JP2000013165A - Surface acoustic wave device and method of manufacturing the same - Google Patents

Abstract

[PROBLEMS] To provide a surface acoustic wave device which has sufficient bonding strength and can be inspected with a wafer probe without a decrease in yield. SOLUTION: An aluminum film is formed on a piezoelectric substrate 1 and patterned to form electrodes 3 and 4 of an interdigital transducer 2, a reflector electrode 6 and a bonding pad 5 together with a pyroelectric countermeasure line 7 for connecting the same potential to each other. I do. The electrodes 3, 4 and the reflector electrode 6 of the interdigital transducer 2 are covered with a resist, and an aluminum film is laminated. The bonding pad 5 is covered with a resist, the pyroelectric protection line 7 is electrically separated, and the aluminum film is etched to remove the resist.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a surface acoustic wave device having improved bonding strength and preventing a decrease in yield, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A surface acoustic wave device is used for a frequency filter of a mobile communication terminal, for example.
The thickness of the metal layer of the bonding pad is about 150 nm. Then, wire bonding is performed to electrically connect the surface acoustic wave element of the frequency filter and the package.

However, when the thickness of the bonding pad is 1
At 50 nm, the connection strength of wire bonding may be insufficient because the film thickness is too small.

For this reason, a surface acoustic wave device is manufactured by increasing the thickness of a bonding pad.

The surface acoustic wave device is configured as shown in FIG. That is, for example, L
An interdigital transducer (IDT) 2 which is an excitation electrode of aluminum (Al) to which copper (Cu) is added is formed on a piezoelectric substrate 1 of iTaO ₃ , and the interdigital transducer 2 has a U-shape with one end opened. It has an electrode 3 and an electrode 4 located between the openings of the electrode 3, and a bonding pad 5 thicker than the electrodes 3 and 4 is formed on each of the electrodes 3 and 4.
A reflector electrode 6 is formed on the side of the interdigital transducer 2. Further, the interdigital transducer 2 and the electrodes 3, 4
Is formed with a pyroelectric countermeasure line 7.

That is, in a photolithography process using a lift-off method, during heating during pre-bake treatment of a resist or post-bake treatment after development, the interdigital transducer 2 is heated due to the pyroelectricity of the piezoelectric substrate 1. Since the patterns of the electrodes 3 and 4, the bonding pad 5 and the reflector electrode 6 may be melted, the patterns of the electrodes 3 and 4 of the interdigital transducer 2 and the bonding pad 5 and the reflector electrode 6 may be changed. The connection is made electrically by the anti-pyroelectric line 7 so as to have the same potential, thereby preventing fusing.

However, in the prober process for selecting non-defective products at the wafer stage, since all the patterns have the same potential, the electrical characteristics cannot be measured. Therefore, the electrodes 3, 4 of the interdigital transducer 2, the bonding pad 5, and the reflection All the patterns such as the electrodes 6 are formed by connecting the pyroelectric lines, and the pyroelectric countermeasure lines 7 are cut by using a photolithography method.

Next, a method of manufacturing the surface acoustic wave device will be described with reference to FIGS.

First, an aluminum film to which copper is added is deposited on the piezoelectric substrate 1 to a thickness of 150 nm by sputtering or the like, and is patterned by a usual photolithography process as shown in FIG. That is, a photoresist is applied on an aluminum film to which copper is added, and the device pattern is printed by an exposure machine using a mask on which a predetermined device pattern is drawn. Then, the exposed portion of the resist is removed with a developing solution, and using the remaining resist pattern as a mask, an aluminum film to which copper is added by, for example, RIE (Reactive Ion Etching) using chlorine gas (Cl ₂ ) or the like is used. By etching and removing the resist, electrodes 3 and 4 of the interdigital transducer 2, an aluminum film 10 to which copper is added as a first layer of the bonding pad 5, a reflector electrode 6, and a pyroelectric countermeasure line 7 are formed.

Next, as shown in FIG. 10, portions other than the bonding pads are covered with a resist 11 by using a photolithography process.

Further, as shown in FIG. 11, an aluminum film 12 is formed on the entire surface by vacuum evaporation.

Next, as shown in FIG. 12, a so-called lift-off method is used in which the resist 11 is removed in a resist stripping step, and the aluminum film 12 laminated on the resist 11 is also removed at the same time. As a result, only the bonding pad 5 is formed of the two layers of the aluminum film 10 to which the copper of the first layer is added and the aluminum film 12 of the second layer to have a thickness of 500 nm.
Therefore, the bonding strength of the bonding can be sufficiently maintained.

As shown in FIG. 13, the electrodes 3 and 4, the bonding pad 5 and the reflector electrode 6 of the interdigital transducer 2 are covered with a resist 15 except for the pyroelectric countermeasure line 7.

Next, as shown in FIG. 14, the pyroelectric measures line 7 is etched.

Further, the resist 15 is peeled off as shown in FIG.

However, the manufacturing method shown in FIGS. 9 to 15 requires an extra photolithography step,
Productivity drops significantly.

In the lift-off method, when the resist 11 is peeled, the copper-added aluminum film 10 laminated on the resist 11 is simultaneously peeled off, so that these metal films float in a lift-off peeling tank. In the next lot, it may reattach to the surface acoustic wave device, which may cause a decrease in yield.

[0018]

As described above, if the thickness of the bonding pad is small, the bonding strength of wire bonding becomes weak. Therefore, it is necessary to increase the thickness of the bonding pad of the surface acoustic wave device by the lift-off method. It is conceivable that during the baking process in the middle of the process, the piezoelectric substrate 1
Electrodes 3, 4 of the interdigital transducer 2, bonding pad 5, and reflector electrode 6 due to the pyroelectricity of
There is a possibility that the pattern may be electrostatically damaged. As a countermeasure against pyroelectricity, all the patterns are electrically connected to each other through a pyroelectricity countermeasure line to have the same potential, thereby preventing fusing. However, if the patterns of the electrodes 3 and 4 of the interdigital transducer 2, the bonding pad 5, and the reflector electrode 6 are all set to the same potential by the pyroelectric countermeasure line 7, the wafer probe inspection becomes impossible, and the yield in the subsequent process is reduced. The pyroelectric countermeasure line is cut because it worsens. This allows
There is a problem that the number of photolithography steps is increased and productivity is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a surface acoustic wave device which has sufficient bonding strength and which can be inspected by a wafer probe or the like without a decrease in yield, and a method of manufacturing the same. I do.

[0020]

SUMMARY OF THE INVENTION The present invention provides a pyroelectric substrate, an excitation electrode and a reflector electrode formed of a first conductive metal layer on the substrate, and A first conductive metal layer is formed together with a pyroelectric countermeasure line for electrically setting the excitation electrode and the reflector electrode to the same electric potential, and the first conductive metal layer is formed on at least a part of the first conductive metal layer. A second conductive metal layer is laminated on the metal layer.
After the conductive metal layer is formed, the pyroelectric countermeasure line is provided with a bonding pad formed while being electrically separated by etching.

By forming the pyroelectric countermeasure line, the excitation electrode, the reflector electrode and the bonding pad are blown by the pyroelectricity due to the pyroelectricity of the substrate when the bonding pad is formed thick to improve the bonding strength. In addition, the wafer probe inspection can be performed by separating the pyroelectric countermeasure line by etching.

The conductive metal layer contains aluminum.

Furthermore, the etching of the pyroelectric countermeasure line is performed as follows.
This is wet etching.

Further, according to the present invention, there is provided a first metal layer forming step of laminating a first conductive metal layer on a substrate having a pyroelectric property, and an excitation electrode formed by patterning the first conductive metal layer. Forming a reflector electrode and a bonding pad together with a pyroelectric countermeasure line for setting the same potential to each other, a first resist process of covering the excitation electrode and the reflector electrode with a resist, and a second conductive metal. A second metal layer forming step of stacking layers, a second resist step of further covering the bonding pads with resist, and electrically separating the pyroelectric protection line and etching the second conductive metal layer Etching process,
A resist removing step of removing the resist.

By forming a pyroelectric countermeasure line in the patterning step, the excitation electrode, the reflector electrode, and the bonding pad are formed by the pyroelectricity of the substrate when the bonding pad is formed thick to improve the bonding strength. And prevents the wafer from being blown, and separates the pyroelectric countermeasure lines in the etching process, thereby making each of them electrically independent, thereby enabling the wafer probe inspection.

The thickness of the bonding pad is larger than that of the excitation electrode and the reflector electrode.

Further, the first conductive metal layer and the second conductive metal layer contain aluminum.

Further, the etching step for etching the pyroelectric countermeasure line is wet etching.

The substrate has piezoelectricity.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a surface acoustic wave device according to the present invention will be described below with reference to the drawings. Parts corresponding to the conventional example shown in FIGS. 8 to 15 are denoted by the same reference numerals and described.

This surface acoustic wave device is configured as shown in FIG. That is, for example, L
An interdigital transducer (IDT) 2, which is an excitation electrode for converting electric energy of aluminum (Al) into elastic energy, is formed on a piezoelectric substrate 1 of iTaO _3. And an electrode 4 located between the openings of the electrode 3, and a bonding pad 5 for connecting a bonding wire is formed on each of the electrodes 3 and 4. In addition, a reflector electrode 6 is formed on the side of the interdigital transducer 2 for confining elastic energy. Further, a pyroelectric countermeasure line 7 is formed on the interdigital transducer 2 and the electrodes 3 and 4.

That is, in the photolithography process, the electrodes 3 and 4 of the interdigital transducer 2 are heated due to the pyroelectricity of the piezoelectric substrate 1 during heating during resist baking and post baking after development. Since the patterns of the bonding pads 5 and the reflector electrodes 6 may be melted, the patterns of the electrodes 3 and 4 of the interdigital transducer 2, the bonding pads 5 and the reflector electrodes 6, etc. By making the same electrical connection and the same potential, it is possible to prevent fusing.

However, in the prober process for selecting non-defective products at the wafer stage, the electric characteristics cannot be measured because all the patterns have the same potential, so that the electrodes 3, 4 of the interdigital transducer 2, the bonding pad 5, and the reflection All the patterns such as the electrodes 6 are formed by connecting pyroelectric lines, and the pyroelectric countermeasure lines 7 are cut off by using an etching method.

Next, a method of manufacturing the surface acoustic wave device will be described with reference to FIGS.

First, an aluminum film is deposited on the piezoelectric substrate 1 to a thickness of 150 nm by a sputtering method or the like, and is patterned by a usual photolithography process as shown in FIG. That is, a photoresist is applied on the aluminum film, and the device pattern is printed by an exposure machine using a mask on which a predetermined device pattern is drawn.
Then, the exposed portion of the resist is removed with a developing solution, and the remaining resist pattern is used as a mask to form, for example, RIE (Reactive Ion) using chlorine gas (Cl ₂ ) or the like.
The aluminum film is etched by an etching method or the like, and the resist is peeled off.
A reflector electrode 6 and a pyroelectric measure line 7 are formed.

Next, as shown in FIG. 3, portions other than the bonding pad 5 and the pyroelectric protection line 7 are covered with a resist 11 by using a photolithography process.

Further, as shown in FIG. 4, an aluminum film 22 as a second conductive metal layer serving as a second layer is formed on the entire surface by vacuum evaporation to obtain a sufficient strength 500
It is formed with a thickness of nm.

Next, as shown in FIG. 5, only the bonding pad 5 is covered with a resist 23 of a photosensitive resin, and the pyroelectric measure line 7 is not covered.

As shown in FIG. 6, portions of the aluminum film 10 and the aluminum film 22 where no resist 23 is provided are formed.
And interdigital transducer 2
The electrodes 3 and 4, the bonding pad 5 and the reflector electrode 6 are protected by the resist 21, but the pyroelectric measure line 7 is cut off.

Further, as shown in FIG. 7, the resist 23 is removed, and the patterning step on the wafer is completed.

According to the above embodiment, the yield is improved as compared with the related art.

That is, first, since the lift-off method is not used, the resist is not removed together with the conductive metal film such as aluminum. Conventionally, since the lift-off method was used, this stripped resist film with the conductive metal film remains as a residue in the stripping solution, and adheres to the wafer in the next lot, causing short-circuit failures. Since the metal film on the resist is completely removed by etching without using the lift-off method and then the resist is peeled off, there is no adhesion of the metal film, and no short circuit failure due to the adhesion of the metal film occurs.

Second, since the number of processes is smaller than in the case where the lift-off method is used, the occurrence of fusing failure due to pyroelectricity is eliminated. That is, in the conventional lift-off method, when the pyroelectric measures line 7 for preventing the occurrence of fusing is cut,
Finally, a patterning step by photolithography must be added once again. Since the pyroelectric countermeasure line 7 is provided, the yield in the wafer process due to electrostatic breakdown due to pyroelectricity can be reduced. If the pyroelectric countermeasure line 7 is not cut, the potential between the electrodes 3 and 4 of the interdigital transducer 2, the bonding pad 5 and the reflector electrode 6 becomes the same, so that the wafer probe cannot be used for inspection. These inspections can also be performed by cutting 7. The reason why the pyroelectric countermeasure line 7 is drawn out from the bonding pad 5 is to prevent the interdigital transducer 2 from being damaged due to a displacement at the time of cutting when pulled out from the interdigital transducer 2. Also, the wet etching is used because it is necessary to remove the metal film on the resist 21 together with the etching of the pyroelectric countermeasure line 7. 2 may be damaged.

Further, by not using the lift-off method, the electrodes 3 and 3 of the interdigital transducer 2 can be used.
4. The thickness of the bonding pad 5 and the thickness of the reflector electrode 6 can be made equal, and the frequency characteristics that change due to the change in the thickness can be stabilized.

Further, by increasing the thickness of the bonding pad 5, the connection strength of the bonding wire can be increased.

The same effect can be obtained by using LiNbO ₃ as the piezoelectric substrate.

[0047]

According to the present invention, by forming a pyroelectric countermeasure line, when forming a thick bonding pad for improving the bonding strength, the excitation electrode,
It is possible to prevent the reflector electrode and the bonding pad from being blown out by pyroelectricity, and to separate the pyroelectric countermeasure line by etching, thereby enabling the wafer probe inspection without lowering the yield.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing an embodiment of a surface acoustic wave device according to the present invention.

FIG. 2 shows one manufacturing process of the surface acoustic wave device according to the first embodiment;
It is sectional drawing of the position corresponding to B2.

FIG. 3 is a sectional view of a position corresponding to B1-B2, which shows the next step of FIG. 2;

FIG. 4 is a sectional view of a position corresponding to B1-B2 showing the next step of FIG. 3;

5 is a cross-sectional view of a position corresponding to B1-B2, which shows the next step of FIG.

FIG. 6 is a sectional view of a position corresponding to B1-B2, which shows the next step of FIG.

FIG. 7 is a sectional view of a position corresponding to B1-B2, which shows the next step of FIG.

FIG. 8 is a plan view schematically showing a conventional surface acoustic wave device.

FIG. 9 is a diagram illustrating one manufacturing process of the surface acoustic wave device according to the first embodiment;
It is sectional drawing of the position corresponding to A2.

FIG. 10 is a cross-sectional view of a position corresponding to B1-B2, showing the next step of FIG. 9;

FIG. 11 is a sectional view of a position corresponding to B1-B2, which shows the next step of FIG.

FIG. 12 is a sectional view of a position corresponding to B1-B2, which shows the next step of FIG.

FIG. 13 is a sectional view of a position corresponding to B1-B2, which shows the next step of FIG.

FIG. 14 is a sectional view of a position corresponding to B1-B2, which shows the next step of FIG.

FIG. 15 is a sectional view of a position corresponding to B1-B2, which shows the next step of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Interdigital transducer as excitation electrode 5 Bonding pad 6 Reflector electrode 7 Pyroelectric countermeasure line 10 Aluminum film as first conductive metal layer 21, 23 Resist 22 Aluminum as second conductive metal layer film

Claims (8)

[Claims] A substrate having pyroelectricity; an excitation electrode and a reflector electrode formed of a first conductive metal layer on the substrate; and an excitation electrode and a reflector electrode on the substrate. A first conductive metal layer is formed together with a pyroelectric countermeasure line for making the same electric potential, and a second conductive metal layer is formed on at least a part of the first conductive metal layer. An elastic surface, comprising: a metal layer laminated thereon; and a bonding pad formed and electrically separated from the pyroelectric countermeasure line by etching after the second conductive metal layer is formed. Wave device. 2. The surface acoustic wave device according to claim 1, wherein the conductive metal layer contains aluminum. 3. The method according to claim 1, wherein the etching of the pyroelectric countermeasure line is wet etching.
The surface acoustic wave device according to claim 1. 4. A first metal layer forming step of laminating a first conductive metal layer on a substrate having pyroelectricity, and an excitation electrode by patterning the first conductive metal layer.
A patterning step of forming a reflector electrode and a bonding pad together with a pyroelectric countermeasure line for setting the same potential to each other; a first resist step of coating the excitation electrode and the reflector electrode with a resist; a second conductive metal layer A second metal layer forming step of laminating a bonding pad, and a second step of coating a bonding pad with a resist.
A surface acoustic wave characterized by comprising: a resist process; an etching process for electrically separating the pyroelectric countermeasure line and etching the second conductive metal layer; and a resist removing process for removing the resist. Device manufacturing method. 5. The method according to claim 4, wherein the thickness of the bonding pad is greater than the thickness of the excitation electrode and the reflector electrode. 6. The method of manufacturing a surface acoustic wave device according to claim 4, wherein the first conductive metal layer and the second conductive metal layer contain aluminum. 7. The method for manufacturing a surface acoustic wave device according to claim 4, wherein the etching step for etching the pyroelectric countermeasure line is wet etching. 8. The method for manufacturing a surface acoustic wave device according to claim 4, wherein the substrate has piezoelectricity.