DE102018200528A1 - Projection exposure apparatus for semiconductor lithography with sensor protection - Google Patents

Abstract

The invention relates to a projection exposure apparatus 1 for semiconductor lithography with a first component 51 movable relative to a second component 51, a sensor 31 for measuring the relative position of the two components 50, 51 to each other, the sensor 31 having a first sensor portion 35 with a reference surface 37 and a a second sensor part 32 with a measuring surface 34 spaced apart by a measuring path, and the first sensor part 35 is arranged on the first component 51 and the second sensor part 32 is arranged on the second component 50. At least one of the sensor parts 32, 35 is mounted relative to that component 50, 51 on which it is arranged to be movable with a movement component in the direction of the measurement path.

Description

The invention relates to a projection exposure apparatus for semiconductor lithography.

For such projection exposure systems, there are extremely high demands on the imaging accuracy in order to be able to produce the desired microscopically small structures as error-free as possible. At the same time the projection exposure systems must be constructed so that in case of external disturbances, such as earthquakes or the like, no damage to the highly sensitive components and components of the projection exposure system arise.

In the WO 2013/004403 is disclosed a projection exposure apparatus for semiconductor lithography with an array of frames and mirrors, the position of which can be measured directly or indirectly with linear scales or any other type of non-contact measuring sensors.

Non-contact measuring sensors usually comprise two sensor parts, wherein a first sensor part comprises a reference surface which contains the zero point of the sensor, ie the point at which the measuring path of the sensor begins. A second sensor part comprises a measuring surface, which comprises the second end point of the measuring path of the sensor.

It is known from the general state of the art to protect components in the event of an external disturbance, such as an earthquake, by means of end stops which limit the relative movement between two components. The distance between the individual sensor parts, as in the cited document the linear scale on one component and the sensor head on the other component, is chosen to be greater than the maximum relative movement, which is permitted by the end stop.

When using sensors, such as linear scales or eddy current sensors, the achievable measurement accuracy depends on the distance of the individual sensor parts. In particular, in EUV and DUV lithography, the demands on the determination of the accuracy of the position of the components of the system increase absolutely and / or to each other due to continuously tightening optical specifications. The resulting increased demands on the accuracy of the sensors and thus the requirement of a decreasing distance between the sensor parts to each other can not be met with the solutions used in the prior art.

Object of the present invention is to provide a sensor arrangement with a small distance of the sensor parts and high collision safety.

This object is achieved by a device having the features of independent claim 1. The subclaims relate to advantageous developments and variants of the invention.

A projection exposure apparatus according to the invention for semiconductor lithography comprises a first component movable relative to a second component and a sensor for measuring the relative position of the two components relative to one another. The sensor has a first sensor part with a reference surface and a second sensor part with a measuring surface spaced apart by a measurement path. The first sensor part is arranged on the first component and the second sensor part is arranged on the second component, wherein at least one of the sensor parts is mounted movably relative to the component on which it is arranged with a movement component in the direction of the measurement path.

The first sensor part with the reference surface is advantageously fastened to a first component which performs no or only slight movements relative to the fixed world, since parts for generating signals and / or electronics for evaluating the measured signals are frequently arranged on the first sensor part. These parts are usually connected to cables with the environment, ie the fixed world, whereby a mechanical connection is formed, via which external disturbances can be transmitted to the component. However, since the first component does not move at all or only to a small extent relative to the fixed world, in this case the potentially disturbing influence of movements is less.

The second sensor part, which is often designed as a passive part, is advantageously arranged on a second component moving relative to the fixed world, since it typically requires no connection to the environment, for example by cables.

The measuring path of the sensor begins at the reference surface of the first sensor part and extends to the measuring surface of the second sensor part. The axis of the measuring direction is defined by the position of the reference surface and the measuring surface.

The measuring surface may be a specially made surface, such as a high surface area reflecting surface in an interferometer or a measuring grid used as a measuring surface by encoders.

According to the invention, at least one of the sensor parts is mounted so as to be movable relative to that component on which it is arranged with a movement component in the direction of the measurement path. In the event of a collision between the two mutually movable components due to interference from the outside, such as an earthquake, this sensor part can thus avoid the other potentially conflicting sensor part or recede from it and thus prevent damage to both sensor parts.

In an advantageous embodiment of the invention, the first component is a forceframe and the second component is a sensor frame of the projection exposure apparatus.

The division into forceframe and sensorframe results from the increasing demands on the accuracy of the positioning of the optical elements, especially in the projection optics of the projection exposure apparatus. It has been found useful to minimize any suggestions that could affect the positioning of optical elements such as mirrors. In addition to the suggestions from outside, a further contribution to these suggestions is the reaction forces of the actuators, which manipulate the mirrors. Actuators and sensors have been affixed to the same fixed environment, in the form of a rigid frame, in the first generations of projection exposure equipment, which resulted in deformation and excitation of the frame directly affecting the reaction forces of the actuators on the mounting points of the sensors. To minimize these effects of reaction forces on the location of the mounting points of the sensors, the rigid frame has been divided into two frames, with a first frame receiving the reaction forces of the actuators and a second frame being used as attachment for the sensors. The two frames are decoupled from each other, for example by decoupling springs, to minimize the transmission of deformations and vibrations. The first frame is called a forceframe due to the absorption of the reaction forces, and the second frame is called the sensor frame because of the sensors.

It is of course also conceivable to apply the invention to further combinations of mutually moving components of the lithographic system.

In a further advantageous variant of the invention, end stops are present on both components, which limit the maximum approach (and thus the minimum distance) of the two components. In addition, in this advantageous embodiment, the distance between the two sensor parts is less than the distance between the two end stops during normal operation of the system.

The end stops can be designed so that the end stop yields in the event of a collision, so deformed. Due to the rising force required for the deformation of the end stop, the movement of the components relative to one another is braked to a standstill. Primarily, the end stops serve to protect the decoupling springs, which typically decouple the two components, such as the forceframe and the sensor frame, from each other, so that the decoupling springs can not deform so much that they are plastically deformed and thereby damaged. Characterized in that the distance of the sensor parts from each other in the prior art is chosen so that it is greater than the maximum movement of the two components out of the static position, protect the end stops and the sensor parts. For the special case of transport, in addition to the end stops, there are additional temporary, fixed connections between the components, so-called transport locks, which are mounted only for the transport of the system and are removed before the system is put into operation.

The normal operation of the system is defined by the fact that no unusual disturbances, such as earthquakes, act on the system from the outside and that it works normally.

In an advantageous embodiment of the invention, at least one sensor part has an elevation extending in the direction of the other sensor part, which contacts the other sensor part in an area which is not used for the measurement when the two sensor parts approach each other.

The measuring surface of the second sensor part is usually a passive component as described above. The measuring surface comprises an area to which the signals of the second sensor part, for example light, strike and a second area, at least partially enclosing the first area, which is not relevant for the measurement. Also, the first sensor part has a reference area at least partially enclosing area, which is not relevant to the measurement. Thus, it is largely harmless if the increase comes into tactile contact with one of the two not relevant for the measurement areas.

In a variant of the invention, the elevation is arranged on the first sensor part. The increase surrounds the usually very sensitive reference surface of the first sensor part, so that in case of contact of the two sensor parts, the increase hits the unused for the measurement area of the measuring surface of the second sensor part and thereby the reference surface of the first sensor part is protected.

In a further advantageous embodiment, the movably mounted sensor part is arranged in a holder which comprises a reference stop for the defined positioning of the sensor part.

The position of the sensor parts is the basis for the measuring path of the sensor and the position and position of the sensor parts must, in order to ensure a sufficiently good alignment of the two sensor parts to each other, are adjusted very accurately. By a suitably designed reference stop, which reliably determines the position and position of the individual sensor parts by its design, the reproducibility of the measurements of the sensor can be ensured.

In a further embodiment of the invention, the movably mounted sensor part is arranged on a means with path-dependent force generation. This ensures that the movably mounted sensor part is pressed by the force that is generated due to the deflection of the agent, after contact with the other sensor part again against the reference stop and thereby assumes the same position as before the contact. This avoids that after a contact of the two sensor parts a new adjustment of the sensor parts to each other must be performed. Especially with absolute measuring sensors, the change of the position and position of the sensor parts is one to one in the measuring section. This would lead to a different positioning of the optical elements after a contact and a change in the position and position of the sensor parts caused thereby, which in turn would affect the imaging properties of the projection optics. The path-dependent force generating means may comprise, for example, a spring, one with a compressible fluid, e.g. Be air-filled cavity or a magnet assembly. The means must also be able to apply a force to the sensor part through a path set during assembly of the sensor part, which presses the sensor part against the reference stop during normal operation of the system.

In addition to the means with path-dependent force generation, the positioning of the movably mounted sensor part can advantageously be improved after contact by further means.

Furthermore, a guide for the guided movement of the movably mounted sensor part may be present. The guide prevents tilting of the sensor part during movement of the sensor part.

In a further embodiment of the invention, the guide is formed as part of the holder.

The guide can in particular be designed without friction, which additionally improves the positioning of the sensor parts after a contact, since no friction effects, such as adhesive, rolling or sliding friction, caused by such a guide. This is particularly advantageous for light contacts, in which the position of the sensor parts was only minimally changed to each other and generates the means with path-dependent force generation by the low deflection only small additional restoring forces against the force set during installation.

Advantageously, of the two components movable sensor part and holder contains the one component stainless steel and the other aluminum bronze.

Due to the very dry air used in the DUV area for flushing the projection optics and the vacuum used in the EUV range with very low partial pressures of hydrogen and possibly oxygen, there is a risk of cold welding during friction of components with the same material , So a solid compound that can not be solved without affecting the surface quality of the components.

• 1 den prinzipiellen Aufbau einer EUV-Projektionsbelichtungsanlage, in welcher die Erfindung verwirklicht sein kann,
• 2a, b eine Sensoranordnung nach dem Stand der Technik im Einbauzustand und im Kollisionsfall,
• 3a, b eine exemplarische Ausführungsform der Erfindung im Einbauzustand und im Kollisionsfall, und
• 4a, b eine Detailansicht zu der Erfindung.

Embodiments and variants of the invention will be explained in more detail with reference to the drawing. Show it

• 1 the basic structure of an EUV projection exposure apparatus in which the invention can be realized,
• 2a, b a sensor arrangement according to the prior art in the installed state and in the event of a collision,
• 3a, b an exemplary embodiment of the invention in the installed state and in the event of a collision, and
• 4a, b a detailed view of the invention.

1 shows an example of the basic structure of an EUV projection exposure system 1 for microlithography, in which the invention can find application. An illumination system of the projection exposure apparatus 1 points next to a light source 3 an illumination optics 4 for illuminating an object field 5 in an object plane 6 on. One by the light source 3 generated EUV radiation 14 as optical useful radiation is by means of a light source in the 3 integrated collector aligned so that they are in the area of a Zwischenfokusebene 15 goes through an intermediate focus, before looking at a field facet mirror 2 meets. After the field facet mirror 2 becomes the EUV radiation 14 from a pupil facet mirror 16 reflected. With the aid of the pupil facet mirror 16 and an optical assembly 17 with mirrors 18 . 19 and 20 become field facets of the field facet mirror 2 in the object field 5 displayed.

Illuminated is a in the object field 5 arranged reticle 7 that of a schematically represented Reticlehalter 8th is held. A merely schematically illustrated projection optics 9 serves to represent the object field 5 in a picture field 10 into an image plane 11 , Pictured is a structure on the reticle 7 on a photosensitive layer in the area of the image field 10 in the picture plane 11 arranged wafers twelve , by a wafer holder also shown in detail 13 is held. The light source 3 can emit useful radiation, in particular in a wavelength range between 5 nm and 30 nm.

The invention can also be used in a DUV system not explicitly shown here. A DUV system is in principle like the EUV system described above 1 constructed, in a DUV system mirrors and lenses can be used as optical elements and the light source of a DUV system emits a useful radiation in a wavelength range of 100 nm to 300 nm.

2a shows a sensor arrangement 30 According to the state of the art. This includes two components 50 , 51 a lithography system 1 that has a decoupling spring 52 are connected. In the embodiment shown, the components 50 . 51 by way of example as a frame 50 . 51 executed, the first frame 51 for storage of another component 20 such as a mirror 20 , and the second frame 50 as a reference frame for measuring the position and position of the other component 20 serves.

The second frame 50 is opposite the first frame 51 through the decoupling spring 52 decoupled, ie the second frame 50 follows the movements of the first frame 51 , which are triggered for example by vibrations of the ground such as an earthquake, only in certain frequency ranges. In general, that applies to soft decoupling springs 52 , so decoupling springs 52 with lower stiffness / spring constant, the amplitudes of the relative motion between the frames 50 . 51 are larger than with hard decoupling springs 52 , ie decoupling springs 52 with high rigidity / spring constant. In the embodiment shown, the second frame 50 as the reference for measuring the position and location of the component 20 serves, also sensor frame 50 (SFr), compared to the first frame 51 for the storage of the component 20 serves, also forceframe 51 (FFr), with a frequency between 1 - 20 Hz decoupled. This frequency is also called decoupling frequency. The type of storage shown on a spring 52 is also referred to as floating storage.

The frames 50 . 51 move in the event of a disturbance from the outside relative to each other, in particular towards each other. Interference may be jolts due to transportation or earthquake and other events that deviate from the standard working conditions in semiconductor production. For transport additionally transport locks or transport locks can be provided, which are the two components 50 . 51 hold each other in a fixed position to each other during transport, thus avoiding relative movements. Due to the soft connection of the sensor frame 51 to the forceframe 50 can the relative movement between the frames 50 . 51 so big that the decoupling spring 52 deformed so much that it is damaged. The in 2a illustrated end stop 53 is to prevent damage to the decoupling spring 52 designed. In case of contact by a relative movement gives the end stop 53 after, that is deformed and by the increasing force by the deformation of the end stop 53 becomes the movement of the frame 50 . 51 braked to a standstill, as in 2a shown. The decoupling spring 52 is not deformed so much that it can be damaged. By a sensor distance 60 which is greater than the maximum movement of the components 50 . 51 to each other from a static position, the sensor parts 32 . 35 also through the end stops 53 protected against damage.

2a also shows a sensor 31 for measuring the relative position of the frames 50 . 51 , the sensor parts as a sensor head 35 and a sensor target 32 includes. Such sensors 31 are usually round in their basic form, but can also have other geometric shapes. The most passive sensor target 32 is usually on that frame 50 mounted, which moves relative to the fixed environment. The sensor head 35 which is often mechanically connected for the transmission of signals and / or energy to the environment, however, as shown in the figure, usually on that frame 51 arranged, which is connected to the fixed environment. This arrangement is particularly advantageous because of the mechanical connection of the sensor head 35 with the associated frame 51 Forces and moments are transmitted in the case of an arrangement of the sensor head 35 on the moving frame 50 an existing regulation of this framework 50 additionally disturb. The sensor head 35 includes a sensor body 36 and a reference surface 37 ,

The accuracy of the sensors 31 is among other things of the size of the working distance 60 , ie the distance between the reference surface and sensor target during operation, and the surface area of the measuring surface 33 of the sensor 31 dependent. This is especially true for eddy current sensors and capacitive sensors, with a small working distance 60 for almost all types of sensors 31 is advantageous, such as eddy current sensors, capacitive sensors, optical encoders, interferometers, confocal sensors or compressed air sensors.

The working distance 60 the sensors 31 is in the prior art by the distance of the end stops 53 at rest, ie the distance required during operation without interference from the outside 62 that also works area 62 is called, the braking distance of the end stops and a safety margin determined, which is composed of manufacturing and assembly tolerances and uncertainties in the design. The working distance 60 at rest is in systems in the prior art at 1.5 - 2.5mm and is exemplified by 0.7 mm operating range, 1.3mm compliance of the end stops 53 and an additional safety margin between the sensor target 32 and sensor head 35 of 0.5 mm together.

Only then can a collision of the sensor parts 32 . 35 and thus avoiding damage to the sensors 31 be assured as in 3b shown.

A disadvantage of the solution of the above-described prior art is that with it the increasing demands on the accuracy of the sensors 31 in the available space for systems of the latest generation can no longer be met, since the necessary for this small working distance 60 the sensors 31 within the range, which is more likely to collide with the sensor target in the event of a failure 32 and sensor head 35 would lead.

3a shows a first embodiment of the invention based on a representation of two as a frame 50 . 51 trained components of a lithography system 1 that with a decoupling spring 52 are connected. In the presentation of the 3a If the arrangement is in the operating state, there is currently no fault on the first frame 51 before, which could lead to relative movements of high amplitude and thus a possible collision.

The decoupling spring 52 and the end stop 53 are basically as already known from the prior art, whereas the working distance 60 of the sensor 31 during normal operation of the system 1 ( 3a) advantageously smaller than the distance 62 of the end stops 53 is. In the case of a large relative movement between the frames triggered by a disturbance from the outside 50 . 51 leads the small working distance 60 of the sensor 31 to a contact between sensor target 32 and sensor head 35 , To avoid damage from the collision of the sensor head 35 and sensor target 32 is the sensor head 35 advantageously floating, ie the sensor head 35 is on a pen 38 mounted, causing the sensor head 35 upon contact of the sensor target 32 is moved to a reserved room. The 3b shows the two frames 50 . 51 and the sensor 31 in case of such a collision.

4a shows an enlarged section of the area of the sensor 31 , The sensor head 35 is in a sensor receptacle 39 attached, in turn, in a holder 41 is mounted. The holder 41 encloses at least partially a space in the deflection direction of the spring 38 between sensor head 35 and forceframe 51 , In this room, the sensor head 35 dodge if the sensor target 32 on the sensor head 35 meets. The sensor head 35 and the sensor receptacle 39 can as in the 4a be shown as separate parts or be designed in one piece, so that the sensor head 35 directly into the holder 41 can be mounted.

4a moreover shows that the sensor head 35 a reference surface 37 and the sensor target 32 a measuring surface 33 and an outdoor area 34 includes. The actual measuring process of the sensor 31 takes place between reference surface 37 and measuring surface 33 instead of. The outdoor area 34 of the sensor target 32 has no function with regard to the measurement. To the sensitive reference surface 37 of the sensor head 35 and the measuring surface 33 of the sensor target 32 to protect against direct contact is at the sensor receptacle 39 on the side that leads to the sensor target 32 shows an increase 40 trained, which also serves as collision protection 40 referred to as. The collision protection 40 can also be an additional component or integral with the sensor mount 39 be executed. By the collision protection 40 is the reference surface 37 opposite the area of the sensor head 35 at which it comes to mechanical contact with the sensor target 32 comes, advantageously by an amount of 25 - 50μm reset. In case of touch of sensor target 32 and sensor head 35 thus meet the insensitive outdoor area 34 of the sensor target 32 on the collision protection 40 of the sensor head 35 so that the sensitive and sensitive reference 37 and measuring surfaces 33 are protected.

In addition, it is 4a still the distance 61 between sensor target 32 and collision protection 40 , shown. This distance 61 is advantageously designed so that during operation of the lithographic system 1 and without consideration of external interference, a touch of sensor target 32 and collision protection 40 is excluded; it is typically in the range of 50 and 200μm and consists of the expected path in operation, tolerances and a safety margin. The distance 61 is also referred to as a workspace.

In the 4a shown spring 38 that the sensor head 35 in the holder 41 must be designed in such a way that on the one hand it ensures that the sensor head 35 in operation always at a stop 42 is applied and on the other hand, a deflection of the sensor head 35 in case of a collision is possible without the sensor head 35 Takes damage. The necessary force and characteristic can not only as in the embodiment in 4a shown by a spring 38 be generated, but in particular by a magnetic field or a pneumatic storage with the same effect.

Also shown in 4a / b is a reference stop 42 in the holder 41 that should make sure the sensor head 35 after a collision reproducible for mounting 41 and thus to the sensor target 32 can be positioned without a re-adjustment and / or calibration of the sensor 31 to make necessary. The accuracy of the sensor 31 is usually in the range of 5-10 microns. To achieve this requirement is a very high reproducibility of the position of the sensor head 35 in the holder 41 necessary, which in turn leads to high demands on the surface accuracy both at the reference stop 42 the holder 41 as well as at the contact surface of the recording 39 or the sensor head 35 leads. The requirements are for a sensor 31 with absolute measurement at a few microns and can with a relatively measuring sensor 31 be greatly reduced. Here the quality of the contact surface only has to ensure a stable position during operation. A measurement during the collision is not necessary.

4a / b continues to show a lead 43 in the example shown as part of the holder 41 is trained. The task of leadership 43 is it, a movement of the sensor head 35 in the direction of the action of the spring force, which is hereinafter referred to as the axis of action to allow, while ensuring that a tilt and / or rotations about the axis of action and a movement perpendicular to the axis of action of the spring 38 minimized or avoided. Advantageously, the leadership 43 frictionless, such as by monolithic joints or a magnetic guide 43 to the formation of in lithography equipment 1 avoid unwanted particles by friction. A frustrated leadership 43 with appropriate precautions to avoid the particles or targeted encapsulation is also possible.

When selecting the material pairing of sensor mount 39 and bracket 41 Different aspects have to be taken into account, such as reproducibility of the attack 42 and machinability of the material. Likewise, the environmental conditions in a lithography system 1 to note, which is easy to cold-weld between parts 39 . 41 can lead from the same material. An advantageous combination that largely meets the above requirements, for example, stainless steel and aluminum bronze. Which of the two partners 39 . 41 which material is not decisive.

LIST OF REFERENCE NUMBERS

1

Projection exposure system

2

Field facet mirror

3

light source

4

illumination optics

5

object field

6

object level

7

reticle

8th

Reticlehalter

9

projection optics

10

field

11

image plane

12

wafer

13

wafer holder

14

EUV radiation

15

Between the focal plane

16

Pupil facet mirror

17

module

18

mirror

19

mirror

20

mirror

30

sensor arrangement

31

sensor

32

sensor target

33

measuring surface

34

outdoors

35

sensor head

36

sensor body

37

reference surface

38

feather

39

sensor recording

40

collision protection

41

bracket

42

reference stop

43

guide

50

Component, frame, sensor frame

51

Component, frame, forceframe

52

decoupling spring

53

end stop

60

working distance

61

Workspace

62

operating range

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2013/004403 [0003]

Claims (11)

A projection exposure apparatus (1) for semiconductor lithography, comprising - a first component (51) movable relative to a second component (50) - a sensor (31) for measuring the relative position of the two components (50, 51) relative to one another - the sensor (31) a first sensor part (35) with a reference surface (37) and a second sensor part (32) with a measuring surface (33) spaced apart by a measuring path and the first sensor part (35) on the first component (51) and the second sensor part (32 ) is arranged on the second component (50), characterized in that at least one of the sensor parts (32, 35) is mounted movably relative to that component on which it is arranged with a movement component in the direction of the measurement path. Projection exposure system (1) according to Claim 1 , characterized in that the first component (51) is a forceframe (51) and the second component (50) is a sensor frame (50) of the projection exposure apparatus. Projection exposure apparatus (1) according to one of the preceding claims, characterized in that - on both components (50, 51) end stops (53) are present, which limit the maximum approximation of the two components (50, 51) and - the distance (60) the two sensor parts (32, 35) is less than the distance (62) of the two end stops (53) during normal operation of the system. Projection exposure apparatus (1) according to one of the preceding claims, characterized in that at least one sensor part (32, 35) has an increase (40) extending in the direction of the other sensor part, which at an approach of the two sensor parts (32, 35) to each other touches the other sensor part (32, 35) in a region (34) that is not used for measurement. Projection exposure apparatus (1) according to one of the preceding claims, characterized in that the elevation (40) is arranged on the first sensor part (35). Projection exposure apparatus (1) according to one of the preceding claims, characterized in that the movably mounted sensor member (35) is arranged in a holder (41) comprising a reference stop (42) for the defined positioning of the sensor part (35). Projection exposure system (1) according to Claim 6 , characterized in that the movably mounted sensor part (35) is arranged on a means with path-dependent force generation (38), so that it is again positioned against the reference stop (42) after contact with the other sensor part (32). Projection exposure apparatus (1) according to one of the preceding claims, characterized in that a guide (43) for the guided movement of the movably mounted sensor part (35) is present. Projection exposure system according to Claims 6 . 7 and 8th , characterized in that the guide (43) is formed as part of the holder (41). Projection exposure system (1) according to Claim 6 or 7 and Claim 8 or 9 , characterized in that the guide (43) is made frictionless. Projection exposure system (1) according to Claim 6 . 7 and one or more of the preceding claims, characterized in that of the two components movable sensor part (35) and holder (41), the one component contains stainless steel, the other aluminum bronze.

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