Plasma chemistry during the deposition of a-C:H films and its influence on film properties

Plasma chemistry in an argon/acetylene expanding thermal plasma was studied by means of a residual gas analyser (RGA) and cavity ring down spectroscopy (CRDS). With RGA, the consumption of acetylene in the plasma and the production of the C4H2 molecule was measured. CRDS was used for C, CH and C-2 radical detection. It is demonstrated that C, CH and C-2 are products of a secondary reaction chain of argon ions and electrons with radical products formed after the primary reaction of argon ions and electrons with acetylene. By increasing the acetylene injection the composition of the plasma, and consequently the film properties, can be controlled. The growth of the films was monitored using in situ real time single wavelength ellipsometry. Films were analysed with Rutherford backscattering combined with elastic recoil detection analysis and with ex situ spectroscopic ellipsometry. The film properties reflect clearly the different plasma composition. Possible consequences for hydrogenated amorphous carbon films with good electronic properties are highlighted. (C) 2003 Elsevier Science B.V. All rights reserved.