CN212381185U

CN212381185U - Air gap type film bulk acoustic resonator beneficial to integration

Info

Publication number: CN212381185U
Application number: CN202020718950.9U
Authority: CN
Inventors: 李国强; 刘红斌; 张铁林; 梁敬晗; 衣新燕; 赵利帅; 刘鑫尧
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2020-04-30
Filing date: 2020-04-30
Publication date: 2021-01-19
Anticipated expiration: 2030-04-30

Abstract

The utility model discloses a do benefit to integrated air gap type film bulk acoustic resonator. The resonator is characterized in that an air-gap type film bulk acoustic resonator is respectively manufactured on the front side and the back side of a double-polished silicon substrate, both the two sides of the resonator are bonding type air-gap type film bulk acoustic resonators, a top electrode, a piezoelectric film, a bottom electrode, a leveling layer, a bonding layer and a transfer substrate are sequentially distributed on the resonator, the bonding layer is respectively grown on the leveling layer and the transfer substrate, and an air gap is formed by the bonding layer, the transfer substrate and the bottom electrode in a surrounding mode. The upper surface and the lower surface of the piezoelectric films of the two resonators are respectively and oppositely connected with a top electrode and a bottom electrode, the bottom electrodes are positioned in the air gaps, and the top electrodes, the piezoelectric films and the bottom electrodes form a sandwich structure. The FBAR device prepared by the method has a simple structure, the influence of the manufacturing process on the core structure is small, the manufacturing cost of the FBAR device can be reduced, the size of the device is reduced, and the FBAR device is suitable for high-frequency fields such as duplexers, multiplexers and the like.

Description

Air gap type film bulk acoustic resonator beneficial to integration

Technical Field

The utility model relates to a film bulk acoustic resonator technical field, concretely relates to do benefit to integrated air gap type film bulk acoustic resonator.

Background

With the development of modern wireless communication technologies like high frequency and high speed, higher requirements are put forward on the front-end filter commonly used in radio frequency communication. The working frequency is continuously improved, and simultaneously, the requirements on the size, the service performance, the stability and the integration of the device are higher, a Film Bulk Acoustic Resonator (FBAR) is a novel filter, the size is small, the power capacity is large, the integration can be realized, the working frequency is high, in addition, better out-of-band suppression and insertion loss are realized, and the wide application is realized in the current 5G communication.

The film bulk acoustic resonator mainly has three structures of a diaphragm type, an air gap type and a solid assembly type, and the three structures all have a sandwich structure of 'electrode-piezoelectric film-electrode'. The principle is that the piezoelectric property of the piezoelectric film is utilized, when alternating voltage is applied to the electrodes, the piezoelectric effect enables electric energy to be converted into mechanical energy, the piezoelectric film is mechanically deformed, and therefore bulk acoustic waves are excited in the piezoelectric film. When the bulk acoustic wave is transmitted to the interface of the piezoelectric surface film on the electrodes, the bulk acoustic wave is reflected back due to the action of the common acoustic layer outside the electrodes, so that the bulk acoustic wave is limited between the two electrodes. In order to reduce the loss of the sound wave, the sound wave should be made to be capable of forming total reflection as much as possible. The acoustic impedance of air can be considered to be approximately zero, so that the top electrode and the surface of the bottom electrode need to be in contact with the air during manufacturing, the top electrode is in contact with the air, the bottom electrode grows on the substrate, and the substrate material at the bottom electrode needs to be removed by using an etching method, so that the substrate material can form solid/air interface contact with the air, and sufficient mechanical strength is ensured, namely the air gap type film bulk acoustic resonator is manufactured.

The preparation method of the mainstream air gap type film bulk acoustic resonator is that a silicon cavity is etched through the silicon cavity, then a sacrificial layer is filled in the cavity, other materials are continuously grown after chemical mechanical polishing, and finally the materials are released and removed. The first disadvantage is that the release of the sacrificial layer needs to use an etching solution, which can corrode other structures of the device to a certain extent, the second is that the sacrificial layer becomes gas when released, the control rate is not appropriate, the pressure in the cavity is too high, the device structure is damaged, and the third is that the release of the sacrificial layer may not be thorough, thereby introducing other influences. Due to the existence of the factors, the yield of the mainstream FBAR device is very low, and the mainstream FBAR devices are grown on one side of a silicon substrate, so that the layout area and the wiring length of the integrated circuit with multi-band operation can be increased.

In order to solve various problems existing in a mainstream process, a recent patent proposes a method for preparing a cavity by metal bonding, but in the metal bonding process, the metal has high fluidity, bonding pressure and bonding temperature are difficult to control, and the metal easily generates an electromagnetic effect. Therefore, the more efficient and reasonable air-gap FBAR structure and the preparation method need to be researched to simplify the preparation process and improve the performance of the device.

SUMMERY OF THE UTILITY MODEL

In order to overcome the defects in the prior art, the utility model aims to provide an air gap type film bulk acoustic resonator which is beneficial to integration and a preparation method thereof.

The utility model provides a preparation method adopts nonmetal bonding preparation two air gap type film bulk acoustic resonators on the positive and negative of a silicon substrate.

Based on this, the utility model aims at providing a thin film bulk acoustic resonator's structure that does benefit to the integration. The FBAR structure adopted is stable, the damage of the manufacturing process to the core structure is small, the introduction of parasitic capacitance is avoided, the controllability is strong, in a multi-filter circuit, compared with a single-face air gap type film bulk acoustic resonator, the area of a double-face structure can be greatly reduced, the integration level of the circuit is improved, and the process can be adopted to process a very thin film, so that the FBAR structure is suitable for the high-frequency field.

The purpose of the utility model is realized through one of the following technical schemes.

The utility model provides an air gap type film bulk acoustic resonator, which comprises two air gap type resonators; the air gap type resonator comprises a top electrode, a piezoelectric film, a bottom electrode, a filling layer, a bonding layer and a double-polished silicon substrate (transfer substrate); the two air gap type resonators are respectively manufactured on the front and back surfaces of the double-polished silicon substrate; the bonding layer grows on the filling layer and the double-polished silicon substrate respectively, and air gaps are formed by the bonding layer, the double-polished silicon substrate and the bottom electrode in a surrounding mode; the upper surface and the lower surface of the two air-gap resonators are respectively connected with a top electrode and a bottom electrode, wherein the bottom electrode is positioned in the air gap; the top electrode, the piezoelectric film and the bottom electrode form a sandwich structure.

Further, the double-polished silicon substrate is high-resistance double-polished monocrystalline silicon; grooves are respectively arranged on the front and back surfaces of the double silicon polishing substrate; the depth of the grooves on the front and back surfaces of the double-polished silicon substrate is 500nm-3 mu m.

Furthermore, an air cavity of the resonator is defined by the bonding layer, the bottom electrode and the groove of the double-polished silicon substrate; the depth of the air cavity is 900nm-8 μm.

Further, the bonding layer is made of SiO₂And SiO₂Bonding to obtain the final product; the bonding layer comprises a first bonding layer and a second bonding layerBonding layer, third bonding layer and fourth bonding layer. The first bonding layer is connected with the third bonding layer; the second bonding layer is connected with the fourth bonding layer.

Further, the piezoelectric film is more than one of AlN, ZnO and PZT; the bottom electrode and the top electrode are both metal electrode layers, and the bottom electrode and the top electrode are made of more than one of Pt, Mo, W, Ti and Au.

Further, the bonding layer has a thickness of 400nm- μm; the thickness of the piezoelectric film is 200nm-3 mu m; the thicknesses of the top electrode and the bottom electrode are both 50nm-500 nm.

The utility model discloses a preparation method of air gap type film bulk acoustic resonator, including following step:

(1) using a single crystal silicon substrate as an epitaxial substrate, cleaning the surface of the epitaxial substrate, and carrying out thermal oxidation treatment for 30min at the temperature of 300-500 ℃; then growing a piezoelectric film on the monocrystalline silicon substrate, growing a bottom electrode on the upper surface of the piezoelectric film, obtaining a required bottom electrode pattern through photoetching and wet etching, and then growing SiO for filling on the bottom electrode by using PECVD (plasma enhanced chemical vapor deposition)₂Protecting the filled part with photoresist, and forming SiO layer on the bottom electrode₂Removing (negative photoresist is adopted here, the exposed area is insoluble in developing solution after exposure and can be used as the protection of a filling and leveling layer), and etching to remove the part covered on the bottom electrode; growing a bonding layer (SiO) using PECVD₂Thin film) on the bottom electrode by photolithography and wet etching to remove SiO coated on the bottom electrode₂The bottom electrode is protected by photoresist, and SiO is treated by HF acid solution₂The surface of the film is sent into a plasma activation system to carry out surface activation treatment on the bonding layer, and a first wafer is obtained; the preparation of the second wafer is the same as that of the first wafer;

(2) selecting double-polished monocrystalline silicon (high-resistance double-polished monocrystalline silicon) as a transfer substrate, and growing SiO on one surface of the transfer substrate by using PECVD (plasma enhanced chemical vapor deposition)₂Photoetching the other side of the protective layer, then sending the protective layer into an ICP-RIE system to etch a groove (silicon cavity), and growing SiO by PECVD₂Removing SiO covered on the groove (in the cavity) by photoetching and wet etching₂Using HFAcid solution treatment of SiO₂The surface of the film is sent into a plasma activation system to carry out surface activation treatment on the bonding layer, and a third wafer is obtained;

(3) protecting a bottom electrode of the first wafer by using photoresist, activating the surface of a bonding layer of the first wafer, aligning the bonding layers of the first wafer and the third wafer after activation treatment, then sending the wafers into a bonding machine together for pre-bonding, annealing, forming firm bonding between the pre-bonded wafers, realizing the transfer of a piezoelectric film and forming an air gap;

(4) separating the silicon substrate on the first wafer from the piezoelectric film by mechanical thinning, chemical polishing and chemical corrosion;

(5) depositing a top electrode on the upper surface of the piezoelectric film of the first wafer, and carrying out imaging processing to enable the top electrode to be opposite to the bottom electrode, wherein the top electrode, the piezoelectric film and the bottom electrode form a sandwich structure;

(6) growing a layer of SiO for protection on the first wafer with deposited top electrode by using PECVD₂A protective layer, which is ground flat and turned over;

(7) after overturning, removing the protective layer on the surface of the third wafer on the back surface, and etching the silicon cavity in ICP-RIE equipment; subsequent growth of SiO using PVD₂Etching and corroding the film to remove SiO in the cavity₂Treatment of SiO with HF acid solution₂The surface of the film is sent into a plasma activation system to carry out surface activation treatment on the bonding layer;

(8) aligning the activated third wafer and the second wafer bonding layer, then sending the aligned third wafer and second wafer bonding layer into a bonding machine for pre-bonding, annealing for 2-4 hours at 800-1000 ℃, forming firm bonding between the pre-bonded wafers, realizing the transfer of the piezoelectric film and forming an air gap;

(9) separating the epitaxial substrate from the piezoelectric film by mechanical thinning, chemical polishing and chemical corrosion;

(10) depositing a top electrode on the upper surface of the piezoelectric film, imaging, making the top electrode opposite to the bottom electrode, forming a sandwich structure by the top electrode, the piezoelectric film and the bottom electrode, and thenWet removal of protective SiO₂And obtaining the air gap type film bulk acoustic resonator.

Further, in the step (1), the method for growing the piezoelectric film comprises more than one of PVD, MOCVD, PLD and the like; the method for growing the bottom electrode is magnetron sputtering; the method for growing the filling layer is PECVD. Growing bonding layer SiO₂The method of thin film is PECVD.

Further, in the step (2), SiO is grown on the transfer substrate₂The method of the protective layer is PECVD; the groove is formed by etching a groove which is consistent with the bottom electrode pattern from top to bottom on the bonding layer and the transfer substrate.

Further, the annealing temperature in the step (3) is 100-600 ℃, and the surface activation in the steps (1) and (3) comprises more than one of plasma activation, HF solution surface roughening and modification methods.

Preferably, the annealing temperature of the step (3) is 150-300 ℃.

Preferably, the bonding layer grown on the third wafer is SiO₂。

Preferably, the bonding layer and the supporting layer grown on the first and second wafer are both SiO₂(ii) a The piezoelectric film is more than one of PZT, AlN and ZnO; the bottom electrode and the top electrode are metal electrode layers, and the metal is more than one of Pt, Mo, W, Ti and Au.

Preferably, the thickness of the bonding layer is 400 nm-5 μm; the thickness of the piezoelectric film is 200nm-3 mu m; the thickness of the top electrode and the bottom electrode is 50nm-500 nm.

The utility model provides a preparation method can prepare different syntonizers and cascade the mode, realize each frequency channel duplexer or multiplexer.

Compared with the prior art, the utility model has the advantages of as follows and beneficial effect:

(1) the utility model provides an among the air gap type film bulk acoustic resonator, to SiO₂After surface active treatment, the surface of the material has higher surface energy, and the material passes through SiO₂- SiO₂Bonding implementationThe method comprises the following steps of (1) transferring a film, namely extending a layer of high-quality monocrystal AlN piezoelectric film on a Si substrate, depositing a metal electrode on the monocrystal AlN piezoelectric film and patterning the monocrystal AlN piezoelectric film, forming a cavity under the monocrystal AlN piezoelectric film through substrate transfer, finally modifying the AlN pattern, depositing metal and patterning the metal to form an electrode-piezoelectric film-electrode sandwich composite structure, forming the cavity through bonding without introducing a sacrificial layer, and applying the high-quality monocrystal AlN piezoelectric layer to FBAR;

(2) the utility model adopts the insulating material SiO₂The film transfer is carried out, the bonding temperature is low and the cost is low.

Drawings

Fig. 1 is a cross-sectional view of an epitaxial substrate on which a piezoelectric film, a bottom electrode, a filling layer, and a bonding layer are grown in this order and patterned in example 1;

FIG. 2 is a cross-sectional view of a transfer substrate after etching a silicon cavity, depositing a bonding layer and patterning in example 1;

FIG. 3 is a cross-sectional view of an air gap cavity obtained by flip-chip bonding the first wafer and the third wafer of example 1;

FIG. 4 is a sectional view of example 1 in which an epitaxial substrate is peeled;

FIG. 5 is a cross-sectional view of a top electrode grown after glass epitaxy of a substrate in example 1;

FIG. 6 is a cross-sectional view of the third wafer bonded to the second wafer after the top electrode of the first wafer is protected and the top electrode is grown in accordance with example 1;

fig. 7 is a sectional view of an air gap type thin film bulk acoustic resonator for facilitating integration obtained after removing a protective layer in example 1;

the figure includes: the piezoelectric device comprises an epitaxial substrate 101, a piezoelectric film 102, a filling-up layer 103, a bottom electrode 104, a first bonding layer 105, a top electrode 106, a piezoelectric layer 202, a filling-up layer 203, a bottom electrode 204, a second bonding layer 205, a top electrode 206, a transfer substrate 301, a third bonding layer 302, a protective layer 303 and a fourth bonding layer 304.

Detailed Description

The following is a further description of the embodiments of the present invention with reference to the examples, but the invention is not limited thereto. It is noted that the processes described below, if not specifically described in detail, are all realizable or understandable by those skilled in the art with reference to the prior art.

Example 1

The present embodiment provides an air gap type thin film bulk acoustic resonator, as shown in fig. 7, the resonator includes an epitaxial substrate 101, a piezoelectric thin film 102, a leveling layer 103, a bottom electrode 104, a first bonding layer 105, a top electrode 106, a piezoelectric layer 202, a leveling layer 203, a bottom electrode 204, a second bonding layer 205, a top electrode 206, a transfer substrate 301, a third bonding layer 302, a protective layer 303, and a fourth bonding layer 304.

The transfer substrate 301 is high-resistance double-polished monocrystalline silicon; the bonding layer is SiO₂The thickness is 400 nm; the protective layer is also SiO₂The thickness is 10-20 mu m; the piezoelectric film is AlN with the thickness of 1.2 mu m; the bottom electrode and the top electrode are both metal electrode layers, the thickness of each electrode layer is 300nm, and the bottom electrode and the top electrode are both Mo.

The present embodiment also provides a method for manufacturing an air gap type thin film bulk acoustic resonator as described above, including the steps of:

(1) selecting Si substrate with (100) crystal orientation as epitaxial substrate 101, and first passing through concentrated H to the epitaxial substrate₂SO₄：H₂O₂：H₂Cleaning with SPM solution of O (volume ratio of 1.6:1.6:4) at 60 deg.C for 15min, and washing with H₂O: BOE solution cleaning with HF (volume ratio 15:1) for 10min (concentrated H)₂SO₄、H₂O₂BOE, HF are commercially available), removing surface organics and contamination, growing a piezoelectric film 102 on the epitaxial substrate 101 using a metal-organic chemical vapor deposition system and a radio frequency magnetron sputtering system, with the reactive gases trimethylaluminum (50 sccm), NH₃A flow rate of (3 slm), a carrier gas Ar (1 slm), a substrate temperature of about 900 ℃ and a total reaction chamber pressure of about 40Torr, and a single crystal AlN having a thickness of 1.2 μm is grown; growing a bottom electrode 104 on the upper surface of the piezoelectric film 102, using a radio frequency magnetron sputtering machine, taking Mo with the purity of 99.99% as a sputtering target material, introducing high-purity Ar as sputtering gas during sputtering, and working alwaysThe pressure is 3-10Pa, the target base distance is 60mm, and the vacuum degree is 4.0 × 10^-4Pa, growing a Mo electrode layer with the thickness of 300nm at the substrate temperature of 200 ℃; after the electrode is patterned, growing a layer of filling-up layer silicon dioxide 103 in the region outside the bottom electrode connected with the upper surface of the bottom electrode and the surface of the pressure film by a Plasma Enhanced Chemical Vapor Deposition (PECVD) method; after the growth of the filling layer is completed, growing a first bonding layer 105 by using PECVD (plasma enhanced chemical vapor deposition), and removing the first bonding layer 105 on the surface of the bottom electrode 104 by photoetching and wet etching; as shown in FIG. 1, the bottom electrode 104 is protected by photoresist, and H is used₂O: HF = 5:1, and then sent to an ICP-RIE system to perform surface activation treatment on the first bonding layer 105, and N with a concentration of 99.99% at a power of 200W is supplied to the ICP-RIE system₂Keeping the atmosphere for 2 minutes to obtain a first wafer;

(2) selecting a high-resistance monocrystalline silicon as the transfer substrate 106, and passing through the epitaxial substrate by concentrated H₂SO₄：H₂O₂：H₂Cleaning with SPM solution of O (volume ratio of 1.6:1.6:4) at 60 deg.C for 15min, and using H₂O: BOE solution cleaning with HF (volume ratio 15:1) for 10min (concentrated H)₂SO₄、H₂O₂BOE, HF are commercially available), removing surface organics and dirt; growing SiO on one side by PECVD₂As a protective layer, manufacturing a silicon cavity with the depth of 800nm on the transfer substrate by an inductively coupled plasma etcher on the other surface of the transfer substrate 301; a third bonding layer 302 having a thickness of 400nm is regrown. As shown in fig. 2, using H₂O: HF = 5:1, then sent to an ICP-RIE system to perform surface treatment on the third bonding layer 302, and then N with a concentration of 99.99% at a power of 200W₂Keeping the atmosphere for 2 minutes to obtain a third wafer, as shown in FIG. 2; FIG. 1, FIG. 2, and the arrow indicates the surface activation of the bonding layer;

(3) respectively taking the first bonding layer 105 and the third bonding layer 302 as contact surfaces, sending the processed first wafer and the processed third wafer into a bonding machine for pre-bonding, applying pressure from the center of the substrate 101 of the first wafer in the bonding process, gradually expanding towards the edge, bonding for 2 hours at the temperature of 300 ℃ after the bonding pressure reaches 2MPa, then annealing, taking out, sending into an annealing furnace, preserving heat for 30 minutes at the temperature of 200 ℃, forming firm bonding between the pre-bonded wafers, and transferring the piezoelectric film to form an air gap, as shown in fig. 3;

(4) separating the epitaxial substrate 101 from the piezoelectric film 102 by mechanical thinning, chemical polishing and chemical etching, and adopting a volume ratio of 5:1, mixing 30 mass percent of KOH and IPA to prepare an etching solution, and etching the piezoelectric film 102 at 80 ℃ until the piezoelectric film is stopped, as shown in FIG. 4;

(5) cleaning the surface residues treated in the step (4), depositing a top electrode 106 on the upper surface of the piezoelectric film 102, and performing imaging treatment, wherein the top electrode 106 is opposite to the bottom electrode 104, and the top electrode 106, the piezoelectric film 102 and the bottom electrode 104 form a sandwich structure, as shown in fig. 5;

(6) growing a layer of protective SiO on the surface of the top electrode 106₂And turning over after mechanical grinding, removing the protective layer grown in the second step, taking the second wafer, repeating the step of bonding the first wafer and the third wafer, and finally performing wet etching to obtain a complete sample, namely the air gap type film bulk acoustic resonator, as shown in fig. 6.

The above-described embodiments are merely illustrative of several embodiments of the present invention, which are described in detail and specific, but not intended to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, without departing from the spirit of the present invention, several variations and modifications can be made, which are within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. An air gap type film bulk acoustic resonator is characterized by comprising two air gap type resonators; the air gap type resonator comprises a top electrode, a piezoelectric film, a bottom electrode, a filling and leveling layer, a bonding layer and a double-polished silicon substrate; the two air gap type resonators are respectively manufactured on the front and back surfaces of the double-polished silicon substrate; the bonding layer is respectively connected with the filling layer and the double-polished silicon substrate, and air gaps are enclosed by the bonding layer, the double-polished silicon substrate and the bottom electrode; the upper surface and the lower surface of the two air-gap resonators are respectively connected with a top electrode and a bottom electrode, wherein the bottom electrode is positioned in the air gap; the top electrode, the piezoelectric film and the bottom electrode form a sandwich structure.

2. The air gap type thin film bulk acoustic resonator according to claim 1, wherein the double-polished silicon substrate is high-resistance double-polished single crystal silicon; grooves are respectively arranged on the front and back surfaces of the double silicon polishing substrate; the depth of the grooves on the front and back surfaces of the double-polished silicon substrate is 500nm-3 mu m.

3. The air gap type film bulk acoustic resonator according to claim 1, wherein the bonding layer, the bottom electrode and the groove of the double polished silicon substrate enclose an air cavity of the resonator; the depth of the air cavity is 900nm-8 μm.

4. The air-gap type thin film bulk acoustic resonator according to claim 1, wherein the bonding layer is made of SiO₂And SiO₂Bonding to obtain the final product; the bonding layer comprises a first bonding layer, a second bonding layer, a third bonding layer and a fourth bonding layer.

5. The air gap type thin film bulk acoustic resonator according to claim 1, wherein the bonding layer has a thickness of 400nm- μm; the thickness of the piezoelectric film is 200nm-3 mu m; the thicknesses of the top electrode and the bottom electrode are both 50nm-500 nm.