Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q70/00—General aspects of SPM probes, their manufacture or their related instrumentation, insofar as they are not specially adapted to a single SPM technique covered by group G01Q60/00
  • G01Q70/02—Probe holders
  • G01Q70/04—Probe holders with compensation for temperature or vibration induced errors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q10/00—Scanning or positioning arrangements, i.e. arrangements for actively controlling the movement or position of the probe
  • G01Q10/04—Fine scanning or positioning
  • G01Q10/045—Self-actuating probes, i.e. wherein the actuating means for driving are part of the probe itself, e.g. piezoelectric means on a cantilever probe
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q40/00—Calibration, e.g. of probes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q70/00—General aspects of SPM probes, their manufacture or their related instrumentation, insofar as they are not specially adapted to a single SPM technique covered by group G01Q60/00
  • G01Q70/06—Probe tip arrays

Definitions

• the present invention relates to a scanning probe microscope and a method for examining a sample surface.
• Scanning probe microscopes use a measuring probe to scan a sample or the surface thereof and thus yield measurement data for generating a representation of the topography of the sample surface.
• Scanning probe microscopes are abbreviated hereinafter to SPM.
• SPM scanning probeling microscopes
• Different SPM types are differentiated depending on the type of interaction between the measuring tip of a probe and the sample surface.
• Use is often made of scanning tunnelling microscopes (STM), in which a voltage is applied between the sample and the measuring tip, which do not touch one another, and the resulting tunnelling current is measured.
• STM scanning tunnelling microscopes
• the measuring tip In the microscope referred to as atomic force microscope (AFM) or scanning force microscope (SFM), the measuring tip is deflected by atomic forces of the sample surface, typically attractive van der Waals forces and/or repulsive forces of the exchange interaction. The deflection of the measuring tip is proportional to the force acting between the measuring tip and the sample surface, and this force is used to determine the surface topography.
• AFM atomic force microscope
• SFM scanning force microscope
• Scanning probe microscopes can be used in different operating modes.
• the measuring tip In the contact mode, the measuring tip is placed onto the sample surface and scanned over the sample surface in this state.
• the distance of the SPM head above the sample can be kept constant and the deflection of the cantilever or of the spring beam carrying the measuring tip is measured and used for imaging the surface. It is also possible to keep the deflection of the cantilever constant in a closed control loop, and to track the distance of the SPM to the contour of the sample surface.
• the measuring tip In a second operating mode, the non-contact mode, the measuring tip is brought to a defined distance from the sample surface and the cantilever is excited to oscillate, typically at or near the resonant frequency of the cantilever. The measuring probe is then scanned over the surface of the sample. Since the measuring tip does not come into contact with the sample in this operating mode, its wear is low.
• the cantilever In a third operating mode, the intermittent mode (or tapping modeTM), the cantilever is likewise caused to carry out a forced oscillation, but the distance between the SPM and the sample surface is chosen such that the measuring tip reaches the sample surface during a small part of an oscillation period.
• the contour of the surface of the sample is derived from the change in the frequency, the amplitude or the phase of the forced oscillation, which change is caused by the interaction of the measuring probe with the sample surface.
• the step-in operating mode the movements perpendicular to the sample surface and parallel to the sample surface are performed sequentially. To that end, the measuring tip of the measuring probe is lowered onto the sample surface and the interaction between the sample surface and the measuring tip is measured at the same time. Afterwards, the measuring tip is brought to its initial position again. Subsequently, the measuring tip is displaced by a defined section parallel to the sample surface and the analysis process is continued with a further lowering process.
• the measuring tip in a working position typically has a height in the two- or three-digit nanometres range, when the measuring tip approaches the surface it is absolutely necessary to ensure that the measuring tip is actually at the smallest distance from the sample and the cantilever and the securing plate thereof does not settle on the sample instead of the measuring tip and possibly damage or even destroy said sample.
• the mount carrying the securing plate of the measuring probe is typically tilted by a specific angle from the horizontal. This tilting of the measuring probe has the effect that the measuring tip of the measuring probe does not settle perpendicularly on the sample surface.
• a cantilever may not be straight along its longitudinal direction, but rather have a curvature.
• the measuring tip therefore describes a curved trajectory in relation to a sample surface to be examined.
• the resolution of a scanning probe microscope is reduced particularly when scanning steep flanks or sample regions having a high aspect ratio.
• the present invention therefore addresses the problem of specifying an apparatus and a method which can be used at least partly to avoid the problem area described above.
• the apparatus comprises a scanning probe microscope for examining a sample surface, the scanning probe microscope comprising: (a) at least one first measuring probe having a first se- curing region and at least one first cantilever, on which at least one first measuring tip is arranged; (b) wherein the at least one first cantilever is configured to adopt an adjustable bending at a free end of the at least one first cantilever before the beginning of a scanning process, which adjustable bending at least partly compensates for or intensifies a tilting of the first securing region and/or a pre-bending of the at least one first cantilever; and (c) at least one optical measuring device configured to determine the adjustable bending.
• tilting means a rotation about a transverse axis of a measuring probe, said transverse axis running in the horizontal direction.
• a sample surface is arranged in a horizontal plane.
• the term "adjustable" means, on the one hand, a temporary variable bending of the free end of a cantilever, which is brought about by an influence from outside. Said term means, on the other hand, a permanent bending of the free end of a cantilever, which substantially compensates for a tilting of the securing region of a measuring probe.
• the adjustable bending can be effected away from the sample surface, such that before the beginning of the scanning process the free end of the at least one first cantilever is aligned substantially parallel to the sample surface to be scanned.
• a mount of a scanning probe microscope measuring head on which mount the securing region of a measuring probe is secured on the SPM measuring head, has an inclination relative to the horizontal or the sample surface, which inclination tilts the cantilever of the scanning probe microscope relative to the sample surface such that the measuring tip is the first part of the measuring probe that comes into contact with the sample surface, rather than the cantilever or even the securing region of the measuring probe. Damage to the scanning probe microscope and/or to the sample to be examined can thereby be prevented. On account of this precautionary measure, the measuring probe of the scanning probe microscope can quickly be brought into a working position for a scanning process, as a result of which the efficiency of this analysis instrument is increased.
• the adjustable bending of the free end of the cantilever, to which the measuring tip is fitted preferably after the measuring probe of the SPM approaches the sample surface to be scanned or to be examined, but before the beginning of the performance of a scanning process, away from the sample surface, enables virtually perpendicular contacting of the measuring tip of the measuring probe with the sample surface during the performance of a scanning process.
• the imaging aberrations of the measuring probe and thus of the scanning probe microscope during the scanning of the sample surface to be examined are minimized as a result. This applies in particular to samples whose surfaces have steep flanks and/or whose surface topography has a high aspect ratio.
• the fact of whether the cantilever actually has the desired bending is ensured by measuring, before the performance of a scanning process of the SPM, whether the cantilever or the free end thereof has actually adopted the desired bending.
• the measuring tip has an unambiguous orientation in relation to the sample surface, as a result of which, firstly, the resolution of the SPM is optimized and, secondly, the interpretation of the measurement data is facilitated.
• a scanning probe microscope according to the invention thus enables even samples hav- ing a high aspect ratio to be scanned with a high resolution capability.
• the measuring probe is guided as perpendicularly as possible over the sample surface to be examined or, in an oscillating operating mode, oscillates as perpendicularly as possible with respect to the sample surface to be scanned.
• the resolu- tion of the scanning probe microscope is thereby maximized.
• the corners and edges of structure elements on the surface of the sample are detected as well as possible. Since the adjustment and the monitoring of the bending of a cantilever take place before an actual scanning process, a scanning probe microscope according to the invention can operate in all conventional operating modes.
• the adjustable bending of the free end of the at least one first cantilever can be effected towards the sample surface to be scanned.
• the free end of the cantilever is that end of the cantilever which is situated opposite the end of the cantilever at which the cantilever has the securing region of the measuring probe.
• the cantilever For scanning steep flanks it may be expedient to bend the cantilever such that the measuring tip approaches the steep flanks at a large angle during scanning as well. As a result of this bending of the cantilever, the measuring tip can scan specific steep flanks or side walls at a large angle (ideally at an angle of up to 90 0 ). In addition, by means of an enlarged bending of the cantilever, specific edges and/ or corners between a steep flank and the sample surface can be analysed with higher resolution. Overall, the adjustable bending of the cantilever of a scanning probe microscope makes it possible to minimize regions of a sample surface that can be detected only with uncertainty or cannot be detected.
• the adjustable bending of the at least one first cantilever can define a zero crossing for an oscillation of the at least one first cantilever during a scanning process.
• Adjusting the adjustable bending of a cantilever in this way ensures that the measuring tip approaches the sample surface to be scanned substantially at a perpendicular angle.
• the at least one mount of a scanning probe microscope measuring head can be configured to have an inclination relative to a horizontal of 0.5 0 to 45 0 , preferably 1.0 0 to 40 0 , more preferably 1.5 0 to 30 0 , and most preferably 2.0 0 to 20 0 .
• the adjustable bending of the at least one first cantilever can be embodied as permanent bending.
• the cantilever of a measuring probe is bent during production such that its measuring tip points substantially perpendicularly to the sample surface after the securing region of the measuring probe has been mounted onto an inclined mount. This means that the measuring probe is produced specifically for the inclination of the mount of the SPM measuring head.
• the orientation of the free end of the cantilever and thus the orientation of the measuring tip is measured and corrected as necessary.
• the at least one first cantilever can comprise at least two material layers which are connected to one another and whose coefficients of thermal expansion are different and which are permanently prestressed with respect to one another.
• a prestress of the two layers with respect to one another can be generated in a number of ways.
• the second layer can be applied to the entire cantilever or to parts of the cantilever at an elevated temperature. After cooling, the two layers are stressed relative to one another and the cantilever has a bending along its longitudinal axis.
• the at least one first cantilever can comprise at least one first actuator.
• the at least one first actuator can be integrated into the at least one first cantilever.
• the at least one first actuator can be arranged in a partial region of the at least one first canti- lever.
• the at least one first actuator is arranged in the vicinity of the free end of the at least one first cantilever.
• a first actuator integrated or fitted on the cantilever has the advantage that the adjustable bending of the cantilever can be adjusted in a defined manner with the aid of a control signal. As a result, different tilting angles of the mount of the SPM measuring head and/or different pre-bendings of the cantilever can be compensated for or corrected.
• the optical measuring device ascertains whether the bending of the cantilever that is appropriate for the respective tilting angle of the securing apparatus has actually been set. Furthermore, by means of the optical measuring device it is possible to determine whether, before the beginning of a scanning process, the free end of the cantilever has actually adopted a bending that substantially compensates for the pre- bending of the cantilever.
• the first actuator can furthermore be configured to scan the cantilever with a constant deflection over the sample surface to be examined. In addition, the first actuator can be configured to excite the cantilever to oscillate at a predefined frequency.
• the first actuator can comprise a multimorph actuator and/or a piezoelectric actuator
• the multimorph actuator can comprise a bimorph actuator.
• the bimorph actuator can comprise a bimetallic element.
• a bimorph actuator can be activated by an optical signal and/or an electrical signal. Furthermore, a bimorph actuator can be activated by means of an electron beam.
• a piezoelectric actuator as bending element of a cantilever has the advantage that the piezo-actuator reacts rapidly to a control signal.
• the free end of the cantilever and thus the measuring probe can be deflected or bent dynamically away from the sample surface and towards the sample surface and can consequently be adapted to the structure of the sample surface to be scanned.
• the scanning probe microscope can furthermore comprise a laser system configured, upon the control signal being applied to the laser system, to cause the at least one first actuator to effect the adjustable bending of the at least one first cantilever.
• a laser beam can be focused to a small focal spot.
• its point of incidence on the actuator can be precisely adjusted.
• part of the material system of the cantilever can be selectively heated with the aid of a laser beam.
• a laser beam is able to bring about a defined temperature change in the actuator. Consequently, a laser beam is very well suited, by means of an adjustable bending of the cantilever along its longitudinal axis, to adapt said cantilever rapidly and in a targeted manner to the topography to be examined of a sample surface.
• a modulation of the heating can be used in order to excite the cantilever and thus the measuring tip of a measuring probe to vibrate.
• the at least one first cantilever can comprise a heating apparatus configured to locally heat the bimorph actuator upon a control signal being applied. Furthermore, the at least one first cantilever can comprise at least one heating resistor configured to locally heat a layer of the bimorph actuator upon a control signal being applied.
• a localized heating apparatus for example in the form of a heating resistor, can selectively heat part of the bimorph actuator and thus bend the free end by an adjustable angle, such that the free end of the cantilever has a predefined orientation.
• At least one of the at least two material layers connected to one another can comprise a heating resistor in the form of implanted material in a partial region.
• the heating resistor can be implemented by doping part of the cantilever.
• the doping atoms can be introduced by implantation or diffusion into the cantilever.
• a cantilever with an applied metallic heating resistor does not have a complex structure and can be produced cost-effectively as a result.
• the two functions are, firstly, being part of a bimorph structure and, secondly, serving as an electrical resistor for generating a local temperature distribution in the cantilever.
• the at least one first actuator can be configured to keep the adjustable bending of the at least one first cantilever substantially constant during the scanning process.
• the adjustable bending of a cantilever can be monitored independently of the mode of operation of the scanning probe microscope during a scanning process by means of the optical measuring device. This makes it possible to ensure that the desired orientation of the measuring tip of the measuring probe in relation to the sample surface is maintained during the examination of the sample.
• the at least one first cantilever can comprise a second actuator.
• the second actuator can be integrated into the at least one first cantilever.
• the second actuator can be configured to excite the at least one first cantilever to carry out a forced oscillation.
• the second actuator can be configured to scan the at least one first cantilever with a constant deflection over the sample surface to be examined.
• the second actuator can be embodied in the form of a bimorph actuator and/ or in the form of a piezoelectric actuator.
• a cantilever comprises two actuators, two parameters for acting on the cantilever are available, in order to monitor or to optimize firstly the bending of said cantilever and secondly the interaction of the measuring probe with the sample surface.
• a piezoelectric actuator can be configured to perform an adjustable bending of the at least one cantilever which at least partly compensates for the inclination of the securing region of the measuring probe, or to perform an adjustable bending of the at least one cantilever which intensifies the inclination of the securing region.
• a piezoelectric actuator can achieve a movement of the cantilever in two opposite directions by reversal of the current direction.
• the at least one first cantilever and the measuring tip can have a resonant frequency that is in the range of 1 kHz - 10 MHz, preferably 5 kHz - 5 MHz, more preferably 10 kHz - 2 MHz, and most preferably 15 kHz - 1 MHz.
• the at least one cantilever can have a spring constant that is in the range of 0.001 N/m - 400 N/m, prefera- bly 0.02 N/m - 200 N/m, more preferably 0.04 N/m - 150 N/m, and most preferably 0.1 N/m - 100 N/m.
• a scanning probe microscope can furthermore comprise a control device configured to provide a control signal for the first actuator and/or the second actuator. Furthermore, the control device can be configured to provide control signals for one or more heating apparatuses.
• Electrical connections can be integrated into the securing region of the at least one first cantilever, said electrical connections leading to the one or the two actuators or the one or the two heating apparatuses.
• Probes of scanning probe microscopes nowadays are preferably automatically changeable.
• the electrical connections for the actuator or actuators or the heating apparatus(es) being integrated into the securing region of the measuring probe, measuring probes can be changed automatically, i.e. without manual interaction.
• Simple operability of a scanning probe microscope is achieved as a result.
• This makes it possible to use the scanning probe microscopes defined above in a manufacturing environment, for example.
• an automatic probe change ensures high reproducibility and reliability.
• the automation of the probe change makes it possible to achieve short probe change times of less than one minute. This is expedient particularly for scanning probe microscopes which operate in a vacuum environment.
• the scanning probe microscope can furthermore comprise a detection device config- ured to determine, from a topography of the sample surface and a contour of the measuring tip of the measuring probe, whether a region to be examined can be examined more accurately with a cantilever bent towards the sample surface in an intensified manner than without a cantilever bent in an intensified manner.
• the at least one optical measuring device can comprise a light pointer system.
• the light pointer system can comprise a laser system and a four-quadrant photodiode, wherein the laser system directs a light beam onto the at least one first cantilever, which light beam is reflected from the at least one first cantilever onto the four-quadrant photodiode.
• the optical measuring device in the embodiment of a light pointer system enables a high precision when determining the adjustable bending of the cantilever along its longitudinal axis.
• scanning probe microscopes often comprise optical measuring devices in the form of a light pointer system, such that there is no need for complex retrofitting of scanning probe microscopes for the purpose of determining the adjustable bending of a cantilever.
• the longitudinal axis of the measuring probe extends symmetrically from the measuring tip to the securing region of the measuring probe.
• the transverse axis of the cantilever is perpendicular to the longitudinal axis in a plane of the measuring probe.
• the at least one first cantilever can comprise a piezoresistive sensor and/or a piezoelectric sensor.
• the piezoelectric sensor can be used for determining the interaction of the measuring probe with the sample surface during a scanning process. Furthermore, the piezoelectric sensor can be used in addition to the optical measuring device for detecting the force acting on the measuring tip during scanning. Furthermore, a piezoresistive sensor can be used for measuring the adjustable bending of the cantilever before or at the be- ginning of a scanning process.
• a scanning probe microscope furthermore comprises a test body for determining the adjustable bending of the at least one first cantilever.
• a test body having defined dimensions which comprises, in particular, one or more structure elements having known dimensions can be used to calibrate a tilting angle of the mount of the SPM measuring head relative to the horizontal, an adjustable bending of the cantilever and/or a response behaviour of the optical measuring device.
• the calibration of the scanning probe microscope can be repeated at regular time intervals.
• the calibration values can be stored in a non-volatile memory of the scanning probe microscope.
• the calibration values can be used for determining the adjustable bending of the cantilever and/or for determining a topography image of the sample surface to be examined from the data of one or more scans of the measuring probe.
• a scanning probe microscope can furthermore comprise: (d) at least one second measuring probe having a second securing region and at least one second cantilever, on which at least one second measuring tip is arranged; (e) wherein the at least one second cantilever is configured to adopt an adjustable bending at a free end of the at least one second cantilever before the beginning of a scanning process, which adjustable bending at least partly compensates for or intensifies a tilting of the second securing region and/or a pre-bending of the at least one second cantilever; and (f) wherein the at least one first cantilever and the at least one second cantilever are arranged substantially in the form of antiparallel vectors.
• the arrangement of the two cantilevers in the form of antiparallel vectors makes it possible to analyse with high accuracy for example two perpendicular side walls of a web that is scanned in a direction perpendicular to the web by an SPM.
• the distance between the two measuring probes is adjustable, the two side walls of the web can be scanned simultaneously by the measuring tips of the two measuring probes.
• the measuring tip of the corresponding cantilever is bent towards the sample. A region of a sample can thus be scanned using a measuring tip, wherein the bending of the cantilever is adapted to the topology of the sample surface.
• a sample region can be scanned in a first scan by means of a measuring tip guided substantially perpendicular to the sample surface. From the image generated from the measurement data, an adjustable bending of the cantilever of the corresponding measuring tip is determined for a second scan. With a bent cantilever, the sample region to be examined, for example a side wall, is then scanned again. A realistic second image of the sample surface is then generated from the measurement data of the two scans of the same region of the sample. If the second image gives occasion to suppose that the second image of the sample surface still does not accord with reality, the sample region to be examined can be scanned again using a cantilever bent differently. This process can be repeated as necessary until a realistic image of a region to be examined of the sample surface is present.
• the adjustable bending of a cantilever requires only the movement of a minimal mass.
• the measuring probe can thus be prepared very rapidly and reproducibly for a scan- ning process. Consequently, the throughput of a scanning probe microscope is reduced only insignificantly by the adjustable bending of the cantilever(s).
• a scanning probe microscope generally comprises easily interchangeable measuring probes and a modularly implementable control device for generating a control signal.
• Existing apparatuses can therefore be retrofitted in a simple manner with a measuring probe described here.
• a scanning probe microscope can comprise at least two first cantilevers and at least two second cantilevers, wherein the at least two first cantilevers and the at least two second cantilevers are arranged substantially in a manner rotated by 90 0 relative to one another.
• a scanning probe microscope comprises four cantile- vers, which are arranged in each case at an angle of substantially 90 0 and the measuring tips of which point towards one another.
• a scanning probe microscope can analyse highly precisely a sample having webs running perpendicularly to one another, for example elements of an absorber pattern of a photolithographic mask.
• the problem explained above is solved by a method for examining a sample surface.
• the method for examining a sample surface using at least one measuring probe comprising a securing region and at least one cantilever comprises a sequence of steps: (a) adjusting an adjustable bending at a free end of the at least one cantilever before the beginning of a scanning process, which adjustable bending at least partly compensates for or intensifies a tilting of the securing region and/or a pre-bending of the at least one cantilever; and (b) determining before the beginning of the scanning process using an optical measuring device whether the at least one cantilever has adopted the adjustable bending.
• Another aspect furthermore comprises the step of: Performing the scanning process in a contact operating mode, in a non-contact operating mode, an intermittent operating mode or a step-in operating mode.
• a further aspect furthermore comprises the step of: Operating the at least one cantilever in a closed control loop when performing the scanning process.
• a scanning probe microscope comprising a cantilever having an adjustable bending along its longitudinal axis can be operated in all conventional operating modes. Conse- quently, the adjustment of an adjustable bending of a cantilever is associated with no disadvantages whatsoever for the use of an SPM comprising a corresponding cantilever.
• Yet another aspect furthermore comprises the steps of: Repeating steps (a) and (b) if the determining in step (b) reveals that the at least one cantilever has not correctly adopted the adjustable bending.
• adjustable bending of a cantilever can be altered until the free end of the cantilever has a predefined orientation.
• the adjustable bending of the free end of the cantilever can compensate for the inclination of the securing region of the measuring probe relative to the horizontal and/or a pre-bending of the cantilever.
• Yet another aspect comprises the step of scanning the at least one measuring tip over the sample surface to be scanned after the determination that the free end of the at least one cantilever has adopted a predefined orientation in relation to the sample surface to be scanned.
• the adjustable bending of the at least one cantilever can make it possible for the sample surface to be scanned to be approached by the measuring tip substantially perpendicularly.
• the adjustable bending can furthermore comprise: Bending the at least one cantilever away from the sample surface to be scanned, such that before the beginning of the scanning process the free end of the at least one cantilever is aligned substantially parallel to the sample surface to be scanned. Furthermore, the adjustable bending can comprise: Bending the free end of the at least one cantilever towards the sample surface to be scanned. Yet another aspect comprises the step of: Detecting a topography of the sample surface, which substantially corresponds to the contour of the measuring tip, in order to determine whether the adjustable bending of the at least one cantilever is intended to be intensified. Another aspect comprises the step of: Deciding whether the cantilever of the measuring probe is bent in an intensified manner on the basis of a detected height gradient of the sample surface.
• the method defined above makes it possible, during a scanning process, to identify a steep high flank and to increase the accuracy of the scanning of a sample surface by means of corresponding intensified bending of the free end of the cantilever with the aid of renewed scanning of the corresponding sample region.
• the scanning probe microscope described above performs a method explained above.
• a computer program can comprise instructions which, if they are executed by one of the scanning probe microscopes described above, cause the scanning probe microscope to perform the method steps from one of the aspects above.
• a control device can be configured to cause a scanning probe microscope to perform the method steps of the methods specified above.
• Figure 1 shows, in the upper partial figure, an excerpt from a photolithographically patterned sample having strips on a substrate of the sample which were scanned by a scanning probe microscope (AFM), and, in the lower partial figure, a scan of a measuring probe of the AFM over the strips along a scan line;
• AFM scanning probe microscope
• Figure 2 substantially represents the excerpt from the sample in Figure 1, which excerpt was captured by a scanning electron microscope;
• Figure 3 schematically illustrates a measuring probe of a scanning probe microscope, the mount of which measuring probe has a tilting angle relative to the hori- zontal and thereby tilts the securing region of the measuring probe by the same angle relative to the horizontal;
• Figure 4 illustrates a schematic illustration of the scanning of a measuring probe over both side walls of an element of the sample from Figure 1 and, in the lower partial figure, reproduces the contour of the scanned region of the sample structure, which contour was determined from the scan;
• Figure 5 illustrates a schematic illustration of the trajectory of the free end of a tilted, oscillating cantilever
• Figure 6 illustrates calculated path movements of the free end of the cantilever and of the measuring tip with changing curvature of the cantilever for a tilting of the mount of 0° (blue and green curves) and of the measuring tip for a tilting of the mount by 8° (red curve);
• Figure 7 presents an excerpt from Figure 6
• Figure 8 illustrates a schematic illustration of the trajectory of the free end of a cantilever that was bent away from the sample surface
• Figure 9 reproduces the calculated path movements of the free end or of the measuring tip from Figure 6, wherein the measuring tip was bent away from the sample surface;
• Figure 10 illustrates an excerpt from Figure 9
• Figure 11 in the upper partial figure represents a tilted cantilever, wherein the tilting is substantially compensated for by the bending of a free end of the can- tilever away from a sample surface, and, in the lower partial figure, illustrates the improvement of the bent cantilever relative to Figure 4;
• Figure 12 schematically reproduces some essential components of a scanning
• Figure 13 schematically illustrates the essential components of the light pointer system from Figure 12;
• Figure 14 schematically shows a plan view (top) and a sectional view (bottom) through a probe and a mount of a scanning force microscope having a V-shape cantilever;
• Figure 15 reproduces the measuring probe from Figure 14 after a heating resistor has been applied over large parts of the arms of the cantilever;
• Figure 16 schematically shows a plan view (top) and a sectional view (bottom) through a measuring probe and a mount of a scanning force microscope, wherein a piezo-actuator has been fitted over large parts of the two arms of the V-shape cantilever;
• Figure 17 schematically illustrates a measuring probe tilted relative to the horizontal, wherein the free end of the cantilever has a permanent bending away from a sample surface;
• Figure 18 schematically illustrates a tilted cantilever, the free end of which has a temporary bending towards the sample surface
• Figure 19 in the upper partial figure, schematically represents two measuring
• Figure 20 schematically illustrates a configuration of four probes, the measuring probes of which point towards one another;
• Figure 21 reproduces a flow diagram of a method for examining a sample surface using a measuring probe, wherein the orientation of the free end of the cantilever and thus of the measuring tip can be adjusted;
• Figure 22 illustrates a flowchart of one exemplary method for adjusting a bending of a free end of a cantilever.
• the exemplary diagram 100 in Figure 1 schematically shows, in the upper partial figure, an excerpt from a structured sample 110, comprising a substrate 120 having a regular pattern of elements of a periodic strip structure 130.
• the side walls of the periodic strips are very steep; ideally, they are perpendicular.
• the excerpt from the sample 110 was scanned using a force microscope (AFM) as an example of a scanning probe micro- scope (SPM).
• AFM force microscope
• SPM scanning probe micro- scope
• the lower partial figure of the diagram 100 represents a scan 140 of the AFM or of the SPM along the line 145 or the scan line 145, i.e. perpendicularly to the elements of the strip structure 130.
• the height of the periodic strips 130 is somewhat more than 60 nm. From the lower partial figure it can likewise be gathered that the periodic strips 130 have a width of approximately 200 nm.
• Both the substrate 120 of the sample 110 and the surface of the elements of the strip structure 130 are substantially planar.
• the scan 140 in the lower partial figure shows that the measurement of the right-hand side walls of the strips 130 slopes with a different angle than the measure- ment of the left-hand side walls.
• From the upper partial figure of the diagram 100 it can additionally be gathered that the central element or the central strip of the strip structure 130 has defects 160 along the right-hand flank or side wall, whereas the left-hand side wall of this element of the strip structure 130 appears not to have any defects.
• the diagram 200 in Figure 2 sub- stantially shows once again the excerpt from the sample 110 comprising the substrate 120 and the periodic strip structure 130 from the diagram 100 in Figure 1.
• the diagram 200 in Figure 2 was captured with the aid of a scanning electron microscope (SEM). Besides the defects 160 along the right-hand side wall of the central element of the strip structure 130, this micrograph reveals that the left-hand flank of the central structure element 130 also has defects 260. This means that the AFM or SPM cannot, or at least cannot unambiguously, image defects 260 along the left-hand side edge of an element of the strip structure 130.
• SEM scanning electron microscope
• Figure 1 represents an example of a sample surface 150 with structure elements 130 on a substrate 120 of a sample 110 which has a high aspect ratio, i.e. the ratio of the height or depth of a structure to its (smallest) width. Furthermore, elements of the strip structure 130 have steep side walls or flanks.
• a sample 110 structured with strips 130 is thus well suited to illustrating the problem addressed by the present invention. Furthermore, the efficacy of the solution to this problem, as disclosed in this application, can be illustrated on the basis of this example.
• a scanning probe microscope described here together with the associated method is not restricted to application to samples 110 having strip structures 130. Rather, a scanning probe microscope according to the invention and a method according to the invention can be used for analysing arbitrary samples.
• the diagram 300 in Figure 3 represents a measuring probe 330 having a securing region 305 or a securing plate 305, a cantilever 310 or spring beam 310 and a measuring tip 320. With the aid of the securing region 305, the measuring probe 330 is secured on the mount 340 of the AFM measuring head. This can be effected by clamping, for ex- ample.
• the measuring probe 330 is thus incorporated into a scanning probe microscope (not shown in Figure 3).
• the measuring tip 320 of the measuring probe 330 or of the probe 330 is preferably fitted in the vicinity of the free end 350 of the cantilever 310.
• the mount 340 and thus also the securing region 305 or the securing plate 305 of the measuring probe 330 are tilted or inclined relative to the horizontal 380 by an angle 390 about a transverse axis, which is perpendicular to the plane of the drawing in the example of the diagram 300.
• the mount 340 is tilted along the longitudinal axis 370 of the cantilever 310.
• the tilting angle 390 is typically in a range of 5 0 to 20 0 .
• the position 315 shows the tilted or inclined cantilever 310 in its rest position.
• the positions 312 and 317 represent the positions of maximum deflection of an oscillating cantilever 310.
• the position 315 represents the zero crossing of a forced oscillation.
• the free end 350 of the cantilever 310 carries out a movement along the trajectory 360.
• the path movement of the tip 325 of the measuring tip 320 of the cantilever 310 follows the trajectory 360.
• the measuring tip 320 is suppressed in the positions 315 and 317 of the cantilever 310.
• the diagram 400 in Figure 4 illustrates how the inclined or tilted probe 330 generates the diagram 100 in Figure 1.
• the measuring probe 330 analyses the sample surface 150, wherein the mount 340 or a piezo-element fitted on the mount excites the cantilever 310 to carry out a forced oscillation.
• the probe 330 scans a surface of an element of the strip structure 130 of the sample 110.
• the measuring tip 320 of the cantilever 310 scans along the right-hand side wall 410 of a strip element 130.
• the top right partial figure shows the scanning of a left-hand side wall 420 of an element of the strip structure 130 of the photomask 110.
• the bottom partial figure illustrates the contour 430 extracted from the scan of the top partial figures in Figure 4.
• the substantially planar surface of the structure element 130 can be examined with high resolution by the measuring tip 320 inclined relative to the perpendicular to the surface of the sample 110. This also holds true for the substrate 120 of the sample 110.
• the analysis of the right-hand side wall of the structure element 130, relative to the surface of which the measuring tip 320 has a small angle different from zero, can also be analysed by the measuring tip 320 with reasonable resolution.
• the tip 325 of the inclined measuring tip 320 moves away from the surface of the side wall 420, however, upon lowering onto the sample surface 150.
• the measurement data of conventional scanning probe microscopes are not very resilient in the region 440 of the contour 430.
• the line 450 symbolizes the explanations given above by means of a measurement uncertainty map.
• the region of the measurement uncertainty i.e. the region of the left-hand side wall of an element of the strip structure 130, is illustrated in a dotted manner in the measurement uncertainty map.
• the diagram 500 in Figure 5 illustrates the division of the movement of the tip 325 of the measuring tip 320 of the cantilever 310 into a height change and a lateral offset during its movement along the path curve 360.
• Figure 6 shows the calculated curves for the free end 350 of the cantilever 310 (blue curve), of the tip 325 of the measuring tip 320 of the cantilever 310 (green curve) and of the tip 325 of the measuring tip 320 of the cantilever 310 in the case of an additional inclination of the mount 340 and thus of the securing region 305 or of the cantilever 310 of 8° towards the sample surface 150 (red curve).
• the curves indicate a highly exaggerated bending of the cantilever 310 extending up to a bending of 90°of the free end 350 of the cantilever 310.
• a height change of the tip 325 of the measuring tip 320 by means of curvature of the cantilever 310 of approximately h 10.23 ⁇ leads to a lat- eral offset in the region of likewise 10.23 ⁇ (green curve). If the cantilever 310 is curved such that the bending is 90 0 , the free end of the cantilever describes a circle segment of 90 0 . In this special case, vertical and horizontal offsets are substantially identical. The additional tilting angle 390 of 8° results in a height change of the tip 325 of the measuring tip 320 of 8.7 ⁇ and in a lateral offset of approximately 11.0 ⁇ (red curve).
• Figure 7 represents an enlarged excerpt from the top right corner of the calculated curves in Figure 6.
• a height change h of the tip 325 of the measuring tip 320 of the cantilever 310 of 1 ⁇ results in a lateral offset of approximately 0.2 ⁇ .
• a height change of 1 ⁇ leads to a lateral offset of the tip 325 of the measuring probe 320 of approximately 0.4 ⁇ .
• the diagram 800 in Figure 8 shows the trajectory 860 of the free end 360 of a bent cantilever 810.
• the bending of the cantilever 810 is effected away from the sample sur- face 150.
• the cantilever 810 has an inclination or tilting relative to the horizontal 380 about a transverse axis of the measuring probe 330.
• the diagram in figure 9 reproduces calculated trajectories of the free end 350 of the bent cantilever 810 for a highly exaggerated oscillation excitation (blue curve).
• the green trajectory represents the path of the tip 325 of the measuring tip 320 of the measuring probe 330.
• the red curve shows the path movement of the tip 325 of the measuring tip 320 of the bent cantilever 810 if the securing plate 305 of the cantilever 810 has a tilting angle of 8°.
• Figure 10 represents an enlarged view of the top right excerpt from the calculated curves in Figure 9.
• a height change of the free end 350 of the cantilever 810 (blue curve) or of the tip 325 of the measuring tip 320 by 1 ⁇ brings about a lateral offset of approximately 10 nm.
• an inclined, bent cantilever 860 tilt angle 8° causes a lateral offset of the tip 325 of the measuring tip 320 of approximately 20 nm.
• Figure 11 shows, in the upper partial figure, a probe 1130 or a measuring probe 1130, the securing region of which is secured on an inclined mount 340.
• the tilting angle 390 of the mount 340 is compensated for by an adjustable bending of the cantilever 810 away from the sample surface 150, such that the free end 350 of the cantilever 810 is aligned substantially parallel to the sample surface 150.
• the tip 325 of the measuring tip 320 of the bent cantilever 810 approaches the sample surface 150 substantially perpendicularly. In an oscillation operating mode of a scanning probe microscope, the tip 325 of the measuring probe 330 substantially performs a vertical movement 1110. The lateral offset of the tip 325 is minimized by the bent cantilever 810.
• FIG 12 schematically shows some components of a scanning probe microscope 1200, the SPM measuring head of which comprises a mount 340 serving for incorporating a measuring probe 330, 1130 into the SPM 1200.
• Scanning probe microscopes are differ- entiated according to the measurement variable used for examining the sample 1210.
• Scanning tunnelling microscopes (STM) use the tunnelling current between the sample 1210 and the measuring tip 320, which tunnelling current occurs upon a voltage being applied between the sample 1210 and the measuring tip 320, in order to analyse the topography of the sample surface 150 of the sample 1210.
• Atomic force microscopes use the tunnelling current between the sample 1210 and the measuring tip 320, which tunnelling current occurs upon a voltage being applied between the sample 1210 and the measuring tip 320, in order to analyse the topography of the sample surface 150 of the sample 1210.
• AFM Magnetic force microscopes
• MFM Magnetic force microscopes
• SNOM Scanning near- field optical microscopes
• SNAM Scanning near-field acoustic microscopes
• the principle for the adjustable bending of the cantilever 810 about a transverse axis of the measuring probe 330 can be applied to the probes of all types of scanning probe microscopes which have a cantilever, i.e. an elastically flexible lever arm or, for short, a spring beam.
• Scanning probe microscopes whose measuring probes do not have a cantilever must be equipped with a cantilever 810 be- fore use in the configuration described in this application.
• An atomic force microscope (AFM) is explained below as one example of a scanning probe microscope 1200.
• the atomic force microscope 1200 illustrated in Figure 12 can be operated under ambient conditions or in a vacuum chamber (not illustrated in Figure 12).
• the sample 1210 to be analysed is arranged on a sample stage 1225.
• the sample stage 1225 can be positioned in three spatial directions by a positioning device 1215.
• the positioning device 1215 comprises for example one or more micro-displacement elements, for example in the form of spindle actuators and/or piezo-actuators (not shown in Figure 12).
• the measuring probe 330, 1130 is secured by means of the mount 340 on a holding apparatus (not shown in Figure 12) of the atomic force microscope (AFM) 1200.
• the holding apparatus can be connected to the measuring head of the AFM 1200 via a pie- zo-actuator (not illustrated in Figure 4).
• the piezo-actuator that connects the mount 340 to the holding apparatus of the AFM measuring head can perform the function of a scanning device.
• the positioning device 1215 performs the movement of the sample 1210 in the sample plane (xy-plane) and the piezo-actuator mentioned above realizes the movement of the measuring tip 320 in the direction of the normal to the sample (z-direction).
• the sample stage 1225 is implemented in a stationary fashion and the measuring tip 320 is brought to the region to be analysed of the sample 1210 by means of micro-displacement elements (not shown in Figure 12).
• the measuring tip 320 of the probe 330, 1130 can operate in a plurality of operating modes. Firstly, it can be scanned at constant height over the surface 150 of the sample 1210. Alternatively, the probe 330, 1130 can be guided over the sample surface 150 with constant force in a closed control loop. Furthermore, it is possible, with the aid of a modulation method, to cause the cantilever 310, 810 to oscillate perpendicular to the sample surface 150 and thereby to scan the surface 150 of the sample 1210 in a closed control loop. In this case, the cantilever 310, 810 can oscillate at its resonant frequency (self-oscillation) or perform a forced oscillation at a predefined frequency. In the first- mentioned case, i.e.
• an FM (frequency modulation) demodulation is effected in which the frequency change brought about by interaction between the measuring tip 320 and the sample 1210 is measured.
• an AM (amplitude modulation) demodulation is carried out in order to detect the amplitude of the oscillation that is changed by the interaction between the measuring tip 320 and the sample surface 150.
• a light pointer system 1300 is illustrated in Figure 12. In Figure 13, for clarification, the essential components of such a system are illustrated separately again.
• a laser system 1260 directs a laser beam 1265 onto the free end of the cantilever 310, 810.
• the laser beam 1275 reflected from the cantilever 310, 810 is picked up by a photodetector 1270.
• the photodetector 1270 is often embodied in the form of a four-quadrant photodiode. It is also possible to use a two-segment photodiode.
• the adjustable bending of the free end 350 of the cantilever 310, 810 for compensating for the tilting angle 390 can be measured just like a pre-bending and/or a twisting of the cantilever 310, 810. Measuring a twisting of the cantilever 310, 810 necessitates a four-quadrant photodiode as photodetector.
• an optical interferometer can be used in order to determine a distance between the measuring tip 320 of the measuring probe 330 and the sample surface 150. Using an optical interferometer it is also possible to determine the movement of the measuring tip in the z-direction, i.e. perpendicular to the sample surface 150 (not shown in Figure 12). In addition, an alignment of the free end 350 of the cantilever 810 can also be detected with the aid of piezoresistive elements or sensors of the cantilever 810 (not illustrated in Figure 12).
• the atomic force microscope 1200 comprises a control device 1280.
• the latter is connected to a second laser system 1290 via a lead 1284 for a control signal.
• the laser beam 1295 of the second laser system 1290 in the vicinity of the securing region 305, is directed at the cantilever 810 onto the two arms of the V-shaped cantilever 810 in order to locally heat a bimorph actuator of the cantilever 810.
• the choice of a cantilever 310 in the form of an individual spring beam makes it possible to work with just one light beam and thereby facilitates the adjustment of the laser beam 1295.
• the second laser system 1290 No particular requirements are made of the second laser system 1290.
• the wavelength thereof can be chosen arbitrarily. However, wavelengths in the visible range of the elec- tromagnetic spectrum facilitate the adjustment of the laser beam 1295. Furthermore, it is expedient to choose the wavelength of the laser radiation such that the proportion of absorbed radiation is as high as possible. An output power of a few mW is sufficient for locally heating part of the cantilever 810. In order to achieve local heating of part of the cantilever 810, focussing to a focal spot of ⁇ 10 ⁇ is necessary.
• the focal spot should be smaller than the width of the cantilever 310 or of an arm of the V-shaped cantilever 810 in order that only very little laser radiation reaches the sample 150, 1210 past the cantilever 310, 810.
• both arms should be irradiated uniformly.
• control device 1280 has a second connection 1282 to the mount 340. Via the connection 1282, control signals from the control device 1280 can be passed to the cantilever 810 of the probe 1130.
• control signals from the control device 1280 can be passed to the cantilever 810 of the probe 1130.
• cantilevers 810 for atomic force microscopes 1200 are presented in the subsequent figures. The person skilled in the art will recognize that other types of cantilevers such as, for instance, the cantilever 310 described in Figure 3 can likewise be used.
• the adjustable bendings of the free end 350 of the cantilever 810 are brought about by applying control signals or adjustment signals to the cantilevers 810 via the connections 1282 and/or 1284.
• the diagram 1400 in Figure 14 shows, in the upper part, a plan view of a probe 1130 and, in the lower part, a sectional view through the plane of symmetry of the probe 1130 or the longitudinal axis 370 and the measuring probe 320.
• the yz-plane illustrated in the lower part of Figure 14 corresponds to the sectional plane through a cantilever 810 and the measuring tip 320 thereof.
• the probe 1130 has a securing region 1105, a measuring tip 320 and a cantilever 810. With the aid of the securing region 1105, the measuring probe 1130 is fitted on the mount 340.
• the cantilever 810 comprises two layers 1442 and 1444 arranged one above the other and having different coefficients of thermal expansion.
• the two layers 1442 and 1444 can be constructed for example from semiconducting and/or electrically insulating materials. Silicon (Si) shall be mentioned here as an example of a semiconducting layer, and silicon nitride (Si 3 N 4 ) by way of example as insu- lator material.
• one of the two layers 1442 and 1444 to comprise a metal layer, for example an aluminium layer or a chromium layer, and the second layer to comprise a semiconducting layer or an electrically insulating layer, for example a polymer layer.
• all materials are conceivable for the two layers 1442 and 1444 as long as said materials have different coefficients of linear thermal expansion.
• the methods and materials known from semiconductor fabrication can be used.
• the implantation can be effected from the top side of the cantilever 310, 810 (i.e. the side facing away from the measuring tip 320) and/or from the underside of the cantilever 310, 810 (i.e. the side having the measuring tip 320).
• the measuring tip 320 can be produced from the material of the lower layer 1444, from the material of the upper layer 1442 of the cantilever 810, or from a different material. This likewise applies to the securing region 1105 or the securing plate 1105. This means that the measuring tip 320, one of the layers 1442 or 1444 and the securing plate 1105 can be embodied integrally. Alternatively, individual or all components can be produced separately from suitable materials and then be connected to one another, for example by adhesive bonding.
• a symmetrical temperature change of the cantilever 310, 810 leads to a bending of the free end 350 of the cantilever 810 in the yz-plane.
• a local heating of the cantilever 810 can be generated for example by local irradiation of a beam at a position 1460 with the laser beam 1295 of the laser system 1290.
• the bending of the cantilever 810 is to a first approximation proportional to the light power introduced at the position 1460.
• the extent of the bending of the free end 350 of the cantilever 310, 810 is also dependent on the position 1460 at which the laser beam 1295 is incident on the cantilever 310, 810.
• the absorption coefficient of the material on which the laser beam 1295 impinges and the specific heat conduction thereof— and thus the time duration of the irradiation— influence the adjustable bending of the free end 350 of the cantilever 310, 810.
• the adjustable bending of the cantilever 810 is effected with a very short time constant in the range of microseconds on account of the low mass of the cantilever 810.
• the time duration from the first incidence of the laser beam 1295 at the position 1460 on the cantilever 810 until a steady state is set within the cantilever 810 is greatly dependent on the thermal conductivity of the materials of the layers 1442 and 1444 ⁇
• said time constant is greatly influenced by the expansion of the cantilever 310, 810 and also the volume and the material of the securing plate 1105.
• the thermal time constant therefore varies in a range of a few microseconds to milliseconds.
• the time constant with which the cantilever 310, 810 returns to thermal equilibrium again after the laser beam 1295 has been switched off by the control device 1280 is generally greater.
• the local temperature gradient must be maintained by continuous supply of energy. If the measuring probe 1130 is operated in a modulated manner, the cantilever 810 oscillates in the z-direction.
• the amplitude of the cantilever oscillation is normally small ( ⁇ 1 ⁇ ), however, and so the latter to a first approximation can be disregarded.
• the local temperature increase in the region of the position 1460 is dependent not only the power of the laser beam 1295 but also on the materials 1442 and 1444 and the position 1460 of the laser beam 1295 on the cantilever 810.
• the exemplary cantilever 810 illustrated in Figure 14 comprises two materials having different coefficients of thermal expansion. It is also possible to arrange three or more materials one above another. In the case of the arrangement of three or more different materials one above another, however, care should be taken to ensure that the resonant frequency of the cantilever 810 remains in the range of 10 kHz to 20 MHz.
• both layers 1442 and 1444 extend over the entire cantilever 810.
• the diagram 1500 in Figure 15 presents the cantilever 810 from Figure 14, comprising two materials 1442 and 1444 having different coefficients of thermal expansion.
• the cantilever 810 comprises a heating apparatus in the form of two heating resistor 1560, which are fitted on the two arms of the cantilever 810.
• the heating resistors 1560 can be embodied for example in the form of a thin coating.
• the currently preferred material is aluminium. Aluminium has firstly a high coefficient of thermal expansion and secondly a relatively high electrical resistance.
• the heating resistors 1560 are illustrated in the form of rectangles in Figure 15, for reasons of simplicity.
• the heating resistors typically comprise meandering electrical conductor structures.
• the width of the conductors is in the range of a few micrometres.
• the length thereof is typically a few hundred micrometres, for example 200 ⁇ to 500 ⁇ .
• An exemplary cantilever 810 comprises a 4.6 ⁇ thick silicon layer. The latter is covered by a 0.6 ⁇ thick layer of silicon oxide.
• a thin chromium layer (approximately 50 nm) as adhesion promoting layer is deposited onto the silicon oxide layer.
• Heating resistors can also be produced by implanting dopants into a semiconducting cantilever 310, 810. This process is described in the book "PRONANO: proceedings of the integrated project on massively parallel intelligent cantilever probe platforms for nanoscale analysis and synthesis", edited by Thomas Sulzbach and Ivo W. Rangelow, Minister: Publishers Monsenstein and Vannerdat, ISBN: 978-3-86991-177-9.
• the heating resistors 1560 are applied in addition to the two layers 1442 and 1444 of the cantilever 810.
• the heating resistors 1560 it is also possible to dispense with one of the two layers 1442 or 1444.
• the heating resistors 1560 which have a linear thermal expansion that is different from the layer 1442 or 1444 of the cantilever 810, then perform the function of the second layer of the cantilever 810.
• the heating resistor 1560 has two leads 1565 and 1575, which pass through the securing region 1105 of the measuring probe 1130 and connect the heating resistor 1560 to the control device 1280 via the connection 1282.
• the heating resistor 1560 allows local heating of the cantilever 810 on which the heating resistors 1560 are fitted.
• the local heating of the cantilever 810 leads to an adjustable bending of the free end 350 and thus of the cantilever 810 of the measuring probe 330 in relation to the sample surface 150.
• the thermal time constant for setting a steady state within the cantilever 810 between local supply of heat by the heating resistors 1560 and the dissipation of heat by the securing plate 1105 is of the same order of mag- nitude as indicated above.
• the heating resistors 1560 can be operated digitally, i.e. when the control signal is applied, a predefined voltage is applied to the heating resistors 1560 and the latter convert a defined electrical power into a corresponding thermal energy.
• the heating resistors 1560 can also operate in an analogue manner, such that the electrical power loss of the heating resistors 1560 can be set in accordance with the voltage present on the leads 1565 and 1575.
• the heating resistors 1560 can also be used in a closed control loop.
• the deviation of the orientation of the free end 350 of the cantilever 810 from the horizontal 370 which can be determined by means of the light pointer system, functions as the controlled variable.
• the heating resistors 1560 are fitted on the top side of the cantilever 810.
• the heating resistors 1560 can be fitted on the underside of the cantilever 810 (not illustrated in Figure 15). This has the advantage that the heating resistor(s) cannot adversely affect the position of the laser beam 1265 for determining the bending and/or the deflection of the free end 350 of the cantilever 810.
• the heating resistor(s) fitted on the underside of the cantilever 640 reduce(s) slightly the distance between the cantilever 810 and the sample surface 150.
• Probes 1130 for atomic force microscopes whose cantilevers are embodied in a V- shaped fashion were described in Figures 14 and 15.
• the atomic force microscopes defined in this application can also use probes 1130 whose cantilevers are configured differently, such as, for example, the strip-shaped cantilever 310 in Figure 3.
• the diagram 1600 in Figure 16 shows a cantilever 810 with piezo-actuators 1660 fitted on the two arms thereof.
• the cantilever 810 comprises a substantially uniform material layer 1442.
• the piezo-actuators 1660 are connected to the control device 1280 of the atomic force microscope 1200 via the leads 1665 and respectively 1675 and 1282.
• Piezo-actuators can be applied to the cantilever 810 for example in the form of zinc oxide (ZnO) actuators, as described above for the heating resistors. This is described for example by the authors S.R. Manalis, S.C. Minne and C.F. Quate in the article "Atomic force microscopy for high speed imaging using cantilevers with an integrated actuator and sensor", Appl. Phys. Lett. 68, 871 (1996). Generally, almost exclusively integrated production methods from the semiconductor industry and MEMS (microelectrome- chanical system) production are used for depositing or implementing the piezo- actuators 1660.
• ZnO zinc oxide
• the adjustable bending of the free end 350 of the cantilever 810 with the aid of the piezo-actuators 1660 has the advantage that the free end of the cantilever 810 can be bent rapidly away from the sample surface 150 or towards the sample surface 150.
• the response time of piezo-actuators is limited by their relatively large capacitance, which leads to a current flow when an applied voltage changes.
• the capacitance of the piezo- actuators in conjunction with the resistance of the leads 1665 and 1675 limits the response of the free end 350 to a change of the voltage signal applied to the leads 1665, 1675 ⁇
• the bending of the cantilever 810 can be adjusted in order to compensate as well as possible for the inclination of the securing region 1105 and/or a pre-bending incorporated into the cantilever 810. It is also possible, however, to equip a cantilever with a fixedly incorporated bending away from the sample surface 150.
• Figure 17 represents a cantilever 1710 having a permanent bending.
• the permanent bending can be produced for example by applying a second layer composed of a material having a coefficient of thermal expansion that differs from that of the material of the first layer on an existing cantilever at a temperature that is above or below room temperature. Cooling or heating to room temperature stresses the two layers and thereby forms a permanent bending of the cantilever 1710.
• a permanent bending can be introduced in a cantilever 1710 comprising two materials having different coefficients of thermal expansion by the cantilever 1710 being heated for a short time period above the extension limit of the material that melts at the lower temperature.
• the cantilever 1710 having a fixed permanent bending is designed for a specific tilting angle 1790 of the mount 340.
• Figure 18 schematically shows an exemplary embodiment in which the cantilever 310, 810 is bent towards the sample surface 150 in a manner different from that in Figures 14 to 16 by an actuator 1560 or 1660 or by the laser beam 1290.
• the mount 340 and thus the securing region 305, 1105 of the cantilever 310, 810 are inclined by an angle 390, 1790 relative to the horizontal 380.
• the tilting angle 390, 1790 can be io°, for example.
• the side wall 410 of an element of the strip structure 130 of the sample 110 can be analysed with higher precision than with a non-bent or an upwardly bent cantilever 310, 810, i.e. cantilever 810 bent away from the sample surface.
• the cantilever 310, 810 comprises one or a plurality of actuators 1660 which enable the free end 350 to be bent in opposite directions, it is possible to perform a first scanning process over the sample surface 150 with a cantilever 310, 810 whose free end 350 compensates as well as possible for the tilting angle of the mount 340 or a pre-bending of the cantilever 310, 810.
• the contour of the sample surface 150 that is generated from the first scan contains indications that the cantilever 310, 810 cannot realistically scan specific regions of the sample surface 150, such as the side wall 410, for example, before a second scan the cantilever 310, 810 is bent in the other direction, i.e. towards the sample surface 150, and the side wall 410 is scanned a second time with the cantile- ver 310, 810 thus prepared. From the superimposition of the data of the two scans, the control device 1280 can determine a realistic contour of the sample surface 150 in the region of the side wall 410.
• the diagram 1900 in Figure 19 shows a configuration comprising two probes 330 and 1930, with the aid of which both side surfaces of a web can be scanned reproducibly.
• the two probes 330 are arranged antiparallel to one another, i.e. the measuring tips 320 and 1920 point towards one another.
• the securing regions 305 and 1905 are inclined by an angle about their longitudinal axes 370 and 1970. Both securing regions 305 and 1905 can have the same inclination angle or different inclination angles.
• the cantilevers 810 and 1910 can be cantilevers of the same type. It is also possible to use different types of cantilever for the cantilevers 810 and 1910. The same applies to the measuring tips 320 and 1920.
• the cantilevers 810 and 1910 of the two measuring probes 330 and 1930 have a bending away from the sample surface 150 in order as far as possible to compensate for the inclination of the securing regions 305 and 1905 by the free end 350, 1950 of the cantilevers 810, 1910.
• this alignment it is possible to scan planar regions of a sample, for example the substrate 120 of the sample 110 or the surface of elements of the strip structure 130 with high resolution.
• the cantilevers 810 and 1910 are bent towards the sample surface 150.
• the measuring probe 330 can scan the left-hand side wall 410 of an element of the strip structure 130 of the sample 110 from Figure 1 with improved accuracy.
• the measuring probe 1930 can scan the right-hand side wall 420 of an element of the strip structure 130 of the sample 110.
• the control device 1280 of the scanning probe microscope 1200 can generate a realistic contour of the sample surface 150.
• Figure 19 the scan of the sample surface 150 is effected in a parallel manner with respect to the arrangement of the two measuring probes 330 and 1930.
• steep side walls oriented parallel to the scanning direction of the probes 330 and 1930 can be scanned by the probes 330 and 1930 only with difficulty.
• Figure 20 shows a configuration which comprises the two measuring probes 330 and 1930 twice in each case.
• the two probes 330 and 1930 are arranged in a manner rotated by in each case 90 0 rela- tive to one another.
• the SPM 1200 can realistically image sample surfaces 150 whose structure elements have a rectangular shape having steep side walls.
• the free ends 350, 1950 of the cantilevers 810 and 1910 can be aligned paral- lei to the sample surface 150 and scan the sample surface individually or in combination.
• a test body which can be procured from the company for example, can be used to calibrate the adjustable bending of the free end 350, 1950 of the cantilever 310, 810, 1710, 1910.
• the key elements of a test body are the overhanging structure elements thereof. If the measuring tip 320, 1920 is symmetrical in relation to the z-direction (i.e. the normal to the sample) and the measuring tip 320, 1920 is additionally perpendicular to the test body, the measuring probe 330, 1930 generates a symmetrical image of the test body. If one of the two conditions is not met, the measuring probe 330, 1930 generates a distorted image of the test body. If the scan of the measuring probe 330,
• Figure 21 reproduces a flow diagram 2100 of a method which can be used for examining a sample surface 150, in particular a surface 150 having a high aspect ratio and/or steep flanks 410, 420.
• the method begins at 2110.
• a free end 350, 1950 of a cantilever 310, 810, 1910 is adjusted by means of an adjustable bending, wherein the adjustable bending at least partly compensates for or intensifies a tilting of a securing region 305, 1905 of a measuring probe 330, 1930 and/or a pre-bending of the cantilever 310, 810, 1910.
• the second step 2130 involves determining with the aid of an optical measuring device 1300 whether the cantilever 310, 810, 1910 actually has the required bending. Both steps are performed before the beginning of a scanning process.
• steps 2120 and 2130 are repeated if the determination of the adjustable bending in step 2120 reveals that the cantilever has not correctly adopted the adjustable bending.
• the method ends in step 2150.
• the method illustrated in the flow diagram 2100 is performed before the scanning of the sample surface 150.
• Step 2230 involves switching of the laser system 1290, which directs a laser beam 1295 onto the cantilever 810, 1910 in the vicinity of the free end 350 of the cantilever 810, 1919.
• the four-quadrant photodiode 1270 of the light pointer system 1300 measures the A-B portion of the light beam 1275 reflected from the free end 350, 1950 of the cantilever 310, 810, 1910.
• a plan view of the four-quadrant photodiode 1270 is illustrated at the bottom left end of the flowchart 2200.
• Alight beam 1275 impinges centrally on the light-sensitive area of the photodiode 1270.
• Step 2230 involves determining the signal portion which the light beam 1275 has in the segments A and B of the four-quadrant photodiode 1270.
• Decision step 2240 involves ascertaining whether the signal portion of the segments A and B is less than a predefined threshold value. If this is the case, in step 2250 the light power of the laser system 1290 is increased and, in step 2230, the signal portion of the segments A and B of the four-quadrant photodiode 1270 is once again measured. Decision step 2240 then involves ascertaining whether the new signal portion of the segments A and B is still less than a predefined threshold value.
• step 2260 involves ascertaining that the instantaneous light power of the laser system 1290 sets the desired bending of the free end 350, 1950 of the cantilever 310, 810, 1910.
• Step 2270 then involves starting the process in which the measuring tip 320, 1920 approaches the sample surface 150.
• the method for adjusting the orientation of the free end 350, 1950 of the cantilever 310, 810, 1910 relative to the sample surface 150 ends in step 2280.
• the method in Figure 22 is performed with the aid of a closed-loop control (for example with a proportional element and an integral element) in combination with a sample-and-hold circuit. After the setpoint value has been reached, a switchover is made from the sample mode to the hold mode.
• a closed-loop control for example with a proportional element and an integral element

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