A dual ion beam deposition system was used to deposit thin films of CNx from a carbon target. A 1 keV nitrogen ion beam from a 3 cm Kaufman source was used to sputter carbon from a graphite target, and a second nitrogen ion beam of 50 eV, from an RF ion source, was used to bombard the growing film with nitrogen ions. Using this technique, rather than direct ion beam deposition from methane, it is possible to reduce the amount of hydrogen in these films to less than 5% (atomic), and to boost the nitrogen content to over 30%. These films were then subjected to isochronal heating up to 900°C to determine the stability of the films as compared to those with much higher concentrations of hydrogen.
CNx is a material that is difficult to fabricate without the inclusion of large amounts of hydrogen. A high hydrogen content has the tendency to make the material sensitive to property changes as it is heated over 200°C. Concomitant with a loss of hydrogen is the loss of nitrogen.
In the films that had lower amounts of hydrogen it was found that the loss of nitrogen during heating was delayed until higher temperatures were reached. However, instead of hydrogen being evolved during heating, the amount of hydrogen in the film increases, reaching a maximum concentration of ∼45% at 800°C.