Improvements in scanning probe microscopy

Abstract

There is provided an apparatus for determining a physical parameter of a sample surface. The apparatus comprises a probe mount, a scanning stage, an optical detection system comprising a light source for positioning a beam of light onto a probe, and a positioning module that is configured to bring an imaging tip into contact with a sample surface for scanning. The positioning module comprises a processor configured to determine a width value of a probe cantilever in a region of an imaging tip and to instruct the scanning stage to initiate a relative movement between the probe mount and a sample surface to vary a position of a region of the imaging tip with respect to the beam of light which is stationary.

Description

[0001] IMPROVEMENTS IN SCANNING PROBE MICROSCOPY

[0002] INCORPORATION BY REFERENCE

[0003] This patent application claims priority to G.B. Patent Application No. GB2416398.2, titled “IMPROVEMENTS IN SCANNING PROBE MICROSCOPY”, filed on 7 November 2024, which is herein incorporated by reference in its entirety.

[0004] TECHNICAL FIELD

[0005] The present disclosure relates, in general, to scanning probe microscopy and improvements for increasing the scanning speed of a scanning probe microscope.

[0006] BACKGROUND

[0007] Scanning probe microscopy enables physical properties of a sample to be measured. Figure 1A is a schematic representation showing a scanning probe microscope (SPM). An SPM 100 generally comprises a probe mount 102 configured to receive a probe 103 formed of a microcantilever 104 with an imaging tip 106 at the free end. One or more sets of scanner motors 108, 110 are operated to generate a relative motion between the imaging tip 106 and a sample surface 112. Relative movement between the imaging tip and sample surface in an X-direction or Y-direction may be controlled by probe scanner motors 108 to move the probe mount within an XY plane, or sample stage motors 110 to move the sample mount within an XY plane. A positioning module 114 can initiate a movement of parts of the SPM within a Z-direction.

[0008] An SPM system can be operated in different scanning modes: tip or probe scanning; sample scanning; or some combination of both. The XY plane is generally considered to correspond to the directions of the probe and / or sample movement relative to one another in an X-direction and Y-direction, for example as initiated by the scanning motors. The XY plane may be considered to correspond to the desired plane of imaging with respect to the sample surface. In probe scanning, the motors may be arranged to move the probe 103 in an XY plane across a stationary sample surface, as shown in figure IB. The SPM can be configured for moving the probe in both of the X-direction and Y-direction, whilst the sample 113 remains stationary in the XY plane. The SPM may be configured for the sample may remain stationary within the XY plane whilst the position of the probe mount is varied in the XY plane, and where the detection system may optionally be moved with the probe mount. There are times when it is preferable or necessary to operate the SPM with the sample stationary (or used for large scale navigation), such as with larger samples where the scanning hardware is not able to move the sample reliably or safely. In these cases, the SPM can be operated in probe scanning mode.

[0009] In sample scanning, the SPM can be configured for moving the sample 113 in the XY plane, as shown in figure 1C. The SPM may comprise a sample stage onto which the sample can be placed, and the motors may be arranged to move the sample stage in an XY plane under a stationary probe 103 and imaging tip 106 (known as sample scanning). A global XY sensor may be used to measure the exact position of the probe on the sample surface.

[0010] In combination scanning, it is also possible to do some combination of both tip and sample scanning, for example where the probe 103 is moved in X and the sample 113 is moved in Y, as shown in figure ID. Both positions of the probe mount and sample may be varied in the XY plane, for example the probe can be moved in X and the sample moved in Y. The SPM system can be provided with a probe with the fast scan axis in the X-direction, where the probe is moving along the fast axis (X-direction), i.e., perpendicular to the length of the probe, and the sample is moving in the Y-direction or slow scan axis, i.e., along the length of the probe, such as for a raster scan pattern.

[0011] It is also possible to move the sample and / or probe in a Z-direction which is generally considered to be perpendicular to the XY plane. For example, this may be to bring the imaging tip into contact with the sample surface for the scanning.

[0012] As the probe traverses the sample surface, an optical detection system 118 measures a motion of the imaging tip of the probe interacting with the sample surface, where the motion relates to an angle of flex of the probe at the free end of the cantilever. The variation in movement of the probe during scanning can be measured to provide height information in a Z-direction.

[0013] Conventional SPMs use an electronic feedback loop to control the distance (Z-direction) between the probe and the sample surface to maintain a desired interaction force between the imaging tip and the sample surface. This may be to prevent damage to the sample or wear to the imaging tip. Typically, an optical beam deflection method is used to measure the force between the probe’s sharp tip and the surface. An electro-mechanical control loop adjusts the distance between the base of the probe and the surface as to attempt to keep this average load constant. Scanning motors 108, 110, as shown in figure 1, are used to control the distance of the probe mount from the sample surface in the Z-direction to maintain a desired interaction force. In conventional SPM systems, an optical detection system 118 and probe mount 102 may be moved in unison during scanning to maintain the desired interaction force and to enable imaging of a sample. The electronic feedback loop compares a process variable, such as the property of the probe’s motion that is being measured, e.g. oscillation amplitude, vertical position, bend angle, etc., against a setpoint value. This allows for calculation of any adjustments needed to bring the process variable back to the setpoint value. The motors then use these adjustments to control the distance in the Z-direction to maintain the desired interaction force.

[0014] In order to measure the vertical motion of the probe, a beam of light 116 is typically reflected or scattered off the back of the probe, and the reflected or scattered light is detected by one or more sensors. For example, in probe scanning mode the probe and light beam used to detect the probe’s vertical motion can be moved in the XY plane. Hence, the vertical motion of the probe as the imaging tip traverses the topography of the sample surface is measured. The vertical motion can be used to determine the vertical displacement of the probe relative to the sample surface such that this information can be used to generate, for example, topographic data for imaging the sample surface topography. The reflected or scattered light signals are processed to output vertical position data which is synced with X and Y location data to form an image or to create a topographic map. In this way, SPMs can generally be used to image nano- and microscale structures.

[0015] In order for the reflected or scattered light signals to provide information about the sample, the light beam must remain on the back of the probe and the reflected or scattered light signals must be detectable by the sensors. The skilled person would understand that there are consequences of light overspill. If the light beam is not returned from the back of the cantilever, then no useful data can be collected about the sample surface. For example, it is well known that light overspill induces image artifacts and reduces the signal to noise ratio in the detection system. If the light beam were to fall off the back of the cantilever this would negatively impact the collection of data that is ‘useful’, or in other words data that can provide information about the sample. Figures 2A-D are schematic representations showing a light beam and probe under different scanning conditions, in which: figure 2A shows no light overspill; figure 2B shows a mis-focussed optical detection system (with light beam overspill); figure 2C shows a mis-aligned SPM system; and figure 2D shows the probe being pushed upwards into a mis-focussed situation (with light beam overspill), for example whilst scanning a sample having a rough surface. To minimise the consequences of light overspill, as shown in figure 2E, the light beam can be aligned on the back of the probe as the probe traverses the sample. If the light beam partially is returned from the back of the cantilever, for example as shown in figure 2E, then the returned signal can be processed to extract useful data containing information about the physical parameter of the sample surface from the data that is not useful which provides no information about the physical parameter of the sample surface, i.e., data processing can be used to ‘bin bad data’.

[0016] If the beam of light partially falls off the probe, then (depending on the detection system) the measured motions of the probe are convoluted with that of the sample which is then also under the beam of light. As such, there is a current, entrenched understanding that a form of beam steering is required to always maintain the light dot at the same location on the probe, where the beam steer mirror must perfectly match the motion of the probe scanner. However, this is increasingly difficult to achieve as the scan frequency and scan speed increases. It is not enough to simply move the probe quicker because the probe motion must be correctly observed to deduce meaningful determinations of physical measurements of a sample surface.

[0017] For the last 30 years or so, SPMs have aligned a light beam or light dot on the back of the probe such that the light dot tracks the probe as the probe traverses the sample surface. By moving the light dot in the XY plane during scanning it is possible to maintain the light dot at an apparent fixed position relative to the back of the cantilever as the probe is moved during scanning, i.e., the light dot is steered to track the movement of the probe. One such alignment approach uses a moving mirror to move the light dot in the XY plane during scanning. Alternatively, a small fibre optic and micro-optics can be used to align the focused light on the back of the probe, where the small fibre optic or micro-lens can be adhered to the probe scanner such that the fibre and light dot move in concert with the probe during scanning. Else, the SPM suffers the consequences of light overspill in the data.

[0018] A conventional alignment approach is shown by the schematic representation in figure 3 A. The optical detection system 318 emits a light beam 316 onto the probe. The SPM has a moving mirror 350 to steer the light beam 316 onto the back of the probe 103 as the sample is scanned. As is shown, this modifies the spatial position of the beam 317 to maintain the focused light dot on the probe at a chosen position 325 on the probe, despite movement of the probe in the XY plane between different positions 303a, 303b within the XY plane and Z-direction. An optical alignment system, such as an objective lens 330, is used to focus the light dot onto the probe surface. This enables deflection measurements to be taken as the probe moves laterally in the XY plane because the light dot is always kept in the same location 325 relative to the probe and imaging tip, i.e. the light dot is apparently static on the probe surface as the probe is moved across the sample surface 312. Alternatively, the light dot can track the back of the cantilever as the probe is moved during scanning using a fibre optic, as shown in figure 3B, where the tip is adhered to the probe and would traditionally follow the trajectory of the probe during scanning.

[0019] However, these traditional alignment methods place limitations on the speed at which the probe can be moved across the sample surface whilst collecting useful data. It becomes increasingly technically challenging to implement at higher scan speeds. For example, whilst lenses or objectives can typically focus the light to a one micron dot, if the light starts falling off the probe, then the resolution (if the detection system works at all) will be linked to the objective element used in the optical system. For example, for scan frequencies above one kilohertz (1kHz) it becomes increasingly difficult to move the focused light dot in phase, and with the exact same motion, as the probe in a scanned probe arrangement, or higher scan frequencies can cause the fibre optic to move out of alignment or lose adherence to the probe. Typically, the light dot is approximately one micron in diameter, where the light dot covers an area on the cantilever surface in the XY plane. The cantilever of the probe may have a width of approximately twenty microns extending along the X-direction. The cantilever of the probe may have a length of approximately two hundred microns extending along the Y-direction. The cantilever may have a thickness or depth (along the Z-direction) of approximately one half of a micron. The imaging tip may have a tip radius of a few tens of nanometers at the sharpest point, with a base diameter of around 5 microns where the cantilever supports the imaging tip. Some example values for dimensions of a probe have been provided but it will be appreciated that dimensions of a probe will vary from probe to probe.

[0020] There are some ways to increase the scan rate or scan speed of the probe over the sample, but these too have limitations. The scan rate or scan speed is generally understood as the traverse speed of the imaging tip over the sample surface at which the surface features of interest can be determined or imaged. The speed at which you can perform measurements of a surface property (typically topography) is understood to be limited by the mechanical bandwidth of the probe (or resonant frequency of the probe). For example, the probe bandwidth can be increased to enable more pixels per second to be imaged, and hence equates to higher resolution images in a shorter time per frame. The probe bandwidth can be increased by making the probe with dimensions and materials that make the probe smaller and stiffer. However, there is a fundamental limit to how small the probe can be made since the detection system must still be able to read the probe’s physical interaction with the surface, particularly because this requires a focused beam of light and the probe cannot be made smaller than the focus spot of the light, otherwise the detection system will read noise (not signal). Further, if the probe is made smaller, then the alignment of the imaging probe with the sample surface becomes very challenging, particularly because the supporting structures for the probe chip can risk becoming a hazard where the support contacts the sample surface (instead of the probe).

[0021] A probe tracking system using beam steering with a moving mirror can maintain the light dot at an apparent static location on the probe surface or relative to the probe during scanning. However, a probe tracking system or beam steering is either not possible or is too costly to implement at higher scan speeds and scan frequencies. As such, at lower scan speeds and frequencies at which conventional SPMs operate, i.e., around 1-100 micrometres per second, it is possible for the light dot to track the back of the probe. However, this is not practical at higher scan speeds and scan frequencies, where it becomes very challenging to ensure that the light dot position on the back of the probe remains constant relative to the probe.

[0022] As technology has progressed, there is a growing requirement for SPMs to operate at faster scan rates.

[0023] SUMMARY OF THE INVENTION

[0024] An objective of the present disclosure is to provide an apparatus for determining a physical parameter of a sample surface. The foregoing and other objectives are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

[0025] A first aspect of the present disclosure provides an apparatus comprising a probe mount that is configured to receive a probe having a cantilever with an imaging tip, a scanning stage that is configured to initiate a relative movement between the probe mount and a sample surface, wherein the relative movement is within an XY plane, an optical detection system comprising a light source, the optical detection system configured to position a beam of light from the light source onto a surface of a cantilever in a region of an imaging tip, maintain the position of the beam of light such that the beam of light remains substantially stationary in the XY plane during scanning, and detect a returned light signal from a surface of a cantilever, and a positioning module that is configured to bring an imaging tip into contact with a sample surface for scanning, the positioning module comprising a processor configured to determine a width value of a cantilever in a region of an imaging tip, the width value substantially relating to a distance that a cantilever is extending along an X-direction of the XY plane, instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in the X-direction, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light, and wherein the movement of the probe mount in the X-direction has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined width value, and receive a returned light signal from a surface of a cantilever, a returned light signal having a Z-component representing a distance along a Z-direction that an imaging tip has moved, wherein the Z- direction is perpendicular to the XY plane.

[0026] The beam of light may remain stationary regardless of the relative movement between the probe mount and a sample surface. The probe mode and / or sample surface may not remain stationary relative to the beam of light.

[0027] The optical detection system may be configured to maintain the position of the beam of light such that the beam of light remains stationary in the Z-direction during scanning regardless of the relative movement between the probe mount and a sample surface.

[0028] Determining the width value may comprise one or more of an automated measurement, and a user-inputted measurement.

[0029] The region of the imaging tip may substantially correspond to an area on the surface of the cantilever where a base of the imaging tip intersects the surface of the cantilever.

[0030] The processor may be configured to determine a further width value of a cantilever in a region of an imaging tip, the further width value substantially relating to a distance extending along a Y-direction of the XY plane.

[0031] The determined width value and / or further width value may be substantially equal to a side-to-side width of the cantilever in the region of the imaging tip.

[0032] The determined width value and / or further width value may be substantially equal to a width of a base of the imaging tip where the base intersects the surface of the cantilever.

[0033] The processor may be configured to instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in a Y-direction of the XY plane, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light. The movement of the probe mount in the Y-direction may have a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined further width value.

[0034] A diameter of the beam of light may comprise a focussed light dot. Further, the optical detection system may be configured to maintain a focal point of the focussed light dot such that the focal point remains stationary in the Z-direction during scanning regardless of the relative movement between the probe mount and a sample surface. A diameter of the beam of light may comprise a focussed light dot. Further, the positioning module may be configured to instruct the optical detection system to initiate a movement of the optical detection system, thereby to vary the position of a focal point of the focussed light dot in the Z-direction during scanning. Yet further, the positioning module may be configured to instruct the scanning stage to initiate movement of the probe mount in the Z-direction during scanning.

[0035] The processor may be further configured to modify the determined width value and / or a further width value subsequent to instructing the scanning stage to initiate the relative movement between the probe mount and a sample surface, wherein the width value is modified by decreasing the determined width value as a function of the Z-component.

[0036] The apparatus may comprise a sample mount that is configured to receive a sample for scanning the sample surface.

[0037] The scanning stage may comprise the probe mount.

[0038] The apparatus may be a scanning probe microscope. Further, the apparatus may be an atomic force microscope.

[0039] The apparatus may comprise a probe having a cantilever with an imaging tip.

[0040] A diameter of the beam of light may be substantially equal to, or less than, the determined width value or further width value.

[0041] The beam of light may be positioned onto a surface of a cantilever above a base of an imaging tip where the base intersects the surface of the cantilever.

[0042] A second aspect of the present disclosure provides a method for determining a physical parameter of a sample surface, the method comprising providing a probe mount that is configured to receive a probe having a cantilever with an imaging tip, providing a scanning stage that is configured to initiate a relative movement between the probe mount and a sample surface, wherein the relative movement is within an XY plane, providing an optical detection system comprising a light source, the optical detection system configured to position a beam of light from the light source onto a surface of a cantilever in a region of an imaging tip, maintain the position of the beam of light such that the beam of light remains stationary in the XY plane during scanning, and detect a returned light signal from a surface of a cantilever, and providing a positioning module that is configured to bring an imaging tip into contact with a sample surface for scanning, the positioning module comprising a processor configured to determine a width value of a cantilever in a region of an imaging tip, the width value substantially relating to a distance that a cantilever is extending along an X-direction of the XY plane, instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in the X-direction, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light, and wherein the movement of the probe mount in the X-direction has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined width value, and receive a returned light signal from a surface of a cantilever, a returned light signal having a Z-component representing a distance along a Z-direction that an imaging tip has moved with respect to time, wherein the Z-direction is perpendicular to the XY plane.

[0043] The processor may be configured to instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface with a mean scan speed or mean traverse speed of at least one millimeter per second or a scan frequency of at least one kilohertz.

[0044] A third aspect of the present disclosure provides a computer-implemented method for determining a physical parameter of a sample surface, the method comprising the steps of configuring a probe mount to receive a probe having a cantilever with an imaging tip, configuring a scanning stage to initiate a relative movement between a probe mount and a sample surface, wherein the relative movement is within an XY plane, configuring an optical detection system comprising a light source to position a beam of light from the light source onto a surface of a cantilever in a region of an imaging tip, maintain the position of the beam of light such that the beam of light remains substantially stationary in the XY plane during scanning, and detect a returned light signal from a surface of a cantilever, and configuring a positioning module to bring an imaging tip into contact with a sample surface for scanning, the positioning module comprising a processor configured to determine a width value of a cantilever in a region of an imaging tip, the width value substantially relating to a distance that a cantilever is extending along an X-direction of the XY plane instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in the X-direction, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light, and wherein the movement of the probe mount in the X-direction has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined width value, and receive a returned light signal from a surface of a cantilever, a returned light signal having a Z-component representing a distance along a Z-direction that an imaging tip has moved, wherein the Z-direction is perpendicular to the XY plane.

[0045] A fourth aspect of the present disclosure provides a machine-readable storage medium encoded with instructions for determining a physical parameter of a sample surface, the instructions executable by a processor, whereby to cause the processor to carry out the computer-implemented method.

[0046] These and other aspects of the invention will be apparent from the embodiment(s) described below.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order that the present disclosure may be more readily understood, embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

[0049] Figure 1 A is a schematic representation of a scanning probe microscope, according to an example;

[0050] Figures IB, 1C and ID are schematic representations of different scanning modes, according to examples;

[0051] Figures 2A, 2 B, 2C and 2D are schematic representations of various probe scanning conditions, according to examples;

[0052] Figure 2E is a schematic representation of light overspill, according to an example;

[0053] Figure 3 A is a schematic representation of a scanning probe microscope comprising beam steering alignment, according to an example;

[0054] Figure 3B is a schematic representation of a probe comprising a fibre optic, according to an example; Figure 4 is a schematic representation of a scanning probe microscope, according to an example;

[0055] Figures 5A, 5B and 5C are schematic representations of determined width amplitudes of probe movement along the X-direction, according to examples;

[0056] Figure 5D is a schematic representation of a determined width amplitude of probe movement along the Y-direction, according to an example;

[0057] Figure 5E is a schematic representation of sample navigation, according to an example;

[0058] Figure 6A is a schematic representation of a region of an imaging tip for a beam cantilever probe, according to an example;

[0059] Figure 6B is a schematic representation of a region of an imaging tip for a V-shaped probe, according to an example;

[0060] Figures 7A and 7B are schematic representations of determined width values for a smooth surface and rough surface respectively, according to examples;

[0061] Figure 8 is a schematic representation of a scanning probe microscope, according to an example;

[0062] Figure 9 is a flow chart of a method for determining a physical parameter of a sample surface, according to an example; and

[0063] Figure 10 is a schematic representation of a machine, according to an example.

[0064] DETAILED DESCRIPTION

[0065] Example embodiments are described below in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

[0066] Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

[0067] The terminology used herein to describe embodiments is not intended to limit the scope. The articles “a,” “an,” and “the” are singular in that they have a single referent, however the use of the singular form in the present document should not preclude the presence of more than one referent. In other words, elements referred to in the singular can number one or more, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and / or “including,” when used herein, specify the presence of stated features, items, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and / or groups thereof. The term “and / or” is only an association relationship for describing associated objects and represents that three relationships may exist such that A and / or B may indicate that A exists alone, A and B exist at the same time, or B exists alone. The character “ / ” generally represents that the associated objects are in an “or” relationship.

[0068] Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealized or overly formal sense unless expressly so defined herein.

[0069] The following contains specific information related to implementations of the present disclosure. The drawings and their accompanying detailed disclosure are merely directed to implementations. However, the present disclosure is not limited to these implementations. Other variations and implementations of the present disclosure will be obvious to those skilled in the art.

[0070] The expression “at least one of A, B and C” or “at least one of the following: A, B and C” means “only A, or only B, or only C, or any combination of A, B and C.”

[0071] For the purposes of explanation and non-limitation, specific details such as functional entities, techniques, protocols, and standards are set forth for providing an understanding of the present disclosure. In other examples, detailed disclosure of well-known methods, technologies, systems, and architectures are omitted so as not to obscure the present disclosure with unnecessary details.

[0072] Movement of the probe in the XY plane with stationary beam

[0073] There is provided an improved SPM system comprising an optical detection system that is configured to position a beam of light from a light source onto a surface of a cantilever, and to maintain the position of the beam of light such that the beam of light remains substantially stationary in the XY plane during scanning. In other words, the beam of light is not steered during scanning and / or does not track a movement of the probe during scanning. Instead, the probe is permitted to move in the XY plane whilst the beam of light is stationary.

[0074] The XY plane is referred to herein as having an X-directional component and a Y- directional component. The Z-directional component has been described as substantially perpendicular to the XY plane and comprising Z-component data. However, it will be appreciated by the skilled person that any suitable referencing co-ordinates may be used, such that reference to an X-direction may be interchangeable with a Y-direction, and vice versa.

[0075] An SPM system 400 according to an example is shown in figure 4. The SPM comprises an optical detection system 418 having a light source that emits a beam of light 416. The beam of light comprises a light dot where it is incident on the probe surface 420. The beam of light may be focused onto the surface of the probe using an objective lens 430 and / or one or more mirrors. In an alternative arrangement, a fibre optic may instead be provided. The focus or focal point of the beam of light may initially be configured at the point 425 at which the beam of light hits the detection surface of the probe in an initial position 403a, for example during a set up process and before the probe movement has been initiated. The optical detection system is configured to position the beam of light onto the detection surface of a probe. The optical detection system may be arranged in a manner to cause the beam of light to fall onto an upper surface 420 of the cantilever, with the upper surface being the surface that faces away from the surface of the sample 412. This is generally considered to be the detection surface of the probe.

[0076] In an example, a suitable light source for the optical detection system may be a laser for emitting a laser beam or may be an LED or super luminescent diode for emitting a beam of light, where the beam can be focused to a light dot. In an example, the optical detection system may comprise an optical alignment system, for example, including an objective lens or one or more fibre optics or mirror.

[0077] The optical detection system is configured to detect a returned light signal from the detection surface of the probe or cantilever. The optical detection system may comprise a data collection module. The returned light signal comprises Z-component data representing a distance along a Z-direction that an imaging tip has moved with respect to time. The Z-direction is substantially perpendicular to the XY plane such that a distance that the imaging tip has moved along the Z-direction can be correlated to a vertical or height measurement of the sample surface (as indicated by the varying positions 403b, 403c of the probe during scanning).

[0078] During set-up, the location of the imaging tip of the probe can be determined. The beam of light may be placed at an initial position 425, at X0 and / or Y0 locations, within the XY plane. The initial position, X0 and / or Y0, may correspond to a location of the imaging tip at the free end of the cantilever beam. For example, the initial position, X0 and / or Y0, could be in a region where there is contact 415 between the imaging tip and the sample surface at the initial position, or above the base of the imaging tip where the tip intersects with the cantilever. However, it will be understood that X and Y co-ordinates corresponding to an initial position can serve as a reference point for tracking movement of the probe into different positions during scanning.

[0079] The term contact is implied to relate to a positioning of the imaging tip relative to the surface of the sample that is suitable for collecting Z-component information about the sample during scanning, for example via interaction forces exerted between the proximity of the imaging tip and sample surface. It is noted that an SPM may operate in ‘noncontact’ or ‘tapping’ mode and still collect information about physical properties of the sample surface during scanning.

[0080] The scanning process is initiated to move the probe mount, and hence a probe mounted thereon, in the XY plane whilst the beam of light is kept at a constant, static position in the XY plane. The X-direction may generally be understood to correspond to a width and the Y-direction to correspond to a length, or vice versa, with the Z-direction substantially being perpendicular to the XY plane. For example, the probe may have a cantilever that extends in the XY plane having a width along the X-direction and a length along the Y- direction, and a thickness or depth along the Z-direction. The probe can be moved in the fast axis, perpendicular to the length of the probe, to obtain faster scanning rates.

[0081] Reference to movement of the probe mount 102 is intended to infer a movement of a probe 103 mounted thereon. For brevity, reference herein may be made simply to movement of a probe 103. The movement of the probe can be caused by a range of motors, such as piezo-electric motors, piezo-electric stacks, voice coils, charge repulsion, etc.. There is provided a drive signal that is generated in the X and / or Y axis to initiate scanning of the sample via a movement of at least one of a sample and a free end of a probe relative to one another in the XY plane. The X axis may correspond to a high frequency or fast scanning axis, and the Y axis may correspond to a comparatively low frequency or slow scanning axis, or vice versa.

[0082] As shown in the example of figure 4, the probe mount can be instructed to move along the X-direction, for example via scanning motors as described above, such that the beam of light and the probe move relative to one another. The apparent movement of the probe relative to the beam of light may be centred about an initial position X0. For example, the probe can have an amplitude of movement, A, centred about X0, where the amplitude of movement of the probe is between maximum positions at XI and X2, or maxima XI and minima X2, and vice versa. The initial position, X0, can be any suitable position along the probe surface and does not have to be limited to being directly above the base of the imaging tip (for example). For example, the amplitude of motion may be limited to 19 microns in the X-direction for a 20 micron wide probe. The amplitude of motion may be chosen accordingly for different probe types, and / or may relate to a diameter of the beam of light incident on the cantilever surface which is used for collecting data or deflection measurements.

[0083] The SPM is provided with a positioning module that is configured to control movement of the probe. The positioning module is used to bring the imaging tip into contact with a sample surface for scanning, and to instruct movement of the probe. For example, the probe can be instructed to follow a pre-determined scan path. The positioning module comprises a processor for instructing the various components of the SPM system. The processor is configured to instruct the scanning stage or motors to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in the X-direction. This will vary the position of the imaging tip with respect to the stationary beam of light.

[0084] Examples of the amplitude of movement of the probe in the X-direction is generally shown in figures 5A-C. The amplitude of movement, A1(X), of the probe can be determined as a width value corresponding to a distance along the X-direction of the XY plane. For example, the width value may substantially relate to the distance that the cantilever or cantilever surface extends along the X-direction of the XY plane. Similarly, a further width value or length value can be determined as corresponding to a distance along the Y-direction of the XY plane. For example, the length value may substantially relate to the distance that the cantilever or cantilever surface extends along the Y-direction of the XY plane.

[0085] The processor is configured to determine the width value and / or length value and to instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface. For example, the movement of the probe mount in the X-direction, and / or Y-direction, can have a peak-to-peak amplitude of movement centred about XO. As the probe moves relative to the sample surface the imaging tip at the free end of the cantilever traverses the sample surface 412 to scan the sample. The system is configured such that the focused light dot remains stationary in the X and / or Y locations, while the probe traverses the sample surface in the XY plane. The light dot generally extends in the Z-direction. The cantilever is deflected as the imaging tip traverses the sample surface and the position of the imaging tip varies in the Z-direction due to the forces on the imaging tip imparted by interactions with the sample surface. The optical detection system receives the returned light signal from the surface of the cantilever, and the Z- component representing the distance that the imaging tip has moved with respect to time in the Z-direction is measured.

[0086] Determining a width value

[0087] The imaging tip and microcantilever together make up the probe of the SPM. For example, an SPM probe may be chosen to have desired dimensions or mechanical properties, such as a given fundamental resonant frequency (known as a bending mode) or a given softness or spring constant. This may be to provide desired interaction forces between the imaging tip and the sample surface. In an example, the material properties of the probe comprise a spring constant equal to or less than 0.01 Newtons per meter. An SPM probe may be provided with a cantilever that is rectangular in shape (known as a beam cantilever probe), or with a cantilever that is triangular in shape (known as a V- shaped probe), among other shapes. An SPM probe may be factory manufactured and as such the position of the imaging tip on the cantilever may fall within a manufacturing tolerance such that the exact location of the imaging tip at the free end of the probe may not be initially known. However, an SPM operator can perform an initial set-up process to determine the location of the imaging tip.

[0088] The width value for the purposes of instructing the scanning stage to initiate the movement of the probe or relative movement between the probe and sample surface may be determined through an automated measurement and / or a user-inputted measurement.

[0089] In an example, the SPM system may comprise an automated alignment module that determines a width value and / or length for the probe. The automated alignment module may be configured to detect the presence of the cantilever and determine dimensions or a shape of the cantilever and / or determine the location of the imaging tip on the cantilever.

[0090] In an example, the SPM system may comprise a user interface to allow a user to input a desired width value and / or length value for movement of the probe or relative movement between the probe and sample. For example, the user may measure the dimensions of the probe directly and input the measurements into the user interface for processing by the positioning module. The SPM can be configured to receive as a user input, a length value of the cantilever where the length value corresponds to distance along the Y-direction of the XY plane, where the instructed amplitude of movement of the probe mount in the Y- direction is less than the length value. For example, the position of the cantilever surface with respect to the light beam in the Y-direction of the XY plane can have an effective amplitude of movement that is much less than the length value of the cantilever.

[0091] As shown in the examples of figures 5 A-C, the oscillation distance or amplitude of motion of the probe in the XY plane can be determined by the width value and / or length value. The probe oscillation may be along the X-direction of the XY plane between a position XI and X2 that is centred about X0. In an example, position X0 corresponds to the base of the imaging tip where the imaging tip intersects the cantilever surface. The amplitude of motion of the probe, A1(X), is the distance or difference between XI and X2, i.e., A1(X)=X2-X1. Similarly, the probe oscillation may be along the Y-direction of the XY plane between a position Y1 and Y2 that is centred about YO. In an example, position YO corresponds to the base of the imaging tip where the imaging tip intersects the cantilever surface. The amplitude of motion of the probe, A1(Y), is the distance or difference between Y1 and Y2, i.e., A1(Y)=Y2-Y1. As the probe is moved in the XY plane relative to the sample the relative movement effectively sweeps out an area, such as that shown in the examples of figures 6 A and 6B.

[0092] The determination of the width value allows for the scanning stage to initiate the relative movement between the probe and sample to vary the position of the light dot or stationary beam of light such that the extent of movement of the probe centred about the initial position XO is such that the light dot always remains on the detection surface of the probe. The light dot remains stationary in the XY plane as the probe is translated along the X or Y direction. The movement of the probe mount in the X-direction has a maximum peak- to-peak amplitude of movement that is substantially the same as, or less than, the determined width value.

[0093] In the examples of figure 5 A and 5B, the amplitude of motion, A1(X), is substantially equal to a side-to-side width of the cantilever extending in the X-direction in the region of the imaging tip. As shown in figure 5B, the two extremes of motion shown with a dashed and dotted outline show that the red focused light dot never falls off of the edge of the probe. In another example, the area swept out may correspond to the region of the imaging tip 650a or area 650b above the base of the imaging tip, as shown in figure 6A, or another area therebetween. In the example of figure 5C, the amplitude of motion, A2(X), is substantially equal to a width of a base of the imaging tip where the base intersects the surface of the cantilever extending in the X-direction in the region of the imaging tip. Similar considerations can be given to movement of the probe in the Y- direction, as shown in figures 5D and 5E. In figure 5D, the probe mount is limited to a movement covering the region of the imaging tip in both the X and Y directions, and optionally, the sample may be moved to navigate between different scan windows on the sample surface. In figure 5E, the probe mount is limited to a movement covering the region of the imaging tip in both the X and Y directions, and optionally the probe and the optical detection system may be moved to navigate between different scan windows on the sample surface. In order to scan a desired area of a sample surface, a navigation module can navigate the surface of the sample to position the probe mount at a desired scan window. This allows for different areas of the sample surface to be scanned by the probe. It is often beneficial to move the probe in the XY plane rather than the sample, i.e. if the sample is too massive or large or fragile to fit on a scanning stage. Moving the probe in the XY plane allows for an arbitrarily large object to be scanned or imaged using the probe. Arbitrarily large areas can be mapped by panning the scan window around and stitching together data frames via image processing. The scan window can be navigated around the surface of the sample by moving the sample and / or the probe in the X and / or Y directions. Once the navigation module has positioned the probe mount at the desired scan window, the navigation module can remain stationary at the desired scan window whilst the data frame is collecting during scanning of the sample.

[0094] In an example, the amplitude of movement of the probe mount in the X and / or Y directions can be limited by a point at which a proportion of light falls off the cantilever in the region of the imaging tip. In an example, a tolerance level for light overspill or the proportion of light falling off the region of the imaging tip may be linked to a width of the incident beam of light falling on the detection surface of the cantilever. The tolerance level may be set according to a requirement that deflection measurements are collected using a minimum proportion of the centre of mass of the gaussian beam at its highest intensity (e.g., such as 2-3 sigma), where the focus of the beam is at the centre of mass of the gaussian beam.

[0095] In an example the physical parameter of the sample to be determined can include one or more of: height data representing a topography of the sample surface; a tribology property of the sample; a mechanical stiffness of a sample; amongst other physical or dimensional properties of the sample.

[0096] In general, the relative movement of the probe, or between the probe mount and the sample surface in the X and / or Y-direction is substantially the same as, or less than, the determined width value and / or length value of the cantilever in the region of the imaging tip. In other words, the position of the probe in the lateral directions (XY plane) varies relative to the position of the light dot as the probe scans over the sample surface. As shown in figure 6A, there is an area 650b at which the base of the imaging tip is attached to the cantilever. This area may be considered the region of intersection between the imaging tip, or base thereof, and the cantilever 620 or cantilever surface 660. The region of the imaging tip may be considered to be the free end of the cantilever and / or to substantially correspond to the region or part 650a of the cantilever which supports the imaging tip. The imaging tip 606 is mounted on the opposite surface 660 (‘bottom’ surface) of the cantilever with respect to the detection surface 665 (‘top’ surface).

[0097] The region of the imaging tip that corresponds to the width value and / or length value is generally shown in figure 6A, where the region may extend from an initial position, X0 and / or Y0, or base of the imaging tip, and out to an edge of the cantilever along the X- direction XI, X2 and / or Y-direction Yl, Y2. The region of the imaging tip relates to the area on the surface of the cantilever onto which the light beam is incident and from which a returned light signal provides a determination of a physical parameter of the sample surface during scanning. In other words, the region of the imaging tip is not limited to the area where the base of the imaging tip intersects the cantilever but rather is a comparatively wider area or zone that surrounds the base of the imaging tip where the returned light signal provides a strong signal to noise measurement.

[0098] Whilst figure 6A shows an example of a beam cantilever probe, an alternative probe is shown in figure 6B for a V-shaped probe. Similarly for a probe having a different shape to a beam cantilever probe, the region of the imaging tip that corresponds to the width value and / or length value may extend from the initial position, X0 and / or Y0, or base of the imaging tip, and out to an edge of the cantilever along the X-direction XI, X2 and / or Y-direction Yl, Y2. In the example of figure 6B, the determined width value may correspond to the width of the base of the imaging tip such that movement of the probe is limited to being within the area 650a defined by the intersection of the base of the imaging tip with the cantilever. The determined width value may be determined as a distance (e.g., X4-X3) relating to a width of the cantilever in the region of the imaging tip, for example between either edge of the cantilever about a desired position in the Y-direction, (e.g., Y0). Similarly, the determined length value may be determined as a distance (e.g., Y4-Y3) relating to a length of the cantilever in the region of the imaging tip, for example between either edge of the cantilever about a desired position in the X-direction, (e.g., X0). Referring to figures 5A and 6A, the determined width value may correspond to the distance that the cantilever extends along the X-direction between either side of the cantilever edges across the cantilever’s full width (i.e., X4-X3). In other words, the determined width value may be considered to be substantially equal to the side-to-side width of the cantilever in the region of the imaging tip. Similarly, referring to figures 5C and 6A, the determined width value may correspond to the distance that the cantilever extends along the X-direction, and which substantially corresponds to the area or base of the imaging tip (i.e., X2-X1). In other words, the determined width value may be considered to be substantially equal to the width of the base of the imaging tip where the base intersects the surface of the cantilever. As shown in figures 5C, it may be preferred for the amplitude of motion of the probe to be centred in the region of the free end of the cantilever above the imaging tip of the probe. The amplitude of movement of the probe mount in the X and / or Y directions can be limited by the area (i.e., width and length) of the base of the imaging tip.

[0099] Similarly, where figures 5A-C have been described with reference to the X-direction, this may instead, or also, refer to movement of the probe in the Y-direction. For example, as shown in figure 6A, there is a region of the imaging tip that effectively moves within the XY plane relative to the stationary light beam.

[0100] During scanning, the movement of the probe back and forth across the surface of the sample can excite bending modes and torsional modes in the cantilever. The excitation of such modes causes the detection surface of the cantilever to change angle, such that it will deflect away from or towards the incident beam of light. The excitation of these bending and torsional modes introduces errors in the deflection measurements of the probe motion at the free end of the probe because the detection surface of the cantilever rapidly changes angle as a result of excited vibrational modes and in effect appears to ‘wobble’. The angular deviation in the plane of the detection surface, with respect to the incident beam of light, results in a deviation in the returned light signal that is reflected from the cantilever surface, and which is detected by the optical detection system. The bending and torsional modes excited in the probe arise due to probe dynamics rather than physical properties of a sample surface, such as a sample surface topography (or other physical effect of interest). It is therefore counter-intuitive to determine a physical parameter of a sample surface based on positioning a beam of light onto the cantilever in order to measure the detection surface at a point that is at an extremity of the cantilever width or length as these regions suffer a greater deflection error compared to the point directly above the imaging tip, i.e., above the point at which the imaging tip is in contact with the sample surface. Torsional modes and bending modes are excited along the probe cantilever due to movement of the imaging tip as it oscillates across the sample surface. The positioning module and / or optical detection system may be configured to modify the determined width value during scanning, for example to reduce the width value in an accordance with the Z-component. The determined width value may be reduced as a function of the Z-component. The magnitude of which the determined width value may be decreased may be inversely proportional to a roughness measurement of the sample. In other words, the determined width value may be modified by a greater magnitude for a rougher sample when compared to a smooth sample.

[0101] In an example, once scanning has been initiated the determined width value or amplitude of movement of the probe can be checked and / or modified accordingly if required. For example, the width value may be determined based on an inverse relationship with a ‘roughness’ of a sample surface, where a rough sample is scanned with a smaller determined width value compared to a smooth sample which is scanned with a larger width value. For example, if scanning is initiated and the processor detects errors in the Z-component data returned, the processor can modify or update the determined width value to reduce the determined width value. The process may incrementally reduce the determined width until no error is detected in the Z-component data from the deflection measurements.

[0102] Figure 7 A shows an example of an imaging tip traversing a ‘smooth’ sample, where the determined width value is set between X3 and X4. These locations along the X-direction can correspond to the full extent of the region of the imaging tip, such as the full width of the cantilever. Figure 7B shows an example of an imaging tip traversing a ‘rough’ sample, where the determined width value is set between XI and X2. These locations along the X-direction can correspond to a sub-section of the region of the imaging tip, such as the width of the base of the imaging tip.

[0103] Movement of the probe in the Z-direction Alternatively, or in addition, to modifying the determined width value according to a sample roughness, a scan range of the SPM may be adapted or modified according to a sample roughness. As the probe moves over the sample surface the cantilever will bend and deflect, which can move the probe outside of a detection range, or optimal detection range, of the optical detection system. For example, as shown in figures 2B and 2D, the scan range of the probe may be linked to a ‘roughness’ of the sample surface, where large scan ranges can be achievable on relatively ‘flat’ surfaces whilst reduced scan ranges can be achievable on ‘rough’ surfaces. A rough surface can exert more force on the imaging tip to deflect the cantilever to a greater extent, whether the imaging tip is deflected into ‘valleys’ or ‘hills’ on the sample surface. Deflection of the cantilever to a greater extent can move the deflection surface in the region of the imaging tip out of an optimal scan. This is shown between figure 2A for an optimal scan range, and figure 2B for a probe that has moved out of focus of the optical detection system. As shown in figure 2D, for a rough surface, the probe can be deflected or pushed up by a feature on the sample surface. A control loop is able to correct for this additional load on the cantilever surface by adjusting the position of the probe and optical detection system along the Z-direction. This maintains a wider scan range for the SPM for rough samples, otherwise it will result in light overspill and errors being introduced into the deflection measurements.

[0104] In an example, the collected light signal can be processed to remove any height offset in the Z-direction due to any twisting in the probe as it moves through different lateral positions within the XY plane over the sample surface. The height offset in the surface of the cantilever can be due to torsional and / or flexural bending modes excited in the probe as the imaging tip moves through different lateral positions. The excitation of higher bending and torsional modes in the probe causes errors in deflection measurements. Data processing can improve the signal to noise ratio of the deflection measurements.

[0105] As mentioned above, the XY plane is generally considered to correspond to the directions of the probe and / or sample movement relative to one another in an X-direction and Y- direction, for example as initiated by the scanning motors. The XY plane may be considered to correspond to the desired plane of imaging with respect to the sample surface. The Z-direction is generally perpendicular to the XY plane. Nevertheless, any suitable referencing system may be used. As shown in figure 8, the SPM may be operated as a mobile unit to scan a large sample. For example, the SPM may be mounted onto a robotic arm and configured to operate as described herein.

[0106] As described above, during scanning of the sample, the position of the light dot in the XY plane remains stationary such that the position or location of the light dot on the probe in the XY plane is static. This is in contrast to conventional SPM systems, for example as shown in Figure 3, where beam steering is employed in order for the light beam to track the movement of the probe during scanning of the sample. For the SPM system described herein, in addition to the position of the light dot remaining stationary in the XY plane during scanning, a focal point of the light dot may also remain stationary in the Z- direction. The system can be configured for the light dot focus to remain stationary in the Z-direction while the probe traverses the sample surface.

[0107] The positioning module can be configured to detect the vertical motion of the probe as the imaging tip traverses the topography of the sample surface. The positioning module and / or optical detection system is configured to measure the vertical displacement of the probe relative to the sample surface. The vertical displacement measurement can be used to generate topographic data for the sample surface. In an example, the focus of the beam of light may remain stationary in the Z-direction during scanning, e.g., for a static optical detection system and mobile probe mount. Alternatively, in addition to movement of the probe mount by scanning motors, the optical detection system of the SPM system described herein may also be moved by scanning motors. Whilst this latter example reduces the rate at which the SPM system is able to scan the sample, due to the increase in load on the scanning motors, it has the benefit of improving the signal to noise by minimising light overspill.

[0108] As shown in figures 2B and 2D, as the imaging tip traverses the sample surface the free end of the probe moves in the Z-direction. The extent to which the imaging tip is deflected on the cantilever can be more pronounced for a rough sample (e.g., figure 2D) compared to a smooth sample (e.g., figure 2B). For a rough sample the increased deflection of the cantilever moves the edges of the cantilever to a greater extent compared to that for a smooth sample and therefore increases the risk of light overspill. The SPM system can therefore be configured for the positioning module to detect the vertical motion or vertical displacement of the probe relative to the sample surface as the imaging tip traverses the topography of the sample surface and adjust the position of the optical detection system in addition to adjusting the position of the probe mount.

[0109] In an example, the optical detection system measures the motion of the probe due to the interaction between the imaging tip and the sample surface. The positioning module is configured to position the imaging tip or probe at a desired location with respect to the sample surface. For example, the positioning module is configured to bring the imaging tip into contact with the sample surface for scanning for the collection of data via the interaction forces between the imaging tip and sample surface. The positioning module comprises a processor configured to instruct the scanning stage to initiate the relative movement between the probe mount and sample surface, whether via motors that control the positioning of the probe mount and / or motors that control the positioning of the sample, or a combination of instructions to both sets of motors. The positioning module processor is configured to receive a returned light signal from the surface of the cantilever and may process the signal to identify a Z-component representing a distance along the Z-direction that the imaging tip has moved with respect to time. The positioning module and / or optical detection system can therefore measure the position of the imaging tip in the Z-direction and check whether the deflection of the probe at the free end is within a predetermined deflection range or tolerance.

[0110] The positioning module processor can instruct a controller to modify a predetermined scan path to keep the interaction forces between the imaging tip and sample surface within the predetermined deflection range. The processor can instruct the scanning stage to move the probe mount and / or a sample mount to initiate a relative movement in a manner to achieve the desired interaction force between the imaging tip and sample surface. As such a control loop is able to maintain a specific load on the sample surface with the imaging tip. The controller provides information on the position of the probe mount and / or optical detection system in the Z-direction whilst the deflection of the probe is measure during scanning. The Z-component information can be used, for example by the processor or controller, to image the physical parameter of the sample surface that is of interest to the SPM user. An image of the sample topography can be constructed based on detection of the motion of the probe.

[0111] Figure 9 is a flow chart 900 of a method for determining a physical parameter of a sample surface. At block 910, a probe mount is provided which is configured to receive a probe having a cantilever with an imaging tip. At block 920, a scanning stage is provided that is configured to initiate a relative movement between the probe mount and a sample surface, wherein the relative movement is within an XY plane. At block 930, an optical detection system comprising a light source is provided, where the optical detection system configured to position a beam of light from the light source onto a surface of a cantilever in a region of an imaging tip, maintain the position of the beam of light such that the beam of light remains substantially stationary in the XY plane during scanning, and detect a returned light signal from a surface of a cantilever. At block 940, a positioning module is provided that is configured to bring an imaging tip into contact with a sample surface for scanning, the positioning module comprising a processor configured to determine a width value of a cantilever in a region of an imaging tip, the width value substantially relating to a distance that the cantilever is extending along an X-direction of the XY plane, instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in the X-direction, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light, and wherein the movement of the probe mount in the X-direction has a maximum peak-to- peak amplitude of movement that is substantially the same as, or less than, the determined width value, and receive a returned light signal from a surface of a cantilever, a returned light signal having a Z-component representing a distance along a Z-direction that an imaging tip has moved with respect to time, wherein the Z-direction is perpendicular to the XY plane.

[0112] Figure 10 is a schematic representation of a machine according to an example. The machine 1000 comprises a processor 1010, a data storage 1020, a memory 1030 to store instructions 1040, executable by the processor 1010, and a positioning module 1050. The machine comprises the data storage 1020 that can be used to store data obtained by the positioning module 1050, which can comprise reference co-ordinates (XYZ data) and timestamps for various scanning paths. The instructions 1040, executable by the processor 1010, can cause the machine 1000 to determine a physical parameter of a sample surface as described herein. Accordingly, the machine 1000 can implement a method for determining a physical parameter of a sample surface. A scan window can generally correspond to an area of the sample surface that is scanned by the probe. It takes time for deflection measurements or other data to be collected for each scan window because data must be collected over a number of scan passes. The greater the scan rate, the lesser time it takes to complete each data frame or scan window. Vertical position (Z) data is collected while the probe or the sample is moved relative to each other in the lateral (XY) directions. To generate an image of the sample topography, the X and Y positions of a data point are combined with its Z position to ensure that the XYZ data being processed correspond to the same physical location on the sample. Different areas of the sample surface can be scanned by the probe at each scan window and the collected data frames can be stitched together via image processing to form a complete image of the sample surface that has been scanned. In an example, the SPM may comprise an image acquisition module having a processor for imaging a topography of the sample surface using the deflection measurements.

[0113] Industrial Application

[0114] The SPM scanning methods described herein instruct the scanning stage to initiate a relative movement between the probe mount and sample surface by moving the probe mount in the X-direction to vary the position of the region of the imaging tip with respect to the stationary beam of light. The movement of the probe mount in the X-direction has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined width value. The width value may be substantially equal to a side- to-side width of the cantilever in the region of the imaging tip, or substantially equal to a width of the base of the imaging tip where the base intersects the surface of the cantilever, or some width therebetween. It is counter intuitive that the SPM scanning methods described herein are possible for determining a physical parameter of a sample surface whilst the light dot is apparently moving around so much on the back of the probe during scanning, particularly in view of bending and torsional modes which cause errors in deflection measurements. At conventional scan rates or scan speeds around 1-100 micrometres per second, the twisting of the probe, or torsional rotation of the microcantilever of the probe, due to oscillation of the probe does not create significant “noise” in the measurement of the motion of the probe as it is twisted during sample scanning. However, as scan speeds are increased the excitation of vibrational modes in the probe start to introduce noise into deflection measurements placing a limit to the rate at which a sample can be scanned whilst still being able to determine the physical parameters of interest for the sample. The solution described allows faster scanning rates whilst maintaining the ability to determine the physical parameters of interest for the sample based on determining a width value for the cantilever and instructing the scanning stage to initiate movement of the probe mount that has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined width value. Therefore bending modes and torsional modes are not readily excited in the probe to an extent that inhibits the ability to gather useful deflection measurements having a Z-component that can be used to determine the physical parameters of interest for the sample. This maintains an angle of the detection surface of the cantilever such that the angle of the probe as the imaging tip traverses the sample surface is not modified to an extent that would otherwise inhibit determination of the physical property of the sample surface of interest. In other words, compared to an SPM scanning at conventional speeds the twist angle is significantly smaller for the SPM described herein allowing scanning in excess of conventional scanning speeds. The SPM system described herein reduces the risk of light overspill due to the reduction in excitation of bending modes and torsional modes at faster scan rates, leading to a larger scan range being achievable. This solution has the benefit of improved signal to noise deflection measurements at faster scan speeds.

[0115] The SPM scanning methods described herein have been shown to allow an SPM to exceed previous expectations by removing previous limitations placed on the SPM system to significantly increase the scan rates that are possible. Conventional scan speeds and frequencies are substantially lower (1-100 micrometres per second) than the scan speeds demonstrated for the dynamic SPM system described herein where scan speeds in excess of one millimetre per second, or scan frequencies above 1kHz, have been achieved. The SPM described herein does not require a beam steering or corrective optics so scan frequencies can be significantly increased. By allowing the light dot to remain stationary in the XY plane and with the probe mount moving within the XY plane, the overall complexity of the SPM can be greatly reduced while enabling the benefits of increased probe scanning speed and high frame rates.

[0116] In light of bending modes and torsional modes, traditional cantilever beam (springboard) probes, or triangular (V-shaped) probes, have a preferred dominant scanning direction. SPM systems generally have a ‘fast’ scanning axis and ‘slow’ scanning axis for a chosen probe. The dominant or fast scanning axis (i.e., the X-axis) is usually perpendicular to the length of the cantilever (extending along the Y-direction) of the probe due to having a lower stiffness of the bending modes relative to the torsional modes. The torsional modes then provide stability to the interaction between the imaging tip and sample in the lateral direction (i.e., X-direction). It may be preferred for the X-axis of the XY plane, or X-direction, to be the fast-scanning axis, depending on the probe chosen. For the SPM systems described herein, the configuration of the system allows for the scanning speed to be increased well beyond conventional scan speeds (around 1-100 micrometres per second). The methods described herein may be applied to any probe shape. This provides versatility between different SPM probes.

[0117] The SPM system described enables the system to be operated without an electronic feedback loop, further reducing the complexity of the system. The SPM systems described herein operate to determine physical properties of a sample whether a control loop (in the Z-direction) is present or not. A control loop is able to maintain a specific load on the surface between the tip and the surface. However, in the absence of a control loop the probe mount and optical detections system may be moved along the Z-direction as the imaging tip is moved over features on the surface. The physical properties of the sample can still be determined provided that the focal depth of the objective is such that the incident beam of light does not fall off the surface of the cantilever, or the optical fiber (if one is used) does not come into contact with the surface of the cantilever.

[0118] The determined width value allows for the sample to be scanned whilst minimising the effects of light overspill to provide a wider scan range. The present system is configured such that the amplitude of the probe’s motion in the lateral plane is less than the width of the probe. The SPM system described herein provides a configuration in which the light dot remains stationary whilst the probe is scanned within the XY plane, where the amplitude of motion of the probe does not exceed the width of the probe. This allows for a wider range of motion as the beam of light is more easily maintained on the detection surface of the probe to minimise occurrences where the light dot would otherwise overspill the edges of the cantilever. This improves the signal to noise ratio of deflection measurements. For a determined width value, such as described above for X2-X1, this provides an amplitude of movement of the probe mount in the X and / or Y directions that is limited by the area (i.e., width and length) of the base of the imaging tip. This has the benefit of further minimising the effects of light overspill because the light dot is more closely located to the base of the imaging tip during scanning due to the smaller extent of movement of the probe in the X-direction. Positioning the light dot at above the imaging tip of the probe means that the returned signal may not be convoluted with the oscillation of excited eigenmodes on the probe. Further, determining the width value based on an inverse relationship with a roughness of a sample surface, where a rough sample is scanned with a smaller determined width value compared to a smooth sample, allows for an optimal amplitude of probe movement can be determined.

[0119] The SPM system described provides a light beam that remains stationary in the XY plane during scanning. This makes it possible for the optical detection system to remain static and for the scanning motors to move only the probe mount during scanning to maintain a desired interaction force between the imaging tip and sample surface. The probe mount has a lower mass than the optical detection system, and a lower mass than the probe mount and optical detection system combined. The load exerted on the scanning motors is therefore smaller when the scanning motors move only the probe mount (and probe thereon) in the XY plane. This allows the SPM system to move the probe mount faster for faster sample scanning. By keeping the incident light beam on the cantilever stationary in the XY plane it allows for faster scanning of the sample because movement of the optical detection system can be decoupled from the movement of the probe mount whilst still enabling properties of the sample to be determined. By moving only the probe without an attachment of an optical system, the scan speed and frequency of the probe can be improved. The area that can be scanned or imaged is limited by the mechanical size of the probe face, so faster scanning rates allow for data to be collected in a more time efficient manner.

[0120] The SPM is configured for the stationary light dot to remain positioned on a fast-moving probe. This reduces the complexity of the SPM and reduces costs because the described configuration negates tracking of the light beam on the probe during scanning and does not require beam steering equipment. Since the position of the beam of light remains substantially stationary in the XY plane during scanning, it is possible to place the optical detection system at a variety of positions, provided the beam of light still falls onto the detection surface of the cantilever. For example, a mirror and / or objective lens may be provided to direct the beam of light onto the detection surface of the probe. The mirror may be considered a “static” mirror in the sense that once the beam of light has been positioned onto the detection surface of the probe prior to scanning, the mirror is not adjusted or moved further during scanning or once the scanning process has been initiated. This enables a more versatile and compact SPM arrangement with less hardware or parts being required within the SPM system. Further, the SPM system is simpler and more user friendly to implement.

[0121] The extent of movement of the probe may be limited such that the light beam does not spill over the edges of the cantilever during scanning. This allows for an optimum signal to noise measurement of the returned light and avoids additional data processing for ‘binning’ bad data. For example, a data collection module comprising a processor may perform the data processing. However, it will be appreciated that some amount of light overspill may be tolerated provided that the SPM still has the ability to determine a physical parameter of the sample surface. For example, this may be influenced by the objective lenses within the SPM system. If the amplitude of motion in the X direction is larger than the width of the cantilever, a processing step can be used to leave only data collected while the light dot was on the cantilever.

[0122] The positioning module is configured to detect the vertical motion of the probe and adjust the position of the optical detection system in addition to adjusting the position of the probe mount. This allows for the full width of the light beam to remain on the detection surface of the cantilever during scanning. The processor (of the positioning module) can be configured to maintain a desired interaction force between the imaging tip and the sample such that the beam of light, or focus thereof, remains on the back of the cantilever in the Z-direction during scanning. The positioning module is configured to instruct movement of the probe mount, and optionally the optical detection system, within the Z- direction (up and / or down) as the sample is scanned. The imaging tip on the cantilever moves over the sample surface to maintain a usable field of detection in the Z-direction for detecting the returned light signal. This prevents the optical detection system from receiving data with errors which can lead to poor imaging and blurring. By moving only the probe without an attachment of an optical system, the scan speed and frequency of the scanning stage and hence SPM can be improved.

[0123] The approaches described herein mean that new scan profiles can be generated under scanning speeds in excess of conventional scanning speeds based on a modification of a conventional SPM, i.e., without requiring complex generation of a new scan stage. For example, an SPM operating with a 1Hz signal can be re-configured to operate using a 2kHz signal as described herein. The systems and methods described herein are modeagnostic, meaning they are compatible with different SPM imaging modes, including contact mode, error signal mode, intermittent contact mode (or tapping mode), and noncontact mode. In an alternative method of operation, the SPM system can be operated in error or deflection mode where the probe tip is moved across the sample surface and the motion of the probe motion is proportional to the surface topography.

[0124] The present solution can be used in atomic force microscopy. For example, it can be used for imaging a topography of a sample surface, or for taking tribology measurements of a sample. One example application of the solution is for taking surface roughness measurements of silicon and other surface of interest in the semiconductor industry. In this field of industry, the solution is beneficial because semiconductor wafers are relatively large, necessitating probe scanning SPMs. As such, advances in probe scanning using fast scan speeds is particularly advantageous as it reduces the time taken for surface measurements, leading to a more efficient use of resources.

[0125] As SPMs attempt to go faster with scan frequencies in excess of 1 kHz, the approaches described herein become increasingly valuable. Although the methods described herein may function on conventional SPMs with conventional scan frequencies, the method described becomes more useful and valuable when the complexity of beam steering to maintain the optical focus in the same location on the probe becomes too difficult or expensive to implement. As mentioned previously, it is not intuitive that an image is able to be formed with the relative location of the focused dot of light moving around so much on the back of the probe. The solution described has yet to find a known limit on the fast scan frequency that an SPM is able to achieve and as such is suitable to video rate SPMs using scan frequencies in excess of 1 kHz or which are able to image arbitrarily large surfaces in significantly reduced timeframes. For example, the solution allows an SPM to image a sample with a resolution in excess of 2 Mega pixels per second.

[0126] Examples in the present disclosure can be provided as methods, systems or machine- readable instructions, such as any combination of software, hardware, firmware or the like. Such machine-readable instructions may be included on a computer readable storage medium (including but not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0127] The present disclosure is described with reference to flow charts and / or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. In some examples, some blocks of the flow diagrams may not be necessary and / or additional blocks may be added. It shall be understood that each flow and / or block in the flow charts and / or block diagrams, as well as combinations of the flows and / or diagrams in the flow charts and / or block diagrams can be realized by machine readable instructions.

[0128] The machine-readable instructions may, for example, be executed by a machine such as a general-purpose computer, apparatus, a platform comprising user equipment such as a smart device, e.g., a smart phone, a special purpose computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams.

[0129] A processor or processing apparatus may execute the machine-readable instructions. The term 'processor' is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, programmable gate set, etc. The methods and modules may all be performed by a single processor or divided amongst several processors.

[0130] Further, the teachings herein may be implemented in the form of a computer or software product, such as a non-transitory machine-readable storage medium, the computer software or product being stored in a storage medium and comprising a plurality of instructions, e.g., machine readable instructions, for making a computer device implement the methods recited in the examples of the present disclosure.

[0131] Such machine-readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode. For example, the instructions may be provided on a non-transitory computer readable storage medium encoded with instructions, executable by a processor. Such machine-readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer-implemented processing, thus the instructions executed on the computer or other programmable devices provide an operation for realizing functions specified by flow(s) in the flow charts and / or block(s) in the block diagrams.

[0132] Persons skilled in the art will immediately recognize that any network function(s) or algorithm(s) disclosed may be implemented by hardware, software or a combination of software and hardware. Disclosed functions may correspond to modules which may be software, hardware, firmware, or any combination thereof. The terms “system” and “network” may be used interchangeably.

[0133] A software implementation may include machine- and / or computer- readable and / or executable instructions stored on a machine- and / or computer-readable medium such as memory or other types of storage devices. One or more microprocessors or general- purpose computers with communication processing capability may be programmed with corresponding executable instructions and perform the disclosed network function(s) or algorithm(s).

[0134] The microprocessors or general -purpose computers may include Applications Specific Integrated Circuitry (ASIC), programmable logic arrays, and / or using one or more Digital Signal Processor (DSPs). Although some of the disclosed implementations are oriented to software installed and executing on computer hardware, alternative implementations implemented as firmware or as hardware or as a combination of hardware and software are well within the scope of the present disclosure. The computer readable medium includes but is not limited to Random Access Memory (RAM), Read Only Memory (ROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), flash memory, Compact Disc Read- Only Memory (CD-ROM), magnetic cassettes, magnetic tape, magnetic disk storage, or any other equivalent medium capable of storing computer-readable instructions.

[0135] In some examples, some methods can be performed in a cloud-computing or networkbased environment. Cloud-computing environments may provide various services and applications via the Internet. These cloud-based services (e.g., software as a service, platform as a service, infrastructure as a service, etc.) may be accessible through a web browser or other remote interface of the user equipment for example. Various functions described herein may be provided through a remote desktop environment or any other cloud-based computing environment.

[0136] While various embodiments have been described and / or illustrated herein in the context of fully functional computing systems, one or more of these exemplary embodiments may be distributed as a program product in a variety of forms, regardless of the particular type of computer-readable-storage media used to actually carry out the distribution. The embodiments disclosed herein may also be implemented using software modules that perform certain tasks. These software modules may include script, batch, or other executable files that may be stored on a computer-readable storage medium or in a computing system. In some embodiments, these software modules may configure a computing system to perform one or more of the exemplary embodiments disclosed herein. In addition, one or more of the modules described herein may transform data, physical devices, and / or representations of physical devices from one form to another.

[0137] The preceding description has been provided to enable others skilled in the art to best utilize various aspects of the exemplary embodiments disclosed herein. This exemplary description is not intended to be exhaustive or to be limited to any precise form disclosed. Many modifications and variations are possible without departing from the spirit and scope of the instant disclosure. The embodiments disclosed herein should be considered in all respects illustrative and not restrictive. Reference should be made to the appended claims and their equivalents in determining the scope of the instant disclosure.

Claims

CLAIMS1. An apparatus for determining a physical parameter of a sample surface, the apparatus comprising: a probe mount that is configured to receive a probe having a cantilever with an imaging tip; a scanning stage that is configured to initiate a relative movement between the probe mount and a sample surface, wherein the relative movement is within an XY plane; an optical detection system comprising a light source, the optical detection system configured to: position a beam of light from the light source onto a surface of a cantilever in a region of an imaging tip; maintain the position of the beam of light such that the beam of light remains substantially stationary in the XY plane during scanning; and detect a returned light signal from a surface of a cantilever; and a positioning module that is configured to bring an imaging tip into contact with a sample surface for scanning, the positioning module comprising a processor configured to: determine a width value of a cantilever in a region of an imaging tip, the width value substantially relating to a distance that a cantilever is extending along an X- direction of the XY plane; instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in the X-direction, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light, and wherein the movement of the probe mount in the X-direction has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined width value; andreceive a returned light signal from a surface of a cantilever, a returned light signal having a Z-component representing a distance along a Z-direction that an imaging tip has moved, wherein the Z-direction is perpendicular to the XY plane.

2. The apparatus according to claim 1, wherein the optical detection system is further configured to: maintain the position of the beam of light such that the beam of light remains stationary in the Z-direction during scanning regardless of the relative movement between the probe mount and a sample surface.

3. The apparatus according to claim 1 or claim 2, wherein determining the width value comprises one or more of: an automated measurement; and a user-inputted measurement.

4. The apparatus according to any preceding claim, wherein the region of the imaging tip substantially corresponds to an area on the surface of the cantilever where a base of the imaging tip intersects the surface of the cantilever.

5. The apparatus according to any preceding claim, wherein the processor is further configured to: determine a further width value of a cantilever in a region of an imaging tip, the further width value substantially relating to a distance extending along a Y-direction of the XY plane.

6. The apparatus according to any preceding claim, wherein the determined width value and / or further width value is substantially equal to a side-to-side width of the cantilever in the region of the imaging tip.

7. The apparatus according to any preceding claim, wherein the determined width value and / or further width value is substantially equal to a width of a base of the imaging tip where the base intersects the surface of the cantilever.

8. The apparatus according to any preceding claim, wherein the processor is further configured to: instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in a Y-direction of the XY plane, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light.

9. The apparatus according to claim 8, wherein the movement of the probe mount in the Y-direction has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined further width value.

10. The apparatus according to any preceding claim, wherein a diameter of the beam of light comprises a focussed light dot, optionally wherein the optical detection system is configured to maintain a focal point of the focussed light dot such that the focal point remains stationary in the Z- direction during scanning regardless of the relative movement between the probe mount and a sample surface.

11. The apparatus according to any of claims 1-9, wherein a diameter of the beam of light comprises a focussed light dot, optionally wherein the positioning module is configured to instruct the optical detection system to initiate a movement of the optical detection system, thereby to vary the position of a focal point of the focussed light dot in the Z-direction during scanning,further optionally wherein the positioning module is configured to instruct the scanning stage to initiate movement of the probe mount in the Z-direction during scanning.

12. The apparatus according to any preceding claim, wherein the processor is further configured to: modify the determined width value and / or a further width value subsequent to instructing the scanning stage to initiate the relative movement between the probe mount and a sample surface, wherein the width value is modified by decreasing the determined width value as a function of the Z-component.

13. The apparatus according to any preceding claim, further comprising a sample mount that is configured to receive a sample for scanning the sample surface.

14. The apparatus according to any preceding claim, wherein the scanning stage comprises the probe mount.

15. The apparatus according to any preceding claim, wherein the apparatus is a scanning probe microscope, optionally wherein the apparatus is an atomic force microscope.

16. The apparatus according to any preceding claim, further comprising a probe having a cantilever with an imaging tip.

17. The apparatus according to any preceding claim, wherein a diameter of the beam of light is substantially equal to, or less than, the determined width value or further width value.

18. A method for determining a physical parameter of a sample surface, the method comprising: providing a probe mount that is configured to receive a probe having a cantilever with an imaging tip; providing a scanning stage that is configured to initiate a relative movement between the probe mount and a sample surface, wherein the relative movement is within an XY plane; providing an optical detection system comprising a light source, the optical detection system configured to: position a beam of light from the light source onto a surface of a cantilever in a region of an imaging tip; maintain the position of the beam of light such that the beam of light remains stationary in the XY plane during scanning; and detect a returned light signal from a surface of a cantilever; and providing a positioning module that is configured to bring an imaging tip into contact with a sample surface for scanning, the positioning module comprising a processor configured to: determine a width value of a cantilever in a region of an imaging tip, the width value substantially relating to a distance that a cantilever is extending along an X- direction of the XY plane; instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in the X-direction, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light, and wherein the movement of the probe mount in the X-direction has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined width value; and receive a returned light signal from a surface of a cantilever, a returned light signal having a Z-component representing a distance along a Z-direction that an imaging tip has moved, wherein the Z-direction is perpendicular to the XY plane.

19. The method according to claim 18, wherein the processor is configured to instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface with a mean scan speed of at least one millimeter per second or a scan frequency of 1 kilohertz.

20. A computer-implemented method for determining a physical parameter of a sample surface, the method comprising the steps of configuring a probe mount to receive a probe having a cantilever with an imaging tip; configuring a scanning stage to initiate a relative movement between a probe mount and a sample surface, wherein the relative movement is within an XY plane; configuring an optical detection system comprising a light source to: position a beam of light from the light source onto a surface of a cantilever in a region of an imaging tip; maintain the position of the beam of light such that the beam of light remains substantially stationary in the XY plane during scanning; and detect a returned light signal from a surface of a cantilever; and configuring a positioning module to bring an imaging tip into contact with a sample surface for scanning, the positioning module comprising a processor configured to: determine a width value of a cantilever in a region of an imaging tip, the width value substantially relating to a distance that a cantilever is extending along an X-direction of the XY plane; instruct the scanning stage to initiate the relative movement between the probe mount and a sample surface, thereby to move the probe mount in the X- direction, thereby to vary a position of a region of an imaging tip with respect to the stationary beam of light, and wherein the movement of the probe mount in theX-direction has a maximum peak-to-peak amplitude of movement that is substantially the same as, or less than, the determined width value; and receive a returned light signal from a surface of a cantilever, a returned light signal having a Z-component representing a distance along a Z-direction that an imaging tip has moved, wherein the Z-direction is perpendicular to the XY plane.

21. A machine-readable storage medium encoded with instructions for determining a physical parameter of a sample surface, the instructions executable by a processor, whereby to cause the processor to carry out the computer-implemented method of claim 20.

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