CONTROL OF CRYSTALLOGRAPHIC ORIENTATION OF A1N FILMS IN APCVD

Crystallographic orientation of ceramic films prepared by CVD methods causes significant deterioration of mechanical properties. This work was attempted to discover the factors that control the orientation in an atmospheric-pressure hot-wall CVD, in forming AlN from AlCl3 with excess NH3. The experiments were carried out in a wide range of operating conditions: temperature 700 to 950-degrees-C. AlCl3 concentration 0.2 to 1.3 vol%, and gaseous flow rate 3 to 100 m.s-1. At 850-degrees-C. various film structures ranging from non-oriented polycrystalline with 100 nm size grains to completely oriented structure were prepared as functions of the above deposition conditions and longitudinal position in a reactor- However, the degree of orientation measured by XRD was a function solely of the film growth rate. The tendency to orientation becomes significant at lower growth rates, and non-orientated fine grain films were obtained at higher growth rates. Experiments made at reaction temperatures 700-degrees-C to 950-degrees-C show that the critical growth rate, GR(CRT), which separates the orientation region from the non-orientation region is expressed as follows GR(CRT) = 400.exp (- E/RT) [m.hr-1], were E = 136 kJ.mol-1. Control of orientation is possible by combining this equation with knowledge of the growth rate.