JP3379166B2 - Ultrasound spectrum microscope - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention analyzes, analyzes, calculates, records and displays the output of reflected ultrasonic waves in order to accurately measure the thickness and quality of a sample. In connection with the ultrasonic spectrum microscope,
In particular, the present invention relates to an ultrasonic spectrum microscope suitable for measuring and evaluating surface physical properties of a sample. [0002] In order to measure the thickness and quality of a sample, an SPP
A lens is used. In general, the SPP lens has a pair of lens structures of a transmitting-side spherical lens and a receiving-side flat lens, and both have a transducer and a delay member. Ultrasonic waves transmitted from the transmitting lens are irradiated on the sample surface. The reflected wave from the sample is received by the receiving lens, and the output of the reflected wave is analyzed, analyzed, calculated, and displayed by an image processing means such as an oscilloscope or a computer. Conventionally, an SPP lens generally used has a paired structure of a spherical lens and a planar lens. For example, a focused ultrasonic wave is transmitted from a transmitting spherical lens to a focal point of a sample, and a divergent ultrasonic wave from the focal point is received. The output of the reflected wave is obtained by receiving the light by the flat lens on the side, and the film thickness and the like are measured based on the output. When measuring the characteristics of a sample surface, the phase velocity of a surface wave is measured. When determining the phase velocity, S
The incident angle is changed by angularly scanning the PP lens. When the incident angle of the ultrasonic wave reaches the critical angle θw, a leaky surface acoustic wave is excited along the surface of the sample. Here, the specular reflection component on the sample surface decreases. The presence of the surface wave can be confirmed by the dip on the intensity of the output of the reflected wave, but the dip may not easily appear.
Assuming that the transmission speed of the ultrasonic wave in the medium (usually water is the medium) on the SPP lens side is V ₁ and the velocity of the surface wave traveling along the surface of the sample, that is, the phase velocity is V ₂ , V ₂ =
V ₁ / sin θw. Since V ₁ is known, the phase velocity V ₂ can be easily obtained by obtaining the critical angle θw. Such a technique is described in the following English literature, for example.
"Measurements of SAW Velocity Using an Ultrasonic
-Micro Stectrometer '' (Proceeding of 10th Symtosium
onUltrasonic Electronics, Tokyo 1909 Japanese Jour
nal of Applied Physics, Vol. 29 (1990) Supplement 29
[0004] As described above, when an ultrasonic wave is incident at a critical angle θw, a surface wave (leakage of the surface wave along the surface of the sample) occurs. Surface acoustic wave, hereinafter referred to as LSAW)
Are excited and almost no reflected wave is generated. The LSAW leaks again from the surface of the sample and proceeds to the flat lens side on the receiving side. As a result, the information of the sample is averaged in the output of the reflected wave by about the distance that the LSAW has propagated.
It was difficult to measure the elastic properties of. The present invention solves the above-mentioned problems. Based on the fact that the reflected wave output changes in a constant manner with respect to the change in the incident angle, the critical angle is determined from the stylized change pattern. In addition to obtaining the phase velocity of the sample surface wave with high accuracy, the physical property information (including anisotropy) of the sample
An object of the present invention is to provide an ultrasonic spectrum microscope that can be obtained with higher spatial resolution than a P lens. SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a transducer which transmits and receives ultrasonic waves, which is disposed to be inclined left and right with respect to a vertical axis perpendicular to the sample surface. And an ultrasonic spectrum microscope having a pair of ultrasonic sensors having a delay member and an image processing means for receiving waves of the ultrasonic sensor, wherein an end portion of the delay member on the sample side of a transmission-side and reception-side lens constituting the ultrasonic sensor Are formed with concave surfaces having different focal positions. As a feature,
The receiving lens is incident from the transmitting transducer.
Component included in the transmitted ultrasonic wave and passing on the center axis of the transmitting lens
However, the reflected wave specularly reflected from the sample
Incident on the sample included in the ultrasonic wave incident from the transducer
Re-emission wave from the sample whose angle matches the critical angle is detected.
This constitutes a known ultrasonic spectrum microscope. When the incident angle of the ultrasonic wave from the transmitting side is smaller than the critical angle θw, the LSAW is not excited, and other than the ultrasonic wave on the central axis of the transmitting side lens, , The reflected wave output has a substantially constant value. next,
When the incident angle matches the critical angle θw, the ultrasonic wave passing through the central axis of the transmitting lens excites the LSAW on the sample, the output of the mirror reflected wave is drastically reduced, and a dip occurs instantaneously. At this time, L
Although the re-emission component of SAW exists, it is not received because it is at a position different from the focal point of the receiving lens. Next, when the incident angle becomes larger than the critical angle θw, a part of the ultrasonic wave from the transmitting lens is directly incident on the receiving lens as a specular reflection wave, and the other part excites the LSAW, and the re-excitation occurs. The emitted wave travels to the receiving lens. Therefore, since a two-component wave is generated, the reflected wave output has a wave shape that repeats a shallow dip due to interference. As described above, by observing the change pattern of the reflected wave output with respect to the incident angle, the position of the critical angle is clarified, and the phase velocity can be accurately obtained with higher spatial resolution than the conventional SPP lens. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic overall configuration diagram of an ultrasonic spectrum microscope to which the present embodiment is applied, FIG. 2 is a perspective view of a concave lens for transmission, FIG. 3 is a perspective view of a concave lens for reception, and FIGS. FIG. 8 is a front view for explaining the operation of the present embodiment, and FIG. 8 is a diagram showing the relationship between the incident angle θi and the reflected wave output. As shown in FIG. 2, a concave lens 1 for transmission is used.
Consists of a transducer 3 and a cylindrical delay member 4,
A concave surface 5 having a focal point P ₁ is formed on the distal end side of the delay member 4.
On the other hand, as shown in FIG. 3, the concave lens 2 for reception includes a transducer 6 and a cylindrical delay member 7, and a concave surface 8 of a focal point P ₂ is formed on the distal end side of the delay member 7. That is, the concave surface 5 and the concave surface 8 form the focal points P ₁ and P ₂ at different positions, and have different concave curvature shapes. Next, the schematic structure of an ultrasonic spectrum microscope 9 to which this embodiment is applied will be described with reference to FIG. The concave lens 1 for transmission is disposed on the right side of the vertical axis 11 of the sample 10, and the concave lens 2 for reception is disposed on the left side. Both lenses 1 and 2 are arranged obliquely to each other. The concave lens 2 is arranged so that its focal point P ₂ coincides with the focal point P of the sample 10, and the concave lens 1 has a central axis 17 passing through the focal point P.
The focal point P ₁ is located above the sample 10. The central axes of the biconcave lenses 1 and 2 intersect at the focal point P. The concave lens 1 transmits a focused spherical wave from the concave surface 5, and a part of the focused spherical wave is reflected from the focal point P as a divergent spherical wave toward the concave lens 2 and received. Further, the concave lens 1 and the concave lens 2 are held by a common lens holder 12, and both are arranged at an intersection angle of the angle θ. By rotating the lens holder 12 about the convergence point P, the incident angle θi of the concave lens 1 changes, and the concave lens 2 becomes θ−θ.
Move to position i. An electric impulse is transmitted from the pulsar & receiver 13 to the transducer 3 of the concave lens 1.
On the other hand, the transducer 6 of the concave lens 2 is connected to a pulser & receiver 13, and the reflected wave output is amplified by the pulser & receiver 13. This data is sent to the computer 15 via the oscilloscope 14, where necessary calculations and recording are performed, and analysis and calculation of the surface wave phase velocity and other characteristics of the sample are performed. The result is displayed by a display means such as a monitor television (not shown). As shown in the figure, water 16 as a medium for transmitting ultrasonic waves is interposed between the concave lens 1 and the concave lens 2 and the sample 10. Next, the operation of this embodiment will be described with reference to FIGS. FIG. 4 illustrates the state of transmission and reception of ultrasonic waves when the incident angle θi is smaller than the critical angle θw and θi <θw. A focused spherical wave is emitted from the concave lens 1, but only the component passing on the central axis 17 of the concave lens 1 (indicated by an arrow C) is received by the concave lens 2. This component is reflected at the focal point P on the sample 10, passes through the concave lens 2 as shown by the arrow D, and is converted into an electric signal by the transducer 6.
(FIG. 1). Therefore, in this case, the output of the reflected wave has a substantially constant value. FIG. 5 shows that the incident angle θi is equal to the critical angle θw.
This shows a state where i = θw. Also in this case, the ultrasonic component traveling to the concave lens 2 side is the center axis 17 of the concave lens 1.
, Which excites the LSAW (indicated by arrow E) at the focal point P as described above. As a result, the power of the reflected wave indicated by the arrow F becomes weak, and almost no input is made to the concave lens 2 side, and the output of the reflected wave is drastically reduced.
Deep dips occur. FIG. 6 shows a state in which the incident angle θi is larger than the critical angle θw and θi> θw. The ultrasonic waves are received by the concave lens 2 side case and components indicated by the arrow C passing through the center axis 17 of the concave lens 1, the components of arrow G toward the sample 10 side through the focal point P ₁ at the critical angle θw It has two components.
As shown in an enlarged manner in FIG. 7, the ultrasonic wave indicated by the arrow C is reflected at the focal point P and is converted into a reflected wave indicated by the arrow H.
Is received. On the other hand, since the ultrasonic wave indicated by the arrow G is incident at the critical angle θw, the LSAW is excited on the surface of the sample 10 as indicated by an arrow I, and a part thereof is weakened as indicated by an arrow J while proceeding to the focal point P (P ₁ ). The light advances to the concave lens 2 side as a re-reflected wave of power. Therefore, the reflected wave output measured on the receiving side has a waveform that repeats a smaller dip in the interference between the two components. FIG. 8 is a diagram showing a change in the output of the reflected wave described with reference to FIGS. The horizontal axis indicates the incident angle θi, and the vertical axis indicates the reflected wave output. In the figure, region 1 shows the state of θi <θw in FIG. 4 and the output of the reflected wave becomes almost constant as described above. Next, the region 2 corresponds to the state of θi = θw in FIG. 5 and a deep dip 18 appears. Next, a region 3 shows the state of θi> θw in FIG. 6, and has a waveform 20 in which shallow dips 19 are repeated. The shape of the waveform 20 changes according to characteristics such as the material and hardness of the sample 10. When observing the change pattern of the reflected wave output with respect to the incident angle θi shown in FIG. 8, a dip 18 occurs at the boundary where the reflected wave output changes from a constant value to a waveform 20. Therefore, the position of the critical incident angle θw can be accurately read. Once the value of the critical angle θw is determined, the phase velocity V ₂ of the LSAW traveling on the surface of the sample 10 can be accurately obtained by the “Snell's law” of V ₂ = V ₁ / sin θw as described above. In addition, as described above, various characteristics of the sample can be obtained by analyzing the shape of the waveform 20, which is effective for ultrasonic microspectroscopy. In the above description, the shapes of the concave surface 5 and the concave surface 8 of the concave lens 1 and the concave lens 2 are not limited to those shown in the drawings as long as the focal positions are different. Further, the overall configuration of the ultrasonic spectrum microscope 9 to which the present embodiment is applied is not limited to that of FIG. According to the present invention, the following remarkable effects are obtained. 1) The LSAW speed in a minute area can be obtained as compared with the conventional SPP lens. That is, the spatial resolution is higher than in the past. 2) By adopting a concave lens having a different focal point and a combination lens of concave lenses as the ultrasonic sensor, a change pattern of the reflected wave output with respect to the incident angle θi can be standardized, and the critical angle position can be accurately determined from this pattern. You can ask. 3) Since the critical angle is accurately grasped, the surface wave phase velocity of the sample can be accurately obtained. 4) The waveform changes periodically with the change pattern of the reflected wave output being θi> θw, and the characteristics (material, hardness, anisotropy, etc.) of the sample can be obtained by analyzing the waveform. 5) The present invention can be implemented at a relatively low cost because the shape of the ultrasonic sensor is devised and no special accessories are used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall schematic configuration diagram of an ultrasonic spectrum microscope to which an embodiment of the present invention is applied. FIG. 2 is a perspective view of a concave lens according to the present embodiment. FIG. 3 is a perspective view of the concave lens of the present embodiment. FIG. 4 is an explanatory front view showing a transmission / reception state of ultrasonic waves in a state of θi <θw according to the present embodiment. FIG. 5 is an explanatory front view showing a transmission / reception state of ultrasonic waves in a state where θi = θw in the present embodiment. FIG. 6 is an explanatory front view showing a transmission / reception state of ultrasonic waves in a state of θi> θw in the present embodiment. FIG. 7 is an enlarged view of a mark A in FIG. 6; FIG. 8 is a diagram illustrating a relationship between an incident angle θi and a reflected wave output in the present embodiment. [Description of Signs] 1 Concave lens 2 Concave lens 3 Transducer 4 Delay member 5 Concave surface 6 Transducer 7 Delay member 8 Concave surface 9 Ultrasonic spectrum microscope 10 Sample 11 Vertical axis 12 Lens holder 13 Pulser & receiver 14 Oscilloscope 15 Computer 16 Water 17 Center Axis 18 Dip 19 Dip 20 Waveform

Claims (1)

(57) Claims 1. A pair of ultrasonic sensors having a transducer for transmitting and receiving ultrasonic waves, which is disposed to be inclined left and right with a vertical axis perpendicular to the sample surface as a boundary, and a delay member, and In the ultrasonic spectrum microscope provided with the image processing means of the received wave, a concave surface having a different focus position is formed at an end of the delay member of the transmitting side and the receiving side lens constituting the ultrasonic sensor on the sample side . The receiving lens is included in the ultrasonic wave incident from the transmitting transducer.
The component passing through the center axis of the transmitting lens is
Included in the reflected wave and the ultrasonic wave input from the transmitting transducer
Of the component whose incident angle to the sample coincides with the critical angle
An ultrasonic spectrum microscope that detects re-emitted waves .