Atomic force microscope (AFM) device and its operation method

Abstract

Atomic force microscope (AFM) device and its operating method An atomic force microscope (AFM) apparatus 1 is disclosed that includes at least one scanning head for scanning a sample 9. A cantilever deflection detector 30 measures the deflection d of the probe relative to the scanning head during scanning and provides an output signal indicative of the measured deflection. A controller 40 of the AFM apparatus receives and analyzes the output signal from the cantilever deflection detector to measure the deflection of the probe, and automatically adjusts one or more imaging parameters during scanning in response to information about sample characteristics near the location of the sample currently being scanned. The information about the sample characteristics includes one or more of information from a specification of the sample, a recipe for manufacturing the sample.

Description

[Technical Field]

[0001] The present invention relates to an atomic force microscope (AFM) device. The present invention further relates to a method of operating an AFM device. [Background technology]

[0002] AFM devices are widely used, for example in the semiconductor industry, to measure the surface topography of (semi-finished) products. The AFM device scans the surface of the sample along a scanning trajectory. Tip and the operation of the AFM device is performed by a scanning head having a force threshold. (force threshold) , baseline offset (baseline offset) , approach profile (approach profile) , receding profile (retract profile) , scanning speed (scanning speed) Various Imaging It is determined by the parameters.

[0003] Real-world inspection samples in the semiconductor industry typically contain 3D samples with narrow, high aspect ratio features, making it necessary to characterize the surface topography with an AFM instrument. Imaging This may result in deviations from the actual surface topography of the sample due to various reasons, such as: Tips is on a relatively narrow feature, a relatively high contact force will Tips may slide off the top edge of the narrow feature and slide to a lower level (height). As a result, for a lateral position x,y Imaging The height value shown in the surface topography will be smaller than the actual height of the sample at that lateral position. Tips It has been found that misalignment can occur when the lateral position of a narrow and relatively deep recess in the sample is Tips is moderately larger than the diameter of the Tips is larger than one diameter of TipsExamples of such features include features having a characteristic lateral dimension that is less than 10 times the diameter of the feature and a depth that is substantially greater than the width, e.g., two or more times the diameter. Such features are, for example, holes whose diameter is the characteristic lateral dimension and grooves whose width is the characteristic lateral dimension. In this case, Tips The contact force is Tips is not enough to overcome the frictional force acting on the Tips In this case, the lateral position x, y is Imaging The height value shown in the surface topography will be larger than the actual height of the sample at that lateral position. Tips If the stiffness of the combination of the cantilever and the sensor is relatively high, such deviations will be small. Tips The stiffness of the combination of the cantilever and the rotational stiffness of the cantilever is Tips Other local device characteristics can also affect the image surface topography. For example, Imaging Features of relatively hard materials tend to be higher than features of relatively soft materials, even though the features are actually at the same level on the surface of the 3D sample. Imaging These may appear to be high levels in the resulting surface topography. Summary of the Invention [Problem to be solved by the invention]

[0004] A first objective of the present disclosure is to provide a method for fabricating a semiconductor device that is based on local device characteristics, such as offset in the presence of narrow, high aspect ratio features, and offset associated with differences in surface hardness. Imaging More accurate 3D sample analysis by reducing deviations in the simulated surface topography from the actual device topography Imaging The object of the present invention is to provide a method for operating an AFM device that enables the above.

[0005] A second objective of the present disclosure is to provide a method for detecting and controlling the presence of a local device characteristic. ImagingMore accurate 3D sample analysis by reducing deviations in the simulated surface topography from the actual device topography Imaging The object of the present invention is to provide an AFM apparatus that enables

[0006] According to a first object, a method of operating an AFM apparatus comprises: Tips Scan the surface of the sample along a first lateral current scan line with the probe having child and, The chip and The aforementioned With sample Between Measuring interactions child and, The aforementioned To sample About Advance information ( prior information ) based on The aforementioned During scanning, the force threshold (force threshold) Contains 1 End of Imaging Parameters (imaging parameter) Adjust child Includes: The aforementioned To sample About Advance information is The aforementioned On the sample taken before scanning About Contains information. The aforementioned Acquired before scanning The aforementioned To sample About Prior information may be, for example, information from the sample specifications and / or information on samples taken during recipe creation. About The sample specification defines the desired topography of the sample and the properties of the materials used in its features. About The information may indicate that the actual topography tends to deviate in a particular way from the designed topography. The information obtained during recipe development does not perfectly describe the actual topography, but it helps predict how the actual topography will deviate. For example, the information obtained during recipe development may indicate that the width of the edge is, on average, narrower than the width originally specified. AboutThe prior information allows the surface elements of the sample to be scanned at optimal settings, so that the output signal obtained at these settings more accurately indicates the actual height of the surface as a function of lateral position. About The information may further include information obtained from a prior device inspection method, for example information obtained from an electron microscope image of the sample.

[0007] The force threshold is Tips is the upper limit of the force exerted on the sample.

[0008] On the sample taken before scanning About Based on the information from the area of ​​the current scanning position, the current scanning point is relatively deep. and A relatively high force threshold is selected to indicate that the device is expected to be in a narrow recess or at the bottom near a steep wall, The aforementioned The information from the region is relatively steep. and Relatively wide recess or wide flat area away from high edge / wall Area (wide flat area) , a relatively low force threshold is selected.

[0009] On the sample taken before scanning About Although the information does not necessarily correspond exactly to the actual topology of the sample, this information allows the force threshold to be optimally set to more accurately determine the actual topology.

[0010] For example, surface elements with high levels close to low levels can be more accurately determined by setting the force threshold relatively low. Imaging This will result in: Tips This reduces the risk of the vehicle skidding towards a lower level. Tips As another example, relatively narrow and deep recesses on the sample surface can be more accurately measured by setting a relatively high force threshold. Imaging This will result in: Tips The force acting on the side wall of the recess is TipsThis allows the force acting on the Imaging In the resulting surface topography, the depth of the recesses is more accurately shown.

[0011] The aforementioned To sample About The information is The aforementioned On the previous scan line in a direction substantially parallel to the current scan line follow It may also include information obtained from the scan.

[0012] The present invention is particularly suited to trigger-based scanning embodiments, where the scanning comprises a scan cycle for each scan position, having the following steps: (a) Tips (b) approaching the sample at a lateral position on the sample surface. Tips retracting from the sample, (c) Tips towards a new lateral position. Tips and sample Between Interaction data indicative of the interaction is acquired during the approach and / or retreat.

[0013] The approach to the sample in step (a) is determined by the approach profile. Imaging Examples of parameters include the initial height before approaching the sample surface and the speed at which the sample is approached.

[0014] The retraction of the sample is determined by the retraction profile. Imaging Examples of parameters include force threshold, displacement threshold, retraction distance, and velocity. Tips When the force exerted by exceeds a predefined force threshold, the sample Tips As another example, retraction is initiated when the measured depth exceeds a depth threshold. As another example, retraction is initiated as soon as either of these conditions occurs, whichever occurs first, or when both conditions are met. Imaging The parameter is the setback distance. Adhesion Where it is determined that the resonant frequency is relatively high, the retraction distance is increased. The retraction distance may also be adjusted depending on the situation. That is, if it is detected that the cantilever resonance has sufficiently decreased before the retraction of a predetermined distance is completed, the retraction may be stopped and the cantilever may be allowed to approach the surface again. This improves the measurement speed.

[0015] During operation, the cantilever Tips The cantilever deflects due to forces acting between the cantilever and the sample surface. Electrostatic forces can also cause cantilever deflection at a distance from the sample. This introduces a bias that can be corrected by taking into account the baseline offset. If necessary, the baseline offset can be updated every measurement cycle.

[0016] Please note that multiple Imaging The parameters may be adjusted, for example, both the baseline offset and the force threshold may be adjusted according to prior knowledge of the sample at the lateral position being scanned, with the force threshold being selected relative to the baseline offset.

[0017] As mentioned above, the sample About The prior information may include information from the sample specification, which may include device design data and / or recipe data. Under normal circumstances, the topography of the sample to be measured is determined by the About It can be assumed that the topography is approximated by a topography derived from a priori information, e.g., sample specifications and / or information obtained during recipe development. End of Imaging By adjusting the parameters, the actual scanned position may deviate slightly from the desired scanned position, Imaging Although the actual topography of the structure may deviate to some extent from the originally designed topography, the overall sample Imaging This provides a significant improvement over using a uniform setting for

[0018] Also, as mentioned above, the sample About The prior information is based on a previous scan line in a direction substantially parallel to the current scan line. follow It may also contain information obtained from the scan. If the current and previous scan lines are close enough together, the topography of the current scan line will be approximated by the topography of the previous scan line, so that the entire sample Imaging Again, this provides a significant improvement compared to using a uniform setting for

[0019] In some embodiments, subsequent scan lines are substantially parallel, i.e., in this case, subsequent scan lines are at a distance Δy from each other. In operation, scanning proceeds by moving the probe in the x direction along scan lines y, y+Δy, y+2Δy, etc. Alternatively, instead of increasing the coordinate y between subsequent scan lines in steps, y may be increased gradually during the scan, resulting in a triangular scan path.

[0020] Note that subsequent scan lines do not have to be exactly parallel to each other.

[0021] In some embodiments, Imaging The parameters are as follows: About Further improvements can be achieved by adjusting the scan during the scan based on prior information obtained from previous scan lines.

[0022] In some embodiments, the sample About The prior information is used in combination with information acquired during the scan. For example, if the topography at position x along the current scan line y appears to deviate significantly from the topography at position x along the previous scan line y-Δy, this deviation may be incorporated in preparing adjustments to the settings for the subsequent position x+Δx along the current scan line.

[0023] In one embodiment, The aforementioned probe, The chip , or the above Sample 1 EndProvides an acoustic signal to child and, The aforementioned Acoustic signals and The aforementioned With sample Between Analyze the output signal based on the interaction child The output signal is indicative of subsurface properties of the sample, thereby enabling both topographical and subsurface information to be obtained in a common measurement, for example, for overlay and / or alignment analysis.

[0024] Tips The force that the probe exerts on the sample is proportional to the cantilever deflection and the stiffness of the cantilever. In one embodiment, vibration of the probe is induced to change the effective force that the probe exerts on the sample. The vibration increases the stiffness of the cantilever, thereby increasing the effective force on the sample.

[0025] This approach is intended to avoid the same location or scan line being scanned multiple times, but analysis of the image data acquired during the scan allows for different Imaging It may be found desirable to perform one or more additional scans with the parameter settings, in which case the image data obtained from the additional scans may replace the original image data, or the original image data may be combined with new image data obtained from the one or more additional scans. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram illustrating a portion of an exemplary improved AFM device and a sample scanned by the device. [Figure 2] FIG. 1 shows an aspect of a controller according to a first embodiment of an improved AFM device. [Figure 3] FIG. 10 is a schematic diagram illustrating two graphs of the Z position signal of the Z actuator and the measured deflection signal from the probe tip in one embodiment of the present invention. [Figure 4] 4 is a diagram showing four probe deflection situations associated with specific positions in FIG. 3. [Figure 5] FIG. 10 shows an embodiment of a controller according to a second embodiment of the improved AFM device. [Figure 6] FIG. 10 shows an embodiment of a controller according to a third embodiment of the improved AFM device. [Figure 7] FIG. 10 shows an aspect of a controller according to a fourth embodiment of the improved AFM device. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further elucidated by describing specific embodiments with reference to the accompanying drawings. The detailed description provides possible examples of the present invention, but does not describe the only embodiments falling within the scope of the present invention. The scope of the present invention is defined by the claims, and the following description should be considered as illustrative rather than limiting.

[0028] One embodiment of an improved atomic force microscope (AFM) apparatus 1 will now be described with reference to Figures 1 and 2. Figure 1 shows a schematic representation of a portion of an exemplary improved AFM apparatus and a sample 9 scanned by the apparatus. Figure 2 shows aspects of a controller according to a first embodiment of the improved AFM apparatus.

[0029] As shown in FIG. 1, the AFM device 1 includes at least one scanning head 10 for scanning a sample 9. attitude The scanning head 10 includes a cantilever 12 and a probe disposed on the cantilever. Tips 13 and attitude Probe 11 Prepared .

[0030] The AFM device 1 further includes a first actuator 20. attitude The first actuator 20 is a probe. Tips In order to scan the surface 91 of the sample with End Probe in the x and y directions Tips 13 and sample 9 To each otherIn other embodiments, the first actuator cooperates with the scan head, and in yet other embodiments, there is provided a first actuator that cooperates with each of the scan head and the substrate holder to effect scanning of the surface 91.

[0031] The AFM device 1 moves the scan head 10 and the probe relative to the sample during scanning. Tips 13. The cantilever deflection sensor 30 is configured to measure the relative movement / position of the cantilever. attitude The detection unit 30 also Tips and sample Between It is configured to provide an output signal Sout indicative of the interaction and deflection of the cantilever due to the applied force (in the static domain).

[0032] The topography of the sample is indicated by the deflection of the cantilever Tips It is derived from the height of the AFM head minus the distance between the heads.

[0033] In the illustrated embodiment, when contacted with the surface 91 of the sample 9 Tips Provides a sense signal Stdf indicating the deformation of 13 Tips The AFM device 1 is also provided with a deformation sensor 15. The AFM device 1 receives an output signal Sout from the cantilever deflection detection unit 30. and Analyzing and characterizing surface 91 and / or subsurface sample characteristics of the sample 9 Imaging The controller 40 is further configured to attitude In the embodiment of FIG. 1, the controller 40 further controls the control signals of the XY actuators 20 and / or the probes indicated by the displacement sensors 21. Tips The controller 40 also receives additional information for analysis, such as position signals x, y indicating the lateral position of the Z actuator 60 and / or the z position of the probe as indicated by the displacement sensor 61. In the illustrated example, the controller 40 also receives additional information for analysis, such as control signals x, y indicating the lateral position of the Z actuator 60 and / or the z position of the probe as indicated by the displacement sensor 61. Tips The controller 40 also receives a sense signal Stdf indicative of the deformation of the 13. TipsAlternatively and / or additionally, the controller 40 may be configured to: Tips The deviation caused by the deformation of 13 compensation The device may be configured to process output signals obtained by the device to:

[0034] The AFM device is configured to perform a scanning cycle for each scan position, which includes the following steps:

[0035] In the first stage, Tips 13 approaches the sample 9 according to an approach profile starting from a reference position z on the sample 9. The reference position z defined by the approach profile is, for example, a predetermined z value higher than any z value on the surface 91 of the sample 9. Alternatively, the reference position z is a relative position at a predetermined distance relative to an expected z value of the surface at the approaching abscissas x, y. The approach profile further defines a speed at which the surface 91 is approached. This speed may be constant, for example. Alternatively, the speed may be variable, for example starting at a relatively high speed and decreasing in steps or gradually as the approach progresses.

[0036] In the second stage, Tips 13 recedes from the sample surface 91. The transition from the first stage to the second stage is determined by one of the following: End One option is to use Tips Or the transition occurs when the probe has advanced a predetermined distance towards the sample. Tips The transition occurs when the force exerted by the robot exceeds a threshold. Another option is to initiate retraction as soon as either of these conditions occurs, whichever occurs first, or to initiate retraction when both conditions are met. Imaging One parameter is the speed of the retraction. The behavior of the second stage is determined by the speed at which the retraction is performed. As with the approach profile, the speed can be a constant value or can vary during the retraction.

[0037] In the third stage, Tips is displaced towards the next lateral position. The magnitude of the lateral distance is further Imaging 10 is an example of a parameter.

[0038] During the first and / or second phase: Tips and sample Between Interaction data indicative of the interaction is obtained. Tips and the force between the sample, Tips as a function of displacement towards and / or away from the sample, Tips - The sample force curve is determined.

[0039] As with many practical types of samples, the sample 9 shown in Figure 1 has surface portions 91B, 91S, and 91T at different levels. Tips 13 is located at the end of a shoulder 91S having a bottom 91B. Tips A downward force acts on the cantilever 12 and / or Tips Deformation occurs in Tips 13 slides toward the bottom 91B, and as a result, the cantilever flexure detection unit 30 Tips This may result in a lower z value than the x,y position where 13 was originally located. This phenomenon only occurs near the edge of a surface with low level surfaces, but the measurement error increases for samples with high aspect ratio surface features. Tips 13 is located at position x, y of the bottom 91B, Tips The wall portion 91BW of the bottom 91B near the 13 Tips force that may prevent the bottom 91B from approaching sufficiently Tips Therefore, the cantilever flexure detection unit 30 Tips This indicates a higher z value than the actual z value at the x, y position of 13. Furthermore, this type of measurement error becomes more pronounced as the aspect ratio, i.e., the ratio of the depth to the lateral dimension of the bottom 91B, increases.

[0040] The improved AFM device 1 disclosed herein includes a controller 40 that controls the sample properties at the lateral position of the sample currently being scanned. About Depending on the information, during scanning End of Imaging These sources of error are mitigated by automatically adjusting the parameters to suit the sample characteristics. About The information may include information from the sample specification, a recipe for manufacturing the sample, and information from a previous scan line in a direction substantially parallel to the current scan line. follow One of the pieces of information obtained from the scan End Additionally, information acquired during the orbital scan may be used to make additional adjustments based on local conditions. Imaging The parameters are locally optimized for proper Z measurement. As an example, a relatively low force threshold is selected at an x,y location predicted to be a location on a relatively high level surface near an edge with a lower level surface. As another example, a relatively high force threshold is selected at a lateral (x,y) location predicted to be part of the bottom near a wall. A further example is adjusting the baseline offset depending on the predicted height at the lateral location. As yet another example, Tips Estimation of the sample surface at the lateral position of Adhesion The retraction profile can be adjusted accordingly.

[0041] As shown schematically in FIG. 1, the AFM device includes a probe 11, Tips 13, 1 of 9 samples End and a signal analysis module 52 for analyzing the output signal based on the interaction between the acoustic signal and the sample 9. Tips The output signal Sout of the deflection sensor further indicates subsurface properties of the sample, allowing both topographical and subsurface information to be obtained in a common measurement, for example for overlay and / or alignment analysis.

[0042] Additionally or alternatively, the AFM device may include a signal source, e.g., signal source 51a, for inducing vibrations in the probe 11 to increase the effective stiffness of the cantilever 12. Vibration increases the stiffness of the cantilever 12, thereby increasing the effective force on the sample. In the absence of induced vibration, the stiffness of the cantilever is determined by the static spring constant of the cantilever. Applying vibration increases the stiffness. The deflection of the cantilever 12 is Tips Since the force exerted by the probe 11 via 13 on the sample 9 is proportional to the ratio of the force divided by the stiffness of the cantilever, the effective force on the sample can be calculated from the deflection of the cantilever and its effective stiffness as a function of the induced vibration, for example using a calculation module 53.

[0043] In the example shown in FIG. 1, the AFM device Tips Showing 13 variants Tips Deformed signal (tip deformation signal) Supply Stdf Tips Equipped with a deformation sensor 15 attitude In this example, the controller 40 of the AFM device is Tips The AFM device may be configured to lower the force threshold if deformation of the AFM exceeds a predetermined limit. Alternatively, or in addition, the AFM device may be configured to correct the reconstructed image for this deformation. This optional functionality may be provided as an alternative to, or in combination with, other measures taken to control the settings of the AFM device.

[0044] For clarity of illustration, the interconnections between the controller 40 and the components controlled by the controller, and the cantilever deflection detection unit 30 and Tips The connection to the deformation sensor 15 is not shown in the drawing. A more detailed configuration will be shown in the following drawings.

[0045] 2 shows in more detail a first embodiment of the improved AFM device 1. In the example shown, the controller 40 comprises a signal analysis unit 41, an image memory 42, and a motion profile generator 45. attitudeAs further shown in FIG. 2, the probe / cantilever deflection detection unit 30 includes a photodetector element 31 (here, a four-quadrant photodetector element) and a deflection signal processing unit 32. attitude The deflection signal processing unit 32 calculates the deflection of the probe from the signal S31 emitted by the photodetector element 31 and supplies the signal to the motion profile generator 45. The motion profile generator 45 generates a control signal Cz for controlling the Z actuator 60 and a control signal Cxy for controlling the XY actuator 20. The motion profile generator 45 further supplies an input signal indicating the z value determined for each pixel of the abscissa coordinates x and y to the image memory 42. For simplicity, in this example, the coordinates x, y, and z stored in the image memory 42 are assumed to be coordinates specified by the motion profile generator 45. In general, the z value is the vertical " Tips In practice, there may be a discrepancy between the specified coordinates and the actual coordinates. Taking this into consideration, position sensors (21, 61, see FIG. 1) are usually provided to sense the lateral position (x, y) of the sample 9 and the vertical position z of the probe 11. The sensed signals from these sensors are supplied as feedback signals to the motion profile generator 45. When the scanning process is completed, the topography of the surface 91 of the sample 9 is calculated. z(x,y) can be read out from the image memory 42.

[0046] As shown in FIG. 2, the signal processing unit 41 calculates a force threshold setting Ft(x,y) for lateral position x,y based on the topography data z(x,y-Δy) from the previous scan line.

[0047] The embodiment of Figure 2 will be further described with reference to Figures 3 and 4. Figure 3 shows a non-resonant version of the embodiment of Figure 2. Imaging 1 shows a schematic graph of the probe deflection signal d51 and the Z-position actuator signal z41 in the mode. The lower graph shows the Z-position actuator signal Cz that drives the probe 11 to approach or move away from the surface 91 of the sample 9. The horizontal axis indicates time t, and the level of the axis a43 indicates the probe Tips13 corresponds to the Z level where the probe 11 just touches the surface 91. As the probe 11 is extended further in the negative Z direction towards the surface 91, the probe Tips 13. Therefore, at Z levels below axis a43, the positive probe-sample interaction force Tips 13. The top graph shows the probe over time. Tips 13. The deflection signal d51 is represented by the parameter d. Starting from the retracted position of the remote Z level, as shown in the lower graph g40, the Z position actuator signal z41 is Tips 13) is further driven toward the surface 91. Vertical lines t45, t46, t47, t48, and t49 indicate characteristic time points, which will be described later. As the Z position signal z41 indicates, when the probe 11 is extended toward the surface 91 of the sample 9, at time t45, the probe Tips 13 first contacts the surface 91 of the sample 9. This corresponds to the point where the signal z41 intersects with the axis a43. In the deflection signal d51, the probe 11 approaches the surface 91 before time t45. In the first stage A of the deflection signal d51, the flatness of the deflection signal d51 at this stage area As shown by the probe Tips 4, stage A is the measurement of the deflection of probe 11 and probe 13 in an undeflected state on surface 91. Tips This is shown diagrammatically in situation s60, which represents the position of 13.

[0048] Immediately after contact, at time t45, the probe TipsThe probe 13 is temporarily attracted to the surface 91, as indicated by the drop in the deflection signal d51. The Z position signal d41 indicates that the probe 11 is being extended further toward the surface 91, increasing the probe-sample interaction force. This is illustrated by the negative Z position z44 of the Z position signal z41. The extension of the probe 11 toward the surface 91 continues until the probe-sample interaction force threshold level Ft(x,y) is reached at time t46. Then, between t46 and t47, the probe 11 retracts again, causing the Z position signal z41 to rise. The period between times t45 and t47, during which the Z position signal z41 is negative, corresponds to phase B of the deflection signal. Phase B consists of two parts, corresponding to the portion before the maximum value of the deflection signal d51 before time t46 and the portion after the maximum value between times t46 and t47. The situation in phase B is shown diagrammatically in FIG. 4 as situation s61. As shown, the positive probe-sample interaction force causes the probe's cantilever 12 to bend backward, thereby providing a positive deflection signal d51 between times t45 and t47 in FIG.

[0049] At time t47, the probe 11 is at a Z position corresponding to the level of the axis a43 where the probe-sample interaction force is zero. Tips 13 is further retracted from surface 91 until it is released. However, before that, between times t47 and t48, Adhesion is the probe Tips Attract 13 and probe Tips A negative force acts on 13, and while the probe is retracting, Tips 13 maintains contact with the sample surface 91. This portion of the deflection signal is designated phase C.

[0050] In FIG. 4, step C is a process for determining whether the surface 91 and the probe Tips Between 13 Adhesion Probes generated by Tips At time t48, the probe 11 is AdhesionThe balance between the force exerted by the probe and the force exerted by the Z actuator 60 cannot be maintained. Tips 13 is released from the surface 91 and begins to vibrate at its natural frequency. This phase D of the deflection signal d51 is called resonance and is shown diagrammatically in FIG. 4 as state s63. The resonance continues until it disappears, and after time t49 the probe is again in an undeflected state corresponding to phase A. The next extension to the surface can then begin. In some embodiments, if the resonance amplitude decreases below a predetermined threshold level, the next extension is initiated before the cantilever is in an undeflected state. In these embodiments, the cantilever is in an undeflected state before reaching the surface. Between time t48 and the next approach to the surface after time t49, the probe may move laterally relative to the sample 9 toward the next pixel in the image. This process continues until all pixels are Imaging The process is repeated until the z(x,y) value is registered for each pixel x,y, resulting in a topographical image of the surface 91 of the sample 9. The choice of force threshold Ft(x,y) used by the motion profile generator 45 is determined by the signal processing unit 41.

[0051] The surface height profile z(x,y) is estimated from the head position and cantilever deflection as described with reference to Figures 3 and 4. The motion profile generator retracts the probe when the deflection d indicates that the current force threshold Ft has been exceeded. The estimated height profile in the vicinity, e.g., z(x,y-Δy), is the sum of the height profile z(x,y) at position x,y. Indication and using this information, an optimal force threshold Ft(x,y) is selected by the signal processing unit 41. As mentioned above, the selection of the optimal force threshold Ft(x,y) may additionally or alternatively depend on the sample About It may be determined by prior knowledge, for example, specified topography data and / or recipe creation data and / or analytical results obtained from the current scan line, i.e., neighborhood z(x-Δx,y).

[0052] In one embodiment, the signal processing unit 41 determines the value of the force threshold Ft(x,y) based on image data acquired for a previous scan line y-Δy having a corresponding x coordinate or having an x ​​coordinate within the region of the currently scanned coordinate x. In some embodiments, not only the z value measured when the force threshold is reached is registered, but instead the complete force-distance curve defining the relationship between distance z and applied force is registered.

[0053] In one example, the force threshold Ft(x,y) for the abscissa position is selected from at least a relatively low threshold Ftlow and a relatively high threshold Fthigh depending on the z value measured in the preceding scan line (y-Δy) according to the following criteria:

number

[0054] For example, it is conceivable to use additional information from earlier scan lines -2Δy, -3Δy. This additional information is less predictive of the characteristics of the sample at the current position x,y, but may be weighted with an appropriate weighting factor. In another example, the selection of the force threshold depends on a region having width Δy defined by the distance to the previous scan line and length dx of the most recently scanned portion of the current scan line, as follows:

number

[0055] That is, features with low z values ​​are predicted based on knowledge of the area at the current scan position (x,y). Indication If there is a force threshold Ft(x,y) at that location, a relatively high force threshold Ft(x,y) is selected. A relatively high force threshold Ft(x,y) is used to minimize the force threshold Ft(x,y) to the bottom surface of such a feature. Tips This choice therefore improves the measurement of features with low z values.

[0056] In another example, the force threshold Ft(x,y) is determined as follows:

number

[0057] This is done by finding features with high z values ​​based on knowledge of the region at the current scan position (x,y). but expected Indication means that a relatively low force threshold Ft(x,y) is selected for that position. A relatively low force threshold Ft(x,y) is Tips This choice is intended to prevent the lens from sliding from high z-value features to lower positions, thus improving measurements of features with high z-values.

[0058] Also, the width of the region may span several preceding scan lines.

[0059] In yet another embodiment, the threshold force is About The sample is adjusted according to the material properties at the x,y location based on prior information and / or information acquired from the sample during scanning of the previous or current scan line. About A relatively low threshold force is used when the surface hardness at the scanned location is predicted to be relatively low based on prior information and / or information obtained from the sample during scanning, and a relatively high threshold force is used when the surface hardness at the scanned location is predicted to be relatively high.

[0060] In these examples, the force threshold Ft(x,y) is determined by selection from a predetermined threshold. In other embodiments, the force threshold is determined by interpolating the sample, for example using a polynomial function, for example an interpolation function, for example a cubic interpolation function. About An interpolated threshold value at a location is calculated from a number of predetermined threshold values ​​known at nearby locations, determined as a continuous function from prior information. In yet another example, a look-up table is used.

[0061] It should be noted that the determination of the force threshold Ft by the signal processing unit 41 is further based on the most recently acquired scan line y. ImagingFor example, the signal processing unit 41 may invalidate a decision based on a previous scan line y-Δy if the z-value z(x-Δx,y) determined for a lateral position of coordinate x-Δx,y deviates significantly from the z-value z(x,y-Δy) determined for a lateral position of coordinate x,y-Δy.

[0062] Alternatively, the signal processing unit 41 may Imaging The threshold FtΔx(x,y) determined based on the data and the Imaging The average value of the threshold FtΔy(x,y) determined based on the data may be calculated using the following formula:

number

[0063] In the above formula, 0 <ax,ay<1であり、ax+ay=1である。

[0064] FIG. 5 illustrates another embodiment. In the example illustrated in FIG. 5, the signal processing unit 41 uses topography information zs(x,y), which can be obtained from the specifications or recipe of the sample 9 and stored in the topography storage unit 43. The motion profile generator 45 and / or the displacement sensor 21 provide the abscissas x,y of the currently scanned position to the signal processing unit 41. The signal processing unit 41 can then retrieve the predicted z-value for that position zs(x,y) and / or predicted z-values ​​for adjacent positions from the topography storage unit 43 in a manner similar to that described for the embodiment of FIG. 2, and determine the force threshold Ft(x,y) to be used by the motion profile generator 45 for that lateral position x,y. In one embodiment, the process of determining the force threshold Ft(x,y) includes estimating the uncertainty of the values ​​involved in determining the threshold. Depending on the magnitude of this uncertainty, different weights may be assigned to each force threshold estimate using various techniques. Estimates with high uncertainty, i.e., low confidence, are assigned a lower weight than estimates with low uncertainty. In this case, the force threshold Ft(x,y) used by the motion profile generator 45 may be determined by a weighted average of the various force threshold estimates according to the assigned weights. As mentioned above, the thresholds may be estimated based on prior knowledge and topographic information obtained from previous scanlines and / or preceding positions on the current scanline.

[0065] Also, in this embodiment, as described above for the embodiment of FIG. 2, the determination of the force threshold Ft by the signal processing unit 41 further depends on the most recently acquired force threshold Ft from the current scan line y. Imaging It may be based on data.

[0066] In yet another embodiment, the signal processing unit 41 is configured to determine a force threshold Ft(x,y) for the positions of the scanned abscissa x,y based on a combination of the topography information zs(x,y) from the specification or recipe of the sample 9 described with reference to FIG. 5 and the topography information z(x,y−Δy) obtained from the previous scan line y−Δy described with reference to FIG. 2. In some of its examples, the signal processing unit 41 is also further configured to use the image data most recently obtained from the same scan line to determine the force threshold Ft(x,y) for the positions of the abscissa x,y.

[0067] As described above, the signal processing unit 41 does not need to calculate the threshold force based on information from a single position near the current scan point. Instead, it may be calculated based on information from the area of the current scan point x,y, for example, from the area of the preceding scan line x−dx<x′<x+dx, or from the area of the current scan point defined by the design data or recipe data, for example, from the area x−dx<x′<x+dx, y−dy<y′<y+dy. In an exemplary embodiment, if the information from the area indicates that the current scan point is expected to be in a narrow groove, the signal processing unit 41 selects a relatively high force threshold, and if the information from the area indicates a wide groove or other relatively flat area, it selects a relatively low force threshold. If within a configurable distance (e.g., Tips 10 times the diameter) the difference between the maximum surface level and the minimum surface level is less than a configurable coefficient (e.g., Tips 0.5 times the height), the current scan point is determined to be in a flat area. The exact values of the configurable distance and the configurable coefficient depend on Tips the stiffness of the combination of Tips and the cantilever. When the stiffness of the combination of Tips and the cantilever is relatively high, the configurable distance may be selected to be relatively small and the configurable coefficient to be relatively high.

[0068] In the above exemplary embodiment, the signal processing unit 41 adjusts Imaging The parameter is the force threshold Ft as a function of the abscissas x and y, but in other embodiments it may be adjusted. Imaging The parameters are a baseline offset, an approach profile, or a receding profile.

[0069] An exemplary embodiment is shown in Figure 6. In the example shown in Figure 6, the controller 40 Adhesion Signal Processing Unit (adhesion signal processing unit) Equipped with 47 attitude do. Adhesion The signal processing unit 47 determines a control signal dr(x,y) that indicates the retraction distance of the retraction profile used by the motion profile generator 45, i.e., the distance that the motion profile generator 45 causes the Z actuator 60 to retract the probe 11 away from the sample 9. In the illustrated example, the deflection curve signal processing unit 46 receives the deflection curve data dz(x,y) for each scan position. The deflection curve data dz(x,y) indicates the deflection d measured as a function of the movement of the probe z, and in particular, the deflection of the probe during the time interval from t47 to t48. and Figure As explained with reference to 4, during this time interval the deflection of the probe 11 is substantially Tips Between 13 and sample 9 Adhesion Using this data, the deflection curve signal processing unit 46 determines the deflection curve at the lateral position x, y of the sample. Adhesion The magnitude Adh(x, y) of the vector is estimated and the value is stored in the memory 44. Adhesion The signal processing unit 47 calculates the signal for the previous scan line x,y-Δy. Adhesion Read the data acquired for Adh(x,y-Δy) and calculate the optimum retraction distance for the retraction profile based on the assumption that Adh(x,y) is approximately equal to Adh(x,y-Δy). Adhesion If this is expected, the setback distance is relatively low. Adhesion is set to a value larger than expected. Adhesion The signal processing unit 47 determines the signal from the specifications or recipe of the sample 9. Adhesion In yet another embodiment, the calculation is based on information about Adhesion The signal processing unit 47 determines the signal from the specifications or recipe of the sample 9. Adhesion information and the previous scan line y-Δy Adhesion In some examples, the method is configured to determine the retraction distance of the retraction profile relative to the scanned abscissa x,y position based on a combination of information about the retraction distance and the position of the scanned abscissa x,y. Adhesion The signal processing unit 47 also processes recently acquired signals from the same scan line. Adhesion The information is further configured to determine a setback distance for a position of abscissas x,y.

[0070] FIG. 7 illustrates yet another embodiment. Similar to the example illustrated in FIG. 6, the deflection curve signal processing unit 48 receives deflection curve data dz(x,y) for each scan position. However, in this embodiment, the deflection curve signal processing unit 48 calculates force-distance data for lateral positions (x,y) determined during the time interval in which the force is positive, from t45 onward until the probe is retracted at t46. The force-distance data may include two or more distances z measured for each force. The signal processing unit 41 can access the force-distance data and, based thereon, determines which threshold force Ft(x,y) to select for the lateral position x,y based on two or more distances z1(x,y-Δy), z2(x,y-Δy) measured for each force stored for the lateral position having the coordinate x' at or near x,y-Δy. In some embodiments, the signal processing unit 41 also performs calculation of the threshold force Ft(x,y) based on the force-distance data obtained from the current scan line, e.g., the force-distance data obtained from the previous scan position x-Δx,y.

[0071] As mentioned above, Imaging Parameter settings are based on design information, recipe information, and previous scan line Imaging Information obtained from the data, recent Imaging Samples of information obtained from data AboutThe decision may be based on a combination of input data from various sources, including two or more pieces of prior information, provided that the prior information used in the combination is consistent. child This is, Those trust It is an indication of sexuality If not, one approach is to set Imaging The values ​​of the input parameters used to predict the parameters may be calculated as an average, e.g., a weighted average, of input data obtained from various sources, i.e., Imaging The parameter settings may be calculated based on input data from various sources and may be used in practice. Imaging The parameter setting may be calculated as an average, e.g., a weighted average, of settings calculated based on various input data. Alternatively, in another approach, the input parameter setting is the most conservative setting among the settings predicted individually based on each input data. For example, the lowest force threshold setting may be selected from multiple force threshold settings to minimize the risk of sample damage.

[0072] While the present invention has been described with reference to specific embodiments thereof, it will be understood that the embodiments shown in the accompanying drawings and herein are merely exemplary 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 foregoing description and 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 may be made within the scope of the appended claims. Kinematic reversals are also inherently disclosed and are considered to be within the scope of the present invention.

[0073] Furthermore, any of the components or elements of the various disclosed embodiments may be combined or incorporated into other embodiments where considered necessary, desirable, or preferred without departing from the scope of the invention as defined in the claims.

[0074] In the claims, reference signs should not be construed as limiting the scope of the claims. The terms "comprising" and "including" used in this specification or the appended claims should not be construed in an exclusive or exhaustive sense, but in an inclusive sense. Therefore, the term "comprising" used in this specification does not exclude the presence of other elements or steps in addition to those recited in a claim. Furthermore, the terms "a" and "an" should not be construed as limiting to "only one," but rather as meaning "at least one," without excluding a plurality. Features not specifically or explicitly described or claimed may also be included in the structure of the present invention within the scope of the present invention. Phrases such as "means for..." should be interpreted as "a component configured for..." or "an element configured for..." and should be interpreted to include equivalents of the disclosed structures. The use of terms such as "important," "preferred," and "particularly preferred" is not intended to limit the present invention. Additions, deletions, and modifications within the knowledge of those skilled in the art can generally be made without departing from the spirit and scope of the present invention, as defined by the claims. This invention may be practiced other than as specifically described herein and is limited only by the scope of the appended claims.

Claims

1. A method of operating an atomic force microscope (AFM) apparatus, the method comprising: scanning a surface of the sample along a first lateral current scan line with a probe having a tip; measuring the interaction between the tip and the sample; adjusting one or more imaging parameters during the scan based on information about the sample. Including, the information about the sample includes information about the sample obtained prior to the scan; the imaging parameters adjusted during the scan based on the information acquired prior to the scan include a force threshold; a relatively high force threshold is selected if information from the region of the current scan position indicates that the current scan point is expected to be within a relatively deep and narrow recess or at the bottom near a steep wall; and If the information from the region indicates a relatively wide recess or a wide flat area away from a relatively steep and high edge / wall, a relatively low force threshold is selected. The method.

2. The method of claim 1 , wherein the information about the sample further comprises information obtained from a scan following a previous scan line in a direction substantially parallel to the current scan line.

3. The method of claim 1 or 2, wherein the one or more imaging parameters that are adjusted further include a baseline offset.

4. The method of claim 1 or 2, wherein the one or more imaging parameters that are adjusted further include an approach profile.

5. The method of claim 1 or 2, wherein the one or more imaging parameters that are adjusted further include a recession profile.

6. The method of claim 1 or 2, wherein the information further comprises one or more pieces of information selected from the approximate geometry of the sample, a profile of a previous line, adhesion, and an indication from a lateral displacement sensor.

7. 3. The method of claim 1, further comprising adjusting one or more image parameter settings based on information about samples acquired for one or more recently scanned positions along the current scan line.

8. applying an acoustic signal to one or more of the probe, the tip, or the sample; analyzing an output signal based on an interaction between the acoustic signal and the sample; The method of claim 1 or 2, further comprising:

9. 3. The method of claim 1 or 2, comprising inducing vibration of the probe to change the effective stiffness of the cantilever (12).

10. obtaining a tip deformation signal indicative of deformation of the tip; and reducing the force threshold if the indicated deformation of the tip exceeds a predetermined limit, and / or processing the output signal obtained by the method to compensate for deviations caused by deformation of the tip.

3. The method of claim 1 or 2, comprising:

11. An atomic force microscope (AFM) apparatus (1), comprising at least one scanning head for scanning a sample (9), said scanning head comprising a probe (11), said probe comprising a cantilever (12) and a probe tip (13) disposed on said cantilever; The device comprises: a first actuator (20) cooperating with at least one of a scan head or a substrate holder (95) for moving the probe tip and the sample relative to one another in one or more directions parallel to the surface (91) of the sample to scan the surface with the probe tip; a cantilever deflection detector (30) arranged to measure the deflection (d) of the cantilever (12) relative to the scan head during said scanning and to provide an output signal indicative of said deflection; a controller (40) configured to receive and analyze the output signal from the cantilever deflection detector, measure deflection of the probe, and automatically adjust one or more imaging parameters during the scan in response to information about sample properties near the location of the sample currently being scanned; It also has the information about the sample characteristics includes information about the sample obtained prior to the scanning; the one or more imaging parameters adjusted during the scan based on the information acquired prior to the scan include a force threshold; a relatively high force threshold is selected if information from the region of the current scan position indicates that the current scan point is expected to be within a relatively deep and narrow recess or at the bottom near a steep wall; If the information from the region indicates a relatively wide recess or a wide flat area away from relatively steep and high edges / walls, a relatively low force threshold is selected. The atomic force microscope device.

12. 12. The atomic force microscope apparatus of claim 11, wherein the information about the sample properties further comprises information obtained from a scan following a previous scan line in a direction substantially parallel to the current scan line.

13. the controller is configured to cause a first actuator (20) to move the probe tip (13) and the sample (9) relative to each other according to a subsequent scan line extending in a first direction (x); The AFM device further comprises a memory (42) for storing information about the sample acquired during scanning of a current scan line; the controller is configured to determine values ​​of each of the one or more imaging parameters at the scan positions along a subsequent scan line based at least on information about samples stored in the memory for an area or position of the current scan line corresponding to the scan position along the subsequent scan line.

13. An atomic force microscope apparatus according to claim 11 or 12.

14. an acoustic signal generator for providing an acoustic signal to one or more of the probe, the tip, or the sample; a signal analysis module that analyzes an output signal based on an interaction between the acoustic signal and the sample; 13. The atomic force microscope apparatus according to claim 11, further comprising:

15. 13. An atomic force microscope apparatus according to claim 11, further comprising a signal source that induces vibration in the probe to increase the effective stiffness of the cantilever.

16. a tip deformation sensor (15) for providing a tip deformation signal (Stdf) indicative of deformation of the tip (13); the AFM device is configured to lower the force threshold when the indicated tip deformation exceeds a predetermined limit, and / or process an output signal obtained by the device to compensate for deviations caused by tip deformation.

13. An atomic force microscope apparatus according to claim 11 or 12.

Images