JPH06244534A - Copper-fine-interconnection formation method and copper fine interconnection - Google Patents

Abstract

PURPOSE:To provide a copper-fine-interconnection formation method wherein a resin in a paste and a resist are burned and burned down completely and their surface is flattened and to provide its copper fine interconnection. CONSTITUTION:An opening part corresponding to an interconnection pattern is formed in a photoresist 2 which is deposited on a ceramic substrate 1. A conductor paste constituted of copper and/or copper oxide and of a glass frit as well as of a vehicle which is composed of a resin, a solvent and a pasticizer is filled into the opening part by using a flat rubber 6. The conductor paste is dried, and the conductor paste is heaved in the air at a temperature of 400 to 600 deg.C. The photoresist 2 and the resin in the conductor paste 5 are burned and burned down completely, and a copper oxide fine interconnection 7 is formed. Then, the copper oxide fine interconnection 7 is reduced at a temperature of 600 to 1000 deg.C in nitrogen gas at 10vol.% or lower, and it is sintered. A copper fine interconnection 8 is formed. In addition, a metal-plated layer is formed on the surface of the copper fine interconnection 8 by an electrolytic plating method, and the copper fine interconnection whose surface has been flattened is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming fine wiring mainly composed of copper on a ceramic substrate on which a semiconductor LSI, a chip component, etc. are mounted, and a fine copper wiring formed.

[0002]

2. Description of the Related Art Due to the miniaturization and high density of electronic devices, ceramic wiring boards for mounting semiconductor LSIs and chip parts are evolving into multi-chip modules with narrower pitch and more pins. The TAB (Tape Automated Bonding) method or the flip chip method is adopted instead of the wire bonding method for the ceramic wiring board, and the line width is 100 μm or less for the wiring of the ceramic wiring board. There is a demand for fine wiring whose wiring material is copper with low conduction resistance and low cost.

As a method of forming fine wiring, there are a thick film method, a thin film method, a plating method and the like. The thick film method is a method of forming a wiring by printing a paste in which a copper powder is dispersed in an organic vehicle on a ceramic substrate through a mesh screen having a required pattern and firing the paste.
This method can form conductor wiring with sufficient adhesion strength on a ceramic substrate at a low cost because the device used is relatively inexpensive, but since the wire diameter of the screen mesh is limited, fine wiring However, there is a limit to the formation, and there is a problem that the printing accuracy is low because the screen bends during printing.

In the thin film method, a thin film forming apparatus such as a vapor deposition apparatus, a sputtering apparatus or an ion plating apparatus is used to deposit a copper thin film having a thickness of several μm on a ceramic substrate, and then a desired pattern is formed by a photolithography method. This is a method of forming the wiring. Since this method uses a photolithography method, it is possible to form fine wiring with high accuracy, but the manufacturing efficiency is low due to the large number of steps,
There is also a problem that the cost is high because the thin film forming apparatus is expensive. The plating method is a method of forming a wiring pattern similarly to the above-described thin film method after depositing copper by, for example, electrolytic plating method, but it has the same problem as the thin film method.

Therefore, a method of introducing a photolithography method, which is a feature of the thin film method, into the thick film method by using a photosensitive copper conductor paste has been attempted. This is a photosensitive copper conductor paste in which copper powder is dispersed in a photoresist in which a photosensitive resin is dissolved in a solvent, is uniformly printed on a ceramic substrate, and the paste is formed using a mask having a required pattern. After the wiring pattern is formed by positively exposing and developing, the photosensitive resin of the photoresist is burned and burned by baking in a nitrogen atmosphere containing a trace amount of oxidizing gas, and at the same time the conductor wiring is baked on the ceramic substrate. It is to bring them together.

[0006] Although this method does not use a thin film forming apparatus, the cost can be reduced, but since the concentration of copper in the photoresist is low, the density of the sintered copper wiring is low, and the conductivity and the adhesiveness to the ceramic substrate are low. In addition, in the sintering of copper, in order to burn and burn away the photoresist without oxidizing the copper, it is necessary to perform baking in a nitrogen atmosphere containing a trace amount of oxidizing gas that is strictly controlled. Follow. Therefore, not only does it take a long time, but when the amount of oxidizing gas is large, the copper is oxidized and the characteristics of the conductor wiring deteriorate, and when it is small, the photosensitive resin in the photosensitive copper conductor paste is completely burned and burned out. However, there is a problem in that it cannot be made to be carbonized and carbonized, which hinders the sintering of copper or reduces the adhesive strength of the conductor wiring to the ceramic substrate.

On the other hand, an opening corresponding to the wiring pattern is formed by negatively exposing and developing the photoresist deposited on the ceramic substrate using a mask having a required pattern, and then copper powder is introduced into the opening. A method has been attempted in which a conductor paste containing a resin and a resin is filled, the resin and the photoresist are burned and burned by firing in a nitrogen atmosphere containing an extremely small amount of oxidizing gas, and at the same time, the conductor wiring is sintered on a ceramic substrate. ing.

[0008]

By the way, in such a conventional method, since the conductor paste as used in the thick film method is used instead of the above-mentioned photosensitive copper conductor paste,
Although the density of the sintered copper wiring does not decrease, it must be fired in a nitrogen atmosphere containing an extremely small amount of oxidizing gas, making it difficult to control the oxidizing gas and reducing production efficiency and quality. Problems such as remain. In addition, the conventional copper fine wiring formed by sintering reduces the flatness of the surface of the copper fine wiring due to volume contraction during sintering.
When soldering, there is a possibility that the adhesiveness may be deteriorated due to subsequent high temperature aging.

The present invention has been made in view of the above circumstances, and an object thereof is to heat the paste filled in the opening formed in the resist in an oxidizing atmosphere to cause the resin and the resist in the paste to be removed. To provide a method for forming a copper fine wiring that completely burns and burns away the copper, a method for forming a copper fine wiring that flattens the surface by forming a metal plating layer on the surface of the sintered copper wiring, and the copper fine wiring. It is in.

[0010]

According to a first aspect of the present invention, there is provided a copper fine wiring forming method, wherein an opening corresponding to a wiring pattern is formed in a photoresist deposited on a ceramic substrate, and copper and resin are contained in the opening. In a method for forming a fine wiring of copper by sintering copper in the paste after filling the paste, the opening containing the paste containing copper and / or copper oxide, and then in an oxidizing atmosphere. Then, the method is characterized by including a step of heating at a temperature at which the photoresist and the resin burn or burn out or higher, and a step of heating at a temperature at which copper is sintered or higher in a reducing atmosphere.

In the method for forming copper fine wiring according to the second aspect of the invention, an opening corresponding to the wiring pattern is formed in the photoresist deposited on the ceramic substrate, and the opening is filled with a paste containing copper and resin. After that, in a method of sintering copper in the paste to form fine wiring of copper,
After filling the opening with the paste containing copper and / or copper oxide, heating in an oxidizing atmosphere at a temperature above the temperature at which the photoresist and the resin burn and burn out; and in a reducing atmosphere, copper oxide. The method is characterized by including a step of heating at or above a temperature at which is reduced, and a step of heating at or above a temperature at which reduced copper is sintered in a neutral atmosphere.

Further, the copper fine wiring forming method according to the third invention is characterized in that, in addition to the first invention or the second invention, it further comprises a step of applying metal plating to the surface of the sintered copper.

Further, in the copper fine wiring according to the fourth aspect of the present invention, in the copper fine wiring baked on a ceramic substrate, a metal plating layer is formed on the surface of the copper and the surface is made flat. Is characterized by.

[0014]

In the copper fine wiring forming method of the present invention, after the paste containing copper and / or copper oxide and the resin is filled in the opening corresponding to the wiring pattern formed on the photoresist, it is placed in an oxidizing atmosphere. Since the step of heating the photoresist and the resin at a temperature at which the photoresist and the resin burn or burn out is included, it is possible to completely burn and burn the photoresist and the resin in a short time. At this time, when a paste containing copper is used, the volume of the photoresist and resin expands due to oxidation of copper in parallel with burning and burning, but this volume expansion is absorbed by densification of the wiring part and expansion in the thickness direction. Therefore, the wiring pattern is not broken. On the other hand, when the paste containing copper oxide is used, the above-mentioned volume expansion does not occur.

Further, since the method includes a step of heating at a temperature at which copper is sintered or higher in a reducing atmosphere, the copper oxide formed in the above-mentioned heating step in an oxidizing atmosphere and / or the copper oxide contained in the paste from the beginning. Are reduced together to form metallic copper, which does not impair the conduction resistance.

On the other hand, the above-mentioned reduction step is carried out at a temperature at which the copper oxide is reduced and lower than the temperature of the above-mentioned reduction / firing step, and thereafter, heating is performed at a temperature above the temperature at which copper is sintered in a neutral atmosphere. Then, when the reduced metallic copper is fired, the reduction step is performed at a relatively low temperature, so that a ceramic material having low reduction resistance can be used.

Since the step of applying metal plating to the surface of the sintered copper after the sintering of the further reduced metallic copper is performed, the surface of the sintered copper wiring is flattened and subjected to high temperature aging after soldering. The adhesiveness does not deteriorate.

Further, in the copper fine wiring of the present invention, the metal plating layer is formed on the surface of the fine copper wiring baked on the ceramic substrate, and the surface is made flat, so that soldering is performed. Subsequent high temperature aging prevents deterioration of solder adhesion.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments thereof. 1 and 2 are process diagrams showing respective manufacturing steps of the method for forming a copper fine wiring of the present invention. Figure 1
As shown in (a), the photoresist layer 2 is formed on the ceramic substrate 1. As the ceramic substrate 1 that can be used in the present invention, known ceramic substrates such as alumina, mullite and glass ceramics can be used. The photoresist layer 2 can be deposited on the ceramic substrate 1 by using a liquid photoresist by a spin coater method, a roll coater method, a dip method, a Wheeler method (spinner method), or the like. It is easiest to perform pressure bonding by a heat lamination method using a resist. The thickness of the photoresist layer 2 is preferably 10 to 50 μm. This is because if the film thickness is outside this range, it will be difficult to fill the paste described later.

Next, as shown in FIG. 1 (b), the photoresist layer 2 deposited on the ceramic substrate 1 is exposed to ultraviolet rays from above the photomask 3 having a required wiring pattern to expose the wiring pattern. As shown in (c), the openings 4 are formed according to the wiring pattern by developing by a spray method, a dipping rocking method, or the like. The poorly developed photoresist remaining in the opening 4 can be removed by dry etching such as plasma ashing.

Then, as shown in FIG. 2D, copper powder and / or copper oxide powder is provided in the opening 4 of the photoresist layer 2.
The conductor paste 5 containing the glass frit and the vehicle is filled with the flat plate rubber 6 and then dried. When copper powder is used for the conductor paste 5, 75 wt% to 87 wt% of copper powder having a particle size of 0.3 μm to 10 μm, a particle size of 0.1 μm to 10 μm, and a softening point of 450 ° C. to 700 ° C. A paste having a composition in which a certain glass frit is 1 wt% to 7 wt% and a vehicle in which a resin and a plasticizer are dissolved in a solvent is 24 wt% to 6 wt% is preferable.

If the particle size of the above-mentioned copper powder is less than 0.3 μm, it becomes bulky, so that a large amount of vehicle is required for forming a paste, and the amount of copper powder in the paste decreases. The filling property of is reduced. If the softening point of the glass frit is less than 450 ° C., the fluidity of the glass frit is large during firing, and the adhesion between the wiring and the ceramic substrate is reduced.
If the temperature exceeds 00 ° C, the wiring may peel off from the ceramic substrate. If the glass frit content is less than 1% by weight, the adhesion of the wiring is low, and if it exceeds 7% by weight, the wettability of the wiring against soldering is reduced. A preferable glass frit is a glass obtained by dissolving lead, copper, zinc, cadmium, barium, calcium, bismuth and the like in borosilicate glass.

On the other hand, the resin constituting the vehicle is a cellulose resin such as ethyl cellulose and nitrocellulose,
Methacrylic resin and acrylic resin, etc., high boiling point solvent such as terpineol, dibutyl carbitol, trimethylpentanediol diisowirate and ester alcohol as the solvent, dibutyl phthalate as the plasticizer are preferable, and the proportion of the vehicle is 6% by weight. If the amount is less than 24% by weight, it becomes difficult to fill the inside of the opening due to the high viscosity of the paste.
If it exceeds, the ratio of the copper powder in the paste becomes too low, so that the conductivity and the adhesiveness with the ceramic substrate are deteriorated as described above.

When copper oxide powder is used for the conductor paste 5, 75 wt% to 90 wt% of copper powder having a particle size of 0.3 μm to 10 μm, 1 wt% to 5 wt% of the glass frit, and the vehicle are used. A paste having a composition of 24 wt% to 5 wt% is preferable. The copper oxide powder,
Cuprous oxide powder, cupric oxide powder, and mixed powder thereof can be used. A mixed powder of copper oxide powder and copper powder can also be used.

Next, the ceramic substrate 1 filled with the conductor paste 5 is transferred into a combustion furnace and heated at a temperature of 400 ° C. to 600 ° C. in the atmosphere as shown in FIG. The resin in 5 and the photoresist layer 2 are burned and burned to form the copper oxide fine wiring 7.
In this case, if the heating temperature is lower than 400 ° C., the resin in the conductor paste 5 and the photoresist layer 2 may not be completely burned and burned. Further, when copper powder is used in the conductor paste 5, the copper powder is simultaneously oxidized in this oxidation step to become copper oxide, so that the volume expands and the wiring accuracy slightly deteriorates. It is possible to perform wiring with high accuracy even with extremely fine wiring having a wiring width of 30 μm or less without the volume expansion as described above.

Next, as shown in FIG. 2 (f), in a reducing atmosphere such as nitrogen gas containing 10% by volume or less of hydrogen, 60
By heating at a temperature of 0 ° C to 1000 ° C,
The copper oxide fine wiring 7 is reduced and fired to form the copper fine wiring 8. In this case, if the heating temperature is less than 600 ° C, the copper will not sinter densely, and if it exceeds 1000 ° C, the melting point of the copper (10
It is not preferable since it is close to 83 ° C. Although volume contraction occurs when copper oxide is reduced to metallic copper, the glass frit in the paste is melted in the above-described oxidation step to bond the copper oxide fine wiring 7 and the ceramic substrate 1 to each other. The fine wiring 8 is not separated from the ceramic substrate 1.

Further, the above-mentioned reduction / firing process can be performed separately. In this case, the copper oxide fine wiring 7 is reduced to metallic copper by heating in the reducing atmosphere described above at a temperature of about 400 ° C., and then 600 ° C. to 1000 ° C. in a neutral atmosphere such as nitrogen.
By heating at a temperature of ° C, the metallic copper is fired to form the copper fine wiring 8.

A plating layer of copper, gold, nickel or the like is further formed on the surface of the copper fine wiring 8 thus formed by an electrolytic plating method or the like. In this case, since the surface of the copper fine wiring 8 is flattened, the adhesiveness does not decrease even if aging is performed at high temperature after soldering.

Specific numerical examples and comparative examples according to the present invention will be described below. (Numerical Example 1) A dry film resist having a film thickness of 40 μm is pressure-bonded onto an alumina substrate by a heat lamination method, and then the resist is exposed through a photomask having a required wiring pattern having a line width and a line spacing of 50 μm. Then, it was developed with a weak alkaline developer to form an opening corresponding to the wiring pattern. Copper containing 82% by weight of copper powder having a particle diameter of 1.5 μm, 3% by weight of lead borosilicate glass frit, and 15% by weight of vehicle (5% by weight of ethyl cellulose, 95% by weight of terpineol) in the opening. The conductor paste was filled with flat rubber and heated at 100 ° C. for 10 minutes to dry the paste. Then, in the air, the resin and the resist in the paste are burned and burned off with a heating profile with a peak temperature of 600 ° C. and a peak holding time of 20 minutes.
Subsequently, the copper oxide generated in the above-mentioned step was treated with a peak temperature of 900 ° C. in a mixed gas atmosphere of 10% hydrogen and 90% nitrogen.
It was reduced to metallic copper and sintered in a heating profile with a peak holding time of 20 minutes to form a copper fine wiring.

The conductivity, adhesive strength, solder wettability and flatness of the copper fine wiring thus formed were measured as follows to evaluate the characteristics of the copper fine wiring. (Conductivity) 4-terminal resistance Using the measured values, the sheet resistance was calculated from the line width and film thickness of the wiring in terms of a film thickness of 20 μm.

(Adhesive Strength) As described above, a 2 mm square copper sheet was formed on an alumina substrate and placed in a 63% tin (Sn) -37% lead (Pb) solder bath maintained at 230 ° C. ± 3 ° C. for 3 ± 0. After dipping for 5 seconds, a 0.6 mmφ tin-plated copper wire was passed through the center of the copper sheet parallel to this, and soldered at a right angle to the two opposite sides, at a position 1 mm from the edge of the copper sheet. The tin-plated copper wire was bent 90 ° perpendicular to the alumina substrate. This was set in a tensile tester, pulled at a speed of 10 cm / min, and the value when the tin-plated copper wire was peeled from the alumina substrate was taken as the adhesive strength.
The adhesive strength is the value immediately after soldering (initial adhesive strength) and 1
The value after aging at 50 ° C. for 1000 hours (aging adhesive strength) was measured. (Solder wettability) 4mm on the alumina substrate as described above
□ Copper sheet was formed and maintained at 230 ℃ ± 3 ℃ 63
After dipping in a% Sn-37% Pb solder bath for 3 ± 0.5 seconds, the coverage of the solder adhered to the copper sheet was visually measured. (Flatness) The surface of the copper fine wiring was measured with a surface roughness meter.

As a result, the sheet resistance value is 1.5 mΩ /
□, initial adhesive strength is 3.0 kg / 4 mm ² , aging adhesive strength is 2.6 kg / 4 mm ² , solder wettability is 10
The flatness was 0% and the flatness was ± 0.5 μm.

Further, a copper plating layer having a thickness of 2 μm was formed on the copper fine wiring by an electrolytic plating method, and its characteristics were evaluated. As a result, the flatness was ± 0.1 μm or less, the initial adhesive strength was 3.0 kg / 4 mm ² , the aging adhesive strength was 3.0 kg / 4 mm ² , and the solder wettability was 100%.

(Numerical Example 2) As in Numerical Example 1, the copper conductor paste is filled in the openings corresponding to the wiring patterns formed on the resist, and the resin and the resist in the copper conductor paste are subjected to heat treatment in the atmosphere. Was burned and burned. Then 10
Peak temperature of 400 in a nitrogen atmosphere containing volume% hydrogen
After carrying out the reduction step by holding at 30 ° C. for 30 minutes, it was sintered in a pure nitrogen atmosphere with a heating profile having a peak temperature of 900 ° C. and a peak holding time of 10 minutes to form a copper fine wiring. In this case, the sheet resistance is 1.4 mΩ /
□, initial adhesive strength is 3.1 kg / 4 mm ² , aging adhesive strength is 2.2 kg / 4 mm ² , solder wettability is 10
The flatness was 0% and the flatness was ± 0.5 μm.

A copper plating layer having a thickness of 2 μm was formed on the copper fine wiring by electrolytic plating, and its characteristics were evaluated. As a result, the flatness was ± 0.1 μm or less, the initial adhesive strength was 3.1 kg / 4 mm ² , the aging adhesive strength was 3.0 kg / 4 mm ² , and the solder wettability was 100%.

(Numerical Example 3) As in Numerical Example 1, a grain size of 3 μm is formed in the opening corresponding to the wiring pattern formed on the resist.
m copper oxide powder 80 wt%, lead borosilicate glass frit 3 wt%, vehicle (ethyl cellulose 5 wt%, terpineol 95 wt%) 17 wt% copper oxide conductor paste was filled. In the same manner as Numerical Example 1, a heat treatment was performed to form copper fine wiring. In this case, the sheet resistance was 1.6 mΩ / □, the initial adhesive strength was 3.0 kg / 4 mm ² , and the aging adhesive strength was 2.2 k.
g / 4mm ² , solder wettability 100%, flatness ±
It was 0.8 μm.

Further, a copper plating layer having a thickness of 2 μm was formed on this copper fine wiring by an electrolytic plating method, and its characteristics were evaluated. As a result, the flatness was ± 0.1 μm or less, the initial adhesive strength was 3.0 kg / 4 mm ² , the aging adhesive strength was 2.9 kg / 4 mm ² , and the solder wettability was 100%.

Numerical Example 4 Using the copper oxide conductor paste of Numerical Example 3, copper fine wiring was formed by the same operation as Numerical Example 2. In this case, the sheet resistance is 1.5 mΩ /
□, initial adhesive strength is 3.1 kg / 4 mm ² , aging adhesive strength is 2.0 kg / 4 mm ² , solder wettability is 10
The flatness was 0% and the flatness was ± 0.6 μm.

A copper plating layer having a thickness of 2 μm was formed on this copper fine wiring by electrolytic plating, and its characteristics were evaluated. As a result, the flatness was ± 0.1 μm or less, the initial adhesive strength was 3.1 kg / 4 mm ² , the aging adhesive strength was 3.0 kg / 4 mm ² , and the solder wettability was 100%.

(Comparative Example) As in Numerical Example 1, a copper conductor paste was filled in the openings corresponding to the wiring patterns formed on the resist. Then, in a pure nitrogen atmosphere, a peak temperature of 9
An attempt was made to burn and burn off the resin and resist in the paste with a heating profile of 00 ° C. and a peak holding time of 1 hour.
As a result, the resist was not completely burned and burned out, but remained in black.

[0041]

As described in detail above, in the copper fine wiring forming method of the present invention, the resin and the resist in the conductor paste can be completely burned and burned off in a short time, so that the manufacturing efficiency and the product quality are improved. On the other hand, in the copper fine wiring of the present invention, since the metal plating layer is formed on the surface of copper, the surface is flattened and the adhesiveness does not decrease due to high temperature aging after soldering. Has an excellent effect.

[Brief description of drawings]

FIG. 1 is a process drawing showing each manufacturing process of a copper fine wiring forming method of the present invention.

FIG. 2 is a process drawing showing each manufacturing process of the copper fine wiring forming method of the present invention.

[Explanation of symbols]

 1 Ceramics Substrate 2 Photoresist 3 Photomask 4 Opening 5 Conductor Paste 6 Flat Rubber 7 Copper Oxide Fine Wiring 8 Copper Fine Wiring

Claims (4)

[Claims] 1. An opening corresponding to a wiring pattern is formed in a photoresist deposited on a ceramic substrate, a paste containing copper and a resin is filled in the opening, and then the copper in the paste is sintered. In the method of forming fine wiring of copper by filling the opening with the paste containing copper and / or copper oxide, at a temperature not lower than a temperature at which the photoresist and the resin burn and burn in an oxidizing atmosphere. A method for forming a copper fine wiring, comprising: a heating step; and a heating step in a reducing atmosphere at a temperature at which copper is sintered or higher. 2. An opening corresponding to a wiring pattern is formed in a photoresist deposited on a ceramic substrate, a paste containing copper and a resin is filled in the opening, and then the copper in the paste is sintered. In the method of forming fine wiring of copper by filling the opening with the paste containing copper and / or copper oxide, at a temperature not lower than a temperature at which the photoresist and the resin burn and burn in an oxidizing atmosphere. It is characterized by including a step of heating, a step of heating in a reducing atmosphere to a temperature at which copper oxide is reduced or higher, and a step of heating in a neutral atmosphere at a temperature at which reduced copper is sintered or higher. Copper fine wiring forming method. 3. The method for forming a copper fine wiring according to claim 1, further comprising the step of applying metal plating to the surface of the sintered copper. 4. A copper fine wiring that is fired on a ceramic substrate, wherein a metal plating layer is formed on the surface of the copper and the surface is made flat.