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

FIELD OF THE INVENTION

This invention relates to vacuum techniques and technologies, in particular to vacuum devices for depositing multilayer thin-film optical coatings on optical elements.

STATE OF THE ART

The vacuum device and its use in the method of manufacturing optical coatings can be applied in the industrial production of narrowband interference filters used in astrophysical research to obtain monochromatic images of space objects, in fiber optic communication networks operating with multi-channel serial data transmission; in the manufacture of optical systems, such as highly reflective mirrors, spectrum splitters with a steep front part and other products containing multilayer thin-film coatings with one hundred or more layers with these properties.

Patent document US6736943 describes a vacuum device consisting of a vacuum process chamber in which a rigid frame is mounted, a holder with a fixed optical substrate, the outer surface of which is exposed in the process chamber for multilayer coating, and process devices for producing the coatings. The process devices are used with targets mounted on the rigid frame. The design of the vacuum device allows you to control the distance from the working surfaces of the targets to the upper surface of the substrate using special motion devices.

In addition to the various process parameter monitoring devices, the vacuum unit is equipped with a device for continuously monitoring the thickness of each thin film layer of the multilayer coating. When optical coatings are applied to a substrate, the thickness of the produced thin film layers is strictly controlled, which must be uniform over the entire outer surface of the substrate. For optical thin films, their optical thickness is a more accurate characteristic than the geometric thickness, since it determines the optical properties of the coating. Therefore, in modern vacuum systems, optical thickness is usually controlled when producing optical thin-film coatings.

The vacuum device described in patent document US6736943 is equipped with an optical inspection system, which is used to perform constant control of the optical thickness of the coating. In order to control the uniformity of the coating on the substrate surface, the inspection is performed in two places - in the center of the substrate and at a certain distance from it.

The main disadvantage of the described vacuum device is that it is impossible to ensure the required technological process efficiency, since the coating production methods used in it are low-performance, and the design of the device does not allow the use of many holders.

Documents US4851095, US5944964, US6207536, US6274014 and US6328865 describe both the specified vacuum device and the method of coating thin films therein. The aforementioned sources describe devices consisting of a vacuum chamber, in the center of which is a cylindrical device for fixing the substrate (substrate holder), designed so that it can be rotated about a central axis. The technological devices used in the coating production process are attached to the side walls of the vacuum process chamber around a cylindrical holder, the internal space of which is divided into separate compartments with one technological device. These compartments are not isolated from each other, but are essentially independent, and the processes occurring in them are controlled autonomously.

The thin film deposition method described in these patent documents involves vacuum deposition of thin film layers onto substrates placed on a rotating cylindrical holder and oxidation thereof. As the cylindrical substrate holder rotates about its central axis, the substrate moves past process devices such as target magnetrons and plasma sources. In this case, the formation of thin film layers on substrates takes place in sections with magnetrons, and their oxidation takes place in other sections containing plasma sources.

The methods for depositing multilayer thin-film optical coatings described in the aforementioned documents are vacuum deposition of coatings onto a heated substrate located on a rotating holder using moving magnetrons and a plasma source. A specific feature of the method is the generation of a working gas plasma for sputtering the material and a gas plasma for oxidizing the sputtered material and maintaining the sputtered material in the total volume of the vacuum process chamber. In this case, the sprayed materials, flying through ionized gas clouds formed by magnetrons and plasma sources, are ionized, gaining additional energy, and oxidized, acquiring the required properties. Due to bulk oxidation and additional energy, the molecules of the deposited material form a thin stoichiometric film, characterized by low porosity and stress on the outer surface of the substrate. The low film stress is due to the fact that the thin film on the substrate surface is formed by stoichiometric molecules with higher energy. This is the main difference between the patented multilayer thin film optical coating production method compared to the method described in the above-mentioned patent documents. In addition, using the entire volume of the vacuum process chamber allows for an increase in the distance from the magnetrons to the substrates, which in turn reduces the impact of the high-energy magnetron plasma on the substrate and the temperature effect on it.

The disadvantage of the described devices and methods is that first a dense film of the target material must be deposited on the substrate, and then its oxidation process must be carried out. When forming an oxide layer in a limited space of a dense metal film along the surface of the substrate, the volume increases, which creates additional mechanical stresses in the thin layer. Such features of the technological process do not allow the deposition of coatings on thin optical glasses, semiconductor elements and plastics, where coatings with low mechanical stress are required to avoid substrate deformation after the evaporation process.

Patent document EP4163416 describes a vacuum apparatus for producing multilayer optical coatings. The vacuum device described in this document is closest in design to the patented device. The device consists of a vacuum process chamber with a rigid frame inside, a substrate mounting device - a holder designed to be rotatable around a central axis, at least two magnetrons with targets whose working surfaces are parallel to the plane of the outer surface 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 technological chamber, and the magnetrons are mounted on autonomous movement devices designed to change the distance from the center of the target to the central axis of the technological chamber during the technological process.

The disadvantage of the vacuum device and method for producing multilayer thin-film optical coatings described in EP4163416 is low throughput due to the use of a single substrate holder, as well as insufficient uniformity and density of the formed coatings required for the production of most precision optical products with multilayer thin-film coatings.

BRIEF DESCRIPTION OF THE INVENTION

The purpose of this invention is to create an industrial vacuum device for producing precise multilayer interference coatings on optical substrates, and a method for producing coatings, which, when used in a vacuum device of the proposed design, would ensure high productivity and stability of the technological process, and the resulting optical coatings should be characterized by high homogeneity, density, adhesion, high stability of parameters under external conditions and have few defects.

The identified technical task is solved by the fact that the vacuum device for the production of multilayer thin-film precision optical coatings has a vacuum process chamber, inside which are mounted holders for fixing 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 designed to measure the optical thickness of the produced coating. The holders are made so that the substrates can be rotated around their axis, and each of the magnetrons is mounted on a movement device that allows the magnetrons with targets to move in the plane of their placement.

The uniqueness of the vacuum device is that it has an even number of magnetrons, so targets of the same materials are mounted on two magnetrons, forming a magnetron sputtering system. Plasma sources are mounted on the side walls of the vacuum process chamber above the working surfaces of the targets. The holders for fixing the substrates are mounted along a planetary mechanism made to rotate the substrates around their axis and around the axis of the vacuum process chamber, and the surfaces of the substrate holders are located in one plane at the level of the plasma sources.

The optical control system also includes an optical control unit with replaceable control elements mounted on a holder fixed so that it cannot be rotated around its axis, with the possibility of changing the position of the control elements. The optical control unit contains at least four control elements.

The device contains planar magnetrons, the working surfaces of the targets of which are located above the surfaces of the magnetron protective elements. The device also contains cylindrical magnetrons. The movement devices are made so that it is possible to change the angle of inclination of the magnetrons relative to the plane of their initial position.

The device has two magnetron sputtering systems and two plasma sources, mounted on the side walls of the vacuum process chamber opposite each other, at the same height above the working surfaces of the targets. The elements of the working gas pumping system from the vacuum process chamber are arranged in such a way that it is possible to direct the flows away from the working surfaces of the targets.

The proposed coating production method uses magnetron sputtering of target materials using plasma sources. The coating method is performed in a vacuum process chamber, where the coatings are deposited on preheated substrates attached to holders rotating around their axis. The substrates are heated in the range from 50^oh up to 300^oh temperature using heaters. The method of magnetron evaporation of target materials using plasma sources is applied, when plasma is produced by technological devices throughout the volume of the vacuum technological chamber, while at the same time optically measuring the optical thickness of the coating by an optical control system. According to 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 corrected.

The coating production method differs in that it uses magnetron sputtering systems consisting of two magnetrons with identical targets and plasma sources located above the working surfaces of the targets outside the plasma combustion zone created by the magnetrons.

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

In the high-density plasma region, substrates enter the evaporation and oxidation zones at different angular coordinates. Each magnetron sputtering system is assisted by multiple plasma sources.

In order to reduce the formation of contamination on the working surfaces of the targets, magnetrons are used so that the working surfaces of the targets are above the surfaces of the protective elements, as well as the locations of the elements of the suction system. The optical control system uses several control elements, therefore the optical structure of the coating is divided into several simple structures, each of which is controlled by a separate control element.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. shows a volumetric view of the interior of the vacuum process chamber of a vacuum device for the production of multilayer thin-film precision optical coatings.

Fig. shows the planetary mechanism holder, on which the optical control unit is mounted.

Fig. shows the bandwidth graph of a super narrowband filter with a wavelength of 777.4 nm.

Fig. shows the transmission curves of super narrowband filters with a wavelength of 777.4 nm manufactured using five technological processes.

DETAILED DESCRIPTION OF THE INVENTION

The device for the production of multilayer thin-film precision optical coatings (Fig. 1) on substrates 8 consists of a vacuum process chamber 1, inside which a planetary mechanism 10 is installed, made so that during the technological process the substrates 8 simultaneously rotate around their central axis and around the central axis of the vacuum process chamber 1.

The dual function of rotating the substrates 8 in the planetary mechanism 10 is performed by the rotation device 11, which transmits the rotation from the motor to the base 13. In this case, the base 13 of the planetary mechanism 10 is equipped with holders 9, designed to fix the substrates 8 in the vacuum process chamber 1 and having the ability to rotate around their central axis. The number and size of the holders 9 can be changed depending on the size of the substrates 8 and the requirements for the uniformity of the coating of their outer surface. The 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 mounting the substrates 8, are in the same plane with a deviation of no more than 0.1 mm.

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 coatings.

The uniformity of thin-film coatings produced on all substrates 8 mounted on the planetary mechanism 10 also depends on whether the rotation speed of the planetary mechanism 10 around the central axis coinciding with the central axis of the vacuum process chamber is correctly selected, and on the rotation speed of the holders 9 with the 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 selected so that each substrate 8 enters the evaporation and oxidation zones at different angular coordinates to avoid repetitive movements that may impair the uniformity of the optical thickness of the produced coatings. In addition to the planetary mechanism 10, an even number of magnetrons 2 with targets 3, on the working surfaces of which the evaporation process of the coating materials takes place, is installed inside the vacuum process chamber 1. Magnetrons 2 are involved 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 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 significantly reducing the formation of curvature on the surface of the targets, which in turn improves the quality of the sprayed coatings.

Holders 9, designed to secure substrates 8 in the vacuum process chamber 1, are mounted on the base 13 so that the outer surface of the substrates 8 open for coating is oriented in a plane parallel to the plane of arrangement of the magnetrons 2.

The uniformity of the thickness of each thin film layer on the substrates 8 during production varies due to the material consumed by the target 3, its erosion and the changing geometry of the working surface. In order to improve the uniformity of the produced coating layers, each magnetron 2 is mounted on a moving device 4, with the help of which the magnetron moves in the plane of its position. In this case, all moving devices 4 are autonomous, i.e. Each magnetron can be moved by its movement device 4 by a predetermined distance both before and during the operation of the magnetron 2. Since each magnetron 2 of the magnetron sputtering system has its own autonomous movement device 4, it can be moved by a distance that does not coincide with the displacement distance of another magnetron of the magnetron sputtering system. In addition to being able to change the position of the magnetrons 2 in the plane, the design of the movement devices 4 allows changing the angle of inclination of the magnetrons 2 relative to the plane of their initial position, and with them the targets 3, in order to ensure the highest evaporation efficiency.

The described vacuum device uses planar magnetrons, which consist of a cooled housing with a magnetic system inside. The target 3 is attached to the housing and pressed against the magnetic system by a pressure ring. All surfaces of the housing and the pressure ring are covered with protective elements to prevent parasitic (incorrect) sputtering. When installing the planar magnetrons 2 of the vacuum device, the target 3 is mounted so that its working surface is above the surfaces of all protective elements. Such an arrangement of the target 3 allows to reduce the spraying of protective elements around the target 3, therefore, no debris is formed on its working surface and electrical failures are avoided, which affect the quality of the resulting coatings.

In addition to planar magnetrons, cylindrical magnetrons are used in vacuum equipment, the targets of which are made in the shape of a cylinder and can rotate around their axis. Cylindrical magnetrons allow to reduce defects in the sputtered layers due to the constant rotation of the target. This movement constantly changes the working surface of the sputtering target and reduces the area of ​​the sputtered surface at any given time, thereby reducing oxidation of the working surface of the target and the likelihood of debris accumulating on it. Such features reduce the likelihood of electrical breakdown and, consequently, the formation of defects in the produced coating, and the process is stabilized by more uniform formation of the target material. In addition, the design of a cylindrical magnetron allows for an increase in the target volume with the same dimensions as a planar magnetron, since the target shape is cylindrical, or for a decrease in the magnetron dimensions with the same amount of target material. As a result, the technological scheme of the optical sputtering process becomes more flexible, since the large overall dimensions of planar magnetrons with flat targets limit the possibility of arranging the magnetrons 2 in the vacuum process chamber 1 relative to each other and to the overall dimensions of the planetary mechanism 10.

The vacuum process chamber 1 contains devices for protecting the working surfaces of the targets 3, which consist of a movement mechanism 6, which ensures the movement of the screen 5 over 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, so it is possible to start and stabilize the sputtering devices located under the screens and protect the working surfaces of the targets 3 from sputtering during the operation of other magnetron sputtering systems. Several screens 5 can be provided in one movement mechanism 6, one for each magnetron of the magnetron sputtering system. In turn, the movement mechanism 6 can be manufactured using various principles of displacement of the screen 5, for example, rotation, shear, reciprocating movement, etc.

In order to ensure high efficiency of the coating production process and improve its quality, induction-coupled plasma generating devices, plasma sources 7, are used. In the presented vacuum device, 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, outside the plasma combustion zone produced by magnetrons 2. The design of the vacuum device ensures the rotation of the substrates 8 around the central axis of the vacuum process chamber 1, when the substrates alternately fly over the working surfaces of the targets 3 and near the plasma sources 7. Thus, the plasma sources 7 and the substrates 8, rotating on the holders 9 in the planetary mechanism 10 at the level of the plasma sources 7, are as close as possible to each other during the technological process in the zone of maximum effective impact in the production process of multilayer thin film precision coatings.

The use of plasma sources 7 in the patented device affects the quality of the produced coatings and their growth rate. The charged particles of the plasma source 7 injected into the combustion zone of the magnetron discharge plasma affect the magnetron plasma and the target 3. As a result, it is possible to reduce the operating pressure of the technological process and thus improve the quality of optical coatings by increasing the mean free path distance of the sprayed material particles. In addition, the density of ionized states (ion density) increases in the plasma, and the sputtering process is supported by ions from two independent sources - its own magnetron discharge and an external plasma beam. In addition, the beam of plasma particles generated by the plasma source 7, injected into the combustion zone of the magnetron discharge plasma, allows you to increase the resistance to the formation of a dielectric film on the working surface of the target 3. This, in turn, allows for a significant increase in the deposition rate and a reduction in the likelihood of bulge formation on the surface of the target 3, thereby improving the quality of thin films deposited on the substrates 8.

The vacuum process chamber 1 contains the process gas suction system outlets. The system elements are arranged in such a way as to separate the process gas flows in order to reduce the influence of the process gas supplied to the plasma sources 7 on the operation of the magnetron sputtering systems. For this purpose, the suction system elements are located behind the substrates 8 so that the flow of the pumped process gas is directed in the opposite direction to the working surfaces of the targets. By reducing the formation of contaminants and chemical reaction products on the working surfaces of the targets 3, the functional characteristics of the magnetrons 2 are improved, expanding the area of ​​existence of the magnetron discharge plasma, which helps to achieve high quality and stability of the physical properties of the deposited coatings in each cycle and shortens the technological cycle time.

In order to ensure the uniformity of the produced thin-layer coating, the corresponding dimensional parameters (hereinafter referred to as X and Y) are maintained in the vacuum device. The distance X is the distance from the surface of the holders 9 for fixing the substrates 8 to the working surfaces of the targets 3. The distance X remains unchanged during the entire technological process and can be changed by switching the vacuum device or during the period between processes, by changing the position of the planetary mechanism 10 or replacing it with another modification. The distance Y is the distance from the central axis of the vacuum process chamber 1 to the centers of the working surfaces of the magnetrons 2 targets 3. The distances X and Y are selected according to the arrangement of the magnetrons 3 and plasma sources 7 so that, taking into account the rotation of the centers of the substrates 8 around the central axis of the vacuum process chamber 1, extremely high uniformity accuracy of the production of multilayer interference coatings in the vacuum device is achieved.

As mentioned above, the optical thickness of the sprayed thin films determines the optical properties of the coating. During the technological evaporation process in a vacuum device, the optical thickness of the coating is continuously monitored as it is deposited on the substrate, the so-called end-to-end control, taking into account changes in the optical properties of the coating during evaporation.

End-to-end monitoring of the optical thickness of the coating can be performed directly on the substrate 8. In this case, an automatic optical control system is used, and optical signal measurements are made during each revolution of the planetary mechanism 10 in the center of the substrate 8. A preferred variant of the optical control system is the use of an optical control unit 14, which is a set of replaceable control elements 15 mounted not on the substrate 8, but on one of the holders 9. One optical control unit 14 contains at least four control elements 15.

When controlling the optical characteristics of the coating on the control element 15, measurements are made at the center of the control element 15, which, like the substrate 8, is located in the center of the holder 9. This reduces the difference in the optical thickness of the coating sprayed on the control element 15 and on the substrate 8.

By using multiple control elements 15, it is possible to increase the total number of sprayed layers without increasing the overall spray error, as is done with a single control element.

In order to perform measurements before starting the technological process, the rotation of the holder 9 around the central axis is blocked, on the surface of which the test substrate 8 is placed or the optical control unit 14 with control elements 15 is installed. The optical control unit 14 is made in such a way that it is possible to change the position of the control elements 15 on the surface of the holder 9, therefore the control element on which measurements are performed can be placed in the center of the surface of the holder 9, and during the technological process it can be replaced with another one.

For thermal stabilization of the technological process, including heating of the substrates 8, heaters 12 are installed in the vacuum technological chamber 1. In the described vacuum device, the heaters 12 are installed at the bottom of the vacuum chamber 1 and directed towards the substrates 8 to heat their outer surfaces.

The above-described method for producing multilayer thin-film precision optical coatings in a vacuum device is described in detail below.

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, determined by calculations taking into account all the parameters of the technological process (the size of the technological chamber, the size of the substrates, the operating characteristics of the technological devices involved in the evaporation process, etc.), is kept constant during one technological process in order to achieve maximum uniformity of each layer of the coating being produced. The distance Y, also calculated before the start of the technological process for each magnetron 2 separately, taking into account the required uniformity, can be repeatedly changed during one technological process, but is maintained within a certain calculated range.

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

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. When the required pressure is reached or during the pumping process, heaters 12 are turned on, which heat the substrates 8 from the outer surface to the set temperature. Plasma sources 7 are turned on and put into operating mode.

Before the coating process begins, the plasma sources 7 clean the outer surface of the substrates 8. During the cleaning operation, the rotating device 11 of the planetary mechanism 10 operates, the substrates 8 rotate around the perimeter of the vacuum process chamber 1 at a speed of 5-60 revolutions per minute, simultaneously rotating about their axis. During the cleaning process, the working surface of the targets 3 of the first magnetron sputtering system is covered by a screen 5. The first magnetron sputtering system is a pair of magnetrons, which will perform the thin layer deposition process first in the process chain. The magnetrons 2, the working surfaces of the targets 3 of which are covered by a screen 5, are turned on to clean the working surfaces from the oxide film.

After the preparatory procedures are completed, the vacuum unit is ready for the coating production process.

The first thin layer of the multilayer precision optical coating is applied to the outer surface of the substrate 8 when both magnetrons 2 and working plasma sources 7 of the first magnetron sputtering system are operating, acting on the working surfaces of the targets of the working magnetrons 2 and the substrate 8. In order to start the technological process, the working surface of the targets 3 of the working magnetron sputtering system is opened by sliding the screens 5 by means of movement mechanisms 6. According to the technological process, working technological gases and electrical energy of a certain magnitude and frequency are supplied to the magnetrons 2 and plasma sources 7 in the technological chamber 1.

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 sputtered, thus preparing their working surface for the technological process.

Due to the special spatial dispersion of the sources of the sputtered material - magnetrons 2 and oxidizers - plasma sources 7, which is ensured by the design of the vacuum device, and the designed minimum distance from the substrates 8 to the plasma sources 7, using the planetary mechanism 10, the substrates 8 enter different areas of high-density ionized plasma. During each rotation of the substrate 8 around the central axis of the vacuum process chamber 1, the substrate is for a certain time in the high-density plasma zone of the magnetron sputtering system (sputtering zone), in which the partially oxidized target material 3 is deposited on the surface of the substrate 8, and in the high-density plasma zone (oxidation zone) of the reactive gases generated by the plasma sources 7, in which the layer deposited on the surface of the substrate 8 is pre-oxidized. This ensures high-quality oxidation of the sprayed material, which increases the density of the sprayed coatings. Increasing the density of the coatings reduces the likelihood of water vapor absorption into the coating, which improves the stability of optical and mechanical parameters under external conditions.

By reducing the distance from the substrates 8 to the plasma sources 7, it is possible to reduce the oxygen pressure in the process chamber 1, which reduces the probability of oxidation of the surface of the target 3 and the probability of warping, thereby reducing the number of defects in the produced coating.

The quality of the produced coating is also influenced by the arrangement of the working surfaces of the sputtered targets 3 in planar magnetrons, which are installed above the surfaces of the protective elements. This reduces the dustiness of the protective elements around the target 3, prevents the formation of dirt on its working surface and thus avoids electrical failures that affect the quality of the resulting coatings.

Achieving the calculated optical characteristics of the deposited coating is ensured by using a system for controlling the optical thickness of the produced thin layers.

The proposed vacuum device is equipped with an automatic coating optical thickness control system, which is located directly on the substrate 8 or on the control elements 15 of the optical control block 14. During the production of the coating, the optical thickness is controlled from end to end in the center of the rotating substrate 8 or in the center of the control element 15. If simple interference coatings are produced, it is sufficient to control in the center of the rotating substrate 8. In this case, all holders 9 of the planetary mechanism 10 are used to secure the substrates 8. An optical control unit 14 with control elements 15 is used to produce more complex optical coatings. In this case, before starting the technological process, one of the holders 9 is not used to secure the substrate 8, it is fixed, except for rotation around the central axis of the holder, and an optical control unit 14 with control elements 15 is mounted on it, which controls the optical thickness of the coating.

The optical thickness control is performed using the monochromatic photometry method. This method records the transmittance maxima and minima resulting from interference phenomena in the applied optical coating during light transmission. The optical signal is measured for each revolution of the planetary mechanism 10 around the central axis of the vacuum process chamber 1.

In order to reduce the overall spraying error, the optical image of an interference coating consisting of more than a hundred thin layers is divided into several simplified images. For this purpose, a certain number of layers is specified for each of the possible control elements in the overall coating production process. In addition, during the technological process, the operating program of the optical control system gives a signal to the optical control unit 14 so that upon reaching a predetermined number of layers according to the production process, it switches to the non-evaporated control element 15.

The more control elements 15 are used during the process, the smaller the overall spraying error will be. In addition, using multiple control elements 15 can simplify the spraying control of complex, non-uniform thickness coatings by breaking down the overall coating structure into several simpler structures, each of which will be controlled by a separately selected control element 15.

If the measured optical characteristics do not match the calculated characteristics, depending on the size of the discrepancy, the optical control system sends a corresponding signal to the vacuum device controller to change the operating parameters of the technological equipment used, including the movement of the magnetrons 2. The optical control system continues to read the received signals, process them and compare them with the calculated characteristics until the set parameters are reached, after which the optical control system generates a signal to stop the production of the first thin layer. Upon receiving the appropriate signal from the optical control system, the production of the thin layer is stopped by turning off the first magnetron sputtering system. Another thin coating layer is applied in the same way, using the second magnetron sputtering system with previously activated plasma sources 7, until a command is received from the optical control system about its readiness.

By changing magnetron sputtering systems with targets 3 made of the required materials, using different operating modes of plasma sources 7, a multilayer optical coating with specified properties is obtained.

Several features of the technological process described above can be distinguished.

In the production of coatings, magnetrons 2 operate in pairs as part of magnetron sputtering systems, and each system is assisted by one or more plasma sources 7 located above the working surfaces of the targets 3. This allows for significantly reducing oxidation and the formation of warping on the working surface of the target 3, which in turn reduces the occurrence of defects on the produced coatings. At the same time, the plasma sources 7 and magnetrons 2 effectively ionize the working gas, as well as the atomic fraction of the sprayed material, resulting in the formation of a high-density plasma region in the vacuum process chamber 1.

During the production of the coating, the substrates 8 rotate around the central axis of the vacuum process chamber 1, alternately flying over the working surface of the targets 3 and near the oxygen plasma sources 7. Due to the special spatial dispersion of the sprayed material and the corresponding movement of the substrates 8 in the process chamber 1, a high density of the produced coatings and high-quality oxidation are ensured. The high density of the coatings reduces the optical scattering of electromagnetic radiation, which is especially important for interference coatings with a large total thickness (more than 30 microns), as well as the probability of water vapor absorption in the film, which improves the stability of the optical and mechanical parameters of the coating under external conditions.

Since the substrates 8 alternately fly over the magnetrons 2 and near the oxygen plasma sources 7, the oxygen concentration in the process chamber 1 decreases, which is necessary for oxidizing the film of the sprayed material formed on the substrate as it moves over the magnetron 2. By reducing the oxygen concentration in the process chamber 1, the probability of oxidation of the working surfaces of the targets 3 also decreases, which in turn reduces the probability of target failures and defects in the produced coating.

Due to the double rotation of the substrates 8 (around their 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 of more than 0.2% is achieved both for each substrate separately and over the entire area of ​​all substrates 8.

The design of the planar magnetrons used, i.e. the working surface of the target 3 is above the surfaces of the protective elements of the magnetron 2, reduces the contamination of the target 3 with film particles falling from the protective elements, therefore fewer bends are formed on the working surfaces of the target 3, and thus fewer defects in the produced coatings.

The following describes the fabrication of an ultra-narrowband interference filter for a wavelength of 777.4 nm and intended for an optical transient detector. Thin-film variable optical filter layers are made of tantalum oxide - Ta2Ū5 and silicon oxide - S1O2, using targets used in magnetron sputtering systems, made of Ta and Si materials, respectively. The coating consists of 163 thin-film layers. The complex coating structure is decomposed into four simpler structures, therefore, four control elements 15 are used in the optical control unit 14. The average thickness of the Ta2O5 and S1O2 layers is 100 and 150 nm, respectively, and the total coating thickness is 18 μm.

A vacuum device (Fig. 1) is used for filter production, which consists of 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 autonomous motion device 4, which is designed as a linear motion drive. Tantalum targets 3 are mounted on two magnetrons 2 - the first is a magnetron sputtering system, the other two magnetrons with silicon targets form a second magnetron sputtering system. In order to reduce the formation of defects in the coating, planar magnetrons are used, the surfaces of the protective elements of which are located below the working surfaces of the targets 3.

Two plasma sources 7 are located at the same height above the working surfaces of the magnetron targets 3, on the side walls of the vacuum chamber 1 opposite each other so that the plasma beams generated by the plasma sources 7 enter the magnetron plasma combustion zones.

The diameter D of the rotation of the centers of the substrate 8 around the central axis of the vacuum process chamber 1 is 720 mm. It is selected taking into account the size of the vacuum technological chamber 1, the arrangement of the magnetrons 2 and the plasma sources 7, taking into account that during the technological process the substrates 8 rotate as close as possible to the plasma sources 7 in order to effectively control the coating production process.

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 so that their central axes coincide with the central axes of the holders 9, and the outer surface of the substrates is parallel to the working surface of the flat targets of the magnetrons 2. During the technological process, the movement devices 4 allow the magnetrons 2 to be moved, maintaining the flatness of the working surface of the targets 3. The initial position of the magnetrons 2 from the center axis of the vacuum technological chamber is Y=200 mm. An optical control unit 14 with four control elements 15 is mounted on a stationary holder 9.

Using low and high vacuum suction systems, the vacuum process chamber 1 is evacuated to a set pressure of 1e-2 Pa. During the evacuation, the rotation of the planetary mechanism 10 is turned on and the speed of fifty revolutions per minute is set. The rotation device 11 remains switched on throughout the technological process until the technological chamber 1 is opened. When the planetary mechanism 10 starts to rotate, the heaters 12 installed at the bottom of the vacuum process chamber 1 are turned on, directed towards the outer surface of the substrates 8. The substrates 8 are heated to 150^oh C. Along with heating, the pressure in process chamber 1 is reduced to 8e-4 Pa.

Before starting the precision optical coating manufacturing process, the outer surface of the substrate 8 is cleaned with an inductive discharge plasma using both plasma sources 7 to remove molecular particles, adsorbed gases, polymer fragments, water vapor, and also to atomically activate the surface bonds of the outer surface of the substrate 8 in order to improve the adhesion of the applied layer. For this purpose, oxygen is supplied to the vacuum processing chamber 1 through plasma sources 7, the pressure is reduced to 0.03-0.05 Pa and the plasma sources 7 are turned on. The processing lasts for at least five minutes. The oxygen pressure in the chamber is maintained by flow meters.

When cleaning substrates 8, the working surface of the targets 3 of the first magnetron sputtering system with tantalum targets is covered by a screen 5. The magnetrons 2, the working surfaces of the targets 3 of which are covered by a screen 5, are turned on so that the working surfaces are cleaned of the oxide film. For this, argon gas is supplied to the magnetrons 2 and the surface of the targets 3 is cleaned for five minutes. The pressure in the chamber reaches 0.07 Pa. The magnetrons 2 are turned on with a power of 1 kW and the working surfaces of the targets 3 are cleaned for five minutes.

After cleaning the substrates 8, the plasma sources 7 continue to operate in an oxygen environment. At the same time, due to the special arrangement of the reactive gas inlets, the RF electrodes of the plasma sources 7 and the elements of the pumping system, the plasma sources 7 create gradients of the oxidant concentration and its reactivity in the vacuum process chamber 1, directed from the pumping openings to the plasma sources 7.

When working under the protective screen 5, the power of the magnetrons 2 is increased to 2-5 kW. After stabilizing the modes for fifteen seconds, the protective screen 5 is moved, the working surfaces of the targets 3 are opened, the magnetron sputtering system is activated and the first layer of the thin-film coating is sprayed.

The formation of a thin layer occurs as follows: the partially oxidized working surfaces of the substrates 8 are bombarded by ions of the magnetron discharge plasma, knocking out the atoms of the target material and their molecular compounds with particles of reactive gases. During one flight of the substrates 8 over the operating magnetrons 2 (in the evaporation zone), a partially oxidized film about 5 angstroms thick is formed on their front surface. 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 for ~300 and ~900 ms, respectively, where the thin layer is completely pre-oxidized. In the described system, the oxidation reaction equilibrium of the target 3 material atoms forming a thin film layer on the outer surface of the substrate 8 can shift between oxidation on the target 3 surface and oxidation on the substrate 8 surface, as the oxygen consumption changes. 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.

When spraying a thin film layer, the power of the magnetrons of the magnetron sputtering system and the argon flow rate are not changed. The power supply unit of the magnetron sputtering system controls the oxygen flows of the plasma sources 7 to maintain the set voltage of the magnetrons 2 by changing the oxygen flow up or down. This is necessary to ensure that the working surface of the targets 3 being sprayed during the technological process is in a stable state, ensuring a constant fiber profile of the sprayed material, spraying speed and minimal curvature formation.

The optical control system controls the optical thickness of each thin layer according to the control elements 15 of the optical control unit 14. The optical signal is measured during each revolution of the planetary mechanism 10 at the center of the control elements 15 mounted in the stationary holder 9.

During the evaporation of the first layer, the second magnetron sputtering system, the targets of which are made of silicon, is covered with a protective screen 5. This prevents the surface of the targets 3 from being contaminated with dust. At the same time as the first thin layer is being sprayed, the second magnetron sputtering system, located under the protective screen 5, is turned 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 sputtering the second thin-film coating layer. The optical control system measures the received signal and compares it with the calculated characteristics, and upon reaching the required parameters, the optical control system generates a signal that stops the thin-film coating process. Spraying is stopped by turning off the power supply of the first magnetron spraying system so that the propagation time of the sprayed material after the shutdown signal is as short as possible.

At this time, the plasma sources 7 continue to operate. The oxygen flow is changed according to the determined composition of the second layer. The power of the second magnetron sputtering system is increased to 3-5 kW. After 15 seconds of stabilization of the modes, the second magnetron sputtering system with silicon targets 3 is opened and the second thin layer is sprayed.

At this time, 1 kW of power is supplied to the first magnetron sputtering system, now covered by the protective shield 5, to prepare the working surface of the targets for further evaporation.

Next, the algorithm for producing thin layers of a multilayer precision optical coating is repeated until an interference coating with the desired optical properties is formed.

The standard working pressure in vacuum process chambers when magnetron sputtering is used is 5e-1 Ra. In this case, using plasma sources 7 together with magnetron sputtering systems allows the working pressure to be reduced to 7e-2 Ra.

Fig. presents the transmission curve of an ultra-narrowband filter with a wavelength of 777.4 nm, obtained by applying the described method in a vacuum device of the described design. The half-width is 0.8 nm, the transmission - up to 90%, the blocking range - 400-1000 nm OD3. The obtained values ​​of the transmission, half-width and blocking level during one technological cycle indicate a high stability of the technological process. At the same time, it is impossible to obtain the aforementioned type of coating without precise control of all technological process parameters and properties of the optical layers produced, without the use of precisely manufactured mechanical assemblies of the vacuum device and the stability of the operation of all technological equipment.

Fig. 1 shows the transmission curves of ultra-narrowband filters fabricated by five independent processes at a wavelength of 777.4 nm. The deviation of the central wavelength of the coating in different processes is 0.6 nm or 0.077%, which indirectly indicates a high stability of the refractive index and thickness of each of the one hundred and sixty-three layers. This in turn indicates high density, homogeneity, adhesion to the substrate and low stress.

Thus, the vacuum device design and the method for producing multilayer thin-film precision optical coatings described in this invention allow solving the identified technical problem and ensuring the specified technical result.

The use of a planetary mechanism in the technological process allows for 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 the formation of thin layers characterized by high density, homogeneity, adhesion to the substrate, and low stresses on the outer surface of the substrate.

Proper arrangement of plasma sources, magnetron sputtering systems and substrates in the vacuum process chamber, design features of magnetron sputtering systems, and arrangement of product extraction system elements 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.