WO1991000842A1 - Manufacture of aluminium nitride - Google Patents

Manufacture of aluminium nitride Download PDF

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Publication number
WO1991000842A1
WO1991000842A1 PCT/GB1990/001038 GB9001038W WO9100842A1 WO 1991000842 A1 WO1991000842 A1 WO 1991000842A1 GB 9001038 W GB9001038 W GB 9001038W WO 9100842 A1 WO9100842 A1 WO 9100842A1
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WO
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Prior art keywords
aluminium
reaction
temperature
nitrogen
mixture
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Application number
PCT/GB1990/001038
Other languages
French (fr)
Inventor
James Anthony Charles
Young Wan Cho
Original Assignee
The Carborundum Company
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Filing date
Publication date
Application filed by The Carborundum Company filed Critical The Carborundum Company
Publication of WO1991000842A1 publication Critical patent/WO1991000842A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/072—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with aluminium
    • C01B21/0726—Preparation by carboreductive nitridation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values

Definitions

  • This invention relates to improvements in aluminium nitride
  • Carbothermic reduction and nitridation of aluminium oxide can also be used to produce a relatively fine powder of aluminium nitride but a high reaction temperature of 1580°C or more is required depending upon the reaction time and the final oxygen content being sought.
  • Another known process for the manufacture of aluminium nitride is to react halides of aluminium (e.g. A1C1-,) and anrmonia to produce a relatively pure and fine aluminium nitride powder.
  • This process has the disadvantages of high materials costs and low productivity as well as presenting prob1ems of corrosion.
  • a method of manufacturing aluminium nitride which comprises the steDs of producing a substantially homogeneous mixture of carbon and aluminium trihydroxide (Al .CH)-,) or its dehydration product, garrma aluminium oxide and reacting the mixture with nitrogen by heating to a temperature of not less than 120CTC.
  • the temperature be not more than 160O°C and preferably in the range of 1450°C to 1550°C.
  • the reaction time is related both to the temperature and to the particle size but, in general, should not be less than 30 minutes and preferably not more than 6 hours.
  • the mixture be heated rapidly to the reaction temperature selected in the presence of nitrogen and that it should be heated from ambient temperature to the reaction temperature in not more than 5 minutes .
  • the nitrogen gas is advantageously " supplied to the reaction at a rate of 100 to 2000 ml/min, preferably 500 to lOOO ml /mi n.
  • the mixture could be a bed fluidised by the nitrogen flow in a continuous production process.
  • the particle size of the start ing mater i al i.e. aluminium trihydroxide is preferably in the range of 0.5 to 1.5 ⁇ , preferably less than 1 p and desirably between 0.6 to 0.8 p .
  • the particle size of the aluminium nitride product is substantially the same as that of the start ing mater ia1 and, if the particle size is too low, there is an increase in oxygen impurities and handling problems. In fact an average particle size of 0.7 ⁇ has given optimum results.
  • the mixture In order to ensure intimate mixing of the aluminium trihydroxide and carbon it is preferred to produce the mixture as a porous compact using an organic solvent.
  • the porosity allows the nitrogen to access the components of the mixture and participate in the reaction to produce aluminium nitride.
  • Carbon black is preferably used to provide the carbon component and some carbon blacks are to be preferred to others, namely carbon blacks having a high specific, surface area, a fine particle size and a good porosity. These qualities enhance the lower reaction times and/or lower reaction temperatures which can be achieved by the present invention.
  • a carbon black having a specific surface area For example, a carbon black having a specific surface area
  • a known amount of the pellets was subsequently heated in a graphite container in a vertical tube furnace under flowing nitrogen supplied at a rate of 1000 ml/min.
  • a reaction temperature of 1500°C was employed and the pellets were brought to this temperature from room temperature in under 5 minutes. The reaction time was found to be 30 minutes.
  • the product shape was the same as that of the starting material but fragile in the sense that it broke up into powder when shaken, the product particle size being of the order of 0.7 ⁇ . It will be appreciated that the lower temperatures made possible by the present invention and the related lesser reaction times reduces the risk of the particles sintering during the reaction and also the risk of grain growth.
  • the aluminium nitride product of the present invention is very suitable for use as electronic substrate material. It can be used as a sintered body to carry integrated circuits and it has other uses including in high temperature electrical insulators as its electrical resistance remains high at elevated temperatures.
  • a known amount of pellets was heated in a graphite container in a vertical tube furnace under flowing nitrogen.
  • the molar ratio of Al(OH), to C was between 1:1.5 and 1:9.
  • the reaction temperature was between 1200 and 1500 C and was achieved in less than 5 minutes.
  • the reaction time was between 0.5 to 6 hours and the nitrogen flow was between 100 and 2000 ml/min. After the reaction was completed, residual carbon was burnt out in air at 700°C for 4 hours.
  • a level of 0.1% wt. carbon is readily obtainable using a material known as Conductex 975.
  • Decarbur i sat ion depends upon the form of the carbon, the decarbur i sat ion temperature and the time.
  • the minimum nitrogen requirement is determined by the mass being treated but varies as the reaction proceeds with the evolution of CO. There will be a minimum theoretical nitrogen flow rate for the process but the reaction rate
  • SUBSTITUTESHEET wi 1 I increase substantially hyperbol i cal ly with less to be gained as the flow rate is increased.
  • Nitrogen flow rate 1000 ml /mi ns .
  • Decarburization temperature 700°C.
  • Average particle size less than 1 jum Crystalline phase: single phase A1N Colour: white.
  • the present invention enables a lower oxygen content in the product to be achieved in a process using aluminium trihydroxide or its dehydration- product, garrma aluminium oxide compared with equivalent processes using alpha aluminium oxide at a lower reaction temperature and/or time.
  • An oxygen content of approximately 1.7 wt . % can be achieved at a reaction temperature of 1500 C for a period of 60 mins.
  • the oxygen content in the finat product can be any reaction temperature and times.
  • the invention more specifically, provides a method of manufacturing aluminium nitride with an oxygen content of 1.0 w . % or less which comprises the steps of producing a subs antially homogeneous mixture of carbon and aluminium

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Ceramic Products (AREA)

Abstract

A process is disclosed for manufacturing aluminium nitride in which a substantially homogeneous mixture of carbon and aluminium trihydroxide (Al(OH))3) or its dehydration product, gamma aluminium oxide is reacted with nitrogen by heating to a temperature of not less than 1200 °C and preferably not more than 1600 °C. The mixture is heated rapidly from ambient temperature to the reaction temperature in the presence of nitrogen in not more than five minutes. The mixture could be a bed fluidised by the nitrogen flow in a continuous production process.

Description

MANUFACTURE OF ALLMINILM NITRIDE
This invention relates to improvements in aluminium nitride
Several processes are known for the manufacture of aluminium nitride in powder form. Direct nitridation of aluminium with nitrogen is believed to be the most coπrmon method. The product powders are, however, generally too coarse to use as a starting powder for s inter ing wi thout corrmi nut i on. High milling costs and a relatively high level of impurities in the final products are the main disadvantages of this method.
Carbothermic reduction and nitridation of aluminium oxide can also be used to produce a relatively fine
Figure imgf000003_0001
powder of aluminium nitride but a high reaction temperature of 1580°C or more is required depending upon the reaction time and the final oxygen content being sought.
Another known process for the manufacture of aluminium nitride is to react halides of aluminium (e.g. A1C1-,) and anrmonia to produce a relatively pure and fine aluminium nitride powder. This process has the disadvantages of high materials costs and low productivity as well as presenting prob1ems of corrosion.
It is an object of the present invention to provide an improved process for the manufacture of aluminium nitride in which the disadvantages referred to above shall be materially reduced if not substantially obviated.
According to the present invention there is provided a method of manufacturing aluminium nitride which comprises the steDs of producing a substantially homogeneous mixture of carbon and aluminium trihydroxide (Al .CH)-,) or its dehydration product, garrma aluminium oxide and reacting the mixture with nitrogen by heating to a temperature of not less than 120CTC.
SUBSTITUTESHEET It is preferred that the temperature be not more than 160O°C and preferably in the range of 1450°C to 1550°C.
The reaction time is related both to the temperature and to the particle size but, in general, should not be less than 30 minutes and preferably not more than 6 hours.
It is highly desirable that the mixture be heated rapidly to the reaction temperature selected in the presence of nitrogen and that it should be heated from ambient temperature to the reaction temperature in not more than 5 minutes .
The nitrogen gas is advantageously " supplied to the reaction at a rate of 100 to 2000 ml/min, preferably 500 to lOOO ml /mi n.
Conceivably, the mixture could be a bed fluidised by the nitrogen flow in a continuous production process.
The particle size of the start ing mater i al , i.e. aluminium trihydroxide is preferably in the range of 0.5 to 1.5 μ , preferably less than 1 p and desirably between 0.6 to 0.8 p . The particle size of the aluminium nitride product is substantially the same as that of the start ing mater ia1 and, if the particle size is too low, there is an increase in oxygen impurities and handling problems. In fact an average particle size of 0.7 μ has given optimum results.
In order to ensure intimate mixing of the aluminium trihydroxide and carbon it is preferred to produce the mixture as a porous compact using an organic solvent. The porosity allows the nitrogen to access the components of the mixture and participate in the reaction to produce aluminium nitride. Carbon black is preferably used to provide the carbon component and some carbon blacks are to be preferred to others, namely carbon blacks having a high specific, surface area, a fine particle size and a good porosity. These qualities enhance the lower reaction times and/or lower reaction temperatures which can be achieved by the present invention.
For example, a carbon black having a specific surface area
2 of 250 m /g, a particle size in a narrow range about 20 x
9 lO m and a porosity defined by an oil absorption value of DBP 165 ml/100 g was homogeneously mixed with aluminium trihydroxide having a particle size in a narrow range about 0.7 μ in a molar ratio of ALCOH /C of 1:3. The mixture was stirred with the addition of a non-polar solvent (absolute alcohol) to give a slurry which was dried while stirring to give a thick paste which was extruded into cylindrical pellets of about 2 rrm diameter and 5 to 10 rrm in length. The pellets were then dried in an oven overnight at 125 C. A known amount of the pellets was subsequently heated in a graphite container in a vertical tube furnace under flowing nitrogen supplied at a rate of 1000 ml/min. A reaction temperature of 1500°C was employed and the pellets were brought to this temperature from room temperature in under 5 minutes. The reaction time was found to be 30 minutes.
The product shape was the same as that of the starting material but fragile in the sense that it broke up into powder when shaken, the product particle size being of the order of 0.7 μ. It will be appreciated that the lower temperatures made possible by the present invention and the related lesser reaction times reduces the risk of the particles sintering during the reaction and also the risk of grain growth.
It will be appreciated that the aluminium nitride product of the present invention is very suitable for use as electronic substrate material. It can be used as a sintered body to carry integrated circuits and it has other uses including in high temperature electrical insulators as its electrical resistance remains high at elevated temperatures.
A number of tests were carried out using aluminium trihydroxide of a particle size in the range of 0.5 to 1 μ homogeneously mixed with carbon black in a non-polar solvent (absolute alcohol) by ball milling for 2 hours. The slurry was dried while stirring to give a thick paste and then extruded to obtain cylindrical pellets of about 2 rrm diameter- and 5 to 10 rrm length. The pellets were dried at 125°C.
A known amount of pellets was heated in a graphite container in a vertical tube furnace under flowing nitrogen. The molar ratio of Al(OH), to C was between 1:1.5 and 1:9. The reaction temperature was between 1200 and 1500 C and was achieved in less than 5 minutes. The reaction time was between 0.5 to 6 hours and the nitrogen flow was between 100 and 2000 ml/min. After the reaction was completed, residual carbon was burnt out in air at 700°C for 4 hours.
» In one such test in which the pellets were heated to a temperature of 1500°C for a period of 120 minutes with a linear nitrτjgen flow rate of 2 metres/min, the product contained 1.7% oxygen and 0.1% carbon.
A level of 0.1% wt. carbon is readily obtainable using a material known as Conductex 975. Decarbur i sat ion depends upon the form of the carbon, the decarbur i sat ion temperature and the time.
The minimum nitrogen requirement is determined by the mass being treated but varies as the reaction proceeds with the evolution of CO. There will be a minimum theoretical nitrogen flow rate for the process but the reaction rate
SUBSTITUTESHEET wi 1 I increase substantially hyperbol i cal ly with less to be gained as the flow rate is increased.
The tests carried out all produced good quality single phase aluminium nitride.
However optimum conditions were found to be : -
Reaction temperature: 150O0C Reaction time: 120 minutes
A1(CH)3/C molar ratio: 1:3
Nitrogen flow rate: 1000 ml /mi ns . Decarburization temperature: 700°C.
The best reaction product powder had the following character i st ics :
Average particle size: less than 1 jum Crystalline phase: single phase A1N Colour: white.
Without wishing to be bound by any theory it is believed that the relatively high temperatures required for the carbothermic reduction and nitridation of aluminium oxide result from the fact that such oxide is generally in the form of stable crystalline .^ alumina. When heated, aluminium trihydroxide dehydrates to the oxide and water and this starts at about 250 to 3θO°C. However, the trihydroxide initially becomes lj alumina and two or three other metastable phases of alumina and these phases react more readily with the carbon and nitrogen to initiate the desired reaction. Consequently, by starting with the trihydroxide and bringing the mixture rapidly to the reaction temperature lower reaction temperatures are possible as are lesser reaction times. As will be understood, the higher the reaction temperature employed, the lesser the reaction time required.
SUBSTITUTESHEET There are many applications where it is required that the product should have a low oxygen content. The present invention enables a lower oxygen content in the product to be achieved in a process using aluminium trihydroxide or its dehydration- product, garrma aluminium oxide compared with equivalent processes using alpha aluminium oxide at a lower reaction temperature and/or time. An oxygen content of approximately 1.7 wt . % can be achieved at a reaction temperature of 1500 C for a period of 60 mins. The oxygen
10 content can, however, be materially reduced using a reaction temperature of 1550UC and a time of 120 mins
Thus by selecting appropriate reaction temperatures and times, the oxygen content in the finat product can be
-- reduced to about 1.0 wt . % or less. The invention, more specifically, provides a method of manufacturing aluminium nitride with an oxygen content of 1.0 w . % or less which comprises the steps of producing a subs antially homogeneous mixture of carbon and aluminium
-- trihydroxide (Al(GH)-,) and reacting the mixture with ni rogen by heating the mixture to a reaction temperature in the range of 1450 C to 1550 C inclusive in a period of not more than 5 mins. and maintaining the reaction temperature for a period of ime of not less than 3θ mins.
-- and not more than 6 hours until the reaction is substantially complete and the oxygen content of the product is not more than 1.0 wt . %.
30
35
SUBSTITUTESHEET

Claims

Cl a ims :
1. A method of manufacturing aluminium nitride which comprises the steps of producing a substantially 5 homogeneous mixture of carbon and aluminium trihydroxide (Al(GH),) or its dehydration product gamma aluminium oxide and reacting the mixture with nitrogen by heating to a temperature of not less than 12CO C.
-- 2. A method according to claim 1 in which the temperature is not more than 16CO°C.
3. A method according to claim 1 or 2 in which the temperature is in the range of 1450 to 1550°C.
15
4. A method according to claim 1, 2 or 3 in which the reaction time is not less than 30 minutes.
5. A method according to any one of the preceding claims
20 in which the reaction time is not more than 6 hours.
6. A method according to any one of the preceding claims in which the mixture is heated from ambient tempera ure to the reaction temperature in the presence of nitrogen in
-- not more than 5 minutes.
7. A method according to any one of the preceding claims in which the nitrogen gas is supplied to the reaction at a rate of 100 to 2000 ml/min.
30
8. A method according to any one of the preceding claims in which the nitrogen gas is supplied to the reaction at a rate of 500 to 1000 ml/min.
■^5 9. A method according to any one of the preceding claims in which the parti.cle size of the aluminium trihydroxide
'IB is in the range of D.5 to 1.5 u.
10. A method according to claim 9 in which the particle size of the aluminium trihydroxide is less than 1 u.
11. A method according to claim 10 in which the particle 5 size of the aluminium trihydroxide is in the range of 0.6 to 0.8 u.
12. A method according to any one of the preceding claims in which the carbon in the form of carbon black and the ° aluminium trihydroxide are mixed in the presence of a non- polar solvent to form a slurry which is dried to a thick paste while stirring and the thick paste is extruded to obtain pellets which are then completely dried.
5 13. A method according to claim 12 in which the pellets are cylindrical with a diameter of about 2 rrm and a length of 5 to 10 rrm and are heated to the reaction temperature in a graphite container in a vertical tube furnace under f lowing n i trαgeπ . 0
14. A method according to any one of the preceding claims in which the mixture is arranged as a bed of particles and the nitrogen is flowed through the bed to fluidise the bed . 5
15. A method of manufacturing aluminium nitride substantiall as herein described.
0
5
PCT/GB1990/001038 1989-07-06 1990-07-05 Manufacture of aluminium nitride WO1991000842A1 (en)

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GB8915465.2 1989-07-06
GB8915465A GB2233969A (en) 1989-07-06 1989-07-06 Improvements in or relating to the manufacture of aluminium nitride.

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4020905A1 (en) * 1990-06-30 1992-03-05 Hoechst Ag METHOD FOR PRODUCING ALUMINUM NITRIDE
AU755863B2 (en) * 1998-04-22 2003-01-02 Gesellschaft Fur Biotechnologische Forschung Mbh Immobilized substrate, separation gels produced therewith and method for detecting enzymatic activity after electrophoretic protein separation

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5891919A (en) * 1981-11-28 1983-06-01 Toyota Motor Corp Connecting rod for internal-combustion engine and its manufacture
JPS6060910A (en) * 1983-09-14 1985-04-08 Tokuyama Soda Co Ltd Manufacture of aluminum nitride
EP0186144A2 (en) * 1984-12-24 1986-07-02 Kabushiki Kaisha Toshiba Process for preparing aluminum nitride powder
JPS6278103A (en) * 1985-09-30 1987-04-10 Toshiba Corp Production of aluminum nitride powder
FR2594109A1 (en) * 1986-02-10 1987-08-14 Int Stamaco System Process for the nitriding of pulverulent oxides by ammonia and furnace making possible the implementation of this process
EP0247907A2 (en) * 1986-04-03 1987-12-02 Elf Atochem S.A. Metal carbide and nitride powders for ceramics obtained by carbothermal reduction, and process for their manufacture
EP0266927A1 (en) * 1986-10-15 1988-05-11 The Carborundum Company Process for the continuous production of high purity, ultrafine, aluminium nitride powder by the carbo-nitridisation of alumina

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0176737B1 (en) * 1984-09-28 1989-08-09 Kabushiki Kaisha Toshiba Process for production of readily sinterable aluminum nitride powder

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5891919A (en) * 1981-11-28 1983-06-01 Toyota Motor Corp Connecting rod for internal-combustion engine and its manufacture
JPS6060910A (en) * 1983-09-14 1985-04-08 Tokuyama Soda Co Ltd Manufacture of aluminum nitride
EP0186144A2 (en) * 1984-12-24 1986-07-02 Kabushiki Kaisha Toshiba Process for preparing aluminum nitride powder
JPS6278103A (en) * 1985-09-30 1987-04-10 Toshiba Corp Production of aluminum nitride powder
FR2594109A1 (en) * 1986-02-10 1987-08-14 Int Stamaco System Process for the nitriding of pulverulent oxides by ammonia and furnace making possible the implementation of this process
EP0247907A2 (en) * 1986-04-03 1987-12-02 Elf Atochem S.A. Metal carbide and nitride powders for ceramics obtained by carbothermal reduction, and process for their manufacture
EP0266927A1 (en) * 1986-10-15 1988-05-11 The Carborundum Company Process for the continuous production of high purity, ultrafine, aluminium nitride powder by the carbo-nitridisation of alumina

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, vol. 103, no. 16, October 1985 Columbus, Ohio, USA Tokuyama Soda Co.: "Aluminum nitride." page 143; ref. no. 125898 A see abstract & JP-A-60060910 (TOKUYAMA SODA CO.), 8 April 1985 *
CHEMICAL ABSTRACTS, vol. 107, no. 2, July 1987 Columbus, Ohio, USA H. Innoue et al.: "High-purity aluminum nitride powder." page 162; ref. no. 9967 F see abstract & JP-A-62078103 (TOSHIBA CORP), 10 April 1987 *
CHEMICAL ABSTRACTS, vol. 99, no. 14, 3 October 1983 Columbus, Ohio, USA Toshiba Corp.: "Aluminum nitride powder." page 123; ref. no. 107504 P see abstract & JP-A-58091919 (TOSHIBA CORP), 30 May 1983 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4020905A1 (en) * 1990-06-30 1992-03-05 Hoechst Ag METHOD FOR PRODUCING ALUMINUM NITRIDE
AU755863B2 (en) * 1998-04-22 2003-01-02 Gesellschaft Fur Biotechnologische Forschung Mbh Immobilized substrate, separation gels produced therewith and method for detecting enzymatic activity after electrophoretic protein separation

Also Published As

Publication number Publication date
AU5938090A (en) 1991-02-06
GB2233969A (en) 1991-01-23
IE902433A1 (en) 1991-06-19
GB8915465D0 (en) 1989-08-23

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