DE102022203299A1 - Procedure for checking the quality of a screw connection - Google Patents

Abstract

Method for checking the quality of a screw connection of at least two components (42, 45, 49) with a predetermined target torque by evaluating torque signals, preload force signals and angle of rotation signals detected during screwing, the quality criteria including that an actually applied torque when the target torque is reached lies in a first corridor (60), - a starting torque detected for a predetermined angle of rotation lies in a second corridor (62), - a preload force for the angle of rotation of the actually applied torque lies in a third corridor (61).

Description

The invention relates to a method for checking the quality of a screw connection, in particular a screw connection in a projection exposure system for semiconductor lithography.

In modern assembly technology, screw connections are still one of the most important types of connections. The variety of screws in screwdriving technology has changed significantly compared to the past. Methods for calculating screw connections and newly developed screwing processes offer the possibility of significantly reducing the dimensions of the screws. The result is smaller and lighter screws, which leads to significant raw material and weight savings and greatly reduces the space required for screw connections.

Screw connections also play an important role in the area of projection exposure systems for semiconductor lithography, especially in EUV projection exposure systems. Due to the typically limited installation space available here and the drastic consequences of a screw connection failure, there are increased requirements here.

A screw connection is a detachable connection that joins two or more parts together in such a way that they behave as one part under all operating forces. Maintaining sufficient residual preload force (residual clamping force) is crucial for operational safety. If the operating force becomes so great during operation that it cancels out the preload force, the screw can loosen or even break, depending on the operating load. The preload force can be increased by increasing the stress cross section by using several or larger screws, by increasing the screw quality, which makes it possible to increase the assembly preload force with the same screw dimensions, or by using more precise screwing processes so that the elastic properties of the screw are better utilized can be increased.

In screwing processes, a more precise statement about the or even a smaller spread of the preload force achieved can be achieved using the parameters monitored during screwing, such as the torque, the slope of the torque and/or the angle of rotation. The measured torque when tightening the screw connection consists of the thread friction, the under-head friction, for example between a nut and a support, and the preload force, whereby the high spread of thread friction and the under-head friction makes it difficult to determine the preload force.

Known tightening procedures are disclosed, for example, in the training documents from IBES Elektronik GmbH, which are published at http://www.ibeselectronic.de/Schulungsmodelle_Neutral.pdf.

A method described there for improving screwing is a torque-controlled tightening method in which the torque D [Nm] is monitored and a minimum D _min [Nm] and maximum torque D _max [Nm] are defined, which describe a range in which the Screw is tightened. This means that the torque used is more reproducible compared to purely subjective tightening of the screw connection. In addition, a range for the exceeded rotation angle W [degrees] is also defined by a minimum W _min [degrees] and maximum rotation angle W _max [degrees], for example to detect seizing of the thread or plastic deformation of the screw head. The quality of the screw connection is defined by reaching the process window, which is defined by the minimum and maximum values of the areas for the torque and the angle of rotation, i.e. is two-dimensional. The method described has the disadvantage that it still involves a high degree of variation in thread friction and underhead friction.

Another known method monitors the angle of rotation, whereby this is only determined from a defined threshold value of the torque D _threshold [N], at which the setting effects in the thread and under the head of the screw connection are complete. This process can bring the screw into the plastic range, regardless of the torque, so that the thread friction and the under-head friction no longer have any influence on the determination of the preload force. Nevertheless, a minimum and maximum torque is also defined in this method for the same reasons as above. The quality of the screw connection is also defined by reaching the two-dimensional process window with a lower and upper torque and a lower and upper rotation angle.

The methods described above have the disadvantage that the screw connections they rate as tolerable do not always meet the requirements.

The object of the present invention is to provide a method which solves the disadvantages of the prior art described above.

This task is solved by a method with the features of the independent claim. The subclaims relate to advantageous developments and variants of the invention.

• - ein tatsächlich anliegendes Drehmoment beim Erreichen des Zieldrehmoments in einem ersten Korridor liegt,
• - ein für einen vorbestimmten Drehwinkel erfasstes Startdrehmoment in einem zweiten Korridor liegt,
• - eine Vorspannkraft für den Drehwinkel des tatsächlich anliegenden Drehmoments in einem dritten Korridor liegt.

A method according to the invention for checking the quality of a screw connection of two components with a predetermined target torque by evaluating torque signals, preload force signals and angle of rotation signals detected during screwing is characterized in that the quality criteria include that

• - an actually applied torque lies in a first corridor when the target torque is reached,
• - a starting torque recorded for a predetermined angle of rotation lies in a second corridor,
• - a preload force for the angle of rotation of the torque actually applied lies in a third corridor.

In this context, in contrast to the windows of envelope monitoring known in the prior art, a corridor is to be understood as a one-dimensional area. For a defined angle of rotation, there is a torque range in which the recorded torque may lie in order to meet the quality criterion. This corresponds to a closer monitoring of the target torque compared to the window, which allows a variation of the angle of rotation and the torque. The difference between the actual torque applied and the target torque depends on the control quality of the control system used for the screw connection, which receives the target torque to be achieved for the screw connection as input. This is not always achieved exactly due to various influences such as friction in the thread and under-head friction on the contact surfaces of the components, such as between a nut and a support, as well as tolerances of the sensors and control parameters. The starting torque is defined by the torque at which the contact surfaces of the components come into contact with one another during and through the screw connection.

For this purpose, the predetermined angle of rotation for determining the starting torque can correspond to a rotation angle which causes the predetermined preload force for the screw connection due to the torque caused by the angle of rotation. This angle of rotation can be determined in advance through tests and depends on the preload force to be applied, the geometry of the screw and other boundary conditions such as the quality of the screw used and setting effects when screwing.

Additionally or alternatively, the preload force can be determined based on a weight force acting on the screw connection and a motor current of a motor exerting a force on the screw connection. The weight force can be caused, for example, by a portal firmly connected to the screw connection, which is connected to the component to be prestressed and acts on the component with its entire weight. The portal can also be moved via a motor, so that in addition to the weight force, a force acting in the direction of the weight force can be exerted on the screw connection. To adjust the preload force, the motor is first regulated via the motor current until the sum of the weight of the portal and the additional force caused by the motor current corresponds to the predetermined preload force. The motor control is then switched to position control and the motor current is continuously recorded. If, when screwing, the preload force is caused by the screw connection itself, i.e. by the torque generated when the screw connection is tightened, the motor current and thus the recorded preload force are reduced. In order to fulfill the quality criterion, as described above, the recorded preload force must be within a certain corridor when the target torque is reached. This depends on the preload required in the screw connection.

Furthermore, another quality criterion can be a total angle of rotation of the screw connection. This is intended to check and thus rule out accidental, incorrect fulfillment of the other quality criteria, for example due to seizing of the thread.

$${\text{Drehwinkel}}_{\text{max}}={\text{W}}_{\text{th}}\left(2160°\right){\text{+/-W}}_{\text{To}}+{\text{W}}_{\text{Vs}}+{\text{W}}_{\text{0max}}\left(360°\right)=2532°{\text{+/-W}}_{\text{To}}$$

In particular, the total angle of rotation can lie in a fourth corridor. The total angle of rotation can be determined by the theoretical angle of rotation of the screw connection, a component tolerance, which is used to apply The angle of rotation required for the preload force and the angle of rotation required until the threads mesh can be determined. The total angle of rotation is therefore made up of the length of the thread, i.e. the theoretical angle of rotation W _th , the angle of rotation W ₀ until the threads mesh, the component tolerances W _To and the angle of rotation Wvs required to apply the preload through the screw connection. This results in the following minimum and maximum values for a theoretical rotation angle of six revolutions and a rotation angle W _Vs of 12°: $${\text{Angle of rotation}}_{\text{min}}={\text{W}}_{\text{th}}\left(2160°\right){\text{+/-W}}_{\text{To}}+{\text{W}}_{\text{Vs}}+{\text{W}}_{\text{0min}}\left(0°\right)=2172°{\text{+/-W}}_{\text{To}}$$

$${\text{Angle of rotation}}_{\text{Max}}={\text{W}}_{\text{th}}\left(2160°\right){\text{+/-W}}_{\text{To}}+{\text{W}}_{\text{Vs}}+{\text{W}}_{\text{0max}}\left(360°\right)=2532°{\text{+/-W}}_{\text{To}}$$

The total angle of rotation must therefore lie within the fourth corridor, which is defined by the angle of rotation _min and angle of rotation _max .

Furthermore, a receptacle of a component can be designed in such a way that a tilting of the longitudinal axes of the two components relative to one another can be compensated for by tilting at least one component about two axes perpendicular to the screwing direction. This prevents tilting when the two components come into contact and thus prevents incomplete contact between the contact surfaces when the target torque is reached. In the event that a heat flow is to flow through the two components, the contact of the contact surfaces is an important factor for the maximum heat flow. This variant can also be used independently of the method described above to check the quality of the screw connection.

In particular, tilting of the component may only be possible in a partial area of the screw connection. This has the advantage that at the beginning of the screw connection, a secure finding of the thread can be ensured by pressing the two components together. Only after one or more threads have been screwed together is the two components tilted relative to one another.

Furthermore, a spring can apply a force to the holder in the direction of the screw connection during screwing. In addition to the secure finding of the thread as already explained above, this also preloads the thread so that the contact of the thread surfaces is always defined, which reduces the play in the thread when screwing.

In particular, the force of the spring can prevent the component from tilting in the receptacle. As a result, tilting, as already explained above, is only possible in a partial area towards the end of the screw connection shortly before or at the time when the two components come into contact.

In addition, the holder can absorb the torque caused by the screw connection. The holder can be designed in such a way that it is possible to absorb the torque and tilt the component in the holder about two axes perpendicular to the screwing direction.

• 1 schematisch im Meridionalschnitt eine Projektionsbelichtungsanlage für die EUV-Projektionslithografie,
• 2 eine Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens,
• 3 einen Ausschnitt eines auf im erfindungsgemäßen Verfahren erfassten Daten basierenden Diagramms,
• 4 ein weiteres auf im erfindungsgemäßen Verfahren erfassten Daten basierenden Diagramm,
• 5 eine Komponente, und
• 6a-e ein Verfahren zum Ausgleich einer Verkippung zweier Bauteile zueinander beim Verschrauben.

Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing. Show it

• 1 schematically in meridional section a projection exposure system for EUV projection lithography,
• 2 a device for carrying out the method according to the invention,
• 3 a section of a diagram based on data recorded in the method according to the invention,
• 4 a further diagram based on data recorded in the method according to the invention,
• 5 a component, and
• 6a-e a method for compensating for tilting of two components relative to one another when screwing together.

Below we will initially refer to the 1 The essential components of a projection exposure system 1 for microlithography are described as an example. The description of the basic structure of the projection exposure system 1 and its components are not intended to be restrictive.

One embodiment of a lighting system 2 of the projection exposure system 1 has, in addition to a radiation source 3, lighting optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a module separate from the other lighting system. In this case, the lighting system does not include the light source 3.

A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced in particular in a scanning direction via a reticle displacement drive 9.

In the 1 A Cartesian xyz coordinate system is shown for explanation. The x direction runs perpendicular to the drawing plane. The y-direction is horizontal and the z-direction is vertical. The scanning direction is in the 1 along the y direction. The z direction runs perpendicular to the object plane 6.

The projection exposure system 1 includes projection optics 10. The projection optics 10 is used to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0 ° is also between the object plane 6 and the Image level 12 possible.

A structure on the reticle 7 is imaged on a light-sensitive layer of a wafer 13 arranged in the area of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced in particular along the y direction via a wafer displacement drive 15. The displacement, on the one hand, of the reticle 7 via the reticle displacement drive 9 and, on the other hand, of the wafer 13 via the wafer displacement drive 15 can take place in synchronization with one another.

The radiation source 3 is an EUV radiation source. The radiation source 3 emits in particular EUV radiation 16, which is also referred to below as useful radiation, illumination radiation or illumination light. The useful radiation in particular has a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be a plasma source, for example an LPP source (Laser Produced Plasma) or a DPP source. Source (Gas Discharged Produced Plasma, plasma produced by gas discharge). It can also be a synchrotron-based radiation source. The radiation source 3 can be a free electron laser (FEL).

The illumination radiation 16, which emanates from the radiation source 3, is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and/or hyperboloid reflection surfaces. The at least one reflection surface of the collector 17 can be exposed to the illumination radiation 16 in grazing incidence (GI), i.e. with angles of incidence greater than 45°, or in normal incidence (normal incidence, NI), i.e. with angles of incidence smaller than 45° become. The collector 17 can be structured and/or coated on the one hand to optimize its reflectivity for the useful radiation and on the other hand to suppress false light.

After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focus plane 18. The intermediate focus plane 18 can represent a separation between a radiation source module, having the radiation source 3 and the collector 17, and the illumination optics 4.

The lighting optics 4 comprises a deflection mirror 19 and, downstream of it in the beam path, a first facet mirror 20. The deflection mirror 19 can be a flat deflection mirror or alternatively a mirror with an effect that influences the bundle beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be designed as a spectral filter which separates a useful light wavelength of the illumination radiation 16 from false light of a wavelength that deviates from this. If the first facet mirror 20 is arranged in a plane of the illumination optics 4, which is optically conjugate to the object plane 6 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 20 includes a large number of individual first facets 21, which are also referred to below as field facets. Of these facets 21 are in the 1 just a few are shown as examples.

The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or part-circular edge contour. The first facets 21 can be designed as flat facets or alternatively as convex or concave curved facets.

Like, for example, from the DE 10 2008 009 600 A1 is known, the first facets 21 themselves can also each be composed of a large number of individual mirrors, in particular a large number of micromirrors. The first facet mirror 20 can in particular be designed as a microelectromechanical system (MEMS system). For details see the DE 10 2008 009 600 A1 referred.

Between the collector 17 and the deflection mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction.

A second facet mirror 22 is located downstream of the first facet mirror 20 in the beam path of the illumination optics 4. If the second facet mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the lighting optics 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006/0132747 A1 , the EP 1 614 008 B1 and the US 6,573,978 .

The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

The second facets 23 can also be macroscopic facets, which can have, for example, round, rectangular or even hexagonal edges, or alternatively they can be facets composed of micromirrors. In this regard, reference is also made to the DE 10 2008 009 600 A1 referred.

The second facets 23 can have flat or alternatively convex or concave curved reflection surfaces.

The lighting optics 4 thus forms a double faceted system. This basic principle is also known as the honeycomb condenser (fly's eye integrator).

It may be advantageous not to arrange the second facet mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the pupil facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as is the case, for example, in FIG DE 10 2017 220 586 A1 is described.

With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path in front of the object field 5.

In a further embodiment of the illumination optics 4, not shown, transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5, which contributes in particular to the imaging of the first facets 21 into the object field 5. The transmission optics can have exactly one mirror, but alternatively also two or more mirrors, which are arranged one behind the other in the beam path of the lighting optics 4. The transmission optics can in particular include one or two mirrors for perpendicular incidence (NI mirror, normal incidence mirror) and/or one or two mirrors for grazing incidence (GI mirror, gracing incidence mirror).

The lighting optics 4 has the version in the 1 is shown, after the collector 17 exactly three mirrors, namely the deflection mirror 19, the field facet mirror 20 and the pupil facet mirror 22.

In a further embodiment of the lighting optics 4, the deflection mirror 19 can also be omitted, so that the lighting optics 4 can then have exactly two mirrors after the collector 17, namely the first facet mirror 20 and the second facet mirror 22.

The imaging of the first facets 21 into the object plane 6 by means of the second facets 23 or with the second facets 23 and a transmission optics is generally only an approximate image.

The projection optics 10 comprises a plurality of mirrors Mi, which are numbered consecutively according to their arrangement in the beam path of the projection exposure system 1.

At the one in the 1 In the example shown, the projection optics 10 includes six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 are double-obscured optics. The projection optics 10 has an image-side numerical aperture that is larger than 0.5 and which can also be larger than 0.6 and which can be, for example, 0.7 or 0.75.

Reflection surfaces of the mirrors Mi can be designed as free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. The mirrors Mi, just like the mirrors of the lighting optics 4, can have highly reflective coatings for the lighting radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optics 10 has a large object image offset in the y direction between a y coordinate of a center of the object field 5 and a y coordinate of the center of the image field 11. This object image offset in the y direction can be approximately like this be as large as a z-distance between the object plane 6 and the image plane 12.

The projection optics 10 can in particular be anamorphic. In particular, it has different imaging scales βx, βy in the x and y directions. The two imaging scales βx, βy of the projection optics 10 are preferably (βx, βy) = (+/- 0.25, +/- 0.125). A positive image scale β means an image without image reversal. A negative sign for the image scale β means an image with image reversal.

The projection optics 10 thus leads to a reduction in size in the x direction, that is to say in the direction perpendicular to the scanning direction, in a ratio of 4:1.

The projection optics 10 leads to a reduction of 8:1 in the y direction, that is to say in the scanning direction.

Other image scales are also possible. Image scales of the same sign and absolutely the same in the x and y directions, for example with absolute values of 0.125 or 0.25, are also possible.

The number of intermediate image planes in the x and y directions in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, can be different. Examples of projection optics with different numbers of such intermediate images in the x and y directions are known from US 2018/0074303 A1 .

One of the pupil facets 23 is assigned to exactly one of the field facets 21 to form an illumination channel for illuminating the object field 5. This can in particular result in lighting based on Köhler's principle. The far field is broken down into a large number of object fields 5 using the field facets 21. The field facets 21 generate a plurality of images of the intermediate focus on the pupil facets 23 assigned to them.

The field facets 21 are each imaged onto the reticle 7 by an assigned pupil facet 23, superimposed on one another, in order to illuminate the object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by overlaying different lighting channels.

The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by an arrangement of the pupil facets. By selecting the illumination channels, in particular the subset of the pupil facets that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the lighting setting.

A likewise preferred pupil uniformity in the area of defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels.

Further aspects and details of the illumination of the object field 5 and in particular the entrance pupil of the projection optics 10 are described below.

The projection optics 10 can in particular have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

The entrance pupil of the projection optics 10 cannot regularly be illuminated precisely with the pupil facet mirror 22. When imaging the projection optics 10, which images the center of the pupil facet mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, an area can be found in which the pairwise distance of the aperture beams becomes minimal. This surface represents the entrance pupil or a surface conjugate to it in local space. In particular, this surface shows a finite curvature.

It may be that the projection optics have 10 different positions of the entrance pupil for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 22 and the reticle 7. With the help of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

At the in the 1 As shown in the arrangement of the components of the illumination optics 4, the pupil facet mirror 22 is arranged in a surface conjugate to the entrance pupil of the projection optics 10. The field facet mirror 20 is tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted to an arrangement plane that is defined by the deflection mirror 19.

The first facet mirror 20 is arranged tilted to an arrangement plane that is defined by the second facet mirror 22.

2 shows a device designed as a portal 30 with which the method according to the invention can be carried out. The portal 30 serves to connect a first component designed as a base body 42 to a base plate 41, the cylindrical base body 42 with a shoulder 43 formed at the upper end being guided from above through a through hole 44 in the base plate 41. The base body 42 additionally includes an interface 46 at the upper end for connection to an optical element, which is in the 5 and 6 is explained in more detail. The base body 42 is screwed to the opposite underside of the base plate 41 with a second component designed as a nut 45. As a result, the base body 42 is firmly connected to the base plate 41, with the screw connection generating a preload which ensures a residual clamping force of the screw connection for all operating states. The base body 42 is subjected to a predetermined preload force, which is continuously recorded during the screwing process. The portal 30 comprises a housing 31, which is connected via a connecting element in the form of a rod 33, which is connected at one end to the portal 30 and at the other end to the base body 42 to be screwed via a thread 47. The portal 30 therefore hangs with its weight on the base body 42 and thereby causes part of the required preload force. The portal 30 is connected to a motor 32 on the underside facing away from the base body 42, which can move the portal 30 in the direction of the screw connection. As a result, when the portal 30 is pulled away from the base body 42, the motor 32 can exert a force on the base body 42 in addition to the weight of the portal 30, as shown by an arrow in the figure 2 is indicated. The prestressing force acting on the base body 42 is therefore composed of the weight of the portal 30 and the force acting on the portal 30 through the motor 32. The known and constant weight of the portal 30 is set to a predetermined value by an additional force of the motor 32 applied via the control of the motor current. Once the predetermined preload force is reached, the control of the motor 32 is switched to position control and the motor current continues to be recorded continuously. This can be used as a quality criterion to check the quality of the screw connection, as in the 3 will be explained in more detail. The nut 45 used to connect the base body 42 to the base plate 41 is screwed to the base body 42 by a screwing unit 35 of the portal 30. The screwing unit 35 is guided in the housing 31 in such a way that both the torque required to screw the nut 45 can be absorbed by the guide and a movement in the direction of the longitudinal axis 48 of the base body 42 is possible. A stop 34 limits the movement of the screw unit 35 in the housing 31. The portal 30 and the screw unit 35 are designed such that they have a recess 36 for the base body 42 and the rod 33. In the in the 2 In the upper position shown by dashed lines, the bearing surface of the nut 45 comes into contact with the underside of the base plate 41. This continues through the screw unit 35 applied torque, the base body 42 is additionally biased by the nut 45, so that the motor current required to maintain the position of the motor 32 drops. The screwing unit 35 detects the angle of rotation and the torque during the entire screwing process, which, like the motor current, are transmitted to a control of the portal 30, not shown. The control of the portal 30 screws on the nut 45 until a predetermined maximum torque is reached. The evaluation of the torque via the angle of rotation and the preload force via the angle of rotation is carried out in the 3 explained in more detail.

3 shows a diagram in which the torque of the screwing unit 35 and the preload force determined from the weight of the portal 30 and the motor current are plotted against the angle of rotation of the screwing unit 35. The signals detected during screwing are processed by the control of the portal 30, with the maximum torque corresponding to the torque detected when screwing is stopped by the screwing unit 35. This must lie in a predetermined first corridor 60 in order to fulfill a first quality criterion of a screw connection that is considered to be good. A corridor in the sense of the invention describes an area in which the torque or the preload force may be at a fixed angle of rotation, i.e. in comparison to the prior art, a one-dimensional area represents a narrower tolerance for the maximum torque. Another quality criterion that must be met for a screw connection to be considered good is a calculated starting torque, which corresponds to the torque at the time of contact of the contact surface of the nut 45 with the underside of the base plate 41. For this purpose, a rotation angle α determined through tests is subtracted from the rotation angle of the maximum torque. The starting torque corresponding to this determined angle of rotation must in turn lie in a second predetermined corridor 62 in order to meet the quality criterion. Furthermore, the preload force corresponding to the angle of rotation of the maximum torque must also lie in a third predetermined corridor 61. The areas of the corridors 60, 61, 62 depend on the various influencing parameters such as screw size, screw quality, hardness of the base plate 41, required preload, to name just a few.

$${\text{Drehwinkel}}_{\text{max}}={\text{W}}_{\text{th}}\left(2160°\right){\text{+/-W}}_{\text{To}}+{\text{W}}_{\text{Vs}}+{\text{W}}_{\text{0max}}\left(0°\right)=2532°{\text{+/-W}}_{\text{To}}$$

4 shows a diagram in which the entire screwing process is shown. The diagram also includes the one already in the 3 shown area of the diagram and also represents the torque and the preload force over the angle of rotation detected by the screwing unit 35. The detection of the angle of rotation is started in the diagram shown when the thread of the nut 45 is in contact with the thread of the base body 42. While the nut 45 is screwed onto the base body 42 by the screwing unit 35, the preload force is adjusted by regulating the motor current of the motor 32, as in 2 already explained, and when the predetermined preload force is reached, the control is switched to position control. Due to the low component tolerances, the total angle of rotation can be used as an additional quality criterion, with the total angle of rotation consisting of the length of the thread, i.e. the theoretical angle of rotation W _th , the angle of rotation W ₀ up to the interlocking of the threads of the nut 45 and the base body 42, the component tolerances W _To and the angle of rotation Wvs required to apply the preload through the nut 45. This results in the following value for a theoretical rotation angle of six revolutions and a rotation angle W _Vs of 12°: $${\text{Angle of rotation}}_{\text{min}}={\text{W}}_{\text{th}}\left(2160°\right){\text{+/-W}}_{\text{To}}+{\text{W}}_{\text{Vs}}+{\text{W}}_{\text{0min}}\left(0°\right)=2172°{\text{+/-W}}_{\text{To}}$$

$${\text{Angle of rotation}}_{\text{Max}}={\text{W}}_{\text{th}}\left(2160°\right){\text{+/-W}}_{\text{To}}+{\text{W}}_{\text{Vs}}+{\text{W}}_{\text{0max}}\left(0°\right)=2532°{\text{+/-W}}_{\text{To}}$$

When the target torque is reached, the total angle of rotation must therefore lie within a fourth corridor 63 of a rotation angle _{of min.} 2172° +/- W _To and a rotation angle _{of max.} 2532° +/- W _To .

If all four quality criteria explained lie within the specified corridors 60, 61, 62, 63, a successful screw connection can be assumed with a very high probability.

5 shows the explanation of the process in the 2 until 4 Assembly 40 explained by way of example, which additionally comprises an optical element designed as a facet 49. The assembly 40 can, for example, be part of one of the 1 be the facet mirror 20, 21 described. The facet 49 is connected to the base body 42 via the interface 46 designed as a screw connection. The two bearing surfaces 50, 51 of the facet 49 and the base body 42 must be aligned parallel to one another when screwing in order to ensure flat contact between the two bearing surfaces 50, 51 and a resulting optimal heat flow across both components 42, 49. This requires the two parts to be securely screwed together. That in the 2 , the 3 and the 4 The method according to the invention explained can also be used for this screw connection, whereby the method for a forced-free screw connection and the method for checking the quality of a screw connection can also stand independently as an invention. A procedure that ensures forced screwing is described in the 6 explained in detail.

The 6a until 6e show a screwing process in which the facet 49 and the base body 42 are screwed in a device 70, which ensures a parallel alignment of the two support surfaces 50, 51 of the facet 49 and the base body 42. This process can also be used independently of the procedure described above to check the quality of the screw connection.

In the 6a In a first method step, the facet 49 is aligned with the base body 42 in such a way that an internal thread 52 formed in the facet 49 and an external thread 53 formed at the interface 46 are centered relative to one another. The facet 49 is held in a screwing device 71 of the device 70, the screwing device 71 being positioned relative to one another in the X/Y plane for centering the longitudinal axis 55 of the facet 49 and the longitudinal axis 48 of the base body 42. The base body 42 is held in a holder 73, which engages with an adapter 72 in a recess 54 in the base body 42. The adapter 72 and the recess 54 are designed in such a way that the base body 42 can be moved in the Z direction, i.e. in the direction of its longitudinal axis 48, in a limited range, and freely around the X axis and Y axis by a certain range can be tilted and the rotation around the Z axis is locked so that the torque required for screwing can be absorbed.

6b shows a second method step in which the screwing device 71 is moved with the facet 49 in the direction of the base body 42 until the facet 49 comes into contact with the base body 42. The base body 42 is thereby initially pressed with the recess 54 against a stop 75 of the adapter 72, whereby the holder 73 is pressed against a compression spring 74 arranged on the side of the holder 73 opposite the adapter 72, whereby it is compressed. The compression spring 74 prestressed in this way causes the stop 75 of the holder 73 to be pressed against the recess 54 of the base body 42 and as a result the thread 53 of the base body 42 is pressed against the thread 52 of the facet 49, whereby this is almost free of play when screwing is.

The 6c shows a third method step in which the screwing device 71 is first fixed in the Z direction and after the threads 52, 53 have meshed with one another, the screwing of the thread 52, 53 begins by rotating the screwing device 70.

6d shows a fourth method step in which the base body 42 was pulled through the thread 52, 53 into the facet 49 supported by the spring force of the compression spring 74 and a first contact occurred between the two bearing surfaces 50, 51 of the base body 42 and the facet 49 is. The holder 73, the adapter 72 and the recess 54 are designed in such a way that before the first contact of the support surfaces 50, 51, the compression spring 74 is completely relaxed and the adapter 72 no longer has any contact with the recess 54 of the base body 42 in the Z direction , so that it can tilt freely around the X-axis and Y-axis in the holder 73. Alternatively, the facet 49 can be raised with the screwing device 70 after screwing, for example, half of the threads in the Z direction, so that the adapter 72 and the recess 54 are contact-free. On the one hand, this can be ensured via a predetermined path in Z or through a force measurement. The two longitudinal axes 48, 55 of the base body 42 and the facet 49 are as in the 6d shown tilted towards each other upon first contact.

6e shows a fifth method step in which, when the two components 42, 49 are further screwed together, the base body 42 is aligned in such a way that the longitudinal axis 48 of the base body 42 and the longitudinal axis 55 of the facet 49 lie on one another and the two support surfaces 50, 51 are aligned parallel, whereby complete contact between the bearing surfaces 50, 51 is achieved. This ensures an optimal heat flow across the contact surfaces 50, 51.

Reference symbol list

1

Projection exposure system

2

Lighting system

3

Radiation source

4

Illumination optics

5

Object field

6

Object level

7

Reticule

8th

Reticle holder

9

Reticle displacement drive

10

Projection optics

11

Image field

12

Image plane

13

wafers

14

wafer holder

15

Wafer displacement drive

16

EUV radiation

17

collector

18

Intermediate focal plane

19

Deflecting mirror

20

Facet mirror

21

facets

22

Facet mirror

23

facets

30

portal

31

Housing

32

engine

33

connecting element

34

attack

35

screw unit

36

recess

40

module

41

Base plate

42

Basic body

43

Paragraph

44

through hole

45

Mother

46

Interface facet

47

thread

48

Longitudinal axis

49

facet

50

Support surface facet

51

Support surface base body

52

Internal thread facet

53

External thread interface

54

Recess base body

55

Longitudinal axis

60

Corridor target torque

61

Corridor preload force

62

Corridor calculated starting torque

63

Corridor total rotation angle

70

contraption

71

screw device

72

adapter

73

bracket

74

Feather

75

attack

α

Angle starting torque

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was 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

• DE 102008009600 A1 [0036, 0040]
• US 20060132747 A1 [0038]
• EP 1614008 B1 [0038]
• US 6573978 [0038]
• DE 102017220586 A1 [0043]
• US 20180074303 A1 [0057]

Claims (10)

Method for checking the quality of a screw connection of at least two components (42, 45, 49) with a predetermined target torque by evaluating torque signals, preload force signals and angle of rotation signals detected during screwing, characterized in that the quality criteria include that - an actually applied torque when reached of the target torque lies in a first corridor (60), - a starting torque detected for a predetermined angle of rotation lies in a second corridor (62), - a preload force for the angle of rotation of the actually applied torque lies in a third corridor (61). Procedure according to Claim 1 , characterized in that the predetermined angle of rotation for determining the starting torque corresponds to an angle of rotation which causes the predetermined preload force for the screw connection through the torque caused by the angle of rotation. Procedure according to one of the Claims 1 or 2 , characterized in that the preload force is determined based on a weight force acting on the screw connection and a motor current of a motor (32) which exerts a force on the screw connection. Method according to one of the preceding claims, characterized in that a further quality criterion is a total angle of rotation of the screw connection. Procedure according to Claim 4 , characterized in that the total angle of rotation lies in a fourth corridor (63). Method according to one of the preceding claims, characterized in that one of the two components (42, 45, 49) is arranged in a holder (73) in such a way that a tilting of the two longitudinal axes (48, 55) of the two components (42, 49 ) is balanced against each other by tilting at least one component (42,49) about two axes perpendicular to the screwing direction. Procedure according to Claim 6 , characterized in that the tilting of the component (42,49) is only possible in a partial area of the screw connection. Procedure according to one of the Claims 6 or 7 , characterized in that a spring (74) applies a force to the holder (73) in the direction of the screw connection during screwing. Procedure according to Claim 8 , characterized in that the force of the spring (74) prevents the component (42,49) from tilting in the holder (73). Procedure according to one of the Claims 6 until 9 , characterized in that the holder (73) absorbs the torque caused by the screw connection.

Images