JP2000321223A - Multilayer thin-film composition measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure composition even if a common element exists in a multilayer film by detecting each fluorescent X-ray intensity of a common element MB and non-common elements MA and MC and calculating the MB intensity of an upper-layer film according to the intensity ratio of MB and MC being calculated from the specific known lower-layer thin-film composition ratio. SOLUTION: In a sample SP, a multilayer thin film consisting of an upper-layer film containing a non-common element MA and a common element MB and a lower-layer film containing the common element MB and the non-common element MC is formed on a substrate. The intensity of fluorescent X rays where the elements MA, MB, and MC are generated is detected by an X-ray detector 4 from a part where an excitation light source X1 of a low incidence angle is applied from an X-ray source 1 to the sample SP. Then, the fluorescent X-ray intensity ration of both the elements originating from the lower-layer film is obtained from the composition ratio of the common element MB and the non-common element MC of the specific known lower-layer film. The fluorescent X-ray intensity of the common element MB originating from the upper-layer film is calculated from the intensity ratio, and the composition ratio between both the elements MA and MB on the upper-layer film is calculated based on the fluorescent X-ray intensity ratio of the common element MB and the non-common element MA of the upper-layer film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the composition of a multilayer thin film by irradiating a sample with excitation X-rays and detecting the fluorescent X-rays generated from the multilayer thin film to measure the composition of the multilayer thin film. .

[0002]

2. Description of the Related Art Recently, a technique in which a perovskite-based metal oxide is formed on a silicon wafer and used as a dielectric for a capacitor of, for example, a DRAM (Dynamic Random Access Memory) has been put into practical use. Among metal oxides, BST {(Ba, Sr) TiO ₃ } has a high dielectric constant, so that it can be formed small and has a large capacitance, and its application to a gigabit-class DRAM is being studied. The use of SRO (SrRuO ₃ ), which exhibits conductivity among the same perovskite-based metal oxides, has been studied as an electrode material having excellent compatibility with such a perovskite-based dielectric.

When these BSTs and SROs are laminated as thin films on a semiconductor wafer, changes in the element composition of each thin film greatly affect the characteristics of the integrated circuit. Further, the composition of the multi-component metal oxide is likely to change due to fluctuations in film forming conditions. Therefore, in order to stabilize product quality, it is important to accurately measure the element composition of a thin film.

As a method of measuring the composition of a thin film, a fluorescent X-ray method capable of nondestructively inspecting is effective. The fluorescent X-ray method is a method of irradiating a sample with excitation X-rays and analyzing the spectrum of fluorescent X-rays generated from the sample, thereby specifying an element corresponding to characteristic X-rays.

[0005]

When a sample is a thin film formed on a substrate, irradiation with excitation X-rays generates characteristic X-rays specific to the constituent elements of the substrate and the constituent elements of the thin film. For example, when a single-layer BST film is formed on a Si (silicon) substrate, Si characteristic X-rays are generated from the Si substrate, and Ba (barium) characteristic X-rays, Sr (strontium) characteristic X-rays, and Ti (Titanium) Characteristic X-rays are generated. In this case, since there is no common element, separation of each characteristic X-ray becomes easy.

However, when a multilayer thin film composed of a BST film and an SRO film is formed on a Si substrate, Si characteristic X-rays are generated from the Si substrate and Ba characteristic X-rays are generated from the BST film.
X-ray, Sr characteristic X-ray and Ti characteristic X-ray
Sr characteristic X-rays and Ru (ruthenium) characteristic X-rays are generated from the film. In this case, since Sr is an element common to both thin films, the composition of each thin film cannot be accurately determined unless it is possible to specify which thin film the Sr characteristic X-ray originates from.

An object of the present invention is to provide a method for measuring the composition of a multilayer thin film which can accurately measure the composition of the multilayer thin film even when a common element is present in the multilayer thin film.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a method of exciting X-rays toward a substrate having a multilayer thin film composed of an upper film and a lower film on which a common element MB and non-common elements MA and MC are present, respectively. A method of measuring the composition of the multilayer thin film by irradiating the X-rays and detecting the fluorescent X-rays generated from the multilayer thin film, comprising:
And specifying the composition ratio Kb of the non-common element MC;
Irradiating excitation X-rays at an incident angle θL to detect respective intensities of fluorescent X-rays of the common element MB and non-common elements MA and MC generated from the multilayer thin film, and based on the composition ratio Kb,
Calculating the intensity ratio ILb of the fluorescent X-rays of the common element MB and the non-common element MC derived from the lower layer at the incident angle θL; and, based on the intensity ratio ILb, the fluorescent X-rays at the incident angle θL derived from the upper layer. Calculating the intensity of the fluorescent X-rays of the common element MB, and the ratio I between the intensity of the fluorescent X-rays of the common element MB derived from the upper layer film and the intensity of the fluorescent X-rays of the non-common element MA
Calculating the composition ratio Kt of the common element MB and the non-common element MA of the upper layer film based on Lt.

According to the present invention, when the excitation thin film is irradiated with the excitation X-ray, the fluorescent X-ray from the common element MB of the upper film, the fluorescent X-ray from the non-common element MA of the upper film, and the common element of the lower film. X-ray fluorescence from MB and non-common element MC in lower layer film
X-rays are mixed and generated. Non-common element MA,
Since the spectrum of MC is different, it can be measured alone, but since the common element MB is present in both thin films,
It cannot be distinguished from which thin film the fluorescent X-rays of the common element MB originate.

Further, in the case of a single film sample formed only of the upper layer film, since there is no common element, the composition ratio of the non-common element MA and the common element MB in the upper layer film and the intensity ratio of each fluorescent X-ray are different. Can be accurately determined. Similarly, in the case of a single film sample formed only of the lower layer film, since the common element does not exist, the non-common element MC and the common element M of the lower layer film do not exist.
The correspondence between the composition ratio of B and the intensity ratio of each fluorescent X-ray can be accurately determined.

[0011] Excited X-rays are incident on a multilayer thin film at a low incident angle θ.
When irradiated with L, the X-ray absorption in the upper layer film increases,
The intensity of the fluorescent X-rays derived from the upper layer film increases, and the amount of composition information on the upper layer film increases.

Therefore, the intensity of the fluorescent X-rays from the non-common element MC of the lower layer film is detected by irradiating at a low incident angle θL.
Since the relationship between the composition ratio and the fluorescent X-ray intensity ratio is known by using the composition ratio Kb of the underlayer film specified in advance, the fluorescence X derived only from the common element MB of the underlayer film is known.
The intensity of the line can be calculated. By subtracting the calculated intensity from the intensity of the fluorescent X-rays of the common element MB derived from both films, the intensity of the fluorescent X-rays derived only from the common element MB of the upper layer film can be calculated.

Next, the calculated common element MB derived from the upper layer film
By referring to the correspondence relationship between the composition ratio of the non-common element MA and the common element MB of the upper layer film specified in advance and the intensity ratio of each fluorescent X-ray by using the intensity of the fluorescent X-ray of the upper layer film, Composition ratio Kt of common element MB and non-common element MA
Can be calculated.

As a method of specifying the composition ratio Kb of the lower film, a) the chemical composition ratio of the compound constituting the lower film is used as it is, and b) a single film sample prepared only with the lower film is quantitatively analyzed. It is possible to use the result.

When a plurality of non-common elements MA and MC and a plurality of common elements MB exist, the present invention can be applied by narrowing down to specific elements.

Further, according to the present invention, the excited X-rays are incident at an incident angle θH (θH
> ΘL) to detect the intensity of the fluorescent X-rays of the common element MB and the non-common elements MA and MC generated from the multilayer thin film, and, based on the composition ratio Kt, the intensity of the upper layer film at the incident angle θH Calculating the intensity ratio IHt of the fluorescent X-rays of the common element MB and the non-common element MA, and
Calculating the intensity of the fluorescent X-rays of the common element MB derived from the lower layer out of the fluorescent X-rays at the incident angle θH based on Ht; The composition ratio Kb of the common element MB and the non-common element MC in the lower layer film is determined based on the ratio IHb of the intensity of the fluorescent X-rays of the MC to the intensity.
And a step of newly calculating

According to the present invention, irradiation is performed at an incident angle θH higher than the incident angle θL, and the common element MB generated from the multilayer thin film is irradiated.
And the intensity of the fluorescent X-rays of the non-common elements MA and MC are detected, and the composition ratio Kt calculated by irradiation at the incident angle θL
Since the relationship between the composition ratio and the fluorescent X-ray intensity ratio is known by using, it is possible to calculate the fluorescent X-ray intensity ratio IHt of the common element MB and the non-common element MA derived from the upper layer film. From the intensity ratio IHt, the intensity of fluorescent X-rays derived only from the common element MB of the lower layer film can be calculated.

Next, the calculated common element MB derived from the lower layer film
Since the relationship between the composition ratio and the fluorescent X-ray intensity ratio is known using the ratio IHb between the intensity of the fluorescent X-ray and the intensity of the fluorescent X-ray of the non-common element MC, the common elements MB and The composition ratio Kb of the non-common element MC can be newly calculated.

Excited X-rays are incident on a multilayer thin film at a high incident angle θ.
When irradiation is performed at H (θH> θL), the X-ray absorption in the upper film is reduced, so that the intensity of the fluorescent X-rays originating from the lower film is increased and the amount of information on the composition of the lower film is increased. for that reason,
The accuracy of measuring the composition ratio Kb of the lower layer film is further improved.

The composition ratio Kb thus calculated is adopted as a new predetermined value, and the above-described calculation steps, ie, the step of calculating the intensity ratio ILb of the fluorescent X-rays originating from the lower layer at the incident angle θL, By repeating the process of calculating the intensity of the fluorescent X-ray of the common element MB and the process of calculating the composition ratio Kt of the upper layer film, the measurement accuracy of the composition ratio Kt can be further improved. The obtained composition ratio Kt is adopted as a new default value, and the above-described calculation steps, that is, the step of calculating the intensity ratio IHt of the fluorescent X-rays derived from the upper layer film at the incident angle θH, and the step of calculating the lower layer film at the incident angle θH By repeating the step of calculating the intensity of the fluorescent X-ray of the common element MB and the step of calculating the composition ratio Kb of the lower layer film, the measurement accuracy of the composition ratio Kb can be further improved. In addition, since the accuracy can be improved by such regression calculation, the accuracy of the composition ratio Kb as an initial value can be relaxed.

Further, according to the present invention, a silicon substrate having a multilayer thin film composed of an upper BST film and a lower SRO film formed thereon is irradiated with excitation X-rays to detect fluorescent X-rays generated from the multilayer thin film. A method for determining the composition ratio KSR of Sr and Ru in the SRO film, and irradiating excited X-rays at a low incident angle θL to obtain Ba, Detecting the intensity of each of the fluorescent X-rays XBa, XSr, XTi, and XRu of Sr, Ti, and Ru; and determining the intensity ratio of the fluorescent X-rays XSr, XRu derived from the SRO film at an incident angle θL based on the composition ratio KSR. Calculating the ILSR, and the incident angle θL based on the intensity ratio ILSR.
Calculating the intensity of the fluorescent X-ray XSr derived from the BST film among the fluorescent X-rays XSr in the above, and the BST film based on the ratio ILSBT between the intensity of the fluorescent X-ray XSr derived from the BST film and the fluorescent X-rays XBa and XTi. Calculating the composition ratio KBST of Ba, Sr, and Ti.

According to the present invention, when the excitation X-ray is irradiated on the multilayer thin film, the fluorescent X-ray XSr from Sr, which is a common element of the upper BST film, and Ba, T, which are non-common elements of the BST film,
The fluorescent X-rays XBa and XTi from i, the fluorescent X-ray XSr from Sr which is a common element of the lower SRO film, and the fluorescent X-ray XRu from Ru which is a non-common element of the SRO film are mixed and generated. Since the non-common elements Ba, Ti, and Ru have different spectra, they can be measured independently, but the common elements Sr
Cannot be distinguished from which thin film the fluorescent X-ray XSr originates from.

In the case of a single film sample formed only of the BST film, since no common element exists, the BST film
a, Sr, Ti composition ratio and each fluorescent X-ray XBa, XSr, XTi
Can be accurately determined. Similarly, S
In the case of a single film sample formed only of the RO film, since there is no common element, the correspondence between the composition ratio of Sr and Ru in the SRO film and the intensity ratio of each of the fluorescent X-rays XSr and XRu is accurately determined. it can.

Excited X-rays are incident on a multilayer thin film at a low incident angle θ.
When irradiated with L 2, the X-ray absorption in the upper BST film increases, so that the intensity of the fluorescent X-rays derived from the BST film increases, and the amount of composition information on the BST film increases.

Therefore, irradiation at a low incident angle θL is performed to
The relationship between the composition ratio and the fluorescent X-ray intensity ratio is known by detecting the intensity of the fluorescent X-ray XRu from the Ru of the O film and using the previously specified composition ratio KSR of the SRO film. Thus, the intensity of the fluorescent X-ray XSr derived only from Sr of the SRO film can be calculated. By subtracting the calculated intensity from the intensity of the fluorescent X-ray XSr derived from both films, the intensity of the fluorescent X-ray XSr derived only from the Sr of the BST film can be calculated.

Next, the calculated fluorescent X-rays X
Using the intensity of Sr, the BST film B
a, Sr, Ti composition ratio and each fluorescent X-ray XBa, XSr, XTi
By referring to the correspondence with the intensity ratio of
The composition ratio KBST of the film can be calculated.

As a method of specifying the composition ratio KSR of the SRO film, a) a chemical composition ratio of Sr and Ru of the SRO compound of 1: 1 is used as it is, and b) a single film sample prepared only with the SRO film. It is possible to use the results of quantitative analysis.

Further, according to the present invention, the excited X-rays are incident at an incident angle θH (θH
> ΘL), Ba, Sr, T generated from the multilayer thin film
i, the step of detecting the intensity of each of the fluorescent X-rays XBa, XSr, XTi, and XRu, and the fluorescent X-rays XBa, XSr, and XTi derived from the BST film at an incident angle θH based on the composition ratio KBST.
Calculating the intensity ratio of the fluorescent X-rays XSr derived from the SRO film among the fluorescent X-rays at the incident angle θH based on the intensity ratio IHBST; Based on the ratio IHSR between the intensity of XSr and the intensity of the fluorescent X-ray XRu, the composition ratio KSR of Sr and Ru of the SRO film is determined.
And a step of newly calculating

According to the present invention, irradiation is performed at an incident angle θH higher than the incident angle θL so that Ba, Sr,
The relationship between the composition ratio and the fluorescent X-ray intensity ratio is obtained by detecting the intensity of each of the fluorescent X-rays XBa, XSr, XTi and XRu of Ti and Ru and using the composition ratio KBST calculated by irradiation at the incident angle θL. Is known, the intensity ratio IHBST of the fluorescent X-rays XBa, XSr, and XTi derived from the BST film can be calculated. From the intensity ratio IHBST, the intensity of the fluorescent X-ray XSr derived from the SRO film can be calculated.

Next, the calculated fluorescent X-rays X
Using the ratio IHSR between the intensity of Sr and the intensity of the fluorescent X-ray XRu,
Since the relationship between the composition ratio and the fluorescent X-ray intensity ratio is known, the composition ratio KSR of the SRO film can be newly calculated.

Excited X-rays are incident on a multilayer thin film at a high incident angle θ.
Irradiation at H (θH> θL) reduces the X-ray absorption in the upper BST film, so the fluorescent X originating from the lower SRO film
The intensity of the line increases, and the amount of composition information on the SRO film increases. Therefore, the accuracy of measuring the composition ratio KSR of the SRO film is further improved.

The composition ratio KSR calculated in this manner is adopted as a new predetermined value, and the intensity ratio ILSR of the fluorescent X-rays derived from the SRO film at the incident angle θL is calculated by using the above-described calculation steps.
, The step of calculating the intensity of the fluorescent X-ray XSr derived from the BST film, and the step of calculating the composition ratio KBST of the BST film can be further improved in the measurement accuracy of the composition ratio KBST. Obtained composition ratio KBS
T is adopted as a new default value, and the fluorescence X derived from the BST film at the incident angle θH
Measuring the composition ratio KSR by repeating the steps of calculating the intensity ratio IHBST of the X-ray, the step of calculating the intensity of the fluorescent X-ray XSr derived from the SRO film at the incident angle θH, and the step of calculating the composition ratio KSR of the SRO film. Accuracy can be further improved. Further, since the accuracy can be improved by such regression calculation, the accuracy of the composition ratio KSR as an initial value can be relaxed.

Further, the present invention is characterized in that monochromatic X-rays are used as excitation X-rays.

According to the present invention, the lower the incident angle of the excited X-ray, the longer the X-ray passage distance in the upper layer film.
The effective extinction length, which defines the distance until the original intensity attenuates to a certain value after the excitation X-rays pass, varies depending on the X-ray energy (wavelength) and the elements constituting the medium. Therefore, as the X-ray passing distance in the upper layer becomes longer, the influence of the energy distribution of the excited X-rays appears as a measurement error. Therefore, it is preferable to make the excited X-rays monochromatic as a countermeasure.

[0035]

FIG. 1 is a block diagram showing an X-ray fluorescence analyzer according to the present invention. An X-ray fluorescence analyzer includes an X-ray source 1 for generating beam-like X-rays, and a spectral crystal 2 for separating a single characteristic X-ray from the X-rays from the X-ray source 1 to monochromatic. And X diffracted in a predetermined direction by the spectral crystal 2
A slit member 3 for extracting a line, an X-ray detector 4 for detecting fluorescent X-rays generated from a portion of the sample SP irradiated with the excitation X-ray X1, and a sample holding unit for holding the sample SP It is composed of a mechanism 5 and the like. Sample holding mechanism 5
Can adjust the angle and the three-dimensional position of the sample SP, thereby changing the incident angle θ and the irradiation area of the excitation X-ray. As the X-ray detector 4, an energy dispersion type or wavelength dispersion type detector is used.

The sample SP to which the present invention is applied is composed of an upper layer containing the non-common element MA and the common element MB and the common element MB.
And a lower layer film including a non-common element MC formed on a substrate.
A silicon wafer on which a multilayer thin film composed of a film and a lower SRO film is formed is illustrated.

Next, the principle of the present invention will be described. First, a method for measuring the composition of the single-layer film will be described. Excitation X
When a line is irradiated at a high incident angle θ, the fluorescent X-ray intensity of each element of the single-layer film is expressed by the following equation (1). Here, Iz is the fluorescent X-ray intensity of element Z, kz is the device sensitivity coefficient of element Z, Cz
z is the content (mass ratio) of the element Z, ρ is the density of the film, and t is the thickness of the film. Iz = kz · Cz · ρ · t (1)

At this time, if the single-layer film is sufficiently thin, the absorption of the excitation X-rays and the absorption of the fluorescent X-rays by the film can be ignored. When the purpose is only the composition analysis, the parameter can be reduced as in the following equation (2) by relative comparison with another arbitrary element ZO. Iz / Izo = (kz.Cz) / (kzo.Czo) (2)

Here, a reference sample whose composition Cz is known for all the elements is prepared, and the fluorescent X-ray intensities Iz of all the elements are measured.
Is required. Here, Iz, R is the fluorescent X-ray intensity of the element Z in the reference sample, and Cz, R is the content (mass ratio) of the element Z in the reference sample. kz / kzo = (Iz, R · Cz, R) / (Izo, R · Cz, R) (3)

If the apparatus sensitivity coefficient is determined in this way, the composition Cz can be determined by solving the following simultaneous equations (4) and (5) by measuring the fluorescent X-ray intensity even for an unknown sample. Czo / Cz = (kz · Izo) / (kzo · Iz) (4) ΣCz = 1 (total for element Z = 1) (5)

Next, when the oblique incidence method is used, the following equations (6) and (7) generally hold. Here, dz and dzo are the effective extinction lengths of the excited X-rays corresponding to the elements Z and ZO. Iz = kz · Cz · ρ · dz (6) Izo = kzo · Czo · ρ · dzo (7)

Dz and dzo are determined by the absorption of excited X-rays by the film. Note that the absorption of fluorescent X-rays by the film is ignored. Similarly to the above-mentioned formula (2) of the high-angle incidence method, the fluorescent X-ray intensity ratio of the elements Z and ZO can be obtained as in the following formula (8). Iz / Izo = (kz.Cz.dz) / (kzo.Czo.dzo) (8)

Therefore, only the element of dz / dzo differs from the high-angle incidence method, but by making the excitation X-ray monochromatic, dz / dzo = 1, which agrees with the equation (2). Therefore, if monochromatic excitation X-rays are used, the same calculation formula as in the high-angle incidence method can be used in the oblique incidence method, and the calculation process can be simplified.

Next, a method for measuring the composition of the multilayer film will be described. FIG. 2 is an explanatory diagram when the excitation X-ray X1 is incident at a low incident angle θL, and FIG. 3 is an explanatory diagram when the excitation X-ray X1 is incident at a high incident angle θH (θH> θL). The measurement sample is a silicon wafer on which a multilayer thin film including an upper BST film and a lower SRO film is formed.

First, as shown in FIG. 2, when the incident angle .theta.L of the excitation X-ray X1 is set to a sufficiently low angle, for example, 0.1 degree, the X-rays of Ba, Sr and Ti are emitted from the upper BST film. XBa, XSr and XTi are generated relatively strongly, and the SR
The fluorescent X-rays XSr and XRu of Sr and Ru are weakly generated from the O film. At this time, since Sr exists in both the BST film and the SRO film, it cannot be distinguished from which film the detected fluorescent X-ray XSr is derived.

In general, when X-rays are obliquely incident on a thin film having a two-layer structure, the intensity of the detected fluorescent X-rays is expressed by the following equations (9) to (1).
It can be described as 1). Here, I1, z and I2, z are the first
X-ray intensity of element Z from layer and second layer, C1, z, C2, z
Is the content (mass ratio) of the element Z in the first and second layers, ρ1,
ρ2 is the density of the first and second layers, d1 and d2 are the first layers,
The effective extinction length of excited X-rays in the second layer, T1, is the transmittance of the first layer for excited X-rays. Iz = I1, z + I2, z (9) I1, z = kz · C1, z · ρ1 · d1 (10) I2, z = T1 · kz · C2, z · ρ2 · d2 (11)

As in the case of the single layer film, the expressions (10) and (11) are simplified to the following expressions (12) and (13) by relative comparison of the fluorescent X-ray dose with the fluorescent X-ray dose of a certain element. Can be I1, z / I1, z1 = (kz.C1, z) / (kzo.C1, zo) (12) I2, z / I2, z2 = (kz.C2, z) / (kzo.C2, zo) …(13)

Next, the above equation is applied to a multilayer thin film composed of a BST film and an SRO film. IBa = I1, Ba ... (14) ISr = I1, Sr + I2, Sr ... (15) ITi = I1, Ti ... (16) IRu = I2, Ru ... (17) I1, Ba / I1, Sr = (kBa・ C1, Ba) / (kSr ・ C1, Sr) (18) I1, Ti / I1, Sr = (kTi ・ C1, Ti) / (kSr ・ C1, Sr) (19) I2, Sr / I2, Ru = (kSr · C2, Sr) / (kRu · C2, Ru) (20)

From the equations (15), (17) and (20), the intensity I1, Sr of the fluorescent X-ray XSr derived from the BST film is obtained. I1, Sr = ISr-I2, Sr = ISr-I2, Ru (kSr.C2, Sr) / (kRu.C2, Ru) = ISr-IRu. (KSr.C2, Sr) / (kRu.C2, Ru) ) …(twenty one)

Here, ISr and IRu are observation quantities, and kSr
/ KRu can be determined by measuring a single-layer film sample of the SRO film. Therefore, the composition ratio of the SRO film C2, Sr / C
2, if Ru is known, the intensity I2 of the fluorescent X-ray XSr derived from the SRO film
Sr is determined, and finally the intensity I1, Sr of the fluorescent X-ray XSr derived from the BST film can be obtained.

The SRO film composition ratio C 2,
A standard chemical composition ratio of 1: 1 can be adopted as Sr / C2, Ru. The reason is that when the excited X-ray is incident at a low angle, the excited X-ray is almost absorbed by the upper BST film,
The transmittance T1 of the excited X-rays of the BST film becomes extremely small, and the SRO is lower than the fluorescent X-ray intensity I1, Sr derived from the BST film.
The fluorescent X-ray intensity I2, Sr derived from the film is only about 1/100. Therefore, even if the set value of the composition ratio C2, Sr / C2, Ru contains, for example, an error of 1/10, it only affects the calculation result of the intensity I1, Sr by about 1/1000. . Further, as will be described later, it is also possible to sequentially refine using the measurement results of the SRO film.

When the amount of the generated fluorescent X-rays XBa, XSr, and XTi generated from the upper BST film is known, the composition of the BST film can be calculated as in the case of the single-layer film. The kBa / kSr and kTi / kSr used at this time can be determined by measuring a single-layer film sample of the BST film.

Next, the measurement of the composition of the lower SRO film will be described. As shown in FIG. 3, when the incident angle θH of the excitation X-ray X1 is set to a sufficiently high angle, for example, 2 degrees, the X-rays Ba, Sr, and Ti fluorescent X-rays XBa, X
Sr and XTi are generated, and fluorescent X-rays XSr and XRu of Sr and Ru are generated from the lower SRO film more strongly than the incident angle θL. At this time, since Sr exists in both the BST film and the SRO film, it cannot be distinguished from which film the detected fluorescent X-ray XSr is derived.

In general, when X-rays are incident on a two-layered thin film at a high angle, the intensity of the fluorescent X-rays detected is expressed by the following equations (9) to (9).
Similar to (11), it can be described as in the following equations (22) to (24). Here, t1 and t2 are the thicknesses of the first layer and the second layer.
Further, the absorption of the excited X-rays and the fluorescent X-rays in the first layer and the second layer can be ignored because the passing distance is short. Iz = I1, z + I2, z (22) I1, z = kz · C1, z · ρ1 · t1 (23) I2, z = kz · C2, z · ρ2 · t2 (24)

As in the case of the single-layer film, the expressions (23) and (24) are simplified to the following expressions (25) and (26) by relative comparison of the fluorescent X-ray dose with the fluorescent X-ray dose of a certain element. Can be I1, z / I1, z1 = (kz.C1, z) / (kzo.C1, zo) (25) I2, z / I2, z2 = (kz.C2, z) / (kzo.C2, zo) … (26)

Next, the above equation is applied to a multilayer thin film composed of a BST film and an SRO film. IBa = I1, Ba ... (27) ISr = I1, Sr + I2, Sr ... (28) ITi = I1, Ti ... (29) IRu = I2, Ru ... (30) I1, Ba / I1, Sr = (kBa・ C1, Ba) / (kSr ・ C1, Sr) (31) I1, Ti / I1, Sr = (kTi ・ C1, Ti) / (kSr ・ C1, Sr) (32) I2, Sr / I2, Ru = (kSr · C2, Sr) / (kRu · C2, Ru) (33)

By transforming equations (31) and (32), the intensity I1, Sr of the fluorescent X-ray XSr derived from the BST film can be obtained.

[0058]

(Equation 1)

In addition to such a calculation method, it is also possible to obtain the intensities I1 and Sr as shown in the following equations (36) and (37) using, for example, equation (31). I1, Ba / I1, Sr = (kBa.C1, Ba) / (kSr.C1, Sr) (36) I1, Sr = (I1, Ba.kSr.C1, Sr) / (kBa.C1, Ba) … (37)

Regarding the measurement accuracy, the higher the intensity of the fluorescent X-ray to be measured, the higher the S / N ratio can be secured. X-ray fluorescence
When measuring the strength of Ba and XTi, for example, the Ba-L characteristic X
When the X-ray and the Ti-K characteristic X-ray are used, there is a situation that both peaks are close to each other. When the sum of these fluorescent X-ray intensities is obtained without separating the peaks, much more stable measurement can be performed than when either one is obtained by separating the peaks. In such a situation, the method using equation (35) is preferable.

Then, using equations (28) and (35), SRO
The intensity I2, Sr of the fluorescent X-ray XSr derived from the film is determined.

[0062]

(Equation 2)

Here, ISr, IBa, and ITi are observation quantities, and kBa / kSr and kTi / kSr can be determined by measuring a single-layer BST film sample. Therefore, BST
If the composition ratio C1, Ba: C1, Sr: C1, Ti of the film is known, the intensity I1, Sr of the fluorescent X-ray XSr derived from the BST film is finally determined, and finally the intensity I2 of the fluorescent X-ray XSr derived from the SRO film. , Sr.

The composition ratio C1, of the BST film used in this calculation
When specifying Ba: C1, Sr: C1, Ti, when comparing the ratio of the lower SRO film at oblique incidence to the ratio of the upper BST film at high angle incidence, the latter is much more pronounced than the former. Big. Therefore, the composition ratio of the BST film is set to the excitation X-ray X1
Is preferably calculated using measurement data obtained by the oblique incidence method in which the light is irradiated at an incident angle θL.

If the amount of the fluorescent X-rays XSr and XRu generated from the lower SRO film is known, the composition of the SRO film can be calculated as in the case of the single-layer film. KSr used at this time
/ KRu can be determined by measuring a single-layer film sample of the SRO film.

Next, the regression calculation of the calculation result will be described. As described above, when calculating the composition of the BST film, a large error does not occur even if a standard chemical composition ratio is used as the composition ratio of the SRO film. However, it is preferable that the error be small. Therefore, by executing the regression calculation in the following procedure, the measurement accuracy of the composition of the BST film and the SRO film can be improved.

1) A standard chemical composition ratio is adopted as the composition C2, z of the SRO film. 2) The composition C of the BST film from the intensity measurement result of the obliquely incident X-ray fluorescence and the composition C2, z of the SRO film
Calculate 1, z. 3) The composition C2, z of the SRO film from the intensity measurement result of the high-angle incident fluorescent X-ray and the composition C1, z of the BST film.
Is newly calculated and corrected. 4) Procedure 2) is performed using the corrected composition of the SRO film C2, z, and the newly calculated B
The procedure 3) is performed using the composition C1, z of the ST film, and the procedures 2) and 3) are repeated as necessary.

Next, an actual measurement example will be described. The table below shows the X-ray energies used as excited X-rays and B
The relationship between the characteristic X-rays to be measured among the fluorescent X-rays generated by the constituent elements of the ST film and the SRO film is shown.

[0069]

[Table 1]

Group 1 has an excitation X larger than the LI absorption edge of Ba (5996 eV) and smaller than the K absorption edge of Sr (16108 eV).
Line. In this case, the Ba-L line (4465 eV, 4827 eV, 5156 eV
V), Sr-L line (1806 eV), Ti-K line (4508 eV, 4931 eV)
, Ru-L lines (2558 eV, 2683 eV) are measured.

Group 2 is larger than the K absorption edge of Sr,
This is an excited X-ray smaller than the K absorption edge of Ru (22120 eV).
In this case, Ba-L line, Sr-K line (14140 eV, 15830 eV)
, Ti-K line and Ru-L line are measured.

Group 3 is an excited X-ray that is larger than the K absorption edge of Ru. In this case, Ba-L line, Sr-K line, T
Characteristic X of i-K line and Ru-K line (19233 eV, 21646 eV)
The line is measured.

In the case of oblique incidence where the upper BST film is mainly measured, it is necessary to measure the Ba-L line and the Ti-K line as accurately as possible. The measurement system of Group 1 in which the intensity of the fluorescent X-rays is larger than that of the first embodiment is preferable.

In the case of high-angle incidence where the lower SRO film is mainly measured, Si-K (1739 eV) of the substrate is detected very strongly, and the energy dispersive X-ray detector 4 is used. In this case, it is difficult to detect the Sr-L line (1806 eV).
As a countermeasure, it is preferable to use the measurement systems of Group 2 and Group 3 in which an Sr-K line different from the Sr-L line is to be measured.

Therefore, in the X-ray fluorescence analyzer as shown in FIG. 1, separate X-rays are used for oblique incidence and for high-angle incidence.
When employing a configuration in which the source 1 is switched, a combination of the group 1 and the group 3 (or the group 2) is preferable.
On the other hand, when the same X-ray source 1 is shared for oblique incidence and high-angle incidence, the measurement system of group 2 is preferable.

FIG. 4 is a graph showing the energy distribution of Ba fluorescent X-rays and Ti fluorescent X-rays. Ba-L line (4465e
V, 4827 eV, 5156 eV) and the Ti-K line (4508 eV, 4931 eV) are close to each other. Therefore, if both occur at the same time, the peak position information may be buried as shown by the solid line graph in FIG. In this case, 1) Separate the measured data into two curves using advanced graph analysis calculations, 2)
Relative comparison with Sr fluorescent X-rays can be performed by a technique such as treating the combined amount of Ba fluorescent X-rays and Ti fluorescent X-rays as one parameter as it is.

[0077]

As explained in detail above, according to the present invention, the intensity of the fluorescent X-rays of the common element MB and the non-common elements MA and MC when the excitation X-ray is irradiated at the incident angle θL is detected.
Based on a predetermined composition ratio Kb of the lower film, the intensity ratio ILb of the fluorescent X-rays of the common element MB and the non-common element MC derived from the lower film at the incident angle θL can be calculated, and further, based on the intensity ratio ILb, The composition ratio Kt of the upper layer film can be calculated by calculating the intensity of the fluorescent X-ray of the common element MB derived from the upper layer film among the fluorescent X-rays at the incident angle θL. Therefore, even when the common element exists in the multilayer thin film, the composition of the multilayer thin film can be accurately measured.

Further, according to the present invention, the composition of a multilayer thin film can be accurately measured by a similar method on a silicon substrate having a multilayer thin film composed of an upper BST film and a lower SRO film formed on the surface.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a fluorescent X-ray analyzer according to the present invention.

FIG. 2 is an explanatory diagram when an excitation X-ray X1 is incident at a low incident angle θL.

FIG. 3 is an explanatory diagram when an excitation X-ray X1 is incident at a high incident angle θH (θH> θL).

FIG. 4 is a graph showing the energy distribution of Ba fluorescent X-rays and Ti fluorescent X-rays.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray source 2 Dispersion crystal 3 Slit member 4 X-ray detector 5 Sample holding mechanism

Claims (5)

[Claims] 1. Excited X-rays are irradiated to a substrate on which a multilayer thin film composed of an upper layer film and a lower layer film each having an element MB common to each other and elements MA and MC not present respectively is formed. A method for measuring the composition of a multilayer thin film by detecting fluorescent X-rays generated from a substrate, comprising: a composition ratio K of a common element MB and a non-common element MC in a lower film.
b) irradiating excited X-rays at an incident angle θL;
Common element MB and non-common element M generated from multilayer thin film
Detecting the intensity of each of the fluorescent X-rays of A and MC, and calculating the intensity ratio ILb of the fluorescent X-rays of the common element MB and the non-common element MC derived from the lower layer at the incident angle θL based on the composition ratio Kb. The fluorescence X at the incident angle θL based on the intensity ratio ILb.
Calculating the intensity of the fluorescent X-rays of the common element MB derived from the upper layer film among the lines; and the ratio ILt between the intensity of the fluorescent X-rays of the common element MB derived from the upper layer film and the intensity of the fluorescent X-rays of the non-common element MA Calculating the composition ratio Kt of the common element MB and the non-common element MA of the upper layer film based on the above formula. 2. a step of irradiating excitation X-rays at an incident angle θH (θH> θL) to detect respective intensities of fluorescent X-rays of a common element MB and non-common elements MA and MC generated from the multilayer thin film; Calculating the intensity ratio IHt of the fluorescent X-rays of the common element MB and the non-common element MA derived from the upper layer film at the incident angle θH based on the composition ratio Kt; and the fluorescence at the incident angle θH based on the intensity ratio IHt. X
Calculating the intensity of the fluorescent X-rays of the common element MB derived from the lower film among the lines, and the ratio IHb between the intensity of the fluorescent X-rays of the common element MB derived from the lower film and the intensity of the fluorescent X-rays of the non-common element MC Calculating the composition ratio Kb of the common element MB and the non-common element MC of the lower layer film based on the following formula: 3. A silicon substrate having a multilayer thin film comprising an upper BST film and a lower SRO film formed thereon is irradiated with excitation X-rays toward a silicon substrate formed on the surface thereof to detect fluorescent X-rays generated from the multilayer thin film. A method for measuring the composition of a multilayer thin film, comprising the steps of specifying the composition ratio KSR of Sr and Ru in an SRO film, irradiating excited X-rays at a low incident angle θL, and generating Ba, Sr, and Ti generated from the multilayer thin film. , Ru fluorescent X-rays XBa, XSr, X
Detecting the intensity of each of Ti and XRu; and determining the SRO at an incident angle θL based on the composition ratio KSR.
Calculating the intensity ratio ILSR of the fluorescent X-rays XSr and XRu derived from the film; and calculating the intensity of the fluorescent X-ray XSr derived from the BST film among the fluorescent X-rays XSr at the incident angle θL based on the intensity ratio ILSR. Step, intensity of fluorescent X-ray XSr derived from BST film and fluorescent X-ray XBa, X
Based on the ratio ILSBT to Ti, Ba, Sr, T
calculating the composition ratio KBST of i. 4. Irradiation with excitation X-rays at an incident angle θH (θH> θL) to detect the respective intensities of fluorescent X-rays XBa, XSr, XTi and XRu of Ba, Sr, Ti and Ru generated from the multilayer thin film. Based on the composition ratio KBST, the BS at the incident angle θH
Calculating the intensity ratio IHBST of the fluorescent X-rays XBa, XSr, and XTi derived from the T film; and, based on the intensity ratio IHBST, the intensity of the fluorescent X-ray XSr derived from the SRO film among the fluorescent X-rays at the incident angle θH. Calculating, and based on the ratio IHSR between the intensity of the fluorescent X-ray XSr and the intensity of the fluorescent X-ray XRu derived from the SRO film, newly calculating the composition ratio KSR of Sr and Ru of the SRO film. 4. The method for measuring the composition of a multilayer thin film according to claim 3, wherein: 5. The method for measuring the composition of a multilayer thin film according to claim 1, wherein monochromatic X-rays are used as the excitation X-rays.