Thermodynamics of AlN deposition by means of the aluminium-trichloride-ammonia process

Equilibrium yields for CVD of AlN dependent on the input ratio AlCl₃/NH₃ and on temperature were computed (A) for AlCl₃ + NH₃ ⇋ AlN + 3 HCl; (B) for additional complexing AlCl₃ + NH₃ ⇋ AlCl₃ · NH₃ at substrate temperature which did not result in changes of yield above 900°C; (C) for AlCl₃ · NH₃ ⇋ AlN + 3 HCl corresponding to complete inhibition of dissociation near the substrate of the complex formed or preformed at lower temperature which resulted in considerably lower yields. A corresponding decrease of experimental results occurred within reactors having a long AlCl₃–NH₃-mixing zone at 350°C or AlCl₃ · NH₃-input with respect to a reactor with a short mixing zone near to the substrate. The dissociation of the complex present in the former two cases was inhibited considerably. – This investigations demonstrate the additional influence of homogeneous reactions, which has to be regarded for CVD especially with complexing reactants in connection with the role of reactor geometry, a problem being increasingly discussed at present.