Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
  • B23H3/00—Electrochemical machining, i.e. removing metal by passing current between an electrode and a workpiece in the presence of an electrolyte
  • B23H3/08—Working media
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
  • B23H3/00—Electrochemical machining, i.e. removing metal by passing current between an electrode and a workpiece in the presence of an electrolyte
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
  • B23H5/00—Combined machining
  • B23H5/06—Electrochemical machining combined with mechanical working, e.g. grinding or honing
  • B23H5/08—Electrolytic grinding
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F7/00—Constructional parts, or assemblies thereof, of cells for electrolytic removal of material from objects; Servicing or operating

Definitions

• FIGS. 8A through 8C illustrate, in sequence of process steps, an example of forming such a substrate W having copper interconnects.
• Some processing methods such as chemical polishing, electrolytic processing, and electrolytic polishing, have been developed in order to solve this problem.
• these methods perform removal processing or the like through chemical dissolution reaction. Therefore, these methods do not suffer from defects, such as formation of an altered layer and dislocation, due to plastic deformation, so that processing can be performed without deteriorating the properties of the materials.
• water molecules 20 in the liquid 18 such as ultrapure water are dissociated efficiently by using the ion exchangers 12a, 12b into hydroxide ions 22 and hydrogen ions 24.
• the hydroxide ions 22 thus produced are carried, by the electric field between the workpiece 10 and the processing electrode 14 and by the flow of the liquid 18, to the surface of the workpiece 10 opposite to the processing electrode 14 whereby the density of the hydroxide ions 22 in the vicinity of the workpiece 10 is enhanced, and the hydroxide ions 22 are reacted with the atoms 10a of the workpiece 10.
• the reaction product 26 produced by this reaction is dissolved in the liquid 18, and removed from the workpiece 10 by the flow of the liquid 18 along the surface of the workpiece 10. Removal processing of the surface of the workpiece 10 is thus effected. ⁇
• an electrolytic processing method utilizes a chemical interaction between OH ⁇ ions and the atoms of a workpiece. Accordingly, the processing phenomenon occurs even when a workpiece and a tool (electrode) is not in contact with each other. Electrolytic processing is thus differentiated in the processing principle from mechanical processing in which processing is effected by physical destruction of a workpiece.
• processing is effected by allowing a workpiece and a tool, which are in contact with each other, to make a relative movement so as to physically destruct the workpiece.
• the progress of processing may be stopped by releasing the contact between the workpiece and the tool e.g. when a processing amount is reached to an intended processing amount.
• the processing does not progress any more even when the tool passes over the surface of the workpiece.
• the electrolytic processing method which utilizes a chemical interaction between the reaction species and a workpiece, as described above, the processing phenomenon occurs when the amount of the reaction species reaches a certain level, even when the tool (electrode) is not in contact with the workpiece. Accordingly, the processing phenomenon inevitably occurs when the tool (electrode) passes over the surface of a portion of the workpiece in which a predetermined amount of processing has been effected.
• the present invention has been made in view of the above situation in the background art. It is therefore an object of the present invention to provide an electrolytic processing apparatus and method that can effect processing of a workpiece, having in the surface an electrically conductive material as a to-be-processed material, with high processing precision and can produce an intended form of processed workpiece with high accuracy of form.
• the present invention provides an electrolytic processing apparatus, comprising: a holder for detachably holding a workpiece; a processing electrode that can come close to or into contact with the workpiece held by the holder; a feeding electrode for feeding electricity to the workpiece held by the holder; an ion exchanger disposed in at least one of the space between the workpiece and the processing electrode and the space between the workpiece and the feeding electrode; a fluid supply section for supplying a fluid between the workpiece and at least one of the processing electrode and the feeding electrode, in which the ion exchanger is present; a power source for applying a voltage between the processing electrode and the feeding electrode; a drive section for allowing the workpiece held by the holder and the processing electrode, facing each other, to make a relative movement; and a numerical controller for effecting a numerical control of the drive section.
• the electrolytic processing apparatus makes it possible to compare the form of a workpiece before or during processing with an intended form of the workpiece after processing and determine the processing amount corresponding to the coordinate difference between the two forms, input parametric data corresponding to the processing amount to the numerical controller and, based on the inputted data, effect a numerical control of the drive section that allows the workpiece held by the holder and the processing electrode, facing each other, to make a relative movement.
• the electrolytic processing apparatus carried out under such a numerical control, can produce the intended form of processed workpiece with high accuracy of form.
• the power source may supply an electric current or a voltage controlled at a constant value between the processing electrode and the feeding electrode.
• the processing rate is constant when the electric current following between a processing electrode and a feeding electrode is controlled at a constant value.
• the processing amount is determined by the product of the electric current value and the processing time. Accordingly, in the case where the electric current flowing between a processing electrode and a feeding electrode is controlled at a constant value, an intended form of processed workpiece can be obtained with high accuracy of form only by numerically controlling the processing time, i.e. a period of time during which the workpiece and the processing electrode face each other, so that the electrolytic processing phenomenon occurs (residence time) .
• the numerical controller may numerically control, for example, the relative movement speed between the workpiece held by the holder and the processing electrode via the drive section.
• the changing relative movement speeds may be numerically controlled. This makes it possible to process a certain point in the processing surface of the workpiece for an optimum processing time (residence time) .
• the numerical controller may numerically control a stop time in a relative step movement of the workpiece held by the holder and the processing electrode via the drive section .
• the stop time in the movement is numerically controlled. This makes it possible to process a certain point in the processing surface of the workpiece for an optimum processing time (residence time) .
• relative step movement refers to such a relative movement that either one or both of the workpiece and the processing electrode move so that the processing electrode makes a repetition of a certain-distance movement and stop over the workpiece.
• FIG. 1 is a longitudinal sectional front view of an electrolytic processing apparatus according to a first embodiment of the present invention
• FIG. 3 is a block diagram illustrating an example of numerical control by the electrolytic processing apparatus of FIG. 1;
• FIG. 4 is a longitudinal sectional front view of an electrolytic processing apparatus according to a second embodiment of the present invention.
• FIG. 5 is a schematic perspective view of an electrolytic processing apparatus according to a third embodiment of the present invention.
• FIGS. 8A through 8C are diagrams illustrating, in sequence of process steps, an example of the formation of copper interconnects.
• FIG. 9 is a diagram illustrating the principle of electrolytic processing as carried out by using an ion exchanger .
• the electrode head 38 is connected directly to a hollow motor 60 as a third drive section for making the relative movement between the substrate W held by the substrate holder 30 and the processing electrodes 32 so as to rotate by the actuation of the hollow motor (third drive section) 60.
• the nonwoven fabric carrying a strongly acidic cation- exchange group can be prepared by the following method: As in the case of the nonwoven fabric carrying a strongly basic anion-exchange group, a polyolefin nonwoven fabric having a fiber diameter of 20-50 ⁇ m and a porosity of about 90 % is subjected to the so-called radiation graft polymerization comprising -ray irradiation onto the nonwoven fabric and the subsequent graft polymerization, thereby introducing graft chains; and the graft chains thus introduced are then treated with a heated sulfuric acid to introduce sulfonic acid groups thereinto. If the graft chains are treated with a heated phosphoric acid, phosphate groups can be introduced. The degree of grafting can reach 500 % at its maximum, and the capacity of the ion-exchange groups thus introduced after graft polymerization can reach 5 meq/g at its maximum.
• the base material of each of the laminated layers 62a, 62b and 62c of the ion exchanger 40 may be a polyolefin such as polyethylene or polypropylene, or any other organic polymer.
• the ion exchanger may be in the form of a woven fabric, a sheet, a porous material, net or short fibers, etc.
• graft polymerization can be effected by first irradiating radioactive rays ( ⁇ -rays or electron beam) onto the base material (pre-irradiation) to thereby generate a radical, and then reacting the radical with a monomer, whereby uniform graft chains with few impurities can be obtained.
• radioactive rays ⁇ -rays or electron beam
• radical polymerization can be effected by impregnating the base material with a monomer and irradiating radioactive rays ( y -rays , electron beam or UV-rays) onto the base material (simultaneous irradiation) . Though this method fails to provide uniform graft chains, it is applicable to a wide variety of base materials.
• each of the laminated layers 62a, 62b and 62c of the ion exchanger 40 has only one of anion-exchange group and cation-exchange group, a limitation is imposed on electrolytically processible materials and, in addition, impurities are likely to form due to the polarity.
• the anion exchangers and the cation exchangers may be superimposed, or each of the laminated layers 62a, 62b and 62c of the ion exchanger 40 may carry both of an anion-exchange group and a cation-exchange group per se, whereby a range of materials to be processed can be broadened and the formation of impurities can be restrained.
• the ion exchanger 40 by making the ion exchanger 40 a multi-layer structure consisting of laminated layers of ion-exchange materials, such as a nonwoven fabric, a woven fabric and a porous membrane, it is possible to increase the total ion exchange capacity of the ion exchanger 40, whereby formation of an oxide, for example, in removal (polishing) processing of copper, can be restrained to thereby avoid the oxide adversely affecting the processing rate .
• the total ion exchange capacity of an ion exchanger 40 is smaller than the amount of copper ions taken in the ion exchanger 40 during removal processing, the oxide should inevitably be formed on the surface or in the inside of the ion exchanger 40, which adversely affects the processing rate.
• the formation of the oxide is governed by the ion exchange capacity of an ion exchanger, and copper ions exceeding the capacity should become the oxide .
• the formation of an oxide can thus be effectively restrained by using, as the ion exchanger, a multi-layer ion exchanger composed of laminated layers of ion-exchange materials which has enhanced total ion exchange capacity.
• the ion exchanger 40 should preferably have water permeability and water-absorbing properties. Further, it is desirable that at least the material to be opposed to the workpiece has a high hardness and good surface smoothness .
• a commercially-available foamed polyurethane "IC 1000" manufactured by Rodel, Inc.
• IC 1000 foamed polyurethane
• this product can be used as a material for each of the laminated layers of the ion exchanger 40. It is possible to provide holes in a resin plate, thereby making the plate water-permeable for use in the ion exchanger 40. It is of course desirable that the quality of the material has "water-absorbing properties".
• a plurality of fan-shaped electrode plates 64 are disposed in the electrode section 36 in the circumference direction, and the cathode and anode of a power source 68 are alternately connected, via a slip ring 66, to the electrode plates 64.
• the electrode plates 64 connected to the cathode of the power source 68 become the processing electrodes 32 and the electrode plates 64 connected to the anode of the power source 68 become the feeding electrodes 34.
• processing of e.g. copper because electrolytic processing of copper proceeds on the cathode side.
• the cathode side can be a feeding electrode and the anode side can be a processing electrode.
• the electrode plates 64 connected to the cathode of the power source 68 should be the processing electrodes 32 and the electrode plates 64 connected to the anode should be the feeding electrodes 34.
• electrolytic processing proceeds on the anode side. Accordingly, the electrode plates connected to the anode of the power source should be the processing electrodes and the electrode plates connected to the cathode should be the feeding electrodes .
• a noble metal-based electrode may, for example, be one obtained by plating or coating platinum or iridium onto a titanium electrode , and then sintering the coated electrode at a high temperature to stabilize and strengthen the electrode.
• Ceramics products are generally obtained by heat-treating inorganic raw materials , and ceramics products having various properties are produced from various raw materials including oxides, carbides and nitrides of metals and nonmetals . Among them there are ceramics having an electric conductivity.
• the value of the electric resistance generally increases to cause an increase of applied voltage.
• a non-oxidative material such as platinum or with a conductive oxide such as an iridium oxide
• the decrease of electric conductivity due to oxidation of the base material of an electrode can be prevented.
• a pure water nozzle 70 as a pure water supply section for supplying pure water or ultrapure water toward the space between the substrate W held by the substrate holder 30 and the lowered electrode head 38 is disposed above the substrate holder 30. Pure water or ultrapure water is thus supplied to the ion exchanger 40. Pure water herein refers to a water having an electric conductivity of not more than 10 ⁇ S/cm, and ultrapure water refers to a water having an electric conductivity of not more than 0.1 ⁇ S/cm . The electric conductivity of the present invention refers herein to that at 25°C, lat . Instead of pure water or ultrapure water, a liquid having an electric conductivity of not more than 500 ⁇ S/cm or any electrolytic solution may be used.
• the electrolytic processing apparatus is provided with a numerical controller 72 for effecting numerical control of the drive sections, i.e. the motor (first drive section) 44, the motor (second drive section) 56 and the motor (third drive section) 60, which allow the substrate W held by the substrate holder 30 and the processing electrodes 32, facing each other, to make a relative movement.
• the motors (drive sections) 44, 56 and 60 are thus numerically controllable servomotors, and their rotation angles and rotational speeds are numerically controlled by an output signal from the numerical controller 72.
• the form of a substrate (workpiece) before processing is measured.
• various coordinate points of the pre-processing form are measured in a X-Y-Z coordinate system (in which the Z axis is orthogonal to the X-Y plane as a datum plane) .
• the measured pre-processing form data is inputted to the numerical controller 72.
• the corresponding coordinate point (x, y, Z 2 ) of an intended post-processing form is also inputted as intended form data to the numerical controller 72.
• unit processing form data (movement speed per motor control signal pulse) e.g. on form and on processing rate is inputted to the numerical controller 72 in advance or at an arbitrary time .
• a substrate W e.g. a substrate W as shown in FIG. 8B which has in its surface a copper film 6 as a conductor film (portion to be processed)
• the electrode head 38 is moved by the pivot arm 48 to a processing position right above the substrate W held by the substrate holder 30.
• the electrode head 38 is then lowered by the actuation of the motor 50 for vertical movement, so that the ion exchanger 40 mounted on the lower surface of the electrode section 36 of the electrode head 38 contacts or gets close to the upper surface of the substrate W held by the substrate holder 30.
• This embodiment shows the case of supplying pure water, preferably ultrapure water, to the space between the electrode section 36 and the substrate W.
• pure water or ultrapure water containing no electrolyte upon electrolytic processing can prevent extra impurities such as an electrolyte from adhering to and remaining on the surface of the substrate W.
• copper ions or the like dissolved during electrolytic processing are immediately caught by the ion exchanger 40 through the ion-exchange reaction. This can prevent the dissolved copper ions or the like from re- precipitating on the other portions of the substrate W, or from being oxidized to become fine particles which contaminate the surface of the substrate W.
• Ultrapure water has a high resistivity, and therefore an electric current is hard to flow therethrough. A lowering of the electric resistance is made by shortening a distance between the electrode and the workpiece , or interposing the ion exchanger between the electrode and the workpiece. Further, an electrolytic solution, when used in combination with electrolytic solutions, can further lower the electric resistance and reduce the power consumption. When electrolytic processing is conducted by using an electrolytic solution, the portion of a workpiece that undergoes processing ranges over a slightly wider area than the area of the processing electrode.
• a liquid obtained by adding a surfactant or the like to pure water or ultrapure water and having an electric conductivity of not more than 500 ⁇ S/cm, preferably not more than 50 ⁇ S/cm, more preferably not more than O.l ⁇ S/cm
• the processing rate can be considerably enhanced by interposing the ion exchanger 40 between the substrate W and the processing and feeding electrodes 32, 34.
• electrochemical processing using ultrapure water is effected by a chemical interaction between hydroxide ions in ultrapure water and a material to be processed.
• the amount of the hydroxide ions acting as reactant in ultrapure water is as small as 10 "7 mol/L under normal temperature and pressure conditions, so that the removal processing efficiency can decrease due to reactions (such as an oxide film-forming reaction) other than the reaction for removal processing. It is therefore necessary to increase hydroxide ions in order to conduct removal processing efficiently.
• a method for increasing hydroxide ions is to promote the dissociation reaction of ultrapure water by using a catalytic material, and an ion exchanger can be effectively used as such a catalytic material. More specifically, the activation energy relating to water-molecule dissociation reaction is lowered by the interaction between functional groups in an ion exchanger and water molecules , whereby the dissociation of water is promoted to thereby enhance the processing rate.
• FIG. 4 shows an electrolytic processing apparatus according to a second embodiment of the present invention.
• the electrolytic processing apparatus has a ring-shaped contact holding plate 80 at the periphery of the upper surface of the substrate holder 30.
• a plurality of inwardly-protruding contacts 82 as feeding electrodes are mounted at a given pitch to the contact holding plate 80.
• the electrode head 38 is provided with a processing electrode 84 instead of the electrode section 36 used in the embodiment of FIG. 1.
• the processing electrode 84 is connected to the cathode of the power source 68 via a slip ring 86, and the contacts (feeding electrodes) 82 are connected to the anode of the power source 68.
• the other construction is the same as the apparatus shown in FIG. 1.
• the pre-processing form data, the intended form data, the unit processing form data are inputted to the numerical controller 72 so as to numerically control: the rotational speed of the substrate W, held by the substrate holder 30, via the motor (first drive section) 44; the speed of the horizontal movement of the electrode head 38, by pivoting of the pivot arm 48, via the motor (second drive section) 56; and the rotational speed of the electrode head 38 via the motor (third drive section) 60.
• the electrolytic processing carried out under such a control can produce an intended form of processed substrate W with high accuracy of form.
• FIG. 5 shows an electrolytic processing apparatus according to a third embodiment of the present invention.
• the electrolytic processing apparatus includes a substrate holder 100 for attracting and holding a substrate W with its front surface facing upward, and a columnar or cylindrical processing electrode 102 disposed above the substrate holder 100.
• the processing electrode 102 is coupled to the free end of a horizontally-extending rotating shaft 104 that is rotatable and vertically movable.
• An ion exchanger 106 is mounted tightly on the outer circumferential surface of the processing electrode 102.
• the substrate holder 100 and the processing electrode 102 are disposed in a processing bath (not shown) filled with a fluid, such as ultrapure water or pure water, that is, they are immersed in the fluid.
• a wire extending from the cathode of a power source 120 is connected to the processing electrode 102, and a wire extending from the anode is connected to a feeding electrode 122 that is connected to an electric conductor, e.g. copper film 6 formed in the substrate W as shown in FIG. 8B, and feeds electricity to the conductor.
• an electric conductor e.g. copper film 6 formed in the substrate W as shown in FIG. 8B
• the electrolytic processing apparatus is provided with a numerical controller 124 for effecting a numerical control of the drive sections, i.e. the motor 110 (first drive section) and the motor 114 (second drive section) , which allow the substrate W, held by the substrate holder 100 , and the processing electrode 102, facing each other, to make a relative movement.
• the motors (drive sections) 110, 114 are thus numerically controllable servomotors, and their rotation angles and rotational speeds are numerically controlled by an output signal from the numerical controller 124.
• a substrate W as shown in FIG. 8B having copper film 6 as a conductive film (to- be-processed portion) in the surface, is attracted and held by the substrate holder 100.
• the ion exchanger 106 mounted on the surface of the processing electrode 102 is brought close to or into contact with the surface (upper surface) of the substrate W. Electrolytic processing is then carried out by supplying an electric current from the power source 120 to between the processing electrode 102 and the feeding electrode 122 at a constant value while rotating the processing electrode 102.
• the area of a portion (point) under processing is small, whereby supply of ultrapure water or pure water to around the processing portion can be made with ease, enabling a stable processing.
• This invention relates to an electrolytic processing apparatus and method useful for processing a conductive material present in the surface of a substrate, such as a semiconductor wafer, or for removing impurities adhering to the surface of a substrate.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

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• 2002
  • 2002-01-08 JP JP2002001737A patent/JP2003205428A/ja active Pending
• 2003
  • 2003-01-07 TW TW092100219A patent/TWI271246B/zh not_active IP Right Cessation
  • 2003-01-07 US US10/500,576 patent/US20050115838A1/en not_active Abandoned
  • 2003-01-07 WO PCT/JP2003/000038 patent/WO2003057948A1/en not_active Ceased

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