JP2699581B2 - Via forming method for aluminum nitride substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for forming a via of an aluminum nitride substrate, with the aim of forming a via having a low resistance, using a tungsten paste containing aluminum nitride added 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 a tungsten paste and fired in a non-oxidizing atmosphere to constitute a via forming method for an aluminum nitride substrate.

[Industrial applications]

The present invention relates to a method for forming a low-resistance via on an aluminum nitride (hereinafter abbreviated as AlN) substrate.

Due to the necessity of processing a large amount of information at high speed, information processing apparatuses have been reduced in size and capacity, and semiconductor integrated circuits, which are the main components of the information processing apparatuses, have been improved in integration degree and LSIs and VLSIs have been put to practical use.

On the other hand, these integrated circuits are mounted on a chip mounting substrate (interposer) made of ceramics in the form of a chip to produce an LSI module, which is then mounted on a printed wiring board as a replacement unit. There are.

As described above, the degree of integration of a semiconductor integrated circuit increases, and the amount of heat generated by the device increases at an accelerated pace as high-density mounting is performed.

In other words, the calorific value per IC was small at about 3.5 W at the beginning, but the calorific value per LSI has now increased to about 10 W, and when a large number of ICs are mounted in a matrix, Are enormous and tend to increase.

Conventionally, a substrate on which an LSI chip or the like is mounted has been made of alumina (Al ₂ O ₃ ) having high thermal conductivity and excellent heat resistance.

However, the thermal conductivity of alumina is excellent ゝ 20 W / mK
This is inadequate as a material for the above-mentioned chip mounting substrate.

Therefore, attention has been paid to AlN having a thermal conductivity as large as 320 W / mK (theoretical value), and the practical use of this substrate has been promoted.

 Table 1 compares the characteristics of the two.

In other words, AlN has a small coefficient of thermal expansion in addition to its excellent thermal conductivity, and the coefficient of thermal expansion of Si constituting the LSI (3.6 × 10
⁻⁶ / ° C.) and a low dielectric constant are also advantageous in that crosstalk can be reduced when forming a multilayer substrate.

[Conventional technology]

The AlN substrate has attracted attention as a substrate for mounting semiconductor integrated circuits. However, since AlN has a high melting point and the substrate is fired at a high temperature exceeding 1800 ° C., a high melting point tungsten (W The conductor line is formed by screen-printing a W paste on a green sheet, laminating and integrating the paste, and then firing.

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

That is, at the stage of the green sheet, a connection position is formed by pressing to form a via hole, and the W paste used for forming the conductor line is filled and filled with the via hole, and the conductor line is patterned by screen printing. After that, the green sheets are laminated and integrated, and heated to 1800 ° C. in this state to form a multilayer circuit board.

However, upon heating, the W powder constituting the W paste starts shrinking at about 1000 ° C, whereas the AlN powder constituting the green sheet does not shrink at all up to 1600 ° C. And a liquid phase is formed to cause firing shrinkage.

For this reason, cracks occur during the firing process, and the adhesion between the substrate and the via is reduced, resulting in poor conduction.

As a countermeasure, there is a method of adding 5% or more AlN powder to the W paste to reduce the difference in the shrinkage rate during the firing process and improve the adhesion.

However, this method increases the resistance of the via,
There is a problem that a multilayer circuit board having good characteristics cannot be formed.

[Problems to be solved by the invention]

As described above, W is used as a constituent material of the conductor line of the AlN multilayer circuit board. However, cracks occur in vias because the firing shrinkage start temperature of AlN and the firing shrinkage start temperature of W differ by about 400 ° C. The problem is that it causes poor conduction, and the solution is a problem.

[Means for solving the problem]

The above-mentioned problem is characterized in that a W paste containing AlN is applied to the inner wall of a via hole provided in an AlN green sheet and dried, and then the via hole is filled with the W paste and fired in a non-oxidizing atmosphere. This problem can be solved by configuring a method for forming a via in a substrate.

[Action]

In the present invention, instead of filling the via hole with the AlN-containing W paste as it is, as shown in FIG. The problem is solved by filling the inside with a W paste 4 and firing it.

In this way, the influence of firing shrinkage of AlN and W is reduced, and a low-resistance via can be formed.

The problem here is how the inner surface of the via hole having a small hole diameter of about 200 μm can be coated with the AlN-containing W paste thinly. Can be applied.

FIG. 2 is a cross-sectional view for explaining the vacuum suction method. A porous water-absorbing paper 7 is placed on a pressure-reducing container 6 having a large number of holes 5 formed on the surface thereof, and an AlN green sheet 1 is placed thereon. A mask 8 precisely positioned in the via hole 2 is placed, and a low-viscosity AlN-containing W paste is supplied on the mask.

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

According to the present invention, a via is formed by applying the AlN-mixed W paste on the inner surface of the via hole 2 in this manner, and then drying and then filling the paste with the W paste.

〔Example〕

Example: A green sheet having a composition shown in Table 2 (a density of 1.70 g / cm ³ and a thickness of 250 μm) was formed by a doctor blade method, the green sheet was punched into a 90 mm square, and 362 via holes having a diameter of 200 μm were formed with a punch. .

Next, an AlN-added W paste having a composition shown in Table 3 (viscosity 3
000 poise), add terepineol to a viscosity of 500 poise and apply paste to the inside of the via hole.
Dry at 15 ° C. for 15 minutes.

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

Six green sheets are laminated as a set, pressurized at a pressure of 50 MPa and integrated, and then heated to 1000 ° C. in a N ₂ stream.
Degreasing is performed by heating at a heating rate of 50 ° C / hour.
Baking was performed at 00 ° C. for 30 hours to form a multilayer substrate.

As a result of the measurement, the volume resistivity of the via was 35 μΩcm, which was slightly higher than that in the case of using the conventional W paste (about 30 μΩcm), but there was no crack between the substrate and the via.

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

The green paste was filled with the W paste (viscosity 3000 poise) shown in Table 4 in the via hole of the green sheet, and dried at 70 ° C. for 15 minutes.

Six green sheets are laminated as a set, pressurized at a pressure of 50 MPa and integrated, and then heated to 1000 ° C. in a N ₂ stream.
After degreasing by heating at a heating rate of 50 ° C / hour,
The firing was performed for a time to form a multilayer substrate.

Then, as a result of the measurement, the volume resistivity of the via was as low as 30 μΩcm, but cracks occurred between the substrate and the via.

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

Fill the via holes of this green sheet with the AlN-added W paste (viscosity 2500 poise) shown in Table 3 at 70 ° C.
Dried for 15 minutes.

Thereafter, as in the example, the six sheets were laminated, degreased, and fired to form a multi-layer substrate.

As a result of the measurement, the volume resistivity of the via was as high as 80 μΩcm, but no crack occurred between the substrate and the via.

〔The invention's effect〕

By implementing the present invention, it is possible to manufacture an AlN multilayer circuit board in which the volume resistivity of the via is low and no crack occurs between the substrate and the via.

[Brief description of the drawings]

 FIG. 1 is a cross-sectional view illustrating the principle of the present invention, and FIG. 2 is a cross-sectional view illustrating a vacuum suction method. In the drawing, 1 is an AlN green sheet, 2 is a via hole, 3 is an AlN mixed W paste, 4 is a W paste, 5 is a hole, and 6 is a decompression container.

Claims (1)

(57) [Claims] 1. An aluminum nitride green sheet is provided with a tungsten paste containing aluminum nitride applied to the inner wall of a via hole provided on the aluminum nitride green sheet and dried. Then, the via hole is filled with a tungsten paste and fired in a non-oxidizing atmosphere. A method for forming a via in an aluminum nitride substrate.