JPH0526826A - Method for measuring thickness of thin film sample and quantitatively analyzing element - Google Patents

Abstract

PURPOSE:To perform both quantitative analysis and film thickness measurement by finding the X-ray intensity ratio of an element, the X-ray intensity ratio which is actually unmeasurable, from the X-ray intensity of another element and chemically coupled form between both of the elements and calculating the thickness of the thin film of the sample from a specific equation. CONSTITUTION:The ratio of a specific X-ray intensity of a radioactive element in a thin film sample of an already known element to that of a radiation characteristic from a single- body standard sample of a component element is found by actual measurement. The X-ray intensity ratio of an element, the X-ray intensity of which is actually unmeasurable, is found from the X-ray intensity ratio of another element and the chemically coupled form between both of the elements. Then the thickness of the thin film is calculated from Equation 1 by using the X-ray intensity ratios of all components. The EO and ECi of the equation respectively represent an applied voltage and X-ray exciting voltage from an element (i). The concentration of each component element and thickness of the thin film are decided by successive approximation by repeating simulation and calculation by assuming the concentration of each component element contained in the thin film from the X-ray intensity ratio, finding the intensity ratio of each component element by simulating the loci of the incident electrons to the sample, correcting the concentration of each component element and film thickness of the thin film so that the calculated X-ray intensity can become equal to that obtained by measurement.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an X-ray spectroscopic method such as EPMA in a thin film quantitative analysis when the thin film and the substrate are different oxides and the composition of the substrate oxide is known. The present invention relates to a method for determining the composition and film thickness of a thin film.

[0002]

2. Description of the Related Art In a quantitative analysis of a thin film sample, when the thin film and the substrate have the same element (O in this application), the intensity of the characteristic X-ray of the common element emitted from the substrate cannot be discriminated between the substrate and the thin film. Moreover, the composition ratio of the elements of the thin film cannot be specified from the characteristic X-ray intensity obtained by the measurement. For example, if the thin film thickness is set to be slightly thin for one measurement result and it is assumed that there is no O, even if the measured OKα comes out only from the substrate, the same result as the experimental value may be obtained. There is. Therefore, when the substrate and the thin film sample thereon have a common element, it was not possible to determine the thickness of the sample thin film and the elemental composition ratio together using EPMA.

[0003]

SUMMARY OF THE INVENTION The present invention is a thin film sample containing the same element in a substrate and a thin film. When the substrate and the thin film element are known, an X-ray spectroscopic method such as EPMA is used. It is an object to provide a method for performing both quantitative analysis and film thickness measurement together.

[0004]

A characteristic X-ray intensity of a component element emitted from a thin film sample of a known constituent element, which is excited by an electron beam accelerated by an appropriate accelerating voltage, and the same accelerating electron beam as described above are used. The ratio of the excited component elements to the characteristic X-ray intensity (X-ray intensity ratio) radiated from a simple substance standard sample is actually obtained in an element for which it can be actually obtained, and the X-ray intensity ratio is actually measured. The X-ray intensity ratio of the element that cannot be obtained from the above is obtained from the X-ray intensity ratio of the other element obtained above and the chemical bond form between the unmeasurable element and the other element, and the X-ray intensity ratio of all the components is obtained. Then, the thickness of the thin film is calculated by the following formula [2], and the concentration of each component element of the thin film of the sample is assumed from the above X-ray intensity ratio ratio. , The sample incident electron trajectories are simulated, and The X-ray intensity ratio by determined by calculation,
Correct the concentration of each element and the film thickness so that the X-ray intensity ratio obtained by the calculation becomes equal to the X-ray intensity ratio obtained by the above measurement.
The same simulation as above is performed using the corrected assumed concentration and film thickness, and by repeating the same calculation,
The element concentration and film thickness of the thin film sample were determined by successive approximation.

[Equation 2] However, ρ Z _ri = 7.0 (E _o ^1.65 −E _Ci ^1.65 ) μg
/ Cm ² E _o ; acceleration voltage, E _Ci ; X-ray excitation voltage of element i

[0005]

Regarding the computer simulation method used in the present invention, the applicant of the present invention filed Japanese Patent Application No. 2-14
The method applied for in No. 9528 is incorporated. The present invention determines the component element concentration C and the thin film thickness t when the common element is contained in the substrate and the thin film layer, or when the thin film contains an element whose X-ray intensity ratio cannot be directly measured. At the same time, they try to seek. In this computer simulation, in a thin film sample and a standard sample of each element, the rate at which the characteristic X-ray of each element is generated, that is, the intensity is calculated by using the Monte Carlo method. The characteristic X-ray intensity of the sample and that of the standard sample are calculated. The ratio with the characteristic X-ray intensity (characteristic X-ray intensity ratio by calculation) is to be obtained by the above calculation. This X-ray intensity ratio has a character proportional to each element concentration without being influenced by the intensity of the excitation ray, the measurement time, the frequency of X-ray generation in each element, and the concentration of each element used in the computer simulation and If the film thickness is correct, the calculated X-ray intensity ratio and the measured X-ray intensity ratio
It was born from the idea that it should be equal to the line intensity ratio, and the elemental concentration and film thickness values used for computer simulation should match the calculated X-ray intensity ratio and the measured X-ray intensity ratio. While correcting the above, calculate the calculated X-ray intensity ratio by computer simulation, and if the calculated X-ray intensity ratio matches the measured X-ray intensity ratio, use the composition ratio and film thickness at that time as the measured value. Therefore, it is intended to obtain a highly accurate measured value. Therefore, in order to use the computer simulation method, first, the composition ratio of the thin film sample, that is, the concentration of each element in the substrate and the thin film, and the thickness of the thin film must be set. However, in the present invention, an element whose X-ray intensity ratio cannot be obtained by measurement is contained, and the analysis is started unless the X-ray intensity ratio of the element that cannot be obtained by this measurement is set by any method. I can't.

Therefore, the present invention is intended to set the X-ray intensity ratio by the measurement of an element such as oxygen O, for which the X-ray intensity ratio cannot be determined by the measurement, by the following principle. The present invention is constructed based on the idea that the X-ray intensity ratio is proportional to the concentration of each element. Therefore, X of oxygen O
The ratio of the line intensity ratio to other X-ray intensity ratios is considered to be equal to the element concentration (weight) ratio. Therefore, even if the total concentration of oxygen is unknown, when oxygen is chemically bound to each element in a known manner, the concentration ratio (weight ratio) between oxygen and the binding element in the chemical formula showing the binding state is: Since it is theoretically known, the X-ray intensity ratio of oxygen in the bound state should be obtained from the product of the weight ratio of oxygen to the bound element in the bound state and the X-ray intensity ratio measured by the bound element. You can However, oxygen is not always in a bonded state with only one element, that is, an oxide,
It may also be in a bonded state with many elements. In such a case, the X-ray intensity ratio of oxygen is calculated for each binding state, and the sum of the calculated X-ray intensity ratios can be estimated as the X-ray intensity ratio of oxygen contained in the sample.

The thickness of the thin film is set by the following [Equation 3].

[Equation 3] However, ρ Z _ri = 7.0 (E _o ^1.65 −E _Ci ^1.65 ) μg
/ Cm ² E _o ; accelerating voltage, E _Ci ; X-ray excitation voltage of element i. A. Waldo: Microbea
m Analysis (1988) P, 310-], it is a formula for calculating the film thickness by using the characteristic X-ray intensity ratio K _i0 for all the constituent elements of the thin film. .. Here, the characteristic X-ray intensity ratio is the ratio of the characteristic X-ray intensity of the sample component element in the sample to the characteristic X-ray intensity of the pure sample of the element, and is obtained by the measurement in applying [Equation 3]. X-ray intensity ratio K of each element
_{Although i0} is used, for O, since the X-ray intensity ratio cannot be directly obtained by measurement as described above,
From the bonding state of the constituent elements and oxygen, the value of the sum of the products of the measured X-ray intensity ratios of these constituent elements and the concentration ratio of oxygen to the constituent elements is used. For example, if the characteristic X-ray intensity ratio of a certain binding element is 0.03 and the weight concentration ratio of O is 40% with respect to the same binding element, the characteristic X-ray of O bound to the certain binding element is The intensity ratio is 0.012. There is another bonding element, and the X-ray intensity ratio of the bonding element is 0.1.
If the weight concentration ratio of O to the same binding element is 60%, the characteristic X-ray intensity ratio of O bound to the binding element is 0.06, and oxygen O is bound only to the above two elements. In the case of, the sum of the X-ray intensity ratios of the two is 0.0
72 is set as the X-ray intensity ratio of oxygen O. After that, the X-ray intensity ratio calculated by the simulation method was calculated using the element concentrations and film thicknesses set above, and the calculated X-ray intensity ratio was compared with the actually measured X-ray intensity ratio to make an assumption. While correcting the thickness and the composition ratio, the calculation is repeated until the component element characteristic X-ray intensity ratio calculated by the simulation method agrees with the actual measurement to obtain the thickness and the composition ratio.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a flowchart of an embodiment of the present invention. In the figure, the sample used in the present invention contains an oxide in both the surface layer (thin film) of the measurement sample and the substrate, and although the constituent elements of the substrate and the constituent elements of the thin film are known, the constituent elements of the thin film are known. The concentration and film thickness of are unknown. The sample S is irradiated with an electron beam with an appropriate acceleration voltage E, and each element i (i =
a, b, c, ..., Z) characteristic X-ray intensity I _iS and each element i
The characteristic X-ray intensity I _iK of the standard sample (pure sample) is measured (a). Based on the measurement data obtained in the operation (A), the X-ray intensity ratio K _i0 = I _iS / I _iK of each element other than the common element O is calculated (B). The X-ray intensity ratio K _o0 of the common element O is set from the bonding state with each element using the X-ray intensity ratio K _i1 of each constituent element. For example, in the case of a film considered to be a superconducting material of Y, Ba, Cu, O, it is a mixture of Y, Ba, Cu oxides in an appropriate ratio and is burned.
Since the ratio of is almost fixed, it is considered that O≈7 for Y = 1. If the oxide in the sample is an oxide of Al, A
As L ₂ O ₃ , the weight ratio is Al: O≈19: 8, and S
If the oxide of i is SiO ₂ , the weight ratio is Si: O≈
Calculate and set at 7: 8 (C). The ratio of the X-ray intensity ratios of the constituent elements obtained by the measurement and calculation is set as the elemental concentration C _i1 of the first approximation in the thin film layer (d). Film thickness t
₁

[Equation 4]However, ρZ_ri= 7.0 (E_o ^1.65 -E_Ci ^1.65) Μg
/ Cm² E_o Accelerating voltage, E_CiSet by the X-ray excitation voltage of element i (e). Depending on the above setting conditions,
Computer simulation and calculate the characteristics of each element by calculation.
X-ray intensity ratio K_ijCalculate (F). Other than common element O
Calculated intensity ratio K for all elements_ijAnd measured by strength
Degree ratio K_i0Error ε_i Is ε_i = [(K_i0-K_ij) /
K_i0], Ε_i And the average value E of_i Deviation range Δε
(Ε_i (Difference between the maximum value and the minimum value of)) (g). Swing range
Whether Δε is larger than the set value α (for example, 0.05)
Judge whether (K). When the swing width Δε is larger than the set value α
If the concentration is C, the concentration C of each element other than the common element O_ij(I; element
Name, j; number of sequential calculations) C_ij= C_ij-1× K_i0/ K_ij-1  (J = 2, 3, ...) Concentration C of common element O_OJTo C_OJ= 1-ΣC_ij  (ΣC_ijIs the element concentration C other than the common element in the thin film layer
_ij(Sum) of the correction calculation
Returning to (f), each element concentration corrected in the jth sequential calculation
C_ij(I = a, b, c, ...)
Data simulation again. Runout width Δε is the set value
If it is not larger than α, the average value E is set value β (for example,
For example, it is determined whether it is larger than 0.1) (ko). average
When the value E is larger than the set value β, the film thickness t_j To

[Equation 5] However, K ₀ : Sum of X-ray intensity ratios measured by elements other than element o K _j-1 ; Correction calculation is performed by the sum of X-ray intensity ratios calculated by elements other than element o (S), and the procedure returns to step (F), Each element concentration C _ij (i =
a, b, c, ...) And the film thickness t _j , the above computer simulation is performed again. When the average value E is not larger than the set value β, the corrected concentration C _{ij of} each element
And the film thickness t _j are displayed on the CRT or the like as measured values (S). In the above embodiment, the case where the thin film and the substrate have a common element (oxygen O) has been described. However, even when the substrate has no common element, a certain element in the sample is
It can be applied even when the X-ray intensity ratio is difficult to measure, and when the bonding state of the element is known. The calculation method by computer simulation is omitted because it is described in detail in Japanese Patent Application No. 2-149528 filed by the applicant of the present application.

[0009]

According to the present invention, even if the thin film sample contains an element for which the measured X-ray intensity ratio is not obtained, the measured X-ray intensity ratio of each element bonded to the element and the bonding element By setting the actually measured X-ray intensity ratio of the element according to the concentration ratio of the element and the element concentration and the film thickness, it becomes possible to perform analysis using a computer simulation method. Even if there is a common element with the substrate, or even if it contains an element whose X-ray intensity ratio cannot be measured, it becomes possible to measure the element quantitatively and simultaneously measure the film thickness by the X-ray spectroscopic method. The performance of the analyzer was further improved.

[Brief description of drawings]

FIG. 1 is a flowchart of an embodiment of the present invention.

Claims (1)

Claim: What is claimed is: 1. A characteristic X-ray intensity of a component element emitted from a thin film sample of a known constituent element excited by an electron beam accelerated by an appropriate acceleration voltage, and the same accelerated electron as above. The ratio of the component element excited by the beam to the characteristic X-ray intensity (X-ray intensity ratio) radiated from the simple substance standard sample has been obtained by actually measuring it with an element for which it can be actually measured. X-ray intensity ratio of the element that cannot be obtained by measurement is obtained from the X-ray intensity ratio of the other element obtained above and the chemical bond form of the unmeasurable element and the other element, and The thickness of the thin film was calculated from the intensity ratio by the following formula [1], and the concentration of each component element of the thin film of the sample was assumed from the ratio of the X-ray intensity ratio,
Based on the assumed constituent element concentrations and the above-mentioned film thickness, the X-ray intensity ratio by calculation of each constituent element is calculated by simulation of the trajectory of the sample incident electrons, and the calculated X-ray intensity ratio is the X-ray intensity ratio by the above measurement. To be equal to the line intensity ratio,
The concentration of each component element and the film thickness are corrected, the same simulation as above is performed by using the corrected assumed concentration and film thickness, and the similar calculation is repeated, and the element concentration and the film thickness of the thin film sample are sequentially approximated. A method for measuring the thickness of a thin film sample and a quantitative elemental analysis method, characterized in that the determination is made. [Equation 1] However, ρ Z _ri = 7.0 (E _o ^1.65 −E _Ci ^1.65 ) μg
/ Cm ² E _o ; acceleration voltage, E _Ci ; X-ray excitation voltage of element i