Synthesis and Electrical Characteristics of Nano-doped Diamond-like Carbon Films*

A carbon atom, which has an electron configuration of [He]2s²2p², makes sp² or sp³ covalent bonds with other atoms. Macroscopic development of these bonds creates various carbonaceous materials: graphite for sp² carbons and diamond for sp³ carbons. Random combination of sp² carbon and sp³ carbon atoms accompanying with hydrogen termination creates amorphous carbon. Remarking on the dielectric properties, it is called “diamond-like carbon (DLC)”.

DLC films are mainly synthesized by plasma-enhanced CVD (PECVD) or sputtering methods using radiofrequency (RF) discharge. The reason why RF discharge is used to make low-energy stable plasma by accelerating collision frequency between electron and particle in the atmosphere. However, there is a drawback in its chemical structure analysis and controlled synthesis: it is difficult to measure voltage and current individually. Capacitance between the apparatus and measurement probes generates displacement current, making accurate electrical measurements difficult. The product of current and voltage, power, is an alternative factor; however, current is an extensive variable and kinetic factor; voltage is an intensive variable and thermodynamic factor. Selectivity and progress of chemical reactions depends on the relationship between these factors (i.e., current‒voltage curves).

To perform precise and tailor-made synthesis of DLC, we have developed “Photoemission-assisted PECVD (PA-PECVD)”. In particular, PA-PECVD activates Townsend discharge, called “photoemission-assisted Townsend discharge (PATD)”, to create precisely controlled DLC films in nanometer scale. Hetero-atoms such as oxygen and nitorgen can be doped into a desired site of the DLC film without destroying the underlayer.