JP3289486B2 - Surface acoustic wave device and method of manufacturing electronic circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a piezoelectric element for precisely adjusting the frequency of a piezoelectric element such as a surface acoustic wave element used as a filter or an oscillator in the field of mobile telephones and various communication devices, and a method of manufacturing the same. The present invention relates to a method for manufacturing an electronic circuit using a piezoelectric element.

[0002]

2. Description of the Related Art A surface acoustic wave device used as a filter or an oscillator in a mobile telephone or various communication fields has a sound velocity of a piezoelectric substrate and a pattern shape of a comb-shaped electrode formed on the surface.
The frequency is uniquely determined by the film thickness. Patterns of comb-shaped electrodes have been widely used because they can be formed using semiconductor technology and can be miniaturized. However,
With the increase in the frequency of the surface acoustic wave device, a reduction in yield due to variations in frequency due to variations in electrode film thickness and pattern width has become a problem. For this reason, conventionally, when the thickness of the electrode is too thick, the frequency is adjusted by immersing the electrode material in a solution for etching to remove a predetermined amount of the electrode on the surface by wet etching. In addition, a method of adjusting the frequency by dry-etching the surface of a piezoelectric crystal by a predetermined amount using plasma has been performed.

[0003]

In the method of removing a predetermined amount of the surface of the electrode by wet etching, the amount of the etching removed can be controlled only by time. There was a problem that variation was increased. Another problem is that when a large power is applied due to surface roughness due to etching of the electrode surface, the electrode surface becomes fragile.

The method of dry etching the surface of a piezoelectric crystal as a substrate using plasma has problems such as the fact that the apparatus is expensive and that it is difficult to accurately control the amount of etching. is not.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a method of manufacturing a piezoelectric element for adjusting the frequency with high accuracy, and a method of manufacturing an electronic circuit using the same.

[0006]

According to the present invention, the frequency of a surface acoustic wave device is controlled to a predetermined value by utilizing the characteristic of a chemically adsorbed film that the growth of a film is stopped when a monomolecular layer is formed. Things.

More specifically, a chemically adsorbed liquid comprising a chlorosilane compound having a different molecular chain length according to the frequency to be adjusted is prepared, and a chemically adsorbed film is formed on at least a region of the surface acoustic wave device where surface waves are excited. By forming it, it is possible to obtain a predetermined frequency.

Further, a predetermined frequency can be obtained by repeatedly laminating the chemical adsorption film according to the frequency to be adjusted using a chemical adsorption film made of a bistrichlorosilane derivative having chlorosilyl groups at both ends of the molecule. It is possible. Further, after forming at least one layer of a chemisorption film made of a bistrichlorosilane-based derivative, a chemisorption film made of a chlorosilane-based compound is formed so that a predetermined frequency can be obtained.

[0009]

When a monomolecular film having a certain molecular structure is formed, the film cannot be formed any more. Therefore, when the film is immersed in the solution, a certain film thickness is obtained regardless of the immersion time. The monolayer thickness is naturally generated. When using chemisorption films with different molecular chain lengths, the longer ones are thicker, the shorter ones are thinner,
An insulating film having a constant thickness is formed. Therefore, the thickness and density of the formed film can be freely and accurately changed by preparing and selectively using chemisorbed substances having various molecular chain lengths. Since the natural frequency of the surface acoustic wave device shifts depending on the mass of the substance on the surface of the surface acoustic wave device, the monolayer film of various thicknesses and densities is formed by the chemisorption film as described above. , The frequency can be adjusted with high accuracy.

Furthermore, a chemically adsorbed film made of a bistrichlorosilane-based derivative can be formed into a stack because an OH group is formed on the film surface by water treatment. , The frequency is adjustable.

[0011]

EXAMPLES (Example 1) In the first example, the frequency was adjusted using four types of chemisorption films having different molecular chain lengths. FIG. 2 is a perspective view of the surface acoustic wave device used in the present embodiment, and FIG. 3 is a diagram showing the vicinity of the surface in the AA ′ section of FIG. In the figure, 1 is a piezoelectric substrate, and 2 is a comb-shaped electrode made of aluminum. 4 and 5 show chemical adsorption films 3 having different molecular weights.
It is a figure which shows the cross-sectional shape which formed 4 and 4. The formation of the chemical adsorption film was performed in the following procedure. First, the frequency of a substrate in a wafer state (multiple-piece state) on which comb-shaped electrodes are formed is measured to determine a deviation from a target frequency. The material of the chemical adsorption film to be used is selected based on this value. In the selection, a solution containing a solute with a short molecular chain length is selected for those with a small deviation from the target frequency (set frequency), and conversely, for those with a large deviation from the set frequency. Select a solution containing a long chain solute. Specifically, a suitable solute is selected from a chemisorption solution obtained by dissolving various types of solutes having different molecular weights, in which a chain hydrocarbon is bonded to chlorosilane.

When a substrate is immersed in a chemisorption solution containing a solute of a chlorosilane compound in a nitrogen atmosphere, OH groups on an aluminum oxide as an electrode and OH groups on a substrate surface
The group and the chlorosilane compound cause a dehydrochlorination reaction to form a strong bond with the substrate. When a predetermined monomolecular film is formed, the chemical adsorption film does not react any more and a constant film thickness is automatically formed. Thereafter, by washing with chloroform and washing with running water, extra molecules and bonds between adjacent molecules are generated by a dehydrochlorination reaction to form strong bonds between the molecules.

As a result, a chemical adsorption film is formed on the oxide film on the aluminum surface of the electrode and on both surfaces of the piezoelectric substrate. This is shown in FIG. 4 and FIG. In the figure, each film thickness is not an accurate scale factor, and the film thickness of the electrode is about 500 n.
The thickness of the chemisorption film is about 1.5 nm to 3 nm with respect to m. FIG. 1 is a diagram showing the bonding state between the molecular structure of the chemisorption film used in FIG. 4 and the comb-shaped electrode, and FIG. 6 is a diagram showing the bonding state of the chemisorption film used in FIG. 5 to the substrate and the electrodes. is there. In these figures, 1 is a piezoelectric substrate, 2 is a comb-shaped electrode made of aluminum, 3 is a monolayer of electrically insulating chemisorption film A made of a chlorosilane compound, and 4 is a monolayer made of a chlorosilane compound. 2 shows an electrically insulating chemisorption film B. Further, although not shown, chemical adsorption films C and D having different molecular weights were formed in the same manner.

The molecular chain lengths of the solutes on which A, B, C and D are based have a relationship of A <B <C <D.

FIG. 7 shows the results of frequency changes obtained by the four types of chemically adsorbed films thus formed.

The difference (frequency change) between the frequency f ₀ before film formation and the frequency f after film formation is shown three times for each solution of each composition on a substrate without any insulating film. .
Each result is represented by a white circle. The longer the molecular chain length,
It can be seen that the frequency change is also large. Although a linear relationship cannot be obtained because the molecular weight differs depending on the material, the frequency change is very good when the same material is used, and the effect of the chemical adsorption film is confirmed.

In the molecular structure diagrams of FIGS. 1 and 6, adjacent Si atoms of each single molecule are bonded by oxygen, but the presence of such a bond is not a necessary condition of the present invention. The specific method of bonding of Si with oxygen will be described in more detail in Example 2.

In the first embodiment, a chemisorption solution containing a solute of a chlorosilane compound was used as the solution. Instead, a solution containing an alkoxysilane compound as a solute, or a chlorosilane compound and an alkoxysilane The same effect can be obtained by using a compound containing both of the system compounds.

Embodiment 2 In the second embodiment, the frequency was adjusted using a bistrichlorosilane-based derivative.
Since the bistrichlorosilane-based derivative has a chlorosilyl group (SiCl ₃ −) at both ends as a molecular structure, it can be laminated. In the present embodiment, it was formed as follows.

The frequency of the surface acoustic wave element of the piezoelectric substrate in the wafer state on which the comb-shaped electrodes are formed is measured to determine the difference from the target value. The number of laminations is determined based on this value. The formation of the chemically adsorbed film is basically the same as in Example 1, except that the same film is laminated by immersing in the same liquid after forming once.

The specific procedure was as follows. First, the substrate is immersed in a solution containing a solute composed of a bistrichlorosilane derivative, and a OH group on the substrate surface and the bistrichlorosilane derivative undergo a dehydrochlorination reaction to form a monomolecular film. Thereafter, excess molecules are removed by washing with chloroform, and further washing with running water is performed to form a bond between adjacent molecules by a dehydrochlorination reaction, and chloro groups on the surface of the monomolecular film are subjected to OH by a dehydrochlorination reaction.
Group. Thus, the formation of one layer is completed. In the case of further laminating, since the OH groups formed by the washing with running water are present on the surface of the monomolecular film, the same procedure as above is repeated to form the second and subsequent monomolecular layers.

8 to 10 show cross-sectional shapes before and after the formation of the surface acoustic wave device. 8 shows a state before formation, FIG. 9 shows a state in which one layer is formed, and FIG. 10 shows a state in which two layers are formed. FIG. 11 shows the molecular structure of the film formed in one layer.
In these figures, 1 is a piezoelectric substrate, 2 is a comb-shaped electrode made of aluminum, 6 is a one-layer chemically adsorbed film made of a bischlorosilane-based derivative, and 7 is a second layer similarly laminated. Is a chemisorption film.

In this example, the effect of frequency adjustment was confirmed using two types of bistrichlorosilane derivatives.

FIG. 12 shows the result. The vertical axis of FIG.
The frequency change is the same as the above. The black circles represent data of one type of bistrichlorosilane-based derivative prototyped three times for each lamination, and the white circles represent data for other types. is there. The frequency change ratio is different between the white circle and the black circle due to the difference in molecular weight, but both are reproducible, and within the tested range (especially after the second time), the frequency change is linear with the number of laminations. Obtained.

In the second embodiment, a solution containing a solute consisting of a bistrichlorosilane derivative was used. Instead of the bistrichlorosilane derivative, a bistrialkoxysilane derivative having alkoxysilyl groups at both ends was used as the solute, or The same effect can be obtained by using a solution containing both a bistrichlorosilane derivative and a bistrialkoxysilane derivative.

(Embodiment 3) In the third embodiment, both the bistrichlorosilane-based derivative and the chlorosilane-based compound were laminated to adjust the frequency. The specific method is as follows. The molecular structure diagram shown in FIG. 11 is one in which one monolayer 6 is formed on the comb-shaped electrode 2 using a bistrichlorosilane-based derivative. This is the same as that described in the second embodiment. By repeating this forming step four times, lamination up to four layers was performed in the same manner as in Example 2, and then a final layer was further laminated using a chlorosilane-based compound. The formation of the chemical adsorption film in this case was performed in the same manner as in the monomolecular layer 4 shown in FIG. The surface acoustic wave device thus prepared is a monolayer 6 of a chemisorption film.
Is formed, and from the frequency change of 110 KHz when the monolayer 4 of the chemisorption film is laminated thereon, four monolayers 6 of the chemisorption film are laminated to form the monolayer 4 of the chemisorption film. 1
A frequency change of up to 185 KHz when the layers were stacked was obtained. In this embodiment, the monomolecular layer 6 is laminated from one to four layers using a bistrichlorosilane-based derivative, and the monomolecular layer 4 is further laminated using a chlorosilane-based compound. However, this combination is not particularly limited. It is possible to laminate not only the material of the present embodiment but also various materials in combination, such as a chemically adsorbed film made of a bistrialkoxysilane-based derivative to a chemically adsorbed film made of a chlorosilane-based compound. The target frequency can be freely obtained by using such a combination of various materials.

Further, by making the surface layer have a molecular structure in which a large number of fluorine-bonded molecular chains are provided, the surface of the chemically adsorbed film can be made water-repellent, and the corrosion of aluminum of the comb-shaped electrode can be prevented. Thus, a highly reliable surface acoustic wave can be obtained.

(Embodiment 4) In the fourth embodiment, the vicinity of a comb-shaped electrode portion of a surface acoustic wave device having a comb-shaped electrode is covered with a water-soluble resin, and then a chemical adsorption film is formed. A chlorosilane compound was used as the chemical adsorption film. The formation of the chemically adsorbed film was performed in the same manner as in Example 1. Finally, the film was washed with water and the water-soluble resin was dissolved to remove the chemically adsorbed film formed on the resin by lift-off. FIG. 13 is a diagram showing a cross-sectional shape of the surface acoustic wave device after lift-off. In the present embodiment, the chemical adsorption film 8 is formed only in the portion between the comb-shaped electrodes 2. In this case, the change in frequency was smaller than that when formed over the entire surface, but the ripple and insertion loss were improved.

(Embodiment 5) In the fifth embodiment, the surface acoustic wave device 10 on which the comb-shaped electrodes 2 are formed is cut into chips and then die-bonded to a metal case 14 as shown in FIG. After performing wire bond connection using, the frequency was measured to determine the deviation from the target frequency. A chemical adsorption solution was selected based on this value, and the whole was immersed in the chemical adsorption solution to form a chemical adsorption film. In this case, the metal case, the aluminum wire, the adhesive, and the like are also immersed in the chemical adsorption solution, and the aluminum wire has an oxide film on its surface, so that a chemical adsorption film is formed.

After the frequency was adjusted in this manner, the lid was seam-welded to produce a surface acoustic wave device as shown in FIG. 14 and 15, reference numeral 1 denotes a piezoelectric substrate,
2 is a comb-shaped electrode made of aluminum, 10 is a surface acoustic wave element containing these, 11 is an aluminum wire, 12
Is an adhesive for bonding the surface acoustic wave element, 13 is an external terminal,
14 is a metal case, 15 is a lid, and 16 is a seam weld. The chemical adsorption film is formed not only on the surface acoustic wave device but also on the case and the aluminum wire, but is not shown. Although the chemical adsorption film was formed on the metal case, no particular problem occurred even in seam welding or the like. This is because the chemically adsorbed film is as thin as several nm or less. In the present embodiment, the mounting is performed after the mounting by the wire bonding method. However, a flip-chip mounting on a ceramic substrate or a glass substrate can be similarly formed.

As described above, even after mounting on the mounting board, the adjustment can be made in accordance with the deviation from the set frequency. There is an advantage that it is possible to accurately adjust the manufacturing variation of the entire electronic circuit including the above components.

Further, since a film having a passivation effect is simultaneously formed on the aluminum wires when the insulating film is formed after mounting, the electronic circuit as a whole has high corrosion resistance.

[0033]

As described above, according to the present invention, a film having a required film thickness and density can be obtained with high precision by using a chemisorption film having a monomolecular structure, and the frequency can be adjusted with very high reproducibility. it can. In addition, since the apparatus for forming the film is inexpensive and can be mass-produced, there is a great effect on improving the accuracy and cost of the surface acoustic wave device. Also, it has a great effect on preventing corrosion of aluminum in the electrode film, and has a great effect on cost reduction and high reliability of the surface acoustic wave device.

The chemically adsorbed film has strong adhesion because it forms a covalent bond with an oxide film on the surface of aluminum, which is an electrode material, and quartz, lithium tantalate, and lithium niobate, which are oxides and substrate materials. It can be formed at very low cost because the film can be easily formed by the method.

A fluorinated carbon chain having a bond to a fluorine atom (C
Since the molecular chain of F ₂ ) _n has water repellency, it has an effect of preventing corrosion of aluminum as an electrode material.

In each of the embodiments, a description has been given mainly of a surface acoustic wave element for a SAW filter whose frequency needs to be adjusted with very high precision. However, the present invention is not limited to this, and it is not limited to this. The present invention can be generally applied to a frequency oscillator or a resonator in which an electrode is formed on the surface of the piezoelectric element.

[Brief description of the drawings]

FIG. 1 is a diagram showing a molecular structure of an insulating film according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a surface acoustic wave device used in the first embodiment of the present invention.

FIG. 3 is a view showing the vicinity of the surface of the AA ′ section in FIG. 2;

FIG. 4 is a diagram showing a cross-sectional shape in which an insulating film is formed.

FIG. 5 is a diagram showing a cross-sectional shape in which an insulating film is formed.

FIG. 6 is a molecular structure diagram of an insulating film according to the first embodiment of the present invention.

FIG. 7 is a graph showing frequency changes due to four types of insulating films according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a cross-sectional shape before an insulating film is formed in a second embodiment of the present invention.

FIG. 9 is a diagram showing a cross-sectional shape in which one insulating film is formed in a second embodiment of the present invention.

FIG. 10 is a diagram showing a cross-sectional shape in which two insulating films are formed according to a second embodiment of the present invention.

FIG. 11 is a molecular structure diagram of an insulating film according to a third embodiment of the present invention.

FIG. 12 is a graph showing the relationship between the number of times of lamination of the insulating film and the frequency change in the second embodiment of the present invention

FIG. 13 is a diagram showing a cross-sectional shape in which an insulating film is formed according to a fourth embodiment of the present invention.

FIG. 14 is a sectional view of an electronic circuit package according to a fifth embodiment of the present invention.

FIG. 15 is a cross-sectional view showing a cover of an electronic circuit package according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Comb-shaped electrode 3, 4, 6, 7, 8 Insulating film consisting of monolayer

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Mamoru Soga 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-63-252212 (JP, A) JP-A-63-178615 (JP, A) JP-A-5-31356 (JP, A) JP-A-2-36350 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H03H 3/10 H03H 9/145

Claims (10)

(57) [Claims] 1. A surface acoustic wave device comprising a substrate having piezoelectricity and electrodes provided on the substrate is immersed in a solution containing a solute having a molecular chain length corresponding to a deviation from a set frequency, A method for manufacturing a surface acoustic wave device, comprising: forming an insulating film made of a monomolecular layer of a chemically adsorbed film on at least a part of a surface thereof and adjusting the frequency to a set frequency . 2. The method for manufacturing a surface acoustic wave device according to claim 1, wherein the solution contains a solute of a chlorosilane derivative and / or an alkoxysilane derivative . 3. A method for preparing a plurality of solutions each containing a solute of a plurality of chlorosilane derivatives and / or alkoxysilane derivatives having different molecular chain lengths, and using the solutions for individual surface acoustic wave devices according to a deviation from a set frequency. 3. The method for manufacturing a surface acoustic wave device according to claim 2, wherein: 4. A surface acoustic wave device having a substrate having piezoelectricity and electrodes provided on the substrate is immersed in a solution containing a solute having a constant molecular chain length, and the surface of the surface acoustic wave device is immersed in the solution. At least part of the solute derivative chemisorption film.
A step of forming an insulating film made of a molecular layer, wherein the surface acoustic wave element is adjusted to the set frequency by repeating the above-described steps according to a deviation from the set frequency.
Child manufacturing method. 5. The method for manufacturing a surface acoustic wave device according to claim 4, wherein the solution contains a solute having a chlorosilyl group and / or an alkoxysilyl group at both ends of the molecule . 6. After mounting a surface acoustic wave device including a substrate having piezoelectricity and electrodes provided on the substrate on a mounting substrate,
An insulating film made of a monomolecular layer of a chemically adsorbed film of the derivative of the solute on at least a part of the surface of the surface acoustic wave device , immersed in a solution containing a solute having a molecular chain length corresponding to a deviation from a set frequency. Forming an electronic circuit and adjusting the frequency to a set frequency. 7. The method according to claim 7, wherein the solution contains a solute of a chlorosilane derivative and / or an alkoxysilane derivative. 8. A method comprising preparing a plurality of solutions each containing a solute of a plurality of chlorosilane derivatives and / or alkoxysilane derivatives having different molecular chain lengths, and using the solutions for individual electronic circuits according to a deviation from a set frequency. The method for manufacturing an electronic circuit according to claim 7. 9. After mounting a surface acoustic wave device including a substrate having piezoelectricity and electrodes provided on the substrate on a mounting substrate,
The surface is immersed in a solution containing a solute of a certain length
The method includes a step of forming an insulating film made of a monomolecular layer of a chemical adsorption film of the solute derivative on at least a part of the surface of the elastic wave element , and setting by performing the above steps repeatedly according to a deviation from a set frequency. A method for manufacturing an electronic circuit, comprising adjusting a frequency. 10. The method according to claim 9, wherein the solution contains a solute having a chlorosilyl group and / or an alkoxysilyl group at both ends of the molecule.