JP2018113366A - Catalyst-referred etching method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a catalyst-referred etching method, water-care already established as a processing method which makes possible to planarize a semiconductor material, a solid oxide material and others to have a flat face or appropriate curved surface without polishing grains nor harmful chemical solution, and which is low in cost and high in processing speed, which enables the optimization of a catalyst substance and enables stable processing for a long time; and a device therefor.SOLUTION: A catalyst-referred etching method arranged to planarize a workpiece 21 with the aid of the effect of hydrolysis by a catalyst comprises an etching process arranged to alternately repeating: a deposition step of putting at least a processing face of a tool 22, and a processed face of the workpiece in a process liquid 25 containing water and transition metal ions, setting the processing face at a negative potential relative to the process liquid, and causing a transition metal to deposit on the processing face, thereby forming a transition metal film having a catalyst function; and a dissolving step of setting the processing face at a positive potential relative to the process liquid, thereby dissolving the transition metal film on the processing face.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a catalyst surface reference etching method and an apparatus therefor, and more particularly, a semiconductor material such as Si, SiC, GaN, or a workpiece such as a solid oxide material typified by optical glass, and the like. The present invention relates to a catalyst surface reference etching method and apparatus capable of flattening into a flat surface or an arbitrary curved surface without using a chemical solution.

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

For the polishing agent for CMP, for example, fine particles of cerium oxide mainly containing colloidal silica (SiO ₂ ), cerium oxide (CeO ₂ ) or lanthanum are 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 caused by abrasive grains on the surface to be processed and internal scratches remain, but also cerium oxide, which is a rare earth, is frequently used. Being exposed to problems is inevitable. Further, since CMP uses fine particles such as colloidal silica, there are problems such as high cost for the treatment of the polishing liquid and poor compatibility with the clean room.

  Therefore, the present inventors have proposed a catalyst surface-based etching (CARE) method that can flatten a workpiece into a flat surface or an arbitrary curved surface without using an abrasive or abrasive grains. Has been. The CARE method is a processing technique that does not use any abrasive or abrasive grains, and is an ideal processing method that does not introduce any scratches or work-affected layers on the work surface by processing, that is, has no crystallographic damage. In the early stages of development, the CARE method was developed for the purpose of processing difficult-to-process materials such as SiC using a hydrogen fluoride solution as the processing liquid. There is a problem that a processing facility is required.

  Under such circumstances, the understanding of the processing principle of the CARE method has also progressed, and the present inventor does not use harmful chemical liquids such as abrasive grains and hydrogen fluoride solution, and does not use semiconductor materials such as Si, SiC, GaN, A catalyst surface reference etching method capable of flattening a workpiece such as a solid oxide material typified by optical glass into a flat surface or an arbitrary curved surface has been proposed (Patent Documents 1 to 3).

In Patent Document 1, a catalytic substance that assists in the generation of decomposition products by hydrolysis by adsorbing the oxygen element constituting the solid oxide by dissociating the back bond between the oxygen element and other elements is used as a processing reference surface. And in the presence of water, the workpiece and the processing reference surface are arranged in contact with or in close proximity to each other, and the potential of the processing reference surface is set to a range that includes a natural potential and does not generate H ₂ and O ₂ , A solid oxide film processing method is disclosed in which the decomposition product is removed from the workpiece surface by relatively moving the workpiece and a processing reference surface.

  The processing method described in Patent Document 1 uses rare earths, does not use any abrasive or abrasive grains, is difficult to handle hydrogen fluoride, etc., does not use any environmentally damaging solution, and in principle water CARE (Water-CARE) using only a material, which was an epoch-making material capable of processing a solid oxide film such as an optical material without introducing a work-affected layer.

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

Japanese Patent No. 5754754 JP2015-162600A Japanese Patent Laying-Open No. 2015-173216

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

  Therefore, in view of the above-mentioned situation, the present invention intends to solve the problem of grinding a workpiece such as a semiconductor material such as Si, SiC, or GaN or a solid oxide material typified by optical glass. Water-CARE has been established as a processing method that can be flattened into a flat or arbitrary curved surface without using grains or harmful chemicals. The catalytic material is optimized, the processing speed is low, and the processing speed is high. The object is to provide a catalyst surface reference etching method and apparatus capable of time-stable processing.

  In order to solve the above-mentioned problems, the present invention provides a catalyst surface reference etching method and apparatus configured as follows.

(1)
Using a tool with a transition metal with a catalytic function that promotes hydrolysis of the work surface of the work piece on the work surface, the work surface and the work surface are contacted at a predetermined pressure in the presence of water. In addition, 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 advanced 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 capable of flattening a workpiece into a flat surface or an arbitrary curved surface by removing
At least the machining surface of the tool and the machining surface of the workpiece are arranged in a machining fluid containing water and transition metal ions, and the machining surface is brought into a negative potential state with respect to the machining fluid and transitioned to the machining surface. Alternating process of depositing a metal to form a transition metal film having a catalytic function and a dissolving process of dissolving the transition metal film on the machined surface by making the machined surface positive with respect to the machining liquid And a catalyst surface reference etching method characterized by including an etching step repeated in step (a).

(2)
The catalyst surface reference etching method according to (1), wherein the precipitation process is a process of depositing the transition metal in a thickness that allows the transition metal film on the processed surface to be removed by dissolution in the dissolution process.

(3)
The dissolution process is a process in which the transition metal film deposited on the processed surface progresses and the transition metal film on the processed surface is dissolved in a positive potential state before the activity as a catalyst is lost (1) or (2) The catalyst surface reference etching method according to the above.

(4)
The etching step further includes a cleaning step of dissolving the inactive transition metal film by maintaining a dissolution process for dissolving the transition metal film on the processing surface while maintaining the processing surface at a positive potential with respect to the processing liquid, for a predetermined time. The catalyst surface reference etching method according to any one of (1) to (3), wherein the step and the cleaning step 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 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 in which an acid is added to a nickel salt is used as the processing liquid.

(7)
Using a tool with a transition metal with a catalytic function that promotes hydrolysis of the work surface of the work piece on the work surface, the work surface and the work surface are contacted at a predetermined pressure in the presence of water. In addition, 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 advanced 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 apparatus capable of flattening a workpiece into a flat surface or an arbitrary curved surface by removing
A tool having a work surface in which a conductive film that is less ionized than the transition metal and chemically stable is formed on the surface of the elastically deformable pad;
A container for disposing at least the processing surface of the tool and the processing surface of the workpiece in a processing liquid containing water and transition metal ions;
A drive mechanism for holding the workpiece, bringing the workpiece surface and the machining surface of the tool into contact with a predetermined pressure, and causing the workpiece surface and the machining surface to move relative to each other;
A counter electrode disposed in the machining liquid facing a portion different from the machining surface of the tool in contact with the workpiece surface;
A power source for applying a voltage between the machining surface of the tool and the counter electrode;
A control unit for controlling the electric potential of the machining surface of the tool with respect to the machining fluid, and for controlling the drive mechanism;
A deposition process of forming a transition metal film having a catalytic function by depositing a transition metal on the processing surface by setting the processing surface to a negative potential with respect to the processing fluid; and A catalytic surface reference etching apparatus comprising an etching step of alternately repeating a dissolution process of dissolving the transition metal film on the processed surface in a positive potential state.

(8)
The etching step further includes a cleaning step of dissolving the inactive transition metal film by maintaining a dissolution process for dissolving the transition metal film on the processing surface while maintaining the processing surface at a positive potential with respect to the processing liquid, for a predetermined time. And the catalyst surface reference etching apparatus according to (7), wherein the cleaning 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 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 reference etching method and apparatus according to 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 formed electrochemically on the machined surface of the tool, and is dissolved electrochemically before the performance of the transition metal film deteriorates. By removing and repeating this, a stable transition metal catalytic function can be maintained at all times, and the processing speed can be stabilized at a high level. In addition, even when the transition metal film that has become inactive cannot be completely removed only by the dissolution process of the etching process, the transition metal film can be completely removed by performing a cleaning process after the etching process to maintain the dissolution process for a certain period of time. Can be dissolved and removed, and the machined surface of the tool can always be kept clean.

  In addition, the present invention is faster and cheaper than chemically stable Pt, but Ni can be used as a catalyst because of its rapid deterioration of the catalyst function. Can be speeded up. Further, the transition metal is nickel, and an aqueous solution of nickel salt is used as the processing liquid, and the deposition process is an electroplating process, so that no extra chemical is required, thereby inhibiting the etching process by hydrolysis. There is nothing. Further, when an aqueous solution obtained by adding an acid to nickel salt is used as the processing liquid, there is an action of promoting the elution of Ni in the dissolution process of 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 base of the present 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 using 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 at the time of processing quartz glass by using Ni as a catalyst by the conventional Water-CARE method. It is the cyclic voltammogram obtained by CV measurement before and after immersing the Ni film | membrane on SUS in a pure water. It is a conceptual diagram of the electronic state in the interface of a working fluid and the Au film | membrane of a tool surface, (a) is the initial state of an Au film | membrane natural potential, (b) is the precipitation state of Au film | membrane negative potential, (c) The membrane shows a dissolved state with a positive potential. 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 planarization processing device of the present invention. It is a graph which shows the voltage application waveform in an etching process. It is a graph which shows a voltage application waveform in the case of repeating an etching process and a cleaning process. It is a graph which shows the time change of the processing speed at the time of processing quartz glass by this invention. It is a graph which shows the time change of the processing speed at the time of processing SiC by the present invention. It is a simplified sectional view of a local processing device of the present invention. Similarly it is an expanded sectional view of an important section.

  The catalyst surface reference etching method of the present invention uses a tool in which a transition metal having a catalytic function for promoting hydrolysis of a work surface of a work piece is provided on the work surface, and the work surface in the presence of water. And the processing surface are brought into contact with each other at a predetermined pressure, and the processing surface and the processing surface are moved relative to each other so that hydrolysis of the processing surface is brought into contact with the processing surface by a catalytic function provided on the processing surface. In the catalytic surface reference etching method, which allows the workpiece to be flattened into a flat surface or an arbitrary curved surface by preferentially proceeding and removing the decomposition products, at least the processing surface of the tool and the workpiece The surface to be processed is disposed 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. Form transition metal film And step out and is characterized in that it comprises an etching step of repeating the processing surface alternating with the dissolution process of dissolving the transition metal film of the pressurized cumene to a positive potential state, the relative dielectric fluid. Here, the transition metal film may be a single transition metal or an oxide having catalytic activity.

  Here, the precipitation process is a process in which the transition metal is deposited to a thickness that allows the transition metal film on the processed surface to be removed by dissolution in the dissolution process. Further, the dissolution process is a process in which the transition metal film deposited on the processed surface is advanced and the transition metal film on the processed surface is dissolved in a positive potential state before 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 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 nickel salt as the processing liquid. In this embodiment, nickel sulfate is used as the nickel salt and sulfuric acid is used as the acid. However, the present invention is not limited to this. It is also possible to use a transition metal having a high d-orbital electron occupancy, which is oxidized to generate a vacant level in the d-orbital to acquire catalytic activity.

<Description of CARE>
The catalyst surface-referenced etching (CARE) method based on the present invention utilizes an etching reaction that proceeds only in the presence of a catalyst. In other words, the CARE method gives a catalytic function to the machining surface of the tool, and brings the machining surface of the workpiece and the machining surface (reference surface) of the tool into contact with each other at a predetermined pressure in a machining liquid mainly composed of water. By relatively moving, an etching region is created only in the vicinity of the processed surface, and the reference surface is chemically transferred. As a result, a flat surface without crystallographic damage is obtained. Here, the processing mechanism of the CARE method is known to be a hydrolysis reaction from the first-principles calculation simulation, and the catalyst supports the dissociative adsorption reaction of water in the reaction path, and the decomposition product by hydrolysis is submerged in water. To be eluted. If the processing surface of the tool is flat, for example, a disk, flattening can be performed, and if the processing surface is spherical or ring-shaped, curved processing can be performed.

  FIG. 1 shows a conceptual diagram in which the work surface is flattened by the CARE method. A state in which the work surface 2 of the work 1 is flattened into a flat shape by a tool 3 is shown. The tool 3 is formed by forming a transition metal film 5 (processed surface) serving as a catalyst on a pad 4 that is sufficiently flat. Here, the pad 4 normally uses Viton rubber hardness 90. The transition metal film 5 of the tool 3 becomes a processed surface having a catalytic function. Then, at least the machining surface of the tool 3 and the workpiece surface 2 of the workpiece 1 are arranged in a machining fluid containing water, and a catalytically active region is created only in the vicinity of the machining 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 liquid and are rotated with each other (see FIG. 1B). Thereby, the processing surface 5 of the tool 3 becomes a transfer surface, chemical etching is promoted, and only the convex portion of the processing surface 2 is selectively removed (see FIG. 1C).

  Up to now, it has been confirmed that the surface of an Si substrate, SiC, or GaN substrate can be planarized to an atomic level by a Water-CARE method using Pt as a catalyst and pure water as a working fluid. Further, it is confirmed that the object to be processed (workpiece) is not limited to these semiconductor materials, and it is possible to planarize a solid oxide material in a crystalline state or an amorphous state (glass). Since the Water-CARE method is performed in room temperature and pure water, various transition metals can be used as a catalyst. However, the conventional CARE method still has problems such as poisoning of the catalyst surface and a reduction in processing speed. As described later, the present invention optimizes the catalyst surface to achieve high efficiency at low cost. Is achieved.

  In addition, the water used in the present invention is pure water or ultrapure water that has few impurities and constant characteristics, so that a pure processing environment is realized and accurate control of processing conditions is necessary. Generally, pure water has an electrical resistivity of about 1 to 10 MΩ · cm, and ultrapure water has an electrical resistivity of 15 MΩ · cm or more.

<Processing speed comparison of various transition metals>
A transition metal can be used as a substance having a catalytic function for promoting hydrolysis of the surface to be processed, and Pd, Ru, Ni, Co, Cr, Mo, etc. can be used as well as Pt having a large work function. Is possible. Among them, as a typical transition metal, Au, Cu, Pt, Ni, and Cr are compared with the processing speeds of quartz glass (SiO ₂ ) and 4H—SiC (0001) under the same processing conditions in FIG. Show. 2 is 5 minutes, and the SiC processing time of FIG. 3 is 1 hour. 2 and 3, the vertical axis on the left is the processing speed (nm / h), the vertical axis on the right is the d-orbital electron occupancy (%) of the transition metal, the white circle is the processing speed, and the black triangle is the d-orbital electron. It represents the occupation rate.

  In both quartz glass and SiC, processing is progressing for a plurality of types of transition metals, and it is apparent that etching is 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. Similar to generally known molecular adsorption characteristics, when Cr, Ni, and Pt are used, processing proceeds and Au is used. In the 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. It should be noted that the processing is progressing in Cu in which the d orbit is completely occupied, which is considered to be caused by the fact that the vacant level is generated in the d orbit because the surface is slightly oxidized. Although different tendencies are shown for Ni and Cr, the dependence of the processing speed on quartz glass and SiC shows a similar tendency, and it is considered that the processing is progressing by an equivalent mechanism. Therefore, the CARE method is effective for oxide materials and semiconductor materials, and a more efficient reaction can be achieved in the CARE method by using a transition metal catalyst having many vacant levels in the d orbital represented by Ni or Cr. It was suggested that it could be induced.

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

  The processing mechanism of the present invention is considered as follows from a phenomenological viewpoint. When a catalytic material having at least a d-electron orbit near the Fermi level is in contact with or close to the surface of the workpiece, that is, when the d-electron orbit approaches the surface of the workpiece, the d-electrons It acts to lower the barrier of reaction against both dissociation and the phenomenon of oxide back bonds becoming loose. Phenomenologically, when the catalytic substance approaches the oxide film, the bonding strength of the back bond between the oxygen element and the other element constituting the oxide film becomes weak, and the water molecules dissociate and the oxygen element in the oxide film and other elements The element's back bonds are cut and adsorbed to produce decomposition products by hydrolysis. In addition, when the catalyst material approaches the surface to be processed, a phenomenon of directly hydrolyzing the surface also occurs. And it is the principle that the decomposition product produced | generated by hydrolysis is eluted in a processing liquid. Here, the work surface of the tool is brought into contact with the work surface at a predetermined pressure and rubbed to give a mechanical force to the decomposition product and promote elution into water.

Although it has been found that the potential of the transition metal having a catalytic function affects the processing speed, the processing proceeds even at a natural potential. If the potential of the transition metal is increased positively, O ₂ is generated, and if it is negatively increased, H ₂ is generated. If bubbles interfere with processing, adjustment should be made within a range in which H ₂ and O ₂ are not generated. is necessary.

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

  FIG. 4 shows the results of processing experiments of quartz glass using a planarization processing apparatus using Ni plating film as a catalyst and processing liquid as pure water. The vertical axis in FIG. 4 represents the machining speed, and the horizontal axis represents the passage of machining time. In addition, the processing frequency was 5 times, and the processing speed was averaged. As a result, it was confirmed that the machining speed tended to greatly decrease with time. This is considered to be because the Ni surface was covered with an oxide film and the catalytically active part was greatly reduced.

  FIG. 5 shows the results of cyclic voltammetry (CV) measurement before (solid line) and after immersion (dotted line) of the Ni plating film formed on the SUS piece. In CV measurement, the potential of the electrode surface to be investigated is changed with respect to the solution, the current value at that time is monitored, and the chemical state of the electrode surface can be considered from the peak of the current value. The waveform obtained thereby is called a cyclic voltammogram. CV measurement after immersion in pure water was performed in a KOH solution (pH 13) immediately after the sample piece was immersed in pure water for 10 minutes. In order to clarify the influence of oxidation by pure water, the potential was scanned from the oxygen adsorption to the oxygen generation region. 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 covered with an oxide film, thereby reducing the enjoyment of electrons. It was confirmed that the decrease in the processing speed was due to oxidation of the Ni film surface. Since the Ni plating film has a weak current response even after immersion in pure water, it is possible to electrochemically suppress oxidation of the catalyst surface. On the other hand, it has been confirmed that the current response disappears after immersion in pure water when the film is formed by sputtering. That is, it is important that the Ni film as the catalyst is formed by electrochemical plating. Electrochemical plating includes electroplating and electroless plating. However, electroless plating uses many types of chemicals, which may interfere with the processing process by hydrolysis, so use simple chemicals. Electrolytic plating was selected.

<Specific method of Ni activation>
In order to maintain Ni that is always active in the processing atmosphere, film formation on the processing surface of the tool in-situ is ideal. However, if only film formation is performed, the surface is hardened, and there is a possibility that the surface is damaged by 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 by electrical control of Ni ions and Ni is used. The conceptual diagram is shown in FIG. In the present invention, Au having excellent electrical conductivity and chemically stable was used for the electrode. A nickel sulfate aqueous solution containing a large number of Ni ions was used as the working fluid. 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 machining liquid and the Au electrode, the right side shows Au and the left side shows the machining liquid. The thick line indicates the machining liquid, and the thin line indicates the potential of the Au electrode. When the natural potential of the Au electrode is measured in a nickel sulfate solution (working solution), the potential becomes positive with respect to the working solution, and the relationship shown in FIG. At this time, movement of electrons from the Au electrode toward the solution does not occur. On the other hand, FIG. 6B shows the case where the potential of the Au electrode is made negative with respect to the machining liquid. At this time, in order to stabilize the interface system, the electrons of the Au electrode move to the working fluid. And it couple | bonds with Ni ion which exists in a process liquid, Ni ion is reduced, and Ni precipitates on the Au electrode surface. In order to dissolve the deposited Ni film again, the potential is changed from the state shown in FIG. 6B to the state shown in FIG. Ni is converted to ions again by the oxidation reaction of Ni and dissolved in the working fluid. By alternately performing the oxidation-reduction reaction corresponding to such precipitation / 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 reaction of Ni on the Au surface by CV measurement. The electrode was formed by sputtering Au 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 center dotted line shows a value of zero current density. The response of the current value is confirmed, and it can be seen that the surface state is surely changed by the potential sweep. First, a gentle decrease in current density (arrow (1)) in the negative direction starting from the vicinity of 0 V vs. standard hydrogen electrode (SHE) indicates precipitation of Ni (hereinafter, the unit of voltage value is all). vs. SHE notation). Further, as indicated by the arrow (2), the current density increases when sweeping from negative to positive potential, which corresponds to dissolution of Ni. From the above, it was shown that the precipitation and dissolution reaction of Ni on the Au film can be controlled by potential sweep. Using the Ni precipitation and dissolution potential obtained from the CV measurement result, the potential control value in actual processing was obtained.

<Apparatus for realizing the method of the present invention>
Next, the planarization 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 processing surface 21A of the workpiece 21 and the processing surface 22A of the tool 22 are immersed in water. Specifically, the flattening processing apparatus A includes a tool 22 having a processing surface 22A in which a conductive film 24 having a smaller ionization tendency and chemically stable than the transition metal is formed on the surface of the elastically deformable pad 23; Holding at least the processing surface 22A of the tool 22 and the processing surface 21A of the workpiece 21 in the processing liquid 25 containing water and transition metal ions, and the workpiece 21; A driving mechanism 27 for bringing the processing surface 21A and the processing surface 22A of the tool 22 into contact with each other with a predetermined pressure and causing the processing surface 21A and the processing surface 22A to move relative to each other, and a tool in contact with the processing surface 21A 22, a counter electrode 28 disposed in the machining liquid 25 so as to face a portion different from the machining surface 22A, a power source 29 for applying a voltage between the machining surface 22A of the tool 22 and the counter electrode 28, It controls the potential of the working surface 22A of the tool 22 relative to the liquid 25, in which a control unit for controlling the drive mechanism 27 (not shown).

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

  In the present invention, Ni remains in the process system and is not taken out of the process system, that is, 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 radius portion of the processed surface 22A of the tool 22 is covered in consideration of the deposition efficiency and dissolution efficiency of the Ni film. The size is set to be displayed. Then, a deposition process in which the processed surface 22A (Au conductive film 24) is in a negative potential state with respect to the processing liquid 25 to deposit Ni on the processed surface 22A to form a Ni film having a catalytic function, and the processing The surface 21A to be processed of the workpiece 21 is flattened by an etching process in which the surface 22A is in a positive potential state with respect to the processing liquid 25 and the dissolution process of dissolving the Ni film on the processing surface 22A is alternately repeated. To do.

  The workpiece 21 was made of quartz glass having a diameter of 35 mm, and the machining liquid was a 0.01 M nickel sulfate aqueous solution. In this embodiment, in principle, the Ni film functions as a catalyst if it has a thickness of several atomic layers. Therefore, the nickel sulfate concentration is very thin, but the concentration is arbitrary. As described above, when Ni is present as a film, the surface is easily oxidized. It is predicted that the potential control of the machining surface 22A of the tool 22 will be difficult due to the generation of the oxide film, and it is necessary to elute the Ni film before the surface oxidation proceeds. In other words, it was considered ideal to alternately deposit and dissolve the Ni film in a short time, and the voltage was applied in pulses. 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 maintained at a negative potential (−0.2V) is the precipitation process, and the state maintained at a positive potential (0.4V) is the dissolution process. Further, after performing the processing by applying the pulse for 5 minutes, in order to confirm that Ni was dissolved from the tool 22, the processing was performed for 5 minutes without applying voltage (the natural potential of Au is 0.4 V). FIG. 10 shows an approximate applied voltage waveform.

  The rotation speed of the tool 22 is 60 rpm, and the processing pressure is 15 kPa. The processing result is shown in FIG. White circles indicate the processing speed when a pulse is applied, and black circles indicate the processing speed by natural potential. When a pulse was applied, the machining speed increased significantly, and when no pulse was applied, the machining speed was almost zero. The processing speed at the third and fifth points is about ½ times the first point, but this is because the Au film is peeled off approximately 1 minute after the first processing starts and the Ni precipitation area is reduced. This 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. However, in the processing with pulse application, the processing speed is about 500 nm / h, which is higher than the precipitated active Ni. High speed machining was realized. Further, the processing hardly progressed at the natural potential. This is considered to be because Ni was dissolved from the pad surface and Au as a base was exposed. It is known that Au has a very small catalytic activity in the CARE method, and its processing speed is almost zero. From the above, it has been shown that by repeating precipitation and dissolution of Ni by applying a pulse, active Ni can always be maintained on the surface and stable and highly efficient processing can be realized. That is, when the natural potential in the machining fluid of the conductive film formed on the machined surface of the tool becomes positive, the deposited transition metal film can be dissolved even at the natural potential, so it is not necessary to apply a voltage from the 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-described positive potential state means a state where the natural potential remains unchanged.

  Here, the inactive Ni film can be completely removed by positively utilizing the natural potential (0.4 V) of Au. Even when the inactivated Ni film cannot be completely removed only by the dissolution process of the etching process (A), as shown in FIG. 10, the cleaning process (B) for maintaining the dissolution process for a predetermined time is used as the etching process (A ), The Ni film can be completely dissolved and removed, and the processed surface 22A of the tool 22 can always be kept clean. FIG. 10 shows an applied voltage waveform in which the etching process (A) and the cleaning process (B) can be performed alternately. The time of each process can be set arbitrarily. Furthermore, it is also effective to add sulfuric acid to the working fluid in order to assist the dissolution of the Ni film. In addition to sulfuric acid, other acids such as nitric acid and hydrochloric acid can be added to assist the dissolution of the Ni film. However, depending on the application of the workpiece, performance may be adversely affected if it remains. Choose the best one.

  Next, the workpiece 21 was set to 4H—SiC (0001) 4 ° off-axis, and the processing liquid was similarly flattened using an aqueous solution of 0.1 M nickel sulfate and sulfuric acid (pH 12). The rotation speed of the tool 22 was 60 rpm, the processing pressure was 25 kPa, and the processing speed was measured every 90 minutes. The result is shown in FIG. It has been confirmed that by using the present invention, the Ni film activity can be maintained and the processing speed can be maintained for a long time. In the etching process (A), if the precipitation process and the dissolution process are at the same time interval, the processing speed is ½ that of continuous etching, and the etching process (A) and the cleaning process (B) are the same. When it is repeated at time intervals, the processing speed becomes 1/4 that of continuous etching. However, in continuous etching, the activity of the catalyst is reduced and the processing speed is greatly reduced. Sex becomes remarkable.

  Finally, the local processing apparatus B will be described based on FIGS. 13 and 14. This local processing apparatus B is an apparatus capable of numerically controlling an arbitrary curved surface in principle. In other words, the local processing device B makes unit processing traces for processing only a partial region of the workpiece by rotating a rotating body having a transition metal formed on the surface as a catalyst while contacting the surface of the workpiece. The processing depth of the workpiece is controlled by scanning the entire surface of the workpiece and controlling the staying time.

  The local processing device B holds a workpiece 43 in a processing liquid 42 stored in a water tank 41 and a tool 46 formed of a rotating body attached to the tip of a vertical rotating shaft 45 connected to a stepping motor 44. It is an apparatus that rotates and processes the surface of the workpiece 43 in a machining liquid 42 while making contact with the surface of the workpiece 43 with a constant contact pressure. More specifically, the water tank 41 and the XY stage 49 are fixed on a horizontal plate 48 provided on the Z stage 47, and a workpiece holder 50 driven by the XY stage 49 extends to the inside of the water tank 41. The workpiece 43 is held. In order to minimize vibration, the rotary shaft 45 is fixed by double bearings 51 and 51, and the connecting portion with the head portion 52 to which the tool 46 is attached is tapered so that it is generated at each attachment / detachment. Misalignment is suppressed. The tool 46 was formed by sputtering a predetermined thickness of Au as a conductive film on the surface of an O-ring. As the O-ring, a P44 standard size (outer diameter 50.7 mm, thickness 3.5 mm) made of fluororubber was used. The stepping motor 44, the rotary 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 mount 54 by a plate spring 55, and the balance-type balancer 56 The verticality is adjusted.

  By operating the X stage, the workpiece 43 can be moved in the direction of the tool 46 by an arbitrary amount, and the surface of the workpiece 43 is controlled by controlling the movement amount of the rotary shaft 45 using an electric micrometer. The contact pressure between the tool 46 and the tool 46 is adjusted. A conductive film (Au film) on the tool 46 is electrically connected to a potentiostat via a rotary joint 57, and is further opposed to the outer periphery of the tool 46 in the machining liquid 42. 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 is formed by sputtering a Pt film having a predetermined thickness on the surface. As the processing liquid 42, an aqueous solution of nickel sulfate or an aqueous solution of sulfuric acid added to nickel sulfate is used as described above, and the conductive film on the rubber ring surface used as the tool 46 is brought into a negative potential state, and the surface of the conductive film Then, a Ni film is deposited 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 apparatus B, the processing conditions and the processing method are the same as those described above.

  In this case, the local processing apparatus B drives each stage by numerically controlling and moving the unit processing traces by changing the relative positions of the workpiece 43 and the tool 46, so that the conductive film of the tool 46 is moved. It becomes a numerical control (NC) processing device capable of creating an arbitrary curved surface smaller than the curvature of the.

A Planarization processing equipment,
B Local processing equipment,
1 Workpiece 2 Workpiece 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 Working fluid 26 Container 27 Drive mechanism 28 Counter electrode 29 Power supply 30 Disk 31 Rotating shaft 32 Rotating shaft 33 Holder 34 Standard electrode 35 Pt electrode 41 Water tank 42 Working fluid 43 Workpiece 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 Base 55 Plate spring 56 Balancer 57 Rotary joint 58 Counter electrode 59 Power supply

Claims (10)

Using a tool with a transition metal with a catalytic function that promotes hydrolysis of the work surface of the work piece on the work surface, the work surface and the work surface are contacted at a predetermined pressure in the presence of water. In addition, 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 advanced 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 capable of flattening a workpiece into a flat surface or an arbitrary curved surface by removing
At least the machining surface of the tool and the machining surface of the workpiece are arranged in a machining fluid containing water and transition metal ions, and the machining surface is brought into a negative potential state with respect to the machining fluid and transitioned to the machining surface. Alternating process of depositing a metal to form a transition metal film having a catalytic function and a dissolving process of dissolving the transition metal film on the machined surface by making the machined surface positive with respect to the machining liquid And a catalyst surface reference etching method characterized by including an etching step repeated in step (a).   2. The catalyst surface reference etching method according to claim 1, wherein the precipitation process is a process of depositing a transition metal in a thickness that allows the transition metal film on the processed surface to be removed by dissolution in the dissolution process.   2. The dissolution process is a process in which the transition metal film deposited on the processed surface advances and the transition metal film on the processed surface is dissolved in a positive potential state before the activity as a catalyst is lost. 3. The catalyst surface reference etching method according to 2.   The etching step further includes a cleaning step of dissolving the inactive transition metal film by maintaining a dissolution process for dissolving the transition metal film on the processing surface while maintaining the processing surface at a positive potential with respect to the processing liquid, for a predetermined time. The catalyst surface reference etching method according to any one of claims 1 to 3, wherein the step and the cleaning step are alternately repeated.   The catalyst surface reference 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 reference 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 with a transition metal with a catalytic function that promotes hydrolysis of the work surface of the work piece on the work surface, the work surface and the work surface are contacted at a predetermined pressure in the presence of water. In addition, 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 advanced 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 apparatus capable of flattening a workpiece into a flat surface or an arbitrary curved surface by removing
A tool having a work surface in which a conductive film that is less ionized than the transition metal and chemically stable is formed on the surface of the elastically deformable pad;
A container for disposing at least the processing surface of the tool and the processing surface of the workpiece in a processing liquid containing water and transition metal ions;
A drive mechanism for holding the workpiece, bringing the workpiece surface and the machining surface of the tool into contact with a predetermined pressure, and causing the workpiece surface and the machining surface to move relative to each other;
A counter electrode disposed in the machining liquid facing a portion different from the machining surface of the tool in contact with the workpiece surface;
A power source for applying a voltage between the machining surface of the tool and the counter electrode;
A control unit for controlling the electric potential of the machining surface of the tool with respect to the machining fluid, and for controlling the drive mechanism;
A deposition process of forming a transition metal film having a catalytic function by depositing a transition metal on the processing surface by setting the processing surface to a negative potential with respect to the processing fluid; and A catalytic surface reference etching apparatus comprising an etching step of alternately repeating a dissolution process of dissolving the transition metal film on the processed surface in a positive potential state.   The etching step further includes a cleaning step of dissolving the inactive transition metal film by maintaining a dissolution process for dissolving the transition metal film on the processing surface while maintaining the processing surface at a positive potential with respect to the processing liquid, for a predetermined time. The catalyst surface reference etching apparatus according to claim 7, wherein the step and the cleaning step 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 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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