WO2024001087A1

WO2024001087A1 - Preparation method for film bulk acoustic resonator, and film bulk acoustic resonator

Info

Publication number: WO2024001087A1
Application number: PCT/CN2022/140678
Authority: WO
Inventors: 李国强
Original assignee: 广州市艾佛光通科技有限公司
Priority date: 2022-06-28
Filing date: 2022-12-21
Publication date: 2024-01-04
Also published as: CN115333497A

Abstract

Disclosed in the present invention are a preparation method for a film bulk acoustic resonator, and a film bulk acoustic resonator. The resonator comprises a silicon substrate, a bottom electrode layer, a piezoelectric layer and a top electrode layer, which are arranged in sequence from bottom to top, wherein the top surface of the silicon substrate is provided with a cavity that is dented downward, and the bottom electrode layer is a diphenylene bottom electrode layer. The preparation method comprises step S1: treating a silicon substrate by means of an RCA cleaning process, then drying same, then etching a surface of the silicon substrate to form a groove by means of a dry etching method, and depositing a sacrificial layer on the groove; step S2: depositing a diphenylene bottom electrode layer material on the silicon substrate; step S3: bonding a piezoelectric layer material; step S4: depositing a top electrode layer material, and etching same to obtain a pattern; and step S5: forming a release window around the cavity by means of a dry etching method, injecting an etchant solution from the release window, and removing the loose sacrificial layer, so as to form an air cavity. The present invention can improve both a Q value and an electromechanical coupling coefficient of the resonator.

Description

Preparation method of thin film cavity acoustic resonator, thin film cavity acoustic resonator

Technical field

The invention relates to the technical field of bulk acoustic wave resonators, and in particular to a preparation method of a thin film cavity acoustic wave resonator and a thin film cavity acoustic wave resonator.

Background technique

As people have higher and higher requirements for high data transmission efficiency and portable mobile terminals, wireless communication technology has developed rapidly. In communication systems, the RF front-end is responsible for receiving and transmitting RF signals. In the RF front-end module, the filter mainly plays the role of effectively filtering the signal, achieving effective transmission of the signal within a specific frequency band, and filtering out signals outside the required frequency band.

fbar filter is the abbreviation of film bulk acoustic resonator filter, which is translated as film cavity acoustic resonance filter. fbar filter is different from previous filters. It is manufactured using silicon substrate, mems technology and thin film technology. At this stage, The fbar filter already has slightly higher characteristics than the ordinary saw filter. The fbar filter has a series of advantages such as integrability, high operating frequency (0.6GHz-24GHz), large power capacity and high Q value. It is formed by a cascade of series and parallel FBAR resonant units. fbar technology combines the advantages of dielectric filtering technology and surface acoustic wave filtering technology, and is widely used in filters, oscillators and other fields, becoming the mainstream technology for next-generation wireless communication filtering. Its working principle is as follows: under the action of an external electric field, the piezoelectric film deforms under the action of reverse piezoelectricity. When the external field is an alternating electromagnetic field, the piezoelectric film undergoes mechanical vibration and generates sound waves. The sound waves are fully reflected on the contact surface between the electrode and the air. , and are all bound inside the device. At a specific frequency, sound waves generate standing waves inside the device, thereby converting mechanical energy into electromagnetic energy, so that the electromagnetic field energy at a specific frequency is transmitted through the resonant unit.

At present, FBAR devices have the advantages of low insertion loss and high frequency selectivity, but the electrode itself has a certain thickness, which is equivalent to extending the sound wave path. Secondly, the electromechanical coupling coefficient (k _t ² ) of FBAR and the Q value are two key factors, and the Q value and k _t ² have mutual constraints. When the Q value is increased, k _t ² will decrease, and if in order to increase k _t ² , then the Q value will be sacrificed so that the transmission characteristics of the resonator cannot be improved.

Contents of the invention

In order to solve the above problems, the main purpose of the present invention is to provide a preparation method of a thin film cavity acoustic resonator and a thin film cavity acoustic resonator, which can simultaneously increase the Q value and the electromechanical coupling coefficient of the resonator, thereby improving the signal conversion efficiency. .

In order to achieve the above objects, the technical solution adopted by the present invention is:

A method for preparing a thin film cavity acoustic resonator. The thin film cavity acoustic resonator includes: a silicon substrate, a bottom electrode layer, a piezoelectric layer and a top electrode layer arranged in sequence from bottom to top. The silicon substrate The top surface of the bottom is provided with a downwardly depressed cavity, and the bottom electrode layer is a diphenylene-based bottom electrode layer;

The preparation method includes the following steps:

Step S1: Process the silicon substrate through the RCA cleaning process, dry it, and then etch a groove on the surface of the silicon substrate through dry etching, and deposit a sacrificial layer at the groove;

Step S2: Deposit diphenylene base electrode layer material on the silicon substrate;

Step S3: Bond the piezoelectric layer material, and etch the piezoelectric layer to form the required pattern;

Step S4: Deposit the top electrode layer material and etch it to obtain a pattern;

Step S5: Obtain a release window by dry etching around the cavity, inject the corrosion solution from the release window, remove the loose sacrificial layer, and form an air cavity, thereby obtaining the thin film cavity acoustic resonator.

Further, depositing the sacrificial layer at the groove includes: depositing a loose SiO ₂ layer on the SiO ₂ layer by PECVD method.

Further, in step S2, it also includes:

A trifluoromethanesulfonylation reagent is added to o-iodophenol, and the resulting product reacts with a lithium reagent in a low-temperature solvent to prepare a diphenylene group. Then, a diphenylene-based electrode layer material is obtained by evaporation deposition.

Further, in step S3, it also includes:

Step S31: Deposit a piezoelectric material film on the silicon substrate through magnetron sputtering, and then perform heat treatment and inert gas protection treatment on the piezoelectric material film;

Step S32: Using the organic metal compound chemical vapor deposition method, the piezoelectric material film processed in step S31 is further grown into a high crystal quality piezoelectric material, and then etching and stripping are performed to remove parts other than the piezoelectric material film to obtain the piezoelectric material. Material.

Further, the horizontal areas of the bottom electrode layer and the top electrode layer are both smaller than the horizontal area of the silicon substrate, and the bottom electrode layer and the top electrode layer respectively extend from both ends of the piezoelectric layer and completely Cover right above the cavity.

Furthermore, an inclination angle of 70° to 86° is provided between the inner wall of the cavity and the bottom surface of the cavity.

Further, the piezoelectric layer includes at least one piezoelectric material selected from AlN, ZnO, and PTZ.

Further, the top electrode layer is composed of at least one of diphenylene, gold, copper, silver, aluminum, tungsten, platinum, molybdenum, rhodium, iridium, and titanium.

Further, the thin film cavity acoustic resonator includes a support base, and the silicon substrate is disposed on the support base.

A kind of thin film cavity acoustic wave resonator, the thin film cavity acoustic wave resonator is made by executing the above-mentioned preparation method of the thin film cavity acoustic wave resonator.

The beneficial effects of the present invention are:

The invention includes a silicon substrate, a bottom electrode layer, a piezoelectric layer and a top electrode layer arranged sequentially from bottom to top. The top surface of the silicon substrate is provided with a downwardly recessed cavity. The bottom electrode layer is diphenylene-based electrode layer. The use of diphenylene base electrode layer can simultaneously improve the Q value and electromechanical coupling coefficient of the resonator, thereby improving signal conversion efficiency.

Description of drawings

Figure 1 is a schematic cross-sectional view of the new thin film cavity acoustic resonator according to the present invention.

Figure 2 is a flow chart of a method for preparing a thin film cavity acoustic resonator according to the present invention.

Figure 3 is a flow chart of a specific embodiment of the method for preparing the thin film cavity acoustic resonator of the present invention.

Explanation of reference numbers: 10. Support base; 20. Silicon substrate; 30. Cavity; 40. Bottom electrode layer; 50. Piezoelectric layer; 60. Top electrode layer.

Detailed ways

Referring to Figures 1-2, the present invention relates to a method for preparing a thin film cavity acoustic resonator.

The thin film cavity acoustic resonator includes: a silicon substrate 20, a bottom electrode layer 40, a piezoelectric layer 50 and a top electrode layer 60 arranged in sequence from bottom to top. The top surface of the silicon substrate 20 has a directional The lower recessed cavity 30, the bottom electrode layer 40 is a diphenylene-based electrode layer 40; it should be noted that the silicon substrate 20 is made of high-resistance silicon material, and the resistivity of the high-resistance silicon is 10000Q· m or above; silicon material is used as the substrate of the thin film cavity acoustic resonator, on the one hand, because the current technology of silicon material is relatively mature, and on the other hand, because silicon material has many advantages in technology. The top surface of the silicon substrate 20 is etched to form a cavity 30. On the one hand, the technical effect of the cavity 30 is to reserve space for the electrode layer (it needs to be emphasized that in this specification, the bottom electrode layer 40 and The top electrode layer 60 (generally referred to as the electrode layer) vibrates, and on the other hand, it can form a sound wave propagation interface, so that the sound wave is fully reflected and does not leak out and propagate. When a high-frequency electrical signal is applied to the above-mentioned electrode layer, the piezoelectric layer 50 sandwiched therein will be internally polarized due to the inverse piezoelectric effect, and will produce reciprocating periodic mechanical deformation and vibration with the same frequency as the input electrical signal. This This kind of mechanical deformation and vibration propagates between the bottom electrode layer 40 and the top electrode layer 60 in the form of bulk acoustic waves, and the propagation direction of the sound wave is related to the electrode layer distribution and the crystallographic orientation of the piezoelectric material. When converting mechanical energy into electrical energy, conductors are needed to transmit signals, so electrodes are needed. It is worth mentioning that the bottom electrode layer 40 is a diphenylene-based bottom electrode layer 40. When the lattice width of the diphenylene material is only 21 atoms, the conductivity is the same as that of metal, while graphite has a lattice width of only 21 atoms. Enene has only the conductivity of a semiconductor at the same thickness; therefore, using diphenylene materials as the FBAR electrode layer can obtain a good Q value and can be made very thin, which is useful for obtaining better electromechanical coupling coefficients, and Frequency control in the design will be greatly improved.

The preparation method includes the following steps:

Step S1: Process the silicon substrate 20 through an RCA cleaning process, dry it, and then etch a groove on the surface of the silicon substrate 20 through dry etching, and deposit a sacrificial layer at the groove; wherein, The depth of the groove is 20um; depositing the sacrificial layer at the groove includes: depositing a loose SiO ₂ layer on the SiO ₂ layer through the PECVD method;

Step S2: Deposit diphenylene base electrode layer 40 material on the silicon substrate 20; in step S2, it also includes:

A trifluoromethanesulfonylation reagent is added to o-iodophenol, and the resulting product reacts with a lithium reagent in a low-temperature solvent to prepare diphenylene. Then, the diphenylene-based bottom electrode layer 40 material is obtained by evaporation deposition. ;

Step S3: Bond the piezoelectric layer 50 material, and etch the piezoelectric layer 50 to form the required pattern; in step S3, it also includes:

Step S31: Deposit a piezoelectric material film on the silicon substrate 20 by magnetron sputtering, and then perform heat treatment and inert gas protection treatment on the piezoelectric material film;

Step S32: Using the organic metal compound chemical vapor deposition method, the piezoelectric material film processed in step S31 is further grown into a high crystal quality piezoelectric material, and then etching and stripping are performed to remove parts other than the piezoelectric material film to obtain the piezoelectric material. Material;

Step S4: Deposit the top electrode layer 60 material and etch it to obtain a pattern;

Step S5: Obtain a release window by dry etching around the cavity 30, inject the corrosion solution from the release window, remove the loose sacrificial layer, and form an air cavity, thereby obtaining the thin film cavity acoustic resonator.

Further, the horizontal areas of the bottom electrode layer 40 and the top electrode layer 60 are both smaller than the horizontal area of the silicon substrate 20 , and the bottom electrode layer 40 and the top electrode layer 60 are respectively formed from the piezoelectric layer 50 The two ends begin to extend and completely cover the cavity 30 directly above.

In this embodiment, an inclination angle of 70° to 86° is provided between the inner wall of the cavity 30 and the bottom surface of the cavity 30 . Since the cavity 30 needs to be filled and released with a sacrificial layer (the so-called sacrificial layer refers to a loose SiO ₂ layer deposited on the SiO ₂ layer by the PECVD method), an inclination angle is set on the inner wall of the cavity 30 .

In this embodiment, the piezoelectric layer 50 includes at least one piezoelectric material selected from AlN, ZnO, and PTZ. Further, the top electrode layer 60 is composed of at least one of diphenylene, gold, copper, silver, aluminum, tungsten, platinum, molybdenum, rhodium, iridium, and titanium. Further, the thin film cavity acoustic resonator includes a support substrate 10 , and the silicon substrate 20 is disposed on the support substrate 10 .

Referring to Figure 3, a specific embodiment of the method for preparing the thin film cavity acoustic resonator includes the following steps:

1) Use the standard RCA cleaning process to process the silicon wafer (silicon substrate 20), and then dry it;

2) Use dry etching to etch a groove on the surface of the silicon wafer with a depth of 20um;

3) Deposit a SiO ₂ layer on the surface of the silicon wafer through thermal oxidation growth;

4) Deposit a loose SiO ₂ layer (as a sacrificial layer) on the SiO ₂ layer by PECVD method;

5) Perform chemical mechanical polishing (CMP) to remove the SiO ₂ layer higher than the edge of the groove, and then clean;

6) Evaporate and deposit the diphenylene base electrode layer 40 material, and etch the bottom electrode pattern;

7) Bond the piezoelectric layer 50 material, and etch the piezoelectric layer 50 to form the required pattern;

8) Deposit the top electrode layer 60 material and etch it to obtain a pattern;

9) Obtain a release window by dry etching around the cavity 30, inject HF solution through the release window, remove the loose SiO ₂ layer, and form an air cavity, thus obtaining a thin film cavity acoustic resonator.

It should be noted:

1. The standard RCA cleaning process was pioneered in 1965 by Kern, Puotinen and others at the RCA Laboratory in Princeton, NJ, and is named after it. RCA is a typical wet chemical cleaning method that is still the most commonly used. This cleaning method mainly includes the following cleaning solutions. (1) SPM: H ₂ SO ₄ /H ₂ O ₂ 120～150℃ SPM has a high oxidizing ability. It can oxidize metals and dissolve them in the cleaning solution, and can oxidize organic matter to generate CO ₂ and H ₂ O. Cleaning silicon wafers with SPM can remove heavy organic contamination and some metals on the surface of the silicon wafer. However, when the organic contamination is particularly severe, the organic matter will be carbonized and difficult to remove. (2) HF (DHF): HF (DHF) 20~25℃ DHF can remove the natural oxide film on the surface of the silicon wafer. Therefore, the metal attached to the natural oxide film will be dissolved into the cleaning solution, and DHF inhibits oxidation. membrane formation. Therefore, Al, Fe, Zn, Ni and other metals on the surface of the silicon wafer can be easily removed. DHF can also remove metal hydroxides attached to the natural oxide film. When cleaning with DHF, when the natural oxide film is corroded away, the silicon on the surface of the silicon wafer is almost not corroded. (3)APM(SC-1): NH ₄ OH/H ₂ O ₂ /H ₂ O 30～80℃ Due to the action of H ₂ O ₂ , there is a natural oxide film (SiO ₂ ) on the surface of the silicon wafer, which is hydrophilic properties, the surface of the silicon wafer and between the particles can be penetrated by the cleaning fluid. Since the natural oxide layer on the surface of the silicon wafer and the Si on the surface of the silicon wafer are corroded by NH ₄ OH, the particles attached to the surface of the silicon wafer fall into the cleaning solution, thereby achieving the purpose of removing the particles. While NH ₄ OH corrodes the surface of the silicon wafer, H ₂ O ₂ forms a new oxide film on the surface of the oxidized silicon wafer. (4)HPM(SC-2): HCl/H ₂ O ₂ /H ₂ O 65～85℃ is used to remove sodium, iron, magnesium and other metal contamination on the surface of silicon wafers. HPM can remove Fe and Zn at room temperature. The general idea of cleaning is to first remove organic contamination on the surface of the silicon wafer, because organic matter will cover part of the surface of the silicon wafer, making it difficult to remove the oxide film and related contamination; then dissolve the oxide film, because the oxide layer is "contamination""Traps" will also introduce epitaxial defects; finally, particles, metal and other contaminants are removed, and the surface of the silicon wafer is passivated.

2. Dry etching is a technology that uses plasma to etch thin films. When gas exists in the form of plasma, it has two characteristics: on the one hand, the chemical activity of these gases in the plasma is much stronger than under normal conditions. Depending on the material being etched, choosing the appropriate gas can make the process faster. React with the material to achieve the purpose of etching removal; on the other hand, the electric field can also be used to guide and accelerate the plasma so that it has a certain energy. When it bombards the surface of the object to be etched, it will be etched. The atoms of the physical material are knocked out, thereby achieving the purpose of etching using physical energy transfer. Therefore, dry etching is the result of a balance between physical and chemical processes on the wafer surface.

3. The PECVD method uses microwaves or radio frequencies to ionize gas containing atoms of film components to form a plasma locally. The plasma is very chemically active and can easily react to deposit the desired film on the substrate. In order to enable chemical reactions to proceed at lower temperatures, the activity of plasma is used to promote the reaction, so this type of CVD is called plasma enhanced chemical vapor deposition (PECVD). Its experimental mechanism is to use microwave or radio frequency to make the gas containing the atoms that make up the film locally form a plasma. The plasma is very chemically active and can easily react to deposit the desired film on the substrate. Its advantages are: low basic temperature, fast deposition rate, good film quality, fewer pinholes, and not easy to crack.

4. Evaporation is a process in which the substance to be formed into a film is placed in a vacuum to evaporate or sublimate, so that it is precipitated on the surface of the workpiece or substrate.

A thin film cavity acoustic wave resonator is produced by executing the above-mentioned preparation method of a thin film cavity acoustic wave resonator.

The beneficial effects of the present invention are: 1. The thickness of the electrode layer is greatly reduced, the thickness of the electrode layer can be effectively ignored, and the actual operating frequency of the device can be calculated and predicted more accurately in the design. 2. Use diphenylene material as the electrode layer, because diphenylene has better conductivity than graphene, which can effectively increase the Q value of the thin film cavity acoustic resonator, improve the device efficiency, and can also Increased power capacity.

The above embodiments are only descriptions of preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, ordinary engineers and technicians in the art may make various modifications and modifications to the technical solutions of the present invention. Improvements should fall within the protection scope determined by the claims of the present invention.

Claims

A method for preparing a thin film cavity acoustic resonator, characterized in that the thin film cavity acoustic resonator includes: a silicon substrate, a bottom electrode layer, a piezoelectric layer and a top electrode layer arranged in sequence from bottom to top, The top surface of the silicon substrate is provided with a downwardly depressed cavity, and the bottom electrode layer is a diphenylene-based bottom electrode layer;

The preparation method includes the following steps:

Step S1: Process the silicon substrate through the RCA cleaning process, dry it, and then etch a groove on the surface of the silicon substrate through dry etching, and deposit a sacrificial layer at the groove;

Step S2: Deposit diphenylene base electrode layer material on the silicon substrate;

Step S3: Bond the piezoelectric layer material, and etch the piezoelectric layer to form the required pattern;

Step S4: Deposit the top electrode layer material and etch it to obtain a pattern;

Step S5: Obtain a release window by dry etching around the cavity, inject the corrosion solution from the release window, remove the loose sacrificial layer, and form an air cavity, thereby obtaining the thin film cavity acoustic resonator.
The method for preparing a thin film cavity acoustic wave resonator according to claim 1, characterized in that: depositing a sacrificial layer at the groove includes: depositing a loose SiO2 layer on the SiO2 layer by a PECVD method.
The method for preparing a thin film cavity acoustic resonator according to claim 1, characterized in that: in step S2, it also includes:

A trifluoromethanesulfonylation reagent is added to o-iodophenol, and the resulting product reacts with a lithium reagent in a low-temperature solvent to prepare a diphenylene group. Then, a diphenylene-based electrode layer material is obtained by evaporation deposition.
The method for preparing a thin film cavity acoustic resonator according to claim 1, characterized in that: in step S3, it further includes:

Step S31: Deposit a piezoelectric material film on the silicon substrate through magnetron sputtering, and then perform heat treatment and inert gas protection treatment on the piezoelectric material film;

Step S32: Using the organic metal compound chemical vapor deposition method, the piezoelectric material film processed in step S31 is further grown into a high crystal quality piezoelectric material, and then etching and stripping are performed to remove parts other than the piezoelectric material film to obtain the piezoelectric material. Material.
The method for preparing a thin film cavity acoustic resonator according to claim 1, wherein the horizontal areas of the bottom electrode layer and the top electrode layer are both smaller than the horizontal area of the silicon substrate, and the bottom electrode layer and The top electrode layer extends from both ends of the piezoelectric layer and completely covers directly above the cavity.
The method for preparing a thin film cavity acoustic resonator according to claim 1, wherein an inclination angle of 70° to 86° is provided between the inner wall of the cavity and the bottom surface of the cavity.
The method for preparing a thin film cavity acoustic resonator according to claim 1, wherein the piezoelectric layer includes at least one piezoelectric material selected from the group consisting of AlN, ZnO, and PTZ.
The method for preparing a thin film cavity acoustic resonator according to claim 1, wherein the top electrode layer is made of diphenylene, gold, copper, silver, aluminum, tungsten, platinum, molybdenum, rhodium, and iridium. , at least one composition of titanium.
The method for preparing a thin film cavity acoustic resonator according to claim 1, wherein the thin film cavity acoustic resonator includes a support base, and the silicon substrate is disposed on the support base.
A thin film cavity acoustic wave resonator, characterized in that the thin film cavity acoustic wave resonator is produced by executing the preparation method of a thin film cavity acoustic wave resonator according to any one of claims 1 to 9.