JPS62295504A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To improve the dielectric strength, to decrease the resistivity and to stabilize the electrode by forming at least a part of the electrode propagating or reflecting a surface acoustic wave by a metallic film made of aluminum added with an impurity of the metal of the group III element other than aluminum having a specific range of wt.%. CONSTITUTION:As a material for the electrode, an aluminum and 0.2-10wt.% of an impurity of the group III, element other than the aluminum are used. For example, reflector electrodes 10, 10' made of 750 metallic strips are provided at both sides of one set of transmitting/receiving electrodes 2,2' to constitute a two-opening surface acoustic wave resonator. The film thickness of the electrodes 2,2, aud 10, 10' is 0.1mum, the resonance frequency is 697MHz and the Q' is 4000. The electrode material is the aluminum added by 2wt.% of Ga, the film is formed by DC magnetron sputter and the pattern is formed by photoetching. As the result of the acceleration test, the time of deterioration is extended by >=three times in comparison with a conventional device made of EB vapor-deposition of aluminum added with Cu and the dielectric strength is remarkably improved.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a surface acoustic wave device that transmits large electric power or an elastic The present invention relates to a surface acoustic wave device that can be used as a surface wave resonator and has high reliability.

[Conventional technology]

The range of applications of surface acoustic wave devices has expanded, and surface acoustic wave filters that transmit large amounts of power and surface acoustic wave resonators that generate large-amplitude surface waves as standing waves during operation have come to be used. .

However, in the surface acoustic wave device used with high power or large amplitude as described above, the fine Al electrode fingers of the wave transmitting/receiving electrodes and reflectors are (March 1984), protrusions due to electromigration that occur on Al wiring electrodes of semiconductor integrated circuits.
Defects similar to defects such as locks) and voids (νoids) occur, and in surface acoustic wave resonators, defects such as shifts in the resonant frequency occur1, and in surface acoustic wave filters that transmit large power, defects due to hillox growth occur. Failures such as short circuits and disconnections were occurring frequently. ” - The mechanism by which such defects occur is that ``distortion of the substrate surface caused by surface acoustic waves generates internal stress in the Al thin film formed on the surface'', and in areas where the stress exceeds a threshold value, Grain boundary movement of A11l occurs, resulting in voids and hillocks. Grain boundary movement due to internal stress is reported in the Journal of the Institute of Electrical and Electronics Engineers, Parts,
Hybrid, and Packaging (IEEE Tr
ans, :Parts, Hybrids and Pac
The mechanism is considered to be the same as in the case of temperature cycling of integrated circuits as shown in Vol. ”. The first document mentioned above describes a method of adding a small amount (1 to 4%) of Cu to Al used in semiconductor integrated circuits as a countermeasure against defects caused by such Al migration, and discusses its effectiveness in suppressing migration. It shows.

Next, regarding electromigration countermeasures for semiconductor integrated circuit wiring, Journal of Applied Physics, Vol. 49 (1,978), 4083-4.
As shown on page 093, a multilayer film using a first Al film doped with, for example, Cu as an impurity, and a second film that does not contain Al, which is much thinner than the first Al film, such as a Hf film. structure is used.

It is also conceivable to apply this second conventional technique to high-power surface acoustic wave devices and surface acoustic wave resonators.

However, in the conventional technique of adding a small amount of Cu to Al according to the above-mentioned first document, the hardness of the film tends to be excessive.
It has the disadvantage of making wire bonding difficult, and when dry etching is applied to high-frequency surface acoustic wave devices to form fine electrodes with high precision, corrosion of the electrodes is likely to occur, resulting in a significant reduction in yield. There was a drawback that it deteriorated.

In addition, at high frequencies, even if the transmitted power or amplitude is not so large, the distortion of the surface wave becomes large, so the Cu-doped AU electrode according to the first document mentioned above has a sufficient lifespan during high power (large vibration m) operation. cannot be guaranteed.

On the other hand, in the conventional technology according to the second document, the second film that does not contain Al has good anti-migration properties;
If a material that easily diffuses into Al and has a high alloy resistivity with Al is used, even at a temperature of about 80°C, if used for a long time, alloying with the first Al film will progress and the entire film will deteriorate. As a result, the resistivity increases rapidly. That is, the loss as a surface acoustic wave device increases rapidly, and it may become unusable.

That is, another failure mode occurs.

[Problem that the invention seeks to solve]

The present invention solves the problems of the above-mentioned conventional techniques, such as the hardness of the film tends to be excessive, the yield decreases significantly during dry etching, sufficient life is not obtained, and the resistivity becomes excessive. However, it is an object of the present invention to provide a surface acoustic wave device having stable electrodes with sufficient power resistance and low resistivity.

[Means for solving problems]

In order to solve the above-mentioned problems, in the present invention, as an electrode material, A and Q are added with 0.2 to 10% by weight of a Group 1 element other than Aρ as an impurity.

This is because the present inventors searched for materials with low bulk resistivity when added to Al, and found that like Al, group Ⅰ elements are preferable, and in particular, the addition of Ga is effective for forming electrode films. This is because it has been found that the resistivity can be reduced and the resistance to power is also excellent.

If the addition rate is less than 0.2% by weight, it is difficult to notice the effect of addition, and if it is more than 10% by weight, the melting point after addition will decrease, so the following addition rates were determined.

[Effect]

Materials added to Al that reduce resistivity are based on the general viewpoint of solid-state electron theory, that is, Linda's law (for example, F. J. Blatt, translated by Masao Doyama, "Electron Theory of Solids J, 1970, Maruzen It is an element with the same valence of electrons as Al.From this point of view, Group Ⅰ elements are suitable, but when we added them to Al and investigated them, we found that
It has become clear that the addition of Ga is effective in improving the power durability of surface acoustic wave devices.

A sputtered film with a thickness of 0.1 μm was created using a target containing Ga added to Al at a concentration of 2% by weight, and its resistivity was measured to be 3.4 μΩ −■.
The resistivity was smaller than that of a Cu-added Aρ sputtered film of the same film thickness made by the conventional technique, which was 3.8 μΩ-■. On the other hand, when examining the power durability, it was found that at the same concentration, when Ga was added, C
The power durability was about twice that of the case with u addition. This increase in power durability is thought to be due to the fact that the atomic radius of Ga is 1.24 A, which is smaller than that of Al, 1.43 A, and it is easier to suppress the movement of Al due to diffusion.

〔Example〕

FIG. 1 is a sectional view of one embodiment of the present invention. 1 is a surface acoustic wave substrate using ST-cut crystal, and on the surface of this substrate, a pair of wave transmitting/receiving electrodes 2, 2' are arranged with an opening of 1000 μm and a number of pairs of electrode fingers.
Eight pairs of electrodes are provided to mutually transmit and receive surface acoustic waves, and these electrodes are connected to a bonding pad 3.3' through a bus electrode (not shown), and the bonding pad 3.3I is made of Al wire or gold. Connect the input/output pins of the stem of the can package using bonding wires (not shown).
4', and a ground side bus electrode (not shown) of the wave transmitting/receiving electrode is grounded to the stem 6 of the can package through a ground side bonding pad (not shown). In addition, 75 mm are placed on both sides of the pair of wave transmitting/receiving electrodes 2.2'.
Reflector electrode 10.10' consisting of 0 metal strips
is provided, constituting a two-aperture surface acoustic wave resonator.

The film thickness of the above-mentioned wave transmitting/receiving electrode 2.2' and reflector electrode 10.10' is 0.1 μm, and the resonance frequency is 697 MIhi, Q'
It is 4000. The electrode material used in this example was Al containing 2% by weight of Ga, which was formed into a film by DC magnetron sputtering and then patterned by photoetching.

FIG. 2 shows the results of an accelerated deterioration test of the surface acoustic wave resonator of this example. This figure shows the E of Cu-added AI2 for comparison.
Test results for samples without B vapor deposition are also shown. The horizontal axis shows the concentration of the additive element in the film in weight percent, and the vertical axis shows the deterioration time TF in terms of the time at which the resonance frequency changed. The accelerated deterioration test conditions were a temperature of 120° C. and an input power of 100 mW. The test results of the present invention example shown by line 9 in FIG.
Compared to the test results of samples using conventional materials made without EB deposition, the time until deterioration was more than three times longer, indicating a significant improvement in power durability, and the film resistivity was approximately 0. 3μ
Ω-■ has decreased, and no deterioration of the 1-frequency characteristics is observed.
In fact, the loss was slightly better.

Although the above embodiment is a two-opening surface acoustic wave resonator using a reflector made of a metal strip, the present invention is applicable to all cases where large amplitude surface waves are handled.

〔Effect of the invention〕

As explained above, according to the present invention, the power durability is more than three times greater than that of the conventional vapor-deposited electrode of Cu-added Al.
In addition, a highly reliable surface acoustic wave device with improved characteristics such as reduced resistivity and reduced loss can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is a diagram showing a comparison of accelerated deterioration test results of the embodiment of the present invention and a conventional example. DESCRIPTION OF SYMBOLS 1...Surface acoustic wave substrate, 2.2'... Wave transmitting/receiving electrode, 9...Line showing the relationship between impurity doping concentration and deterioration time of the embodiment of the present invention, 10.10'...Surface acoustic wave reflection vessel.

Claims (1)

[Claims] 1. At least one wave transmitting/receiving electrode is provided on the surface acoustic wave substrate, and at least a part of the electrode that propagates or reflects surface acoustic waves, including this electrode, is made of Al, 0 A surface acoustic wave device comprising a metal film doped with 2 to 10% by weight of a Group III element other than Al as an impurity. 2. The surface acoustic wave device according to claim 1, wherein Ga is used as a Group III element impurity other than Al.