JP3382038B2 - Manufacturing method of surface acoustic wave device - Google Patents

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 improvement of a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, a surface acoustic wave device used as a filter or a resonator has an electrode wire of a metal electrode formed on a piezoelectric substrate and an electrode wire of a metal electrode formed on a piezoelectric substrate as the frequency band of the surface acoustic wave device is increased. The size reduction of the surface acoustic wave element is remarkable, and the miniaturization of the surface acoustic wave element is required in accordance with the miniaturization for the mobile phone and the like.

With the miniaturization of these electrode structures and the miniaturization of the surface acoustic wave device chip size, when mounting the surface acoustic wave device in a package, a pattern defect is caused on the metal electrode due to contact with a mounting jig. Caused by the metal splash caused by the metal splash generated by welding during sealing of the package, resulting in defects and increased production defects, resulting in a marked decrease in yield during production. Was there.

Therefore, conventionally, the metal electrode provided on the piezoelectric substrate is covered with a protective film made of silicon oxide (SiO ₂ ) and having a thickness of about 600 Å to prevent the occurrence of defects in the metal electrode. .

However, since the frequency characteristic of the surface acoustic wave element greatly changes with the film thickness of silicon oxide, if the frequency characteristic standard is strict, the frequency standard is deviated, yield is generated, and productivity is lowered. Was causing problems.

For this reason, conventionally, at the time of forming a silicon oxide layer, for example, a stylus type film thickness measuring device such as .alpha.-step manufactured by TENCOR or RUDOLPH RE.
Using an optical non-contact type film thickness measuring device such as an ellipsometer such as SEARCH Auto EL IV,
The film thickness was strictly controlled.

However, in the former stylus-type film thickness measuring apparatus, in order to measure the film thickness of the silicon oxide layer, a step must be provided in the silicon oxide layer by a photolithography process after forming the layer. However, the measurement result of the film thickness is obtained after the photolithography process performed after the layer formation process, and the next process is performed after waiting for the feedback, so that the process control is significantly delayed and If the film thickness is out of specification,
The first problem is that the photolithography process is also wasted.

Furthermore, since the thickness of the protective film is as thin as about 600 Å, there is a second problem that the measured values vary greatly. Actually, the standard deviation when measuring 15 samples with a film thickness of about 600 angstroms was about 30 angstroms. This is because in addition to the reproducibility of the device itself, fine unevenness on the silicon oxide layer is formed. This is because it is read as a thickness measurement value.

In order to solve the problems of these stylus type film thickness measuring devices, the latter optical non-contact type film thickness measuring devices such as ellipsometers are used. The reproducibility of the value is high, and the variation of the film thickness value of about 600 angstrom is about 1/3 of that of the stylus type film thickness measuring device, and the standard deviation when measuring 15 samples is about 10 angstrom. Becomes

In this ellipsometer, when polarized light is incident on the measurement sample layer laminated on the substrate from an oblique direction, the reflection polarization is the optical constant of the sample substrate and the refractive index which is the optical constant of the sample layer. -The absorption coefficient and the thickness of the sample layer determine the phase and amplitude ratio. Therefore, if the optical constants of the sample substrate and the sample layer are known, the film thickness value of the sample layer can be obtained.

However, in the optical film thickness measuring device such as an ellipsometer having the above-mentioned principle, since the optical constant of the substrate in the measurement region must be constant, there are two types of piezoelectric substrate and a metal electrode such as aluminum (Al). There is a problem that the thickness of the protective film formed on the substrate cannot be measured.

For this reason, conventionally, in order to measure the film thickness of the protective layer of the surface acoustic wave device using an ellipsometer, a film thickness measuring dummy that does not pattern the metal layer for the metal electrode on the piezoelectric substrate is used. -Put the substrate into each deposition batch,
By measuring the film thickness formed on this dummy substrate, it is represented as the data of the film thickness of all the substrates of the same film deposition batch.

[0013]

Conventionally, in place of a stylus-type film thickness measuring device, which has a large variation in measured values and requires a photolithography step to provide a step on the protective film at the time of measurement, In order to measure the film thickness with an optical film thickness measuring device such as an ellipsometer with a small variation in measured values, a dummy substrate that does not pattern the metal layer for the metal electrode at all is thrown in for each deposition batch, and The film thickness was represented as the data of the film deposition batch film thickness.

However, in this method, the film thickness is measured only on the dummy substrate, and since the film thickness on the substrate which is actually manufactured cannot be directly measured, there arises a problem that the reliability of the data is low. As a result, the number of product substrates in the film deposition batch is reduced by the number of dummy substrates input, which causes a problem of poor production efficiency.

Therefore, the present invention solves the above-mentioned problems, and suppresses the variation of the film thickness measurement value to the minimum without lowering the production efficiency, and further, the protective film formed directly on the piezoelectric substrate to be the product. Since the film thickness can be directly measured immediately after film formation, highly reliable data can be measured with high accuracy and speed, improving reliability and improving production efficiency by efficiently managing production. It is an object of the present invention to provide a method for manufacturing a surface acoustic wave device capable of achieving the above.

[0016]

In order to solve the above-mentioned problems, the first aspect of the present invention provides a step of forming a metal electrode portion on a piezoelectric substrate, and a step of selectively removing the metal electrode portion. Forming a comb-shaped electrode, forming a transparent insulating layer covering the main surface of the piezoelectric substrate on which the comb-shaped electrode is formed,
Detecting the film thickness of the transparent insulating layer by injecting polarized light into a region where the transparent insulating layer is directly deposited on the piezoelectric substrate without interposing the comb-shaped electrode and measuring reflected polarized light from the region. And steps.

In order to solve the above problems, the second aspect of the present invention is that the transparent insulating layer in the first aspect is a silicon oxide layer.

In order to solve the above-mentioned problems, the third aspect of the present invention is that, in the first aspect, the region into which polarized light is incident can include a circle having a diameter of 3 mm.

In order to solve the above-mentioned problems, a fourth aspect of the present invention is the same as the first aspect, wherein the region into which the polarized light is incident is surrounded by the region in which the comb-shaped electrode is formed. .

[0020]

The present invention is formed as described above, and is formed on a product substrate by providing an exposed portion of the piezoelectric substrate where a metal layer having a predetermined area is not formed on the piezoelectric substrate on which the metal electrode pattern is formed. The protective film is directly measured by an ellipsometer and compared with the conventional stylus type film thickness measuring device, the film thickness is measured quickly and with high accuracy, so the occurrence of defects is reduced.
The production efficiency can be improved. Further, compared to the conventional film thickness measurement with an ellipsometer using a dummy substrate, the dummy substrate is not required, and the production efficiency can be improved, and the reliability of the data to be measured is improved, and the measured value can be improved. The accuracy can be further improved, and the production efficiency can be improved because the occurrence of defects can be more surely prevented.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in FIGS. FIG. 1 shows lithium niobate (Li
3 is a schematic plan view showing a state in which a metal electrode 11 made of an alloy of aluminum (Al) and copper (Cu) is patterned on the entire surface of a piezoelectric substrate 10 made of NbO3),
Are areas where the comb-shaped metal electrodes 11 are formed on the piezoelectric substrate 10, as shown in FIG. On the other hand, a region B, which is a film thickness measurement region on the piezoelectric substrate 10 and is an exposed portion of the piezoelectric substrate, is a region in which a metal electrode is not formed, which has an area capable of including a circle having a diameter of 3 mm.

One pattern in the area A is the piezoelectric substrate 10.
One surface acoustic wave element 12 is provided with one comb-shaped metal electrode 11 on the top.

Here, according to the flow chart shown in FIG.
The process of forming the metal electrode 11 will be described. Step 20
First, a metal layer made of aluminum (Al) and copper (Cu) is formed on the piezoelectric substrate 10 by a sputtering method to a thickness of about 2000.
Stack to a thickness of Angstrom and proceed to step 21.
In step 21, a negative photoresist (THMR-
iN200: Tokyo Ohka Kogyo Co., Ltd. is applied on the alloy layer, prebaked in step 22, and then proceeds to step 23.

In step 23, a negative exposure photoresist is sequentially exposed by using a step-and-repeat type reduction exposure apparatus. At this time, the reduction exposure apparatus is programmed in advance so that the exposure is performed in a comb shape in the area A and only the steps are performed in the area B without exposing the exposure. The unexposed area corresponding to the region B is set to a size capable of including a circle having a diameter of 3 mm.

In step 23, a negative photoresist is sequentially exposed using a step-and-repeat type reduction exposure apparatus. At this time, the reduction exposure apparatus is programmed in advance so that the exposure is performed in a comb shape in the area A and only the steps are performed in the area B without exposing the exposure. The unexposed area corresponding to the region B is set to a size capable of including a circle having a diameter of 3 mm.

In step 27, the metal layer is patterned by wet etching using a photoresist patterned with a mixed acid containing phosphoric acid as a main component, and in the region A, a comb-shaped metal is formed on the piezoelectric substrate 10. Electrode 1
1 is continuously formed, and in the region B, the metal layer is entirely removed to expose the piezoelectric substrate 10. Then step 2
At 8, the photoresist is removed, and the metal electrode forming step is completed. After that, the protective film 16 made of silicon oxide is formed on the metal electrode 11 by the sputtering method.

However, the filter center frequency of the surface acoustic wave element 12 varies depending on the film thickness of the protective film 16 due to the mass load effect, and the RF for mobile band communication using the 800 MHz band is used.
In the case of the filter, the center frequency is shifted to the low frequency side by about 1 MHz with respect to 100 Å of the silicon oxide layer.

Therefore, the pattern of the metal electrode 11 is designed in consideration of the frequency shift caused by the protective film 16.

Therefore, if the protective film 16 on the metal electrode 11 has the designed film thickness, there is no problem without deviating from the frequency standard. However, due to fluctuations and variations in film forming conditions when forming the protective film 16, a predetermined value is obtained. If the designed film thickness cannot be obtained, the product will be defective, and therefore the film formation of the protective film 16 will be performed while strictly measuring the film thickness and controlling it.
That is, the piezoelectric substrate 10 having an A region where the metal electrode 11 is patterned on the entire surface and a B region where the metal substrate is not present and the piezoelectric substrate is exposed is placed in a reaction vessel, and a silicon oxide target is formed. Argon (Ar) gas for sputtering is introduced, RF (Radio Frequency) power is supplied from a high frequency power source to excite glow discharge, and a predetermined time is set so that the region A and the region B have a film thickness of 600 angstroms. After forming the silicon oxide film, the supply of the RF power is stopped, and the formation of the protective film 16 is completed.

After that, the piezoelectric substrate 1 is measured with an ellipsometer.
The film thickness is measured by measuring the polarized light reflected from the region B of 0.

When the film thickness is measured by the ellipsometer, the film thickness cannot be measured in the area A due to reflection from both the piezoelectric substrate 10 and the metal electrode 11, but the area B is measured.
In that case, only the reflection is received from the piezoelectric substrate 10, and the film thickness can be satisfactorily measured by the ellipsometer.

When the protective film 16 has a thickness of about 600 Å and is found to be within the standard range, the piezoelectric substrate 10 is made into a chip, and the chipped surface acoustic wave element 12 is packaged (not shown). ) To complete a surface acoustic wave device (not shown). On the other hand, when the film thickness of the protective film 16 does not satisfy the standard range,
The frequency adjustment process is performed without proceeding to the next chip forming process.

According to this structure, the surface acoustic wave element 12
Since the metal electrode 11 is covered with the protective film 16 at the time of mounting in the package of, the metal electrode 11 is miniaturized or the surface acoustic wave element 12 is downsized, and
Even if a slight contact with the jig occurs, the metal electrode 11 is not damaged, and the fine metal electrode 11 is not short-circuited due to the metal splash generated during the sealing welding of the package.

Moreover, in the manufacturing process of the surface acoustic wave element 12, since the film thickness of the protective film 16 can be measured immediately by the ellipsometer immediately after the protective film 16 is formed, it is more than the conventional stylus type film thickness measuring device. Since the variation in the measured film thickness can be reduced and more accurate film thickness can be obtained, the reliability of the device can be improved without causing defects after the surface acoustic wave device is manufactured. It is not necessary to form a step, and after the protective film 16 is formed, the film thickness measurement value can be quickly obtained, and the subsequent manufacturing process can be immediately performed according to the measurement result, and the production management can be efficiently performed. You can also

Further, as compared with the conventional film thickness measurement by an ellipsometer using a dummy substrate, the dummy substrate is not required, the production efficiency can be improved significantly, and the measurement target is a substrate directly commercialized. The reliability of data can be improved, the accuracy of measured values can be further improved, and production efficiency can be improved because the occurrence of defects can be prevented more reliably.

The present invention is not limited to the above-mentioned embodiment, but can be modified within the scope of the invention.
For example, the photoresist serving as a mask for patterning the metal layer formed on the piezoelectric substrate to form the metal electrode and the film thickness measurement region is not limited to the negative type and may be a positive type. However, when a positive photoresist is used, the unexposed area remains as a mask without being dissolved during development,
When the metal layer is etched using the photoresist thus patterned, the metal electrode is patterned, while in the film thickness measurement region, the metal layer remains as it is without being removed. If there is
The protective film will be formed on the metal layer, but this metal layer may have different reflectance depending on the components, film thickness, film formation method, etc. during layer formation. However, it is desirable to use a negative photoresist so that the piezoelectric substrate is exposed in the film thickness measurement region.

The exposure apparatus may also be one which performs exposure by a proximity exposure method, a projection exposure method or the like if an unexposed area is provided in the film thickness measurement area.

Further, the size of the film thickness measuring region may be arbitrary, but in view of the performance of the ellipsometer, it is at least 3 mm in diameter.
An area on the order of a mm circle is required.

[0039]

As described above, according to the present invention, since the metal electrode formed on the piezoelectric substrate is covered with the transparent insulating layer, it is possible to increase the frequency utilization band or downsize the device. Also, when the surface acoustic wave element is mounted on the package, the metal electrode is not damaged and defects are not generated, and the yield in the mounting process can be improved.

Moreover, by providing a film thickness measuring region in which the metal layer is not patterned on the piezoelectric substrate, the film thickness of the transparent insulating layer can be measured immediately after film formation by an ellipsometer. Since more accurate film thickness with less variation compared to the thickness measurement device can be obtained, the reliability of the device can be improved without causing defects after the surface acoustic wave device is manufactured. It is not necessary to form a film, and the film thickness measurement value can be quickly obtained after the transparent insulating layer is formed, and the production control can be performed efficiently.

Furthermore, the film thickness measurement by the ellipsometer can be performed directly on the substrate to be manufactured, not on the dummy substrate, and the reliability of the data can be improved to improve the accuracy of the measured value, and the occurrence of defects can be more reliably caused. The production efficiency can be improved also by preventing it. In addition, the production of dummy substrates becomes unnecessary,
The production efficiency is significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing an array of metal electrode patterns and exposed portions of a piezoelectric substrate formed on a piezoelectric substrate according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a state in which protective films are formed in regions A and B formed on a piezoelectric substrate according to a position example of the present invention.

FIG. 3 is a plan view showing a surface acoustic wave device according to an embodiment of the present invention.

FIG. 4 is a flowchart showing a process of forming a metal electrode according to an embodiment of the present invention.

[Explanation of symbols]

10 ... Piezoelectric substrate 11 ... Metal electrode 12 ... Surface acoustic wave element 16 ... Protective film

Claims (4)

(57) [Claims] 1. A step of forming a metal electrode portion on a piezoelectric substrate, a step of selectively removing the metal electrode portion to form a comb-shaped electrode, and a main electrode on which the comb-shaped electrode of the piezoelectric substrate is formed. Forming a transparent insulating layer covering the surface, and injecting polarized light into a region where the transparent insulating layer is directly deposited on the piezoelectric substrate without interposing the comb electrodes, and measuring reflected polarized light from the region. And a step of detecting the film thickness of the transparent insulating layer. 2. The method of manufacturing a surface acoustic wave device according to claim 1, wherein the transparent insulating layer is a silicon oxide layer. 3. The area into which polarized light is incident has a diameter of 3 m.
The method of manufacturing a surface acoustic wave device according to claim 1, wherein a circle of m can be included. 4. The method of manufacturing a surface acoustic wave device according to claim 1, wherein the region where polarized light is incident is surrounded by a region where the comb electrode is formed.