JP2906506B2 - X-ray spectroscopy for thin film determination - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a thin film quantification method based on X-ray spectroscopy measured using computer simulation.

[Prior art]

There are few methods for non-destructively measuring the thickness of a thin film and the composition ratio of thin film elements of a sample in which a thin film is formed on a substrate by plating or the like. Usually, the thickness and composition ratio of a thin film are measured by measuring the composition ratio of the surface layer while removing the surface layer by etching or the like using an apparatus for analyzing the surface layer. In the method, since the measurement sample is destroyed, a sample that cannot be destroyed cannot be measured. As a non-destructive measurement method, there is a method utilizing the fact that the depth that can be analyzed by EPMA changes depending on the electron beam acceleration voltage, but there is a problem that the analysis accuracy is low.

[Problems to be solved by the invention]

An object of the present invention is to make it possible to easily perform quantitative measurement even when both the thickness of a thin film of a measurement sample and the concentration of each element are unknown.

[Means for Solving the Problems]

As a thin film quantitative method by X-ray spectroscopy, the characteristic X-ray intensity of the component elements emitted from the thin film of the sample excited by the electron beam accelerated at a certain appropriate accelerating voltage, and the same Assuming the concentration of each component element in the thin film of the sample from the X-ray intensity ratio with the characteristic X-ray intensity radiated from the simple standard sample of the component element, and changing the film thickness for the sample model having the assumed component element concentration Calculate the X-ray intensity ratio of one component element by computer simulation,
The X-ray intensity ratio by this calculation and the X
Assuming a film thickness such that the line intensity ratio appropriately matches, a computer simulation is performed using the assumed thin film element concentration and the thin film thickness, the X-ray intensity ratio of each component element is calculated by calculation, and the X Correcting each component element concentration so that the line intensity ratio becomes equal to the X-ray intensity ratio obtained by the above measurement,
The same computer simulation as described above was performed using the corrected thin film element concentration as the assumed concentration, and the same calculation was repeated to determine the thin film composition and the film thickness successively and approximately.

[Action]

The present invention intends to measure the element concentration C and the film thickness Z of a thin film of a sample by using an X-ray intensity calculation method by computer simulation in Japanese Patent Application No. 63-45287 filed by the present applicant. is there. In the computer simulation, the X-ray intensity is calculated from the acceleration voltage E of the electron beam, the concentration C of each element, the thickness Z of the thin film, and the composition of the sample substrate. According to the present invention, the thin film thickness Z and the respective element concentrations C _A , C _B , and C _{c are obtained} from the measurement data of the sample in which the thin film thickness Z and the respective element concentrations C are unknown under the above set conditions by the computer simulation calculation. Is what you want. Even when the composition ratio of the constituent elements A, B, C,... Of the thin film is constant, the mutual ratio of the characteristic X-ray intensity of each element changes depending on the film thickness. If the mutual ratio of the X-ray intensities does not change with the film thickness, the composition ratio can be immediately obtained from the mutual ratio of the characteristic X-ray intensities of the constituent elements of the sample. The film thickness can be determined from the change due to the film thickness, and the component ratio and the film thickness can be determined independently of each other. However, as described above, since the mutual ratio of the characteristic X-ray intensities of the component elements changes depending on the film thickness, the film thickness and the composition ratio cannot be determined independently as described above. However, in the case of a multi-component thin film, the change in characteristic X-ray intensity depending on the film thickness differs for each element, so that the film thickness and the composition ratio can be determined by the successive approximation method. First, let's clarify the definition of words. The ratio of the characteristic X-ray intensity of each element of the sample to the characteristic X-ray intensity of each single reference sample of the component elements A, B, C,... Of the sample is referred to as the X-ray intensity ratio of the component element. When the concentrations of the thin film component elements are determined, a change in the X-ray intensity ratio of each component depending on the film thickness is obtained by calculation as described later. The actual X-ray intensity ratios K _A0 , K _B0 ,... Of each component are determined from the actual measurement of the sample and each component standard sample. The first approximate concentrations C _A1 , C _B1 ,... Of each component are relatively determined from this intensity ratio.
When the composition of the sample is determined as described above, the change in the X-ray intensity ratio of one component A depending on the film thickness can be calculated as described above. From this calculation, it is obtained first approximation Z ₁ of film thickness. That is, the feature of the present invention is to first obtain an approximate value of the concentration of the component element,
The two steps of obtaining an approximate value of the thickness of the thin film by using it are one step of the successive approximation. As above, the first approximations C _A1 , C _B1 ,... And Z ₁
, The X-ray intensity ratio K _A1 ,
K _B1 , ... can be calculated. This intensity ratio often does not coincide with the actual measurement except for the component A. So one component A
The concentrations of the other elements B, C,... _Are corrected by C _B2 = C _B1 × K _B0 / K _B1 or the like. However, since C _A2 + C _B2 +... = 1, the concentration of the element A is also corrected to C _A2 . The C _A2, C _B2, under the component ratio of ......, X-ray intensity ratio of the element A is determined the thickness Z ₂ fit with the measured. The X-ray intensity ratio of each element is determined from the film thickness and the component composition. Hereinafter, the same procedure as described above is repeated to successively approximate. Given the composition and thickness of a thin film, the intensity ratio of characteristic X-rays of each component element can be calculated by computer simulation described later. That is, the ratio between the calculated value of the characteristic X-rays for each component standard sample and the calculated value of the characteristic X-ray intensity of each element when the film thickness and composition are set is the X-ray value of each element. It is an intensity ratio. The details of this calculation are
It is described in Japanese Patent Application No. 63-45287 filed by the present applicant.

【Example】

1 and 2 show a flowchart of one embodiment of the present invention. FIG. 1 shows a flowchart of the first stage, and FIG. 2 shows a flowchart of the second stage. In Figure 1, previously investigated surface layer (thin film) and the constituent elements of the substrate of the measurement sample before the measurement, the electron beam is irradiated to the sample S by a suitable acceleration voltage E _0, each element A thin film, B , C, the X-ray intensities I _AS , I _BS , and I _cS were measured (A), and the X-ray intensities I _AK ,
I _BK and I _cK were measured, and X of each element in the thin film and the standard sample was measured.
The line intensity ratios K _A0 , K _B0 , and K _c0 are calculated (A). Each element concentration C
_A1, a _{C B1, C c1, C A1} ; C B1; C c1 = K A0; K B0; K c0, C A1
+ C _B1 + C _c1 = 1, set the acceleration voltage of the electron beam to E ₀ , change the thin film thickness Z, perform computer simulation, and create a calibration curve between the thin film thickness Z and the intensity ratio K _A to using a calibration curve prepared (c), to set the film thickness Z ₁ corresponding to the intensity ratio K _A0 by measuring a first film thickness set value (d). The acceleration voltage is set to E ₀ , the concentration of each element is C _A1 , C _B1 , C _c1 , the thickness of the thin film Z ₁ , and the standard sample of each element are computer-simulated, and the intensity ratios K _A1 , K _B1 , K _c1 Is calculated (E). The concentrations C _Ai , C _Bi , and C _ci of the elements A, B, and C are represented by C _Ai ′ = C _Ai-i × K _A0 / K _Ai-i C _Bi ′ = C _Bi-i × K _B0 / K _{Bi− i} C _ci '= C _ci-i × K _c0 / K _ci-i C _Ai = C _Ai ' / (C _Ai '+ C _Bi ' + C _ci ') C _Bi = C _Bi ' / (C _Ai '+ C _Bi ' + C _ci ′) Set as C _ci = C _ci ′ / (C _Ai ′ + C _Bi ′ + C _ci ′) (f). Here, i is the number of successive approximation calculations, and the first time (i = 1) has already been assumed in the operation (c). Therefore, i = 2, 3,... Acceleration voltage E ₀ , each element concentration C _Ai , C _Bi , C _ci , thin film thickness Z
Is changed and computer simulation is performed to create a calibration curve between the thin film thickness Z and the intensity ratio K _A (g). , Using a calibration curve prepared obtains the film thickness Z ₁ corresponding to the intensity ratio K _A0 by measuring an acceleration voltage E _0, the element concentration K _Ai, K _Bi,
A computer simulation is performed on the sample with K _ci and the thin film thickness Z _i to calculate the intensity ratios K _Ai , K _Bi , and K _ci (h).
It is determined whether or not the obtained intensity ratios K _Ai , K _Bi , and K _ci match the intensity ratios K _A0 , K _B0 , and K _c0 obtained by the measurement (q).
If they match, the analysis operation ends as the values of the film thickness and the concentration of each component set in step (f). In this embodiment, the same operation as described above is performed by further changing the electron acceleration voltage in order to confirm the correctness of each value determined in the above step (v). FIG. 2 shows the operation. If they do not match, the process returns to operation (f). In FIG. 2, the acceleration voltage varied to different appropriate values E ₁ and the first stage, each element A thin film, B, X-ray intensity I _AS of C ', I _BS', to measure the I _cS ' (A), X-ray intensities I _AK ′ of standard samples of each element A, B, C
I _BK ′ and I _cK ′ are measured, and the X-ray intensity ratios K _A0 ′, K _B0 ′, and K _c0 ′ of each element in the thin film and the standard sample are calculated (i). The accelerating voltage of the electron beam and E _1, the element concentration C _Ai, C _Bi, C
_ci, a sample of the film thickness Z _1, performs a computer simulation in a standard sample of each element, the intensity ratio K _Ai ',
Calculate K _Bi ′ and K _ci ′ (U). The calculated intensity ratios K _Ai ′, K _Bi ′, and K _ci ′ are the intensity ratios obtained by measurement.
It is determined whether they are equal to K _A0 ′, K _B0 ′, and K _c0 ′ (E). If they are equal, the concentrations C _Ai , C _Bi , and C _ci are displayed on a CRT or the like as the concentrations of the _constituent elements A, B, and C of the sample, and Z ₁ is the thin film thickness. If not equal, each element concentration C _Ai , C _Bi , C
_{Let ci} be 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 ') C _ci = C _ci ' / ( C _Ai ′ + C _Bi ′ + C _ci ′), and returns to the operation (g) in FIG.

【effect】

According to the present invention, it is possible to obtain the concentration of each element and the thickness of a thin film in which the measured intensity ratio and the calculated intensity ratio of each element are equal by computer simulation using two different acceleration voltages. Qualitative analysis by X-rays can be performed even when both of the thin film thickness are unknown.

[Brief description of the drawings]

FIG. 1 is a flowchart of a first step of an embodiment of the present invention;
FIG. 2 is a flowchart of the second stage of the above embodiment.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-244844 (JP, A) JP-A-1-219550 (JP, A) JP-A-3-209148 (JP, A) JP-A-4- 42037 (JP, A) JP-A-4-2956 (JP, A) JP-A-4-43944 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 23/22-23 / 227

Claims (1)

(57) [Claims] 1. A certain suitable accelerating voltage each component element A is radiated from the thin film of the excited sample at an accelerated electron beam at E _0,
X-ray intensity ratio K _A0 between the characteristic X-ray intensity of B ... and the characteristic X-ray intensity of each element emitted from the single reference sample of each of the above-mentioned component elements A, B ... excited by the same accelerated electron beam as above. , K _B0 …
From the first approximation concentration C _A1 , C _B1 of each element of the sample thin film
The X-ray intensity ratio K _A of one component element _A is calculated by computer simulation using a sample model having the respective assumed component element concentrations and varying film thicknesses, and the calculated value and the measured X-ray First such that the intensity ratio K _A0 matches
Obtains an approximate thickness Z _1, first approximation concentration C _A1 of the assumed thin film elements, C _B1 ... and performs a computer simulation in a sample model having a film thickness Z ₁ described above assumption, X-rays intensity ratio K by computing _A1 , K _B1 ... are obtained, and the component element concentrations are corrected so that the X-ray intensity ratio obtained by the same calculation becomes equal to the X-ray intensity ratio K _A0 , K _B0 . The thin film element concentrations C _A2 , C _B2 ... Are assumed concentrations, the film thickness is changed, and the same computer simulation as above is performed.
_A0 and second seek thickness Z ₂ approximate matching, the C _A2, C _B2 ...
Using this Z ₂ and the same computer simulation as above, the concentration of each component element is corrected so that the calculated X-ray intensity ratio of each component element becomes equal to the actually measured X-ray intensity ratio K _A0 , K _B0 . A thin film quantification method by X-ray spectroscopy, wherein a thin film composition and a film thickness are determined by successively and approximately repeating a calculation of obtaining a third approximate concentration.