THICKNESS-DEPENDENT STRESS IN SPUTTERED CARBON-FILMS

The intrinsic compressive stress in thin carbon films up to 350 nm in thickness, deposited on Si(100) substrates via dc magnetron sputtering, has been measured using ex situ optical interferometry. A plateau value in compressive stress (approximately 1.5 X 10(9) Pa) is observed for carbon films thicker than 85 nm, but an anomalously large stress (up to 50% increase) occurs for film thicknesses between 18 and 85 nm. The carbon film stress data are interpreted in terms of a simple structural model in which the average film density influences the macroscopic stress. Ultrathin carbon films (< 10 nm) in the initial stages of growth were further investigated by atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). AFM images of approximately 1-nm-thick carbon films and uncoated substrates reveal topographic features with average heights of 4 and 1.5 angstrom, respectively, but no obvious island film growth structures. XPS measurements, in which the native SiO2 peak is used as a marker of exposed substrate area, suggest that films of less-than-or-equal-to 2 nm thickness are not continuous. The reported enhanced film stresses are therefore associated with a continuous film structure.