BAW device preparation method based on novel sacrificial layer process

Abstract

The invention discloses a preparation method of a BAW device based on a novel sacrificial layer technology, and the preparation method employs ZnO as the material of a sacrificial layer, employs a diluted hydrochloric acid solution as an etchant solution, can prevent the diluted hydrochloric acid solution from corroding an insulating layer and a dielectric layer while completely corroding ZnO, and obtains a high-performance BAW device. And meanwhile, on-chip integration with other passive devices is realized. According to the invention, ZnO is adopted as the sacrificial layer, and the sacrificial layer has the same wurtzite structure as the piezoelectric layer, so that the sacrificial layer can be used for inducing grain arrangement of the first electrode of the piezoelectric oscillation stack, and preferred orientation growth of the first electrode film is facilitated, so that preferred orientation growth of the piezoelectric layer film is further realized, and the piezoelectric layer film has relatively good piezoelectric performance. According to the invention, SiO2 is used as a passivation protection layer and an insulating layer, so that the function of the passivation protection layer and the insulating layer is achieved, and the function of temperature compensation can be additionally realized at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of MEMS devices, and in particular relates to a method for preparing a BAW device based on a novel sacrificial layer process. Background Art

[0002] In mobile phones, in addition to the rapid increase in frequency bands for communications, there are also dedicated frequency bands for applications such as WiFi, Bluetooth, and navigation, making the spectrum increasingly crowded. The mutual interference of signals between frequency bands has become an important problem that must be solved by the communication system. Filters are key components in the system that filter out other frequency bands and malicious interference signals. With the rapid increase in mobile phone frequency bands, the number of filters in a single mobile phone has rapidly increased from more than 30 in the 4G era to more than 60 in the 5G era, and the number of filters in flagship phones exceeds 100.

[0003] The crowded spectrum and the increase in the number of filters have put forward new requirements for the comprehensive performance of the filters: higher Q value, smaller frequency temperature coefficient and smaller volume. A higher Q value can ensure that the filter has a narrower transition band and achieve better filtering effect; a smaller frequency temperature coefficient means a smaller protection bandwidth reserved for useful signals, and fewer interference signals entering the receiving end of the system, ensuring that the system maintains better performance within a higher temperature range; a smaller volume can help achieve miniaturization and lightweighting of mobile phones, leaving more space for batteries.

[0004] The development of communication systems and weapons and equipment has put forward requirements for high frequency, miniaturization and high temperature stability for bulk acoustic wave (BAW) filters. BAW filters have significant advantages in high frequency and miniaturization. Although their frequency temperature coefficient is large (-25~-30 ppm / ℃), by adding a temperature compensation layer, their frequency temperature coefficient can be controlled within a lower range. Therefore, the temperature-compensated thin-film bulk acoustic wave filter with miniaturization and low frequency temperature coefficient in BAW filters is of great significance to the current and future development of mobile communications, complete systems and weapons and equipment.

[0005] The invention patent application with publication number CN109995342A discloses a method for preparing an air-gap thin-film bulk acoustic wave resonator, comprising the following steps: a sacrificial layer preparation step, in which a first sacrificial layer and a second sacrificial layer are sequentially prepared in the air gap of a supporting substrate, and the upper surface of the second sacrificial layer is flush with the upper surface of the supporting substrate; a piezoelectric sandwich structure preparation step, in which a piezoelectric sandwich structure is prepared on the upper surface of the sample obtained in the sacrificial layer preparation step, and the piezoelectric sandwich structure at least covers the upper surface of the second sacrificial layer; and a sacrificial layer removal step, in which the first sacrificial layer and the second sacrificial layer are removed; wherein the material of the first sacrificial layer is molybdenum oxide, and the material of the second sacrificial layer is phosphosilicate glass. The preparation method of the above patent application reduces the time of immersing the device in hydrofluoric acid and improves the device yield.

[0006] In the conventional BAW device preparation process disclosed in the above patent application, phosphosilicate glass (PSG) is usually used as a sacrificial layer material, which needs to be released by hydrofluoric acid (HF). However, using PSG as a sacrificial layer material is not conducive to the preferred orientation growth of the lower electrode metal molybdenum (Mo) film (110), and it is usually necessary to grow an additional AlN seed layer on the sacrificial layer to induce the preferred orientation growth of the Mo electrode. At this time, additional process steps are introduced, increasing the difficulty of the process. At the same time, the passivation protective layer also uses the same AlN. Summary of the invention

[0007] The invention provides a method for preparing a BAW device based on a novel sacrificial layer process. The BAW device prepared by the method has high integration and high performance.

[0008] A specific embodiment of the present invention provides a method for preparing a BAW device based on a novel sacrificial layer process, comprising: S1, forming a cavity on a substrate; S2. Form an insulating layer on the cavity and the substrate, wherein the insulating layer is made of SiO 2 ; S3, forming a first sacrificial layer on the insulating layer to fill the cavity, wherein the material of the first sacrificial layer is ZnO; S4, etching the insulating layer to expose the substrate, and forming a piezoelectric oscillation stack on the exposed substrate, the first sacrificial layer and the insulating layer, wherein the piezoelectric layer of the piezoelectric oscillation stack is a wurtzite structure; S5, etching the piezoelectric oscillator stack to form a first window and a release hole, and exposing the first electrode through the first window; S6, forming a metal pad layer on the first electrode and the second electrode of the piezoelectric oscillator stack to lead out the first electrode and the second electrode; S7. Corrode the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

[0009] Preferably, a reserved window for placing passive components is also formed on the substrate in step S1; According to steps S2-S4, an insulating layer, a second sacrificial layer and a piezoelectric layer of a piezoelectric oscillator stack are sequentially formed on the reserved window for placing the passive device; In step S5, the piezoelectric layer of the piezoelectric oscillator stack is also etched to expose a reserved window for placing passive components; In step S6, a metal pad layer is further formed on the piezoelectric layer at a side away from the first electrode and the second electrode of the piezoelectric oscillator stack; In step S7, the second sacrificial layer is further etched with a dilute hydrochloric acid solution to open a reserved window for placing a passive device to obtain a BAW device.

[0010] The present invention reserves a reserved window for placing passive devices on the BAW device, so that when a cover plate with passive devices is subsequently bonded, there is space for storing the passive devices, thereby improving the integration.

[0011] The present invention also provides a method for preparing a BAW device based on a novel sacrificial layer process, comprising: S1, forming a first insulating layer on a substrate, and forming a patterned first sacrificial layer on the first insulating layer, wherein the material of the first sacrificial layer is ZnO; S3, a second insulating layer is covered on the first insulating layer and the first sacrificial layer to form a new insulating layer, wherein the material of the insulating layer is SiO 2 ; S4, etching the new insulating layer to expose the substrate and the first sacrificial layer, and forming a piezoelectric oscillator stack on the exposed substrate, the first sacrificial layer and the new insulating layer; S5, etching the piezoelectric oscillator stack to form a first window and a release hole, and exposing the first electrode through the first window; S6, forming a metal pad layer on the first electrode and the second electrode of the piezoelectric oscillator stack to lead out the first electrode and the second electrode; S7. Corrode the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

[0012] Preferably, the concentration of the dilute hydrochloric acid solution is 0.1%-30%. At this concentration, the release rate will not be too slow due to too low a concentration, nor will the hydrochloric acid be too high to cause the SiO 2 The insulating layer is partially corroded.

[0013] Preferably, the material of the piezoelectric layer is AlN or AlxSc(1-x)N. The present invention uses ZnO as a sacrificial layer. Since it has the same wurtzite structure as AlN, it can be used to induce the grain arrangement of Mo, which is conducive to the preferred orientation growth of the Mo (110) film, thereby further enabling the preferred orientation growth of the piezoelectric layer AlN (002) film, so that it has better piezoelectric properties; therefore, the present invention can omit the preparation of the AlN seed layer, and ZnO can be completely released by the release material dilute hydrochloric acid used in the present invention, thereby improving the operating frequency of the device.

[0014] Preferably, forming the piezoelectric oscillating stack comprises the following steps: forming a first electrode on the exposed substrate and the first sacrificial layer; forming a piezoelectric layer on the first electrode and the insulating layer, and etching the piezoelectric layer to expose the first electrode; forming a second electrode on the piezoelectric layer; A protection layer is formed on the second electrode, and the protection layer is etched to expose the second electrode.

[0015] Further preferably, the material of the protective layer is SiO 2 .

[0016] Preferably, the piezoelectric oscillator stack further includes a temperature compensation layer, which is formed on the first sacrificial layer before forming the first electrode on the exposed substrate and the first sacrificial layer. The material of the temperature compensation layer is silicon dioxide, doped silicon dioxide, chromium or tellurium oxide.

[0017] A specific embodiment of the present invention further provides a method for preparing a BAW device based on a novel sacrificial layer process, comprising: S1, forming a cavity on a substrate; S2. Form an insulating layer on the cavity and the substrate, wherein the insulating layer is made of SiO 2 ; S3, forming a first sacrificial layer on the insulating layer to fill the cavity, wherein the material of the first sacrificial layer is ZnO; S4, etching the insulating layer to expose the substrate, and forming a first electrode on the exposed substrate, the first sacrificial layer and the insulating layer; S5, forming a piezoelectric layer on the first electrode, and forming a dielectric layer on the insulating layer and the first electrode and on a side away from the piezoelectric layer, wherein the material of the dielectric layer is SiN; S6, etching a window and a release hole on the piezoelectric layer to expose the first electrode through the window; S7, depositing a second electrode and an upper electrode on the piezoelectric layer and the dielectric layer respectively, depositing a protective layer on the second electrode and the upper electrode, and etching the protective layer to expose the second electrode and the upper electrode; S8, depositing a metal pad layer on the exposed first electrode, second electrode and upper electrode to lead out the first electrode, second electrode and upper electrode; S9. Corrode the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

[0018] Compared with the prior art that uses hydrofluoric acid as a corrosive solution that easily corrodes the dielectric layer, the present invention uses zinc oxide as the material of the sacrificial layer, so that the dielectric layer material SiN used to construct the passive device is less corroded, thereby avoiding damage to the performance of the passive device.

[0019] Preferably, in step S4, before forming the first electrode on the exposed substrate, the first sacrificial layer and the insulating layer, a temperature compensation layer is formed on the first sacrificial layer.

[0020] The present invention provides a method for preparing a BAW device based on a novel sacrificial layer process. Compared with the traditional BAW device preparation process, the process has a significant change. Zinc oxide (ZnO) is used as the sacrificial layer material, and dilute hydrochloric acid (HCl) is used for release. Zinc oxide provides a sacrificial layer filler and eliminates the need for the preparation of an AlN seed layer. The passivation protective layer uses silicon dioxide (SiO 2 ), in addition to playing its own role, it also provides an additional temperature compensation function.

[0021] The present invention uses ZnO as the material of the sacrificial layer and adopts a dilute hydrochloric acid solution as the etching solution. While completely etching ZnO, the dilute hydrochloric acid solution can be prevented from etching the insulating layer and the dielectric layer, so that the active device and the passive device have better performance, and the Q value of the prepared BAW device is higher.

[0022] The present invention adopts ZnO as a sacrificial layer. Since it has the same wurtzite structure as the piezoelectric layer, it can be used to induce the grain arrangement of the first electrode of the piezoelectric oscillator stack, which is beneficial to the preferential orientation growth of the first electrode film, thereby further enabling the piezoelectric layer film to preferentially grow in an oriented manner, so that it has better piezoelectric properties; therefore, the present invention can omit the preparation of the seed layer and the subsequent removal process, and the ZnO can be completely released by the release material dilute hydrochloric acid used in the present invention, and the process of removing the AlN seed layer can improve the operating frequency of the device.

[0023] In addition, compared with the use of hydrofluoric acid (HF) for sacrificial layer release, dilute hydrochloric acid is not corrosive to temperature compensation materials such as silicon dioxide, doped silicon dioxide, chromium or tellurium oxide, and can be conveniently used as a temperature compensation layer and passivation protection layer to reduce the temperature frequency coefficient of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1a It is the ladder topology diagram of BAW filter; Figure 1b The corresponding transmission response diagram of the BAW filter; Figure 2 A flow chart of a method for preparing a bulk acoustic wave resonator based on a novel sacrificial layer process provided in a specific embodiment of the present invention; Figure 3a-Figure 3n A processing flow chart of the first BAW 10 provided for a specific embodiment of the present invention; Figure 4a-4k A processing flow chart of a second BAW 30 provided for a specific embodiment of the present invention; Figure 5a-5m A processing flow chart of the third BAW50 provided for a specific embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the embodiments and drawings. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0026] A specific embodiment of the present invention provides a method for preparing a BAW device based on a novel sacrificial layer process, and wafer processing of resonators before cutting into individual filter packages. The various resonators of the filter assembly are manufactured on a large array of wafers, and then the wafers are cut to form individual filters, each filter being formed by a different combination of BAW resonators, such as step-type, lattice-type, and combination-type arrangements. These resonators are electrodes with piezoelectric films, and each side has a cavity for them to vibrate, thereby acting as a filter, transmitting signals at the resonant frequency and filtering signals at other frequencies, specifically, such as Figure 1a-1b As shown, including: Figure 1a The topology of a ladder filter is shown. The circuit is realized by arranging BAW resonators in series and in parallel. The series resonant frequency of the parallel resonator corresponds to the left zero point of the filter, and the parallel resonant frequency of the series resonator corresponds to the right zero point of the filter. The series resonant frequency of the series resonator is close to the parallel resonant frequency of the parallel resonator. If the series resonant frequency of the series resonator is too far away from the parallel resonant frequency of the parallel resonator, a notch will be formed in the passband of the filter, that is, the loss in the middle of the filter passband is large. Reference Figure 1b This is the transmission response curve corresponding to the ladder filter circuit. Increasing the order of the ladder filter can improve the out-of-band suppression of the filter.

[0027] The specific embodiment of the present invention provides a resonator with multiple different structures, which is a bulk acoustic wave resonator, and the bulk acoustic wave resonators are respectively a first BAW10, a second BAW30, and a third BAW50. Among them, the first BAW10 is prepared with a reserved window on the cover plate for placing passive devices, the second BAW30 realizes the integration of on-chip passive devices, and the third BAW50 has a cavity structure on a silicon wafer.

[0028] A method for preparing a BAW device based on a novel sacrificial layer process provided in a specific embodiment of the present invention, specifically, a method for preparing a first BAW 10, includes: like Figure 3a As shown, the substrate 100 is ultrasonically cleaned with SPM solution, and a cavity 101 and a reserved window 101-1 for placing passive devices are formed on the silicon substrate 100 by a dry etching process. The lateral width of the cavity 101 and the reserved window 101-1 for placing passive devices can be changed according to actual needs. The etching angle of the cavity sidewall is 100° to 120°, which is convenient for fully filling the sacrificial layer. The etching depth is about 3.5 μm. The cavity depth under BAW only needs to be sufficient to accommodate the displacement generated by the piezoelectric layer. The acoustic device substrate must have a high resistivity to prevent the substrate from coupling with the resonator.

[0029] For those skilled in the art, other substrate materials are also optional. For example, the substrate material is one of silicon, silicon carbide, sapphire, ceramic, etc. or any combination thereof.

[0030] Preferably, the substrate 100 used in the specific embodiment of the present invention is generally made of Si, and its resistivity is generally greater than 1000 Ω·cm.

[0031] like Figure 3b As shown, a layer of thermal oxide SiO is grown on the surface of the substrate. 2 As an insulating layer 102, to prevent Zn in ZnO from diffusing into the layer, such diffusion will cause the surface of the silicon substrate 100 to conduct electricity, thereby shunting the radio frequency signal from the thin film bulk acoustic wave resonator and interfering with the electrical operation of the final device. The thermal oxidation growth method has a better film density than the PECVD or LPCVD method, so as to protect the substrate when the sacrificial layer is released. Preferably, the thickness of the insulating layer is 100 nm to 5000 nm.

[0032] like Figure 3c and 3d As shown, zinc oxide (ZnO) is deposited on the insulating layer 102 by a PECVD method as a sacrificial layer material, and the wafer surface is flattened by a CMP process to form sacrificial layer fillings 103 - 1 and 103 - 2 with an edge gap of less than 30 nm.

[0033] The specific embodiment of the present invention uses ZnO as the sacrificial layer material. The AlN piezoelectric film has a wurtzite structure and a hexagonal crystal form. The (002) preferred orientation growth requires that the lower electrode film has the same crystal form, or is a face-centered cubic crystal form with a (111) orientation, or a body-centered cubic (110) orientation. When the lattice arrangement of the electrode material is closer to the lattice arrangement of the (002) plane of the AlN film, it is more conducive to the preferred orientation growth of the AlN film. In the traditional BAW device preparation process, a layer of AlN seed layer is deposited before depositing the lower electrode to induce the grain arrangement of Mo, which is conducive to the preferred orientation growth of the Mo (110) film, thereby further enabling the piezoelectric layer AlN (002) film to grow in a preferred orientation, so that it has better piezoelectric properties. When ZnO is used as the sacrificial layer material, since ZnO has the same wurtzite structure as AlN, the preparation of the seed layer and the subsequent removal process can be omitted.

[0034] Since the rough surface is not conducive to the columnar growth of piezoelectric materials in the plane perpendicular to the electrode, the smooth surface after CMP treatment in the specific embodiment of the present invention can provide a basis for the deposition of highly textured c-axis piezoelectric materials, so that the subsequent steps can have excellent piezoelectric performance. A higher quality piezoelectric layer can realize a higher quality resonator, thereby realizing a higher quality filter circuit.

[0035] like Figure 3e As shown, the specific embodiment of the present invention selectively treats SiO 2 The insulating layer 102 is dry-etched.

[0036] like Figure 3f As shown, a layer of SiO is deposited on the surface of the insulating layer 102 and the sacrificial layer filling 103-1 by thermal oxidation. 2 As the temperature compensation layer 104 .

[0037] For those skilled in the art, other materials are also optional. For example, the temperature compensation layer can be tellurium oxide (TeO x ), chromium (Cr), doped silicon dioxide and silicon dioxide (SiO 2 ) and other materials.

[0038] In particular, the temperature compensation layer can be located at other positions, such as in the middle of the electrode or above the upper electrode. In the embodiment of the present invention, the temperature compensation layer can be omitted here, and the subsequent passivation protection layer is made of SiO 2 It can also play the role of a temperature compensation layer. For different embodiments, it is necessary to specifically study the different positions of the temperature compensation layer to achieve the optimal effect.

[0039] In a specific embodiment, the material of the temperature compensation layer 104 provided in this embodiment is SiO 2 .

[0040] like Figure 3g As shown, after cleaning the surface after the CMP step, a layer of metal molybdenum (Mo) is deposited on the substrate 100 and the temperature compensation layer 104 by thermal evaporation or magnetron sputtering, and the first electrode 105 of the BAW device is formed by dry etching.

[0041] For those skilled in the art, other materials are also optional. For example, the first electrode is Al, W, Au, Pt or Ti.

[0042] In one embodiment, the electrode material of the first electrode 105 deposited in this embodiment is molybdenum. Since the temperature is extremely high when manufacturing the piezoelectric film, the electrode is mostly made of heavy metals such as molybdenum that can withstand high heat. The mass recombination effect of the electrode will be particularly prominent and compatible with the etching of AlN. Preferably, the thickness of the first electrode 105 is 100 nm to 1000 nm.

[0043] like Figure 3h As shown, a layer of scandium-doped aluminum nitride (AlScN) is deposited on the substrate 100, the first electrode 105, and the surface of the sacrificial layer as the piezoelectric layer 106 by magnetron sputtering or MOCVD.

[0044] The AlxSc(1-x)N piezoelectric layer 106 is typically c-axis oriented and is typically 0.5≤x≤1, and preferably 0.57≤x≤1. These films have a root mean square (RMS) surface roughness of less than 1 nm and a rocking curve value of less than 500 arc seconds.

[0045] The more ideal candidates for the piezoelectric layer 106 material are: crystalline BaxSr(1-x)TiO3 (BST) or C-axis AlxSc(1-x)N, AlN and AlxGa(1-x)N. The AlN and AlxSc(1-x)N provided in the specific embodiment of the present invention are HCP-type wurtzite crystal structures (C-plane orientation). A strong C-axis structure is the most important prerequisite for AlxGa(1-x)N and AlxSc(1-x) BAW filters, because the sound mode of BAW requires longitudinal activation, and the piezoelectric axis of AlN and AlxGa(1-x)N is along the C-axis direction. Adding gallium or scandium to the AlN lattice can improve the coupling coefficient for a wider bandwidth resonator.

[0046] In a specific embodiment, the resonance layer provided in this embodiment is made of scandium-doped aluminum nitride piezoelectric resonance material. Preferably, the thickness of the piezoelectric layer is 100 nm to 4000 nm.

[0047] like Figure 3iAs shown, a ZnO sacrificial material is deposited on the surface of the piezoelectric layer 106 as a filler 107, 107-1 of the BAW resonator air bridge structure. After the metal pad layer of the BAW device is formed, the sacrificial material needs to be released to form the air bridge structure.

[0048] Optionally, the filler 107, 107-1 of the air bridge may be other dielectric or metal materials to provide the required acoustic impedance discontinuity, and no release is performed in subsequent steps.

[0049] This embodiment uses an air bridge structure. The acoustic impedance mismatch provided by the air bridge causes the sound waves at the boundary to reflect when the active area of ​​the resonator resonates. Otherwise, these sound waves may propagate out of the active area and disappear, resulting in energy loss. Reducing these helps to improve the quality factor of the BAW device, thereby improving the overall performance of the BAW device.

[0050] like Figure 3j As shown, a layer of metal molybdenum (Mo) is deposited on the surface of the piezoelectric layer 106 by magnetron sputtering or MOCVD, and then dry-etched to form the second electrode 108 of the BAW device.

[0051] For those skilled in the art, other materials are also optional. For example, the electrode can be made of Al, W, Au, Pt or Ti, and the material of the protrusion structure can be different from the electrode material.

[0052] Preferably, the thickness of the second electrode 108 is 100 nm to 1000 nm.

[0053] like Figure 3k As shown, a layer of silicon dioxide (SiO2) is deposited on the surface of the second electrode 108 by magnetron sputtering or MOCVD. 2 ), and after dry etching, a passivation protection layer 109 is formed, exposing a window 110 of the second electrode 108 of the BAW device.

[0054] The passivation protection layer 109 provided in the specific embodiment of the present invention may be, for example but not limited to, SiO 2 , AlN, TiN, silicon, chromium or any other suitable material or combination of materials. The passivation layer is part of the resonator and affects the performance of the resonator. The passivation layer is generally made of an inert material that is not easily interacted with the environment. It can prevent the upper electrode from being exposed to air and oxidized. At the same time, adjusting the thickness of the passivation layer can adjust the operating frequency of the resonator.

[0055] Preferably, the material of the passivation protection layer 109 used in this embodiment is SiO 2 , which is the same as the material of the insulating layer and the temperature compensation layer. Preferably, the thickness of the passivation protection layer 109 is about 100 nm to 2000 nm.

[0056] like Figure 3l As shown, the piezoelectric layer 106 is dry-etched to form a window 111 exposing the first electrode 105 of the BAW device, a release hole 111-1, and a piezoelectric layer portion 111-2 for preparing the window. The lateral widths of the windows 111 and 111-2 can be changed according to actual needs. The release hole 111-1 is not in the same cross section and is indicated by a dotted line.

[0057] like Figure 3m As shown, a layer of gold is deposited on the piezoelectric layer 106, the passivation protection layer 109 and the windows 110 and 111 by thermal evaporation or magnetron sputtering, and a first metal pad layer 112, a second metal pad layer 112-1 and a third metal pad layer 112-2 are formed by dry etching or wet etching. The first metal pad layer 112 is not connected to the BAW second electrode 108.

[0058] The metal pad layer may be one of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, nickel or any group thereof.

[0059] Preferably, in this embodiment, gold is used as the material of the metal pad layer. Preferably, the thickness of the metal pad layer is 50 nm to 12000 nm.

[0060] like Figure 3n As shown, a dilute hydrochloric acid (HCl) solution is used to etch the ZnO sacrificial layer 103 and the ZnO fillers in the air bridges 107 and 107 - 1 to form a cavity 113 , a substrate portion 113 - 1 for placing a window, and air bridge structures 113 - 2 and 113 - 3 .

[0061] The preparation method of the second BAW30 provided in the specific embodiment of the present invention is as follows: Figure 2 As shown, including: like Figure 4a-4e As shown, in this embodiment, the preparation method of sequentially depositing an insulating layer 302, a sacrificial layer 303, a temperature compensation layer 304 and a first electrode 305 on a substrate 300 having a sacrificial layer groove is the same as the preparation method of the first BAW 30. Among them, a part of the first electrode 305 will be used as the lower electrode 305-1 of the passive capacitor, and the lateral width of the lower electrode 305-1 can be changed according to actual needs.

[0062] like Figure 4f As shown, a layer of silicon nitride (SiN) is deposited and etched on the surface of the insulating layer 302 and the first electrode 305 by magnetron sputtering or MOCVD to form a dielectric layer 306 as a passive capacitor dielectric. The lateral width of the dielectric layer 306 can be changed according to actual needs.

[0063] like Figure 4gAs shown, a layer of scandium-doped aluminum nitride (AlScN) is deposited on the substrate 300, the first electrode 305, the insulating layer 302, and the dielectric layer 306 by magnetron sputtering or MOCVD as a piezoelectric layer 307, and the piezoelectric layer 307 is dry-etched to form a window 308 and a release hole 308-1 exposing the first electrode 305 of the BAW device. The release hole 308-1 is not in the same cross section and is indicated by a dotted line.

[0064] like Figure 4h As shown, a ZnO sacrificial material is deposited on the surface of the piezoelectric layer 307 as a filler for the BAW resonator air bridge structure. After the metal pad layer of the BAW device is formed, the sacrificial material needs to be released to form the air bridge structure. The fillers 309 and 309-1 of the air bridge can be other dielectric or metal materials to provide the required acoustic impedance discontinuity, and the subsequent steps will not release it. A layer of metal molybdenum (Mo) is deposited on the surface of the piezoelectric layer 307 by magnetron sputtering or MOCVD, and the second electrode 310 of the BAW device and the upper electrode 310-1 of the passive capacitor are formed by dry etching. By controlling the lateral width of the upper electrode 310-1, a passive capacitor of the required area can be formed.

[0065] like Figure 4i As shown, a layer of silicon dioxide (SiO2) is deposited on the surface of the second electrode 310 by magnetron sputtering or MOCVD. 2 ), and after dry etching, a passivation protection layer 311, 311-1 is formed, and at the same time, the window 312 of the second electrode 310 of the BAW device and the window 312-1 of the upper electrode 310-1 of the passive capacitor device are exposed.

[0066] like Figure 4j As shown, a layer of gold is deposited on windows 308, 312 and 312-1 by thermal evaporation or magnetron sputtering, and a first metal pad layer 313, a second metal pad layer 313-1 and a third metal pad layer 313-2 are formed by dry etching or wet etching. The first metal pad layer 313 is not connected to the BAW second electrode 310, and the third metal pad layer 313-2 is connected to the upper electrode 310-1 of the passive capacitor device.

[0067] like Figure 4k As shown, a dilute hydrochloric acid (HCl) solution is used to etch the ZnO sacrificial layer 303 and the ZnO fillers in the air bridge fillers 309 and 309 - 1 to form a cavity 314 and air bridge structures 314 - 1 and 314 - 2 .

[0068] It is understandable that if there is no need to manufacture passive components, the manufacturing step of the passive components can be omitted in the above steps.

[0069] The preparation method of the third BAW50 provided in a specific embodiment of the present invention includes: like Figure 5a As shown, the substrate 500 is ultrasonically cleaned using an SPM solution, and a layer of thermal oxide SiO is grown on the surface of the substrate. 2 As the insulating layer 501.

[0070] like Figure 5b As shown, a layer of ZnO is deposited on the insulating layer 501 by using the PECVD method, and is patterned by dry etching to form a sacrificial layer 502.

[0071] refer to Figure 5c and Figure 5d , a layer of SiO covering the sacrificial layer 502 is grown by thermal oxidation method 2 The sacrificial layer 502 is exposed by CMP treatment, and then the insulating layer 501 is dry-etched to expose part of the surface of the substrate 500.

[0072] Figure 5e-5m The steps shown are Figure 3f-Figure 3n The steps are the same as those of the embodiment to form a temperature compensation layer 504, a first electrode 505, a piezoelectric film 506, a second electrode 508, a passivation protection layer 509, a sacrificial layer release hole 511-1 for preparing a cavity, a first metal pad layer 512, a second metal pad layer 512-1, a cavity 513, and air bridge structures 513-1, 513-2.

Claims

1. A method for preparing a BAW device based on a novel sacrificial layer process, characterized in that: include: S1, forming a cavity on a substrate; S2, forming an insulating layer on the cavity and the substrate, wherein the material of the insulating layer is SiO2; S3, forming a first sacrificial layer on the insulating layer to fill the cavity, wherein the material of the first sacrificial layer is ZnO; S4, etching the insulating layer to expose the substrate, and forming a piezoelectric oscillation stack on the exposed substrate, the first sacrificial layer and the insulating layer, wherein the piezoelectric layer of the piezoelectric oscillation stack is a wurtzite structure; S5, etching the piezoelectric oscillator stack to form a first window and a release hole, and exposing the first electrode through the first window; S6, forming a metal pad layer on the first electrode and the second electrode of the piezoelectric oscillator stack to lead out the first electrode and the second electrode; S7. Corrode the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

2. A method for preparing a BAW device based on a novel sacrificial layer process, characterized in that: include: S1, forming a first insulating layer on a substrate, and forming a patterned first sacrificial layer on the first insulating layer, wherein the material of the first sacrificial layer is ZnO; S3, covering the first insulating layer and the first sacrificial layer with a second insulating layer to form a new insulating layer, wherein the insulating layer is made of SiO2; S4, etching the new insulating layer to expose the substrate and the first sacrificial layer, and forming a piezoelectric oscillator stack on the exposed substrate, the first sacrificial layer and the new insulating layer; S5, etching the piezoelectric oscillator stack to form a first window and a release hole, and exposing the first electrode through the first window; S6, forming a metal pad layer on the first electrode and the second electrode of the piezoelectric oscillator stack to lead out the first electrode and the second electrode; S7. Corrode the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

3. The method for preparing a BAW device based on a novel sacrificial layer process according to claim 1 or 2, characterized in that: The concentration of the dilute hydrochloric acid solution is 0.1%-30%.

4. The method for preparing a BAW device based on a novel sacrificial layer process according to claim 1 or 2, characterized in that: Forming a piezoelectric oscillating stack includes the following steps: forming a first electrode on the exposed substrate and the first sacrificial layer; forming a piezoelectric layer on the first electrode and the insulating layer, and etching the piezoelectric layer to expose the first electrode; forming a second electrode on the piezoelectric layer; A protection layer is formed on the second electrode, and the protection layer is etched to expose the second electrode. 5 . According to the method for preparing a BAW device based on a novel sacrificial layer process according to claim 4 , the material of the protective layer is SiO 2 .

6. The method for preparing a BAW device based on a novel sacrificial layer process according to claim 4, characterized in that: The piezoelectric oscillation stack further includes a temperature compensation layer, which is formed on the first sacrificial layer before forming the first electrode on the exposed substrate and the first sacrificial layer.

7. The method for preparing a BAW device based on a novel sacrificial layer process according to claim 6, characterized in that: The material of the temperature compensation layer is silicon dioxide, doped silicon dioxide, chromium or tellurium oxide.

8. A method for preparing a BAW device based on a novel sacrificial layer process, characterized in that: include: S1, forming a cavity on a substrate; S2, forming an insulating layer on the cavity and the substrate, wherein the material of the insulating layer is SiO2; S3, forming a first sacrificial layer on the insulating layer to fill the cavity, wherein the material of the first sacrificial layer is ZnO; S4, etching the insulating layer to expose the substrate, and forming a first electrode on the exposed substrate, the first sacrificial layer and the insulating layer; S5, forming a piezoelectric layer on the first electrode, and forming a dielectric layer on the insulating layer and the first electrode and on a side away from the piezoelectric layer, wherein the material of the dielectric layer is SiN; S6, etching a window and a release hole on the piezoelectric layer to expose the first electrode through the window; S7, depositing a second electrode and an upper electrode on the piezoelectric layer and the dielectric layer respectively, depositing a protective layer on the second electrode and the upper electrode, and etching the protective layer to expose the second electrode and the upper electrode; S8, depositing a metal pad layer on the exposed first electrode, second electrode and upper electrode to lead out the first electrode, second electrode and upper electrode; S9. Corrode the first sacrificial layer with a dilute hydrochloric acid solution through the release hole to form an air gap below the resonant cavity.

9. The method for preparing a BAW device based on a novel sacrificial layer process according to claim 8, characterized in that: In step S4 , before forming the first electrode on the exposed substrate, the first sacrificial layer and the insulating layer, a temperature compensation layer is formed on the first sacrificial layer.

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