JPH05177451A - Manufacture of metal probe - Google Patents

Abstract

PURPOSE:To provide an industrially advantageous method for manufacturing an excellent metal probe in which the curvature radius of the probe top end part is extremely small, and the length of the electrolytic part of the probe is equal to or less than the diameter of the probe. CONSTITUTION:In a method for manufacturing a metal probe by dipping the top end part of a probe metal base material 4 in an electrolyte 3 and electrolytically polishing it, the metal base material 4 is lowered substantially following the lowering of the meniscus surface 3' of the electrolyte formed along the metal base material 4, and the meniscus surface 3' of the electrolyte 3 is regularly kept on the boundary between a part 4' to be polished and an unpolished part thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a metal probe, and more specifically, the radius of curvature of the tip of the metal probe is extremely small and the length of the electrolytic portion of the probe is very small. The present invention relates to an industrially advantageous method for producing an excellent metal probe having a diameter equal to or smaller than the diameter.

[0002]

2. Description of the Related Art Various scanning probe microscopes (Scanning
In Probe Microscope) and the like, a metal probe having an extremely sharp tip shape is used for observing / evaluating the sample surface structure, operating / processing. In particular, the scanning tunnel microscope (Scanning T
In fields such as unneling Microscop (hereinafter abbreviated as “STM”), it is essential to develop an extremely sharp metal probe having a radius of curvature on the nanometer level.

Conventionally, as a method of manufacturing a metal probe,
Although various methods are known, the most commonly used method is a preparation method using an electrolytic polishing method. The above-mentioned preparation methods are roughly classified into two types, one of which is a method of completely terminating the electrolytic reaction of a part of the probe base material in a two-phase system solution composed of an electrolytic solution and a non-electrolytic solution, The other one is a method in which the electropolishing reaction is allowed to stand until it reaches the interface between the electrolytic solution and the atmosphere, and the electrolytic polishing is stopped by decreasing the electrolytic current or stopping the current due to the decrease of the base material in the electrolytic solution. ..

[0004]

However, in any of the above-mentioned methods, fluctuations in physical conditions at the end of electrolysis (fine voltage and current due to the tip shape of the probe at the interface between the electrolyte and the atmosphere) Therefore, there is a problem in sharpening the shape of the tip of the probe (minimizing the radius of curvature of the tip) and its reproducibility. In order to ensure reproducibility, it is conceivable to constantly monitor current and voltage fluctuations during electropolishing and perform feedback control to stabilize them, but this requires expensive monitoring and feedback control. Various equipment is required, and there is a limit to the minimization of the radius of curvature of the tip.

In addition, in order to obtain a high resolution image in STM or the like, in addition to the radius of curvature of the tip of the probe being extremely small, in order to avoid the influence of external vibration during scanning, the metal probe is used. It is necessary that the natural frequency of the needle is high. In order to increase the natural frequency of the metal probe, it is desirable that the length of the electrolytic portion of the metal probe be about the same as its diameter.

However, in the conventional method, the above-mentioned 2
It is extremely difficult to create a metal probe that satisfies the two conditions at the same time. For example, in Japanese Patent Laid-Open No. 1-135430,
Although a method of pulling up the metal base material while contacting the portion to be polished with the electrolytic solution is disclosed, this method can sufficiently minimize the radius of curvature of the tip portion of the probe, and the electrolytic portion of the probe is also minimized. Is likely to be large. The present invention has been made in view of the above circumstances, and an object thereof is that the radius of curvature of the tip portion of the metal probe is extremely small, and the length of the electrolytic portion of the probe is equal to or less than its diameter. Another object of the present invention is to provide an industrially advantageous method for producing an excellent metal probe.

[0007]

That is, the gist of the present invention is to provide a method for producing a metal probe by immersing the tip of a probe metal base material in an electrolytic solution and electrolytically polishing the metal base material. The method for producing a metal probe is characterized in that the metal base material is moved down substantially following the downward movement of the surface of the meniscus of the formed electrolyte solution.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of an electrolytic polishing apparatus for explaining an embodiment of the present invention. In the figure, (1) is an AC power supply, (2) is an electrode, (3) is an electrolytic solution, (4) is a metal base material for a probe,
(5) is a stereomicroscope, (6) is an AC ammeter, (7) is an AC voltmeter, (8) is a probe holder, and (9) is a holder position fine adjuster. When a DC power source is used as (1), (6) is a DC ammeter and (7) is a DC voltmeter.

In the present invention, the electrolytic solution (3) is
NaOH, KOH, KNO ₃ or the like is used, and tungsten (W), platinum (Pt) or the like is used as the material of the probe metal base material (4).

The method of manufacturing the metal probe of the present invention is carried out as follows. First, the electrode (2) and the tip of the probe metal base material (4) to be polished are immersed in the electrolytic solution (3). As the electrode (2), for example, a carbon rod can be used, and its dimensions are, for example, a diameter of 7 mm and a length of 5 cm.
Is. As the metal base material (4) for a probe, for example, a tungsten cylindrical rod can be used, and its dimensions are
As an example, the diameter is 0.25 mm and the length is 3 cm. As the electrolytic solution (3), for example, 1N-NaOH can be used. The probe metal member (4) is adjusted by the probe holder (8) and the holder position fine adjuster (9) so that the immersed portion at its tip is, for example, about 2 mm. Then, the focus of the stereomicroscope (5) is adjusted to the probe immersed portion.

Next, the output voltage of the AC power source (1) is set to, for example, 10 volts to start electrolytic polishing. Figure 2
It is explanatory drawing which shows an example of the process time schedule (change with time of an electrolysis current) showing the change of the electric current amount with progress of an electrolysis reaction. The electrolysis current during the electropolishing step is usually controlled so as to gradually decrease as the electropolishing progresses, as shown in FIG. Then, from the latter half of the electrolytic polishing step, referring to the display of the AC ammeter (6), while observing the tip of the polished portion of the probe metal base material (4) with the stereoscopic microscope (5), the holder position By operating the adjuster (9), the amount of immersion of the probe metal base material (4) in the electrolytic solution (3) is controlled.

In the above control, it is especially important to control the interface between the surface of the probe and the electrolyte in the gas phase. Figure 3
FIG. 4 is an explanatory view showing the state of the surface of the electrolytic solution (3) and the portion to be polished (4 ′) of the metal base material (4) during electrolytic polishing. When the metal base material (4) is dipped in the electrolytic solution (3), the electrolytic solution (3) rises around the metal base material (4) due to the surface tension of the electrolytic solution (3) to form a meniscus surface (3 '). (FIG. 3 (a)). The part where the above meniscus surface (3 ') is formed (the part indicated by (*) in Fig. 3 (b))
Has a high polishing rate, so if electrolytic polishing is continued,
The surface of the metal base material (4) is sharply polished to form a polished portion (4 ') (Fig. 3 (b)). As the polishing progresses further, the surface of the meniscus (3 ') descends and moves to the lower part of the portion to be polished (4') (Fig. 3 (c)). If the polishing is continued in such a state, the length of the electrolytic portion of the manufactured metal probe becomes long.

Therefore, in the present invention, the electrolytic solution (3)
The metal base material (4) is lowered by substantially following the lowering of the meniscus surface (3 '). As a result, in the present invention, as shown in FIG. 3 (c), the meniscus surface (3 ') is substantially always on the boundary line between the polished portion (4') and the unpolished portion on the polished portion (4 '). Maintained. The metal base material (4) is lowered by the probe holder (8) and the holder position fine adjuster (9). By controlling the drop of the metal base material (4), the length of the electrolytic portion of the metal probe to be manufactured can be made shorter than its diameter. The holder position fine adjuster (9) may be driven by either manual operation or operation by an automatic control electronic circuit.

After continuing the above operation, in the final step of electropolishing which can be judged from the process time schedule based on the change curve of the amount of current accompanying the progress of the electrolytic reaction (for example, FIG. 2 described above) and observation with a stereoscopic microscope. , A metal probe produced by making the output voltage of the AC power supply (1) several times the initial set value (for example, the initial set value of 5 V is 20 V) for a short time (for example, 1 to 2 seconds). The tip of the needle can be made extremely sharp.

FIG. 4 and FIG. 5 are explanatory views of an example of the shape of the metal probe manufactured by the above method, which is prepared on the basis of photographs observed by a scanning electron microscope (SEM). FIG. 4 is based on a photograph of SEM observation at low magnification (about 40 times) and shows the shape of the entire metal probe including the non-electrolytic polishing portion. Figure 5 shows a high magnification of SEM (about 30
(000 times), and is based on the photograph of observation, and shows the shape of the tip of the metal probe. In the above example, the length of the electrolytic portion of the metal probe is equal to or less than its diameter, and the radius of curvature of the tip of the probe can be judged to be about 5 nanometers. It is understood that there is. Therefore,
The metal probe obtained by the manufacturing method of the present invention makes use of its excellent characteristics, and is a scanning tunneling microscope (Scanning Tunneli
ng Microscope), Atomic Force Mic
roscope), Magnetic Force Microscop
e), Near Field Optical Microscope
), Scanning Photon Microscop
e) various scanning probe microscopes (Scanning Probe microscope)
Microscope), and is also useful as a metal probe in field ion microscopes, ion beam electrodes, etc.

[0016]

According to the present invention described above, the radius of curvature of the tip of the metal probe is extremely small, and the length of the electrolytic portion of the probe is about the same as or less than its diameter. The metal probe can be easily manufactured with excellent reproducibility with an extremely simple device configuration.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an electrolytic polishing apparatus for explaining an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a process time schedule (an example of changes over time in electrolytic current) showing changes in the amount of current with the progress of an electrolytic reaction.

FIG. 3 is an explanatory diagram showing a state of a portion to be polished of a metal base material and a surface of an electrolytic solution during electrolytic polishing.

FIG. 4 is an explanatory diagram of an example of a shape of a metal probe manufactured by the method of the present invention, which is created based on a photograph (magnification: about 40 times) observed by a scanning electron microscope (SEM).

FIG. 5 is an explanatory diagram of the shape of an example of a metal probe manufactured by the method of the present invention, which is created based on a photograph (magnification: about 30,000 times) observed by a scanning electron microscope (SEM). ..

[Explanation of symbols]

 1: AC power supply 2: Electrode 3: Electrolyte solution 3 ': Surface of meniscus of electrolyte solution 4: Probe 4': Part to be polished 5: Stereomicroscope 6: AC ammeter 7: AC voltmeter 8: Probe holder 9: Holder position fine adjuster

Claims (1)

[Claims] 1. A method for producing a metal probe by dipping the tip of a metal base material for a probe in an electrolytic solution and electrolytically polishing the metal base material, wherein the surface of the meniscus of the electrolytic solution formed along the metal base material is lowered. A method of manufacturing a metal probe, which is characterized in that the metal base material is lowered substantially following the metal base material.