Apparatus and method for determining cantilever deflection in a scanning probe microscopy system

Abstract

The present invention is directed to an apparatus for determining cantilever deflection in a scanning probe microscopy system. The system includes a scanning head supporting a probe, the probe including a cantilever and a probe tip, the cantilever including a specular reflective surface. The apparatus includes a light source providing a light beam. The light beam is directed onto the specular reflective surface. An optical sensor receives the reflected beam from the specular reflective surface, forming a light spot on the sensor. The optical sensor provides a sensor signal from which position information of the light spot on the sensor can be obtained. The optical sensor includes an array of photodiode elements. Each photodiode element is configured to provide a photodiode signal included in the sensor signal, and includes a photosensitive surface having an active area in a plane transverse to the direction of the beam, the active area being smaller than the cross-sectional area of ​​the reflected beam. Thus, the active area is smaller than the size of the light spot.

Description

[Technical Field]

[0001] The present invention relates to an apparatus for determining cantilever deflection in a scanning probe microscopy system, the scanning probe microscopy system including a scan head supporting a probe, the probe including a cantilever and a probe tip, at least one surface of the cantilever or the probe tip including a specular reflective surface, an apparatus including a light source providing a light beam, the apparatus configured to direct the light beam at the specular reflective surface to produce a reflected beam reflected from the specular reflective surface, an optical sensor configured to receive the reflected beam at the optical sensor and form a light spot on the optical sensor, the optical sensor configured to provide a sensor signal from which position information of the position of the light spot on the optical sensor can be obtained.

[0002] The invention further relates to a scanning probe microscopy system, a method for determining cantilever deflection, and a computer program product. [Background technology]

[0003] Scanning probe microscopy (SPM) systems, such as atomic force microscopes (AFM), typically apply a light beam to determine cantilever deflection. The method is largely as described above. In optical beam detector (OBD) devices, a laser beam is typically reflected by a specular surface at the probe tip or the backside of the cantilever. This can be achieved by appropriately positioning and orienting a light source so that the beam is directed toward the specular surface of the cantilever, or by including an optical system such as a target, mirror, or optical element that modifies the direction of the optical beam. The reflected beam strikes an optical sensor, allowing the precise location of the light spot formed by the impact of the reflected beam on the sensor's surface to be determined. Optical sensors, called position-sensitive detectors (PSDs), are typically formed by quadrant cells. A quadrant cell contains four adjacent cells, the edges of which together form a cross. The system is adjusted so that the reflected beam spot overlaps the crosshairs, so that the amount of light captured by each cell together allows for precise identification of where the center of the spot is located. The cells provide sensor signals indicative of the amount of light received, and the ratio between the cell signals allows for identification of the center of the spot (assuming the shape of the spot is known, e.g., a circular spot). Very small deflections of the cantilever are important in this method, as they provide leverage over the distance between the probe tip and the quadrant cell.

[0004] The exact location of the reflected beam's light spot and thus the "zero point," or origin of measurement, on the sensor depends on the cantilever's curvature. This curvature can vary slightly between individual cantilevers. In SPM systems, probe tips are prone to wear due to continuous or intermittent contact between the probe tip and the surface during scanning. Therefore, probes, including cantilevers on which the probe tip is formed, must be replaced frequently. As a result of frequent replacement, individual variations, and other factors, the zero point must be repeatedly adjusted to ensure it overlaps with the cross formed by the quadrant cell. Furthermore, the signal-to-noise ratio (SNR) of a quadrant cell (or simply "quad cell") is maximized when the zero point is optimally centered on the optical sensor's cross. However, during scanning, the zero point location can shift over time for various reasons. This results in the need to adjust the quadrant cell position from time to time, even during probe changes, to prevent the SNR from deteriorating over time.

[0005] For the reasons mentioned above, the position of the quad cell must be adjusted very precisely and frequently to tune the system. As mentioned above, several solutions exist for mechanically adjusting the position of the PSD or quad cell to ensure sufficient SNR. In most SPM systems, manual adjustment screws typically allow the quad cell to be moved laterally. The quad cell in these SPM systems is then adjusted to ensure the light spot is centered on the quad cell crosshair. In some advanced SPM systems, integrated electromechanical actuators allow tuning to be performed automatically. The disadvantages are clear: manual adjustment slows the measurement process and is labor-intensive and therefore cumbersome. These disadvantages have been partially overcome by automatic adjustment. However, the downside of automatic adjustment is that it increases the system's complexity, making it more expensive to manufacture, and even if the adjustment is performed faster than manually, it still slows the overall process. For this reason, better options are needed, especially for industrial applications, which typically require high yields. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide an apparatus and method for determining cantilever deflection that overcomes the above disadvantages and provides accurate measurements and is preferably unaffected by cantilever replacement. [Means for solving the problem]

[0007] To this end, there is now provided an apparatus as previously mentioned, wherein the optical sensor comprises an array of photodiode elements, each photodiode element configured to provide a photodiode signal included in the sensor signal, each photodiode element comprising a photosensitive surface having an active area in a plane transverse to the direction of the beam, the active area being smaller than the cross-sectional area of ​​the reflected beam such that the active area is smaller than the size of the light spot, a first subset of adjacent photodiodes of the array of photodiodes comprising photodiode elements sensitive in a first wavelength range, a second subset of adjacent photodiodes of the array of photodiodes comprising photodiode elements sensitive in a second wavelength range, and the photodiode elements forming the first subset being different from the photodiode elements forming the second subset.

[0008] In the device according to the present invention, an array of photodiode elements, each smaller than the light spot, allows the position of the light spot to be directly captured without any adjustment or tuning. In the device according to the present invention, due to the size of the photodiode elements being smaller than the effective beam diameter, the light spot of the beam on the surface of the light sensor always overlaps with more than one photodiode element. Therefore, again assuming a known beam cross-sectional shape, the center position of the light spot can be accurately determined from the photodiode signals due to the known shape of the light spot. For example, this may be achieved by comparing the amounts of light received or their ratios.

[0009] In particular, the present invention makes it possible to provide an optical sensor in an OBD device that includes different regions sensitive to different wavelengths. This allows the use of different light sources with different wavelengths, or the wavelength of the light source to be changed, without the need to recalibrate the OBD's optical sensor. In many cases, the wavelengths of the two beams used must be sufficiently different to prevent interference. This is important, at least in those applications and embodiments where more than one light beam is applied simultaneously.

[0010] In the device according to the invention, if the position of the zero point of the reflected beam on the light sensor changes, for example due to an exchange or movement of the cantilever, the light spot will always overlap at least two photodiodes. Therefore, since the photodiode elements have an active area in a plane transverse to the beam direction that is smaller than the cross-sectional area of ​​the reflected beam (and therefore also smaller than the light spot), the position of the light spot can always be accurately determined by the light spot always hitting more than one photodiode.

[0011] Preferably, according to the embodiment, the photodiode elements are arranged side by side to form the sensor surface of the light sensor. In preferred embodiments, the light sensitive surfaces of the photodiode elements are arranged in a plane to form the surface of the light sensor. The photodiode elements in these embodiments are arranged side by side, adjacent to each other.

[0012] Most preferably, in this method, the array of photodiode elements includes at least two parallel rows or columns of photodiode elements, each row or column preferably including at least three photodiode elements. Thus, in some embodiments, the array of photodiode elements includes an arrangement of N*M photodiode elements, with the photodiode elements arranged in N rows and M columns, where at least N is greater than 2 or M is greater than 2. More preferably, in these embodiments, at least one of N or M is at least 2, and the other of N or M is at least 3. Having more than two photodiode elements in at least one direction (column or row), with these photodiodes having an active area smaller than the cross-section of the reflected beam, allows for easy and rapid detection of movement of the light spot in this direction. Due to the addition of photodiode elements in (at least) one direction, movement of the light spot in these embodiments does not cause the light spot to move off scale. Rather, movement of the light spot such that the light spot overlaps with another photodiode element allows the position of the light spot to remain detectable. Thus, if the number of photodiodes is sufficiently large, any movement of the light spot remains detectable. As a result, the probe can be constantly replaced as long as the new position of the light spot is immediately known. This overcomes the need for frequent retuning of the OBD device. Furthermore, if the photodiode elements form an N × M matrix, where both N and M are greater than 3, it is possible to detect not only the movement of the light spot due to differences in the angle of cantilever deflection, but also the movement of the light spot due to cantilever twist. This can therefore be provided in an OBD device and advantageously applied, for example, in an SPM system that applies cantilever twist to measure high-aspect-ratio features on a substrate surface. High-aspect-ratio features are structural features with high walls or deep grooves that cannot be easily measured and mapped using standard SPM systems.

[0013] The device may use either analog or digital photodiode signals to determine the position of the light spot. For example, the analog signal of each photodiode may be preprocessed using analog electronics to obtain a position-determining signal. Such analog electronics may include, for example, a variable gain amplifier followed by analog normalization, followed by normalization in the digital domain. In other embodiments, the photodiode signals may be digitized, and the digital signals may be further processed to generate the position of the light source. In some embodiments, the device includes a digitizer for digitizing one or more photodiode signals of the photodiode elements. For example, each photodiode signal may be digitized individually, or the signals of multiple photodiodes (e.g., all photodiodes in the same column or row) may be digitized together.

[0014] In some embodiments, the device further includes or is configured to cooperate with a controller, the controller configured to receive sensor signals including photodiode signals, and the controller configured to process the sensor signals to identify the position of the light spot on the light sensor. This can be achieved in various ways. A rough identification can already be obtained by simply comparing the photodiode signals, followed by a position estimation based on this comparison. However, in other or further embodiments, to identify the position of the light spot on the light sensor, the controller is configured to perform a centroid calculation based on the photodiode signals. The centroid calculation can, of course, be more precise in identifying the center position of the light spot and can be performed in multiple ways using the photodiode signals as input. In some of these embodiments, the array of photodiode elements includes an N*M photodiode element array, where the photodiode elements are arranged in N vertically aligned rows and M horizontally aligned columns, and the controller is configured to apply the following algorithm to perform the centroid calculation in the vertical direction among the N rows:

number

[0015] The algorithm calculates the centroid of the light spot in the vertical direction (up and down or column direction). For example, if only one direction of bending is considered (i.e., ignoring lateral bending or twisting), such as the bending of a normal cantilever, it may be sufficient to analyze the movement of the light spot in only one direction, aligned with the cantilever. The algorithm may be applied to the signal values ​​of the photodiode signals, which in the algorithm are denoted S, which indicates the signal value of the photodiode signal of the ith photodiode in the column. i (Note that i is the row counter, so the ith photodiode in a column is the photodiode element found in the ith row within each column.) This signal value indicates the amount of light received by each photodiode element. Therefore, the signal value S iis a digitized version of the photodiode signal of the photodiode, which may be, for example, a current signal, or, if converted, for example, by a resistor, a voltage signal corresponding to the amount of light received by the photodiode element. Typically, the current received from the photodiode element is linearly dependent on the amount of light received, and therefore the voltage signal obtained by such analog conversion is also linearly dependent on the amount of light received. The photodiode signal thus obtained or converted is used as the signal value S i The signal value S of the photodiode in the ith row of the column may be digitized using any kind of analog-to-digital converter (ADC) (e.g., an on-chip ADC such as an ultra-fast on-chip ADC, a flash ADC, a half-flash ADC, a successive approximation ADC, a sigma-delta ADC, etc.). i In the vertical direction (i.e., columns), instead of using all signal values ​​S ij It is also possible to apply the algorithm to the sum of (where j ranges from 1 to M, j∈N) or its equivalent (eg, the average or maximum signal value).

[0016] If deflection in two directions, e.g., lateral deflection or twist, needs to be analyzed in addition to normal cantilever deflection, the additional direction may be analyzed by applying a similar algorithm in the horizontal direction (i.e., side-to-side or row direction). In these embodiments, the array of photodiode elements may include an array of N*M photodiode elements, where the photodiode elements are arranged in M ​​vertically aligned rows and M horizontally aligned columns, and the controller is configured to apply the following algorithm to perform the centroid calculation in the horizontal direction among the M rows:

number

[0017] The algorithm calculates the center of gravity of the light spot in the horizontal direction (up and down or column direction). The algorithm may be applied to the signal value of the photodiode signal, which is denoted in the algorithm as S , which indicates the signal value of the photodiode signal of the j-th photodiode in the row. j (Note that j is the column counter, so the jth photodiode in a row is the photodiode element found in the jth column within each row.) This signal value indicates the amount of light received by each photodiode element. Therefore, the signal value S j is a digitized version of the photodiode signal of the photodiode element, which may be, for example, a current signal, or, if converted, for example, by a resistor, a voltage signal corresponding to the amount of light received by the photodiode element. Typically, the current received by the photodiode element is linearly dependent on the amount of light received, and therefore the voltage signal obtained by such analog conversion is also linearly dependent on the amount of light received. The photodiode signal thus obtained or converted is used as the signal value S jThe signal value S of the photodiode in the j-th row and column may be digitized using any kind of analog-to-digital converter (ADC) (e.g., an on-chip ADC such as an ultra-high speed on-chip ADC, a flash ADC, a half-flash ADC, a successive approximation ADC, a sigma-delta ADC, etc.) to obtain the signal value S of the photodiode in the j-th row and column. j In the horizontal direction (i.e., row), instead of using all signal values ​​S in the j-th column, ij It is also possible to apply the algorithm to the sum of (where i ranges from 1 to N, i∈N, as described above) or its equivalent (e.g., the average signal value or the maximum signal value).

[0018] Those skilled in the art will appreciate that the array of photodiode elements may be of any desired size, for example, with respect to the number of photodiode elements in the array.

[0019] In some embodiments, the controller is configured to perform a time-dependent analysis of the photodiode signals, and the time-dependence of the photodiode signals of at least two of the photodiode elements is compared to identify intensity variations of the light source, for example, the photodiode signals of a plurality or all of the photodiode elements are analyzed in a time-dependent manner and compared to each other to identify intensity variations of the light source (e.g., laser).

[0020] In some embodiments, the device is further configured to filter the photodiode signals to include only photodiode signals associated with photodiodes that at least partially overlap with the light spot. Removing photodiode signals that are too weak (e.g., have an absolute value below a threshold) prevents the accuracy of the location determination from being compromised by noise from photodiodes not illuminated by the reflected beam. Filtering may be accomplished in various ways. For example, in some embodiments, the device includes at least one of an analog or digital multiplexer, one or more high-pass filters, or a digital filter to perform the filtering. A multiplexer may be used to analyze a group of channels (i.e., where a channel is formed by a row sum of photodiode signals, a column sum of photodiode signals, or the photodiode signals of individual photodiode elements). A high-pass filter or digital filter may be applied to each photodiode signal, for example, to pass only signals that exceed a threshold. In some embodiments, to perform the filtering, the controller is adapted to at least one of: compare the photodiode signals with a threshold value; set each photodiode signal having a signal value below the threshold value to 0; or select photodiode signals having a signal value above the threshold value. The filtering may be performed by the controller (e.g., by setting weak signals to, e.g., 0).

[0021] In some embodiments of the present invention, the light source includes one or more light sources to provide a first light beam at a first wavelength and a second light beam at a second wavelength, and the device is configured to direct the first light beam and the second light beam toward a specular reflective surface to produce a first reflected beam and a second reflected beam, directing the first reflected beam toward a first subset of adjacent photodiodes in the array and directing the second reflected beam toward a second subset of adjacent photodiodes in the array. As will be appreciated, the first and second light beams are typically produced by different light sources, often monochromatic (e.g., lasers). However, in some embodiments, the same polychromatic light source may provide both the first and second optical beams. For example, a splitter and subsequent filters may provide separate beams from the same source providing a broadband light spectrum. There are several applications in which this may be advantageously applied.

[0022] For example, in some embodiments, mirrored reflective surfaces are located both at the mid-region of the cantilever near the base of the cantilever and at the end-region of the cantilever below the probe tip, and the apparatus is configured to direct a first light beam at the end-region of the cantilever and a second light beam at the mid-region of the cantilever to provide a first reflected beam and a second reflected beam. In these embodiments, the first light beam provides a probe tip sensor signal indicative of the deflection of the probe tip. An additional second light beam is directed at the mid-region of the cantilever to obtain information about a particular harmonic mode. Locations on the cantilever may be selected and configured to be most sensitive to particular modes. For example, the fundamental mode (mode 1) is most strongly sensed at the probe tip, while the first harmonic mode (mode 2), second harmonic mode (mode 3), and third harmonic mode (mode 4) are strongest at other locations along the length of the cantilever. Thus, using this embodiment of the present invention, highly effective simultaneous measurements of multiple vibrational modes of a scanning probe can be performed, which has many applications.

[0023] In other or further embodiments, the probe is supported by a probe tip, a specular reflective surface is located on the probe tip, a further specular reflective surface is located on the probe tip, and the apparatus is configured to direct a first optical beam at the probe tip and a second optical beam at the probe tip to provide a first reflected beam and a second reflected beam. These embodiments may be used to monitor tip dynamics and, for example, to filter these from probe tip dynamics. For example, tip dynamics may be subtracted from probe tip dynamics to account for any disturbing dynamics signals in the apparatus, thus improving sensing accuracy.

[0024] In yet further embodiments, the apparatus is configured to direct the first and second light beams onto the same region of the mirror-reflective surface of the probe tip or cantilever, and the optical sensor is configured to provide a sensor signal from at least one of the first or second subsets of adjacent photodiodes, preferably from at most one of the first or second subsets of photodiode elements at a time. These embodiments offer distinct advantages. In particular, these embodiments may apply one of several light beams at a time, each of which is formed from light energy of a specific wavelength corresponding to a wavelength to which a coating on the probe is sensitive. For example, depending on the functional requirements of the probe, different probes may have different coatings. In these embodiments, different probes having such different coatings can be applied, while the same apparatus can be used when exchanging probes without having to recalibrate the light source. For example, if various cantilevers are used with different coatings having different reflection coefficients, lasers corresponding to each type of cantilever coating may be used to maximize reflection intensity and, therefore, sensitivity. The multiple pre-aligned lasers and sensors with multiple subsets of photodiodes make the operation of the scanning probe microscope faster, as there is no need to retune the system for different types of cantilevers.

[0025] In yet further embodiments, the apparatus includes a plurality of probes, each probe including a cantilever and a probe tip, such that each probe includes a specular reflective surface, and at least one of the cantilever and the probe tip includes the specular reflective surface. The apparatus of these embodiments is configured to provide a first reflected beam and a second reflected beam by directing a first light beam onto a probe tip or cantilever of a first probe of the plurality of probes and directing a second light beam onto a probe tip or cantilever of a second probe of the plurality of probes. The probe tip of the scanning probe microscopy system may have multiple cantilevers on the same tip. In this case, multiple lasers may be focused on different cantilevers and reflected onto corresponding subsets of photodiodes. This sensing method enables various scanning techniques (i.e., FFTP mode, AM mode) to be performed without any type of mechanical readjustment. Furthermore, because the cantilevers do not change their relative position between measurements, it is important that the offset between the multiple cantilevers is known, and this offset can then be easily adjusted.

[0026] As explained above, the photodiode element has an active area in a plane transverse to the beam direction, which is smaller than the cross-sectional area of ​​the reflected beam (and therefore smaller than the light spot). In some embodiments, for one or more photodiodes, the ratio between the active area of ​​the photosensitive surface in a plane transverse to the beam direction and the cross-sectional area of ​​the reflected beam is between 0.3 and 1.0, preferably between 0.4 and 0.75, more preferably between 0.4 and 0.6, and even more preferably between 0.4 and 0.45. A desirable size of the photodiode element provides sufficient resolution while also providing a sufficiently strong signal when the photodiode element is illuminated. Making the photodiode element too small can cause the photodiode signal to be too small, thereby degrading the SNR. Making the photodiode element larger produces a stronger signal but reduces the resolution for determining the location. On the other hand, using multiple small photodiode elements provides more information about the reflected beam and the formed light spot. For example, a small photodiode allows analysis of the shape of the beam or the shape of the light spot, which analysis may be used to correct for optical distortions, such as aberrations caused by optical elements.

[0027] According to a second aspect, the present invention provides a scanning probe microscopy system comprising at least one scanning head and a substrate carrier for supporting a substrate, the scanning head including a probe comprising a cantilever and a probe tip for scanning a surface of the substrate for performing measurements on the substrate, the scanning head further comprising apparatus as described above for determining cantilever deflection of the cantilever.

[0028] According to a third aspect, the present invention provides a method for determining cantilever deflection in a scanning probe microscopy system, the scanning probe microscopy system including a scan head supporting a probe, the probe including a cantilever and a probe tip, at least one surface of the cantilever or probe tip including a specular reflective surface, the method comprising: providing a light beam using a light source and directing the light beam at the specular reflective surface to produce a reflected beam that is reflected from the specular reflective surface; receiving the reflected beam with a light sensor to form a light spot on the light sensor; and providing a sensor signal from which position information of the position of the light spot on the light sensor can be obtained, the sensor signal being derived from an array of photodiode elements including a plurality of photodiodes. the sensor signal is provided by photodiode signals of the photodiode elements, the cross section of the reflected beam being larger than the effective area of ​​the photosensitive surface of each photodiode in a plane transverse to the beam direction of the reflected beam such that the effective area is smaller than the size of the light spot; the sensor signal is provided by at least one of a first subset of adjacent photodiodes of the array of photodiodes, the first subset comprising photodiode elements sensitive in a first wavelength range, and a second subset of adjacent photodiodes of the array of photodiodes, the second subset comprising photodiode elements sensitive in a second wavelength range, the photodiode elements forming the first subset being different from the photodiode elements forming the second subset.

[0029] wherein in some embodiments the array of photodiode elements comprises an array of N*M photodiode elements, the photodiode elements being arranged in N vertical rows and M horizontal columns, and the sensor signals including the photodiode signals are processed using a controller to identify a position of the light spot on the light sensor. In some of these embodiments, to identify the position of the light spot, a centroid calculation is performed by the controller, and at least one of the controllers applies the following algorithm to perform the centroid calculation in the vertical direction among the N rows:

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[0030] In some embodiments, the method may further include performing a time-dependent analysis of the photodiode signals, wherein the time-dependence of the photodiode signals of at least two photodiode elements is compared to ascertain intensity variations of the light source. In some embodiments, the method may further include filtering the photodiode signals to include only photodiode signals for photodiodes that at least partially overlap with the light spot. In some embodiments, such filtering may be performed by at least one of comparing the photodiode signals to a threshold, setting each photodiode signal having a signal value below the threshold to zero, or selecting photodiode signals having a signal value above the threshold.

[0031] According to a fourth aspect, there is provided a computer program product suitable for loading into a memory of an analysis system of a scanning probe microscopy system, the computer program product comprising instructions for enabling a controller of the analysis system to carry out the method described above according to the third aspect. [Brief explanation of the drawings]

[0032] The present invention will be further explained by the description of several specific embodiments with reference to the accompanying drawings. The detailed description provides possible embodiments of the invention, but should not be considered as describing the only embodiments within the scope. The scope of the invention is defined in the claims, and the description should be considered as an example, not a limitation, of the invention.

[0033] [Figure 1] 1 shows a schematic diagram of a scanning probe microscopy system to which the device of the present invention is applied; [Figure 2A] 1A and 1B are schematic front and side views of a conventional position sensitive detector; [Figure 2B] 1A and 1B are schematic front and side views of a conventional position sensitive detector; [Figure 3] 1 illustrates a schematic diagram of an apparatus according to an embodiment of the present invention; [Figure 4]2 shows a schematic representation of an optical sensor for use in a device according to the invention; [Figure 5] 2 shows a schematic representation of an optical sensor for use in a device according to the invention; [Figure 6A] 2 shows a schematic representation of a digital signal processing scheme used in a device according to the invention; [Figure 6B] Continuing with Figure 6A, Fig. 6 shows a schematic diagram of the digital signal processing scheme used in the device according to the invention. [Figure 7] 1 illustrates a schematic diagram of an apparatus according to an embodiment of the present invention; [Figure 8] 4 shows a graph of the various vibration modes of the cantilever that can be detected using the apparatus shown in FIG. 3. [Figure 9] 1 illustrates a schematic diagram of an apparatus according to an embodiment of the present invention; [Figure 10] 1 illustrates a schematic diagram of an apparatus according to an embodiment of the present invention; [Figure 11] 1 illustrates a schematic diagram of an apparatus according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0034] FIG. 1 shows a schematic diagram of a scanning probe microscopy system 1. The scanning probe microscopy system 1 includes a sample stage 3 on which a substrate sample 4 may be placed. As shown in FIG. 1, a first actuator system 6 provides for precise movement of the sample stage 3 in the X and Y directions. As shown, a piezoelectric actuator system 8 provides for precise movement of the sample stage 3 in the vertical direction Z. The actuator system 6 and the piezoelectric actuator 8 are controlled by controller electronics 10.

[0035] In use, the probe 17, which includes a cantilever 18 and a probe tip 19, is scanned relative to the surface of the substrate 4 while the probe tip 19 is in continuous or intermittent contact with the surface of the substrate 4. Scanning in the X and Y directions is performed by the SPM system using the controller 10 and actuator system 6. The probe tip 19 is brought into contact with the sample surface 4 by operating the piezoelectric actuator system 8, which moves the substrate 4 in the Z direction to reduce the distance between the probe tip 19 and the surface. While the substrate 4 and probe tip 19 are moved relative to each other in the X and Y directions, the probe tip 19 may optionally be oscillated to enable said intermittent contact with the surface.

[0036] Typically, the height of the substrate surface at the position where the probe tip 19 touches the substrate 4 is measured very accurately by the SPM system 1. By performing such precise height measurements at each position where the probe tip 19 touches the substrate 4, a map of the surface topography of the substrate 4 can be provided, with the surface structure visible on the map. To determine this precise height, the cantilever deflection of the cantilever 18 needs to be determined with high precision, allowing for very precise and accurate determination of the Z position of the apex of the probe tip 19 when it touches the surface of the substrate 4. To measure this cantilever deflection, an optical beam deflection (OBD) device is applied. For this purpose, a specular reflective surface 20, such as a mirror, may be arranged behind the probe tip 19. This surface 20 is illuminated with a light beam, typically a laser, from a light source 22, and a light beam 25 is directed onto the specular reflective surface 20. A reflected beam 27 is emitted from the specular reflective surface 20 towards an optical sensor 30. The optical sensor 30 is capable of precisely determining the location of a light spot 28 formed by the reflected beam 27 on the face of the optical sensor 30. The detection electronics 15 receives the sensor signal from the optical sensor 30 and performs an analysis to determine the location of the light spot 28.

[0037] 2A and 2B respectively provide a front view of optical sensor 30 and a side view of an optical beam deflection device (OBD device) to which optical sensor 30 is applied. In FIG. 2A, it can be seen that optical sensor 30 consists of four optical cells 31, 32, 33, and 34. Optical cells 31-34 are positioned adjacent to one another with their edges adjacent to one another so as to form a cross 35 in the center of optical sensor 30.

[0038] In FIG. 2B, it can be seen that incident beam 25 is reflected toward optical sensor 30, providing reflected beam 27. The divergence of incident beam 25 and reflected beam 27 is exaggerated in this illustration. Typically, a laser beam 25 is used to form light spot 28, and therefore, beam divergence is very limited or even negligible. As can be seen in FIG. 1, reflected beam 27 forms light spot 28 on the surface of optical detector 30. Light spot 28 in FIG. 2B is located where reflected beam 27 strikes the surface of optical sensor 30. In FIG. 2B, optical cells 33 and 34 are shown in side view. FIG. 2B also shows that cantilever 18 is slightly deflected at deflection angle α. This may be due to probe tip 19 touching the surface of substrate 4 (not shown). However, if each probe experiences a slight deviation of ±1.5 degrees of offset deflection, angle α in FIG. 2B may be better at this offset deflection. Due to the deflection angle α, the reflected beam 27 is not directed towards the center of the optical sensor 30, but is mostly formed on cell 34. Cell 33 receives only a small portion of the light energy from the reflected beam 27.

[0039] Depending on how precisely the light spot 28 is formed on the optical cells 31, 32, 33, and 34, each of the cells 31-34 receives an amount of light coming from the reflected beam 27. By comparing the magnitude of the sensor signals from each of the cells 31-34, it is possible to determine to what extent the light spot 28 is centered on the cross 35. Here, the optical cell 33 receives only a small portion of the light energy, while the optical cell 34 receives a large portion of the light energy. In many conventional SPM systems 1, the position of the optical sensor 30 is adjusted after each probe exchange and occasionally during a scanning operation to adjust the system so that the light spot 28 is formed precisely at the center of the cross 35. Thereafter, to measure the local height of the substrate 4 during scanning, the piezoelectric actuator 8 is controlled for each deflection that results in a shift of the light spot 28 so that the light spot 28 is again precisely at the center of the cross 35 on the optical sensor 30. Using this feedback method, the local height can be measured by recording the Z-direction correction applied using the piezoelectric actuator 8. By recording how much the sample stage Z position has been adjusted to return the position of the light spot 28 to the center 35 of the optical sensor 30, the height of the substrate 4 at this particular position is known precisely. As mentioned earlier, a disadvantage of this type of optical sensor is that although the cantilever deflection can be determined precisely in this way, the optical sensor 30 must often be adjusted to enable measurements.

[0040] FIG. 3 illustrates a schematic diagram of an optical beam deflection device in accordance with an embodiment of the present invention. This device may be applied in system 1 of FIG. 1 or in other SPM designs that apply OBD to measure cantilever deflection. FIG. 3 shows probe 17, including cantilever 18 and probe tip 19. Similar to SPM 1 of FIG. 1, a specular reflective surface 20 is located behind probe tip 19. An incident beam 25 is applied to the backside of probe tip 19 and is reflected as reflected beam 27 back toward foldable mirror 26. Mirror 26 redirects reflected beam 27' toward optical sensor 30. This additional mirror 26 is applied in the illustrated embodiment in a design that allows for various placements of optical sensor 30 to accommodate any desired size of optical sensor 30. However, in other embodiments, mirror 26 may be omitted, and the optical sensor may be conveniently designed to fit in the same location as a conventional optical sensor 30.

[0041] The optical sensor 30 includes an array 41 of photodiode elements 40. Figures 4 and 5 show various configurations of such an array 41. In accordance with the present invention, the size of the photodiode elements 40 is such that each photodiode element 40 is smaller than the cross-sectional diameter of the light spot 28. The light spot 28 formed by the reflected beam 27 of the laser beam 25 has an intensity value of 1 / e of the axis value. 2The photodiode elements 40 may have a radius as small as 0.5-1.5 mm. This is merely a typical range and is not intended to limit the invention; light spots of various sizes may be applied. In this regard, the photodiode elements 40 are therefore relatively small. In an embodiment of the present invention, the photodiode elements 40 together form an array 41, such as an array of columns and rows as shown in FIGS. 4 and 5. While the number of photodiode elements may be selected as desired, the array 41 includes at least one column or one row having three or more photodiode elements 40. In particular, the photodiode element array 41 may comprise an array of N×M photodiode elements, where N is the number of rows and M is the number of columns, and at least one of N or M may comprise at least three photodiode elements 40, while the other of N or M may comprise at least two photodiode elements 40. Thus, the smallest array 41 of photodiode elements 40 according to an embodiment of the present invention comprises an array of 2×3 photodiode elements. However, optionally, the array may consist of an arrangement of 10 x 10 photodiode elements or 20 x 15 photodiode elements 40 or any other configuration desired. In very specific applications, the number of photodiode elements may be much larger, for example even consisting of 100 x 50 photodiode elements.

[0042] FIG. 4 shows a schematic diagram of a photodiode array 41 in a device according to the present invention. The photodiode array 41 includes eight photodiode elements 40 horizontally and two photodiode elements 40 vertically, thereby forming two rows of eight photodiode elements 40 or eight columns of two photodiode elements 40, depending on the sensor orientation. A light spot 28 is shown impinging on a number of photodiode elements 40. Light intensity signal profiles 42-1 and 42-2 are shown adjacent to the diagram. When the probe 17, including the cantilever 18 and the probe tip 19, is replaced with a new probe, the difference in the bending angle of the cantilever 18 of the new probe causes the light spot 28 to move to a new position 28', as indicated by arrow 29. As is clear from FIG. 4, the movement 29 of the light spot 28 does not result in the new light spot 28' being lost. Due to the fact that the photodiode elements 40 are smaller in size than the diameter of the light spots 28, 28', the light spots 28, 28' are always spread over multiple photodiode elements 40, which allows for accurate location of the light spots 28, 28' on the light sensor 30. Furthermore, according to the format of Figure 4 and its implementations where this would be advantageous, it is even possible to form multiple spots 28 on the array 41 of light sensors 30 and to simultaneously locate them.

[0043] FIG. 5 shows a schematic representation of an alternative photodiode array 41, consisting of photodiode elements 40. Again, the light spot 28 is shown impinging on multiple photodiode elements 40. Light intensity signal graphs 42-1 and 42-2 along axes 43-1 and 43-2 are shown adjacent to the figure. The size of the photodiode elements 40 relative to the size of the light spot 28 is smaller than in FIG. 4, approximately 0.4 times the radius of the light spot 28. Although not very visible, the light spot 28 is not perfectly round, but rather oval. The fact that the photodiode elements 40 are relatively small compared to the size of the light spot 28 allows for accurate identification of the shape of the light spot 28. In FIG. 5, an equal intensity line 45 is shown next to the array 41. From the line 45, it is clear that the shape of the light spot 28 is slightly oval rather than round. This may cause a deviation in the location determination, but the fact that the shape of the light spot is detectable makes it possible to correct for this deviation and accurately identify the center of the light spot. Beam graphs are shown next to the equal intensity field lines 45 .

[0044] FIG. 6 illustrates a digital implementation of signal processing for an OBD device according to an embodiment of the present invention. In FIG. 6, a digital signal processor 48 is connected to a photodiode array 41 consisting of photodiodes 40, with each row of photodiode signals being sent to an adder 50. In a first portion 51 of the digital implementation logic, signals s1 through s8 are further summed in an adder 52 to obtain a grand total. This grand total is used as the denominator in a divider 55. Each row sum obtained from the adder 50 is then multiplied by a factor corresponding to the normalized segment size times the row number, and an offset is subtracted as described above. This is done for each row in a multiplier unit 53. An adder 54 then calculates the grand total of the multiplied signal values ​​and provides it to a divider 55 for use as the numerator of the division. The output of the divider 55 provides an absolute point position 58 in millimeters. The first portion 51 may be used when the size of the light spot 28 is large compared to the size of the photodiode elements 40, such as in the case shown in FIG. 5. However, in cases where the size of the light spot is relatively small compared to the size of the photodiode elements 40, the digital signal processing logic may be implemented according to portion 60 shown in FIG. 6 . In portion 60, multiplexer 63 uses a subset of the channels s1 through s8 of the row signals and calculates the position of the light spot from these subsets of channels. In adder 64, the total sum of the subsets is calculated for use in divider 75. Furthermore, in 68, an offset can be set in the system to ensure that the position of the light spot is centered around zero. This offset is subtracted in subtractor 69 from a value 67 representing the normalized segment size times a factor depending on the row number. The results are then multiplied by each of the row signals in multiplier 70 and summed in 73 to provide the numerator of divider 75. Divider 75 provides the position of the light spot as part of the output signal 77 of the photosensor 30.

[0045] FIG. 7 schematically illustrates an apparatus according to a further embodiment of the present invention. In FIG. 7, a probe tip 17, including a probe having a cantilever 18 and a probe tip 7, is illuminated using a first optical beam 25-1 and a second optical beam 25-2. The first optical beam 25-1 is formed from an optical signal at a first wavelength, while the second optical beam 25-2 is formed from an optical signal at a second wavelength. These wavelengths may be selected freely, but it is preferable to select wavelengths sufficiently separated to prevent interference. In the embodiment of FIG. 7, the first optical beam 25-1 is directed toward the back side of the probe tip 19. A mirrored reflective surface on the back side of the probe tip 19 reflects the incident optical beam 25-1, thereby forming a reflected beam 27-1. A mirror 26-1 (or another directing optical element) redirects the reflected optical beam 27-1 toward a photodiode array 41, which includes a plurality of photodiode elements 40 as described above. The redirected beam is designated by reference numeral 27'-1. On the array 41, the redirected reflected beam 27'-1 forms a first light spot 28-1 in a first area of ​​the array. The first light spot 28-1 formed in the first area of ​​the array 41 makes it possible to obtain a sensor signal indicative of the deflection of the probe tip 19. The movement and direction of the probe tip 19 can thereby be measured.

[0046] The second light beam 25-2 is directed toward the back side of the cantilever 18. The back side of the cantilever 18 therefore also contains a specularly reflective portion. This specularly reflective portion may extend from the probe tip 19 along the entire or partial back side of the cantilever 18, or several specularly reflective regions may be formed on this side of the probe and extend across it. The second light beam 25-2 is reflected as a reflected beam 27-2, which is redirected to the array 41 using a mirror 26-2 (or another redirecting optical element). Here, the redirected reflected beam 27'-2 forms a second light spot 28-2. The motion of the cantilever 18 can be monitored by a signal coming from a photodiode element 40 in the area where the second light spot 28-2 is formed. Here, one or more harmonic modes of the probe can be measured depending on the specific location where the second light beam 25-2 strikes. As can be appreciated, instead of the one shown in Figure 7, more than two optical sensing beams 25 may be directed to strike different portions of the probe tip 19 and cantilever 18 in this manner. Each position will be sensitive to one or more harmonic modes with different behavior, and sensing several positions in this manner allows more than one mode to be monitored simultaneously with greater precision.

[0047] FIG. 8 shows a simulation of harmonic modes of a probe similar to that of FIG. 7. The probe is a semi-confined, vibrating lever with a free end and confined at one end by being fixed to the probe tip 17. In vibration, the free end is free to move, thereby mechanically establishing a second boundary requirement (the first being the confined first end). The fundamental mode is labeled "Mode 1" in the graph and designated by reference numeral 80. The fundamental mode is provided by approximately one-quarter of a standing wave. This is due to the boundary requirement above, where the free end of the cantilever 18, where the probe tip 19 is located, is free to move, thereby providing the maximum local amplitude. The first harmonic mode, "Mode 2" in the graph, is characterized by one antinode and one-quarter of the next half-wave, i.e., three-quarters of the total standing wave, thereby including the first antinode. Furthermore, the second harmonic mode, designated "Mode 3" in the graph, is provided by one full standing wave and one-quarter of the next full standing wave, and therefore by one-and-a-quarter (one-and-a-quarter) of the standing wave, which includes two antinodes and a free edge. And similarly, the third harmonic mode consists of three antinodes and a free edge, and thereby includes approximately one-and-three-quarters (one-and-three-quarters) of the standing wave.

[0048] From the graph in FIG. 8, it becomes clear that at any given position along the length of the cantilever 18, there is a varying mix of positional sensitivities for each of the first four illustrated modes. At the free end formed by the probe tip 18, all modes contribute to their full potential due to the boundary requirements of the free end. At any other point along the cantilever 18, one of the modes always dominates. The optimal position for investigating a particular preselected mode can be obtained, for example, from FIG. 8. At this point, the contributions of other modes are also identified. In this way, various light beams 25 can be used to monitor various excitation frequencies (modes) of the cantilever 19. The greater the amplitude of the mode at the point where the second light beam 25-2 strikes the cantilever 19, the more sensitive the sensor signal obtained from spot 28-2 will be to this particular mode. By measuring with two or more beams at a number corresponding to the position, the accuracy and amount of information about all these modes is improved and increased.

[0049] In the embodiment shown in FIG. 9, second beam 25-2 impinges on probe tip 17. A specular reflection on probe tip 17 reflects beam 25-2, providing reflected beam 27-2. This reflected beam 27-2 is redirected toward array 41 using mirror 26-2 (or another redirecting optical element). Redirected reflected beam 27'-2 forms spot 28-2 on the surface of the array, thereby illuminating photodiode elements 40 in that area of ​​the array. Sensor 40 illuminated by redirected reflected beam 27'-2 provides a sensor signal that allows the dynamic behavior of probe tip 17 to be monitored. As can be seen, the dynamic behavior of probe tip 17 provides a disturbance to the movement of probe tip 19. Thus, measuring the dynamic behavior of probe tip 17 allows it to be subtracted from the signal indicative of the movement of probe tip 19. The signal indicative of the movement of probe tip 19 is obtained using light spot 28-1 formed by first beam 25-1. For example, the movement of probe tip 17 may be subtracted from the probe tip 19 signal to improve the accuracy of the probe tip signal.

[0050] In the embodiment of FIG. 10 , first light beam 25-1 and second light beam 25-2 both strike the same point on the backside of probe tip 19. These light beams 25-1 and 25-2 are reflected together to provide reflected beams 27-1 and 27-2, respectively, which are redirected to form points 27'-1 and 27'-2, forming two points 28-1 and 28-2 in different areas on array 41. The wavelengths of the optical signals in beams 25-1 and 25-2 are different and are selected specifically in relation to the probes used in the scanning probe microscopy system. For example, scanning probe microscopy system 1 may subsequently be designed to use several different types of probes, each type of probe having a different function. Such probes may be made of different materials or may include specific coatings on surface 18 that are most sensitive to certain wavelengths and less sensitive to other wavelengths. In the apparatus shown in FIG. 10, light beams 25-1 and 25-2 are each sensitive to a different wavelength. The wavelengths are selected to provide strong reflection signals in reflected light beams 27-1 and 27-2, respectively, for each probe. Thus, the wavelength of first light beam 25-1 is selected to be a wavelength that is well reflected by probe tip 19 of a first type of probe. The wavelength of second light beam 25-2 is selected to be a wavelength that is well reflected by probe tip 19 of a second type of probe. When the first type of probe is replaced with a second type of probe, second light beam 25-2 provides a sufficiently well-reflected light signal to allow measurement of the movement of probe tip 19. Therefore, probe replacement does not require replacement or readjustment of the light source, making the replacement process more efficient.

[0051] In the embodiment shown in FIG. 11, the probe tip 17 includes multiple probes that allow simultaneous measurements to be performed. In the example shown, the probe tip includes four probes consisting of cantilevers 18-1, 18-2, 18-3, and 18-4. Cantilevers 18-1 through 18-4 include probe tips 19-1, 19-2, 19-3, and 19-4, respectively. In the example shown, multiple light beams 25-1, 25-2, 25-3, and 25-4 impinge on the backsides of the probe tips 19-1 through 19-4. Thus, each of the probe tips 19-1 through 19-4 is illuminated by one of the incident light beams 25-1 through 25-4. The different wavelengths of the beams 25-1 through 25-4 allow these beams to be located sufficiently close to one another without interfering with one another. In an apparatus according to the embodiment of FIG. 11, multiple lasers 25-1 to 25-4 can be focused on separate probe tips 19-1 to 19-4, and the reflected beams 27-1 to 27-4 are directed to corresponding subsets of photodiodes 40 in the array 41. This method of detection allows various scanning techniques (i.e., FFTP mode, AM mode) to be performed without any mechanical realignment. Furthermore, because the cantilevers do not change their relative position during the measurement, it is important that the offset between the multiple cantilevers 18-1 to 18-4 is known, and this offset can then be easily adjusted. The various scanning techniques may include, for example, a feed-forward trajectory planner (FFTP) mode. FFTP measures high-aspect ratio structures, such as trench spaces or holes with diameters less than 20-40 nm and depths of approximately 200 nm. This mode controls the probe motion over such a range, minimizes sidewall interactions, and ensures the probe reaches the bottom of such complex structures. Other scanning techniques available include, for example, dynamic force modes, which refer to a collection of AFM modes in which the cantilever oscillates at high frequencies or near resonance. A particular type of dynamic mode called amplitude modulation mode (AM-AFM) is the most common AFM imaging mode.In AM-AFM, the amplitude of vibration is the feedback parameter, while in other dynamic modes there are various parameters for the feedback loop, such as frequency (frequency modulation) or phase (phase modulation). The terms amplitude modulation mode, tapping mode, intermittent contact mode, and dynamic force mode can be used interchangeably.

[0052] The present invention has been described with respect to several specific embodiments. It will be understood that the embodiments shown and described herein are intended for illustrative purposes only and are not intended to limit the invention in any manner or manner. The context of the invention as described herein is limited only by the appended claims.

[0053] (Addendum) (Appendix 1) 1. An apparatus for determining cantilever deflection in a scanning probe microscopy system, comprising: the scanning probe microscopy system includes a scan head supporting a probe; the probe includes the cantilever and a probe tip; at least one surface of the cantilever or the probe tip comprises a specular reflective surface; the apparatus includes a light source providing a light beam; the apparatus is configured to direct the light beam onto the specular reflective surface to produce a reflected beam that is reflected from the specular reflective surface; the device includes an optical sensor; the device is configured to receive the reflected beam at the light sensor and form a light spot on the light sensor; the optical sensor is configured to provide a sensor signal from which position information of the position of the light spot on the optical sensor can be obtained; the optical sensor includes an array of photodiode elements; each photodiode element configured to provide a photodiode signal included in the sensor signal; each photodiode element includes a photosensitive surface having an effective area in a plane transverse to the direction of said beam, said effective area being smaller than a cross-sectional area of ​​said reflected beam such that said effective area is smaller than the size of said light spot; a first subset of adjacent photodiodes of the array of photodiodes includes photodiode elements sensitive to a first wavelength range; a second subset of adjacent photodiodes of the array of photodiodes includes photodiode elements sensitive to a second wavelength range; the photodiode elements forming the first subset are different from the photodiode elements forming the second subset; Device.

[0054] (Appendix 2) the array of photodiode elements comprises an arrangement of N*M photodiode elements; The photodiode elements are arranged in N rows and M columns, At least one of N is greater than 2 or M is greater than 2, 10. The apparatus described in Appendix 1.

[0055] (Appendix 3) the device further comprising or configured to cooperate with a controller; the controller is configured to receive the sensor signal including the photodiode signal; the controller is configured to process the sensor signal to identify a position of the light spot on the light sensor; To determine the location of the light spot on the light sensor, the controller is configured to perform a centroid calculation based on the photodiode signals. 10. The apparatus of claim 1 or 2.

[0056] (Appendix 4) the controller is configured to apply an algorithm to perform the centroid calculation in a vertical direction among N rows; The algorithm is:

number

[0057] (Appendix 5) the controller is configured to apply an algorithm to perform the centroid calculation in a horizontal direction among M rows; The algorithm is:

number

[0058] (Appendix 6) the controller is configured to perform a time-dependent analysis of the photodiode signal; the time dependence of the photodiode signals of at least two photodiode elements is compared to ascertain intensity variations of the light source; 6. The apparatus of any one of claims 1 to 5.

[0059] (Appendix 7) 7. The apparatus of any one of claims 1 to 6, wherein the apparatus is further configured to filter the photodiode signals to include only photodiode signals for photodiodes that at least partially overlap with the light spot.

[0060] (Appendix 8) Clause 7 and the apparatus of at least one of Clauses 3 to 6, wherein to perform the filtering, the controller is adapted to at least one of: compare the photodiode signals with a threshold value; set each photodiode signal having a signal value below the threshold to zero; or select photodiode signals having a signal value above a threshold.

[0061] (Appendix 9) the light source includes one or more light sources to provide a first light beam at a first wavelength and a second light beam at a second wavelength; the apparatus is configured to direct the first light beam and the second light beam onto the specular reflective surface to produce a first reflected beam and a second reflected beam, the first reflected beam onto the first subset of adjacent photodiodes of the array, and the second reflected beam onto the second subset of adjacent photodiodes of the array. 9. The apparatus of any one of claims 1 to 8.

[0062] (Appendix 10) the specular reflective surface is located on both the cantilever and the probe tip; the apparatus is configured to provide the first reflected beam and the second reflected beam by directing the first light beam to the probe tip and the second light beam to the cantilever. 10. The apparatus described in Appendix 9.

[0063] (Appendix 11) the probe is supported by a probe tip that attaches to the probe; the specular reflective surface is located at the probe tip, and a further specular reflective surface is located on the probe tip; the apparatus is configured to provide the first reflected beam and the second reflected beam by directing the first light beam at the probe tip and directing the second light beam at the probe tip. 10. The apparatus described in Appendix 9.

[0064] (Appendix 12) the apparatus is configured to direct the first light beam and the second light beam at the same area of ​​the specular reflective surface of the probe tip or the cantilever; the photosensor is configured to provide the sensor signal from at least one of the first or second subsets of adjacent photodiodes, preferably from at most one of the first or second subsets of photodiode elements at a time; 10. The apparatus described in Appendix 9.

[0065] (Appendix 13) the device includes a plurality of probes; each probe includes a cantilever and a probe tip, such that each probe includes a specular reflective surface, and at least one of the cantilever and the probe tip includes said specular reflective surface; the apparatus is configured to provide the first reflected beam and the second reflected beam by directing the first light beam to the probe tip or the cantilever of a first probe of the plurality of probes and directing the second light beam to the probe tip or the cantilever of a second probe of the plurality of probes. 10. The apparatus described in Appendix 9.

[0066] (Appendix 14) 14. The apparatus of any one of claims 1 to 13, wherein for one or more photodiodes, the ratio between the effective area of ​​the photosensitive surface in a plane transverse to the direction of the beam and the cross-sectional area of ​​the reflected beam is between 0.3 and 1.0, preferably between 0.4 and 0.75, more preferably between 0.4 and 0.6, and even more preferably between 0.4 and 0.45.

[0067] (Appendix 15) 1. A scanning probe microscopy system comprising: at least one scanning head; a substrate carrier for supporting the substrate; Including, the scanning head includes a probe including a cantilever and a probe tip for scanning a surface of the substrate to perform measurements of the substrate; the scanning head further comprising an apparatus according to any one of clauses 1 to 14 for determining cantilever deflection of the cantilever. Scanning probe microscopy system.

[0068] (Appendix 16) 1. A method for determining cantilever deflection in a scanning probe microscopy system, comprising: the scanning probe microscopy system includes a scan head supporting a probe; the probe includes a cantilever and a probe tip; at least one surface of the cantilever or the probe tip comprises a specular reflective surface; The method comprises: providing a light beam using a light source and directing the light beam at the specular reflective surface to produce a reflected beam that is reflected from the specular reflective surface; receiving the reflected beam with an optical sensor to form a light spot on the optical sensor, and providing a sensor signal from which position information of the position of the light spot on the optical sensor can be obtained; Including, the sensor signal is provided by photodiode signals of a plurality of photodiode elements from an array of photodiode elements; the cross section of the reflected beam is larger than the effective area of ​​the photosensitive surface of each photodiode in a plane transverse to the beam direction of the reflected beam, so that the effective area is smaller than the size of the light spot; The sensor signal is a first subset of adjacent photodiodes of the array of photodiodes, the first subset including photodiode elements sensitive to a first wavelength range; a second subset of adjacent photodiodes of the array of photodiodes, the second subset including photodiode elements sensitive to a second wavelength range; provided by at least one of the photodiode elements forming the first subset are different from the photodiode elements forming the second subset; method.

[0069] (Appendix 17) the array of photodiode elements comprises an array of N*M photodiode elements; The photodiode elements are arranged in N vertical rows and M horizontal columns, the sensor signals, including the photodiode signal, are processed using a controller to identify the position of the light spot on the light sensor; The method described in Appendix 16.

[0070] (Appendix 18) a centroid calculation is performed by the controller to identify the location of the light spot; At least one of the controllers applies an algorithm to perform the centroid calculation in a vertical direction among N rows; The algorithm is:

number

number

[0071] (Appendix 19) further comprising performing a time-dependent analysis of the photodiode signal; the time dependence of the photodiode signals of at least two photodiode elements is compared to ascertain intensity variations of the light source; 19. The method of any one of appendices 16 to 18.

[0072] (Appendix 20) 20. The method of any one of claims 16 to 19, further comprising filtering the photodiode signals to include only photodiode signals for photodiodes that at least partially overlap with the light spot.

[0073] (Appendix 21) 21. The method of claim 20, wherein the filtering is performed by at least one of comparing the photodiode signals to a threshold, setting each photodiode signal having a signal value below the threshold to 0, or selecting photodiode signals having a signal value above the threshold.

[0074] (Appendix 22) 1. A computer program product suitable for loading into a memory of an analysis system of a scanning probe microscopy system, comprising: comprising instructions that enable a controller of the analytical system to perform the method of any one of claims 16 to 21, Computer program products.

Claims

1. 1. An apparatus for determining cantilever deflection in a scanning probe microscopy system, comprising: the scanning probe microscopy system includes a scan head supporting a probe; the probe includes the cantilever and a probe tip; at least one surface of the cantilever or the probe tip comprises a specular reflective surface; the apparatus includes a light source providing a light beam; the apparatus is configured to direct the light beam onto the specular reflective surface to produce a reflected beam that is reflected from the specular reflective surface; the device includes an optical sensor; the device is configured to receive the reflected beam at the light sensor and form a light spot on the light sensor; the optical sensor is configured to provide a sensor signal from which position information of the position of the light spot on the optical sensor can be obtained; the optical sensor includes a single array of photodiode elements; each photodiode element configured to provide a photodiode signal included in the sensor signal; each photodiode element includes a photosensitive surface having an effective area in a plane transverse to the direction of said beam, said effective area being smaller than a cross-sectional area of ​​said reflected beam such that said effective area is smaller than the size of said light spot; a first subset of adjacent photodiode elements of the single array of photodiode elements includes photodiode elements sensitive to a first wavelength range; a second subset of adjacent photodiode elements of the single array of photodiode elements includes photodiode elements sensitive to a second wavelength range different from the first wavelength range; the single array of photodiode elements includes an area of ​​the photodiode elements constituting the first subset and an area of ​​the photodiode elements constituting the second subset that are different from each other, and the area of ​​the photodiode elements constituting the first subset and the area of ​​the photodiode elements constituting the second subset are adjacent to each other; Device.

2. the single array of photodiode elements comprises an arrangement of N*M photodiode elements; The photodiode elements are arranged in N rows and M columns, At least one of N is greater than 2 or M is greater than 2; 10. The apparatus of claim 1.

3. the device further comprising or configured to cooperate with a controller; the controller is configured to receive the sensor signal including the photodiode signal; the controller is configured to process the sensor signal to identify a position of the light spot on the light sensor; To determine the location of the light spot on the light sensor, the controller is configured to perform a centroid calculation based on the photodiode signals.

3. The device according to claim 1 or 2.

4. the controller is configured to apply an algorithm to perform the centroid calculation in a vertical direction among N rows; The algorithm is: [Equation 1] where i is a row counter indicating that the i-th row is being considered, P ＴＢ is the vertical coordinate of the point, W ＴＢ，ｓｅｇｍｅｎｔ is the normalized segment size, given by dividing the photodiode element size in the vertical direction by the row pitch distance of the row; P ＴＢ，ｏｆｆｓｅｔ is an offset that allows to set a zero offset coordinate in the vertical direction, S ｉ is a row sum indicating the sum of the signal values ​​of the photodiode signals in the i-th row, 4. Apparatus according to claims 2 and 3.

5. the controller is configured to apply an algorithm to perform the centroid calculation in a horizontal direction among M rows; The algorithm is: [Equation 2] where j is the column counter indicating that the jth row is being considered, P ＬＲ is the horizontal coordinate of the point, W ＬＲ，ｓｅｇｍｅｎｔ is the normalized segment size, given by dividing the size of the photodiode element in the horizontal direction by the column pitch distance of the column; P ＬＲ，ｏｆｆｓｅｔ is an offset that allows to set a zero offset coordinate in the horizontal direction, S ｊ is a column sum value indicating the sum of the signal values ​​of the photodiode signals in the jth column, 5. Apparatus according to claim 2 and 3, or claim 4.

6. the controller is configured to perform a time-dependent analysis of the photodiode signal; the time dependence of the photodiode signals of at least two photodiode elements is compared to ascertain intensity variations of the light source; 6. An apparatus according to any one of claims 1 to 5.

7. 7. The apparatus of claim 1, further configured to filter the photodiode signals to include only those photodiode signals relating to photodiode elements that at least partially overlap with the light spot.

8. 7. The apparatus according to claim 7 and at least one of claims 3 to 6, wherein to perform the filtering, the controller is adapted to at least one of: compare the photodiode signals with a threshold value, set each photodiode signal having a signal value below the threshold to 0, or select photodiode signals having a signal value above a threshold.

9. the light source includes one or more light sources to provide a first light beam at a first wavelength and a second light beam at a second wavelength; the apparatus is configured to direct the first light beam and the second light beam onto the specular reflective surface to produce a first reflected beam and a second reflected beam, the first reflected beam onto the first subset of adjacent photodiode elements of the single array, and the second reflected beam onto the second subset of adjacent photodiode elements of the single array.

9. An apparatus according to any one of claims 1 to 8.

10. the specular reflective surface is located on both the cantilever and the probe tip; the apparatus is configured to provide the first reflected beam and the second reflected beam by directing the first light beam to the probe tip and the second light beam to the cantilever.

10. The apparatus of claim 9.

11. the probe is supported by a probe tip that attaches to the probe; the specular reflective surface is located at the probe tip, and a further specular reflective surface is located on the probe tip; the apparatus is configured to provide the first reflected beam and the second reflected beam by directing the first light beam at the probe tip and directing the second light beam at the probe tip.

10. The apparatus of claim 9.

12. the apparatus is configured to direct the first light beam and the second light beam onto the same area of ​​the specular reflective surface of the probe tip or the cantilever; the optical sensor is configured to provide the sensor signal from at least one of the first or second subsets of adjacent photodiode elements, preferably from at most one of the first or second subsets of photodiode elements at a time; 10. The apparatus of claim 9.

13. the device includes a plurality of probes; each probe includes a cantilever and a probe tip, such that each probe includes a specular reflective surface, and at least one of the cantilever and the probe tip includes said specular reflective surface; the apparatus is configured to provide the first reflected beam and the second reflected beam by directing the first light beam to the probe tip or the cantilever of a first probe of the plurality of probes and directing the second light beam to the probe tip or the cantilever of a second probe of the plurality of probes.

10. The apparatus of claim 9.

14. 14. An apparatus according to any one of claims 1 to 13, wherein for one or more photodiode elements, the ratio between the effective area of ​​the photosensitive surface in a plane transverse to the direction of the beam and the cross-sectional area of ​​the reflected beam is between 0.3 and 1.0, preferably between 0.4 and 0.75, more preferably between 0.4 and 0.6, and even more preferably between 0.4 and 0.

45.

15. 1. A scanning probe microscopy system comprising: at least one scan head; a substrate carrier supporting the substrate; Including, the scanning head includes a probe including a cantilever and a probe tip for scanning a surface of the substrate to perform measurements of the substrate; The scanning head further comprises an apparatus according to any one of claims 1 to 14 for determining cantilever deflection of the cantilever. Scanning probe microscopy system.

16. 1. A method for determining cantilever deflection in a scanning probe microscopy system, comprising: the scanning probe microscopy system includes a scan head supporting a probe; the probe includes a cantilever and a probe tip; at least one surface of the cantilever or the probe tip comprises a specular reflective surface; The method comprises: providing a light beam using a light source and directing the light beam at the specular reflective surface to produce a reflected beam that is reflected from the specular reflective surface; receiving the reflected beam with an optical sensor to form a light spot on the optical sensor, and providing a sensor signal from which position information of the position of the light spot on the optical sensor can be obtained; Including, the sensor signal is provided by photodiode signals of a plurality of photodiode elements from a single array of photodiode elements; the cross section of the reflected beam is larger than the effective area of ​​the photosensitive surface of each photodiode element in a plane transverse to the beam direction of the reflected beam, so that the effective area is smaller than the size of the light spot; The sensor signal is a first subset of adjacent photodiode elements of the single array of photodiode elements, the first subset including photodiode elements sensitive to a first wavelength range; a second subset of adjacent photodiode elements of the single array of photodiode elements, the second subset including photodiode elements sensitive to a second wavelength range different from the first wavelength range; provided by at least one of the single array of photodiode elements includes an area of ​​the photodiode elements constituting the first subset and an area of ​​the photodiode elements constituting the second subset that are different from each other, and the area of ​​the photodiode elements constituting the first subset and the area of ​​the photodiode elements constituting the second subset are adjacent to each other; method.

17. the single array of photodiode elements comprises an array of N*M photodiode elements; The photodiode elements are arranged in N vertical rows and M horizontal columns, the sensor signals, including the photodiode signal, are processed using a controller to identify the position of the light spot on the light sensor; 17. The method of claim 16.

18. a centroid calculation is performed by the controller to identify the location of the light spot; At least one of the controllers applies an algorithm to perform the centroid calculation in a vertical direction among N rows; The algorithm is: [Equation 3] where i is a row counter indicating that the i-th row is being considered, P ＴＢ is the vertical coordinate of the point, W ＴＢ，ｓｅｇｍｅｎｔ is the normalized segment size, given by dividing the photodiode element size in the vertical direction by the row pitch distance of the row; P ＴＢ，ｏｆｆｓｅｔ is an offset that allows to set a zero offset coordinate in the vertical direction, S ｉ is a row sum indicating the sum of the signal values ​​of the photodiode signals in the i-th row, the controller applies an algorithm to perform the center of gravity calculation in the horizontal direction between M columns; The algorithm is: [Equation 4] where j is a column counter indicating that the jth row is being considered, P ＬＲ is the horizontal coordinate of the point, W ＬＲ，ｓｅｇｍｅｎｔ is the normalized segment size, given by dividing the size of the photodiode element in the horizontal direction by the column pitch distance of the column; P ＬＲ，ｏｆｆｓｅｔ is an offset to allow setting a zero offset coordinate in the horizontal direction, S ｊ is a column sum indicating the sum of the signal values ​​of the photodiode signals in the j-th column, 18. The method of claim 17.

19. further comprising performing a time-dependent analysis of the photodiode signal; the time dependence of the photodiode signals of at least two photodiode elements is compared to ascertain intensity variations of the light source; 19. The method of any one of claims 16 to 18.

20. 20. The method of any one of claims 16 to 19, further comprising filtering the photodiode signals to include only photodiode signals relating to photodiode elements that at least partially overlap with the light spot.

21. 21. The method of claim 20, wherein the filtering is performed by at least one of comparing the photodiode signals to a threshold, or setting each photodiode signal having a signal value below the threshold to 0, or selecting photodiode signals having a signal value above the threshold.

22. 1. A computer program product suitable for loading into a memory of an analysis system of a scanning probe microscopy system, comprising: comprising instructions that enable a controller of the analytical system to carry out the method of any one of claims 16 to 21, Computer program products.

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