JPH0626945A - Method for measuring residual stress, and measuring device used for this method - Google Patents

Abstract

PURPOSE:To quickly measure residual stress by providing a laser oscillator, a Raman spectrophotometer, a sample base for stress test, and an arithmetic device. CONSTITUTION:A sample base 12 for stress test is driven 14 to add a stress to a base 16. A stress value is inputted to an arithmetic device 13 from the device 14. The laser beam emitted to a sample 17 from a laser oscillator 10 in the state where the stress is added to the sample 17 generates a Raman scattered light 20 near the surface of the sample 17, and the scattered light 20 is converged by a converging mirror 15 and incident to a spectroscope 11a followed by spectral diffraction, and the light is detected by a multi-channel detector 11b, converted into an electric signal, and transmitted to the device 13. In the device 13, arithmetic processing is conducted on the basis of the measurement data of the change quantity in Raman shift based on the change of the lattice frequency transmitted from a spectrophotometer 11 and the data of stress value. In this way, even the residual stress of an extremely thin oxidized film such as MnCr2O4 in which elastic constant and mode Bruneisen's constant are not known can be easily and quickly measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a residual stress measuring method and a measuring apparatus used for the method, and more particularly to a thin film, particularly MnCr ₂ O _4, Cr ₂ O _3, NiFe ₂ O _4, FeCr ₂ O. _{4. A} method for measuring residual stress for enabling measurement of residual stress applied to an oxide film such as Ti ₂ O ₃ and a measuring device used for the method.

[0002]

_2. Description of the Related Art Recently, in order to improve the corrosion inhibitory effect of stainless steel, MnCr ₂ O _4, Cr ₂ O _3, NiFe ₂ O _4, FeCr ₂ O _{4, and} Ti have been previously prepared.
A method of forming an oxide film such as ₂ O _{3 on} the surface of stainless steel is used. At this time, stress may be applied to the oxide film due to the difference in thermal expansion coefficient between the oxide film and the stainless steel that is the substrate, and the stress applied to the oxide film is closely related to peeling of the oxide film and corrosion resistance. Therefore, it is necessary to measure the stress applied to the oxide film.

Conventionally, the residual stress is measured by measuring the deformation of the measured object, calculating the residual stress applied to the measured object from constants such as Young's modulus and Poisson's ratio, or by X-ray diffraction or electron beam diffraction. The residual stress was measured by measuring the lattice constant of the object to be measured and checking the deviation from the standard value, or the residual stress was estimated from the shift amount of the peak position by Raman spectroscopy.

An example of determining the residual stress of an object to be measured using Raman spectroscopy is, for example, Solid State Electronics v
ol 23 (1980) 333.

A method for obtaining the stress from the Raman shift amount will be described below.

Now, when a stress is applied to a certain crystal, the wave number change of a certain mode can be expressed as shown in the following mathematical expression (1) using the mode Grueneisen constant γ.

[0007]

[Equation 1]

Where ω is the lattice frequency and ∂V / V is the change in volume ratio.

The rate of change of the lattice frequency is expressed by the following equation using the mode Grueneisen parameter.

[0010]

[Equation 2]

Here, ε represents strain.

On the other hand, the stress δ ₀ is simply expressed as follows.

Δ ₀ = Eε (3) where E is an elastic constant.

Substituting equation (2) into equation (3),

[0015]

[Equation 4]

Therefore, the stress δ ₀ can be obtained from the equation (4).

[0017]

However, Si, Ge, GaAs, GaSb, InAs, ZnSe, and graphite are the only substances for which the mode-Gruneisen constant γ indicating the relationship between the lattice frequency and the stress is known. The exact value of the Mode-Gruneisen constant of oxides such as MnCr ₂ O _4, FeCr ₂ O _{4 and} Ti ₂ O ₃ is unknown, and there is little information on the elastic constants. Therefore, the above equation (4) is used. Then, the residual stress of the above oxide could not be obtained. Furthermore, since the oxide film has an extremely thin film thickness of about several tens of nm, it is difficult to obtain the Young's modulus and Poisson's ratio, and therefore it is impossible to calculate using these constants, and the residual stress cannot be measured. There was a problem that it was difficult.

The present invention has been made in view of the above problems, and when measuring the residual stress of an object to be measured, the physical constants such as the elastic constants of the object to be measured and the Mode-Gruneisen constant are unknown. Moreover, it is an object of the present invention to provide a residual stress measuring method capable of easily measuring the residual stress even when the film thickness is extremely thin such as about 20 nm or less, and a measuring device used for this measuring method.

[0019]

In order to achieve the above-mentioned object, a method for measuring residual stress according to the present invention comprises: forming an object to be measured on a substrate, and applying the stress to the substrate to add the object to be measured. To the standard spectrum of the Raman shift amount due to the lattice vibration of the object to be measured, after which a calibration curve was created from the relationship between the stress value to the and the change in the Raman shift amount due to the lattice vibration of the crystal structure. The change is measured, the residual stress of the object to be measured is obtained by comparing the measured value with the calibration curve, and the residual stress measuring device according to the present invention further comprises a laser oscillator and a Raman. A spectrophotometer and a sample table for stress test are provided, and further a computing means for computing the residual stress of the object to be measured from the Raman shift amount due to lattice vibration measured by the Raman spectrophotometer. It is characterized.

[0020]

When the stress X is applied to the object to be measured, the lattice constant changes and the coupling force changes.
₀ changes. The relationship between the change in Raman shift Δω with the change in frequency ω ₀ and the stress X is expressed by the following equation.

Δω = −kX (5) Therefore, by preparing a calibration curve from the relationship between Δω and X and obtaining the value of k, Δω is measured and the stress is calculated by using the equation (5). The value X is sought.

Further, according to the above measuring device, the value of k can be easily obtained from the measured values of the Raman shift amount change Δω and the stress X by the calculating means, and the value of k and Δω can be calculated. The stress X is easily calculated from the measured value.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the residual stress measuring device according to the present embodiment includes a laser oscillator 10, a laser Raman spectrophotometer 11, and a four-point bending stress test sample table 12, and the laser Raman spectrophotometer 11 and the stress are measured. The test sample table 12 is connected to a central controller 13 that performs arithmetic processing. The laser Raman spectrophotometer 11 is a spectroscope 11a.
And a multi-channel detector 11b, and a drive mechanism 14 for applying stress to the sample is arranged below the stress test sample table 12. A condenser mirror 15 is provided between the laser oscillator 10 and the stress test sample table 12.
Are arranged at predetermined positions.

In the above-described measuring apparatus, the sample 17 formed on the substrate 16 is a stress test sample table 1 together with the substrate 16.
The stress test sample table 12 is placed on the substrate 2 and is driven by a driving mechanism 14 to apply stress to the substrate 16. A stress value is input from the drive unit 14 to the central control unit 13.

The laser light applied to the sample 17 from the laser oscillator 10 in a state where the sample 17 is under stress is the sample 1
Raman scattering occurs near the surface of No. 7. The scattered light 20 generated by Raman scattering is collected by the condenser mirror 15, is incident on the spectroscope 11a and is dispersed, and then the multi-channel detector 1 having about 1000 $ 2000 photodiodes is provided.
Light is detected by 1b, converted into an electric signal, and transmitted to the central controller 13.

The central controller 13 performs arithmetic processing based on the measurement data of the amount of change in the Raman shift amount based on the change in the lattice frequency and the data of the stress value sent from the laser Raman spectrophotometer 11. In addition, the central controller 13
Also sends a control signal for instructing the measurement procedure to the drive mechanism 14 and the laser Raman spectrophotometer 11.

Using the above residual stress measuring device, MnCr
The residual stress of the ₂ O ₄ thin film was measured. The standard sample of MnCr ₂ O ₄ is powder, and it is not possible to apply stress directly because there is no large single crystal, and elastic constant and Grueneisen constant have not been obtained.

As sample 17, high purity Ar (9
9.999%) Using a MnCr ₂ O ₄ thin film (400 Å) produced by heat treatment at 1000 ℃ × 2 min in gas, sample 17
The change in the Raman shift amount due to the stress change was measured while stress was applied to.

A stress value was plotted on the abscissa and a Raman shift change amount was plotted on the ordinate to obtain a calibration curve as shown in FIG. From the calibration curve, the relationship between the stress X and the Raman shift change amount Δω is expressed by the following equation in the case of uniaxial stress. Δω = −0.24 × 10 ⁻⁹ X (6) In the Raman spectrum of the standard sample of MnCr ₂ O ₄ , as shown in FIG. 2, a peak was recognized at the 679 cm ⁻¹ position.

Next, when the Raman spectrum of the MnCr ₂ O ₄ thin film formed on the SUS 304L steel was measured, the above-mentioned peak was shifted to the position of 690 cm ^-1 as shown in FIG.

In this embodiment, the Raman shift change amount Δω
= 11, and assuming that sample 17 is under biaxial stress, from formula (6), MnCr ₂ O ₄ thin film has a density of 2.3 × 10 ¹⁰ (d
It means that the compressive stress of yne / cm ² ) is applied as the residual stress.

As described above, using the apparatus and method according to the present embodiment, the elastic constant and the mode Grueneisen constant are unknown, and the residual stress of an extremely thin oxide film such as MnCr ₂ O ₄ can be easily and quickly obtained. Can be measured.

[0033]

As is apparent from the above description, in the residual stress measuring method according to the present invention, an object to be measured is generated on a substrate and the stress is applied to the substrate to be measured. A calibration curve was created from the relationship between the stress value on the object and the change in the Raman shift amount due to the lattice vibration of the crystal structure, and after that, the shift from the standard spectrum of the Raman shift amount due to the lattice vibration of the DUT. By measuring the amount change, by comparing the measured value and the calibration curve, since it is a method of obtaining the residual stress of the measured object, constants such as Young's modulus and Poisson's ratio of the measured object and Grueneisen constant is The residual stress can be easily measured even if the substance is unknown and the film thickness is extremely thin, about 20 nm or less. Moreover, since laser light is used, it is presumed that it is possible to converge the stress with a lens and measure stress with a spatial resolution of 1 μmX.

Further, the residual stress measuring device according to the present invention comprises a laser oscillator, a Raman spectrophotometer, and a stress test sample stage, and the Raman shift amount due to the lattice vibration measured by the Raman spectrophotometer is used to measure the residual stress. Since the calculation means for calculating the stress of the measurement object is provided, it is possible to calculate the residual stress almost simultaneously with the measurement of the Raman shift change amount and the stress. Can be measured.

[0035]

[Brief description of drawings]

FIG. 1 is a schematic partial cross-sectional view showing an embodiment of a residual stress measuring device according to the present invention.

FIG. 2 is a diagram showing the relationship between the Raman shift amount and the intensity in the Raman spectrum of a standard sample of MnCr ₂ O ₄ .

FIG. 3 is a diagram showing the relationship between the Raman shift amount and the intensity in the Raman spectrum of the MnCr ₂ O ₄ thin film formed on SUS 304L steel.

FIG. 4 is a diagram showing a calibration curve.

[Explanation of symbols]

 10 laser oscillator 11 laser Raman spectrophotometer 12 sample table for stress test 13 central processing unit (processing means)

Claims (2)

[Claims] 1. A calibration is performed based on the relationship between a stress value applied to the object to be measured by generating an object to be measured on the substrate and applying a stress to the substrate, and a change in Raman shift amount due to lattice vibration of a crystal structure. A line is created in advance, and after that, the shift amount change of the Raman shift amount of the measured object due to the lattice vibration is measured, and the measured value is compared with the calibration curve to obtain the measured object. A method for measuring residual stress, which comprises determining the residual stress of an object. 2. A laser oscillator, a Raman spectrophotometer, and a stress test sample stage are provided, and the residual stress of the object to be measured is calculated from the Raman shift amount due to lattice vibration measured by the Raman spectrophotometer. An apparatus for measuring residual stress, characterized in that it comprises a computing means.