Investigations on tip-based large area nanofabrication and nanometrology using a planar nanopositioning machine (NFM-100)

This paper explores large area application of tip-based nanofabrication by field emission scanning probe lithography and showcases the simultaneous possibility of atomic force microscopy on macroscopic scales. This is made possible by the combination of tip-based technology and a planar nanopositioning and nanomeasuring machine. Using long range atomic force microscopy measurement of regular grating structures, the performance of the machine is thoroughly characterized over the full 100 mm range of motion of the positioning machine, which was confirmed by repeated measurements. After initially focussing on achieving the minimum line width of < 40 nm in microscopic areas, a grating with a pitch of 1 μm is additionally fabricated over a total length of 10 mm, whereby the dimensions and deviations are also considered.


Introduction
In recent decades, a new level of complexity and miniaturization has been achieved in micro-and nanotechnology manufacturing [1].As described in various predictions of * Author to whom any correspondence should be addressed.
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the International Technology Roadmap for Semiconductors or the International Roadmap for Device and Systems, structure sizes will decrease while wafer sizes will continue to increase to achieve the highest possible throughput [2].Accordingly, when fabricating structures at the nano-scale, the allowable tolerances need to decrease to keep defects to a minimum.Nanostructures manufactured in this manner now have a wide range of applications as semiconductor components and form the basis of modern integrated circuits, whose possible areas of application are in semiconductor technology, biology, chemistry, medical as well as agricultural, communications technology and optoelectronics [3,4].
Due to the high cost of mask fabrication and other complex problems, EUV lithography is only useful for extreme mass production.Meanwhile, various, alternative lithographic technologies, such as electron beam lithography , direct laser writing (DLW), scanning probe lithography (SPL), nanoimprint lithography (NIL) and directed self-assembly have been established for specific applications [5][6][7][8].In contrast to extreme ultra violet (EUV) lithography, these alternative processes can be used for customized, flexible, and maskless structuring.
Especially tip-based systems are typically characterized by the possibility of high-precision surface scanning, but the scanning range of these in commercial available systems is usually limited to a range of several hundred µm 2 [9].In addition to high-precision surface scanning, there is the possibility of fabricating nanostructures by repurposed, conventional atomic force microscopy (AFM) systems based on various lithographic techniques.To transfer the limited range of motion to wafer-based sizes, the combination with highprecision nanopositioning technology with large ranges of motion is necessary to extend high-resolution inspection as well as nanofabrication over long ranges.
This work demonstrates the synergy of a planar nanopositioning machine with tip-based nanometrology and highly localised nanofabrication, which now enables repeatable highprecision AFM measurements over the full range of motion of 100 mm and furthermore nanopatterning over macroscopic lengths up to 10 mm with minor deviation from the given trajectory.The focus is initially on the positionability of the NFM-100, followed by experimental investigations and analyses on nanometrology and nanofabrication in macroscopic ranges, which could be demonstrated and analysed for the first time in the aforementioned areas.

SPL
The flexibility and the simplicity of alternative manufacturing processes has led to a steady development of direct writing processes in the last decades, which are based on a variety of physical and chemical approaches.SPL technologies in particular offer a number of advantages, such as structuring with nanoscale precision as well as the possibility of in-situ pre-and post-inspection of the surface to be structured and the fabricated structuring results, which takes place with minimal effort compared to other processes [10].In general, in tip-based nanostructuring, there are several processes that offer the possibility of producing a pattern transfer with very small dimensions and low deviations.These processes can be divided into chemical, physical and physical-chemical functional principles.However, each process is characterized by individual advantages and disadvantages due to the different operating principles.Fan et al [11] summarise different methods with their operating principles, resolution and velocity limits of SPL.It is shown that the resolution limits are in a similar order of magnitude of less than 10 nm for the respective principles of SPL.With most tip-based systems, however, compromises have to be made in terms of measuring/fabrication velocities and the expected accuracy, which are typically in the range of several µ ms −1 .Furthermore, the problem of tip wear is present in all processes.
Despite the partially low fabrication velocity of maskless methods and the limited penetration depth, when using resists for nanomanufacturing, the use of a low-energy electron beam, in which a cantilever tip is brought near a sample and a field emission (FE) current is used for patterning, offers numerous advantages over other fabrication methods [12].Due to the advantages such as the absence of the proximity effect, the possibility of flexible production of arbitrarily shaped samples, operation under normal environmental conditions and reduced acquisition costs [12], this tip-based fabrication technology, so-called FE-SPL, is applied in this work by using active (self-actuated and self-sensing) microcantilevers.Additionally, these types of cantilevers can be used for preand postinspection of the samples, due to the possibility of simple switching between the measuring and writing mode.In FE-SPL, a voltage is applied between a cantilever tip and a sample.Due to a small distance (∆d < 5 nm) between the tip and the sample, electrons can be emitted despite a low voltage (30-50 V) and contribute to a reaction in an electron-sensitive resist coated sample through a current flow.The described FE can be described by the Fowler-Nordheim (FN) theory, which was first published in 1928 [13]: Using this formula, the dependence of the emitted current density J on the electric field E and the work function Φ 0 of the tip material can be described (a, b, and c are constants) [14].The choices of tip shape, tip material and tip radius play an important role for the FN emission current density due to the work function [13,15].However, with these processes for creating nanostructures, it should be noted that deposits, contamination and tip wear can lead to changes in the tip shape and thus have a direct influence on the structuring result.In order to minimise tip wear during patterning as well as surface scanning, which is particularly important for macroscopic areas, only diamond tips are used for this application.In comparison to tips made of silicon, diamond tips have been identified as having almost no tip wear and, in addition, significantly more stable FE currents can be expected.Nevertheless, the tip can also be altered by contamination, which can have an influence on the homogeneity of the structures, especially with long structuring lengths.
Experience and knowledge regarding the fabrication of the used active microcantilevers as well as the use of special resist types or additionally resistless nanopatterning through nanoscale oxidation could be gained to further improve the process and ultimately fabricate structures in the sub-5 nm range [14,[16][17][18][19].The fact that the SPL systems can also be used as an ordinary AFM system means that the result can be inspected directly after the fabrication step.This is done without any tool change, which also eliminates the need to realign the cantilever sensor.The possibility of measuring the sample surface before and after the structuring step and the requirement to find the fabricated structures again also allows alignment with existing structures at the same time.Moreover, the tip-based SPM lithography with active is capable to be employed in diverse modes like STM Mode at UHV on hydrogen in the voltage range of 0.3-3 V [18], or as local anodic oxidation of 2D-Materials in the voltage range of 4-25 V [19,20] and FN FE lithography on resist in the voltage range of 35-110 V [21].
So far, the development has focused on small-scale processes of SPL, with its findings now being transferred to macroscopic areas in the foreground.For reproducible, error-free fabrication and imaging of structures at wafer level, highprecision nanomeasuring technology is required [22].

Nanopositioning and nanomeasuring technology
To meet the challenges of large-area positioning and at the same time of positioning with nm-accuracy, nanopositioning and nanomeasuring machines (NMM) can fill this gap [23].
For these machines, various approaches are used, such as sample scanning mode, scanning probe mode and mixed scanning mode [24].In sample scanning mode, the measuring tool is fixed while the sample is moved using a machine table.In scanning probe mode, the measuring tool is moved while the sample to be investigated is fixed.In mixed scanning mode, the two previously mentioned modes are used in combination.
To avoid length measurement deviations in these setups caused by systematic and random tilting, the Abbe principle should be applied consistently [25,26].Ernst Abbe described this important principle of length measurement technology, in which the measuring apparatus must be arranged in such a way that the distance to be measured forms the straight-line continuation of the graduation serving as a scale [25,27,28].This Abbe comparator principle [27] was further developed into the extended three-dimensional Abbe-comparator [2,24], which is implemented in various coordinate measuring machines (for example the ISARA 100 and 400 [29]) and nanopositioning machines.However, the highest accuracy can only be expected with machines, which are using laser interferometers for length measurement and consistently fulfill the Abbe principle.Furthermore, some of these machines are consistently developed as coordinate measuring machines and do not allow any nanopositioning, which we define as the ability to freely position the sample with nanometer resolution anywhere in the working area.
Based on many years of research in the field of nanometrology, a first NMM-1 was developed at the Technische Universität Ilmenau by the Institute of Process Measurement and Sensor Technology [24,26].The design of this NMM-1 is based on the principle of Sample Scanning Mode.The measuring tool and the length measuring systems are in a fixed position while the sample is moved in the x-, y-and z-directions.This concept makes it possible to arrange the measuring systems in such a way that their axes intersect at the touching point of the sample at all times.In this way, the Abbe-principle is fulfilled in all three measuring directions over the entire range of motion [26,27,30].The position of the machine table is measured by three laser interferometers in the x-, y-and zdirections with a resolution of 20 pm and a laser wavelength stability of <2 × 10 −9 .Due to the basic design based on the Abbe-principle and the high-resolution measuring systems, the NMM-1 offers a large positioning range of 25 mm × 25 mm × 5 mm with sub-nm accuracy and a measurement uncertainty of 9 nm under defined measurement conditions [26,31].By using stabilized lasers for position determination, metrological traceability can be guaranteed [32,33].
With the possibility of using, for example, optical as well as tactile measuring tools, this NMM has already been combined with an atomic force microscope and scans over several millimeters could been demonstrated [25,34].The outstanding measurement results with the NMM-1 triggered the demand to extend its extraordinary properties to a larger scale and therefore stimulated the development of a machine with a larger range of motion.This led to the development of the nanopositioning and nanomeasuring machine 200 (NPMM-200), which is based on the same concept as the NMM-1, but offers a significantly larger range of motion of 200 mm × 200 mm × 25 mm with the same picometer resolution.The main reasons for the high measuring accuracy of the NMM-1 and the NPMM-200 are the described 3D implementation of the Abbe comparator principle and the additional control compensation of the inclination angles of the guidance systems.These machines are specially designed to position the machine table in all three dimensions.
In contrast, the positioning of the machine used in this work is performed by a planar direct drive system with a movement range of 100 mm in diameter.This machine is intended for 2D wafer positioning, where any remaining adaption to height differences and wafer tilt has to be carried out by the installed measuring or writing system.Besides a cost reduction, one focus in the development of the, so-called, nanofabrication machine (NFM-100) was to achieve higher stability in the z-direction, which is necessary for a sensitive tip-based system.Due to the high stability in the z-direction, the NFM-100 represents a special platform for research into new tip-based nanomeasuring processes and alternative lithography methods in extended macroscopic working ranges and, in particular, allow arbitrary nanopositioning within its range of motion.

Setup of the combination of nanopositioning and nanomeasuring technology and the tip-based system
Within this work, a tip-based system has been combined with the NFM-100, which is installed directly above the Abbepoint of the machine's coordinate system (see figure 1).Like the other machines developed at the Technische Universität Ilmenau, the NFM-100 is based on the sample scanning mode.
The entire set-up of the NFM and the manufacturing/measuring tool including the enclosure is operated in an air-conditioned (controlled temperature and humidity) and vibration-isolated environment.

The NFM-100
The machine slider is aerostatically guided on three elements.Natural hard stone serves the base of the machine.The top surface is machined to achieve a flatness of less than 1 µm and serves as a guide surface for the aerostatic guide elements of the machine slider [35].These enable high repeatability and, above all, high stiffness in the z-direction as well as low friction during the x-y-movement [36].
Direct drives in form of ironless linear actuators are used to position the machine table (see figure 2 (left)).The drive system is realised in such a way that the coils are fixed to the granite base, while the magnetic array is attached directly to the machine table, as are the measuring mirrors for length measurement.This basic arrangement of the direct drive system is shown in figure 3. It has the advantage that a low magnetic stray field can be assumed.As two-phase actuators are used in this case, it is necessary to work with commutation [28].The advantage of this configuration is the elimination of heating through the passive slider and the fact that no cabling is required.Furthermore, the influence of material wear is minimised by the contactless movement of the slider using aerostatic guiding elements.By using this direct drive without a rigid mechanical connection, frictional defects can be reduced to a minimum [37].Due to the absence of stick-slip effects, this drive is suitable for use in high-precision positioning in the nm-range.They are also characterized by high dynamics and repeatability during positioning.
The position of the machine table is tracked with differential interferometers, which have a particularly high thermal stability due to their symmetrical optical design [38].The laser source for this is a stabilised He-Ne laser (λ = 632.8nm) with a relative frequency stability of 2 • 10 −8 [28].The evaluation electronics uses Arctan demodulation with a resulting path resolution of 5 pm [28,39].The laser interferometers are the only measuring systems for the x and y-plane, which means that the laser wavelength serves as a length scale for these coordinates.To calibrate the laser wavelength, it was compared with a traceable laser that was stabilised with an iodine absorption cell.The resulting actual laser wavelength is taken into account in the machine control system.These length values are used for high precision closed-loop control of the machine slider by the NFM-100 control system.The direct drive systems, as well as the length and angle measuring system, are arranged in a 3 × 120 • orientation and can apply three independent forces on the machine table in the x, y-plane.Correspondingly, this arrangement provides three degrees of freedom: movement in the x-and y-directions and rotation around the z-axis.The machine table is therefore equipped with three measuring mirrors for the length and angle measuring systems (see figure 2 (right)).Two of the interferometers are used to measure the x-y-position of the machine table, while the third interferometer serves as an angular interferometer for measuring the rotation φ z .The maximum permissible rotation for the angle interferometer here is 30 ' as a higher rotation leads to a loss of signal.The rotation must therefore be measured and actively set to zero.
The two interferometers for length measurement are also arranged in such a way that their measuring axes virtually intersect at the probing point of the measuring tool.Accordingly, the Abbe-principle can be fulfilled in the x-, yand z-directions with an Abbe offset l Abbe,i = 0 and an uncertainty u Abbe,i < 100 µm [40]: In this way, rotation-related first-order length measurement errors can be reduced to a minimum.Otherwise, tilting φ of the slider around the x-, y-or z-axis would lead to an Abbe error ∆l i,j [40]: As the measuring mirrors attached to the machine table define the coordinate system of the machine in the x-y-plane,   A thermomechanical actuator is used for oscillation (coloured in orange) and a Wheatstone-bridge is used to detect the deflection of the cantilever at the clamping point (coloured in green).The measuring/fabrication tip is placed at the free end of the cantilever [35,44].
their deviations from the ideal shape are essential parameters.For this reason, the slider and mirror are made of quartz to minimize thermal and mechanical drift [40].

The AFM/SPL system
After decades of research on microcantilevers and their potential applications, various principles have been established alongside AFM and SPL.Active cantilevers in particular, however, find a wide range of applications beyond the fields mentioned, such as in the areas of inertial, pressure, biological and chemical, as well as flow and acoustic sensor technology [41][42][43].
The active microcantilevers utilized in this work emply a thermomechanical actuator to excite an oscillation (see figure 4).
The thermomechanical actuator works according to the bimorph effect and consists of two different layers with different coefficients of thermal expansion.In this case, silicon and aluminium are used.The inequality of the thermal resistance coefficients leads to a higher efficiency of the actuator [12].If a periodic signal is now applied to the meander actuator, this results in an oscillation of the cantilever due to a periodic temperature change and periodic thermal expansion [44].
By using these type of self-actuating and self-sensing microcantilevers, it is possible to switch sequentially between the measuring and writing modes.With scanning probe systems using active microcantilevers, the surface can be inspected prior to the actual patterning step, allowing subsequent alignment of the nanostructures [45].The structuring step is carried out with the application of FE-SPL, using a resistcoated silicon sample.Calixarenes with macromolecular sizes of around 0.5-1 nm are used in this contribution as resists to achieve minimum feature widths of less than 50 nm.This resist is a multi-tone resist, which can be used to create both positive and negative tones.However, this depends on the electron dose used and the resist material selected, as well as the ambient conditions, such as room temperature and humidity.In general, FE lithography technology is controlled to a specified current setpoint, which is also influenced by the peakto-sample distance, which is why this is also controlled to a constant distance value and adjusted accordingly in the case of height fluctuations.In order to generate an electron beam at all, a bias voltage is required, which can be set to a value of up to 100 V with the existing system.
Since the focus is on manufacturing minimum structure widths and the penetration depth of the Fowler-Nordheim emission current is limited, it is important at this point to use particularly homogeneous resist layers with low surface roughness and, especially, a thin resist layer with a thickness of 5-20 nm [21].The line dose (LD) with which the structures are manufactured and which also largely determines the generation of positive or negative tone is calculated by the emission current I e and the movement velocity v [45]: With the use of active cantilevers, it is therefore possible to fabricate nanostructures and inspect the surface properties several times with one and the same cantilever.In order to minimize tip wear, long-life diamond tips are used, which are commercially available, as this is particularly important for applications in large measuring ranges.The tip radius is in the order of < 25 nm (see figure 5).

Characterization of the NFM-100
In order to analyze the performance and the influences of the nanopositioning system used for large area atomic force microscopy measurements as well as fabrication of long range nanostructures, this section presents various measurements regarding the trajectory deviation of the machine slider in static and dynamic mode, whose deviations of the given trajectory can have a direct effect on the measurement and/or fabrication results of the tip-based system.Different parameters of the NFM-100 are varied and analyzed with respect to the position values in x-, y-and φ z -direction.

Static mode
To investigate the positioning behavior in static operation, the position noise of the machine table is first considered with a sampling frequency of 10 kHz for a duration of 10 s in the xand y-direction in the coordinate center in the activated controlled state, as well as in the deactivated state.In the latter case, the machine table is deactivated, i.e. the aerostatic guide elements are switched off and the table rests directly on the base made of natural hard stone.The slider can be regarded as practically mechanically stabilized.Figure 6 shows the recorded position noise for both cases at the center point of the NFM-100.
The maximum deviation (peak-to-valley) within the measurement duration of 10 s in the activated state is 1.92 nm in the x-direction and 2.75 nm in the y-direction, while 2.03 nm was determined in the x-direction and 3.64 nm in the y-direction in the deactivated state.The standard deviations (1σ) of the various recorded measured values are listed in table 1.As can be seen in table 1, the values meet the requirement for an extremely low position noise of well below 0.5 nm, especially in the controlled state, which is necessary for precise local AFM measurements.
Nevertheless, the position noise σ y shows minimally higher values than σ x in both the activated and deactivated mode, which can be attributed to the coordinate transformation.It can also be seen that the position noise σ x and σ y is lower in the activated state than in the deactivated state.This can be attributed to effects such as creep, which influence the position values of the interferometers.
The angular noise σ φz is slightly higher in the controlled state than in the uncontrolled, deactivated state.In the activated state of the machine, there is no mechanical rotation lock for φ z , which must therefore be actively controlled to zero by the NFM-100 controller, which obviously results in higher σ φz values.
The magnitudes of the position noise in the x-, y-and φ zdirections in the activated and controlled state confirm the suitability for sub-10 nm-fabrication processes within the range of motion [28].

Dynamic mode
In addition to the static behavior of the planar nanopositioning machine, the dynamic behavior is particularly important for high-quality nanofabrication.For this reason, the trajectory deviations at different movement velocities are now being analyzed.For this purpose, motion scenarios such as linear motion in a specific coordinate direction are implemented and analyzed.In particular, the lateral path deviations are a quality feature of how the machine can follow the specified trajectory.
The maximum positioning velocity of the NFM-100 is 20 mm s −1 [28].For this reason, the maximum trajectory deviation is analyzed for straight-line movement and in the velocity range of 0.1-20 mm s −1 .
For this purpose, linear movements are carried out over a length of 100 mm and the recorded position data is shown in figure 7(top).The angular deviation is also recorded and analyzed during the x-movement of the table over the entire length of 100 mm (figure 7 (bottom)).
The graphs show that the deviation of the given trajectory increases with increasing movement velocities.Nevertheless, the maximum trajectory deviation perpendicular to the movement direction at the maximum movement velocity of v = 20 mm s −1 is less than 5.5 nm (see table 2).This proves the suitability of the NFM-100 for high-precision linear movements.The maximum angular deviation of the maximum velocity is below 700 nrad (1.4 ′ ), which is also still a very good value.The calculated RMSE values for the trajectory and angular deviation are summarized in table 2. The deviations from the predefined trajectory increase with increasing movement speed, especially at the beginning of the drive.This can be attributed to effects of acceleration at the start of the movement.
Furthermore, circular movements with a diameter of 80 mm are carried out in order to be able to assess the path deviations up to the maximum speed in circular scenarios.Figure 8(above) shows the path deviation of the circular path movement for one revolution.
The angular deviation over the circular position is also shown (figure 8  radius and angular deviations at different movement speeds, which clearly show that the deviation for all position values (x,y,φ z ) increases with increasing movement velocities (see table 3).The RMSE at an r = 40 mm and the maximum velocity of 20 mm s −1 is 7.27 nm.The maximum angular deviation is 689 nrad.

(bottom)). The different graphs show the
The measured values presented in the static and dynamic mode show that the NFM-100 meets the requirements of high-precision technology even at very high speeds.Even if the maximum movement velocity is for now not suitable for tip-based measuring and/or writing systems, other systems based on other alternative methods such as DLW could cope with these velocity ranges.

Results
Through the use active microcantilevers, it is possible to simple switch between scanning and fabrication mode.First,  the focus will be on large area AFM analysis and their repeatability.Then, nanofabrication in microscopic as well as macroscopic areas will be shown due to the use of the combined tip-based system and the NFM-100.After the structuring step, the manufactured nanostructures are observed and analysed.

Long range AFM scans over 100 mm
The application of the combined NFM-100 and AFM system in a real scenario is the quality control for arbitrary periodic structures such as scales, diffraction gratings, metamaterials on long ranges, or large area scans through several parallel scan lines, as could be shown for example in [46][47][48][49].
To demonstrate macroscopic line scans with the NFM-100 in combination with the AFM system, a measurement is carried out on a periodic grating utilizing the full movement range of 100 mm to overcome the usual measuring range limitations of conventional tip-based systems several times.A commercially available length scale [50] with a pitch of 100 µm and a structure height of 120 nm serves as an test object for this investigation.The measurement object used is initially measured with a movement velocity of 200 µ ms −1 .Figure 9 (top) shows the complete scan line of the measured sample and figure 9(bottom) a section of the scan line with a length of 0.5 mm.A scan time of 500 s is required for this measurement, which can be further improved in the future, for example by using high-frequency microcantilevers and adapting the control system.
The mean period is determined using the centre of gravity (COG) method presented in [51], which has already been investigated and successfully applied to previously investigated samples and associated measurement series in [49].In an investigation of various methods for determining grid periods, the COG method was found to be an effective algorithm [49].With this method, the centres of gravity of the positive and negative profile areas of a threshold value are used to evaluate the division.A total of 1000 divisions with an average period of 99.9512 µm ± 8.6 nm and an average height of 120.2 nm ± 2.8 nm were measured over the entire scan length.
This investigation demonstrates the ability of the NFM-100 to provide long range and high resolution measurement at high measuring velocities (200 µ ms −1 ).Compared to conventional AFM systems, the range of motion in combination with the NFM-100 is larger by a factor of 10 4 .
Furthermore, the repeatability in the scanning mode by combining the planar nanopositioning machine with the tipbased system is also investigated and presented.Therefore, the sample [50] with a pitch of 100 µm and a step height of 120 nm, which was already used in the previous section (see figure 9) to demonstrate repeated line scans over a total length of 100 mm, is used for this investigation.The measurements are repeated ten times with a velocity of 100 µ ms −1 and are shown in figure 10.
The mean height of the sample measured results in a value of 120.7 nm ± 0.6 nm (k = 1) and with a mean pitch of Figure 9. Line scan over a total length of 100 mm (top) and a section of this line scan with a length of 0.5 mm (bottom).The x-and y-movement is realized by the machine table, while the movement in z-direction is carried out by the tip-based system.The movement speed is 200 µ ms −1 .
Figure 10.Overview of the mean distances and mean heights of the respective measurement series (based on [35]).99.974 µm ± 29 nm (k = 1).For this investigation with a movement speed of 100 µ ms −1 and a total length of 100 mm, the path deviation of the NFM-100 is less then 2 nm.As the deviations of the mean pitch (29 nm) are significantly greater, the path deviations can be neglected.
It could be demonstrated that repeatable results in the nmrange can be achieved with the combination of AFM and NFM-100.With a total length of 100 mm, the average pitch is 99.974 µm with a small deviation < 30 nm.Error influences that contribute to deviations are drift and thermal expansion of the sample.
This type of measurement can be used very well for proofing the periodicity of samples and as a tool for detecting defects over large areas by combining the NFM-100 and AFM.

Nanomanufacturing in microscopic areas
In most polymer-based resists, which are used for nanofabrication, the cross-linked macromolecules achieve a structure size between 5-10 nm, which are not suitable for the fabrication of structure sizes below 10 nm.In order to be able to produce the smallest possible line widths in the range of sub-5 nm, it is particularly necessary to use the thinnest possible resist layer (<20 nm) as well as especially stable resists.Even the smallest changes at the molecular level in the resist layer can have a major impact on the manufacturing process.Especially for nanofabrication, the broad use of calixarenes is conceivable in the future years, since a good resistance to plasma etching processes as well as a high heat resistance and chemical stability could be shown [21,52].By using calixarenes, stable surfaces can be generated with structural resolutions below 5 nm [45,53].
The following section focusses on nanofabrication with the thinnest possible line widths.After carrying out dose tests with varying parameters (bias voltage, current, velocity), settings are selected with which a small line width < 50 nm can be generated.
After determining the most suitable machine settings, the piezo scanning unit (x, y, z) of the SPL system was used to manufacture ten lines each with a pitch of 100 and 200 nm on a calixarene-coated silicon substrate.After this fabrication step, an AFM image was recorded, which is shown in figure 11.The  according height profile of the fabricated structures is shown in figure 12.With a line depth of 5.7 nm ± 0.47 nm (k = 1), a line width of 67.5 nm ± 6.2 nm (k = 1) and a pitch of 200.7 nm ± 5.4 nm (k = 1) for the ten lines with a preset distance of 200 nm, the structures generated show a high degree of homogeneity.For the line field with a distance of 100 nm, the pitch is 101.5 nm ± 7.8 nm (k = 1), the line depth is 4.6 nm ± 0.5 nm (k = 1) and the line width is 36.5 nm ± 3.6 nm (k = 1).In a comparison of the two line fields with 100 nm and 200 nm pitch, both were generated with a slight deviation for the pitch.Nevertheless, it is that the line width and depth vary, which can probably be attributed to the convolution effect [45].This means that the geometry of the measuring tip broadens or narrows the real topography.

Nanomanufacturing in macroscopic areas (1 mm)
By combining high-precision nanopositioning and nanomeasuring technology with tip-based lithography, the positioning accuracy, which is characterized in particular by low positioning noise and high trajectory fidelity, can be transferred directly to nanofabrication.The aim is to extend the previous small-area precision in the tip-based fabrication of nanostructures to macroscopic areas.
In the following, the structuring capability of the NFM-100 and the SPL system over even larger areas will be demonstrated and analyzed.For this purpose, a grating with ten lines and a pitch of 1 µm is fabricated over a respective length of 1 mm.In this case, the microcantilever was in a fixed position in x-and y-direction, while only moving in z-direction.The slider of the NFM-100 serves the movement in x-and ydirection.An AFM image with a section of 8 µm × 10 µm is shown in figure 13.
In order to be able to evaluate the line width, line depth and pitch over a length of 1000 µm, additional line scans at seven different positions along the total length were performed transverse to the writing direction and are shown in figure 14.An average line width of 60.7 nm ± 19.46 nm (k = 1) is achieved.The average line depth is 2.69 nm ± 0.74 nm (k = 1).The average pitch is 1.0036 µm ± 21.5 nm (k = 1).The relatively high deviation of the line width can be explained by various influences.These include the fluctuations in resist thickness over large areas used, which can occur when generating layer thicknesses below 20 nm and have to be investigated further, to achieve high homogeneity over macroscopic areas.
Furthermore, deviations can be caused by particles contained in the resist as well as impurities on the resist/substrate surface.Also it can be expected that the tip shape will change over the entire processing length of over 10 mm due to adhering residues, i.e. particles can adhere to the cantilever, but can also detach again during the entire processing time, which affects the consistency of the structures produced.In the scanning mode the adhering particles can narrow or widen the topography through the convolution effect [45].The almost absence of tip wear of the used diamond-tips was confirmed through SEM images in [35].13 (left) at seven different positions in the y-direction.The measuring velocity was 1 µ ms −1 .An offset in the z-direction has been added for better visualization.

Conclusion and outlook
In this contribution, the synergy of a planar nanopositioning machine with tip-based nanometrology and highly localised nanofabrication has been demonstrated, whereby the usual limited working range of tip-based AFM/SPL technology can be extended to macroscopic dimensions (≫ mm).
The new combined system is suitable for small-area inspection, as interesting areas on macroscopic samples can be targeted and positioned by the NFM-100 and then micro-/ nanoscopic detailed images can be recorded by the AFM system.This was successfully demonstrated, for example, in [54,55].&percentage;This approach can additionally be used because large-area AFM measurements are not possible for reasons of time alone.The characterisation of nanostructures on a wafer-based on the NFM-100 with many small, locally distributed but nanometre-precise scans appears to be a much more sensible application in the future [35].
Furthermore, by combining the highly efficient AFM system with the planar nanopositioning machine, AFM measurements up to the maximum range of motion over a length of 100 mm have been demonstrated and analyzed.The small deviations of less than 30 nm regarding repeated pitch measurements over the full movement range demonstrate the suitability of the combination of tip-based measuring technology and nanopositioning and nanomeasuring technology.In addition, due to the use of active microcantilevers and corresponding option for simple switching to SPL mode, through investigations and further optimisation steps, line widths below 40 nm were generated by the tip-based system.Minimisation down to the sub-10 nm range seems possible with further optimisation of various influencing variables [45].The combination of nanopositioning technology and SPL enables large-area structuring in particular, in which the x-ydeviation from the specified path is less than 1 nm at the applicable patterning velocities.In addition, the machine table can be used to create any desired and, above all, flexible shapes of nanostructures.It has been shown that nanostructures in form of a grating can be produced over a total length of 10 mm with minimal deviations in the line distance.
In the future, further contributions regarding pattern transfer into the used substrate will be shown.In [56], it could be shown, that with the use of reactive ion etching, pattern transfer of such nanostructures in calixarene-resist is possible.The fact that silicon dioxide is generated on the surface of the silicon substrate during FE-SPL means that this can be used in addition to the modified resist for pattern transfer.
In order to overcome the remaining discrepancy between the generation of nm-structures and structuring speeds, laserbased manufacturing processes can be combined with the SPL process to generate microstructures in the mm-range in a short time.By using NIL, the micro-and nanostructures produced in this way can be multiplied in a short time [56].Due to the high-precision positioning of the NFM-100, a large number of small-area nanostructures can be generated over the entire movement range of 100 mm in diameter and new approaches to mix-and-match lithography can be developed and applied in the future [35,56].
In addition, high-frequency cantilevers can contribute to shorter measuring times due to their smaller dimensions [57] and the use of multi-cantilever arrays [58], which can contribute to shorter measuring/fabrication times.
The NFM-100 can also be equipped with various tools for surface measurement and structuring.By further combining laser-based and optomechanical manufacturing processes with the NFM-100, structures can be analyzed, fabricated and transferred to large surfaces in the shortest possible time.The use of different tools for a combined structuring of the sample is possible with an appropriate tool changing system with high reproducibility, for which initial approaches already exist [59,60].The presented approach could also be applied to positioning systems even larger travel ranges and 6D capabilities as are currently in development [61].These can extend the scope of application for alignment problems or macroscopicly 3Dshaped surfaces.

Figure 1 .
Figure 1.Sideview of the used combined setup of planar nanomeasuring and positioning machine and tip-based system.

Figure 2 .
Figure 2. Top-view of the direct drive system (left) and the interferometric setup (right) of the NFM-100.

Figure 3 .
Figure 3. Working principle of the electromagnetic direct drive.

Figure 4 .
Figure 4. Illustration of the used active microcantilever.The cantilever has a length of 350 µm, a width of 150 µm and a thickness of 5 µm.A thermomechanical actuator is used for oscillation (coloured in orange) and a Wheatstone-bridge is used to detect the deflection of the cantilever at the clamping point (coloured in green).The measuring/fabrication tip is placed at the free end of the cantilever[35,44].

Figure 5 .
Figure 5. Scanning electron microscope (SEM) image of an active microcantilever with diamond tip.Commercially available from the company nano analytik GmbH [44].

Figure 6 .
Figure 6.x-and y-position values of the length interferometers in the controlled, activated (red) and deactivated (blue) state, recorded with a sampling frequency of 10 kHz.

Figure 7 .
Figure 7. Trajectory and associated angular deviation (bottom) during a linear movement over a length of 100 mm at different movement velocities.

Table 2 .
Overview of the RMSE values of a linear movement over 100 mm and different movement velocities.

Figure 8 .
Figure 8. Trajectory deviation (top) and associated angular deviation (bottom) during a circular movement with a radius of 40 mm at different movement velocities.

Figure 11 .
Figure 11.AFM image of FESPL-generated structures with a line spacing of 200 nm and 100 nm.The nanostructuring is carried out with a bias voltage of 50 V and a writing speed of 1.5 µ ms −1 .The current is regulated to a value of 9 pA, which results in a dose of 60 nC cm −1 .

Figure 12 .
Figure 12.Height profile of the 20 structures generated with a pitch of 200 nm and 100 nm from figure 9 (y = 2.5 µm).

Figure 13 .
Figure 13.Sketch of the fabricated nanostructures over a length of 1 mm each with marked corresponding line profiles at different locations and corresponding AFM image of a of these fabricated structures with a pitch of 1 µm.The fabrication velocity was 10 µ ms −1 .The current is regulated to a value of 200 pA, which results in a dose of 20 nC cm −1 .

Figure 14 .
Figure 14.Comparison of the line profiles from figure 13 (left) at seven different positions in the y-direction.The measuring velocity was 1 µ ms −1 .An offset in the z-direction has been added for better visualization.

Table 1 .
[28]erent values of the position noise in the closed loop of the NFM-100 as well as in the deactivated mode for a duration of 10 s and a sampling frequency of 10 kHz (see figure6)[28].

Table 3 .
Overview of the path deviations and the angular deviations at different velocities.