Classifications

• • 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]
  • G01Q10/00—Scanning or positioning arrangements, i.e. arrangements for actively controlling the movement or position of the probe
• • 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
  • G01Q10/06—Circuits or algorithms therefor
• • 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
  • G01Q10/06—Circuits or algorithms therefor
  • G01Q10/065—Feedback mechanisms, i.e. wherein the signal for driving the probe is modified by a signal coming from the probe itself
• • 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
  • G01Q70/08—Probe characteristics
  • G01Q70/14—Particular materials

Definitions

• the present invention relates to a scanning probe microscope and a method of inspecting a high aspect ratio surface.
• Scanning probe microscopes use a probe to scan a sample or its surface and thus provide measurement data for generating a representation of the topography of the sample surface.
• scanning probe microscopes are abbreviated by SPM - English for Scanning Probe Microscope.
• SPM Scanning Probe Microscope
• SPM types are distinguished.
• STMs Scanning Tunneling Microscopes
• atomic force microscopy In atomic force microscopy (AFM for Atomic Force Microscope or SFM for Scanning Force Microscope) the probe tip is deflected by atomic forces of the sample surface, typically van der Waals forces. The deflection of the probe tip is proportional to the force acting between the probe tip and the sample surface and this force is used to determine the surface topography.
• Authors Y. Sarov, T. Ivanov, and IW Rangelow describe in the article "Controllable off-plane deflection of cantilevers for multiple scanning proximity probe arrays", Appl. Phys. A (2008), 92: 525-530, DOI io.ioo7 / soo339-oo8-4668-y the production of a measuring probe with a two-dimensional arrangement of 4 x 32 measuring tips.
• Fig. 1a shows schematically the problem of an SPM probe when scanning a web.
• the dotted lines of Fig. Lb symbolize the difficulties in measuring the flanks of a high ridge with steep flanks.
• pivoting the AFM probe or Z-scanner ⁇ 40 ° from the normal of the sample surface, thereby passing the probe tip of the AFM probe 2 shows schematically the pivoting or tilting of the Z-scanner, which is the application note "High Throughput and Non-Destructive Sidewall Roughness Measurement Using 3-Dimensional Atomic Force Microscopy" of the company Park Systems Corporation (https://www.parkafm.com/images/applications/ semiconduetors / note / i_Park_Systems_App_ Note_Sidewall _Roughness_2012_03_14.pdf).
• the technical effort for producing the precision mechanism for pivoting the entire AFM measuring head is enormous.
• the space required for the AFM is very large.
• tilting the AFM probe also leads to a lateral displacement of the probe tip of the AFM probe, which makes navigation on the probe much more difficult.
• a measuring tip in the form of a so-called elephant's foot is used instead of a needle-shaped measuring tip.
• Fig. 3 shows schematically such a measuring tip, which is guided perpendicular to a web over this away.
• This principle was first described by the authors Yves Martin and H. Kumar Wickramashing in the article "Method for imaging sidewalls at atomic force microscopy" in Appl. Phys. Lett., 64 (19), 9 May 1994, pp. 2498-2500.
• a second control in the x direction (the fast scan direction) is used to guide the elephant foot probe over steep flanks or under overhangs.
• US Pat. No. 8,458,810 B2 discloses a cantilever of an AFM probe having two materials in an asymmetrical arrangement with respect to the longitudinal axis of the AFM probe.
• the two materials have different coefficients of linear expansion.
• a thermal signal component lateral deflection
• a topographic signal component deflection of the cantilever in the normal direction
• the present invention is therefore based on the problem to provide an apparatus and a method by means of which structures with a high aspect ratio can be reliably analyzed.
• the apparatus comprises a scanning probe microscope, comprising: (a) scanning means for scanning a probe tip over a surface; (b) a cantilever for the probe tip, the cantilever having a torsion region; (c) wherein the winding region is designed such that it twists upon application of a control signal and thereby pivots the measuring tip; and (d) a controller for outputting the control signal when the probe tip scans a portion of the surface that can be more accurately inspected with a pivoted probe tip than without pivoting the probe tip.
• An embodiment of a device according to the invention makes it possible to use measuring probes with normal radius of curvature and opening angle of a cone-shaped measuring tip and thus enables the high resolving power of conventional scanning probe microscopes when scanning surfaces without a high aspect ratio for samples which have a high aspect ratio.
• the defined scanning probe microscope provides access to corners or overhanging portions of edges that are not accessible to conventional SPMs.
• the angle of the probe tip relative to the home position without pivoting is set by performing a raster or scan operation. This allows an area of a sample to be scanned with a measuring tip whose pivoting angle is adapted to the topology of the sample surface.
• a sample area in a first scan can be scanned without pivoting the probe tip. From the image generated from the measured data, a pivoting angle of the measuring tip is determined for a second scan. Then the sample area to be examined is scanned again with the probe tip pivoted. From the measurement data of the two scans of the same area of the sample then becomes a realistic second image the sample surface are generated. If the second image gives rise to the assumption that the second image of the sample surface still does not coincide with the reality, the region of the sample to be examined can be scanned again with a different pivoting angle of the measuring tip. This process can be repeated until a close-to-reality image of a sample area to be examined is present.
• pivoting the probe requires only moving a minimum mass.
• the measuring tip can thus be swiveled or deflected very quickly and reproducibly during a scanning process.
• a scanning probe microscope usually has easily interchangeable measuring probes and a modular executable control device for generating a control signal.
• Existing systems can therefore be retrofitted with the device defined above.
• the twisting region comprises at least two interconnected material layers whose thermal expansion coefficients are different, at least in a partial region.
• at least a portion of the twisting portion comprises implanted material so that the portion and the twisting portion have different thermal expansion coefficients.
• the twisting region comprises at least a first region with at least two first interconnected material layers for setting a coarse pivoting of the measuring tip and comprises at least a second region with at least two second material layers connected to one another Adjusting a fine pivoting of the measuring tip or the twisting region comprises at least two partial regions of implanted material for setting a coarse pivoting and a fine tilting of the measuring tip.
• asymmetric material is implanted in the twisting area of the cantilever.
• a symmetrical arrangement of at least two materials in the twisting area and / or implanted material with respect to the cutting plane defined in the preceding paragraph also leads to a twisting of the twisting area and thus of the cantilever and ultimately to a pivoting or tilting of the asymmetrical temperature change with respect to the cutting plane Probe.
• the twisting region By having two or more regions of two or more interconnected material layers or two or more subregions of implanted material, the twisting region provides two or more parameters for inducing a local temperature change to selectively and precisely direct the deflection of the measurement tip out of the cutting plane to adapt the examining surface of a sample.
• the twisting area extends over the entire receiving unit.
• the area of the at least two interconnected material stretches layers over the entire cantilever or at least a portion implanted material extends over the entire cantilever.
• This embodiment of a cantilever is simple and therefore inexpensive to manufacture, since the two or more layers of material can extend over the entire cantilever. For example, by choosing a local asymmetric temperature change with respect to the cutting plane defined above within the twisting region, the twisting of the cantilever and thus the pivoting of the measuring tip can be adapted flexibly to the requirements of different applications.
• the region of the at least two interconnected material layers or the at least one partial region of implanted material comprises a bimetallic element.
• the twisting region comprises a material in an arrangement which, when the control signal is applied, holds a first part of the device substantially at a first temperature and keeps a second part of the device essentially at a second temperature, wherein the first and the second temperature are different.
• a twisting area defined in this way comes with a material and is therefore also favorable with regard to the production of a cantilever.
• By adjusting the configuration of the twisting Reichs can easily cover the requirements of various applications.
• the scanning probe microscope further includes a laser system configured to locally heat the twisting area upon application of the control signal.
• a laser beam can be focused on a small focal spot.
• its impact point can be precisely adjusted to the twisting area.
• a part of the material system of the twisting region can be selectively heated with the aid of a laser beam.
• a laser beam is able to bring about the above-mentioned preferred asymmetric temperature change.
• a laser beam is very well suited, by a deflection of the measuring tip from the specified cutting plane to adapt these quickly and selectively to the examined topography of a sample surface.
• the scanning probe microscope has a heating device which is designed to locally heat the twisting area when the control signal is applied.
• the scanning probe microscope has at least one heating resistor, which is mounted in the region of the twisting region, and which is designed to locally heat the twisting region when the control signal is applied.
• a localized heating device for example in the form of a heating resistor, can selectively heat part of the twisting region and thus bring about a preferred asymmetric temperature distribution with respect to the above-mentioned cutting plane in the twisting region.
• At least one of the at least two interconnected material layers or at least one subregion of implanted material comprises at least one heating resistor.
• the twisting area comprises at least one piezo actuator.
• a piezoelectric actuator as a twisting area of a receiving unit of a measuring probe has the advantage that the piezoactuator reacts quickly to a control signal.
• the measuring tip can be deflected dynamically on both sides of the above-defined cutting plane and thus adapted to the structure of the sample surface to be scanned.
• the receiving unit is designed as a microelectromechanical system.
• the controller is configured to modulate the control signal to excite the probe tip to vibrate.
• a modulation of the heating can be used to excite the measuring tip to vibrate.
• the vibration of the measuring tip takes place essentially in the z-direction, ie in a direction perpendicular to the sample surface.
• an asymmetric variation of the temperature takes place within a symmetrical connection region the vibration of the measuring tip predominantly in the x-direction, ie perpendicular to the defined cutting plane.
• the twisting area of the cantilever is designed to pivot the measuring tip in an angular range of ⁇ 5 °, preferably ⁇ 10 °, more preferably ⁇ 15 °, and most preferably ⁇ 20 °.
• the cantilever and the probe tip have a resonant frequency that is in the range of 100 Hz-5 MHz, preferably 500 Hz-1 MHz, more preferably 1 kHz-500 kHz, and most preferably 2 kHz-200 kHz ,
• the cantilever has a spring constant ranging from 0.001 N / m - 600 N / m, preferably 0.02 N / m - 300 N / m, more preferably 0.04 N / m - 150 N / m, and most preferably 0.08 N / m - 80 N / m.
• the scanning device is designed to expand a z-motion distance control loop into a z-x movement, wherein the x-direction designates a fast scan direction.
• the scanning device is configured to add a z-motion signal to an x-motion signal.
• the movement of the probe tip is essentially a movement in the x direction, ie, a movement parallel to the sample surface.
• the scanning movement of the measuring tip in the x direction can be superimposed on a vibration of the measuring tip in the z direction, ie a movement perpendicular to the sample surface.
• the measuring tip is controlled at the largest possible angle to the edge to be scanned. This can be achieved at least in part by mixing the z-movement of the measuring tip with the movement in the fast scanning direction. It is also possible to mix the movement of the measuring tip in the z-direction with the slow scan direction.
• the fast scan direction in this application refers to the direction in which a scanning probe microscope scans a given surface line by line.
• the direction on the sample surface perpendicular to the line-wise scan direction is referred to as the slow scan direction.
• the cantilever has a fixing unit, in which electrical connections are integrated, which lead to the twisting area.
• Probes from scanning probe microscopes are today preferably automatically interchangeable.
• probes with pivotable measuring tips can also be automatically, i. to be changed without manual interaction.
• a simple operability of a scanning probe microscope is achieved.
• the above-defined scanning probe microscopes can be used, for example, in a manufacturing environment.
• automatic probe replacement ensures high reproducibility and reliability.
• the short probe change times of less than a minute can be achieved by automating the probe change. This is particularly beneficial for probe microscopes operating in a vacuum environment.
• the cantilever has at least one sensor to determine the pivoting of the measuring tip.
• Sensors for determining the pivoting of the measuring tip can borzo be attached in the form of piezoresistive sensors on the top and / or bottom of the twisting portion of a cantilever.
• the scanning probe microscope further comprises a detection device which is designed to determine from a topography of the surface and a contour of the measuring tip whether a region to be scanned can be examined more precisely with the pivoted measuring tip than without pivoting of the measuring tip.
• a method of inspecting a high aspect ratio surface comprises: (a) scanning a probe tip over the surface, wherein the probe tip is attached to a cantilever and the cantilever has a twisted region; (b) applying a control signal when the probe tip scans a portion of the surface that can be more accurately inspected with a pivoted probe tip than without pivoting the probe tip; and (c) twisting the twisting portion to pivot the measuring tip.
• the method comprises the step of: detecting a topography of the surface, which substantially corresponds to the contour of the measuring tip for determining whether the measuring tip is to be pivoted.
• the method includes the step of: deciding whether the probe tip is pivoted based on the detected change in height of the surface.
• the angle of the probe tip relative to the home position is adjusted without pivoting prior to performing a scan.
• This allows an area of a sample with a measuring tip to be whose waste angle is adapted to the topology of the sample surface.
• a method according to the invention makes it possible to detect a steep high flank during a scanning process and to increase the accuracy of scanning a sample surface by appropriately tilting the measuring tip.
• a method according to the invention for examining irregular structural elements having a high aspect ratio is suitable.
• a scanning probe microscope according to any one of the preceding aspects is used to perform at least one of the above-identified method steps.
• 1a schematically shows the scanning of a probe tip of a probe
• FIG. 1b schematically illustrates the regions around the steep high web of FIG. 1a, which can not be reliably analyzed with a measuring tip of a scanning probe microscope from the prior art;
• Fig. 2 shows schematically the pivoting of the measuring head of an atomic force microscope for scanning the overhanging flanks of a web
• 3 is a schematic representation of the scanning of a probe in the form of an elephant foot via a web with substantially vertical flanks, the scanning being carried out in the region of the flanks with a control of the probe of the x-direction or in the scanning direction;
• Fig. 4 illustrates a schematic representation of some important components of an atomic force microscope according to the invention
• Fig. 5 shows schematically a plan view (top) and a section (bottom) through a probe of an Atomic Force Microscope with V-shaped cantilever;
• Fig. 6 shows the probe of Fig. 5 after a heating resistor has been applied to a beam of the V-shaped cantilever
• Fig. 6a shows symmetrically with respect to a plane of symmetry formed by the measuring tip and the cantilever on the underside of the cantilever, heating resistors having the form of folded electrical leads;
• FIG. 7 shows schematically a plan view (top) and a section (bottom) through a probe of an atomic force microscope with a beam-shaped cantilever;
• Fig. 8 shows the probe of Fig. 7, after a part of the
• FIG. 9 schematically illustrates a plan view (top) and a section (bottom) through a probe of an atomic force microscope whose cantilever has only one material; 10 shows schematically a plan view (top) and a section (bottom) through a probe of an atomic force microscope, wherein the twisting region of a cantilever comprises two piezoactuators;
• FIG. 11 is a flowchart of a first embodiment of a method of scanning a high aspect ratio sample surface with a scanning probe scanning microscope with a pivotable probe tip;
• FIG. 12 is a flowchart of a second embodiment of a method of inspecting a surface of a high aspect ratio sample with a scanning probe microscope with a pivotable probe tip.
• the diagram 100 of FIG. 1 a schematically shows a sample 110 having a sample surface 120 with a high web 130.
• the web 130 has steep 140 and partly an overhanging flank 135.
• a measuring tip 150 of a conventional scanning probe microscope can scan the sample surface 120 and the surface of the web 130 with great lateral resolution. As symbolized schematically by the dotted lines 170 and 190 in FIG. 1b, the measuring tip 150 can only insufficiently analyze the flanks 135 and 140 of the web 130, so that a conventional scanning probe microscope in the regions 160 and 180 around the web 130 does not provide loadable measurement data can deliver.
• FIG. 4 schematically shows some components of a scanning probe microscope 400 defined in the third section. Scanning probe microscopes are differentiated according to the measured variable used for examining the sample 410.
• Scanning Tunneling Microscopes use the tunneling current between the sample 410 and the measuring tip 430, which occurs upon application of voltage between the sample 410 and the measuring tip 430, to analyze the topography of the surface 415 of the sample 410.
• Atomic Force Microscopes AFM determine the surface contour of sample 410 from the deflection of probe 430 by sample 410.
• Magnetic Force Microscopes MFM measure the magnetic forces between sample 410 and probe 430.
• Near-field optical microscopes (SNOM) use evanescent electromagnetic waves as an interaction between the sample 410 and the probe tip 430.
• Scanning Near-field Acoustic Microscopes use near-field acoustic interactions to sense the surface topography Sample 410. This list of scanning probe microscopes is not complete.
• the principle for pivoting the measuring tip 430 disclosed in this application can be applied to the probes of all types of scanning probe microscopes which have a cantilever, i.e. a cantilever. have an elastically flexible lever arm or short a spring bar. Scanning probe microscopes whose probes have no cantilever must be equipped with a cantilever before use in the configuration described in this application. In the following, this principle is explained using exemplary probes for an atomic force microscope (AFM).
• AFM atomic force microscope
• the atomic force microscope 400 shown in FIG. 4 can not be used under ambient conditions or in a vacuum chamber (in FIG. 4) shown).
• the sample 410 to be analyzed is placed on a sample table 425.
• the sample table 425 can be moved in three spatial directions by a scanning device 420.
• the scanning device 420 comprises, for example, one or more micro-displacement elements, for example in the form of piezo-actuators (not shown in FIG. 4).
• the probe 455 or probe 455 includes a tip 430 or a probe tip 430 and a cantilever 440 for the probe tip 430.
• the cantilever 440 includes an elastically flexible lever arm or a cantilever.
• the cantilever 440 has a mounting unit 450 at the end opposite the probe tip 430, with which the probe 455 is attached to a fixture (not shown in FIG. 4) of the atomic force microscope (AFM) 400.
• the holding device can be connected via a piezo actuator to the measuring head of the AFM 400 (not shown in FIG. 4).
• the piezoactuator which connects the probe 455 to the fixture of the AFM probe, can also perform the function of a scanning device.
• the relative movement between the sample surface 415 and the measuring tip between the scanning device 420 and the piezo actuator connecting the measuring probe 455 to the holding device can be divided.
• the scanning device 420 performs the movement of the sample 410 in the sample plane (xy plane) and the above-mentioned piezo actuator accomplishes the movement of the measuring tip 430 in the direction of the sample normal (z-direction).
• the sample table 425 is stationary and the measuring tip 430 is brought to the region of the sample 410 to be analyzed by means of micro-displacement elements (not shown in FIG. 4).
• the probe tip 430 of the probe 455 can operate in multiple modes. On the one hand, it can be rasterized at constant height over the surface 415 of the sample 410. Alternatively, the de 455 are guided over the sample surface 415 with a constant force in a closed control loop. It is also possible, by means of a modulation method, to cause the cantilever 440 to oscillate perpendicular to the sample surface 415 and thereby scan the surface 415 of the sample 410 in a closed loop. In this case, the cantilever 440 may oscillate at its resonant frequency or perform a forced oscillation at a predetermined frequency.
• FM Frequency Modulation
• AM amplitude modulation
• a laser system 460 directs a laser beam 465 onto the tip of the cantilever 440.
• the laser beam 475 reflected by the cantilever 440 becomes taken by a photodetector 470.
• the photodetector 470 often has a four-quadrant configuration.
• the signal of a four-quadrant configuration of a photodetector 470 may be used to determine a pivoting of the probe tip 430 that does not result from a control signal or adjustment signal applied to the cantilever 440.
• an interferometer can be used to detect the pivoting of a probe tip 430 (not shown in FIG. 4).
• interferometer types which can be used for this purpose are a Michelson interferometer or a Mach-Zehnder interferometer.
• a deflection of the measuring tip 430 can also be detected with the aid of piezoresistive elements or sensors of the cantilever 440 (not shown in FIG. 4).
• the atomic force microscope 400 has a control device 480. This is connected to a second laser system 490 via a supply line 484 for a control signal.
• the laser beam 495 of the second laser system 490 is directed to one of the beams of the cantilever 440 of the probe 455 to effect local heating of the beam or arm of the cantilever 440.
• the second laser system 490 has no special requirements. Its wavelength can be chosen arbitrarily. However, wavelengths in the visible region of the electromagnetic spectrum facilitate adjustment of the laser beam 495. For locally heating part of the cantilever 440, an output power of a few mW is sufficient. In order to achieve a local heating of a part of the cantilever 440, a focus on a focal spot ⁇ 10 ⁇ is necessary. For modern laser systems, these requirements pose no problem. It is advantageous if the wavelengths of the two laser systems 460 and 490 differ. It is then possible Use filters to prevent interference of the signal of the photodetector 470 by the laser 490 (for example, by stray light).
• control device 480 has a second connection 482 to the fastening unit 450. Via the connection 482, control signals can be fed to the cantilever 440 of the probe 455.
• control signals can be fed to the cantilever 440 of the probe 455.
• cantilevers 440 of probes 455 for atomic force microscopes 400 are presented. Furthermore, the deflections of the measurement tips are discussed, which are caused by the application of control signals or adjustment signals via the connections 482 and / or 484 to the cantilevers of the probes.
• the diagram 500 of FIG. 5 shows in the upper part a plan view of a probe 555 and in the lower part a section through the plane of symmetry of the probe 555 and the measuring tip 530.
• the yz plane shown in the lower part of FIG. 5 corresponds to that in the third Part defined cutting plane by a cantilever and its measuring tip.
• the probe 555 has a measuring tip 530, a cantilever 540 and a fastening unit 550.
• the cantilever 540 has a twisting region 545 that extends over the entire cantilever 540.
• the twisting area 545 comprises two superimposed layers 542 and 544, which have different thermal expansion coefficients.
• the two layers 542 and 544 of the twisting region 545 can be constructed, for example, from semiconductive and / or electrically insulating materials. Silicon (Si) may be mentioned here as an example of a semiconducting layer and silicon nitride (Si 3 N 4 ) as an insulator material by way of example. Furthermore, it is possible for one of the two layers 542 and 544 to comprise a metal layer, for example an aluminum or a chromium layer, and the second a semiconducting or an electrically insulating layer. In addition, for the two layers 542 and 544, all materials are bar, as long as they have different thermal expansion coefficients.
• implant in the material of the cantilever 540 over the entire surface or in sub-regions material of another element or another compound to a certain depth, so as to produce a second layer whose length is different from the material of the cantilever 540th
• the methods and materials known from semiconductor manufacturing can be used. Implantation may occur from the top of the cantilever 540 (i.e., the side remote from the probe tip 530) and / or from the bottom of the cantilever 540 (i.e., the side having the probe tip 530).
• the measuring tip 530 may be made of the material of the lower layer 544, of the material of the upper layer 542 of the cantilever 540 or of another material. This also applies to the fastening unit 550. That is, the probe tip 530, one of the layers 542 or 544, and the attachment unit 550 may be integrally formed. Alternatively, individual or all components of the probe 555 may be manufactured separately from suitable materials and then joined together, for example by gluing.
• a uniform temperature change of the twisting portion 545 of the cantilever 540 leads to a movement or deflection of the measuring tip 530 in the yz plane.
• an uneven or a local temperature change of the twisting region 545 results in a movement of the measuring tip 530 predominantly in the xy plane, more precisely an additional tilting of the measuring tip in the -x or the + x direction.
• a local temperature change of the twisting region leads to a superposition of the deflection of the measuring tip 530 in the yz and the xy plane.
• Local heating of an arm or beam of the cantilever 540 may be produced, for example, by locally irradiating a beam at a position 560 with the laser beam 495 of the laser system 490.
• the tilting or pivoting of the measuring tip 530 is, to a first approximation, proportional to the light power introduced at the position 560 into the winding area 545.
• the extent of the tilting of the measuring tip 530 also depends on the position 560 at which the laser beam 495 impinges on the twisting region 545.
• the absorption coefficient of the material that hits the laser beam 495 and its specific heat conduction influence the pivoting angle of the measuring tip 530.
• the deflection of the measuring tip 530 in -x or in the + x-direction takes place when a control signal of the control device 480 via the connection 484 to the laser system 490 due to the low mass of the cantilever 540 with a very short time constant in the range of microseconds.
• the time constant with which the cantilever 540 returns to thermal equilibrium after the laser beam 495 has been switched off by the control device 480 is generally greater.
• the probe tip 530 remains pivoted during a scan, so the local temperature gradient must be maintained by continuous energy supply. If the probe 555 is operated modulated, the cantilever 540 oscillates in the z direction. The amplitude of the cantilever oscillation is normally small ( ⁇ 1 ⁇ ), so that this has only a negligible influence on the local heating by the laser beam 495 of the laser 490.
• the local temperature increase in the region of the position 560 in addition to the power of the laser beam 495, also depends on the materials 542 and 544 as well as the position 560 of the laser beam 495 within the twisting region 545.
• Maximum local temperature increases ⁇ are in the range of a few K (Kelvin).
• a single laser beam 495 locally heats the warp region 545 at position 560.
• two or more laser beams can be derived from the laser beam 495 of the second laser system 490.
• a separate laser system can be used for each laser beam (not shown in FIG. 4).
• an elliptical focus may be generated by means of a cylindrical lens to uniformly heat a larger area of the twisting portion 545.
• the use of a cylindrical lens can be dispensed with since semiconductor lasers typically already have an elliptical output beam (not shown in FIG. 4).
• the exemplary twisting region 545 shown in FIG. 5 has two materials with different thermal expansion coefficients. It is also possible to arrange three or more materials one above the other in the twisting area 545. However, in the arrangement of three or more different materials one above the other, care should be taken that the resonance frequency of the cantilever 540 remains in the range of 10 kHz to 100 kHz. Furthermore, in the weaving area 545 shown in FIG. 5, both layers 542 and 544 extend over the entire winding area 545. However, it is also possible that one of the layers 542 and 544 or both layers does not extend over the entire twist area 545 extend. A twisting area may be composed of sub-layers comprising different materials.
• first partial layers of the twisting region 545 which are arranged, for example, in the vicinity of the measuring tip 530, are used for coarse guidance of the measuring tip 530.
• Second sub-layers of the twisting portion 545 which are attached closer to the fixing unit 550 within the twisting portion 545, may be used to finely align the measuring tip 530.
• the two layers 542 and 544 fill the twisting area 545 in its entire area.
• An arrangement is also possible in which one of the layers 542 or
• one of the layers 542 or 544 may be in multiple sub-areas within the warp area
• the laser beam 495 may impinge on the warp region 545 at a position having one or both of the layers 542 and 544.
• the various portions within which the two layers 542 and 544 are arranged can be individually irradiated with the laser beam 495.
• the different subareas can the Having two or more interconnected layers are selectively heated with different laser sources.
• the laser beam 495 of the laser system 490 can be used to generate a plurality of laser beams that are directed individually at the different subregions of the layers 542 and 544 (not shown in FIG. 5).
• the winding region 545 represented in FIG. 5 extends over the entire cantilever 540.
• the cantilever 540 is simple and inexpensive to manufacture.
• the laser beam 495 is directed at the position 560 on the left arm or beam of the twisting area 545 of the cantilever 540.
• Local heating at position 560 results in pivoting of measuring tip 530 in the -x or + x directions, depending on whether the material of layer 542 or 544 has the greater thermal expansion coefficient. If the surface topography 415 of the sample 410 to be examined requires tilting of the measurement tip 530 in the opposite direction, the laser beam 495 is directed to a position of the right-hand beam of the warp region 545 and the right-hand beam of the warp region 545 is locally heated (in FIG 5 not shown).
• the diagram 600 of FIG. 6 presents a probe 655. This corresponds in dimensions and material composition to the probe 555 of FIG. 5, ie it comprises the measuring tip 630, the cantilever 640 and the fastening unit 650.
• the twisting region 645 extends over the entire cantilever 640 and has two materials 642 and 644 with different thermal expansion coefficients.
• the probe 650 has a heater in the form of a heating resistor 660 mounted on an arm or beam of the twisting unit 645 and the cantilever 640, respectively.
• the heating resistor 660 may, for example, be designed in the form of a thin coating.
• the currently preferred material is aluminum. Aluminum has a high coefficient of thermal expansion and a relatively high electrical resistance. Other metals with similar properties can also be used.
• the heating resistor 660 is shown in the form of a rectangle for reasons of simplicity. Typically, the heating resistors have meandering electrical conductor structures. 6a shows the underside of a measuring probe with two heating resistors in the form of folded electrical conductors. The width of the conductors is in the range of a few micrometers. Their length is typically a few hundred micrometers, for example 200 ⁇ to 500 ⁇ .
• the exemplary cantilever 640 has a 4.6 ⁇ thick silicon layer. This is covered by a 0.6 ⁇ thick layer of silicon oxide.
• a thin chromium layer (about 50 nm) is deposited on the silicon oxide layer as an adhesion-promoting layer.
• a 1 ⁇ thick aluminum layer is deposited, for example in the form of the conductor structure shown in Fig. 6a, which acts as a heating resistor.
• Heating resistors may also be created by implanting dopants into a semiconducting cantilever 640. This process is described in the book "PRONANO: proceedings of the integrated project on massively parallel intelligent cantilever sample platforms for nanoscale analysis and synthesis", edited by Thomas Sulzbach and Ivo W. Rangelow, Weg: Monsenstein and Vannerdat Publishers, ISBN: 978-3- 86991-177-9.
• the heating resistor 660 is applied in addition to the two layers 642 and 644 of the cantilever 640. When applying a heating resistor 660, however, it is also possible to dispense with one of the two layers 642 or 644.
• the heating resistor 660 which has a thermal expansion that is different from the cantilever layer 642 or 644, then takes over the function of the second layer of the cantilever 640.
• the heating resistor 660 has two leads 665 which lead through the fastening unit 650 and connect the heating resistor 660 via the connection 482 to the control device 480.
• the heating resistor 660 allows for local heating of the beam of the twisting portion 645 on which the heating resistor 660 is mounted. As explained in the context of the discussion of FIG. 5, locally heating a beam of the twist region 645 causes the tip 630 to tilt in the -x or + x direction.
• the thermal time constant for setting a thermal equilibrium within the cantilever 640 between local heat input by the heating resistor 660 and the heat dissipation through the mounting unit 650 is of the same order of magnitude as stated above.
• the heating resistor 660 can be operated digitally, ie when applying the control signal, a predetermined voltage is applied to the heating resistor 660 and this converts a defined electrical power into a corresponding heat energy.
• the heating derstand 660 also work analogously, so that the electrical power loss of the heating resistor 660 can be adjusted according to the voltage applied to the leads 665 voltage. If the atomic force microscope shown in FIG. 4 is used, the heating resistor 660 can also be used in a closed control loop.
• the controlled variable is the tilting of the measuring tip, which can be determined by means of an interferometer or a piezoresistive sensor. It is also possible to determine the tilt of the measuring tip from the measurement of a temperature change of the twisting area.
• the heating resistor 660 extends over a majority of the area of a beam of the cantilever 640 and thus over a greater part of the twisting area 645. It is alternatively possible to concentrate the heating resistor on a small part of a twisting area 645 (not shown in FIG. 6). Further, the heating resistor 660 may be divided into a plurality of smaller distributed heating resistors (also not shown in FIG. 6). The smaller distributed heating resistors can be connected in series and thus controlled with a single control signal. It is also possible to provide several heating resistors individually or in groups with supply lines and thus operate independently of each other.
• the heating resistor 660 may be applied to the right arm or beam of the twisting portion 645 of the receiving unit 640.
• only one heating resistor 660 is provided on the left-hand beam of the twisting region 645. orderly. This allows an active deflection of the measuring tip 630 in one of the directions -x or + x as a function of the coefficients of thermal expansion of the layers 642 and 644.
• a second heating resistor can be provided on the right-hand beam of the twisting portion 645 (not shown in Fig. 6). This may be done in various forms as discussed above in connection with the heating resistor 660.
• the heating resistor 660 is mounted on the winding area 645.
• the heating resistor 660 or the heating resistors may be attached to the underside of the twisting portion 645 (not shown in FIG. 6 but shown in FIG. 6a).
• the heater resistor (s) mounted on the underside of the cantilever 640 slightly reduces the distance of the cantilever 640 from the surface 415 of the sample 410.
• one or more sensors can additionally be mounted on the canvases 440, 540, 640 (not shown in FIGS. 4 to 6). With their help, the extent of distortion of the cantilever 440, 540, 640 and thus the pivoting of the measuring tip 430, 530, 630 can be determined.
• the sensor (s) may be mounted on the side of the heater resistor (s) 660 or on the opposite side of the cantilever 440, 540, 640.
• the sensors can be designed, for example, in the form of piezoresistive sensors which indicate a bend in a cantilever arm by a voltage change at their terminals.
• FIGS. 4 to 6 probes for atomic force microscopes have been described, whose cantilevers are V-shaped. However, the atomic force microscopes defined in this application can also use probes whose cantilevers are designed differently.
• the diagram 700 of FIG. 7 schematically shows a measuring probe 755 whose cantilever 740 has the form of a bar.
• the upper part of FIG. 7 shows a plan view of the measuring probe 755 and the lower part represents a section through the cantilever 740 and the measuring tip 730 of the probe 755.
• the probe 755 also has a fastening unit 750 ,
• the cantilever 740 includes a twist region 745 that extends over the right half of the cantilever 740.
• the cantilever beam 740 has a first layer 744 occupying the entire length and width of the beam of the cantilever 740.
• a second layer 742 is applied on the right half of the cantilever 740 (as viewed in plan view).
• the two layers 742 and 744 have materials with different thermal expansion coefficients.
• the surface of the second layer 742 forms the twist region 745 within the cantilever 740.
• the twisting portion 745 of the cantilever 740 twists.
• the measuring tip 730 of the probe 755 pivots in the -x or the + x direction depending on the thermal Constants of the Layers 742 and 744.
• the probe tip 730 may also be tilted in the direction opposite to the tilt of the probe tip 730, when the laser beam 495 is focused on the twisting area 745. It is further it is possible to separate the left and right parts of the cantilever 740 by a slot to minimize heat transfer from one part to the other part of the cantilever 730.
• the local heating of the layer 742 and thus of the twisting region 745 takes place only indirectly via the heat conduction in the layer 744.
• the laser beam 495 is directed onto the layer 744, twisting takes place of the twisting region 745 slower and on the other hand, the local heating has a lower spatial resolution.
• the wavelength of the laser 490 such that the layer 744 is substantially transparent to the laser beam 495.
• silicon is transparent in the infrared (IR) spectral region.
• silicon nitride is substantially transparent.
• the position of the impact of the laser beam 495 may be selected to adjust the amount of pivoting of the probe tip 730.
• the twisting portion 745 may be locally heated at a plurality of positions (not shown in Fig. 7).
• the twisting region 745 extends only over the right half of the receiving unit 740. This has the disadvantages explained above. In a preferred alternative embodiment, therefore, the twisting area 745 is extended to the entire receiving unit 740 by the layer 742 also covering the entire cantilever 740 (not shown in FIG. 7).
• the sequence of layers 742 and 744 can be reversed from the illustration in FIG. Similar to the twisting region 545 of FIG. 5, the twisting region 745 can have both layers 742 and 744 in only one partial area.
• all of the modifications of the twisting region 545 discussed in connection with FIG. 5 are also possible for the twisting region 745 of FIG. 7.
• the measuring probe 855 corresponds to the probe 755 shown in FIG Heating device in the form of a heating resistor 860, the supply lines 865 are guided by the fixing unit 850.
• the heating resistor 860 is applied to the left half of the cantilever 840.
• Local heating of the layer 844 causes the twisting region 845 to twist.
• the layer 844 conducts the heat absorbed in the left part into the right part of the layer 844 and from there into the layer 842, resulting in local heating of the two layers 842 and 844 results and ultimately leads to a tilting of the measuring tip 830.
• the direction of pivoting of the measuring tip 830 depends on the thermal constants of the materials of the layers 842 and 844.
• the heating resistor 860 heats the twisting region 845 only indirectly and thus with the above-mentioned disadvantages.
• the heating resistor 860 may be mounted on the right half of the cantilever 840, resulting in direct local heating of the twisting region.
• the heating resistor 860 whose thermal expansion is normally different from the thermal expansion of the layers 842 and 844, can take over the function of the second layer 842 so that the layer 842 can be saved (not shown in FIG. 8).
• the heating resistor 86o occupies most of the left portion of the receiving unit 840.
• the heating resistor 860 and / or a second heating resistor on the right half of the receiving unit 840 can be divided into a plurality of smaller heating resistors which are placed at different locations placed at different locations of the receiving unit (in FIG Fig. 8 not shown).
• FIG. 6b shows a symmetrical arrangement of heating resistors with respect to the plane of symmetry (yz plane).
• the various heating resistors that replace the heating resistor 860 can be controlled individually, together or in groups. If the various resistors are individually connected to the controller 480, various heater resistors may be used for coarse steering and fine deflection of the probe tip 830.
• the heating resistor (s) may be mounted on or below the cantilever 840, as illustrated in FIG.
• a second substantially identical resistor 860 is applied to the winding region 845 on the measuring probe 855 shown in FIG. 8, the asymmetry remains that the heating resistor 860 mounted on the layer 844 remains the twisting region 845-in contrast to that on the layer 842 arranged heating resistor - only indirectly heated.
• This asymmetry can be removed by extending the layer 842 over the entire layer 842, whereby the twist region 845 extends over the entire cantilever 840.
• this asymmetry can be circumvented by installing heating resistors above and / or below the cantilever 840 symmetrically with respect to the symmetry plane of the measuring probe 855 instead of the second layer 842 on or below the cantilever 840 (see FIG.
• FIG. 9 represents a measuring probe 955.
• This has a cantilever 940, at one end of which the measuring tip 930 is fastened and which is fastened with its opposite end to the fastening unit 950.
• FIG. 9 shows a top view of the measuring probe 955 in the upper part and a section through the cantilever 940 and the measuring tip 930 in the lower part.
• the cantilever 940 of FIG. 9 has only a single material. Semiconductor materials, in particular silicon, are preferred materials for the Cantilever 940.
• the cantilever 940 includes two legs 960 and 970 that are secured to the mounting unit 950. In the region of the measuring tip 930, the two legs 960 and 970 are connected to one another via a thin connecting web 980. The upper 960 and lower legs 970 are connected to the controller 480 of the atomic force microscope 400 via the leads 965 and 482.
• the lower leg 970 is over a majority of the length of the cantilever 940 by a multiple wider than the upper leg 960. As can be seen from the upper part of Fig. 9, the upper leg 960 and the lower leg 970 of Cantilever 940 of the probe 955 the same thickness. Due to the geometry, the lower leg 970 has an ohmic resistance that is several times smaller than the ohmic resistance of the upper leg 960.
• the twisting region 945 extends at the measuring probe 955 over the entire cantilever 940.
• the two legs 960 and 970 heat unevenly.
• the upper leg 960 heats up much more than the lower leg 970 and therefore expands more than the lower leg 970.
• the upper leg 960 has a first temperature and the lower leg 980 has a second temperature, wherein the first temperature is greater than the second temperature.
• the measuring tip 930 of the probe 955 is tilted in the direction of the negative y direction.
• the thermal time constant is greater than for the cantilevers 540, 640, 740 and 840.
• the diagram 1000 of FIG. 10 shows a measuring probe 1055 with a cantilever 1040, the twisting region 1045 of which comprises two piezoactuators 1060 and 1070.
• the cantilever 1040 is V-shaped similar to FIGS. 4 through 6.
• the probe tip 1030 is attached to the tip of the V-shaped cantilever 1040.
• the cantilever 1040 is secured to the attachment unit 1050 of the 1055 probe.
• the cantilever 1040 has a substantially uniform material layer 1042.
• a piezoelectric actuator 1060 and 1070 is respectively applied on the left and on the right beam of the cantilever 1040.
• the piezo actuators are connected via the supply lines 1065 or 1075 and 482 to the control device 480 of the atomic force microscope 400.
• Piezo actuators can be applied to the Cantilever 1040, 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 SR Manalis, SC Minne and CF Quate in the article "Atomic force microscopy for high speed imaging using cantilevers with integrated actuators and sensors", Appl. Phys. Lett., 68, 871 (1996) almost exclusively integrated manufacturing methods from the semiconductor industry and the MEMS (micro-electro-mechanical system) manufacturing are used for the deposition or implantation of piezo actuators 1060, 1070.
• ZnO zinc oxide
• piezo actuators change their dimensions when applying an electrical voltage in the longitudinal direction conceivable, piezo actuators with a complex
• geometry to the cantilever 1040 which can change in one (for example, the longitudinal direction), two (for example in the two lateral directions) or three spatial directions (ie, both in the longitudinal direction and in the lateral directions).
• a twisting region 1045 in the form of one or more piezoactuators 1060, 1070 has the advantage that the measuring tip 1030 can be deflected rapidly in a positive or a negative direction.
• the response time of the piezo actuators 1060, 1070 is limited by their relatively large capacitance, which leads to a current flow when changing an applied voltage.
• the capacitance of the piezoactuators in conjunction with the resistance of the leads 1065 limits the response of the probe tip 1030 to a change in the voltage signal applied to the leads 1065.
• the measuring probe 1055 reproduced in FIG. 10 has a piezoactuator 1060, 1070 on both arms or beams of the cantilever 1040. This makes it possible to pivot the measuring tip in the -x and + x directions.
• the use of a piezoactuator 1060, 1070 as a twisting area 1045 is usually sufficient, as a piezoactuator 1060, 1070 can normally bend in its longitudinal direction on both sides of its equilibrium configuration.
• the large piezo actuators 1060, 1070 may be replaced by a plurality of smaller piezo actuators, for example, to define a rough steering and a fine steering of the probe tip 1030 defined.
• FIG. 11 depicts a flowchart 1100 of a first embodiment of a method employing a scanning probe microscope 400 having a pivotable probe tip 530, 630, 730, 830, 930, and 1030 to inspect a sample surface 415 having a high aspect ratio.
• the procedure starts at 1110.
• the measuring tips 530, 630, 730, 830, 930 and 1030 are brought into the basic position, ie the position in which the measuring tip is not tilted.
• a scanning probe microscope 400 scans the measuring tip 530, 630, 730, 830, 930, 1030 over an area of a sample surface 415 to be examined.
• an image of the examined sample surface 415 is generated in step 1140.
• the generated image is analyzed and it is determined whether there are indications in the image that the measurement tip 530, 630, 730, 830, 930, 1030 could not sample the sample surface 415 in a realistic manner. If not, the method ends at step 1160.
• the probe tip 530, 630, 730, 830, 930, 1030 is pivoted through a defined angle.
• the three-dimensional contour of a measuring tip is normally known.
• the three-dimensional contour data can be supplied by the manufacturer of the measuring tip.
• the contour of the measuring tip can be determined by measurement, for example by means of a scanning electron microscope.
• the contour of the measuring tip 530, 630, 730, 830, 930, 1030 can be determined by scanning a sample with known surface topography.
• the measuring tip Since the measuring tip is subject to wear, it may be necessary to re-determine the contour of the measuring tip 530, 630, 730, 830, 930, 1030 from time to time.
• the author J.S. Villarubbia describes in the article "Algorithms for Scanned Probe Microscope Image Simulation, Surface Reconstruction, and Tip Estimation" in J. Res. Natl. Inst. Stand. Technol., Vol. 102, No. 4, July-August , Pages 425-454, in detail as from the measured image data of a sample surface with a known contour of the measuring tip, the topography of the sample surface can be determined.
• Displays for a non-realistic image of the sample surface 415 are present, for example, if the change of the sample surface 415, ie whose surface topography in at least part of the region of the sample 410 to be examined approaches or reaches the contour of the measuring tip. From the analysis of the image generated from the measured data, the direction of the pivoting of the measuring tip for the second scanning process also results.
• the pivotal unwanted motion components of the measurement tip 530, 630, 730, 830, 930, 1030 are corrected.
• An undesired component of the movement of the measuring tip is, for example, a change in the distance between the measuring tip 530, 630, 730, 830, 930, 1030 and the sample surface 415 and / or a change in the lateral position of the measuring tip relative to the sample surface.
• the area to be examined of the sample surface 415 with pivoted measuring tip 530, 630, 730, 830, 930, 1030 is scanned again. If the image now being generated has no indication of a resolution limit by the probe tip, the method ends at 1160. If not, the process described above is repeated with a changed probe tip pivot.
• the image generated after the second scan is composed of the scan data of the first data taken with the probe tip not swiveled and the second data taken with the probe tip swiveled together.
• FIG. 12 shows a flowchart 1200 of a second embodiment of a method employing a scanning probe microscope 400 having a pivotable probe tip 530, 630, 730, 830, 930 and 1030 to inspect a sample surface 415 having a high aspect ratio.
• the method begins at step 1205.
• a scanning probe microscope 400 scans a probe tip 530, 630, 730, 830, 930, 1030 over a region of a sample surface 415 to be examined.
• decision block 1215 a decision is made as to whether the probe tip 530, 630 , 730, 830, 930, 1030 is just scanning a portion of the sample surface 415 having a high aspect ratio or not. This decision can be made, for example, based on a comparison of the just-detected topography of the sample surface 415 with the contour of the measuring tip 530, 630, 730, 830, 930, 1030.
• decision step 1240 determines if the probe tip 530, 630, 730, 830, 930, 1030 has reached the end of the scan range. If this is the case, the method ends with step 1250. If not, at step 1245, the controller 480 pivots the probe tip 530, 630, 730, 830, 930, 1030 by applying a corresponding control signal. The method then proceeds to step 1210 and scans over the sample surface 415 with the pivoted measuring tip 530, 630, 730, 830, 930, 1030.
• the method continues to decision step 1220, where it is detected if the measurement tip 530, 630 , 730, 830, 930, 1030 is pivoted or not. If the probe tip 530, 630, 730, 830, 930, 1030 is not pivoted, it is determined at decision step 1230 whether or not the probe tip 530, 630, 730, 830, 930, 1030 has reached the end of the scan range. If so, the method ends with step 1235. Otherwise, the method continues with step 1210 and the probe tip 530, 630, 730, 830, 930, 1030 continues to scan across the sample surface 415.
• step 1220 If it is determined at decision step 1220 that the probe tip 530, 630, 730, 830, 930, 1030 is pivoted, tilting of the probe tip 530, 630, 730, 830, 930, 1030 is reversed in step 1225. The method then proceeds to decision step 1230 and ends with either step 1235 or proceeds to step 1210 with the scanning of the sample surface with non-pivoted measuring tip 530, 630, 730, 830, 930, 1030 continued.

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