JPH04127044A - Analysis of surface structure - Google Patents

Abstract

PURPOSE:To find the position of an element near a surface by determining an angle distribution of fluorescent X-rays emitted from a sample or near the surface of the sample. CONSTITUTION:Excitation X-rays 1 impinge upon a sample substrate 5 almost vertically using characteristic X-rays from a target. The characteristic X-rays 2 from a substrate adhesion layer are detected with an X-ray detector 4 passing through a slit 3. An intake angle thetat is determined by a position at which the excitation X-rays impinges on the sample and a geometrical position of the slit 3. The detector 4 employs a semiconductor detector capable of analyzing energy to discriminate desired characteristic X rays alone by a pulse height discrimination to remove effect of scattered X rays or the like otherwise serving as other backgrounds. To vary the intake angle thetat, it is so arranged to rotate the sample substrate 5 with the slit 3 fixed. The slit 3 may be replaced with a duct-shaped collimator or a collimator can be used utilizing a Bragg reflection of a crystal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses an X-ray analyzer to determine the position of elements near the surface by determining the angular distribution of fluorescent X-rays emitted from a sample or near the surface of the sample. Concerning how to identify.

[Conventional technology]

Conventionally, as a method for measuring one-dimensional bridge structures near the substrate surface, Physical Repulsion Letters Vol. 62 (1989) 1
Discussed on pages 376-1379. In the above method, when X-rays are totally reflected on a smooth substrate surface,
This method takes advantage of the fact that standing waves are generated due to interference between incident X-rays and reflected X-rays. Here, the -dimensional structure (in the vertical direction) of the deposited layer on the substrate is measured by detecting the characteristic X-rays emitted from the atoms due to the interaction between the standing wave of X-rays and the atoms in the layer near the surface. It is something that will be done.

The present invention has the same purpose as the above method, and the physical phenomena utilized are very similar. However, it differs from the conventional method in the following points. That is, the present invention has the characteristic X emitted from the adhesion layer.
This method utilizes the interference effect between the characteristic X-rays that reach the detector directly without being reflected and the characteristic X-rays that reach the detector after being reflected when the radiation is reflected at the interface with the substrate. be.

1. As a prior art related to the present invention, Japanese Journal of Applied Physics 24
(1985), pages L387 to L390. X shown in Figure 3 in the above paper
The angular dependence of the line intensity is analyzed using the theory of the present invention, and shows the state in which atoms are attached to the substrate surface (that is, when the distance between the substrate surface and the attached atoms is zero). I can understand that. The above paper has the same configuration as the device of the present invention, but since the relationship between the fluorescent X-ray intensity and the attached atom position was not clarified, it was found that the relationship between the attached atoms and the substrate was determined from the fluorescent X-ray angle distribution measurement data. It could not be used as a method to find the distance between.

[Problem to be solved by the invention]

The above-mentioned conventional technology requires parallel and monochromatic incident X-rays in order to utilize the interference effect between incident X-rays and reflected X-rays.

The present invention aims to measure the surface structure on a substrate using the interference effect of X-rays, which is the same objective as the above-mentioned conventional technology, but the present invention aims to measure the surface structure on a substrate using the interference effect of X-rays. Eliminates the need for X-rays and does not require any excitation method (electron beam,
The purpose of the present invention is to provide a method that can analyze the position of the element of interest in the adhesion layer on the substrate in the same way as conventional methods even when using excitation methods such as ion beams and gamma rays from internal conversion elements). do.

Means for Solving CHM] In order to achieve the above object, in an apparatus having an X-ray detector that detects characteristic X-rays from elements contained in a sample substrate and a layer on the substrate, By limiting the angle (takeout angle) between the sample surface and the characteristic X-ray detection method and by making the sample or slit movable, the angular distribution of the characteristic X-rays (i.e., the dependence of the characteristic X-ray intensity on the takeoff angle) It is used to measure. Furthermore, in the present invention, the structure of the surface layer attached to the substrate is determined by correlating the obtained angular distribution of the characteristic X-rays with a calculated value that takes into account reflection and interference effects of the characteristic X-rays at the interface. It is.

[Effect]

In the present invention, characteristic X-rays generated near the substrate surface are detected when they are emitted at an angle θ defined by a slit, as shown in FIG. Here, by measuring the intensity of the characteristic X-rays while changing the angle θt by moving the slit up and down or rotating the sample substrate, the extraction angle (θt
) Dependency can be found. The angle dependence of this characteristic X-ray intensity can be calculated as follows. As shown in FIG. 2, when an atom 6, which is the emission point of characteristic X-rays, exists at a distance d from the surface of the substrate 5, the X-rays that reach the detector
The intensity of 4I is determined by the interference effect of the X-rays passing through the two optical paths, considering the optical path 7 of the X-rays, which reach the detector directly without being reflected by the substrate, and the optical path 8, which once hits the substrate and is reflected and then heads to the detector. is expressed as follows.

Here, Eo is the electric field of the X-rays passing through the optical path 7. ER is the electric field of the X-rays passing through the optical path 8.

The relationship between ER and Eo can be approximately expressed, for example, by the following equation by considering Fresnel reflectance and optical path difference.

sinθt + (sin2θ, -26-2iβ) Here, λ is the wavelength of the X-ray, δ and β are quantities related to the complex refractive index, and if the complex refractive index of the substrate is n, then n=1-δ -1β.

Therefore, by measuring the dependence of the characteristic X-ray output on the take-off angle (θt) and analyzing it using the above formula, it is possible to determine that if the refractive index n and the X-ray wavelength λ are known, the atomic position d from the substrate surface is can be found. Further, even if n is unknown, it is possible to simultaneously obtain n and d by parameter fitting.

The reflectance of X-rays is usually extremely small, usually on the order of 10-10. Therefore, the interference effect caused by this is practically unobservable. However, in the present invention, a sufficiently strong interference effect is produced by obtaining sufficient reflectance by using an angle near the critical angle of total reflection.

FIG. 3 shows an example of an interference pattern calculated using the above theoretical formula. The horizontal axis of the figure is the extraction angle normalized by the critical angle of total reflection (θC), and the vertical axis is the point where θ1 is sufficiently large (
It is the characteristic X-ray intensity normalized by the characteristic X-ray intensity of θ, )θC). It is shown that strong interference occurs on the low angle side of the total reflection critical angle, and as θ becomes larger, the interference effect becomes smaller.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The excitation X-ray 1 uses characteristic X-rays from the target, and the sample substrate 5
incident almost perpendicularly to. Characteristics from the substrate adhesion layer Xg2
passes through the slit 3 and is detected by the X-ray detector 4. The extraction angle θ is determined by the irradiation position of the excitation X-ray 1 onto the sample and the geometrical position of the slit 3. In this embodiment, a semiconductor detector capable of energy analysis is used as the detector, and the desired characteristic XI! is determined by the wave height valve array. The effects of other bank grounds such as scattered X-rays were eliminated. In addition, in order to change the extraction angle θ, without moving the slit,
The structure was such that the sample substrate could be rotated. The slit 3 may be replaced with a duct-shaped collimator or a solar slit, or a collimator utilizing Bragg reflection of a crystal may be used. In this example, in order to find the distance d, which is an unknown parameter, the value of d that best matches the experimental value is selected by comparing and contrasting the angle dependence graph calculated in advance with the data obtained from the experiment. method was used. An example of this is shown in FIG. Here, experimental values are taken from the literature (Japanese Journal of Applied Physics, Vol. 24 (1985), pp. L387 to 5390).
We used the results of measuring the angular distribution of AgLα rays on a Si substrate, as reported in Page). Theoretical calculations were performed using the wavelength of AgLα rays (4,147 people) and the critical angle of total reflection (0.6°) determined from the density of Si. β/α is 0.0
Assuming 5, d=o people, 50 people.

This is a request for three cases of 100 people. This experimental value uses a sample that is expected to be d=o (thin film attached to the substrate surface) based on the sample preparation method.
In fact, as is clear from FIG. 4, the case where d=o person best matched the experimental data, and the distance clO person was determined by the analysis method of the present invention.

〔Effect of the invention〕

According to the invention, characteristic XI! There is no need to use parallel monochromatic X-rays as an excitation method; equivalent data can be obtained using divergent X-rays or white X-rays, and the excitation method is not X-rays but electron beams or ion beams.

Neutral particles or the like may be used, which has the effect of simplifying the apparatus.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the present invention in detail. Second
The figure is an enlarged view of the optical path of the X-rays in FIG. 1. FIG. 3 is an example of a theoretical calculation result of the dependence of the characteristic X-ray output on the extraction angle. FIG. 4 is a comparison of theoretical calculation results and experimental results in one embodiment of the present invention.

Claims (1)

[Claims] 1. Among the X-rays emitted from near the sample surface of the sample,
By detecting the angle formed with a specific sample surface and by measuring and analyzing the angular dependence of the emitted X-ray intensity near the critical angle of total reflection, A surface structure analysis method characterized by determining the position measured from .