JPH0738366A - Inspecting method for surface acoustic wave device - Google Patents

Abstract

PURPOSE:To provide the inspecting method for a surface acoustic wave device, by which an inspection can be executed efficiently. CONSTITUTION:This inspecting method is applied to a surface acoustic wave device in which at least one IDT 12 is formed on a piezoelectric substrate 10. The electrical capacity of the IDT 12 in a prescribed inspection frequency being lower than a working frequency of the surface acoustic wave device is measured by an LCR meter 20, and based on the measured electrical capacity value, a frequency characteristic in the working frequency of the surface acoustic wave device is inspected.

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 a method for inspecting a surface acoustic wave device used in a high frequency band.

[0002]

2. Description of the Related Art A surface acoustic wave device has an IDT on a piezoelectric substrate.
A high-frequency element that forms an (Interdigital Transducer) and excites and propagates a surface acoustic wave on the surface of a piezoelectric substrate to function as a filter, a resonator, a delay line, or the like. The frequency of the surface acoustic wave device is almost determined by the acoustic velocity of the surface acoustic wave of the piezoelectric substrate and the electrode pitch of the IDT, but it also changes depending on the film thickness of the electrode, the ratio of the electrode width to the electrode pitch of the IDT (metallization ratio), and the like. . Therefore, when manufacturing a surface acoustic wave device with high frequency accuracy, it is necessary to suppress variations in the electrode film thickness and the IDT metallization ratio.

In particular, in the case of a piezoelectric substrate having a large electromechanical coupling coefficient such as a 36 ° cut lithium tantalate substrate, the change in sound velocity due to the presence or absence of an electrode layer is larger than that due to the difference in electrode film thickness. The frequency characteristic greatly depends on the metallization ratio. In order to inspect the frequency characteristics of such a surface acoustic wave device, conventionally, the measurement is performed using the actually used frequency, or the IDT is measured by a microscope.
Was visually observed to measure the metallization ratio.

[0004]

However, in the conventional method of inspecting by using the actually used frequency, there is a problem that the inspection takes time because the sweep is performed in a predetermined frequency range. In addition, although it is necessary to inspect the used frequency even in the state of the wafer before being divided into individual element chips, in the case of a high frequency, it is difficult to perform the inspection with sufficient accuracy by the measurement with a normal RF probe.

Further, the conventional method of inspecting using a microscope has problems that it requires skill in inspection and it is difficult to realize sufficient inspection accuracy. An object of the present invention is to provide a method of inspecting a surface acoustic wave device that can efficiently inspect.

[0006]

SUMMARY OF THE INVENTION The above object is to provide a method of inspecting a surface acoustic wave device in which at least one IDT is formed on a piezoelectric substrate, in which the electric power of the IDT at an inspection frequency lower than the operating frequency of the surface acoustic wave device. It is achieved by a method for inspecting a surface acoustic wave device, which comprises measuring a static capacitance and inspecting a frequency characteristic at a use frequency of the surface acoustic wave device based on the measured electric capacitance value.

In the method of inspecting the surface acoustic wave device, it is desirable that the equivalent resistance of the IDT be measured and the surface acoustic wave device be inspected based on the measured equivalent resistance value.

[0008]

In the surface acoustic wave device in which at least one IDT is formed on the piezoelectric substrate, the input capacitance changes and the matching state changes due to the variation of the metallization ratio of the IDT. It was found that there is a strong correlation between the ratios. Similarly, it is known that there is a strong correlation between the metallization ratio of the IDT and the frequency characteristic. Therefore, according to the present invention, if the electric capacity of the IDT at a predetermined inspection frequency lower than the operating frequency of the surface acoustic wave device is measured, the electric capacity of the surface acoustic wave device at the operating frequency is measured based on the measured electric capacity value. The frequency characteristic can be inspected.

Further, if the IDT of the surface acoustic wave device is broken or short-circuited, the electric capacity of the IDT changes.
By measuring the electric capacity of T, the presence or absence of disconnection or short circuit of the IDT can be inspected. Furthermore, according to the present invention, even when the wafer is inspected before it is divided into individual element chips, the electric capacity of the IDT can be measured at a predetermined inspection frequency lower than the operating frequency of the surface acoustic wave device. Since it is good, simple inspection is possible without using an RF probe.

Further, if the equivalent resistance of the IDT is measured in addition to the electric capacity of the IDT, the ID is calculated from the measured equivalent resistance value.
An abnormality such as a short circuit of T can be detected.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An inspection method for a surface acoustic wave device according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the surface acoustic wave device to be inspected in this embodiment has an input ID made of an alloy containing aluminum at the center of a 36 ° -cut lithium tantalate substrate 10.
It is a surface acoustic wave filter in which T12 and an output IDT 13 adjacent thereto are formed. The IDT 12 is configured by combining a pair of comb-shaped electrodes 12a and 12b.

In the inspection method of this embodiment, as shown in FIG. 1, the impedance (real part: equivalent resistance value; imaginary part: electric capacity) between terminals of the IDT 12 of the surface acoustic wave device is L.
It is measured by the CR meter 20. Even if the operating frequency of the surface acoustic wave device is 800 MHz, the inspection frequency is IDT.
The electric capacitance of the IDT may be within a range in which it can be accurately measured, and the radiation conductance of the IDT is small with respect to the capacitance and may be within a frequency range that can be ignored. That is, even if the operating frequency of the surface acoustic wave device is 800 MHz,
The electrical capacity may be measured at 1 MHz or less, for example, 10 KHz.

As described above, in the surface acoustic wave device, there is a strong correlation between the electric capacity of the IDT and the metallization ratio, and a strong correlation between the metallization ratio of the IDT and the frequency characteristic. Therefore, various characteristics such as frequency characteristics at the operating frequency of the surface acoustic wave device can be inspected from the electric capacitance value measured at the low inspection frequency in this way.

FIG. 2 shows the measurement results. The vertical axis represents the center frequency [relative value] of the surface acoustic wave device, and the horizontal axis represents the electrical capacitance value [pF]. From the graph of FIG. 2, it can be seen that the magnitude of the deviation of the center frequency of the surface acoustic wave device can be accurately inspected from the electric capacitance value of the IDT. Even if resistors, inductors, capacitors, etc. are inserted between the signal and ground for the purpose of impedance matching, etc., the phase change can be ignored at low frequencies, so the real and imaginary parts of the impedance are Can measure with high accuracy. Since the surface acoustic wave device can be inspected by the measurement at a single low inspection frequency, the inspection speed can be significantly improved as compared with the inspection at the operating frequency of the surface acoustic wave device.

Further, the presence or absence of disconnection of the IDT can be inspected from the difference between the capacitance values of the input IDT 12 and the output IDT 13. In a symmetric circuit in which the input capacitance value and the output capacitance value should be the same, the difference between the input capacitance value and the output capacitance value may be detected as it is, and efficient inspection is possible. Further, in the asymmetric circuit, if the respective capacitance values are weighted, then it is possible to perform the efficient inspection as well. Further, in the case of surely inspecting the disconnection, the center frequency of the surface acoustic wave device is measured in advance, and the surface acoustic wave device within a certain value is obtained from the relational expression between the electric capacitance value and the center frequency in a normal surface acoustic wave device. As a non-defective product, the load in the visual inspection process can be reduced. Such an inspection is particularly effective for a multi-electrode surface acoustic wave device having a plurality of input IDTs and output IDTs.

In FIG. 1, the surface acoustic wave device which is divided into individual pieces is inspected, but a low inspection frequency is sufficient even in the state of the wafer before division into individual element chips, so that a normal RF probe is used. Without this, a simple inspection is possible. A method of inspecting a surface acoustic wave device according to another embodiment of the present invention will be described with reference to FIG.

In this embodiment, the wafer 30 before being divided into individual element chips is an inspection target. Waha 3
Although a plurality of surface acoustic wave devices (not shown) are formed on the surface of the wafer 0, in the present embodiment, the inspection patterns 32 are further formed at various places in the wafer 30. Inspection pattern 32
For example, as shown in FIG. 3, an IDT having a pair of comb-shaped electrodes is used. The comb electrodes have the same line width of the surface acoustic wave device. The impedance (real number part: equivalent resistance value; imaginary number part: electric capacity) between the input and output terminals of the IDT for this inspection pattern 32 is measured by the LCR meter 20. Since the inspection frequency only needs to be within the range in which the electric capacity of the IDT can be accurately measured, it does not depend on the operating frequency of the surface acoustic wave device, and is 1 MHz or less, for example, 10 KH.
It may be measured at a low frequency of z.

According to this embodiment, it is possible to easily control the line width ratio during the manufacturing process, and it is possible to inspect variations in the wafer surface. The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, the case of inspecting a surface acoustic wave filter in which two IDTs are formed on the piezoelectric substrate has been described, but the present invention is not limited to the IDT and other resonator types such as a resonator type in which a reflector is provided. It is also effective for the inspection of the surface acoustic wave device.

[0019]

As described above, according to the present invention, since the electric capacity of the IDT may be measured at a predetermined inspection frequency lower than the operating frequency of the surface acoustic wave device, a sufficiently accurate inspection can be performed efficiently. Can be done.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a method of inspecting a surface acoustic wave device according to an embodiment of the present invention.

FIG. 2 is a graph showing the correlation between the capacitance value of the IDT and the frequency characteristic of the surface acoustic wave device.

FIG. 3 is an explanatory diagram of a method of inspecting a surface acoustic wave device according to another embodiment of the present invention.

[Explanation of symbols]

 10 ... Lithium tantalate substrate 12 ... Input IDT 12a, 12b ... Comb-shaped electrode 13 ... Output IDT 20 ... LCR meter 30 ... Wafer 32 ... Inspection pattern

Claims (1)

[Claims] 1. At least one IDT on a piezoelectric substrate.
In the method of inspecting a surface acoustic wave device having the above-mentioned structure, the electric capacity of the IDT is measured at a predetermined inspection frequency lower than the operating frequency of the surface acoustic wave device, and the electric capacity is measured based on the measured electric capacity value. A method for inspecting a surface acoustic wave device, which comprises inspecting a frequency characteristic at a use frequency of the surface acoustic wave device.