JPH11243273A - Method of forming metal wiring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of realizing a deposited film separated out thick enough at a enough separating speed through a simple process, when a metal thin film is separated out by irradiation with light rays at arbitrary positions on the surface of a non-conductive and/or conductive board to serve as a copper electric wiring. SOLUTION: A metal pattern is provided as a conductive path through a method, where metal colloids whose skins serve as films are deposited on a base as a thin film which serves as a precursor, the surface of the thin film is spatially and selectively irradiated with light rays to decompose or break the skins of the colloids to turn the thin film into a metal thin film, and then the unexposed metal colloids are removed off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metal pattern on a substrate using a metal colloid by photochemical and / or thermochemical action of a light beam, and more particularly to a wiring of a printed wiring board or a semiconductor device. The present invention relates to a method for manufacturing

[0002]

2. Description of the Related Art A technique of providing a wiring pattern of a metal such as copper on a surface of an electrically non-conductive material such as a resin substrate or a passivation film of a semiconductor device is a technique for forming a semiconductor element or various electronic components at a high density. It is extremely important as the basis for the means of implementation. As means for forming a copper wiring pattern on the surface of a resin base or the like, two main methods are conventionally roughly classified.

One of the methods is to remove a copper foil provided in advance on the entire surface of the substrate by immersing the copper foil in a liquid having a copper solubility except for a desired portion and etching the solution, which is called a subtractive method. . In order to perform such position-selective etching, it is necessary to cover a portion of the surface of the copper foil to be a wiring pattern in advance with a resin called a resist.

A resist used for such a purpose usually has photosensitivity, and an arbitrary resist pattern can be obtained by exposing the resist to a desired light image.

Another means for forming a copper wiring pattern on the surface of a resin substrate or the like is called an additive method, which is to form a wiring pattern on a desired portion of a substrate such as a resin by electroless plating. .

In this method, first, an adhesive layer is provided on the resin substrate to roughen the surface thereof, and a nucleus serving as a catalyst when performing electroless copper plating performed in a later step is attached to the surface. Next, a photosensitive plating resist film is provided on the entire surface of the substrate, and a light image corresponding to a desired wiring pattern is exposed on the surface and developed, whereby the substrate surface can be coated with the plating resist in a desired pattern. . Subsequently, the substrate is immersed in an electroless copper plating solution to deposit copper on a portion not covered with the resist, and then the plating resist is removed. In this way, a copper wiring pattern can be formed on the surface of a resin substrate or the like by the additive method.

The above two methods have been most widely used in the art as means for obtaining a printed wiring board. However, in any case, a complicated process of coating and stripping with a resist is essential to obtain a desired wiring pattern, and this limits the improvement in productivity of a printed wiring board.

In addition to the above two methods, there has been proposed a method of forming a metal wiring pattern without using a resist. One of the typical ones is to provide a thin film of a soluble copper precursor compound to be a metal foil on a substrate, and to irradiate this specific site with ultraviolet light to precipitate copper. However, this method has a disadvantage that it is difficult to obtain a film thickness sufficient to form a conductive path, and amplification by electroless plating or the like is required subsequently. Another method of forming a metal wiring pattern without using a resist is that Ap.
plied Physics Letters, Vol. 64, pp. 3404-3406 (1994). According to this, a thin film of a metal such as copper of about 200 ° is previously deposited on the entire surface of a dielectric or glass substrate, and then a thin film of A is formed in an electrolytic solution containing copper sulfate, sulfuric acid, and glycol.
Irradiation with an r @ + ion laser generates an electromotive force at a site irradiated with the laser beam, causing an electrochemical reaction to lead to copper deposition.

This method has the advantage that it is difficult for substances other than copper to deposit on the substrate surface, and that the thickness of the copper deposited by changing the sweep speed of the laser beam can be varied within a certain width. However, there are many restrictions such as that the deposited film thickness is not sufficient, the sweep speed must be considerably reduced, and that a copper thin film must be provided on the entire surface of the substrate in advance.

The deposited copper thin film is not uniform and has a structure in which copper particles having a particle size of 0.1 to 0.3 μm are mutually bonded. When attempting to deposit a copper thin film in a metallic state from copper ions in a solution, it is necessary to sequentially reduce the amount of ions corresponding to the amount of deposited copper, which affects the speed of the process and the properties of the film. ing.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to deposit a thin film of a metal such as copper which can be used as an electric wiring at an arbitrary position on the surface of a non-conductive and / or conductive substrate by irradiation with a light beam. It is an object of the present invention to provide a method capable of realizing a sufficient deposition film thickness by a simple process and a sufficient deposition rate.

[0012]

The present inventor has made various studies in view of the above-mentioned disadvantages of the prior art, and as a result, has found that a simple thin film of metal such as copper can be deposited on a substrate by irradiating a light beam. We came up with a way. That is, 1 according to the present invention
In one embodiment, by using colloidal particles composed of ultrafine metal particles in an oxidized state mainly having a zero-valent state as a precursor substance to be converted into a metal upon irradiation with light,
It has been found that the disadvantages of the prior art can be solved.

It is a fact well known among those skilled in the art as the additive method that a metal in a colloidal state is deposited on a trace amount of a substrate and used as a catalyst in electroless plating of copper or the like.

However, the principle of the present invention is different from that in principle, and is characterized in that the metal itself in a colloidal state is substantially changed into a metal thin film to form a direct conductive pattern, and the catalyst of the metal colloid is used. It does not rely on chemical reactions by action. Of course, it goes without saying that even if the metal thin film produced by the method of the present invention is used for the purpose of causing a catalytic action, it does not depart from the gist of the present invention. A typical example of a metal colloid is
In order to prevent aggregates of atoms having a diameter of several nm to several tens of nm, that is, clusters and colloids, from agglomerating and coalescing with each other, it is necessary to form a structure in which the outer skin of a certain organic compound is covered. Normal. Such a structure is usually called a protective colloid.

In the present invention, after a colloid having such a form is deposited on a substrate as a thin film, the stable structure is intentionally destroyed by the chemical and / or thermal action of light to fuse with the metal thin film. Is what you do. Therefore, the substance that may be included as a foreign substance in the thin film is only a minimum decomposition residue of the outer skin. About 3n
In a metal colloid having a diameter of about m, usually about 100 atoms are contained in the metal colloid, whereas the outer skin is a relatively sparse monomolecular film of a surfactant made of an organic compound. It is normal that there is. The use of a high molecular weight compound in the outer skin instead of a low molecular weight surfactant is also effective in stabilizing the metal colloid, but even in such a case, the components of the organic substance are much larger than the metal atoms contained therein. Not be.

According to the present invention, the advantage that the ratio of the number of atoms to be a metal thin film in the precursor thin film is much larger than that of the conventional example is apparent when compared with the case of the copper precursor compound described above. It is. In the precursor of the reference, an overwhelmingly large number of non-copper atoms are contained compared to the number of copper atoms,
This is significantly different from the case of the present invention. For this reason, the difference between the film thickness of the precursor thin film and the film thickness after forming the metal thin film is smaller than in the case of the above-described conventional technology.

As described above, in the present invention, the precursor to be a metal thin film contains an element other than the metal element at an overwhelmingly small ratio as compared with the prior art. Together with the fact that the oxidation state consists of a zero-valent metal element, it constitutes a remarkable feature of the present invention.

The advantage of forming a metal thin film using zero-valent colloidal particles is that the metal thin film can be formed quickly and efficiently by light irradiation because it is not necessary to reduce the target metal ions one by one. The result is that the step of precipitation proceeds promptly. If a metal element susceptible to oxidation is used, it may be unavoidable that part or all of the metal thin film obtained by light irradiation is in the form of an oxide.

In such a case as well, by reducing the thin film containing the oxide in one part or all of the oxide at once, it is possible to finally obtain a thin film having excellent conductivity. It is possible. Such a method is overwhelmingly advantageous in terms of speed as compared with a method in which metal ions are reduced one by one chemically or electrochemically and deposited on a substrate as a metal thin film. It is a well-known fact that ultrafine particles of metal oxides form colloids like zero-valent metals, and therefore the object of the present invention should not be limited to colloids composed of zero-valent metals.

In addition, colloids of oxides of magnetic atoms such as iron and manganese exhibit an interesting magnetic behavior when they have a size smaller than or equal to the magnetic coherence length. It is also effective to apply the method as a spatially selective method for depositing colloids. In this case, it is not necessary that the colloid particles of the respective oxides are fused, and it is sufficient that the outer skin is destroyed and the difference in solubility between the non-irradiated portion and the non-irradiated portion becomes significant during 'development'.

There are many known examples in which a single colloid particle substantially contains a plurality of types of metal elements.
Another advantage of the present invention is that a metal thin film in which a plurality of metal elements are mixed can be used even when a metal colloid precursor in which such a single colloid particle is composed of a plurality of metal elements is used. It can be easily obtained. It is a well-known fact that various kinds of metal elements form a colloidal state, and various reports have been made on a method for producing a relatively stable colloid in a state of covering the outer skin.

For example, the preparation of platinum-protected colloids with polyvinyl alcohol is described by John Kiwi et al. In Journal.
of the American Chemical Society, Volume 101,
Pages 7214 to 7217 (1979). According to this method, it is obtained by heating a weakly alkaline aqueous solution of chloroplatinic acid in the presence of polyvinyl alcohol. Another example is H. Bonnema
nn et al. by Angewandte Chemie, International Edition
Engl., Vol. 30, pages 1312 to 1314 (1991). Here is chrome,
Manganese, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, and platinum halides are reduced by a reducing agent and obtained as colloids of these elements protected by quaternary ammonium salts.

A method for producing a metal powder of nanometer size by reacting a metal halide with an alkali metal hydride or an alkaline earth metal hydride is disclosed in JP-A-8-325.
No. 613. Alternatively, it is also possible to electrochemically reduce metal ions into a colloid based on an electrode process.

At that time, if an organic substance to be a skin is previously coexisted in the electrolytic solution, it can be easily obtained as a colloid protected by the organic substance. At that time, by selecting the organic group to be the outer skin from one having an appropriate molecular structure, it can be prepared so as to be soluble in an organic solvent or water. An electrochemical production method of a metal colloid protected and solubilized by the outer coat is described in, for example, JP-A-7-310107. It is also known that by reducing a copper salt with hydrazine in the presence of a polymer compound, ultrafine particles of copper protected by the polymer compound can be obtained.

By applying a spin coating method or the like to a metal colloid solution obtained by the chemical reduction method or the electrochemical reduction method, a thin film can be easily formed.

The gist of the present invention is to substantially convert the deposited metal colloid into a metal thin film, so it must be emphasized that the present invention is not limited to the particular metal colloid to be its precursor. This is not dependent on the manufacturing method, which is obvious in light of the spirit of the present invention.
In addition to the use of the above-described colloids composed of a plurality of types of metal elements, the use of a metal colloid composed of two or more different elements stacked or mixed with each other is also consistent with the gist of the present invention. Also, when a part or all of the metal colloid is oxidized to be an oxide, it can be finally reduced by various methods, which does not depart from the gist of the present invention.

The metal colloid thin film protected by the outer skin generally exhibits not only low electrical conductivity but also is mechanically and physicochemically unstable such as easily peeling off or being dissolved by a solvent. . In order to form such a colloidal deposit into a thin metal film, it is important that the outer skin is substantially destroyed and removed from the colloid particles protected by the outer skin, and the metal colloids or clusters are brought into contact with each other and fused. is there.

When the metal colloid is used as a precursor for forming a metal thin film, it is important to minimize the intervening of other substances in order to maximize the effect of the present invention. This is extremely important for minimizing impurities in the finally obtained metal thin film as described above. Specifically, the metal colloid precursor protected by the outer coat is not mixed and diluted with other film-forming substances as much as possible.

However, even if the precursor film according to the present invention contains a minimum amount of inclusions that do not substantially affect the electrical properties of the finally obtained metal thin film, It does not depart completely from the gist.

When light is applied to a precursor thin film made of a metal colloid provided on a substrate, the irradiated light is absorbed by the outer skin of the colloid and the metal atom aggregates constituting the colloid. At that time, the following two effects can be mainly interposed. One is that the energy of the light is converted into heat, which destroys the outer skin and fuses the colloid into a thin film. When a colloid, which is an aggregate of metal atoms, receives heat, the thermal vibration of its constituent atoms is activated, and the colloid comes into contact with another cluster or colloid whose outer skin has been destroyed. It is important to improve the effect of the present invention that the colloid skin is destroyed more efficiently by the light irradiation.

One method is to enable the organic compound or colloid aggregate forming the skin to efficiently absorb the irradiation light. Unless the energy of the absorbed light is further used for light emission, electrical phenomena, or photochemical reactions described later, it is finally converted to heat.
Therefore, it is preferable that the precursor has good light absorption and conversion to heat energy.

It is advisable to include a substituent suitable for light absorption in the hull compound for such a purpose. Conversely, it is important that the precursor use light having a wavelength convenient for such absorption of light and conversion to heat energy. For example, in the case of gold or copper, visible light irradiation causes light absorption corresponding to excitation from the d-electron level to the Fermi level or plasmon excitation based on free electrons, and is ultimately converted into lattice vibration energy to become heat. It has been known.

At that time, it is convenient to use a substance whose structure and adsorptivity of the material constituting the outer skin of the colloid are thermally weak so that the colloid of the precursor is easily destroyed by heat. For example, there is a case in which a specific bond of the organic compound in the outer skin is cleaved or isomerized by light irradiation, so that the adsorption performance on the metal colloid is lost.

Another effect expected when the precursor is irradiated with light is a case where a photochemical reaction is caused. According to the photochemical reaction, the organic compound in the outer skin is destroyed by a different route from the thermal case, and fusion of the metal colloid is promoted. In this case as well, the coexistence of thermal effects is important and helps the reaction to the metal thin film.

Also in the case of utilizing this photochemical reaction, it is important to use a substance having a molecular structure suitable for this as the outer coat. For example, diorganopolysilane can be used for the purpose of the present invention because the Si-Si bond of the main chain is photochemically cleaved by irradiation with ultraviolet light. In addition, polyethylene glycols are also effective as an outer skin for protecting the colloid. An example in which the outer skin provided for the purpose of protecting the metal colloid is chemically modified to have a function other than the protection in addition to the outer skin is disclosed in Japanese Patent Application Publication No. Sho 62-51138.
No.

In this case, the catalytic action of the noble metal colloid is combined with the function of electron transfer by using an electron-accepting outer skin. Even when irradiated with light of a wavelength that causes a photochemical action, a significant proportion of the energy is ultimately converted to heat. Therefore, a thermal effect can be greatly involved even when an ultraviolet ray that irradiates the outer skin photochemically is irradiated.

Most metal elements, except for some noble metal elements, are more or less oxidized by oxygen gas in the air. Therefore, a part or all of the deposited metal thin film is oxidized, so that an operation such as a reduction treatment may be required subsequently. In order to avoid such inconveniences, it is preferable to carry out the present invention under a vacuum or an inert gas atmosphere as much as possible.

However, even if the metal colloid component is oxidized to an oxide during the preparation of the metal colloid, during the subsequent process of preparing the precursor thin film, or during the light irradiation reaction, the reaction is finally completed in a reducing atmosphere such as hydrogen. It is possible to return to a metal state by performing a heat treatment in the inside.

It is relatively easy to remove a portion remaining as a precursor on the substrate, except for a portion formed into a metal thin film by light irradiation. That is, the portion irradiated with the light beam becomes a metal and is no longer dissolved by the solvent, whereas the region not irradiated with the light beam is not chemically changed and can be eluted away by the solvent. Thus, it becomes possible to easily draw a metal thin film pattern by light irradiation.

According to the present invention, when changing from a metal colloid to a metal thin film, only the outer skin is removed.
When changing from the precursor thin film to the metal thin film, the change in the film thickness can be extremely small as compared with the known example of the aforementioned reference.
The light source that can be used for the light irradiation of the present invention can be from the ultraviolet region to the infrared region, and a laser light source can be used in addition to a normal light source. In particular, when a fine metal pattern is required, it is preferable to use a light source having a shorter wavelength such as ultraviolet light.

The irradiation wavelength depends not only on the absorption wavelength of the molecules constituting the outer skin described above, but also on the plasma band of the colloid particles themselves. When irradiating a metal colloid thin film as a precursor with light to form a metal thin film, in many cases, a process from destruction of the outer skin to fusion of the metal colloid is a mixture of a photochemical process and a thermal process. Therefore, it is more preferable to set the structure of the outer skin and the irradiation wavelength so that the irradiation light can exert a photochemical action and a thermochemical action.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

EXAMPLE 1 Copper (II) chloride in 1500 ml of ethanol purged with tetrahydrofuran purged and purged with nitrogen gas
While 0.01 mmol was suspended and stirred, 0.02 mmol of tetradecyl ammonium tetrahydroborate was added and stirred. This solution was filtered under a nitrogen atmosphere, the solvent was distilled off, and tetrahydrofuran was added to dissolve the solution. Next, n-hexane was added to this solution to obtain a powder. To 0.5 g of this powder, 1000 ml of tetrahydrofuran and 5 mg of polyoxyethylene were added and dissolved under a nitrogen atmosphere.
Then, the solvent was distilled off under reduced pressure and concentrated.

This solution was dropped on a silicon wafer, spin-coated and dried. The surface of the silicon substrate was irradiated with a xenon lamp through a mask for 1.5 hours. Then, the substrate was immersed in 500 ml of tetrahydrofuran,
The solvent was gently stirred to dissolve the non-irradiated portion, thereby obtaining a copper wiring pattern.

Example 2 Nickel (II) chloride in place of copper chloride
The same operation as in Example 1 was performed except for using, to obtain a nickel wiring pattern.

[0046]

As described above, by irradiating a metal colloid film protected with an organic substance according to the present invention with light, a wiring pattern having a film quality and a film thickness which can substantially form a conductive path can be easily prepared. Obtainable.

Claims (6)

[Claims] 1. A method of providing a metal pattern on a substrate, which may be substantially a conductive line, comprising: depositing the metal colloid having a protective shell as a precursor on the substrate as a thin film; Forming a metal thin film by decomposing or destroying the outer skin by performing a typical light irradiation, and then removing a metal colloid in an unexposed portion. 2. The method according to claim 1, wherein the outer skin is a tetraalkylammonium salt. 3. The method according to claim 1, wherein the outer shell is a polymer compound having an ethylene oxide skeleton. 4. The method according to claim 1, wherein the outer skin is a diorganopolysilane. 5. The metal colloid comprises copper, palladium, nickel, chromium, zinc, cobalt, molybdenum, tungsten, ruthenium, osmium, iridium, iron, manganese, platinum, silver, gold, germanium, tin, gallium, indium. 2. The method for forming a metal wiring according to claim 1, comprising one or more selected elements. 6. The film thickness of the precursor of the metal colloid thin film is 5
2. The method for forming a metal wiring according to claim 1, wherein the thickness of the metal wiring is in the range of from 600 to 600 nm.