JP2013007076A - Method for producing metal fine particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing metal fine particles for desorbing a surfactant and amine from the metal fine particles at a low temperature, when a base material is coated with a dispersing liquid in which metal fine particles are stably dispersed without being flocculated in a solvent, and also, the metal fine particles are dispersed in an isolated state, and firing is performed.SOLUTION: A metal raw material and a solvent including a surfactant and imine are stored into a tank, the metal raw material is heated under reduced pressure so as to be evaporated, and the evaporated matter is collected and is introduced into the solvent to obtain a metal fine particle-containing liquid made by dispersing into the solvent, the metal fine particles in which the entire surface is coated with the surfactant and the amine obtained by hydrolyzing the imine. Next, a polar solvent is added to the metal fine particle-containing liquid, thus the metal fine particles are settled. The solvent is removed, and the settled metal fine particles are recovered.

Description

  The present invention relates to a method for producing metal fine particles, and more particularly to a method for producing metal fine particles used for forming a predetermined film such as a metal wiring or a transparent conductive film by an ink jet method.

  In the manufacturing process of a semiconductor device, it is conventionally known to use a so-called inkjet method for forming a predetermined film such as a metal wiring film or a transparent conductive film. In this apparatus, using an in-jet type coating apparatus, a dispersion liquid in which metal fine particles are dispersed is directly applied to the surface of the substrate, and the applied dispersion liquid is dried and baked to obtain a predetermined film. According to this, a lithography process, an etching process, etc. can be skipped, and there exists an advantage that equipment cost and production cost can be reduced.

  As a method for producing the metal fine particles, for example, Patent Document 1 discloses the use of a gas evaporation method. In this method, a metal raw material and a predetermined organic solvent are accommodated in a tank, the metal raw material is evaporated in an inert gas atmosphere under reduced pressure, and when the evaporated metal vapor is cooled and collected, The surface of the metal is brought into contact with an organic solvent at the stage where the vapor of the solvent is introduced by introducing a vapor of the solvent, and a metal fine particle-containing liquid in which the obtained metal particles are singly and uniformly dispersed in a colloidal form in the organic solvent is obtained. Then, in order to improve the dispersion stability of the metal fine particles, at least one selected from alkylamines, carboxylic acid amides, and aminocarboxylates is added to and mixed with the metal fine particle-containing liquid thus obtained. .

  Next, a step of adding a low molecular weight polar solvent to precipitate the metal fine particles and allowing the supernatant liquid to flow out by decantation is repeated a plurality of times to remove the organic solvent. Thereby, metal fine particles having a particle size of 100 nm or less are recovered. In addition, the metal fine particles which are the precipitates thus obtained are subjected to solvent substitution by adding one or more kinds of solvents for dispersing the fine metal particles in the isolated state, and the dispersion liquid in which the fine metal particles are dispersed in the isolated state. And applied to the substrate surface as described above.

  By the way, in recent years, various substrates such as resin and paper are used as a base material in addition to a glass substrate, and further performance improvement and productivity improvement of a semiconductor device are required. For this reason, a further reduction in resistance is required for the predetermined film formed by the above method, and low temperature firing (for example, 150 ° C.) is required when the dispersion is dried and fired. In order to achieve such an object, the dispersant for coating the metal fine particles in the dispersion needs to be detached from the metal fine particles at a low temperature. When the dispersant is detached from the surface of the metal fine particles, the surfaces of the metal fine particles become active, and the metal fine particles are sintered and fused together. As a result, the fired film exhibits conductivity. As a dispersant that desorbs from metal fine particles at a low temperature, an organic dispersant having a low carbon number and a low boiling point is generally used.

  However, when a low boiling point dispersant having a small number of carbon atoms is used, the dispersion stability of the metal fine particles is reduced, and the metal fine particles aggregate and settle in the dispersion. Even if such a dispersion having low dispersion stability is applied, a uniform coating film cannot be formed, and as a result, the dispersant cannot be detached from the surface of the metal fine particles at a low temperature.

JP 2002-121606 A

  In view of the above points, the present invention is a method in which metal fine particles are stably dispersed without agglomerating in a solvent, and a dispersion liquid in which metal fine particles are dispersed in an isolated state is applied to a substrate and fired. Thus, an object of the present invention is to provide a method for producing metal fine particles exhibiting excellent conductivity when the dispersant is detached from the surface of the metal fine particles and the fine particles are sintered together.

  In order to solve the above-mentioned problems, the metal fine particle production method of the present invention contains a metal raw material and a solvent containing a surfactant and an imine in a tank, and heats and vaporizes the metal raw material under reduced pressure. Collecting the evaporated material and bringing it into contact with a solvent to obtain a metal fine particle-containing liquid in which metal fine particles are dispersed in the solvent; and adding a polar solvent to the metal fine particle-containing liquid to add a metal fine particle And a step of removing the solvent and recovering the precipitated fine metal particles.

  According to the present invention, the metal raw material is evaporated under reduced pressure (may be an inert gas atmosphere), and the evaporated material is collected and introduced into the solvent and brought into contact in the metal grain growth stage. . At this time, since the solvent contains a surfactant and imine and nothing is adsorbed on the surface of the metal fine particles, the imine is hydrolyzed on the surface of the metal fine particles to produce amine, and the metal fine particles in contact with the solvent Is covered with amine and surfactant over its entire surface. As a result, the metal fine particles of the present invention have higher dispersibility, and the metal fine particles exhibit excellent dispersion stability, so that aggregation of the metal fine particles can be reliably prevented. Furthermore, if the surfactant or amine that coats the metal fine particles has a low boiling point, a low temperature of 60 ° C. or higher and 150 or lower is required when a dispersion in which the metal fine particles are dispersed in an isolated state is applied to the substrate and fired. The dispersing agent such as the surfactant and amine can be removed from the surface of the metal fine particles by calcination. As a result, since the fine particles sinter, the fired film exhibits excellent conductivity. In the present invention, the metal fine particles mean those having a particle size of 100 nm or less (typical particle size is 1 nm to 10 nm). In the present invention, the metal fine particle dispersion includes metal fine particle ink and metal fine particle paste.

  In the present invention, organic solvents such as methyl oleate, benzyl acetate, ethyl stearate, ethyl phenylacetate and glyceride, tetradecane, hexadecane and terpineol can be preferably used as the solvent.

  In the present invention, the imine is obtained by dehydration condensation of a ketone and an amine having 4 to 14 carbon atoms having at least one structure selected from linear, branched and cyclic. Can be used. As this ketone, at least one selected from acetone, methyl ethyl ketone and methyl propyl ketone can be preferably used. Further, as this amine, butylamine having 4 carbon atoms; pentylamine having 5 carbon atoms; hexylamine, cyclohexylamine, aniline having 6 carbon atoms; heptylamine having 7 carbon atoms; octylamine having 8 carbon atoms, 2-ethylhexylamine; At least one selected from nonylamine having 9 carbon atoms; decylamine having 10 carbon atoms; dodecylamine having 12 carbon atoms; and tetradodecylamine having 14 carbon atoms can be preferably used. If the amine has less than 4 carbon atoms, the dispersion stability of the metal fine particles may be reduced, and when the metal fine particles are produced by the evaporation method, the amine is exhausted from the tank for producing the metal fine particles. In some cases, the surface of the metal fine particles cannot be coated. On the other hand, when the number of carbon atoms exceeds 14, it is difficult for amine to be detached from the surface of the metal fine particles at a low temperature during firing, resulting in an increase in firing temperature.

  In the present invention, as the surfactant, a carboxylic acid having 6 to 12 carbon atoms having at least one structure selected from linear, branched, and cyclic can be used. As this carboxylic acid, C6 hexanoic acid, 2-ethylbutyric acid; C7 heptanoic acid, 2-methylhexanoic acid, cyclohexanecarboxylic acid; C8 octanoic acid, neohexanoic acid, 2-ethylhexane At least one selected from acid; nonanoic acid having 9 carbon atoms; neooctanoic acid and decanoic acid having 10 carbon atoms; undecanoic acid having 11 carbon atoms; neodecanoic acid and dodecanoic acid having 12 carbon atoms; and tetradecanoic acid having 14 carbon atoms. These carboxylic acids can be preferably used. When the carbon number of the carboxylic acid is less than 6, the dispersion stability of the metal fine particles may be lowered. When the metal fine particles are generated by the evaporation method, the carboxylic acid is removed from the tank for generating the metal fine particles. May be exhausted and the surface of the metal fine particles may not be covered. On the other hand, if the number of carbon atoms exceeds 12, it becomes difficult for carboxylic acid to be detached from the surface of the metal fine particles at a low temperature during firing, leading to an increase in firing temperature.

  The amount of imine used in the present invention is preferably set so that the imine is 0.01 g to 1 g, more preferably 0.05 g to 0.5 g, with respect to 1 g of the metal fine particles. . The amount of carboxylic acid used in the present invention is preferably set so that the amount of carboxylic acid is 0.1 g to 10 g with respect to 1 g of imine, and is set to be 0.2 g to 1.0 g. Is more preferable. By setting the amounts of imine and carboxylic acid in this way, it becomes possible to more appropriately control the amounts of amine and carboxylic acid covering the surface of the metal fine particles.

  The metal used in the present invention is composed of at least one metal selected from Ag, Au, Cu, Ni, Pd, In, Sn, Rh, Ru, Pt, In, and Sn, or at least two of these metals. It is an alloy and can be appropriately selected depending on the purpose and application.

The electron micrograph of the metal microparticle obtained by this invention. (A) And (b) is a graph which shows the result of the thermogravimetric-differential thermal analysis of the metal microparticle of this invention.

  Hereinafter, the method for producing fine metal particles according to the embodiment of the present invention will be described by taking the case of producing fine Ag particles as an example. The tank contains an Ag raw material, which is a metal raw material, and a solvent containing a surfactant and an imine. The Ag raw material is heated and evaporated by high-frequency induction heating under a reduced pressure of 10 Pa or less, and the evaporated material is captured. Collect and contact with the solvent in the tank. At this time, the imine contained in the solvent is easily hydrolyzed on the surface of the Ag fine particle to produce an amine, and the entire surface of the Ag fine particle is covered with the produced amine and the surfactant. As a result, an Ag fine particle-containing liquid (product liquid) is obtained in which Ag fine particles whose entire surface is covered with an amine and a surfactant are dispersed in a solvent.

  Here, as the solvent, organic esters such as methyl oleate, benzyl acetate, ethyl stearate, ethyl phenylacetate and glyceride, tetradecane, hexadecane and terpineol can be preferably used.

  As the imine, one obtained by dehydration condensation of a ketone and an amine can be used. As the ketone used as a raw material for obtaining imine, it is preferable to use at least one selected from acetone, methyl ethyl ketone and methyl propyl ketone. As the amine used as a raw material for obtaining imine, an aliphatic amine or aromatic amine having 4 to 14 carbon atoms and having at least one structure selected from linear, branched and cyclic is used. Can do. Specifically, butylamine having 4 carbon atoms; pentylamine having 5 carbon atoms; hexylamine, cyclohexylamine, aniline having 6 carbon atoms; heptylamine having 7 carbon atoms; octylamine having 8 carbon atoms, 2-ethylhexylamine; It is preferable to use at least one amine selected from nonylamine having 9 carbon atoms; decylamine having 10 carbon atoms; dodecylamine having 12 carbon atoms; and tetradodecylamine having 14 carbon atoms. When the number of carbon atoms of the amine is less than 4, the dispersion stability of the metal fine particles may be lowered, and when the metal fine particles are generated by the evaporation method, the amine is removed from the tank used for obtaining the metal fine particles. The surface of the metal fine particles may be unable to be coated with amine due to exhaust. On the other hand, if the number of carbon atoms of the amine exceeds 14, it is difficult for the amine to be detached from the surface of the metal fine particles at a low temperature during firing, leading to an increase in the firing temperature.

  As the surfactant, a carboxylic acid having 6 to 12 carbon atoms having at least one structure selected from linear, branched and cyclic can be used. Specifically, C6 hexanoic acid, 2-ethylbutyric acid; C7 heptanoic acid, 2-methylhexanoic acid, cyclohexanecarboxylic acid; C8 octanoic acid, neohexanoic acid, 2-ethylhexane At least one selected from acid; nonanoic acid having 9 carbon atoms; neooctanoic acid and decanoic acid having 10 carbon atoms; undecanoic acid having 11 carbon atoms; neodecanoic acid and dodecanoic acid having 12 carbon atoms; and tetradecanoic acid having 14 carbon atoms. It is preferable to use it. When the carbon number of the carboxylic acid is less than 6, the dispersion stability of the metal fine particles may be lowered. When the metal fine particles are generated by the evaporation method, the carboxylic acid is removed from the tank for generating the metal fine particles. May be exhausted, and the surface of the metal fine particles may not be covered with carboxylic acid. On the other hand, when the carbon number of the carboxylic acid exceeds 12, it becomes difficult for the carboxylic acid to be detached from the surface of the metal fine particles at a low temperature during firing, resulting in an increase in the firing temperature.

  Further, as the metal raw material, for example, in addition to Ag, at least one metal selected from Au, Cu, Ni, Pd, Rh, Ru, Pt, In, and Sn, or at least two of these metals is used. The alloy can be appropriately selected depending on the purpose and application.

  The Ag fine particle-containing liquid obtained as described above is discharged from the discharge port of the tank, a polar solvent such as acetone is added to the Ag fine particle-containing liquid to precipitate the Ag fine particles, and the supernatant liquid is discharged by decantation or the like. (Hereinafter, this operation is referred to as “cleaning step”). This washing step is repeated a plurality of times to remove the solvent and collect the precipitated Ag fine particles. A solvent for dispersing the collected Ag fine particles in an isolated state is added to obtain an Ag fine particle dispersion. As the solvent for obtaining the Ag fine particle dispersion, it is preferable to use an organic solvent having a weak polarity and having 6 to 18 carbon atoms in the main chain. For example, toluene, hexane, heptane, octane, Long chain hydrocarbons such as decane, undecane, dodecane, tridecane, tetradecane, tetradecene, hexadecane, and cyclics such as cyclohexane, cycloheptane, cyclooctane, cyclododecene, benzene, ethylbenzene, xylene, trimethylbenzene, dodecylbenzene These hydrocarbons, hexanol, heptanol, octanol, decanol, cyclohexanol, and terpineol can be used alone or in admixture.

  Next, the Ag fine particle dispersion is heated and concentrated to a predetermined concentration (for example, 60% by weight when used as an Ag fine particle ink and 80% by weight when used as an Ag fine particle paste). Then, the concentrated Ag fine particle dispersion is directly applied to the surface of the glass as a base material by an inkjet method, and the applied dispersion is dried and baked at a temperature of 60 ° C. or higher and 150 ° C. or lower to form an Ag wiring. The As the substrate, in addition to glass, for example, polyimide, PEN film, polycarbonate, PET film, or a substrate in which a TFT (thin film transistor) is formed on glass can be used.

  In the embodiment described above, the material obtained by evaporating the Ag raw material is collected in the tank under reduced pressure, and introduced into the solvent and brought into contact in the Ag grain growth stage. At this time, the solvent contained a surfactant and an imine. For this reason, when the imine contacts the surface of the metal fine particle, the imine is hydrolyzed back to the amine, and the surface of the metal fine particle is coated with the amine and the surfactant. When the imine is brought into contact with the surface of the metal fine particle in this way, the surface of the metal fine particle is coated in the process where the imine is hydrolyzed to become an amine. The surface of the fine particles is more strongly coated with the amine. As a result, the metal fine particles can improve dispersion stability without agglomeration.

  Here, in order to coat the metal fine particle surface with an amine, it is conceivable to introduce an amine into the tank from the beginning. However, it is difficult for the amine and the carboxylic acid used as the surfactant to coexist stably in the tank, and the amine easily reacts with the carboxylic acid as the surfactant to form a salt or an amide. As described above, when the reaction between the amine and the carboxylic acid as the surfactant occurs, the reaction between the surface of the metal fine particles and the amine and the surfactant is inhibited. As a result, the entire surface of the metal fine particles is not covered with the amine and the carboxylic acid as the surfactant, and the dispersion stability of the metal fine particles is lowered. If an attempt is made to form a coating film by an ink jet method using a dispersion liquid having such a low dispersion stability, there arises a problem that the nozzles of the ink jet head for discharging droplets are blocked.

  On the other hand, in this embodiment, since imine is introduced into the tank, unnecessary reaction between the amine and the carboxylic acid as the surfactant can be avoided. Therefore, the reaction between the surface of the metal fine particle and the amine and the surfactant is not inhibited, and the entire surface of the metal fine particle is coated with the amine and the carboxylic acid as the surfactant as described above, and the dispersion stability of the metal fine particle is improved. improves.

  Further, it is obtained when a carboxylic acid having 4 to 12 carbon atoms is used as a surfactant, and at least one selected from acetone, methyl ethyl ketone and methyl propyl ketone and an amine having 4 to 14 carbon atoms are used as a raw material for imine. Since the metal fine particles also have high dispersion stability, when a dispersion liquid in which the metal fine particles are dispersed in an isolated state is applied to a substrate and fired, the surfactant is applied from the surface of the metal fine particles at a low temperature of 60 ° C. or more and 150 or less. And the amine can be eliminated.

  Hereinafter, a solvent containing methyl oleate containing octanoic acid and an imine described later is used to produce Ag fine particles using Ag raw materials, and to produce an Ag fine particle dispersion that can be applied by an inkjet method using Ag fine particles. The case where it does is demonstrated.

  Prior to the production of Ag fine particles, acetone and dodecylamine are dehydrated and condensed to produce the imine. And while containing 400g of Ag raw materials in the crucible in a vacuum chamber, what contains 50g of octanoic acid and the said imine in 5kg of methyl oleate as a solvent is accommodated in the bottom part in a vacuum chamber. And the inside of a vacuum chamber is evacuated, He gas is supplied in a vacuum chamber, and the pressure in a vacuum chamber is controlled to 10 Pa or less.

  Next, the Ag raw material is evaporated by high-frequency induction heating, the evaporated material is collected, introduced into the solvent in the Ag grain growth stage, and brought into contact with it to contain Ag fine particles dispersed in the solvent. A liquid is obtained. At this time, imine is easily hydrolyzed on the surface of the Ag fine particles to produce dodecylamine, and the Ag fine particles are covered with dodecylamine and octanoic acid over the entire surface. In this case, the amount of imine is set in the range of 0.01 to 1 g with respect to 1 g of the Ag raw material, and the amount of octanoic acid as a surfactant is set in the range of 0.1 to 10 g with respect to 1 g of the Ag raw material. Then, the average particle diameter of Ag fine particles can be controlled to 2 to 20 nm.

  Acetone is added to the Ag fine particle-containing liquid taken out from the vacuum chamber to precipitate the Ag fine particles, and the supernatant liquid is discharged by decantation or the like (cleaning step). This washing step is repeated a plurality of times to remove the solvent and collect the precipitated Ag fine particles. Tetradecane is added to the collected Ag fine particles to obtain an Ag fine particle dispersion.

  Next, the Ag fine particle dispersion is heated under reduced pressure and concentrated to a concentration of 60% by weight. The concentrated Ag fine particle dispersion is directly applied to the surface of the glass as a base material by an ink jet method, and the applied dispersion is dried. And baking at a temperature of 150 ° C. to form an Ag wiring. At this time, since the dispersion stability of the Ag fine particle dispersion is high, the nozzles of the inkjet head will not be blocked.

  In the embodiment described above, the material obtained by evaporating the Ag raw material is collected under reduced pressure and obtained by dehydration condensation of octanoic acid and the above imine (acetone and dodecylamine) to methyl oleate in the Ag grain growth stage. It was introduced and brought into contact with a product containing imine). At this time, imine is hydrolyzed on the surface of the Ag fine particles to produce dodecylamine, and the Ag fine particles are covered with dodecylamine and octanoic acid over the entire surface. Thereby, the dispersibility of Ag fine particles can be further improved, and the dispersion stability of Ag fine particles can be improved.

  The octanoic acid and dodecylamine covering the entire surface of the Ag fine particles have 8 and 12 carbon atoms, respectively, and the Ag fine particles have high dispersion stability as described above, so that the Ag fine particles are in an isolated state. When the dispersion liquid dispersed in (1) is applied to a substrate and baked, octanoic acid and dodecylamine can be eliminated at a low temperature of 150 ° C. or lower.

  Next, in order to confirm the effect of the above embodiment, the following experiment (Experiment 1) was performed. In this experiment 1, an Ag fine particle dispersion in which Ag fine particles whose entire surface was covered with octanoic acid and 2-ethylhexylamine was dispersed in tetradecane in an isolated state was heated to concentrate to a concentration of 60% by weight, and concentrated. The Ag fine particle dispersion is applied to the surface of the substrate by spin coating, dried, and then baked in an air atmosphere at a temperature of 150 ° C. for 1 hour in a hot plate to form a silver glossy Ag film on the surface. Formed (Invention 1).

  When an SEM photograph of this product 1 (average particle size: 10.8 nm, total weight ratio of 2-ethylhexylamine and octanoic acid to Ag fine particles: 19.4%) was taken, as shown in FIG. Was confirmed to be highly dispersible without condensing. And when surface resistance and a film thickness were measured in three places of the invention product 1, and the specific resistance value was calculated | required from the measurement result, as shown in Table 1, the specific resistance value similar to pure Ag was obtained. According to this, it can be seen that the Ag film can be reduced in resistance and fired at a low temperature. For measurement of the surface resistance, a Lorester made by Mitsubishi Chemical was used.

  Next, another experiment (Experiment 2) was performed in the same manner as Experiment 1 above. In this experiment 2, an Ag film (invention 2) formed using Ag fine particles whose entire surface was covered with 2-ethylhexanoic acid and octylamine, and Ag fine particles whose entire surface was covered with trimethylacetic acid and octylamine were used. The Ag film (Invention product 4) formed using the Ag film (Invention product 3) and the Ag film (Invention product 4) using Ag fine particles whose entire surface was covered with cyclohexanecarboxylic acid and octylamine were compared in the same manner as in Experiment 1 above. When the resistance value was determined, specific resistance values as shown in Table 2 were obtained. According to this, it was found that the Ag film can be reduced in resistance and fired at a low temperature.

  Next, for comparison with the above invention products 1 to 4, the Ag film (comparative product 1) formed using Ag fine particles having oleic acid (carbon number 18) and dodecylamine adsorbed on the surface, and stearic acid With respect to an Ag film (Comparative Product 2) formed using Ag fine particles (carbon number 18) and octylamine adsorbed on the surface, measurement of the specific resistance value was attempted in the same manner as in Experiment 1 (Experiment 3). However, it was found that the Ag films according to the comparative product 1 and the comparative product 2 were burnt and did not conduct at all and could not be fired at a low temperature.

  Next, when the firing temperature of the invention product 1 was changed in the range of 50 ° C. to 350 ° C. and differential thermal-thermogravimetric analysis (TG-DTA analysis) was performed (Experiment 4), the results shown in FIG. 2 were obtained. It was. FIG. 2 also shows the results of the comparative product 1 for comparison with the inventive product 1. According to this, since the TG-DTA peak of Invention Product 1 was seen on the lower temperature side than that of Comparative Example 1, it was confirmed that low-temperature firing was possible.

  In addition, this invention is not limited to the said embodiment, It can deform | transform.

Claims (6)

A metal raw material and a solvent containing a surfactant and imine are accommodated in the tank, the metal raw material is heated and evaporated under reduced pressure, and the evaporated material is collected and brought into contact with the solvent. Obtaining a metal fine particle-containing liquid in which metal fine particles are dispersed in a solvent;
Adding a polar solvent to the metal fine particle-containing liquid to precipitate the metal fine particles;
And a step of recovering the precipitated fine metal particles after removing the solvent.   The imine is obtained by dehydration condensation of a ketone and an amine having 4 to 14 carbon atoms having at least one structure selected from linear, branched and cyclic structures. The method for producing metal fine particles according to claim 1.   The said surfactant is C6-C12 carboxylic acid which has at least 1 sort (s) of structure chosen from linear, branched, and cyclic, The Claim 1 or Claim 2 characterized by the above-mentioned. A method for producing fine metal particles.   The method for producing metal fine particles according to any one of claims 1 to 3, wherein the amount of imine relative to 1 g of metal fine particles is set within a range of 0.01 g to 1 g.   The method for producing metal fine particles according to any one of claims 1 to 4, wherein the amount of the surfactant with respect to 1 g of the metal fine particles is set within a range of 0.1 g to 10 g.   The raw material of the metal fine particles is at least one metal selected from Ag, Au, Cu, Ni, Pd, In, Sn, Rh, Ru and Pt, or an alloy composed of at least two of these metals. The method for producing metal fine particles according to any one of claims 1 to 5, characterized in that: