RU2522667C2 - Method of determining elemental composition and thickness of surface film of solid body with external action on surface - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention can be used to determine elemental composition and thickness of the surface film of a solid body. The method includes measuring energy spectra of ions reflected and knocked from the surface of the solid body, wherein the energy spectra are measured directly in the process of applying external action on the surface of the solid body or immediately after said action by successive irradiation of the surface of the solid body with inert gas ions and hydrogen ions that are mass-separated according to mass-to-charge ratio by applying a corresponding accelerating voltage across an ion source operating on a mixture of inert gases and hydrogen, wherein the elemental composition of the surface layer of the solid body is determined from the energy spectra of reflected inert gas ions and the thickness of the film is determined from the energy spectra of reflected hydrogen ions.

EFFECT: broader functional capabilities of determining elemental composition of a surface film of a solid body.

3 cl, 4 dwg

Description

The invention relates to experimental physics and methods for controlling the surface of materials when applying (forming) or removing thin layers of substances from it, which differ in average atomic number from the substrate material, including under conditions of plasma exposure.

To analyze the composition of the surface and the layers deposited on it, the methods of secondary emission spectroscopy with spraying the surface with a probe beam are widely used. However, the depth resolution in these methods is limited and is accompanied by sample destruction [Woodruff DP., Delchar T.A. Modern techniques of durface science, Cambridge, Cambridge University Press, 1986]. Rutherford backscattering spectroscopy can be used as a non-destructive analysis method, but requires the use of expensive accelerators [B. Breeger, E. Wendler, W. Trippensee, Ch. Schubert, W. Wesch; Nuclear instruments and methods in physics research; B174, 199-204; 2001].

The closest method to the present invention and adopted as a prototype is a method for determining the elemental composition of a solid [RU 2017143 C1], in which, by measuring the mass spectrum of secondary particles obtained from the material and measuring the energy distributions of the analyzed particles, the desired concentration of each component.

However, this method is implemented in a prototype device [Gordeev Yu.S., Kablukov SB, Makarenko BN, Popov AB, Shergin AP Determination of the component composition of HTSC using mass spectrometry of secondary atoms. Factory laboratory, t.56, N 8, pp.52-55, 1990], does not allow to determine the thickness of the surface layers, and also because of the need for analysis in high vacuum ~ 10 ^-8 Torr does not allow to study the dynamics of changes in the state of the surface directly during its technological processing, for example during plasma exposure or during etching by an ion beam or during sputtering using ion beams.

The technical result of the invention is the expansion of the functionality to determine the elemental composition of the surface film of a solid, namely the determination of the elemental composition and thickness of the surface layer of a solid when exposed to the surface.

The technical result is achieved in that the measurement of the energy spectra of hydrogen ions and inert gas ions reflected and knocked out of the surface of a solid is carried out directly in the process of external action on the surface of a solid or immediately after it by sequentially irradiating in time the surface of a solid body with masses separated by mass to a charge by hydrogen ions and inert gas ions with energies, while alternately irradiating with hydrogen and inert gas ions is carried out by supplying corresponding accelerating voltage to an ion source operating on a mixture of inert gases and hydrogen, while the elemental composition of the surface layer of a solid is judged by the energy spectra of singly reflected inert gases and recoil ions, and the thickness of the surface layer of a solid by the energy spectra of scattered hydrogen ions . Helium, neon or argon are used as inert gas ions, and external action is carried out by etching with an ion beam, or by sputtering using ion beams, or by irradiation with plasma or heating.

Ion beams of hydrogen and inert gases are generated using a single ion source, for example, a duoplasmatron operating on a mixture of inert gases and hydrogen. This makes it possible to simultaneously obtain ions providing an analysis of atoms on the surface, as well as ions providing a measurement of the layer thickness with an average atomic number different from the average atomic number of the substrate. Inert gas ions with a high ionization potential reflected from a solid surface at a fixed angle within 5-30 ° particle flows form narrow peaks of singly scattered ions or knocked-out recoil ions, the energy of which is uniquely related to the mass of surface atoms. From the laws of conservation of energy and momentum, it follows that the ion energy after elastic scattering by an atom

$$E_{\mathrm{one}}=E_0{\left(\frac{\gamma \cos \varphi +\sqrt{\mathrm{one}-{\mathrm{<figure-callout\; id="2"\; label="\gamma "\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">\gamma </figure-callout>}}^2{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2\varphi }}{\mathrm{one}+\gamma }\right)}^2,\left(\mathrm{one}\right)$$

where γ = m / M, m is the mass of the incident particle, M is the mass of the atom on which the electron is scattered. In this case, energy is transferred to the surface atom

$${\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">E</figure-callout>}}_2=\mathrm{four}\gamma E_0\frac{{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="00000007.png,00000008.png"\; state="\{\{state\}\}">cos</figure-callout>}}^{{}_2}\varphi }{{(\mathrm{one}+\gamma )}^2},\left(2\right)$$

where φ is the angle between the direction of the momentum transferred to the atom as a result of scattering and the direction of the initial ion trajectory. To analyze thin near-surface layers, hydrogen ions are necessary, which, due to the small cross section of elastic scattering (compared to heavier ions), penetrate deep into the surface and, being reflected from atoms deep in the solid and losing their energy along the way due to inelastic collisions, form wide domed energy distributions of reflected particles, the shape of which depends on the atomic number of the particles of the medium and the thickness of the corresponding layers on the target surface. Moreover, when using hydrogen ions (or atoms), narrow peaks of single scattering are practically not observed. The thickness of the surface layer is determined by the formula:

$$L=\frac{2}{k}(\sqrt{E_0}-\sqrt{E_m})\left(3\right)$$

where E ₀ is the energy of the incident ions, E _m is the most probable ion energy after reflection from the test surface, k is the stopping power, calculated by the Lindhard-Schaffer formula k _LS = 0.082 eV ^{l / 2} / A (other literature data can be used [ Gott Yu.V. Interaction of Particles with Matter in Plasma Studies (Moscow: Atomizdat, 1978, 270 s]).

The essence of the proposed method is to provide alternate irradiation of the test sample with those and other ions. In this case, the type and energy of ions used to determine the elemental composition of the surface layer of a solid body should ensure the formation of components of once elastically reflected ions and knocked-out recoil ions [Kurnaev VA, Mashkova B.C., Molchanov VA // Reflection of light ions from the surface of a solid // M. Energoatomizat. 1985, 192 s], while the energy of hydrogen ions used to measure the thickness of the layer on the surface of the sample should be sufficient for penetration to the entire depth of the layer, reflection from the substrate, and flight back into vacuum [Kurnaev VA, Trifonov N .N., M.N. Drozdov, Salashenko N.N. // Letters to the ZhTF, vol. 25 issue 11, 1999]. This method of studying the surface film of a solid body provides a monolayer resolution of the analyzed surface, and also allows you to study films consisting of atoms that differ in average atomic number from the atoms of the substrate, for example, a surface layer consisting of water molecules and hydrocarbons on the surface of metals. Moreover, this method allows not to destroy the investigated surface film of a solid.

This method was implemented using the experimental setup "Big Mass Monochromator MEPhI" Crocodile "[Kurnaev VA, Mamedov N.V. A modernized setup for studying the interaction with the surface of ions with an energy of up to 40 keV. “Brief Communications in Physics” No. 4, p. 45, 2010].

Figure 1 presents a diagram of one of the options for implementing this method, where 1 is an ion source duoplasmatron, 2 is a separating electromagnet, 3 is a target, 4 is a plasma source for affecting the surface of the sample, 5 is an electrostatic energy analyzer, 6 is an ion detector, 7 is the sample heater, α is the angle of incidence of the primary beam, θ is the angle of registration of scattered ions.

The beam extracted from the ion source 1 is separated by the ratio of mass to charge, and for the ion accelerating potential U ₀ , mass M, charge Z, and the magnitude of the separating field B, the relation (U ₀ M / Z) ^1/2 / B = const is satisfied. By changing the current in electromagnet 2, the desired component of the beam U ₀ M / Z = const is extracted and sent to target 3 located in the collision chamber. After that, the reflected particles pass through the electrostatic energy analyzer 5 and are recorded using the detector 6. In this case, the target can be subjected to plasma exposure 4 or heating 7.

к ионам ⁴He⁺ сводится к двукратному уменьшению величины ускоряющего потенциала. В рассмотренном случае слоя карбида бора на поверхности молибдена U₀ должно попеременно составлять 5 и 2,5 кВ как показано на фиг.2 (где τ_анализ - время снятия энергоспектра), а масс-монохроматор настраивается на значение U₀·M/Z=10 КэВ·а.е.м. При этом энергия ионов гелия обеспечивает формирование узких пиков однократно рассеянных ионов, а энергия ионов водорода наличие в энергетическом распределении отраженных частиц ионов, отраженных от слоя более тяжелых атомов подложки. При толщине слоя В₄С порядка 4 нм и облучении ионами $$H_2^{+}$$

с начальной энергией 5,0 кэВ при регистрации под углом рассеяния 30° толщина слоя определяется с точностью ±0,03 нм На фиг.3 представлен характерный энергетический спектр ионов водорода отраженный от исследуемой поверхности (где 1 - энергетический спектр первичного пучка ионов водорода - дельта функция, 2 - энергетический спектр ионов водорода отраженных от исследуемой поверхности, 3 - положение наиболее вероятной энергии ионов после отражения от исследуемой поверхности). Ионы же гелия формируют спектр с узкими пиками, соответствующими частицам, однократно рассеянным от атомов бора и углерода, а также первично выбитым ионам отдачи тех же элементов. Поскольку атомы углерода обладают большим сродством к электрону, то для их детектирования измерялись энергетические спектры отрицательно заряженных атомов отдачи при облучении ионами ⁴He⁺. На фиг.4 представлен характерный энергетический спектр отрицательно заряженных ионов отдачи и ионов гелия выбитых и отраженных от исследуемой поверхности (где 1 - положение пика, соответствующего атомам отдачи кислорода, 2 - положение пика, соответствующего атомам отдачи углерода, 3 - куполообразная часть спектра соответствующая отрицательным ионам гелия, отраженным от поверхности) На фиг.4 четко видны два пика, которые соответствуют атомам отдачи углерода и кислорода (атомы кислорода являются остатками адсорбированных на поверхности молекул воды). Высокоэнергетическая часть этого спектра по форме полностью соответствует высокоэнергетической части спектра положительных ионов. Таким образом, куполообразная часть спектра соответствует отрицательным ионам гелия.For example, in order to simultaneously determine the composition and thickness of a layer of light boron carbide atoms on the surface of a substrate of heavy molybdenum atoms, it is necessary to alternately direct hydrogen and helium ions onto the target, changing the ion accelerating voltage on the ion source in accordance with the condition U ₀ M / Z = const. When using helium ions for analysis, the transition from ion irradiation $$H_{}^{}$$$${}_2^{+}$$

to ⁴ He ⁺ ions is reduced to a twofold decrease in the value of the accelerating potential. In the case considered, the boron carbide layer on the molybdenum surface U ₀ should alternately be 5 and 2.5 kV as shown in Fig. 2 (where τ _analysis is the energy spectrum removal time), and the mass monochromator is set to U ₀ · M / Z = 10 KeV · a.m. In this case, the energy of helium ions ensures the formation of narrow peaks of singly scattered ions, and the energy of hydrogen ions is the presence in the energy distribution of reflected particles of ions reflected from a layer of heavier substrate atoms. When the thickness of the layer In ₄ With about 4 nm and ion irradiation $$H_{}^{}$$$${}_2^{+}$$

with an initial energy of 5.0 keV, when recording at a scattering angle of 30 °, the layer thickness is determined with an accuracy of ± 0.03 nm. function, 2 - energy spectrum of hydrogen ions reflected from the investigated surface, 3 - position of the most probable ion energy after reflection from the studied surface). Helium ions, on the other hand, form a spectrum with narrow peaks corresponding to particles once scattered from boron and carbon atoms, as well as primary knocked-out recoil ions of the same elements. Since carbon atoms have a high electron affinity, the energy spectra of negatively charged recoil atoms upon irradiation with ⁴ He ⁺ ions were measured to detect them. Figure 4 shows the characteristic energy spectrum of negatively charged recoil ions and helium ions knocked out and reflected from the surface under study (where 1 is the position of the peak corresponding to oxygen atoms, 2 is the position of the peak corresponding to carbon atoms, 3 is the domed part of the spectrum corresponding to negative helium ions reflected from the surface) In figure 4, two peaks are clearly visible, which correspond to the atoms of the return of carbon and oxygen (oxygen atoms are residues adsorbed on the surface of the mole water molecules). The high-energy part of this spectrum in shape is fully consistent with the high-energy part of the spectrum of positive ions. Thus, the domed part of the spectrum corresponds to negative helium ions.

с энергией 20 кэВ, а при уменьшении U₀ до 2 кВ - ионы Ne⁺ с энергией 2 кэВ. Протоны позволят измерить по энергетическому спектру толщину слоя, а ионы неона - его состав.To analyze an order of magnitude thicker layers, a mixture of Ne and H ₂ gases can be used. In this case, the mass monochromator is tuned, for example, to a ratio of U ₀ · M / Z = 40 KeV · amu. In this case, when applying an accelerating potential of 40 kV to the source, ions will fall on the target $$H_{}^{}$$$${}_2^{+}$$

with an energy of 20 keV, and with a decrease in U ₀ to 2 kV - Ne ⁺ ions with an energy of 2 keV. Protons will make it possible to measure the thickness of a layer from the energy spectrum, and neon ions - its composition.

A sharp difference in the energies of primary ions allows continuous recording of the spectrum of scattered particles. If the characteristic sections of the energy spectra for different ions coincide, then by synchronizing the measurements of the spectra with a change in the accelerating voltage, one can obtain independent spectra for different ions.

The degree of simultaneity in measuring the thickness and composition of the layer on the surface of the sample is determined by the frequent changes in U ₀ . So, at a frequency of change of U ₀ 10 Hz, the analysis of the thickness and surface composition will be carried out with a time difference of 0.1 s, at 100 Hz - with a difference of 10 ms.

Thus, it follows from the above that the proposed method allows one to determine the elemental composition and thickness of the surface layer of a solid under plasma irradiation in order to study the laws and mechanisms of interaction of TNR plasma with candidate materials of the first wall of the TCB. And also to improve the control of the surface of materials when applying (forming) or removing from it thin layers of substances used in the electronic industry.

Claims (3)

1. The method of determining the elemental composition and thickness of the surface film of a solid when exposed to the surface, which consists in measuring the energy spectra of ions reflected and knocked out of the surface of a solid, characterized in that the energy spectra are measured directly in the process of external action on the surface of a solid or immediately after it, by alternately irradiating in time the surface of a solid mass-separated with respect to masses to charge by hydrogen ions and inert ions a call by applying a corresponding accelerating voltage to an ion source operating on a mixture of inert gases and hydrogen, while the elemental composition of the surface layer of a solid is judged by the energy spectra of the reflected inert gas ions, and the film thickness by the energy spectra of the reflected hydrogen ions. 2. The method according to claim 1, characterized in that helium, neon, argon or xenon are used as inert gas ions. 3. The method according to claim 1, characterized in that the external action is carried out by etching with an ion beam, or by spraying with ion beams, or by irradiation with plasma, or by the action of atoms or molecules of a gas medium, or by heating.

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