JPH09289430A - Method for forming electrode of surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave(SAW) device which has high electric power resistance and is superior in mass-productivity. SOLUTION: On a piezoelectric substrate 2, a lower electrode 13 is formed to less than desired thickness by using a converged ion beam vapor-depositing method, and then an upper electrode part 14 is formed by a PVD method so as to the obtain desired thickness. The crystallinity of the upper electrode part 14 is affected by that of the lower electrode part 13. Therefore, the upper electrode part 14 having good crystallinity can be formed. Further, the upper electrode part 14 is formed by the PVD method, so an electrode having the desired thickness can be formed in a shorter time than the converged ion beam vapor-deposition method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, and more particularly to the shape of its electrodes.

[0002]

2. Description of the Related Art Today, SAW (surface acoustic wave) devices using surface acoustic waves are known. This SAW device will be described with reference to FIG.

An input side electrode 3 and an output side electrode 5 are formed on the surface of the piezoelectric substrate 2. When an electric signal is applied to the input side electrode 3, the surface of the piezoelectric substrate 2 is distorted and the surface acoustic wave 6
Occurs. This surface acoustic wave 6 is transmitted to the output side electrode 5. That is, the electric signal given to the input side electrode 3 can be taken out at the output side electrode 5.

[0004] Waves transmitted through the piezoelectric substrate 2 (surface acoustic waves)
The amplitude and phase of are determined by the cross length and pitch of the input side electrode 3 and the output side electrode 5. The input side electrode 3 and the output side electrode 5 are formed into a comb shape, and by changing the cross length and pitch of each of the interdigital transducers (IDTs), a complicated shape such as a band pass filter is obtained. A filter with frequency characteristics can be created. SAW devices are suitable for miniaturization, weight reduction, and thinning, and are expected to have more functions and higher performance as key devices for mobile portable terminals and the like.

The SAW device is generally manufactured by forming aluminum on the entire surface, patterning it by lithography, performing dry etching, and then removing the resist.

At this time, the crystallinity is increased by epitaxially growing an aluminum thin film on the substrate,
The power resistance can be improved.

However, when the above epitaxial growth is performed, it takes time to form the electrode surface to a desired thickness, and the mass productivity is lowered.

An object of the present invention is to provide a method of forming electrodes of a surface acoustic wave device which has high mass productivity and improved power resistance.

[0009]

According to a first aspect of the present invention, there is provided an electrode forming method for a surface acoustic wave device, wherein a focused ion beam is used as a vaporizable energy in the electrode forming method for forming an electrode of a surface acoustic wave device. Irradiate the substrate surface with
It is characterized in that a plurality of electrode surfaces are formed, the electrode surfaces are covered with a resist, and etching is performed to form electrodes.

In the method of forming an electrode of a surface acoustic wave device according to a second aspect of the present invention, the electrode surface is formed so as to have a thickness smaller than a desired thickness, and the PVD is applied after the irradiation of the focused ion beam.
The method is characterized in that an electrode surface having a desired thickness is formed by a method.

The electrode surface means a surface for forming an electrode for forming an electrode, and in the embodiment, 100 × 30.
It was set to 0 μm. In the embodiment, the size of one resonator is configured, but the size is not limited to this.
For example, the size may include a plurality of resonators.

The PVD method is a method of physically depositing a metal, and includes, for example, a resistance heating type vacuum evaporation method, an electron beam evaporation method, and a sputtering method.

[0013]

In the method of forming an electrode of a surface acoustic wave device according to claim 1, a plurality of electrode surfaces are formed by a focused ion beam, the electrode surfaces are covered with a resist and etched to form an electrode. To do. The electrode deposited by the focused ion beam has high crystallinity. Therefore, the power resistance can be improved.

In the method of forming an electrode of a surface acoustic wave device according to a second aspect of the present invention, the electrode surface is formed so as to be thinner than a desired thickness, and after the irradiation of the focused ion beam, PVD is performed.
Method, an electrode surface having a desired thickness is formed. The crystallinity of the portion formed by the PVD method is determined by the crystallinity of the underlying portion. Therefore, it is possible to obtain an electrode having a desired thickness in a shorter time as compared with the case where the whole is deposited by the focused ion beam while maintaining the crystallinity.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a surface acoustic wave device according to the present invention will be described with reference to the drawings with reference to FIG. In this embodiment, a plurality of lower electrode portions 13 of the surface acoustic wave element are formed by using the device shown in FIG.

The focused ion beam direct vapor deposition apparatus 10 shown in FIG. 2 will be briefly described. The focused ion beam direct vapor deposition apparatus 10 has a vacuum chamber 20, and the focused ion beam direct vapor deposition is performed in the vacuum chamber 20 as follows.

For the liquid metal ion source 21, for example, Al
-Au-Ge alloy tip is set,
Generates ion species such as u ⁺ and Al ⁺ . The generated metal ions are accelerated to 20 keV by the acceleration electrode 22 and focused by the condenser lens 23. Since the ion beam generated by the liquid metal ion source 21 contains various ion species, only the desired ion source is selected by the mass analyzer for the beam containing the various ion species. This selection is performed by the mass filter 24. The ion beam that has passed through the beam aperture 25 is deflected by the deflection electrode 26. The ion beam is focused on the objective lens 27 and applied to the substrate 31 mounted on the stage 28. The substrate 31 on the stage 28 is in an electrically floating state by the insulator 32. Therefore, by applying a deceleration voltage of 0 to 20 KV to the stage 28 by the deceleration power supply 12, the final energy of the focused ion beam continuously changes in a wide range of 0 to 20 KeV. For example, if 19.9 KV is applied as the deceleration potential, 20 Ke
The metal ions accelerated to V were decelerated to 100 eV when they reached the substrate. In this way, the once focused ion beam is decelerated near the surface of the substrate to generate the piezoelectric substrate 2.
The metal ions can be directly vapor-deposited by irradiating the metal ions.

The focused ion beam direct vapor deposition device 10
In (1), the ion beam having a high flux (particle beam flux density) is narrowed down to a spot diameter of a submicron diameter by using a focusing optical system including a beam aperture 25 and an objective lens 27 for shaping a beam profile, and a minute pattern is directly It is vapor-deposited.

In this embodiment, it is necessary to form the electrode surface. Therefore, the beam spot diameter is increased by reducing the beam current limitation by the beam aperture 25. As a result, the lower electrode portion 13 having high crystallinity can be formed without losing the high flux required for direct vapor deposition.

In this embodiment, 36 ° Y rotation Li
As shown in FIGS. 1A and 1B, a plurality of lower electrode portions 13 having L1 = 300 μm and L2 = 100 μm were formed on a TaO ₃ 3-inch piezoelectric substrate.

Next, as shown in FIG. 1C, additional vapor deposition of 900 Å is performed on the entire surface by PVD.

In this embodiment, the piezoelectric substrate 2 having the lower electrode 3 formed thereon was put into an electron beam vapor deposition apparatus, and 900 angstroms of additional vapor deposition was performed on the entire surface to form an electrode surface having a total thickness of 1000 angstroms.

From this state, desired patterning is performed (not shown) using a photoresist as in the conventional case. As a result, the electrode portion of the SAW filter is formed.

In this embodiment, an aluminum electrode having a line width W = 0.7 μm of the input side electrode 3 and the output side electrode 5, an electrode finger pitch d = 0.7 μm, and a film thickness t = 1000 angstrom is formed. The center frequency is 1.5
A GHz SAW filter could be obtained.

As described above, the lower electrode portion 13 is once formed to be thinner than a desired thickness by using the focused ion beam evaporation method, and then the upper electrode portion 14 is formed by the PVD method so as to have a desired thickness. Is forming. The crystallinity of the upper electrode portion 14 is affected by the crystallinity of the lower electrode portion 13. Therefore, the upper electrode portion 14 having good crystallinity can be formed. Further, since the upper electrode portion 14 is formed by the PVD method, an electrode having a desired thickness can be formed in a shorter time than the focused ion beam vapor deposition method.

The electrodes may be formed by the focused ion beam vapor deposition method until the electrode has a desired thickness.

In this embodiment, a single crystal piezoelectric substrate 2 such as LiTaO ₃ is used as the substrate having piezoelectricity. However, as the material of the piezoelectric substrate 2, LiNbO ₃ , Li ₂ B
A single crystal substrate such as ₄ O ₇ or quartz may be used. Further, instead of the piezoelectric substrate itself, a glass substrate or a sapphire substrate (AL ₂ O ₃ ) on which a piezoelectric thin film is formed may be used.

In this embodiment, the case where the SAW device is applied as a surface acoustic wave device has been described.
However, the surface acoustic wave is not limited to this, and SSB
W (surface skimming bulk wave) or SBW (sha
llow bulk wave) may be used. These waves are SH (shear horizontal) wave type bulk waves whose main displacement is parallel to the substrate surface, so their propagation velocity is 1.5 times higher than that when Rayleigh waves are used, and the frequency-temperature characteristics Is excellent.

Further, in the present embodiment, the focused ion beam is decelerated to the energy capable of vapor deposition so that the surface of the substrate is selectively irradiated. However, the present invention is not limited to this, and any other manufacturing method may be used as long as it is a method capable of selectively irradiating a focused ion beam on the surface of the substrate with energy capable of vapor deposition.

Further, in the present embodiment, the metal ions are generated from the liquid ion source and then focused. However, the method is not limited to this, and any method may be used as long as it can obtain a focused ion beam.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a surface acoustic wave device according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a focused ion beam direct vapor deposition device 10.

FIG. 3 is a diagram for explaining the function of a SAW device (prior art).

[Explanation of symbols]

 1 ... Surface acoustic wave element 2 ... Piezoelectric substrate 3 ... Input side electrode 5 ... Output side electrode 10 ... Focused ion beam direct vapor deposition device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shinji Nagamachi, No. 1 Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto City, Kyoto Prefecture Shimadzu Corporation Co., Ltd. Within

Claims (2)

[Claims] 1. An electrode forming method for forming an electrode of a surface acoustic wave device, wherein a focused ion beam is irradiated onto a substrate surface with energy capable of vapor deposition to form a plurality of electrode surfaces, and the electrode surfaces are resisted. And forming an electrode by etching, and forming an electrode of the surface acoustic wave device. 2. The method for forming an electrode of a surface acoustic wave device according to claim 1, wherein the electrode surface is formed so as to be thinner than a desired thickness, and after the focused ion beam irradiation, a desired PVD method is applied. A method of forming an electrode of a surface acoustic wave device, comprising forming an electrode surface having a thickness.