Methods for classifying leaks in semiconductor technology

Abstract

The invention relates to a method for classifying leaks (35,40,46) of a wall (34,38,43) surrounding a test volume (33,37,42) of a component (32,36,41) for semiconductor technology, comprising the following method steps: - Filling the test volume (33, 37, 42) with a test fluid (31) and applying a predetermined differential pressure (50, 61, 3) to the environment to the test volume (33, 37, 42), - Recording a leak rate (62,63,64) from the test volume (33,37,42) over a predetermined period, - Determination of a slope (S1,S2,S3) of the leakage rate (62,63,64) over at least a sub-section of the period, - Classification of the leakage (35,40,46) based on the determined slope (S1, S2, S3).

Description

[0001] The invention relates to a method for classifying a leakage of a wall of a component surrounding a test volume, in particular of a semiconductor technology system, such as a projection exposure system.

[0002] In a prior art method for leak testing, i.e. the detection of leaks in a wall surrounding a closed volume, hereinafter referred to as the test volume, the class, i.e. the type of leak, cannot be reliably determined.

[0003] In the event of a leak, i.e. damage to the wall completely surrounding the closed volume, a test fluid, hereinafter referred to as test gas, escapes into the test chamber surrounding the component to be tested, which is usually designed as an evacuated vacuum chamber.

[0004] The test gas 31 ( Fig. 3a) preferably comprises predominantly or exclusively helium, which, in addition to its small atomic size, which enables the detection of comparatively small leaks, has the particular advantage that it only occurs in very small amounts of approximately 5 ppm in air. The gas released during the evacuation of the test chamber 30 ( Fig. 3a) The remaining residual gas also predominantly consists of air, which enters the test chamber through back diffusion through the vacuum pumps. The background noise of the partial pressure of helium in the vacuum, which is relevant for detection, is therefore comparatively low or close to zero, allowing a good signal-to-noise ratio to be achieved when determining a leak rate for leak classification in test chamber 30.

[0005] Two classes of leaks can be distinguished. A typical leak 35 is characterized by its cross-section, as shown in the Fig. 3a, is almost constant over the thickness of the wall 34 of a component 32 or has a single constriction. The curve of the leak rate 51 determined by a residual gas analyzer and / or a pressure gauge, which is shown in the Fig. 3d is shown in dash-dotted lines, follows a test volume 33 ( Fig. 3a) applied test pressure 50 almost without time delay and thus corresponds in terms of its qualitative course to the course of the test pressure 50.

[0006] Atypical leaks 40, 46 as they occur in the Fig. 3b and the Fig. 3c are characterized by the fact that the cross sections of the leaks 40, 46 are not constant over the thickness of the walls 38, 43 of the components 36, 41, for example, they have a cavity 39, 45. The cavity can, on the one hand, as in the Fig. 3b, be formed by a pore 39 in the wall 38 of the test volume 37, such as can occur in weld seams. On the other hand, the leakage 46, as shown in the Fig. 3c, a cavity formed as an intermediate space 45 between a seal 44 comprising two O-rings 44.1, 44.2. The leakage 46 can be caused, for example, by damage to the sealing surfaces, such as a scratch, or alternatively by damage to one or both O-rings 44.1, 44.2. This results in a first leak rate from the test volume 37, 42 into the cavity 39, 45 and a second leak rate from the cavity 39, 45 into the test chamber 30, whereby only the second leak rate is detected by the detector in the test chamber 30. Depending on the relationship between the two leak rates, there may be a time-delayed increase in the detected leak rate 52 ( Fig. 3d) in the test chamber 30. Furthermore, due to a lower pressure gradient from the cavity 39, 45 to the test chamber 30 compared to a typical leak, a lower gradient of the detected leak rate 52 may develop. Fig. Figure 3d shows an exemplary atypical leak rate 52 in dashed lines. It shows a curve proportional to the increase in test pressure 50 with a reduced gradient and a time delay 53 compared to the application of test pressure 50.

[0007] Compared to a seal damaged on at least one of the two sealing surfaces, permeation through an undamaged double O-ring seal 44 is in the range of hours, and can therefore be neglected during the leak test, which is usually carried out over a period of several minutes.

[0008] In the method used in the prior art, the leak rate is determined at a predetermined time 54. This has the disadvantage that, as shown in the Fig. As shown in Figure 3d, the leak rate determined in this way cannot distinguish between a typical and an atypical leak. This can necessitate a very time-consuming search for the location of the leak on the component.

[0009] The object of the present invention is to provide a method which eliminates the disadvantages of the prior art described above.

[0010] This object is achieved by a method having the features of independent claim 1. The subclaims relate to advantageous developments and variants of the invention.

[0011] A method according to the invention for classifying leaks in a wall surrounding a test volume of a component for semiconductor technology comprises the following method steps: - Filling the test volume with a test fluid and subjecting the test volume to a predetermined differential pressure relative to the environment. - Recording a leak rate from the test volume over a predetermined period of time. - Determination of an increase in the leak rate over at least part of the period. - Classification of the leak based on the determined gradient.

[0012] The wall of the test volume can be designed, for example, as the wall of a fluid line or the wall of a pressure or expansion vessel and represents the boundary between the test volume and the environment. The test volume corresponds to the volume that is subjected to a pressure differential, referred to as the test pressure, to determine a leak from the test volume relative to the environment.

[0013] Leaks can have various causes, which can provide clues to the location of the leak. Classifying the leak makes it possible to narrow down the location of the leak and thus simplify and, in particular, accelerate the detection of the leak in the wall. A distinction can be made between typical and atypical leaks. While a typical leak corresponds to damage with at least a nearly constant cross-section across the thickness of the wall, an atypical leak is characterized by a cavity formed in the wall, which can, for example, lead to a delayed detection of the leak.

[0014] Helium is usually used as the test fluid, hereinafter referred to as test gas, which is particularly suitable as explained above.

[0015] In particular, the process can be carried out in a test chamber designed as a vacuum chamber. The vacuum chamber has the advantage that, due to the very low residual air volume, the detection of the test gas, which is usually helium, is significantly simplified.

[0016] In a further embodiment of the method, the measurement period may comprise three subsections.

[0017] In a first section of the measurement, the leak rate can be determined without applying test pressure to the test volume. This section, also known as the preliminary measurement, can be used to determine the background noise of the partial pressure of the test gas present in the residual air volume and to rule out parasitic leakage into the vacuum chamber.

[0018] Furthermore, during a second sub-section of the measurement, the test volume can be pressurized with the previously defined test pressure. This sub-section of the measurement, also known as the leak test, corresponds to a state-of-the-art measurement in terms of the measurement sequence. In the event of a leak in the wall, the partial pressure of the test gas in the vacuum chamber increases during this sub-section, which can be detected by a detector designed as a residual gas analyzer. The residual gas analyzer can be calibrated before the measurement using one or two or more calibration leaks with a known leak rate. Because the vacuum pumps run continuously to maintain the vacuum in the vacuum chamber, a flow develops between the leak and the vacuum pumps in the event of a leak. This results in a constant flow at a constant leakage, which can be determined by the residual gas analyzer.In the case of an atypical leak, which is usually not constant over the period of the leak test, the residual gas analyzer detects a flow that changes over the period of the leak test.

[0019] Depending on the class of leakage, a different leak rate curve can develop during the leakage test.

[0020] Finally, in a third subsection of the measurement, the test volume can no longer be subjected to test pressure. This subsection, also known as the re-measurement, can provide additional information about the class or subclass of the leak and can also ensure that even a leak with a significant delay, i.e., a leak that occurs outside the leak test period, can still be detected.

[0021] In a further embodiment of the invention, the gradient can be determined for each subsection of the measurement. The gradient of the leak can be different for each class of leaks as well as within a class, thus enabling a classification of the detected leak.

[0022] In particular, the gradient can be determined as the average gradient over the period of the section. Determining the gradient over the period of the leak test can simplify the evaluation of the measurement, with sufficient discriminatory power to reliably distinguish between a typical and atypical leak.

[0023] Subsequently, a difference between the gradients of all three sections can be determined, resulting in three differences.

[0024] In addition, the magnitude of the differences can be determined. This can simplify the evaluation of the measurement, since the direction of the gradient is irrelevant for determining the leakage class.

[0025] Furthermore, the maximum of the three differences determined can be compared with a predetermined threshold. The threshold can be set such that if the threshold is exceeded, an atypical leak occurs, and if the threshold is undershot, a typical leak or a leak-tight system exists. If the maximum of the differences is zero or almost zero, it can be assumed that there is no leak or that there is a typical leak in the wall surrounding the test volume. A typical leak can be differentiated from a leak-tight system by checking whether the leak rate exceeds a second predetermined threshold. If the leak rate is above the threshold, it is a typical leak; otherwise, the system is leak-tight.

[0026] A further classification of leaks within a class can be based on a further evaluation of the curves, such as areas of gradients or duration of a delay or even on the basis of a non-linear gradient, whereby this can be done with the support of artificial intelligence if necessary.

[0027] The method can be used to classify a leak from any test volume, with the method being particularly suitable for classifying a leak from a test volume of a component of a semiconductor technology system. A semiconductor technology system can be configured, for example, as a mask inspection system, mask repair system, mask measurement system, wafer inspection system, or a projection exposure system.

[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 schematically shows in meridional section a projection exposure system for DUV projection lithography, Fig. 3a-d a detailed view of a test volume to explain the effect on the slope of the leak rate, Fig. 4a,b diagrams explaining the procedure, and Fig. 5 a flowchart of a method according to the invention.

[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 illuminated. 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° relative to the normal direction of the mirror surface, 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 a numerical aperture on the image side 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] It is possible that the projection optics 10 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. 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.

[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. 2 shows a schematic meridional section of another projection exposure system 101 for DUV projection lithography, in which the invention can also be used.

[0073] The structure of the projection exposure system 101 and the principle of imaging is comparable to that in Fig. 1 described structure and procedure. Identical components are provided with a 100 Fig. 1 raised reference numerals, the reference numerals in Fig. So 2 start with 101.

[0074] In contrast to a Fig. 1, due to the longer wavelength of the DUV radiation 116 used as useful light in the range from 100 nm to 300 nm, in particular from 193 nm, refractive, diffractive and / or reflective optical elements 117, such as lenses, mirrors, prisms, cover plates and the like, can be used in the DUV projection exposure system 101 for imaging or for illumination.The projection exposure system 101 essentially comprises an illumination system 102, a reticle holder 108 for receiving and precisely positioning a reticle 107 provided with a structure, by means of which the later structures on a wafer 113 are determined, a wafer holder 114 for holding, moving and precisely positioning this wafer 113 and a projection lens 110 with a plurality of optical elements 117, which are held via mounts 118 in a lens housing 119 of the projection lens 110.

[0075] The illumination system 102 provides DUV radiation 116 required for imaging the reticle 107 on the wafer 113. A laser, a plasma source, or the like can be used as the source for this radiation 116. The radiation 116 is shaped in the illumination system 102 via optical elements such that the DUV radiation 116 has the desired properties regarding diameter, polarization, wavefront shape, and the like when it strikes the reticle 107.

[0076] The structure of the subsequent projection optics 101 with the lens housing 119 does not differ in principle from that in Fig. 1 and is therefore not described further.

[0077] The Fig. 3a-d have already been explained above.

[0078] The Fig. 4a, Fig. 4b shows resulting curves of a method according to the invention for classifying a typical leak and an atypical leak in a fluid system or volume of a component of a Fig. 1 explained projection exposure system 1. The component can be designed, for example, as a fluid line or as a pressure or compensation tank.

[0079] To check the tightness of the test volume 33, the component 32, 36, 41 ( Fig. 3a-3c) or at least the area of ​​the component to be tested into a test chamber 30 designed as a vacuum chamber ( Fig. 3a-3c). The test chamber 30 is first evacuated and then the method according to the invention is started.

[0080] The detectors used to detect potential leaks are typically designed as residual gas analyzers (RGAs) and are calibrated before a measurement using a so-called calibration leak with a known leak rate, i.e. leakage per time. Due to the continuously running vacuum pumps used to maintain the vacuum in the test chamber 30, a leak results in a flow of helium, usually used as test gas 31, from the leak towards the vacuum pumps. The calibration serves to determine one or two reference values, each of which can be assigned to the known leak rate of the calibration leak(s). Based on this calibration, the proportion of the helium partial pressure recorded during the measurement can be assigned to a leak rate or converted into a corresponding leak rate.The time required to reach a constant flow and the distance between a leak and the detector can be neglected at a helium velocity in a vacuum of approximately 1 km / s; thus, the helium escaping from a leak is detected by the detector without any noticeable time delay. Alternatively, detection can also be achieved via a change in the pressure in the vacuum, although this is not the preferred approach.

[0081] Fig. Figure 4a shows a curve of a leak rate 62 determined by the method according to the invention for a typical leak, which is shown in the Fig. 4a is shown as a dashed-dotted line. The curve of the test volume 33 ( Fig. 3b) applied test pressure 61 is in the Fig. 4a shown as a solid line.

[0082] The measurement 60 for determining the leak rate is divided into three subsections 60.1, 60.2, and 60.3, which are explained in more detail below. The detector records the partial pressure of helium in the vacuum over the entire measurement period, i.e., over all three subsections 60.1, 60.2, and 60.3 of the inventive method, for example, every second. Thus, if the three subsections 60.1, 60.2, and 60.3 each last, for example, 5 minutes, a total of 300 measured values ​​are recorded per subsection.

[0083] In the first section, designated as preliminary measurement 60.1, the composition of the residual gas in the already evacuated test chamber 30 ( Fig. 3a) using the residual gas analyzer (RGA). This subsection 60.1 ensures that the test chamber 30 does not make any parasitic contributions to the determination of a possible leak rate 62 of the test volume 33, 37, 42 ( Fig. 3a-3c) and determines the background noise of the partial pressure of helium present in the vacuum. The leak rate curve 62.1 in section 60.1 is therefore constant at a value just above zero.

[0084] In the second part of the measurement, known as leakage test 60.2, the test volume 33 ( Fig. 3a) with the test gas 31 ( Fig. 3a) is filled and subjected to the test pressure 61, whereby the pressure build-up occurs in a very short time compared to the measurement period, so that the gradient 61.2 of the test pressure at the beginning of the second sub-section 60.2 is comparatively steep. After reaching the previously defined test pressure 61.3, this is kept constant for the duration of sub-section 60.2 and reduced back to 0 at the end of sub-section 60.2. The gradient 61.4 between the test pressure 61.3 and the subsequent test pressure 61.5 (0 bar) is comparable to the increase 61.2 when the test volume 33, 37, 42 is subjected to the test pressure 61.3. The course of the leak rate 62 follows the course of the test pressure 61 with almost no time delay, whereby a constant leak rate 62.3 is also established comparatively quickly.

[0085] In the third subsection 60.3 of the measurement 60, the test pressure 61.5 remains constant at 0 bar, whereby the leak rate 62.5 also comparatively quickly reaches the value of the partial pressure of helium in the residual gas of the vacuum determined in the first subsection 60.1.

[0086] Fig. Figure 4b shows two curves of leak rates 63, 64 for atypical leaks determined by the method according to the invention, which are in the Fig. 4b are shown as dash-dotted line 63 and dashed line 64 respectively. The curve of the test volume 37, 42 ( Fig. 3b, Fig. 3c) applied test pressure 61 is as in the Fig. 4a shown as a solid line.

[0087] The curve 63 can be one in the Fig. 3b shown leakage with a cavity formed as pore 39 in the wall 38 of the component 36 and the curve 64 of a Fig. 3c, with a cavity formed as a gap 45 between two O-rings 44.1, 44.2 of a seal 44. It goes without saying that, depending on the leak, a variety of different curve profiles are conceivable.

[0088] The curve 63 has a continuous slope 63.3 in the area of ​​the leakage test 60.2, which in the area of ​​the re-measurement 60.3 changes into a slope which is continuous over the remaining period of the measurement 60, as shown in the Fig. 4b upon closer inspection, a slightly declining gradient can be seen. This progression can be explained by the fact that when the test pressure 61 is applied at the beginning of the leak test 60.2, the pore 39 is first filled with test gas 31 and a pressure must be built up within the pore 39 before a leak can occur from the pore 39 into the test chamber 30. The lower differential pressure between the pore 39 and the test chamber 30 compared to the differential pressure between the test pressure 61 and the evacuated test chamber 30 can explain the lower gradient 63.3 compared to the leak rate 62 of a typical leak. This circumstance can also lead to a Fig. 3d, the increase in the leak rate 63 in the area of ​​the leak test 60.2. Even after reducing the test pressure 61 to 0 bar, the leak rate remains at a comparatively high value over the period of the follow-up measurement 60.3 of the measurement 60, but drops slightly, as explained above. This behavior is due to the continued overpressure in the pore 39 compared to the vacuum of the test chamber 30. The increase in the leak rate 63 depends largely on the leak rate from the pore 39 back into the test volume 37 ( Fig. 3b) and the size of the test volume 37, resulting in a drop in the differential pressure between the pore 39 and the test chamber 30.

[0089] In a further analysis, the change in the gradient in the area of ​​the leakage test 60.2, i.e., when the leak rate 63 is built up, and in the area of ​​the final measurement 60.3, i.e., when the leak rate 63 is reduced, can be used to determine the range in which the pressure in the pore 39 lies during the measurement 60. Based on this, further conclusions can be drawn about the size of the leakage 40 and / or the pore 39, whereby, for example, a gap can be drawn between a pore 39 and a seal 44 ( Fig. 3c), which can show a similar course.

[0090] In the leak test area 60.2, curve 64 initially exhibits a constant partial pressure of helium, which corresponds to the background noise of the preliminary measurement 60.1. The leak rate 64.3 exhibits an ever-increasing gradient, reaching its maximum when the test pressure 61 is switched off. In the final measurement area 60.3, the leak rate 64.5 exhibits a continuously decreasing gradient. The course of the leak rates 64.3, 64.5 can be explained, for example, by a combination of a gap 45 and permeation through at least one of the two O-rings 44.1, 44.2.

[0091] Curve 64 merely represents one embodiment of how a leak in a wall of a test volume can be represented as a curve of a continuously recorded leak rate.

[0092] Based on a large number of determined curves and the leaks assigned to the curves, the classification and, if necessary, the location of the leak in the wall surrounding the test volume can be further refined, for example through the use of artificial intelligence. This has the advantage of simplifying the search for leaks on components that are often not visually detectable, thus reducing the time required.

[0093] To do this, first, the average gradient S1, S2, S3 of one of the curves 62, 63, 64 in the three subsections 60.1, 60.2, 60.3 is determined. Subsequently, differences are calculated from the gradients S1, S2, S3, and the absolute values ​​of the differences D12, D13, D23 are determined. If the maximum of the absolute values ​​of the three differences D12, D13, D23 is above a predetermined threshold, the leak is assigned to the class of atypical leaks. If the maximum of the absolute values ​​of the differences D12, D13, D23 is below the predetermined threshold, the leak is assigned to the class of typical leaks.

[0094] The method has the advantage that the determination of the leakage class, i.e. whether it is a typical leak or an atypical leak, significantly simplifies the search for the leak in the component. While a typical leak, as in the Fig. 4a, indicates a hole in the wall of the component, the cause of an atypical leak could be, for example, a weld seam or a double O-ring seal. The search area can thus be significantly restricted, which has a beneficial effect on the duration of the search for the leak in the component. On the basis of the determined curves 63, 64, in the case of an atypical leak, further indications of the type of leak can be determined using the gradient or change in gradient in the individual sections 60.1, 60.2, 60.3 of the measurement 60 and the temporal progression of the curves 63, 64 in comparison to the test pressure 61, thus the atypical leaks can be divided into further subclasses. This has the advantage that the more precisely the cause of the leak can be determined based on the curves 63, 64, the easier the search for the leak in the component can be.

[0095] Fig.5 describes a possible method for classifying leaks 35, 40, 46 in a wall 34, 38, 43 surrounding a test volume 33, 37, 42.

[0096] In a first method step 71, the test volume 33, 37, 42 is filled with a test fluid 31 and the test volume 33, 37, 42 is subjected to a previously determined test pressure 61.3, which corresponds to a differential pressure.

[0097] In a second method step 72, a leak rate 62, 63, 64 is recorded over a predetermined period of time.

[0098] In a third method step 73, the gradient of the leak rates 62, 63, 64 is determined over at least part of the period. In a fourth method step 74, the leaks 35, 40, 46 are classified based on the determined gradient of the leak rates 62, 63, 64. 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 test chamber 31 Test gas 32 components 33 test volumes 34 Wall Component 35 Typical leakage 36 components 37 test volumes 38 Wall Component 39 cavity 40 Leakage in cavity / in test chamber 41 Component 42 test volumes 43 Wall Component 44, 44.1,44.2 Seal, O-rings 45 cavity 46 Leakage in cavity / in test chamber 50 Curve test pressure 51 Curve leak rate typical leakage 52 Leak rate curve atypical leakage 53 Time delay (delay time) 54 Time of measurement State of the art 60,60.1-60.3 Measurement, measuring sections 61,61.1-61.5 Curve test pressure 62,62.1-62.5 Curve leak rate typical leakage 63,63.1,63.5 Curve leak rate atypical leakage cavity 64,64.1-64.5 Leak rate curve atypical leakage double O-ring 71 Process step 1 72 Process step 2 73 Process step 3 74 Process step 4 101 Projection exposure system 102 Lighting system 107 reticles 108 reticle holders 110 Projection optics 113 wafers 114 wafer holders 116 DUV radiation 117 optical element 118 versions 119 lens housings M1-M6 mirrors S1-S3 slope leak rates D12,D13,D23 Differences of gradients QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] DE 10 2008 009 600 A1 [0040, 0044] US 2006 / 0132747 A1

[0042] EP 1 614 008 B1

[0042] US 6,573,978

[0042] DE 10 2017 220 586 A1

[0047] US 2018 / 0074303 A1

[0061]

Claims

[1] Method for classifying leaks (35,40,46) of a wall (34,38,43) surrounding a test volume (33,37,42) of a component (32,36,41) for semiconductor technology, comprising the following method steps: - filling the test volume (33,37,42) with a test fluid (31) and applying a predetermined differential pressure (50,61.3) to the environment to the test volume (33,37,42), - Recording a leak rate (62,63,64) from the test volume (33,37,42) over a predetermined period of time, - Determination of a gradient (S1,S2,S3) of the leak rate (62,63,64) over at least a portion of the period, - Classification of the leakage (35,40,46) based on the determined gradient (S1, S2, S3). [2] Method according to claim 1, characterized by that the process is carried out in a vacuum chamber (30). [3] Method according to claim 1 or 2, characterized bythat the measurement period (60) comprises three sub-sections (60.1,60.2,60.3). [4] Method according to claim 3, characterized by that in a first subsection (60.1) of the measurement (60) the leak rate (62,63,64) is determined without subjecting the test volume (33,37,42) to test pressure (50,61.3). [5] Method according to claim 3 and 4, characterized by that during a second subsection (60.2) of the measurement (60) the test volume (33,37,42) is subjected to the previously determined test pressure (50,61.3). [6] Method according to claims 3-5, characterized by that in a third subsection (60.3) of the measurement (60) the test volume (33,37,42) is no longer subjected to a test pressure (50,61.3). [7] Method according to one of claims 3 to 6, characterized by that the gradient (S1, S2, S3) is determined for each section (60.1,60.2,60.3) of the measurement (60). [8] Method according to claim 7, characterized bythat the gradient (S1,S2,S3) is determined as the average gradient over the period of the subsection (60.1,60.2,60.3). [9] Method according to one of claims 7 or 8, characterized by that a difference (D12,D13,D23) of the gradients (S1,S2,S3) of all three sections (60.1,60.2,60.3) is determined from each other. [10] Method according to claim 9, characterized by that the amount of the differences (D12,D13,D23) is determined. [11] Method according to claim 10, characterized by that the maximum of the amounts of the determined differences (D12,D13,D23) is compared with a previously defined threshold value. [12] Method according to one of the preceding claims, characterized by that the leak rate (62,63,64) is recorded using a residual gas analyzer. [13] Method according to claim 12, characterized by that the residual gas analyzer is calibrated before measurement (60).

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