The properties of diamond are ascribed to C-C sp³ bondings from the point of chemical bonding. Diamond-like carbon (DLC) thin film is defined as a carbon film which is composed of chiefly C-C sp³ bondings. The characteristics of DLC films are approaching those of diamond crystals. DLC films have been formed in non-equilibrium states such as plasma processes, because sp² bondings are stable under atomospheric pressure and ordinary temperature.
Among plasma processes, we have concentrated on reactive sputtering which is distinguished from usual physical sputtering. In reactive sputtering deposition, H radicals are thought to sputter graphite target chemically and deposit sp³ rich thin films selectively on substrates. We have also discussed characterization techniques which are applied to distinguish the chemical bondings and the micro structures in DLC thin films.