X-ray or gamma ray systems or devices – Specific application – Fluorescence
Patent
1998-02-06
2000-03-21
Porta, David P.
X-ray or gamma ray systems or devices
Specific application
Fluorescence
378 45, G01N 23223
Patent
active
060410965
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns a method and an apparatus for total reflection X-ray spectroscopy for conducting analysis by measuring characteristic X-rays emitted from a measured sample when the measured sample is irradiated with primary X-rays at a small angle near a critical total reflection angle.
BACKGROUND ART
The method for total reflection X-ray spectroscopy is adapted for irradiating primary X-rays to a measured sample, by which an element present in the measured sample emits secondary X-rays referred to as characteristic X-rays, and conducting elemental analysis for the sample by using the characteristic X-ray, and this has been known long seen.
Since the wavelength of the characteristic X-rays is inherent to the element which is present, an element present in the sample can be analyzed qualitatively based on the wavelength of each of characteristic X-rays appearing in the characteristic X-rays of the measured sample. Further, since each characteristic X-ray intensity reflects the existing quantity of the element, it is also possible to recognize the existing quantity of the element based on the analysis of the characteristic X-ray spectrum. In this case, it is generally required that a standard sample having a known quantity of an analyzed element is provided and a relation between the quantity and the characteristic X-ray intensity is determined previously.
What should be noted in the method for X-ray fluorescence spectroscopy is that not only the characteristic X-rays appears in the characteristic X-ray spectrum for the sample irradiated with primary X-rays but also scattered X-rays scattered in the inside of the sample is also included, and the scattered X-ray intensity constitutes a major factor for determining a detection limit of the X-ray fluorescence spectroscopy. That is, if the element present in the sample emits characteristic X-rays only at an intensity equal with or lower than the fluctuation of the scattered X-rays, the element can not be analyzed quantitatively.
By the way, while the X-ray fluorescence spectroscopy is applicable also to the analysis of microelements localized only at the surface of a semiconductor or the like, a problem due to scattered X-rays is caused in this case. That is, since the analyzed element is present only on the surface of the sample, the characteristic X-rays thereof are also emitted only from the surface, whereas scattered X-rays are emitted also from the inside of the sample. Accordingly, for the intensity of both of them, the latter is outstandingly great and no sufficient detection limit can be obtained.
As an analyzing method for overcoming the problem, it has been known total reflection X-ray fluorescence spectroscopy of irradiating primary X-rays to a sample at a smaller angle than a critical total reflection angle and conducting elemental analysis for the surface of the sample by using the characteristic X-rays excited therewith. In this total reflection X-ray fluorescence spectroscopy, the intruding depth of the primary X-rays into the sample is extremely shallow and it is considered to be an order of several nm, for example, in single crystals of silicon. Therefore, the scattered X-ray intensity emitted in the sample is reduced greatly, and an analyzed element present only on the surface of the sample can be analyzed at a low detection limit. The feature of the method for total reflection X-ray fluorescence spectroscopy, as can be seen from the principle thereof, resides in that the characteristic X-rays for the analyzed element on the surface of the sample are excited substantially only by the primary X-rays.
For obtaining an analysis value by the total reflection X-ray fluorescence spectroscopy, calibration with a standard sample is required like that in the case of a usual X-ray fluorescence spectroscopy. In the case of the total reflection X-ray fluorescence spectroscopy, since the object is measurement, particularly, for the quantity of the analyzed element on the surface of the sample calibration is conducted by us
REFERENCES:
patent: 4573181 (1986-02-01), Gronberg et al.
patent: 5246216 (1993-09-01), Ohsugi et al.
patent: 5457726 (1995-10-01), Miyazaki
patent: 5497407 (1996-03-01), Komatsu et al.
Doi Ichiro
Tonomura Shoichiro
Asahi Kasei Kogyo Kabushiki Kaisha
Porta David P.
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