TRANSVERSALLY EXCITED ACOUSTIC FILM VOLUME RESONATOR WITH Etching Stop Layer

Abstract

Acoustic resonator device comprising: a substrate (120) with a surface; a piezoelectric plate (110, 310, 410, 510, 610) with front and back surfaces (412, 114) and at least one opening (342, 442, 542, 642) extending through the piezoelectric plate (110, 310, 410, 510, 610); an etch stop layer (450) sandwiched between the surface of the substrate (120) and the back surface (114) of the piezoelectric plate (110, 310, 410, 510, 610), wherein a region of the piezoelectric plate (110, 310, 410, 510, 610) and the etch stop layer (450) form a membrane form a cavity in the substrate (120);and an interdigital transducer (130) (interdigital transducer, IDT) formed on the front surface (412) of the piezoelectric plate (110, 310, 410, 510, 610), wherein nested fingers (136) of the IDT (130) are arranged on the membrane, wherein the etch stop layer (450) is impermeable to an etching process using an etchant introduced through the at least one opening (342, 442, 542, 642) used to form the cavity in the substrate (120), the thickness of the etch stop layer (450) being less than or equal to 20% of the thickness of the piezoelectric plate (110, 310, 410, 510, 610), and wherein the spacing of the IDT (130) between the 2- and 20 times the thickness of the piezoelectric plate (110, 310, 410, 510, 610), wherein the distance is a center-to-center distance between an adjacent pair of fingers (136) of the nested fingers (136).

Description

BACKGROUND area

[0001] This disclosure relates to high-frequency filters that use acoustic wave resonators, and in particular filters for use in communication equipment. Description of the related prior art

[0002] A high-frequency filter (HF filter) is a two-port device configured to pass some frequencies and block others, where "pass" means transmission with relatively little signal loss and "block" means blocking or significant attenuation. The range of frequencies passed by a filter is called the filter's "passband." The range of frequencies blocked by such a filter is called the filter's "stopband." A typical RF filter has at least one passband and at least one stopband. Specific requirements for a passband or stopband depend on the specific application. For example, a "passband" might be defined as a frequency range in which the insertion loss of a filter is better than a defined value such as 1 dB, 2 dB, or 3 dB.A "stopband" can be defined as a frequency range in which the suppression of a filter is greater than a defined value such as 20 dB, 30 dB, 40 dB or more, depending on the application.

[0003] RF filters are used in communication systems where information is transmitted wirelessly. Examples include the RF front ends of cellular base stations, mobile phones and computers, satellite transceivers and ground stations, IoT (Internet of Things) devices, laptops and tablets, fixed-point radio links, and other communication systems. RF filters are also used in radar and electronic warfare systems.

[0004] RF filters typically require many design compromises to achieve the best balance between performance parameters such as insertion loss, suppression, isolation, power handling, linearity, size, and cost for each specific application. Specific design and manufacturing methods and improvements can simultaneously benefit one or more of these requirements.

[0005] Improvements to the RF filters in a wireless system can have a broad impact on system performance. RF filter enhancements can be used to implement system performance improvements such as larger cells, longer battery life, higher data rates, greater network capacity, lower costs, improved security, and higher reliability. These improvements can be implemented at many levels of the wireless system, both individually and in combination, for example, at the RF module, RF transceiver, mobile or fixed subsystem, or network level.

[0006] The desire for wider communication channel bandwidths will inevitably lead to the use of higher-frequency communication bands. The current LTE™ (Long Term Evolution) specification defines frequency bands from 3.3 GHz to 5.9 GHz. Some of these bands are currently unused. Future proposals for wireless communications include millimeter-wave communication bands with frequencies up to 28 GHz.

[0007] High-performance RF filters for current communication systems typically incorporate acoustic wave resonators, including surface acoustic wave resonators (SAW resonators), bulk acoustic wave resonators (BAW resonators), film bulk acoustic wave resonators (FBAR resonators), and other types of acoustic resonators. However, these existing technologies are not well-suited for use at the higher frequencies proposed for future communication networks. List of characters Fig. Figure 1 contains a schematic top view and two schematic cross-sectional views of a transversely excited acoustic film volume resonator (XBAR). Fig. Figure 2 is an extended schematic cross-sectional view of an area of ​​the XBAR. Fig. 1. Fig. Figure 3 is an alternative schematic cross-sectional view of the XBAR. Fig. 1. Fig. 4A is a schematic cross-sectional view of an XBAR with an etch stop layer and backside etched cavities. Fig. 4B is a schematic cross-sectional view of an XBAR with an etch stop layer and cavities etched on the front. Fig. 5A is a schematic cross-sectional view of an XBAR with an etch stop layer, a bonding layer and backside etched cavities. Fig. 5B is a schematic cross-sectional view of an XBAR with an etch stop layer, a bonding layer and front-etched cavities. Fig. Figure 6A is a schematic cross-sectional view of an XBAR with an etch stop layer, a backside dielectric layer and backside etched cavities. Fig. Figure 6B is a schematic cross-sectional view of an XBAR with an etch stop layer, a bonding layer, a backside dielectric layer and frontside etched cavities. Fig. Figure 7 is a flowchart of a process for manufacturing an XBAR with an etch stop layer.

[0008] In this description, elements appearing in drawings are assigned three- or four-digit reference identifiers, where the two least significant digits are specific to the element and the one or two most significant digits are the drawing number in which the element is first introduced. For an element not described in connection with a drawing, it can be assumed to have the same characteristics and function as a previously described element with the same reference identifier. DETAILED DESCRIPTION Device description

[0009] Fig. Figure 1 shows a simplified schematic top view and orthogonal cross-sectional views of a transversely excited acoustic film volume resonator (XBAR) 100 XBAR resonators, such as the resonator 100 XBARs can be used in a variety of RF filters, including bandstop filters, bandpass filters, duplexers, and multiplexers. They are particularly well-suited for use in filters for communication bands with frequencies above 3 GHz.

[0010] The XBAR 100 consists of a thin-film conductor structure mounted on the surface of a piezoelectric plate 110 with parallel front and back surfaces 112 or 114The piezoelectric plate is a thin single-crystal layer of a piezoelectric material such as lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, or aluminum nitride. The piezoelectric plate is cut such that the orientation of the X, Y, and Z crystal axes with respect to the front and back surfaces is known and consistent. In the examples shown in this patent, the piezoelectric plates are Z-cut, i.e., the Z-axis is perpendicular to the surfaces. However, XBARs can be fabricated on piezoelectric plates with other crystallographic orientations.

[0011] The back surface 114 the piezoelectric plate 110 is on a substrate 120 attached to the piezoelectric plate 110 provides mechanical support. The substrate 120 The substrate can consist of, for example, silicon, sapphire, quartz, or another material. 120It can be a composite material made of two or more materials. For example, the substrate can be... 120 They consist of a first material such as silicon with an inserted island of a second material such as silicon dioxide or phosphosilicate glass (PSG). The inserted island can then be removed to form a cavity, which is described below. The piezoelectric plate 110 can be bonded to a surface of the substrate using a wafer bonding process 120 bonded or onto the substrate 120 The piezoelectric plate can be grown on the substrate or attached to it in some other way. It can be attached directly to the substrate or via a bonding interlayer. 122 to be attached to the substrate. If the substrate 120 For example, silicon can form the bonding layer 122 consist of silicon dioxide.

[0012] The ladder structure of the XBAR 100contains an interdigital transducer (IDT) 130 The IDT 130 contains a first multitude of parallel fingers, such as the finger 136 , which branch off from a first busbar 132 extend, and a second multitude of fingers extending from a second busbar 134 extend. The first and second sets of parallel fingers are nested. The nested fingers overlap over a distance AP, commonly referred to as the "aperture" of the IDT. The center-to-center distance L between the outermost fingers of the IDT 130 is the "length" of the IDT.

[0013] The first and second busbar 132 , 134 serve as connections of the XBAR 100 A high-frequency or microwave signal that is transmitted between the two busbars 132 , 134 of the IDT 130 When applied, it stimulates an acoustic wave within the piezoelectric plate.110 As will be explained in more detail below, the excited acoustic wave is a volume shear wave that propagates along a direction orthogonal to the surface of the piezoelectric plate. 110 The XBAR's path runs perpendicular or transversely to the direction of the electric field generated by the IDT fingers. Therefore, the XBAR is considered a transversely excited film volume wave resonator.

[0014] A cavity 140 is in the substrate 120 so formed that an area 115 the piezoelectric plate 110 , which the IDT 130 contains, above the cavity 140 is suspended without the substrate 120 to touch. “Cavity” has its usual meaning of “an empty space within a solid body”. The cavity 140 It could be a hole that goes completely through the substrate. 120passes through (as shown in Section AA and Section BB) or a recess in the substrate 120 (as below in Fig. 3 shown). The cavity 140 can be achieved, for example, by selectively etching the substrate 120 before or after attaching the piezoelectric plate 110 and the substrate 120 be formed. As in Fig. As shown in 1, the cavity 140 a rectangular shape with an extent that is larger than the aperture AP and the length L of the IDT 130 The cavity of an XBAR can have a different shape, such as a regular or irregular polygon. The cavity of an XBAR can have more or fewer than four sides, which can be straight or curved.

[0015] The area 115 the piezoelectric plate that is above the cavity 140The suspended element is referred to here (for lack of a better term) as a "diaphragm" due to its physical similarity to the diaphragm of a microphone. The diaphragm can be continuously and seamlessly connected to the rest of the piezoelectric plate. 110 around the entire or almost the entire circumference of the cavity 140 be connected around.

[0016] To display in Fig. To facilitate the process, the geometric spacing and width of the IDT fingers are greatly exaggerated in relation to the length (dimension L) and aperture (dimension AP) of the XBAR. A typical XBAR has more than ten parallel fingers in the IDT. 110 An XBAR can have hundreds, possibly thousands, of parallel fingers in the IDT. 110 The thickness of the fingers in the cross-sectional views is also greatly exaggerated.

[0017] Fig. Figure 2 shows a detailed schematic cross-sectional view of the XBAR. 100 from Fig. 1. The piezoelectric plate 110 is a single-crystal layer of piezoelectric material with a thickness ts. ts can be, for example, 100 nm to 1500 nm. When used in filters for LTE™ bands from 3.4 GHz to 6 GHz (e.g., bands 42 , 43 , 46 ) the thickness ts can be, for example, 200 nm to 1000 nm.

[0018] A front-side dielectric layer 214 can optionally be placed on the front of the piezoelectric plate 110 be formed. The "front side" of the XBAR is, by definition, the surface facing away from the substrate. The front-side dielectric layer 214 has a thickness tfd. The front-side dielectric layer 214 is between the IDT fingers 238 formed. Although in Fig. 2 not shown, the front-side dielectric layer 214 also over the IDT fingers 238 be deposited. A backside dielectric layer 216can optionally be placed on the back of the piezoelectric plate 110 be formed. The rear dielectric layer 216 has a thickness of tbd. The front and back dielectric layers 214 , 216 They can consist of a non-piezoelectric dielectric material, such as silicon dioxide or silicon nitride; tfd and tbd can be, for example, 0 to 500 nm thick. tfd and tbd are typically smaller than the thickness ts of the piezoelectric plate; tfd and tbd are not necessarily equal; and the front and back dielectric layers 214 , 216 They do not necessarily consist of the same material. One or both of the front and back dielectric layers. 214 , 216 can be formed from multiple layers of two or more materials.

[0019] The IDT fingers 238They can be made of aluminum or an alloy essentially of aluminum, copper or an alloy essentially of copper, beryllium, gold, or another conductive material. Thin (relative to the overall thickness of the conductors) layers of other metals, such as chromium or titanium, can be formed under and / or over the fingers to improve adhesion between the fingers and the piezoelectric plate. 110 to improve and / or to passivate or encapsulate the fingers. The busbars ( 132 , 134 in Fig. 1) The IDTs can be made of the same or different materials as the fingers.

[0020] Dimension p is the center-to-center distance or "pitch" of the IDT fingers, which can be referred to as the IDT spacing and / or the XBAR spacing. Dimension w is the width or "mark" of the IDT fingers. The IDT of an XBAR differs significantly from the IDTs used in surface acoustic wave resonators (SAW resonators). In a SAW resonator, the IDT spacing is half the acoustic wavelength at the resonant frequency. Furthermore, the mark-to-pitch ratio of a SAW resonator IDT is typically close to 0.5 (i.e., the mark or finger width is about one-quarter of the acoustic wavelength at the resonant frequency). In an XBAR, the IDT spacing p is typically 2 to 20 times the width w of the fingers. Additionally, the IDT spacing p is typically 2 to 20 times the thickness ts of the piezoelectric plate. 212The width of the IDT fingers in an XBAR is not limited to a quarter of the acoustic wavelength at resonance. For example, the width of the XBAR IDT fingers can be 500 nm or more, allowing the IDT to be fabricated using optical lithography. The thickness tm of the IDT fingers can range from 100 nm to approximately equal to the width w. The thickness of the busbars ( 132 , 134 in Fig. 1) The IDT can be equal to or greater than the thickness tm of the IDT fingers.

[0021] Fig. 3 is an alternative cross-sectional view along the in Fig. 1 defined cutting plane AA. In Fig. 3 is a piezoelectric plate 310 on a substrate 320 applied. A bonding layer 322 can be between the piezoelectric plate 310 and the substrate 320 be present. A cavity 340 , which the substrate 320 does not penetrate completely, is in the substrate320 (and the bonding layer) 322 , if present) under the area of ​​the piezoelectric plate 310 formed, which contains the IDT of an XBAR. The cavity 340 can be done, for example, by etching the substrate 320 formed with a selective etching agent that passes through the substrate through one or more openings 342 achieved in the piezoelectric plate 310 are provided. If the bonding layer 322 If present, the bonding layer can also be etched with a selective etching agent that passes through the one or more openings of the bonding layer. 342 reached.

[0022] The in Fig. 3 XBARs shown 300 is referred to here as a "front-side etching configuration" because the cavity 340 from the front of the substrate 320 is etched. The XBAR 100 from Fig. 1 is referred to here as a "backside etching configuration" because the cavity 140 from the back of the substrate 120 after attaching the piezoelectric plate 110 is etched.

[0023] Fig. 4A is a schematic cross-sectional view of an XBAR device. 400A with an etch-stop layer and back-etched cavities. The XBAR device 400A contains two XBARs, each of which corresponds to the XBAR 100 from Fig. 1 is similar. A back surface 414 a piezoelectric plate 410 is on a substrate 420 Attached to the front surface. 412 the piezoelectric plate 410 An electrode structure is formed. The electrode structure comprises nested fingers. 430 of the respective IDTs for the two XBARs. The IDT fingers 430 are above corresponding cavities 440A arranged in the substrate 420The materials of the piezoelectric plate, the substrate, and the electrode structure are as previously described.

[0024] The main difference between the XBAR device 400A and the XBAR 100 from Fig. 1 is the presence of an etch stop layer 450 , sandwiched between the piezoelectric plate 410 and the substrate 420 is arranged. The term "sandwich-like" means that the etch stop layer 450 both between a surface of the substrate 420 and the back surface 414 the piezoelectric plate 410 is arranged and physically connected to these. In some embodiments, as described below, layers of additional materials can be placed between the etch stop layer. 450 and the surface of the substrate 420 and / or between the etch stop layer 450 and the back surface 414the piezoelectric plate 410 be arranged. With the XBAR device 400A is the piezoelectric plate 410 not directly attached to the substrate 420 bonded, but via the etch stop layer 450 on the substrate 420 appropriate.

[0025] The cavities 440A These are formed using an etching process to remove material from the substrate. The etching process can be a "wet process," using a liquid etchant, or a "dry process," such as reactive ion etching or sputter etching, using a gaseous etchant. As indicated by the dashed arrow 460A As shown, the etching process starts from the back surface of the substrate and gradually removes material from the substrate until the cavities are filled. 440A are formed. In the absence of the etch stop layer 450 would at least one area of ​​the back surface 414 the piezoelectric plate410 the etching process 460 be suspended. The performance of the XBAR 400A It is sensitive to the thickness of the piezoelectric plate and – at least to some extent – ​​to the flatness of the back surface. 414 Any erosion of the back surface 414 through the etching process 460 can the performance of the XBAR 400A negatively affect.

[0026] The etch stop layer 450 protects the back surface 414 before the etching process. For this purpose, the etch stop layer is used. 450 impermeable to the force indicated by the dashed arrow 460A The etching process is described. The word "impermeable" has several definitions, including "not affected by" and "not permeable to liquid." Both definitions apply to the etch stop layer. 450The etch stop layer is not significantly affected by the etching process and prevents the liquid or gaseous etchant used in the etching process from reaching the piezoelectric layer. 410 penetrate. The etch stop layer does not need to be inert to the etchant, but it must exhibit high resistance to the etchant so that a substantial area of ​​the etch stop layer remains after the cavity etching is complete. The remaining etch stop layer 450 after the formation of the cavities 440A not removed and becomes part of the membranes of the XBAR devices.

[0027] The etch stop layer 450The etch stop material is formed from an etch stop material. This etch stop material must be a dielectric with very low conductivity and low acoustic loss. It must exhibit strong adhesion to the surface(s) on which it is formed. Furthermore, the etch stop material must be compatible with the attachment of the piezoelectric plate to the substrate using a wafer bonding process. Most importantly, as previously defined, the etch stop material must be impermeable to the processes and chemicals used to etch the substrate material. Suitable etch stop materials include oxides such as aluminum oxide and silicon dioxide, sapphire, nitrides including silicon nitride, aluminum nitride, and boron nitride, silicon carbide, and diamond.

[0028] If the etch stop material is a dielectric with high thermal conductivity, such as aluminum nitride, boron nitride or diamond, the etch stop layer helps to dissipate heat from the XBAR membrane.

[0029] As described in patent 10,491,192, a dielectric layer can 470 selectively on the front side of the piezoelectric plate 410 about the IDTs 430Some XBARs may be formed. For example, a frequency-tuning dielectric layer can be formed over the IDTs of shunt resonators to lower their resonant frequencies compared to the resonant frequencies of series resonators in a filter. The electromechanical coupling efficiency of an XBAR can be reduced and interference modes improved if the total thickness of the dielectric layers on the front and back surfaces of the piezoelectric plate exceeds approximately 35% of the plate's thickness. Furthermore, filters designed for wide communication bands, such as the 10 band, can be further enhanced. N77 and band N79 They are designed to require a frequency-setting layer with a thickness of 20% to 30% of the thickness of the piezoelectric plate. To allow flexibility in choosing the thickness of the frequency-setting layer, the thickness t can be es the etch stop layer 450less than or equal to 10% of the thickness of the piezoelectric plate, and preferably about 4% to 6% of the thickness of the piezoelectric plate. If no frequency-adjusting dielectric layer is used, the thickness t can be es less than approximately 20% of the thickness of the piezoelectric plate.

[0030] Fig. 4B is a schematic cross-sectional view of an XBAR device. 400B with an etch-stop layer and cavities etched on the front. The XBAR device 400B contains two XBARs, each of which corresponds to the XBAR 100 out of Fig. 1 is similar. A back surface of a piezoelectric plate 410 is on a substrate 420 applied. An etch stop layer. 450 is sandwich-like between the piezoelectric plate 410 and the substrate 420 An electrode structure is arranged on the front surface of the piezoelectric plate. 410formed. The electrode structure contains nested fingers. 430 of the respective IDTs for the two XBARs. The IDT fingers 430 are above the corresponding cavities 440B arranged in the substrate 420 are formed. The materials and properties of the piezoelectric plate 410 , of the substrate 420 , the etch stop layer 450 and the electrode structure 430 are as described above.

[0031] The main difference between the XBAR device 400B and the XBAR device 400A from Fig. 4A is the etching process used to create the cavities. 440B is used. The cavities 440B are produced using an etching process, represented by the dashed arrow 460B , formed using an etching agent that passes through the openings 442 in the piezoelectric plate 410 and the underlying etch stop layer 450is introduced.

[0032] Fig. 5A is a schematic cross-sectional view of an XBAR device. 500A with an etch-stop layer and back-etched cavities. The XBAR device 500A contains two XBARs, each of which corresponds to the XBAR 100 from Fig. 1 is similar. A back surface 514 a piezoelectric plate 510 is above an etch stop layer 550 on a substrate 520 An electrode structure is attached to the front surface. 512 the piezoelectric plate 510 formed. The electrode structure contains nested fingers. 530 of the respective IDTs for the two XBARs. The IDT fingers 530 are about the corresponding one in the substrate 520 formed cavities 540A arranged. The materials of the piezoelectric plate 510 , of the substrate 520 and the electrode structure 530 are as described above.

[0033] The main difference between the XBAR device 500A and the XBAR device 400A from Fig. 4A is the presence of a bonding layer 522 between the etch stop layer 550 and the substrate 520 In this case, the etch stop layer 550 not directly attached to the substrate 520 bonded, but via the bonding layer 522 on the substrate 520 attached. The bonding layer 522 is a material that is both on the substrate 520 as well as on the etching stop layer 550 adheres to or bonds with them. If the substrate consists of silicon, for example, the bonding layer can consist of grown or deposited silicon dioxide.

[0034] The cavities 540A are produced using an etching process (represented by the dashed arrow). 560A)Etching is a process formed to remove material from the substrate. The etching process can be a "wet process," using a liquid etchant, or a "dry process," such as reactive ion etching or sputter etching, using a gaseous etchant. The etching process starts from the back surface of the substrate and gradually removes material until the cavities are filled. 540A through the substrate 520 are open through it. The same or a different etching process can then be used to remove the bonding layer on the top side (as in Fig. (shown in 5A) of the cavity. The etch stop layer 550 It is at least impermeable to the bonding layer removal process. The etch stop layer can consist of one of the previously identified etch stop materials.

[0035] Fig. 5B is a schematic cross-sectional view of an XBAR device. 500Bwith an etch-stop layer and cavities etched on the front. The XBAR device 500B contains two XBARs, each of which corresponds to the XBAR 100 from Fig. 1 is similar. The back surface of a piezoelectric plate 510 is over an etch stop layer 550 and a bonding layer 522 on a substrate 520 applied. The etch stop layer 550 It is sandwiched between the piezoelectric plate 510 and the bonding layer 522 The bonding layer 522 is sandwiched between the etch stop layer 550 and the substrate 520 On the front surface of the piezoelectric plate 510 An electrode structure is formed. The electrode structure comprises nested fingers. 530 of the respective IDTs for the two XBARs. The IDT fingers 530 are above corresponding cavities 540B arranged in the substrate 520are formed. The materials and properties of the piezoelectric plate 510 , of the substrate 520 , the etch stop layer 550 , the bonding layer 522 and the electrode structure 530 are as described above.

[0036] The main difference between the XBAR device 500B and the XBAR device 500A from Fig. 5A is the etching process used to create the cavities 540B is used. The cavities 540B are produced using an etching process, represented by the dashed arrow 560B , formed using an etching agent that passes through openings 542 in the piezoelectric plate 510 , the underlying etch stop layer 550 and the bonding layer 522 is introduced.

[0037] Fig. 6A is a schematic cross-sectional view of an XBAR device. 600Awith an etch-stop layer and back-etched cavities. The XBAR device 600A contains two XBARs, each of which corresponds to the XBAR 100 from Fig. 1 is similar. A back surface 614 a piezoelectric plate 610 is via a rear-side dielectric layer 616 and an etch stop layer 650 on a substrate 620 Attached to the front surface. 612 the piezoelectric plate 610 An electrode structure is formed. The electrode structure comprises nested fingers. 630 of the respective IDTs for the two XBARs. The IDT fingers 630 are above corresponding cavities 640A arranged in the substrate 620 are formed. The materials of the piezoelectric plate 610 , of the substrate 620 , the etch stop layer 650 and the electrode structure 630 are as described above.

[0038] The main difference between the XBAR device 600A and the XBAR device 400A from Fig. 4A is the presence of the backside dielectric layer 616 between the piezoelectric plate 610 and the etch stop layer 650 The rear dielectric layer 616 This could, for example, be a layer of silicon dioxide to ensure temperature compensation, i.e., the temperature coefficient of the resonator's frequency. 600A to reduce. As described in application 16 / 819,623, the backside dielectric layer can be 616 Another example would be a layer of silicon dioxide with half the wavelength. The backside dielectric layer 616 It can be made of a different dielectric material and have a thickness other than half a wavelength.

[0039] The cavities 640A are produced using an etching process (represented by the dashed arrow).660A) Formed to remove material from the substrate. The etch stop layer 650 It is impermeable to the etching process used to create the cavities. The etch stop layer can consist of one of the previously identified etch stop materials.

[0040] Fig. Figure 6B is a schematic cross-sectional view of an XBAR device. 600B with an etch-stop layer and cavities etched on the front. The XBAR device 600B contains two XBARs, each of which corresponds to the XBAR 100 from Fig. 1 is similar. A back surface of a piezoelectric plate 610 is via a rear-side dielectric layer 616 and an etch stop layer 650 on a substrate 620 applied. The etch stop layer 650 is sandwiched between the rear dielectric layer 616 and the substrate 620 On the front surface of the piezoelectric plate 610An electrode structure is formed. The electrode structure comprises nested fingers. 630 the respective IDTs for the two XBARs The IDT fingers 630 are above corresponding cavities 640B arranged in the substrate 620 are formed. The materials and properties of the piezoelectric plate 610 , of the substrate 620 , the etch stop layer 650 , the rear dielectric layer 616 and the electrode structure 630 are as described above.

[0041] The main difference between the XBAR device 600B and the XBAR device 600A from Fig. 6A is the etching process used to form the cavities. 640B is used. The cavities 640B are produced using an etching process, represented by the dashed arrow 660B , formed using an etching agent that passes through openings 642 in the piezoelectric plate 610, the underlying backside dielectric layer 616 and the etch stop layer 650 is introduced.

[0042] An XBAR device can create both a bonding layer (e.g., the bonding layer) 522 from Fig. 5A and Fig. 5B) as well as a rear-side dielectric layer (e.g. the rear-side dielectric layer) 616 from Fig. 6A and Fig. 6B). Procedure description

[0043] Fig. 7 is a simplified flowchart that shows a process 700 for the manufacture of a device that can be an XBAR or a filter with XBARs. The process 700 It begins at 705 with a substrate and a plate made of piezoelectric material and ends at 795 with a finished device. The flowchart of Fig. Section 7 contains only important process steps. Various conventional process steps (e.g., surface preparation, cleaning, inspection, curing, annealing, monitoring, testing, etc.) can be performed before, between, after, and during the process. Fig. The 7 steps shown must be carried out.

[0044] The flowchart of Fig. Figure 7 shows four variations of the process. 700 for the production of devices that differ in when and how cavities are formed in the substrate and whether or not there is a bonding layer separate from the etch stop layer. The cavities can be created in the following steps. 760A or 760B be formed. In each of the four variants of the process. 700 Only one of these steps is performed. The activity at 710 may or may not be carried out. The four variations of the process lead to the six configurations of the XBAR devices, as shown in Fig. 4A, Fig. 4B, Fig. 5A, Fig. 5B, Fig. 6A and Fig. 6B is shown.

[0045] The piezoelectric plate can be made of, for example, lithium niobate or lithium tantalate, in which case the crystalline orientation can be Z-cut, twisted Z-cut, or twisted YX-cut. The piezoelectric plate can be made of a different material and / or have a different cut. The substrate can preferably be silicon. The substrate can be made of a different material that allows the formation of deep cavities by etching or other processing.

[0046] At 710A bonding layer can be formed either by growing or depositing a bonding material onto the substrate surface. The bonding material must be a dielectric with very low conductivity and exhibit high adhesion to the substrate surface. Furthermore, the bonding material must be compatible with the wafer bonding process used to attach the piezoelectric plate to the substrate. For example, if the substrate is silicon, the bonding material can be silicon dioxide, which is either grown or deposited onto the substrate. A bonding layer is not strictly necessary on a silicon substrate. Other substrate materials, such as glass, quartz, and sapphire, may not require a bonding layer.

[0047] At 715Optionally, a backside dielectric layer can be formed by depositing a dielectric material onto the back surface of the piezoelectric plate. The backside dielectric must consist of a dielectric material with very low conductivity and exhibit high adhesion to the surface of the piezoelectric plate. Furthermore, the backside dielectric material must possess specific acoustic properties to improve the function of the XBAR device. For example, the backside dielectric material could be silicon dioxide, which can lower the temperature coefficient of the XBAR device's frequency response.

[0048] At 720An etch stop layer is formed by depositing an etch stop material onto the back surface of the piezoelectric plate (or the back surface of the backside dielectric layer, if present), the substrate surface (above the bonding layer, if present), or both. The etch stop material can be deposited by atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), or another method. The etch stop material must be a dielectric with very low conductivity and low acoustic loss. The etch stop material must exhibit high adhesion to the surface(s) on which it is deposited. Furthermore, the etch stop material must be compatible with the attachment of the piezoelectric plate to the substrate using a wafer bonding process.It is important that the etch stop material is impermeable to the processes and chemicals used to etch the substrate material and, if present, the bonding layer.

[0049] At 730The piezoelectric plate is bonded to the substrate. The piezoelectric plate and the substrate can be bonded using a wafer bonding process. When the etch stop layer is deposited onto the piezoelectric plate, wafer bonding occurs between the etch stop layer and the bonding layer, if present, or the substrate. Alternatively, if the etch stop layer is deposited onto the bonding layer, if present, or the substrate, wafer bonding occurs between the etch stop layer and the piezoelectric plate. One or both mating surfaces can be activated, for example, by a plasma process. The mating surfaces can then be pressed together with considerable force to create molecular bonds between the piezoelectric plate and the substrate or intermediate material layers.

[0050] A ladder structure, including the IDTs of each XBAR, is used at 740The conductor layer is formed by depositing and structuring one or more conductive layers on the front surface of the piezoelectric plate. The conductive layer can be made of, for example, aluminum, an aluminum alloy, copper, a copper alloy, or another conductive metal. Optionally, one or more layers of other materials can be placed beneath (i.e., between the conductive layer and the piezoelectric plate) and / or over the conductive layer. For example, a thin film of titanium, chromium, or another metal can be used to improve adhesion between the conductive layer and the piezoelectric plate. A conductivity-enhancing layer of gold, aluminum, copper, or another metal with higher conductivity can be applied over areas of the conductor structure (e.g., the IDT busbars and connections between the IDTs).

[0051] The ladder structure can be used at 740The conductive layer, and optionally one or more other metal layers, are formed by successively depositing it onto the surface of the piezoelectric plate. The excess metal can then be removed by etching through a structured photoresist. The conductive layer can be etched, for example, by plasma etching, reactive ion etching, wet chemical etching, and other etching techniques.

[0052] Alternatively, the ladder structure can be used at 740 The photoresist is formed using a lift-off process. It can be deposited and structured onto the piezoelectric plate to define the conductor structure. The conductor layer, and optionally one or more other layers, can be deposited sequentially onto the surface of the piezoelectric plate. The photoresist can then be removed, eliminating the excess material and leaving the conductor structure.

[0053] At750One or more front-side dielectric layers can be formed by depositing one or more layers of dielectric material onto the front of the piezoelectric plate. These dielectric layers can be deposited using conventional deposition techniques such as sputtering, evaporation, or chemical vapor deposition. The dielectric layers can be deposited over the entire surface of the piezoelectric plate, including the top surface of the conductor structure. Alternatively, one or more lithographic processes (using photomasks) can be employed to restrict the deposition of the dielectric layers to selected areas of the piezoelectric plate, for example, only between the nested fingers of the IDTs.Masks can also be used to enable the deposition of different thicknesses of dielectric materials on different areas of the piezoelectric plate.

[0054] In one version of the process 700 will be 760A One or more cavities are formed in the back of the substrate. A separate cavity can be formed for each resonator in a filter device. The one or more cavities can be formed using an anisotropic or orientation-dependent dry or wet set to create holes through the back of the substrate to the piezoelectric plate. In this case, the resulting resonator devices will have a cross-section as shown in Fig. 1 shown, exhibit.

[0055] In a second variant of the process 700 can at 760BBy etching the substrate with an etchant introduced through openings in the piezoelectric plate and the etch stop layer, one or more cavities in the form of depressions are created in the substrate. A separate cavity can be created for each resonator in a filter device. The one or more cavities that are created during 760B The resulting resonator devices do not penetrate the substrate, and the resulting resonator devices have a cross-section as shown in Fig. 3 shown, exhibit.

[0056] In all variations of the process 700The filter device is completed at step 770. Activities that may occur at 770 include depositing an encapsulation / passivation layer, such as SiO2 or Si3N4, over the entire device or a portion thereof; forming bonding pads or solder bumps, or other means to connect the device to an external circuit; cutting individual devices from a wafer containing multiple devices; other packaging steps; and testing. Another activity that may occur at 770 is tuning the resonant frequencies of the resonators within the device by adding or removing metal or dielectric material from the front of the device. Once the filter device is complete, the process ends at step 795. Closing remarks

[0057] Throughout this entire description, the embodiments and examples shown should be considered as models and not as limitations of the disclosed or claimed devices and procedures. Although many of the examples presented here involve specific combinations of process activities or system elements, it should be understood that these activities and elements can be combined in other ways to achieve the same objectives. With regard to flowcharts, additional or fewer steps can be taken, and the steps shown can be combined or further refined to achieve the procedures described herein. Activities, elements, and features discussed only in connection with one embodiment are not intended to exclude a similar role in other embodiments.

[0058] As used here, "multiple" means two or more. As used here, a "set" of elements may comprise one or more such elements. In the form used here, whether in the written description or in the claims, the terms "comprising," "including," "bearing," "having," "containing," "incorporating," and the like are to be understood as being unlimited, i.e., including but not limited to. Only the transitional phrases "consisting of" and "consisting substantially of" are closed or semi-closed transitional phrases with respect to claims. The use of ordinal expressions such as "first," "second," "third," etc.In the claims, the use of "and / or" to modify a claim element does not in itself imply a priority, precedence, or order of one claim element over another, nor does it indicate the temporal order in which the activities of a process are carried out. Rather, it is merely used as a distinguishing term to differentiate one claim element with a particular name from another element with the same name (but for the use of the ordinal expression to distinguish the claim elements). As used here, "and / or" means that the listed elements are alternatives, but the alternatives also include every combination of the listed elements. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 16 / 819623

[0038]

Claims

[1] Acoustic resonator device, comprising: a substrate with a surface; a single-crystal piezoelectric plate with front and back surfaces; an etch stop layer arranged sandwich-like between the surface of the substrate and the back surface of the piezoelectric plate, wherein a region of the piezoelectric plate and the etch stop layer form a membrane spanning a cavity in the substrate; and an interdigital transducer (IDT) formed on the front surface of the single-crystal piezoelectric plate, wherein nested fingers of the IDT are arranged on the membrane, wherein the etch stop layer is impermeable to an etching process used to form the cavity, and The thickness of the etch stop layer is less than or equal to 20% of the thickness of the piezoelectric plate. [2] Device according to claim 1, wherein the single-crystal piezoelectric plate consists of lithium niobate or lithium tantalate. [3] Device according to claim 1, wherein the etch stop layer consists of an oxide, sapphire, nitride, silicon carbide or diamond. [4] Device according to claim 3, wherein the etch stop layer consists of aluminium oxide. [5] Device according to claim 3, wherein the etch stop layer consists of a material with high thermal conductivity selected from aluminium nitride, boron nitride and diamond. [6] Device of claim 1, further comprising: a rear dielectric layer between the piezoelectric plate and the etch stop layer, wherein the membrane contains the piezoelectric plate, the rear dielectric layer and the etch stop layer. [7] Device according to claim 6, wherein the rear dielectric layer consists of silicon dioxide. [8] Device of claim 1, further comprising: a bonding layer between the etch stop layer and the substrate, wherein the membrane contains the piezoelectric plate and the etch stop layer, but not the bonding layer. [9] Device according to claim 8, wherein the substrate consists of silicon and the bonding layer consists of silicon dioxide. [10] Device of claim 1, further comprising: a frequency-adjusting dielectric layer arranged on the front surface between the fingers of the IDT. [11] Device according to claim 10, wherein the sum of the thickness of the etch stop layer and the thickness of the frequency-adjusting dielectric layer is less than or equal to 35% of the thickness of the dielectric plate. [12] Method for manufacturing an acoustic resonator device, comprising: Forming an etch stop layer sandwiched between a surface of a device substrate and a first surface of a single-crystal piezoelectric plate with a second surface attached to a sacrificial substrate; Removing the sacrificial substrate to expose the second surface of the piezoelectric plate; Using an etching process to create a cavity in the substrate, wherein an area of ​​the piezoelectric plate and the etch stop layer form a membrane spanning the cavity; and Forming an interdigital transducer (IDT) on the second surface of the piezoelectric plate such that nested fingers of the IDT are arranged on the membrane, wherein The etch stop layer is impermeable to an etching process used to create the cavity. [13] Method according to claim 12, wherein the single-crystal piezoelectric plate consists of lithium niobate or lithium tantalate. [14] Method according to claim 12, wherein the etch stop layer consists of an oxide, sapphire, nitride, silicon carbide or diamond. [15] Method according to claim 14, wherein the etch stop layer consists of aluminium oxide. [16] Method according to claim 14, wherein the etch stop layer consists of a material with high thermal conductivity selected from aluminium nitride, boron nitride and diamond. [17] The method of claim 12, further comprising: forming a backside dielectric layer between the piezoelectric plate and the etch stop layer, wherein the membrane contains the piezoelectric plate, the backside dielectric layer and the etch stop layer. [18] Method according to claim 17, wherein the rear dielectric layer consists of silicon dioxide. [19] The method of claim 12, further comprising: forming a bonding layer between the etch stop layer and the substrate, wherein the membrane contains the piezoelectric plate and the etch stop layer, but not the bonding layer. [20] Method according to claim 19, wherein the substrate consists of silicon and the bonding layer consists of silicon dioxide.

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