A film bulk acoustic wave device with a cavity structure obtained by stress control and a method for manufacturing the same

Abstract

The application discloses a preparation method of a thin film bulk acoustic wave device with a cavity structure obtained by stress control, which comprises the following steps: forming a natural oxidation layer on a substrate, setting an effective area on the natural oxidation layer, respectively forming a piezoelectric seed layer and a sacrifice layer in the effective area, forming a first electrode on the piezoelectric seed layer, and the height of the sacrifice layer is not lower than the height sum of the piezoelectric seed layer and the first electrode, and removing the natural oxidation layer outside the effective area to expose the substrate; depositing a piezoelectric thin film with internal stress on the exposed surfaces of the substrate, the sacrifice layer and the first electrode, depositing a second electrode on the piezoelectric thin film, connecting a metal pad layer with the first electrode and the second electrode, removing the sacrifice layer and the natural oxidation layer in the effective area through a sacrifice layer release hole to form a cavity. The method can effectively solve the problem of difficult removal of the sacrifice layer in the traditional process, and the preparation method is simple and efficient. The application further discloses a cavity thin film bulk acoustic wave device.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of resonators, and relates to a thin film bulk acoustic wave device with a cavity structure obtained through stress control and a preparation method thereof. BACKGROUND

[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 wave resonators (FBARs) have the advantages of small size, low loss, high quality factor, large power capacity and high resonant frequency, and therefore have a broad application prospect in related fields, especially in high-frequency communication, and have become a research hotspot in the industry and academia.

[0003] The performance level of a filter is determined by its factor of merit (FOM), which is defined as FOM=Q*K2eff, wherein Q is the quality factor, which describes the vibration attenuation of an oscillator or resonator and represents the bandwidth of the resonator relative to the center frequency, and is related to the structure and process integration of the FBAR device. The Q factor of the most advanced FBAR filter can reach 2500 to 5000. K2eff is called the effective coupling coefficient, which is related to the properties of the piezoelectric thin film material.

[0004] The preparation of the cavity required for the operation of a thin film bulk acoustic wave resonator (FBAR) is a very critical process. The traditional preparation method is to first etch a cavity on a substrate, then fill the cavity with a releasable material, then perform a CMP process to make the filler in the cavity flush with the surface of the substrate, then deposit a first electrode, a piezoelectric layer and a second electrode on the substrate after the CMP process in sequence, then etch a through hole, and finally release the sacrificial layer to form the cavity required for the operation of the thin film bulk acoustic wave resonator (FBAR).

[0005] A cavity thin film bulk acoustic wave resonator is disclosed in Chinese Patent No. 202111442142.X, which comprises a first substrate, a bonding layer, an opaque medium layer, a piezoelectric oscillation stack and a metal pad layer. 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, and the cavity is formed between the opaque medium layer and the piezoelectric oscillation stack. The metal pad layer is connected to the piezoelectric oscillation stack. The resonator has a low surface roughness, and the thickness of each region of the thin film can be measured conveniently and accurately. The patent also discloses a preparation method of the cavity thin film bulk acoustic wave resonator.

[0006] The Chinese patent with the patent number 202010923553.X discloses a cavity type film bulk acoustic resonator packaging structure and a preparation method thereof. The structure comprises a substrate, a substrate, a piezoelectric oscillation stack and a metal bonding layer. The piezoelectric oscillation stack and the metal bonding layer are located between the substrate and the substrate. The metal bonding layer is arranged around the piezoelectric oscillation stack and is formed by the cross-bonding of the metal columns arranged on the substrate and the substrate. There is a first cavity between the piezoelectric oscillation stack and the substrate, which is formed by directly etching or corroding the substrate. There is a second cavity between the piezoelectric oscillation stack and the substrate, which is formed by releasing the sacrificial layer. The piezoelectric oscillation stack comprises a lower electrode, a piezoelectric layer and an upper electrode. The structure is prepared by directly cross-bonding the substrate part and the substrate part treated in a specific way, and then releasing the sacrificial layer.

[0007] However, the above-mentioned patent is affected by the sacrificial layer factor, and the preparation process of the piezoelectric layer has certain limitations, and the optimization of the quality of the piezoelectric layer film has an upper limit. SUMMARY

[0008] The application provides a preparation method of a film bulk acoustic wave device with a cavity structure obtained by stress control. The method can effectively solve the problem of difficult removal of the sacrificial layer in the traditional process, and prepare a cavity film bulk acoustic wave device meeting the performance requirements through a relatively simple process.

[0009] A preparation method of a film bulk acoustic wave device with a cavity structure obtained by stress control, comprising:

[0010] (1) forming a natural oxidation layer on the substrate, setting an effective area on the natural oxidation layer, forming a piezoelectric seed layer and a sacrificial layer in the effective area respectively, forming a first electrode on the piezoelectric seed layer, and the sacrificial layer is located on both sides of the piezoelectric seed layer or surrounds the piezoelectric seed layer, wherein the height of the sacrificial layer is not less than the height sum of the piezoelectric seed layer and the first electrode, and the natural oxidation layer outside the effective area is removed to expose the substrate;

[0011] (2) depositing a piezoelectric film with an internal stress of 600-1500 MPa on the surface of the exposed substrate, the sacrificial layer and the first electrode, depositing a second electrode on the piezoelectric film, depositing a first metal pad layer on the second electrode, etching a metal pad filling hole to the first electrode on the piezoelectric film, depositing a second metal pad layer on the first electrode through the metal pad filling hole, and etching a sacrificial layer release hole on the piezoelectric film;

[0012] (3) adding etching liquid to the sacrificial layer release hole for removing the sacrificial layer and the natural oxidation layer in the effective area, so that the piezoelectric film in the effective area is deformed under the action of the internal stress, the piezoelectric seed layer is separated from the silicon substrate to form a cavity, and then a cavity film bulk acoustic wave device is obtained.

[0013] The substrate is one or any combination of silicon, silicon carbide, sapphire, ceramic.

[0014] The natural oxide layer is obtained by thermal oxidation of the substrate and has a thickness of 10-50 nm.

[0015] The piezoelectric seed layer is aluminum nitride and has a thickness of 10-100 nm. The piezoelectric seed layer can improve the quality of the electrode film and prevent oxidation of the electrode.

[0016] The first electrode is one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten or nickel.

[0017] The first electrode has a thickness of 50-400 nm and a lateral width of 60-400 μm.

[0018] The sacrificial layer is amorphous silicon, polysilicon, silicon nitride, organic matter, phosphoric acid glass or doped silicon oxide.

[0019] The sacrificial layer has a thickness of 50-500 nm and a lateral width of 5-30 μm.

[0020] The sacrificial layer is immediately adjacent to the first electrode or partially remains on the first electrode.

[0021] The first electrode and the sacrificial layer are both patterned by plasma etching or wet etching.

[0022] The piezoelectric film is aluminum nitride, doped aluminum nitride, zinc oxide, lithium nickelate or lead zirconate titanate.

[0023] The piezoelectric film has a thickness of 0.3-2 μm.

[0024] The piezoelectric film is deposited by a method comprising:

[0025] The Ar / N2 gas flow is 10-50 / 50-150 sccm, the growth temperature is 200-300 °C, the chamber pressure is 2-4 mT, the Target / RF power is 5000-6000 / 120-200 W, and the growth rate is 1-5 nm / min.

[0026] The second electrode is one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten or nickel.

[0027] The second electrode has a thickness of 100-300 μm and a lateral width of 50-300 μm.

[0028] The second electrode is patterned by plasma etching, wet etching or Lift-off.

[0029] A metal pad filling hole and a sacrificial layer releasing hole are formed on the piezoelectric film by plasma etching or wet etching.

[0030] The first metal pad layer and the second metal pad layer are one of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, nickel or any combination thereof.

[0031] The thickness of the first metal pad layer and the second metal pad layer is 200-4000nm, and the first metal pad layer is patterned by a lift-off method and is not connected to the second electrode.

[0032] The cavity has a depth of 50-2000nm and a lateral width of 50-250μm, and the lateral width of the cavity is greater than the lateral width of the first electrode.

[0033] The application further provides a cavity film bulk acoustic wave device obtained by the preparation method for preparing a cavity film bulk acoustic wave device by stress control, and the cavity film bulk acoustic wave device has an effective area on the cavity film bulk acoustic wave device, and comprises:

[0034] A substrate;

[0035] A piezoelectric oscillation stack, in the effective area, the piezoelectric oscillation stack and the substrate form a cavity, and outside the effective area, the piezoelectric oscillation stack is located on the substrate; and

[0036] A metal pad layer, located on the piezoelectric oscillation stack.

[0037] The piezoelectric oscillation stack comprises:

[0038] A first metal pad layer, located on the piezoelectric film and connected to the first electrode through a metal pad filling hole in the piezoelectric film;

[0039] A second metal pad layer, located on the second electrode;

[0040] A second electrode, located on the piezoelectric film;

[0041] The piezoelectric film, in the effective area, the piezoelectric film and the substrate form a cavity, and outside the effective area, the piezoelectric film is located on the substrate;

[0042] The first electrode, in the cavity, is located between the piezoelectric seed layer and the piezoelectric film; and

[0043] The piezoelectric seed layer, in the cavity, the first electrode is deposited on the piezoelectric seed layer, and the piezoelectric seed layer is separated from the substrate.

[0044] Compared with the prior art, the application has the following beneficial effects:

[0045] The application releases the sacrifice layer and the natural oxidation layer in the effective area, so that the piezoelectric film can be deformed by the self stress, the piezoelectric seed layer is separated from the substrate to form a cavity, the preparation process is simplified, the generation cost is reduced, the device preparation efficiency is improved, and the production capacity is improved.

[0046] The natural oxidation layer outside the effective area is removed before the sacrifice layer and the natural oxidation layer are released, so that the piezoelectric film outside the effective area is not peeled off from the substrate during the release of the sacrifice layer and the natural oxidation layer in the effective area; and the metal pad filling hole is set in the piezoelectric film to release the stress in the area, so that the first electrode is prevented from being separated from the piezoelectric film when the cavity is formed, and the piezoelectric film is prevented from being peeled off from the first electrode and being broken during the deformation of the piezoelectric film, based on the above reasons, the cavity film bulk acoustic wave device can be successfully prepared. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 A cross-sectional view of preparing the natural oxidation layer is provided for the specific embodiment, wherein 100 is the substrate, and 101 is the natural oxidation layer;

[0048] Figure 2 A cross-sectional view of preparing the first electrode is provided for the specific embodiment, wherein 102 is the piezoelectric seed layer, and 103 is the first electrode;

[0049] Figure 3 A cross-sectional view of preparing the sacrifice layer is provided for the specific embodiment, wherein 104 is the sacrifice layer;

[0050] Figure 4 A cross-sectional view of growing the piezoelectric film is provided for the specific embodiment, wherein 105 is the piezoelectric film;

[0051] Figure 5 A cross-sectional view of growing the second electrode is provided for the specific embodiment, wherein 106 is the second electrode;

[0052] Figure 6 A cross-sectional view of etching the piezoelectric film via is provided for the specific embodiment, wherein 107 is the first electrode pad deposition via, 107-1 is the release hole, and the dashed line represents that the section is invisible;

[0053] Figure 7 A cross-sectional view of growing the metal pad is provided for the specific embodiment, wherein 108 is the metal pad connected with the first electrode, 108-1 is the metal pad connected with the second electrode, and the dashed line represents that the section is invisible;

[0054] Figure 8 A cross-sectional view of the cavity prepared for the specific embodiment, wherein 104-1 is the formed cavity;

[0055] Figure 9 Actual anatomical diagram of the thin-film bulk acoustic resonator (FBAR) prepared for a specific embodiment;

[0056] Figure 10 The actual test impedance curve of the thin-film bulk acoustic resonator (FBAR) prepared for a specific embodiment;

[0057] Figure 11 The actual Q-value curve of the thin-film bulk acoustic resonator (FBAR) prepared for a specific embodiment is shown in the figure. Detailed Implementation

[0058] This embodiment provides a method for fabricating a thin-film bulk acoustic resonator (FBAR), the specific steps of which are as follows:

[0059] (1) The silicon substrate 100 was ultrasonically cleaned with SPM solution and the silicon substrate orientation was C(001).

[0060] (2) Figure 1 As shown, the cleaned substrate 100 is subjected to thermal oxidation treatment, so that a natural oxide layer 101 of about 10 nm is formed on the surface of the substrate 100.

[0061] (3) Figure 2 As shown, a 30 nm AlN seed layer 102 and a 160 nm molybdenum layer are deposited on a substrate 100 that has undergone thermal oxidation treatment using methods such as thermal evaporation or magnetron sputtering, and a first electrode 103 is patterned to form the first electrode. The lateral width of the first electrode is 260 μm. The AlN seed layer 102 outside the first electrode region is removed by etching with a diluted KOH solution.

[0062] (4) Figure 3 As shown, a 200nm SiO2 layer is deposited as a sacrificial layer using PECVD and patterned to form a sacrificial layer 104. The lateral width of the sacrificial layer 104 is 10μm. Here, the sacrificial layer acts as a spacer, closely adjacent to or partially remaining on the first electrode 103. This step can simultaneously remove the natural oxide layer 101 in the area outside the pattern of the sacrificial layer 104.

[0063] (4) Figure 4As shown, before depositing the piezoelectric thin film 105, a dilute HF solution is used to remove the silicon oxide film layer on the surface of the substrate, and then a 600 nm ALN thin film 105 is deposited on the structure prepared in step (3) using a magnetron sputtering or MOCVD method. The growth process of the ALN thin film is as follows: Ar / N2 gas flow is 20 / 100 sccm, growth temperature is 200°C, chamber pressure is 3.4 mT, Target / RF power is 6000 / 160 W, growth rate is about 6 nm / min, and the stress of the film layer after growth should be controlled in the range of 600-1500 Mpa. The control of the film layer stress is a very critical parameter. If the stress is too small, the cavity cannot be formed after the sacrificial layer is etched; if the stress is too large, the film layer will be broken after the sacrificial layer is etched due to too large deformation of the film layer.

[0064] (5) As shown in Figure 5 , a 170 nm metal molybdenum is deposited on the piezoelectric layer 105 using a thermal evaporation or magnetron sputtering method, and is patterned to form a second electrode 106. The lateral width of the second electrode is 200 μm. In general, a metal protective layer with a thickness of about 100 nm is also deposited, which is not shown in the figure.

[0065] (6) As shown in Figure 6 , a via hole 107 and 107-1 are formed on the piezoelectric layer 105 using a wet etching or dry etching process. The via hole 107 is a metal pad filling hole, and the via hole 107-1 is a sacrificial layer releasing hole. The lower end of the via hole 107 is connected to the first electrode 103, and the lower end of the via hole 107-1 is connected to the sacrificial layer 104. The via hole etching process is as follows: RF power is 800 / 300 W, chamber pressure is 7 mT, etching gas BCL3 / CL2 flow is 120 / 20 sccm, and etching rate is about 100 nm / min.

[0066] (7) As shown in Figure 7 , a 400 nm gold is deposited on the piezoelectric layer 105, the filling hole 107 and the second electrode 106 using a thermal evaporation or magnetron sputtering method, and is patterned to form a metal pad 108 and 108-1 through a Lift-off process. In general, a 10 nm adhesion layer is deposited before depositing the metal pad 108 to increase the adhesion of the metal pad to the electrode, which is not shown in the figure. The metal pad 108 is not connected to the second electrode 106.

[0067] (8) As shown in Figure 8As shown, the sacrificial layer 104 and part of the oxide layer 101 formed on the substrate under the seed layer 102 are removed by releasing hole 107-1 through the sacrificial layer by dilute BOE soaking corrosion. Due to the stress of the film layer, the film layer of the effective area of the device is deformed, the piezoelectric seed layer 102 is separated from the substrate, and the cavity 104-1 required for the operation of the FBAR device is formed. Because the silicon oxide film layer on the surface of the substrate has been removed by dilute HF solution before the piezoelectric layer is deposited, the entire device will not be separated from the substrate due to stress. The metal pad 108 will not be obviously separated from the substrate due to the etching of the piezoelectric layer and the release of stress. The prepared cavity type thin film bulk acoustic wave device is as shown in Figure 9 As shown, the BAW device prepared by the present application has the measured impedance data as shown in Figure 10 As shown, the BAW device prepared by the present application has the measured frequency quality factor of about 2500. Figure 11

[0068] The substrate 100 supports the device, and the material can be one or any combination of silicon, silicon carbide, sapphire, and ceramic.

[0069] The substrate 100 is formed on the surface of the substrate 100 after thermal oxidation treatment, and the thickness is about 10 nm.

[0070] The seed layer 102 is grown on the oxide layer 101, and the material is generally aluminum nitride, and the thickness is 10-100 nm.

[0071] The first electrode 103 is deposited on the seed layer 102, and the material can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, and nickel, and the thickness is 50-400 nm. The first electrode 102 is formed into a designed pattern by plasma etching and wet etching, and the lateral width of the first electrode 102 is 60-400 μm.

[0072] The sacrificial layer 104 is deposited on the oxide layer 101, and the material can be amorphous silicon, polycrystalline silicon, silicon nitride, organic matter, phosphoric acid glass, and doped silicon oxide, and the thickness is 50-500 nm. The sacrificial layer 104 is patterned by plasma etching and wet etching, and the lateral width of the sacrificial layer 104 is 10 μm. The sacrificial layer functions as a gasket and is close to the first electrode 103 or partially remains on the first electrode 103.

[0073] The piezoelectric film 105 is deposited on the substrate 100, the sacrificial layer 104, and the first electrode 103, and the material can be aluminum nitride, doped aluminum nitride, zinc oxide, lithium nickelate, lead zirconate titanate, etc., and the thickness is 0.3-2 μm. The stress of the film layer is controlled to be 600-1500 Mpa.

[0074] ​106 is a second electrode deposited on the piezoelectric layer 105, the material can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, nickel, the thickness is 500-500nm, and the designed pattern is formed by plasma etching, wet etching, lift-off, etc., the lateral width of the second electrode 105 is 50-300μm.

[0075] 107, 107-1 are metal pad filling holes and sacrificial layer releasing holes formed by plasma etching, wet etching, etc.

[0076] 108 is a metal pad deposited on the piezoelectric layer 105 and the filling hole 107, 108-1 is a metal pad deposited on the second electrode 106, the material of the metal pad can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, nickel, the thickness is 200-4000nm, and the pad 108 is patterned by lift-off, the pad 108 is not connected to the second electrode 106.

[0077] The cavity 104-1 required for the FBAR device to work is formed by the stress of the film layer causing the deformation of the effective area film layer of the device, the seed layer 102 is separated from the substrate, and the depth of the cavity formed by the deformation is 50-2000nm.

[0078] The present application forms the cavity required for the FBAR device to work by using the stress of the piezoelectric film itself to cause the deformation of the film layer, and this method of forming the cavity has not been reported yet, and currently, the FBAR device has been successfully prepared by using this technology, and the corresponding test has been carried out, the device test Q factor is about 2500. It can be proved that the method of using the stress of the piezoelectric film itself to cause the deformation of the film layer to form the cavity required for the FBAR device to work is feasible, and this technology can be applied in more advanced piezoelectric film preparation process to improve the quality of the piezoelectric film and optimize the device performance. This technology can even be applied to the preparation of single crystal FBAR devices.

Claims

1. A method for fabricating a thin-film bulk acoustic wave device with a cavity structure obtained by stress control, characterized in that, The method comprises the following steps: (1) forming a natural oxide layer on a substrate, setting an effective area on the natural oxide layer, forming a piezoelectric seed layer and a sacrificial layer in the effective area respectively, forming a first electrode on the piezoelectric seed layer, and the sacrificial layer is located on both sides of the piezoelectric seed layer or surrounds the piezoelectric seed layer, wherein the height of the sacrificial layer is not less than the height sum of the piezoelectric seed layer and the first electrode, and the natural oxide layer outside the effective area is removed to expose the substrate; (2) depositing a piezoelectric film with an internal stress of 600-1500 MPa on the exposed surface of the substrate, the sacrificial layer and the first electrode, depositing a second electrode on the piezoelectric film, depositing a first metal pad layer on the second electrode, etching a metal pad filling hole on the piezoelectric film to the first electrode, depositing a second metal pad layer on the first electrode through the metal pad filling hole, and etching a sacrificial layer release hole on the piezoelectric film; (3) adding an etching liquid to the sacrificial layer release hole for removing the sacrificial layer and the natural oxide layer in the effective area, so that the piezoelectric film in the effective area is deformed under the action of the internal stress to separate the piezoelectric seed layer from the silicon substrate to form a cavity and then obtain a cavity film bulk acoustic wave device.

2. The method of claim 1, wherein the method further comprises: forming a cavity in the thin film bulk acoustic wave device. The substrate is one or any combination of silicon, silicon carbide, sapphire and ceramic.

3. The method of claim 1, wherein the method further comprises: forming a cavity in the thin film bulk acoustic wave device. The processing technology of the natural oxide layer is obtained by heat oxidation treatment of the substrate, and the thickness is 10-50 nm.

4. The method of claim 1, wherein the method further comprises: forming a cavity in the thin film bulk acoustic wave device. The piezoelectric seed layer is aluminum nitride, and the thickness is 10-100 nm.

5. The method of claim 1, wherein the method further comprises: forming a cavity in the thin film bulk acoustic wave device. The sacrificial layer is adjacent to the first electrode or partially remains on the first electrode.

6. The method of claim 1, wherein the method further comprises: forming a cavity in the thin film bulk acoustic wave device. The piezoelectric film is aluminum nitride, doped aluminum nitride, zinc oxide, lithium nickelate or lead zirconate titanate.

7. The method of claim 1, wherein the method further comprises: forming a cavity in the thin film bulk acoustic wave device. The deposition method of the piezoelectric film comprises: The Ar / N2 gas flow is 10-50 / 50-150 sccm, the growth temperature is 200-300℃, the chamber pressure is 2-4 mT, the Target / RF power is 5000-6000 / 120-200 W, and the growth rate is 1-5 nm / min.

8. The method of claim 1, wherein the method further comprises: forming a cavity in the thin film bulk acoustic wave device. The cavity depth is 50-2000 nm, the lateral width is 50-250 μm, and the lateral width of the cavity is greater than the lateral width of the first electrode.

9. A cavity film bulk acoustic resonator device obtained by the method of any one of claims 1-8, wherein, The effective area on the cavity film bulk acoustic wave device comprises: a substrate; a piezoelectric oscillation stack, in the effective area, the piezoelectric oscillation stack and the substrate form a cavity, and outside the effective area, the piezoelectric oscillation stack is located on the substrate; and a metal pad layer located on the piezoelectric oscillation stack.

10. The FBAR device prepared by the method of claim 9, wherein, The piezoelectric oscillation stack comprises: a first metal pad layer located on the piezoelectric film and connected to the first electrode through a metal pad filling hole in the piezoelectric film; a second metal pad layer located on the second electrode; a second electrode located on the piezoelectric film; a piezoelectric film, in the effective area, the piezoelectric film and the substrate form a cavity, and outside the effective area, the piezoelectric film is located on the substrate; a first electrode, in the cavity, located between the piezoelectric seed layer and the piezoelectric film; and a piezoelectric seed layer, in the cavity, the first electrode is deposited on the piezoelectric seed layer, and the piezoelectric seed layer is separated from the substrate.

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