JPH04372843A - Sample positioning method - Google Patents

Abstract

PURPOSE:To obtain the method for determining the accurate position of a sample in the machining process of a material and at the analysis of the material. CONSTITUTION:The laser light from an illuminating laser 1 is modulated with a specified frequency in a modulator 2, and the light is cast on a sample 6 so as to emit heat wave. The change in refractive index of fluid generated at immediately upper part of the sample by the heat wave is detected with a bisected photodiode 7 as the polarized probe laser light from a probe laser 4. The position of the sample can be accurately determined by measuring the phase delay of the polarizing period from the illuminating period of the modulated laser light.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for positioning a sample.

0002

[Prior Art] Conventionally, methods for accurately placing a sample in a predetermined position during material processing or analysis are as follows:
For example, there is a method in which a sample is irradiated with a laser beam, the reflected light is divided by a knife edge, the beam is focused, the intensity is measured with a photodiode, and the sample is placed at a position where the intensity reaches a predetermined value. , the method of measuring the reflected light with a two-split photodiode and setting the sample so that the intensity ratio of the two photodiodes is constant, or the method of setting the sample so that the interference intensity between the incident light and the reflected light is constant. There are known methods for installing.

0003

[Problems to be Solved by the Invention] However, since all of the above-mentioned conventional positioning methods require measurement of reflected light, there is a problem that they cannot be applied to samples with low reflectance. there were. Furthermore, it is difficult to apply this method to cases where the surface of the sample is rough and causes diffused reflection. The present invention has been made in order to solve the problems of the prior art as described above, and is applicable to samples that do not reflect light or have low reflectance, or samples that have rough surface conditions. It is also an object of the present invention to provide a method for accurate positioning.

0004

[Means for Solving the Problems] The present invention irradiates a sample with a laser beam modulated at a predetermined frequency, and uses a probe laser that passes directly above the sample to detect changes in the refractive index of a fluid directly above the sample caused by heat release from the sample. This method of positioning a sample is characterized in that the polarization of light is measured, and the phase delay of this polarization period from the modulated laser beam irradiation period is measured.

[0005]

[Operation] When a sample is irradiated with laser light modulated at a predetermined frequency, heat waves are emitted from the sample to the fluid directly above the sample due to photothermal conversion. The propagation of this heat wave in the fluid is expressed by the following equation (Equation 1) as a general solution to the thermal diffusion equation. T(x,t)=T0 exp(-x/μ)・c
os(ωt-x/μ) (Equation 1) where x: distance from the sample surface, t: time from the time of laser beam irradiation, T(
x, t): temperature at position x and time t, T0: sample surface temperature, μ: thermal diffusion length, ω: angular frequency.

Since the refractive index of the fluid changes depending on the temperature of the fluid, when a probe laser beam different from the modulated laser beam is passed through the fluid directly above the sample, the refractive index of the fluid changes as shown in the above equation (Equation 1). Due to the resulting refractive index change, this probe laser light becomes periodically polarized. Since the temperature change of this fluid includes a phase delay expressed by (x/μ) in equation (1), the polarization period also has a phase of (x/μ) with respect to the modulated laser beam irradiation period. There will be a delay. Therefore, if the passing position of the probe laser beam is fixed, the phase delay changes according to changes in the sample position.

That is, according to the present invention, based on the above facts, it is possible to accurately position the sample by making constant the phase delay of the polarization period from the modulated laser beam irradiation period.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of the configuration of a measuring device for carrying out the method of the present invention. In the figure, 1 is an irradiation laser, 2 is a modulator, 3 is a condensing lens, 4 is a probe laser, 5 is a condensing lens, 6 is a sample, 7 is a two-split photodiode, 8 is a modulator power supply, 9 is a lock-in amplifier.

Therefore, when the laser beam from the irradiation laser 1 is modulated at a predetermined frequency by the modulator 2 and then irradiated onto the sample 6 through the condenser lens 3, heat waves are emitted from the sample 6 directly above it. . On the other hand, when the probe laser beam from the probe laser 4 is irradiated directly above the sample 6 through the condensing lens 5, the refractive index of the fluid directly above the sample changes due to the heat wave from the sample 6, which causes the probe laser beam to Polarize. By detecting this polarized light with the two-split photodiode 7 and inputting it to the lock-in amplifier 9, the phase delay of the polarization period from the modulated laser beam irradiation period is measured. The sample 6 is then positioned by determining the distance between the sample and the probe laser beam using a calibration curve prepared in advance using a sample whose film thickness is known.

Now, as the sample 6, a coated steel plate with black paint applied to the surface of the steel plate is used, and as the irradiation laser 1, 30
An mWAr+ ion laser was used, and the modulation frequency of modulator 2 was 500 Hz. Further, as the probe laser 4, a 5 mWHe-Ne laser was used. FIG. 2 shows the relationship between the sample position and phase delay at this time. From this result, a positional deviation of 1 μm can be detected as a phase delay of 0.34°, and positioning on the order of submicrons can be performed.

[0011]

As explained above, according to the present invention, the change in refractive index due to the heat wave generated from the sample when the sample is irradiated with laser light is measured as the polarized light of the probe laser beam. Even samples with low reflectance or rough surfaces can be accurately positioned, greatly contributing to improving sample positioning accuracy.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the configuration of a measuring device for implementing the method of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between sample position and phase delay obtained by the present invention.

[Explanation of symbols]

1 Laser for irradiation 2 Modulator 3. Condensing lens 4 Laser for probe 5 Condensing lens 6 Sample 7 Two-split photodiode 8 Modulator power supply 9 Lock-in amplifier

Claims (1)

[Claims] Claim 1: A sample is irradiated with a laser beam modulated at a predetermined frequency, and a change in the refractive index of a fluid directly above the sample caused by heat emission from the sample is measured as the polarization of a probe laser beam passing directly above the sample. A method for positioning a sample, comprising measuring a phase delay of a polarization period from the modulated laser beam irradiation period.