JPH0731169Y2 - Ultrasonic probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an ultrasonic microscope for irradiating a sample with a focused ultrasonic beam and measuring the acoustic characteristics of the sample based on the reflected wave. It relates to an ultrasonic probe used.

[Prior Art] In recent years, an ultrasonic microscope has come to be used as a means of knowing the physical properties of the surface layer of an object (sample), such as the thickness of the surface layer and the magnitude of residual stress. The ultrasonic beam used in such an ultrasonic microscope needs to be focused. An ultrasonic probe (hereinafter, simply referred to as a probe) for emitting the focused ultrasonic beam is shown in FIG.
This will be described with reference to (b).

FIG. 2 (a) is a plan view of a conventional probe, and FIG. 2 (b) is a sectional view taken along line IIb-IIb shown in FIG. 2 (a). In each figure, 1 is an acoustic lens, 1a is an upper surface of the acoustic lens 1, and 1b is a concave surface of the lower portion of the acoustic lens 1. 2 is a piezoelectric element, 3a, 3
Reference numeral b is an electrode provided on both surfaces of the piezoelectric element 2. A vibrator is composed of the piezoelectric element 2 and the electrodes 3a and 3b. This vibrator is attached to the upper surface 1a of the acoustic lens 1 so that the piezoelectric element 2 is located at the center. In the figure, reference numeral 4 indicated by a broken line indicates a sample, Z indicated by an alternate long and short dash line represents a central axis of the acoustic lens 1, and B indicated by an alternate long and two short dashed line indicates an ultrasonic beam.

When a pulse voltage is applied between the electrodes 3a and 3b, the piezoelectric element 2 is excited and ultrasonic waves are generated. This ultrasonic wave is focused on the concave surface 1b of the acoustic lens 1 and is emitted to the sample 4 as a conical ultrasonic beam B, and the reflected wave from the sample 4 returns to the piezoelectric element 2 through the same path. The reflected wave causes the piezoelectric element to output an electrical signal proportional to the reflected wave, which is generated by the electrodes 3a, 3
It is taken out by b and is imaged through a predetermined process.
The inspection of the sample 4 can be performed by this image.

By the way, as described above, in recent years, means for investigating the physical properties of the surface layer of the sample 4 using focused ultrasonic waves has been developed.
This means will be described below. When the above-described operation is performed while the probe is brought close to the sample 4 along the Z-axis direction, the signal output from the piezoelectric element 1a has the waveform shown in FIG. In FIG. 3, the horizontal axis represents the distance (Z) in the Z-axis direction between the probe and the sample 4, and the vertical axis represents the voltage level (V) of the signal output from the piezoelectric element 2. There is. The distance (Z) between the probe and the sample 4 is 0 at a predetermined position of the probe, the direction in which the probe is away from the sample 4 is positive, and the direction in which the probe approaches is negative. . The waveform shown in FIG. 3 is called a V (Z) curve, and changes with a constant period ΔZ when the probe is close to the sample 4 by a certain distance or less.

As described above, the V (Z) curve changes with the period ΔZ is
When the sample 4 is irradiated with the ultrasonic beam B, the sample 4
This is because a surface acoustic wave is generated in the surface layer of, and the surface acoustic wave and the reflected wave of the ultrasonic beam B interfere with each other to generate an interference wave. The period ΔZ has a constant relationship with the propagation velocity of the surface acoustic wave propagating through the surface layer of the sample 4. That is, normally, a liquid medium such as water is interposed between the acoustic lens 1 and the sample 4, and when the speed of sound of this liquid medium is V _W and the wavelength of the sound wave in the liquid medium is λ _W ,
The propagation velocity V _R of the surface acoustic wave is expressed by the following equation.

V _R = V _W (ΔZ / λ _W ) ^1/2 (1) In the equation (1), the values V _W and λ _W are known, so V
By measuring the period ΔZ from the (Z) curve, the propagation velocity V _R of the surface acoustic wave can be obtained. The propagation velocity V _R changes depending on the physical properties of the surface layer of the sample 2, and thus the physical properties of the surface layer of the sample 4 can be known based on the propagation velocity V _R. For example, when the surface of the sample 4 is a processed surface, the residual stress and thickness of the processed layer can be known.

[Problems to be solved by the invention] By the way, some objects have anisotropy in their crystal structure, and it is strongly demanded to detect the acoustic velocity of surface acoustic waves in the direction of this anisotropy with an ultrasonic microscope. Has been done.
However, it is difficult for the above-described conventional ultrasonic microscope to meet such a demand. That is, the above V (Z)
The curve is detected in a minute portion of the sample 4, but the component of the ultrasonic beam B has its central axis Z (beam axis).
Since the sound velocity of the obtained surface acoustic wave is an average value in all directions because the sound velocity of the surface acoustic wave is all around, the detection of the sound velocity of the surface acoustic wave in the anisotropic direction of the sample 4 is impossible. Is.

For a sample having anisotropy, a probe using a cylindrical lens has been proposed to detect the sound velocity of the anisotropic surface acoustic wave. Such a probe will be described with reference to the drawings. FIG. 4 is a perspective view of a probe including a cylindrical lens. In the figure, 6 is a cylindrical lens, 6a is the upper surface of the cylindrical lens 6, and 6b is the concave surface below the cylindrical lens 6. The concave surface 6b is formed as a semi-cylindrical surface. Reference numeral 7 denotes a vibrator composed of a piezoelectric element and both electrodes sandwiching the piezoelectric element, which is attached to the upper surface 6a.

When such a cylindrical lens 6 is used, surface acoustic waves are generated in one direction (left and right direction in the figure), and if this direction and the anisotropic direction of the sample 4 are matched, different The speed of sound of the surface acoustic wave in the direction of the direction can be obtained.

However, since the probe uses the cylindrical lens 6, the surface on the sample 4 on which the ultrasonic beam is incident is inevitably dispersed in the cylindrical length portion of the concave surface 1b formed in a semi-cylinder, The sound velocity of the surface acoustic wave detected is the average value of the sound velocity of the surface acoustic wave of each part along the length of the cylinder,
It is impossible to obtain the accurate sound velocity of the surface acoustic wave at a predetermined point.

An object of the present invention is to solve the above problems of the prior art and to provide an ultrasonic probe capable of detecting the sound velocity of a surface acoustic wave in an anisotropic direction in a predetermined minute region of a sample.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an acoustic lens and a transducer attached to the acoustic lens, and an ultrasonic beam focused at one point by the excitation of the transducer. In the radiating ultrasonic probe, the transducer is arranged in a center of an acoustic lens and two transducers arranged symmetrically with respect to the center of the transducer to focus the radiated ultrasonic wave at a Rayleigh critical angle. A plurality of sets of other oscillators, each of which is another set, is configured to simultaneously excite the oscillator arranged at the center and the other oscillators of the set, and receive signals of the respective oscillators. Are combined to form one received signal.

[Operation] One or both of the oscillator arranged in the center of the acoustic lens and the other oscillators in a set by aligning the arrangement direction of the oscillators in the set with the anisotropic direction of the sample. When and are simultaneously excited, the ultrasonic wave from the former transducer returns as a normal reflected wave, and the ultrasonic wave from the other or both of the latter transducer returns as a reflected surface acoustic wave. Accordingly, if the reflected wave signals of the transducers are combined for each distance between the probe and the sample, the V (Z) curve in the anisotropy direction in the minute portion of the sample can be obtained, Based on this, the speed of sound of the surface acoustic wave in the relevant direction can be obtained.

[Examples] Hereinafter, the present invention will be described based on illustrated examples.

FIG. 1A is a plan view of a probe according to an embodiment of the present invention,
FIG. 1 (b) is a sectional view taken along the line Ib-Ib shown in FIG. 1 (a). In the figure, 1 is the same acoustic lens as that shown in FIGS. 2 (a) and 2 (b). Reference numeral 9 is a disc-shaped electrode attached to the upper surface 1a of the acoustic lens 1. In this embodiment,
The piezoelectric element is divided into five and arranged on the electrode 9. Three of these piezoelectric elements 10b ₁ , 10b ₂ , 10c
The cross section of FIG. 1 appears in FIG. 1 (b). 11a ₁ , 11a ₂ , 11
b _1, 11b _2, 11c together with each electrode 9 is an electrode sandwiching the divided piezoelectric elements, there is a corresponding respective piezoelectric elements substantially the same shape. The piezoelectric element 10c and the electrode 11c are formed in a substantially disc shape, and are arranged at the center of the upper surface 1a of the acoustic lens 1 with the central axis Z of the acoustic lens 1 as the center. Piezoelectric elements 10a ₁ and 10a ₂ (none shown in the figure) and electrodes
11a ₁ and 11a ₂ are formed in a substantially fan shape, and are arranged symmetrically with respect to the axis Z in the peripheral portion of the upper surface 1a of the upper surface 1a of the acoustic lens 1. Further, the piezoelectric elements 10b ₁ and 10b ₂ and the electrodes 11b ₁ 11b ₂ are also formed in a substantially fan shape, and are arranged in the peripheral portion of the upper surface 1a of the acoustic lens 1 at positions symmetrical to each other with respect to the Z axis. Piezoelectric elements 10a ₁ and 10a ₂ , electrode 11
The arrangement of each set of a ₁ and 11a ₂ , the piezoelectric elements 10b ₁ and 10b ₂ , the electrode 11
The arrangement of each pair of b ₁ and 11b ₂ is shifted by about 90 degrees. A vibrator is composed of these piezoelectric elements and electrodes.

Next, the operation of this embodiment will be described. When a pulse voltage is applied simultaneously between the electrodes 11b ₁ and 11c and the electrode 9, the piezoelectric element 10
Ultrasonic waves are output from c, 10b ₁ . The ultrasonic wave output from the piezoelectric element 10c propagates along the Z axis at the center of the acoustic lens 1 and is incident on the sample 4 substantially vertically. Therefore, this ultrasonic wave does not generate a surface acoustic wave in the sample 4, is reflected as it is, returns through the propagation path, and reaches the piezoelectric element 10c.

In contrast, the ultrasonic wave output from the piezoelectric element 10 ₁ passes through the peripheral portion of the acoustic lens 1 and radiated to the focusing direction by the concave 1b. Therefore, the emitted ultrasonic waves are incident on the sample 4 at a certain angle. This angle is an angle determined by the sample 4 (the Leeley critical angle), and the ultrasonic wave incident on the sample 4 at this angle propagates inside the sample 4 as a surface acoustic wave. Position of the shape and the piezoelectric elements 10b ₁ of the acoustic lens 1 is preselected as ultrasonic piezoelectric element 10b ₁ emitted from the acoustic lens 1 is incident at the critical angle of the Rayleigh the sample 4. In this way, the ultrasonic wave from the piezoelectric element 10b ₁ becomes a surface acoustic wave in the sample 4, and this surface acoustic wave returns from the surface of the sample 4 to the acoustic lens 1 again. However, since this surface acoustic wave returns at the same angle in the opposite direction to the incident angle with respect to the normal line of the surface of the sample 4, the piezoelectric element 10b ₂ is excited instead of the piezoelectric element 10b ₁ .

After all, the piezoelectric element 10c is excited by the direct reflected wave of the ultrasonic wave, and the piezoelectric element 10b ₂ is excited by the reflected wave of the surface acoustic wave, so that the electric signals output from both electrodes 11b ₂ and 11c are transmitted. If synthesized, the same interference wave data as the conventional probe can be obtained.

As described above, in this embodiment, since the oscillators divided into the center of the upper surface 1a of the acoustic lens 1 and the symmetrical position with respect to this center (the position for transmitting and receiving ultrasonic waves at the Rayleigh critical angle) are arranged, The two transducers are arranged in the same direction as the anisotropic direction of the sample 4, and ultrasonic waves are output from one of the center transducer and the symmetrical transducer.
In addition, if the reflected wave signal is received by the other vibrator of the vibrator at the center and the vibrator at the symmetrical position, the reflected wave signals are combined, and this is performed at each position in the Z-axis direction between the probe and the sample 4. , V (Z) curve for the anisotropic direction of Sample 4 can be obtained. In this case, the acoustic lens 1 emits one ultrasonic beam.
Since it has a property of focusing on a point, it is possible to inspect a specific minute region of the sample 4.

By the way, the V (Z) curve is a reflected wave of ultrasonic waves radiated to the sample at an angle other than the Rayleigh critical angle and a reflected wave of ultrasonic waves radiated to the sample at the Rayleigh critical angle (surface acoustic wave). If the signal levels of the two reflected waves are almost the same, the difference between the peaks and valleys of the V (Z) curve becomes large, and the period ΔZ can be obtained with high accuracy. But,
If one signal level is lower than the other signal level, the difference between the peaks and valleys of the V (Z) curve becomes small, and the cycle ΔZ cannot be obtained accurately. Further, the ratio of the signal levels of the two differs depending on the reflection level of the sample and the critical angle of Rayleigh and is not always constant.

In this example, since the oscillator that radiates ultrasonic waves at an angle other than the Rayleigh critical angle and the oscillator that radiates ultrasonic waves at the Rayleigh critical angle were separated, depending on the reflection level of the sample and the Rayleigh critical angle. By selecting the size (diameter) of the vibrator arranged at the center, the both signal levels can be made substantially the same level, and the cycle ΔZ can be accurately obtained.

In the description of the above embodiment, one set of piezoelectric elements 11
Although an example in which ultrasonic waves are output from the piezoelectric element 11b ₁ using b ₁ and 11b ₂ and the reflected wave is input to the piezoelectric element 11b ₂ has been described, the input and output may be reversed, or both may be simultaneously applied. You can also input and output. Further, it goes without saying that another set of piezoelectric elements 11a ₁ and 11a ₂ may be used depending on the anisotropic direction.

Furthermore, the shape of each piezoelectric element and electrode is not limited to a circular shape or a fan shape, and may be any shape. Further, the number of piezoelectric element and electrode groups is not limited to two, and a plurality of groups may be provided. You can Further, the piezoelectric element may not be divided and only one electrode may be divided, or the piezoelectric element and the electrodes sandwiching the piezoelectric element may be divided.

Also, if the number of sets to be divided is increased, it is possible to cope with the anisotropy of the sample in various directions without rotating the probe, but on the other hand, the received signal level is also lowered. U To avoid this, if the number of groups to be divided is reduced and the probe can be rotated by an angle corresponding to the number, it is possible to secure a sufficient received signal level, and also to make the difference in all directions. It can also be used for orientation.

[Advantages of Device] As described above, in the present embodiment, the probe is divided into the transducer arranged in the center of the acoustic lens and the plurality of sets of transducers arranged in symmetrical positions. Therefore, the sound velocity of the surface acoustic wave in the anisotropic direction of the sample can be detected in the minute region. Further, by selecting the size of the oscillator arranged at the center according to the reflection level of the sample and the critical angle of Rayleigh, both signal levels can be made almost the same level, and the cycle ΔZ can be obtained accurately. be able to.

[Brief description of drawings]

1 (a) and 1 (b) are plan views and sectional views of a probe according to an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are plan views of a conventional probe, respectively. A sectional view, FIG. 3 is a waveform diagram of a V (Z) curve, and FIG. 4 is a perspective view of a cylindrical lens. 1 ... Acoustic lens, 9,11a ₁ , 11a ₂ , 11b ₁ , 11b ₂ , 11c ……
Electrodes, 10b ₁ , 10b ₂ , 10c ... Piezoelectric element, 4 ... Sample.

Claims (4)

[Scope of utility model registration request] 1. An ultrasonic probe comprising an acoustic lens and a transducer attached to the acoustic lens, and radiating an ultrasonic beam focused at one point by exciting the transducer, wherein the transducer is the acoustic lens. The oscillator placed in the center of
This oscillator is composed of a plurality of sets of other oscillators, one set of which is a set of two other oscillators arranged at symmetrical positions with respect to the center of the oscillator and converging the radiated ultrasonic waves at the Rayleigh critical angle. The ultrasonic probe is characterized in that the transducer and the other transducer of the set are simultaneously excited, and the reception signals of the respective transducers are combined into one reception signal. 2. The oscillator according to claim 1, wherein
An ultrasonic probe comprising a piezoelectric element and electrodes provided on both surfaces of the piezoelectric element. 3. The ultrasonic probe according to claim 2, wherein the piezoelectric element and one of the electrodes are divided for each transducer, and the other of the electrodes is a common electrode. Tentacles. 4. The super device according to claim 2, wherein one of the electrodes is divided for each of the vibrators, and the other of the piezoelectric element and the electrode is commonly used for each of the vibrators. Sonic probe.