UA36209C2 - Method for producind a holographic diffraction grating - Google Patents

Abstract

The proposed method for producing a holographic diffraction grating can be used for holographic protection of industrial goods and securities, in optical devices, and other fields. The method consists in applying an adhesive layer and a chalkogenide glass resist layer, which corresponds to the As40S60-xSex triple system where 20 x 40, exposing the substrate to coherent laser radiation and selective etching in the solution containing ethylenediamine, acetone, glycerol, and dimethylsulfoxide with the following content of components (in percent by volume): ethylenediamine of 5 … 30 %, acetone of 55 … 90 %, glycerol of 2 … 8 %, and dimethylsulfoxide as the reminder. In order to improve the characteristics of the diffraction grating, coating with a layer having high reflection coefficient is used. The proposed method provides for improving parameters of the process used for producing diffraction gratings. By the stable resist layer with the triple system structure and an etching solution for treating the substrate provides for the possibility to form the diffraction gratings with sinusoidal slits and copy the diffraction gratings in industrial conditions.

Description

Description of the invention

The invention relates to holography and can be used for holographic protection of industrial goods and securities, in optical instrumentation, in laser technology, in optoelectronics, etc.

In its essence, the invention belongs to the methods of obtaining relief images using inorganic photoresists based on layers of chalcogenide glasses (CS) thermally sprayed in a vacuum. They are characterized by high resolution, a wide spectral range of light sensitivity, a small number of defects due to the vacuum application technology, and high uniformity of the film thickness, which makes them advantageously different from organic photoresists. Particularly successful is the use of inorganic photoresists based on CS for recording holographic diffraction gratings (HDGs), which

And they are characterized by high values of diffraction efficiency and low levels of scattered light (-- 1079), which is achieved due to the high quality of the surface relief (Herke R.R., Koreshov

S.N., Semenov G.B., Smirnov V.V. Holographic optics at the GOII named after S.I. Vavilova - Optical Journal - 1994. - 719 Mo1, - p. 26 - 39),

The formation of GDH with optimal characteristics, in general, depends on the choice of a light-sensitive medium and a selective herbarium, which must be able to reproduce relief images with low light scattering and high resolution. Known methods of producing GDH with the help of photoresists based on XC layers include the sequential application of an adhesive layer (Cg) and an inorganic photoresist in the form of a three-layer film structure Ad-Av8253-Av8oez on the substrate in a vacuum, its exposure by projecting an interference pattern formed by coherent beams onto it laser radiation, formation of relief with the help of selective etching of the photoresist and application of an AI layer on it to increase the diffraction efficiency of GDH. At the same time, selective etching is carried out using solutions containing ethylenediamine - 20 - 75wt.9o and ethyl alcohol - 25 - 8wt. 905 (Ukrainian patent "Mo7442, IPC? 0285/18, 1995), or methylamine - 20 - UBmas.ov and ethyl alcohol - 80 - Bmas. 96 (patent (o)

Mo4737 of Ukraine, IPC? SOZNI/18, 1994). These methods ensure the production of GDH with high values of diffraction efficiency (60 - 7095) and spatial frequency (up to b000 mm') and large geometric dimensions ((200 7 200) mm2 and more). The disadvantages of these methods include: the low quality (o) of diffraction gratings due to the defect of the etched surface of the relief, which leads to an increase in the level of scattered light and a low yield of suitable products, as well as the difficulty of implementing these methods in the conditions o of industrial production. Gee!

As a prototype, a method of manufacturing holographic diffraction gratings was chosen, which includes applying an adhesive layer, an AvobZez layer, to the substrate, projecting onto it an interference pattern formed by two i-o kCoherent beams of laser radiation and exposure, selective etching in a solution containing Ho) ethylenediamine - 5 - 80 wt.9uo and dimethylformamide - 20 - 95 wt.9uo and application of a layer with a high reflection coefficient (patent of Ukraine Mo7443, IPK 5 soZnNI/18, p0285/32, 1995). Unlike those described above, this method is more promising due to the ease of application (one layer of photoresist instead of three), high quality "etching with the help of an anhydrous selective organic herbalizer, which allows you to simplify the manufacturing technology and increase the yield of high-quality GDH. The main drawback of the prototype is the instability of the sensitometric characteristics (light sensitivity and contrast) of the Avobez resist layers, which significantly limits their shelf life after preparation. For commercial light-sensitive materials (which are produced in serial batches), an important characteristic is the warranty period of storage, during which their sensitometric characteristics undergo minor changes that do not significantly affect image quality. This term, for various light-sensitive materials, can range from several months to several years. So, for example, for serial plates with organic photoresist, which are used for the production of GDH, because the warranty period of storage must be at least 3 months. Due to the instability of the properties of the resistance layers of AvozZez, the period of use for the production of GDH is limited to 3 - 5 days from the time of their application (namely) to the substrates. o 50 Also, a significant drawback of the prototype method from the point of view of its manufacturability is the impossibility of obtaining grids with a symmetrical surface relief profile (for example, sinusoids) when exposing a resistive

Me, AvzoZez layer by radiation from He-Ca and Ag lasers, which are the main industrial sources of radiation in the production of GDH. Due to the strong absorption of the radiation of these lasers by the layers

Avozez, the dependence of the speed of their selective etching on the exposure has a non-linear character, as a result of which a relief with an asymmetric profile is formed, for example, in the form of a cycloid. All this limits the use of the prototype method in the mass production of GDH, which involves the use of electroplating or photopolymerization methods for replicating identical copies of diffraction gratings. (Obviously, there is) such copies can be obtained only under the condition that the original grid has a surface relief with a symmetrical profile). 60 The task of this invention is to improve the manufacturability of the method of manufacturing holographic diffraction gratings and bring it as close as possible to the requirements of mass production, by making it possible to use inorganic photoresists with stable properties and highly selective herbicides for their processing, the combination of which allows forming high-quality gratings with a sinusoidal profile of strokes, as well as industrial methods to reproduce identical copies from them. 65 To solve the problem, an adhesive layer, a resist layer of the CS triple system AvloZvokhOeu de 20 "x" 40 is successively applied to the substrate by vacuum evaporation, which, after exposure of the interference pattern, is processed in a selective herbarium containing ethylenediamine, acetone, glycerin and dimethyl sulfoxide with the following ratio of ingredients (06.90): ethylenediamine - 5 - 30; acetone - 55 - 90; glycerin - 2 - 8; dimethyl sulfoxide - the rest, and a reflective coating is applied.

One of the essential features of the proposed invention is the use as a recording medium for holographic recording of diffraction gratings thermally deposited in a vacuum layers of CS of the ternary composition of AvloZvokhOeh, where 20 " x " 40. As established by the authors, these layers are advantageously different from the CS layers of binary systems. So, for example, the resistive layers of the binary composition of AvzoZez are characterized by stable properties, but in the visible spectral range their light sensitivity is low. Av 5523 7/0 layers are characterized by high photosensitivity, however, as already mentioned, their properties are inherently unstable. From a practical point of view, layers of AvlobZvokhZeh de 20 " x " 40 have optimal characteristics, namely: they combine the best qualities of the indicated resistive layers of binary compositions and are characterized by high light sensitivity and stable properties. (Resistive layers of CS of ternary compositions AvzloZvohZeu, selected outside the specified interval, in their properties approach 75 resistive layers of binary compositions Avobez (at x » 40) and Avozez (at x « 20)).

Another essential feature of the proposed invention is its use as an alkaline component of the solution for selective etching of ethylenediamine, as well as the possibility of the formation of fragments with a more complex structure - polychelate and macrocyclic compounds when interacting with the surface of the resist - during the interaction of ethylenediamine with acetone during the preparation of the herb. and macrocyclic effects, which consist in increasing the stability constants of complex compounds compared to those containing monodentate ligands. During the interaction of chelate, polychelate and macrocyclic ligands with irradiated parts of the resist surface with a significantly higher degree of structural organization (compared to non-irradiated ones), steric complications also arise, which should be an additional factor that increases the selectivity of negative etching.

Thus, the increase in the selectivity of negative etching of resists when using the solutions proposed in this invention occurs, according to the authors, primarily due to the formation of more active components of selective negative etching than the original compounds during the preparation of the herbicide solution. In addition, due to the formation of compounds with a relatively high molecular weight, the evaporation of components during the storage of such solutions is practically excluded, which ensures the reproducibility of the properties of the herb during repeated use. The authors established that the dependence of the etching speed of layers Av4o0560-x5eu, Ge) where 20 " x " 40, on the exposure value (for the exposure interval determined by the rectilinear section of the characteristic curve of resistance) in these selective etchants is linear. This makes it possible to ensure the formation of the relief of the GDH with a high-quality etched surface, the profile of which has a symmetrical Ge shape - a sinusoid. Thanks to this, the resulting GDH can be used to reproduce identical copies by known industrial methods of electroplating or photopolymerization. oh

The proposed method of production of GDH is carried out as follows. An adhesive layer (Cg) and a layer of inorganic photoresist based on ЧС of the ternary composition of AvloZvokhZeh, where 20 " x " 40 )nm, and the thickness of the XS layer - from the known (theoretically calculated) condition of "obtaining the maximum diffraction efficiency of the GDH with a sinusoidal profile, which is achieved at the modulation depth and / and -0.3, where n is the stroke height, 4 is the lattice period (i.e., the initial thickness yo x 0.34). From c Exposure of the resist layers was carried out on a holographic installation using Ag laser radiation. "» By changing the angle of convergence of the interfering beams, it was possible to change the spatial frequency of the grating from 600 to "3b00mm". Depending on this, the initial thickness of the CS layer was chosen in accordance with the above condition for obtaining the maximum diffraction efficiency of the GDH with a sinusoidal profile. The value of 75 exposure H was chosen individually for the specific composition of the photoresist on the linear section of its characteristic curve (the dependence of the reduced thickness and / on the exposed resist layer that remains (is) on the substrate after development, on the amount of exposure H: and / on - E (Н), where on - initial thickness of the resist layer). In this case, when the resist layer was exposed to an interference light field from two plane o waves, a relief was formed, which reproduced the sinusoidal distribution of light intensity in the layer. After 20 o, the exposure mixing was carried out using a selective negative action herbator prepared by ethylenediamine, acetone, glycerin and dimeth lsulfoxide at the following ratio of ingredients (vol. 90):

Ethylenediamine 5 - 30; acetone 55 - 90;

GF) glycerin 2-8; 7 dimethyl sulfoxide rest.

Preparation of a selective herb for a resist layer of a specific composition was carried out by mixing ethylenediamine, acetone, glycerin and dimethylsulfoxide in a ratio selected from the above concentration intervals. When using compositions of herbalists selected outside these intervals, the characteristics of selective digestion deteriorate. As a result of chemical treatment of the resist layer

CS in it was formed a relief-phase lattice, the profile of the relief surface of which reflects the distribution of radiation intensity in the layer during its exposure. The reflective ability of the grating is characterized by the diffraction efficiency H, the value of which depends on the depth of modulation of the topography of the PNYA / y, where n is the stroke height. To increase the diffraction efficiency, a reflective coating of AI was applied to the resulting grating.

The quality control of GDH consisted in determining the diffraction efficiency H for radiation with light wavelengths of 7, - 441; 488; 514 and 632 nm according to the expression: ptE іє Lo, b where Iі is the intensity of light diffracted to the first order of diffraction, Io is the intensity of light falling on the grating. The topography of the microrelief of the obtained GDH was studied using an atomic force microscope

Oitepvsiop 3100.

The proposed invention is illustrated by drawings in which: 70 fig. 1 - depicts the general view of the microrelief of the original GDH formed in the photoresist layer of AvzlaoZoozelo; Fig. 2 - shows the profilogram of the microrelief of the original GDH formed in the photoresist layer Avzlo52032e40; Fig. 3 - depicts the general view of the microrelief of a photopolymer copy of the GDH removed from the original GDH; Fig. 4 - shows the profilogram of the microrelief of the original GDH photopolymer copy of the GDH removed from the original GDH.

The proposed invention is also explained by the following examples of its specific implementation. 12 Example 1.

Layers of St and chalcogenide glasses Avl0Z4o05e20, AvloZzobezo and AvloZooZelo With thicknesses of 60 and 90 Ohm, respectively, were applied to glass substrates (Zsht.) measuring (100 7 40) mm2 by thermal evaporation in a vacuum of 2 7 10 Pa (on each substrate in particular). Each of the prepared samples was half covered (longitudinally) with black opaque paper, and the open half was exposed to collimated integral radiation of mercury 720 lamp DRSH-250. At a radiation power density of 0.15 W/cm 2, the exposure was 2 J/cm 2. Then, the samples were cut into 5 equal parts so that each of them contained exposed and unexposed areas of the CS layer. After that, it was studied how the selectivity of the etching of Г layers of CS with different compositions changes depending on the time of their aging (the time of their storage after vacuum sputtering). Digestion was carried out at room temperature (293K) in freshly prepared solutions consisting of ethylenediamine, acetone, glycerol, and dimethylsulfoxide, taken with the content of the ingredients (06.90): (o) for AeaoZaoZego 0 vshcheyuui svter in F zo o for AvaoZ305e3o s

F z o for AeaoZ2oZedo 7 aeyun| in h! ! ! ! . -

The etching selectivity Г was estimated by the ratio of the times of complete dissolution of the exposed (Yi ee) and c unexposed (Ce) sections of the CS layer (in "z i. / (le). The quantitative characteristic of the aging process of the resist layer :z" XO was the relative change in the etching selectivity du - у ;/ уд, where уд and уу are the selectivity of the etching of the freshly prepared and aged, respectively, during the time of the XO layer. The dependence of the relative changes in the etching selectivity of the XO layers on the time of their aging is presented in Table 1. (95)

Phew

Fo Mon Sun Fri No o000111ovt

IF) The given data show that the aging of AzloZvohOeh resist layers, where 20 " x " 40, accelerates with an increase in the Ze content. However, if we compare the resistive layers of the binary composition Av»5ez (prototype) and the above-mentioned ternary compositions, the aging of the latter proceeds much more slowly. Reproducible phototechnical characteristics 60 (light sensitivity, contrast) can be obtained if AG»0.95. This value can be a criterion for establishing the warranty period for the use of Az40560.xZeh resist layers. As can be seen from the table. 1, depending on the composition, this period ranges from 3 months for Аг405205е40 to 1 year for Аз40Б640reg20.

Example 2.

On glass substrates (12 pieces) measuring (76 7 76) mm2, pre-coated with adhesive layers of Cg, samples (by Z pieces) with resistive layers of Av 40Z405e20 chalcogenide glasses were prepared by thermal evaporation in a vacuum.

AzvaloZzoZezo and AvzloZ2oZelo. The conditions of sputtering and after exposure processing were similar to those described in example 1. In order to study the influence of the aging process of resist layers on the value of the diffraction efficiency of 1 GDH, samples with layers of CS of different composition were exposed after a certain period of time

After their preparation. Exposure was carried out on a holographic installation by projecting an interference pattern with a spatial frequency of - 1800mm'', formed by coherent beams of Ag laser radiation with a light wavelength of ;, - 488nm, onto the resist layer. The amount of exposure for each type of resist was chosen based on its characteristic curve (on its linear section). After exposure of the resist layer, relief formation was carried out in it by processing photoresist 70 in a suitable selective herbarium and applying a layer of AI to it to increase the diffraction efficiency of GDH. The quality control of gratings consisted in determining the diffraction efficiency of 1 for radiation with a wavelength of 75, - 6bZ2nm. The results of the investigation of the diffraction efficiency of n gratings formed with the help of resist layers of CS of different composition, depending on the aging time of Ii, are shown in Table 2.

As can be seen from Table 2, the reproducible characteristics of the GDH recording process on AzloZvohOZeh layers, where x is 20; 30; with 29 DAO, can be obtained within the terms established for the indicated resistive layers in example 1. (Reproducible characteristics of the GDH recording process on Azosez layers can be obtained within 3 - 5 days).

Example 3.

Layers of St and chalcogenide glass Avzl0Z2oZelo with thicknesses of 60 and ZOOnm, respectively, were successively deposited on a glass substrate measuring (102 7 102) mm 2 by thermal evaporation in a vacuum of 2 7 10 Pa. Exposure F was carried out on a holographic installation by projecting an interference pattern from av! spatial frequency y - 1800 mm", formed by coherent beams of Ag laser radiation at a wavelength of 5 - 514 nm with a power density of xx 10 W/cm2. The amount of exposure, which was selected from the linear section of the characteristic curve of the resistance layer Av40Z2oZedo, was 0.3 J/cm? In this case, when exposing ke,

35 of the resistive layer, the interference light field from two plane waves should form a relief with a sinusoidal shape of the profile. Post-exposure processing of the resist was carried out at room temperature (293K) in a solution consisting of ethylenediamine, acetone, dimethylsulfoxide and glycerin, taken with the content of ingredients (06.95): "

Ethylenediamine - 22; in acetone - 63; glycerin -4; :z» dimethylsulfoxide - the rest.

After washing and drying the obtained original diffraction grating, a layer of liquid photopolymer composition with a thickness of about 500 μm was applied to it, which was covered with a clean glass substrate of size (102 x 102) mm2 and irradiated through it with the collimated integral radiation of the DRT-220 mercury lamp.

Me At a radiation power density of 0.5 W/cm 2, the exposure was 20 J/cm 2. As a result of the exposure, the photopolymer composition hardened, and after unlocking the substrates, a photopolymer copy of the diffraction grating remained on the second substrate 5p. To compare the quality of the microrelief of the original and their copy, the topography was studied using an atomic force microscope Oitepviop 3100. Figures 1 and 3 show, respectively (Che) images of the general types of microrelief of the original GDH and its photopolymer copy. Also, Fig. 2 and 4 respectively depict microrelief profilograms of the original GDH and its photopolymer copy. A comparison of the presented results convincingly shows the high quality of the microrelief of both the original lattice and its photopolymer copy, the relief profiles have a sinusoidal shape and practically coincide. So, for example, the depth of the relief of the lattice-original and the copy coincide with the accuracy of zh-inm. their identity is also confirmed by measurements

F) diffraction efficiency of n gratings (in - 441; 488; 514 and 632 nm) after applying a reflective layer AI, the results of which are shown in Table 3. in wavelengths 7, - 441; 488; 514 and b632nm. drone vv

Thus, the proposed method allows the use of GDH obtained on the basis of a resistive layer

AzvaloZgoozZelo, for duplicating high-quality copies by the photopolymerization method.

Claims (1)

The formula of the invention is a method of manufacturing holographic diffraction gratings, which includes vacuum application of an adhesive layer, a resistive layer of chalcogenide glass, to the substrate, its exposure to coherent beams of laser radiation, selective etching in a solution containing ethylenediamine, application of a reflective coating, which differs in that the layer is applied chalcogenide glass of the AvloZvokhZeh ternary system, where 20 5 x 540, which after exposure is processed in a selective herbarium, which additionally contains acetone, glycerin and dimethyl sulfoxide with the following ratio of ingredients (volume 9): ethylenediamine 5-30 acetone 55-90 glycerin 2-8 dimethyl sulfoxide is the rest. Official bulletin "Industrial Property". Book 1 "Inventions, useful models, topographies of integrated microcircuits", 2003, M 1, 15.01.2003. State Department of Intellectual Property of the Ministry of Education and Science of Ukraine. s shchi 6) (o) "c) s (Se) so - and? (95) (o) name) («c) 3e) name) 60 b5