JPH06100585B2 - Ultrasound microscope probe - Google Patents

Description

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. The present invention relates to a probe of an ultrasonic microscope used.

[Conventional technology]

In recent years, an ultrasonic microscope has come to be used as a means for 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 systematic diagram of an ultrasonic microscope. In the figure, X, Y, and Z indicate coordinate axes (Y axis is perpendicular to the paper surface). An ultrasonic probe (sensor) 1 is composed of a piezoelectric element 1a and an acoustic lens 1b to which the piezoelectric element 1a is attached. 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, and 5 is on the X and Y axes of the sample 2. It is an XY positioning device for positioning. 6 is a scanning control device, which is an XY positioning device 5
And controlling the Y-axis scanning device 4 and driving the sensor 1 in the X-axis and Z-axis directions. The drive 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. Reference numeral 9 is a high-frequency pulse oscillator that applies a high-frequency pulse voltage to the piezoelectric element 1a, 10 is a receiver that receives and processes the signal from the piezoelectric element 1a, and 11 is a display device that displays based on the signal processed by the receiver 10. is there.

FIG. 6 is a perspective view of the sensor 1 shown in FIG. In the figure,
The same parts as those shown in FIG. 5 are designated by the same reference numerals. As is clear from the figure, the ultrasonic wave generated by the piezoelectric element 1a propagates in the acoustic lens 1b, is focused on the lower concave surface, and is irradiated onto the sample 2 as a point-shaped focused ultrasonic beam B. That is, the illustrated acoustic lens 1b is a point focusing lens. Here, 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 generated by the acoustic lens 1b as described above.
And is emitted as a focused ultrasonic beam B. The ultrasonic beam B is applied to the sample 2, and the reflected wave returns to the radiation path and reaches the piezoelectric element 1a. Upon arrival of this reflected wave, the piezoelectric element 1a outputs an electric signal proportional to the magnitude of the reflected wave. The receiver 10 receives the electric signal, performs amplification and detection, and then uses this signal as a brightness modulation signal to display an image of one pixel corresponding to the electric signal on the display device 11 (an ultrasonic microscope image). ) Is displayed.
By moving the sample 2 by the scanning control device 6 and performing two-dimensional scanning with the ultrasonic beam B, one ultrasonic image is obtained.

By the way, as described above, in recent years, the physical properties of the surface layer of the sample 2 are investigated by using focused ultrasonic waves (the surface of the material is evaluated).
Means are being developed. This means will be described below. When the above-described operation is performed while the sensor 1 is brought 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 horizontal axis represents the distance (Z) in the Z-axis direction between the sensor 1 and the sample 2, and the vertical axis represents the voltage level (V) of the signal output from the piezoelectric element 1a. There is. The distance (Z) between the sensor 1 and the sample 2 is 0 at a predetermined position of the sensor 1, 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 called a V (Z) curve, and changes with a constant period ΔZ when the sensor 1 is close to the sample 2 by a certain distance or less.

As described above, the curve of X (Z) changes with the period ΔZ because the surface acoustic wave is generated on the surface layer of the sample 2 when the sample 2 is irradiated with the ultrasonic beam B, and the radiation of the surface acoustic wave is generated. This is because the waves interfere with the reflected waves of the ultrasonic beam B. The period ΔZ has a constant relationship with the propagation velocity of the surface acoustic wave propagating through the surface layer of the sample 2.
That is, when the sound velocity of the liquid medium 7 is V _W and the wavelength of the sound wave in the liquid medium 7 is λ _W , the propagation velocity V _R of the surface acoustic wave is represented 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 2 can be known based on the propagation velocity V _R. 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 with an ultrasonic microscope. For example, a certain object has anisotropy in its crystal structure, and even such an object must be subjected to a required measurement with an ultrasonic microscope. However, with the conventional ultrasonic microscope using the point focusing lens as described above, it is difficult to perform the required measurement on an anisotropic sample. That is, the detection of the V (Z) curve is performed in a minute portion of the sample 2, but the component of the ultrasonic beam B in the irradiation region extends in all directions around the central axis (beam axis). The sound velocity of the obtained surface acoustic wave is an average value in all the directions, and therefore the measurement of the sample 2 having anisotropy is impossible.

FIG. 8 is a perspective view of a special sensor for measuring a sample having such anisotropy. In the figure, 1a '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. With such a cylindrical surface, this sensor can focus a linear ultrasonic beam only in one axis direction as shown in the figure, and therefore, the ultrasonic beam is incident beyond the Rayleigh critical angle. A surface acoustic wave in only one direction can be generated on the surface of the sample 2 by the ultrasonic beam. By measuring the propagation velocity of the surface acoustic wave at each angle while rotating the sample 2 as indicated by the arrow, the anisotropy of the sample 2 can be obtained and the measurement along that direction can be performed.

However, the sensor shown in FIG. 8 has the following problems. That is, since this sensor has a structure in which only one axis is focused, there is a limit in reducing the length L of the acoustic lens 1b 'in the major axis direction, and it is usually about 2 mm. Therefore, the ultrasonic information obtained from this sensor is an average value within the above 2 mm. On the other hand, the ultrasonic microscope is configured to capture the change in elastic property of a substance from an extremely minute area to obtain an ultrasonic microscope image, and therefore, the irradiation area on the sample 2 is as large as 2 mm. In that case, a desired ultrasonic microscope image cannot be obtained. That is, the acoustic lens 1 shown in FIG.
The b '(line focusing lens) can measure the anisotropy of the sample, but cannot obtain an ultrasonic microscope image of the sample.

For this reason, a person who uses an ultrasonic microscope to perform measurement needs to replace the point focusing lens and the line focusing lens as necessary, but such conversion requires a lot of time and effort. However, there has been a problem that the burden on the measurer is increased and the efficiency of the measurement work is significantly reduced.

Furthermore, in the case of measurement using the line focusing lens 1b ', the surface of the sample 2 and the focal plane of the linear ultrasonic beam must be perfectly parallel, and if a slight inclination occurs between them. There is an error in measurement accuracy. The allowable angle of this tilt is 1/10
Since it is 0 degree, it takes a long time to adjust the inclination of both to be less than the allowable angle, and there is a problem that the burden on the measurer and the fixed price of the efficiency of the measurement work are further increased.

The object of the present invention is to solve the above-mentioned problems in the conventional technology,
An ultrasonic microscope probe that can measure anisotropy and collect an ultrasonic microscope image without changing the probe, which in turn reduces the burden on the measurer and improves the efficiency of measurement work. To provide a child.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention provides an ultrasonic device including an element for transmitting and receiving ultrasonic waves, and an acoustic lens for focusing the ultrasonic waves generated by the element and emitting the focused ultrasonic beam to a sample. In the probe of the acoustic microscope, the lens surface of the former acoustic lens is formed in a shape such that the opening angle of the acoustic lens has directionality.

[Action]

The ultrasonic waves generated by the element that transmits and receives ultrasonic waves are focused by the acoustic lens, and emitted from the lens surface as a focused ultrasonic beam. In this case, the beam focused in the predetermined direction of the focused ultrasonic beam has a portion having an incident angle larger than the Rayleigh critical angle, and the beam of this portion generates a surface acoustic wave on the surface layer of the sample. Therefore, surface acoustic waves are generated only in one direction. And
Since the acoustic lens is a point focusing type, the irradiation area of the sample is minute.

Therefore, both the measurement of anisotropy and the acquisition of the ultrasonic microscope image can be performed with one probe.

〔Example〕

 Hereinafter, the present invention will be described based on the illustrated embodiments.

1 (a), (b), and (c) are a front view, a side view, and a bottom view of an acoustic lens of a probe (sensor) of an ultrasonic microscope according to an embodiment of the present invention. In the figure, 20 indicates an acoustic lens used in the sensor of this embodiment. This acoustic lens
20 is formed by cutting the lens surface 1c of the acoustic lens 1b shown in FIGS. 5 and 6. The cutting mode is shown in FIG. Figure 2 shows a conventional acoustic lens
It is a sectional view taken along the central axis of 1b. 1c shows the lens surface, a two-dot chain line _{C 1 -C 2, C 3 -C} 4 shows the cutting line. That is, the lens surface 1c is cut along a plane that passes through the two-dot chain lines C ₁ -C ₂ and C ₃ -C ₄ and is perpendicular to the paper surface. The acoustic lens 20 shown in FIGS. 1A to 1C is the acoustic lens after being cut in this way. 20C _{1 to} C ₄ indicate cut surfaces passing through the chain double-dashed lines C _{1 to} C ₄ shown in FIG. 2, respectively. Due to such cutting, acoustic lens
On the lower surface of 20, there is formed an elongated lens surface 21 having a dimension in the length direction (direction perpendicular to the paper surface in FIG. 1A) considerably larger than the dimension in the width direction.

Next, the operation of this embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a line III-III shown in FIG. 1 (b).
4 shows a portion of the lens surface 21 in a cross section taken along the line, and FIG. 4 shows a portion of the lens surface 21 in the cross section taken along the line IV-IV shown in FIG. Reference numeral 2 represents a sample, and the acoustic lens 1b
The description of the liquid medium interposed between the sample 2 and the sample 2 is omitted.

In FIG. 3, the ultrasonic waves that have reached the lens surface 21 are radiated as an ultrasonic beam indicated by a broken line and focused on the focal point F. f indicates the focal length. In this way, the maximum value of the radiation angle of the ultrasonic beam (lens opening angle in the width direction) θmax when the width direction of the lens surface 21 is viewed is small because the lens surface 21 has an elongated shape and the dimension in the width direction is small. Therefore, it is smaller than the Rayleigh critical angle θ _R , and accordingly, the surface acoustic wave is not generated.

On the other hand, as shown in FIG. 4, when the length direction of the lens surface 21 is viewed, the maximum value of the emission angle of the ultrasonic beam emitted from the lens surface 21 (lens opening angle in the length direction) θ ′
max is the Rayleigh critical angle θ because there are no cuts.
Greater than _R. Then, when the ultrasonic beam B ₁ (shown by the solid line in FIG. 4) emitted at an angle near the Rayleigh critical angle θ _R is incident on the sample 2, the surface acoustic wave B ′ ₁ ( (Indicated by the solid line in FIG. 4).

In summary, the ultrasonic beam emitted from the elongated lens surface 21 generates surface acoustic waves in the length direction of the elongated lens surface 21 on the surface layer of the sample 2, but does not generate the surface acoustic waves in other directions. . That is, the surface acoustic waves can be generated only in one direction, and the anisotropy of the sample 2 can be measured. Moreover, since the acoustic lens 20 is originally a point-focusing type lens, the irradiation area on the sample 2 is minute (thus, the surface acoustic wave is also generated in the minute area). Microscopic images can be obtained without any trouble.

As described above, in this embodiment, since the lens surface of the point-focusing acoustic lens is cut to form the elongated lens surface,
One sensor can perform anisotropy measurement and ultrasonic microscopic image acquisition, and in the anisotropy measurement, adjustment for maintaining parallelism is unnecessary. As a result, the burden on the measurer can be significantly reduced, and the efficiency of the measurement work can be significantly improved.

The lens surface formed by cutting can be selected in any shape according to various conditions (that is, the cutting mode can be selected arbitrarily).

〔The invention's effect〕

As described above, according to the present invention, the lens surface of the point-focusing type acoustic lens is formed in such a shape that the opening angle thereof has directionality. Microscopic images can be collected, and adjustment of parallelism at the time of measurement regarding anisotropy can be eliminated, which significantly reduces the burden on the measurer and greatly improves the efficiency of measurement work. Can be improved.

[Brief description of drawings]

1 (a), (b) and (c) are front views of an acoustic lens of a probe of an ultrasonic microscope according to an embodiment of the present invention, respectively.
FIG. 2 is a side view and a bottom view, FIG. 2 is an explanatory view of a cutting mode of the acoustic lens, FIGS. 3 and 4 are cross-sectional views of a lens surface of the 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. 20 …… Acoustic lens, 20C _{1 to} 20C ₄ …… Cut plane, 21 …… Lens plane.

Claims (1)

[Claims] 1. A probe of an ultrasonic microscope comprising an element for transmitting and receiving ultrasonic waves, and an acoustic lens for focusing the ultrasonic waves generated by the element and emitting the focused ultrasonic beam to a sample. A probe for an ultrasonic microscope, wherein the lens surface of the acoustic lens is formed in a shape such that the opening angle of the acoustic lens has directionality.