JP2580766B2 - Ultrasonic microscope lens and reflected wave sampling method using the lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial application field> The present invention obliquely enters an ultrasonic wave at an intended incident angle onto a surface of a subject, collects a reflected wave thereof, and depends on the incident angle of the ultrasonic wave. The present invention relates to an ultrasonic microscope lens used for performing film thickness measurement, adhesion measurement, and the like based on the shape of the obtained frequency distribution, and a method for collecting reflected waves using the ultrasonic microscope lens.

<Prior Art> A V (z) curve method using a lens of an ultrasonic microscope is known as a method for non-destructively quantitatively measuring the structure and elastic constant of a subject using ultrasonic waves. The V (z) curve method corresponds to the phase velocity of the surface acoustic wave due to excitation of the surface acoustic wave on the surface of the object when the lens of the ultrasonic microscope is moved up and down perpendicular to the surface of the object. Since the output oscillates in a cycle, the phase velocity of the surface acoustic wave is determined from the oscillation cycle. Since the phase velocity of the surface acoustic wave can be obtained as a function of the structural parameters of the subject and the elastic constant,
Conversely, the structural parameter and elastic constant of the subject can be measured from the observed phase velocity of the surface acoustic wave.

Japanese Patent Application Laid-Open No. 61-20803 discloses a technique for measuring the structure of an object such as an elastic constant and a film thickness by using an excitation phenomenon of a surface acoustic wave excited on the surface of the object. There is a technique described in Japanese Patent Application No. 63-202569 to evaluate the properties. These receive the ultrasonic waves oscillated by the transmitting transducer 23 as shown in FIG.
When an object 21 having a film 19 formed on the sample 18 is incident at a certain range of incident angle θ1 determined by the substrate, the film, and the substance constituting the ultrasonic wave propagation liquid, the object is exposed at the same angle as the incident angle. Ultrasonic waves are emitted from the sample 21. The emitted reflected wave is detected by the receiving transducer 24 to obtain the frequency distribution 26 shown in FIG. 3B.
It takes advantage of the fact that the reflected output takes a minimum at a frequency that depends on the structural parameters and elastic properties of. In the film thickness measuring method, the film thickness is measured by the equation (1).

fxd = C (constant) (1) where d is the film thickness. f is the frequency at which the reflected wave output minimum phenomenon occurs in the frequency distribution 26 of the reflected wave obtained by the receiving transducer 24. C is a constant determined by the constituent materials of the substrate and the film, the liquid for ultrasonic wave propagation, and the incident angle of ultrasonic waves.

On the other hand, in the adhesion determination method, the presence or absence of an intermediate layer made of another substance between the film and the substrate, and separation are detected from the manner in which the frequency of the reflected wave output is minimized at each incident angle when the incident angle is shifted. Things. Japanese Unexamined Patent Publication No. Sho 61-79 discloses a document relating to an ultrasonic microscope lens used in these measuring methods.
157 and JP-A-61-79158. However, these ultrasonic microscope lenses cannot change the angle of incidence, and if the constituent materials of the film and the substrate change, the angle of incidence for exciting the surface acoustic wave changes, making measurement impossible. In particular, when a measurement is to be performed on a sample made of an unknown substance, the incident angle must be continuously changed to find the optimum incident angle at which the reflected wave output minimum phenomenon occurs, which requires a great deal of time and effort. Therefore, from the above demand, there is a demand for an ultrasonic microscope lens that can easily collect reflected waves at different incident angles.

Furthermore, when measuring a micro area on the surface of the subject based on the above-described film thickness measurement method and adhesion determination method, the ultrasonic wave is converged on the surface of the object, or only from the micro area on the surface of the object. Must be detected. In the lenses described in the above-mentioned JP-A-61-79157 and JP-A-61-79158, ultrasonic waves can be incident at a fixed incident angle, but when trying to measure in a minute area, oscillation occurs. In addition, there is no other way than to reduce the area of the receiving piezoelectric material, and since the reception output is reduced in this way, there is a limit to the measurement in a minute region naturally.

<Problems to be Solved by the Invention> As described above, 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, a film is formed on a substrate. For the formed subject,
When trying to non-destructively measure the film thickness and the adhesion between the substrate and the film using ultrasonic waves, the incident angle at which ultrasonic waves are incident when the constituent material of the subject changes with a conventional ultrasonic microscope lens Therefore, it is necessary to replace the lens with an ultrasonic microscope having a different incident angle. Furthermore, obtaining high resolution has been difficult with conventional techniques. The present invention solves these problems of the prior art.

<Means for Solving the Problems> The present invention applies an electric signal to a piezoelectric body, oscillates ultrasonic waves, and irradiates the oscillated ultrasonic waves obliquely to the surface of a subject,
In an ultrasonic microscope lens configured to receive the reflected wave of the ultrasonic wave using a piezoelectric body, either the transmitting side or the receiving side of the transducer transmits a plane wave when an electric signal is applied. The other transducer is a point-focusing beam transducer that focuses sound waves at one point or a linear focusing beam transducer that focuses sound waves in a straight line when an electric signal is applied. A point focusing beam transducer or a linear focusing beam transducing device having the focusing point or the linear focusing portion on the surface of the subject, and the parallel beam transducing device having the receiving surface thereof. Is an ultrasonic microscope lens directed toward the focal point or the linear focal point.

Furthermore, such an ultrasonic microscope lens is used to oscillate the ultrasonic waves in the parallel beam transducer within a range where the oscillated ultrasonic waves are obliquely applied to the object surface and the reflected waves are received. This is a reflected wave collecting method using an ultrasonic microscope lens, characterized in that an output of a reflected wave from a subject at an intended incident angle or a frequency distribution thereof is obtained by inclining in a direction in which the incident angle changes.

<Detailed Description of the Invention> As shown in FIG. 1 or FIG. 2, in an ultrasonic microscope lens for irradiating an ultrasonic wave to a subject and collecting a reflected wave thereof, a ultrasonic wave oscillating side and a receiving side are used. The principle of characteristics of an ultrasonic microscope lens composed of two transducers, one composed of a point convergent beam transducer or a linear convergent beam transducer and the other composed of a parallel beam transducer, will be described.

First, a case is considered in which a linear convergent beam transducer as shown in FIG. 1 is focused on the surface of the subject, and is installed on the subject so that the reflected wave is received by the parallel beam transducer.

As shown in FIG. 4, a convergent beam 30 oscillated by a linear convergent beam transducer 28 whose objective surface has a cylindrical side surface shape.
Is a linear focusing beam transducer on the surface of the subject 36
Incidence and focus with an incident angle width θ2 determined by the aperture angle of 28
It converges to a very narrow area of 32. This incident sound wave is reflected,
It is re-emitted into the ultrasonic wave propagation liquid again with the same reflection angle width θ2. Here, based on the concept of Fourier optics, this reflected wave can be expressed as follows.

As shown in FIG. 5, the wave (FIG. 5A) radiated from a very small area 34 corresponding to the focal point 32 of the transducer is a plane wave (FIG. 5B, C, D) propagating in the color direction. It can be considered as a superposition. Of the decomposed plane wave components propagating in various directions, those components which are perpendicularly incident on the parallel beam transducer 29 as shown in FIG. 5C are converted into electric signals without causing a phase shift on the piezoelectric body surface. However, as shown in FIG. 5B and FIG. 5D, components decomposed in a direction shifted from the direction perpendicular to the piezoelectric body and reflected are:
Since the sound wave obliquely enters the piezoelectric body and causes a phase shift, the contribution of these components to the output becomes relatively weak.
From this, the electric signal received by the ultrasonic microscope lens has a large amount of elasticity information in a minute area 34 corresponding to the focal point 32 of the linear convergent beam transducer 28 on the surface of the subject, and a parallel beam. Transducer
This is a signal corresponding to the case where an ultrasonic wave is incident at an incident angle of 29.

As shown in FIG. 6A, similarly, when the receiving and transmitting transducers of FIG. 4 are reversed, the elasticity information at the time of incidence at the incident angle defined by the parallel beam transducer is used as the object information. 41 can be obtained for a small area 42 corresponding to the focal point 40 of a linear convergent beam transducer on the surface. As shown in FIG. 6A, the plane wave transmitted from the parallel beam transducer 38 is
The light is irradiated on the surface of the subject 41 at a constant incident angle, and is reflected by the surface of the subject 41. Based on the Fourier engineering concept, a plane wave can generally be considered as a superposition of cylindrical waves radiated from each point 45 on the surface of the subject 41. Of the components reflected on the surface of the subject, only the component of the reflected wave from the area 42 corresponding to the focal point 40 of the convergent beam transducer as shown in FIG. Is converted into an electric signal without causing the focal point of the convergent beam transducer as shown in FIGS. 6C and 6E.
The components of the reflected waves from regions other than the region 42 cause a phase shift on the surface of the piezoelectric body, and the magnitude of the electric signal contributing to the output of these components is relatively weak. As a result, the linear convergent beam transducer Small area 42 equivalent to 39 focal points
Only the elastic properties of appear in the received signal.

The above is because the normal 51 on the surface of the subject as shown in FIG.
When the center line 52 of the ultrasonic microscope lens is tilted with respect to
In the case of FIG. 7A, an ultrasonic wave is applied at an incident angle θ5 defined by a parallel beam transducer, and in the case of FIG.
Means that a response to the ultrasonic wave of the subject when irradiated to 48 is obtained, which means that the physical properties of the subject at any incident angle by simply tilting the entire ultrasonic microscope lens with respect to the subject 48, or A signal reflecting the structure can be extracted.

In the case of a point convergence transducer, the explanation can be made using the concept of Fourier optics as in the case of the linear convergence beam transducer described above. In this case, since the focal point is a point, measurement with high spatial resolution is possible. .

If one of the ultrasonic oscillation and the reception transducer is constituted by a point-converging or linear-converging beam transducer and the other transducer is constituted by a parallel beam transducer, as shown in FIG. In order to construct a convergent beam transducer by making the piezoelectric body itself cylindrical or concave,
As shown in FIG. 1 and FIG. 2, a convergent beam transducer is formed by radiating an ultrasonic wave into a delay member with a planar piezoelectric body and processing the object surface of the delay member into a cylindrical side surface shape or a concave shape. The technical scope of the present invention is not limited by this. Similarly, the parallel beam transducer is not limited by whether or not a delay member is used.

<Example 1> Example 1 The thickness of a substrate and a film formed on the substrate whose constituent materials are unknown is measured using the ultrasonic microscope lens of the present invention according to the following procedure. Was possible.

An ultrasonic microscope lens having a structure as shown in FIG. 1 was used. The transducer on the receiving side constitutes a linear convergent beam transducer 1 by cutting the objective surface 5 of the fused silica delay member 4 into a cylindrical side surface shape, and the parallel beam transducer 2 is fused on the transmission side into the delay member 4. It was configured using quartz. The linear convergent beam transducer and the parallel beam transducer were fixed using the fixing member 8 so as to have an inclination of 55 deg. The aperture angle of the linear convergent beam transducer is 30 deg. The measurement was performed using water as the liquid for ultrasonic propagation, and the ultrasonic microscope lens was moved from the angle θ7 = 15 deg to the angle θ8 = 6 with respect to the surface of the object as shown in FIG. 9A.
The reflected wave was collected while tilting so as to continuously change to 0 deg, and its frequency analysis was performed. As a result, as shown in FIG. 9A, the angle of incidence of the ultrasonic microscope lens of the present invention was θ = 30 de.
At g, it was found that a minimal phenomenon caused by surface acoustic wave excitation on the surface of the subject was well observed. For this reason,
As shown in FIG. 9B, the angle of incidence θ of the parallel beam transducer on the surface of the subject is measured using the ultrasonic microscope lens.
The following measurement was continuously performed by tilting the ultrasonic microscope lens so that 9 was always 30 deg.

A reflected wave was collected from a specimen having the same material composition as that of the above-mentioned specimen and whose film thickness was found to be 5 μm, and as a result of frequency analysis, a minimum was observed at 50 MHz. From this, it was found that the value of C in the equation (1) at the given incident angle of the specimen of 30 deg was 250, and thereafter, the specimen of unknown film thickness composed of the same substance Against
As shown in FIG. 9B, the measurement was performed with θ9 = 30 deg as shown in FIG. 9B by setting the value of C to 250.

Example 2 As shown in FIG. 10, gold plating was performed on a fused quartz substrate 70.
In the determination of the close contact of the subject, which was performed in 71, it was possible to detect an area where the oil film 75 was present between the gold film and the substrate as follows.

In the ultrasonic sensor, as shown in FIG. 2, the transmitting side parallel beam transducer 11 is constituted by using a delay material made of fused silica, and the receiving side transducer is formed by cutting the object surface 14 of the delay material into a concave surface. The point convergent beam transducer 10 was constituted by.

The angle between the center line of the point convergent beam transducer and the normal of the parallel beam transducer is fixed by the fixing member 15 so as to be about 40 deg. The diameter of the circular piezoelectric body is
1 mm. The aperture angle of the point convergent beam transducer is 20 deg. Water was used as the liquid for ultrasonic propagation. The spatial resolution of the ultrasonic microscope lens having the above configuration at the focal point at 50 MHz was 6 μm down to 50 μm. It can be seen that the value of the spatial resolution is much improved compared to 550 μm in the case of using a parallel beam transducer for both conventional transmitting and receiving transducers.

According to the theoretical calculation in elasticity engineering, when the film and the substrate are completely adhered and water is used as the liquid for ultrasonic propagation, the incident angle of the ultrasonic wave to this object surface is 17deg to 20deg.
When an ultrasonic wave is incident at an incident angle between the surface acoustic waves are excited on the surface of the subject, a minimum appears in the frequency distribution of the reflected wave, and the frequency causing the minimum is a certain film thickness,
It was found that the angle of incidence was 202 MHz at an incident angle of θ10 = 17.3 deg, and 281 MHz at an incident angle of θ11 = 19.2 deg. Adhesion judgment was performed by the following procedure using the calculation results. First, the ultrasonic microscope lens is set so that the focal point of the point converging beam transducer is located on the surface of the object, and the normal of the parallel beam transducer is θ10 = 17.3 de with respect to the object.
The ultrasonic beam emitted from the parallel beam transducer was applied to the subject, and the reflected wave was set to be received by the point convergent beam transducer, and the frequency distribution of the reflected wave was obtained. Similarly, the entire ultrasonic microscope lens was tilted so that the normal line of the parallel beam transducer was set to have a tilt of θ11 = 19.2 deg with respect to the subject, and the same processing was performed. The value of the minimum frequency that appears in the frequency distribution obtained in this experiment is
At each point b, c, ...

Next, the ratio to the minimum frequency in each case when perfect contact is assumed is as follows.

At points A and C, the ratio between the minimum frequency when the incident angle was changed and the minimum frequency when perfect contact determined from the theoretical calculation was the same at each incident angle was judged to be perfect contact. Is not completely adhered. The same determination was made over the entire surface of the subject to detect a poor adhesion portion. An oil film was found between the gold and the fused quartz in an area determined to be poorly adhered by a destructive test later.

<Effects of the Invention> Since the present invention has the above-described configuration, it is common to the first, second, and third inventions that the ultrasonic wave is incident on the subject and the reflected wave is collected to measure the film thickness and determine the adhesion. In performing
It is possible to measure reflected waves at different incident angles only by tilting the entire ultrasonic microscope lens with respect to the surface of the subject.

Further, the first aspect of the present invention enables measurement of the film thickness and determination of adhesion in a minute area, and is particularly useful when used as a sensor section of a spectrum ultrasonic microscope.

[Brief description of the drawings]

The drawings show and explain the principles and embodiments of the present invention. FIGS. 1 and 2 are perspective explanatory views of an ultrasonic microscope lens of the present invention. FIG. 3 illustrates the principle of a conventional film thickness measurement method, in which A is a cross-sectional explanatory view of a measurement example, and B is a frequency distribution diagram of the obtained reflected wave. 4 to 7 illustrate the principle of the ultrasonic microscope lens. FIG. 4 is a cross-sectional explanatory view of a measurement example, and FIGS.
D is a plane wave division explanatory diagram of reflected ultrasonic reception when the receiving transducer is a parallel beam transducer. FIGS. 6A, 6B, 6C, D, and E show cases where the receiving transducer is a linear converging beam transducer. FIG. 7 is an explanatory diagram of plane wave division for reflected ultrasonic reception, and FIG. 7 is an explanatory diagram of reception when the ultrasonic microscope lens is tilted. FIG. 8 is an explanatory view of another embodiment of the present invention. Ninth
FIG. A is an explanatory diagram showing a change in the frequency distribution of the reflected wave with a change in the incident angle obtained by using the present invention. FIG. 9B is a perspective explanatory diagram showing the actual measurement, and FIG. It is a perspective explanatory view of the measurement at an incident angle. DESCRIPTION OF SYMBOLS 1 ... Linear converging beam transducer 2 ... Parallel beam transducer 3 ... Piezoelectric body 4 ... Delay material 5 ... Cylinder side surface objective surface 6 ... Linear focal point 7 ... Subject 8 ... Fixed Material 9: Liquid for ultrasonic wave propagation 10: Point convergent beam transducer 11: Parallel beam transducer 12: Piezoelectric body 13: Delay member 14: Concave object surface 15: Fixing member 16 ... Point focal point 17 ... Subject 18 ... Substrate 19 ... Film 20 ... Ultrasonic propagation liquid 21 ... Subject 23 ... Transducer 24 ... Transducer 26 ... Receiver Frequency distribution of the obtained reflected wave 28 Linear convergent beam transducer 29 Parallel beam transducer 30 Focused beam 32 Focus 34 Small area 36 Subject 38 Sjudder 39… Focused beam transducer for reception 40… Focus 41 defined by the focused beam transducer for reception 41… Subject 42… Small area 43… Normal to the subject surface 45… Subject surface Oscillation source point of cylindrical wave assumed at 48 ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. The center line of the beam 54 ... The focal point of the convergent beam transducer 55 ... The normal line of the parallel beam transducer 56 ... The center line of the ultrasonic microscope lens 57 ... The normal line of the surface of the subject 58 ... The delay material 59 ... The piezoelectric Body 60… Ultrasonic wave propagation liquid 61… Subject 64… Linear convergent beam transducer 65… Parallel beam transducer 67… Substrate 68… Film 69… Subject 70… Substrate 71… Gold plating film 72 Subject 73 Point convergent beam transducer 74 Parallel beam transducer 75 Oil film 77 Focus (measurement point) of point convergent beam transducer θ1 Ultrasonic incident angle θ2 Incident Angle width = reflection angle width θ3: incident angle defined by parallel beam transducer θ4: incident angle defined by transmitting parallel beam transducer θ5: incident angle defined by parallel beam transducer θ6 ... The incident angle defined by the parallel beam transducer θ7: The minimum incident angle of the measurement defined by the parallel beam transducer θ8: The maximum incident angle of the measurement defined by the parallel beam transducer θ9: The minimum phenomenon Incident angle defined by parallel beam transducer that appeared most strongly θ10: Defined by parallel beam transducer Angle of incidence defined by the incident angle θ10 θ11 ...... parallel beam transducer that

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Katsumi Ohira 1-5-1, Taito, Taito-ku, Tokyo Toppan Printing Co., Ltd. (56) References JP-A-2-35353 (JP, A) JP-A-1 -284752 (JP, A) JP-A 1-254859 (JP, A) JP-A-61-245055 (JP, A)

Claims (3)

(57) [Claims] An ultrasonic wave is oscillated by applying an electric signal to a piezoelectric body, and the oscillated ultrasonic wave is irradiated obliquely onto a surface of a subject,
In an ultrasonic microscope lens configured to receive the reflected wave of the ultrasonic wave using a piezoelectric body, either the transmitting side or the receiving side of the transducer transmits a plane wave when an electric signal is applied. The other transducer is a point focusing beam transducer that focuses a sound wave to one point when an electric signal is applied, and the point focusing beam transducer is An ultrasonic microscope lens having the focal point on the surface of the subject, and the parallel beam transducer having its receiving surface facing the focal point. 2. An ultrasonic signal is oscillated by applying an electric signal to a piezoelectric body, and the oscillated ultrasonic wave is irradiated obliquely on the surface of the subject,
In an ultrasonic microscope lens configured to receive the reflected wave of the ultrasonic wave using a piezoelectric body, either the transmitting side or the receiving side of the transducer transmits a plane wave when an electric signal is applied. The other transducer is a linear focusing beam transducer that focuses a sound wave linearly when an electric signal is applied, and the linear focusing beam transducer is An ultrasonic microscope lens comprising: a linear focusing portion for focusing the sound wave on the surface of the subject; and a parallel beam transducer having a receiving surface facing the focusing portion. 3. An ultrasonic microscope lens according to claim 1 or 2, wherein an ultrasonic wave oscillated on the surface of the object is radiated obliquely onto the surface of the object, and a reflected wave of the ultrasonic wave is applied to the surface. In the direction in which the incident angle of the ultrasonic wave in the parallel beam transducer changes in the range where the light is received, thereby obtaining the output of the reflected wave from the subject or the frequency distribution thereof at the intended different incident angles. A method of collecting reflected waves using an ultrasonic microscope lens.