JP2633858B2 - Probe microscope - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a probe microscope, for example, a scanning tunneling microscope, and more particularly to, for example, a case where a tunneling current is first obtained in a scanning tunneling microscope. The present invention relates to a probe microscope devised for simplifying an operation for establishing an initial state of the probe microscope. Hereinafter, a scanning tunneling microscope will be described for simplicity.

[Conventional technology]

In order to observe a sample with a scanning tunneling electron microscope (STM), the distance between the probe and the sample surface must be close to the order of microns. As a means of bringing a sample closer to a probe, Science Magazine Vol. 15, No. 10, (1985)
The driving mechanism described on pages 14 to 15 can be mentioned. This drive mechanism is composed of a piezoelectric plate and three static fixing plates. Due to the expansion and contraction of the piezoelectric plate and the action of fixing and releasing by the electrostatic fixing plate, it is possible to move in a plane.
With this drive mechanism, the sample is brought closer to the probe, and stops moving when a tunnel current is detected.

In addition to the above drive mechanism, review of Scientific Instruments 56, 10 (1985) (Rev. Sc
i.instrum.56 (10). (1985).

When stopping these sample moving mechanisms, the operator confirms the detection of the tunnel current and immediately stops it manually. In order to avoid collision between the probe and the sample, the moving amount of one step is reduced or the moving distance is relaxed from the time when it is considered that the probe is appropriately approached.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technology, it is difficult to detect the tunnel current and stop the movement of the sample at the same time because the operation is performed by the operator. . In addition, the operator also requires meticulous attention and time, and the work load is heavy.

An object of the present invention is to automate the operation of stopping movement of a sample at the same time that a tunnel current is detected, in order to prevent the sample and probe from being damaged by collision between the sample and the probe and to bring them closer in a short time. is there.

[Means for solving the problem]

An object of the present invention is to provide a coarse movement mechanism which is a second driving means for moving a sample or a probe over a wide range, and a coarse movement mechanism control circuit for moving the coarse movement mechanism until a tunnel current is detected, and detecting and stopping the tunnel current at the same time. This is achieved by providing

[Action]

The coarse movement mechanism control circuit determines whether a tunnel current is detected based on a signal from the current detector. Only when no detection is made, the coarse movement mechanism is moved by a certain distance to bring the sample closer to the probe.

As described above, when the sample and the probe are brought close to each other, the coarse movement mechanism is operated so as to be within the operating distance of the first driving means, which is a fine movement mechanism, and the coarse movement mechanism is stopped simultaneously with the detection of the tunnel current. Thus, collision between the sample and the probe does not occur. The operator can obtain the tunnel current only by activating the coarse movement mechanism control circuit without paying any other attention.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to FIG.

On the table 13, there is a scanning mechanism 8 for scanning the sample 11 two-dimensionally in a plane parallel to the sample surface. The probe 10 facing the sample and the Z-axis piezoelectric element 9 that can hold the probe and adjust the distance between the probe and the sample are held by the coarse movement mechanism including the fixing mechanisms 5 and 4 and the piezoelectric element 3. Have been. A voltage is applied between the probe 10 and the sample 11, and a current detector 12 for detecting a tunnel current causes a tunnel current flowing between the probe and the sample to be kept constant by controlling the Z-axis piezoelectric element 9. A display mechanism 7 for displaying a tunneling electron microscope STM image or the like from the Z-axis control circuit 6, the scanning mechanism 8 and signals from the Z-axis control circuit 6.
A servo circuit 2 for controlling the piezoelectric element 3 so as to keep the tunnel current constant, and a coarse circuit for detecting the tunnel current signal from the Z-axis control circuit and controlling the servo circuit 2 and the fixing mechanisms 5 and 4. The control and display system is formed by the dynamic mechanism control circuit 1.

Next, the operation will be described. Consider a state in which the coarse movement mechanism is fixed on the table by the fixing mechanisms 5 and 4 in a state where the probe 10 and the sample 11 are separated by several mm.

A voltage is applied between the sample 11 and the probe 10 by the current detector 12 and at the same time, a certain set current is caused to flow between the probe 10 and the sample 11 by the function of the feedback function of the Z-axis control circuit 6. Then, a voltage is applied to the Z-axis piezoelectric element 9, and the probe approaches the sample. The amount of expansion and contraction of the Z-axis piezoelectric element is 100 nm,
No tunnel current or very low voltage field emission current flows, and the probe must be brought closer to the sample by the coarse movement mechanism.

In such a case, the coarse movement mechanism control circuit 1 operates. First, the fixing of the fixing mechanism 5 is released, and the servo circuit 2 is started. The servo circuit 2 extends the piezoelectric element 3 by a maximum of 10 μm. If no current is detected at this time, the fixing mechanism 5 is fixed and the fixing of the fixing mechanism 4 is released. Next, the servo circuit is turned off, the piezoelectric element 3 is contracted, and the fixing mechanism 4 is turned off.
Is fixed.

By repeating this series of operations, the coarse movement mechanism and the probe 10 supported by the coarse movement mechanism approach the sample in steps of 10 μm. Finally, the sample,
It stops when the current flowing between the probe 11 and the probe 10 is detected. FIG. 2 shows the cyclic operation of the coarse movement mechanism up to the stop.

Next, the voltage applied to the piezoelectric element 3 is fixed at an appropriate voltage, or the fixing mechanism 5 is fixed and the fixing mechanism 4 is released, and then the servo circuit is turned off. As a result, the coarse movement mechanism stops, and an image of the sample is obtained by the operation of the scanning mechanism 8, the Z-axis control circuit 6, and the like.

Due to the feedback caused by the current flowing between the probe and the sample, the response speed for driving the Z-axis piezoelectric element 9 and the piezoelectric element 3 is significantly slower in the latter than in the former. For example, when controlling the Z-axis piezoelectric element 9 at a speed of 0.5 msec, the piezoelectric element 3 is controlled at a speed of 50 msec. Thus, oscillation due to mutual interference can be avoided.
Alternatively, the feedback function on the Z-axis piezoelectric element side may be stopped until a tunnel current is generated.

According to this embodiment, an STM image can be obtained by the operation of the piezoelectric element 3 and the servo circuit 2. The usage range is
This is the case where the amount of expansion and contraction of the Z-axis piezoelectric element 9 exceeds 100 nm, and is suitable for observation of a sample at a low magnification and observation of a sample with severe irregularities.
After roughly observing the sample surface with the piezoelectric element 3, an arbitrary place may be observed with high resolution using the Z-axis piezoelectric element. However, at this time, it is necessary to adjust the response of the servo circuit 2 so as to be fast.

Further, according to this embodiment, the probe can be brought closer to the sample in steps larger than the amount of expansion and contraction of the Z-axis piezoelectric element 9.

FIG. 3 shows another embodiment for controlling the coarse movement mechanism. In this embodiment, the servo circuit 2 is always operating,
A switch 15 provided between the servo circuit and the piezoelectric element 3
Controls the piezoelectric element 3 to operate. In this case, as long as no tunnel current is detected, a certain voltage is output from the servo circuit, and the moment the switch 15 is turned on, the piezoelectric element 3 operates rapidly, and the probe and the sample may collide. There is. Therefore, a resistor 14 is added between the servo circuit and the piezoelectric element 3. The piezoelectric element 3 has an electrostatic capacitance C, and the piezoelectric element does not operate rapidly due to the action of the capacitance C and the resistor 14.

FIG. 4 shows an embodiment in which an electromagnetic system is used as the coarse movement mechanism. The sample 11 is mounted on a coarse movement mechanism including an electromagnetic coil 17 mounted below the table 13, a sample table 18 which moves smoothly on the table 12, and a permanent magnet 16 mounted on the lower part of the sample table 18. The magnetization direction of the permanent magnet 16 is perpendicular to the axis of the coil 17 and the plane of the table. By instantaneously passing a current through the electromagnetic coil 17, the sample stage moves by a certain distance. This is due to the interaction between the electromagnetic coil 17 and the permanent magnet 16 due to the magnetic field. The amount of movement for one step can be adjusted by the amount of current flowing through the coil. The amount of movement of one step is determined within a range smaller than the amount of expansion and contraction of the Z-axis piezoelectric element 9.

Until the Z-axis control circuit 6 detects a current flowing between the probe 10 and the sample 11, the coarse movement mechanism control circuit 1
Continue to give a current pulse. When the current is detected,
The coarse movement mechanism is automatically stopped by a signal from the axis control circuit.

FIG. 5 shows an embodiment of an STM having a coarse movement mechanism comprising a coater 19 and a differential screw 20.

By the rotation of the motor 19 and the function of the differential screw 20, the sample approaches the probe very little by little. At the same time as the detection of the tunnel current by the Z-axis control circuit 6, the motor 19 is stopped.
To avoid collision between the probe 10 and the sample 11, the Z-axis voltage element 9
The step motor 19 is controlled to be equal to or less than the amount of expansion and contraction. Alternatively, by moving the sample slowly, the distance the sample moves from the detection of the tunnel current to the actual stop of the sample is kept to be equal to or less than the amount of expansion and contraction of the Z-axis piezoelectric element 9.

In this embodiment, since the positioning accuracy of the coarse movement mechanism is lower than in the other embodiments, the amount of expansion and contraction of the Z-axis piezoelectric element needs to be at least several μm. About 10μm piezoelectric element and 100n
It is preferable to form a Z-axis control element with about m piezoelectric elements, and to add a field back mechanism to each of them.

〔The invention's effect〕

According to the present invention, only by activating the Z-axis control circuit and the coarse movement mechanism control circuit, the probe and the sample automatically come close to the distance where the tunnel current flows. Further, there is no danger that the probe will collide with the sample.

By providing the coarse motion mechanism with a field back function by a tunnel current, the amount of one movement can be increased. Therefore, the sample can be brought closer to the probe in a short time. Also, in the case of a worm-type coarse movement mechanism,
The danger of collision between the probe and the sample due to backlash when fixing or releasing fixing is also reduced.

[Brief description of the drawings]

1 and 3 to 5 are block diagrams showing an embodiment of the present invention, and FIG. 2 is a timing chart showing a control operation of the coarse movement mechanism. DESCRIPTION OF SYMBOLS 1 ... Coarse movement mechanism control circuit, 2 ... Servo circuit, 3 ... Piezoelectric element, 4 ... Fixing mechanism, 5 ... Fixing mechanism, 6 ... Z-axis control circuit, 7 ... Display mechanism, 8 ... Scanning mechanism, 9 ... Z
Axial piezoelectric element, 10 probe, 11 sample, 12 current detector, 13 base, 14 resistance, 15 switch, 16 permanent magnet, 17 electromagnetic coil, 18 …… Sample stand, 19 …… Motor, 20 …… Differential screw.

Claims (5)

(57) [Claims] 1. Means for detecting physical information between a probe having a sharply pointed tip and a sample surface of a sample disposed opposite to the probe, and the probe based on the physical information Servo means for controlling the distance between the probe and the sample surface; a scanning mechanism for moving the probe and the sample relative to each other two-dimensionally; and scanning the movement of the probe or the sample and the physical information. A probe microscope having display means for displaying information corresponding to information from a mechanism, another driving means for adjusting the distance between the probe and the sample surface in a stepwise manner in a wider moving range than the servo means, A means for outputting a signal for stopping the operation of the other driving means in accordance with the physical information. 2. The probe microscope according to claim 1, wherein said servo means is restrained from operating when another driving means is in an operating state. 3. The probe microscope according to claim 1, wherein the speed of the drive response of the other drive means is set to be slower than the speed of the drive response of the servo means. 4. The probe microscope according to claim 1, wherein physical information between the probe and the sample surface is a tunnel current. 5. The probe microscope according to claim 1, wherein an amount of step movement per operation by said another driving means is set smaller than a maximum amount of movement by said servo means.