RU2727762C1 - Method to determine thickness of thin films - Google Patents

Abstract

FIELD: measurement.SUBSTANCE: use: to determine thickness of thin films. Essence of the invention lies in the fact that thin films with different layer thickness are deposited on the substrate, thickness of the layer is measured by atomic force microscopy, measuring the analytical X-ray fluorescence signal from the film and substrate elements, constructing the calibration curve, wherein the analytical X-ray fluorescence signal is recorded by energy-dispersive X-ray spectroscopy at two different energies of the primary electron beam from the marker element which is included only in the substrate of different titanium alloys, on which titanium nitride-based film is applied by ion-plasma method, based on the constructed calibration curve of attenuation of the signal from the marker element, the actual thickness of the applied film is determined.EFFECT: possibility of obtaining data on thickness of films based on titanium nitride with thickness of up to 100 nm without their destruction and modification.1 cl, 2 tbl, 10 dwg

Description

The invention relates to the field of non-destructive testing and physicochemical analysis, namely to a method for determining the thickness of thin (up to 100 nm) films based on titanium nitride, formed by ion-plasma methods on substrates of various titanium alloys according to X-ray fluorescence recorded by the energy dispersive X-ray method spectroscopy.

A known method for determining the thickness of a homogeneous coating (patent RU 2619133C1, published 05/12/2017, bulletin No. 14) by pressing a cylindrical indenter into the surface of the material. The disadvantage of this method is that its application to a thin coating can lead to local destruction of the coating, which in some cases is undesirable. In addition, this method gives a large error in measuring the thickness of the titanium nitride-based coating deposited on the titanium alloy substrate due to the high hardness of the investigated composition.

There is a known method for determining the thickness of two-layer materials and their constituent layers using pulses of elastic waves (patent RU 2625261C1, published on 12.07.2017, bulletin No. 20) by registering and analyzing the time of arrival of acoustic pulses reflected from the surfaces of the test object and the boundaries of its layers. The disadvantages of this method are the obligatory presence of a clearly defined coating-substrate boundary and a large value of the measurement error for a thin coating applied to a thick substrate.

There is also a known method for measuring in real time the thickness of a film of a chromium-free coating on the surface of a strip steel (patent RU 2498215C1, published on November 10, 2013, bull. No. 31), based on the construction of a correlation function according to X-ray data of two water-soluble chemicals, not reacting with the coating fluid. The disadvantage of this method is the use of two chemical marker elements that are not part of the film or substrate. In addition, this method is used only for liquid-chemical methods of coating and cannot be used for ion-plasma coating methods.

The closest technical solution adopted as a prototype is a method for assessing the thickness of micro- and nanoscale films of lead sulfide [Abzalov RF, Syatynova AV, Astafieva AG, Sidorova MI, Sopin VF ... A technique for evaluating the thickness of the crystallite layer of micro- and nanosized PbS films by X-ray fluorescence. Bulletin of Technological University, 2015, V.18, No. 19, pp. 144–146], based on the measurement of analytical signals from the film and the substrate, followed by the construction of calibration dependences of the ratio of the intensities of the analytical signals Pb (II) and Ni (II) on the concentration of the reference Pb (II) solutions. The disadvantage of this method is the complexity, complexity in the preparation of analyzed samples and measurements. In addition, this method for determining the thickness of coatings is destructive, because peeling and transfer of the film into solution is required by using concentrated nitric acid.

The objective of this invention is to develop a method for determining the thickness of up to 100 nm thin films based on titanium nitride without their destruction and modification, based on the analysis of X-ray fluorescence data recorded at different depths by energy dispersive X-ray spectroscopy.

To solve this problem, a method is proposed that consists in depositing films on substrates, measuring their thickness by atomic force microscopy (AFM), recording analytical signals from film and substrate elements, plotting a calibration dependence of signal attenuation from a marker element, which is only a part of substrate, on the thickness of the applied film (Fig. 1). To plot the calibration dependence, the energy-dispersive X-ray spectra of the substrate S (Fig.1a), as well as samples with films C of known thickness d1 (Fig.1b) and d2 (Fig.1c) are measured at two different energies of the primary electron beam (10 and 20 kV) ... On the calibration graph, the film thickness is plotted along the abscissa axis, and the corresponding ratio of the atomic concentration of the marker element, which is determined from the energy dispersive X-ray spectra, is plotted along the ordinate axis, and is measured using different energies of exciting radiation.

The method allows you to obtain data on the thickness of the films based on titanium nitride with a thickness of up to 100 nm without their destruction and modification. Applying this technical result, it is possible to avoid laborious and time-consuming methods for determining the thickness of films based on the use of surface-sensitive analysis methods.

Below is an example of implementation of the invention, allowing to estimate the thickness of a film based on titanium nitride deposited by the ion-plasma method on a substrate of a titanium alloy of VT-5 grade. Aluminum, which is part of the VT-5 grade alloy, was selected as a marker element. The samples used are a sample of an alloy without a film, as well as samples of an alloy with films, the thickness of which was 37 and 91 nm, respectively. The thickness of the films was certified by the AFM method on the MFP-3D SA microscope (Asylum Research) by measuring the height difference between the sprayed film and the substrate [Shupenev AE, Pankova NS, Korshunov IS, Grigoryants A.G. Analysis of destructive methods for measuring and controlling the thickness of thin films. Proceedings of higher educational institutions. Mechanical engineering, 2019, No. 3, pp. 31–39, doi: 10.18698 / 0536-1044-2019-3-31-39]. The preparation of a sample for AFM investigation consists in the formation of a sharp step at the film – substrate interface by etching a part of the coating with argon ions with an average energy of 1 keV to the VT-5 substrate. The other part of the sample is covered with a fixed stainless steel mask to reduce the likelihood of damage to the film. FIG. 2 shows an AFM image of the surface of a titanium nitride film with a thickness of 91 nm on a VT-5 substrate after ion etching. The titanium nitride film has a clear separation between the dark (etched) and light (non-etched) regions on the sample surface. The construction of the profile of the change in the height of the film from the distance traveled by the probe was carried out across the boundary between the etched and untouched regions along the profile 1 in Fig. 2.

FIG. 3 shows the profile of the change in the heights between the deposited titanium nitride film and the VT-5 substrate after ion etching according to AFM data. Evaluation of the film thickness consists in determining the maximum and minimum values of heights and finding their difference. In this case, the film thickness is 91 nm. Energy dispersive X-ray spectra are measured using 10 and 20 kV exciting radiation. A sample with a film thickness of 64 nm is used as a control sample.

The normalized energy dispersive X-ray spectra for the VT-5 grade substrate are shown in FIG. 4 (electron beam energy 10 kV) and FIG. 5 (electron beam energy 20 kV).

The energy dispersive X-ray spectra recorded on a 37 nm thick titanium nitride film formed on a VT-5 grade substrate are shown in FIG. 6 (electron beam energy 10 kV) and FIG. 7 (electron beam energy 20 kV).

The energy dispersive X-ray spectra recorded on a titanium nitride film with a thickness of 91 nm formed on a VT-5 grade substrate are shown in FIG. 8 (electron beam energy 10 kV) and FIG. 9 (electron beam energy 20 kV).

FIG. 4 - 9 it can be seen that the intensity of the aluminum marker element for all samples increases with the transition from the electron beam energy of 10 kV to 20 kV. With increasing film thickness, a significant attenuation of the signal from aluminum is observed when using an electron beam energy of 10 kV.

The data of energy dispersive X-ray spectroscopy, which were used to construct the calibration dependence, are presented in Table 1.

Table 1

VT-5 (without film) Energy [Al], at. % [Al] 20 / [Al] 10 20 kV 8.5 1.3 10 kV 6.5 VT-5 with 37 nm film Energy [Al], at. % [Al] 20 / [Al] 10 20 kV 6.0 2.6 10 kV 2.3 VT-5 with 91 nm film Energy [Al], at. % [Al] 20 / [Al] 10 20 kV 3.2 5.3 10 kV 0.6

Energy dispersive X-ray spectroscopy data for the control sample are presented in Table 2.

table 2

VT-5 with a film with a thickness of 64 nm (control sample) Energy [Al], at. % [Al] 20 / [Al] 10 20 kV 4.1 3.7 10 kV 1.1

FIG. 10 shows a graph, as well as point 2, corresponding to the control sample. It can be seen that the results for the control sample are in good agreement with the obtained calibration dependence, which indicates the possibility of using the proposed method for assessing the thickness of thin films.

The applicability of this method is limited by the values of the film thickness at which the atomic concentration of the marker element in the energy dispersive X-ray spectra will decrease to zero. However, the results obtained show that the method can be applied in the range of ~ 37-91 nm of film thickness values.

Thus, the proposed invention makes it possible to evaluate the thickness of a film based on titanium nitride without destroying it and modifying it by measuring X-ray fluorescence recorded by energy dispersive X-ray spectroscopy and constructing a calibration dependence of signal attenuation from a marker element included in the substrate on the thickness of the applied film ... To plot the calibration dependence, it is necessary to measure the energy dispersive X-ray spectra of the substrate samples without a film, as well as at least two samples with a film of known thickness, certified by the AFM method, at two different energies of the primary electron beam of 10 and 20 kV. This method avoids the use of laborious and time-consuming methods for determining the thickness of the films based on the use of surface-sensitive methods of analysis.

Claims (1)

A method for determining the thickness of thin films, including their deposition with different layer thicknesses on a substrate, measuring the layer thickness by atomic force microscopy, measuring the analytical signal of X-ray fluorescence from the elements of the film and the substrate, plotting a calibration dependence, characterized in that the analytical signal of X-ray fluorescence is recorded by the method energy dispersive X-ray spectroscopy at two different energies of the primary electron beam from a marker element, which is only a part of a substrate made of various titanium alloys, on which a titanium nitride-based film is applied by the ion-plasma method, based on the constructed calibration dependence of the signal attenuation from the marker element, determine actual applied film thickness.

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