Argon-Hydrogen rf plasma study for carbon film deposition

In this work the effect of hydrogen addition on the physical properties and the sputtering efficiency of a rf (13.56 MHz) Ar plasma was investigated. The discharges in Ar-H2 were used to sputter-deposit carbon films from a graphite cathode, with a hydrogen concentration in the feedgas ranging from 0 to 100 % (the useful range for film growth was however limited to 0-85%). The physical plasma parameters were determined by means of a Langmuir probe which, coupled with a chemical modeling of the ion-molecule and electron-molecule reactions in gas phase, enabled to define the energy flux conditions at the cathode. The results show that hydrogen exerts a positive effect on the film deposition rate at the lowest end of the hydrogen concentration range, an enhancing deposition effect correlated with a high density of ArH+ ions in the plasma and a high energy flux carried by the ions to the cathode. Nonetheless, an analysis of the processes at the cathode indicates that the sputtering mechanism was essentially physical in the low [H2] range (3-20%) but that a chemical assistance of the process should be considered too for the remaining [H2] range. Besides, even in the physical sputtering regime, the target material removal occurred with a reactive sputtering mechanism, which implies a chemical modification of the target surface layers and surface binding energy