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

Abstract

Hydrogenated amorphous carbon (a-C:H) films were deposited using inductively coupled C 2 H 2 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 C 2 H 2 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 C 2 H 2 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 CF 4 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. • The effects of ions and CH radicals were investigated on sp 2 /sp 3 ratios of a-C:H. • Ions in C 2 H 2 plasma make a-C:H films sp 2 -rich because ions remove H atoms in films. • CH radicals make more sp 3 structure in a-C:H due to incorporation of H atoms