JPH0799400B2 - High reflectivity, high resolution X-ray dispersive reflective structure and spectroscopic analysis method using the same - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to high reflectivity, high resolution X-ray dispersive reflective structures for use in the analysis of carbon, beryllium and boron.

This synthetic structure is free of crystal symmetry constraints and allows the use of the more restrictive prior art vapor deposition methods and materials. This improved structure has excellent properties with regard to the particular analytical tool of interest.

X-ray dispersible structure is industrially LiF, metal acid phthalate (map), pyrolytic graphite, Langmuir Broger (LB)
It is formed from a crystalline structure such as a film. The materials listed above have very tight lattice spacing restrictions. In addition, the LB device and the map device have severe environmental restrictions, and it is necessary to operate them near room temperature in a dry environment. LB equipment may generate pollutants under certain conditions, making it unsuitable for very high vacuum applications. In addition, it is not suitable for applications where the incident beam energy is high, because it may decompose. LB devices also have poor mechanical properties such as scratch resistance, mechanical puncture strength, and wear resistance. A further disadvantage of all prior art structures is that the reflectivity is not as high as required.

Many attempts have been made to construct natural and novel crystalline-like materials with the aim of improving their X-ray properties, which were limited by the availability of natural crystalline materials. One of such attempts is to adjust the composition by performing molecular beam epitaxial growth (MBE) on a single crystal substrate. For example, Dingle et al. U.S. Pat.
No. 261,771 describes a method of manufacturing a monolayer semiconductor using a kind of MBE technology. Such prior art conditioning structures are commonly referred to as "superlattices". Superlattices have been developed as a unitary periodic potential as a result of the material layers forming homo- or hetero-epitaxially grown planes or layers. The maximum period of a superlattice is usually several hundred angstroms, but a monoatomic layer structure is also constructed.

The characteristics of the superlattice are that a pair of layers of A layer (GaAs, etc.) and then B layer (AlAs) are alternately stacked in layers, and that they have a good crystal quality and a long-range order. The point is that it is formed on the crystal synthetic material. The thickness of each layer pair (A and B) is "d"
Defined as an interval. Since such a structure has a small electron density contrast between layers, it is often not suitable as a reflective or dispersive structure. Since these structures are essentially single crystals having an extra superlattice periodicity, the d-spacing is also accompanied by the constraint that the entire structure is a single crystal.

In addition to MBE type superlattice construction technology, stacked synthetic microstructures (lsm) have been developed using various vapor deposition methods including diode and magnetron sputtering, reactive gas injection method, standard multi-source evaporation method, etc. . Control of the layer size is performed by using a shutter, or by moving the substrate with respect to the material source, or by using both shutter and substrate movement. In the case of the multi-source evaporation method, control of the required thickness is achieved by in-situ monitoring the X-ray reflectivity of the film as it is being deposited. It is said that this material is composed of crystalline layer, amorphous layer and their mixture. However, as far as reported so far, when the deposition conditions are periodically repeated, it is necessary to perform it precisely based on this. It is usual to try to synthesize a superlattice type structure by. Some structures have d steps in the structure.

Such materials are considered to be synthetic crystals or crystal analogs where the long-range periodicity or repetition of a particular layer combination is important. It is both structurally and chemically homogeneous in the xy plane and periodic in the third (Z) direction. Compared with the evaporation method, various materials can be used for these construction methods, especially sputtering.

SUMMARY OF THE INVENTION In the present invention, the above-mentioned drawbacks of the prior art are overcome by a structure and material having high reflectivity and resolution and dispersiveness and reflectivity of X-rays. This structure exhibits excellent properties in certain low energy X-ray wavelength ranges such as those used for carbon, beryllium, and boron analysis. The structure of the present invention includes an alternating stack of metallic and non-metallic materials. Cr: C or N for carbon analysis
i: C or V: C, M for analysis of beryllium and boron
Form these layers with o: B ₄ C. The laminated structure can also be formed of Ni: C and used for both carbon and boron analysis.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1-8 show the prior art and the systems, materials and configurations described and claimed in the original patent application US Pat. No. 501,659 (JP 60-7399). . The applicability of the disclosure of the original patent application to the present invention is described in connection with these figures, while the novel materials and structures of the present invention are also described in the tables and legends below.

Referring first to FIG. 1, a conventional X-ray analysis system 10 is schematically illustrated. The system 10 includes an x-ray source 12, which impinges an x-ray beam 14 on a sample 16. Fluorescent beam 18 exits sample 16 and is aligned to pass through aperture 20 and reach x-ray dispersive structure 22.
X-ray dispersive structure 22 reflects beam 18 'toward detector 24. Although the curvature of structure 22 is exaggerated, it is actually only slightly curved so that the reflected beam 18 'of the desired wavelength can be focused on the detector 24.

FIG. 2 shows the distribution pattern of a typical prior art laminated structure 22. Although only three layer pairs with the layer spacing d are shown in the figure, many layer pairs are commonly used, for example 100 to 2000 pairs. The incident beam 18 has a wavelength band of which λ is an example. The reflected beam 18 'has a component corresponding to a single wavelength λ substantially reflected at an angle θ, that is, λ' / 2, λ / 3, λ ', according to Bragg's law of nλ'-2d sin θ.
It consists of / n. The reflected beam 18 'therefore includes all of these wavelengths in proportion to the intensity of the incident beam and the high unit reflections resulting from the rectangular electron density distribution as shown in FIG. I _i (λ) is the incident intensity distribution of λ, I _r (λ ′) is λ ′
Is a reflection intensity distribution of. (Perfect theoretical treatment results in a modification of Bragg's law resulting from diffraction of the X-ray beam.) Each layer pair contributes to the reflected beam intensity at similar angles.
In the figure, only the reflection from one layer pair is shown. Structure 22
Are typically curved to focus the reflected beam of the required wavelength from each layer pair onto the detector 24. The structure 22 is formed of a plurality of layers, and each layer includes a pair of layers A and B made of different materials. This aims to make the junction between the layers stepwise. Functionally, it means that the reflection index density is essentially a square wave 26, blocking the beam 18.

FIG. 3 shows the diffraction pattern 28 that results from the impinging beam 18 striking a prior art LB X-ray dispersive structure. Each peak is the order n of reflection with respect to the wavelength λ '(required wavelength) guided by the approximate relation nλ' = 2d sin θn. Prior art lsm devices show a similar diffraction pattern, but control of this pattern is essentially achieved by the deposited material and the d-spacing used.

The deposition parameters can be controlled by providing the material in an ion beam system to control layer deposition throughout the structure. One embodiment of a suitable ion beam system 34 is shown in FIGS. 4 and 5.

Ion beam technology has not been used to deposit X-ray dispersive reflective structures to date, but the technology employed in the original patent application is preferred. Not only for accuracy and control of deposition parameters, but also for breaking the bond between the ion plasma and the substrate to minimize unwanted components in the deposition of the desired structure. Ion beam 38 produced by ion source 36
Is neutralized and irradiated onto a suitable target 40. Beam 38 sputters material from the target into a substantially collimated, homogeneous stream 42 which is deposited on a suitable substrate 44. Substrate 44 is mounted on a holder (not shown) to evacuate system 34. At this time, the vacuum degree can be substantially lower than the vacuum degree used in magnetron sputtering or diode sputtering.
Substrate 44 may also be heated or cooled as needed to affect the structure of the deposited material as described below.

As best shown in FIG. 5, the ion source 36 is preferably a square cross section ion source that produces a substantially square cross section beam 38. Board 44 preferably frequency
Rotate at f ₁ to equalize across board 44, preferably 10-20
Allows deposition in the rpm range. Target 40 is 2
It is divided into four parts 46 and 48. These two parts are made of different materials C and D as described above. In order to form the rectangular electron distribution structure, the ion source may be turned off while translating the target, or it may be cut off to completely separate the material layers. The term "frequency" as used herein is defined as a repetition of relative orientation at a given velocity, not necessarily a sinusoidal repetition.

It is desirable that the frequency f ₁ is considerably larger than the frequency f ₂ , and for example, f _{1 is set} to about 100 times. F ₁ and f ₂ are also different for different materials and structures, allowing section 46 to be moved in front of beam 38 at a different speed than section 48, or at a different beam power. Further, the portions 46 and 48 may be separate targets, and the number of portions may be two or more.
In this case as well, it can be controlled by a shutter (not shown) as necessary. A single element material, a compound, an alloy, or a combination thereof can be used for forming the layer.

FIG. 6 is a graph showing the reflection wavelength resolution.

Since the narrower the bandwidth, the higher the resolution obtained from the reflected signal, the reflected bandwidth 50 has a much lower resolution than the same reflected signal of bandwidth 52. Due to the accuracy of the system 34,
The system 34 has a much narrower reflection bandwidth than the prior art lsm x-ray structure 22.

FIG. 7 shows the ion beam stem 58 of FIG.
This system can also be the same as the system 34 except that a second ion beam source 60 is provided. An ion beam source 60 produces an ion beam 62. Ion beam 62 may be a reactive ion beam formed of argon and / or nitrogen or other suitable material or combination thereof. Reactive ion beams can be used to control the material density of a given layer or layers, or all layers. Also in this case, the substrate 44 is rotated at the speed of the frequency f ₁ ,
The target 40 is oscillated in front of the beam 38 at a frequency f ₂ . The flow of the reactive beam 62 is controlled by the third frequency,
Modulates and assists the deposition of material on 44. The deposition process can be further controlled by changing the ion flow of the ion source 36 at the frequency f ₄ . It is also possible to mill the substrate 44 with the ion beam source 60 prior to layering with the ion source 36.

A third type of deposition system 66 is shown in FIG. System 66
Is a magnetron sputtering deposition system for confining plasma in the vicinity of a plurality of substrates 68 fixed to a rotary drum 70 and a plurality of targets 74, 76, 78, 80 provided separately. The outer surface of the drum 70 can also be used as the substrate 72 if desired. The drum 70 may be heated or cooled as needed and rotated at a frequency f ₅ to allow the substrate 68 to pass a plurality of targets 74, 76, 78, 80 mounted on the shell 81 of the system.

Separation shield 82 with variable height for each target 74,76,78,80
Are separated by. Each target 74,76,78,80 is accompanied by a shutter 84,86,88,90 and a deposition rate monitor 9
Equipped with 2,94,96,98 respectively, deposition rate monitor 92,9
4,96,98 are connected to respective power sources 100,102,104,106. Therefore, each target has its own power supply, shutter,
A deposition monitor would be provided, providing a control loop to each deposition station. Although four stations are shown in the figure, this number can be increased or decreased.

The space "S" between the drum surface 72 and the shell 81 is varied to control the impact of secondary electrons on the substrate, and the deposition is well controlled by maximizing the coupling of the magnetron's confined plasma to the substrate. Are equalized. System 66
Operates with a sputtering gas such as argon under vacuum. In addition, a reactive gas such as hydrogen or a compound containing hydrogen may be injected into the plasma adjacent to the target to achieve the above effect. The system can fabricate multiple substantially identical modulation structures on multiple substrates 68, or a single structure on cylinder 72.

The present invention also includes selecting the optimum material that can fully utilize the above synthesis techniques in a particular wavelength range. As is well known, the control of the reflection characteristics of the lsm device can be achieved by controlling the electron density as a function of the depth of the lsm device. For example, in order to obtain the maximum reflectivity, it is necessary to select the component by maximizing the electron density between layers. Therefore, it is predominant in the prior art lsm device to choose the W: C layer or the W-Re: C layer.

As another important factor in maximally controlling the composition gradient in the original patent application and the present invention, relative electronegativity, as described in the original patent application or incorporated herein by reference, Atom diameter and bond distance can be mentioned.

According to the original patent application, carbon and boron can be used as the main components of the laminated structure. The buffer layer is used to form the layer as described in the original patent application.

The higher electron density in the original carbon and boron containing structure improves reflectivity and resolution for a particular x-ray wavelength range. This particular X-ray wavelength range is usually a subrange of the low energy X-ray range of 9.75 to 120 Angstroms defined in that original patent application. The prior art describes structures formed from W: C and ReW: C layer pairs A, B. The original patent application is generally Hf: C, HfW: C, R with the buffer layer (the buffer layer may not be used).
e: C, HfRe: C and Hf: B ₄ C, W: B ₄ C, Re: B ₄ C, HfW: B ₄ C, HfRe: B
_It describes the structure formed by ₄ C, HfWRe: B ₄ C.
The present invention also includes a structure containing a certain amount of carbon and boron as described below.

In accordance with the present invention, it has been discovered that structures containing carbon, specifically Cr: C, Hi: C, V: C, improve properties for carbon analysis. The structures were analyzed for both flat and curved shapes, and the results are shown in Table 1 and Table 2, respectively.
A comparison of CKα reflections is shown in two tables.

The W: C structure is a prior structure of the present applicant and is also used industrially. These structures were formed by a planar magnetron or ion beam assisted deposition technique as described above. Measurements were made with a Philips 4-position wavelength dispersive spectrometer under substantially the same operating conditions for all tests. The net peak-to-background ratio (p−b /
The peak-to-background ratio (p / b) was measured, but not b). If necessary, p-b / b can be calculated from the above table. For carbon analysis, generally in the 40-70 Angstrom wavelength range, more specifically, 4
The performance of the V: C, Ni: C, Cr: C structure at a wavelength of 4.7 Å is substantially superior to that of the prior art.

When examining the test results of Table 1 and the tables that follow, the following points should be noted. That is, for the convenience of the test, there are many structures in which the number of layer pairs to be deposited is 100 or less, which is an optimal number or less. Applicants have found that peak intensity and p / b increase and bandwidth (dE / E) decreases with increasing number of layer pairs. The W: C structure is representative of Applicant's own prior structure. A representative structure was selected by examining the results of tests performed on 380 of these structures. The metal-to-nonmetal ratio of the layer pair or layer set was 1: 1 to 1: 3. The improved structure exhibits superior properties in peak, p / b and dE / E at d intervals of 35-80 Å compared to the prior art.

The above measurements were taken by standard techniques using a JEOL WDS (FCS-35) spectrometer under substantially the same operating conditions for all tests. W: C was not chosen as a prior art for curved (micro-pulp) structures because the peaks were excellent, but both bandwidth and p-b / b were poor. Another factor was analyzed in the above results. That is, the lower limit of detection (11d) is shown as a percentage, which is used as the measurement value of the sensitivity and the throughput in the test environment. This 11d is divided by the square root of the same measurement time t (t is 100 seconds in this example). Therefore Cr: C (XRO
1184) and Ni: C (XRO1188) structures have measurement sensitivities more than twice that of the myristate prior art.
All three curved structures were also tested in flat form to allow comparison between the two structures. DE / E should decrease while (p−b) / b increases with increasing number of layers log. Peak intensity and
11d far exceeds prior art structures.

In addition, according to the present invention, it was found that the composition of the Mo: B ₄ C structure can improve the characteristics for analysis of boron and beryllium. Tables 3 and 4 show the results for BKα analysis of flat and curved structures, respectively.

The above measured values are obtained by the same method as in Table 1. Regarding the analysis of the flat structure, the above-mentioned structure is a new analysis because the structure of the prior art does not exist industrially.
The Ni: C structure (XRO1186) is a structure that can be used for both boron analysis and carbon analysis (see 1).

The above measurements are taken in the same way as in Table 2. Ni: C
(XRO1188) is a structure that can be used for both boron analysis and carbon analysis (see Table 2). MoB ₄ C has a large peak increase and 11d is less than half that of prior art myristate crystals.

Table 5 shows the results for curved structures for BeKα analysis.
This is because beryllium analysis of flat structures is not expected to give valid results.

The above measurements were taken in the same way as in Table 2. Lead serotonate (p-b) / b is good, but peak intensity is poor. The Mo: B ₄ C structure of the present invention is reasonably good in (p−b) / b and dE / E, but is excellent in peak intensity and 11d. Applicants believe that Mo: B ₄ C structures with d-spacings of about 139 angstroms or greater are structures that can be used for boron and beryllium analysis. Although W: C is not a commercially available prior art structure, it shows an example of the results that can be obtained for the composition. The Mo: B ₄ C structure has a d-spacing of 35-200 Angstroms, preferably 40-100 Angstroms. It can be used as an angstrom for boron and beryllium analysis, but is usually in the range of 55 to 130 angstroms, more specifically 67.6 angstroms and 114 angstroms, respectively.

Many modifications and variations of the present invention can be considered with reference to the above teachings. Sputtering targets are easier to form with B ₄ C compounds, but essentially pure boron targets can also be used to form boron stacks. A layer pair includes a set of layers sandwiching another layer. The ion beam or sputtering flux can be profiled to control the uniformity of the structure deposited over the substrate. By doing so, it is possible to construct a structure in which the d-distance is controlled and changed from the substrate surface to the subsequent layer. The type of substrate is not critical and may be any of the prior art lsm-type substrates including polished silicon wafers, glass, metal, quartz, sapphire, flexible plastics and the like. It is therefore to be understood that the invention can be practiced other than as specifically described above in the claims.

[Brief description of drawings]

FIG. 1 is a partial schematic view showing an embodiment of an X-ray analysis system in which the X-ray dispersible structure of the present invention can be used. FIG. 2 is an exploded partial sectional view of a prior art X-ray dispersive structure, showing an X-ray dispersion pattern. FIG. 3 is a diffraction pattern produced by the prior art structure of FIG. FIG. 4 is a schematic partial side view showing one embodiment of an ion beam deposition technique that may be used to form the structures of the present invention. FIG. 5 is a schematic partial end view showing the deposition technique of FIG. FIG. 6 is a graph showing the reflection wavelength resolution. FIG. 7 is a partial schematic diagram showing a second embodiment of an ion beam deposition technique that may be used to form the structure of the present invention. FIG. 8 is a partial schematic diagram showing a third ion beam deposition technique that may be used to form the structures of the present invention. 10 …… X-ray analysis system, 12 …… X-ray source, 16 …… Sample,
22 …… X-ray dispersive structure, 24 …… detector, 34,58 …… ion beam system, 36,60 …… ion source, 44 …… substrate.

Claims (11)

[Claims] 1. An X-ray dispersive structure for spectroscopic analysis of lightweight elements, the structure comprising a plurality of alternating layer pairs, said layer pairs being X in a predetermined first target wavelength range. One having a linear dispersion characteristic and having a maximum net peak-to-background ratio in a narrow second wavelength range of the first target wavelength range; Is formed of amorphous vacuum-deposited carbon, and the other layer of the layer pair is formed by vacuum-depositing a transition metal selected from the group consisting of vanadium, nickel, and chromium. Or in a device for the analysis of boron, one of the layer pairs being formed from vacuum-deposited B ₄ C and the other layer of the layer pair being formed from vacuum-deposited molybdenum. X-ray dispersible structure. 2. An X-ray dispersive structure for wavelength dispersive spectroscopy of beryllium or boron having a maximum net peak-to-background ratio in the 55 to 130 angstrom wavelength range. An improved X-ray dispersible structure according to claim 1. 3. An improved x-ray dispersive structure according to claim 2 wherein said layer pairs have a d-spacing of 35 to 200 angstroms, preferably 40 to 100 angstroms. 4. The method of claim 1 wherein the layer pair is deposited on a curved substrate such that the beam in the narrow second wavelength range reflected from the layer pair is focused on the detector. An improved X-ray dispersive structure as described in 1. 5. An improved X-ray dispersive structure according to claim 4, wherein the curved substrate has the shape of a Rowland circle. 6. An X-ray dispersive structure for wavelength dispersive spectroscopy of carbon, having a maximum net peak-to-background ratio in the wavelength range of 40 to 70 angstroms. An improved X-ray dispersive structure as described in 1. 7. The improved x-ray dispersive structure of claim 6 wherein said layer pairs have a d-spacing of 35-80 angstroms. 8. An X-ray dispersive structure for spectroscopic analysis of boron and beryllium, said structure comprising a plurality of layer pairs, said layer pairs having a predetermined first portion.
It has X-ray dispersion characteristics in the target wavelength range, and its net peak-to-background ratio is maximized in the narrow second range of 55 to 130 angstroms in the predetermined target wavelength range, and one of the layer pairs layers are formed by B ₄ C, the other layer of the layer pair is formed by vacuum deposition of molybdenum, improved X-ray dispersive structure d-spacing of the layer pair is 35-200 Å. 9. An X-ray dispersive structure for spectroscopic analysis of carbon, comprising a plurality of layer pairs in which the structures are alternately formed, and the layer pairs are X-ray in a predetermined first target wavelength range. Has a dispersion characteristic and has a maximum net beam-to-background ratio in a narrow second range of 40 to 70 angstroms within the predetermined wavelength range of interest, one layer of the layer pair being formed of carbon, An improved X wherein the other layer of the layer pair is formed by vacuum deposition of a transition metal selected from the group consisting of nickel, vanadium and chromium, and the d spacing of the layer pair is 35-80 angstroms. Line dispersive structure. 10. A method of wavelength dispersive spectroscopy of beryllium and boron, the method comprising setting a sample, setting an X-ray dispersive structure, and irradiating the sample with an X-ray beam. The sample emitting fluorescent X-rays, and irradiating the dispersive structure with the emitted X-rays to reflect the X-rays from the X-ray dispersible structure. The structure includes a plurality of layer pairs formed alternately, the layer pairs having X-ray dispersion characteristics in a predetermined first target wavelength range, and 55 in the predetermined target wavelength range.
The peak to background ratio is maximized in a narrow second range of ~ 130 Å, one layer of the layer pair is formed of B ₄ C and the other of the layer pair is formed of vacuum deposited molybdenum. And the d-spacing of the layer pair is
35-200 angstroms, the method further comprising the step of detecting and analyzing the reflected X-rays. 11. A method for spectroscopic analysis of carbon, comprising the steps of: setting a sample; setting an X-ray dispersive structure; and irradiating the sample with an X-ray beam, Emitting fluorescent X-rays, and irradiating the dispersive structure with the emitted X-rays to reflect the X-rays from the X-ray dispersible structure composed of a plurality of layer pairs alternately stacked. The layer pair has X-ray dispersion characteristics in a predetermined wavelength range of interest, and the net beam pair background in a narrow second range of 40 to 70 angstroms in the wavelength range of interest. The ratio is maximized, one layer of the layer pair being formed of carbon and the other layer of the layer pair being formed by vacuum evaporation of a transition metal selected from the group consisting of nickel, chromium and vanadium. , The layer pair has a d-spacing of 35 to 80 angstroms A beam, said method further comprising the step of detecting detects the reflected X-ray.