JP3118108B2 - Scanning probe microscope and its measuring method - Google Patents

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 and a method for measuring the same, and more particularly, to controlling the movement of a probe by setting an appropriate scanning speed in accordance with the degree of unevenness of an area to be measured. The present invention relates to a scanning probe microscope and a measuring method therefor.

[0002]

2. Description of the Related Art In a scanning tunneling microscope (STM), a bias voltage is applied between a conductive probe and a sample, and the probe is brought closer to the surface of the sample to an atomic level distance (about 1 nm). A three-dimensional shape (irregular shape) of the sample surface is measured using a tunnel current sometimes flowing between the probe and the sample. When the probe is scanned and moved along the sample surface, the height of the probe relative to the sample surface is controlled so that the tunnel current flowing between the probe and the sample becomes a set constant value. By detecting the amount of displacement in the height direction, information on the uneven shape of the sample surface is obtained. The spatial position coordinates of the probe are such that the direction from the tip of the probe toward the root is the Z axis, and two directions included in a plane perpendicular to the Z axis and orthogonal to each other are the X axis and the Y axis, respectively. Is determined by the respective coordinate values of X, Y, and Z. Using the spatial coordinates, a bird's-eye view of the surface of the sample to be observed and a luminance modulation image with respect to the Z coordinates are displayed on the CRT monitor. The image obtained in this way reflects the information on the unevenness of the surface of the sample, and it is possible to analyze a fine shape on the surface of the sample by using this image.

In the above-mentioned STM, the sample stage surface on which the sample is placed is configured so that the axis direction of the probe is perpendicular to the sample stage surface. A predetermined area on the surface of the sample on the sample stage is scanned to measure the unevenness of the area.

[0004]

The conventional STM described above.
In such a case, in order to measure the fine irregularities on the atomic level of the sample surface, even a slight change in the measurement conditions may cause distortion in the measurement image. Therefore, when two-dimensional scanning for measurement is started in the measurement target area, it is desirable to complete the measurement in a short time by moving the probe at a scanning speed as high as possible.

On the other hand, in the two-dimensional scanning of the measurement area, the probe stops at a plurality of measurement points set in the measurement area, and the distance between the probe and the sample is kept constant while detecting and monitoring the tunnel current. Until the probe approaches the sample by moving in the Z-axis direction. After the approach operation is completed, the probe is moved to the next measurement point by horizontal movement in the XY plane, and the same approach operation is repeated. Perform a scanning operation. The scanning speed of the probe in two-dimensional scanning for measurement is basically determined by the approach speed based on the number of servo control repetitions at each measurement point. For this reason, if the scanning speed is set to a high speed state regardless of the unevenness of the sample surface, if the degree of unevenness of the sample surface changes suddenly, the probe collides with the sample surface, A defect that the sample is damaged occurs.

An object of the present invention has been made in view of the above problems, at the appropriate scan speed corresponding to the unevenness degree of the sample surface is scanned with the probe, scanning probe that enables highly accurate measurement with avoiding collision A microscope and a measuring method thereof are provided.

[0007]

SUMMARY OF THE INVENTION A scanning probe microscope according to the present invention is, for example, a scanning tunneling microscope or the like, a probe disposed close to a sample, and a probe moved with respect to the sample. Moving means for moving forward or backward, voltage applying means for applying a voltage for generating a tunnel current between the probe and the sample, measuring means for measuring the tunnel current, and a probe for keeping the tunnel current constant Control means for controlling the distance between the probe and the sample, scanning means for causing the probe to scan the surface of the sample, and data storage and processing means for recording and processing measurement data on the sample surface obtained using the probe. An unevenness degree estimating means for estimating the degree of unevenness of the sample surface based on data obtained by line scanning in a region to be measured, and setting an appropriate scanning speed based on the estimated unevenness degree Scan speed setting It has the means. In the above configuration, preferably, the unevenness degree estimating means is an altitude difference calculating means for obtaining a difference between adjacent data of the line data. In addition, in the measuring method of the scanning probe microscope according to the present invention, before performing the two-dimensional scanning for the measurement, the measurement target area is scanned in a line, and the measurement is performed using the data obtained by the line scanning. This is a measurement method of estimating the degree of unevenness of a target area, setting an optimal scanning speed in accordance with the estimated degree of unevenness, and performing measurement by performing two-dimensional scanning at an appropriate scanning speed in the measurement target area. . The linear scanning can be performed manually by an operator or automatically by a program incorporated in a microcomputer.

[0008]

According to the present invention, a linear scan is performed on the measurement target area before the original measurement, and the degree of unevenness of the measurement target area is estimated using data based on the linear scan. Generally, when regular unevenness is formed in a measurement target area, it is possible to estimate the degree of unevenness of the measurement target area by one or more line scans. The direction of the linear scanning can be arbitrarily selected. It is preferable that the measurement area can be covered as much as possible. For example, a difference between data, a change rate, a differential value, or the like is used for estimating the degree of unevenness of the measurement region. After the degree of unevenness is estimated, a scanning speed suitable for the degree of unevenness is set. To set an appropriate scanning speed,
It is desirable to use a scanning speed table. This is because the processing time can be reduced. By setting an appropriate scanning speed, a desired measurement can be performed in the two-dimensional scanning for the measurement, and the measurement can be performed quickly and with high accuracy without causing damage to the sample and the probe.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a configuration of a probe portion of the STM, a device configuration for controlling the position of the probe, and a configuration of a portion for detecting and processing measurement data obtained by the probe. The general configuration and operation of the main part of the STM will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a probe having conductivity. The tip of the probe 1 is sharply pointed and faces the surface of the sample 2. The probe 1 is attached to an intersection of rod-like fine-movement piezoelectric elements 3, 4, and 5 arranged at right angles to each other in a tripod head (not shown). The piezoelectric element 3 is an actuator related to the movement in the X-axis direction, the piezoelectric element 4 is an actuator related to the movement in the Y-axis direction, and the piezoelectric element 5 is an actuator related to the movement in the Z-axis direction. Further, the probe 1 can be brought close to the surface of the sample 2 to a distance where a required tunnel current is detected by a manual device (not shown) equipped with a tripod head, a stepping motor, or a piezoelectric element for coarse movement having a large stroke.

When a power source 6 is connected between the probe 1 and the sample 2, a required bias voltage is applied between them. In this state, the probe 1 is brought closer to the sample 2, and when the distance between the probe 1 and the sample 2 becomes a required minute distance, a tunnel current flows between them. A tunnel current flowing through the conductive probe 1 is detected by a tunnel current detection unit 7,
Thereafter, the detected tunnel current is converted into a distance between the probe 1 and the sample 2 by the tunnel current / distance converter 8. In the measurement of the normal uneven shape, in the scanning of the probe 1 in the measurement area, the detected tunnel current is predetermined in the axial position control of the probe 1 at each of a plurality of set measurement points. The height position of the probe 1 is controlled so as to be maintained at a constant value. In order to perform such control, the next-stage servo circuit 9 inputs the distance data output from the tunnel current / distance converter 8 and performs servo control so that the distance data always matches the internally set reference distance. Control is performed to control the amount of expansion and contraction of the piezoelectric element 5 in the Z-axis direction so that the distance between the probe and the sample is kept constant. The servo circuit 9 may be configured as an analog servo circuit, or may be configured as a digital servo circuit using a microcomputer. To realize high controllability, a digital servo circuit is desirable.

The scanning unit 10 moves the probe 1 on the measurement surface of the sample 2 for scanning in the X-axis and Y-axis directions. The scanning unit 10 includes the piezoelectric element 3 for the X-axis direction.
And a driving signal for expansion / contraction to the piezoelectric element 4 for the Y-axis direction.
Is performed two-dimensionally.

The piezoelectric elements 3, 4, 4 in the X, Y, and Z axial directions
With the movement of the probe 1 by 5, the load voltage of the piezoelectric elements 3, 4, and 5, ie, the amount of expansion and contraction of each piezoelectric element, is stored in the measurement data storage unit 11 as spatial coordinates. Measurement data storage unit 1
The position data of the probe 1 stored in 1 is appropriately extracted and supplied to the data processing unit 12. Data processing unit 12
Then, the image processing is performed on the uneven shape of the measurement surface of the sample 2, and the monitor unit 13 uses the data obtained by the image processing.
Then, an image of the surface unevenness of the sample 2 is displayed. Note that the monitor unit 13 as an output device is an example, and a printer, for example, may be used. The measurement data storage unit 11 and the data processing unit 12 are included in the calculation / control unit 14. The arithmetic and control unit 14 is configured by a CPU and a memory. Necessary functional means are realized by the arithmetic and control unit 14.
For example, reference numeral 15 denotes a scanning control unit.
Supplies a scanning control signal to the scanning unit 10 described above. The scanning control signal is a control signal for moving the probe 1 to each of a plurality of measurement points in the measurement area.

In the above configuration, when a tunnel current flows between the probe 1 and the sample 2, the distance between the probe 1 and the sample 2 is about 1 nm at the atomic level, and the unevenness of the sample surface is detected. Therefore, it is necessary to control the operation of the piezoelectric element 5 so as to keep this distance constant. The tunnel current is sensitive to a change in the distance between the probe and the sample, so that a high resolution can be obtained.

Based on the above STM, a series of operations can obtain information on the uneven shape of the measurement surface of the sample 2. In order to obtain this information, the movement for scanning of the probe 1 is stopped at each of a plurality of measurement points, that is, sampling points set in the measurement area, and the distance between the probe 1 and the surface of the sample 2 is reduced. Servo control for maintaining the constant is repeatedly performed by the servo circuit 9 a plurality of times. The number of servo control repetitions at each measurement point is
The overall measurement time, ie the scanning speed, is determined. The scanning speed is usually empirically determined by assuming a standard sample uneven surface, but when the surface of the sample 2 has severe unevenness, the measurement is performed at the standard scanning speed. Since the probe 1 cannot follow irregularities on the surface of the sample, it is necessary to increase the number of servo control repetitions. In other words, the number of servo control repetitions, that is, the scanning speed, for the Z-axis movement of the probe 1 at each measurement point is set to an appropriate one, preferably an optimum one, according to the degree of irregularities on the sample surface to be measured. Hopefully you can.

Therefore, in the STM of the present embodiment, as shown in FIG.
6 is provided. When the measurement target area is determined, the scanning speed setting unit 16 performs a two-dimensional scan for measurement.
A function of performing one or more line-shaped scans in a measurement area in an arbitrary direction to estimate the degree of unevenness of the measurement area and setting an appropriate scanning speed or preferably an optimal scanning speed according to the degree of unevenness. Have The line-shaped scanning before performing the two-dimensional scanning can be performed manually by an operator, or can be automated by incorporating it in a program. The specific configuration of the scanning speed setting unit 16 is shown in FIG.

The scanning speed setting section 16 is constituted by a line data extracting means 21, an unevenness estimating means 22, a scanning speed (repetition number) setting means 23, and a scanning speed (repetition number) table 24. The operation of the scanning speed setting unit 16 will be described with reference to the flowchart of FIG. Sample 2
When the measurement area is determined on the surface of the image, first, the scanning range and the number of measurement points in the range are set (step 3).
1). Next, in the measurement area, one or more linear scans are performed manually or automatically in an arbitrary direction before the two-dimensional scan for measurement is performed (step 32).
The measurement data obtained by the linear scanning is stored in the measurement data storage unit 11 as line data. The line data extracting means 21 reads out the line data from the measurement data storage unit 11 and sends it to the unevenness degree estimating means 22. The unevenness degree estimating means 22 estimates the unevenness degree based on the line data (step 33).

Various methods can be employed for estimating the degree of unevenness. For example, the degree of unevenness can be estimated by calculating a change state and a change ratio between adjacent data. When the change state of the data is used, for example, means for calculating a difference between adjacent data, that is, a difference in height (altitude difference) is provided, and when a change rate is used, a change rate calculating means is provided. Can be In addition, a method of estimating the degree of unevenness by obtaining a differential value as a continuous change rate is also conceivable. In this case, a differential value calculation means is provided.

The unevenness information estimated by the unevenness degree estimating means 22 is provided to a scanning speed setting means 23. The scanning speed setting means 23 selects an appropriate scanning speed according to the degree of unevenness from the scanning speed table 24 prepared in advance (step 34). The scanning speed determined in this way is provided from the scanning speed setting means 23 to the servo circuit 9. In the servo circuit 9, information on the given scanning speed is set as an element for determining the number of servo control repetitions at each measurement point. Then, two-dimensional scanning for measurement is performed by the servo circuit 9 in such a state (step 35).

In the above operation, it is desirable to use the absolute value of the difference (height difference) between adjacent data in the line data for estimating the degree of unevenness. The difference in height is used when the unevenness of the sample surface is severe, and becomes small when the unevenness is gentle. Then, it is desirable to determine the scanning speed by comparing the maximum value of the absolute values of the height differences with a plurality of preset reference values. The same can be applied to the case where a change ratio or a differential value is used.

Although the above embodiment has described the STM,
Needless to say, the present invention can be generally applied to a scanning probe microscope having a probe and configured to control the position of the probe in the axial direction by servo control.

[0021]

As is apparent from the above description, according to the present invention, the degree of unevenness of a region to be measured is checked in advance, an appropriate scanning speed is determined according to the degree of unevenness, and an appropriate scanning speed is determined. In order to perform two-dimensional scanning for measurement at, in addition to preventing damage due to collision between the probe and the sample,
Since the measurement can be completed in a time as short as allowable, high-precision measurement can be performed. In particular, when irregularities formed on the surface of a sample have regularity, the present invention can find the regularity in advance and is suitable for measurement of a sample having such a surface.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of a scanning tunnel microscope.

FIG. 2 is a block diagram showing an internal configuration of a scanning speed setting unit.

FIG. 3 is a flowchart illustrating an operation of a scanning speed setting unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Probe 2 ... Sample 3, 4, 5 ... Piezoelectric element 6 ... Power supply 7 ... Tunnel current detection part 8 ... Tunnel current / distance conversion part 9 ... Servo circuit 10 ... Scanning part 11 ... Measurement data storage part 12 ... Data processing Unit 13: Monitor unit 14: Calculation / control unit 15: Scan control unit 16: Scan speed setting unit 21: Line data extraction unit 22: Estimation unit of unevenness degree 23: Scan speed setting unit 24: Scan speed table

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01B ^7/ 00-7/34 102 G01B 21/00-21/32 G01N 37/00 H01J 37/28

Claims (3)

(57) [Claims] A probe arranged close to a sample, a moving unit for moving the probe forward or backward with respect to the sample, a control unit for controlling a distance between the probe and the sample, A scanning type probe comprising: a scanning unit for causing the probe to scan the surface of the sample; and a data recording and processing unit for recording and processing measurement data of the sample surface obtained using the probe.
In a needle microscope, unevenness degree estimating means for estimating the degree of unevenness of the sample surface based on data obtained by line-shaped scanning in an area to be measured, and scanning speed setting means for setting an appropriate scanning speed based on the degree of unevenness A scanning probe microscope comprising: 2. The scanning probe microscope according to claim 1, wherein said unevenness degree estimating means is means for estimating unevenness based on a difference between adjacent line data. Tip microscope. 3. Before performing a two-dimensional scan for measurement, scan the measurement target area in a line, and estimate the degree of unevenness of the measurement target area using data obtained by the linear scan. A scanning type wherein an appropriate scanning speed is set in accordance with the estimated degree of unevenness, and the two-dimensional scanning is performed at an appropriate scanning speed in the measurement target area.
Measurement method of probe microscope.