JPH0251060A - Spectrum ultrasonic microscope - Google Patents

Abstract

PURPOSE:To observe the surface of an object to be inspected quantitatively with a two-dimensional outputting of information on an object to be inspected by a method wherein a wide-range ultrasonic wave enters at a fixed angle of incidence making an X-Y scanning of the surface of the object to be inspected to sample reflected wave thereof and a frequency distribution is obtained to be computed and stored. CONSTITUTION:An an output of a wide-range high frequency pulse oscillator 1, an ultrasonic wave enters an object to be inspected from an oscillating section 2 and reflected wave thereof is received with a receiving section 3. An output of the receiving section 3 is inputted into a wide-range amplifying section 4 and undergoes a frequency analysis with a frequency analyzer 5 comprising a spectral analyze to be converted into digital from analog. Thus, a frequency distribution thus obtained undergoes a frequency distribution digital computation made with a computer and a feature extraction programed by an operator with a memory 6and the results are stored and displayed on an image output device 7. An X-Y scanning is performed for an X-Y stage driver8 linked to a sample base synchronizing a signal of the oscillator 1. This enables a short-time measurement of a film thickness distribution, film thickness and detection of cracking and peeling and the like.

Description

[Detailed description of the invention] <Industrial application field> Regarding spectrum ultrasound microscopy performed in between.

<Conventional technology> In recent years, piezoelectric materials have been used to oscillate ultrasonic waves and perform sound detection. The subject through the liquid for ultrasound propagation is refracted by lenses.

An ultrasonic microscope has been developed that displays the elastic properties of the object in two dimensions by scanning the surface of the object in an X-Y manner while converging on the surface and obtaining the output of the reflected or transmitted waves. .

To give an overview of a typical ultrasonic microscope, as shown in Fig. 2, a high frequency burst signal is created using a high frequency oscillator 9 that oscillates at a constant frequency of several tens to several hundred MHz.
A voltage is applied to the piezoelectric body 10. The high-frequency burst signal is converted into a sound wave by a piezoelectric material (a device that converts the applied electric signal into a sound wave and enters the subject, and converts the reflected sound wave back into an electric signal is called a "transducer"). It propagates through a delay material 11 made of fused silica, sapphire, etc., is refracted by the difference in sound speed between the delay material and the ultrasonic propagation liquid 12, and is focused onto the subject 13. The reflected wave of the sound wave reflecting the acoustic properties of the sample is emitted again into the ultrasonic propagation liquid 12, phase-matched by the delay material 11, and then converted into an electric signal by the piezoelectric body 10 again. The obtained electrical signal is amplified and diode-detected, and the output is used as a video signal.

Displayed as a two-dimensional reflection intensity image.

Conventional ultrasound microscopes irradiate the subject with sound waves of a certain frequency through an acoustic lens at a wide angle of incidence, including the vertical component, and the reflected waves of1. ib: Most display the output as brightness and darkness of the image.\5,2,[ Energy leakage due to surface acoustic waves toward the deep force of the substrate, and energy is detected from the position of the transducer as surface acoustic waves. The output can only be obtained as a result of integrating the effects of many phenomena, such as the phenomenon of reflected wave components escaping into impossible regions, and it always provides only the relative output relationship within one image. As described above, today's ultrasound microscopes have difficulties in performing quantitative measurements due to their principles.

There is a method based on the ■(z) curve method described in Japanese Patent Application Laid-Open No. 61-20857 that allows quantitative measurement using an ultrasonic microscope. 1'! propagating on V(z) and onto the surface of the subject without mechanical scanning such as that due to interference of re-emitted components. 1＼・The sound velocity of the excited surface acoustic wave or the surface acoustic wave is
- If the frequency of the excited ultrasonic wave is obtained accurately as an absolute value and in a short time with two-dimensional high resolution on the sample surface, it is possible to quantitatively obtain the film thickness or crack depth from such information. This makes it a useful evaluation device in a wide range of fields, such as destructive inspection means in current precision machining and physical property research.

<Problem to be solved by the invention> It takes a huge amount of time to create a point transducer with high accuracy (it needs to be moved up and down). There was a problem that it took a while.

Means for Solving the Problems> The present invention has been made in consideration of the above problems, and includes a means for oscillating a broadband high-frequency pulse, a transducer for making the oscillator enter a body, and receiving the reflected wave. We have developed a method for frequency analysis of the obtained signals, quantitatively extracting or observing changes in the characteristics of the frequency distribution, and are able to provide important information for actual non-destructive testing and physical property research. Obviously, the frequency of the reflected wave depends on the angle of incidence of the transducer on the sample, or the structural parameters such as the thickness, or the presence of cracks or peeling.
This makes it possible to measure and detect infarction two-dimensionally and quantitatively on the surface of a subject.

If the frequency distribution of the reflected wave and the frequency dependence of the reflection coefficient are obtained, it can be obtained using equation (1).

PI (θ, f) R (θ f ) P2 (θ f ) ... (1) Here, P2 is the frequency distribution of the response function of the device, and Pl is the frequency distribution of the reflected wave at the test object. This is the frequency distribution. 1 If the incident angle θ is kept 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 Figure 4, when the reflection coefficient has a minimum at a certain frequency 23 as a function of physical property constants or structural parameters, the constant information that takes the minimum reflection coefficient has an influence on the energy of the entire reflected wave. ``You can get without receiving.

In this way, unlike conventional ultrasound microscopes that use the relative value of output within the screen as information, the spectrum ultrasound microscope of the present invention uses the reflected waves at each point on the surface of the subject. By using the shape of the frequency distribution as the measurement target, the surface condition of the test object and the transformer 1! After removing the electrical and mechanical instability factors of the characteristics of the Juicer and the entire device, we investigated the frequency detection frequency dependence of the reflected waves at various incident angles of ultrasonic waves with respect to the sound waves specific to the subject. Even if the angle of incidence has a certain range depending on the physical properties and structure of the object, the shape of the frequency distribution will be almost the same as when the incidence is at the center of the spread of the angle of incidence. By making the shape of the transducer as shown in Figure 6, it is possible to focus the ultrasonic waves on the surface of the subject and observe an area narrower than the area of the piezoelectric material of the transducer. It is possible to obtain images with high resolution.

<Example> The present invention will be described in detail below with reference to the drawings and examples.

Figure 1 shows an example of a block diaphragm for a spectrum ultrasound microscope.

An impulse transmitter is used as a wideband high-frequency pulse transmitter 1, and a transducer is installed to inject ultrasonic waves into a subject and receive reflected waves.

The receiving section 3 of the transducer is connected to a broadband amplifier 4, and the amplified signal is frequency-analyzed by a frequency analyzer 5 consisting of a spectrum analyzer.
converted. The obtained frequency distribution is subjected to feature extraction programmed by the operator by a frequency distribution digital calculation and storage device 6 comprised of a computer and stored, and then the result is displayed on an image output device 7. The X-Y stage drive device 8 connected to the sample stage is subjected to X-Y scanning in synchronization with the signal output from the impulse oscillator.

The following measurements were possible with the apparatus configured as described above.

Ultrasonic waves are incident on a sample consisting of a membrane at a certain angle of incidence determined by the combination of the substrate, membrane, and ultrasonic propagation liquid,
If there is a frequency at which the reflectance becomes minimum, we can find that the film thickness d and the minimum reflectance frequency f have the following relationship with a constant C determined by the combination of the substrate, film, and ultrasonic propagation liquid. I'm finding out.

f*d-C...(2) Store the frequency distribution 24 when sampled using the same transducer for those that do not exhibit a minimum due to singular absorption at a specific frequency at the incident angle. at the same angle of incidence as shown in Figure 5B.

Ryo! −・□
Assuming that a component of the 1゛ frequency distribution 25 of the reflected wave at each frequency obtained by the subject is obtained, subtracting the value of the frequency distribution 24 from the value of the frequency distribution 25 at each frequency results in the 5th component. As shown in Figure C, a frequency distribution 26 is obtained that clearly shows the minimum phenomenon unique to the subject. Obtain the frequency 27 that takes the minimum value in the obtained frequency distribution 26, and (
2) Calculate the film thickness d from the formula and set the magnitude of d to be bright and dark. When ultrasonic waves are incident on the monitor screen of the image output device at approximately 30 degrees, a surface wave called pseudo-elastic surface hemorrhage is excited on the surface of the subject. , is known to propagate while emitting energy to the substrate. From this, the incident angle of the sound wave of the transducer was set to 30 deg, and the frequency distribution digital calculation and storage device of the spectral ultrasound microscope was stored as shown in Figure 5A.
・5. - Set to obtain a film thickness distribution map for the entire surface of the subject, and use 1 drop.

As a result of the measurement, a high spatial resolution of 1·τ was achieved over the entire surface of the subject.
A two-dimensional film thickness distribution map was obtained using Z1, and later investigation by destructive inspection and inspection revealed that the film thickness distribution map obtained using a spectrum ultrasound microscope showed correct values. has been proven.

Furthermore, when an ultrasonic wave is incident on a sample containing a membrane at a certain angle of incidence determined by the combination of the substrate, membrane, and ultrasonic propagation liquid, waves called surface acoustic waves are strongly excited on the sample surface. In this case, if an extremely small area is irradiated with ultrasonic waves and the reflected sound waves are collected from that area, they will propagate as surface acoustic waves to areas that cannot be detected by the receiving transducer without emitting energy to the substrate. We found that only the frequency component that excited the surface acoustic wave was large, and the reflected wave output reached a minimum.

Therefore, as shown in Fig. 6, the central incidence angle is 40 degrees,
In the digital calculation and storage device for zero frequency distribution with a transducer set to an incident angle width of 4 degrees, as in the previous example, find the minimum frequency of the frequency distribution of the resulting reflected wave, and calculate the constant when the film is chromium and the substrate is copper. C was determined, the film thickness d was determined, and measurements were taken over the entire surface of the object.
As a result, by irradiating ultrasonic waves onto a very small area and collecting one reflected wave from that area, the phenomenon of the minimum reflected wave output appears greatly, and it is possible to accurately and quickly measure the thickness of the film under test. The film thickness was measured over the entire surface.

It is known that when a sample with a gold film deposited on a fused silica substrate is immersed in hydrochloric acid, the gold film peels off from many parts in a short time and in a small area due to the hydrochloric acid entering the boundary. .

However, until now it has been difficult to continuously observe this peeling process. For this purpose, hydrochloric acid was used as the ultrasound propagation medium, and measurements were performed using the spectrum ultrasound microscope of the present invention. When the film is peeled off from the substrate, the minimum phenomenon at a certain frequency in the reflected wave output, which existed when the film was in close contact due to the influence of pseudo surface acoustic waves propagating while leaking energy to the substrate, no longer occurs. Because we found
In the digital calculation and storage device of the frequency distribution, the monitor screen is displayed as 11 bright at the part of the subject where the minimum phenomenon occurred, and the monitor screen is displayed in darkness at the point where the minimum phenomenon did not occur. Equation (2) was performed.

Through this measurement, the peeling of the gold film was observed over time. Furthermore, after the observation, when the film thickness distribution was displayed as an image based on the minimum reflected wave output frequency stored in the spectrum ultrasound microscope, it was found that more peeling occurred from the thinner parts of the film.

If the relationship in equation (3) holds for a sample with a film formed on a substrate, it means that there is an intermediate layer made of different materials between the film and the substrate, or that the boundary is completely bonded. Collect the reflected waves in the region where the fused silica A gold film is deposited on top, and the incident angle θ1
=17. Odeg and incident angle θ2 - 25°Qdeg, and the incident angle width θ3 = 3deg. Using the birch sensor shown in Figure 7, set so that reflected waves can be collected independently at each incident angle. went.

Furthermore, it is determined whether equation (3) holds for fl and f2 obtained in advance, and if it does not hold, then
If it holds true, set the frequency distribution digital calculation and storage device to display darkness on both sides of the monitor as the state of the measurement point, and perform the measurement7. - As a result, a bright area was observed on the replacement object, so a destructive test was conducted to confirm the presence of an oil film in the area where the bright color was displayed on both sides of the monitor fl f2 ≠ fl' f2.

Ta.

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

The frequency distribution digital calculation and storage device further stores the frequency distribution of the obtained reflection coefficient from OMHz to 30MHz.
up to green, 30MHz to 60MHz blue, 6
An area represented by a --shape indicates settings for converting the integral value of the reflection coefficient in each frequency range into the luminance of the corresponding color and sending a signal to be displayed on the color monitor screen, with the range from 0MHz to 100MHz in red. The area is roughly divided into two areas, the area shown in green. After this observation, the subject;
When we investigated the chemical composition ratio of each part of the body using a chemical analyzer, we found that the areas represented as yellowish <- on the color monitor screen had a different chemical composition ratio than the areas represented as green. found.

<Effects of the Invention> As explained above, according to the present invention, the surface of the subject is
While performing Y-scanning, ultrasonic waves in a wide range of 5 areas are incident on the subject at a constant angle of incidence, and the reflected waves can be collected and quantitatively observed.It is used as an extremely versatile measurement device. Ru.

The spectrum ultrasound microscope was set to express the characteristics of the frequency distribution by color, and the entire surface of the subject was observed using the x-Y stage drive device.The measurement results were displayed on the color monitor screen. Additionally, it can be measured quantitatively at 1°.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a typical embodiment of the present invention, Figure 2 is a block diagram of a conventional ultrasound microscope, and Figure 3 is a block diagram when the V(z) curve method is performed using an ultrasound microscope. Fig. 4 is an example of a frequency distribution with an output minimum, Fig. 5, A, B, and C are explanatory diagrams of how to obtain the reflection coefficient, and Fig. 6 is set to the center incident angle θl and the 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. l...J...Broadband high frequency pulse oscillator 2...
Transducer transmitting section 3... Transducer receiving section 4... Broadband amplifier 5... Frequency analyzer 6... Digital calculation and storage device 7...
・Image output device 8...X-Y stage drive device 9...
High frequency oscillator IO... Piezoelectric material l... Delay material 2... Liquid family for ultrasonic propagation 3... Test object 4... Circhierator 5...Amplifier 6...Output detection device 7...Image output device 8...X-Y stage drive device 9...・
Acoustic lens 0...Output detection device l...V(z) curve output analysis device 2...
・Z stage drive device 3...Reflection coefficient minimum frequency 4...Frequency distribution ridge with no peculiar minimum 5...Frequency distribution obtained in the subject 26 ...Reflectance of the obtained test object 27 ... Frequency at which the obtained reflectance of the test object is minimized 28 ... Substrate 9 of the test object... ...Membrane of subject 0 ... Liquid for ultrasound propagation 1 ... Center incidence angle 2 ... Incident angle width 3 ... Ultrasonic propagation Liquid 4... Central incident angle θ1 5... Center incident angle θ2 6... Incident angle width θ3 Patent Permission Applicant Toppan Printing Co., Ltd. Representative Kazuo Suzuki No. 1 Figure 2 Figure 4 Figure 10 J5 Figure C

Claims (1)

[Claims] 1) means for oscillating a broadband high-frequency pulse, a transducer for converting the oscillated electrical signal into a sound wave, making it incident on a subject at a constant angle of incidence, and receiving the reflected wave; It is equipped with a means for frequency analysis of the detected signal and a means for quantitatively extracting or storing the characteristics of the frequency distribution. It has a drive means that moves the object two-dimensionally with respect to the transducer by synchronizing the processes of oscillation and reception of sound waves and frequency analysis, and has a driving means that moves the object two-dimensionally with respect to the transducer, and the ultrasonic wave at each point of the object moves the object two-dimensionally. 1. A spectrum ultrasound microscope characterized by having means for two-dimensionally outputting information on a frequency distribution depending on the incident angle or quantitative object information obtained from the information. 2) A means of oscillating a broadband high-frequency pulse, and converging the sound wave on the surface of the object by giving a width to the angle of incidence to an extent that does not impair the characteristics of the frequency distribution that depends on the angle of incidence, or emitting reflected wave components from minute parts. A transducer that receives reflected waves from only a minute region of a subject by a method such as receiving only a small area of the subject, a means for frequency analysis of the obtained signal, and a means for quantitatively extracting or storing the characteristics of the frequency distribution. Furthermore, in conjunction with these steps, the transducer is moved relative to the object parallel to the surface of the object, or the object is moved relative to the transducer, and the steps of emitting and receiving sound waves and frequency analysis are performed. It has a driving means for synchronized two-dimensional movement, and provides information on the frequency distribution depending on the angle of incidence of ultrasonic waves on the sample at each point of the object, or quantitative information on the object obtained from it. A spectrum ultrasonic microscope characterized by having means for outputting in two dimensions.