JPH04157302A - Scanning tunneling microscope - Google Patents

Abstract

PURPOSE:To correctly measure the state of the surface roughness of a sample by the atomic level by driving an actuator in the X-axis or Y-axis direction which is provided orthogonal to an inclining direction of the sample surface seen from a probe. CONSTITUTION:Actuators 4, 5 in the X-axis, Y-axis directions are driven when a voltage for scanning a probe is applied. Since the Y-axis actuator 5 is directed in an inclining direction of a sample 2 seen from a probe 1, the probe l is moved in a direction not to sense the inclination of the surface of the sample 2 if the X-axis actuator 4 directed orthogonal to the actuator 5 is driven. Accordingly, the scanning data of the image is obtained in this moving direction of the probe. Since there is only a small displacement corresponding to the roughness of the surface of the sample 2 by the atomic level, the change of the signal resulting from tone inclination of the surface of the sample 2 is not brought about. Therefore, the surface state of the sample can be correctly measured by the atomic level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a scanning tunneling microscope used for surface analysis of a sample.

Conventional technology A scanning tunneling microscope is configured to measure the state of a sample surface by measuring the tunneling current flowing between the surface of the sample to be observed and a probe facing the sample surface. ing. The conventional scanning tunneling microscope described above will be described below with reference to the drawings.

Figure 4 (al, (b), (C1 shows a conventional scanning tunneling microscope, Figure 4 (al is a plan view of the main part, Figure 4 f)
bl is a front view of the main part, and FIG. 4 (C1 is a side view of the main part).

In Fig. 4 (Tal to fc), 1 is a probe for measuring the surface condition of the sample 2, and 3 is a support made of insulating material that supports the probe 1 on the upper surface so as to face the surface of the sample 2. stand,
4 and 5 are X points perpendicular to the probe 1 along the in-plane direction of the sample 2.
Actuators 6 and 7 are made of piezoelectric elements to move the probe 1 in the axial and Y-axis directions, and coarse movement actuators and fine movement actuators are made of piezoelectric elements that move the probe 1 in the X-axis direction, which is almost perpendicular to the surface of the sample 2. It is an actuator for
The inner end of the actuator 4 in the axial direction, the inner end of the actuator 5 in the Y-axis direction, the inner end of the actuator 5 in the X-axis direction, and the upper end of the fine movement actuator 6 in the X-axis direction are joined to the support base 3, The outer end of the actuator 4 in the X-axis direction, the outer end of the actuator 5 in the Y-axis direction, and the lower end of the coarse movement actuator 6 in the Z-axis direction are joined to a frame (not shown). Reference numeral 8 denotes a support member, which supports the sample 2 in a dotted manner to make it less susceptible to vibrations.

Each of these members is housed in a vacuum container (not shown). Then, the actuator 4 in the X-axis direction and the actuator 5 in the Y-axis direction move in the direction of inclination of the surface of the sample 2 as seen from the probe 1, that is, in the direction in which the axial direction of the probe 1 deviates from the normal direction of the surface of the sample 2. (Journal of Vacuum Science and Technology: Journal of Vacuum 5ci)
ence and Technology＾, Vol.
ume 8. No. 1. Published in 1990, 234 pages).

The operation of the above configuration will be described below.

By driving the actuators 4 and 5 in the X-axis direction and the Y-axis direction by applying voltage, the probe 1 is caused to scan the surface of the sample 2 in the in-plane direction. At this time, the fine movement actuator 7 in the Z-axis direction is driven by applying a control voltage to move the probe 1.
The distance of the probe 1 from the surface of the sample 2 is controlled so that the value of the tunnel current flowing between the probe 1 and the sample 2 is constant. This control amount corresponds to the amount of unevenness on the surface of the sample 2. Since the tunneling current changes extremely sensitively to this distance, extremely minute irregularities on the surface of the sample 2 can be observed as large changes in the current. In this way, the probe 1 approaches the surface of the sample 2 as much as possible, and the tunnel current is scanned in the in-plane direction of the surface of the sample 2 under constant control. If the surface of the sample 20 is uneven, the probe 1 moves along the unevenness, and when a two-dimensional image is drawn by the amount of movement, the unevenness of atoms on the surface of the sample 2 is displayed.

Problems to be Solved by the Invention However, in the conventional scanning tunneling microscope described above, the probe 1
The information on the surface of the sample 2 obtained by scanning the surface of the sample 2 included not only the atomic level unevenness of the surface but also the inclination of the surface of the sample 2 with respect to the probe 1.

The situation will be explained with reference to FIGS. 3 and 5.

FIG. 3 shows the locus of the probe 1 scanned over the surface of the sample 2. By driving the actuator 4 in the X-axis direction and the actuator 5 in the Y-axis direction by applying a scanning voltage, the probe 1 located at the coordinates X^ and Y^ is moved to the surface of the sample 2 at time t^. Coordinates XB, Y at time t in the inward direction
After passing through the position ^, the coordinates Xa at time is are scanned to the position 'f8 (However, the X-axis and Y-axis are set in the driving directions of the actuator 4 in the X-axis direction and the actuator 5 in the Y-axis direction. ). At this time, the fine and coarse movement actuators 7 and 6 in the Z-axis direction operate as shown in FIGS. In order to achieve large and stable displacements, we use an actuator that cannot handle high-speed changes.On the other hand, we use an actuator for fine movement that can handle high-speed changes, although the amount of displacement that can be controlled is small. and the third
By performing the scanning shown in the figure, the fine movement actuator 7 moves from t^ to 1C, which reflects the unevenness of atoms on the surface of the sample 2.
At the same time, it also shows a -like slope displacement ΔV between t^ and tC, which corresponds to the slope of the surface of the sample 2. However, since the coarse movement actuator 6 cannot respond to high-speed changes as described above, it cannot follow this inclination displacement Δ■. As the scanning range becomes wider, the change in the signal obtained by the inclination of the surface of the sample 2 far exceeds the change in the signal obtained by the unevenness of the surface at the atomic level. For example, when reading the displacement amount of the fine movement actuator 7 with a 12-bit AD converter as image data of a scanning tunneling microscope, the change in ΔV is read with a resolution of 12 bits, but when wide-area scanning is performed, the change in ΔV>>ΔW. As a result, the resolution for reading changes in the data ΔW, which is originally intended to be obtained, deteriorates. In this way, there is a problem in that the originally desired information about the atomic level unevenness on the surface of the sample 2 is buried by the information about the inclination of the surface of the sample 2.

The present invention solves the conventional problems as described above, and can suppress changes in the signal obtained due to the tilt of the sample surface due to wide-range scanning, and therefore,
The object of the present invention is to provide a scanning tunneling microscope that can accurately measure the state of unevenness at the atomic level on the surface of a sample.

Means for Solving the Problems The technical solution of the present invention for achieving the above object is as follows:
A probe arranged to face the surface of a sample to be observed, an actuator that moves and scans the probe in the X-axis direction and the Y-axis direction orthogonal to each other in the in-plane direction of the sample, and the above-mentioned probe. an actuator that scans the probe by making coarse and fine movements in the Z-axis direction perpendicular to the surface of the sample, and one of the actuators in the X-axis direction and the Y-axis direction moves the probe The probe is configured to move in the direction of inclination of the sample surface as seen from the probe.

Therefore, according to the present invention, by driving the actuator in the X-axis direction or the Y-axis direction, which is arranged in a direction perpendicular to the inclination direction of the sample surface as seen from the probe,
The probe moves in a direction that does not feel the slope of the sample surface, so
By obtaining the scanning line data of the image in this direction, the scanning line data mostly corresponds to the atomic level unevenness of the sample surface, and no signal change occurs due to the inclination of the sample surface. By driving the actuator in the Y-axis or X-axis direction to obtain the next scanning line data, the probe moves in the direction of the inclination of the sample surface, and the signal obtained changes depending on the inclination. The change is absorbed by the coarse movement actuator in the Z-axis direction. In this way, the coarse movement actuator in the Z-axis direction is responsible for tracking the inclination of the sample surface, and by configuring the image from the drive voltage of the fine movement actuator in the Z-axis direction, changes in the signal obtained due to the inclination of the sample surface can be detected. can be kept small.

゛Example Hereinafter, an example of the present invention will be described with reference to the drawings.

Figures 1 (a), (b), and (C) show a scanning tunneling microscope according to an embodiment of the present invention. Front view, Figure 1 (C1
is a side view of the main part.

In this embodiment, the same parts as those in the conventional example described above are given the same reference numerals, and the explanation thereof will be omitted, and the different configuration will be explained.

In this embodiment, as shown in FIGS. 1(a) to (C1), actuators 4 and 5 are used to scan the probe 1 in the X-axis and Y-axis directions perpendicular to the surface of the sample 2 in the in-plane direction. In the illustrated example, the actuator 5 in the Y-axis direction moves the probe 1 in the direction of inclination of the surface of the sample 2 when viewed from the probe 1, that is, in the direction in which the axial direction of the probe 1 is in the direction of the surface of the sample 2. Therefore, the remaining actuator 4 in the X-axis direction is configured to be able to move the probe 1 in a direction that does not feel the inclination of the surface of the sample 2.

The operation of the above configuration will be described below.

By driving the actuator 4 in the X-axis direction and the actuator 5 in the Y-axis direction by applying voltage for probe scanning, the coordinates X^, Y are set at time t^ as shown in FIG.
The probe 1 located at ^ is scanned in the in-plane direction of the surface of the sample 2 through the position of coordinates XB and Y^ at time ic to the position of coordinates XB and YB at time js. At this time, the actuators 7 and 6 for fine movement and coarse movement in the Z-axis direction operate as shown in FIG. Since the probe 1 faces in the direction of inclination of the surface, by driving the actuator 4 in the X-axis direction, which faces in the direction perpendicular to the direction, the probe 1 moves in a direction in which it does not feel the inclination of the surface of the sample 2. By obtaining scanning line data of the image at the position t^, the displacement position ΔV as shown in Fig. There is only a small wave-like displacement ΔW corresponding to the unevenness of the sample 2, and the signal does not change due to the inclination of the surface of the sample 2.After passing the position t, the actuator 5 in the Y-axis direction is moved to obtain the next scanning line data. By driving, the probe 1 moves in the direction of climbing (or descending) the slope of the surface of the sample 2, but the speed of this climbing is slower than that of the conventional example described above. Then, probe 1 reaches the fifth point at time t・-t^.
Although the height of the displacement ΔV shown in Figure (al) had to be climbed, in the present invention, the height can be sufficiently smaller than ΔV in the same time. This speed can be followed by the coarse movement actuator 6. Figure 5 (a) takes a long time to-t^.
Climb a height of ΔV' which roughly corresponds to Δ■ of l. In other words, by driving the fine movement actuator tough, the probe 1 can trace the atomic-level irregularities on the surface of the sample 2 to obtain an image, and it is possible to suppress changes in the signal obtained due to the slope of the surface of the sample 2. can.

Effects of the Invention As described above, according to the present invention, the
Alternatively, by driving the actuator in the Y-axis direction, the probe moves in a direction that does not feel the slope of the sample surface, so by obtaining the scanning line data of the image in this direction, the scanning line data can be The surface of the bulk sample becomes uneven at the atomic level, and the signal changes as the sample surface tilts.

doesn't happen. By driving the actuator in the Y-axis or X-axis direction to obtain the next scanning line data, the probe moves in the direction of the inclination of the sample surface, and the signal obtained changes depending on the inclination. The change is absorbed by the coarse movement actuator in the Z-axis direction. In this way, the coarse movement actuator in the Z-axis direction is responsible for following the inclination of the sample surface, and the image is constructed from the drive voltage of the fine movement actuator in the Z-axis direction.
Changes in the signal obtained due to the inclination of the sample surface can be suppressed to a small level. Therefore, the state of unevenness at the atomic level on the sample surface can be accurately measured.

[Brief explanation of the drawing]

1(a), (bl, and (C) show a scanning tunneling microscope according to an embodiment of the present invention. FIG. 1 (al is a plan view of the main part, and FIG. 1 fbl is a front view of the main part. , Figure 1 (C1
2 is a side view of the main part, and FIG. 2 is an explanation of the operation of the actuator of the above embodiment. Figure 3 is an explanatory diagram showing the trajectory of the probe scanned on the surface of the sample, Figure 4 (a), (bl, (C)
1 shows a conventional scanning tunneling microscope, and Fig. 4(a)
is a plan view of the main part, FIG. 4(C) is a front view of the main part, FIG. 4(C) is a side view of the main part, and FIG. Figures (al is an explanatory diagram of the operation of the actuator for fine movement, and Figure 5 (bl is an explanatory diagram of the operation of the actuator for coarse movement. 1... Probe, 2... Sample, 4... Actuator (X-axis direction ), 5...actuator (Y-axis direction),
6... Coarse movement actuator (Z-axis direction), 7...
Fine movement actuator (Z-axis direction), 8... Support member. Figure 1 Figure 6Y Figure 4 (a) (b) (c)

Claims (1)

[Claims] A probe arranged to face the surface of a sample to be observed, an actuator that moves and scans the probe in the X-axis direction and the Y-axis direction orthogonal to each other in the in-plane direction of the sample, and the above-mentioned probe. an actuator that scans the probe by making coarse and fine movements in the Z-axis direction perpendicular to the surface of the sample, and one of the actuators in the X-axis direction and the Y-axis direction moves the probe A scanning tunneling microscope configured to move the probe in the direction of inclination of the sample surface as viewed from the probe.