Atomic force microscope with probe distancer

Abstract

Method of measuring a dimension of a nanometer sized high aspect ratio structure of a sample using a scanning probe microscope, the nanometer sized high aspect ratio structure comprising a recess having a height dimension in a direction transverse to the surface and a lateral dimension in a direction parallel to the surface, wherein the height dimension is greater than the lateral dimension; wherein the method comprises the steps of: - scanning the surface of the sample in a scanning direction parallel to the surface by a probe including a probe tip attached to the scanning probe microscope, and lowering, during the step of scanning, the probe tip into the recess such as to determine the dimension of the nanometer sized high aspect ratio structure; - wherein the recess comprises a recess width between at least two opposing sidewalls in a direction parallel to the scanning direction; - wherein the probe tip, which is lowered into the recess, comprises a base, an apex at an end of the base arranged to interface with the surface of the sample, and a distancer, wherein said base extends parallel to a longitudinal axis of the probe tip and wherein the distancer extends from the base such as to extend radially outward for defining a width of the probe tip including the distancer; and - wherein the width of the probe tip is smaller than the recess width.

Description

[0001] P137501NL00

[0002] Title: Atomic force microscope with probe distancer

[0003] The invention relates to a probe tip for an atomic force microscope for measuring nanometer sized high aspect ratio structures on a surface of a sample, an atomic force microscope and a method of scanning a surface of a sample using an atomic force microscope.

[0004] Scanning probe microscopy is a widespread class of microscopy methods that is based upon the scanning of a surface by means a probe tip in continuous or periodic, i.e. intermittent, contact with the surface. The method enables the detection and mapping of surface features — e.g. trenches, dimples, edges, roughness, etcetera — on the surface of a sample and below the surface of a sample with great accuracy and at high resolution. Measurements below the surface are performed using ultrasound in combination with scanning the surface using a probe. The high resolution enables the detection of even nanometer sized structures, and as a result of this high resolution has become very popular for example as a tool in the production of semiconductor elements. However, scanning probe microscopy is used in many other applications as well, for example the imaging and analysis of soft tissue or biological samples.

[0005] Atomic force microscopy is a type of scanning probe microscopy that uses a sharp tip attached to a cantilever to scan the surface of a sample and measure the forces between the tip and the sample's surface atoms. The cantilever's motion is monitored and used to produce high-resolution images of the on-surface and sub-surface features and topography of the sample, with a resolution on the order of a few nanometers. Atomic force microscopy can be used in a variety of environments, including vacuum, air, and liquids, and can provide information on a wide range of sample properties, including mechanical, electrical, and magnetic properties.

[0006] The surface of a sample to be mapped by atomic force microscopy may comprise nanometer sized high aspect ratio structures. A nanometer sized high aspect ratio structure is a shape or feature on the surface of the sample that is relatively high, or deep, compared to its width and I or length. As an example, a small and high structure, viewed from a side of the surface, can be considered a structure having a high aspect ratio.

[0007] Nanometer sized high aspect ratio structures are commonly measured, or mapped, using probe tips that are cylindrical, conical or spike-shaped and are more thin than a conventional probe tip. These shapes may be inserted in between nanometer sized high aspect ratio structures, thus allowing the nanometer sized high aspect ratio structures to be measured where a conventional probe tip would not be able to.

[0008] In particular when characterising high aspect ratio structures at the nanometer scale, conventional probe tips exhibit significant limitations. Sidewall friction and undesired lateral contact between the base and the structure wall result in deformation or wear of the tip and in systematic measurement artefacts, such as apparent broadening of narrow features and incorrect depth profiles. These effects become increasingly severe when nanoscale structures, for example with lateral and / or vertical dimensions in the range of 5—100 nm, are to be imaged with high accuracy. For example, Van der Waals or electrostatic forces deflect the probe tip up to a few nanometers before or during contact with the substrate surface. This consequently alters the effective interaction and resonance of the probe, resulting in misinterpretation of changes in amplitude, phase, or frequency of the readout signal as true height or material contrast. These effects introduce measurement uncertainties in both topography and other derived properties of substrates being scanned, and are impractical if not impossible to correct for since such bending of probe tips cannot be measured.

[0009] A downside of using cylindrical, conical or spike-shaped probe tips, i.e. commonly used probe tips for nanometer sized high aspect ratio structure measurements, is that there may be a high interaction between the surface of the probe tip and the nanometer sized high aspect ratio structure, specifically the sidewall of the structure. As a result, it is necessary to use higher forces to measure the surface while the lifetime of the probe, and specifically the probe tip, is limited. At the same times artifacts, e.g. incorrectly measured and mapped structures, may be created. For example, the depth between two structures may not correctly be measured as a result of the high interaction between the surface of the probe tip and the structures. Furthermore, lateral dimensions of the nanometer sized high aspect ratio structures may not be reliably measured due to the formation of artifacts as a result of the side wall of the probe tip coming in to contact with the side wall of the structure instead of the end of the probe tip coming in to contact with the surface of the sample, adjacent the structure.

[0010] The invention aims to counteract the above disadvantages, preferably while retaining the advantages. More specifically, the invention aims to provide for method and an atomic force microscope that is able to more accurately measure and map the surface of a sample having nanometer sized high aspect ratio structures, in particular the depth of an nanometer sized high aspect ratio structure, e.g. measure and map the surface of the sample while producing less artifacts, and increase the lifetime of the probe tip of the atomic force microscope.

[0011] Therefore, the invention provides for a method of measuring a dimension of a nanometer sized high aspect ratio structure of a sample using a scanning probe microscope, e.g. an atomic force microscope, in particular the method according to claim 1. The nanometer sized high aspect ratio structure of the method comprises a recess having a height dimension in a direction transverse to the surface and a lateral dimension in a direction parallel to the surface. In the context of the invention, a nanometer sized high aspect ratio structure should be understood as a structure having a height dimension that is greater than the lateral dimension. The method comprises the steps of: scanning the surface of the sample in a scanning direction parallel to the surface by a probe including a probe tip attached to the scanning probe microscope, and lowering, during the step of scanning, the probe tip into the recess such as to determine the dimension of the nanometer sized high aspect ratio structure, preferably at least the height of the nanometer sized high aspect ratio structure by lowering the probe tip of the scanning probe microscope in the recess until the probe tip reaches the bottom of said recess; wherein the recess comprises a recess width between at least two opposing sidewalls in a direction parallel to the scanning direction; wherein the probe tip, which is lowered into the recess, comprises a base, an apex at an end of the base arranged to interface with the surface of the sample, and a distancer, wherein said base extends parallel to a longitudinal axis of the probe tip and wherein the distancer extends from the base such as to extend radially outward for defining a width of the probe tip including the distancer; and wherein the width of the probe tip is smaller than the recess width. For example, the width of the probe tip can be between 0.1 and 0.999 times the recess width, preferably 0.2 and 0.999, more preferably 0.3 and 0.999, or even 0.3 and 0.95 times the recess width (i.e. the ratio between the widths being between 0.3 and 1.0). For example, depending on the width of the features, the size of the distancer can be anywhere between 2 and 100, preferably 2 nm and 70 nm, more preferably 2 nm and 50 nm.

[0012] The methods and probe tips according to the present concepts are particularly suitable for use in atomic force microscopy (AFM) and related scanning probe techniques for characterizing structures at the nanometer scale. It goes without saying that the method naturally includes the step of determining the desired dimensions of the nanometer sized high aspect ratio structure. In some embodiments, the methods and probe tips are configured for measuring features having lateral and / or vertical dimensions in the range of about 5—100 nm. Probes may for example be manufactured using chemical vapor deposition, or via etching. The tip radius may therefore for example be less than 5 nm or smaller, such as below 3 nm. The skilled person will however appreciate that other manufacturing methods may also be applied to obtain a probe tips with nanoscale probe tip radii. In the context of the present description, the term “distancer” is used to denote a structural protrusion or enlargement that extends radially outward from the probe tip, at a position between the base and the apex of the tip. The distancer is dimensioned and positioned such that, during scanning of a nanometer scale high aspect ratio structure, it makes controlled contact with the sidewall of the structure and thereby maintains a defined minimum radial separation between the base and the sidewall. In this way, the distancer acts as a physical spacer that limits unwanted lateral interaction of the base with the structure while allowing the apex of the probe tip to follow the surface profile at nanometer scale.

[0013] A “nanometer sized high aspect ratio structure” as used herein refers to a recess or protrusion whose height (or depth) is greater than its lateral width, e.g. 2:1, 3:1, 4:1, 7:3, etc. The invention is particularly advantageous for high aspect ratio structures that comprise nanoscale features, for example trenches, vias, lines or pillars having lateral dimensions and / or spacings in the nanometer range, such as between about 5 nm and about 100 nm. Typical dimensions of the width of a nanometer sized high aspect ratio structure is between 10-50 nm and depths or heights as small as 50 nm. In such cases, conventional probe tips tend to suffer from pronounced sidewall interaction and measurement artefacts, whereas the present probe tip with distancer allows the nanoscale geometry of these structures to be more accurately determined.

[0014] Advantageously, by providing a distancer that extends, or protrudes, radially outward, interfacing between the probe tip and the surface of the sample can be better controlled. Since the distancer locally broadens the probe tip at the end of the base, it may be prevented that a side of an structure on the surface comes in to contact with the base of the probe tip, reducing interaction between the probe tip and the structure. In the context of the invention, interaction between the probe tip and the structure is to be understood as forces acting upon the probe tip and the structure as a result of them being in proximity of each other, e.g. in physical contact with each other. By providing a distancer, the contact area between the probe tip and the wall of the structure interacting with each other may be reduced, reducing forces such as capillary forces and adhesive forces acting upon the probe tip and wall. In other words, the distancer may ensure that, even at small dimensions and high aspect ratios, the base of the probe tip is kept at a controlled distance from the sidewalls of the structure, thereby enabling accurate nanoscale profiling while limiting tip wear and sidewall-induced artefacts. As a result lifetime of the probe tip may be increased by reducing scraping or interference to diminish wearing of the probe tip. Also the risk of artifacts may be reduced that are normally caused as a result of such interaction with a sidewall or other structure. The probe tip is provided with a distancer having a regular shape. Therefore, due to the known shape of the distancer, the point of contact between the distancer and the sidewall is predictable. Thereby, the deviations caused by interaction between the probe tip and the sidewall, which in turn result in the error underlying the artifacts, can be calculated and are quantifiable. Therefore, the artifacts can be resolved. The influence of any deviations caused by for example Van der Waals or electrostatic forces acting on the probe tip can in other words be advantageously compensated for during or after measurements. Thereby, the invention advantageously also effectively enables to account for the measurement errors in measurement data associated therewith and thereby increases the precision and accuracy with which high aspect ratio features at nanoscales can be measured.

[0015] Furthermore, the shape of the distancer allows for less force needed to be applied for the probe tip to reach the bottom of the recess, because the probe tip more easily slides into the recess to reach the bottom.

[0016] To elaborate on the above, as may be appreciated, by limiting contact with the sidewalls, wear and tear on the probe tip is reduced, resulting in an extended operational lifespan. This means fewer replacements and lower operational costs. The reduction in interaction also helps to reduce measurement artifacts, such as false readings or inaccurate dimensions, particularly in the measurement of narrow or deep structures. This allows for more precise mapping of the sample's surface, ensuring reliable data. Furthermore, because the distancer reduces (diminishes) direct contact with the sidewalls, less force is needed to lower the probe tip into the recess or structure. This reduces the risk of damaging sensitive structures on the sample. It allows the probe to smoothly reach the bottom of the recess without being hindered by unnecessary resistance. The smooth motion results in less artefacts.

[0017] In addition to this, the reduction in direct contact not only results in less wear to the probe tip, but likewise to a reduction of risk of damage to the sample. In turn, since damage and wear to the sample results in remnants of the sample left behind, this likewise lowers the risk of contamination of the probe tip and / or the sample surface. The reduced level of wear to or contamination of the probe tip also improves repeatability of measurements performed with a same probe more than once.

[0018] Furthermore, by reducing unwanted lateral contact between the probe tip and the sidewalls of nanometer sized high aspect ratio structures, the probe tip can maintain improved vertical positioning stability within a recess. Such an improved vertical positioning stability may be achieved by due to the distancer providing a single and known contact point between the probe tip and the sidewalls of the nanometer sized high aspect ratio structure. When the probe tip is lowered during measurements of the scanning probe microscope, only the distancer will interact with the sidewall of the nanometer sized high aspect ratio structure, while the rest of the probe tip does not interact with said sidewall. A known probe tip, not having a distancer, may have multiple contact points with the sidewall at the same time and I or may have a contact point at an unknown height from the apex of the probe tip. This may negatively affect the measurement precision, as in both cases it is not known what point of the probe tip has been interacting with the surface such that it is not known at what vertical position the measurement data has been collected. The distancer provides a known contact point between the probe tip and sidewalls of high aspect ratio structures. As a result, stable positioning allows for increased vertical precision when measuring the depth of narrow or deep features, thereby enhancing the accuracy of depth profiles obtained from samples. Vertical positioning stability refers to the ability of the probe tip to maintain a consistent and precise vertical orientation relative to the sample surface while being lowered into and withdrawn from nanometer sized high aspect ratio structures. This stability ensures that the probe tip’s movements in the depth direction remain controlled, reducing the likelihood of lateral shifts or unintended contact with the structure’s sidewalls. Maintaining such stability is essential for accurate depth measurement, as even minor deviations in vertical alignment can introduce errors in the recorded depth and overall topography of the sample. Such vertical precision is especially beneficial in applications where nanoscale accuracy is required, for example, in the production of semiconductor elements or in the structural analysis of biological samples. Consequently, the risk of positional deviation due to unintended sidewall interaction is minimized, supporting more reliable and accurate measurements of high aspect ratio features with nanometer-level detail.

[0019] The distancer, in some implementations, can have a stiffness such that, during said lowering upon an engagement of the distancer with one of said sidewalls, the distancer can engage the sidewall without a bending of the distancer. When a probe tip having a distancer is lowered into a recess of a nanometer sized high aspect ratio structure, the distancer may experience various forces acting upon it. For example, if the distancer interfaces directly with a sidewall, interaction forces and I or shear forces may act on the distancer. Bending or otherwise deforming of the distancer may result in inaccurately determining the dimensions of the nanometer sized high aspect ratio structure, such as the depth of the recess. When the distancer does not bend relative to the probe tip, more accurate measurements may be taken. This may be achieved by manufacturing the probe tip out of a sufficiently stiff material. Additionally or alternatively, the distancer can be shaped such as to provide said stiffness in at least one direction sideways to a direction wherein the distancer extends from the base.

[0020] The distancer can comprise a remote end away from the base of the probe tip, the remote end can include a rounded shape. A rounded end of the distancer, at a location away of the probe tip, i.e. a distal end of the distancer, reduces the amount of surface of the distancer that interfaces with the side wall of the a recess of a nanometer sized high aspect ratio structure. For example, assuming that a probe tip that during operation has a horizontally provided distancer. When such a distancer has a rounded end at a remote end, it has an apex in the horizontal direction. When this probe tip is now lowered into a recess, only the apex of the distancer may interact with the sidewall. As a result, the rounded shape thus further reducing the interaction between the wall of the nanometer sized high aspect ratio structure and the probe tip.

[0021] The distancer has a regular shape, which means that its shape is well definable in mathematical formulas. This enables easy deconvolution and predictable contact points between the distancer and the substrate surface. For example, the distancer can be rotationally symmetric around the longitudinal axis of the probe tip. This may allow, in particular in relatively narrow recesses of a nanometer sized high aspect ratio structure, for the forces action upon the distancer to act symmetrically around the probe tip. When forces acting upon the distancer are equal, bending of the probe tip and I or the distancer may be mitigated. In an implementation, the distancer can be spherically, or ovoid, shaped such that it has a rounded cross-section, preferably the center of the spherically shaped distancer can coincide with the longitudinal axis of the probe tip. The distancer thus protrudes in all directions equally, e.g. by forming a disc-shaped distancer, when viewed in a direction parallel to the longitudinal axis. In alternative embodiments however, the distancer may be asymmetrical with respect to the longitudinal axis of the probe tip, such as by extending transversely in one or more directions from the base. This may ensure that, regardless of the orientation of the probe tip relative to the surface of a sample, the distancer interfaces with the surface instead of the base of the probe tip. As an example, when the distancer is a flat disc and the probe tip is lowered in the center of a nanometer sized high aspect ratio structure, forces acting upon the distancer by the walls of the nanometer sized high aspect ratio structure are equal, and thus the probe tip will not bend as a result. In case the distancer is only provided partially around the base of the probe tip, e.g. at a single side of the probe tip, forces may act upon one side of the probe tip and may cause bending as a result. This may thus be prevented by a distancer that is rotationally symmetric around the longitudinal axis of the probe tip. In a further example of provided a rotationally symmetric distancer around the longitudinal axis of the probe tip is that the probe tip may be used in any direction and the benefits of the distancer may still be achieved. Since the distancer is present in all directions in which the probe tip may move in lateral direction during scanning of the scanning probe microscope, the distancer will be positioned between the base of the probe tip and a wall of a recess of a nanometer sized high aspect ratio structure when the probe tip is lowered in such a nanometer sized high aspect ratio structure.

[0022] In an implementation, wherein the distancer is a spherical distancer provided at the tip of the probe such that the apex of the probe tip is located on the distancer, the distancer reduces the complexity of deconvolution during or after scanning of the surface. When the distancer is a spherical distancer, it has a constant radius. The midpoint can coincide with the longitudinal axis of the base, such that spherical distancer is rotational symmetric around the longitudinal axis of the base with a constant radius. Since the radius of the distancer is constant, angling of the probe tip or deformation of the probe tip can be conveniently accounted and corrected for. For example, if the probe tip is angled relative to its original position, the width and height of the spherical probe tip projected on the sample remains the same. Comparing this to the behavior of non-spherical apexes of a probe tip, angling or rotation of the probe tip mostly also affects the projection of the width and / or height of the probe tip on the surface of the sample. This may result in incorrect measurements, e.g. artifacts, or additional errors which may need to be corrected or accounted for. A spherical distancer provided at the tip of the probe alleviate this as it reduces the complexity of deconvolution during or after scanning. In particular, the spherical shape of the probe tip renders deconvolution to be independent of the angle of the probe relative to the surface of the sample, and will therefore result in less complexity and thus an advantage during deconvolution. Reduced complexity during processing of measurement results is a clear advantage, especially for high throughput scanning probe microscopy applications e.g. in industrial environments.

[0023] In further implementations, the distancer of the probe tip that can be used for lowering into the recess can be formed by a disc shape, star shape or bar shape such as to provide the distancer extending in more than a single direction. Such a distancer protrudes more than the other parts of the distancer or probe tip. As a result it may be more clearly defined where the structure on the surface of the sample interfaces, or comes in to contact with, the distancer. Therefore, accuracy of measurement results may improve compared to conventional probe tips, or a probe tip having a sphering end.

[0024] The distancer can be provided at the apex of the probe tip. This may advantageously facilitate that when the probe tip is lowered in the recess of a nanometer sized high aspect ratio structure, the distancer interfaces with a wall of the nanometer sized high aspect ratio structure instead of the apex the probe tip. When the walls of the nanometer sized high aspect ratio structure are sloped, uneven or otherwise not perpendicular to the surface of the sample, it may occur that the apex of the probe tip interfaces with, e.g. a sloped, wall before the distancer does. This would mean that the distancer may be bypassed and its aforementioned positive effects negated. Therefore, providing a distancer at the apex of the probe tip can facilitate the contact between the probe tip and the nanometer sized high aspect ratio structure in case the high aspect ratio is sloped, or uneven.

[0025] The base can be tapered such that the base has a larger width than the distancer, measured in a direction transverse to the longitudinal axis, at a first length from the end of the probe tip in a direction parallel to the longitudinal axis. Such tapering provides structural integrity and allows the probe tip to access narrow recesses while maintaining stability. By having the distancer protruding more radially outward than the width of the base, e.g. when the length is smaller than the first length, it may be ensured that the distancer interfaces with the structures on the surface of the sample. The larger the first length is, the more suitable the probe tip may be to scan high resolution structures. Conversely, by having the side of the base of the probe tip opposite the apex being relatively wide compared to the width of the base of the probe tip between the apex and the first length, it may be facilitated that the probe tip may be conveniently attached to the scanning probe microscope. Additionally, a relatively wide probe tip may increase the structural integrity of the probe tip when exposed to forces acting upon the probe tip when scanning. Thus, the skilled person will need to consider the advantages of having a relatively long first length to the advantages of having a relatively short first length. For example, the first length can be larger than 1 / 3 the length of the probe tip measured parallel to the longitudinal axis, such as 1 / 2 the length or 3 / 4 the length or the full length of the probe tip.

[0026] In some implementations of the present concept, in conjunction with the step of scanning, the method further comprises a step of mapping of said structures by moving the probe tip relative to the substrate surface and bringing the probe tip in contact with the surface, wherein for performing said mapping of the structures the method comprises sensing a deflection of the probe caused by interaction of the probe tip with a structure for obtaining a measurement signal, and performing a step of deconvolution of the measurement signal with a shape of the probe tip for establishing the shape of the structure, wherein the probe comprises a probe tip including a spherical shaped distancer forming the apex of the probe tip. The use of a spherical shaped probe tip makes deconvolution invariant of the angle of orientation, thereby reducing the complexity of this process and increasing the accuracy of the calculated shape of the structure.

[0027] In a second aspect of the invention, there is provided for a probe tip for a scanning probe microscope. The probe tip is arranged to be attached to a probe of a scanning probe microscope, e.g. an atomic force microscope. The probe tip comprises a base, an apex at an end of the base arranged to interface with the surface of the sample and a distancer. The base extends parallel to a longitudinal axis of the probe tip. The distancer extends from the base such as to extend radially outward for defining a width of the probe tip including the distancer. In an implementation, the distancer can be rotationally symmetric around the longitudinal axis of the probe tip and additionally or alternatively be provided away from the apex of the base. If it is known that the walls of the high aspect ratio are sufficiently perpendicular to the surface of the sample, providing the distancer away from the probe tip, or at a distance from the probe tip, may allow for the scanning of even deeper recesses of nanometer sized high aspect ratio structures, i.e. high aspect ratios of which the lateral dimension is even further reduced. If the distancer is provided at a distance chosen such that the interaction between the side wall of the nanometer sized high aspect ratio structure and the probe tip is sufficiently low, e.g. by providing the distancer at l / 5th, l / 4thor even l / 3rdof the length of the probe tip measured from the apex, the interaction may be still sufficiently low to increase probe tip lifetime and reduce the forces needed by the scanning probe microscope to scan the surface and the nanometer sized high aspect ratio structure in particular. For example, if the distancer is provided at l / 5thde distance of the probe tip measured from the apex, only l / 5thof the probe tip may be exposed to the side wall of the nanometer sized high aspect ratio structure before the movement into the recess is limited by the distancer, as the distancer may interface with the surface of the sample, e.g. the top of the nanometer sized high aspect ratio structure, or the side wall of the nanometer sized high aspect ratio structure.

[0028] Further advantageous aspects of the invention are set out in the description and appended claims.

[0029] The technical features described in the paragraphs and sentences above can be isolated from the context, and the isolated technical features from the different paragraphs and sentences can be combined. Such combinations are herewith specifically disclosed in this description.

[0030] The invention will further be elucidated on the basis of exemplary embodiments which are represented in the drawings. The exemplary embodiments are given by way of non-limitative illustration of the invention.

[0031] In the drawings:

[0032] Figs. 1A and IB show a schematic view of a probe tip scanning a surface of a sample according to the prior art;

[0033] Fig. 2 shows a schematic view of an example of a probe tip according to the invention;

[0034] Figs. 3A and 3B show a schematic the probe tip according to Fig. 2 and a probe tip according to the prior art scanning a surface of a sample respectively;

[0035] Fig. 4 shows a schematic view of a further example of a probe tip according to the invention;

[0036] Figs. 5A and 5B show a schematic view of the example of the probe tip according to Fig. 4 and a probe tip according to the prior art scanning a surface of a sample respectively; Figs. 6A and 6B depict a schematic view of a probe tip according to another example of the invention, wherein in Fig. 6B the probe tip of Fig.

[0037] 6A is angled;

[0038] Figs. 7 A — 7C depict a schematic view of a further probe tip according to an example of the invention, wherein in Fig. 7B and 7C the probe tip of Fig. 7 A is angled; and

[0039] Figs. 8A — 8C depict a schematic view of an even further probe tip according to an example of the invention, wherein in Fig. 8B and 8C the probe tip of Fig. 8A is angled.

[0040] Figure 9 schematically illustrates a system for executing a method according to the present concept.

[0041] Figure 10A and 10B schematically illustrates a method in accordance with the third aspect.

[0042] It is noted that the figures are only schematic representations that are given by way of non-limited examples. In the figures, the same or corresponding parts are designated with the same reference numerals.

[0043] Figure 9 schematically illustrates a system for executing a method according to an embodiment of the invention. The system comprises a scanning probe microscopy device comprising a scan head 202 with a probe 203 including a probe tip 1. The scan head 202 cooperates with the substrate carrier 205, which supports the substrate 206, for mapping features on or below the substrate surface 261. The probe tip 1 includes a distancer 4, which will be further described in relation to the figures discussed in the description below. The distancer 4 at the apex of the probe tip 1 is to be brought in contact with the substrate surface 261. In the presently described invention, the scanning probe microscopy system is used in order to map high aspect ratio features on the surface.

[0044] Mapping of features on surface 261 is performed by moving the probe tip 1 relative to the substrate surface 261 and bringing the probe 203 in contact with the substrate surface 261. This contact may be established continuously, i.e. in contact mode of the system wherein the probe tip 1 remains in contact with the surface 261, or intermittently by vibrating the probe tip such that it impacts (i.e. taps) the surface regularly in tapping mode. The measurements are performed by monitoring the deflection of the probe tip. To established the shape of surface features, a deconvolution step is to be performed between the measurement signal and the shape and orientation of the probe tip.

[0045] In contact mode, for example, a constant force is maintained continuously between the probe tip 1 and the substrate surface 261. As the probe tip 1 moves across the substrate surface 261, variations in surface topography cause changes in the interaction forces between the probe and the substrate. A light source 207 emits a light beam 209 onto the back of the probe 203, typically onto a specular reflective surface on the back of probe tip 1. Changes in the interaction forces between the probe 203 and substrate 206 will cause a deflection of the probe tip 1. These deflections will cause the light beam 209 to be reflected by the probe 203 at a changed angle. This change is detected by an optical sensor 210 and used by a controller 211 to correct the probe position on the substrate 261. This correction may be done using a correction signal from the controller 211, or based on the deflection signal detected by the sensor 210, or by a combination of both signals. The correction is used to determine a dimension of an on-surface feature on the substrate 206 and to generate an image of the features on the substrate surface 261. Alternatively to contact mode, in tapping mode the probe tip 1 oscillates at high frequencies near its resonant frequency, such that contact between the rounded shape 241 and the substrate surface 261 is made intermittently. As the rounded shape 241 taps on the substrate surface 261, changes in amplitude, phase, or frequency of the oscillatory movement are monitored to detect variations in the topography of the substrate surface 261 and used to generate an image thereof. In the context of this document, and not limited to the present embodiment alone, but also with respect to each and every alternative embodiment, scanning of the probe tip 1 relative to the substrate surface 261 may be performed in a variety of geometries. Typically, the scan proceeds laterally in the x— y plane, for example in a linear or raster pattern where successive scan lines are displaced in the y-direction while motion occurs along the x-direction. Alternatively, in cylindrical coordinates, the probe tip 1 may follow an arcuate or spiral trajectory defined by a radial coordinate r and angular coordinate cp while maintaining a constant height relative to the surface 261. In other embodiments, arbitrary user-defined trajectories (such as circular, radial, or polygonal patterns) can be executed to image selected regions of interest. In all these examples, the scanning direction is substantially parallel to the surface 261 of the sample, while approach or retraction of the probe tip 1 occurs along the perpendicular height axis.

[0046] The method using a probe 203 and probe tip 1 can also be used for mapping features below the substrate surface 261, including buried interfaces of layers, or subsurface defects or inclusions such as the subsurface feature 212. This would involve applying an acoustic vibration 213 to the probe 203 or to the substrate 206. This vibration 213 then propagates through the substrate 206 and has signal components which can be detected again at the substrate surface 261. For example, the vibration may have signal components with high frequencies (for example above 100 MHz), or signal components with lower frequencies (for example below 100 MHz). In the case of higher frequencies, the vibration 213 propagates through the substrate 206 and scatters from the feature 212. Some of the scattered vibration propagates back to the surface; this backscattered output signal may then be detected by the probe 203. In the case of lower frequencies, the feature 212 may be detected based on a mechanical response of the probe-substrate interaction caused by the vibration 213. For example, the substrate 206 may deform less when the vibration 213 is applied directly above the feature 212 than it would when the vibration 213 would be applied elsewhere on the substrate surface 261. In both cases, the probe will detect a signal component that has a frequency equal to the difference between two signal components of the applied acoustic vibration 213.

[0047] In the present concept, a system such as briefly described above and illustrated in figure 9 will be used for mapping nanometer sized high aspect ratio structures. A nanometer sized high aspect ratio structure, as referred to herein, is a structure of which the height dimensions (transverse to the surface) are typically more pronounced (i.e. larger) than the width dimensions (in the directions parallel to the surface).

[0048] Figs. 1A and IB show a schematic example of a probe tip 100 scanning a surface 101 of a sample 102 according to the prior art. The surface 101 comprises an structure 103, specifically a nanometer sized high aspect ratio structure 103 being a recess. The structure 103 is considered to be a nanometer sized high aspect ratio structure as the structure 103 is relatively high, in a height direction H, compared to its width in a width direction W. Specifically, the object has a height dimension in the height direction H being larger than a lateral dimension in the width direction W. The probe tip 100, which is mounted to a probe of an atomic force microscope (not depicted) is used to scan the surface 101. This may be done by dragging the probe tip 100 over the surface, i.e. having a minimal amount of movement in the height direction H while moving in a direction parallel to the width direction W, or may be done by tapping the surface 101, i.e. by also significantly moving in the height direction H while moving in the direction parallel to the width direction W. In the shown example of Figs. 1A and IB, the surface 101 is scanned by a tapping movement. The probe tip 100 is a conventional probe tip, being rotational symmetric around a longitudinal axis Al, being tapered along the longitudinal axis Al towards an end 104 of the probe tip 100. Turning to Fig. 1A, the probe tip 100 taps the surface 101, and is lowered in the nanometer sized high aspect ratio structure 103 and reaches the surface 101 at the bottom of the nanometer sized high aspect ratio structure 103 where the end 104 of the probe tip 100 interfaces with said surface 101. As can be seen from the schematic image, this is indeed the surface 101 and as a result data of the surface is correctly registered by the atomic force microscope to which the probe tip 100 is mounted. Turning to Fig. IB, the same probe tip 100 as in Fig. 1A attempts to interface with the surface 101 again, however the tapered probe tip 100 comes in to contact with the nanometer sized high aspect ratio structure 103. As a result, the probe tip 100 experiences a significant amount of interaction with the nanometer sized high aspect ratio structure 103, which may result in increased wear on the probe tip or may prevent the probe tip 100 from moving further down and not registering it still has a distance D to bridge before the actual surface 101 is reached. As a result, the atomic force microscope to which the probe tip 100 is attached incorrectly registers that the surface 101 is at the end of the probe tip 104 and the atomic force microscope incorrectly registers the surface data.

[0049] Turning to Figs. 2, 3A and 3B, a schematic view illustrates an example of a probe tip 1 according to the invention. The probe tip 1 is designed to provide a probe tip of a probe of an atomic force microscope (not depicted). The probe tip comprises a base 3 and an apex 5 at an end of the base 3 arranged to interface with a surface of a sample. The probe tip 1 further comprises a distancer 4, in the shown example the distancer 4 is provided at the apex 5 of the probe tip 1. As a result, the distancer 4 in the shown example is arranged to scan a surface 11 of a sample 10. The base 3 extends parallel to a longitudinal axis A of the probe tip 1. In this example, the base 3 is tapered towards the apex 5 of the probe tip 1. Such tapering provides structural integrity and allows the probe tip to access narrow recesses while maintaining stability. In the example, to minimize contact with sidewalls and ensure compatibility with nanometer sized high aspect ratio structures, the distancer 4 is spherically shaped, with a rounded crosssection, and is rotationally symmetric around the longitudinal axis A. The distancer 4 extends from the base 3 such as to extend radially outward and defining a width W2 of the probe tip 1, said width W2 including the distancer 4. In the shown example, the distancer 4 furthermore protrudes radially in a direction transverse to the longitudinal axis A. Specifically, the distancer 4 is spherically shaped, such that it has a rounded cross-section. The center C of the spherically shaped distancer 4 coincides with the longitudinal axis A of the probe tip 1. The base 3 is tapered such that the base 3 has a larger width W1 than the distancer W2, measured in a direction transverse to the longitudinal axis A, at a first length L from the end 5 of the probe tip 1 in a direction parallel to the longitudinal axis A. The distancer 4 has a first dimension DI parallel to the longitudinal axis A and a second dimension, in the example corresponding to the width W2 of the distancer 4, transverse to the first dimension DI. The second dimension, or width W2 of the distancer 4 is larger than the first dimension DI, effectively causing the distancer element 4 to be relatively thin in a direction parallel to the longitudinal axis A, comparable to a disc-shape.

[0050] Turning to Figs. 3A and 3B, the probe tip 1 according to an example of the invention and a probe tip 100 according to the state of the art are shown respectively. Both probe tips 1, 100 are used by an atomic force microscope (not depicted) in a tapping mode to scan the surface 11 of a sample 10 on which a nanometer sized high aspect ratio structure 12 is provided. In both Figs. 3A and 3B, the corresponding probe tip 1, 100 is lowered, during the tapping motion of the atomic force microscope, at the same position relative to the nanometer sized high aspect ratio structure 12 measured from the most distal end 13, 13’ of both probe tips 1, 100, e.g. at the bottom of the corresponding probe tip 1, 100. Comparing the surface of the probe tip 1, 100 of the example of the invention and the prior art interfacing with the wall 14 of the nanometer sized high aspect ratio structure 12, it can be seen that the probe tip 1 according to the invention has significantly less surface interfacing with the wall 14 compared to the probe tip 100 of the prior art. In particular, the distancer element 4 in the inventive probe limits lateral contact, ensuring that only a small section of the probe tip interacts with the sidewall. As a result, the probe tip 1 of the invention will have less interaction with the nanometer sized high aspect ratio structure 103 than the commonly used probe tip 100, which leads to an increased probe tip lifetime, a reduced chance of artifacts, and greater accuracy in depth and lateral measurements of the nanometer sized high aspect ratio structure. Additionally, by reducing unwanted lateral contact between the probe tip 1 and sidewalls 14 of the high-aspect-ratio structure 12, the probe tip 1 maintains improved vertical stability within the high-aspect ratio structure 12. This stability is achieved as the distancer 4 ensures a single, known contact point with the sidewall 14. During measurements, only the distancer 4 contacts the sidewall 14, leaving the rest of the probe tip 1 unaffected. In contrast, probes without a distancer may have multiple or variable-height contact points, reducing measurement precision.

[0051] Turning to Fig. 4 a schematic side view of a probe tip 1 according to a further example of the invention is depicted. The probe tip 1 comprises a base 3, an apex 5 at an end of the base, and a distancer 4 positioned away from the apex 5. The apex 5 is arranged to interface with a surface of a sample. The distancer 4 of the probe tip 1 extends from the base 3 such as to extend radially outward for defining a width W2 of the probe tip 1 including the distancer 4. The distancer 4 is rotationally symmetric around a longitudinal axis A of the probe tip 1, in the shown example the distancer is spherically shaped, forming a disc-like structure having its center C coincide with the longitudinal axis A. In further implementations, the distancer 4 may take on alternative shapes or positions along the probe tip, allowing customization based on specific sample or structural characteristics. The distancer is provided away from the apex 5 of the base 3, i.e. the distancer is provided at a distance D2 from the apex 5 of the probe tip. By positioning the distancer at the distance D2 from the apex 5, the probe tip 1 is kept narrow and sharp, providing a very small contact point, whereas advantages of the distancer 4 such as reducing the contact area with the sidewalls are maintained. In Figs. 5 A and 5B the use of the probe tip 1 according to the example of Fig. 4 has been shown. Specifically, Fig. 5A depicts the probe of Fig. 4 scanning a surface 11 of a sample 10 comprising nanometer sized high aspect ratio structure 12. In Fig. 5B a probe tip 100 according to the prior art is depicted scanning the surface 11 of the same sample 10 as shown in Fig. 5A. As can be seen, both probe tips 1, 100 interface with the wall 14 of the nanometer sized high aspect ratio structure 12. However, the probe tip 1 of Fig. 5A is limited in height direction by the distancer 4 and as a result cannot be moved down further. Alternatively, the probe tip 1 may deform slightly or slip over the surface 11 of the sample 10 such that the probe tip 1 can move down the recess formed by the nanometer sized high aspect ratio structure 12. When moving down the recess 12 in such a situation, the distancer 4 interfaces with the wall 14 of the nanometer sized high aspect ratio structure, and not the base of the probe tip 100 as will be the case in the example depicted in Fig. 5B. The probe tip 1 according to an example of the invention however either cannot move down further without lateral movement in the scan direction W or will slip such that the distancer 4 prevents the base 3 of the probe tip 1 from interfacing with the wall 14. Thus, compared to the conventionally used probe tip depicted in Fig. 5B, the probe tip 1 according to the invention interacts less with the side wall 14 of the nanometer sized high aspect ratio structure 12 and as a result has less interaction with the probe tip 1.

[0052] The rounded, spherically shaped distancer which is for example depicted in Figs. 2 and 4 provides additional advantages by minimizing the contact area between the distancer and the sidewalls of nanometer sized high aspect ratio structures. By limiting contact primarily to the apex of the distancer’s rounded shape, interaction between the probe tip 1 and the sidewalls is significantly reduced. This design ensures that only a minimal portion of the distancer interacts with the structure, facilitating smoother movement of the probe tip within narrow recesses and thereby further enhancing measurement accuracy while reducing wear. In addition to reducing wear on the probe tip itself, this limited contact minimizes potential damage to delicate samples and lowers the risk of sample and probe tip contamination. The limited sidewall interaction further enables the probe tip to maintain stable vertical positioning within a recess, contributing to more accurate depth measurements. By ensuring consistent orientation and reducing probe deformation, the design also enhances repeatability across multiple measurements, allowing for more reliable results when scanning similar structures with the same probe.

[0053] Turning to Figs. 6A and 6B, an example of a probe tip 1 according to the invention is depicted. The distancer 4 is a spherical distancer 4 provided at the tip 5 of the probe 1 such that the apex of the probe tip 1 is located on the distancer 5. The spherical distancer 4 has a constant radius, and its midpoint coincides with the longitudinal axis of the base 3 such that the distancer 4 is rotational symmetric around the longitudinal axis of the probe tip 1. In Fig. 6A the probe tip 1 is in an upright position, in Fig. 6B the probe tip 1 is angled. This angling may be the result of the suspension from the scan head of the scanning probe microscope, a periodic motion of the probe tip 1, or of external forces acting upon the probe tip 1. Comparing Fig. 6A and 6B, it can be seen that the projected width of the probe tip, wO and wl of Fig. 6A and 6B respectively, is the same. As a result, the spherical distancer 4 renders deconvolution to be independent of the angle of the probe relative to the surface of the sample. As a result, the process of deconvolution is less complex. In Figs. 7A-7C and 8A-8C a comparison is given with different probe tip 4 shapes.

[0054] Turning to Figs. 7A-7C and 8A-8C further examples of the probe tip 1 according to the invention have been depicted. As an example, the spherical distancer 4 of Figs. 6A and 6B has been replaced by a square probe tip 4 (in Figs. 7A - 7C) and a ovoid shaped distancer 4 in Figs. 8A - 8C. In Figs. 7 A and 8A, the probe tip 1 is in an upright position, having a projected width of wO on the surface of a sample during use. In Figs. 7B and 8B, the probe tip 1 has been angled relative to the upright position over an angle ct. Due to the angling, it can be seen that both probe tips 1 of Figs. 7B and 8B tilt, and have a displacement height dz and a projected width of wl. The projected width wl in Figs. 7B and 8B is larger than the projected width wO of Figs. 7 A and 8A due to the tilting. The incorrect projected width wl needs to be corrected for, of which an example is shown in Figs. 7C and 8C. The incorrect projected width wl is the sum of the projected width wO and the displacement width dx. Although, it is possible to deconvolute the angled probe tip 1 of Figs. 7B and 8B, doing so will result in an error of value dx in x-direction and dz in z-direction. The displacement width dx and height dz of the probe tip of Figs. 7 A — 7C can be determined using the following equations respectively: dx = hO * cos (a) and dz = wO * sin (a), in which hl is the length of the probe tip 1. For Figs. 8A-8C, the displacement width dx and height dz of the probe tip 1 can be determined using the following equations respectively: dx = 4r — (2r + 2r * cos(a)) and dz = 2r *

[0055] sin (a). Hence, in either case of figures 7 and 8, the angle must be determined in order for the correction to be carried out. Comparing to the spherically shaped probe tip 1 of Figs. 6A and 6B, it can be seen that the deconvolution process is less complex and results in less error when a spherical distancer 4 is used.

[0056] Figure 10A schematically illustrates a probe 203 scanning a substrate surface 261 as the spherical shape 241 of the probe tip 1 makes contact with a sidewall 262 of an on-surface feature 264. The direction of the probe 203 relative to the surface 261 is indicated by arrow 266. The probe 203 in figure 10A is oriented at an angle 9 with respect to the substrate surface 261. As the probe tip 1 moves over the feature 264, the probe tip 1 will encounter the edge 265 thereof. Upon going over the edge 265, the probe 203 will be deflected, resulting in a deflection signal being measured. An example of resulting measurement data 300, in the form of a deflection signal u against a horizontal probe position x is depicted in figure 10B. The measurement data 300 are deconvolved with probe tip shape data associated with the shape at the end of probe tip 1. In embodiments of the first aspect of the invention where the rounded shape is spherical, and in the method according to the third aspect of the invention, the deconvolution is invariant with respect to the angling 0 of the probe 203 because the constant radius of the spherical shape 241 of the probe tip 1. Therefore, the measurement signal 300 of deflection u will be invariant to angle 0. The shape of edge 265 can be obtained by deconvolving the round shape 301 of the measurement signal thereof with the shape of the probe tip 1. In other embodiments, the probe tip may be provided with partially spherical rounded shapes, such as hemi- spherical shapes. If the probe tip 1 were instead provided with a non-spherical shape, such as elliptical shape 243, scanning the substrate surface 261 with that probe will result in a measurement signal that is dependent on the orientation angle 0 of the probe 203, which is therefore more difficult to deconvolve. This is an example of how the deconvolution of the measurement data 300 would be more complex than when a probe tip 1 with a spherically shaped tip is used, because additional uncertainties are contained within the measurement data. The rotational symmetry of spherical shapes alleviates these effects, significantly simplifying the deconvolution process.

[0057] During use at nanometer scale, the probe tip 1 with distancer 4 enables stable scanning with reduced risk of tip collapse or sticking to the sidewalls of high aspect ratio structures 12. By maintaining a controlled spacing between the base 3 and the sidewall 14, the effective contact area between the probe 203 and the structure 12 is reduced, which in turn lowers lateral forces acting on the tip 1. This allows the probe 203 to follow steep sidewalls and narrow recesses more faithfully, improving the fidelity of the acquired height data and thereby enhancing the accuracy and reproducibility of nanometer-scale measurements.

[0058] Many variations will be apparent to the skilled person in the art. For example, the base of the probe tip may have a different cross-sectional shape than shown in the examples, i.e. round, for example triangular, square or hexagonal. As may be appreciated by the skilled person, additional implementations not explicitly depicted in the drawings are possible, wherein the distancer’s dimensions, shape, and positioning may be varied to achieve similar advantages. Furthermore, it will be apparent to the skilled person that the disclosed probe tip can be used on various surfaces to detect structures having various, preferably nanometer sized high aspect ratio structures, and not merely a flat surface and a rectangular structure.

Claims

Claims1. Method of measuring a dimension of a nanometer sized high aspect ratio structure of a sample using a scanning probe microscope, the nanometer sized high aspect ratio structure comprising a recess having a height dimension in a direction transverse to the surface and a lateral dimension in a direction parallel to the surface, wherein the height dimension is greater than the lateral dimension; wherein the method comprises the steps of:- scanning the surface of the sample in a scanning direction parallel to the surface by a probe including a probe tip attached to the scanning probe microscope, and lowering, during the step of scanning, the probe tip into the recess such as to determine the dimension of the nanometer sized high aspect ratio structure;- wherein the recess comprises a recess width between at least two opposing sidewalls in a direction parallel to the scanning direction;- wherein the probe tip, which is lowered into the recess, comprises a base, an apex at an end of the base arranged to interface with the surface of the sample, and a distancer, wherein said base extends parallel to a longitudinal axis of the probe tip and wherein the distancer extends from the base such as to extend radially outward for defining a width of the probe tip including the distancer; and- wherein the width of the probe tip is smaller than the recess width.

2. Method according to claim 1, wherein the distancer has a stiffness such that, during said lowering upon an engagement of the distancer with one of said sidewalls, the distancer engages the sidewall without a bending of the distancer.

3. Method according to claim 2, wherein the distancer is shaped such as to provide said stiffness in at least one direction sideways to a direction wherein the distancer extends from the base.

4. Method according to any of the preceding claims, wherein the width of the probe tip is between 0.3 and 1 times the recess width.

5. Method according to any of the preceding claims, wherein the distancer comprises a remote end away from the base of the probe tip, the remote end including a rounded shape.

6. Method according to any of the preceding claims, wherein the distancer is rotationally symmetric around the longitudinal axis of the probe tip.

7. Method according to any of the preceding claims, wherein the distancer of the probe tip that is used for lowering into the recess is formed by a disc shape, star shape or bar shape such as to provide the distancer extending in more than a single direction.

8. Method according to any of the preceding claims, wherein the distancer is provided at the apex of the probe tip.

9. Method according to any of the preceding claims, wherein the distancer is spherically, or ovoid, shaped such that it has a rounded crosssection.

10. Method according to any of the preceding claims, wherein the base is tapered such that the base has a larger width than the distancer, measured in the direction of travel, at a first length from the end of the probe tip in a direction parallel to the longitudinal axis.

11. Method according to any one or more of the preceding claims, wherein in conjunction with the step of scanning, the method further comprises a step of mapping of said structures by moving the probe tip relative to the substrate surface and bringing the probe tip in contact with the surface, wherein for performing said mapping of the structures the method comprises sensing a deflection of the probe caused by interaction of the probe tip with a structure for obtaining a measurement signal, and performing a step of deconvolution of the measurement signal with a shape of the probe tip for establishing the shape of the structure, wherein the probe comprises a probe tip including a spherical shaped distancer forming the apex of the probe tip.

12. Method according to any one or more of the preceding claims, wherein the nanometer sized high aspect ratio structure has lateral and / or vertical dimensions in the range of 5—100 nm13. Probe tip for a scanning probe microscope arranged to be attached to a probe of a scanning probe microscope comprising a base, an apex at an end of the base arranged to interface with a surface of a sample, and a distancer, wherein said base extends parallel to a longitudinal axis of the probe tip and wherein the distancer extends from the base such as to extend radially outward for defining a width of the probe tip including the distancer.

14. Probe tip for a scanning probe microscope according to claim 13, wherein the distancer is rotationally symmetric around the longitudinal axis of the probe tip.

15. Probe tip according to claim 13 or 14, wherein the distancer is provided away from the apex of the base.

Images