JPH03120791A - Via formation method on aluminum nitride substrate - Google Patents

Abstract

PURPOSE:To prevent the occurrence of cracks in via boles which result in inferior continuity by filling the via holes provided in an AlN green sheet with W paste after applying W paste to which AlN is added to the inner surface of the via holes and calcining the green sheet in a non-oxidative atmosphere. CONSTITUTION:After W paste 3 mixed with AlN is thinly applied to the inner surface of via holes 2 provided in an AlN green sheet 1, the via holes 2 are filled up with W paste and the green sheet 1 is burned. When such process is used, effects of the burning shrinkage of the AlN and W can be relieved and low-resistance via holes can be formed. In addition, after a piece of porous water absorbing paper 7 is placed on a pressure reducing container 6 with numerous holes 5, the green sheet 1 and a mask 6 which is accurately positioned to the via holes 2 are successively put on the paper 7 and low-viscosity W paste mixed with AlN is fed onto the mask. When the pressure is reduced through the paper 7 by operating an exhaust system, the W paste mixed with AlN gets into the via holes 2 and adheres to the inner surface of the holes. Therefore, via holes which are free from cracks can be obtained.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for forming a via in an aluminum nitride substrate, for the purpose of forming a via with low resistance, a tungsten paste added with aluminum nitride is applied to the inner wall of a via hole provided in an aluminum nitride green sheet. After coating and drying, the via hole is filled with tungsten paste 1- and fired in a non-oxidizing atmosphere.

[Industrial application field]

The present invention relates to a method for forming a low resistance via on an aluminum nitride (AρN) substrate.

Due to the need to process a large amount of information at high speed, information processing devices are becoming smaller and larger in capacity, and the degree of integration of semiconductor integrated circuits that form the main body of these devices has improved, and LSI and VLSI have been put into practical use.

On the other hand, these integrated circuits are still chips and are mounted on a chip mounting substrate (interposer) made of ceramics.
A mounting system is being adopted in which an LSI module is created by mounting it on a printed wiring board or the like as a replacement unit.

As described above, as the degree of integration of semiconductor integrated circuits increases and high-density packaging is performed, the amount of heat generated by devices is also increasing at an accelerating pace.

In other words, in the beginning, the amount of heat generated per IC was as low as about 35W, but now the amount of heat generated per LSI has increased to about 10W, and when many of these are installed in a matrix, the amount of heat generated increases. The amount is enormous and is likely to increase further.

Conventionally, alumina ([203)], which has high thermal conductivity and excellent heat resistance, has been used for substrates on which LSI chips and the like are mounted.

However, alumina has excellent thermal conductivity\20W/
mK, which is insufficient as a material for the above-mentioned chip mounting substrate.

Table 1 So, AI has a large thermal conductivity of 320 W/liK (theoretical value)! , N has attracted attention, and the practical use of this substrate is progressing.

Table 1 compares the characteristics of both.

In other words, in addition to its excellent thermal conductivity, AIN has a small coefficient of thermal expansion, and has a coefficient of thermal expansion (3
, 6XIO-6/'C) (and the small dielectric constant causes crosstalk when forming a multilayer substrate.
It is also advantageous in that it is possible to reduce lk).

[Conventional technology]

1/2N substrates are attracting attention as substrates for mounting semiconductor integrated circuits, but iN has a high melting point and the baking time of the substrate is 1800℃.
Since the process is carried out at a high temperature exceeding 100% Celsius, tungsten (W), which has a high melting point, is used as the constituent metal of the conductor line, and the conductor line is formed by screen printing W paste on a green sheet and laminating it to form an integral piece. This is done by baking after converting into

Here, the electrical connection of the conductor lines constituting each layer of the multilayer board is performed by vias provided in each layer.

That is, at the green sheet stage, a via hole (ν1ahole) is created by punching a hole at the connection position using a press, and the hole is filled with the W paste used to form the conductor line, and the conductor line is patterned using a screen printing method. Thereafter, the green sheets are laminated and integrated, and heated to 1800°C in this state to form a multilayer circuit board.

However, when heated, the W powder that makes up the W paste begins to shrink at about 1000°C, whereas the IN powder that makes up the green sheet does not shrink at all until 1600°C, and cannot be sintered at temperatures higher than this. The difference is that a reaction with the auxiliary agent occurs, forming a liquid phase and causing shrinkage during firing.

As a result, cracks occur during the firing process, which reduces the adhesion between the substrate and the via, causing poor conductivity.

As a countermeasure for this, 5% or more of Aj2N is added to the W paste.
There is a method of adding powder to alleviate the difference in shrinkage rate during the firing process and improve adhesion.

However, this method has the problem that the resistance value of the via increases, making it impossible to form a multilayer circuit board with good characteristics.

[Problem to be solved by the invention]

As mentioned above, W is used as a constituent material for the conductor lines of the 11 multilayer circuit board, but cracks occur in vias because the firing shrinkage start temperature of An and the firing shrinkage start temperature of W differ by about 400°C. The problem is that it causes poor conduction, and the challenge is to solve this problem.

[Means to Solve the Problem] The above problem is solved by applying W paste containing AIN to the inner wall of the via hole provided in the AJ2N green sheet, drying it, filling the via hole with W paste, and placing it in a non-oxidizing atmosphere. This problem can be solved by configuring the via formation method for the AIN substrate so that the via formation method is characterized by firing inside the AIN substrate.

[Effect]

In the present invention, instead of directly filling the via hole with Al2N mixed base, as shown in FIG.
The problem is solved by coating the inner surface of the via hole 2 of the green sheet 1 with the W paste 3 containing I<An, and then filling the W paste 4 therein and firing it.

In this way, the influence of firing shrinkage of iN and W is alleviated, and it becomes possible to form a via with low resistance.

The problem here is how to coat the inner surface of a via hole with a small diameter of about 200 μm with a thin layer of W paste mixed with An, but this is done by vacuum suctioning the W paste mixed with IN whose viscosity has been adjusted to a low viscosity. It can be applied by

FIG. 2 is a sectional view illustrating the vacuum suction method, in which a porous water-absorbing paper 7 is placed on a vacuum container 6 with many holes 5 on its surface.
The An green sheet 1 and the mask 8 accurately aligned with the via hole 2 are placed thereon, and a low viscosity AlN-containing W paste is supplied onto this mask.

After application with a squeegee, when the exhaust system is operated, the pressure is reduced through the water-absorbing paper 7, and as a result, the Al2N-mixed W paste is sucked into the via hole 2 and adheres to the inner wall.

In the present invention, the iN-containing W paste is applied to the inner surface of the via hole 2 in this manner, and after drying, the W paste is applied as in the conventional method.
Vias are formed by filling them with paste.

〔Example〕

Example: Green sheet with the composition shown in Table 2 (density 1.70 g/c
m3+thickness 250 μm) was formed using a doctor blade method, this green sheet was punched into a 90 mm square, and 362 via holes each having a diameter of 200 μm were formed using a punch.

Next, terpineol was added to the composition shown in Table 3 (AβNβN addition-paste degree 3000 voids), and the viscosity was reduced to 5.
The paste was applied to the inner surface of the via hole at a void of 0.00, and dried at 70°C for 15 minutes.

Table 3 Next, W paste (viscosity 3000 voids) having the composition shown in Table 4 was printed in the conventional manner to fill via holes and print conductor lines, and then dried at 70°C for 15 minutes. did.

Table 4 Six of these green sheets are laminated as a set, and the pressure is 50MPa.
After pressurizing and integrating at a pressure of 1,000 yen in a N2 stream,
Degreasing was performed by heating to 50° C. at a heating rate of 50° C./hour, and then baking was performed at 1800° C. for 930 hours to form a multilayer substrate.

As a result of measurement, the volume resistivity of the via was 35 μΩcm.
When using conventional W paste (approximately 30μΩcm
), but there were no cracks between the substrate and the via.

Comparative Example 1: A green sheet was made in the same manner as in Example 1, and 362 via holes were punched out.

The via holes of this green sheet were filled with W paste (viscosity 3000 voids) shown in Table 4, and heated at 70°C for 1 hour.
Dry for 5 minutes.

Six of these green sheets were laminated as a set, and the pressure was 50MPa.
After pressurizing and integrating at a pressure of 1,000 yen in a N2 stream,
After degreasing by heating at a temperature increase rate of 50° C./hour to 1,800° C., a multilayer substrate was formed by firing at 1800° C. for 930 hours.

As a result of measurement, the volume resistivity of the via was 30 μΩcm.
However, cracks were observed between the substrate and the via.

Example 2: A green sheet was made in the same manner as in Example 1, and 362 via holes were punched out.

The via holes of this green sheet were filled with iN-added W paste (viscosity 2500 poise) shown in Table 3, and
Dry at °C for 15 minutes.

Thereafter, in the same manner as in the example, a set of six sheets was laminated, degreased, and fired to form a multilayer board.

As a result of measurement, the volume resistivity of the via was 80 μΩcm.
However, no crank occurred between the board and the via.

〔Effect of the invention〕

By carrying out the present invention, it is possible to manufacture an AIN multilayer circuit board in which the volume resistivity of the vias is low and there is no cranking between the substrate and the vias.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the principle of the present invention, FIG. 2 is a sectional view illustrating the vacuum suction method. In the figure, l is An green sheet, 2 is a beer hall, 3 is AI! , N mixed W paste, 4 is W paste, 5 is hole, 6 is a vacuum container; 1 2 It is. ) 3

Claims (1)

[Claims] Aluminum nitride characterized by applying tungsten paste added with aluminum nitride to the inner wall of a via hole provided in an aluminum nitride green sheet, drying it, filling the via hole with tungsten paste, and firing in a non-oxidizing atmosphere. How to form vias on a board.