JP4205393B2 - Method for forming fine wiring pattern - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a fine copper-based wiring pattern, and more specifically, after drawing an ultrafine pattern using a dispersion of copper oxide nanoparticles, the copper oxide nanoparticles in the pattern are reduced. And firing the produced copper nanoparticles to form a sintered copper-based wiring pattern having a low impedance and a very fine size corresponding to digital high-density wiring.
[0002]
[Prior art]
As a method for forming an ultrafine wiring pattern using metal nanoparticles, for example, when gold nanoparticles or silver nanoparticles are used, a methodology has already been established. Specifically, an extremely fine circuit pattern drawing using an ultrafine printing dispersion containing gold nanoparticles or silver nanoparticles, and then sintering between the metal nanoparticles is performed. In the combined wiring layer, the wiring width and the space between the wirings are 5 to 50 μm, and the volume resistivity is 1 × 10. ^-Five Wiring formation of Ω · cm or less is possible. However, when gold nanoparticles are used, the material gold itself is expensive, so the production unit price of such a dispersion for ultra-fine printing is high, which is a major economic obstacle to widespread use as a general-purpose product. It has become. On the other hand, by using silver nanoparticles, the unit cost of the dispersion can be reduced considerably, but as the wiring width and inter-wiring space become narrower, disconnection due to electromigration has emerged as a new problem. Yes.
[0003]
In order to avoid the disconnection caused by this electromigration phenomenon, the use of copper-based wiring is prominent. For example, with the further increase in integration, the use of copper-based materials for wiring patterns on semiconductor elements has been promoted. ing. That is, copper exhibits high conductivity like gold and silver, and also has good ductility and malleability, but its electromigration is much less than gold and silver. Therefore, when the current density increases with fine wiring, it is possible to avoid disconnection due to the electromigration phenomenon by using the copper-based wiring.
[0004]
Similarly, in a printed wiring board, when a fine wiring pattern is produced with a sintered body type wiring layer obtained by sintering metal nanoparticles, it is desired to use copper with less electromigration. Furthermore, compared to gold and silver, the unit price of the material itself is considerably cheaper, and copper can be used from the viewpoint of cost reduction in a printed wiring board having a fine wiring pattern that is more versatile. Expected.
[0005]
[Problems to be solved by the invention]
However, unlike noble metals such as gold and silver, copper is susceptible to oxidation and oxidation proceeds from its surface. In addition, when copper is made into a fine powder like nanoparticles, it easily binds to oxygen in the air even at room temperature, and forms an oxide film on the surface. This copper oxide is not passivated, and further, as a result of the oxidation proceeding into the interior of the nanoparticle, when exposed to air for a long period of time, most of it eventually becomes copper oxide. In particular, the progress of the oxidation is promoted in air containing moisture. The present inventors have tried to prevent oxidation of copper nanoparticles using various methods, for example, by dispersing them in an organic solvent, thereby preventing direct contact with air, thereby reducing the thickness of the oxide film. However, no means for completely avoiding surface oxidation could be found.
[0006]
When the copper nanoparticles are heated with the oxide film remaining on the surface and subjected to a sintering treatment, the copper nanoparticles partially sinter to form a sintered body, but at the grain boundaries. Is a state in which a thin copper oxide layer is interposed. Therefore, as a whole sintered body, formation of a dense current channel is not achieved, and it is difficult to produce a fine wiring pattern having desired good conductivity with high reproducibility. Therefore, when a reducing agent is added in advance to a dispersion containing copper nanoparticles having a surface oxide film, and the dispersion is applied on a substrate and heated, the surface of the surface is affected by the action of the added reducing agent. The copper oxide is reduced, and copper in a non-oxidized state appears on the surface of the nanoparticles. At the same time, the heating and firing proceeds, and a sintered copper wiring layer is formed. When this method is used, a hydrogenating agent such as a borohydride derivative is used as the reducing agent to be blended in the dispersion. However, sufficient reducing reaction is achieved, reproducibility and good conductivity. In order to obtain a sintered copper wiring layer, it is necessary to select a processing temperature of 400 ° C. or higher. As a substrate material that can withstand the above-mentioned processing temperature, it is limited to some heat-resistant materials such as ceramics. As a result, the method of blending this reducing agent in the dispersion cannot be expected to have a wide range of applications.
[0007]
Recently, as a solder material, tin alloy solder not containing lead, that is, so-called lead-free solder has been used, and heating at about 300 ° C. has sufficient heat resistance corresponding to the high melting temperature of such lead-free solder. Although the use of the substrate material is expanding, it is desired to develop a means that can achieve a sufficient reduction reaction even when the temperature of the reduction treatment is suppressed to 300 ° C. or lower.
[0008]
The present invention solves the above-mentioned problems, and an object of the present invention is to form such a fine wiring pattern when forming a fine copper-based wiring pattern that uses inexpensive and less electromigration copper as a conductive medium. The nanoparticle dispersion is used for drawing, and the copper oxide coating layer on the surface of the nanoparticles contained in the dispersion coating layer is sufficiently reduced under heating conditions of 300 ° C. or less, And it is providing the method of forming the fine sintered compact copper-type wiring pattern in which the precise | minute baking process between the copper nanoparticles obtained is possible. More specifically, in the case of nanoparticles having an average particle diameter of 100 nm or less, for example, an average particle diameter of about 1 to 10 nm, which is suitable for drawing an extremely fine wiring pattern, the surface of the copper oxide coating layer is the average particle. Although it reaches half or more of the diameter and the copper remains in the non-oxidized state in the center and remains a little, as a whole, it reaches a state that can be regarded as nanoparticles of copper oxide, but even in that case, heating conditions of 300 ° C. or less The present invention provides a method for forming a fine sintered copper-based wiring pattern that is sufficiently reduced and that can be subjected to a dense firing process between obtained copper nanoparticles.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present inventors applied a dispersion on a substrate, and then effectively reduced the copper oxide coating layer covering the surface of the copper nanoparticles contained in the coating layer. We have conducted extensive research on ways to do this. At that time, for example, in the case of nanoparticles having an average particle diameter of about 1 to 10 nm, the layer thickness of the copper oxide coating layer on the surface often reaches more than half of the fine average particle diameter. As a result of the increase in the ratio of copper oxide in the dispersion, it has been found that there is a case where a necessary amount of the reducing agent may not be supplied by a method in which the reducing agent is blended in advance in the dispersion. As a result of further studies based on such knowledge, in order to complete the desired reduction reaction without depending on the average particle diameter of the nanoparticles, after forming the coating layer, the reactive species involved in the reduction reaction are selected from the gas phase. Inspired by the optimal supply method. In that case, the oxygen-containing compound itself produced as a by-product by the reduction reaction is vaporized and evaporated, and does not remain in the coating layer.In addition, the reactive species involved in the reduction reaction are also gaseous, It has been found that it is preferable to reach deeper than narrow gaps between the densely stacked nanoparticles.
[0010]
In addition, the present inventors have confirmed that the reduction of the copper oxide coating layer on the nanoparticle surface is achieved by a thermal reduction reaction using, for example, hydrogen, which is a reducing gas. It was found that the processing temperature must be selected to be 400 ° C. or higher in order to proceed the chemical reduction reaction quickly. In order to promote an efficient reaction with the reactive species derived from the reducing gas at a treatment temperature of 300 ° C. or lower, the reaction was converted to an active reactive species derived from the reducing gas in an atmosphere in which plasma was generated in advance. From the above, it has been found that it is effective to act on the copper oxide coating layer on the nanoparticle surface. In addition, in the reduction reaction by such plasma-excited active reactive species, the by-product oxygen-containing compound itself is excellent in vaporization and transpiration, and in addition, a non-oxidized state generated on the surface by the reduction reaction As a result of the solid-state reaction between the copper atoms of the copper atoms and the copper oxide molecules present inside, the internal copper oxide is converted to non-oxidized copper atoms, and instead copper oxide is generated on the surface, resulting in copper oxide It was found that the coating layer gradually decreased and eventually the entire nanoparticle reverted to copper nanoparticles. It is also confirmed that when copper nanoparticles without oxide film come into contact with each other on this surface, sintering proceeds rapidly even at a relatively low temperature, and the entire coating layer forms a dense sintered body layer of copper nanoparticles. did. In addition to the above knowledge, even if the atmospheric temperature at which the plasma is generated is 300 ° C. or less, for example, a reducing gas is mixed in a gas suitable for plasma maintenance, such as argon or helium. Thus, the plasma-excited active reactive species can be stably supplied, and the reduction reaction to the copper oxide coating layer on the surface of the nanoparticles and the subsequent formation of a sintered body layer between the regenerated copper nanoparticles, The present inventors have also confirmed that this can be done efficiently, and have completed the present invention.
[0011]
That is, the method for forming a fine wiring pattern of the present invention includes:
A method of forming a fine copper-based wiring pattern comprising a sintered body layer of copper nanoparticles on a substrate,
Drawing the coating layer of the fine wiring pattern on the substrate using a dispersion containing nanoparticles having a copper oxide coating layer on the surface, the average particle diameter being selected in the range of 1 to 100 nm;
The nanoparticles having a copper oxide coating layer on the surface thereof contained in the coating layer are subjected to a treatment for reducing the copper oxide on the surface, and further, the nanoparticles subjected to the reduction treatment are fired and sintered. Forming a body layer,
The reduction treatment and firing treatment carried out in the same process are as follows:
Select the heating temperature to be 300 ° C or lower,
It is a method for forming a fine wiring pattern, which is performed by exposing the nanoparticles contained in a coating layer in a plasma atmosphere generated in the presence of a reducing gas. At that time, at least the nanoparticles having a copper oxide coating layer on the surface contained in the dispersion, the copper oxide coating layer is made of cuprous oxide, cupric oxide or a mixture of these copper oxides. In addition, the nanoparticles may be mixed particles containing two or more of cuprous oxide, cupric oxide or a mixture of these copper oxides, and metallic copper. it can.
[0012]
On the other hand, the reducing gas to be present in the plasma atmosphere is preferably hydrogen, ammonia, carbon monoxide, or a mixture of two or more thereof.
[0013]
In the method for forming a fine wiring pattern of the present invention,
As a technique to draw a fine wiring pattern coating layer on the substrate,
Any drawing method of screen printing, inkjet printing, or transfer printing can be selected. In addition, in the coating layer of the fine wiring pattern drawn on the substrate,
Corresponding to the minimum wiring width of the wiring pattern in the range of 0.1 to 50 μm, the minimum inter-wiring space is selected in the range of 0.1 to 50 μm,
It is desirable that the average particle diameter of the nanoparticles contained in the dispersion is selected to be 1/10 or less of the minimum wiring width and the minimum inter-wiring space.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the method for forming a fine sintered copper-based wiring pattern of the present invention, unlike metal nanoparticles using gold or silver, which are noble metals, copper nanoparticles are very susceptible to oxidation, and their oxidation In consideration of the fact that there is no means to completely prevent this, a dispersion of nanoparticles having a copper oxide coating layer on the surface is prepared, and a desired wiring pattern is drawn on the substrate using this dispersion of nanoparticles. After that, by reducing the copper oxide coating layer present on the surface of the nanoparticles, the copper nanoparticles are regenerated into a copper nanoparticle and subjected to a firing treatment, so that the copper nanoparticles are densely sintered in the coating layer. By using the body layer, a copper-based wiring pattern with low cost and less electromigration is formed.
[0015]
In particular, in the method for forming a fine wiring pattern according to the present invention, in the step of reducing the copper oxide coating layer present on the surface of the nanoparticles, the heating temperature is selected to be 300 ° C. or lower, and it is generated in the presence of a reducing gas. In the plasma atmosphere, the nanoparticles contained in the coating layer are exposed to the nanoparticle after being converted into an active reactive species derived from a reducing gas in an atmosphere in which plasma is generated in advance. By acting on the copper oxide coating layer on the surface, even if the heating temperature is as low as room temperature (25 ° C.) or more and 300 ° C. or less, the reduction reaction of the surface copper oxide can proceed rapidly. Once the solid-state reaction between the non-oxidized copper atoms generated on the surface and the copper oxide molecules present inside the copper atoms, the internal copper oxide is converted to non-oxidized copper atoms and oxidized on the surface instead. Copper is produced, but the copper oxide produced on this surface is reduced to non-oxidized copper atoms by the reducing action of active reactive species derived from the reducing gas continuously supplied from the gas phase. The As a result of repeating the series of reaction cycles described above, the copper oxide coating layer that has reached the depth of the nanoparticles at the beginning is gradually reduced, and finally the entire nanoparticle is restored to the copper nanoparticle. .
[0016]
If the state returned to the copper nanoparticles is brought into contact with the atmosphere again, surface oxidation occurs rapidly. However, in the method for forming a fine wiring pattern of the present invention, the reducing gas is not brought into contact with the atmosphere again. The clean surfaces of the regenerated copper nanoparticles are closely packed with each other even at a heating temperature selected from room temperature (25 ° C.) to 300 ° C. while being kept in the generated plasma atmosphere. As a result of the contact state, sintering proceeds rapidly even at a relatively low temperature, and the entire coating layer is formed in a dense sintered body layer of copper nanoparticles.
[0017]
That is, in the method for forming a fine wiring pattern of the present invention, finally, in a state where the clean surfaces of the regenerated copper nanoparticles are in close contact with each other, the room temperature is 25 ° C. or higher and 300 ° C. or lower. Depending on the heating temperature selected, it is desirable to select the average particle size of the nanoparticles to be used within a range in which sintering can proceed rapidly. From this viewpoint, the copper oxide coating layer is used on the surface to be used. The average particle size of the nanoparticles having a diameter is selected in the range of 1 to 100 nm, more preferably in the range of 1 to 10 nm. Furthermore, the method for forming a fine wiring pattern according to the present invention is, first of all, when an extremely fine wiring pattern is formed, the disconnection caused by the electromigration phenomenon that is most prominently found in the portion of the minimum wiring width. In order to avoid the above, the sintered copper-based wiring is used, and the minimum wiring width of the wiring pattern corresponds to the range of 0.1 to 50 μm, practically the range of 5 to 50 μm. Thus, when the minimum inter-wiring space is selected within the range of 0.1 to 50 μm, and practically within the range of 5 to 50 μm, this is a more preferable method. In drawing the above extremely fine wiring pattern with a dispersion of nanoparticles with high uniformity of the wiring width, the average particle diameter of the nanoparticles used is the minimum wiring width and the minimum target. It is desirable to select 1/10 or less of the space between wirings. At the same time, depending on the minimum wiring width, the layer thickness of the sintered copper-based wiring layer is also determined as appropriate, but usually the layer thickness of the wiring layer is significantly smaller than the minimum wiring width, By controlling the average particle size of the nanoparticles to be in the range of 1 to 100 nm, more preferably in the range of 1 to 10 nm, it is possible to suppress variations in the thickness of the wiring layer and uneven local height. Is possible.
[0018]
On the other hand, as a technique for drawing a desired wiring pattern on a substrate using a dispersion liquid containing the nanoparticles, it has been conventionally used in the formation of a fine wiring pattern using a dispersion liquid containing metal nanoparticles. Any drawing method of screen printing, inkjet printing, or transfer printing can be used in the same manner. Specifically, in consideration of the shape of the desired fine wiring pattern, the minimum wiring width, and the layer thickness of the wiring layer, a more suitable one of these screen printing, ink jet printing, or transfer printing should be selected. Is desirable.
[0019]
On the other hand, it is desirable that the dispersion containing the nanoparticles to be used is prepared to have a liquid viscosity suitable for each according to the drawing technique employed. For example, when screen printing is used for drawing a fine wiring pattern, it is desirable that the dispersion containing the nanoparticles has a liquid viscosity of 50 to 200 Pa · s (25 ° C.). Moreover, when using transfer printing, it is desirable to select a liquid viscosity in the range of 150 to 300 Pa · s (25 ° C.). When using inkjet printing, it is desirable to select the liquid viscosity in the range of 5 to 30 mPa · s (25 ° C.). The liquid viscosity of the dispersion containing the nanoparticles is determined depending on the average particle diameter of the nanoparticles to be used, the dispersion concentration, and the type of the dispersion solvent being used. The liquid viscosity can be adjusted.
[0020]
Further, in the dispersion containing the nanoparticles, it is preferable that the contained nanoparticles maintain a uniform dispersion state. For example, in order to improve the dispersibility of the nanoparticles, Metal element, that is, a terminal amino group (-NH ₂ ), A hydroxy group (—OH), a sulfanyl group (—SH), or an organic compound having ether (—O—) and sulfide (—S—) in the molecule. One or more excellent materials can be added. Although these dispersants improve the dispersibility by forming a dispersant layer covering the surface of the nanoparticles, finally, in the firing step, when the copper nanoparticles are brought into contact with each other, they are hindered. It is preferable not to become. If necessary, the terminal amino group (—NH ₂ ), A hydroxy group (—OH), a sulfanyl group (—SH), a compound that reacts when heated and accelerates the release of the dispersant molecule from the nanoparticle surface, depending on the type and amount of the dispersant added. They can be blended as appropriate. For example, the terminal amino group (—NH ₂ ), A hydroxy group (—OH), and a sulfanyl group (—SH), a cyclic acid anhydride derived from a dicarboxylic acid can be used.
[0021]
A nanoparticle having a copper oxide coating layer on the surface thereof has an average particle diameter in the above range, and the production method thereof is not limited as long as the average particle diameter is known in advance. For example, a copper nanoparticle may have a copper oxide coating layer formed on the surface thereof, or the nanoparticle as a whole may be copper oxide. Therefore, the nanoparticles having a copper oxide coating layer on the surface thereof, at least the copper oxide coating layer comprises cuprous oxide, cupric oxide or a mixture of these copper oxides, and the nanoparticles Can be a mixed particle comprising two or more of cuprous oxide, cupric oxide or a mixture of these copper oxides, and metallic copper. Although the surface copper oxide coating layer is restored to metallic copper again by the reduction treatment in the above plasma atmosphere, depending on the thickness of the surface copper oxide coating layer, the treatment time is extended. A thinner copper oxide coating layer on the surface is generally preferable. However, when the average particle diameter of the nanoparticles is selected within the range of 1 to 10 nm, the time required for the reduction treatment may become long enough to be a problem even if the entire nanoparticles are made of copper oxide. Absent.
[0022]
In addition, when this nanoparticle dispersion is used for wiring formation, a resin component such as an epoxy resin that functions as an organic binder in order to uniformly disperse, increase the concentration of the dispersion, and improve adhesion to the substrate, It is preferable to prepare a nanoparticle dispersion by adding an organic acid anhydride or organic acid that functions to remove the dispersant, and an organic solvent serving as a solvent thereof, and further mixing and stirring.
[0023]
After drawing the wiring pattern using the nanoparticle dispersion liquid, the wiring board is subjected to a heating temperature of room temperature (25 ° C., for example) in the plasma processing apparatus shown in FIG. In the above manner, the temperature is selected to be 300 ° C. or lower, and the nanoparticles contained in the coating layer are exposed to the plasma atmosphere generated in the presence of the reducing gas.
[0024]
First, after the wiring board is installed in the apparatus, the inside of the apparatus is depressurized to 150 Pa or less in advance to remove air remaining in the system. Next, a mixed gas of an inert gas and a reducing gas is supplied from the gas inlet at a constant flow rate, plasma is generated in the presence of the reducing gas, and reduction treatment is performed in the plasma atmosphere. For example, the flow rate of the mixed gas of inert gas and reducing gas is adjusted to 1 to 1000 ml / min (regular state equivalent flow rate), and the internal pressure in the apparatus is maintained and the plasma is generated and maintained by the pressure adjustment function of the exhaust system. Is adjusted to a pressure suitable for the pressure, for example, in the range of 1 to 120,000 Pa. As the internal pressure in the apparatus, it is desirable to select a pressure suitable for the generation and maintenance of plasma according to the frequency of high-frequency power to be used, the amount of power, the gas composition, and the flow rate. Specifically, in various plasma CVD methods, for example, a low pressure plasma CVD method, it is preferable to set conditions with reference to conditions that are beneficial to the stability of the plasma state.
[0025]
On the other hand, the plasma is generated, for example, by applying a high frequency power to the electrode, which is widely used in a plasma CVD method with a frequency of 13.56 MHz, and setting the amount of power in a range of 100 to 5000 W, and a desired plasma density. It is desirable to maintain In that case, nitrogen, helium, argon, etc. can be utilized as inert gas which dilutes reducing gas, such as hydrogen and ammonia. For example, helium and argon also have an advantage that contributes to the generation and maintenance of plasma under the above-described conditions. In addition, the mixing ratio (volume ratio) of the inert gas and the reducing gas is selected in the range of 50:50 to 99.9: 0.1, and preferably in the range of 80:20 to 99: 1. In the plasma atmosphere, the temperature rises due to the plasma, but the temperature of the printed circuit board itself installed in the processing apparatus is set so that it is maintained at 300 ° C. or lower, that is, in the range of 20 ° C. to 300 ° C.・ Adjust. Although depending on the set temperature and the plasma generation conditions, the plasma treatment time can be selected in the range of 1 second to 1 hour, preferably 1 minute to 20 minutes. Specifically, the set temperature and plasma generation conditions are appropriately selected in consideration of the thickness of the copper oxide coating layer covering the nanoparticle surface and the time required for the reduction. After the reduction of the copper oxide coating layer covering the nanoparticle surface by this plasma treatment, the nanoparticles contacting the cleaned copper surface are subjected to low-temperature sintering in a reducing atmosphere and oxidized at the interface. It is possible to form a sintered body layer without any physical film. Specifically, under the plasma processing conditions, the printed circuit board itself installed in the processing apparatus is cleaned at 300 ° C. or lower, that is, maintained in a range of 20 ° C. to 300 ° C. after reduction is completed. The nanoparticles that come into contact with the copper surface are continuously irradiated with plasma in a reducing atmosphere, so that the energy of the locally irradiated plasma particles is supplied, and low-temperature sintering using the thermal energy proceeds. .
[0026]
Since the drawing of the wiring pattern can be performed using a dispersion liquid containing nanoparticles, its fine drawing characteristics are comparable to conventional fine wiring pattern formation using gold and silver nanoparticles. . Specifically, the fine wiring pattern to be formed has a minimum wiring width of 0.1 to 50 μm, practically a range of 5 to 50 μm, and a corresponding minimum inter-wiring space of 0.1 to 0.1 μm. It is possible to achieve good line width uniformity and reproducibility by selecting in the range of ˜50 μm, practically in the range of 5˜50 μm. In addition, the obtained wiring layer becomes a sintered layer of copper nanoparticles without an oxide film at the interface, and the volume resistivity at the minimum wiring width is also 1 × 10. ^-Five Ω · cm or less can be achieved, and good conduction characteristics can be achieved.
[0027]
In addition, since the sintered body layer to be formed is a conductive material with little electromigration, the wiring thickness is reduced due to electromigration and the occurrence of disconnection even in the above fine wiring pattern. Can be suppressed.
[0028]
【Example】
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.
[0029]
Example 1
A paste liquid containing copper oxide nanoparticles in a uniform dispersion state was prepared by the following procedure.
[0030]
Commercially available copper oxide nanoparticle dispersion (trade name: Independently dispersed ultrafine particle perfect copper, Vacuum Metallurgical Co., Ltd.), specifically, as alkylamine per 100 parts by mass of copper oxide nanoparticles having an average particle diameter of 8 nm A copper oxide nanoparticle dispersion containing 15 parts by mass of dodecylamine and 75 parts by mass of terpineol as an organic solvent is used.
[0031]
10 parts by mass of methyl hexahydrophthalic anhydride (Me-HHPA) is added as an acid anhydride to 100 parts by mass of the copper oxide nanoparticles contained in the dispersion of the copper oxide nanoparticles, followed by stirring and defoaming Mix thoroughly with a machine to prepare a copper oxide nanoparticle paste liquid. The liquid viscosity of the copper oxide nanoparticle paste liquid was 100 Pa · s (25 ° C.).
[0032]
The dodecylamine, which is an alkylamine contained in the paste liquid, has an amino group as a group capable of coordinative bonding to copper, and non-oxidized copper is exposed on the surface. Then, it functions as a surface protective molecular layer by forming a coordinate bond with the copper atom. On the other hand, Me-HHPA, which is an acid anhydride, exhibits reactivity to the amino group of the alkylamine when heated, and has a function of promoting the release of dodecylamine that forms a surface protective molecular layer from the copper surface. . As a result, copper in a non-oxidized state is exposed on the surface, and the adjacent nanoparticles are brought into contact with each other and the sintering proceeds at a low temperature. At the same time, the alkylamine constituting the surface protective molecular layer, specifically, dodecylamine, is dispersed in nanoparticles in a dispersion solvent (organic solvent) contained in the paste liquid using its hydrocarbon chain. It also contributes to improved characteristics.
[0033]
Using this copper oxide nanoparticle paste liquid, a wiring pattern was drawn on a printed wiring board by screen printing. The wiring pattern to be drawn was a stripe pattern having a line width and space of 30/30 μm. At that time, the paste coating film thickness at the time of drawing was selected to be 20 μm.
[0034]
After drawing, the wiring board was placed in the plate electrode type plasma processing apparatus shown in FIG. 1, and the internal pressure of the plasma processing apparatus was reduced to 10 Pa by the exhaust system. After the depressurization, a mixed gas of argon gas: hydrogen gas = 95: 5 (volume ratio) is supplied into the apparatus at a flow rate of 100 ml / min (normal state converted flow rate), and between the plate electrodes 2 and 3, A high frequency power (frequency: 13.56 MHz) 500 W was applied, and plasma treatment was performed at 150 ° C. for 5 minutes. During this plasma treatment, the internal pressure of the apparatus was maintained at about 30-40 Pa.
[0035]
As a result of processing in a plasma atmosphere generated in a mixed gas containing hydrogen as the reducing gas, the copper oxide nanoparticles in the wiring pattern undergo plasma reduction and are once restored to copper nanoparticles. Furthermore, the dispersion solvent contained in the coating layer is evaporated, and the surface protective molecular layer of dodecylamine covering the surface of the copper nanoparticles is removed by the acid anhydride Me-HHPA, and the plasma reduction treatment is performed to the inside of the coating layer. Is achieved, and a state in which the copper nanoparticles are in close contact with each other throughout the coating layer is achieved. By applying low-temperature heating in this state, low-temperature sintering of copper nanoparticles having no oxide film on the surface progressed, and as a whole, a copper sintered body type wiring layer was formed.
[0036]
The obtained copper wiring had a wiring width and space of 30/30 μm, and an average layer thickness of 2 μm. When the resistance value of the copper wiring layer was measured, and the volume resistivity was calculated assuming a homogeneous body having the wiring width and the average layer thickness, the value was 4.5 × 10. ^-6 It was Ω · cm. The resistivity (20 ° C.) of copper itself is 1.673 × 10 ^-6 Compared with the value, it is judged that the obtained sintered copper-type wiring layer has achieved a close sintering between the copper nanoparticles. Moreover, also in the result of SEM observation, the interposition of copper oxide is not recognized in the grain boundary part between the copper nanoparticles, and it is judged that a sintered body showing good conductivity is formed.
[0037]
(Example 2)
In the same manner as in Example 1, with respect to a dispersion of copper oxide nanoparticles having an average particle diameter of 8 nm (trade name: independent dispersed ultrafine particle perfect copper, Vacuum Metallurgy Co., Ltd.), acid anhydride per 100 parts by mass of copper oxide nanoparticles. As a product, 10 parts by mass of methylhexahydrophthalic anhydride (Me-HHPA) is added and sufficiently stirred with a stirring deaerator to prepare a copper oxide nanoparticle paste liquid. The liquid viscosity of the copper oxide nanoparticle paste liquid was adjusted to 10 mPa · s (25 ° C.), and using this paste liquid, a wiring pattern was drawn on a printed wiring board by inkjet printing. The drawn wiring pattern was a stripe pattern having a line width and space of 15/15 μm. At that time, the paste coating film thickness at the time of drawing was selected to be 3 μm.
[0038]
After drawing, the wiring substrate was subjected to plasma treatment using a mixed gas of argon gas: hydrogen gas = 95: 5 (volume ratio) under the conditions described in Example 1 above, with the substrate heating temperature set to 50 ° C. .
[0039]
As a result of processing in a plasma atmosphere generated in a mixed gas containing hydrogen as the reducing gas, the copper oxide nanoparticles in the wiring pattern undergo plasma reduction and are once restored to copper nanoparticles. Furthermore, by applying low-temperature heating in this state, low-temperature sintering of copper nanoparticles having no oxide film on the surface progressed, and as a whole, a copper sintered body type wiring layer was formed.
[0040]
The obtained copper wiring had a wiring width and space of 15/15 μm, and an average layer thickness of 0.8 μm. When the resistance value of the copper wiring layer was measured, and the volume resistivity was calculated assuming a homogeneous body having the wiring width and the average layer thickness, the value was 6.6 × 10 6. ^-6 It was Ω · cm.
[0041]
Along with the difference in drawing method, there is a slight difference in the layer thickness variation of the coating layer in the substrate and the ratio of the organic solvent contained after coating, so there is a slight difference in the evaluated volume resistivity. However, similarly to Example 1 using screen printing, also in Example 2 using ink jet printing, the obtained sintered copper-type wiring layer achieves dense sintering between copper nanoparticles. It is judged that
[0042]
(Example 3)
Using the same copper oxide nanoparticle paste solution as in Example 1, a wiring pattern was drawn on the printed wiring board by screen printing. The wiring pattern to be drawn was a stripe pattern having a line width and space of 30/30 μm. At that time, the paste coating film thickness at the time of drawing was selected to be 20 μm.
[0043]
After drawing, the wiring board was placed in the plate electrode type plasma processing apparatus shown in FIG. 1, and the internal pressure of the plasma processing apparatus was reduced to 10 Pa by the exhaust system. After the depressurization, a mixed gas of argon gas: hydrogen gas: ammonia gas = 94: 3: 3 (volume ratio) is supplied into the apparatus at a flow rate of 100 ml / min (normal state converted flow rate), and the plate electrode 2 A high-frequency power (frequency: 13.56 MHz) of 500 W was applied between the three and plasma treatment was performed at 150 ° C. for 5 minutes. During this plasma treatment, the internal pressure of the apparatus was maintained at about 30-40 Pa.
[0044]
As a result of processing in a generated plasma atmosphere in a mixed gas containing hydrogen and ammonia as the reducing gas, the copper oxide nanoparticles in the wiring pattern are subjected to plasma reduction and are once restored to copper nanoparticles. Furthermore, by applying low-temperature heating in this state, low-temperature sintering of copper nanoparticles having no oxide film on the surface progressed, and as a whole, a copper sintered body type wiring layer was formed.
[0045]
The obtained copper wiring had a wiring width and a space of 30/30 μm, and an average layer thickness of 3 μm. When the resistance value of the copper wiring layer was measured, and the volume resistivity was calculated assuming a homogeneous body having the wiring width and the average layer thickness, the value was 3.2 × 10. ^-6 It was Ω · cm.
[0046]
Although there is a slight difference in the evaluated volume resistivity, which is considered to be derived from the difference in reducing gas used in the plasma treatment, the obtained copper is also obtained in this Example 3 as in Example 1 above. This sintered body type wiring layer is judged to have achieved a close sintering between the copper nanoparticles.
[0047]
(Example 4)
A paste liquid containing copper oxide nanoparticles in a uniform dispersion state was prepared by the following procedure.
[0048]
Commercially available copper oxide nanoparticles (trade name: Nanotech, CI Chemical Co., Ltd.), specifically, copper oxide nanoparticles with an average particle diameter of 47.6 nm, ethanol, propyl at a dispersion concentration of 15% by mass A slurry dispersion dispersed in an alcohol mixture is used.
[0049]
To the dispersion of copper oxide nanoparticles, 20 parts by mass of polyethyl alcohol 2-ethylhexanediol is added as a high boiling point solvent per 100 parts by mass of the copper oxide nanoparticles contained, and the alcohol solvent has a low boiling point. After removing the solvent, the mixture is sufficiently stirred with a stirring deaerator to prepare a copper oxide nanoparticle paste liquid. The liquid viscosity of the copper oxide nanoparticle paste liquid was 70 Pa · s (25 ° C.).
[0050]
Using this copper oxide nanoparticle paste liquid, a wiring pattern was drawn on a printed wiring board by screen printing. The wiring pattern to be drawn was a stripe pattern having a line width and space of 30/30 μm. At that time, the paste coating film thickness at the time of drawing was selected to be 20 μm.
[0051]
After drawing, the wiring substrate was subjected to plasma treatment using a mixed gas of argon gas: hydrogen gas = 95: 5 (volume ratio) under the conditions described in Example 1 above. In addition, since the average particle diameter of the nanoparticles was larger than that of Example 1, the time required for the reduction was longer, and the plasma treatment time was 10 minutes.
[0052]
As a result of processing in a plasma atmosphere generated in a mixed gas containing hydrogen as the reducing gas, the copper oxide nanoparticles in the wiring pattern undergo plasma reduction and are once restored to copper nanoparticles. Furthermore, by applying low-temperature heating in this state, low-temperature sintering of copper nanoparticles having no oxide film on the surface progressed, and as a whole, a copper sintered body type wiring layer was formed.
[0053]
The obtained copper wiring had a wiring width and a space of 30/30 μm, and an average layer thickness of 5 μm. When the resistance value of the copper wiring layer was measured, and the volume resistivity was calculated assuming a homogeneous body having the wiring width and the average layer thickness, the value was 6.0 × 10. ^-6 It was Ω · cm.
[0054]
Due to the difference in the average particle diameter of the nanoparticles used, it is thought that it is derived from the difference in the low-temperature sintering characteristics. Also in Example 4, it is judged that the obtained sintered copper-type wiring layer has achieved a close sintering between the copper nanoparticles.
[0055]
(Example 5)
Using the same copper oxide nanoparticle paste solution as in Example 1, a wiring pattern was drawn on the printed wiring board by screen printing. The wiring pattern to be drawn was a stripe pattern having a line width and space of 30/30 μm. At that time, the paste coating film thickness at the time of drawing was selected to be 20 μm.
[0056]
After drawing, the wiring board was placed in the plate electrode type plasma processing apparatus shown in FIG. 1, and the internal pressure of the plasma processing apparatus was reduced to 10 Pa by the exhaust system. After the depressurization, a mixed gas of argon gas: hydrogen gas: carbon monoxide gas = 94: 3: 3 (volume ratio) is supplied into the apparatus at a flow rate of 100 ml / min (normal state converted flow rate), and a flat plate A high frequency power (frequency: 13.56 MHz) 500 W was applied between the electrodes 2 and 3, and plasma treatment was performed at 50 ° C. for 5 minutes. During this plasma treatment, the internal pressure of the apparatus was maintained at about 30-40 Pa.
[0057]
As a result of processing in a generated plasma atmosphere in a mixed gas containing hydrogen and carbon monoxide as the reducing gas, the copper oxide nanoparticles in the wiring pattern are subjected to plasma reduction and are once restored to copper nanoparticles. To do. Furthermore, by applying low-temperature heating in this state, low-temperature sintering of copper nanoparticles having no oxide film on the surface progressed, and as a whole, a copper sintered body type wiring layer was formed.
[0058]
The obtained copper wiring had a wiring width and a space of 30/30 μm, and an average layer thickness of 3 μm. When the resistance value of the copper wiring layer was measured, and the volume resistivity was calculated assuming a homogeneous body having the wiring width and the average layer thickness, the value was 7.8 × 10. ^-6 It was Ω · cm.
[0059]
Although there is a slight difference in the evaluated volume resistivity, which is considered to be derived from the difference in reducing gas used in the plasma treatment, the obtained copper is also obtained in this Example 5 as in Example 1 above. This sintered body type wiring layer is judged to have achieved a close sintering between the copper nanoparticles.
[0060]
【The invention's effect】
In the method for forming a fine wiring pattern of the present invention, a fine wiring pattern drawn using a nanoparticle having a copper oxide film layer on its surface or a dispersion containing copper oxide nanoparticles is used as a boron hydride derivative or the like. Instead of reducing treatment using a general reducing agent, plasma treatment in a reducing gas atmosphere reduces the copper oxide film layer on the surface and regenerates it into copper nanoparticles. The plasma treatment temperature can be a low temperature of 300 ° C. or lower compared to the reduction treatment temperature when using a general reducing agent such as 400 ° C. or higher. Even in this low-temperature treatment, the reduction of copper oxide and subsequent firing of the resulting copper nanoparticles can be achieved, so the heat resistance required for the substrate material to be used is greatly eased, and the usage range is greatly expanded Have In addition, since the obtained fine copper-based wiring is a conductive material with less electromigration, the copper thickness is reduced due to electromigration even in the above fine wiring pattern. Can be suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration of a plasma processing apparatus that can be used for performing a plasma reduction process in a method for forming a fine sintered copper-based wiring pattern according to the present invention.
[Explanation of symbols]
1 Plasma processing equipment container
2 Electrode for applying high frequency power
3 Grounding electrode
4 Substrate
5 Gas inlet
6 Gas outlet
7 High frequency power supply

Claims (7)

A method of forming a fine copper-based wiring pattern comprising a sintered body layer of copper nanoparticles on a substrate,
Drawing the coating layer of the fine wiring pattern on the substrate using a dispersion containing nanoparticles having a copper oxide coating layer on the surface, the average particle diameter being selected in the range of 1 to 100 nm;
The nanoparticles having a copper oxide coating layer on the surface thereof contained in the coating layer are subjected to a treatment for reducing the copper oxide on the surface, and further, the nanoparticles subjected to the reduction treatment are fired and sintered. Forming a body layer,
The reduction treatment and firing treatment carried out in the same process are as follows:
Select the heating temperature to be 300 ° C or lower,
Performed by exposing the nanoparticles contained in the coating layer in a plasma atmosphere generated in the presence of a reducing gas,
The reducing gas is selected from the group consisting of hydrogen gas, a combination of hydrogen gas and ammonia, a combination of hydrogen gas and carbon monoxide,
An inert gas selected from the group consisting of helium and argon and the reducing gas are selected such that the mixing ratio (volume ratio) of the inert gas: reducing gas is in the range of 80:20 to 99: 1. In a mixed state,
The plasma atmosphere generated in the presence of the reducing gas is generated by supplying high-frequency power in a state where the pressure is reduced to at least 150 Pa or less;
A dispersion containing nanoparticles having a copper oxide coating layer on the surface, the average particle diameter of which is selected in the range of 1 to 100 nm,
Containing a dispersant, uniformly dispersing the nanoparticles in a dispersion solvent,
As the dispersant , one or more alkylamines having an amino group (—NH ₂ ) having excellent affinity with the dispersion solvent and capable of coordinative bonding with copper are contained,
The dispersing agent forms a dispersing agent layer that coats the surface of the nanoparticles, and improves the dispersibility of the nanoparticles in the dispersing solvent. Method. Nanoparticles having a copper oxide coating layer on the surface, contained in the dispersion,
At least the copper oxide coating layer comprises cuprous oxide, cupric oxide or a mixture of these copper oxides, and the nanoparticles comprise cuprous oxide, cupric oxide or these copper oxides. 2. The method according to claim 1, wherein the mixture is a mixture of two or more of metal oxides and metallic copper. In the plasma atmosphere, the reducing gas to be present is selected from the group consisting of hydrogen gas, a combination of hydrogen gas and ammonia, and a combination of hydrogen gas and carbon monoxide, and argon and the reducing gas are combined with the inert gas. The method according to claim 1, wherein the mixing ratio (volume ratio) of the reducing gas is selected in the range of 80:20 to 99: 1 to form a mixed state . As a technique to draw a fine wiring pattern coating layer on the substrate,
The method according to claim 1, wherein a drawing method of screen printing, ink jet printing, or transfer printing is selected. In the coating layer of the fine wiring pattern drawn on the substrate,
Corresponding to the minimum wiring width of the wiring pattern in the range of 0.1 to 50 μm, the minimum inter-wiring space is selected in the range of 0.1 to 50 μm,
2. The average particle diameter of the nanoparticles contained in the dispersion is selected to be 1/10 or less of the minimum wiring width and the minimum inter-wiring space. the method of. A dispersion containing nanoparticles having a copper oxide coating layer on the surface, the average particle diameter of which is selected in the range of 1 to 100 nm,
The dispersant contains at least one alkylamine having an amino group (—NH ₂ ) terminal, which has excellent affinity with the dispersion solvent and can coordinately bond with metallic copper. ,
The cyclic acid anhydride derived from a dicarboxylic acid, when heated, claim response to an amino group of the terminal (-NH ₂₎ is a compound capable, characterized <br/> that blended 1 The method as described in any one of -5. The method according to any one of claims 1 to 6, wherein an average particle diameter of nanoparticles having a copper oxide coating layer on the surface is selected in a range of 1 to 10 nm.

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