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

Equilibrium yields for CVD of AlN dependent on the input ratio AlCl 3 /NH 3 and on temperature were computed (A) for AlCl 3 + NH 3 ⇋ AlN + 3 HCl; (B) for additional complexing AlCl 3 + NH 3 ⇋ AlCl 3 · NH 3 at substrate temperature which did not result in changes of yield above 900°C; (C) for AlCl 3 · NH 3 ⇋ 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 AlCl 3 –NH 3 ‐mixing zone at 350°C or AlCl 3 · NH 3 ‐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.