JP2727652B2 - Method for firing aluminum nitride substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding a method for firing an aluminum nitride substrate, an object of the present invention is to provide a firing method suitable for mass production. Aluminum nitride powder is used as a main constituent material, and a binder, a plasticizer, and a dispersion agent are dispersed in the powder. Add the agent, make a green sheet using the kneaded material, after drying the green sheet,
After placing a tungsten wire or a molybdenum wire around the green sheet, or printing a paste that can be fired simultaneously with the green sheet to form a spacer, performing a degreasing treatment, and then laminating in a firing vessel or firing vessel After vertically setting the substrates, sandwiching the correcting substrate made of boron nitride on both sides, insert the substrate fixing deformed body between the firing container and the correcting substrate, and fire in a non-oxidizing atmosphere. Thus, a method for firing the aluminum nitride substrate is formed.

[Industrial applications]

The present invention relates to aluminum nitride (hereinafter abbreviated) suitable for mass production.
AlN) substrate manufacturing method.

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

These integrated circuits are mounted in a chip form on a chip mounting substrate (interposer) made of ceramic.
There is a mounting type in which an LSI module is mounted on a printed circuit board and mounted on a printed wiring board or the like as a replacement unit.

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, Is enormous, and the calorific value tends to further increase.

Conventionally, alumina (α-Al), which is a material with high thermal conductivity and excellent heat resistance, has
₂ O ₃ ) Substrates have been used.

However, the thermal conductivity of alumina is excellent.
It is about 20 W / mK, which is insufficient as a material for the substrate for mounting a chip.

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 properties of AlN and Al ₂ O ₃ .

That is, in addition to having excellent thermal conductivity, the coefficient of thermal expansion is small, and the coefficient of thermal expansion of Si constituting the Si chip (3.6 × 10
⁻⁶ / ° C.) and a low dielectric constant are advantageous in that cross-talk can be reduced when forming a multilayer substrate.

However, AlN is sublimable and its decomposition temperature is 2200 ° C.
There is a problem that decomposition starts around 000 ° C.

Therefore, a special technique is required for the production of an AlN substrate.

[Conventional technology]

To manufacture an AlN substrate, a slurry containing AlN as a main component is formed like an alumina substrate, and a green sheet is formed from the slurry by a doctor blade method. To decompose and remove the binder to form a sheet made of AlN.

Next, this sheet is heated at a high temperature of about 1800 ° C. in a non-oxidizing atmosphere, and liquid phase sintering is performed with a sintering aid, whereby an AlN substrate is produced.

Table 2 shows a typical configuration of the AlN slurry.

In the table, PVB is an abbreviation for polyvinyl butyral, DBP is an abbreviation for diptyl phthalate, and a specific treatment method is that a green sheet formed to a thickness of about 400 μm by the doctor blade method is dried at room temperature and dispersed in a dispersion medium. After removing the (solvent), the binder is removed by heating at a temperature of about 900 ° C. in a non-oxidizing atmosphere, for example, a nitrogen (N ₂ ) stream, and the sheet is fired at a high temperature.

Here, in the conventional firing method, a sheet without binder is placed on a setter made of boron nitride (BN), a BN center is placed on it, and this is placed in a graphite container or BN container and fired. The way you are used.

However, in this method, only one sheet can be fired per one BN setter, which is not suitable for mass production.

Therefore, for mass production, as shown in FIG. 4, a plurality of (in this case, nine) AlN sheets 1 are
The AlN substrate 3 which has already been fired at a high temperature is placed thereon, and this is set in a firing vessel 4 made of BN or graphite, and fired.

However, when firing at a high temperature of about 1800 ° C., the AlN sheets 1, especially the bottom AlN sheet 1, are naturally fused and cannot be separated.

[Problems to be solved by the invention]

In order to mass-produce AlN substrates, it is necessary to stack and fire the sheets that have undergone the binder decomposition process.To do so, it is necessary to prevent fusion of the AlN sheets to each other, and the method must be put to practical use. Is the challenge.

[Means for solving the problem]

The above-mentioned problem is that AlN powder is used as a main constituent material, a binder, a plasticizer and a solvent are added to this powder, and a green sheet is made using the kneaded material. After drying the green sheet, a tungsten wire is formed around the green sheet. Or put a molybdenum wire, or print a paste that can be co-fired with the AlN green sheet to make a spacer, and after performing degreasing treatment, stack in a firing container or set vertically in a firing container, After sandwiching the straightening substrate made of BN on both sides, insert a substrate fixing deformed body between the firing container and the straightening substrate, and fire in a non-oxidizing atmosphere to obtain Al.
This can be achieved by configuring a method for firing the N substrate.

[Action]

The present invention relates to a method of firing an AlN sheet having undergone binder decomposition treatment without causing mutual fusion, by using a tungsten (W) wire, a molybdenum (Mo) wire, or a thick film paste containing W or Mo as a main component. A frame pattern formed by printing is used as a spacer.

Substrates obtained by sintering AlN sheets at high temperatures require high sintering conditions of, for example, 1800 ° C., 30 hours, and a long time, and it is difficult to maintain the temperature distribution of the sintering furnace uniformly throughout sintering. From, deformation around the substrate (sag)
And it is necessary to cut off the peripheral part for commercialization.

The present inventors have paid attention to this point, and have considered placing a separator in an area to be cut, and removing this portion using a diamond cutter or an ultrasonic cutter after firing.

When the AlN sheets are stacked with the separator interposed therebetween, it is possible to prevent mutual fusion from occurring due to the presence of a gap between the sheets.

The next problem is the deformation that occurs during high temperature firing of the AlN sheet.

As a result of the experiment, the inventors have confirmed that although some deformation occurs, the deformation does not occur to the extent that mutual fusion occurs.

That is, the sheet from which binder has been removed by treatment at about 900 ° C. for several hours is made of only AlN powder, and there is no other material.

Therefore, when sintering at a temperature of 1800 ° C and sintering by liquid phase sintering with a sintering aid, some deformation is unavoidable, but deformation such that the separated stacked sheets fuse together. Does not occur.

According to the present invention, when the green sheet is dried at room temperature and the removal of the solvent is completed, as shown in FIG. 1 (A), a spacer 6 made of a W line or a Mo line is placed around the AlN green sheet 5. Alternatively, as shown in FIG. 2B, a paste such as a W conductor paste or a Mo conductor paste whose sintering temperature is similar to the sintering temperature of the AlN sheet is screen-printed around the periphery to form spacers.

Thus, the green sheet provided with the spacer is
Usually, a tunnel furnace is used, and the binder is removed by firing at a temperature of about 900 ° C. in a non-oxidizing atmosphere, for example, N ₂ , one by one, but after this step is completed, the spacer made of W wire or Mo is fused with the AlN sheet. I am wearing it, but there is no problem at all,
Such an AlN sheet is laminated in a BN container and fired at a high temperature.

FIG. 2 shows that an AlN sheet 1 having a linear spacer 6 fused thereto is laminated on a BN setter 2 placed at the bottom of a firing container 4 made of BN or graphite, and an AlN substrate 3 is placed thereon. The state is shown.

Next, in consideration of mass production, when a large number of AlN sheets are stacked, deformation or fusion is likely to occur in the bottom sheet due to the load of the sheets themselves.

Therefore, as a countermeasure, as shown in FIG. 3, a plurality of AlN sheets 1 provided with spacers 6 on one surface are arranged vertically, and are sandwiched between non-reactive correcting substrates 9 having high melting points from both sides. Sintering may be performed, and BN is suitable for this purpose because it has a high melting point of 3000 ° C. and is non-reactive.

In this high-temperature firing, shrinkage occurs as the sintering of the AlN sheet proceeds, which may cause the AlN sheets 1 arranged vertically to be inclined. As a method for preventing this, the firing container 4 and the straightening substrate are used. The substrate fixing deformable body 10 which is deformed at a high temperature may be placed between the green paste 9 and a green paste. A green sheet having a layered structure may be inserted, and a curving may be intentionally caused by high-temperature firing, so that the straightening substrate is pushed out.

〔Example〕

Example 1: (Example of use of Mo wire spacer, related to FIG. 2) A slurry having the composition shown in Table 2 was prepared, and a molding interval of 450 was used.
The green sheet was formed at a feed rate of 2.3 m / min, and a green sheet was formed.

Next, the green sheet from which the dispersion medium was removed by drying at room temperature for 6 hours was punched into a 90 mm square, and as shown in FIG.
70m consisting of Mo wire with a diameter of 25μm on N-green sheet 5
The m-square spacer 6 was placed, and a degreasing treatment was performed at 900 ° C. for 4 hours in a N ₂ atmosphere using a tunnel furnace.

As shown in FIG. 2, these 10 AlN sheets are laminated on the BN setter 2 in a firing vessel 4 made of graphite,
The firing was performed at 1800 ° C. for 30 hours while flowing N ₂ gas.

Thereafter, the substrate was cut along the inside of the spacer 6 using a diamond cutter to obtain an AlN substrate, all of which were flat and had good surface roughness.

Example 2: (Use example of W thick film spacer, related to FIG. 2) W thick film paste is screen-printed on a 90 mm square green sheet formed in the same manner as in Example 1, and FIG. As shown in the figure, a 70 mm square conductor pattern having a width of 1 mm, a height of 50 μm and a spacer 7 was formed.

Thereafter, a degreasing treatment was performed at 900 ° C. for 4 hours in a N ₂ atmosphere using a tunnel furnace in the same manner as in Example 1.

Next, as shown in FIG. 2, these 10 AlN sheets were laminated on the BN setter 2 in a firing vessel 4 made of graphite, and fired at 1800 ° C. for 30 hours while flowing N ₂ gas. .

Thereafter, the substrate was cut along the inside of the spacer 6 using a diamond cutter to obtain an AlN substrate, all of which were flat and had good surface roughness.

Example 3: (Example of vertical sintering, related to FIG. 3) A 90 mm square, 2 mm thick BN substrate was used as a correction substrate, and a 100 μm thick AlN was used as a substrate fixing deformable body.
A green sheet coated with a W thick film paste on one side was used.

By doing so, the AlN side can be curved inside.

After forming a green sheet in the same manner as in Example 1, W
The wire was placed and subjected to a degreasing treatment at 900 ° C. for 4 hours in an N ₂ atmosphere.

Next, the AlN sheets 1 provided with the spacers 6 are vertically arranged in the baking container 4 made of BN, and the correction substrates 9 are placed on both sides thereof, and between the correction substrate 9 and the baking container 4. The gap was eliminated by inserting the deformable body 10 for fixing the substrate.

Then, baking was performed at 1800 ° C. for 30 hours while flowing N ₂ gas, and then cut along the inside of the spacer 6 using a diamond cutter to obtain an AlN substrate. It was also good.

〔The invention's effect〕

Implementation of the present invention enables mass production of AlN substrates,
This makes it possible to reduce the cost of the AlN substrate.

[Brief description of the drawings]

1 (A) and 1 (B) are plan views of a green sheet showing a method of practicing the present invention, FIG. 2 is a sectional view showing a firing method according to the present invention, and FIG. 3 is another firing method according to the present invention. FIG. 4 is a cross-sectional view showing a method for firing AlN. In the figure, 1 is an AlN sheet, 2 is a BN setter, 3 is an AlN substrate, 4 is a firing container, 5 is an AlN green sheet, 6 and 7 are spacers, 9 is a correction substrate, and 10 is a substrate fixing deformable body. is there.

Claims (2)

(57) [Claims] An aluminum nitride powder is used as a main component, a binder, a plasticizer, and a dispersant are added to the powder, and a kneaded material is used to form a green sheet. After drying the green sheet, the green sheet is dried. Place a tungsten wire or molybdenum wire around, or print a paste that can be fired at the same time as the green sheet to make it a spacer, perform degreasing treatment, stack it in a firing vessel, and fire in a non-oxidizing atmosphere A method for firing an aluminum nitride substrate. 2. The green sheet subjected to the degreasing treatment according to claim 1 is set vertically in a firing container, and a correction substrate made of boron nitride is sandwiched on both sides. And a baking method in which an aluminum nitride substrate is fired in a non-oxidizing atmosphere.