Thin Film Production Under Elevated Gravity Conditions

The effect of elevated gravity has been reported for crystallization of various semiconductor materials and alloys. The results have shown many unique properties never attained under normal gravity or microgravity conditions. Although no attempt has, so far, been made to produce thin films under elevated gravity, it is expected that a higher gravity condition would yield a higher nucleation site density, which should increase the deposition rate. The grain size and therefore crystal morphology should also be under the strong influence of gravity so that the thermal, physical, electrical and mechanical properties of the thin films produced under elevated gravity condition may show unexpected characteristics suitable for practical applications.From this standpoint, we plan to produce thin films at moderate pressures under elevated gravity conditions at the Electrotechnical Laboratory. A centrifuge facility for chemical vapour deposition (CVD) up to 100 g was designed and constructed. For the first step of a demonstrative study with the facility, we plan diamond thin film production by DC-plasma CVD.The present paper is divided into two parts. The first part briefly reviews the main features of DC-plasma CVD processes and examines the potential advantages in using DC-plasma CVD in conjunction with high gravity. The second part introduces the mathematical model that describes the macroscopic heat and mass transport phenomena with chemical reactions occurring in a DC-plasma CVD (HGCVD) reactor under high gravity. Numerical evaluations were accomplished aimed at investigating the fluid dynamic performances of several reactor configurations under normal gravity and high gravity conditions, with and without the influence of the plasma source. Selected results are presented that show the criteria for optimal hardware configurations of DC-plasma CVD reactor chambers under high gravity.