JP2007212328A - Sensitivity coefficient measurement method for Auger electron spectroscopy - Google Patents

Abstract

The present invention relates to a sensitivity coefficient measurement method for Auger electron spectroscopy of an Auger electron spectrometer for analyzing the chemical state of a solid surface.
[Solution]
An Auger electron spectroscopic analyzer that scans an electron beam and detects Auger electrons emitted from the sample surface. Between each element to obtain the element concentration of the sample surface from the intensity of a plurality of elements detected from the sample surface A sensitivity coefficient measurement method for obtaining a sensitivity coefficient, comprising the following steps: A sensitivity coefficient measurement method for Auger electron spectroscopy.
1) a step of arranging two or more solid materials composed of a single element in the scanning range of the electron beam;
2) A step of measuring a spectrum in the scanning range to obtain the intensity of an element constituting the solid material,
3) obtaining an area ratio of the solid material in the scanning range;
4) A step of obtaining a sensitivity factor between each element from the intensity of the element obtained from the spectrum measurement and the area ratio of the solid material.
[Selection] Figure 1

Description

  The present invention relates to a sensitivity coefficient measurement method for Auger electron spectroscopy of an Auger electron spectrometer that analyzes the chemical state of a solid surface.

  Examples of methods for analyzing the chemical state of the solid surface include Auger electron spectroscopy (hereinafter referred to as AES method), X-ray photoelectron spectroscopy (XPS method), secondary ion mass spectrometry (SIMS method) and the like. in use.

  Among them, Auger electron spectroscopy is used as a method for quickly knowing the surface composition in a production line at a semiconductor factory or the like. A great number of surface chemical analysis methods have been proposed. (For example, refer to Patent Document 1 and Patent Document 2.)

  The AES method is a method for identifying the type and amount of an element present on a solid surface by irradiating the surface of the solid with an electron beam finely focused in a high vacuum and measuring the energy and number of Auger electrons generated. It is.

  Since the electron beam used in the AES method can be narrowed down, it is possible to irradiate a minute area with a diameter of several tens of nanometers.

  Further, since the escape depth of Auger electrons is about several nanometers from the sample surface, it has a feature that local region analysis with a diameter of several tens of nanometers and a depth of several nanometers is possible.

  In the AES method, the horizontal axis represents the kinetic energy inherent to the element, and the vertical axis represents the spectrum indicating the electron count or its differential type.

  Then, mapping analysis and line analysis are performed on a specific peak (kinetic energy). Further, depth direction analysis (depth profile) is possible by combining with an ion gun.

  In addition, the peak intensity of Auger electrons detected by the AES method changes according to the abundance in the detection area. For this reason, it is possible to estimate the element concentration present on the sample surface from the Auger electron spectrum.

  In general, the calculation of element concentration is the relative concentration of the element to be analyzed. The total abundance of all detected elements is 100%, and this is expressed as a fraction for each element. Called analysis.

  Since the generation efficiency of Auger electrons, which is the basis of quantitative analysis, differs depending on the element, even if a plurality of elements are present in the same amount in the measurement region, the detected peak intensity differs between the elements.

  A sensitivity coefficient is used as a coefficient used to correct such a difference in sensitivity between elements when determining the element concentration. Then, the relative intensity can be calculated by multiplying the obtained peak intensity of each element by the sensitivity coefficient to obtain the element concentration.

Prior art documents are shown below.
JP 2002-195965 A JP 2004-325262 A

  The sensitivity coefficient of each element is usually shown in a reference book or a collection of spectra as the relative intensity when pure silver is 1. However, in the AES method, the sensitivity and transmittance depending on the energy value of Auger electrons change depending on factors derived from the spectroscope and detector of the Auger electron spectroscopic analyzer (hereinafter referred to as AES apparatus).

  For this reason, in order to obtain an accurate quantitative result, it is necessary to correct the Auger electron generation efficiency and the device factors (sensitivity, transmittance) for each AES device.

  As a method for obtaining the sensitivity coefficient, there are a method of obtaining a sensitivity coefficient from the obtained peak intensity by sequentially measuring a solid sample made of a single element, and a method of using a known solid sample having a composition of two or more elements.

  In the method of obtaining the sensitivity coefficient by sequentially measuring a solid sample made of a single element, there is a possibility that the peak intensity may change depending on the degree of vacuum or the sample height in the measurement chamber due to replacement of the sample. And it was difficult to obtain an accurate sensitivity factor.

  In the method using a known solid sample having a composition of two or more elements, the AES method is the measurement of the outermost surface several nm from the surface. Therefore, when there is oxidation of the sample surface or composition change, such information is mainly used. There was a problem of being detected.

  Furthermore, in the case of metal samples such as nickel, copper, and iron, and alloys in which a plurality of metal elements are mixed, the sample surface is generally oxidized in a normal storage state.

  Further, it is also known that a trace component contained in the alloy is locally present, such as being deposited on the outermost surface. It has been difficult to produce a standard sample having a completely uniform composition up to the local surface.

  In addition, when surface etching with argon ions or the like is performed in the AES apparatus for the purpose of removing the surface oxide film, the ion etching rate differs among the constituent elements depending on the sample. And only a specific element may be etched previously.

  That is, there is a problem that the composition of the surface of the solid sample is changed by etching and the sensitivity coefficient cannot be calculated accurately.

  For example, in a tin-nickel alloy, it is known from the phase diagram that a composition of nickel 3 -tin 4 exists in an atomic weight ratio. In addition, when a standard sample analyzed by electron beam microanalysis and confirmed to be a composition of nickel 3 -tin 4 is analyzed by the AES method, the etching rate of tin is higher than that of nickel. For this reason, a high nickel ratio is detected on the alloy surface after etching.

  If the relative sensitivity coefficient of nickel and tin is calculated assuming that this spectrum is measured correctly, the sensitivity of nickel is estimated to be lower than that of tin, and an incorrect result is calculated in the subsequent actual sample measurement. There was a problem.

The present invention is intended to solve such problems of the prior art. In the AES method, a sensitivity coefficient measurement method for Auger electron spectroscopy that can accurately obtain a sensitivity coefficient when performing quantitative calculation is provided. The purpose is to provide.

The present invention has been made to solve the above problems, and the invention according to claim 1 of the present invention is an Auger electron spectroscopic analysis in which an electron beam is scanned to detect Auger electrons emitted from the sample surface. A sensitivity coefficient measurement method of Auger electron spectroscopy for obtaining a sensitivity coefficient between elements for obtaining an element concentration on the sample surface from the intensity of a plurality of elements detected from the sample surface by an apparatus, comprising the following steps: It is a sensitivity coefficient measuring method of Auger electron spectroscopy which is characterized by comprising:
1) a step of arranging two or more solid materials composed of a single element in the scanning range of the electron beam;
2) A step of measuring a spectrum in the scanning range to obtain the intensity of an element constituting the solid material,
3) obtaining an area ratio of the solid material in the scanning range;
4) A step of obtaining a sensitivity factor between each element from the intensity of the element obtained from the spectrum measurement and the area ratio of the solid material.

  According to a second aspect of the present invention, in the step of obtaining the area ratio of the solid material in the scanning range of the electron beam, the method of obtaining the area ratio of the solid material is the surface of the solid material at the scanning location by the scanned electron beam. 2. The sensitivity coefficient measuring method of electron spectroscopy in Auger electron spectroscopy according to claim 1, wherein the area ratio is obtained from an electron image obtained by electrons emitted from the electron beam.

  According to a third aspect of the present invention, in the step of obtaining the area ratio of the solid material in the scanning range of the electron beam, the method for obtaining the area ratio of the solid material emits from the solid surface at the scanning position by the scanned electron beam. The method according to claim 1 or 2, wherein the area ratio is obtained from an Auger electron mapping image obtained by Auger electrons.

  The invention according to claim 4 of the present invention is the sensitivity coefficient measurement method for Auger electron spectroscopy according to any one of claims 1 to 3, wherein the solid material comprising the single element is a metal. is there.

  Since the sensitivity coefficient measurement method of the Auger electron spectroscopic analysis method of the present invention has the above-described configuration, it is possible to accurately estimate the sensitivity coefficient between each element for each AES measurement device by performing sensitivity correction. The composition of the solid material to be determined can be accurately determined.

  Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing an outline of an embodiment of an AES apparatus of the sensitivity coefficient measurement method of Auger electron spectroscopy of the present invention.

  As shown in FIG. 1, the AES apparatus includes an electron gun 1, an electron lens system 2, a secondary electron detector 3, an energy spectrometer 4, a detector 5, a sample stage 6, a sample stage operating mechanism 7, an etching gun 8, and a vacuum. The chamber 9 and the preliminary exhaust chamber 10 are configured.

  The vacuum chamber 9 covers the tip direction portion of all configurations except the preliminary exhaust chamber 10. The preliminary exhaust chamber 10 exhausts the sample 11 and the like in the vacuum chamber 9.

  The electron lens system 2 is formed to focus and scan the electron beam emitted from the electron gun 1. The secondary electron detector 3 is formed to obtain a secondary electron image. And in order to isolate | separate the energy of the Auger electron discharge | released from the sample, the energy spectrometer 4 is formed.

  The detector 5 detects Auger electrons separated by the energy spectrometer 4. Further, a sample stage 6 on which the sample 11 is placed, and a sample stage operating mechanism 7 for operating the sample stage 6 are formed. An etching gun 8 is formed to etch the surface of the sample 11.

  As the electron gun 1, a tungsten (W) filament type in which the electron beam cannot be narrowed as compared with a field emission type that can focus an electron beam and a field emission (FE) type is generally used.

  In addition, the energy spectrometer 4 includes what are called a concentric cylindrical mirror type (CMA) and a concentric hemisphere type (CHA). In the CMA type spectroscope, two cylinders are arranged on the same axis, the inner cylinder is grounded, and a negative voltage is applied to the outer cylinder.

  The electrons entering the CMA-type spectroscope are bent in the orbit by the negative voltage of the outer cylinder, and only electrons having energy corresponding to the negative voltage are concentrated on the axis.

  In addition, since the CMA type spectroscope has a larger electron capture angle than the CHA type spectroscope, electrons can be efficiently captured. For this reason, high-sensitivity and quick measurement is possible.

  The surface of the sample 11 is irradiated with an electron beam focused from the electron gun 1 through the electron lens system 2. Then, secondary electrons, Auger electrons, and the like are emitted from the surface of the sample 11 by the incident electron beam, and electrons reflected from the surface of the sample 11 become reflected electrons.

  These electrons are dispersed by the CMA type spectroscope 4 and only the electrons having a predetermined kinetic energy are detected by the detector 5. Then, by combining with the position information of the electron beam to be scanned, line analysis and surface analysis are possible.

  Further, secondary electrons and the like emitted from the surface of the sample 11 are detected by the secondary electron detector 3, and a secondary electron image (SEM image) can be obtained by synchronizing with the scanning electron beam.

  Further, it is desirable that the sample stage operating mechanism 7 can rotate (rotate) and tilt (tilt) in addition to the three axes of X, Y, and Z.

  Next, the vacuum degree of the vacuum chamber 9 at the time of measurement is preferably a high vacuum. Specifically, it is desirable to measure at 1 × 10 −6 Pa or less. Further, when the degree of vacuum is poor (low vacuum), residual gas components in the vacuum chamber 9 mainly composed of carbon adhere to the surface of the electron beam irradiation part sample 11 during electron beam irradiation, and accurate measurement cannot be performed. .

  The etching gun 8 is preferably of a type using rare gas ions such as argon. The etching gun 8 using oxygen oxidizes the surface of the sample 11 and is not desirable for use in the present invention.

  Next, the sensitivity coefficient measuring method of the present invention will be described. Hereinafter, although the case where two types of solid materials which consist of a single element are demonstrated is demonstrated, three or more types of solid materials may be sufficient.

  First, the solid sample A made of the element A and the solid sample B made of the element B are placed on the sample stage 6 without any gap. At this time, the sample heights of the solid sample A and the solid sample portion are preferably the same. Further, the solid material A and the solid material B are electrically connected to the sample stage 6. As the solid material A and the solid material B, it is desirable to use a pure substance, but a trace amount of impurities may be included.

  The solid material A and the solid material B fixed to the sample stage 6 are sufficiently exhausted after being introduced into the preliminary exhaust chamber 10 and moved to the sample stage holding movable mechanism 7 in the vacuum chamber 9. The sample table holding movable mechanism 7 is arbitrarily moved to align the measurement position with the electron beam irradiation position and the etching gun 8 irradiation position.

  Next, surface etching is performed on the surface of each sample 11 of the solid material A and the solid material B using the etching gun 8 in order to remove the surface oxide layer and the contamination layer.

  For the surface etching, rare gas ions such as argon ions are used. Then, the ion beam is irradiated in a range sufficiently larger than the measurement range until the surface contamination and the oxide film are removed. At this time, in order to confirm surface contamination and oxide film removal, even if it is confirmed that the peak intensity of carbon and oxygen is at the noise level by depth direction analysis on the surface of each of the single element sample A and single element sample B good.

  Further, the sample stage is moved so that the solid materials A and B can be measured together in the measurement region. Then, both the solid material A and the solid material B are included in the scanning range of the electron beam which is the measurement region. Further, an Auger spectrum is measured under measurement conditions when measuring a sample whose element concentration is unknown.

  For the surface including the boundary between the solid material A and the solid material B, an Auger spectrum is measured until the peak intensity of each sample is sufficient.

  Next, the area ratio of the solid material A and the solid material B in the electron beam scanning region is obtained. In the method of obtaining the area ratio from the secondary electron image, the secondary electron image is acquired before the Auger spectrum measurement or after the Auger spectrum measurement, and the solid material in the electron beam irradiation range at the time of spectrum acquisition is obtained by binarization image processing. The area ratio between A and the solid material B is calculated.

  If the brightness of solid material A and solid material B does not change in the SEM image and it is difficult to binarize by image processing of the SEM image, mapping of element A and / or element B in the same field of view as the spectrum acquisition range Measure. Then, the area ratio of the solid materials A and B in the electron beam scanning range is calculated from the mapping image.

  Further, as a method for obtaining the area ratio of the solid materials A and B in the electron beam scanning region, there is a method of rotating the sample stage 6 during the Auger spectrum measurement.

  In this method, the sample stage 6 is rotated around one point on the boundary line between the solid material A and the solid material B as the rotation center, and the rotation center and the center of the electron beam scanning region are made coincident. Since the electronic scanning area is usually rectangular, the intersection of diagonal lines is the center. At this time, the area ratio of the solid material A and the solid material B is equal to 1: 1.

  Finally, the correction coefficient of the element B with respect to the single element A is determined from the intensities of the elements A and B in the obtained spectrum and the area ratio of the solid material A and the solid material B at the time of spectrum measurement. At this time, the following calculation formula (1) is used.

X = Ac * (1-As) / (Bc * As) (1)
However, X: Correction coefficient of element B with respect to element A Bc: Signal intensity (count number) of solid material B Ac: Signal intensity (count number) of solid material A As: Ratio of solid material A in the measurement area.

  Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited thereto.

As the single element sample, pure nickel (purity 99.99%) manufactured by High Purity Chemical Laboratory and pure tin (purity 99.99%) manufactured by High Purity Chemical Laboratory were used.
In addition, SAM680 manufactured by ULVAC-PHI is used for spectrum measurement and SEM image acquisition.
A scanning Auger electron spectrometer was used.

  After pure nickel and pure tin were fixed on the sample stage without gaps, the preliminary exhaust chamber was sufficiently evacuated and introduced into the analysis position of the measurement chamber. With an attached ion gun, Ar ion sputter etching was performed with an etching area of 2 mm × 2 mm, an acceleration voltage of 4 kV, and an etching time of 120 seconds centering around the boundary between pure nickel and pure tin.

  After the etching is completed, the range including the boundary between pure nickel and pure tin is observed at a magnification of 500 times with a scanning electron microscope image (SEM image) at an acceleration voltage of 10 kV and a sample current of 9.8 nA, which are the conditions for Auger spectrum measurement. SEM images were acquired.

<Observation>
After the SEM image is taken, the Auger electron spectrum is scanned in the range of kinetic energy 50 eV to 1200 eV while the electron beam is scanned in the observation range. Measured with
After the measurement, the Auger spectrum was differentiated once, and the difference (intensity) between the maximum and minimum of the peak of each element was determined. As shown in FIG.
Nickel KLL peak (849 eV) 11920 counts Tin MNN peak (432 eV) 13799 counts.

At this time, the area ratio of pure nickel and pure tin in the scanning range was determined by binarizing the SEM image,
Nickel: Tin = 51: 49
Met.
Therefore, the correction coefficient of tin with respect to nickel was calculated as 0.8300.

  The sensitivity coefficient measurement method of the Auger electron spectroscopy of the present invention is not only excellent as a sensitivity coefficient measurement method of Auger electron spectroscopy that can be used for the sensitivity coefficient measurement method, but can also be used for elucidating member compositions in the field of precision instruments. It is a wonderful invention.

It is the schematic which shows the outline of one Example of the AES apparatus of the sensitivity coefficient measuring method of the Auger electron spectroscopy method of this invention. Auger electron spectrum of pure nickel-pure tin measured at an area ratio of 51:49

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron gun 2 ... Electron lens system for electron beam focusing scanning 3 ... Secondary electron detector 4 ... CMA type spectroscope 5 ... Detector 6 ... Sample stand 7 ... Sample stand movable mechanism 8 ... Etching gun 9 ... Vacuum chamber 10 ... Preliminary exhaust chamber 11 ... Sample

Claims (4)

An Auger electron spectrometer that scans an electron beam and detects Auger electrons emitted from the sample surface. Between each element to obtain the element concentration of the sample surface from the intensity of a plurality of elements detected from the sample surface A method for measuring a sensitivity coefficient of an Auger electron spectroscopy method for obtaining a sensitivity coefficient, comprising the following steps.
1) a step of arranging two or more solid materials composed of a single element in the scanning range of the electron beam;
2) A step of measuring a spectrum in the scanning range to obtain the intensity of an element constituting the solid material,
3) obtaining an area ratio of the solid material in the scanning range;
4) A step of obtaining a sensitivity factor between each element from the intensity of the element obtained from the spectrum measurement and the area ratio of the solid material.   In the step of obtaining the area ratio of the solid material in the scanning range of the electron beam, a method for obtaining the area ratio of the solid material is obtained from an electron image obtained by electrons emitted from the surface of the solid material at the scanning position by the scanned electron beam. The sensitivity coefficient measurement method for electron spectroscopy in Auger electron spectroscopy according to claim 1, wherein the area ratio is obtained.   In the step of obtaining the area ratio of the solid material in the scanning range of the electron beam, the method for obtaining the area ratio of the solid material is an Auger electron mapping image obtained by Auger electrons emitted from the solid surface at the scanning location by the scanned electron beam 3. The method for measuring the sensitivity coefficient of Auger electron spectroscopy according to claim 1, wherein the area ratio is obtained from   4. The method for measuring a sensitivity coefficient of Auger electron spectroscopy according to claim 1, wherein the solid material made of a single element is a metal.

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