Method for analyzing probe tip deflection signals in scanning probe microscopy systems

Abstract

The present invention relates to a method for analyzing probe tip deflection signals in a scanning probe microscopy system. The system includes a probe head with a probe including a probe tip disposed on a cantilever, the probe head configured to scan the probe tip along one or more directions parallel to a substrate surface. The probe head includes an actuator for applying a periodic motion to the probe, and a tip position detector provides a probe tip deflection signal indicative of a deviation of the probe tip from a reference position. The method includes acquiring multiple samples of the probe tip deflection signals at scan positions over time to provide a signal profile, and identifying a signal profile associated with a grazing collision of the probe tip against a sidewall. Position coordinates of the sidewall structure are provided by the acquired z-position.

Description

[Technical Field]

[0001] The present invention relates to a method for analyzing probe tip deflection signals of a scanning probe microscopy system comprising at least one probe head comprising a probe including a probe tip disposed on a cantilever, the probe head configured to scan the probe tip along one or more directions parallel to a substrate surface, the probe head comprising an actuator for applying a periodic motion to the probe tip during said scanning, and a tip position detector for providing a probe tip deflection signal indicative of a deviation of an actual position of the probe tip from a reference position along a z direction across the substrate surface, the method comprising acquiring, at a first scan position on the substrate surface, a first plurality of samples of probe tip deflection signals over time at one or more positions of the probe tip along the z direction during at least one first cycle of the periodic motion, and providing a signal profile at the first scan position using the first plurality of samples. [Background technology]

[0002] Scanning probe microscopy (SPM) is an imaging technique that can provide images of surface and subsurface structures on the nanometer scale. The technique is non-optical and therefore not constrained by the diffraction limit, making it applicable, for example, to semiconductor manufacturing processes where the features of integrated circuits become so small that optical imaging is no longer sufficient due to diffraction limitations. However, scanning probe microscopy is also applied in other situations as well, making it a good alternative to optical imaging or scanning electron microscopy (SEM).

[0003] Scanning probe microscopy operates on the basis of a probe having a cantilever and a probe tip (typically at the end of the cantilever) that moves relative to the surface of a substrate while continuously or intermittently contacting the surface. By "contact" herein, we mean that the probe tip is at least close enough to the surface that the effect of the surface becomes significant in the transfer function of the probe's dynamic or static response / behavior. SPM can be performed in a variety of different modes, the most common of which are contact mode, intermittent contact mode, and non-contact mode. In contact mode, the probe tip remains in contact with the surface during scanning. When a structure on the surface is encountered, the probe tip is either pushed up (e.g., in the case of a block) or lowered (e.g., in the case of a trench). This change in the deflection of the probe tip can be compensated for in feedback, allowing the height or depth of the structure to be accurately measured. In intermittent contact mode, the probe oscillates above the surface at a frequency well below its first resonant frequency and intermittently contacts the surface. The difference in deflection amplitude thereby indicates a change in height or depth, which can also be accurately measured using a compensation feedback loop to re-establish the original minimum (or maximum).In non-contact mode, the probe tip is moved very close to encounter the surface's influence on the dynamic behavior of the probe.

[0004] Above we have briefly described on-surface measurements, also called surface topography measurements. In the case of subsurface measurements, ultrasonic vibrations may additionally be applied to the probe or sample or both, which can be measured at the surface, and the presence of subsurface features can be detected in the generated waves or from changes in contact stiffness, which also allows imaging of the subsurface features.

[0005] While SPMs such as those described above offer exceptional performance for high-precision imaging of structures on and within samples and substrates down to the nanometer scale, characterization of high-aspect-ratio features (i.e., features with relatively steep and tall walls and structural components) is more challenging. Various measurement techniques using SPMs have been developed to perform such measurements. However, a further challenge in this regard is accurately characterizing and measuring sidewall structures, i.e., structures that reside on or extend into the sidewalls of regular surface features. As the structures that need to be fabricated to manufacture modern semiconductor devices become more complex, the need for methods to accurately characterize these sidewall features will increase. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide a method for analyzing probe tip deflection signals of a scanning probe microscopy system, which allows for characterization of sidewall structures present on or in the sidewalls of surface features present on the surface of a substrate.

[0007] To this end, provided herein is a method for analyzing probe tip deflection signals of a scanning probe microscopy system to determine position coordinates of sidewall structures on or in the sidewall of a surface feature present on the surface of a substrate. The scanning probe microscopy system includes at least one probe head, the at least one probe head including a probe having a probe tip disposed on a cantilever. The system may include a single probe head, but may also include multiple probe heads. These probe heads may be independently movable relative to one another; for example, in certain embodiments, the system may include a collection of probe heads independently positionable at various locations relative to the substrate surface, thereby enabling simultaneous and parallel scanning of multiple regions on the surface. However, more basic embodiments may include only a single probe head movably connected to another system component, such as a metrology frame or another structure of the system. The at least one probe head is configured to scan the probe tip along one or more directions parallel to the substrate surface. For example, these directions may be orthogonal directions across the surface, and scanning may be performed to scan regions of the surface. The probe head comprises an actuator for applying a periodic motion to the probe (tip) during said scanning, and a tip position detector for providing a probe tip deflection signal indicative of the deviation of the actual position of the probe tip from a reference position along the z direction across the substrate surface. For example, those skilled in the art will recognize various tip position detectors that may be applied, such as an optical beam detector (OBD) arrangement or a piezoresistive sensor. [Means for solving the problem]

[0008] The method according to the present invention includes the following steps: At a first scanning position on the substrate surface, a first plurality of samples of probe tip deflection signals are acquired over time at one or more positions of the probe tip along the z-direction during at least one first cycle of cyclic motion. This is performed to provide a signal profile at the first scanning position, the signal profile being based on or generated using the first plurality of samples. As described above, the first plurality of samples are acquired during at least one first cycle of cyclic motion, thereby acquiring a signal profile of signals during this at least one cycle. The signal profile during at least a portion of the cycle provides desired data for the method and also allows for characterization of the signal profile in other steps. The method further includes identifying a signal profile associated with a grazing impact of the probe tip against the sidewall. This characterization and identification step can be performed based on sufficient data collected during at least one cycle (e.g., a force-distance curve (FDC)), as described above. Additionally, it should be noted that the term "grazing impact" herein refers to the probe tip grazing past the sidewall while lightly contacting the sidewall. Alternatively, this type of motion may be referred to as sliding impact or sliding motion, i.e., the probe tip slides over the sidewall while moving downward toward the base of the sidewall (or upward or both, depending on the system setup).

[0009] The method further includes detecting one or more variations in the slope or shape of a signal profile associated with probe tip motion in the z-direction toward the substrate surface. In other words, while moving toward the substrate surface, e.g., downward toward the bottom of a trench or sliding along the sidewall of a surface feature, the probe tip may encounter obstacles. These obstacles may be formed, for example, by sidewall structures. For example, a hole or opening in the sidewall may catch the probe tip as it moves toward the base of the sidewall. This may temporarily stop the probe tip motion, while the remainder of the probe, including the cantilever, continues to move the probe tip under the influence of the translational motion imparted by the z-actuator. Thus, the probe will bend, which is directly observed as a wave-like change or fluctuation in the slope of the probe tip deflection signal. At some point after being caught, the probe tip will break free, and the probe tip motion will continue. In that case, the velocity will be subject to additional thrust from the energized cantilever, resulting in a higher-than-average velocity. Similarly, positive structures (ie, structures extending from the sidewall) will also catch the probe tip and cause deflection.

[0010] The variations identified in the probe tip deflection signal can be analyzed to derive z-positions where they occurred. These z-positions can be considered estimates of the z-position of the structure. Thus, the method can further include associating at least one of the variations with an interaction between the probe tip and the sidewall structure during probe tip motion and obtaining a z-position of the probe tip at the at least one variation. The method then includes providing the obtained z-position of the at least one variation as a position coordinate of the sidewall structure.

[0011] As noted above, the claimed invention provides the advantage of providing an ingenious scheme for detecting the presence of sidewall features and providing a scheme for estimating the z-position of sidewall features. This is a significant advantage because conventional methods of performing scanning probe microscopy are unable to achieve detection, sensing, and inspection of sidewall features with their actual z-position. The present invention uses the principle of grazing impact of a probe tip against a sidewall and the probe tip being captured by a sidewall structure to identify the presence of a sidewall structure and provide an estimate of the z-position.

[0012] In some embodiments of the present invention, the one or more fluctuations relate to one or more of: undulations in the (slope of) the signal profile, or local extrema in the slope of the signal profile, such as local maxima or local minima. As explained, fluctuations in the probe tip velocity during a periodic motion cycle of the probe tip velocity are visible as undulations in the slope of the signal. In some situations, the presence of a sidewall structure extending on or into the sidewall briefly slows (but does not completely stop) the probe tip motion during sliding over the sidewall, and after passing the obstacle, the probe tip accelerates to catch up with the cantilever, similar to a leaf spring that is released. In these situations, which may occur, for example, when a small structure (e.g., a dent, depression, or scratch) is encountered, the fluctuations are visible as undulations in the slope, but in most cases, there is no actual local minima or maximum due to the fact that the probe tip velocity remains non-zero during the event. However, in some situations, for example, when encountering an opening or hole in a sidewall, the probe tip may accelerate in order to be released into the opening and then stopped by being captured and held by the opposing wall of the opening. In a deflection signal, deceleration results in an increase in deflection (the probe bending backward), while acceleration of the probe tip results in a decrease in deflection (the probe returning to equilibrium or continuing to bend forward), although it should be noted that "increase" and "decrease" depend on the sign convention used, and that bending backward and forward accurately describes what physically occurs. Thus, when encountering an opening, a local extremum, such as a local minimum or local maximum, is formed as the probe tip is released into the opening or stops on the other side of the opening. In still other situations, a sidewall structure distinctly extending from the sidewall may obstruct the probe tip during its grazing collision, causing the probe tip to stop and bend backward. Upon release, depending on when this occurs, the probe tip may immediately accelerate to the base of the sidewall, e.g., the bottom of a trench. The variations can be fully analyzed to determine each step in the dynamic behavior of the probe during glazing impact or sliding movement over the sidewall.

[0013] In some embodiments, identifying a signal profile associated with a glazing collision includes providing the signal profile to a pattern recognition algorithm or pattern recognition data model to perform the identification. In other or further embodiments, identifying a signal profile associated with a glazing collision includes comparing the signal profile to one or more reference profiles. The signal profile of a probe tip in a sliding motion (glazing collision) past a sidewall is distinguished from the regular motion of the probe tip freely approaching the surface. Thus, recognition of this signal profile of the deflection signal can be automated, for example, in the manner described above, making automated inspection of sidewall structural features a potential application of the methods and systems of the present invention. Automatic recognition of the signal profile can also be achieved based on other characteristics of the signal.

[0014] In other or further embodiments, the one or more sidewall structures include at least one of a structure extending from the sidewall or an opening or depression extending into the sidewall, as described above, and the present invention is not limited to any particular type of sidewall structure.

[0015] In other or further embodiments, detecting one or more variations includes detecting multiple variations, and associating includes associating at least a first variation with an interaction between the probe tip and a first sidewall structure, associating at least a second variation with an interaction between the probe tip and a second sidewall structure, and obtaining a first z-position of the probe tip at the first variation and obtaining a second z-position of the probe tip at the second variation to associate the first z-position and the second z-position with the first sidewall structure and the second sidewall structure. The method of the present invention can be applied to identify and determine the position coordinates of multiple sidewall structures that may be present on or in the sidewall of a surface feature. For example, a surface feature may include a sidewall where multiple structures at different z-positions may be present, and the method can be applied to identify and determine the z-positions of all of these structures.

[0016] In some embodiments, the one or more sidewall structures include at least one opening or depression extending into the sidewall of the surface feature, and the method further includes acquiring a second plurality of samples of probe tip deflection signals over time during at least one second cycle of the periodic motion at a second scan position, the second scan position coinciding with the top surface of the surface feature, and an acoustic signal is applied to at least one of the substrate or the probe tip to perform subsurface feature detection measurements at the second scan position during the second cycle. In this particularly advantageous class of embodiments, the method of the present invention is combined with subsurface scanning probe microscopy. A key advantage achievable thereby is that the method of the present invention enables the determination of the z-position of sidewall structures, such as openings in sidewalls at a particular z-level, and this class of embodiments enables the measurement of the depth or shape of such openings by performing subsurface measurements below the top surface of the surface feature. Thus, in some of these embodiments, the method further includes analyzing a second plurality of samples of the probe tip deflection signal (while the acoustic signal is being applied) to obtain measurement data indicative of, for example, the depth of the opening or depression extending into the sidewall. The idea in this embodiment is to use the subsurface signal to obtain this measurement data indicative of the depth of the opening or depression extending into the sidewall.

[0017] In other or further embodiments, the reference position is an equilibrium position, which is the in-use position assumed by the probe tip in the absence of any forces applied to the probe tip and in the absence of cyclic motion. In principle, any other position could be used as the reference position, but using the equilibrium position as the reference position allows for accurate calibration of the instrument.

[0018] In other or further embodiments, the surface features relate to fin structures of a semiconductor device present on or formed on the surface, the fin structures extending in a first direction along the substrate surface, and the method includes scanning a probe tip in a scanning direction relative to the surface such that the scanning direction is parallel to the first direction. Aligning the scanning direction with the direction of the fin structures facilitates establishing grazing collision of the probe tip with the sidewalls. Furthermore, when the scanning direction is aligned with the fin structures, grazing collision can be established over a range of adjacent positions along the scanning direction. In substrates with multiple parallel fins, where many or each of the fins have sidewall structures, the z-positions of the sidewall structures can be conveniently verified at multiple positions across the surface spanning some of the fins.

[0019] According to a second aspect of the present invention, the present invention relates to a method of operating a scanning probe microscopy system to perform a method according to the present invention according to the first aspect and analysing probe tip deflection signals of the scanning probe microscopy system to determine position coordinates of sidewall structures present on or in a sidewall of a surface feature present on the surface of a substrate, the system comprising: at least one probe head comprising a probe including a probe tip arranged on a cantilever, the probe head being configured to scan the probe tip along one or more directions parallel to the substrate surface, the probe head comprising an actuator for applying a periodic motion to the probe (tip) during said scanning; and a tip position detector for providing a probe tip deflection signal indicative of a deviation of an actual position of the probe tip from a reference position along a z direction across the substrate surface, the scanning probe microscopy system further comprising a controller and a memory, the memory being loaded with instructions which cause the controller to and storing instructions for performing the steps of: controlling the system to scan the probe tip relative to the substrate surface; acquiring first multiple samples of probe tip deflection signals over time at one or more positions of the probe tip along the z direction during at least one first cycle of periodic motion at a first scan position on the substrate surface to provide a signal profile at the first scan position using the first multiple samples; identifying a signal profile associated with grazing collisions of the probe tip against the sidewall; detecting one or more variations in slope or shape in the slope of the signal profile associated with probe tip motion in the z direction towards the substrate surface; associating at least one of the variations with an interaction between the probe tip and a sidewall structure during the probe tip motion to acquire a z position of the probe tip at the at least one variation; and providing the acquired z position at the at least one variation as a position coordinate of the sidewall structure.

[0020] Furthermore, according to a third aspect thereof, the present invention is directed to a computer program product embodied on a distribution medium readable by a computing device and comprising program instructions which, when loaded into a scanning probe microscopy system, carry out a method according to the first or second aspect.

[0021] The present invention will be further detailed by the description of some specific embodiments thereof with reference to the accompanying drawings. The detailed description provides examples of possible implementations of the invention, but should not be considered as describing the only embodiments within the scope. The scope of the invention is defined in the claims, and the description should be considered illustrative rather than limiting of the invention. The drawings are as follows: [Brief explanation of the drawings]

[0022] [Figure 1] 1A-1C are diagrams illustrating various exemplary three-dimensional structures of semiconductor devices. [Figure 2A] FIG. 1 shows a cross-sectional image of the three-dimensional structure of a finFET. [Figure 2B] 1 is a schematic diagram of the three-dimensional structure of a finFET. [Figure 3] FIG. 1 shows a scanning probe microscopy apparatus for use in a method according to the present invention. [Figure 4] FIG. 1 is a schematic diagram illustrating the inventive method according to some embodiments of the present invention. [Figure 5] FIG. 10 shows a probe tip deflection signal including multiple periodic motion cycles. [Figure 6] 6 shows a portion of the probe tip deflection signal of FIG. 5 that can be used in a method according to the present invention. [Figure 7] 1A-1C are schematic diagrams illustrating methods according to some embodiments of the present invention; [Figure 8] 2A-2C show diagrammatically the principle of the method according to the invention for a sidewall with multiple openings or recesses therein; [Figure 9]1A-1C show diagrammatically the principle of the method according to the invention for side walls with openings or recesses therein; [Figure 10] 1A-1C show diagrammatically the principle of the method according to the invention for sidewalls with depressions; [Figure 11] 3A-3C show diagrammatically the principle of the method according to the invention for sidewalls with sidewall structures extending on the sidewalls; DETAILED DESCRIPTION OF THE INVENTION

[0023] The terms used to describe particular embodiments are not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of the listed elements but do not exclude the presence or addition of one or more other elements. When a particular step of a method is referred to as following another step, it will be further understood that the particular step may directly follow the other step, unless otherwise specified, or that one or more intermediate steps may be performed before performing the particular step. Similarly, when a connection between structures or elements is described, it will be understood that this connection may be established directly or through intermediate structures or elements, unless otherwise specified.

[0024] The present invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and / or cross-sectional illustrations of possible idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms and their derivatives should be construed to refer to the orientation as described or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require the system to be constructed or operated in a particular orientation, unless specifically stated otherwise.

[0025] 1 shows a schematic representation of various exemplary three-dimensional structures 30 of semiconductor devices that may be present on the surface 8 of a substrate 7. Element A on the left side of FIG. 1 shows a conventional field effect transistor (FET). The FET 36 includes a gate 30 that is structured on the surface 8 of the substrate 7. Beneath the gate 30, silicon source and drain structures 31 extend below the surface 8. The gate 30 allows for control of the conductivity of the region of the source / drain structure 31 below the gate 30.

[0026] To the right of Device A, Device B shows a finFET 37. The finFET 37 comprises a gate structure 30 through which source and drain structures 31 extend. Thus, the gate 30 is present on three sides of the source and drain structures 31, thereby providing much better control of conductivity within the source and drain structures 31. Reference numeral 34 denotes the sidewalls of the gate structure 30. In Device C, to the right of Device B, the substrate 7 includes a gate-all-around nanowire structure. The gate-all-around nanowire structure comprises a gate 30 with sidewalls 34. Extending through the gate 30 are several nanowires 31′. The nanowires 31′ provide the source and drain of the gate-all-around field-effect transistor. It will be understood that by nanowire, the gate 30 is present on all sides of the nanowire 31′, thereby giving rise to the name gate-all-around.

[0027] Another gate-all-around structure is provided on the right side of Figure 1 by Element D of Figure 1. In Element D, the gate-all-around device comprises multiple lobes 31" extending through gate 30, with multiple lobes 31" forming the source and drain of the gate-all-around device.

[0028] A cross section of device 39 is shown in FIG. 2B, an image of which is provided in FIG. 2A. This image shows gate 30 in cross section, including sidewall structure 31′ extending from sidewall 34. The base of the trench formed between structures 30 is designated by reference numeral 35. In reality, sidewall structure 31″ extends from sidewall 34, but in cross section, sidewall structure 31″ can also be said to be formed by recesses between lobes 31″. Furthermore, interface 33 provides an interface between gate 30 and first source / drain structure 31″.

[0029] FIG. 3 schematically illustrates a scanning probe microscopy (SPM) system 1. System 1 is suitable for use in a method according to the present invention. For example, system 1 includes a processing device 26 and memory 27 and / or 27′ suitable for storing instructions that, when executed by processing device 26, cause processing device 26 to perform a method as described herein according to one or more implementations of the present invention. Processing device 26 in FIG. 3 is shown as a single entity in SPM system 1. However, those skilled in the art will appreciate that while all of the described method steps may be implemented using a single processing device 26, processing device 26 may also be implemented using multiple elements that together perform the described method steps. Thus, processing device 26 may comprise a cluster of multiple processing devices, or may be implemented by various entities that individually perform certain (sub)steps and cooperate to implement the present invention. Furthermore, as shown, memory 27 may be an internal memory 27, an external memory 27′, or another external entity reachable via a data communication network 29. For communication with data communication network 29, system 1 may include a communication unit 28. In Figure 3, data storage element 27, data processing element 26, and data communication element 28 are all shown as being part of analyzer unit 25 of system 1. While this may often be implemented in this manner (as already suggested above), this is not always the case. The illustration of a single entity 25 in Figure 3 is for the sole purpose of not unnecessarily complicating the drawing.

[0030] In the figures, technically and functionally equivalent elements, i.e., elements that perform the same or similar functions in the same or similar manner with respect to the invention described herein, may be designated by the same reference number or by the same reference number followed by a prime (') or a subnumber ("-1," "-2," ...). These entities, such as data repositories 27 and 27', may be of the same nature or of different technical nature or may be implemented (e.g., connected or controlled) in different ways, but with respect to the present invention, both provide the functionality of allowing the storage of data or operating instructions for processing device 26. Memory 27' in FIG. 3 is designated with a prime (') to indicate that this element performs (or can perform) a similar function to, or in certain embodiments, even performs (or can perform) the same function as, internal memory 27 of system 1', but differs in the sense that this memory 27' (which may be implemented as a server or as an externally stored data file or database) is an external memory rather than an internal memory, without departing from the functionality of memory 27' in embodiments of the present invention. The above are merely examples and may apply to other entities described below as well. In principle, unless specifically indicated to the contrary elsewhere in this document, it should be assumed that any entity or element described may be implemented differently in alternative embodiments. The described or illustrated embodiments should not be considered as limiting the invention, which is limited only by the scope of the appended claims, which define the scope and spirit of the invention.

[0031] In the system 1 of FIG. 3 , a substrate carrier 3 is configured to support a substrate or sample 7 to be inspected by the SPM system 1. The substrate carrier 3 is configured to include or be connected to an actuator (not shown) to move the substrate 7 in a plane parallel to the carrier 3, which is typically referred to as the XY plane of the system. Apart from the ability to move the substrate 7 in the X and Y directions, the substrate carrier 3 is connected to a metrology frame 5 that provides a fixed reference for the system. The SPM system 1 further includes one or more scan heads 15 that are movable in the Z direction. Each of the scan heads 15 includes a tip holder 16 capable of holding a probe tip 13, which in turn includes a probe 10 that forms the sensing element of the SPM system 1. The probe 10 includes a cantilever 12 and a probe tip 11. The probe tip 11 typically includes a very sharp tip that allows for very precise (with nanometer accuracy) scanning and measurements to be made on the surface 8 of the substrate 7.

[0032] In addition to the above, the scan head 15 typically also includes a sensor system for determining the exact position of the cantilever relative to the scan head. For example, the sensing system in FIG. 3 consists of an optical beam deflection (OBD) unit provided by a laser unit 20 for generating an optical beam 23 and a four-quadrant optical sensor 21 for receiving the reflected beam 23. The optical system directs the beam 23 toward the back surface of the probe cantilever 12, which includes a specular surface. The specular surface of the probe cantilever 12 reflects the beam 23 onto the optical detector 21. Any displacement of the probe tip 11 similarly displaces the position where the beam 23 impinges on the optical detector 21. In the four-quadrant optical detector 21, the light spot formed by the beam 23 is preferably set by default to be precisely centered in the four different quadrants of the detector. Thus, equal portions of the light spot fall on each quadrant of the four-quadrant optical detector 21. It will be appreciated that even if in practice the laser beam 23 is not aligned exactly in this manner, the principle of detecting the displacement of the light spot remains the same. All that is required to detect the displacement is that each of the four quadrants of the photodetector 21 receive a portion of the light from the beam 23. For example, the relative vertical deflection of the cantilever (above or below relative to the cantilever equilibrium position) can be determined by taking the signal from the top half (T) of the detector 21 minus the signal from the bottom half (B) of the detector, i.e., the up-down signal (TB signal).

[0033] When the probe tip 11 is displaced or bent relative to the scanning head 15 including the laser unit 20, the light spot formed on the photodetector 21 is slightly displaced such that the ratio between the different areas illuminated by the light spot on each quadrant of the photodetector 21 changes. This allows the exact position and / or orientation of the probe tip 11 relative to the scanning head 15 to be determined. Since the Z position of the probe 10 applied by the Z actuator 18 is also known (from the control data of the Z actuator 18 or a dedicated Z sensor), the orientation and position of the probe tip 11 in the Z direction can be determined. Furthermore, the XY position of the probe tip 11 indicates the position of the probe tip 11 relative to the sample 7 in the plane of the substrate carrier 3 and is known from the actuators or corresponding sensors of the substrate carrier 3. In this way, at each position in the XY plane, the exact orientation of the probe tip 11 in the Z direction can be determined in combination with the Z level applied via the Z actuator 18 or a dedicated Z sensor. As an alternative to the OBD sensor system described above, a different sensor system may be applied to determine the position of the probe tip 11. For example, a piezoresistive sensor may alternatively be applied. The manner in which piezoresistive sensors are applied in the SPM system 1 will not be further described herein.

[0034] In the system 1 shown in FIG. 3 , the above information allows the precise height of the surface 8 at each point in the XY plane to be determined with great accuracy. Thus, the surface topography 9, consisting of various different structures on the surface 8 of the sample 7, can be accurately measured and mapped to provide a surface topography map. At each point in the XY plane parallel to the sample surface 8, the precise Z level of the surface 8 can be determined from data provided to control the Z-level actuator 18 and data obtained from the light beam detector optical sensor 21 or a dedicated Z sensor. The data may be registered as three-dimensional measurement data, for example, in the memory 27 of the system 1. In addition to the above-described analysis of the data from the Z-level actuator 18 or Z sensor and the light detector 21, several other processing steps need to be performed to provide a three-dimensional surface topography map of the surface 8. These include, for example, noise reduction and the identification and removal of measurement artifacts.

[0035] Thus, in SPM system 1, the position and orientation of probe tip 11 are acquired and recorded by acquiring measurements with the OBD detector formed by laser unit 20 and photodetector 21 in combination with Z-level data acquired from Z-level actuator 18 or actuator control data of the Z sensor. Furthermore, system 1 performs subsurface measurements of any structures that may be below the surface 8 of sample 7. For this purpose, substrate carrier 3 further includes a vibration actuator that allows vibrations 4 to be applied to sample 7 from below. In alternative SPM systems, vibration signals 4 may be applied in different ways, for example, by a vibration actuator on the surface 8 of sample 7 or on a side of sample 7. The vibration signal 4 can also be applied via probe 10 using a vibration transducer on scan head 15 or via probe tip 11 by periodic power intensity fluctuations in laser beam 23 provided by laser unit 20. Such alternative ways of applying vibration signals 4 to sample 7 have been described in the literature and will not be discussed further herein. The present invention can be applied to measurements obtained from an SPM system, such as when SPM system 1 performs surface topography measurements of surface topography 9 or performs subsurface measurements of structures below top surface 8. The subsurface structures may be, for example, previous layers of a semiconductor device during its manufacture to detect whether the overlay of subsequent layers is accurate enough to result in a fully functional semiconductor device, or whether critical dimensions are specified with the correct tolerances. In methods according to the present invention, in some specific embodiments thereof, subsurface measurements are performed to further characterize sidewall structures extending inward into the surface that have been characterized on surface 8. For example, the subsurface measurements may enable obtaining information regarding the shape or depth of sidewall recesses.

[0036] In the system 1 of FIG. 3, a vibration acoustic input signal applied to the substrate 7 via the substrate carrier 3 is acquired at the surface 8 of the sample 7 via the probe tip 11. The vibration periodically displaces the Z-level of the probe tip 11 at the frequency applied via the acoustic signal 4. Various acoustic measurement techniques are known in the art, including, for example, heterodyne techniques that use very high-frequency gigahertz acoustic signals containing two frequencies in the gigahertz range. The difference frequency between the two applied frequencies in the gigahertz range is relatively small, typically in the megahertz range. Using the principle of heterodyne signal mixing, a low-frequency signal at the difference frequency (in the megahertz range) can be acquired by the probe tip 11 and detected by analyzing the output signal acquired via the optical beam deflector unit 21. Again, this measurement data needs to be further analyzed to acquire three-dimensional surface topography data. For example, amplitude and phase data can be acquired, and measurement artifact identification and noise reduction should be performed as described above.

[0037] 4 shows schematically a probe tip 13 comprising a probe 10 including a cantilever 12 and a probe tip 11. The figure also shows (very) schematically a substrate 7 having, on a surface 8 of the substrate 7, a pattern 42 of fin structures 44 having sidewalls 34. The fin structures 44 are densely packed and parallel to one another. Optional source or drain structures 31, 31′, or 31″ (not visible in FIG. 4 ) extend from the sidewall 34 of each fin 44. To implement the method according to the invention, the top-bottom signal (TB signal) of the SPM is analyzed to obtain a signal indicative of a grazing collision of the probe against the sidewall 34. A grazing or sliding collision is a situation in which the probe tip 11 slides off the top 36 of the fin (see, for example, FIG. 7 ) while remaining in contact with the sidewall 34. Capturing a grazing collision signal is required to be able to detect the location of any side lobes or other structures on the sidewall 34. FIG. 4 shows an effective way to obtain such a signal. This is certainly not the only way that can be applied to obtain a TB signal indicative of a grazing collision, but it is an effective method.

[0038] To acquire a TB signal indicative of a grazing collision, the probe 10 can be moved 45 in a periodic motion in a relative direction parallel or slightly off-parallel to the direction of the fin 44. This mode is characterized by periodic motion of the probe 10, during each oscillation of which the probe tip 11 contacts the surface 8 of the substrate 7. As shown in FIG. 4, the probe tip 11 can be scanned in the direction of the fin 44, while graph 50 in FIG. 5 represents a TB signal 53 acquired from the SPM system 1. While the probe tip 11 is above the fin 44 and in contact with the top surface 36 of the fin 44, a somewhat standard output signal is acquired, such as the first four cycles 52 of the signal 53. However, as the probe tip 11 begins to approach the edge of the surface 36 of the gate 30, a typical transition behavior 54 can be identified in the TB signal 53. The probe tip 11 then remains in a sliding or grazing collision state for some time, which is characterized by a signal portion 56 of the TB signal 53.

[0039] FIG. 6 shows a close-up of signal portion 56 of TB signal 53. The TB signal on its upward slope shows several local peaks 62 and 63. These peaks indicate the z-levels at which probe tip 11 encounters various side lobe or sidewall structures 31, 31' or 31". This is shown with reference to FIG. 7.

[0040] FIG. 7 schematically illustrates a cross section of a finFET, including a gate 30 extending from a base 35 with side lobes 31 extending from the sidewalls 34. A trench 70 extends between the sidelobes 31. The gate 30 has a flat top surface 36, with an edge 33 between the gate 30 and the sidewalls 34. FIG. 7 also illustrates the probe 10 at four positions I, II, III, and IV as the probe 10 passes the sidewalls 34 and moves toward the base 35 in a grazing motion. The four positions I-IV correspond to various portions of the TB signal at local maxima 62 and 63. For example, the flat portion of the signal 53 before peak 62 corresponds to a situation where the cantilever has no deflection while moving downward at position I. The deflection of the cantilever 12 increases toward the edge 33 at position II and rapidly decreases at position III as it encounters a valley 70. The same effect is seen toward position IV, resulting in a local maximum 63. Subsequently, as the probe moves further towards the base 35, smaller maxima 60 can also be identified. Because for every position on the TB signal 53 the corresponding z-level is known (from the driver signal of the SPM driving the probe motion downwards or from the corresponding Z-sensor), it is possible to correlate the various positions of each local maxima 62, 63 and 60 with the corresponding z-position of the probe tip 11. Furthermore, if the dimensions of the probe tip 11 and its shape are known, potentially the widths of the trenches 70 and their z-positions can also be derived. This data is valuable during the manufacturing process to enable correct manufacturing of the side lobes to be verified.

[0041] Figures 8, 9, 10, and 11 show schematically various structures that may be present on the sidewall 34 and how they may be detected in the TB signal. For example, Figure 8 shows the situation with multiple sidelobes, which was also identified in Figures 6 and 7. Locations a, b, c, d, and e on the sidewall are shown in the schematic signal plot 53 on the right side of the figure. The sidelobes appear as several local maxima and minima on the slope of the TB signal 53.

[0042] Figure 9 shows side lobes with a wide, deep trench. From the onset of a local peak in the TB signal 53 at location a, the deflection increases toward location b, where it reaches a maximum. The deflection then decreases again toward the bottom of the trench, leading to the onset of the next peak at location c. At location d, the probe tip emerges from the trench.

[0043] Figure 10 shows a situation where there is a shallow small trench on the sidewall 34. At position a, the deflection begins to decrease towards a minimum at position b, then increases again until a normal deflection signal is again obtained at position c.

[0044] 11 shows the situation of a sharp depression on the side wall 34. Here, at position a, an increase in deflection is detected. The deflection is at a maximum at position b. Then, at position c, the deflection reaches its minimum value, from which it returns to its normal value.

[0045] The present invention has been described with reference to several specific embodiments thereof. It will be understood that the embodiments shown in the drawings and described herein are intended for illustrative purposes only and are not intended to limit the invention in any manner or manner. The operation and construction of the present invention will be apparent from the foregoing description and the accompanying drawings. It will be apparent to those skilled in the art that the present invention is not limited to any of the embodiments described herein, and modifications are possible that are to be considered within the scope of the appended claims. Also, kinematic reversals are considered inherently disclosed and are considered within the scope of the present invention. Furthermore, any of the components and elements of the various disclosed embodiments may be combined or incorporated into other embodiments where deemed necessary, desirable, or preferred without departing from the scope of the present invention as defined in the claims.

[0046] In the claims, any reference signs should not be construed as limiting the claims. The terms "comprising" and "including," when used in this description or the appended claims, should not be construed in an exclusive or exhaustive sense, but rather in an inclusive sense. Thus, the term "comprising" as used herein does not exclude the presence of elements or steps other than those recited in any claim. Expressions such as "consisting of," when used in this description or the appended claims, should not be construed as an exhaustive list, but rather in the inclusive sense of "at least consisting of." Furthermore, the words "a" and "an" should not be construed as being limited to "only one," but instead are used to mean "at least one," and do not exclude a plurality. Features not specifically or explicitly described or claimed may still be included in the structure of the invention within its scope. Any of the claimed or disclosed devices or portions thereof may be combined together or divided into further parts unless specifically stated otherwise without departing from the claimed invention. Phrases such as "means for" should be read as "a component configured for" or "a member constructed for" and should be interpreted to include equivalents of the disclosed structures. The use of phrases such as "critical," "preferred," and "especially preferred" is not intended to limit the invention. Additions, deletions, and modifications within the purview of those skilled in the art may generally be made without departing from the spirit and scope of the invention, as determined by the claims. The invention may be practiced otherwise than as specifically described herein and is limited only by the appended claims.

Claims

1. 1. A method of analyzing a probe tip deflection signal of a scanning probe microscopy system to determine position coordinates of a sidewall structure on or in a sidewall of a surface feature present on a surface of a substrate, comprising: the system comprises: at least one probe head comprising a probe including a probe tip disposed on a cantilever, the probe head configured to scan the probe tip along one or more directions parallel to the substrate surface, the probe head comprising an actuator for applying a periodic motion to the probe tip during the scanning; and a tip position detector for providing a probe tip deflection signal indicative of a deviation of an actual position of the probe tip from a reference position along a z direction across the substrate surface; acquiring a first plurality of samples of the probe tip deflection signals over time at one or more positions of the probe tip along the z-direction during at least one first cycle of the periodic motion at a first scan position on the substrate surface to provide a signal profile at the first scan position using a first plurality of samples; identifying the signal profile associated with a grazing impact of the probe tip against the sidewall; detecting one or more variations in the gradient of the signal profile associated with probe tip motion in the z-direction towards the substrate surface, the variations including a local maximum or minimum; correlating at least one of the variations with an interaction between the probe tip and the sidewall structure during the probe tip movement to obtain a z-position of the probe tip during the at least one variation; providing the acquired z-position of the at least one variation as the position coordinate of the sidewall structure; A method comprising:

2. 2. The method of claim 1, wherein the one or more variations relate to one or more of local extrema in the slope of the signal profile, such as undulating changes in the slope of the signal profile, local maxima or local minima.

3. identifying the signal profile associated with a glazing collision, providing the signal profile to a pattern recognition algorithm or a pattern recognition data model for performing the identification; or comparing said signal profile to one or more reference profiles; The method of claim 1 or claim 2, comprising at least one of:

4. 10. A method according to any one or more of the preceding claims, wherein the one or more sidewall structures comprise at least one of a structure extending from the sidewall, or an opening or a depression extending into the sidewall.

5. Detecting one or more variations comprises detecting a plurality of variations, and correlating comprises: associating at least a first variation with an interaction between the probe tip and a first sidewall structure; associating at least a second variation with an interaction between the probe tip and a second sidewall structure; obtaining a first z-position of the probe tip at the first variation; and obtaining the second z-position of the probe tip at the second variation to associate the first z-position and the second z-position with the first sidewall structure and the second sidewall structure.

10. A method according to any one or more of the preceding claims.

6. the one or more sidewall structures include at least one opening or depression extending into the sidewall of the surface feature, and the method further comprises: acquiring a second plurality of samples of the probe tip deflection signal over time during at least one second cycle of the periodic motion at a second scan position, the second scan position coinciding with a top surface of the surface feature; during the second cycle, an acoustic signal is applied to at least one of the substrate or the probe tip to perform a subsurface feature detection measurement at the second scan position; 10. A method according to any one or more of the preceding claims.

7. 7. The method of claim 6, wherein the method further comprises analyzing the second plurality of samples of the probe tip deflection signals to obtain measurement data indicative of a depth of the opening or depression extending in the sidewall.

8. 10. A method according to any one or more of the preceding claims, wherein the reference position is an equilibrium position, the equilibrium position being the in-use position assumed by the probe tip in the absence of any force applied to the probe tip and in the absence of the cyclic motion.

9. 10. A method according to any one or more of the preceding claims, wherein the surface features relate to fin structures of a semiconductor device present on or formed on the surface, the fin structures extending in a first direction along the substrate surface, and the method comprising scanning the probe tip relative to the surface in a scanning direction such that the scanning direction is parallel to the first direction.

10. 10. A method of operating a scanning probe microscopy system to perform the method of claim 1 , comprising analyzing a probe tip deflection signal of the scanning probe microscopy system to determine position coordinates of sidewall structures on or in sidewalls of surface features present on a surface of a substrate, the method comprising: the system comprising at least one probe head comprising a probe including a probe tip disposed on a cantilever, the probe head configured to scan the probe tip along one or more directions parallel to the substrate surface, the probe head comprising an actuator for applying a periodic motion to the probe tip during the scanning, and a tip position detector for providing a probe tip deflection signal indicative of a deviation of an actual position of the probe tip from a reference position along a z direction across the substrate surface; The scanning probe microscopy system includes a controller and a memory, the memory being loaded with instructions that cause the controller to: controlling the system to scan the probe tip relative to the substrate surface; acquiring a first plurality of samples of the probe tip deflection signals over time at one or more positions of the probe tip along the z-direction during at least one first cycle of the periodic motion at a first scan position on the substrate surface to provide a signal profile at the first scan position using a first plurality of samples; identifying the signal profile associated with a grazing impact of the probe tip against the sidewall; detecting one or more variations in the gradient of the signal profile associated with probe tip motion in the z-direction towards the substrate surface, the variations including a local maximum or minimum; Associating at least one of the variations with an interaction between the probe tip and the sidewall structure during the probe tip movement to obtain a z-position of the probe tip during the at least one variation; providing the acquired z-position of the at least one variation as the position coordinate of the sidewall structure; A method comprising:

11. 11. A computer program product embodied on a distribution medium readable by a computing device and comprising program instructions which, when loaded into a scanning probe microscopy system, perform the method of any one of claims 1 to 10.

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