JP2507484B2 - Polarized total reflection X-ray fluorescence structure analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laminated film formed by laminating thin films constituting an electronic device such as a semiconductor device, and the atomic arrangement of each thin film and each interface in the laminated state. The present invention relates to a polarized total reflection fluorescent X-ray structure analysis device suitable for an evaluation device for analyzing.

[Conventional technology]

As an X-ray generator, an electron beam excitation type or a synchrotron radiation generated when an electron or a positron is circulated in a synchrotron which has recently been actively used is generally used. X removed from these devices
The line is not polarized in the electron beam excitation type and is strongly polarized in the synchrotron radiation. The polarization direction is such that the electric vector of the X-ray is aligned with the orbiting plane of the electron or positron with respect to the traveling direction of the emitted light, and is generally horizontal polarization in view of the installation state of the synchrotron. Even when the electron beam excitation type X-ray generator is used, when the X-ray to be used is extracted by the crystal monochromator, it becomes polarized light having an electric vector in the crystal rotation axis direction of the monochromator crystal.

The conventional device is Photon Factory Activity Report 1982/83, V-28 (Photon Factory Activ
1982/83, V-28), the sample to be measured is allowed to absorb all incident X-rays to generate fluorescent X-rays or to cause total reflection on the sample surface in the atmosphere, It is an apparatus for measuring the intensity of the fluorescent X-rays and the total reflection X-rays generated from the above, and no particular consideration has been given to the polarization of the X-rays that irradiate the sample.

[Problems to be solved by the invention]

Since the above-mentioned conventional technique is a device that performs measurement in the atmosphere, by setting the incident X-ray photon energy low due to the influence of absorption and scattering of X-rays by air, for example, fluorescent X-rays of silicon and secondary electrons are It is impossible to obtain data on the atomic arrangement structure of silicon compounds by measurement,
It is impossible to collect data on the changes in the atomic arrangement structure in the depth direction of the thin film and the structure changes near the film interface by deleting the multi-layered film used for semiconductor elements from the surface by several nm in the depth direction. However, there is a problem in that the entire evaluation of the multilayer thin film cannot be performed sufficiently.

The object of the present invention is to make it possible to analyze, for example, the atomic arrangement structure of a silicon compound thin film even when the incident X-ray photon energy is set low, and to change the three-dimensional atomic arrangement structure in the depth direction of a multilayer thin film. An object of the present invention is to provide a polarized total reflection fluorescent X-ray structure analysis device capable of analysis.

[Means for solving problems]

The above-mentioned purpose is to measure the incident X-ray intensity, the fluorescent X-ray intensity, the secondary electron intensity, and the total reflection X-ray intensity, and the axis of the incident X-ray beam so that the incident X-ray is totally reflected on the surface of each detector and the sample. It is possible to evacuate to a high vacuum a mechanism capable of relatively finely adjusting the angle between the sample surface and the sample surface and rotating the sample around the axis of the incident X-ray beam in accordance with the deflection direction of the incident X-ray beam. By installing in a vacuum container, fluorescent X of silicon
By making it possible to measure the intensity of the secondary electron emitted from the line (about 1.7 keV) and the sample, and also to remove (etch) the sample surface by attaching an ion gun in the vacuum container. To be achieved. The features of the device of the present invention will be described in more detail as follows.

(1) A means for detecting at least the intensity of an incident X-ray in a vacuum container, and a sample which is inclined with respect to the axis of the incident X-ray beam at an angle capable of at least totally reflecting the incident X-ray beam on the sample. Sample placing means provided with a sample elevating mechanism for setting the X-ray beam at an arbitrary position and a sample rotating mechanism capable of rotationally moving the sample parallel or perpendicular to the polarization direction of the incident X-ray beam, and the sample is emitted. X-ray fluorescence,
A particle beam detecting means for detecting the respective intensities of the secondary electrons and the totally reflected X-rays, and the incident X-ray intensity, the fluorescent X-ray intensity, and the secondary electron intensity while scanning the energy of the incident X-ray photons. It is possible to analyze the three-dimensional array structure of atoms in the depth direction from the sample surface by measuring the total reflection X-ray intensity.

(2) A focused ion beam irradiation means is further provided in the vacuum container so that the sample surface can be etched.

Furthermore, the measurement principle of the device of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing the state of total reflection of an X-ray beam on the sample surface. In the figure, the incident X-ray beam Xi is totally reflected by the surface S of the sample 1 at a reflection angle θ. The incident X-ray penetrates from the surface to the depth d, total reflection occurs within this range, and a total reflection beam Xr having an X-ray intensity almost equal to Xi is emitted. At this time, the penetration depth d of the incident X-ray beam is
If the thickness is smaller than the thickness da of the thin film layer 2 (first layer) as a sample, Xr is due to the surface first layer only. In addition, 21 shows a thin film of the second layer.

The efficiency η of total reflection is defined by the following equation (1) and takes a value close to 1.

η = I (Xr) / I (Xi) (1) where I (Xi) is the incident X-ray intensity and I (Xr) is the total reflection X.
It is the line strength. η1, which is the result of X-rays that have not been totally reflected scattered on the sample surface or fluorescently excite atoms in the thin film up to the penetration depth d to cause fluorescent X-rays X _f and secondary electrons e _s on the sample surface. By releasing from.

In fluorescence excitation, the energy of the fluorescent X-ray _Xf differs depending on the target element, and the fluorescent X-ray intensity I ( _Xf ) changes depending on the energy of the incident X-ray Xi. The fluorescent X-ray yield α is represented by the formula (2).

α = I (X _f ) / I (Xi) (2) α obtained by scanning the photon energy E of the incident X-ray Xi from the energy of the fluorescent X-ray X _f to near 1 keV higher energy
The spectrum α (E) of is called fluorescence EXAFS, and X-ray fluorescence X
It is known to include information on the atomic arrangement around the element generating _f .

Secondary electron yield β (E) is an amount having the same information as α (E). β (E) is expressed by equation (3).

β = I (e _s ) / I (Xi) (3) where I (e _s ) is the intensity of the secondary electron. These spectra, α and β, have information on the atomic arrangement within the depth d of the sample surface that causes total internal reflection.

The depth d that penetrates into the sample surface layer depends on the density ρ of the sample surface and the total reflection angle θ, but is about 5 to 10 nm. The maximum energy (total reflection critical energy, Ec) at which the sample can totally reflect X-rays is shown by equation (4), and X is smaller than Ec.
It produces total internal reflection for linear energy.

To measure the EXAFS spectrum of Si using SiO ₂ as a sample, if θ = 0.5 °, Ec = 4.4 keV according to the equation (4), and measurement is possible.

The thickness of the thin film laminated as a film for semiconductor is 20 to 10
If it is about 0 nm and d = 10 nm, it is possible to obtain only the atomic arrangement structure of the uppermost layer in the stacked state.

When the incident X-ray Xi is polarized light, if the direction of the electric vector incident on the sample is changed, the spectra of α (E) and β (E) may change. This is because the atomic arrangement structure on the surface of the sample differs between the depth direction of the sample and the plane direction of the sample. When the electric vector of the polarized X-rays incident on the sample is set in a state perpendicular to the surface as shown in Fig. 2 (a), the electric vector is directed to the outermost atomic layer and the second layer. , Spectra α (E) and β (E) containing structural information such as the interatomic distance in this direction are obtained. Considering the case of exciting the outermost surface atoms to measure a fluorescent X-ray or a secondary electron spectrum, the elements of the outermost surface atomic layer and the second layer are different, and in particular, as shown in FIG. When there are plural kinds of elements, the spectrum becomes complicated as shown in FIG. 2 (c). On the other hand, when the X-ray electric vector of polarized light is set parallel to the surface as shown in FIG. 3 (a), the electric vector is parallel to the outermost atomic layer as shown in FIG. 3 (b). , Structural information of a single atom is obtained, and a relatively simple α as shown in FIG.
(E) and β (E) spectra are obtained. Therefore,
By measuring the spectra as shown in FIG. 2 (c) and FIG. 3 (c) and analyzing each, FIG. 2 (b)
The atomic arrangement in FIG. 3B can be analyzed, and three-dimensional structural information can be obtained.

After collecting each data, the sample surface can be deleted by colliding ionized ions such as Ar ions accelerated by an ion gun attached to the vacuum chamber with the surface of the sample. The thickness to be removed can be electrically controlled by the operating time of the ion gun or the ion current, and it is easy to select this thickness to about 10 nm. EXAFS as above
It is possible to analyze the changes in the three-dimensional atomic arrangement structure in the depth direction of the sample with a resolution of about 10 nm by repeating the measurement of 1 and the removal of the sample surface by the ion gun.

[Action]

In the present invention, since the detector for measuring the X-ray intensity is set in a vacuum container evacuated to a high vacuum, there is no absorption or scattering of X-rays by the air, and therefore, it is possible to use a detector such as a fluorescent X-ray of silicon. The intensity of low-energy X-rays and the intensity of secondary electrons emitted from the sample surface can be measured with high accuracy. Further, by providing a mechanism for setting the angle and position of the sample with respect to the incident X-ray beam inside the vacuum container and controlling from outside the vacuum container, it is possible to easily observe the total reflection condition requiring high accuracy while observing the output of the X-ray detector. It is adjustable. Furthermore, the energy of incident X-rays is scanned and the sample position with respect to the polarization direction of incident X-rays is changed after each data acquisition by each detector is completed, and the sample surface is deleted by the ion gun installed in the vacuum container. Thus, a series of data in the depth direction can be obtained from the sample surface. That is, if the plane of polarization of the incident X-ray is parallel to the sample plane, information on the plane direction of the sample surface (related to the atomic arrangement structure) is obtained, and if the plane of polarization is perpendicular to the sample plane, Information in the depth direction can be obtained from the surface. Furthermore, by irradiating the sample surface with a focused ion beam using an ion gun, it is possible to process with any width and depth depending on the irradiation conditions (ion beam current and irradiation time). Information on the atomic arrangement structure about the surface can be obtained.

〔Example〕

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 4 shows a conceptual view from the front of the embodiment apparatus according to the present invention. In FIG. 4, the vacuum container 6 is evacuated to a high vacuum by a vacuum pump 10. The positions of 1a and 1b of the sample can be selected so that the sample surface is vertical or horizontal (parallel) with respect to the polarization direction of the incident X-ray. The fluorescent X-ray detector 3 is used at the position 1a, and the fluorescent X-ray detector 4 is used at the position 1b. The sample surface is deleted by setting the sample at the position 1c and irradiating it with ionized ions from the ion gun 5. In order to keep the vacuum container 6 always at a high vacuum, the sample is replaced through the preliminary exhaust chamber 8 and the valve 7. Reference numeral 9 is an exhaust means using a vacuum pump.

FIG. 5 shows a perspective view of an apparatus according to the present invention. The incident X-ray Xi, which is polarized light, is incident on the incident slit 11, the cross-sectional shape is shaped by the slit, and the incident X-ray detector 12 measures the sample incident X-ray intensity. FIG. 5 shows an example in which the electric vector of the polarized light is in the horizontal direction, but this does not affect the effect of the present invention if the installed state of the device is rotated in any direction. Although not shown in the inside of the vacuum chamber of the apparatus of this embodiment, it can be rotated by 90 degrees or more with a rotation axis substantially parallel to the direction of the incident X-ray on the sample surface as shown by 1a, 1b and 1c in FIG. The sample stage is built in, and the angle of the electric vector of the incident X-ray of polarized light with respect to the sample surface is selected. The fluorescent X-ray detectors 3 and 4 and the secondary electron detectors 13 and 14 are installed so that the projections on the rotation axis of the sample are 90 degrees,
In the case of the present embodiment, the detectors 3 and 13 and the detectors 4 and 14 form a pair, and the projection angles of the detectors of the same type are 90 degrees. Even if the incident state on the sample surface is different, it is not constant which angle of the detector has a superior signal-to-noise ratio for each surface state of the sample. α (E), β (E)
Get the spectrum. The total reflection X-ray intensity of the sample is measured by the incident X-ray detector 12 and the total reflection X-ray detector 15.

〔The invention's effect〕

As described above, according to the present invention, X is stored in a high vacuum container.
A line detector and a secondary electron detector are installed, the polarization direction of X-rays incident on the sample is selected from two types, parallel and perpendicular to the sample surface, and α (E), β ( Since E) is measured, it is possible to collect three-dimensional information of the atomic arrangement structure of a silicon compound having a thickness of about 10 nm, and further, the sample surface is deleted (etched) by an ion gun attached to the vacuum container of this device, By repeating the data measurement of α (E) and β (E) by total reflection, it is possible to obtain the information of the structural change in the depth direction with the resolution of about 10 nm of the thickness of the laminated thin film, which is often used for semiconductors. There is.

[Brief description of drawings]

FIG. 1 is a schematic diagram of total reflection of X-rays on a sample surface for explaining the principle of the present invention, and FIG. 2A is a schematic diagram of total reflection of polarized X-rays for explaining the principle of the present invention. 2 (b) shows the arrangement state of the atoms (the arrangement state of the outermost atomic layer and the second layer), in which the X-ray electric vector of is set perpendicular to the sample surface.
FIG. 2 (c) is a schematic view for explaining α (E), β (E)
A spectrum curve diagram and FIG. 3 (a) are also schematic diagrams of total reflection of polarized X-rays for explaining the principle of the present invention. An example in which the X-ray electric vector of polarized light is set in a state parallel to the sample surface, FIG. 3B is a schematic diagram for explaining the arrangement state of atoms (the arrangement state of the outermost atomic layer and the second layer), and FIG. 3C is α (E),
β (E) spectrum curve diagram, FIG. 4 and FIG. 5 are a front conceptual diagram and a perspective conceptual diagram of an apparatus showing an embodiment of the present invention, respectively. In the figure, 1 ... Sample, 2 ... Surface thin film layer 3, 4 ... Fluorescent X-ray detector 5 ... Ion gun, 6 ... Vacuum container 7 ... Valve, 8 ... Preliminary exhaust chamber 9, 10 ... … Vacuum pump, 11 …… Injection slit 12 …… Injection X-ray detector, 13,14 …… Secondary electron detector 15 …… Total reflection X-ray detector

Claims (2)

(57) [Claims] 1. A means for detecting at least the intensity of an incident X-ray in a vacuum container, and a sample which is inclined with respect to the incident X-ray beam axis at an angle capable of at least totally reflecting the incident X-ray beam. A sample elevating mechanism for setting the X-ray beam at an arbitrary position above and a sample rotating mechanism capable of rotationally moving the sample plane in parallel or perpendicular to the direction in which the electric vector of the polarized incident X-ray beam has the maximum value. And a particle beam detecting means for detecting the intensities of the fluorescent X-rays emitted from the sample, the secondary electrons, and the totally reflected X-rays, respectively, and scanning the energy of incident X-ray photons. However, it is possible to analyze the three-dimensional array structure of atoms in the depth direction from the sample surface by measuring the incident X-ray intensity, the fluorescent X-ray intensity, the secondary electron intensity, and the total reflection X-ray intensity. Polarized light Reflection fluorescent X-ray structural analysis apparatus. 2. The polarized total reflection fluorescence X according to claim 1, characterized in that a focused ion beam irradiation means is further provided in the vacuum container so that the sample surface can be etched. Line structure analysis device.