JPH02203204A - Method for measuring scanning type tunnel microscope - Google Patents

Abstract

PURPOSE:To freely select a measurement area and a follow-up area within the movement range of a sample stage by measuring a sample by utilizing the movement of a probe by a fine adjusting element and the movement of the sample by the movement of the sample stage. CONSTITUTION:When the ruggedness of a surface is measured by STM(scanning type tunnel microscope) by using a tunnel current, the probe 1 is moved by the fine adjusting element 4 in three axial directions to the surface of the sample 2 and the sample 2 is moved by X, Y, and Z stages 8, 9, and 7 in the three axial directions. Consequently, the movement of the probe 1 by the element 4 and the movement of the sample 2 by the movement of the stages 7, 8, and 9 are both utilized. Therefore, the sample can be measured while the follow-up area of the probe 1 and the observation scan area of the sample 2 are expanded by the movement of the stages 7, 8, and 9 even outside the movable range of the element 7.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to measurement using a scanning tunneling microscope (STM) that uses tunneling current to measure surface irregularities and work functions, and is particularly applicable to measurements in large areas and , S on a highly uneven surface
This invention relates to a TM measurement method.

[Summary of the invention]

INDUSTRIAL APPLICABILITY The present invention is very useful industrially because it is possible to expand the measurement area and the follow-up area in the height direction by moving the probe relative to the sample on a stage together with a fine movement element.

[Conventional technology]

Figure 2 shows the principle of STM. When a bias voltage 3 is applied between the probe 1 and the sample 2 and the two are brought close to each other to about 1 μ, a current called a tunnel current flows. This current changes exponentially as the distance between the two changes. In order to keep this value constant, the probe 1 is moved up and down using a fine movement element 4 made of piezoelectric material equipped with electrodes for 3-axis drive that can be driven on 3 wheels, while the X and Y scanner 5 searches in the in-plane direction. Scan the needle l. By processing these signals with the computer 6, the irregularities on the surface of the sample 2 can be displayed.

Next, a conventionally used scanning method is shown in FIG. The probe 1 scans the surface of the sample 2 with the servo applied so that the tunneling current is constant, that is, the distance between the two is kept constant, and Z-axis information is sampled at each measurement position 7. . The Z-axis information and each measurement position 7 are taken in as a voltage applied to the fine movement element 4, and converted into a displacement amount from the voltage-displacement characteristic of the fine movement element 4.

FIG. 4 shows another conventional example. The probe 1 is moved up and down so that a predetermined tunneling current value is reached only at each measurement position, and Z-axis information (voltage applied to the fine movement element 4) at this point is sampled. At other points, that is, when moving between measurement points, the fine movement element 4 keeps the probe l in a raised state. This method has the advantage of being able to move quickly between measurement points when the measurement area is wide.

The conventional example shown above is that only the fine movement element is used for scanning the probe and tracking the sample surface, so it is not possible to measure objects larger than the movement area of the fine movement element or objects with large steps. . Note that for the Z-axis tracking area, the fifth
As shown in the figure, this amount could not be fully utilized. For example, as shown in the same figure, the surface 201 of the sample 2 is located at the center of the range l in which the fine movement element 4 can be expanded and contracted by the Z-axis servo.
Suppose that a certain tunnel current is flowing between the That is, the probe 1 moves up and down 1 from this state.
2/2 L will not be able to follow. Therefore 202
When scanning to the side, if the step difference is larger than 1/2, it becomes impossible to follow. Normally, when the sample 2 and the probe l are brought close to a region where a tunnel current flows (tunnel region), the surrounding unevenness is unknown, so as described above, the sample 2 and the probe l are brought to the center of the expansion/contraction range by the Z-axis servo. In other words, the floating voltage was controlled by adding a floor raising voltage (floating voltage) to the Z-axis servo voltage.

[Invention tries to solve! 18) As mentioned above, in the conventional method, the scanning area (area in the plane direction of the sample) and the tracking area (area in the height direction of the sample) cannot be made larger than the movable range of the fine movement element. was about 101 at maximum, and the follow-up area was only about a few. For this reason, it was not possible to perform positioning by zooming up from a larger area (for example, Equation 1) or to measure large differences in surface roughness or the like.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a measurement method in which a sample is measured using both movement of a probe using a fine movement element and movement of a sample by movement of a sample stage.

[Effect]

According to the method of the present invention, by moving the sample stage even outside the movable range of the fine movement element, measurement can be performed by enlarging the probe tracking area and the sample observation scanning area.

〔Example〕

FIG. 1 shows a flow diagram of this embodiment. Use STl to capture position information using a computer, etc. In Sr2, the sample is moved to that position using the X and Y stages. In Sr3, the probe and sample are brought closer using the Z-axis stage until a specified tunnel current flows (auto approach). At 5T4ST5, the amount of displacement of the Z-axis stage and the amount of Z-axis displacement of the fine movement element are taken in. Sr6 separates the sample probes from each other sufficiently compared to the unevenness of the sample, and Sr1 updates the measurement position. Repeat at Sr8 until measurement is completed at all measurement points. Thereafter, data processing is performed in ST9.

This means adding the displacement amount of the Z stage and the displacement amount due to the fine movement element to obtain the Z-axis displacement amount, and converting it into three-dimensional data together with the position data. Note that since the position data is set in advance, there is also a method in which the position data is not taken in for each measurement point.

FIG. 6 shows a list of transportation means used in this embodiment shown in FIG. 1.

-1, both the scanning area and the following area can be expanded to the maximum stage movement amount.

That is, the scanning area can be enlarged by moving the sample using the X and Y stages.

The following region will be explained using FIG. 7. Figure 7 1a
1 is a state in which the sample 2 and the probe 1 are separated from each other.

In this case, the maximum voltage that can be supplied is applied to the fine movement element 4 in order to bring the probe 1 closer to the sample 2 until a tunnel current flows by the Z-axis servo. In other words, the fine movement element 4 is in a fully extended state. Note that the sample 2 is supported by a Z-axis stage 7, an X-stage 8, and a Y-stage 9. The figure shows a state in which the sample 2 is brought close to the probe 1 on the Z stage 7, and a specified tunnel current is flowing.In this case, the amount of movement of the Z-axis stage is expressed as The amount of shrinkage is LP
The sample 2 and the probe 1 are separated by the zero-order Z-axis stage 7 or the fine movement element 4, which is denoted by I, and the sample 2 is moved to the next measurement point and approached in the same manner. In this state, if the amount of movement of the Z-axis stage is LZ2 and the amount of contraction of the fine movement element is LP2, the step difference in the sample is (LZ2-LZI) + (LP2-L
PI) ... (It can be found using 11.

In this way, even if the difference in the unevenness of the sample surface exceeds the moving range of the probe attached to the fine movement element, the uneven surface can be measured by moving the sample using the stage to within the movable range of the probe. be able to.

Magnetic 2 is a case in which when the unevenness of the sample is sufficiently large compared to the tracking area of the fine movement element, the first approach is performed with the Z-axis stage, and the movement and approach to each measurement point is performed only with the fine movement element. Since Z-axis movement can be performed by displacement of only the fine movement element, l
Measurements can be made faster than 1 hl. In this case, this example can be used if the unevenness of the sample is less than (fine movement element Z-axis movement amount - margin)/2. The margin is
This is the distance between the probe and the largest convex part of the sample, and is a value of 0 or more.

In -3, instead of moving the sample with X and Y stages, the probe is scanned with a fine movement element, and a Z-axis stage is also used as a tracking means. The scanning area is sufficient to be the scanning area of a fine movement element, but it is possible to measure a sample with large steps.

Since scanning is performed using a fine movement element, measurement can be performed at a higher speed than in the method described in Part 1.

In case 4, a fine movement element and an X and Y stage are used together as a scanning means, and the tracking method is the same as in case 1.

As shown in Fig. 8, the scanning means used in combination is one in which a fine movement element is used for the range of movement (dotted line), and the stage movement step amount is increased to reduce the number of stage movements (-dot chain IJil). be. The figure shows 50 lines per line.
This is an example where the maximum in-plane displacement of the fine movement element is 10-1 and the measurement point is 100/line, and the stage is 10
．． This is an example of moving in 5um steps. By using this means, the number of times the stage is moved can be reduced, allowing high-speed measurement. Note that when this method is used for x and y, the nonlinearity of the fine movement element can be corrected for each block scanned using the fine movement element as shown in FIG. As shown in FIG. 10, nonlinearity means that the voltage-displacement characteristic applied to the fine movement element is not linear, and measuring and correcting this characteristic is called nonlinearity correction.

A.5 uses the scanning method shown in Fish 4 and uses the tracking method described in Magnetic.2.

〔Effect of the invention〕

As explained above, according to this method, the measurement area and the tracking area can be freely selected within the stage movement range. For this reason, it is possible to scan a large area, find the place you want to measure, and then zoom in. In this case, it is effective to use it in combination with STM measurement, which is performed by scanning and tracking using only the fine movement element.

Furthermore, according to this method, it is possible to measure samples with large steps.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram showing this embodiment, FIG. 2 is an explanatory diagram showing the principle of STM, FIG. 3 is an explanatory diagram showing a scanning method according to the prior art, and FIG. 4 is an explanatory diagram showing another scanning method according to the prior art. FIG. 5 is an explanatory diagram showing the Z-axis tracking area, FIG. 6 is an explanatory diagram showing the moving means of this embodiment, FIG. 7 is an explanatory diagram of follow-up opening, and FIG. 8 is an explanatory diagram of the scanning means used together. FIG. 9 is an explanatory diagram showing a nonlinearity correction block, and FIG. 10 is an explanatory diagram showing nonlinearity. ■ ・Probe/sample 4 ・・Fine movement element/Z-axis stage or higher

Claims (4)

[Claims] (1) A scanning tunneling microscope measurement method consisting of a fine movement element that drives the probe in three axes relative to the sample surface and a stage that moves the sample in three axes. A measurement method for a scanning tunneling microscope characterized by measuring a sample by using a combination of movement and movement of the sample by movement of a sample stage. (2) The method for measuring a scanning tunneling microscope (STM) according to claim 1, characterized in that the sample is measured using a fine movement element in the height direction and a stage in the in-plane direction. (3) The method for measuring a scanning tunneling microscope according to claim 1, wherein the sample is measured using a fine movement element and a stage in the height direction and a stage in the in-plane direction. (4) The method for measuring a scanning tunneling microscope according to claim 1, wherein the sample is measured using a fine movement element and a stage in the height direction, and a fine movement element and a stage in the in-plane direction.