JPH0120367B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grazing incidence spectrometer using a concave diffraction grating.

Conventionally, when trying to analyze and measure light in the vacuum ultraviolet region, a grazing incidence spectrometer using a concave diffraction grating has been used.

Conventionally, in this type of spectrometer, light from a certain space passing through an entrance slit is incident on the grating plane of a so-called concave diffraction grating at a considerable angle, and the light is diffracted by this grating plane. In this way, spectral lines of specific wavelengths are imaged at different positions on the Rowland circle. Each spectral line is then measured by a photodetector.

However, in the above-mentioned apparatus, when light from a certain space is separated and measured, one photodetector is arranged for a spectral line of a certain specific wavelength, and photometry is performed. Therefore, when measuring light of the above-mentioned specific wavelength coming from a different space, it is necessary to shift the position of the spectrometer each time.

An object of the present invention is to obtain a spectrometer that can separate light from a plurality of spaces and measure spectral lines of specific wavelengths for each space without shifting the position of the spectrometer.

Each spectral line obtained in an oblique incidence spectrometer using a concave diffraction grating extends long in the direction of the grooves of the grating, and this has traditionally been considered a drawback of this type of spectrometer. In the present invention, by reducing the length of the entrance slit in the direction of the grating grooves to some extent, the light in each space located in the direction of the grooves of the grating and the light of each part located in the length direction of the spectral lines extending in the direction of the grooves of the grating are reduced. Based on the discovery that light corresponds to each other, it was possible to measure the light in each space to be measured without moving the spectrometer by measuring the light in each part of the spectral line. .

Embodiments of the present invention will be described below based on the accompanying drawings.

1 to 3 schematically show a first embodiment of the present invention, in which FIG. 1 is a side view of the device of this embodiment, FIG. 2 is a plan view of the device shown in FIG. 1, and FIG. FIG. 3 is a perspective view of the apparatus shown in FIGS. 1 and 2.

In these figures, the grating surface 1a of the diffraction grating 1, which is always in a fixed position, is a concave spherical surface.
Parallel grooves 1b are formed at equal intervals on this grating surface 1a. That is, the diffraction grating 1 is what is called a "concave diffraction grating." R indicates a Rowland circle in contact with the concave lattice surface 1a. The slit length direction of the entrance slit 2a is parallel to the groove direction of the diffraction grating (hereinafter referred to as the x direction). In the figure, the slit length is indicated by d, and the slit width is indicated by e. This entrance slit 2a is arranged on the Rowland circle R. Slit length limiting plate 2b
As shown in the figure, a light shielding plate has an opening extending in a direction perpendicular to the x direction (hereinafter referred to as the y direction), and limits the slit length d of the entrance slit 2a. Of course, the slit width e and the slit length d may be made variable. 3a-3e, 4
A to 4e are rows of photodetectors, and each detector is arranged in the x direction. 3c of detectors
The photodetectors 4c and 4c are located on the Rowland circle R. And these elements 1, 2, 3a-3e, 4
a to 4e are built into this spectrometer.

Now, light from the measurement space s is guided to the grating surface 1a of the diffraction grating 1 through the entrance slit 2a having a slit length d and a slit width e. The lattice plane 1a reflects this light, but even if the incident angle α is the same, the diffraction angle β differs depending on the wavelength of the light, and spectral lines of specific wavelengths are connected to different positions on the Rowland circle R. imaged. In the figure, l ₁ is a spectral line on which light with a certain wavelength λ ₁ is imaged, and l ₂ is a spectral line on which light with a certain wavelength λ ₂ is imaged.
The concave grating 1 described above has an imaging ability in the width direction of the groove (referred to as the z direction) due to the relationship between the concave surface and the incident angle of light, but has almost no imaging ability in the groove direction (x direction). travels in the x direction as a diverging light beam, and the image of the entrance slit portion 2a is linearly formed as a so-called astral image on the Rowland circle R, resulting in spectral lines l ₁ and l ₂ extending in the x direction.

Conventionally, the resolution of the spectral line was adjusted by changing the slit width e, and the light intensity of the spectral line was adjusted by changing the slit length d using the limiting plate 2b. By reducing the slit length d, each space s ₁ , s ₂ , s ₃ , aligned in the x direction in the measurement space s
This was made based on the discovery that s ₄ and s ₅ correspond to each portion located in the length direction (x direction) on the spectral line.

That is, in this embodiment, the light from the measurement space s is imaged onto the Rowland circle R for each wavelength through the entrance slit, and spectral lines l ₁ and l ₂ extending in a plurality of x directions are formed.
However, since the slit length d is set sufficiently small by the light amount adjustment member 2b,
The light in each space s ₁ to _{s 5} arranged in the x direction in the spatial plane s corresponds to the light in each part arranged in the x direction on the spectral line. Therefore, for example, if a plurality of photodetectors 4a to 4e are arranged on the spectral line _l2 of light with a wavelength _λ2 , the light with a wavelength _λ2 coming from the space _s1 in the measurement space s will be on the photodetector 4a. guided by the spaces s ₂ , s ₃ , s ₄ , s ₅
The light coming from the photodetectors 4b, 4c, 4
d, guided above 4e. In this way, the light in a plurality of spaces s ₁ to s ₅ within the measurement space can be measured simultaneously.

Furthermore, if a plurality of photodetectors 3a to 3e are arranged on the spectral line _l1 of light with wavelength _λ1 , some of the light coming from each space _s1 , _s2 , _s3 , _s4 , _s5 in the measurement space will be Light with wavelength λ ₁ is transmitted to photodetectors 3a, 3b, 3c, 3d, respectively.
3e, it is possible to simultaneously measure light from a plurality of measurement portions s ₁ to _{s 5} even for light of different wavelengths λ ₁ .

In the first embodiment described above, a plurality of photodetectors were placed on a spectral line on which light of a certain specific wavelength was imaged, and the light of each part of this spectral line was measured. 1st
Numerical examples for Examples are shown below.

The size of the spectrometer is expressed by the radius of curvature of the concave diffraction grating 1: R = 3 m, incident angle α = 87°, entrance slit 2a, slit length d = 0.5 mm, slit width e =
20μm, diffraction grating 1 has 1200 grooves/mm, dimensions are
It is 50 mm (width) x 37 mm (length), and the measurement wavelength range of this spectrometer is 50 to 500 Å. The distance between the entrance slit 2a and the diffraction grating 1 is ra, and the distance between the diffraction grating and the image point is
If rb, then ra=Rcos α=157mm, rb=Rcos β.

However, sinα−sinβ=λ/σ Here, only the first-order diffracted light is considered, λ is its wavelength, and σ is the reciprocal of the number of grooves. As mentioned above, even if the incident angle α is the same, the diffraction angle β differs depending on the wavelength of the light, so the measurement wavelengths are λ ₁ = 100 Å, λ ₂ =
If we choose two wavelengths of 300 Å, β and rb will be as follows.

λ ₁ = 100 Å, β = 80.62°, rb = 489 mm λ ₂ = 300 Å, β = 74.29°, rb = 812 mm From this, the photodetector can be placed on the Rowland circle 489 mm or 812 mm away from the diffraction grating.
The plasma we want to measure is 25cm in size and 2m away from the spectrometer. This is measured for each of the measurement spaces S ₁ , S ₂ , S ₃ , S ₄ , and S ₅ . The spatial positions and intensities of the obtained spectral line images for the center space S ₃ and the spaces S ₁ and S ₅ at both ends will be explained based on FIG. 2. However, the image plane is taken perpendicular to the straight line (direction of the main diffracted light) connecting the diffraction grating and the center of the image point by _S3 . The light from the central space _S3 is
The length of the entrance slit is limited by d = 0.5 mm, and diffraction occurs only near the center of the diffraction grating. space at both ends
If S ₁ and S ₅ are the edges of the plasma that are 11.5 cm away from the plasma center, the light from these ends will be similarly restricted by the entrance slit and will be incident near the center of the diffraction grating by 9 mm in the longitudinal direction. , is diffracted.
As a result, the spatial positions and intensity distributions of spectral images at two wavelength values (100 Å and 300 Å) obtained by the photodetector are shown in FIGS. 4 and 5, respectively.
In this figure, the spectral image due to light from space S ₁ or S ₂ at the edge is generated at a location shifted in the x direction by 40 mm at a wavelength of 100 Å and by 60 mm at a wavelength of 300 Å with respect to the image from space S ₃ at the center, so By placing photodetectors (or a combination of an exit slit and a photodetector) at separate locations, it is possible to separate and detect the light from the spatial points S ₁ to S ₅ . In the diagram showing the image intensity distribution, the image caused by the light from the spaces S ₁ and S ₅ at both ends is slightly more spread out than the image caused by the light from the center space S ₃ . This is because the images S ₁ and S ₅ are slightly tilted, and this can be seen from the spatial position diagram of the images. Therefore, when combining an exit slit and a photodetector, the exit slit is installed to match this inclination to improve wavelength resolution. As a result, it is possible to obtain a resolution comparable to that of an image created by light from the central space _S3 . The magnitude of the inclination is approximately 0.6 to 0.7° in the examples shown in FIGS. 4 and 5. The second embodiment is an example in which one photodetector is arranged for a spectral line on which light of a specific wavelength is imaged. That is, the second embodiment includes a plurality of photodetectors 4a to 4 arranged on the spectral line _l2 in FIG.
One photodetector (not shown) having a light-receiving surface in the length direction of this spectral line _l2 is placed in place of spectral line e, and one slit is placed on the spectral line in front of this detector. By running along the length of spectral line _l2 , the light of each part of spectral line _l2 is selectively guided to the photodetector, making it possible to measure the light of each part of spectral line _l2 . It is something.

In the embodiments described so far, each spectral line l ₁ ,
l ₂ are each equipped with a dedicated photodetector. The third example described below is a certain spectral line l ₂
The photodetectors 4a to 4e that photometer the other spectral lines _l1 can also measure the light. That is, the photodetectors 3a to 3e shown in FIG. 3 are omitted,
The photodetectors 4a to 4e are all moved in the direction of the Roland circle R. As is clear from FIG. 2, the spectral lines become longer as they move away from the diffraction grating 1, and the intervals between the parts on the spectral lines corresponding to the spaces s ₁ to _{s 5} also widen as the spectral lines are farther away from the diffraction grating. Therefore, when the photodetectors 4a to 4e located on the spectral line _l2 are moved in the direction of the Rowland circle R to reach the top of the spectral line _l1 , the intervals between the photodetectors 4a to 4e are gradually narrowed, and each When the detectors arrive on the spectral line _l1 , it is desirable that the respective detectors be located at the positions of the detectors 3a to 3e shown in FIG.

In this embodiment, the photodetectors 4a to 4e are all moved simultaneously, but each of the photodetectors 4a to 4e may be moved independently.

In the examples so far, a concave spherical surface is used as a lattice surface,
Although the description has been made using a so-called "concave diffraction grating," the present invention may also use a diffraction grating whose grating plane is a concave cylindrical surface. Of course, the generatrix of the cylindrical surface is oriented in the x direction, and the grating grooves are also oriented in the x direction. Even if such a diffraction grating is used, the same effect as in the embodiment described above can be obtained only by increasing the lengths of the spectral lines l ₁ and l ₂ . The concave diffraction grating referred to in the present invention includes not only the so-called "concave diffraction grating" described above, but also a diffraction grating having a concave cylindrical grating surface as described above. It goes without saying that a diffraction grating having a concave toroidal surface as a grating surface is also included in the concave diffraction grating in the present invention.

In the embodiment, a case has been described in which the slit and the photodetector are arranged on the Rowland circle, but the present invention is not necessarily limited to the arrangement of the slit and the photodetector on the Rowland circle. When a spectral line is imaged, each part on the spectral line may be photometered.

As described in detail above, according to the present invention, it is possible to separate light from a plurality of spaces and measure a spectral line of a specific wavelength for each space without shifting the position of the spectrometer.

[Brief explanation of drawings]

1 to 3 schematically show a first embodiment of the present invention, with FIG. 1 being a side view, FIG. 2 being a plan view, and FIG.
The figure is a perspective view. Figure 4 shows the A spatial position and B intensity distribution of a spectral image (distance unit is mm) at a wavelength of 100 Å in the numerical example of the first embodiment, and Figure 5 shows the spectral image (distance) at a wavelength of 300 Å in the same numerical example. A is the spatial position and B is the intensity distribution (unit: mm). [Explanation of symbols of main parts] 1... Concave diffraction grating, 1a... Grating surface, 1b... Grating groove, R... Rowland circle, 2a... Entrance slit, d... Slit length,
l ₂ ...spectral line, 4a to 4e...photodetector (measurement point).

Claims (1)

[Scope of Claims] 1. In a grazing incidence spectrometer that forms a spectral line of a specific wavelength using a concave diffraction grating whose grating surface has curvature at least in the width direction of the groove, and performs photometry of the spectral line, an entrance slit is used. The length in the groove direction of the diffraction grating is defined as the light in each space located in the groove direction of the diffraction grating and the light in each part located in the length direction of the spectral line extending in the groove direction of the diffraction grating. are short enough to correspond to each other, and a plurality of measurement points are provided along the length direction of the spectral lines, so that photometry of the spectral lines can be performed at each measurement point. vessel. 2. The spectrometer according to claim 1, wherein a photodetector is provided corresponding to each measurement location. 3 1 having a light-receiving surface in the length direction of the spectral line
Claims characterized in that two photodetectors are arranged, and a slit arranged on the spectral line guides light from each photometric point to the photodetector by traveling along the spectral line. The spectrometer according to paragraph 1. 4. The spectrometer according to claim 1, wherein a plurality of measurement points are provided on each of the plurality of spectral lines, and light from each measurement point can be photometered.