Total reflection X-ray fluorescence apparatus

Abstract: A total reflection X-ray fluorescence apparatus comprises a base material (6) having an optically flat surface for totally reflecting X-rays radiated at a small glancing angle, a first detector (13) such as an SSD for detecting fluorescent X-rays emerging from a specimen (7) located near the optically flat surface of the base material (6) and a second detector (11) such as a scintillation counter for detecting an intensity of an X-rays coming from the base material (6).

Description: Background of the Invention (Field of the Invention) The present invention relates to a total reflection X-ray fluorescence apparatus used in a trace analysis of particles located near surface such as surface contaminations by total reflection X-ray fluorescence, and a method for adjusting a glancing angle of X-ray beam in a total reflection X-ray fluorescence apparatus. (Related Background Art) The total reflection X-ray fluorescence will be briefly described below. When X-rays are radiated on an optically flat surface at a small glancing angle, the X-rays are reflected at the same angle as the glancing angle without being absorbed by a radiated material. In other words, the X-rays are totally reflected. In this case, if a specimen is placed on the surface by which the X-rays are totally reflected, since X-ray other than those radiated on the specimen are totally reflected, fluorescent X-rays emerging from the specimen can be detected in a state wherein scattered X-ray can be apparently ignored. Therefore, spectral measurement with a high S/N ratio can be attained (Nippon Kinzoku Gakkai Kaiho, vol. 24, No. 11 (1985) pp. 956-961). Such an analysis method is called the total reflection X-ray fluorescence. Qualitative/quantitative analysis of the specimen is performed based on the result of the spectral measurement. As analysis examples, for qualitative/quantitative analysis of a specimen placed on a wafer surface, "Progress in X-ray Analysis 19" (Agune Technical Center) pp. 217-226, Technical Reports of University of Electro-Communications, Osaka, "Natural Science Edition" 22 (1986), from p.87), and the like are known, and for qualitative/quantitative analysis of a solution dripped on a wafer surface, "Progress in X-ray Analysis 19" (Agune Technical Center) pp. 237-249, and the like are known. According to the prior technique, it was difficult to make X-rays radiate at small glancing angle to the optically flat surface on which a specimen is placed so as to meet conditions for total reflection of X-rays. And, if X-ray total reflection conditions are satisfied, X-rays enter to a depth of about 100 Å of a surface portion of an optically flat surface. For this reason, X-rays detected by the above-mentioned total reflection X-ray fluorescence include fluorescent X-rays radiated from a base material having the optically flat surface, and X-rays unique to an X-ray source target (Mo, W, or the like) and continuous X-rays (white X-rays). Since those X-rays are detected as a background level of the analysis result, they induce an increase in detection lower-limit density of a small amount of element placed as a specimen on the optically flat surface of the base material, and also induce a decrease in quantitative precision of the element. Further, the conventional total reflection X-ray fluorescence apparatus, however, can designate an analysis position on a surface for totally reflecting X-rays, it cannot be discriminated by only analysis of the designated position whether the designated region can represent an attaching state of a particle on the entire surface for totally reflecting X-rays or corresponds to a region where a large amount of particle is locally present. For this reason, the surface for totally reflecting the X-rays is divided into a plurality of regions. The amount of particle cannot be determined unless analysis is independently performed for all the divided regions to confirm an attaching state of a particle, resulting in much time and poor work efficiency. Furthermore, NUCLEAR INSTRUMENTS AND METHODS, vol.114, 1974, pages 157, 158, North-Holland Publishing Co.; H. Aiginger et al.: "A method for quantitative X-ray fluorescence analysis in the nanogram region" discloses a total reflection X-ray fluorescence apparatus which comprises a base material having an optically flat surface for totally reflecting X-rays radiated at a small glancing angle, a first detection means for detecting fluorescent X-rays emerging from a specimen located near the optically flat surface of said base material, and a second detection means for detecting an intensity of X-rays coming from said base material. The specimen is adjusted by an adjusting lever so that it is irradiated and the X-ray beam is totally reflected on the surface of the base material. EP-A-0265618 discloses a method for measuring the penetration depth of X-rays toward a sample. After an incident angle has been set by varying the height of an X-ray tube and after the sample has been replaced by a stepped ring diaphragm, the first measurement is performed by varying the height of a slit diaphragm to obtain maximum intensity I 0 of the primary radiation. Thereafter, the ring diaphragm is replaced by the sample and the slit diaphragm is moved by 2h (wherein h is the distance between the zero point and the point of maximum intensity) and a second measurement is performed to obtain the reflected intensity I R. The penetration depth T may be calculated by using the measurement results. NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH, SECTION A, vol.A-246, nos.l/3, 1986, pages 736-738, Amsterdam, NL; A. Iida et al.: "Grazing incidence X-ray fluorescence analysis" discloses a total reflection X-ray fluorescence apparatus in which the sample is mounted on translational and rotational stages, driven by step motors, and the intensities of the incident and reflected beams are monitored by two ionization chambers. The ionization chambers and the detector for detecting fluorescent X-rays emerging from the sample are connected to electronics. The intensity of the fluorescent X-rays is measured as a function of the glancing angle. Summary of the Invention It is an object of the invention to provide an apparatus and method by which an optical glancing angle can be set automatically in a precise manner. This object is solved by the features described in claims 1 and 12, respectively. Particular embodiments of the invention are set out in the dependent claims. Brief Description of the drawings Fig. 1 is a schematic diagram showing a total reflection X-ray fluorescence apparatus according to the present invention, Figs. 2A to 2C are flow charts showing a method for adjusting glancing angle of X-rays which can be used for the present invention, Fig. 3 is a graph showing an analysis result obtained by using the total reflection X-ray fluorescence apparatus according to the present invention, Fig. 4 is a graph showing an analysis result obtained by using a conventional total reflection X-ray fluorescence apparatus, Fig. 5 is a schematic diagram of a total reflection X-ray fluorescence apparatus according to the present invention, Figs. 6A and 6B are views showing analysis result by the total reflection X-ray fluorescence apparatus according to the present invention, Figs. 7A, 7B and Fig. 8 are views showing inspection results by a surface inspection system according to the present invention, and Fig. 9 is a view showing an inspection result by the surface inspection system according to the present invention, which result is different from that shown in Fig. 8. Description of the Preferred Embodiment The first embodiment of the present invention will now be described with reference to Figs. 1 to 4. X-rays radiated from an X-ray source 1 such as an X-ray emission tube are converted to a collimated X-ray beam by a slit 2, and the X-ray beam is monochromatized by an monochromator means 3. For X-rays source, a sealed X-ray tube having Mo as its target and an X-ray source having W rotating anode target (see Fig. 2) can be used as an exciting source. The latter X-ray source can generate higher power of R-rays than the former X-ray tube since the latter X-ray source uses a rotating target. As the monochromator means 3, a crystal of lithium fluoride (LiF) can be used, and X-rays radiated from the X-ray source 1 are reflected (diffracted) by its crystal plane of (200), thus monochromatizing X-rays. For the monochromator means 3, a crystal of topaz, Si, NaCl, calcite CaCO3, Ge, α-quartz, graphite, InSb and pentaerythritol, etc. can be used. The X-rays monochromatized are radiated on an optically flat surface of a base material 6 at a small glancing angle. Note that the monochromator means 3 can change its fixing angle to the glancing angle of X-rays, so that X-ray monochromatized in any wavelength range after the monochromatization can be radiated on the base material 6. Therefore, only X-rays unique to a target used as the X-ray source 1 can be radiated on the base material 6. A specimen 7 is placed on the surface of the base material 6, which surface is irradiated with the X-rays. As the specimen 7 is fixed by an chuck utilizing electrostatic force provided with the base material 6, the wapage of the base material 6 having a specimen 7 thereon is straightened to allow the surface of the specimen 7 to be flat. The base material 6 is placed on a stage 8a of the positioning table 8, and the positioning table 8 is subjected to positioning control by a controller 10. In this case, the positioning for the specimen 7 may be performed by positioning the monochromator means 3 controlled by controller 10 instead of positioning the positioning table 8. X-rays reflected by the base material 6 are incident on a scintillation counter 11 via a slit 5. The scintillation counter 11 measures an X-ray intensity. Prior scintillation counter having a phototube can be used for the scintillation counter 11. The measured X-ray intensity is input to a central processing unit 12 comprising, e.g., a CPU. On the basis of this intensity, a table position control instruction is output from the central processing unit 12 to the controller 10 to perform positioning control of the base material 6, thus satisfying X-ray total reflection conditions. Next, a method for adjusting a glancing angle of X-ray to a base material which can be applied for the present invention is explained in reference with Figs. 2A to 2C. The optimized angle of X-ray is about 0.06 degree where the base material 6 having an optically flat surface is a Si wafer for example. The specimen 7 is attached on the optically flat surface of the base material 6. The positioning of the base material 6 is performed as follows. First of all, X-rays radiated from an X-ray source are directly incident into a scintillation counter 11 and an intensity of the X-rays is measured by the scintillation counter 11 (Fig. 2A). After that, the optically flat surface of the base material 6 is coincided with the X-rays so that the X-rays may contact wholly with the optically flat surface (Fig. 2B). If the coincidence between them could not be perfectly made, the intensity of X-rays should be changed due to scattering or absorption of the X-rays. Therefore, it is possible to make a precise coincidence by monitoring the intensity changes. After the coincidence, the stage 8a of positioning table 8 is precisely inclined by 0.06 degree on an axis perpendicular to the direction of X-rays rays radiation on the optically flat surface so as to obtain the glancing angle of 0.06 degree which meets a condition of total reflection for X-rays (Fig. 2C). The critical angle (maximum angle) of c which meets the condition of total reflection can be calculated by next equation of; c = {(5.4 x 10 10 )Zρ/A} 1/2 λ where Z is an atomic number of constitutional element, A is weight of atom and λ is wavelength of glancing beam. Generally, an optimized angle which is different in material and at which on maximum intensity of fluorescent X-rays can be obtained is approximately one third of critical angle. It is experimentally confirmed by the present inventors that the optimized angle for GaAs is 0.09 degree and that for InP is 0.07 degree for example (Peter Wobrauschek and Hannes Aiginger, Analytical Chemistry, Vol. 44B, No. 5 (1989) 483). A semiconductor X-ray detector 13 such as a SSD (Solid State Detector) is arranged above the base material 6 to oppose the optically flat surface of the base material 6. The semiconductor X-ray detector 13 utilizes a phenomenon in which X-rays radiated onto Si diode applied with inverse voltage results in current flow to generate pulses. Concretely, Si material is doped by Li to form a P-i-n type diode and the P-i-n type diode is applied with inverse voltage for use. The Si(Li) itself is sealed in A vacuum tube and X-rays are incident thereon through a window made of beryllium foil with several micrometers of thickness. Since the diode has Li doped, a certain number of electron-hole pairs corresponding to the energy of X-rays incident on the i-layer of the diode is generated to output pulses. The energy of the X-rays can be detected by measuring the wave height (voltage) and the intensity of the X-rays can be detected by counting the number of pulses. The SSD published by K. Nishihagi et al in the Extended Abstracts of Electro Chemical Society of Vol. 89-2 and the Si(Li) type SSD made of Link Co. Ltd. (detection area: 80 mm 2 , diameter: 10 mm) may be used for the semiconductor X-ray detector 13. The semiconductor X-ray detector 13 detects fluorescent X-rays radiated from the specimen 7 placed on the base material 6. This detection output is amplified by a preamplifier 15 and a linear amplifier 16, and is extracted as a pulse output having a peak value proportional to the magnitude of a fluorescent X-ray energy. The preamplifier 15 may be directly connected to the semiconductor X-ray detector 13 to prevent S/N ratio from lowering. Further, the semiconductor X-ray detector 13 and the preamplifier 15 may be cooled by liquid nitrogen in order to reduce thermal noise as much as possible. This pulse output is converted into a digital output by an A/D converter 17, and the digital output is accumulated according to energy by a multichannel analyzer. The accumulated output is then subjected to data processing in the central processing unit 12. Further, if air exists on the path of fluorescent X-rays between the specimen 7 and the semiconductor X-ray detector 13, the detection intensity is lowered due to scattering and absorption by particulate in the air. In this case, as fluorescent X-rays of Ar existed in the air is excited by X-rays, it becomes difficult to detect fluorescent X-rays of Cl and K since the energy values of them are very cross to that of Ar. Accordingly, it is preferable that the chamber in which the fluorescent X-rays are measured is in vacuum atmosphere. In this case, the degree of vacuum is preferably below 13.3 Pa (0.1 Torr). For example, a peak energy intensity for Si is 0.1 cps (counts per second) where the degree of vacuum is 101324 Pa (760 Torr), but the peak energy intensity increases to 2.2 cps (counts per second) where the degree of vacuum is 1.33 Pa (0.01 Torr) since the vacuum atmosphere prevent the every intensity from lowering an efficiency for detecting light elements is improved. Fig. 3 shows an analysis result of the above-mentioned total reflection X-ray fluorescent apparatus. This analysis was performed using tungsten (W) for the X-ray source, and a spectral crystal of lithium fluoride (LiF) as the monochromator means, and X-rays were spectrally diffracted by a (200) plane of the spectral crystal. Contamination particles as a specimen became attached onto an optically flat finished surface of a silicon wafer, and were analyzed. Note that this analysis was performed by an energy dispersion type detection method. In Fig. 3, energy values of detected fluorescent X-rays are plotted along the abscissa, and X-ray counts (detection frequency) of the respective energy values are plotted along the ordinate, thus representing an analysis result. Upon evaluation of this analysis result, peaks of the count numbers appear at energy values unique to Si, X, Ca, Cr, Fe, Ni, and Zn, respectively, and almost no continuous X-rays (white X-rays) are detected. Therefore, peaks of these elements can be prevented from being concealed behind a background level caused upon detection of continuous X-rays, and these elements can be easily identified. Since peak areas and corresponding element densities have predetermined correlations, amounts of elements can be determined by performing calibration of a specimen whose density is known. Fig. 4 shows an analysis result by a conventional total reflection X-ray fluorescent apparatus. In this analysis, molybdenum (Mo) was used for an X-ray source, and X-rays radiated from the X-ray source were radiated on an optically flat surface of a silicon wafer without being monochromatized into monochromatized X-rays. Note that contamination particles attached as a specimen onto the silicon wafer are not the same as those attached in Fig. 3. Upon evaluation of this analysis result, peaks of counts appear at energy values unique to Si, Ar, Cr, Fe, W, and Zn, respectively, and these elements can be identified. However, in this analysis result, since detected X-rays include continuous X-rays, these continuous X-rays are present as a background level of the peak values. For this reason, peaks other than those of Ar and Fe are not easily discriminated from the background level, and peaks may be erroneously judged. When a small amount of element is to be detected, since its peak is concealed behind the background level, a detection lower-limit density of the small amount of element is increased, and the corresponding element cannot often be identified. When a detected element is to be quantitatively measured, a value from which the background level is subtracted must be used as a peak area. However, an error occurs depending on the way of setting the background level, resulting in a decrease in quantitative precision. Contrast to this, when the total reflection X-ray fluorescence apparatus according to the present invention is used, only monochrome X-ray components in a specific wavelength range monochromatized by the monochromator means are radiated on the optically flat surface of the base material on which the specimen is placed. Therefore, continuous X-rays are removed from the X-rays radiated on the base material, and can be prevented from being detected by the semiconductor X-ray detector. Therefore, in the obtained analysis result, since the background level caused upon detection of continuous X-rays can be greatly reduced, as shown in Fig. 3, a small amount of element can be easily identified, and peak areas can be precisely obtained, thus improving quantitative precision. In the above embodiment, the spectral crystal of lithium fluoride (LiF) is used for the monochromator means. In place of this crystal, a spectral crystal of, e.g., ethylenediamine ditartarate (EDDT), pentaerythritol (PET), or the like, or a diamond type crystal body may be used. In particular, when the diamond type crystal body is used and X-rays are monochromatized by its (111) plane, X-rays in a wavelength range to be extracted can be efficiently monochromatized, line-spectral monochrome X-ray components with a uniform wavelength can be radiated on the optically flat surface of the base material. Therefore, the above-mentioned identification and quantitative precision can be further improved. X-ray monochromatized by the monochromator means and radiated on the base material may be any unique X-rays radiated from the X-ray source as long as they have a higher energy than that of an X-ray absorption spectrum of an element to be detected form a specimen. For example, when Kα rays as unique X-rays of tungsten (W) are monochromatized by the monochromator means and are radiated on the base material, elements corresponding to atomic numbers below lanthanum (La) are detected since they have a high energy value. However, when Lβ1 rays are monochromatized and radiated on the base material, only elements having atomic numbers equal to or smaller than that of zinc (Zn) are detected. Therefore, elements constituting the base material can be appropriately selected according to X-rays to be radiated so as not to detect a corresponding element. Thus, a background level can be further reduce, and analysis precision can be improved. In particular, the present invention is effective for detection of a transition-metal element on a GaAs or InP wafer. By unique and an energy gap between elements is small where the elements have light weights. For example, in case of detecting Na and Mg, the energy value of Kα rays for Na is 1.0410 keV and that of Kα rays for Mg is 1.2536 keV. Therefore, the energy gap between them is 212.6 eV. In this case, it is impossible to identify peaks if the semiconductor X-ray detector 13 does not have a resolution power to be able to identify the energy gap below 212.6 eV. Accordingly, it is preferable that the semiconductor X-ray detector 13 with resolution power below 200 eV is used for identifying light elements. It is generally known that the energy resolution power of the semiconductor X-ray detector 13 is reversely proportional to the size of detecting portion of the semiconductor X-ray detector 13. For example, a semiconductor X-ray detector 13 with size of 150 mm 2 ⊘ has a resolution power of 250 eV and a semiconductor X-ray detector 13 with size of 80 mm 2 ⊘ has a resolution power of 150 to 180 eV. Accordingly, it is enough to identify light elements if the size of detecting portion of the semiconductor X-ray detector 13 is 80 mm 2 ⊘. The second embodiment of the present invention will be described below with reference to Figs. 5 to 9. The apparatus illustrated in Fig. 5 can be mainly constituted by an X-ray analysis system A for performing a total reflection X-ray fluorescence, and a surface inspection system B for inspecting a state of a surface where the total reflection X-ray fluorescence is performed. In the X-ray analysis system A, X-rays are radiated from an X-ray source 1 such as an X-ray emission tube, and are collimated to a fine X-ray beam by a slit 2 as described before. The X-ray beam is radiated on an optically flat surface of a base material 6 at a small glancing angle after monochromatization by the monochromater means 3 fixed with a member inclinable to the X-rays. The base material 6 is, for example, a silicon wafer, and a specimen 7 is attached to a surface of the base material 6 where X-rays are radiated. The base material 6 is placed on a stage 8a of a positioning table 8, and is positioned by the positioning table 8. The positioning table 8 has a predetermined coordinate system (x,y,z), and is subjected to positioning control by a position controller 10 according to the coordinate system. Therefore, when the base material 6 is placed on the stage 8a, a coordinate system is set on the optically flat surface of the base material 6 for totally reflecting X-rays. X-rays radiated on the surface for totally reflecting X-rays (total reflection surface) of the base material 6 are reflected by the surface, and are incident on a scintillation counter 11 via a slit 5. The scintillation counter 11 measures an X-ray intensity. The scattered X-ray intensity is input to a first central processing unit 12 comprising a CPU, a ROM, a RAM, and the like, and a stage position control instruction is output based on the input intensity. The base material 6 is positioned on the basis of the control instruction to satisfy X-ray total reflection conditions. On the total reflection surface of the base material 6, elementary analysis of a particle by the total reflection X-ray fluorescence is performed for a position (region) according to the control instruction. Information associated with a coordinate position corresponding to the control instruction at that time is stored in the RAM of the first central processing unit 12. A semiconductor X-ray detector 13 such as a SSD (Solid State Detector) is arranged above the base material 6 to oppose the optically flat surface (total reflection surface) of the base material 6. The semiconductor X-ray detector 13 detects fluorescent X-rays radiated from a specimen 7 attached onto the base material 6. The detection output is amplified by a preamplifier 15 and a linear amplifier 16, and is extracted as a pulse output having a peak value proportional to a magnitude of the fluorescent X ray energy. The pulse output is converted into a digital output by an A/D converter 17, and the digital output is accumulated by a multichannel analyzer, and is then subjected to data processing in the first central processing unit 12. The total reflection X-ray fluorescence apparatus according to the present invention has the surface inspection system B for performing surface inspection of the total reflection surface such as an attaching condition of the specimen 7 to the total reflection surface of the base material 6, a distribution and particle size of attached specimen particles, scratches or defects on the total reflection surface, and the like. The surface inspection system B obtains inspection information of each point on the total reflection surface in correspondence with coordinates set on the surface of the base material 6, and can store the information. The surface inspection system B comprises a stage 14 on which the base material 6 is placed, a laser 18 for radiating a laser beam to be radiated on the base material 6 placed on the stage, a reflection mirror 19 for reflecting the laser beam to radiate it on the base material 6, a photomultiplier 20 for detecting a reflection light intensity of the laser beam reflected by the base material 6, and a second central processing unit 21 for receiving an output signal digitalized by A/D converter 17 from the photomultiplier 20. The reflection mirror 19 changes its position to be able to scan the laser beam on the entire total reflection surface of the base material 6. The laser beam radiated onto the base material 6 is reflected by the base material 6. If a foreign matter is present on the base material 6 or in the neighborhood of the surface, the laser beam is scattered by the foreign matter, and an intensity of reflected light is changed. Therefore, information such as a distribution condition of the specimen 7 attached to the total reflection surface can be obtained based on the change in reflected light intensity. The reflected light is focused by an elliptic reflection mirror 22, and is incident on the photomultiplier 20. The light incident on the photomultiplier 20 is converted into an electrical signal according to its intensity, and the electrical signal is amplified at output. The output signal from the photomultiplier 20 is converted into digital data by an A/D converter 23, and is input to the second central processing unit 21. The signal input to the second central processing unit 21 is processed in correspondence with the coordinates set on the total reflection surface, and the processed signal is stored as inspection information such as a distribution condition, particle size, and the number of particles of the specimen 7 attached to the total reflection surface, the number of particles of the specimen present in a region subjected to the total reflection X-ray fluorescence, a ratio of the number of particles to a total number of particles of the specimen attached to the entire total reflection surface, scratches or defects on the total reflection surface, and the like. The surface inspection system B is connected to the X-ray analysis system A via the position controller 10, as shown in Fig. 5. Note that as the surface inspection system B, a surfscan 4500 available from TENCOR INSTRUMENTS can be used. As described above, in the total reflection X-ray fluorescence apparatus of the present invention with the surface inspection system B, the base material 6 is placed on the stage 14 to perform surface inspection of the total reflection surface of the base material 6 before or after X-ray analysis is performed for the base material 6 placed on the stage 8a. Therefore, in order to discriminate whether a region on the base material 6 where the total reflection X-ray fluorescence is performed represents an attaching state of a particle on the entire total reflection surface or corresponds to a region where a large amount of particle is locally present, no time-consuming operation for dividing the total reflection surface into a plurality of regions and independently performing total reflection X-ray fluorescence on all the divided regions to confirm an attaching state and the like of a specimen is required unlike in the conventional apparatus. A coordinate region most suitable for performing the X-ray fluorescence can be searched from the inspection result by the surface inspection system B, and efficient X-ray analysis can be performed. For example, when the total reflection X-ray fluorescence is to be performed for a portion having a highest distribution density of the specimen 7, a region having a highest distribution density is searched from the inspection result of the surface inspection system B, and the X-ray analysis can be performed for only this region. After the total reflection X-ray fluorescence is performed, whether the region on the base material 6 subjected to the fluorescence represents an attaching state of a particle on the entire total reflection surface or corresponds to a region where a large amount of particle is locally present can be easily discriminated. Furthermore, since a ratio of a specimen attached to a portion subjected to the analysis to the entire specimen can be obtained based on the inspection result of the surface inspection system B, the amount of the specimen 7 can be easily determined with high precision using this ratio. In the total reflection X-ray fluorescence apparatus according to the present invention with the surface inspection system B, as described above, since the X-ray analysis and the surface inspection can be performed as a series of operations, an opportunity that a foreign matter becomes additionally attached to the base material can be reduced, and the analysis with higher precision can be performed. Figs. 6A and 6B show analysis results of the X-ray analysis system A described above, and Figs. 7A and 7B show inspection results of the surface inspection system B. Fig. 6A shows an analysis result of the total reflection X-ray fluorescence as follows. That is, N 2 gas was sampled from a pipe for introducing N 2 gas to, e.g., a semiconductor manufacturing device, the sampled N 2 gas was blown on a silicon wafer used as the base material for two hours to specimen contamination particles included in the N 2 gas as a specimen, and the total reflection X-ray fluorescence was performed for the contamination particles. Fig. 6B shows an analysis result for the silicon wafer surface before the N 2 gas is blown to attach the contamination particles. In these figures, energy values of fluorescent X-rays are plotted along the abscissa, and X-ray counts (detection frequency) of the respective energy values are plotted along the ordinate. Note that this analysis was performed by an energy dispersion type detection method. Upon examination of this analysis result, peaks appear at energy values unique to Cr, Fe, Cu, and Zn, and corresponding metal elements are identified by them. Upon comparison with the analysis result shown in Fig. 6B, it can be determined that these metal elements are contained in the N 2 gas. Since these elements are constituting elements of stainless steel and brass, it can be estimated that contamination sources of the N 2 gas are pipes and their joints. Since the axis of ordinate represents the counts, a peak area for each element reflects a corresponding element density, and the amount of element can be determined by performing calibration using a specimen whose density is known. Fig. 7A shows an inspection result of a distribution condition of contamination particles attached to the surface of the above-mentioned silicon wafer after the N 2 gas is blown, using the surface inspection system A, and Fig. 7B shows an inspection result of the silicon wafer surface before the N 2 gas was blown. As can be seen from these inspection results, a very small amount of contamination particles are attached to the silicon wafer surface before the N 2 gas is blown, but a large amount of contamination particles are uniformly distributed and attached to the surface of the silicon wafer after the N 2 gas is blown. These results can demonstrate that these contamination elements are particles containing the metal elements identified in Figs. 6A and 6B. The analysis position in Fig. 6A corresponds to an area having a diameter of 6 mm at the central portion of the wafer, and it can be determined based on the inspection result of the surface inspection system B that the number of contamination particles attached to that portion is about 10 % of the total number of contamination particles. Therefore, if attaching efficiency of the contamination particles can be detected, a density of each element contained in the N 2 gas can be calculated based on a peak area of the corresponding element and the total amount of blown N 2 gas. Fig. 8 shows another inspection result of the surface inspection system B, which is different from that in Figs. 7A and 7B. This inspection result was obtained as follows. That is, a magnet was attached to the central portion of the lower surface of the silicon wafer, and the N 2 gas was similarly blown on the upper surface. As can be seen from Fig. 8, since the magnet is attached, contamination particles are concentrated around the magnet. Contamination particles about 20 % of the overall contamination particles are attached to an area having a diameter of 6 mm at the central portion of the wafer. Therefore, coordinates of the area where the contamination particles are concentrated and attached are read out, and the positioning table 8 is controlled by the position controller 10 so that the total reflection X-ray fluorescence is performed for this area. When the total reflection X-ray fluorescence is then performed, an analysis result having larger peak values than those in the analysis result shown in Fig. 6A can be obtained, contamination elements can be detected with high sensitivity, and precision of quantitative analysis can also be improved. Note that the surface inspection system B can detect the total number of contamination particles attached to the wafer or the number of particles in units of particle sizes. Fig. 9 shows these detection results. The particle sizes of contamination particles can be an important clue to clear up the cause of contamination. In the above embodiment, the stage 8a used for the total reflection X-ray fluorescence and the stage 14 used for surface inspection of the total reflection surface are independently arranged, and the base material 6 is transferred between these two stages. Therefore, when the base material 6 is transferred, the base material 6 is preferably parallelly transferred without changing its position so that the coordinates set on the total reflection surface during the total reflection X-ray fluorescence can be directly used in surface inspection of the total reflection surface, that is, the relative positional relationship between the X-ray analysis system A and the base material 6 is the same as the positional relationship between the surface inspection system B and the base material 6. Even when different coordinates are set for the X-ray analysis and surface inspection, a coordinate setting reference need only be provided to the base material 6, so that the different coordinates can be converted based on the reference as if common coordinates were set. As the reference, when a semiconductor wafer is used as the base material 6, an orientation flat can be used. Alternatively, the surface inspection system B may be added to the X-ray analysis system A to have one common stage, so that coordinates common to the X-ray analysis and surface inspection can be set. In this case, a transfer process of the base material 6 can be omitted, and additional attachment of a contamination material on the base material 6 during transfer can be avoided. Further, although the surface inspection system B uses a laser 18 and a photomultiplier 20 to make an inspection by scanning laser beam from laser 18 two-dimensionally, a CCD instead of the photomultiplier 20 may be used to make an inspection by linear scanning with laser beams enlarged in certain direction and radiated onto the CCD. And a lamp instead of the laser 18 and a CRT instead of the phohomultiplier 20 may be used to make an inspection based on image data obtained by CRT. From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims: A total reflection X-ray fluorescence apparatus comprising: a base material (6) having an optically flat surface for totally reflecting X-rays radiated thereonto at a small glancing angle; first detection means (13) for detecting fluorescent X-rays emerging from a specimen (7) located near the optically flat surface of said base material (6); and second detection means (11) for detecting an intensity of an X-rays coming from said base material (6); monochromator means (3) for monochromatizing the X-rays radiated from an X-ray source (1) and radiating the monochromatized X-rays onto said optically flat surface; and positioning means (8) for setting coordinates on the optically flat surface and positioning said base material (6); characterized by control means (10, 12) for controlling said positioning means (8) to determine coincidence between the X-rays and the optically flat surface of said base material (6) in accordance with said intensity of said X-rays detected by said second detection means (11) and to set said coordinates to obtain said small glancing angle which meets the condition of total reflection for X-rays. An apparatus according to claim 1, wherein said first detection means comprise a semiconductor X-ray detector (13) and/or said second detection means comprise a scintillation counter (11). An apparatus according to claim 1 or 2, wherein said X-ray source (1) comprises a rotating cathode type X-ray source. An apparatus according to any of claims 1 to 3, wherein said monochromator means (3) use a diamond type crystal body, a crystal of lithium fluoride (LiF), a crystal of ethylenediamine ditartarate (EDDT) or a crystal of pentaerythritol (PET), and the X-rays radiated from said X-ray source (1) are reflected by a crystal surface thereof. An apparatus according to any of claims 1 to 4, wherein said monochromator means (3) are supported on a support member for changing a fixing angle of said monochromator means (3) so as to radiate X-rays onto said base material (6) in any wavelength range after the monochromatization. An apparatus according to any of the claims 1 to 5, wherein said monochromator means (3) radiate monochrome X-rays having a higher energy than that of an X-ray absorption spectrum of an element to be detected from said specimen (7) onto the optically flat surface. An apparatus according to any of the claims 1 to 6, wherein said X-ray source (1) uses tungsten, and said monochromator means (3) use a crystal of lithium fluoride (LiF). An apparatus according to any of the claims 1 to 7, further comprising: a surface inspection system (B) for performing state inspection of the optically flat surface and obtaining inspection data of each point on the optically flat surface in correspondence with the coordinates. An apparatus according to claim 8, wherein said surface inspection system (B) comprises a laser scanner (18, 19) for radiating and scanning a laser beam onto said base material (6), and reflected light detection means (20) for detecting a reflected light intensity of the laser beam reflected by said base material (6). An apparatus according to claim 9, wherein said laser scanner comprises a laser oscillator (18) for radiating the laser beam and a reflection mirror (19) for reflecting and scanning the laser beam toward said base material (6). An apparatus according to claim 9 or 10, wherein said reflected light detection means comprises a photomultiplier (20). A method for adjusting a glancing angle of X-ray beam in a total reflection X-ray fluorescence apparatus according to any of the preceding claims, said method comprising the steps of: providing a base material having an optically flat surface; radiating an X-ray beam directly into a detection means; measuring the intensity of the X-ray beam by means of the detection means; positionally adjusting at least one of said optically flat surface and said X-ray beam under monitoring the intensity changes so that said X-ray beam is parallel to and coincides with said optically flat surface of the base material; maintaining relative positions of said optically flat surface and said X-ray beam just before the intensity of said X-ray beam changes due to the adjustment of relative positions between said optically flat surface and said X-ray beam; and inclining said optically flat surface by the predetermined glancing angle about an axis perpendicularly intersecting said X-ray beam on said optically flat surface.

Inventors: KYOTO MICHIHISA, NISHIHAGI KAZUO, OHSUGI TETSUYA, KYOTO, MICHIHISA, NISHIHAGI, KAZUO, OHSUGI, TETSUYA, KYOTO, MICHIHISA, C/O YOKOHAMA WORKS OF, OHSUGI, TETSUYA, C/O YOKOHAMA WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, TECHNOS CO LTD, SUMITOMO ELECTRIC INDUSTRIES, LTD., TECHNOS CO., LTD.,
Application year: 1990
Main classification: G01N23
IPC codes: G01N23