Scanning probe microscopy system and method for mapping nanostructures on a sample surface of a sample.

Abstract

The invention is directed at a scanning probe microscopy system and method for mapping nanostructures on a sample surface. The system comprises a scan head, a sample carrier, a probe including a cantilever and probe tip, and a probe position sensor. The system further comprises scanning motion actuators and a Z-level adjustment actuator, and a controller. The controller is configured for providing a control signal to the adjustment actuator for controlling operation of the adjustment actuator. The controller uses a Z-level signal indicative of said position of the scan head relative to the sample surface in the Z-direction for providing a topography signal indicative of a local height of the substrate surface. The controller is also configured for providing a correction signal for correcting the topography signal for a response delay in the Z-level signal caused by a response of the adjustment actuator to the control signal. The correction signal depends on the current probe tip sensor signal.

Description

[0001]Title: Scanning probe microscopy system and method for mapping nanostructures on a sample surface of a sample. Field of the invention The present invention is directed at a scanning probe microscopy system for mapping nanostructures on a sample surface of a sample, the scanning probe microscopy system comprising scan head including a sample carrier for supporting the substrate, a probe including a cantilever and a probe tip, and a probe position sensor arranged for providing a probe tip sensor signal indicative of a position of a probe tip relative to a setpoint reference position, wherein the scanning probe microscopy system further comprises one or more scanning motion actuators for enabling a scanning motion of the probe relative to the sample parallel to the sample surface, and a Z-level adjustment actuator arranged for adjusting a position of the scan head in a Z- direction, wherein the Z-direction is a direction transverse to the sample surface. The present invention is further directed at a method for mapping nanostructures on a sample surface of a sample. Background Although the present document includes references to various other documents, no admission is made that any reference constitutes prior art. The discussion of references refers to their content as presented therein, and does not acknowledge nor confirm the accuracy or pertinency thereof. It will be understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art in any country. Typically, in amplitude modulation (AM) mode, topographic mapping of nanostructures requires to obtain accurate Z-level measurements of the surface topography at many scan positions along a scan trajectory. The Z-level is thereby very accurately determined using a feedback loop, which adapts the Z-position of the probe tip in order to maintain an equilibrium orientation thereof. This equilibrium orientation is typically referred to as the setpoint reference position, because it is a predetermined reference position that is set in the system as an adjustable system parameter. The orientation of the probe tip can be monitored by a probe position sensor, for example an optical beam deflector. A controller of the system receives the current probe tip orientation, or at least the deviation thereof from the setpoint reference position, as a sensor signal from the probe position sensor. A control signal that is dependent on this deviation, is provided to an adjustment actuator for adjusting the Z-position of the probe or scan head to which it is attached, in order to reestablish the position of the probe tip to adopt the setpoint reference position. The Z- level measurement that will provide the topography signal is then based on a reading of the Z-position set via the adjustment actuator. This can often accurately be determined from the control signal used to control the adjustment actuator, although alternatively it may also be obtained from an additional Z-level sensor measuring the Z-level of the probe. If it is taken from the control signal, the system may comprise an internal circuit that converts the control signals to Z-values. Both these implementations are considered to be suitable for providing a Z-level signal in the present disclosure. This method works well in laboratory environments, where throughput of the number of topographic images is not a limiting factor (i.e. it does not matter whether the imaging takes place in a slow pace, whereas accuracy of the image is more important than speed of obtaining the image). However, in commercial or industrial environments, the feedback loop limits the throughput of the imaging process too much. A low yield of images per unit of time results in a low yield of wafer inspection, for example in a semiconductor manufacturing process. Summary of the invention It is an object of the present invention to overcome the above disadvantages of the prior art, and to provide a scanning probe microscopy system and method of operating it, which enables a high yield of images per unit of time without diminishing image quality. To this end, there is provided herewith a scanning probe microscopy system for mapping nanostructures on a sample surface of a sample. The scanning probe microscopy system comprises a scan head including a sample carrier for supporting the substrate, a probe including a cantilever and a probe tip, and a probe position sensor arranged for providing a probe tip sensor signal indicative of a position of a probe tip relative to a setpoint reference position. The scanning probe microscopy system further comprises one or more scanning motion actuators. These scanning motion actuators enable a scanning motion of the probe relative to the sample parallel to the sample surface. This motion may be achieved by moving the whole scan head including the probe, or only the probe carrier or probe itself. A Z-level adjustment actuator is arranged for adjusting a position of the scan head relative to the sample surface in a Z-direction, wherein the Z-direction is a direction transverse to the sample surface. For enabling mapping of the nanostructures, the device further comprises a controller which is arranged for receiving during scanning a current probe tip sensor signal from the probe position sensor indicative of a current position of the probe tip relative to the setpoint reference position. Based on the current probe tip sensor signal, the controller is further configured for providing a control signal to the adjustment actuator for controlling operation of the adjustment actuator for adjusting the position of the scan head such as to reestablish the position of the probe tip to adopt the setpoint reference position. The system is further configured for providing a Z-level signal indicative of said position of the scan head relative to the sample surface in the Z-direction, wherein the controller is configured for providing, based on the Z- level signal, a topography signal indicative of a local height of the substrate surface. For providing the topography signal, the controller is further configured for providing a correction signal for correcting the topography signal for a response delay in the Z- level signal caused by a response of the adjustment actuator to the control signal, wherein the correction signal is dependent on the current probe tip sensor signal. In accordance with the present invention, the current probe tip sensor signal is not only used within the feedback loop in order to obtain the Z-level measurements, but it is thereafter used again in order correct the Z-level measurements for inconsistencies caused by slow response of the adjustment actuator. Defining the term ‘time constant’ to be the time representative of the speed with which a particular system can respond to a change, it may be appreciated that the probe itself has a time constant that is mainly determined by the response of the cantilever and the response of the probe tip. Thus, during scanning, the probe tip will respond very quickly to a change in Z-level on the sample surface compared to the response of the feedback loop in order to adjust the Z-level, because characteristic response of the feedback loop is determined amongst others by how quickly the adjustment actuator (which is typically – but not limited to – a piezo type element) can adjust the Z- position of the scan head above the surface in order to reestablish the setpoint reference position. The adjustment actuator is a slow response system, and hence in terms of throughput provides a bottleneck. When measuring in order to provide a topographic signal, in conventional systems it is necessary to lower the scan speed in order to allow the adjustment actuator to respond to the change in Z-level of the sample surface, such that the Z-level signal correctly represents the actual Z-level of the sample at the scan position. If this is not done, and the Z-level signal is obtained too fast, the adjustment actuator would not have had enough time to adjust the Z- position of the scan head (or probe) and the Z-level signal will deviate from the real Z- level of the surface. This is typically encountered when the scan rate, i.e. indicative of the scan velocity with which the scanning is performed, is set too fast. The resulting topographic signal will show many errors caused by the system’s inability to quickly respond to changes in Z-level. Typical also in this case, is that such errors are dependent on the direction of motion of the probe relative to the sample. In the present invention, the fast responsive probe tip sensor is used in order to provide a correction signal for the topographic signal. Therefore, any deviations caused by the slow response of the adjustment actuator to a change in Z- position, can be corrected retrospectively on the basis of the current probe tip sensor signal coming from the probe tip sensor. Such correction can be performed already during scanning as a subsequent step following the obtaining of the Z-level signal by the controller, but may also be performed in a post-processing procedure if the correction signal has been stored along with the other measurement data. The fast responsive current probe tip sensor signal provides the actual amplitude and phase data of the probe tip during scanning, and thus a deviation between the real Z-level and the measured Z-level from the Z-level signal caused by a lag of the system can effectively be corrected using the fast responsive amplitude data obtained from the current probe tip sensor signal. For completeness it is to be understood, as already explained above, that the Z-level signal may be obtained from a reading of the Z-position set via the adjustment actuator, and thus can accurately be determined from the control signal used to control the adjustment actuator. However, alternatively it may also be obtained from an additional Z-level sensor measuring the Z-level of the probe. If it is taken from the control signal, the system may comprise an internal circuit that converts the control signals to Z-values. Both these implementations are considered to be suitable for providing a Z-level signal in the present disclosure. The term Z-level sensor in connection with the present invention is to be interpreted broadly. The Z- level sensor can be implemented in many different manners, that may also be dependent on the type of scanning probe microscopy system used. For example, the Z- level sensor may be a real sensor measuring the Z-level of the probe or a relevant part of the scan head relative to the sample surface. For example, such as sensor can be capacitive or optical. In some cases, the Z-level sensor may measure the Z-position of the probe or the probe carrier in relation to the sample surface. In some cases, a Z- position of a probe or probe carrier in relation to the metrology frame of the system may be measured instead. In some cases, especially for high throughput in an industrial setting, the system may include multiple scan heads, each equipped with at least one probe. In that case, each scan head may include a Z-level sensor. In particular embodiments, the scan heads of such a high throughput SPM system may be separate entities that may be freely placed onto a reference grid surface at will, thereby providing miniature atomic force microscopes, for example. Each of these may include a Z-level sensor that determines the relative Z-level in relation to the sample surface. Another possibility is thus that the Z-level is directly obtained from a signal that drives the adjustment actuator. For example, a signal that drives the piezo type element. Furthermore, the SPM system or the or each scan head (e.g. in a multi scan head system) may alternatively also include an internal circuit that converts the control signals to Z-values. Some SPM systems comprise a single scan head attached to a metrology frame, including at least one probe. Here also the Z-level sensor may measure the Z-position of the probe or the probe carrier in relation to the sample surface; or alternatively it may measure a Z-position of a probe or probe carrier in relation to the metrology frame of the system. All these implementations are considered to be either suitable for (or configured for) obtaining a Z-level signal or include Z-level sensors, in the present disclosure. Furthermore, it is also to be understood that the term ‘current probe tip sensor signal’ may be dependent on the measuring mode of the SPM system that is being applied. If the SPM system operates in tapping mode, the current probe tip sensor signal will include the amplitude and phase of the probe tip periodic motion and in this case, the amplitude will be used in order to correct the topography signal in accordance with the present invention. However, if the SPM system operates in contact mode, the current probe tip sensor signal includes the deflection of the probe tip, and the deflection will be used in order to correct the topography signal in accordance with the present invention. More broadly, therefore, the invention is directed at the concept of correcting the topography signal (affected by slow response of the feedback loop) using the fast responsive current probe tip sensor signal. In some embodiments, the scanning probe microscopy system further comprises a first demodulator filter, wherein the first demodulator filter is connected to receive the probe tip sensor signal from the probe position sensor, wherein the system further comprises a second filter, the second filter being connected to receive the Z-level signal, wherein the first demodulator filter and the second filter are identical such as to match a delay in the current probe tip sensor signal caused by the first demodulator filter with an equivalent delay in the Z-level signal caused by the second filter. Here, also the relatively small lag of the probe system (including probe and filter) itself is taken into account in the correction of the topographic signal. The probe tip sensor signal, typically obtained using an optical beam deflection type detector arrangement, is filtered in these embodiments using a demodulation filter in order to yield an amplitude and phase therefrom. The demodulation filter has a characteristic response time, which also leads to a minor time delay in the receipt of the current probe tip sensor signal. In these embodiments, correction of the topographic signal further benefits from correcting for this delay as well. In the present embodiments, this is implemented by the system comprising a second filter that is connected to receive the Z-level signal, and which is identical. The Z-level positions associated with the current XY-positions, which are read in this manner, are thereby slightly delayed in order to correspond to the XY-positions associated with the amplitude or phase signals from the current probe tip position sensor signal used for correction. In some embodiments, the system further comprises a further filter connected to receive the Z-level signal, wherein the further filter is configured for modelling a response of the cantilever, for filtering the Z-level signal such as to match a delay in the current probe tip sensor signal caused by dynamics of the cantilever with an equivalent delay in the Z-level signal caused by the further filter. As may be appreciated, also the probe itself – i.e. the cantilever and the probe tip – is characterized by a time constant indicative of its response. Therefore, additional benefit is achieved when also this potential lag is taken into account. The recited ‘further’ filter may therefore advantageously include (or be provided by) a filter that takes into account the cantilever dynamics or probe dynamics. In one embodiment, the further filter is first order low pass filter having a bandwidth equivalent to a bandwidth of the probe. Cantilever dynamics can be modeled as a first order lowpass filter, whose bandwidth is at resonance frequency of probe divided by two times the effective Q-factor of probe in contact. In other words, this means the cantilever cannot follow sharp topography and high frequency vibrations beyond its bandwidth so tip- sample distance will be underestimated by the amplitude based on the cantilever bandwidth. In the present embodiments, this effect is also taken into account in order to match the lag of the Z-level signal with that of the probe. In some embodiments, the second filter and the further filter are integrated in a Z-level filter, for matching a delay in the current probe tip sensor signal caused by both of the dynamics of the cantilever and the first demodulation filter with an equivalent delay in the Z-level signal caused by the Z-level filter. A single filter (or system of filters) can be applied to take both the demodulation filter and the cantilever dynamics into account. This may be embodied as a digital filter or analog filter. In some embodiments, the controller is configured for determining the correction signal from the current probe tip sensor signal during scanning of the probe relative to the substrate surface, such as to perform a real-time correction of the topography signal. With the above filters, the lag of the current probe tip sensor signal and the Z-level signal are well matched, enabling real time correction of the topography signal during scanning. The resulting topography signal may thus be shown real-time. This has many advantages. For example, this allows instantaneous verification of semiconductor device topography during a lithographic manufacturing process, at high throughput. In other or further embodiments, during said scanning at a plurality of scan positions along a scan trajectory of the probe tip relative to the sample surface the controller obtains a topography signal measurement and a current probe tip sensor signal measurement at each scan position, the system further comprising or being connected to a data storage, wherein the system is configured for storing, for each scan position and associated therewith, the topography signal measurement and the current probe tip sensor signal measurement in the data storage. Naturally, this provides the advantage of making this data available after completion of the scan for later use. It also allows, in accordance with some of these embodiments, the controller to correct the topography signal measurements based on the associated current probe tip sensor signal measurements for each scan position stored in the data storage. In accordance with a second aspect of the present invention, there is provided a method mapping nanostructures on a sample surface of a sample using a scanning probe microscopy system, the scanning probe microscopy system comprising scan head including a sample carrier for supporting the substrate, a probe including a cantilever and a probe tip, a probe position sensor arranged for providing a probe tip sensor signal indicative of a position of a probe tip relative to an setpoint reference position, one or more scanning motion actuators for enabling scanning of the probe relative to the sample parallel to the sample surface, a Z-level adjustment actuator for adjusting a position of the scan head in a Z-direction, wherein the system is configured for providing a Z-level signal indicative of said position of the scan head in the Z- direction, wherein the Z-direction is a direction transverse to the sample surface; wherein the method comprises the steps of: scanning, using the one or more scanning motion actuators, the probe tip relative to the sample surface; receiving, by a controller during the scanning, a current probe tip sensor signal from the probe position sensor indicative of a current position of the probe tip relative to the setpoint reference position; providing, by the controller based on the current probe tip sensor signal, a control signal to the adjustment actuator, and adjusting by the adjustment actuator based on the control signal the position of the scan head such as to reestablish the position of the probe tip to adopt the setpoint reference position; obtaining, by the controller, the Z-level signal and using the Z-level signal for providing a topography signal indicative of a local height of the substrate surface; wherein the step of providing the topography signal comprises providing, by the controller, a correction signal and correcting the topography signal using the control signal for a response delay in the Z-level signal caused by a response of the adjustment actuator to the control signal, wherein the correction signal is dependent on the current probe tip sensor signal. Brief description of the drawings The invention will further be elucidated by description of some specific embodiments thereof, making reference to the attached drawings. The detailed description provides examples of possible implementations of the invention, but is not to be regarded as describing the only embodiments falling under the scope. The scope of the invention is defined in the claims, and the description is to be regarded as illustrative without being restrictive on the invention. In the drawings: Figure 1 schematically illustrates a feedback loop of a scanning probe microscopy system wherein the principles of the present invention may be applied; Figures 2A and 2B schematically provide a front view and side view of a conventional position sensitive detector; Figure 3 illustrates an alternative scanning probe microscopy system wherein the principles of the present invention may be applied; Figure 4 schematically and functionally illustrates a Z-position feedback loop; Figure 5 shows an exemplary correction method based on the principles of the present invention. Detailed description Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as subsequent to another step, it can directly follow said other step or one or more intermediate steps may be carried out before carrying out the particular step, unless specified otherwise. Likewise it will be understood that when a connection between structures or components is described, this connection may be established directly or through intermediate structures or components unless specified otherwise. The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and / or cross-section illustrations of possibly idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms as well as derivatives thereof should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation unless stated otherwise. In figure 1, the principles of a scanning probe microscopy system 1 are schematically illustrated. The scanning probe microscopy system 1 comprises a sample stage 3 onto which a substrate sample 4 may be placed. A first actuator system 6 enables to accurately move the sample stage 3 in the X and Y directions as illustrated in figure 1. A piezo type actuator system 8 enables to accurately move the sample stage 3 in the vertical direction Z as illustrated in the figure. The actuator system 6 and the piezo type actuator 8 are controlled by controller electronics 10. In use a probe 17, comprising a cantilever 18 and a probe tip 19, is scanned relative to the surface of substrate 4 while the probe tip 19 is brought in continuous or intermittent contact with the surface of the substrate 4. The scanning in the X and Y direction is performed by the SPM system using controller 10 and actuator system 6. The probe tip 19 is brought in contact with the sample surface 4 by operating the piezo type actuator system 8, for moving the substrate 4 in the Z-direction in order to decrease the distance between the probe tip 19 and the surface. While the substrate 4 and the probe tip 19 move relative to each other in the X and Y directions, the probe tip 19 may optionally be vibrated for enabling said intermittent contact with the surface. Typically, the height of the substrate surface at the position where the probe tip 19 touches the substrate 4 is very accurately measured by the SPM system 1. By performing such a highly accurate height measurement at each location where the probe tip 19 touches the substrate 4, a map of the topography of the surface of substrate 4 may be provided on which surface structures are visible. To determine this height accurately, the cantilever deflection of cantilever 18 needs to be determined with high precision, in order to enable very accurate and exact determination of the Z location of the apex of probe tip 19 when it touches the surface of substrate 4. To measure this cantilever deflection, an optical beam deflection (OBD) arrangement is applied. For this, on the back side of the probe tip 19, a specular reflective surface 20 such as a mirror surface may be located. This surface 20 is illuminated with an optical beam 25 from a light source 22, typically a laser, which optical beam 25 is impinged on the specular reflective surface 20. A reflected beam 27 emits from the specular reflective surface 20 towards an optical sensor 30. The optical sensor 30 enables to exactly determine the position of a light spot 28 that is formed by the reflected beam 27 on the surface of the optical sensor 30. The detector electronics 15 receives the sensor signal coming from optical sensor 30 and performed an analysis to determine the position of the light spot 28. Figures 2A and 2B respectively provide a front view of the optical sensor 30, and a side view of the optical beam deflection arrangement (OBD arrangement) wherein the optical sensor 30 is applied. In figure 2A, it can be seen that the optical sensor 30 consists of four optical cells 31, 32, 33 and 34. The optical cells 31-34 are arranged adjacent each other, with their edges contiguous to each other to form a cross 35 in the middle of the optical sensor 30. In figure 2B, it can be seen that the incoming beam 25 is reflected towards the optical sensor 30 providing the reflected beam 27. The divergence of the incoming beam 25 and the reflected beam 27 are exaggerated in this figure. Typically, a laser beam 25 is used for forming the light spot 28, and therefore beam divergence is very limited or even negligible. As can be seen in figure 1, the reflected beam 27 forms a light spot 28 on the surface of the optical detector 30. This light spot 28 in figure 2B is located where the reflected beam 27 impinges the surface of the optical sensor 30. In figure 2B, optical cells 33 and 34 are illustrated in side view. It further follows from figure 2B that the cantilever 18 slightly bends backwards providing a deflection angle α. This may be due to the probe tip 19 touching the surface of substrate 4 (not shown). However, as each probe comes with a slight deviation of + / - 1.5 degrees in offset deflection, the angle α in figure 2B may as well be this offset deflection. Due to the deflection angle α, the reflected beam 27 is not directed towards the center of the optical sensor 30, but for a major part is formed on cell 34. Cell 33 only receives a small part of the optical energy from reflected beam 27. Dependent on exactly how the light spot 28 is formed on the optical cells 31, 32, 33 and 34, each of the cells 31-34 receives an amount of light coming from the reflected beam 27. By comparing the magnitude of the sensor signals from each of the cells 31-34, it is possible to determine how well the light spot 28 falls onto the center of the cross 35. Here, optical cell 34 receives a lot of optical energy whereas optical cell 33 only receives a small part of the optical energy. In many conventional SPM systems 1, after each probe exchange and occasionally between scanning operations, the position of the optical sensor 30 is adjusted in order to tune the system such that light spot 28 is formed exactly in the center of cross 35. Thereafter, to measure the local height of the substrate 4 during scanning, the piezo type actuators 8 are controlled for each deflection resulting in a deviation of the light spot 28, such as to bring back the light spot 28 exactly into the center of the cross 35 of the optical sensor 30 again. Using this feedback method, the local height can be measured by registering the modifications in the Z-direction that are applied using the piezo type actuator 8. By registering how much the Z position of the sample stage has been adapted in order to bring back the position of the light spot 28 into the center 35 of the optical sensor 30, the height of the substrate 4 at this specific location is exactly known. Figure 3 illustrates an alternative scanning probe microscopy system 1, which may, for example, be used for performing high-throughput industrial scanning probe microscopy. The system 1 applies one or more miniature atomic force microscopy modules that provide scan heads 2, one of which is schematically illustrated in the figure. The scan heads 2 may be placed onto a carrier surface, which in the present example is provided by reference grid plate 16 of the system 1. The reference grid plate 16 provides a positional XY reference enabling highly accurate placement of the scan head 2 in a desired location of the grid plate 16. The system 1 may comprise a plurality of scan heads such as scan head 2, which can be place at multiple locations on the grid plate 16 in order to perform measurements on multiple sites on the surface 5 of sample 4. Sample 4 resides in a sample stage 3 that may be fixed on a metrology frame, whereas a XY scanning motion may be applied to the probe using piezo actuator 6 and a Z-position of the probe can be set by piezo type actuator 8; the actuator 8 serving as adjustment actuator for the Z-position of the probe, as referred to in descriptions of the present invention. Piezo type actuators 6 serve as scanning actuators that enable the scanning motion of the probe tip 19 across the surface 5 of the sample 4. Same reference numerals are applied across the various systems and embodiments described, where these refer to elements having a same or similar function within the whole. Because in the system 1 illustrated in figure 3 use is made of multiple scan heads 2 that can be placed freely on the grid plate 16, the scan heads 2 are preferably not attached to the system 1 using wiring, and hence any data or signal transmission is preferably performed wirelessly from the scan head 2 to the system electronics (not shown). To this end, the scan head 2 includes a wireless transmission element 12 for wireless data communication. Optionally, the scan head 2 may include a memory 11 or other data repository where desired, but this is certainly not preferred under all circumstances. Typically, namely, the scan heads 2 are small in size, such as to allow many scan heads 2 on a grid plate 16 enabling simultaneous scanning in many sites on the surface 5 of the sample 4. Remember, the system 1 of figure 3 is especially designed for it’s high throughput. As may be appreciated, the feedback loop that is schematically illustrated in figure 1, in the present invention is integrated on the scan head 2. If the scan head 2 includes a memory 11, in addition to or alternative to the use of the wireless transmission 12, data from any measurements may likewise be temporarily stored in the memory of the scan head 2 for later use or analysis. In alternative systems, the scan head 2 may be integrated in the main system, for example by being fixed to the metrology frame of the system. Although no figure shows such an implementation thereof, this is certainly an implementation that is foreseen and in which the present invention may be implemented. In such implementations, the actuators for performing the XY-scanning motion and the Z- position adjustment may for example be implemented underneath the sample 4 on the sample stage 3 (although they could as well be present on the head 2 in that case). Alternatively, it could also be the case that either one of the XY-motion actuators 6 and the Z-position adjustment actuator 8 is present underneath the sample 4 whereas the other one is present on the scan head 2 to directly move the probe 21. Furthermore, in the system 1 illustrated in figure 3, a Z-level sensor 13 is implemented. The Z-level sensor 13 cooperates with a structural element 14 in order to allow accurate determination of a Z-level to provide a Z-level signal. As mentioned already above, the application of a Z-level sensor – also on a scan head 2 as illustrated in figure 3 – is completely optional and may even not be preferred in all implementations. It is just an alternative implementation, but it may as well be implemented by analyzing the control signal provided by controller 10 to the Z-level adjustment actuator 8 to determine the present Z-level and provide a Z-level signal. Figure 4 schematically and functionally illustrates a Z-position feedback loop, similar to the feedback loops described above. As illustrated in figure 4, a setpoint reference position 50 can be set in scanning probe microscopy system 1. During scanning of the probe tip 19 across the surface 5, the probe tip 19 will encounter nanostructures such as trenches, step-ups or walls. In contact mode, these nanostructures will cause the deflection of the probe tip 19 to change. In tapping mode, the amplitude of the probe tip 19 will change under influence of the encountered nanostructures. In figure 4, reference numeral 64 indicates the actual tip-sample distance. The actual tip-sample distance 64 will change instantaneously upon encountering the nanostructure, however the cantilever dynamics 65 schematically implement in the feedback loop the response of the probe 21 to the change in actual tip-sample distance 64. Thus, the signal 66 will be the raw signal obtained from the optical sensor 30 and is indicative of the actual cantilever response to the change in tip-sample distance 64. In the SPM system 1 in tapping mode, this raw signal 66 will typically be filtered by demodulation filter 67 in order to derive therefrom the amplitude and phase of the probe tip 19. Therefore, in absence of the demodulator filter 67, the current probe tip sensor signal referred to in this document may be based directly on the raw signal 66 from the optical sensor 30. However, including the demodulator filter 67, the current probe tip sensor signal referred to in this document may be based on the filtered signal 54 in figure 4. In general, the current probe tip sensor signal will be referred to with reference numeral 54 (also B in figure 4). Combiner 51 is provided as a function of the controller 10 and will provide at the output thereof a control signal 55, indicative of the position of the probe tip relative to the setpoint reference position. The controller 10 will use this in order to provide a control signal to the adjustment actuator 8 for controlling operation of the adjustment actuator 8 for adjusting the position of the scan head 2 such as to reestablish the position of a probe tip 19 to adopt the setpoint reference position 50. The response of the adjustment actuator 8 to the control signal 55 is illustrated by Z- scanner dynamics filter 57 in the feedback loop of figure 4. This will yield an actual or current Z-level signal 58, indicative of the momentary Z-level of the probe tip 19 relative to the surface 5. As may be appreciated, the adjustment takes place rather slow in comparison to the cantilever response to a change in tip-sample distance. In conventional high-throughput SPM systems, this slow response provides a bottleneck to the efficiency of the system, because the scan rate must be diminished in order to allow the system to response first to the change in tip-sample distance 64, before determining a present Z-level. Otherwise, the Z-level determined will not truly be representative of the surface level, because the system would not have had enough time to adapt to the new Z-level. Thus, the feedback loop, although providing a very accurate manner of determining Z-level changes on the surface 5 during scanning, to a large extends slows down the measurement. In the present invention, the above is overcome in the manner illustrated in figure 5. The method of figure 5 may be applied ‘on-the-fly’ thus during scanning of the probe tip 19 across the surface, but it may also be applied in retrospect on measurements already stored in a memory or data repository provided that the current probe tip sensor signal (e.g. any one of signals 66, 54 or 55 from which this can be derived) has been stored as well. Figure 5 shows the cantilever dynamics 65 (illustrated as a filter) and demodulator filter 67 that were also illustrated in figure 4. The cantilever dynamics 65 is a property of the probe 21, and thus each individual probe 21 provides for its own dynamics. The demodulator filter 67 is part of the detector electronics 15 and provides the amplitude and phase signal of the probe tip 19. In principle, a significant improvement in scan rate is already achievable if the Z- level signal 58 is corrected based on the current probe tip sensor signal (e.g. any one of signals 66, 54 or 55 from which this can be derived). These signals, namely, respond to the actual tip-sample distance changes very quickly, and thereby directly enable to correct – at any given time – the Z-level signal 58 for deviations caused by lagging due to the slow response of the adjustment actuator 8. The current probe tip sensor signal provides a fast adapting probe signal indicative of a change in the tip-sample distance, whereas the Z-level signal adapts slowly to the correction signal. By correcting the Z- level signal 58 on the basis of the actual deviations indicated by the current probe tip sensor signal 54 (i.e. any one of signals 66, 54 or 55 from which this can be derived), the real current tip-sample distance is always derivable. Therefore, the topography signal can be obtained directly on the basis of these two signals. In some embodiments, the results of this correcting step are even further improved by also taking into account the (relatively small) lag caused by one or more of the cantilever response provided by the cantilever dynamics 65 and the demodulation filter response caused by demodulation filter 67. Each of these, as explained, likewise provides for a characteristic response that introduces a small lag in the current probe tip sensor signal 54 as compared to the actual tip-sample distance 64. For example, upon encountering a step-down on the surface 5 of the sample 4, the cantilever responds such that the amplitude will increase, however the rate with which this happens dependent on e.g. the material properties of the probe 21, the dimensions of the cantilever 18, and other characteristic parameters for the probe 21. Thus also the current probe tip sensor signal 54 will likely have a small lag in comparison to the actual tip-sample distance. The topographic signal can be corrected for this lag as well, by introducing a similar lag in the Z-level signal 58. If both the lag of current probe tip sensor signal 54 and Z-level signal 58 match, correcting the Z-level signal using this (in time lag ) matching current probe tip sensor signal 54 will provide the best accuracy. The present invention has been described in terms of some specific embodiments thereof. It will be appreciated that the embodiments shown in the drawings and described herein are intended for illustrated purposes only and are not by any manner or means intended to be restrictive on the invention. It is believed that the operation and construction of the present invention will be apparent from the foregoing description and drawings appended thereto. It will be clear to the skilled person that the invention is not limited to any embodiment herein described and that modifications are possible which should be considered within the scope of the appended claims. Also kinematic inversions are considered inherently disclosed and to be within the scope of the invention. Moreover, any of the components and elements of the various embodiments disclosed may be combined or may be incorporated in other embodiments where considered necessary, desired or preferred, without departing from the scope of the invention as defined in the claims. In the claims, any reference signs shall not be construed as limiting the claim. The term 'comprising' and ‘including’ when used in this description or the appended claims should not be construed in an exclusive or exhaustive sense but rather in an inclusive sense. Thus the expression ‘comprising’ as used herein does not exclude the presence of other elements or steps in addition to those listed in any claim. Expressions such as "consisting of", when used in this description or the appended claims, should be construed not as an exhaustive enumeration but rather in an inclusive sense of "at least consisting of". Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. Features that are not specifically or explicitly described or claimed may be additionally included in the structure of the invention within its scope. Any of the claimed or disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise, without departing from the claimed invention. Expressions such as: "means for ...” should be read as: "component configured for ..." or "member constructed to ..." and should be construed to include equivalents for the structures disclosed. The use of expressions like: "critical", "preferred", "especially preferred" etc. is not intended to limit the invention. Additions, deletions, and modifications within the purview of the skilled person may generally be made without departing from the scope of the invention, which is determined by the claims. The invention may be practiced otherwise then as specifically described herein, and is only limited by the appended claims.

Claims

Claims 1. Scanning probe microscopy system for mapping nanostructures on a sample surface of a sample, the scanning probe microscopy system comprising scan head including a sample carrier for supporting the substrate, a probe including a cantilever and a probe tip, and a probe position sensor arranged for providing a probe tip sensor signal indicative of a position of a probe tip relative to a setpoint reference position, wherein the scanning probe microscopy system further comprises one or more scanning motion actuators for enabling a scanning motion of the probe relative to the sample parallel to the sample surface, and a Z-level adjustment actuator arranged for adjusting a position of the scan head relative to the sample surface in a Z-direction, wherein the Z-direction is a direction transverse to the sample surface, wherein for enabling mapping of the nanostructures the device further comprises a controller, wherein the controller is arranged for receiving during scanning a current probe tip sensor signal from the probe position sensor indicative of a current position of the probe tip relative to the setpoint reference position during said scanning, wherein the controller is further configured for providing, based on the current probe tip sensor signal, a control signal to the adjustment actuator for controlling operation of the adjustment actuator for adjusting the position of the scan head such as to reestablish the position of a probe tip to adopt the setpoint reference position, wherein the system is further configured for obtaining a Z-level signal indicative of said position of the scan head relative to the sample surface in the Z- direction, and wherein the controller is configured for providing, based on the Z-level signal, a topography signal indicative of a local height of the substrate surface; wherein, for providing the topography signal, the controller is further configured for providing a correction signal for correcting the topography signal for a response delay in the Z-level signal caused by a response of the adjustment actuator to the control signal, wherein the correction signal is dependent on the current probe tip sensor signal; wherein the system further comprises a first demodulator filter, wherein the first demodulator filter is connected to receive the probe tip sensor signal from theprobe position sensor, wherein the system further comprises a second filter, the second filter being connected to receive the Z-level signal, wherein the first demodulator filter and the second filter are identical such as to match a delay in the current probe tip sensor signal caused by the first demodulator filter with an equivalent delay in the Z- level signal caused by the second filter.

2. Scanning probe microscopy system according to claim 1, further comprising a further filter connected to receive the Z-level signal, wherein the further filter is configured for modelling a response of the cantilever, for filtering the Z-level sensor such as to match a delay in the current probe tip sensor signal caused by dynamics of the cantilever with an equivalent delay in the Z-level signal caused by the further filter.

3. Scanning probe microscopy system according to claim 2, wherein the further filter is first order low pass filter having a bandwidth equivalent to a bandwidth of the probe.

4. Scanning probe microscopy system according to at least one of claims 2 or 3, wherein the second filter and the further filter are integrated in a Z-level filter, for matching a delay in the current probe tip sensor signal caused by both of the dynamics of the cantilever and the first demodulation filter with an equivalent delay in the Z- level signal caused by the Z-level filter.

5. Scanning probe microscopy system according to any one or more of the preceding claims, wherein the controller is configured for determining the correction signal from the current probe tip sensor signal during scanning of the probe relative to the substrate surface, such as to perform a real-time correction of the topography signal.

6. Scanning probe microscopy system according to any one or more of the claims 1-4, wherein during said scanning at a plurality of scan positions along a scan trajectory of the probe tip relative to the sample surface the controller obtains a topography signal measurement and a current probe tip sensor signal measurement at each scan position, the system further comprising or being connected to a data storage,wherein the system is configured for storing, for each scan position and associated therewith, the topography signal measurement and the current probe tip sensor signal measurement in the data storage.

7. Scanning probe microscopy system according to claim 6, wherein the controller is configured for correcting the topography signal measurements based on the associated current probe tip sensor signal measurements for each scan position stored in the data storage.

8. Method mapping nanostructures on a sample surface of a sample using a scanning probe microscopy system, the scanning probe microscopy system comprising scan head including a sample carrier for supporting the substrate, a probe including a cantilever and a probe tip, a probe position sensor arranged for providing a probe tip sensor signal indicative of a position of a probe tip relative to a setpoint reference position, one or more scanning motion actuators for enabling scanning of the probe relative to the sample parallel to the sample surface, a Z-level adjustment actuator for adjusting a position of the scan head relative to the sample surface in a Z-direction, wherein the system is configured for providing a Z-level signal indicative of said position of the scan head relative to the sample surface in the Z-direction, wherein the Z-direction is a direction transverse to the sample surface; wherein the method comprises the steps of: scanning, using the one or more scanning motion actuators, the probe tip relative to the sample surface; receiving, by a controller during the scanning, a current probe tip sensor signal from the probe position sensor indicative of a current position of the probe tip relative to the setpoint reference position; providing, by the controller based on the current probe tip sensor signal, a control signal to the adjustment actuator, and adjusting by the adjustment actuator based on the control signal the position of the scan head such as to reestablish the position of the probe tip to adopt the setpoint reference position; obtaining, by the controller, the Z-level signal and using the Z-level signal for providing a topography signal indicative of a local height of the substrate surface; wherein the step of providing the topography signal comprises providing, by the controller, a correction signal and correcting the topography signal using thecontrol signal for a response delay in the Z-level signal caused by a response of the adjustment actuator to the control signal, wherein the correction signal is dependent on the current probe tip sensor signal; further comprising a step of filtering the current probe tip sensor signal from the probe position sensor using a first demodulator filter for providing at least one of an amplitude signal or a phase signal, and filtering the Z-level signal using a second filter, wherein the first demodulator filter and the second filter are identical, for matching a delay in the current probe tip sensor signal caused by the first demodulator filter with an equivalent delay in the Z-level signal caused by the second filter.

9. Method according to claim 8, wherein the correction signal is at least one of the current probe tip sensor signal of a filtered signal obtained by filtering the current probe tip sensor signal by one or more filters.

10. Method according to any one or more of claims 8-9, further comprising filtering the Z-level signal using a further filter, wherein the further filter is configured for modelling a response of the cantilever, for matching a delay in the current probe tip sensor signal caused by dynamics of the cantilever with an equivalent delay in the Z-level signal caused by the further filter.

11. Method according to claim 10, wherein the further filter is first order low pass filter having a bandwidth equivalent to a bandwidth of the probe.

12. Method according to any one or more of the claims 8-11, further comprising determining the correction signal from the current probe tip sensor signal during scanning of the probe relative to the substrate surface, such as to perform a real-time correction of the topography signal.

13. Method according to any one or more of the claims 8-12, further comprising obtains a topography signal measurement and a current probe tip sensor signal measurement at each scan position during said scanning at a plurality of scan positions along a scan trajectory of the probe tip relative to the sample surface, and storing, for each scan position and associated therewith, the topography signalmeasurement and the current probe tip sensor signal measurement in a data storage; and correcting, by the controller after completion of said scanning, the topography signal measurements based on the associated current probe tip sensor signal measurements for each scan position stored in the data storage.

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