JP2002116163A - Spectrum peak position correcting method for surface analyzing instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spectrum peak position correcting method for a surface analyzing instrument, requiring no installation of charge removing mechanism nor specimen treatment such as vapor deposition of a reference substance for a correction reference. SOLUTION: This spectrum peak position correcting method is used for a surface analyzing instrument for analyzing the chemical conditions of elements in a sample by detecting the positions of peaks in an energy spectrum in the depth direction of the specimen obtained by irradiating the surface of the sample with X rays or electron beam while etching it. The position of a peak in the energy spectrum of an element to be analyzed existing in the upper layer part of the sample is corrected based on the amount of shifts of the peak positions due to a charge in the energy spectrum of elements constituting a substrate part at the interface area of the substrate part in contact with the upper layer part where the element to be analyzed exists.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a correction of a peak position of an energy spectrum in a surface analyzer such as a photoelectron spectrometer or an Auger electron spectrometer which measures photoelectrons or Auger electrons using an electron beam or X-ray as an excitation source. About the method.

[0002]

2. Description of the Related Art In a surface analyzer such as a photoelectron spectrometer or an Auger electron spectrometer which measures photoelectrons or Auger electrons using an electron beam or X-ray as an excitation source, a sample is measured based on a measured energy spectrum peak. The constituent elements are detected, but when the chemical bonding state of the elements changes, the peak position and the peak shape change.
Therefore, the state of the chemical bond of the element can be determined by observing the shift of the peak position.

Conventionally, in order to determine the chemical bonding state of elements in this way, reference is made to literature values measured in advance,
The chemical bond state of the target element to be analyzed is determined based on the matched literature values.

However, when the state of the chemical bond is determined with reference to the literature value as described above, the peak position of the energy spectrum fluctuates due to the electrification during the measurement of the sample. It is necessary to verify whether the method and sample pretreatment were appropriate, and to verify that the energy analyzer of the measuring device used to determine the literature values was correctly calibrated.

In order to solve the problem of necessity of such verification, conventionally, the spectrum of the target element is measured while monitoring the neutralization state of the charge, or the peak position is corrected on the sample to be measured. For this purpose, a technique such as vapor deposition of a reference substance used as a reference is used.

[0006]

When a surface analyzer having a charge neutralizing mechanism as described above is used, the charge neutralizing action can be properly performed by monitoring a spectrum waveform during measurement. Must be monitored at all times. In addition, in the case of a method in which a reference material serving as a correction reference is deposited, not only special sample processing is required, but also the deposited reference material is ion-etched as the analysis in the depth direction progresses. There is a problem that the spectrum peak cannot be corrected in the analysis in the depth direction since the spectrum peak disappears.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional surface analysis apparatus, and is provided with a charge neutralization mechanism or special sample processing such as deposition of a reference substance for correction reference. An object of the present invention is to provide a method of correcting a spectral peak position in a surface analyzer that is not required.

[0008]

In order to solve the above problems, the invention according to claim 1 is directed to an energy spectrum in a depth direction of a sample obtained by irradiating an X-ray or an electron beam while etching the surface of the sample. In a method of correcting a spectrum peak position in a surface analyzer for detecting a peak position of a sample and analyzing a chemical state of an element of a sample, a substrate portion in an interface region of a substrate portion in contact with a sample upper layer portion in which an element to be analyzed exists is formed. The peak position of the energy spectrum of the element to be analyzed existing in the upper layer is corrected based on the shift amount of the peak position of the energy spectrum of the element to be charged due to charging.

When performing a depth direction analysis on a sample to be measured having an insulator layer in an upper layer portion, an element to be analyzed particularly present in an upper layer portion of the sample to be measured is different from an element constituting the substrate portion. When the substrate has conductivity, the purpose of measurement in the upper layer is to utilize the peak shift amount due to the charging of the spectral peaks of the elements constituting the substrate observed from the interface region between the upper layer and the substrate. It is possible to estimate the peak shift amount due to element charging. Therefore, in such a sample, the energy of the target element present in the upper layer portion is determined based on the shift amount due to the charging of the spectral peak of the element observed from the substrate portion, as described in the first aspect of the present invention. By correcting the peak position of the spectrum, it is possible to estimate a true chemical shift value corresponding to the chemical state of the target element existing in the upper layer portion and correcting the shift due to the influence of charging.

According to a second aspect of the present invention, in the method of correcting a spectral peak position in the surface analyzer according to the first aspect, the element to be analyzed among the elements constituting the sample upper layer is included in the substrate. In the case of coincidence with an element, the energy spectrum of the detected interface region is subjected to waveform separation processing to separate and obtain each spectrum peak of the element belonging to the upper layer portion and the element belonging to the substrate portion. It is.

In the sample to be measured having an insulator layer in the upper layer, when the element to be analyzed among the elements constituting the upper layer coincides with the element constituting the substrate, the spectrum of the element in the substrate is determined. Since the peak and the spectral peak of the element in the upper layer portion are close to each other, it is difficult to simply measure the shift amount due to charging of the spectral peak of the element in the substrate portion in the interface region.

In a sample in which the target element present in the upper layer portion is also included in the substrate portion, the proximity spectrum peak in the interface region is assigned to the substrate portion by the waveform separation processing as in the invention according to the second aspect. It is separated into the spectral peak of the element and the spectral peak of the element belonging to the upper layer. Then, the peak position of the energy spectrum of the target element belonging to the upper layer portion is corrected based on the shift amount of the spectrum peak of the element belonging to the substrate portion obtained in this waveform separation processing, so that the upper layer portion which is an insulator can be obtained. It is possible to estimate the true spectral peak position of the target element in the chemical state to which it belongs, that is, the chemical shift value.

[0013]

Next, an embodiment will be described. FIG. 1 is a block diagram showing an embodiment of a surface analyzer for performing a method of correcting a spectral peak position in the surface analyzer according to the present invention. This embodiment shows an embodiment in which the present invention is applied to an Auger electron spectrometer. In FIG. 1, reference numeral 1 denotes an analysis chamber for disposing a sample to be measured and the like, and 2 denotes an electron gun, which emits an electron beam on the sample. It serves as an excitation source for irradiating and exciting Auger electrons. Reference numeral 3 denotes an ion gun which irradiates the sample with an ionized inert gas or the like and etches the sample surface so that a depth direction analysis (sputter depth profile analysis) can be performed. Reference numeral 4 denotes an energy analyzer that measures the Auger spectrum of the Auger electrons generated from the sample and measures the Auger spectrum. Reference numeral 5 denotes an electron gun control unit that controls an acceleration voltage, an emission current, an irradiation position of the electron beam, and the like. An ion gun control unit for controlling the acceleration voltage, emission current, ion irradiation position, etc. of the gun 3, an energy analyzer / detection system control unit 7, which controls the voltage of the energy analyzer 4 and converts the detected Auger electrons into electric signals. Is what you do. Reference numeral 8 denotes an analysis function control computer which manages a schedule of spectrum measurement and etching for performing a depth direction analysis, and controls an electron gun 2, an ion gun 3, and an energy analyzer 4 for performing Auger spectrum measurement and ion etching. Control, and further performs waveform separation processing and quantitative calculation processing on the spectrum measured by the depth direction analysis, corrects the peak shift position based on the chemical state, and corrects the corrected peak shift position and the quantitative result. And the like to create a table.

Next, the operation of the embodiment configured as described above will be described. In this embodiment, the operation until the energy spectrum group of each level is obtained in the depth direction analysis of the sample using the electron beam by the electron gun and the ion beam by the ion gun is exactly the same as the conventional one. Is omitted, and a process of correcting the peak shift position based on the chemical state of the spectrum group obtained by the above operation will be described with reference to the flowchart shown in FIG.

First, a group of spectra obtained by applying a depth direction analysis method to a sample to be measured having an upper layer on a substrate is loaded into an analysis function control computer 8 (step S1). Then, with respect to the sample to be measured, it is determined whether or not the element to be analyzed among the elements constituting the sample upper layer is the same as the element contained in the substrate (step S).
2). If they are not the same, the peak shift amount of the energy spectrum due to the influence of the sample electrification of the elements constituting the substrate portion is obtained, and a peak shift table is created (step S3).

Here, the peak shift amount of the energy spectrum due to the influence of the charging of the sample is obtained as follows. That is, in the present invention, it is assumed that the substrate portion is a conductor or a semiconductor, but the depth direction analysis (sputter depth) is performed while etching only the elements from the substrate portion while etching the sample surface. By performing the profile analysis), spectra for the elements on the substrate that are not affected by the charging can be obtained. Therefore,
The spectrum of this part (level) is adopted as a reference spectrum, the peak shift amount of the spectrum of the part (level) mixed with the element in the upper layer is obtained, and the peak position is corrected.

Next, in step S2, when the element to be analyzed in the upper layer portion is the same as the element contained in the substrate portion, the spectral peak of the element in the substrate portion and the spectral peak of the element contained in the upper layer portion are obtained. Are close to each other, and it is not possible to simply measure the shift amount due to the charging of the spectral peak of the element in the substrate portion near the interface, and thus the waveform separation processing is performed on the measured energy spectrum. Then, a reference spectrum used for the waveform separation processing is determined (step S4), and the waveform separation processing is executed based on the reference spectrum (step S5). As the reference spectrum waveform used for this waveform separation processing,
For example, waveform separation is performed using an actual spectrum obtained by the depth direction analysis as a reference spectrum. Here, as a real spectrum used as a reference spectrum, a spectrum in a compound state indicating a target chemical state is used, and this is a separated spectrum. That is, SiO ₂ / Si ₃
In the case of a sample having a layer of N ₄ / Si, SiO ₂ ,
The spectra corresponding to each state of Si ₃ N ₄ and Si are set as respective reference spectra. If Si O ₂ and the Si ₃ N ₄ film is thin, in the case of the sample that can not identify each peak by itself, not from the sample itself that are measured at that time, the other Si O ₂ or Si ₃ The spectrum obtained by measuring the sample formed from N ₄ alone is used as a reference spectrum.

At this time, it is also possible to use a spectrum shape generated by a mathematical function as a reference spectrum. For the mathematical function, use Gauss type, Lorentz type or a mixed function of these. Gauss type: G (x) = I ₀ exp (−A / 2) where I ₀ : spectral intensity A = (x−u) ² / b ² u = peak position b = (peak half width) / 2 Lorentz type : L (x) = I ₀ / (1 + A) where I ₀ : spectral intensity A = (x−u) ² / b ² Gauss-Lorentz mixed type M (x) = I ₀ exp ｛− (1-M) ln ₂ B｝ / (1 + M
B) where I ₀ : spectral intensity B = (x−u) ² / (Zb) ² Z = Σ _{i = 0 to 6} A _i M ⁱ M ⁱ : mixture ratio A _i : coefficient Peak for the above equation It is calculated by giving the intensity (spectral intensity) and the peak half width.

As described above, a component ratio table which records the component ratio of each component obtained when the measured spectrum of each level obtained by the depth direction analysis is subjected to waveform separation processing, a peak shift amount with respect to the reference spectrum Is created (step S6).

Here, the component ratio of each component obtained when performing the waveform separation processing is obtained as follows. For the integral type waveform, the minimum value in the target energy range is subtracted from the observed spectrum and the reference spectrum (removal of the baseline), and the maximum value of the intensity of the observed spectrum and the reference spectrum is normalized to “1”. Using these, the count value is optimized by the nonlinear least squares method so that the residual spectrum by the following equation is minimized. Residual spectrum = (observed spectrum−coefficient × reference spectrum) ² The shift of the peak position is included in this optimization process, and the coefficient ratio obtained in this optimization process is obtained when performing waveform classification processing. It becomes a component ratio.

Next, based on the peak shift table due to the influence of charging prepared for the element belonging to the substrate portion obtained in step S3 and the peak position shift table of the spectrum representing the chemical state obtained in step S6. Correct the spectral peak position of the target element or the spectral peak value belonging to the chemical state (step S
7). More specifically, the peak position with respect to the target element or the chemical state is corrected by the peak shift amount of the element belonging to the conductive substrate layer with respect to the peak position observed at the substrate level. That is, based on the peak position of the element belonging to the substrate layer measured at the substrate layer portion from the result of the depth profile analysis, the peak value of the element contained in the substrate layer at the interface between the upper layer and the substrate layer is compared with this reference value. The shift amount is regarded as a peak shift amount due to charging at each level.

On the other hand, the concentration ratio of each element is determined by quantitative calculation based on a spectrum group to be processed at each level obtained by the depth analysis of the sample taken into the computer 8 in step S1 (step S8). Then, with respect to the concentration ratio determined by the quantitative calculation, step S
In step 6, the component ratio of the target element in each chemical state obtained by the waveform separation is multiplied to convert the component ratio of the target element in each chemical state into a concentration ratio (step S9). Next, a level number matching the stoichiometric ratio corresponding to the target chemical state is searched (step S10). Here, the level number search is performed by performing a quantitative calculation on the spectrum intensity corresponding to the chemical state of the target element separated by the waveform separation processing, and on the element constituting the compound and the atomic concentration ratio. And searching for a level where the atomic concentration ratio for each level created here matches (coincides with) the estimated composition ratio (stoichiometric ratio) of the compound.

Next, the spectrum peak position of the level number corresponding to the target chemical state retrieved in step S10 is set as the peak position of this chemical state, and the peak shift table of the target chemical state is reconstructed based on this position. (Step S11). As a result, a corrected spectrum peak position / element concentration ratio table from which the influence of charging is excluded is created (step S12).

To further explain this point, the peak shift table indicates a relative position with respect to a certain reference peak position, while the corrected spectrum peak position is recorded in the peak shift table at the reference peak position. It shows the absolute position of the peak obtained by adding (or subtracting) the calculated relative position. That is, (corrected peak position) = (reference peak position) +
(Peak shift value), and the peak shift value indicates a displacement amount with respect to the reference value, and has a negative or positive value. Note that the peak shift table used here is based on the shift amount (displacement amount) with respect to the peak position used as a reference when performing waveform separation, and the charge amount is determined by the shift amount of the peak position corresponding to the chemical state of the element in the substrate portion. The results are shown in which the influence is removed and the displacement of the peak position of each level is determined based on the peak position of the level having the composition ratio corresponding to the target chemical state of the target element based on this value.

Next, the peak shift correction for a specific sample will be described. The graph shown in FIG.
Figure 3 of the depth profile analysis using an ion etching technique with respect to (B) are shown as Si on a substrate having a Si ₃ N ₄ layer on the uppermost layer oxide Si (Si O ₂₎ samples with layer The graph shows the change in the peak shift of the Si peak of Si nitride and the substrate Si obtained by applying the waveform separation technique to the obtained Si spectrum. In FIG. 3A, the horizontal axis of the graph shows the repetition of ion etching and peak measurement, the left side shows the vicinity of the sample surface, and the right side shows the inside of the sample.

In this graph, the spectrum of level number 13 of the graph is used as a standard spectrum of Si nitride,
Level number 37 is used as the standard spectrum of Si. In FIG. 3A, a curve a indicates a peak shift amount of SixNy (uncorrected) obtained by the waveform separation process, and a curve b indicates a peak shift amount of Si obtained by the waveform separation process. . Curve c is a result of correcting the peak shift amount of SixNy (uncorrected) (curve a) with the peak shift amount of Si (curve b) obtained by the waveform separation processing (Si).
(SixNy peak shift corrected by). Further, in this graph, with respect to the SixNy peak shift amount (curve c) corrected by Si, the peak at level number 17 is regarded as the peak corresponding to Si ₃ N _4, and the peak value of this level number 17 is used as a reference. And Six corrected by Si
The Ny peak shift (curve c) is corrected, and the amount of SixNy peak shift based on the level number 17 is shown by the curve d.

Next, a modification of the embodiment of the Auger electron spectroscopy apparatus shown in FIG. 1 will be described with reference to FIG. In this modification, an X-ray source 2a is provided instead of an electron gun, and is used as an excitation source for irradiating a sample with X-rays to excite photoelectrons and Auger electrons. Is provided, and the other configuration is the same as that of the embodiment shown in FIG.

FIG. 5 is a diagram showing another modification of the embodiment of the Auger electron spectroscopy apparatus shown in FIG. In this modification, an X-ray source 2a is provided together with an electron gun 2 as an excitation source for exciting photoelectrons and Auger electrons from a sample, and an X-ray source control unit 5a is provided together with an electron gun control unit 5 correspondingly. The other configuration is the same as that of the embodiment shown in FIG.

In the above-described embodiment of the Auger electron spectroscopy apparatus and its modified example, the apparatus constituted by the Auger electron spectroscopy main body and the analysis function control computer is shown. However, as shown in FIG. A separate analysis result processing computer 12 for the surface analysis device 11
Provided, the energy spectrum data obtained in the depth direction analysis in the surface analysis device 11, read into the analysis result processing computer 12 by data communication or recording medium,
A peak position correction process may be performed on the data by a process such as waveform separation.

[0030]

As described above with reference to the embodiments, according to the first aspect of the present invention, the object existing in the upper layer portion based on the shift amount of the spectral peak of the element observed from the substrate portion. Since the peak position of the energy spectrum of the element is corrected, it is possible to estimate a true chemical shift value obtained by correcting the shift due to the influence of charging on the chemical state of the target element present in the upper layer. According to the invention according to claim 2, even in a sample in which the target element present in the upper layer portion is also included in the substrate portion, based on the shift amount of the spectrum peak of the element belonging to the substrate portion obtained by performing the waveform separation processing. This makes it possible to correct the spectral peak position of the target element.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an Auger electron spectrometer for performing a method of correcting a spectrum peak position in a surface analyzer according to the present invention.

FIG. 2 is a flowchart for explaining a main operation of the embodiment shown in FIG. 1;

FIG. 3 is a graph showing the results of a depth direction analysis using an ion etching method on a sample composed of a Si substrate having a Si ₃ N ₄ layer having a Si oxide layer on the surface as an upper layer, and Si and Si obtained by the analysis. FIG. 7 is a graph illustrating correction of a peak shift of FIG.

FIG. 4 is a diagram showing a modification of the embodiment shown in FIG. 1;

FIG. 5 is a diagram showing another modification of the embodiment shown in FIG. 1;

FIG. 6 is a diagram showing still another modification of the embodiment shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Analysis room 2 Electron gun 2a X-ray source 3 Ion gun 4 Energy analyzer 5 Electron gun control part 5a X-ray source control part 6 Ion gun control part 7 Energy analyzer and detection system control part 8 Analysis function control computer 11 Surface analysis device 12 Analysis result processing computer

Claims (2)

[Claims] 1. A surface analyzer for analyzing a chemical state of an element of a sample by detecting a peak position of an energy spectrum in a depth direction of the sample obtained by irradiating an X-ray or an electron beam while etching the surface of the sample. In the method of correcting the spectral peak position in the above, based on the shift amount due to the charging of the peak position of the energy spectrum of the element constituting the substrate portion of the interface portion of the substrate portion in contact with the sample upper layer portion where the element to be analyzed is present, A method of correcting a spectrum peak position in a surface analyzer, wherein a peak position of an energy spectrum of an existing analysis target element is corrected. 2. When the element to be analyzed among the elements constituting the upper layer portion of the sample matches the element contained in the substrate portion, the energy spectrum of the detected interface region is subjected to waveform separation processing. 2. The method of correcting a spectral peak position in a surface analyzer according to claim 1, wherein spectral peaks of an element belonging to an upper layer portion and a spectrum portion of an element belonging to a substrate portion are separately obtained.