JPH11326347A - Scan type probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly measure a breadth, etc., of a bumpy part of a sample surface by representing a shape of the bumpy part and specifying an edge of the bumpy part. SOLUTION: This microscope has a probe 15 opposite to a sample 11, a tripod 12 for applying a relative shift between the sample 11 and probe 15, and an optical shift detection device (17, 18) for detecting a physical amount generated between the probe 15 and sample 11. The microscope further includes a control circuit 20 which keeps the physical amount generated between the probe 15 and sample 11 at a set value s0, and a subtractor 22 which combines a signal s2 obtained from the control circuit 20 and a deviation signal Δs between the physical amount generated between the probe 15 and sample 11 and the set value, thereby outputting a signal s3 including a bump information and an edge specification information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope capable of easily specifying the edge of a measurement target portion on a sample surface and suitable for measuring the shape and size of the measurement target portion.

[0002]

2. Description of the Related Art A scanning probe microscope (SPM) is a technique in which a probe having a sharp tip is brought close to a sample at a distance of the order of nanometers (nm). This is a device that measures the shape and the like of the sample surface at the atomic dimension level by measuring the physical interaction such as the generated atomic force. Among them, a force microscope typified by a scanning atomic force microscope (hereinafter referred to as AFM) uses a cantilever having a very low spring constant, and acts between a probe provided at the tip of the cantilever and a sample. This is a device that measures the unevenness of the sample surface by detecting the amount of displacement due to the bending deformation of the cantilever due to the interatomic force.

With reference to FIG. 6, a description will be given of the configuration and operation of a main part of a mechanical system and a control system of a conventional AFM. This AFM
Is a general contact mode AFM.

A cantilever 82 having a probe 81 at its tip
Is fixed at its proximal end. The displacement caused by the bending deformation of the cantilever 82 is caused by the laser light source 83 and the photodetector 84.
It is measured by an optical displacement detection device called an optical lever made of. Optical levers are generally and widely used as means for detecting the displacement of the cantilever of the AFM. The tripod 85 includes a sample table 87 on which a sample 86 is placed, and a sample table 87.
And piezoelectric elements 88a and 88b (Y-axis piezoelectric elements are not shown) of three axes (X, Y, and Z axes orthogonal to each other) that support
This is a three-dimensional actuator for performing scanning in the XY directions and operation in the Z-axis direction for controlling the distance between the probe and the sample. At the time of measurement, the probe 81 is arranged close to the surface of the sample 86.

When measuring the surface shape of the sample 86,
The cantilever 82 is moved closer to the sample 86 by an approach / retreat mechanism (not shown) until an atomic force is generated between the probe 81 and the sample 86. At this time, the probe 81 receives a force from the surface of the sample 86, and the cantilever 82 is bent and deformed. When the bending deformation of the cantilever 82 occurs, the control circuit 89 causes the displacement amount of the bending deformation of the cantilever 82 detected by the optical lever (the probe 81).
The displacement of the tripod 85 in the Z-axis direction is controlled such that the deviation signal Δs as the difference between the displacement signal s1 representing the displacement amount of the tripod and a preset set value s0 becomes zero.
That is, the amount of displacement of the cantilever 82 due to the bending deformation is controlled so as to always coincide with the set value s0. Therefore, the probe 81 is kept pressed against the sample 86 with a constant force. When the piezoelectric element of the tripod 85 is driven by an XY scanning circuit (not shown) to scan the surface of the sample 86 while controlling the pressing force to be constant, the control signal s2 in the Z-axis direction becomes irregular on the surface of the sample. It changes according to. Therefore, according to the control signal s2, unevenness information on the sample surface can be obtained.

Next, an example of measuring a convex portion 91 having a rectangular cross section as shown in FIG. 7 by the AFM will be described. Edges 92 and 93 are formed on both sides of the cross section of the convex portion 91. In the measurement of the protrusion 91, the tip of the probe 81 moves from left to right in FIG. Probe 8
The movement of 1 is relative, and the sample 86 is moved by the tripod 85 in practice. In the measurement of the convex portion 91 on the surface of the sample 86, as described above, control is performed so that the pressing force of the probe 81 against the sample 86 is constant. Accordingly, the cantilever 82 is deformed by a constant amount of displacement. In this state, the probe 81 is
When the measurement of the convex portion 91 is performed while scanning is performed, the Z-axis piezoelectric element 88b of the tripod 85 is controlled so as to contract by a distance corresponding to the step in the convex portion 91 and to extend to the original length again. Therefore, in the control signal s2, the signal level decreases at the edge 92 of the convex portion 91 and changes so as to return to the original state at the edge 93 (FIG. 8). The actual change is accompanied by a control delay. Therefore, the control signal s2 changes as shown in FIG. The change state of the control signal s2 shown in FIG. 8 corresponds to the uneven shape of the convex portion 91 on the sample surface. In the AFM, image processing of the control signal s2 is performed by an image processing device (not shown), an image of the AFM is created, and the image is displayed on the display device. Since the configuration and method of image processing are well known, detailed description will be omitted.

The degree of control delay in the control signal s2 shown in FIG. 8 is an example. The control delay varies variously depending on the state of the control system and the magnitude of the scanning speed. Further, in the illustrated example, an example of a piezoelectric element that extends in the axial direction with an increase in the applied voltage has been described. However, a piezoelectric element having the opposite polarity also exists. The polarity of the piezoelectric element does not affect the principle part of the AFM, and therefore does not need to be considered here.

[0008]

According to the conventional AFM measurement method, when the width dimension is to be calculated for the cross-sectional shape of the convex portion 91 obtained by the measurement, the edges 92 and 93 are specified by the control signal s2. Very difficult to do in practice,
A problem arises in that it is impossible to calculate the width dimension. FIG.
Measurement signal obtained from the circuit configuration of FIG.
Since the control signal s2 output from the control signal includes a control delay as shown in FIG. 8, the portion corresponding to the edges 92 and 93 becomes dull, causing a problem that the edge cannot be clearly specified. In FIG. 7, it is considered that the edge is relatively easy to identify because the convex portion 91 is completely square for convenience of explanation. However, in actuality, there are many convex portions having rounded edges whose edges are not clear. This is more difficult, and it is difficult to measure the width dimension of the convex portion with good reproducibility.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and it is possible to represent the uneven shape of the measurement target portion on the sample surface, to clearly specify the edge of the measurement target portion, and to measure the width dimension of the measurement target portion. It is an object of the present invention to provide a scanning probe microscope capable of accurately measuring the characteristics of a scanning probe microscope.

[0010]

The scanning probe microscope according to the present invention is configured as follows to achieve the above object. The first scanning probe microscope (corresponding to claim 1) includes a probe facing the sample, a means (fine movement mechanism or the like) for giving a relative displacement between the sample and the probe, and a probe between the probe and the sample. It has detecting means (for example, an optical lever type optical displacement detecting device) for detecting the generated physical quantity,
Control means for maintaining a physical quantity generated between the probe and the sample at a set value; a signal obtained from the control means; a deviation signal between the physical quantity generated between the probe and the sample and a set value; And synthesizing means for outputting a signal including edge identification information. In the above-mentioned scanning probe microscope, for example, in the case of an AFM, an atomic force is generated between the probe and the sample as a physical quantity, and at the time of measurement, a change in the atomic force is detected by, for example, an optical lever type detection means, and the atomic force is detected. The distance between the probe and the sample is adjusted by the control means so that the force matches the set value, and control is performed so as to keep the distance between the probe and the sample constant. The optical lever-type detecting means includes a cantilever having a probe at a tip thereof, and a position detector for detecting a displacement amount of the cantilever due to bending deformation. During the measurement, the surface of the sample is scanned by the needle, and during that time, the distance between the probe and the sample is kept constant by the control signal output from the control means as described above. Since the control signal output from the control means controls the probe so as to follow the uneven shape of the sample surface, the control signal can obtain unevenness information of the sample surface. Further, information reflecting the change rate of the unevenness on the sample surface can be obtained from the deviation signal between the physical quantity generated between the probe and the sample and the set value. Because,
This is because the larger the rate of change of the unevenness, the greater the control delay by the control means, and thus a larger signal is generated as the deviation signal. Since the edge of the measurement target part on the surface of the sample is the point where the rate of change of unevenness is the largest, the control delay is maximized, the absolute value of the deviation signal is maximized, and the edge of the measurement target part is accurately detected. Can be. Therefore, by synthesizing the signal output from the control means and the deviation signal, it is possible to obtain a signal that indicates the uneven shape of the sample surface and can specify the edge of the uneven shape. If the edge of the measurement target portion on the sample surface can be specified, the width dimension and the like of the measurement target portion can be accurately measured. Even when the edge portion is rounded, the deviation signal is a signal reflecting the differential coefficient of the cross-sectional shape of the sample surface, and thus can be used as an effective signal when specifying the edge. In the second scanning probe microscope (corresponding to claim 2), in the above configuration, preferably, the synthesizing unit is a subtractor that calculates a difference between a signal obtained from the control unit and a deviation signal. In a third scanning probe microscope (corresponding to claim 3), in the above configuration, preferably,
An adjuster is provided for adjusting the signal level of the deviation signal with respect to the signal obtained from the control means.

[0011]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention. The scanning probe microscope (SPM) of the present embodiment has a cantilever as an example, and particularly shows an example of a contact mode atomic force microscope (AFM). The amount of displacement caused by the bending deformation of the cantilever is detected by using a general optical lever type optical displacement detecting device.

In FIG. 1, a sample 11 is a tripod 1
It is mounted on the second sample stage 13. Tripod 1
Reference numeral 2 denotes a three-axis piezoelectric element that supports the sample table 13, that is, an X-axis piezoelectric element 14a, a Y-axis piezoelectric element (not shown), and a Z-axis piezoelectric element (not shown).
XY direction scanning and probe
This is a three-dimensional actuator for driving in the Z-axis direction for controlling the distance between the samples (or between the cantilever and the sample). Above the sample 11, a cantilever 16 having a probe tip 15 facing the sample 11 at its tip is arranged.
Above the cantilever 16, an optical lever type optical displacement detecting device including a laser light source 17 and a photodetector 18 is arranged. The laser light 17 a emitted from the laser light source 17 is reflected on the back surface of the cantilever 16 and enters the light detector 18. An atomic force acts between the surface of the sample 11 and the probe 15, and the amount of displacement generated in the cantilever 16 when the cantilever 16 bends and deforms according to the atomic force is an optical lever type optical displacement detection device. Is measured by

Next, the configuration of the control system and the operation related to measurement will be described.

In FIG. 1, when measuring the shape of the surface of the sample 11, the probe 15 is brought close to a region where an atomic force acts on the sample 11 by a well-known approach / retreat mechanism (not shown). At that time, the probe 15 receives a force from the sample surface, and the cantilever 16 bends.
Cantilever 16 detected by optical displacement detection device
(The displacement of the probe 15) is extracted from the photodetector 18 as a displacement signal s1. In the subtractor 19, a difference between a preset set value s0 and the displacement signal s1 is calculated as a deviation signal Δs.
0 is supplied. The control circuit 20 determines the Z of the tripod 12
It controls the operation in the axial direction, that is, the Z-axis piezoelectric element 14b, and the deviation signal Δs output from the subtractor 19 is 0.
The control signal s2 is generated and output so that That is, the displacement amount of the cantilever 16 due to the bending deformation is controlled so as to always coincide with the set value s0, and the probe 15 is kept pressed against the surface of the sample 11 with a constant force. The XY scanning circuit 21 drives the tripod 12 to control the sample 11
Is moved and the surface of the sample 11 is scanned by the probe 15, Z
The control signal s2 in the axial direction changes according to the uneven shape of the surface of the sample 11.

The control signal s2 and the deviation signal Δs are supplied to a subtractor 22, which outputs a difference signal s3 obtained by subtracting the deviation signal Δs from the control signal s2. The difference signal s3 output from the subtractor 22 is input to the signal processing device 23. In the signal processing device 23, the difference signal s3 and X
An image signal is generated based on the output signal s <b> 4 of the Y-scanning circuit 21, and information on the unevenness of the surface of the sample 11 is displayed on the display device 24 based on the image signal.

The difference signal s3 output from the subtractor 22 is
The signal is a signal representing the uneven shape of the surface of the sample 11 and a signal that can clearly specify the edge of the uneven shape. That is, the difference signal s3 is a signal including the unevenness information on the sample surface and the edge identification information. Next, the characteristics of the difference signal s3 will be described.

The difference signal s3 will be described with reference to FIGS. Here, as an example, a difference signal s3 obtained by relatively moving the probe 15 from the left to the right and scanning the protrusion 91 shown in FIG. 7 will be described. 2 and 3, reference numeral 91 denotes an example of the cross-sectional shape of the convex portion on the sample surface, and reference numerals 92 and 93 denote the edges of the convex portion 91. When measuring the convex portion 91 on the surface of the sample 11, the change state of the signal obtained as the control signal s2 is the same as the conventional one, and the control signal s as shown in FIG.
2 is output from the control circuit 20. This control signal s2 is input to the subtractor 22. On the other hand, the deviation signal Δs generated in the measurement of the convex portion 91 changes like the waveform shown in FIG. In FIG. 2, the correspondence between the deviation signal Δs and the convex portion 91 is clear. In the deviation signal Δs, a peak 31 occurs downward corresponding to the edge 92 of the convex portion 91 and the edge 93
, A peak 32 is generated in the upward direction. FIG. 2
In the above, 0 indicates a reference potential (0 volt). As described above, in the deviation signal Δs, as apparent from FIG.
It has a characteristic that peaks 31 and 32 are generated corresponding to the edges 92 and 93 of one. Next, peaks 31 and 32
The reason for the occurrence will be described.

When the probe 15 is brought close to the surface of the sample 11 to the extent that an atomic force is generated, and the probe 15 is scanned from left to right with respect to the convex portion 91 on the sample surface, the left side of the convex portion 91 is obtained. Is bent at the edge 92 of the cantilever 16. The bending deformation of the cantilever 16 is caused by a decrease in the distance between the tip of the probe 15 and the sample surface. The probe 15 is controlled so that the pressing force of the cantilever 16 is always constant.
When the flexure 6 is deformed, the Z-axis piezoelectric element 14b of the tripod 12 is controlled to contract rapidly so as to increase the distance between the probe 15 and the sample surface. However, in this control, since a delay occurs in the feedback control, the control signal s2 actually changes as shown in FIG. 8 as described in the related art. Therefore, in such control, the control delay at the edge occurs most remarkably, and the deviation signal Δs becomes maximum in the downward direction, that is, the minus side at the left edge 92 as shown in FIG. 2, and thereafter, when the control is completed, the deviation signal Δs Becomes 0. As a result, a peak 31 occurs.
The same occurs in the right edge 93 of the convex portion 91. At the edge 93, the Z-axis piezoelectric element 14b is controlled to extend rapidly. However, since the control is delayed as described above, the edge 9
In the portion corresponding to No. 3, it changes so as to be maximum in the upward direction, that is, on the plus side. As a result, a peak 32 occurs.

As described above, when the probe 15 is relatively moved from the left side to the right side to scan the convex portion 91 of the sample surface along the shape, as shown in FIG. , 93 corresponding to the peaks 31, 32. This means that the edges 92 and 93 of the projection 91 on the sample surface can be specified by monitoring the deviation signal Δs. In the case of the present embodiment, for the sake of convenience of explanation, the convex portion 91 on the sample surface is shown as a convex portion having a perfect rectangular cross section, and the peaks 31 and 32 appear remarkably in the deviation signal Δs. Even in the case of a convex portion, a peak that can specify the edge can be generated in the deviation signal Δs.

The difference signal Δs having the above-described characteristics is supplied to the subtractor 22, and the difference signal Δs is subtracted from the control signal s2 to output the difference signal s3. FIG. 3 shows a waveform of the difference signal s3.
In FIG. 3, 0 is a reference potential, which is the level of the potential 0.
Peaks 33 and 34 also occur in the difference signal s3. The peaks 33 and 34 respectively correspond to the edges 92 and
93. Therefore, if the peaks 33 and 34 in the difference signal s3 are extracted, the edge 9 of the convex portion 91 can be obtained.
The location where 2,93 exists can be found. Convex part 9
Obviously, if the locations of the edges 92 and 93 are found, the width dimension of the projection 91 can be obtained. The measurement signal (control signal s) obtained by the conventional AFM shown in FIG.
In contrast to 2), the difference signal s3 obtained by the configuration of the present embodiment shown in FIG. 3 includes the information of the uneven shape of the surface of the sample 11 and has a peak corresponding to the edge of the uneven shape of the surface of the sample 11. Since it is a signal possessed, it is easy to specify the edge when it is desired to measure the width dimension of the measurement target portion. For this reason, it becomes possible to accurately and reproducibly measure the width and the like of the uneven shape on the sample surface.

It goes without saying that the deviation signal and the control signal shown in FIGS. 2 and 8 change variously depending on the state of the control system and the magnitude of the operation speed. In the description of the present embodiment, an example that is easy to understand is shown for convenience of explanation.

In the above-described embodiment, the signal for specifying the edge of the uneven shape on the sample surface is obtained as the difference signal s3 using the subtractor 22, but the signal for specifying the edge is It is not limited to the difference signal. As long as a signal capable of specifying the edge of the uneven shape on the surface of the sample 11 can be generated, it goes without saying that any combining means for combining the control signal and the deviation signal can be used other than the subtractor.

Next, a second embodiment of the present invention will be described with reference to FIGS. The basic part of the configuration shown in FIG. 4 is substantially the same as the configuration shown in FIG. FIG.
In FIG. 7, the same reference numerals are given to substantially the same elements as those shown in FIG. 1, and detailed description thereof will be omitted. The characteristic configuration of this embodiment is that an adjuster 25 (amplifier or attenuator) is provided for the deviation signal Δs output from the subtractor 19, and the signal level of the deviation signal Δs is appropriately adjusted. It is. The subtracter 22 subtracts the deviation signal Δs whose signal level has been appropriately adjusted by the adjuster 25 from the control signal s2. As the adjuster 25, for example, an attenuator that attenuates the level of the deviation signal Δs to 1/10 is used. Note that the signal level is 1/10
In the sense of doubling, it can also be called an amplifier. When the subtracter 22 subtracts the attenuated deviation signal Δs from the control signal s2 by 1/10, the difference signal s3 is generated as shown in FIG. Also in the difference signal s3 shown in FIG.
1, 42 have occurred. Therefore, the difference signal s shown in FIG.
According to 3, it is possible to identify the edges 92 and 93 of the convex portion 91 by detecting the peaks 41 and 42. The magnitude of the deviation signal Δs varies depending on the state of control, the scanning speed, and the shape of the sample surface. According to the configuration of the present embodiment, the deviation signal Δs is adjusted to an appropriate magnitude (amplification) by providing the adjuster 25. Or attenuation). Further, according to the configuration of the present embodiment, it is possible to clearly specify the edge of the uneven shape while maintaining the waveform of the control signal s2 including the information on the uneven shape of the sample surface as it is.

Although the AFM has been described in the above embodiment, it goes without saying that the characteristic configuration of the present invention can be generally applied to an SPM provided with a similar control system that generates a deviation signal.

[0026]

As apparent from the above description, the present invention has the following effects. Focusing on the SPM having a control system for maintaining the distance between the probe and the sample surface at a constant distance, a deviation signal generated in the control system has a characteristic that the edge of the measurement target portion on the sample surface can be specified. By synthesizing the deviation signal and a control signal including the unevenness information of the sample surface to generate a signal including the unevenness information and the information on the edge of the unevenness, the image of the unevenness shape of the sample surface is displayed. The edge can be specified clearly, and accurate and highly reproducible measurement can be performed. Further, an image reflecting the change rate of the sample surface can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing a change state of a deviation signal.

FIG. 3 is a waveform diagram of an edge specifying signal obtained by subtracting a deviation signal from a control signal.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a waveform diagram of an edge specifying signal obtained in a second embodiment.

FIG. 6 is a main part configuration diagram of a conventional typical scanning probe microscope.

FIG. 7 is a diagram showing an example of a cross section of a convex portion on a sample surface.

FIG. 8 is a waveform diagram showing a change in a control signal generated when measuring the projection of FIG. 7 with a conventional scanning probe microscope.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Sample 12 Tripod 13 Sample stand 15 Probe 16 Cantilever 17 Laser light source 18 Photodetector 19 Subtractor 22 Subtractor 31, 32 Peak 41, 42 Peak

Claims (3)

[Claims] 1. A scanning probe having a probe facing a sample, means for giving a relative displacement between the sample and the probe, and detection means for detecting a physical quantity generated between the probe and the sample. In the microscope, control means for maintaining the physical quantity generated between the probe and the sample at a set value, a signal obtained from the control means, a deviation signal between the physical quantity generated between the probe and the sample and a set value, And a synthesizing means for synthesizing and outputting a signal including the unevenness information and the edge specifying information. 2. The scanning probe microscope according to claim 1, wherein said synthesizing means is a subtractor for calculating a difference between a signal obtained from said control means and said deviation signal. 3. The scanning probe microscope according to claim 1, further comprising an adjuster for adjusting a signal level of the deviation signal with respect to a signal obtained from the control unit.