Dependence of growth and nanomechanical properties of ultrathin amorphous carbon films on radio frequency sputtering conditions

Ultrathin films of amorphous carbon (a-C) were deposited on Si(100) substra tes by radio frequency (rf) sputtering using pure Ar as sputtering gas, rf power of 80-1000 W, and substrate bias voltage between 0 and -300 V. The fi lms possessed a thickness of 6-95 nm, nanohardness of 12-40 GPa, and root-m ean-square surface roughness of 0.15-32 nm, depending on the deposition con ditions. Plasma parameters of the film growth environment were correlated t o the deposition conditions to obtain insight into the phenomena responsibl e for changing the growth characteristics and nanomechanical properties of the a-C films. The surface binding energies of carbon atoms in the films we re interpreted in terms of measured sputter etching rates due to energetic Ar ion bombardment at a kinetic energy of 850 eV. Higher etching rates were found for a-C films with higher growth rates and lower hardness. Ultrathin (10 nm) a-C films of maximum nanohardness (similar to 39 GPa) were synthes ized at 3 mTorr working pressure, 750 W rf power, -200 V substrate bias, an d 5 min deposition time. Results are presented to elucidate the effects of rf power, working pressure, and substrate bias on the quality of a-C films deposited by controlling the ion-current density, mean free path, and sheat h voltages in the rf discharges. The latter are important parameters affect ing the ratio of ion to atom fluxes and the intensity (power density) of io n bombardment on the growing film surface. (C) 1999 American Institute of P hysics. [S0021-8979(99)08015-9].