JP2021038468A - Metal probe and method for producing metal probe - Google Patents

Abstract

To provide a convenient production method for a metal probe with a sharp tip and a metal probe produced by the method.SOLUTION: The metal probe has a fine linear substrate containing a metal or an alloy to have sublimability by oxidation, and a conical tip part with its diameter to decrease from the substrate to the tip. The substrate has a diameter of 200 μm or less. The width of an error bar in a tip curvature radius of the tip part is 100 nm or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a metal probe and a method for manufacturing the metal probe.

Atomic force microscope (AFM) and scanning tunneling microscope (STM) are known as devices for observing micron-order surface structures from the atomic level. AFM observes the surface structure of the sample by detecting the force acting between the sample and the atom of the probe. The STM uses the tunneling current flowing between the sample and the metal probe to observe the surface structure of the sample.

As described above, metal probes processed in nano-order to micron-order sizes are used in various fields. In addition to this, it is also used in probers and the like for integrated circuits (LSIs).

As a method for producing a metal probe, a method using an electrolytic polishing method, an ion beam, or the like is known. For example, Patent Documents 1 and 2 describe a method in which one end of a thin metal wire is immersed in a solution, an electric current is applied between the metal wire and the electrode, and one end of the thin metal wire is electropolished. Further, Patent Document 3 describes a method of irradiating the tip of a probe with an ion beam, etching a part of the tip, and sharpening the tip.

Japanese Unexamined Patent Publication No. 5-261625 Japanese Unexamined Patent Publication No. 2001-74634 Japanese Unexamined Patent Publication No. 2003-240700

However, the electrolytic polishing method as described in Patent Documents 1 and 2 requires the use of harmful chemicals such as potassium hydroxide and nitric acid in order to perform etching. In addition, equipment for processing these chemicals and electrochemical equipment for applying electricity to thin metal wires are required.

Further, the electrolytic polishing method is easily affected by external factors such as a change in the concentration of the etching solution and shaking. Therefore, the uniformity of the produced metal probe is poor, and the production yield is also low. Furthermore, the time required to manufacture one metal probe is long, and it takes about 15 minutes for each metal probe.

On the other hand, the method using an ion beam described in Patent Document 3 does not require the use of chemicals. However, in order to stably generate an ion beam, a larger-scale facility such as a vacuum facility is required. Further, the irradiation of the ion beam is required to have high accuracy, and the time required to manufacture one metal probe becomes longer.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a simple method for manufacturing a metal probe having a sharp tip and a metal probe manufactured by the manufacturing method.

As a result of diligent studies, the present inventors have found that a metal probe having a sharp tip can be easily produced by heating a part of a thin wire of a metal or alloy having sublimation property while oxidizing it. It was also found that the metal probe produced by this manufacturing method has high uniformity and small variation in characteristics.
The present invention provides the following means for solving the above problems.

(1) The method for manufacturing a metal probe according to the first aspect includes a step of heating while oxidizing a part of a thin wire of a metal or alloy having sublimation property by oxidation, and the heated portion is sublimated. Sharpen.

(2) In the method for manufacturing a metal probe according to the above aspect, the metal or alloy may contain tungsten or molybdenum.

(3) In the method for manufacturing a metal probe according to the above aspect, the heating may be performed using a flame discharged from a burner.

(4) In the method for manufacturing a metal probe according to the above aspect, the burner may simultaneously discharge a combustion system gas and an oxygen gas, and the flame discharged from the burner may be an oxidizing flame.

(5) In the method for manufacturing a metal probe according to the above aspect, the tip sharpened by the sublimation may be subjected to ultrasonic treatment or acid treatment.

(6) The metal probe according to the second aspect contains a metal or alloy having sublimation property by oxidation, and has a thin linear substrate extending in the first direction and a diameter reduced from the substrate toward the tip. It has a cone-shaped tip portion, and the inclination angle of the inclined surface of the tip portion with respect to the first direction is substantially constant.

(7) The metal probe according to the above aspect may have cilia made of an oxide of the metal or alloy attached to the inclined surface of the tip portion.

(8) The metal probe according to the above aspect may have a root portion that clings to the inclined surface of the tip portion and has cilia made of an oxide of the metal or alloy removed.

(9) The device according to the third aspect includes the metal probe according to the above aspect.

According to the method for manufacturing a metal probe according to the above aspect, the metal probe can be manufactured easily and inexpensively. Further, the metal probe produced by this method has high uniformity and little variation.

It is a schematic diagram of the manufacturing method of the metal probe which concerns on this embodiment. It is an electron microscope image after oxidative heating of various thin metal wires. It is an electron microscope image of a part of the metal probe according to the 2nd embodiment. It is an electron microscope image of a part of the metal probe according to the 1st embodiment. It is a graph which shows the change of the inclination angle of the inclined surface when the diameter of a thin line is changed. It is an electron microscope image of a metal probe whose tip is sharpened by electrolytic polishing. It is an electron microscope image of a part of the metal probe according to the third embodiment. The result of the composition analysis of the metal probe using the electron probe microanalyzer is shown. It is an electron microscope image of the metal probe of Example 2. It is the measurement result of the electric resistance of the metal probe of Example 2, Comparative Examples 1 and 2. It is a graph which shows the relationship between the thin line and the tip curvature radius of the tip of a metal probe.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

"Manufacturing method of metal probe"
FIG. 1 is a diagram schematically showing a method for manufacturing a metal probe according to the present embodiment. In the method for manufacturing a metal probe according to the present embodiment, a part 1a of a thin wire 1 of a metal or alloy having sublimation property by oxidation is heated while being oxidized. The heated part 1a of the thin wire 1 is sublimated and sharpened. Hereinafter, a method for manufacturing a metal probe according to the present embodiment will be specifically described.

First, a thin wire 1 as a base material for a metal probe is prepared. As the thin wire 1, a commercially available one may be purchased.

For the thin wire 1, a metal or alloy that sublimates by oxidative heating is used. FIG. 2 is an electron microscope image of various thin metal wires after being oxidized and heated. Generally, when a metal is heated, it tends to become round due to surface tension. On the other hand, the sublimation speed of a metal or alloy that sublimates by oxidative heating is faster than the speed at which it tends to be rounded by surface tension. Therefore, the portion sublimated by oxidative heating is not rounded but sharpened.

As shown in FIG. 2, tungsten (W), molybdenum (Mo) and the like have sublimation property by oxidative heating. For example, tungsten oxide (WO ₃ ) has a sublimation temperature of 800 ° C., and molybdenum oxide (MoO ₃ ) has a sublimation temperature of 1000 ° C. At temperatures above this temperature, tungsten oxide and molybdenum oxide sublimate.

In FIG. 1, the thin wire 1 is fixed by the fixing jig 10. The fixing jig 10 merely supports the thin wire 1, and does not apply an external force in the extending direction of the thin wire 1. In the method for manufacturing a metal probe according to the present embodiment, the sharpening of the tip of the metal probe is caused by the sublimation of a part of the fine wire 1. Therefore, it is not necessary to sweep the thin wire 1 with the fixing jig 10, and the fixing direction of the thin wire 1 may be perpendicular to the ground, parallel to the ground, or diagonally. Of course, an external force may be applied to the thin wire 1.

Next, a part 1a of the thin wire 1 is heated while being oxidized. The heating means may be indirect heating using electricity or the like, or direct heating using a flame. Considering that a part 1a of the thin wire 1 is heated pinpointly, it is preferable to use the flame f discharged from the burner 20.

For example, when the flame f discharged from the burner 20 is used as shown in FIG. 1, the oxygen required for oxidation is the oxygen forcibly supplied to the burner 20 even if it is present in the air. You may use it. A gas in which a combustion system gas 21 and oxygen 22 are mixed is supplied to the burner 20 shown in FIG.

When a gas in which the combustion system gas 21 and the oxygen 22 are mixed is supplied to the burner 20 at the same time, the flame f discharged from the burner 20 stably becomes an oxidizing flame. "Oxidation flame" is a flame containing excess air or oxygen, and means a portion where an oxidation reaction close to complete combustion is occurring. Generally, it is said that the outer flame part of the flame has a high temperature and is an oxidative flame.

Oxidation reaction is likely to occur in the portion heated by the oxidative flame. That is, by using the flame f discharged from the burner 20 as an oxidizing flame, oxidation and sublimation of a part 1a of the thin wire 1 are efficiently generated.

It is generally practiced to supply hydrogen gas to the burner 20 in order to increase the amount of heat of the flame discharged from the burner 20. In this case, the gas discharged from the burner 20 tends to become a reducing flame. Prone to reducing flame means that the ratio of reducing internal flame to the total flame is high.

A hydrocarbon gas can be used as the combustion system gas 21 supplied to the burner 20. As the hydrocarbon gas, known ones such as alkane gas and alkene gas can be used. For example, propane (C ₃ H ₈ ) and butane (C ₄ H ₁₀ ) are easily available and highly flammable. Therefore, these gases can be suitably used as the combustion system gas 21.

When a part 1a of the thin wire 1 is oxidatively heated, the heated part of the thin wire 1 is gradually sublimated. Then, when heated to some extent, a part 1a of the thin wire 1 is completely sublimated, and the thin wire 1 is divided into two. The heating time required for the thin wire 1 to be divided into two is about 30 seconds, although it varies depending on the conditions such as the heating temperature.

FIG. 3 is an electron microscope image of a part of the metal probe according to the present embodiment. The metal probe shown in FIG. 3 corresponds to the two divided ends of the thin line 1.

As shown in FIG. 3, at this stage, the cilia 2 are attached to the inclined surface 1Aa of the tip portion 1A of the metal probe. Cilia 2 are oxides of sublimated metals or alloys. The cilia 2 can be easily removed by ultrasonic treatment or acid treatment of the tip portion 1A sharpened by sublimation.

As described above, according to the method for manufacturing a metal probe according to the present embodiment, the metal probe can be easily manufactured with almost no use of harmful chemicals or the like. Moreover, since the tip of the metal probe is formed by the sublimation of the thin wire, it is not easily affected by disturbance. That is, a uniform metal probe can be obtained with high accuracy.

"Metal probe"
(First Embodiment)
FIG. 4 is an electron microscope image of a part of the metal probe according to the first embodiment. The metal probe according to the first embodiment has a substrate (not shown) and a tip portion 1A.

The substrate corresponds to the portion of the thin line 1 (see FIG. 1) that has not been sublimated. That is, it refers to a portion of the thin wire 1 other than the heated portion 1a. Therefore, the substrate is a thin line extending in the first direction and contains a metal or alloy having sublimation property when oxidized. Here, the main component of the thin wire 1 is a metal or an alloy, and other substances are often impurities. Therefore, it may be said that the substrate 1 is made of a metal or an alloy.

The tip portion 1A is a cone-shaped portion whose diameter is reduced from the substrate toward the tip t. That is, it is the part corresponding to the tip of the metal probe. The shape of the tip portion 1A may be any of a conical shape, a triangular pyramid shape, a quadrangular pyramid shape, and the like. If heating is performed isotropically, the shape of the tip portion 1A is usually conical.

Since the tip portion 1A has a conical shape, the side surface of the tip portion 1A becomes an inclined surface 1Aa. The inclination angle θ of the inclined surface 1Aa with respect to the first direction in which the substrate extends is substantially constant from the substrate toward the tip t. Here, "substantially constant" does not mean that it is constant without allowing even a slight error, but means constant with a certain range.

That is, on any of the cut surfaces passing through the tip t of the tip 1A and the center of the cross section of the thin line 1, the line segment L connecting the boundary between the tip t of the tip 1A and the substrate and an arbitrary point on the inclined surface 1Aa. If the angle formed by the tangent line is within 20 °, it can be said that the inclination angle θ of the inclined surface 1Aa is substantially constant from the substrate toward the tip t.

FIG. 5 is a graph showing a change in the inclination angle θ of the inclined surface 1Aa when the diameter of the thin line 1 is changed. As shown in FIG. 5, the angle variation with respect to the average value of the inclination angle θ is 15.1 ° at the maximum, and the angle variation is within 20 °, which is substantially constant. Especially in a region where the diameter of the thin line 1 is narrow, the angle variation with respect to the average value of the inclination angle θ is 10 ° or less at the maximum, and it can be said that the inclination surface 1Aa has an extremely constant inclination angle from the substrate to the tip. ..

Therefore, the shape of the inclined surface 1A is neither upwardly convex nor downwardly convex with respect to the line segment L connecting the tip t of the tip portion 1A and the boundary between the substrates, but is an intermediate shape.

FIG. 6 is an electron microscope image of a metal probe whose tip is sharpened by electrolytic polishing. As shown in FIG. 6, the tip of the metal probe sharpened by electrolytic polishing exponentially shrinks from the substrate toward the tip. That is, the inclined surface is recessed toward the center of the thin line, and the inclination angle of the inclined surface at the tip portion gradually decreases from the substrate toward the tip. Such a shape is affected by the surface tension of the solution and is peculiar to a metal probe manufactured by electrolytic polishing.

Further, the inclined surface of the metal probe whose tip is sharpened by electrolytic polishing may have protrusions that stand up against the inclined surface. It is considered that this is because air bubbles generated immediately after the start of polishing adhere to the tip and the polishing speed of the tip becomes uneven.

As described above, the metal probe according to the present embodiment is different from the metal probe produced by electrolytic polishing. The tip shape of such a metal probe is a unique shape obtained by the above-mentioned method for manufacturing a metal probe.

The radius of curvature of the tip of the tip 1A of the metal probe according to the present embodiment depends on the diameter of the thin line 1 (see FIG. 1) prepared at the time of processing. When the diameter of the thin wire 1 is large, the radius of curvature of the tip is large, and when the diameter of the thin wire 1 is small, the radius of curvature of the tip is small. In other words, the radius of curvature of the tip of the tip 1A of the metal probe according to the present embodiment can be arbitrarily set. For example, if the diameter of the thin wire 1 is 0.5 mm, the radius of curvature of the tip is about 500 nm, and if the diameter of the thin wire 1 is 0.1 mm, the radius of curvature of the tip is about 50 nm.

(Second Embodiment)
FIG. 3 is an electron microscope image of a part of the metal probe according to the second embodiment. The lower part of the metal probe according to the second embodiment shown in FIG. 3 is not subjected to ultrasonic waves or acid treatment in the above-mentioned method for manufacturing a metal probe.

The metal probe according to the second embodiment is different from the metal probe according to the first embodiment in that it has cilia 2. Other points are the same as those of the metal probe according to the first embodiment. That is, the metal probe according to the second embodiment has a substrate (not shown), a tip portion 1A, and cilia 2.

As shown in FIG. 3, the cilia 2 are formed so as to cling to the inclined surface 1Aa of the tip portion 1A. The cilia 2 are formed by reattaching a part of the thin line 1 (see FIG. 1) that has been oxidized and sublimated. Therefore, the cilia 2 are made of an oxide of a metal or alloy constituting the fine wire 1.

The cilia 2 are unique to the method for manufacturing a metal probe according to the present embodiment. When measuring the surface of an object to be measured or the like using a metal probe, it is the tip t of the tip portion 1A that directly faces the metal probe. Therefore, it is possible to perform the measurement even if the cilia 2 are clinging to the inclined surface 1Aa of the tip portion 1A.

(Third Embodiment)
FIG. 7 is an electron microscope image of a part of the metal probe according to the third embodiment. The metal probe according to the third embodiment shown in FIG. 7 is an enlargement of the upper part of the metal probe in FIG.

The metal probe according to the third embodiment is different in that it has a root 3 with respect to the metal probe according to the first embodiment. Other points are the same as those of the metal probe according to the first embodiment. That is, the metal probe according to the third embodiment has a substrate (not shown), a tip portion 1A, and a root portion 3.

As shown in FIG. 7, the root portion 3 is formed so as to cling to the inclined surface 1Aa of the tip portion 1A. The root portion 3 is in a state in which the cilia 2 shown in FIG. 3 have been removed. Depending on the conditions of ultrasonic waves or acid treatment, the portion of the cilia 2 that corresponds to the hair root remains as the root portion 3. Like the cilia 2, the root portion 3 is made of an oxide of a metal or alloy constituting the fine wire 1.

The root portion 3 is unique to the method for manufacturing a metal probe according to the present embodiment. When measuring the surface of an object to be measured or the like using a metal probe, it is the tip t of the tip portion 1A that directly faces the metal probe. Therefore, it is possible to perform the measurement even if the root portion 3 is attached to the inclined surface 1Aa of the tip portion 1A.

The metal probe may have cilia 2 and root 3 at the tip 1A at the same time. As described above, FIG. 7 is an enlarged view of the upper part of FIG. 3, and may have cilia 2 and root 3 at the same time. In the method of manufacturing a metal probe, the shape changes depending on the extent to which ultrasonic waves or acid treatment is applied.

The metal probe according to this embodiment is used for various devices. Devices include atomic force microscope (AFM), scanning tunneling microscope (STM), 4-terminal measurement probe, failure analysis probe for semiconductor elements such as LSI, electrical measurement probe such as probe station, neural potential, and brain. Examples thereof include a probe for measuring a bioelectric signal. Further, the metal probe is not limited to one device, and can be used for a device such as a probe manufactured by collecting a large number of a plurality of metal probes according to the present embodiment.

Among these devices, for example, the AFM and STM include a metal probe in a portion close to the measurement sample. Observe the surface structure of the sample by detecting the atomic force between the sample and the probe and the tunnel current. Further, for example, the inspection probe is provided with a metal probe at a portion in contact with the measurement target. The metal probe functions as a metal electrode and measures nerve transmission in the brain or the like as an electrical signal. The test probe may have multiple metal probes to simultaneously measure neurotransmission at multiple locations.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and varies within the scope of the gist of the present invention described in the claims. Can be transformed / changed.

"Example 1"
First, a thin wire made of molybdenum having a diameter of 0.2 mm was prepared. Then, one end of the thin wire was fixed, and a flame discharged from the burner was applied to a part of the thin wire. Butane (C ₄ H ₁₀ ) and oxygen (O ₂ ) were supplied to the burner in equal amounts. The temperature of the flame corresponding to the thin line was about 3000 degrees.

Then, when the flame was continuously applied to a part of the thin line for 30 seconds, the thin line was cut. Then, the cut end was ultrasonically cleaned in ethanol (30 seconds in a 55 W ultrasonic bath) to prepare a metal probe. FIG. 3 is an electron microscope image of the produced metal probe, and FIG. 7 is an electron microscope image of the portion subjected to ultrasonic treatment.

Moreover, the composition analysis of the metal probe of Example 1 was performed using an electron probe microanalyzer (EPMA). As a result, it was confirmed that the tip of the metal probe was made of molybdenum, and the cilia clinging to the tip were made of molybdenum oxide.

FIG. 8 shows the results of composition analysis of a metal probe using an electron probe microanalyzer. FIG. 8A is an electron microscope image, FIG. 8B is the result of composition analysis using the specific element as molybdenum, and FIG. 8C is the result of composition analysis using the specific element as oxygen. Is. From FIG. 8 (b), it can be confirmed that the tip portion and the cilia contain molybdenum, and from FIG. 8 (c), it can be confirmed that the cilia contain more oxygen than the other parts. That is, it can be confirmed that the cilia are composed of molybdenum oxide.

"Example 2"
The second embodiment differs only in that the thin wire is changed to tungsten. Other conditions were the same as in Example 1.

9A and 9B are electron microscope images of a metal probe having a diameter of 0.2 mm, in which FIG. 9A is a photograph taken at a magnification of 500 and FIG. 9B is a photograph in which the tip is enlarged at a magnification of 10,000.

In both the metal probes shown in Examples 1 and 2, the inclination angle of the inclined surface of the tip portion with respect to the first direction was constant from the substrate to the tip.

Next, the electrical resistance of the metal probe produced in Example 2 was measured. Electricity when a probe made of a tungsten wire having a diameter of 0.2 mm and a length of 15 mm is placed on a manipulator of a probe station and the probe is brought into contact with a gold electrode pad having a thickness of 30 nm formed on a silicon substrate. By measuring the resistance, the electrical resistance on the surface of the probe was measured. At the same time, the electrical resistance of the thin wire before processing (Comparative Example 1) and the metal probe produced by electrolytic polishing (Comparative Example 2) were also measured. The result is shown in FIG.

As shown in FIG. 10, the metal probe of Example 2 had a lower electric resistance than the metal probe produced by electrolytic polishing (Comparative Example 2). For example, STM and the like observe the surface structure of the sample using the tunnel current flowing between the sample and the metal probe. Therefore, if the electrical resistance of the metal probe is low, more precise measurement can be performed.

Further, as shown in FIG. 10, the metal probe of Example 2 has a smaller error bar than the metal probe of Comparative Example 2. That is, it can be said that the metal probe of Example 2 has excellent uniformity and less noise than the metal probe of Comparative Example 2.

"Example 3"
The radius of curvature of the tip of the tip of the metal probe was measured by changing the diameter of the thin wire used to make the metal probe. Molybdenum and tungsten were used as the materials constituting the fine wire. The tip radius of curvature was determined as the average value of five metal probes with each diameter. The result is shown in FIG.

As shown in FIG. 11, a correlation was found between the diameter of the thin wire used for manufacturing the metal probe and the radius of curvature of the tip of the tip of the metal probe. Further, in the region where the diameter of the thin wire is 200 μm or less, the width of the error bar of the radius of curvature of the tip is small. The range that is expected to be actually used as a metal probe is this region, and a metal probe having particularly excellent uniformity was obtained in this region.

1 ... Fine wire, 1a ... Part, 1A ... Tip, 1Aa ... Inclined surface, 2 ... Cilia, 3 ... Root, 10 ... Fixing jig, 20 ... Burner, 21 ... Combustion gas, 22 ... Oxygen, f ... Flame , T ... tip

Claims (4)

A fine linear substrate containing a metal or alloy that is sublimable by oxidation,
It has a cone-shaped tip portion whose diameter is reduced from the substrate toward the tip end, and has a conical tip portion.
The diameter of the substrate is 200 μm or less.
A metal probe in which the width of the error bar having the radius of curvature of the tip of the tip is 100 nm or less. A fine linear substrate containing a metal or alloy that is sublimable by oxidation,
It has a cone-shaped tip portion whose diameter is reduced from the substrate toward the tip end, and has a conical tip portion.
The diameter of the substrate is less than 200 μm.
A metal probe having an angle variation of 10 ° or less with respect to an average value of the inclination angles of the inclined surface of the tip portion. A method for manufacturing a metal probe, which comprises a step of heating while oxidizing a part of a thin wire of a metal or alloy having a diameter of 200 μm or less and having sublimation property by oxidation, and the heated portion is sharpened by sublimation. The method for manufacturing a metal probe according to claim 3, wherein the heating is performed using an oxidizing flame discharged from a burner that simultaneously discharges a combustion system gas containing a hydrocarbon and an oxygen gas.