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JPH02300658

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DESCRIPTION JPH02300658
[0001]
[Industrial field of application] The present invention is directed to an ultrasonic microscope used
in an ultrasonic microscope which irradiates a sample with a focused ultrasonic beam and
measures the acoustic characteristics of the sample based on the reflected wave. It relates to a
tentacle. 2. Description of the Related 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 outline of this
ultrasonic microscope will be described with reference to the drawings. FIG. 5 is a system
diagram of an ultrasonic microscope. In the figure, x, 'y, z indicate coordinate axes (Y axis is
perpendicular to the paper surface). An ultrasonic probe (sensor) 1 comprises a piezoelectric
element 1a and an acoustic lens 1b attached thereto. 2 is a sample to be inspected by an
ultrasonic microscope, 3 is a sample table on which the sample 2 is placed, 4 is a Y-axis scanning
device for moving the sample table 3 in the Y-axis direction, 5 is an xy axis of the sample 2 Is an
xy positioning device that performs positioning of Reference numeral 6 denotes a scan control
device, which controls driving of the X-Y positioning device 5 and the Y-axis scanning device 4
and controls driving of the sensor 1 in the X-axis and Z-axis directions. The driving mechanism of
the sensor 1 is not shown. Reference numeral 7 denotes a liquid medium, such as water,
interposed between the sensor 1 and the sample 2. A high frequency pulse oscillator 9 applies a
high frequency pulse voltage to the piezoelectric element 1a, a receiver 10 receives and
processes a signal from the piezoelectric element 1a, and a display 11 displays an image based
on the signal processed by the receiver 10. is there. 6 is a perspective view of the sensor 1 shown
in FIG. In the figure, the same parts as those shown in FIG. As apparent from the figure, the
ultrasonic wave generated by the piezoelectric element 1a propagates in the acoustic lens lb, is
focused by the lower concave surface, and is irradiated to the sample 2 as a point-like focused
ultrasonic beam B. Immediately, the illustrated acoustic lens 1b is a point focusing lens. Here,
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when a pulse voltage is applied to the piezoelectric element 1a from the high frequency pulse
oscillator 9 shown in FIG. 5, the piezoelectric element 1a generates an ultrasonic wave, and the
ultrasonic wave is focused by the acoustic lens b as described above. It is emitted as a focused
ultrasound beam B. The ultrasonic beam B is irradiated to the sample 2, and the reflected wave
returns to the radiation path and reaches the piezoelectric element 1a. Due to the arrival of the
reflected wave, the piezoelectric element 1a outputs an electrical signal proportional to the
magnitude of the offending wave. The receiver 10 receives the electric signal, amplifies and
detects it, and then uses this signal as a luminance modulation signal to display an image of one
pixel corresponding to the electric signal (ultrasound microscope) on the display device 11 ′ ′
Image) is displayed.
By moving the sample 2 by the scan control device 6 and performing two-dimensional scanning
with the ultrasonic beam B, a single ultrasonic image is obtained. By the way, as mentioned
above, in recent years, means for examining the physical properties of the surface layer of the
sample 2 (evaluating the material surface) using a focusing ultrasonic wave has been developed.
The means will be described below. When the above operation is performed while bringing the
sensor 1 close to the sample 2 along the Z-axis direction, the signal output from the piezoelectric
element 1a has a waveform shown in FIG. In FIG. 7, the abscissa represents the distance (Z)
between the sensor 1 and the sample 2 in the Z-axis direction, and the ordinate represents the
voltage level (V) of the signal output from the piezoelectric element 1a. It is. The distance (Z)
between the sensor 1 and the sample 2 is set to O at a predetermined position of the sensor 1,
and the direction in which the sensor 1 separates from the sample is positive and the direction in
which the sensor 1 approaches is negative. The waveform shown in FIG. 7 is referred to as a V
(Z) curve, and changes with a constant period ΔZ when the sensor 1 approaches a certain
distance or less on the sample 2. As described above, when the V (Z) curve changes at a period
ΔZ, when the sample 2 is irradiated with the ultrasonic beam B, a surface acoustic wave is
generated on the surface layer of the sample 2 and a radiation wave of this surface acoustic wave
is generated. And the opposite wave of the ultrasonic beam B interfere with each other. The
period ΔZ has a fixed relationship with the propagation velocity at which the surface acoustic
wave propagates. That is, assuming that the sound velocity of the liquid medium 7 is ■ 8, and
the waveform of the sound wave in the liquid medium 7 is λ, the propagation velocity VR of the
surface acoustic wave is expressed by the following equation %% (1). Since λ is known, the
propagation velocity of the surface acoustic wave can be obtained by measuring the period ΔZ
from the V (Z) curve. The propagation velocity {circle over (3)} changes according to the physical
properties of the surface layer of the sample 2, and therefore, the physical properties of the
surface layer of the sample 2 can be known based on the propagation velocity VR. For example,
when the surface of the sample 2 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, although
each object has different physical properties, it is desirable that any object can be measured by
an ultrasonic microscope. For example, some objects have anisotropy in their crystal structure,
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but even such objects have to be measured by an acoustic microscope. However, in the
conventional acoustic microscope using a point focusing lens as described above, the required
measurement for a sample having anisotropy is difficult.
That is, although the detection of the V (Z) curve is performed in a minute portion of the sample
2, the component of the ultrasonic beam B in the irradiation region is in all directions around the
central axis (beam axis) Therefore, the sound velocity of the obtained surface acoustic wave is an
average value in all the directions, and therefore, measurement of the sample 2 having
anisotropy is impossible. FIG. 8 is a perspective view of a special sensor for measurement of a
sample having such anisotropy. In the figure, la 'is a rectangular piezoelectric element and 1b' is
an acoustic lens. Since the acoustic lens 1b 'is also formed in a rectangular shape, the concave
surface formed in the lower part is a cylindrical surface. Such a cylindrical surface enables this
sensor to focus a linear ultrasonic beam in only one axial direction as shown, and therefore,
among the ultrasonic beams, the ultrasonic wave incident beyond the Rayleigh critical angle. The
beam can generate surface acoustic waves in only one direction on the surface of the sample 2. If
the propagation velocity of the surface acoustic wave is measured at each angle while rotating
the sample 2 as shown by the arrows, the anisotropy of the sample 2 can be determined and
measurement can be performed along that direction. However, the sensor not shown in FIG. 8
has the following problems. That is, since this sensor is a uniaxial focusing structure, there is a
limit to reducing the length I of the acoustic lens lb 'in the long-side direction, which is usually
about 21 m. For this reason, the ultrasonic information obtained from this sensor 6 is an average
value between the two records. On the other hand, the ultrasound microscope is configured to
capture changes in the elastic properties of the substance from a very small area to obtain an
ultrasound microscope image, and thus, when the irradiation area on the sample 2 is also 2111,
It will not be possible to obtain the desired ultrasound microscopy image. That is, the acoustic
lens 1b '(line focusing lens) shown in FIG. 8 can measure the anisotropy of the sample but can
not obtain an ultrasonic microscopic image of the sample. For this reason, the measurer who
performs measurement with an ultrasonic microscope has performed measurement by
exchanging the point focusing lens and the line focusing lens as needed, but such exchange
requires much time and effort and time. There is a problem that the burden on the measurer is
increased and the efficiency of the measurement operation is significantly reduced. Furthermore,
in the case of measurement using a line focusing lens 1b ', the surface of the sample 2 and the
focal plane of the linear ultrasonic beam must be completely parallel, with a slight tilt between
them. An error occurs in measurement accuracy. The allowable angle of this inclination is 1/100
degrees, and it takes a long time to make both inclinations equal to or less than the allowable
angle, which further increases the burden on the measurer and the decrease in efficiency of the
measurement operation. There was also.
The object of the present invention is to solve the problems in the above-mentioned prior art, and
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it is possible to measure anisotropy and acquire an ultrasonic microscope image without
replacing the probe, thereby reducing the burden on the measurer and performing measurement
An object of the present invention is to provide an ultrasonic microscope probe which can
improve the efficiency of operation. [Means for Solving the Problems] In order to achieve the
above object, the present invention provides an element for transmitting and receiving an
ultrasonic wave, and an ultrasonic beam generated by point-focusing an ultrasonic wave
generated by the element with respect to a sample. In a probe of an ultrasonic microscope
provided with an acoustic lens for emitting light, a lens surface of the acoustic lens is covered
with a sound absorbing material except a slit-like non-coated portion. [Operation] The ultrasonic
waves generated by the element transmitting and receiving the ultrasonic waves are focused by
the acoustic lens and emitted as a focused ultrasonic beam from the slit-like portion. In this case,
the incident angle of the ultrasonic beam focused in the width direction of the slit-like portion is
smaller than the Rayleigh critical angle and no surface acoustic wave is generated. On the other
hand, the ultrasonic beam focused in the longitudinal direction of the slit-like portion has a
portion having an incident angle larger than the Rayleigh critical angle, and the beam of this
portion generates a surface acoustic wave in the surface layer of the sample. Therefore, surface
acoustic waves in only one direction are generated. And, since the acoustic lens is a point
focusing type, the critical region of the sample is minute. Therefore, both the measurement of the
anisotropy and the acquisition of the ultrasound microscopy image can be performed with one
probe. The present invention will be described below based on the illustrated embodiments. 1 (a)
i, (b) are a cross-sectional view and a bottom view of a probe (sensor) of an acoustic microscope
according to a first embodiment of the present invention. In the figure, the same parts as those
shown in FIG. In this embodiment, the sound absorbing material is attached to the lens surface
(concave surface) of the bottom of the point focusing type acoustic lens 1b, leaving a part.
Reference numeral 13 denotes a sound absorbing material layer made of the attached sound
absorbing material, and 14 denotes a portion to which the sound absorbing material is not
attached. The portion 14 is formed in a slit shape long in one direction as shown in FIG. 1 (b).
That is, the portion 14 is a curved slit-like surface. The ultrasonic wave generated by the
piezoelectric element 1a is emitted as a beam only at the portion 14 and the one reaching the
sound absorbing material layer I3 is absorbed by the sound absorbing material layer 13 and is
not emitted to the outside. FIGS. 2 (a) and 2 (b) are a sectional view and a bottom view of a
sensor of an ultrasonic microscope according to a second embodiment of the present invention.
The lens surface of this embodiment leaves the slit-shaped portion 14 and the sound absorbing
portion lfA '13' is attached to the other portion. Also in this embodiment, as in the first
embodiment, only the ultrasonic waves reaching the portion 14 are emitted, and the ultrasonic
waves reaching the sound absorbing member 13 'are absorbed by the sound absorbing member
13'. Next, the operation of each of the above embodiments will be described with reference to
FIGS. 3 and 4. The operation of each embodiment is the same. 3 is an enlarged view of the lens
surface portion in the cross sectional view shown in FIG. 1 (a) and FIG. 2 (a), and FIG. 4 is a line
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shown in FIG. 1 (a) and FIG. 2 (a) It is an expanded sectional view of the lens surface portion in
the section which meets V-IV. The description of the sound absorbing material layer 13 and the
sound absorbing member 13 'is omitted in each of the drawings. Reference numeral 2 denotes a
sample, and the description of the liquid medium interposed between the acoustic lens 1 b and
the sample 2 is also omitted. FIG. 3 is a view of the slit-shaped portion 14 in the width direction.
The ultrasonic waves reaching the portion 14 are emitted as an ultrasonic beam shown by a
broken line and focused on the focal point F. f indicates the focal length. As described above, the
maximum value of the radiation angle of the ultrasonic beam (opening angle of the lens in the
width direction) θmax when the width direction of the portion 14 is viewed is because the
portion 14 has a slit shape and the dimension in the width direction is small. Rayleigh critical
angle θ, smaller, thus no surface acoustic wave is generated. On the other hand, as shown in FIG.
4, when the length direction of the portion 14 is viewed, the maximum value of the radiation
angle of the ultrasonic beam emitted from the portion 14 (opening angle of lens in the length
direction) θ max Is larger than the Rayleigh critical angle .theta. Because there is no sound
absorbing material layer 13 or sound absorbing member 13 '. Then, the ultrasonic beam B
emitted at an angle near the Rayleigh critical angle θ 8 (shown by a solid line in FIG. 4) is a
surface elastic wave (FIG. 4 in FIG. 4) when it is incident on the sample 2. Generate a solid line B
'+). Taken together, the ultrasonic beam emitted from the slit-shaped portion 14 generates
surface acoustic waves in the longitudinal direction of the slit-shaped portion 14 in the surface
layer of the sample 2 but not in the other direction. That is, surface acoustic waves can be
generated only in one direction, and measurement of the anisotropy of the sample 2 becomes
possible. Moreover, since the acoustic lens 1b is originally a point focusing type lens, the
irradiation area on the sample 2 is also minute (therefore, the surface acoustic wave is also
generated in the minute area), and thereby an ultrasonic microscope image Can be obtained
without problems.
As described above, in each of the above embodiments, the slit-shaped ultrasonic wave
transmitting portion is formed on the lens surface of the point focusing type acoustic lens, and
the radiation of the ultrasonic wave from the other portion is absorbed by the sound absorbing
material layer or the sound absorbing member As a result, measurement with respect to
anisotropy and acquisition of an acoustic microscope image can be performed with one sensor,
and in measurement with respect to anisotropy, adjustment for maintaining parallelism is not
necessary. As a result, the burden on the measurer is greatly reduced and the efficiency of the
measurement operation is greatly improved. In the description of each of the above
embodiments, an example has been described in which the portion in the lengthwise direction of
the slit shape is the entire lens surface of that portion, but covering the end of the lens surface in
the lengthwise direction with a sound absorbing material Naturally, it is possible to freely select
the size in the length direction and the size in the width direction in consideration of the
characteristics of the acoustic lens. As described above, according to the present invention, since
the lens surface of the point focusing type acoustic lens is covered with the sound absorbing
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material except for the slit-shaped non-covered portion, it is possible to use a single probe. It is
possible to measure anisotropy and to collect an ultrasonic microscope image, and it is not
necessary to adjust parallelism when measuring anisotropy, which greatly improves the burden
on the measurer. 'I can do it.
[0002]
Brief description of the drawings
[0003]
1 (aL (b), 2 (a) and 2 (b) are respectively the first embodiment of the present invention.
Sectional view and bottom view of a probe of an ultrasonic microscope according to the second
embodiment, FIGS. 3M and 4 are enlarged sectional views of a lens surface of an acoustic lens,
and FIG. 5 is a system diagram of a conventional ultrasonic microscope 6 is a perspective view of
the probe shown in FIG. 5, FIG. 7 is a waveform diagram of an ultrasonic signal obtained by
moving the probe, and FIG. 8 is a perspective view of another probe. is there. 1a · · · · · ·
Piezoelectric element, 1b · · · · · · · · · · · · · acoustic lens, 13 · · · · · sound absorbing material layer,
13 '· · · · · · · · · · · · · · · · · · · · · Slit shaped part. To 麹
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