Electrolytic processing apparatus and method

TECHNICAL FIELD

This invention relates to an electrolytic processing apparatus and method, and more particularly to an electrolytic processing apparatus and method useful for processing a conductive material formed in a surface of a substrate, such as a semiconductor wafer, or for removing impurities adhering to a surface of a substrate.

BACKGROUND ART

In recent years, instead of using aluminum or aluminum alloys as a material for forming circuits on a substrate such as a semiconductor wafer, there is an eminent movement towards using copper (Cu) which has a low electric resistivity and high electromigration endurance. Copper interconnects are generally formed by filling copper into fine recesses formed in the surface of a substrate. There are known various techniques for forming such copper interconnects, including chemical vapor deposition (CVD), sputtering, and plating. According to any such technique, a copper film is formed in the substantially entire surface of a substrate, followed by removal of unnecessary copper by chemical mechanical polishing (CMP).

FIGS. 1A through 1C illustrate, in sequence of process steps, an example of forming such a substrate W having copper interconnects. As shown in FIG. 1A, an insulating film 2, such as an oxide film of SiO₂or a film of low-k material, is deposited on a conductive layer la in which semiconductor devices are formed, which is formed on a semiconductor base 1. Contact holes 3 and trenches 4 for interconnects are formed in the insulating film 2 by the lithography/etching technique. Thereafter, a barrier layer 5 of TaN or the like is formed on the surface, and a seed layer 7 as an electric supply layer for electroplating is formed on the barrier layer 5 by sputtering or CVD, or the like.

Then, as shown in FIG. 1B, copper plating is performed onto the surface of the substrate W to fill the contact holes 3 and the trenches 4 with copper and, at the same time, deposit a copper film 6 on the insulating film 2. Thereafter, the copper film 6 and the barrier layer 5 on the insulating film 2 are removed by chemical mechanical polishing (CMP) so as to make the surface of the copper film 6 filled in the contact holes 3 and the trenches 4 for interconnects and the surface of the insulating film 2 lie substantially on the same plane. Interconnects composed of the copper film 6 as shown in FIG. 1C are thus formed.

Components in various types of equipments have recently become finer and have required higher accuracy. As sub-micron manufacturing technology is becoming common, the properties of materials are more and more influenced by the processing method. Under these circumstances, with a conventional mechanical processing method in which a processing object in a workpiece is physically destroyed and removed from the workpiece by a tool, many defects may be produced, deteriorating the properties of the workpiece. Thus, it is increasingly important to perform processing without deteriorating the properties of the materials.

Some processing methods, such as chemical polishing, electrolytic processing, and electrolytic polishing, have been developed in order to solve this problem. In contrast with the conventional physical processing, 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.

In an electrochemical processing, ions as reactant species move onto the surface of a workpiece due to the electric field created between a processing electrode, feeding electrode and the workpiece. Accordingly, generation of an obstacle to the movement of ions will affect constancy and uniformity in processing. Such an obstacle may include a processing product which is generated during processing by the electrochemical reaction between the workpiece and the ions at the surface of the workpiece, a substance produced and released from an ion exchanger during a relative movement between the ion exchanger and the workpiece, and bubbles (gas) generated by a side reaction at the surfaces of the workpiece and the electrode, etc. Such an obstacle, present between the electrode and the workpiece, impedes the migration of ions, and therefore prevents obtaining a constant and uniform processing amount. Bubbles, in particular, can also cause the formation of pits in the surface of the workpiece. Accordingly, there is a strong desire for suppression of the generation of bubbles.

Bubbles are formed due to aggregation of gas (microbubbles) generated at the electrode surface and the surface of the workpiece. Accordingly, to suppress the aggregation of gas is considered to be one method to suppress the generation of bubbles. The degree of the gas aggregation depends on (1) the affinity of gas molecules for water and (2) the gas generation speed and the unevenness of gas distribution at the electrode surface and the surface of the workpiece. Regarding (2), the generation of gas is influenced by a disproportion in the distribution of an amount of ions (H⁺ions and OH⁻ions) supplied to the electrode and the workpiece. The distribution of the amount of ions supplied is in turn influenced by the electric field distributions in the vicinities of the electrodes and the workpiece as well as the electric field distribution between the electrodes. It is therefore necessary to design electrodes taking into consideration the distributions of electric field intensity in the vicinities of the electrodes and the workpiece as well as between the electrodes.

DISCLOSURE OF INVENTION

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 which can suppress the growth of a gas, which is inevitably generated during electrochemical processing, into bubbles thereby effectively preventing the formation of pits in a surface of a workpiece.

In order to achieve the above objects, the present invention provides an electrolytic processing apparatus, comprising: an electrode section including a plurality of processing electrodes and feeding electrodes both having a diameter of not more than 1 mm, said processing electrodes being electrically isolated from said feeding electrodes; a substrate holder for holding a workpiece and bringing the workpiece close to the electrode section; a power source for applying a voltage between the processing electrodes and the feeding electrodes; a fluid supply section for supplying a fluid between the electrode section and the workpiece which is held by the substrate holder and has been brought close to the electrode section; and a drive section for moving the electrode section and the workpiece relative to each other in such a manner that a plurality of said processing electrodes pass every point in a processing surface of the workpiece held by the substrate holder.

FIGS. 2 and 3 illustrate the principle of processing according to the present invention. FIG. 2 shows the ionic state in the reaction system when an ion exchanger 12a mounted on a processing electrode 14 and an ion exchanger 12b mounted on a feeding electrode 16 are brought into contact with or close to a surface of a workpiece 10, while a voltage is applied from a power source 17 to between the processing electrode 14 and the feeding electrode 16, and a fluid 18, such as ultrapure water, is supplied from a fluid supply section 19 to between the processing electrode 14, the feeding electrode 16 and the workpiece 10. FIG. 3 shows the ionic state in the reaction system when the ion exchanger l2a mounted on the processing electrode 14 is brought into contact with or close to the surface of the workpiece 10 and the feeding electrode 16 is directly contacted with the workpiece 10, while a voltage is applied from the power source 17 to between the processing electrode 14 and the feeding electrode 16, and the fluid 18, such as ultrapure water, is supplied from the fluid supply section 19 to between the processing electrode 14 and the workpiece 10.

When using a liquid, like ultrapure water, which itself has a large resistivity, it is preferred to bring the ion exchanger 12a into “contact” with the surface of the workpiece 10. This can lower the electric resistance, lower the voltage applied, and reduce the power consumption. Thus, the “contact” in the processing according to the present invention does not imply “press” for giving a physical energy (stress) to a workpiece as in CMP.

In FIGS. 2 and 3, water molecules 20 in the liquid 18, such as ultrapure water, are dissociated by the ion exchangers 12a and 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 facing the processing electrode 14, whereby the density of the hydroxide ions 22 in the vicinity of the workpiece 10 is increased, and the hydroxide ions 22 are reacted with the atoms 10a of the workpiece 10. The reaction product 26 produced by reaction is dissolved in the liquid 18 such as ultrapure water, 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 layer of the workpiece 10 is thus effected.

As will be appreciated from the above, the removal processing according to the present method is effected purely by the electrochemical interaction between the reactant ions and the workpiece. The present electrolytic processing thus clearly differs in the processing principle from a processing as by CMP according to which processing is effected by the combination of a physical interaction between a polishing member and a workpiece, and a chemical interaction between a chemical species in a polishing liquid and the workpiece. According to the present method, the portion of the workpiece 10 facing the processing electrode 14 is processed. Therefore, by moving the processing electrode 14, the workpiece 10 can be processed into a desired surface configuration.

The electrolytic processing apparatus according to the present invention performs removal processing of a workpiece solely by the dissolution reaction based on the electrochemical interaction, as distinct from a CMP apparatus which performs processing by the combination of the physical interaction between a polishing member and a workpiece, and the chemical interaction between a chemical species in a polishing liquid and the workpiece. Therefore, this electrolytic processing apparatus can perform removal processing of a material without impairing the properties of the material. Even when the material is of a low mechanical strength, such as the above-described low-k material, removal processing of the material can be effected without causing any physical interaction. Further, as compared to conventional electrolytic processing apparatuses, the apparatus of the present invention, because of the use as an electrolysis liquid a liquid having an electric conductivity of not more than 500 μS/cm, preferably pure water, more preferably ultrapure water, can remarkably reduce contamination of the surface of a workpiece with impurities, and can facilitate disposal of waste water after the processing.

Further, according to the electrolytic processing apparatus of the present invention, the electrode section is provided with a plurality of processing electrodes and feeding electrodes both having a diameter of not more than 1 mm, the processing electrodes being electrically isolated from the feeding electrodes, and such electrode section and a workpiece are moved relative to each other in carrying out processing. This makes it possible to equalize the electric field distributions in the vicinities of the electrodes (processing electrodes and feeding electrodes) and the workpiece as well as the electric field distribution between the processing electrodes and the feeding electrodes, thereby suppressing the growth of a gas, which is generated at the surfaces of the electrodes and the workpiece, into bubbles.

The distance between each processing electrode and each feeding electrode, adjacent to each other, is preferably at least equal to the distance between the workpiece and the processing electrodes or the feeding electrodes.

This allows electricity to pass preferentially between the substrate and each processing electrode or each feeding electrode rather than between each electrode and each feeding electrode, thereby preventing an electric current from flowing between each processing electrode and each feeding electrode, adjacent to each other, without passing through the substrate W. The distance between each processing electrode and each feeding electrode, adjacent to each other, is preferably at least 4.5 times, more preferably at least 9 times the distance between the workpiece and the processing electrodes or the feeding electrodes.

Preferably, an ion exchanger is disposed between the workpiece and at least one of the processing electrodes and the feeding electrodes.

An ion exchanger which integrally covers the processing electrodes and the feeding electrodes may be disposed between the workpiece and the processing and feeding electrodes. With this arrangement, the electrode section and the ion exchanger may be produced with ease.

In the preferred aspect of the present invention, the ion exchanger extends between a supply shaft and a take-up shaft, and is taken up sequentially.

By thus taking up the ion exchanger sequentially, a change of the ion exchangers can be carried out automatically, enabling a speedy change. Accordingly, the downtime of the apparatus for a change of the ion exchanger can be shortened, leading to an increased throughput.

In the aspect of the present invention, the electrolytic processing apparatus further comprises an ion exchanger regeneration section for regenerating the ion exchanger. The of the ion exchanger regeneration section in the apparatus, the ion exchanger that has been used in electrolytic processing is regenerated automatically, thereby lowering the running cost and, at the same, shortening the downtime of the apparatus.

The fluid supply section may comprise a fluid supply passage penetrating the electrode section. This enables the liquid, which has passed through the electrode section, to be supplied to between the workpiece, which is held by the substrate holder and has been brought close to the electrode section, and the electrode section.

The electrode section may comprise an electrode plate made of a liquid-permeable porous insulating material. This enables the liquid to pass through the electrode plate without providing the electrode plate with a through-hole or the like by troublesome processing.

The fluid may be pure water, ultrapure water, a fluid having an electric conductivity of not more than 500 μS/cm, or an electrolytic solution. Pure water may be water having an electric conductivity (referring herein to that at 25° C., 1 atm) of not more than 10 μS/cm. Ultrapure warer is herein meant water having an electric conductivity of not more than 0.1 μS/cm (resistivity of not less than 10 MΩ·cm). The use of pure water in electrolytic processing enables a clean processing without leaving impurities on the processed surface of a workpiece, whereby a cleaning step after the electrolytic processing can be simplified. Specifically, one or two-stages of cleaning may suffice after the electrolytic processing.

The present invention also provides an electrolytic processing method, comprising: opposing a workpiece to an electrode section including a plurality of processing electrodes and feeding electrodes both having a diameter of not more than 1 mm, said processing electrodes being electrically isolated from said feeding electrodes; supplying a liquid between the electrode section and the workpiece; and moving the electrode section and the workpiece relative to each other in such a manner that a plurality of said processing electrodes pass every point in a processing surface of the workpiece held by the substrate holder, while applying a voltage between the processing electrodes and the feeding electrodes.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A through 1C are diagrams illustrating, in sequence of process steps, an example of the production of a substrate with copper interconnects;

FIG. 2 is a diagram illustrating the principle of electrolytic processing according to the present invention as carried out by allowing a processing electrode and a feeding electrode to be close to a substrate (workpiece), and supplying pure water or a fluid having an electric conductivity of not more than 500 μS/cm between the processing electrode, the feeding electrode and the substrate (workpiece);

FIG. 3 is a diagram illustrating the principle of electrolytic processing according to the present invention as carried out by mounting the ion exchanger only on the processing electrode and supplying the fluid between the processing electrode and the substrate (workpiece);

FIG. 4 is a plan view illustrating the construction of a substrate processing apparatus incorporated an electrolytic processing apparatus according to an embodiment of the present invention.

FIG. 5 is a vertical sectional view showing the electrolytic processing apparatus of the substrate processing apparatus shown in FIG. 4;

FIG. 6 is a plan view of the electrolytic processing apparatus of FIG. 5;

FIG. 7 is a plan view of the electrode section of the electrolytic processing apparatus of FIG. 5;

FIG. 8 is an enlarged view of a portion of the electrode section shown in FIG. 7;

FIG. 9A is a graph showing the relationship between electric current and time, as observed in electrolytic processing of the surface of a substrate having a two-layer film of two different materials formed in the surface, and FIG. 9B is a graph showing the relationship between voltage and time, as observed in electrolytic processing of the surface of a substrate having a two-layer film of two different materials formed in the surface;

FIG. 10 is a view corresponding to FIG. 8, showing a variation of the electrode section; and

FIG. 11 is a diagram showing an ion exchanger and its circulation system in an electrolytic processing apparatus according to another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described with reference to the drawings. Though the below-described embodiments refer to application to electrolytic processing apparatuses that use a substrate as a workpiece to be processed and process the substrate, the present invention is, of course, applicable to workpiece other than substrates.

FIG. 4 is a plan view illustrating the construction of a substrate processing apparatus incorporated an electrolytic processing apparatus according to an embodiment of the present invention. As shown in FIG. 4, the substrate processing apparatus comprises a pair of loading/unloading section 30 as a carry-in/carry-out section for carrying in and out a substrate, e.g. a substrate W as shown in FIG. 1B, a first cleaning machine 31a for performing a primary cleaning of the substrate, a second cleaning machine 31b for performing a secondary cleaning (finish cleaning) of the substrate, a reversing machine 32 for reversing the substrate, and an electrolytic processing apparatus 34. These devices are disposed in series. A transport robot 36 as a transport device, which can move parallel to these devices for transporting and transferring the substrate W therebetween, is provided. The substrate processing apparatus is also provided with a monitor section 38, disposed adjacent to the loading/unloading units 30, for monitoring a voltage applied between the bellow-described processing electrodes 76 and the feeding electrodes 78 upon electrolytic processing in the electrolytic processing apparatus 34, or an electric current flowing therebetween.

FIG. 5 is a vertical sectional view showing the electrolytic processing apparatus 34 in the substrate processing apparatus, and FIG. 6 is a plan view of the apparatus of FIG. 5. As shown in FIG. 5, the electrolytic processing apparatus 34 includes a arm 40 that can move vertically and pivot horizontally, a substrate holder 42, supported at the free end of the arm 40, for attracting and holding the substrate W with its front surface facing downward (face-down), a disc-shaped electrode section 44 disposed below the substrate holder 42, and a power source 46 to be connected to the electrode section 44.

The arm 40 is mounted to the upper end of a pivot shaft 50 which is coupled to a pivoting motor 48, so that the arm 40 pivots horizontally by the actuation of the pivoting motor 48. The pivot shaft 50 is coupled to a vertically-extending ball screw 52 and moves vertically together with the arm 40 by the actuation of a vertical movement motor 54 which is coupled to the ball screw 52.

The substrate holder 42 is coupled to a rotating motor 56 and rotates (about its axis) by the actuation of the rotating motor 56. The arm 40 is movable vertically and pivotable horizontally, as described above, and the substrate holder 42 can move vertically and pivot horizontally together with the arm 40.

The electrode section 44 is mounted on the upper surface of a tabular base 60 which is coupled to a hollow motor 62. Thus, by the actuation of the hollow motor 62, the electrode section 44 rotates together with the base 60. The electrode section 44 rotates about the axis of rotation O₁, while the substrate holder 42 rotates about the axis of rotation O₂. There is provided a distance d between the axis of rotation O₁of the electrode section 44 and the axis of rotation O₂of the substrate holder 42.

A supply shaft 64 on which an ion exchanger 68 is wound and a take-up shaft 66 for taking up the ion exchanger 68 are disposed rotatably at the both ends of the base 60 and on opposite sides of the electrode section 44, and the ion exchanger 68, which has a long length, extends between the supply shaft 64 and the take-up shaft 66. The take-up shaft 66 is coupled to a take-up motor 70. By rotating the take-up shaft 66 by the take-up motor 70, the ion exchanger 68 wound on the supply shaft 66 is taken up sequentially, whereby a change of the ion exchanger 68 is carried out automatically. This enables a speedy change of the ion exchanger 68, thus shortening the downtime of the apparatus for a change of the ion exchanger 68 and increasing the throughput.

The ion exchanger 68 may be composed of a nonwoven fabric that has an anion-exchange group or a cation-exchange group. A cation exchanger preferably carries a strongly acidic cation-exchange group (sulfonic acid group); however, a cation exchanger carrying a weakly acidic cation-exchange group (carboxyl group) may also be used. Though an anion exchanger preferably carries a strongly basic anion-exchange group (quaternary ammonium group), an anion exchanger carrying a weakly basic anion-exchange group (tertiary or lower amino group) may also be used.

The nonwoven fabric carrying a strongly basic anion-exchange group can be prepared by, for example, the following method: A polyolefin nonwoven fabric having a fiber diameter of 20-50 μm and a porosity of about 90% is subjected to the so-called radiation graft polymerization, comprising γ-ray irradiation onto the nonwoven fabric and the subsequent graft polymerization, thereby introducing graft chains; and the graft chains thus introduced are then aminated to introduce quaternary ammonium groups thereinto. The capacity of the ion-exchange groups introduced can be determined by the amount of the graft chains introduced. The graft polymerization may be conducted by the use of a monomer such as acrylic acid, styrene, glicidyl methacrylate, sodium styrenesulfonate or chloromethylstyrene, or the like. The amount of the graft chains can be controlled by adjusting the monomer concentration, the reaction temperature and the reaction time. Thus, the degree of grafting, i.e. the ratio of the weight of the nonwoven fabric after graft polymerization to the weight of the nonwoven fabric before graft polymerization, can be made 500% at its maximum. Consequently, the capacity of the ion-exchange groups introduced after graft polymerization can be made 5 meq/g at its maximum.

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 μm and a porosity of about 90% is subjected to the so-called radiation graft polymerization comprising γ-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 the ion exchanger 68 may be a polyolefin such as polyethylene or polypropylene, or any other organic polymer. Further, besides the form of a nonwoven fabric, the ion exchanger may be in the form of a woven fabric, a sheet, a porous material, or short fibers, etc.

When polyethylene or polypropylene is used as the base material, graft polymerization can be effected by first irradiating radioactive rays (γ-rays and 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. When an organic polymer other than polyolefin is used as the base material, on the other hand, radical polymerization can be effected by impregnating the base material with a monomer and irradiating radioactive rays (γ-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.

By using a nonwoven fabric having an anion-exchange group or a cation-exchange group as the ion exchanger 68, it becomes possible that pure water or ultrapure water, or a liquid such as an electrolytic solution can freely move within the nonwoven fabric and easily arrive at the active points in the nonwoven fabric having a catalytic activity for water dissociation, so that many water molecules are dissociated into hydrogen ions and hydroxide ions. Further, by the movement of pure water or ultrapure water, or a liquid such as an electrolytic solution, the hydroxide ions produced by the water dissociation can be efficiently carried to the surfaces of the processing electrodes 76 (see FIG. 8), whereby a high electric current can be obtained even with a low voltage applied.

When the ion exchanger 68 has only one of anion-exchange groups and cation-exchange groups, a limitation is imposed on electrolytically processible materials and, in addition, impurities are likely to form due to the polarity. In order to solve this problem, the anion exchanger and the cation exchanger may be superimposed, or the ion exchanger 68 itself may carry both an anion-exchange group and a cation-exchange group, whereby the range of materials to be processed can be broadened and the formation of impurities can be restrained.

Further, a pure water nozzle 72 as a pure water supply section, extending entirely in the crosswise direction of the ion exchanger 68, is disposed at the upstream of the ion exchanger 68 which has a long length. The pure water nozzle (pure water supply section) 72 has a plurality of supply ports for supplying pure water, preferably ultrapure water, to the upper surface of the electrode section 44. Pure water herein refers to water having an electric conductivity of not more than 10 μS/cm, and ultrapure water refers to water having an electric conductivity of not more than 0.1 μS/cm. The use of pure water or ultrapure water containing no electrolyte upon electrolytic processing can prevent impurities such as an electrolyte from adhering to and remaining on the surface of the substrate W. Further, copper ions or the like dissolved during electrolytic processing are immediately caught by the ion exchanger 68 through the ion-exchange reaction. This prevents 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.

It is possible to use, instead of pure water or ultrapure water, a liquid having an electric conductivity of not more than 500 μS/cm, for example, an electrolytic solution obtained by adding an electrolyte to pure water or ultrapure water. The use of such an electrolytic solution can further lower the electric resistance and reduce the power consumption. A solution of a neutral salt such as NaCl or Na₂SO₄, a solution of an acid such as HCl or H₂SO₄, or a solution of an alkali such as ammonia, may be used as the electrolytic solution, and these solutions may be selectively used according to the properties of the workpiece.

Further, it is also possible to use, instead of pure water or ultrapure water, 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 μS/cm, preferably not more than 50 μS/cm, more preferably not more than 0.1 μS/cm (resistivity of not less than 10 MΩ·cm). Due to the presence of a surfactant in pure water or ultrapure water, the liquid can form a layer, which functions to inhibit ion migration evenly, at the interface between the substrate W and the ion exchanger 68, thereby moderating concentration of ion exchange (metal dissolution) to enhance the flatness of the processed surface. The surfactant concentration is desirably not more than 100 ppm. Whenthevalue of the electric conductivity is too high, the current efficiency is lowered and the processing rate is decreased. The use of the liquid having an electric conductivity of not more than 500 μS/cm, preferably not more than 50 μS/cm, more preferably not more than 0.1 μS/cm, can attain a desired processing rate.

FIG. 7 is a plan view of the electrode section 44, and FIG. 8 is an enlarged view of a portion of the electrode section 44 shown in FIG. 7. As shown in FIGS. 7 and 8, the electrode section 44 includes a disc-shaped electrode plate 74 made of an insulating material, and a large number of processing electrodes 76 having a diameter d₁of not more than 1 mm and a large number of feeding electrodes 78 having a diameter d₂of not more than 1 mm, which electrodes 76 and 78 are embedded in the electrode plate 74 and arranged alternately and uniformly distributed over the entire surface of the electrode plate 74. The processing electrodes 76 are electrically isolated from the feeding electrodes 78 by the electrode plate 74 made of an insulating material. The upper surfaces of the processing electrodes 76 and the feeding electrodes 78 are integrally covered with the above-described ion exchanger 68. The processing electrodes 76 and the feeding electrodes 78 are of the same shape, and are arranged in almost the entire surface of the electrode plate 74 such that when the substrate W and the electrode section 44 are moved relative to each other, the presence frequencies of the electrodes at every points in the processing surface of the substrate W become substantially equal.

According to this embodiment, the processing electrodes 76 are connected via a slip ring 80 (see FIG. 5) to the cathode of the power source 46, and the feeding electrodes 78 are connected via the slip ring 80 to the anode of the power source 46. In processing of copper, for example, the electrolytic processing action occurs on the cathode side. Accordingly, the electrodes connected to the cathode become processing electrodes and the electrodes connected to the anode become feeding electrodes. Depending upon the material to be processed, the feeding electrodes may be connected to the cathode of the power source, while the processing electrodes may be connected to the anode of the power source. In particular, when the material to be processed is, for example, aluminum or silicon, the electrolytic processing action occurs on the anode side. Accordingly, the electrodes connected to the anode of the power source become processing electrodes, while the electrodes connected to the cathode become feeding electrodes.

With respect to the processing electrodes 76 and the feeding electrodes 78, oxidation or dissolution thereof due to an electrolytic reaction is generally a problem. In view of this, it is preferred to use, as a base material for the electrodes, carbon, a noble metal which is relatively inactive, a conductive oxide or a conductive ceramic, rather than a metal or metal compound widely used for electrodes. A noble metal-based electrode may, for example, be one obtained by plating or coating platinum or iridium on a titanium electrode, and then sintering the coated electrode at a high temperature to stabilize and strengthen the electrode. Ceramic products are generally obtained by heat-treating inorganic raw materials, and ceramic products having various properties are produced from various raw materials including oxides, carbides and nitrides of metals and nonmetals. Among them are ceramics having an electric conductivity. When an electrode is oxidized, the electric resistance of the electrode increases to cause an increase of applied voltage. However, by protecting the surface of an electrode with a material hard to oxidize, such as platinum, or with a conductive oxide, such as iridium oxide, the decrease in electric conductivity due to oxidation of the base material of the electrode can be prevented.

Next, substrate processing (electrolytic processing) by using the electrolytic processing apparatus 34 of this embodiment will be described. First, a substrate, e.g. a substrate W as shown in FIG. 1B which has in its surface a copper film 6 as a conductive film (processing object), is taken by the transport robot 36 out of the cassette housing substrates and set in the loading/unloading unit 30. If necessary, the substrate W is transported to the reversing machine 32 by the transport robot 36 to reverse the substrate W so that the front surface of the substrate W having the conductive film (copper film 6) faces downward.

The transport robot 36 receives the reversed substrate W and transports it to the electrolytic processing apparatus 34, and the substrate W is attracted and held by the substrate holder 42. The arm 40 is moved to move the substrate holder 42 holding the substrate W to a processing position right above the electrode section 44. Next, the vertical movement motor 54 is driven to lower the substrate holder 42 so as to bring the substrate W held by the substrate holder 42 close to or into contact with the surface of the ion exchanger 68, which covers the upper surface of the electrode section 44. Thereafter, the hollow motor 62 is driven to rotate the electrode section 44, and the rotating motor 56 is driven to rotate the substrate holder 42 and the substrate W, so that the substrate W and the electrode section 44 make a relative movement. Pure water, preferably ultrapure water, at the same time, is supplied from the supply ports of the pure water nozzle 72 to between the substrate W and the electrode section 44. Then, a predetermined voltage is applied between the processing electrodes 76 and the feeding electrodes via the power source 46, whereby electrolytic processing of the conductive film (copper film 6) facing the processing electrodes (cathode) 76 is effected with hydrogen ions and hydroxide ions produced by the ion exchanger 68.

According to this embodiment, the electrode section 44 is provided with the plurality of processing electrodes 76 having a diameter of not more than 1 mm and the plurality of feeding electrodes 78 having a diameter of not more than 1 mm, the processing electrodes 76 being electrically isolated from the feeding electrodes 78 and the electrodes 76, 78 being distributed uniformly, and the electrode section 44 and the substrate W are moved relative to each other during processing. This makes it possible to equalize the electric field distributions in the vicinities of the processing electrodes 76, the feeding electrodes 78 and the substrate W as well as the electric field distribution between the processing electrodes 76 and the feeding electrodes 78, thereby suppressing the growth of a gas, which is generated at the surfaces of the processing electrodes 76, the feeding electrodes 78 and the substrate W, into bubbles.

Further, by providing the large number of processing electrodes 76 and allowing a plurality of processing electrodes 76 to pass every point in the processing surface of the substrate W, held by the substrate holder 42, during electrolytic processing, a possible variation in the processing rates between the processing electrodes 76 can be equated, enabling a nm/min order equalization of the processing rates in the entire surface of the substrate W.

It is preferred that the processing electrodes 76 and the feeding electrodes 78 be embedded in the electrode plate 74 with the same height so that the level of their surfaces (upper surfaces) is the same as or different by a certain distance from the surface of the electrode plate 74. This avoids a variation in the distances between the substrate and the surfaces of the electrodes. Such a variation would vary the resistances between the substrate and the surfaces of the electrodes, leading to a variation in the electric current.

The distance between each processing electrode 76 and each feeding electrode 78, adjacent to each other, is set at least equal to, preferably at least 4.5 times, more preferably at least 9 times the distance between the substrate W and the processing electrodes 76 or the feeding electrodes 78. This allows electricity to pass preferentially between the substrate W and each processing electrode 76 or each feeding electrode 78 rather than between each electrode 76 and each feeding electrode 78, thereby preventing an electric current from flowing between each processing electrode 76 and each feeding electrode 78, adjacent to each other, without passing through the substrate W.

It is possible to group one processing electrode 76 and one feeding electrode 78, or a plurality of processing electrodes 76 and a plurality of feeding electrodes 78, and control the voltage or electric current applied independently for each group.

During the electrolytic processing, the voltage applied between the processing electrodes 76 and the feeding electrodes 78 or the electric current flowing therebetween is monitored with the monitor section 38 to detect the end point of processing. It is noted in this connection that in electrolytic processing, the electric current (applied voltage) may vary depending upon the material to be processed even with the same voltage (electric current). For example, as shown in FIG. 9A, when an electric current is monitored in electrolytic processing of the surface of a substrate W on which a film of material B and a film of material A are laminated in this order, a constant electric current is observed during the processing of material A, but it changes upon the shift to the processing of the different material B. Likewise, as shown in FIG. 9B, though a constant voltage is applied between a processing electrode and a feeding electrode during the processing of material A, the voltage applied changes upon the shift to the processing of the different material B. FIG. 9A illustrates a case in which the electric current is harder to flow in electrolytic processing of material B compared to electrolytic processing of material A, and FIG. 9B illustrates a case in which the voltage becomes higher in electrolytic processing of material B compared to electrolytic processing of material A. As will be appreciated from the above-described example, the monitoring of a change in electric current or voltage can surely detect the end point.

Though in this embodiment the voltage applied between the processing electrodes 76 and the feeding electrodes 78, or the electric current flowing therebetween is monitored with the monitor section 38 to detect the end point of processing, it is also possible to monitor with the monitor section 38 a change in the state of a substrate being processed to detect an arbitrarily set end point of processing. In this case, the end point of processing refers to a point at which a desired processing amount is reached for a specified region in the processing surface of the substrate, or a point at which a parameter correlated with processing amount has reached a value corresponding to a desired processing amount for a specified region in the processing surface. By thus arbitrarily setting and detecting the end point of processing even in the course of processing, it becomes possible to carry out a multi-step electrolytic processing.

For example, the processing amount may be determined by detecting a change in frictional force due to a difference in friction coefficient produced when a different material is reached in a substrate, or a change in frictional force produced by removal of irregularities in the surface of the substrate. The endpoint of processing maybe detected based on the processing amount thus determined. During electrolytic processing, heat is generated by the electric resistance of the processing surface of a substrate, or by collision between water molecules and ions moving in the liquid (pure water) between the processing surface of the substrate and the surface of the electrode section. In processing e.g. a copper film deposited on the surface of a substrate under a controlled constant voltage, when a barrier layer or an insulating film becomes exposed with the progress of electrolytic processing, the electric resistance increases and the current value decreases, and the heat value decreases. Accordingly, the processing amount maybe determined by detecting the change in the heat value. The end point of processing may therefore be detected. Alternatively, the film thickness of a to-be-processed film on a substrate may be determined by detecting a change in the intensity of reflected light due to a difference in reflectance produced when a different material is reached in the substrate. The end point of processing may be detected based on the film thickness thus determined. The film thickness of a to-be-processed film on a substrate may also be determined by generating an eddy current within a to-be-processed conductive film, for example a copper film, and monitoring the eddy current flowing within the substrate to detect a change in e.g. the frequency or the impedance of a sensor monitoring the eddy current, thereby detecting the end point of processing. Further, in electrolytic processing, the processing rate depends on the value of the electric current flowing between the processing electrode and the feeding electrode, and the processing amount is proportional to the quantity of electricity, determined by the product of the current value and the processing time. Accordingly, the processing amount may be determined by integrating the quantity of electricity, and detecting the integrated value reaching a predetermined value. The end point of processing may thus be detected.

After completion of the electrolytic processing, the power source 46 is disconnected from the processing electrodes 76 and the feeding electrodes 78, and the rotations of the electrode section 44 and the substrate holder 42 are stopped. Thereafter, the substrate holder 42 is raised and the arm 40 is moved to transfer the substrate W to the transport robot 36. The transport robot 36 transports the substrate W to the reversing machine 32, according to necessity, where the substrate W is reversed. The transport robot 36 then transports the substrate W to the first cleaning machine 31a, where a primary cleaning of the substrate e.g. with a sponge roll or rinsing (primary cleaning) with pure water or a chemical liquid is carried out. The substrate W after the primary cleaning is then transported to the second cleaning machine 31b with the transport robot 36, where a secondary cleaning (finish cleaning) of the substrate e.g. with pure water is carried out. The substrate is then rotated at a high speed for spin-drying. Thereafter, the substrate W is returned to the cassette of the loading/unloading section 30.

When electrolytic processing is continued and the ion exchange capacity of an ion exchanger 68 reaches its limit, a need arises to change the ion exchangers. According to the electrolytic processing apparatus of this embodiment, a change of the ion exchanger 68 can be carried out automatically by driving the take-up motor 70, enabling a speedy change of the ion exchanger 68. Accordingly, the downtime of the apparatus for a change of the ion exchanger 68 can be shortened, leading to an increased throughput. The change of the ion exchanger 68 is preferably carried out after completion of electrolytic processing, or during the internal between one processing and the next processing.

When using a liquid, like ultrapure water, which itself has a large resistivity, the electric resistance can be lowered by bringing the ion exchanger 68 into contact with the substrate W. This enables a low-voltage application and a reduction in the power consumption. The term “contact” herein does not imply “press” for giving a physical energy (stress) to a workpiece as in CMP. Thus, while the electrolytic processing apparatus of this embodiment is provided with the vertical movement motor 54 to bring the substrate W close to or into contact with the electrode section 44, it is not provided with a press mechanism, as employed in a CMP apparatus, for pressing the substrate against the polishing member. It is noted in this connection that in CMP a substrate is pressed against a polishing surface generally at a pressure of about 20 to 50 kPa. According to the electrolytic processing apparatus of this embodiment, on the other hand, the ion exchanger 68 may be in contact with the substrate W at a pressure of, for example, not more than 20 kPa. A sufficient removal processing effect could be produced even at a pressure of not more than 10 kPa.

Though in this embodiment the electrode section 44 and the substrate W are both rotated such that they make an eccentric rotational movement, any relative movement may be employed insofar as it allows a plurality of processing electrodes to pass every point in the processing surface of a workpiece. Such a relative movement may include a rotational movement, a reciprocating movement, an eccentric rotational movement, a scroll movement, and any combination of these movements.

According to this embodiment, the electrodes (processing electrodes) 76 positioned in every other longitudinal line are connected via the slip ring 80 (see FIG. 5) to the cathode of the power source 46, and the electrodes (feeding electrodes) 78 positioned in the other longitudinal lines are connected via the slip ring 80 to the anode of the power source 46. The processing electrodes 76 and the feeding electrodes 78 are thus arranged alternately so that when the electrode section 44 and the substrate W are moved relative to each other, the presence frequencies of processing electrodes 76 and feeding electrodes 78 at every points in the processing surface of the substrate W become substantially equal. In particular, according to this embodiment, the processing electrodes 76 and the feeding electrodes 78 are arranged such that when any adjacent three electrodes are connected by lines, an equilateral triangle is formed and the respective electrodes are situated at the apexes of the equilateral triangle. Accordingly, the distances between adjacent processing electrode 76 and feeding electrode 78, the distances between adjacent processing electrodes 76 and the distances between adjacent feeding electrodes 78 are all equal.

According to this embodiment, the number of the processing electrodes 76 is made substantially the same as the number of the feeding electrodes 78. Depending upon the processing conditions, however, the respective numbers of the processing electrodes 76 and of the feeding electrodes 78 may arbitrarily be changed. For example, the number of processing electrodes may be increased in order to increase the processing rate. Further according to this embodiment, the entire surface of the electrode plate 74 is covered with the ion exchanger 68 so that electrolytic processing can be carried out with the use of ultrapure water. When using an electrolytic solution, however, it is possible to cover the entire surface of the electrode plate with a scrubbing member (liquid-permeable one such as a porous material).

Further, it is possible to arrange the processing electrodes 76 and the feeding electrodes 78 in lines in a lattice pattern, as shown in FIG. 10, with the processing electrodes 76 arranged in every other longitudinal line and the feeding electrodes 78 arranged in the other longitudinal lines, so that the distances between adjacent processing electrode 76 and feeding electrode 78, the distances between adjacent processing electrodes 76 and the distances between adjacent feeding electrodes 78 are all equal.

FIG. 11 shows an ion exchanger and its circulation system in an electrolytic processing apparatus according to another embodiment of the present invention. An ion exchanger 68 of an endless form is employed in this embodiment. The ion exchanger 68 runs around a pair of reels 91, 92, which are spaced apart by a predetermined spacing, and runs between a pair of opposing rollers 97c, 97d and between a pair of opposing rollers 97a, 97b, which rollers are disposed below the reels 91, 92. The ion exchanger 68 circulates in this manner between the reels and rollers. A regeneration section 100 for regenerating the ion exchanger 68 is disposed between the pair of rollers 97a, 97b and the pair of rollers 97c, 97d. When carrying out electrolytic processing of copper by using as the ion exchanger 68 a cation exchanger having cation-exchange groups, a considerable proportion of the ion-exchange groups of the ion exchanger (cation exchanger) 68 is occupied by copper after the processing, leading to lowering of the processing efficiency of the next processing. When carrying out electrolytic processing of copper by using as the ion exchanger 68 an anion exchanger having anion-exchange groups, on the other hand, fine particles of copper oxide are generated and the particles adhere to the surface of the ion exchanger (anion exchanger) 68. Such particles on the ion exchanger 68 can contaminate the surface of the next substrate to be processed. The regeneration section 100 is provided to regenerate such a consumed or contaminated ion exchanger 68, thereby removing the above drawbacks.

The regeneration section 100 includes a regeneration electrode holder 102 having a downwardly-open depressed portion 102a, a regeneration electrode 104 disposed in the depressed portion 102a, a partition 106 closing the bottom opening of the depressed portion 102a, and a regeneration electrode plate 112 disposed below the partition 106. A counter electrode 108 is embedded in the upper surface of the regeneration electrode plate 112. The ion exchanger 68 to be regenerated is disposed between the partition 106 and the counter electrode 108. A discharge portion 110, defined by the depressed portion 102a and the partition 106, is formed in the regeneration electrode holder 102. Further, a liquid inlet 102b and a liquid outlet 102c, both communicating with the discharge portion 110, are formed in the regeneration electrode holder 102. A liquid is supplied from the liquid inlet 102b into the discharge portion 110. The liquid supplied fills the discharge portion 110, so that the regeneration electrode 104 is immersed in the liquid, while the liquid flows in one direction in the discharge portion 110 and is discharged sequentially from the liquid outlet 102c.

Further, positioned almost in the center of the regeneration electrode plate 112, there is provided a through-hole 112a vertically penetrating the electrode plate 112. A pure water supply pipe 114 for supplying pure water or ultrapure water is connected to the lower end of the through-hole 112a. Accordingly, pure water or ultrapure water, supplied from the pure water supply pipe 114, passes through the through-hole 112a and reaches the upper surface side of the regeneration electrode plate 112. By thus supplying pure water or ultrapure water between the regeneration electrode plate 112 and the ion exchanger 68 during regeneration of the ion exchanger 68, a gas and a heat generated by regeneration of the ion exchanger 68 can be removed.

It is desired that the partition 106 do not hinder the migration therethrough of impurity ions removed from the ion exchanger 68 and inhibit permeation therethrough of the liquid (including ions in the liquid) flowing between the partition 106 and the regeneration electrode 104 in the discharge portion 110 into the ion exchanger 68 side. In this regard, ion exchangers permit selective permeation therethrough either cations or anions. Further, a film-type ion exchanger as a partition can prevent intrusion of the liquid flowing between the partition 106 and the regeneration electrode 104 into the ion exchanger 68 side. Thus, a suitably selected film-type ion exchanger can meet the above requirements for the partition 106.

According to this embodiment, the ion exchanger used as the partition 106 has the same type of ion-exchange group as the ion exchanger 68 to be regenerated. That is, when a cation exchanger having a cation-exchange group is used as the ion exchanger 68, a cation exchanger is used also as the partition (ion exchanger) 106. When an anion exchanger having an anion-exchange group is used as the ion exchanger 68, an anion exchanger is used also as the partition (ion exchanger) 106.

It is desired that the liquid to be supplied into the discharge portion 110 be a liquid, such as an electrolytic solution, which has a high electric conductivity and does not form a hardly soluble or insoluble compound through a reaction with ions removed from the ion exchanger to be processed. Thus, the liquid is for discharging those ions, which have moved from the ion exchanger 68 and passed through the partition 106, out of the system by the flow of the liquid. The above liquid having a high conductivity, because of its low electric resistance, can reduce the power consumption in the regeneration section 100. Further the above liquid, which does not form an insoluble compound (by-product) through a reaction with the impurity ions, can prevent adhesion of a solid matter to the partition 106. A suitable liquid may be chosen depending upon the kind of the impurity ion to be discharged. For example, when regenerating the ion exchanger 68 that was used in electrolytic polishing of copper, sulfuric acid with a concentration of 1 wt % or higher may be used.

The regeneration electrode 104 is to be connected to one of the electrodes (e.g. cathode) of the power source, while the counter electrode 108 is to be connected to the other electrode (e.g. anode) of the power source. Such control is made that, for example, when a cation exchanger is used as the ion exchanger 68, the regeneration electrode 104 should become a cathode, and when an anion exchanger is used as the exchanger 68, the regeneration electrode 104 should become an anode.

One of the electrodes (e.g. cathode) of the power source is connected to the regeneration electrode 104 and the other electrode (e.g. anode) is connected to the counter electrode 108, thereby applying a voltage between the regeneration electrode 104 and the counter electrode 108. At this time, a liquid is supplied into the discharge portion 110 provided inside the regeneration electrode holder 102 so as to fill the discharge portion 110 with the liquid, thereby immersing the regeneration electrode 104 in the liquid and allowing the liquid to flow in one direction in the discharge portion 110 and to be discharged from the liquid outlet 102c. Pure water or ultrapure water, at the same time, is supplied between the upper surface of the regeneration electrode plate 112 and the ion exchanger 68.

Upon the electrical connection, such control is made that the regeneration electrode 104 should have the opposite polarity to the polarity of the ion exchanger 68 (and of the partition 106). Thus, when a cation exchanger is used as the ion exchanger 68 (and as the partition 106), the regeneration electrode 104 should become a cathode and the counter electrode 108 should become an anode. Conversely, when an anion exchanger is used as the ion exchanger 68 (and as the partition 106), the regeneration electrode 104 should become an anode and the counter electrode 108 should become a cathode. By the above operation, ions in the ion exchanger 68 are moved toward the regeneration electrode 104, passed through the partition 106, and introduced into the discharge portion 110. The ions thus moved into the discharge portion 110 are discharged out of the system by the flow of the liquid supplied into the discharge portion 110. Regeneration of the ion exchanger 68 is thus effected. By supplying pure water or ultrapure water between the regeneration electrode plate 112 and the ion exchanger 68, at the same time, a gas and a heat generated by regeneration of the ion exchanger 68 can be removed. When a cation exchanger is used as the ion exchanger 68, cations taken in the ion exchanger 68 pass through the partition 106 and move into the discharge portion 110; when an anion exchanger is used as the ion exchanger 68, anions taken in the ion exchanger 68 pass through the partition 106 and move into the discharge portion 110, whereby the ion exchanger 68 is regenerated.

In the above regeneration treatment, as descried above, an ion exchanger having the same type of ion-exchange group as the ion exchanger 68 is used as the partition 106. This prevents migration of impurity ions in the ion exchanger 68 through the partition (ion exchanger) 106 from being hindered by the partition 106, thereby preventing an increase in the power consumption. Further, this inhibits permeation through the partition 106 of the liquid (including ions in the liquid) flowing between the partition 106 and the regeneration electrode 104, thus inhibiting movement of the liquid to the ion exchanger 68 side and preventing re-contamination of the regenerated ion exchanger 68. Furthermore, preferably used as the liquid to be supplied between the partition 306 and the regeneration electrode 104 is a liquid which has an electric conductivity of not less than 50 μS/cm and does not form a hardly soluble or insoluble compound through a reaction with ions removed from the ion exchanger 68. Such a liquid, because of its low electric resistance, can reduce the power consumption in the regeneration section 100. Moreover the liquid does not form an insoluble compound (by-product) through a reaction with an impurity ion. In this regard, an insoluble compound, if formed, will adhere to the partition 106 whereby the electric resistance between the regeneration electrode 104 and the counter electrode 108 will be changed, making it difficult to control the electrolysis current. Such a problem can thus be prevented. Instead of using pure water or ultrapure water, it is possible to use a liquid having an electric conductivity of not more than 500 μS/cm or an electrolytic solution.

Thus, according to the embodiment of the electrolytic apparatus, the ion exchanger 68 that has been used in electrolytic processing is regenerated automatically, thereby lowering the running cost and, at the same, shortening the downtime.

In the preceding embodiment, the pure water nozzle 72 is disposed above the ion exchanger 68, and pure water, preferably ultrapure water, is supplied from the pure water nozzle 72 onto the upper surface of the electrode section 44. However, it is also possible to provide the electrode plate with a through-hole (fluid supply passage) vertically penetrating the electrode plate and insert a pure water pipe, extending from a pure water supply source and communicating with the through-hole, into the hollow motor so that pure water, preferably ultrapure water, is supplied to the upper surface of the electrode plate from below the electrode plate. In this case, the electrode plate may be made of a liquid-permeable porous insulating material. This eliminates the need to provide the electrode plate with a through-hole or the like.

As described hereinabove, the present invention makes it possible to equalize the electric field distributions in the vicinities of the electrodes (processing electrodes and feeding electrodes) and a workpiece as well as the electric field distribution between the processing electrodes and the feeding electrodes, thereby suppressing the growth of a gas, which is generated at the surfaces of the electrodes and the workpiece, into bubbles. This effectively prevents the formation of pits in the surface of the workpiece.

While the present invention has been described with reference to the preferred embodiments thereof, the present invention is not limited to such embodiments and changes and modifications could be made within the technical concept of the invention.

INDUSTRIAL APPLICABILITY

This invention is suitable for use in an electrolytic processing apparatus useful for processing a conductive material formed in the surface of a substrate, especially a semiconductor wafer, or for removing impurities adhering to the surface of a substrate.

Electrolytic processing apparatus and method

Information

Publication Number

Date Filed

Date Published

Inventors

CPC

US Classifications

International Classifications

Abstract

Description

Claims

Priority Claims (1)

PCT Information