JPH06147821A - Inclination correcting method for scanning probe microscopic image - Google Patents

Abstract

PURPOSE:To remove inclination components from measured data obtained through a scanning probe microscope and to obtain a corrected measured data representative of an accurate irregular image. CONSTITUTION:Surface of a sample 2 is scanned by means of a probe 1 set close thereto and the height of the probe, corresponding to the irregular profile of the sample surface, is measured by taking advantage of the physical amounts of tunnel current flowing between the probe and the sample surface. The data is employed in a measuring method for producing an irregular image, wherein linear scanning is performed in X and Y axis directions on the measuring region of a sample and an inclination angle of the measuring surface in the measuring region is calculated thus defining a scanning range. Signal level in the direction intersecting the measuring surface perpendicularly is then calculated based on the scanning range and the measured data and a signal level at the time of constant sampling pitch is determined according to interpolation method based on the scanning range, number of samples, and the signal level thus calculated and used as a final data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting inclination of a scanning probe microscope image, and more particularly, in measuring an uneven surface shape of a sample using a scanning probe microscope and creating an image, an inclination component is measured from measurement data. The present invention relates to a tilt correction method capable of accurately reproducing an original shape without deforming an uneven shape of an image formed by measurement data after correction when removing.

[0002]

2. Description of the Related Art A typical example of a scanning probe microscope (also referred to as a scanning probe microscope) is a scanning tunneling microscope (hereinafter referred to as STM). In STM, the tunnel current flowing between the probe and the sample is detected, and while the measurement surface of the sample (the plane defined by the X axis and the Y axis orthogonal to each other) is scanned by the probe, the tunnel current is constant, for example. The height position of the probe (the amount of displacement in the Z-axis direction orthogonal to the XY plane) is controlled so that the probe becomes the spatial coordinate of the probe, that is, the piezoelectric element in each of the X, Y, and Z axis directions. A drive applied voltage for expanding and contracting the (actuator for displacing the probe position) is used as measurement data, and a bird's-eye view or the like is displayed on the CRT monitor regarding the uneven shape of the sample measurement surface. The fine shape on the surface of the sample is observed and analyzed based on the thus obtained unevenness information of the measurement region of the sample.

In the surface shape measurement by the above-mentioned STM, since the tunnel current is extremely sensitive to the change in the distance between the probe and the sample, it is known that it has a high resolution capable of discriminating at the atomic level. .

[0004]

The STM for performing the above measurement
The information obtained in step 1 is the uneven shape of the sample surface. However, if the measurement surface of the sample is not substantially perpendicular to the axial direction of the probe but is inclined, the detected height information of the probe includes the required surface irregularity information as well as the sample surface. The information includes the inclination of. Therefore, when a brightness modulation image or a stereoscopic shadow image is created using the data obtained by the measurement and displayed on a CRT monitor for analysis, the inclination of the sample measurement surface becomes an obstacle and proper correction is required. It is necessary to do it.

As a method of correcting the inclination of the sample measuring surface,
For example, based on the inclination angle of the measurement surface obtained based on the measurement data by the line scan in each of the X and Y directions, or the equation of the inclination surface obtained by using the least square method for the two-dimensional measurement data, A concept of correcting by subtracting or adding the height amount due to the inclination has been proposed. These methods are gradation corrections having a mapping meaning, and can be said to be simple and useful correction methods when the degree of inclination is small. However, since it is only an approximate method, it may not be strictly appropriate when the degree of inclination is large. Particularly when the degree of inclination is large, the uneven shape (FIG. 6B) of the image created by the corrected measurement data becomes the actual uneven shape (FIG. 6A) as shown in FIG. In comparison, when it is remarkably deformed and the inclination is corrected, there is a problem that the uneven shape cannot be maintained as it is. If the surface of the sample is analyzed using the thus-corrected uneven image, the risk of misjudgment increases.

The above problem is not only caused by the STM but also caused by the inclination correction of the image obtained by the scanning probe microscope having the similar structure such as the atomic force microscope.

In view of the above problems, an object of the present invention is to accurately remove the tilt component from the measurement data obtained by the scanning probe microscope regardless of the tilt degree, and to accurately obtain the uneven image drawn by the corrected measurement data. Another object of the present invention is to provide a method for correcting inclination of a scanning probe microscope image capable of showing an actual uneven shape.

[0008]

A method for correcting inclination of a scanning probe microscope image according to the present invention scans a sample surface with a probe in a state of being close to the surface of the sample, and a plurality of measurement points during the scanning. For each of the above, the height position of the probe corresponding to the uneven shape of the sample surface is measured using physical quantities such as tunneling current and atomic force generated in the minute gap between the probe and the sample surface. The present invention is applied to a measuring method for creating an image of a concave-convex shape on the surface of a sample using position data, and a line is formed on the measuring area of the sample, preferably in each of two biaxial directions defined at right angles. -Like scanning is performed to calculate the tilt angle of the measurement surface in the measurement region, the scan range is determined based on this tilt angle, and the scan range and measurement data are used to tilt in the direction orthogonal to the above-described measurement surface. Calculate the signal level, scan range and sampling The signal levels at evenly spaced sampling pitches based on the number and the calculated signal levels are determined by interpolation, and the signal levels at evenly spaced sampling pitches determined by interpolation are used to create the final image for creating the concavo-convex shape image. This is a tilt correction method that is used as temporary data.

[0009]

In the present invention, when the image of the uneven shape of the measurement area of the sample is created by using the measurement data obtained by the scanning probe microscope, the surface of the measurement area is inclined and is included in the measurement data. When it is necessary to perform the tilt correction to remove the tilt component that is generated, the tilt correction calculation is performed to obtain the signal level related to the new coordinate system, and this signal level is calculated by using the interpolation method. To the signal level corresponding to. This makes it possible to remove the tilt component without deforming the actual concavo-convex shape even if the initially obtained measurement data is subjected to tilt correction calculation. In other words, even when the inclination correction is performed on the scanning probe microscope image, the uneven shape image can be displayed with the same profile as the actual uneven shape.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In this embodiment, an STM will be described as an example of a scanning probe microscope.

FIG. 1 shows the structure of the STM probe part, the device structure for controlling the position of the probe, and the structure of the detection / processing unit for the measurement data obtained by the probe. With reference to FIG. 1, a general configuration and operation of main parts of the STM will be described. Reference numeral 1 is a probe, and 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-shaped 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 involved in movement in the X-axis direction, the piezoelectric element 4 is an actuator involved in movement in the Y-axis direction, and the piezoelectric element 5 is an actuator involved in movement in the Z-axis direction. Further, the probe 1 is brought close to the surface of the sample 2 to a distance at which a required tunnel current is detected by a manual device (not shown) having a tripod head attached, a stepping motor, or a coarse-movement piezoelectric element having a large stroke.

A power source 6 is connected between the probe 1 and the sample 2 and a required voltage is applied between them. In this state, when the probe 1 is brought close to the sample 2 and the distance between the probe 1 and the sample 2 becomes a required minute distance, a tunnel current flows between them. The tunnel current flowing through the conductive probe 1 is
The tunnel current is detected by the tunnel current detector 7, and then the tunnel current / distance converter 8 converts the detected tunnel current into a voltage signal corresponding to the distance between the probe 1 and the sample 2. In the measurement of the uneven shape, the height position of the probe 1 is controlled so that the tunnel current detected during scanning of the probe 1 is maintained at a constant value. In order to perform this control, the servo circuit 9 in the next stage inputs the distance signal output from the tunnel current / distance converter 8 and compares this distance signal with a preset reference distance so that they match. By controlling, the expansion / contraction amount of the piezoelectric element 5 in the Z-axis direction is controlled so that the probe and the sample are held at a constant distance.

The X axis and Y of the probe 1 on the measurement surface of the sample 2
Scanning in each direction of the axis is performed by the scanning unit 10. The scanning unit 10 gives an expansion / contraction driving signal to the piezoelectric element 3 for the X-axis direction and the piezoelectric element 4 for the Y-axis direction, and the expansion / contraction operation of these piezoelectric elements 3, 4 causes the probe 1 to two-dimensionally move. Scanning is performed. The expansion and contraction operations of the piezoelectric elements 3 and 4 are independently performed, and the scanning position of the probe on the XY plane is determined by the combination of the expansion and contraction amounts of the piezoelectric elements 3 and 4.

Piezoelectric elements 3, 4, in the directions of the X, Y and Z axes
With the movement of the probe 1 by 5, the load voltage of the piezoelectric elements 3, 4, and 5, that is, the data regarding the expansion and contraction amount of each piezoelectric element is stored in the measurement data storage unit 11 as spatial coordinates. The position data of the probe 1 stored in the measurement data storage unit 11 is appropriately extracted and supplied to the data processing unit 12. The data processing unit 12 performs image processing on the uneven shape of the measurement surface of the sample 2, and displays the surface uneven shape of the sample 2 on the monitor unit 13 using the data obtained by the image processing. The data processing unit 12 of this embodiment is provided with a tilt correction means for executing a tilt correction method described later. The measurement data storage unit 11 and the data processing unit 12 described above are included in the calculation / control unit 14. The arithmetic / control unit 14 is composed of a CPU and a memory. The arithmetic / control unit 14 realizes necessary functional means.

The calculation / control unit 14 further includes the scan control unit 1.
Have 5. The scan control unit 15 is provided with a procedure of how to move the probe in the probe scan of this region when the target region to be measured on the surface of the sample 2 is set, and the scan is performed. The control unit 15 has a function of giving a control signal for executing this procedure to the scanning unit 10.

In the above structure, 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. In order to do so, it is necessary to control the expansion / contraction operation of the piezoelectric element 5 so as to keep this distance constant. The tunnel current is sensitive to the change in the distance between the probe and the sample, and thus high resolution can be obtained.

Based on the above structure of the STM, the series of operations makes it possible to obtain information on the uneven shape of the measurement surface of the sample 2. In order to obtain this information, the movement for scanning the probe 1 is stopped at each of the plurality of measurement points set in the measurement region, and the distance between the probe 1 and the surface of the sample 2 is kept constant. The servo control is performed by the servo circuit 9 repeatedly a plurality of times.

As for the measurement area of the sample 2, the height information of the uneven shape is measured at a plurality of predetermined measurement points as described above, whereby the uneven information of the measurement area can be obtained. It is assumed that the measurement data as shown in FIG. 2 is obtained by such measurement. As shown in FIG. 2, the measurement surface 2a of the sample created by the measurement data has an inclination. The inclination angle of the measurement surface 2a is defined with respect to the reference surface 2b. The reference plane is a plane parallel to the mounting stage (not shown) of the sample 2 and is orthogonal to the axial direction of the probe 1, that is, the Z-axis direction. For example, by performing a line scan in the X-axis direction and the Y-axis direction on the measurement surface 2a of the sample 2 having an inclination, or by performing a two-dimensional measurement for obtaining two-dimensional measurement data,
The measurement data of a line in an arbitrary direction is obtained, and the inclination angle of the measurement surface 2a with respect to the reference surface 2b is obtained. The two-dimensional measurement is to scan a partial area within the measurement area two-dimensionally.
By this, the unevenness data on an arbitrary line is obtained.

As an example, when the measurement data at the time of line scanning in the Y-axis direction is obtained as shown in FIG. 3, using this measurement data, the sample surface with respect to the reference surface 2b (a surface assumed to be an average plane) is used. The inclination angle θy of 2c) is obtained.
The inclination angle in the X-axis direction can be similarly obtained. Hereinafter, for convenience of description, tilt correction for the tilt angle θy will be described.

A method of correcting the inclination of the measured data will be described with reference to FIGS. 4 (A), (B) and (C). Figure 4
(A) is a graph in which measurement data (probe height position data) obtained as a result of line scanning in the Y-axis direction on the measurement surface 2a set for the sample 2 are arranged in the Y-axis direction. The horizontal axis is the Y ₀ axis and the vertical axis is the Z ₀ axis, and Y ₀ -Z ₀ is the reference coordinate system. In this graph, the sampling pitch P ₀ is evenly spaced. In FIG. 4A, 16 indicates the scanning direction, and ΔY ₀ indicates the scanning range in the Y-axis direction at the time of measurement. In addition, the height of the measured data is Z _{i, 0} (i = 1 to
n _y ; n _y is the number of sampling points or the number of measurement data). The coordinate system Y ₁ -Z ₁ corresponding to the sample surface 2c is further shown in the graph of FIG. The angle with respect to the reference coordinate system is θy.

When the measured data Z _{i, 1} for the inclined sample surface 2c is obtained using Z _{i, 0} , the following (Equation 1) is obtained. Refer to FIG. 5 for the guidance of (Equation 1) and the like.
FIG. 5 shows a part of FIG. 4A in an enlarged manner, and points A to G are shown in the figure. For these points A to G, the line segment CA = Z
_{i, 0} and line segment CD = Z _{i, 1} are defined, and the following equation holds. CD = {AC-AB} cos θy P _{i, 1} = (CF ² -CG ² ) ^1/2 CF ² = EF ² + P ₀ ² = (Z _{i + 1,0} -Z _{i, 0} ) ² + P
₀ ² CG ² = (Z _{i + 1,1} −Z _{i, 1} ) ² (Equation 1) and the like are obtained using the above relational expressions.

[Expression 1] Z _{i, 1} = {Z _{i, 0} − (i−1) P ₀ tan θy} cos θy The sampling pitch P _{i, 1} at unequal intervals in the Y ₁ axis direction with respect to the measurement data Z _{i, 1} When calculated, it is given by the following formula.

## EQU2 ## P _{i, 1} = {((Z _{i + 1,0} −Z _{i, 0} ) ² + P ₀ ² ) −
(Z _{i + 1,1} −Z _{i, 1} ) ² } ^{1/2 The} scanning range ΔY ₁ (corrected scanning range) along the Y ₁ axis direction of the sample surface 2c is the result of the above (Formula 2). Using,
It is given by the following formula.

Equation 3] ΔY ₁ = ΣP _{i, 1} except i = 1~ (n _y -1) The above information is different for each scan line in accordance with the degree of strictly surface irregularities. Therefore, ΔY ₁ ′, which is approximately given by the following equation, is adopted as the scanning range.

[Formula 4] ΔY ₁ ′ = ΔY ₀ / cos θy However, ΔY ₀ is the ratio ΔY ₁ / Δ of the scanning range set by the measurement before correction (Formula 3) and each value obtained by (Formula 4).
Y ₁ ′ is multiplied by the non-equidistant scanning pitch P _{i, 1} to obtain P _{1
i, 1} ′, and using this value and the height component Z _{i, 1} with respect to the inclined sample surface 2c obtained from (Equation 1) _, an equal pitch ΔY
The height component at ₁ '/ ( _ny- 1) is calculated by the interpolation method.

In connection with the above tilt correction calculation, FIG.
(B), the measurement data Z _{i, 1} unequally spaced pitch P with respect to the sample surface 2c which is inclined in the coordinate system Y ₁ -Z ₁
It is a graph shown by _{i, 1} . FIG. 4C shows the coordinate system Y ₁
At Z ₁ , the equidistant pitch Δ calculated by the interpolation method
Y ₁ '/ is a graph showing the height component data in (n _y -1). The height component data shown in FIG. 4C is used to display as a brightness modulation image or a stereoscopic shadow image.

In order to clarify the problem that the scanning range ΔY ₁ along the direction of the sample surface 2c is approximated by (Equation 4) in the calculation of the inclination correction described above, the following points will be considered.
From the measurement data, the height direction component of the sample 2 with respect to the inclined surface is

[Expression 5] Y _{i, 1} = {(i−1) P ₀ } sin θy + Z _{i, 0} cos θy

Z _{i, 1} = {(i−1) P ₀ } cos θy + Z _{i, 0} sin θy
Ask in. As the scanning pitch at equal intervals with respect to the corrected scanning range ΔY ₁ ,

(7) Adopt P _i = P ₀ / cos θy. Obtained in (6) and (7) the above _{(Y i, 1, Z i} , 1) except i = based on data from 1 to n _y, the data for the specimen rotation plane by interpolation new It can be calculated and used as corrected height direction data.

In any of the above two inclination correction methods, in the actual measurement in which the fine probe scanning is performed on the surface unevenness shape of about several percent with respect to the scanning range,
The tilt correction can be performed without any problem. According to the inclination correction method of each of the above-described embodiments, it is possible to avoid that the STM image created by the STM image creation data after the tilt correction has a profile different from the actual uneven shape of the sample surface.

In the above description, the method of correcting and tilting an image by STM has been described, but the present invention can be generally applied to a scanning probe microscope.

[0026]

As is apparent from the above description, according to the present invention, when performing tilt correction on an image obtained by a scanning probe microscope, the signal level obtained by removing the tilt component from the measurement data is Further, since the processing is performed so that the signal level is converted into a sampling pitch of equal intervals, an image having the same shape as the actual uneven shape can be obtained even if the inclination correction is performed, and accurate information about the unevenness of the inclined sample surface is obtained. Therefore, the analysis can be easily performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a main configuration of an STM which is an example of a scanning probe microscope.

FIG. 2 is a perspective view showing an inclined measurement surface of a sample.

FIG. 3 is a diagram for explaining an inclined measurement surface of a sample.

FIG. 4 is a diagram for explaining a tilt correction method according to the present embodiment.

FIG. 5 is an enlarged view for assisting the description of the tilt correction method.

FIG. 6 is a diagram for explaining a problem of the tilt correction method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Probe 2 ... Samples 3, 4, 5 ... Piezoelectric element 7 ... Tunnel current detection unit 8 ... Tunnel current / distance conversion unit 9 ... Servo circuit 10 ... Scan unit 11 ... Measurement data storage unit 12 ... Data processing unit 13 ... Monitor unit 14 ... Calculation / control unit

Claims (1)

[Claims] 1. The sample surface is scanned by a probe close to the surface of the sample, and a physical quantity generated in a minute interval between the probe and the sample surface is used at each of a plurality of measurement points to obtain the In the image forming method of the scanning probe microscope image, the height position of the probe corresponding to the uneven shape of the sample surface is measured, and the image of the uneven shape of the sample surface is created using the data of the height position. , Calculating the inclination angle of the measurement surface of the measurement region based on the measurement data of the line in an arbitrary direction on the measurement region of the sample, determining the scanning range based on the inclination angle, and using the scanning range and the measurement data The signal level in the direction orthogonal to the inclined measurement surface, and obtain the signal level at the sampling pitch at equal intervals based on the scanning range, the number of samplings, and the signal level by the interpolation method. Tilt correction method of a scanning probe microscopic image, characterized in that to create the uneven shape image using the signal level obtained at the sampling pitch.