JPH10282117A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an accurate image even if the image is scanned speedily when sampling a moving image by previously generating the amount of operation to a Z-directional drive mechanism on a next scanning based on image data that are obtained by previous scannings. SOLUTION: Data on amount of operation in Z direction of a probe 2 at each scanning position of a sample W are stored at an image memory 5. A part 7 for generating a signal on the amount of foresight operation reads the previous amount-of-operation signal of the image memory 5, uses an xy scanning signal on a next scanning as a timing signal, and generates an amount-of- foresight-operation signal so that the same amount of z-axis operation can be obtained at the same xy scanning position. Then, the amount-of-operation signal from a controller 24 and the amount-of-foresight-operation signal from the part 7 for generating a signal on the amount of foresight operation are added by an addition point 32 and a signal after the addition is supplied to a piezoelectric driver 22 as the amount-of-operation signal, thus increasing the probability following the surface of the sample W faithfully due to the Z-direction drive mechanism and obtaining a highly accurate image information at a relatively high scanning speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning probe microscope, such as a scanning tunnel microscope and an atomic force microscope.

[0002]

2. Description of the Related Art In a scanning probe microscope such as a scanning tunneling microscope (STM) or an atomic force microscope (AFM), a probe or a sample is generally scanned in xy directions (two-dimensional directions along the sample surface). And during that scan,
A specific physical quantity such as a tunnel current or an atomic force acting between the probe and the sample is detected, and the probe or the sample is moved in the z direction (approach / separation between the probe and the sample) so that the detected value matches the set value. Direction), and the control amount in the z direction is used as image data of the sample surface at each scanning position as C data.
Display on a display such as RT.

With such a scanning probe microscope,
2. Description of the Related Art A moving image of an active surface of a reaction, a biological membrane, or the like is collected, and a temporal change of the structure is tracked. At present, for example, one screen has a resolution of 256 × 256 pixels and data of a scan of an area of about 10 nm square is collected at a scan speed of 5 screens / sec, and an image with a sufficient contrast is obtained.

[0004] Various uses have been made to increase the scanning speed of a scanning probe microscope even in uses other than the collection of moving images. The scanning speed in a scanning probe microscope is usually selected according to the tracking characteristics of a servo system that drives in the z direction that operates so as to keep the tunnel current and the interatomic force constant. There is known a system in which constants of a servo system are automatically and adaptively switched according to a surface state and a set scanning speed. That is, within the scanning area of one screen,
There may be localized areas with severe irregularities.If the scanning speed is simply increased, the servo system that controls the z-direction cannot keep up with the areas with severe irregularities, and specific physical quantities such as tunnel currents and interatomic forces. Is scanned in a state where is deviated from the set value, and the measurement accuracy is reduced. In the above countermeasure, the deviation is reduced by automatically switching the constant of the servo system to the high response side in such a region with severe unevenness.

[0005]

In capturing moving images, there is a strong demand for scanning at a higher speed than the above-described scanning speed in order to investigate a structure that changes rapidly.

[0006] Further, even in uses other than moving images, it is desired to further increase the scanning speed and to increase the measurement accuracy. A first object of the present invention is to provide a scanning probe microscope capable of obtaining a high-precision image even when scanning at a higher speed than before in capturing a moving image.

A second aspect of the present invention is a scanning probe capable of obtaining a high-precision image at a high scanning speed without using a method of changing a constant of a servo system for controlling in the z direction. It is to provide a microscope.

[0008]

Means for Solving the Problems In order to achieve the first object, the invention according to claim 1 is an embodiment of the invention shown in FIG.
, An xy direction scanning system 10 for scanning the sample W or the probe 2 in the xy direction along the surface of the sample W, and a probe or a sample in the z direction where the probe 2 and the sample W approach / separate. And a servo control system 20 for driving the probe 2 and scanning the probe 2 and the sample W relatively in the xy directions so that a specific physical quantity acting between them is constant. In a scanning probe microscope that controls the direction driving mechanism 21 and obtains image data of the sample surface from the operation amount given to the z-direction driving mechanism 21 and displays the image data on the display 6,
Means for predictively generating an operation amount to be given to the z-direction drive mechanisms 21 and 22 at the next scan based on the image data of the sample surface already collected, and superimposing the operation amount on the operation amount signal of the servo control system 20 (foreseeing operation It is characterized by having a quantity generation circuit 7 and an addition point 23).

The present invention according to claim 1 focuses on repeatedly scanning the same area of the sample W at the time of capturing a moving image, and performs the next scanning based on the image data obtained by the previous scanning. The operation amount to the z-direction drive mechanisms 21 and 22 is generated in a foreseeable manner, thereby substantially improving the followability of the system.

That is, there are various possible changes in the surface of the sample over time. Unless the scanning area is completely changed instantaneously, for example, a fine concavo-convex pattern or the like may be used. It is considered that there are many common or similar parts in at least a part of the image data obtained in (1) and the image data to be obtained next time. Therefore, when a moving image is collected by repeatedly scanning the same area, the z-direction driving mechanism 21 and the next scanning in the next scanning are performed by the image data obtained up to the previous time rather than the z-direction control by the simple servo control system. Foreseeing the operation amount to be supplied to 22 and superimposing it on the operation amount signal of the servo control system 20, even if the same scanning speed is set, there is a high probability that the deviation between the set value of the specific physical amount and the detection value decreases. As a result, the z-direction driving mechanisms 21 and 22 more faithfully
The probability of following the surface is increased, and highly accurate image information can be obtained at a relatively high scanning speed.

On the other hand, in order to achieve the second object, the invention according to claim 2 is directed to an embodiment of the present invention, as shown in FIG. 2. An xy-direction scanning system 10 for scanning 2, a probe 1 and a sample W
Are provided with z-direction driving mechanisms 21 and 22 for driving the probe 2 or the sample W in the z direction in which the probe 2 approaches / separates and the servo control system 20 thereof, while relatively scanning the probe 2 and the sample W in the xy directions. , A specific physical quantity acting between them is detected, and the z-direction drive mechanism 21 is controlled so that the detected value coincides with the set value. In a scanning probe microscope that obtains image data and displays the image data on a display unit 6, a storage unit 8 that stores a deviation between a set value of the physical quantity and a detected value during scanning, and the image based on the content of the storage unit 8. It is characterized by having image correction means 9 for correcting data.

According to the second aspect of the present invention, the deviation between the set value of the physical quantity and the detected value during scanning is sequentially stored, and the sample image caused by the decrease in the followability of the z-direction driving mechanisms 21 and 22 is stored. By correcting the decrease in accuracy of the z-direction information according to the magnitude of the deviation, it is possible to obtain a high-accuracy image even when scanning at a relatively high speed.

That is, the followability of the z-direction drive mechanisms 21 and 22 operated by the operation amount signal from the servo control system 20 to the sample surface is different from the detection value in the servo control system 20 when the response of the system is constant. There is a high correlation between the magnitude of the deviation from the set value. Therefore, the image data obtained at a high scanning speed is converted into high-precision data by storing the instantaneous deviation during scanning and correcting each pixel of the image data according to the magnitude of the deviation. be able to. The relationship between the magnitude of the deviation and the correction amount is determined, for example, by examining in advance the dependence of the specific physical quantity on the distance between the probe and the sample. It can be set in advance by empirically determining the characteristics of the system related to the state of the sample surface by performing a measurement or the like.

According to a third aspect of the present invention, as another configuration for achieving the second object, as shown in FIG. An xy direction scanning system 100 for scanning the sample W or the probe 2
And z-direction driving mechanisms 21 and 22 for driving the probe or the sample in the z-direction in which the probe 2 and the sample W approach / separate from each other, and a servo control system 20 for moving the probe 1 and the sample W in the xy directions. While scanning relatively, a specific physical quantity acting between them is detected, and the z-direction drive mechanism 21 is controlled so that the detected value matches the set value.
In a scanning probe microscope that obtains image data of the sample surface from the manipulated variables given to the operator and displays the image data on the display 6, the deviation between the set value of the physical quantity and the detected value falls within a predetermined range during the scanning process. And an xy direction scanning system 100 executes a scan step for the next pixel only when it is determined that the deviation is within a predetermined range. It is characterized by being constituted in.

According to the third aspect of the present invention, the scanning speed is substantially changed at any time according to the surface condition of the sample W, so that the followability of the z-direction driving mechanisms 21 and 22 to the sample surface is ensured. The scanning is performed while increasing the average scanning speed to obtain a highly accurate image.

That is, the step of scanning the next pixel of the xy direction scanning system 100 is not executed until the deviation between the detected value and the set value falls within the predetermined range. In other words, the deviation is within the predetermined range. By performing the scanning step to the next pixel after confirming that the current value is within the range, the physical quantity such as the tunnel current or the atomic force is always set to the set value regardless of the surface state of the sample and the set scanning speed. The z-direction control is performed so as to fall within a predetermined range, and a highly accurate sample surface image is obtained.

[0017]

FIG. 1 is a block diagram showing an embodiment in which the invention according to claim 1 is applied to a scanning tunneling microscope. Both a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration are shown. FIG.

A sample W is placed on a sample table 1, and a probe 2 is disposed opposite to the sample W. The sample stage 1 is in a two-dimensional direction along the surface of the sample W with respect to the probe 2 by an xy direction scanning system 10 including an xy direction driving unit 11 using a piezoelectric element as an actuator and an xy direction scanning circuit 12. x
A scan is provided in the y direction.

The probe 2 is made up of a sample by a z-direction drive unit 21 also using a piezoelectric element as an actuator, a servo control system 20 for controlling the z-direction drive unit 21 and a preview operation amount signal generation unit 7 which will be described later. It is moved in the z direction, which is a direction approaching / separating from the table 1.

A predetermined potential difference is given between the probe 2 and the sample W by the tunnel voltage power supply 3, and a tunnel current flowing between the probe 2 and the sample W due to the potential difference is
After being amplified by the tunnel current amplifying circuit 4, it is taken into the servo control system 20 as a detected tunnel current value.

The servo control system 20 includes a piezoelectric driver 22 for supplying a driving voltage signal to the piezoelectric element of the z-direction driving unit 21, and an addition point 23 for the piezoelectric driver 22.
And a tunnel current setting unit 25 for supplying a tunnel current setting value to the controller 24 as main components. The controller 24 includes a tunnel current setting value and a tunnel current amplification value. The deviation ε from the detected value of the tunnel current from the circuit 4 is input, an operation amount signal corresponding to the deviation ε is generated, and supplied to the piezoelectric driver 22 through the addition point 23.

The operation amount signal supplied to the piezoelectric driver 22 is stored in the image memory 5 after being digitized by an AD converter (not shown). In the image memory 5,
At the same time, the scan data of the sample stage 1 in the x and y directions by the xy direction scanning system 10 is also supplied, and the operation amount signal is stored in the image memory 5 in association with the xy scan data. The sample W is stored in the image memory 5.
Is stored in the z direction operation amount data of the probe 2 at each scanning position. The contents of this image memory 5 are
An image is formed by the CRT 6 and becomes an STM image of the sample W.

The feature of this embodiment is that the operation amount signal from the controller 24 and the preview operation amount signal generating section 7 are added by the addition point 23, and the added signal is sent to the piezoelectric driver 22. On the other hand, it is supplied as an operation amount signal.

The foreseeable manipulated variable signal generator 7 is provided with an image memory 5
This has a function of predictively generating and outputting the operation amount to be supplied next time using the operation amount signal at the previous scanning position stored in the previous operation, in other words, using the previous image data. Then, the same operation amount as the momentary operation amount in the previous scan is applied to the piezoelectric driver 22 in the next scan.
, A preview manipulated variable signal is generated. Specifically, the previous operation amount signal stored in the image memory 5 is read out, and the same z-direction operation amount is obtained at the same xy scanning position by using the xy scanning signal at the next scanning as the timing signal. A foreseeable manipulated variable signal is generated so as to be operated.
It should be noted that it is desirable to give the preview operation amount signal in accordance with the amount of change because bias drift in the z direction is likely to occur.

In the above embodiment of the present invention, the reason why the preview operation amount signal from the preview operation amount signal generator 7 is added to the operation amount signal from the controller 24 at the addition point 23 is that the sample W This is only in the case where a moving image is obtained by repeatedly measuring the same area. Hereinafter, an operation at the time of collecting such a moving image will be described.

When the same area of the sample W is repeatedly measured, if there is no change in the surface state of the sample W and no disturbance is present, the same operation amount as the previous time is given at each scanning position. As a result, the deviation ε does not occur because the set value from the tunnel current setting unit 25 and the detection value from the tunnel current amplifier circuit 4 match, and the same image data as the previous time is obtained. Should be done. When the surface state of the sample W changes, or when some kind of disturbance is present, by supplying the above-mentioned preview scanning amount signal, only the part where the surface state changes or only the part affected by the disturbance is provided. Deviation ε during scanning
Occurs.

When data is not stored in the image memory 5 in the first measurement when the same area of the sample W is repeatedly measured, the operation amount signal from the controller 24 of the servo control system 20 is transmitted to the piezoelectric driver 22. Is supplied, and the same measurement as that of the conventional scanning tunneling microscope is performed. In the second and subsequent measurements, an operation amount equivalent to the previous operation amount stored in the image memory 5 is supplied to the addition point 23 at each scanning position. When the surface state of the sample W has changed from the previous state, the deviation ε occurs only when the probe 2 scans the changed portion when the influence of the disturbance is removed, and is supplied to the piezoelectric driver 22. The operation amount signal changes with respect to the previous operation, and the image data changes, but no deviation ε occurs during scanning of other areas. Therefore, the addition point 23 and the preview operation amount signal generation unit 7
As in the case of using the normal servo control system 20 without
Compared to a case where the deviation ε from the detected value of the tunnel current with respect to the constant tunnel current set value is operated to cancel the deviation ε, the deviation ε that appears in this embodiment is
Is more likely to be small, and the followability of the probe 2 to the surface of the sample W is better when the scanning speed is the same, and when the same followability is sufficient, the scanning speed is higher. It is possible to increase the speed.

Here, the method of generating the preview scanning amount signal is as follows.
As described above, in addition to obtaining the same operation amount as the previous operation amount at the same scanning position, the deviation amount at the time of the previous scan and the dynamic characteristics of the probe are added to the previous operation amount. Modifications such as a method of giving an operation amount or obtaining an average value of several operation amounts in the past are possible.

Further, by adding a function of displaying a difference image obtained by performing a difference operation between the same pixels on the time-series image in the same region obtained as described above, the sample in the measurement region can be obtained. Recognition of the change area on the surface is facilitated. In addition, providing a function of changing the scanning area to an arbitrary area designated by the operator on a screen displaying such a difference image is intended to facilitate the work of analyzing a sample by collecting a moving image. Extremely effective.

Next, an embodiment of the invention according to claim 2 will be described. FIG. 2 is a configuration diagram in which the invention is applied to a scanning tunneling microscope, and shows a schematic diagram illustrating a mechanical configuration and a block diagram illustrating an electrical configuration.

In FIG. 2, members having the same functions as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. The feature of this embodiment is that the deviation ε between the tunnel current set value and the detected tunnel current value of the servo control system 20 that controls the driving of the probe 2 in the z direction.
Is supplied to the controller 24 and simultaneously stored in the deviation memory 8. Each pixel data in the image memory 5 is corrected by the image correction unit 9 using the contents of the deviation memory 8. This is the point displayed on the CRT 6.

When the constant of the servo control system 20 is constant, the magnitude of the instantaneous deviation ε during scanning has a strong relationship with the followability of the probe 2 in the z direction with respect to the unevenness of the surface of the sample W. , The greater the deviation ε, the worse the tracking performance. Therefore, the relationship between the deviation ε and the followability is experimentally examined in advance, the dependence of the tunnel current on the distance between the probe 2 and the sample W is examined, or the scanning speed of the same sample is sufficiently reduced. Then, based on the image data obtained by maintaining the deviation ε at or near 0,
If a correction coefficient representing the relationship between the amount of the deviation ε and the amount of image correction is obtained from the magnitude of the deviation ε and the image data when the same area is scanned at a higher scanning speed, the correction can be performed. Image data can be corrected using the coefficient and the instantaneous deviation ε.

That is, the deviation memory 8 stores the instantaneous deviation ε together with the xy-direction scanning signal. Therefore, the deviation memory 8 stores the deviation ε corresponding to each pixel data stored in the image memory 5. Is stored when the pixel data is obtained. By using the deviation ε of each pixel and a correction coefficient obtained in advance, pixel data obtained at a relatively high scanning speed can be substantially maintained at a deviation ε of 0 or near. Pixel data that can be obtained at a scanning speed that can be obtained can be corrected, and a high-precision STM image can be obtained at a high scanning speed.

In the above embodiment, the deviation memory 8
Even if a function of displaying the instantaneous deviation ε stored in the image together with the image is provided, it can be a measure of the reliability of the image. next,
An embodiment of the invention according to claim 3 will be described. FIG.
FIG. 3 is a configuration diagram showing both a schematic diagram showing the mechanical configuration and a block diagram showing the electrical configuration. In FIG. 3, members having the same functions as those shown in FIGS. Are given the same reference numerals and their detailed description is omitted.

The feature of this embodiment is that the deviation ε between the tunnel current setting value and the tunnel current detection value of the servo control system 20 that controls the driving of the probe 2 in the z direction is within a predetermined range. The xy direction scanning system 100 is provided only when the deviation amount determination unit 101 determines that the deviation ε is within a predetermined range. The feature is that step scanning is performed on pixels.

That is, as shown in the flowchart of FIG. 4 showing the operation at the time of scanning in this embodiment, the deviation amount discriminating unit 101 takes in the deviation ε every predetermined minute interval, and the value of the deviation ε is It is determined whether it is within a predetermined range. x of the xy direction scanning system 100
The y-direction scanning circuit 120 continuously outputs a scanning command in the x-direction to the xy-direction driving unit 11 only when the deviation ε falls within a predetermined range. In the state where the deviation ε is not settled, the deviation ε is fetched at the above-mentioned interval while the scanning is stopped without giving a scan command, and time is waited until the deviation ε falls within a predetermined range.

Accordingly, the scanning voltage signal supplied from the xy-direction scanning circuit 120 to the xy-direction driving unit 11 in this example is, as illustrated in FIG.
The presence or absence of step scanning is repeated as appropriate according to the surface condition of the device, and the difference is that the voltage signal for normal scanning in this type of apparatus constantly changes as shown in FIG. It will be.

According to this embodiment, the xy-direction scanning system 100 performs step scanning to the next pixel after confirming that the deviation ε is substantially within a predetermined range. In other words, scanning is performed after assuring that the deviation ε is within a predetermined range, and high-precision image data is accumulated in the image memory 5. Therefore, even if the initial scanning speed is set to a relatively high speed, a high-precision STM image can be obtained while the scanning speed automatically changes according to the surface state of the sample W.

In each of the above embodiments, an example in which each invention is applied to a scanning tunnel microscope has been described.
Of course, each invention can be equally applied to a scanning probe microscope that detects other physical quantities obtained by the interaction between the probe and the sample, such as an atomic force microscope.

[0040]

As described above, according to the first aspect of the present invention, the z direction (approach / proximity between the probe and the sample) in the next scan is determined using the image data obtained by the previous scan. Since the z-direction drive mechanism is controlled by predictively generating the operation amount in the (separation direction), a normal servo control system is used when repeatedly measuring the same area of the sample as when collecting a moving image. Compared to the case where the specific physical quantity is kept constant by feedback control, the deviation amount is more likely to be small, and the followability between the probe and the sample in the z direction is improved. As a result, high accuracy is achieved by a relatively high scanning speed. Is obtained.

According to the second aspect of the present invention, z
The deviation between the set value and the detected value of the specific physical quantity in the servo control system that controls the direction is stored every moment, and the image data at each scanning position is corrected using the stored contents, so that the deviation amount becomes large. Even if the scanning speed is set to a very high scanning speed, a high-precision image can be obtained.

According to the third aspect of the present invention, z
Scanning in the xy direction is step-scanned to the next pixel only when the deviation between the set value and the detected value of the specific physical quantity in the servo control system that controls the direction is within a predetermined range. Because it is configured to
Since the magnitude of the deviation is substantially guaranteed to be within a predetermined range, the image data is taken in while automatically changing the scanning speed according to the surface condition of the sample, etc.
A high-precision image can be obtained at a scan speed without waste.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the invention according to claim 1,
Diagram showing both a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration.

FIG. 2 is a configuration diagram of an embodiment of the invention according to claim 2,
Diagram showing both a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration.

FIG. 3 is a configuration diagram of an embodiment of the invention according to claim 3,
Diagram showing both a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration.

FIG. 4 is a flowchart showing the operation of the embodiment of FIG. 3;

FIG. 5 is an explanatory diagram of an example of a scanning voltage signal waveform output from the xy direction scanning circuit 120 according to the embodiment of FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sample stage 10 xy-direction scanning system 11 xy-direction driving unit 12, 120 xy-direction scanning circuit 2 probe 20 servo control system 21 z-direction driving unit 22 piezoelectric driver 23 addition point 24 controller 25 tunnel current setting unit 3 tunnel voltage power supply 4 Tunnel current amplifier circuit 5 Image memory 6 CRT 7 Preview operation amount signal generation unit 8 Deviation memory 9 Image correction unit 101 Deviation amount discrimination unit W Sample

Claims (3)

[Claims] 1. An xy-direction scanning system that scans a sample or a probe in an xy direction along a surface of the sample, and a z-direction drive that drives the probe or the sample in a z-direction in which the probe approaches / separates from the sample. A mechanism and its servo control system are provided, and while the probe and the sample are relatively scanned in the xy directions, a z-direction drive mechanism is controlled so that a specific physical quantity acting between them is constant, and the z-direction driving mechanism is controlled. In a scanning probe microscope that obtains image data of the sample surface from the amount of operation given to the drive mechanism and displays it on the display, based on the image data of the sample surface already collected, the operation to be given to the z-direction drive mechanism at the next scan A scanning probe microscope comprising means for predictively generating an amount and superimposing the amount on the operation amount signal of the servo control system. 2. An xy-direction scanning system for scanning the sample or the probe in the xy direction along the surface of the sample, and a z-direction drive for driving the probe or the sample in the z direction where the probe approaches / separates from the sample. A mechanism and its servo control system are provided, and while scanning the probe and the sample relatively in the xy directions, a specific physical quantity acting between them is detected, and z is set so that the detected value matches the set value. A scanning probe microscope that controls a directional driving mechanism, obtains image data of a sample surface from an operation amount given to the z-direction driving mechanism, and displays the image data on a display unit. A scanning probe microscope, comprising: storage means for storing a deviation; and image correction means for correcting the image data based on the contents of the storage means. 3. An xy-direction scanning system for scanning the sample or the probe in the xy direction along the surface of the sample, and a z-direction drive for driving the probe or the sample in the z direction where the probe approaches / separates from the sample. A mechanism and its servo control system are provided, and while scanning the probe and the sample relatively in the xy directions, a specific physical quantity acting between them is detected, and z is set so that the detected value matches the set value. A scanning probe microscope that controls a directional drive mechanism, obtains image data of the sample surface from an operation amount given to the z-direction drive mechanism, and displays the image data on a display device. In addition to the determination means for determining whether the deviation is within a predetermined range set in advance, the xy-direction scanning system is provided only when it is determined that the deviation is within the predetermined range. To the next pixel A scanning probe microscope configured to perform a scanning step.