STRESS-RELAXATION AND THERMAL EVOLUTION OF FILM PROPERTIES IN AMORPHOUS-CARBON

A model for the stress relaxation of amorphous carbon films containing high concentrations of fourfold coordinated carbon is presented. The onset of stress relaxation in these materials occurs following thermal annealing at temperatures as low as 100 degrees C, and near full stre ss relaxation occurs after annealing at 600 degrees C. The stress rela xation is modeled by a series of first order chemical reactions which lead to a conversion of some fourfold coordinated carbon atoms into th reefold coordinated carbon atoms. The distribution of activation energ ies for this process is derived from the experimental measurements of stress relaxation and is found to range from 1 eV to over 3 eV. Perman ent increases in the electrical conductivity of the carbon films are a lso found following thermal annealing. The electrical conductivity is found to be exponentially proportional to the number of additional thr eefold atoms which are created upon annealing, with the increase in th reefold atom concentration being deduced from the stress relaxation mo del. This indicates that the increase in electrical conductivity and t he stress relaxation originate from the same fourfold to threefold con version process and that electrical transport through these films is d ominated by a hopping conduction process.