JP2003321800A - Electrolytic polishing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic polishing method by which the sticking of generated bubbles on an article to be electrolytically polished can be reduced. <P>SOLUTION: The tip of a metal wire is immersed into an electrolytic solution from a lower surface of the electrolytic solution, and a counter electrode is brought into contact with the electrolytic solution. Thereafter, the tip of the metal wire is electrolytically polished by applying voltage between the metal wire and the counter electrode and passing a current through the electrolytic solution. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electropolishing method, and more particularly to an electropolishing method for forming a sharp tip on a metal wire.

[0002]

BACKGROUND OF THE INVENTION Sometimes a metal wire with a sharp tip is required. For example, scanning tunneling electron microscope (ST
The resolution in M) largely depends on the shape of the tip of the probe. The smaller the radius of curvature of the tip, the better the resolution. Ideally, a size of about 1 atom is desirable. In addition, a probe of an atomic force microscope and a metal wire having a sharp tip are required for the cathode of a field emission electron gun.

As a method of producing a metal wire having a sharp tip, electrolytic polishing is generally well used. A conventional electrolytic polishing method will be described with reference to the drawings. As shown in FIG. 5 (A), the electrolytic solution 2 is contained in the container 9,
For example, the annular electrode 3 is immersed in the surface layer of the electrolytic solution 2.

The tip of the metal wire 1 which is the material of the probe is immersed in the liquid surface surrounded by the annular electrode 3 for about 1 mm. Metal wire 1
For example, a wire of platinum, platinum-iridium alloy, tungsten or the like having a diameter of 0.1 to 0.3 mm. As the electrolytic solution 2, a calcium chloride aqueous solution, a cyanide compound aqueous solution, an alkali metal hydroxide aqueous solution, an inorganic acid or the like is used in combination with the probe material. Power supply 4 between metal wire 1 and ring electrode 3
Voltage is applied to perform electrolytic polishing. The current detector 5 detects a change in current during electropolishing, and based on the change in current, the voltage applied to the power source 4 is turned off, and electropolishing is terminated.

In electropolishing, the tip of the metal wire 1 immersed in the electrolytic solution 2 is etched. The current decreases as the surface area of the metal wire 1 in contact with the electrolyte solution 2 decreases. When the surface of the metal wire 1 in contact with the electrolytic solution 2 is completely etched, the current becomes zero.

As shown in FIG. 5B, the applied voltage is cut off before and after the current becomes 0, so that a sharp projection is left at the tip of the metal wire 1. Depending on the type of metal wire used as the probe material,
The type and concentration of the electrolytic solution, the material of the annular electrode, the magnitude and waveform of the applied voltage, the electrolytic polishing termination conditions, etc. are selected.

In order to efficiently manufacture a probe having a desired shape, it is desired that electrolytic polishing can be performed with good reproducibility. If the aspect of electrolytic polishing changes each time, electrolytic polishing with good reproducibility is difficult.

As shown in FIG. 5C, the electrolytic solution 2 is electrolyzed by the electrolytic polishing, and the metal wire 1 and the annular electrode 3 are formed.
Bubbles 6 are generated from the surface of the. When the bubbles 6 come into contact with each other, they can form large bubbles that are bound together.

As shown in FIG. 5D, when the bubbles 6 are bonded to each other on the surface 8 of the electrolytic solution, they sometimes grow into large bubbles 7. The large bubbles 7 adsorb to the metal wire 1 and hinder the electrolytic polishing in the bubble portion. Large bubbles grow steadily and eventually burst and disappear. At this time, the electropolishing current decreases with the growth of the large bubbles 7, and returns to the original value due to the disappearance of the large bubbles 7. Since the large bubbles 7 are irregularly generated during the electropolishing, the history of the electropolishing reaction differs for each probe, and it is difficult to produce a sharp probe with high yield.

Japanese Patent No. 2965180 proposes to change the liquid surface shape of the electrolytic solution. As shown in FIG. 6, after the annular electrode 3 is immersed in the electrolytic solution 2, the annular electrode 3 is lifted. Due to the surface tension, the liquid surface 8 of the electrolytic solution 2 rises together with the annular electrode 3. Ring electrode 3 as shown
Inside, the liquid surface is formed that is lowered downward toward the central portion. Bubbles 6 generated by electrolytic polishing of the metal wire 1
Flies upward, but moves toward the annular electrode 3 from the vicinity of the metal 1 because the liquid surface 8 has a gradient. Therefore, it is described that the bubbles do not stick to the probe material and hinder the etching.

The present inventors tried to carry out this method, but it was not easy to carry out it well. There is a demand for an electrolytic polishing method that can easily and surely prevent the generation of large bubbles and can perform electrolytic polishing with good controllability.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrolytic polishing method capable of forming a sharp tip at the end of a metal wire with good controllability.

Another object of the present invention is to provide an electropolishing method in which bubbles generated are reduced from adhering to an electropolishing object.

[0014]

According to one aspect of the present invention, from the lower surface of the electrolytic solution, the tip of the metal wire is dipped in the electrolytic solution to bring the counter electrode into contact with the electrolytic solution, and the metal wire and the There is provided an electrolytic polishing method for electrolytically polishing the tip of the metal wire by applying a voltage between the counter electrode and a current flowing through the electrolytic solution.

[0015]

1A is a schematic sectional view showing an electrolytic polishing method according to an embodiment of the present invention. Container 9a
Indicates an inverted state. The container 9a is glass,
It is made of an insulating material such as synthetic resin, has an inner diameter of about 10 mm and an opening at one end 20, and has a counter electrode 10a at the bottom 30. The electrolytic solution 2 of, for example, an aqueous solution of calcium chloride is stored in the container 9a and fixed with the opening facing downward. Since the bottom of the container 9a is hermetically closed, the electrolytic solution 2 does not drop even if the opening of the container faces downward.

As described above, the electrolytic solution is contained in the container having one end opened, and the electrolytic solution can be held in the container while keeping the opening downward by utilizing the atmospheric pressure or the action of the atmospheric pressure and the surface tension. it can. An exposed lower surface is formed in the electrolytic solution. It becomes possible to immerse the electrolytic polishing object in the electrolytic solution from the lower surface of the electrolytic solution.

The metal wire is a metal wire having a diameter of about 0.1 to 0.5 mm which can be inserted into the opening. For example, a platinum-iridium alloy (platinum 9
0% -iridium 10%) line is used. The metal wire 1 is dipped from below, for example, vertically into the exposed lower surface 7 of the electrolytic solution 2 and penetrates into the electrolytic solution by about 1 mm.

In this state, the metal wire 1 and the counter electrode 10a are connected to the power source 4 and the current detector 5 using the wires L1, L2 and L3. A voltage is applied between the metal wire 1 and the counter electrode 10a from the power source 4, and a current is caused to flow through the electrolytic solution 2, for example, in the form of direct current, alternating current, or pulse. When an electric current flows through the electrolytic solution 2, the electrolytic solution 2 is electrolyzed and the tip of the metal wire 1 is electropolished. The current detector 5 detects the flowing current. Monitor the current change and shut off the current at the desired time. In this way, the electrolytic polishing of the tip of the metal wire 1 is performed.

Bubbles 6 generated from the surface of the metal wire 1 during electrolytic polishing are directed upward due to buoyancy. That is, the bubbles are not adsorbed on the surface of the metal wire 1 inserted into the electrolytic solution 2 from below, and the bubbles move upward away from the surface of the metal wire 1. Even if air bubbles are accumulated in the upper part of the container 9a and a gas phase space is formed, the counter electrode 1
0a is arranged so as to maintain a sufficient contact area with the electrolytic solution 2.

The counter electrode 10a does not have to be embedded in the bottom of the container 9a, and may be provided at any place where it comes into contact with the electrolytic solution 2. For example, a counter electrode may be provided in the middle portion of the container 9a as shown by the broken line 10b. Also,
The counter electrode 10a is preferably provided at a position other than directly above the metal stopper. Bubble 6 rising from the metal stopper is the counter electrode 1
It is possible to reduce the possibility of reducing the current flowing by adsorbing to 0a.

Since bubbles have buoyancy in the electrolytic solution, they always move upward in the electrolytic solution. When the metal wire to be electrolytically polished is introduced from above the electrolytic solution, it is unavoidable that the bubbles generated near the lower end of the metal wire come into contact with the side wall of the metal wire 1 and are adsorbed when moving upward. Large bubbles are generated when many bubbles are combined. If the metal wire 1 is made to enter from below the electrolytic solution 2, rising bubbles are less likely to be adsorbed on the surface of the metal wire 1.

Therefore, the possibility that large bubbles are generated is small, and the electrolytic polishing is prevented from being hindered by the bubbles 6. Therefore, a sharp tip can be formed at the end of the metal wire 1 with good controllability.

FIG. 1B shows a modification of the counter electrode.
An annular electrode 10c is provided near the open end of the container 9a. The metal wire 1 is inserted toward the space defined by the annular electrode 10c. Similar to the embodiment shown in FIG. 1A, it is possible to reduce the possibility that bubbles are adsorbed on the surface of the metal wire 1. According to this configuration, it is possible to prevent bubbles generated from the surface of the metal wire 1 from decreasing the contact area between the counter electrode 10c and the electrolytic solution 2.

FIG. 1C shows a further modification of the container. Both ends 20, 30 of the container 9b are open. The upper end 30 forms a large diameter portion, and the lower end 20 forms a small diameter portion. The small-diameter portion is selected to have a size and shape such that the electrolytic solution does not flow down when the electrolytic solution 2 is contained in the container 9b.

In the shape shown in the figure, the container 9b is formed with a small diameter portion at a constant distance from the lower end 20, and the diameter is stepwise enlarged to be continuous with the large diameter portion. An annular electrode 10d is provided at the lower end of the large diameter portion. Even with this configuration, FIG.
Similar to the embodiment shown in (A), bubbles generated from the surface of the metal wire are not adsorbed on the surface of the metal wire 1 and face upward, so that electrolytic polishing can be performed with good controllability.

The counter electrode 10d is also arranged at a position largely separated laterally from the extending direction of the metal wire 1.
The possibility that the bubbles generated from 0d will be adsorbed on the surface of the metal wire 1 is extremely low, and the possibility that the bubbles generated from the surface of the metal wire 1 will be adsorbed to the counter electrode 10d is also extremely low.

FIG. 1D shows a further modified example. The container 9c has a small diameter opening 21 and a large diameter opening 22 at the top,
The bottom portion 30 has a closed bottle shape. The small-diameter opening 21 is selected in such a size and shape that the electrolytic solution 2 does not flow down even if the electrolytic solution 2 is housed in the container 9c and inverted. Large diameter opening 22
Has a shape suitable for injecting the electrolytic solution 2, and the stopper 11
It can be closed with a. A counter electrode 10e is formed on the surface of the plug 11a, and a lead portion penetrates the plug 11a and is drawn to the outside.

The electrolytic solution 2 is contained in the container 9c, the large-diameter opening 22 is closed by the plug 11a, and the container 2 is inverted to obtain the state shown in the drawing. The lower surface 7 of the electrolytic solution is exposed in the small-diameter opening 21. The metal wire 1 is immersed in the electrolytic solution from the lower surface 7 of the electrolytic solution exposed in the small-diameter opening 21. Electrolytic polishing is performed by applying a voltage between the metal wire 1 and the counter electrode 10e. As in the above-described embodiment, bubbles generated on the surface of the metal wire 1 are less likely to be adsorbed on the surface of the metal wire.

In the embodiment shown in FIGS. 1A to 1D, the lower surface 7 exposed to the electrolytic solution is formed, and the metal wire 1 to be electrolytically polished penetrates into the exposed lower surface 7 from below. Therefore, the bubbles generated from the surface of the metal wire 1 separate from the surface of the metal wire 1 as they move upward, and are less likely to be adsorbed on the surface of the metal wire 1. In FIGS. 1A and 1B, a cylindrical container having one end closed and the other end open is used, and the electrolytic solution is held in the container mainly by atmospheric pressure. Figure 1
In (C) and (D), the upper end of the container may be open or closed. The electrolytic solution 2 in the small-diameter opening 21 is retained mainly by surface tension.

When the probe is used in a scanning tunneling microscope or an atomic force microscope, the probe is held by a probe fixing jig. It is also possible to carry out electrolytic polishing of a metal wire in a state of being connected to a jig. The jig is insulative.

FIG. 2A is a schematic sectional view showing an electrolytic polishing method according to another embodiment of the present invention. The container 9d is a cylindrical container with both ends 23 and 32 open. The metal wire 1 is fixed to the jig 12, and projected from the surface of the jig 12 by about 1 mm. A jig 2 in which one end 23 of the container 9d is fixed to the metal wire 1
Close with. The electrolytic solution 2 is housed in the container 9d, and the counter electrode 10 is brought into contact with the electrolytic solution 2 from above. A current is caused to flow from the power source 4 between the counter electrode 10 and the metal wire 1, the flowing current is detected by the current detector 5, and electrolytic polishing is performed.

In this embodiment, a jig having a fixed metal wire is used instead of the exposed lower surface 7 of the electrolytic solution of the embodiment shown in FIG. 1A, and the metal wire is inserted into the electrolytic solution from the lower surface of the electrolytic solution. is doing. The counter electrode 10 is inserted into the electrolytic solution from above the electrolytic solution 2. The other points are the same as those of the embodiment shown in FIG.

In FIG. 2B, a jig 12 to which the metal wire 1 is fixed is used instead of the exposed electrolytic solution lower surface 7 of the embodiment shown in FIG. 1C. The counter electrode 10f is an annular electrode and penetrates into the electrolytic solution 2 from above. Other points are the same as those of the embodiment shown in FIG.

It will be apparent to those skilled in the art that the electropolishing as shown in FIGS. 1B and 1D can be performed by using the jig 12 to which the metal wire is fixed. Also in these modes, as in the examples shown in FIGS. 1A to 1D, bubbles generated on the metal wire surface are less likely to be adsorbed on the metal wire surface.

FIGS. 3A to 3C are schematic sectional views showing still another embodiment of the present invention. As shown in FIG. 3 (A), one end 32 of a cylindrical container 9d having an inner diameter of about 5 mm and open at both ends 23, 32 is closed with a lid 14 to accommodate the electrolytic solution 2 in the container 9d halfway. Stopper 1 with metal wire 1 fixed
3, the opening of the other end 23 of the container 9d is closed, and the metal wire 1
The tip is penetrated into the electrolytic solution 2 by about 1 mm. A vapor phase space 14 is formed between the surface of the electrolytic solution and the plug 13.

As shown in FIG. 3 (B), the container 9d is turned upside down, and the stopper 13 to which the metal wire 1 is fixed is placed below. The gas phase space 14 formed above the electrolytic solution 2 is not separated from the stopper 13 and is held at the position as it is.

Therefore, the length of contact of the tip of the metal wire 1 with the electrolytic solution 2 does not change. The root portion of the metal wire 1 protruding from the plug 13 is wrapped in the gas phase space 14 and does not come into contact with the electrolytic solution 2. Next, the lid 14 arranged above is removed.

As shown in FIG. 3C, the counter electrode 10 is inserted into the electrolytic solution 2 from above and brought into contact with the electrolytic solution 2. In this state, the counter electrode 10 and the metal wire 1 are connected to the power source 4 and the current detector 5, and electrolytic polishing is performed. The electropolishing is carried out in the same way as in the above-mentioned embodiment. The bubbles generated from the surface of the metal wire 1 rarely move upward and are adsorbed on the surface of the metal wire 1. Since the metal wire portion surrounded by the vapor phase space is not electrolytically polished, the metal wire portion can be gripped by the subsequent handling, and the metal wire can be easily handled.

FIG. 3D shows a modified example of the container 9d.
One end 23 of the container 9d forms a small-diameter open portion, and the other end 32
Forms a large diameter open part. The small-diameter open portion is closed with a stopper to which a metal wire is fixed, and the counter electrode is inserted from above. By keeping the lower portion of the container 9d small in diameter, it is possible to reliably hold the gas phase space. By making the upper portion of the container 9d to have a large diameter, it is possible to reduce the possibility that bubbles are combined and large bubbles are formed.

FIG. 4 is a schematic sectional view for explaining another embodiment of the present invention. The container 9e is a cylindrical container with one end 35 opened, and the metal wire 1 is fixed to the bottom surface. First, the insulating liquid 15 is poured into the container 9e so that the upper end of the metal wire 1 is exposed above the surface of the insulating liquid 15 by about 1 mm. For example, carbon tetrachloride can be used as the insulating liquid.

Next, the electrolytic solution 2 is placed in the container 9e.
The insulating liquid 15 has a higher specific gravity than the electrolytic solution 2 and is immiscible with the electrolytic solution 2. Therefore, the insulating liquid 1
5 keeps the state arranged at the bottom of the container 9e. Metal wire 1
Has penetrated into the electrolyte solution 2 only at its upper end. Stopper 13
The root portion of the metal wire 1 protruding from is covered with the insulating liquid 15.

The counter electrode 10 is brought into contact with the electrolytic solution 2 from above, and a current is supplied from the power source 4 to carry out electrolytic polishing. The metal wire 1 in contact with the electrolytic solution 2 is electropolished. Electrolytic polishing is not performed on the root portion of the metal wire 1 which is immersed in the insulating liquid 15, and the metal wire 1 is not etched. In this way, electrolytic polishing can be performed only on the tip of the metal wire 1. The counter electrode, the container shape, etc. can be selected in various ways.

The insulating liquid is not limited to carbon tetrachloride, and various liquids can be used as long as they are insulating, do not float in the electrolytic solution, and are immiscible with the electrolytic solution. For example, a halogenated hydrocarbon other than carbon tetrachloride or a sol-like or gel-like substance may be used. Since the portion of the metal wire 1 that was immersed in the insulating liquid is not electropolished, the portion can be gripped by subsequent handling, and the metal wire can be handled easily.

The present invention has been described above according to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, and combinations can be made.

The features of the present invention will be described below. (Supplementary Note 1) From the lower surface of the electrolytic solution, the tip of the metal wire is immersed in the electrolytic solution, the counter electrode is brought into contact with the electrolytic solution, and a voltage is applied between the metal wire and the counter electrode to remove the electrolytic solution. An electropolishing method of electropolishing the tip of the metal wire by passing an electric current therethrough.

(Supplementary Note 2) The electrolytic polishing method according to Supplementary Note 1, wherein the counter electrode is arranged at a position other than directly above the metal wire. (Supplementary Note 3) A step of accommodating the electrolytic solution in a container having the counter electrode therein and having an opening capable of preventing the electrolytic solution from falling, and exposing the electrolytic solution with the opening facing downward through the opening. 3. The electrolytic polishing method according to appendix 1 or 2, further comprising: forming a liquid surface, and immersing the tip of the metal wire in the exposed liquid surface from below.

(Supplementary Note 4) One end of the container is opened,
4. The electrolytic polishing method according to any one of appendices 1 to 3, which is a cylindrical container having the other end closed. (Supplementary note 5) The electrolytic polishing according to any one of Supplementary notes 1 to 3, wherein the container has a small diameter portion that forms the opening at one end and a large diameter portion that has a larger diameter than the small diameter portion at the other end. Method.

(Supplementary Note 6) The supplementary note 1 to any one of Supplementary Notes 1 to 3, wherein the container has a small-diameter opening forming the opening and a large-diameter opening that can be closed with a plug and has a larger diameter than the small-diameter opening. Electrolytic polishing method.

(Supplementary Note 7) A step of sealing one end of a cylindrical container having open both ends by using a jig having the metal wire penetrating, the cylindrical container being arranged with the one end facing downward, and the electrolysis from above. 3. The electropolishing method according to appendix 1 or 2, including a step of housing a liquid in the cylindrical container, and a step of bringing the counter electrode into contact with the electrolytic solution.

(Supplementary Note 8) A step of closing one end of a cylindrical container having open both ends with a first stopper and placing the electrolytic solution in the cylindrical container with the one end facing downward, and penetrating the metal wire A step of immersing the tip of the metal wire in the electrolytic solution and closing the other end of the cylindrical container so as to leave a gas phase above the electrolytic solution by using the second stopper that has been set; And the step of contacting the counter electrode with the electrolytic solution, the other end of the cylindrical container and the electrolytic solution 3. The electropolishing method according to appendix 1 or 2, which is selected so as to maintain the vapor phase at the other end.

(Supplementary Note 9) In a container in which the metal wire is fixed to the bottom surface, a liquid that is insulative and immiscible with the electrolyte solution and has a higher specific gravity than the electrolyte solution is stored, and only the tip of the metal wire is stored. Appendix 1 or 2 including a step of exposing the electrolyte solution above the electrolyte solution and a step of accommodating the electrolyte solution above the liquid solution
The electrolytic polishing method described.

(Supplementary Note 10) The electrolytic polishing method according to Supplementary Note 9, wherein the liquid is carbon tetrachloride.

[0053]

As described above, according to the present invention,
It is possible to effectively prevent bubbles generated by electropolishing from adsorbing on the surface of the material to be polished.

Electrolytic polishing can be performed with good controllability.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view for explaining an electrolytic polishing method according to another embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view for explaining an electrolytic polishing method according to still another embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view for explaining an electrolytic polishing method according to another embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view for explaining an electrolytic polishing method according to a conventional technique.

FIG. 6 is a schematic cross-sectional view for explaining another electrolytic polishing method according to the related art.

[Explanation of symbols]

1 metal wire 2 Electrolyte 4 power supply 5 Current detector 6 bubbles 7 Lower surface (of electrolyte) 9 containers 10 Counter electrode 11 stoppers 12 jigs 13 stopper 14 Lid L lead

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B23H 9/08 B23H 9/08 C25F 3/00 C25F 3/00 C (72) Inventor Yuji Kataoka Kawasaki, Kanagawa Prefecture 4-1-1 Kamiodanaka, Nakahara-ku, Yokohama F-Term inside Fujitsu Limited (reference) 3C059 AA02 AB01 GC01

Claims (5)

[Claims] 1. From the lower surface of the electrolytic solution, the tip of the metal wire is immersed in the electrolytic solution, the counter electrode is brought into contact with the electrolytic solution, and a voltage is applied between the metal wire and the counter electrode. An electrolytic polishing method in which the tip of the metal wire is electrolytically polished by passing an electric current therethrough. 2. The electrolytic polishing method according to claim 1, wherein the counter electrode is arranged at a position other than directly above the metal wire. 3. A step of accommodating the electrolytic solution in a container having the counter electrode therein and having an opening capable of preventing the electrolytic solution from falling, and exposing the electrolytic solution to the electrolytic solution with the opening facing downward. 3. The electrolytic polishing method according to claim 1, further comprising the step of: forming a liquid surface of the metal wire and immersing the tip of the metal wire in the exposed liquid surface from below. 4. The electrolytic polishing method according to claim 1, wherein the container is a cylindrical container having one end open and the other end closed. 5. The container according to claim 1, wherein the container has a small diameter portion that forms the opening at one end and a large diameter portion that has a diameter larger than the small diameter portion at the other end. Electropolishing method.