DE102022203299B4 - 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 recorded during screwing, characterized in that the quality criteria include that - an actually applied torque when the target torque is reached lies in a first corridor (60), - a starting torque recorded 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, the screw connection is still one of the most important types of connection. The variety of screws in screw 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 a significant saving in raw materials and weight and greatly reduces the space required for screw connections.

Screw connections also play an important role in the field of projection exposure systems for semiconductor lithography, especially in EUV projection exposure systems. Due to the typically small installation space available here and the drastic consequences of 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 that occur. Maintaining a sufficient residual preload force (residual clamping force) is of crucial importance for operational safety. If the operating force during operation becomes so great 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 more 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 can be better utilized.

In screwing processes, a more precise statement about the achieved preload force or a smaller scatter of it can be made on the basis of the parameters monitored during screwing, such as the torque, the torque gradient and/or the angle of rotation. The measured torque when tightening the screw connection is made up of the thread friction, the underhead friction, for example between a nut and a support, and the preload force, whereby the high scatter of the thread friction and the underhead friction makes it difficult to determine the preload force.

Known tightening procedures are described, for example, in the training materials of IBES Elektronik GmbH, which are available at http://www.ibes-electronic.de/Schulungsmodelle_Neutral.pdf published.

A method described there for improving the screw connection 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 makes the torque used more reproducible compared to a purely subjective tightening of the screw connection. In addition, a range for the exceeded angle of rotation W [degrees] is defined by a minimum W _min [degrees] and maximum angle of rotation W _max [degrees] in order to detect, for example, seizure 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 ranges for the torque and the angle of rotation, i.e. is two-dimensional. The method described has the disadvantage that it still includes the high scatter of the thread friction and the 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 method can bring the screw into the plastic range regardless of the torque, so that the thread friction and the underhead 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 angle of rotation.

In the German Disclosure Specification DE 10 2019 201 549 A1 A method for monitoring screw connections, in particular for use in projection exposure systems for semiconductor lithography, is described in which a torque is monitored and a minimum and maximum permissible torque is defined, which describe a range in which the screw connection is considered to be good.

Furthermore, the German disclosure document DE 10 2005 019 258 A1 A method is described in which intermittently operating screwing tools such as hydraulic torque wrenches can be controlled with the aim of switching off the tool after the yield point is reached. In this way, design errors and material defects can be detected.

In addition, the German disclosure document DE 32 22 156 A1 a screwing method is disclosed in which a control of the screwing process with complex torque-angle characteristics is achieved by entering sets of maximum and minimum torque signals as well as maximum and minimum angle signals into a computer. An error signal is generated if, for at least one of these sets, the minimum angle of rotation is not yet reached when the maximum torque is reached or the minimum torque is not yet reached when the maximum angle of rotation is reached.

Furthermore, the European patent specification EP 3 571 017 B1 a method and a device for tightening a screw connection with a motor-driven screwdriver unit are presented, wherein the angle of rotation and the torque are determined during tightening in order to be able to stop the tightening process when a desired tightening tension is reached. In a first tightening range, an increase in the torque over the angle of rotation is determined and in a second, subsequent tightening range, a change in the increase in the torque over the angle of rotation is determined. When a maximum permissible change in the increase and/or rate of change, which is determined based on the increase occurring in the first tightening range, is reached or exceeded, the screwdriver unit is stopped.

The methods described above have the disadvantage that the screw connections they consider 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 object is achieved by a method having 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 recorded during screwing is characterized in that the quality criteria include that

• - an actual torque when reaching the target torque lies within a first corridor,
• - 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 actually applied torque lies in a third corridor.

In this context, a corridor is to be understood as a one-dimensional range, in contrast to the envelope curve monitoring windows known in the prior art. For a defined angle of rotation, there is therefore a range for the torque within which the recorded torque may lie in order to meet the quality criterion. This corresponds to 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 screwing, which receives the target torque to be achieved for the screwing 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 in 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 screwing.

For this purpose, the predetermined angle of rotation for determining the starting torque can correspond to an angle of rotation which, through the torque caused by the angle of rotation, causes the preload force predetermined for the screw connection. This angle of rotation can be determined in advance through tests and depends on the preload force to be caused, 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 on the basis of a weight acting on the screw connection and a motor current of a motor exerting a force on the screw connection. The weight force can, for example, be caused by a portal that is firmly connected to the screw connection, which is connected to the component to be preloaded and acts on the component with its entire weight. The portal can also be moved by 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 controlled via the motor current until the sum of the weight force 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 the preload force is caused by the screw connection itself during screwing, i.e. by the torque generated when tightening the screw connection, the motor current and thus the recorded preload force decreases. In order to meet the quality criteria, 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.

A further quality criterion can be the overall angle of rotation of the screw connection. This is intended to check and thus exclude any accidental, incorrect fulfillment of the other quality criteria, for example due to seizure of the thread.

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

In particular, the total angle of rotation can be 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, the angle of rotation required to apply the preload force and the angle of rotation required until the threads mesh. 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 W _Vs required to apply the preload through the screw connection. This results in the following minimum and maximum values for a theoretical angle of rotation of six revolutions and an angle of rotation W _Vs of 12°: $${\text{Drehwinkel}}_{\text{min}}={\text{W}}_{\text{th}}\left(2160°\right)+/-{\text{W}}_{\text{To}}+{\text{W}}_{\text{Vs}}+{\text{W}}_{0\text{min}}\left(0°\right)=2172°+/-{\text{W}}_{\text{To}}$$

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

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 component holder can be designed in such a way that a tilting of the longitudinal axes of the two components relative to each other 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 incomplete contact of 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 for checking the quality of the screw connection.

In particular, the tilting of the component may only be possible in a part of the screw connection. This has the advantage that at the beginning of the screw connection, the thread can be found reliably by pressing the two components together. Only after the thread has been screwed together by one or more thread turns is the tilting of the two components relative to each other possible.

Furthermore, a spring can apply a force to the bracket in the direction of the screw connection during screwing. In addition to reliably finding the thread as explained above, this also pre-tensions the thread so that the contact between 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 holder. As explained above, this means that tilting 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 the torque can be absorbed and the component can be tilted in the holder about two axes perpendicular to the screw connection 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.

In the following, embodiments and variants of the invention are explained in more detail with reference to the drawing.

• 1 schematic meridional section of 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 acquired in the method according to the invention,
• 4 another diagram based on data acquired in the method according to the invention,
• 5 a component, and
• 6a -e a method for compensating the tilting of two components relative to each other when screwing them together.

In the following, first with reference to the 1 The essential components of a projection exposure system 1 for microlithography are described by way of example. The description of the basic structure of the projection exposure system 1 and its components are not to be understood as limiting.

One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a radiation source 3, an illumination 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 rest of the illumination system. In this case, the illumination 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 via a reticle displacement drive 9, in particular in a scanning direction.

In the 1 For explanation, a Cartesian xyz coordinate system is shown. The x-direction runs perpendicular to the drawing plane. The y-direction runs horizontally and the z-direction runs vertically. The scanning direction runs in the 1 along the y-direction. The z-direction is perpendicular to the object plane 6.

The projection exposure system 1 comprises a projection optics 10. The projection optics 10 serves 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° between the object plane 6 and the image plane 12 is also possible.

A structure on the reticle 7 is imaged onto 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 via a wafer displacement drive 15, in particular along the y-direction. The displacement of the reticle 7 on the one hand via the reticle displacement drive 9 and the wafer 13 on the other hand via the wafer displacement drive 15 can be synchronized 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 has in particular 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, plasma generated using a laser) or a DPP source (gas discharged produced plasma, plasma generated by means of 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 that emanates from the radiation source 3 is bundled by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and/or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 17 can be exposed to the illumination radiation 16 in grazing incidence (Gl), i.e. with angles of incidence greater than 45°, or in normal incidence (NI), i.e. with angles of incidence less than 45°. 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 stray light.

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

The illumination optics 4 comprise a deflection mirror 19 and a first facet mirror 20 arranged downstream of this in the beam path. The deflection mirror 19 can be a flat deflection mirror or alternatively a mirror with a beam-influencing effect 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 different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 which is optically conjugated to the object plane 6 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21, which are also referred to below as field facets. Of these facets 21, only one is shown in the 1 only a few examples are shown.

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

As for example from the DE 10 2008 009 600 A1 As is known, the first facets 21 themselves can also be composed of a plurality of individual mirrors, in particular a plurality 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 to.

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

In the beam path of the illumination optics 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20. 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 illumination 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 the 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 be round, rectangular or hexagonal, for example, or alternatively facets composed of micromirrors. In this regard, reference is also made to the DE 10 2008 009 600 A1 referred to.

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

The illumination optics 4 thus forms a double-faceted system. This basic principle is also known as a 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 conjugated 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 the DE 10 2017 220 586 A1 described.

With the help of the second facet mirror 22, the individual first facets 21 are imaged in the object field 5. The second facet mirror 22 is the last bundle-forming 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), a 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 in 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 illumination optics 4. The transmission optics can in particular comprise one or two mirrors for vertical incidence (NI mirrors, normal incidence mirrors) and/or one or two mirrors for grazing incidence (GI mirrors, gracing incidence mirrors).

The lighting optics 4 have in the version shown in the 1 As shown, after the collector 17 there are 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 illumination optics 4, the deflection mirror 19 can also be omitted, so that the illumination 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 by means of the second facets 23 or with the second facets 23 and a transmission optics into the object plane 6 is usually only an approximate imaging.

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

In the 1 In the example shown, the projection optics 10 comprises 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 doubly obscured optics. The projection optics 10 have a numerical aperture on the image side that is greater than 0.5 and can also be greater than 0.6 and can be, for example, 0.7 or 0.75.

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

The projection optics 10 have 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 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 image scales βx, βy in the x and y directions. The two image 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 inversion. A negative sign for the image scale β means an image with image inversion.

The projection optics 10 thus leads to a reduction in the ratio 4:1 in the x-direction, i.e. in the direction perpendicular to the scanning direction.

The projection optics 10 leads to a reduction of 8:1 in the y-direction, i.e. in the scanning direction.

Other image scales are also possible. Image scales with 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-direction in the beam path between the object field 5 and the image field 11 can be the same or can be different depending on the design of the projection optics 10. Examples of projection optics with different numbers of such intermediate images in the x- and y-direction are known from US 2018/0074303 A1 .

Each 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 result in particular in illumination according to the Köhler principle. The far field is broken down into a plurality 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 associated pupil facet 23, superimposing one another, 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%. The field uniformity can be achieved by superimposing different illumination channels.

By arranging the pupil facets, the illumination of the entrance pupil of the projection optics 10 can be defined geometrically. 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 set. This intensity distribution is also referred to as the illumination 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 a redistribution of the illumination channels.

In the following, further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optics 10 are described.

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 usually be illuminated precisely with the pupil facet mirror 22. When the projection optics 10 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, a surface can be found in which the pairwise determined distance of the aperture rays is minimal. This surface represents the entrance pupil or a surface conjugated to it in spatial space. In particular, this surface shows a finite curvature.

It is possible that the projection optics 10 have different positions of the entrance pupil for the tangential and the sagittal beam path. 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.

In the 1 In the arrangement of the components of the illumination optics 4 shown, the pupil facet mirror 22 is arranged in a surface conjugated to the entrance pupil of the projection optics 10. The field facet mirror 20 is arranged tilted 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 which 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, wherein the cylindrical base body 42 is guided from above through a through hole 44 in the base plate 41 with a shoulder 43 formed at the upper end. The base body 42 additionally comprises an interface 46 at the upper end for connection to an optical element, which interface is in the 5 and 6 The base body 42 is screwed to the opposite underside of the base plate 41 with a second component designed as a nut 45. This firmly connects the base body 42 to the base plate 41, whereby the screw connection is a tension is generated, which ensures a residual clamping force of the screw connection for all operating conditions. The base body 42 is subjected to a predetermined pre-tensioning force, which is continuously recorded during the screwing process. The portal 30 comprises a housing 31, which has 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 thus hangs with its weight on the base body 42 and thereby causes part of the required pre-tensioning 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 2 is indicated. The pre-tensioning force acting on the base body 42 is therefore made up of the weight of the portal 30 and the force acting on the portal 30 by 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 pre-tensioning force is reached, the control of the motor 32 is switched to a 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 screw unit 35 of the portal 30. The screw unit 35 is guided in the housing 31 in such a way that both the moment 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 in such a way that they have a recess 36 for the base body 42 and the rod 33. In the 2 In the upper position shown by dashed lines, the support surface of the nut 45 comes into contact with the underside of the base plate 41. The torque applied by the screw unit 35 additionally preloads the base body 42 through the nut 45, so that the motor current required to hold the position of the motor 32 drops. The screw unit 35 records 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 the nut 45 until a predetermined maximum torque is reached. The evaluation of the torque over the angle of rotation and the preload force over the angle of rotation is carried out in the 3 explained in more detail.

3 shows a diagram in which the torque of the screw 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 screw unit 35. The signals recorded during screwing are processed by the control of the portal 30, with the maximum torque corresponding to the torque recorded when the screw unit 35 stops screwing. In order to meet a first quality criterion for a screw connection that is considered good, this must lie in a predetermined first corridor 60. A corridor in the sense of the invention describes a range in which the torque or the preload force can lie at a fixed angle of rotation, i.e., compared to the prior art, represents a narrower tolerance for the maximum torque due to a one-dimensional range. Another quality criterion that must be met for a screw connection that is considered good is a calculated starting torque, which corresponds to the torque at the time of contact between the support surface of the nut 45 and 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 rotation angle must in turn be in a second predetermined corridor 62 in order to meet the quality criterion. Furthermore, the preload force corresponding to the rotation angle of the maximum torque must also be in a third predetermined corridor 61. The ranges 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.

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

4 shows a diagram in which the entire screwing process is shown. The diagram also includes the already in the 3 shown area of the diagram and also represents the torque and the preload force over the angle of rotation recorded by the screw 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 screw unit 35, the preload force is set by regulating the motor current of the motor 32, as in 2 As already explained, and when the predetermined preload force is reached, the control is switched to position control. Due to the small component tolerances, the total angle of rotation can be additional quality criterion can be used, whereby the total angle of rotation is 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 of the nut 45 and the base body 42 mesh, the component tolerances W _To and the angle of rotation W _Vs required to apply the preload by the nut 45. This results in the following value for a theoretical angle of rotation of six revolutions and an angle of rotation W _Vs of 12°: $${\text{Drehwinkel}}_{\text{min}}={\text{W}}_{\text{th}}\left(2160°\right)+/-{\text{W}}_{\text{To}}+{\text{W}}_{\text{Vs}}+{\text{W}}_{0\text{min}}\left(0°\right)=2172°+/-{\text{W}}_{\text{To}}$$

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

When reaching the target torque, the total angle of rotation must therefore be within a fourth corridor 63 of a _minimum angle of rotation 2172° +/- W _To and a maximum angle of rotation 2532° +/- W _To .

If all four of the quality criteria described are within the specified corridors 60, 61, 62, 63, it can be assumed with a very high degree of probability that the screw connection was successful.

5 shows the explanation of the process in the 2 to 4 The assembly 40 is 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 The facet 49 is connected to the base body 42 via the interface 46, which is designed as a screw connection. The two contact 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 a flat contact between the two contact surfaces 50, 51 and a resulting optimal heat flow across both components 42, 49. For this purpose, a force-free screwing of the two parts is necessary. 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 non-constrained screw connection and the method for checking the quality of a screw connection can also stand independently as an invention. A method which ensures a non-constrained screw connection is described in the 6 explained in detail.

The 6a to 6e show a screwing process in which the facet 49 and the base body 42 are screwed together 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 method described above for checking 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 screw device 71 of the device 70, wherein the screw device 71 is positioned in the X/Y plane to center the longitudinal axis 55 of the facet 49 and the longitudinal axis 48 of the base body 42 relative to one another. The base body 42 is held in a holder 73, which engages with an adapter 72 in a recess 54 of the base body 42. The adapter 72 and the recess 54 are designed such that the base body 42 can be moved in the Z direction, i.e. in the direction of its longitudinal axis 48, within a limited range, can be freely tilted about the X axis and Y axis within a certain range, and the rotation about the Z axis is locked so that the torque required for screwing can be absorbed.

6b shows a second method step in which the screw device 71 with the facet 49 is moved 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, thereby compressing it. The compression spring 74 pre-tensioned 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.

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

6d shows a fourth method step in which the base body 42, supported by the spring force of the compression spring 74, was pulled through the thread 52, 53 into the facet 49 and a first contact was made between the two contact surfaces 50, 51 of the base body 42 and the facet 49. The holder 73, the adapter 72 and the recess 54 are designed in such a way that before the first contact of the contact 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 about the X-axis and Y-axis in the holder 73. Alternatively, the facet 49 can be raised with the screw 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. This can be ensured either by a predetermined path in Z or by a force measurement. The two longitudinal axes 48, 55 of the base body 42 and the facet 49 are as shown in the 6d shown tilted towards each other at first contact.

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

list of reference symbols

1

projection exposure system

2

lighting system

3

radiation source

4

lighting optics

5

object field

6

object level

7

reticle

8

reticle holder

9

reticle displacement drive

10

projection optics

11

image field

12

image plane

13

wafers

14

wafer holder

15

wafer relocation drive

16

EUV radiation

17

collector

18

intermediate focal plane

19

deflecting mirror

20

faceted mirror

21

facets

22

faceted mirror

23

facets

30

portal

31

Housing

32

Motor

33

connecting element

34

stop

35

screw unit

36

recess

40

module

41

base plate

42

base body

43

Paragraph

44

through hole

45

Mother

46

interface facet

47

thread

48

longitudinal axis

49

facet

50

contact surface facet

51

support surface base body

52

internal thread facet

53

external thread interface

54

recess base body

55

longitudinal axis

60

target torque corridor

61

corridor prestressing force

62

corridor calculated starting torque

63

corridor total angle of rotation

70

device

71

screw device

72

adapter

73

bracket

74

Feather

75

stop

α

angle starting torque

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 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). 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 preload force predetermined for the screw connection through the torque caused by the angle of rotation. Method according to one of the Claims 1 or 2 , characterized in that the preload force is determined on the basis of a weight force acting on the screw connection and a motor current of a motor (32) exerting 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) relative to one another is compensated by a tilting of 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. Method according to one of the Claims 6 or 7 , characterized in that a spring (74) applies a force in the direction of the screwing to the holder (73) during screwing. procedure according to claim 8 , characterized in that the force of the spring (74) prevents the tilting of the component (42,49) in the holder (73). Method according to one of the Claims 6 until 9 , characterized in that the holder (73) absorbs the torque caused by the screw connection.

Images