JPH10282123A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a surface shape even if an entire sample surface is inclined by generating an observation image signal based on a control signal and finely moving a probe in Z-direction in response to an output signal where an inclination correction signal is added to the control signal. SOLUTION: An inclination detection circuit 90 for detecting the inclination of a sample surface, an inclination correction circuit 81 for generating an inclination correction signal S4 for correcting an error that is generated in Z-direction due to the inclination of the sample surface, and an addition circuit 82 for adding the inclination correction signal S4 to a control signal S6 are added. The inclination correction circuit 81 outputs an inclination correction signal S4 in X and Y directions. A PI control part 76 outputs the synthetic signal of an error signal S2 and its integral value as a control signal S6. The correction circuit 81 generates the correction signal S4 for each scanning position (x) in X direction and is added to the control signal S6 by the addition circuit 82. Therefore, an inclination signal is eliminated from the measurement signal S6 that is outputted from the PI control part 76, thus obtaining a clear image with less noise via an observation image signal amplifier 77.

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 a scanning atomic force microscope (AFM), and more particularly to a case where an observation surface of a sample is entirely inclined. However, the present invention relates to a scanning probe microscope capable of accurately detecting its 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 scanning probe in order to detect a fine structure or structure on the surface of the sample by utilizing the interaction between the sample surface and the scanning probe. With such a cantilever,
When the probe is scanned on the surface of the sample, an attractive force or a repulsive force based on an atomic force is generated between the surface of the sample and the probe. Therefore, this atomic force is detected as the amount of bending of the cantilever, and control is performed to finely move the sample stage in the Z-axis direction so that the amount of bending is constant, that is, the gap between the sample surface and the probe is constant. Is executed, the control signal at that time or the detected amount of deflection itself becomes representative of the shape of the sample surface. FIG. 5 is a block diagram showing an example of a conventional signal processing device of a scanning probe microscope. The sample 52 is placed on the three-dimensional sample stage 55, and a probe 54 attached to a free end of a 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 amount of laser light 7 emitted from the laser generator 71 and reflected by the back surface of the cantilever 53.
The second spot position is detected by measuring the spot position with the position detector 73.

The position detector 73 is composed of, for example, four divided light detection electrodes. When the amount of deflection of the cantilever 53 is 0, the position of the laser beam 72 is adjusted to be at 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 S2 output from the comparator 75 is input to a proportional-integral (PI) control unit 76, and the error signal S2
And a signal obtained by synthesizing the integrated value is input to the actuator drive amplifier 70 and the observation image signal amplifier 77 as a control signal S3 also serving as an observation image signal. The observation image signal amplifier 77 amplifies the control signal S3 and converts it to the observation image signal S3.
5 is supplied to an image display device (for example, a CRT) 80. The scanning signal generator 78 outputs a fine movement signal for finely moving the sample 52 in the X and Y directions to the actuator drive amplifier 70.
Supply to

[0005]

In the scanning probe microscope having the above-described structure, unevenness on the surface of the sample is observed on the display device 80 as the intensity of the luminance. The maximum amplitude of the signal supplied from the image signal amplifier 77 to the display device 80 and the display device 8
It is desirable to make the input rating substantially equal to 0. For this reason, the amplification degree of the observation image signal amplifier 77 is controlled in accordance with the magnitude of the input signal. On the other hand, even if the surface shape of the sample is the same, the case where the sample surface is entirely inclined as shown in FIG. 6 and the case where it is not inclined and flat as shown in FIG. By comparison, if the sample surface is not inclined, the detected amplitude Δd2 matches the amplitude of the unevenness component on the sample surface as shown in FIG. Therefore, if the control signal S3 is amplified so that the amplitude Δd2 matches the rating of the display device 80 as shown in FIG.
An image having an excellent N ratio can be obtained.

On the other hand, when the sample surface is totally inclined as shown in FIG. 6, the displacement Δd1 becomes relatively large because the control signal S3 contains an inclination component. I will. Therefore, the observation image signal amplifier 77 cannot increase the amplification degree, and has a problem that the amplitude of the concavo-convex component becomes smaller as compared with the case where the observation image signal amplifier is not inclined, so that the resolution and the SN ratio are reduced.

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 sample surface is entirely inclined. Is to do.

[0008]

In order to achieve the above object, according to the present invention, a probe is brought close to the surface of a sample, and at least the probe and the sample are placed so that a gap between them is maintained at a predetermined value. A scanning probe microscope that scans a probe in the X and Y directions on the sample surface while slightly moving one in the Z direction is characterized by the following means. (1) A control means for generating a control signal for maintaining the gap between the sample surface and the probe at a predetermined value, and correcting a deviation generated in the Z direction separately from the sample surface shape due to the inclined sample surface. Tilt correction means for generating a tilt correction signal to be generated as a function of a scanning position, addition means for adding a tilt correction signal to a control signal, means for generating an observation image signal based on the control signal, and output signal of the addition means. Z direction fine movement means for finely moving the probe in the Z direction in response. (2) A control means for generating a control signal for maintaining a gap between the sample surface and the probe at a predetermined value, and correcting a deviation generated in the Z direction separately from the sample surface shape due to the inclined sample surface. Tilt correction means for generating a tilt correction signal to be generated as a function of the scanning position, addition means for adding the tilt correction signal to the control signal, means for generating an observation image signal based on the output signal of the addition means, Z direction fine movement means for finely moving the probe in the Z direction in response.

According to the above configuration (1), the observation image signal generating means amplifies the control signal which does not include the tilt component of the sample, so that the control signal as the observation image signal is sufficiently amplified. And a clear, low-noise image can be obtained. According to the above configuration (2),
Although the control signal contains the tilt component of the sample, the tilt component is removed from the signal input to the observation image signal generating means. Therefore, the observation image signal generation stage can sufficiently amplify the control signal as the observation image signal, and a clear and low-noise image can be obtained.

[0010]

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 a first embodiment of the present invention, wherein the same reference numerals as those described above denote the same or equivalent parts. As is clear from comparison with the block diagram of the related art described with reference to FIG. 5, in the present embodiment, the inclination detection circuit 90 for detecting the inclination of the sample surface, and the surface shape of the sample because the sample surface is inclined Apart from this, a feature is that a tilt correction circuit 81 for generating a tilt correction signal S4 for correcting a deviation generated in the Z direction and an addition circuit 82 for adding the tilt correction signal S4 to the control signal S6 are added. . Hereinafter, the operation of the inclination detection circuit 90 and the inclination correction circuit 81 will be described. When the operator scans the probe in the X direction on the surface of the sample prior to the actual observation, the inclination detection circuit 90 determines the height of one end on the scan line by using a control signal detected immediately after the start of scanning. It is determined based on S6. further,
The height of the other end on the scan line is obtained based on the control signal S6 detected immediately before the end of the scan. And FIG.
As shown in the figure, the inclination angle θ (θX in the X direction) is determined based on the detected height deviation ΔZ0 and the scanning distance therebetween.
) Is obtained and registered in the inclination correction circuit 81. Also in the Y direction, an inclination angle θ (θY) in the Y direction is obtained based on the control signal S6 detected immediately before and immediately after the end of scanning and the scanning distance, and this is registered in the inclination correction circuit 81.

Next, the operation of the inclination correction circuit 81 will be described. The tilt correction circuit 81 of the present invention outputs a tilt correction signal S4 in each of the X direction and the Y direction. Here, only the operation in the X direction will be described, and the description of the operation in the Y direction will be omitted. FIG.
As shown in the above, a linear function Δ representing the relationship between the scanning position x in the X direction and the tilt correction amount Δz at the scanning position x
z = f (x) is registered based on the tilt angle θ, and the correction amount Δz is set for each scanning position based on the X scanning signal output from the scanning signal generator 78 and the linear function f (x).
Is calculated and output as the inclination correction signal S4. That is, when the sample surface is inclined upward to the right as shown in FIG. 2, the inclination correction circuit 81 uses the linear function f (x) corresponding to the inclination angle θ to obtain the data shown in FIG. As shown in (1), the inclination correction signal S4 that increases as the scanning position of the probe 54 moves from the left end to the right end is output.

FIG. 3 is a diagram showing an example of a specific configuration of the inclination correction circuit 81. The scanning signal output from the scanning signal generator 78 is input to a connection between the resistors R1 and R2. Here, when the sample surface is inclined upward to the right, the resistor R1 is connected to the input terminal of the operational amplifier OP1 by 0 V
(Ground potential) is applied, and the resistance R2
Is adjusted so that a voltage responsive to the tilt angle θ is applied to the input terminal of the operational amplifier OP2. As a result,
From the inclination correction circuit 81, as shown in FIG.
An inclination correction signal S4 proportional to the scanning position in the direction is output.

If the surface of the sample is inclined downward to the right, the resistance R1 is adjusted so that a voltage corresponding to the inclination angle θ is applied to the input terminal of the operational amplifier OP1, and the resistance R2 is adjusted to the input of the operational amplifier OP2. It is adjusted so that 0 V (ground potential) is applied to the input terminal. In such a configuration, when the sample stage is scanned in the X direction with the probe 54 being close to the surface of the sample 52, the sample surface and the probe 5
4, the cantilever 53 bends due to the atomic force between
This is detected by the position detector 73 and the differential amplifier 74. The gap between the probe 54 and the sample surface is determined by the PI control unit 76.
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, and the error signal S2 output from the comparator 75 is Represents the difference between the sample surface shape detected by the method and the actual sample surface shape.

The PI control section 76 outputs a signal obtained by synthesizing the error signal S2 and its integral value as a control signal S6 also serving as an observation image signal. At this time, the tilt correction circuit 81 generates a tilt correction signal S4 for each scanning position x in the X direction, and the tilt correction signal S4 is added to the control signal S6 by the adding circuit 82. Therefore, from the control signal S6 output from the PI control unit 76, as shown in FIG. 9B, the inclination component is removed. Therefore, the observation image signal amplifier 77 can sufficiently amplify the input signal (control signal S6), and a clear image with less noise can be obtained. FIG. 4 is a block diagram showing the configuration of the second embodiment of the present invention, and the same reference numerals as those described above denote the same or equivalent parts. The present embodiment is characterized in that a tilt component is removed from a signal input to the observation image signal generation unit 77 by adding a tilt correction signal S4 to a signal input to the observation image signal amplifier 77. .

In this embodiment, since the polarity of the tilt correction signal S4 needs to be opposite to that of the first embodiment, the tilt correction circuit 81 uses the resistor R2 when the sample surface is tilted to the right. Is 0V to the input terminal of the operational amplifier OP2.
(Ground potential) is adjusted so that the resistance R1
Is adjusted so that a voltage responsive to the inclination angle θ is applied to the input terminal of the operational amplifier OP1. If the sample surface is inclined downward to the right, the resistance R1 is adjusted so that 0 V (ground potential) is applied to the input terminal of the operational amplifier OP1, and the resistance R2 is adjusted to the input terminal of the operational amplifier OP2. It is adjusted so that a voltage responsive to the angle θ is applied.

In such a configuration, the control signal S3 output from the PI control unit 76 includes a tilt component, but a signal from which the tilt component has been removed is input to the observation image signal amplifier 77. You. Therefore, the observation image signal amplifier 77 can sufficiently amplify the input signal, and a clear and low-noise image can be obtained. In each of the above embodiments, the sample stage 55 is used as a fine movement mechanism for bringing the probe 54 close to the sample surface, and the sample 5
2 has been described as finely moving with respect to the cantilever 53, but the present invention is not limited to this. If the probe 54 can be finely moved relative to the sample 52, The drive mechanism is a cantilever 5
A mechanism for driving the probe 3 (or the probe 54 itself) in the Z-axis direction may be used.

In each of the embodiments described above, the inclination angle θ of the sample surface is automatically obtained by the inclination detection circuit 90 and registered in the inclination correction circuit 81. However, the present invention is not limited thereto. The present invention is not limited to this. The operator may manually adjust the resistances R1 and R2 of the inclination correction circuit 81 without operating the inclination detection circuit 90 to register the inclination angle θ.

Further, in each of the above-described embodiments, the present invention has been described by exemplifying a case where the sample surface is entirely inclined. However, the sample surface is inclined due to a shift between the center of the Z axis and the probe 54. The same can be applied to the case where it seems to be present. Further, since the voice coil motor has excellent linearity, if the voice coil motor is used as a driving unit for finely moving the sample stage 55 in the XYZ directions,
The effect of the present invention is even more remarkable.

[0019]

According to the present invention, even if the sample surface is totally inclined, the inclination component is removed from the signal supplied to the video signal amplification section, and only the unevenness component to be observed is supplied. You. Therefore, the amplifying unit can sufficiently amplify the input signal, and a clear image with less noise can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a scanning probe microscope according to a first embodiment of the present invention.

FIG. 2 is a diagram schematically illustrating an operation of a tilt detection circuit.

FIG. 3 is a diagram illustrating an example of a specific configuration of a tilt correction circuit.

FIG. 4 is a block diagram of a scanning probe microscope according to a second embodiment of the present invention.

FIG. 5 is a block diagram of a signal processing system of a conventional scanning probe microscope.

FIG. 6 is a diagram for explaining a problem of the related art.

FIG. 7 is a diagram for explaining a problem of the related art.

FIG. 8 is a diagram for explaining a problem of the related art.

FIG. 9 is a signal waveform diagram of a main part of FIG. 1;

[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 at least one of the probe and the sample is slightly moved in the Z 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 scanning signal generating means for generating a scanning signal in the XY directions, and an XY direction for finely moving the probe in the XY directions relative to the sample in response to the scanning signal. Fine movement means, 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; based on the error signal, A control means for generating a control signal for maintaining a gap between the probe and the probe at a predetermined value, and a tilt correction signal for correcting a deviation generated in the Z direction separately from the surface shape of the sample due to the tilt of the sample surface. Tilt correcting means generated as a function of position, adding means for adding the tilt correcting signal to the control signal, means for generating an observation image signal based on the control signal, and output signal of the adding means In response, the scanning probe microscope characterized by comprising a Z direction fine movement means for finely moving the relative Z-direction the probe relative to the sample. 2. A probe is brought close to the surface of the sample while moving at least one of the probe and the sample in the Z direction so that the gap between the two is maintained at a predetermined value.
In a scanning probe microscope that scans in the Y direction,
Scanning signal generation means for generating a scanning signal in the XY directions, XY direction fine movement means for finely moving the probe relative to the sample in the XY directions in response to the scanning signal, Means for comparing a signal representative of the gap with a signal representative of the predetermined value, and generating a difference between the two as an error signal; and, based on the error signal, for maintaining the gap between the sample surface and the probe at the predetermined value. Control means for generating a control signal, and tilt correction means for generating, as a function of the scanning position, a tilt correction signal for correcting a deviation generated in the Z direction separately from the surface shape of the sample because the sample surface is tilted; An adding unit that adds the tilt correction signal to the control signal; a unit that generates an observation image signal based on an output signal of the adding unit; In the Z direction A scanning probe microscope comprising: a Z-direction fine movement means for moving. 3. A tilt detection for detecting a tilt of a sample surface in at least one of the X direction and the Y direction based on control signals obtained at one end and the other end of scanning in at least one of the X direction and the Y direction. 3. The scanning probe microscope according to claim 1, further comprising a unit, wherein the tilt correction unit generates a tilt correction signal based on the detected tilt. 4. A cantilever having a probe formed at a free end thereof, and means for detecting a deflection of the cantilever, wherein a gap between the sample surface and the probe is determined by the detected deflection of the cantilever. 2. The method of claim 1, wherein
4. The scanning probe microscope according to any one of claims 3 to 3.