ENHANCED DIFFUSION OF C IN FE UNDER CVD DIAMOND DEPOSITION CONDITIONS

It has been reported, by other authors [1-3], that under DC plasma con ditions the diffusion of C into Fe is much greater than that obtained under thermal equilibrium conditions. They postulated that the excepti onally high C uptake is due to rapid infusion (mass transfer) of C int o the surface from the plasma, and not to an anomalously high diffusio n rate in the bulk. The aim of the current investigation was to determ ine whether the rapid infusion of C and classical C diffusion rates ob tained from high CH4 concentration plasmas are also observed in the lo wer C content (1% CH4) plasma employed in CVD diamond deposition. A se ries of experiments were conducted for short deposition times (up to 5 min) under plasma-CVD diamond deposition conditions at a substrate te mperature of 950 degrees C. The C profile was analysed using Auger ele ctron spectroscopy (AES) and Rutherford backscattering spectroscopy (R ES). The diffusion coefficient (D-o) calculated from thermodynamic dat a for 950 +/- 20 degrees is (3.0 +/- 0.6) x 10(-11) m(2) s(-1), wherea s that estimated from the AES depth profile using a constant surface c oncentration solution to Fick's second law was found to be 4.2 +/- 1.3 x 10(-10) m(2) s(-1). Hence, even though the carbon content in the pl asma is very low the diffusion occurring under plasma conditions at a sample temperature of 950 +/- 20 degrees C is equivalent to that expec ted from thermal diffusion at 1244 +/- 42 degrees C. Possible mechanis ms for this enhancement are discussed.