Positive and negative direct current bias effects on the microstructures and physical properties of hydrogenated amorphous carbon films prepared by radio frequency plasma chemical vapor deposition

Abstract

Positive and negative direct current (dc) bias effects were investigated for the synthesis of hydrogenated amorphous carbon films in radio frequency plasma chemical vapor deposition at 0.025 Torr and 200 °C. The applied bias ranged from +250 to −500 V. Both the positive and negative dc bias effects are discussed on the basis of surface and cross-sectional morphology by scanning electron microscopy, deposition rate, threshold energy for photoelectron emission, contact angle, and adhesive strength of these films. For a negative bias, the surface of the film is very flat. The surface of the film deposited with no bias is somewhat pebbly while that of the film deposited with a positive bias is very rough and shows the presence of pores in the cross section. A negative bias substantially increases the deposition rate, refractive index, wettability, and adhesive strength. With no bias (ground potential), as compared to with a positive bias, there is a little increase in the wettability and adhesive force. The no bias case did not affect the properties arising from structural change, such as refractive index (density) and threshold energy for photoelectron emission (incorporated hydrogen). A positive bias did not affect these physical properties of the hydrogenated amorphous carbon films. These positive, negative, and no bias effects depend on the kinds of collision species and their collision energy against the substrate in the radio frequency plasma according to the additional bias conditions.