A method for preparing a single crystal piezoelectric thin film bulk acoustic resonator

Abstract

The application discloses a preparation method of a single-crystal piezoelectric thin film bulk acoustic resonator, which comprises the following steps: growing a single-crystal piezoelectric thin film on a substrate, and preparing an upper electrode above the piezoelectric thin film; patterning to form a discrete resonator device area; etching the upper electrode and the piezoelectric thin film through a via hole formed on the device by lithography; forming a cavity below the device area through the via hole; depositing metal on the upper electrode, inside the via hole, the back of the piezoelectric thin film and inside the cavity through ALD; and patterning the upper electrode to obtain a single-crystal piezoelectric thin film bulk acoustic resonator composed of the upper electrode, the single-crystal piezoelectric thin film and a lower electrode. The application can realize the resonator structure with a cavity without a wafer bonding process, effectively avoids the complex wafer bonding process, potential damage to the epitaxial single-crystal AlN thin film on a hetero-substrate caused by lattice mismatch and thermal mismatch, and the resonator failure caused by the potential damage. Moreover, the process is simple and easy for batch processing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor process, and particularly relates to a preparation method of a single-crystal piezoelectric thin film bulk acoustic resonator. BACKGROUND

[0002] The radio frequency filter is a core device of a radio frequency front end, and has very wide application in the fields of mobile communication and Internet of Things. At present, mainstream radio frequency filters have two types of surface acoustic wave and bulk surface wave. The bulk surface wave filter is suitable for a high-frequency scene, and along with the popularity of high-frequency communication represented by 5G, the demand for the bulk surface wave filter is more urgent.

[0003] In order to have greater out-of-band rejection, greater bandwidth, better insertion loss and other more excellent device performances, the resonator structure based on single-crystal AlN thin film has become a focus of research in the industry. However, the related preparation technology of the single-crystal AlN filter and resonator is not mature enough. Generally, a thin AlN single-crystal thin film is grown on a substrate, and then is transferred to a high-resistance silicon substrate for subsequent device processing. Since the single-crystal AlN thin film is very thin, and generally has problems such as lattice mismatch and thermal mismatch with the epitaxial substrate, the single-crystal thin film is prone to breakage, which can easily cause the collapse and damage of the resonant structure in the subsequent process, and further cause the device failure or abnormality. SUMMARY

[0004] The application aims to provide a preparation method of a single-crystal piezoelectric thin film bulk acoustic resonator, which solves the problems existing in the prior art, i.e. without using the transfer method such as bonding, a single-crystal thin film bulk acoustic resonator with a cavity structure can be constructed, and the potential damage to the single-crystal AlN thin film in the bonding transfer process is avoided.

[0005] The technical solution for achieving the object of the application is as follows: a preparation method of a single-crystal piezoelectric thin film bulk acoustic resonator, comprising the following steps:

[0006] 1) growing a single-crystal piezoelectric thin film on a substrate, and then preparing an upper electrode above the piezoelectric thin film;

[0007] 2) patterning the upper electrode and the piezoelectric thin film respectively to form discrete resonator device regions;

[0008] 3) etching a through hole above the device, and etching the upper electrode and the piezoelectric thin film respectively until the upper surface of the substrate;

[0009] 4) forming a cavity below the device region through the through hole by dry etching or wet etching;

[0010] 5) depositing a metal on the upper electrode, inside the through hole, the back of the piezoelectric thin film and inside the cavity by ALD;

[0011] 6) patterning the metal deposited on the upper electrode by ALD to obtain a single crystal piezoelectric thin film bulk acoustic resonator composed of an upper electrode, a single crystal piezoelectric thin film, and a lower electrode.

[0012] Compared with the prior art, the single crystal piezoelectric thin film bulk acoustic resonator has the advantages that the resonator structure with a cavity can be realized without a wafer bonding process, potential damage to the epitaxial single crystal AlN film on a hetero-substrate caused by lattice mismatch and thermal mismatch is effectively avoided, and the resonator failure problem caused by the potential damage is avoided. The process is simple and easy for batch processing. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a schematic diagram of growing a single crystal piezoelectric thin film and an upper electrode on a substrate.

[0014] Figure 2 is a schematic diagram of patterning the upper electrode and the piezoelectric thin film.

[0015] Figure 3 is a schematic diagram of etching a via to the upper surface of the substrate in the area above the resonator device.

[0016] Figure 4 is a schematic diagram of forming a cavity below the device area.

[0017] Figure 5 is a schematic diagram of depositing metal on the upper electrode, inside the via, the back of the piezoelectric thin film, and inside the cavity.

[0018] Figure 6 is a schematic diagram of patterning the metal deposited on the upper electrode by ALD.

[0019] In the figure: 1 is an upper electrode, 2 is a single crystal piezoelectric thin film, 3 is a substrate, 4 is a via, 5 is a cavity, and 6 is a lower electrode. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be further described below with reference to the accompanying drawings.

[0021] A preparation method of a single crystal piezoelectric thin film bulk acoustic resonator, comprising the following steps:

[0022] 1) growing a single crystal piezoelectric thin film 2 on a substrate 3, and then preparing an upper electrode 1 above the single crystal piezoelectric thin film 2, wherein the substrate 3 is a Si, SiC, or GaN substrate; the thickness of the substrate is 100 μm to 2 mm; the single crystal piezoelectric thin film 2 is a piezoelectric material such as aluminum nitride or zinc oxide; the thickness of the piezoelectric material is 10 nm to 5 μm; the upper electrode material includes but is not limited to one of metal compounds TaN and TiN or metals Pt, Co, Ru, and Mo; the thickness of the metal is 10 nm to 1 μm, such asFigure 1 as shown.

[0023] 2) The upper electrode 1 and the single-crystal piezoelectric thin film 2 are patterned respectively to form discrete resonator device regions, wherein the patterning methods include dry etching or wet etching after lithography, etc.; the resonator device region size is 30 μm x 30 μm to 2 mm x 2 mm, as shown. Figure 2 as shown.

[0024] 3) A via hole 4 is lithographically formed above the device, and the upper electrode 1 and the piezoelectric thin film 2 are etched respectively until the upper surface of the substrate 3, wherein the size of the via hole 4 is 3 μm to 50 μm, as shown. Figure 3 as shown.

[0025] 4) A cavity 5 is formed below the device region through the via hole 4 by dry etching or wet etching, wherein the depth of the cavity 5 is 100 nm to 100 μm, as shown. Figure 4 as shown.

[0026] 5) Metal is deposited on the upper electrode, inside the via hole, the back of the piezoelectric thin film, and inside the cavity by ALD, wherein the deposited metal includes but is not limited to one of metal compounds such as TaN, TiN, or metals such as Pt, Co, Ru, Mo, etc., and the thickness of the metal is 10 nm to 1 μm, as shown. Figure 5 as shown.

[0027] 6) The metal deposited on the upper electrode by ALD is patterned to obtain a single-crystal piezoelectric thin film bulk acoustic resonator composed of the upper electrode 1, the single-crystal piezoelectric thin film 2, and the lower electrode 6, wherein the patterning methods include dry etching or wet etching after lithography, etc., as shown. Figure 6 as shown.

[0028] Embodiment

[0029] A method for preparing a single-crystal piezoelectric thin film bulk acoustic resonator, comprising the following steps:

[0030] ①On a single-crystal Si substrate with a (111) crystal orientation, a 300 nm thick single-crystal AlN thin film is first epitaxially grown by MOCVD, and then 100 nm of metal Mo is deposited on the single-crystal AlN thin film by PVD.

[0031] ②The metal Mo is lithographically patterned, and a resonator device upper electrode is etched by using a chlorine-based gas; then the AlN thin film is lithographically patterned, and a resonator region is etched by using a fluorine-based gas, to form a discrete resonator structure with a size of 200 μm x 200 μm.

[0032] ③A via hole with a size of 10 μm x 10 μm is lithographically formed above the device, and chlorine-based gas and fluorine-based gas are used for etching respectively until the surface of the Si substrate stops.

[0033] (4) The through hole etched by the above steps is used to etch the Si substrate by XeF2 gas, to form a cavity with a depth of about 50 μm and a width of about 50 μm x 50 μm.

[0034] (5) A metal Mo with a thickness of about 200 nm is deposited on the upper electrode, inside the through hole, the back of the piezoelectric film and inside the cavity by an ALD device.

[0035] (6) The metal Mo deposited on the upper electrode is subjected to photoetching, and the metal Mo is etched by a chlorine-based gas to obtain a single crystal piezoelectric film bulk acoustic resonator composed of the upper electrode, the single crystal piezoelectric film and the lower electrode.

[0036] The above steps realize the preparation method of the single crystal piezoelectric film bulk acoustic resonator.

[0037] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application should not be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be regarded as falling within the protection scope of the present application.

Claims

1. A method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator, characterized in that, Includes the following steps: 1) A single-crystal piezoelectric thin film is grown on a substrate, and then an upper electrode is fabricated on top of the piezoelectric thin film; 2) Pattern the upper electrode and the piezoelectric thin film separately to form discrete resonator device regions; 3) Photolithographically create vias above the device, and then etch the top electrode and piezoelectric thin film separately until the top surface of the substrate is reached; 4) A cavity is formed below the device area through a via by means of dry etching or wet etching; 5) Metal is deposited above the upper electrode, inside the via, on the back of the piezoelectric film, and inside the cavity via ALD; 6) Pattern the metal deposited above the upper electrode by ALD to obtain a single-crystal piezoelectric thin film bulk acoustic resonator composed of an upper electrode, a single-crystal piezoelectric thin film, and a lower electrode.

2. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, In step 1), the substrate is a Si, SiC or GaN substrate with a thickness of 100 μm to 2 mm.

3. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, In step 1), the single-crystal piezoelectric thin film is aluminum nitride or zinc oxide, and the thickness of the piezoelectric material is 10 nm to 5 μm.

4. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, In step 1), the upper electrode material includes, but is not limited to, metal compounds TaN, TiN, or one of the metals Pt, Co, Ru, and Mo, with the thickness of the metal ranging from 10 nm to 1 μm.

5. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, The patterning methods in step 2) include dry etching or wet etching after photolithography.

6. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, In step 2), the size of the resonator device region ranges from 30μm×30μm to 2mm×2mm.

7. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, The size of the through hole in step 3) is between 3 μm and 50 μm.

8. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, The cavity depth in step 4) is between 100 nm and 100 μm.

9. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, The deposited metal in step 5) includes, but is not limited to, metal compounds TaN, TiN, or one of the metals Pt, Co, Ru, and Mo, with a thickness of 10 nm to 1 μm.

10. The method for fabricating a single-crystal piezoelectric thin-film bulk acoustic resonator according to claim 1, characterized in that, The patterning methods in step 6) include dry etching or wet etching after photolithography.

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