DE3126539A1 - X-ray crystal spectrometer and a method of evaluating measurement results obtained with an x-ray crystal spectrometer - Google Patents

Abstract

An x-ray crystal spectrometer consists of a device for producing an electron beam for irradiating a sample and has a chamber for receiving a crystal, a proportional counter and a semiconductor detector for detecting x-rays. The crystal and the semiconductor detector are approximately within the same polychromatic radiation, so that the evaluation can be carried out with a multichannel analyser taking account of a single geometrical position of the sample with respect to the crystal or the semiconductor detector. All in all, this simplifies the analysis and improves the quantitative evaluation.

Description

The invention relates to an X-ray crystal spectrometer which is attached to a device for generating an electron beam for irradiating a sample is flanged and from a chamber for receiving a crystal and a Proportional counter tube for capturing X-rays.

Such spectrometers are very often with a scanning electron microscope coupled. This device is used to generate and focus an electron beam with which a sample is applied. The sample surface can be made visible with a very high resolution, moreover when electron beams strike a sample, X-rays are produced, the evaluation of which provides information about the

BATH ORIGINAL

provides the chemical composition of the irradiated sample. Essentially two different types of evaluation are used, namely the energy dispersive and the wavelength dispersive analysis.

In the wavelength dispersive analysis, the dex Sample emitted X-rays are diffracted in a crystal, causing the polychromatic radiation to form a monochromatic fan Radiation is decomposed. The energy density in a wavelength range is now derived from this fan with the help of a proportional counter tube determined. There is one between the sample, the crystal and the proportional counter tube special geometrical assignment adhered to in order to fully follow to obtain sizing X-ray optics. For example, the crystal moves along a straight line and is rotated while the proportional counter tube executes a hypocyclic movement

As a rule, four analysis crystals, namely TAP, PET, LiF and Bb sterate are provided, with which a wavelength range of approx. 0.1 - 9.24 nm can be covered. So can all elements from boron to uranium can be detected.

In the energy dispersive analysis, the total spectrum the X-rays simultaneously with the help of a silicon semiconductor detector detected, the result passed on to a so-called Vie channel analyzer and finally on a Screen brought to the display. Due to the characteristic X-ray radiation that can be assigned to each element, a Most of the chemical elements, namely sodium to uranium, can be detected at the same time. Evidence easier Elements that emit a softer X-ray radiation cannot usually be achieved with energy-dispersive analysis Their radiation is absorbed in a beryllium window in front of the detector.

So far, with the appropriate equipment on the scanning electron microscope (REM) both analysis methods can be carried out. While for the movement of the crystal and the proportional counter tube in the given geometric relation to each other a relatively large structural effort is required, it is necessary to attach the semiconductor detector, which is in the rest is not moved during the analysis, a breakthrough in the sample chamber of the scanning electron microscope for Introduction of the semiconductor detector. The detector must also be cooled with liquid nitrogen to ensure good To ensure freedom from noise.

In practice, the energy dispersive analysis is given preference, because especially with the downstream Multi-channel analyzer gives a reliable result on the composition of the sample in approx. 100 - 200 seconds is present. The same analysis process can take up to 8 hours when using wave-dispersive analysis. However If the energy-dispersive method fails with the light elements, then inevitably the wave-dispersive method Procedure must be applied.

With the help of an extensive correction program, this succeeds it to get a quantitative analysis of the chemical elements contained in the sample. In the quantitative evaluation 'evaluation' Correction factors must be taken into account that depend on the presence of other elements contained in the sample and also depend on the respective position of the sample in relation to the crystal or in relation to the semiconductor detector. The usage of the same program with the same correction factors for be4 <3e analysis systems is excluded for this reason alone, because the semiconductor detector is in a different place than in all previously implemented X-ray spectrometers

BATH ORIGINAL

312653E

_ the .. crystal. The correction factors that take into account the geometry are therefore always correct for only one analysis method. _ yy

It is therefore an object of the invention to provide an X-ray crystal spectrometer of the type mentioned at the beginning, or the procedure used so far for the overall analysis to that effect to improve that the measurement of energy and wave dispersive spectrometers and the evaluation of the data and so that the analysis time is significantly reduced.

The proposal according to the invention to improve the process provides that the crystal and the semiconductor detector are moved into approximately the same beam path that for the same geometric position of the sample is selected for both analyzes, and that the comparison and the display are taken into account only this geometric position is carried out.

The invention therefore provides for both the measurement with the proportional counter tube in a single sample setting this is indispensable for the detection of light elements - as well as to be carried out with the semiconductor detector. In order to two very important advantages are achieved with regard to the evaluation. On the one hand, there is only a single calculation program the quantitative evaluation of the measurement results is necessary because the same correction factors are now due to the identical geometry are valid for both measuring methods. On the other hand, the energy dispersive quantitative analysis is improved, since the light elements can now be determined with the same computer program, which up to now could only be determined by subtraction 100% calculated. . ·

To adapt the radiation density to the lower requirement of the semiconductor detector is a further development of the invention provided that a diaphragm is arranged in front of the semiconductor detector, which is optionally adjustable.

To further optimize a measurement with a constant geometric position of the sample in relation to the measuring instruments, the Semiconductor detector, if necessary with the associated screen, be moved back and forth within the plane which is perpendicular to the direction of the 'X-ray radiation.

The limit of detection of relatively light elements such as sodium or magnesium due to the energy dispersive analysis is therefore relatively high in the devices implemented so far, since the actual detector is arranged behind a beryllium window, with the result that the beryllium is relatively soft X-rays are partially absorbed. In order to create better conditions here, the invention is being developed provided that the semiconductor detector is located inside the vacuum chamber and the chamber by a turbo-molecular pump is evacuated.

In this way it is possible to create such a good vacuum within the chamber that the semiconductor detector cannot must be protected by a beryllium window. Its sensitivity to soft X-rays increases accordingly, since there is no absorption. However, omitting the window alone would not bring the benefits that come with help of the invention are achievable. No rays are absorbed without a window, which is the resolution of the detectors However, it is so bad in the area of the soft rays (light elements) that there is only a gradual difference results.

An exemplary embodiment of the invention, which is shown in the drawing, is explained in more detail below; the single figure shows:

a schematic plan view of an X-ray crystal spectrometer according to the invention with the chamber lid open.

In the figure, a partially open chamber 1 is shown, which is part of an X-ray crystal spectrometer is? - It is complete in the operating position covered and evacuated. It is used to hold a Krista] 2 and a semiconductor detector 3. The chamber 1 is flanged to the side of a scanning electron microscope 4 / generally can be regarded as a device for generating an electron beam. It allows one to be made visible Sample arranged in the lower part of the microscope with the aid of electron beams. When the Electron beams on the sample distort X-rays that hit the crystal 2 and the semiconductor detector 3 meet. The X-rays are evaluated for qualitative and quantitative analysis of the sample.

The X-rays incident on the crystal 2 become bent and directed at a proportional counter tube (not shown) within chamber 1. The one emanating from the sample X-ray radiation is polychromatic, which with the help of crystal 2 is fanned out into monochromatic radiation will. In order to cover the entire spectrum, the crystal must be adjusted, both one straight-line movement along a rail 6 shown as a dashed line as well as a rotation about the vertical Adhse of the crystal. Depending on the position of the Crystal 2 also adjusts the proportional tube in a hypocyclic movement, which is, however, related is not essential to the invention.

The one from the sample in the lower area of the scanning electron microscope 4 emitted polychromatic radiation is relatively strongly bundled, but leaves the sample more or less than a cone of rays, the radiation intensity of which is approximately the same at every point of the cone. The quality of the beam cone and to a certain extent also its position and opening angle can be determined by aligning the sample are influenced compared to the electron beam.

As a rule, the crystal 2 emits a stronger radiation intensity coped with than by the semiconductor detector 3. In order to avoid "overexposure" of the semiconductor detector, as it were, an optionally adjustable diaphragm 7 is provided, with which a part of the directed onto the semiconductor detector 3 Radiation can be covered. In the event that an adjustment is provided, be it for the diaphragm 7 or the position of the semiconductor detector 3, its actuation is passed through the wall of the chamber 1 in a gas-tight manner or possible via a remote control, so that the chamber 1 can remain closed for the adjustment.

In order to obtain noise-free spectra, the silicon semiconductor must be cooled with liquid nitrogen. This is on a cryostat 5 flanged to the chamber 1, its cooling potential with the aid of a cold finger 8 up to the semiconductor element is transmitted. The cold finger 8 may have to be designed to be flexible, for example in the form of a flexible braided one Band when an adjustment of the semiconductor detector 3 within the chamber 1 is provided. Otherwise treads the invention here known ways, so that a further explanation can be dispensed with.

Commonly, the commercially available semiconductor detectors are 3 encapsulated, the radiation falling on the actual measuring element through a beryllium window. This will cause any x-rays from elements lighter than beryllium to go out of this window absorbed. Therefore, in the X-ray crystal spectrometer according to the invention provided in a further development to use an unencapsulated semiconductor detector 3, which, however requires that the chamber 1 is evacuated. A Tu'rbo molecular pump is used for this, which is seen in isolation is known.

The signals received by the proportional counter tube and the semiconductor detector are fed to a multi-channel analyzer.

31265!

leads, which with the help of an iteration process also a quantitative determination, i.e. a statement about the concentration of a chemical element in the sample. There are corrections to the respective interim results required, depending on the elements contained in the sample and according to the geometric position of the sample opposite the counter tube and the detector. For the first time, a very complete correction can now be made - it If all elements are recorded using both analysis methods, the geometry-related correction does not change when moving from one analysis method to the other.

BAD ORIGINM-

Claims (8)

anv; älte 30612 y .. \ / Y.r S. Kalkoff - "." -. "..". June 25, 1981 Ruhrstr. 26 ::;: .--: "":, "" Postfach 2448 '■ * "-.".: .. Witten / Ruhr patent claims; 1. X-ray crystal spectrometer, consisting of a device for generating an electron beam for irradiating a sample and a chamber for receiving it a crystal and a proportional counter tube for the detection of X-rays, thereby characterized in that in the region of the radiation thrown from the sample onto the crystal (2) a semiconductor detector (3) known per se is arranged within the chamber (1). 2. X-ray crystal spectrometer according to claim 1, characterized in that in front of the semiconductor detector (3) a diaphragm (7) is arranged. 3. X-ray crystal spectrometer according to claim 2, characterized in that the diaphragm (7) is adjustable is. 4. X-ray crystal spectrometer according to one of the claims 1-3, characterized in that the semiconductor detector (3) optionally together is attached to the diaphragm (7) displaceably transversely to the direction of the rays. 5. X-ray crystal spectrometer according to claim 3 or 4, characterized in that the actuation the respective adjustment is led out gas-tight from the chamber (1). 6. X-ray crystal spectrometer according to one of the preceding Claims, characterized in that that the semiconductor detector (3) with the chamber (1) is atmospherically in exchange, and that a turbo-molecular pump is connected to the chamber (1) is. 7. Procedure for evaluating the measurement results of a proportional counter tube, its received radiation. one crystal is bent and fanned out, and one Semiconductor detector in the course of a wavelength-dispersive or energy-dispersive analysis of a sample in an X-ray crystal spectrometer, in which the measurement results with standard values of reference samples taking into account the geometric position of the sample to the crystal or to the semiconductor detector compared and be brought to the display, thereby g e k e η η ζ e ichnet that the crystal and the semiconductor detector be moved approximately into the same beam path, the same geometric position for both analyzes the sample is chosen, and that the comparison and the display taking into account only this geometric Location is carried out. 8. The method according to claim 7, characterized in that g e k e η η ζ It is assumed that the crystal and the semiconductor detector are arranged within a beam whose radiation has an essentially identical quality at all points.