Transparent polymer and diamond-like hydrogenated amorphous carbon thin films by PECVD technique

Optical, electrical and structural properties of hydrogenated amorphous carbon films deposited by radio frequency plasma enhanced chemical vapour deposition technique (RF-PECVED) have been investigated thoroughly. The films were deposited using a mixture of hydrogen and acetylene gases at a low substrate temperature of 200 deg. C. The electrical resistivities of the films are ≥ 109 Ω cm. The ratio of hydrogenated sp3 to sp2 bonded carbon atoms in the films is obtained by deconvoluting the infrared spectra over the 2800 cm-1-3100 cm-1 range. Polymer-like hydrogenated amorphous carbon films are grown at a low power (50 mW cm-2) having a high hydrogen content (30.3-46.1 at%). Increase in hydrogen dilution increases the total hydrogen content as well as the ratio of hydrogenated sp3 to sp2 carbon bonding and it becomes a maximum at an optimum hydrogen dilution. Similarly the grain density also increases with the increase in hydrogen dilution. On the other hand, at a higher RF power of 150 mW cm-2 much stronger C-C sp3 and C-C sp2 bonds are formed and the total hydrogen content drastically reduces to a very low value of 1.1-1.8 at%. This indicates the growth of hydrogenated diamond-like carbon (DLC) structure. The stronger C-C sp3 bonds present in the DLC film make the films harder as well as Raman active