Characterization of sp2/sp3 hybridization ratios of hydrogenated amorphous carbon films deposited in C2H2 inductively coupled plasmas

Hydrogenated amorphous carbon (a-C:H) films were deposited using inductively coupled C2H2 plasma, and the effect of process parameters on the sp(2)/sp(3) hybridization ratio of the films was investigated. The sp(2)/sp(3) ratio was deduced from the intensity ratios of the D and G peaks (I-D/I-G) observed in Raman spectra. The ion density in the C2H2 plasma was determined using an ion probe, and the relative density of CH and H radicals was quantified using optical actinometry. A high I-D/I-G ratio was observed at high substrate temperatures, and the high sp(2)/sp(3) ratio is attributed to the loss of hydrogen atoms at high temperatures. A high I-D/I-G ratio was also observed with high plasma power and low pressure. The I-D/I-G ratio of the a-C:H films increased with increasing ion density in the C2H2 plasmas generated under various conditions, but decreased with the relative density of CH radicals. Ions remove hydrogen atoms from a-C:H films, and CH radicals introduce hydrogen atoms into a-C:H films. The etching resistance of a-C:H films was also investigated, wherein the etch rates of the a-C:H films decreased by 83.3% in the CF4 plasma and by 70.2% in the O-2 plasma when the sp(2)/sp(3) ratio was increased from 0.97 to 1.62.

Automated summary

Hydrogenated amorphous carbon (a-C:H) films were deposited using inductively coupled C2H2 plasma, and the effect of process parameters on the sp(2)/sp(3) ratio was investigated. Higher I-D/I-G ratio was observed at high substrate temperatures, high plasma power, and low pressure. The I-D/I-G ratio increased with ion density in the C2H2 plasmas, but decreased with the relative density of CH radicals.