JP2006159014A - Method of forming metallic film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a metallic film by which the metallic film having high adhesion to a substrate is stably formed without the limitation by the shape of the substrate and the cost on the formation is reduced. <P>SOLUTION: A metal fine particle dispersed solution 3 prepared by dispersing the metal fine particles in a volatile solvent is applied on a required part of the substrate 10 by an inkjet method and the applied metal fine particle dispersed solution 3a is heated to evaporate the solvent to deposit a metal 3b on the substrate 10. The deposited metal (a metallic film 11) is heat treated. The above steps can be repeated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a metal film, and more particularly to a method for forming a metal film using an inkjet method.

  Conventionally, as a method of forming a metal film such as a wiring pattern, an electrolytic plating method and an electroless plating method are known. In the electroplating method, since plating is performed by using an object to be plated immersed in a plating solution (an object to be plated) as a cathode, current must be applied to the area to be plated of the object. For this reason, depending on the wiring pattern, it is necessary to employ a method in which a dummy wiring, a seed layer, or the like is provided and energized therethrough. However, it has become very difficult to adopt such a method due to recent pattern miniaturization.

  In addition, since the object to be plated is immersed in the plating solution and the plating reaction occurs at the place where it is in contact with the plating solution, the plating reaction occurs uniformly if the current density is the same. The current density varies depending on the shape (irregularity etc.) of the film, and it is very difficult to make the deposition rate uniform over the entire surface. For this reason, when the surface area of the object to be plated is large, the thickness of the film varies, which causes an increase in cost.

  In addition, in the conventional electrolytic plating, as a pretreatment such as plating or resist coating, alkali degreasing (treatment to remove oils and fats adhering to the metal surface), acid cleaning (oxide generated on the metal surface is converted to sulfuric acid or hydrochloric acid) For example, a large-scale capital investment such as plating equipment, pure water production equipment, and drainage equipment is required.

  On the other hand, the electroless plating method is a “chemical” plating process in which a metal is reduced with a reducing agent or deposited by metal replacement on the surface of an object to be plated immersed in a plating solution without passing an electric current. Therefore, there is a merit that dummy wiring and the like required by the electrolytic plating method are unnecessary. However, as in the case of the electrolytic plating method, a large capital investment is required, and particularly when performing electroless gold (Au) plating, the problem is that the plating solution is unstable. That is, the lifetime of the plating solution is limited, and the cost is very high depending on the frequency of renewal, and it is particularly not suitable for thick Au plating.

  In addition, what can be said in common with wet electrolysis / electroless plating methods is that the process from the pretreatment of the base (such as surface cleaning activation) to plating to drying treatment is very long, and partial plating with a limited plating area is required. In order to do this, there is a problem that an expensive device (equipment) is required.

  In recent years, a technique using an ink jet method has been proposed as a method for forming a film by a relatively simple method against such a wet plating method. In film formation using this ink jet method, for example, an ink obtained by dispersing metal fine particles such as gold (Au) in an alcohol solvent is used as ink, and the ink conveyed from the ink supply unit is ejected from the nozzle. Thus, ink is applied to a required portion on the base (substrate), and the solvent evaporates to obtain a wiring pattern composed of metal fine particles.

As a technique related to such an ink jet method, for example, as described in Patent Document 1, a plating layer is formed by applying an electroless plating solution by an ink jet method onto a conductive pattern previously formed on a base substrate. Some of them are designed to control the thickness. Further, as described in Patent Document 2, a conductive pattern is directly formed on an insulating substrate by an ink jet method using an ink made of an independent dispersion of ultrafine metal particles, and after firing, electroplating is performed thereon to conduct the conductive process. Some have a pattern formed.
JP 2002-26491 A JP 2003-209341 A

  As described above, in the film formation using the conventional inkjet method, although the solvent of the ink applied on the base (substrate) evaporates and the metal fine particles remain, the metal fine particles only adhere to the substrate and the adhesion strength is increased. Since it is not so high, a highly reliable wiring pattern (metal film) is not always obtained. For this reason, there is a demand for a technique for forming a metal film having high adhesion to a base by an ink jet method.

  Note that neither Patent Document 1 nor Patent Document 2 considers the problem of low adhesion to the base when the conductive pattern is formed using the inkjet method.

  The present invention was created in view of the problems in the prior art, and can stably form a metal film having high adhesion to the base without being limited to the shape of the base, and can reduce the cost of manufacturing. An object is to provide a method of forming a metal film that can contribute.

  In order to solve the above-described problems of the prior art, according to the basic form of the present invention, a metal fine particle dispersion solution in which metal fine particles are dispersed in a volatile solvent is applied to a required portion of a base by an inkjet method. Heating the applied metal fine particle dispersion to evaporate the solvent, depositing the metal on the underlayer to form a metal film, and subjecting the formed metal film to a heat treatment And a method of forming a metal film.

  According to the method for forming a metal film according to the present invention, after the metal fine particle dispersion applied on the base by the inkjet method is heated to evaporate the solvent, the metal is deposited on the base to form the metal film, Since the heat treatment is performed on the metal film, the metal film is formed with high adhesion strength to the base.

  In addition, since the metal fine particle dispersion solution (ink) is sprayed toward a required portion of the object (base) by the ink jet method, the metal is almost uniformly applied to the surface without being limited by the shape of the surface of the base. Fine particles can be deposited (formation of a uniform metal film). Furthermore, since the metal film is directly formed on the surface of the base by the ink jet method, the apparatus (equipment) for manufacturing is compared with the conventional method of forming the metal film using plating, photolithography, or the like. Is simplified, and the process is also simplified, so that the manufacturing cost can be reduced.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  1 and 2 schematically show a method for forming a metal film according to an embodiment of the present invention in the order of steps, and FIG. 3 shows an inkjet method related to processing performed in a part of the steps. It is a figure for demonstrating.

  The metal film formed by the method for forming a metal film according to the present embodiment is used as a wire bonding pad or a solder ball bonding pad, as will be described later. Therefore, required wire bonding characteristics or solder wettability is used. The metal film is formed so as to satisfy the above. Further, an object (base) to which the metal film forming method according to the present embodiment is applied is a metal portion in a printed circuit board wiring, a semiconductor hermetic component, a semiconductor ceramic package, or the like. The metal film forming method according to the present embodiment can be carried out, for example, using a patterning apparatus previously proposed by the applicant (April 21, 2003, Japanese Patent Application No. 2003-115240).

  First, in the first step (see FIGS. 1A and 3), a base 10 on which a metal film is to be formed is placed on the support 1 (in this case, the stage in the patterning apparatus), and the patterning is performed. The ink 3 is ejected from the inkjet nozzle 2 in the apparatus toward a required portion (a portion where a metal film is formed) on the base 10 and applied onto the base 10.

  In this embodiment, as the ink 3, a solution (Au fine particle dispersion solution) in which fine particles of gold (Au) are dispersed in a volatile solvent (alcohol, toluene, ethyl acetate, butyl acetate, ether, etc.) is used. Yes. In addition, the object to be the base 10 is a metal body in the present embodiment, for example, a connector made of an alloy (steel) containing iron (Fe) as a main component and containing nickel (Ni), manganese (Mn), or the like. Part of the terminal.

  As the means for applying the ink 3, there are several types as illustrated in FIG.

  FIG. 3A shows an example of a bubble jet (registered trademark) coating means. On the left side, a state in which the ink 3 supplied from the ink supply unit 6 in the patterning device is filled in the nozzle 2 is shown, and in this state, the ink jet control unit 5 in the patterning device has When the heating element 4 provided in the nozzle 2 is heated based on the control, bubbles 7 are generated in the ink 3 as shown on the right side, and a part of the ink 3 is pushed out from the tip of the nozzle 2 by the bubbles 7. Erupt outside.

  FIG. 3B shows an example of a piezoelectric conversion (piezo) drive type application means. As shown on the left side, the nozzle 2 is provided with a piezo element 8 that generates distortion based on the piezoresistive effect. When a predetermined voltage is applied to the piezo element 8 from the inkjet control unit 5a, the piezo element 8 is illustrated. The ink 3 is injected into the nozzle 2 from the ink supply unit 6. Then, as shown on the right side, by changing the voltage applied to the piezo element 8, the piezo element 8 swells as shown by the arrow in the figure, whereby a part of the ink 3 is pushed out from the tip of the nozzle 2. Spouts outside.

  The diameter and number of the nozzles 2 are not particularly limited. For example, when forming a wiring pattern on a wiring board, the diameter of the tip of the nozzle 2 is 30 μm to 80 μm (preferably about 50 μm), and the number is approximately 30 to 90. (Preferably about 60). As a result, even when the width, film thickness, etc. of the metal film pattern changes, it can be easily handled. Then, the nozzle 2 for ejecting the ink 3 is selected by the ink jet control units 5 and 5a, and the ejection amount and ejection timing of the ink 3 are controlled. In addition, the ejection time per time of the ink 3 is selected as 1 second in this embodiment.

  When the ink 3 is ejected from the inkjet nozzle 2 in this way, an ink coating layer 3a is formed on a required portion on the base 10, as shown in FIG. The thickness of the ink coating layer 3 a is about 0.4 μm per drop (50 μm) of the ink 3 ejected from the nozzle 2.

  In the next step (FIG. 1C), the ink coating layer 3a (Au fine particle dispersion solution) formed on the base 10 is heated at a predetermined temperature for a predetermined time to evaporate the solvent in the Au fine particle dispersion solution 3a. Let In this embodiment, the heating temperature is selected to be around 200 ° C., and the heating time is selected to be about 30 minutes. As the heating means, the whole support 1 may be put in a furnace previously maintained at a specified temperature (in this case, around 200 ° C.), or a heating means such as a heater is provided inside the support 1 in advance. It may be built in and used.

  By this heat treatment, the solvent evaporates as shown in the figure, and Au fine particles 3b are deposited on the base 10, thereby forming a thin Au film. The thickness of the Au film is about 0.13 to 0.18 μm with respect to the thickness of the ink coating layer 3a: 0.4 μm. At this stage, an Au film is formed on a required portion on the base 10, but the adhesiveness with the base 10 is not necessarily sufficient as it is.

Therefore, in the next step (FIG. 1D), the Au film 11 formed on the base 10 is further heat-treated in a nitrogen (N ₂ ) atmosphere so as to improve the adhesion with the base 10. To. In this step, the heating temperature is selected to be around 150 ° C., and the heating time is set to about 2 hours. At this stage, basically, the Au film 11 is formed in a state where the adhesion strength to the base 10 is high.

  However, when this Au film 11 is used as a pad for wire bonding, in order to satisfy the required wire bonding characteristics (gold (Au) wire, the tensile strength is 3 to 4 [gf]) Since the adhesiveness is not yet sufficient, a process for further increasing the thickness of the Au film 11 is performed by the following steps (FIGS. 2A to 2C).

  That is, in the process shown in FIG. 2A, the Au film 11 formed on the base 10 is formed from the inkjet nozzle 2 in the same manner as the process performed in the process of FIGS. 1A and 1B described above. Ink 3 is ejected toward the Au film 11 to form an ink coating layer 3a (indicated by a broken line in FIG. 2B).

  In the next step (FIG. 2B), the ink coating layer 3a (Au fine particle dispersion solution) formed on the Au film 11 is formed in the same manner as the processing performed in the step of FIG. The solvent in the Au fine particle dispersion solution 3a is evaporated by heating at a temperature around 30 ° C. for about 30 minutes. Then, Au fine particles 3b are deposited on the Au film 11 to form a thin Au film.

Further, in the next process (FIG. 2C), nitrogen (N ₂ ) is applied to the Au film 12 formed on the Au film 11 in the same manner as the process performed in the process of FIG. In the atmosphere, the film is heated at a temperature of about 150 ° C. for about 2 hours to enhance the adhesion of the Au film 12 to the base 10.

  Through the above steps, a metal film (Au film 12) having the required wire bonding characteristics intended in the present embodiment is formed.

As described above, according to the method for forming a metal film (FIGS. 1 to 3) according to the present embodiment, the ink 3 applied on the base 10 is heated by the ink jet method to evaporate the solvent, and the base 10 After Au fine particles 3b are deposited thereon to form a metal film (Au films 11 and 12), heat treatment (heating at about 150 ° C. for about 2 hours in a nitrogen (N ₂ ) atmosphere) is performed on the metal film. As a result, the metal films (Au films 11 and 12) are formed on the base 10 with high adhesion strength.

  FIG. 4 shows an example of the effect in comparison with the comparative example. Wire bonding characteristics when the Au film 12 is used as a wire bonding pad (when a gold (Au) wire is used as a bonding wire) The tensile strength [gf]) is shown. In the example shown in the figure, three characteristics are shown. Among these, the characteristics of “inkjet × twice” are related to the present embodiment, and the other two “current products (method using electrolytic plating)”, “Au strike plating + inkjet” shows a comparative example. The tensile strength of the gold (Au) wire is usually sufficient if it is 3 to 4 [gf] or more, and those according to this embodiment sufficiently satisfy this condition.

  Further, since the ink 3 is ejected toward a desired portion of the object (base 10) by the ink jet method, the metal particles (Au) are almost uniformly formed on the surface without being limited by the shape of the surface of the base 10. Particles) can be deposited (formation of a uniform Au film). In addition, since the metal films (Au films 11 and 12) are directly formed on the surface of the base 10, compared to the conventional method of forming a metal film using plating, photolithography, or the like, it is easier to manufacture. Since such an apparatus (equipment) is simplified and a process (process) is also simplified, manufacturing costs can be reduced.

  In addition, since the ink 3 only needs to be applied to the necessary part on the base 10, the required metal film can be formed without wasting materials unlike the case of using conventional plating or photolithography. Can do. This contributes to further reduction in manufacturing costs. In particular, compared with the case where electroless Au plating is used, it is possible to significantly reduce the cost spent for renewing the conventional plating solution, which is advantageous.

  In addition, in the conventional metal film forming method using plating, photolithography, or the like, there is a problem that it takes a long time to form the film to increase the film thickness. However, the method according to the present embodiment has been described above. As described above, since the process for forming the metal film is simplified as compared with the conventional process, the process shown in FIGS. 1A to 1D is further repeated as necessary, so that the metal film having a required film thickness can be obtained in a short time. Can be formed. This contributes to a reduction in manufacturing costs.

  In the metal film formation method (FIGS. 1 and 2) according to the above-described embodiment, the Au film 11 adheres to the base 10 by performing a heat treatment (about 150 ° C./2 hours) in the process of FIG. The case where the adhesiveness is improved has been described as an example, but it is needless to say that the means for improving the adhesiveness is not limited to this. For example, “roughening treatment” that is generally used in the process of wiring substrates such as plastic packages and ceramic packages can be substituted.

  In this case, the roughening process is desirably performed on the base 10 at a stage before the ink 3 is applied in the first step (FIG. 1A). For example, the surface of the base 10 is roughened by a dry process using plasma or the like. As a result, an anchor effect can be given to the surface of the base 10, so that the ink coating layer 3a is formed in the subsequent process (FIG. 1B) and heated to evaporate the solvent (FIG. 1C). )), Since the precipitated Au particles 3b enter the anchor portion of the base 10, the adhesion of the Au film 11 to the base 10 can be improved. However, when this Au film 11 (finally the Au film 12) is used as a wire bonding pad, the surface of the Au film 12 exhibits an uneven shape if the surface of the base 10 is excessively roughened. The portion (pad) may not be able to hit the wire, and it is necessary to fully consider the degree of roughening. On the other hand, when this Au film 11 (Au film 12) is used as a solder ball bonding pad, such inconvenience does not occur.

It is sectional drawing which shows the process (the 1) of the formation method of the metal film which concerns on one Embodiment of this invention. FIG. 3 is a cross-sectional view showing a process (No. 2) following the process of FIG. 1. It is explanatory drawing of the inkjet method which concerns on the process performed at the process of Fig.1 (a). It is the characteristic view which showed the effect acquired by one Embodiment of this invention in contrast with the comparative example.

Explanation of symbols

2 ... (inkjet) nozzle,
3. Ink (metal fine particle dispersion),
3a: Ink coating layer (metal fine particle dispersion),
3b: Au particles deposited,
4 ... heating element,
5, 5a ... inkjet control unit,
6 ... Ink supply unit,
7 ... Bubbles,
8 ... Piezoelectric conversion (piezo) element,
10 ... Underlying object (object on which a metal film is deposited),
11, 12 ... Au film (metal film).

Claims (4)

A step of applying a metal fine particle dispersion solution in which metal fine particles are dispersed in a volatile solvent to a required portion of a base by an inkjet method;
Heating the applied metal fine particle dispersion to evaporate the solvent, depositing the metal on the base, and forming a metal film;
And a step of heat-treating the formed metal film.   A method for forming a metal film, wherein the steps constituting the method for forming a metal film according to claim 1 are further repeated. Roughening the surface of the substrate;
Applying a fine metal particle dispersion solution in which fine metal particles are dispersed in a volatile solvent to a required portion of the base by an ink jet method;
Heating the coated metal fine particle dispersion to evaporate the solvent, and depositing the metal on the base to form a metal film.   4. The method of forming a metal film according to claim 1, wherein the base is a metal body, and gold (Au) is used as a metal dispersed in the metal fine particle dispersion solution. 5.

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