JPH0825801B2 - Aluminum nitride sintered body and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel aluminum nitride sintered body, particularly an aluminum nitride sintered body having a large Weibull coefficient, and a method for producing the same.

(Problems to be Solved by Conventional Techniques and Inventions) Aluminum nitride sintered bodies have high thermal conductivity, corrosion resistance, and
Because of its high strength and electrical insulating properties, it is attracting attention as a new material. For example, JP-A-59
The aluminum nitride sintered body described in Japanese Patent Publication No. 50078 is a high-purity sintered body having a high purity with an oxygen content of 0.8% by weight or less and a cation impurity of 0.3% by weight or less. Therefore, the above aluminum nitride sintered body is excellent in thermal properties, chemical properties, and mechanical properties,
In particular, it is a material that exhibits translucency and has excellent optical properties.

By the way, generally, the mechanical strength of ceramic materials shows a large variation. This is because the mechanical strength is determined by the weakest point existing in the ceramic material.

Even in the case of the aluminum nitride sintered body, large variations in mechanical strength are observed. The variation in mechanical strength can be expressed by a Weibull coefficient, and the greater the Weibull coefficient, the smaller the variation. Generally, it is said that the Weibull coefficient of an aluminum nitride sintered body is about 10 (published by "Industrial Technology Center" of "Ceramics Material Technology Collection"), but at this level, the probability of defective products due to insufficient mechanical strength High and unreliable.

The Weibull coefficient of the aluminum nitride sintered body having the excellent properties described in the above publication is 13 when measured by the present inventors. Although this value is superior to the above-mentioned general aluminum nitride sintered body, it is not yet a sufficiently satisfactory value in order to reduce the probability of defective products due to insufficient mechanical strength.

(Means for Solving Problems) The inventors of the present invention have conducted repeated studies for the purpose of obtaining a highly reliable aluminum nitride sintered body having a small variation in mechanical strength, a low probability of defective products. It was as a result,
It was found that an aluminum nitride powder having a small average primary particle diameter of the raw material aluminum nitride powder, and an aluminum nitride sintered body having excellent properties that achieved the above objects can be obtained when using one having a small number of coarse particles. He came to propose an invention.

That is, the present invention, the oxygen content is 0.5 wt% or less, the cationic impurities contained when the aluminum nitride composition is AlN is 0.3 wt% or less, the carbon content is 0.07 wt% or less,
The aluminum nitride sintered body has a density of 3.20 g / cm ³ or more and a Weibull coefficient of 17 or more.

The aluminum nitride in the present invention means a 1: 1 compound of aluminum and nitrogen, and all other substances are treated as impurities. However, the surfaces of the aluminum nitride powder and the sintered body are inevitably oxidized in air and Al-N bonds are replaced with Al-O bonds, but this bonded Al is not regarded as a cation impurity. Therefore, Al-
Metallic aluminum having no N, Al-O bond is a cationic impurity.

The aluminum nitride sintered body of the present invention has an oxygen content of 0.
5% by weight or less, 0.3% by weight or less of cationic impurities, and 0.07% by weight or less of carbon content, the content of impurities is extremely low and the sintered density is 3.20 g / cm ³ or more. It is a union. The Weibull coefficient showing the variation in mechanical strength shows a good value of 17 or more.

The Weibull coefficient in the present invention is a value obtained by measuring the three-point bending strength of 50 test pieces and obtaining it according to the formula described later.

The aluminum nitride sintered body of the present invention tends to show a favorable Weibull coefficient as the content of impurities decreases. Here, the impurities consist essentially of oxygen as an anion, and as a cation, a metal or other cation and a substance capable of becoming a cation, and carbon. If the content of these impurities is further reduced, for example, if the oxygen content is 0.3 wt% or less, the cationic impurities are 0.1 wt% or less, and the carbon content is 0.07 wt% or less, a better Weibull coefficient is obtained. For example, an aluminum nitride sintered body having a Weibull coefficient of 18 or more can be used. Among the above-mentioned impurities, especially the carbon content has a large influence on the Weibull coefficient, and therefore it can be considered as a cation because it can bind to an anion, but the content of carbon is specified separately, and 0.07 wt. % Or less, and a smaller amount is preferable. For example, it is preferably 0.06% by weight or less, and more preferably 0.05% by weight or less.

The aluminum nitride sintered body of the present invention not only has the excellent properties as described above, but also has a feature that the surface roughness is small. The surface of the aluminum nitride sintered body is generally polished after sintering for the purpose of improving the smoothness of the surface of the sintered body. When the surface roughness is low as in the aluminum nitride sintered body of the present invention, the time required for surface polishing after sintering can be omitted, and further the surface polishing itself can be omitted. The surface roughness of the unpolished surface of the aluminum nitride sintered body of the present invention is 1.0 μm or less in _Ra , which is far smaller than 7.0 μm of a general aluminum nitride sintered body.

Further, the aluminum nitride sintered body of the present invention has a remarkably high translucency to visible light to infrared light because the content of impurities is extremely small. For example, the following Lambert-Bee
In the formula of r, the absorption coefficient for light with a wavelength of 6 μm is 60c
There are also sintered bodies having excellent performance such as m ⁻¹ or less.

I = I _o e ^−μt I _o : Intensity of incident light I: Intensity of transmitted light t: Material thickness μ: Absorption coefficient The aluminum nitride sintered body having the above-mentioned excellent characteristics has various requirements described above. Can be obtained only when satisfied.
That is, the oxygen content in the aluminum nitride sintered body is 0.5 wt% or less, the cationic impurities contained is 0.3 wt% or less, the carbon content is 0.07 wt% or less and the sintered density is 3.20.
The four requirements of g / cm ³ or more cannot be the aluminum nitride of the present invention even if any one of the requirements is lacking.
Among the above requirements, the content of oxygen is 0.3% by weight or less, the content of cationic impurities is 0.1% by weight or less, the carbon content is 0.07% by weight or less and the sintering density is 3.22 g / cm ³ or more of an aluminum nitride sintered body. It has an excellent property that the Weibull coefficient is 18 or more.

The aluminum nitride sintered body of the present invention is not particularly limited as long as it satisfies the above requirements regardless of the manufacturing method. The following is an example of a typical manufacturing method that is generally suitably used.

Mainly composed of aluminum nitride powder having an average primary particle size of 0.1 to 1.5 μm and primary particles of 20 μm or more and 10% by weight or less, oxygen content of 1.5% by weight or less, and when the aluminum nitride composition is AlN, it is contained. Cationic impurities
This is a method of sintering an aluminum nitride powder compact having a carbon content of 0.3% by weight or less and a carbon content of 0.07% by weight or less.

Therefore, the present invention also has an average primary particle size of 0.1 to 1.5 μm.
m, 2.0μm or more primary particles are mainly 10% by weight or less of aluminum nitride powder, oxygen content is 1.5
Wt% or less, when the aluminum nitride composition is AlN, the cation impurities contained are 0.3% or less by weight, and the carbon content is
Oxygen content characterized by sintering an aluminum nitride powder compact of 0.1 wt% or less is 0.5 wt% or less,
When the aluminum nitride composition is AlN, the content of cation impurities is 0.3 wt% or less, the carbon content is 0.07 wt% or less, the density is 3.20 g / cm ³ or more, and the Weibull coefficient is 17 or more. A method of manufacturing the same is also provided.

The aluminum nitride powder compact to be sintered has an average primary particle size of 0.1 to 1.5 μm and 10 or more primary particles of 2.0 μm or more.
It is mainly composed of aluminum nitride powder which is less than or equal to wt%. The average primary particle diameter is a value obtained from an electron micrograph as described later. The particle size of the aluminum nitride powder has a great influence on the Weibull coefficient of the obtained aluminum nitride sintered body, and when it is out of the above range, the aluminum nitride sintered body having the excellent properties described above is obtained. I can't. The above average primary particle diameter is preferably 0.
2 to 1.0 μm. The number of primary particles of 2.0 μm or more is 3
It is preferably not more than wt%, and more preferably not present at all.

The aluminum nitride powder compact to be sintered has an extremely low content of impurities and an oxygen content of 1.5% by weight or less,
When the aluminum nitride composition is AlN, the content of cationic impurities must be 0.3% by weight or less and the carbon content must be 0.07% by weight or less. The smaller the content of these impurities, the better the properties of the obtained aluminum nitride sintered body. Therefore, the oxygen content is 0.3-1.2% by weight, the cationic impurities are less than 0.1% by weight, the carbon content is 0.06% by weight.
The following aluminum nitride powder compacts are preferably used.

The above-mentioned aluminum nitride powder molded body preferably has a high molding density, and is preferably 1.70 g / cm ³ or more, and more preferably 1.75 g / cm ³ or more in consideration of the properties of the obtained aluminum nitride sintered body.

The above-mentioned aluminum nitride powder compact may be obtained by any method, but a suitable method is as follows.

(1) The average primary particle size is 0.1 to 1.5 μm, the primary particles of 2.0 μm or more are 10% by weight or less, and the oxygen content is 1.5.
A method of press-molding aluminum nitride powder having a weight percentage of not more than 0.3, a cationic impurity of not more than 0.3 wt% and a carbon content of not more than 0.07 wt% by a pressure device at a pressure of, for example, 200 to 4000 kg / cm ² .

In the case of this method, known additives can be added to improve the moldability of the aluminum nitride powder compact, but the oxygen content, the amount of cation impurities and the carbon content in the resulting aluminum nitride powder compact are not limited. The amount of addition must be such that the content is below the specified value. In order to reduce the amount of impurities in the aluminum nitride powder compact, it is preferable to perform compacting only by applying pressure without adding additives.

(2) The average primary particle size is 0.1 to 1.5 μm, the primary particles of 2.0 μm or more are 10% by weight or less, and the oxygen content is 1.5.
A method in which a binder is added to aluminum nitride powder having a weight percentage of less than or equal to 0.3, a cationic content of less than or equal to 0.3 and a carbon content of less than or equal to 0.07% by weight, the obtained mixture is molded, and the binder is heated and removed. .

As the binder that can be used in the above method (2), known compounds used as a binder for ceramic powder can be used without any limitation. For example, 1100 ℃
Organic polymer compounds that decompose at the following temperatures are preferably used. Examples of the binder preferably used in the present invention include, for example, polyvinyl gutylal, polymethyl methacrylate, cellulose acetate butyrate, nitrocellulose, polyacrylic acid ester, polyvinyl alcohol, methyl cellulose, hydroxymethyl cellulose and polyethylene oxide. Oxygen-containing organic polymer compound: Other hydrocarbon type synthetic resins such as petroleum resin, polyethylene, polypropylene and polystyrene are used alone or in combination of two or more. The amount of these admixtures used is generally 100 parts by weight of aluminum nitride powder.
It may be selected from the range of 2.5 to 15 parts by weight, preferably 4 to 10 parts by weight.

A peptizer or a plasticizer may be added to the mixture of the aluminum nitride powder and the binder for the purpose of improving the dispersibility of these. Examples of the deflocculants include glycerin or sorbitol esters of fatty acids such as glycerin trioleate and sorbitan trioleate; natural fish oils; nonionic synthetic surfactants; higher fatty acids; benzenesulfonic acid and the like. Examples of the plasticizer include polyethylene glycol and its derivatives; phthalic acid esters such as dimethyl phthalate, dibutyl phthalate, butylbenzyl phthalate and dioctyl phthalate; stearic acid esters such as butyl stearate;
Tricresol phosphate; tri-N-butyl phosphate; glycerin and the like. The amount of these peptizers and plasticizers is generally 0.01 to 5 parts by weight of peptizer and 0.4 to 15 parts of plasticizer per 100 parts by weight of aluminum nitride powder.
It may be selected from the range of parts by weight.

As the additive to be added to the aluminum nitride powder, compounds that can be decomposed and removed by the heat treatment described later are allowed, but they are not removed by heating and become cation impurities or other impurities. Compounds which remain in the shaped body are not suitable. Therefore, in the present invention, addition of various metal compounds known as sintering aids is not preferable.

The above aluminum nitride powder is mixed with a binder, and if necessary, a deflocculant and a plasticizer are mixed with, for example, ketones such as acetone and methyl ethyl ketone; non-aqueous solvents such as alcohols such as ethanol, propanol and butanol. Wet mixing is preferred.

The mixture of the aluminum nitride powder thus obtained and the binder is molded into a desired shape such as a sheet or a plate by a rubber press or a sheet molding method, for example, a doctor blade type sheet molding machine or a press molding machine. To be done. Then, the binder is decomposed and removed by heating next. For decomposition and removal of the binder by heating, it is preferable to adopt conditions that can also remove carbon generated by decomposition of the binder. When the residual amount of carbon increases and exceeds 1.0% by weight, the aluminum nitride sintered body of the present invention may not be obtained. The heating condition is preferably in the temperature range of 300 to 1100 ° C. under an atmosphere of oxygen or nitrogen, or under vacuum, and the heating time is in order to almost completely remove the carbon generated by the decomposition of the binder. The range of 5 to 24 hours is preferably adopted.

Aluminum nitride powder molded body used by the method of the present invention is preferably produced by the method described above,
In any of the methods, it is necessary to control the oxygen content, the cation impurity content, and the carbon content contained in the aluminum nitride powder molded body obtained to be equal to or less than the above specific values.

 The aluminum nitride powder compact is then subjected to sintering.

Examples of the sintering include a method of firing at a high temperature in a non-oxidizing atmosphere of vacuum or atmospheric pressure, for example, in an atmosphere of nitrogen gas, helium gas, argon gas or the like or under a nitrogen gas pressure of about 2 to 100 atm. Particularly, a method of firing under atmospheric pressure can be preferably adopted. The firing temperature is 1700 to 2100 ° C in the case of a non-oxidizing atmosphere of vacuum or atmospheric pressure, preferably 17
A temperature of 50 to 2050 ° C is preferably adopted, and 1700 to 2400 ° C, preferably 1750 to 2300, under nitrogen gas pressure of 2 to 100 atm.
A temperature of ° C is preferably adopted. The temperature in the present invention is a value obtained by measuring the surface of a graphite crucible containing an aluminum nitride powder compact with a radiation thermometer and compensating for the gas temperature in the graphite crucible.

In the present invention, in order to increase the Weibull coefficient of the obtained aluminum nitride sintered body and make it dense,
At the time of firing, it is preferable that the average heating rate in the temperature range of at least 1300 to 1700 ° C. be in the range of 1 ° C./min to 40 ° C./min. It is more preferable to raise the temperature in the range of 5 to 30 ° C / min.

By the above manufacturing method, the aluminum nitride sintered body of the present invention described above is obtained.

(Effect) As described above, the aluminum nitride sintered body of the present invention has a high Weibull coefficient as described above, has a very small variation in mechanical strength, and is a defective product due to insufficient mechanical strength. The occurrence probability of is extremely small. For example, comparing the Weibull coefficient 17 of the aluminum nitride sintered body of the present invention with the Weibull coefficient 13 of the already known aluminum nitride sintered body, the defective product occurrence probability is compared, and the three-point bending strength is 90% of the average strength of the population. The probability of breaking with% stress is about 8 in the former case.
%, But about 16% for the latter. Therefore, it can be said that the aluminum nitride sintered body of the present invention is a highly reliable ceramic material. Of course, the three-point bending strength is equal to or higher than that of a known aluminum nitride sintered body,
It shows a good value of 30 kg / mm ² or more.

Furthermore, the aluminum nitride sintered body of the present invention has a small surface roughness after sintering. Therefore, it is possible to shorten the time for polishing the surface after sintering as in the conventional aluminum nitride sintered body, and it is also possible to omit the surface polishing itself.

Further, the aluminum nitride sintered body of the present invention is an epoch-making material having a wide light transmission range in the visible light to infrared light region as described above. Therefore, the aluminum nitride sintered body of the present invention is expected as a new nitride material such as a high temperature window material, an optical filter, a frequency conversion element, and a heat dissipation substrate of an integrated circuit, and its industrial value is extremely large.

(Examples) Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

In the examples, the Weibull coefficient of the aluminum nitride sintered body and the average primary particle diameter of the aluminum nitride powder are values obtained by the following method.

(1) Weibull coefficient When the statistical display of the strength of the ceramic material is shown by the Weibull statistical display based on the weakest link theory, the Weibull fracture probability distribution function is given by the following formula.

F _i: in fracture probability (cumulative probability) sequence number of the strength (test piece, the one most sigma _R small i
= 1, the number sequentially added in ascending order) is i, and the number of test pieces (number of samples) is N Calculated from

m: Weibull coefficient σ _R : Maximum stress (strength of test piece) μ: Average strength Is plotted on the vertical axis and l _n σ _R is plotted on the horizontal axis, and the Weibull coefficient is obtained from the slope of the straight line.

Incidentally, in the present invention, for 50 test pieces, JIS
The three-point bending strength was measured according to R-1601 and the Weibull coefficient was determined from these data.

(2) Average primary particle size An arbitrary 20-screen photograph of AlN powder was taken with a scanning electron microscope at a magnification of 20,000. Parallel lines were drawn on the obtained photograph at intervals of 0.5 μm. Of the particles on the parallel lines, only those with a perfect outline were selected as target particles, and more than 500 target particles were picked up from 20 screens. The particle size of each particle is
Two lines which are perpendicular to the parallel lines applied to the respective particles and which are tangential lines to the particles were drawn, and the distance was calculated from the distance (l) between the intersections of these lines and the above parallel lines. In addition, when two or more lines were applied to one particle, only the maximum value of the distance (l) between the intersections was counted. When the total particle size was considerably large, parallel lines with a 2μ interval were drawn on a photograph at 5000 times and the same treatment was performed with a larger size, and parallel lines with a 5μ interval were drawn at 2000 times.

Based on the obtained data of 500 or more, the weight-based average primary particle size and primary particle size distribution were calculated by a usual method.

Example 1 7.3 parts by weight of polyvinyl butyral as a binder with respect to 100 parts by weight of the aluminum nitride powder shown in Table 1,
1.6 parts by weight of glycerin trioleate as a deflocculant and 12.2 parts by weight of dibutyl phthalate as a plasticizer were mixed in 61 parts by weight of a toluene-ethanol mixed solvent to prepare a slurry. This slurry was formed into a sheet using a doctor blade type sheet forming machine, sufficiently dried, and then a 65 mm square test piece was punched out. This test piece was heated in a small muffle furnace at 600 ° C. for 8 hours. The obtained aluminum nitride powder compact had a thickness of 1.19 mm and a compacting density of 1.
It was 80 g / cm ³ , and the chemical composition was as shown in Table 1.

The obtained aluminum nitride powder molded body was placed in a graphite crucible coated with boron nitride, in an electric furnace,
Sintered under normal pressure in a nitrogen gas atmosphere. Sintering from room temperature to 18
The temperature was raised up to 50 ° C. at a heating rate of 10 ° C./min and maintained at 1850 ° C. for 7 hours. The flow rate of nitrogen gas is 1
/ Min. The obtained aluminum nitride sintered body was light gray and had translucency. Its physical properties are second
It was as shown in the table.

Example 2 Various aluminum nitride powders were used to prepare aluminum nitride powder compacts in the same manner as in Example 1, and after heat treatment, sintering was performed. The physical properties of the obtained aluminum nitride sintered body are
Shown in the table.

For comparison, No. 5 shows an example in which the aluminum nitride powder described in JP-A-59-50078 was used and the same procedure as above was performed. In addition, No. 6 shows an example using an aluminum nitride powder having more coarse particles.

Example 3 An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that the addition amount of the binder and the heat treatment conditions were changed as shown in Table 4. The results are shown in Table 4.

Example 4 Approximately 1.5 g of the aluminum nitride powder of Example 1 was put into a 20 mmφ die and preformed at 200 kg / cm ² , and then 3000 kg /
Cold isostatic pressing was performed at a pressure of cm ² . The density of the obtained molded body was 1.82 g / cm ³ . This molded body was used in Example 1.
Pressureless sintering was performed in the same manner as in. The obtained sintered body was a light gray translucent body. The physical properties of this sintered body are shown in Table 5.

Comparative Example An aluminum nitride sintered body was obtained in the same manner as in Example 1 except that 3% by weight of CaO powder as a sintering aid was added to and mixed with the aluminum nitride powder used in Example 1. The results are shown in Table 6.

Claims (2)

[Claims] 1. An oxygen content of 0.5% by weight or less, and when the aluminum nitride composition is AlN, the cation impurities contained are
0.3% by weight or less, carbon content 0.07% by weight or less, density
^{3. An} aluminum nitride sintered body characterized by having a Weibull coefficient of 17 or more and 3.20 g / cm ³ or more. 2. An average primary particle diameter of 0.1 to 1.5 μm, 2.0 μ
Mainly composed of aluminum nitride powder with primary particles of m or more of 10% by weight or less, oxygen content of 1.5% by weight or less, cationic impurities contained when the aluminum nitride composition is AlN is 0.3% by weight or less, carbon content The method for producing an aluminum nitride sintered body according to claim 1, wherein an aluminum nitride powder compact having an amount of 0.07% by weight or less is sintered.