JPH079418B2 - Spectrum ultrasound microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to two-dimensional observation of elastic properties of a subject,
In particular, the present invention relates to a spectrum ultrasonic microscope that performs two-dimensional quantitative measurement of a subject in a short time.

<Prior Art> In recent years, an ultrasonic wave is oscillated using a piezoelectric body, refracted by an acoustic lens, and converged on the surface of the object via an ultrasonic wave propagating liquid, and an XY scan is performed on the surface of the object. Ultrasonic microscopes have been developed that two-dimensionally display the elastic properties of a subject by obtaining the output of waves or transmitted waves.

An outline of a typical ultrasonic microscope will be described. As shown in FIG. 2, a high frequency burst signal is generated using a high frequency oscillator 9 that oscillates a constant frequency of several tens to several hundreds of MHz and applied to the piezoelectric body 10. To do. High-frequency burst signals are converted into sound waves by a piezoelectric body (a device that converts applied electric signals into sound waves, enters the subject, and converts the reflected sound waves back into electric signals is called a "transducer") and melts. The light propagates through the delay material 11 made of quartz or sapphire, and is refracted by the difference in sound velocity between the delay material and the ultrasonic wave propagating liquid 12 to be converged on the subject 13. The reflected wave of the acoustic wave that reflects the acoustic properties of the sample is emitted again to the ultrasonic wave propagating liquid 12, and the delay member 11
After being phase-matched with each other, it is converted into an electric signal again by the piezoelectric body 10. After the obtained electric signal is amplified and diode-detected, its output is used as a video signal. The above steps are simultaneously performed on the sample while the transducer is scanning XY, and the two-dimensional reflection intensity image of the subject is displayed.

Most acoustic microscopes up to now irradiate a subject with a wide incidence angle including a vertical component by an acoustic lens, and display the output of the reflected wave as the brightness of the image. Is.

However, the roughness of the surface of the specimen, the leakage of energy due to the surface acoustic waves excited on the surface of the specimen to the depth direction of the substrate, and the energy escaping from the transducer position to an undetectable area as surface acoustic waves. Only the output as a result of the integration of the effects of many phenomena such as the phenomenon of the reflected wave component due to is obtained, and only the relation of the relative output in one image can be always provided. As described above, today's ultrasonic microscopes have difficulty in performing quantitative measurement based on its principle.

One that enables quantitative measurement using an ultrasonic microscope is disclosed in Japanese Patent Application Laid-Open No. 61-20857, which uses the V (z) curve method as a principle. As shown in FIG. 3 by the V (z) curve method, the acoustic lens 19 is moved vertically in the direction perpendicular to the surface of the subject, and is vertically incident on the surface of the subject. , Once propagated as a surface acoustic wave on the surface of the subject, and the sound velocity of the surface acoustic wave is measured from the oscillation period Δ _{z of the} output due to the interference of the components re-emitted, and from that value, the elastic constant or structure of the subject is measured. Can be quantitatively measured.
However, with this method, when attempting two-dimensional measurement on the surface of the subject, it is necessary to move up and down the point-by-point transducer with high accuracy, so it may take a huge amount of time to create one image. It is a drawback.

Accurate as an absolute value, such as the speed of sound of a surface acoustic wave excited on the surface of the subject or the frequency of ultrasonic waves that can excite the surface acoustic wave without mechanically moving the transducer up and down with respect to the subject. In addition, if the sample surface can be obtained two-dimensionally with high resolution in a short time, the elastic constant of the object that could not be achieved with the conventional ultrasonic microscope or the film thickness or the crack depth in the case of an object with a film. Since it becomes possible to quantitatively obtain the information from the information, it becomes a useful evaluation device in an extremely wide field such as the destructive inspection means in the current precision machining or the field of physical property research.

<Problems to be Solved by the Invention> As described above, in the conventional ultrasonic microscope, it is difficult to quantitatively measure the physical constants and structural parameters of the object, and V
(Z) If a two-dimensional quantitative measurement of an object is performed using the curve method or the like, there is a problem that the measurement takes a long time.

<Means for Solving Problems> The present invention has been made by omitting the above problems, and a means for oscillating a high-frequency pulse in a wide band and an oscillated electric signal converted into a sound wave at a constant incident angle. The method further comprises a transducer for entering a subject and receiving the reflected wave thereof, means for frequency-analyzing the obtained signal, and means for quantitatively extracting or storing the characteristics of the frequency distribution thereof, and the steps of these steps. Drive to move the transducer relative to the subject in parallel with the surface of the subject, or to move the subject two-dimensionally with respect to the transducer by synchronizing the oscillation and reception of sound waves and the process of frequency analysis. With a means, the information of the frequency distribution of the reflected wave depending on the incident angle of the ultrasonic wave at each point of the subject to the sample, or the quantitative information of the subject obtained from it is two-dimensionally obtained. By using a device having a means for outputting, the physical property constant of the subject,
It is possible to two-dimensionally and quantitatively measure and detect the structural parameters such as the film thickness, or the presence or separation of cracks on the surface of the subject.

<Operation> Generally, an ultrasonic wave is incident on a subject at a constant angle, and the frequency distribution of the reflected wave and the frequency dependence of the reflection coefficient show a change corresponding to the elastic constant of the subject or a structural parameter. We have revealed that it can provide important information for nondestructive inspection and physical property research.

The reflection coefficient of the subject when ultrasonic waves are incident on the subject at a certain angle can be obtained by the equation (1) if the frequency response function of the apparatus is obtained in advance.

Here, P2 is the frequency distribution of the response function of the device, and P1 is the frequency distribution of the reflected wave at the subject.

If the incident angle θ is constant in this way, the reflection coefficient as a function of the frequency f, which is dimensionless data, can be obtained.

In particular, as shown in FIG. 4, when the reflection coefficient has a minimum at a certain frequency 23 as a function of a physical property constant or a structural parameter, the frequency at which the reflection coefficient has the minimum is the transducer and the object under XY scanning. It is possible to obtain information that is relatively stable with respect to fluctuations in the relative distance of the signal without being affected by the energy of the entire reflected wave.

As described above, the spectrum ultrasonic microscope of the present invention is different from the conventional ultrasonic microscope that uses the relative value of the output within one screen as information, in the frequency distribution of the reflected wave at each point on the surface of the subject. By using the shape as the measurement target, it is possible to remove the surface condition of the subject, the characteristics of the transducer, the electrically or mechanically unstable element of the entire apparatus, and purely take out the response to the sound wave peculiar to the subject.

Furthermore, we investigated the frequency dependence of the reflected wave at various incident angles of ultrasonic waves on many subjects with known physical properties and structures. Since it has been found that the shape of the frequency distribution is almost the same as that of the case where the light is incident at the center angle of the spread of the incident angle even when the width is given, the shape of the transducer is shown in FIG. With such a structure, the ultrasonic waves can be focused on the surface of the subject, an area smaller than the piezoelectric area of the transducer can be observed, and an image can be obtained with high resolution.

<Examples> The present invention will be described in detail below with reference to the drawings based on examples.

FIG. 1 shows an example of a block diagram of a spectrum ultrasonic microscope.

The impulse oscillator is used as the broadband high frequency pulse oscillator 1, and the transducer injects ultrasonic waves into the subject,
Install to receive reflected waves. The receiving unit 3 of the transducer is connected to a wide band amplifier 4, and the amplified signal is a frequency analyzer 5 including a spectrum analyzer.
The frequency is analyzed according to the A / D conversion. The obtained frequency distribution is subjected to feature extraction programmed by an operator by the frequency distribution digital calculation and storage device 6 and stored by the operator, and the result is displayed on the image output device 7. The XY stage driving device 8 connected to the sample stage is scanned in XY in synchronization with the signal output from the impulse oscillator.

The following measurement was possible with the device having the above configuration.

An ultrasonic wave is incident on a sample composed of a film at a specific incident angle determined by the combination of the substrate, the film, and the ultrasonic wave propagating liquid,
If there is a frequency at which the reflectance becomes a minimum, we find that the film thickness d and the reflectance minimum frequency f have the following relationship with the constant C determined by the combination of the substrate, the film, and the ultrasonic wave propagating liquid. Is heading.

f * d = C (2) When using this to measure the thickness of gold as a test object on a fused quartz plate plated with gold, ultrasonic waves are applied.
It is known that when incident at 30 deg, a surface wave called a pseudo-surface acoustic wave is excited on the surface of the subject and propagates while releasing energy to the substrate. From this, the incident angle of the sound wave of the transducer is set to 30 deg, and the sample is stored in the digital operation and storage device of the frequency distribution of the spectrum ultrasonic microscope as shown in FIG. The frequency distribution 24 in the case where the same transducer is used for samples that do not show a local minimum due to peculiar absorption in (3) is stored. Next, as shown in FIG. 5B, if the components of the frequency distribution 25 of the reflected wave at each frequency obtained at the subject at the same incident angle are obtained, from the value of the frequency distribution 25 at each frequency, When the value of the frequency distribution 24 is subtracted, a frequency distribution 26 clearly showing the minimal phenomenon peculiar to the subject is obtained as shown in FIG. 5C. Obtained frequency distribution
The frequency 27, which has the minimum value at 26, is obtained, and the film thickness d is calculated from the equation (2).
Was calculated, and the magnitude of d was set as light and dark and displayed on the monitor screen of the image output device. The above processing was performed over the entire surface of the subject using the XY stage drive device, and settings were made so as to obtain a film thickness distribution chart of the entire subject.

As a result of the measurement, a distribution map of the film thickness was obtained two-dimensionally with a high spatial resolution over the entire surface of the subject, and when it was later examined by destructive inspection, the film thickness distribution map obtained by the spectrum ultrasonic microscope It has been proved that shows the correct value.

Further, when an ultrasonic wave is incident on a sample having a film, which is determined by a combination of the substrate, the film, and the ultrasonic wave propagating liquid, a wave called a surface acoustic wave is strongly excited on the sample surface. In this case, if ultrasonic waves are applied to a very small area and the reflected sound waves in that area are collected, they propagate as surface acoustic waves to areas that cannot be detected by the receiving transducer without releasing energy to the substrate. , We found that only the frequency component excited by the surface acoustic wave has a large minimum output of the reflected wave.

Therefore, as shown in FIG. 6, the transducer was set to have a central incident angle of 40 deg and an incident angle width of 4 deg. In the digital operation and storage device of the frequency distribution, as in the previous example, the minimum frequency of the frequency distribution of the obtained reflected wave is calculated, the constant C is calculated when the film is chromium and the substrate is copper, and the film thickness d is calculated. After setting, measurement was performed over the entire surface of the subject. As a result, by radiating ultrasonic waves to a very small area and collecting the reflected wave in that area, a minimal phenomenon of reflected wave output appears significantly, and the film thickness of the entire surface of the subject can be measured accurately and in a short time. Was done.

It is known that when a sample with a gold film deposited on a fused quartz substrate is immersed in hydrochloric acid, the gold film will peel off from many parts in a short time due to the entry of hydrochloric acid at the boundary. .

However, until now, it was difficult to continuously observe this peeling process. Therefore, hydrochloric acid was used as the ultrasonic wave propagation medium, and measurement was performed using the spectrum ultrasonic microscope of the present invention. If the film peels off from the substrate, the minimal phenomenon at a certain frequency of the reflected wave output that was present due to the influence of the pseudo surface acoustic wave propagating while leaking energy to the substrate when the film was in close contact does not occur. Since we found, in the digital operation of frequency distribution and storage device, the part of the subject where the minimal phenomenon occurred shows the monitor screen as bright, and at the point where the minimal phenomenon did not occur, the monitor screen was displayed as dark. Meanwhile, the film thickness obtained by the equation (2) was set to be stored, and the entire surface of the subject was repeatedly observed for a long time.

By this measurement, the peeling of the gold film was observed over time. In addition, after observation, when the film thickness distribution distribution was image-displayed from the reflected wave output minimum frequency stored in the spectrum ultrasonic microscope, it was found that more peeling occurred from the thin film portion.

When the relation of the expression (3) is established in the sample in which the film is formed on the substrate, there is an intermediate layer made of a different kind of material between the film and the substrate, or the boundary is completely joined. We found that it did not.

Ultrasonic waves are incident on the subject at two different incident angles, the reflected waves in that region are sampled, and the output of the reflected waves is minimized at each of the incident angles. , f2, and f1 ′ and f2 ′ in the subject, For this reason, a gold film is vapor-deposited on fused silica and the incident angle θ1
= 17.0 deg and incident angle θ2 = 25.0 deg, and the incident angle width θ3 = 3 deg was set so that the reflected wave could be independently collected at each incident angle using the sensor as shown in FIG. .

Furthermore, it is judged whether or not the formula (3) holds for f1 and f2 obtained in advance, and if it does not hold, the light distribution is displayed on the monitor screen as the state of the measuring point, and the dark distribution is displayed on the monitor screen. And the storage device was set and the measurement was performed. As a result, since a bright portion was observed in the subject, the presence of an oil film was confirmed in the area where the bright display was made on the monitor screen when confirmed by the destructive test.

The following useful experiments were conducted on a subject whose physical properties were unknown.

The wideband pulse oscillator is set to transmit signals with frequency components up to around 100MHz, and the output is a digital operation and storage device for the frequency distribution independently of the brightness of each of the three primary colors of red, blue and green on the color monitor screen. I set it up to be expressed by the command from.

The frequency distribution of the response function of the device is stored in advance in the digital operation and storage device of the frequency distribution, and the reflection coefficient of the subject is calculated using the formula (1) from the frequency distribution of the reflected wave obtained in the subject. Then, the frequency distribution of the obtained reflection coefficient is calculated from 0MHz to 30MHz in green, and from 30MHz to 60MH.
By setting up to z in blue and from 60MHz to 100MHz in red, the settings were made to send the signal to be displayed on the color monitor screen by converting the integrated value of the reflection coefficient in each frequency region into the brightness of the corresponding color. As described above, the spectrum ultrasonic microscope is set so that the characteristic of the frequency distribution of the reflection coefficient at each point on the surface of the subject is expressed by the color, and the entire surface of the subject is observed by the XY stage drive device.

As a result of the measurement, the subject was roughly classified into two regions, a region expressed in yellow on the color monitor screen and a region expressed in green. After this observation, the chemical composition ratio of each part of the subject was examined by using a chemical analyzer, and the area displayed in yellowish color on the color monitor screen had a different chemical composition ratio from the area expressed in green. It turned out that

<Effects of the Invention> As described above, according to the present invention, the surface of the subject is exposed to X-
While performing Y-scan, a wide-band ultrasonic wave is incident on the subject at a constant angle of incidence, the reflected wave is sampled, and the frequency distribution can be obtained and calculated and stored. And can be observed quantitatively,
It is used as an extremely versatile measuring device.

Further, according to the second aspect of the present invention, it is possible to quantitatively measure the acoustic characteristics over two dimensions of the subject in a short time with sufficient spatial resolution.

[Brief description of drawings]

FIG. 1 is a block diagram of a typical embodiment of the present invention, FIG. 2 is a block diagram of a conventional ultrasonic microscope, and FIG. 3 is a block diagram when the V (z) curve method is performed by an ultrasonic microscope. FIG. 4 is an example of a frequency distribution having an output minimum, FIGS. 5A, 5B and C are explanatory views of how to obtain the reflection coefficient, and FIG. 6 shows a transducer set to a central incident angle θ1 and an incident angle width θ2. FIG. 7 is an explanatory diagram of a transducer having two incident angles θ1 and θ2 and an incident angle width θ3. 1 ... Broadband high frequency pulse oscillator 2 ... Transducer transmitter 3 ... Transducer receiver 4 ... Broadband amplifier 5 ... Frequency analyzer 6 ... Digital operation and storage device 7 ... Image output device 8 …… XY stage drive device 9 …… High frequency oscillator 10 …… Piezoelectric body 11 …… Delay material 12 …… Ultrasonic wave propagation liquid 13 …… Subject 14 …… Circulator 15 …… Amplifier 16 …… Output Detector 17 …… Image output device 18 …… XY stage driver 19 …… Acoustic lens 20 …… Output detector 21 …… V (z) curve output analyzer 22 …… Z stage driver 23 …… Reflector Coefficient minimum frequency 24 …… Frequency distribution that does not have a peculiar minimum 25 …… Frequency distribution obtained in the subject 26 …… Reflectance of the obtained subject 27 …… Minimum reflectance of the obtained subject Frequency 28 ... the basis of the subject 29 …… Subject film 30 …… Ultrasonic wave propagation liquid 31 …… Center incident angle 32 …… Incident angle width 33 …… Ultrasonic wave propagation liquid 34 …… Central incident angle θ1 35 …… Central incident angle θ2 36 ...... Incident angle width θ3

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Claims (2)

[Claims] 1. A means for oscillating a wide-band high-frequency pulse,
A transducer that converts an oscillated electrical signal into a sound wave and makes it incident on the subject at a constant angle of incidence and receives the reflected wave, a means for analyzing the frequency of the obtained signal, and the characteristics of its frequency distribution quantitatively. Means for extracting or storing and moving the transducer with respect to the object parallel to the surface of the object, or oscillating and receiving the sound wave with respect to the object, in parallel with these steps. It has a driving means to move the frequency analysis process two-dimensionally in synchronization with each other, and the information of the frequency distribution depending on the incident angle of the ultrasonic wave at each point of the subject to the sample or the quantitative information obtained from it. Spectrum ultrasonic microscope having means for outputting two-dimensional information of various subjects. 2. A means for oscillating a wide band high frequency pulse,
The angle of incidence is wide enough not to impair the characteristics of the frequency distribution depending on the angle of incidence, and the sound waves are focused on the surface of the object, or only the reflected wave component from the minute part is received. It is equipped with a transducer for receiving a reflected wave from only a region, a means for frequency-analyzing the obtained signal, and a means for quantitatively extracting or storing the characteristics of the frequency distribution thereof, and further interlocking with these steps. Driving means for moving the transducer with respect to the subject parallel to the surface of the subject or for moving the subject two-dimensionally with respect to the transducer by synchronizing the processes of oscillating and receiving sound waves and frequency analysis. It has two-dimensionally output the information of the frequency distribution depending on the incident angle of the ultrasonic wave at each point of the subject to the sample or the quantitative information of the subject obtained from it. Spectrum acoustic microscope, characterized in that it has a means.