Vacuum device and method of manufacturing of multilayer thin-film precision optical coatings

Abstract

The proposed vacuum device and the method for producing multilayer thin-film optical coatings therein can be used in industrial production of precision optical products comprising multilayer thin-film coatings having one hundred or more layers. The vacuum device differs from known prototypes of similar purpose in that an even number of magnetrons is installed in the process chamber, each capable of moving within its placement plane, and two magnetrons forming a magnetron sputtering system are equipped with targets made of identical materials. Plasma sources assisting the operation of the magnetron sputtering systems are mounted on the side walls of the vacuum process chamber above the working surfaces of the targets, and holders for securing the substrates are mounted on the side walls of the vacuum process chamber at the level of the target working surfaces. According to the proposed coating production method, a magnetron sputtering process assisted by plasma sources is used, wherein plasma is generated throughout the entire volume of the vacuum process chamber, and coatings are deposited onto preheated substrates fixed on holders in a planetary mechanism. The substrates move through the high-density plasma zone alternately passing through sputtering and oxidation zones, and the optical thickness of the coatings is measured end-to-end using an optical control system.

Description

[0001] VACUUM DEVICE AND METHOD OF MANUFACTURING OF MULTILAYER THIN-FILM PRECISION OPTICAL COATINGS

[0002] FIELD OF THE INVENTION

[0003] This invention relates to vacuum technology and equipment, in particular to vacuum devices intended for coating multilayer thin-film optical coatings on optical elements.

[0004] BACKGROUND OF THE INVENTION

[0005] The vacuum device and its use in the method of producing optical coatings can be applied in the industrial manufacturing of narrowband interference filters used in astrophysical research to obtain monochromatic images of celestial objects, in fiber-optic communication networks operating with multichannel sequential data transmission, and in the manufacturing optical systems such as highly reflective mirrors, spectral beam splitters with steep edges, and other products containing multilayer thin-film coatings with one hundred or more layers exhibiting the following properties.

[0006] Patent document US6736943 describes a vacuum unit comprising a vacuum process chamber within which a rigid frame, a holder with an affixed optical substrate whose front surface is exposed in the process chamber for applying multilayer coatings, and technological devices for making the coatings are installed. It uses technological devices with targets mounted on a rigid frame. The design of the vacuum unit allows controlling the distance from the working surfaces of the targets to the front surface of the substrate by means of special motion devices.

[0007] In addition to various process parameter monitoring devices, the vacuum device includes a unit designed to continuously control the thickness of each thin-film layer in the multilayer coating. During the coating of optical layers onto the substrate, the thickness of the produced thin-film layers is strictly monitored to ensure uniformity across the entire outer surface of the substrate. For optical thin films, optical thickness is a more accurate characteristic than geometric thickness, as it determines the optical properties of the coating. Therefore, in modern vacuum systems used for producing optical thin-film coatings, optical thickness is typically controlled.

[0008] The vacuum unit described in patent document US6736943 is equipped with an optical control system, which is used for end-to-end control of the optical thickness of the coating. To control the uniformity of the coating on the substrate surface, the control is carried out in two areas - in the center of the substrate and at a certain distance therefrom.

[0009] The main disadvantage of the described vacuum unit is the impossibility to provide the necessary productivity of the technological process, as the methods of applying of coatings thereon are of limited productivity, and the design of the unit does not allow to use a large number of holders.

[0010] Documents US4851095, US5944964, US6207536, US6274014, and US6328865 describe analogues of both the specified vacuum device and the method for thin-film coating performed therein. The mentioned sources disclose devices comprising a vacuum chamber with a cylindrical substrate holder positioned at its center, designed to rotate around a central axis. During the coating process, the technological units used for producing the coatings are mounted on the side walls of the vacuum process chamber around the cylindrical holder, the inner space of which is divided into separate sections, each containing one technological unit. These sections are not isolated from one another but are essentially independent, with the processes taking place in each section being controlled autonomously.

[0011] The thin-film coating method described in these patent documents involves vacuum deposition of thin-film layers onto substrates placed on a rotating cylindrical holder, followed by their oxidation. As the cylindrical substrate holder rotates around its central axis, the substrate moves past various processing units, such as target magnetrons and plasma sources. In this setup, the formation of thin-film layers on the substrates takes place in sections equipped with magnetrons, while their oxidation occurs in other sections containing plasma sources.

[0012] The methods for depositing multilayer thin-film optical coatings described in the aforementioned documents involve vacuum coating onto a heated substrate mounted on a rotating holder, using moving magnetrons and a plasma source. A specific feature of these methods is the generation of plasma from working gases for sputtering the material, and plasma from other gases for oxidizing the sputtered material and maintaining it within the overall volume of the vacuum process chamber. In this case, the sputtered materials, passing through ionized gas clouds created by the magnetrons and plasma sources, become ionized, gaining additional energy, and are oxidized, acquiring the desired properties. Due to volumetric oxidation and the additional energy, the deposited material molecules form a thin stoichiometric film with low porosity and low stress on the outer surface of the substrate. The low stress of the film is a result of the stoichiometric molecules forming the thin film having higher energy. This is the main distinguishing feature of the patented method for producing multilayer thin-film optical coatings, compared to the methods described in the aforementioned patent documents. Moreover, utilizing the entire volume of the vacuum process chamber allows for increasing the distance between the magnetrons and the substrates, which in turn reduces the impact of high-energy magnetron plasma on the substrate as well as the thermal effect.

[0013] The disadvantages of the described devices and method are that a dense layer of the target material must first be deposited onto the substrate, followed by its oxidation process. When forming an oxide layer within the limited volume of the dense metal film along the surface of the substrate, the volume increases, resulting in additional mechanical stresses in the thin layer. Such characteristics of the technological process prevent the deposition of coatings onto thin optical glass, semiconductor elements, and plastics, where low-stress coatings are required in order to avoid substrate deformation after the evaporation process. Patent document EP4163416 describes a vacuum apparatus for producing multilayer optical coatings. The construction of the vacuum device described in this document is the closest to the patented device. The apparatus comprises a vacuum process chamber with a rigid internal frame, a substrate mounting device, a holder, designed to rotate around a central axis, at least two magnetrons with targets whose working surface planes are parallel to the outer surface plane of the substrate, an optical control system with two optical channels, a plasma source, and a substrate heater. In this case, the central axis of the holder coincides with the central axis of the vacuum process chamber, and the magnetrons are mounted on independent movement devices intended to adjust the distance from the target center to the central axis of the process chamber during the technological process.

[0014] The disadvantages of the vacuum device and the method of manufacturing multilayer thin- film coatings described in the document EP4163416 are low productivity due to the use of a holder designed for a single substrate, as well as insufficient uniformity and density of the formed coatings required for the majority of precision optical products with multilayer thin- film coatings.

[0015] SUMMARY OF THE INVENTION The purpose of this invention is to develop an industrial vacuum device for producing precision multilayer interference coatings on optical substrates, as well as a coating production method that, when used with the proposed vacuum device design, ensures high productivity and technological process stability. The resulting optical coatings are characterized by high homogeneity, density, adhesion, strong parameter stability under external conditions, and low defect levels.

[0016] The identified technical problem is solved in that the vacuum device for producing precision multilayer thin-film optical coatings comprises a vacuum process chamber in which holders for securing substrates, magnetrons with targets made of materials that form coatings on the outer surface of the substrate, plasma sources, heaters, and an optical control system for measuring the optical thickness of the produced coating are installed. The holders are designed so that the substrates can rotate around their own axis, and each of the magnetrons is mounted on a movement mechanism that allows the magnetrons with targets to move within their mounting plane.

[0017] The uniqueness of the vacuum device is that it includes an even number of magnetrons, allowing identical material targets to be mounted on two magnetrons that together form a magnetron sputtering system. The plasma sources are installed on the side walls of the vacuum process chamber, positioned above the working surfaces of the targets. The substrate holders are arranged along a planetary mechanism, which is designed to rotate the substrates both around their own axis and around the central axis of the vacuum process chamber. The surfaces of the substrate holders lie in a single plane at the level of the plasma sources.

[0018] The optical control system also comprises an optical control unit with interchangeable control elements mounted on a holder that is fixed in place to prevent rotation around its own axis, while allowing adjustment of the control elements' positions. The optical control unit contains at least four control elements.

[0019] The device includes planar magnetrons with the working surfaces of the targets positioned above the surfaces of the magnetron protective elements. It also includes cylindrical magnetrons. The movement mechanisms are designed to allow adjustment of the magnetrons’ tilt angle relative to their initial positioning plane.

[0020] The device is equipped with two magnetron sputtering systems and two plasma sources mounted on opposite side walls of the vacuum process chamber positioned at the same height above the working surfaces of the targets. The elements of the working gas evacuation system from the vacuum process chamber are arranged so as to direct the flow away from the working surfaces of the targets.

[0021] According to the proposed coating production method magnetron sputtering of target materials is used in combination with plasma sources. The coating process is carried out in a vacuum process chamber, where coatings are deposited onto preheated substrates mounted on holders that rotate around their own axis. The substrates are heated within a temperature range of 50°C to 300°C using heaters. The method involves magnetron evaporation of target materials using plasma sources, with plasma being generated by the technological devices throughout the entire volume of the vacuum process chamber. Simultaneously, the optical thickness of the coating is measured by an optical control system. Based on the data obtained by comparing the measured values with the calculated ones, the position of the magnetrons and the parameters of the technological process are adjusted accordingly.

[0022] The coating production method is characterized by the use of magnetron sputtering systems consisting of two magnetrons with identical targets and plasma sources positioned above the working surfaces of the targets, outside the plasma discharge zones created by the magnetrons.

[0023] The substrates mounted on rotating holders in a single plane are additionally rotated around the central axis of the vacuum process chamber, ensuring their movement through the high-density plasma zone alternately between the evaporation and oxidation zones. The coatings are produced under reduced pressure.

[0024] In the high-density plasma region, the substrates enter the evaporation and oxidation zones at different angular coordinates. Each magnetron sputtering system is supported by several plasma sources.

[0025] To reduce contamination on the working surfaces of the targets, the magnetrons are operated in such a way that the working surfaces of the targets are positioned above both the surfaces of the protective elements and the locations of the vacuum pumping system components. The optical control system uses multiple control elements, allowing the optical design of the coating to be divided into several simpler structures, each monitored by a separate control element.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a three-dimensional view of the interior of the vacuum process chamber of the vacuum device intended for producing precision multilayer thin-film optical coatings. Figure 2 shows the planetary mechanism holder with the optical control unit mounted on it. Figure 3 shows the transmission graph of a super-narrowband filter with a wavelength of 777.4 nm.

[0027] Figure 4 shows the transmission graphs of super-narrowband filters with a wavelength of 777.4 nm produced using five different technological processes.

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] The device for producing multilayer thin-film precision optical coatings (see Fig. 1) on substrates 8 comprises a vacuum process chamber 1, inside which a planetary mechanism 10 is installed. This mechanism is designed so that during the technological process, the substrates 8 simultaneously rotate around their own central axis and around the central axis of the vacuum process chamber 1.

[0030] The dual rotation function of the substrates 8 in the planetary mechanism 10 is performed by a rotation device 11, which transmits the rotational motion from a motor to the base 13 of the planetary mechanism. In this configuration, holders 9 are mounted on the base 13 of the planetary mechanism 10 to fix the substrates 8 within the vacuum process chamber 1, and these holders are capable of rotating around their own central axis. The number and size of the holders 9 can be adjusted depending on the size of the substrates 8 and the required uniformity of coating on their outer surfaces. Substrate 8 is mounted in the holder 9 so that the central axis of the holder 9 coincides with the central axis of the substrate 8, and the surfaces of the holders 9 intended for securing the substrates 8 lie in the same plane with a deviation not exceeding 0.1 mm.

[0031] The dimensions of the substrates 8 correspond to the dimensions of the holders 9, respectively. Other parameters of the planetary mechanism 10, for example, the dimensions of its base 13, the arrangement of the holders 9 in the base 13 of the planetary mechanism 10, i.e. the diameter D of rotation of the substrate centers around the central axis of the vacuum process chamber 1, are calculated taking into account the mutual arrangement of the technological devices in the vacuum process chamber 1, in order to obtain the required homogeneity and density of the coating.

[0032] The uniformity of the thin-film coatings deposited on all substrates 8 mounted on the planetary mechanism 10 also depends on the correct selection of the rotation speed of the planetary mechanism 10 around its central axis (which coincides with the central axis of the vacuum process chamber) and the rotation speed of the holders 9 with substrates 8 during the coating process. The rotation speed of each individual holder 9 is determined by selecting the gear ratio of the base 13 of the planetary mechanism 10. The gear ratio is chosen so that each substrate 8 enters the evaporation and oxidation zones at different angular coordinates, thereby avoiding repetitive motion patterns that could negatively affect the uniformity of the optical thickness of the produced coatings.

[0033] In addition to the planetary mechanism 10, an even number of magnetrons 2 with targets 3 are installed inside the vacuum process chamber 1, on the working surfaces of which the evaporation process of coating materials takes place. Magnetrons 2 participate in the technological process of manufacturing multilayer thin-film optical coatings in pairs. Each pair of magnetrons 2 is equipped with targets 3 of the same materials, respectively, each pair of magnetrons 2 covers layers of a thin film of a certain composition. A pair of magnetrons 2 operating simultaneously form a magnetron sputtering system. The magnetron sputtering system operates using alternating current power sources. At each moment of time, one of the targets 3 of the magnetron sputtering system is at a positive potential, and the second - at a negative potential, and vice versa. Thus, at each moment of time, material is sprayed from one target 3 at a certain frequency, and the accumulated charge is removed from the working surface of the second target 3. This allows for a significant reduction in the formation of curvature on the surface of the targets, which in turn improves the quality of the sprayed coatings. The holders 9 used to fix the substrates 8 in the vacuum process chamber 1 are mounted on the base 13 in such a way that the outer surface of the exposed substrates 8 intended for coating is oriented toward a plane parallel to the mounting plane of the magnetrons 2.

[0034] The holders 9 used to secure the substrates 8 inside the vacuum process chamber 1 are mounted on the base 13 in such a way that the outer surface of the exposed substrates 8 intended for coating is oriented toward a plane parallel to the mounting plane of the magnetrons 2.

[0035] The uniformity of each thin-film layer's thickness on the substrates 8 during production varies due to consumption of material from the target 3, its erosion, and the changing geometry of the working surface. To improve the uniformity of the produced coating layers, each magnetron 2 is mounted on a movement mechanism 4, which allows the magnetron to move within its mounting plane. In this case, all movement mechanisms 4 are autonomous, i.e. each magnetron can be shifted by its respective movement mechanism 4 by a predetermined distance, either before or during operation. Since each magnetron 2 in the sputtering system has its own autonomous movement mechanism 4, it can be shifted by a distance different from that of the other magnetron in the system. In addition to allowing planar position adjustments, the design of the movement mechanisms 4 also enables the tilt angle of the magnetrons 2 to be adjusted relative to their initial mounting plane and along with the tilt of the targets 3 ensuring optimal evaporation efficiency.

[0036] The described vacuum device employs planar magnetrons, which consist of a cooled housing containing an internal magnetic system. The target 3 is attached to the housing and pressed against the magnetic system using a clamping ring. All surfaces of the housing and the clamping ring are covered with protective elements to prevent parasitic (unwanted) sputtering. In the installation of planar magnetrons 2 in the vacuum device, the target 3 is positioned so that its working surface is located above all surrounding protective element surfaces. This arrangement reduces the deposition of material onto the protective elements around the target 3, preventing the formation of debris on its working surface and avoiding electrical failures that could negatively affect the quality of the resulting coatings.

[0037] In addition to planar magnetrons, the vacuum device also includes cylindrical magnetrons, in which the targets are cylindrical in shape and capable of rotating around their own axis. The use of cylindrical magnetrons reduces defects in the deposited layers due to the continuous rotation of the target. This movement constantly changes the portion of the target’s surface being sputtered and reduces the area exposed to sputtering at any given moment, thereby decreasing oxidation of the target’s working surface and the accumulation of debris. These properties lower the likelihood of electrical breakdowns and associated coating defects, while stabilizing the process through more uniform target material consumption. Moreover, the cylindrical magnetron design allows the target volume to be increased while maintaining the same overall dimensions as a planar magnetron, due to the cylindrical shape of the target, or allows for a reduction in magnetron size while keeping the same amount of target material. This increases the flexibility of the optical sputtering process layout, since the large dimensions of planar magnetrons with flat targets can limit the spatial arrangement of magnetrons 2 relative to each other and to the overall size of the planetary mechanism 10 within the vacuum process chamber 1.

[0038] The vacuum process chamber 1 includes devices designed to protect the working surfaces of the targets 3. These devices consist of a movement mechanism 6 that enables the motion of a screen 5 above the working surfaces of the targets 3. During the technological process, the screens 5 cover the working surfaces of the targets 3 in one of the magnetron sputtering systems. This allows the sputtering units located beneath the screens to be started up and stabilized while protecting the targets' working surfaces from unintended deposition caused by other operating magnetron sputtering systems. A single movement mechanism 6 can hold multiple screens 5, each dedicated to a respective magnetron in a magnetron sputtering system. The movement mechanism 6 may operate according to different displacement principles, such as rotational, sliding, return movement, etc.

[0039] To ensure high efficiency in the coating production process and to improve coating quality, the system uses induction-coupled plasma generation devices, plasma sources 7. In the presented vacuum device, the plasma sources 7 are installed on the side walls of the vacuum process chamber 1 at the same height as the working surfaces of the sputtered targets 3 and outside the plasma discharge zones created by the magnetrons 2. The construction of the vacuum device enables the substrates 8 to rotate around the central axis of the vacuum process chamber 1 , such that the substrates alternately pass above the working surfaces of the targets 3 and adjacent to the plasma sources 7. In this way, the plasma sources 7 and the rotating substrates 8, mounted on holders 9 in the planetary mechanism 10, are positioned at the same level and in close proximity to one another in the zone of maximum effective influence during the technological process for producing multilayer thin-film precision coatings.

[0040] The use of plasma sources 7 in the patented device significantly influences both the quality and the growth rate of the deposited coatings. Charged particles from the plasma source 7, when injected into the magnetron discharge plasma zone, interact with the magnetron plasma and the target 3. This allows the working pressure of the technological process to be reduced, thereby improving the quality of the optical coatings by increasing the mean free path of the sputtered material particles. Furthermore, the ionized state density (ion density) in the plasma increases, and the sputtering process is sustained by ions from two independent sources - the intrinsic magnetron discharge and the external plasma beam. The particle beam generated by the plasma source 7, when injected into the magnetron discharge plasma zone, increases resistance to the formation of dielectric films on the working surface of the target 3. This, in turn, enables a significantly higher deposition rate and reduces the likelihood of arcing on the target 3 surface, thereby improving the quality of the thin films deposited on the substrates 8.

[0041] The vacuum process chamber 1 includes outlets for the process gas evacuation system. The system components are arranged in such a way as to separate the flows of the process gases, minimizing the influence of gases supplied to the plasma sources 7 on the operation of the magnetron sputtering systems. For this purpose, the evacuation system elements are positioned behind the substrates 8, so that the flow of exhausted process gases is directed opposite to the working surfaces of the targets 3. By reducing the formation of contaminants and chemical reaction byproducts on the working surfaces of the targets 3, the functional characteristics of the magnetrons 2 are improved. This expands the operating range of the magnetron discharge plasma, helping to achieve high-quality and stable physical properties of the coated films in each cycle and to shorten the overall process cycle time.

[0042] To ensure the uniformity of the produced thin-film coating, the vacuum device maintains specific dimensional parameters (hereinafter referred to as X and Y). Distance X is defined as the distance from the surface of the holders 9, which secure the substrates 8, to the working surfaces of the targets 3. This distance X remains constant throughout the entire technological process and can only be changed when reconfiguring the vacuum device or between processing cycles, for example, by adjusting the position of the planetary mechanism 10 or replacing it with another modification. Distance Y refers to the distance from the central axis of the vacuum process chamber 1 to the center of the working surfaces of the targets 3 in the magnetrons 2. The X and Y distances are selected based on the positioning of the magnetrons 3 and plasma sources 7 in such a way that, taking into account the rotation of the centers of the substrates 8 around the central axis of the vacuum process chamber 1, exceptionally high coating uniformity for multilayer interference coatings is achieved.

[0043] As previously mentioned, the optical thickness of the deposited thin films determines the optical properties of the coating. During the evaporation process in the vacuum device, the optical thickness of the coating is continuously monitored as it is deposited onto the substrate, so-called, based on changes in the optical properties of the coating throughout the evaporation process.

[0044] This optical thickness monitoring, end-to-end control, can be performed directly on the substrate 8. In such cases, an automatic optical control system is used, and optical signal measurements are taken at the center of substrate 8 during each full rotation of the planetary mechanism 10. A preferred variant of the optical control system includes the use of an optical control unit 14, which comprises a set of interchangeable control elements 15 mounted not on the substrate 8 itself, but on one of the holders 9. A single optical control unit 14 contains at least four control elements 15. When monitoring the optical characteristics of the coating on a control element 15, measurements are taken at the center of the control element 15, which, like the substrate 8, is positioned at the center of the holder 9. This minimizes the difference in optical thickness between the coating applied to the control element 15 and the coating applied to the substrate 8.

[0045] Using multiple control elements 15 makes it possible to increase the total number of sputtered layers without increasing the overall deposition error, as would typically occur when using only a single control element.

[0046] In order to perform measurements prior to starting the technological process, the rotation of the holder 9, on which either the test substrate 8 or the optical control unit 14 with the control elements 15 is mounted, is united. The optical control unit 14 is designed to allow the position of the control elements 15 on the surface of holder 9 to be changed, enabling the element undergoing measurement to be placed in the center of the holder 9 surface and then replaced by another during the process.

[0047] To stabilize the thermal conditions of the technological process, including the heating of substrates 8, heaters 12 are installed in the vacuum process chamber 1. In the described vacuum device, the heaters 12 are mounted in the bottom of the vacuum chamber 1 and directed toward the substrates 8 to heat their outer surfaces.

[0048] The method for producing multilayer thin-film precision optical coatings in the vacuum device described above is detailed below.

[0049] In the vacuum process chamber 1 the height X of the holders 9 of the planetary mechanism 10 above the working surfaces of the targets 3 is adjustable. The distance X calculated in advance considering all technological process parameters (such as the chamber size, substrate dimensions, and operating characteristics of the devices involved in deposition etc.), is maintained constant throughout a single coating cycle to achieve maximum uniformity of each coating layer. The distance Y, also pre-calculated for each magnetron 2 individually to meet required uniformity, can be adjusted during the process but must remain within a defined, calculated range.

[0050] Substrates 8 are secured in the holders 9 of the planetary mechanism 10. The testing elements 15 of the optical control unit 14 are attached to a fixed holder, which does not rotate during the technological process, after which the sealed door of the vacuum technological chamber 1 is closed.

[0051] Using low and high vacuum pumping systems, the vacuum technological chamber 1 is pumped up to the pressure set for the start of the technological process. Once the target pressure is reached or during the evacuation process the heaters 12 are activated to heat the substrates 8 from the outer surface to the required temperature. The plasma sources 7 are then activated and brought to operational mode.

[0052] Before starting the coating process, the plasma sources 7 are used to clean the outer surfaces of the substrates 8. During this cleaning operation, the rotation device 11 of the planetary mechanism 10 is activated, causing the substrates 8 to rotate around the perimeter of the vacuum process chamber 1 at a speed of 5 to 60 revolutions per minute, while also rotating around their own axis. During this cleaning phase, the working surfaces of the targets 3 in the first magnetron sputtering system are covered with screen 5. The first magnetron sputtering system refers to the pair of magnetrons that will perform the first layer deposition step in the process chain. The magnetrons 2 whose targets 3 are covered by the screen 5 are activated to clean the working surfaces of any oxide layer.

[0053] Once these preparatory steps are completed, the vacuum device is ready for the coating deposition process.

[0054] The first thin layer of the multilayer precision optical coating is deposited onto the outer surface of substrate 8 when both magnetrons 2 of the first magnetron sputtering system are operating, along with the working plasma sources 7 that act upon the working surfaces of both the targets in the active magnetrons 2 and the substrate 8. To initiate the technological process, the working surface of the targets 3 in the active magnetron sputtering system is exposed by shifting the screens 5 using the movement mechanisms 6. During this process, working process gases and electrical power of specific magnitude and frequency are supplied to the magnetrons 2 and plasma sources 7 within the process chamber 1.

[0055] At the same time as the first thin layer production process begins, the second magnetron sputtering system is turned on. At that time, the working surface of its targets 3 is covered by a screen 5 moved by the movement mechanism 6, under which the targets 3 are "sprayed", thus preparing their working surface for the technological process.

[0056] Due to the specific spatial distribution of the sputtering material sources, magnetrons 2 and the oxidizing sources and plasma sources 7, which is enabled by the design of the vacuum device, and due to the minimized distance from substrates 8 to plasma sources 7 ensured by the planetary mechanism 10, the substrates 8 enter different zones of high- density ionized plasma. During each rotation of a substrate 8 around the central axis of the vacuum process chamber 1 , it spends part of the time in the high-density plasma zone of the magnetron sputtering system (sputtering zone), where partially oxidized target material is deposited onto the substrate surface, and part of the time in the high-density plasma zone of the plasma sources 7 (oxidation zone), where the deposited layer undergoes preoxidation on the substrate surface. This ensures high-quality oxidation of the sputtered material, resulting in increased coating density. By increasing the density of the coatings, the likelihood of water vapor absorption into the layer is reduced, thereby improving the stability of the optical and mechanical properties of the coatings under external conditions. Reducing the distance between the substrates 8 and the plasma sources 7 allows the oxygen pressure in the process chamber 1 to be lowered. This, in turn, reduces the likelihood of oxidation of the target 3 surface and the risk of warping, thereby decreasing the number of defects in the resulting coating.

[0057] The arrangement of the working surfaces of the sputtered targets 3 in planar magnetrons, positioned above the surfaces of the protective elements, also plays an important role in the quality of the deposited coatings. This configuration minimizes dust accumulation on the protective elements around the target 3, prevents contamination on its working surface, and thus avoids electrical failures that could negatively impact coating quality.

[0058] Accurate achievement of the calculated optical characteristics of the deposited coating is ensured by a system for monitoring the optical thickness of the produced thin films. The proposed vacuum device is equipped with an automatic optical thickness monitoring system, which can measure directly on the rotating substrate 8 or on the control elements 15 of the optical control unit 14. During coating, optical thickness is monitored end-to-end at the center of the rotating substrate 8 or at the center of a control element 15. To produce simple interference coatings, monitoring at the center of the rotating substrate 8 is sufficient. In this case, all holders 9 of the planetary mechanism 10 are used for securing substrates 8. To produce more complex optical coatings, an optical control unit 14 with control elements 15 is used. In such cases, one of the holders 9 is not used to hold a substrate 8 and is instead fixed, with the exception for rotation around its central axis, with the optical control unit 14 installed on it to monitor the optical thickness via its control elements 15.

[0059] The monochromatic photometry method is used for optical thickness monitoring. In this method, transmission maxima and minima caused by interference effects in the deposited optical coating are recorded as light passes through it. The optical signal is measured during each revolution of the planetary mechanism 10 around the central axis of the vacuum process chamber 1.

[0060] To reduce total sputtering error, when manufacturing interference coatings made of more than 100 thin layers, the optical design is divided into several simplified designs. In the overall coating process, a defined number of layers is assigned to each of the available control elements. During the process, the operating program of the optical control system sends a signal to the optical control unit 14 to switch to an unused control element 15 once a predefined number of layers has been reached.

[0061] The more control elements 15 are used during the process, the lower the overall sputtering error. Additionally, using multiple control elements 15 makes it possible to simplify the control of complex coatings with non-uniform layer thicknesses by breaking the total coating structure into several simpler sub-structures, each monitored separately by a selected control element 15.

[0062] If the measured optical characteristics do not match the calculated ones, the optical control system sends a corresponding signal to the vacuum device controller, depending on the degree of deviation, to adjust the operating parameters of the technological equipment in use including the movement of the magnetrons 2. The optical control system continues to read the received signals, processes them, and compares them with the calculated characteristics until the target parameters are reached. Once the required characteristics are achieved, the optical control system generates a signal to stop the production of the first thin layer. Upon receiving this signal from the optical control system, the first thin layer deposition is stopped by turning off the first magnetron sputtering system. The next thin coating layer is then deposited in the same way using the second magnetron sputtering system along with the already activated plasma sources 7, until a readiness signal is again received from the optical control system.

[0063] By alternating magnetron sputtering systems with targets 3 made of the required materials and by using different operating modes for the plasma sources 7, a multilayer optical coating with predefined properties can be produced.

[0064] Several key features of the above-described technological process can be highlighted.

[0065] During coating production, the magnetrons 2 operate in pairs as part of a magnetron sputtering system, and each system is supported by one or more plasma sources 7 located above the working surfaces of the targets 3. This configuration significantly reduces oxidation and warping of the target 3 working surface, thereby reducing defects in the resulting coatings. At the same time, the plasma sources 7 and magnetrons 2 effectively ionize both the process gases and the sputtered material atoms, creating high-density plasma zones within the vacuum process chamber 1.

[0066] During the coating process, the substrates 8 rotate around the central axis of the vacuum process chamber 1, alternately passing over the working surfaces of the targets 3 and near the oxygen plasma sources 7. Due to the specific spatial distribution of the sputtered material and the coordinated motion of the substrates 8 within the process chamber 1 , high film density and high-quality oxidation of the deposited material are achieved. High coating density reduces the optical scattering of electromagnetic radiation, which is particularly important for interference coatings with a total thickness greater than 30 microns. It also reduces the likelihood of water vapor absorption into the film, thus improving the stability of the optical and mechanical properties under external conditions.

[0067] Because the substrates 8 alternately move over the magnetrons 2 and near the oxygen plasma sources 7, the required oxygen concentration for oxidizing the film formed while the substrate passes over the magnetron 2 is lowered. This reduction in overall oxygen concentration in the process chamber 1 also reduces the risk of oxidation of the target 3 working surfaces, thereby lowering the likelihood of target failure and coating defects.

[0068] Due to the dual rotation of the substrates 8 (around their own axis and around the central axis of the vacuum processing chamber), and their entry into the evaporation and oxidation zones at different angular coordinates, an optical thickness uniformity more than 0.2% is achieved both for each individual substrate and across the entire surface area of all substrates 8.

[0069] The design of the planar magnetrons used, specifically, the working surface of the target 3 being positioned above the protective surfaces of the magnetron 2, reduces contamination of the target 3 by film particles falling from the protective elements. This results in fewer deformations on the target’s working surface and consequently fewer defects in the finished coatings.

[0070] The following describes the production of an ultra-narrowband interference filter for a wavelength of 777.4 nm, intended for an optical transient process detector. The thin-film, multilayer optical coating of the filter is made from tantalum oxide (Ta2Os) and silicon oxide (SiC>2) using magnetron sputtering systems with targets made of Ta and Si, respectively. The coating consists of 163 thin-film layers. The complex structure is divided into four simpler sub-structures, each monitored by one of four control elements 15 in the optical control unit 14. The average thickness of the Ta2Os and SiC>2 layers is approximately 100 nm and 150 nm, respectively, with a total coating thickness of 18 pm.

[0071] A vacuum device (Fig. 1) is used for filter production, which comprises a vacuum process chamber 1 , inside which are installed: a planetary mechanism 10 with ten holders 9 for round substrates 8 with a diameter of 200 mm, four planar magnetrons 2 with round targets 3 with a diameter of 200 mm, two induction plasma sources 7 and two infrared heaters 12. Each magnetron 2 is mounted on an independent movement mechanism 4, designed as a linear drive system. Two of the magnetrons 2 are equipped with tantalum targets 3 forming the first magnetron sputtering system, while the other two are equipped with silicon targets forming the second sputtering system. To minimize coating defects, the protective surfaces of the planar magnetrons are positioned below the working surfaces of the targets 3.

[0072] The two plasma sources 7 are located at the same height as the working surfaces of the magnetron targets 3, mounted on opposing side walls of the vacuum chamber 1 in such a way that the plasma beams generated by the plasma sources 7 intersect the plasma discharge zones of the magnetrons.

[0073] The diameter D of the rotation path of the substrate 8 centers around the central axis of the vacuum process chamber 1 is 720 mm. This value is selected based on the size of the vacuum chamber 1 and the arrangement of the magnetrons 2 and plasma sources 7, ensuring that the substrates 8 rotate as close as possible to the plasma sources 7 during the process, thereby maximizing control over the coating process.

[0074] The optical glass substrates 8 are mounted on the surface of the holders 9 of the planetary mechanism 10 at a calculated height X = 210 mm above the working surfaces of the targets 3. The substrates 8 are mounted such that their central axes align with those of the holders 9, and the outer substrate surface is parallel to the working surface of the flat targets 3 in the magnetrons 2. During the coating process, the movement mechanisms 4 allow the magnetrons 2 to move while maintaining the planarity of the target surfaces. The initial position of the magnetrons 2 relative to the center axis of the vacuum chamber is Y = 200 mm. The optical control unit 14 with four control elements 15 is mounted on a stationary holder 9.

[0075] Using low and high vacuum pumping systems, the vacuum process chamber 1 is evacuated to a pressure of 1 xio-2Pa. During evacuation, the planetary mechanism 10 is activated and set to rotate at a speed of 50 revolutions per minute. The rotation device 11 remains active throughout the entire technological process until the process chamber 1 is opened. Once the planetary mechanism 10 begins rotating, heaters 12 located at the bottom of the vacuum process chamber 1 are activated, directing heat toward the outer surfaces of substrates 8, which are heated to a temperature of 150°C. Simultaneously, the pressure in the process chamber 1 is reduced further to 8x1 O'4Pa.

[0076] Before the precision optical coating process begins, the outer surface of the substrates 8 is cleaned using inductively coupled plasma generated by both plasma sources 7. This cleaning removes molecular particles, adsorbed gases, polymer fragments, and water vapor, and activates surface atomic bonds to improve adhesion of the deposited layer. For this purpose, oxygen is supplied through the plasma sources 7, and the pressure in the vacuum processing chamber 1 is maintained between 0.03-0.05 Pa, while the plasma sources 7 are turned on. This treatment lasts for no less than five minutes, with the oxygen pressure controlled by mass flow controllers.

[0077] During substrate 8 cleaning, the working surfaces of the tantalum targets in the first magnetron sputtering system are shielded by screen 5. The corresponding magnetrons 2, though covered by the screen, are turned on to clean the working surfaces of the targets 3 from any oxide films. Argon gas is supplied to the magnetrons 2, and the chamber pressure is raised to 0.07 Pa. The magnetrons 2 are operated at 1 kW power for five minutes to clean the surfaces of the targets 3.

[0078] After the substrates 8 are cleaned, the plasma sources 7 continue to operate in an oxygen environment. Due to the specific arrangement of reactive gas inlets, RF electrodes of the plasma sources 7, and the pumping system elements, the plasma sources 7 create gradients of oxidizer concentration and reactivity, directed from the exhaust outlets toward the plasma sources 7 inside the vacuum process chamber 1.

[0079] While still working under the protective screen 5, the power of the magnetrons 2 is increased to 2-5 kW. After a 15-second stabilization, the protective screen 5 is retracted, exposing the working surfaces of the targets 3, and the magnetron sputtering system begins depositing the first thin-film coating layer.

[0080] The thin layer is formed as follows: the partially oxidized outer surfaces of substrates 8 are bombarded by ions from the magnetron discharge plasma, which eject target material atoms and their molecular compounds with reactive gas particles. During one pass over the operating magnetrons 2 (sputtering zone), a partially oxidized film of about 5 A angstroms is deposited on the front surface of each substrate 8. Each individual substrate 8, after flying through the evaporation zone, flies through the first and second high-density reactive gas plasma regions (oxidation zones) created by the plasma sources 7, where the thin layer is completely pre-oxidized, within -300 and -900 ms. In the described system, the oxidation equilibrium of the target 3 material atoms forming the thin-film layer on the outer surface of substrate 8 can shift between oxidation on the target surface and oxidation on the substrate surface, depending on oxygen consumption. Thus, the implemented method for producing thin-layer coatings in a vacuum device of the described design allows reducing the oxygen concentration in the vacuum technological chamber 1 , necessary for the complete oxidation of the formed coating, and working with less oxidized target surfaces, thus reducing the formation of curvature on the working surface of the target 3 and the probability of defects in the produced coating.

[0081] During the deposition of a thin-film layer, the power of the magnetrons in the magnetron sputtering system and the argon flow rate remain constant. The power supply unit of the magnetron sputtering system regulates the oxygen flows of the plasma sources 7 in order to maintain a constant voltage on the magnetrons 2 by adjusting the oxygen flow rate up or down. This is essential to ensure that the working surface of the sputtered targets 3 remains in a stable state throughout the process, providing a consistent sputtered material beam profile, steady deposition rate, and minimal warping.

[0082] The optical control system monitors the optical thickness of each thin layer based on the control elements 15 of the optical control unit 14. The optical signal is measured at each revolution of the planetary mechanism 10 at the center of the control elements 15 mounted on the stationary holder 9.

[0083] During the sputtering of the first layer, the second magnetron sputtering system, whose targets are made of silicon, is covered with a protective screen 5. This prevents contamination of the surface of the targets 3 with dust. At the same time as the first thin layer is sprayed, the second magnetron sputtering system, located under the protective screen 5, is switched on. For this purpose, 1 kW of power is supplied to the magnetrons of the second magnetron sputtering system, thus preparing the working surface of the targets 3 for spraying the second thin layer of coating. The optical control system measures the received signal and compares it with the calculated characteristics, and when the required parameters are reached, the optical control system generates a signal that stops the thin film coating process. Spraying is stopped by turning off the power supply unit of the first magnetron sputtering system, so that the propagation time of the sprayed material after the shutdown signal is as short as possible.

[0084] At this point, the plasma sources 7 continue operating, and the oxygen flow is adjusted according to the composition required for the second layer. The power of the second magnetron sputtering system is increased to 3-5 kW, and after 15 seconds of stabilization, the screen 5 is retracted, exposing the silicon targets 3, and the second thin layer is sputtered.

[0085] Simultaneously, 1 kW of power is supplied to the first magnetron sputtering system, now covered by the screen 5, to prepare the working surface of its targets for the next sputtering cycle. This algorithm for producing multilayer precision optical thin-film coatings is repeated until an interference coating with the desired optical properties is fully formed.

[0086] The standard working pressure in vacuum process chambers during magnetron sputtering is approximately 5x10“1Pa. However, when plasma sources 7 are used in combination with magnetron sputtering systems, the working pressure can be reduced to 7X 10“2Pa.

[0087] Figure 3 shows the transmission graph of an ultra-narrowband filter with a center wavelength of 777.4 nm, obtained using the described method in the vacuum device of the invention. The full width at half maximum (FWHM) is 0.8 nm, transmission reaches up to 90%, and the uniting range is 400-1000 nm at OD3. These values achieved in a single process cycle demonstrate high process stability. Such coating performance would be unattainable without precise control over all technological parameters and the properties of the optical layers being fabricated, as well as the mechanical precision of the vacuum device components and the stability of all equipment operations.

[0088] Figure 4 shows the transmission curves of ultra-narrowband filters made in five independent runs, each targeting the same 777.4 nm center wavelength. The central wavelength deviation between the different processes is 0.6 nm, or 0.077%, which indirectly indicates the exceptional stability of the refractive index and thickness across all 163 layers in each coating. This, in turn, reflects high density, homogeneity, substrate adhesion, and low internal stress.

[0089] In summary, the vacuum device design and the manufacturing method for multilayer precision optical thin films described in this invention effectively solve the identified technical problem and ensure the achievement of the desired technical result.

[0090] The use of a planetary mechanism in the technological process allows to ensure a high yield percentage not only by increasing the number of substrate holders, but also by improving the uniformity of each produced thin layer and the entire coating due to the double rotation of the substrates. The dimensions of the planetary mechanism, the mounting of the holders in it and the selected mutual positions of the magnetrons and plasma sources create the conditions for producing coatings in different zones of high- density ionized plasma generated by technological equipment, which allows to form thin layers characterized by high density, homogeneity, adhesion to the substrate and low stresses on the outer surface of the substrate.

[0091] Proper arrangement of plasma sources, magnetron sputtering systems and substrates in the vacuum process chamber, design features of magnetron sputtering devices, and arrangement of elements of the product extraction system from the vacuum process chamber improve the quality of the produced coatings, as they prevent the formation of dielectric films and other contaminants on the working surfaces of sputtering targets, which impair the performance of magnetrons and increase the likelihood of warping.

Claims

CLAIMS1. A vacuum device for producing multilayer thin-film precision optical coatings, comprising a vacuum process chamber, holders for securing substrates inside the vacuum process chamber, each holder being capable of rotating about its own axis, magnetrons with targets made from materials forming coatings on the outer surface of the substrates, plasma sources, heaters, and an optical control system for measuring the optical thickness of the produced coating, wherein the holders are configured so that the substrates rotate about their own axis, and each magnetron is mounted on a movement device that enables the magnetron with the target to move in its placement plane, characterized in that: the number of magnetrons is even, and targets of identical material mounted on two magnetrons form a magnetron sputtering system; the plasma sources are mounted on the side walls of the vacuum process chamber above the working surfaces of the targets; the substrate holders are mounted in a circular arrangement in a planetary mechanism that ensures rotation of the substrates about their own axis and about the central axis of the vacuum process chamber, and the surfaces of the holders for securing the substrates lie in a single plane at the level of the plasma sources.

2. The vacuum device according to claim 1 , characterized in that the optical control system includes an optical control unit with interchangeable control elements mounted on a holder fixed so that it does not rotate about its own axis, and the position of the control elements is adjustable.

3. The vacuum device according to claim 1 or 2, characterized in that the optical control unit comprises at least four control elements.

4. The vacuum device according to any one of claims 1-3, characterized in that the working surfaces of the targets in the planar magnetrons are positioned above the surfaces of the protective elements of the magnetrons.

5. The vacuum device according to any one of claims 1-4, characterized in that the magnetrons are mounted on movement devices enabling movement in their placement plane and adjustment of their inclination angle relative to the initial plane.

6. The vacuum device according to any one of claims 1-5, characterized in that the device additionally comprises screens for protecting the working surfaces of the targets, said screens being movable by movement mechanisms to cover or uncover the working surfaces during the technological process.

7. The vacuum device according to any one of claims 1-6, characterized in that the movement devices are configured to allow adjustment of the inclination angle of the magnetrons relative to their initial placement plane.

8. The vacuum device according to any one of claims 1-7, characterized in that it comprises two magnetron sputtering systems and two plasma sources mounted on the opposite side walls of the vacuum process chamber at the same height above the working surfaces of the targets.

9. The vacuum device according to any one of claims 1-8, characterized in that the elements of the system for evacuating working gases from the vacuum process chamber are arranged to direct the flow away from the working surfaces of the targets.

10. The vacuum device according to any one of claims 1-9, characterized in that it comprises planar magnetrons.

11. The vacuum device according to any one of claims 1-9, characterized in that it comprises cylindrical magnetrons.

12. A method for producing multilayer thin-film precision optical coatings, comprising: fixing the substrates on holders rotating about their own axis inside the vacuum process chamber; heating the substrates within a temperature range from 50°C to 300°C using heaters; generating plasma by technological devices throughout the volume of the vacuum process chamber;depositing thin-film layers by magnetron sputtering of target materials, using plasma sources; rotating the substrates about their own axis and the central axis of the vacuum process chamber to ensure movement alternately through high-density plasma zones during sputtering and oxidation; measuring the optical thickness of the coating using an optical control system; characterising in that: magnetron sputtering systems are used, each consisting of two magnetrons with identical targets, and plasma sources located above the working surfaces of the targets and outside the plasma discharge zones generated by the magnetrons; the substrates rotate both about their own axis and about the central axis of the vacuum process chamber, ensuring movement through high-density plasma zones alternately during sputtering and oxidation; and coatings are produced under reduced pressure.

13. The method according to claim 12, characterized in that the optical control system uses multiple control elements, wherein the optical coating structure is divided into several simpler structures, each being controlled by a separate control element.

14. The method according to claim 12 or 13, characterized in that in the high-density plasma region, the sputtering and oxidation zones of the substrate are located at different angular coordinates.

15. The method according to any one of claims 12-14, characterized in that the operation of each magnetron sputtering system is supported by at least two plasma sources.

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