JP6957306B2 - Elastic wave device and its manufacturing method - Google Patents

Description

The present invention relates to an elastic wave device and a method for manufacturing the same, for example, an elastic wave device having a comb tooth electrode and a method for manufacturing the same.

As an elastic wave device using an elastic wave, an elastic surface acoustic wave (SAW) device including an IDT (Interdigital Transducer) composed of a pair of comb tooth electrodes on a piezoelectric substrate is known. Surface acoustic wave devices are used, for example, as bandpass filters in various circuits for processing radio signals having a frequency of 45 MHz to 2 GHz (for example, Patent Document 1). It is known that the comb tooth electrode is formed by using the lift-off method (for example, Patent Document 2-4). It is known that an additional film is provided on the piezoelectric substrate between the electrode fingers of the comb tooth electrode (for example, Patent Document 5-7).

JP-A-2015-89069 Japanese Unexamined Patent Publication No. 2001-267868 Japanese Unexamined Patent Publication No. 2009-147818 Japanese Unexamined Patent Publication No. 2007-267117 Japanese Unexamined Patent Publication No. 2011-78072 Japanese Unexamined Patent Publication No. 2011-124745 Re-table 2010/100967

Since the comb tooth electrode is formed by the lift-off method, an additional film is provided between the piezoelectric substrate and the mask layer. If the additional film is removed after the comb tooth electrode is formed, damage may be introduced to the surface of the piezoelectric substrate. If an insulating film is provided as a protective film on the comb tooth electrode and the additional film without removing the additional film, the covering property of the insulating film may deteriorate.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the covering property of the insulating film.

The present invention is adjacent to a piezoelectric substrate and a pair of comb tooth electrodes provided on the piezoelectric substrate, each having a plurality of electrode fingers, and at least a part of each electrode finger being alternately arranged in an arrangement direction. An additional film provided on the piezoelectric substrate between the electrode fingers, having a film thickness of 1/2 or less of the film thickness of at least one of the plurality of electrode fingers and separated from the adjacent electrode fingers, and the plurality of electrode fingers. e Bei an insulator film covering the electrode fingers and the additional film, the width of the additional layer in the arrangement direction of the plurality of electrode fingers is 3/4 or less of the width between adjacent electrode fingers in the array direction An elastic wave device.

In the above configuration, the pair of comb-tooth electrodes each has a bus bar to which a plurality of corresponding electrode fingers are connected, and additions provided on both sides of one electrode finger of the pair of comb-tooth electrodes in the arrangement direction. The film may be configured to be connected via one electrode finger of the pair of comb-tooth electrodes and the other bus bar of the pair of comb-tooth electrodes.

In the above configuration, the additional film may be provided so as to surround the pair of comb tooth electrodes.

In the above configuration, the separation distance between the additional film and the pair of comb tooth electrodes can be substantially constant.

In the above configuration, a dielectric film provided so as to cover the insulator film is provided, the insulator film is thinner than the plurality of electrode fingers, and the dielectric film is thicker than the plurality of electrode fingers. Can be done.

In the above configuration, the additional film may be made of the same material as the insulator film.

In the above configuration, the acoustic impedance of the additional film may be closer to the acoustic impedance of the insulator film than the acoustic impedance of the plurality of electrode fingers.

The present invention includes a step of forming an additional film on a piezoelectric substrate, a step of forming a mask layer having a first opening on the additional film, and the mask layer so that the additional film is smaller than the mask layer. The step of removing the additional film on the mask to form the second opening of the additional film communicating with the first opening, and on the piezoelectric substrate and the mask layer in the first opening and the second opening. A step of forming a metal film having a film thickness larger than the film thickness of the additional film, and removing the mask layer to remove the metal film on the mask layer, and a plurality of each from the metal film on the piezoelectric substrate. The step of forming a pair of comb tooth electrodes having the electrode fingers of the above, and the respective electrode fingers are alternately arranged in the arrangement direction in at least a part thereof, and the plurality of electrode fingers and the additional film are formed on the piezoelectric substrate. to cover, seen including a step of forming an insulating film, wherein the thickness of the additional film is 1/2 or less of at least one of thickness of the plurality of electrode fingers, said plurality of sequences of the electrode fingers The width of the additional film in the direction is 3/4 or less of the width between adjacent electrode fingers in the arrangement direction, which is a method for manufacturing an elastic wave device.

According to the present invention, the covering property of the insulating film can be improved.

1 (a) to 1 (d) are cross-sectional views (No. 1) showing a method of manufacturing an elastic wave device according to the first embodiment. 2 (a) to 2 (c) are cross-sectional views (No. 2) showing a method of manufacturing an elastic wave device according to the first embodiment. FIG. 3 is a schematic diagram of an SEM image corresponding to FIG. 1 (d). FIG. 4 is a plan view of the elastic wave resonator according to the first embodiment. 5 (a) is a cross-sectional view taken along the line AA of FIG. 4, and FIG. 5 (b) is an enlarged view of FIG. 6 (a) and 6 (b) are cross-sectional views showing a method of manufacturing an elastic wave device in Comparative Example 1 and Comparative Example 2. FIG. 7 is a cross-sectional view of the elastic wave device according to the first modification of the first embodiment. FIG. 8A is a circuit diagram of the filter according to the second embodiment, and FIG. 8B is a circuit diagram of the duplexer according to the first modification of the second embodiment.

Examples of the present invention will be described below with reference to the drawings.

1 (a) to 2 (c) are cross-sectional views showing a method of manufacturing an elastic wave device according to the first embodiment. As shown in FIG. 1A, the additional film 14 is formed on the piezoelectric substrate 10. The piezoelectric substrate 10 is, for example, a lithium tantalate substrate or a lithium niobate substrate. The piezoelectric substrate 10 may be bonded to the support substrate. The additional film 14 is, for example, an insulating film such as a silicon oxide film, a silicon nitride film, a silicon carbide film, a tantalum oxide film or a niobium oxide film, a metal film such as an aluminum film, or a conductor film such as a silicon film. The additional film 14 is formed by using, for example, a vacuum deposition method, a sputtering method, or a CVD (Chemical Vapor Deposition) method.

As shown in FIG. 1 (b), a mask layer 50 having an opening 52 is formed on the additional film 14. The mask layer 50 is, for example, a photoresist, and is formed by coating, exposing, and developing.

As shown in FIG. 1 (c), the additional film 14 is removed by using the mask layer 50 as a mask. For the removal of the additional film 14, for example, a wet etching method or a dry etching method is used. At this time, the additional film 14 is side-etched. As a result, the opening 53 of the additional film 14 becomes larger than the opening 52. The side surface of the additional film 14 is provided inside the side surface of the mask layer 50. Overhangs 54 without an additional film 14 are formed between the mask layer 50 and the piezoelectric substrate 10 at both ends of the mask layer 50.

As shown in FIG. 1 (d), the metal films 12 and 13 are formed on the piezoelectric substrate 10 and the mask layer 50 in the openings 52 and 53. For the formation of the metal films 12 and 13, for example, a vacuum vapor deposition method is used. The metal films 12 and 13 are, for example, a film containing an aluminum film or a copper film, and are thicker than the additional film 14. Since the overhang 54 is formed, the metal film 12 formed on the piezoelectric substrate 10 in the openings 52 and 53 and the metal film 13 formed on the mask layer 50 are not connected as in the region 56. It is divided into.

An SEM (Scanning Electron Microscope) image corresponding to FIG. 1 (d) was acquired for an example of the method for manufacturing an elastic wave device according to Example 1. FIG. 3 is a schematic diagram of an SEM image corresponding to FIG. 1 (d). As shown in FIG. 3, the metal film 13 and the metal film 12 formed on the side surface of the mask layer 50 are separated in the region 56. The metal film 12 has a ruthenium film 12a and a copper film 12b.

As shown in FIG. 2A, by removing the mask layer 50, the metal film 13 formed on the mask layer 50 is lifted off. Since the metal films 12 and 13 are separated, the metal film 13 can be easily removed. For example, when the metal films 12 and 13 are partially connected, burrs and the like are formed at the ends of the metal films 12.

As shown in FIG. 2B, the insulator film 16 is formed on the piezoelectric substrate 10 so as to cover the metal film 12 and the additional film 14. The insulator film 16 is, for example, a silicon nitride film or a silicon oxide film. The insulator film 16 is formed by, for example, a vacuum vapor deposition method or a CVD method. The insulator film 16 is thinner than, for example, the metal film 12.

As shown in FIG. 2C, the dielectric film 18 is formed on the insulator film 16. The dielectric film 18 is, for example, a silicon oxide film. The dielectric film 18 is formed by, for example, a vacuum vapor deposition method or a CVD method. The dielectric film 18 is thicker than, for example, the metal film 12. The upper surface of the dielectric film 18 is flattened by using, for example, a CMP (Chemical Mechanical Polishing) method.

FIG. 4 is a plan view of the elastic wave resonator according to the first embodiment. 5 (a) is a cross-sectional view taken along the line AA of FIG. 4, and FIG. 5 (b) is an enlarged view of FIG. 4 and 5 (b) show the metal film 12 and the additional film 14. The propagation direction of elastic waves (that is, the arrangement direction of the electrode fingers) is the X direction, the extension direction of the electrode fingers is the Y direction, and the normal direction of the upper surface of the piezoelectric substrate 10 is the Z direction. The X-direction, Y-direction, and Z-direction do not necessarily correspond to the X-axis direction, Y-axis direction, and Z-axis direction of the crystal orientation of the piezoelectric substrate 10.

As shown in FIG. 5A, the metal film 12 is provided on the piezoelectric substrate 10. An additional film 14 is provided on the piezoelectric substrate 10 between the metal films 12. An insulator film 16 is provided so as to cover the metal film 12 and the additional film 14. A dielectric film 18 is provided on the insulator film 16. The film thickness H2 of the additional film 14 is smaller than the film thickness H1 of the metal film 12. That is, the height of the upper surface of the additional film 14 from the piezoelectric substrate 10 is lower than the height of the upper surface of the metal film 12 from the piezoelectric substrate 10.

The dielectric film 18 has, for example, a temperature coefficient of elastic modulus of the piezoelectric substrate 10 and a temperature coefficient of elastic modulus having an inverse sign. As a result, the frequency temperature coefficient of the elastic wave device can be reduced. When the piezoelectric substrate 10 is a lithium tantalate substrate or a lithium niobate substrate, the insulator film 16 is, for example, a silicon oxide film. By adding fluorine to the silicon oxide film, the temperature coefficient of frequency of the elastic wave device can be made smaller. The insulator film 16 is a protective film that protects the upper surface of the piezoelectric substrate 10 and the metal film 12. For example, it suppresses the diffusion of atoms of the metal film 12 into the dielectric film 18.

As shown in FIGS. 4 and 5 (b), the IDT 24 and the reflector 26 are provided on the piezoelectric substrate 10. The IDT 24 and the reflector 26 are formed of a metal film 12. The IDT 24 includes a pair of opposing comb tooth electrodes 20a and 20b. The comb tooth electrode 20a includes a plurality of electrode fingers 21a (comb teeth) and a bus bar 22a to which the plurality of electrode fingers 21a are connected. The comb tooth electrode 20b includes a plurality of electrode fingers 21b (comb teeth) and a bus bar 22b to which the plurality of electrode fingers 21b are connected. The pair of comb tooth electrodes 20a and 20b are provided so as to face each other so that the electrode fingers 21a and 21b are substantially staggered at least in part.

The region where the electrode fingers 21a and 21b of the pair of comb tooth electrodes 20a and 20b intersect is the intersection region. The elastic waves excited by the electrode fingers 21a and 21b in the intersecting region propagate mainly in the X direction. The reflector 26 reflects elastic waves. As a result, elastic waves are confined in the intersection region of IDT24. The pitch λ of the electrode fingers 21a and 21b in the same comb tooth electrodes 20a and 20b is approximately the wavelength of the elastic wave.

The additional film 14 is provided between the electrode fingers 21a and 21b. The additional films 14 provided on both sides of the electrode finger 21a in the X direction are connected between the electrode finger 21a and the bus bar 22b. The additional films 14 provided on both sides of the electrode finger 21b in the X direction are connected between the electrode finger 21b and the bus bar 22a. The additional film 14 between the electrode fingers in the reflector 26 is isolated. The additional film 14 is provided so as to surround the IDT 24 and the reflector 26. The width W2 of the additional film 14 between the adjacent electrode fingers 21a and 21b is smaller than the width W1 between the adjacent electrode fingers 21a and 21b.

The piezoelectric substrate 10 is, for example, a rotating Y-cut X propagating lithium niobate substrate. The metal film 12 is, for example, a ruthenium film having a film thickness of 20 nm and a copper film having a film thickness of 125 nm from the piezoelectric substrate 10 side. The insulator film 16 is, for example, a silicon nitride film having a film thickness of 20 nm.

[Comparison example]
6 (a) and 6 (b) are cross-sectional views showing a method of manufacturing an elastic wave device in Comparative Example 1 and Comparative Example 2. As shown in FIG. 6A, in Comparative Example 1, the width of the additional film 14 and the width of the mask layer 50 are about the same. The metal film 12 and the additional film 14 are not separated from each other. The metal film 13 on the side surface of the mask layer 50 and the metal film 12 on the piezoelectric substrate 10 are not separated. Therefore, it becomes difficult to lift off the metal film 13. Further, when the metal film 12 (electrode fingers 21a and 21b) and the additional film 14 come into contact with each other, the excitation efficiency of elastic waves deteriorates.

As shown in FIG. 6B, in Comparative Example 2, the film thickness H2 of the additional film 14 is larger than the film thickness H1 of the metal film 12. If the insulator film 16 is formed so as to cover the metal film 12 and the additional film 14, the coverage of the insulator film 16 deteriorates. For example, the insulator film 16 has poor coverage on the side surface of the metal film 12, the side surface of the additional film 14, and / or the upper surface of the piezoelectric substrate 10. Therefore, the function of the insulator film 16 as a protective film is reduced.

[Effect of Example 1]
According to the first embodiment, as shown in FIG. 1A, the additional film 14 is formed on the piezoelectric substrate 10. As shown in FIG. 1B, a mask layer 50 having an opening 52 (first opening) is formed on the additional film 14. As shown in FIG. 1 (c), the opening 53 (second opening) of the additional film 14 which removes the additional film 14 by using the mask layer 50 as a mask and communicates with the opening 52 so that the additional film 14 is smaller than the mask layer 50. To form. As shown in FIG. 1D, metal films 12 and 13 having a film thickness larger than that of the additional film 14 are formed on the piezoelectric substrate 10 and the mask layer 50 in the openings 52 and 53. As shown in FIG. 2A, the metal film 13 on the mask layer 50 is removed by removing the mask layer 50. As shown in FIG. 4, a pair of combs having a plurality of electrode fingers 21a and 21b, respectively, from the metal film 12 on the piezoelectric substrate 10, and the electrode fingers 21a and 21b are alternately arranged in the arrangement direction at least in a part thereof. The tooth electrodes 20a and 20b are formed. As shown in FIG. 2B, the insulator film 16 is formed on the piezoelectric substrate 10 so as to cover the metal film 12 and the additional film 14.

Since the insulator film 16 is formed without removing the additional film 14, damage to the piezoelectric substrate 10 and the electrode fingers 21a and 21b caused by the step of removing the additional film 14 can be suppressed. Since the additional film 14 is smaller than the mask layer 50 in FIG. 1 (b), the lift-off of FIG. 2 (a) can be performed more easily than in Comparative Example 1. Further, since the additional film 14 is separated from the electrode fingers 21a and 21b, it is possible to suppress a decrease in the excitation efficiency of the electrode fingers 21a and 21b. Further, since the volume (weight) of the additional film 14 can be reduced, it is possible to suppress the influence of the additional film 14 on the elastic wave. Further, since the film thickness of the additional film 14 is smaller than the film thickness of at least one of the plurality of electrode fingers 21a and 21b, deterioration of the coating property of the insulator film 16 as shown in FIG. 6B of Comparative Example 2 can be suppressed. ..

When a large amount of electric power is applied to the pair of comb tooth electrodes 20a and 20b, the atoms of the electrode fingers 21a and 21b migrate at the interface between the piezoelectric substrate 10 and the insulator film 16 between the electrode fingers 21a and 21b. This may destroy the comb tooth electrodes 20a and 20b. In Example 1, by providing the additional film 14, the migration of atoms between the electrode fingers 21a and 21b can be suppressed.

When the comb tooth electrodes 20a and 20b are formed as in the first embodiment, the additional film 14 is provided on the piezoelectric substrate 10 between the adjacent electrode fingers 21a and 21b as shown in FIGS. 4 and 5 (b). , Separated from adjacent electrode fingers 21a and 21b.

Further, the additional films 14 provided on both sides of the electrode finger 21a of the comb tooth electrode 20a in the X direction are connected via between the electrode finger 21a and the bus bar 22b of the comb tooth electrode 20b. The additional film 14 is provided so as to surround the comb tooth electrodes 20a and 20b. The separation distance between the additional film 14 and the pair of comb tooth electrodes 20a and 20b is substantially constant to the extent of manufacturing error.

In order to improve the coverage of the insulator film 16, the film thickness H2 of the additional film 14 is preferably 50% (1/2) or less of at least one film thickness H1 of the electrode fingers 21a and 21b, and is 25% (1/4) or less. Is more preferable. Since a gap is provided between the mask layer 50 and the piezoelectric substrate 10, the film thickness H2 is preferably 10% (1/10) or more of H1.

In order to easily lift off the metal film 12, the width W2 of the additional film 14 is preferably 90% (9/10) or less, and 75% (3/4) or less of the width W1 between the electrode fingers 21a and 21b. More preferred. The width W2 is preferably 30% or more of W1 so as to mechanically reinforce the mask layer 50 in FIG. 1B.

If the acoustic impedance of the additional film 14 is significantly different from that of the insulator film 16 and / or the dielectric film 18, it will affect the elastic wave. Therefore, the acoustic impedance of the additional film 14 is preferably closer to the acoustic impedance of the insulator film 16 and / or the dielectric film 18 than the acoustic impedance of the plurality of electrode fingers 21a and 21b.

For example, when the electrode fingers 21a and 21b are mainly copper films, the acoustic impedance of copper is 34.1 MPa · s / m ³ . When the insulator film 16 is a silicon nitride film, its acoustic impedance is 15.2 MPa · s / m ³ . When the dielectric film 18 is a silicon oxide film to which fluorine is added, its acoustic impedance is 10.9 MPa · s / m ³ . In this case, as a material closer to the acoustic impedance of the insulator film 16 and / or the dielectric film 18 than the acoustic impedance of the electrode fingers 21a and 21b, there are silicon nitride, silicon oxide (SiO ₂ ), silicon and aluminum. The acoustic impedances of silicon oxide, silicon and aluminum are 12.5 MPa · s / m ³ , 20.8 MPa · s / m ³ and 13.8 MPa · s / m ³ , respectively.

[Modification 1 of Example 1]
FIG. 7 is a cross-sectional view of the elastic wave device according to the first modification of the first embodiment. As shown in FIG. 7, an additional film 14 is provided on the piezoelectric substrate 10 between the electrode fingers 21a and 21b. The addition film 14 and the insulator film 16 are made of the same material, and are, for example, a silicon nitride film. Other configurations are the same as those in the first embodiment, and the description thereof will be omitted.

In the first modification of the first embodiment, since the additional film 14 is made of the same material as the insulator film 16, the acoustic impedance of the additional film 14 is substantially the same as the acoustic impedance of the insulator film 16. As a result, it is possible to suppress the influence of the additional film 14 on the elastic wave.

In the modified example 1 of the first embodiment, the interface between the additional film 14 and the insulator film 16 becomes unclear, and the additional film 14 and the insulator film 16 may be seen as an integral film. Between the electrode fingers 21a and 21b, the film thickness H4 in which the addition film 14 and the insulator film 16 are integrated at the center thereof is the insulator film on both sides between the electrode fingers 21a and 21b. It becomes larger than the film thickness H3 of 16.

Example 2 is an example of a filter and a duplexer using an elastic wave resonator of Example 1 and its modifications. FIG. 8A is a circuit diagram of the filter according to the second embodiment. As shown in FIG. 8A, one or more series resonators S1 to S4 are connected in series between the input terminal T1 and the output terminal T2. One or more parallel resonators P1 to P4 are connected in parallel between the input terminal T1 and the output terminal T2. The elastic wave resonators of Example 1 and its modifications can be used for at least one of one or more series resonators S1 to S4 and one or more parallel resonators P1 to P4. The number of resonators of the ladder type filter can be set as appropriate. The filter may be a multiple mode filter.

[Modification 1 of Example 2]
FIG. 8B is a circuit diagram of the duplexer according to the first modification of the second embodiment. As shown in FIG. 8B, a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes a signal in the transmission band among the high-frequency signals input from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 passes a signal in the reception band among the high frequency signals input from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment. Although the duplexer has been described as an example as the multiplexer, a triplexer or a quadplexer may be used.

Although the examples of the present invention have been described in detail above, the present invention is not limited to such specific examples, and various modifications and modifications are made within the scope of the gist of the present invention described in the claims. It can be changed.

10 piezoelectric substrate 12, 13 metal film 14 additional film 16 insulator film 18 dielectric film 20a, 20b comb tooth electrode 21a, 21b electrode finger 22a, 22b bus bar 24 IDT
26 Reflector 40 Transmit filter 42 Receive filter 50 Mask layer 52, 53 Aperture

Claims (8)

Piezoelectric board and
A pair of comb tooth electrodes provided on the piezoelectric substrate, each having a plurality of electrode fingers, and at least a part of which the respective electrode fingers are alternately arranged in the arrangement direction.
An additional film provided on the piezoelectric substrate between adjacent electrode fingers and having a film thickness of 1/2 or less of the film thickness of at least one of the plurality of electrode fingers and separated from the adjacent electrode fingers.
An insulator film covering the plurality of electrode fingers and the additional film,
Bei to give a,
An elastic wave device in which the width of the additional film in the arrangement direction of the plurality of electrode fingers is 3/4 or less of the width between adjacent electrode fingers in the arrangement direction. The pair of comb tooth electrodes each has a bus bar to which a plurality of corresponding electrode fingers are connected.
The additional films provided on both sides of one electrode finger of the pair of comb tooth electrodes in the arrangement direction are between one electrode finger of the pair of comb tooth electrodes and the other bus bar of the pair of comb tooth electrodes. The elastic wave device according to claim 1, which is connected via. The elastic wave device according to claim 2, wherein the additional film is provided so as to surround the pair of comb tooth electrodes. The elastic wave device according to claim 3, wherein the separation distance between the additional film and the pair of comb tooth electrodes is substantially constant. A dielectric film provided so as to cover the insulator film is provided.
The elastic wave device according to any one of claims 1 to 4 , wherein the insulator film is thinner than the plurality of electrode fingers, and the dielectric film is thicker than the plurality of electrode fingers. The elastic wave device according to any one of claims 1 to 5 , wherein the additional film is made of the same material as the insulator film. The elastic wave device according to any one of claims 1 to 6 , wherein the acoustic impedance of the additional film is closer to the acoustic impedance of the insulator film than the acoustic impedance of the plurality of electrode fingers. The process of forming an additional film on the piezoelectric substrate and
A step of forming a mask layer having a first opening on the additional film and
A step of removing the additional film by using the mask layer as a mask to form a second opening of the additional film communicating with the first opening so that the additional film is smaller than the mask layer.
A step of forming a metal film having a film thickness larger than that of the additional film on the piezoelectric substrate and the mask layer in the first opening and the second opening.
By removing the mask layer, the metal film on the mask layer is removed, and each of the metal films on the piezoelectric substrate has a plurality of electrode fingers, and the electrode fingers are alternately arranged at least in a part thereof. The process of forming a pair of comb-tooth electrodes arranged in the direction,
A step of forming an insulator film on the piezoelectric substrate so as to cover the plurality of electrode fingers and the additional film.
Only including,
The film thickness of the additional film is ½ or less of the film thickness of at least one of the plurality of electrode fingers.
A method for manufacturing an elastic wave device, wherein the width of the additional film in the arrangement direction of the plurality of electrode fingers is 3/4 or less of the width between adjacent electrode fingers in the arrangement direction.

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