JP2009070727A - Forming method of metal nanoparticle sintered body layer having fine pattern form - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a metal nanoparticle sintered body capable of attaining a high adhesion property in an interface of a base layer and a sintered body layer, by restraining degradation of bulk density, mechanical strength, and conductivity of the sintered body layer as a whole formed, and further, by heightening density of the sintered body layer as a whole obtained, in manufacturing a metal nanoparticle sintered body on a substrate by sintering metal nanoparticles at low temperature. <P>SOLUTION: Dispersion liquid with metal nanoparticles with a mean particle size of 1 to 100 nm having the surface coated with alkylamine dispersed in a hydrocarbon solvent with a boiling point of 150°C or more is coated on a substrate, and then is put under heat treatment at a temperature of 150 to 300°C under a non-pressurized reduction atmosphere to efficiently take off the alkylamine coating the surface and have the sintered body formed with excellent adhesiveness with the substrate through dense fusion among the metal nanoparticles themselves. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of forming a metal nanoparticle sintered body layer having a fine pattern shape. The present invention is particularly applicable to fine pattern shape drawing, and a dispersion of metal nanoparticles is applied on a substrate in a desired pattern shape, and the metal nanoparticles contained in the coating layer are sintered at a low temperature. It is related with the method of forming the metal nanoparticle sintered compact layer which has high electroconductivity on a board | substrate by processing.

  In recent years in the field of electronic equipment, miniaturization of wiring patterns on a wiring board to be used is progressing. In addition, regarding a metal thin film layer used for forming various electrode pattern portions, utilization of an extremely thin metal thin film layer is being promoted. For example, when fine wiring formation or thin film formation is achieved using screen printing, the application of a metal particle dispersion with a very small particle diameter is required for drawing ultrafine patterns or forming thin film coating layers with extremely thin film thickness. Is planned. At present, gold and silver fine particle dispersions that can be applied to the above-mentioned applications have already been commercialized.

In particular, regarding the method of forming an ultrafine wiring pattern using metal nanoparticles, for example, when using gold nanoparticles or silver nanoparticles, a methodology has already been established. For example, a sintered-type wiring obtained by drawing an extremely fine circuit pattern using a dispersion for ultra fine printing containing gold nanoparticles or silver nanoparticles, and then performing sintering between metal nanoparticles. In the layer, it is possible to form a wiring having a wiring width and a space between the wirings of 5 to 50 μm and a volume resistivity of 1 × 10 ⁻⁵ Ω · cm or less (see Patent Document 1 and Patent Document 2).

Specifically, in a dispersion for ultra fine printing containing gold nanoparticles or silver nanoparticles, the surface of gold nanoparticles or silver nanoparticles is coated with a coating molecule such as an amine compound, and then dispersed in a dispersion solvent. Distributed. After applying the dispersion for ultra fine printing in a desired pattern, it is dried to evaporate the dispersion solvent, and the coating molecules covering the surface of the metal nanoparticles are removed by heating to remove the metal of the metal nanoparticles. The surfaces are brought into contact with each other and sintered at a relatively low temperature.
JP 2002-334618 A Japanese Patent Laid-Open No. 2004-218055

  The method for producing the metal nanoparticle sintered body by sintering the above metal nanoparticles at a low temperature is to produce a metal nanoparticle sintered body excellent in conductivity by performing heat treatment at a relatively low temperature. It is possible. However, the obtained sintered body has a problem that the intended high conductivity cannot be achieved under conditions where the separation of the amine compound covering the metal nanoparticles cannot be sufficiently achieved.

  That is, after evaporating a dispersion solvent having a relatively low boiling point in advance, when the heat treatment is further performed, the amine compound covering the surface of the metal nanoparticles is detached from the metal surface, and the gas molecules of the amine compound are separated. And evaporates into the gas phase. At that time, in a state where the metal nanoparticles are laminated in layers, the gap space inside the laminated structure is occupied by the vaporized gas molecules of the amine compound. That is, in the state where the metal nanoparticles are laminated in layers, when the dispersion solvent having a relatively low boiling point evaporates and reaches a dry state, the interstitial space in the laminated structure is vaporized by the amine compound. It becomes a full state, and the detachment of the amine compound from the surface of the metal nanoparticles in the gap space proceeds only slowly. Even at this stage, since the coating layer of the amine compound that coats the surface of the metal nanoparticles has partially disappeared, if the metal nanoparticles contact each other in the local region where the coating layer has disappeared, The fusion of the nanoparticles proceeds and a sintered body layer is formed.

  On the other hand, the ratio of the local region in which the coating layer disappears with respect to the entire surface of the entire metal nanoparticles is determined by the local partial pressure of the amine compound molecules in the gas phase of the gap space at the heating temperature, As a result of achieving an equilibrium relationship between the surface density of the amine compound adsorbed on the surface of the metal nanoparticle, it becomes “saturated”. When the “saturated” state is reached, the separation of the amine compound stops in the interstitial space inside the laminated structure, and the fusion between the metal nanoparticles cannot proceed any further. As a result, in the formed sintered body layer, conductivity is imparted through the conduction path formed by the fusion of the metal nanoparticles, but the metal nanoparticles are fused. When the density of the locations is low, the overall conductivity remains low. In other words, when the density of the portions where the metal nanoparticles are in contact with each other is low at the time when the dispersion solvent having a relatively low boiling point is evaporated and dried to obtain a sintered state that is finally formed. A decrease in conductivity of the entire bonded layer is caused.

  In addition, as the fusion of metal nanoparticles progresses with the low temperature sintering process, the gap space existing inside the laminated structure of metal nanoparticles decreases, and the bulk density of the formed sintered body layer as a whole becomes Decrease. At that time, if the density of the portions where the metal nanoparticles are in contact with each other is low, the degree of reduction of the gap space is relatively low, and the bulk density of the entire sintered body layer finally formed is relatively low. It becomes a low state. In other words, when the bulk density of the entire sintered body layer is relatively low, a large amount of gap space remains inside the sintered body layer. If the density of the places where the metal nanoparticles are in contact with each other is low, the density of the connection places due to the fusion of the metal nanoparticles will be low, and the mechanical strength of the entire sintered body layer that will eventually be formed will also be low. It is relatively small.

  That is, the density of the places where the metal nanoparticles are in contact with each other is low, and if the contact area at the connection site due to the fusion between the metal nanoparticles is relatively small at each contact place, finally, The bulk density of the formed sintered body layer is relatively low. At that time, the density of the connection sites due to the fusion of the metal nanoparticles, the conductivity of the entire sintered body layer to be formed, and the mechanical strength are relatively low depending on the contact area. Become.

The present invention solves the aforementioned problems. The object of the present invention is to suppress the reduction in bulk density, mechanical strength, and conductivity of the entire sintered body layer when the metal nanoparticles are sintered at low temperature to produce a metal nanoparticle sintered body. The sintered metal layer produced in a fine pattern shape has high reproducibility, and the volume resistivity is in the range of 1 × 10 ⁻⁵ Ω · cm or less. It is in providing the manufacturing method of a zygote. In particular, when the sintering treatment temperature is selected in the range of 150 ° C. or more and 300 ° C. or less, which can be applied to the production of a fine patterned conductive layer on the substrate, the sintering treatment time can be suppressed to 1 hour or less. , Metal nanoparticles capable of reducing the bulk density, mechanical strength, and conductivity of the entire sintered body layer to be formed, and increasing the density of the entire sintered body layer, for example, with high reproducibility It is providing the manufacturing method of a sintered compact. Furthermore, by increasing the density of the entire sintered body layer obtained, a method for producing a metal nanoparticle sintered body capable of achieving high adhesion at the interface between the underlayer and the sintered body layer Is to provide.

  First, when manufacturing metal nanoparticle sintered bodies according to conventional procedures and conditions, the present inventors have factors that cause a decrease in the bulk density, mechanical strength, and conductivity of the entire sintered body layer to be formed. Further details were discussed. In the examination process, after applying a dispersion of metal nanoparticles, when the dispersion solvent having a relatively low boiling point contained in this coating layer is evaporated, the dispersed metal nanoparticles have a laminated structure. At this stage, the surface of the metal nanoparticles was found to have a considerable amount of coating molecule layer remaining. In that case, in the part where the coating material molecular layer remains, the metal nanoparticles are brought into contact with each other through the coating material molecular layer. At the site where the metal nanoparticles are in contact with each other via the coating molecule layer, heating is then performed to vaporize the coating molecules on the surface of the metal nanoparticles and remove the metal. It has been found that the metal surfaces of the nanoparticles are in contact with each other and have a low probability of causing fusion.

  In addition, when the dispersion solvent is evaporated and the gap space remaining around the metal nanoparticles becomes a gas phase, gas molecules contained in the surrounding atmosphere enter the gap space. For example, when oxygen molecules are included in the surrounding atmosphere, oxygen molecules gradually invade from the surface of the laminated structure of metal nanoparticles into the interior due to the diffusion process through the gap. In the heated state, the metal molecule on the surface is oxidized due to the invading oxygen molecules at the site where the coating molecule layer covering the metal nanoparticles is removed and the clean metal surface is exposed. As a result, an oxide film is formed on a part of the surface of the metal nanoparticles. Of course, the oxide film inhibits the progress of fusion between the metal nanoparticles at the site where the oxide film is partially formed on the surface. For example, in a state in which metal nanoparticles are laminated, fusion of metal nanoparticles starts from the point where metal nanoparticles are in contact with each other at that time, but then an oxide film is formed on the surface of metal nanoparticles At that stage, it was found that the progress of fusion was stopped.

On the other hand, in the state immersed in the dispersion solvent, when the surface density of the coating molecule that covers the surface of the metal nanoparticles is low, the ratio of the portions where the metal nanoparticles in the stacked state are in contact with the metal surface It has also been found that the ratio of the sites where the metal nanoparticles contact each other via the coating agent molecular layer rapidly decreases. In the part where the metal nanoparticles in the laminated state are in contact with each other on the metal surface, the fusion proceeds by low-temperature heating. Therefore, if the ratio of the part in which the metal nanoparticles are in contact with the metal surface increases, It was also confirmed that the entire metal nanoparticles showed significantly “bulk volume shrinkage” as the fusion progressed. As this “bulk volume shrinkage” proceeds, the metal nanoparticles are brought into contact with each other even at a site where a slight gap is initially present between the metal nanoparticles, and fusion is possible. Including this secondary effect, when the surface density of the coating molecule that covers the surface of the metal nanoparticles is lowered, the metal nanoparticles contained in the coating layer constitute a laminated structure, The fusion sites between the metal nanoparticles are formed at a high density. Furthermore, the contact area of each fusion site increases as the fusion of metal nanoparticles progresses. Therefore, in the laminated structure, the fusion sites between the metal nanoparticles are formed at a high density, the contact area of each fusion site is widened, and the sintered body in which the “bulk volume shrinkage” has sufficiently progressed. It was found that a layer was formed. As a result, the bulk density, mechanical strength, and electrical conductivity of the entire sintered body layer are excellent. For example, the electrical conductivity of the entire sintered body layer is high reproducibility and the volume resistivity is 1 × 10 ^−5. It has been found that it is possible to make the range Ω · cm or less.

  As a result of investigating the conditions for reducing the surface density of the coating agent molecules covering the surface of the metal nanoparticles at the time of the heat treatment, after applying the metal nanoparticle dispersion liquid, On the other hand, it was confirmed that the conditions for performing the heat treatment in the range of 150 ° C. to 300 ° C. in a non-pressurizing reducing atmosphere were suitable. That is, when the coating layer is heated in a non-pressurizing reducing atmosphere without being dried, the transpiration rate of the dispersion solvent contained in the dispersion is lowered. In the state where the coating is immersed, the detachment of the coating molecule proceeds, the surface density of the coating molecule covering the surface of the metal nanoparticle can be lowered, and a dense sintered metal nanoparticle is produced. It was confirmed.

  That is, when the heat treatment is carried out in a non-pressurizing reducing atmosphere, the transpiration of the dispersion solvent proceeds, and when the gap space remaining around the metal nanoparticles becomes a gas phase, Although gas molecules contained therein penetrate, the phenomenon that an oxide film is formed on the surface of the metal nanoparticles is avoided. Therefore, the phenomenon in which the progress of the fusion is hindered due to the formation of the oxide film is avoided, so that the fusion sites between the metal nanoparticles are formed at a high density inside the laminated structure, It was confirmed that the contact area of the fusion part was increased and a sintered body layer in which “bulk volume shrinkage” sufficiently progressed was formed.

  As a result of sufficient progress of “bulk volume shrinkage”, the density of the entire sintered body layer is increased, so that high adhesion can be achieved at the interface between the underlying layer and the sintered body layer. It was also confirmed that.

  Based on the above-described series of findings, the inventors have completed the present invention.

That is, the method of forming a finely patterned metal nanoparticle sintered body layer according to the present invention is:
A method of forming a conductive layer having a fine pattern shape composed of sintered layers of metal nanoparticles on a substrate,
Drawing an application layer having a desired fine pattern shape on a substrate using a dispersion containing metal nanoparticles, selecting an average particle size in the range of 1 to 100 nm;
Performing a firing process of metal nanoparticles contained in the coating layer to form a metal nanoparticle sintered body layer having a fine pattern shape on a substrate;
The metal nanoparticles contained in the dispersion have a boiling point of 150, which enables a coordinate bond to a metal atom on the surface of the metal nanoparticle using a lone electron pair on a nitrogen atom of an amino group. The surface is coated with an alkylamine of ℃ or higher,
The metal nanoparticles whose surface is coated with the alkylamine are dispersed in a hydrocarbon solvent having a boiling point of 150 ° C. or higher,
In the dispersion, the hydrocarbon having a boiling point of 150 ° C. or higher is contained in the range of 10 to 100 parts by mass per 100 parts by mass of the metal nanoparticles;
Firing treatment of the metal nanoparticles,
Select the heating temperature in the range of 150 ° C or higher and 300 ° C or lower,
It is a method for forming a metal nanoparticle sintered body layer having a fine pattern, which is carried out in a reducing atmosphere composed of hydrogen gas or a mixed gas of hydrogen gas and inert gas.

At that time, metal nanoparticles contained in the dispersion,
A nanoparticle made of one kind of metal or an alloy made of two or more kinds of metal selected from the group of gold, silver, platinum, palladium, rhodium, ruthenium, iridium and osmium. Is preferred.

  In this invention, it is preferable that the content rate of the hydrogen gas in a reducing atmosphere used for the baking process process of the said metal nanoparticle is selected in the range of 1 volume%-100 volume%. Particularly, in the mixed gas of hydrogen gas and inert gas, the inert gas used may be nitrogen, helium, argon, krypton, xenon, or a mixture of two or more thereof. preferable.

Usually, in the firing process of the metal nanoparticles,
Flow hydrogen gas or a mixed gas of hydrogen gas and inert gas at a predetermined flow rate,
It is desirable to select a form that is heated in a non-pressurizing reducing atmosphere.

In addition, in the dispersion,
When heated, the rosin derivative having a function as a hydrogen atom supply source is preferably contained in the range of 0.5 to 5 parts by mass per 100 parts by mass of the metal nanoparticles. At that time, in the dispersion, as the rosin derivative,
At least one compound selected from abietic acid, neoabietic acid, parastrinic acid, levopimaric acid, pimaric acid, isopimaric acid, sandaracopimaric acid, dehydroabietic acid, acrylated rosin, maleated rosin, polymerized rosin, hydrogenated rosin It is more preferable to select a form in which is contained.

When the rosin derivative is contained in the dispersion,
The substrate has a surface formed of a metal material;
An oxide film containing an oxide of the metal material is formed on the surface of the metal material,
The oxide of the metal material contained in the oxide film is a basic metal oxide,
The basic metal oxide can be removed by a flux treatment using the rosin derivative.

  One of conductive layers having a fine pattern shape formed of a sintered body layer of metal nanoparticles formed on the substrate by applying the method for forming a finely patterned metal nanoparticle sintered body according to the present invention. The part may be configured to be used as a wire bonding pad. In that case, it is preferable to select the film thickness of the sintered body layer in the range of 0.5 μm to 10 μm for the part of the sintered body layer between the metal nanoparticles used as the wire bonding pad.

  In the method for forming a finely patterned metal nanoparticle sintered body according to the present invention, first, a fine pattern drawn on a substrate is formed using a dispersion of metal nanoparticles having a surface coating layer made of alkylamine. The coating film which has is formed. At that time, a hydrocarbon solvent having a boiling point of 150 ° C. or higher is contained in the dispersion as a dispersion solvent for dispersing the metal nanoparticles having the surface coating layer. Therefore, when the heating temperature is selected in the range of 150 ° C. or higher and 300 ° C. or lower and the heat treatment is performed in a non-pressurizing reducing atmosphere, a state where a dispersion solvent at least enough to immerse the metal nanoparticles remains. Thus, the alkylamine is released from the surface of the metal nanoparticles, and the metal surfaces of the metal nanoparticles can be brought into contact with each other. That is, the surface of the metal nanoparticle is covered with a liquid layer of a dispersion solvent, and as a result of the fusion of the metal nanoparticles starting, the metal nanoparticle contained therein is maintained while maintaining the original planar shape of the coating film. It is possible to form a sintered body layer in which the particles are fused closely. That is, the alkylamine of the coating molecule covering the surface of the metal nanoparticles is once eluted in the dispersion solvent and then evaporated when the heat treatment is performed. Compared to the coated state, the alkylamine covering the metal surface can be detached more quickly. Subsequently, when the heat treatment is advanced, all of the dispersion solvent in which the metal nanoparticles are immersed is evaporated, but the surface oxidation of the metal nanoparticles is avoided under a non-pressurizing reducing atmosphere. As a result, the fusion proceeds continuously, so that the fusion sites between the metal nanoparticles are formed at a high density, the contact area between the individual fusion sites is widened, and the “bulk volume shrinkage” is sufficiently advanced. The sintered body layer thus formed is formed. In particular, at the interface between the substrate and the sintered body layer, the time for which the dispersion solvent remains is relatively long, and as a result of sufficient “bulk volume shrinkage”, the resulting denseness of the entire sintered body layer Therefore, high adhesion is achieved at the interface between the base layer and the sintered body layer on the substrate surface.

  The present invention is described in detail below.

  In the method for producing a metal nanoparticle sintered body with a fine pattern according to the present invention, a dispersion of metal nanoparticles having a surface coating layer made of alkylamine is used to draw and apply a desired fine pattern shape on a substrate. A coated layer is formed. Next, the coating molecules covering the surface of the metal nanoparticles contained in the coating layer are released by heating in a non-pressurizing reducing atmosphere, causing fusion between the metal nanoparticles. To form a sintered body. In the process of releasing the coating agent molecules covering the surface of the metal nanoparticles, the state where the dispersion solvent remains in the coating layer of the metal nanoparticle dispersion at least to the extent that the metal nanoparticles are immersed is maintained. For this reason, a hydrocarbon solvent having a boiling point of 150 ° C. or higher is used as a dispersion solvent, and the heating is performed at a temperature slightly lower than the boiling point of the hydrocarbon solvent after the surrounding atmosphere is a non-pressurizing reducing atmosphere. Selected to avoid the generation of “bubbles” due to rapid vaporization of the dispersion solvent.

  When heating is performed at a temperature slightly lower than the boiling point of the hydrocarbon solvent in the non-pressurizing reducing atmosphere, the hydrocarbon solvent having a boiling point of 150 ° C. or higher at 1 atm is not in a “boiling state”, but at this heating temperature. Can exist as a liquid. In this state, the hydrocarbon solvent contained in the coating layer gradually evaporates from the surface, but does not cause rapid vaporization and form “bubbles” unlike the “boiling state”. Therefore, when the coating molecules that coat the surface of the metal nanoparticles contained in the coating layer are released due to heating, the dispersibility is impaired, and the metal nanoparticles settle and deposit on the substrate surface. Thus, a laminated structure is formed. At that time, the larger the particle size of the metal nanoparticles and the higher the degree of detachment of the coating molecules covering the surface, the greater the decrease in dispersibility, and the smaller the particle size of the metal nanoparticles, The lower the degree of detachment of the coating molecules that are, the smaller the decrease in dispersibility. Therefore, metal nanoparticles having a large particle diameter and the highest degree of detachment of the coating agent molecules are deposited at a high ratio at the interface with the substrate surface. On the other hand, as the distance from the interface with the substrate surface increases, the ratio of metal nanoparticles with a small particle size and a low degree of detachment of the coating agent molecules covering the surface increases. In the laminated structure formed by the metal nanoparticles settled on the substrate surface, the particle size distribution is formed in the thickness direction as described above. In the laminated structure of the metal nanoparticles, the dispersion solvent covering the surface of the laminated structure gradually evaporates in a state where the dispersion solvent is immersed in the gap between the metal nanoparticles.

On the other hand, at the temperature T of the liquid phase, the coating molecule that coats the surface of the metal nanoparticles is in an equilibrium state with the coating molecule dissolved in the liquid phase through the adsorption / desorption process. ing. That is, at the temperature T, the area density of the coating molecules covering the surface of the metal nanoparticles: C _absorb (T) is the concentration of the coating molecules dissolved in the dispersion solvent covering the surface: C _sol (T),
C _absorb (T) / C _sol (T) = K _absorb · exp {ΔE _absorb / (kT)}
Is in an equilibrium state that can be described approximately.

Further, the saturation solubility of the coating agent molecule in the dispersion solvent at the temperature T: C _eq . (T) is approximately
C _eq . (T) / C _eq . (T ₀ ) = exp {−ΔE _sol. / (KT)} / exp {−ΔE _sol. / (KT ₀ )}
Shows the temperature dependence that can be described by.

Furthermore, the coating agent molecule dissolved in the dispersion solvent and the gaseous coating agent molecule existing in the gas phase at the temperature T are in an equilibrium relationship between the gas phase and the liquid phase. At that time, the concentration of the coating molecule dissolved in the dispersion solvent at the temperature T: C _sol (T) and the partial pressure of the gaseous coating molecule existing in the gas phase: P _vapor (T) When the total pressure P _total (T) in the gas phase is constant,
C _sol (T) / C _sol (T ₀ ) = {P _vapor (T) / P _vapor (T ₀ )} · exp {ΔE _vol. / (KT)} / exp {ΔE _vol. / (KT ₀ )}
Shows the temperature dependence that can be described by.

Thus, the room temperature (T _1), During coated dispersion, the concentration of the coating agent molecules dissolved in the dispersion solvent: in C _sol (T ₁₎ and the equilibrium surface density _C absorb (T ₁₎ The surface of the metal nanoparticles is covered with coating molecules. When the temperature is raised, the release of the coating molecules covering the surface of the metal nanoparticles proceeds, and the concentration of the coating molecules dissolved in the dispersion solvent: C _sol (T) increases. At that time, the surface density of the coating molecules covering the surface of the metal nanoparticles: C _absorb (T) is greatly reduced from the initial surface density C _absorb (T ₁ ). As a result, at the heating temperature T, a considerable portion of the surface of the metal nanoparticles is not coated with the coating agent molecules, and the dispersibility is significantly lowered and settles. Then, the precipitated metal nanoparticles are brought into contact with the metal surface and start fusion.

  On the other hand, as the heat treatment proceeds, the transpiration of the dispersion solvent proceeds, and similarly, the transpiration of the coating agent molecules dissolved therein also proceeds. When the content ratio of the dispersion solvent and the coating agent molecules contained in the coating layer of the dispersion liquid of metal nanoparticles is compared, the content ratio of the dispersion solvent is remarkably high at the start of the heat treatment. Therefore, the transpiration rate of the dispersion solvent having a remarkably high content ratio is superior to the transpiration rate of the coating agent molecule, and thus the transpiration of the dispersion solvent proceeds with priority. As a result, the concentration of coating molecules dissolved in the dispersion solvent proceeds on the surface of the coating layer where transpiration is actually proceeding.

As the concentration of the coating molecules proceeds, the concentration of the coating molecules dissolved in the dispersion solvent: C _sol (T) increases rapidly. The concentration of the coating molecule dissolved in the dispersion solvent: C _sol (T) rapidly rises at the stage where the deposited metal nanoparticles are fused to each other by forming a laminated structure on the substrate surface. , Causing re-adsorption of coating molecules on the surface of the metal nanoparticles. As a result, the surface density of the coating molecule covering the surface of the metal nanoparticle: C _absorb decreases from the initial surface density C _absorb (T ₁ ) after the start of heating, and once shows a minimum value. To rise. When the surface density of the coating molecule covering the surface of the metal nanoparticle: C _absorb exceeds the threshold at the heating temperature T: C _absorb-0 (T), the progress of fusion between the metal nanoparticles is inhibited.

Furthermore, when the dispersion solvent evaporates and the dispersion solvent completely evaporates, the surface of the metal nanoparticle is densely coated with the coating molecule layer at least over the entire surface by re-adsorption of the coating molecule. It has returned to the state. Thereafter, the coating molecule covering the surface of the metal nanoparticle exposed to the non-pressurized atmosphere is detached again, becomes a gas, and starts discrete. Therefore, when the surface density of the coating molecule covering the surface of the metal nanoparticle: C _absorb gradually decreases and becomes lower than the threshold value: C _absorb-0 (T), the fusion between the metal nanoparticles is resumed.

  However, if oxygen molecules are present in the non-pressurized atmosphere to which the metal nanoparticle surface is exposed, the oxygen molecules act on the metal surface from which the coating agent molecules are detached at the heating temperature. Oxidation proceeds. Due to this surface oxidation, when an oxide film is formed on the surface of the metal nanoparticles, the progress of fusion between the metal nanoparticles is inhibited. In the present invention, a phenomenon in which an oxide film is formed on the surface of the metal nanoparticles is avoided by proceeding the heat treatment in a non-pressurizing reducing atmosphere. As a result, the coating molecule covering the surface of the metal nanoparticles exposed to the non-pressurizing reducing atmosphere is detached again, becomes a gas, and starts to dissociate. Is done. Finally, a sintered body layer in which the metal nanoparticles are sintered at a low density at a low density is formed on the substrate.

  First, in the method of the present invention, a coating layer of the dispersion is drawn in a desired fine pattern shape using a dispersion containing metal nanoparticles having a coating agent molecular layer on the surface. In that case, the average particle diameter of the metal nanoparticle which has a coating agent molecular layer on the surface made into a dispersoid is 100 nm or less, and it can apply also to formation of a very fine pattern.

  For example, in the method for producing a metal nanoparticle sintered body with a fine pattern according to the present invention, the drawing accuracy of the desired fine pattern shape is sufficiently high, and the minimum wiring width of the fine pattern is in the range of 1 to 300 μm. In practice, it is more suitable for selecting the minimum inter-wiring space in the range of 1 to 300 μm, and practically in the range of 5 to 200 μm, corresponding to the range of 5 to 200 μm. It becomes.

In consideration of the minimum wiring width, at least nanoparticles having an average particle diameter of 100 nm or less are used as metal nanoparticles that can be used for forming a sintered body layer that can cope with the accuracy. On the other hand, corresponding to the minimum wiring width (W _Lmin ) of about several μm, the film thickness (t _L ) of the sintered body layer is also selected in the range of sub μm to several μm. Therefore, also from the viewpoint of sufficiently satisfying the flatness in the film thickness, the average particle diameter of the metal nanoparticles to be used is selected in the range of 1 to 100 nm, more preferably in the range of 1 to 20 nm. At least, when applying the method for producing a metal nanoparticle sintered body according to the present invention to the formation of a fine pattern, the above-mentioned extremely fine pattern is formed using a nanoparticle dispersion liquid with a high wiring width. When drawing with uniformity, the average particle size of the nanoparticles used is selected to be less than 1/10 of the target minimum wiring width (W _Lmin ) and minimum inter-wiring space (W _Smin ). It is desirable to do. At the same time, the layer thickness of the sintered body wiring layer is also appropriately determined according to the minimum wiring width (W _Lmin ), but the layer thickness of the sintered body layer is usually compared with the minimum wiring width (W _Lmin ). (T _L ) is a significantly smaller form. Usually, the ratio between the minimum wiring width (W _Lmin ) and the thickness of the sintered body layer (t _L ): t _L / W _Lmin is 1/100 ≦ (t _L / W _Lmin ) ≦ 1, preferably 1 / A range of 50 ≦ (t _L / W _Lmin ) ≦ 1/2 is selected. At that time, by selecting the average particle size of the nanoparticles in the range of 1 to 100 nm, more preferably in the range of 1 to 20 nm, variation in the layer thickness (t _L ) of the sintered body layer, local It becomes possible to suppress unevenness in height.

  In the method for producing a sintered metal nanoparticle according to the present invention, the average particle diameter of the metal nanoparticles having a coating molecular layer on the surface to be used is in the range of 1 to 100 nm, more preferably in the range of 1 to 20 nm. Therefore, when forming an extremely thin conductive layer having an average film thickness of sub μm to several μm, for example, 0.3 μm to 2 μm, high film thickness uniformity and controllability can be achieved. On the other hand, the method for producing a metal nanoparticle sintered body according to the present invention can be applied to the formation of a conductive layer having an average film thickness of several μm to several tens of μm, for example, 4 μm to 20 μm.

The metal nanoparticles having a coating molecule layer on the surface thereof contained in the dispersion liquid have a lone electron pair on the nitrogen atom of the amino group as a coating molecule with respect to the metal atoms on the surface of the metal nanoparticles. An alkylamine capable of coordinative bonding is utilized. Therefore, the liquid phase part of the dispersion is a concentration of C _sol (T) which is in equilibrium with the surface density of the alkylamine covering the surface of the metal nanoparticles: C _absorb (T) at a temperature of 50 ° C. or less. The alkylamine of the coating agent molecule is dissolved in the dispersion solvent.

  At this time, the alkylamine maintains dispersibility in the dispersion solvent by forming at least a coating agent molecular layer corresponding to a monomolecular layer on the surface of the metal nanoparticles. In order to surely form the coating agent molecular layer, the alkylamine is contained in the range of 2 to 25 parts by mass, more preferably in the range of 5 to 20 parts by mass per 100 parts by mass of the metal nanoparticles. It is preferable to select the state that is being performed. The alkylamine of the coating molecule needs to be able to be detached from the surface of the metal nanoparticle by heat treatment. However, while the dispersion is stored at a temperature of 50 ° C. or less, it easily evaporates from the dispersion. Those which do not do are preferable. Therefore, it is preferable to use an alkylamine having a boiling point at 1 atmosphere of 150 ° C. or more and 300 ° C. or less, preferably 150 ° C. or more and 280 ° C. or less.

As the alkylamine, any of monoalkylamine, dialkylamine, and trialkylamine can be used. When using a monoalkylamine, a monoalkylamine having an alkyl group having 8 to 14 carbon atoms is preferred. Alkylamines having the form of H ₂ N (CH ₂ R ′) such as dodecylamine (melting point 28.3 ° C., boiling point 248 ° C.), decylamine (melting point 14 ° C., boiling point 218 ° C.), etc. can be used.

When dialkylamine is used, the total number of carbon atoms of the two alkyl groups is preferably in the range of 8 to 16, and the alkyl groups used may be the same or different. For example, as the dialkylamine, dialkylamines having 5 to 9 carbon atoms can be suitably used as the two alkyl groups. In particular, a dialkylamine having an alkyl group having 5 to 9 carbon atoms and having the shape of HN (CH ₂ R ′) ₂ , such as bis (2-ethylhexyl) amine ((CH ₃ —CH ₂ — CH ₂ —CH ₂ —CH (C ₂ H ₅ ) —CH ₂ ) ₂ NH (boiling point: 281 ° C.) can be used.

At room temperature (T ₁ ), in the dispersion, the surface of the metal nanoparticles to be dispersed contains the alkylamine of the coating molecule with an areal density: C _absorb (T ₁ ) so that it equilibrates with it. In the dispersion solvent, alkylamine is dissolved at a concentration of C _sol (T ₁ ). Therefore, in the entire dispersion, the amount of the alkylamine used for coating the surface of the metal nanoparticles is {S · C _absorb (T ₁ )} where S is the total surface area of the metal nanoparticles. The amount of alkylamine dissolved in the dispersion solvent is {V _total (T ₁ ) · C _sol (T ₁ )}, where V _total (T ₁ ) is the _total amount of the liquid phase portion of the dispersion. . Therefore, the total amount of alkylamine is {S · C _absorb (T ₁ )} + {V _total (T ₁ ) · C _sol (T ₁ )}.

When heated and the liquid temperature rises to T ₂ , the dispersion solvent partially evaporates and the total amount of the remaining liquid phase becomes V _total (T ₂ ). In this state, the dispersion solvent, alkylamine concentrations were dissolved in C _sol (T _2), therewith to equilibrium, the surface of the metal nanoparticles alkylamine, surface _density: C absorb (T ₂ ). At that time, the total amount of alkylamine is {S · C _absorb (T ₂ )} + {V _total (T ₂ ) · C _sol (T ₂ )}.

In this heating state, it is desirable that the _total amount of the remaining liquid phase portion: V _total (T ₂ ) is at least the state in which the entire metal nanoparticles present in the coating layer are immersed. In that case, it is desirable that the remaining amount of the dispersion solvent is an amount capable of filling the entire gap between the metal nanoparticles present in the coating layer. Therefore, in the dispersion to be used, a hydrocarbon solvent having a boiling point of 150 ° C. or higher at 1 atm, usually 150 ° C. or higher and 300 ° C. or lower, preferably 200 ° C. or higher and 300 ° C. or lower of boiling point at 1 atm. A hydrocarbon solvent is included as a dispersion solvent. The hydrocarbon solvent is at least in the range of 10 to 100 parts by weight, preferably in the range of 20 to 100 parts by weight, more preferably in the range of 20 to 80 parts by weight per 100 parts by weight of the metal nanoparticles. It is desirable to be included in the range.

  In the present invention, the hydrocarbon solvent has a function of a dispersion solvent and a function of a solvent for alkylamines and rosin derivatives. Therefore, in order to dissolve the rosin derivative having a high melting point to obtain a solution, the ratio of the content of the rosin derivative / the content of the hydrocarbon solvent is 1/2 or less, preferably 1/5 or less. It is desirable. On the other hand, the alkylamine itself is a liquid and can form a uniform mixture with the hydrocarbon solvent. When the total amount of alkylamine contained forms a mixture with the hydrocarbon solvent, the ratio of the alkylamine content / the content of the hydrocarbon solvent is at most 3/2, generally 2/2. In the following, it is desirable to set it to 1/2 or less. In general, it is desirable to select the content ratio so that the content of the hydrocarbon solvent is larger than the total content of the alkylamine and the rosin derivative. For example, the ratio of the total content of alkylamine and rosin derivative / the content of the hydrocarbon solvent is at most 3/2 or less, generally 2/2 or less, preferably 3/5 or less. desirable.

  In the method for producing a metal nanoparticle sintered body according to the present invention, formation of a sintered body between metal nanoparticles utilizes a phenomenon in which mutual fusion occurs at a low temperature when the metal nanoparticles contact the metal surface. . In addition, after the dispersion solvent evaporates, the heat treatment is continued in a non-pressurizing reducing atmosphere to further advance the metal nanoparticle mutual fusion. In the present invention, a reducing atmosphere composed of hydrogen gas or a mixed gas of hydrogen gas and inert gas is used as the non-pressurizing reducing atmosphere. The hydrogen gas content in the reducing atmosphere is selected in the range of 1% to 100% by volume, preferably in the range of 2% to 100% by volume. In the mixed gas of hydrogen gas and inert gas, the inert gas used is preferably nitrogen, helium, argon, krypton, xenon, or a mixture of two or more thereof. In a non-pressurized reducing atmosphere, a dispersion solvent evaporating from the coating layer of the dispersion and an alkylamine gas used as a coating agent molecule are mixed. In particular, it is preferable to reduce the partial pressure of the alkylamine used as the coating agent molecule in a non-pressurized reducing atmosphere. For that purpose, in the firing process of the metal nanoparticles, hydrogen gas or a mixed gas of hydrogen gas and inert gas is flowed at a predetermined flow rate, and heating is performed in a non-pressurizing reducing atmosphere. It is desirable to select a form.

  On the other hand, after the fusion of metal nanoparticles progresses and a dense sintered body of metal nanoparticles is formed as a whole, no dispersion solvent remains in the gap space inside the sintered body. That is, when the baking treatment is completed, the unnecessary dispersion solvent needs to be a dispersion solvent that is vaporized and evaporated at the heat treatment temperature.

  Therefore, the dispersion solvent to be used must be liquid at room temperature, and the melting point is at least 20 ° C. or less, preferably 10 ° C. or less. On the other hand, at the heat treatment temperature selected to be non-pressurized 300 ° C. or lower, it is also necessary to show transpiration of a certain level or higher. Therefore, it is desirable that the boiling point of the hydrocarbon solvent used as the dispersion solvent is at least 320 ° C. or less, preferably 300 ° C. or less, more preferably 280 ° C. or less. However, when the boiling point is lower than 150 ° C., the evaporation of the dispersion solvent proceeds considerably in the process of drawing the coating film layer, which causes variations in the amount of metal nanoparticles contained in the coating film layer. It also becomes. Therefore, the dispersion solvent is a hydrocarbon solvent having a boiling point of preferably 150 ° C. or more and 300 ° C. or less, more preferably a hydrocarbon solvent having a boiling point of 200 ° C. or more and 300 ° C. or less. select. Specifically, the boiling point of the hydrocarbon solvent used as the dispersion solvent becomes higher than the temperature at which the fusion of the metal nanoparticles starts, for example, the temperature at which the fusion of the silver nanoparticles starts, about 220 ° C. Thus, it is more preferable to make the selection.

  Examples of the dispersion solvent used for preparing a dispersion containing metal nanoparticles having a coating agent molecular layer on the surface include chains having a high boiling point such as tetradecane (melting point 5.86 ° C., boiling point 253.57 ° C.). Formula hydrocarbon solvents can be utilized. In particular, the dispersion solvent needs to have a function of easily dissolving the alkylamine when heated. Therefore, it is preferable to use a chain hydrocarbon solvent having a high boiling point such as tetradecane (melting point 5.86 ° C., boiling point 253.57 ° C.). As the hydrocarbon solvent having a boiling point in the range of 200 ° C. to 300 ° C., straight chain alkanes having 12 to 18 carbon atoms and branched alkanes having 11 to 16 carbon atoms can be suitably used.

  On the other hand, it is indispensable for the metal nanoparticles to cause fusion at a portion in contact with the metal surface by heating at a temperature of 150 ° C. or more and 300 ° C. or less. In order to cause fusion by this low-temperature heating, the average particle diameter is selected in the range of 1 to 100 nm, more preferably in the range of 1 to 20 nm. At that time, the metal constituting the metal nanoparticle is selected from the group of metal species of gold, silver, platinum, palladium, rhodium, ruthenium, iridium, and osmium, or one or more metal species. An alloy can be used. Since metal nanoparticles are far more susceptible to oxidation than ordinary metal fine powders, they are dispersed in a dispersion with alkylamine coated on the surface as a coating molecule. At the stage of preparing the dispersion, there is a concern that an oxide film is formed at a site covering the surface of the metal nanoparticles where the coating agent molecules are detached. The effect of surface oxidation by oxygen molecules, which occurs during the preparation of this dispersion, is caused by metals that are not easily oxidized, such as noble metals, that is, metals composed of gold, silver, platinum, palladium, rhodium, ruthenium, iridium, and osmium. There is no problem when using nanoparticles.

  In the present invention, the metal nanoparticles are fired by selecting a heating temperature in the range of 150 ° C. or more and 300 ° C. or less, and a reducing atmosphere composed of hydrogen gas or a mixed gas of hydrogen gas and inert gas. Implement below. At that time, during the heat treatment, as described above, first, the detachment of the coating agent molecules covering the surface of the metal nanoparticles is advanced while being immersed in the dispersion solvent. With the release of the coating agent molecules that coat the surface of the metal nanoparticles, the metal nanoparticles come into contact with each other and the fusion starts. Thereafter, after the dispersion solvent evaporates, the coating molecules remaining on the surface of the metal nanoparticles exposed to the non-pressurizing reducing atmosphere are thermally dissociated (vaporized), and the metal nanoparticles are mutually bonded. The fusion is further advanced. As described above, the firing treatment of the metal nanoparticles is composed of two partial processes. In the first half of the process, in the state where the metal nanoparticles are immersed in the dispersion solvent, the coating molecules covering the entire surface of the metal nanoparticles are detached. In the latter half of the process, after the dispersion solvent evaporates, the coating molecules remaining on the surface of the metal nanoparticles are thermally dissociated (vaporized) while exposed to a non-pressurized reducing atmosphere. Yes.

Therefore, in the first half of the process, it is preferable to select a heating temperature T ₂ that can avoid the generation of “bubbles” due to rapid vaporization of the dispersion solvent. In the coating layer of the dispersion, since the coating agent molecules are dissolved in the dispersion solvent as described above, “boiling point rise” occurs, and “boiling state” occurs at a temperature higher than the original boiling point of the dispersion solvent. It becomes. In other words, in the first half of the process, if the heating temperature T ₂ is selected within the range below the original boiling point of the dispersion solvent, the generation of “bubbles” due to the rapid vaporization of the dispersion solvent can be avoided. That is, in the first half of the process, the heating temperature T ₂ is in the range of 150 ° C. or higher and 300 ° C. or lower, and is within the original boiling point (T _sb ) of the dispersion solvent, preferably the dispersion solvent boiling point (T _sb ). The temperature difference of ( _Tsb− T ₂ ) is preferably selected so as to be in the range of 10 ° C. to 50 ° C.

On the other hand, in the latter process, the alkylamine of the coating molecule is used to thermally dissociate (vaporize) the coating molecule remaining on the surface of the metal nanoparticles exposed to the non-pressurizing reducing atmosphere. However, it is desirable to select a heating temperature (T ₃ ) that can quickly vaporize. That is, in the first half of the process, the heating temperature T ₃ is preferably selected in the range of 150 ° C. or more and 300 ° C. or less in the range of the boiling point (T _cb ) of the alkylamine of the coating agent molecule.

For example, as described above, the firing process of the metal nanoparticles is performed in two stages in which the heating temperature T ₂ and the heating temperature T ₃ are selected in accordance with the first half process and the second half process, respectively. It is also possible. At that time, the heating temperature T ₂ and the heating temperature T ₃ are selected so that at least 150 ° C. ≦ T ₂ ≦ T ₃ ≦ 300 ° C., preferably 200 ° C. ≦ T ₂ ≦ T ₃ ≦ 300 ° C. desirable. For example, when the boiling point (T _cb ) of the alkylamine is higher than the boiling point (T _sb ) of the dispersion solvent, at least a relationship of 150 ° C. ≦ T ₂ ≦ T _sb <T _cb ≦ T ₃ ≦ 300 ° C., It is desirable to select so as to satisfy the relationship of 200 ° C. ≦ T ₂ ≦ T _sb <T _cb ≦ T ₃ ≦ 300 ° C. Further, when the boiling point (T _cb ) of the alkylamine is lower than the boiling point (T _sb ) of the dispersion solvent, at least a relationship of 150 ° C. ≦ T _cb ≦ T ₂ ≦ T _sb ≦ T ₃ ≦ 300 ° C., preferably It is desirable to select so as to satisfy the relationship of 200 ° C. ≦ T _cb ≦ T ₂ ≦ T _sb ≦ T ₃ ≦ 300 ° C.

  In addition, the metal nanoparticles themselves dispersed in the dispersion liquid are coated with coating molecules to avoid oxidation, but are adsorbed and desorbed between the coating molecules dissolved in the dispersion solvent. Is in an equilibrium state. Occasionally, when desorption occurs, oxygen molecules may act on the metal surface of the metal nanoparticles to locally generate an oxide film. In consideration of this point, when using metal nanoparticles composed of a metal that is susceptible to oxidation, a rosin derivative that functions as a hydrogen atom supply source when heated in a dispersion is used as a metal. It can also be set as the form added in the range of 0.5 mass part-5 mass parts per 100 mass parts of nanoparticles, Preferably, it is 0.7 mass part-3 mass parts. At that time, as the rosin derivative, which is added to the dispersion and has a function as a hydrogen atom supply source when heated, abietic acid (molecular weight 302.4, melting point 172 ° C.), neoabietic acid (molecular weight 302.4). , Melting point 172 ° C.), parastrinic acid (molecular weight 302.4, melting point 165 ° C.), levopimaric acid (molecular weight 302.4, melting point 150 ° C.), pimaric acid (molecular weight 302.4, melting point 218 ° C.), isopimaric acid (molecular weight 302). .4, melting point 160 ° C.), sandaracopimaric acid (molecular weight 302.4, melting point 174 ° C.), dehydroabietic acid (molecular weight 300.4, melting point 172 ° C.), acrylated rosin, maleated rosin, polymerized rosin, hydrogenated At least one compound among rosins can be used.

  When the heat treatment proceeds, the dispersion solvent remains as a liquid phase, and the rosin derivative, which functions as a hydrogen atom supply source, dissolves in the dispersion solvent and locally forms on the surface of the metal nanoparticles. It is used as a source of hydrogen used for reducing the oxidized film. By the reduction treatment, the locally formed oxide film that inhibits the progress of fusion between the metal nanoparticles is removed. Therefore, when metal nanoparticles composed of a metal that is susceptible to oxidation are used, the metal nanoparticle formed by adding a rosin derivative having a function as a supply source of the hydrogen atom is added. The bonded body exhibits a dense sintered state.

  Furthermore, as will be described below, the rosin derivative added can also function as a flux component that removes an oxide film present on the surface of the metal material when the heat treatment is performed. In this invention, when forming a metal nanoparticle sintered compact layer on a board | substrate, it is possible to utilize the surface formed with a metal material as the base layer. For example, an oxide film containing an oxide of a metal material may be formed on the surface of the metal material due to oxidation of the metal material. In that case, it is preferable to apply the dispersion after removing the oxide film in advance. Even when the treatment for removing the oxide film is performed, an oxide film containing an oxide of the metal material may be slightly formed due to factors such as subsequent oxidation. When this oxide film remains slightly, and the oxide of the metal material contained in the oxide film is a basic metal oxide, the basic metal is obtained by flux treatment using a rosin derivative. Oxide removal is possible. For example, copper and copper contained in a copper alloy contain an M (II) O type metal oxide containing a divalent metal cation in the oxide film. When a rosin derivative is allowed to act on this basic metal oxide, the M (II) O type metal oxide can be removed using the carboxyl group (—COOH). Since the flux treatment using this rosin derivative generally proceeds under heating conditions, in the present invention, when the above-mentioned heat treatment is performed, the liquid temperature of the dispersion rises and the flux treatment proceeds.

  In this invention, when forming a metal nanoparticle sintered compact layer on a board | substrate, copper or a copper alloy can be utilized as the base layer, for example. For example, the metal nanoparticle sintered body layer can be formed on the surface of a copper frame material or a copper alloy frame material containing copper as a main component.

  When forming a metal nanoparticle sintered body layer on the surface of this copper or copper-based alloy as a base layer, the rosin derivative added in the hydrocarbon solvent with a high boiling point is the oxidation remaining on the metal surface. It also has the function of a flux component that is used to remove the coating. All the rosin derivatives are carboxylic acids having a boiling point of 200 ° C. or higher. The oxide film remaining on the metal surface is generally composed of a metal oxide in the form of M (II) O. When a carboxylic acid (R-COOH) acts on the metal oxide M (II) O during the heat treatment, a basic metal salt of the carboxylic acid is first generated by the following reaction.

M (II) O + R—COOH → R—COO ⁻ [M ²⁺ · OH ⁻ ]
On the other hand, an alkylamine, for example, a monoalkylamine (R′—NH ₂ ) used as a metal nanoparticle coating molecule is dissolved in the dispersion solvent. This alkylamine (R′—NH ₂ ) is much easier to cause coordination with the metal ion M ²⁺ than with the metal atom M. Accordingly, alkylamine (R′—NH ₂ ) acts on the basic metal salt of the carboxylic acid to produce an amine complex as described below, for example.

^{R-COO - [M 2+ ·} OH -] + 4R'-NH 2 → R-COO - [M 2+ (R'-NH 2) 4] OH -
When the above amine complex is constituted, dissolution in the dispersion solvent becomes easier. At that time, since the concentration of the alkylamine (R′—NH ₂ ) itself dissolved in the dispersion solvent decreases, the alkylamine (Coordinatively bonded to the metal atom on the metal surface of the metal nanoparticle ( R'-NH ₂₎ dissociation is accelerated.

R′—NH ₂ : M → R′—NH ₂ + M
Therefore, the rosin derivative added in the hydrocarbon solvent can be used to remove the oxide film remaining on the metal surface through the above mechanism in addition to the function of the flux component. It also exhibits the function of promoting the release of alkylamines, coating molecules that coat the surface.

  The produced amine complex is then exposed to a non-pressurized reducing atmosphere, and when it comes into contact with hydrogen molecules, it is reduced to produce a metal atom. The generated metal atoms are deposited on the surface of the metal nanoparticle in the surface of the base layer of copper or a copper-based alloy or the metal nanoparticle sintered body layer. When removal of the oxide film remaining on the surface of the copper or copper-based alloy underlayer is achieved, when the clean metal surface comes into contact with the metal nanoparticles, fusion proceeds at the interface between the two. . As a result, high adhesion is achieved at the interface between the copper or copper alloy underlayer and the metal nanoparticle sintered body layer due to the progress of the fusion.

  In the present invention, when forming a metal nanoparticle sintered body layer on a substrate having a metal surface, in particular, an underlayer having a copper or copper alloy surface, dispersion of metal nanoparticles to which a rosin derivative is added. Use liquid. The coating layer of the dispersion of metal nanoparticles to which the rosin derivative is added is heated at a relatively low temperature in a non-pressurizing reducing atmosphere, and the metal nanoparticles are baked to provide excellent conductivity. The metal nanoparticle sintered body type conductor shown can be formed, and the adhesion to the copper or copper alloy substrate can be improved.

Utilizing the advantage of excellent adhesion to the copper or copper alloy substrate, the metal nanoparticle-sintered sintered body layer formed by the method of the present invention can be used as a wire bonding pad. When used as a wire bonding pad, the bonding wire is bonded to the surface of the sintered body layer between the metal nanoparticles by welding. Therefore, the film thickness of the sintered body layer between the metal nanoparticles used as the wire bonding pad is selected according to the wire diameter of the bonding wire to be joined. For example, when the wire diameter (diameter) d _{w of} the bonding wire is in the range of 5 μm to 500 μm, the thickness t _{pad of the} sintered body layer of the metal nanoparticles for the wire bonding pad is correspondingly set. Is selected in the range of 0.5 μm to 10 μm, preferably in the range of 1 μm to 5 μm. Of course, the size of the sintered metal layer between the metal nanoparticles for the wire bonding pad (pad surface size) is appropriately set according to the bonding method and the wire diameter (diameter) d _w of the bonding wire. The For example, when adopting the wet bonding method, the size of the pad surface is selected in consideration of the amount of deformation of the bonding wire at the welded joint.

  In addition, the metal material of the metal nanoparticle utilized for preparation of the sintered compact layer between the metal nanoparticles for wire bonding pads is selected according to the metal material of the bonding wire. In general, it is desirable to select the same metal material as the metal material of the metal nanoparticles used for the sintered body layer between the metal nanoparticles for the wire bonding pad and the metal material of the bonding wire. Of course, as long as sufficiently high bonding strength can be obtained by welding bonding, a combination of metal materials of metal nanoparticles and bonding wire metal materials used for the sintered layer of metal nanoparticles, A combination of different metal materials is also possible.

  Moreover, in the sintered metal layer between the metal nanoparticles formed by the method of the present invention, the alkylamine covering the metal nanoparticles is removed, and no organic matter remains. Therefore, in wire bonding, when forming a welded joint, the metal material of the sintered metal layer between the metal nanoparticles and the metal material of the bonding wire form a dense metal bond with each other. The bonding strength is sufficiently high.

  Hereinafter, the present invention will be described more specifically with reference to examples. These examples are examples of the best mode according to the present invention, but the present invention is not limited by these examples.

Example 1
As a silver nanoparticle raw material, a commercially available silver ultrafine particle dispersion (trade name: independent dispersed ultrafine particle Ag1T manufactured by ULVAC MATERIAL), specifically, 35 mass parts of silver ultrafine particles, alkylamine as dodecylamine (molecular weight) 185.36, melting point 28.3 ° C., boiling point 248 ° C., specific gravity d ₄ ⁴⁰ = 0.7841) 7 parts by mass, as an organic solvent, toluene (boiling point 110.6 ° C., specific gravity d ₄ ²⁰ = 0.867) 58 mass A dispersion of ultrafine silver particles having an average particle diameter of 3 nm including a part was used. The liquid viscosity of the silver ultrafine particle dispersion is 1 mPa · s (20 ° C.).

  First, 5.8 g of dodecylamine was added to and mixed with 500 g (containing 35 wt% of Ag) of silver ultrafine particle dispersion Ag1T in a 1 L eggplant-shaped flask, and the mixture was heated and stirred at 80 ° C. for 1 hour. After completion of the stirring, the dispersion solvent toluene contained in Ag1T was removed by concentration under reduced pressure.

N14 (tetradecane, viscosity: 2.0 to 2.3 mPa · s (20 ° C.), melting point: 5.86 ° C., boiling point: 253 per 175 parts by mass of the ultrafine silver particles contained in the mixture after the solvent removal. .57 ° C., specific gravity d ₄ ²⁰ = 0.7924, manufactured by Nikko Petrochemical Co., Ltd.) 95 parts by mass, abietic acid (manufactured by Wako Pure Chemical Industries, Ltd.) 1.2 parts by mass, and stirred at room temperature (25 ° C.) A uniform dispersion was obtained. After the stirring, the dispersion was filtered with a 0.2 μm membrane filter. The resulting dispersion was a uniform dark blue high flow paste silver nanoparticle dispersion (silver nanoparticle ink) having a liquid viscosity (B-type rotational viscometer, measurement temperature 20 ° C.) of 8 mPa · s. . Bulk silver alone has a density of 10.49 g · cm ⁻³ (20 ° C.) and a resistivity of 1.59 μΩ · cm (20 ° C.).

  First, a silver nanoparticle dispersion (silver nanoparticle ink) is applied onto a copper plate using an ink jet apparatus, and a pad pattern is drawn. Immediately after this drawing, the layer thickness of the silver nanoparticle dispersion coating layer was about 20 μm.

  After installing the substrate on which the coating layer has been formed in a gas baking furnace, an argon 96% -hydrogen 4% mixed gas is allowed to flow into the furnace to form a reducing atmosphere. The temperature is raised from room temperature to 220 ° C. over 10 minutes and held at a heating temperature of 220 ° C. for 10 minutes. Next, the temperature is raised from 220 ° C. to 270 ° C. over 2 minutes and 30 seconds, and held at a heating temperature of 270 ° C. for 9 minutes. Next, the temperature is lowered to room temperature over 10 minutes.

  The film thickness of the sintered body layer produced by the firing treatment in the reducing atmosphere was an average film thickness of 2.0 μm in a planar pattern portion having a width of 200 μm and a length of 200 μm. When the obtained sintered body layer was subjected to cross-sectional observation, it had a bulk structure without voids as shown in FIG.

  Further, when a wire bonding test was performed on the produced sintered body layer bonding pad using a gold wire (wire diameter: 30 μm), the average pull strength was as high as 13.9 g and the variation was small.

  That is, it is confirmed that the adhesion at the interface between the copper plate and the sintered body layer bonding pad produced thereon is good and the reproducibility is high.

(Comparative Example 1)
According to the procedure described in Example 1, a silver nanoparticle dispersion liquid (silver nanoparticle ink) to which abietic acid is added is applied to produce an ink jet drawing pattern. Immediately after drawing, the layer thickness of the coating layer of the silver nanoparticle dispersion was about 20 μm. The ink jet drawing pattern formed on the copper plate is placed on a hot plate and held in air at a heating temperature of 220 ° C. for 10 minutes. Subsequently, it hold | maintains for 1 minute at the heating temperature of 270 degreeC, and cools down over 10 minutes to normal temperature.

  The film thickness of the sintered body layer produced by the above-described firing treatment in the atmosphere was an average film thickness of 3.0 μm in a planar pattern portion having a width of 200 μm and a length of 200 μm. When the obtained sintered body layer was subjected to cross-sectional observation, a large number of voids were present and the bulk structure was not formed (FIGS. 2 and 3).

  Further, when a wire bonding test was performed on the produced sintered body layer bonding pad using a gold wire (wire diameter: 30 μm), the average pull strength was 13.0 g and the variation was large.

  That is, the adhesion at the interface between the copper plate and the sintered body bonding pad produced thereon is slightly inferior to that of Example 1, and it is judged that the reproducibility is also low.

(Comparative Example 2)
According to the procedure described in Example 1, a silver nanoparticle dispersion liquid (silver nanoparticle ink) to which abietic acid is added is applied to produce an ink jet drawing pattern. Immediately after drawing, the layer thickness of the coating layer of the silver nanoparticle dispersion was about 20 μm.

  After installing the substrate on which the coating layer has been formed in the gas firing furnace, nitrogen gas is allowed to flow into the furnace. The temperature is raised from room temperature to 220 ° C. over 10 minutes and held at a heating temperature of 220 ° C. for 10 minutes. Next, the temperature is raised from 220 ° C. to 270 ° C. over 2 minutes and 30 seconds, and held at a heating temperature of 270 ° C. for 9 minutes. Next, the temperature is lowered to room temperature over 10 minutes.

  The film thickness of the sintered body layer produced by the firing treatment under the nitrogen atmosphere was 4.0 μm on the average film thickness in a planar pattern portion having a width of 200 μm and a length of 200 μm.

  Further, when a wire bonding test was performed on the fabricated sintered body layer bonding pad using a gold wire (wire diameter: 30 μm), the bonding property was poor and the pull strength measurement was not achieved.

  Separately, the volume resistivity of the sintered body layer produced under the same conditions was measured, which was about 10 times higher than the bulk silver resistivity of 1.59 μΩ · cm (20 ° C.). . When the volume resistivity of the sintered body layer produced in Comparative Example 1 is compared with the volume resistivity of the sintered body layer produced in Comparative Example 2, it is about 8 times.

  From the above results, in Comparative Example 2 in which the baking treatment is performed in a nitrogen atmosphere, the removal of the alkylamine of the coating molecule is suppressed as compared with Comparative Example 1 in which the baking treatment is performed in the air. It is judged. Therefore, it is judged that the sintered body layer bonding pad manufactured in Comparative Example 2 is inferior in wire bondability even when compared with the sintered body layer bonding pad manufactured in Comparative Example 1.

(Comparative Example 3)
As a silver nanoparticle raw material, a commercially available silver ultrafine particle dispersion (trade name: independent dispersed ultrafine particle Ag1T manufactured by ULVAC MATERIAL), specifically, 35 mass parts of silver ultrafine particles, alkylamine as dodecylamine (molecular weight) 185.36, melting point 28.3 ° C., boiling point 248 ° C., specific gravity d ₄ ⁴⁰ = 0.7841) 7 parts by mass, as an organic solvent, toluene (boiling point 110.6 ° C., specific gravity d ₄ ²⁰ = 0.867) 58 mass A dispersion of ultrafine silver particles having an average particle diameter of 3 nm including a part was used. The liquid viscosity of the silver ultrafine particle dispersion is 1 mPa · s (20 ° C.).

  First, 5.8 g of dodecylamine was added to and mixed with 500 g (containing 35 wt% of Ag) of silver ultrafine particle dispersion Ag1T in a 1 L eggplant-shaped flask, and the mixture was heated and stirred at 80 ° C. for 1 hour. After completion of the stirring, the dispersion solvent toluene contained in Ag1T was removed by concentration under reduced pressure.

N14 (tetradecane, viscosity: 2.0 to 2.3 mPa · s (20 ° C.), melting point: 5.86 ° C., boiling point: 253 per 175 parts by mass of the ultrafine silver particles contained in the mixture after the solvent removal. .57 ° C., specific gravity d ₄ ²⁰ = 0.7924, manufactured by Nikko Petrochemical Co., Ltd.) was added 96.2 parts by mass and stirred at room temperature (25 ° C.) to obtain a uniform dispersion. After the stirring, the dispersion was filtered with a 0.2 μm membrane filter. The resulting dispersion was a uniform dark blue high flow paste silver nanoparticle dispersion (silver nanoparticle ink) having a liquid viscosity (B-type rotational viscometer, measurement temperature 20 ° C.) of 8 mPa · s. . Therefore, no rosin derivative is added to the silver nanoparticle dispersion (silver nanoparticle ink).

  First, a silver nanoparticle dispersion (silver nanoparticle ink) is applied onto a copper plate using an ink jet apparatus, and a pad pattern is drawn. Immediately after this drawing, the layer thickness of the silver nanoparticle dispersion coating layer was about 20 μm.

  The film thickness of the sintered body layer produced by the firing treatment in the atmosphere was an average film thickness of 4.0 μm in a planar pattern portion having a width of 200 μm and a length of 200 μm. When the obtained sintered body layer was subjected to cross-sectional observation, many voids existed and the bulk structure was not formed (FIG. 3).

  Further, when a wire bonding test was performed on the produced sintered body layer bonding pad using a gold wire (wire diameter: 30 μm), the average pull strength was 12.0 g and the variation was large.

  That is, the adhesion at the interface between the copper plate and the sintered body bonding pad produced thereon is slightly inferior to that of Example 1, and it is judged that the reproducibility is also low.

(Example 2)
Using the silver nanoparticle dispersion liquid (silver nanoparticle ink) prepared in Comparative Example 3, a silver nanoparticle dispersion liquid (silver nanoparticle ink) is applied onto a copper plate using an inkjet device, and a pad pattern is drawn. To do. Immediately after this drawing, the layer thickness of the silver nanoparticle dispersion coating layer was about 20 μm. Therefore, no rosin derivative is added to the silver nanoparticle dispersion (silver nanoparticle ink).

  After installing the substrate on which the coating layer has been formed in a gas firing furnace, a 96% argon-hydrogen 4% mixed gas is flowed into the furnace to create a reducing atmosphere. The temperature is raised from room temperature to 220 ° C. over 10 minutes and held at a heating temperature of 220 ° C. for 10 minutes. Next, the temperature is raised from 220 ° C. to 270 ° C. over 2 minutes and 30 seconds, and held at a heating temperature of 270 ° C. for 9 minutes. Next, the temperature is lowered to room temperature over 10 minutes.

  The film thickness of the sintered body layer produced by the firing treatment in the reducing atmosphere was an average film thickness of 2.5 μm in a planar pattern portion having a width of 200 μm and a length of 200 μm.

  Further, when a wire bonding test was performed on the produced sintered body layer bonding pad using a gold wire (wire diameter: 30 μm), the average pull strength was 13.3 g and the variation was small.

  In other words, even if the flux treatment using the rosin derivative is not performed, the adhesion at the interface between the copper plate and the sintered body bonding pad produced thereon is performed by performing the firing treatment in a reducing atmosphere. Is sufficiently high.

  In the method for forming a metal nanoparticle sintered body layer having a fine pattern according to the present invention, when the metal nanoparticle sintered body is produced on a substrate, the bulk density and mechanical strength of the entire sintered body layer to be formed are as follows. It is possible to achieve high adhesion at the interface between the underlying layer and the sintered body layer by suppressing the decrease in conductivity and further increasing the density of the entire sintered body layer obtained. . Therefore, for example, the present invention can be applied to the production of a metal nanoparticle sintered body layer that can be used as a conductive layer for a bonding pad that exhibits good adhesion on the surface of a copper or copper alloy substrate.

It is the printout of the image which shows the result of having observed the cross section about the sintered compact layer produced in Example 1 by SIM (Scanning Ion Microscope). It is the printout of the image which shows the result of having observed the cross section about the sintered compact layer produced in the comparative example 1 by SIM (Scanning Ion Microscope). It is the printout of the image which shows the result of having observed the cross section in the other area | region about the sintered compact layer produced in the comparative example 1 in SIM (Scanning Ion Microscope).

Claims (10)

A method of forming a conductive layer having a fine pattern shape composed of sintered layers of metal nanoparticles on a substrate,
Drawing an application layer having a desired fine pattern shape on a substrate using a dispersion containing metal nanoparticles, selecting an average particle size in the range of 1 to 100 nm;
Performing a firing process of metal nanoparticles contained in the coating layer to form a metal nanoparticle sintered body layer having a fine pattern shape on a substrate;
The metal nanoparticles contained in the dispersion have a boiling point of 150, which enables a coordinate bond to a metal atom on the surface of the metal nanoparticle using a lone electron pair on a nitrogen atom of an amino group. The surface is coated with an alkylamine of ℃ or higher,
The metal nanoparticles whose surface is coated with the alkylamine are dispersed in a hydrocarbon solvent having a boiling point of 150 ° C. or higher,
In the dispersion, the hydrocarbon having a boiling point of 150 ° C. or higher is contained in the range of 10 to 100 parts by mass per 100 parts by mass of the metal nanoparticles;
Firing treatment of the metal nanoparticles,
Select the heating temperature in the range of 150 ° C or higher and 300 ° C or lower,
A method for forming a metal nanoparticle sintered body layer having a fine pattern, which is performed in a reducing atmosphere composed of hydrogen gas or a mixed gas of hydrogen gas and an inert gas. The metal nanoparticles contained in the dispersion are
A nanoparticle made of one kind of metal or an alloy made of two or more kinds of metal selected from the group of gold, silver, platinum, palladium, rhodium, ruthenium, iridium and osmium. The method of claim 1, wherein: The content of hydrogen gas in the reducing atmosphere used for the firing process of the metal nanoparticles is:
3. The method according to claim 1, wherein the method is selected in the range of 1% by volume to 100% by volume. In the mixed gas of the hydrogen gas and the inert gas, the inert gas used is:
The method according to claim 3, wherein nitrogen, helium, argon, krypton, xenon, or a mixture of two or more thereof is used. In the firing process of the metal nanoparticles,
Flow hydrogen gas or a mixed gas of hydrogen gas and inert gas at a predetermined flow rate,
The method according to any one of claims 1 to 4, wherein heating is performed in a non-pressurizing reducing atmosphere. In the dispersion,
The rosin derivative having a function as a hydrogen atom supply source when heated is contained in the range of 0.5 to 5 parts by mass per 100 parts by mass of the metal nanoparticles. The method as described in any one of -8. In the dispersion, as the rosin derivative,
At least one compound selected from abietic acid, neoabietic acid, parastrinic acid, levopimaric acid, pimaric acid, isopimaric acid, sandaracopimaric acid, dehydroabietic acid, acrylated rosin, maleated rosin, polymerized rosin, hydrogenated rosin The method according to claim 6, further comprising: The substrate has a surface formed of a metal material;
An oxide film containing an oxide of the metal material is formed on the surface of the metal material,
The oxide of the metal material contained in the oxide film is a basic metal oxide,
The method according to claim 6 or 7, wherein the basic metal oxide can be removed by a flux treatment using the rosin derivative. 9. A part of a conductive layer having a fine pattern formed of a sintered body layer of metal nanoparticles formed on the substrate is used as a wire bonding pad. The method as described in any one of. The portion of the sintered body layer between the metal nanoparticles used as the wire bonding pad has a thickness of the sintered body layer selected in a range of 0.5 μm to 10 μm. The method described.