JP3010598B2 - X-ray spectroscopic analysis method of a sample covered with a thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quantitatively analyzing a sample covered with a thin film by X-ray spectroscopy.

[0002]

2. Description of the Related Art Usually, in an X-ray analyzer such as EPMA,
Quantitative analysis is performed by measuring the wavelength and intensity of X-rays emitted from a sample by electron irradiation, and examining the type of element based on the wavelength of the X-rays and the concentration based on the X-ray intensity. Conventionally, in the case of a sample covered with a thin film, the measurement was performed ignoring the effect of the thin film. In particular, in the case of depositing a conductive thin film on an insulator sample or the like to prevent electrification due to electron irradiation, it was almost ignored. However, since the absorption of characteristic X-rays in a thin film differs depending on the wavelength, the effect of the thin film differs depending on the sample component element, which affects the measurement result, and it is difficult to obtain a highly accurate measurement result. there were.

[0003]

SUMMARY OF THE INVENTION The present invention provides an X-ray spectroscopic quantitative analysis of a sample covered with a thin film, and a correction for removing the influence of the thin film when the thickness and the composition of the thin film are known. To obtain a highly accurate measurement result.

[0004]

In an X-ray spectroscopic analysis method, an electron beam is irradiated with an electron beam accelerated at a predetermined accelerating voltage.
Are, each property characteristic X-ray measuring the intensity of the component elements to be emitted from the measurement sample coated with a thin film due to absorption of the surface film X
The characteristic X-ray intensity before attenuation is obtained by dividing by the attenuation rate of the linear intensity, and this intensity and the standard sample of each component element are converted to the above-mentioned electronic beam.
Irradiation with an electron beam accelerated at the same accelerating voltage as the beam
Then, X of the characteristic X-ray intensity radiated from the standard sample
Assuming each element concentration of the measurement sample from the line intensity ratio, the X-ray intensity ratio of each characteristic X-ray of the standard sample and the measurement sample is theoretically calculated from the assumed element concentration of the measurement sample by the theoretical calculation. Is adjusted to be equal to the X-ray intensity ratio obtained by the above measurement, and the same theoretical calculation as above is performed by using the corrected respective element concentration as the assumed concentration. The composition of the measurement sample was determined approximately.

[0005]

The present invention is based on Japanese Patent Application No. 63-63, filed by the present applicant.
No. 45287 is intended to perform quantitative analysis correction of a sample covered with a vapor-deposited film by using an X-ray intensity calculation method by computer simulation. By the computer simulation, the X-ray intensity can be theoretically calculated from the acceleration voltage E of the electron beam and the element concentrations C of the deposited film and the sample. In this calculation, the concentration of each component element needs to be known. However, from the measurement data of the sample in which the concentration C of each element is unknown, it is assumed that the concentration of the component element is assumed, and the above-described theoretical calculation is successively performed. Element concentration C
_A , C _B , C _C ,... Are obtained. That is, the concentration of each component is determined so that the mutual ratio of the characteristic X-ray intensity ratios of the respective components according to the theoretical calculation matches the mutual ratio of the characteristic X-ray ratios measured for the sample.

Since the measured X-ray intensity of the sample used in the above-described successive approximation calculation is a value when there is no thin film, if there is a thin film, it is necessary to correct the measured intensity for absorption by the thin film. Even if the composition ratio of the constituent elements A, B, C,... Of the sample is constant, the mutual ratio of the characteristic X-ray intensity of each element changes depending on the composition and thickness of the deposited film. However, since the composition and thickness of the deposited film are known, the effect of the deposited film on the characteristic X-ray intensity of each component element of the sample, that is, the surface thin film of the characteristic X-ray intensity of each component element radiated from the sample, The attenuation factor due to absorption is obtained by calculation, and it is possible to obtain each characteristic X-ray intensity when there is no surface film from each characteristic X-ray intensity directly measured for the sample. Just do it.

Since the characteristic X-ray intensity when there is no surface film is obtained and the successive approximation calculation is started, the convergence of the successive approximation is faster than when the calculation is started without the absorption correction of the surface film.

[0008]

FIG. 1 is a flowchart showing one embodiment of the present invention. In the figure, previously examined qualitative composition and thickness of the constituent elements and deposited film of sample S, an electron beam with an appropriate acceleration voltage E ₀ is applied to the sample S prior to measurement, the measurement sample S
The characteristic X-ray intensities I _AS , I _BS , and I _CS of each of the elements A, B, and C were measured (A), and the pure standard sample K of each of the elements A, B, and C was placed on top.
The same standard sample when irradiated with an electron beam at the accelerating voltage E _O
Characteristic X-ray intensity of each component element to be emitted from the I _AK, I _BK,
I _CK was measured (a), and sample S obtained by the above measurement was measured.
From the characteristic X-ray intensities I _AS , I _BS , and I _CS of the standard sample K and the characteristic X-ray intensities I _AK , I _BK , and I _{CK of} the standard sample K,
The linear intensity ratio K _A0 = I _AK / I _AS (the same applies hereinafter), K _B0 , and K _C0 are calculated (C). For the absorption correction by the thin film of the X-ray intensity ratio K _Z0 (Z = A, B, C), a correction coefficient may be obtained experimentally for each characteristic X-ray, but when the surface thin film is an artificial film. Since the film thickness, composition, and composition are known, the attenuation factor due to absorption can be obtained by calculation. Therefore, by dividing the K _Z0 attenuation rate due to the surface film of the elements characteristic X-ray by any method performs attenuation correction of the X-ray intensity ratio K _Z0, corrected X-ray intensity at which the film does not exist _{Determine the} ratio H _Z0 . The correction by calculation is calculated, for example, as follows. _{H Z0 = K Z0 / exp (} -μρz) [ where, [rho; density, z; _{depth] b μ = Σ μ Fn C} n [ where, n = a, b] n = a , however, mu _Fn; element Z Mass absorption coefficient C _{n of} X-rays generated from element n due to element n; concentration of element n in thin film First approximate concentration of each element A, B, C using corrected X-ray intensity ratio H _Z0 obtained by the above calculation C _A1 , C _B1 , C _C1
C _Z1 = H _Z0 / ΣH _Z0 [where Z = A, B, C] Z = A, and the composition and film thickness of the deposited film, the acceleration voltage E _{0 of the} electron beam, etc. Set (D). The characteristic X-ray intensities of the measurement sample S of each element concentration C _A1 , C _B1 , C _C1 set in the above operation and the elements A, B, C of the standard sample K of each element are theoretically calculated, and the first approximate concentration is calculated. C _A1 , C _B1 , C _C1
X-ray intensity ratio K _A1 , K _B1 , K _C1 of each element A, B, C
Is calculated (E). The error value E (i) is calculated by E (i) = Σ
| (K _Z0 −K _Zi ) / K _Z0 |
(I) It is determined whether <ε ₀ (g). Here, Z is the element A, B, C, and i is the number of successive approximation calculations, and ε ₀ is an appropriate value. If E (i) <ε _0, it is determined that the correction calculation has been properly performed, and the respective element concentrations C _Z obtained by the calculation are displayed on the display device (h). In the (i-1) th successive approximation calculation,
When E (i−1) <ε ₀ is not satisfied, the calculation of the assumed elemental concentrations C _{Zi in} the i-th successive approximation calculation is performed as in the following equation. Each element A, B, the concentration C _Ai of C, C _Bi, a _{C Ci, C Ai '= C} Ai-1 × K A0 / K Ai-1 C Bi' = C Bi-1 × K B0 / K Bi- _{1 C Ci '= C Ci-} 1 × K C0 / K Ci-1 C Ai = C Ai' / (C Ai '+ C Bi' + C Ci ') C Bi = C Bi' / (C Ai '+ C Bi' + C _{Ci ′} ) It is obtained as C _Ci = C _{Ci ′} / (C _{Ai ′} + C _{Bi ′} + C _{Ci ′} ), and the i-th approximate density C _Zi is set (q). Each element concentration C _Ai , C _Bi , C set in the above operation (g)
The characteristic X of each component of the measurement sample is determined by _Ci and the acceleration voltage E ₀ .
The theoretical calculation of the line intensity is performed, and the intensity ratios K _Ai , K _Bi , and K _Ci are calculated (コ). Hereinafter, the operations from the operation (f) to the operation (h) are repeated until a determination of YES is made in the operation (g).

In the above embodiment, the component elements are described as being limited to the three elements A, B, and C. However, even when the number of component elements is four or more, the element concentration can be determined by the same method. is there.

The details of the calculation for obtaining the characteristic X-ray intensity of each component element of the sample based on the theory described above are described in Japanese Patent Application No. 63-45287 filed by the present applicant, and are incorporated into the sample. The trajectory of the electrons in the sample is traced by the Monte Carlo simulation method, and the X-ray intensity is calculated from the probability of interaction of the sample components with atoms during that time.

[0011]

According to the present invention, the concentration is determined so that the measured value of the X-ray intensity ratio and the theoretically calculated value assuming the concentration are determined, whereby the measurement of each element in the sample covered with the thin film is performed. The concentration of each element is obtained successively approximately. However, as a first approximate concentration, the absorption of the thin film is corrected for the measured X-ray intensity, and the concentration of each component is assumed from the corrected element characteristic X-ray intensity. sequential convergence calculation becomes faster, high-precision quantitative analysis of a sample covered with a thin film, and Tsu name so that it can be performed at high speed.

[Brief description of the drawings]

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 23/22-23/227

Claims (1)

(57) [Claims] A predetermined acceleration of a measurement sample covered with a thin film;
When irradiating with an electron beam accelerated by a voltage, the characteristic X-ray measurement intensity of the component element radiated from the measurement sample is divided by the attenuation rate of each characteristic X-ray intensity due to absorption of the surface thin film, and the intensity before the attenuation is determined. Each characteristic X-ray intensity is obtained, and the intensity and the same accelerating voltage for exciting the standard sample of each component element to the above measurement sample
Assuming each element concentration of the measurement sample from the X-ray intensity ratio with the characteristic X-ray intensity emitted from the standard sample when irradiated with the electron beam accelerated at The X-ray intensity ratio of each characteristic X-ray of the standard sample and the measurement sample is calculated from the theoretical calculation, and the concentration of each component element is corrected 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 theoretical calculation as above is performed using the corrected component element concentrations as assumed concentrations, and thereafter, by repeating the same calculations, the composition of the sample covered with the thin film is characterized in that the measurement sample composition is successively and approximately determined. X-ray spectroscopy method.