JP2989975B2 - Method for manufacturing aluminum nitride substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a substrate having an aluminum nitride sintered body as an insulating substrate and a through hole formed therein.

[0002]

2. Description of the Related Art In a multi-layer wiring board on which a semiconductor element or the like is mounted, how to emit heat from the element has become a major problem with the increase in circuit integration. Therefore, recently, it has been proposed to use an aluminum nitride-based substrate having high thermal conductivity from the Al ₂ O ₃ -based substrate which has been generally used so far, and its practical use has been promoted.

Generally, in a multilayer wiring board, as shown in FIG. 1, internal conductors 2 are arranged between insulating layers 1, and conductors 2 of each layer are led out to the surface of the board through through holes 3. Further, a wiring layer 6 is formed on the surface of the substrate including the surface conductor 4 by, for example, a thin film method such as an evaporation method.

On the other hand, the aluminum nitride substrate has low chemical resistance to acids, alkalis, and the like, so that when immersed in an etching solution in the process of forming a wiring pattern, the substrate surface is corroded, causing discoloration. Due to the problem of roughening, chemical resistance has been conventionally achieved by forming the oxide layer made of Al ₂ O ₃ by heat-treating the substrate in air before forming a conductor pattern on the surface of the aluminum nitride substrate. Enhancements have been made.

[0005]

However, when an aluminum nitride substrate is provided with a conductor inside and the conductor is exposed to the surface through a through hole, the substrate is oxidized in the air. Since an oxide film is formed even on the surface of the conductor led out to the surface, when a conductor is further connected to the surface of the conductor to form a wiring pattern, there is a problem that the resistance between the two conductors increases. Was.

Further, it has been found that when a wiring pattern is formed on the surface of a substrate on which an oxide film has been formed by a conventional method, there arises a problem that the adhesive strength between the wiring pattern and the substrate is reduced.

[0007]

SUMMARY OF THE INVENTION The inventor of the present invention has made it possible to provide a chemical resistance of an aluminum nitride substrate and to reduce the resistance between the surface conductor 4 led out to the substrate surface and the wiring layer 6 on the substrate surface. When a method for reducing the increase was examined, a heat treatment for forming an Al ₂ O ₃ film on an aluminum nitride substrate having a conductor exposed to the surface was performed at an oxygen concentration of 5%.
By performing the treatment at a temperature of 1100 ° C. or more in a nitrogen atmosphere of 0 to 1500 ppm, it is possible to form an oxide film without increasing the resistance and to improve the adhesion of a wiring pattern formed on the substrate surface to the substrate. Was found.

[0008]

According to the present invention, the oxidation treatment is carried out at 50 to 1500.
By performing in a nitrogen atmosphere with a low oxygen concentration of ppm,
Oxidation of the conductor surface led to the surface of the substrate becomes difficult to progress, and when connecting the conductor led to this surface and the conductor formed on the substrate surface, there is no oxide film or even if the oxide film exists. Since the thickness is very small, good electrical conduction can be achieved without increasing the electrical resistance between the conductors.

Further, even when a wiring pattern is formed on the surface of the substrate on which the oxide film is formed, the wiring pattern is not peeled off, and good adhesive strength can be obtained.

[0010]

The present invention will be described below in detail. The aluminum nitride substrate in the present invention is formed, for example, from a multilayer structure as shown in FIG. According to FIG. 1, an internal conductor 2 is formed between layers of an insulating layer 1 made of an aluminum nitride sintered body. The internal conductors 2 of each layer are connected by through-hole conductors 3 filled with conductors, and are led out as surface conductors 4 on the substrate surface.

Such a multi-layer substrate is formed by molding a powder obtained by adding aluminum nitride and a sintering aid such as an oxide of Group 3a or Group 2a of the periodic table to the surface of a green sheet formed of W or Mo. A conductor paste containing a high melting point metal powder is applied and laminated in a predetermined pattern, a through hole is formed, and the conductor paste is filled therein.
It can be obtained by simultaneously firing the aluminum nitride molded body and the conductive paste in a non-oxidizing atmosphere at 500 to 1900 ° C.

At this time, the portion of the substrate where the conductor is not formed has aluminum nitride exposed. Aluminum nitride itself has high reactivity with water and is inferior in durability against an alkaline solution. Therefore, an oxide film 5 made of Al ₂ O ₃ is formed on the exposed aluminum nitride surface. According to the present invention, it is important that the oxide film 5 is formed in an inert atmosphere having a low oxygen concentration in the range of 50 to 1500 ppm. That is, if the oxygen concentration at this time is lower than 50 ppm, a predetermined oxide film cannot be formed on the substrate surface on which sufficient aluminum nitride is exposed, and if the oxygen concentration is higher than 1500 ppm, the oxide film formed on the substrate surface cannot be formed. WO ₃ up to the surface of the surface conductor 4
Then, an oxide film is formed, and a resistive layer is formed at the interface with the wiring layer formed on the surface conductor 4 after that, and the electric resistance between the two conductors increases. In addition, when performed in a high oxygen atmosphere such as air, the thickness of the oxide film on the aluminum nitride substrate surface increases, and when a wiring pattern is formed on the oxide film, the adhesive strength of the wiring layer decreases due to a difference in thermal expansion and the like. Problems occur.

In forming the oxide film, the treatment temperature may be any temperature that is sufficient for aluminum nitride to combine with oxygen and oxidize, specifically, 1100 ° C. or more.
In particular, 1200-1400 ° C is desirable. If the temperature at this time is lower than 1100 ° C., no oxide film is formed, or even if it is formed, it takes a very long time.

The thickness of the oxide film formed on the surface of the aluminum nitride insulating layer as described above is 0.5 to 7 μm.
When the thickness is less than 0.5 μm, the durability against exposed water or alkali is insufficient, and when the thickness is more than 7 μm, an oxide film is peeled off due to a difference in thermal expansion with an aluminum nitride substrate. This is because the problem described above occurs.

Next, on the surface of the multi-layer substrate thus obtained, a thin film method such as a vapor deposition method or a conductor paste The wiring layer 6 is formed by a method of applying and baking, and a plating layer (not shown) may be formed on the surface of the wiring layer 6 in some cases.

The present invention is further described in the following examples. EXAMPLE An organic binder was added to a mixture of aluminum nitride powder (average particle size: 1.6 μm, oxygen content: 0.9% by weight) and 8% by weight of Y ₂ O ₃ as a sintering aid, and mixed in an organic solvent. Thus, a slurry was prepared. This slurry was formed into a green sheet having a thickness of 300 μm by a doctor blade method.

On the surface of the green sheet, a conductor pattern containing a solid content obtained by adding 5% by weight of aluminum nitride powder to W powder was formed into a conductor pattern by screen printing. Further, through holes were formed at desired positions in the green sheet. After laminating and pressing the plurality of green sheets thus formed, the conductor paste was filled in through holes and fired in a nitrogen atmosphere at 1800 ° C. for 3 hours. Next, this substrate was heat-treated in a nitrogen atmosphere having an oxygen concentration and a processing temperature shown in Table 1 to perform an oxidation treatment. Thereafter, a thin film conductor of Ti having a thickness of 1.0 μm was formed on the surface of the conductor on the substrate by a vacuum evaporation method.

The obtained substrate is immersed in an alkaline solution for one hour in order to measure the electric resistance between the thin film conductor and the through-hole conductor, and to evaluate the chemical resistance of the substrate. Then, changes in the substrate surface after the test were observed.
Further, the adhesive strength of the thin film conductor to the substrate was measured.

[0019]

[Table 1]

According to Table 1, in Sample No. 1 having an oxygen concentration lower than 50 ppm, formation of an oxide film was insufficient, and although the electrical resistance was low, the chemical resistance was low. In Sample No. 6 having an oxygen concentration of more than 1500 ppm, there was no problem in chemical resistance, but the electrical resistance between conductors was large. On the other hand, all the samples treated with the oxygen concentration of the present invention had excellent chemical resistance, and the electrical resistance between the conductors was not affected at all.

Further, the adhesion strength of the thin film is reduced even in the case of samples No. 1 and No. 8 where the oxidation treatment of the substrate is insufficient, and in the case of samples No. 7 and No. 9 having a high oxygen concentration.
It can be seen that the strength is maximized by the treatment in a predetermined low oxygen concentration atmosphere.

[0022]

As described above in detail, according to the present invention, in a multilayer wiring board in which a conductor is led out through its surface by a through-hole, the electrical connection between the conductors due to the multilayering is not affected at all. In addition, the chemical resistance of the substrate can be improved. Thereby, the reliability as a substrate can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic view of an aluminum nitride substrate according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating layer 2 Inner conductor 3 Through hole 4 Surface conductor 5 Oxide film 6 Wiring layer

Claims (1)

(57) [Claims] 1. A substrate having an internal conductor layer formed between insulating layers containing aluminum nitride as a main component and having the internal conductor layer led out to the surface through a through hole is placed in a nitrogen atmosphere having an oxygen concentration of 50 to 1500 ppm. A heat treatment at a temperature of 1100 ° C. or more to form an oxide film made of Al ₂ O _{3 on the} surface of the substrate, and then form a wiring layer on the surface of the substrate. .