Hydrogen-Free Carbon Films Deposited by a High Density Plasma Assisted Sputtering Source

概要

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Hydrogen-free carbon films were synthesized by a high density plasma assisted sputtering source (HiPASS). In the HiPASS a high density (> 1012 cm-3) remote Ar plasma was used to sputter a graphite cathode. As a direct current sputtering voltage was changed from -400 to -800 V the deposition rate was linearly increased from 3.5 to 8 nm/min. Raman spectroscopy showed that the ratio of D- and G-peaks (I(D)/I(G)) was increased 0.89 to 1.68 and the position of G-peak was shifted from 1573.8 to 1575.1 cm-1 as the sputtering voltage is negatively increased. This corresponds to the phase transition from amorphous carbon to nano-crystalline graphite with the decrease of sp3 fraction, which causes the decreases of nano hardness from 23 to 22 GPa. In an asymmetric pulsed sputtering with fixed voltage (Vp-p = -600 V), the ratio of I(D)/I(G) was increased 1.10 to 1.41 as a positive duty is increased from 0 to 14%. The electron heating of graphite target during a positive duty increased the target temperature, resulting in the formation of sp2 dominant carbon film and the decreases of nano hardness from 22 to 21 GPa.