JPS63169554A - Ultrasonic microscope lens - Google Patents

Abstract

PURPOSE:To accurately find the film thickness of the film of a sample by making an ultrasonic wave incident on the same at the characteristic angle of incident that a combination of a cylindrical sample and liquid for ultrasonic wave propagation has, and finding the frequency at which its reflection factor is minimum. CONSTITUTION:The ultrasonic wave is made incident on the sample 10 at the characteristic angle theta of incidence that the combination of the cylindrical sample, a film, and liquid for ultrasonic wave propagation has. A conic lens 20 for transmission with a vertical angle 2theta is combined with a conic lens 30 for reception across the liquid for ultrasonic wave propagation and a piezoelectric body 22 for transmission and a piezoelectric body 32 for reception are provided on the surfaces of the lenses 20 and 30. Then the cylindrical sample 10 which has the film provided on its surface is inserted into the cavities in the centers of both lenses 20 and 30. Then the piezoelectric body 22 sends the ultrasonic wave to the sample 10 at the angle theta of incidence and the wave is reflected in the order of paths P, R, S, T, and (and received by the piezoelectric body 32. Then the frequency at which the intensity ratio between the reflected wave and incident wave, i.e. reflection factor is minimum is found. Then this frequency and the characteristic values of the sample, film, and liquid are used to calculate the film thickness from a specific expression. Thus, the film thickness can be measured accurately and speedily.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is based on the principle described in Japanese Patent Application Laid-Open No. 61-79157, and is directed to a film formed on the surface of a test object such as a cylindrical body or a linear body. This ultrasonic microscope lens is suitable for continuously measuring film thickness across various parts of a subject.

[Conventional technology]

Ultrasonic microscopes that have been developed in recent years generate ultrasonic waves by applying high-frequency electric pulses to a piezoelectric material, converge them with an acoustic lens, and irradiate them onto the sample surface while scanning the acoustic lens or the sample in an X-Y manner. At that time, the intensity or phase of the reflected ultrasound from the sample surface or the transmitted ultrasound transmitted through the sample is received by an acoustic lens and a piezoelectric material, and recorded in synchronization with the X-Y scan. This is to obtain elastic information directly below as an image.

Here, the role of the acoustic lens is to focus the ultrasonic beam generated by the piezoelectric material onto a minute area on the sample surface, thereby improving the resolution of the ultrasonic microscope image. Acoustic lenses used for this purpose are typically made of a cylinder made of sapphire, quartz glass, etc., with a piezoelectric material closely attached to one end surface and a concave spherical surface provided on the other end surface. The ultrasonic waves generated by the piezoelectric body propagate in the cylinder as plane waves, and when they reach the concave spherical surface, they are refracted there and converge on a minute area on the sample surface. In addition, a concave spherical surface is provided on one end surface of a similar cylinder, and a piezoelectric material is closely attached along that surface to create a piezoelectric material with a concave spherical surface, thereby creating an ultrasonic wave for the purpose of directly generating convergent spherical waves. Microscope lenses have also been announced.

All of these aim to obtain high resolution by converging an ultrasound beam onto a minute area on the sample surface, but one of the measurement methods using an ultrasound microscope is the so-called V (
Z) Also used in the curve method.

This is done by changing the distance between the sample surface and the acoustic lens while fixing the sample or the acoustic lens at a fixed position on the sample surface without X-Y scanning, and changing the intensity of the reflected ultrasound from the two surfaces of the sample. When recording, it is observed that the intensity changes periodically with a period specific to the material of the sample, so this method measures the elastic characteristics of the sample surface and just below the surface from the recording period obtained by this method. It is. This periodic change in reflection intensity is caused by the interference between the vertically incident component and the component incident on the sample surface at the so-called Rayleigh angle of the convergent ultrasound generated from the concave spherical lens.
Its period depends on the sound speed of Rayleigh waves near the sample surface.

As described above, most conventional acoustic lenses for ultrasonic microscopes are characterized by generating spherically focused ultrasonic waves and converging them on the sample surface.

In addition, there are Japanese Patent Application Laid-open No. 61-79157 and Japanese Patent Application Publication No. 61-79158, which are based on the film thickness measurement method described in Japanese Patent Application Laid-Open No. 61-20803. When measuring the thickness of a film formed on a substrate, ultrasonic waves are incident on the sample at a certain angle determined by the substrate, liquid, and film material, and the reflected waves are collected using the same lens. It was invented for the purpose of It generates ultrasonic waves with a fixed angle of incidence on the body.

Furthermore, there is an ultrasonic lens described in Japanese Patent Application Laid-Open No. 58-166258, which uses a piezoelectric material on the bottom of one end of a cylindrical delay material and a conical groove on the bottom of the other end. By converging in a straight line perpendicular to the body, the purpose is to obtain a deep depth of focus in ultrasonic flaw detection, etc.

In this way, most of these ultrasonic lenses are designed in such a way that the lens is positioned perpendicular to the flat object under test, and the ultrasonic waves it oscillates are received by the same piezoelectric material. be.

[Problem that the invention seeks to solve]

In a film thickness measurement method based on the film thickness measurement principle described in JP-A No. 61-20803, the film thickness is measured by injecting ultrasonic waves onto the surface of a sample film at a fixed angle and collecting reflected waves. When the object is cylindrical or linear, conventional ultrasound microscope lenses cannot make the ultrasonic wave incident on the side of the object at a fixed angle of incidence other than right angles. If the cross-sectional radius is small, the surface to be irradiated with ultrasonic waves is small, making it difficult to obtain sufficient irradiation intensity and its reflection intensity, and the phase of the reflected waves is disturbed. It was difficult to measure the thickness of the film formed on the side surface based on the measurement principle described above.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention
The apex angle of the cone is set to 20 times the angle defined in Publication No. 20803, a positive potential is placed on a curved surface other than the base of the cone, and a cylindrical or linear object is placed on the center line of the cone. When the center lines are aligned, the ultrasonic waves emitted by the piezoelectric material are focused toward the surface of the object with high energy density, and the ultrasonic waves can be incident on the surface of the object at a constant angle of incidence. Taking advantage of this fact, by positioning a similar lens opposite to the oscillation side lens, by passing or inserting the subject through the cavity opened at the center line of these lenses, the reflected waves from the sample surface can be continuously reflected. We have created a lens that can receive signals over a wide area and obtain sufficient output for film thickness measurement without causing minimum phenomena due to interference when observing the frequency distribution of the received signal due to phase shift. This is what we provide.

[In the detailed description of the invention, when applying the measurement method described in JP-A-61-20803 to the measurement of the film thickness on the side surface of a cylindrical body or a linear body, The incident angle of the ultrasonic wave incident on the core material is a value (θ) specific to the core material, film, and liquid substance, and the ratio of the ultrasonic wavelength to the film thickness (d) is When the value (H) is specific to the liquid substance,
Utilizing the fact that the reflectance of ultrasonic waves decreases, measure the wavelength (λ) of the ultrasonic waves at which the intensity of the reflected waves decreases, and calculate the film thickness using the formula (A) below (% formula %) (see Figure 6). By positioning the piezoelectric substance on the surface of a cone with an apex angle of 2θ, and positioning the ultrasonic microscope lens used for the determination so that the center line of the cylindrical or linear object coincides with the center line of the cone, It is possible to make ultrasonic waves incident on the surface of the subject with high energy density and at the above-mentioned specific incident angle θ, and even if the subject is long, a cavity can be created near the center line of the lens to allow it to pass through. This is an ultrasonic microscope lens that allows continuous measurement of film thickness.

In a conical shape with an apex angle of 2θ, normal lines from a circle having the same height V always converge at v −1 tanθ on the center line, as shown in FIG. Therefore, even if a piezoelectric material is stretched to an arbitrary width on the side surface of a cone, the ultrasonic waves always converge on the center line of the cone and always have an incident angle of θ with respect to the center line.

Next, when a cylindrical body with radius m is installed along the center of the cone, the ultrasonic waves emitted from the piezoelectric material on the back of the cone converge on the surface of this cylindrical body, as shown in Figure 3, and the ultrasonic waves at this time The energy density is equal to the energy density at the side of the cone.
You can see that it is twice as much.

As described above, when piezoelectric bodies are arranged in a conical shape, it is possible to make a focused ultrasonic wave incident at a constant angle of incidence θ and obtain a high energy density, which also holds true when a delay material is used. , in the cross section including the center line, if the center line is the X axis, the plane corresponding to the position of the piezoelectric body is y = -tanθ-x+h O≦x O<y-■
It is expressed as Also, the objective plane 26 of the delay material is y = −
tanθ−x+k O≦X O≦y”'■ Here, if a hollow section is provided along the center line of the cone so that the subject 10 can pass through, the hollow section is expressed as x=t , O≠t<k...■ (see Fig. 4). When the lens 20.30 is configured in this way, when similar lenses are positioned oppositely, As shown in FIG. 1, the ultrasonic wave emitted from point P on the piezoelectric body 22 for transmission is
→The reflected wave can be received by the receiving piezoelectric body 32 through the path U, and by moving the subject 10 passed through the cavity, the film thickness of each part of the cylindrical surface can be continuously measured.

Furthermore, if the receiving piezoelectric body 32 is divided and stretched as shown in FIG. 5, it is possible to measure the distribution of the film thickness at each portion of the cylindrical surface in the circumferential direction.

〔Example〕

When measuring the gold plating film thickness of a cylindrical test object with a gold plating film on a long N-Fe 42% alloy core material, the incident angle θ when water is used as the ultrasonic propagation material is 31@
Met. For this purpose, a conical lens with an apex angle of 62'' is made of quartz and is combined as shown in FIG. The frequency was 70MHz (see Figure 6). From this, when calculating the gold film thickness d using A2,
d=3.9 μm.

〔Effect of the invention〕

Since the present invention has the above-described configuration, the combination of materials for the core material and membrane of the cylindrical or linear test object is determined.
Furthermore, once the ultrasonic propagation liquid has been determined, ultrasonic waves are irradiated at their specific angle of incidence, and the ratio of the intensity of the reflected wave to the incident wave, that is, the frequency at which the reflectance is minimum, is measured using a frequency measuring instrument. Find the frequency, then use formula A,
If applied to the measurement method to calculate the film thickness of the measured object,
The thickness of the film formed on the surface of a cylindrical body or linear body,
By simply moving the subject along the lens center line, the distribution can be measured quickly and accurately. Furthermore, if the piezoelectric body on the receiving side is divided and constructed so that electric signals can be extracted independently, the film thickness distribution around the auxiliary measurement object can be obtained all at once.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIG. 1 is an explanatory view from the front showing an applied state of the present invention (liquid 16 is removed), FIG. 2, FIG. 3, and FIG. 4. 5 is an explanatory diagram showing the shape of a lens, FIG. 5 is a perspective view showing an applied state of the present invention, and FIG. 6 is a spectral distribution diagram of an electric signal obtained from a receiving piezoelectric body. Further, FIG. 7 is an explanatory diagram showing the principle of a conventionally known ultrasonic film thickness measurement technique. 10... Subject 12... Membrane to be measured 14... Core material (or substrate) 16... (For ultrasound propagation) Liquid 20... Lens for transmission 22... (For transmission) Piezoelectric body 24... Delay material 26 (for transmission)... Objective surface 30 (of delay material)... Receiving lens 32... Piezoelectric material 34 (for reception)... Delay (for reception) Material 36...piezoelectric body

Claims (1)

[Claims] When measuring the film thickness of a film formed on a cylindrical body or a linear body, the incident angle of the ultrasonic wave incident on the surface of the subject from the liquid for ultrasonic propagation is determined by the angle of incidence between the core material, the liquid, and the membrane. The characteristic value of the substance (
θ), and when the ratio of the ultrasonic wavelength (λ) to the film thickness (d) is a value (H) specific to the core material, liquid, and film material, measure the ultrasonic wavelength (λ). In the ultrasonic microscope lens used to determine the film thickness using the following formula (A), d=λ・H... (A), the delay material is in orthogonal x, y space, and h>k y =-tanθ・x+h 0≦x 0≦y...(1) y=-tanθ・x+k 0≦x 0≦y...(2) x=-t 0≠t<k... ...(3) Is it composed of a solid formed by rotating the plane enclosed by equations (1), (2), and (3) above by 360° around the x-axis?
Or a part of it, in which a piezoelectric body is formed along the surface of the plane created by rotating equation (1) around the x-axis, and the normal of the plane on which the piezoelectric body is formed and (2
) and a plane rotated around the x-axis exist on the surface of the delay material.