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The main objective of this study is to characterize the prominent features of a thermal plasma CVD, and to investigate the principal deposition mechanism in this method. The materials chosen in this study were SiC, Si3N4 and BN. The deposition rate achieved was from 5 to 27μm/min. The relationships between the structures of the coatings and the dwell time of reactants (td) were investigated under reactant partial pressure of about 1 Torr, substrate temperature of 850° to 1300°C, and td of 50 to 400μs. In SiC, columnar, flat dense, or powder-like coatings were deposited at td of 80 to 200, 200 to 400, or over 200μs, respectively. In Si3N4, on the other hand, flat dense and powder-like or whisker-like porous films were deposited at td longer or smaller than 200μs, respectively. These results suggest that in this process the clusters produced in the flame may play an important role in the formation of dense films. One of the essentials to obtain dense films at a high deposition rate is to regulate td as well as deposition temperature.