CZ309261B6 - Thin optical semiconducting film, producing it, equipment for producing this layer and reading devices - Google Patents

Abstract

The invention is an optical semiconductor device (1) which has an optical absorption gradient and an impedance spectrum gradient in the high frequency range. The optical semiconductor element (1) comprises a thin layer (11) which is applied to a substrate (14). The method comprises the steps of spraying the reaction gases by at least two magnetrons (M1 and M2), a diaphragm (3) is between the magnetrons (M1 and M2), which can move vertically. Another type is a plasma deposition system (5) that carries out a method of forming an optical semiconductor device (1). Another type relates to a reading device (9) that can determine the authenticity of an object which has a security element with an optical semiconductor layer.

Description

Optical semiconductor thin layer, method of its production, equipment suitable for the production of this layer and reading device

Field of technology

In the first embodiment, the present invention falls into the field of the method of manufacturing optical semiconducting thin layers and elements, suitable in particular as a security protection element for marking the authenticity of products, wherein the optical semiconducting element contains a surface-gradient optical thin layer.

In a second embodiment, the present invention relates to a product, in particular a thin layer that can be produced in the above-mentioned manner and an optical semiconductor element. A thin optical semiconductor layer exhibits surface gradient material and optical properties.

In a third embodiment, the present invention relates to a plasma deposition system capable of performing a method of manufacturing an optical semiconductor thin layer.

The fourth embodiment relates to a device that is adapted to read an optical semiconductor element with a surface gradient layer and to determine the authenticity of the product on which this layer is provided.

Current state of the art

Currently, there are a number of optical protection elements that can be used to guarantee the authenticity of the product in which this element is implanted. By default, these are various thin-film holograms with a defined relief. These holographic or otherwise functional optical reliefs must be provided with a protective layer or a system of protective layers that will ensure protection against mechanical damage and also provide a safety element against copying the optical relief. In order to preserve the optical function of the protective element in such a case, the optical relief must be separated from the other layers by at least one layer with a different refractive index. As a standard, simple, deposited layers with a high refractive index are used (metallic, such as aluminum, silver, or transparent, such as ZnS, TiO ₂ , etc.).

The current trend is to try to protect these holographic elements more sophisticatedly against forgery with other optical elements or optically functional elements that have defined optical properties that form parameters for unambiguous identification of the element and this element is difficult to counterfeit. US 2004/0126669 AI describes a method of depositing an optical thin layer on a hologram. Deposition is carried out using printing methods with possible thermal sharpening. Moreover, this document describes only a transparent layer with a high refractive index.

In patent document US 4851095 A, reactive magnetron sputtering of optical thin layers or multilayers with a defined dependence of the absorption coefficient on the wavelength is described. However, the system does not address the implementation of the deposition of surface-inhomogeneous thin layers, which we will hereinafter call "surface-gradient thin layers", when for these layers there is a gradient of the chemical composition of the thin layer and its optical constants not along its thickness profile, but this gradient exists in the direction of one suitably chosen the coordinate axis of the rectangular Cartesian coordinate system, which is parallel to the surface of the thin layer and is chosen in the direction of this gradient.

Reactive magnetron sputtering of thin films operating at extremely low pressures in the HiPIMS mode combined with a radio frequency (RF) inductively coupled (ICP) electrode in the form of a single turn of a ribbon conductor operating in a stationary magnetic field with an electron cyclotron wave resonance (RF-ECWR) where particles move from the target to the substrate almost without collisions is described in the article: V. Straňák, A.P. Herrendorf, S. Drache, M. Čada, Z. Hubička,

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M. Tichý, R. Hippier, Highly ionized physical vapor deposition plasma source working at very low pressure, Appl. Phys. Lett. 100, 141604 (2012) and the application of this system with two sputtering reactive magnetrons for the deposition of semiconducting CuFeO ₂ layers is described in: Z. Hubička, M. Zlámal, J. Olejníček, D. Tvarog, M Čada, J. Krysa, Semiconducting p-Type Copper Iron Oxide Thin Films Deposited by Hybrid Reactive-HiPIMS +ECWR and Reactive-HiPIMS Magnetron Plasma System, Coatings 2020, 10, 232.

The application of the RF-ECWR plasma system in combination with other plasma sources such as MW surfatrons is described in patent file PV 2018-555, i.e. CZ 2018555 A3.

The essence of the invention

The object of this invention is to provide a production method and the safety element of the product itself.

In a first embodiment, the present invention relates to a method of producing a surface-gradient optical semiconductor thin layer. The method includes the steps:

- injecting reactive gases into the vacuum chamber,

- during the reactive sputtering of these injected reactive gases, the sputtered particles from the two magnetrons mix in the space above the surface of the substrate; whereas

- a height-adjustable planar vertical screen is placed in the space above the dielectric substrate between the magnetrons, and the essence of the invention consists in the fact that

- the height-adjustable flat vertical screen changes its position by moving in a direction that is perpendicular to the surface of the substrate.

The method according to the present invention makes it possible to effectively create a surface-gradient semi-conductive layer, which changes optical, especially color, and semi-conductive properties linearly with the spatial coordinate on the surface. This defined surface gradient is achieved in a deposition system with two sputtering magnetrons located in a vacuum chamber and a movably adjustable planar vertical diaphragm located in the space above the substrate between the magnetrons. There is an adjustable gap d between the lower edge of the aperture and the surface of the substrate, which determines the size of the surface gradient of the composition of the deposited layer in the direction of the coordinate, which is parallel to the surface of the substrate. The size of this gradient and the composition of the thin layer is influenced by the size of the gap d between the aperture and the substrate, or by the movement of the aperture, which is perpendicular to the surface of the substrate. The method can be carried out at a pressure lower than 0.05 Pa.

In a preferred embodiment of the invention, the pressure in the vacuum chamber is lower than 10 ^-2 Pa. In this case, the mean free path of the sputtered particles is large, and the sputtered particles can effectively diffuse through a gap of size d between the screen and the substrate, and their effective diffusion length is a function of the distance d. In order to achieve a higher effect of the deposition method of creating a surface gradient structure, it is preferable to use the lowest possible pressure in a two-magnetron deposition system, when the sputtered particles move towards the substrate almost without collision.

In another advantageous embodiment, sputtering takes place in a stationary magnetic field, whereby a high-frequency plasma operating in the wave resonance of an electron cyclotron wave is formed.

The use further contributes to the achievement of sprayed particles moving towards the substrate almost without collision.

The second embodiment of the invention relates to the final product, i.e. a thin layer that can be manufactured above

-2CZ 309261 B6 in the indicated method according to the invention. The thin layer deposited on the substrate exhibits surface gradient properties. Advantageously, this thin layer is implemented as an optical semiconductor element suitable as part of a security element determining the authenticity of the product.

The optical semi-conductor element comprises surface-gradient optical thin layers, wherein the thin layer of the optical semi-conductor element exhibits:

- a gradient of chemical composition and optical properties in the direction of at least one axis that is parallel to the surface of the thin layer; and

- the gradient of the measured impedance spectrum in the high-frequency range from 10 ⁴ Hz to 10 ⁸ Hz.

By using a suitable combination of various reactively dedusted materials according to the production method, a thin-film optical semiconductor element can be created that exhibits a defined surface gradient of chemical composition and optical properties, such as the coefficient of optical absorption, i.e. color, or refractive index. The individual reactively sputtered layers from both magnetrons have a different width of the band gap and a different concentration of donors formed, for example, by oxygen vacancies in the semiconductor and a different size of the mobility of electrical carriers.

Furthermore, for analogous reasons, a gradient of the measured impedance spectrum will arise in the high-frequency region in the interval of high frequencies from 10 ⁴ Hz to 10 ⁸ Hz. This easily measurable information, i.e. the surface distribution of the optical absorption of the thin layer (color) and the impedance spectrum at a given point on the surface in a simplified method of measurement on the protective element using a high-frequency reading device, can be used for an optical safety protective element.

An area gradient layer is a thin layer in which there is a gradient of the chemical composition of the thin layer and optical quantities, especially optical absorption and/or refractive index. The areal gradient is not along the thickness profile of the thin layer, but this gradient exists in the direction of at least one suitably chosen coordinate axis of the rectangular Cartesian coordinate system which is parallel to the surface of the thin layer.

An optical thin layer is a dielectric or semiconductor layer at least partially transparent in the optical region, which has a thickness from tens of nm, e.g. from 10 nm, 50 nm, 100 nm to several units of micrometers, e.g. 1 pm, 2 pm, 5 pm or 9.9 p.m.

In a preferred embodiment, the optical semiconductor element has a suitable combination of sputtered materials. This combination of materials is sputtered from two magnetrons. In certain examples, Fe ₂ O 3 material can be reactively sputtered from the first magnetron and WCh-x material can be sputtered from the second magnetron, where x is 0 to 2. Any semiconducting material that exhibits partial transmission of light in the optical region and exhibits a measurable absorption coefficient can be used a change in relative composition that varies along a gradient. As sputtered targets, metals such as Fe, W, Cu, Ti, Zn, Zr or metal alloys CuFe, CulnGa, InSn, etc. can be used. As reactive gases for sputtering, O ₂ can be used for the formation of semiconducting oxides, H ₂ S for the formation of semiconducting sulfides in this case, a mixture of O ₂ +N ₂ for the formation of semiconducting oxynitrides.

In another embodiment, the optical semiconductor layer can be used as a security element, i.e. it is included in the security element. The surface gradient layer works as a protective optical element, where information about the authenticity is included in the surface gradient of the optical absorption coefficient of the layer, i.e. in the surface gradient of its color and in the surface gradient of the impedance spectrum of this layer.

The third embodiment of the invention relates to a plasma deposition system suitable for the production of an optical semiconductor thin layer according to the present invention. The plasma deposition system according to this embodiment does not have to be exclusively used for the production of an optical semiconductor element, it can also be used for other purposes. The plasma deposition system includes:

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- two sputtering magnetrons working at extremely low pressures and a movable height-adjustable vertical screen, which enables a defined mixing of the sputtered particles from both magnetrons in the space above the surface of the substrate, while the essence of the invention is that the system contains

- a movable adjustable planar vertical screen placed above the substrate, with a distance d between the substrate and the screen. The height-adjustable movable vertical screen is perpendicular to the surface of the substrate.

In another preferred embodiment, the system includes a vacuum pump that is capable of reaching a pressure in the chamber that is lower than 10 ^-2 Pa.

In another preferred embodiment, the system contains a radio frequency electrode capable of creating an inductively coupled plasma, the electrode is placed above the substrate and surrounds the aperture. With another advantage, the radio frequency electrode is connected to a high frequency source.

In another advantageous embodiment, both magnetrons are connected to a high-power pulsed magnetron sputtering (HiPIMS) power source, which is preferably powered by two DC sources.

In another advantageous embodiment, both magnetrons are pulse magnetrons generating voltage pulses with a pulse length in the range of 30 to 200 ps and a voltage amplitude of up to 1000 V and current pulses with a pulse length in the range of 30 to 200 ps and a current amplitude of up to 140 A.

The fourth embodiment of the invention relates to a reading device suitable for determining the impedance properties of an optical semiconductor element according to the invention. The reading device includes

- a dielectric substrate on which the above-mentioned optical semiconductor element can be placed;

- a cover layer, e.g. a plastic film covering an optical semiconductor element;

- measuring contacts that are pressed onto the surface of the cover layer and are simultaneously connected to a measuring device measuring the impedance parameters of the semiconductor element (1), e.g. impedance spectrography, and operating in a defined interval of high frequencies.

The reading device makes it possible to determine the impedance spectrum of the semiconductor layer even through the covering dielectric plastic film.

Clarification of drawings

Giant. 1 represents a schematic arrangement of a two-magnetron deposition system with a moving plane aperture for the deposition of an area-gradient semiconducting optical thin layer.

Giant. 2 is a view of the target plane of a two-magnetron deposition system with a moving plane aperture for surface gradient semiconductor optical thin layer deposition.

Giant. 3 shows an example of a two-magnetron deposition system with a moving plane aperture for the deposition of an areally gradient semiconducting optical thin layer at extremely low pressures using a combination of two high-power pulsed magnetron sputtering (HiPIMS) sources and a radio frequency (RF) inductively coupled plasma operating in the electron cyclotron wave resonance mode

-4CZ 309261 B6 waves.

Giant. 4 represents the time course of the pulse voltage and current on the cathode and magnetron Ml in the arrangement according to Fig. 3.

Giant. 5 represents the time course of the pulse voltage and current on the cathode and magnetron M2 in the arrangement according to Fig. 3.

Giant. 6 represents an example of a reading device of a protective optical semiconductor thin-film element with a surface gradient structure when measuring the impedance spectrum at a defined position on the surface through a covering thin plastic film.

Giant. 7 represents an example of measuring the real component R _{p of the} impedance spectrum of thin semiconductor layers WO3-X and Fe ₂ C>3 in an arrangement according to the example of the reading device shown in Fig. 6 through a covering plastic film.

Giant. 8 presents an example of a photograph of a surface gradient layer and examples of various transmission optical spectra measured on this layer at marked points 1 to 4 on the surface of the layer. A gradient of the layer's chemical composition and its optical and other physical properties exists along the x-axis of the chosen rectangular coordinate system.

Giant. 9 presents a) an example of a photograph of a surface gradient layer on a glass substrate, where the area marked G represents the surface gradient region b) examples of two layers with different sizes of the surface gradient region prepared for two different aperture distances d above the substrate.

Examples of implementation of the invention

Giant. 1 is a basic diagram of a plasma deposition system 5 according to the present invention. The plasma deposition system 5 contains a substrate holder 14 on which a substrate 14 suitable for the deposition of the optical semiconductor element 1 according to the invention is placed. The plasma deposition system 5 further includes at least two magnetrons Ml and M2, which are located above the substrate 14, respectively above the place for the deposition of the optical semiconducting thin layer 11 suitable for the optical semiconductor element 1. Between the magnetrons Ml and M2 is placed an aperture 3, which is capable of of vertical movement from the substrate 14, respectively the optical semiconductor element 1, towards the magnetron heads Ml and M2. The aperture 3 is placed at a distance d from the substrate 14 so that it never touches it. Using the distance d, it is possible to adjust the area gradient of the impedance spectrum of the optical semiconductor element 1 according to the requirements. The above structural elements are placed in the vacuum chamber 2, which is a vacuum vacuum chamber 2. The vacuum chamber 2 is capable of maintaining a pressure of less than 0.05 Pa, preferably the plasma deposition system 5 is also equipped with a vacuum pump 6, which is capable of reaching a pressure in the vacuum chamber 2, which is less than 10 ^-2 Pa. Low pressure and the presence of the working gases 24 is ensured by means of a supply which brings the working gases 24 into the vacuum chamber 2. The working gases 24 can be, for example, oxygen and argon. Magnetrons M1 and M2 spray reactive gases 21 and 22 towards substrate 14.

Giant. 2 represents a cross-section of the vacuum chamber 2. The cross-section shows two magnetron heads M1 and M2 and a movable diaphragm 3, which is located between the magnetron heads.

Giant. 3 represents a preferred embodiment of the plasma deposition system 5, which contains the above-mentioned structural elements, i.e. features according to Figure 1. The preferred embodiment in Fig. 3 also contains an electrode 7 capable of creating inductively coupled plasma. Electrode 7 generates a stationary magnetic field 4. Electrode 7 capable of creating inductively coupled plasma surrounds aperture 3 and is placed above substrate holder 14, respectively above substrate 14 of optical semiconductor element L. Reaction gases 21 and 22 enter the area between aperture 3 and electrode 7.

-5CZ 309261 B6 which atomizes the magnetron Ml and M2. Electrode 7 is further connected to the radio frequency circuit 71, which consists of two coils LI and L2, at least two capacitors Cl and C2, and a radio frequency source. The vacuum chamber 2 also contains an electrically insulating grommet 51 intended for electrical separation of the attachment of the substrate holder to the walls of the grounded vacuum chamber. The vacuum pump, as mentioned above, is preferably such a pump 6 which is capable of reaching a pressure which is less than 10 ^-2 Pa. The pressure is further influenced by the inputs 241 of working gases 24. in this case four working gases F1 to F4 which supply gases: argon, oxygen, nitrogen and a mixture of nitrogen and hydrogen gases. The inlets are preferably equipped with flow meters. Magnetrons M1 and M2 are preferably connected to a high-power pulsed magnetron sputtering source 8, which is further connected to two DC sources 81. The high-power pulsed magnetron sputtering pulse source 8 is further connected to a pulsed synchrotron 82 generating two pulses 821, which are fed to channels CHI and CH2 of the high-power pulsed magnetron sputtering source 8. As a further advantage, the high-power pulsed magnetron sputtering source 8 is dual-channel and is connected to an oscilloscope 80 that monitors voltage and current pulses.

Giant. 4 represents the time course of the voltage and current generated by the high-power pulsed magnetron sputtering source 8 on the first magnetron ML. The length of the voltage pulse is approximately 10 ^-4 s, the maximum voltage amplitude is 800 V. The length of the current pulse is also 10 ^-4 s, while the current amplitude is a maximum of 80 A .Pulses can follow in a row or overlap. The relative length of the pulses affects the dust removal intensity of the individual targets and the density of the plasma in front of the substrate, which affects the semiconducting properties of the deposited layers.

Figure number 5 represents the course of voltage and current on magnetron M2, while the length of the voltage pulse was approximately 8x10 ^-5 with a voltage amplitude of 800 V. The length of the current pulse is also 8x10 ^-5 with a current amplitude on the cathode up to 140 A at most.

Giant. 6 schematically represents a reading device 9, which can be used to read an optical semiconductor element 1, which can be used as a security element for determining authenticity, or counterfeit of the product on which this element 1 is provided. The reading device 9 contains a dielectric substrate 14 on which a semiconductor optical layer 11 according to the present invention is placed and which for these purposes is characterized by a capacitance 911 and a resistance 912. The optical semiconductor layer 11 with a gradient impedance spectrum is provided with a cover layer, e.g. a plastic film 92 , which has its own capacity 93. At least two measuring contacts 921 are provided on the cover layer 92, which are connected to a device measuring the impedance parameters of the semiconductor layer, e.g. to an impedance spectrograph 94. The measuring device 94 also has its own parasitic capacitance 941. Thanks to the measuring device 94, it is possible to determine the characteristics of the optical semiconductor layer 11 according to the present invention, especially the impedance gradient at high frequencies.

Giant. 7 presents examples of impedance spectra measured on a security element containing a thin layer 11 deposited by the method of the present invention. Giant. 7 specifically shows the dependencies of the impedance R _{p of the} optical semiconductor element 1 on the applied frequency of the measuring signal. The record originates from the reading device 9, which device 9 was applied to the optical semiconductor element j_ which was formed according to the present invention. The optical semiconductor element 1 exhibits an impedance gradient of two layers that are deposited on the substrate 14.

Giant. 8 presents an example of a photograph of a surface gradient layer and examples of various transmission optical spectra measured on this layer at marked points 1 to 4 on the surface of the layer. A gradient of the layer's chemical composition and its optical and other physical properties exists along the x-axis of the chosen rectangular coordinate system.

Giant. 9 represents a) an example of a photo of a surface gradient layer on a glass substrate, where the area marked G represents the surface gradient region, b) examples of two layers with different sizes of the surface gradient region prepared for two different distances d of the aperture 3 above the substrate L

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Industrial applicability

The protective element production process can be used in industry in the production of multi-stage optical thin-film protective elements for foils and thin-film holograms.

Claims (15)

PATENT CLAIMS 1. A method of producing a surface-gradient optical semiconductor thin layer (11) by magnetron sputtering, comprising steps: - injecting reactive gases (21 and 22) into the vacuum chamber (2), - mixing of sprayed particles from two magnetrons (M1 and M2) in the space above the surface of the dielectric substrate (14) during reactive spraying of the introduced gases (21 and 22); and - placement of an adjustable planar vertical screen (3) in the space above the dielectric substrate (14) between the magnetrons (Ml and M2), characterized by the fact that during sputtering it leaves to - changing the position of the height-adjustable planar vertical aperture (3) in a direction that is perpendicular to the surface of the substrate (14), thereby creating a surface-gradient optical semiconducting thin layer (11). 2. The production method according to claim 1, characterized in that the pressure in the vacuum chamber (2) is lower than 10' ² Pa. 3. The method according to claim 1 or 2, characterized in that sputtering takes place in a stationary magnetic field (4), while a high-frequency plasma operating in the wave resonance of an electron cyclotron wave is formed. 4. The method according to any one of claims 1 to 3, characterized in that the sputtering takes place using pulsed magnetrons generating voltage pulses with a pulse length ranging from 30 ps to 200 ps and a voltage amplitude of up to 1000 V and current pulses with a pulse length ranging from 30 ps to 200 ps and current amplitude up to 140 A. 5. Surface-gradient optical semiconducting thin layer (11) producible by the method according to any one of claims 1 to 4, characterized in that the layer (11) exhibits a gradient of chemical composition and optical properties in the direction of at least one axis that is parallel to the surface of the thin layer (11); and the gradient of the measured impedance spectrum in the high-frequency region from 10 ⁴ Hz to 10 ⁸ Hz. 6. An optical semiconducting element (1), characterized in that it contains a surface-gradient optical semiconducting thin layer (11) according to claim 5, deposited on a dielectric substrate (14). 7. Optical semiconductor element (1) according to claim 6, characterized in that the thin layer (11) contains a combination of two sputtered optical semiconductor materials that have different absorption coefficients in the optical region of the spectrum and different electrical impedance in the frequency range 10 ⁴ to 10 ⁸ Hz. 8. Safety protective element, characterized in that it contains an optical semiconductor element (1) according to claim 6 or 7. 9. A plasma deposition system (5) for carrying out the production method according to any one of claims 1 to 4, which contains: - two sputtering magnetrons (Ml and M2) capable of working at pressures lower than 0.05 Pa located in a vacuum chamber (2), - a movably adjustable planar vertical screen (3) placed above the dielectric substrate (14), whereby there is a non-zero distance (d) between the dielectric substrate (14) and the screen (3), and the screen (3) is located between two magnetrons (Ml and M2 ), characterized by the fact that the height-adjustable planar vertical screen (3) is adapted for perpendicular movement with respect to the substrate (14). 10. Plasma deposition system (5) according to claim 9, characterized in that it contains a vacuum pump (6) for achieving a pressure in the chamber (2) that is lower than 10 ^-2 Pa. -8 CZ 309261 B6 11. Plasma deposition system (5) according to claim 9 or 10, characterized in that the system further comprises a radio frequency electrode (7) for creating an inductively coupled plasma, which is placed above the substrate (14), while the inside of the electrode (7) is a screen (3). 12. Plasma deposition system (5) according to any one of claims 9 to 11, characterized in that both magnetrons (M1 and M2) are connected to a high-power pulsed magnetron sputtering power source (8) which is preferably powered by two DC sources (81). 13. Plasma deposition system (5) according to any one of claims 9 to 12, characterized in that the magnetrons (M1 and M2) are pulsed magnetrons generating voltage pulses with a pulse length ranging from 30 to 200 ps and a voltage amplitude of up to 1000 V and current pulses with a pulse length ranging from 30 to 200 ps and a current amplitude of up to 140 A. 14. Plasma deposition system (5) according to any one of claims 9 to 13, characterized in that the radio frequency electrode (7) is connected to the high frequency source (71). 15. A reading device (9) for determining the impedance properties of an optical semiconductor element (1) according to claim 6 or 7, characterized in that it contains - a dielectric substrate (14) on which the aforementioned optical semiconductor element (1) is placed; - a cover layer (92) covering the optical semiconductor element (1); and - measuring contacts (93), which are pressed onto the surface (921) of the covering layer (92) and are simultaneously connected to the measuring device (94), which measures the impedance gradient parameters of the semiconductor element (1) and operates in the high frequency range from 10 ⁴ dolO ⁸ Hz.