Image correction method and scanning probe microscope

Abstract

This scanning probe microscope includes: a sample stage on which a sample is placed; a cantilever having a probe at the tip thereof; and a control device that controls the position of the sample stage or the position of the cantilever so that a physical quantity acting between the probe and the sample becomes a predetermined target value. This image correction method comprises: a step for acquiring a deviation signal (A) based on the difference between a target value and a physical quantity acting between a probe and a sample; a step for converting a value of the deviation signal into a displacement amount (C) of the distance between the probe and the sample; a step for creating a primary image (B) of the sample on the basis of the position of a cantilever or the position of a sample stage; and a step for creating a secondary image (D) obtained by correcting the primary image with the displacement amount.

Description

Image correction method and scanning probe microscope

[0001] The present invention relates to an image correction method and a scanning probe microscope.

[0002] A scanning probe microscope (SPM) uses a cantilever with a probe tip formed thereon. In an SPM, changes in the bending or vibration of the cantilever are detected by converting them into a detection signal such as a voltage at a detection unit.

[0003] When measuring a sample with an SPM, the probe scans the sample surface while feedback-controlling the distance between the probe and the sample so that the physical quantity acting between the probe and the sample reaches a predetermined target value. Specifically, a "deviation signal" indicating the difference between the physical quantity actually acting between the probe and the sample and the target value is acquired from the detection unit of the SPM. The SPM's control device then changes the height of the sample stage on which the sample is placed, etc., so that the deviation signal becomes zero.

[0004] In this way, if feedback control based on the deviation signal is performed appropriately, the shape of the sample can be calculated correctly from the position information of the sample stage and the like.

[0005] However, in actual measurements, depending on the parameter settings of the feedback control, the actual distance between the sample and the probe may deviate significantly from the target distance, making it impossible to accurately calculate the shape of the sample from the position information of the sample stage, etc.

[0006] In view of this situation, Japanese Patent No. 3360792 (Patent Document 1) discloses a configuration for predicting the unevenness of a sample by displaying an image in which the magnitude of the deviation signal value corresponds to color information.

[0007] Patent No. 3360792

[0008] As described above, conventionally, there has been a problem in that the shape of the sample cannot be accurately calculated depending on the parameter settings of the feedback control. Furthermore, even with the technique of Patent Document 1, although it is possible to predict the positions of the unevenness of the sample, it is not possible to obtain an image showing the actual shape of the sample.

[0009] An object of the present invention is to provide an image correction method for obtaining an image that shows the actual shape of a sample.

[0010] An image correction method according to one aspect of the present invention is an image correction method for a scanning probe microscope. The scanning probe microscope includes a sample stage on which a sample is placed, a cantilever with a probe at its tip, and a control device that controls the position of the sample stage or the cantilever so that a physical quantity acting between the probe and the sample becomes a predetermined target value. The image correction method includes the steps of acquiring a deviation signal based on the difference between the physical quantity acting between the probe and the sample and the target value, converting the value of the deviation signal into an amount of displacement in the distance between the probe and the sample, creating a primary image of the sample based on the position of the cantilever or the position of the sample stage, and creating a secondary image by correcting the primary image using the amount of displacement.

[0011] A scanning probe microscope according to one aspect of the present invention is a scanning probe microscope including a sample stage on which a sample is placed, a cantilever having a probe at its tip, and a control device that controls the position of the sample stage or the cantilever so that a physical quantity acting between the probe and the sample becomes a predetermined target value. The control device acquires a deviation signal based on the difference between the physical quantity acting between the probe and the sample and the target value, converts the value of the deviation signal into a displacement amount of the distance between the probe and the sample, creates a primary image of the sample based on the position of the cantilever or the sample stage, and creates a secondary image by correcting the primary image for the displacement amount.

[0012] According to the present invention, it is possible to provide an image correction method for creating an image showing the actual shape of a sample.

[0013] FIG. 1 is a schematic diagram showing the configuration of a scanning probe microscope according to an embodiment; FIG. 2 is a diagram showing the configuration of a feedback signal generating unit; FIG. 3 is a diagram for explaining ideal feedback control; FIG. 4 is a diagram for explaining a primary image when a feedback parameter is too large; FIG. 5 is a diagram for explaining a primary image when a feedback parameter is too small; FIG. 6 is a diagram for explaining image correction when a feedback parameter is too large; FIG. 7 is a diagram for explaining image correction when a feedback parameter is too small; A flowchart showing image correction processing according to an embodiment; A flowchart showing image correction processing according to a first modification; A flowchart showing image correction processing according to a second modification; A flowchart showing image correction processing according to a third modification.

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are denoted by the same reference numerals, and their description will not be repeated in principle.

[0015] [Device Configuration] FIG. 1 is a schematic diagram showing the configuration of a scanning probe microscope (SPM) 1 according to an embodiment. In this embodiment, the SPM 1 is an atomic force microscope (AFM), but this embodiment can also be applied to other types of scanning probe microscopes. Examples of other types of scanning probe microscopes include a magnetic force microscope (MFM), a Kelvin force microscope (KFM), a lateral force microscope (LFM), or a scanning tunneling microscope (STM). In this embodiment, the SPM is used in a contact mode in which the cantilever deflection is controlled to be constant. However, this embodiment can also be applied to a dynamic mode in which the cantilever vibration is controlled to be constant.

[0016] Referring to FIG. 1, the SPM 1 includes a control device 2 , a piezo scanner 111 , a sample stage 112 , a cantilever 113 , a displacement detection mechanism 120 , a feedback signal generating unit 131 , and a scanning signal generating unit 133 .

[0017] In this specification, a plane parallel to the sample stage 112 (more specifically, the upper surface 1121 of the sample stage 112) is sometimes referred to as the XY plane, and a direction perpendicular to the XY plane is sometimes referred to as the Z-axis direction. Furthermore, the positive direction of the Z axis is sometimes referred to as "upward" (the direction from the sample stage 112 toward the probe 114), and the negative direction of the Z axis is sometimes referred to as "downward" (the direction from the probe 114 toward the sample stage 112).

[0018] The sample 110 is placed on the sample stage 112. The sample stage 112 is placed on the upper surface of the piezo scanner 111.

[0019] The piezoelectric scanner 111 includes a Z scanner 111z that moves the sample stage 112 in the Z-axis direction based on a control voltage Vz (described later), and an XY scanner 111xy that moves the sample stage 112 in the X-axis direction based on control voltages Vx and Vy. By moving the piezoelectric scanner 111 in the X-axis direction, the sample stage 112 and the sample 110 can be moved in the X-axis direction, the Y-axis direction, and / or the Z-axis direction.

[0020] The cantilever 113 has a probe 114 at its tip end. The cantilever 113 is a cantilever beam, and one end of the cantilever 113 is supported by a support member 121.

[0021] The displacement detection mechanism 120 detects the displacement of the cantilever 113. More specifically, the displacement detection mechanism 120 detects the deflection of the cantilever 113 in the Z-axis direction. The displacement detection mechanism 120 includes a laser diode 115 and a photodetector 119. Laser light emitted from the laser diode 115 is reflected by the back surface of the cantilever 113, and the reflected light is received by the photodetector 119. When the cantilever 113 deflects, the position at which the laser light emitted from the laser diode 115 is reflected on the back surface of the cantilever 113 changes, and the position on the photodetector 119 at which the reflected light is received also changes. The photodetector 119 is composed of, for example, a photodetection electrode divided into four segments. The position of the photodetection electrode is adjusted so that the laser light spot is located at the center of the divided electrode when the deflection of the cantilever 113 is zero. When the cantilever 113 is bent, the spot of the laser light moves on the divided electrodes, causing a change in the voltage output from the divided electrodes.

[0022] FIG. 2 shows the configuration of the feedback signal generating unit 131. The feedback signal generating unit 131 includes a target value signal input unit 151, a comparator 152, and a proportional integral differential (PID) control unit 153. The non-inverting input terminal (+) of the comparator 152 receives a change in voltage output from the photodetector 119 as a signal indicating the amount of deflection of the cantilever 113. The inverting input terminal (−) of the comparator 152 receives a target value signal input from the target value signal input unit 151. The target value signal corresponds to a signal output from the photodetector 119 when a physical quantity (atomic force in the case of an AFM) acting between the probe 114 and the sample 110 reaches a predetermined target value. With this configuration, the comparator 152 outputs a deviation signal based on the difference between the amount of deflection of the cantilever 113 and the amount of deflection of the cantilever 113 when the physical quantity acting between the probe 114 and the sample 110 reaches a predetermined target value. In other words, the comparator 152 outputs a deviation signal based on the difference between the target value and the physical quantity acting between the probe 114 and the sample 110. More specifically, the deviation signal correlates with the difference between the target value and the physical quantity acting between the probe 114 and the sample 110.

[0023] The feedback signal generating unit 131 controls the position of the sample stage 112 so that the deviation signal becomes zero. In one embodiment, the PID control unit 153 outputs a signal obtained by combining the deviation signal, its integral value, and its differential value to the Z scanner 111z as a control voltage Vz of the Z scanner 111z based on the deviation signal. This controls the distance between the probe 114 and the sample 110 so that the physical quantity acting between the probe 114 and the sample 110 becomes a predetermined target value. Note that the "distance between the probe 114 and the sample 110 at which the physical quantity acting between the probe 114 and the sample 110 becomes a predetermined target value" is also referred to as the "target distance" in this specification. As described above, in the SPM 1, the distance between the probe 114 and the sample 110 is controlled so that it becomes a constant target distance.

[0024] The feedback signal generator 131 also transmits the deviation signal and the control voltage Vz to the control device 2 .

[0025] The scanning signal generating unit 133 calculates a control voltage Vx in the X-axis direction and a control voltage Yy in the Y-axis direction so that the sample 110 moves relative to the probe 114 in the XY plane according to a preset scanning pattern, and outputs the control voltages Vx and Vy to the XY scanner 111xy.

[0026] The control device 2 includes a processor 20, a memory 21, an input device 23, and a display device 22. The control device 2 is, for example, a computer and its peripheral devices.

[0027] The processor 20 loads a program stored in the memory 21 into a RAM or the like and executes it.

[0028] The memory 21 includes, for example, a read-only memory (ROM), a random access memory (RAM), and a non-volatile memory. The program stored in the ROM is a program that describes the processing procedures of the control device 2. The program includes a program that executes the image correction method according to the embodiment when executed by a computer. The non-volatile memory stores data sent from the feedback signal generating unit 131. Note that the memory 21 may include a hard disk drive instead of or in addition to the non-volatile memory.

[0029] The input device 23 is a device for inputting user instructions to the control device 2. For example, the input device 23 includes a keyboard and a pointing device such as a mouse.

[0030] The display device 22 includes a liquid crystal display or the like. The control device 2 creates a primary image of the sample 110 based on the position of the sample stage 112. The control device 2 calculates the height of the sample 110 based on the position of the sample stage 112 in the Z-axis direction. More specifically, the control device 2 calculates the height of the surface 1101 of the sample 110 from the upper surface 1121 of the sample stage 112. Even more specifically, the control device 2 calculates the Z coordinate of the surface 1101 of the sample 110 when the upper surface 1121 of the sample stage 112 is set to Z=0.

[0031] The position of the sample stage 112 in the Z-axis direction correlates with the control voltage Vz. The control device 2 calculates the height of the surface 1101 from the control voltage Vz based on correlation information indicating the relationship between the control voltage Vz and the height of the surface 1101. The correlation information is stored in advance in the memory 21.

[0032] The control device 2 calculates the height of the surface 1101 of the sample 110 at each (X, Y) coordinate on the surface 1101 of the sample 110, thereby creating a primary image, which is a three-dimensional image of the surface 1101 of the sample 110. The data of the primary image is stored in the memory 21. The data of the primary image includes (X, Y) coordinates indicating a position on the XY plane and the Z coordinate of the sample 110 at the (X, Y) coordinate. The primary image may be displayed on the display device 22. As described above, in this embodiment, the position of the sample stage 112 is precisely controlled three-dimensionally, and a primary image is created based on the position of the sample stage 112. Note that the position of the cantilever 113 may be precisely controlled three-dimensionally instead of the sample stage 112, and a primary image may be created based on the position of the cantilever 113. More specifically, the position of the cantilever 113 supported by the support member 121 may be precisely controlled, and a primary image may be created based on that position.

[0033] As will be described later, the control device 2 creates a secondary image showing the actual shape of the sample 110 by implementing an image correction method according to the embodiment.

[0034] [Acquisition of Primary Image] Next, a primary image acquired by the SPM according to the embodiment will be described.

[0035] (Ideal State) FIG. 3 is a diagram for explaining ideal feedback control. FIG. 3(A) shows the shape of the actual sample 110. FIG. 3(B) shows the shape of the sample 110 in an acquired primary image. In FIGS. 3(A) and 3(B), the horizontal axis is the X coordinate, and the vertical axis is the Z coordinate. Referring to FIG. 3(A), the surface 1101 of the sample 110 includes two convex portions that rise at X=X1 and X3 and fall at X=X2 and X4. FIG. 3(B) shows the Z coordinate acquired when the probe 114 is scanned in the X direction on the sample 110 shown in FIG. 3(A). FIG. 3(C) shows the deviation signal acquired when the probe 114 is scanned in the X direction on the sample 110 shown in FIG. 3(A). In FIG. 3(C), the horizontal axis is the X coordinate, and the vertical axis is the value of the deviation signal. If the scanning speed in the X direction is constant, the horizontal axes of FIGS. 3(A) to 3(C) may represent time T.

[0036] In an ideal situation, if the position of the sample 110 is controlled so that the deviation signal is always zero, the distance between the probe 114 and the sample 110 is always constant. Therefore, the height of the sample 110 at each (X, Y) point corresponds to the position of the sample stage 112 in the Z-axis direction. Therefore, the shape of the sample 110 in the primary image acquired by the SPM matches the actual shape of the sample 110.

[0037] More specifically, at X=X1, X3, which are the rising portions of the convex portion, the sample stage 112 moves down as the surface 1101 approaches the probe 114, so the distance between the probe 114 and the surface 1101 remains the target distance and the deviation signal remains 0. As a result, the Z coordinate of the surface 1101 in the primary image coincides with the Z coordinate of the surface 1101 of the actual sample 110.

[0038] Similarly, at X=X2 and X4, which are the falling portions of the convex portion, the Z coordinate of the surface 1101 in the primary image coincides with the Z coordinate of the surface 1101 of the actual sample 110.

[0039] However, in order to perform appropriate feedback control as shown in Figure 3, it is necessary to set the feedback parameter appropriately. When the feedback parameter is large, feedback control is performed so that the distance between probe 114 and surface 1101 quickly approaches the target distance. When the feedback parameter is small, feedback control is performed so that the distance between probe 114 and surface 1101 slowly approaches the target distance.

[0040] However, in actual SPM measurements, the feedback parameters are often too large or too small, and in this case, the shape of the sample 110 in the primary image deviates from the actual shape of the sample 110.

[0041] (Primary Image When Feedback Parameter is Too Large) Figure 4 is a diagram for explaining a primary image when the feedback parameter is too large. For example, those skilled in the art who use SPMs desire to increase the image acquisition speed, but in that case, the feedback parameter must also be increased from its original value. As a result, overshoot and / or undershoot, as described below, may occur depending on the rise and / or fall of the surface 1101 of the sample 110.

[0042] If the feedback parameter is too large, at the rising portions of the convex portion, X=X1, X3, the sample stage 112 will move down too far in an attempt to quickly return the distance between the probe 114 and the sample 110 to the target distance, resulting in an overshoot, as shown by the arrow OS in Figure 4(B), in which the detected Z coordinate is larger than the actual Z coordinate of the surface 1101. Corresponding to this overshoot, the atomic force between the probe 114 and the surface 1101 will also become smaller than the target value, and the absolute value of the deviation signal will also become larger.

[0043] In the SPM according to the embodiment, when the distance between the probe 114 and the surface 1101 becomes larger than the target distance and the atomic force between the probe 114 and the surface 1101 becomes smaller than the target value, the deviation signal is set to be larger than 0. Conversely, when the distance between the probe 114 and the surface 1101 becomes smaller than the target distance and the atomic force between the probe 114 and the surface 1101 becomes larger than the target value, the deviation signal is set to be smaller than 0.

[0044] On the other hand, at X=X2 and X4, which are the falling portions of the convex portion, the sample stage 112 rises too much in an attempt to quickly return the distance between the probe 114 and the sample 110 to the target distance, resulting in an undershoot, as shown by the arrow US in Figure 4(B), in which the detected Z coordinate is smaller than the actual Z coordinate of the surface 1101. Corresponding to this undershoot, the atomic force between the probe 114 and the surface 1101 also becomes larger than the target value, and the deviation signal also becomes smaller than 0.

[0045] As described above, if the feedback parameter is too large, overshooting and undershooting occur in the primary image in areas where there is a large change in height (change in the Z-axis direction) of the surface 1101, making it impossible to acquire the correct shape of the surface 1101. Note that in the example of Figure 4, in areas where there is a small change in height following an area where there is a large change in height of the surface 1101 (for example, the area where X1' < X < X2), an appropriate Z-axis value is acquired and the deviation signal returns to 0, but in an example where the feedback parameter is even larger, overshooting and undershooting are repeated even in those areas.

[0046] (Primary Image When Feedback Parameter is Too Small) Figure 5 is a diagram for explaining a primary image when the feedback parameter is too small. When the feedback parameter is too small, at X = X1, X3, which is the rising portion of the convex portion, the sample stage 112 descends in an attempt to return the distance between the probe 114 and the sample 110 to the target distance, but the descending speed is too slow, and the distance between the surface 1101 and the probe 114 becomes smaller than the target distance. Therefore, as shown by arrow AR1 in Figure 5(B), the detected Z coordinate is smaller than the actual Z coordinate of the surface 1101. Correspondingly, the atomic force between the probe 114 and the surface 1101 also becomes larger than the target value, and the deviation signal also becomes smaller than 0.

[0047] On the other hand, at X=X2 and X4, which are the falling portions of the convex portion, the sample stage 112 rises to return the distance between the probe 114 and the sample 110 to the target distance, but the rising speed is too slow, and the distance between the sample 110 and the probe 114 becomes too large. Therefore, as shown by arrow AR2 in Figure 5(B), the detected Z coordinate is larger than the actual Z coordinate of the surface 1101. Correspondingly, the atomic force between the probe 114 and the surface 1101 also becomes smaller than the target value, and the deviation signal also becomes larger than 0.

[0048] As described above, if the feedback parameter is too small, the correct shape of the surface 1101 cannot be acquired in areas where the height of the surface 1101 changes significantly. Specifically, the corners of the rectangular irregularities on the surface 1101 are detected as rounded, and the centers of the concave and convex portions are detected later than they actually are (shifted toward the positive X coordinate). In the example of FIG. 5 , in areas where the height changes less following areas where the height changes more significantly (for example, areas where X1″<X<X2), appropriate Z-axis values ​​are acquired, and the deviation signal returns to zero. However, in an example where the feedback parameter is even smaller, there is a possibility that the acquired Z-axis values ​​will not catch up with the actual Z-axis values, or that the probe 114 will collide with the surface 1101, even in these areas.

[0049] As described above, if the feedback parameter is too large or too small, an accurate shape image cannot be obtained, making it difficult to set an appropriate value for the feedback parameter. Moreover, since the feedback parameter can also vary depending on the optical lever sensitivity (described later), accurate feedback control requires readjusting the feedback parameter each time. Furthermore, an image that perfectly matches the sample shape, as shown in Figure 3, is not actually obtained. Instead, an image that contains some overshoot and undershoot, as shown in Figure 4, or an image with rounded corners, as shown in Figure 5, is obtained. In other words, it is inevitable that the primary image will deviate to some extent from the actual shape.

[0050] [Creation of Secondary Image by Image Correction] (Image Correction When Feedback Parameter is Too Large) FIG. 6 is a diagram for explaining image correction when the feedback parameter is too large.

[0051] In the SPM according to the embodiment, the deviation signal ( FIG. 6A ) is first converted into a displacement ( FIG. 6C ) of the distance between the sample 110 and the probe 114 using a predetermined conversion coefficient. This conversion coefficient may also be referred to as optical lever sensitivity, device sensitivity, or the like by those skilled in the art. In the case of an AFM, a voltage change (unit: volts, for example) on the photodetector 119 is converted into a displacement (unit: μm, for example) using a predetermined conversion coefficient. The horizontal axis of FIG. 6C represents the X coordinate, and the vertical axis of FIG. 6C represents the Z coordinate displacement. The displacement is the value obtained by subtracting the target distance from the actual distance between the probe 114 and the surface 1101. Therefore, the displacement is greater than 0 when the actual distance between the probe 114 and the surface 1101 is greater than the target distance, and is less than 0 when the actual distance between the probe 114 and the surface 1101 is less than the target distance.

[0052] Next, the Z coordinate of the secondary image (FIG. 6(D)) is calculated by subtracting the displacement (FIG. 6(C)) from the Z coordinate of the primary image (FIG. 6(B)). In other words, the Z coordinate of the secondary image is a value obtained by subtracting the displacement of the distance between the probe 114 and the surface 1101 from the Z coordinate position of the surface 1101 obtained from the position of the sample stage 112. Therefore, the Z coordinate of the secondary image coincides with the Z coordinate of the actual surface 1101.

[0053] More specifically, for example, at X=X1, the Z coordinate of the primary image becomes too large in response to the sample stage 112 being lowered too much, but the amount by which the distance between the probe 114 and the surface 1101 is larger than the target distance is subtracted from the Z coordinate. The amount by which the sample stage 112 is lowered too much corresponds to the amount by which the distance between the probe 114 and the surface 1101 is larger than the target distance. In this way, in the secondary image, the overshoot and undershoot of the primary image are canceled out by the amount of displacement in the distance between the probe 114 and the surface 1101.

[0054] (Image Correction When Feedback Parameter is Too Small) According to the image correction method according to the embodiment, appropriate correction can be performed even when the feedback parameter is too small.

[0055] FIG. 7 is a diagram for explaining image correction when the feedback parameter is too small.

[0056] As in FIG. 6, the deviation signal (FIG. 7A) is converted into the amount of displacement of the distance between the sample 110 and the probe 114 (FIG. 7C) using a predetermined conversion coefficient.

[0057] Then, the Z coordinate of the secondary image (FIG. 7D) is calculated by subtracting the displacement (FIG. 7C) from the Z coordinate of the primary image (FIG. 7B).

[0058] In the example of FIG. 7 , the Z coordinate of the secondary image also coincides with the Z coordinate of the actual sample 110. As shown in FIGS. 6 and 7 , the SPM according to this embodiment can create a secondary image that shows the shape of the actual sample 110. This makes it possible to acquire a secondary image in which overshoot and undershoot have been corrected, even when image acquisition is accelerated. Furthermore, regardless of the image acquisition speed, an image with an accurate shape can be acquired without strictly setting the feedback parameters.

[0059] The method for acquiring the deviation signal varies depending on the type and / or settings of the SPM. For example, in an STM, the deviation signal is acquired as a change in the current flowing between the sample 110 and the probe 114. Also, in a dynamic mode such as an AFM, a deviation signal is acquired based on a change in the amplitude of vibration of the cantilever 113. However, regardless of the type and / or settings of the SPM, a secondary image showing the actual shape of the sample 110 can be created by implementing the deviation signal-based image correction method according to this embodiment. Furthermore, since each type of SPM performs measurements based on different physical quantities, the above-mentioned "distance" and "shape" are also distances and shapes based on the physical quantities of the SPM.

[0060] [Flowchart] FIG. 8 is a flowchart showing the image correction process according to the embodiment.

[0061] Each step (hereinafter also referred to as "ST") in Figure 8 is performed by the processor 20 of the control device 2 of the SPM 1, which controls the position of the sample stage 112 so that the physical quantity acting between the probe 114 and the sample 110 becomes a predetermined target value.

[0062] In ST01, the processor 20 updates the conversion coefficient from the deviation signal to the displacement amount when replacing the cantilever 113. Specifically, when the cantilever 113 of the SPM 1 is replaced, the processor 20 remeasures the conversion coefficient between the deviation signal and the displacement amount and records the conversion coefficient.

[0063] The conversion coefficient can change depending on the individual differences of the cantilever 113, and can also change depending on the installation state of the cantilever 113. Therefore, the conversion coefficient can change when the cantilever 113 is replaced. Therefore, by performing ST01, a conversion coefficient according to the state of the installed cantilever 113 can be obtained, enabling more accurate image correction.

[0064] In ST02, the processor 20 acquires a deviation signal based on the difference between the physical quantity acting between the probe 114 and the sample 110 and a target value.

[0065] In ST 04 , the processor 20 converts the value of the deviation signal into the amount of change in the distance between the probe 114 and the sample 110 .

[0066] In ST06 , the processor 20 creates a primary image of the sample 110 based on the position of the sample stage 112 .

[0067] In ST08, the processor 20 creates a secondary image by correcting the primary image with the amount of displacement.

[0068] 8, even when the distance between the probe 114 and the sample 110 is too small or too large compared to a target value, a secondary image can be acquired in which the Z coordinate of the primary image is corrected using a deviation signal correlated with the deflection of the probe 114. Therefore, the Z coordinate of the secondary image coincides with the Z coordinate of the actual sample 110. Therefore, an image correction method can be provided for creating an image that shows the shape of the actual sample 110.

[0069] 8 may be applied to an STM 1 in which the processor 20 controls the position of the cantilever 113 so that the physical quantity acting between the probe 114 and the sample 110 becomes a predetermined target value. In this case, in ST06, the processor 20 creates a primary image of the sample 110 based on the position of the cantilever 113.

[0070] [Modification 1] FIG. 9 is a flowchart showing image correction processing according to Modification 1.

[0071] In the flowchart of Fig. 9, ST01 in Fig. 8 is deleted. As shown in Fig. 9, if measurement accuracy can be maintained without updating the conversion coefficients, measurement may be performed without updating the conversion coefficients.

[0072] [Modification 2] FIG. 10 is a flowchart showing image correction processing according to Modification 2.

[0073] In the flowchart of FIG. 10, the process of ST08A is performed instead of ST08 in FIG.

[0074] In ST08A, the processor 20 creates a secondary image by correcting the primary image only for portions where the absolute value of the corresponding deviation signal exceeds a predetermined threshold.

[0075] 10, the primary image can be corrected only for portions where the Z coordinate of the primary image is significantly different from the Z coordinate of the secondary image. For example, only the portions corresponding to the undershoot and overshoot in FIG. 4B can be corrected. More specifically, it is possible to correct only the portion from Xn to Xn' (n = 1, 2, 3, 4) and not the portion from Xn' to Xn+1 (n = 1, 2, 3).

[0076] This allows a secondary image to be obtained by correcting only the portions of the primary image that deviate from the actual shape, which means that corrections to the raw data can be kept to a minimum.

[0077] The threshold value used in ST08A may be predetermined or may be set by the user as appropriate. The threshold value may be determined according to the value of the deviation signal, for example, a value that is a predetermined multiple of the average value of the absolute values ​​of the deviation signals of the entire primary image.

[0078] [Modification 3] FIG. 11 is a flowchart showing image correction processing according to Modification 3.

[0079] In the flowchart of Fig. 11, ST09 is added after ST08 in Fig. 9. In ST09, the processor 20 displays the primary image and the secondary image.

[0080] 11, the user can view the primary image, which is raw data, and the secondary image, which is a corrected image, and decide whether to use the raw data or the corrected image as the measurement result. For example, if the primary image and the secondary image are not very different, the primary image, which is raw data, can be used as the measurement result, and if the primary image and the secondary image are significantly different, the secondary image, which is a corrected image, can be used as the measurement result.

[0081] The processing of ST09 may be performed by the processor 20. The processor 20 may compare the primary image and the secondary image through image processing, and determine to use the primary image if the deviation is small, and to use the secondary image if the deviation is large. More specifically, the processor 20 may create a secondary image by correcting the primary image if the average value of the absolute values ​​of the deviation signals of the entire primary image exceeds a predetermined threshold.

[0082] As an image correction method related to variant 3, the processor 20 may display the primary image before creating and / or displaying the secondary image and accept a user's selection as to whether or not to create and / or display the secondary image.

[0083] Aspects It will be understood by those skilled in the art that the above-described embodiments are specific examples of the following aspects.

[0084] (Item 1) An image correction method according to one aspect is an image correction method for a scanning probe microscope. The scanning probe microscope includes a sample stage on which a sample is placed, a cantilever with a probe at its tip, and a control device that controls the position of the sample stage or the cantilever so that a physical quantity acting between the probe and the sample becomes a predetermined target value. The image correction method includes the steps of acquiring a deviation signal based on the difference between the physical quantity acting between the probe and the sample and the target value, converting the value of the deviation signal into a displacement amount of the distance between the probe and the sample, creating a primary image of the sample based on the position of the cantilever or the position of the sample stage, and creating a secondary image by correcting the primary image using the displacement amount.

[0085] According to the image correction method described in paragraph 1, a secondary image showing the actual shape of a sample can be created. In particular, even when image acquisition is performed quickly, a secondary image in which overshoot and undershoot have been corrected can be acquired.

[0086] (Item 2) The image correction method according to item 2 further comprises a step of updating a conversion coefficient from the deviation signal to the displacement amount when the cantilever is replaced.

[0087] According to the image correction method described in paragraph 2, a conversion coefficient according to the state of the installed cantilever can be obtained, thereby enabling more accurate image correction.

[0088] (Clause 3) In the image correction method described in clause 1 or 2, the correcting step includes a step of creating a secondary image by correcting only the portion of the primary image where the absolute value of the corresponding deviation signal exceeds a predetermined threshold.

[0089] According to the image correction method described in paragraph 3, a secondary image can be obtained by correcting only the portions of the primary image that deviate from the actual shape. In other words, corrections to the raw data can be kept to a minimum.

[0090] (4) The image correction method according to any one of the above paragraphs 1 to 3, further comprising the step of displaying the primary image and the secondary image.

[0091] According to the image correction method described in paragraph 4, it is possible to determine whether to use the raw data or the corrected image as the measurement result by looking at the primary image, which is raw data, and the secondary image, which is a corrected image.

[0092] (Item 5) The scanning probe microscope described in item 5 is a scanning probe microscope comprising a sample stage on which a sample is placed, a cantilever having a probe at its tip, and a control device that controls the position of the sample stage or the position of the cantilever so that a physical quantity acting between the probe and the sample becomes a predetermined target value. The control device acquires a deviation signal based on the difference between the physical quantity acting between the probe and the sample and the target value, converts the value of the deviation signal into an amount of displacement in the distance between the probe and the sample, creates a primary image of the sample based on the position of the cantilever or the position of the sample stage, and creates a secondary image by correcting the primary image for the amount of displacement.

[0093] The scanning probe microscope described in paragraph 5 can create a secondary image that shows the actual shape of the sample. In particular, even when image acquisition is performed quickly, a secondary image in which overshoot and undershoot have been corrected can be acquired.

[0094] 1 SPM, 2 control device, 20 processor, 21 memory, 22 display device, 23 input device, 110 sample, 111 piezo scanner, 111xy XY scanner, 111z Z scanner, 112 sample stage, 113 cantilever, 114 probe, 115 laser diode, 119 photodetector, 120 displacement detection mechanism, 121 support member, 131 feedback signal generator, 133 scanning signal generator, 151 target value signal input unit, 152 comparator, 153 PID controller, 1101 surface, 1121 upper surface.

Claims

1. An image correction method for a scanning probe microscope, wherein the scanning probe microscope includes: a sample stage on which a sample is placed; a cantilever having a probe at its tip; and a control device that controls the position of the sample stage or the position of the cantilever so that a physical quantity acting between the probe and the sample becomes a predetermined target value, the image correction method comprising the steps of: acquiring a deviation signal based on the difference between the physical quantity acting between the probe and the sample and the target value; converting the value of the deviation signal into an amount of displacement of the distance between the probe and the sample; creating a primary image of the sample based on the position of the cantilever or the position of the sample stage; and creating a secondary image by correcting the primary image with the amount of displacement.

2. The image correction method according to claim 1, further comprising the step of updating a conversion coefficient from the deviation signal to the displacement amount when the cantilever is replaced.

3. The image correction method according to claim 1, wherein the correcting step includes a step of creating the secondary image by correcting only the portion of the primary image where the absolute value of the corresponding deviation signal exceeds a predetermined threshold.

4. The image correction method of claim 1, further comprising the step of displaying the primary image and the secondary image.

5. A scanning probe microscope comprising: a sample stage on which a sample is placed; a cantilever having a probe at its tip; and a control device that controls the position of the sample stage or the position of the cantilever so that a physical quantity acting between the probe and the sample becomes a predetermined target value, wherein the control device: acquires a deviation signal based on the difference between the physical quantity acting between the probe and the sample and the target value; converts the value of the deviation signal into an amount of displacement in the distance between the probe and the sample; creates a primary image of the sample based on the position of the cantilever or the position of the sample stage; and creates a secondary image by correcting the primary image with the amount of displacement.

Images