DIAGNOSTICS IN O-2 HELICON PLASMAS FOR SIO2 DEPOSITION

O-2 and O-2/TEOS helicon plasmas used for plasma enhanced chemical vap our deposition of SiO2 films are investigated in the 1-10 mTorr pressu re and 0-800 W rf power ranges. The positive oxygen ions are analysed by energy selective mass spectrometry and Langmuir probes. The oxygen atom concentration is monitored by actinometry and ionization threshol d mass spectrometry. In oxygen plasmas it is shown that O-2(+) is the major positive ion, and that the oxygen molecules are far from being c ompletely dissociated, due to a very high oxygen atom recombination fr equency on the reactor wails. The dissociation degree increases with t he rf power reaching 10% at 500 W. In O-2/TEOS plasmas, the plasma den sity and electron temperature decrease as the TEOS fraction increases. In contrast, the degree of oxygen dissociation increases sharply with the addition of a few per cent TEOS, is maximum for about 5% TEOS and decreases as TEOS fraction is further increased. In a 95:5 O-2/TEOS p lasma (5 mTorr, 300 W) the fluxes of oxygen positive ions and atoms im pinging onto a floating substrate are estimated to be 4 x 10(15) cm(-2 ) and 10(18) cm(-2) s(-1) respectively. Under these plasma conditions, near-stoichiometric SiO2 films, with low OH content, are deposited at ambient temperature. The corresponding atom to ion flux ratio is abou t 250, which suggests the dominant role of oxygen atoms in the deposit ion kinetics. The comparison of the compositions of layers grown in a 5 mTorr 95:5 O-2/TEOS plasma at two rf powers confirms the major role of oxygen atoms.