JPH05288729A - Ultrasonic microscope - Google Patents

Abstract

PURPOSE:To reduce a size and a cost of an ultrasonic microscope and realize highly reliable sample evaluation by means of a measured sound speed value including little error. CONSTITUTION:An ultrasonic microscope for measuring a V(z) curve of a sample to evaluate the sample comprises a means for obtaining complex V(z) data including from the V(z) curve to phase information and a sound speed measuring means 8 as a sound speed calculating means for obtaining a sound speed of a supersonic wave propagating medium 3 from the phase data of the complex V(z) data in a range where a distance between the sample and an acoustic lens is larger than a focal distance of the acoustic lens 2. A reflectance measuring means 9 for obtaining reflectance of the sample from the sound speed information obtained by the means 8 and the complex V(z) data is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic microscope capable of measuring V (z) characteristics of a sample and analyzing the properties of the sample.

[0002]

2. Description of the Related Art In order to quantify the elastic properties of a sample and to evaluate the structure of a thin film, there is a so-called V (z) curve analysis method that utilizes the acoustic characteristics of the sample. This V (z) curve can be obtained by using the basic functions of the ultrasonic microscope.

In a general ultrasonic microscope, ultrasonic waves converged by an acoustic lens are incident on a sample, and reflected ultrasonic waves from the sample are incident on the acoustic lens again and converted into electrical reflection signals. The peak detection value of this reflected signal is A / D
It is stored in the memory via the converter.

The above series of operations is performed by moving the acoustic lens to each position in the ultrasonic wave incident direction (Z direction), and each peak detection value at each position in the Z direction of the acoustic lens is calculated as Z of the acoustic lens. It is stored in association with each position in the direction. When the stored peak detection value is plotted on the vertical axis and the acoustic lens-sample distance z is plotted on the horizontal axis, a V (z) curve is obtained. This V (z) curve has a shape peculiar to a material consisting of peaks and valleys.

Here, between the pitch of the peak and the valley of the V (z) curve
Δz, the surface acoustic wave velocity of the sample (Sonic velocity of Rayleigh wave)
To V_R, The working frequency is f, and the space between the acoustic lens and the sample is
The speed of sound in the coupler liquid as an ultrasonic wave propagation medium
If Vo, the following relational expression holds. Δz = V_R ² / (F ・ Vo) V_R= (Δz · f · Vo)^1/2  Therefore, from the pitch interval Δz of the V (z) curve,
The surface wave velocity can be obtained. As mentioned above, conventional
In the evaluation of the substance using the V (z) curve of
I was paying attention only to the size.

On the other hand, it has recently been found that more effective information can be obtained by measuring the complex V (z) curve including the phase of the reflected ultrasonic wave. For example, complex V
The reflection function of the sample can be obtained by performing an inverse Fourier transform on the (z) curve, and it is possible to know not only the surface wave sound velocity of the sample but also the longitudinal and transverse wave sound velocities from the reflection function.

By the way, when the sample is analyzed using the complex V (z) curve, the sound velocity information of the coupler liquid filled between the sample and the acoustic lens is required. Conventionally, the speed of sound of the coupler liquid has been indirectly obtained by measuring the ambient temperature and water temperature of the coupler liquid.

For example, when water is used as the coupler liquid, the temperature of the water is measured or controlled, or the ambient air temperature is regarded as the temperature of the water to obtain the water temperature, and the sound velocity at the water temperature is converted into a conversion table. Wanted from.

[0009]

However, in order to measure or control the temperature of the coupler liquid,
Since a temperature measuring device and a temperature control device are required, the size of the device becomes large and the cost increases.

Further, due to the influence of impurities eluted into water from the sample, or impurities mixed into water for other reasons, or the local change in water temperature, the temperature between the actual propagation path of ultrasonic waves and the measured temperature is There may be an error in.

Further, the temperature-sound velocity characteristics of coupler liquids other than water may not be clear. In such a case,
Before starting the measurement, it is necessary to measure the temperature-sonic velocity characteristic of the coupler liquid used.

The present invention has been made in view of the above circumstances, and in a series of processes for analyzing complex V (z) data without using an external device such as a temperature measuring device and a temperature control device. By obtaining the sound velocity information of the coupler liquid, it is possible to reduce the size of the device and reduce the cost, and by measuring the sound velocity information of the path through which the ultrasonic waves propagate, it is possible to obtain a sound velocity measurement value that contains almost no error. It is an object of the present invention to provide an ultrasonic microscope that can perform sample evaluation with high reliability.

[0013]

In order to achieve the above object, the ultrasonic microscope of the present invention is configured such that an ultrasonic wave converged by an acoustic lens is incident on a sample, and reflected ultrasonic waves from the sample are electrically reflected signals. V (z) curve representing the relationship between the position Z of the acoustic lens or the sample in the Z-axis direction and the signal value V of the reflected signal corresponding to that position, with the incident direction of the ultrasonic wave as the Z-axis. To obtain information about the sample by analyzing the V (z) curve of the V
A means for obtaining complex V (z) data including the (z) curve to the phase information of the reflected ultrasonic wave, and the complex V (in the range where the sample-acoustic lens distance is larger than the focal length of the acoustic lens. z) sound velocity measuring means for obtaining the sound velocity information of the ultrasonic wave propagation medium filled between the sample and the acoustic lens from the phase data of the data, the sound velocity information obtained by the sound velocity measuring means, and the complex V (z) data. And reflectance measuring means for obtaining the reflectance of the sample.

[0014]

In the ultrasonic microscope of the present invention, the ultrasonic wave is incident on the sample from the acoustic lens at each position where the distance between the sample and the acoustic lens is changed, and the reflected ultrasonic wave from the sample is converted into a reflected signal each time. It is taken in and taken. Then, complex V (z) data in which the complex reflection signal of each reflection signal and the position of the acoustic lens or the sample in the ultrasonic wave incident direction are associated with each other is measured. The complex V (z) data of the sample thus measured is given to the sound velocity measuring means, and from the phase data of the reflected ultrasonic wave in the range where the distance between the sample and the acoustic lens is larger than the focal length of the acoustic lens, Sound velocity information of the ultrasonic propagation medium is required. The sound velocity information obtained by the sound velocity measuring means and the complex V (z) data are given to the reflectance measuring means to obtain the reflectance of the sample.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows functional blocks of an ultrasonic microscope according to an embodiment of the present invention. The ultrasonic microscope according to the present embodiment is provided with a high-frequency transmission / reception unit 1 with a duration of 10 cycles.
A burst wave consisting of a pulse wave of about 100 times is generated. This burst wave is supplied to the acoustic lens 2 and converted into ultrasonic waves by a transducer (not shown), and the ultrasonic waves are converged by the acoustic lens 2. The ultrasonic waves focused by the acoustic lens 2 are the coupler liquid 3
It propagates through the inside and enters the sample 4.

On the other hand, the reflected ultrasonic wave reflected by the sample 4 enters the acoustic lens 2 again, and the reflected ultrasonic wave is converted into an electric reflected signal by the transducer, and the high frequency transmitting / receiving section 1 is obtained.
Has been entered into. Then, the reception intensity (V) of the reflected signal input by the high frequency transmission / reception unit 1 is sent to the data storage unit 5,
The data storage unit 5 stores the reception intensity (V) in association with the position of the acoustic lens 2 in the ultrasonic wave incident direction (Z direction).

The acoustic lens 2 is held by a Z stage 6 so as to be movable in the Z direction. The Z stage 6 receives the Z position signal from the controller 7 and operates to move the acoustic lens 2 to the Z position instructed by the controller 7. Further, in this embodiment, the sound velocity calculator 8 as the complex V (z) data creating means and the sound velocity measuring means.
And a reflectance calculating section 9 as a reflectance measuring means.

The sound velocity calculation unit 8 operates under the control of the controller 7 and V stored in the data storage unit 5 is controlled.
(Z) Complex V that includes the phase information of the reflected ultrasonic wave
(Z) It has a function of converting it into data and storing it again in the data storage unit 5. It also has a function of calculating the sound velocity of the coupler liquid 3 from the complex V (z) data according to an algorithm described later, and storing the obtained sound velocity information in the data storage unit 5 again.

Further, the reflectance calculating section 9 operates under the control of the controller 7, and the complex V (z) data stored in the data storage section 5 and the calculated sound velocity information are used in accordance with an algorithm to be described later. 4 has a function of calculating the reflectance and storing the obtained reflectance information in the data storage unit 5 again. Here, a method of measuring the temperature of the coupler liquid 3 and the reflectance of the sample from the complex V (z) data of the sample will be described. The complex V (z) curve of the sample is
It can be expressed by equation (1).

[0021]

[Equation 1]

Where Z is the distance between the sample and the acoustic lens, and P is
Is the pupil function of the acoustic lens, Kr is the radial component of the wave number of the sound wave,
R is the reflectance of the sample, Kz is the z component of the wave number of the sound wave, and C is a constant. The equation (1) is modified as follows. Complex V (z) = A (z) · B (z) (3) A (z) = exp [−j · 2K · Z] (4)

[0023]

[Equation 2] However, K has shown the magnitude of the wave number of a sound wave.

By dividing the complex V (z) curve as described above, A (z) represents the phase change of the reflected ultrasonic wave in proportion to the Z change. Further, B (z) is an amount that reflects the surface characteristics of the sample, and the amplitude component and phase component due to B (z) are as shown in FIGS. In addition,
In the graphs shown in FIGS. 2 (a) and 2 (b), the point where the focal length of the acoustic lens and the interval between the sample and the acoustic lens match is taken as O, and the direction in which the acoustic lens is closer to the sample than the focal length is minus. On the contrary, the direction in which the acoustic lens is farther from the sample than the focal length is positive. From FIG. 2 (b), Z>
It can be seen that the phase of B (z) is constant in the range of Zo> 0, that is, where Z is sufficiently longer than the focal length. Therefore, only the effect of A (z) is included in the range of Z>Zo> 0 in the measured complex V (z) data. In this embodiment, the sound velocity of the coupler liquid is calculated by the following procedures (1) to (3).

(1) From the measured complex V (z) data, the portion where the phase component curve of B (z) becomes a straight line, that is, Z
The part where the phase is almost constant when> 0 is taken out. Specifically, the B (z) curve is displayed and visually searched for the Z position (Zo) from the focal length where the phase has a substantially constant value. (2) The slope L of the phase in the portion where the phase has a substantially constant value is determined by the method of least squares. (3) Obtain λ or c from the relational expression L = 4π / λ = 4πν / c. Here, ν is frequency, λ is phase, and c is speed of sound. The reflectance R (2cos θ) of the sample is calculated based on the following equation. R (u) = F ^-1 [V (t)] / P ² (U) (6) where u is 2cos θ, t is Z / λ, and F is Fourier transform. The pupil function P is obtained in advance by another method. The operation of this embodiment configured as described above will be described.

First, the V (z) curve of Sample 4 is measured.
In this case, a position command in the Z direction is sent from the controller 7 to the Z stage 6, and when the Z position of the acoustic lens 2 is determined, a transmission trigger signal is given from the controller 7 to the high frequency transmitting / receiving unit 1 and the ultrasonic wave is applied to the sample 4. Is incident.
The reception intensity (V) of the reflected signal for this ultrasonic wave is stored in the data storage unit 5. The data storage unit 5 stores the reception intensity (V) input from the high frequency transmission / reception unit 1 and the position command value in the Z direction input from the controller 7 in association with each other. By repeating such an operation at a plurality of Z positions from the position where the acoustic lens 2 is closest to the sample 4 to the position where it is farthest from the sample 4, data of the V (z) curve is stored in the data storage unit 5. ..

In this way, the controller 7 whose V (z) curve has been measured gives an operation start command to the sonic velocity calculator 8. Sound velocity calculator 8 to which this operation start command is given
Executes the process of the first step. In the first step, the measured V (z) data is read from the data storage unit 5 and converted into complex V (z) data. In the second step, a B (z) curve as shown in FIG. 2 (b) is calculated from the complex V (z) data. The calculated B (z) curve is displayed on the display device 10 by the controller 9.

When the operator inputs Zo where the phase becomes a straight line when Z is sufficiently larger than 0 with respect to the displayed B (z) curve, the sound velocity calculation unit 8 performs the processing of the third step. Run. In this third step, a straight line most approximated to the range of Z> Zo of the B (z) curve is determined by the least squares method, and the slope L (argV = L.multidot.L) of the straight line is determined.
Z + const) is calculated. When the slope L of the straight line is obtained, the process of step 4 is executed next. In step 4, L =
The wavelength λ of the underwater acoustic wave is obtained using the relational expression of 4π / λ.

When the sound velocity calculator 8 completes the processing of steps 1 to 4 and obtains the wavelength λ of the underwater sound wave, the controller 7 gives the wavelength λ of the underwater sound wave to the reflectance calculator 9 and the reflectance R of the sample. To calculate. The reflectance calculator 9 measures the reflectance of the sample from the above equation (6) using the input wavelength λ.

As described above, according to this embodiment, the complex V (z) data including the phase is measured, and the sound velocity of the coupler liquid 3 is measured from the complex V (z) data. It is possible to reduce the number of external devices such as the temperature measurement device and the temperature control device, which can reduce the size of the device and reduce the cost.

Further, since the sound velocity information of the path through which the ultrasonic wave propagates in the coupler liquid is obtained, the obtained sound velocity measurement value has almost no error as compared with the case where the temperature of the coupler liquid is indirectly measured. .. As a result, the reliability of sample evaluation can be improved.

[0032]

As described in detail above, according to the present invention, the coupler liquid is analyzed in a series of processes for analyzing complex V (z) data without using an external device such as a temperature measuring device and a temperature control device. It is possible to reduce the size and cost of the device by obtaining the sound velocity information of, and it is possible to obtain a sound velocity measurement value that contains almost no error by measuring the sound velocity information of the path through which the ultrasonic waves propagate, An ultrasonic microscope that can realize highly reliable sample evaluation can be provided.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an ultrasonic microscope according to an embodiment of the present invention.

FIG. 2 is a diagram showing amplitude characteristic and phase characteristic curves of B (z).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... High frequency transmission / reception part, 2 ... Acoustic lens, 3 ... Coupler liquid, 4 ... Sample, 5 ... Data storage part, 6 ... Z stage, 7
... controller, 8 ... sound velocity calculation unit, 9 ... reflectance calculation unit,
10 ... Display device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsugu Sakai 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd.

Claims (1)

[Claims] 1. An ultrasonic wave converged by an acoustic lens is incident on a sample, reflected ultrasonic waves from the sample are converted into an electric reflection signal and taken in, and the incident direction of the ultrasonic wave is set as a Z axis.
V (z) representing the relationship between the position Z of the acoustic lens or the sample in the Z-axis direction and the signal value V of the reflected signal corresponding to that position
In an ultrasonic microscope that measures a curve and analyzes the V (z) curve to obtain information about the sample, the complex V (z) data including the V (z) curve to the phase information of the reflected ultrasound is obtained. A means for obtaining the ultrasonic propagation medium filled between the sample and the acoustic lens based on the phase data of the complex V (z) data in a range in which the distance between the sample and the acoustic lens is larger than the focal length of the acoustic lens. It is characterized by further comprising sonic velocity measuring means for obtaining sonic velocity information, and reflectance measuring means for obtaining the reflectance of the sample from the sonic velocity information obtained by the sonic velocity measuring means and the complex V (z) data. Ultrasonic microscope.