Method of forming thin metal films on substrates

A solution containing a metal component of composite ultrafine metal particles each having a core substantially made of metal component and a covering layer made of an organic compound chemically bonded to the core having an average diameter ranging from 1 to 10 nm, uniformly dispersed in a solvent, forms a thin metal film on the surface of a transfer sheet, after which the transfer sheet, after which the transfer sheet is thermally decomposed to transfer the thin metal film to a substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solution containing a metal component, and a method of and an apparatus for forming a thin metal film, and more particularly to a solution containing a metal component for use in forming a conductive thin metal film on a semiconductor substrate of silicon or the like, and a method of and an apparatus for forming a thin metal film using such a solution, and a method of and an apparatus for forming a thin metal film in embedding a conductive metal such as copper (Cu) or the like in minute interconnection recesses defined in the surface of a substrate of silicon or the like thereby forming interconnections.

2. Description of the Related Art

Aluminum or aluminum alloys are generally used as metal materials for forming interconnection circuits on semiconductor substrates. One recent trend is to use copper as such a metal material for forming interconnection circuits. Since copper has an electric resistivity of 1.72 μΩcm which is about 40% lower than aluminum, it is more effective to prevent signal delays. In addition, because copper has much better electromigration resistance than presently available aluminum and can be embedded more easily into minute recesses by the dual damascene process than aluminum, it allows complex and minute multilayer interconnection structures to be manufactured relatively inexpensively.

Metal such as copper or the like can be embedded into interconnection grooves and via holes by the dual damascene process according to three methods, i.e., CVD, sputtering reflow, and plating. Of these methods, the plating method has a stronger tendency to be able to form highly conductive paths with a relatively easy and inexpensive process, because conductive material can be embedded more easily into minute recesses by the plating, making it customary to incorporate a design rule of 0.18 μm generation into semiconductor mass-production lines.

FIGS. 16A through 16Cshow a basic process for plating the surface of a semiconductor substrate with copper to produce a semiconductor device with copper interconnections. As shown inFIG. 16A, an insulating film2of SiO2is deposited on a conductive layer1aon a semiconductor base1with semiconductor elements formed thereon. A small recess5comprising a contact hole3and an interconnection groove4is formed in the insulating film2by lithography and etching. A diffusion barrier layer6made of TaN or the like and a base film7as a seed layer for supplying an electric current for electroplating are successively formed on the surface formed so far.

As shown inFIG. 16B, the entire surface of the substrate18is plated with copper according to electrolytic copper plating to fill the recess5with a copper layer8and deposit a copper layer8on the base film7. Thereafter, the surface formed so far is polished by chemical mechanical polishing (CMP) to remove the base film7, the copper layer8thereon, and the diffusion barrier layer6, and planarize the copper layer8filled in the contact hole3and the interconnection groove4flush with the insulating film2. In this manner, an embedded interconnection made of the copper layer8is formed as shown inFIG. 16C.

The base film7(seed layer) is formed prior to the electrolytic copper plating because its surface will serve as an electric cathode for supplying a sufficient current to reduce metal ions by reduction in the electrolytic solution and to precipitate them as a metal solid. The surface of the substrate may be plated with copper according to electroless copper plating. According to the electroless copper plating, it is the widespread practice to employ a catalytic layer as the base film7instead of the seed layer.

Other general known method of forming a conductive thin metal film on a ceramic substrate comprises the steps of coating (printing) a metal paste such as an Ag—Pd-based paste, a silver-based paste, or the like on the surface of the substrate, and then baking the coated metal paste. The metal paste is generally in the form of a solution that comprises a metal powder of silver, copper, or the like and a resin or glass component which are dispersed in an organic solvent. The resin or glass component enables the paste to be formed as a film, and the particles of the metal powder are held in point-to-point contact to make the thin metal film electrically conductive.

To meet demands in recent years for higher-speed and finer-circuit semiconductor devices, there is a need for growing films of materials that are poorly evaporated by CVD, and a pattern is produced which is too small to be embedded by sputtering. While the plating technology is inexpensive and technically highly complete, the electrolytic plating process allows films to be grown on only conductive materials, and the electroless plating process is open to environmental pollution as materials contained in the plating solution adversely affect the natural environment and the working and labor environment. For these reasons, there has been a strong demand for a new film growing technique in place of the conventional film growing technique.

If a thin metal film is formed of a conventional metal paste as interconnections on a ceramic substrate, then the conductivity is limited to a certain level because the thin metal film is rendered conductive by point-to-point contact between metal particles. To increase the conductivity, the thickness of the thin metal film needs to be increased to provide more sites of-point-to-point contact between metal particles. The thicker metal film is more expensive to manufacture.

There has been developed a dispersion liquid comprising ultrafine metal particles dispersed in an organic solvent. However, available processes of producing ultrafine metal particles are of low productivity. One example of such processes is a gas evaporation process in which is metal is evaporated under vacuum in the presence of a small amount of gas to aggregate ultrafine particles made of only the metal from the gas phase. The processes of producing ultrafine metal particles also disadvantageous in that it is difficult to keep the ultrafine particles in safe storage because once the solvent is evaporated, the particles stick to each other and cannot be reused.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a solution containing a metal component for use in inexpensively and easily forming a conductive thin metal film which has a sufficient conductivity and whose thickness can easily be adjusted, and a method of and an apparatus for forming a thin metal film using such a solution.

Another object of the present invention to provide a method of and an apparatus for stably forming a thin metal film of good quality on a surface of a base to embed a conductor reliably in fine interconnection recesses that are defined in a surface of a substrate, for example.

According to an aspect of the present invention, there is provided a solution containing a metal component, comprising composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core; wherein the core has an average diameter ranging from 1 to 10 nm; and the composite ultrafine metal particles are uniformly dispersed in a solvent.

It is known in the art that the melting point of a metal particle is lower as the diameter of the metal particle is smaller. The effect starts to develop when the diameter of the metal is 50 nm or smaller, and becomes apparent particularly when the diameter of the metal is 20 nm or smaller, or more evident when the diameter of the metal is 10 nm or smaller. Therefore, cores substantially made of a metal component and having an average diameter ranging from 1 to 20 nm, preferably from 1 to 10 nm, are melted and joined together at a temperature considerably lower than the melting point of the metal component itself.

It is believed that the composite ultrafine metal particles are bonded such that the cores and the organic compound share metal molecules or make an ionic bond to form a complex-like structure, although no details of such a bonded structure are clearly given. Since the composite ultrafine metal particles can be produced according to a chemical process in a liquid phase, they can be mass-produced inexpensively in the ordinary atmosphere with a simple apparatus without the need for a large-scale vacuum system. Because the composite ultrafine metal particles are of a uniform particle diameter, all the composite ultrafine metal particles are fused together at a constant temperature. Since the cores are covered with the organic compound, the aggregation of the composite ultrafine metal particles is small, and hence the composite ultrafine metal particles can uniformly be distributed over a surface of a substrate. The composite ultrafine metal particles are also stable and can be handled with ease. Even after the solvent is evaporated, the composite ultrafine metal particles remain chemically stable until they are thermally decomposed. Therefore, the process control for the processing of the composite ultrafine metal particles is facilitated.

According to another aspect of the present invention, there is provided a solution containing a metal component, comprising composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core; wherein the core has an average diameter ranging from 1 to 50 nm; and the composite ultrafine metal particles are uniformly dispersed in a solvent.

According to still another aspect of the present invention, there is provided a solution containing a metal component, comprising: at least one of composite ultrafine metal particles and an organic metal compound; and a metal powder having an average particle diameter ranging from 1 to 10 μm; wherein each of the composite ultrafine metal particles has a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core; the core has an average diameter ranging from 1 to 10 nm; and the at least one of the composite ultrafine metal particles and the organic metal compound and the metal powder are uniformly dispersed in a solvent.

With this arrangement, the proportion of the metal component in the solution can be increased by the metal powder which is relatively inexpensive. Further, the metal powder serves as a skeleton and a conductor, and at least one of the composite ultrafine metal particles and the organic metal compound serves as a binder, preventing the solution from being lowered in conductivity.

According to yet another aspect of the present invention, there is provided a solution containing a metal component, comprising: at least one of composite ultrafine metal particles and an organic metal compound; and a metal powder having an average particle diameter ranging from 1 to 10 μm; wherein each of the composite ultrafine metal particles has a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core; the core has an average diameter ranging from 1 to 50 nm; and the at least one of the composite ultrafine metal particles and the organic metal compound and the metal powder are uniformly dispersed in a solvent.

According to yet still another aspect of the present invention, there is provided a method of forming a thin metal film, comprising: preparing a solution containing a metal component, comprising composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core, the core having an average diameter ranging from 1 to 10 nm, the composite ultrafine metal particles being uniformly dispersed in a solvent; bringing the solution into contact with a surface of a substrate; evaporating the solvent in the solution on the surface of the substrate to form an ultrafine particle coating layer on the surface of the substrate; and thermally decomposing the ultrafine particle coating layer into a thin metal film having a thickness ranging from 0.01 to 10 μm.

The above method is capable of forming a thin metal film uniformly over the surface of the substrate, which is composed of only cores (metal component) contained in the composite ultrafine metal particles and having a relatively small thickness.

In the above method, the metal component in the solution has a total amount ranging from 30 to 90 weight %. The thickness of the thin metal film can be adjusted by adjusting the total amount of the metal component in the solution.

According to a further aspect of the present invention, there is provided a method of forming a thin metal film, comprising: preparing a solution containing a metal component, comprising composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core, the core having an average diameter ranging from 1 to 50 nm, the composite ultrafine metal particles being uniformly dispersed in a solvent; bringing the solution into contact with a surface of a substrate; evaporating the solvent in the solution on the surface of the substrate to form an ultrafine particle coating layer on the surface of the substrate; and thermally decomposing the ultrafine particle coating layer into a thin metal film having a thickness ranging from 0.01 to 10 μm.

In the above method, the metal component in the solution has a total amount ranging from 30 to 90 weight %.

According to a still further aspect of the present invention, there is provided a method of forming a thin metal film, comprising: preparing a solution containing a metal component, comprising at least one of composite ultrafine metal particles and an organic metal compound, and a metal powder having an average particle diameter ranging from 1 to 10 μm; bringing the solution into contact with a surface of a substrate; evaporating the solvent in the solution on the surface of the substrate to form an ultrafine particle coating layer on the surface of the substrate; and thermally decomposing the ultrafine particle coating layer into a thin metal film having a thickness ranging from 10 to 1000 μm; wherein each of the composite ultrafine metal particles has a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core; the core has an average diameter ranging from 1 to 10 nm; and the at least one of the composite ultrafine metal particles and the organic metal compound and the metal powder are uniformly dispersed in a solvent.

With the above method, the thickness of the thin metal film can be increased by the metal powder. The ultrafine metal particles that are formed by reducing the cores (metal component) of the composite ultrafine metal particle or the organic metal compound are melted and joined by thermal decomposition. At this time, at least one of the ultrafine metal particles and the organic metal compound are closely bonded to the metal powder to achieve high conductivity.

In the above method, the metal component in the solution has a total amount ranging from 30 to 90 weight %.

According to a yet still further aspect of the present invention, there is provided a method of forming a thin metal film, comprising: preparing a solution containing a metal component, comprising at least one of composite ultrafine metal particles and an organic metal compound, and a metal powder having an average particle diameter ranging from 1 to 10 μm; bringing the solution into contact with a surface of a substrate; evaporating the solvent in the solution on the surface of the substrate to form an ultrafine particle coating layer on the surface of the substrate; and thermally decomposing the ultrafine particle coating layer into a thin metal film having a thickness ranging from 10 to 1000 μm; wherein each of the composite ultrafine metal particles has a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core; the core has an average diameter ranging from 1 to 50 nm; and the at least one of the composite ultrafine metal particles and the organic metal compound and the metal powder are uniformly dispersed in a solvent.

In the above method, the metal component in the solution has a total amount ranging from 30 to 90 weight %.

According to another aspect of the present invention, there is provided an apparatus for forming a thin metal film, comprising: a solution supply device for bringing a solution containing a metal component into contact with a surface of a substrate, the solution comprising composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core, the composite ultrafine metal particles being uniformly dispersed in a solvent; and a heating device for evaporating the solvent in the solution on the surface of the substrate to form an ultrafine particle coating layer on the surface of the substrate, and thermally decomposing the ultrafine particle coating layer into a thin metal film.

In the above apparatus, the metal component in the solution has a total amount ranging from 30 to 90 weight %.

The above apparatus further comprises a supplementary drying device for drying the solvent in the solution on the surface of the substrate. The supplementary drying device is effective to completely dry the organic solvent that cannot be dried out by a spin drying (air-drying) process such as a spin coating process, so that voids are prevented from being formed in the thin metal film.

According to still another aspect of the present invention, there is provided a method of forming a thin metal film, comprising: preparing an ultrafine particle dispersion liquid containing ultrafine particles at least partly made of metal, the ultrafine particles being dispersed into a solvent; ejecting the ultrafine particle dispersion liquid in a vacuum atmosphere from an ejection nozzle toward a surface of a substrate to evaporate the solvent in the solution to cause the ultrafine particles to collide with the surface of the substrate; and bonding the metal, of which at least a part of the ultrafine particles is made, on the surface of the substrate.

With the above method, a thin metal film composed of only the metal, of which at least a part of the ultrafine particles is made, can uniformly be formed on the surface of the substrate in intimate contact therewith.

In the above method, the metal is brought into collision with the surface of the substrate in a naked state, or ionized in a naked state and accelerated at a predetermined voltage to be brought into collision with the surface of the substrate. The ionized metal can easily and reliably be introduced to embed grooves or plugs having an aspect ratio of 5 or more.

In the above method, the ultrafine particles comprise composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core.

According to still another aspect of the present invention, there is provided an apparatus for forming a thin metal film, comprising: a processing chamber which can be evacuated; a substrate holder disposed in the processing chamber for holding a substrate; a heater housed in the substrate holder for heating the substrate held by the substrate holder; and an ultrafine particle ejector head having an ejection nozzle disposed in the processing chamber for ejecting an ultrafine particle dispersion liquid containing ultrafine particles at least partly made of metal toward a surface of the substrate held by the substrate holder, the ultrafine particles being dispersed into a solvent.

The above apparatus further comprises at least one of a device for bringing the metal, of which at least part of the ultrafine particles is made, of the ultrafine particle; dispersion liquid ejected from the ultrafine particle ejector head with the solvent being evaporated, into a naked state, and a device for ionizing the metal in the naked state.

In the above apparatus, the ultrafine particles comprise composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core.

According to yet another aspect of the present invention, there is provided a method of forming a thin metal film, comprising: placing a thin-film precursor on one surface of a film thereby to form a transfer sheet; transferring the transfer sheet onto a surface of a base; and thermally decomposing the transfer sheet and the film to form a thin metal film from the thin-film precursor on the surface of the base.

With the above method, a thin metal film can stably be formed on the surface of the base from the thin-film precursor according to a relatively simple process including the step of transferring the transfer sheet and the step of thermally decomposing the transfer sheet and the film.

In the above method, the base comprises a substrate having recesses defined in a surface thereof for embedding a conductor therein; the transfer sheet is transferred onto the surface of the substrate with the recesses filled up with a portion of the thin-film precursor; and after the thin metal film is formed, the surface of the substrate is polished to remove an excessive thin metal film therefrom.

With the above method, the metal contained in the thin-film precursor can reliably be embedded in the recesses, and the surface of the substrate is then polished to form interconnections of the metal.

In the above method, the thin-film precursor is composed of an ultrafine particle dispersion liquid comprising uniformly dispersed ultrafine particles having an average diameter ranging from 1 to 20 nm; and the ultrafine particles have at least a portion made of metal. With this method, it is possible to form a uniform thin metal film of pure metal on the surface of the substrate.

In the above method, the ultrafine particles comprise composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core.

In the above method, the thin-film precursor is composed of an ultrafine particle dispersion liquid comprising uniformly dispersed ultrafine particles having an average diameter ranging from 1 to 50 nm; and the ultrafine particles have at least a portion made of metal.

In the above method, the ultrafine particles comprise composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core.

In the above method, the film is made of an organic material of C, H, O, and N. When the transfer sheet and the film are thermally decomposed, the film can easily be gasified, and the gas does not chemically bonded to the produced thin metal film.

According to yet still another aspect of the present invention, there is provided a method of forming a thin metal film, comprising: placing a thin-film precursor on one surface of a film thereby to form a transfer sheet; transferring the transfer sheet onto a surface of a base; and peeling the film and thermally decomposing the transfer sheet to form a thin metal film from the thin-film precursor on the surface of the base.

In the above method, the base comprises a substrate having recesses defined in a surface thereof for embedding a conductor therein; the transfer sheet is transferred onto the surface of the substrate with the recesses filled up with a portion of the thin-film precursor; and after the thin metal film is formed, the surface of the substrate is polished to remove an excessive thin metal film therefrom.

In the above method, the thin-film precursor is composed of an ultrafine particle dispersion liquid comprising uniformly dispersed ultrafine particles having an average diameter ranging from 1 to 20 nm; and the ultrafine particles have at least a portion made of metal.

In the above method, the ultrafine particles comprise composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core.

In the above method, the thin-film precursor is composed of an ultrafine particle dispersion liquid comprising uniformly dispersed ultrafine particles having an average diameter ranging from 1 to 50 nm; and the ultrafine particles have at least a portion made of metal.

In the above method, the ultrafine particles comprise composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core.

In the above method, the film is made of an organic material of C, H, O, and N.

According to a further aspect of the present invention, there is provided an apparatus for forming a thin metal film, comprising: a transfer device for transferring a transfer sheet comprising a thin-film precursor placed on one surface of a film, onto a surface of a base; and a heating device for thermally decomposing the transfer sheet or the transfer sheet and the film to form a thin metal film from the thin-film precursor on the surface of the base.

In the above apparatus, the base comprises a substrate having recesses defined in a surface thereof for embedding a conductor therein; the transfer sheet is transferred onto the surface of the substrate with the recesses filled up with a portion of the thin-film precursor; and the apparatus further comprises a polishing device for, after the thin metal film is formed, polishing the surface of the substrate to remove an excessive thin metal film therefrom.

In the above apparatus, the thin-film precursor is composed of an ultrafine particle dispersion liquid comprising uniformly dispersed ultrafine particles having an average diameter ranging from 1 to 20 nm; and the ultrafine particles have at least a portion made of metal.

In the above apparatus, the ultrafine particles comprise composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core.

In the above apparatus, the thin-film precursor is composed of an ultrafine particle dispersion liquid comprising uniformly dispersed ultrafine particles having an average diameter ranging from 1 to 50 nm; and the ultrafine particles have at least a portion made of metal.

In the above apparatus, the ultrafine particles comprise composite ultrafine metal particles each having a core substantially made of a metal component and a covering layer made of an organic compound chemically bonded to the core.

In the above apparatus, the film is made of an organic material of C, H, O, and N.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIGS. 1A and 1B, a composite ultrafine metal particle14comprising a core10substantially made of a metal component and a covering layer12made of an organic compound is prepared. The composite ultrafine metal particle14is stable because it has the covering layer12made of an organic compound, and is less liable to be aggregated in a solvent.

The composite ultrafine, metal particle14is composed of the organic compound and the metal component which derives from a metal salt as a starting material, e.g., a carbonate, a formate, or an acetate. The core10is made of the metal component, and surrounded by the covering layer12of the ionic organic compound. The organic compound and the metal component are partly or wholly chemically coupled to each other. The composite ultrafine metal particle14is highly stable, and stable in a higher metal concentration, unlike the conventional ultrafine particles which are stabilized by being coated with a surface active agent.

The core10has an average diameter ranging from 1 to 50 nm, preferably from 1 to 20 nm, and more preferably from 1 to 10 nm. With this structure, the core10can be melted at a temperature that is considerably lower than the melting point of the metal of the core10.

The composite ultrafine metal particle14can be manufactured by heating a metal salt, e.g., a carbonate, a formate, or an acetate at or higher than its decomposing reducing temperature and at or lower than the decomposing temperature of a ionic organic compound in a nonaqueous solvent in the presence of the ionic organic compound.

The temperature at which the metal salt is heated is equal to or higher than the decomposing reducing temperature of the metal salt, e.g., a carbonate, a formate, or an acetate, and equal to or lower than the decomposing temperature of the ionic organic compound. For example, since the decomposing temperature of silver acetate is 200° C., silver acetate may be held at a temperature equal to or higher than 200° C. at which the ionic organic compound is not decomposed. In order to make the ionic organic compound resistant to decomposition, the atmosphere in which the metal salt is heated should preferably be an inactive gas atmosphere. However, the metal salt may be heated in the atmosphere by selecting a nonaqueous solvent.

For heating the metal salt, any of various alcohols may be added for promoting the reaction. The alcohols that can be added are not limited to any particular alcohol insofar as they can promote the reaction, and may include lauryl alcohol, glycerin, ethylene glycol, etc. The amount of an alcohol that is added may be determined depending on the type of the alcohol added. Usually, 5 to 20 parts by weight, preferably 5 to 10 parts by weight, of an alcohol may be added to 100 parts by weight of the metal salt.

After the metal salt is heated, it is refined by any of various known refining processes including the centrifugal separation process, the membrane refining process, the solvent extracting process, etc.

FIGS. 2A through 2Cshow successive steps of a method of forming a thin metal film using the composite ultrafine metal particles14shown inFIGS. 1A and 1B.

As shown inFIG. 2A, a metal powder16of silver, copper, iron, etc. whose average particle diameter ranges from 1 to 10 μm, preferably is about 8 μm, is uniformly dispersed in an ultrafine particle dispersion liquid15which comprises composite ultrafine metal particles14dispersed in a given organic solvent, thus preparing a solution17containing a metal component. When the composite ultrafine metal particles14are mixed and stirred, the ultrafine particle dispersion liquid15is substantially transparent as the dispersed composite ultrafine metal particles14are very small. The properties, such as surface tension, viscosity, etc. of the ultrafine particle dispersion liquid15can be adjusted by selecting the type of the solvent, the concentration of the composite ultrafine metal particles14, and the temperature of the ultrafine particle dispersion liquid15.

If a thin metal film having a relatively small thickness is to be formed, then the solution17comprises a dilute solution which contains 30 weight % of the metal component. If a thin metal film having a relatively large thickness is to be formed, then the solution17comprises a dense solution which contains 90 weight % of the metal component. In this manner, the thickness of the thin metal film is adjusted by adjusting the total amount of the metal component in the solution.

Then, as shown inFIG. 2B, the solution17is brought into contact with the surface of a substrate18, and then the organic solvent in the solution17applied to the surface of the substrate18is evaporated. The above cycle is repeated several times as desired to form an ultrafine particle coating layer19of a desired thickness which comprises the composite ultrafine metal particles14and the metal powder16.

The solution17may be brought into contact with the surface of the substrate18by an immersion process, a spray coating process, or a spin coating process. According to the immersion process, the solution17is put into a receptacle, and the substrate18is immersed in the solution17in the receptacle. According to the spray coating process, the solution17is sprayed to the substrate18. According to the spin coating process, the solution17is dropped onto the substrate18, and the substrate18is then rotated. Regions of the substrate surface which are not to be coated may be masked. The solvent may be dried off at normal temperature or with heat.

Then, as shown inFIG. 2C, the ultrafine particle coating layer19is thermally decomposed at about 300° C. to melt and join cores10(seeFIG. 1A) of the metal component of the composite ultrafine metal particles together, thus forming a thin metal film20which is composed of the cores10and the metal powder16and has a thickness ranging from 10 to 1000μm, preferably from 10 to 200 μm. Specifically, when the ultrafine metal particles are heated to a temperature equal to or higher than the temperature at which the covering layer (organic compound)12is separated from the core10or the decomposing temperature of the covering layer12, the covering layer12is separated from the core10or the covering layer12is decomposed and disappear, and at the same time the cores10are melted and joined together.

At this time, the cores10serve as a solder and the metal powder16as a skeleton. Since the melted cores10and the metal powder16are held in close contact with each other, the thin metal film20has a high conductivity. Because the metal powder16used is relatively inexpensive, it is possible to easily and inexpensively manufacture a thin metal film20which is of an increased thickness, whose thickness can easily be adjusted, and which has a high conductivity.

While the metal powder16is uniformly dispersed in the ultrafine particle dispersion liquid15to produce the solution17in the above example, the ultrafine particle dispersion liquid15may be used directly as the solution17. According to this modification, a thin metal film whose thickness ranges from 0.01 to 10 μm is formed which is composed of only melted and joined cores of the metal component by thermally decomposition of the composite ultrafine metal particles.

The composite ultrafine metal particles may be replaced with an organic metal compound, and the organic metal compound and a metal powder may be uniformly dispersed in an organic solvent to prepare a solution containing a metal component. In this case, it is necessary to reduce the organic metal compound into ultrafine metal particles. The organic metal compound may be reduced using a reducing agent or in its own reducing decomposing reaction with heat.

The organic metal compound collectively refers to organic compounds containing various metals, and may include a fatty acid salt such as naphthenate, octanoate, stearate, benzoate, paratoluate, n-decanoate, or the like, a metal alkoxide such as isopropoxide, ethoxide, or the like, and acetylacetone complex salts of the above metals.

FIGS. 3 through 10show an apparatus for carrying out the above method of forming a thin metal film.

FIG. 3shows a rectangular indoor facility21which houses the apparatus for forming a thin metal film therein. The rectangular indoor facility21has two air discharge ducts22,24and an air-conditioning device26which are mounted on the ceiling thereof. The rectangular indoor facility21also has, on a side wall thereof, an inlet/outlet port30for placing a cassette28housing substrates18therethrough into and out of the rectangular indoor facility21, and a control panel32.

As shown inFIG. 4, the rectangular indoor facility21is disposed in a utility zone34in a clean room which is separated from a clean zone36by a partition wall38, for example. The rectangular indoor facility21has an end positioned in an opening defined in the partition wall38, with the inlet/outlet port30and the control panel32exposed in the clean zone36. The air discharge ducts22,24are connected to a single common air discharge duct25, which is extends out of the utility zone34.

As shown inFIG. 5, the rectangular indoor facility21has its interior divided into a loading/unloading section40having the inlet/outlet port30, a solution supply section44having a solution supply device42therein, a supplementary drying section48having a supplementary drying device46therein, and a heating section52having a heating device50therein. The solution supply device42, the supplementary drying device46, the heating device50are arranged in a sequence along the direction in which substrates are fed, so that steps of forming a thin metal film can successively be performed. While the rectangular indoor facility21is shown as having one inlet/outlet port for holding one cassette therein, the rectangular indoor facility21may have two inlet/outlet ports each holding respective cassettes therein.

FIGS. 6 and 7show the solution supply device42which supplies the solution17(seeFIG. 2A) to the surface of the substrate18. The solution supply device42comprises a substrate holder60for holding and rotating the substrate18with an interconnection forming surface thereof facing upwardly, and a bottomed cup-shaped scattering prevention member62surrounding the substrate18that is held by the substrate holder60. The substrate holder60has a vacuum chuck for attracting and holding the substrate18on its upper surface, and is connected to the upper end of a rotatable shaft66that extends upwardly from a servomotor64. When the servomotor64is energized, the substrate holder60is rotated about its own axis. The bottomed cup-shaped scattering prevention member62is made of a material resistant to an organic solvent, e.g., stainless steel.

The solution supply device42includes a solution supply nozzle68positioned above either the center of the surface of the substrate18held by the substrate holder60or a position slightly displaced from the center of the surface of the substrate18. The solution supply nozzle68is oriented downwardly to drop the solution17onto the substrate18. The solution supply nozzle68is connected to the free end of an arm70which houses therein a pipe extending from a constant-quantity supply device72such as a syringe pump or the like for supplying a metered amount of solution17. The pipe in the arm70is held in communication with the solution supply nozzle68for supplying a metered amount of solution17from the constant-quantity supply device72to the solution supply nozzle68.

The solution supply device42also includes a bevel cleaning nozzle74extended radially downwardly above the peripheral edge of the substrate18held by the substrate holder60for supplying a cleaning liquid to a bevel portion of the substrate18, and a plurality of reverse side cleaning nozzles76extended radially outwardly below the substrate18held by the substrate holder60for supplying a gas or a cleaning liquid to the backside of the substrate18. The bottomed cup-shaped scattering prevention member62has a drain hole62adefined in its bottom.

When the servomotor64is energized, the substrate18held by the substrate holder60is rotated at a rotational speed of 300 to 500 rpm, preferably 400 to 500 rpm. At the same time, a desired amount of solution17is supplied from the solution supply nozzle68and dropped onto the central region of the surface of the substrate18. When the surface of the substrate18is covered with the solution17, the supply of the solution17from the solution supply nozzle68is stopped. In this manner, the solution17is uniformly coated on the surface of the substrate18. At this time, a hydrophilic organic solvent such as methanol or acetone, or a cleaning liquid such as ethanol or isopropyl alcohol is supplied from the bevel supply nozzle74to the bevel portion of the substrate18, for thereby preventing the outer circumferential surface and the backside surface of the substrate18from being coated with the solution17. A gas such as an N2gas or air, or a cleaning liquid which is the same as the cleaning liquid supplied from the bevel supply nozzle74is supplied from the backside cleaning nozzle76to the backside of the substrate18to prevent the backside of the substrate18from being contaminated.

With the supply of the solution17being stopped, the servomotor64is energized to rotate the substrate18to spin-dry the substrate18with air, thereby evaporating the solvent from the solution17coated on the substrate18.

The above process of coating the solution17on the interconnection forming surface of the substrate18and then drying the solution17with air is repeated a plurality of times as desired. The process is stopped when the ultrafine particle coating layer19, as shownFIG. 2A, is deposited to a desired thickness.

The substrate18may finally be rotated at a higher rotational speed to promoting the drying process of the solvent. Any excessive solution17and the cleaning liquid that has been used to clean the bevel portion of the substrate18and the backside of the substrate18are discharged out of the bottomed cup-shaped scattering prevention member62through the drain hole62a.

FIG. 8shows the supplementary drying device46in cross section. The supplementary drying device46comprises a substrate holding base80for holding the substrate18with its surface facing upwardly and a heating device84having lamp heaters82disposed above the substrate holding base80, for example.

The supplementary drying device46serves to dry out the solvent that has not been fully evaporated by the solution supply device42. If the solution17is coated to a very small thickness on the surface of the substrate18or the solvent has been fully evaporated by the solution supply device42, then the supplementary drying device46may be dispensed with.

Specifically, if the ultrafine particle coating layer19(seeFIG. 2B) deposited on the surface of the substrate18were heated while the organic solvent is remaining in the ultrafine particle coating layer19, then voids would tend to be formed in the thin metal film. Such voids are prevented from being formed in the thin metal film by fully drying out the solvent in the supplementary drying device46. The supplementary drying device46heats the ultrafine particle coating layer19at a temperature where the ultrafine particles are not decomposed, e.g., at a temperature of about 100° C., so that the supplementary drying device46is prevented from being contaminated by decomposed ultrafine particles.

FIGS. 9 and 10show the heating device50which heats the ultrafine particle coating layer19(seeFIG. 2B) to melt the composite metal ultrafine particles and join them together. The heating device50comprises a heating plate90for holding and heating the substrate18with its surface facing upwardly, a housing94for surrounding a space above the substrate18held by the heating plate90to define a gas chamber92between itself and the heating plate90, and a frame96surrounding the periphery of the heating plate90.

The heating plate90is in the form of a disk of aluminum or copper that is of a high thermal conductivity and can be heated uniformly at a high speed. The heating plate90houses therein a heater98and a temperature sensor100for detecting the temperature of the heating plate90. The heating plate90also has a coolant passage104defined therein which communicates with a coolant inlet pipe103for introducing a coolant such as a cooling gas, air, or the like. The coolant passage104communicates with a coolant discharge pipe106.

The housing94is made of ceramics, for example, and fixed to the free end of a vertically movable arm108. The housing94has a conical recess94adefined in the lower surface thereof which defines a gas chamber92between itself and the substrate18placed on and held by the heating plate90. The housing94also has a gas supply port94bdefined centrally therein and connected to a gas supply pipe110. The housing94further has slit portions94cand pressing portions94dalternately formed on the lower peripheral edge thereof. When the housing94is lowered, the pressing portions94dcontact the peripheral edge of the substrate18on the heating plate90, gripping the peripheral edge of the substrate18between the pressing portions94dand the heating plate90. At this time, the slit portions94cprovide a gas discharge port112on the peripheral edge of the substrate18.

The frame96has a ring-shaped gas intake port114defined therein. A discharge duct116is fixed to the lower surface of the frame96in communication with the gas inlet port114. The discharge duct116is connected to a discharge blower118.

The heating device50operates as follows. The substrate18is placed on the upper surface of the heating plate90. The heating plate90heats the substrate18to 300° C., for example, in 5 minutes. After the substrate18is kept at 300° C. for 5 minutes, it is cooled to the room temperature in 10 minutes. In this manner, the cores10of the metal component of the composite ultrafine metal particles14are melted and joined together. An inactive gas of N2or the like containing a small amount of oxygen or ozone is introduced from the gas supply pipe110into the gas chamber92, and thereafter an inactive gas of N2or the like alone is introduced from the gas supply, pipe110into the gas chamber92. The introduced oxygen or ozone serves as a catalyst for separating the organic substance and the metal from each other thereby to promote the decomposition of the composite ultrafine metal particles14. The N2gas serves to remove soot produced when the composite ultrafine metal particles14are decomposed, from the surface of the substrate18, for thereby preventing the surface of the substrate18from being contaminated by soot.

The oxygen or ozone should be introduced in a small quantity because if it were introduced in a large quantity, it would tend to oxidize the composite ultrafine metal particles14.

If interconnections are to be formed using ultrafine cupper particles, then the substrate18is heated (baked) while a nitrogen gas containing a small amount of oxygen or ozone is being introduced, and then a nitrogen gas containing hydrogen is introduced to prevent the cupper from being oxidized. After interconnections of pure copper are formed, a nitrogen gas is introduced. In this manner, interconnections can be formed efficiently.

The apparatus for forming a thin metal film, which is constructed as described above, operates as follows. The cassette28with substrates18housed therein is placed into the inlet/outlet port30, and one of the substrates18is taken from the cassette28into the solution supply device42in the solution supply section44. The solution supply device42supplies the solution17containing a metal component to the surface of the substrate18, and dries the substrate18by spin-drying process, thereby evaporating the solvent from the solution17coated on the substrate18. The above process of coating and drying the solution17is repeated a plurality of times as desired. When the ultrafine particle coating layer19(seeFIG. 2B) is deposited to a desired thickness, the substrate18is fed to the supplementary drying device46in the supplementary drying section48. The supplementary drying device46evaporates the solvent in the ultrafine particle coating layer19. Thereafter, the substrate18is fed to the heating device50in the heating section52. The heating device50heats the ultrafine particle coating layer19to melt and join the metal cores together, thereby forming the thin metal film20(seeFIG. 2C), after which the substrate18is returned to the cassette28. The apparatus according to the present invention is capable of performing the above steps successively.

FIG. 11shows an apparatus for forming a thin metal film according to another embodiment of the present invention. The apparatus has a processing chamber120which can be evacuated by a vacuum pump (not shown) connected to an evacuating port120a. The processing chamber120houses therein a substrate holder122disposed vertically movably and rotatably for placing a substrate18on its upper surface. The substrate holder122accommodates therein a heater124for heating the substrate18held by the substrate holder122and a cooling mechanism for cooling the substrate18with cooling water. A liquid nitrogen trap device126is disposed below the substrate holder122in the processing chamber120.

An ultrafine particle ejector head130having a number of ejection nozzles130adefined in a lower surface thereof is positioned above the substrate holder122in the processing chamber120. The ultrafine particle ejector head130is connected to an ultrafine particle dispersion liquid passage132which introduces an ultrafine particle dispersion liquid into the processing chamber120. The ultrafine particle dispersion liquid which is supplied from an external source is uniformly ejected from the ejection nozzles130atoward the surface of the substrate18that is held by the substrate holder122.

Between the substrate holder122and the ultrafine particle ejector head130, there is disposed an openable/closable shutter134that is rotatable to open and close a region above the substrate holder122.

In this embodiment, the ultrafine particle dispersion liquid comprises, as shown inFIGS. 1A and 1B, composite ultrafine metal particles14, each having a core10substantially made of a metal component and a covering layer12made of an organic compound, uniformly dispersed in a suitable solvent of cyclohexane or the like. The composite ultrafine metal particles14are stable because the cores10are covered with the covering layers12made of an organic compound, and have a small tendency to be aggregated in a solvent. The core10has an average diameter ranging from 1 to 50 nm, preferably from 1 to 20 nm, and more preferably from 1 to 10 nm.

The ultrafine particle ejector head130is connected to a high-frequency power supply140, and acts as a discharge electrode for generating a plasma in a plasma generating region142below the ultrafine particle ejector head130. An electron beam generator144for applying an electron beam inwardly is positioned laterally and downwardly of the plasma generating region142. The electron beam generator144may be replaced with an ion generator.

A method of forming a thin metal film, carried out by the apparatus shown inFIG. 11, to form copper interconnections on the semiconductor substrate18using an ultrafine particle dispersion liquid which comprises ultrafine copper particles (composite ultrafine metal particles) dispersed in cyclohexane will be described below. Each of the ultrafine copper particles comprises a core10of copper covered with a covering layer12of an organic compound. For example, the ultrafine copper particles can be produced by adding a stearic acid as an anionic substance and copper carbonate as a metal source to a paraffin-based high-boiling-point solution having an initial boiling point of 250° C., heating the mixture at 300° C. for 3 hours, adding methanol to the mixture, and subjecting the mixture to precipitation refinement.

First, the substrate18is placed on the upper surface of the substrate holder122, and heated to a desired temperature by the heater124. Then, the processing chamber120is evacuated to keep under vacuum atmosphere in the processing chamber120. The ultrafine particle dispersion liquid is introduced into the ultrafine particle ejector head130, and ejected through the ejection nozzles130ato the surface of the substrate18. At the same time, the high-frequency power supply140applies high-frequency electric energy to the ultrafine particle ejector head130to produce a plasma in the plasma generating region142, and the shutter134is opened. When necessary, the electron beam generator144is energized to ionize the ultrafine particles.

The solvent contained in the ultrafine particle dispersion liquid ejected through the ejection nozzles130ais quickly vaporized, and either trapped by the liquid nitrogen trap device126or discharged via the evacuating port120aby the vacuum pump. The ultrafine copper particles that have been left upon evaporation of the solvent pass through the plasma generating region142, and are heated upon passage through the plasma generating region142. When heated, the covering layer12of the organic compound (seeFIGS. 1A and 1B) is decomposed and disappears, producing an ultrafine particle beam composed of highly active copper alone (core10).

Since the copper cores10are uniformly dispersed in the solvent stably out of contact with each other, the ultrafine copper particles which are of a very small diameter can easily be handled, and the ultrafine particle beam composed of copper (core10) has a uniform distribution.

The electron beam is applied to the ultrafine particle beam to ionize the ultrafine particle beam into an ultrafine particle ion beam, which is accelerated, if necessary, with a given voltage into collision with the surface of the substrate18. Because the copper cores10are very active and the substrate18is heated by the heater124, the copper cores10are melted and joined together, forming and depositing a uniform, spot-free copper film on the surface of the substrate18in intimate contact therewith.

Heretofore, as shown inFIGS. 16A through 16C, after the diffusion barrier layer6and the base film7have successively been formed on the small recesses5, the surface of the substrate is plated with copper. According to the method carried out by the apparatus shown inFIG. 11, however, the diffusion barrier layer6and the primary film7are not formed, but a copper layer is deposited directly on the surface of the insulating film2in intimate contact therewith to form copper interconnections free of voids and seals therein.

When the copper cores10are ionized and the energy to accelerate the ions is optimized, it is possible to embed copper in contact holes whose aspect ratio is 5 or more.

As indicated by the imaginary lines inFIG. 11, a laser beam source150may be positioned outside of the processing chamber120, and the processing chamber120may have a window152made of a material capable of passing a laser beam generated by the laser beam source150. With this modification, the laser beam that has passed through the window152is applied to the composite ultrafine metal particles14, from which the solvent has been evaporated, to remove the covering layers12. The laser beam may be replaced with an ultraviolet ray. Alternatively, a particle beam such as an electron beam, an ion beam, or a neutron beam may be applied to remove the covering layers12from the composite ultrafine metal particles14, from which the solvent has been evaporated.

In the above embodiments, the composite ultrafine metal particles14are used as ultrafine particles, and the ultrafine particle dispersion liquid is prepared by dispersing the composite ultrafine metal particles14in the solvent. However, the composite ultrafine metal particles14may be replaced with generally known ultrafine particles made of metal only, and the ultrafine particle dispersion liquid may be prepared by dispersing the known ultrafine particles in the solvent.

FIGS. 12A through 12Fshow successive steps of a method of forming a thin metal film according to another embodiment of the present invention. According to this method, a conductor such as copper, silver, or the like is embedded in interconnection grooves defined in the surface of the semiconductor substrate or small recesses such as vertical holes interconnecting layers, known as contact holes, making up interconnections of the embedded conductor.

As shown inFIGS. 12A and 12B, there are prepared a substrate212having small recesses210such as interconnection grooves formed by lithography and etching, and a transfer sheet218comprising a film214of synthetic resin, for example, and a thin-film precursor216of given thickness deposited on one surface of the film214.

The thin-film precursor216is prepared from a paste-like ultrafine particle dispersion liquid which comprises composite ultrafine metal particles14, each comprising a core10substantially made of a metal component and a covering layer12made of an organic compound, uniformly dispersed in a given solvent, as shownFIGS. 1A and 1B, in this embodiment. The composite ultrafine metal particles14are stable because the cores10are covered with the covering layers12made of an organic compound, and have a small tendency to be aggregated in a solvent.

The proportion of the metal component in the composite ultrafine metal particles14may be normally in the range from 50 to 90 weight %. For use in interconnection grooves, it is preferable for the metal component to be in the range from 60 to 90 weight %, particularly from 70 to 90 weight %. The core10has an average diameter ranging from 1 to 50 nm, preferably from 1 to 20 nm, and more preferably from 1 to 10 nm.

When the composite ultrafine metal particles14are mixed and stirred, the thin-film precursor (ultrafine particle dispersion liquid)216, which is prepared by uniformly dispersing the composite ultrafine metal particles14in the solvent, is substantially transparent as the dispersed composite ultrafine metal particles14are very small. The properties, such as surface tension, viscosity, etc. of the thin-film precursor216can be adjusted by selecting the type of the solvent, the concentration of the composite ultrafine metal particles14, and the temperature of the thin-film precursor216.

The film214is made of an organic material such as polyethylene composed of C, H, O only or an organic material such as nylon composed of C, H, O, N only. If the film214is made of an organic material composed of C, H, O, N only, then when the film214is thermally decomposed, it can easily be gasified, and the generated gas and a formed thin film232(seeFIG. 12E) are not chemically bonded together.

Then, as shown inFIG. 12C, the surface of the substrate212where the recesses210are defined and the thin-film precursor216on the transfer sheet218are brought into contact with each other, and then pressed against each other by a pressure roller230. As shown inFIG. 12D, the thin-film precursor216is transferred to the substrate212with the recesses210filled up with a portion of the thin-film precursor216.

Then, after the film214is peeled off the thin-film precursor216, a thin metal film232is formed from the thin-film precursor216on the surface of the substrate212where the recesses210are defined. Specifically, the solvent contained in the thin-film precursor (ultrafine particle dispersion liquid)216is evaporated, and the covering layers (organic compound)12(seeFIGS. 1A and 1B) of the composite ultrafine metal particles14are decomposed away. At the same time, the cores10of the metal component are melted and joined together, forming a thin metal film232made of only the metal component contained in the thin-film precursor216.

At this time, the recesses210in the substrate212are fully filled up with a portion of the thin-film precursor216that is pressed. In this manner, a conductor free of voids and cavities is formed in the recesses210in the substrate212.

Then, as shown inFIG. 12F, the surface of the substrate is polished by chemical mechanical polishing (CMP) to remove the excessive thin metal film232, other than the thin metal film232filled in the recesses210, from the substrate212. Embedded interconnections made of the thin metal film232are now fabricated.

FIGS. 13A through 13Fshow a modification of the method of forming a thin metal film shown inFIGS. 12A through 12F. The modified method differs from the method shown inFIGS. 12A through 12Fin that, as shown inFIG. 13D, the film214is not peeled off the thin-film precursor216, but is thermally decomposed to form a thin metal film232from the thin-film precursor216on the surface of the substrate212where the recesses210are defined, as shown inFIG. 13E. Specifically, the film214is gasified away, and the solvent contained in the thin-film precursor (ultrafine particle dispersion liquid)216is evaporated, and the covering layers (organic compound)12(seeFIGS. 1A and 1B) of the composite ultrafine metal particles14are decomposed away. At the same time, the cores10of the metal component are melted and joined together, forming a thin metal film232made of only the metal component contained in the thin-film precursor216.

FIGS. 14 and 15show an apparatus for carrying out the methods shown inFIGS. 12A through 12Fand13A through13F.

As shown inFIGS. 14 and 15, the apparatus comprises a central feed chamber242having a feed robot240disposed therein, a transfer section246housing a transfer device244therein, a heating section250housing a heating device248therein, a polishing chamber254housing a polishing device252therein, and a plurality of stock yards (temporary stock chambers)256. The transfer section246, the heating section250, the polishing chamber254, and the stock yards256are disposed radially outwardly of the central feed chamber242, with the stock yards256being positioned between the transfer section246, the heating section250, and the polishing chamber254. The apparatus also includes a second feed chamber262disposed between the feed chamber242and a loading/unloading chamber258and housing a movable robot260.

As shown inFIGS. 12C and 13C, the transfer device244brings the surface of the substrate212where the recesses210are defined and the thin-film precursor216on the transfer sheet218into contact with each other, and then presses the substrate212and the thin-film precursor216against each other with the pressure roller230, for thereby transferring the thin-film precursor216to the substrate212with the recesses210filled up with a portion of the thin-film precursor216, as shown inFIGS. 12D and 13D.

The heating device248is of a structure identical to the heating device50shown inFIGS. 9 and 10. In the heating device248, after the film214is peeled off the thin-film precursor216, or with the film214remaining unremoved on the thin-film precursor216, the substrate212is placed on the upper surface of the heating plate90. The heating plate90heats the substrate18to 300° C. in 5 minutes. After the substrate18is kept at 300° C. for 5 minutes, it is cooled to the room temperature in 10 minutes. In this manner, the cores of the metal component of the composite ultrafine metal particles are melted and joined together.

The polishing device removes excessive metal from the surface of the substrate212in a chemical mechanical polishing action. As shown inFIG. 15, the polishing device comprises a polishing table322with a polishing pad320attached to its upper surface to provide a polishing surface, and a top ring324for holding the substrate212with its surface to be polished facing toward the polishing table322. The polishing table322and the top ring324are rotated about their own axes independently of each other. While an abrasive liquid is being supplied from an abrasive liquid nozzle326positioned above the polishing table322to the polishing pad320, the top ring324presses the substrate212against the polishing pad320under a constant pressure to polish the surface of the substrate212. The abrasive liquid supplied from the abrasive liquid nozzle326comprises an alkaline solution with fine abrasive particles of silica or the like suspended therein. Therefore, the surface of the substrate212is polished to a flat mirror finish by a chemical mechanical polishing action which is a combination of a chemical polishing action performed by the alkali and a mechanical polishing action performed by the fine abrasive particles.

Continued polishing of substrates on the polishing device results in a reduction of the polishing capability of the polishing surface of the polishing pad320due to the loading of the polishing pad320. To recover the polishing capability, the polishing pad320is dressed by a dresser328when the polished substrate212is replaced with another substrate212, for example. Specifically, the lower dressing surface of the dresser328is pressed against the polishing pad320, and the dresser328and the polishing table322are independently rotated about their own axes to remove the abrasive liquid and debris from the polishing pad320. The polishing surface of the polishing pad320is thus planarized and dressed into a regenerated state.

The transfer section246housing the transfer device244therein, the heating section250housing the heating device248therein, and the polishing chamber254housing the polishing device252therein can be unitized, and the processes in the transfer section246, the heating section250, and the polishing chamber254can individually be performed and combined to form interconnections on substrates.

In the above embodiment, the composite ultrafine metal particles14are used as ultrafine particles, and the ultrafine particle dispersion liquid for the thin-film precursor is prepared by dispersing the composite ultrafine metal particles14in the solvent. However, the composite ultrafine metal particles14may be replaced with generally known ultrafine particles made of metal only, and the ultrafine particle dispersion liquid may be prepared by dispersing the known ultrafine particles in the solvent.

With the arrangement of the present invention, it is possible to easily and inexpensively manufacture a thin metal film which has a sufficient conductivity and whose thickness can easily be adjusted. A thin metal film of good quality can stably be formed on the surface of a substrate to embed a conductor reliably in small interconnection grooves or recesses defined in the surface of the substrate.