JP3172165B2 - Manufacturing method of surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a surface acoustic wave having an electric / acoustic transducer, a lead wire, and a bonding pad on one main surface of a piezoelectric substrate. The present invention relates to a device manufacturing method.

(Prior Art) The structure of a surface acoustic wave device will be described using a surface acoustic wave filter as an example. As shown in FIGS. 4 and 5, a piezoelectric substrate 2 is disposed in an envelope 1 of the surface acoustic wave filter, and one main surface of the piezoelectric substrate 2 is formed of a metal thin film. In addition, a plurality of (two in this example) electric / acoustic transducers 3 are arranged.

These electric / acoustic transducers 3 are composed of comb-teeth-shaped electrode finger pairs, one of which is an input transducer connected to a power supply, and the other is an output transducer connected to a load. By changing the number and shape of the electrode fingers of the electric / acoustic transducer 3 or the interval (period) of the electrode fingers, a bandpass filter having a desired frequency selection characteristic is realized.

In order to connect the electric / acoustic transducer 3 to a power supply and a load (not shown), a lead wire 5 and a bonding pad 6 formed of a metal thin film are provided on one main surface of the piezoelectric substrate 2. 3 and are arranged. Then, the bonding pad 6 is connected to the external lead lead terminal 8 by a bonding wire 7 so as to be electrically pulled out.

By the way, in such a surface acoustic wave filter, low loss is often required, and efforts have conventionally been made to eliminate the cause of the loss as much as possible.

One of the factors that increase the loss is the electrical resistance loss of the lead wire 5. In order to reduce the resistance of the lead 5, it is conceivable to increase the thickness of the metal thin film forming the lead 5.

However, the thickness of the electric / acoustic transducer 3 is
Since the thickness is set to be constant in design, it is necessary to increase only the film thickness of the portion of the lead wire 5 and the bonding pad 6 excluding the electric / acoustic transducer 3. As a method for realizing this, a technique has been proposed in which a metal thin film portion excluding the electric / acoustic transducer 3 is formed into two layers.

Hereinafter, a conventional method for increasing the thickness of the metal thin film of the lead wire 5 and the bonding pad 6 by the two-layer structure will be described with reference to FIG.

First, an electric / acoustic transducer 3 having a predetermined thickness and a lead wire 5 (and a bonding pad 6) are formed on a piezoelectric substrate 2 in the same manner as in a normal case (a).

Thereafter, a resist film 10 is formed on the upper surface, and light 21 is irradiated through a mask (not shown) having a predetermined pattern corresponding to the pattern of the part to be formed into two layers, thereby performing exposure (b).

Next, a developing solution 22 is brought into contact with the resist film 10 to perform development, and the resist film 10 in an exposed portion (or a non-exposed portion) is removed to form an opening 31. Usually, in such a lift-off method, the resist pattern 32 is formed in an inverted trapezoidal shape (c).

Thereafter, a metal film 11 for forming a second layer is deposited (d).

Then, the resist film 10 is dissolved and removed, and the metal film 11 in other portions is removed together with the resist film 10 while leaving the second-layer metal film 11 only in a desired portion (e).

According to the above method, only the metal film of the lead wire 5 and the bonding pad 6 can be made into two layers without changing the metal film thickness of the electric / acoustic transducer 3, and only the film thickness of this portion can be increased. .

(Problems to be Solved by the Invention) However, in the above-described conventional method of manufacturing a surface acoustic wave device, as in the case of the surface acoustic wave device shown in FIG. As shown in FIG. 2, in the case of a surface acoustic wave device having a complicated pattern in which a plurality of lead lines 5 are adjacent to each other, a second-layer metal film is formed on the first-layer pattern. The accuracy of the alignment for forming is a problem.

For example, as shown in FIG. 7, in the case of a wiring pattern in which the lead-out lines 5 are adjacent to each other and have a small interval, if the mask positioning accuracy is poor, the resist pattern 32 is formed so as to be shifted from a predetermined position indicated by a dotted line in the figure. (A), and as a result,
The second metal film 11 is formed so as to be shifted from a predetermined position, and this second metal film 11 may cause an electrical short circuit between the lead wires 5 (b).

For this reason, there are problems such as a decrease in yield during mass production and a decrease in productivity due to the necessity of performing high-accuracy alignment.

The present invention has been made in view of such a conventional situation, and even if the surface acoustic wave device has a fine lead line pattern on the piezoelectric substrate, it does not cause a decrease in yield or a decrease in productivity and a low loss. It is an object of the present invention to provide a method of manufacturing a surface acoustic wave device capable of efficiently manufacturing a high-performance surface acoustic wave device.

[Configuration of the Invention] (Means for Solving the Problems) That is, the present invention is formed on one main surface of a piezoelectric substrate,
A surface acoustic wave comprising: a plurality of electric / acoustic transducers each including a pair of comb-shaped electrode fingers; and a lead wire and a bonding pad formed on one main surface of the piezoelectric substrate and connected to the electric / acoustic transducers. A method for manufacturing the device, wherein an electro-acoustic transducer forming step of forming the electro-acoustic transducer made of a metal film on a predetermined area on one main surface of the piezoelectric substrate; and the predetermined area on one main surface of the piezoelectric substrate. A lead wire and a bonding pad forming step for forming the lead wire and the bonding pad formed of a metal film thicker than the electro-acoustic transducer in a region other than the electro-acoustic transducer and the lead wire The connection is made by overlapping one part of these with the other To.

(Operation) In the method for manufacturing a surface acoustic wave device according to the present invention having the above configuration,
On the piezoelectric substrate, the electric / acoustic transducer, the lead wire, and the bonding pad can be formed by different processes.

That is, for example, only the electric / acoustic transducer is formed by the electric / acoustic transducer forming step, and thereafter, the lead line and the bonding pad formed of the thick metal film are formed by the lead line and the bonding pad forming step. be able to.

The electrical connection between the electric / acoustic transducer and the lead wire and the bonding pad is made by, for example, forming a part of these parts so as to overlap each other.

Therefore, unlike the conventional method of forming two layers, it is not necessary to perform high-precision alignment of the mask, and there is no shift between the first and second metal films. Therefore, even if the surface acoustic wave device has a fine lead line pattern on the piezoelectric substrate, it is possible to efficiently manufacture a low-loss surface acoustic wave device without lowering the yield or lowering the productivity.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing the steps of one embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing an electrode pattern layout of the surface acoustic wave filter in the present embodiment, and FIG. 3 is a diagram showing a connection portion between the electric / acoustic transducer 3 and the lead wire 5.

The surface acoustic wave filter manufactured in this embodiment has an electrode pattern layout as shown in FIG. 2, and a plurality of electric / acoustic transducers 3 and electric / acoustic transducers are provided on one main surface of the piezoelectric substrate 2. A lead wire 5 and a bonding pad 6 connected to 3 are formed. The electric / acoustic transducer 3, the lead wire 5 and the bonding pad 6 are all formed of a single-layer metal thin film by the following method. 3 is set to be thicker than the metal film.

Next, the steps of the method of this embodiment will be described with reference to FIG.

In this embodiment, first, an electro-acoustic transducer 3 made of a metal thin film having a predetermined thickness (360 nm in this example) is formed on one main surface of a piezoelectric substrate 2. Note that the lead wire 5 and the bonding pad 6 are not formed in this step (A).

Next, a resist is coated on one main surface of the piezoelectric substrate 2 to form a resist film 10, and light is applied thereto through a mask (not shown) having a predetermined pattern corresponding to the pattern of the lead wire 5 and the bonding pad 6. Exposure is performed by irradiating 21 (B).

Thereafter, development is performed by bringing the developing solution 22 into contact with the resist film 10, and the exposed portion (or unexposed portion) of the resist film 10 is developed.
Is removed to form an opening 31. Usually, in such a lift-off method, the resist pattern 32 is formed in an inverted trapezoidal shape (C).

Thereafter, a metal film 11 (900 nm in this example) for forming the lead wire 5 and the bonding pad 6 which is thicker than the electric / acoustic transducer 3 is deposited (D).

Then, the resist film 10 and the metal film 11 deposited on the undesired portions are removed (E).

From the above steps, the electric / acoustic transducer 3, the lead wire 5, and the bonding pad 6 can be formed of a single-layer metal thin film, and the metal thin film of the lead wire 5 and the bonding pad 6 can be used as the electric / acoustic transducer 3. Thicker than the metal thin film.

FIG. 3 shows such an electric / acoustic transducer 3
FIG. 5 shows a state of connection between the lead wire 5 and the lead wire 5. Third
In the figure, reference numeral 9 denotes a bus bar connected to the transducer 3, which is formed simultaneously with the formation of the transducer 3. The lead wire 5 is formed such that its end is overlapped with the bus bar 9.

Here, as shown in FIG. 3, if the deviation of the exposure position when providing the lead line 5 is l, at least l or more lengths a and b where the lead line 5 and the bus bar 9 overlap are provided. The length W and the width H of the bus bar 9 are W> b + 1, H
> A + 1. As a result of an actual experiment, the displacement is within about 50 μm, and if the size of the bus bar 9 is 100 μm or more for both W and H, the lead wire 5 and the transducer 3 are in the open state or the lead wire 5 Overlapped with the electrode finger, and it was possible to prevent the transducer 3 from becoming short-circuited.

In the electrode pattern layout of the present embodiment shown in FIG. 2, LiNbO ₃ is used as the piezoelectric substrate 2, and the transducer 3 has five electrodes in which 7-pair normal type and 26-pair avodic weighting (Blackman function) are alternately arranged. The structure, the opening length was 1 mm, and Al was used for the electrode material. The Al film thickness was 360 nm for the transducer 3 and the lead wire 5 and the bonding pad 6 were 900 nm. The insertion loss was improved by 0.7 dB as compared with the case where the thickness of Al in the portion of the lead wire 5 and the bonding pad 6 was not increased (in the case of 360 nm).
This means that the resistance loss has been reduced. Further, since the thickness of the bonding pad 6 is similarly increased, the effect of improving the bonding property (bonding strength) was also obtained.

As described above, in this embodiment, the first and second metal films do not need to be positioned with high accuracy as in the case of the two-layer deposition method. The resistance loss can be improved without causing an electric short circuit due to the displacement. For this reason, even if the lead-out line pattern 5 on the piezoelectric substrate 2 is a fine surface acoustic wave device, it is possible to efficiently manufacture a low-loss surface acoustic wave device without reducing the yield or the productivity. it can. Further, the bonding property of the bonding wire can be improved.

[Effects of the Invention] As described above, according to the present invention, even if the lead line pattern on the piezoelectric substrate is a fine surface acoustic wave device,
A low-loss, high-performance surface acoustic wave device can be efficiently manufactured without lowering the yield or lowering the productivity.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of one embodiment of the present invention, FIG. 2 is a view showing an electrode pattern layout of a surface acoustic wave filter in one embodiment, and FIG. FIG. 4 and FIG.
The figure shows the configuration of a general surface acoustic wave filter.
FIG. 7 is a view showing a manufacturing process in the conventional method, and FIG. 7 is a view for explaining a problem of the conventional method. 2. Piezoelectric substrate 3. Electric / acoustic transducer 5. Lead wire 6. Bonding pad

 ──────────────────────────────────────────────────続 き Continuing on the front page Referee Mikio Kawana Judge Nobuaki Yoshimi Judge Masahiro Hashimoto (56) References JP-A-4-21205 (JP, A) JP-A-1-103011 (JP, A) 1964-16729 (JP, U)

Claims (1)

(57) [Claims] 1. A plurality of electric / acoustic transducers formed on one main surface of a piezoelectric substrate and comprising a pair of comb-shaped electrode fingers;
A method of manufacturing a surface acoustic wave device, comprising: a lead wire and a bonding pad formed on one main surface of the piezoelectric substrate and connected to the electric / acoustic transducer; An electro-acoustic transducer forming step of forming the electro-acoustic transducer made of a metal film in a region; and a metal film thicker than the electro-acoustic transducer in a region other than the predetermined region on one main surface of the piezoelectric substrate. Forming a lead line and a bonding pad for forming the lead line and the bonding pad, wherein the connection between the electric / acoustic transducer and the lead line overlaps a part of one of them with the other. A method for manufacturing a surface acoustic wave device.