JPH07119718B2 - Analytical method in the depth direction of the sample surface layer - Google Patents

Description

The present invention relates to a method for analyzing a thin surface layer of a sample in the depth direction using soft X-rays.

(Prior Art) A sample can be subjected to elemental analysis by exciting the sample with accelerated electrons, dispersing the X-rays emitted from the sample, and detecting the characteristic X-rays of sample constituent elements. In this case, when the characteristic X-ray exists in the hard X-ray region, the profile of the characteristic X-ray peak in the X-ray spectrum is hardly affected by the binding state of the element in the sample, but the soft X-ray is not affected. Area characteristics X
In the line, the peak profile changes depending on the binding state of the element in the sample, and from this change, the binding state of the element in the sample can be known. Utilizing such a property of the characteristic X-rays in the soft X-ray region, a thin film grown on a substrate, for example, a thickness or a structure of a thin film when SiC is epitaxially grown on the substrate surface of Si single crystal Analysis can be performed. In the structural analysis of such a thin film, in addition to the measurement of the soft X-ray spectrum, it is necessary to utilize that the penetration depth of the sample excited electrons from the sample surface varies depending on the electron acceleration voltage. The movement of the electrons incident on the sample in the sample can be estimated by a simulation method when the composition of the sample is known, and the electron acceleration voltage and the penetration depth of the electron from the sample surface, that is, the X-ray generation region. Relationship with the depth of is required. Figure 2 shows Si single crystal and β-SiC single crystal Si-
The profile of the X-ray spectrum of the L _2,3 line is shown in FIG.
The figure shows the change of the peak profile of Si-L _2,3 of the X-ray spectrum of the sample in which the SiC single crystal was epitaxially grown on the surface of the Si single crystal, depending on the accelerating voltage of the irradiation electrons, and when the accelerating voltage was 4 kV. The profile is almost that of the Si single crystal, and the profile gradually deforms as the accelerating voltage is lowered, and becomes almost the same as that of the SiC single crystal at the accelerating voltage of 0.85 kV. From this crystal and the above-mentioned knowledge of the electron acceleration voltage and the penetration depth of electrons from the sample surface, the film thickness of SiC is estimated to be about 20 nm in the case of this illustrated example.

The conventional apparatus that has performed the above-described analysis uses an apparatus in which a sample is placed at a target position of a Henke type X-ray tube as an electron beam irradiation apparatus for a sample, and a soft X-ray emitted from the sample is diffracted by a diffraction grating. It was configured to disperse with a spectroscope (Magazine Applied Physics Vol. 57, No. 8, 1988, page 68, "Soft X-ray spectroscopy (SXS)".
New Application to Surface Layer / Interface Research ”).

(Problems to be Solved by the Invention) In the above-mentioned conventional apparatus, since the electron beam is made incident on a certain area of the sample surface, average information of a certain area of the sample surface can be obtained, and the surface of the sample surface can be obtained. It was not suitable for the analysis when there was a structure in the spreading direction. Further, since there is no means for simultaneously observing the shape of the sample surface, it is difficult to say that a specific place on the sample surface is selected for analysis.

INDUSTRIAL APPLICABILITY According to the present invention, when performing structural analysis or the like of a sample surface thin layer using soft X-rays, the operation of narrowing the excitation region of the sample surface to a minute region and selecting the analysis point of the sample surface is easy and simple. An object of the present invention is to provide a method for selecting an analysis point while observing the shape of the surface and dividing the sample in the depth direction from the sample surface at that point.

(Means for Solving the Problems) An electron optical system with a variable electron acceleration voltage for converging an electron beam on the sample surface, an electron beam scanning means for scanning the electron beam on the sample surface, and a soft X-ray emitted from the sample A diffraction grating spectroscope for spectroscopic analysis, an electron detector for detecting secondary electrons emitted from the sample, a means for displaying an image of the output of the detector in synchronization with scanning of the sample surface by an electron beam, and a desired sample surface An optical microscope,
Using the means for recording the X-ray spectrum data obtained by the X-ray spectroscope and the apparatus having the sample stage that can move in the X, Y and Z three-axis directions and rotate about the Z-axis and rotate about the horizontal axis, An analysis point on the sample surface is selected from the image and the image obtained on the image display means by converging and scanning the electron beam on the sample surface, and the electron beam irradiates the selected analysis point by the sample moving means. As described above, while changing the accelerating voltage of the electron beam, the soft X-rays emitted from the sample are dispersed by the X-ray spectroscope to measure the peak profile of the characteristic X-rays of the sample constituent elements. The shape of the sample surface layer was analyzed in the depth direction based on the change in the electron beam acceleration voltage of the shape and the penetration depth of the electron beam into the sample calculated from the electron acceleration voltage.

(Embodiment) FIG. 1 shows an embodiment of the present invention. In the figure, 1 electron gun, 2
Is a condenser lens, 3 is an objective lens, and each of these parts constitutes an electron optical system for converging and irradiating an electron beam on the sample surface. A scanning coil 4 deflects the electron beam in the X and Y directions on the sample surface. 5 is a scanning signal generator,
The scanning coil 4 and the scanning signal generator 5 constitute electron beam scanning means. An electron detector 6 is arranged on the side of the sample S and detects secondary electrons emitted from the sample irradiated with the electron beam. A video signal amplifier 7 amplifies the output signal of the electronic detector 6 and switches
To CRT9 for display via. The display CRT 9 forms a raster for a display screen by the output signal of the scanning signal generation unit 5, is brightness-modulated by the output signal of the video signal amplification unit 7, and is a secondary surface of the sample surface on the display surface of the CRT 9. An electron image, that is, a scanning electron microscope image is displayed. The video signal amplifying section 7, CRT 9, scanning signal generating section 5 and the like constitute a video display means. m is a reflecting mirror, L is an optical lens system,
These constitute an optical microscope that looks at the sample surface. G is a concave diffraction grating coated with platinum and has a radius of curvature of 2 m.
It has a lattice groove of 1200 lines / mm. D is an X-ray detector that slides on a guide rail T arranged along the Rowland circle. The diffraction grating G, the X-ray detector D, etc. constitute an X-ray spectroscope. The extension of the Rowland circle passes through the electron beam irradiation point on the sample, and the diffraction grating is arranged along this Rowland circle. X-ray detector D
Is moved along the Roland circle, and X-ray spectrum data is collected. An X-ray detection signal processing unit 10 converts the X-ray detection pulse into count rate data. When the changeover switch 8 is switched, the output signal of the X-ray detection signal processing unit 10 is input to the CRT 9, and an image of the characteristic wavelength of the sample surface by X-ray is displayed. Reference numeral 11 denotes an X-ray spectrum data recording section, which uses a memory in this embodiment to store X-ray spectrum data obtained by moving the X-ray detector D. 12 is a sample stage, which is a moving unit in the X, Y, and Z axis directions.
It is composed of five parts: X, Y, Z, A for rotating around the Z axis, and I for changing the inclination of the sample surface. Reference numeral 13 denotes the sample stage control unit, which sends drive pulses to the drive pulse motors (not shown) of the angular movement units X, Y, Z, A and I, respectively. An electron optical system control unit 14 arbitrarily sets an electron accelerating voltage and the like. Reference numeral 15 is a control device that controls the entire device. V is a vacuum container that houses an electron optical system, an X-ray spectrometer, and the like.

With the above configuration, the sample S is set on the sample stage in the apparatus, the sample is moved while observing the entire sample with an optical microscope, an approximate analysis point is brought to the center of the visual field, and finely moved up and down to focus. And the analysis point of the sample coincides with the X-ray incident point of the X-ray spectroscope. In this state, the sample surface is irradiated with an electron beam, the sample surface is scanned, the secondary electron image is displayed on the CRT9, the details of the analysis point on the sample surface are selected, and X, Y fine movement is performed to analyze. Center the point on the CRT image. After setting the analysis points of the sample in this way, the X-ray spectroscope is driven while changing the acceleration voltage of the electron beam stepwise, and the X-ray spectrum for each acceleration voltage is stored in the memory 11.
To memorize. When this memory is read and displayed, the third
A spectrum display is obtained as shown.

(Effects of the Invention) According to the present invention, it is possible to analyze a sample in the soft X-ray region and to analyze its structure by arbitrarily selecting minute points on the sample surface, and to analyze the thin film formed on the sample surface and to analyze the structure. It will be possible to provide a powerful means.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention, and FIG.
An X-ray spectrum of each single crystal of SiC, and FIG. 3 is a diagram showing a change in X-ray spectrum due to a change in electron acceleration voltage when a SiC film is formed on Si. 1 ... Electron gun, 2 ... Condenser lens, 3 ... Objective lens, 4 ... Scanning coil, 5 ... Scanning signal generator, 6 ...
... Electron detector, 9 ... CRT, 11 ... Memory for recording X-ray spectrum data, 12 ... Sample stage, 14 ... Electron optical system controller, 15 ... Control device, S ... Sample, G ... Diffraction grating, D ... X-ray detector, m ... Mirror, L ... Lens system of optical microscope.

Claims (1)

[Claims] 1. An electron optical system having a variable electron accelerating voltage for focusing an electron beam on a sample surface, an electron beam scanning means for scanning the electron beam on the sample surface, and a diffraction for separating soft X-rays emitted from the sample. A grating spectroscope, an electron detector for detecting electrons emitted from the sample, a means for displaying an image of the output of the detector in synchronization with the scanning of the sample surface by an electron beam, an optical microscope which desires the sample surface, and The above-mentioned optical microscope is used by using a device for recording X-ray spectrum data obtained by an X-ray spectroscope and a device including a sample stage that can move in the X, Y, and Z axis directions and rotate about the Z axis and rotate about the horizontal axis. An analysis point on the sample surface is selected according to the image of the material surface obtained by the image display means, the point is located at the convergence point of the electron beam, and the X-ray is spectrally dispersed while changing the electron beam acceleration voltage. Characteristic X-ray peak pro of sample constituent elements File, and analyze the depth direction of the sample surface layer by the change in the peak profile shape due to the electron beam accelerating voltage and the electron penetration depth data into the sample calculated from the electron beam accelerating voltage. A method for analyzing a surface layer of a sample in the depth direction.