Optical gap of fluorinated amorphous carbon films prepared by electron cyclotron resonance trifluromethane and benzene plasmas

Abstract

The optical gap of fluorinated amorphous carbon (a-C:F) films, which were prepared by electron cyclotron resonance plasma chemical vapor deposition using trifluromethane (CHF 3) and benzene (C 6H 6) as the source gases, is investigated. The optical gap E g of the a-C:F films, which were deposited at input microwave power of 140–700 W, pressure of 0.1–1.0 Pa and CHF 3/C 6H 6 flow ratio of 1:1–10:1, is in the range of 1.76–3.98 eV and is dependent on the amount of fluorine and CC bonding in the films. The optical gap E g increases with raising the amount of fluorine but decreases as the amount of CC bonding increased. This is because of the decrease in the amount of π bonding formed by CC and the increase in that of σ bonding formed by CF. As a result, the density of state near band edgy reduces and the optical gap becomes wide.