CN114883479A - Preparation method of high-quality single crystal piezoelectric film applied to FBAR (film bulk acoustic resonator) and resonator structure - Google Patents

Abstract

The invention discloses a method for preparing a high-quality single crystal piezoelectric film applied to FBAR (film bulk acoustic resonator) and a resonator structure, wherein the method for preparing the film comprises the following steps: adopting SiC as a substrate, and pretreating the SiC substrate; depositing an AlN thin layer on the pretreated substrate through MOCVD, wherein the AlN thin layer is used as a transition layer; sputtering a polycrystalline AlN film on the transition layer by a low-temperature magnetron sputtering method; performing high-temperature face-to-face annealing treatment on the AlN thin film; under the action of high temperature, the crystal grains of the AlN thin film are recrystallized to grow up the crystal grains, and then the interfaces among the crystal grains are reduced through combination to form the high-quality monocrystal AlN thin film. According to the invention, SiC is used as the substrate of the AlN piezoelectric film, so that the influence caused by thermal expansion coefficient and lattice mismatch can be reduced, and the performance of the FBAR piezoelectric film AlN is improved.

Description

Preparation method of high-quality single crystal piezoelectric film applied to FBAR (film bulk acoustic resonator) and resonator structure

Technical Field

The invention relates to a method for preparing a single crystal piezoelectric film and a resonator structure, in particular to a method for preparing a high-quality single crystal piezoelectric film and a resonator structure applied to FBAR.

Background

FBAR has the advantages of small size, high Q value, high operating frequency, large power capacity, and low loss, and is the most likely filter for realizing full integration of radio frequency modules at present. The quality of FBAR performance depends mainly on the quality of the piezoelectric layer. As a piezoelectric thin film material, AlN has the advantages of low intrinsic loss of the material, high resonant frequency, high thermal conductivity, and the like, and along with the development of radio frequency technology, AlN is a very small number of piezoelectric thin film materials capable of adapting to high-frequency signals.

In order to cooperate with an integrated MEMS (micro-electromechanical systems) technology, currently used FBARs (film bulk optical resonators) directly grow AlN thin films on the basis of Si substrates, and because the lattice constant of the Si substrates is greatly different from that of AlN piezoelectric thin films, the influence of the thermal expansion coefficient and lattice mismatch on the performance of the piezoelectric thin films is large.

Disclosure of Invention

The present invention is directed to overcoming the above-mentioned problems, and to provide a method for manufacturing a high-quality single-crystal piezoelectric thin film for FBAR, which uses SiC as a substrate of an AlN piezoelectric thin film, and can reduce the influence of thermal expansion coefficient and lattice mismatch, thereby improving the performance of the AlN piezoelectric thin film for FBAR.

Another object of the present invention is to overcome the above problems and to provide a method for fabricating a resonator structure applied to an FBAR.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a high-quality single crystal piezoelectric film applied to FBAR comprises the following steps:

adopting SiC as a substrate, and pretreating the SiC substrate;

depositing an AlN thin layer on the pretreated substrate through MOCVD, wherein the AlN thin layer is used as a transition layer; sputtering a polycrystalline AlN film on the transition layer by a low-temperature magnetron sputtering method;

performing high-temperature face-to-face annealing treatment on the AlN thin film; under the action of high temperature, the crystal grains of the AlN thin film are recrystallized to grow up the crystal grains, and then the interfaces among the crystal grains are reduced through combination to form the high-quality monocrystal AlN thin film.

In a preferred embodiment of the present invention, the operation of the pretreatment is:

firstly, carrying out chemical mechanical double-sided polishing on the silicon surface and the carbon surface of SiC by using a diamond abrasive material, then carrying out single-sided chemical mechanical polishing on the silicon surface, and reducing the influence of substrate warping on a film and avoiding cracking of the substrate before use by a two-step polishing method.

In a preferred embodiment of the present invention, in MOCVD, the reactants are TMAL and NH ₃ While H is ₂ As a carrier gas.

The invention discloses a preferable scheme, wherein in the magnetron sputtering, the magnetron sputtering target material is pure aluminum with the purity of 99.999 percent, the sputtering power is 3000-;

the reaction gas for sputtering was a mixed gas of nitrogen and argon, and the ratio of the mixed gas was 0.33.

A preparation method of a resonator structure applied to FBAR comprises the following steps:

sputtering and growing a Mo layer electrode on the monocrystal AlN film by magnetron sputtering, and taking the Mo layer electrode as a bottom electrode;

bonding the bottom electrode to the substrate with the cavity in the reverse direction;

etching to remove the SiC substrate on the uppermost layer, so that the AlN thin film under the SiC substrate is exposed;

and polishing the exposed AlN film, sputtering a Mo layer electrode on the AlN film, and taking the Mo layer electrode as a bottom electrode to finally form the substrate-Mo-AlN-Mo four-layer FBAR resonator structure.

In a preferred embodiment of the present invention, the substrate with an open cavity is obtained by:

selecting Si or SiC or sapphire as a substrate, and carrying out planarization treatment of cleaning and polishing on the substrate; a groove is etched on the substrate by adopting dry etching or wet etching to form a cavity with the depth of 3-30 mu m, so that the oscillation of the resonator is ensured.

Compared with the prior art, the invention has the following beneficial effects:

1. according to the preparation method of the high-quality single crystal piezoelectric film, SiC is used as the substrate of the AlN piezoelectric film, so that the influence caused by thermal expansion coefficient and lattice mismatch can be reduced, and the AlN performance of the FBAR piezoelectric film is improved.

2. The process method of magnetron sputtering is used for replacing MOCVD, the preparation cost is reduced, meanwhile, the thermal decomposition of the film is inhibited by opposite annealing after sputtering, and the performance of the film is improved.

Drawings

Fig. 1 to 6 are preparation flows of the resonator structure preparation method applied to FBAR of the present invention, in which 1 represents a SiC substrate, 2 represents an MOCVD AlN thin layer, 3 represents an AlN sputtered thin film, 4 represents a Si substrate, and 5 represents a Mo bottom electrode.

Detailed Description

In order to make those skilled in the art understand the technical solutions of the present invention well, the following description of the present invention is provided with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Referring to fig. 1 to 6, the method for manufacturing a resonator structure applied to an FBAR of the present invention includes the steps of:

(1) and selecting a substrate for the FBAR resonator and pretreating the substrate before deposition to obtain the required substrate. Firstly, polishing treatment is carried out on a single crystal 4H-SiC substrate. Firstly, carrying out chemical mechanical double-sided polishing on the silicon surface and the carbon surface of SiC by using a diamond abrasive material, then carrying out single-sided chemical mechanical polishing on the silicon surface, and reducing the influence of substrate warping on a film and avoiding cracking of the substrate before use by a two-step polishing method.

(2) And preparing the monocrystal AlN piezoelectric film on the processed substrate. A thin layer of AlN (about 50 nm) was deposited on the polished SiC substrate using MOCVD, with TMAL and NH3 as reactants, with H2 as a carrier gas. A thin layer of single crystal aluminum nitride was obtained as a transition layer for the subsequent magnetron sputtered AlN layer, as shown in fig. 1. And then sputtering an AlN film (800nm) by a method of low-temperature magnetron sputtering (the target material of magnetron sputtering is pure aluminum with the purity of 99.999 percent, the sputtering power is 3000-. An SiC substrate, an MOCVD-completed AlN thin layer, and a magnetron-sputtered AlN thin film were sequentially formed (fig. 2).

(3) And (3) processing the sputtered film by a heat treatment method to improve the film performance. The sputtered AlN thin film is a polycrystalline thin film, and is subjected to face-to-face annealing treatment at 1700 ℃, crystal grains of the thin film can be recrystallized at high temperature to cause the growth of the crystal grains, the crystal grain boundaries are combined and disappear, and finally a single crystal is formed, so that dislocation and stress generated by the crystal grain boundaries are reduced, and the performance is improved. As AlN is thermally decomposed at high temperature, in order to avoid the high-temperature decomposition of the film, the method of surface-to-surface annealing treatment is adopted to inhibit the thermal decomposition of the film and ensure the recrystallization of the film at high temperature.

(4) After obtaining a desired high-quality single crystal thin film, polishing is performed, and electrode preparation of the FBAR resonator is performed on the single crystal thin film. And sputtering and growing a Mo layer electrode on the AlN thin film after sputtering annealing to be used as a bottom electrode (figure 4), wherein the target material is Mo, and the FBAR resonator structure is a three-layer structure of SiC-AlN-Mo. It is then reverse bonded to a substrate that has been coated with a cavity of a bonding agent, the cavity substrate being shown in fig. 3. Constituting a substrate-Mo-AlN-SiC structure (fig. 5). The method can obtain the high-quality monocrystal AlN piezoelectric film and is convenient for the piezoelectric film to be applied to different substrates.

Further, the preparation method of the substrate with the cavity comprises the following steps: firstly, carrying out planarization treatment of cleaning and polishing on a substrate, wherein the substrate can be a series of common substrates such as SiC, sapphire, Si and the like, and then etching a groove by using a dry method or a wet method to form a cavity with the depth of 3-30 mu m so as to ensure the oscillation of a resonator.

(5) And preparing the top electrode to obtain the final FBAR resonator structure. And removing the uppermost SiC substrate by dry etching or wet etching to expose the AlN piezoelectric film under the SiC substrate, polishing the exposed AlN piezoelectric film, and sputtering an MO layer electrode on the substrate to be used as a bottom electrode to finally form the substrate-Mo-AlN-Mo four-layer FBAR resonator structure (figure 6).

The present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents and are included in the scope of the present invention.

Claims (6)

1. A preparation method of a high-quality single crystal piezoelectric film applied to FBAR is characterized by comprising the following steps:

adopting SiC as a substrate, and pretreating the SiC substrate;

depositing an AlN thin layer on the pretreated substrate through MOCVD, wherein the AlN thin layer is used as a transition layer; sputtering a polycrystalline AlN film on the transition layer by a low-temperature magnetron sputtering method;

performing high-temperature face-to-face annealing treatment on the AlN thin film; under the action of high temperature, the crystal grains of the AlN thin film are recrystallized to grow up the crystal grains, and then the interfaces among the crystal grains are reduced through combination to form the high-quality monocrystal AlN thin film.

2. The method for preparing a high-quality single crystal piezoelectric thin film for FBAR according to claim 1, wherein said pre-treating is performed by:

firstly, carrying out chemical mechanical double-sided polishing on the silicon surface and the carbon surface of SiC by using a diamond abrasive material, then carrying out single-sided chemical mechanical polishing on the silicon surface, and reducing the influence of substrate warping on a film and avoiding cracking of the substrate before use by a two-step polishing method.

3. The method of preparing a high quality single crystal piezoelectric thin film for FBAR as claimed in claim 1, wherein reactants are TMAL and NH in MOCVD ₃ While H is ₂ As a carrier gas.

4. The method as claimed in claim 1, wherein in the magnetron sputtering, the magnetron sputtering target is pure aluminum with a purity of 99.999%, the sputtering power is 3000-;

the reaction gas for sputtering was a mixed gas of nitrogen and argon, and the ratio of the mixed gas was 0.33.

5. A preparation method of a resonator structure applied to FBAR is characterized by comprising the following steps:

sputtering and growing a Mo layer electrode on the monocrystal AlN film by magnetron sputtering, and taking the Mo layer electrode as a bottom electrode;

reversely bonding the bottom electrode to the substrate with the cavity;

etching to remove the SiC substrate on the uppermost layer, so that the AlN thin film under the SiC substrate is exposed;

and polishing the exposed AlN film, sputtering a Mo layer electrode on the AlN film, and taking the Mo layer electrode as a bottom electrode to finally form the substrate-Mo-AlN-Mo four-layer FBAR resonator structure.

6. The method of claim 5, wherein the substrate with the cavity is obtained by:

selecting Si or SiC or sapphire as a substrate, and carrying out planarization treatment of cleaning and polishing on the substrate; a groove is etched on the substrate by adopting dry etching or wet etching to form a cavity with the depth of 3-30 mu m, so that the oscillation of the resonator is ensured.

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