Effects of applied power on hydrogenated amorphous carbon (a-C:H) film deposition by low frequency (60 Hz) plasma-enhanced chemical vapor deposition (PECVD)

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass substrates using low frequency (60 Hz) plasma-enhanced chemical vapor deposition and the effects of the applied power on a-C:H films deposition were investigated. During deposition, the electron temperature and the density of CH4–H2 plasma were 2.4–3.1 eV and about 108 cm−3, respectively. The main optical emission peak of the carbon species observed in the CH4–H2 plasma is shown to be excited carbon CH* at 431 nm. The sp3/sp2 ratio, band gap, hydrogen content, and refractive index of a-C:H films gradually increased up to a power of 25 W and then saturated at higher power. This tendency is similar to the variation of plasma parameters with varying applied power, thereby indicating that a strong relationship exists between the properties of the films and the plasma discharge.

► a-C:H films were deposited using H2–CH4 plasma generated by 60 Hz power source.
► Electron temperature and density increased up to 25 W and then saturated at higher power.
► The excited carbon CH* (431 nm) was not only good indicator but also main reactive species.
► Fraction of sp3 was gradually raised with the increase of applied power.
► The change on film properties had similar patterns compared to plasma parameters.