Methods for checking the quality of a screw connection

Abstract

Method for checking the quality of a bolted joint 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 acquired during bolting, characterized in that the quality criteria include that - an actual applied torque when reaching the target torque lies within 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 actual applied torque lies in a third corridor (61).

Description

[0001] 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.

[0002] In modern assembly technology, the screw connection remains one of the most important connection types. The variety of screws used 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 significant savings in raw materials and weight, and significantly reduces the space required for screw connections.

[0003] Screw connections also play an important role in projection exposure systems for semiconductor lithography, especially in EUV projection exposure systems. Due to the typically limited installation space available in these systems and the drastic consequences of screw connection failure, increased requirements apply.

[0004] A bolted connection is a detachable joint that joins two or more parts together in such a way that they behave as one under all operating forces. Maintaining a sufficient residual preload (residual clamping force) is crucial for operational reliability. If the operating force during operation becomes so great that it cancels out the preload, the bolt can loosen or even break depending on the operating load. The preload can be increased by increasing the stress cross-section by using more or larger bolts, by improving the bolt quality, which makes it possible to increase the assembly preload with the same screw dimensions, or by using more precise screwing methods so that the elastic properties of the bolt can be better utilized.

[0005] In screwdriving processes, parameters monitored during screwing, such as torque, torque gradient, and / or angle of rotation, can provide a more precise statement about the achieved preload force, or even reduce the variance of the preload force. The measured torque when tightening a screw connection is composed of the thread friction, the friction between the head (e.g., between a nut and a support), and the preload force. The high variance of the thread friction and the friction between the head (e.g., between a nut and a support), makes determining the preload force difficult.

[0006] Known tightening procedures are disclosed, for example, in the training materials of IBES Elektronik GmbH, which are published at http: / / www.ibes-electronic.de / Schulungsunterlagen_Neutral.pdf.

[0007] One method described there to improve 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], which describes a range in which the screw is tightened. This makes the applied torque more reproducible compared to a purely subjective tightening of the screw. In addition, a range for the exceeded angle of rotation W [degrees] is also defined by a minimum W min [degrees] and maximum angle of rotation W max[degrees] to detect, for example, thread scuffing or plastic deformation of the screw head. The quality of the screw connection is determined by reaching the process window, which is defined by the minimum and maximum values ​​of the torque and angle ranges, thus being two-dimensional. The described method has the disadvantage that it still includes the high scatter of thread friction and underhead friction.

[0008] Another known method monitors the angle of rotation, whereby this only occurs above a defined threshold value of the torque D Schwell[N], at which the setting effects in the thread and under the head of the screw connection are complete, is determined. This method can bring the screw into the plastic range, independent of the torque, so that thread friction and underhead friction no longer influence the determination of the preload force. However, for the same reasons as above, a minimum and maximum torque are also defined in this method. 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.

[0009] The German patent application DE 10 2019 201 549 A1 describes a method for monitoring screw connections, in particular for use in projection exposure systems for semiconductor lithography, 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.

[0010] Furthermore, German patent application DE 10 2005 019 258 A1 describes a method in which intermittently operating screwdriving tools, such as hydraulic torque wrenches, can be controlled with the goal of shutting off the tool after the yield point is reached. This allows for the detection of design errors and material defects.

[0011] In addition, German patent application DE 32 22 156 A1 discloses a screwdriving method in which control of the screwdriving process with complex torque-angle characteristics is achieved by inputting 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 is reached when the maximum torque is reached, or if the minimum torque is not yet reached when the maximum angle is reached.

[0012] Furthermore, European patent EP 3 571 017 B1 presents a method and a device for tightening a screw connection using a motor-driven screwdriver unit, 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 torque over the angle of rotation is determined, and in a second, subsequent tightening range, a change in the increase in 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.

[0013] The methods described above have the disadvantage that the screw connections they consider tolerable do not always meet the requirements.

[0014] The object of the present invention is to provide a method which solves the disadvantages of the prior art described above.

[0015] This problem is solved by a method having the features of the independent claim. The subclaims relate to advantageous developments and variants of the invention.

[0016] 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 - the actual torque applied when reaching the target torque lies within a first corridor, - a starting torque detected 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.

[0017] In this context, a corridor is understood as a one-dimensional range, in contrast to the envelope monitoring windows known in the prior art. Thus, for a defined angle of rotation, there is a torque range within which the measured torque may lie in order to meet the quality criterion. This corresponds to a tighter monitoring of the target torque compared to the window that allows variation of the angle of rotation and the torque. The difference between the actually applied torque and the target torque depends on the control quality of the control system used for tightening, which receives the target torque to be achieved for the tightening as input.This is not always precisely achieved due to various influences, such as friction in the thread and underhead friction on the contact surfaces of the components, such as between a nut and a support, as well as tolerances in the sensor technology and control parameters. The starting torque is defined by the torque at which the contact surfaces of the components come into contact during and through the screw connection.

[0018] For this purpose, the predetermined angle of rotation for determining the starting torque can correspond to a rotation angle that, through the torque generated by the angle of rotation, produces the preload force specified for the screw connection. This angle of rotation can be determined in advance through tests and depends on the preload force to be achieved, the geometry of the screw, and other boundary conditions such as the quality of the screw used and settling effects during screwing.

[0019] Additionally or alternatively, the preload force can be determined based on 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 gantry that is firmly connected to the screw connection, is connected to the component to be preloaded and acts on the component with its entire weight. The gantry 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 gantry and the additional force exerted 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 during screwing is caused by the screw connection itself, i.e., by the torque generated when tightening the screw connection, the motor current decreases and thus the measured preload force decreases. To meet the quality criterion, as described above, the measured preload force must be within a certain range when the target torque is reached. This range depends on the preload required in the screw connection.

[0020] Another quality criterion can be the overall 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 thread seizure.

[0021] In particular, the total angle of rotation can lie within 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 composed of the length of the thread, i.e., the theoretical angle of rotation W. th , the angle of rotation W0 until the threads mesh, the component tolerances W To and the angle of rotation W required to apply the preload through the screw connection Vs This results in a theoretical angle of rotation of six revolutions and a rotation angle W Vs of 12° the following minimum and maximum value: Rotation anglemin=Wth(2160°)+ / −WTo+WVs+W0min(0°)=2172°+ / −WTo Rotation angle max=Wth(2160°)+ / −WTo+WVs+W0max(360°)=2532°+ / −WTo

[0022] The total angle of rotation must therefore be within the fourth corridor, which is defined by the angle of rotation min and angle of rotation max is defined.

[0023] Furthermore, a component holder can be designed such 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 screw connection 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 case where 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.

[0024] In particular, the 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, the two components can be pressed together to ensure that the thread is securely located. Only after the thread has been screwed together for one or more thread turns is the tilting of the two components relative to each other possible.

[0025] Furthermore, a spring can apply a force to the bracket in the direction of the screw connection during screwing. This not only ensures secure thread location as explained above, but also preloads the thread so that the contact between the thread surfaces is always defined, thus reducing play in the thread during screwing.

[0026] In particular, the force of the spring can prevent the component from tilting in the holder. As explained above, tilting is only possible in a specific area toward the end of the screw connection, shortly before or at the point at which the two components come into contact.

[0027] 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.

[0028] In the following, embodiments and variants of the invention are explained in more detail with reference to the drawings. Fig. 1 schematically shows in meridional section a projection exposure system for EUV projection lithography, Fig. 2 a device for carrying out the method according to the invention, Fig. 3 shows a section of a diagram based on data acquired in the method according to the invention, Fig. 4 shows another diagram based on data acquired in the method according to the invention, Fig. 5 a component, and Fig. 6a-e a method for compensating for a tilting of two components relative to each other when screwing together.

[0029] In the following, with reference to the Fig. 1 describes, by way of example, the essential components of a projection exposure system 1 for microlithography. The description of the basic structure of the projection exposure system 1 and its components is not intended to be limiting.

[0030] 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 separate module from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0031] 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.

[0032] In the Fig. 1 shows a Cartesian xyz coordinate system for explanation. The x-direction is perpendicular to the plane of the drawing. The y-direction is horizontal and the z-direction is vertical. The scanning direction is in the Fig. 1 along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0033] 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.

[0034] A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the image plane 12 in the region of the image field 11. 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 of the reticle 7, on the one hand, via the reticle displacement drive 9, and the displacement of the wafer 13, on the other hand, via the wafer displacement drive 15, can be synchronized with each other.

[0035] 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) or a DPP source (gas discharged produced plasma). It can also be a synchrotron-based radiation source. The radiation source 3 can be a free-electron laser (FEL).

[0036] The illumination radiation 16 emanating 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 hyperboloidal reflection surfaces. The at least one reflection surface of the collector 17 can be exposed to the illumination radiation 16 at grazing incidence (Gl), i.e., at angles of incidence greater than 45°, or at normal incidence (NI), i.e., at 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.

[0037] 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.

[0038] The illumination optics 4 comprises a deflecting mirror 19 and, downstream of this in the beam path, a first facet mirror 20. The deflecting mirror 19 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugated to the object plane 6 as the 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, Fig. 1 only some examples are shown.

[0039] 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 convexly or concavely curved facets.

[0040] As is known, for example, from DE 10 2008 009 600 A1, 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, reference is made to DE 10 2008 009 600 A1.

[0041] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction.

[0042] 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 US 2006 / 0132747 A1, EP 1 614 008 B1, and US Pat. No. 6,573,978.

[0043] 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.

[0044] The second facets 23 can also be macroscopic facets, which can, for example, be round, rectangular, or hexagonal, or alternatively facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

[0045] The second facets 23 can have planar or alternatively convex or concave curved reflection surfaces.

[0046] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (fly's eye integrator).

[0047] It may be advantageous to arrange the second facet mirror 22 not 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 described, for example, in DE 10 2017 220 586 A1.

[0048] 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 before the object field 5.

[0049] 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 transmission optics 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 illumination optics 4. The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (GI mirrors, grazing incidence mirrors).

[0050] The illumination optics 4 has in the version shown in the Fig. 1, 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] In the Fig. In the example shown in Figure 1, the projection optics 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or a different number of mirrors M1 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 is a doubly obscured optic. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0055] Reflection surfaces of the mirrors Mi can be designed as freeform 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, 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.

[0056] 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 as large as a z-distance between the object plane 6 and the image plane 12.

[0057] The projection optics 10 can, in particular, be anamorphic. It has, in particular, different magnifications βx, βy in the x- and y-directions. The two magnifications βx, βy of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, + / - 0.125). A positive magnification β means imaging without image inversion. A negative sign for the magnification β means imaging with image inversion.

[0058] 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.

[0059] The projection optics 10 results in a reduction of 8:1 in the y-direction, i.e. in the scanning direction.

[0060] Other magnifications are also possible. Magnifications with the same sign and absolutely identical in the x and y directions, for example, with absolute values ​​of 0.125 or 0.25, are also possible.

[0061] 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 can vary 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-directions are known from US 2018 / 0074303 A1.

[0062] Each of the pupil facets 23 is assigned to exactly one of the field facets 21 to form a respective illumination channel for illuminating the object field 5. This can, in particular, result in illumination according to the Köhler principle. The far field is divided 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.

[0063] The field facets 21 are each imaged onto the reticle 7 by an associated pupil facet 23, superimposed on 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%. Field uniformity can be achieved by superimposing different illumination channels.

[0064] By arranging the pupil facets, the illumination of the entrance pupil of the projection optics 10 can be geometrically defined. 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 illumination setting.

[0065] 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.

[0066] 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 below.

[0067] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0068] The entrance pupil of the projection optics 10 cannot usually be precisely illuminated 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 minimized. This surface represents the entrance pupil or a surface conjugate to it in spatial space. In particular, this surface exhibits a finite curvature.

[0069] The projection optics 10 may have different entrance pupil positions 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. This optical element can be used to account for the different positions of the tangential entrance pupil and the sagittal entrance pupil.

[0070] In the Fig. In the arrangement of the components of the illumination optics 4 shown in Figure 1, 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 relative to the object plane 6. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the deflection mirror 19.

[0071] The first facet mirror 20 is arranged tilted to an arrangement plane which is defined by the second facet mirror 22.

[0072] Fig. Figure 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 46 is inserted into the Fig. 5 and Fig. 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. This firmly connects the base body 42 to the base plate 41, the screw connection generating a preload which ensures a residual clamping force of the screw connection for all operating conditions. The base body 42 is subjected to a predetermined preload force which is continuously recorded during the screwing process. The gantry 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 gantry 30 and at the other end to the base body 42 to be screwed via a thread 47. The gantry 30 thus hangs with its weight on the base body 42 and thereby effects part of the required preload force.The gantry 30 is connected to a motor 32 on the underside facing away from the base body 42, which can move the gantry 30 in the direction of the screw connection. As a result, when the gantry 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 gantry 30, as indicated by an arrow in the figure. Fig. 2. The preload force acting on the base body 42 is therefore composed of the weight of the gantry 30 and the force acting on the gantry 30 by the motor 32. The known and constant weight of the gantry 30 is adjusted to a predetermined value by an additional force applied by the motor 32 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 to check the quality of the screw connection as a quality criterion, as shown in the Fig. 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 Fig. 2, the contact surface of the nut 45 comes into contact with the underside of the base plate 41. Due to the torque still applied by the screw unit 35, the base body 42 is additionally preloaded by the nut 45, so that the motor current required to maintain 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 gantry 30 (not shown). The control of the gantry 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 Fig. 3 is explained in more detail.

[0073] Fig. 3 shows a diagram in which the torque of the screwing unit 35 and the preload force determined from the weight of the gantry 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 gantry 30, with the maximum torque corresponding to the torque detected when the screwing unit 35 stops. In order to fulfill a first quality criterion for a screw connection to be considered good, this torque must lie within a predetermined first corridor 60. A corridor within the meaning of the invention describes a range in which the torque or the preload force may lie at a fixed angle of rotation, thus representing a narrower tolerance for the maximum torque compared to the prior art due to a one-dimensional range.A further 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 the contact surface of the nut 45 makes contact with the underside of the base plate 41. For this purpose, a rotation angle α determined through testing is subtracted from the rotation angle of the maximum torque. The starting torque corresponding to this determined rotation angle must in turn lie within 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 lie within a third predetermined corridor 61. The ranges of the corridors 60, 61, 62 depend on various influencing parameters such as screw size, screw quality, hardness of the base plate 41, and required preload, to name just a few.

[0074] Fig. 4 shows a diagram illustrating the entire screwing process. The diagram also includes the Fig. 3 and also represents the torque and preload force over the angle of rotation detected 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 contacts 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 adjusted by regulating the motor current of the motor 32, as shown in Fig. 2, 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 used as an additional quality criterion, whereby the total angle of rotation is determined from the length of the thread, i.e., the theoretical angle of rotation W th, the angle of rotation W0 until the threads of the nut 45 and the base body 42 mesh, the component tolerances W To and the angle of rotation W required to apply the preload by the nut 45 Vs This results in a theoretical angle of rotation of six revolutions and a rotation angle W Vs of 12° the following value: Rotation anglemin=Wth(2160°)+ / −WTo+WVs+W0min(0°)=2172°+ / −WTo Rotation angle max=Wth(2160°)+ / −WTo+WVs+W0max(360°)=2532°+ / −WTo

[0075] When the target torque is reached, the total angle of rotation must therefore be within a fourth corridor 63 of a rotation angle min 2172° + / - W To and a rotation angle max 2532° + / - W To lay.

[0076] If all four of the quality criteria explained are within the specified corridors 60, 61, 62, 63, it can be assumed with a very high probability that the screw connection was successful.

[0077] Fig. 5 shows the process used to explain the Fig. 2 to 4, which additionally comprises an optical element designed as a facet 49. The assembly 40 can, for example, be a part of one of the Fig. 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 each other during screwing in order to ensure flat contact between the two contact surfaces 50, 51 and the resulting optimal heat flow across both components 42, 49. For this purpose, a force-free screwing of the two parts is necessary. The Fig. 2, the Fig. 3 and the Fig. The method according to the invention explained in Figure 4 can also be applied to 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 be considered as independent inventions. A method that ensures a non-constrained screw connection is described in Fig. 6 explained in detail.

[0078] The Fig. 6a to 6e show a screwing process in which the facet 49 and the base body 42 are screwed together in a fixture 70, which ensures 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 testing the quality of the screw connection.

[0079] In the Fig. 6a, in a first method step, the facet 49 is aligned with the base body 42 such 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 rotation about the Z axis is locked so that the torque required for screwing can be absorbed.

[0080] Fig. 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 the holder. The compression spring 74 pretensioned 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 the facet 49 is virtually free of play during screwing.

[0081] The Fig. 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 engaged, the screwing of the thread 52, 53 begins by rotating the screwing device 70.

[0082] Fig. 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 initial contact occurred between the two bearing surfaces 50, 51 of the base body 42 and the facet 49. The holder 73, the adapter 72, and the recess 54 are designed such that before the first contact of the bearing surfaces 50, 51, the compression spring 74 is completely relaxed and the adapter 72 no longer has contact with the recess 54 of the base body 42 in the Z direction, so that the recess 54 can tilt freely about the X-axis and Y-axis in the holder 73. Alternatively, the facet 49 can be raised in the Z direction with the screw device 70 after screwing, for example, half of the threads, 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 . Fig. 6d shown tilted towards each other at first contact.

[0083] Fig. Figure 6e shows a fifth process step, in which, as the two components 42, 49 are further screwed together, the base body 42 aligns such that the longitudinal axis 48 of the base body 42 and the longitudinal axis 55 of the facet 49 are aligned and the two contact surfaces 50, 51 are aligned parallel, thereby achieving complete contact 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 reticles 8 reticle holders 9 Reticle displacement drive 10 Projection optics 11 Image field 12 Image plane 13 wafers 14 wafer holders 15 Wafer relocation drive 16 EUV radiation 17 Collector 18 Intermediate focal plane 19 Deflecting mirrors 20 facet mirrors 21 facets 22 facet mirrors 23 facets 30 Portal 31 housings 32 engine 33 Connecting element 34 stop 35 screw unit 36 recess 40 assembly 41 Base plate 42 basic bodies 43 paragraph 44 through hole 45 Mother 46 Interface facet 47 threads 48 Longitudinal axis 49 facets 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 corridor target torque 61 Corridor prestressing force 62 Corridor calculated starting torque 63 Corridor total rotation angle 70 Device 71 Screwing device 72 adapters 73 Bracket 74 spring 75 stops α angle starting torque

Claims

[1] 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 by that the quality criteria include that - an actual torque when reaching 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). [2] Method according to claim 1, characterized by that the predetermined angle of rotation for determining the starting torque corresponds to an angle of rotation which, through the torque caused by the angle of rotation, causes the preload force predetermined for the screw connection. [3] Method according to one of claims 1 or 2, characterized by 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. [4] Method according to one of the preceding claims, characterized by that another quality criterion is the overall angle of rotation of the screw connection. [5] Method according to claim 4, characterized by that the total angle of rotation lies in a fourth corridor (63). [6] Method according to one of the preceding claims, characterized by 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. [7] Method according to claim 6, characterized bythat the tilting of the component (42,49) is only possible in a partial area of ​​the screw connection. [8] Method according to one of claims 6 or 7, characterized by that a spring (74) applies a force in the direction of the screw connection to the holder (73) during screwing. [9] Method according to claim 8, characterized by that the force of the spring (74) prevents the component (42,49) from tilting in the holder (73). [10] Method according to one of claims 6 to 9, characterized by that the bracket (73) absorbs the torque caused by the screw connection.

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