Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
  • G01N23/223—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material by irradiating the sample with X-rays or gamma-rays and by measuring X-ray fluorescence
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2223/00—Investigating materials by wave or particle radiation
  • G01N2223/07—Investigating materials by wave or particle radiation secondary emission
  • G01N2223/076—X-ray fluorescence

Definitions

• the invention relates to a method for setting the effective angle of incidence of X-rays emerging from an X-ray source onto a material sample for analysis of layers of the material near the surface by means of a total reflection X-ray fluorescence analysis method.
• the fundamentally known total reflection X-ray fluorescence analysis method can be used very effectively for non-destructive element analysis of layers near the surface. Methods of this type are used, among other things, to check compliance with the extremely high purity requirements in the course of production control in the production of highly integrated electronic components.
• a known total reflection X-ray fluorescence analysis method is described for example in DE-PS 36 06 748.
• This well-known process Similar other methods, which work according to this principle, are based on the fact that X-ray radiation emerging from an X-ray source is directed at an extremely flat angle of incidence onto a surface of a material sample to be examined, the X-radiation only due to the total reflection effect penetrates a few nanometers into the surface. In this way, a layer close to the surface is isolated by measurement technology, without the material sample undergoing a change in any way due to the X-ray radiation. If the condition for the total reflection of the X-rays is met, only the atoms of the uppermost surface layer are excited to emit fluorescent radiation, to be precise by the primary X-rays penetrating the surface only a few nanometers.
• a precondition for the fact that an exact quantitative statement about the element concentration in said surface layer can be obtained from the fluorescence signal is a highly precise setting of the angle of incidence of the primary radiation. It is known (DE-PS 36 06 748) that in devices with which the total reflection X-ray fluorescence analysis described here is to be carried out, the angle of incidence of the primary X-ray radiation is accurate to about 0.1 to 0 , 2 arc minutes must be determined or adjusted, because the fluorescence intensity of the elements from the surface layer strongly depends on the angle of incidence of the primary X-ray radiation which excites the fluorescence.
• the x-ray beam is sufficiently precise on the material sample with an angle of incidence is set that the total refection condition is approximately met and the resulting fluorescence count rate can be determined by measurement
• the advantage of the method according to the invention essentially consists in the fact that the effective angle of incidence of the divergent primary radiation for different material samples can be optimally adjusted in a simple manner, so that the induced fluorescence radiation reaches its optimum in each case and thus a highly precise measurement of impurities in a material sample. as is required, for example, in the case of highly integrated electronic components.
• Another significant advantage of the method according to the invention is that it does not merely cover the plane Surfaces of a material sample can be analyzed, but also curved surfaces.
• the first setting of the angle of incidence is carried out in accordance with method step a. with an accuracy in the arc minute range, i.e.
• the initial value of the angle of incidence only needs to be set with an accuracy of a few minutes of arc. It should be pointed out that for the total refraction x-ray fluorescence analysis, cf. above, the angle of incidence must be set for an exact measurement with an accuracy of 0.1 to 0.2 arc minutes, because of the strong Dependence of the fluorescence intensity on the angle of incidence of the stimulating primary X-rays.
• the angle of incidence is preferably varied according to method step b. in steps of arc minutes, advantageously in steps of one arc minute.
• the angle of incidence is advantageously varied by changing the height of the x-ray source relative to the material sample or, according to another advantageous embodiment of the invention, the angle of incidence is varied by tilting the material sample relative to the incident x-ray radiation.
• At least method step d. carried out automatically with computer support.
• This, but also the other method steps, can be defined in accordance with a software program following a predetermined algorithm and also easily, ie with simple, in relation to the different measurement parameters Funds can be changed by intervention in the software program.
• the setting of the angle of incidence to the value recognized as optimal for the desired analysis in question can also be carried out automatically, preferably also with computer support, and also according to a software program following an algorithm. It is also conceivable for the entire method, including the automatic setting of the angle of incidence, which was recognized as optimal, to be set automatically according to the method result by means of a device in which the method according to the invention is used.
• the method according to the invention is carried out as follows.
• the material sample is positioned on a carrier in a total reflection X-ray fluorescence analysis device, as was described, for example, in DE-PS 36 06 748.
• An x-ray source which is preferably a normal x-ray tube, emerges X-ray flow, which is aimed at the material probe under investigation.
• the X-ray beam is now set on the material sample with an angle of incidence so sufficiently precise that the total reflection condition is fulfilled, i.e. The set angle between the primary X-rays and the surface of the material sample is below the critical angle of the total reflection.
• the resulting fluorescence count rate is then detected by measurement, in a known manner by means of a detector that is provided in such total reflection X-ray fluorescence analysis devices.
• the angle of incidence is then varied, the changing fluorescence count rate being detected by measurement in accordance with this step.
• a theoretical fluorescence count rate function ascertained on the basis of a model calculation, which is carried out on the basis of the dispersion theory for X-radiation, depending on different angles of incidence of the X-rays on the material sample, which is recorded, for example can happen in a computer.
• the fluorescence count rates detected by measurement for different angles of incidence in accordance with the method steps described above are compared with the theoretical fluorescence count rate function determined on the basis of the model calculation, with each being made by a comparison which can be carried out by a suitably chosen mathematical algorithm a corresponding effective angle of incidence can be assigned by the measurement of the fluorescence count.
• the comparison of the measured curve with the theoretically determined curve in particular determines which fluorescence count corresponds to the excellent effective angle of incidence 0 n under the current measurement conditions.
• 0 Q is generally outside the angular range that is favorable for measuring the surface contaminate, this can be determined particularly expediently by comparing the calculated with the measured fluorescence count rate, because at this particular angle 0 Q , cf. 2, the influence of the instru ential divergence on the fluorescence count rate minimal, that of a change in the effective one
• the arithmetic and control process according to the method according to the invention takes little time if appropriately designed and, as mentioned, can run completely automatically under computer control.

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• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Analysing Materials By The Use Of Radiation (AREA)

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Citations (1)

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• 1988
  • 1988-05-11 DE DE19883816081 patent/DE3816081A1/de active Granted
• 1989
  • 1989-05-11 WO PCT/DE1989/000300 patent/WO1989011094A1/de unknown

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