JPH10265267A - Aluminum nitride sintered body and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure high heat conductivity and superior light shielding property by using high purity single crystals as aluminum nitride grains forming a skeleton part and accumulating components of a sintering aid and an additive at specified points of grain boundaries. SOLUTION: High purity aluminum nitride, a sintering aid such as Y2 O3 powder and an additive such as basic calcium carbonate powder are added to an org. solvent and they are mixed, press-molded and temporarily fired at 1,000-1,400 deg.C. A soln. of a metallic salt such as nickel nitrate, neodymium acetate or molybdenum heterotungstate is impregnated into the resultant temporarily fired body and this body is subjected to concluding firing at 1,600-1,950 deg.C in an atmosphere of gaseous N2 . The resultant sintered body is heat-treated at 1,000-1,400 deg.C and rapidly cooled at >=100 deg.C/min rate to obtain the objective aluminum nitride sintered body contg. aluminum nitride grains as high purity single crystals and components of the sintering aid and the additive accumulated at specified points of the grain boundaries and having 190-210 W/mK heat conductivity, 4.4×10<-6> -4.6×10<-6> /K coefft. of thermal expansion and a dielectric constant of 8.9-9.2 at 25 deg.C and 1 MHz.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride sintered body fired using a ceramic containing aluminum nitride as a main component and a method for producing the same.

[0002]

2. Description of the Related Art Generally, a sintered body using aluminum nitride is widely used as a substrate for high heat radiation of a semiconductor circuit. At that time, in semiconductor circuits, high integration, high functionality,
Higher current and higher frequency of switching current are required, and high thermal conductivity is required for a high heat dissipation substrate of this type of semiconductor circuit.

[0003] Further, in addition to the above-mentioned high thermal conductivity, a high heat dissipation substrate is required to have a thermal expansion coefficient close to that of a semiconductor and to have characteristics such as light shielding properties, low dielectric properties, and high insulating properties. .

[0004]

However, in the normally manufactured aluminum nitride sintered body, impurities such as impurities in the raw material, sintering aid, and molding binder also exist in the crystal, and the grain boundary is reduced. Is thickly dispersed. For this reason, it has been pointed out that the impurities impede the heat conductivity and decrease the heat conductivity, making it impossible to obtain a high thermal conductivity.

[0005] Therefore, in order to achieve a high thermal conductivity, high purity to reduce impurities in the raw material as much as possible, high densification to reduce barriers at grain boundaries, and search for a sintering aid with a low addition amount, etc. Various ideas have been devised. However, when trying to achieve high purity, problems such as a decrease in light-shielding properties occur, and the problem that the manufacturing cost rises considerably becomes apparent.

SUMMARY OF THE INVENTION The present invention solves this kind of problem, and provides an aluminum nitride sintered body which can secure desired characteristics and can be easily and efficiently manufactured, and a method for manufacturing the same. With the goal.

[0007]

In the aluminum nitride sintered body according to the present invention, the aluminum nitride particles constituting the skeleton have a high-purity single crystal, and the sintering aid component and the additive component have a grain boundary. , Heat transfer disturbances are reduced and heat transfer is improved. Thereby, the aluminum nitride sintered body can secure a desired high thermal conductivity, for example, 170 W / mK or more, and can reliably maintain a desired light-shielding property and the like.

Further, in the method for manufacturing an aluminum nitride sintered body according to the present invention, first, a formed body is formed using a ceramic containing aluminum nitride as a main component (FIG. 1).
Middle, step S1). At that time, aluminum nitride
In addition to containing impurities such as oxygen and carbon, a densification additive as a sintering aid is mixed.

[0009] The sintering aid component is usually selected from C and a Group III element or a Group II element containing a lanthanum element added during sintering of aluminum nitride.
The sintering aid component is required not to react with the metal salt solution when the calcined body is impregnated with the metal salt solution in a later step, and the sintering aid component is selected based on this request. .

[0010] The molded body is preliminarily fired in a temperature range of 1000 ° C to 1400 ° C to obtain a preliminarily fired body (step S2). Next, a metal salt that reacts with impurities in the raw material, sintering aid components, and the like is added to the calcined body. Here, the calcined body has continuous voids of about 40 to 50%, and the solution impregnates the inside of the calcined body by osmotic pressure (step S3).

The metal salt, which is an additive, tends to lower the thermal conductivity of aluminum nitride, and is required to have a large effect with as little as possible. For this reason, it is desirable to perform the addition in atomic units and in the form of a solution in order to achieve the addition in the smallest size and in the smallest amount. The solution may be in the form of a nitrate, an acetate or a chloride, or may be an organic ester so as not to hinder the densification and physical properties of the sintered body. Further, tungsten or molybdenum hetropolyacid is suitable because it is a liquid and is easy to use and does not impair physical properties or hinder densification.

[0012] The calcined body after the impregnation with the metal salt solution and the drying treatment is fully calcined in a temperature range of 1600 ° C to 1950 ° C to obtain a calcined body (step S4). Then, the fired body is subjected to a heat treatment in a temperature range of 1000C to 1400C (step S5). As a result, impurities in the raw material, crystallization aid components, and the like react with the additive (metal salt) and are fixed, and are deposited and accumulated at a specific point on the grain boundary. Therefore, high-purity single crystallization of the aluminum nitride particles is achieved,
Since impurities and the like are deposited and accumulated at a specific point on the grain boundary to remove a factor that hinders heat conduction, it is possible to secure light shielding properties by the precipitates in addition to high thermal conductivity.

After the heat treatment, the fired body is cooled at a cooling rate of 100 ° C./min or more (step S6). For this reason, it is possible to prevent the accumulated impurities and the like from diffusing again to the periphery.

The metal salt solution is composed of Ni, Co, Nd, Sm,
At least one or more nitrates, acetates or chlorides selected from Ce, Cr, Mn, Mo, V, Ti, Zr or Y, or heterotungstic acid and M
o, V or Cr salts.

The Ni and Co elements combine with oxygen as an impurity in aluminum nitride. These become oxides at high and low temperatures, but in N ₂ , 1000 ° C. to 14 ° C.
Metallization in the temperature range of 00 ° C. Therefore, when the fired body is heat-treated in this temperature range, it reacts with the grain boundary glass layer and other impurities while being metallized to form spinel, etc., and is deposited and accumulated at a specific point.

Nd, Sm, Ce, Y and La elements are
It is considered to have strong activity and strongly bond with oxygen.However, when alkaline earth metal enters, it forms perovskite and the amount of oxygen deviates from the stoichiometric ratio, and acts as a carrier for oxygen. . These elements are easily affected by the oxygen partial pressure and the temperature, and conversely can metallize or oxidize other oxides, and have an effect as a densifying agent for aluminum nitride. Therefore, for example, Ni, Co, Cr, impurities in the raw material, etc. are selected as the components to be reacted and controlled at a specific temperature and a specific partial pressure, whereby it is possible to react and precipitate at a specific point.

The Cr, Mn, Mo and V elements, including W, react with oxygen to form spinels. On the other hand, these elements are relatively easily turned into carbides and nitrides, and have a function of effectively suppressing the oxidization of the grain boundaries to lower the thermal conductivity. In addition, the oxide can easily make the sintered body light-transmitting, but by precipitating it as carbide or nitride, it can have an effective light-shielding property.

The Ti and Zr elements have a function of reacting with other additives or reacting with impurities such as oxygen in the raw material. These form stable oxides with oxygen, but also have a perovskite structure, which can cause partial nitridation and carbonization. Therefore, by controlling the temperature and the atmosphere, nitrides and carbides can be precipitated at specific points.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Aluminum nitride powder having a purity of 99.0% (average particle size of 1.8 μm) contains 0.9% of oxygen and 0.06% of carbon as impurities and calcium, silicon and the like. , Several tens of ppm of iron and nickel.

Therefore, the aluminum nitride powder is mixed with 97 w
t%, 1.0 wt% of yttrium oxide having an average particle size of 1.0 μm, and 2.0 wt% of basic calcium carbonate having an average particle size of 1.5 μm were sufficiently mixed in an organic solvent. The purity of yttrium oxide and calcium carbonate was 99.9% and 99.2%, respectively. At this mixing ratio, if a sintered body is manufactured by a conventional manufacturing method, about 4% of a glass layer will be generated.

After the mixing, the liquid content was adjusted to 17% in volume ratio, and then 61 × 61 × 7 by hydrostatic pressure molding in a mold.
mm was molded. After being subjected to a drying treatment, the molded body is heated at a heating rate of 10 ° C./min under nitrogen gas flow, kept at 650 ° C. for 30 minutes, and further heated to a temperature of less than 1000 ° C. to 1410 ° C. The resultant was held for 1 hour to obtain a calcined body.

The calcined body was impregnated with a 25% nickel nitrate solution, a 10% neodymium acetate solution and a molybdenum heterotungstate solution as a metal salt solution. At that time, in the calcined body having a calcining temperature of less than 1000 ° C., cracks and cracks occurred to 30% or more due to liquid penetration during impregnation with the metal salt solution. This phenomenon decreases with increasing temperature, up to 10% at 1000 ° C., up to 1450 ° C.
At a temperature exceeding, no defects were visually observed during the impregnation.

The calcined body impregnated with the metal salt solution was subjected to a drying treatment, followed by a main calcination treatment in a nitrogen gas atmosphere. The main firing temperature range was arbitrarily selected from 1550 ° C. to 2050 ° C., and was maintained for 90 minutes in each temperature range.
At that time, when the main firing temperature was lower than 1600 ° C., the relative density was 95% or less, and high densification was not achieved. When the firing temperature is 1600 ° C. or higher, the relative density is 98%.
% From 1700 <0> C to 1850
In the temperature range of ° C., the relative densities are all 98% or more,
Further, in the temperature range of 1730 ° C. to 1800 ° C., the relative density was almost all 100%.

However, when the above-mentioned sintering process was performed using a sintering body having a sintering temperature exceeding 1400 ° C.,
It was found that the metal salt as an additive was not impregnated to the center. Therefore, the calcination temperature is 1000 ° C. to 1400 ° C.
° C, and the final firing temperature is 1600 ° C to 19 ° C.
50 ° C temperature range, more preferably 1730 ° C to 180 ° C
It is preferable to set the temperature to 0 ° C.

Next, the fired body fired at a temperature of 1730 ° C. to 1800 ° C. has a pressure of 0.5 bar to 3.5 ba.
r, and heat treatment was performed by maintaining the temperature in a temperature range of 900 ° C. to 1500 ° C. for 2 hours.
Here, when the heat treatment temperature is 1400 ° C. or higher, the reaction precipitation of impurities in the raw material and the sintering aid component does not occur.
If the temperature was lower than 000 ° C., the reaction was too slow and the accumulation did not proceed. Therefore, the temperature range of the heat treatment is 1000 ° C. to 1 ° C.
The temperature was set to 400 ° C. Next, the fired body after the heat treatment is 1
It was quenched at a rate of 00 ° C./min or more. This allows
It is possible to reliably prevent the reactant precipitated at the grain boundary from dissolving again.

The fired body thus obtained is 190
２１０210 W / mK and a thermal expansion coefficient and a dielectric constant of 4.4 × 10 ^{−6 /} k to 4.6, respectively.
× 10 ^{−6 /} k, 8.9 to 9.2 (25 ° C., 1 MHz). Further, since the reaction precipitate is distributed at a specific point on the grain boundary, the fired body is grayish. In addition, due to the presence of heavy metals such as tungsten, high-performance electronic circuit substrates having high heat conductivity and having a light-shielding effect with X-rays and ultraviolet rays have been manufactured.

[0027]

As described above, in the aluminum nitride sintered body and the method for producing the same according to the present invention, the aluminum nitride particles constitute a high-purity single crystal, have high thermal conductivity, and have a sintering aid component. And additive components accumulate at specific points in the grain boundaries to have desired light-shielding properties. Thus, it is possible to obtain an aluminum nitride sintered body that can be suitably applied to a substrate for a high-performance electronic circuit or the like that secures desired properties such as thermal conductivity and light-shielding properties with a simple process.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for manufacturing an aluminum nitride sintered body according to an embodiment of the present invention.

Claims (6)

[Claims] An aluminum nitride sintered body fired using ceramics containing aluminum nitride as a main component, wherein the aluminum nitride particles constituting a skeleton portion are high-purity single crystals, and a sintering aid component And a sintered body of aluminum nitride, wherein an additive component is accumulated at a specific point of a grain boundary. 2. The aluminum nitride sintered body according to claim 1, wherein said aluminum nitride sintered body has a thermal conductivity of 1
An aluminum nitride sintered body characterized by being at least 70 W / mK. 3. A step of obtaining a molded body using ceramics containing aluminum nitride as a main component; a step of temporarily firing the molded body in a temperature range of 1000 ° C. to 1400 ° C .; A step of drying the calcined body after impregnating the calcined body with the metal salt solution; a step of main-baking the calcined body after the drying treatment in a temperature range of 1600 ° C. to 1950 ° C .; The obtained fired body is heated at 1000 ° C to 140 ° C.
A method for producing an aluminum nitride sintered body, comprising: a heat treatment in a temperature range of 0 ° C .; and a cooling treatment of the fired body after the heat treatment at a cooling rate of 100 ° C./min or more. 4. The production method according to claim 3, wherein said metal salt solution comprises Ni, Co, Nd, Sm, Ce, Cr, M
A method for producing an aluminum nitride sintered body, comprising at least one of a nitrate, an acetate and a chloride selected from n, Mo, V, Ti, Zr and Y. 5. The production method according to claim 3, wherein said metal salt solution comprises heterotungstic acid and its Mo, V
Or a method for producing an aluminum nitride sintered body, which is a Cr salt. 6. The method according to claim 3, wherein a sintering aid is added when the molded body is obtained, and the sintering aid component is a group III element containing C and a lanthanum element or A method for producing an aluminum nitride sintered body, comprising at least one oxide, hydroxide or carbonate selected from Group II elements.