JP3832214B2 - SAW device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a SAW device including a surface acoustic wave (SAW) that is provided with an IDT composed of crossed finger electrodes formed on a substrate surface and a reflector, and that is excited from the IDT, and a method for manufacturing the SAW device.
[0002]
[Prior art]
In recent years, SAW devices such as resonators, filters, and oscillators using SAW elements in which an IDT and a reflector are formed on the surface of a piezoelectric substrate have been widely used in information communication equipment, OA equipment, consumer equipment, and the like. Conventionally, an interdigitated electrode constituting an IDT is formed by etching a metal thin film deposited on the surface of a piezoelectric substrate into a desired pattern using a photolithography technique.
[0003]
Although dry etching is suitable for forming a fine electrode pattern, it is difficult to control the etching depth, and overetching may occur, or damage to the substrate surface by an etching gas may change the piezoelectric characteristics of the substrate. For example, in Japanese Patent Application Laid-Open No. 62-71317, a metal thin film on a substrate surface is etched by dry etching until just before the substrate is exposed, and then the remaining metal thin film is completely removed by wet etching, thereby A method of manufacturing a surface acoustic wave device for patterning is described.
[0004]
[Problems to be solved by the invention]
In particular, in recent years, high-frequency and high stability of SAW devices have been demanded in response to rapid communication with rapid development of network technology in the communication field. In order to increase the frequency of the SAW device, it is necessary to make the electrode width of the IDT smaller and further refine the electrode pattern. However, in the above-described conventional method of patterning the interdigital electrodes by etching, it is difficult to make the electrode width narrower corresponding to the increase in frequency, for example, about 0.7 μm or less currently used.
[0005]
Therefore, the present invention has been made in view of the above-described conventional problems, and its purpose is to use as much as possible dry etching that may damage the substrate surface or affect its piezoelectric characteristics. An object of the present invention is to provide a SAW element that can form a fine electrode pattern of IDT and can cope with high frequency, and a manufacturing method thereof.
[0006]
[Means for Solving the Problems]
According to the present invention, in order to achieve the above object, a metal thin film is deposited on the surface of the substrate and patterned to form an electrode region including at least one set of IDTs composed of interdigitated electrodes, By applying a resist material on the electrode region and forming a resist pattern so as to leave a portion to be a crossed finger electrode, and using the resist pattern, the metal thin film in the exposed electrode region is completely oxidized And a process for forming an IDT. A method for manufacturing a SAW device is provided.
[0007]
In this way, by exposing and oxidizing the portion of the metal thin film other than the portion where the crossed finger electrodes are formed, as in the case of removing by conventional etching, and without damaging the substrate surface by dry etching, An IDT having a fine electrode pattern suitable for high frequency can be formed.
[0008]
According to the present invention, a metal thin film is deposited on the surface of the substrate and patterned to form an electrode region including at least one set of IDTs composed of cross-finger electrodes, and a resist is formed on the electrode region. A process of applying a material and forming a resist pattern so as to leave a portion to become a crossed finger electrode; a process of partially removing the metal thin film in the exposed electrode region by etching halfway using the resist pattern; And a process for forming an IDT by completely oxidizing the remaining portion of the exposed metal thin film in the electrode region.
[0009]
In general, the oxidation treatment of a metal thin film becomes faster as the film thickness becomes thinner, whereas the etching of a metal thin film with a larger film thickness is relatively easy to control, so that a fine electrode suitable for higher frequency as described above. In addition to being able to form a pattern, it is possible to shorten the processing time and increase the working efficiency.
[0010]
In an embodiment, a fine electrode pattern can be formed relatively easily by oxidizing the metal thin film in the exposed electrode region by anodization.
[0011]
In another embodiment, after the IDT is formed by an oxidation process, a flat insulating film is further formed on the IDT, thereby preventing a short circuit between fine electrodes and at the same time exciting a good surface acoustic wave. Can be made easier.
[0012]
In still another embodiment, the insulating film is formed of a material having piezoelectricity, so that the surface acoustic wave propagates through the insulating film. Therefore, it is not always necessary to use a piezoelectric material for the substrate. Therefore, when the substrate is made of a non-piezoelectric material having a high surface acoustic wave propagation speed, a higher-frequency SAW element can be obtained.
[0013]
In one embodiment, the substrate is a wafer having a large number of electrode regions formed on the surface thereof, and the wafer is divided into individual element pieces after forming an IDT by an oxidation process, whereby a plurality of high frequency SAW elements are formed. Can be manufactured in large quantities.
[0014]
According to another aspect of the present invention, a substrate, at least one pair of IDTs formed of crossed finger electrodes formed on the substrate surface, and one reflector each disposed on both sides of the substrate surface with the IDT interposed therebetween, And the adjacent cross finger electrodes are separated by a metal oxide formed on the surface of the substrate, and a SAW element capable of increasing the frequency by miniaturizing the electrode pattern is provided.
[0015]
In an embodiment, the interdigital electrodes and the metal oxide are covered with a flat insulating film, so that it is possible to easily prevent a short circuit between the electrodes and excite good surface acoustic waves.
[0016]
In another embodiment, since the insulating film is made of a material having piezoelectricity, a non-piezoelectric material can be used for the substrate, and further, the substrate is a non-piezoelectric material having a high surface acoustic wave propagation speed. Therefore, higher frequency can be achieved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1A shows an embodiment of a SAW resonator element to which the present invention is applied. The SAW resonator element 1 has a rectangular substrate 2 made of a piezoelectric material such as quartz, lithium tantalate, or lithium niobate, and an IDT 4 made up of a pair of crossed finger electrodes 3a and 3b is formed at the approximate center of the surface. In addition, lattice-like reflectors 5a and 5b are formed on both sides in the longitudinal direction. In each of the interdigitated electrodes 3a and 3b, connection lands 6a and 6b connected to the bus bars are formed in the vicinity of the edges in the longitudinal direction of the substrate 2. The crossed finger electrode, the reflector, and the connection land of this embodiment are formed of an aluminum thin film in consideration of workability and cost, but other conductive metal materials such as an aluminum alloy can be used.
[0018]
In the IDT 4, the adjacent interdigitated electrodes 3 a and 3 b are separated by an alumina (Al ₂ O ₃ ) thin film 7 which is an oxide of aluminum formed on the substrate 2 as shown in FIG. 1B. . In this embodiment, the reflectors 5a and 5b and the adjacent interdigital electrodes 3a and 3b are similarly separated by the Al ₂ O ₃ thin film 7. The IDT 4 is entirely covered with a flat insulating film 8. By providing such an insulating film 8, a surface acoustic wave is easily and satisfactorily excited from the IDT.
[0019]
The insulating film 8 can be formed of a piezoelectric insulating material such as ZnO. In this case, a voltage change is generated in the insulating film 8 by the piezoelectric effect and an output is obtained. Therefore, the substrate 2 may not necessarily be a material having piezoelectricity. Therefore, a higher-frequency SAW element can be obtained by using a non-piezoelectric material having a high surface acoustic wave propagation speed. As such a substrate material, for example, there is DLC (Diamond-like-Carbon). A substrate in which the surface of a normal substrate material is coated with a DLC film is used, and an IDT can be formed on the DLC-coated surface.
[0020]
A process for manufacturing the SAW resonator element of FIG. 1 will be described below with reference to FIGS. First, an aluminum thin film is formed on the surface of the wafer 9 by an appropriate method such as vapor deposition. Next, by patterning this aluminum thin film, as shown in FIG. 2, an electrode region 10 including the IDT 4 and both reflectors 5a and 5b and connection lands 6a and 6b are formed. Further, a connection line 11 is formed for connecting them to a common terminal provided at one end of the wafer. In FIG. 2, only an electrode area for one SAW element is shown for simplification, but a large number of electrode areas are formed on the actual surface of the wafer 9.
[0021]
Next, a resist material is applied to the surface of the wafer, and the electrode region portion 12a between the adjacent cross finger electrodes is exposed, leaving a portion to be the cross finger electrode of the electrode region 10, as shown in FIG. 3A. A resist pattern 12 is formed. The portion of the aluminum thin film exposed from the resist pattern 12 is completely oxidized by anodic oxidation to form an Al ₂ O ₃ thin film 7 as shown in FIG. 3B. The Al ₂ O ₃ thin film 7 becomes thicker than the original aluminum thin film due to the adhesion of oxygen.
[0022]
FIG. 4 schematically shows the configuration of an apparatus for performing the anodizing treatment. The wafer 9 is immersed in the electrolytic cell 14 containing the anodizing solution 13 while holding the terminal 15 with the clip 16. The clip is connected to the anode (+) of the DC power source 17 and the cathode (−) is connected to the cathode electrode plate 18 immersed in the electrolytic cell 14. When a predetermined voltage is applied from the DC power source 17, the aluminum thin film is oxidized. In this embodiment, an aqueous solution of ammonium dihydrogen phosphate or the like is used as the anodizing solution, but an aqueous solution of a neutral salt such as citrate or adipate can be used. Further, the temperature of the anodizing solution 13 is preferably about room temperature so that a non-porous oxide film is formed rather than porous.
[0023]
Thus, after the aluminum thin film is completely oxidized to form the Al ₂ O ₃ thin film 7, the resist pattern 12 is removed to form an IDT 4 having a desired fine electrode pattern. The wafer 9 is finally diced along the cutting line 19, whereby a predetermined number of SAW resonance pieces are obtained.
[0024]
FIG. 5 shows a manufacturing process of the SAW resonator element according to the second embodiment of the present invention. First, as in the first embodiment, an aluminum thin film is formed on the surface of the wafer 9, and this is patterned to form electrode regions 10 and connection lands 6a and 6b, and then a resist material applied to the wafer surface. As shown in FIG. 5A, a resist pattern 12 is formed, leaving a portion to be a cross finger electrode in the electrode region. Next, in the second embodiment, as shown in FIG. 5B, the electrode region 10 exposed from the resist pattern 12, that is, the aluminum thin film is partially removed by dry etching. Then, the portion of the aluminum thin film remaining on the substrate is anodized until it is completely oxidized using the apparatus shown in FIG. 4 as described above in connection with the first embodiment. Then, after removing the resist pattern 12, the wafer 9 is diced to obtain a predetermined number of SAW resonance pieces.
[0025]
The preferred embodiments of the present invention have been described in detail above. However, as will be apparent to those skilled in the art, the present invention may be implemented with various modifications and variations within the technical scope thereof. Can do.
[0026]
【The invention's effect】
According to the method of the present invention, as described above, the metal thin film portion other than the portion for forming the interdigital electrode is oxidized, not etched, to form an IDT having a fine electrode pattern without damaging the substrate surface. Therefore, a SAW element capable of higher frequency can be easily realized. Therefore, a SAW element corresponding to the recent demand for higher speed of communication and a SAW device such as a resonator, a filter or an oscillator using the SAW element can be obtained.
[Brief description of the drawings]
FIG. 1A is a perspective view showing a SAW resonator element according to the present invention, and FIG. 1B is an enlarged cross-sectional view taken along line II.
FIG. 2 is a plan view showing a part of a wafer in which a large number of electrode regions and bus bars connecting them are formed on the surface thereof.
FIG. 3 is a cross-sectional view of FIGS. A to C showing a process of forming an IDT by the method of the first embodiment of the present invention in the order of steps.
FIG. 4 is a schematic diagram showing the configuration of an apparatus for anodizing a wafer.
FIG. 5 is a cross-sectional view of FIGS. A to D showing the process of forming an IDT by the method of the second embodiment of the present invention in the order of steps.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 SAW resonance piece 2 Board | substrate 3a, 3b Cross finger electrode 4 IDT
5a, 5b Reflector 6a, 6b Connection land 7 Al ₂ O ₃ thin film 8 Insulating film 9 Wafer 10 Electrode region 11 Connection line 12 Resist pattern 12a Electrode region portion 13 Anodizing solution 14 Electrolyzer 15 Terminal 16 Clip 17 DC power supply 18 Cathode Electrode plate 19 cutting line

Claims (6)

A process of forming a metal thin film on the surface of the substrate and patterning to form an electrode region including at least one set of IDTs composed of cross finger electrodes, and applying a resist material on the electrode regions, A process of forming a resist pattern so that the resist material remains in a portion to become, a process of partially removing the metal thin film in the exposed electrode region by etching halfway, and a residual metal thin film in the exposed electrode region A process for forming an IDT by completely oxidizing a portion to be formed. 2. The method of manufacturing a SAW element according to claim 1 , wherein the exposed metal thin film in the electrode region is oxidized by anodization. 3. The method of manufacturing a SAW element according to claim 1, further comprising a step of forming a flat insulating film on the IDT after forming the IDT. The method of manufacturing a SAW element according to claim 3 , wherein the insulating film is made of a material having piezoelectricity. 5. The method of manufacturing a SAW element according to claim 4 , wherein the substrate is made of a material containing DLC ( Diamond - Like - Carbon ) . Said substrate is a wafer formed with a large number of the electrode regions on the surface thereof, according to any one of claims 1 to 5, characterized in that dividing the wafer into individual element pieces after the oxidation process A method for manufacturing a SAW element.

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