JPH06331634A - Method and device for measuring surface atom distribution - Google Patents

Abstract

PURPOSE:To measure an element constitution and an atomic structure at an atomic level near a sample surface by alternately repeating an operation for measuring the element constitution or atomic arrangement of an atom layer using surface analysis method and an operation for peeling the atoms of the sample surface using a reaction gas. CONSTITUTION:A surface analysis method comprises either ion scattering spectroscopy for detecting a surface first atom layer, electron spectroscopy, or secondary ion mass spectrometry, or a combination of the plurality of methods. A reaction gas for use is either chlorine, fluorine or bromine, or a mixture of them, and exciting energy is imparted by ultraviolet irradiation and/or ion irradiation, in addition to heating of a sample. A measuring apparatus for use comprises a peeling chamber 9 and a measuring chamber 5 connected to each other with airtightness maintained. The sample 7 is set in a positioning device 6 and transported to the peeling chamber 9, and the reaction gas is fed from a reaction gas introducing device 10 and a reaction is excited using an excitation device 11 to peel surface atoms, and then the sample 7 is shifted to the measuring chamber 5 and analyzed using a surface analysis system 8. The above operations are repeated alternately to enable analysis in the depth of the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for measuring the surface composition and atomic arrangement of solid materials.

[0002]

2. Description of the Related Art Among the methods for analyzing the elemental composition and atomic arrangement near the surface, the method for extracting the signal from the outermost first atomic layer or the extreme surface is a scanning tunneling electron microscope (STM), low energy. Ion scattering spectroscopy (ISS)
And low energy electron diffraction (LEED). However, these methods cannot obtain the distribution of elemental composition from the surface to the inside or the atomic arrangement. A field ion microscope (FIM) can separate atoms at an atomic level by utilizing a field emission phenomenon and perform depth direction analysis. However, in this method, the sample is processed into a needle shape and the number of tips is 1
There is a large restriction on the measurement site selection that only the 0 nm portion is required for measurement, and it is difficult to apply it to a normal sample surface. (Reference: “Surface Science and Fundamentals and Applications”, edited by The Surface Science Society of Japan, 1991, published by NTS STM: p222, ISS: p246, LEED: p.
540, FIM: p562) In addition to this, as a method for investigating the atomic distribution from the surface to the inside, there are also methods capable of performing depth direction analysis, such as medium energy ion scattering spectroscopy (MEID) and angle-resolved photoelectron spectroscopy. (XPS or UPS), secondary ion mass spectrometry (SIMS), glow discharge emission spectrometry (GDS),
Ion sputtering method and surface analysis method such as glow discharge mass spectrometry (GD-MS) [Auger electron spectroscopy (AE
S), X-ray photoelectron spectroscopy (XPS), etc.], a method using chemical etching and a surface analysis method, and the like.

[0003]

In the conventional surface atom distribution measuring method, the resolution in the depth direction is limited to several atomic layers, and the depth direction analysis cannot be performed for each single atomic layer. An object of the present invention is to eliminate the above problems and provide a surface atomic distribution measuring method and apparatus for measuring the elemental composition and atomic structure at the atomic level near the surface by a completely original method.

[0004]

In order to achieve the above object, in the present invention, an operation for measuring the elemental composition or atomic arrangement of one atomic layer or several atomic layers on a sample surface by a surface analysis method and a reactive gas are used. By repeating the operation of peeling the sample surface atoms in atomic layer units alternately,
The depth distribution of the elemental composition or atomic arrangement near the surface is measured. As the surface analysis method, a method in which the surface first atomic layer is detected is used. Any one of ion scattering spectroscopy, electron spectroscopy, secondary ion mass spectrometry, or a combination of a plurality of methods is used, and any one of chlorine, fluorine, bromine, iodine, and oxygen or a mixed gas is used as a reactive gas. In order to apply the excitation energy for desorbing the surface compound in which the surface atom is strongly chemically bonded to the gas atom, in addition to sample heating, light irradiation such as ultraviolet light on the sample surface, ion irradiation, and electron beam irradiation are used. .

The device capable of measuring the surface atom distribution includes a highly airtight container, a surface analysis device, and
An apparatus for adjusting the position of the measurement sample, an apparatus for introducing the minimum required amount of the reactive gas, and an apparatus for exciting the sample surface are provided. As a surface analysis device in this, an ion scattering spectrometer,
An electron spectrometer or a secondary ion mass spectrometer is installed, and a sample heating device, an electron irradiation device, a light irradiation device, or an ion irradiation device is installed as a device for exciting the sample surface.

[0006]

[Function] When a reactive gas is adsorbed and reacted on the sample surface,
A surface compound in which the surface atom is strongly chemically bonded to the gas atom is generated to easily break the bond with the internal atom, and the surface compound is desorbed by applying a relatively small excitation energy.
Since this surface phenomenon occurs at the outermost surface atom layer, only the surface atom layer can be peeled off. As the reactive gas, one of chlorine, fluorine, bromine, iodine and oxygen, which is a gas that easily adsorbs and reacts with the sample surface to be measured and easily forms a compound with sample surface atoms, or a mixed gas is used. The introduction of the reactive gas is necessary for further adsorption on the measurement surface, and is preferably as small as possible and for a short time in order not to corrode the inside of the apparatus with the reactive gas, usually 10 ⁻³
It is effective to blow it on the measurement surface at a low pressure of about Pa and exhaust it within a short time of several tens of seconds. Further, application of excitation energy for desorption of the surface compound is performed by heating the sample when the compound generated on the surface sublimes at a low temperature. However, in this case, the condition is that heating is performed at a temperature at which the atomic arrangement near the sample surface to be measured is not disturbed.
As a sample heating method, infrared irradiation is effective because it is difficult to raise the temperature inside the sample. In addition to sample heating, light irradiation such as ultraviolet light, ion irradiation, or electron beam irradiation is used. The ultraviolet irradiation is effective because the surface atoms can be exfoliated without disturbing the arrangement of the sample atoms by selecting the energy that breaks the bond between the sample surface atoms and the atoms immediately below. Ion irradiation is
Ion irradiation-induced desorption of the surface compound is performed under weak ion irradiation conditions where ion sputtering of sample atoms hardly occurs.

As the surface analysis method, a method of detecting the surface first atomic layer is used. Ion scattering spectroscopy is preferred. In particular, ion scattering spectroscopy using low-energy ions can measure the elemental composition of the surface first atomic layer and the atomic arrangement of the surface diatomic layer. AES, XPS
Electron spectroscopy or SIMS is a method to detect several atomic layers on the surface, not necessarily information only on the first layer on the surface, but AES is minute part analysis, XPS is chemical state analysis, SI
MS is used to take advantage of each feature that enables high sensitivity analysis. With the surface atomic layer peeling,
By repeating the measurement of the surface after peeling by the surface analysis method, the elemental composition and the distribution in the depth direction near the surface of the atomic arrangement can be measured at the atomic level. Moreover, since the surface atom exfoliation used in the present invention can be performed with almost no damage to the atoms inside the sample, the original elemental composition and atomic arrangement of the sample can be measured.

The concept of the mechanism for exfoliating surface atoms at the atomic level and the method for measuring the exfoliated surface according to the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows the measurement procedure. First, the composition or atomic arrangement of this outermost atomic layer is measured by the surface analysis method. FIG. 2A is a sectional view showing the arrangement of atoms near the surface of the sample to be measured. Next, FIG. 2B shows a state in which a reactive gas is introduced and adsorbed on this surface. As for the adsorption method, the space in which the sample is placed is evacuated to a vacuum, and then the reactive gas is introduced at a low pressure.
To confirm whether the adsorption to the surface was successful,
It is effective to use the above-mentioned surface analysis method. The strong bond between the surface atom and the reactive gas atom weakens the bonding force between the surface atom and the atom inside the sample, which facilitates desorption.

Excitation energy is applied to this surface to sublimate and desorb the compound of the sample outermost surface atom and the adsorbed atom, thereby peeling off one surface atom layer. FIG. 2C shows a state in which one surface layer is peeled off in this way, and the elemental composition or atomic arrangement of the surface atomic layer on this surface is measured again. After that, by repeating the peeling of the surface atomic layer and the measurement of the peeled surface, the distribution of the elemental composition or the atomic arrangement in the depth direction near the sample surface can be measured at the atomic level.

Next, the concept of the measuring apparatus of the present invention will be described with reference to the schematic diagram of FIG. The device of the present invention is usually composed of a measuring chamber 5 and a peeling chamber 9. Both rooms are connected airtightly. Further, the vacuum exhaust system 4 is connected to each of them. A sample position adjusting device 6 and a surface analyzer 8 are arranged in the measuring chamber 5, and a reactive gas introducing device 10 is provided in the peeling chamber 9.
An excitation device 11 for peeling is installed. There is a case where the measurement chamber and the peeling chamber are not separated but are combined into one chamber. The reason why the two chambers are separated is to prevent the reactive gas from being introduced into the measurement chamber 5 in order to avoid the reactive gas from invading the component materials of the surface analysis device 8. The measurement chamber has a highly airtight structure having a function as a vacuum chamber in order to prevent contamination and deterioration of the surface of the sample whose polar surface is to be measured by the atmosphere. The sample position adjusting device 6 controls the sample position by placing a sample on the sample position adjusting device 6, and may have a sample heating function. When the measuring chamber 5 and the peeling chamber 9 are separate chambers, the sample position adjusting device 6 also moves between the two chambers. The reactive gas introduction device 10 introduces a required amount of the reactive gas to be adsorbed on the sample surface for surface atom separation, and has a function of finely adjusting the introduced amount. The excitation device 11 for peeling introduces excitation energy for desorbing the compound generated on the surface. In addition to the above configuration, the control unit 13 and the sample introduction mechanism 12 may be installed. The control unit 13 efficiently performs an alternating operation of surface peeling and surface analysis, and preferably has a control function of automatically performing it. The sample introduction mechanism 12 is for efficiently introducing and discharging the sample.

[0011]

【Example】

(Embodiment 1) As an embodiment of the measuring apparatus of the present invention, an example in which ISS is adopted as a surface analyzer is shown. FIG. 4 is a side view of the embodiment. An ion gun 16 for irradiating ions for ISS and a time-of-flight analyzer 17 for analyzing the energy of scattered ions are arranged around a measurement sample 7 placed in a vacuum container 15 pulled by a molecular turbo pump 14. Further, a reactive gas introducing device 10 and an ultraviolet laser 18 for irradiating ultraviolet rays as excitation energy for surface atom exfoliation are also arranged. As the reactive gas, chlorine gas and fluorine gas can be switched and supplied.

Next, an example in which the present invention is actually applied to the measurement of the elemental composition near the surface will be described. The measuring device used was the device shown in the embodiment of FIG. The sample is a film in which a total of 4 layers of tungsten and nickel are alternately deposited for 8 atomic layers on a silicon substrate by an electron beam evaporation method. As the surface analysis method, ISS using neon ions of 1 keV was used. Chlorine gas was used as a reactive gas for the surface stripping method, and ultraviolet irradiation was used as excitation energy for stripping. First, the surface is subjected to ISS measurement. Chlorine gas is sprayed on the sample surface and exhausted after 30 seconds. Next, an ultraviolet laser is irradiated. This series of operations is repeated. The results obtained by this measurement are shown in FIG. The abscissa represents the number of times that ISS measurement, chlorine gas spraying, and ultraviolet ray irradiation make up one cycle, and one cycle corresponds to peeling one atomic layer of the sample. The vertical axis is the value converted from the ISS measurement spectrum into the concentrations of tungsten and nickel. That is, FIG. 5 shows the depthwise distribution of the elemental composition near the surface. From the steep change of the elements near the interface as a result, it can be seen that the depth distribution is obtained with almost the resolution of the atomic layer. Moreover, the depth resolution does not deteriorate to the silicon substrate.

(Comparative Example) FIG. 5 shows the results of depth direction analysis of the same multilayer film as the sample of Example 1 by a method combining Auger electron spectroscopy and ion sputtering. Ar
The operation of irradiating ions at 1 keV for 8 seconds to sputter the sample surface and the Auger electron spectroscopy measurement were alternately performed. The sputter integration time is plotted on the horizontal axis, and the concentration of each element calculated from the obtained Auger spectrum is plotted on the vertical axis. As can be seen from this, the depth resolution by this method is about 5 atomic layers even at the interface of the 1-2nd layer from the surface,
The interface between the fourth layer and the substrate is approximately 6 atomic layers. This is due to the atomic mixing of the sample atoms by ion irradiation, and it can be seen that such distribution analysis of thin layers is not useful.

On the other hand, it can be seen that the result of measuring the same sample by the method of the present invention has a sufficient depth resolution, and can be sufficiently applied to the evaluation of the film formation of such a thin layer.

Example 2 An example in which the present invention is applied to the measurement of atomic arrangement near the surface will be described. The measured sample is a nickel thin film prepared by the molecular beam epitaxial method.
As the surface atomic arrangement analysis method, ISS using neon ion of 1 keV was used. In ISS, when the scattered ion intensity is measured while changing the incident angle of the ion beam on the sample surface, the scattering intensity changes due to the shadowing effect of the ion beam. Therefore, the relation of the atomic arrangement between the first layer and the second layer on the surface is determined. You can ask. The stripping of the sample atoms was performed by spraying chlorine gas and irradiating with ultraviolet rays as in Example 1. FIG. 7A shows the obtained results as a view (top view) viewed from the direction perpendicular to the sample surface. FIG. 7B shows a top view obtained by measuring the atomic arrangement of the second layer and the third layer after the surface first layer was separated by the surface separation method using chlorine gas. FIG. 7C shows the result when the first, second, and third layers are displayed together. FIG. 8A is also possible as a possibility of arranging the second layer and the third layer (the arrangement of the first to third layers in this case is shown in FIG. 8B). I confirmed that it is not.

[0016]

Industrial Applicability As described above, the present invention enables the distribution measurement of elemental composition and atomic arrangement near the surface with depth resolution at the atomic level, and through the evaluation of highly functional thin film materials, It makes a great contribution to the development of these materials.

[Brief description of drawings]

FIG. 1 is a diagram showing a procedure for measuring an atomic composition near a surface according to the present invention.

FIG. 2 is a diagram schematically showing surface atom exfoliation according to the present invention. (A) is a sectional view showing the arrangement of elements in the vicinity of the surface of the sample to be measured. (B) shows a state in which a reactive gas is adsorbed on this surface. (C) is a figure which shows the cross-section arrangement | sequence of the sample atom after peeling one atomic layer of a sample surface.

FIG. 3 is a diagram conceptually showing a measuring apparatus according to the present invention.

FIG. 4 is a diagram showing an embodiment of a measuring device according to the present invention.

FIG. 5 is a diagram showing the results of measuring the distribution in the depth direction of the elemental composition near the surface according to the present invention.

FIG. 6 is a diagram showing the results of measuring the same sample as in FIG. 5 by a method combining Auger electron spectroscopy and ion sputtering.

FIG. 7 is a diagram showing a result of measuring a surface atomic arrangement according to the present invention. (A) is a diagram showing the atomic arrangement of the surface first layer and the second layer obtained by ISS from the direction perpendicular to the sample surface (as a top view). (B) is a diagram showing the atomic arrangement of the second layer and the third layer after peeling off the first surface layer by the surface peeling method using chlorine gas of the method of the present invention and displaying it as a top view. (C) is a diagram in which the obtained surface atomic arrangement is displayed together with the first, second, and third layers.

FIG. 8 is a diagram showing an atomic arrangement considered other than the analysis result. (A) is a diagram showing a possible arrangement of the second layer and the third layer other than the analysis result. (B)
[Fig. 4] is a view showing the arrangement of the first to third layers together.

[Explanation of symbols]

 1 Matrix atoms constituting sample (○) 2 Sample impurity element (△) 3 Adsorption reactive atom (●) 4 Vacuum exhaust system 5 Measuring chamber 6 Measuring position adjusting device 7 Measuring sample 8 Surface analysis device 9 Stripping chamber 10 Reactivity Gas introduction device 11 Excitation device for peeling 12 Sample introduction mechanism 13 Control unit 14 Turbo molecular pump 15 Vacuum container 16 Ion gun 17 TOF type analyzer 18 Ultraviolet laser

Claims (4)

[Claims] 1. A sample in which an elemental composition or atomic arrangement of an atomic layer or several atomic layers on a sample surface is measured by a surface analysis method, and a reactive gas is reacted with a sample surface atom to release a bonded sample atom A method for measuring a surface atomic distribution, characterized in that the elemental composition or atomic distribution in the vicinity of the surface in the depth direction is measured by repeating the operation of peeling the surface in units of a monoatomic layer. 2. A surface analysis method using any one of ion scattering spectroscopy, electron spectroscopy, secondary ion mass spectrometry, or a combination thereof, and chlorine or fluorine as a reactive gas,
The surface atom distribution measuring method according to claim 1, wherein any one of bromine, iodine and oxygen or a mixed gas is used. 3. A surface analysis device, a device for adjusting the position of a measurement sample, a device for introducing a reactive gas, and a device for exciting a sample surface are provided in an airtight container. Surface atomic distribution measuring device. 4. A surface analysis device, which is installed in combination with any one of an ion scattering spectroscope, an electron spectroscope, a secondary ion mass spectroscope, or a combination thereof, and which excites a sample surface, a sample heating device, an electron irradiation device, and a light irradiation 4. An apparatus or an ion irradiation apparatus is installed.
The surface atom distribution measuring device according to the item.