JP2008020386A - Method and apparatus for analyzing chemical state by auger electron spectroscopy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for analyzing samples in which different chemical states are mixed through the use of AES. <P>SOLUTION: FeO (II) and Fe<SB>2</SB>O<SB>3</SB>(III) are used as standard samples, and Fe<SB>3</SB>O<SB>4</SB>is used as a sample to be tested. The standard samples of FeO and Fe<SB>2</SB>O<SB>3</SB>are used to perform waveform separation operations on spectra from Fe<SB>3</SB>O<SB>4</SB>by fitting operations by the least square method. A convolution curve is a spectrum synthesized by multiplying each standard sample of FeO and Fe<SB>2</SB>O<SB>3</SB>with a coefficient employed when the best fitting results are derived. On the basis of the coefficients of FeO and Fe<SB>2</SB>O<SB>3</SB>at this time, it is possible to determine an abundance radio between divalent and trivalent iron atoms in Fe<SB>3</SB>O<SB>4</SB>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for analyzing a very small area on the extreme surface of a sample using an Auger electron spectrometer (AES), and more particularly to a technique for analyzing a chemical state using AES.

  For example, iron (hereinafter sometimes referred to as the element symbol “Fe”) is a metal material that is widely used for structural materials of buildings and automobile bodies, but it is prone to rust depending on the environment. Also have. Therefore, it is important to analyze the chemical state of iron oxides and hydroxides (rust components) generated on the surface of the sample containing iron.

  Typical analyzers used for investigating the cause of corrosion on the sample surface and developing materials include an electron probe microanalyzer (EPMA), an X-ray photoelectron spectrometer (XPS), and AES. When these apparatuses are compared from the viewpoint of chemical state analysis, they have the following characteristics.

  EPMA is an apparatus that detects and analyzes characteristic X-rays generated by irradiating a sample with an electron beam. Since the characteristic X-rays generated in the region where the electrons incident on the sample diffuse are used for the analysis, the minimum analysis region (spatial resolution) is 0. 0 in both the horizontal and depth directions. It is about several μm to several μm. For elemental analysis of transition metals such as iron, Kα rays are usually used. However, when chemical state analysis is performed, characteristic X-ray waveform changes and peak shifts of Lα and Lβ rays are used. Although the generation efficiency of L-series characteristic X-rays is not so good, it is suitable for chemical state analysis (see, for example, JP-A-63-205550 of Patent Document 1).

  XPS can directly know the energy level of the electron orbit by irradiating the sample surface with soft X-rays and measuring the kinetic energy of the generated photoelectrons. Therefore, it is generally the most suitable analyzer for analyzing the chemical state among EPMA, XPS, and AES. However, the analysis area of XPS is about several nanometers in the depth direction, but it is usually several hundred μm to several mm in the horizontal direction, and an apparatus called micro XPS has a spread of several tens of μm. .

  AES irradiates a sample with a finely focused electron beam, similar to EPMA, but because the generated Auger electrons are used for analysis, the depth direction is several nanometers as in XPS, and the horizontal direction is a submicron region. Domain analysis is possible. This is because, unlike characteristic X-rays in EPMA, only Auger electrons generated in the vicinity of the incident position of the electron beam incident on the sample can contribute to the analysis. Characteristic X-rays and Auger electrons are common in that they are generated based on the surplus energy generated when the outer shell orbital electrons transition to fill the vacancies generated in the electron inner orbitals of the atoms. Have sex. In fact, the transition probability of the outer shell orbital electrons is equal to the addition probability of the characteristic X-rays (fluorescence yield) and the probability of the Auger electrons. Therefore, in the chemical state analysis using Auger electrons, as in the case of characteristic X-rays, the Auger electrons that involve more outer orbital electrons generally have larger waveforms and peak shifts depending on the chemical state. Change. As an example of chemical state analysis using AES, for example, Japanese Patent Application Laid-Open No. 7-294464 of Patent Document 2 focuses on the fact that the intensity ratio of two peaks varies depending on the chemical state in the Auger electron spectrum. Techniques to do are disclosed.

  In addition, for example, titanium (hereinafter sometimes referred to as “Ti” and element symbols) materials are hard and lighter than Fe, so they are used in a wide variety of applications from carbide tools to glasses frames. . Among them, TiCN (“C” is carbon and “N” is an element symbol of nitrogen) is a typical compound used for cemented carbide tools and the like. The TiCN compound does not have a fixed composition ratio, but the composition ratio of Ti, C, and N can have a continuous value. Quantitative analysis is very important for investigating the material characteristics. However, in an analyzer using characteristic X-rays, N and Ti peaks overlap, so it is particularly difficult to quantify N. N-Kα line and Ti-Ll line overlap even in EPMA with high quantification accuracy. Therefore, N intensity can be determined by estimating and subtracting the intensity of Ti-Ll line considered to be overlapping from the intensity of Ti-Kα line. (See, for example, Japanese Patent Laid-Open No. 1-115045 of Patent Document 3).

JP-A 63-205550 JP 7-294464 A Japanese Patent Laid-Open No. 1-115045 A. G. Sault: Appl. Surf. Sci 74, p249 (1994)

  When analyzing the chemical state of the sample surface, using EPMA makes it difficult to obtain a spatial resolution of submicron or less because the diffusion region of characteristic X-rays is wide no matter how narrow the electron beam is.

When XPS is used, the spatial resolution in the horizontal direction is limited to about several tens of μm. Therefore, meaningful analysis can be performed only in the case of a sample having a uniform chemical state in a wider area. In particular, for iron oxides, the peak waveform of the photoelectron spectrum from FeO and Fe ₂ O ₃ (“O” is the element symbol of oxygen) is almost indistinguishable, so it can be used practically for chemical state analysis of iron. There is also a problem of not.

  When AES is used, chemical state analysis with the highest spatial resolution can be expected as compared with EPMA and XPS. However, for example, when analyzing the chemical state of iron, even if trying to analyze using the peak shape of the Fe-MVV peak (Auger electron energy is around 50 eV), other coexisting elements have peaks near the same energy position. They tend to overlap each other and cannot be used when other elements are mixed. In addition, since the change of the Auger spectrum due to the change of the chemical state is generally as small as several eV, it is not easy to determine which Auger spectrum can be used to analyze the chemical state of the element to be analyzed.

  Further, when a TiCN compound is analyzed by AES, there is a problem that the Ti-LMM Auger spectrum and the N-KLL Auger spectrum overlap as in the case of using characteristic X-rays. Since the accuracy of the quantification method using the relative sensitivity factor generally used in AES is low, this problem can be solved by adopting a method of subtracting the Ti overlap as in EPMA. difficult.

  The present invention has been made in view of the above problems, and an object thereof is to provide a method for analyzing a sample having different chemical states using AES. Another object of the present invention is to provide a method capable of correctly analyzing the oxidation state of iron by determining the abundance ratio of iron in different chemical states using AES. Another object of the present invention is to provide a method for determining the abundance ratio of titanium in different chemical states using AES and analyzing the composition of a compound of titanium, carbon and nitrogen.

In order to solve the above problems, the present invention provides:
A chemical state analysis method using an Auger electron spectrometer that performs ultra-surface analysis of a sample by irradiating the sample surface with a finely focused electron beam,
Obtaining an Auger spectrum of the analysis element from a plurality of standard samples containing the analysis element having different chemical states;
Obtaining an Auger spectrum of the analysis target element from a test sample;
Performing waveform separation calculation for obtaining the coefficient when the residual between the spectrum obtained from the standard sample multiplied by each coefficient and the spectrum from the test sample gives the minimum. And

The present invention also uses an Fe-LMM Auger spectrum from at least two standard samples of Fe, FeO, Fe ₂ O ₃ , and Fe ₃ O ₄ when the test sample contains iron as the element to be analyzed. The waveform separation calculation is performed on the Fe-LMM Auger spectrum from the test sample, and the abundance ratio for each chemical state of iron contained in the test sample is obtained based on the obtained coefficient. To do.

  In the present invention, when the test sample contains titanium and nitrogen simultaneously, and titanium or nitrogen is the element to be analyzed, Ti— obtained from a plurality of standard samples of a compound containing either or both of titanium and nitrogen. Using an LMM Auger spectrum, an N-KLL Auger spectrum, or an Auger spectrum in which Ti-LMM and N-KLL are superimposed, the Auger spectrum in which Ti-LMM and N-KLL from the test sample are superimposed Waveform separation calculation is performed, and the abundance ratio for each chemical state of a compound containing either or both of titanium and nitrogen contained in the test sample is obtained based on the obtained coefficient.

  In the present invention, when the test sample contains titanium as the element to be analyzed and is a compound of at least one element of carbon, nitrogen, and oxygen and titanium, titanium metal, titanium carbide, titanium nitride, and titanium oxide. Using the Ti-LMM Auger spectrum from at least two kinds of standard samples, the waveform separation calculation is performed on the Ti-LMM Auger spectrum from the test sample, and the test is performed based on the obtained coefficient. The chemical state analysis method according to claim 3, wherein an abundance ratio for each chemical state of titanium contained in the sample is obtained.

Further, the present invention is a method in which the analysis target element of the test sample is nitrogen, and includes a base made of a compound containing titanium, and a thin film made of a nitrogen compound of an element other than titanium formed on the base. Is less than the effective analysis depth of Auger electron spectroscopy,
N-KLL Auger spectrum from a sample consisting only of a nitrogen compound of an element other than titanium and Ti-LMM Auger spectrum from at least two kinds of standard samples of metal titanium, titanium carbide, titanium nitride and titanium oxide, or N Using the Auger spectrum in which -KLL and Ti-LMM are superimposed, the waveform separation calculation is performed on the Auger spectrum in which N-KLL and Ti-LMM are superimposed from the test sample, and based on the obtained coefficient An abundance ratio of nitrogen contained in the base and the thin film is obtained.

  The present invention further comprises background removal means for removing a spectrum background from the standard sample and a spectrum from the test sample in order to perform the waveform separation calculation, and the background removal method includes: The differential spectrum is used as the spectrum of the above and the spectrum from the test sample.

In the present invention, when measuring the standard spectrum and the spectrum from the test sample by the electron energy analyzer provided in the Auger electron spectrometer,
Electrons having an energy resolution of 0.35% or more in the method of measuring the energy of Auger electrons generated from the sample with a constant reduction ratio with respect to the energy of Auger electrons generated from the sample and the energy when incident on the electron energy analyzer. An energy analyzer is used.

Further, the present invention is an Auger electron spectrometer for performing an extreme surface analysis of a sample by irradiating a finely focused electron beam onto the sample surface,
Means for obtaining an Auger spectrum of the analysis element from at least two kinds of standard samples containing the analysis element having different chemical states;
Means for obtaining an Auger spectrum of the analysis target element from a test sample;
Waveform separation calculation means for obtaining the coefficient when a residual between a spectrum obtained from the standard sample multiplied by each coefficient and a spectrum from the test sample gives a minimum is provided. .

According to the present invention, there is provided a chemical state analysis method by an Auger electron spectroscopic device for performing an extreme surface analysis of a sample by irradiating the sample surface with a finely focused electron beam,
Obtaining an Auger spectrum of the analysis element from a plurality of standard samples containing the analysis element having different chemical states;
Obtaining an Auger spectrum of the analysis target element from a test sample;
Performing a waveform separation calculation to obtain the coefficient when the residual between the spectrum obtained from the standard sample multiplied by each coefficient and the spectrum from the test sample gives the minimum,
Even if the chemical states of the elements to be analyzed are mixed, the ratio for each chemical state can be known.

According to the invention, when the test sample contains iron as the element to be analyzed, an Fe-LMM Auger spectrum from at least two kinds of standard samples of Fe, FeO, Fe ₂ O ₃ , and Fe ₃ O ₄ is used. The waveform separation calculation is performed on the Fe-LMM Auger spectrum from the test sample, and the abundance ratio for each chemical state of iron contained in the test sample is obtained based on the obtained coefficient. So
Even if the chemical state of iron is mixed, the ratio for each chemical state can be known.

Further, according to the present invention, when the test sample contains titanium and nitrogen at the same time, and titanium or nitrogen is the element to be analyzed, it was obtained from a plurality of standard samples of a compound containing either or both of titanium and nitrogen. Using a Ti-LMM Auger spectrum, N-KLL Auger spectrum, or an Auger spectrum in which Ti-LMM and N-KLL are superimposed, an Auger spectrum in which Ti-LMM and N-KLL from the test sample are superimposed The waveform separation calculation was performed, and the abundance ratio for each chemical state of the compound containing either or both of titanium and nitrogen contained in the test sample was determined based on the obtained coefficient.
To solve the problem that the Auger spectrum of titanium and nitrogen overlap because the test sample contains titanium and nitrogen simultaneously, waveform separation into the chemical state of the titanium compound and nitrogen compound is possible, and the abundance ratio for each chemical state is obtained. Can do. Furthermore, the quantitative value for each element contained in the test sample can be known from the obtained existence ratio for each chemical state.

According to the invention, when the test sample contains titanium as the element to be analyzed and is a compound of at least one element of carbon, nitrogen, and oxygen and titanium, metal titanium, titanium carbide, and titanium nitride; Using the Ti-LMM Auger spectrum from at least two standard samples of titanium oxide, the waveform separation calculation is performed on the Ti-LMM Auger spectrum from the test sample, and based on the obtained coefficient Since the existence ratio for each chemical state of titanium contained in the test sample was determined,
Even if the chemical states of titanium are mixed, the ratio of each titanium in different chemical states can be known.

According to the present invention, the element to be analyzed of the test sample is nitrogen, and comprises a base made of a compound containing titanium, and a thin film made of a nitrogen compound of an element other than titanium formed on the base, When the thickness of the thin film is thinner than the effective analysis depth of Auger electron spectroscopy,
N-KLL Auger spectrum from a sample consisting only of a nitrogen compound of an element other than titanium and Ti-LMM Auger spectrum from at least two kinds of standard samples of metal titanium, titanium carbide, titanium nitride and titanium oxide, or N Using the Auger spectrum in which -KLL and Ti-LMM are superimposed, the waveform separation calculation is performed on the Auger spectrum in which N-KLL and Ti-LMM are superimposed from the test sample, and based on the obtained coefficient Since the ratio of nitrogen contained in the base and the thin film was determined,
Conventionally, analysis of only an extremely thin nitride layer of about 1 to 2 nm formed on an underlayer containing titanium and nitrogen, which has been difficult even by Auger electron spectroscopy that can analyze only the extreme surface, is possible. .

In addition, according to the present invention, in order to perform the waveform separation, a background removal unit that removes a spectrum background from the standard sample and a spectrum from the test sample is provided, and the background removal method includes the standard sample. Since the differential spectrum was used as the spectrum from and the spectrum from the test sample,
The waveform separation calculation can be performed using a spectrum after removing a different background for each sample by a certain method.

According to the present invention, when the standard spectrum and the spectrum from the test sample are measured by the electron energy analyzer provided in the Auger electron spectrometer, the energy of Auger electrons generated from the sample and the electron energy analyzer are incident on the electron energy analyzer. Since the energy resolution in the method of measuring the energy of Auger electrons generated from the sample with a constant reduction ratio with respect to the time energy is 0.35% or more,
The chemical state analysis of iron using the Fe-LMM Auger spectrum and the chemical state analysis of titanium using the Ti-LMM Auger spectrum can be performed correctly.

Further, according to the present invention, there is provided an Auger electron spectroscopic apparatus for performing an extreme surface analysis of a sample by irradiating the sample surface with a finely focused electron beam,
Means for obtaining an Auger spectrum of the analysis element from at least two kinds of standard samples containing the analysis element having different chemical states;
Means for obtaining an Auger spectrum of the analysis target element from a test sample;
Since the waveform separation calculation means for obtaining the coefficient when the residual between the addition spectrum of the spectrum from the standard sample multiplied by each coefficient and the spectrum from the test sample gives the minimum,
Even if the chemical states of the elements to be analyzed are mixed, an Auger electron spectrometer capable of obtaining the ratio for each chemical state by analysis can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. However, the technical scope of the present invention is not limited by this illustration.

  Note that all Auger peaks used in the following description are differential spectra. This is because the Auger electron peak is on a large background so that it is not affected by the background when performing waveform separation calculation. The spectrum background removal method used for waveform separation calculation includes the method of removing low frequency components by differentiating the spectrum, the method of theoretically obtaining and subtracting the background curve, and the analyst drawing and subtracting the spline curve. There are methods. Since the theoretical method can be applied only to a specific sample and the spline method depends on the judgment of the analyst, the present invention uses a method of differentiating the spectrum. However, other methods can be used depending on conditions, and the method of differential spectrum is not necessarily essential.

  Here, a waveform separation calculation method used for the analysis described below will be described. However, the Auger spectra from the standard sample and test sample used for waveform separation calculation are all data measured under the same conditions (or data normalized to the same conditions). The calculation method itself performs the least-squares fitting of the spectrum, and aims to solve the following determinant.

…（１）
波形分離に用いるスペクトルのエネルギー幅をｎ点で分割する。式（１）の左辺が被験試料からのスペクトルのｙ成分（オージェ電子強度）であり、右辺はそれに相当する標準試料スペクトル（Ｓ１〜Ｓｍ）のｙ成分の集合行列である。ここで示すａ₁,ａ₂,…,ａ_ｍが各標準スペクトルの係数であり、ｂが定数ベクトルである。この左辺から右辺を引いたものが残差Σであり、式（２）に示すように、この残差が最小になる係数ａと定数ｂを計算する。

... (1)
The energy width of the spectrum used for waveform separation is divided at n points. The left side of equation (1) is the y component (Auger electron intensity) of the spectrum from the test sample, and the right side is the set matrix of the y components of the standard sample spectrum (S1 to Sm) corresponding thereto. A _1, a ₂ indicated here, ... is _{a m} is the coefficient of each standard spectrum, b is a constant vector. Subtracting the right side from the left side is a residual Σ, and a coefficient a and a constant b that minimize this residual are calculated as shown in Equation (2).

…（２）
残差Σ^２は、必ず正の値となることが明らかなので、この式をａ₁,ａ₂,…,ａ_ｍで偏微分し、その偏微分した値が０となる点が最小の残差である。よって、次式を満たすように方程式の解を求めれば、各標準試料からのスペクトルの係数ａと定数ｂが求まる。

... (2)
Since it is clear that the residual Σ ² is always a positive value, this equation is partially differentiated by a ₁ , a ₂ ,..., A _m and the point where the partial differentiated value becomes 0 is the smallest residual. It is. Therefore, if the solution of the equation is obtained so as to satisfy the following equation, the coefficient a and the constant b of the spectrum from each standard sample can be obtained.

…（３）
これらの偏微分方程式を解いて、ａ₁,ａ₂,…,ａ_ｍの各標準スペクトルの係数と定数ｂを求めることができる。ただし、条件としてａ₁,ａ₂,…,ａ_ｍはすべて正の数であるという条件を付加して解を求める。以上のようにして、最小二乗法によるピーク分離を行う。
このようにして求められた各標準スペクトルの係数ａ₁,ａ₂,…,ａ_ｍは、被験試料における化学状態毎の存在比率に相当する。なお、実際に波形分離計算を行う際は、ピークシフト等を考慮して非負拘束条件付の最小二乗法を用いることが望ましい。

... (3)
Solve these _{PDEs, a 1, a 2, ...} , it is possible to find coefficients and constant b of each standard spectrum of _{a m.} However, as a condition, a solution is obtained by adding a condition that a ₁ , a ₂ ,..., _Am are all positive numbers. As described above, peak separation is performed by the method of least squares.
Coefficient a ₁ of each standard spectrum determined in this way, a _2, ..., _{a m} corresponds to the existence ratio of each chemical state in a test sample. When actually performing the waveform separation calculation, it is desirable to use a least square method with a non-negative constraint condition in consideration of a peak shift or the like.

(Embodiment 1)
First, the result of examining the method for evaluating the oxidation state of iron using the Fe-LMM Auger spectrum will be described. FIG. 1 and FIG. 2 show Fe-LMM Auger spectra measured with an electron energy analyzer with energy resolutions of 0.5% and 0.1% for standard samples of FeO, Fe ₂ O ₃ and Fe ₃ O ₄ , respectively. ing. Here, the definition of the energy resolution is ΔE / E where E is the path energy of electrons passing through the entrance slit to the electron energy analyzer, and ΔE is the energy width of the detected electrons. The path energy E is a value determined by a mode (CRR: Constant Retarding Ratio) in which the energy of the Auger electrons generated from the sample and the reduction ratio Eo / E with respect to the path energy E are kept constant. is there.

FIG. 1 is an Fe-LMM spectrum measured with an energy resolution ΔE / E = 0.5%. The shape of the Fe-LMM spectrum including three large Auger peaks hardly changes, and it is impossible to determine the oxidation state of iron. In the paper of Non-Patent Document 1, Saul states that it is difficult to determine the oxidation state of iron by the Auger spectrum of Fe-LMM, but the resolution of the AES electronic energy analyzer used by Saul is ΔE. /E=0.6%. On the other hand, FIG. 2 is a Fe-LMM spectrum measured with higher energy resolution ΔE / E = 0.1%. The peak as a whole is sharp, peaks of L _2,3 M _2,3 M _2,3 and L _2,3 M _2,3 M _4,5 Despite overlap in the same intensity, It can be seen that the peak intensities of L _2,3 M _4,5 M _4,5 are different for each of FeO, Fe ₂ O ₃ and Fe ₃ O ₄ . This is clearly a change due to the difference in the oxidation state of iron, and shows the possibility that the chemical state of iron can be evaluated from the Fe-LMM spectrum only in practice.

Therefore, in order to verify whether the Fe-LMM spectrum of FIG. 2 really shows the divalent and trivalent chemical states of iron, spectra from FeO (divalent) and Fe ₂ O ₃ (trivalent) are used as standard spectra. As a result, the waveform separation calculation was performed on the spectrum from Fe ₃ O ₄ by the least square fitting method.

FIG. 3 shows the waveform separation results. In FIG. 3, the convolution curve is a spectrum synthesized from the standard spectra of FeO and Fe ₂ O ₃ when giving the best fitting result. It can be seen that Fe ₃ O ₄ almost overlaps with this convolution curve. Table 1 shows the spectrum coefficients of FeO and Fe ₂ O ₃ obtained by waveform separation of Fe ₃ O ₄ and the atomic concentrations of Fe ²⁺ , Fe ^3+, and O ²⁻ converted based on the coefficients.

オージェピークの強度は、原理的にそのオージェ電子が放出される元素の原子濃度に依存することから、表１中の係数は、Ｆｅ_３Ｏ_４を構成するＦｅ原子のうちＦｅ^２＋の状態にある原子とＦｅ^３＋の状態にある原子個数のそれぞれ標準試料ＦｅＯとＦｅ_２Ｏ_３に対する個数比を示すことになる。但し、係数から各々の原子濃度に換算するときは、標準試料中のその元素の原子濃度を各係数に乗じる必要が有る。例えば、Ｆｅ^２＋の原子濃度は、
ＦｅＯの係数×ＦｅＯ中のＦｅ原子濃度＝０．２７７４×０．５
Ｆｅ^３＋の原子濃度は、
Ｆｅ_２Ｏ_３の係数×Ｆｅ_２Ｏ_３中のＦｅ原子濃度＝０．７２２６×０．４
として、波形分離計算により求めた係数からＦｅ_３Ｏ_４を構成するＦｅ原子の化学状態の存在比率を求めることができる。
表１における換算された原子濃度をみると、Ｆｅ^２＋とＦｅ^３＋の原子濃度がＦｅ_３Ｏ_４の理論値に近い値が得られており、ＦｅＯとＦｅ_２Ｏ_３のスペクトルを２価と３価の標準スペクトルとして、Ｆｅ_３Ｏ_４の化学状態を分離できることが分かった。

Since the intensity of the Auger peak depends in principle on the atomic concentration of the element from which Auger electrons are emitted, the coefficients in Table 1 are in the Fe ²⁺ state among the Fe atoms constituting Fe ₃ O _4. The ratio of the number of atoms and the number of atoms in the state of Fe ^{3+ to} the standard samples FeO and Fe ₂ O ₃ respectively will be shown. However, when converting from a coefficient to each atomic concentration, it is necessary to multiply each coefficient by the atomic concentration of the element in the standard sample. For example, the atomic concentration of Fe ²⁺ is
Coefficient of FeO × Fe atom concentration in FeO = 0.774 × 0.5
The atomic concentration of Fe ³⁺ is
Fe atomic concentration in the coefficient × _Fe 2 _{O 3} of Fe ₂ O ₃ = 0.7226 × 0.4
As described above, the abundance ratio of the chemical state of Fe atoms constituting Fe ₃ O ₄ can be obtained from the coefficient obtained by waveform separation calculation.
Looking at the converted atomic concentrations in Table 1, the atomic concentrations of Fe ²⁺ and Fe ³⁺ are close to the theoretical values of Fe ₃ O ₄ , and the spectra of FeO and Fe ₂ O ₃ are divalent and 3 As a standard spectrum of valence, it was found that the chemical state of Fe ₃ O ₄ can be separated.

(Embodiment 2)
Next, a method for obtaining the ratio of TiC and TiN in a titanium carbonitride (hereinafter referred to as TiCN) compound using chemical state analysis by Ti-LMM Auger spectrum will be described. This method is a method of estimating the abundance ratio of TiC and TiN by utilizing the fact that the Ti-LMM Auger spectrum changes depending on the bond partner of Ti atoms depending on C and N. At this time, the Ti and N spectra overlapping in TiN are handled as if they are one spectrum, thereby solving the problem that the Ti and N spectra overlap and cannot be quantified.

  FIG. 4 is a Ti-LMM spectrum measured with standard samples of Ti having different chemical states. The energy resolution of the used electronic energy analyzer is 0.05%. Thus, when the Ti compound is measured with high energy resolution (ΔE / E = 0.1% or less), it is measured in completely different shapes as shown in FIG. Therefore, using these as standard spectra and applying waveform separation calculations to Auger spectra obtained with unknown concentrations of TiCN compounds, the abundance ratios of the chemical states of TiC and TiN can be obtained, respectively, and the concentrations of C and N can be determined from the results. You can ask.

FIG. 5 shows an Auger spectrum measured with TiCN compounds having known concentrations prepared as C: N concentration ratios of C: N = 3: 7, 5: 5, and 7: 3, respectively, as samples for evaluating quantitative accuracy. It is. Table 2 shows the result of waveform separation calculation of only Ti-LMM using four standard spectra of Ti, TiC, TiN, and TiO ₂ with respect to the spectrum of FIG. The converted atomic concentration of Ti is a value obtained by multiplying each coefficient of TiC and TiN obtained by the waveform separation calculation result by multiplying the atomic concentration of Ti in each compound (both TiC and TiN is 0.5).

表２において波形分離計算結果の係数から換算した各元素の原子濃度を見ると、理論値と非常によい一致が得られている。ＡＥＳの従来の定量法における相対感度因子を用いて原子濃度を求める方法では、他の元素のオージェピークがオーバーラップすると、正しい濃度を求めることが非常に困難であった。その理由は、ある元素が他の元素と結合してピーク形状が変化すると、純物質のピーク形状から求めた相対感度因子の値そのものの誤差が大きくなるからである。しかし、今回のように同じ条件で測定した標準スペクトルをもとに、高エネルギー分解能のオージェスペクトルを使って化合物毎（即ち化学状態毎）の存在比率を求めると、非常に精度の良い定量結果が得られることがわかった。

Looking at the atomic concentration of each element converted from the coefficient of the waveform separation calculation result in Table 2, a very good agreement with the theoretical value is obtained. In the method of obtaining the atomic concentration using the relative sensitivity factor in the conventional quantitative method of AES, it is very difficult to obtain the correct concentration when the Auger peaks of other elements overlap. The reason is that when a certain element is combined with another element to change the peak shape, an error in the value of the relative sensitivity factor obtained from the peak shape of the pure substance increases. However, based on the standard spectrum measured under the same conditions as this time, using the high energy resolution Auger spectrum to determine the abundance ratio for each compound (that is, for each chemical state), a very accurate quantitative result is obtained. It turns out that it is obtained.

(Embodiment 3)
Next, a method for analyzing an extremely thin nitride layer of about 1 to 2 nm formed on a base containing titanium and nitrogen as shown in FIG. 11 will be described. Auger electrons are generated inside the sample by the electron beam incident on the sample. However, since the mean free path of the Auger electrons in the sample is short, generally the depth of generation of Auger electrons that contribute to the analysis (in the present invention, “ The effective analysis depth of Auger electron spectroscopy ”is about 5 nm as shown in FIG. Therefore, even if a thin film having a thickness of about 1 to 2 nm is formed on the base, it is extremely difficult to analyze only the thin film using Auger electron spectroscopy. In particular, when the analysis target element is nitrogen, as shown in FIG. 11, it is impossible to know whether or not there is a nitride layer not containing titanium on the underlayer containing titanium and nitrogen as shown in FIG. . The invention of Embodiment 3 can exert an effect on such a sample.

The Auger spectrum shown in FIG. 12 is an electronic energy analyzer having an energy resolution of 0.05% on a sample surface in which a thin film of Si ₃ N ₄ (silicon nitride) having a thickness of 1 to 2 nm is formed on a TiCN alloy. It is an Auger spectrum measured by. The peak near 375 to 390 eV seen in this spectrum is a superposition of the Auger peaks of Si ₃ N ₄ , TiN N-KLL and Ti-LMM. At an energy resolution of about 0.5% of an AES electronic energy analyzer that is generally used, the chemical state analysis of Ti cannot be performed because the energy resolution is low. Therefore, it has been considered difficult to quantitatively analyze an extremely thin nitride layer of about 1 to 2 nm formed on a base containing titanium and nitrogen. However, if an Auger spectrum in the energy region including N-KLL and Ti-LMM is measured with an electronic energy analyzer with an energy resolution of 0.05%, chemical state analysis is possible by waveform separation processing using the least square method. .

FIG. 13 shows a standard spectrum from each standard sample of Si ₃ N ₄ , Ti, TiN, and TiC used for waveform separation, measured at an energy resolution of 0.05%. FIG. 14 shows the result of the waveform separation calculation of the Auger spectrum from the base and thin film of the Si ₃ N ₄ thin film sample formed on the TiCN alloy. Further, Table 5 shows the coefficient of each standard spectrum obtained from the waveform separation result and the atomic concentration converted from the coefficient.

表５の結果から、ＴｉＣＮ合金上に形成された極薄いＳｉ_３Ｎ_４から発生したオージェ電子によるＮ−ＫＬＬスペクトルのみを分離できていることがわかる。即ち、エネルギー分解能の高い電子エネルギーアナライザを用いれば、従来はＡＥＳでも分析が困難とされてきたＴｉＣＮ合金上の極表面に存在する窒化物層の分析が可能であることを示している。さらに、Ｓｉ−ＫＬＬオージェスペクトル等を用いてシリコンのみの組成値を求めれば、表５に示される窒素の原子濃度Ｎ（−Ｓｉ）とから、シリコン窒化物層の定量分析が可能である。

From the results in Table 5, it can be seen that only the N-KLL spectrum due to Auger electrons generated from ultrathin Si ₃ N ₄ formed on the TiCN alloy can be separated. That is, if an electron energy analyzer with high energy resolution is used, it is possible to analyze the nitride layer existing on the extreme surface on the TiCN alloy, which has conventionally been difficult to analyze even with AES. Further, if the composition value of only silicon is obtained using Si-KLL Auger spectrum or the like, the silicon nitride layer can be quantitatively analyzed from the atomic concentration N (-Si) of nitrogen shown in Table 5.

  As a result of the inventors examining the analysis contents of the iron sample and the titanium-based sample described above, in order to perform a reliable chemical state using the Fe-LMM Auger spectrum or Ti-LMM and N-KLL Auger spectrum, the energy resolution It has been found that it is necessary to use an electronic energy analyzer having ΔE / E of 0.35% or more.

Next, the example which implemented this invention with respect to the real sample is demonstrated.
(Example 1)
First, an example in which iron rust around us is analyzed using a waveform separation method based on an Fe-LMM spectrum is shown. The secondary electron images shown in FIG. 6 are both naturally oxidized by exposing an iron sample to the atmosphere for a long period of time. FIG. 6A is a so-called black rust sample which is visually black. FIG. 6 (b) is a red rust sample, but even when viewed with the naked eye, a reddish place and a blackish place are mixed depending on the place. When the region that appeared to be red and uniform was observed with a secondary electron image, it was found that there were two types of regions, region A and region B, as shown in FIG.

First, in order to investigate what elements are detected on the surface, Auger spectra were measured at an energy resolution of 0.5% in regions A and B of black rust and red rust. The result is shown in FIG. Although trace amounts of C, S, and Cl were detected, it was found that the main components were composed of Fe and O. However, with an energy resolution of 0.5%, the oxidation state of Fe cannot be distinguished from changes in the spectrum. Therefore, all samples were measured again with a high energy resolution of 0.1%, and waveform separation calculations were performed. FIG. 8 shows an example of the result of waveform separation in the red rust region A.
The result shown in FIG. 8 does not completely overlap with the convolution curve shown by the sum of the spectra of Fe, FeO, and Fe ₂ O ₃ as in FIG. This was the same at the other analysis points and did not overlap completely. This reason seems to be because Fe in a different chemical state such as hydroxide exists. However, here, only the spectra of Fe, FeO, and Fe ₂ O ₃ were used for peak separation calculation and evaluation.

  Table 3 shows the atomic concentration converted to the coefficient of the standard spectrum in each sample obtained by the waveform separation calculation.

表３の結果を見ると、黒錆と赤錆とでは、赤錆の方がＦｅの原子濃度が小さく、よく酸化が進行していると思われる。また、黒錆からは赤錆の成分と考えられているＦｅ_２Ｏ_３の成分は検出されず、赤錆からはＦｅＯとＦｅ_２Ｏ_３の両方の成分が検出された。図６（ａ）の二次電子像で確認された赤錆の領域Ａと領域Ｂとの差は、Ｆｅ^２＋とＦｅ^３＋の存在比率が異なっていることがわかった。

From the results shown in Table 3, it is considered that the red rust has a lower atomic concentration of Fe and the oxidation proceeds well between black rust and red rust. Further, from the black rust components of Fe ₂ O ₃ which is considered a component of red rust is not detected, both components of FeO and Fe ₂ O ₃ was detected from the red rust. The difference between the red rust region A and the region B confirmed in the secondary electron image of FIG. 6A was found to be different in the abundance ratio of Fe ²⁺ and Fe ³⁺ .

(Example 2)
Next, the result of analyzing the segregation in the TiCN compound will be described. As already described in the embodiment, the analysis result of TiC ₃ N ₇ using waveform separation by Ti-LMM Auger spectrum is in good agreement with the theoretical value of TiC ₃ N ₇ if the average value of the analysis is taken. Has been obtained. However, it was found from the secondary electron image in FIG. 9 that two different types of crystal grains exist in TiC ₃ N ₇ . From the secondary electron image of FIG. 9, it can be seen that two types of TiC ₃ N ₇ are present at almost the same rate: crystal grains having a smooth surface and crystal grains having slight irregularities. FIG. 10 shows Auger spectra measured at the analysis points P1 and P2 representing the respective crystal grains. FIG. 10 shows that the Ti-LMM spectrum is slightly different between P1 and P2. Table 4 shows the atomic concentrations converted into the coefficients of the standard spectrum obtained by performing waveform separation calculation on the spectra measured at P1 and P2.

表４から分かるように、分析点Ｐ１とＰ２では、それぞれＴｉＣとＴｉＮの係数が異なり、それに従って換算された原子濃度も異なっていた。つまりこの試料は、ＴｉＣとＴｉＮの存在比率が異なる２種類の結晶粒が混在した試料であることが明らかにされた。

As can be seen from Table 4, at the analysis points P1 and P2, the coefficients of TiC and TiN were different, and the atomic concentrations converted accordingly were also different. That is, it was revealed that this sample was a sample in which two types of crystal grains having different ratios of TiC and TiN were mixed.

  As described above, taking an iron sample and a titanium-based sample as an example, a method for obtaining the chemical state abundance ratio of a sample in which different chemical states are mixed by waveform separation of the AES Auger spectrum and an example of application to an actual sample Explained. In actual samples, there are many cases where more complicated and fine crystal grains are mixed than the sample shown in FIG. In such a case, it is clear that the chemical state analysis using the waveform separation calculation by AES of the present invention has a greater effect.

Fe-LMM Auger spectrum measured with an electronic energy analyzer with an energy resolution of 0.5% Fe-LMM Auger spectrum measured with an electron energy analyzer with an energy resolution of 0.1% The result of waveform separation of the Auger spectrum from Fe ₃ O _{4 using} FeO and Fe ₂ O ₃ as standard samples. Ti-LMM spectrum from each Ti standard sample measured by an electronic energy analyzer with an energy resolution of 0.05%. Auger spectrum from TiCN compound of known concentration measured by an electronic energy analyzer with an energy resolution of 0.05%. Secondary electron image of iron black rust and red rust. Auger spectrum from iron black rust and red rust measured by an electronic energy analyzer with an energy resolution of 0.5%. The result of waveform separation of Auger spectra from black rust and red rust of iron using Fe, FeO and Fe ₂ O ₃ as standard samples. Secondary electron image of the surface of TiC ₃ N ₇ . Auger spectra measured on two different grains of TiC ₃ N ₇ . The schematic diagram of the sample which consists of a very thin nitride layer about 1-2 nm formed on the foundation | substrate containing titanium and nitrogen. Auger spectrum measured on the surface of a sample in which a thin film of Si ₃ N ₄ having a thickness of 1 to 2 nm is formed on a TiCN alloy. Standard spectra from Si ₃ N ₄ , Ti, TiN and TiC standard samples used for waveform separation calculation. The result of waveform separation of the base and the Auger spectrum from the thin film of the Si ₃ N ₄ thin film sample formed on the TiCN alloy.

Explanation of symbols

(Those that perform the same or similar operations are denoted by a common reference.)
P1 and P2 analysis points

Claims (8)

A chemical state analysis method using an Auger electron spectrometer that performs ultra-surface analysis of a sample by irradiating the sample surface with a finely focused electron beam,
Obtaining an Auger spectrum of the analysis element from a plurality of standard samples containing the analysis element having different chemical states;
Obtaining an Auger spectrum of the analysis target element from a test sample;
Performing waveform separation calculation for obtaining the coefficient when the residual between the spectrum obtained from the standard sample multiplied by each coefficient and the spectrum from the test sample gives the minimum. Chemical state analysis method. When the test sample contains iron as the element to be analyzed, the test sample is obtained using Fe-LMM Auger spectra from at least two kinds of standard samples of Fe, FeO, Fe ₂ O ₃ , and Fe ₃ O _4. 2. The abundance ratio for each chemical state of iron contained in the test sample is obtained based on the obtained coefficient by performing the waveform separation calculation on the Fe-LMM Auger spectrum from The chemical state analysis method described. Ti-LMM Auger spectra obtained from a plurality of standard samples of a compound containing either or both of titanium and nitrogen when the test sample contains titanium and nitrogen simultaneously, and titanium or nitrogen is the element to be analyzed, N Using the -KLL Auger spectrum or the Auger spectrum in which Ti-LMM and N-KLL are superimposed, the waveform separation calculation is performed on the Auger spectrum in which Ti-LMM and N-KLL are superimposed from the test sample. The chemical state analysis method according to claim 1, wherein an abundance ratio for each chemical state of a compound containing either or both of titanium and nitrogen contained in the test sample is obtained based on the obtained coefficient. . When the test sample contains titanium as the element to be analyzed and is a compound of at least one element of carbon, nitrogen, and oxygen and titanium, at least two of metal titanium, titanium carbide, titanium nitride, and titanium oxide Using the Ti-LMM Auger spectrum from various types of standard samples, the waveform separation calculation is performed on the Ti-LMM Auger spectrum from the test sample, and the titanium contained in the test sample based on the obtained coefficient The chemical state analysis method according to claim 3, wherein an abundance ratio for each chemical state is obtained. The analysis target element of the test sample is nitrogen, and comprises a base made of a compound containing titanium and a thin film made of a nitrogen compound of an element other than titanium formed on the base, and the thickness of the thin film is Auger When thinner than the effective analysis depth of electron spectroscopy,
N-KLL Auger spectrum from a sample consisting only of a nitrogen compound of an element other than titanium and Ti-LMM Auger spectrum from at least two kinds of standard samples of metal titanium, titanium carbide, titanium nitride and titanium oxide, or N Using the Auger spectrum in which -KLL and Ti-LMM are superimposed, the waveform separation calculation is performed on the Auger spectrum in which N-KLL and Ti-LMM are superimposed from the test sample, and based on the obtained coefficient The chemical state analysis method according to claim 3, wherein an abundance ratio of nitrogen contained in the base and the thin film is obtained. In order to perform the waveform separation calculation, a background removing unit that removes a spectrum background from the standard sample and a spectrum from the test sample is provided, and the background removal method includes the spectrum from the standard sample and the test sample. The chemical state analysis method according to claim 1, wherein a differential spectrum is used as the spectrum from. When measuring the standard spectrum and the spectrum from the test sample with an electronic energy analyzer provided in the Auger electron spectrometer,
Electrons having an energy resolution of 0.35% or more in the method of measuring the energy of Auger electrons generated from the sample with a constant reduction ratio with respect to the energy of Auger electrons generated from the sample and the energy when incident on the electron energy analyzer. The chemical state analysis method according to claim 1, wherein an energy analyzer is used. An Auger electron spectrometer that performs ultra-surface analysis of a sample by irradiating the sample surface with a finely focused electron beam,
Means for obtaining an Auger spectrum of the analysis element from at least two kinds of standard samples containing the analysis element having different chemical states;
Means for obtaining an Auger spectrum of the analysis target element from a test sample;
Waveform separation calculation means for obtaining the coefficient when a residual between a spectrum obtained from the standard sample multiplied by each coefficient and a spectrum from the test sample gives a minimum is provided. Auger electron spectrometer.

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