JPH06100511B2 - Scanning stress measurement method - Google Patents

Description

The present invention relates to a stress measurement method applying Raman spectroscopy using laser light as a light source, and is particularly suitable for measurement when a stress distribution exists in a sample to be measured. Scanning stress measurement method.

[Conventional technology]

When the sample to be measured is irradiated with strong monochromatic visible light, the incident light changes in frequency due to the molecular vibration of the sample, and Raman scattered light having a frequency different from that of the incident light is generated. What measured the Raman scattered light intensity with respect to the frequency change is called a Raman spectrum, and qualitative analysis can be performed from the frequency position where this Raman spectrum shows a peak, and quantitative analysis can be performed from the scattered light intensity. When stress is applied, the frequency position showing the peak of the Raman spectrum shifts, and the stress can be quantitatively evaluated by detecting the shift amount.

The current laser Raman spectroscopy is disclosed in, for example, JP-A-55-11254.
As disclosed in No. 9, if it is a solid sample, place it on the sample table, if it is a liquid sample, put it in the cell, and introduce the Raman scattered light generated by irradiating the sample with laser light in the sample chamber into the spectrometer. The Raman scattered light intensity at the frequency is measured.

[Problems to be solved by the invention]

In the above-mentioned laser Raman spectroscopy method, positioning of the measurement point of the sample in the XY direction was performed by moving the sample itself and manually, so if moving the sample may damage the sample or put the sample in the sample chamber. If the sample itself cannot be moved in the sample chamber, such as when it cannot be performed, measurement was impossible. Even if the sample itself can be moved in the sample chamber, it is difficult to perform accurate positioning in the XY directions because it is manual. Further, since the positioning in the Z direction is not performed, it is difficult to hold the optical fiber at a constant distance from the sample surface when the sample surface has irregularities. Therefore, there is a drawback that the accuracy of the obtained stress distribution is lowered.

An object of the present invention is to provide a scanning stress measurement method for automatically measuring the stress distribution in the sample surface and in the depth direction.

[Means for solving problems]

In the method for measuring stress by guiding a laser to a sample to be measured with a first optical fiber and irradiating the sample with Raman scattered light generated from the sample to a Raman spectrometer with a second optical fiber, the above-mentioned object is This is achieved by carrying out the stress determination while horizontally scanning or horizontally and vertically scanning the first optical fiber, the second optical fiber or the sample while keeping the distance between the first and second optical fibers and the sample constant, and Raman. The Raman spectrum is obtained by a spectrometer, then the stress of the sample is obtained from the shift amount of the frequency (or wavelength is the same) position where the Raman spectrum shows a peak by the computer, and the stress is finally obtained according to the scanning. This is achieved by finding the distribution.

Further, the above object is to provide a laser light source, an optical fiber for guiding the laser light emitted from the laser light source to a sample to be measured,
A device comprising an optical fiber for guiding a Raman spectrometer generated from the sample, wherein a mechanical stage supporting the optical fiber, a stage for mounting the sample, and a horizontal scanning or horizontal scanning for the mechanical stage or the stage for mounting the sample. And a means for vertical scanning, a sensor for detecting the distance between the optical fiber and the sample, a scanning control / data processing computer, and an image processing device.

[Action]

As described above, by horizontally scanning the optical fiber or the sample, or by scanning the optical fiber or the sample horizontally and vertically while keeping the distance between the sample and the optical fiber constant, by guiding the Raman scattered light to the Raman spectrometer, It is possible to understand the stress distribution of a sample having a stress distribution that has been impossible in the past.

When stress is applied, the frequency position showing the peak of the Raman spectrum shifts, and it is possible to quantitatively evaluate the stress by detecting this shift amount, and thus the stress distribution can be accurately grasped. Becomes Further, by making the distance between the optical fiber and the sample constant, it is possible to grasp the change in the position of the frequency (horizontal axis) indicating the peak value of the spectrum intensity without the influence of the distance variation. The inventor has found that the shift amount of the frequency (wavelength) represents the stress distribution and the shift amount is influenced by the distance (distance) between the optical fiber and the sample.

Further, as described above, a mechanical stage that supports the optical fiber, a table on which the sample is placed, a means for horizontally scanning or horizontally and vertically scanning the mechanical stage or the table on which the sample is placed, the optical fiber and the sample. By providing a sensor that detects the interval between the scanning points, a scanning control / data processing computer, and an image processing device, the position and stress of each scanning point can be grasped with high precision, and therefore highly accurate measurement is performed. be able to.

〔Example〕

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

The embodiment shown in FIG. 1 is a basic mode of the present invention. Laser light oscillated from a laser light source 1 such as an argon ion laser passes through an optical fiber 2 for laser light, and a laser condensing lens 3 causes a laser beam of a sample 4 to be emitted. Focus on the measurement section. Then, the optical fiber 2 for laser light and the optical fiber 5 for Raman light were attached to an XY axis stage 6 and installed in an XY mechanism driven by two stepping motors (a DC motor may be used, not shown). Raman scattered light 8 is generated from the sample 4 by program-controlling the stepping motor to automatically scan in the XY directions and irradiating the laser light 7 at each scanning point. The generated Raman scattered light 8 is condensed by the Raman condensing lens 9, passes through the Raman light optical fiber 5 and is dispersed in a known Raman spectrometer 10 to measure the Raman spectrum, and the Raman spectrum shows a peak by the computer 11. The stress distribution of the sample 4 is obtained from the shift amount of the frequency position, and the stress distribution is image-processed by the image processing device 11a.

The Raman spectrum obtained by the Raman spectrometer 10 is processed by the computer 11 to obtain the gradient of the stress distribution, and the stepwise scanning step width and the data sampling interval are determined by the computer 11 according to their magnitudes, and the two stepping motors ( It is also possible to drive (not shown). When the gradient of the stress distribution becomes large, the scan step width and the data sampling interval are made small, and when the gradient becomes small, they become large. Then, the Raman spectrum is measured by the Raman spectrometer 10 at each scanning point, the stress distribution of the sample 4 is obtained from the shift amount of the frequency position where the Raman spectrum shows a peak by the computer 11, and the stress distribution is calculated by the image processing device 11a. It is for image processing.

The embodiment shown in FIG. 2 is a basic mode of another invention, and is a laser fiber 2 and a Raman light fiber 5.
Is mounted on the XYZ axis stage 6a together with the Z-direction positioning sensor 12 and installed in an XYZ mechanism driven by two stepping motors (not shown) and one motor (not shown). The stepping motor is program-controlled to automatically scan in the XY directions, and at the same time, the Z-direction positioning sensor 12 and the motor drive by this signal keep the positions of the optical fibers 2 and 5 in the Z-direction constant from the surface of the sample 4. The distance is maintained and the laser light 7 is emitted at each scanning point. Sample 4
The Raman scattered light 8 generated from the light is condensed by the Raman condensing lens 9, passes through the Raman light optical fiber 5 and is dispersed in the Raman spectrometer 10 to measure the Raman spectrum, and the computer 11 vibrates the Raman spectrum at the peak. The stress distribution of the sample 4 is obtained from the shift amount at several positions, and the stress distribution is image-processed by the image processing device 11a.

The stress of the sample 4 obtained from the Raman spectrum measured by the Raman spectrometer 10 is processed by the computer 11, the gradient of the stress distribution is obtained, and the sequential scanning step width and the data sampling interval are determined by the magnitude thereof.
2 stepping motors (not shown)
It is also possible to drive. As the gradient of the stress distribution becomes larger, the scanning step width and the data sampling interval are made smaller. On the contrary, when the gradient of the stress distribution becomes smaller, they become larger. Then, the Raman spectrum is measured at each scanning point, and the stress distribution of the sample 4 is obtained by the computer 11 from the shift amount of the frequency position where the Raman spectrum shows a peak.
The stress distribution is image-processed by 11a.

FIG. 3 shows the stage on which the sample 4 is placed without moving the stage 6b.
In the embodiment in which 13 is moved, such a structure has an effect that the laser light source 1, the stage 6b, the Raman spectrometer 10, the scanning control / data processing computer 11 and the image processing device 11a can be integrated.

FIG. 4 shows an embodiment in which the reflected laser light 14 is received by the Z-direction positioning sensor 12 and the fibers 2 and 5 and the surface of the sample 4 are kept at a constant distance. Has the effect of being easy.

FIG. 5 shows an embodiment in which a laser is used as the positioning sensor 12.

In the figure, the laser beam 15 emitted from the positioning sensor 12 to the surface of the sample 4 to be measured becomes a bright spot 16 when the distance to the surface of the sample 4 to be measured is large. The diffusely reflected light from the laser light 15 is condensed by the lens 17 and forms an image on the image forming point 18a on the image sensor 18. When the distance to the surface of the sample 4 to be measured becomes small and the sample reaches the position 4a, it moves to the bright spot 16a. Accordingly, the image forming point 18a on the image sensor 18 becomes the image forming point 1
Move to 8b. The image sensor 18 is formed by arranging a large number of light receiving elements on a straight line, and the distance between the positioning sensor 12 and the surface of the measured sample 4 can be known by reading the position of the image forming point. Therefore, if the distance between the positioning sensor 12 and the tips of the optical fibers 2 and 5 in the Z direction is defined in advance, the optical fiber 2
And the distance between the tip of 5 and the surface of the sample 4 to be measured is known. Thus, by processing the signal from the positioning sensor 12 by the computer 11 and driving a motor (not shown),
The positions of the optical fibers 2 and 5 in the Z direction can be maintained at a constant distance from the surface of the measured sample 4. Then, the Raman spectrum is measured at each scanning point, the processing is performed by the computer 11, the stress distribution is obtained, and the image processing is performed by the image processing apparatus 11a.

The embodiment shown in FIG. 6 is an example of an optical non-contact type sensor using a laser as the positioning sensor 12. In the figure, the laser light 20 emitted from the laser light source 19 of the positioning sensor 12 includes lenses 21 and 22, and a half mirror 23.
And a diameter of 1 on the surface of the sample 4 to be measured through the objective lens 24.
It is condensed to less than μm. The reflected light is the objective lens 24,
The light enters the light receiving element 26 through the half mirror 23 and the lens 25. The diameter of the beam incident on the light receiving element 26 changes depending on the size of the bright spot 27 on the surface of the sample 4 to be measured, and the size of this bright spot 27 is the distance L between the objective lens 24 and the surface of the sample 4 to be measured.
Depends on. For example, when the distance L is equal to the focal length of the objective lens 24, the size of the bright spot 27 is minimum and the incident beam diameter on the light receiving element 26 is also minimum. When the distance L is smaller or larger than the focal length of the objective lens 24, the bright spot 27a and the incident beam diameter increase. If the relationship between the incident beam diameter to the light receiving element 26 and the distance L is obtained, the distance L can be obtained by measuring the incident beam diameter. Therefore, if the distance in the Z direction between the positioning sensor 12 and the tips of the optical fibers 2 and 5 is defined in advance, the distance between the tips of the optical fibers 2 and 5 and the surface of the sample 4 to be measured can be known. Thus, the signal from the positioning sensor 12 is processed by the computer 11, and the motor (not shown)
By driving, the positions of the optical fibers 2 and 5 in the Z direction can be maintained at a constant distance from the surface of the measured sample 4. Then, the Raman spectrum is measured at each scanning point, the stress distribution is obtained by processing with the computer 11,
Image processing is performed by the image processing device 11a.

The embodiment shown in FIG. 7 is an example in which a non-contact type sensor using a light emitting / receiving element is used as the positioning sensor 12. In the figure, the light emitting element of the positioning sensor 12
A voltage is applied to 28 to project light on the surface of the sample 4 to be measured. When the reflected light 29 from the surface of the measured sample 4 is received by the light receiving element 30, the distance L between the positioning sensor 12 and the surface of the measured sample 4 can be obtained by measuring the amount of received light.

FIG. 8 shows the relationship between the distance L and the amount of received light. In FIG. 8, if the areas (a) and (c) are used, the distance L
And the amount of received light can be obtained in a linear relationship. Therefore, if the distance between the positioning sensor 12 and the tips of the optical fibers 2 and 5 in the Z direction is defined in advance, the optical fiber 2
And the distance between the tip of 5 and the surface of the sample 4 to be measured is known. Thus, by processing the signal from the positioning sensor 12 by the computer 11 and driving a motor (not shown),
The positions of the optical fibers 2 and 5 in the Z direction can be maintained at a constant distance from the surface of the measured sample 4. Then, the Raman spectrum is measured at each scanning point, the processing is performed by the computer 11, the stress distribution is obtained, and the image processing is performed by the image processing apparatus 11a.

The embodiment shown in FIG. 9 is an example in which a non-contact type sensor using a semiconductor laser is used as the positioning sensor 12. This sensor utilizes the optical feedback effect of intensity-modulating the output light by changing the phase of the light returning to the semiconductor laser. In the figure, when the emitted light 32 of the semiconductor laser 31 of the positioning sensor 12 is reflected on the surface of the sample 4 to be measured and returns to the semiconductor laser 31, the output of the laser changes depending on the phase of the returned light 33. The intensity-modulated outgoing light 34 is made incident on the photoelectric conversion element 35, and the optical output is measured.

FIG. 10 shows the relationship between the distance L between the positioning sensor 12 and the surface of the sample 4 to be measured and the output light power. In FIG. 10, if the regions (f) and (h) are used, the distance L And the light output can be obtained in a linear relationship. In FIG. 9, if the output from the photoelectric conversion element 35 is linearized using a linearizer (not shown) and then the signal is sent to the computer 11, a wider range than that shown in FIG. In the area, the distance L and the light output can be obtained in a linear relationship. Therefore, if the distance in the Z direction between the positioning sensor 12 and the tips of the optical fibers 2 and 5 is defined in advance, the distance between the tips of the optical fibers 2 and 5 and the surface of the sample 4 to be measured can be known. Thus, the signal from the positioning sensor 12 is processed by the computer 11 and the motor (not shown) is driven to keep the positions of the optical fibers 2 and 5 in the Z direction at a constant distance from the surface of the sample 4 to be measured. You can Then, the Raman spectrum is measured at each scanning point, the processing is performed by the computer 11, the stress distribution is obtained, and the image processing is performed by the image processing device 11a.

The embodiment shown in FIG. 11 is an example in which a non-contact type sensor using ultrasonic waves is used as the positioning sensor 12. In the figure, the ultrasonic oscillator 36 of the positioning sensor 12 is
Pulsed electrical energy generated by the ultrasonic transmitter 37
In addition, this is converted into ultrasonic energy by the electrostrictive effect and emitted in the vertical direction. This ultrasonic pulse 38 propagates in the vertical direction in the air, and when it hits the surface of the sample 4 to be measured, it is reflected and returned. This is received by the wave receiver 39, converted into electric energy again, amplified by the receiver 40, and output. If the sound velocity in the air is checked, the distance L between the positioning sensor 12 and the surface of the sample 4 to be measured can be known from the time required for the ultrasonic waves to reciprocate at this time. Therefore, if the distance in the Z direction between the positioning sensor 12 and the tips of the optical fibers 2 and 5 is defined in advance, the distance between the tips of the optical fibers 2 and 5 and the surface of the sample 4 to be measured can be known. Thus, the positioning sensor
The signal from 12 is processed by the computer 11 and a motor (not shown) is driven to drive the optical fibers 2 and 5.
The position in the Z direction can be maintained at a constant distance from the surface of the sample 4 to be measured. Then, the Raman spectrum is measured at each scanning point, the processing is performed by the computer 11, the stress distribution is obtained, and the image processing is performed by the image processing apparatus 11a.

The embodiment shown in FIG. 12 is an example in which a capacitance type non-contact type sensor is used as the positioning sensor 12. In the figure, when a potential is applied between the measurement electrode 41 at the tip of the positioning sensor 12 and the surface of the sample 4 to be measured, electric charge is accumulated, and the capacitance C is expressed by the following equation.

C = (ε _o · ε _s · S) / L (1) where ε _o : dielectric constant of vacuum, ε _s : relative dielectric constant of dielectric, S: area of measuring electrode 41, L: measuring electrode The distance between 41 and the surface of sample 4 to be measured.

If the relative permittivity ε _s and the area S are constant, the capacitance C is determined by the distance L from the equation (1). That is, the distance L between the positioning sensor 12 and the surface of the measured sample 4 is obtained by measuring the electrostatic capacitance C. In the present embodiment, a guard ring (a type of electrode) is provided around the measurement electrode 37 so that the lines of electric force 42 between the measurement electrode 41 and the surface of the sample 4 to be measured are uniform as shown in the figure. , The same potential as that of the measurement electrode 41 is applied. By using this guard ring 43, the equation (1) is accurately established. From the above, if the distance in the Z direction between the positioning sensor 12 and the tips of the optical fibers 2 and 5 is defined in advance, the distance between the tips of the optical fibers 2 and 5 and the surface of the sample 4 to be measured can be known. Thus, the signal from the positioning sensor 12 is processed by the computer 11 and the motor (not shown) is driven to keep the positions of the optical fibers 2 and 5 in the Z direction at a constant distance from the surface of the sample 4 to be measured. You can Then, the Raman spectrum is measured at each scanning point, the processing is performed by the computer 11, the stress distribution is obtained, and the image processing apparatus 11
Image processing is performed by a.

The embodiment shown in FIG. 13 is an example in which a non-contact type sensor using an eddy current is used as the positioning sensor 12. In the figure, a high frequency (about 1 MHz) current is passed through the active coil 44 of the positioning sensor 12 to generate a magnetic field 45. When the positioning sensor 12 is brought close to the surface of the sample 4 to be measured in this state, eddy currents flow concentrically on the surface of the sample 4 to be measured, and the impedance of the active coil 44 changes.
If the distance between the positioning sensor 12 and the surface of the sample to be measured 4 decreases, the coil impedance decreases in proportion to this. Therefore, if the Wheatstone bridge is formed and the impedance of the coil is measured, The distance from the surface of the measurement sample 4 is known. Therefore, the Z of the positioning sensor 12 and the tips of the optical fibers 2 and 5 is previously set.
If you specify the distance in the direction, the optical fibers 2 and 5
The distance between the tip and the surface of the sample 4 to be measured can be known. Thus,
By processing the signal from the positioning sensor 12 by the computer 11 and driving a motor (not shown), the positions of the optical fibers 2 and 5 in the Z direction can be kept at a constant distance from the surface of the sample 4 to be measured. . Then, the Raman spectrum is measured at each scanning point, the processing is performed by the computer 11, the stress distribution is obtained, and the image processing is performed by the image processing apparatus 11a. In the figure, 46 is an inactive coil.

〔The invention's effect〕

As described above, the method according to the present invention scans the optical fiber or the sample horizontally, or scans the optical fiber or the sample horizontally and vertically while keeping the distance between the sample and the optical fiber constant, and Raman scattered light is subjected to Raman spectroscopy. Since it leads to the measurement, it has an effect of grasping the stress distribution of a sample having a non-uniform stress distribution and a sample having an uneven surface, which has been impossible in the past, without giving a disturbance.

[Brief description of drawings]

1 to 4 are explanatory views of a scanning type stress measuring device according to the present invention. FIG. 1 is a schematic diagram of the basic embodiment, FIG. 2 is another schematic diagram of the basic embodiment, and FIG. FIG. 4 is a further schematic diagram of the basic embodiment, FIG. 4 is a further schematic diagram of the basic embodiment, and FIG.
FIG. 6, FIG. 7, FIG. 7, FIG. 9, FIG. 11, FIG. 12, and FIG. 13 are schematic diagrams of non-contact sensor examples, and FIG.
FIG. 10 is a relationship diagram between the distance and the light receiving amount in the diagram model, and FIG. 10 is a relationship diagram between the distance and the light output in the model diagram of FIG. 1,19 ... Laser light source, 2 ... Laser light fiber, 3 ... Laser condensing lens, 4, 4a ... Sample, 5 ...
Optical fiber for Raman light, 6 ... XY axis stage, 6a ...
… XYZ axis stage, 6b …… Stage, 7,14,15,20 ……
Laser light, 8 ... Raman scattered light, 9 ... Raman condenser lens, 10 ... Raman spectrometer, 11 ... Scan control / data processing computer, 12 ... Z direction positioning sensor, 13 ...
… Mounting table, 16,16a, 27,27a …… Bright spot, 17,21,22,25 …… Lens, 18 …… Image sensor, 18a, 18b …… Imaging point, 23
...... Half mirror, 24 …… Objective lens, 26,30 …… Light receiving element, 28 …… Projecting element, 29 …… Reflected light, 31 …… Semiconductor laser, 32 …… Emitted light, 33 …… Returned light, 34 ... Intensity-modulated outgoing light, 35 ... Photoelectric conversion element, 36 ... Ultrasonic oscillator, 37 ... Ultrasonic wave transmitter, 38 ... Ultrasonic wave, 39 ... Ultrasonic wave receiver, 40 ... … Ultrasonic receiver, 41 …… Measuring electrodes, 42 ……
Electric lines of force, 43 ... Guard ring, 44 ... Active coil, 45 ... Magnetic field, 46 ... Inactive coil.

Claims (1)

[Claims] 1. A method for measuring a stress by guiding laser light to a sample to be measured with a first optical fiber and irradiating the sample with Raman scattered light generated from the sample to a Raman spectrometer by a second optical fiber. Guide the Raman scattered light to the Raman spectrometer, determine the Raman spectrum by the Raman spectrometer, then determine the stress of the sample from the shift amount of the frequency position where the Raman spectrum shows a peak by a computer, further the sample and the The stress distribution is obtained by horizontally or vertically scanning the first optical fiber, the second optical fiber, or the sample while keeping the distance between the first and second optical fibers constant. A scanning stress measuring method characterized by the above.