JPH08122340A - Method and apparatus for surface shape measurement - Google Patents

Abstract

PURPOSE: To enable the measuring of the shape of the surface of a sample containing a vertical way at a high accuracy with a high resolving power by obtaining a band- shaped lattice image following a step of the surface of the sample using a scan control signal in the direction vertical to the surface of the sample and a two-dimensional lattice image to calculate coordinates with the results as reference coordinates. CONSTITUTION: A scanning mechanism 14 for ZX axis is sent in the X axis direction scanning with a probe 17 for crystal observation in the Z axis direction to obtain a lattice image of a reference crystal 16 for a scale. Here, the probe 19 for observing a sample follows the surface of a sample 12 and when a step exists, the probe 19 is controlled to keep the distance from the sample surface constant. Hence, the reference crystal 16 is also moved equally in the Z axis direction to obtain a lattice image distorted in the Z axis direction. So, when a control signal in the Z axis direction applied to the mechanism 14 is added to a scan signal in the Z axis direction of the scanning mechanism 18, a corrected lattice image closely resembling the shape of an actual scanning area is obtained. Thus, coordinates at respective lattice points indicating the upper and lower ends of the lattice image are collated with the coordinates of the reference crystal 16 thereby enabling detecting of the shape of the step of the sample 12 as coordinates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a surface shape of a scanning probe microscope or the like and a measuring method therefor.

[0002]

2. Description of the Related Art In recent years, various surface shape measuring devices have been researched and developed in order to obtain information on the surface of a substance. As a conventional device for measuring the level difference, shape, and roughness of the surface of the sample, a level difference measuring device, a scanning electron microscope, an electron beam three-dimensional roughness analyzer, or the like is used. In the case of an apparatus using an electron beam, it is not possible to directly obtain information on the step direction (direction perpendicular to the surface of the sample), and complicated simulation is required.
In the case of the stylus type device, the information on these surfaces is directly obtained as the displacement of the probe, and the operating transformer system in which the probe is pressed and scanned for reading is used. On the other hand, Scanning Probe Microscope
pe (SPM) uses the interaction between the probe and the surface of the sample as a control signal and positions the probe in the step direction on the surface of the sample with a three-dimensional scanning mechanism and Two-dimensional scanning is performed, and the surface shape is obtained from the displacement of the probe. For example, in a scanning tunneling microscope (STM), a metal probe is brought close to a conductive sample to about 1 nm.
When a minute voltage is applied between the two, a current flows due to the tunnel effect, and the surface of the sample can be accurately measured by scanning the surface of the sample while moving the probe up and down so that the tunnel current becomes constant. A scanning atomic force microscope (AFM) detects an atomic force acting between the surface of a sample and a probe, and scans the surface so that it becomes constant. A minute spring called a cantilever is used to detect the atomic force, and an STM, an optical lever, an interferometer, etc. are used to detect the displacement of the spring.
In addition, there are a friction force microscope that detects a change in frictional force as a lateral deflection amount of a cantilever, a magnetized probe, and a magnetic force microscope that resonates the cantilever to detect a magnetic force.

Since these SPMs have a lower contact pressure than the stylus type and can be ignored, they do not scratch the surface of the sample. In addition, the lateral resolution of detection is a few 100 nm at most with the stylus method, but it is the highest in SPM and reaches the atomic level. However, the control signal of SPM is 10 at maximum for the displacement of the probe or sample.
There is an error of more than a percentage. Therefore, calibration with a capacitance gauge or an interferometer was performed. There was also a calibration method using a reference crystal lattice only in the plane parallel to the surface of the sample (XY plane).

When measuring the depth and spacing of pits on the surface of an optical disc, the depth of the pits is 100 nm and the spacing is 1.6 μm in the case of a compact disc. Further, it is important that the thickness of the optical thin film, the multilayer film of the X-ray reflecting mirror, etc. is as thin as several tens of nm or less, and that the thickness is accurately measured. As described above, the measurement range is small and high accuracy and high resolution are required for the measurement of the sample in the step direction.

[0005]

However, in the calibration method, the capacitance gauge has a slow detection speed and a long measurement time, so that it is particularly unsuitable for measuring in the step direction among SPMs having a high lateral resolution and a fast response. Further, when an interferometer is used for the calibration method, the absolute value can be known only in terms of accuracy, so it can be used as a reference, but it is large and expensive as seen in commercially available devices.

On the other hand, the calibration method using the reference crystal lattice is small and inexpensive, and the detection resolution is extremely high because it is determined by the distance between the reference crystal lattices. If the quality of the lattice image is good, the sub-angstrom is obtained by interpolation. Also reaches. In the calibration method using the reference crystal lattice, the scanning probe overcomes atoms or molecules forming a known atomic interval, counts the number of irregularities, and uses it as a scale for length measurement.

However, the crystal lattice has an orientation. Also,
Even if scanning is performed in the azimuth direction of the crystal lattice, the position where the atoms are crossed over differs depending on the scanning position, the size of the unevenness becomes small, and the number of atoms may not be accurately counted. As described above, it is not possible to accurately measure the displacement by only one-dimensionally scanning the surface of the reference crystal lattice with the scanning probe. Therefore, in order to use the reference crystal lattice as a scale for length measurement, it is necessary to scan two-dimensionally and form a lattice image in order to know the unevenness and orientation of atoms. However, since the measurement including the step direction (Z-axis direction) in the surface shape consists of one-dimensional scanning and movement in the feedback control direction and becomes an irregular one-dimensional line drawing, it is necessary to know the relative position of each grid point. I can't. Therefore, the conventional calibration method using the reference crystal lattice cannot measure the planes other than the XY plane, that is, the ZX plane and the YZ plane.

An object of the present invention is to solve the above problems.

[0009]

The present inventors have found that SPM and S
We have earnestly conducted research on a calibration method using a reference crystal lattice that can measure only the XY plane in PM. As a result, they have found that it is possible to measure the ZX plane and the YZ plane including the step direction with the following device and measuring method. Therefore, the present invention, in any one of the sample measurement probe and the sample surface, in at least one direction of the sample surface and a method of scanning the surface shape of the sample by a scanning mechanism in a direction perpendicular to the sample surface, When the sample surface has a step, a two-dimensional lattice image is obtained using a reference crystal lattice that is displaced according to the scanning of the scanning mechanism and a crystal lattice image observing probe that can scan in a direction perpendicular to the sample surface. , A two-dimensional lattice image and a control signal of a scanning mechanism in a direction perpendicular to the sample surface are used to obtain a belt-shaped lattice image that follows the steps of the sample surface, and the belt-shaped lattice image is used as reference coordinates to calculate coordinates. Provided is a surface shape measuring method characterized by measuring a step on the surface of a sample by obtaining it.

The present invention also provides a sample measuring probe,
A scanning mechanism capable of scanning in at least one direction of the sample surface and in a direction perpendicular to the sample surface, and a sample or sample measurement probe fixed, and scanning in a direction perpendicular to the scanning direction of the sample surface and parallel to the sample surface. Provided is a surface shape measuring device including a reference crystal lattice provided on a side surface of a mechanism and a crystal lattice image observation probe capable of scanning the reference crystal lattice in a direction perpendicular to a sample surface.

The level difference in the present invention means the height of the sample surface having undulations in the Z-axis direction, that is, in the direction perpendicular to the sample surface. FIG. 4 shows an example of an XY plane calibration method using a reference crystal lattice. The X-axis is the direction of the scan line (2
It is the scanning direction of the dimensional scanning). The present invention is characterized in that the conventional two-dimensional scanning direction is changed to the XY axis scanning mechanism and the ZX or ZY axis scanning mechanism in which the scanning direction is rotated by 90 ° is used. It is not possible to measure in the vertical direction (Z-axis direction). ZX
In addition to the axis scanning mechanism, it is necessary to simultaneously scan and modulate the crystal lattice observation probe.

In the conventional calibration method using the crystal lattice as the scale, the displacement of the probe in the direction perpendicular to the surface of the sample cannot use the crystal lattice as the scale, which is inaccurate and the displacement of the actual probe Had to use a control signal with a maximum error of 10 percent.
On the other hand, the present invention can measure a plane including the Z-axis direction with high accuracy and high resolution at the atomic level.

[0013]

The crystal lattice reference shape measuring apparatus for measuring the surface shape according to the present invention comprises a fixed portion and a shape trace serving as a measurement reference for measuring the shape trace movement by scanning at least one dimension of at least one of a probe and a sample. This device consists of a moving part, one of which has a reference crystal lattice that serves as a measurement scale, and the other has a crystal lattice observation probe.

The shape tracing motion mentioned here is to scan the surface of the sample by using the interaction between the probe and the sample surface as a control signal. Using this device, the surface of the sample is measured. A reference crystal that becomes a scale during measurement,
By scanning at least one of the crystal lattice observation probes in a direction perpendicular to the surface of the sample at a slow period and a small amplitude so that a two-dimensional image of the reference crystal lattice can be obtained, distortion due to a step on the surface of the sample occurs. A two-dimensional lattice image of the obtained reference crystal lattice is obtained.

The two-dimensional lattice image of the reference crystal lattice obtained here is obtained by scanning the reference crystal lattice or the crystal lattice observation probe in the Z-axis direction and the scanning signal in the X-axis direction of the scanning mechanism as in the case of the usual SPM processing. Since the coordinates are displayed on the screen plane, a lattice image with distorted atomic positions can be obtained as it is, as shown in FIG. Therefore, the atomic position cannot be used as a scale as it is.

Therefore, by using the control signal in the direction perpendicular to the surface of the sample to recover the distortion of the atomic position, a band-shaped lattice image having a surface shape as shown in FIG. 3C can be obtained. it can. This image contains an error because it is an image of a control signal, but has sufficient accuracy to obtain the orientation of the reference crystal. Since the arrangement of atoms in the crystal lattice is measured with sufficient accuracy if the cleavage plane is known, the upper and lower boundaries of the band-shaped lattice image are accurately measured if the atoms are reproduced so that they are aligned correctly. Is expressed, and its value can be easily obtained from the coordinates of the lattice image.

Since the probe has a finite length, an Abbe error occurs due to the Abbe offset when the scanning mechanism has a rotational movement, but the Abbe error can be minimized by using a parallel spring. Although the reference crystal lattice has sufficient accuracy for practical use,
When used as an absolute value or for verifying the accuracy of the device, it is effective to incorporate an optical wave interferometer for calibration.

Further, it is desirable that the reference crystal lattice can easily obtain a crystal lattice image and a clean cleavage plane. In STM, since conductivity is required, graphite is particularly desirable. Examples of the present invention will be shown below, but the present invention is not limited thereto.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the main configuration of the apparatus. Sample (1
STM was used for the observation of 2) and the reference crystal lattice observation, and the scale reference crystal (1) was used for the ZX axis scanning mechanism (14) on the sample side.
6) was fixed. As the sample 12, the one in which Pt was vapor-deposited on the cleavage plane of MgO was used, and the graphite crystal was used as the scale reference crystal. A parallel spring is used for 14, and a calibration function (13, 15, 21, 22,
23, 24, 25, 26).

As the sample scanning mechanism, a cylindrical piezoelectric element (11) movable in a three-dimensional direction is used, and a sample observing probe, that is, an STM probe (19) is moved in a shape trace. Reference numeral 11 is mounted on a Y-direction approach coarse movement mechanism using a DC gear motor and screws. The sample 12 is mounted on 11.

A reference numeral 19 for observing 12 is fixed to the reference numeral 14. 12 is 1 so that three-dimensional observation can be performed independently on the sample side.
Fixed to 1. 11 is mounted on a coarse movement mechanism that can move not only in the Z-axis approaching direction but also in the X-axis direction so that a specific point on the sample can be easily located. A calibration function by an interferometer using light is added to 14, and interferometer measuring mirrors (13, 15) are attached to two surfaces for calibrating the grating.

In this device, the quality of the lattice image is important.
It is necessary to avoid making the movable part of the robot heavy because it deteriorates the shape tracing motion performance. Therefore, it is necessary to avoid the use of a corner cube used as a normal measuring mirror and a tilt mechanism that is necessary when a plane mirror is used.
Therefore, a steering alignment mechanism is used for the Z-axis and X-axis interferometer polarization beam splitters (Polarizing Beam Splitters, 21, 22) and the laser beam introduction section.
As a result, the thickness of 14 movable parts is increased as a measuring mirror of the interferometer.
Plane mirrors 13 and 15 without a 300-micron tilt mechanism
It can be mounted only, and the mass load on 14 moving parts
I was able to keep it around 100 mg.

As the interferometer, a Michelson type orthogonal polarization dual frequency heterodyne interferometer was used. Since sub-nanometer resolution is required, the heterodyne frequency is 100 kHz and the stabilized HeNe laser is used as the light source. The Z-axis and X-axis interferometer polarization beam splitters 21 and 22 are integrated with a wavelength plate and a reference mirror necessary for polarization interference in order to downsize the device. In FIG. 1, the plates attached to the two surfaces of the polarization beam splitter are wavelength plates, and the plates that are stacked are reference mirrors. Reference numeral 21 is a beam splitter for measurement in the direction perpendicular to the surface of the sample, that is, the Z-axis direction, and 22 is a beam splitter in the X-axis direction which is the line width.

Non-Polarized Beam Splitter
The Beam Splitter, 25) splits the interferometer laser beam into two axes. When nanometer precision is required, polarization heterodyne interferometry poses a problem of nonlinear error of wavelength period due to polarization mixing. In addition, alignment with a beam splitter increases the error in the optical system installation, so the nonlinear detection device (Ba
lanced Detector Unit, 23, 24) is used for the detection system.

FIG. 2 is a diagram in which an integral type two-dimensional parallel spring driven by a laminated piezoelectric element is used for the ZX axis scanning mechanism 14 and an interferometer measuring mirror is provided. The parallel spring is made of aluminum and is manufactured by wire electric discharge machining. The cutouts on the arc serve as elastic hinges, and the four locations on one axis act as hinges, and the rectangle enclosed thereby is sheared to form a parallelogram. When the movement is small, the cosine error due to the subduction is small, so it can be regarded as almost linear movement. 1
Another shaft is manufactured inside the shaft.

FIG. 3 shows the principle of measurement including a direction (step direction) perpendicular to the surface of a sample using a reference crystal lattice as a scale. By sending the parallel spring ZX-axis scanning mechanism 14 in the X-axis direction while scanning 17 in the Z-axis direction, the 17 scans the graphite 16 in a raster scan.
16 grid images are obtained. At the same time, the scanning mechanism for ZX axis 1
19 is traced on the surface of 12 by the feeding operation of 4 in the X-axis direction. Here, as shown in FIG.
Is present, 19 is controlled in the Z-axis direction to keep the probe-sample constant, and 16 integral with 19 also moves equally in the Z-axis direction. The scanning area of 17 is forcibly distorted in the Z-axis direction by the movement of 16 in the Z-axis direction.
As a result, the lattice image of FIG. 3 (a) is obtained.

In FIG. 3 (a), the distortion of the scanning region due to the step C of 12 is ignored, and the scanning signal in the X-axis direction given to 14 is the width and the scanning signal in the Z-axis direction added to 18. Since only the vertical width is used for drawing, the effect of the step appears as distortion of the lattice image. The control signal of the shape trace motion in the Z-axis direction applied to 14 is applied to Z
By drawing in addition to the scanning signal in the axial direction, it is possible to correct the lattice image of FIG. 3A so as to be close to the shape of the actual scanning region. As a result, FIG. 3 (c) is obtained.

The lattice image of graphite becomes almost the same as the actual arrangement of the reference crystal lattices, and the distortion of the scanning region due to the step of the sample 12 appears on the contour of the lattice image. That is, FIG.
By comparing the coordinates of the respective lattice points representing the lower end and the upper end of the lattice image of (c) with the coordinates of the reference crystal lattice used as the scale, the shape of 12 steps C can be known as the coordinates. In addition, the surface shape of the sample could be reproduced with high accuracy and high resolution by converting the positional relationship of each lattice point in FIG. 3 (c) to the coordinates of the reference crystal lattice used for the scale and restoring. .

[0029]

As described above, according to the present invention, by using the reference crystal lattice as a scale, it becomes possible to measure the shape including the direction perpendicular to the surface of the sample with high accuracy and high resolution.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of the present invention, which is an example in which a calibration interferometer is incorporated.

FIG. 2 is an example in which a parallel spring is used for a ZX axis scanning mechanism and an interferometer measuring mirror is provided in the present invention.

FIG. 3 is a principle diagram of measurement including a direction perpendicular to the surface of a sample using a reference crystal lattice as a scale. (A) A lattice image in which the relative positions of lattice points are distorted in the Z-axis direction. (B) A schematic view of the movement of the sample observation probe. (C) A lattice image in which distortion of the lattice is corrected by using a control signal in the Z-axis direction of the ZX-axis scanning mechanism.

FIG. 4 is a perspective view showing an example of an XY plane calibration method using a reference crystal lattice. (A) It is a perspective view from the surface which fixed the reference crystal lattice. (B) It is a perspective view from the surface which fixed the sample.

[Explanation of symbols]

 11 Sample Scanning Mechanism 12 Sample 13 X-Axis Interferometer Measuring Mirror 14 Z X-Axis Scanning Mechanism 15 Z-Axis Interferometer Measuring Mirror 16 Scale Crystal 17 Crystal Observation Probe 18 Scanning Mechanism 19 Sample Observation Probe 21 Z-Axis Interferometer Polarization beam splitter 22 Polarization beam splitter for X-axis interferometer 23 Z-axis photodetection system 24 X-axis photodetection system 25 Non-polarization beam splitter 26 Beam bender 27 XY-axis scanning mechanism 28 Z-axis positioning mechanism

Claims (10)

[Claims] 1. A method for measuring a surface shape of a sample by scanning one of a sample measuring probe and a sample surface in at least one direction of the sample surface and a direction perpendicular to the sample surface by a scanning mechanism. When the sample surface has a step, a two-dimensional lattice image is obtained using a reference crystal lattice that is displaced according to the scanning of the scanning mechanism and a crystal lattice image observation probe that can scan in a direction perpendicular to the sample surface, Using the control signal of the scanning mechanism in the direction perpendicular to the sample surface and the two-dimensional lattice image, a band-shaped lattice image that follows the steps on the sample surface is obtained, and the band-shaped lattice image is calculated as reference coordinates to obtain the coordinates. The surface shape measuring method is characterized by measuring the level difference on the sample surface. 2. A method for measuring a surface shape of a sample by scanning one of a sample measuring probe and a sample surface in at least one direction of the sample surface and a direction perpendicular to the sample surface by a scanning mechanism. When the sample surface has a step, a two-dimensional lattice image is obtained by using a crystal lattice image observing probe and a reference crystal lattice that can be displaced in response to scanning by the scanning mechanism and can be independently scanned in a direction perpendicular to the sample surface. Using the control signal of the scanning mechanism in the direction perpendicular to the sample surface and the two-dimensional lattice image to obtain a band-shaped lattice image that conforms to the steps on the sample surface, and the band-shaped lattice image is used as a reference coordinate for calculation. A surface shape measuring method characterized by measuring a step on the surface of a sample by obtaining coordinates. 3. A method for measuring a surface shape of a sample by scanning one of a sample measuring probe and a sample surface in at least one direction of the sample surface and a direction perpendicular to the sample surface by a scanning mechanism. When the sample surface has a step, a two-dimensional lattice image is displaced using a reference crystal lattice and a crystal lattice image observing probe that can be displaced in response to scanning by the scanning mechanism and can be independently scanned in a direction perpendicular to the sample surface. Using the control signal of the scanning mechanism in the direction perpendicular to the sample surface and the two-dimensional lattice image to obtain a band-shaped lattice image that conforms to the steps on the sample surface, and the band-shaped lattice image is used as a reference coordinate for calculation. A surface shape measuring method characterized by measuring a step on the surface of a sample by obtaining coordinates. 4. A method for measuring a surface shape of a sample by scanning one of a sample measuring probe and a sample surface in at least one direction of the sample surface and a direction perpendicular to the sample surface by a scanning mechanism. When the sample surface has a step, a two-dimensional lattice image is obtained using a crystal lattice image observing probe that is displaced according to the scanning of the scanning mechanism and a reference crystal lattice that can be scanned in a direction perpendicular to the sample surface, Using the control signal of the scanning mechanism in the direction perpendicular to the sample surface and the two-dimensional lattice image, a band-shaped lattice image that follows the steps on the sample surface is obtained, and the band-shaped lattice image is calculated as reference coordinates to obtain the coordinates. The surface shape measuring method is characterized by measuring the level difference on the sample surface. 5. A sample measuring probe, a scanning mechanism capable of scanning in at least one direction of the sample surface and a direction perpendicular to the sample surface, and a sample or sample measuring probe fixed thereto, and a scanning direction of the sample surface. A reference crystal lattice provided on the side surface of the scanning mechanism in a direction perpendicular to and parallel to the sample surface,
A surface shape measuring device comprising a crystal lattice image observing probe capable of scanning the reference crystal lattice in a direction perpendicular to the sample surface. 6. A sample measuring probe, a scanning mechanism capable of scanning in at least one direction of the sample surface and a direction perpendicular to the sample surface, and a sample or a sample measuring probe fixed thereto, and a scanning direction of the sample surface. And a crystal lattice image observation probe that is provided on the side surface of the scanning mechanism in a direction perpendicular to and parallel to the sample surface and that can scan in a direction perpendicular to the sample surface independently of the scanning mechanism, and that is scanned by the crystal lattice image observation probe. Topography measuring device comprising a reference crystal lattice as described above. 7. A sample measuring probe, a scanning mechanism capable of scanning in at least one direction of the sample surface and a direction perpendicular to the sample surface, and a sample or a sample measuring probe fixed thereto, and a scanning direction of the sample surface. A reference crystal lattice which is provided on the side surface of the scanning mechanism in a direction perpendicular to and parallel to the sample surface and which can be scanned independently of the scanning mechanism in a direction perpendicular to the sample surface, and a crystal lattice for observing the reference crystal lattice image A surface shape measuring device including an image observation probe. 8. A sample measurement probe, a scanning mechanism capable of scanning in at least one direction of the sample surface and a direction perpendicular to the sample surface, and a sample or sample measurement probe fixed thereto, and a scanning direction of the sample surface. And a crystal lattice image observing probe provided on a side surface of the scanning mechanism in a direction perpendicular to and parallel to the sample surface, and a reference crystal lattice capable of scanning in a direction perpendicular to the sample surface by the crystal lattice image observing probe. Surface shape measuring device. 9. The surface profile measuring apparatus according to claim 5, wherein a parallel spring is used as the scanning mechanism. 10. The surface profile measuring apparatus according to claim 5, which has a calibration function by an optical wave interferometer.