JPH06185987A - Dimension measuring method - Google Patents

Abstract

PURPOSE:To accurately measure the inside dimension of an object to be measured under a nondestructive condition by measuring and processing a photo-acoustic signal generated by a photo-acoustic effect in the vicinity of the invisible end face of the object. CONSTITUTION:After a sample 12 having a tapered section 12a is housed in a closed cell 13 and the cell 13 is sealed, the sample 12 is placed on the stage of an optical microscope 6 and set near the optical focal point of the microscope 6. Then the surface of the sample 12 is irradiated with a laser beam of an adequate power by oscillating an argon laser 3. When photo-acoustic measurement is performed on the tapered section A of the sample 12 by using a microphone 14, personal computer 10, etc., a phase change is generated by the edge effect of the end face 12 of the sample 12. Namely, the phase value gradually decreases as approaching the end face 12b and abruptly rises and forms an edge at the end face 12b after decreasing to a minimum value. Since the maximum variation of the phase change and dimension (depth) of the end face 12b are in a proportional relation, the dimension of the end face 12b can be found from the maximum variation. Thus the inside dimension of the sample can be accurately measured in the order of over ten to several hundred m under a nondestructive condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel dimensional measurement method for structural dimensional analysis of an optically opaque structure.

[0002]

2. Description of the Related Art For example, when considering the manufacture of a magnetic head for magnetic recording on a floppy disk, a hard disk, a video tape, an audio tape, etc., the inspection of defective products currently depends on visual inspection under a microscope. is there. Also,
The measurement of the finished dimension of the magnetic head (for example, the depth of the gap) is performed by relying on an indirect method such as observing under a microscope by shining light from the side. However, in such an indirect measurement, an internal defect is not known and an error is large, which makes accurate measurement / evaluation difficult.
Therefore, it is necessary to develop a device that can directly observe the internal structure in a chip state.

An ultrasonic microscope is known as a measuring device capable of measuring internal dimensions and having sufficient accuracy. Then, there are two types of measurement techniques in this ultrasonic microscope, one using a reflected wave of a longitudinal wave used for flaw detection and the other using a surface acoustic wave excited on a sample. The former is effective for relatively thick ones (millimeter order or more), and the latter is effective for extremely thin ones of several μm or less.

[0004]

However, for example, the depth of the gap (so-called depth) of the magnetic head as described above is about ten and several .mu.m, which is measured by an ultrasonic microscope regardless of which of the above measurement techniques is adopted. Not suitable for. Also,
In the measurement with the above-mentioned ultrasonic microscope, it is necessary to use water (coupler) or the like at the time of measurement, and there is a risk that the sample will be soiled. Therefore, the present invention has been proposed in view of such conventional circumstances, and provides a dimension measuring method capable of nondestructively measuring an internal dimension of the order of ten and several μm to several hundreds μm. With the goal. Another object of the present invention is to provide a dimension measuring method that can perform measurement in the atmosphere and does not require an environment such as immersion in water.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and have completed the present invention by focusing on the photoacoustic effect. That is, the present invention is
It is characterized in that a photoacoustic signal generated by a photoacoustic effect is measured in the vicinity of the invisible end surface of the measured object, and the dimension of the invisible end surface of the measured object is nondestructively obtained.

The acoustic signal due to the photoacoustic effect can be measured by various devices, and the photoacoustic devices applicable to the present invention are listed below. 1. Thermal waves and thermoelasticity generated by absorption of irradiated light by converging a periodically oscillating continuous-wave laser beam on a sample installed in a photoacoustic cell through a microscopic optical system such as a microscope objective lens. A wave is detected by a sensor such as a microphone or a piezoelectric element, and the signal is directly captured by an A / D converter, or is synchronously detected by a lock-in amplifier and then a data bus such as GP / IB or an A / D converter. The photoacoustic device is characterized in that it is incorporated into the signal processing device.

2. By replacing the modulation of the laser light of the device of 1 above with the modulation in a random time series, and taking the time correlation between the photoacoustic signal generated by the correlator and the random excitation light pulse series, A photoacoustic device characterized by obtaining information about an internal structure.

3. A pulse laser is used in place of the laser and modulator of the above-mentioned devices 1 and 2, and a high-speed response piezoelectric element or surface displacement meter is used as a sensor, and the detected photoacoustic signal is combined with a technique such as Fourier transform. A photoacoustic apparatus characterized by obtaining information about the internal structure under the surface of the sample.

4. The photoacoustic apparatus according to the above-mentioned 1 based on a method of processing information based on an amplitude image of a photoacoustic signal generated from a sample.

5. The photoacoustic apparatus according to the above-mentioned 1 which is based on a method of processing information based on a phase image of a photoacoustic signal generated from a sample.

6. In the above apparatus 1, when the position where the sample is irradiated with laser light is (x, y), the amplitude image of the photoacoustic signal is A (x, y), and the phase image is φ (x, y), the formula H (X, y) = A (x, y) · [1 + cos (φ (x,
y))] or H (x, y) = A (x, y) ² · [1 + cos (φ
(X, y))] A photoacoustic apparatus based on a method of processing information by a "hologram" defined by

7. The photoacoustic apparatus according to any one of 1 to 6 above, which is provided with the above-mentioned function by systematically controlling and scanning a position of a laser beam with respect to a sample.

8. The photoacoustic apparatus according to any one of 1 to 6 above, wherein the sample is controlled and scanned by a mechanical method such as a pulsus stage to have the above-mentioned functions with high accuracy.

9. In each of the above devices 1 to 8, more information about the sample can be obtained by utilizing the wavelength change of the laser scanning the sample to separate the optical property from the thermal / acoustic property of the sample. A photoacoustic device characterized by obtaining.

10. The photoacoustic apparatus according to any one of the above 1 to 9, wherein noise is reduced by using an optical or electrical difference method.

[0016]

As shown in FIG. 1, the photoacoustic effect is the generation of heat due to the absorption of modulated light by the substance (measurement object 1), and the substance itself and the gas in contact with the surface of the substance show an alternating temperature change and expand. ，
This is a phenomenon in which an acoustic signal is generated by repeating contraction. For example, an acoustic signal obtained via the microphone 2 or the like is
It includes information on the light absorption property in the light irradiation region 1a and the heat property in the thermal diffusion length region 1b determined by the following equation 1.

[Formula 1] Therefore, photoacoustic measurement has been used as a method for detecting defects inside opaque materials that are not optically observable.

On the other hand, the present invention quantitatively obtains the dimension of this end face by utilizing the edge effect in the vicinity of the invisible end face of the object to be measured. That is, when the photoacoustic measurement is performed near the edge of the object to be measured, a phenomenon called "edge effect" is observed. For example, it is a phenomenon in which the amplitude intensity of the photoacoustic signal exponentially increases from the inside toward the edge. Here, paying attention to the edge effect in the measured object having a thickness of about the thermal diffusion length, the photoacoustic signal changes in proportion to the dimension of the end surface of the measured object. Therefore,
By measuring the photoacoustic signal, the size of the invisible end surface of the measured object can be obtained.

[0018]

EXAMPLES Specific examples to which the present invention is applied will be described below in detail based on experimental results relating to phase measurement as an example. First, the photoacoustic apparatus used in this example is
As shown in FIG. 2, it comprises an optical system, a scanning system, a sample storage section and a signal processing system. The optical system includes an Ar gas laser device 3 as a light source, a light chopper 4 as a modulator, a plano-convex lens 5 for condensing, and an optical microscope 6. Here, the plano-convex lens 5 is attached at a position separated from the mirror described later by a focal length so that the light beams to be scanned are parallel. As the objective lens of the optical microscope 6, a lens having an ultra long working distance was used so as not to contact the photoacoustic cell. A modulated laser can be used instead of the Ar gas laser device 3 and the light chopper 4.

As the scanning system, two mirrors 7,
8, a scanner control driver 9 for controlling these mirrors 7, 8 and a control personal computer 10 (including a D / A conversion board 11) are provided. On the other hand, in order to store the sample 12, a closed cell 13 is used for measurement by a microphone method, and in addition to the space for storing the sample 12, the microphone 14 and the preamplifier 15 are stored in the cell 13. There is a space for you.

The signal processing system includes a microphone 14 as a detector, a preamplifier 15 for signal amplification, and a lock-in amplifier 16, and the output from the lock-in amplifier 16 is passed through the A / D converter 17 to the personal computer. It is directly imported into the computer 10. Although the microphone 14 is used as the detector here, it is also possible to detect it with a sensor such as a piezoelectric element. Further, the output from the lock-in amplifier 16 is directly taken in through the A / D converter 17, but various variations such as passing through the GP-IB bus are possible.

In the photoacoustic apparatus having the above-described structure, it is expected that electrical noise and vibration noise will occur. The former is one that is picked up from the outside by a cord between the microphone 14 and the amplifier 15, and one that uses the elements of the microphone 14 and the preamplifier 15 as a generation source. Therefore, batteries are used for the power sources of the microphone 14 and the preamplifier 15, and the sealed cell 13 is grounded to the outside so that it is not affected by the outside. In addition, the latter uses the microphone 14 to generate various vibrations that are transmitted to the floor.
It is thought that this is due to picking up. Therefore, the entire device was placed on a vibration isolation table to eliminate external vibrations as much as possible.

On the other hand, the software in the above-mentioned photoacoustic apparatus is, as shown in FIG. 3, a part 18 for controlling the scanning system.
And a portion 19 for processing the measurement data and displaying an image. The parameters for processing the scanning system include the scanning width and the scanning speed, and several values can be selected for each. Then, the set parameters are stored in the database 20 at the time of measurement. X-
The scanner control signal processed in the Y mirror control processing step 21 is sent from the personal computer 10 to the D /
It is adapted to be sent to the scanner control driver 9 via the A conversion board 11, and the X-axis scanning 22 and Y are provided.
Two-channel signals are used for axis scanning 3.

The electric signal emitted from the microphone 14 passes through the preamplifier 15 and the lock-in amplifier 16 to
Sent to the / D converter 17 and the personal computer 1
Input to 0. The input data captured during measurement is
It is processed so as to be displayed in pseudo color on the display as a two-dimensional image, and is sequentially transferred to the database 20 via the data input step 24, the data imaging step 25 and the data output step 26.

The above is the hardware and software configuration of the photoacoustic apparatus used in the present embodiment. The photoacoustic apparatus was used to actually measure the sample 12 shown in FIG. The measurement results will be described in detail below. The measured sample is ferrite having a tapered portion 12a as shown in FIG. The sample 12 is housed in the closed cell 13 and bolted to make the inside of the closed cell 13 tightly closed.
The optical image was set at a position near the optical focus. Then, the Ar gas laser 3 was oscillated to irradiate the surface of the sample 12 with an appropriate power, and the laser was used to focus again.

Then, the photoacoustic measurement of the tapered portion (indicated by the arrow A in the figure) of the sample 12 was performed. As a result,
As shown in FIG. 5, a change in phase due to the edge effect of the end face 12b of the sample 12 was observed. That is, as shown in FIG. 5, the phase value gradually decreases toward the end face 12b, and after the minimum value is shown in the vicinity of the end face 12b, the end face 1
In 2b, it rises sharply and an edge is observed.

Then, when the same measurement was repeated for the samples having different end faces 12b, the difference between the maximum value and the minimum value (change amount B) in the phase change and the size (depth) of the end face 12b are shown in FIG. It was found that there is a proportional relationship as shown in. In addition, in FIG. 6, frequencies of 400 Hz, 6
The relationship between the change amount B and the depth when 00 Hz and 800 Hz are displayed, respectively. Therefore, it has been found that by obtaining the change amount B, the dimension of the end face 12b can be obtained based on the correlation, which can be applied to, for example, the depth measurement of the magnetic head.

[0027]

As is apparent from the above description, in the present invention, the size of the invisible end face of the object to be measured is determined by utilizing the photoacoustic effect, and it is nondestructive and does not exceed 10 μm.
It is possible to accurately measure internal dimensions on the order of m to several hundreds of μm. In addition, in the present invention, the measurement can be performed in the atmosphere, and the problem of contamination due to immersion in water can be avoided. Therefore, for example, it is possible to quantitatively measure the internal dimensions of the components that make up the magnetic circuit of the magnetic head, and it is also possible to nondestructively evaluate and inspect the internal quality. The sex is great.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating the principle of a photoacoustic effect.

FIG. 2 is a schematic diagram showing a hardware configuration of a photoacoustic apparatus used in Examples.

FIG. 3 is a schematic diagram showing a software configuration of a photoacoustic apparatus used in an example.

FIG. 4 is a schematic perspective view showing the actually measured shape of the sample.

FIG. 5 is a characteristic diagram showing a change in phase due to an edge effect.

FIG. 6 is a characteristic diagram showing the correlation between the amount of change in phase and the dimension (depth) of the end face.

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[Procedure amendment]

[Submission date] May 1, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

As the scanning system, two mirrors 7,
8, a scanner control driver 9 for controlling these mirrors 7, 8 and a control personal computer 10 (including a D / A conversion board 11) are provided. On the other hand, in order to store the sample 12, a closed cell 13 is used for measurement by a microphone method, and in addition to a space for storing the sample 12, a microphone 14 and a preamplifier 15 are stored in the cell 13. There is a space for you. In this example, the closed cell
The example used was described above, but the sample was used as a photoacoustic cell.
Airtightness is maintained by sealing with a ring etc.
The same effect can be obtained by using the open cell.
it can.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiro Hiroshi Suto 6-5-6 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Magne Products Co., Ltd. (72) Tsutomu Hoshimiya 1-13 Chuo, Tagajo-shi, Miyagi -1 Tohoku Gakuin University

Claims (1)

[Claims] 1. In the vicinity of the invisible end surface of the object to be measured,
A dimension measuring method comprising measuring a photoacoustic signal emitted by a photoacoustic effect and non-destructively obtaining a dimension of an invisible end surface of the object to be measured.