Acetylene–argon plasmas measured at an rf-biased substrate electrode for diamond-like carbon deposition: II. Ion energy distributions**This paper was presented as an invited talk at the 19th European Sectional Conference on Atomic and Molecular Physics of Ionized Gases, Granada, Spain, 15–19 July 2008. See stacks.iop.org/PSST/18/3.

Abstract

Ion energy distributions (IEDs) have been determined at the radio frequency (rf)-biased electrode in an inductively coupled acetylene–argon plasma for various substrate bias voltages and frequencies under conditions suitable for diamond-like carbon (DLC) and polymer-like film deposition. These are compared with those obtained at a capacitively coupled plasma grounded wall. In the former, for pressures <25 mTorr, the IEDs exhibit bimodal structures with peak separation values that follow the expected voltage and frequency dependences. At higher pressures, 120 mTorr, the bimodal structure is replaced by a single peak. For all conditions the dominant ion is Ar+ or ArH+ despite the set flow ratio of C2H2 : Ar of 2 : 1 and this can be attributed to the high electron dissociation of the parent molecule. DLC films indicate a peak hardness at an ion energy of around 90 eV and a very sharp fall in hardness is noted beyond this value. This is similar to the observed sp3-bond formation in hydrogen-free tetrahedral amorphous carbon or bias-sputtered films. However, due to the lack of carbon-based ions, an alternative mechanism is likely based on argon knock-on implantation of surface adsorbed carbon species. The results have shown that the use of high-frequency bias or bias harmonics may lead to much narrower IEDs.