TWM638118U - A vacuum unit for producing multilayer interference coatings on an optical element - Google Patents

Abstract

The technical solution refers to vacuum technology, in particular to vacuum units for depositing thin film multilayer interference coatings and is aimed at solving the problem of providing a commercial-scale unit for producing high-precision optical products.

Set problem is solved by using planar magnetrons mounted on autonomous motion devices in a vacuum unit, with a variable distance from the center of the working surfaces of the targets to the axis of rotation of the optical element holder and from the working surface of the targets to the front surface of the optical element clamped in the holder. The control signal for changing mentioned distances is generated by the optical control system according to the optical signal values provided by optical properties of the deposited coating at different points of the front surface of the optical element and obtained from two geometrically spaced optical channels.

The vacuum unit makes it possible to reduce the duration of the technological process while increasing the uniformity of the produced thin-film layers, thereby increasing the efficiency of equipment use and increasing the yield of valid high-precision optical products.

Description

Vacuum Apparatus for Generating Multilayer Interference Coatings on Optical Components

The requested technical solution concerns vacuum technology, in particular vacuum devices for depositing thin-film multilayer optical coatings. The device can be used for commercial-scale production of narrowband interference filters, which can be used in astrophysics research to obtain monochromatic images of space objects. Used in optical fiber communication networks for serial data transmission, the device can be used in the production of optical systems, such as highly reflective mirrors, beam splitters with steep front edges, and others including multilayer thin film coatings with hundreds or more layers combined product.

A vacuum apparatus is known for producing multilayer interference coatings on optical components [1], in which the ion source is directed towards the surface of an alternative flat rectangular target. The ion source and target are fixed relative to each other on a moving device so that they move simultaneously in a direction perpendicular to the long profile of the source. To improve coating uniformity, the optics are mounted in a rotatable holder. At the same time, in order to improve the quality of the coating produced, the device uses a second auxiliary ion source directed at the optical element. It is used to smooth the surface of optical components and suppress the formation of additional roughness as the number of films and coating thicknesses increase. It can also be used to oxidize the deposited material.

The main disadvantage of this vacuum device lies in the coating deposition techniques used, which do not ensure a high deposition rate and cannot produce them at a high rate. Therefore, in a single vacuum cycle deposition The process of multilayer coatings with hundreds or more layers takes several days, which makes it difficult to use the above-mentioned vacuum devices on an industrial scale. Furthermore, ion beam methods for depositing coatings have disadvantages related to the heterogeneity of multilayer coatings due to non-uniform extraction of the ion beam from the ion source, and non-uniform sputtering of the target material.

Magnetron sputtering devices or magnetrons can also be used to produce optical components with complex multilayer coatings. Magnetrons are also ion sputtering devices and are distinguished by their high sputtering rates due to strong transverse magnetic fields, which localize the plasma near the surface of the sputtering (working) target and thereby increase the ion current density. The use of magnetrons significantly speeds up the manufacture of optical products with coatings comprising a large number of thin film layers and thus increases the yield of the final product. In the field of magnetron sputtering, however, there is a need to reduce the corrosion inhomogeneity of the target on its sputtered surface. This needs to be considered, not only for efficient use of the target material, but also as a factor that adversely affects the quality of the film deposited on the optical element.

One of the reasons for non-uniform corrosion of the target working surface is that corrosion increases in regions where the magnetic field lines are parallel to the sputtering surface. There are known technical solutions in which the matrix of magnets located behind the target can be rotated relative to the target, or the sputtering target itself can be moved relative to the magnets in order to achieve a more uniform erosion of its working surface.

Patent document [2] describes a vacuum device with a planar magnetron comprising a movable flat target. The vacuum apparatus includes a vacuum processing chamber having a holder for fixing the optical element inside the chamber and rotating it along its central axis coincident with the rotation axis of the holder. A modified magnetron inside the vacuum processing chamber is used as the coating device, the magnetron comprising a flat target whose working surface is partly covered by a shielding device and a magnet system. The target is mounted on a movable support such that it can move relative to the magnet, and the magnet system behind the target is immovable relative to the process chamber, while the magnetron itself is fixed on a non-moving mounting surface . Thus, this vacuum device utilizes a magnetron with a movable target that slides along a magnetic system to form a homogeneous erosion profile on its working surface, and also rotates to maintain a stationary deposition cloud.

The moving erosion zone of the target working surface is both an advantage and a disadvantage of the technical solutions described above, since it leads to uneven coating and reduces the precision of thin film deposition. Furthermore, with a moving target, it becomes problematic to cover areas of the target that are not subject to corrosion with a masking device. Dielectric film layers containing unwanted materials produced by backscattering coating materials or chemically active gases can form on exposed areas of the target working surface not involved in the sputtering process. But this technical solution does not contain guidelines on how to increase the magnetron resistance to form a dielectric film on the target surface, but this is required to achieve high quality and stable reproducibility of the optical properties of the deposited coating.

There are known vacuum devices whose design allows reducing possible technical influences on the quality of the deposited coating. As an example, patent document [3] describes a vacuum device with a rigid frame for the production of multi-layer coatings, the design of which is the closest to the technical solution claimed. The frame is used for the installation technology and other devices involved in the technical processing of coating manufacture. It is installed and designed to reduce the effects of vibration and flexing of the processing chamber during technical processing. Such disturbances may be caused by the operation of various devices involved in the vacuum technology process, such as vacuum pumps, or by environmental shocks. The frame can be designed as a separate component set up from the vacuum processing chamber, or as a device mounted on one of the stationary surfaces, or it can be designed in another effective way to allow isolation of the frame from vibrations and flexing as described above. The main function of the frame is to fix the devices mounted on it in a stable position relative to each other during technical processing.

In addition to the vacuum processing chamber and frame, the apparatus described in the patent document [3] includes: an optical element holder; an optical element with an open front surface to be coated; a planar magnetron; a sputtering target material with its working surface parallel to and facing the front surface of the optical element. The design of the vacuum unit includes special motion equipment on which the magnetron is fixed and allows control of the distance from the working surface of the target to the front surface of the optic. In addition to means for monitoring the various process parameters, the apparatus also includes means for continuously monitoring the thickness of each coating layer. During optical coating deposition, the thickness of each layer must be tightly controlled and must be the same over the entire front surface of the optical element. The film optical thickness determines the final Properties of optical coatings, such as reflectivity, transmission, and wavelength of maximum transmission, are more precise than the geometric thickness of the film. Therefore, there is an end-to-end control method called optical thickness, which is widely used to monitor layer optical thickness and takes into account optical property changes of thin films during deposition on optical components. The described vacuum apparatus is equipped with an optical control system to perform end-to-end control of the optical thickness at or at a distance from the center of the optical element.

The vacuum devices described above cannot provide the required throughput of the desired product after each vacuum cycle of multilayer interference coating fabrication. Most coated optical elements do not have the necessary optical properties: the coating only corresponds to the prescribed requirements in a narrow ring on the front surface of the optical element. Coatings meeting specified requirements are placed in a narrow ring on the front surface of the optic. In order to increase the yield of suitable products, the area of the annulus must be increased. Therefore, to deposit a coating it is not only necessary to control the distance from the front surface of the optical element to the working surface of the target (as provided in the device according to patent document [3]), but also to control the distance from the optical element. The distance from the axis of rotation to the center of the target.

This technical solution aims to solve the technical problem of inventing an industrial-scale vacuum device for producing multilayer interference coatings suitable for the manufacture of high-precision optical products. At the same time, the vacuum device should ensure an increased yield of useful products due to the high reproducibility of the optical parameters of the multilayer coating, as well as the quality and homogeneity of the individual layers.

This object in the claimed technical solution is achieved by mounting the magnetron on an autonomous movement device with a variable distance Y from the center of the target working surface to the axis of rotation of the gripper possibility. Specifically, the distance Y may vary in the range of 200 to 400 mm, and the distance X from the working surface of the target to the front surface of the fixed optical element is 150 to 450 mm.

The claimed vacuum device comprises a rigid frame; a holder for an optical element, which is rotatable and movable along its central axis coincident with the central axis of the optical element held in the holder; At least two magnetrons whose working surfaces are parallel to the plane of the front surface of the optical element; means for shielding the working surface of the target; a dual-channel optical control system for the two geometries of the optical element during deposition Optical properties of the coating are measured in the upper compartment region; at least one plasma source and an optical element heating device.

Preferably, the plasma source is mounted in a processing chamber which affects the working surface of the target and the front surface of the optical element.

In one possible design, the vacuum device comprises four magnetrons mounted on a frame comprising two separate parallel surfaces connected by stiffening ribs. Optical element holders and heaters are also mounted on the frame.

One example of a magnetron target shielding device includes at least one shield mounted on a movement mechanism.

1: Vacuum processing chamber

2: Magnetron

3: Sports device

4: Target

5: screen

6: Mobile mechanism

7: Holder

8: Optical components

9: Rotating device

10: Plasma source

11: Launcher

12: Receiver

13: frame

14: heater

X, Y: distance

Figure 1 schematically illustrates a vacuum apparatus for producing multilayer interference coatings on an optical element.

The essence of the claimed technical solution can be explained by the representation of FIG. 1 , which schematically illustrates a vacuum device for producing a multilayer interference coating on an optical element.

The vacuum apparatus comprises a processing chamber 1 having at least two planar magnetron sputtering devices 2 (hereinafter also referred to as magnetrons) with mounted targets 4 inside, the working surfaces of which are sputtered deal with. The magnetrons 2 are involved in the process in turn, since they have targets 4 of different materials, and each magnetron 2 deposits a thin film layer of a specific composition, which provides a manufacturing process for a multilayer interference thin film coating on the optical element 8 .

Means for shielding the working surface of the target 4 are also provided inside the processing chamber 1 . In one possible design version, the shielding device is constituted by a movement mechanism 6 with at least one attached shield 5 , which ensures movement of the shield 5 over the working surface of the target 4 . Thus, during the technical processing, the shield 5 covers the working surface of one of the targets 4, allowing to open and stabilize the magnetron below the shield 5, and to shield the surface of the target 4 from the other magnetron. The pipe 2 is free from coating deposition during operation.

If more than two magnetrons 2 are installed in the processing chamber 1 , the shield 5 can be designed to provide a target working surface 4 covering multiple magnetrons 2 at the same time.

At the same time, there may be several shields 5 on one or more moving mechanisms 6 for each respective magnetron. The moving mechanism 6 can be adapted to use various principles of moving the shutter 5, such as rotation, shear, reciprocation motion, and the like.

During the deposition process, the thickness uniformity of each thin film layer on the optical element 8 changes due to erosion of the target working surface 4 and to changing geometry due to target material consumption.

In order to improve the uniformity of the layers in the produced coating, each magnetron 2 is mounted on a moving device 3 . It allows moving the magnetron, maintaining the plane of the target working surface 4 and/or changing the inclination angle of the target 4 of the magnetron 2 towards the plane of the front surface of the optical element 8 . Each magnetron 2 is equipped with autonomous movement means 3 . This means that for a vacuum device with two magnetrons 2 each magnetron 2 can be moved by its movement means 3 to a desired position before or during operation.

If more than two magnetrons 2 are installed in the processing chamber 1, these technical devices can work sequentially or in pairs. If the number of installed magnetrons 2 is an even number, the paired magnetrons operating simultaneously form a magnetron sputtering system. Since each magnetron 2 in the magnetron sputtering system has its own Its own autonomous displacement device 3, so it can be displaced by a distance that is inconsistent with the displacement distance of another magnetron in the magnetron sputtering system.

In order to ensure high efficiency of the deposition process and improve film quality, at least one inductively coupled plasma generator 10 (hereinafter referred to as "plasma source") directed to the sputtering area is used in the patented vacuum device. Since the plasma source 10 may perform various functions during coating deposition, it may preferably be mounted to affect the working surface of the target 4 and the front surface of the optical element 8 . In this case, the plasma source 10 can be used to pre-clean the front surface of the optical element 8 immediately before the coating process, as well as to assist the technical process because it can speed up the technical process due to its ability to control the ion density in the sputtering zone and Improve coating quality. The plasma beam generated by the plasma source 10 and injected into the sputtering zone, or more precisely into the magnetron discharge plasma zone, allows increased resistance to the formation of the dielectric film on the working surface of the target 4 Resistance. It thus allows a significant increase in the coating deposition rate and reduces the impact of the arc on the target surface 4 , thereby improving the quality of the film deposited on the optical element 8 . The use of the plasma source 10 reduces the time of the technology cycle by minimizing the formation of contaminants and chemical reaction products on the working surface of the target 4, thereby increasing the magnetic field by enlarging the area where the magnetron discharge plasma exists. Controls the functional properties of 2 and contributes to the high quality of the deposited coating and the stable reproducibility of its physical properties.

If the processing chamber 1 comprises two magnetrons 2 and one plasma source 10, when the magnetrons 2 are alternated during the technological process, the plasma source 10 is kept on, or switched to a different mode of operation, or only with One of the magnetrons 2 is switched on together. If more than two magnetrons 2 are installed in the processing chamber 1, several plasma sources 10 can be used. In this case, each plasma source can perform the optical element 8 front surface treatment before the start of the deposition process, and/or together with one of the magnetrons 2 or the magnetron sputtering system and the start of the operation of the assisted deposition on, and/or continue to work.

The holder 7 inside the vacuum processing chamber 1 is used to fix the optical element 8 , and the front surface is parallel to the plane of the working surface of the target 4 . The optical element 8 is based on the central axis of the holder 7 and the optical element 8 It is fixed in the holder 7 in such a way that the central axes coincide. The holder 7 of the optical element 8 is designed to rotate and move along its central axis.

Since the azimuthal uniformity of the produced thin film coating depends on the rotational speed of the optical element 8 during the coating manufacturing process, the patented vacuum apparatus includes a rotating device 9 which provides a rotational speed of the optical element 8 up to 3000 revolutions per minute .

In order to avoid contamination of the sputtering zone, all mechanisms of the vacuum device can be removed from the sputtering zone. Thus, the rotating device 9 of the holder 7 is located inside the processing chamber 1 , outside the sputtering zone, or outside the processing chamber 1 itself, as shown in FIG. 1 . For the same reason, the moving device 3 of the magnetron 2 and the moving mechanism 6 of the screen 5 are also outside the sputtering zone of the vacuum device. To reduce contamination, more suitable mechanisms can be used in the device, such as magnetic couplings in the rotating device 9 .

A specific position, such as X and Y, of the magnetron 2 and the holder 7 in the sputtering zone shown in FIG. 1 is maintained to achieve a specific uniformity of the deposited thin film coating.

The distance X is the distance from the front surface of the optical element 8 to the working surface of the target 4 (the front surface of the optical element is the surface facing the sputtering zone where the coating takes place).

The distance Y is the distance from the center rotation axis of the optical element 8 to the center of the target 4 .

The distances X and Y are determined by experiments, X is 150 to 450mm, and Y is 200 to 400mm. Distances X and Y in these ranges allow setting the vacuum device to achieve ultra-high precision in the uniformity of multilayer interference coating deposition.

If the optical element 8 in the holder 7 is not moved along the central axis of the holder inside the vacuum processing chamber 1 during the technical process, the distance X will be fixed throughout the technical process and can be obtained in the vacuum device. Change during interoperability period or readjustment. In this case, during the coating deposition process, the optical element 8 and the holder 7 are rotated along their central axes by means of the rotating device 9 and the spatial position of the optical element 8 in the deposition zone remains unchanged.

The distance Y is calculated before the technical processing of each magnetron 2 begins, and can be changed repeatedly during the processing according to the required uniformity, but kept within the above-mentioned range.

The possibility to achieve computational optical properties of the deposited coating depends on the control method used. For optical films, their optical thickness determines the optical properties of the coating itself and is a precise characteristic. The patented vacuum unit is equipped with an automated system for end-to-end control of coating optical thickness, which has two optical channels. The presence of two optical channels is ensured by the presence of two transmitters 11 and two receivers 12 in the optical control system. The method of optical thickness control is monochromatic photometry, which is based on recording the maximum and minimum values of transmission caused by interference phenomena and by changing the thickness of the optical film.

The end-to-end control of the optical thickness is carried out during the coating deposition in two different points of the optical element 8 at different radii from the axis of rotation: in the region of maximum uniformity of the resulting coating.

The difference in coating optical thickness at these two points is determined from the difference in signals through the two optical control channels.

The optical control software compares the values obtained from the two optical channels, performs calculations based on the magnitude of the signal difference, and sends an appropriate signal to control the deposition process. It is a signal used to change a specified parameter of the technical equipment, for example the position of the magnetron 2 .

For heating and thermal stabilization of the optical element 8 at least one heater 14 is installed in the vacuum processing chamber 1 oriented towards the optical element 8 . The position of the heater in the vacuum processing chamber can be different: above or below the optical element 8, on the holder 7, etc.

For the purpose of arranging technical devices, motors and other components for vacuum technology processing in the vacuum processing chamber 1 a special rigid frame 13 can be used. The frame is used to minimize the vibration and bending shocks experienced by the technical chamber during technical processing. For this purpose, the frame 13 can be completely isolated from the processing chamber 1 or mounted on one of its stationary surfaces, for example on a pedestal. The frame 13 consists of two flat horizontal surfaces joined by vertical stiffeners. Magnetron 2 and screen 5 can be installed in its On one of the lower surfaces, on the side of the magnetron discharge plasma generation area. The holder 7 with the optical element 8 can be fixed on the upper plane of the frame 13 . In this case, the moving means 3 of the magnetron 2 , the moving means 6 of the screen 5 , the rotating means 9 of the holder 7 are mounted outside the frame 13 . With this configuration of the device, the sputtering area is not contaminated by mechanical parts of the listed device. Furthermore, the orientation of the components relative to each other, as well as the distance between them, remains stable, ie both X and Y parameters can be adjusted reliably and precisely.

The requested vacuum device consists of four planar magnetrons 2 working in pairs and mounted on a frame 13, equipped with a circular target 4 with a diameter of 250 mm; two inductively coupled plasma sources 10 are installed , which can simultaneously process the working surface of the target 4 and the front surface of the optical element 8 , as well as the flat holder 7 mounted on the frame 13 . This vacuum device operates as follows. A 9-inch flat optical element 8 made of optical glass is clamped in the holder 7. The purpose of the holder 7 is to hold an optical element 8 in the processing chamber 1, in the deposition area, on the target 4 at a calculated height X above the work surface. The central axis of the clamped optical element 8 coincides with the central axis of the holder 7 , and its front surface is parallel to the working surface of the flat target 4 of the magnetron 2 .

Using low and high vacuum pumping systems (not shown in the drawings), the vacuum processing chamber 1 is evacuated to a suitable initial pressure to start the technical process. During evacuation or after reaching a suitable initial pressure, the heater 14 located above the optical element 8 on the holder 7 is turned on and heats the optical element 8 to a desired temperature. Then, the plasma source 10 installed on the wall of the vacuum processing chamber 1, which is located above the magnetron 2 of the first spraying system, is switched on and starts to operate. The plasma source 10 performs pre-cleaning of the front surface of the optical element 8 before the coating process. During the cleaning operation, the rotating device 9 of the holder 7 rotates the optical element 8 at a speed of 400 to 2000 revolutions per minute, and the working surface of the target 4 of the first magnetron sputtering system is covered by the screen 5 . Next, the first magnetron sputtering system is turned on under the screen 5 , and pre-sputtering is performed to remove the oxide film on the working surface of the target 4 . After the preparatory procedure, the vacuum unit is ready for coating deposition.

The deposition of the first thin film layer of the multilayer interference coating on the front surface of the optical element 8 was performed while both magnetrons 2 of the first magnetron sputtering system were in operation and the plasma source 10 was processing its target material. Occurs when working on the surface. To start the technical process, the working surface of the target 4 of the active magnetron sputtering system is opened by deflecting the screen 5 using the movement mechanism 6 . Working gas and electric power of a certain value and frequency are supplied to the processing chamber 1 , to the magnetron 2 and to the plasma source 10 according to the skill of the art.

Simultaneously with the start of the deposition of the first thin film layer, the second magnetron sputtering system is switched on, covered by the screen 5 displaced by the moving mechanism 6, performing pre-sputtering, thus preparing its target working surface for Perform technical processing.

After obtaining the corresponding signal from the optical control system monitoring the optical thickness of the growing thin film layer, the deposition of the first thin film layer by the first magnetron sputtering system is stopped. Using a transmitter 11 and a receiver 12 , the optical control system monitors the optical thickness of the deposited coating in two points of the optical element 8 through two optical channels. The system then compares the values obtained via the two optical channels with each other. The result of comparing the magnitude of the optical signal is used as a feedback signal to generate a corresponding control signal for the moving device 3 to change the distance Y of the working magnetron 2 . Since the monitoring of the optical parameters of the thin film layer via the two optical channels takes place during the entire deposition technology cycle, their matching also takes place between the entire technology cycles. At the same time, since each magnetron 2 is installed on a separate moving device 6 , the parameter Y can be calculated and independently changed for each magnetron 2 .

The next thin film coating is deposited in the same manner using a second magnetron sputtering system in cooperation with a previously unused plasma source until an instruction to terminate it is received from the optical control system. By alternating the operation of the magnetron sputtering system with different target 4 materials and with different plasma sources 10, a multilayer interference coating with specified characteristics can be produced with two alternating thin film layer types.

By maintaining the specified distances X and Y, a high degree of uniformity in the deposited thin film layer can be achieved. In vacuum devices, uniformity is also provided by using an optical control system with two optical channels. The measured optical parameters of the prepared coating are received by the optical control system through the optical channel and compared with each other Compare. If the obtained comparative value of the optical signal does not comply with the allowable variation, the magnetron is automatically moved within the distance Y in the device to match the measured optical characteristic.

The quality of the coating produced and the deposition rate in the vacuum apparatus of this patent is also affected by the plasma source, which shoots charged particles into the magnetron discharge plasma region, which affects the plasma and the target. Therefore, it becomes possible to reduce the working pressure of technical processing, and in this way to increase the free path distance of atomized materials to improve the quality of optical coatings. At the same time, the operation of the plasma source increases the density of ionized states in the plasma, and in this case the sputtering process becomes controlled by two independent sources (its own magnetron discharge and an external plasma beam) supported by ions.

Coating cycle time will be reduced due to the reduction of technological process time due to the high-speed sputtering by the vacuum device using technological devices, ie a combination of magnetron and auxiliary plasma source. Compared with vacuum devices using ion beam sputtering technology, magnetrons not only have a higher productivity (ie multi-layer coating deposition rate), but also have a longer operation time without maintenance. Thus, a vacuum device equipped with a magnetron has a higher availability, ie increased operating efficiency. At the same time, by mounting the magnetron on the moving device, the target in the magnetron sputtering device can be used up to the maximum target corrosion.

Therefore, for the proposed vacuum device of this design, it is possible to solve the technical task, to ensure the reduction of the technical processing time, and to improve the uniformity of the deposited thin film layers, thereby increasing the efficiency of the vacuum equipment and increasing the yield of effective high-precision optical products .

source:

1. Patent No. RU 2654991, published on May 23, 2018

2. Patent No. US 9771647, published on September 26, 2017

3. Patent No. US 6736943, published on May 18, 2004

1: Vacuum processing chamber

2: Magnetron

3: Sports device

4: Target

5: screen

6: Mobile mechanism

7: Holder

8: Optical components

9: Rotating device

10: Plasma source

11: Launcher

12: Receiver

13: frame

14: heater

X, Y: distance

Claims (6)

A vacuum apparatus for producing multilayer interference coatings on a fixed optical element, comprising a processing chamber with a rigid frame inside; a holder for an optical element, the holder being movable along its center Axis rotation and movement, the central axis coincides with a central axis of the optical element whose front surface is subjected to multilayer coating deposition in the processing chamber; at least two magnetrons with targets, which work The surface plane is parallel to a plane of the front surface of the optical element, and the distance X from the working surface of the targets to the front surface of the optical element is kept within 150 to 450 mm, and the magnetrons are Installed on the autonomous movement device that can change the distance Y from the center of the working surface of the targets to the rotation axis of the fixture, and the distance Y is limited to an interval of 200 to 400 mm; for A device for shielding the working surfaces of the targets; an optical control system having two geometrically separated optical channels capable of measuring The optical properties of the coating formed at different points of the substrate; at least one plasma source, disposed in the processing chamber, and the plasma source is installed so that it affects the working surface of the targets and the optical element the front surface; and a heater for the optical element. The vacuum device as claimed in claim 1, wherein it comprises four magnetrons. The vacuum device of claim 1, wherein the rigid frame has two separate parallel planar surfaces connected by stiffening ribs. The vacuum device as claimed in claim 1, wherein the magnetrons and the holder are mounted on the frame. The vacuum device as claimed in claim 1, wherein the means for shielding consists of a moving mechanism on which at least one shielding member is mounted. The vacuum device as claimed in claim 1, wherein the optical element heater is mounted on the holder.

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