Thermal decomposition kinetics of amorphous carbon nitride and carbon films

Abstract

Kinetic thermal degradation of amorphous carbon and carbon nitride films is studied. Significantly improved thermal stability was observed for films intensified with C-N, C=N, and C≡N bonds. When the N2% (percentage of nitrogen) in Ar/N2 during film deposition was varied from 0 to 30 at pressures of 3 × 10-3 and 16 × 10-3 Torr, the onset decomposition temperatures increased from 396 to 538 and from 340 to 360 °C, while the apparent activation energy ΔE at 60% residual weight increased from 149 to 158 and from 96 to 120 kJ mol-1, respectively. A change in the thermal stability was observed when the N2% reached 50. The films of higher bonding ratio and structural integration showed a single-step decomposition mechanism. They had ΔE values decreasing with the decomposition process, following convex-trend isothermal weight-loss curves. Films deposited using low-energy carbon plasma had higher contents of loosely bonded molecules; this resulted in a seemingly two-step decomposition and ΔE increasing with weight loss over a certain range. They followed concave-trend isothermal weight-loss curves. The overall decomposition mechanism could best be expressed in terms of nth-order reactions with the value of n closely related to film structures and reaction temperatures. Lower n-values are related to densely packed structure and higher temperature due to the increased diffusion barrier of the products.