JP3827447B2 - Multilayer wiring board and manufacturing method thereof - Google Patents

Description

【００４５】
【表２】

【００４６】
表１に示すように、同時焼成時の露点が−２０℃よりも高い試料Ｎo.１では、導体抵抗の上昇、銅の拡散距離が２０μｍを超え且つ表面荒さも低下した。また、雰囲気中に水素を含まない試料Ｎo.１９、２０では、メタライズの酸化が起こり、導体抵抗が上昇した。
【００４７】
また、内部配線層組成において、Ｃｕ／（Ｃｕ＋Ｗ＋Ｍｏ）の体積比が０．３よりも小さい試料Ｎo.９、１３では、導体抵抗が８ｍΩ／□よりも大きくなった。また、同時焼成の温度が１５００℃よりも高い試料Ｎo.１７では、銅拡散距離が２０μｍよりも大きくなることにより絶縁基板の絶縁性が劣化した。
【００４８】
これらの比較例に対して、本発明の多層配線基板によれば、シート抵抗が８ｍΩ／□以下、銅の拡散距離２０μｍ以下であり、これにより配線層間の抵抗を１０⁹ Ω以上に高めることができた。しかも、いずれも表面粗さＲａが１μｍ以下であり、表面平滑性に優れるものであった。
【００４９】
【発明の効果】
以上詳述した通り、本発明の銅含有導体からなる内部配線層を形成する場合、水素を含む露点が−２０℃以下の非酸化性雰囲気中で同時焼成することにより、銅の絶縁基板中への拡散を２０μｍ以下に抑制でき、これにより配線層間の絶縁劣化を防止し、高信頼性の高密度の配線層を形成することができる。しかも、焼成後の基板表面の平滑性に優れ、研磨工程等を必要としない安価な多層配線基板を提供できる。
【図面の簡単な説明】
【図１】本発明の多層配線基板の一実施態様を示す概略断面図である。
【図２】本発明の多層配線基板における内部配線層中の銅の拡散状態を説明するための図である。
【符号の説明】
１ 絶縁基板
１ａ，１ｂ、１ｃ 絶縁層
２ａ 内部配線層
２ｂ 表面配線層
３ ビアホール導体
４ 銅元素[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer wiring board using an oxide ceramic as an insulating substrate, and in particular, can be sintered at a temperature of 1400 ° C. to 1500 ° C., has good thermal conductivity, and has low resistance and low migration. The present invention relates to a multilayer wiring board having a wiring layer and a manufacturing method thereof.
[0002]
[Prior art]
In recent years, heat generated from a semiconductor device has been increased with higher integration of semiconductor elements. In order to eliminate the malfunction of the semiconductor device, a wiring board capable of releasing such heat to the outside of the device is necessary.
[0003]
On the other hand, as an electrical characteristic, signal delay becomes a problem due to an increase in calculation speed, and it has been required to use a conductor having a small conductor loss, that is, a low resistance. Conventionally used conductors mainly composed of tungsten can only be reduced to about 8 mΩ / □. Therefore, a multilayer wiring board using so-called glass ceramics that can be fired simultaneously with copper and silver which are low resistance conductors has been proposed.
[0004]
However, since the thermal conductivity of glass ceramics is only a few W / m · K, it is difficult to solve the thermal problem. Thus, as a method for simultaneously solving the thermal problem and the electrical problem, a method of simultaneously forming a conductor layer of copper or a combination of copper and tungsten or molybdenum on aluminum oxide is disclosed in Japanese Patent Laid-Open No. 7-15101. No. 1, JP-A-8-8502, and Japanese Patent No. 2666744.
[0005]
[Problems to be solved by the invention]
However, JP-A-8-8502 is based on the premise that firing is performed at a high temperature of 1600 ° C. or higher in order to densify the aluminum oxide. As a result, the copper component in the wiring layer is fired. There is a problem that the insulation between the wiring layers deteriorates due to diffusion into the ceramic of the insulating substrate.
[0006]
In order to suppress the diffusion of copper, it is considered effective to improve the sinterability at low temperatures of ceramics and lower the firing temperature. Preventing diffusion or volatilization during firing because copper is oxidized by the generated oxygen or water vapor generated by the reaction of this oxygen and hydrogen in the atmosphere, resulting in copper oxide that easily diffuses. There is a problem that the insulation between the wiring layers cannot be prevented from being deteriorated.
[0007]
Moreover, according to Japanese Patent Laid-Open No. 7-15101, after all the wiring layers are disposed inside the insulating substrate and fired at the same time, the surface insulating layer is removed by polishing or the like to expose the conductors on the surface, and the surface wiring Although it is disclosed that a layer is formed, the method of course adds a step such as polishing, which leads to an increase in cost.
[0008]
Furthermore, Japanese Patent No. 2666744 discloses a method of co-firing with gold, silver, copper, etc. at a low temperature of 1200 ° C. or lower using fine alumina powder having an average particle diameter of 5 to 50 nm. Use of such fine powder is accompanied by great difficulty in the process, leading to an increase in cost.
[0009]
Therefore, the present invention forms an internal wiring layer made of a low-resistance conductor containing copper by simultaneous firing, prevents insulation deterioration between wiring layers due to copper diffusion, can form a high-density wiring layer, and is polished. An object of the present invention is to provide an inexpensive multilayer wiring board that does not require a process or the like and a manufacturing method thereof.
[0010]
[Means for Solving the Problems]
As a result of repeated studies on the above problems, the present inventors have found that, in a multilayer wiring board using an oxide ceramic as an insulating substrate, the diffusion distance of copper in the wiring layer into the ceramic is substantially 20 μm or less. In addition, the insulation between the wiring layers does not deteriorate, and by optimizing the firing temperature and atmosphere, the diffusion or volatilization of copper in the wiring layer can be suppressed, the copper diffusion distance can be reduced, and the burnt surface The present inventors have found that the surface roughness of can be reduced, leading to the present invention.
[0011]
That is, the multilayer wiring board of the present invention includes an insulating substrate formed by laminating a plurality of insulating layers made of aluminum oxide ceramics having an average crystal grain size of a main crystal phase of 1.5 to 5.0 μm,
An internal wiring layer made of a conductor composed mainly of a composite material containing copper and tungsten and / or molybdenum and having a volume ratio of Cu / (Cu + W + Mo) of 0.3 to 0.9, disposed inside the insulating substrate When,
A composite composed of a conductive component of W and / or Mo disposed on the surface of the insulating substrate or containing copper and tungsten and / or molybdenum and having a volume ratio of Cu / (Cu + W + Mo) of 0.3 to 0.9 A surface wiring layer made of a conductor mainly composed of a material,
The diffusion length of copper into the ceramic around the internal wiring layer is not more 20μm or less, and the insulating surface of the substrate to the surface wiring layer is formed is a surface roughness (Ra) of less burnt skin surface 1μm substrate It is characterized by comprising.
[0012]
The aluminum oxide ceramics preferably has a thermal conductivity of 15 W / m · K or more. Furthermore, the minimum distance between the wiring layers is 100 μm or less, a plurality of via-hole conductors are formed in the insulating layer, the minimum separation distance between the via-hole conductors is 100 μm or less, and the insulating substrate surface is It is desirable that it is not polished.
[0013]
In addition, as a method for manufacturing such a multilayer wiring board, on the surface of a sheet-like molded body made of a mixed powder mainly composed of an aluminum oxide ceramic powder having an average particle size of 0.5 to 2.5 μm , at least for an internal wiring layer Conductive paste containing a composite material of copper and tungsten and / or molybdenum as a conductive component, and for a surface wiring layer, tungsten and / or molybdenum as a conductive component, or at least a composite of copper and tungsten and / or molybdenum After laminating a plurality of sheet-like molded bodies obtained by printing and applying a conductor paste containing a material as a conductor component in a wiring pattern, the laminated body is 1400 to 1400 ° C. in an atmosphere containing hydrogen and nitrogen at a dew point of −20 ° C. or lower. It is characterized by firing at a temperature of 1500 ° C.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Below, it demonstrates based on the schematic sectional drawing which shows one embodiment of the multilayer wiring board of this invention. The multilayer wiring board of FIG. 1 includes an insulating substrate 1 in which a plurality of insulating layers 1a, 1b, and 1c made of oxide ceramics are laminated, and an internal wiring layer 2a and further between the insulating layers 1a, 1b, and 1c. A surface wiring layer 2b is provided on the surface of the insulating layer 1a. Of the above wiring layers, the internal wiring layer 2a is formed of a conductor whose main component is at least copper or a composite material of copper and tungsten and / or molybdenum. The internal wiring layer 2a is insulated. It is formed by simultaneous firing with the substrate 1.
[0015]
In addition, the wiring layers of each layer are electrically connected by a via-hole conductor 3 formed so as to penetrate the insulating layer. The via-hole conductor 3 is also preferably formed by simultaneous firing with a conductor similar to the internal wiring layer 2a.
[0016]
According to the present invention, as shown in FIG. 2, it is important that the diffusion distance x of copper to the ceramic of the insulating substrate 1 around the internal wiring layer 2a containing at least copper is 20 μm or less, particularly 10 μm or less. is there. That is, if the diffusion distance of copper into the ceramic exceeds 20 μm, the insulation between the wiring layers is lowered, and the reliability as the wiring board cannot be guaranteed. The diffusion distance x is an average value obtained by measuring 10 distances x from the end of the wiring layer 2a to the outermost part of the region where the copper element is detected in the same plane in EPMA (X-ray microanalyzer) analysis. It is.
[0017]
As the oxide ceramics forming the insulating substrate 1, aluminum oxide, mullite, although the forsterite or the like is known, the insulating substrate 1 in the present invention is made of a ceramic mainly containing aluminum oxide is there. This is because mullite and forsterite ceramics generally have low thermal conductivity and are not effective in solving the thermal problem. In addition, the thermal conductivity of the insulating substrate 1 is desirably 15 W / m · K or more, particularly 20 W / m · K or more.
[0018]
In the case where the insulating substrate 1 is made of aluminum oxide, in ceramics, SiO ₂ and MgO, CaO, SrO are used as sintering aids to achieve simultaneous sintering with the internal wiring layer 2a. In addition, alkaline earth element oxides such as tungsten and molybdenum and other transition metals may be included as colorants.
[0019]
In addition, it is desirable to contain these sintering aid components in a proportion of 0.3 to 10% by weight in total. If the amount of these sintering aids is less than 0.3% by weight, the co-sinterability with the internal wiring layer 2a made of a copper-containing conductor is reduced, and if more than 10% by weight, the insulating substrate 1 This is because the thermal conductivity is lowered, and the advantages of the insulating substrate 1 over the glass ceramics are not exhibited. In particular, in order to improve the co-sinterability with the copper-containing conductor, it is desirable to contain SiO _2, MgO, and CaO at a ratio of 0.4 to 8% by weight in terms of oxides.
[0020]
Aluminum oxide crystals constituting the main crystal phase of the oxide ceramic forming the insulating substrate 1 exist as granular or columnar crystals, and the average crystal grain size of these main crystal layers is 1.5 to 5.0 μm. It is necessary to be. In addition, when the main crystal phase is composed of columnar crystals, the average crystal grain size is based on the minor axis diameter.
[0021]
When the average crystal grain size of the main crystal phase is smaller than 1.5 μm, it is difficult to achieve high thermal conductivity, and when the average grain size is larger than 5.0 μm, the grain boundary is a path when copper diffuses into the ceramic. This is because the diffusion length exceeds 30 μm because the length of the film becomes shorter and the diffusion speed becomes faster, and sufficient strength required for use as a substrate material cannot be obtained. The sintering aid component exists as an amorphous phase or a crystalline phase at the grain boundary of the main crystalline phase, but suppresses the diffusion of copper and improves the thermal conductivity. Is preferably formed.
[0022]
According to the present invention, in the multilayer wiring board, the internal wiring layer 2a and the via-hole conductor 3 are both formed by simultaneous firing with the insulating substrate 1, but the ceramics forming the insulating substrate 1 is fired. It is desirable to change the conductor forming the wiring layer according to the temperature.
[0023]
For example, when the firing temperature of the insulating substrate 1 is 1100 ° C. or lower, it is possible to use copper alone, but when it is 1400 ° C. or higher, by adding tungsten or molybdenum to the copper, The firing temperature can be gradually increased, and the firing temperature with the oxide ceramic can be matched. However, when the compounding amount of tungsten or molybdenum increases, the resistance of the conductor increases and the advantages of using a copper conductor cannot be utilized.
[0024]
In matching the firing temperature at 1400 ° C. or more and making the resistance of the conductor resistance 8 mΩ / □ or less, the volume ratio of copper and tungsten and / or molybdenum is Cu / (Cu + W + Mo) is 0.3 or more, In particular, 0.4 or more is desirable, but 0.9 or less is preferable in order to enable simultaneous sintering with oxide ceramics, to prevent wiring bleeding and to reduce the thermal expansion difference .
[0025]
In the multilayer wiring board of the present invention, the surface wiring layer 2b can be formed by co-firing with the insulating substrate 1 using the copper-containing conductor, as with the internal wiring layer 2a. When firing at a temperature higher than the firing temperature, the conductor tends to melt and aggregate due to surface tension. Accordingly, the surface wiring layer 2b may be formed of a metallized layer having a composition in which about 2 to 10% by weight of a powder of the same component as that of aluminum oxide or an insulating substrate is added to a conductor component made of W and / or Mo. desirable.
[0026]
In the multilayer wiring board of the present invention, the minimum distance between the wiring layers formed in the same plane among the wiring layers is 100 μm by setting the copper diffusion distance in the internal wiring layer 2a to 20 μm or less. In the following, particularly high-density wiring of 90 μm or less can be achieved. Similarly, as shown in FIG. 1, when a plurality of via-hole conductors 3 are formed in one insulating layer, the minimum separation distance between the via-hole conductors 3 is also 100 μm or less, particularly 90 μm or less for the same reason as described above. It is possible to control.
[0027]
Furthermore, the multilayer wiring board of the present invention has a smoothness of 1 μm or less, particularly 0.7 μm or less, of the average surface roughness Ra of the surface of the insulating substrate 1 by firing by controlling the firing temperature and atmosphere as described later. An excellent surface can be formed. As a result, when the surface wiring layer 2b is formed on the surface of the insulating substrate 1, the surface of the insulating substrate 1 does not need to be polished.
[0028]
Next, the manufacturing method of the multilayer wiring board of this invention is demonstrated concretely. First, in order to form an insulating substrate, a powder having an average particle size of 0.5 to 2.5 μm, particularly 0.5 to 2.0 μm is used as the oxide ceramic powder. This is because if the average particle size is smaller than 0.5 μm, it is difficult to handle the powder, and the cost of the powder becomes high, and if it is higher than 2.5 μm, it is difficult to fire at a temperature of 1500 ° C. or less. It is.
[0029]
In addition, a sintering aid can be appropriately added to the oxide ceramic powder. For example, with respect to the aluminum oxide raw material powder, SiO _2, MgO, CaO powder and the like are added and mixed at a ratio of 0.4 to 8 wt% as a sintering aid component. And the sheet-like molded object for forming an insulating layer using this mixed powder is produced.
[0030]
The sheet-like molded body can be produced by a known molding method. For example, after preparing a slurry by adding an organic binder or solvent to the above mixed powder, it is formed by a doctor blade method, or an organic binder is added to the mixed powder, and sheet-like molding with a predetermined thickness is performed by press molding, rolling molding, or the like. The body can be made.
[0031]
The volume ratio of Cu / (Cu + W + Mo) is 0.3 or more, particularly 0.4 or more, with respect to the sheet-like molded body thus produced, copper powder or copper powder and tungsten powder and / or molybdenum powder. Furthermore, a conductor paste mainly composed of a mixed powder having a ratio of 0.9 or less is prepared, and this paste is printed and applied to each sheet-like insulating layer by a technique such as screen printing or gravure printing. Further, as the surface wiring layer, instead of the copper-containing conductor paste, a conductor paste containing tungsten and / or molybdenum as a conductor component as a solid component may be printed and applied on the surface of a predetermined sheet-like molded body.
[0032]
In addition, when forming a via-hole conductor, after forming a via hole with a diameter of 50-250 micrometers with respect to a sheet-like molded object by a micro drill, a laser, etc., the said copper containing conductor paste or the said copper in this via hole Fill with additive-free conductor paste.
[0033]
In these conductor pastes, in order to improve the adhesion to the insulating layer, the same aluminum oxide powder as the main component of the oxide ceramic forming the insulating layer, or the same composition as the insulating layer forming composition is used. It is desirable to add at a ratio of -10 wt%.
[0034]
Thereafter, the sheet-like molded body on which the conductive paste is printed and applied is aligned and laminated and pressure-bonded. At this time, the sheet-like molded body on which the copper-containing conductor paste is printed is laminated with another sheet-like molded body on the conductor paste application surface so as to form an internal wiring layer.
[0035]
Next, according to the present invention, this calcination needs to be performed at a temperature of 1400 to 1500 ° C. in a non-oxidizing atmosphere containing hydrogen and nitrogen and having a dew point of −20 ° C. or lower, particularly −30 ° C. or lower. Under this firing condition, hydrogen is necessary for reducing and removing the oxide film inevitably generated in the manufacturing process before firing the copper-containing conductor. Moreover, you may mix inert gas, such as argon gas, as desired.
[0036]
If the dew point during firing is higher than −20 ° C., oxide ceramics react with moisture in the atmosphere during firing to form an oxide film, and this oxide film and copper of the copper-containing conductor react, This is because it not only prevents the resistance of the conductor from being lowered, but also promotes copper diffusion.
[0037]
Further, when the firing temperature is higher than 1500 ° C., the grain size of the main crystal phase of the oxide ceramics becomes large and abnormal grain growth occurs, and the grain boundary length, which is a path when copper diffuses into the ceramics. This is because it becomes difficult to suppress the diffusion distance to 30 μm or less as a result of shortening the length and increasing the diffusion speed. Preferably, the range of 1430-1480 degreeC is good.
[0038]
【Example】
Hereinafter, the present invention will be described based on examples.
After mixing aluminum oxide powder (average particle size 0.65 μm) as a main component with various sintering aids as shown in Table 1, acrylic binder as molding organic resin (binder), and toluene as solvent, doctor It was formed into a sheet having a thickness of 250 μm by the blade method. Then, a via hole having a hole diameter of 120 μm was formed by a laser at a predetermined location.
[0039]
Next, copper powder (average particle size: 5 μm) and W powder (average particle size: 1.2 μm) or Mo powder (average particle size: 1 μm) are mixed at a ratio shown in Tables 1 and 3, and an acrylic binder is added to acetone. A conductor paste for internal wiring layers was produced as a solvent. Further, W powder (average particle size: 1.2 μm) and an acrylic binder were mixed with acetone as a solvent to prepare a conductor paste for a surface wiring layer and a via-hole conductor.
[0040]
And the conductor paste for internal wiring layers was printed on the sheet-like molded body, and drying was repeated. Moreover, the conductor paste for surface wiring layers was printed on the surface of the sheet-like molded body for the outermost insulating layer and dried. The via-hole conductor of each sheet-like molded body was filled with the above-described surface wiring layer conductor paste.
[0041]
Each sheet-like molded body produced as described above was positioned and laminated and pressure-bonded to produce a molded body laminate. Thereafter, this molded body laminate was degreased in an oxygen-containing atmosphere substantially free of moisture (N ₂ + O ₂ or air), and then fired at the temperature and atmosphere shown in Table 1.
[0042]
After measuring the conductor resistance, length, width and thickness of the internal resistance of the obtained sintered body, the sheet resistance (mΩ / □) converted to a conductor having a thickness of 15 μm was calculated. At the same time, the inter-conductor resistance was obtained by measuring the resistance value between conductors having a line distance of 100 μm. Moreover, about the sample, the diffusion distance of copper was measured using EPMA (X-ray microanalyzer).
[0043]
The thermal conductivity of each insulating substrate was measured by a laser flash method, and the results are shown in Table 1. In addition, the average crystal grain size of the main crystal grains in the insulating substrate was obtained from the scanning electron microscope (SEM) photograph based on the intercept method. Furthermore, the average surface roughness Ra on the outermost surface of the insulating substrate was measured with a stylus type surface roughness meter.
[0044]
[Table 1]

[0045]
[Table 2]

[0046]
As shown in Table 1, in sample No. 1 in which the dew point during co-firing was higher than −20 ° C., the conductor resistance increased, the copper diffusion distance exceeded 20 μm, and the surface roughness also decreased. Further, in samples No. 19 and 20 that did not contain hydrogen in the atmosphere, oxidation of metallization occurred and the conductor resistance increased.
[0047]
Further, in the internal wiring layer composition, in the samples No. 9 and 13 in which the volume ratio of Cu / (Cu + W + Mo) was smaller than 0.3, the conductor resistance was larger than 8 mΩ / □. Further, in sample No. 17 in which the co-firing temperature is higher than 1500 ° C., the insulating property of the insulating substrate deteriorated due to the copper diffusion distance becoming larger than 20 μm.
[0048]
In contrast to these comparative examples, according to the multilayer wiring board of the present invention, the sheet resistance is 8 mΩ / □ or less and the copper diffusion distance is 20 μm or less, thereby increasing the resistance between the wiring layers to 10 ⁹ Ω or more. did it. Moreover, in all cases, the surface roughness Ra was 1 μm or less, and the surface smoothness was excellent.
[0049]
【The invention's effect】
As described above in detail, when forming the internal wiring layer made of the copper-containing conductor of the present invention, by co-firing in a non-oxidizing atmosphere having a dew point of hydrogen of -20 ° C. or lower, into a copper insulating substrate. Diffusion can be suppressed to 20 μm or less, whereby insulation deterioration between the wiring layers can be prevented, and a highly reliable high-density wiring layer can be formed. Moreover, it is possible to provide an inexpensive multilayer wiring board that is excellent in the smoothness of the substrate surface after firing and does not require a polishing step.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a multilayer wiring board according to the present invention.
FIG. 2 is a view for explaining a diffusion state of copper in an internal wiring layer in the multilayer wiring board of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Insulation board | substrate 1a, 1b, 1c Insulation layer 2a Internal wiring layer 2b Surface wiring layer 3 Via-hole conductor 4 Copper element

Claims (6)

An insulating substrate formed by laminating a plurality of insulating layers made of an aluminum oxide ceramic whose main crystal phase has an average crystal grain size of 1.5 to 5.0 μm;
An internal wiring layer made of a conductor composed mainly of a composite material containing copper and tungsten and / or molybdenum and having a volume ratio of Cu / (Cu + W + Mo) of 0.3 to 0.9, disposed inside the insulating substrate When,
A composite composed of a conductive component of W and / or Mo disposed on the surface of the insulating substrate or containing copper and tungsten and / or molybdenum and having a volume ratio of Cu / (Cu + W + Mo) of 0.3 to 0.9 A surface wiring layer made of a conductor whose main component is a material,
The diffusion length of copper into the ceramic around the internal wiring layer is not more 20μm or less, and the insulating surface of the substrate to the surface wiring layer is formed is a surface roughness (Ra) of less burnt skin surface 1μm substrate multilayer wiring substrate characterized by comprising the. The multilayer wiring board according to claim 1, wherein the aluminum oxide ceramic has a thermal conductivity of 15 W / m · K or more. 3. The multilayer wiring board according to claim 1, wherein the minimum distance between the wiring layers is 100 [mu] m or less. 4. The multilayer wiring board according to claim 1, wherein a plurality of via hole conductors are formed in the insulating layer, and a minimum separation distance between the via hole conductors is 100 [mu] m or less. 5. The multilayer wiring board according to claim 1, wherein the surface of the insulating substrate is not polished. A composite material of at least copper and tungsten and / or molybdenum for use as an internal wiring layer on the surface of a sheet-like formed body composed of a mixed powder mainly composed of an aluminum oxide ceramic powder having an average particle size of 0.5 to 2.5 μm For the surface wiring layer, a conductor paste containing tungsten and / or molybdenum as a conductor component, or a conductor paste containing at least a composite material of copper and tungsten and / or molybdenum as a conductor component After laminating a plurality of sheet-like molded bodies formed by printing and applying in a pattern, the laminate is fired at a temperature of 1400 to 1500 ° C. in an atmosphere containing hydrogen and nitrogen at a dew point of −20 ° C. or lower. A method for manufacturing a multilayer wiring board.

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