JPH04193765A - Production of aluminum nitride substrate - Google Patents

Abstract

PURPOSE:To improve thermal conductivity, electrical insulating property and stability of appearance by sustaining a definite temp. in the case of calcining an AlN substrate in the temp. increasing stage of the calcining temp. pattern and accelerating the decarburization. CONSTITUTION:To an AlN powder consisting of 0.5-1.0wt.% oxygen as impurity and <=0.05wt.% carbon, an oxide sintering aid (e.g. Y2O3) is added to control total quantity of oxygen at 1.0-2.0wt.% and is molded in the presence of an organic binder and calcined to obtain the AlN substrate 4 of <=0.7wt.% residual carbon. Then, into an AlN crucible 2 housed in a crucible 1, a setter 4 laminated with an AlN substrate 3 is disposed and covered with a lid 6 via spacer 5. Then, heat-up is started while blowing gaseous N2 7 from the outside, and when temp. arrives to 1500-1600 deg.C and is sustained for 2-10 hours to accelerate the decarburization, temp. is further increased and sintering is completed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an ARN (aluminum nitride) substrate, and particularly relates to a method for manufacturing an ARN (aluminum nitride) substrate. The present invention relates to a manufacturing method for obtaining a stable appearance of a sintered body.

[Prior Art 1 Highly thermally conductive AlN sintered bodies are specifically used as insulating materials, typified by semiconductor substrates. High integration of semiconductors,
With the trend toward higher speeds and higher outputs, the following problems have come into focus. In other words, (a) How efficiently can the heat generated by the semiconductor chip be released to the outside of the system?

(b) As operational accuracy improves, signal delays in the substrate or package portion become a problem.

(C) As the chip size increases, the difference in thermal expansion with the chip increases.

(d) The operating voltage of high-power chips is increasing, and the insulation resistance and dielectric strength of the substrate are becoming problems.

In order to solve these problems faced by semiconductor devices, a new substrate or package material is desired to replace the conventional alumina. Such materials have: ■ High thermal conductivity.

■Excellent electrical insulation.

■ Good high frequency characteristics (low dielectric constant, low dielectric loss).

■Thermal expansion is similar to silicon.

■ Chemically stable.

■ High mechanical strength.

■ Circuit formation is easy.

■ Can be airtightly sealed.

It is desirable to have the following characteristics. AlN is seen as a promising material that can meet these demands.

Research into the use of ΔffN as a substrate material has focused on obtaining the properties described above using sintering aids that are effective in non-oxidizing atmospheres. The specific technology is
As shown in Japanese Patent Publication No. 46-4.1003, Y
203 as a sintering aid, or
As shown in Publication No. 9510, Cab, Bad, S
Using r○ etc. as a sintering aid, the thermal conductivity is 100W/m
A sintered body of about K was obtained.

In addition, Ceramics Association Journal, 25th Ceramics Basics Debate, ID03
．． In 3HO3 (January 1988), a sintered body with high thermal conductivity is obtained by firing an AffN molded body at 1850 to 1950°C for 2 to 96 hours in a reducing atmosphere. This method has a problem in that the manufacturing cost is high because the fired substrate is refilled in a graphite crucible and fired.

JP-A-62-52181 reports that thermal conductivity is improved by adding carbon, which acts as a reducing agent, to AgN in addition to Y2O3, which is a sintering aid.

It can be seen that active use of a reducing agent or reducing atmosphere is effective in reducing residual oxygen.

On the other hand, possible ways to reduce residual carbon include optimizing the decarburization process during raw material powder synthesis, selecting an organic binder that can be efficiently removed even in a non-oxidizing atmosphere, or debinding in the atmosphere. However, these are all treatments or countermeasures taken before firing, and although they are effective in reducing residual carbon, they are not always compatible with deoxidation during firing.

Zunawaji: If sufficient carbon is removed before firing, deoxidation during firing will be insufficient, resulting in a decrease in thermal conductivity. In addition, during firing, we actively use a reducing agent (reducing atmosphere).
If this is used, not only the carbon left behind but also foreign carbon will be taken in from the furnace internal structure, increasing the amount of carbon in the sintered body and causing a decrease in insulation resistance and dielectric strength.

[Problem to be solved by the invention 1 With the conventional firing technology using oxide sintering aids such as Y203, (1) Sufficient thermal conductivity cannot be obtained (Japanese Patent Publication No. 46-41
003, JP-A-62-52181).

(2) In order to obtain sufficient thermal conductivity, the manufacturing cost is high because the -degree-fired substrate is packed back into the graphite crucible and re-fired (25th Ceramic Industry Basics Forum, IDO3,
There are problems such as 3I (03).

The present invention does not only remove or reduce either oxygen or carbon contained in the fired product during firing, but also
The object of the present invention is to provide a firing technique that can reduce both of these factors at the same time.

[Means for Solving the Problems 1] In the present invention, in order to efficiently remove oxygen and carbon impurities contained in the product to be fired before firing, the form of these oxygen and carbon is grasped, and the firing pattern is adjusted accordingly. Achieved optimization.

That is, the present invention removes oxygen impurities or carbon impurities contained in the AgN raw material powder in the form of alumina or the like, and the residual amount of organic binder added during green sheet forming by optimizing the following reaction. When firing the substrate, it is possible to remove oxygen and carbon from the fired product to the outside of the system.

Oxygen impurities (oxides) +C (internal carbon) -COT (1) Specifically, a holding step in which the temperature is maintained at a constant temperature at an appropriate temperature during the heating process in the firing temperature pattern. This is a method for manufacturing an AlN substrate, characterized in that a method is provided to promote decarburization.

In this case, the holding step is preferably performed at a temperature of 1500 to 1700
'C12 to 10 hours is preferable.

In addition, using raw material powder containing 0.5 to 1.0% by weight of oxygen impurities and 0.05% by weight or less of carbon, the total oxygen content at the time of adding the oxide sintering aid is 1. .0~2.
0% by weight, and the amount of residual carbon after removing the organic binder added during green sheet molding is 0.7% by weight.
The following is preferable. Furthermore, it is preferable to adjust the amount of gas discharged from the AlN substrate.

[Function] The AlN sintered body produced according to the present invention had high thermal conductivity (and electrical properties such as insulation resistance and dielectric strength were comparable to those of alumina).

In the present invention, in the decarburization reaction shown by the above formula (1),
After controlling the forms of oxygen and carbon, we limited the optimal temperature and time range for intermediate holding. In addition, the removal of the generated gas from the system (control of Co gas pressure) is as described in (1) above.
This is important for promoting the decarburization reaction shown in the equation, and was achieved by controlling the discharge rate.

Regarding carbon, the temperature and time range of the oxidation reaction are different depending on what is mixed in during the synthesis of the raw material powder and the residue of the organic binder added during molding, and therefore the timing of CO gas generation is also different. Further, when the temperature (late 1700° C.) at which a liquid phase that promotes sintering is formed is reached, it becomes difficult to remove carbon.

Therefore, at 15oO to 16oooC, which is the oxidation peak of carbon caused by the organic binder, and in the first half of 1700'C, which is the oxidation peak of carbon mixed during raw material powder synthesis,
By providing a hold during the temperature raising process, sufficient CO gas was generated.

This makes it possible to reduce residual oxygen and carbon without relying on active oxidation or reduction from the outside.

[Example 1 Example-1 Average particle size 1.2 μm (OAρN powder (oxygen content 0.
65% by weight, carbon content 0.02% by weight), 2.5% by weight of Y2O3 having an average particle size of 0.5 μm was added, and an appropriate amount of polyvinyl butyral (PVB) was added to prepare an AgN slurry. A green sheet was formed from this slurry by a doctor blade method, and further punched into a 65 x 65 mm square.

This green sheet was heated at 600°C in a nitrogen stream of 1 atm.
It was degreased in 3 hours. Subsequently, in the firing furnace shown in Figure 6,
In a nitrogen flow of 1 atm (5 (1!/m1n), 1900
C. for 4 hours. The firing furnace shown in Fig. 6 contains Ag,
A crucible 2 with a lid 6 is placed in an N-coated graphite crucible 1 through a spacer 5, and this AlN crucible 2 is
Inside, the AlN sheet 3 to be fired is placed on the BN setter 4 and heated and fired. N2 gas from the bottom of the graphite Ruppol 7
A nitrogen gas flow is created in the crucible into which the nitrogen gas is introduced.

Processing amount per batch (7 to 8k in this example)
g) and the amount of residual carbon after degreasing (0.6 in this example)
% by weight) and the amount of CO gas discharged, the conditions for holding during firing were 1625° C. for 8 hours. FIG. 2 shows a conventional firing heat pattern, whereas in the present invention, firing is performed using the heat pattern shown in FIG. The time change in the amount of co gas generated at this time is also shown.

After the obtained AlN substrate was subjected to a normal honing treatment, appearance measurements such as brightness and color tone, and measurements of thermal conductivity and insulation resistance were performed. The results are shown in Table 1 and No. 1 in FIG.

Example 2 Firing was carried out in the same manner as in Example 1, and the holding temperature in the heating process was 1450 to 1750°C, and the holding time was 2 to 12 hours. The results are No., 2-No., 1 in Table 1 and Figure 5.
0.

Comparative Example-1 Same as Example-1 with temperature pattern shown in Section 2/1f2
N was fired. The temperature is not maintained during the heating process,
It was fired in one stage as before. The results are shown in Table 1 and No. 11 in FIG.

Comparative Example-2 Firing was performed in the same manner as in Example-1. However, the processing amount per batch was (a) 1.5 mm as in Example-1, and (b) as in Example-1. The results are shown in Table 1 and Figure 5 as No. 12.
．． It was shown as 13.

Comparative Example-3 Firing was performed in the same manner as in Example-1. By controlling the amount of CO gas generated, the amount of CO gas around the fired product can be reduced.
The partial pressure of O gas was adjusted. Specifically, the height of the scrubber 5 shown in Fig. 6 is adjusted, and the opening degree of the CO gas outlet is adjusted to (a).
(b) twice as much as that of Example-1; The results are shown in Table 1 and FIG. 5 as No. 14 and No. 015.

Furthermore, from the results of the above examples, the relationship between the holding temperature and the amount of residual carbon when the holding time is 2 hours is shown in Figure 3.
FIG. 4 shows the relationship between the holding time and the amount of residual carbon when the holding temperature was 1625°C.

FIG. 5 shows No. 091 to No.], 5 in Table 1 on a graph of tone and lightness. When the tone Y is large, the color is yellowish brown, and when the lightness is large, the color is bright. The preferred value is Y=3.4-5. O, L=64 or more"2. Further, the most preferable values are Y=4 to 5 and L-75 to 85%. No. 1 in terms of thermal conductivity, insulation resistance, and appearance
is the most suitable.

[Effect of the invention] In the present invention, an active reducing action from the outside is used,
In addition, by adopting a firing heat pattern that allows the oxygen and carbon contained in the fired product to react efficiently without actively removing the binder, the generated CO gas can be discharged outside the system. By adjusting this, we were able to significantly reduce residual oxygen and carbon in the sintered body. According to the present invention, it is possible to obtain a /IN sintered body that has high thermal conductivity, excellent insulation resistance, and stable appearance such as brightness and color tone.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the firing heat pattern of the embodiment of the present invention, Fig. 2 is a graph showing the conventional firing heat pattern, Fig. 3 is a graph showing the relationship between holding temperature and residual carbon amount, Fig. 4 5 is a graph showing the relationship between retention time and amount of residual carbon, FIG. 5 is a graph showing color tone and brightness, and FIG. 6 is a schematic cross-sectional view of a firing furnace used in carrying out the present invention. 1... Crucible 2... AlN crucible 3... AlN sheet 4... BN setter 5... Spacer 6... Lid 7... N2 gas

Claims (1)

[Scope of Claims] 1. A method for producing an AlN substrate, characterized in that during firing of the AlN substrate, a holding step is provided in which the temperature is maintained at a constant temperature during the heating process in the firing temperature pattern to promote decarburization. 2. Claim 1, wherein the holding step has a holding temperature of 1500 to 1700°C and a holding time of 2 to 10 hours.
The method for manufacturing the AlN substrate described above. 3 Using a raw material powder containing 0.5 to 1.0% by weight of oxygen impurities and 0.05% by weight or less of carbon, the total oxygen content at the time of adding the oxide sintering aid is 1. 0-2.0
% by weight, and the amount of residual carbon after removing the organic binder added during green sheet molding is 0.7% by weight or less.
Substrate manufacturing method. 4. The method for manufacturing an AlN substrate according to claim 1, 2 or 3, characterized in that the amount of gas discharged from the AlN substrate is adjusted.