance to shear stress, as can be seen in the graphical representation in Figure 17. The bumps on the sample thin film broke when subjected to shear forces ranging from 125 g (1.22 N) to 160 g (1.57 N). The bumps of the comparative thin film broke when subjected to shear forces ranging from 50 g (0.49 N) to 150 g (1.47 N). It was also observed that the bumps of the comparative thin film showed greater variation in shear strength.

[0133] Furthermore, resonators made using the sample thin films were observed to have smaller variations in fs (series resonance frequency) and dry gain than resonators made from the control thin films. The electrical performance of the resonators was measured by making electrical contact with the thin films. The variation in fs of the resonators made from the sample thin films was less than ±100 MHz, while the variation in fs of the resonators made from the control thin films exceeded ±100 MHz. The variation in dry gain of the resonators made from the sample thin films was less than 2%, while the variation in dry gain of the resonators made from the control thin films exceeded 2%.

[0134] The results of Examples 1-3 demonstrate that the disclosed method, in which deposition in the second step is performed at a normal incidence angle, can be used to deposit a bulk layer in two steps, resulting in a bulk layer that is at least comparable to, or superior to, bulk layers deposited using prior art methods. The bulk layer exhibits reduced surface roughness and greater thickness uniformity. Structures fabricated using the bulk layer exhibit greater shear strength. The improved quality of the bulk layer leads to process improvements, such as greater process throughput and lower processing costs.

Claims

1. a substrate comprising a wafer or a portion of said wafer; a piezoelectric bulk material layer including a first portion deposited on the substrate and a second portion deposited on the first portion, the second portion having an outer surface with a surface roughness (Ra) of 4.5 nm or less; A structure comprising:

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

3. 3. The structure of claim 1 or 2, further comprising a bump disposed at least partially in the bulk material layer, the bump being capable of withstanding a shear force of 120 g (1.18 N) or greater.

4. The structure of any one of claims 1 to 3, further comprising a bump disposed at least partially in the bulk material layer, the bump being capable of withstanding a shear force of 125g (1.23N) or greater.

5. The structure of any one of claims 1 to 4, wherein the first portion has a first c-axis tilt and the second portion has a second c-axis tilt substantially aligned with the first c-axis tilt.

6. 6. The structure of claim 5, wherein the first c-axis tilt is between about 35 degrees and about 52 degrees.

7. 7. The structure of claim 1, wherein the first portion has a first bulk grain orientation and the second portion has a second bulk grain orientation, the second bulk grain orientation being different from the first portion.

8. 8. The structure of claim 7, wherein the second bulk grain orientation is substantially vertical.

9. The structure of any preceding claim, wherein the bulk piezoelectric material layer comprises AlN.

10. 10. The structure of any one of claims 1 to 9, wherein the bulk material layer exhibits a shear bond to longitudinal bond ratio of 1.25 or greater during excitation.

11. The structure of any one of claims 1 to 10, wherein the bulk material layer has a thickness of about 1,000 Angstroms to about 30,000 Angstroms, the thickness varying by less than 2% across the area of ​​the bulk material layer.

12. The structure is depositing a first portion of the bulk material layer having a first c-axis tilt onto a substrate at a first angle of incidence; depositing a second portion of the bulk material layer having a second c-axis tilt substantially aligned with the first c-axis tilt onto the first portion at a second angle of incidence less than the first angle of incidence; The structure of any one of claims 1 to 11, produced by

13. 13. The structure of claim 12, wherein the first portion, the second portion, or both are deposited under deposition conditions comprising a pressure of less than 5 mTorr (0.67 Pa).

14. 14. The structure of claim 13, wherein the pressure is between about 1 mTorr (0.13 Pa) and about 4 mTorr (0.53 Pa).

15. 15. A bulk wave resonator comprising the structure of any one of claims 1 to 14, further comprising a first electrode and a second electrode, wherein at least a portion of the piezoelectric bulk material layer is between the first electrode and the second electrode.

16. a plurality of acoustic resonator structures fabricated from a single wafer, the wafer having a surface and a piezoelectric bulk material layer deposited on the surface, the piezoelectric bulk material layer having a first portion of the bulk material layer deposited at a first angle of incidence and a second portion of the bulk material layer deposited on the first portion at a second angle of incidence less than the first angle of incidence; the plurality of acoustic resonator structures exhibit a variation in resonant frequency of up to 100 MHz above or below a nominal frequency; A plurality of acoustic resonator structures.

17. 17. The plurality of acoustic resonator structures of claim 16, wherein the plurality of acoustic resonator structures exhibit a variation in dry gain of 10% or less between test conditions.

18. 18. The plurality of acoustic resonator structures of claim 16 or 17, wherein the second portion has an outer surface with a surface roughness (Ra) of 4.5 nm or less.

19. a plurality of acoustic resonator structures fabricated from a single wafer, the wafer having a surface and a piezoelectric bulk material layer deposited on the surface, the piezoelectric bulk material layer having a first portion of the bulk material layer deposited at a first angle of incidence and a second portion of the bulk material layer deposited on the first portion at a second angle of incidence less than the first angle of incidence; the plurality of acoustic resonator structures exhibiting a dry gain variation of 10% or less between test conditions; A plurality of acoustic resonator structures.

20. 20. The plurality of acoustic resonator structures of claim 19, wherein the second portion comprises an outer surface having a surface roughness (Ra) of 4.5 nm or less.

Images