REACTION OF TA THIN-FILM WITH SINGLE-CRYSTALLINE (001) BETA-SIC

The reaction between a sputter-deposited Ta film (320 nm thick) and a single crystalline (001) beta-SiC substrate induced by vacuum annealing at temperatures of 600-1200-degrees-C for 1 h (30 min at 1100-degrees-C) is investigated by 3 MeV He++ backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, and transmission and scanning electron microscopies. No significant reaction is observed at 800-degrees-C or at lower temperatures. At 900-degrees-C, the main product phases are Ta2C and carbon-stabilized Ta5Si3. A minor amount of unreacted Ta is also present. After annealing at 1000-degrees-C, all the tantalum has reacted; the reaction zone possesses a multilayered structure of beta-SiC/TaC/carbon-stabilized Ta5Si3/alpha-Ta5Si3/Ta2C. The diffusion path at 1000-degrees-C is plotted on the isothermal section of the Ta-Si-C phase diagram. At 1100-degrees-C, the reacted layer has an interface with the SiC substrate that is still quite flat but has a rough surface due to the formation of macroscopic voids within the reacted layer. The equilibrium products predicted by the phase diagram are TaC and TaSi2. This final state is reached by annealing at 1200-degrees-C for 1 h. At that point, the reacted layer has a laterally very uneven structure and morphology.