Single crystal FBAR piezoelectric thin film and method of making same

Abstract

The application discloses a cavity film bulk acoustic resonator, comprising a first substrate, a bonding layer, an opaque medium layer, a piezoelectric oscillation stack and a metal pad layer; wherein the bonding layer is formed on the first substrate, the opaque medium layer is formed on the bonding layer, the piezoelectric oscillation stack is formed on the opaque medium layer, the cavity is arranged between the opaque medium layer and the piezoelectric oscillation stack, and the metal pad layer is connected with the piezoelectric oscillation stack. The resonator has low surface roughness, and the thickness of each region of the film can be conveniently and accurately measured. The application further discloses a preparation method of the cavity film bulk acoustic resonator, and the preparation method is simple, efficient and saves preparation procedures.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a single-crystal FBAR piezoelectric thin film and its preparation method. Background Technology

[0002] With the rapid development of mobile communication technology, the market demand for high-frequency resonators and filters is increasing. Compared with traditional microwave ceramic resonators and surface acoustic wave resonators, thin-film bulk acoustic resonators (FBARs) have advantages such as small size, low loss, high quality factor, large power capacity, and high resonant frequency. Therefore, they have broad application prospects in related fields, especially in high-frequency communication, and have become a research hotspot in industry and academia.

[0003] The performance level of a filter is determined by its Factor of Merit, which is defined as FOM = Q * K. 2 eff, where Q is the quality factor, describes the vibration attenuation of an oscillator or resonator and characterizes the bandwidth of the resonator relative to its center frequency. It is related to the structure and process integration of FBAR devices. Currently, the most advanced FBAR filters have Q factors ranging from 2500 to 5000. K2eff is called the effective coupling coefficient, a property related to the properties of piezoelectric thin film materials.

[0004] The thickness of the piezoelectric film in FBAR filters is negatively correlated with the operating frequency. Filters operating at extremely high frequencies, such as 10 GHz, have an ALN ​​film thickness of approximately 200 nm. This ultra-thin specification presents significant challenges to the fabrication of piezoelectric films; the thinner the piezoelectric film, the more difficult it is to maintain the required rigidity, and its own crystal defects and stress make it more prone to cracking. Therefore, next-generation high-frequency FBARs require defect-free single-crystal films.

[0005] To obtain high-quality single-crystal piezoelectric thin films, they are typically fabricated on 300-500 μm thick silicon carbide or sapphire substrates using metal-organic chemical vapor deposition (MOCVD) or magnetron sputtering. However, to fabricate a complete FBAR device, the substrate on which the single-crystal piezoelectric thin film is grown needs to be removed to form the second electrode required for FBAR device operation and subsequent device packaging. Currently, there are two process routes for removing the substrate on which the single-crystal piezoelectric thin film is grown: traditional mechanical substrate thinning and laser substrate lift-off.

[0006] The traditional mechanical thinning substrate process includes mechanical thinning, mechanical grinding, dry etching, chemical mechanical grinding and other processing technologies, the traditional mechanical thinning substrate process is not only complex but also can easily cause single crystal piezoelectric film damage in the substrate thinning process and substrate removal failure caused by bonding quality problems, and the substrate cannot be reused by using mechanical grinding to remove the substrate, especially the cost of silicon carbide substrate is high, if the recycling of silicon carbide substrate cannot be realized, the device preparation cost will be greatly increased, and the product market competitiveness will be reduced.

[0007] The laser stripping process is to grow a stripping layer on the silicon carbide substrate or sapphire substrate, the band gap of the stripping layer and the substrate and the single crystal piezoelectric film is different, and different band gaps have different absorption rates for ultraviolet laser. For example, the band gap of sapphire substrate is 9.9eV, the band gap of GaN is 3.3eV, and the band gap of AlN is 6.4eV, so only 248nm KrF excimer laser (5eV radiation energy) is needed to irradiate the three materials, the band gap of sapphire substrate and AlN is greater than 5eV radiation energy, and the laser energy cannot be absorbed, and the laser directly transmits, and the band gap of GaN is less than 5eV radiation energy, and the laser energy is strongly absorbed to cause decomposition. However, the stripping layer will not be completely decomposed, and the remaining stripping layer needs to be removed, and in the process of removing the remaining stripping layer in the prior art, the single crystal piezoelectric film is damaged, and in addition, the substrate and the grown film used in the prior art, such as: ALN piezoelectric film, SiO2 bonding layer, are transparent layers, which poses a certain challenge to the online accurate measurement of the thickness of the piezoelectric film in different areas by using mature optical film thickness instrument technology.

[0008] Therefore, it is urgent to solve the technical problem of damage to the single crystal piezoelectric film caused by the stripping layer removal process, which affects the surface uniformity of the single crystal FBAR piezoelectric film, and the thickness of the single crystal piezoelectric film in different areas cannot be accurately measured, which affects the subsequent Trimming process and directly affects the yield of the device. SUMMARY

[0009] The present application provides a kind of cavity type film bulk acoustic resonator, the surface roughness of this resonator is lower, and the thickness of each area of the film can be more conveniently and accurately measured.

[0010] A kind of cavity film bulk acoustic resonator, comprising a first substrate, a bonding layer, an opaque dielectric layer, a piezoelectric oscillation stack and a metal pad layer;

[0011] Wherein, the bonding layer is formed on the first substrate, the opaque dielectric layer is formed on the bonding layer, the piezoelectric oscillation stack is formed on the opaque dielectric layer, the opaque dielectric layer and the piezoelectric oscillation stack have a cavity, and the metal pad layer is located on the piezoelectric oscillation stack.

[0012] The present application forms an opaque medium layer on the bonding layer, and the thickness of each area of the single crystal piezoelectric film can be accurately and conveniently measured online by using the opaque medium layer. Compared with the prior art of measuring the thickness of the single crystal piezoelectric film in the partial area by using a measuring block, the present application can save the process while increasing the accuracy of the single crystal piezoelectric film thickness detection, and provide accurate data support for subsequent trimming process preparation.

[0013] The piezoelectric oscillation stack comprises a first electrode, a single crystal piezoelectric film and a second electrode, wherein the first electrode is formed on the surface of the opaque medium layer, the opaque medium layer has a cavity between the first electrode, the single crystal piezoelectric film is formed on the surface of the first electrode, the second electrode is formed on the surface of the single crystal piezoelectric film, and the metal pad layer is respectively located on the first electrode and the second electrode.

[0014] The metal pad layer is divided into a first metal pad layer and a second metal pad layer, the first metal pad layer is located on the first electrode through the single crystal piezoelectric film, and is separated from the second electrode;

[0015] The second metal pad layer is located on the second electrode, and is separated from the first metal pad layer.

[0016] The metal pad layer can thicken the first electrode and the second electrode respectively according to the needs, facilitate online testing, and can be used as a solder point for subsequent packaging bonding.

[0017] The first substrate is one or more of silicon, silicon carbide, sapphire, glass, and ceramic.

[0018] The bonding layer is inorganic or organic, and the inorganic is one or more of silicon oxide, polysilicon, amorphous silicon, silicon nitride, and phosphoric acid glass.

[0019] The thickness of the bonding layer is 0.5-10 μm, and the roughness is less than 0.5 nm.

[0020] The opaque medium layer is one or more of silicon nitride, silicon, aluminum nitride, and ceramic.

[0021] The thickness of the opaque medium layer is 0.1-5 μm.

[0022] The cross section of the cavity is one or more of ladder type, rectangular, and square, the depth of the cavity is 0.5-2 μm, and the lateral width is 40-200 μm.

[0023] The single crystal piezoelectric film is one or more of aluminum nitride, doped aluminum nitride, zinc oxide, and lithium nickelate.

[0024] The thickness of the single crystal piezoelectric film is 0.3-2 μm.

[0025] The material of the first electrode and the second electrode is one or more of molybdenum, gold, aluminum, silver, titanium, tungsten and nickel.

[0026] The thickness of the first electrode and the second electrode is 150-500 nm, and the lateral width is 100-600 μm.

[0027] The metal pad layer is one or more of gold, platinum, aluminum, titanium, tungsten and nickel, and the thickness is 300-2000 nm.

[0028] The application further provides a preparation method of the cavity type film bulk acoustic resonator.

[0029] (1) a second substrate with a stripping layer is selected, a single-crystal piezoelectric film is prepared on the surface of the second substrate, a first electrode is applied on the surface of the single-crystal piezoelectric film, a sacrificial layer is prepared on the surface of the first electrode, an opaque dielectric layer is prepared on the surface of the sacrificial layer, a bonding layer is prepared on the surface of the opaque dielectric layer, and a first substrate is bonded on the surface of the bonding layer;

[0030] (2) the second substrate with the stripping layer is stripped from the single-crystal piezoelectric film by first laser irradiation, the residual stripping layer on the surface of the single-crystal piezoelectric film is dry etched, and then the residual stripping layer after the dry etching is secondly laser irradiated to obtain the single-crystal piezoelectric film with a surface roughness of 0.5 nm or less;

[0031] (3) the single-crystal piezoelectric film obtained in step (2) is provided with a first through hole and a second through hole, a first metal pad layer is applied into the first through hole so that the first metal pad layer is connected with the first electrode, an etching solution is added into the second through hole, the sacrificial layer is removed by fumigation to form a cavity, a second electrode layer is applied on the surface of the single-crystal piezoelectric film obtained in step (2), and a second metal pad layer is deposited on the surface of the second electrode layer to obtain the cavity type film bulk acoustic resonator.

[0032] The application dry etches the residual stripping layer after the first laser irradiation to remove more residual stripping layer, and then performs second laser irradiation to remove most of the residual stripping layer, because the band gap of the single-crystal piezoelectric film is much larger than that of the stripping layer, the stripping layer can absorb laser energy and decompose through specific wavelength laser irradiation, the single-crystal piezoelectric film does not absorb laser energy and does not decompose, so that the stripping layer is completely removed without any damage to the single-crystal piezoelectric film, the single-crystal piezoelectric film has good surface roughness, and the removal efficiency is improved due to the dry etching before the second laser irradiation.

[0033] In step (1),

[0034] The peeling layer is deposited on the surface of the second substrate by magnetron sputtering or metal organic chemical vapor deposition (MOCVD), and the peeling layer is one or more of gallium nitride, tantalum nitride and niobium nitride, and the thickness of the peeling layer is 100-500 nm.

[0035] Before the single-crystal piezoelectric thin film is prepared on the surface of the second substrate, the selected second substrate with the peeling layer is subjected to ultrasonic washing with acetone and / or isopropyl alcohol.

[0036] The single-crystal piezoelectric thin film is deposited on the surface of the peeling layer by magnetron sputtering, metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0037] The electrode is deposited on the surface of the single-crystal piezoelectric thin film by thermal evaporation or magnetron sputtering deposition.

[0038] The sacrificial layer is deposited on the surface of the first electrode by plasma enhanced chemical vapor deposition (PECVD) or chemical vapor deposition (CVD), and the sacrificial layer is one or more of organic matter and inorganic matter, and the inorganic matter is one or more of amorphous silicon, polysilicon, silicon nitride, silicon oxide and doped silicon oxide.

[0039] The opaque dielectric layer is deposited on the surface of the sacrificial layer by low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD) or physical vapor deposition (PVD).

[0040] The bonding layer is deposited on the surface of the opaque dielectric layer by chemical vapor deposition (CVD), atmospheric pressure chemical vapor deposition (APCVD) or plasma enhanced chemical vapor deposition (PECVD).

[0041] In step (2), the thickness of the residual peeling layer is 100-4000 nm, the parameters of dry etching are as follows: RF power is 500-1000 W, Cl2 / Ar gas flow is 30-100 / 5-40 sccm, chamber pressure is 5-40 mT, and the parameters of the second laser irradiation are as follows: wavelength of light is ≤248 nm, and laser energy density is 400-600 mJ / cm 2 .

[0042] The residual peeling layer is removed by dry etching with appropriate parameters, and the single-crystal piezoelectric thin film is not lost, then the residual peeling layer on the surface of the single-crystal piezoelectric thin film is efficiently removed by the second laser irradiation with appropriate parameters, and the surface of the single-crystal piezoelectric thin film is not damaged, and the surface roughness is good.

[0043] Further, the surface roughness obtained by the second laser irradiation is 0.1-0.5 nm.

[0044] In step (3), a metal pad layer is deposited in the first via and on the surface of the second electrode by thermal evaporation or magnetron sputtering.

[0045] Compared with the prior art, the present application has the following advantages:

[0046] (1) Compared with the prior art in which a dry etching is used to remove the residual release layer, the present application uses a dry etching to remove most of the release layer, and then uses a laser irradiation method to obtain a good surface roughness without damaging the single-crystal piezoelectric thin film. Compared with the prior art in which an etching stop layer is introduced, the single-crystal piezoelectric thin film prepared by the above-mentioned release layer removal process has a higher half-width and a better quality factor, thereby obtaining a cavity-type film bulk acoustic resonator with excellent performance.

[0047] (2) The present application can accurately measure the thickness of the single-crystal piezoelectric thin film of the entire wafer in line, compared with the prior art in which a measuring block is used to measure the thickness of only a partial area of the single-crystal piezoelectric thin film, and the thickness of the single-crystal piezoelectric thin film is calculated by subtracting the thickness of other layers during the measurement process. The single-crystal piezoelectric thin film thickness measurement method provided by the present application can directly and accurately measure the thickness of the entire area of the single-crystal piezoelectric thin film, saving the measuring block process while improving the accuracy of the thickness measurement. Accurate testing of the thickness of the piezoelectric thin film in different areas is crucial for the subsequent Trimming process, which directly determines the yield of the device. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 Cross-sectional view of the second substrate and the release layer thereon provided for Example 1;

[0049] Figure 2 Cross-sectional view of the second substrate and the release layer, single-crystal piezoelectric thin film thereon provided for Example 1;

[0050] Figure 3 Cross-sectional view of the second substrate and the release layer, single-crystal piezoelectric thin film, first electrode thereon provided for Example 1;

[0051] Figure 4 Cross-sectional view of the second substrate and the release layer, single-crystal piezoelectric thin film, first electrode, sacrificial layer thereon provided for Example 1;

[0052] Figure 5 Cross-sectional view of the second substrate and the release layer, single-crystal piezoelectric thin film, first electrode, sacrificial layer, opaque medium layer thereon provided for Example 1;

[0053] Figure 6Cross-sectional view of the second substrate and the release layer, the single-crystal piezoelectric thin film, the first electrode, the sacrificial layer, the opaque dielectric layer, the bonding layer thereon provided for Example 1;

[0054] Figure 7 Cross-sectional view of the second substrate and the release layer, the single-crystal piezoelectric thin film, the first electrode, the sacrificial layer, the opaque dielectric layer, the bonding layer, the second substrate thereon provided for Example 1;

[0055] Figure 8 Cross-sectional view of the device after the first laser irradiation provided for Example 1;

[0056] Figure 9 Cross-sectional view of the device after the second laser irradiation and dry etching provided for Example 1;

[0057] Figure 10 Cross-sectional view of the second substrate and the bonding layer, the opaque dielectric layer, the sacrificial layer, the first electrode, the single-crystal piezoelectric thin film, the second electrode thereon provided for Example 1;

[0058] Figure 11 Cross-sectional view of the device after via etching provided for Example 1;

[0059] Figure 12 Cross-sectional view of the second substrate and the bonding layer, the opaque dielectric layer, the sacrificial layer, the first electrode, the single-crystal piezoelectric thin film, the second electrode, the metal pad layer thereon provided for Example 1, wherein the first filling hole and the second filling hole are provided in the single-crystal piezoelectric thin film;

[0060] Figure 13 Cavity type thin film bulk acoustic resonator prepared for Example 1;

[0061] In the figure, 101 - release layer, 102 - single-crystal piezoelectric thin film, 103 - first electrode, 104 - sacrificial layer, 105 - opaque dielectric layer, 106 - bonding layer, 107 - first substrate, 108 - second electrode, 109-1 is the first filling hole, 109-2 is the second filling hole, 110 - metal pad layer;

[0062] Figure 14 XRD pattern of the single-crystal piezoelectric thin film prepared for Example 1;

[0063] Figure 15 XRD pattern of the single-crystal piezoelectric thin film prepared for Comparative Example 1;

[0064] Figure 16 Thickness mapping of the single-crystal piezoelectric thin film prepared for Example 1;

[0065] Figure 17 Thickness mapping of the single-crystal piezoelectric thin film prepared for Comparative Example 1;

[0066] Figure 18 A surface roughness map of the single-crystal piezoelectric thin film prepared for Example 1 is shown in FIG. 1.

[0067] Figure 19 A surface roughness map of the single-crystal piezoelectric thin film prepared for Comparative Example 1 is shown in FIG. 2. DETAILED DESCRIPTION

[0068] A cavity film bulk acoustic resonator includes a first substrate 107, a bonding layer 106, an opaque dielectric layer 105, a piezoelectric oscillation stack, and a metal pad layer 110.

[0069] The bonding layer 106 is formed on the first substrate 107, the opaque dielectric layer 105 is formed on the bonding layer 106, the piezoelectric oscillation stack is formed on the opaque dielectric layer 105, the cavity 104-1 is between the opaque dielectric layer 105 and the piezoelectric oscillation stack, and the metal pad layer 110 is connected to the piezoelectric oscillation stack.

[0070] The piezoelectric oscillation stack includes a first electrode 103, a single-crystal piezoelectric thin film 102, and a second electrode 108. The first electrode 103 is formed on the opaque dielectric layer 105, the single-crystal piezoelectric thin film 102 is formed on the first electrode 103, and the second electrode 108 is formed on the single-crystal piezoelectric thin film 102. The metal pad layer 110 is connected to the first electrode 103 and the second electrode 108, respectively.

[0071] The metal pad layer 110 is divided into a first metal pad layer 110-a and a second metal pad layer 110-b. The first metal pad layer 110-a is connected to the first electrode 103 through the single-crystal piezoelectric thin film 102 and is separated from the second electrode 108.

[0072] The second metal pad layer 110-b is connected to the second electrode 108 and is separated from the first metal pad layer 110-a.

[0073] 100 is a first substrate, which can be one or any combination of silicon carbide, sapphire, etc.

[0074] 101 is a separation layer, which can be one or any combination of gallium nitride, tantalum nitride, niobium nitride, etc., and has a thickness of 100-5000 nm.

[0075] 102 is a single-crystal piezoelectric thin film grown on the separation layer 101. The piezoelectric layer can be one or any combination of aluminum nitride, doped aluminum nitride, zinc oxide, lithium nickelate, etc., and has a thickness of 0.3-2 μm.

[0076] 103 is the first electrode deposited on the single-crystal piezoelectric film 102, which can be one of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, nickel, or any combination thereof, with a thickness of 100-300 nm, and is formed into a designed pattern by plasma etching, wet etching, lift-off, etc., and the lateral width of the first electrode 103 is 100-600 μm.

[0077] 104 is the sacrificial layer deposited on the single-crystal piezoelectric film 102 and the first electrode 103, which can be amorphous silicon, polysilicon, silicon nitride, organic matter, phosphoric acid glass, doped silicon oxide, etc., with a thickness of 0.5-3 μm, and is patterned by plasma etching, wet etching, etc., and the cross section of the cavity can be one of trapezoidal, triangular, rectangular, square, or any combination thereof, and the lateral width of the sacrificial layer 104 is 50-250 μm.

[0078] 105 is the opaque dielectric layer deposited on the single-crystal piezoelectric film 102, the first electrode 103, and the sacrificial layer 104, which can be one of silicon nitride, silicon, tantalum nitride, ceramic, or any combination thereof, with a thickness of 0.1-5 μm.

[0079] 106 is the bonding layer deposited on the opaque dielectric layer 105, which can be one of silicon oxide, polysilicon, silicon nitride, organic matter, phosphoric acid glass, doped silicon oxide, or any combination thereof, with a thickness of 0.5-10 μm, and a roughness of less than 0.5 nm after CMP treatment.

[0080] 107 is the second substrate, which can be one of glass, silicon, silicon carbide, sapphire, ceramic, or any combination thereof.

[0081] After the device is bonded, the first substrate 100 is irradiated with a 248 nm wavelength laser, the release layer 101 absorbs energy and decomposes, and the first substrate separates, leaving a 0.5-3 μm defect on the surface of the separated device, which is removed by a dry etching and laser irradiation decomposition combined process.

[0082] 108 is the second electrode deposited on the single-crystal piezoelectric film 102, which can be one of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, nickel, or any combination thereof, with a thickness of 100-400 nm, and is formed into a designed pattern by plasma etching, wet etching, lift-off, etc., and the lateral width of the second electrode 108 is 50-300 μm.

[0083] 109-1 and 109-2 are metal pad filling holes and sacrificial layer release holes formed in the single-crystal piezoelectric film by plasma etching, wet etching, etc.

[0084] 110 is a metal pad deposited on the single-crystal piezoelectric thin film 102, the filling hole 109-1 and the second electrode 108. The material can be one of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten and nickel or any combination thereof, with a thickness of 100-4000nm, and patterned by lift-off.

[0085] The cavity 104-1 required for the operation of the FBAR device is created by releasing the sacrificial layer 104 through wet etching, fumigation, or other methods. The cavity has a depth of 0.5-2 μm and a lateral width of 40-200 μm.

[0086] Example 1

[0087] This invention also provides a method for fabricating a cavity-type thin-film bulk acoustic resonator, the specific steps of which are as follows:

[0088] (1) Clean the double-polished sapphire substrate 100 by ultrasonic water washing with acetone and isopropanol. The sapphire substrate orientation is C(0001).

[0089] (2) Figure 1 As shown, a 1 μm GaN film is deposited on the surface of a double-polished sapphire substrate 100 as a release layer 101 using magnetron sputtering or MOCVD. The GaN film growth process is as follows: TMGa gas flow rate is 20 sccm, NH3 gas flow rate is 800 sccm, growth temperature is 1000℃, chamber pressure is 30 mbar, and growth rate is approximately 10 nm / min. Sometimes, in order to make the GaN film more compatible with the sapphire substrate, an ALN ​​film of about 100 nm is sputtered before growing the GaN film.

[0090] (3) Figure 2 As shown, an 800 nm ALN single crystal piezoelectric thin film 102 is deposited on the release layer 101 using magnetron sputtering or MOCVD. The growth process of the single crystal ALN is as follows: TMAl gas flow rate is 10 sccm, NH3 gas flow rate is 900 sccm, growth temperature is 1200℃, chamber pressure is 45 mbar, and growth rate is approximately 5 nm / min.

[0091] (4) Figure 3 As shown, a 150 nm thick layer of metallic molybdenum is deposited on a single-crystal piezoelectric thin film 102 using methods such as thermal evaporation or magnetron sputtering, and a first electrode 103 is formed by plasma etching or wet etching. The lateral width of the first electrode is 300 μm. Typically, an ALN ​​thin film of about 30 nm is also deposited as a protective layer, which is not shown in the figure.

[0092] (5) Figure 4As shown, a SiO2 layer of approximately 150 nm is deposited on the first electrode 103 using PECVD as a buffer layer for sacrificial layer deposition (not shown in the figure). Next, a 1.2 μm layer of amorphous silicon is deposited as a sacrificial layer, and then plasma etched to form sacrificial layer 104, which has a lateral width of 200 μm.

[0093] (6) Figure 5 As shown, a 2μm thick SiN film was deposited on the surfaces of the single-crystal piezoelectric thin film 102, the first electrode 103, and the sacrificial layer 104 using LPCVD. x 105 serves as the online thickness testing structure for the single-crystal piezoelectric thin film 102. (SiN) x Thin film growth process: SiH2Cl2 gas flow rate is 25 sccm, NH3 gas flow rate is 150 sccm, growth temperature is 350℃, chamber pressure is 100 mbar, and growth rate is approximately 100 nm / min.

[0094] (7) Figure 6 As shown, a 5μm SiO2 layer is deposited on the opaque dielectric layer 105 by LPCVD and then subjected to CMP treatment to form a bonding layer 106 with a surface roughness of less than 0.5nm.

[0095] (8) Figure 7 As shown, the device is bonded to the second substrate 107 through the bonding layer 106 and is ready for laser lift-off;

[0096] (9) such as Figure 8 As shown, a laser of a specific wavelength is used to irradiate the first substrate 100. The GaN lift-off layer 101 absorbs the laser irradiation energy and decomposes to generate Ga metal and nitrogen gas. The nitrogen gas is discharged through a gas path. After the laser irradiation process, part of the GaN lift-off layer 101 becomes opaque Ga metal. The melting point of Ga metal is 29.8℃. The lifted device can be directly separated from the first substrate 100 by placing it on a hot plate at 40℃. The specific laser lift-off process is as follows: the laser wavelength is 248nm and the laser energy density is 500mJ / cm². 2 The laser operates by irradiating the substrate edge in pulses, with one pulse covering a range of 250μm x 250μm.

[0097] (10) such as Figure 9As shown, after the first substrate is separated, there is a part of the residual peeling layer, i.e. GaN peeling layer and Ga metal generated after decomposition, on the surface of the device, the thickness of the residual peeling layer is 1000 nm, and the generated Ga metal is generally removed by using dilute hydrochloric acid. The remaining undecomposed GaN is first etched by dry etching, and the remaining part of the GaN is removed by decomposition through laser irradiation after dry etching, and the generated Ga metal is still removed by using dilute hydrochloric acid. When the laser irradiation is no longer generating bright white Ga metal, it indicates that the residual peeling layer GaN is completely removed. The advantage of the GaN removal process is that it can ensure that the single-crystal piezoelectric thin film is not damaged while retaining the initial growth morphology of the thin film, thereby making the single-crystal piezoelectric thin film have a relatively good roughness. The dry etching process parameters in the GaN removal process are: RF power 1000 W, chamber pressure 20 mT, etching gas Cl2 / Ar flow rate 60 / 10 sccm, and etching rate about 520 nm / min; the laser decomposition process parameters are: laser wavelength 248 nm, laser energy density 450 mJ / cm 2 , chamber pressure 30 mT;

[0098] (11) As shown in Figure 10 , 150 nm of metal aluminum is deposited on the single-crystal piezoelectric thin film 102 by using a magnetron sputtering method, and a second electrode 108 is formed by using a plasma etching or wet etching method, the lateral width of the second electrode is 230 μm;

[0099] (12) As shown in Figure 11 , a through hole 109-1, 109-2 is formed on the single-crystal piezoelectric thin film 102 by using a wet etching or dry etching process, wherein 109-1 is a metal pad filling hole, and 109-2 is a sacrificial layer release hole, the lower end of the through hole 109-1 is connected with the first electrode 103, and the lower end of the through hole 109-2 is connected with the sacrificial layer 104;

[0100] (13) As shown in Figure 12 , 1 μm of metal aluminum is deposited on the single-crystal piezoelectric thin film 102, the filling hole 109-1 and the second electrode 108 by using an electron beam evaporation or a magnetron sputtering method, and a metal pad 110 is patterned by using a Lift-off process, the metal pad 110 filled in the 109-1 is not connected with the second electrode 108;

[0101] (14) As shown in Figure 13 , the exposed sacrificial layer buffer layer SiO2 is removed through the 109-2 release hole by using an HF solution, and then the amorphous silicon sacrificial layer 104 is removed through the sacrificial layer release hole 109-2 by using a XeF2 fumigation method to form a cavity 104-1 required for FBAR device operation, and finally a cavity type film bulk acoustic resonator is obtained.

[0102] Performance test:

[0103] As shown in Figure 14 , the full width at half maximum (FWHM) of the prepared single-crystal piezoelectric film is 109 sec measured by a high-resolution XRD test method, and a better FWHM value can obtain a better quality factor, thereby obtaining a better filter performance;

[0104] As shown in Figure 16 , the single-crystal piezoelectric film thickness mapping of the prepared single-crystal piezoelectric film is measured by an automatic optical film thickness measurement test method, and the thickness value of each region of the single-crystal piezoelectric film can be accurately obtained from the figure, and the single-crystal piezoelectric film thickness is thick and uniform;

[0105] As shown in Figure 18 , the roughness of the prepared single-crystal piezoelectric film is 0.34 nm measured by an atomic force microscope test method, and the roughness is low.

[0106] Comparative Example 1

[0107] Compared with Example 1, no opaque medium layer is added, an etching stop layer is introduced between the peeling layer and the single-crystal piezoelectric film, and the residual peeling layer is removed by dry etching in step (10).

[0108] Performance test:

[0109] As shown in Figure 15 , the full width at half maximum (FWHM) of the prepared single-crystal piezoelectric film is 1703 sec measured by a high-resolution XRD test method;

[0110] As shown in Figure 17 , the single-crystal piezoelectric film thickness mapping of the prepared single-crystal piezoelectric film is measured by an automatic optical film thickness measurement test method, and it can be seen from the figure that the thickness value obtained is the thickness of the single-crystal piezoelectric film to the first substrate. If the thickness of the single-crystal piezoelectric film is to be obtained, it needs to be converted. Due to the bonding layer and the instability of the thickness of the opaque medium layer, the accuracy of the thickness of the single-crystal piezoelectric film obtained by conversion is poor;

[0111] As shown in Figure 19 , the roughness of the prepared single-crystal piezoelectric film is 8.85 nm measured by an atomic force microscope test method.

Claims

1. A cavity film bulk acoustic resonator, characterized by, The piezoelectric oscillation stack comprises a first substrate, a bonding layer, an opaque dielectric layer, a piezoelectric oscillation stack and a metal pad layer. The piezoelectric oscillation stack comprises a first substrate, a bonding layer, an opaque dielectric layer, a piezoelectric oscillation stack and a metal pad layer. The preparation method of the cavity film bulk acoustic resonator comprises the following steps: (1) selecting a second substrate with a release layer, preparing a single-crystal piezoelectric film on the surface of the second substrate, applying a first electrode on the surface of the single-crystal piezoelectric film, preparing a sacrificial layer on the surface of the first electrode, preparing an opaque dielectric layer on the surface of the sacrificial layer, bonding a first substrate on the surface of the opaque dielectric layer, and bonding the first substrate on the surface of the bonding layer; (2) performing first laser irradiation on the release layer, peeling the second substrate with the release layer from the single-crystal piezoelectric film, dry etching the residual release layer on the surface of the single-crystal piezoelectric film, and then performing second laser irradiation on the dry-etched residual release layer to obtain a single-crystal piezoelectric film with a surface roughness of 0.5 nm or less; (3) forming a first through hole and a second through hole in the single-crystal piezoelectric film obtained in step (2), applying a first metal pad layer to the first through hole so that the first metal pad layer is located on the first electrode, adding an etching solution to the second through hole, removing the sacrificial layer by fumigation to form a cavity, applying a second electrode layer to the surface of the single-crystal piezoelectric film obtained in step (2), and depositing a second metal pad layer on the surface of the second electrode layer to obtain a cavity type film bulk acoustic resonator.

2. The cavity film bulk acoustic resonator of claim 1, wherein, The piezoelectric oscillation stack comprises a first substrate, a bonding layer, an opaque dielectric layer, a piezoelectric oscillation stack and a metal pad layer.

3. The cavity film bulk acoustic resonator of claim 1, wherein, The metal pad layer is divided into a first metal pad layer and a second metal pad layer, the first metal pad layer passes through the single-crystal piezoelectric film and is located on the first electrode, and is separated from the second electrode; The second metal pad layer is located on the second electrode and is separated from the first metal pad layer.

4. The cavity film bulk acoustic resonator of claim 1, wherein, The opaque dielectric layer is one or more of silicon nitride, silicon, silicon nitride, and ceramic.

5. The cavity film bulk acoustic resonator of claim 1 or 4, wherein, The thickness of the opaque dielectric layer is 0.1-5 μm.

6. The cavity film bulk acoustic resonator of claim 1, wherein, The cross section of the cavity is one or more of trapezoidal, rectangular and square, the depth of the cavity is 0.5-2 μm, and the lateral width is 40-200 μm.

7. The cavity film bulk acoustic resonator of claim 2, wherein, The single-crystal piezoelectric film is one or more of aluminum nitride, doped aluminum nitride, zinc oxide and lithium nickelate.

8. The cavity film bulk acoustic resonator of claim 2 or 7, wherein, The thickness of the single-crystal piezoelectric film is 0.3-2 μm.

9. The method of claim 8, wherein the cavity film bulk acoustic resonator is a film bulk acoustic resonator (FBAR) or a bulk acoustic wave resonator (BAWR). In step (2), the thickness of the residual stripping layer is 100-4000 nm, the dry etching parameters are as follows: radio frequency power is 500-1000 w, Cl2 / Ar gas flow is 30-100 / 5-40 sccm, chamber pressure is 5-40 mT, and the second laser irradiation parameters are as follows: light wavelength ≤ 248 nm, and laser energy density is 400-600 mJ / cm2. 2 .

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