Transient effects during sputtering of a-C:H surfaces by nitrogen ions

Sputtering of polymer-like amorphous hydrogenated carbon (a-C:H) thin films by 0.5–1 keV N2+ molecular ions has been studied in situ and real-time using a highly sensitive quartz crystal microbalance technique. During bombardment of a fresh, plasma-deposited a-C:H layer with nitrogen ions the measured sputtering yield decreases exponentially with ion fluence until a steady state value is reached at a fluence of typically about 3.5 × 1015 N2+ ions per cm2. A chemical sputtering mechanism has to be considered in addition to physical sputtering to explain the observed steady state sputtering values. Simulations based on the code TRIDYN, which take into account a change of surface composition due to implantation and erosion, are performed to understand the transient development of sputtering yields.