JPH02251752A - Ultrasonic microscope lens and reflected wave collecting method using same - Google Patents

Abstract

PURPOSE:To facilitate the selective control of the inclination of transmitting-receiving apparatuses with an object to be inspected and to perform measurement of high accuracy with high resolving power by holding a converging type transmitting-receiving apparatus and non- converging type transmitting-receiving apparatus at a predetermined angle. CONSTITUTION:A converging type transmitting-receiving apparatus 10a is constituted so that a piezoelectric body 101a composed of a curved plate-shaped body is held between a pair of curved plate-shaped electrodes 102a and the ultrasonic wave transmitting/incident surface thereof is formed into a concave surface. A non-converging type transmitting-receiving apparatus 10b is constituted so that piezoelectric body 101b composed of a flat plate-shaped body is held between a pair of planar electrodes 102b and the ultrasonic wave transmitting/ incident surface thereof is made planar. The apparatuses 10a, 10b are supported by an ultrasonic transmitting-receiving apparatus holder 100C so as to hold the angle formed by the ultrasonic wave transmitting/incident directions of both apparatuses 10a, 10b to constitute a microscopic lens. The concave surface of the apparatus 10a can be formed into a spherical or cylindrical surface. When the concave surface is the spherical surface, said apparatus 10a becomes a point converging lens and, when said concave surface is the cylindrical surface, the apparatus 10a becomes a line converging lens. Further, either one of the apparatuses 10a, 10b may be set to an ultrasonic wave transmitting means and the other may be set to a receiving means.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention obliquely injects an ultrasonic wave onto the surface of a subject at an intended angle of incidence, collects the reflected waves, and detects the reflected waves depending on the angle of incidence of the ultrasonic wave. The present invention relates to an ultrasonic microscope lens used to measure film thickness, adhesion, etc. from the shape of the resulting frequency distribution, and a method for collecting reflected waves using the ultrasonic microscope lens.

<Prior Art> As a method for non-destructively and quantitatively measuring the structure and elastic constants of an object using ultrasound, there is a V(z) curve method using a lens of an ultrasound microscope. The V(z) curve method corresponds to the phase velocity of surface acoustic waves due to the fact that surface acoustic waves are excited on the surface of the object when the lens of the ultrasound microscope is moved up and down perpendicular to the surface of the object. Since the output oscillates with a period, the phase velocity of the surface acoustic wave is determined from the oscillation period.The phase velocity of the surface acoustic wave can be determined as a function of the structural parameters and physical constants of the object, so it is difficult to observe. In turn, the structural parameters and physical constants of the object can be measured from the phase velocity of the surface acoustic waves.

Furthermore, JP-A-61-20803 discloses a method for measuring structures such as elastic constants and film thickness of a test object using the excitation phenomenon of surface acoustic waves excited on the surface of the test object. Patent application No. 63-20256 for evaluating gender
There is a technique described in Publication No. 9. As shown in FIG. 3A, these transmit ultrasonic waves oscillated by a transmitting transducer 23 to a subject 21 on which a membrane 19 is formed on a substrate 18. When the ultrasonic wave is incident at an incident angle θ1 within a certain range determined by the substance constituting the liquid, the subject 21 emits an ultrasonic wave at the same angle as the incident angle. When the emitted reflected waves are detected by the receiving transducer 24 to obtain the frequency distribution 26 shown in FIG. This takes advantage of taking the minimum value. The WA film thickness measurement method measures the film thickness using equation (1).

F This is a constant determined by the constituent materials of the ultrasonic propagation liquid and the incident angle of the ultrasonic waves.

On the other hand, the adhesion judgment method detects the presence or absence of an intermediate layer made of another material between the film and the substrate, as well as peeling, from the way the frequency of the minimum reflected wave output changes at each incident angle when the incident angle is shifted. It is something. Japanese Patent Application Laid-Open No. 1983-1989 is a document regarding ultrasonic waves @ mirror lenses used in these measurement methods.
There are examples such as Japanese Patent Application No. 79157 and Japanese Patent Application Laid-open No. 79158/1983. However, these ultrasonic microscope lenses cannot change the angle of incidence, and if the constituent materials of the film and substrate change, the angle of incidence at which surface acoustic waves are excited changes, making measurement impossible. Particularly when trying to measure a specimen made of an unknown substance, it is necessary to continuously change the angle of incidence to find the optimum angle of incidence at which the reflected wave output minimum phenomenon occurs, which requires a great deal of time and effort. Therefore, in view of the above requirements, there is a need for an ultrasonic microscope lens that can easily collect reflected waves at different incident angles.

Furthermore, when measuring a minute area on the surface of a subject based on the film thickness measurement method and adhesion judgment method described above, the ultrasonic waves are focused on the surface of the subject, or only from a minute area on the surface of the subject. It is necessary to detect the reflected waves of The lenses described in JP-A-61-79157 and JP-A-61-79158 allow ultrasonic waves to be incident at a constant angle of incidence, but when trying to measure in a minute area, oscillation occurs. However, there is no choice but to narrow the area of the receiving piezoelectric body, and in this case, the receiving output becomes small, which naturally limits the ability to measure in a minute area.

<Problem to be Solved by the Invention> As described above, a film is formed on a substrate based on the method described in Japanese Patent Application Laid-Open No. 61-20803 or Japanese Patent Application No. 63-202569 filed by the same applicant. When trying to non-destructively measure film thickness or adhesion between a substrate and film on a formed specimen using ultrasound, conventional ultrasonic microscope lenses measure the constituent materials of the specimen. If the angle of incidence changes, it is necessary to change the angle of incidence of the ultrasonic waves, so it is necessary to replace the ultrasonic microscope lens with a different angle of incidence.

Furthermore, it has been difficult to obtain high resolution using conventional techniques.The present invention solves these problems of conventional techniques.

Means for Solving the Problems> The present invention oscillates ultrasonic waves by applying an electric signal to a piezoelectric body, irradiates the oscillated ultrasonic waves obliquely onto the surface of a subject, and transmits the reflected waves to the piezoelectric body. In an ultrasonic microscope lens that is configured to receive signals using This is an ultrasonic U microscopic lens characterized by being configured with a point convergence beam transducer that converges sound waves to one point when an electric signal is applied or a linear convergence beam transducer that converges sound waves in a straight line.

Furthermore, the ultrasonic wave is incident on the parallel beam transducer within a range where such an ultrasonic microscope lens is applied to the surface of the object to be examined, and the emitted ultrasonic wave is obliquely irradiated onto the object surface and the reflected wave is received. This is a method of collecting reflected waves using an ultrasonic microscope lens, which is characterized by obtaining the output of reflected waves from a subject at an intended incident angle or its frequency distribution by tilting the lens in the direction in which the angle changes.

<Detailed Description of the Invention> As shown in Figure 1 or Figure 2, in an ultrasound microscope lens that irradiates an object with ultrasound and collects the reflected waves, there are two sides: one that emits ultrasound waves and one that receives ultrasound waves. We will explain the characteristics principles of an ultrasound microscope lens that is composed of two transducers, one consisting of a point convergence beam transducer or a linear convergence beam transducer, and the other consisting of a parallel beam transducer. .

First, consider the case where a linear converging beam transducer as shown in FIG. 1 is installed on the subject so that it focuses on the subject's surface and the reflected wave is received by the parallel beam transducer.

As shown in FIG. 4, a convergent beam 3 is oscillated by a linear convergent beam transducer 28 whose objective surface has a cylindrical side surface shape.
0 is incident on the surface of the object 36 with an incident angle width θ2 determined by the aperture angle of the linear converging beam transducer 28, and is converged in an extremely narrow area of the focal point 32. This incident sound wave is reflected and enters the ultrasonic propagation liquid again with the same reflection angle width θ.
It is re-radiated with 2. Based on the concept of Fourier optics, this reflected wave can be expressed as follows.

As shown in FIG. 5, a very narrow 614 j! corresponds to the focal point 32 of the transducer. The wave radiated from If 34 (Fig. 5 A) can be considered as a superposition of plane waves (Fig. 5 B, C, D) propagating in various directions.
Among the decomposed plane wave components propagating in various directions, the fifth
As shown in FIG. Components that are reflected in a direction shifted from the direction perpendicular to the piezoelectric material cause a phase shift because the sound waves are obliquely incident on the piezoelectric material, so the contribution of these components to the output becomes relatively weak. From this, the electric signal received by the second ultrasound microscope lens has elastic information in the micro head area 34 corresponding to the focal point 32 of the linear converging beam transducer 28 on the surface of the subject. , and the signal corresponds to the case where the ultrasonic wave is incident at the incident angle of the parallel beam transducer 29.

As shown in Figure 6A, even when the receiving and transmitting transducers in Figure 4 are reversed, the elastic information when the incidence angle defined by the parallel beam transducer is 41 surface can be obtained for a minute region 42 corresponding to the focal point 40 of a linear converging beam transducer. As shown at A in FIG.
reflected by the surface of Based on the concept of Fourier engineering, a plane wave can generally be considered as a superposition of cylindrical waves emitted from each point 45 on the surface of the object 410.

Among the components reflected from the object surface, only the component of the reflected wave from the region 42 corresponding to the focal point 40 of the converging beam transducer is out of phase on the piezoelectric surface having a cylindrical side surface, as shown in D in FIG. The components of the reflected waves from areas other than the area 42 corresponding to the focal point 40 of the converging beam transducer cause a phase shift on the piezoelectric surface, as shown in Fig. 601 and Fig. 6E. , the magnitude of the electrical signals contributing to the output of these components is relatively weak, and as a result, only the elastic properties of the minute region 42 corresponding to the focal point of the linear focusing beam transducer 39 appear in the received signal.

The above is based on the normal 51 of the surface of the object as shown in FIG.
When the center line 52 of the ultrasonic microscope lens is tilted relative to This means that when ultrasonic waves are irradiated onto the object 4B at an incident angle θ6, a response to the ultrasonic waves of the object 4B can be obtained. A signal reflecting the physical properties or structure of the object at the incident angle can be extracted.

The case of a point convergence transducer can be explained using the concept of Fourier optics in the same way as the linear convergence beam transducer described above, and in this case, since the focus is a point, measurement with high spatial resolution is possible. .

If either the ultrasonic oscillation or reception transducer is configured with a point convergence or linear convergence beam transducer, and the other transducer is configured with a parallel beam transducer, then In order to construct a converging beam transducer, the piezoelectric material itself has a cylindrical side surface shape or a concave shape, but as shown in Figs. The technical scope of the present invention is not limited by whether a convergent beam transducer is constructed by processing the object surface of the material into a cylindrical side surface shape or a concave shape.Also, the technical scope of the present invention is not limited depending on whether a convergent beam transducer is constructed by processing the object surface of the material into a cylindrical side surface shape or a concave shape. It is not limited by whether or not it is used.

<Example> Example 1 The film thickness of a specimen whose constituent materials are unknown for both the substrate and the film formed thereon was measured using the ultrasonic 3gl microscopic lens of the present invention according to the following procedure. It was possible to do so.

The ultrasonic microscope lens used had a structure as shown in FIG. The transducer on the receiving side forms a linear converging beam transducer l by cutting the objective surface 5 of the delay material 4 made of fused silica into a cylindrical side shape, and the parallel beam transducer 2 on the transmitting side is constructed by cutting the object surface 5 of the delay material 4 made of fused silica into the shape of a cylindrical side surface. It was constructed using fused silica. The linear convergent beam transducer and the parallel beam transducer were fixed using a fixing member 8 so that they were at an angle of 55 degrees. The aperture angle of the linear converging beam transducer is 30 degrees. In the measurement, water was used as the liquid for ultrasonic propagation, and the ultrasonic microscope lens was attached to the birch shown in Figure 9A, and the incident angle of the ultrasonic waves from the parallel beam transducer was set to 07 = 15d with respect to the surface of the specimen.
Reflected waves were collected while tilting continuously from eg to θ8=60 degrees, and their frequency was analyzed. As a result, as shown in FIG. 9A, it was found that when using the ultrasonic microscope lens of the present invention at an incident angle of 09 = 30 deg, the minimum phenomenon caused by the excitation of surface acoustic waves on the surface of the object to be examined was often observed. did. Therefore, as shown in Fig. 9B, the present ultrasound microscope lens is tilted so that the incident angle θ9 of the parallel beam transducer on the surface of the subject is always 30 degrees, and then the following steps are performed. Measurements were taken.

Reflected waves were collected from a specimen with the same material composition as the specimen described above and known to have a film thickness of 5 μm, and as a result of frequency analysis, a minimum was observed at 50 MHz. From this, at a given incident angle of 30 deg of the object, (
1) The value of C in the formula was found to be 250, and from now on, for a specimen of unknown film thickness made of the same substance, the value of C was set to 250 and the formula was calculated according to formula (1). As shown in FIG. 9B, the measurement could be performed at 09=30 deg.

Example 2 As shown in FIG. 10, when determining the close contact of a subject with gold plating 71 on a fused silica substrate 70, the presence of an oil film 75 between the gold film and the substrate was performed as follows. It was possible to detect the area.

As shown in FIG. 2, the ultrasonic sensor consists of a parallel beam transducer 11 on the transmitting side using a delay material made of fused silica, and an objective surface 14 of the delay material on the receiving transducer being cut into a concave surface. A point converging beam transducer 10 was constructed.

The diameter of the 0-circular piezoelectric body fixed by the fixing member 15 is 1 mm so that the angle between the center line of the point converging beam transducer and the normal line of the parallel beam transducer is about 40 degrees. Further, the aperture angle of the point converging beam transducer is 20 degrees. In addition, ultrasonic microscope lenses with 0 or more configurations using water as the liquid for ultrasonic propagation,
The spatial resolution at the focus at 50 MHz was 50 μm down 6 dB. This spatial resolution value is 550 II m when using parallel beam transducers for both conventional transmitting and receiving transducers.
It can be seen that this is a significant improvement compared to what was before.

Theoretical calculations in elastic engineering have shown that when the membrane and substrate are in perfect contact and water is used as the liquid for ultrasonic propagation, the incident angle of the ultrasonic waves on the surface of the object will vary from 17 deg to 2 deg.
When an ultrasonic wave is incident at an incident angle between 0 degrees, a minimum appears in the frequency distribution of the reflected wave due to surface acoustic waves being excited on the surface of the object, and the frequency at which this minimum occurs is at a certain film thickness. 202M at an incident angle of θ10-17.3deg
) iz1θ11-19, 281M at an incident angle of 2deg
It turned out to be H2. Using this calculation result, adhesion was determined according to the following procedure. First, set the ultrasound microscope lens so that the focal point of the point converging beam transducer is located on the surface of the subject, and the normal line of the parallel beam transducer is θ10 = 17.3 deg with respect to the subject.
The ultrasonic beam emitted from the parallel beam transducer was irradiated onto the object, and the reflected wave was received by the point convergence beam transducer to obtain the frequency distribution of the reflected wave. Similarly, the entire ultrasonic microscope lens was tilted, and the normal line of the parallel beam transducer was set to have an inclination of θ11=19.2 degrees with respect to the subject, and similar processing was performed. The value of the minimum frequency that appeared in the frequency distribution obtained in this experiment was 2, 5, 5, 0. The results for each point are as follows.

Incident angle 17.3deg 19.2deg point
101MHz 141MHz mouth reading 130M
Hz 160MHz 120MHz
Taking the ratio of the minimum frequency of 167 MHz and the minimum frequency in each case assuming perfect contact, the results are as follows.

Incident angle 17.3deg 19.2deg point
0.50 0.50 points 0.64
0.57 points 0.60 0.60
At points A and C, the minimum frequency when changing the incident angle,
The ratio of the minimum frequencies at the time of complete contact determined from theoretical calculations is equal at each angle of incidence, so it is determined that there is complete contact, but it is determined that the mouth point is not in complete contact. Similar judgments were made over the entire surface of the object to detect areas with poor adhesion. A subsequent destructive test revealed an oil film between the gold and fused quartz in areas where adhesion was determined to be poor.

<Effects of the Invention> Since the present invention has the above configuration, it is possible to measure film thickness, judge adhesion, etc. by injecting ultrasonic waves into the object and collecting the reflected waves, in common with the i2nd and 3rd inventions. In carrying out this method, reflected waves at different angles of incidence can be measured simply by tilting the entire ultrasound microscope lens with respect to the surface of the subject.

Furthermore, the first invention makes it possible to measure film thickness and determine adhesion in minute areas, and is particularly useful when used as part of a sensor for a spectrum ultrasound microscope.

[Brief explanation of drawings]

The drawings show and explain the principles and embodiments of the present invention, and FIGS. 1 and 2 are perspective explanatory views of the ultrasonic microscope lens of the present invention. FIG. 3 explains the principle of the conventional film thickness measurement method, and A is a cross-sectional explanatory diagram of a measurement example, and B is a frequency distribution diagram of the obtained reflected waves. Figures 4 to 7 explain the principle of this ultrasonic microscope lens, Figure 4 is a cross-sectional explanatory diagram of a measurement example, and Figures 5A, B, C, and D.
is an explanatory diagram of plane wave division of reflected ultrasound reception when the receiving transducer is a parallel beam transducer,
Figures 6A, B, C, D, and E are explanatory diagrams of plane wave division of reflected ultrasound reception when the receiving transducer is a linear convergent beam transducer, and Figure 7 is an illustration of plane wave division when the ultrasound microscope lens is tilted. Each shows an explanatory diagram of reception,
FIG. 8 is an explanatory diagram of another embodiment of the present invention. Figure 9A
is an explanatory diagram showing changes in the frequency distribution of reflected waves with changes in the incident angle obtained using the present invention, FIG. 9B is a perspective explanatory diagram showing the actual measurement situation, and FIG. FIG. 1 Linear converging beam transducer 2 Parallel beam transducer 3 Piezoelectric body 4 Delay material 5 Objective surface with cylindrical side surface 6 Linear focal point 7 Object 8 Fixing material 9 Ultrasonic propagation liquid 10 Point bundle beam transducer II Parallel beam Transducer I Piezoelectric delay material Concave objective surface fixing material Point focus Object substrate film Liquid for ultrasound propagation Object Transmitting transducer Receiving transducer Receiving transducer Frequency distribution of reflected waves obtained from transducer Linear convergence Beam transducerParallel beam transducerConvergent beamFocal micro areaObject for transmissionParallel beam transducerFor receptionConvergent beam transducerFor receptionConvergent beam transducerFocus defined by the transducerMinimum area of the objectNormal to the object surfaceObject Assumed cylindrical wave oscillation source point at the surface.Object focus of the focused beam transducer.Normal of the parallel beam transducer.Normal to the object surface.Center line of the ultrasound microscope lens.Focus of the focused beam transducer. Normal ultrasound! Center line of J microscopic lens Normal to the surface of the object Delay material Piezoelectric material Liquid for ultrasonic propagation Transducer oil film point number flux Beam transducer focal point (measuring point) Ultrasonic incident angle Width of incident angle - Reflection angle width Incident angle defined by parallel beam transducer Parallel beam for transmission Incidence defined by transducer Angle θ5 Angle of incidence defined by parallel beam transducer θ6 Angle of incidence defined by parallel beam transducer θ7 Minimum angle of incidence for measurement defined by parallel beam transducer θB Maximum incidence for measurement defined by parallel beam transducer Angle θ9 Incident angle defined by the parallel beam transducer where the minimum phenomenon appeared most strongly θlO Incident angle defined by the parallel beam transducer θ10 θ11 Incident angle defined by the parallel beam transducer

Claims (1)

[Claims] 1) Ultrasonic waves are oscillated by applying an electrical signal to a piezoelectric body, the oscillated ultrasound waves are irradiated obliquely onto the surface of a subject, and the reflected waves are received using the piezoelectric body. In the ultrasonic microscope lens configured as follows, either the transmitting side or the receiving side is a parallel beam transducer that oscillates a plane wave when an electric signal is applied, and the other side is a parallel beam transducer that oscillates a plane wave when an electric signal is applied. An ultrasonic microscope lens comprising a point-converging beam transducer that converges sound waves to a single point. 2) It is configured to oscillate ultrasonic waves by applying an electrical signal to the piezoelectric body, irradiate the oscillated ultrasonic waves obliquely onto the surface of the subject, and receive the reflected waves using the piezoelectric body. In an ultrasound microscope lens, either the transmitting side or the receiving side is a parallel beam transducer that emits a plane wave when an electric signal is applied, and the other side is a parallel beam transducer that emits a plane wave when an electric signal is applied. An ultrasound microscope lens comprising a linear converging beam transducer. 3) The ultrasonic microscope lens described in claim 1 or 2 is applied to the surface of a subject, and the oscillated ultrasonic waves are obliquely irradiated onto the surface of the subject and the reflected waves are received. An ultrasonic microscope lens characterized by obtaining the output of reflected waves from a subject or its frequency distribution at different intended incident angles by tilting the parallel beam transducer in a direction in which the incident angle of the ultrasonic waves changes within a range. Reflected wave collection method used.