JP3505753B2 - Ultrasound spectrum microscope - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic spectrum microscope, and more particularly to an ultrasonic spectrum microscope capable of suppressing frequency dispersion. 2. Description of the Related Art Conventionally, an ultrasonic spectrum microscope has been used to measure film characteristics of a sample. The ultrasonic spectrum microscope has a great feature in that the reflection coefficient of a sample can be measured over a wide frequency range as its name implies. As shown in FIG. 6, the ultrasonic spectrum microscope includes a pair of SPP lenses including a planar lens 1a and a spherical lens 2,
It comprises an impulse input means (not shown) and an analyzer for analyzing and analyzing reflected waves. The SPP lens is joined to a sample 4 to be measured via a coupler (usually water) 3. The plane lens 1a and the spherical lens 2 are each composed of a cylindrical delay member 5 and a rectangular or circular transducer 6. The spherical lens 2 forms a concave spherical surface 7 on the coupler 3 side of the delay member 5. The spherical lens 2 driven by the impulse input means makes the ultrasonic wave enter the coupler 3 via the transducer 6 and the delay member 5. The ultrasonic wave is reflected by the sample 4, and the reflected wave is converted into an electric signal by the transducer 6 via the delay member 5 of the plane lens 1a and sent to the analyzer side. On the other hand, when the angle of incidence selected by the plane lens 1a is near the critical angle θw, a surface wave traveling along the surface of the sample 4 (leakage surface acoustic wave, hereinafter referred to as LsAw) is generated. This LsAw phase velocity is generally not related to the frequency of the incident ultrasonic wave, but is related to the frequency of the incident ultrasonic wave when a film is present on the surface. Generally, if the transmission speed of the ultrasonic wave in the coupler is V ₁ and the phase speed is V ₂ , V
₂ = V ₁ / sin θw, and V ₂ can be easily obtained by obtaining V ₁ and θw. To evaluate the sample properties by analyzing the frequency dependence of V _2. Note that the critical angle θw is
It can be easily obtained by detecting the change in amplitude or the change in phase of the component reflected by the surface. FIG. 7 is a diagram showing the relationship between the frequency [MHz] and the phase velocity [m / s] when fused quartz is used as a sample. In the figure, a line C (indicated by a dashed line) and a curve B '(indicated by a dotted line) are calculated values, which are obtained by an output equation introduced in the following document (Y · Tsukahar).
a, N. Nakaso, and K. Ohira, “Angular spectral appro
ach to reflection of focus beams with oblique inci
dence in spherical-planar-pair lenses "," IEEE Trans
・ UFFC "vol38, no5, pp.468-480,1991). Curve B 'is shown in FIG.
Shows the calculation results according to the prior art shown in FIG. Note that line C
Is the calculated value when the area of the transducer is infinite. Therefore, the flat frequency characteristics of the fused quartz surface are almost faithfully represented. A curve A '(shown by a solid line) shows a result of measurement by the conventional ultrasonic spectrum microscope shown in FIG. In the drawing, there is a difference between the line C and the curve B 'because the transverse leakage or the like caused by the refraction of the ultrasonic wave between the planar lens 1a and the coupler 3 causes the transducer 6 having a finite size.
Because it cannot be caught. The difference between the curve B 'and the curve A' is due to the difference between the actual value and the theoretical value due to the shape and size errors of the flat lens 1a and the spherical lens 2 and the influence of the diffraction and refraction of ultrasonic waves. is there. [0004] As described above, the difference between the calculated value line C and the actually measured value curve A 'must be corrected by interpolation using the calculated value curve B'. Is possible. However, if the difference g ₂ (FIG. 7) between the calculated value curve B ′ and the actually measured value curve A ′ is large, the effect of complementation is reduced, and an accurate phase velocity cannot be obtained. For example, in FIG.
When the speed is 5 m / s, the maximum value g ₂ of the difference between the phase velocities of the curve A ′ and the curve B ′ is about 16 m / s and about 0.5%
Error occurs. Therefore, in order to perform precise sample measurement, a lens structure having originally flat frequency dispersion is desired without relying on complementation. However, in reality, conventional SPP lenses have a relatively large dispersion. The present invention has been made in view of the above circumstances, and has as its object to provide an ultrasonic spectrum microscope provided with a planar SPP lens which has a small frequency dispersion and requires an accurate phase velocity. . [0006] In order to achieve the above object, the present invention comprises an SPP lens having a spherical lens and a flat lens as a sensor that engages with a sample via a transmission medium . the ultrasonic spectrum microscope, to suppress an error caused by diffraction or refraction in the plane lens so as to reduce the frequency dispersion in the measurement of the phase velocity, Rights
Put the piezoelectric surface of the surface lens transducer on the coupler side
Place and form a coating layer on the piezoelectric surface of the transducer and input to the transducer
To match the ultrasonic wave, the thickness of the coating layer and (n / 2) · λ + λ / 4 (n = 0,1,2 ···)
It is characterized by having. According to the present invention, the transducer is fixed to the coupler side of the flat lens. For this reason, errors due to diffraction and refraction errors in the planar lens are reduced, and the frequency dispersion in measuring the phase velocity is greatly reduced. Further, in the present invention, since the transducer directly contacts the coupler, the transducer is covered with a coating layer as a waterproof layer. In addition, the coating layer has a thickness substantially equal to that of the wavelength to achieve matching of ultrasonic waves input to the transducer. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a front view of the flat lens of the present embodiment, FIG. 2 is a schematic configuration diagram of an ultrasonic spectrum microscope using the flat lens of the present embodiment, FIG. 3 is a diagram for explaining the effect of the present embodiment, 4 and 5 are front views showing an embodiment provided with a coating layer. As shown in FIG. 1, the planar lens 1 comprises a transducer 6 and a cylindrical backing 8 having the transducer 6 fixed to the lower surface. The transducer 6 is disposed in contact with the coupler 3, and an electrode (not shown) is connected to its piezoelectric surface. The coupler 3 is interposed between the sample 4 and the flat lens 1. The backing 8 has a function of suppressing the natural vibration of the transducer 6 and a function of flattening the frequency characteristics, and also holds the transducer 6. In FIG. 2, the flat lens 1 and the spherical lens 2 of this embodiment are inclined in opposite directions to each other and are integrally held by a lens holder 9. The lens holder 9 is rotated by a moving means (not shown) to change the inclination angle of the flat lens 1 and the spherical lens 2 with respect to the sample 4. The coupler 3 is interposed between the flat lens 1 and the spherical lens 2 and the sample 4 as described above. Electrodes (not shown) on the piezoelectric surface of the transducer 6 of the flat lens 1 are connected to an analyzer 11 via an amplifier 10 to receive an electric signal of the transducer 6. The analyzer 11 performs necessary analysis and analysis to calculate and display the relationship between the frequency and the phase velocity. on the other hand,
An electric impulse input means 12 is connected to the transducer 6 of the spherical lens 2 to excite ultrasonic waves in a predetermined frequency band. With the above structure, the input wave from the spherical lens 2 enters the coupler 3, is reflected by the sample 4, and is converted into an electric signal by the transducer 6 of the flat lens 1. The transducer 6 of this embodiment is a coupler 3
, The reflected wave is directly input to the transducer 6. Therefore, the phase velocity at the critical angle θw can be accurately obtained without the diffraction in the delay member 5 or the loss of the ultrasonic wave due to the refraction between the coupler 3 and the delay member 5 as in the related art. In FIG. 3, a line C shows a calculated value when the infinite transducer 6 is used as in the case of the line C in FIG. Indicates a value. Also, a solid curve A
Is a measured value using the flat lens 1 of the present embodiment. As shown in the figure, the difference between the line C and the curve B is extremely small as compared with the related art. The difference between the curves B and A is also small. About 10 m / s is only a maximum value at fluctuations g ₁ is prior art under the same conditions of the actually measured curve A. That is, only a variance of about 0.3% with respect to the absolute value occurs. For this reason, extremely high-precision phase velocity measurement can be performed. On the other hand, when the conventional planar lens is used, the velocity dispersion reaches 30 m / s at the maximum, and there is an error of about 1% with respect to the absolute value. FIG. 4 shows the transducer 6 of the planar lens 1 shown in FIG. Since the transducer 6 of the flat lens 1 of the embodiment shown in FIG. 1 is in direct contact with the coupler 3, there is a problem of waterproofness. By providing the coating layer 13, the transducer 6 is waterproofed and its function is prevented from being deteriorated. In this case, the film thickness δ ₁ of the coating layer 13 is a thin film having a value sufficiently smaller than the wavelength λ of the ultrasonic wave. FIG. 5 shows a transducer 6 of the flat lens 1.
Is coated with a coating layer 14. The coating layer 14 is made of those of approximately equal thickness [delta] ₂ and wavelength lambda of the ultrasonic wave used, is employed as in the present embodiment about lambda / 4 (or n / 2 · λ + λ / 4). Note that λ
The setting of / 4 is based on experimental trials. The coating layer 14 waterproofs the transducer 6, suppresses re-reflection from the lower surface of the backing 8, and functions as an acoustic matching layer. According to the present invention, the following remarkable effects are obtained. 1) Since no lateral leakage of the sound wave occurs due to sound wave diffraction or refraction in the plane lens, dispersion in the frequency direction is small, and a highly accurate frequency-phase velocity relationship can be obtained. 2) By covering the transducer of the flat lens with the coating layer, waterproofness can be obtained even if the transducer is arranged on the coupler side, and deterioration is prevented. 3) Waterproofing and acoustic matching can be obtained by coating the transducer with a coating layer having a film thickness substantially equal to the wavelength of the ultrasonic wave used. 4) The present invention is a relatively simple one that changes the mounting position of the transducer of the flat lens, and can be implemented easily and at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view showing the structure of a flat lens according to one embodiment of the present invention. FIG. 2 is a schematic overall configuration diagram of an ultrasonic spectrum microscope using the flat lens of the present embodiment. FIG. 3 is a diagram showing the relationship between frequency and phase velocity according to the embodiment. FIG. 4 is a front view of another embodiment of the present invention. FIG. 5 is a front view of still another embodiment of the present invention. FIG. 6 is a front view showing the structure of a conventional SPP lens. FIG. 7 is a diagram showing the relationship between frequency and phase velocity in a conventional planar lens. [Description of Signs] 1 Planar lens 1a Planar lens 2 Spherical lens 3 Coupler 4 Sample 5 Delay material 6 Transducer 7 Concave sphere 8 Backing 9 Lens holder 10 Amplifier 11 Analyzer 12 Electric impulse input means 13 Coating layer 14 Coating layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 29/00-29/28

Claims (1)

(57) [Claim 1] In an ultrasonic spectrum microscope equipped with an SPP lens having a spherical lens and a planar lens as a sensor that engages with a sample via a transmission medium, the diffraction and diffraction of the planar lens Suppress errors due to refraction,
To reduce the frequency dispersion in the measurement of the phase velocity
Then, the piezoelectric surface of the flat lens transducer is
And a coating layer is formed on the piezoelectric surface of the transducer.
And align the ultrasound input to the transducer
As described above, the film thickness of the coating layer is (n / 2) · λ + λ
/ 4 (n = 0,1,2 ···) and ultrasonic spectrum microscope, characterized in that the.