Scanning probe microscope system and method of operating same - Patents.com

Abstract

This document relates to a scanning probe microscope system comprising a sample support structure, a sensor head including a probe, a deflection sensor unit, and an actuator including a Z-motion actuator and a scanning actuator. The system further comprises a control unit capable of receiving the deflection sensor signals and controlling the actuator. The control unit comprises a number of signal processing units, each of which is capable of receiving the deflection signals, providing a processed signal, and cooperating with a trigger unit which compares the processed signals with predefined trigger conditions and generates a trigger when the conditions are met.

Description

[Technical field]

[0001] The present invention relates to a scanning probe microscope system comprising a sample support structure for supporting a sample including a sample surface, a sensor head including a probe with a cantilever and a probe tip arranged on the cantilever, a deflection sensor unit for acquiring a deflection sensor signal indicative of a deflection of the probe tip during scanning, and one or more actuators including a Z motion actuator for moving the probe tip in a direction perpendicular to the sample surface and a scanning actuator for moving the probe tip laterally / parallel to the substrate surface, the system further comprising a control unit configured to receive the deflection sensor signal from the deflection sensor unit and to control the one or more actuators. The present invention further relates to a method of operating a scanning probe microscope. [Background technology]

[0002] Topographic imaging of 3D samples with certain structures, especially those characterized by narrow width and large height aspect ratios, common in the semiconductor or biomedical industries, using scanning probe microscope (SPM) systems (such as atomic force microscopes (AFM)) requires the use of non-resonant vibration imaging methods. Existing methods, although implemented differently, usually have some common features. This involves moving the probe or the sample in a repetitive motion profile in a direction perpendicular to the surface (Z direction), which extracts the topography of each pixel of the image when the probe-sample interaction force reaches a predefined value. During the motion profile, these features include retracting the probe from the surface and moving the probe relative to the surface in a plane parallel to the surface (XY).

[0003] Therefore, conventional non-resonant vibration imaging modes also usually include a number of drawbacks. For example, topographic height data is extracted based on predefined values ​​of the probe-sample interaction force, but the shape and nature of surface features, as well as the height differences within and between surface features, may vary widely. Even using a predefined probe-sample interaction force, not all features can be imaged correctly. This may be partly solved by performing a second scan of the substrate surface with a different predefined probe-sample interaction force. However, this leads to reduced throughput and further wear of the probe. Furthermore, drift of the probe position relative to the sample surface (e.g., due to temperature differences or vibrations) may adversely affect the accuracy and even prevent or obscure the imaging.

[0004] Another drawback is that in conventional non-resonant vibration imaging modes, the retraction of the probe from the surface is usually performed using a fixed, user-defined retraction distance. This predefined retraction distance may in some cases not be sufficient to completely pull the probe away from the surface, which may lead to damage to the probe and / or the sample surface when moving the probe to the next pixel. In other cases, this predefined retraction distance may be too large, which makes the pixel-by-pixel procedure unnecessarily slow, again leading to reduced throughput.

[0005] Furthermore, when the probe tries to leave the surface, the surface forces slightly delay the departure, which biases the probe. As a result, the probe tip vibrates at the natural frequency of the probe upon release. This vibration, also called ringing, needs to be minimized before the next pixel is measured, and a certain settling time is required before the next pixel is measured. This settling time is also usually pre-set in the system. Thus, if the settling time is too short, the probe is still ringing and the image quality is affected by the probe vibration. If the settling time is too long, this also has a negative impact on the measurement throughput.

[0006] In industrial applications, the throughput of an SPM system is of great importance. This directly impacts, for example, the throughput of semiconductor manufacturing. However, it is not only in this application field where throughput plays a key role. For example, the use of SPMs to inspect large numbers of, for example, biological samples would also benefit from an increased throughput. Similarly, the quality and precision of the imaging is crucial to achieve the required quality levels. Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide an SPM system and method that overcomes the above-mentioned drawbacks and is capable of achieving high throughput with excellent quality and accuracy. [Means for solving the problem]

[0008] For this purpose, the above-mentioned system is provided, in which the control unit comprises a plurality of signal processing units, each of which is configured to receive the deflection sensor signal provided by the deflection sensor unit and to provide a processed signal, and each of the signal processing units is configured to cooperate with an associated trigger unit, which is configured to compare the processed signal of the corresponding processing unit with a predetermined trigger condition and to generate a trigger signal when the trigger condition is met.

[0009] In the system of the invention, the application of multiple signal processing units, each associated with a trigger unit, allows for the inspection of the deflection sensor signal in real time upon the occurrence of multiple different conditions. The occurrence of such conditions is signaled by the trigger unit generating a trigger signal, thus allowing for more sophisticated control of one or more actuators of the system. This can be used in multiple different ways to improve throughput or accuracy or to prevent damage to the probe or sample. For example, if multiple carefully selected force thresholds are monitored in this way, it is not necessary to perform multiple passes to properly image different depths and shapes of surface features, resulting in less probe replacement.

[0010] In some embodiments, each of the signal processing units is exclusively associated with a trigger unit, and the number of processing units associated with the number of trigger units is equal. This allows each processed signal to be tested against a trigger condition uniquely associated therewith. In other or further embodiments, one or more signal processing units are associated with multiple trigger units. For example, if a processed signal is indicative of a particular physical parameter of the deflection signal and that physical parameter is tested against multiple conditions, the processed signal from the corresponding signal processing unit may be provided directly to multiple trigger units to reduce the processing power required and increase the processing speed.

[0011] The control unit of the present invention may be a single integrated circuit or may be a system of multiple integrated circuits, e.g., an electronic circuit including one or more integrated circuits. The control unit may be embodied as multiple logic circuits, e.g., digital components combined with analog circuit elements. Each of the various functions described may be embodied as a dedicated element of one or more electronic circuits. Furthermore, it will be understood that many of the described functions, e.g., a comparison function to perform a processing function or a trigger, may be embodied in computer instructions that, when loaded into a memory onboard a scanning probe microscope (SPM) system (or a data repository remotely accessible by the SPM system), enable a controller circuit or a central processing unit (CPU) or other circuit to perform the desired function. Such instructions may, for example, include an algorithm or may enable an operator to provide such an algorithm to the SPM system. Those skilled in the art will recognize possible ways to implement the above in light of the description provided herein.

[0012] In some embodiments, one or more of the plurality of signal processing units are configured to process the deflection sensor signal to provide the processed signal indicative of a static deflection of the probe tip. The term "static deflection" as applied herein is intended to refer to a non-oscillating deflection behavior of the probe. For example, a low frequency component of the motion of the probe tip, below the first resonant frequency of the cantilever. In other or further embodiments, one or more of the plurality of signal processing units are configured to process the deflection sensor signal to provide the processed signal indicative of a dynamic deflection of the probe tip. The term "dynamic deflection" as applied herein is intended to refer to a high frequency oscillatory behavior of the system, for example starting at or near or above the first resonant frequency of the cantilever. Both types of behavior of the probe tip may be examined to allow the generation of trigger signals that may be applied to control certain aspects of the motion of the probe and / or sample in the system. Each actuator or aspect of motion may in principle be controlled in this way, as will be further explained below.

[0013] The actuator or actuators may consist of a single actuator unit or of multiple actuator units, without any limitation of the claimed invention. For example, a system of multiple actuator units may be applied, each actuator being responsible for driving the movement of one or more elements of the SPM system in one or more degrees of freedom. These actuators may additionally comprise vibration actuators or acoustic actuators for applying, for example, vibrations to the probe and / or sample. Furthermore, the actuators may comprise translational or rotational actuators in or about the X, Y or Z directions of the system.

[0014] In some embodiments, each trigger unit is configured to compare the processed signal of the corresponding processing unit with a different trigger condition. This means that each trigger unit among all trigger units of the system applies a trigger condition different from the trigger conditions of the other trigger units, thereby being unique within the system. Although this feature is not essential, it allows validating the deflection sensor signal against several different criteria at the same time. For example, the criteria may include processing the signal to obtain a measurement of the probe-sample interaction force and comparing this to several force thresholds. The deflection sensor signal may also be processed to measure the amplitude of a high frequency signal, for example around the natural frequency of the probe, and compared to a threshold to determine whether the vibration of the probe after it has left the surface has subsided. Alternatively or additionally, some of the trigger conditions of two or more trigger units may be the same, the advantage being that this may be used to perform different actions in response to one and the same trigger. For example, one and the same trigger condition may be used in a combination of a low pass filter and a combination of a high pass filter to perform a first action if the sensed frequency is below a certain threshold and a second action (different from the first action) if the sensed frequency is above the certain threshold. Other situations are also possible where one and the same trigger condition may result in different actions depending on the situation.

[0015] In some embodiments, at least two of the trigger units are configured to evaluate one and the same physical parameter for the comparison of the processed signals, and the trigger conditions for the physical parameter of the at least two trigger units are different from each other. Thus, for example, the processed signals may indicate a certain physical parameter (e.g., the amplitude of the dynamic deflection signal), and the trigger conditions compare the amplitude of this dynamic signal with a first threshold and a second threshold. The first threshold may, for example, trigger the detection of ringing of the probe upon contact release, and the second threshold indicates that the ringing has settled sufficiently to allow access to the surface again (to obtain a new measurement result). Alternatively or additionally, the probe-sample interaction force may also be compared with different thresholds or other conditions to improve the quality of the measurement. In a non-resonant vibration imaging mode, the probe is pressed against the surface and may slightly depress the surface in response to this force. By generating triggers at different force thresholds, the probe deflection signal may be recorded at particularly predefined values ​​of the applied probe-sample interaction force.

[0016] In some embodiments, the physical parameter is at least one of the group including: deflection of the probe tip, force on the probe tip, twist of the probe tip, amplitude of the deflection sensor signal, frequency of the deflection signal, phase of the deflection sensor signal, the invention is not limited to these parameters and multiple simultaneous processing of the deflection sensor signals may be performed to gain insight into other physical parameters not explicitly mentioned herein.

[0017] In some embodiments, each of the at least two trigger units compares the deflection sensor signal with a threshold value according to a trigger condition associated with each of them for evaluating the physical parameter, the threshold value of the at least two trigger units being different from each other. The advantages of these embodiments have already been mentioned herein. For example, in a non-resonant vibration imaging mode, this is advantageous in order to be able to obtain deflection signals at the occurrence of various conditions regarding the probe-sample interaction force. The force on the probe tip may be determined by examining the bending of the probe tip due to said force, which may be done by analyzing the deflection sensor signal. The bending occurs while the probe tip is pressing down on the surface, but also before the release due to the adhesive force that the surface exerts on the probe tip. When both parameters are of interest, they can be analyzed in the method of the invention using a combination of a dedicated signal processing unit and a trigger unit.

[0018] In some embodiments, the control unit further comprises a motion profile generator configured to generate motion signals for controlling the one or more actuators, the motion profile generator configured to receive the trigger signal from the trigger unit and to control the motion of the one or more actuators in response to the trigger signal. This allows for direct control of the motion of the probe in response to the generation of a trigger. For example, in a non-resonant vibration imaging mode, the settling time can be made dependent on the amplitude of a high frequency ringing motion of the probe, as described above. As another example, the acquisition and registration of a topography signal when the probe-sample interaction force reaches a certain value can be implemented in this way. Furthermore, by detecting the occurrence of a high frequency ringing signal (e.g. by its amplitude or frequency content in the deflection sensor signal), the moment when the probe leaves the surface can be detected and a trigger can be generated to stop the retraction motion. In this way, the probe is not retracted more than necessary (optimized) to prevent damage to the surface, after which a motion of the probe parallel to the surface can be performed and moved to the next pixel. By optimizing this, this parallel motion can be performed faster, thereby increasing the throughput of the system.

[0019] In some embodiments, the system further comprises a Z-displacement sensor configured to generate a Z-displacement sensor signal indicative of a Z-position of the probe in a direction perpendicular to the sample surface, the system being configured to store current Z-position data in a data repository, such as a memory or a database, upon generation of a trigger signal by at least one of the trigger units. The advantages of these embodiments have already been mentioned, but the acquisition and registration of a Z-displacement signal when a probe-sample interaction force reaches a particular value may be implemented in this way.

[0020] In some embodiments, a plurality of the signal processing units comprise low pass filters for providing the processed signals indicative of static deflection of the probe tip, the trigger units associated with the plurality of the signal processing units each compare the processed signal to a threshold force on the probe tip, and the control unit is configured to operate the Z-motion actuator to initiate retraction of the probe tip from the sample surface upon receipt of a predefined trigger signal of the trigger unit, thereby obtaining many values ​​at different threshold forces and automatically retracting the probe at a desired threshold force.

[0021] In some embodiments, at least one of the signal processing units comprises a lock-in amplifier configured to provide data of an amplitude of the oscillatory motion of the probe tip, and the trigger unit associated with the at least one signal processing unit is configured to generate a trigger signal when the amplitude falls below an amplitude threshold level. In this embodiment, a ringing motion of the probe after disengagement is monitored. Once the ringing is sufficiently settled, the probe may resume movement towards the surface using the Z-displacement actuator.

[0022] As described above, in some embodiments, the control unit is configured, upon receiving the trigger signal of the trigger unit associated with the at least one signal processing unit, to at least one of operate the scanning actuator to move the probe tip parallel to the surface to a next position, operate the Z-motion actuator to start retracting the probe tip from the surface, or operate the Z-motion actuator to stop retracting the probe tip from the surface.

[0023] The present invention is not limited with respect to the type of deflection sensor applied. In some embodiments, the deflection sensor unit comprises at least one of an optical beam deflection unit, a piezoelectric sensor unit, a piezoresistive sensor unit, or a capacitive deflection sensor unit. In principle, any type of deflection sensor that is sufficiently accurate depending on the requirements of the SPM system may be used in combination with the present invention.

[0024] In a second aspect of the present invention there is provided a method of operating a scanning probe microscope system for performing scanning probe microscopy of a sample including a sample surface, the system comprising a control unit, a sensor head including a probe with a cantilever and a probe tip disposed on the cantilever, a deflection sensor unit for acquiring a deflection sensor signal indicative of a deflection of the probe tip during scanning, and one or more actuators including a Z movement actuator for moving the probe tip in a direction perpendicular to the sample surface and a scanning actuator for moving the probe tip relative to the substrate surface, the method comprising receiving, by the control unit, the deflection sensor signal from the deflection sensor unit, and controlling, by the control unit, the one or more actuators in response to the deflection sensor signal received, wherein to perform the controlling step, the deflection sensor signals are simultaneously processed by a plurality of signal processing units of the control unit, each of the plurality of signal processing units providing a processed signal, each of the signal processing units cooperating with an associated trigger unit, whereby each trigger unit performs the step of comparing the processed signal with a predetermined trigger condition and generating a trigger signal when the trigger condition is satisfied. [Brief description of the drawings]

[0025] The present invention will be further elucidated by describing some specific embodiments with reference to the accompanying drawings. The following detailed description provides examples of possible implementations of the present invention, but should not be considered as describing all of the embodiments falling within the scope of the present invention. The scope of the present invention is defined in the claims, and the following description should be considered as illustrative rather than limiting on the present invention.

[0026] [Figure 1] FIG. 1 is a schematic diagram of a scanning probe microscope system according to one embodiment of the present invention. [Diagram 2] FIG. 2 shows two schematic graphs of the Z position signal of the Z actuator and the measured deflection signal from the probe tip according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a schematic diagram illustrating four probe deflection situations associated with particular positions in FIG. [Figure 4A] FIG. 4A shows a schematic diagram of a scanning probe microscope system according to one embodiment of the present invention and associated deflection and Z position signals during operation. [Figure 4B] FIG. 4B shows a schematic diagram of a scanning probe microscope system according to an embodiment of the present invention and associated deflection and Z position signals during operation. [Figure 5A] FIG. 5A is a schematic diagram of a scanning probe microscope system and associated Z position signal and probe deflection in accordance with an embodiment of the present invention. [Figure 5B] FIG. 5B is a schematic diagram of a scanning probe microscope system and associated Z position signal and probe deflection in accordance with an embodiment of the present invention. [Figure 6A] FIG. 6A is a schematic diagram of a scanning probe microscope system and associated Z position signal and probe deflection in accordance with an embodiment of the present invention. [Figure 6B] FIG. 6B is a schematic diagram of a scanning probe microscope system and associated Z position signal and probe deflection in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] FIG. 1 is a schematic diagram of a scanning probe microscope system 1 according to an embodiment of the present invention. Only a part of the SPM system is shown in FIG. 1 in order not to obscure the description with other parts of the system that are less important to the present invention. FIG. 1 shows a schematic diagram of a sample carrier 2 carrying a sample 5 having a sample surface 6. The sample carrier 2 comprises an XY actuator 12 capable of moving the sample 5 in a direction parallel to the carrier 2 relative to a probe 7 of the system 1. The system 1 further comprises a probe 7 with a cantilever 8 and a probe tip 9. In use, for example to perform measurements of the topography of the sample 5, the probe tip 9 needs to be at least temporarily in contact with the surface 6, for example to determine the local height of the surface 6. When the probe tip 9 is in contact with the surface 6, the deflection of the tip 9 is generally different than when the probe tip 9 is not in contact with the surface 6. By oscillating the tip 9 during sensing or by periodically contacting the probe tip 9 with the surface 6, the amplitude of this periodic or oscillatory movement varies depending on the local height of the surface 6. Measurements can therefore be made by monitoring the deflection of the probe tip 9, which may result from deformation of the cantilever 8. The probe 7 is attached to a Z-position actuator 10, which in use allows the probe 7 to contact and retract from the sample surface 6. The actuators 10 and 12 are operated by a control unit 20, which comprises a motion profile generator 30, which controls the operation of these actuators. During the measurement, in principle, the probe tip 9 does not move, or only moves slightly, in the XY direction relative to the sample surface 6. Thus, to move the probe tip 9 to the next pixel of the image to be created, the probe tip 9 is retracted from the surface by the Z-position actuator 10, and the XY actuator 12 is operated to move the probe 7 and the sample 5 relative to each other to the next pixel. The Z-position actuator 10 is then operated again to extend the probe 7 towards the surface 6, bringing the probe tip 9 into contact with the surface 6.

[0028] The measurement is performed using an optical beam deflection unit comprising a laser 15 and an optical sensor 17. The optical sensor 17 is for example a four-quadrant optical sensor which determines the shift of the spots formed by the laser beams 16 and 16' on the surface of the sensor 17. The beam 16 is provided by the laser unit 15 and is reflected off the back surface of the probe 9 into a reflected beam 16'. The optical beam deflector unit uses the optical sensor 17 to provide at its output a deflection sensor signal which is provided to a control unit 20.

[0029] According to the present invention, the control unit 20 comprises a number of signal processing units 22-1, 22-2, 22-i to 22-N. The number of signal processing units may be freely determined in the design as required. Each of the signal processing units 22 is associated with a corresponding trigger unit 24. The processing unit 22-1 is associated with the trigger unit 24-1, the processing unit 22-2 is associated with the trigger unit 24-2, and so on, the processing unit 22-N is associated with the trigger unit 24-N. It is not necessary that each processing unit 22 is exclusively associated with one trigger unit. For example, in some embodiments, one processing unit 22 may be associated with multiple different trigger units 24. In other or further embodiments, multiple processing units 22 may be connected to one and the same trigger unit 24. This depends on the application and design requirements. Furthermore, each trigger unit compares the output of the associated processing unit 22 with a condition 25. The trigger conditions 25-1 to 22-N may be pre-set by the operator of the SPM system 1. For example, each of the trigger conditions 25-1 to 25-N may be different, whereby a different trigger condition may be matched by each of the triggers 24-1 to 24-N. Furthermore, trigger signals are provided at the output of the trigger units 24-N, all of which are provided to a registration unit 35, which will be described later. Furthermore, each of the output signals of the trigger units 24-1 to 24-N may also be selectively provided to the motion profile generating device 30. For this purpose, a selector unit 28-1 to 28-N is associated with each of the trigger units 24-1 to 24-N. It should be noted that a selector unit is not mandatory in the system. In the absence of the selectors 28-1 to 28-N, the trigger signals may be processed in a different way by the motion profile generating device. The registration unit 35 may perform a registration of the actuator positions of the actuators 10 and 12 upon receiving a trigger signal from any of the trigger units 24-1 to 24-N. Furthermore, the control unit 20 may also be configured to register the output signal 17 upon receiving a trigger signal via the connection 33.The registered measurement data and actuator positions are stored in the memory 38 of the SPM system.

[0030] FIG. 2 is a graph showing a schematic of the probe deflection signal 51 and the Z-position actuator signal 41 in an SPM system during a non-resonant vibration imaging mode according to one embodiment. The bottom graph shows the Z-position actuator signal 41 driving the probe 7 to and from the surface 6 of the substrate 5. The horizontal axis shows time, and the level of the axis 43 corresponds to the Z level where the probe tip 9 just touches the surface 6. As the probe 7 is further extended in the negative Z direction towards the surface 6, the reaction force of the surface 6 on the probe tip 9 increases. Thus, at Z levels below the axis 43, a probe-sample interaction force acts on the probe tip 9. The top graph shows a schematic of the deflection signal 51 of the probe tip 7 over time. The deflection signal 51 is represented by the parameter d. As can be seen in the bottom graph 40, the Z-position actuator signal 41 drives the probe 7 (and the probe tip 9) further towards the surface 6, starting from an extraction position away from the Z level. Vertical lines 45, 46, 47, 48, 49 mark characteristic points that will be described later. During extension of the probe 7 towards the surface 6 of the sample 5, at point 45, as shown by the Z position signal 41, the probe tip 9 first contacts the surface 6 of the sample. This is the point where the signal 41 crosses the axis 43. During the approach of the probe 7 to the surface 6 prior to point 45 in the deflection signal 51, in a first phase A of the deflection signal 51, no deflection of the probe tip 9 is measured, as shown by the flat line 51 in this phase. In FIG. 3, phase A is shown diagrammatically in situation 60, showing the position of the probe tip 9 and the probe 7 in a relaxed state above the surface 6.

[0031] Immediately after contact, at time 45, the probe tip 9 is briefly attracted to the surface as indicated by a drop in the deflection signal 51. The Z position signal 41 indicates that the probe 7 is further extended towards the surface 6, increasing the probe-sample interaction force. This is explained by the portion 44 of the Z position signal 41 indicating a negative Z position. The extension of the probe 7 towards the surface 6 continues until the probe-sample interaction force reaches a threshold value at time 46. Then, between 46 and 47, the probe 7 is retracted again, indicating an increase in the Z position signal 41. The period between the instants 45 and 47 when the Z position signal 41 is negative corresponds to phase B of the deflection signal. Phase B actually consists of a first portion corresponding to the portion before the maximum of the deflection signal 51, before point 46, and a second portion corresponding to the portion after the maximum, between times 46 and 47. The situation of phase B is shown diagrammatically by situation 61 in FIG. 3. As can be seen, a positive probe-sample interaction force causes the probe 9 to bend backwards, resulting in a positive deflection signal 51 between points 45 and 47 in FIG.

[0032] At point 47, the probe 7 is in a Z position corresponding to the level of the axis 43 where the probe-sample interaction force is zero. The probe 7 is further retracted from the surface 6 until the probe tip 9 is released. However, before this moment, between times 47 and 48, the adhesion forces attract the probe tip 9, thereby exerting a negative force on the probe tip 9, which maintains contact with the sample surface 6 during the retraction of the probe. This part of the deflection signal is shown in phase C. In FIG. 3, phase C is shown in situation 62, which shows the negative deflection of the probe tip 9 caused by the adhesion forces between the surface 6 and the probe tip 9. At time 48, the probe 7 has been retracted so far that the balance of the combination of the adhesion forces and the force exerted by the Z actuator on the probe tip can no longer be maintained. Now the probe tip 9 is released from the surface 6 and starts to oscillate at its natural frequency. This phase D of the deflection signal 51 is called ringing and is shown diagrammatically in FIG. 3 in situation 63. The ringing continues until it gradually disappears and the probe again goes into a relaxed state corresponding to stage A from time 49, after which the next extension towards the surface may commence. Between point 48 and the next approach to the surface after moment 49, the probe may move laterally relative to the sample 5 towards the next pixel of the image. This process is repeated until all pixels have been imaged.

[0033] In the following description many different embodiments and possibilities that can be realized with the present invention are outlined. The present invention is not limited to these embodiments. In principle, each signal processing unit 22 of the control unit 20 may perform any desired signal processing method to provide a processed signal that allows obtaining any desired signal parameter. Also, the trigger unit 24 may verify any desired trigger condition 25 to control the imaging process of the SPM system. Some examples are shown in Figures 4 to 6 and are described below. Reference to the deflection signal 51 and the Z position signal 41 is repeated in Figures 4B, 5B and 6B below Figures 4A, 5A and 6A, respectively.

[0034] 4A and 4B show an embodiment in which the control unit 20 is configured to analyze the probe-sample interaction force against a number of different threshold levels. The deflection sensor signal 51 is provided to the control unit 20 by the deflection sensor 17 and is received in the control unit 20 by a number of signal processing units 22-1, 22-2 to 22-N. Although the units 22-1 to 22-N are shown as separate units in FIG. 4A, it is in principle possible to combine the signal processing into a single processing unit 22 and a number of trigger units 24-1 to 24-N. In the trigger units 24-1 to 24-N, each trigger unit verifies whether an associated trigger condition 25 is fulfilled. In the embodiment of FIG. 4A, the probe-sample interaction force is analyzed against a number of different threshold levels provided by the trigger conditions 25-1 to 25-N. 1 ~th N 4A , the trigger conditions 25-1 to 25-N are checked against the trigger conditions 25-1 to 25-N. A trigger is generated for each fulfilled condition 25-1 to 25-N by each of the trigger units 24-1 to 24-N. As a trigger is generated by each trigger unit 24-1 to 24-N, it is sent to a registration unit 35 which registers the current deflection signal 51, the Z position signal 41 and the XY position signal indicative of the pixel to be imaged. This data is stored in the memory 38 of the SPM system. Furthermore, the control unit 20 is configured to keep track of at least one of the trigger conditions 25-1 to 25-N to be fulfilled in order to control the motion profile generator 30. In the embodiment of FIG. 4A , this is shown diagrammatically by the selectors 28-1 to 28-N. A selector showing “0” indicates that the trigger signal is to be discarded. A selector showing “1” indicates that the respective trigger signal is selected by the control unit 20. In the embodiment shown in FIG. 4A , the trigger signal 28-2 is selected to control the motion profile generator 30. This is done by selecting the trigger signal 28-2 from the threshold th 2 is satisfied, which means that if so, this controls the motion profile generator 30 to start the retraction of the probe 7 from the surface 6 again.

[0035] In FIG. 4B, the respective trigger conditions 25-1 to 25-N verified by each trigger unit 24-1 to 24-N are indicated diagrammatically by levels 25-1 to 25-N in graph 50. These trigger conditions 25-1 to 25-N have been arbitrarily selected to allow the explanation of the working principle. In practice, they may be selected differently, for example the level of trigger condition 25-1 may be selected lower than the level of trigger condition 25-2. Also, further trigger conditions may be added or some of the trigger conditions 25-1 to 25-N may not be present. In the example shown in FIG. 4A and FIG. 4B, level 25-2 is the threshold level verified to retract the probe 7 from the surface 6 again. As can be seen from the signal 51, when level 25-2 is reached the probe-sample interaction force decreases again, which corresponds to an increase in the Z position signal 41 in graph 40 of FIG. 4B. This increase appears to occur immediately in FIG. 4B, but in reality it may occur with some delay due to system delays such as the inertia of the Z scanner. Other levels 25-1 to 25-N may be matched to perform specific actions, such as controlling specific parts of the system or registering the deflection sensor signal 51, the Z position signal 41 and the XY actuator signals of the SPM. For trigger condition 25-N, this condition is met at time 45, which corresponds to point 65 of the deflection signal 51. Upon receiving a trigger signal at time 46 shown in FIG. 4B, the motion profile generator 30 of FIG. 4A is programmed to start the retraction of the probe 7 from the sample surface 6 again and, after a certain settling time, control the XY actuator 12 to move to the next pixel. In the embodiment of FIG. 4A, only the probe-sample interaction forces are analyzed for multiple triggers 25. Optionally, there may be no settling time, in the sense that the probe may be moved while still ringing.

[0036] In a further embodiment shown in Figures 5A and 5B, one of the signal processing units 22 is configured to analyze a portion of the frequency spectrum of the deflection sensor signal 51. Here, the signal processing unit 22-N is embodied by a lock-in amplifier providing at least a portion of the deflection signal 51 corresponding to a frequency band including the natural frequency of the probe 7. As a result, a trigger unit 24-N associated with the signal processing unit 22-N can determine whether a signal component of sufficient strength is present in this frequency band. Here, the trigger condition 25-N is a threshold th indicative of a sufficiently strong signal indicative of ringing of the probe 7. N5B when a ringing signal occurs at stage D of the deflection signal 51. The signal processing unit 22-2 and the trigger unit 24-2 cooperate to generate a trigger signal when the maximum desired threshold force of the probe-sample interaction force is reached. As in the example of FIG. 1, in the example of FIG. 5, each output signal of the trigger units 24-1 to 24-N may be selectively provided to the motion profile generator 30, which can be indicated by using the selector units 28-1 to 28-N. Each of these selectors 28-1 to 28-N is associated with one of the trigger units 24-1 to 24-N. To indicate that the trigger signals 24-N and 24-2 are to be used by the motion profile generator 30, the selectors 28-N and 28-2 are each set to "1" to provide their corresponding trigger signals to the motion profile generator 30. Thus, at the instant 46, point 71 of the Z position signal 41 and point 66 of the deflection sensor signal 51 may be marked as the moment when the probe 7 retracts from the surface 6 again. From the instant 48 (i.e. point 68 of the deflection sensor signal 51) onwards, the occurrence of ringing of the probe 7 can be detected by the trigger unit 24-N. At this point, the Z position signal is at point 73 of the graph 40. Upon receiving a trigger signal from the trigger unit 24-N, the motion profile generator 30 is informed that the probe tip 9 is away from the surface 6 and the probe 7 is ringing. Thus, the XY actuator 12 may be controlled to move to the next pixel and, after a settling time set by the control unit 20, the Z position actuator 10 may be controlled to extend the probe 7 towards the surface 6 again. In the embodiment of Figures 5A and 5B, no trigger is generated when the ringing of the probe 7 settles. In principle, it is possible to check whether the probe 7 has settled by checking against one of the lowest threshold levels of the deflection signal 51. This may be used to advantage in other or further embodiments of the present invention.4A and 4B, in the embodiment shown in FIG. 5A, when each trigger is received from trigger units 24-1 to 24-N, data from the actuator signal and deflection sensor signal 51 are registered in memory 38 by registration unit 35.

[0037] In Fig. 6A and 6B, a further embodiment of the SPM system according to the invention is shown. Here, a lock-in amplifier 22-N is present as one of the signal processing units 22 to check the occurrence of ringing after time 48. In addition, a further lock-in amplifier 22-1 is associated with the trigger unit 24-1 to check the settling of the ringing signal from the probe 7. The embodiment of Fig. 6A and 6B is similar in many respects to the embodiment of Fig. 5A and 5B, at least except for the additional lock-in amplifier 22-1. As mentioned above, although different lock-in amplifiers are shown, they may all be implemented by a single lock-in amplifier combined with multiple trigger units. Each of the selectors 28-1, 28-2 to 28-N (the dots between units 22-2 and 22-N indicate that any number of processing units can be added at any time) can provide these trigger signals to the motion profile generator 30 as well by setting the value to "1" (or "true" or another corresponding Boolean value). Additional trigger units, not specifically shown in FIG. 6A, may generate a trigger under any circumstances, for example at time 45 for registering data in memory 38. In the embodiment of FIG. 6A, trigger unit 24-2 generates a trigger according to trigger condition 25-2 at time 46 when the probe-sample interaction force reaches a maximum at point 66 of deflection sensor signal 51. After this moment, motion profile generator 30 retracts probe 7 from surface 6. The next trigger is generated by lock-in amplifier 22-N combined with trigger unit 24-N. This trigger is generated when probe tip 9 is released from sample surface 6 and probe 7 starts ringing. Motion profile generator 30 recognizes that probe tip 9 is now away from sample surface 6 and may therefore be moved to the next pixel by control of XY actuator 12. Furthermore, a further trigger signal is generated at time 49 when the natural frequency of deflection sensor 51 falls below the threshold level indicated by condition 25-1. The trigger unit 24-1 then generates a trigger signal which is sent to the motion profile generator 30 via the selector 28-1.To the motion profile generator 30, this marks the point where the ringing of the probe 7 has stopped, and the probe 7 may safely be extended towards the surface 6 in the next pixel. Thus, after time 49 on the graph 40 of Figure 6B, the Z position signal 41 decreases again, indicating that the probe 7 is being extended towards the surface 6. This has begun the process of imaging the next pixel.

[0038] The present invention has been described with respect to 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 present invention in any manner or means. The operation and construction of the present invention will be apparent from the above description and the accompanying drawings. It will be apparent to those skilled in the art that the present invention is not limited to the embodiments described herein, but that modifications are possible that are contemplated within the scope of the appended claims. Also, kinematic inversion is inherently disclosed and is considered to be 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 as deemed necessary, desirable or preferred without departing from the scope of the present invention as defined in the claims.

[0039] In the claims, any reference signs should not be construed as limiting the claims. If a decrease or increase in a particular parameter is described, this should not be construed as limiting, since the reversed parameter is equally applicable. If a decrease in Z level is mentioned, it means that the probe is extending towards the surface, while an increase means that the probe is retracted from the surface. Of course, this depends on the definition of the positive direction of Z, and may be reversed if a different definition is used. The terms "comprises" and "includes" as 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 expression "comprises" as used herein does not exclude the presence of other elements or steps in addition to those recited in any claim. Furthermore, the words "a" and "an" should not be construed as being limited to the meaning of "only one". Instead, they are used to mean "at least one" and do not exclude a plurality. Features not specifically or explicitly recited herein or in the claims may additionally be included in the structure of the invention within the scope of the invention. Phrases such as "means for" should be read as "a component configured for" or "a member configured for" and should be interpreted to include equivalents of the disclosed structures. The use of phrases such as "important," "preferred," and "particularly preferred" is not intended to limit the invention. In general, additions, deletions, and modifications may be made within the scope of the skilled artisan's knowledge without departing from the spirit and scope of the invention, which is determined by the claims. The invention may be embodied in forms other than those specifically described herein, and the invention is limited only by the appended claims.

Claims

1. a sample support structure for supporting a sample including a sample surface; a sensor head including a probe having a cantilever and a probe tip disposed on the cantilever; a deflection sensor unit for acquiring a deflection sensor signal indicative of a deflection of the probe tip of the probe during scanning; a Z motion actuator for moving the probe tip in a direction perpendicular to the sample surface and one or more actuators including a scan actuator for moving the probe tip relative to the substrate surface, The system further comprises a control unit configured to receive the deflection sensor signal associated with the probe from the deflection sensor unit and to control the one or more actuators; said control unit comprising a plurality of signal processing units for simultaneously providing a plurality of processed signals; A scanning probe microscope system, wherein each of the plurality of signal processing units is configured to receive the deflection sensor signal provided by the deflection sensor unit and provide at least one processed signal among the plurality of processed signals, and each of the signal processing units is configured to cooperate with an associated trigger unit, the trigger unit being configured to compare the processed signal of a corresponding processing unit with a predetermined trigger condition and to generate a trigger signal when the trigger condition is satisfied.

2. The plurality of signal processing units include at least one first signal processing unit for providing a first processed signal; at least one second signal processing unit for providing a second processed signal; the first signal processing unit is associated with a first trigger unit configured to compare the first processed signal with a first trigger condition; The scanning probe microscope system of claim 1 , wherein the second signal processing unit is associated with a second trigger unit configured to compare the second processed signal with a second trigger condition.

3. 3. A scanning probe microscope system according to claim 1 or claim 2, wherein each of the signal processing units is exclusively associated with a trigger unit, and the number of trigger units and the number of associated processing units are equal.

4. one or more of the signal processing units are configured to process the deflection sensor signal to provide the processed signal indicative of a static deflection of the probe tip; or 4. A scanning probe microscope system as claimed in claim 1 , wherein one or more of the plurality of signal processing units are configured to process the deflection sensor signal to provide the processed signal indicative of dynamic deflection of the probe tip.

5. 5. A scanning probe microscope system according to claim 1, wherein each trigger unit is configured to compare the processed signal of a corresponding processing unit with a different trigger condition.

6. At least two of the trigger units are configured to evaluate one and the same physical parameter for comparison of the processed signals; The scanning probe microscope system according to claim 1 , wherein the trigger conditions regarding the physical parameters of the at least two trigger units are different from each other.

7. 7. The scanning probe microscope system of claim 6, wherein the physical parameter is at least one of the group including: deflection of the probe tip, force on the probe tip, torsion of the probe tip, amplitude of the deflection sensor signal, frequency of the deflection sensor signal, and phase of the deflection sensor signal.

8. each of the at least two trigger units compares the deflection sensor signal with a threshold value according to a trigger condition associated therewith for evaluating the physical parameter; The scanning probe microscope system according to claim 6 or 7, wherein the threshold values ​​of the at least two trigger units are different from each other.

9. the control unit further comprises a motion profile generator configured to generate motion signals for controlling the one or more actuators; 9. A scanning probe microscope system according to claim 1 , wherein the motion profile generating device is configured to receive the trigger signal from the trigger unit and to control the motion of the one or more actuators in response to the trigger signal.

10. the scanning probe microscope system further comprising a Z-displacement sensor configured to generate a Z-displacement sensor signal indicative of a Z position of the probe in a direction perpendicular to the sample surface; 10. A scanning probe microscope system as claimed in any one or more of claims 1 to 9, wherein the system is configured to store current Z position data in a data repository, such as a memory or a database, when at least one of the trigger units generates a trigger signal.

11. At least one of the signal processing units comprises a low pass filter for providing the processed signal indicative of static deflection of the probe tip; 11. A scanning probe microscope system as claimed in any one or more of claims 1 to 10, wherein each of the trigger units associated with at least one of the signal processing units compares the processed signal with a threshold force applied to the probe tip, and the control unit is configured to operate the Z movement actuator to initiate retraction of the probe tip from the sample surface upon receiving a predetermined trigger signal of the trigger unit.

12. At least one of the signal processing units comprises a lock-in amplifier configured at least to provide amplitude data of the vibrational motion of the probe tip; 12. A scanning probe microscope system according to claim 1 , wherein the trigger unit associated with the at least one signal processing unit is configured to generate a trigger signal when the amplitude falls below an amplitude threshold level.

13. 13. The scanning probe microscope system of claim 12, wherein the control unit is configured to, upon receiving the trigger signal of the trigger unit associated with the at least one signal processing unit, at least one of operate the scanning actuator to move the probe tip parallel to the surface to a next position, operate the Z motion actuator to start retracting the probe tip from the surface, or operate the Z motion actuator to stop retracting the probe tip from the surface.

14. A scanning probe microscope system, wherein the deflection sensor unit comprises at least one of a light beam deflection unit, a piezoelectric sensor unit, a piezoresistive sensor unit, or a capacitive deflection sensor unit.

15. 1. A method of operating a scanning probe microscope system for performing scanning probe microscopy of a sample including a sample surface, comprising: the system comprises a control unit, a sensor head including a probe with a cantilever and a probe tip disposed on the cantilever, a deflection sensor unit for acquiring a deflection sensor signal indicative of a deflection of the probe tip of the probe during scanning, and one or more actuators including a Z motion actuator for moving the probe tip in a direction perpendicular to the sample surface and a scan actuator for moving the probe tip relative to the substrate surface; The method comprises: receiving, by the control unit, the deflection sensor signal associated with the probe from the deflection sensor unit; and controlling, by the control unit, the one or more actuators in response to the received deflection sensor signal; To perform the controlling step, the deflection sensor signals are simultaneously processed by a plurality of signal processing units of the control unit, each of the plurality of signal processing units providing at least one processed signal of a plurality of processed signals; each of said signal processing units cooperates with an associated trigger unit, whereby each trigger unit performs the step of comparing said at least one processed signal with a predetermined trigger condition and generates a trigger signal when said trigger condition is satisfied.

16. The step of simultaneously processing comprises: processing the deflection sensor signal by one or more of the plurality of signal processing units to provide the processed signal indicative of static deflection of the probe tip; or 16. The method of claim 15, comprising at least one of processing the deflection sensor signal by one or more of the plurality of signal processing units to provide the processed signal indicative of dynamic deflection of the probe tip.

17. In at least two of the trigger units, the comparing step includes evaluating one and the same physical parameter; The method of claim 16 , wherein the trigger conditions for the physical parameters are different from one another.

18. 18. The method of claim 17, wherein the physical parameter is at least one of the group including: deflection of a probe tip, a force on the probe tip, a twist of the probe tip, or, if the deflection sensor signal is a dynamic signal, an amplitude of the deflection sensor signal, or a frequency of the deflection sensor signal, or a phase of the deflection sensor signal.

19. each of the at least two trigger units compares the deflection sensor signal with a threshold value according to a trigger condition associated therewith for evaluating the physical parameter; 19. The method according to claim 17 or 18, wherein the threshold values ​​of the at least two trigger units are different from each other.

20. 19. The method according to any one or more of claims 15 to 18, wherein the method further comprises generating an operation signal for controlling the one or more actuators, the generating comprising receiving the generated trigger signal from the trigger unit and controlling operation of the one or more actuators in response to the trigger signal.

21. said processing said deflection signal includes low pass filtering to provide said processed signal indicative of a static deflection of said probe tip; the comparing step includes comparing the processed signal to a threshold force applied to the probe tip; 21. A method according to any one or more of claims 15 to 20, wherein the controlling step comprises operating the Z movement actuator to initiate retraction of the probe tip from the sample surface upon receipt of a predetermined trigger signal.

22. Processing the deflection sensor signal includes providing data on the amplitude of the vibratory motion of the probe tip; 23. A method according to any one or more of claims 15 to 22, wherein the comparing step comprises generating a trigger signal when the amplitude falls below an amplitude threshold level.

23. 23. The method of claim 22, wherein in response to receiving the trigger signal, the method includes at least one of moving the probe tip parallel to the surface to a next position, retracting the probe tip from the surface, or stopping retraction of the probe tip from the surface.

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