DE102020118150A1 - Method, test structure, test device and device - Google Patents

Abstract

A method for determining a geometry of a measuring tip (100) for a scanning probe microscope is proposed. The method comprises the steps: a) Generating (S1) at least one test structure (200) which has elevations (210) alternating with depressions (220) in a first direction (I), the elevations (210) and depressions (220 ) are aligned parallel to one another in a second direction (II) perpendicular to the first direction (I);b) scanning (S2) the test structure (200) with the measuring tip (100) to determine a profile (300) of the test structure (200); andc) determining (S3) the geometry of the measuring tip (100) as a function of the determined profile (300).

Description

The present invention relates to a method for determining a geometry of a measuring tip for a scanning probe microscope, a test structure, a test device and a device for analyzing and/or processing a sample.

Microlithography is used to produce microstructured components such as integrated circuits. The microlithography process is carried out using a lithography system which has an illumination system and a projection system. The image of a lithography mask (reticle) illuminated by the illumination system is projected by the projection system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example a silicon wafer, in order to place the mask structure on the light-sensitive coating of the substrate transferred to.

In order to achieve small structure sizes and thus increase the integration density of the microstructured components, light with very short wavelengths is increasingly being used, which is known, for example, as deep ultraviolet (DUV, from English "deep ultra-violet") or extreme ultraviolet (EUV, from English "". extreme ultra-violet”). DUV has a wavelength of 193 nm, for example, and EUV has a wavelength of 13.5 nm, for example. The lithography masks themselves have structure sizes in the range of 5-100 nm. The production of such lithography masks is very complex and therefore expensive, in particular since the lithography masks must be free of defects, since otherwise it cannot be ensured that a structure produced with the lithography mask has the desired function. For this reason, lithography masks are verified, for example, that is to say that the lithography mask is checked for freedom from defects. Defects are detected and localized in the process, which enables the defects to be repaired in a targeted manner. Typical defects are the absence of intended structures, for example because an etching process did not run successfully, or structures that were not intended are present because, for example, an etching process progressed too quickly or worked at the wrong place. These defects can be eliminated by targeted etching of excess material or targeted deposition of additional material at the appropriate positions, which is possible in a very targeted manner, for example, using electron beam induced processes (FEBIP).

During the repair process, the progress of the process is continuously monitored, preferably by means of a scanning electron microscope. The electron microscope offers a spatial resolution suitable for this, which is in the range of a few nanometers. However, it is disadvantageous that the surface to be examined can be represented solely on the basis of contrasts due to different interactions of the electron beam with the surface atoms. Therefore, the image of an electron microscope typically contains no information about the height of the surface.

Scanning probe microscopy (SPM) is an imaging method that can be used to determine height information of the surface to be examined. A measuring probe is used for this purpose, which interacts directly with the surface and which is scanned over the surface. In atomic force microscopy (AFM), the interaction can be based on direct contact, on a van der Waals interaction or on other physical interactions and mixtures thereof. For example, the interaction is kept constant for each grid position of the measuring probe by adjusting a height of the measuring probe above the surface using a microactuator. The measuring probe is also referred to as a tip. The geometry of the tip has a significant impact on the interaction between the tip and the surface, especially for sharp structures. The result of such a measurement roughly corresponds to a convolution of the tip geometry with the surface geometry. It is therefore advantageous to know the tip geometry precisely in order to be able to correctly interpret the measurement result.

The following publications deal with the consideration of the influence of the geometry or shape of a measuring tip of an SPM on SPM images of a sample surface: V. Bykov et al.: "Test structure for SPM tip shape deconvolution", Appl. physics A 66, pp. 499-502 (1998) ; G. Reiss et al.: "Scanning tunneling microscopy on rough surfaces: Deconvolution of constant current images", Appl. physics Latvia 57(9), 27 Aug 1990 , pp. 867-869; Y. Martin and HK Wickramasinghe: "Method of imaging sidewalls by atomic force microscopy", Appl. physics Latvia 64 (19), 9 May 1984 , pp. 2498-2500; L. Martinez et al., Aspectratio and lateral resolution enhancement in force microscopy by attaching nanoclusters generated by an ion cluster source at the end of a silicon tip, Rev. Sci. instruments 82, (2011) , p. 02370-1 - 023710-7; X. Qian et al.: "Image simulation and surface reconstruction of undercut features in atomic force microscopy", SPIE Proc. Vol. 6518, (2007) , pp. 1-12; L. Udpa et al.: “Deconvolution of atomic force microscopy data for cellular and molecular imaging”, IEEE, Sig. Proc. Mag. 23, 73 (2006) ; Ch Wong et al, Tip dilation and AFM capabilities in the characterization of nanoparticles, JO Min 59, 12 (2007) ; JS Villarrubbia: "Algorithms for scanned particle microscope image simulation, surface reconstruction, and tip estimation", J. Res. Natl. Inst. Stand. Technol. 102, pp. 425-454 (1997) ; X. Qian and JS Villarrubia: "General three-dimensional image simulation and surface reconstruction in scanning probe microscopy using a dexel representation", Ultramicroscopy 1008 (2007) , pp. 29-42.

For example, using test structures whose geometry is known and which are measured with the measuring tip, the geometry of the tip can be deduced by “unfolding” the measurement signal with the known test structure geometry. The tip geometry that is then known can be used to "unfold" the measurement signal of an unknown structure and thus draw conclusions about its actual geometry. However, a measuring tip changes during its use due to the constant interaction with the surface, which is why the tip geometry should be checked regularly. This can be very time-consuming, especially if the measuring tip has to be moved to a separate test structure or even has to be removed from the measuring device. It is therefore desirable to have an option for characterizing the geometry of the measuring tip that is exact and yet does not involve a great deal of effort, and in particular requires little time.

DE 10 2016 223 659 A1 describes a method for providing a measuring tip for a scanning probe microscope. In a first step, at least a first and at least a second measuring tip are provided, the first and the second measuring tip being arranged on a common measuring tip carrier such that only the first measuring tip interacts with a sample to be examined. In a second step, the first measuring tip is processed irreversibly, so that after irreversible processing only the second measuring tip interacts with the sample to be examined.

DE 10 2018 221 304 A1 describes a device for determining in situ a process resolution of a particle beam-induced machining process of an element for photolithography. This includes a processing unit that is designed to generate at least two reference structures on the element within a process environment that differ in at least one dimension, and an analysis unit that is designed to determine the dimensions of the at least two reference structures in the process environment in order to to determine the process resolution of the particle beam-induced machining process from this.

DE 10 2017 211 957 A1 describes a method for examining a measuring tip of a scanning probe microscope, a test structure being produced and the measuring tip being examined with the aid of the test structure produced.

Against this background, one object of the present invention is to improve the use of a measuring tip in processes for analyzing or processing surfaces, in particular microstructured surfaces.

According to a first aspect, a method for determining a geometry of a measuring tip for a scanning probe microscope is proposed. In a first step a), at least one test structure is produced which has elevations alternating with depressions in a first direction, the elevations and depressions being aligned parallel to one another in a second direction perpendicular to the first direction. In a second step b), the test structure is scanned with the measuring tip in the first direction and in a third direction perpendicular to the first and second directions to determine a profile of the test structure. In a third step c), the geometry of the measuring tip is determined as a function of the determined profile.

This method has the advantage that the geometry of the measuring tip can be determined quickly and easily with a comparatively simple test structure. Due to the parallelism of the structures, it can be safely avoided that the measuring tip (partially) misses the test structure, as can be the case with columnar elevations or depressions, which can lead to measurement errors. This can in particular take place in situ, with the test structure being produced specifically for this purpose, for example, on a sample surface to be examined. Because of the simple geometry of the test structure, it can be generated or manufactured precisely. In addition, relevant dimensions of the test structure can be easily determined and thus checked with supplementary measuring equipment, such as an electron microscope. Furthermore, using the proposed test structure, the geometry of the measuring tip can be determined in a targeted manner on different flanks of the measuring tip.

A scanning probe microscope can be operated in different operating modes. In addition to being used as an imaging measuring instrument with which a three-dimensional structure of a surface can be recorded, the measuring tip can also be used as a micromanipulator. The measuring operating modes have in common that the sample surface to be measured is scanned with the measuring tip. A height value, ie a value of a z-coordinate, is determined for each measurement point, which is determined, for example, by a tuple of (x,y) coordinates. The horizontal and also the vertical resolution of a scanning probe microscope is in the range of less than one nanometer. The scanning probe microscope is designed, for example, as an atomic force microscope.

The measuring tip is arranged, for example, at a free end of a cantilever. The end of the cantilever opposite the free end is held by a probe holder or measuring head, which can be moved in all three spatial directions, for example by means of a piezoelectric actuator. In addition, it can be provided that the probe holder is rotatably and/or tiltably mounted. The basic resolution of the scanning probe microscope is determined, for example, by the piezo actuator, since this is responsible for the exact approach to the measuring points arranged in a grid. The cantilever with the measuring tip arranged on it can be referred to overall as a measuring probe. The cantilever consists, for example, of monocrystalline silicon, but depending on the application, other materials and/or material combinations can also be provided.

Various types of scanning probe microscopes are known, such as scanning tunneling microscopes and atomic force microscopes. In scanning tunneling microscopes, a voltage is applied between the probe tip and the sample surface, and the current that flows when the tip is not in direct contact with the surface (the “tunneling current”) is measured. The current is an indicator of the distance between the probe tip and the sample surface. In atomic force microscopes, the measuring tip interacts directly with the sample surface at the atomic level. This is explained in more detail below.

In order to record the height of the sample surface at a respective measuring point, the measuring tip interacts with the sample surface. For example, the measuring tip is brought into contact with the sample surface. To do this, the measuring probe is approached to the sample surface from above. As soon as bending of the cantilever is detected, which is determined optically, for example, by deflecting a laser beam reflected on the upper side of the cantilever, contact is made. The measuring tip is then held in contact with the surface and moved (scanned) over the surface. The deflection of the cantilever is a measure of the height of the surface at a given grid point. In this mode, for example, a height of the probe holder is kept constant. Alternatively, the deflection of the cantilever can be kept constant by controlling the height of the probe holder using an appropriate control loop. Then the modulation of the probe holder in the z-direction corresponds to the height of the sample surface. In addition to the contact mode, in which the measuring tip wears out comparatively quickly, other measuring modes are possible, such as a non-contact mode or an intermittent mode, which differ in particular in the type of interaction between the measuring tip and the surface. In these modes, the cantilever is brought into a forced oscillation with a predetermined frequency, for example, which is preferably close to a resonant frequency of the cantilever. The vibration is excited in such a way that the free end of the cantilever vibrates with the measuring tip in the z-direction. In this case, the resonant frequency depends in particular on the properties of the cantilever and an existing interaction of the measuring tip with the sample surface. As soon as the interaction changes, the resonant frequency changes, for example, and with it the amplitude of the forced oscillation at the specified frequency. For example, the probe holder is tracked in the z-direction by means of a closed control loop in such a way that the oscillation is maintained, whereby the modulation of the probe holder in the z-direction corresponds to the height of the sample surface. These measurement methods described by way of example can be expanded and/or modified in various ways. Various other measurement methods are also possible.

The measuring tip itself has, for example, a pyramid-like or needle-like shape. Depending on the application, a particularly fine measuring tip is advantageous, for example if very fine structures with a high aspect ratio are to be measured with the measuring tip. The geometry of the measuring tip has a significant influence on the profile of a sample surface recorded with the measuring tip, which is why it is advantageous to know the geometry as precisely as possible.

Depending on the geometry of a measuring tip, incorrect or incomplete measurement results can occur. Two examples for this. A probe tip with a tip diameter of, for example, 60 nm cannot detect a depression, for example a ditch or hole in the sample surface, with a width or diameter of only 30 nm, since the probe tip cannot enter the depression. Likewise, a measuring tip with a length of 50 nm cannot completely detect an indentation with a height of 100 nm.

The geometry of the measuring tip can be characterized by various parameters. For example, a diameter and a length can fully characterize a rod-shaped measuring tip. If the measuring tip has a different basic shape, such as a cone or pyramid, an opening angle of the cone or pyramid can also be a helpful parameter. However, a measuring tip can also have different geometries on different flanks, so that the geometry of the measuring tip is preferably determined in relation to a respective flank. Such parameters characterizing the geometry can be determined by scanning the test structure and subsequent analysis of the profile recorded in the process.

The test structure is generated, for example, on a surface of a sample to be examined. The surface of the sample to be examined, on which the test structure is produced, is preferably flat and smooth. “Flat” is understood in particular to mean that the surface lies in the plane spanned by the first and the second direction, at least in the area of the test structure. “Smooth” means in particular that the surface does not have any significant unevenness or structures deviating from this level before the test structure is created. "Significant unevenness" is to be understood, for example, as unevenness that has more than 10% of a structure size of the test structure. For example, if the test structure has an elevation with a height of 20 nm and a width of 10 nm, then the limit from insignificant to significant would be 2 nm in height and 1 nm in width. Depending on the application, the skilled artisan's understanding of what is essential or non-essential may differ from this example.

The at least one test structure has elevations alternating with depressions in a first direction, which are aligned parallel to one another in a second direction perpendicular to the first direction. The elevations are, for example, structures that are raised with respect to a lower point in a depression, and the depressions are, for example, hollows with respect to an upper point of a projection. This means that the terms elevation and depression are to be understood relative to one another. For example, elevations and depressions can be represented in the form of at least one trench in a smooth surface. Then, the surface adjacent to the depression (trench) corresponds to a bump. Conversely, with respect to a ridge that is an elevation relative to the surface, the surface adjacent to the ridge may form a depression. The elevations and depressions preferably extend in the direction of a surface normal relative to the surface that carries the test structure. However, deviations from this are also possible.

The fact that the elevations and depressions alternate with one another means in particular that if the test structure is cut along the first direction, elevations and depressions are found in an alternating sequence. The various elevations and depressions can be designed differently, that is, for example, have a variation in width, height, flank angle and the like. The test structure is preferably designed periodically, at least in sections, so that a plurality of pairs of elevations and depressions following one another in the first direction are each of the same design, ie have the same geometry. Such a regular test structure makes it possible to determine the profile with a significant statistic of measuring points for determining the geometry of the measuring tip.

The fact that the elevations and depressions are aligned parallel to one another in a second direction perpendicular to the first direction means in particular that, for example, a tangent applied to an edge between an elevation and the adjacent depression extends in the second direction. The elevations and depressions can thus have a curvilinear course, in the sense that the tangents of two points at the edge that are spaced apart from one another do not have to be parallel to one another.

In step b), the test structure is preferably scanned with the measuring tip in the first direction and in a third direction perpendicular to the first and second directions to determine a profile of the test structure.

As described above, the scanning takes place in step b) in such a way that the probe holder scans the test structure with the measuring probe. A height value is determined at each grid point of the grid. The height value describes a distance from the point of the test structure corresponding to the grid point to a reference level, which is given for example by a surface of a sample bearing the test structure, in a third direction orthogonal to the first and the second direction. The third direction is also referred to below as the z-direction.

The test structure is preferably scanned with the measuring tip linearly, for example along the first direction, but directions deviating from this are also possible. A line comprises 1000 grid points, for example, and extends over a distance of 1 µm. This means that the resolution of the grid points is ent 1 nm long in the first direction. A respective line is preferably scanned in forward and reverse directions, whereby each raster point is detected twice. A height value is assigned to each grid point. When a first line is detected, the probe tip is offset perpendicular to the first line by one grid point and a second line parallel to the first line is scanned. In this way, for example, a 1 μm ² area of the test structure is scanned with a spatial resolution of 1 nm ² . The profile determined in this way thus comprises 10 ⁶ (one million) measurement points. Depending on the application, the resolution can be varied along the different directions. For example, the deflection along the first and/or second direction can be up to 10 μm or up to 100 μm. Furthermore, in embodiments, a profile can also include only a few lines, for example ten lines, down to just a single line. Fewer lines are captured in less time, which can be beneficial. On the other hand, fewer measuring points are then available to determine the geometry of the measuring tip. In addition, it is possible to use a varying resolution, using a higher resolution in an area of interest where, for example, a sharp edge of the test structure is located than in other areas where the test structure is flat.

In the third step c), the geometry of the measuring tip is determined as a function of the determined profile. It should be noted that the profile obtained by scanning does not reflect the height profile of the test structure, but corresponds to a convolution of the test structure geometry with the tip geometry. However, the test structure geometry or the measuring tip geometry can be determined from the profile by unfolding the profile. For this purpose, the respective other geometry should be known as precisely as possible. In the present case, the test structure is generated according to precise specifications, so that its geometry is known. The geometry of the measuring tip can therefore be determined from the determined profile.

Steps b) and c) can be carried out again and again, for example before and after a structure to be examined has been scanned with the measuring tip. In this way, changes in the geometry of the measuring tip that affect a measurement result can be detected early and taken into account accordingly.

According to one embodiment of the method, an electron microscope image of the at least one test structure is captured and a feature size of the at least one test structure is determined from the captured electron microscope image. In step c), the geometry of the measuring tip is determined as a function of the determined profile and the determined structure size.

This embodiment has the advantage that a structure size of the test structure produced is checked using a reliable method. The electron microscope image of the test structure makes it possible to precisely determine dimensions of the test structure in the plane spanned by the first and second directions. The structure size of the test structure is thus precisely known, at least in two dimensions. The structure parameters, which are determined from the electron microscope image, are referred to as length and width, for example. A distinction must be made here between an overall length/overall width, which describes the test structure as a whole, and a length/width of individual elevations or depressions that are part of the test structure. The structure size relates in particular to the length/width of individual elevations or depressions.

According to a further embodiment of the method, at least two test structures are produced in step a), which have a different aspect ratio in relation to the elevations or depressions, the aspect ratio specifying a height relative to a width of the elevation or depression. In step b), the at least two test structures are scanned with the measuring tip to determine a respective profile.

The geometry of the measuring tip can be determined very precisely by varying the aspect ratio. For example, a first test structure has rectangular elevations/depressions with a height of 50 nm and a width of 25 nm. The aspect ratio is therefore 2:1. The second test structure has rectangular projections/depressions with a height of 50 nm and a width of 10 nm. The aspect ratio is therefore 5:1. If, for example, when scanning these two test structures, it is determined that the profile of the first test structure has a height of 50 nm between a top point of a projection and a bottom point of a depression, then the measuring tip has a front section with a length of more than 50 nm and a diameter (along the scanning direction, which is here along the first direction) of less than 25 nm. Further geometric details of the front section of the measuring tip can be determined from the steepness of the flanks of the profile during the transition from an elevation to a depression and vice versa. In contrast, the profile of the second test structure has a maximum height of only 10 nm between an upper point of an elevation and a lower point of a depression. From this it can be determined that the measuring tip cannot completely dip into the indentations and the bottom of the indentation not reached. It can also be deduced, for example, that the front ten nanometers of the measuring tip have a diameter of less than ten nanometers.

By combining a large number of different test structures with a wide variety of aspect ratios, the geometry of the measuring tip can be determined very precisely.

Aspect ratio is a measure of how "fine" or "thin" a structure is. However, the aspect ratio alone does not determine the geometry of a test structure; one of the two dimensions, i.e. the height or the width, must also be specified.

According to a further embodiment of the method, the at least two test structures are scanned sequentially one after the other with an increasing or decreasing aspect ratio. The scanning is terminated when it is determined on the basis of the determined profiles in a sequence with a decreasing aspect ratio that a deepest point of a depression is reached, or when it is determined on the basis of the determined profiles in a sequence with an increasing aspect ratio that a deepest point of a Deepening is no longer achieved.

This sequential procedure is advantageous in order to purposefully determine a limit variable that can still be measured or recorded without errors using the measuring tip. The sequence with decreasing aspect ratio can have the advantage that the front section of the measuring tip is characterized very precisely or in detail. The sequence with increasing aspect ratio can have the advantage that with a smaller aspect ratio, which can be resolved by the measuring tip without any problems, basic properties of the measuring tip can be determined and the successful creation of the test structures can also be checked.

As an alternative to a sequentially increasing or decreasing aspect ratio of the test structures to be scanned one after the other, an alternating scheme is also possible, with a row comprising every second test structure to be scanned having a sequentially increasing aspect ratio or sequentially decreasing aspect ratio, and a row with the test structures to be scanned in between also having a sequentially increasing aspect ratio or has a sequentially decreasing aspect ratio.

According to a further embodiment of the method, in step a) at least a first test structure and a second test structure are produced having elevations alternating with depressions in a first direction in each case, with the first direction of the first test structure having an angle not equal to 0 with the first direction of the second test structure ° includes, in particular an angle in the range of 45 ° - 90 °. In step b), the at least two test structures are scanned with the measuring tip to determine a respective profile.

This embodiment has the advantage that the geometry of the measuring tip can be determined even more precisely. In particular, a flank geometry of different flanks of the measuring tip can be precisely determined.

For example, the first test structure is scanned along its first direction, which in this example is called the x-direction. The probe holder thus moves the measuring tip back and forth along the x-direction. The trajectory of the measuring tip in the x-direction therefore hits an edge between an elevation and a depression perpendicularly. In this case, the geometry of the front edge or the rear edge of the measuring tip is decisive for the determined profile. The second test structure is also scanned along its first direction, which however is perpendicular to the first direction of the first structure, which is therefore called the y-direction. The probe holder thus moves the measuring tip back and forth along the y-direction. In this case, too, the measuring tip strikes an edge between an elevation and a depression perpendicularly. If the measuring tip or the probe holder has the same orientation as before, then the side flanks of the measuring tip are now decisive for the determined profile.

Further or other flank areas can also be determined more precisely, for example, by rotating the probe holder by a specific angle, so that another flank area is decisive for the determined profile when the measuring tip approaches an edge.

According to a further embodiment of the method, steps a) and b) take place in the same vacuum chamber and/or without breaking the vacuum.

The test structure is thus generated in particular in situ and then scanned without breaking the vacuum. There is thus no need for a time-consuming introduction of a test structure and/or the measuring tip into a process environment. In particular, a process environment comprises an atmosphere with very precisely controlled physico-chemical properties such as pressure, temperature and composition, in particular the partial pressure of various species present in the atmosphere

According to a further embodiment of the method, step a) includes generating the at least one test structure using a focused particle beam, in particular an electron beam, and at least one precursor gas or etching gas.

The generation of structures by means of particle beam-induced processes is possible with a very high level of accuracy, in particular a high spatial resolution. It is therefore possible to create test structures with very small structure sizes, which are in the atomic range. The test structures produced in this way can, for example, have elevations with a width of 1 nm alternating with depressions with a width of 1 nm and an aspect ratio of 10:1 or even more. This is possible in a particularly advantageous manner by means of electron beam-induced processes (EBIP).

Alkyl compounds of main group elements, metals or transition elements are particularly suitable as precursor gases which are suitable for the deposition or growth of raised structures. Examples include cyclopentadienyl trimethyl platinum (CpPtMe ₃ Me = CH ₄ ), methylcyclopentadienyl trimethyl platinum (MeCpPtMe ₃ ), tetramethyltin (SnMe ₄ ), trimethylgallium (GaMe ₃ ), ferrocene (Cp ₂ Fe), bis-aryl Chromium (Ar ₂ Cr), and/or carbonyl compounds of main group elements, metals or transition elements, such as chromium hexacarbonyl (Cr(CO) ₆ ), molybdenum hexacarbonyl (Mo(CO) ₆ ), tungsten hexacarbonyl (W( CO) ₆ ), dicobalt octacarbonyl (Co ₂ (CO) ₈ ), triruthenium dodecacarbonyl (Ru ₃ (CO) ₁₂ ), iron pentacarbonyl (Fe(CO) ₅ ), and/or alkoxide compounds of main group elements, metals or transition elements, such as tetraethoxysilane (Si(OC ₂ H ₅ ) ₄ ), tetraisopropoxytitanium (Ti(OC ₃ H ₇ ) ₄ ), and/or halide compounds of main group elements, metals or transition elements, such as tungsten hexafluoride (WF ₆ ), tungsten hexachloride (WCl ₆ ), titanium tetrachloride (TiCl ₄ ), boron trifluoride (BCl ₃ ), silicon tetrachloride (SiCl ₄ ), and/or complexes with main group elements, metals or transition elements, such as copper bis-hexa-fluoroacetylacetonate (Cu(C ₅ F ₆ HO ₂ ) ₂ ), dimethyl gold trifluoro-acetylacetonate (Me ₂ Au(C ₅ F ₃ H ₄ O ₂ )), and/or organic compounds such as carbon monoxide (CO), carbon dioxide (CO ₂ ), aliphatic and/or aromatic hydrocarbons, and the like.

The etching gas may include, for example: xenon difluoride (XeF ₂ ), xenon dichloride (XeCl ₂ ), xenon _{tetrachloride (XeCl 4} ), water vapor (H ₂ O), heavy water (D ₂ O), oxygen (O ₂ ), ozone (O ₃ ) , ammonia (NH ₃ ), nitrosyl chloride (NOCl) and/or one of the following halide compounds: XNO, XONO ₂ , X ₂ O, XO ₂ , X ₂ O ₂ , X ₂ O ₄ , X ₂ O ₆ , where X is a halide is. Other etchant gases for etching one or more of the deposited test structures are disclosed in Applicant's US Patent Application Serial No. 13/0103,281

Other additive gases that can be used in creating the test structure include, for example, oxidizing gases such as hydrogen peroxide (H ₂ O ₂ ), nitrous oxide (N ₂ O), nitrous oxide (NO), nitrogen dioxide (NO ₂ ), nitric acid (HNO ₃ ) and others Oxygen-containing gases and/or halides such as chlorine (Cl ₂ ), hydrogen chloride (HCl), hydrogen fluoride (HF), iodine (I ₂ ), hydrogen iodide (HI), bromine (Br ₂ ), hydrogen bromide (HBr), phosphorus trichloride (PCl ₃ ), phosphorus pentachloride (PCl ₅ ), phosphorus trifluoride (PF ₃ ) and other halogen-containing gases, and/or reducing gases such as hydrogen (H ₂ ), ammonia (NH ₃ ), methane (CH ₄ ) and other hydrogen-containing gases. These additional gases can be used, for example, for etching processes, as buffer gases, as passivating agents and the like.

According to a further embodiment of the method, the at least one test structure has a line-like structure in plan view with a comb-like cross-section, the comb-like cross-section in particular comprising a substantially rectangular profile.

Ideally, the test structure has a rectangular profile. Since the particle beam, for example the electron beam, typically has a Gaussian beam profile, the edges of a built-up structure at the atomic level are not sharp but rounded. Structures with rounded corners are also understood to be “substantially rectangular”. Which structures are still to be regarded as "substantially rectangular" depends on the expert understanding using the relevant measurement methods. Beam profile is understood to mean, for example, an intensity distribution along a cross section through the particle beam perpendicular to its direction of propagation.

In further embodiments, the at least one test structure has a curvilinear shape in plan view. For example, curvilinear means that the first direction at a first position is a different direction than the first direction at a second position different from the first. A radius of curvature of the curvilinear course is preferably greater than a width of an elevation or depression, in particular more than twice the radius of curvature and up to 20 times the radius of curvature. The elevations and depressions can, for example, be arc-shaped, in particular arc-shaped being. The parallelism criterion is maintained at every point of the test structure.

In further embodiments, the test structure has a regular arrangement of cubes or cuboids. In the top view, this test structure would resemble a chess board, for example. This test structure corresponds to a superposition of two line-like test structures with orthogonal alignment at the same position. This embodiment is particularly space-saving.

According to a further embodiment of the method, in step c) a length of a front section of the measuring tip, the diameter of which is less than a width of the depression of the test structure, is determined.

According to a further embodiment of the method, before step a) a structure size of a sample to be measured or manipulated using the measuring tip is determined and in step a) the at least one test structure is generated as a function of the determined structure size.

This embodiment is advantageous when it is primarily important to determine whether a specified limit structure size can still be measured with the respective measuring tip. If, for example, in an application it is sufficient for the probe tip to detect a structure with an aspect ratio of 1:1 and a height of 25 nm without errors, then it may be sufficient to create a test structure with precisely these geometric properties and scan it with the probe tip.

The measuring tip is set up in particular for measuring and/or for manipulating a photomask for microlithography.

According to a further embodiment of the method, the test structure produced in step a) is removed again after the geometry of the measuring tip has been determined.

In this case, the test structure is preferably removed by means of a particle beam-induced etching process with a precursor gas suitable for this purpose. The precursor gas may include, for example: xenon difluoride (XeF ₂ ), xenon dichloride (XeCl ₂ ), xenon _{tetrachloride (XeCl 4} ), water vapor (H ₂ O), heavy water (D ₂ O), oxygen (O ₂ ), ozone (O ₃ ), ammonia (NH ₃ ), nitrosyl chloride (NOCl) and/or one of the following halide compounds: XNO, XONO ₂ , X ₂ O, XO ₂ , X ₂ O ₂ , X ₂ O ₄ , X ₂ O ₆ , where X is a halide. Other etchant gases for etching one or more of the deposited test structures are disclosed in Applicant's US Patent Application Serial No. 13/0103,281.

Such an etching process can advantageously be carried out in situ, ie without a vacuum having to be broken and/or the sample having to be brought into another device.

According to a second aspect, a method for analyzing and/or processing a sample, in particular a photomask for microlithography, is proposed. In a first step a), the sample is analyzed and/or processed using a measuring tip of a scanning probe microscope. In a step b), which can be carried out before and/or after step a), a geometry of the measuring tip is determined according to the method according to the first aspect.

According to one embodiment of the method, steps a) and b) take place in the same vacuum chamber and/or without breaking the vacuum.

According to a further embodiment of the method, in step b) the at least one test structure is produced on the sample and/or a substrate within a vacuum chamber of the scanning probe microscope.

According to a third aspect, a test structure for determining a geometry of a measuring tip of a scanning probe microscope is proposed. The test structure has elevations alternating with depressions in a first direction, with the elevations and depressions being aligned parallel to one another in a second direction perpendicular to the first direction.

The embodiments and features of the test structure described in the context of the first aspect apply correspondingly to the proposed test structure and vice versa.

In particular, the test structure has elevations and depressions whose width is in a range of 1-50 nm and whose height is in a range of 1-100 nm. It can also be said that the test structure has a structure at spatial frequencies in the range of 10/µm - 1000/µm, which can also be referred to as the resolution of the test structure. The test structure can be designed in such a way that the resolution varies spatially and two-dimensionally, that is to say it becomes larger/smaller along the first direction, for example. The function that describes the variation is, for example, a step function with a resolution that is constant in sections, or a constant, continuous function. For example, the resolution can increase linearly, or also increase logarithmically or exponentially and/or the function has a combination of different components.

The test structure can be designed in such a way that an aspect ratio of the elevations and depressions varies along the first direction. In this case, for example, one pair of elevations and depressions can have a specific first aspect ratio, and the following pair of elevations and depressions can have a different aspect ratio.

The test structure can also be designed in such a way that the structure size of the elevations and depressions varies along the first direction with a constant aspect ratio. In this case, one elevation-depression pair can have a specific first structure size with a specific aspect ratio, and the following elevation-depression pair can have a different structure size with the same specific aspect ratio.

Such a variation of the aspect ratio or the structure size can take place continuously according to a step function or also according to a continuous function. Sections with a constant geometry of the test structure along the first direction are preferably larger than a lower limit value. The lower limit value can be determined, for example, in such a way that a respective section comprises at least ten pairs of elevations and depressions.

The test structure is preferably produced by means of a particle beam-induced process, in particular with an electron beam in connection with a suitable precursor gas. Etching processes that remove material and/or deposition processes that apply material can be used here.

In embodiments, the test structure can also have a plurality of rounded, for example circular, columnar elevations and/or depressions, which are preferably arranged regularly and have a specific aspect ratio.

According to a fourth aspect, the use of a test structure according to the third aspect for determining a geometry of a measuring tip of a scanning probe microscope is proposed.

According to a fifth aspect, a testing device for determining a geometry of a measuring tip for a scanning probe microscope is proposed. The testing device includes a generating unit for generating at least one test structure which has elevations alternating with depressions in a first direction, the elevations and depressions being aligned parallel to one another in a second direction perpendicular to the first direction. Furthermore, the testing device has a scanning unit for scanning the test structure with the measuring tip to determine a profile of the test structure. A determination unit of the testing device is set up to determine the geometry of the measuring tip as a function of the determined profile.

The embodiments and features described for the proposed method according to the first aspect apply accordingly to the proposed testing device.

The testing device is advantageously set up to carry out the method according to the first aspect.

The generation unit is set up in particular to generate a test structure according to the third aspect.

The determination unit can be implemented in terms of hardware and/or software. In the case of a hardware implementation, the determination unit can be embodied, for example, as a computer or as a microprocessor. In the case of a software implementation, the determination unit can be embodied as a computer program product, as a function, as a routine, as an algorithm, as a neural network, as part of a program code or as an executable object.

According to a sixth aspect, a device for analyzing and/or processing a sample, in particular a photomask for microlithography, is proposed. The device includes an analysis and processing unit for analyzing and/or processing the sample using a measuring tip of a scanning probe microscope. Furthermore, the device comprises a testing device according to the fifth aspect, wherein the testing device is set up to determine a geometry of the measuring tip before and/or after the analysis and/or processing of the sample.

The embodiments and features described for the proposed method according to the second aspect apply accordingly to the proposed device.

The device is advantageously set up to carry out the method according to the second aspect.

"A" is not necessarily to be understood as being limited to exactly one element. Rather, a plurality of elements, such as two, three or more, can also be provided. Any other count word used here should also not be understood to mean that there is a restriction to precisely the stated number of elements. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with regard to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

• 1a zeigt eine schematische Ansicht einer Messsonde für ein Rastersondenmikroskop;
• 1b zeigt drei verschiedene Messspitzen mit unterschiedlichen Geometrien;
• 2 zeigt eine schematische Ansicht einer ersten Ausführungsform einer Prüfstruktur;
• 3 zeigt schematisch ein Abtasten einer Prüfstruktur mit einer Messspitze und ein resultierendes Profil;
• 4 zeigt ein schematisches Elektronenmikroskop-Bild einer Probe mit mehreren Prüfstrukturen;
• 5 zeigt Querschnitte durch zwei Prüfstrukturen mit unterschiedlichem Aspektverhältnis;
• 6 zeigt eine Sequenz mit drei Prüfstrukturen mit abnehmendem Aspektverhältnis und die korrespondierenden Profile;
• 7 zeigt ein Elektronenmikroskop-Bild einer Prüfstruktur und das korrespondierende Profil;
• 8 zeigt ein Diagramm in dem beispielhaft die Eindringtiefe einer Messspitze als Funktion einer Strukturgröße der Prüfstruktur dargestellt ist;
• 9 zeigt eine Anordnung einer Mehrzahl unterschiedlicher Prüfstrukturen;
• 10 zeigt drei weitere unterschiedliche Ausführungsformen von Prüfstrukturen;
• 11 zeigt schematisch eine zu analysierende Probe;
• 12 zeigt ein beispielhaftes Blockdiagramm eines Ausführungsbeispiels einer Vorrichtung zum Analysieren und Bearbeiten einer Probe mit einer Prüfvorrichtung; und
• 13 zeigt ein schematisches Blockschaltbild eines Ausführungsbeispiels eines Verfahrens zum Bestimmen einer Geometrie einer Messspitze.

Further advantageous refinements and aspects of the invention are the subject matter of the dependent claims and of the exemplary embodiments of the invention described below. The invention is explained in more detail below on the basis of preferred embodiments with reference to the enclosed figures.

• 1a shows a schematic view of a measuring probe for a scanning probe microscope;
• 1b shows three different measuring tips with different geometries;
• 2 shows a schematic view of a first embodiment of a test structure;
• 3 shows schematically a scanning of a test structure with a measuring tip and a resulting profile;
• 4 shows a schematic electron micrograph of a sample with multiple test structures;
• 5 shows cross-sections through two test structures with different aspect ratios;
• 6 shows a sequence with three test structures with decreasing aspect ratio and the corresponding profiles;
• 7 shows an electron microscope image of a test structure and the corresponding profile;
• 8th shows a diagram in which the penetration depth of a measuring tip is shown as a function of a structure size of the test structure;
• 9 shows an arrangement of a plurality of different test structures;
• 10 shows three further different embodiments of test structures;
• 11 shows schematically a sample to be analyzed;
• 12 12 shows an exemplary block diagram of an embodiment of an apparatus for analyzing and processing a sample with a test device; and
• 13 shows a schematic block diagram of an embodiment of a method for determining a geometry of a measuring tip.

Elements that are the same or have the same function have been provided with the same reference symbols in the figures, unless otherwise stated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

1a shows a schematic view of a measuring probe 110 for a scanning probe microscope 514 (see 12 ). The measuring probe 110 has a holding bar 120 which is arranged on a fastening section 130 and is known in the art as a cantilever. The measuring tip 100 is arranged at the free end of the cantilever 120 . In this example, the measuring tip has two sections 101, 102. The front section 101 is of particularly fine design. The front section 101 has a length of 200 nm with a diameter of 20 nm, for example. Alternatively, the measuring tip 100 does not have such a subdivision into different sections with different geometries.

The cantilever 110 and the measuring tip 100 can be made in one piece. For example, the cantilever 120 and probe tip 100 may be fabricated from a metal such as tungsten, cobalt, iridium, a metal alloy, a semiconductor such as silicon, silicon nitride, silicon carbide, or silicon oxide. The measuring tip 100 is preferably grown on the cantilever 120 by means of a particle beam-induced process. The measuring tip 100 can also be made of different materials, such as having a base made of a first material and a tip made of a second material. It is also possible to manufacture the cantilever 110 and the measuring tip 100 as two separate components and then to connect them to one another. This can be done, for example, by gluing.

the 1b shows, for example, three different measuring tips 100a, 100b, 100c with different geometries. In the left column of 1b is a side view of the respective measuring tip and in the right column of the 1b shows the cross section through the respective measuring tip at different positions.

The first measuring tip 100a has a conical geometry, for example. This one is running tapered towards the tip, the cross-section being circular in each case, as shown in the exemplary cross-sections C1, C2, C3.

The second measuring tip 100b has, for example, a pyramid-like geometry with a triangular base area C1, C2, C3. The respective corner of the triangular base forms a flank F1, F2, F3 of the measuring tip 100b. The flank F1 runs essentially perpendicularly in relation to the cross sections C1, C2, C3, and the two flanks F2, F3 are tilted. This measuring tip 100b is therefore suitable for detecting vertical edges of a structure when the measuring tip 100b is approached with the flank F1 of the structure.

The third measuring tip 100c has a cylindrical profile, with the cross section C1 being essentially constant along the length of the measuring tip 100c.

2 12 shows a schematic perspective view of a first embodiment of a test structure 200. In this example, the test structure 200 is arranged on a substrate 230, which can be a semiconductor substrate, for example. The test structure 200 has a line-like geometry in plan view with a comb-like cross section. In this case, elevations 210 are arranged in a first direction I in alternation with depressions 220 . The elevations 210 and depressions 220 extend parallel to one another in a second direction II, which is perpendicular to the first direction I.

In this example, the test structure 200 was produced by depositing material at the positions of the elevations 210 . It can be said that the elevations were raised in 210. In this case, the growth took place along the third direction III, which is perpendicular to the first direction I and the second direction II. The third direction III is here, for example, parallel to a surface normal (not shown) of the substrate 230.

The elevations 210 and depressions 220 are designed uniformly in this example, that is, the width of an elevation 210 and the width of a depression 220 are the same in each case. For example, the width is 10 nm and the height of the projections 210 above the substrate is 30 nm. Thus, the projections 210 and the depressions 220 have an aspect ratio of 3:1.

3 shows schematically a scanning of a test structure 200 with a measuring tip 100 and a resulting profile 300. For example, it is about the measuring tip 100a of FIG 1b , which has a conical geometry, and the test structure 200 of FIG 2 . On the left of the 3 is shown schematically, like the measuring probe 110, which is held by a probe holder 140 (see 12 ) is held, is scanned over the test structure 200 in order to scan it. This example is an atomic force microscope.

The measuring probe 110 is moved back and forth parallel to the first direction I, with a control loop (not shown) keeping the interaction of the measuring tip 100 with the surface of the test structure 200 constant by adjusting the probe holder 140 with the measuring probe 110 in the third direction III will. Schematically and for easier understanding is in the 3 the measuring tip 100 is shown in contact with the test structure 200, but this does not necessarily have to be the case in other operating modes of the atomic force microscope. At the time shown, the measuring tip 100 is in a depression 220 of the test structure 200, a front edge of the measuring tip 100 just coming into contact with an edge between the depression 220 and the following elevation 210. If the measuring probe 110 is now advanced further, the probe holder 140 must be moved upwards in the third direction III. In this case, an angle of the trajectory of the probe holder 140 with respect to the horizontal direction corresponds to the angle of the front flank of the measuring tip 100 with respect to the horizontal direction.

Therefore, the profile 300 shown in the diagram on the right is the scanning result of the test structure 200. The dashed lines represent the actual geometry of the test structure 200. This example shows that the profile 300, which is determined by scanning, is not corresponds to the actual structure. Rather, the profile 300 is a convolution of the geometry of the test structure 200 and the geometry of the measuring tip 100. If one or the other geometry is known, the respective other geometry can be determined by unfolding the profile 300. So if the geometry of the test structure 200 is known, the geometry of the measuring tip 100 can be determined.

An advantageous design of the test structure 200 can be used in this way to determine various geometric parameters of the measuring tip 100, such as a length, a diameter as a function of the length, an angle of attack, a flank of the measuring tip in different directions and the like. Determining the geometry of the measuring tip is understood here to mean that at least one of the geometry parameters is determined.

4 shows a schematic electron microscope image 400 of a sample 10 (see 11 or 12 ) with several different test structures 200a - d. In this example, four different test structures 200a-d are shown. All four test structures 200a-d have a linear structure with a comb-like cross section, as shown in FIG 2 explained in detail. For example, the hatched bars represent bumps 210 (see 2 ) is, alternatively, it can also be depressions 220 (see 2 ) Act. Without restricting the generality, the test structures 200c, 200d in this example each have three elevations/depressions and the test structures 200a, 200b each have four elevations/depressions. The test structures 200a, 200c have the same orientation and the test structures 200b, 200d have an orthogonal orientation thereto. In addition, the test structures 200a, 200b have a smaller structure size than the corresponding test structures 200c, 200d. The width B1 of an elevation 210 and the width B2 of a depression 220 are shown on the test structure 200a as an example of the structure size. One can say that the test structures 200a and 200c have a different spatial resolution or have information at different spatial frequencies. The same applies to the test structures 200b and 200d. The structure size or the resolution of a respective test structure 200a - d can advantageously be determined from the electron microscope image 400 .

Due to the different resolution of the test structures 200a, 200c or 200b, 200d, different geometry parameters of a measuring tip 100 (see 1a , 1b or 12 ) determine or certain geometry parameters can be determined with varying degrees of accuracy. In addition, by aligning two of the test structures 200a-d orthogonally, the geometry of the measuring tip 100 can be measured with respect to different flanks F1-F3 (see 1b ) more precisely. The respective test structure 200a-d is preferably scanned perpendicular to the respective line direction. In the case of the test structures 200a, 200c, for example, a front and a rear flank are decisive, so that from the profile 300 determined here (see 3 ) whose geometry can be determined, and in the case of the test structures 200b, 200d, the left and right flanks are decisive, so that their geometry can be determined from the profile 300 determined there.

5 shows cross sections through two test structures 200a, 200b with different aspect ratios AV1, AV2. The two test structures 200a, 200b have a comb-like cross section. In this example, the aspect ratio AV1, AV2, which results from the quotient of the height H1, H2 of the respective depression 220 and the width B1, B2 of the respective depression 220, is shown for each depression 220. In this example, aspect ratio AV1 is greater than aspect ratio AV2. For the additional elevations 210 or additional depressions 220 of the respective test structure 200a, 200b, the respective aspect ratio can be specified accordingly. In this example, the test structures 200a, 200b are formed uniformly, which means that the aspect ratio AV1, AV2 is the same for each elevation 210 or depression 220.

6 shows a sequence with three test structures 200a - c with decreasing aspect ratio AV1, AV2 (see 5 ) and corresponding profiles 300a-300c. In this example, the respective test structure 200a-c has a linear structure with a comb-like cross section. The hatched areas correspond to elevations 210 (see 2 , 3 , 5 ). These have a height H1, H2 (see 5 ) from 30 nm. The aspect ratio of the test structure 200a on the left is 3:1, for example, which means that the elevations 210/depressions 220 have a width B1, B2 (see 5 ) from 10 nm. The aspect ratio of the middle test structure 200b is 6:1, for example, that is to say the elevations 210/depressions 220 have a width B1, B2 of 5 nm. The aspect ratio of the right test structure 200c is 10:1, for example, that is to say the elevations 210/depressions 220 have a width B1, B2 of 3 nm.

The three test structures 200a - c shown are measured sequentially with an increasing aspect ratio with a measuring tip 100 (see 1a , 1b , 3 or 12 ) is sampled to obtain a corresponding profile 300a-c. In this case, the scanning takes place along the first direction I of the respective test structure 200a-c. The profiles 300a-c shown in the diagrams are obtained as an example. The horizontal axis I corresponds to a position of the respective test structure 200a-c along the first direction I, the vertical axis III corresponds, for example, to a height value at which the interaction of the measuring tip with the surface of the respective test structure 200a-c is constant. The left test structure 200a is completely covered by the measuring tip 100, in particular the measuring tip 100 reaches the bottom of the depressions 210. At the edges between an elevation 210 and a depression 220, a slight angle of incidence of the measuring tip 100 can be seen in the profile 300a. In the middle test structure 200b, the measuring tip 100 just about reaches the bottom of a depression 220 between two elevations 210, which can be seen from a short flat section in the profile 300b. In contrast, in the case of the right-hand test structure 200c, the measuring tip 100 penetrates only a small distance into the depressions 220, but the bottom of the depressions 220 is no longer reached.

From these three measurements it can be seen at a glance that this measuring tip 100 is not suitable for analyzing wells with a diameter of 5 nm and an aspect ratio of 10:1. The structure size of the middle test structure 200b could be specified as a limit value for the suitability of the measuring tip 100 . From the rising flanks of the profiles 300a - c, a geometry of the respective flank F1 - F3 (see 1b ) of the measuring tip 100 can be closed. In particular, it can be derived from the profile 300c that the measuring tip 100 has a diameter of 5 nm at the maximum penetration depth, since this is the width of the indentations 220 . The penetration depth of the measuring tip 100 can be represented as a function of the width of the indentations 220, which is exemplified in FIG 8th is shown.

7 shows an electron microscope image of a test structure 200 and the corresponding profile 300, which is obtained by scanning the test structure 200 with a measuring tip 100 (see 1a , 1b , 3 , 12 ) was detected. In this example, the test structure 200 has a linear structure with a comb-like cross section. The light lines that can be seen in the electron microscope image correspond to elevations 210, and darker areas in between correspond to depressions 220. Test structure 200 has an aspect ratio of 3:1, for example, with the elevations being 60 nm in height, for example. The test structure 200 was constructed with an electron beam, for example, using tetraethoxysilane as the deposition gas. The elevations 210 have a width of 20 nm, for example, and the depressions 220 have a width of 60 nm. The test structure 200 was scanned with an atomic force microscope and the profile 300 was thus recorded. The profile 300 shows rounded corners of the elevations 210 and downwardly tapering depressions 220. Such a profile 300 is referred to herein as being essentially rectangular. As already explained, the corners of the test structure 200 are often slightly rounded, for example due to a Gaussian beam profile. This is all the more important, the narrower the elevations or depressions are. The profile 300 shows that the probe tip 100 reaches the substrate between the elevations 210. FIG. From this it can be deduced that the measuring tip 100 at its front section 101 (see 1a ) has a diameter of less than 60 nm.

8th shows a diagram in which the penetration depth ΔH of a measuring tip 100 (see 1a , 1b , 3 or 12 ) as a function of a structure size B1 of the test structure 200 (see 2 - 7 , 9 , 10 ) is shown. For example, the horizontal axis B1 refers to a width B1 (see 5 ) of a recess 220 (see 2 , 3 , 5 ) of the test structure 200. For example, here twelve test structures 200 (each point in the diagram corresponds to a test structure) each with a different width B1 of the depressions 220, but with a constant height H1 (see 5 ) is generated and sampled with a measuring tip 100. From the resulting profiles 300 (see 3 , 6 ) a maximum penetration depth ΔH of the measuring tip was determined and entered in the diagram shown here. The height H of the depressions 220 is 70 nm, for example. Instead of the width B1, the aspect ratio could also be plotted on the horizontal axis.

It can be seen that the penetration depth ΔH is essentially 0 up to a width B1 of 20 nm. From this it can be concluded that the measuring tip 100 has a diameter of approximately 20 nm at the front end. The penetration depth ΔH then increases steadily, and the diameter of the measuring tip 100 can be read from a respective value at a distance from the front end of the measuring tip 100 that corresponds to the penetration depth ΔH. This is shown as an example for the depression 220 with a width B1 of 40 nm. With a penetration depth ΔH of 20 nm, the measuring tip 100 thus has a diameter of 40 nm. From a width B1 of 70 nm, the measuring tip 100 reaches the bottom of the depression 220 at a penetration depth ΔH of 70 nm.

9 shows an arrangement of a plurality of different test structures 200a-f. The test structures 200a-f are linear structures with a comb-like cross section. The test structures 200a, 200c and 200e have the same alignment with different structure sizes or different aspect ratios. The test structures 200b, 200d and 200f are aligned orthogonally thereto and have correspondingly different structure sizes or aspect ratios. the 9 FIG. 12 is an example of an arrangement of multiple test structures 200a-f with different orientations and a variation of the aspect ratio.

10 shows three further examples of embodiments of test structures 200a - c. All three test structures 200a-c comprise elevations 210 alternating with depressions 220 in a first direction I, elevations 210 and depressions 220 being aligned parallel to one another in a second direction II perpendicular to the first direction I

In the case of the test structure 200a, the elevations 210 and depressions 220 have the shape of a circular arc, with a respective circular arc spanning an angle of 90°. The test structure 200a also has a variation in structure size, in particular whose width B1, B2, which is shown as an example for two of the circular arcs, in the radial direction. Elevations 210 and depressions 220, which are designed as arcs of a circle, have a common center point. A tangent T is drawn in on each of three edges between an elevation 210 and a depression 220 . The respective tangent T relates to a point of the respective circular arc, which corresponds to an intersection with a line I running in the radial direction. The elevations 210 and depressions 220 are aligned parallel to one another in relation to this radial direction. The radial direction thus corresponds to the first direction I and the tangential direction corresponds to the second direction II.

In addition to structures in the shape of a circular arc, the elevations 210 and depressions 220 can have other curvilinear or curved profiles.

The test structure 200b has a chessboard-like arrangement of the elevations 210 and depressions 220 . This embodiment combines two test structures 200 arranged orthogonally to one another in a small area. In this example, the structure size is uniform, but the structure size can also be varied, for example increasing or reducing the structure size or the aspect ratio line by line.

The test structure 200c has a linear structure with a comb-like cross section, a width B1 of the depressions 220 being gradually reduced along the first direction I. This results in the possibility of determining a limit variable with a single scanning process, which can still be detected without any problems using the respective measuring tip 100 . This embodiment can therefore contribute to a more rapid determination of the geometry of the measuring tip 100.

11 FIG. 1 schematically shows a sample 10 to be analyzed, for example a section of a structured lithography mask. In particular, the lithography mask 10 has a structure formed by a coating 14 on the substrate 12 of the sample 10 . The structure size B of these structures can be different at different positions of the lithography mask 10 . An example is in the 11 the width B of an area is drawn in as structure size. The structure size B is, for example, in a range of 20-200 nm. In the production of lithography masks, there are isolated defects D, since etching processes, for example, do not run exactly as intended. In the 11 such a defect D is shown hatched. There is excess material since the coating 14 was not removed in this area, although the two adjacent coating areas 14 are provided separately in the template for the lithography mask 10 . One can also say that the defect D forms a ridge. In this case, a size of the defect D corresponds to the structure size B. Other defects are also known which are smaller than the structure size B, for example in a range of 5-20 nm. Such defects D, and also defects of other types, can be corrected in devices suitable for this purpose. In this example it is necessary to remove the ridge in a targeted manner, for example by means of particle beam-induced etching. It is advantageous here if the defect location is checked using imaging methods before, during and/or after the etching process. A scanning probe microscope, preferably an atomic force microscope, is particularly suitable for obtaining a three-dimensional image.

As above based on the 3 described, for an exact interpretation of the measurement data obtained, the profile 300 (see 3 and 6 ), the geometry of the measuring tip 100 used (see 1a , 1b , 3 , and 12) must be known as precisely as possible. One of the test structures 200 described above can advantageously be used for this purpose (see 2 - 7 , 9 , 10 or 12 ) are used. Depending on the type of defect D and how it is remedied, it may be sufficient if it is ensured that the measuring tip 100 does not exceed a specific limit value with regard to its width. In the example of 11 for example, it may be sufficient to note that after the defect D is removed, the substrate 12 is reached along a narrow line and the two substrate regions 12 above and below the defect D shown are connected. It may therefore be sufficient to produce the test structure 200 in such a way that it has, for example, a structure size such as that of the defect D, ie in particular a width B as shown here. The height of the coating 14 is fixed and constant for the lithography mask 10, which is why an aspect ratio AV1, AV2 (see Fig 5 ) fixed. It can therefore be said that the test structure 200 is generated on the basis of or as a function of the structure size B of the sample 10. Determining the geometry of the measuring tip 100 used can thus be limited to one or a few test structures 200, which can save time. The analysis of the defect D or the defect site after the defect D has been removed can also be speeded up and made more reliable.

12 10 shows an exemplary block diagram of an embodiment of an apparatus 500 for analyzing and processing a sample 10 with a testing apparatus 510. The apparatus Device 500 is mostly arranged in a vacuum housing 501, which is kept at a certain gas pressure by a vacuum pump 502.

The device 500 is particularly suitable for analyzing and processing lithography masks 10 (see FIG 11 ) furnished. For example, it is a verification and/or repair tool for lithography masks, in particular for lithography masks for EUV (“extreme ultra-violet”) or DUV (“deep ultra-violet”) lithography. A sample 10 to be analyzed or processed is placed on a sample table 11 . The sample table 11 is set up in particular to adjust the position of the sample 10 in three spatial directions and in three axes of rotation with an accuracy of a few nanometers. The device 500 has an electron column 540 . This includes an electron source 541 for providing an electron beam 542 and an electron microscope 543, which detects the electrons scattered back from the sample 10 in this arrangement. A further detector for secondary electrons can also be provided (not shown). The electron column 540 can, in cooperation with supplied process gases, which are supplied from a gas supply unit 530 from the outside via a valve 532 and a gas line 534 into the area of a focus point of the electron beam 542 on the sample 10, electron beam-induced machining processes (EBIP: " electron-beam induced processing”). This includes in particular a deposition and/or an etching of material. The electron column 540 together with the gas supply unit 530 can be referred to as a generation unit 512, for example. It should be noted that the electron microscope 543 is not absolutely necessary for EBIP, but is advantageous for monitoring the processes.

The device 500 also has an analysis and processing unit 520, which is embodied here as an atomic force microscope. The atomic force microscope 520 comprises a scanning unit 514 which has a probe holder 140 which can be moved in at least three spatial directions by means of a plurality of piezo actuators (not shown). In addition, the probe holder 140 can be rotatably mounted in one or more axes in order to compensate for or specifically bring about a tilting and/or to adjust a relative goniometric alignment in relation to the sample 10 . The probe holder 140 is intended in particular for receiving a measuring probe 110 (see FIG 1 ) having a cantilever 120 and a measuring tip 100 set up. The probe holder 140 is set up to scan a surface of the sample 10 with the measuring tip 100 in a raster fashion. For this purpose, the scanning unit 514 preferably comprises a closed control circuit (not shown), which, for example, keeps an interaction of the measuring tip 100 with the sample 10 constant. In this way, in particular, a height profile of the sample surface is recorded. In order to obtain the height profile from the raw measurement data, an assumption about the geometry of the measuring tip 100 must be made, for example.

In order to determine the geometry of the measuring tip 100 in situ, a test structure 200 with a predetermined geometry, in particular with a predetermined aspect ratio, can be generated by means of the generating unit 512 . The test structure 200 can, as shown in FIG 2 - 7 , 9 or 10 described be trained. In this example, the test structure 200 is placed on the sample 10 itself. The test structure 200 can be both on the substrate 12 (see 11 ) or on the coating 14 (see 11 ) be arranged a lithography mask. The test structure 200 is preferably designed in such a way that it can be removed without leaving any residue in a subsequent process step. As an alternative to the position on the sample 10, the test structure 200 can be produced on a position of the sample table specially provided for this purpose or on a separate sample (not shown).

The device 500 also includes a determination unit 516 which is embodied here as a component of a control computer 503 arranged outside of the vacuum housing 501 . The determination unit 516 is in particular for determining the geometry of the measuring tip 100 on the basis of a profile 300 recorded with the measuring tip 100 (see FIG 3 and 6 ) of the test structure 200 is set up. The control computer 503 is set up to control the electron column 540 and the atomic force microscope 520 .

The atomic force microscope 520 can also be used as a micromanipulator. In this case, for example, the measuring tip 100 is moved to a position of the sample 10 that is to be manipulated and is brought into contact with the sample there, for example. In this way, for example, dirt adhering to the sample surface, such as dust particles, can be picked up by the measuring tip 100 and thus removed.

The test device 510 comprises at least the generation unit 512, the sampling unit 514 and the determination unit 516.

13 shows a schematic block diagram of an embodiment of a method for determining a geometry of a measuring tip 100 (see 1a , 1b , 3 or 12 ). In a first step S1, at least one test structure 200 (see 2 - 7 , 9 , 10 ) generates which elevations 210 (see 2 , 3 , 5 or 10 ) alternating with deepening gen 220 (see 2 , 3 , 5 or 10 ) in a first direction I (see 2 , 3 or 10 ), wherein the elevations 210 and depressions 220 are parallel to one another in a second direction II (see 2 and 10 ) are aligned perpendicular to the first direction I. The test structure 200 has, for example, one of the 2 - 7 , 9 or 10 structures shown. The test structure 200 is preferably generated by the generation unit 512 (see 12 ) of the test device 510 (see 12 ) or the device 500 (see 12 ) generated. In a second step S2, the test structure 200 is measured with the measuring tip 100 to determine a profile 300 (see 3 or 6 ) of the test structure 200 is sampled. This is done in particular by means of the scanning unit 514 (see 12 ) of the testing device 510 or the device 500. In a third step S3, the geometry of the measuring tip 100 is determined as a function of the determined profile 300. This is done, for example, by the determination unit 516 (see 12 ) of test device 510 or device 500.

Once the geometry of the probe tip 100 is determined, the probe tip 100 can be used to analyze and/or process a sample 10 . In particular, the suitability of the measuring tip 100 for a specific analysis task or processing task is then known. Profiles 300 determined with the measuring tip 100 can be converted with high reliability into height profiles of the scanned surface on the basis of the known geometry of the measuring tip 100 .

Advantageously, by repeatedly scanning the test structure 200 with the measuring tip 100, a change in the geometry of the measuring tip, which can occur, for example, due to wear or tear, can be detected, so that the actual geometry of the measuring tip 100 can be monitored and erroneous measurements can be avoided .

Furthermore, the test structure 200 produced can be removed again in situ, that is to say without breaking the vacuum, for example by means of a particle beam-induced etching process.

Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

Reference List

10

sample

11

rehearsal table

12

substrate

14

coating

100

measuring tip

100a - c

measuring tip

101

section

102

section

110

measuring probe

120

cantilever

130

attachment section

140

probe holder

200

test structure

200a-f

test structure

210

elevation

220

deepening

230

substrate

300

profile

300a - c

profile

400

Electron Microscope Image

500

contraption

501

vacuum housing

502

vacuum pump

503

tax calculator

510

testing device

512

generating unit

514

scanning unit

516

unit of determination

520

Analysis and processing unit

530

gas supply unit

532

Valve

534

management

540

electron column

541

electron source

542

electron beam

543

electron microscope

ΔH

penetration depth

AV1

aspect ratio

AV2

aspect ratio

B

structure size

B1

broad

B2

broad

C1

cut

C2

cut

C3

cut

D

defect structure

H1

height

H2

height

I

first direction

II

second direction

III

third direction

S1

process step

S2

process step

S3

process step

T

tangent

QUOTES INCLUDED IN DESCRIPTION

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

Patent Literature Cited

• DE 102016223659 A1 [0008]
• DE 102018221304 A1 [0009]
• DE 102017211957 A1 [0010]

Non-patent Literature Cited

• V. Bykov et al.: "Test structure for SPM tip shape deconvolution", Appl. physics A 66, pp. 499-502 (1998) [0006]
• G. Reiss et al.: "Scanning tunneling microscopy on rough surfaces: Deconvolution of constant current images", Appl. physics Latvia 57 (9), 27 August 1990 [0006]
• Y. Martin and H.K. Wickramasinghe: "Method of imaging sidewalls by atomic force microscopy", Appl. physics Latvia 64 (19), 9 May 1984 [0006]
• L. Martinez et al., Aspectratio and lateral resolution enhancement in force microscopy by attaching nanoclusters generated by an ion cluster source at the end of a silicon tip, Rev. Sci. instruments 82, (2011) [0006]
• X. Qian et al.: "Image simulation and surface reconstruction of undercut features in atomic force microscopy", SPIE Proc. Vol. 6518, (2007) [0006]
• L. Udpa et al.: "Deconvolution of atomic force microscopy data for cellular and molecular imaging", IEEE, Sig. Proc. Mag. 23, 73 (2006) [0006]
• Ch. Wong et al.: "Tip dilation and AFM capabilities in the characterization of nanoparticles", J.O.Min. 59, 12 (2007) [0006]
• J.S. Villarrubbia: "Algorithms for scanned particle microscope image simulation, surface reconstruction, and tip estimation", J. Res. Natl. Inst. Stand. Technol. 102, pp. 425-454 (1997) [0006]
• X.Qian and J.S. Villarrubia: "General three-dimensional image simulation and surface reconstruction in scanning probe microscopy using a dexel representation", Ultramicroscopy 1008 (2007) [0006]

Claims (18)

Method for determining a geometry of a measuring tip (100) for a scanning probe microscope, with the steps: a) Generating (S1) at least one test structure (200) which has elevations (210) alternating with depressions (220) in a first direction (I), the elevations (210) and depressions (220) being parallel to one another in a second direction (II) perpendicular to the first direction (I); b) scanning (S2) of the test structure (200) with the measuring tip (100) to determine a profile (300) of the test structure (200); and c) determining (S3) the geometry of the measuring tip (100) as a function of the profile (300) determined. procedure after claim 1 , further comprising: acquiring an electron microscope image (400) of the at least one test structure (200); determining a structure size (B1, B2) of the at least one test structure (200) from the captured electron microscope image (400); and determining the geometry of the measuring tip (100) as a function of the determined profile (300) and the determined structure size (B1, B2) in step c). procedure after claim 1 or 2 , wherein: in step a) at least two test structures (200) are generated which have a different aspect ratio (AV1, AV2) in relation to the elevations (210) or depressions (220), the aspect ratio (AV1, AV2) having a height (H) relative to a width (B1, B2) of the peak (210) or valley (220); and in step b) the at least two test structures (200) are scanned with the measuring tip (100) to determine a respective profile (300). procedure after claim 3 , wherein the at least two test structures (200) are scanned sequentially one after the other with an increasing or decreasing aspect ratio (AV1, AV2), the scanning being terminated when: in a sequence with a decreasing aspect ratio (AV1, AV2) based on the determined profiles (300 ) it is determined that a deepest point of a depression (220) is reached, or in the case of a sequence with an increasing aspect ratio (AV1, AV2) based on the determined profiles (300) it is determined that a deepest point of a depression (220) is no longer reached is reached. Procedure according to one of Claims 1 - 4 , wherein: in step a) at least a first test structure (200) and a second test structure (200) having elevations (210) alternating with depressions (220) are produced in a respective first direction (I), the first direction (I ) the first test structure (200) with the first direction (I) of the second test structure (200) at an angle not equal to 0 °, in particular in the range of 45 ° - 90 °; and in step b) the at least two test structures (200) are scanned with the measuring tip (100) to determine a respective profile (300). Procedure according to one of Claims 1 - 5 , wherein steps a) and b) take place in the same vacuum chamber (501) and/or without breaking the vacuum. Procedure according to one of Claims 1 - 6 , wherein step a) comprises generating the at least one test structure (200) using a focused particle beam (542), in particular an electron beam, and at least one precursor gas or etching gas. Procedure according to one of Claims 1 - 7 , wherein the at least one test structure (200) has a line-like structure in plan view with a comb-like cross section, wherein the comb-like cross section comprises in particular a substantially rectangular profile. Procedure according to one of Claims 1 - 8th , wherein in step c) a length of a front section (101) of the measuring tip (100) whose diameter is less than a width (B1, B2) of the depression (220) of the test structure (200) is determined. Procedure according to one of Claims 1 - 9 , wherein: before step a), a structure size (B) of a sample (10) to be measured or manipulated using the measuring tip (100) is determined; and in step a) the at least one test structure (200) is generated as a function of the determined structure size (B). Procedure according to one of Claims 1 until 10 , further comprising: removing the test structure (200) produced in step a) after the geometry of the measuring tip (100) has been determined. Method for analyzing and/or processing a sample (10), in particular a photomask for microlithography, with the steps: a) analyzing and/or processing a sample (10) using a measuring tip (100) of a scanning probe microscope (520); and b) determining a geometry of the measuring tip (100) according to the method according to one of Claims 1 - 11 before and/or after step a). procedure after claim 12 , wherein steps a) and b) take place in the same vacuum chamber (501) and/or without breaking the vacuum. procedure after claim 12 or 13 , wherein in step b) the at least one test structure (200) on the sample (10) and / or a substrate within a vacuum chamber (501) of the scanning probe microscope (520) is generated. Test structure (200) for determining a geometry of a measuring tip (100) of a scanning probe microscope (520), having elevations (210) alternating with depressions (220) in a first direction (I), the elevations (210) and depressions (220) parallel to each other in a second direction (II) perpendicular to the first direction (I). Use of a test structure (200) according to claim 15 for determining a geometry of a measuring tip (100) of a scanning probe microscope (520). Testing device (510) for determining a geometry of a measuring tip (100) for a scanning probe microscope, with: a generating unit (512) for generating at least one test structure (200), which has elevations (210) alternating with depressions (220) in a first direction (I), the elevations (210) and depressions (220) being parallel to one another in one second direction (II) perpendicular to the first direction (I); a scanning unit (514) for scanning the test structure (200) with the measuring tip (100) to determine a profile (300) of the test structure (200); and a determination unit (516) for determining the geometry of the measuring tip (100) as a function of the determined profile (300). Device (500) for analyzing and/or processing a sample (10), in particular a photomask for microlithography, having: an analysis and processing unit (520) for analyzing and/or processing the sample (10) using a measuring tip (100) a scanning probe microscope; and a testing device (510) according to Claim 17 , wherein the testing device (510) is set up to determine a geometry of the measuring tip (100) before and/or after analyzing and/or processing the sample (10).

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