JPH0783650A - Measured data correction and measured angle error detection in scanning probe microscope - Google Patents

Abstract

PURPOSE:To provide a measured data correction method in the Z-axis direction and to provide a measurement accuracy detection method regarding a scanning probe microscope which measures the surface shape of a sample at an atomic measure. CONSTITUTION:A standard sample which is provided with a plurality of stages of X-Y plane parts having flat parts on X-Y planes is prepared. Differences in level on the X-Y plane parts are worked in advance to a prescribed value Hn and an angle is worked to 90 deg.. While the interval between the tip of a probe and the standard sample is kept at an atomic measure T, the probe is scanned from the X-Y plane part at the uppermost stage of the standard sample along its plane direction, and the length Hi of an oblique line and a measured difference hi in level are measured whenever the X-Y plane part comes down by one stage. Hi/hi gives a correction factor in the X-axis direction in positions of the individual X-Y plane parts, and cos<-1>(hi/ri) gives an angle error.

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 for measuring the surface shape and the like of a sample with an atomic scale using a sharp probe, and more particularly to a measurement data correction method and a measurement angle error detection method.

[0002]

2. Description of the Related Art In recent years, a scanning probe microscope utilizing the quantum effect has attracted attention as a means for observing the state of an object surface on an atomic scale. The scanning probe microscope includes a scanning tunneling microscope (STM), a scanning atomic force microscope (SAFM), a scanning magnetic force microscope (SMFM), etc., depending on the operation principle.

In both cases, a sharply pointed probe is brought very close to the sample surface, and at this time, the quantum effect that acts between the two is used to measure the surface irregularities and the like on an atomic scale. Among them, in STM, when two conductive objects are brought close to each other on an atomic scale, wave functions of electrons in a solid are superposed on each other, and a tunnel current flows when a voltage V lower than a work function φ is applied. It was used.

The distance at which the wave function is attenuated in the atmosphere outside the metal is 0.1 to 0.2 nm because φ = 1 to 5 eV for a clean surface of a normal metal. If metals of φ = 5 eV are brought close to 1 nm, the tunnel current value is about 1
The current value increases or decreases by one digit as the distance between the two increases or decreases by 0.1 nm. Therefore, if the Z coordinate of the probe is controlled while monitoring the tunnel current value to be constant, the uneven shape of the sample can be measured.

On the other hand, SAFM is suitable for observing the surface of a material having no electrical conductivity or the surface of an organic material on the nm scale. This utilizes a phenomenon in which a weak (about 10 ⁻⁹ N) attractive force due to a dispersive force is exerted at a long distance and a repulsive force is exerted at a short distance between nonpolar substance surfaces. Usually, in order to amplify and observe this weak force, the probe is connected to a leaf spring-shaped cantilever part, and the bending of the lever is detected by a displacement amount measurement system such as a piezoelectric element, and between them, The movement in the Z-axis direction is controlled so that a constant force acts, and the XY plane is scanned.

The SMFM is for detecting and measuring the mutual attractive force ( ^{-10 -10} N) acting between the ferromagnetic probe and the magnetic sample, and a decomposition state of 0.01-0.1 μm has been obtained. By the way, in these scanning probe microscopes, a coarse position drive system and a fine position drive system are provided as scanning means for observing the fine shape and the like of the sample surface. For the coarse position drive system, each of the Y-shaped tripods is electrostatically adsorbed and clamped on the holding table, and the attraction force is released and moved one by one, or the electric system drive method or lever A mechanical drive system is used to reduce the movement of the micrometer by utilizing.

The most important one is a fine position drive system that controls the movement of the sample stage or the probe on the order of nm. A standard configuration of the STM, which is a typical scanning probe microscope, is shown in FIG.

In FIG. 3, the fine movement device drive system comprises an X, Y and Z axis fine movement mechanism and an electric control system which are orthogonal to each other, and the fine movement mechanism is connected to the probe. The fine movement mechanism is usually formed by three orthogonal arms (X, Y, Z) made of piezoelectric ceramics such as PZT and electrodes provided on the surface thereof. By controlling the voltage applied to the fine movement mechanism in the Z-axis direction perpendicular to the sample stage, the distance between the sample and the probe can be kept constant. It is easy to fabricate an element that deforms about 1 nm with application of 1 V, and if raster scanning is performed in the XY plane, the shape of the sample surface is recorded in the wave memory as the voltage applied to the Z-axis fine movement element, and the microcomputer is used. Read in. Therefore, the surface shape of the sample can be magnified and displayed by outputting as an image a screen with the coordinate values of the voltages applied to the piezoelectric elements in the three axis directions. The resolution is about 100p in the XY direction.
It is 1 pm in the m and Z axis directions.

[0009]

The piezoelectric material used in the fine movement mechanism of the prior art described above has an undesirable phenomenon of non-linearity and hysteresis in the relationship between pressure and voltage. For example, the PZT described above makes a displacement of 1 nm / V in the linear range with respect to the applied voltage, and the enlarged scanning range is 1 μm.
It is a degree. However, in such a large amplitude operation, the non-linearity becomes remarkable. Further, there is a hysteresis of about 20%, and a long-term relaxation phenomenon called creeping after applying a large voltage is also observed. It is pointed out that this hysteresis changes depending on the voltage width and the voltage value at the time of start, and the locus is different. Therefore, in the STM and SAFM, the hysteresis curve of the piezoelectric element used for the fine movement mechanism is made into a mathematical expression in advance, and the parameters are applied to this mathematical expression to correct the scanning coordinates. As shown in FIG. 3, a test pattern (for position correction and angle correction) prepared in advance is incorporated in the XY writer scanner,
This is scanned in the preliminary measurement stage. From the ratio of the numerical value (x, y, ψ) obtained by actually measuring the test pattern and the true value (X, Y, Φ) of the test pattern, the correction coefficient of the device at the present time is calculated, and the actual measurement of the sample is performed. If applied to the stage, an accurate value will be obtained.

The same correction formula is applied to the Z-axis direction to correct the Z-axis fine movement measurement value, but there is no test pattern with a guaranteed true value in the Z-axis direction, that is, the height direction. However, there is a problem that the accuracy of the correction value cannot be confirmed. An object of the present invention is to provide a measurement data correction method and an accuracy detection method for a scanning probe microscope that can accurately provide the position of the probe in the Z-axis direction and the measurement accuracy.

[0011]

According to the present invention, a probe held in the Z-axis direction perpendicular to an XY plane sample stage is brought close to a sample surface mounted on the sample stage, and a piezoelectric element is used. In a scanning probe microscope that measures the surface shape of a sample by moving the sample table while keeping the distance between the surface and the tip of the probe constant, a known step _Hi (where i = 1) in the Z-axis direction. The first of the n XY planes having
A standard sample having a plurality of stages from the stage to the n-th stage is prepared, and the known step H _i (i = 1 to n) is measured by scanning the probe in the surface direction of each XY plane portion. Step h
_{i (i} = _1~n) and is stores Searching for the correction coefficient k _{i (i} = _1~n) to conform via the correction coefficient k _i, the correction coefficient k _{i (i} = 1 (1) to (n) disclose a method for correcting measurement data of a scanning probe microscope, which is configured to perform hysteresis correction of a piezoelectric element when measuring a material to be measured.

Further, according to the present invention, a probe held in the Z-axis direction perpendicular to the XY plane sample stage is brought close to the sample surface placed on the sample stage, and the surface and the probe are detected by a piezoelectric element. In a scanning probe microscope that measures the surface shape of a sample by moving the sample table while keeping the distance of the tip of the needle constant, a known step H _i (where i = 1 to 1) in the Z-axis direction.
The standard sample in which a plurality of n X-Y plane portions having n) are provided from the first stage to the n-th stage, and the angle of the adjacent X-Y plane portions in the Z-axis direction is accurately set to 90 °. Is mounted on a sample table, the change of Z coordinate is measured while scanning the probe of the scanning probe microscope in the surface direction of the XY plane, and the probe moves the XY plane to 1 The length r _i (i = 1 to 1) of the measurement trajectory in the diagonal direction until the step is completely descended
n) and the measurement step h _i of the XY plane portion are recorded,
Disclosed is a measurement angle error detection method for a scanning probe microscope in which θ _i = cos ⁻¹ (h _i / r _i ) is calculated and θ _i is a measurement angle error for evaluation.

[0013]

The step H _i of each XY plane is known, and the measured step error h _i should be H _i = h _i . However, H _i ≠ h _i may occur, which is caused by the hysteresis characteristic of the piezoelectric element. Therefore, in the present invention, the correction coefficient through k _i Searching for the correction coefficient k _i as to match the H _i and h _i for each stage, the correction coefficient k _i in the piezoelectric element at the time of measurement of the measured material It was decided to perform the hysteresis correction of. Further, even when the adjacent steps have an angle of 90 °, the measurement locus does not become a 90 ° step locus in this 90 ° step portion, but becomes a diagonal locus. Therefore, in the present invention, the angle θ _i of the diagonal line is obtained from the trajectory of the diagonal line, and the measurement locus at the time of measurement is evaluated.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a Z of STM in one embodiment of the present invention.
An explanatory view and a flow chart of a preliminary measurement step for determining a probe coordinate correction coefficient in the axial direction are shown. In FIG. 1A, 1 is a probe, 2 is a standard sample, and 3 is a standard sample base. In this embodiment, for the sake of simplicity, the number of XY plane portions is four, and the steps H _{i of} each step are all equal and H _i.
= A (i = 1 to 4). Standard sample 2 is XY of the device
When installed on the stage, the base 3 of the standard sample provided on the lower surface of the standard sample 2 is adjusted so that the flat portion is XY in each stage.
Try to match the plane exactly. Although not shown,
The probe 1 is connected to a fine movement mechanism composed of a piezoelectric element as shown in FIG. The probe 1 is the first X-Y plane portion X-
It is arranged on the Y plane. The preliminary measurement step is first performed in the XY plane using the test pattern, but since this step is not directly related to the present invention, the operation description is omitted. After that, preliminary measurement in the Z-axis direction is performed according to the program shown in FIG. 1B, which is an embodiment of the present invention. Figure 1 (B)
First, the probe 1 starts to move in the plane direction of the XY plane portion of FIG. 1A by "start". This is "X
The process of "moving the probe in the Y-plane direction". The probe 1 descends from the XY plane portion 4 to the XY plane portion 3 and detects the measurement step h ₄ at this time. In the preliminary measurement stage as well as in the actual measurement stage, the Z coordinate of the probe 1 is controlled so that the distance between the probe 1 and the sample XY plane maintains a constant atomic scale T (for example, 1 nm). Has been done. Here, as shown in FIG. 1, h _i is a measurement step from the atomic scale T and should originally be h _i = H _i . However, if the piezoelectric element has a hysteresis characteristic, then h _i ≠ H _i .

When the probe 1 is moved from the XY plane portion 4 to the surface of the base 3 of the standard sample which is parallel to the XY plane through the XY plane portion 1, a measurement step h _{1 of} each XY plane portion is obtained. ~ H ₄
Are all detected. Here, for the measurement probe tip plane portion 4 at a position Z ₄ as shown in FIG. 1, the voltage applied to the piezoelectric element V _4, the following positions Similarly for flat site 3,2, l Z ₃ , Z ₂ , Z ₁ are applied voltages V ₃ ,
Assuming V ₂ and V ₁ , this functional relationship between V and Z draws a hysteresis characteristic. Originally, it should be h _i = H _i , but if this hysteresis characteristic exists, h _i ≠ H _i . Then, find the coefficient such that h _i and H _i match via a certain coefficient. This coefficient becomes a correction coefficient k _i = (i = 1 to n) for eliminating the influence of the hysteresis characteristic. The procedure for finding this correction coefficient is as follows.
It is checked whether all the detected steps h _i (i = 1 to 4) are equal to H _i , that is, a. If "NO", then proceed to the process of "converting (a / h _i ) into a correction coefficient". Next, for re-measurement, “Tip the probe in the XY plane section 4
"Move to" and simultaneously perform "program setting of new correction coefficient" in a control device (not shown) such as a microcomputer.

The "movement of the probe in the X-Y plane direction" is performed again to enter the "step h _i detection". However, the actual measurement value of h _i this time is corrected by the correction coefficient k _i . After the measurement of all of h _{1 to} h ₄ is completed, this measurement value is h _i , that is, a
Check if it is equal to. If the previous measurement value h _i was detected with good reproducibility,
The current measurement confirms h _i (i = 1 to 4) = a, and the preliminary measurement step “ends”. However, h _i (n =
1-4) .noteq.a, the correction process is re-entered and h _i
Routine measurements are repeated until (i = 1-4) = a is achieved. If it finds h _i = H _i become such a correction coefficient k _i in all the X-Y plane portion 4 to 1, stores it as optimum correction coefficient k _i.

After the preliminary measurement step is completed, the sample to be inspected is set on the XY plane sample table, and the surface shape is measured while scanning the sample table in the X and Y directions. At this time, the fine movement mechanism adjusts the probe 1 so as to maintain the distance T with respect to the sample surface. XY
The coordinates (x, y) of the plane and the Z-axis coordinates are calibrated by the correction coefficient determined in the preliminary measurement step and output to the wave memory. The correction information once stored in memory is input to the image device and displayed as the enlarged surface shape of the sample.

On the other hand, FIG. 2 is a diagram showing a measuring angle error detecting method of the microscope according to the embodiment. As shown in FIG. 2A, the angle of the XY plane portion of the standard sample 2 having a multi-stage XY plane portion (four steps in the illustrated example) is precisely processed to a predetermined angle, for example, 90 °. In the figure, for simplicity, XY
The flat portion 1 and the base of the standard sample are omitted. A standard sample is placed on a sample table (not shown) such that each XY plane is formed along the X axis of the sample table. Therefore, the movement of the probe 1 along the XY plane is limited to the Y-axis and Z-axis directions.

Now, the process of detecting the measurement accuracy is shown in FIG.
As shown in FIG. 2B, the probe 1 is first located on the flat portion of the XY plane portion 4 of FIG. 2A.
At this position, the Z-axis fine movement mechanism is adjusted as described above to maintain the distance between the probe 1 and the standard sample 2 at T. After that,
Along with "start", "probe movement along the XY plane" is performed. First, when the probe 1 is scanned in the Y-axis direction, a shift in the Z-axis direction is added from a position slightly past the edge of the XY plane portion 4. The shift in the Z-axis direction continues up to a position away from the flat portion of the XY plane portion 3 by T, but the locus of the probe 1 at this time forms oblique lines between steps as shown by the dotted lines in the figure. It is normal to do. Of course, also in the case of FIG. 1 described above, to be precise, an oblique locus as shown in FIG. 2A is obtained, but in the Z-axis position correction of FIG. 1, only the height between the flat portions of the XY plane portion is obtained. Is important, so it is omitted for simplicity.

The reason why the trajectory of the probe 1 draws a slanted line between the steps is that the tip of the probe 1 is not sharp on an atomic scale and the shape thereof is also various. Normally, the probe 1 is used by electrolytically polishing a tungsten wire or the like having a diameter of about 0.1 mm, but it is difficult to completely control the curvature and shape of the tip of the probe. The trajectory of probe 1 is XY
When covering the flat portion of the flat portion 4 to the flat portion of the X-Y plane portion 3 "detection of the oblique line length r _4" is completed. At this time, when the moving distance of the probe 1 in the Z-axis direction is measured, the “step h
₄ detections ”are possible. From r ₄ and h ₄ , the inclination angle θ ₄ of the above-mentioned diagonal line is

## EQU1 ## It can be calculated that θ ₄ = cos ^-1 (h ₄ / r ₄ ). This is the “calculation of the angle θ ₄ ”. After "recording" this θ ₄ value, it is checked whether or not "i = 1".
Where i is the XY plane part number. At first, of course, the answer is "NO", so the routine enters to move the probe to the next XY plane. When “i = 1”, the work ends. Instead of the length r ₄ , the width d ₄ in the XY direction may be detected. At this time, it becomes the following.

[Equation 2] θ ₄ = tan ⁻¹ (d ₄ / h ₄ ) Similarly, the tilt angles θ ₃ , θ ₂ , and θ ₁ are obtained. Then, these are stored in the memory. θ _{4 to} θ ₁ are values indicating the state of the measurement trajectory at each step, and mean the so-called measurement angle error (so-called measurement angle error).

Since h _i does not include the correction in the Z-axis direction shown in FIG. 1, it includes an error due to the piezoelectric characteristic. In order to avoid this, it is necessary to use pre-measurement in the Z-axis direction shown in FIG. 1 in advance and use the coefficient-corrected h _i . And
When measuring the shape of the sample surface, for example, the difference between the measured angle error θ _i and the preset angle (90 °) is used as a correction amount to correct the actual measurement value.

Although the present invention has been described based on the embodiments, the present invention is not limited to these. It is also applicable to SAFM and SMFM other than STM. Also,
In the above-mentioned embodiment, the steps h _i of the standard sample for calibrating the measurement value in the Z-axis direction are all set to a, but of course the steps may be different for each XY plane section. Further, when the angle is corrected, the difference may be used, but the ratio between the measured angle error θ _i and the set angle may be used as the correction amount.

[0023]

As described above, according to the present invention, the scanning accuracy of the scanning probe microscope in the Z-axis direction can be confirmed and the Z coordinate of the measured value can be corrected. As a result, it is considered that the accuracy of the scanning probe microscope can be improved.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a Z coordinate correction process according to an embodiment.

FIG. 2 is a diagram for explaining an accuracy detection process in the Z-axis direction of the microscope according to the embodiment.

FIG. 3 is a diagram showing a general circuit configuration of an STM.

[Explanation of symbols]

 1 probe 2 standard sample 3 standard sample base

Claims (2)

[Claims] 1. A probe held in a Z-axis direction perpendicular to an XY plane sample stage is brought close to a sample surface placed on the sample stage, and a piezoelectric element is used to provide the surface and the tip of the probe. In the scanning probe microscope for measuring the surface shape of the sample by moving the sample table while keeping the distance of n constant, the number of n steps having a known step H _i (where i = 1 to n) in the Z-axis direction is measured. By preparing a standard sample having a plurality of stages of the XY plane portion from the first stage to the n-th stage, and scanning the probe in the plane direction of each XY plane portion, a known step H
_{i (i} = _1~n) and the measurement step h _{i (i} = _1~n) thereof and as to match via a correction coefficient k _i correction coefficient k _i (i =
1 to n) are calculated and stored, and the correction coefficient k _i (i
= 1 to n), the method for correcting the measurement data of the scanning probe microscope is adapted to perform the hysteresis correction of the piezoelectric element during the measurement of the material to be measured. 2. A probe held in the Z-axis direction perpendicular to an XY plane sample stage is brought close to a sample surface placed on the sample stage, and the surface and the probe tip end portion are formed by a piezoelectric element. In the scanning probe microscope for measuring the surface shape of the sample by moving the sample table while keeping the distance of n constant, the number of n steps having a known step H _i (where i = 1 to n) in the Z-axis direction is measured. A plurality of XY plane portions from the first stage to the nth stage are provided, and the angle in the Z-axis direction of the adjacent XY plane portions is 90.
The standard sample set at a temperature of 0 ° is placed on a sample table, and the change in Z coordinate is measured while scanning the probe of the scanning probe microscope in the direction of the XY plane. Measure and record the length r _i (i = 1 to n) of the measurement locus in the oblique direction until completely descending the flat part by one step and the measurement step h _i of the XY flat part, and θ _i = cos A measurement angle error detection method for a scanning probe microscope in which θ _i obtained by calculating ⁻¹ (h _i / r _i ) is used as an evaluation measurement angle error.