JP3884729B2 - Method for manufacturing surface acoustic wave element and method for evaluating electrode film - Google Patents

Description

  The present invention relates to a method for manufacturing a surface acoustic wave device and a method for evaluating an electrode film.

  In recent years, instead of filters and resonators using dielectrics, surface acoustic wave filters and surface acoustic wave resonators, which are types of surface acoustic wave devices, have been used as high-frequency circuits for mobile communication devices such as mobile phones and cordless phones. More and more are being adopted. This is because the surface acoustic wave filter is smaller in size than the dielectric filter and has high electrical characteristics in the same dimension.

Such a surface acoustic wave device mainly includes a piezoelectric substrate and a comb-shaped electrode (interdigital transducer, hereinafter abbreviated as “IDT”) obtained by molding an electrode film laminated on the piezoelectric substrate. And a package containing the piezoelectric substrate and the IDT. As the material of the piezoelectric substrate, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), quartz, and the like are used, and particularly when an RF band filter is manufactured, it has a large electromechanical coupling coefficient. Lithium niobate or lithium tantalate is often used. Since lithium niobate has a large electromechanical coupling coefficient, a 64 ° rotation Y-cut is used. Lithium tantalate has a large electromechanical coupling coefficient and a relatively low frequency temperature coefficient, so that it is 34 to 44. A rotation Y cut type is used. In many cases, aluminum having characteristics such as low specific gravity and low resistance is used as a material for the electrode film.

  As described above, the surface acoustic wave device may be used in an RF band (800 MHz to 2 GHz) of a cellular phone or the like. For example, when used in a 1 GHz band, the electrode finger width (line width) and electrode gap of the IDT are used. Must be reduced to about 1 μm. However, during the operation of the surface acoustic wave device, a repetitive stress proportional to the frequency is applied to the IDT on the piezoelectric substrate, and migration of aluminum atoms due to this repetitive stress occurs, and the IDT has a hillock (projection) or void. Since defects such as (depletion) occur, there is a problem that the life of the apparatus is shortened. That is, the power durability of the IDT (that is, the electrode film) is a very important factor for the life of the device. The deterioration phenomenon of IDT appears not only by increasing the frequency but also by increasing the applied voltage. In addition, as the frequency increases in design, the electrode film must be thinner and the electrode finger width narrower, and as a result, such a deterioration phenomenon is promoted.

  In order to reduce the size of a mobile phone, it is effective to reduce the size of a duplexer that occupies a large space in the high-frequency part of the mobile phone. Therefore, a change from a dielectric duplexer that has been adopted as a duplexer to a surface acoustic wave duplexer has been proposed. However, although this surface acoustic wave duplexer is a very small component, there is a problem in power durability against large power applied to the transmission side of the duplexer, in particular. In addition, it is not impossible to improve the power durability by designing the IDT formation region of the surface acoustic wave device broadly and reducing the effective power density. There is a problem that cannot be achieved.

  For the above reasons, there has been a strong demand for improving the power durability of the IDT of the surface acoustic wave device, that is, the power durability of the electrode film formed on the piezoelectric substrate.

  Therefore, first, as a means for improving the deterioration phenomenon of the electrode film due to migration of aluminum atoms, a technique of adding a trace amount of a different metal such as Cu to aluminum to make the electrode film made of an Al—Cu alloy is described in Non-Patent Document 1 below. Is disclosed. Such Al alloying of the electrode film suppresses the occurrence of hillocks and voids in the electrode film, thereby improving the power durability of the IDT. In addition, the technique for forming an electrode film into an Al alloy is disclosed in Patent Documents 1 to 4 listed below. In any of these techniques, migration of aluminum atoms is suppressed and an IDT deterioration phenomenon is suppressed by adding a small amount of a different metal to aluminum as an electrode film material. By using such a technology, it is possible to improve the power durability. However, even a surface acoustic wave device that has been improved in this way has a duplexer to which a large amount of power is applied. It does not have enough power resistance to be used.

  By the way, it is considered that the diffusion rate of aluminum is higher in the crystal grain boundary than in the crystal grain, that is, the grain boundary diffusion is preferential. Therefore, migration of aluminum atoms due to repetitive stress in the surface acoustic wave device is considered to occur mainly at the crystal grain boundary, which has been pointed out in the past.

  Therefore, it is predicted that the electric power durability can be greatly improved by reducing or removing the crystal grain boundary of the aluminum electrode film, and more preferably by making it into a single crystal, and the electrode film is almost in a single crystal state. The technique is disclosed in Patent Document 5 below. This Patent Document 5 discloses a technique for producing an electrode film using a molecular beam epitaxy method in order to obtain an electrode film that is substantially single crystal.

  A technique for applying an aluminum film oriented in a single crystal or a crystal orientation in a fixed direction to an electrode film of a surface acoustic wave device is disclosed in Patent Document 6 below. Here, as the piezoelectric substrate, a rotated Y-cut quartz substrate in the range of 25-degree rotated Y-cut to 39-degree rotated Y-cut is used, and vapor deposition is performed at a high speed (film formation speed of 4 nm / second) and at a low temperature (substrate temperature of 80 ° C.). By doing so, a (311) orientation film is obtained, and this film is assumed to be an epitaxial film close to a single crystal.

  Patent Document 7 below also discloses that an aluminum single crystal is used as an electrode film for a surface acoustic wave element, and describes a method for producing such an aluminum single crystal film. More specifically, ST-cut or LST-cut quartz is used as the piezoelectric substrate, and an island-like structure in which minute hemispherical islands exist substantially uniformly on the surface of the substrate on which the electrode film is laminated is formed by etching or the like. Forming. An aluminum single crystal film can be obtained by laminating aluminum on the surface of such an island structure by vapor deposition or sputtering.

  Patent Document 8 below shows that an aluminum single crystal film can be obtained when film formation is performed at a very low film formation rate. More specifically, formation of an aluminum single crystal film by vacuum deposition on an LST cut quartz substrate, formation of an aluminum single crystal film by vacuum deposition on a 128-degree rotated Y-cut lithium niobate substrate, 112 degrees X An aluminum single crystal film can be formed on a cut lithium tantalate substrate by vacuum deposition.

Patent Document 9 and Patent Document 10 below are surface acoustic wave devices in which an IDT is formed on a 64-degree rotated Y-cut lithium niobate piezoelectric substrate and a 38-44-degree rotated Y-cut lithium tantalate single crystal substrate. IDT is composed of a titanium base metal film and an aluminum film laminated on the metal film, and it is shown that the aluminum film is monocrystallized by the titanium base metal film.
Japanese Examined Patent Publication No. 7-107967 Japanese Patent No. 2555072 JP-A-64-80113 Japanese Patent Laid-Open No. 1-128607 JP 55-49014 A Japanese Patent No. 2545983 JP-A-5-199062 JP-A-6-132777 International Publication No. 99/16168 Pamphlet International Publication No. 00/74235 Pamphlet JP-A-8-204483 JP 2003-101372 A J. et al. I. Latam, Thin Solid Films 64 (1979), pp 9-15

  In the conventional surface acoustic wave device and surface acoustic wave element described above, there is a problem in the method for evaluating the crystallinity of the electrode film. That is, the electrode film of the surface acoustic wave device is evaluated for its crystallinity by any of the X-ray diffraction method, the RHEED (reflection high-energy electron diffraction) method, and the limited-field electron diffraction method. Time and labor, and expensive equipment is required. Therefore, there is a problem that it is difficult to easily evaluate the crystallinity of the electrode film. A technique for evaluating the crystallinity of the electrode film by the RHEED method and the X-ray diffraction method is also disclosed in Patent Document 11 and the like.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a method for manufacturing a surface acoustic wave device and a method for evaluating an electrode film, in which the crystallinity of the electrode film is evaluated by a simple method. To do.

The method of manufacturing a surface acoustic wave device according to the present invention measures the specific resistance value of an aluminum electrode film formed on a piezoelectric substrate so that the surface orientation is the (311) plane, and this aluminum electrode film constitutes a step of aluminum to assess whether a single crystal, by patterning the aluminum electrode film was evaluated as a single crystal by measurement of specific resistance value, have a forming a comb-shaped electrode When evaluating whether or not the aluminum constituting the aluminum electrode film is a single crystal, if the specific resistance value is equal to or higher than the reference value, the aluminum constituting the aluminum electrode film is evaluated to be a single crystal. Features.

The inventors of the present invention have made researches on the crystallinity of the aluminum electrode film formed on the piezoelectric substrate so that the surface orientation is the (311) plane when producing a surface acoustic wave device. It was newly found that it is possible to evaluate whether or not it is a single crystal based on the value of. Therefore, in this method of manufacturing a surface acoustic wave device, the specific resistance value between the single crystal and the polycrystal is used as a reference value, and the aluminum electrode film having a specific resistance value higher than the reference value is single-crystallized. By evaluating the aluminum electrode film formed on the piezoelectric substrate so that the surface orientation is the (311) plane , the specific resistance value is measured, and the constituent material aluminum is a single crystal. Whether it is evaluated. And the aluminum electrode film | membrane evaluated that aluminum is a single crystal by the evaluation is patterned, and a comb-shaped electrode is formed. The evaluation of the crystallinity of the aluminum electrode film based on this specific resistance value is less time consuming and time consuming than the conventional methods for evaluation using the X-ray diffraction method, the RHEED method, and the limited-field electron diffraction method. The apparatus used for evaluation is also relatively inexpensive. Therefore, the crystallinity evaluation of the aluminum electrode film in the method for manufacturing the surface acoustic wave device according to the present invention can be performed more easily than the crystallinity evaluation of the aluminum electrode film in the conventional method for manufacturing the surface acoustic wave device. .

  When the thickness of the aluminum electrode film is 350 nm or more and 400 nm or less, the reference value of the specific resistance value of the aluminum electrode film is preferably 2.98 μΩcm. When the thickness of the aluminum electrode film is 230 nm or more and 270 nm or less, the reference value of the specific resistance value of the aluminum electrode film is preferably 3.10 μΩcm. When the thickness of the aluminum electrode film is 100 nm or more and 200 nm or less, the reference value of the specific resistance value of the aluminum electrode film is preferably 3.20 μΩcm.

When the thickness of the aluminum electrode film is d (nm), the reference value r (μΩcm) of the specific resistance value of the aluminum electrode film is expressed by the following formula (1)
r = −0.000984d + 3.349 (1)
It is preferable to satisfy.

  Further, Cu is segregated in the aluminum constituting the aluminum electrode film, and when the film thickness of the aluminum electrode film is 350 nm or more and 400 nm or less, the reference value of the specific resistance value of the aluminum electrode film is 3. When the film thickness of the aluminum electrode film is 230 nm or more and 270 nm or less, the reference value of the specific resistance value of the aluminum electrode film is preferably 3.40 μΩcm, and the aluminum electrode film When the film thickness is 100 nm or more and 200 nm or less, the reference value of the specific resistance value of the aluminum electrode film is preferably 3.50 μΩcm.

In addition, Cu is segregated in the aluminum constituting the aluminum electrode film. When the film thickness of the aluminum electrode film is d (nm), the reference value r (μΩcm) of the specific resistance value of the aluminum electrode film is Following formula (2)
r = −0.000984d + 3.649 (2)
It is preferable to satisfy.

The method for evaluating an electrode film according to the present invention comprises measuring the specific resistance value of an aluminum electrode film formed on a piezoelectric substrate so that the surface orientation is the (311) plane, and constituting the aluminum electrode film. It is characterized in that it is evaluated whether the aluminum to be formed is a single crystal, and in that case, when the specific resistance value is equal to or higher than a reference value, it is evaluated that the aluminum constituting the aluminum electrode film is a single crystal .

As described above, the inventors of the present invention have made researches on the crystallinity of an aluminum electrode film formed on a piezoelectric substrate so that the surface orientation is (311) plane . It was newly found that it is possible to evaluate whether or not it is a single crystal by evaluating that the aluminum electrode film having a higher specific resistance value than the reference value is single-crystallized. It was. Therefore, in this electrode film evaluation method for evaluating the crystallinity of an aluminum electrode film based on the value of specific resistance, a conventional method of evaluating using an X-ray diffraction method, a RHEED method, or a limited-field electron diffraction method Compared to, it does not take time and effort, and the apparatus used for evaluation is relatively inexpensive. Therefore, in the electrode film evaluation method according to the present invention, the crystallinity of the aluminum electrode film can be easily evaluated as compared with the conventional electrode film evaluation method.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the surface acoustic wave element by which the crystallinity of an electrode film is evaluated by a simple method, and the evaluation method of an electrode film are provided.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments that are considered to be the best for carrying out a surface acoustic wave device manufacturing method and an electrode film evaluation method according to the present invention will be described below in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  FIG. 1 is a schematic cross-sectional view of a surface acoustic wave device according to an embodiment of the present invention. As shown in FIG. 1, a surface acoustic wave device 10 according to the present invention includes a surface acoustic wave element 12, a mounting substrate 14 on which the surface acoustic wave element is mounted, and a cover 16 that seals the surface acoustic wave element 12. And. On the lower surface 12 a of the surface acoustic wave element 12, a pad electrode 22 (described later) in which raised electrodes 20 are stacked on three pairs of input / output electrodes 18 is formed. A gold plating electrode 24 for applying a voltage necessary for the operation of the surface acoustic wave element 12 is formed on the surface 14 a of the mounting substrate 14 on which the surface acoustic wave element 12 is mounted. As shown in the figure, the corresponding pad electrode 22 of the surface acoustic wave element 12 and the gold plating electrode 24 of the mounting substrate 14 are connected via a gold bump 26. The cover 16 is a member for hermetically sealing and protecting the surface acoustic wave element 12, and is a cap part that covers the dam part 16 </ b> A surrounding the side surface of the surface acoustic wave element 12 from four sides and the upper surface 12 b of the surface acoustic wave element 12. It is composed of two members 16B.

  Next, the surface acoustic wave element 12 constituting the surface acoustic wave device 10 will be described in more detail with reference to FIG. FIG. 2 is a schematic perspective view showing the surface acoustic wave element 12. As shown in FIG. 2, the surface acoustic wave element 12 is formed via a piezoelectric substrate 28, a buffer layer 30 laminated on the piezoelectric substrate 28, and the buffer layer 30 on the piezoelectric substrate 28. Pad electrode 22.

  The piezoelectric substrate 28 is a single crystal substrate made of lithium tantalate and has a prismatic shape with a substantially square horizontal cross section.

  Each of the six pad electrodes 22 has an input / output electrode 18 formed with a single crystal aluminum electrode film (described later) in which Cu is segregated, and a raised electrode 20 for increasing the thickness of the input / output electrode 18 portion. . Three pad electrodes 22 are arranged along two opposing sides of the piezoelectric substrate 28. The three pad electrodes 22 along each side are arranged so as to be separated by an equal distance from the pad electrode 22 located at the center of the side. By arranging the pad electrode 22 in this manner, when the surface acoustic wave device 12 is flip-chip mounted on the mounting substrate 14, the center of gravity of the surface acoustic wave device 12 and the center of gravity of the piezoelectric substrate 28 are the surface of the mounting substrate 14. Therefore, the surface acoustic wave elements 12 have high stability. Note that the single crystal aluminum in this specification is an aluminum film epitaxially grown on a single crystal piezoelectric substrate. In addition to a complete single crystal aluminum film having no grain boundary, a single crystal aluminum or a high crystal An oriented polycrystalline film is also included. In addition, the single crystal in this specification includes a single crystal including a few grain boundaries and a polycrystal having high orientation, in addition to a complete single crystal having no grain boundaries.

  The buffer layer 30 is made of TiN having a lattice constant between the lattice constant of lithium tantalate as the substrate 28 material and the lattice constant of aluminum as the electrode 18 material.

  Although not shown in FIG. 2, on the surface 12a of the surface acoustic wave element 12, a comb electrode and a predetermined wiring pattern are formed in addition to the pad electrode 22, as shown in FIG. FIG. 3 is a schematic configuration diagram showing an electrode pattern formed on the surface acoustic wave element 12. 3 correspond to the pad electrodes 22A to 22F shown in FIG. 2, and four of the pad electrodes 22A, 22B, 22E, and 22F correspond to the six ladder-type comb electrodes 32, respectively. It is connected. Specifically, four comb-shaped electrodes 32 (series arm resonators 32A) are connected in series between the pad electrode 22B and the pad electrode 22E located in the center. Further, the wiring is drawn from the wiring position sandwiching the center two of the four series arm resonators 32A, and connected to the pad electrode 22A and the pad electrode 22F via the comb-shaped electrode 32 (parallel arm resonator 32B), respectively. Has been. The pad electrode 22A and the pad electrode 22F are connected to the ground.

  The electrode pattern is not limited to that shown in FIG. 3, and the number of comb electrodes 32, the wiring pattern, and the like may be changed as appropriate. However, when the surface acoustic wave element 12 is flip-chip mounted on the mounting substrate 14 by adopting an electrode pattern having a point-symmetrical relationship like the electrode pattern shown in FIG. Since the center of gravity of the piezoelectric substrate 28 and the center of gravity of the piezoelectric substrate 28 can be aligned in the normal direction of the surface of the mounting substrate 14, the stability of the surface acoustic wave device 12 can be improved.

  Next, a procedure for producing the surface acoustic wave device 10 shown in FIG. 1 will be described with reference to FIG. FIG. 4 is a diagram showing a procedure for producing the surface acoustic wave device 10 shown in FIG.

  First, a piezoelectric substrate 28 having a diameter of 3 inches is prepared, the surface 28a of the piezoelectric substrate 28 is subjected to a water washing treatment to remove impurities, and then the sputtering substrate is placed in the sputtering apparatus so that the surface 28a faces the target material. set. Then, using titanium metal having a purity of 99.9% as a target material, sputtering is performed in a mixed gas atmosphere of nitrogen and argon, and a TiN buffer layer 30 is formed on the entire surface 28a of the piezoelectric substrate 28 (FIG. 4 ( a)).

  After the buffer layer 30 is formed on the piezoelectric substrate 28, the target material is changed to aluminum added with Cu at a concentration of 0.5 wt% while the inside of the sputtering apparatus is kept in a vacuum state. Then, an aluminum electrode film 34 having a thickness of about 300 nm is formed (see FIG. 4B). Cu is segregated in the aluminum film 34 thus formed, and the power durability of the aluminum film is improved by such Cu segregation. It is considered that the aluminum electrode film 34 is single-crystallized because the lattice mismatch with the piezoelectric substrate 28 is relaxed by the TiN buffer layer 30. Therefore, whether or not the aluminum electrode film is surely single-crystallized, that is, the crystallinity of the aluminum electrode film 34 is evaluated by an evaluation method described later.

  With respect to the piezoelectric substrate 28 in which single crystallization of the aluminum electrode film 34 is confirmed by the evaluation of crystallinity, the number of elements in which the buffer layer 30 and the electrode film 34 are manufactured using a known photolithography (photoetching) technique. The number of the above-described electrode patterns (input / output electrodes 18, comb electrodes 32, wiring patterns, etc.) corresponding to (for example, 200) is produced (see FIG. 4C).

After the patterning, the raised electrode 20 having a thickness of about 500 nm is formed on the input / output electrode 18 of the electrode pattern by the same procedure as that of the input / output electrode 18, and the surface acoustic wave device 12 is completed. At this time, an insulating film made of Al ₂ O ₃ is formed on the surface of the raised electrode 20 when exposed to the atmosphere. Further, each raised electrode 20 is pressed with spherical Au made by a bump bonder and is subjected to ultrasonic vibration to form a bump 26 penetrating the insulating film formed on the surface of the raised electrode 20 (FIG. 4 (d)). In addition, a chromium (Cr) film or an input / output electrode 18 and the raised electrode for preventing the Au atoms of the bumps 26 from diffusing into the input / output electrode 18 are appropriately provided between the input / output electrode 18 and the raised electrode 20. A TiN film for improving the adhesiveness with 20 may be interposed.

  After the bump 26 is formed, the surface acoustic wave element 12 is flip-chip mounted on the mounting substrate 14 made of BT resin. That is, with the surface 12a on which the bump 26 of the surface acoustic wave element 12 is formed facing the element mounting surface 14a of the mounting substrate 14, the bump 26 and the gold plating electrode 24 of the mounting substrate 14 are in contact with each other. The surface acoustic wave element 12 is mounted on the mounting substrate 14 while performing the above. Then, after the surface acoustic wave element 12 is mounted on the mounting substrate 14, the surface acoustic wave element 12 is supported by vacuum suction with a collet (not shown) and ultrasonically vibrated in the surface direction of the mounting substrate 14, thereby causing bumps. 26 and the gold plating electrode 24 are joined (see FIG. 4E). Finally, a BT resin dam plate (thickness: 0.4 mm) having a lattice pattern and a flat cap plate (thickness: 0.2 mm) made of BT resin are placed on the mounting substrate 14 to provide each surface acoustic wave. After the element 12 is hermetically sealed, dicing is performed to complete the fabrication of each surface acoustic wave device 10 (see FIG. 4F). The mounting substrate 14 and the dam part plate (dam part 16A) and the dam part plate and the cap plate (cap part 16B) are bonded with a resin adhesive.

  Next, a method for evaluating the crystallinity of the aluminum electrode film formed on the piezoelectric substrate 28 will be described. The above-mentioned aluminum electrode film was measured for its specific resistance value and evaluated for crystallinity based on the measurement result. The relationship between the crystallinity of the aluminum electrode film and the specific resistance value will be described in detail with reference to the following examples.

  A plurality of 39 ° rotated Y-cut lithium tantalate substrates are prepared as piezoelectric substrates, the surface of the piezoelectric substrate is washed with water to remove impurities, and then the same sputtering method as described above is performed on each piezoelectric substrate. A TiN buffer layer and an aluminum electrode film were sequentially laminated by the method. As a target material for forming an aluminum electrode film, aluminum to which Cu was added at a concentration of 0.5 wt% was used to segregate Cu on the aluminum electrode film. In addition, an aluminum electrode film was formed so that the surface orientation was the (311) plane.

  The thickness of the TiN film on each piezoelectric substrate was selected to be 4 nm. In addition, as the film thickness of the aluminum electrode film of each piezoelectric substrate, three locations of around 150 nm (100 nm to 200 nm), 250 nm (230 nm to 270 nm) and 375 nm (350 nm to 400 nm) were selected. In addition, as for the thickness of the aluminum electrode film of each piezoelectric substrate, a plurality of dispersions having respective thicknesses of 150 nm, 250 nm, and 375 nm with a median value were prepared.

  For each sample, the thickness of the aluminum electrode film and the specific resistance value were measured. Although the fluorescent X-ray film thickness meter was used for the measurement of the film thickness, it may be measured using another known measuring instrument. Further, the specific resistance value is measured by equidistant (20 mm intervals) with the measurement point A in the center position of the aluminum electrode film surface 36a of each sample 36 and the measurement point A in the direction perpendicular to the orientation flat OF. Measurement point B and measurement point C arranged in parallel with measurement point D and measurement point E arranged at equal distances (20 mm intervals) across measurement point A in a direction parallel to orientation flat OF. The average value was taken as the specific resistance value (see FIG. 5). In addition, although the resistivity measuring device VR-30A by Kokusai Electric Inc. was used for the measurement of a specific resistance value, you may measure using another well-known resistivity measuring device.

  And about each sample which measured the film thickness of the aluminum electrode film, and the measurement of the specific resistance value, the crystallinity was confirmed using the X ray diffraction method. The apparatus used for the X-ray diffraction method is a thin film material crystallinity analysis X-ray diffraction apparatus X'Pert-MRD manufactured by Philips. The crystallinity of each sample was confirmed by both spot confirmation by pole figure method and X-ray rocking curve half width (FWHM) of this spot.

  FIG. 6A is a graph showing the relationship between the crystallinity of the aluminum electrode film and the resistivity (that is, the specific resistance value) when the film thickness of the aluminum electrode film is around 375 nm. In this graph, black circles are data of a sample confirmed to be a single crystal, and black squares are data of a sample confirmed not to be a single crystal. As can be seen from this graph, the specific resistance value between the single crystal sample and the non-single crystal sample is separated around 3.28 μΩcm, and the specific resistance value of the single crystal sample is not a single crystal sample. The specific resistance value is higher.

  FIG. 6B is a graph showing the relationship between the crystallinity of the aluminum electrode film and the resistivity when the film thickness of the aluminum electrode film is around 250 nm. In this graph, black circles are data of a sample confirmed to be a single crystal, and black squares are data of a sample confirmed not to be a single crystal. As can be seen from this graph, the specific resistance value between the single crystal sample and the non-single crystal sample is separated around 3.40 μΩcm, and the specific resistance value of the single crystal sample is not a single crystal sample. The specific resistance value is higher.

  FIG. 6C is a graph showing the relationship between the crystallinity of the aluminum electrode film and the resistivity when the film thickness of the aluminum electrode film is around 150 nm. In this graph, black circles are data of a sample confirmed to be a single crystal, and black squares are data of a sample confirmed not to be a single crystal. As can be seen from this graph, the specific resistance value between the single crystal sample and the non-single crystal sample is separated from the center of 3.50 μΩcm, and the specific resistance value of the single crystal sample is not a single crystal sample. The specific resistance value is higher.

  According to Example 1 as described above, the inventors have determined that a sample in which the aluminum electrode film is a single crystal and a sample in which the aluminum electrode film is not a single crystal are a standard regardless of the thickness of the aluminum electrode film. It was newly found that the specific resistance value is separated around the value, and the specific resistance value of the sample in which the aluminum electrode film is a single crystal is higher than the specific resistance value of the sample in which the aluminum electrode film is not. That is, by measuring the specific resistance value of the aluminum electrode film, the crystallinity of the aluminum electrode film can be easily evaluated as compared with the conventional evaluation method that requires labor and time and requires an expensive apparatus.

  Moreover, since evaluation can be performed easily, it can be easily incorporated into the manufacturing process flow of the surface acoustic wave device 12 as described above. Accordingly, the surface acoustic wave device 12 and the surface acoustic wave device 10 are manufactured by patterning only the aluminum electrode film 34 evaluated as a single crystal by such a crystallinity evaluation method to form the comb-shaped electrode 32. Before the process is completed, the piezoelectric substrate on which the aluminum electrode film that is not a single crystal is laminated can be detected and eliminated. Therefore, it is possible to efficiently produce a surface acoustic wave element and a surface acoustic wave device with good characteristics.

  The inventors also measured the specific resistance value of the aluminum electrode film with respect to the crystallinity of the aluminum electrode film in which Cu is not segregated by the same method as in Example 1, and based on the measurement result. evaluated. That is, a plurality of 39 ° rotated Y-cut lithium tantalate substrates are prepared as piezoelectric substrates, the surface of the piezoelectric substrate is washed with water to remove impurities, and the same method as described above is applied to each piezoelectric substrate. A TiN buffer layer and an aluminum electrode film were sequentially laminated by the sputtering method. Note that pure aluminum having a purity of 99.999% was used as a target material for forming an aluminum electrode film.

  FIG. 7A is a graph showing the relationship between the crystallinity of the aluminum electrode film and the resistivity (that is, the specific resistance value) when the film thickness of the aluminum electrode film is around 375 nm. In this graph, black circles are data of a sample confirmed to be a single crystal, and black squares are data of a sample confirmed not to be a single crystal. As can be seen from this graph, the specific resistance value between the single crystal sample and the non-single crystal sample is separated around 2.98 μΩcm, and the specific resistance value of the single crystal sample is not a single crystal sample. The specific resistance value is higher.

  FIG. 7B is a graph showing the relationship between the crystallinity of the aluminum electrode film and the resistivity when the film thickness of the aluminum electrode film is around 250 nm. In this graph, black circles are data of a sample confirmed to be a single crystal, and black squares are data of a sample confirmed not to be a single crystal. As can be seen from this graph, the specific resistance value between the single crystal sample and the non-single crystal sample is separated from the center of 3.10 μΩcm, and the specific resistance value of the single crystal sample is not a single crystal sample. The specific resistance value is higher.

  FIG. 7C is a graph showing the relationship between the crystallinity of the aluminum electrode film and the resistivity when the film thickness of the aluminum electrode film is around 150 nm. In this graph, black circles are data of a sample confirmed to be a single crystal, and black squares are data of a sample confirmed not to be a single crystal. As can be seen from this graph, the specific resistance value between the single crystal sample and the non-single crystal sample is separated from the center of 3.20 μΩcm, and the specific resistance value of the single crystal sample is not a single crystal sample. The specific resistance value is higher.

  According to Example 2 described above, the inventors have obtained a sample in which the aluminum electrode film is a single crystal and a sample in which the aluminum electrode film is not a single crystal, even when Cu is not segregated in the aluminum electrode film. Is that the resistivity value is separated around a certain reference value, and the resistivity value of the sample whose aluminum electrode film is single crystal is higher than the resistivity value of the sample whose aluminum electrode film is not single crystal. Obtained. In other words, even when measuring the specific resistance value of an aluminum electrode film in which Cu is not segregated, the crystallinity of the aluminum electrode film can be easily improved as compared with the conventional evaluation method that requires labor and time and requires an expensive apparatus. Can be evaluated.

  Next, the experimental results of both Example 1 and Example 2 will be described with reference to FIG. FIG. 8 is a graph showing the relationship between the median value of each film thickness and the reference value of the specific resistance in Example 1 and the relationship between the median value of each film thickness and the reference value of the specific resistance in Example 2. It is. In this graph, the thickness (nm) of the aluminum electrode film is shown on the horizontal axis, and the specific resistance value (μΩcm) is shown on the vertical axis. In this graph, the black diamonds are data according to Example 1, and the black squares are data according to Example 2.

From the graph of FIG. 8, it can be seen that both the data according to Example 1 and Example 2 decrease linearly. Further, from the graph of FIG. 8, even when the number of data according to Example 1 and Example 2 is increased by changing the film thickness of the aluminum electrode film, at least a general aluminum electrode film employed in the surface acoustic wave device In the range of 100 nm or more and 500 nm or less which is the thickness of the film, it is presumed that they are also linearly arranged. Therefore, when the data of Example 1 was linearly approximated, assuming that the film thickness was d (nm) and the specific resistance value was r (μΩcm),
r = −0.000984d + 3.649 (1)
It became. That is, in Example 1, when the specific resistance value of an aluminum electrode film is larger than r calculated | required by said Formula (1), it can be evaluated that the aluminum electrode film is a single crystal.

On the other hand, when the data of Example 2 was linearly approximated, assuming that the film thickness was d (nm) and the specific resistance value was r (μΩcm),
r = −0.000984d + 3.349 (2)
It became. That is, in Example 2, when the specific resistance value of the aluminum electrode film is larger than r obtained by the above formula (2), it can be evaluated that the aluminum electrode film is a single crystal.

  The present invention is not limited to the above embodiment, and various modifications are possible. That is, in the above-described example, when the resistance value of the aluminum electrode film is larger than a reference value, it is evaluated as a single crystal. However, depending on the surface orientation of the surface of the aluminum electrode film, there is a resistance value of the aluminum electrode film. When it is smaller than the reference value, it may be evaluated as a single crystal. Such differences are determined by investigating various elements (e.g., reference values and film thicknesses) of single crystal evaluation with respect to a desired plane orientation by the same or equivalent method as in Example 1 or Example 2 described above. What is necessary is just to change suitably.

  In Example 1 and Example 2, 4 nm was selected as the film thickness of the TiN buffer layer. However, even if this film thickness is changed in the range of 2 to 6 nm, the above-described evaluation method is not changed. The sex could be evaluated. Furthermore, although the example which used 39 degree rotation Y cut lithium tantalate as a piezoelectric substrate was demonstrated, for example, if it is 38-44 degree rotation Y cut lithium tantalate, crystallinity of an aluminum electrode film will be carried out by the same evaluation method. Can be evaluated.

1 is a schematic cross-sectional view of a surface acoustic wave device according to an embodiment of the present invention. It is the schematic perspective view which showed the surface acoustic wave element. It is the schematic block diagram which showed the electrode pattern formed in the surface acoustic wave element. It is the figure shown about the procedure which produces the surface acoustic wave apparatus shown in FIG. It is the figure which showed the state of the sample which concerns on Example 1 and Example 2 of this invention. 4 is a graph showing the relationship between the crystallinity and resistivity of an aluminum electrode film when the film thickness of the aluminum electrode film is (a) in the vicinity of 375 nm, (b) in the vicinity of 250 nm, and (c) in the vicinity of 150 nm. 4 is a graph showing the relationship between the crystallinity and resistivity of an aluminum electrode film when the film thickness of the aluminum electrode film is (a) in the vicinity of 375 nm, (b) in the vicinity of 250 nm, and (c) in the vicinity of 150 nm. It is the graph which showed the relationship between the film thickness calculated | required in Example 1 and Example 2, and a specific resistance value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Surface acoustic wave apparatus, 12 ... Surface acoustic wave element, 14 ... Mounting board, 18 ... Input-output electrode,
20 ... Raised electrode, 22 ... Pad electrode, 24 ... Gold-plated electrode, 26 ... Bump, 28 ... Piezoelectric substrate, 30 ... Buffer layer, 32 ... Comb electrode, 34 ... Aluminum electrode film.

Claims (10)

The resistivity value of the aluminum electrode film formed on the piezoelectric substrate so that the surface orientation is the (311) plane is measured, and it is determined whether or not the aluminum constituting the aluminum electrode film is a single crystal. An evaluation step;
Patterning the aluminum electrode film was evaluated as a single crystal by the measurement of the resistivity, have a forming a comb-shaped electrode,
When evaluating whether or not the aluminum constituting the aluminum electrode film is a single crystal, if the specific resistance value is equal to or higher than a reference value, the aluminum constituting the aluminum electrode film is evaluated as a single crystal. A method for manufacturing a surface acoustic wave device. When the thickness of the aluminum electrode film is 350nm or more 400nm or less, the reference value of the specific resistance of the aluminum electrode film is 2.98Myuomegacm, the method of manufacturing a surface acoustic wave device according to claim 1. When the thickness of the aluminum electrode film is less than 270nm or more 230 nm, the reference value of the specific resistance of the aluminum electrode film is 3.10Myuomegacm, the method of manufacturing a surface acoustic wave device according to claim 1. When the thickness of the aluminum electrode film is 100nm or more 200nm or less, the reference value of the specific resistance of the aluminum electrode film is 3.20Myuomegacm, the method of manufacturing a surface acoustic wave device according to claim 1. When the film thickness of the aluminum electrode film is d (nm), the reference value r (μΩcm) of the specific resistance value of the aluminum electrode film is expressed by the following formula (1)
r = −0.000984d + 3.349 (1)
The method for manufacturing a surface acoustic wave device according to claim 1 , wherein: Cu is segregated in the aluminum constituting the aluminum electrode film, and when the thickness of the aluminum electrode film is 350 nm or more and 400 nm or less, the reference value of the specific resistance value of the aluminum electrode film is 3.28 μΩcm. The method for producing a surface acoustic wave device according to claim 1 , wherein Cu is segregated in the aluminum constituting the aluminum electrode film, and when the thickness of the aluminum electrode film is 230 nm or more and 270 nm or less, the reference value of the specific resistance value of the aluminum electrode film is 3.40 μΩcm. The method for producing a surface acoustic wave device according to claim 1 , wherein Cu is segregated in the aluminum constituting the aluminum electrode film, and when the film thickness of the aluminum electrode film is 100 nm or more and 200 nm or less, the reference value of the specific resistance value of the aluminum electrode film is 3.50 μΩcm. The method for producing a surface acoustic wave device according to claim 1 , wherein Cu is segregated in the aluminum constituting the aluminum electrode film, and when the film thickness of the aluminum electrode film is d (nm), the reference value r (μΩcm) of the specific resistance value of the aluminum electrode film is: Following formula (2)
r = −0.000984d + 3.649 (2)
The method for manufacturing a surface acoustic wave device according to claim 1 , wherein: The resistivity value of the aluminum electrode film formed on the piezoelectric substrate so that the surface orientation is the (311) plane is measured, and it is determined whether or not the aluminum constituting the aluminum electrode film is a single crystal. Evaluate and
In that case, when the said specific resistance value is more than a reference value, the aluminum which comprises the said aluminum electrode film is evaluated as a single crystal, The evaluation method of an electrode film.

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