JP6797409B2 - Catalyst surface standard etching method and its equipment - Google Patents

Description

The present invention relates to a catalyst surface reference etching method and its apparatus, and more specifically, a workpiece such as a semiconductor material such as Si, SiC, GaN or a solid oxide material represented by optical glass is subjected to abrasive grains or harmful substances. The present invention relates to a catalyst surface-based etching method and an apparatus thereof capable of flattening a flat surface or an arbitrary curved surface without using a chemical solution.

Conventionally, in the field of manufacturing semiconductor devices, various methods (polishing) have been provided for flattening or polishing the surface of a Si substrate including a Si wafer with high quality. Typically, the surface chemical action of the polishing agent (abrasive grains) itself or the action of chemical components contained in the polishing liquid increases the mechanical polishing (surface removal) effect due to the relative movement between the polishing agent and the object to be polished. There is CMP (Chemical Mechanical Polishing) that obtains a high-speed and smooth polished surface.

As the polishing agent for CMP, for example, fine particles of cerium oxide containing colloidal silica (SiO ₂ ), cerium oxide (CeO ₂ ) or lanthanum are mainly used for polishing a Si substrate, and for polishing a harder SiC substrate. , Diamond abrasive grains are used. However, as long as abrasive grains are used, not only scratches and latent scratches due to the abrasive grains remain on the surface to be processed, but also cerium oxide, which is a rare earth element, is heavily used, so resources will be depleted in the future. It is inevitable to be exposed to problems. Further, since CMP uses fine particles such as colloidal silica, there are problems that the treatment of the polishing liquid is costly and the compatibility with the clean room is poor.

Therefore, the present inventors have proposed a catalyst surface reference etching (CARE: CAtalyst-Referred Etching) method capable of flattening a workpiece to a flat surface or an arbitrary curved surface without using an abrasive or abrasive grains. Has been done. The CARE method is a processing technique that does not use any abrasives or abrasive grains, and is an ideal processing method that does not introduce any scratches or work-altered layers on the surface to be processed by processing, that is, there is no crystallographic damage. In the early stages of development, the CARE method was developed for the purpose of processing difficult-to-process products such as SiC using a hydrogen fluoride solution as the processing liquid, but the airtightness of the processing space, exhaust gas, and waste liquid have been developed. There was a problem that the processing equipment was required.

Under these circumstances, the understanding of the processing principle of the CARE method has progressed, and the present inventor has made semiconductor materials such as Si, SiC, and GaN without using harmful chemicals such as abrasive grains and hydrogen fluoride solution. A catalyst surface-referenced etching method capable of flattening a workpiece such as a solid oxide material represented by optical glass into a flat surface or an arbitrary curved surface has been proposed (Patent Documents 1 to 3).

Patent Document 1 uses a catalytic substance as a processing reference surface, which assists the formation of decomposition products by hydrolysis by cutting and adsorbing back bonds between oxygen elements and other elements that dissociate water molecules to form solid oxides. In use, in the presence of water, the workpiece and the machining reference surface are placed in contact with or very close to each other, and the potential of the machining reference surface is set to a range including natural potential and H ₂ and O ₂ are not generated. A method for processing a solid oxide film, which comprises removing the decomposition product from the surface of the workpiece by relatively moving the workpiece and the machining reference plane, is disclosed.

The processing method described in Patent Document 1 does not use any abrasives or abrasive grains such as rare earths, is difficult to handle hydrogen fluoride, etc., does not use any solution having a large environmental load, and in principle water. It is a CARE (Water-CARE) that uses only a single oxide, and is an epoch-making one that can process a solid oxide film such as an optical material without introducing a processing alteration layer.

Patent Document 2 is to process a Si substrate in the presence of water by using a catalytic substance that promotes both oxidation of Si and hydrolysis of a Si oxide film as a processing reference plane. Further, Patent Document 3 has a function of using a single crystal of SiC, GaN, AlGaN, or AlN as a workpiece and promoting direct hydrolysis of the workpiece or hydrolysis of an oxide film on the surface of the workpiece. Using the catalyst substance as the processing reference surface, in the presence of water, the workpiece and the processing reference surface are placed in contact with or extremely close to each other at a predetermined pressure, and the potential of the processing reference surface is set to the oxygen generation potential. A state in which oxygen is adsorbed on the catalyst surface is set as a reference in the range of ± 1 V, the workpiece and the machining reference surface are moved relative to each other, and the catalyst function provided on the machining reference surface allows the surface of the workpiece to be moved. Direct hydrolysis or oxidation of the surface of the work piece and hydrolysis of the oxide film are preferentially promoted from the surface convex portion close to the processing reference surface to remove the decomposition product.

Japanese Patent No. 5754754 JP-A-2015-162600 JP 2015-173216

In the CARE method, catalyst optimization is important. Until now, Pt, which has excellent oxidation and chemical resistance, has been mainly used as a catalyst substance. However, Pt is expensive and difficult to remove if it adheres to the surface to be processed, and the contamination can significantly reduce the performance of the electronic device. In the processing principle of CARE, the d-electrons of the catalyst play an essential role. Among such transition metals having d-electrons, it has been confirmed from basic experiments that Ni, which has a d-orbital electron occupancy lower than Pt, has a high processing speed (removal speed) and is effective as a catalyst. The shift to Ni was significant because of the reduction in processing cost and the ease of cleaning after processing, but the catalytic function deteriorated significantly due to oxidation, and it could not be put into practical use.

Therefore, in view of the above-mentioned situation, the present invention has been trying to solve the problem by grinding semiconductor materials such as Si, SiC, and GaN and workpieces such as solid oxide materials represented by optical glass. In Water-CARE, which has been established as a processing method that can flatten a flat surface or an arbitrary curved surface without using grains or harmful chemicals, the catalytic material is optimized, the processing speed is fast, and the processing speed is long. The point is to provide a catalyst surface-referenced etching method and an apparatus thereof capable of time-stable processing.

The present invention provides a catalyst surface-based etching method and an apparatus therefor for solving the above-mentioned problems.

(1)
Using a tool provided with a transition metal having a catalytic function to promote hydrolysis of the work surface of the work piece on the work surface, the work surface and the work surface are brought into contact with each other at a predetermined pressure in the presence of water. At the same time, the surface to be processed and the surface to be processed are moved relative to each other, and the hydrolysis of the surface to be processed is preferentially promoted from the portion in contact with the surface to be processed by the catalytic function provided on the surface to be processed. In the catalyst surface reference etching method, which can flatten the workpiece to a flat surface or an arbitrary curved surface by removing
At least the machined surface of the tool and the machined surface of the work piece are placed in a machining liquid containing water and transition metal ions, and the machining surface is brought into a negative potential state with respect to the machining liquid to transition to the machining surface. The precipitation process of precipitating metal to form a transition metal film having a catalytic function and the melting process of putting the processed surface in a positive potential state with respect to the processing liquid to dissolve the transition metal film of the processed surface are alternated. A catalyst surface-referenced etching method comprising an etching step repeated in the above.

(2)
The catalyst surface reference etching method according to (1), wherein the precipitation process is a process of precipitating a transition metal having a thickness that can be removed by melting the transition metal film on the processed surface by the melting process.

(3)
The dissolution process is a process of dissolving the transition metal film on the processed surface in a positive potential state before the transition metal film deposited on the processed surface is oxidized and loses its activity as a catalyst (1) or. (2) The catalyst surface reference etching method according to (2).

(4)
The etching step further includes a cleaning step of melting the inactive transition metal film by sustaining the melting process of melting the transition metal film of the machined surface in a positive potential state with respect to the machining liquid for a certain period of time. The catalyst surface-based etching method according to any one of (1) to (3), wherein the process and the cleaning process are alternately repeated.

(5)
The catalyst surface reference etching method according to any one of (1) to (4), wherein the transition metal is nickel and an aqueous solution of a nickel salt is used as the processing liquid.

(6)
The catalyst surface reference etching method according to any one of (1) to (4), wherein the transition metal is nickel, and an aqueous solution obtained by adding an acid to a nickel salt is used as the processing liquid.

(7)
Using a tool provided with a transition metal having a catalytic function to promote hydrolysis of the work surface of the work piece on the work surface, the work surface and the work surface are brought into contact with each other at a predetermined pressure in the presence of water. At the same time, the surface to be machined and the surface to be machined are moved relative to each other, and the hydrolysis of the surface to be machined is preferentially promoted from the portion in contact with the surface to be machined by the catalytic function provided on the surface to be machined. In a catalyst surface reference etching apparatus capable of flattening a work piece to a flat surface or an arbitrary curved surface by removing
A tool having a machined surface on the surface of an elastically deformable pad that has a lower ionization tendency than the transition metal and a chemically stable conductive film.
A container for arranging at least the machined surface of the tool and the machined surface of the work piece in a working liquid containing water and transition metal ions.
A drive mechanism for holding the work piece, bringing the work surface and the work surface of the tool into contact with each other at a predetermined pressure, and making the work surface and the work surface move relative to each other.
A counter electrode arranged in the machining fluid so as to face a portion different from the machining surface of the tool in contact with the workpiece surface.
A power supply for applying a voltage between the machined surface of the tool and the counter electrode,
A control unit that controls the potential of the machined surface of the tool with respect to the working liquid and controls the drive mechanism.
The process of forming a transition metal film having a catalytic function by depositing a transition metal on the processing surface in a negative potential state with respect to the processing liquid, and the processing surface with respect to the processing liquid. A catalyst surface reference etching apparatus including an etching step of alternately repeating a melting process of melting a transition metal film on a processed surface in a positive potential state.

(8)
The etching step further includes a cleaning step of melting the inactive transition metal film by sustaining the melting process of melting the transition metal film of the machined surface in a positive potential state with respect to the machining liquid for a certain period of time. (7) The catalyst surface reference etching apparatus according to (7), wherein the process and the cleaning process are alternately repeated.

(9)
The catalyst surface reference etching apparatus according to (7) or (8), wherein the transition metal is nickel and an aqueous solution of a nickel salt is used as the processing liquid.

(10)
The catalyst surface reference etching apparatus according to (7) or (8), wherein the transition metal is nickel, and an aqueous solution obtained by adding an acid to a nickel salt is used as the processing liquid.

The catalyst surface-based etching method and the apparatus thereof of the present invention as described above have the following effects.

According to the etching process of the present invention, a transition metal film having a catalytic function is electrochemically formed on the machined surface of the tool, and the transition metal film is electrochemically dissolved before the performance of the transition metal film deteriorates. By removing and repeating this, the catalytic function of the transition metal can always be maintained stable, and the processing speed can be stabilized in a high state. Further, even if the inactive transition metal film cannot be completely removed only by the melting process of the etching process, the transition metal film can be completely removed by executing the cleaning step of sustaining the melting process for a certain period of time after the etching process. Can be melted and removed, and the machined surface of the tool can always be kept clean.

Further, in the present invention, the processing speed is faster and cheaper than that of the chemically stable Pt, but Ni, whose catalytic function is rapidly deteriorated, can be used as a catalyst, and the processing speed can be significantly reduced at the same time as the cost can be significantly reduced. Can be speeded up. Further, since the transition metal is nickel and an aqueous solution of nickel salt is used as the processing solution and the precipitation process is an electroplating process, an extra chemical solution is not required, so that the etching process by hydrolysis is inhibited. There is no such thing. Further, when an aqueous solution obtained by adding an acid to a nickel salt is used as the processing liquid, it has an effect of promoting the elution of Ni in the process of dissolving the Ni film, and the Ni film can be removed more completely.

It is a processing conceptual diagram of the CARE method which is the basis of this invention. It is a graph which shows the example which processed quartz glass by using various transition metals as a catalyst by the conventional Water-CARE method. It is a graph which shows the example which processed SiC by various transition metals as a catalyst by the conventional Water-CARE method. It is a graph which shows the time change of the processing speed when quartz glass is processed using Ni as a catalyst by the conventional Water-CARE method. It is a cyclic voltammogram obtained by CV measurement before and after immersing the Ni film on SUS in pure water. It is a conceptual diagram of the electronic state at the interface between the working liquid and the Au film on the tool surface, (a) is the initial state of the Au film having a natural potential, (b) is the state of precipitation of the Au film having a negative potential, and (c) is the Au The membrane shows a positive potential dissolved state. It is a cyclic voltammogram obtained by CV measurement showing the process of precipitation and dissolution reaction of Ni on the Au surface. It is a simplified sectional view of the flattening processing apparatus of this invention. It is a graph which shows the voltage application waveform in the etching process. It is a graph which shows the voltage application waveform at the time of repeating an etching process and a cleaning process. It is a graph which shows the time change of the processing speed when quartz glass is processed by this invention. It is a graph which shows the time change of the processing speed when SiC is processed by this invention. It is a simplified sectional view of the local processing apparatus of this invention. Similarly, it is an enlarged sectional view of a main part.

The catalyst surface reference etching method of the present invention uses a tool provided with a transition metal having a catalytic function to promote hydrolysis of the work surface of the work piece on the work surface in the presence of water. And the machined surface are brought into contact with each other at a predetermined pressure, and the surface to be machined and the machined surface are moved relative to each other, and the catalyst function provided on the machined surface causes hydrolysis of the machined surface to come into contact with the machined surface. In a catalyst surface-based etching method capable of flattening a work piece to a flat surface or an arbitrary curved surface by preferentially advancing from the above and removing decomposition products, at least the machined surface and the work piece of the tool. The surface to be processed is placed in a processing liquid containing water and transition metal ions, and the processing surface is placed in a negative potential state with respect to the processing liquid to deposit a transition metal on the processing surface to provide a catalytic function. It is characterized by including an etching process in which a precipitation process for forming a transition metal film and a melting process in which the processing surface is brought into a positive potential state with respect to the processing liquid to dissolve the transition metal film on the processing surface are alternately repeated. It is something to do. Here, the transition metal film may be a simple substance of the transition metal or an oxide having catalytic activity.

Here, the precipitation process is a process of precipitating the transition metal to a film thickness that can be removed by melting the transition metal film on the processed surface by the melting process. Further, the dissolution process is a process of dissolving the transition metal film on the processed surface in a positive potential state before the oxidation of the transition metal film deposited on the processed surface proceeds and the activity as a catalyst is lost.

In the present invention, in principle, various transition metals having a low d-orbital electron occupancy can be used as the catalyst, but Ni is the most preferable. That is, the transition metal is nickel, and it is preferable to use an aqueous solution of nickel salt as the processing liquid, and it is also preferable to use an aqueous solution obtained by adding an acid to the nickel salt as the processing liquid. In the present embodiment, nickel sulfate is used as the nickel salt and sulfuric acid is used as the acid, but the present invention is not limited to this. It is also possible to use a transition metal having a high d-orbital electron occupancy rate, which is oxidized to generate an empty level in the d-orbital and acquire catalytic activity.

<Explanation of CARE>
The Catalyst-Referred Etching (CARE) method based on the present invention utilizes an etching reaction that proceeds only in the presence of a catalyst. That is, in the CARE method, a catalytic function is imparted to the machined surface of the tool, and the machined surface of the work piece and the machined surface (reference surface) of the tool are brought into contact with each other at a predetermined pressure in a water-based machining liquid. By relatively moving, an etching region is created only in the vicinity of the machined surface, and the reference surface is chemically transferred. Therefore, a flat surface without the introduction of crystallographic damage can be obtained. Here, the processing mechanism of the CARE method is known to be a hydrolysis reaction from the first-principles calculation simulation, and in the reaction path, the catalyst supports the dissociation and adsorption reaction of water, and the decomposition product by hydrolysis is put into water. It is intended to be eluted in. If the machined surface of the tool is flat, for example, a disk, flattening can be performed, and if the machined surface is spherical or ring-shaped, curved surface can be machined.

FIG. 1 shows a conceptual diagram in which the surface to be machined is flattened by the CARE method. The state in which the workpiece surface 2 of the workpiece 1 is flattened into a flat surface by a tool 3 is shown. As the tool 3, a tool in which a transition metal film 5 (processed surface) serving as a catalyst is formed on a pad 4 whose flatness is sufficiently guaranteed is used. Here, the pad 4 usually uses a Byton rubber hardness 90. The transition metal film 5 of the tool 3 serves as a machined surface having a catalytic function. Then, at least the machined surface of the tool 3 and the machined surface 2 of the workpiece 1 are arranged in a working liquid containing water, and a catalytically active region is created only in the immediate vicinity of the machined surface 5 of the tool 3 (FIG. 1 (a)). Next, the workpiece 1 and the tool 3 are brought into contact with each other at a predetermined pressure in the machining fluid and rotated with each other (see FIG. 1 (b)). As a result, the machined surface 5 of the tool 3 becomes a transfer surface, chemical etching is promoted, and only the convex portion of the machined surface 2 is selectively removed (see FIG. 1C).

So far, it has been confirmed that the surface of a SiC or GaN substrate, including a Si substrate, can be flattened at the atomic level by the Water-CARE method using Pt as a catalyst and pure water as a processing liquid. Further, it has been confirmed that the object to be processed (workpiece) is not limited to these semiconductor materials, and that a solid oxide material in a crystalline state or an amorphous state (glass) can be flattened. Since the Water-CARE method is carried out at room temperature and in pure water, various transition metals can be used as catalysts. However, the conventional CARE method still has problems such as poisoning of the catalyst surface and a decrease in processing speed. As will be described later, the present invention optimizes the catalyst surface to reduce cost and high efficiency. Achieves various processing.

Further, as the water used in the present invention, it is necessary to use pure water or ultrapure water having few impurities and constant characteristics in order to realize a pure processing environment and to accurately control the processing conditions. Generally, pure water has an electric resistivity of about 1 to 10 MΩ · cm, and ultrapure water has an electric resistivity of 15 MΩ · cm or more.

<Comparison of processing speeds of various transition metals>
Then, a transition metal can be used as a substance having a catalytic function to promote hydrolysis of the surface to be processed, and Pd, Ru, Ni, Co, Cr, Mo and the like having a large work function can be used. Is possible. Among them, FIG. 2 shows the results of comparing the processing speeds of quartz glass (SiO ₂ ) and 4H-SiC (0001) under the same processing conditions for Au, Cu, Pt, Ni, and Cr as typical transition metals. Shown. The processing time of the quartz glass of FIG. 2 is 5 minutes, and the processing time of SiC of FIG. 3 is 1 hour. In FIGS. 2 and 3, the vertical axis on the left side is the processing speed (nm / h), the vertical axis on the right side is the d-orbital electron occupancy rate (%) of the transition metal, the white circles are the processing speeds, and the black triangles are the d-orbital electrons. It represents the occupancy rate.

In both quartz glass and SiC, processing is proceeding with a plurality of types of transition metals, and it is clear that etching is also possible by the CARE method using transition metals other than Pt. In addition, there is a clear correlation between the d-orbital electron occupancy and the processing speed, and similar to the generally known adsorption characteristics of molecules, processing proceeded when Cr, Ni, and Pt were used, and Au was used. In that case, the processing did not proceed at all. The above results are in good agreement with the simulation results that the catalyst promotes the dissociation of water molecules in the CARE method. The processing is proceeding in Cu where the d-orbital is completely occupied, and it is considered that this is because the surface is slightly oxidized and an empty level is generated in the d-orbital. Although different tendencies are shown for Ni and Cr, the dependence of the machining speed on quartz glass and SiC shows similar tendencies, and it is considered that machining is proceeding by the same mechanism. Therefore, the CARE method is effective for oxide materials and semiconductor materials, and by using a transition metal catalyst with many empty levels in the d-orbital represented by Ni and Cr, a more efficient reaction can be performed in the CARE method. It was suggested that it could be induced.

From the above, it is considered that transition metals such as Cr, Ni, and Pt, which have many vacant levels in the d-orbital, function effectively as catalysts in this processing method. However, it is known that Cr cannot exist as a simple substance in a bare state in the region where hydrogen and oxygen are not generated in the pH-potential diagram, but since quartz glass can be processed, it is not in a simple metal state. However, it can be inferred that it has catalytic activity in the oxide state. On the other hand, even if Au, whose d-orbital is completely occupied by electrons, is used as a catalyst, the processing does not proceed at all. Although Cu can be processed for the reasons described above, it is known that the processing speed is slow. These are only phenomena in the conventional type Water-CARE, but there is a possibility that both Cr and Cu can be used as catalysts by the method according to the present invention.

The processing mechanism of the present invention is considered to be phenomenologically as follows. When a catalytic material whose d-electron orbital is near the Fermi level is in contact with or very close to the surface of the work piece, that is, when the d-electron orbital is close to the surface of the work piece, the d-electrons are of water molecules. It acts to lower the barrier of reaction to both dissociation and the loosening of the back bond of the oxide film. Phenomenonically, when the catalytic substance approaches the oxide film, the binding force of the back bond between the oxygen element constituting the oxide film and other elements weakens, the water molecules dissociate, and the oxygen element and others in the oxide film dissociate. The back bond of the element is cut and adsorbed to produce a decomposition product by hydrolysis. In addition, when the catalytic substance approaches the surface to be processed, a phenomenon of directly hydrolyzing the surface also occurs. Then, the principle is that the decomposition product produced by hydrolysis is eluted into the processing liquid. Here, the machined surface of the tool is brought into contact with the machined surface at a predetermined pressure and rubbed, thereby applying a mechanical force to the decomposition product and promoting elution into water.

It is known that the potential of the transition metal having a catalytic function affects the processing speed, but the processing proceeds even if the natural potential remains. If the potential of the transition metal is positively increased, O ₂ is generated, and if it is negatively increased, H ₂ is generated, and if bubbles interfere with processing, adjust within a range in which H ₂ and O ₂ are not generated. is required.

<Ni activation of the machined surface of the tool>
Ni, which exhibits excellent catalytic action in the dissociation reaction of water molecules, is considered to function effectively as a catalyst in the CARE method. In fact, as shown in FIGS. 2 and 3, it is known that by using Ni, a processing speed of about 13 times that of SiC and about 3 times that of quartz glass can be obtained as compared with Pt. Further, metal contamination on the surface of a semiconductor substrate such as SiC or GaN causes a significant decrease in its performance, but metal contamination by Ni can be easily removed by cleaning with an acidic chemical solution as compared with Pt. From the above, Ni is considered to be very promising as a catalyst in the CARE method. On the other hand, due to its high chemical activity, surface oxidation and poisoning by decomposition products become remarkable, and the processing speed of Ni sharply decreases with the passage of time. Therefore, it is important to maintain the active state of Ni.

FIG. 4 shows the results of a processing experiment using a flattening processing apparatus using quartz glass, a Ni plating film as a catalyst, and a processing liquid of pure water. The vertical axis of FIG. 4 represents the machining speed, and the horizontal axis represents the passage of machining time. The number of times of processing was set to 5, and the average processing speed was taken. As a result, it was confirmed that the processing speed tends to decrease significantly as time passes. It is considered that this is because the Ni surface is covered with an oxide film and the catalytically active portion is significantly reduced.

FIG. 5 shows the results of cyclic voltammetry (CV) measurement before (solid line) and after (dotted line) immersion of the Ni plating film formed on the SUS piece in pure water. In CV measurement, it is possible to change the potential of the electrode surface to be investigated with respect to the solution, monitor the current value at that time, and consider the chemical state of the electrode surface from the peak of the current value. The resulting waveform is called a cyclic voltammogram. The CV measurement after immersion in pure water was carried out by immersing the sample piece in pure water for 10 minutes and immediately after that, in a KOH solution (pH 13). In order to clarify the effect of oxidation by pure water, the potential was scanned in the oxygen evolution region from oxygen adsorption. As a result, it was found that when the Ni plating film was immersed in pure water, the current response was weak, that is, the activity was greatly reduced. This is because the surface of the Ni plating film is coated with the oxide film, so that the enjoyment of electrons is reduced. It was confirmed that the decrease in processing speed was the oxidation of the Ni film surface. Since the Ni plating film has a weak but current response even after being immersed in pure water, it is possible to electrochemically suppress the oxidation of the catalyst surface. On the other hand, it has been confirmed that when the film is formed with a sputtering film, the current response disappears after immersion in pure water. That is, it is important that the Ni film as a catalyst is formed by electrochemical plating. In addition, there are electrolytic plating and electroless plating in electrochemical plating, but since there are many types of chemicals used in electrochemical plating and there is a risk of interfering with the processing process due to hydrolysis, a simple chemical is used. Electroplating was selected.

<Specific method of Ni activation>
In order to maintain active Ni at all times in the machining atmosphere, it is ideal to form a film on the machined surface of the tool in-situ. However, if only film formation is performed, the surface may be hardened and damage may be left on the surface after processing due to mechanical action. Therefore, in order to keep the film thickness constant, it was decided to continuously deposit and dissolve the Ni film in-situ. Therefore, a reversible reaction between Ni ions and Ni by electrical control is used. FIG. 6 shows the conceptual diagram. In the present invention, Au, which has excellent electrical conductivity and is chemically stable, is used for the electrode. A nickel sulfate aqueous solution containing a large number of Ni ions was used as the processing liquid. Of course, it is possible to use various nickel salts such as nickel sulfamate that can be used in a normal Ni plating solution. The vertical axis in FIG. 6 shows the potential of the working liquid and the Au electrode, the right side shows Au, and the left side shows the working liquid. The thick line shows the processing liquid, and the thin line shows the potential of the Au electrode. When the natural potential of the Au electrode is measured in a nickel sulfate solution (processing solution), it becomes a positive potential with respect to the processing solution, so that the relationship shown in FIG. 6A is obtained. At this time, the movement of electrons from the Au electrode to the solution does not occur. On the other hand, FIG. 6B shows the case where the potential of the Au electrode is set to a negative potential with respect to the processing liquid. At this time, in order to stabilize the interface system, the electrons of the Au electrode move to the processing liquid. Then, by combining with Ni ions existing in the processing liquid, Ni ions are reduced and Ni is deposited on the surface of the Au electrode. In order to dissolve the Ni film precipitated in this way again, the potential is changed from FIG. 6 (b) to the state shown in FIG. 6 (c) to make the Au electrode a positive potential, so that electrons are transferred from the processing liquid to the Au electrode. After being moved, Ni becomes ions again by the oxidation reaction of Ni and dissolves in the processing liquid. By alternately performing such redox reactions corresponding to precipitation and dissolution, the chemical state of Ni can be controlled on the Au electrode surface.

FIG. 7 shows the results of investigating the precipitation and dissolution reactions of Ni on the Au surface by CV measurement. As the electrode, Au was sputtered on a fluororubber used as a pad by the CARE method, and a 0.01 M nickel sulfate aqueous solution was used as the processing liquid. The dotted line in the center shows the value of zero current density. The response of the current value is confirmed, and it can be seen that the surface state is definitely changed by the potential sweep. First, a gentle decrease in current density in the negative direction (arrow (1)) starting near 0 V vs. standard hydrogen electrode (SHE) indicates Ni precipitation (hereinafter, all voltage value units are all). vs. SHE notation). Further, as shown by the arrow (2), the current density increases when sweeping from the negative potential to the positive potential, which corresponds to the dissolution of Ni. From the above, it was shown that the precipitation and dissolution reactions of Ni on the Au film can be controlled by potential sweep. The precipitation and dissolution potentials of Ni obtained from the CV measurement results were used as potential control values in actual processing.

<Device for realizing the method of the present invention>
Next, the flattening processing apparatus A of the present invention is shown in FIG. The flattening processing apparatus A has a structure in which processing is performed in a state where the work surface 21A of the work piece 21 and the work surface 22A of the tool 22 are immersed in water. Specifically, the flattening apparatus A includes a tool 22 having a processed surface 22A having a conductive film 24 formed on the surface of an elastically deformable pad 23 having a lower ionization tendency than the transition metal and being chemically stable. A container 26 for arranging at least the machined surface 22A of the tool 22 and the machined surface 21A of the work piece 21 in the work liquid 25 containing water and transition metal ions, and the work piece 21 are held. A drive mechanism 27 for bringing the work surface 21A and the work surface 22A of the tool 22 into contact with each other at a predetermined pressure and for relatively moving the work surface 21A and the work surface 22A, and a tool in contact with the work surface 21A. A counter electrode 28 arranged in the machining fluid 25 facing a portion different from the machining surface 22A of the tool 22, a power supply 29 for applying a voltage between the machining surface 22A and the counter electrode 28 of the tool 22, and a machining fluid. It is provided with a control unit (not shown) that controls the potential of the machined surface 22A of the tool 22 with respect to 25 and controls the drive mechanism 27.

The work piece 21 is assumed to have a flat plate shape, and the purpose is to flatten the work surface 21A into a flat surface. As the tool 22, a fluororubber pad 23 was provided on the upper surface of the metal disk 30, and Au was sputtered to a thickness of 100 nm as a conductive film 24 on the pad 23. As the processing liquid 25, an aqueous solution of nickel sulfate containing water was used. Therefore, the processing liquid 25 contains Ni ions. The disk 30 as the tool 22 is rotatable by a vertical rotation shaft 31. On the other hand, the work piece 21 is held by a holder 33 provided with a vertical rotating shaft 32 and a pressurizing mechanism in the axial direction, and the work surface 21A of the work work 21 is changed to the work surface 22A of the tool 22. The axes of each other are brought into contact with each other at a predetermined pressure in an eccentric state. The drive mechanism 27 is composed of a rotary shaft 31 of the tool 22, a rotary shaft 32 of the holder 33, and a pressurizing mechanism, and the rotation speed and the machining pressure are controlled by the control unit. It also includes a standard electrode 34 for accurate potential measurement.

In the present invention, Ni stays in the process system and is not taken out of the process system, that is, it is not consumed. Therefore, it is not necessary to use Ni for the anode as in ordinary electrolytic nickel plating. As the counter electrode 28, a Pt electrode 35 having a thickness of 10 nm formed by sputtering is used, and substantially the entire radial portion of the machined surface 22A of the tool 22 is covered in consideration of the precipitation efficiency and dissolution efficiency of the Ni film. It is set to a size that can be used. Then, the process of placing the processed surface 22A (Au conductive film 24) in a negative potential state with respect to the processing liquid 25 and depositing Ni on the processed surface 22A to form a Ni film having a catalytic function, and the processing. The work surface 21A of the work piece 21 is flattened by an etching process in which the surface 22A is brought into a positive potential state with respect to the work liquid 25 and the melting process of dissolving the Ni film of the work surface 22A is repeated alternately. To do.

The workpiece 21 was made of φ35 quartz glass, and the working liquid was a 0.01 M nickel sulfate aqueous solution. In the present embodiment, in principle, the Ni film functions as a catalyst if it has a thickness of several atomic layers. Therefore, a nickel sulfate having a very low concentration is used, but the concentration is arbitrary. As mentioned above, it has been clarified that when Ni is present as a film, its surface is easily oxidized. It is predicted that the formation of the oxide film will make it difficult to control the potential of the machined surface 22A of the tool 22, and it is necessary to elute the Ni film before the surface oxidation progresses. That is, considering that it is ideal to alternately deposit and dissolve the Ni film in a short time, the voltage was applied in a pulse shape. The applied voltage values were −0.2 V for Ni precipitation and 0.4 V for Ni dissolution, and the holding time of each potential was 1 second. FIG. 9 shows the waveform of the applied voltage in the etching process. In FIG. 9, the state of maintaining the negative potential (−0.2 V) is the precipitation process, and the state of maintaining the positive potential (0.4 V) is the dissolution process. Further, after the machining by applying the pulse was performed for 5 minutes, the machining was performed for 5 minutes without applying a voltage (Au's natural potential of 0.4 V) in order to confirm that Ni was dissolved from the tool 22. FIG. 10 shows an approximate applied voltage waveform.

The rotation speed of the tool 22 is 60 rpm, and the machining pressure is 15 kPa. The processing result by this is shown in FIG. White circles indicate the processing speed when a pulse is applied, and black circles indicate the processing speed due to the natural potential. When the pulse was applied, the machining speed increased significantly, and when no pulse was applied, the machining speed showed a value close to zero. At the 3rd and 5th points, the processing speed is about 1/2 times that of the 1st point, but this is because the Au film is significantly peeled off about 1 minute after the start of processing at the 1st point, and the Ni precipitation region is reduced. It is the cause. When pure water is used as the processing liquid and Pt is used as the catalyst, the processing speed is about 100 nm / h, but in the processing with pulse application, it is about 500 nm / h, which is due to the precipitated active Ni. High-speed machining was realized. In addition, the processing hardly proceeded at the natural potential. It is considered that this is because Ni melted from the pad surface and Au, which is the base, was exposed. It is known that Au has extremely low catalytic activity in the CARE method and its processing speed is almost zero. From the above, it was shown that stable and highly efficient processing can be realized by constantly maintaining active Ni on the surface by repeating precipitation and dissolution of Ni by applying a pulse. That is, when the natural potential of the conductive film formed on the machined surface of the tool becomes a positive potential in the working liquid, the precipitation transition metal film can be dissolved even at the natural potential, so it is necessary to apply a voltage by a power source. Absent. That is, since the natural potential of the Au film placed in the nickel sulfate aqueous solution is 0.4 V, the above-mentioned positive potential state means the state of the natural potential.

Here, the natural potential (0.4 V) of Au can be positively utilized to completely remove the inactive Ni film. Even if the inactive Ni film cannot be completely removed by the melting process of the etching step (A) alone, as shown in FIG. 10, the cleaning step (B) that sustains the melting process for a certain period of time is performed by the etching step (A). ), The Ni film can be completely dissolved and removed, and the machined surface 22A of the tool 22 can always be kept in a clean state. FIG. 10 shows an applied voltage waveform capable of alternately performing the etching step (A) and the cleaning step (B). The time of each process can be set arbitrarily. Further, it is also effective to add sulfuric acid to the processing liquid to support the dissolution of the Ni film. In addition to sulfuric acid, it is possible to add other acids such as nitric acid and hydrochloric acid to support the dissolution of the Ni film, but depending on the application of the work piece, if it remains, it may adversely affect the performance. , Choose the best one.

Next, the workpiece 21 was set to 4H-SiC (0001) 4 ° off-axis, and the processing liquid was an aqueous solution of 0.1 M nickel sulfate and sulfuric acid (pH 12), and the same flattening process was performed. The rotation speed of the tool 22 was 60 rpm, the machining pressure was 25 kPa, and the machining speed was measured every 90 minutes. The result is shown in FIG. By using the present invention, it was confirmed that the activity of the Ni film can be maintained and the processing speed can be maintained for a long time. In the etching step (A), if the precipitation process and the melting process have the same time interval, the processing speed is halved as in the case of continuous etching, and the etching step (A) and the cleaning step (B) are the same. When repeated at time intervals, the processing speed is 1/4 that of continuous etching, but continuous etching reduces the activity of the catalyst and significantly reduces the processing speed, which is advantageous in the present invention in long-time processing. The sex becomes remarkable.

Finally, the local processing apparatus B will be described with reference to FIGS. 13 and 14. In principle, this local processing device B is a device capable of numerically controlling an arbitrary curved surface. That is, the local processing apparatus B creates a unit processing mark that processes only a part of the work piece by bringing the rotating body having the transition metal formed on the surface as a catalyst into contact with the surface of the work piece while rotating it. The machining depth is controlled by scanning the entire surface of the workpiece to be machined and controlling the staying time thereof.

The local processing device B holds a work piece 43 in a processing liquid 42 stored in a water tank 41, and uses a tool 46 made of a rotating body attached to the tip of a vertical rotation shaft 45 connected to a stepping motor 44. It is an apparatus for processing by rotating the surface of the workpiece 43 in the processing liquid 42 while contacting the surface with a constant contact pressure. More specifically, the water tank 41 and the XY stage 49 are fixed on the horizontal plate 48 provided on the Z stage 47, and the workpiece holder 50 driven by the XY stage 49 extends to the inside of the water tank 41. Holds the work piece 43. The rotating shaft 45 is fixed by double bearings 51 and 51 in order to minimize runout, and the connection portion with the head portion 52 to which the tool 46 is attached has a tapered shape so that it is generated for each attachment / detachment. The misalignment is suppressed. As the tool 46, a tool having a predetermined thickness of Au sputtered on the surface of the O-ring as a conductive film was used. For the O-ring, a fluororubber P44 standard size (outer diameter 50.7 mm, thickness 3.5 mm) was used. The stepping motor 44, the rotating shaft 45, and the bearings 51, 51 are attached to the same vertical plate 53, the upper end of the vertical plate 53 is connected to the gantry 54 by a leaf spring 55, and the rotating shaft 45 is connected by a balance type balancer 56. It is designed to adjust the verticality.

The workpiece 43 can be moved by an arbitrary amount in the direction of the tool 46 by operating the X stage, and the surface of the workpiece 43 is controlled by controlling the amount of movement of the rotating shaft 45 using an electric micrometer. Adjust the contact pressure between the tool and the tool 46. The conductive film (Au film) on the tool 46 is electrically connected to the potentiostat via a rotary joint 57, and further, in the working liquid 42, the counter electrode 58 faces the outer periphery of the tool 46. Is arranged, and a voltage is applied from the power source 59 between the conductive film on the tool 46 and the counter electrode 58 so that the potential of the conductive film of the tool 46 can be controlled. The counter electrode 58 has a Pt film having a predetermined thickness formed on the surface thereof by sputtering. Similarly, as the processing liquid 42, an aqueous solution of nickel sulfate or an aqueous solution of nickel sulfate added with sulfuric acid is used to bring the conductive film on the surface of the rubber ring used as the tool 46 into a negative potential state, and the surface of the conductive film is brought into a negative potential state. A Ni film is precipitated as a catalyst, and the conductive film of the tool 46 is brought into a positive potential state to dissolve the Ni film. In this device B as well, the processing conditions and processing method are the same as those described above.

In this case, the local machining apparatus B numerically controls and drives each stage and changes the relative positions of the workpiece 43 and the tool 46 to move the unit machining marks and conduct the conductive film of the tool 46. It is a numerical control (NC) processing device that can create an arbitrary curved surface smaller than the curvature of.

A flattening machine,
B Local processing equipment,
1 Work piece 2 Work surface 3 Tool 4 Pad 5 Transition metal film (machined surface)
21 Work piece 21A Work surface 22 Tool 22A Work surface 23 Pad 24 Conductive film (Au film)
25 Machining liquid 26 Container 27 Drive mechanism 28 Opposite electrode 29 Power supply 30 Disk 31 Rotating shaft 32 Rotating shaft 33 Holder 34 Standard electrode 35 Pt electrode 41 Water tank 42 Machining liquid 43 Work piece 44 Stepping motor 45 Rotating shaft 46 Tool 47 Stage 48 Horizontal Plate 49 Stage 50 Workpiece holder 51 Bearing 52 Head 53 Vertical plate 54 Stand 55 Leaf spring 56 Balancer 57 Rotary joint 58 Opposite electrode 59 Power supply

Claims (10)

Using a tool provided with a transition metal having a catalytic function to promote hydrolysis of the work surface of the work piece on the work surface, the work surface and the work surface are brought into contact with each other at a predetermined pressure in the presence of water. At the same time, the surface to be processed and the surface to be processed are moved relative to each other, and the hydrolysis of the surface to be processed is preferentially promoted from the portion in contact with the surface to be processed by the catalytic function provided on the surface to be processed. In the catalyst surface reference etching method, which can flatten the workpiece to a flat surface or an arbitrary curved surface by removing
At least the machined surface of the tool and the machined surface of the work piece are placed in a machining liquid containing water and transition metal ions, and the machining surface is brought into a negative potential state with respect to the machining liquid to transition to the machining surface. The precipitation process of precipitating metal to form a transition metal film having a catalytic function and the melting process of putting the processed surface in a positive potential state with respect to the processing liquid to dissolve the transition metal film of the processed surface are alternated. A catalyst surface-referenced etching method comprising an etching step repeated in the above. The catalyst surface-based etching method according to claim 1, wherein the precipitation process is a process of depositing a transition metal to a thickness such that the transition metal film on the processed surface can be removed by dissolution by the dissolution process. The dissolution process is a process of dissolving the transition metal film on the processed surface in a positive potential state before the transition metal film deposited on the processed surface is oxidized and loses its activity as a catalyst. 2. The catalyst surface reference etching method according to 2. The etching step further includes a cleaning step of melting the inactive transition metal film by sustaining the melting process of melting the transition metal film of the machined surface in a positive potential state with respect to the machining liquid for a certain period of time. The catalyst surface-referenced etching method according to any one of claims 1 to 3, wherein the process and the cleaning step are alternately repeated. The catalyst surface-based etching method according to any one of claims 1 to 4, wherein the transition metal is nickel, and an aqueous solution of a nickel salt is used as the processing liquid. The catalyst surface-based etching method according to any one of claims 1 to 4, wherein the transition metal is nickel, and an aqueous solution obtained by adding an acid to a nickel salt is used as the processing liquid. Using a tool provided with a transition metal having a catalytic function to promote hydrolysis of the work surface of the work piece on the work surface, the work surface and the work surface are brought into contact with each other at a predetermined pressure in the presence of water. At the same time, the surface to be processed and the surface to be processed are moved relative to each other, and the hydrolysis of the surface to be processed is preferentially promoted from the portion in contact with the surface to be processed by the catalytic function provided on the surface to be processed. In a catalyst surface reference etching apparatus capable of flattening a work piece to a flat surface or an arbitrary curved surface by removing
A tool having a machined surface on the surface of an elastically deformable pad that has a lower ionization tendency than the transition metal and a chemically stable conductive film.
A container for arranging at least the machined surface of the tool and the machined surface of the work piece in a working liquid containing water and transition metal ions.
A drive mechanism for holding the work piece, bringing the work surface and the work surface of the tool into contact with each other at a predetermined pressure, and making the work surface and the work surface move relative to each other.
A counter electrode arranged in the machining fluid so as to face a portion different from the machining surface of the tool in contact with the workpiece surface.
A power supply for applying a voltage between the machined surface of the tool and the counter electrode,
A control unit that controls the potential of the machined surface of the tool with respect to the working liquid and controls the drive mechanism.
The process of forming a transition metal film having a catalytic function by depositing a transition metal on the processing surface in a negative potential state with respect to the processing liquid, and the processing surface with respect to the processing liquid. A catalyst surface reference etching apparatus including an etching step of alternately repeating a melting process of melting a transition metal film on a processed surface in a positive potential state. The etching step further includes a cleaning step of melting the inactive transition metal film by sustaining the melting process of melting the transition metal film of the machined surface in a positive potential state with respect to the machining liquid for a certain period of time. The catalyst surface reference etching apparatus according to claim 7, wherein the process and the cleaning process are alternately repeated. The catalyst surface reference etching apparatus according to claim 7 or 8, wherein the transition metal is nickel, and an aqueous solution of a nickel salt is used as the processing liquid. The catalyst surface reference etching apparatus according to claim 7 or 8, wherein the transition metal is nickel, and an aqueous solution obtained by adding an acid to a nickel salt is used as the processing liquid.

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