JPH05101797A - X-ray light source device - Google Patents

Abstract

PURPOSE:To provide an X ray light source device being able to realize an X ray spectral system, in which the light amount variation of a dispersed X ray is small so as to be excellent in stability, in a laser plasma light source which disperses and utilizes the X ray. CONSTITUTION:In an X ray light source, a laser light is irradiated to target material 6 placed in a vacuum vessel 2, and the target material is turned into a plasma state so as to generate an X ray. Here the target material 6 is composed of elements whose atomic numbers are larger than nineteen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray light source device.

[0002]

2. Description of the Related Art In recent years, the analysis of semiconductor material surfaces has begun,
In particular, in the fields of analysis of organic substances containing carbon, semiconductor manufacturing processes such as CVD, evaluation of organic electronic devices and analysis of biological materials, fluorescent X-ray analysis using light in the soft X-ray region of several Å or more as a probe, ESCA (Electr
There is a need for an evaluation device that uses a method such as on spectrocopy for chemical analysis) or Auger spectroscopy.

However, since the evaluation apparatus currently on the market uses an X-ray tube, only a so-called characteristic X-ray having a short wavelength of several Å or less can be used. In such a short-wavelength characteristic X-ray region, the absorption coefficient for an organic substance composed mainly of carbon is reduced, the production rate of secondary electrons and Auger electrons is reduced, and the analysis sensitivity is deteriorated. Furthermore, since only X-rays of a specific wavelength can be used, the scope of application of the device is limited and multifaceted analysis cannot be performed.

On the other hand, research on an artificial lattice for superconductivity of about several tens of liters has progressed, and there is a demand for nondestructive observation of the internal structure of such an artificial lattice. However, since the conventional X-ray tube can only use X-rays having a wavelength of several Å at most, analysis by the X-ray diffraction method in the direct incidence region is impossible. For this reason, the above analysis has been performed using a synchrotron radiation (SOR) light source that emits white light up to the soft X-ray region. Since a large-scale facility is required to generate this SOR light, it is extremely difficult for general users to obtain it.

By the way, recently, a compact white X-ray light source has been developed, and the above-mentioned analysis method of this kind has become popular. That is, in the X-ray light source called a laser plasma light source, it is, 10 ^-4 Tor
When a target such as a metal is irradiated with a laser beam having an intensity of 10 ¹² W / cm ² or more in a vacuum of r or less, the target metal becomes a plasma state and a white X-ray light source having a wavelength of 5 Å or more is generated. Is to do.
Since this laser plasma light source is a high-intensity and white X-ray light source, a soft X-ray diffractometer, a photoelectron spectrometer, an X-ray acoustic spectroscopy method and the like using the same have already been proposed (Japanese Patent Application No. 2- No. 26241, Japanese Patent Application No. 3-161746, etc.).

Here, the principle of X-ray generation of the laser plasma light source will be described. When a high energy laser beam is applied to the surface of an appropriate substance in a vacuum, the atoms constituting the substance violently vibrate due to the strong electric field, and undergo processes such as multiphoton absorption and collision with surrounding atoms. As a result, a plasma state is established. Further, the ionized ions and the electrons repeatedly violently collide with each other, resulting in a plasma state at an even higher temperature.

In the plasma state in which ions and electrons are separated in this way, X-rays of the following three types i) to iii) are mainly generated. i) Free-Free Transition When free electrons freely moving around in the plasma change their trajectories by the attractive force of ions, X-rays are generated by the bremsstrahlung of the free electrons. At this time, the spectrum of the free electrons in the plasma is almost continuous because the free electrons are moving at various speeds and directions. ii) Free-bound transition When free electrons are trapped in the electron orbits of ions, surplus kinetic energy and thermal energy of the free electrons are emitted as X-rays. In this case, although it is essentially a continuous spectrum, in the final state, it has a discontinuous energy level determined by the main quantum number, the angular momentum, and the spin state, so that it becomes a sawtooth continuous spectrum. iii) Bound-bound transition When the ions are excited to a discontinuous high energy level by collision of ions and electrons in the plasma, they are deexcited to a low energy level again. X-rays are also generated at this time, but in this case, since the energy levels of the initial state and the final state are determined, the line spectrum has an extremely narrow width.

2 and 3 show X-ray emission spectra of each element. Generally, in the case of a light element such as Al, the number of energy levels in the bound state is small.
The narrow spectrum corresponding to the form of iii) becomes dominant, and their intensities become dominant (FIG. 2, graph (A)).
reference). Further, as is clear from FIGS. 2 and 3, the X-ray emission spectrum becomes a continuous spectrum in the case of a heavy element. On the other hand, the above tendency becomes stronger as the level of the outer shell having a large number of states such as the L, M, N, and O shells of the electron orbit is involved. FIG. 4 shows the X-ray emission intensities for the transitions involving the K, L, M, N, and O shell electrons for each element, and shows strong emission in the case of transitions involving electrons in the orbits outside the L shell. It can be seen that it has strength. In FIG. 4, the solid line indicates that the photon energy E is 700 eV.
<E, and a dotted line shows 250 <E <800 eV.

[0009]

However, the conventional measuring system such as the soft X-ray diffractometer using the laser plasma light source based on the above X-ray generation principle has the following problems. When the target is an element having a relatively small atomic number such as Al, as shown in the graph (A) of FIG. 2, the emission process of X-rays may be caused by the bound-bound transition of iii) above. It has a spectral characteristic in which a line spectrum having a dominant and extremely narrow wavelength width is scattered over a wide wavelength range. Such a line spectrum exhibits high intensity for a specific wavelength, but if such X-rays are spectrally used, the following inconvenience occurs.

The emission intensity due to the bound-to-bound transition is defined by the number of ions in the initial state of the transition generated in plasma, and the number of ions is significantly influenced by the way of energy injection by laser light irradiation. .. Therefore, the emission intensity due to the bound-to-bound transition changes depending on how the energy is injected by the irradiation of the laser light. On the other hand, the commercially available strong Nd:
The YAG laser or the excimer laser does not have sufficient oscillation stability, and the power, the beam diameter, the position of the optical axis, the wavelength, and the like change. Therefore, X due to the above binding-binding transition
When the rays are used as a probe for a diffractometer or an analyzer, the light quantity of the X-ray, which is a probe, fluctuates abruptly during measurement, and the measurement result is significantly adversely affected. And this has become a very serious problem especially in the experiment for monitoring the X-ray intensity.

In view of the above situation, the present invention is an X-ray spectroscopic system which can realize an X-ray spectroscopic system excellent in stability with a small fluctuation in the amount of X-rays dispersed in a laser plasma light source device for spectrally utilizing X-rays. An object is to provide a light source device.

[0012]

An X-ray light source device according to the present invention irradiates a target material placed in a vacuum container with a laser beam to convert the target material into a plasma state to emit X-rays.
Although a line is generated, the target material is composed of an element having an atomic number larger than 19.

[0013]

First, the free-free transition and the free-bound transition in the X-ray generation mode described above are characterized in that the energy level of the initial state is a continuous spectrum, and the distribution of the initial state is ionized. Corresponds to the energy distribution of free electrons. Moreover, in the laser plasma light source, the energy distribution of the free electrons substantially follows the Boltzmann distribution, which is quite broad. Therefore, even if the plasma generation conditions change to some extent, when focusing on the number of free electrons having a specific kinetic energy, the number of free electrons does not change rapidly. The intensity of X-rays generated by these transition processes does not greatly depend on the way of energy injection by laser light irradiation. Furthermore, in the free-free transition, the energy level in the final state is also a continuous spectrum, so that even if the plasma generation conditions change, the number of free electrons having a specific kinetic energy does not change much more.

On the other hand, in the bound-bound transition, the initial state is
Due to the very limited discontinuous quantum states with specific angular momentum, energy levels and spin states for specific ions, such special initial states can almost occur unless specific plasma generation conditions are satisfied. Absent. For this reason, when the X-ray generated by the bound-bound transition is used as a probe after being separated, the intensity of the X-ray often decreases sharply when the laser energy decreases for some reason, and thus stable. From the viewpoint of sex, it is preferable to use X-rays by free-free transition or free-bound transition.

According to the present invention, the target substance is
It is made up of elements with atomic numbers greater than 19. Generally, only when the atomic number of an element is small, the intensity of X-rays due to the bound-bound transition is large in many cases when the steeple intensity of the spectrum is examined. On the other hand, when the atomic number is large, the number of valence electrons is large, so that the generation rate of X-rays due to free-free transitions and free-bound transitions is increased, whereby a sufficient X-ray intensity can be obtained. In addition, the larger the atomic number and the outer shell electrons, the narrower the energy level interval in the bound state, so that the light emission due to the free-bound transition exhibits a behavior similar to that in the free-free transition. In the present invention, since the target material is selected so that the atomic number is relatively large in the X-ray generation process and the outer shell orbital outside the L shell is involved, X-rays due to free-free transitions and free-bound transitions are obtained. Can be used with high efficiency.

[0016]

EXAMPLE An example of the X-ray light source device according to the present invention will be described below with reference to FIG. 1 by taking the case of an X-ray diffraction / scattering analyzer as an example. In the figure, reference numeral 1 is a vibration isolation table that supports each component of the apparatus while dampening vibrations, and 2 is a vacuum container installed on the vibration isolation table 1, which has a glass transparent window 3 and openings 4 and 5. The target 6 has a shaft 7 inside.
A transparent shielding plate 8 made of glass and having substantially the same size as the transparent window 3 is provided inside the transparent window 3.

Here, the target material is made of an element having an atomic number larger than 19, and is, for example, vanadium (V), copper (Cu), samarium (Sm), tantalum (Ta), tungsten (W), niobium. (Nb), chromium (Cr), gadolinium (Gd), yttrium (Y), platinum (Pt), gold (Au), lead (Pb), silver (Ag), iron (Fe), nickel (Ni), cobalt Any one of (Co), scandium (Sc), titanium (Ti) and bismuth (Bi) is used.

9 is mainly Nd: Y installed on the vibration isolation table 1.
A high-power pulse laser light source 10 such as an AG is a condenser lens for condensing laser light, and the laser light from the pulse laser light source 9 is condensed by the condenser lens 10 through the transparent window 3 and the shielding plate 8 to form a target 6 When the target 6 is irradiated, a part of the target 6 is melted and evaporated to form plasma, and this high temperature
Soft X-rays are generated from high-density plaza. At this time, the shielding plate 8 prevents the scattered pollutants from being deposited on the transparent window 3. The transparent window 3 and the shielding plate 8
Is installed at an angle of about 3 ° with respect to the optical axes of the pulse laser light source 9 and the condenser lens 10 so that the reflected light of the laser light by them does not return to the pulse laser light source 9 to make the oscillation of the laser light unstable. Further, an antireflection film is applied so that the target 6 can be efficiently irradiated with laser light. The above members are the soft X-ray light source unit 1
Make up one.

Reference numeral 12 denotes another vacuum container installed on the vibration isolation table 1 and connected to the vacuum container 2 through the opening 4.
In addition to having the openings 13 and 14, an entrance slit 15 and an oblique incidence type diffraction grating (concave surface diffraction grating) 16 are installed inside. The above-described members constitute the spectroscope 21.

One end of the vacuum container 1 has an opening 13 through the opening 13.
Telescopic bellows connected to 2, 18 is bellows 1
7 is another vacuum container connected to the other end of the diffraction grating 16, and the vacuum container 18 is movable in both the longitudinal direction and the lateral direction of the bellows 17 so that the circumference of the Rowland circle of the diffraction grating 16 is reduced. It is installed on the anti-vibration table 1 via a pedestal 19 that can be moved along. 20 is a vacuum container 1
8 is an exit slit which is installed in a position corresponding to the pedestal 19 within the position 8, that is, moves along the Rowland circle of the diffraction grating 16 with the movement of the pedestal 19. Reference numeral 22 is a sample table rotatably installed in the vacuum container 18, and 23 is a first soft X-ray detector such as a channeltron installed rotatably around the sample table 22 in the vacuum container 18. The center of the diffraction grating 16, the exit slit 20 and the center of the sample table 22 are always positioned on a straight line. The above-mentioned members constitute the measuring unit 27.

Reference numeral 24 denotes a soft X which is installed in the vacuum container 2.
This is a second soft X-ray detector that monitors the intensity of soft X-rays in the line light source unit 11. Reference numeral 25 is a computer that performs arithmetic processing according to a predetermined equation based on the output signals from the first soft X-ray detector 23 and the second soft X-ray detector 24, and displays the result on the display device 26. The computer 25 also controls the oscillation of the pulse laser light source 9, the rotation of the target 6, the movement of the pedestal 19, the rotation of the sample table 11, and the rotation of the soft X-ray detector 23.

28 is a magnetic levitation type turbo molecular pump, one end of which is connected to the vacuum container 2 through the opening 5 and which is installed on the vibration isolation table 1, and which has little vibration. 29 is a rubber tube 30 which hardly transmits vibration. Is a rotary pump for rough evacuation, which is connected to the other end of the turbo molecular pump 28 via the and is installed outside the vibration isolation table 1, and which is a vacuum pump part for performing evacuation in the vacuum container 2. 31 is configured. 32 is a magnetic levitation type turbo molecular pump, one end of which is connected to the vacuum container 12 through the opening 14 and which is installed on the vibration isolation table 1, and 33 is the other end of the turbo molecular pump 32, which is connected through a rubber tube 34. And a rotary pump for roughing, which is installed outside the vibration isolation table 1 and constitutes a vacuum pump unit 35 for performing vacuuming in the vacuum container 12, the bellows 17 and the vacuum container 18. ing.

Further, 36 is a detector 23 from the light source unit 11.
It is a transmission filter which is arranged at a proper position in the optical path up to, that is, at a position corresponding to the aperture 13 in this example, shields light in the vacuum ultraviolet wavelength range and can transmit X-rays of extremely short wavelength (20 Å or less). This transmission filter 36 has a thickness of 1200 Å, for example.
The transmission filter 36 is also detachably attached to the optical path by operating the manipulator 37 from the atmosphere side, that is, the outside of the vacuum container 12 in this example, although it is constituted by a boron filter of a certain degree.

The X-ray light source device of the present invention is configured as described above, and the laser light formed by oscillating the pulsed laser light source 9 passes through the condenser lens 10 and is placed in the vacuum target. 6 Focused on the surface. Then, the white X-rays generated from the target 6 pass through the entrance slit 15 and reach the oblique incidence type diffraction grating 16, and are separated by the oblique incidence type diffraction grating 16. X separated
The line is further passed through the transmission filter 36,
The long wavelength component which is the scattered light from the oblique incidence type diffraction grating 16 is cut. As a result, the X-rays having improved monochromaticity in the short wavelength region pass through the injection slit 20 that can move on the Rowland circle and enter the vacuum container 18 having the sample stage 22 and the first soft X-ray detector 23 built therein. Be guided. Then, in the vacuum container 18, the X-rays are incident on the surface of the sample S rotatably installed, and the diffracted light at this time is soft X-ray detector 2
3 is detected.

The transmission filter 36 can be inserted into and removed from the optical path by operating the manipulator 37. Contrary to the above case, by removing the transmission filter 36 from the optical path, long wavelength X-rays can be emitted. Even when used, the X
It is possible to measure without attenuating the line. In the case of long-wavelength X-rays as described above, even if the sample S is not passed through the transmission filter 36, the sample S is installed at a sufficient distance from the oblique-incidence diffraction grating 16 and has a large diffraction angle. The scattered light from the grating 16 has almost no effect.

By the way, when Ti (atomic number 22) is used as the material of the target 6, in the light source spectrum of the target 6 by laser plasma,
X-rays of the free-bound transition generated by the involvement of the L shell in the wavelength region of 150Å were observed with extremely high intensity. Starting with this Ti example, if a material having an atomic number larger than 19 is used as the material of the target 6, the number of valence electrons increases, so that the generation rate of X-rays due to free-free transitions and free-bound transitions increases. Thereby, sufficient X-ray intensity can be obtained. In addition, the larger the atomic number and the outer shell electrons, the narrower the energy level interval in the bound state, so that the light emission due to the free-bound transition exhibits a behavior similar to that in the free-free transition.

As the material of the target 6, as can be understood from FIGS. 2 and 3, in particular, Cu, Ta, Nb,
Although elements such as Fe and Ti are excellent in terms of light source characteristics of laser plasma, they also have excellent advantages in terms of price and processability. That is, especially when the target 6 has a rotating cylindrical shape, its rotating surface needs to be always at the focus position of the laser light from the pulsed laser light source 9, which causes an axis shift of the target 6 and a change in the surface shape. For example, the plasma generation conditions change and the light source intensity changes. On the other hand, since Cu, Ta, Nb, Fe, Ti and the like are extremely easy to process such as polishing and cutting, it is possible to easily form a highly accurate rotating surface. And besides, these elements are extremely cheap.

[0028]

As described above, according to the present invention, it is possible to realize an X-ray spectroscopic system in which there is little fluctuation in the amount of dispersed X-rays in a laser plasma light source device that disperses and uses X-rays. There are advantages such as being able to guarantee highly accurate measurement or analysis.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an X-ray light source device according to an embodiment of the present invention.
It is a schematic block diagram of a line diffraction / scattering analyzer.

FIG. 2 is a diagram showing X-ray emission spectra of aluminum, iron, tin, copper and samarium.

FIG. 3 is a diagram showing X-ray emission spectra of ytterbium, hafnium, tungsten and lead.

FIG. 4 is a graph showing the relationship between each element and X-ray conversion efficiency.

[Explanation of symbols]

 1 Vibration Isolation Table 2 Vacuum Container 3 Transparent Window 6 Target 8 Shielding Plate 9 Pulse Laser Light Source 10 Condensing Lens 11 Soft X-ray Light Source Part 12 Vacuum Container 15 Incident Slit 16 Glancing Incidence Diffraction Grating 17 Bellows 18 Vacuum Container 20 Emission Slit 21 Spectrometer 22 Sample stage 23 First soft X-ray detector 24 Second soft X-ray detector 25 Computer 26 Display unit 27 Measuring unit 28 Turbo molecular pump 29 Rotary pump 31 Vacuum pump unit 32 Turbo molecular pump 33 Rotary pump 35 Vacuum pump unit 36 Transmission filter 37 Manipulator

Claims (2)

[Claims] 1. An X-ray light source device in which a target material placed in a vacuum container is irradiated with laser light to generate a X-ray by converting the target material into a plasma state, and the target material has an atomic number of An X-ray light source device comprising an element larger than 19. 2. The target material is vanadium,
Copper, samarium, tantalum, tungsten, niobium, chromium, gadolinium, yttrium, platinum, gold, lead, silver,
The X-ray light source device according to claim 1, which is one of iron, nickel, cobalt, scandium, titanium, and bismuth.