JPH10111300A - Scanning probe microscope - Google Patents

Abstract

(57) [Problem] To provide a scanning probe microscope capable of accurately detecting a surface shape even when a spatial frequency related to unevenness of a sample surface is high. SOLUTION: A comparator 75 which compares a gap between the surface of a sample 52 and a probe 54 with a target value and generates a difference between them as an error signal S2, and a probe 54 which is XYZ relative to the sample 52. The control signal S3 for maintaining the gap between the sample surface and the probe at the predetermined value is generated based on the actuator 55 and the drive amplifier 70 for finely moving the probe 55 and the error signal S2, and the position detector 73, Differential amplifier 74,
A PI control unit 76 constituting a feedback circuit together with the comparator 75 and the actuator drive amplifier 70, and the error signal S2 and the control signal S3 are combined to form an observation image signal S
4 is provided.

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 represented by an atomic force microscope (AFM), and more particularly to a scanning probe microscope having a high spatial frequency related to irregularities on a sample surface. The present invention relates to a scanning probe microscope capable of accurately detecting a surface shape.

[0002]

2. Description of the Related Art In a scanning probe microscope such as an AFM,
A cantilever having a probe attached to the tip of a cantilever is used as a probe in order to detect a fine structure or structure on the sample surface by utilizing the interaction between the sample surface and the probe. When such a cantilever is used, if the probe is scanned on the sample surface, an attractive force or a repulsive force based on an atomic force is generated between the sample surface and the probe, and the atomic force is detected as a bending amount of the cantilever. Then, if the sample stage is finely moved in the Z-axis direction so that the amount of deflection is constant, that is, the gap between the sample surface and the probe is constant,
At this time, the fine movement signal or the detected amount of deflection itself represents the shape of the sample surface.

FIG. 2 is a block diagram showing an example of a signal processing device of a conventional scanning probe microscope. The sample 52 is placed on the three-dimensional sample stage 55, and a probe 54 attached to the free end of the cantilever 53 is arranged above the sample 52 so as to face the sample 52. The amount of deflection of the cantilever 53 is determined by the laser light 7 output from the laser generator 71.
2 is detected by measuring the incident position with the position detector 73.

The position detector 73 is composed of, for example, four divided photodetecting electrodes. When the amount of deflection of the cantilever 53 is zero, the position of the laser beam 72 is adjusted so as to come to the center of the four divided electrodes. Have been. For this reason,
When the cantilever 53 bends, the laser light 72
Spot moves on the four-divided electrode, and a difference occurs in the voltage output from the four-divided electrode. This voltage difference is amplified by the differential amplifier 74 and input to the non-inverting input terminal (+) of the comparator 75 as the deflection signal S1. Comparator 75
A target value signal relating to the amount of deflection of the cantilever 53 is input from the target value setting unit 79 to the inverting input terminal (−).

The error signal S 2 output from the comparator 75 is input to a proportional-integral (PI) control unit 76, and the error signal S 2
The signal obtained by synthesizing the integrated value and the integrated value is input to the actuator drive amplifier 70 and the observation image signal amplifier 77 as the actuator drive signal S3 also serving as the observation image signal. In the observation image signal amplifier 77, the actuator drive signal S3 is amplified and an image display device (not shown) (for example,
CRT). The scanning signal generating unit 78
A fine movement signal for finely moving 2 in the XY directions is supplied to the actuator drive amplifier 70. The position detector 73, the differential amplifier 74, the comparator 75, the PI control unit 76, and the actuator drive amplifier 70 constitute a feedback circuit.

[0006]

As shown in FIG. 3 (a), when the spatial frequency related to the unevenness on the sample surface is high, the scanning speed of the probe 1 is relatively fast, and the probe 1 follows the unevenness. If it is not possible, or if the gain of the feedback circuit is insufficient, an error occurs between the deflection amount signal S1 and the target value, and the error signal S2 as shown in FIG.
Is output from the comparator 75. The PI control unit 76, based on the error signal S2, as shown in FIG.
An actuator drive signal S3 also serving as an observation image signal is generated, and feedback control for making the error signal S2 close to zero is executed.

However, since the error signal S2 cannot be completely reduced to zero by such feedback control, a signal component corresponding to the error signal S2 is always lacking in the actuator drive signal S3. The part becomes dull. Since the actuator drive signal S3 also serves as an observation image signal, the conventional technique described above has a problem that the surface shape of the sample cannot be accurately displayed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a scanning probe microscope which solves the above-mentioned problems of the prior art and can accurately detect the surface shape even when the spatial frequency related to the unevenness of the sample surface is high. It is in.

[0009]

According to the present invention, at least one of the probe and the sample is moved in the Z-axis direction so that the gap between the sample surface and the probe is maintained at a predetermined value. A scanning probe microscope for scanning a probe in the X and Y directions on the surface of a sample while finely moving the probe, comparing a gap between the surface of the sample and the probe with a predetermined value, and generating a difference between the two as an error signal; A fine movement mechanism for finely moving the probe relative to the sample in the XYZ directions, feedback control means for generating a control signal for maintaining a gap between the sample surface and the probe at a predetermined value based on the error signal, Means for synthesizing the signal and the control signal and means for generating an observation image signal based on the synthesized signal are provided.

In such a configuration, since the error signal represents a difference between the sample surface shape detected by the probe and the actual sample surface shape, the error signal is generated based on the error signal. If the synthesized signal is combined with the drive signal for feedback control and the synthesized signal is supplied as an observation image signal, the error of the error signal is eliminated on the observation image signal, and the actual sample surface shape can be accurately expressed. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of a signal processing device of a scanning probe microscope according to an embodiment of the present invention,
The same reference numerals as those described above denote the same or equivalent parts.

As is clear from comparison with the prior art block diagram described with reference to FIG. 2, in this embodiment, the amplifier 6 amplifies the error signal S2 output from the comparator 75.
1 and the output signal of the amplifier 61 and the actuator drive signal S3 output from the PI control unit 76, and the synthesized signal is used as an observation image signal S4.
And an adder 62 that supplies the data to the computer.

In such a configuration, when the sample stage is scanned in the X and Y directions with the probe 54 approaching the surface of the sample 52, the cantilever 53 bends due to the atomic force between the sample surface and the probe, This is detected by the position detector 73 and the differential amplifier 74. If the gap between the probe 54 and the sample surface is controlled by the feedback circuit, the deflection signal S1 output from the operational amplifier 74 is representative of the gap between the surface of the sample 52 and the probe 54. The error signal S2 output from 75 indicates the difference between the sample surface shape detected by the probe and the actual sample surface shape. In other words, the actuator drive signal S3 output from the PI control unit 76 is the error signal S2
Means that the surface shape of the sample 52 is not correctly represented.

However, in the present embodiment, an adder 62 is provided to combine the error signal S2 and the actuator drive signal S3, and supplies this as an observation image signal S4 to the observation image signal amplifier 77 separately from the actuator drive signal S3. I am trying to do it. As a result, the observation image signal S4 is
As shown in (d), the surface shape of the sample 52 is accurately represented.

Further, the error signal S2 and the actuator drive signal S3 are originally used for different purposes, and it may not be possible to obtain an accurate observation image signal S4 simply by combining them. Therefore, in the present embodiment, the amplifier 61 is provided between the comparator 75 and the adder 62, and the actuator drive signal S3 is combined with the amplified error signal S2.

According to this embodiment, the error signal S2 representing the difference between the sample surface shape detected by the probe 54 and the actual sample surface shape is converted into a feedback control signal generated based on the error signal S2. Actuator drive signal S3
And supplies this as the observation image signal S4, so that the error of the error signal S2 is eliminated on the observation image signal S4, and the observation image signal S4 can accurately represent the surface shape of the sample 52. become.

In the above embodiment, the sample stage 55 is used as a fine movement mechanism for bringing the probe 54 close to the sample surface, and the error signal S2 is combined with the actuator drive signal S3 for driving the sample stage 55. However, the present invention is not limited to this. If an error signal is combined with a drive signal for finely moving the probe relative to the sample, the drive mechanism is a cantilever. 53 (or the probe 54 itself)
May be driven in the Z-axis direction.

[0018]

As described above, according to the present invention, the error signal obtained by comparing the gap between the sample surface and the probe with a predetermined value is used for driving the feedback control generated based on the error signal. Since the signal is synthesized with the signal and the synthesized signal is supplied as the observation image signal, the detection error of the error signal is eliminated on the observation image signal, and the observation image signal can accurately represent the actual sample surface shape. become.

[Brief description of the drawings]

FIG. 1 is a block diagram of a signal processing circuit of a main part of a scanning probe microscope according to an embodiment of the present invention.

FIG. 2 is a block diagram of a main part of a signal processing circuit of a conventional scanning probe microscope.

FIG. 3 is a diagram showing a signal waveform of a main part of a signal processing circuit of a scanning probe microscope in correspondence with a surface shape of a sample.

[Explanation of symbols]

 52 sample 53 cantilever 54 probe 55 three-dimensional sample stage 61 amplifier 62 adder 70 actuator drive amplifier 71 laser generator 73 position detector 74 differential amplifier 75 comparator 76 proportional integration (PI) control unit 77 observation image signal amplifier 79 Target value setting section

Claims (4)

[Claims] 1. A probe is brought close to the surface of a sample while moving at least one of the probe and the sample in the Z-axis direction so that a gap between the two is maintained at a predetermined value.
A scanning probe microscope for scanning in the Y direction, a signal representing a gap between the sample surface and the probe is compared with a signal representing the predetermined value, and a means for generating a difference between the two as an error signal; A fine movement mechanism for finely moving the sample in the XYZ directions relative to the sample; a feedback control means for generating a control signal for maintaining a gap between the sample surface and the probe at a predetermined value based on the error signal; A scanning probe microscope comprising: means for synthesizing a signal and a control signal; and means for generating an observation image signal based on the synthesized signal. 2. A cantilever having the probe formed at a free end thereof, and means for detecting an amount of deflection of the cantilever, wherein a gap between the sample surface and the probe is a detected amount of deflection of the cantilever. The scanning probe microscope according to claim 1, wherein the scanning probe microscope is represented by: 3. The scanning probe microscope according to claim 1, further comprising a unit that amplifies the error signal, wherein the control signal is combined with the amplified error signal. 4. The scanning probe microscope according to claim 1, wherein the fine movement mechanism is a sample stage capable of finely moving the sample in the Z direction.