RF PACVD DIAMOND-LIKE CARBON COATINGS ON INSULATING OBJECTS

Bias voltage variations along the surface of an insulating cylinder (height 5.5 cm) placed on a capacitively coupled powered electrode during the presence of an r.f. methane discharge are determined. The measurement technique consists of analysing the IR absorption properties of the locally deposited amorphous hydrogenated carbon films along the 2850-3300 cm-1 absorption band (C-H stretching vibration) and making use of a previously determined correlation between the bias voltage during film deposition and structural properties such as the sp3/sp2 C-H bonding ratio, the bonded hydrogen content, etc. Various kinds of insulating materials were selected covering a wide range of dielectric constants: Teflon (epsilon(r) almost-equal-to 2), alumina Al2O3(epsilon(r) almost-equal-to 7) and rutile TiO2(epsilon(r) almost-equal-to 110). The experimental results suggest that the bias voltage variation across insulating objects is governed by their capacitance.