Excimer laser etching of diamond-like carbon films: spalling effect

Etching of diamond-like amorphous hydrogenated carbon films by 20 ns pulses of a KrF excimer laser has been investigated. In addition to previously reported etching mechanisms realized via either carbon oxidation or vaporization, a new etching mode based on a spalling effect was observed. It was found that there is a narrow window in laser fluences in which the etch rate of the carbon films examined exceeds by nearly two orders of magnitude the etch rates measured at fluences beyond this interval. The effect of anomalously fast etching occurs below a threshold for normal laser ablation (vaporization), and is ascribed to stress-induced lift-off of the material in the form of 30–60 nm thick macroscopic sheets. Very smooth surface relief in the etched crater and a reduced degree of film graphitization are characteristic features of this new etching mode.