Synthesis and Processing of Aluminum Nitride

Powders Aluminum nitride is customarily synthesized by the carbothermal reduction of a mixture of aluminum oxide and carbon black, under a nitrogen pressure of 0.2-0.3MPa at 1800-1900 °G, and with a variable isothermal soaking time. The best results are obtained at 1800 °G and with a nitrogen pressure of 0.3 MPa, from a charge of stoichiometric composition. The resultant powders, with an AIN content up to 99 mass%, consist of isometric grains with a narrow size range of between 2 and 6(xm (Makarenko and Mahajan, 2002). 

Aluminum nitride powder has been synthesized by combustion and thermal explosion modes of the self-propagating high-temperature synthesis (SHS). The addition of small amounts of ammonium chloride appears to activate the reaction (Rosenband and Gany, 2004). 

Alternatively, aluminum nitride can be obtained by the direct nitridation of aluminum powder compacts between 500 and 700 °C, under a nitrogen atmosphere, between 0.5 and 7MPa pressure. Complete nitridation was achieved at a temperature as low as 540 °C by controlling the nitrogen pressure. The nitridation process and the structures of the aluminum nitride obtained were drastically influenced by the nitrogen pressure (Okada et al., 2000). As it is extremely difficult to obtain AIN without some unreacted metallic aluminum in the core of the particles, milling and acid washing is required to remove the metallic contaminant (Baik and Drew, 1996). 

The ammonolysis of AlCfl results in a crystalline AIN which remains contaminated with chlorine that, even under thermal treatment at 900 °C in an ammonia atmosphere, cannot be completely removed (Patzold, 2001). 

Chemical Vapor Deposition In this process, semiconductor wafers are heated to between 300 °C and about 550 °C in a diffusion furnace. Ammonia and/or hydrazine are introduced into the chamber, followed by the introduction of an aluminum carrier such as triethylaluminum. With time, a layer of AIN is simultaneously formed at the surface of each wafer. A subsequent annealing of the AIN layer can be carried out in situ, thus improving its crystallinity (Kraus et al., 2002). 

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