JP7622863B2 - Scanning probe microscope and program - Google Patents

Description

The present disclosure relates to a scanning probe microscope and a program.

JP 2000-275159 A (Patent Document 1) discloses a scanning probe microscope (SPM) that has a probe at the tip of a cantilever and brings the probe close to a sample to obtain information about the sample surface. This scanning probe microscope generates image data based on the obtained information and displays an observation image of the sample surface based on the image data.

JP 2000-275159 A

The image data includes values indicating the height at each position on the sample surface. This height corresponds to the surface height at each position on the substrate on which the sample is placed, and at positions where the sample is present, it corresponds to the height including the sample. If the sample is a powder sample, the particles placed on the substrate surface can be extracted based on the height values included in the image data.

However, if the surface of the substrate has a depression due to a scratch or other cause, determining the height at each position on the sample surface using the height of this depression as a reference may result in protrusions or other convex parts on the substrate being mistakenly extracted as particles. As a result, there is a concern that it may be difficult to accurately extract particles present on the substrate surface.

The present disclosure has been made to solve these problems, and its purpose is to provide a scanning probe microscope and program that can accurately extract particles within an observation area from image data obtained by the scanning probe microscope.

A scanning probe microscope according to one aspect of the present disclosure includes an observation device that acquires image data of an observation field including a sample placed on a substrate, and a data processing unit that corrects the image data acquired by the observation device. The image data includes a plurality of measurement data indicating heights at each position on a plane extending horizontally on the surface of the substrate. The data processing unit creates a histogram of height distribution for the plurality of measurement data. The data processing unit sets the height that is the most frequent value in the histogram as a reference point in the height direction of the observation field, and corrects the height of each of the plurality of measurement data based on the set reference point.

According to the present disclosure, particles within the observation area can be accurately extracted from image data obtained by a scanning probe microscope.

1 is a diagram illustrating a schematic configuration of a scanning probe microscope according to an embodiment. FIG. 2 is a diagram illustrating an example of a hardware configuration of an information processing device. 4 is a flowchart for explaining the procedure of image data acquisition processing executed by a scanning probe microscope. FIG. 10 is a diagram illustrating an example of a setting screen for setting processing conditions for image data. FIG. 13 is a diagram illustrating an example of a setting screen for setting processing conditions for particle analysis. FIG. 1 shows image data of a powder sample placed on a substrate. FIG. 13 is a diagram showing a histogram illustrating the distribution of heights of powder samples placed on a substrate. 6B is an image showing data extracted from the image data of FIG. 6A. 11A and 11B are diagrams for explaining a zero point adjustment process for image data. 11 is a histogram showing the distribution of heights in image data whose Z values have been corrected by zero point adjustment processing. 6B is an image showing data extracted from the image data of FIG. 6A. 10 is a flowchart illustrating a procedure for processing and extracting image data. 13 is a flowchart illustrating a modified example of the processing procedure of the step of processing and extracting image data.

Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings are designated by the same reference numerals and their description will not be repeated.

[Configuration of Scanning Probe Microscope]
1 is a diagram showing a schematic configuration of a scanning probe microscope (SPM) according to an embodiment. A scanning probe microscope 100 according to this embodiment is typically an atomic force microscope (AFM: Automatic Force Microscope) that observes the shape of the surface of a sample S by utilizing an atomic force (attractive or repulsive force) acting between a probe (needle) 3 and the surface of a sample S. The present disclosure can also be similarly applied to other scanning probe microscopes, such as a scanning tunneling microscope (STM: Scanning Tunneling Microscope).

With reference to FIG. 1, the sample S is fixed to the surface of a hard, flat substrate 15. In this embodiment, the sample S is a powder sample composed of fine particles. The sample S may be any sample that contains powder, and may be, for example, a liquid sample containing powder. The substrate 15 is formed of glass, mica, a silicon wafer, or the like. The scanning probe microscope 100 according to this embodiment can be used for particle analysis of powder samples, etc.

The scanning probe microscope 100 comprises, as its main components, an observation device 10, an information processing device 20, a display device 30, and an input device 40. The observation device 10 comprises, as its main components, an optical system 1, a cantilever 2, a scanner 12, a sample holder 14, an XY-direction drive unit 16, a Z-direction drive unit 18, a feedback signal generator 22, and a scanning signal generator 24.

The scanner 12 has a cylindrical shape and is a moving device for changing the relative positional relationship between the sample S and the probe 3. The substrate 15 on which the sample S is placed is held by a sample holder 14 provided on the scanner 12. The scanner 12 has an XY scanner 12xy that moves the sample S in two mutually orthogonal X and Y axis directions in a plane parallel to the upper surface of the sample holder 14, and a Z scanner 12z that slightly moves the sample S in a Z axis direction orthogonal to the X and Y axes. The XY scanner 12xy has a piezoelectric element that is deformed by a voltage applied from the XY direction drive unit 16. The Z scanner 12z has a piezoelectric element that is deformed by a voltage applied from the Z direction drive unit 18. Note that the XY scanner 12xy and the Z scanner 12z are not limited to piezoelectric elements.

The cantilever 2 is formed in the shape of a leaf spring, one end of which is supported by a holder 4. The other end of the cantilever 2 is a free end, which is arranged above the sample S in the Z-axis direction. The cantilever 2 has a front surface which faces the sample S, and a back surface opposite the front surface. A probe 3 is arranged on the front surface of the tip of the free end of the cantilever 2 so as to face the sample S. A reflective surface that reflects light is provided on the back surface of the tip. The tip of the cantilever 2 is displaced in the Z-axis direction due to the atomic force acting between the probe 3 and the sample S on the other side of the probe 3.

An optical system 1 is provided above the cantilever 2 in the Z-axis direction to detect the amount of deflection of the cantilever 2 (i.e., the amount of displacement of the tip). When observing the sample S, the optical system 1 irradiates the back surface (reflecting surface) of the cantilever 2 with laser light and detects the laser light reflected by the reflecting surface. Specifically, the optical system 1 has a laser light source 6, a beam splitter 5, a reflecting mirror 7, and a photodetector 8.

The laser light source 6 has a laser oscillator that emits laser light. The photodetector 8 has a photodiode that detects the incident laser light. The laser light LA emitted from the laser light source 6 is reflected by the beam splitter 5 and irradiated onto the back surface (reflection surface) of the cantilever 2. The laser light reflected by the back surface of the cantilever 2 is further reflected by the reflector 7 and enters the photodetector 8.

The photodetector 8 has a light receiving surface divided into multiple (usually two) parts in the Z-axis direction (displacement direction) of the cantilever 2. Alternatively, the photodetector 8 has a light receiving surface divided into four parts in the Z-axis and Y-axis directions. When the tip of the cantilever 2 is displaced in the Z-axis direction, the ratio of the amount of light irradiated to the multiple light receiving surfaces changes, and the amount of deflection (displacement) of the cantilever 2 can be detected based on the multiple amounts of light received.

The feedback signal generating unit 22 calculates the amount of deflection of the cantilever 2 by processing the detection signal provided by the photodetector 8. The feedback signal generating unit 22 controls the Z-direction position of the sample S so that the atomic force between the probe 3 and the sample S is always constant. Specifically, the feedback signal generating unit 22 calculates the deviation Sd between the calculated amount of deflection of the cantilever 2 and a target value, and calculates a control amount for driving the Z scanner 12z so that the deviation Sd becomes zero. The feedback signal generating unit 22 calculates a voltage value Vz for displacing the Z scanner 12z corresponding to this control amount. The feedback signal generating unit 22 outputs a signal indicating the voltage value Vz to the Z direction driving unit 18. The Z direction driving unit 18 applies the voltage value Vz to the Z scanner 12z.

The scanning signal generating unit 24 calculates a voltage value Vx in the X-axis direction and a voltage value Vy in the Y-axis direction so that the sample S moves in the X-axis and Y-axis directions relative to the probe 3 according to preset scanning conditions. The scanning signal generating unit 24 outputs a signal indicating the calculated voltage values Vx and Vy to the XY direction driving unit 16. The XY direction driving unit 16 applies the voltage values Vx and Vy to the XY scanner 12xy. The scanning conditions include information on the scanning range (i.e., the observation field of view) in the XY plane and the scanning speed.

The information processing device 20 mainly controls the operation of the observation device 10 and has a data processing unit 26 and a memory unit 28.

A signal indicating the amount of feedback in the Z-axis direction (applied voltage Vz and deviation Sd to the Z scanner 12z) is sent from the Z-axis direction driver 18 to the data processor 26 and stored in the memory 28. The data processor 26 calculates the amount of displacement of the sample S in the Z-axis direction from the voltage Vz based on correlation information indicating the relationship between the voltage Vz and the corresponding amount of displacement of the sample S in the Z-axis direction, which is previously stored in the memory 28. The calculated amount of displacement reflects a value indicating the position of the sample S in the Z-axis direction (hereinafter also referred to as the "Z value"). The data processor 26 creates three-dimensional image data representing the shape of the surface of the sample S by calculating the amount of displacement of the sample S in the Z-axis direction at each position in the X-axis and Y-axis directions in the scanning range.

This image data includes values (Z values) that indicate the position in the Z-axis direction at each position on the XY plane. The Z value corresponds to the surface height at each position on the substrate 15, and at the position where the sample S is present, it corresponds to the height including the sample S. The data processing unit 26 displays the created image data on the display device 30 and stores it in the memory unit 28.

[Hardware configuration of information processing device]
2 is a diagram showing an example of the hardware configuration of the information processing device 20. Referring to FIG. 2, the information processing device 20 has, as main components, a central processing unit (CPU) 160, a read only memory (ROM) 162, a random access memory (RAM) 164, a hard disk drive (HDD) 166, a communication interface (I/F) 168, a display I/F 170, and an input I/F 172. The components are connected to each other by a data bus. At least a part of the hardware configuration of the information processing device 20 may be located inside the observation device 10. Alternatively, the information processing device 20 may be configured as a separate entity from the scanning probe microscope 100, and configured to communicate bidirectionally with the scanning probe microscope 100.

The communication I/F 168 is an interface for communicating with the observation device 10. The display I/F 170 is an interface for communicating with the display device 30. The input I/F 172 is an interface for communicating with the input device 40.

ROM 162 stores the programs executed by CPU 160. RAM 164 can temporarily store data generated by the execution of the programs in CPU 160 and data input via communication I/F 168. RAM 164 can function as a temporary data memory used as a working area. HDD 166 is a non-volatile storage device. A semiconductor storage device such as a flash memory may be used instead of HDD 166.

The program stored in ROM 162 may be stored in a storage medium and distributed as a program product. Alternatively, the program may be provided by an information provider as a so-called product program that can be downloaded via the Internet or the like. The information processing device 20 reads the program provided on a storage medium or via the Internet or the like. The information processing device 20 stores the read program in a specified storage area (e.g., ROM 162). By executing the program, the CPU 160 can execute the image data acquisition process described below.

The display device 30 can display a setting screen for setting the conditions for acquiring image data. In addition, while acquiring image data, the display device 30 can display image data created by the information processing device 20 and data obtained by processing this image data.

The input device 40 accepts inputs including instructions from a user (e.g., an analyst) to the information processing device 20. The input device 40 includes a keyboard, a mouse, and a touch panel that is integrated with the display screen of the display device 30, and accepts image acquisition conditions, etc.

[Operation of Scanning Probe Microscope]
Next, the operation of the scanning probe microscope 100 shown in FIG. 1 will be described.

In this embodiment, in order to evaluate the particle size of sample S (powder sample), a scanning probe microscope 100 is used to obtain image data, which is an observation image of the surface shape of sample S.

Figure 3 is a flow chart for explaining the steps of the image data acquisition process executed by the scanning probe microscope 100. As shown in Figure 3, the image data acquisition process includes a step of setting image data acquisition conditions (S01), a step of tuning the cantilever 2 (S02), a step of acquiring image data (S03), a step of processing and extracting the image data (S04), a step of saving the image data (S05), and a step of displaying the image data (S06). The process of each step is explained below.

(1) Step of setting image data acquisition conditions (S01 in FIG. 3)
In the step of setting the image data acquisition conditions (S01 in FIG. 3), the tuning conditions of the cantilever 2 (S10), the scanning conditions of the scanner 12 (S11), the processing conditions of the image data (S12), the processing conditions of the particle analysis (S13), and the display conditions of the image data and the data based thereon (S14) are set. Note that the conditions set in step S01 are not limited to these. The order in which these conditions are set is also not limited, and the user can set them in any order. In this embodiment, the display device 30 is configured to be able to display a setting screen for setting the image data acquisition conditions. The user can set various conditions on the setting screen by operating the input device 40.

(1-1) Cantilever Tuning Conditions (S10)
The tuning conditions (S10) of the cantilever 2 are conditions that are set when the operation mode of the scanning probe microscope 100 is the dynamic mode. The tuning conditions include items such as the type of the cantilever 2, the frequency range and amplitude for exciting the cantilever 2, etc. The user can set each item using the input device 40.

In dynamic mode, the cantilever 2 is brought close to the surface of the sample S and excited at a frequency near its resonance point. The amplitude of the vibration of the cantilever 2 changes due to the atomic force acting between the probe 3 and the surface of the sample S. The feedback signal generating unit 22 (see Figure 1) feedback controls the Z scanner 12z to slightly move the sample S in the Z-axis direction so that the amplitude of this vibration remains constant. Image data of the surface shape of the sample S can be created by processing the control amount for this feedback control in the data processing unit 26.

(1-2) Scanning conditions of the scanner (S11)
In setting the scanning conditions of the scanner 12 (S11), conditions related to the movement of the XY scanner 12xy in the X-axis and Y-axis directions are set. The user can set the scanning range (i.e., the observation field) in the XY plane and the scanning speed. The scanning speed is the speed of scanning one line. The scanning speed when scanning one line back and forth in one second is 1 [Hz]. The user can also set the conditions of the feedback control executed by the feedback signal generating unit 22 (proportional gain, integral gain, etc.) and the number of pixels of the image data.

(1-3) Image data processing conditions (S12 in FIG. 3)
In the step of setting the image data processing conditions (S12 in FIG. 3), conditions related to the processing of the acquired image data are set. FIG. 4 is a diagram showing a schematic example of a setting screen for setting the image data processing conditions. As shown in FIG. 4, the setting screen displays a tab for setting the type of signal to be subjected to image processing, and a tab for setting the signal direction. Note that the input means for accepting the setting of the processing conditions by the user is not limited to tabs, and any interface (such as a GUI (Graphical User Interface)) can be adopted.

The signals to be subjected to image processing include a signal indicating a value (Z value) indicating the position of the sample S in the Z-axis direction (hereinafter also referred to as the "height signal") and a signal indicating the deviation Sd. The direction of the signal to be subjected to image processing corresponds to the direction in which the probe 3 scans the surface of the sample S. There are two scanning directions: the forward direction, which is the trace direction, and the reverse direction, which is the retrace direction. Usually, the same area is scanned twice in the forward and reverse directions (i.e., reciprocating scans), and image data is generated independently for each direction. Note that reciprocating scans are performed because the image data may differ depending on the scanning direction due to the tip shape of the probe 3 or the characteristics of the cantilever 2 (such as the spring constant).

The settings screen also displays a tab for setting whether or not to perform image processing. In Figure 4, tilt correction processing and zero point adjustment processing are shown as examples of data processing. However, image processing other than these processes can also be included.

Tilt correction processing is a process for detecting and correcting the tilt of the sample surface. If the sample surface is tilted overall, the detection signal given from the optical system 1 (photodetector 8) to the feedback signal generating unit 22 will contain a tilt component. In this case, the height of the sample surface displayed as an image will contain a tilt component in addition to the unevenness component of the sample surface, making it difficult to distinguish the fine shape of the sample surface. Therefore, a tilt correction process is performed to correct the height before displaying the image.

The user can select the signal to be used for the tilt correction process on the setting screen. In the example of Figure 4, the options shown are the average value in the X direction, the average value in the Y direction, the median value in the X direction, and the median value in the Y direction. The option selected by the user is displayed in the processing content column on the setting screen.

The zero point adjustment process is a process of adjusting the reference point (hereinafter also referred to as the "zero point") in the height direction for the height (Z value) at each position on the XY plane contained in the image data. The details of the zero point adjustment process will be described later.

The user can set the execution of tilt correction processing and zero point adjustment processing by checking each tab displayed on the settings screen in Figure 4.

(1-4) Processing conditions for particle analysis (S13 in FIG. 3)
In the step of setting the processing conditions for particle analysis (S13 in FIG. 3), conditions related to the processing of the acquired image data are set. FIG. 5 is a diagram showing an example of a setting screen for setting the processing conditions for particle analysis. As shown in FIG. 5, the setting screen displays tabs for setting the conditions for data to be extracted from the image data. These tabs include tabs for setting the Z value range, XY threshold value, and target shape of the data to be extracted. Each of the Z value range and the XY threshold value can be specified by an absolute value or a relative value (%). The shape of the target can be specified as a particle or a hole. It is to be noted that conditions other than these conditions can be further included.

The user can set the range of Z values (start value ZH and/or end value ZL) of the data to be extracted from the image data that has been subjected to image processing in step S12. The start value ZH corresponds to the upper limit of the range of Z values of the data to be extracted, and the end value ZL corresponds to the lower limit of the range of Z values. This identifies the particle as being present at a position in the XY direction where the Z value is within the range below the upper limit value ZH and above the lower limit value ZL.

Here, in the observation image shown by the image data, the positions where particles are present have a different height than positions where no particles are present, and therefore the Z value will also be different. Therefore, by appropriately setting the range of Z values to be extracted, it is possible to identify the positions where particles are present. This makes it possible to extract particles present within the observation field of view and determine their number.

In this embodiment, the particle diameter is calculated as the difference between the height (Z value) at the position where the particle is present and the height at the position where the particle is not present (i.e., the average height of the surface of the substrate 15). The particle diameter may be calculated for each position within the particle, or may be calculated as the average value for all positions within the particle.

This configuration is based on the fact that in the scanning probe microscope 100, when the particle diameter is generally smaller than the diameter of the probe 3, the particle diameter cannot be accurately determined from the width of the planar image of the particle in the image data. Since height information can be acquired without being affected by the diameter of the probe 3, the particle diameter can be determined more accurately than when the width of the planar image of the particle is used. Thus, by calculating the particle diameter of each particle based on the height (Z value) at each position in the image data, particle size distribution data for the sample S can be created.

(1-5) Display Conditions (S14 in FIG. 3)
In the step of setting display conditions (S14 in FIG. 3), the user can set conditions related to the display of image data. In this step, the user can set a display method for the image data and the particle size distribution data generated by particle analysis.

(2) Step of tuning the cantilever (S02 in FIG. 3)
3, the information processing device 20 starts acquiring image data in response to a user input instructing the start of image data acquisition. The information processing device 20 first tunes the cantilever 2 in step S02. If the operation mode of the scanning probe microscope 100 is the dynamic mode, the cantilever 2 is excited according to the tuning conditions of the cantilever 2 set in step S10.

(3) Step of acquiring image data (S03 in FIG. 3)
In step S03, the information processing device 20 (scanning signal generating unit 24) drives the XY scanner 12xy according to the scanning conditions of the scanner 12 set in step S10. The data processing unit 26 acquires image data of the observation area based on a signal indicating the feedback amount in the Z-axis direction (the applied voltage Vz and the deviation Sd to the Z scanner 12z) transmitted from the feedback signal generating unit 22.

The image data acquired in step S03 is an image (height image) reproduced from data obtained by moving the sample S in the XY directions by the XY scanner 12xy and searching for the relative position in the height direction (Z direction) with respect to the probe 3 by the Z scanner 12z. The acquired image data is not limited to a height image, and may be an image (deviation image) obtained from the deviation signal Sd output from the feedback signal generating unit 22.

(4) Processing and extracting image data (S04 in FIG. 3)
In step S04, the information processing device 20 (data processing unit 26) processes the image data acquired in step S03 according to the image data processing conditions set in step S13. If the signal to be processed is a height signal, the height image is processed. If the signal to be processed is a deviation signal Sd, the deviation image is processed. In this embodiment, a case where image data of a height image is processed will be described. A similar procedure can be used when processing image data of a deviation image.

If the image data processing conditions (S13 in FIG. 3) are set to execute zero point adjustment processing of the image data, zero point adjustment processing is executed on the image data of the height image. The following describes the zero point adjustment processing of the image data in detail.

<Zero point adjustment process>
6 to 9 are diagrams for explaining an overview of the zero point adjustment process for image data. Fig. 6A is a diagram showing a sample S (powder sample) placed on a substrate 15. Particles having various sizes are placed on the surface of the substrate 15. In the image data, the height (Z value) is larger at positions where particles are present than at positions where particles are not present (the surface of the substrate 15). Moreover, the height (Z value) differs depending on the particle diameter.

Figure 6B shows a histogram showing the distribution of heights (Z values) for the image data in Figure 6A. The horizontal axis of the histogram is the Z value, and the vertical axis is frequency. The histogram can be created by dividing the multiple Z values contained in the image data into multiple classes (intervals) and determining the number of data points (frequency) contained in each class.

In this histogram, particles are identified as being present within the range of the start value ZH or less and the end value ZL or more set in the processing conditions for particle analysis (S13 in Figure 3). Data within the range of the start value ZH or less and the end value ZL or more is extracted from the image data.

Normally, the surface of substrate 15 is flat, so a height distribution (histogram) is formed with the Z value of the surface of substrate 15 as the lowest value. In contrast, consider a case where there is a scratch on the surface of substrate 15, as shown in Figure 6A. In this case, a recess is formed in the scratched area, so the Z value is smaller than in other parts of substrate 15. If the Z value of this recess is used as the reference point (zero point) to find the Z value at each position in the X and Y directions, the found Z value will be larger than when the surface of substrate 15 is used as the zero point.

Figure 7 is an image showing data extracted from the image data of Figure 6A using a start value ZH and an end value ZL. In the extracted image data, each position in the XY direction is binarized and expressed as either a position where a particle exists or a position where no particle exists. Based on this binarized data, the number of particles present within the observation field of view can be calculated.

6B, when particles present on substrate 15 are extracted using a start value ZH and an end value ZL, particles whose Z value exceeds the start value ZH may not be extracted and may be missed. Alternatively, when the Z value of a protrusion such as a bump on substrate 15 is greater than the end value ZL, the protrusion may be erroneously extracted as a particle. As a result, particles may not be extracted accurately, and there is a concern that the number of particles present in the observation field of view may be calculated erroneously.

Furthermore, if the surface height of substrate 15 is calculated based on the average Z value of the positions where no particles were detected, the calculated surface height of substrate 15 will be lower than the actual surface height of substrate 15. As a result, the difference between the height lower than the actual surface of substrate 15 and the height of the position where the particle is present will be calculated as the particle diameter, and there is a concern that the calculated particle diameter will be larger than the actual particle diameter.

Therefore, in the zero point adjustment process, as shown in Figure 8, the height (Z value) that is the most frequent value in the histogram showing the distribution of heights (Z values) is set as the reference point (zero point) in the height direction of the observation field of view. The most frequent value is the class value (Z value) with the highest frequency in the histogram. In the histogram shown in Figure 8, the most frequent value is Z1, so this Z1 is set as the zero point. As a result, the Z values at each position in the X and Y directions are corrected with Z1 as the zero point. Figure 9 shows a histogram showing the distribution of heights (Z values) for image data whose Z values have been corrected by the zero point adjustment process.

The reason why the mode of the histogram is set as the reference point (zero point) in the height direction in this way is based on the assumption that, among the multiple Z values that make up the image data, the frequency of the Z value indicating the surface of substrate 15 is the highest. This typically applies to the case where particles are sparsely present on the surface of substrate 15, as shown in Figure 6A. In the example of Figure 6A, the frequency of the Z value indicating the surface of substrate 15 is greater than the total frequency of the Z values indicating the positions where particles are present. Therefore, the mode in the histogram can be regarded as the height of the surface of substrate 15.

By setting the histogram's most frequent value Z1 as the reference point (zero point) in this way, Z values below reference point Z1 can be deleted from the image data. As a result, it becomes possible to remove the effects of depressions such as scratches on the surface of substrate 15 in particle analysis. Specifically, since the Z value at each position on the XY plane represents the height from the surface of substrate 15, it becomes possible to properly extract particles present on the surface of substrate 15. It also becomes possible to accurately calculate the particle diameter of each particle.

Figure 10 is an image showing data extracted from the image data of Figure 6A using the start value ZH and end value ZL. In the extracted image data, each position in the XY direction is expressed as a binary value depending on whether a particle is present or not. As shown in Figure 10, the Z value at each position in the XY plane is corrected using Z1 as the reference point (zero point), so that particles present on the surface of the substrate 15 can be appropriately extracted according to the start value ZH and end value ZL set in the processing conditions of the particle analysis (S13 in Figure 3). In addition, in the image shown in Figure 9, particles with a large particle diameter are extracted without omission, compared to the image shown in Figure 7. In addition, the protuberances on the substrate are removed from the image.

As mentioned above, the zero point adjustment process is based on the assumption that the frequency of the height of the surface of the substrate 15 is the highest in a histogram showing the distribution of heights in the image data. Therefore, if this assumption does not hold true, for example, if particles are densely present on the substrate 15, it is not appropriate to perform the zero point adjustment process.

Therefore, in this embodiment, the image data processing conditions (S12 in FIG. 3) are configured so that the user can select whether or not to perform zero point adjustment processing. The user can set whether or not to perform zero point adjustment processing depending on the state of the sample S on the setting screen in FIG. 4. This allows the zero point adjustment processing to be performed appropriately depending on the state of the sample S.

Figure 11 is a flowchart illustrating the processing steps for processing and extracting image data.

With reference to FIG. 11, when image data for the observation target area is acquired by the image data acquisition step (S03 in FIG. 3), the data processing unit 26 of the information processing device 20 determines in step S41 whether or not the execution of the tilt correction process is set in the image data processing conditions (S12 in FIG. 3). If the execution of the tilt correction process is set (YES in S41), the data processing unit 26 proceeds to step S42 and executes the tilt correction process of the image data. The tilt correction process can use a known method. As an example, when the average value in the X direction and the average value in the Y direction are selected as the signal to be used for the tilt correction process in the setting screen of FIG. 4, the average value in the X direction and the average value in the Y direction are calculated for the multiple Z values constituting the image data. Then, the calculated average value is used to obtain the tilt component of the sample surface, and each Z value is corrected using the obtained tilt component. On the other hand, if the execution of the tilt correction process is not set (NO in S41), the process of step S42 is skipped.

Next, in step S43, the data processing unit 26 creates a histogram showing the distribution of heights (Z values) for the image data. Then, in step S44, the data processing unit 26 determines whether or not the execution of a zero point adjustment process is set in the processing conditions for the image data.

If the execution of the zero point adjustment process is set (YES in S44), the data processing unit 26 proceeds to step S45 and sets the most frequent value in the histogram created in step S43 as the reference point (zero point) in the Z direction. Then, in step S46, the data processing unit 26 corrects the multiple Z values that make up the image data using the set reference point. On the other hand, if the execution of the zero point adjustment process is not set (NO in S44), the processes of steps S45 and S46 are skipped.

In step S47, the data processing unit 26 extracts data from the image data using the start value ZH and end value ZL set in the processing conditions for particle analysis (S13 in FIG. 3). Particles are identified as existing at positions in the XY directions that are less than the start value ZH and greater than or equal to the end value ZL, and the particles are extracted from the image data.

In step S48, the data processing unit 26 calculates the number of particles present in the observation field based on the extracted data. In step S49, the data processing unit 26 associates the calculated number of particles with the image data and stores them in the memory unit 28.

(5) Step of displaying image data (S06 in FIG. 3)
In step S06, information processing device 20 causes display device 30 to display the image data in accordance with the display conditions set in step S14.

As described above, according to this embodiment, a histogram of height distribution is created for image data obtained by the scanning probe microscope 100, and the height that is the most frequent value of the created histogram is set as the reference point (zero point) in the height direction, so that data with heights smaller than the zero point can be deleted from the image data. This makes it possible to remove the effects of depressions such as scratches on the surface of the substrate 15, making it possible to properly extract particles present on the surface of the substrate 15. In addition, the particle diameter of each particle can be accurately calculated. Therefore, particles within the observation target area can be accurately extracted from the image data obtained by the scanning probe microscope 100.

(Other configuration examples)
In the above-described embodiment, a configuration example has been described in which the user sets whether or not to perform zero point adjustment processing on image data, but a configuration in which the information processing device 20 sets whether or not to execute zero point adjustment processing may also be used.

As an example of such a configuration, the information processing device 20 can be configured to set whether or not to perform zero point adjustment processing based on a histogram showing the distribution of heights (Z values) created from image data. In this configuration, whether or not to perform zero point adjustment processing is set according to the cumulative relative frequency of classes in the histogram that are greater than the mode. In the histogram shown in FIG. 8, the cumulative relative frequency of classes greater than Z1, the mode, is calculated. The cumulative relative frequency is the sum of all relative frequencies up to that class. In the example of FIG. 8, the cumulative relative frequency can be calculated by summing up the relative frequencies from the class with the largest Z value to the class that is one greater than the class of the mode Z1.

In this configuration example, the calculated cumulative relative frequency is compared with a predetermined threshold, and if the cumulative relative frequency is less than the threshold, a zero point adjustment process is executed. The threshold can be set to any value less than 0.5.

As the number of particles present within the observation field of view increases, the histogram showing the distribution of heights shows a decrease in the frequency of heights at the surface of substrate 15 and an increase in the frequency of heights higher than the surface of substrate 15. Therefore, the cumulative relative frequency of classes higher than the mode also increases. In this configuration example, by configuring the zero point adjustment process not to be performed when the cumulative relative frequency is equal to or greater than a threshold value, it is possible to prevent the zero point adjustment process from being performed inappropriately.

Figure 12 is a flowchart for explaining a modified example of the processing procedure for processing and extracting image data. In the flowchart shown in Figure 12, step S44 in the flowchart of Figure 11 is replaced with S44A and S44B.

Referring to Figure 12, when image data for the observation target area is acquired by the image data acquisition step (S03 in Figure 3), the data processing unit 26 of the information processing device 20 executes the same steps S41 to S43 as in Figure 11 to create a histogram showing the distribution of heights (Z values) for the image data.

In step S44A, the data processing unit 26 extracts the most frequent value in the created histogram. The data processing unit 26 calculates the cumulative relative frequency for the height class greater than the most frequent value. Next, in step S44B, the data processing unit 26 compares the cumulative relative frequency with a threshold value. If the cumulative relative frequency is smaller than the threshold value, the data processing unit 26 proceeds to step S45 and executes a zero point adjustment process. That is, the data processing unit 26 sets the most frequent value in the histogram as the reference point (zero point) in the Z direction. Then, in step S46, the data processing unit 26 corrects the multiple Z values constituting the image data using the set reference point. On the other hand, if the cumulative relative frequency is equal to or greater than the threshold value (NO in S44B), the processes of steps S45 and S46 are skipped.

The data processing unit 26 executes the same processes as in steps S47 and S48 in Fig. 11 to extract data from the image data using the start value ZH and end value ZL set in the processing conditions for particle analysis (S13 in Fig. 3), and calculates the number of particles present in the observation field based on the extracted data. In step S49, the data processing unit 26 associates the calculated number of particles with the image data and stores them in the memory unit 28.

[Aspects]
It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

(Section 1) A scanning probe microscope according to one embodiment includes an observation device that acquires image data of an observation field including a sample placed on a substrate, and a data processing unit that corrects the image data acquired by the observation device. The image data includes a plurality of measurement data indicating heights at each position on a plane extending horizontally on the surface of the substrate. The data processing unit creates a histogram of height distribution for the plurality of measurement data. The data processing unit sets the height that is the most frequent value in the histogram as a reference point in the height direction of the observation field, and corrects the height of each of the plurality of measurement data based on the set reference point.

According to the scanning probe microscope described in paragraph 1, a histogram of height distribution is created for image data obtained by the observation device, and the height that is the most frequent value of the created histogram is set as the reference point in the height direction, so that data with heights below the reference point can be deleted from the image data. As a result, the effects of depressions such as scratches on the surface of the substrate can be eliminated, and particles within the observation target area can be accurately extracted from the image data.

(2) The scanning probe microscope described in 1 further includes an input means for receiving an instruction to execute correction of image data. When the data processing unit receives the instruction, it creates a histogram.

According to the scanning probe microscope described in paragraph 2, if the assumption that the frequency of the height of the substrate surface is the highest in the histogram does not hold (for example, if the substrate surface is densely populated with sample particles), the user can set the microscope not to perform zero point adjustment. This allows the zero point adjustment to be performed appropriately according to the state of the sample.

(Clause 3) In the scanning probe microscope described in paragraph 1, the data processing unit is configured to calculate the cumulative relative frequency of a class greater than the mode in the histogram. When the cumulative relative frequency is smaller than a preset threshold, the data processing unit sets the height at which the mode is obtained as the reference point.

According to the scanning probe microscope described in paragraph 3, when the assumption that the frequency of the height of the substrate surface is the highest in the histogram does not hold (for example, when sample particles are densely present on the substrate surface), it is possible to automatically determine this and not perform zero point adjustment processing. This allows the zero point adjustment processing to be performed appropriately.

(4) In the scanning probe microscope described in paragraphs 1 to 3, the observation device is configured to obtain image data by feedback-controlling the distance between the probe and the surface of the sample so that the amount of displacement of the cantilever on which the probe is mounted is a target value, and by scanning the observation field with the probe. The image data is obtained from at least one of the amount of displacement at each position in the observation field and the deviation between the amount of displacement and a target value.

According to the scanning probe microscope described in paragraph 4, image data can be created based on a signal (displacement and deviation of the sample) reflecting feedback control in the Z-axis direction in the observation device, and zero point adjustment processing can be performed using the signal.

(Clause 5) A program in one embodiment is a program for correcting image data using a computer having a data processing unit described in clauses 1 to 4.

According to the program described in paragraph 5, particles within the observation area can be accurately extracted from image data obtained by the observation device.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 Optical system, 2 Cantilever, 3 Probe, 4 Holder, 5 Beam splitter, 6 Laser light source, 7 Reflector, 8 Photodetector, 10 Observation device, 12 Scanner, 12xy XY scanner, 12z Z scanner, 14 Sample holder, 15 Substrate, 16 XY direction drive unit, 18 Z direction drive unit, 20 Information processing device, 22 Feedback signal generator, 24 Scanning signal generator 26 Data processing unit, 28 Memory unit, 30 Display device, 40 Input device, 100 Scanning probe microscope, 160 CPU, 162 ROM, 164 RAM, 166 HDD, 168 Communication I/F, 170 Display I/F, 172 Input I/F.

Claims (4)

an observation device that acquires image data of an observation field including a sample placed on a substrate;
a data processing unit that corrects the image data acquired by the observation device,
the image data includes a plurality of measurement data indicating heights at respective positions on a plane extending horizontally to a surface of the substrate;
The data processing unit includes:
creating a histogram of the distribution of the heights for the plurality of measurement data;
A height that is a most frequent value in the histogram is set as a reference point in the height direction of the observation field of view, and
correcting heights of the plurality of measurement data based on the set reference point ;
the data processing unit is configured to calculate a cumulative relative frequency of a class higher than the mode in the histogram;
The data processing unit sets the height at which the cumulative relative frequency is most frequent as the reference point when the cumulative relative frequency is smaller than a preset threshold value . further comprising an input unit for receiving an instruction to execute the correction of the image data;
The scanning probe microscope according to claim 1 , wherein the data processing unit creates the histogram when the execution instruction is received. the observation device is configured to feedback-control a distance between the probe and a surface of the sample so that a displacement amount of a cantilever provided with the probe reaches a target value, and to acquire the image data by scanning the observation field with the probe;
3. The scanning probe microscope according to claim 1, wherein the image data is obtained from at least one of the amount of displacement at each position in the observation field and a deviation between the amount of displacement and a target value. 4. A program for correcting the image data by using a computer having the data processing unit according to claim 1.

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