JP2006176885A - Working method with hydroxy group in ultrapure water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a completely new working method with hydroxy groups in ultrapure water where, based on the recognition that, at the time when the concentration of OH<SP>-</SP>in ultrapure water is increased, by utilizing the OH<SP>-</SP>, working can be sufficiently performed, clean working can be performed using OH<SP>-</SP>in ultrapure water without leaving impurities in the working face of a work. <P>SOLUTION: Using only ultrapure water excepting a trace amount of inevitable impurities, electric current is made to flow between a pair or more electrodes arranged at intervals in ultrapure water. Thus, the ultrapure water is electrolyzed, so as to increase an ion product, and a work dipped into the ultrapure water in which the concentration of hydroxy groups or the ions of hydroxy groups is increased is subjected to removal working or oxide film formation working by chemical elution reaction or oxidation reaction with the hydroxy groups or the ions of the hydroxy groups. The work is Si, and an oxide film is formed on the surface thereof. Alternatively, the work is Cu, and the Cu is subjected to removal working. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a processing method using a hydroxyl group in ultrapure water, and more specifically, using only ultrapure water, the ionic product is increased to remove a workpiece by hydroxyl group or hydroxyl ion or to form an oxide film. It relates to a processing method that can be performed.

  In recent years, the development of new materials has progressed one after another with the development of science and technology, but effective processing technology for these new materials has not been established yet, and it is always in a position to follow the development of new materials. ing.

  In addition, as the miniaturization and high precision of the components of all devices have recently progressed and the manufacturing in the sub-micron region has become common, the influence of the processing method itself on the material properties has become even greater. . Under these circumstances, the machining method in which the tool removes the workpiece while physically destroying it, as in conventional machining, creates many defects in the workpiece due to machining. The properties of things deteriorate. Therefore, it becomes a problem how the processing can be performed without impairing the characteristics of the material.

  As a means for solving this problem, firstly developed special processing methods include chemical polishing, electrolytic processing, and electrolytic polishing. In contrast to conventional physical processing, these processing methods perform removal processing by causing a chemical elution reaction. Accordingly, defects such as a work-affected layer and dislocation due to plastic deformation do not occur, and the problem of processing without damaging the properties of the above-mentioned material is solved.

Further, a processing method using chemical interaction between atoms is attracting more attention. This utilizes fine particles or radicals with high chemical reactivity. Since these processing methods perform removal processing by a chemical reaction between the workpiece and the atomic order, it is possible to control the processing of the atomic order. Examples of this processing method include EEM (Elastic Emission Machining) (Patent Document 1) and Plasma CVM (Chemical Vaporization Machining) (Patent Document 2 etc.) developed by the present inventors. EEM uses a chemical reaction between fine particles and a workpiece, and realizes atomic order processing without impairing material properties. The plasma CVM utilizes radical reaction between a radical generated in atmospheric pressure plasma and a workpiece, and realizes atomic order processing.
JP-A-1-236939 Japanese Patent Laid-Open No. 1-125829

By the way, in the above-mentioned electrolytic processing and electrolytic polishing, processing is conventionally advanced by electrochemical interaction between a workpiece and an electrolytic solution (aqueous solutions of NaCl, NaNO ₃ , HF, HCl, HNO ₃ , NaOH, etc.). ing. Moreover, as long as the electrolytic solution is used, it is inevitable that the workpiece is contaminated with the electrolytic solution.

Therefore, the present inventor considers that the hydroxyl group (OH ⁻ ) acts on the processing in the neutral and alkaline electrolytes, and if that is the case, the processing can be performed even with a small amount of water containing OH ^−. It came to. If processing can be performed using OH ⁻ in ultrapure water, clean processing without leaving impurities on the processed surface can be performed, and its use is expected to be very wide including in the semiconductor manufacturing field. However, it is a well-known fact that the OH ⁻ concentration contained in ultrapure water is very dilute and is about 10 ⁻⁷ mol / l at 25 ° C. and 1 atm. For example, Si is contained in ultrapure water. So far, there has been no report of the content that etching is performed by immersion.

Based on the recognition that the present invention can be sufficiently processed using OH ⁻ if the OH ⁻ concentration in the ultrapure water is increased in view of the above situation. It is to provide an entirely new processing methods capable of performing clean processing without leaving impurities on the processed surface of the workpiece using a ^- ultrapure water OH.

  In order to solve the above-mentioned problems, the present invention uses only ultrapure water except for a small amount of inevitable impurities, and allows a current to flow between a pair of or more electrodes arranged at intervals in ultrapure water. Electrolyzes pure water to increase the ion product, and removes the workpiece immersed in ultrapure water with an increased concentration of hydroxyl groups or hydroxyl ions by chemical elution reaction or oxidation reaction with hydroxyl groups or hydroxyl ions Alternatively, a processing method using a hydroxyl group in ultrapure water, characterized in that an oxide film is formed (claim 1).

  Here, it is preferable that the workpiece is an anode, or the potential of the workpiece is kept high, and hydroxyl ions are attracted to the surface of the workpiece.

  Furthermore, a work piece that is an anode is provided with a rotating electrode that can be rotated with a predetermined gap provided as a cathode, and the work is performed while rotating the rotating electrode to create a constant flow of water between the gaps. More preferably, the product is processed (claim 3).

  Further, the workpiece is made of Si and an Si oxide film is formed on the surface thereof (Claim 4), or the workpiece is Cu and the Cu is removed (Claim). Item 5) is preferred.

According to the processing method using the hydroxyl group in the ultrapure water of the present invention as described above, the following remarkable effects can be obtained.
(1) Since the processing is based on the chemical action of OH ^- ions and the workpiece, the properties of the workpiece are not impaired.
(2) electrolytic processing in ultrapure water Unlike aqueous solution used in such H ^+, OH ^- and H only ₂ O is present, since there are impurities such as metal ions, completely cut off the impurities from the outside Then, processing in a completely clean atmosphere is possible.
(3) Since only ultrapure water is used, the processing cost can be significantly reduced.

The origin of the processing method of various materials using the ultrapure water of the present invention is in doubt about the reaction mechanism in conventional electrolytic processing. Electrolytic machining (Electrolytic Machining) is a machining method that obtains the required shape, dimensions, and surface condition by concentrating and limiting the electrochemical dissolution action (anodic elution or electrolytic elution) to the required part of the material. Specifically, a cathode formed in a required shape in the electrolytic solution is opposed to an anode as a workpiece with a gap of 0.02 to 0.7 mm, and a DC voltage of 5 to 20 V (current density is 30 to 200 A). / Cm ² ) is applied to perform processing. Under these conditions, electrolytic elution is caused to concentrate and restrict in the vicinity of the anode, thereby processing the workpiece into a shape obtained by reversing the shape of the cathode, which is a tool.

Next, the conventional theory of reaction mechanism in conventional electrolytic processing will be briefly described. For example, when Fe electrolytic processing is performed using a NaCl aqueous solution as the electrolytic solution, the reaction process at both electrodes is generally as follows.
(Positive) Fe → Fe ²⁺ + 2e Further Fe ²⁺ + 2Cl ⁻ → FeCl ₂ .. (1)
(Shade) 2Na ⁺ + 2H ₂ O + 2e → 2NaOH + H ₂ (2)
Thus, FeCl ₂ generated at the cathode and NaOH generated at the anode react in the liquid, and FeCl ₂ + 2NaOH → Fe (OH) ₂ + 2Na ⁺ + 2Cl ⁻ (3)
It becomes. Thus, when formula (1) to formula (3) are added side by side, the pre-reaction formula is
Fe + 2H ₂ O → Fe (OH) ₂ + H ₂ (4)
It becomes.

Therefore, what is questioned is equation (3), in which NaOH appears to react with FeCl ₂ as it is. However, since NaOH has a large ionization tendency with respect to NaOH, it is considered that NaOH is ionized into Na ⁺ and OH ⁻ as shown in the following formula (5). That is,
^{NaOH → Na + + OH - ··················} (5)
It becomes. Considering this process, the formula (2) and the formula (3) are respectively expressed as 2H ₂ O + 2e → 2OH ⁻ + H ₂ (6)
FeCl ₂ + 2OH ⁻ → Fe (OH) ₂ + 2Cl ⁻ (7)
Then, when Expression (1), Expression (6), and Expression (7) are added side by side, Expression (4) is similarly derived.

Comparing both the reaction process of the formula (1) to the formula (3) and the reaction process of the formula (1) → the formula (6) → the formula (7), NaOH itself contributes to the reaction in the former. On the other hand, in the latter, it can be seen that OH ⁻ generated by the ionization of NaOH contributes to the reaction. That is, the latter is considered to proceed if OH ^- is present. Here, OH ⁻ is present in a trace amount (10 ⁻⁷ mol / l at 25 ° C.) not only in the solution but also in pure water. Therefore, based on the above-mentioned idea, it is possible to process the same material as in the alkaline solution by using OH ⁻ in ultrapure water.

However, as described above, since the amount of OH ^{− in} ultrapure water is very small, in order to enable practical processing, the OH ⁻ concentration must be increased by some method. The present invention consists in processing the material in an extremely cleaned environment by increasing the OH ^- concentration in ultrapure water without adding other solutions. Therefore, contamination of the workpiece surface does not occur in the processing of the present invention.

  The processing principle of the present invention is to ionize water molecules in ultrapure water, supply the generated hydroxyl group or hydroxyl ion to the surface of the workpiece, and react the workpiece atom with the hydroxyl group or hydroxyl ion to generate a surface of the material. Then, a clean oxide film is formed, or material surface atoms are removed, and a desired shape is obtained by accumulation thereof.

  In other words, if hydroxyl groups or hydroxyl ions that serve as processing tools are generated by chemical reactions on the surface of an electrode placed near the surface of the workpiece or a solid surface having an ion exchange function or catalytic function, such hydroxyl groups or hydroxyl ions The surface of the workpiece in the vicinity of the surface of the solid material that generates the is preferentially processed. Therefore, so-called transfer processing is possible in which the shape of a material that generates hydroxyl groups or hydroxyl ions is transferred to the surface of the workpiece. Moreover, when the shape of the material that generates hydroxyl groups or hydroxyl ions is linear, the plate-like material can be cut. It is possible to select whether the reaction induced on the surface of the material is an oxidation reaction or a removal processing reaction by adjusting processing parameters such as the supply amount of hydroxyl groups or hydroxyl ions.

In the processing method of the present invention, a hydroxyl group increasing treatment is important in order to increase the processing speed (processing efficiency). A hydroxyl group increases processing, OH at thermal equilibrium state ^- and a method of increasing the ^- OH in a method of increasing a thermal nonequilibrium (not utilize thermal equilibrium) state. Looking at the hydroxyl increasing process from the viewpoint of processing, OH ^- at a method which does not utilize the thermal equilibrium to limit the machining area by localized OH ^- although it is preferred to increase the in thermal equilibrium state Even if OH ⁻ is increased, if only OH ⁻ can be separated or accumulated and supplied to the processing surface of the workpiece, the processing region can be similarly limited.

  As the hydroxyl group increasing treatment, a treatment (electrolytic treatment) in which ultrapure water is electrolyzed by passing an electric current between one or more electrodes arranged at intervals in ultrapure water, or ultrapure water Is a process that maintains high temperature and high pressure (high temperature and high pressure treatment), or current between a pair of electrodes or more disposed at intervals in ultra pure water while maintaining ultra pure water at high temperature and high pressure. Treatment by electrolyzing ultrapure water (high temperature, high pressure, electrolytic treatment), or treatment using an electrochemical reaction on a solid surface with ion exchange function disposed in ultrapure water (ion Exchange treatment), treatment using a reaction on a solid surface having a catalytic function disposed in ultrapure water (catalyst treatment), or applying high frequency voltage with a frequency as low as possible in dielectric loss to ultrapure water Water plasma is generated and water is ionized or dissociated. Physical (plasma treatment) can be adopted.

In combination with the above-described hydroxyl group increasing treatment, the workpiece is used as an anode, or the potential of the workpiece is kept high, and hydroxyl ions are attracted to the surface of the workpiece by an electric field, and the workpiece It is practical to increase the concentration of nearby hydroxyl ions for processing. Further, in order to prevent the generated OH ⁻ and H ^{+ from} recombining and returning to H ₂ O, a strong electric field is applied to attract OH ⁻ to the work piece or a hydrogen storage alloy is used. ^{+ A} method to force exclusion of ions is effective.

Next, each hydroxyl group increase process is demonstrated. First, the electrolytic treatment is a treatment in which an electric current is passed between one or more electrodes disposed at intervals in ultrapure water to electrolyze the ultrapure water. Usually, the anode side is covered. This is done by using a pair of electrodes as a workpiece and applying a DC bias voltage between the electrodes. Here, in order to increase OH ⁻ acting on the workpiece surface per unit time, the electric field strength between the electrodes is increased, that is, the DC bias applied between the electrodes is increased or the gap between the electrodes is decreased. good. In this case, the ions existing in the ultrapure water are only H ⁺ and OH ⁻ , and therefore, when a DC bias is applied, many OH ⁻ exist in the vicinity of the anode. The workpiece to be the anode is processed by OH ^{− in the} vicinity of the anode. The amount of work to be processed is generally determined by Faraday's law, and the amount of electricity required to elute 1 gram equivalent of the element in the work is F (Faraday constant) coulomb, the higher the current density. The processing speed will be fast.

The high-temperature and high-pressure treatment is a treatment in which ultrapure water is maintained at a high temperature and high pressure, and utilizes the fact that the ionic product of water changes in its absolute amount depending on the pressure and temperature in the liquid state. . FIG. 1 is a graph showing the relationship between the ionic product Kw of water and the density ρ obtained by measuring the electrical conductivity of water in an ultrahigh temperature and ultrahigh pressure region up to 100 kbar (10 ¹⁰ Pa), 1000 ° C. The relationship between ion product and pH is
pH (H ₂ O) = − log [H ⁺ ] = − log Kw ^1/2
Given in.

The trend of the relationship between ion product, pressure and temperature is as follows. First, under the condition of constant pressure in the range of 1 to 10 kbar, the ion product increases as the temperature rises, but the slope gradually decreases, and after reaching a limit value at a certain temperature, the ion product increases. Decrease. Under the condition of constant pressure in the range of 30 to 100 kbar, the ion product increases monotonously. Next, under a constant temperature condition, the ion product increases as the pressure increases. Even under a constant density condition, the ion product increases as the temperature and pressure increase. For example, when the density is increased from room temperature (25 ° C.) to 200 ° C. at a density of 1.0 g / cm ³ , the water ion product Kw increases from about 10 ⁻¹⁴ to about 10 ^−10.118 while the pressure is 3 kbar (3 × 10 ⁸ Pa, about 3000 atm).

  High-temperature, high-pressure / electrolytic treatment is to electrolyze ultrapure water by passing a current between one or more electrodes arranged at intervals in ultrapure water while maintaining ultrapure water at high temperature and high pressure. This is a combination of the above-described electrolytic treatment and high-temperature and high-pressure treatment.

The ion exchange treatment is a treatment using an electrochemical reaction on a solid surface having an ion exchange function disposed in ultrapure water, and the ion exchange resin particles between the ion exchange resin membrane or the water-permeable partition membrane. Or what filled a solid electrolyte etc. can be utilized. Then, an anode and a cathode are arranged on both sides of the solid surface having an ion exchange function, and OH ⁻ generated on the solid surface is drawn to the anode side and H ⁺ is drawn to the cathode side to be separated and used as an anode. The workpiece disposed in the vicinity of the workpiece or the anode is processed with OH ⁻ . The catalyst treatment is a treatment in which water molecules are excited or activated on a solid surface having a catalytic function, and the water molecules are ionized or dissociated by a voltage applied between the anode and the cathode.

The plasma treatment is a treatment in which water plasma is generated by applying a high frequency voltage with a frequency as low as possible in dielectric loss to ultrapure water, and water is ionized or dissociated. In a typical non-equilibrium state, OH ⁻ Is a method of generating In this case, OH ⁻ in the plasma is forced to act on the processed surface of the workpiece by applying a strong electric field or the like. It is also considered that plasma is generated by applying a high-frequency voltage to water-purified ultrapure water.

Here, the processing principle of the present invention is that the workpiece is processed by OH ^{− in} ultrapure water, but the processing is removal processing by chemical elution reaction or oxide film formation processing by oxidation reaction. It can be selected by adjusting processing parameters such as the amount of hydroxyl group supplied. However, this processing parameter differs depending on the method of hydroxyl group increasing treatment, and at present, the range of processing parameters for selecting both processing cannot be specified.

  Next, the present invention will be further described based on a specific example in which a workpiece is actually processed. Example 1 employs electrolytic treatment, Example 2 employs high-temperature and high-pressure treatment, Example 3 employs ion exchange treatment, and demonstrates the machining using Si as the workpiece and several other types of metals. A test was conducted.

(Example 1-1)
As shown in FIG. 2, a verification test was performed using a processing apparatus in which the anode side was Si and the cathode side was a rotating electrode. The advantages of using a rotating electrode are that a constant flow of water is created between the electrodes, processing in a stable field is possible, and constantly supplying fresh water between the electrodes keeps the field clean. What can be done. As for the former, if the two flat electrodes face each other with a small gap (1 mm or less), bubbles generated from the surfaces of both electrode plates accumulate between the gaps, so that stable processing cannot be expected. Because. Regarding this point, even in the conventional electrolytic processing, the flow of the electrolytic solution is created to remove the bubbles.

  As shown in FIG. 2, the processing apparatus of the present example immerses the sample 1 made of an Si plate and the rotating electrode 2 in ultrapure water 4 filled with a water tank 3 with a gap provided, and the sample 1 is XY. The rotating electrode 2 is held by a support member 6 fixed to the stage 5, and the rotating electrode 2 is fixed to the tip of the rotating shaft 9 (Z-axis direction) of the motor 8 fixed to the Z stage 7. The processed surface of the sample 1 is disposed perpendicular to the XY plane, for example, parallel to the YZ plane. Therefore, by driving the XY stage 5 and the Z stage 7, the relative position including the gap interval between the sample 1 and the rotating electrode 2 can be changed. The sample 1 and the rotating electrode 2 are electrically connected to a power source 10 via lead wires 11 and 11 respectively, a positive voltage is applied to the sample 1, and the rotating electrode 2 is maintained at the ground potential. Yes. The current flowing between the sample 1 and the rotating electrode 2 is measured by an ammeter 12. Further, most of the mechanical part including the water tank 3 is accommodated in an airtight chamber 13, and the inside of the airtight chamber 13 is purged with Ar gas.

As the material of the rotating electrode 2, it is necessary to use a material that is not affected by OH ^- or H ⁺ , and Au or Pt is most preferable. In this example, the surface of the Al sphere coated with Ni to a thickness of 10 μm by electroless plating and Au coated thereon by electrolytic plating was used as the rotating electrode 2.

First, the DC bias applied between both electrodes (between the anode sample 1 and the cathode rotating electrode 2) is made constant, the gap is changed, the electric field strength is increased, and the amount of OH ⁻ acting on Si is increased. The state of the change of Si when it was made to observe was observed. The processing conditions and processing results are shown in Table 1 below.

Here, the thickness of the oxide film in Table 1 was measured using a stylus roughness meter (Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.). As a result, the oxide film formed on the sample 1 grows thickest in the central portion where the rotating electrode 2 is closest, and the growth of the oxide film decreases as the distance from the center increases. Since the rotating electrode is used, the gap increases as the distance from the center of the rotating electrode increases, and the electric field strength decreases accordingly. As a result, the amount of OH ⁻ acting on Si per unit time Is estimated to have decreased. From the above results, it can be seen that the oxide film forming process is performed at least when the current density is about 0.9 mA / cm ² or less.

(Example 1-2)
Next, in order to increase the current density and make the concentration of OH ⁻ acting on Si uniform, processing using parallel plate electrodes was attempted. FIG. 3 shows an outline of the processing apparatus. In this processing apparatus, samples 22 and 22 made of Si flat plates are placed in parallel through an insulating spacer 23 in ultrapure water 21 filled in a container 20 made of tetrafluoroethylene resin (PTFE). It is immersed in a fixed state, a positive voltage is applied to one sample 22 from a power source 24, the other sample 22 is maintained at zero potential, and the opening of the container 20 is covered with a lid 25 and is gas impermeable. The inside of the bag 26 is purged with Ar gas. In the figure, reference numeral 27 denotes a thermometer.

  In the same manner as in Example 1-1 described above, a DC bias was applied to both samples 22 and 22, and processing was attempted. The processing conditions and processing results are shown in Table 2 below, and the processing was oxide film formation processing even at this current density.

(Example 1-3)
Next, in order to further increase the current density, an attempt was made to process the cathode as a needle-like electrode. FIG. 4 shows an outline of the processing apparatus. In this processing apparatus, a water tank 31 disposed in an airtight container 30 is filled with ultrapure water 32, a sample 34 made of a Si flat plate fixed to a holding base 33 is immersed in the ultrapure water 32, and is made of a gold wire. The needle-like electrode 35 is fixed to the holding table 33 with a predetermined gap perpendicular to the sample 34 and similarly immersed in ultrapure water 32, and a positive voltage is applied from the power source 36 to the sample 34. The electrode 35 is maintained at zero potential, and the sealed container 30 is purged with Ar gas. In the figure, reference numeral 37 denotes a thermometer.

  In the same manner as in Example 1-1 described above, processing was attempted by applying a DC bias between both the sample 34 and the needle electrode 35. The processing conditions and processing results are shown in Table 3 below, and the processing was oxide film forming processing even at this current density.

From the above results, when the workpiece was Si, the processing was oxide film forming processing when the current density was in the range of 0.11 to 7.9 mA / cm ² . Currently, in the semiconductor industry, Si oxide films are used in various fields of manufacturing Si devices such as gate insulating films and capacitor insulating films. There are various methods for generating this Si oxide film, but the Si oxide film used in today's device manufacturing is a thermal oxide film that is uniformly formed mainly by exposing Si to a high temperature atmosphere. Conventionally, dry oxidation, humidified oxidation, steam oxidation, pressure oxidation, plasma oxidation, electrolytic anodic oxidation, and the like are known as methods for forming a Si oxide film.

  In the other methods except electrolytic anodic oxidation, the characteristics of the oxide film are almost the same, whereas in the electrolytic anodic oxidation method, the density of the oxide film is considerably smaller than the other methods and the resistivity is also compared with the other methods. 4 digits smaller. This is presumably because, in the electrolytic anodic oxidation method, the electrolyte in the electrolytic solution greatly affects the Si oxide film. The Si oxide film formed on the anode by the processing method of the present invention is due to the anode electrode reaction in ultrapure water. Therefore, the oxide film and the thermal oxide film according to the present invention were analyzed by FT-IR (Fourier Transfer-Infrared Spectroscopy) (manufactured by JASCO, FT / IR-3 type) and AES (Auger Electron Spectroscopy). From the results of FT-IR analysis, it was found that the oxide film of the present invention generally has a smaller amount of Si—O bonds than the thermal oxide film used for device manufacture. However, on the other hand, it was found from the analysis result of AES that the oxide film of the present invention has a structure comparable to the thermal oxide film. Therefore, by optimizing the processing conditions for forming the oxide film, if an Si electrode reaction is performed in ultrapure water, a Si oxide film comparable to the thermal oxide film may be obtained.

(Example 1-4)
Using the processing apparatus of Example 1-3 described above, processing of Cu, Mo, Fe, and Al as samples was attempted. The processing conditions and processing results are shown in Table 4 below. Under these processing conditions, Cu and Mo were removal processing, and Fe and Al were oxide film formation processing.

Here, the surfaces of Cu and Mo processed immediately after the processing were changed to brown and black, respectively. These appear to be the Cu oxide CuO and the Mo oxide MoO. In particular, Cu had a green haze appearing in the water during processing, and a part of the water after the processing of Mo had a blue haze. Therefore, it is estimated that the processed Cu and Mo surfaces were oxidized. From these results, one model of processing mechanism by electrode reaction in ultrapure water can be considered. That is, in ultrapure water, the substance is first oxidized due to the relationship with OH ^- and H ₂ O, and the oxide is further removed by some reason related to OH ^- and H ₂ O. It is a model that changes to processing.

In this example, the ultrapure water was maintained at a high temperature and a high pressure to increase the OH ⁻ concentration in the ultrapure water, and an attempt was made to process the workpiece immersed in the ultrapure water. As shown in FIG. 1, when the temperature is raised to 200 ° C. with a constant density of 1.0 g / cm ³ of water at atmospheric pressure at a temperature of 25 ° C. near room temperature, the pressure becomes 3000 atm. I understand. Therefore, in this processing apparatus, as shown in FIG. 5, a container 43 made of tetrafluoroethylene resin filled with ultrapure water 42 is disposed in the internal reaction chamber 41 of the pressure vessel 40, and A sample 44 made of Si is immersed, and a heating ceramic heater 45 is wound around the outer periphery of the pressure vessel 40 and further covered with a heat insulating material 46. The ceramic heater 45 is provided with a slidac 47. A current is supplied through this. The temperature is measured with a thermocouple 48 brought into contact with the pressure vessel 40. The pressure vessel 40 is designed to withstand 3000 atm. The vessel main body 40a having the accommodation space 41 and the lid body 40b are fastened by eight bolts 40c, and the vessel main body 40a and the lid body 40b are made of copper. Sealed with a gasket 40d. The container body 40a and the lid body 40b are made of stainless steel (SUS304), and the bolt 40c is made of HPM2 steel having a linear expansion coefficient smaller than that of stainless steel. When the temperature rises, the coefficient of thermal expansion is increased. It has a self-linking structure that increases the tightening force due to the difference.

  As the sample 44, a Si wafer having a thickness of 400 μm and a length and width of 1 × 2 cm is used. As pretreatment, first, oil and other dirt on the surface of the Si wafer were wiped off with ethyl alcohol, and then washed with 5% hydrofluoric acid for 30 seconds to remove the oxide film. And finally, it wash | cleaned for 10 second in ultrapure water (running water), and made it fully dry. Prior to processing, the weight of the Si wafer was measured on the mg order. Table 5 shows the weight before processing and the weight after processing as processing conditions and processing results.

  Here, regarding the processing time, after the thermocouple monitor indicated 200 ° C., it waited for the temperature of ultrapure water in the internal reaction chamber to reach 200 ° C. (10 minutes), and then processing was performed for 1 hour. The thickness reduction amount in the table was calculated by mass difference / (density × surface area).

  An attempt was made to process a Cu plate using a processing apparatus as shown in FIGS. In this processing apparatus, a platinum electrode plate 52 serving as a cathode and a Cu sample 53 serving as an anode are immersed in ultrapure water 51 filled in a container 50 while maintaining a certain gap, and between the electrodes. A cation exchange membrane (Nafion 117) 54 is provided, the entire container 50 is accommodated in an airtight container 55, and the inside is purged with Ar gas. More specifically, the platinum electrode plate 52 is fixed on one side of the gap spacer 56 having an opening inside with the cation exchange membrane 54 interposed therebetween, and the sample 53 is fixed on the other side of the gap spacer 56. Soak in ultrapure water 51. In this case, the ultrapure water 51 is also filled in the opening 56 a of the gap spacer 56. A DC voltage was applied from the power source 57 between the platinum electrode plate 52 and the sample 53 so that the current value was constant during processing. The processing conditions and processing results are shown in Table 6 below.

  Here, in processing 1 in Table 6, as a result of processing by immersing the cation exchange membrane in ultrapure water while being dried, the cation exchange membrane is super Only the contact portion with pure water absorbed water and expanded to the sample side. As a result, there was almost no gap between the cation exchange membrane and the sample. On the other hand, in the processing 2 in Table 6, after the cation exchange membrane was previously immersed in ultrapure water for a sufficient time to make the expansion of the membrane uniform, the gap was further washed thoroughly with ultrapure water. I set it on the spacer. As a result, the voltage applied to secure a current value of 40 mA in machining 1 was several tens of volts, whereas the voltage applied to secure a current value of 30 mA in machining 2 was 600 to 1400 V. .

In this processing method of increasing the OH ⁻ concentration by ion exchange treatment, if the tool with a specific shape having an ion exchange material on the surface is used as the cathode and the workpiece is used as the anode, the shape of the tool is transferred to the workpiece. If a wire electrode having an ion exchange material on its surface is used as the cathode, a process for cutting the workpiece of the anode (cutting process) is possible.

It is a graph which shows the relationship between the density of water and ion product which made temperature and pressure a parameter. It is a simplified cross-sectional view of a processing apparatus that employs electrolytic treatment as a hydroxyl group increasing treatment and uses a rotating electrode. FIG. 3 is a simplified cross-sectional view of a processing apparatus that employs electrolytic treatment as a hydroxyl group increasing treatment and uses parallel plate electrodes. It is a simplified cross-sectional view of a processing apparatus that employs an electrolytic treatment as a hydroxyl group increasing treatment and uses a needle-like electrode. It is a simplified cross-sectional view of a processing apparatus that employs high-temperature and high-pressure treatment as a hydroxyl group increasing treatment. The processing apparatus which employ | adopted the ion exchange process as a hydroxyl group increase process is shown, (a) is a simplified sectional view of an apparatus, (b) is an exploded perspective view which shows an electrode periphery structure.

Explanation of symbols

1 Sample (workpiece)
2 Rotating electrode 3 Water tank 4 Ultrapure water 5 XY stage 6 Support member 7 Z stage 8 Motor 9 Rotating shaft 10 Power supply 11 Lead wire 12 Ammeter 13 Airtight chamber 20 Container 21 Ultrapure water 22 Sample (workpiece)
23 Spacer 24 Power supply 25 Lid 26 Bag 27 Thermometer 30 Sealed container 31 Water tank 32 Ultrapure water 33 Holding stand 34 Sample (Workpiece)
35 Needle electrode 36 Power source 37 Thermometer 40 Pressure vessel 40a Container body 40b Lid 40c Bolt 40d Gasket 41 Internal reaction chamber 42 Ultrapure water 43 Container 44 Sample (workpiece)
45 Ceramic heater 46 Insulating material 47 Slidac 48 Thermocouple 50 Container 51 Ultrapure water 52 Platinum electrode plate 53 Sample (workpiece)
54 Cation Exchange Membrane 55 Airtight Container 56 Gap Spacer 56a Opening 57 Power Supply

Claims (5)

Use only ultrapure water, excluding trace amounts of inevitable impurities, and pass an electric current between one or more electrodes arranged at intervals in ultrapure water to electrolyze the ultrapure water and increase the ion product. The workpiece immersed in ultrapure water having an increased concentration of hydroxyl groups or hydroxyl ions is subjected to removal processing or oxide film formation processing by chemical elution reaction or oxidation reaction with hydroxyl groups or hydroxyl ions. Processing method using hydroxyl groups in pure water. The processing method using a hydroxyl group in ultrapure water according to claim 1, wherein the workpiece is used as an anode, or the potential of the workpiece is maintained high to attract hydroxyl ions to the surface of the workpiece. A work piece made into an anode is provided with a predetermined gap and a rotatable rotating electrode arranged as a cathode, and the work piece is moved while rotating the rotating electrode to create a constant flow of water between the gaps. The processing method by the hydroxyl group in the ultrapure water of Claim 2 formed by processing. The processing method using a hydroxyl group in ultrapure water according to any one of claims 1 to 3, wherein the workpiece is Si and a Si oxide film is formed on the surface thereof. The processing method using a hydroxyl group in ultrapure water according to any one of claims 1 to 3, wherein the workpiece is Cu, and the Cu is removed.

Images