JPH04301501A - Reference scale plate and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a reference scale for calibrating the moving distance of a probe moving device at the hyperfine processing/measuring time by nanometer(nm) or so in a usable constitution for a long term, and to establish a manufacture thereof. CONSTITUTION:A liquid crystal (PYP-909) is applied on the cleavage of a substrate of highly orientative graphite (HOPG). Stick-like molecules of the liquid crystal are made to be adsorbed into a striped pattern with a distance of the molecular length (2.5nm). Then, a pulse voltage is impressed between a probe of an STM and the substrate corresponding to the electric conductivity at the surface of the pattern measured by the STM. As a result, a reference scale of the substrate having the corrugated surface corresponding to the striped pattern of the stick-like molecules is obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Fields] Standard scale plates used in ultra-fine machining, ultra-fine characteristic measurement, etc., where technology is currently becoming more sophisticated.
The present invention relates to a manufacturing method thereof.

0002

[Prior Art] Recently, scanning tunneling (STM) is
It has become widely used as a means of evaluating the processing accuracy of various microfabricated products such as plates and LSIs.

[0003] In STM, a metal probe with an extremely sharp tip is brought close to a conductive object to be measured within a few nanometers, and the tunnel current that flows due to the bias voltage (about several volts) applied between these probes is measured. Since the tunneling current responds sensitively to extremely small changes in the distance between the probe and the object to be measured, it is possible to measure the size of even a single atom on the object to be measured. In the above STM, if the tunneling current flowing through the probe is kept constant and scanned over the surface of the sample to be measured, the shape of the sample can be determined from the trajectory of the probe (constant current mode). {G. Binnin
g and h. Rohrer: Helv. Phy
s. Acta, 55 (1982) 726}. As described above, STM can have extremely high resolution and is also used in research to measure the atomic arrangement on the surfaces of various materials. Furthermore, recently, instead of detecting tunneling current in STM, atomic force microscopes (AFM), which measure by the atomic force acting between the probe and the sample surface, and magnetic force microscopes (MFM), which measure by the magnetic force between them, have been developed. ) and other microscopes with new functions based on STM have been developed and are being applied to various fields. In addition, for the movement of the probe in the STM and other microscopes described above (scanning in the vertical direction and on the sample surface), a piezoelectric element using piezoelectric ceramics, etc., which can move extremely smoothly, is used. It was used. Research is also being conducted to apply this movement method using piezoelectric elements to extremely fine surface processing on the order of nanometers (nm).

0004

[Problem to be solved by the invention] STM explained above
Although the method described above allows smooth movement even in the nanometer range, the piezoelectric element used for movement does not necessarily move in a straight line with respect to the applied voltage. Therefore, it is necessary to calibrate the moving device by comparing it with a reference scale within the range to be moved using the STM method.

The atomic arrangement pattern on the surface of a crystal such as highly oriented graphite (HOPG) can be used as a standard scale in the conventional sub-nanometer region.If the atomic arrangement pattern of HOPG etc. has the accuracy to detect this atomic arrangement, the atomic arrangement pattern of HOPG etc. can be used as the reference scale. However, not all instruments have the precision to detect such atomic arrangements. ST
M and the like are actually used in the nanometer range, but a reference scale in this range cannot be produced using conventional techniques (photolithography, electron beam processing, etc.).

The present invention solves the problem of creating a reference scale in nanometer units in the range of several nm to about 10 nm, in which the STM technology described above is actually used, and is suitable for calibrating mobile devices such as STM. The purpose is to provide a standard scale and its manufacturing method.

[0007]

[Means for Solving the Problems] The scale that achieves the object of the present invention described above uses a flat crystal substrate having relatively high resistance and conductivity as a semiconductor such as HOPG or molybdenum disulfide. . On the surface of the substrate, an organic compound that adsorbs to a monolayer thickness is coated in stripes with rod-shaped molecules separated by a molecular length of about several nanometers, and the coated film is subjected to STM.
A striped uneven shape corresponding to the striped pattern is created on the surface of the substrate by scanning with a probe and applying electric pulses corresponding to the electrical conductivity of the film.

By selecting the organic compound above, S
It is possible to produce a reference scale with irregularities of approximately several nanometers, which is suitable as a reference scale for movement such as TM.

[0009]

[Function] In STM, etc., which is expected to be used for microstructure measurement and microfabrication, the scanning range of the device is This makes it possible to control the movement of the probe with high precision.

0010

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. As the material of the substrate used in this example, HOPG was used because the substrate required flatness and mechanical stability on an atomic scale.

The organic compound coated on the conductive substrate described above is also an organic material composed of various rod-shaped molecules including liquid crystal materials, and when adsorbed onto the substrate surface, it forms on the substrate at intervals corresponding to the molecular length. STM observation revealed that the stripes were arranged in a striped pattern. The above-mentioned organic materials can be relatively easily synthesized with various molecular lengths (up to several nanometers) depending on the molecular configuration, so it is possible to fabricate a material suitable for calibration as a reference scale for an STM device.

In this example, pyrimidine liquid crystal PYP-909{5-n-Nony
l-2-(4-nonyl Oxyphenyl)-
pyrimidine} using {J. K. Spong
et al.: Nature, 339 (1989) 137}. This liquid crystal exhibits sequential phase transitions depending on the following temperature ranges. Crystal phase<35°C<Smectic C<60°C<Smectic A<75°C<Isotropic liquid.

In this example, first, PYP-909 powder was placed on the cleavage surface of a substrate made by cleavage of HOPG, and the temperature was raised to 80° C. to turn the powder into a liquid state. Subsequently, the substrate was gradually cooled down to room temperature (20°C) at a cooling rate of 0.5°C/min, and then lightly immersed in acetone to dissolve and remove only the solid crystal portion on the substrate surface. The surface of the HOPG from which only the solid crystals were removed showed the same level of metallic luster as when it was cleaved.

After the above steps, the surface of the substrate was observed using an STM (USM-301, manufactured by Unisoku Co., Ltd.). A perspective view of the outline of the bright and dark images observed above is shown in FIG. 2. FIG. 2 shows a state in which rod-shaped molecules are arranged in a striped pattern with an interval of about 2.5 nm. The STM probe used for this observation was a 0.4 mmφ tungsten wire formed by mechanical polishing, and the bias voltage Vt = 1.0 V.
The tunnel current It was set to 0.1 nA and measured in variable current mode. This variable current mode is a method in which the probe is kept at a constant height from the substrate surface and scanned, and irregularities on the substrate surface are measured as changes in tunnel current.

The brightness and darkness of the image in FIG. 2 indicates the magnitude of the tunnel current at that position, and the larger the current value, the brighter (whiter) the image becomes. The stripe spacing shown in FIG. 2 is in good agreement with the value reported by Spong et al. The data presented above indicate that such a molecular arrangement pattern can be produced with good reproducibility, and that the formed stripe spacing pattern can be used on a reference scale of about nanometers.

However, when we continuously observed the molecular arrangement pattern on the HOPG substrate formed above, we found that it was stable for about 10 days, but it is hoped that the arrangement of adsorbed molecules can be maintained for a longer period of time. I found out that I can't do it. Therefore, in this example, in order to maintain the striped pattern of the molecular arrangement obtained above in a stable uneven shape on the underlying HOPG substrate, the following experiment was conducted.

That is, in the bright part of the striped pattern shown in FIG. 2, that is, the part with high electrical conductivity, a voltage pulse higher than that in the measurement state was applied between the probe and the substrate. The voltage of the high voltage pulse is 3.0V to 4.0V,
The pulse width was varied from 100 μsec to 500 μsec. The PYP-
An uneven image on the surface of the HOPG substrate having the same pattern as the striped pattern of 909 was formed as shown in FIG. The depth of the groove in FIG. 1 was 0.3 nm.

As described above, the formation of grooves on the HOPG surface is presumed to be caused by local electrical discharge machining caused by the voltage applied between the extremely sharp tip of the SEM probe. The depth of the grooves formed above can be changed by applying a pulse voltage, and in the pattern of this example, even if the depth of the grooves is changed in the range of 0.1 nm to 0.5 nm, a good shape can be obtained. A standard has been obtained. FIG. 1 shows Vt=0.
It was measured in constant current mode at 5V and It=0.6nA.

As can be seen from the embodiments of the present invention explained above, in this embodiment, the scale is formed based on the arrangement pattern of liquid crystal molecules. By calibrating nonlinearity with respect to applied voltage, the effect on processing and measurement accuracy can be reduced to a negligible level. The reference scale prepared above has a striped concavo-convex pattern formed at regular intervals depending on the length of the liquid crystal molecules used, and can be used for calibrating a piezoelectric element for moving a probe in SEM, etc. It is also possible to check the characteristics of the probe used based on the measurement curve.

The present invention has been described above with reference to Examples, but the present invention is not limited to the Examples. For example, the substrate used is Mo, which is a conductive layered compound.
The hexagonal surface of S2 may be used, and 8CB (4-octyl-4'-c
The same effect as in the example can be obtained by using yanobihenyl).

In addition to the above materials, semiconductor materials such as silicon (Si) and gallium arsenide (GaAs) can also be used as long as they are electrically conductive and can form a flat surface. Furthermore, the molecular length is different,
By using organic materials arranged in stripes on a conductive substrate, it is possible to form striped reference scales with various spacings (2 to 10 nm) on the order of nanometers, allowing specifications to be tailored to the purpose. It can be made into

In the above, the reference scale of the present invention is STM
Although the calibration of a probe moving device using a piezoelectric element has been described, it can also be used to calibrate a particle beam scan of an electromagnetic scan of an STM electron beam.

[0023]

[Effects of the Invention] The method using the molecular length of rod-shaped molecules according to the present invention can produce a nanometer-sized striped reference scale with high precision and good reproducibility, which cannot be produced using conventional photolithography technology. . Therefore, it can be used as a reference scale to improve the accuracy of ultra-fine processing and ultra-fine shape measurement that will be developed in the future.

[Brief explanation of the drawing]

FIG. 1 is a reference scale STM image of a striped groove pattern formed on a cleaved substrate of HOPG.

FIG. 2 is an STM image of a PYP-909 monomolecule striped array pattern formed on a conductive substrate.

Claims (4)

[Claims] 1. A reference scale plate characterized in that the surface of a conductive substrate has a shape in which wavy grooves having a wavelength of 2 nm to 10 nm and a depth of 0.1 nm to 1.5 nm are arranged in parallel. 2. The conductive substrate of claim 1 is made of highly oriented graphite (HOPG), molybdenum disulfide (MoS2
), silicon (Si), gallium arsenide (GaAs), or the like. 3. An organic compound to which a monomolecular layer of rod-shaped molecules is arranged and adsorbed in stripes is applied to the surface of a conductive substrate with a flat surface, and the surface of the striped pattern formed is scanned. Scanning is performed using a tunneling microscope (STM), and a pulse voltage corresponding to the electrical conductivity in the striped pattern is applied between the metal probe of the STM and a discharge, which corresponds to the striped arrangement pattern of the adsorbed molecules. A method for manufacturing a reference scale plate, characterized in that a groove is formed on the surface of the substrate. 4. The pulse voltage applied to form the groove according to claim 3 has a voltage of 3.0 V to 4.0 V and a pulse width of 10 V.
4. The method of manufacturing a reference scale plate according to claim 3, wherein the time is in a range of 0 μsec to 500 μsec.