JPH0310901B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a sample cooling device for spectrometry that cools a sample when analyzing different elements contained in a single crystal such as silicon by spectrometry. [Prior Art] In general, spectrometry is a measurement method in which the elements contained in the sample are analyzed by shining light onto the sample and analyzing the transmitted or reflected light using a spectrometer. Widely used for qualitative or quantitative analysis. As such spectroscopic measurement methods, there are two known methods: one in which the sample is measured at room temperature, and the other in which the sample is cooled. The latter method of spectrometry is a method in which the sample is cooled to an extremely low temperature for measurement, and compared to the former measurement method, a more complex spectrum is obtained, which allows a variety of analytical results to be obtained. Therefore, it is a measurement method that can obtain excellent measurement accuracy in both qualitative and quantitative analysis. BACKGROUND ART Conventionally, in the above-mentioned spectrometry method in which a sample is cooled and measured, a sample cooling device A for spectrometry as shown in FIG. 5 has been provided as a device for cooling the sample. This spectroscopic measurement sample cooling device A has an entrance optical window 2 formed on a side circumferential surface 1a of a container 1, and an output optical window 3 formed on a side circumferential surface 1a of the container 1, which faces the incident optical window 2. The entrance optical window 2 and the exit optical window 3 are each equipped with light-transmitting plates 4, 4, and a refrigerant is supplied to the inside of the top plate 1b of the container 1 through a pipe 5 protruding to the outside of the container 1. It is formed by connecting tanks 6. The refrigerant tank 6 has a bottom plate 6a.
The sample 7 can be fixed to the lower surface of the holder.
Furthermore, liquid helium is fed into the refrigerant tank 6 from outside the container 1 through a pipe 5, thereby lowering the atmospheric temperature within the container 1 and cooling the sample 7. ing. The spectroscopic measurement sample cooling device A configured as described above cools a sample to an extremely low temperature during spectroscopic measurement of the sample.
The light incident inside the container 1 is transmitted through the sample 7, and the transmitted light can be emitted from the exit optical window 3 to the outside of the container 1. The light thus emitted is analyzed by a spectrometer (not shown). [Problems to be Solved by the Invention] By the way, in the above-mentioned conventional sample cooling device for spectroscopic measurements, the plates attached to the entrance optical window and the output optical window are perpendicular to the optical axis. Therefore, as shown by the dashed-dotted arrow in Figure 6, the light that has passed through the sample is reflected on the surface of the plate attached to the output optical window, and the reflected light is then reflected on the plate attached to the input optical window. It is reflected by the surface of the body, and the reflected light is emitted to the outside of the container through the exit optical window.
Such light (hereinafter referred to as multiple reflected light) is the light that passes through the sample and exits from the exit optical window to the outside of the container (hereinafter referred to as light on the optical axis), as shown by the solid arrow in the figure. ), which caused the problem of increased measurement errors and variations in measured values. Note that although the path of the light ray indicated by the dashed line in the figure is inclined with respect to the optical axis for convenience of explanation, it is actually coaxial with the optical axis. [Means for solving the problem] In the present invention, at least one of the plate attached to the input optical window and the plate attached to the output optical window is inclined with respect to the optical axis. The inclination angle is set at a critical angle such that the rays that enter from the input optical window, are sequentially reflected once on the plate of the output optical window and the plate of the input optical window, and hit the inner peripheral surface of the container outside the outer periphery of the output optical window. The above problem is solved by setting it larger. [Effect] The light reflected on the surface of the plate is tilted with respect to the optical axis according to the inclination angle set on the plate, and as a result, the multiple reflected light is largely deviated from the optical axis, making it difficult to analyze using a spectrometer. The influence of multiple reflected light on the results is reduced. [Embodiment] FIG. 1 is a diagram showing an embodiment of the present invention. In this figure, reference numeral A denotes a sample cooling device for spectrometry, and its components are the same as those of the conventional sample cooling device for spectrometry. In this sample cooling device A for spectrometry, the plates 4, 4 are attached to the entrance optical window 2 and the exit optical window 3, respectively, at a predetermined angle with respect to the optical axis indicated by the solid arrow in the figure. ing. In the sample cooling device A for spectrometry configured in this way, the multiple reflected light deviates significantly from the optical axis as shown by the dashed-dotted arrow in the figure, thereby distorting the analysis results of the spectrometer (not shown). The influence of multiple reflected light on the image can be reduced, and measurement errors and variations in measured values can be reduced. Further, in the above embodiment, if the inclination angle of the plates 4, 4 with respect to the optical axis (hereinafter referred to as the plate inclination angle) is made larger, the multiple reflected light hits the inner wall surface of the container 1 other than the output optical window 3. , measurement errors and variations in measured values can be further reduced. That is, the plate inclination angle (hereinafter referred to as critical angle) at which the multiple reflected light hits the edge 3a of the output optical window 3 is α, the aperture diameter of the input optical window 2 and the output optical window 3 is D, and the input optical When the distance between the window 2 and the output optical window 3 is L, the critical angle α is given by the following equation. TAN・α=D/2L……(1) Therefore, by making the plate inclination angle larger than the above critical angle α, the multiple reflected light can be directed from the output optical window 3 to the outside of the container 1. There is no emission,
The influence of multiple reflected light on the analysis results by the spectrometer can be completely eliminated. Hereinafter, in the above example, the results of spectroscopic measurement of a sample while changing the plate inclination angle will be explained. In this spectroscopic measurement, the concentration of oxygen contained in a silicon single crystal (sample) was measured using infrared spectroscopy. Spectroscopic measurement sample cooling device A used for spectroscopic measurement
Here, the aperture diameters of the entrance optical window 2 and the exit optical window 3 were set to 25 mm, and the distance L between the entrance optical window 2 and the exit optical window 3 was set to 100 mm. By substituting these values into equation 1, it is possible to obtain the critical angle α of the plate inclination angle of 7°. In this spectroscopic measurement, the plate inclination angle was set to 5°, which is smaller than the critical angle.
A silicon single crystal was cooled to 20°K using a sample cooling device A for spectrometry with a plate inclination angle of 8°, which is larger than the critical angle, and infrared light was applied to the silicon single crystal. , we measured the magnitude of light absorption by oxygen that appeared at a light wave number of 1136 cm ^-1 . Then, the oxygen concentration (number of oxygen atoms/cm ³ ) was determined using a calibration curve determined in advance. In this way 3
Table 1 shows the results of repeated measurements five times for each type of silicon single crystal. In addition, Table 2 shows the results of spectroscopic measurements of the same three types of silicon single crystals as described above using a conventional sample cooling device for spectroscopic measurements. The results are shown in Table 3 for reference. As shown in Table 1, in the measurement results when using sample cooling device A for spectrometry with a plate inclination angle of 5°, the average value of dispersion was ±0.21 × 10 ¹⁷ /cm ³ , which was higher than before. also became a small value. Moreover, the median value for each sample was close to the measurement result at room temperature. Furthermore, in the measurement results when using sample cooling device A for spectrometry with a plate inclination angle of 8 degrees, the average value of dispersion was ±0.08 × 10 ¹⁷ /cm ³ , which was better than the measurement results at room temperature. also became a small value.
Moreover, the median value for each sample was almost the same value as the measurement result at room temperature. As explained above, in the above embodiment,
By tilting the plates 4, 4 with respect to the optical axis, measurement errors and variations in measured values can be reduced.Furthermore, by making the plate inclination angle larger than the critical angle, it is possible to It is possible to obtain measurement results that are almost the same as the measurement results at room temperature, and moreover, it is possible to obtain measurement results with smaller variations than the measurement results at room temperature. FIG. 2 is a diagram showing still another embodiment of the present invention. In this embodiment, only one of the plates 4, 4 is inclined with respect to the optical axis, and the same effect as the above embodiment can be obtained. In this embodiment, the critical angle α is given by TAN·2α=D/2L (2) for equation 1. FIG. 3 is a diagram showing still another embodiment of the present invention. In this embodiment, each of the plates 4, 4 is inclined in an eight-shape with respect to the optical axis, and the same effect as the above embodiment can be obtained. In this embodiment, the critical angle α is given by TAN·3α=D/2L (3) for equation 1. The above describes how, in spectroscopic measurements, light is applied to the sample,
This is an embodiment in which the transmitted light is detected, but as shown in FIG. 4, even in the case of detecting the reflected light, at least one of the plates 4, 4 is tilted with respect to the optical axis. By doing so, the same effects as in the above embodiment can be obtained. [Effects of the Invention] In this invention, at least one of the light-transmitting plate attached to the input optical window and the light-transmitting plate attached to the output optical window is aligned with the optical axis. In contrast, by tilting it, it is possible to obtain measurement results with less measurement error and less variation in measurement values. Furthermore, the inclination angle with respect to the optical axis of at least one of the plate attached to the input optical window and the plate attached to the output optical window is adjusted so that the inclination angle between the plate attached to the input optical window and the plate attached to the output optical window is adjusted. By specifying that the light that has been sequentially reflected once by the plate attached to the plate and the plate attached to the input optical window hits the inner circumferential surface of the container other than the output optical window, there will be less variation than the method of measuring the sample at room temperature. It is possible to obtain the effect of being small and being able to obtain almost the same measurement results as the method of measuring at room temperature.

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【table】 [Brief explanation of the drawing]

1, 2, 3, and 4 each show an embodiment of the present invention, and a cross-sectional view similar to FIG. 6, and FIGS. 5 and 6 show conventional spectroscopy. 5 is a side sectional view thereof, and FIG. 6 is a sectional view taken along the - line arrow in FIG. 5. FIG. DESCRIPTION OF SYMBOLS 1... Container, 2... Incoming optical window, 3... Outgoing optical window, 4... Plate, 7... Sample.

Claims (1)

[Claims] 1. A container for cooling the sample is provided with an entrance optical window and an exit optical window each equipped with a light-transmitting plate, and the sample enters the container through the entrance optical window and is cooled in the container. light passing through the sample,
Alternatively, in a sample cooling device for spectrometry configured to emit light from the exit optical window reflected from the surface of the sample to the outside of the container, a plate attached to the input optical window and a plate attached to the output optical window may be used. At least one of the plates is tilted with respect to the optical axis, and this angle of inclination is such that the angle of inclination is such that when the light enters from the input optical window, it is reflected once by the plate of the output optical window and the plate of the input optical window. 1. A sample cooling device for spectroscopic measurements, characterized in that the angle is set larger than a critical angle at which the light beam hits the inner peripheral surface of the container outside the outer periphery of the output optical window.