DIRECT OBSERVATION OF LASER-INDUCED CRYSTALLIZATION OF A-C-H FILMS

The post-growth modification of diamond-like amorphous hydrogenated ca rbon a-C:H films by laser treatment has been studied by transmission e lectron microscopy and Raman spectroscopy. a-C:H films grown on Si sub strates by benzene decomposition in a rf glow discharge were irradiate d with 15 ns pulses of a KrF-excimer laser with fluences in the ran e of E = 50-700 mJ/cm(2). At fluences below 100 mJ/cm(2) an increase in the number of graphitic clusters and in their ordering was evidenced f rom Raman spectra, while the film structure remained amorphous accordi ng to electron microscopy and electron diffraction observations. At hi gher fluences the appearance of diamond particles of 2-7 nm size, embe dded into the lower crystallized graphitic matrix, was observed and si multaneously a progressive growth of graphite nanocrystals with dimens ions from 2 nm to 4 nm was deduced from Raman measurements. The maximu m thickness of the crystallized surface layer (approximate to 400 nm) and the degree of laser annealing are limited by the film ablation whi ch starts at E > 250 mJ/cm(2). The laser-treated areas lose their chem ical inertness. In particular, chemical etching in chromium acid becom es possible, which may be used for patterning the highly inert carbon films.